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Title: The Economic Aspect of Geology
Author: Leith, C. K. (Charles Kenneth), 1875-1956
Language: English
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THE ECONOMIC ASPECTS OF GEOLOGY
C. K. LEITH
UNIVERSITY OF WISCONSIN
[Illustration]
NEW YORK
HENRY HOLT AND COMPANY
COPYRIGHT, 1921
BY
HENRY HOLT AND COMPANY
_August, 1923_
PRINTED IN THE U. S. A.
CONTENTS
PAGE
CHAPTER I. INTRODUCTION 1
SURVEY OF FIELD 1
ECONOMIC APPLICATIONS OF THE SEVERAL BRANCHES OF GEOLOGY
AND OF OTHER SCIENCES 3
Mineralogy and petrology 3
Stratigraphy and paleontology 4
Structural geology 5
Physiography 6
Rock alterations or metamorphism 10
Application of other sciences 10
TREATMENT OF THE SUBJECT IN THIS VOLUME 11
CHAPTER II. THE COMMON ELEMENTS, MINERALS, AND
ROCKS OF THE EARTH AND THEIR ORIGINS 13
RELATIVE ABUNDANCE OF THE PRINCIPAL ELEMENTS OF THE
LITHOSPHERE 13
RELATIVE ABUNDANCE OF THE PRINCIPAL MINERALS OF THE
LITHOSPHERE 14
RELATIVE ABUNDANCE OF THE PRINCIPAL ROCKS OF THE LITHOSPHERE 16
WATER (HYDROSPHERE) 18
SOILS AND CLAYS 18
COMPARISON OF LISTS OF MOST ABUNDANT ROCKS AND MINERALS WITH
COMMERCIAL ROCKS AND MINERALS 18
THE ORIGIN OF COMMON ROCKS AND MINERALS 18
Igneous processes 19
Igneous after-effects 19
Weathering of igneous rocks and veins 20
Sedimentary processes 22
Weathering of sedimentary rocks 23
Consolidation, cementation, and other sub-surface
alterations of rocks 24
Cementation 24
Dynamic and contact metamorphism 25
THE METAMORPHIC CYCLE AS AN AID IN STUDYING MINERAL DEPOSITS 27
CHAPTER III. SOME SALIENT FEATURES OF THE GEOLOGY
AND CLASSIFICATION OF MINERAL DEPOSITS 29
VARIOUS METHODS OF CLASSIFICATION 29
NAMES 31
MINERAL DEPOSITS AS MAGMATIC SEGREGATIONS IN IGNEOUS ROCKS 34
MINERAL DEPOSITS WITHIN AND ADJACENT TO IGNEOUS ROCKS,
WHICH WERE FORMED IMMEDIATELY AFTER THE COOLING AND
CRYSTALLIZATION OF THE MAGMAS THROUGH THE AGENCY OF HOT
MAGMATIC SOLUTIONS 36
Evidence of igneous source 37
Possible influence of meteoric waters in deposition of ores
of this class 41
Zonal arrangement of minerals related to igneous rocks 42
The relation of contact metamorphism to ore bodies of the
foregoing class 45
SECONDARY CONCENTRATION IN PLACE OF THE FOREGOING CLASSES OF
MINERAL DEPOSITS THROUGH THE AGENCY OF SURFACE SOLUTIONS 46
RESIDUAL MINERAL DEPOSITS FORMED BY THE WEATHERING OF
IGNEOUS ROCKS IN PLACE 50
MINERAL DEPOSITS FORMED DIRECTLY AS PLACERS AND SEDIMENTS 51
Mechanically deposited minerals 51
Chemically and organically deposited minerals 52
SEDIMENTARY MINERAL DEPOSITS WHICH HAVE REQUIRED FURTHER
CONCENTRATION TO MAKE THEM COMMERCIALLY AVAILABLE 54
ANAMORPHISM OF MINERAL DEPOSITS 57
CONCLUSION 58
CHAPTER IV. MINERAL RESOURCES--SOME GENERAL
QUANTITATIVE CONSIDERATIONS 60
WORLD ANNUAL PRODUCTION OF MINERALS IN SHORT TONS 60
WORLD ANNUAL PRODUCTION OF MINERALS IN TERMS OF VALUE 62
SIGNIFICANCE OF GEOGRAPHIC DISTRIBUTION OF MINERAL PRODUCTION 63
THE INCREASING RATE OF PRODUCTION 63
CAPITAL VALUE OF WORLD MINERAL RESERVES 64
POLITICAL AND COMMERCIAL CONTROL OF MINERAL RESOURCES 65
RESERVES OF MINERAL RESOURCES 65
CHAPTER V. WATER AS A MINERAL RESOURCE 67
GENERAL GEOLOGIC RELATIONS 67
DISTRIBUTION OF UNDERGROUND WATER 68
MOVEMENT OF UNDERGROUND WATER 71
WELLS AND SPRINGS 72
COMPOSITION OF UNDERGROUND WATERS 73
RELATION OF GEOLOGY TO UNDERGROUND WATER SUPPLY 75
SURFACE WATER SUPPLIES 76
UNDERGROUND AND SURFACE WATERS IN RELATION TO EXCAVATION
AND CONSTRUCTION 78
CHAPTER VI. THE COMMON ROCKS AND SOILS AS MINERAL
RESOURCES 80
ECONOMIC FEATURES OF THE COMMON ROCKS 80
Granite 82
Basalt and related types 82
Limestone, marl, chalk 82
Marble 83
Sand, sandstone, quartzite (and quartz) 84
"Sand and gravel" 84
Clay, shale, slate 85
The feldspars 86
Hydraulic cement (including Portland, natural, and
Puzzolan cements) 86
GEOLOGIC FEATURES OF THE COMMON ROCKS 88
Building stone 88
Crushed stone 90
Stone for metallurgical purposes 91
Clay 91
Limitations of geologic field in commercial investigation
of common rocks 92
SOILS AS A MINERAL RESOURCE 94
Origin of soils 94
Composition of soils and plant growth 96
Use of geology in soil study 97
CHAPTER VII. THE FERTILIZER GROUP OF MINERALS 99
GENERAL COMMENTS 99
NITRATES 101
Economic features 101
Geologic features 102
PHOSPHATES 104
Economic features 104
Geologic features 105
PYRITE 107
Economic features 107
Geologic features 108
SULPHUR 109
Economic features 109
Geologic features 110
POTASH 111
Economic features 111
Geologic features 112
CHAPTER VIII. THE ENERGY RESOURCES--COAL, OIL, GAS
(AND ASPHALT) 115
COAL 115
ECONOMIC FEATURES 115
World production and trade 115
Production in the United States 117
Coke 118
Classification of coals 119
GEOLOGIC FEATURES 123
PETROLEUM 127
ECONOMIC FEATURES 127
Production and reserves 128
Methods of estimating reserves 134
Classes of oils 136
Conservation of oil 137
GEOLOGIC FEATURES 140
Organic theory of origin 140
Effect of differential pressures and folding on oil
genesis and migration 142
Inorganic theory of origin 143
Oil exploration 144
OIL SHALES 150
NATURAL GAS 151
Economic features 151
Geologic features 151
ASPHALT AND BITUMEN 151
Economic features 151
Geologic features 153
CHAPTER IX. MINERALS USED IN THE PRODUCTION OF
IRON AND STEEL (THE FERRO-ALLOY GROUP) 154
GENERAL FEATURES 154
IRON ORES 158
ECONOMIC FEATURES 158
Technical and commercial factors determining use of iron
ore materials 158
Geographic distribution of iron ore production 160
World reserves and future production of iron ore 162
GEOLOGIC FEATURES 166
Sedimentary iron ores 166
Iron ores associated with igneous rocks 171
Iron ores due to weathering of igneous rocks 171
Iron ores due to weathering of sulphide ores 173
MANGANESE ORES 173
Economic features 173
Geologic features 176
CHROME (OR CHROMITE) ORES 178
Economic features 178
Geologic features 179
NICKEL ORES 180
Economic features 180
Geologic features 181
TUNGSTEN (WOLFRAM) ORES 182
Economic features 182
Geologic features 184
MOLYBDENUM ORES 185
Economic features 185
Geologic features 186
VANADIUM ORES 187
Economic features 187
Geologic features 188
ZIRCONIUM ORES 189
Economic features 189
Geologic features 189
TITANIUM ORES 190
Economic features 190
Geologic features 190
MAGNESITE 191
Economic features 191
Geologic features 192
FLUORSPAR 193
Economic features 193
Geologic features 194
SILICA 195
Economic features 195
Geologic features 196
CHAPTER X. COPPER, LEAD AND ZINC MINERALS 197
COPPER ORES 197
Economic features 197
Geologic features 199
Copper deposits associated with igneous flows 200
Copper veins in igneous rocks 201
"Porphyry coppers" 203
Copper in limestone near igneous contacts 204
Copper deposits in schists 204
Sedimentary copper deposits 205
General comments 206
LEAD ORES 209
Economic features 209
Geologic features 211
ZINC ORES 213
Economic features 213
Geologic features 216
CHAPTER XI. GOLD, SILVER, AND PLATINUM MINERALS 221
GOLD ORES 221
Economic features 221
Geologic features 226
SILVER ORES 231
Economic features 231
Geologic features 234
PLATINUM ORES 237
Economic features 237
Geologic features 239
CHAPTER XII. MISCELLANEOUS METALLIC MINERALS 241
ALUMINUM ORES 241
Economic features 241
Geologic features 243
ANTIMONY ORES 246
Economic features 246
Geologic features 248
ARSENIC ORES 249
Economic features 249
Geologic features 251
BISMUTH ORES 252
Economic features 252
Geologic features 252
CADMIUM ORES 253
Economic features 253
Geologic features 254
COBALT ORES 254
Economic features 254
Geologic features 255
MERCURY (QUICKSILVER) ORES 255
Economic features 255
Geologic features 258
TIN ORES 260
Economic features 260
Geologic features 261
URANIUM AND RADIUM ORES 263
Economic features 263
Geologic features 264
CHAPTER XIII. MISCELLANEOUS NON-METALLIC MINERALS 267
NATURAL ABRASIVES 267
Economic features 267
Geologic features 269
ASBESTOS 270
Economic features 270
Geologic features 271
BARITE (BARYTES) 272
Economic features 272
Geologic features 273
BORAX 274
Economic features 274
Geologic features 275
BROMINE 277
Economic features 277
Geologic features 278
FULLER'S EARTH 278
Economic features 278
Geologic features 279
GRAPHITE (PLUMBAGO) 279
Economic features 279
Geologic features 282
GYPSUM 283
Economic features 283
Geologic features 284
MICA 285
Economic features 285
Geologic features 287
MONAZITE (THORIUM AND CERIUM ORES) 288
Economic features 288
Geologic features 289
PRECIOUS STONES 289
Economic features 289
Geologic features 291
SALT 294
Economic features 294
Geologic features 295
TALC AND SOAPSTONE 299
Economic features 299
Geologic features 299
CHAPTER XIV. EXPLORATION AND DEVELOPMENT 301
THE GENERAL RELATIONS OF THE GEOLOGIST TO EXPLORATION AND
DEVELOPMENT 301
PARTLY EXPLORED VERSUS VIRGIN TERRITORIES 303
THE USE OF ALL AVAILABLE INFORMATION 304
COÖPERATION IN EXPLORATION 305
ECONOMIC FACTORS IN EXPLORATION 306
GEOLOGIC FACTORS IN EXPLORATION 307
MINERAL PROVINCES AND EPOCHS 308
CLASSIFICATION OF MINERAL LANDS 309
OUTCROPS OF MINERAL DEPOSITS 311
Some illustrative cases 312
Topography and climate as aids in searching for mineral
outcrops 314
Size and depth of ore bodies as determined from outcrops 315
The use of placers in tracing mineral outcrops 316
The use of magnetic surveys in tracing mineral ledges 317
THE USE OF ELECTRICAL CONDUCTIVITY AND OTHER QUALITIES OF
ROCKS IN EXPLORATION 319
THE USE OF STRUCTURE AND METAMORPHISM IN EXPLORATION 319
DRILLING IN EXPLORATION 320
QUANTITATIVE ASPECTS OF GEOLOGIC EXPLORATION 321
ORIGIN OF MINERAL DEPOSITS AS A FACTOR IN EXPLORATION 322
LAKE SUPERIOR IRON ORE EXPLORATION AS AN ILLUSTRATION 323
DEVELOPMENT AND EXPLOITATION OF MINERAL DEPOSITS 326
CHAPTER XV. VALUATION AND TAXATION OF MINERAL
RESOURCES 328
POPULAR CONCEPTION OF MINERAL VALUATION 328
VALUATION AND TAXATION OF MINES 329
Intrinsic and extrinsic factors in valuation 329
Values of mineral deposits not often established by
market transfers 331
The ad valorem method of valuation 331
Other methods of mineral valuation and taxation 335
GENERAL COMMENTS ON TAXATION OF MINERAL RESOURCES 338
CHAPTER XVI. LAWS RELATING TO MINERAL RESOURCES 342
I. LAWS RELATING TO OWNERSHIP AND CONTROL OF MINERAL
RESOURCES 342
On alienated lands 343
On the public domain 344
Nationalization of mineral resources 345
Effect of ownership laws on exploration 347
Use of geology in relation to ownership laws 349
II. LAWS RELATING TO EXTRACTION OF MINERAL RESOURCES 355
III. LAWS RELATING TO DISTRIBUTION AND TRANSPORTATION OF
MINERAL RESOURCES 355
IV. OTHER RELATIONS OF GEOLOGY TO LAW 356
CHAPTER XVII. CONSERVATION OF MINERAL RESOURCES 359
THE PROBLEM 359
DIFFERENCES BETWEEN PRIVATE AND PUBLIC EFFORTS IN
CONSERVATION 363
THE INTEREST RATE AS A GUIDE IN CONSERVATION 364
ANTI-CONSERVATIONAL EFFECTS OF WAR 365
CONSERVATION OF COAL 366
MEASURES INTRODUCED OR PROPOSED TO CONSERVE COAL 367
(A) Mining and preparation of coal 368
Progress in above methods 370
(B) Improvement of labor and living conditions at the
mines 372
(C) Introduction or modification of laws to regulate or to
remove certain restrictions on the coal industry 373
(D) Distribution and transportation of coal 376
(E) Utilization of coal 377
(F) Substitutes for coal as a source of power 378
DIVISION OF RESPONSIBILITY BETWEEN GOVERNMENT AND PRIVATE
INTERESTS IN THE CONSERVATION OF COAL 379
CONSERVATION OF MINERALS OTHER THAN COAL 382
CHAPTER XVIII. INTERNATIONAL ASPECTS OF MINERAL
RESOURCES 383
WORLD MOVEMENT OF MINERALS 383
Movement of minerals under pre-war conditions of
international trade 385
Changes during the war 385
Post-war condition of the mineral trade 387
TENDENCIES TOWARD INTERNATIONAL COÖPERATION AND POSSIBILITY
OF INTERNATIONAL CONTROL OF MINERALS 389
Methods of international coöperation 391
CONSERVATION IN ITS INTERNATIONAL RELATIONS 393
EXPLORATION IN ITS INTERNATIONAL RELATIONS 395
VALUATION IN ITS INTERNATIONAL RELATIONS 396
RELATIVE POSITION OF THE UNITED STATES IN REGARD TO SUPPLIES
OF MINERALS 396
THE COAL AND IRON SITUATION OF WESTERN EUROPE UNDER THE
TERMS OF THE PEACE 400
CONCLUSION 403
LITERATURE 403
CHAPTER XIX. GEOLOGY AND WAR 405
GEOLOGY BEHIND THE FRONT 405
GEOLOGY AT THE FRONT 408
EFFECT OF THE WAR ON THE SCIENCE OF ECONOMIC GEOLOGY 412
CHAPTER XX. GEOLOGY AND ENGINEERING CONSTRUCTION 413
FOUNDATIONS 413
SURFACE WATERS 414
TUNNELS 414
SLIDES 415
SUBSIDENCE 417
RAILWAY BUILDING 417
ROAD BUILDING 418
GEOLOGY IN ENGINEERING COURSES 419
CHAPTER XXI. THE TRAINING, OPPORTUNITIES AND
ETHICS OF THE ECONOMIC GEOLOGIST 420
PURE VERSUS APPLIED SCIENCE 420
COURSE OF STUDY SUGGESTED 422
Field work 425
Specialization in studies 426
A degree of Economic Geology 427
THE OPPORTUNITIES OF THE ECONOMIC GEOLOGIST 428
ETHICS OF THE ECONOMIC GEOLOGIST 430
ILLUSTRATIONS
FIGURE PAGE
1. Graphic representation of volume change in weathering
of a Georgia granite 21
2. Commercial (financial) control of the mineral
resources of the world 64
3. Political (territorial) control of the mineral
resources of the world 64
4. The fertilizer situation in the United States 100
5. Diagram showing the chemical composition and heat
efficiency of the several ranks of coal 122
6. Origin and development of coal 123
7. Chart showing the present tendency of the United
States in respect to its unmined reserve of petroleum 134
8. The annual output of the principal oil fields of the
United States for the last twenty years 135
9. Curve showing the usual decline in oil field
production after the period of maximum output is
reached 136
10. Chart showing the relative values of the principal
petroleum products manufactured in the United States
from 1899 to 1914 138
11. Alteration of Lake Superior iron formation to iron
ore by the leaching of silica 168
12. Representing in terms of weight the mineralogical
changes in the katamorphism of serpentine rocks to
iron ore, eastern Cuba 172
13. Diagram showing gradation from syenite to bauxite in
terms of volume 245
CHAPTER I
INTRODUCTION
SURVEY OF FIELD
In adapting ourselves to physical environment it has been necessary to
learn something about the earth. Mainly within the last century has this
knowledge been organized into the science of geology, and only within
the last few decades have the complex and increasing demands of modern
civilization required the applications of geology to practical uses,
resulting in the development of the science generally known as _economic
geology_. This science is not sharply marked off from the science of
geology proper; almost any phase of geology may at some time or some
place take on its economic aspect.
The usefulness of economic geology was first recognized in relation to
mineral resources,--and particularly in relation to metallic resources,
their discovery and development,--but the science has been found to have
much wider practical application. The practice of the economic geologist
in recent years has taken on many new phases.
The geologist is called upon to study the geologic features of mineral
deposits, their occurrence, structure, and origin. The basic information
thus acquired is useful in estimating reserves and life of mineral
deposits. This leads naturally to considerations of valuation. Because
valuation plays such a large part in any tax program, the geologist is
being used by tax boards of the federal and state governments.
Both in the formulation of laws relating to mineral resources, and in
the litigation growing out of the infraction of these laws, the economic
geologist plays a part.
One cannot go very far with the study of mineral resources without
consideration of the question of conservation. Geologists are called on
not only for broad surveys of the mineral reserves, but for the
formulation of general principles of conservation and their application
to specific mines and minerals.
The geologist's familiarity with the distribution and nature of mineral
resources has given him a part in coping with broad questions of
international use of natural resources. War conditions made it necessary
to use new sources of supply, new channels of distribution, and new
methods of utilization. The economic geologist came into touch with
questions of international trade, tariffs, and shipping.
But economic geology is not solely confined to mineral resources. In
relation to engineering enterprises of the greatest variety--canals,
aqueducts, tunnels, dams, building excavations, foundations,
etc.--geology now figures largely, both in war and in peace.
The nature, amount, and distribution of underground water supplies are
so involved with geologic considerations that a considerable number of
geologists give up their time wholly to this phase of the subject.
It might seem from this list of activities that geology is spreading too
far into the fields of engineering and commerce, but there are equally
rapid extensions of other fields of knowledge toward geology. The
organization of these intermediate fields is required both in the
interest of science and in the interest of better adaptation of the race
to its environment. The geologist is required to do his part in these
new fields, but not to abandon his traditional field.
It is proposed in this volume to discuss the economic aspects of geology
without exhaustive discussion of the principles of geology which are
involved. Practically the whole range of geologic science has some sort
of economic application, and it would be futile to attempt in one volume
even a survey of the science of geology as a whole. Our purpose is
rather to indicate and illustrate, in some perspective, the general
nature of the application of geology to practical affairs.
In professional preparation for the practice of economic geology there
is no easy short-cut. Students sometimes think that a smattering of
geological principles, combined with a little business and economic
information, may be sufficient. Analysis of professional successes
should make it clear that economic geologists are most effective and in
most demand, not primarily because of business aptitude, though this
helps, but because of their proficiency in the science of geology
itself. In short, to enter successfully the field of economic geology
one should first become a scientist, if only in a limited field.
The traditional conception of the geologist as a musty and stooped
individual, with a bag, hammer, and magnifying glass, collecting
specimens to deposit in a dusty museum, will doubtless survive as a
caricature, but will hardly serve to identify the economic geologist in
his present-day work. In writing this book, it is hoped in some measure
to convey an impression of the breadth and variety in this field. Few
other sciences offer so wide a range of opportunity, from the purely
scientific to the practical and commercial, coupled with travel,
exploration, and even adventure.
ECONOMIC APPLICATIONS OF THE SEVERAL BRANCHES OF GEOLOGY AND OF OTHER
SCIENCES
There is no phase of geology which at some time or place does not have
its economic application. Many references to these applications are made
in other chapters. It is proposed here to indicate briefly some of the
phases of geologic science which are most necessary to the practice of
economic geology. The student in his preparation cannot afford to
eliminate any of them on the ground that they are merely "scientific" or
"academic" or "theoretical."
MINERALOGY AND PETROLOGY
Mineralogy, the study of minerals, and petrology, the study of rocks
(aggregations of minerals), are of course elementary requisites in
preparation. There must be familiarity with the principal minerals and
rocks, and especially with the methods and processes of their
identification, with their nature, and with their origin. This involves
a study of their crystallography, chemical composition, physical
qualities, and optical properties as studied with the microscope. In
recent years the microscopical study of polished and etched surfaces of
ores has proved a valuable tool.
STRATIGRAPHY AND PALEONTOLOGY
Stratigraphy and paleontology are concerned with the sedimentary and
life history of the earth. The determination of the ages of the earth's
strata and of the conditions of their deposition is required in the
practice of economic geology. For example, a detailed knowledge of the
succession of rocks and their ages, as determined by fossils and other
stratigraphic evidence, is vital to the interpretation of conditions in
an oil or coal field, and to the successful exploration and development
of its deposits. The success of certain paleontologists and
stratigraphic specialists in oil exploration is an evidence of this
situation. Certain iron ores, phosphates, salts, potash, and other
minerals, as well as many of the common rocks used for economic
purposes, are found in sedimentary deposits, and require for their
successful exploration and development the application of stratigraphic
and paleontologic knowledge.
Closely related to stratigraphy (as well as to physiography, see pp.
6-10) is the study of sedimentation,--_i. e._, the study of the
physical, chemical, climatic, and topographic conditions of the
deposition of sediments. This is coming to play an increasingly large
part in geologic work, and is essential to the interpretation of many
mineral deposits, particularly those in which stratigraphic and
physiographic questions are involved.
Still another aspect of the problem of stratigraphy and sedimentation is
covered by the study of _paleogeography_, or the areal distribution of
the faunas and sediments of geologic periods caused by the alternating
submergence and emergence of land areas. In the search for the treasures
of sedimentary deposits, a knowledge of ancient geographies and of
ancient faunas makes it possible to eliminate certain regions from
consideration. From a study of the faunas of eastern Kansas and
Missouri, and of those along the eastern part of the Rocky Mountains, it
has been inferred that a ridge must have extended across eastern Kansas
during early Pennsylvanian time,--a conclusion which is of considerable
economic importance in relation to oil exploration.
STRUCTURAL GEOLOGY
Structural geology is the study of the physical forms and relations of
rocks which result mainly from deformation by earth forces. If rocks
remained in their original forms the structural problem would be a
comparatively easy one, but usually they do not. Often they are faulted
and folded and mashed to such an extent that it is difficult to go
behind the superposed structural features to the original conditions in
order to work out the geologic history. Not only is structural study
necessary for the interpretation of geologic history, but it is often
more directly applicable to economic problems,--as when, for instance,
ore deposits have been formed in the cracks and joints of rocks, and the
ore deposits themselves have been faulted and folded. Water resources
are often located in the cracks and other openings of rocks, and are
limited in their distribution and flow because of the complex attitude
of deformed rocks. Oil and gas deposits often bear a well-defined
relation to structural features, the working out of which is almost
essential to their discovery.
It is not desirable to stop with the merely descriptive aspects of
structural geology, as is so often done; for much light can be thrown on
the economic applications of this subject by consideration of the
underlying principles of mechanics,--involving the relations of earth
stresses to rock structures. The mere field mapping and description of
faults and joints is useful, but in some cases it is necessary to go a
step further and to ascertain the mechanical conditions of their origin
in order to interpret them clearly. If, for illustration, there are
successive groups of mineralized veins in a mining camp, the later ones
cutting the earlier ones, these might be treated as separate structural
units. But if it can be shown that the several sets of veins have formed
from a single movement, that there is no sharp genetic separation
between the different sets and that they are a part of a single system,
this interpretation throws new light on exploration and development, and
even on questions of ownership and extralateral rights (Chapter XVI).
PHYSIOGRAPHY
Physiography is a phase of geology which investigates the surface
features of the earth. It has to do not only with the description and
classification of surface forms, present and past (physical geography or
geomorphology), but with the processes and history of their development.
The subject is closely related to geography, climatology, sedimentation,
and hydrology. As one of the latest phases of geology to be organized
and taught, its economic applications have been comparatively recent and
are not yet widely recognized. Because of this fact its economic
applications may be summarized at somewhat greater length than those of
the other branches of geology above mentioned, which are to be more or
less taken for granted.
The central feature of physiography is the so-called erosion cycle or
topographic cycle. Erosion, acting through the agencies of wind, water,
and ice, is constantly at work on the earth's surface; the eroded
materials are in large part carried off by streams, ultimately to be
deposited in the ocean near the continental margins. The final result is
the reduction of the land surface to an approximate plain, called a
_peneplain_, somewhere near sea level. Geological history shows that
such peneplains are often elevated again with reference to sea level, by
earth forces or by subsidence of the sea, when erosion again begins its
work,--first cutting narrow, steep gulches and valleys, and leaving
broad intervening uplands, in which condition the erosion surface is
described as that of _topographic youth_; then forming wider and more
extensive valleys, leaving only points and ridges of the original
peneplains, in which stage the surface is said to represent _topographic
maturity_; then rounding off and reducing the elevations, leaving few or
none of the original points on the peneplain, widening the valleys still
further and tending to reduce the whole country to a nearly flat
surface, resulting in the condition of _topographic old age_. The final
stage is again the peneplain. This cycle of events is called the
_erosion cycle_ or _topographic cycle_. Uplift may begin again before
the surface is reduced to base level; in fact, there is a constant
oscillation and contest between erosion and relative uplift of the land
surface.
The action of the erosion cycle on rocks of differing resistance to
erosion and of diverse structure gives rise to the great variety of
surface forms. The physiographer sees these forms, not as heterogeneous
units, but as parts of a definite system and as stages in an orderly
series of events. He is able to see into the topographic conditions
beyond the range of immediate and direct observation. He is able to
determine what these forms were in the past and to predict their
condition in the future. He is able to read from the topography the
underground structure which has determined that topography. A given
structure may in different stages of topographic development give quite
diverse topographic forms. In such a case it is important to realize
that the diversity is only superficial. On the other hand, a slight
local divergence from the usual topographic forms in a given region may
reflect a similar local divergence in the underground structure. Thus it
is that an appreciation of the physiographic details may suggest
important variations in the underground structure which would otherwise
pass undiscovered.
Many mineral deposits owe their origin or enrichment to weathering and
other related processes which are preliminary to erosion. These
processes vary in intensity, distribution, and depth, with the stage of
erosion, or in relation to the phase of the erosion cycle. They vary
with the climatic conditions which obtain on the erosion surface.
Mineral deposits are therefore often closely related to the topographic
features, present and past, in kind, shape, and distribution. A few
illustrative cases follow.
Many of the great copper deposits of the western United States owe their
values to a secondary enrichment through the agency of waters working
down from the surface. When this fact of secondary enrichment was
discovered, it was naturally assumed that the process was related to the
present erosion surface and to present climatic and hydrologic
conditions. Certain inferences were drawn, therefore, as to depth and
distribution of the enriched ores. This conception, however, proved to
be too narrow; for evidences were found in many cases that the copper
deposits had been concentrated in previous erosion cycles, and therefore
in relation to erosion surfaces, now partly buried, different from the
present surface. The importance of this knowledge from an exploring and
development standpoint is clear. It has made it possible to find and
follow rich ores, far from the present erosion surface, which would
otherwise have been disclosed solely by chance. Studies of this kind in
the copper camps are yet so recent that much remains to be learned. The
economic geologist advising exploration and development in copper ores
who does not in the future take physiographic factors into account is
likely to go wrong in essential ways, as he has done in some cases in
the past.
Not only is it necessary to relate the secondary enrichment of copper
deposits to the erosion surface, present or past, but by a study of the
conditions it must be ascertained how closely erosion has followed after
the processes of enrichment. In some cases erosion has followed so
slowly as to leave large zones of secondary enrichment. In other cases
erosion has followed up so closely after the processes of secondary
enrichment as to remove from the surface important parts of the
secondarily enriched deposits.
The iron ores of the Lake Superior region are the result of the action
of waters from the surface on so-called iron formations or jaspers. Here
again it was at first supposed that the enrichment was related to the
present erosion surface; but upon further studies the fact was disclosed
that the concentration of the ores took place in the period between the
deposition of Keweenawan and Cambrian rocks, and thus a new light was
thrown on the possibilities as to depth and distribution of the ores.
The old pre-Cambrian surface, with reference to which the concentration
took place, can be followed with some precision beneath the present
surface. This makes it possible to forecast a quite different depth and
distribution of the ores from that which might be inferred from present
surface conditions. Present surface conditions, of low relief,
considerable humidity, and with the water table usually not more than
100 feet from the surface, do not promise ore deposits at great depth.
The erosion which formed the old pre-Cambrian surface, however, started
on a country of great relief and semi-arid climate, conditions which
favored deep penetration of the surface waters which concentrated the
ores.
The iron ores of eastern Cuba are formed by the weathering of a
serpentine rock on an elevated plateau of low relief, where the sluggish
streams are unable rapidly to carry off the products of weathering.
Where streams have cut into this plateau and where the plateau breaks
down with sharp slopes to the ocean, erosion has removed the products of
weathering, and therefore the iron ore. An important element, then, in
iron ore exploration in this country is the location of regions of
slight erosion in the serpentine area. One of the largest discoveries
was made purely on a topographic basis. It was inferred merely from a
study of topography that a certain large unexplored area ought to carry
iron ore. Subsequent work in the thick and almost impenetrable jungle
disclosed it.
Bauxite deposits in several parts of the world require somewhat similar
conditions of concentration, and a study of the physiographic features
is an important factor in their location and interpretation.
A physiographic problem of another sort is the determination of the
conditions surrounding the origin of sedimentary ores. Certain mineral
deposits, like the "Clinton" iron ores, the copper ores in the "Red
Beds" of southwestern United States and in the Mansfield slates of
Germany, many salt deposits, and almost the entire group of placer
deposits of gold, tin, and other metals, are the result of
sedimentation, from waters which derived their materials from the
erosion of the land surface. It is sometimes possible from the study of
these deposits to discover the position and configuration of the shore
line, the depth of water, and the probable continuity and extent of the
deposits. Similar questions are met in the study of coal and oil.
This general problem is one of the phases of geology which is now
receiving a large amount of attention, not only from the standpoint of
ore deposition, but from a broader geologic standpoint. In spite of the
fact that sedimentary processes of great variety can be observed in
operation today, it is yet extremely difficult to infer from a given
sedimentary deposit the precise conditions which determined its
deposition and limited its distribution. For instance, sedimentary iron
formations furnish a large part of the world's iron ore. The surface
distribution, the structure, the features of secondary enrichment, are
all pretty well understood; likewise the general conditions of
sedimentation are reasonably clear,--but the close interpretation of
these conditions, to enable us to predict the extent of one of these
deposits, or to explain its presence in one place and absence in
another, is in an early and sketchy stage.
An understanding of the principles and methods of physiography is also
vital to an intelligent application of geology to water resources, to
soils, to dam and reservoir construction, and to a great variety of
engineering undertakings, but as these subjects involve the application
of many other phases of geology, they are considered in separate
chapters. (Chapters V, VI, and XX.)
ROCK ALTERATIONS OR METAMORPHISM
This is one of the newer special phases of geology which for a long time
was regarded as the plaything of the petrographer or student of rocks.
With the systematic development of the subject, however, it was found
that the extremely numerous and complex alterations of rocks and
minerals may be definitely grouped, and that they are controlled by
broad principles. It became apparent also that these principles apply
both to the economic and non-economic minerals and rocks,--in other
words, that the segregation of economic minerals is a mere incident in
pervasive cycles of the alterations which affect all rocks. Metamorphic
geology, therefore, for some geologists becomes a convenient approach to
the subject of economic geology. It has the great advantage that it
tends to keep all minerals and all processes of ore deposition in proper
perspective with relation to rocks and rock processes in general. It is
not argued that this is the only approach or that it is the best for all
purposes. A brief account of this phase of geology is given in Chapter
II.
APPLICATION OF OTHER SCIENCES
Geology is sometimes defined as the application of other sciences to the
earth. Considered broadly, there is no phase of science which is not
involved in economic geology. In other chapters in this book many
references are made to applications of engineering, mathematics,
physics, chemistry, metallurgy, biology, and economics.
At different times and places the requirements for earth materials are
quite different. In the Stone Age there was little use for metals; in
later ages the use of metals broadened. The multiplicity of demands of
modern civilization, the increasing knowledge of processes of
metallurgy, chemistry and physics, better transportation, better
organization of commercial life, and many other factors, tend to bring
new earth materials into use,--and, therefore, into the field of
economic geology. A comparatively few years ago alumina, one of the most
common and abundant substances of the earth's crust, was in no general
demand except for very limited use as an ornament. Little attention was
paid to it by economic geologists as a commercial product; now, however,
aluminum is in great demand, and the raw materials which produce it have
become the subjects of intensive study by economic geologists.
In short, economic geology includes the consideration of man in reaction
to his physical environment. There are some earth materials and some
conditions of the earth environment which do not yet come within the
field of economic geology. But so large a proportion of them do, that
the "complete economic geologist" should indeed be almost omniscient.
When one considers what an insignificantly small portion of this field
can be covered by any individual, it is apparent that the title of
economic geologist implies no mastery of the entire field. There is yet
no crowding.
TREATMENT OF THE SUBJECT IN THIS VOLUME
In scope and manner of treatment this volume follows somewhat the
writer's presentation of the subject in university teaching. The purpose
is to explain the nature of the economic demands for the science of
geology, and to discuss something of the philosophy of the finding and
use of raw materials.
Somewhat generalized statistics are used as a means of gaining
perspective. No effort has been made for detailed accuracy or for
completeness. So far as possible the quantitative features are expressed
in general proportions, and where specific figures are given they are
meant to indicate only such general proportions. The thought has been
not to be so specific that the figures would soon be out of date. All
standard statistical sources have been drawn on, but the principal
sources have been the results of the various special investigations
called out by the war, in which the writer had a part.
On the geologic side many sources have been drawn on outside of the
writer's own experience. For the most part, no specific references or
acknowledgments are made, on the ground that the book aims to present
the general features which are now the more or less common knowledge of
economic geologists. To make the references really adequate for
exhaustive study would not only burden the text, but would require a
specificity of treatment which it has been hoped to avoid.
The illustrative cases chosen for discussion are often taken from the
writer's field of experience. This field has been principally the Lake
Superior region, but has included also the principal mineral deposits of
North America, Cuba, and limited areas in South America and Europe. Thus
the Lake Superior iron and copper region might seem to be brought
forward more than is warranted by its scientific or economic importance.
For this, the writer offers no apology. An author's perspective is
largely determined by his background of training and experience, and a
frank recognition of this fact may aid in determining the weight to be
given to his conclusions. It might even add to scientific efficiency if
each writer were to confine his discussion almost solely to matters
within his own range of observation and study.
The writer's indebtedness for information derived from the printed page
and for personal discussion and advice is of wide range. He would
express his warm appreciation of the friendly spirit of coöperation and
advice with which this effort has been aided--a spirit which he likes to
think is particularly characteristic of the profession of economic
geology. In particular he would acknowledge the efficient aid of Mr.
Julian D. Conover in preparation and revision of the manuscript.
CHAPTER II
THE COMMON ELEMENTS, MINERALS, AND ROCKS OF THE EARTH AND THEIR ORIGINS
A list of the solid substances of the earth making up the so-called
lithosphere (or rock sphere) in order of their abundance, does not at
all correspond to a list made in order of commercial importance. Some of
the most valuable substances constitute such a small proportion of the
total mass of the lithosphere that they hardly figure at all in a table
of the common substances.
RELATIVE ABUNDANCE OF THE PRINCIPAL ELEMENTS OF THE LITHOSPHERE
When reduced to the simplest terms of elements the outer ten miles of
the lithosphere consists of:[1]
PERCENTAGE OF PRINCIPAL ELEMENTS IN THE LITHOSPHERE
Oxygen 47.33
Silicon 27.74
Aluminum 7.85
Iron 4.50
Calcium 3.47
Magnesium 2.24
Sodium 2.46
Potassium 2.46
-----
98.05
The remainder of the elements exist in quantities of less than 1 per
cent. None of these principal elements occur separately in nature and
none of them are mined as elements for economic purposes.
RELATIVE ABUNDANCE OF THE PRINCIPAL MINERALS OF THE LITHOSPHERE
Minerals exceptionally consist of single elements, but ordinarily are
combinations of two or more elements; for instance, quartz consists of a
chemical combination of silicon and oxygen. The proportions of the
common minerals in the outer ten miles of the lithosphere are in round
numbers as follows:
PERCENTAGE OF COMMON MINERALS IN LITHOSPHERE
Feldspar 49
Quartz 21
Augite, hornblende, and olivine 15
Mica 8
Magnetite 3
Titanite and ilmenite 1
Kaolin, limonite, hematite, dolomite,
calcite, chlorite, etc. 3
---
100
In making up this table it is assumed that the rocks to a depth of ten
miles are about 95 per cent of igneous type, that is, crystallized from
molten magma, and about 5 per cent of sedimentary type, that is, formed
from the weathering and erosion of igneous rocks or preëxisting
sediments, and deposited in beds or layers, either by water or by air
(see pp. 16-17).
More reliable figures for the relative abundance of the minerals are
available for each of the two classes of rocks, igneous and sedimentary.
The igneous rocks contain minerals in about the following proportions:
PERCENTAGE OF COMMON MINERALS IN IGNEOUS ROCKS
Feldspar 50
Quartz 21
Augite, hornblende, olivine, etc. 17
Mica 8
Magnetite 3
Titanite and ilmenite 1
---
100
The sedimentary rocks contain minerals in about the following
proportions:
PERCENTAGE OF COMMON MINERALS IN SEDIMENTARY ROCKS
Quartz 35
Feldspar 16
White mica 15
Kaolin (clay) 9
Dolomite 9
Chlorite 5
Calcite 4
Limonite 4
Gypsum, carbon, rutile, apatite, magnetite,
etc. 3
---
100
The sedimentary rocks comprise three main divisions: (1) The muds and
clays, with their altered equivalents, shale, slate, etc.; (2) the
sands, with their altered equivalents, sandstone, quartzite,
quartz-schist, etc.; (3) the marls, limestones, and dolomites, with
their altered equivalents, marble, talc-schist, etc. For brevity these
groups are referred to respectively as shale, sandstone, and limestone.
The proportions of minerals in each of these groups of rocks are as
follows:
PERCENTAGE OF COMMON MINERALS IN SHALE, SANDSTONE, AND LIMESTONE
-----------+----------+-----------+-----------
| Average | Average | Average
| shale | sandstone | limestone
-----------+----------+-----------+-----------
Quartz | 31.91 | 69.76 | 3.71
Kaolin | 10.00 | 7.98 | 1.03
White mica | 18.40 | |
Chlorite | 6.40 | 1.15 |
Limonite | 4.75 | .80 |
Dolomite | 7.90 | 3.44 | 36.25[1]
Calcite | | 7.21 | 56.56
Gypsum | 1.17 | .12 | .10
Feldspar | 17.60 | 8.41 | 2.20
Magnetite | | .58 |
Rutile | .66 | .12 | .06
Ilmenite | | .25 |
Apatite | .40 | .18 | .09
Carbon | .81 | |
-----------+----------+-----------+-----------
Total | 100.00 | 100.00 | 100.00
-----------+----------+-----------+-----------
1: Includes small amount of FeCO_{3}.
In comparing the mineral composition of igneous and sedimentary rocks,
it will be noted that the most abundant single mineral of the igneous
rocks, and the most abundant mineral of the lithosphere as a whole, is
_feldspar_; that next in order is _quartz_; and that third comes a group
of dark green minerals typified by augite and hornblende, commonly
called _ferro-magnesian silicates_ because they consist of iron and
magnesia, with other bases, in combination with silica. The sedimentary
rocks, which are ultimately derived from the destruction of the igneous
rocks, contrast with the igneous rocks mainly in their smaller
proportions of feldspars and ferro-magnesian minerals, their higher
proportions of quartz and white mica (sericite or muscovite), and their
content of kaolin, dolomite, calcite, chlorite, limonite, etc., which
are nearly absent from the unaltered igneous rocks. Evidently the
development of sediments from igneous rocks has involved the destruction
of much of the feldspars and ferro-magnesian silicates, and the building
from the elements of these destroyed minerals of more quartz, white
mica, clay, dolomite, calcite, chlorite and limonite. The composition of
the minerals of the sedimentary rocks is such as to indicate that the
constituents of the air and water have been added in important amounts
to accomplish this change of mineral character. For instance, carbon
dioxide of the atmosphere has been added to lime and magnesia of the
igneous rocks to make calcite and dolomite, water has been added to some
of the alumina and silica of the igneous rocks to make kaolin or clay,
and both oxygen and water have been added to the iron of the igneous
rocks to make limonite.
RELATIVE ABUNDANCE OF THE PRINCIPAL ROCKS OF THE LITHOSPHERE
Just as elements combine chemically to form minerals, so do minerals
combine mechanically, either loosely or compactly, to form rocks. For
instance, quartz is a mineral. An aggregation of quartz particles forms
sand or sandstone or quartzite. Most rocks contain more than one kind of
mineral.
Sedimentary rocks occupy considerable areas of the earth's surface, but
they are relatively superficial. It has been estimated that if spread
evenly and continuously over the earth, which they are not, they would
constitute a shell scarcely a half mile thick.[2] Igneous rocks are
relatively more abundant deep below the surface. If the sediments be
assumed to be limited to a volume equivalent to a half-mile shell, and
the remainder of the rocks be assumed to be igneous, it is evident that
to a depth of ten miles 95 per cent of the rocks are igneous. Our actual
observation is confined to a shallow superficial zone in which sediments
make up at least half of all the rocks.
Igneous rocks can be divided for convenience into two main types: (1)
granite and allied rocks, containing a good deal of silica and therefore
_acid_ in a chemical sense, and (2) basalt and allied types, containing
less silica and more lime, magnesia, iron, soda and potassa, and
therefore _basic_ in a chemical sense. The former are light-colored gray
and pink rocks while the latter are dark-colored green and gray rocks.
Granite and basalt as technically defined are very common igneous
rocks,--so common that the names are sometimes used to classify igneous
rocks in general into two great groups, the granitic and the basaltic.
It has been estimated that about 65 per cent of the igneous rocks are of
the granitic group and 35 per cent of the basaltic group.
Sedimentary rocks, as already indicated, consist principally of three
groups, which for convenience are named shale, sandstone, and limestone.
If we approximate the average composition of each group and the average
composition of the igneous rocks from which they are ultimately derived,
it can be calculated that sedimentary rocks must form in the proportions
of 82 per cent shale, 12 per cent sandstone, and 6 per cent limestone.
Only this combination of the three sediments will yield an average
composition comparable with that of the parent igneous rocks. As
actually observed in the field the sandstones and limestones are in
relatively higher percentage than is here indicated, suggesting that
part of the shales may have been deposited in deep seas where they
cannot be observed, and that part may have been so changed or
metamorphosed that they are no longer recognized as shales.
SOILS AND CLAYS
Weathered and disintegrated rocks at the surface form soils and clays.
No estimate is made of abundance, but obviously the total volume of
these products is small as compared with the major classes of earth
materials above noted, and in large part they may be included with these
major classes.
WATER (HYDROSPHERE)
It has been estimated that all the water of the earth, including the
ocean, surface waters, and underground waters, constitutes about 7 per
cent of the volume of the earth to a depth of 10 miles.[3]
COMPARISON OF LISTS OF MOST ABUNDANT ROCKS AND MINERALS WITH COMMERCIAL
ROCKS AND MINERALS
Of the common rocks and minerals figuring as the more abundant materials
of the earth's crust, only a few are prominently represented in the
tables of mineral resources. Of these water and soils stand first.
Others are the common igneous and sedimentary rocks used for building
and road materials. Missing from the lists of the most abundant minerals
and rocks, are the greater part of the commercially important mineral
resources--including such as coal, oil, gas, iron ore, copper, gold, and
silver,--implying that these mineral products, notwithstanding their
great absolute bulk and commercial importance, occur in relatively
insignificant amounts as compared with the common rock minerals of the
earth.
THE ORIGIN OF COMMON ROCKS AND MINERALS
The common rocks and minerals develop in a general sequence, starting
with igneous processes, and passing through stages of weathering,
erosion, sedimentary processes, and alterations beneath the surface. The
commercial minerals are incidental developments under the same
processes.
IGNEOUS PROCESSES
The earliest known rocks are largely igneous. Sedimentary rocks are
formed from the breaking down of igneous rocks, and the origin of rocks
therefore starts with the formation of igneous rocks. Igneous rocks are
formed by the cooling of molten rock material. The ultimate source of
this molten material does not here concern us. It may come from deep
within the earth or from comparatively few miles down. It may include
preëxisting rock of any kind which has been locally fused within the
earth. Wherever and however formed, its tendency is to travel upward
toward the surface. It may stop far below the surface and cool slowly,
forming coarsely crystallized rocks of the granite and gabbro types.
Igneous rocks so formed are called _plutonic_ intrusive rocks. Or the
molten mass may come well toward the surface and crystallize more
rapidly into rocks of less coarse, and often porphyritic, textures. Such
intrusive rocks are porphyries, diabases, etc. Or the molten mass may
actually overflow at the surface or be thrown out from volcanoes with
explosive force. It then cools quickly and forms finely crystalline
rocks of the rhyolite and basalt types. These are called effusives or
extrusives, or lavas or volcanics, to distinguish them from intrusives
formed below the surface. The intrusive masses may take various forms,
called stocks, batholiths, laccoliths, sills, sheets and dikes,
definitions and illustrations of which are given in any geological
textbook. The effusives or volcanics at the surface take the form of
sheets, flows, tuffs, agglomerates, etc.
Some of the igneous rocks are themselves "mineral" products, as for
instance building stones and road materials. Certain basic intrusive
igneous rocks contain titaniferous magnetites or iron ores as original
constituents. Others carry diamonds as original constituents. Certain
special varieties of igneous rocks, known as pegmatites, carry coarsely
crystallized mica and feldspar of commercial value, as well as a
considerable variety of precious gems and other commercial minerals.
Pegmatites are closely related to igneous after-effects, discussed under
the next heading. As a whole, the mineral products formed directly in
igneous rocks constitute a much less important class than mineral
products formed in other ways, as described below.
=Igneous after-effects.= The later stages in the formation of igneous
rocks are frequently accompanied by the expulsion of hot waters and
gases which carry with them mineral substances. These become deposited
in openings in adjacent rocks, or replace them, or are deposited in
previously hardened portions of the parent igneous mass itself. They
form "contact-metamorphic" and certain vein deposits. Pegmatites,
referred to above, are in a broad sense in this class of "igneous
after-effects," in that they are late developments in igneous intrusions
and often grade into veins clearly formed by aqueous or gaseous
solutions. Among the valuable minerals of the igneous after-effect class
are ores of gold, silver, copper, iron, antimony, mercury, zinc, lead,
and others. While mineral products of much value have this origin, most
of them have needed enrichment by weathering to give them the value they
now have.
WEATHERING OF IGNEOUS ROCKS AND VEINS
No sooner do igneous rocks appear at or near the earth's surface, either
by extrusion or as a result of removal by erosion of the overlying
cover, than they are attacked vigorously by the gases and waters of the
atmosphere and hydrosphere as well as by various organisms,--with
maximum effect at the surface, but with notable effects extending as far
down as these agents penetrate. The effectiveness of these agents is
also governed by the climatic and topographic conditions. Under
conditions of extreme cold or extreme aridity, weathering takes the form
mainly of mechanical disintegration, and chemical change is less
conspicuous. Under ordinary conditions, however, processes of chemical
decomposition are very apparent. The result is definitely known. The
rocks become softened, loose, and incoherent. Voids and openings appear.
The volume tends to increase, if all end products are taken into
account. The original minerals, largely feldspar, ferro-magnesian
minerals, and quartz, become changed to clay, mixed with quartz or sand,
calcite or dolomite, and iron oxide, together with residual particles of
the original feldspars and ferro-magnesian minerals which have only
partly decomposed. In terms of elements or chemical composition, water,
oxygen, and carbon dioxide, all common constituents of the atmosphere
and hydrosphere, have been added; and certain substances such as soda,
potassa, lime, magnesia, and silica have in part been carried away by
circulating waters, to be redeposited elsewhere as sediments, vein
fillings, and cements. Figure 1 illustrates the actual mineral and
volume changes in the weathering of a granite--one of the most common
rocks. The minerals anorthite, albite, and orthoclase named in this
figure are all feldspars; sylvite and halite are chlorides of potash
and soda. The weathering processes tend to destroy the original
minerals, textures, and chemical composition. They are collectively
known as _katamorphic_ alterations, meaning destructive changes. The
zone in which these changes are at a maximum is called the _zone of
weathering_. This general zone is principally above the surface or level
of the ground-waters, but for some rocks it extends well below this
level. In some regions the ground-water level may be nearly at the
surface, and in others, especially where arid, it may be two thousand or
more feet down. Disintegrated weathered rocks form a blanket of variable
thickness, which is sometimes spoken of as the residual mantle, or
"mantle rock."
[Illustration: FIG. 1. Graphic representation of volume change
in weathering of a Georgia granite.]
Mineral products formed by weathering from common igneous rocks include
soils, clay, bauxite, and certain iron, chromite, and nickel ores. Again
the commercial importance of this group is not large, as compared with
products formed in other ways described below.
The same weathering processes described above for igneous rocks cause
considerable changes of economic significance in deposits formed as
igneous after-effects. In some cases they result in removing the less
valuable minerals, thus concentrating the more valuable ones, as well as
in softening the rock and making it easier to work; and in other cases
they tend to remove the valuable constituents, which may then be
redeposited directly below or may be carried completely out of the
vicinity. The _oxide zones_ of many ore bodies are formed by these
processes.
SEDIMENTARY PROCESSES
Sedimentary rocks are formed by the removal and deposition of the
weathered products of a land surface. Air, water, and ice, moving under
the influence of gravity and other forces, all aid in this transfer. The
broken or altered rock materials may be merely moved down slopes a
little way and redeposited on the surface, forming one type of
_terrestrial_ or _subaërial deposits_, or they may be transferred and
sorted by streams. When deposited in streams or near their mouths, they
are known as _river_, _alluvial_, or _delta deposits_. When carried to
lakes and deposited they form _lake deposits_. Ultimately the greater
part of them are likely to be carried to the ocean and deposited as
_marine sediments_.
Part of the weathered substances are carried mechanically as clay and
sand, which go to make up the _shale_ and _sandstone_ sediments. Part
are carried in solution, as for example lime carbonate and magnesium
carbonate, which go to make up _limestone_ and _dolomite_. Some of the
dissolved substances are never redeposited, but remain in solution as
salts in the sea, the most abundant of which is sodium chloride. Some of
the dissolved substances of weathering, such as calcite, quartz, and
iron oxide, are carried down and deposited in openings of the rocks,
where they act as cements.
The sediments as a whole consist of three main types,--_shales_ (kaolin,
quartz, etc.), _sandstones_ (quartz, feldspar, etc.), and _limestones_
or _dolomites_ (carbonates of lime and magnesia). Of these, the shale
group is by far the most abundant. There are of course many sediments
with composition intermediate between these types. There are also
sediments made up of large undecomposed fragments of the original rocks,
cemented to form _conglomerates_, or made up of small fragments of the
original rocks cemented to form _arkoses_ and _graywackes_. These,
however, may be regarded as simply stages in the alteration, which in
repeated cycles of weathering must ultimately result in producing the
three main groups,--shales, sandstones, and limestones.
Mineral products formed by sedimentary processes include sandstones,
limestones, and shales, used as building stone and road materials;
certain sedimentary deposits of iron, like the Clinton ores of the
southeastern United States and the Brazilian ores; important phosphate
deposits; most deposits of salt, gypsum, potash, nitrates, etc.;
comparatively few and unimportant copper deposits; and important placer
deposits of gold, tin, and other metals, and precious stones. With the
aid of organic agencies, sedimentary processes also account for the
primary deposition of coal and oil.
WEATHERING OF SEDIMENTARY ROCKS
After sedimentary rocks are formed, and in many cases covered by later
sediments, they may be brought again by earth movements and erosion to
the surface, where they in turn are weathered. The weathering of
sedimentary rocks proceeds along lines already indicated for the igneous
rocks. Residual mantles of impure clay and sand are commonly formed.
The mineral composition of sedimentary rocks being different from that
of igneous rocks to start with, the resulting products are in slightly
different proportions; but the changes are the same in kind and tend
merely to carry the general process of alteration farther in the same
direction,--that is, toward the production of a few substances like
clay, quartz, iron oxide, and calcite, which are transported and
redeposited to form clay, sand, and limestone. Cycles of this kind may
be repeated indefinitely.
By weathering of sedimentary rocks are produced some soils, certain
commercial clays, iron ores, lead and zinc ores, and other valuable
mineral products.
CONSOLIDATION, CEMENTATION, AND OTHER SUBSURFACE ALTERATIONS OF ROCKS.
=Cementation.= No sooner are residual weathered mantles formed or
sedimentary rocks deposited, whether under air or water, than processes
of consolidation begin. Settling, infiltration of cementing materials,
and new growths, or recrystallization, of the original minerals of the
rock all play a part in the process. The mud or clay becomes a shale,
the sand becomes sandstone or quartzite, the marl becomes limestone or
marble. All the minute openings between the grains, as well as larger
openings such as fissures and joints, may thus be filled. At the same
time the cementing materials may replace some of the original minerals
of the rock, the new minerals either preserving or destroying the
original textures. This process is sometimes called _metasomatic
replacement_. Igneous rocks as a rule are compact, and hence are not so
much subject to the processes of cementation as sedimentary rocks; but
certain of the more porous phases of the surface lavas, as well as any
joints in igneous rocks, may become cemented. All of these changes may
be grouped under the general term _cementation_.
A special phase of consolidation and cementation is produced near
intrusive igneous rocks through the action of the heat and pressure and
the expelled substances of the igneous rock. This is called _contact
metamorphism_ or _thermal metamorphism_. The processes are even more
effective when acting in connection with the more intense metamorphism
described under the next heading.
By cementation some of the common rocks, especially the sediments,
become sufficiently compact and strong to be useful as commercial
products, such as building stones and road materials.
More important as mineral products are the cementing materials
themselves. These are commonly quartz, calcite, or iron oxide, of no
especial value, but locally they include commercially valuable minerals
containing gold, copper, silver, lead, zinc, and many other mineral
products.
It is a matter of simple and direct observation, about which there is no
controversy, that many minerals are deposited as cements in the openings
in rocks or replacing rocks. As to the source of the solutions bringing
in these minerals, on the other hand, there has been much disagreement.
In general, the common cementing materials such as quartz and calcite,
as well as some of the commercial minerals, are clearly formed as
by-products of weathering, and are transported and redeposited by the
waters penetrating downward from the surface. The so-called _secondary
enrichment_ of many valuable veins is merely one of the special phases
of cementation from a superficial source. In other cases it is believed
that deep circulation of ordinary ground-waters may pick up dispersed
mineral substances through a considerable zone, and redeposit them in
concentrated form in veins and other trunk channels. For still other
cementing materials, it is suspected that the ultimate source is in
igneous intrusions; in fact, deposits of this general character show all
gradations from those clearly formed by surface waters, independently of
igneous activity, to those of a contact-metamorphic nature and others
belonging under the head of "igneous after-effects."
Hypothesis and inference play a considerable part in arriving at any
conclusion as to the source of cementing materials,--with the result
that there is often wide latitude for difference of opinion and of
emphasis on the relative importance of the different sources of ore
minerals.
=Dynamic and contact metamorphism.= Beneath the surface rocks are not
only cemented, but may be deformed or mashed by dynamic movements caused
by great earth stresses; the rocks may undergo rock flowage. The result
is often a remarkable transformation of the character of the rocks,
making it difficult to recognize their original nature. Also, igneous
intrusions may crowd and mash the adjacent rocks, at the same time
changing them by heat and contributions of new materials. This process
may be called _contact metamorphism_, but in so far as it results in
mashing of the rocks it is closely allied to _dynamic metamorphism_. The
former term is also applied to less profound changes in connection with
igneous intrusions, which result merely in cementation without mashing.
Dynamic and contact metamorphism may in some cases produce rocks
identical in appearance with those produced by ordinary processes of
cementation and recrystallization without movement. For instance, it is
difficult to tell how much movement there has been in the production of
a marble, because both kinds of processes seem to produce much the same
result. Commonly, however, the effect of dynamic metamorphism is to
produce a parallel arrangement of mineral particles and to segregate the
mineral particles of like kind into bands, giving a _foliated_ or
_schistose_ or _gneissic_ structure, and the rocks then become known as
slates, schists, or gneisses. Commonly they possess a capacity to part
along parallel surfaces, called _cleavage_. The development of the
schistose or gneissic structure is accompanied by the recrystallization
of the rock materials, producing new minerals of a platy or columnar
type adapted to this parallel arrangement. Even the composition of the
rock may be substantially changed, though this is perhaps not the most
common case. Whereas by weathering the rock is loosened up and
disintegrated, substances like carbon dioxide, oxygen, and water are
abundantly added, and light minerals of simple composition tend to
develop,--by dynamic metamorphism on the other hand, carbon dioxide,
oxygen, and water are usually expelled, the minerals are combined to
make heavier and more complex minerals, pore space is eliminated, and
altogether the rock becomes much more dense and crystalline. While
segregation of materials is characteristic of the surficial products of
weathering, the opposite tendency, of mixing and aggregation, is the
rule under dynamic metamorphism, notwithstanding the minor segregation
above noted.
Dynamic metamorphism is for the most part unfavorable to the development
of mineral products. Ore bodies brought into a zone where these
processes are active may be profoundly modified, but not ordinarily
enriched. One of the exceptions to this general rule is the development
of the cleavage of a slate, which enables it to be readily split and
thereby gives it value. Contact metamorphism, on the other hand, may
develop valuable mineral deposits (see pp. 20, 45-46).
THE METAMORPHIC CYCLE AS AN AID IN STUDYING MINERAL DEPOSITS
All of the chemical, mineralogical, and textural changes in rocks above
described may be collectively referred to as _metamorphism_. The phase
of metamorphism dealing with surficial weathering, similar changes below
the surface, and the formation of sediments, is called _katamorphism_ or
destructive change. The phase of metamorphism dealing with the
constructive changes in rocks, due to cementation, dynamic movements,
and igneous influences, is called _anamorphism_. Some geologists confine
the term metamorphism to the changes involved in contact and dynamic
metamorphism, and call the resulting products _metamorphic rocks_.
The zone in which katamorphism is most active, usually near the surface,
is called the _zone of katamorphism_. The deeper zone in which
anamorphism is preponderant is called the _zone of anamorphism_. There
are no definite limits of depth to these zones. A given rock may be
undergoing katamorphism while rocks on either side at the same depth are
suffering anamorphism.
By katamorphism rocks break down to produce the surficial rocks, and by
anamorphism the surficial rocks are again consolidated and altered to
produce highly crystalline rocks, which are not dissimilar in many of
their characteristics to the igneous rocks from which all rocks trace
their ultimate origin. In other words, anamorphism tends toward the
reproduction of igneous rocks, though it seldom fully accomplishes this
result. These two main groups of changes together constitute the
_metamorphic cycle_. Some rocks go through all phases of the cycle, but
others may pass directly from one phase to an advanced phase without
going through the intermediate stages. For instance, an igneous rock may
become a schist without going through the intermediate stage of
sedimentation.
Rocks are not permanent in their condition, but at practically all times
and places are undergoing some kind of metamorphism which tends to adapt
them to their environment. The conception of rocks as representing
phases or stages in a progressive series of changes called the
metamorphic cycle aids greatly in correlating and holding in mind many
details of rock nature and origin, and brings into some sort of
perspective the conditions which have produced rocks. A schistose
sediment comes to be regarded as an end product of a long series of
alterations, beginning with igneous rocks and passing through the stages
of weathering, sedimentation, cementation, etc., each of which stages
has been responsible for certain mineralogical, chemical, and textural
features now characterizing the rock. The alternation of constructive
and destructive changes of the metamorphic cycle, and the repetitions of
the cycle itself, periodically work over the earth materials into new
forms. Usually the cycles are not complete, in the sense that they
seldom bring the rock back to exactly the same condition from which it
started. More sediments are formed than are changed to schists and
gneisses, and more schists and gneisses are formed than are changed back
to igneous rocks. Salts in the ocean continuously accumulate. The net
result of the metamorphic cycle, is, therefore, the accumulation of
materials of the same kinds. Incidental to these accumulations is the
segregation of commercial mineral products.
The metamorphic cycle becomes a logical and convenient geologic basis
for correlating, interpreting, and classifying mineral products. Because
of the great variety of materials and conditions represented in mineral
deposits, prodigious efforts are required to remember them as
independent entities; but as incidents or stages in the well-known
progress of the metamorphic cycle, their essential characteristics may
be easily remembered and kept in some perspective.
Ores of certain metals, such as iron, occur in almost every phase of the
metamorphic cycle,--as igneous after-effects, as weathered products, as
sediments, and as schists. The ores of each of these several phases have
group characteristics which serve to distinguish them in important
particulars from ores belonging to other phases of the cycle. Having
established the position of any particular ore in the metamorphic cycle,
a number of safe inferences are possible as to mineralogical
composition, shape, extent, and other conditions, knowledge of which is
necessary for an estimate of commercial possibilities.
FOOTNOTES:
[1] Clarke, F. W., Data of geochemistry: _Bull. 695, U. S. Geol.
Survey_, 1920, p. 35.
[2] Clarke, F. W., Data of geochemistry: _Bull. 695, U. S. Geol.
Survey_, 1920, p. 33.
[3] Clarke, F. W., Data of geochemistry: _Bull. 695, U. S. Geol.
Survey_, 1920, pp. 22-23.
CHAPTER III
SOME SALIENT FEATURES OF THE GEOLOGY AND CLASSIFICATION OF MINERAL
DEPOSITS
VARIOUS METHODS OF CLASSIFICATION
Mineral products may be classified according to use, commercial
importance, geographic distribution, form and structure, mineralogical
and chemical composition, or origin. Each of these classifications is
useful for some purposes. The geologist usually prefers a classification
based on origin or genesis. In the following chapters on mineral
resources, however, such a classification is not the primary one,
because of the desire to emphasize economic features. The mineral
commodities are treated as units and by group uses. Some mineral
commodities have so many different kinds of origin in different regions
that to distribute them among several genetic groups in description
would make it impossible to preserve the unity necessary for
consideration of the economic features.
While in the descriptive chapters many references are made to origin, it
may be difficult for the reader to assemble them in perspective; for
this reason we summarize at the outset some of the salient features of
origin of mineral deposits and of their geologic classification.
To the layman the reason for emphasis on origin is often not clear. The
"practical" man frequently regards this phase of the subject as merely
incidental to the immediate economic questions--a playground for
harmless theorists. The answer of the economic geologist is that in no
other way than by a knowledge of origin is it possible to arrive at an
understanding of conditions which so well enables one to answer many
practical questions. In the exploration for mineral deposits, it is
obvious that an understanding of the kinds of geologic conditions and
processes under which a given type of deposit is known to develop
results in the elimination of much unpromising territory, and the
concentration of work on favorable localities. In forming any estimate
of mineral deposits beyond the ground immediately opened up,--for
instance, in estimating depth, form, change in values, mineralogical
character, or interruptions due to faulting,--it is difficult to form
any intelligent conception of the probabilities unless the history of
the deposit is understood. If, for instance, the ore is known to be
formed by hot waters, associated with the cooling of igneous rocks,
different conditions are to be expected below the zone of observation
than if the ore is formed by surface waters. If the ore body is formed
as a single episode under simple geologic conditions, the interpretation
of the possibilities in the situation may be quite different from the
interpretation applied where the history has been more complex. If the
surface conditions suggest possibilities of secondary enrichment of the
ores, the interpretation of the conditions underground will be different
from those applied where there is no evidence of such enrichment.
Where a mineral deposit is completely opened up in three dimensions, it
is often possible to work out economic questions of tonnage, grade,
shape, and values, without the aid of geology. Also, where conditions
are comparatively simple and uniform throughout a district, the local
knowledge of other mines may be a sufficient basis for answering these
questions for any new property developed. Empirical methods may suffice.
However, it is seldom that the conditions are so simple that some
geological inference is not necessary. Even where problems are settled
without calling in the geologist, geological inferences are required in
the interpretation of, and projection from, the known facts. It is often
the case that the practical man has in his mind a rather elaborate
assortment of geologic hypotheses, based on his individual experience,
which make the so-called theories of the geologist seem conservative in
comparison. The geologist comes to the particular problem with a
background of established geologic principles and observations, and his
first thought is to ascertain all the local conditions which will aid in
deciphering the complete history of the mineral deposit. There is no
fact bearing on the history, however remote from practical questions,
which may not be potentially valuable.
With this digression to explain the geologist's emphasis on origin of
mineral products, we may return to a consideration of a few of the
principles of rock and mineral genesis which have been found to be
significant in the study of mineral products.
In the preceding chapters it has been indicated that mineral deposits
are mere incidents in the mass of common rocks; that they are made by
the same processes which make common rocks, that none of the processes
affecting mineral deposits are unique for these minerals, and that most
common rocks are on occasion themselves used as mineral resources. These
facts are emphasized in order to make it clear that the study of mineral
deposits cannot be dissociated from the study of rocks, and that the
study of the latter is essential to bring mineral deposits into their
proper perspective. Absorption in the details of a mineral deposit makes
it easy for the investigator to forget or minimize these relations.
Nevertheless, in the study of mineral deposits, and especially deposits
of the metallic minerals, certain geologic features stand out
conspicuously against the common background indicated above. Our
discussion of these features will follow the order of rock genesis
indicated in the description of the metamorphic cycle.
NAMES
Any classification of mineral deposits on the basis of origin is more or
less arbitrary. The sharp lines implied by the use of class names do not
exist in nature. Mineral deposits are so complex and so interrelated in
origin, that a classification according to genesis indicates only the
essential and central class features; it does not sharply define the
limits of the classes.
It is practically impossible for any geologist to present a
classification which will be accepted without qualification by other
geologists, although there may be agreement on essential features.
Difficulties in reaching agreement are increased by the inheritance from
the past of names, definitions, and classifications which do not exactly
fit present conceptions based on fuller information,--but which,
nevertheless, have become so firmly established in the literature that
it is difficult to avoid their use. In the progress of investigation
many new names are coined to fit more precisely the particular situation
in hand, but only in fortunate cases do these new names stand up against
the traditional currency and authority of old names. The geologist is
often in despair in his attempt to express his ideas clearly and
precisely, and at the same time to use terms which will be
understandable by his readers and will not arouse needless controversy.
As illustrative of the above remarks reference may be made to a few
terms commonly used in economic geology, such as _primary_, _secondary_,
_syngenetic_, _epigenetic_, _supergene_, _hypogene_, _protore_, etc.
The most commonly used of these terms are _primary_ and _secondary_. It
is almost impossible to define them in a way which will cover all the
conceptions for which they have been used, and yet in their context they
have been very useful in conveying essential ideas. An ore formed by
direct processes of sedimentation has sometimes been called primary,
whereas an ore formed by later enrichment of these sediments has been
called secondary. An ore formed directly by igneous processes has been
called primary, while an ore formed by enrichment of such primary ore by
later processes has been called secondary. It is clear, however, that
these terms are merely relative, with application to a specific
sequence, and that they do not fix the absolute position of the ore in a
sequence applying to all ores. For instance, ores deposited directly as
sediments or placers may be derived from the erosion of preëxisting ore
bodies,--in which case it may sometimes be convenient to refer to the
sedimentary ores or placers as secondary and the earlier ores as
primary. Or a sulphide deposit originating through igneous agencies may
undergo two or three successive enrichments, each successive one
secondary to the preceding, but primary to the one following. In spite
of these obvious difficulties, the terms primary and secondary may be
entirely intelligible as indicating relative order of development under
a given set of conditions.
The term _syngenetic_ has been used for mineral deposits formed by
processes similar to those which have formed the enclosing rocks and in
general simultaneously with them, and _epigenetic_ for those introduced
into preëxisting rocks. In certain cases _syngenetic_ may be roughly
synonymous with _primary_, and _epigenetic_ with _secondary_, and yet a
primary ore may be epigenetic. For instance, zinc sulphides in the
Mississippi valley limestones (pp. 54-55) are epigenetic, and yet are
primary with reference to a later enrichment. The two sets of terms are
meant to convey somewhat different ideas and are not interchangeable.
Ransome[4] has suggested, especially for vein and contact deposits, a
series of names which has the considerable advantage of
definiteness:--_hypogene ores_, formed in general by ascending
non-oxidizing solutions, perhaps hot; _supergene ores_, formed in
general by oxidizing and surface solutions, initially cold and downward
moving; and _protores_, or metallized rock or vein substances which are
too low in tenor to be classed as ores, but which would have been
converted into ores had the enriching process been carried far enough.
In this connection Ransome defines primary ore as unenriched material
that can be profitably mined. In view of the general use of the terms
primary and secondary as expressing a sequential relation of ore
development, it is doubtful whether this more precise definition will
supersede the older usage. Also it may be noted that commercial
conditions might require, under these definitions, the designation of an
ore as a protore at one time or place and as a primary ore at another.
Hypogene ores are dominantly primary, and supergene ores are dominantly
secondary, but either may include both primary and secondary ores.
The terms of these several classifications overlap, and seek to express
different aspects of the same situation. While almost synonymous in
certain applications they are not in others.
In this text the writer has certainly not escaped the difficulties in
regard to names above referred to, nor in fact has he made any
exceptional effort to do so. His chief purpose is to convey, in somewhat
elementary terms, an understandable idea of the central features of
economic geology. In the main, the most widely accepted terms are used.
Almost at every turn it would be possible, in the interests of
precision, to introduce qualifying discussions of names,--but at the
expense of continuity and perspective in the presentation of the
principal subject-matter. The writer does not wish to minimize the
necessity for careful and precise nomenclature; but he regards it
important that the student focus his attention on the central objective
facts of the subject, and that he do not become misled by the sometimes
over-strenuous advocacy of certain names or classifications in
preference to others. If the facts are understood, he will ordinarily
have no difficulty in judging the significance of the variety of names
proposed to express these facts. If, on the other hand, the student
approaches the subject with a ready-made set of names and definitions
learned by rote, he is in danger of perceiving his facts from one angle
only and through a distorted perspective.
MINERAL DEPOSITS AS MAGMATIC SEGREGATIONS IN IGNEOUS ROCKS
In this class are included deposits which crystallize within the body of
igneous rock, almost, if not quite, simultaneously with the adjacent
rock. These deposits form one of the main types of _syngenetic_
deposits.
The titaniferous magnetites constitute a widely distributed but at
present commercially unavailable class of iron ores. The magnetite
crystals of these deposits interpenetrate with the other constituents of
an igneous rock, commonly of a gabbro type, and the deposits themselves
are essentially igneous rocks. Their shapes are for the most part
irregular, their boundaries ill-defined, and their concentration
varying. While their magmatic origin is clear, there is little agreement
as to the precise conditions which determined their segregation in the
molten rock. There is often a tendency for the ores to follow certain
primary sheeted structures in the igneous mass, a fact for which the
reason is not obvious.
The Sudbury nickel ores, of Ontario, Canada, the principal source of the
world's nickel, lie mainly within and along the lower margin of a great
intrusive igneous mass of a basic type called _norite_, and locally the
ores project beyond the margin into adjacent rocks. Their textures and
their intercrystallization with the primary minerals of the igneous rock
have suggested that they are essentially a part of the norite mass, and
that they crystallized during some segregative processes which were
effective before the magma had solidified. Near the ores there are
likely to be granitic rocks, which, like the ores, seem to be
segregations from the norite magma. Locally both the ores and the
associated granitic rocks replace the main norite body in such a fashion
as to indicate their slightly later crystallization. However, the
intimate association of the ores with the primary minerals in the
magma, together with their absence from higher parts of the norite and
from the extraneous rocks far from the contact, indicate to other
investigators that they were not brought in from outside in vagrant
solutions which followed the intrusion of the main magma, but that they
were segregated within the magma essentially in place. The occurrence of
these heavy ores near the base of the norite naturally suggests that
they were segregated by sinking to the bottom of the molten magma, but
this conclusion implies certain physical conditions of the magma which
have not yet been proved. Again the precise nature of the process and
the part played in it by aqueous and gaseous solutions are subject to
some doubt and controversy. The settlement of this problem awaits the
solution of the more general problem of the origin and crystallization
of magmas.
In this general class of igneous deposits may be mentioned also
diamonds, platinum, chromite, corundum, and other mineral products,
although for the formation of commercial ores of many of these
substances further concentration by weathering and sedimentation has
been required.
Pegmatites are coarsely crystalline acid dike rocks which often
accompany a large igneous intrusion and which have obviously
crystallized somewhat later than the main igneous mass. They may
constitute either sharply delimited dikes or more irregular bodies which
grade into the surrounding igneous mass. They have a composition roughly
similar to the associated igneous rock, but usually a different
proportion of minerals. They are probably the result of the
differentiation of the parent magma. The pegmatites are of especial
interest to the economic geologist because of the frequency with which
they carry commercial minerals, such as the precious stones, mica,
feldspar, cassiterite (tin ore), and others. They show a complete
gradation from dikes of definitely igneous characteristics to veins
consisting largely of quartz in which evidence of igneous origin is not
so clear. The pegmatites thus afford a connecting link between ores of
direct igneous sources and ores formed as "igneous after-effects," which
are discussed in the next paragraph. Aplites are fine-grained acid
igneous rocks of somewhat the same composition as the pegmatites and
often show the same general relations to ores.
MINERAL DEPOSITS WITHIN AND ADJACENT TO IGNEOUS ROCKS WHICH WERE FORMED
IMMEDIATELY AFTER THE COOLING AND CRYSTALLIZATION OF THE MAGMAS THROUGH
THE AGENCY OF HOT MAGMATIC SOLUTIONS.
These deposits are closely associated in place and age with igneous
rocks, either intrusive or extrusive, and are usually considered to have
come from approximately the same source; and yet they afford distinct
evidence of having been deposited after the adjacent igneous rocks were
completely crystallized and fractured. They are thus _epigenetic_
deposits. They are not themselves igneous rocks and they do not
constitute pegmatites, but they often grade into pegmatites and belong
to the same general stage in the sequence of events. They include
deposits formed by contact metamorphism. They are sometimes designated
by the general term "igneous after-effects"--a term also applied in some
cases to pegmatites. Some geologists discriminate between "deep vein"
deposits (p. 43) and "contact-metamorphic" deposits, but the two are so
closely related in place and origin that for our purposes they will be
considered together.
The ores of this class are clearly deposited from vagrant solutions
which wander through openings of all kinds in the igneous rock and
outward into the adjacent country rocks. They also replace the wall
rocks; limestone is especially susceptible. This is a phase of contact
metamorphism. Some of the most important metalliferous deposits belong
in this class, including most of the gold, silver, copper, iron, lead
and zinc ores of the western United States and the copper deposits of
Lake Superior.
In general, ores of this class are more abundant about intrusive igneous
rocks, that is about igneous rocks which have stopped and cooled before
reaching the surface,--than in association with extrusive igneous rocks
which have poured over the surface as lava flows--but the latter are by
no means insignificant, including as they do such deposits as the Lake
Superior copper ores, the Kennecott copper ores of Alaska, some of the
gold-silver deposits of Goldfield and other Nevada camps, and many
others.
There is general similarity in the succession of events shown by study
of ore bodies related to intrusives. First, the invasion of the magma,
resulting in contact metamorphism of the adjacent rocks, sometimes with,
and often without conspicuous crowding effects on the invaded rocks;
second, the cooling, crystallization, and cracking of both the igneous
rock and the adjacent rock; third, the introduction of ore-bearing
solutions into these cracks,--sometimes as a single episode, sometimes
as a long continued and complex process forming various types of
minerals at successive stages. This order may in some cases be repeated
in cycles, and overlapping of the successive events is a common feature.
One of the interesting facts is the way in which the igneous mass has
invaded and extensively altered the country rocks in some mineral
districts,--in some cases by crowding and crumpling them, and in others
without greatly disturbing their structural attitudes. The latter is
illustrated in the Bingham district of Utah and the Philipsburg district
of Montana. In such cases there is so little evidence of crowding of the
country rocks as to raise the question how such large masses of
intrusives could be introduced without greater disturbing structural
effect. This leads naturally to consideration of the general problem of
the manner of progress of magmas through adjacent rocks,--a subject
which is still largely in the realm of speculation, but which is not
thereby eliminated from the field of controversy. Facts of this kind
seem to favor the position of certain geologists that magmas may
assimilate the rocks they invade.
EVIDENCE OF IGNEOUS SOURCE
No one ever saw one of these deposits in the process of formation; the
conclusion, therefore, that they originated from hot solutions, either
aqueous or gaseous, or both, which were essentially "after-effects" of
igneous activity and came from the same primary source as the associated
igneous rocks, is an inference based on circumstantial evidence of the
kind below summarized:
(1) The close association both in place and age with igneous rocks. This
applies not only to individual deposits, but to certain groups of
deposits which have common characteristics, and which constitute a
metallogenic province; also to groups of the same geologic age, which
indicate a metallogenic epoch (pp. 308-309). The association with
igneous rocks in one place might be a coincidence but its frequent
repetition can hardly be so explained. A zonal arrangement of minerals
about intrusives is often noted. Geologic evidence often shows the
processes of ore deposition to have been complete before the next
succeeding geologic event,--as for instance in the Tonopah district of
Nevada (p. 236), where the ores have been formed in relation to certain
volcanic flows and have been covered by later flows not carrying ore,
without any considerable erosion interval between the two events.
(2) The general contrast in mineralogical and chemical composition,
texture, and mineral associations, between these ore minerals and the
minerals known to be formed by ordinary surficial agencies under
ordinary temperatures. The latter carry distinctive evidences of their
origin. When, therefore, a mineral group is found which shows
contrasting evidences, it is clear that some other agencies have been at
work; and the natural assumption is that the solutions were hot rather
than cold; that they came from below rather than above.
(3) The contrast between the character and composition of these ores
(and their associated gangue) and the character and composition of the
wall rocks, together with the absence of leaching of the wall rocks,
favor the conclusion that the ore minerals are foreign substances
introduced from extraneous sources. The source not being apparent above
and the processes there observed not being of a kind to produce these
results, it is concluded that the depositing solutions were hot and came
from below.
(4) The fact that many of the ore minerals are never known to develop
under ordinary temperatures at the surface. For some of them,
experimental work has also indicated high temperature as a requisite to
their formation.
Quartz, which is a common associate of the ores and often constitutes
the principal gangue, serves as a geologic thermometer in that it
possesses an inversion point or temperature above which it crystallizes
in a certain form, below which in another. In deposits of this class it
has often been found to crystallize at the higher temperatures.
The quartz sometimes shows bubbles containing liquid, gas, and small
heavy crystals, probably of ferric oxide, as in the Clifton-Morenci
district of Arizona. It is clear that the ore-bearing solutions in
these cavities, before the crystallization of the heavy mineral
inclusions, held dissolved not only much larger quantities of mineral
substances than can be taken up by water at ordinary temperatures, but
also a substance like ferric oxide which is entirely insoluble under
ordinary cool conditions.
(5) The association of the ores with minerals carrying fluorine and
boron, with many silicate minerals, such as garnet, amphiboles,
pyroxenes, mica (sericite) and others, and with other minerals which are
known to be characteristic developments within or near igneous masses
and which are not known to form under weathering agencies at the
surface. Various characteristic groupings of these associated minerals
are noted. In limestone much of the mass may be replaced by garnet and
other silicates in a matrix of quartz. In igneous rock the ore-bearing
solutions may have altered the wall rock to a dense mixture of quartz,
sericite, and chlorite. Where sericite is dominant, the alteration is
called sericitic alteration. Where chlorite is important, it is
sometimes called chloritic or "propylitic" alteration. The chloritic
phases are usually farther from the ore deposit than the sericitic
phases, indicating less intense and probably cooler conditions of
deposition. Locally other minerals are associated with the ores, as, for
instance, in the Goldfield district of Nevada (p. 230), where alunite
replaces the igneous rock. Alunite is a potassium-aluminum sulphate,
which differs from sericite in that sulphur takes the place of silicon.
In the quartzites of the lead-silver mines of the Coeur d'Alene district
of Idaho (p. 212), siderite or iron carbonate is a characteristic gangue
material replacing the wall rock.
Quartz in some cases, as noted above, gives evidence of high temperature
origin and therefore of igneous association. Jasperoid quartz, as well
illustrated in the Tintic district of Utah (p. 235), may show texture
and crystallization suggestive of deposition from colloidal solution,--a
process which can occur under both cold and hot conditions, but which is
believed to be accelerated by heat.
Certain minerals, such as magnetite, ilmenite, spinel, corundum, etc.,
are often found as primary segregations within the mass of igneous rock.
These and other minerals, including minerals of tin and tungsten,
monazite, tourmaline, rutile, and various precious stones, are
characteristically developed in pegmatites, which are known to be
igneous rocks, crystallized in the later stages of igneous intrusion.
When, therefore, such minerals are found in other ore deposits an
igneous source is a plausible inference. For instance, in the copper
veins of Butte, Montana (p. 201), are found cassiterite (tin oxide) and
tungsten minerals. Their presence, therefore, adds another item to the
evidence of a hot-water source from below.
(6) The occasional existence of hot springs in the vicinity of these ore
deposits. Where hot springs are of recent age they may suggest by their
heat, steady flow, and mineral content, that they are originating from
emanations from the still cooling magmas. In the Tonopah camp (p. 236),
cold and hot springs exist side by side, exhibiting such contrasts as to
suggest that some are due to ordinary circulation from the surface and
that others may have a deep source below in the cooling igneous rocks.
This evidence is not conclusive. Hot springs in general fail to show
evidence of ore deposition on any scale approximating that which must
have been involved in the formation of this class of ore bodies. Much
has been made of the slight amounts of metallic minerals found in a few
hot springs, but the mineral content is small and the conclusion by no
means certain that the waters are primary waters from the cooling of
igneous rocks below.
In this connection the mercury deposits of California (p. 259),
contribute a unique line of evidence. In areas of recent lavas, mercuric
sulphide (cinnabar) is actually being deposited from hot springs of
supposed magmatic origin, the waters of which carry sodium carbonate,
sodium sulphide, and hydrogen sulphide,--a chemical combination known
experimentally to dissolve mercury sulphide. The oxidation and
neutralization of these hot-spring solutions near the surface throws out
the mercury sulphide. At the same time the sulphuric acid thus formed
extensively leaches and bleaches the surrounding rocks. Such bleaching
is common about mercury deposits. When it is remembered that the mercury
deposits contain minor amounts of gold and silver and sulphides of other
metals; that they are closely associated with gold and silver deposits;
and further that such gold, silver, and other sulphide deposits often
contain minor amounts of mercury,--it is easy to assume the possibility
that these minerals may likewise have had their origin in hot solutions
from below. The presence of mercury in a deposit then becomes suggestive
of hot-water conditions.
(7) Ores sometimes occur in inverted troughs indicating lodgment by
solutions from below, as, for instance, in the saddle-reef gold ores of
Nova Scotia and Australia, and in certain copper ores of the Jerome camp
of Arizona (p. 204.) This occurrence does not indicate whether the
solutions were hot or cold, magmatic or meteoric, but in connection with
other evidences has sometimes been regarded as significant of a magmatic
source beneath.
Perhaps no one of these lines of evidence is conclusive; but together
they make a strong case for the conclusion that the solutions which
deposited the ores of this class were hot, came from deep sources, and
were probably primary solutions given off by cooling magmas.
The conclusion that some ores are derived from igneous sources, based on
evidence of the kind above outlined, does not mean necessarily that the
ore is derived from the immediately adjacent part of the cooling magma.
In fact the evidence is decisive, in perhaps the majority of cases, that
the source of the mineral solutions was somewhat below; that these
solutions may have originated in the same melting-pot with the magma,
but that they came up independently and a little later,--perhaps along
the same channels, perhaps along others.
POSSIBLE INFLUENCE OF METEORIC WATERS IN DEPOSITION OF ORES OF THIS CLASS
It is hardly safe, with existing knowledge, to apply the above
conclusion to all ore deposits with igneous associations, or in any case
to eliminate entirely another agency,--namely, ground-waters of surface
or meteoric origin, which are now present and may be presumed often to
have been present in the rocks into which the ores were introduced. Such
waters may have been heated and started in vigorous circulation by the
introduction of igneous masses, and thereby may have been enabled to
effectively search out and segregate minutely disseminated ore particles
from wide areas. This has been suggested as a probability for the
Kennecott copper ores of Alaska (p. 200) and for the copper ores of Ely,
Nevada. In the Goldfield camp (p. 230) the ores are closely associated
with alunite in such a manner as to suggest a common origin. It has been
found difficult to explain the presence of the alunite except through
the agency of surface oxidizing waters acting on hydrogen sulphide
coming from below.
In the early days of economic geology there was relatively more emphasis
on the possible effectiveness of ground-waters in concentrating ores of
this type. With the recognition of evidence of a deeper source related
to magmas, the emphasis has swung rapidly to the other extreme. While
the evidence is sound that the magmatic process has been an important
one, it is difficult to see how and to just what extent this process may
have been related to the action of ground-waters,--which were probably
present in a heated condition near the contact. It may never be possible
to discriminate closely between these two agencies. It seems likely that
at some stages the two were so intimately associated that the net result
of deposition cannot be specifically assigned either to one or to the
other.
ZONAL ARRANGEMENT OF MINERALS RELATED TO IGNEOUS ROCKS
Evidence is accumulating in many mining districts that ore deposits of
these igneous associations were deposited with a rough zonal arrangement
about the igneous rock. At Bingham, Tintic, and Butte (pp. 204, 208,
235), copper ores are on the whole closest to the igneous rock, and the
lead, zinc, and silver ores are farther away. Furthermore, the quartz
gangue near the igneous rock is likely to contain minerals
characteristic of hot solutions, while farther away such minerals as
dolomite and calcite appear in the gangue, suggestive of cooler
conditions. In Cornwall (p. 262), tin ores occur close to the
intrusives, and lead-silver ores farther away. The gradations are by no
means uniform; shoots of one class of ore may locally cut abruptly
across or through those of another class.
The existence of zones horizontally or areally arranged about intrusives
suggests also the possibility of a vertical zonal arrangement with
reference to the deep sources of the solutions. Of course when secondary
concentration from the surface, described later, is taken into account,
there may be a marked zonal distribution in a vertical direction, but
this is not primary zoning. A few veins and districts show evidence of
vertical zoning apparently related to primary deposition; for the most
part, however, in any one mine or camp there is yet little evidence of
primary vertical zoning. On the other hand, certain groups of minerals
are characteristic of intense conditions of heat and pressure, as
indicated by the coarse recrystallization and high degree of
metamorphism of the rocks with which they are associated; and other
groups have such associations as to indicate much less intense
conditions of temperature and pressure. Depth is only one factor
determining intensity of conditions, but it affords a convenient way to
indicate them; so mineral deposits associated with igneous rocks are
sometimes classified by economic geologists on the basis of deep,
intermediate, and shallow depths of formation.
There are a considerable number of minerals which are formed in all
three of these zones, although in differing proportions. There are
comparatively few which are uniformly characteristic of a single zone.
On the whole, it is possible to contrast satisfactorily mineral deposits
representing very intense metamorphic conditions, usually associated
with formation at great depth, with those formed at or near the surface;
but there are many deposits with intermediate characteristics which it
is difficult to place satisfactorily.
The accessible deposits of the deep zone are associated with plutonic
igneous rocks which have been deeply eroded, and not with surface lavas.
They are characterized by minerals of gold, tin, iron, titanium, zinc,
and copper, and sometimes of tungsten and molybdenum, in a gangue of
quartz, which contains also minerals such as garnet, corundum,
amphibole, pyroxene, tourmaline, spinel, and mica. The deep-zone
minerals are not unlike the pegmatite minerals in their grouping and
associations.
Deposits formed at shallow depths are related to extrusive rocks and to
intrusives near the surface. Erosion has not been deep. Mercury, silver
and gold (tellurides, native metals, and silver sulphides), antimony,
lead, and zinc minerals are characteristic, together with alunite,
adularia, and barite. Metallic copper also is not infrequent. Very often
the gangue material is more largely calcite than quartz, whereas calcite
is not present in the deep zone.[5]
The trend of evidence in recent years has favored the conclusion that
the principal ores associated with igneous rocks have not developed at
very great depths. Even within our narrow range of observation there is
a difference in favor of the shallower depths, and the greatest depths
we can observe are after all but trivial on the scale of the earth.
A survey of the ore deposits of Utah has suggested the generalization
that ores are more commonly related to intrusive stocks than to the
forms known as laccoliths, and that within and about intrusive stocks
the ores are much more abundant near the top or apex of a stock than
lower down.[6] In parts of the region where erosion has removed all but
the deeper portions of the stocks, ore bodies are less abundant. It will
be of interest to follow the testing of this generalization in other
parts of the world.
The scientist is constantly groping for underlying simple truth. Such
glimpses of order and symmetry in the distribution of ore around igneous
rocks as are afforded by the facts above stated, tempt the imagination
to a conception of a simple type or pattern of ore distribution around
intrusions. For this reason we should not lose sight of the fact that,
in the present state of knowledge, the common and obvious case is one of
irregular and heterogeneous distribution, and that there are many
variations and contradictions even to the simplest generalization that
can be made. The observer is repeatedly struck by the freakish
distribution of ores about igneous masses, as compared with their
regularity of arrangement under sedimentary processes to be discussed
later. It is yet unexplained how an intrusive like the Butte granite can
produce so many different types of ores at different places along its
periphery or within its mass, and yet all apparently under much the same
general conditions and range of time. It is difficult also to discern
the laws under which successive migrations of magma, from what seems to
be a single deep-seated source or melting-pot, may carry widely
contrasting mineral solutions. Far below the surface, beyond our range
of observation, it is clear that there is a wonderful laboratory for the
compounding and refinement of ores, but as to its precise location and
the nature of its processes we can only guess.
Other features of distribution of minerals associated with igneous rocks
are indicated by their grouping in metallogenic provinces and epochs
(see pp. 308-309).
THE RELATION OF CONTACT METAMORPHISM TO ORE BODIES OF THE FOREGOING CLASS.
The deposition of ores of igneous source in the country rock into which
the igneous rocks are intruded is a phase of contact metamorphism.
Ordinarily where this deposition occurs there are further extensive
replacements and alterations of the country rock, resulting in the
development of great masses of quartz, garnet, pyroxene, amphibole, and
other silicates, and in some cases of calcite, dolomite, siderite,
barite, alunite, and other minerals. Looked at broadly, the deposition
of ores at igneous contacts under contact metamorphism is a mere
incident in the much more widespread and extensive alterations of this
kind. Hence it is that the subject of contact metamorphism is of
interest to economic geologists. The minerals here formed which do not
constitute ores throw much light on the nature of the ore-bearing
solutions, the conditions of temperature and pressure, and the processes
which locally and incidentally develop the ore bodies. The subject,
however, is a complex one, the full discussion of which belongs in
treatises on metamorphism.[7] We may note only a few salient features.
For many hundreds of yards the rocks adjacent to the intrusions may be
metamorphosed almost beyond recognition. This is especially true of the
limestone, which may be changed completely to solid masses of quartz and
silicates. The shales and sandstones are ordinarily less vitally
affected. The shales become dense, highly crystalline rocks of a
"hornstone" type, with porphyritic developments of silicate minerals.
The sands and sandstones become highly crystalline quartzites, spotted
with porphyritic developments of silicates. Occasionally even these
rocks may be extensively replaced by other minerals, as in the Coeur
d'Alene district, where quartzites adjacent to the ore veins may be
completely replaced by iron carbonate.
A question of special interest to economic geologists is the source of
the materials for the new minerals in these extensively altered zones.
In some cases the minerals are known to be the result of
recrystallization of materials already in the rock, after the
elimination of certain substances such as carbon dioxide and lime, under
the pressures and temperatures of the contact conditions. In such cases
there has obviously been large reduction in volume to close the voids
created by the elimination of substances. In the majority of cases, the
new substances or minerals are clearly introduced from the igneous
source, replacing the wall rock volume for volume so precisely that such
original textures and structures as bedding are not destroyed. In many
cases the result is clearly due to a combination of recrystallization of
materials already present and introduction of minerals by magmatic
solutions from without. So obvious is the evidence of the introduction
of materials from without, that there has been a tendency in some
quarters to overlook the extensive recrystallization of substances
already present; and the varying emphasis placed on these two processes
by different observers has led to some controversy.
SECONDARY CONCENTRATION IN PLACE OF THE FOREGOING CLASSES OF MINERAL
DEPOSITS THROUGH THE AGENCY OF SURFACE SOLUTIONS
Mineral deposits of direct magmatic segregation are seldom much affected
by surficial alteration, perhaps because of their coarse crystallization
and their intermingling with resistant crystalline rocks. Mineral
deposits of the "igneous after-effect" type may be profoundly altered
through surficial agencies. The more soluble constituents are taken
away, leaving the less soluble. The parts that remain are likely to be
converted into oxides, carbonates, and hydrates, through reaction with
oxygen, carbon dioxide, and water, which are always present at the
surface and at shallow depths. These processes are most effective at the
surface and down to the level of permanent ground-water, though locally
they may extend deeper. This altered upper part of the ore bodies is
usually called the _oxide zone_. It may represent either an enrichment
or a depletion of ore values, depending on whether the ore minerals are
taken into solution less rapidly or more rapidly than the associated
minerals and rocks; all are removed to some extent. In certain deposits,
there is evidence that both zinc and copper have been taken out of the
upper zone in great quantity; but they happen to be associated with
limestone, which has dissolved still more rapidly, with the result that
there is a residual accumulation of copper and zinc values. Manganese,
iron, and quartz are usually more resistant than the other minerals and
tend to remain concentrated above. The same is true to some extent of
gold and silver. The abundance of iron oxide thus left explains the name
"iron cap" or "gossan" so often applied to the upper part of the oxide
zone. Not infrequently, and especially in copper ores, the upper part of
the oxide zone is nearly or entirely barren of values and is called the
_capping_.
The depth or thickness of the oxide zone depends on topography, depth of
water table, climatic conditions, and speed of erosion. A fortunate
combination of conditions may result in a deep oxide zone with important
accumulations of values. In other cases erosion may follow oxidation so
rapidly as to prevent the growth of a thick oxide zone.
It is clear from the study of many ore deposits that the process of
oxidation has not proceeded uniformly to the present, but has depended
upon a fortunate combination of factors which has not been often
repeated during geologic time. As illustrative of this, the principal
oxidation of the Bisbee copper ores of Arizona (p. 204) occurred before
Tertiary time, with reference to a place that has since been covered by
later sediments. The conditions in the Ray, Miami, and Jerome copper
camps of Arizona (pp. 203-205) likewise indicate maximum oxidation at an
early period. The Lake Superior iron ore deposits (pp. 167-170) were
mainly concentrated before Cambrian time, during the base-leveling of a
mountainous country in an arid or semi-arid climate. The oxide zone of
these deposits has no close relation to the present topography or to the
present ground-water level. In the Kennecott (Alaska) copper deposits
all oxidation has been stopped since glacial time by the freezing of the
aqueous solutions. At Butte and at Bingham the main concentration of the
ores is believed to have occurred in an earlier physiographic cycle than
the present one. The _cyclic_ nature of the formation of oxide zones is
of comparatively recent recognition, and much more will doubtless be
found out about it in the comparatively near future. Its practical
bearing on exploration is obvious (see p. 325).
It should be clearly recognized that oxidizing processes are not limited
to the zone above the ground-water level. Locally oxidizing solutions
may penetrate and do effective work to much greater depths, especially
where the rocks traversed at higher elevations are of such composition
or in such a stage of alteration as not to extract most of the oxygen.
Consequently the presence of oxide ores below the water table is not
necessarily proof that the water table has risen since their formation.
On the other hand, the facts of observation do indicate generally a
marked difference, in circulation and chemical effect, between waters
above and below this horizon, and show that oxidation is dominantly
accomplished above rather than below this datum surface.
During the formation of the oxide zone, erosion removes some of the ore
materials entirely from the area, both mechanically and in solution.
Part of the material in solution, however, is known to penetrate
downward and to be redeposited in parts of the ore body below the oxide
zone,--that is, usually below the water table. Evidence of this process
is decisive in regard to several minerals. Copper is known to be taken
into solution as copper sulphate at the surface, and to be redeposited
as chalcocite where these sulphate solutions come in contact with
chalcopyrite or pyrite below. Not only has the process been duplicated
in the laboratory, but the common coating of chalcocite around grains of
pyrite and chalcopyrite below the water level indicates that this
process has been really effective. Sulphides of zinc, lead, silver, and
other metals are similarly concentrated, in varying degrees. The zone of
deposition of secondary sulphides thus formed is called the zone of
_secondary sulphide enrichment_. Ores consisting mainly of secondary
sulphides are also called _supergene_ ores (p. 33). In some deposits, as
in the copper deposits of Ray and Miami, there is found, below the
secondary sulphide zone, a lean sulphide zone which is evidently of
primary nature. The mineralized material of this zone, where too lean to
mine, has been called a _protore_.
With the discovery of undoubted evidence of secondary sulphide
enrichment, there was a natural tendency to magnify its importance as a
cause of values. Continued study of sulphide deposits, while not
disproving its existence and local importance, has in some districts
shown clearly that the process has its limitations as a factor in ore
concentration, and that it is not safe to assume its effectiveness in
all camps or under all conditions. At Butte for instance, secondary
chalcocite is clearly to be recognized. The natural inference was that
as the veins were followed deeper the proportion of chalcocite would
rapidly diminish, and that a leaner primary zone of chalcopyrite,
enargite and other primary minerals would be met. However, the great
abundance of chalcocite in solid masses which have now been proved to a
depth of 3500 feet, far below the probable range of waters from the
surface in any geologic period, seems to indicate that much of the
chalcocite is primary. The present tendency at Butte is to consider as
secondary chalcocite only certain sooty phases to be found in upper
levels. The solid masses of chalcocite in the Kennecott copper mines
seem hardly explainable as the result of secondary sulphide enrichment.
No traces of other primary minerals are present and the chalcocite here
is regarded as probably primary.
The possible magnification of the process of secondary enrichment above
referred to has had for its logical consequence a tendency to
over-emphasize the persistence of primary ores in depth. The very use of
the terms "secondary" and "primary" has suggested antithesis between
surficial and deep ores. Progress in investigation, as indicated on
previous pages, seems to indicate that the primary ores are not
uniformly deep and that in many cases they are distinctly limited to a
given set of formations or conditions comparatively near the surface.
In general the processes of oxidation and secondary sulphide enrichment
have been studied mainly by qualitative methods with the aid of the
microscope and by considerations of possible chemical processes. These
methods have disclosed the nature but not the quantitative range and
relations of the different processes. Much remains to be done in the way
of large scale quantitative analysis of ores at different depths, as a
check to inferences drawn by other methods. One may know, for instance,
that a mineral is soluble and is actually removed from the oxide zone
and redeposited below. The natural inference, therefore, is that the
mineral will be found to be depleted above and enriched below. In many
cases its actual distribution is the reverse,--indicating that this
process has been only one of the factors in the net result, the more
rapid solution and deposition of other materials being another factor.
If one were to approach the study of the concentration of iron ores with
the fixed idea of insolubility of quartz from a chemical standpoint, and
were to draw conclusions accordingly, he would fail to present a true
picture of the situation. While quartz is insoluble as compared with
most minerals, it is nevertheless more soluble than iron oxide, and
therefore the net result of concentration at the surface is to
accumulate the iron rather than the silica. Descriptions of enrichment
processes as published in many reports are often misleading in this
regard. They may be correct in indicating the actual existence of a
process, but may lead the reader to assumptions as to net results which
are incorrect.
RESIDUAL MINERAL DEPOSITS FORMED BY THE WEATHERING OF IGNEOUS ROCKS IN
PLACE
Igneous rocks not containing mineral deposits may on weathering change
to mineral deposits. The lateritic iron ores such as those of Cuba (p.
172), many bauxite deposits, many residual clays, and certain chromite
and nickel deposits are conspicuous representatives of this class. The
chemical and mineralogical changes involved in the formation of these
deposits are pretty well understood. Certain constituents of the
original rock are leached out and carried away, leaving other
constituents, as oxides and hydrates, in sufficiently large percentage
in the mass to be commercially available. The accumulation of large
deposits depends on the existence of climatic and erosional conditions
which determine that the residual deposit shall remain in place rather
than be carried off by erosion as fast as made. In the glaciated parts
of the world, deposits of this nature have usually been removed and
dispersed in the glacial drift.
When the minerals of these deposits are eroded, transported, and
redeposited in concentrated form, they come under the class of placer or
sedimentary deposits described under the following heading. There are of
course many intermediate stages, where the residual deposit is only
locally moved and where the distinction between this class of deposits
and that next described is an arbitrary one.
MINERAL DEPOSITS FORMED DIRECTLY AS PLACERS AND SEDIMENTS
Mineral deposits of this class are of large value, including as they do
salt, gypsum, potash, sulphur, phosphates, nitrates, and important
fractions of the ores of iron, manganese, gold, tin, tungsten, platinum,
and precious stones; also many common rocks of commercial importance.
The minerals of these deposits are derived from the weathering and
erosion of land surfaces, either igneous or sedimentary. They are
deposited both under air and under water, both mechanically and
chemically (in part by the aid of organisms). These deposits form the
principal type of _syngenetic_ deposits (p. 32); the term _sedigenetic_
deposits has also been applied to them.
MECHANICALLY DEPOSITED MINERALS
Mechanical erosion of preëxisting mineral deposits or rocks and their
transportation, sorting, and deposition are responsible for the placers
of gold, tin, tungsten, platinum, and various precious stones, and for
certain iron sands and conglomerates. Sands, sandstones, shales, and
certain clays and bauxites also belong in this group. These deposits may
be formed under air or under water, and under various climatic and
topographic conditions. During the process of formation the minerals of
differing density are more or less sorted out and tend to become
segregated in layers. The process is not unlike the artificial process
of mechanical concentration where ores are crushed, shaken up, and
treated with running water. The process is most effective for minerals
which are resistant to abrasion and to solution, and of such density as
to differentiate them from the other minerals of the parent rock.
The origin of deposits of this kind is fairly obvious where they are of
recent age and have not been subsequently altered or buried. A
considerable amount of experimental work has brought out clearly the
main elements of the processes. Physiographic and climatic conditions
play an important part, and cannot be safely overlooked by anyone
studying such deposits.
Extensive copper deposits exist as sediments (pp. 205-206). It is not
clear to what extent they are mechanically or to what extent chemically
deposited. For the most part the concentration of copper in this manner
has not been sufficient to yield deposits of large commercial value; the
mineral is too much dispersed. Relatively small amounts are mined in the
Mansfield shales of Germany and the Nonesuch shales and sandstones of
the Lake Superior country.
The Clinton and similar iron ores of the United States and Newfoundland,
the pre-Cambrian iron ores of Brazil, and the Jurassic iron ores of
England and western Europe (pp. 166-167) are now commonly agreed to be
direct sedimentary deposits in which mechanical agencies of sorting and
deposition played a considerable part. How far chemical and bacterial
agencies have also been effective is not clear. The climatic,
topographic, and other physiographic and sedimentary conditions which
cause the deposition of this great group of ores present one of the
great unsolved problems of economic geology. The study of present-day
conditions of deposition affords little clue as to the peculiar
combination of conditions which was necessary to accomplish such
remarkable results in the past.
On the whole, minerals of this mechanically deposited group are not
greatly affected by later surficial alteration and concentration,
because, having already been subjected to weathering, they are in a
condition to resist such influences.
CHEMICALLY AND ORGANICALLY DEPOSITED MINERALS
The products of surface weathering and erosion are in part carried away
in chemical solution and redeposited as sediments. Sediments thus formed
include limestone and dolomite, siderite, salt, gypsum, potash, sulphur,
phosphates, nitrates, and other minerals. Precipitation may be caused by
chemical reactions, by organic secretion, or by evaporation of the
solutions. The processes are qualitatively understood and it is usually
possible to ascertain with reasonable accuracy the conditions of depth
of water, relation to shore line, climate, nature of erosion, and other
similar factors; yet the vast scale of some of these deposits, and their
erratic areal and stratigraphic distribution, present unsolved problems
as to the precise combinations of factors which have made such results
possible.
Chemically and organically deposited minerals of this class are usually
susceptible to further alteration by surface weathering, and some of
them, for instance the phosphates and siderites, are thus secondarily
concentrated. These processes are discussed under the next heading.
In general the great unsolved problem of the origin of the entire group
of mineral deposits in placers and sediments relates to the scale of the
results. Observation of present-day processes and conditions of
deposition of these minerals affords satisfactory evidence of their
nature, but fails to give us a clear idea of the precise combinations of
agencies and conditions necessary to produce such vast results as are
represented by the mineral deposits. For example, solution of iron on a
land surface and redeposition in bogs and lagoons (as actually observed
to be taking place today) show how some iron-ore sediments may be
formed; but these processes are entirely inadequate to explain the
deposition of iron ores in thick masses over broad areas without
intermingling of other sediments--as represented by the Clinton iron
ores of North America, the Jurassic ores of Europe and England, and the
ancient iron ores of Brazil. The Paleozoic seas in northern and eastern
United States encroached over land areas to the north and east and
deposited ordinary sediments such as sandstone, shale, and limestone.
Suddenly, without, so far as known, tapping any new sources of supply on
the ancient land areas, and without any yet ascertainable change in
topographic or climatic conditions, they deposited enormous masses of
iron ore. There is clearly some cyclic factor in the situation which we
do not yet understand.
The various deposits of salt, gypsum, potash, sulphur, and other
minerals are known to be the result of evaporation, and the deposition
of each of these minerals is known to be related to the degree of
evaporation as well as to temperature, pressure, and factors such as
mass action and crystallization of double salts. The nature of the
processes is fairly well understood; but again, observation of the
present-day operation of these processes fails to give us much clue to
the enormous accumulations at certain times and places in the past. It
is difficult to say just what conditions of climate, in combination with
particular physiographic factors, could have preserved uniformity of
conditions for the long periods necessary to account for some of the
enormously thick salt deposits. Again some cyclic factor in the
situation remains to be worked out.
SEDIMENTARY MINERAL DEPOSITS WHICH HAVE REQUIRED FURTHER CONCENTRATION
TO MAKE THEM COMMERCIALLY AVAILABLE
The conditions for the direct deposition of sedimentary mineral deposits
of the foregoing class are also responsible for the deposition of
minerals in more dispersed or disseminated form, requiring further
concentration through surface agencies to render them commercially
available. Some of these deposits are discussed below.
The lead and zinc ores of the Mississippi Valley, Virginia, Tennessee,
Silesia, Belgium, and Germany (pp. 211-212, 216-219) are in sedimentary
rocks far removed from igneous sources. Lead and zinc were deposited in
more or less dispersed form with the enclosing sediments. It is supposed
that deposition was originally chemical and was favored by the presence
of organic material, which is a rather common accompaniment of the
sediments. It is supposed further that these organic participants were
originally localized during sedimentation in so-called estuarine
channels and shore-line embayments. When subsequently exposed to
weathering, the lead and zinc minerals were dissolved and redeposited in
more concentrated form in fissures and as replacements of limestone.
Agreement as to origin of these deposits, so far as it exists, does not
go beyond these broad generalizations. There is controversy as to
whether the original sources of the ore minerals were the sediments
directly above, from which the mineral solutions have been transferred
downward during weathering and erosion, or whether the original minerals
were below and have been transferred upward by artesian circulation, or
whether they were situated laterally and have been brought to their
present position by movement along the beds, or whether there has been
some combination of these processes. It is the writer's view that the
evidence thus far gathered favors on the whole the conclusion of direct
downward concentration from overlying sources which have been removed by
erosion, although this conclusion fails to explain why certain sulphide
deposits give so little evidence of important downward transfer from
their present position. This matter is further discussed on pages
216-219. The choice of the various alternatives has some practical
bearing on exploration.
Since these ores were brought into approximately their present
position, they have undergone considerable oxidation near the surface
and secondary sulphide enrichment below. The chemical and mineralogical
changes are pretty well understood, but the quantitative range of these
changes and their relative importance in determining the net result are
far from known. Undoubted evidence of secondary sulphide enrichment has
led in some quarters to an assumption of effectiveness in producing
values which is apparently not borne out by quantitative tests.
A group of mineral deposits in sandstones in Utah is regarded as due to
chemical concentration of material originally disseminated in the rock.
They include silver, copper, manganese, uranium, and radium deposits.
The Silver Reef deposits, including silver, copper, uranium, and
vanadium, are commercially the most important of this type.[8] The ore
minerals are commonly associated with carbonized material representing
plant remains, and have replaced the calcareous and cementing material
of the rock, and also some of the quartz grains. The deposits are
regarded as having been formed by circulating waters which collected the
minerals disseminated through the sedimentary rocks, and deposited them
on contact with carbonaceous matter, earlier sulphides, or other
precipitating agents. The circulation in some places is believed to have
been of artesian character and to have been controlled to a large extent
by structural features. The Silver Reef deposits are near the crest of a
prominent anticline. Most of the minerals have been later altered by
surface solutions.
Another great group of ores to be considered under this head are the
iron ores of Lake Superior,--which were originally deposited as
sediments, called jaspers or iron formations, with too low a percentage
of iron to be of use, and which have required a secondary concentration
by surficial agencies to render them valuable. The process of
concentration has been a simple one. The iron minerals have been
oxidized in place and the non-ferrous minerals have been leached out,
leaving iron ores. This process contrasts with the concentration
described above, in that there is little evidence of collection of iron
minerals from disseminated sources. The Lake Superior iron ores are
essentially residual concentrations in place. The outstanding problems
of secondary concentration relate to the structural features which
determined the channels through which the oxidizing and leaching waters
worked, and to the topographic and climatic conditions which existed at
the time the work was done. As with many other classes of ores, it was
first assumed that these processes were related to the present erosion
surface; but it is now known that concentration happened long ago under
conditions far different from those now existing. These deposits
contribute to the rapidly accumulating evidence of the _cyclic_ nature
of ore concentration.
Our least satisfactory knowledge of the Lake Superior ores relates to
the peculiar conditions which determined the initial stage of
sedimentation of the so-called iron formation. As in the case of the
Clinton iron ores, no present-day sedimentation gives an adequate clue.
Students of the problem have fallen back on the association of the iron
formation with contemporaneous volcanic rocks, as affording a possible
explanation of the wide departure from ordinary conditions of
sedimentation evidenced by these formations.[9]
Coal deposits are direct results of sedimentation of organic material.
They are mainly accumulations of vegetable matter in place. To make them
available for use, however, they undergo a long period of condensation
and distillation. Conditions of primary deposition may be inferred from
modern swamps and bogs; but, as in the case of sediments described under
the preceding heading, we are sometimes at a loss to explain the
magnitude of the process, and especially to explain the maintenance of
proper surface conditions of plant growth and accumulation for the long
periods during which subsidence of land areas and encroachment of seas
are believed to have been taking place. The processes of secondary
concentration are also understood qualitatively, but much remains to be
learned about the influences of pressure and heat, the effect of
impervious capping rocks, and other factors.
Various oil shales and asphaltic deposits are essentially original
sediments which have subsequently undergone more or less decay and
distillation. The migration of the distillates to suitable underground
reservoirs is responsible for the accumulation of oil and gas pools.
Oil and gas are distillates from these oil shales and asphaltic
deposits, and also from other organic sediments such as carbonaceous
limestones. The distillates have migrated to their present positions
under pressure of ground-waters. The stratigraphic horizons favorable to
their accumulation are generally recognized. The geologist is concerned
in identifying these horizons and in ascertaining where they exist
underground. He is further concerned in analysis of the various
structural conditions which will give a clue to the existence of local
reservoirs in which the oil or gas may have been accumulated. So
capricious are the oil migrations that the most intensive study of these
conditions still leaves vast undiscovered possibilities.
ANAMORPHISM OF MINERAL DEPOSITS
Mineral deposits formed in any one of the ways indicated above may
undergo repeated vicissitudes, both at the surface and deep below the
surface, with consequent modifications of character. They may be
cemented or replaced by introduction of mineral solutions from without.
They may be deformed by great earth pressures, undergoing what is called
dynamic metamorphism (pp. 25-27), which tends to distort them and give
them schistose and crystalline characters. They may be intruded by
igneous rocks, causing considerable chemical, mineralogical, and
structural changes. All these changes may take place near the surface,
but on the whole they are more abundant and have more marked effects
deep below the surface.
In general all these changes of the deeper zone tend to make the rocks
more crystalline and dense and to make the minerals more complex.
Cavities are closed. The process is in the main an integrating and
constructive one which has been called _anamorphism_, to contrast it
with the disintegrating and destructive processes near the surface,
which have been called _katamorphism_ (see also pp. 27-28). There is
little in the process of anamorphism in the way of sorting and
segregation which tends to enrich and concentrate the metallic ore
bodies. On the contrary the process tends to lock up the valuable
minerals in resistant combinations with other substances, making them
more difficult to recover in mining. Later igneous intrusions or the
ordinary ground-waters may bring in minerals which locally enrich ores
under anamorphic conditions, but these are relatively minor effects. An
illustration of the general effect is afforded by a comparison of the
Cuban iron ores, which are soft and can be easily taken out, with the
Cle Elum iron ores of Washington, which seem to be of much the same
origin, but which have subsequently been buried by other rocks and
rendered hard and crystalline. In the first case the ores can be mined
easily and cheaply with steam shovels at the surface. In the second,
underground methods of mining are required, which cost too much for the
grade of ore recovered.
On the other hand, the same general kind of anamorphic processes, when
applied to coal, result in concentration and improvement of grade. The
same is true up to a certain point in the concentration of oil; but
where the process goes too far, the oil may be lost (pp. 140-141).
CONCLUSION
Mineral deposits are formed and modified by practically all known
geologic processes, but looked at broadly the main values are produced
in three principal ways:
(1) As after effects of igneous intrusion, through the agency of aqueous
and gaseous solutions given off from the cooling magma.
(2) Through the sorting processes of sedimentation,--the same processes
which form sandstone, shale, and limestone. Organic agencies are
important factors in these processes.
(3) Through weathering of the rock surface in place, which may develop
values either by dissolving out the valuable minerals and redepositing
them in concentrated form, or by dissolving out the non-valuable
minerals and leaving the valuable minerals concentrated in place. The
latter process is by far the more important.
The overwhelming preponderance of values of mineral deposits as a whole
is found in the second of the classes named.
Under all these conditions it appears that the maximum results are
obtained at and near the surface. On the scale of the earth even the
so-called deep veins may be regarded as deposits from solutions reaching
the more open and cooler outer portions of the earth. However, valuable
mineral deposits are found in the deepest rocks which have been exposed
by erosion, and the question of what would be found at still greater
depths, closer to the center of the earth, is a matter of pure
speculation.
Ultimately all minerals are derived from igneous sources within the
earth. The direct contributions from these sources are only in small
part of sufficient concentration to be of value; for the most part they
need sorting and segregation under surface conditions.
We can only speculate as to causes of the occurrence of valuable
minerals in certain igneous rocks and not in others. Many granites are
intruded into the outer shell of the earth, but only a few carry
"minerals"; also, of a series of intrusions in the same locality, only
one may carry valuable minerals. It is clear that in some fashion these
minerals are primarily segregated within the earth. Causes of this
segregation are so involved with the problem of the origin of the earth
as a whole that no adequate explanation can yet be offered. Our
inductive reasoning from known facts is as yet limited to the
segregation within a given mass of magma, and even here the conditions
are only dimly perceived. A discussion of these ultimate problems is
beyond the scope of this book.
FOOTNOTES:
[4] Ransome, Frederick Leslie, Copper deposits near Superior, Arizona:
_Bull. 540, U. S. Geol. Survey_, 1914, pp. 152-153; The copper deposits
of Ray and Miami, Arizona: _Prof. Paper 115, U. S. Geol. Survey_, 1919,
p. 156; Discussion: _Econ. Geol._, vol. 8, 1913, p. 721.
[5] For more specific definitions of vertical zones of ore deposition in
association with igneous rocks see Spurr, J. E., Theory of ore
deposition: _Econ. Geol._, vol. 7, 1912, pp. 489-490; Lindgren, W.,
_Mineral deposits_, McGraw-Hill Book Co., 2d ed., 1919, Chapters
XXIV-XXVI; and Emmons, W. H., _The principles of economic geology_,
McGraw-Hill Book Co., 1918, Chapters VI-VIII.
An excellent discussion of a case of vertical and areal zoning of
minerals is contained in _Ore deposits of the Boulder batholith of
Montana_, by Paul Billingsley and J. A. Grimes, Bull. Am. Inst. Min.
Engrs., vol. 58, 1918, pp. 284-368.
[6] Butler, B. S., Loughlin, G. F., Heikes, V. C., and others, The ore
deposits of Utah: _Prof. Paper 111, U. S. Geol. Survey_, 1920, p. 201.
[7] Leith, C. K., and Mead, W. J., _Metamorphic Geology_, Pt. 2, Henry
Holt and Company, New York, 1915.
[8] Butler, B. S., Loughlin, G. F., Heikes, V. C., and others, The ore
deposits of Utah: _Prof. Paper 111, U. S. Geol. Survey_, 1920, pp.
152-158.
[9] Van Hise, C. R., and Leith, C. K., Geology of the Lake Superior
region. _Mon. 52, U. S. Geol. Survey_, 1911, pp. 506-518; and references
there given.
CHAPTER IV
MINERAL RESOURCES--SOME GENERAL QUANTITATIVE CONSIDERATIONS
Of the 1,500 known mineral species, perhaps 200 figure in commerce as
mineral resources.
For the mineral substances used commercially, the term "mineral" is used
in this chapter with a broad significance to cover any or all of the
materials from which the needed elements are extracted,--whether these
materials be single minerals or groups of minerals; whether they be
rocks or ores; whether they be liquid or solid.
The following figures are generalizations based on the miscellaneous
information available. The purpose is to indicate the general
perspective rather than the detail which would be necessary for precise
statement.
WORLD ANNUAL PRODUCTION OF MINERALS IN SHORT TONS
Exclusive of water, but inclusive of petroleum, the world's annual
output of mineral resources amounts to two billions of tons. This figure
refers to the crude mineral as it comes from the ground and not to the
mineral in its concentrated form.
Of this total extraction, coal amounts to nearly 70 per cent, stone and
clay 10 per cent, iron ore about 9 per cent, petroleum 4 per cent,
copper ore 3 per cent, and all the remaining minerals constitute less
than 6 per cent.
If spread out on the surface in a uniform mass with an estimated average
density based on relative proportions of the crude minerals, this annual
production would cover a square mile to a depth of 2,300 feet.
Of the total annual production 85 per cent comes from countries
bordering the North Atlantic basin; 75 per cent is accounted for by the
United States, England, and Germany; the United States has 39 per cent
of the total, England 18 per cent, and Germany 18 per cent. By
continents, Europe accounts for nearly 51 per cent, North America for
nearly 42 per cent, Asia for nearly 4 per cent, and the remaining
continents for nearly 4 per cent. The United States mineral production
in recent years has been about 900,000,000 tons.
According to the United States census of 1920, nearly half of all the
establishments or businesses engaged in quarrying or mining operations
in this country are operating in oil and gas.
Of the crude materials extracted from the ground perhaps 10 per cent,
including gold, silver, copper, lead, zinc, nickel, and other ores, are
concentrated mainly at the mine, with the result that this fraction of
the tonnage in large part does not travel beyond the mine. About 90 per
cent of the total production, therefore, figures largely in the
transportation of mineral resources.
It is estimated that roughly two-thirds of the annual world production
is used or smelted within the countries of origin, the remaining
one-third being exported. Of the minerals moving internationally, coal
and iron constitute 90 per cent of the tonnage.
The metal smelting capacity of the world in terms of yearly production
of crude metal is estimated at nearly 100,000,000 short tons. Of this
amount about 80 per cent is located in the United States, England, and
Germany. The United States alone has over half of the total. Of the
oil-refining capacity the United States controls nearly 70 per cent.
One of the significant features of the situation above summarized is the
concentration of production and smelting in a comparatively few places
in the world. This statement applies with even more force to the
individual mineral commodities.
Water may be regarded as a mineral resource in so far as it is utilized
as a commodity for drinking, washing, power, irrigation, and other
industrial uses. For purposes of navigation and drainage, or as a
deterrent in excavation, it would probably not be so classed. While it
is not easy to define the limits of water's use as a mineral resource,
it is clear that even with a narrow interpretation the total tonnage
extracted from the earth as a mineral resource exceeds in amount all
other mineral resources combined.
WORLD ANNUAL PRODUCTION OF MINERALS IN TERMS OF VALUE
In terms of value, mineral resources appear in different perspective.
The annual world value of mineral production, exclusive of water, is
approximately $9,000,000,000. This figure is obtained by dividing the
annual value of the United States output of each of the principal
minerals by the percentage which the United States output constitutes in
the world output, and adding the figures thus obtained. The values here
used are mainly selling prices at the mines. It is impossible to reduce
the figures absolutely to the value of the mineral as it comes from the
ground; there are always some items of transportation included. This
method of figuring is of course only the roughest approximation; the
values as obtained in the United States cannot be accurately
exterpolated for the rest of the world because of locally varying
conditions. However, the figures will serve for rough comparative
purposes.
Of this total value coal represents roughly 61 per cent, petroleum 12
per cent, iron 6 per cent, copper 5 per cent, and gold 3 per cent.
In terms of value, about 25 per cent of the world's mineral production
is available for export beyond the countries of origin. Of this
exportable surplus the United States has about 40 per cent, consisting
principally of coal, copper, and formerly petroleum.
The value of the United States annual mineral production in recent years
has been from about $3,500,000,000 to $5,500,000,000. Annual imports of
mineral products into the United States have averaged recently in the
general vicinity of $450,000,000, the larger items being copper, tin,
fertilizers, petroleum, gems and precious stones, manganese, nickel, and
tungsten.
Again the perspective is changed when the value of water resources is
considered. As a physiologically indispensable resource, the value of
water in one sense is infinite. There is no way of putting an accurate
value on the total annual output used for drinking and domestic
purposes,--although even here some notion of the magnitude of the
figures involved may be obtained by considering the average per capita
cost of water in cities where figures are kept, and multiplying this
into the world population. This calculation would not imply that any
such amount is actually paid for water, because the local use of
springs, wells, and streams can hardly be figured on a cash basis; but,
if human effort the world over in securing the necessary water is about
as efficient as in the average American city, the figures would indicate
the total money equivalent of this effort.
SIGNIFICANCE OF GEOGRAPHIC DISTRIBUTION OF MINERAL PRODUCTION
The remarkable concentration of the world's mining and smelting around
the North Atlantic basin, indicated by the foregoing figures, does not
mean that nature has concentrated the mineral deposits here to this
extent. It is an expression rather of the localized application of
energy to mineral resources by the people of this part of the world. The
application of the same amount of energy in other parts of the world
would essentially change the distribution of current mineral production.
The controlling factor is not the amount of minerals present in the
ground; this is known to be large in other parts of the world and more
will be found when necessary. Controlling factors must be looked for in
historical, ethnological, and environmental conditions. This subject is
further discussed in the chapters on the several resources, and
particularly in relation to iron and steel.
THE INCREASING RATE OF PRODUCTION
The extraction of mineral resources on the huge scale above indicated is
of comparatively recent date.
From 1880 to the end of 1918 the value of the annual mineral production
of the United States has increased from $367,000,000 to more than
$5,500,000,000, or nearly fifteen times; measured in another way, it has
increased from a little over $7 per capita to more than $52.[10]
More coal has been mined in the United States since 1905 than in all the
preceding history of the country. More iron ore has been mined since
1906 than in all the preceding history. The gold production of the
United States practically started with the California gold rush in
1849. The great South African gold production began in 1888. Production
of diamonds in South Africa began about 1869. The large use of all
fertilizer minerals is of comparatively recent date. The world's oil
production is greater now each year than it was for any ten years
preceding 1891, and more oil has come out of the ground since 1908 than
in all the preceding history of the world. The use of bauxite on a large
scale as aluminum ore dated practically from the introduction of
patented electrolytic methods of reduction in 1889.
In one sense the world has just entered on a gigantic experiment in the
use of earth materials.
The most striking feature of this experiment relates to the vast
acquisition of power indicated by the accelerating rate of production
and consumption of the energy resources--coal, oil, and gas (and water
power). Since 1890 the per capita consumption of coal in the United
States has trebled and the per capita consumption of oil has become five
times as great as it was. If the power from these sources used annually
in recent years be translated roughly into man power, it appears that
every man, woman, and child in the United States has potential control
of the equivalent of thirty laborers,--as against seven in 1890. Energy
is being released on a scale never before approximated, with
consequences which we can yet hardly ascertain and appraise. This
consideration cannot but raise the question as to the ability of modern
civilization to control and coödinate the dynamic factors in the
situation.
CAPITAL VALUE OF WORLD MINERAL RESERVES
It is impossible to deduce accurately the capital value of mineral
resources from values of annual output, but again some approximation may
be made. The profit on the extraction of mineral resources on the whole,
considering the cost of exploration, is probably no greater than in
other industries (p. 330). If we assume a 6 per cent return, which
perhaps is somewhere near the world-wide standard of interest rate for
money, and capitalize the value of the world's annual output at this
rate, we obtain a world capital value for mineral resources, exclusive
of water, of 150 billions of dollars. This assumes an indefinitely long
life for reserves. This assumption may need some qualifications, but
it is the writer's view (Chapter XVII) that it is justified for a
sufficiently long period to substantiate the above method of
calculation.
[Illustration: FIG. 2. Commercial (financial) control of the
mineral resources of the world.]
[Illustration: FIG. 3. Political (territorial) control of the
mineral resources of the world.]
POLITICAL AND COMMERCIAL CONTROL OF MINERAL RESOURCES
The occurrence of a mineral resource within a country does not
necessarily mean control by that particular political unit. A citizen of
the United States may own a mineral resource in South America.
Commercial control of this sort was demonstrated during the war to be of
more far-reaching significance than had been supposed, and it became
necessary to ascertain, not only the output of the different countries,
but the commercial control of this output. Investigation of this subject
for twenty-three leading commodities shows that the political and
commercial control are by no means the same. These are partly summarized
in the accompanying graphs from Spurr.[11] It is to be noted that the
graphs show the control of many commodities as it existed in 1913, the
last normal year before the war. Changes during and since the war have
of course largely altered the situation for certain commodities, notably
for iron, coal, and potash. These developments are summarized in the
discussion of the individual resources. It is also to be noted that the
commercial or financial control of the world's minerals, under the
influence of the fostering and protective policies of certain
governments discussed in Chapter XVIII, is at present in a state of
flux. Considerable changes are taking place today and are to be looked
for in the future.
RESERVES OF MINERAL RESOURCES
Annual production figures are only to a very partial extent an
indication of the distribution of the great reserves of mineral
resources. For instance, there are enormous reserves of coal in China
which are not yet utilized to any large extent. The minerals of South
America and Africa are in a very early stage of development. The total
world reserves will of course not be known until exploration and
development of the world's resources are complete--a time which will
probably never come. Figures of reserves represent only our present
partial state of knowledge and are likely to be considerably modified in
the future. Furthermore, the quantitative accuracy of knowledge of
reserves is so variable in different parts of the world that it is
almost impossible to make up world figures which have any great
validity. There are, however, certain broad facts ascertainable.
Every country in the globe is deficient in supplies of some minerals.
The United States is better off than any other country, but still lacks
many mineral commodities (see pp. 396-399.) No single continent has
sufficient reserves of all mineral commodities.
For the world, however, it may be stated with reasonable certainty that
the reserves of the principal minerals are now known to be ample with
the exception of those of oil, tin, and perhaps gold and silver. By
_ample_ we mean sufficient to give no cause for worry for the next few
decades. For many mineral commodities the amounts now actually in sight
will not last long, but the possibilities of extension and discovery are
so great that a long future availability of these commodities can be
counted upon with reasonable safety.
The present shortages in oil, tin, and other minerals mentioned may be
only temporary. There is a large part of the world still to be explored,
and the present reserves merely mark a stage in this exploration.
Nevertheless, the ratio of reserves and discovery on the one hand to
accelerated use on the other gives cause for much concern. Looking
forward to the future, the problem of mineral reserves in general is not
one of the possible ultimate amount which the earth may
contain--presumably in no case is this deficient--but of the success
with which the resource may be found and developed to keep up with the
rapid acceleration of demand. In the chapter on conservation the
suggestion is made that future difficulties are more likely to arise
from failure to coödinate the dynamic factors of supply and demand, than
from absolute shortage of material in the earth.
FOOTNOTES:
[10] Bastin, Edson S., and McCaskey, H. D., The work on mineral
resources done by the U. S. Geological Survey: _Min. Res. of the United
States for 1918, U. S. Geol. Survey_, pt. 1, 1920, p. 3a.
[11] Spurr, J. E., Who owns the earth?: _Eng. and Min. Jour._, vol. 109,
1920, pp. 389-390.
CHAPTER V
WATER AS A MINERAL RESOURCE
GENERAL GEOLOGIC RELATIONS
With the solid earth as the special care of geology, it may seem
presumptuous for the geologist to claim the waters thereof, but he does
not disclaim this inheritance. Water is so all-pervasive that it is more
or less taken for granted; and so many and so intricate are its
relations that it is not easy to make an objective survey of the water
problem in its relation to geology.
The original source of water, as well as of air, is in molten magmas
coming from below. These carry water and gases,--some of which are
released and some of which are locked up in the rocks on cooling, to be
later released during the alterations of the rocks. It is supposed,
whatever theory of the origin of the earth we favor, that in its early
stages the earth lacked both hydrosphere and atmosphere, and that during
the growth of the earth these gradually accumulated on and near the
surface in the manner stated.
During alterations at the surface water is added to the mineral
constitution of the rocks, and by alterations deep below the surface it
may be subtracted. Water is the agent through which most mineral and
chemical changes of rocks are accomplished. It is the agent also which
is mainly responsible for the segregation of mineral deposits. Water,
both as running water and in the solid form of ice, plays an important
part in determining the configuration of the earth's surface. Water is
the medium in which most sedimentary rocks are formed. It is an
important agent in the development of soil and in organic growth. These
various influences of water on geological processes touch the economic
field at many points, especially in relation to the concentration of
ores and to the development of soils and surface forms.
Water comes even more directly into the field of economic geology as a
mineral resource. Water supplies, for the greatest variety of purposes,
involve geologic considerations at almost every turn.
Finally, water may be an aid or a hindrance to excavation and to a great
variety of structural operations, both in war and in peace; and in this
relation it again affords geologic problems.
The part played by water in geologic processes, such as that of mineral
segregation, is more or less incidentally discussed in other chapters.
We may consider more fully in this chapter the application of geology to
the general subject of water supplies.
From the geological point of view, water is a mineral,--one of the most
important of minerals,--as well as a constituent of other minerals. It
becomes a mineral resource when directly used by man. It is ordinarily
listed as a mineral resource when shipped and sold as "mineral water,"
but there is obviously no satisfactory line between waters so named and
water supplies in general, for most of them are used for the same
purposes and none of them are free from mineral matter. Water which is
pumped and piped for municipal water supply is as much a mineral
resource as water which is bottled and sold under a trade name. Likewise
water which is used for irrigation, water power, and a wide variety of
other purposes may logically be considered a mineral resource.
Notwithstanding the immense economic importance of water as a mineral
resource its value is more or less taken for granted, and considerations
of valuation and taxation are much less in evidence than in the case of
other mineral resources. Water must be had, regardless of value, and
market considerations are to a much less extent a limiting factor.
Economic applications of geology to this resource are rather more
confined to matters of exploration, development, total supply, and
conservation, than to attempts to fix money value.
DISTRIBUTION OF UNDERGROUND WATER
Free water exists in the openings in rocks where it is sometimes called
_hygroscopic_ water. There is also a large amount of water combined
molecularly with many of the minerals of rocks, in which form it is
called _water of constitution_. This water is fixed in the rock so that
it is not available for use, though some of the processes of rock
alteration liberate it and contribute it to the free water. The
immediate source of underground water, both free and combined, is mainly
the surface or rain waters. A subordinate amount may come directly from
igneous emanations or from destruction of certain hydrous minerals.
Ultimately, as already indicated, even the surface water originates from
such sources.
The openings in rocks consist of joints and many other fractures, small
spaces between the grains of rocks (pore space), and amygdaloidal and
other openings characteristic of surface volcanic rocks. Many of these
openings are capillary and sub-capillary in size. Most rocks, even dense
igneous rocks, are porous in some degree, and certain rocks are porous
in a very high degree. The voids in some surface materials may amount to
84 per cent of the total volume. In general the largest and most
continuous openings are near the surface,--where rocks on the whole are
more largely of the sedimentary type and are more fractured,
disintegrated, and decomposed, than they are deep within the earth. The
largest supplies of water are in the unconsolidated sediments. The water
in igneous and other dense rocks is ordinarily in more limited quantity.
APPROXIMATE QUANTITY OF WATER WHICH WILL BE ABSORBED BY SOILS AND
ROCKS[1]
------------------------------------------------------
_Volume of water asborbed
_Material_ per 100 of material_
------------------------------------------------------
Sandy soil[2] 45.4
Chalk soil[2] 49.5
Clay[2] 50-52.7
Loam[2] 45.1-60.1
Garden earth [2] 69.0
Coarse sand [2] 39.4
Peat subsoil[2] 84.0
Sand 30-40
Sandstone 5-20
Limestone and dolomite 1-8
Chalk 6-27
Granite 03.-.8
------------------------------------------------------
1: Mead, Daniel W., _Hydrology_: McGraw-Hill Book Co.,
New York, 1919, p. 393.
2: Woodward, H. B., _Geology of soils and substrata_:
Edward Arnold, London, 1912.
Immediately at the surface, the openings of rocks may not be filled with
water; but below the surface, at distances varying with climatic and
topographic conditions, the water saturates the openings of the rocks
and forms what is sometimes called the _zone of saturation_ or the _sea
of underground water_. The top surface of this zone is called the _water
table_, or the _ground-water level_. The space between the water table
and the earth's surface is sometimes referred to as the _vadose zone_ or
the _zone of weathering_, since it is the belt in which weathering
processes are most active. The zone of weathering is not necessarily
dry. Water from the surface enters and sinks through it and water also
rises through it from below; it may contain suspended pockets of water
surrounded by dry rocks; it is not continuously and fully saturated.
The water table or ground-water level may be near or at the surface in
low and humid areas, and it may be two thousand feet or more below the
surface in arid regions of high topographic relief. Because of the
influence of capillarity, the water table is not a horizontal surface.
It shows irregularities more or less following the surface contours,
though not nearly so sharply accentuated.
The lower limit of the ground-water is more irregular than the upper
surface and is less definitely known. In general, openings in rocks tend
to diminish with depth, due to cementation and to closing of cavities by
pressures which are too great for the rock to withstand. But rocks
differ so widely in their original character, and in their response to
physical and chemical environment, that it is not unusual to find dense
and impervious rocks above, and open and porous rocks below. The lower
limit of the zone of abundant underground water varies accordingly. A
well may encounter nearly dry rock at a comparatively shallow depth, or
it may reach a porous water-bearing stratum at considerable depth. At
the greater depths pockets of water are sometimes found which have a
composition different from that of the surface water, and which
evidently are isolated from the surface water by zones of non-pervious
rock.
Attempts have been made to calculate the total volume of underground
water by measuring the openings of rocks and making assumptions as to
the depth to which such openings may extend. In this manner it has been
estimated that, if all the ground-water were assembled in a single body,
it would make a shell between eighty and two hundred feet thick
(depending on the assumptions) over all the continental areas.
MOVEMENT OF UNDERGROUND WATER
Availability of water supplies is determined by the movement or flow of
water as well as by its distribution and amount. The natural flow of
water underground is caused by gravity in the larger openings, but in
the smaller openings adhesion and capillarity are also important forces.
Of all the water falling on the surface, some may not go below the
surface at all but may immediately evaporate or join the runoff--that
is, the surface streams. Another part may penetrate a little distance
into the zone of weathering and then join the runoff. Of the water which
reaches the zone of saturation, a part may soon come to the surface in
low areas and join the runoff, and a part may penetrate deeply.
Above the zone of saturation gravity carries the water downward in
devious courses until it reaches the water table. Thereafter its course
is determined largely by the lowest point of escape from the water
table. In other words, the water table is an irregular surface; and
under the influence of gravity the water tends to move from the high to
the low points of this surface. Between the point of entrance and the
point of escape from the water table, the water follows various courses,
depending upon the porosity and the openings in the rocks. In general it
fills all of the available openings, and uses the entire available cross
section in making its progress from one point to another. The difference
in height or the "head" between the point of entrance and the point of
escape, together with the porosity of the rock and other factors,
determine the general speed of its movement (see p. 73). With equal
porosity the flow is at a maximum along a line directly connecting the
two points, and on more devious courses the flow is less.
The surface water first enters the ground through innumerable small
openings. Soon, however, it tends to be concentrated into channels of
easiest flow, with the result that in the later part of its underground
course it may be much concentrated in large trunk channels. These
channels may consist of joints, or frequently of very coarse and
pervious beds. The sedimentary rocks as a whole contain the most voids,
and therefore the largest flow and largest supply of water is often
localized in them. Of the sedimentary rocks, sandstones and limestones
usually contain the largest and most continuous openings, and thus
afford the freest circulation for water. The voids in fine-grained
shales may equal in volume those in sandstones and limestones, but the
openings are so small and discontinuous that the water does not flow
freely. Regardless of total amount of water, unless there are continuous
openings of some size the flow may be small.
The relations of more porous rocks to containing impervious strata also
profoundly affect the flow of underground water. Between impervious
strata the circulation may be concentrated and vigorous within the
porous bed. Where the porous bed is not so contained, the movement may
be more dispersed and less vigorous locally. The inclination of the
beds, of course, also affects the direction and amount of the flow.
The influence of gravity upon underground water may locally tend toward
a state of equilibrium in which there is little movement. In such a case
the water is substantially ponded, and moves only when tapped by
artificial openings.
WELLS AND SPRINGS
Underground water becomes available for use by means of springs and
through wells or bore holes. Water rises to the surface in natural
springs at points where the pressure or _head_, due to its entrance into
the ground at a higher level, is sufficient to force it to the surface
after a longer or shorter underground course. The movement may be all
downward and lateral to the point of escape, or it may be downward,
lateral, and upward. Ordinarily, the course of spring waters does not
carry them far below the surface. Heat and gases may be added beneath
the surface by contact with or contributions from cooling igneous rocks.
These may accelerate the upward movement of spring waters, and yield
thermal and gas-charged waters, as in the springs and geysers of
Yellowstone Park.
When a well is sunk to tap the underground water supply, the water may
not rise in the artificial opening but may have to be lifted to the
surface.
If, however, the water is confined beneath an impervious stratum and is
under pressure from the water of higher areas, a well opening may simply
allow it to move upward under its own pressure or head. This pressure
may carry it upward only a few feet or quite to the surface or beyond,
in which latter case the well is called an _artesian_ well. The
essential condition for an artesian circulation is a porous zone,
inclining downward from the surface beneath an impervious stratum which
tends to confine and pond the water. The water at any point in the
water-bearing rock is under pressure which is more or less equivalent to
the weight of the column of water determined by the difference in height
between this point and the point of entrance or feeding area of the
water. If the feeding area is higher than the collar of the well, the
water will rise quite to the surface; if not, it will rise only part
way. Capillary resistance, however, may and usually does lessen the
theoretical pressure so figured.
The flow in deep artesian circulations is ordinarily a slow one. For the
artesian wells of southern Wisconsin, it has been calculated that waters
entering the outcrop of the southward dipping sandstone and limestone
layers in the northern part of the state have required two or three
hundred years to reach a point in the southern part of the state where
they are tapped. Because of this slow movement, a large number of wells
in any one spot may exhaust the local supply faster than it is
replenished from the remainder of the formation. The drilling of
additional wells near at hand in such cases does not increase the total
yield, but merely divides it among a larger number of wells.
The porosity of the rocks, and therefore the flow of an artesian
circulation, may in some cases be artificially increased by blasting and
shattering.
COMPOSITION OF UNDERGROUND WATERS
Underground waters are never entirely free from dissolved mineral
substances, and seldom are they free from suspended particles. Some
waters are desired because they contain very small quantities of
dissolved mineral matter. Others are prized because they have an
unusually high content of certain mineral substances. In determining the
deleterious or beneficial effect of dissolved substances, much depends
on the purpose for which the water is to be used,--whether for drinking,
washing, steam boilers, or irrigation. Near the surface underground
waters may carry bacteria, as well as animal and vegetable refuse,
which from a sanitary standpoint are usually objectionable. Deeper
waters are more likely to lack this contamination because of filtration
through rocks and soils.
The dissolved mineral substances of underground water are derived for
the most part from the solution of rocks with which the waters come in
contact, particularly at or near the surface. Through the agency of
underground water most of the mineral and chemical changes of rocks are
produced. The dissolved substances in solution at any time and place may
therefore be regarded as by-products of rock alterations. Locally they
may to some extent be derived from direct emanations from cooling
igneous masses.
The most common mineral substances contained in waters are lime and
magnesia. Less common, but abundant locally, are soda, potash, iron, and
silica. Waters contain also certain acid and gaseous substances, the
most common of which is carbon dioxide; and less widespread, but locally
abundant, are chlorine and sulphur dioxide. Where lime and magnesia are
abundant the water is ordinarily classed as a hard water. Where absent,
or subordinate to soda and potash, the water is ordinarily classed as a
soft water. Large amounts of the acid substances like chlorine and
sulphur are detrimental for most purposes. Where there are unusual
amounts of carbon dioxide or other gases present, they may by expansion
cause the water to bubble.
If we were to attempt to describe and define the characteristics, with
reference to dissolved mineral content and temperature, which make a
given water more desirable than another, we should enter a field of the
most amazing complexity and one with many surprising contradictions. For
the most widespread use, the most desirable water is a cold water as
free from mineral content as possible, and especially one lacking an
excess of lime and magnesia which make it hard; also lacking an excess
of acid constituents like sulphur dioxide, carbon dioxide, or chlorine,
which give the water a taste, or which make impossible its use in
boilers. Locally and for special reasons, waters of other qualities are
in demand. Waters so excessively carbonated as to bubble, sulphureted
waters, chlorine waters, waters high in iron, high in silica, high in
potash, high in soda, or high in magnesia, or waters of high
temperature, may come to be regarded as desirable. It is an interesting
fact that any water with unusual taste, or unusual mineral content, or
unusual temperature, is likely to be regarded as having medicinal value.
Sometimes this view is based on scientific knowledge; sometimes it is an
empirical conclusion based on experience; and again it may be merely
superstition. In one case the desirable feature may be the presence of a
large amount of carbon dioxide; in another case it may be its absence.
In one case the desirable feature may be high temperature; in another
case low temperature. The same combination of qualities which in a
certain locality may be regarded as highly desirable, may be regarded as
highly detrimental somewhere else where certain other types of waters
are in vogue.
Proprietary rights and advertising have brought certain waters into use
for drinking purposes which are not essentially different from more
widely available waters which are not regarded as having special value.
Two springs located side by side, or a spring and a deep well, whose
waters have exactly the same chemical characteristics, may be used and
valued on entirely different scales. Any attempt to classify mineral
waters sold to the public in any scientific way discloses a most
intricate and confused situation. One can only conclude that the
popularity of certain waters is not based alone on objective qualities
of composition, but rather on causes which lie in the fields of
psychology and commerce.
The part played by sentiment in putting value on water is well
illustrated by the general preference for spring waters as compared with
well waters. In the public mind, "spring water" denotes water of unusual
purity and of more desirable mineral content than well water.
Illustrations could be cited of districts in which the surface or spring
waters have a composition not different from that of the deeper well
waters, and are much more likely to be contaminated because of proximity
to the surface; and yet people will pay considerable sums for the spring
water in preference to the cheaply available well water.
RELATION OF GEOLOGY TO UNDERGROUND WATER SUPPLY
It is obvious that a knowledge of geology is helpful in locating an
underground water supply. Locally the facts may become so well known
empirically that the well driller is able to get satisfactory results
without using anything but the crudest geologic knowledge; but in
general, attention to geologic considerations tends to eliminate
failures in well drilling and to insure a more certain and satisfactory
water supply.
In drilling for water, it is essential to know the nature, succession,
and structure of the rocks beneath the surface in order to be able to
identify and correlate them from drill samples. The mere identification
of samples is often sufficient to determine whether a well has been
drilled far enough or too far to secure the maximum results. In order to
arrive at any advance approximation of results for a given locality, a
knowledge of the general geology of the entire region may be necessary.
Especially for expensive deep artesian wells it is necessary to work out
the geologic possibilities well in advance. It is useless, for instance,
to look for artesian water in a granite; but in an area of gently
inclined strata, with alternations of porous and impervious layers, the
expert may often figure with a considerable degree of certainty the
depth at which a given porous stratum will be found, and the pressure
under which the water will be in this particular stratum at a given
point. Even the mineral content of the water may in some cases be
predicted from geologic study.
One of the most obvious and immediately useful services of the geologist
in most localities is the collection and preservation of well samples
for purposes of identification and correlation of rock formations, and
as a guide to further drilling. Failure to preserve samples has often
led to useless and expensive duplication of work.
The problem of water supply in some localities is comparatively simple
and easy. In other areas there is an infinite variety of geologic
conditions which affect the problem, and the geologist finds it
necessary to bring to bear all the scientific knowledge of any sort
which can be used,--particularly knowledge in relation to the type of
rock, the stratigraphy and the structure.
SURFACE WATER SUPPLIES
Where underground water is not abundant or not cheaply available, or
where larger amounts of water are needed, as in large cities or for
irrigation purposes, surface water is used. In general, surface waters
are more likely to be contaminated by vegetable and animal matter and
to require purification for drinking purposes.
Surface waters are also used for irrigation, water power, drainage, the
carrying of sewage, etc. This great variety of uses brings the
consideration of surface waters into many fields other than geology, but
an understanding and interpretation of the geological conditions is none
the less fundamental. This is evidenced by the inclusion of geologic
discussions in most textbooks of hydrology, and in the reports of the
Hydrographic Branch of the U. S. Geological Survey. The very fact that
this important branch of governmental investigation is in a charge of
the U. S. Geological Survey indicates its close relation to geology.
The principles of geology used in the study of surface waters relate
chiefly to physiography (see Chapter I). It is usually necessary to know
the total quantity of flow, its annual and seasonal variation, and the
possible methods of equalization or concentration; the maximum quantity
of flow, the variation during periods of flood, and the possibilities of
reduction or control; the minimum flow and its possible modification by
storage or an auxiliary supply. These questions are obviously related to
the size and shape of the catchment area, the topography, the rock
structure, the relation between underground flow or absorption and the
runoff, and other physiographic factors. Quoting from D. W. Mead:[12]
Geological conditions are frequently of great importance in
their influence on the quantity and regularity of runoff. If
the geological deposits of the drainage area are highly
impervious, the surface flow will receive and transmit the
water into the mass only through the cracks and fissures in
the rock. Pervious materials, such as sandstones, sands,
gravels, and cracked or fissured rocks, induce seepage, retard
runoff, and, if such deposits are underlaid with an impervious
bed, provide underground storage which impounds water away
from the conditions which permit evaporation, and hence tends
to increase runoff and equalize flow. On the other hand, if
such pervious deposits possess other outlets outside of the
stream channel and drainage area, they may result in the
withdrawal of more or less of the seepage waters entirely from
the ultimate flow of the stream. Coarse sands and gravels
will rapidly imbibe the rainfall into their structure. Fine
and loose beds of sand also rapidly receive and transmit the
rainfall unless the precipitation is exceedingly heavy under
which conditions some of it may flow away on the surface.
Many of the highly pervious indurated formations receive water
slowly and require a considerable time of contact in order to
receive and remove the maximum amount.
In flat, pervious areas, rainfalls of a certain intensity are
frequently essential to the production of any resulting stream
flow. In a certain Colorado drainage area, the drainage
channel is normally dry except after a rainfall of one-half
inch or more. A less rainfall, except under the condition of a
previously saturated area, evaporates and sinks through the
soil and into the deep lying pervious sand rock under the
surface which transmits it beyond the drainage area. Such
results are frequently greatly obscured by the interference of
other factors, such as temperature, vegetation, etc.
* * * * *
The natural storage of any drainage area and the possibilities
of artificial storage depend principally upon its topography
and geology. Storage equalizes flow, although the withdrawal
of precipitation by snow or ice storage in northern areas
often reduces winter flow to the minimum for the year. Both
surface and sub-surface storage sometimes hold the water from
the streams at times when it might be advantageously used.
Storage, while essential to regulation, is not always an
advantage to immediate flow conditions.
UNDERGROUND AND SURFACE WATERS IN RELATION TO EXCAVATION AND CONSTRUCTION
Scarcely more than a mention of this subject is necessary. In mining,
the pumping charge is one of the great factors of cost. A forecast of
the amount and flow of water to be encountered in mining is based on the
geologic conditions. The same is true in excavating tunnels, canals, and
deep foundations. Detailed study of the amount and nature of water in
the rock and soil of the Panama Canal has been vital to a knowledge of
the cause and possibilities of prevention of slides. Rock slides in
general are closely related to the amount and distribution of the water
content.
The importance of ground-water as a detriment in military operations was
shown during the recent war in trenching and other field works. At the
outset, with the possible exception of the German army, a lack of
scientific study of ground-water conditions led to much unnecessary
difficulty. It soon became necessary to study and map the water
conditions in great detail in advance of operations. Much of this work
was done by geologists (see Chapter XIX).
Geological considerations are involved in a great variety of engineering
undertakings related to river and harbor improvements, dam sites, etc.,
mentioned in Chapter XX.
FOOTNOTES:
[12] Mead, Daniel W., _Hydrology_: McGraw-Hill Book Co., New York, 1919,
pp. 447-448, 456.
CHAPTER VI
THE COMMON ROCKS AND SOILS AS MINERAL RESOURCES
ECONOMIC FEATURES OF THE COMMON ROCKS
Under the general heading of common rocks are included the ordinary
igneous, sedimentary, and "metamorphic" rocks, and the unconsolidated
clays, sands, and gravels characteristic of surface conditions, which
are mined and quarried for commercial use. Soils are closely related to
this group; but since they present special problems of their own, they
are discussed under a separate heading at the end of the chapter. Names
of the common rocks will be used with the general commercial
significance given them by the United States Geological Survey in its
mineral resource reports.
Because of their inexhaustible quantity and ready availability, the
value of the common rock products is not large per unit of weight; but
in the aggregate it ranks high among mineral products. In respect to
tonnage, common rocks constitute perhaps 10 per cent of the world annual
output of all mineral commodities (exclusive of water).
The greater tonnage of the common rocks is used commercially in crushed
or comminuted forms for road material, for railroad ballast, and for
cement, brick, concrete, and flux. In blocks and structural shapes, of
less aggregate tonnage, they are used as building stone, monumental
stone, paving blocks, curbing, flagging, roofing, refractory stone, and
for many other building and manufacturing purposes.
The common rocks are commodities in which most countries of the globe
are self-sufficing. International trade in these commodities is
insignificant, being confined to small quantities of materials for
special purposes, or to local movements of short distances, allowed by
good transportation facilities.
The common rocks are so abundant and widespread that the conservation
of raw materials is not ordinarily a vital problem. Conservational
principles do apply, however, to the human energy factor required for
their efficient use. In the valuation of common rocks, also, the more
important factors are not the intrinsic qualities of the stones, but
rather the conditions of their availability for use.
Because of bulk and comparatively low intrinsic value, the principal
commercial factors in the availability of the common rocks are
transportation and ease of quarrying, but these are by no means the only
factors determining availability. Their mineral and chemical
composition, their texture and structure, their durability, their
behavior under pressure and temperature changes, and other factors enter
in to important degrees. The weighting and integration of these factors,
for the purpose of reaching conclusions as to the availability of
particular rock materials, depend also on the purposes for which these
materials are to be used. The problem is anything but simple. The search
for a particular rock to meet a certain demand within certain limits of
cost is often a long and arduous one. On account of the abundance and
widespread distribution of common rocks and their variety of uses, there
is a good deal of popular misapprehension as to their availability. Many
building and manufacturing enterprises have met disastrous checks,
because of a tendency to assume availability of stone without making the
fullest technical investigation. Many quarrying ventures have come to
grief for the same reason. It is easy to assume that, because a granite
in a certain locality is profitably quarried and used, some other
granite in the same locality has equal chances. However, minor
differences in structure, texture, and composition, or in costs of
quarrying and transportation, may make all the difference between profit
and loss. Even though all these conditions are satisfactorily met,
builders and users are often so conservative that a new product finds
difficulty in breaking into the market. A well-established building or
ornamental stone, or a limestone used for flux, may hold the market for
years in the face of competition from equally good and cheaper supplies.
The very size of a quarry undertaking may determine its success or
failure.
GRANITE
The term granite, as used commercially, includes true granite and such
allied rocks as syenite and gneiss. In fact even quartzite is sometimes
called granite in commerce, as in the case of the Baraboo quartzites of
Wisconsin, but this is going too far. For statistical purposes, the
United States Geological Survey has also included small quantities of
diorite and gabbro. The principal uses of granite are, roughly in order
of importance, for monumental stone, building stone, crushed stone,
paving, curbing, riprap and rubble. Thirty states in the United States
produce granite, the leaders being Vermont, Massachusetts, North
Carolina, Maine, Wisconsin, Minnesota, and California.
BASALT AND RELATED TYPES
Basalt and related rocks are sometimes included under the name "trap
rock," which comprises,--besides typical basalt and diabase,--fine-grained
diorite, gabbro, and other basic rocks, which are less common in
occurrence and are similar in chemical and physical properties. The
principal use of these rocks is as crushed stone for road and ballast
purposes and for concrete. They are produced in some fifteen states, the
leaders being New Jersey, Pennsylvania, California, and Connecticut.
LIMESTONE, MARL, CHALK
In the United States limestone is used principally as crushed stone for
road material, railroad ballast, concrete, and cement, as fluxing stone
for metallurgical purposes, and in the manufacture of lime. Minor uses
are as building stones, paving blocks, curbing, flagging, rubble, and
riprap; in alkali works, sugar factories, paper mills, and glass works;
and for agricultural purposes. For the making of cement, in
metallurgical fluxes, and in most of the manufacturing and agricultural
uses, both limestone and lime (limestone with the CO_2 driven out by
heating) are used. Lime is also extensively used in the making of mortar
for building operations, in tanning leather, and in a great variety of
chemical industries. The total quantity of limestone used for all
purposes in the United States nearly equals that of iron ore. Nearly
every state in the union produces limestone, but the more important
producers are Pennsylvania (where a large amount is used for fluxing),
Ohio, Indiana, New York, Michigan, and Illinois.
Closely associated with limestone in commercial uses, as well as in
chemical composition, is calcareous marl, which is used extensively in
the manufacture of Portland cement.
Chalk is a soft amorphous substance of the same composition as
limestone. The main uses of chalk are as a filler in rubber, and as a
component of paint and putty. It is also used for polishing. The
principal producers of this commodity are England, Denmark, and France,
and the chief consumer is the United States. The United States depends
upon imports for its supply of chalk for the manufacture of whiting.
Before the war two-thirds came from England and a third from France.
During the war importation was confined to England, with a small tonnage
from Denmark. No deposits of domestic chalk have been exploited
commercially. A somewhat inferior whiting, but one capable of being
substituted for chalk in most cases, is manufactured from the waste fine
material of limestone and marble quarries.
MARBLE
Marble is limestone which has been coarsely recrystallized by
metamorphism. The marble of commerce includes a small quantity of
serpentine as quarried and sold in Massachusetts, California, Maryland,
Pennsylvania, and Vermont, and also a small amount of so-called onyx
marble or travertine obtained from caves and other deposits in Kentucky
and other states. The principal uses of marble are for building and
monumental stones. Of the twenty-two states producing marble, the
leaders are Vermont, Georgia, and Tennessee.
A small amount of marble of special beauty, adapted to ornamental
purposes, is imported from European countries, especially from Italy.
Marble imports from Italy constitute about two-thirds, both in tonnage
and value, of all stone imported into the United States.
SAND, SANDSTONE, QUARTZITE (AND QUARTZ)
Sand is composed mainly of particles of quartz or silica, though
sometimes feldspar and other minerals are present. Sandstones are
partially cemented sands. Quartzites are completely cemented sands. To
some extent these substances are used interchangeably for the same
purposes.
The principal uses of sand in order of commercial totals are for
building purposes--for mortar, concrete, sand-lime brick, etc.,--as
molding sand in foundries, as a constituent of glass, in grinding and
polishing, in paving, as engine sand, as fire or furnace sand, in the
manufacture of ferrosilicon (a steel alloy), and in filters. Reference
is made to sand as an abrasive and in the manufacture of steel in
Chapters XIII and IX. Almost every state produces some sand, but for
some of the more specialized uses, such as glass sand, molding sand, and
fire or furnace sand, the distribution is more or less limited. The
United States Geological Survey has collected information concerning the
distribution of various kinds of sand and gravel, and serves a very
useful function in furnishing data as to supplies of material for
particular purposes. Fine molding sands have been imported from France,
but during the war domestic sources in New York and Ohio were developed
sufficiently to meet any requirements.
The sandstone of commerce includes the quartzites of Minnesota, South
Dakota, and Wisconsin, and the fine-grained sandstones of New York,
Pennsylvania, and elsewhere, known to the trade as "bluestone." In
Kentucky most of the sandstone quarried is known locally as "freestone."
The principal uses of sandstone are for building stone, crushed stone,
and ganister (for silica brick and furnace-linings). Other uses are for
paving blocks, curbing, flagging, riprap, rubble, grindstones,
whetstones, and pulpstones (see also Chapter XIII). Sandstone is
sometimes crushed into sand and is used in the manufacture of glass and
as molding-sand. Most of the states of the union produce sandstone, the
principal producers being Pennsylvania, Ohio, and New York.
"SAND AND GRAVEL"
Where sand is coarse and impure and mixed with pebbles, it is Ordinarily
referred to as "sand and gravel." For sand and gravel the principal
uses are for railroad ballast, for road building, and for concrete. Sand
and gravel are produced in almost every state in the union, the largest
producers being Pennsylvania, Ohio, Illinois, New Jersey, and North
Carolina.
CLAY, SHALE, SLATE
Shale is consolidated clay, usually with a fine lamination due to
bedding. Slate is a more dense and crystalline rock, produced usually by
the anamorphism of clay or shale under pressure, and characterized by a
fine cleavage which is usually inclined to the sedimentary bedding.
Clays are used principally for building and paving brick and tile,
sewer-pipe, railroad ballast, road material, puddle, Portland cement,
and pottery. Clay is mined in almost every state. Ohio, Pennsylvania,
New Jersey, and Illinois have the largest production. There has been a
considerable importation of high-grade clays, principally from England,
for special purposes--such as the filling and coating of paper; the
manufacture of china, of porcelain for electrical purposes, and of
crucibles; and for use in ultramarine pigments, in sanitary ware, in
oilcloth, and as fillers in cotton bleacheries. War experience showed
the possibility of substitution of domestic clays for most of these
uses; but results were not in all cases satisfactory, and the United
States will doubtless continue to use imported clays for some of these
special purposes.
Shales, because of their thinly bedded character and softness, are of no
value as building stones, but are used in the manufacture of brick,
tile, pottery, and Portland cement.
Slates owe their commercial value primarily to their cleavage, which
gives well-defined planes of splitting. The principal uses are for
roofing and, in the form of so-called mill stock for sanitary,
structural, and electrical purposes. Small amounts are used for
tombstones, roads, slate granules for patent roofing, school slates,
blackboard material, billiard table material, etc. The color, fineness
of the cleavage, and size of the flakes are the principal features
determining the use of any particular slate. Ten states produce slate,
the principal production coming from Pennsylvania and Vermont.
THE FELDSPARS
Feldspars are minerals, not rocks, but mention of them is made here
because, with quartz, they make up such an overwhelming percentage of
earth materials. It is estimated that the feldspars make up 50 per cent
of all the igneous rocks and 16 per cent of the sedimentary rocks. As
the igneous rocks are so much more abundant than the sedimentary rocks,
the percentage of feldspars in the earth approaches the former rather
than the latter figure. In most rocks feldspar is in too small grains
and is too intimately associated with other minerals to be of commercial
importance; in only one type of rock, pegmatite, which is an igneous
rock of extremely coarse and irregular texture, are the feldspar
crystals sufficiently large and concentrated to be commercially
available.
Feldspar is used principally in the manufacture of pottery, china ware,
porcelain, enamel ware, and enamel brick and tile. In the body of these
products it is used to lower the fusing point of the other ingredients
and to form a firm bond between their particles. Its use in forming the
glaze of ceramic products is also due to its low melting point. A less
widespread use of feldspar is as an abrasive (Chapter XIII). One of the
varieties of feldspar carries about 15 per cent of potash, and because
of the abundance of the mineral there has been much experimental work to
ascertain the possibility of separating potash for fertilizer purposes;
but, because of cost, this source of potash is not likely for a long
time to compete with the potash salts already concentrated by nature.
Feldspar is mined in eleven states, but the important production comes
from North Carolina and Maine. The United States also imports some
feldspar from Canada.
HYDRAULIC CEMENT (including Portland, natural, and Puzzolan cements)
Cement is a manufactured product made from limestone (or marl) and clay
(or shale). Sometimes these two kinds of substances are so combined in
nature (as in certain clayey limestones) that they are available for
cement manufacture without artificial mixing. It is not our purpose in
this volume to discuss manufactured products; but the cement industry
involves such a simple transformation of raw materials, and is so
closely localized by the distribution of the raw materials, that a
mention of some of its outstanding features seems desirable.
Hydraulic cement is used almost exclusively as a structural material. It
is an essential ingredient of concrete. Originally used chiefly for the
bonding of brick and stone masonry and for foundation work, its uses
have grown rapidly, especially with the introduction of reinforced
concrete. It is being used in the construction of roads, and its latest
use is in ship construction.
With the exception of satisfactory fuels, the raw materials required for
the manufacture of cement are found quite generally throughout the
world. While practically all countries produce some cement, much of it
of natural grade, only the largest producers make enough for their own
requirements and as a result there is a large world movement of this
commodity. The world trade is chiefly in Portland cement.
Next to the United States, the producing countries having the largest
exportable surplus of cement in normal times are Germany and Great
Britain. France and Belgium were both large producers and exporters
before the war, but the war greatly reduced their capacity to produce
for the time being. Sweden, Denmark, Austria, Japan, and Switzerland all
produce less extensively but have considerable surplus available for
export. Italy and Spain have large productions, which are about
sufficient for their own requirements. Holland and Russia import large
amounts from the other European countries. The far eastern trade absorbs
the excess production of Japan. In South Africa and Australasia,
production nearly equals demand. In Canada, although the industry has
been growing very rapidly, the demand still exceeds production. In South
and Central America, Mexico and the West Indies, the demand is
considerable and will probably increase; production has thus far been
insufficient. Several modern mills are either recently completed or
under construction in these countries, and concessions have been granted
for several others. These new mills are largely financed by American
capital.
The United States is the largest single producer of cement in the world,
its annual production being about 45 per cent of the world's total.
Domestic consumption has always been nearly as great as the production,
and exports have usually not exceeded 4 per cent of the total shipments
from the mills. South and Central America offer fields for exportation
of cement from the United States.
GEOLOGIC FEATURES OF THE COMMON ROCKS
To describe the geologic features of the common rocks used in commerce
would require a full treatise on the subject of geology. These are the
bulk materials of the earth and in them we read the geologic history of
the earth. In preceding chapters a brief outline has been given of the
relative abundance of the common earth materials and of the processes
producing them. In comparison, the metalliferous deposits are the merest
incidents in the development of this great group of mineral resources.
In this section reference will be made only to a few of the rock
qualities and other geologic features which require first attention in
determining the availability of a common rock for commercial use. The
list is very fragmentary, for the reason that the uses are so many and
so varied that to describe all the geologic features which are important
from the standpoint of all uses would very soon bring the discussion far
beyond the confines of a book of this scope.[13]
BUILDING STONE
For building stones, the principal geologic features requiring attention
are structure, durability, beauty, and coloring.
The structures of a rock include jointing, sedimentary stratification,
and secondary cleavage. Nearly all rocks are jointed. The joints may be
open and conspicuous, or closed and almost imperceptible. The closed
joints or incipient joints cause planes of weakness, known variously as
rift, grain, etc., which largely determine the shapes of the blocks
which may be extracted from a quarry. Where properly distributed, they
may facilitate the quarrying of the stone. In other cases they may be
injurious, in that they limit the size of the blocks which can be
extracted and afford channels for weathering agents. Some rocks of
otherwise good qualities are so cut by joints that they are useless for
anything but crushed stone. The bedding planes or stratification of
sedimentary rocks exercise influences similar to joints, and like
joints may be useful or disadvantageous, depending on their spacing. The
secondary cleavage of some rocks, notably slates, enables them to be
split into flat slabs and thus makes them useful for certain purposes.
Proper methods of extraction and use of a rock may minimize the
disadvantageous effects of its structural features. The use of
channelling machines instead of explosives means less shattering of the
rock. By proper dressing of the surface the opening of small crevices
may be avoided. Stratified rocks set on bed, so that the bedding planes
are horizontal, last longer than if set on edge.
The durability of a rock may depend on its perviousness to water which
may enter along planes of bedding or incipient fracture planes, or along
the minute pore spaces between the mineral particles. The water may
cause disastrous chemical changes in the minerals and by its freezing
and thawing may cause splitting. For this reason, the less pervious
rocks have in general greater durability than the more pervious. Highly
pervious rocks used in a dry position or in a dry climate will last
longer than elsewhere.
Durability is determined also by the different coefficients of expansion
of the constituent minerals of the rock. Where the minerals are
heterogeneous in this regard, differential stresses are more likely to
be set up than where the minerals are homogeneous. Likewise a
coarse-textured rock is in general less durable than a fine-textured
one. Expansion and contraction of a stone under ordinary temperature
changes, and also under fire and freezing, must necessarily be known for
many kinds of construction.
Minerals resist weathering to different degrees, therefore the mineral
composition of a rock is another considerable factor in determining its
durability. Where pyrite is present in abundance it easily weathers out,
leaving iron-stained pits and releasing sulphuric acid which decomposes
the rock. Abundance of mica, especially where segregated along the
stratification planes, permits easy splitting of the rock under
weathering. Likewise the mica often weathers more quickly than the
surrounding minerals, giving a pitted appearance; in marbles and
limestones its irregular occurrence may spoil the appearance. Flint or
chert in abundance is deleterious to limestones and marbles, because,
being more resistant, it stands out in relief on the weathered surface,
interferes with smooth cutting and polishing, and often causes the rock
to split along the lines of the flint concretions. Abundance of
tremolite may also be disadvantageous to limestones and marbles, because
it weathers to a greenish-yellow clay and leaves a pitted surface.
The crushing strength of a rock has an obvious relation to its
structural uses. The rock must be strong enough for the specified load.
Most hard rocks ordinarily considered for building purposes are strong
enough for the loads to which subjected, and this factor is perhaps
ordinarily less important than the structural and mineral features
already mentioned.
It is often necessary to know the modulus of elasticity and other
mechanical constants of a rock, as in cases where it is to be combined
with metal or other masonry or to be subjected to exceptional shock.
The beauty and coloring of a rock are its esthetic rather than its
utilitarian features. They are particularly important in the
construction of buildings and monuments for public or ornamental
purposes.
CRUSHED STONE
The largest use of rock or stone is in the crushed form for road
building, railway embankments, and concrete, and the prospect is for
largely increased demands for such uses in the future. For the purpose
of road building, it is necessary to consider a stone's resistance to
abrasion, hardness, toughness, cementing value, absorption, and specific
gravity. Limestone cements well, but in other qualities it is not
desirable for heavy traffic. Shales are soft and clayey, and grind down
to a mass which is dry and powdery, and muddy in wet weather. Basalt and
related rocks resist abrasion, and cement well. Granites and other
coarse-grained igneous rocks do not cement well and are not resistant to
abrasion. Many sandstones are very hard and brittle and resist abrasion,
but do not cement.
The application of geology on a large scale to the study of sources and
qualities of crushed stone is now being required in connection with the
great state and national projects of highway building. This work is by
no means confined to a mere testing of the physical qualities of
road-building materials found along the proposed route, but includes a
careful study of their geologic occurrence, distribution, and probable
amounts. In certain of the northern states specialists in glacial
geology are preferred for this purpose.
STONE FOR METALLURGICAL PURPOSES
The use of limestone and other rock for metallurgical fluxes is
dependent very largely on chemical composition. Comparatively few
limestones are sufficiently pure for this purpose. For furnace linings,
the quartzite or ganister must be exceptionally pure. The field search
for rocks of the necessary composition has required geologic service.
CLAY
For a variety of uses to which clay is put, it is necessary to know its
degree of plasticity, tensile strength, shrinkage (both under air and
fire), fusibility, color, specific gravity, and chemical properties. The
testing of clay for its various possible uses is a highly specialized
job, usually beyond the range of a geologist, although certain
geologists have been leaders in this type of investigation. More
commonly within the range of a geologist are questions concerning
origin, field classification, distribution, quantities, and other
geologic conditions affecting quality and production.
Clay originates from the weathering of common rocks containing
silicates, by pretty well understood weathering processes (see Chapter
II). It may remain in place above the parent rock, or may be transported
and redeposited, either on land or under water, by the agencies of air,
water, and ice. The kind of parent rock, the climatic conditions and
nature of the weathering, and the degree of sorting during
transportation, all determine the composition and texture of the
resulting clay,--with the result that a classification on the basis of
origin may indicate the broad group characteristics which it is
desirable to know for commercial purposes. For instance, residual clays
from the weathering of granite may be broadly contrasted with residual
clays formed by the weathering of limestone, and both differ in group
characteristics from clays in glacial deposits. Classification according
to origin also may be useful in indicating general features of depth,
quantity, and distribution. However, a genetic classification of clays
is often not sufficient to indicate the precise characteristics which
it is necessary to know in determining their availability for narrow and
special technical requirements. Furthermore, clays suitable for certain
commercial requirements may be formed in several different ways, and
classification based on specific qualities may therefore not correspond
at all to geologic classification based on origin.
Geologists have been especially interested in the causes of plasticity
of clay and in its manner of hardening when dried. In general these
phenomena have been found to be due to content of colloidal substances
of a clayey nature, which serve not only to hold the substance together
during plastic flow but to bind it during drying. The part played by
colloids in the formation of clays, as well as of many other mineral
products, is now a question which is receiving intensive study.
The same processes which produce clay also produce, under special
conditions, iron ores, bauxites, the oxide zones of many sulphide ore
bodies, and soils, all of which are referred to on other pages.
LIMITATIONS OF GEOLOGIC FIELD IN COMMERCIAL INVESTIGATION OF COMMON ROCKS
In general the qualities of the earth materials which determine their
availability for use are only to a minor extent the qualities which the
geologist ordinarily considers for mapping and descriptive purposes. The
usual geological map and report on a district indicate the distribution
and general nature of the common rocks, and also the extent to which
they are being used as mineral resources. Seldom, however, is there
added a sufficiently precise description, for instance of a clay, to
enable the reader to determine which, if any, of the many different uses
the material might be put to. The variety of uses is so great, and the
technical requirements for different purposes are so varied and so
variable, that it is almost impossible to make a description which is
sufficiently comprehensive, and at the same time sufficiently exact, to
give all the information desired for economic purposes. If the geologist
is interested in disclosing the commercial possibilities in the raw
materials of an area, he may select some of the more promising features
and subject them to the technical analysis necessary to determine their
availability for special uses. In this phase of his work he may find it
necessary to enlist the coöperation of skilled technicians and
laboratories in the various special fields. The problem is simplified if
the geologist is hunting for a particular material for a specific
purpose, for then he fortifies himself with a knowledge of the
particular qualities needed and directs his field and laboratory study
accordingly.
Too often the geologist fails to recognize the complexity and
definiteness of the qualities required, and makes statements and
recommendations on the use of raw materials based on somewhat general
geologic observations. On the other hand, the engineer, or the
manufacturer, or the builder often goes wrong and spends money
needlessly, by failing to take into consideration general geologic
features which may be very helpful in determining the distribution,
amount, and general characters of the raw materials needed.
It is difficult to draw the line between the proper fields of the
geologist and those of the engineer, the metallurgist, and other
technicians. It is highly desirable that the specialist in any one of
these fields know at least of the existence of the other fields and
something of their general nature. Too often his actions indicate he is
not acutely conscious even of the existence of these related branches of
knowledge. The extent and detail to which the geologist will familiarize
himself with these other fields will of course vary with his training
and the circumstances of his work. Whatever his limit is, it should be
definitely recognized; his work should be thorough up to this limit and
his efforts should not be wasted in fields which he is not best
qualified to investigate.
These remarks apply rather generally to mineral resources, but they are
particularly pertinent in relation to the common rock materials which
the geologist is daily handling,--for he is likely to assume that he
knows all about them and that he is qualified to give professional
advice to industries using them. In connection with metallic resources,
the metallurgical and other technical requirements are likely to be more
definitely recognized and the lines more sharply drawn, with the result
that the geologist is perhaps not so likely to venture into problems
which he is not qualified to handle.
The limits to geologic work here discussed are not necessarily limits
separating scientific from non-scientific work. The study and
determination of the qualities of rocks necessary for commercial
purposes is fully as scientific as a study of the qualities commonly
considered in purely geologic work, and the results of technical
commercial investigations may be highly illuminating from a purely
geological standpoint. When a field of scientific endeavor has been
established by custom, any excursion beyond traditional limits is almost
sure to be regarded by conservatives in the field as non-scientific, and
to be lightly regarded. The writer is fully conscious of the existence
of limits and the necessity for their recognition; but he would explain
his caution in exceeding these limits on the ground of training and
effectiveness, rather than on fear that he is becoming tainted with
non-scientific matters the moment he steps beyond the boundaries of his
traditional field.
SOILS AS A MINERAL RESOURCE
Soils are not ordinarily listed as mineral resources; but as weathered
and altered rock of great economic value, they belong nearly at the head
of the list of mineral products.
ORIGIN OF SOILS
Soil originate from rocks, igneous, sedimentary, and "metamorphic" by
processes of weathering, and by the mixing of the altered mineral
products with decayed plant remains or _humus_. The humus averages
perhaps 3 or 4 per cent of the soil mass and sometimes constitutes as
much as 75 per cent. Not all weathered rock is soil in the agricultural
sense. For this purpose the term is mainly restricted to the upper few
inches or feet penetrated by plant roots.
The general process of soil formation constitutes one of the most
important phases of katamorphism--the destructive side of the
metamorphic cycle, described in Chapter II. Processes of katamorphism or
weathering, usually accompanied by the formation of soils, affect the
surface rocks over practically all the continental areas.
The weathering of a highly acid igneous rock with much quartz produces a
residual soil with much quartz. The weathering of a basic igneous rock
without quartz produces a clay soil without quartz, which may be high
in iron. Where disintegration has been important the soil contains an
abundance of the original silicates of the rock, and less of the altered
minerals.
The production of soil from sedimentary rocks involves the same
processes as alter igneous rocks; but, starting from rocks of different
composition, the result is of course different in some respects.
Sandstones by weathering yield only a sandy soil. Limestones lose their
calcium carbonate by solution, leaving only clay with fragments of
quartz or chert as impurities. A foot of soil may represent the
weathering of a hundred feet of limestone. Shales may weather into
products more nearly like those of the weathering of igneous rocks.
Silicates in the shales are broken down to form clay, which is mixed
with the iron oxide and quartz.
In some localities the soil may accumulate to a considerable depth,
allowing the processes of weathering to go to an extreme; in others the
processes may be interrupted by erosion, which sweeps off the weathered
products at intermediate stages of decomposition and may leave a very
thin and little decomposed soil.
Soils formed by weathering may remain in place as residual soils, or
they may be transported, sorted, and redeposited, either on land or
under water. It is estimated by the United States Bureau of Soils[14]
that upward of 90 per cent of the soils of the United States which have
been thus far mapped owe their occurrence and distribution to
transportation by moving water, air, and ice (glaciers), and that less
than 10 per cent have remained in place above their parent rock.
Glaciers may move the weathered rock products, or they may grind the
fresh rocks into a powder called _rock flour_, and thus form soils
having more nearly the chemical composition of the unaltered rocks.
Glacial soils are ordinarily rather poorly sorted, while wind and
water-borne soils are more likely to show a high degree of sorting.
The character of a transported soil is less closely related to the
parent rock than is that of a residual soil, because the processes of
sorting and mixture of materials from different sources intervene to
develop deposits of a nature quite different from residual soils; but
even transported soil may sometimes be traced to a known rock
parentage.
Where deposited under water, soil materials may be brought above the
water by physiographic changes, and exposed at the surface in condition
for immediate use. Or, they may become buried by other sediments and not
be exposed again until after they have been pretty well hardened and
cemented,--in which case they must again undergo the softening processes
of weathering before they become available for use. Where soils become
buried under other rocks and become hardened, they are classed as
sedimentary rocks and form a part of the geologic record. Many residual
and transported soils are to be recognized in the geologic column; in
fact a large number of the sedimentary rocks ordinarily dealt with in
stratigraphic geology are really transported soils.
The development of soils by weathering should not be regarded as a
special process of rock alteration, unrelated to processes producing
other mineral products. Exactly the same processes that produce soils
may yield important deposits of iron ore, bauxite, and clay, and they
cause also secondary enrichment of many metallic mineral deposits. For
instance the weathering of a syenite rock containing no quartz, under
certain conditions, as in Arkansas, results in great bauxite deposits
which are truly soils and are useful as such,--but which happen to be
more valuable because of their content of bauxite. The weathering of a
basic igneous rock, as in Cuba, may produce important residual iron ore
deposits, which are also used as soils. Weathering of ferruginous
limestone may produce residual iron and manganese ores in clay soils.
COMPOSITION OF SOILS AND PLANT GROWTH
The mineral ingredients in soils which are essential for plant growth
include water, potash, lime, magnesia, nitrates, sulphur, and phosphoric
acid--all of which are subordinate in amount to the common products of
weathering (pp. 20-22, 23-24). Of these constituents magnesia is almost
invariably present in sufficient quantity; while potash, nitrates, lime,
sulphur, and phosphoric acid, although often sufficiently abundant in
virgin soil, when extracted from the soils by plant growth are liable to
exhaustion under ordinary methods of cultivation, and may need to be
replenished by fertilizers (Chapter VII). Some soils may be so
excessively high in silica, iron, or other constituents, that the
remaining constituents are in too small amounts for successful plant
growth.
Even where soils originally have enough of all the necessary chemical
elements, one soil may support plant growth and another may not, for the
reason that the necessary constituents are soluble and hence available
to the plant roots in one case and are not soluble in the other. Plainly
the mineral combinations in which the various elements occur are
important factors in making them available for plant use. Similarly a
soil of a certain chemical and mineralogical composition may be fruitful
under one set of climatic conditions and a soil of like composition may
be barren at another locality--indicating that availability of
constituents is also determined by climatic and other conditions of
weathering. Even with the same chemical composition and the same
climatic conditions, there may be such differences in texture between
various soils as to make them widely different in yield.
The unit of soil classification is the _soil type_, which is a soil
having agricultural unity, as determined by texture, chemical character,
topography, and climate. The types commonly named are clay, clay loam,
silt loam, loam, fine sandy loam, sandy loam, fine sand, and sand. In
general the soil materials are so heterogeneous and so remote from
specific rock origin, that in such classification the geologic factor of
origin is not taken into account. More broadly, soils may be classified
into provinces on the basis of geography, similar physiographic
conditions, and similarity of parent rocks; for instance, the soils of
the Piedmont plateau province, of the arid southwest region, of the
glacial and loessal province, etc. In such classification the geologic
factors are more important. Soils within a province may be subdivided
into "soil series" on the basis of common types of sub-soils, relief,
drainage, and origin.
USE OF GEOLOGY IN SOIL STUDY
While the desirability of particular soils is related in a broad way to
the character of the parent rocks, and while by geologic knowledge
certain territories can be predicated in advance as being more favorable
than others to the development of good soils, so many other factors
enter into the question that the geologic factor may be a subordinate
one. A soil expert finds a knowledge of geology useful as a basis for a
broad study of his subject; but in following up its intricacies he gives
attention mainly to other factors, such as the availability of common
constituents for plant use, the existence and availability of minute
quantities of materials not ordinarily regarded as important by the
geologist, the climatic conditions, and the texture. As the geologic
factors are many of them comparatively simple, much of the expert work
on soils requires only elementary and empirical knowledge of geology.
The geologist, although he may understand fully the origin of soils and
may indicate certain broad features, must acquire a vast technique not
closely related to geology before he becomes effective in soil survey
work and diagnosis.
For these reasons the mapping and classification of soils, while often
started by geologists of state or federal surveys, have in their
technical development and application now passed largely into the hands
of soil experts in the special soil surveys affiliated with the U. S.
Department of Agriculture and with agricultural colleges.
FOOTNOTES:
[13] A good summary of this subject may be found in _Engineering
Geology_, by H. Ries and T. L. Watson, Wiley and Sons, 2d ed., 1915.
[14] Marbut, Curtis F., Soils of the United States: _Bull. 96, Bureau of
Soils_, 1913, p. 10.
CHAPTER VII
THE FERTILIZER GROUP OF MINERALS
GENERAL COMMENTS
Soils are weathered rock more or less mixed with organic material. The
weathering processes forming soils are in the field of geologic
investigation, but the study of soils in relation to agriculture
requires attention to texture and to several of their very minor
constituents which have little geologic significance. Soil study has
therefore become a highly specialized and technicalized subject,--for
which a geological background is essential, but which is usually beyond
the range of the geologist. To supply substances which are deficient in
soils, however, requires the mining, quarrying, or extraction of
important mineral resources, and in this part of the soil problem the
geologist is especially interested.
Soils may be originally deficient in nitrates, phosphates, or potash; or
the continued cropping of soils may take out these materials faster than
the natural processes of nature supply them. In some soils there are
sufficient phosphates and potash to supply all plant needs indefinitely;
but the weathering and alteration processes, through which these
materials are rendered soluble and available for plant life, in most
cases are unable to keep up with the depletion caused by cropping. A ton
of wheat takes out of the soil on an average 47 pounds of nitrogen, 18
pounds of phosphoric acid, 12 pounds of potash. On older soils in Europe
it has been found necessary to use on an average 200 pounds of mixed
mineral fertilizers annually per acre. On the newer soils of the United
States the average thus far used has been less than one-seventh of this
amount. The United States has thus far been using up the original
materials stored in the soil by nature, but these have not been
sufficient to yield anything like the crop output per acre of the more
highly fertilized soils of Europe.
In addition to the nitrates, phosphates, and potassium salts, important
amounts of lime and sulphuric acid, and some gypsum, are used in
connection with soils. Lime is derived from crushed limestone (pp.
82-83), and is used primarily to counteract acidity or sourness of the
soil; it is, therefore, only indirectly related to fertilizers.
Sulphuric acid is used to treat rock phosphates to make them more
soluble and available to plant life. It requires the mining of pyrite
and sulphur. Gypsum, under the name of "land-plaster," is applied to
soils which are deficient in the sulphur required for plant life;
increase in its use in the future seems probable. There are also
considerable amounts of inert mineral substances which are used as
fillers in fertilizers to give bulk to the product, but which have no
agricultural value. The proportions of the fertilizer substances used in
the United States are roughly summarized in Figure 4.
The United States possesses abundant supplies of two of the chief
mineral substances entering into commercial fertilizers,--phosphate rock
and the sulphur-bearing materials necessary to treat it. For potash the
United States is dependent on Europe, unless the domestic industry is
very greatly fostered under protective tariff. For the mineral nitrates
the United States has been dependent on Chile, and because of the
cheapness of the supply will doubtless continue to draw heavily from
this source. However, because of the domestic development of plants for
the fixation of nitrogen from the air, the recovery of nitrogen from
coal in the by-product processes, and the use of nitrogenous plants, the
United States is likely to require progressively less of the mineral
nitrates from Chile.
The fertilizer industry of the United States is yet in its infancy and
is likely to have a large growth. Furthermore much remains to be learned
about the mixing of fertilizers and the amounts and kinds of materials
to be used. The importance of sulphur as a plant food has been realized
comparatively recently. The use of fertilizers in the United States has
come partly through education and the activity of agricultural schools
and partly through advertising by fertilizer companies. The increased
use of potash has been due largely to the propaganda of the German sales
agents. An examination of a map showing distribution of the use of
fertilizers over the country indicates very clearly the erratic
distribution of the effects of these various activities. One locality
may use large amounts, while adjacent territory of similar physical
conditions uses little. The sudden withdrawal of fertilizers for a
period of three or four years during the war had very deleterious
effects in some localities, but was not so disastrous as expected in
others,--emphasizing the fact that the use of fertilizers has been
partly fortuitous and not nicely adjusted to specific needs.
[Illustration: FIG. 4. FERTILIZER SITUATION IN THE UNITED
STATES. SMITHSONIAN INSTITUTION--UNITED STATES NATIONAL MUSEUM]
NITRATES
ECONOMIC FEATURES
There are several sources of nitrogen for fertilizer purposes: mineral
nitrates, nitrogen taken from the air by certain plants with the aid of
bacteria and plowed into the soil, nitrogen taken directly from the air
by combining nitrogen and oxygen atoms in an electric arc, or by
combining nitrogen and hydrogen to form ammonia, nitrogen taken from the
air to make a compound of calcium, carbon, and nitrogen (cyanamid),
nitrogen saved from coal in the form of ammonia as a by-product of
coke-manufacture, and nitrogen from various organic wastes. Nitrogen in
the form of ammonia is also one of the potential products of oil-shales
(p. 150). While the principal use of nitrogenous materials is as
fertilizers, additional important quantities are used in ammonia for
refrigerating plants, and in the form of nitric acid in a large number
of chemical industries. During the war the use of nitrates was largely
diverted to explosives manufacture. The geologist is interested
principally in the mineral nitrates as a mineral resource, but the other
sources of nitrogen, particularly its recovery from coal, also touch his
field.
Almost the single source of mineral nitrates for the world at present is
Chile, where there are deposits of sodium nitrate or Chile saltpeter,
containing minor amounts of potassium nitrate. About two-thirds of the
Chilean material normally goes to Europe and about one-fourth to the
United States. The supply has been commercially controlled chiefly by
Great Britain and by Chilean companies backed by British and German
capital.
The dependence of the world on Chile became painfully apparent during
the war. Germany was the only nation which had developed other sources
of nitrogenous material to any great extent. The other nations were
dependent in a very large degree on the mineral nitrates, both for
fertilizer and munition purposes. Total demands far exceeded the total
output from Chile, requiring international agreement as to the division
of the output among the nations. The stream of several hundred ships
carrying nitrates from Chile was one of the vital war arteries. This
situation led to strenuous efforts in the belligerent countries toward
the development of other sources of nitrogen. The United States, under
governmental appropriation, began the building of extensive plants for
the fixation of nitrogen from the air, and the building of by-product
coke ovens in the place of the old wasteful beehive ovens was
accelerated. Germany before the war had already gone far in both of
these directions, not only within her own boundaries, but in the
building of fixation plants in Scandinavia and Switzerland. War
conditions required further development of these processes in Germany,
with the result that this country was soon entirely self-supporting in
this regard. One of the effects was the almost complete elimination in
Germany of anything but the by-product process of coking coal.
War-time development of the nitrogen industry in the United States for
munition purposes brought the domestic production almost up to the
pre-war requirements for fertilizers alone. With the increasing demand
for fertilizers and with the cheapness of the Chilean supply of natural
nitrates, it is likely that the United States will continue for a good
many years to import considerable amounts of Chilean nitrates. It may be
noted that, although this country normally consumes about one-fourth of
the Chilean product, American interests commercially control less than
one-twentieth of the output. Presumably, if for no other purpose than
future protection, effort will be made to develop the domestic industry
to a point where in a crisis the United States could be independent of
Chile. Particularly may an increase in the output of by-product ammonia
from coke manufacture be looked for (see also pp. 118-119), since
nitrogenous material thus produced need bear no fixed part of the cost
of production, and requires no protective tariff.
The reserves of Chilean nitrate are known to be sufficient for world
requirements for an indefinitely long future.
GEOLOGIC FEATURES
Mineral nitrates in general, and particularly those of soda and potash,
are readily soluble at ordinary temperatures. Mineral nitrate deposits
are therefore very rare, and are found only in arid regions or other
places where they are protected from rain and ground-water. The only
large deposits known are those of northern Chile and some extensions in
adjacent parts of Peru and Bolivia. These are located on high desert
plateaus, where there is almost a total absence of rain, and form
blankets of one to six feet in thickness near the surface. The most
important mineral, the sodium nitrate or Chile saltpeter, is mingled
with various other soluble salts, including common salt, borax minerals,
and potassium nitrate, and with loose clay, sand, and gravel. The
nitrate deposits occur largely around and just above slight basin-like
depressions in the desert which contain an abundance of common salt. The
highest grade material contains 40 to 50 per cent of sodium nitrate, and
material to be of shipping grade must run at least 12 to 15 per cent.
The origin of the nitrate beds is commonly believed to be similar to
that of beds of rock salt (pp. 295-298), borax, and other saline
residues. The source of the nitrogen was probably organic matter in the
soil, such as former deposits of bird guano, bones (which are actually
found in the same desert basin), and ancient vegetable matter. By the
action of nitrifying bacteria on this organic matter, nitrate salts are
believed to have formed which were leached out by surface and ground
waters, and probably carried in solution to enclosed bodies of water.
Here they became mingled with various other salts, and all were
precipitated out as the waters of the basins evaporated. Deliquescence
and later migration of the more soluble nitrates resulted in their
accumulation around the edges of the basins. The nitrate beds are thus
essentially a product of desiccation.
While the origin just set forth is rather generally accepted, several
other theories have been advanced. It has been suggested that the
deposits were not formed in water basins, but that ground water carrying
nitrates in solution has been and is rising to the surface,--where,
under the extremely arid conditions, it evaporates rapidly, leaving the
nitrates mixed with the surface clays. One group of writers accounts for
the deposits by the fixation of atmospheric nitrogen through electrical
phenomena. Still others note the frequent presence of nitrogen in
volcanic exhalations and the association of the Chilean nitrate beds
with surface volcanic rocks; they suggest that these rocks were the
source of the nitrogen, which under unusual climatic conditions was
leached out and then deposited by evaporation.
PHOSPHATES
ECONOMIC FEATURES
The principal use of natural phosphates is in the manufacture of
fertilizers. They are also used in the manufacture of phosphorus,
phosphoric acid, and other phosphorus compounds, for matches, for
certain metallurgical operations, and for gases used in military
operations.
The material mined is mainly a phosphate of lime (tricalcium phosphate).
To make it available for plant use, it is treated with sulphuric acid to
form a soluble superphosphate; hence the importance of sulphuric acid,
and its mineral sources pyrite and sulphur, in the fertilizer industry.
A small percentage of the phosphate is also ground up and applied
directly to the soil in the raw form. Other phosphatic materials are the
basic slag from phosphatic iron ores made into Thomas-process steel,
guano from the Pacific islands, and bone and refuse (tankage) from the
cattle raising and packing countries. These materials are used for the
same purposes as the natural phosphates.
The United States is the largest factor in the world's phosphate
industry, with reference both to production and reserves.
The largest and most available of the European sources are in Tunis and
Algeria, under French control, and in Egypt, under English control.
Belgium and northern France have been considerable producers of
phosphates, but, with the development of higher grade deposits in other
countries, their production has fallen to a very small fraction of the
world's total. There also has been very small and insignificant
production in Spain and Great Britain. Russia has large reserves which
are practically unmined.
While there is comparatively little phosphate rock in western Europe, a
considerable amount of the phosphate supply is obtained as a by-product
from Thomas slag, derived from phosphatic iron ores. These ores are
chiefly from Lorraine and Sweden, but English and Russian ores can be
similarly used.
Outside of Europe and the United States, there are smaller phosphate
supplies in Canada, the Dutch West Indies, Venezuela, Chile, South
Australia, New Zealand, and several islands of the Indian and South
Pacific Oceans. None of these has yet contributed largely to world
production, and their distance from the principal consuming countries
bordering the North Atlantic basin is so great that there is not likely
to be any great movement to this part of the world. On the other hand,
some of the South Sea islands have large reserves of exceptionally high
grade guano and bone phosphates, which will doubtless be used in
increasing amounts for export to Japan, New Zealand, and other nearby
countries. The most important of these islands are now controlled by
Great Britain, Japan, and France.
A striking feature of the situation is that the central European
countries, which have been large consumers of phosphate material, have
lost not only the Pacific island phosphates but the Lorraine phosphatic
iron ores, and are now almost completely dependent on British, French,
and United States phosphate.
In the United States, reserves of phosphate are very large. They are
mined principally in Florida, Tennessee, and South Carolina; but great
reserves, though of lower grade, are known in Arkansas, Montana, Idaho,
Wyoming, and Utah. There are possibilities for the development of local
phosphate industries in the west, in connection with the manufacture of
sulphuric acid from waste smelting gases at nearby mining centers. The
Anaconda Copper Mining Company has taken up the manufacture of
superphosphate as a means of using sulphuric acid made in relation to
its smelting operations. The United States is independent in phosphate
supplies and has a surplus for export. This country, England, and France
exercise control of the greater part of the world's supply of phosphatic
material. In competition for world trade, the Florida and Carolina
phosphates are favorably situated for export, but there is strong
competition in Europe from the immense fields in French North Africa,
which are about equally well situated.
GEOLOGIC FEATURES
Small amounts of phosphorus are common in igneous rocks, in the form of
the mineral apatite (calcium phosphate with calcium chloride or
fluoride). Apatite is especially abundant in some pegmatites. In a few
places, as in the Adirondacks where magnetic concentration of iron ores
leaves a residue containing much apatite, and in Canada and Spain where
veins of apatite have been mined, this material is used as a source of
phosphate fertilizer. The great bulk of the world's phosphate, however,
is obtained from other sources--sedimentary and residual beds described
below.
Phosphorus in the rocks is dissolved in one form or another by the
ground-waters; a part of it is taken up by land plants and animals for
the building of their tissues, and another part goes in solution to the
sea to be taken up by sea plants and animals. In places where the bones
and excrements of land animals or the shells and droppings of sea
animals accumulate, deposits of phosphatic material may be built up.
In certain places where great numbers of sea birds congregate, as on
desert coasts and oceanic islands, guano deposits have been formed. Some
of them, like the worked-out deposits of Peru and Chile, are in arid
climates and have been well preserved. Others, like those of the West
Indies and Oceania, are subjected to the action of occasional rains; and
to a large extent the phosphates have been leached out, carried down,
and reprecipitated, permeating and partially replacing the underlying
limestones. In this way deposits have been formed containing as high as
85 per cent calcium phosphate.
Even more important bodies of phosphates have been produced by the
accumulation of marine animal remains, probably with the aid of joint
chemical, bacterial, and mechanical precipitation. These processes have
formed the chief productive deposits of the world, including those of
the United States, northern Africa, and Russia, and also the phosphatic
iron ores of England and central Europe. The sedimentary features of
many phosphate rocks, particularly their oölitic textures, show a marked
similarity to the features of the Clinton type of iron ores (pp.
166-167).
The marine phosphate beds originally consist principally of calcium
phosphate and calcium carbonate in varying proportions. Depending on the
amount of secondary enrichment, they form two main types of deposits.
The extensive beds of the western United States (in the upper
Carboniferous) are hard, and very little enrichment by weathering has
taken place; they carry in their richer portions 70 to 80 per cent
calcium phosphate, and large sections range only from about 30 to 50 per
cent. In the southeastern deposits (Silurian and Devonian in Tennessee
and Tertiary in the Carolinas and Florida), there has been considerable
enrichment, the rock is softer, and the general grade ranges from 65 to
80 per cent. Both calcium carbonate and calcium phosphate are soluble in
ordinary ground waters, but the carbonate is the more soluble of the
two. Thus the carbonate has been dissolved out more rapidly, and in
addition descending waters carrying the phosphate have frequently
deposited it to pick up the carbonate. These enriching processes,
sometimes aided by mechanical concentration, have formed high-grade
deposits both in the originally phosphatic beds and in various
underlying strata. Concretionary and nodular textures are common. The
"pebble" deposits of Florida consist of the phosphatic materials broken
up and worked over by river waters and advancing shallow seas.
PYRITE
ECONOMIC FEATURES
The principal use of pyrite is in the manufacture of sulphuric acid.
Large quantities of acid are used in the manufacture of fertilizers from
phosphate rock, and during war times in the manufacture of munitions.
Sulphuric acid converts the phosphate rock into superphosphate, which is
soluble and available for plant use. Other uses of the acid are referred
to in connection with sulphur. Pyrite is also used in Europe for the
manufacture of paper from wood-pulp, but in the United States native
sulphur has thus far been exclusively used for this purpose. The residue
from the roasting of pyrite is a high-grade iron ore material frequently
very low in phosphorus, which is desirable in making up mixtures for
iron blast furnaces.
Most of the countries of Europe are producers of pyrite, and important
amounts are also produced in the United States and Canada. The European
production is marketed mainly on that continent, but considerable
amounts come to the United States from Spain.
Before the war domestic sources supplied a fourth to a third of the
domestic demand for pyrite. Imports came mainly from Spain and Portugal
to consuming centers on the Atlantic seaboard. The curtailment of
overseas imports of pyrite during the war increased domestic production
by about a third and resulted also in drawing more heavily on Canadian
supplies, but the total was not sufficient to meet the demand. The
demand was met by the increased use of sulphur from domestic deposits
(p. 109). At the close of the war supplies of pyrite had been
accumulated to such an extent that, with the prospect of reopening of
Spanish importation, pyrite production in the United States practically
ceased. War experience has demonstrated the possibility of substitution
of sulphur, which the United States has in large and cheaply mined
quantities. The future of the pyrite industry in the United States
therefore looks cloudy, except for supplies used locally, as in the
territory tributary to the Great Lakes, and except for small amounts
locally recovered as by-products in the mining of coal or from ores of
zinc, lead, and copper. Pyrite production in the past has been chiefly
in the Appalachian region, particularly in Virginia and New York, and in
California.
GEOLOGIC FEATURES
Pyrite, the yellow iron sulphide, is the commonest and most abundant of
the metallic sulphides. It is formed under a large variety of conditions
and associations. Marcasite and pyrrhotite, other iron sulphide
minerals, are frequently found with pyrite and are used for the same
purposes.
The great deposits of Rio Tinto, Spain, which produce about half of the
world's pyrite, were formed by replacement of slates by heated solutions
from nearby igneous rocks. The ores are in lenticular bodies, and
consist of almost massive pyrite with a small amount of quartz and
scattered grains and threads of chalcopyrite (copper-iron sulphide).
They carry about 50 per cent of sulphur, and the larger part carries
about 2 per cent of copper which is also recovered.
Similar occurrences of pyrite on a smaller scale are known in many
places. Pyrite is very commonly found in vein and replacement deposits
of gold, silver, copper, lead, and zinc. In the Mississippi valley it is
extracted as a by-product from the lead and zinc ores, and in the
Cordilleran region large quantities of by-product pyrite could easily be
produced if there were a local demand. The pyrite deposits of the
Appalachian region are chiefly lenses in schists; they are of uncertain
origin though some are believed to have been formed by replacement of
metamorphosed limestones and schists.
Under weathering conditions pyrite oxidizes, the sulphur forming
sulphuric acid,--an important agent in the secondary enrichment of
copper and other sulphides,--and the iron forming the minerals hematite
and limonite in the shape of a "gossan" or "iron-cap."
Pyrite is likewise frequently found in sediments, apparently being
formed mainly by the reducing action of organic matter on iron salts in
solution. In Illinois and adjacent states it is obtained as a by-product
of coal mining.
SULPHUR
ECONOMIC FEATURES
Sulphur is used for many of the same purposes as pyrite. Under pre-war
conditions, the largest use in the United States was in the manufacture
of paper pulp by the sulphite process. Minor uses were in agriculture as
a fungicide and insecticide, in vulcanizing rubber, and in the
manufacture of gunpowder. About 5 per cent of the sulphur of the United
States was used in the manufacture of sulphuric acid. During the war
this use was greatly increased because of the shortage of pyrite and the
large quantities of sulphuric acid necessary for the manufacture of
explosives. The replacement of pyrite by sulphur in the manufacture of
sulphuric acid has continued since the war, and in the future is likely
to continue to play an important part. Sulphuric acid is an essential
material for a great range of manufacturing processes. Some of its more
important applications are: in the manufacture of superphosphate
fertilizer from phosphate rock; in the refining of petroleum products;
in the iron, steel, and coke industries; in the manufacture of
nitroglycerin and other explosives; and in general metallurgical and
chemical practice.
The United States is the world's largest sulphur producer. The principal
foreign countries producing important amounts of sulphur are Italy,
Japan, Spain, and Chile. Europe is the chief market for the Italian
sulphur. In spite of increased demands in Europe the Italian production
has decreased as the result of unfavorable labor, mining, and
transportation conditions, and the deficit has had to be met from the
United States. Japan's sulphur production has been increasing. Normally
about half of the material exported comes to the United States to supply
the needs of the paper industry in the Pacific states, and half goes to
Australia and other British colonies. Spain's production is relatively
small and has been increasing slowly; most of it is consumed locally.
Chile's small production is mainly consumed at home and large additional
amounts are imported.
The sulphur output of the United States, which in 1913-14 was second to
Italy, now amounts to three-fourths of the entire output of the world,
and the United States has become a large exporter of sulphur. Supplies
are ample and production increasing, with the result that the United
States can not only meet its own demands, but can use this commodity
extensively in world trade. Small amounts of sulphur are mined in some
of the western states, but over 98 per cent of the production comes from
Louisiana and Texas.
GEOLOGIC FEATURES
Native sulphur is found principally in sedimentary beds, where it is
associated with gypsum and usually with organic matter. Deposits of this
type are known in many places, the most important being those of Sicily
and of the Gulf Coast in the United States. In the latter region beds of
limestone carry lenses of sulphur and gypsum which are apparently
localized in dome-like upbowings of the strata. The deposits are
overlain by several hundred feet of loose, water-bearing sands, through
which it is difficult to sink a shaft. An ingenious and efficient
process of mining is used whereby superheated water is pumped down to
melt the sulphur, which is then forced to the surface by compressed air
and allowed to consolidate in large bins. The Sicilian deposits are
similar lenses in clayey limestones containing 20 to 25 per cent of
sulphur, associated with gypsum and bituminous marl; they are mined by
shafts.
Concerning the origin of these deposits several theories have been
advanced. It has been thought that the materials for the deposits were
precipitated at the same time as the enclosing sediments; and that the
sulphur may have been formed by the oxidation of hydrogen sulphide in
the precipitating waters through the agency of air or of
sulphur-secreting bacteria, or that it may have been produced by the
reduction of gypsum by organic matter or bacteria. Others have suggested
that hot waters rising from igneous rocks may have brought in both the
sulphur and the gypsum, which in crystallizing caused the upbowing of
the strata which is seen in the Gulf fields (see also p. 298).
Native sulphur is also found in mineral springs from which hydrogen
sulphide issues, where it is produced by the oxidation of the hydrogen
sulphide. It likewise occurs in fissures of lava and around volcanic
vents, where it has probably been formed by reactions between the
volcanic gases and the air. The Japanese and Chilean deposits are of the
volcanic type.
POTASH
ECONOMIC FEATURES
Potash is used principally as a component of fertilizers in agriculture.
It is also used in the manufacture of soap, certain kinds of glass,
matches, certain explosives, and chemical reagents.
For a long time potash production was essentially a German monopoly. The
principal deposits are in the vicinity of Stassfurt in north central
Germany (about the Harz Mountains). Stassfurt salts are undoubtedly
ample to supply the world's needs of potash for an indefinite future.
However, other deposits, discovered in the Rhine Valley in Alsace in
1904, have been proved to be of great extent; and though the production
has hitherto been limited by restrictions imposed by the German
Government, it has nevertheless become considerable.[15] The grade (18
per cent K_{2}O) is superior to the general run of material taken from
the main German deposits, and the deposits have a regularity of
structure and uniformity of material favorable to cheaper mining and
refining than obtains in the Stassfurt deposits.
Other countries have also developed supplies of potash, some of which
will probably continue to produce even in competition with the deposits
of recognized importance referred to above. Noteworthy among the newer
developments are those in Spain.[16] These have not yet produced on any
large scale, but their future production may be considerable. Less
important deposits are known in Galicia, Tunis, Russia, and eastern
Abyssinia, and the nitrate deposits of Chile contain a small percentage
of potash which is being recovered in some of the operations.
Prior to the war the United States obtained its potash from Germany. The
German potash industry was well organized and protected by the German
Government, which made every effort to maintain a world monopoly. During
the war the potash exports from Germany were cut off, excepting exports
to the neutrals immediately adjoining German territory. The result in
the United States was that the price of potash rose so far as to greatly
diminish its use as fertilizer.
The consequent efforts to increase potash production in the United
States met with considerable success, but the maximum production
attained was only about one-fourth of the ordinary pre-war requirements.
The principal American sources are alkaline beds and brines in Nebraska,
Utah, and California, and especially at Searles Lake, California. These
furnished 75 per cent of the total output. Minor amounts have been
extracted in Utah from the mineral alunite (a sulphate of potassium and
aluminum), in Wyoming from leucite (a potassium-aluminum silicate), in
California from kelp or seaweed, and in various localities from
cement-mill and blast-furnace dusts, from wood ashes, from wool
washings, from the waste residues of distilleries and beet-sugar
refineries, and from miscellaneous industrial wastes. At the close of
the war, sufficient progress had been made in the potash industry to
indicate that the United States might become self-supporting in the
future, though at high cost. The renewal of importation of cheap potash
from Germany, with probable further offerings from Alsace and Spain,
makes it impossible for the United States potash production to continue;
except, perhaps, for the recovery of by-products which will go on in
connection with other industries. Demand for a protective tariff has
been the inevitable result (see Chapters XVII and XVIII).
GEOLOGIC FEATURES
Potassium is one of the eight most abundant elements in the earth. It
occurs as a primary constituent of most igneous rocks, some of which
carry percentages as high as those in commercial potash salts used for
fertilizers. It is present in some sediments and likewise occurs in many
schists and gneisses. Various potassium silicates--leucite, feldspar,
sericite, and glauconite--and the potassium sulphate, alunite, have
received attention and certain of them have been utilized to a small
extent, but none of them are normally able to compete on the market.
Potential supplies are thus practically unlimited in amount and
distribution. Deposits from which the potash can be extracted at a
reasonable cost, however, are known in only a few places, where they
have been formed as saline sediments.
In the decomposition of rocks the potash, like the soda, is readily
soluble, but in large part it is absorbed and held by clayey materials
and is not carried off. Potash is therefore more sparingly present in
river and ocean waters than is soda, and deposits of potash salts are
much rarer than those of rock salt and other sodium compounds. The large
deposits in the Permian beds of Stassfurt, as well as those in the
Tertiary of Alsace and Spain, have been formed by the evaporation of
very large quantities of salt water, presumably sea water. They consist
of potassium salts, principally the chloride, mixed and
intercrystallized with chlorides and sulphates of magnesium, sodium, and
calcium. In the Stassfurt deposits the potassium-magnesium salts occupy
a relatively thin horizon at the top of about 500 feet of rock salt
beds, the whole underlying an area about 200 miles long and 140 miles
wide. The principal minerals in the potash horizon are carnallite
(hydrous potassium-magnesium chloride), kieserite (hydrous magnesium
sulphate), sylvite (potassium chloride), kainite (a hydrous double salt
of potassium chloride and magnesium sulphate), and common salt (sodium
chloride). The potash beds represent the last stage in the evaporation
of the waters of a great closed basin, and the peculiar climatic and
topographic conditions which caused their formation have been the
subject of much speculation. This subject is further treated in the
discussion of common salt beds (pp. 295-298).
In the United States the deposits at Searles Lake, California, have been
produced by the same processes on a smaller scale. In this case
evaporation has not been carried to completion, but the crystallization
and separation out of other salts has concentrated the potassium (with
the magnesium) in the residual brine or "mother liquor." The deposits of
this lake or marsh also contain borax (see p. 276), and differ in
proportions of salts from the Stassfurt deposits. This is due to the
fact that they were probably derived, not from ocean waters, but from
the leaching of materials from the rocks of surrounding uplands,
transportation of these materials in solution by rivers and ground
waters, and concentration in the desert basin by evaporation.
The alkali lakes of Nebraska are believed to be of very recent geologic
origin. They lie in depressions in a former sand dune area, and contain
large quantities of potash supposedly accumulated by leaching of the
ashes resulting from repeated burnings of the grass in the adjacent
country.
Of other natural mineral sources, alunite is the most important. The
principal deposits worked are at Marysville, Utah, but the mineral is a
rather common one in the western part of the United States, associated
with gold deposits, as at Goldfield, Nevada. Alunite occurs as veins and
replacement deposits, often in igneous associations, and is supposed to
be of igneous source. Its origin is referred to in connection with the
Goldfield ores (p. 230).
FOOTNOTES:
[15] Gale, Hoyt S., The potash deposits of Alsace: _Bull. 715-B, U. S.
Geol. Survey_, 1920, pp. 17-55.
[16] Gale, Hoyt S., Potash deposits in Spain: _Bull. 715-A, U. S. Geol.
Survey_, 1920, pp. 1-16.
CHAPTER VIII
THE ENERGY RESOURCES--COAL, OIL, GAS (AND ASPHALT)
COAL
ECONOMIC FEATURES
Coal overshadows all other mineral resources, except water, in
production, value, and demand. It is the greatest of the energy
sources--coal, petroleum, gas, and water power. Roughly two-thirds of
the world's coal is used for power, one-sixth for smelting and
metallurgical industries, and one-sixth for heating purposes. Coal
constitutes over one-third of the railroad tonnage of the United States
and is the largest single tonnage factor in international trade; 70 per
cent of the pre-war tonnage of outgoing cargoes from England was coal.
=World production and trade.= The great coal-producing countries of the
world border the North Atlantic basin. The United States produces about
40 per cent of the world's total, Great Britain about 20 per cent, and
Germany about 20 per cent. Other countries producing coal stand in about
the following order: Austria-Hungary, France, Russia, Belgium, Japan,
China, India, Canada, and New South Wales. There is similarity in the
major features of the distribution of coal production and of iron ore
production. The great centers of coal production--the Pennsylvania and
Illinois fields of the United States, the Midlands district of England,
and the lower Rhine or Westphalian fields of Germany--are also the great
centers of the iron and steel industries of these countries. As in the
case of iron ore, there is rather a striking absence of important coal
production in the southern hemisphere and in Asia. A significant item in
the world's distribution of coal supplies is England's world-wide system
of coaling stations for shipping.
The principal coal-producing countries all have large reserves of coal.
Outside of these countries the world's most important reserves are in
China, which may be looked to for great future development. For the most
part, except for the probable Chinese development, it is likely that
countries now producing most of the coal will continue to do so in the
future, and that outlying parts of the world will continue to be
supplied mainly from these countries.
The quantity and distribution of the coal reserves of the world have
been estimated with perhaps a greater degree of accuracy than those of
any other mineral resource. From these estimates it appears that the
North American continent contains about half of the world reserves
(principally in the United States, with lesser amounts in Canada) and
Asia about one-fourth (principally in China, with some in India). Europe
contains only one-sixth of the world total, chiefly in the area of the
former German Empire and in Great Britain, with smaller quantities in
Russia, Austria-Hungary, France, and Belgium. Australasia (New South
Wales), Africa (British South Africa), and South America (Chile, Brazil,
Peru, and Colombia), together contain less than a tenth of the total
reserves. Coal being one of the great bases for modern industrialism,
the large reserves of high grade-coals in China have led to the belief
that China may some day develop into a great manufacturing nation.
Similarly, the deficiency in coal of most of the South American and
African countries seems to preclude their developing any very large
manufacturing industries, except where water power is available. Coal
reserves and the conservation of coal are further discussed in Chapter
XVII.
The war resulted in considerable disturbances in coal production and
distribution. There has not yet been a return to normal conditions, and
some of the changes are probably permanent. The great overseas movement
of coal from Germany was stopped and that from England curtailed. To
some extent the deficiency was supplied by coal exports from the United
States, particularly to South America. The shutting off of the normal
German export to France and Mediterranean countries, the occupation of
the French and Belgian coal fields by the Germans, and the partial
restriction of German exports to Scandinavian countries, resulted in
Europe's absorbing most of the British coal available for export, and in
addition requiring coal from the United States. The stress in the
world's coal industry to meet the energy requirements of war is too
recent and vivid to require more than mention. The world was made to
realize almost for the first time the utterly vital and essential nature
of this industry.
Since the war, there has been a gradual resumption of England's export
of coal along old lines of international trade. The German overseas
export trade has not been reëstablished, and cannot be for a long time
to come if Germany fulfills the terms of the Peace Treaty. Indeed,
because of slow recovery in output of German coal, there is yet
considerable lag in the supply available for European countries. The
terms of the Peace Treaty lessened the territory of German coal reserves
and required considerable additional contributions of coal to be
delivered to France, Belgium, Luxemburg, and Italy.
The increased export of coal from the United States during the war is
likely to be in part continued in the future, although the great bulk of
the United States production will in the future, as in the past, be
absorbed locally. Most of the coal in the United States available for
export is higher in volatile matter than the British and German export
coal. This quality will in some degree be a limiting factor in
exportation. On the other hand, it may result in wider introduction of
briquetting, coking, and other processes, which will tend to improve the
local industry and be conservational in their effect.
Japan will doubtless hold some of the Asiatic coal market gained during
the war.
International coal relations are further discussed in Chapter XVIII.[17]
=Production in the United States.= The main features of the distribution
of coal supplies in the United States are:
(1) Localization of the anthracite production and reserves in a limited
area in the Lawton region of Pennsylvania. Low-grade anthracite coal
also occurs in Rhode Island, North Carolina, Colorado, and Idaho.
(2) Localization of the bituminous production in the eastern and
interior states of Pennsylvania, West Virginia, Ohio, Indiana, Illinois,
and Kentucky. The principal reserves of bituminous coal occur in the
same provinces, but important additional reserves are known in Texas, in
North and South Carolina, and in the Rocky Mountain and Pacific Coast
provinces.
(3) The existence of large tonnages of subbituminous coal in the west,
which have not been mined to any extent.
(4) The existence of large fields of lignite in the Gulf Coast region,
and in the Northern Plains region, which have not been mined.
=Coke.= About one-sixth of the bituminous coal mined in the United
States is made into _coke_, that is, it is subjected to heat in ovens
from which oxygen is excluded in order to drive off the volatile gases
(chiefly hydrocarbons and water) which constitute about 40 per cent of
the weight of the coal. The residual product, the coke, is a light,
porous mass with a considerably higher percentage of fixed carbon than
bituminous coal. In regard to composition, coking accomplishes
artificially somewhat the same result reached by nature in its slow
development of high-grade coals, but the texture of coke is far
different from that of coal. Not all bituminous coals are suitable for
coke manufacture; and such coals are frequently divided into two
classes, known as _coking_ and _non-coking_ coals. Coke is used
principally for smelting purposes. Because of its spongy, porous
texture, it burns more rapidly and intensely than coal.
The gases eliminated in coking are wasted in the old-fashioned "beehive"
ovens, but in modern "by-product" coke ovens these gases by proper
treatment yield valuable coal tar products and ammonia. It is estimated
that the sum of the value of the products thus recovered from a ton of
coal multiplies the value of the ton of coal at the mine by at least
thirteen times. The importance of this fact from the conservational
standpoint cannot be too much emphasized. At present over half of the
total coke produced in the United States comes from by-product ovens,
and this proportion will doubtless increase in the future.
BALANCE SHEET SHOWING CONTRAST BETWEEN VALUE OF 1 TON OF BITUMINOUS COAL
AT MINE AND VALUE OF PRODUCTS WHICH IT CONTAINS, BASED ON CONDITIONS
PREVAILING IN 1915.[1]
_Value at _Value at point of
mine 1915_ _Quantity_ production, 1915_
-------------------------------------------------------------------------
1 ton (2,000 pounds) |(1,500 pounds smokeless fuel $5.00[2]
bituminous coal |(10,000 cubic feet gas, at
contains $1.13 | 90c. per 1,000 9.00[3]
|(22 pounds ammonium sulphate at 2.8c. .61
|(2-1/2 gallons benzol, at 30c. .75[4]
|(9 gallons tar, at 2.6c. .23[4]
Total $1.13[5]| $15.59
-------------------------------------------------------------------------
1: Gilbert, Chester G., and Pogue, Joseph E., The energy resources of
the United States--A field for reconstruction: _Bull. 102, U. S.
National Museum_, vol. 1, 1919, p. 11.
2: Figure based upon approximate selling price of anthracite.
3: Figure based upon average price of city gas.
4: These figures would be much higher if an adequate coal products
industry were in existence.
5: This figure shows clearly that lowering the cost of production cannot
be expected to lower the price of coal. Even if the cost of production
were eliminated, the price of coal would merely be a dollar less.
=Classification of coals.= The accurate naming and classification of
different varieties of coal is not an easy matter. The three main
classes,--anthracite, bituminous, and lignite,--have group
characteristics determined by their composition, color, texture, origin,
and uses, and for general purposes these names have reasonably definite
significance. However, there is complete gradation in coal materials
from peat through lignite to bituminous and anthracite coals; many
varieties fall near the border lines of the main groups, and their
specific naming then becomes difficult. In addition, coal is made up of
several substances which vary unequally in their proportions. It is
difficult to arrange all of these variables in a graded series in such a
fashion as to permit of precise naming of the coal. Furthermore, the
scientific naming of a coal may not serve the purpose of discriminating
coals used for different commercial purposes. Even the commercial names
vary among themselves, depending on the use for which the coal is being
considered.
Thus it is that the naming and classification of coals is a perennial
source of difficulty and controversy. The earliest and most widely used
classification is based on the ratio between fixed (or non-volatile)
carbon and volatile constituents, called the "fuel ratio." For this
purpose "proximate" analyses of coal are made, in terms of fixed carbon,
volatile matter, moisture, ash, and sulphur. Anthracite has a higher
fuel ratio than bituminous coal; that is, it has more fixed carbon in
relation to volatile matter. Similarly bituminous coal has a higher fuel
ratio than lignite. The fuel ratio measures roughly the heat or
calorific power of the coal, in other words, its fuel value. However,
some bituminous coals have a higher calorific power than some
anthracites, because a large part of their volatile matter is
combustible and yields more heat than the corresponding weight of fixed
carbon in the anthracite. The fuel ratio pretty well discriminates coals
of the higher ranks, and gives a classification corresponding roughly
with their commercial uses. For the lower ranks of coal it is not so
satisfactory, because the volatile constituents of such coals contain
large and varying percentages of non-combustible hydrogen, oxygen, and
nitrogen. Also such coals contain larger and more variable amounts of
moisture, which is inert to combustion and requires heat for its
evaporation. Two coals of the lower ranks with the same fuel ratio may
have very different fuel qualities and different commercial uses,
because of their different amounts of inert volatile matter and of
water. For these coals it is sometimes desirable to supplement the
chemical classification by physical criteria. For instance,
subbituminous coal may be distinguished from lignite, not by its fuel
ratio alone, but by its shiny, black appearance as contrasted with the
dull, woody appearance of lignite. Bituminous may be distinguished from
subbituminous by the manner of weathering. Other classifications have
attempted to recognize these difficulties and still maintain a purely
chemical basis by considering separately the combustible and
non-combustible volatile constituents. For this purpose, it is necessary
to have not merely approximate analyses, but the ultimate analyses in
terms of elements.
Definitions of the principal kinds of coal by Campbell,[18] of the
United States Geological Survey, are as follows:
_Anthracite._ Anthracite is generally well known and may be
defined as a hard coal having a fuel ratio (fixed carbon
divided by the volatile matter) of not more than 50 or 60 and
not less than 10.
_Semianthracite._ Semianthracite is also a hard coal, but it
is not so hard as true anthracite. It is high in fixed carbon,
but not so high as anthracite. It may be defined as a hard
coal having a fuel ratio ranging from 6 to 10. The lower limit
is uncertain, as it is difficult to say where the line should
be drawn to separate "hard" from "soft" coal and at the same
time to divide the two ranks according to their fuel ratio.
_Semibituminous._ The name "semibituminous" is exceedingly
unfortunate, as literally it implies that this coal is half
the rank of bituminous, whereas it is applied to a kind of
coal that is of higher rank than bituminous--really
superbituminous. Semibituminous coal may be defined as coal
having a fuel ratio ranging from 3 to 7. Its relatively high
percentage of fixed carbon makes it nearly smokeless when it
is burned properly, and consequently most of these coals go
into the market as "smokeless coals."
_Bituminous._ The term "bituminous," as generally understood,
is applied to a group of coals having a maximum fuel ratio of
about 3, and hence it is a kind of coal in which the volatile
matter and the fixed carbon are nearly equal; but this
criterion cannot be used without qualification, for the same
statement might be made of subbituminous coal and lignite. As
noted before, the distinguishing feature which serves to
separate bituminous coal from coals of lower rank is the
manner in which it is affected by weathering.
_Subbituminous._ The term "subbituminous" is adopted by the
Geological Survey for what has generally been called "black
lignite," a term that is objectionable because the coal is not
lignitic in the sense of being distinctly woody, and because
the use of the term seems to imply that this coal is little
better than the brown, woody lignite of North Dakota, whereas
many coals of this rank approach in excellence the lowest
grade of bituminous coal. Subbituminous coal is generally
distinguishable from lignite by its black color and its
apparent freedom from distinctly woody texture and structure,
and from bituminous coal by its loss of moisture and the
consequent breaking down of "slacking" that it undergoes when
subjected to alternate wetting and drying.
_Lignite._ The term "lignite," as used by the Geological
Survey, is restricted to those coals which are distinctly
brown and either markedly woody or claylike in their
appearance. They are intermediate in quality and in
development between peat and subbituminous coal.
[Illustration: FIG. 5. Diagrams showing the chemical
composition and heat efficiency of the several ranks of coal. Upper
diagram: Comparative heat value of the samples of coal represented in
the lower diagram, computed on the ash-free basis. Lower diagram:
Variation in the fixed carbon, volatile matter, and moisture of coals of
different ranks, from lignite to anthracite, computed on samples as
received, on the ash-free basis. After Campbell.]
GEOLOGIC FEATURES
Geologic features of coal may be conveniently described in terms of
origin or genesis. Coal has essential features in common with asphalt,
oil, and gas. They are all composed of carbon, hydrogen, and oxygen,
with minor quantities of other materials, combined in various
proportions. They are all "organic" products which owe their origin to
the decay of the tissues of plants and perhaps animals. They have all
been buried with other rocks beneath the surface. The common geologic
processes affecting all rocks have in the main determined the evolution
of these organic products and the forms in which we now find them.
Originating at the surface, they have participated in the constructive
or anamorphic changes of the metamorphic cycle, which occur beneath the
surface, and under these influences have undergone various stages of
condensation, refinement, distillation, and hardening.
All stages in the development of coal have been traced. In brief, the
story is this:
[Illustration: FIG. 6. Origin and development of coal. After
Gilbert.]
This exhibit shows the successive chemical stages in the
evolution of coal. The striking qualities of the original are
lost in the reproduction through the use of designs in the
place of realistic coloring, but the effect is retained
sufficiently to indicate the nature of the sequence and the
directness with which it leads back to an origin in vegetal
accumulations. The evolutionary process is seen to take the
form of increasing density through the progressive expulsion
of volatilizable matters in the course of geologic time. This
inference is substantiated beyond reasonable question by the
actual presence of organic remains in coal beds.
Grasses, trees, and other plants growing in swamps and bogs decay and
form a vegetable mold in the nature of _peat_. A peat bog from the top
downward consists of (1) living plants, (2) dead plants, and (3) a dense
brownish-black mass, of decayed and condensed vegetable material, in
which the vegetable structure is more or less indistinct. Peat consists
chiefly of fixed carbon and volatile matter, also of sulphur, moisture,
and ash. The volatile matter consists mainly of various combinations of
hydrogen and carbon, called hydrocarbons; it goes off in gas or smoke
when the peat is heated to a red heat. The fixed carbon is the carbon
left after the volatile matter has been driven off. The ash represents
the more incombustible mineral matter, usually of the nature of clay or
slate. The moisture in peat may be as high as 90 per cent.
The essential condition for thick accumulation of peat seems to be
abundance of moisture, which favors luxuriant growth and protects the
plant remains from complete oxidation or decay. Without moisture the
vegetable material would completely oxidize, leaving practically no
residue, as it does in dry climates. For the formation of thick peat
beds, there seems to be implied some sort of a balance between the slow
building up of organic accumulations and the settling of the area to
keep it near the elevation of the water table. Present day bog deposits
are known in some cases to have a thickness of forty feet. This
thickness is not enough to account for some of the great coal seams
within the earth; but there seems to be no escape from the conclusion
that the same sort of deposits, formed on a larger scale in the past,
were the first step in the formation of the coal seams. Flat, swampy
coastal plains are believed to furnish the best conditions for thick
accumulation of peat. There is good evidence that most of the deposits
accumulate essentially in place, without appreciable transportation.
In time these surface accumulations of vegetable material may subside
and be buried under clay, sand, or other rock materials. The processes
of condensation begun in the peat bog are then carried further. They
result in the second stage of coal formation, that of _lignite_ or
_brown coal_. This is brown, woody in texture, and has a brown streak.
It has a higher percentage of fixed carbon, and less volatile matter and
water, than peat.
Continuation of the processes of induration produces _subbituminous
coal_, or _black lignite_, which is usually black and sometimes has a
fairly bright luster. It is sometimes distinguished from bituminous
coal, where weathered or dried, by the manner in which it checks
irregularly or splits parallel to the bedding,--the characteristic
feature of bituminous coal being columnar fracture.
The next stage in coal formation is _bituminous coal_. It has greater
density than the lignites or subbituminous coals, is black, more
brittle, and breaks with a cubical or conchoidal fracture. It is higher
in fixed carbon, lower in volatile matter and water. A variety of
bituminous coal, called _cannel coal_, is characterized by an unusually
high percentage of volatile matter, which causes it to ignite easily.
This material has a dull luster and a conchoidal fracture. It is
composed almost entirely of the spores and spore cases, which are
resinous or waxy products, of such plants as lived in the parent coal
swamp.
There are gradations from bituminous coal into _anthracite coal_.
_Semibituminous_ and _semianthracite_ are names used to some extent for
these intermediate varieties. The final stage of coal formation is
anthracite,--hard, brittle, black, with high luster and conchoidal
fracture. It has a higher percentage of fixed carbon and correspondingly
less of the volatile constituents, than any of the other coals.
The coals form a completely graded series from peat to the hard
anthracite. Comparison of the compositions of the coal materials at
different stages shows clearly what has happened. Moisture has
diminished, certain volatile hydrocarbons have been eliminated as gases,
and oxygen has decreased. On the other hand, the residual fixed carbon,
sulphur, and usually ash, have remained in higher percentage. This
change in composition is graphically represented in Figure 6.
During this process volume has been progressively reduced and density
increased. Five feet of wood or plant may produce about one foot of
bituminous coal, or six-tenths of a foot of anthracite.
The exact physical conditions in the earth which determine the
progressive changes in coals, above outlined, cannot be fully specified.
Time is one of the factors--the longer the time, the greater the
opportunity for accomplishing these results. Another factor is
undoubtedly pressure, due to the weight of overlying sediments, or to
earth movements. In peat condensational changes of this nature are
accomplished artificially by the pressure of briquetting machines.
Another factor is believed to be the heat developed by earth movements
and vulcanism, which presumably facilitates the elimination of volatile
materials, and thus accelerates the gradational changes above
described. This is suggested by the fact that in places where hot
volcanic lavas have gone through coal beds they have locally produced
coals of anthracitic and coke-like varieties. In general, however, it
has not been possible to determine the degree to which heat has been
responsible for the changes. Coals which have been developed in
different localities, under what seem to be much the same heat
conditions, may show quite different degrees of progress toward the
anthracite stage. Another factor that has been suggested as possibly
contributing to the change, is the degree of permeability of the rocks
overlying the coal to the volatile materials which escape from the coal
during its refinement. It is argued that in areas of folding or of
brittle rock where the cover is cracked, volatile gases have a better
chance to escape, and that the change toward anthracite is likely to
advance further here than elsewhere.
Bacterial action is an important factor in the earlier stages, in the
partial decay of vegetable matter to form peat; accumulation of waste
products from this action, however, appears to inhibit further bacterial
activity.
Coal deposits have the primary shapes of sedimentary beds. They are
ordinarily thin and tabular, and broadly lenticular,--on true scale
being like sheets of thin paper. At a maximum they seldom run over 100
feet in thickness, and they average less than 10 feet. Seldom is a
workable coal bed entirely alone; there are likely to be several
superposed and overlapping seams of coal, separated by sandstones,
shales, or other rocks. In Illinois and Indiana there are nine workable
coal seams, in Pennsylvania in some places about twenty, and in Wales
there are over one hundred, many of which are worked. Some of the seams
are of very limited extent; others are remarkably persistent, one seam
in Pennsylvania having an average thickness of 6 to 10 feet over about
6,000 square miles of its area. Only 2 per cent of the coal-bearing
measures of the eastern United States is actually coal.
Even where not subsequently disturbed by deformation, coal beds are not
free from structural irregularity. They are originally deposited in
variable thicknesses on irregular surfaces. During their consolidation
there is a great reduction of volume, resulting in minor faults and
folds. Subsequent deformation by earth forces may develop further faults
and folds, with the result that the convolutions of a coal bed may be
very complex. The beds of a coal-bearing series are usually of differing
thickness and competency, and as a consequence they do not take the same
forms under folding. Shearing between the beds may result in an
intricate outline for one bed, while the beds above and below may have
much more simple outlines. In short, the following of a coal seam
requires at almost every stage the application of principles of
structural geology. It is obvious, also, that the identification and
location of sedimentary geologic horizons are essential, and hence the
application of principles of stratigraphy.
The folios of the United States Geological Survey on coal-bearing areas
present highly developed methods of mapping and representing the
geologic features of coal beds. On the surface map are indicated the
topography, the geologic horizons, and the lines of outcrop of the coal
seams. In addition, there are indicated the sub-surface contours of one
or more of the coal seams which are selected as datum horizons. The
sub-surface structure, even though complex, can be readily read from one
of these surface maps. With the addition of suitable cross sections and
comparative columnar sections, the story is made complete. In the study
of the occurrence of coal seams, the reader cannot do better than
familiarize himself with one or more of the Geological Survey folios.
The high-grade coals of the eastern and central United States are found
in rocks of Carboniferous age. The very name Carboniferous originated in
the fact that the rocks of this geologic period contain productive coal
beds in so many parts of the world. The coal measures of Great Britain,
of Germany, Belgium, and northern France, of Russia, and the largest
coal beds of China are all of Carboniferous age. Deposits of this period
include the bulk of the world's anthracite and high-grade bituminous
coal. Coal deposits of more recent age are numerous, but in general they
have had less time in which to undergo the processes of condensation and
refinement, and hence their general grade is lower. In the western
United States there are great quantities of subbituminous coal of
Cretaceous age, and of Tertiary lignites which have locally been
converted by mountain upbuilding into bituminous and semibituminous
coals. Jurassic coals are known in many parts of the world outside of
North America, and lignites of Tertiary age are widely distributed
through Asia and Europe.
PETROLEUM
ECONOMIC FEATURES
Petroleum is second only to coal as an energy resource. The rapid
acceleration in demand from the automobile industry and in the use of
fuel oil for power seems to be limited only by the amounts of raw
material available.
=Production and reserves.= The distribution by countries of the present
annual production of petroleum, the past total production, and the
estimated reserves, is indicated in terms of percentages of the world's
total in the table[19] on the opposite page.
This table indicates the great dominance of the United States both in
present and past production of petroleum, as well as the concentration
of the industry in a few countries. In addition the United States
controls much of the Mexican production as well as production in other
parts of the world, making its total control of production at least 70
per cent. of the world's total. Notwithstanding its large domestic
production, the United States has recently consumed more oil than it
produces. Imports of crude oil are about balanced by exports of
kerosene, fuel oils, lubricants, etc. The per capita consumption of
petroleum in the United States is said to be twenty times greater than
in England. On the other hand, the remaining principal producers consume
far less than they produce, the excess being exported.
The oil from the United States, Russia, the Dutch East Indies, India,
Roumania, and Galicia is for the most part treated at refineries near
the source of supply or at tidewater, and exports consist of refined
products. The Mexican oil is largely exported in crude form to the
United States though increasing quantities are being refined within
Mexico.
The figures shown in the table for oil reserves are of course the
roughest approximations, particularly for some of the less explored
countries. However, they are compiled from the best available sources
and may serve at least to show the apparent relative positions of the
different countries at this time. Further exploration is likely to
change the percentages and add very greatly to the totals. The
significant feature of these figures is the contrast which they indicate
between distribution of reserves and distribution of past production.
Particularly do they show that the reserves of the United States, which
are more closely estimated than those of any other country, are in a far
lower ratio to past production than are the reserves in other countries.
It was estimated in 1920 that about 40 per cent of the United States
reserves are exhausted.[20]
PRESENT AND PAST PRODUCTION AND RESERVES OF OIL, BY COUNTRIES, IN TERMS
OF PERCENTAGE OF WORLD'S TOTAL
-------------------------+--------------+--------------+-------------
| | _Per cent | _Per cent
Country |_Per cent of | of total | of total
| production, | production, | oil
| 1918_ | 1857-1918_ | resources_
-------------------------+--------------+--------------+-------------
United States and Alaska | 69.15 | 61.42 | 16.26
Mexico | 12.40 | 3.80 | 10.51
Russia (southeastern | | |
Russia, southwestern | | |
Siberia, region of the | | |
Caucasus, northern | | |
Russia, and Saghalien) | 7.86 | 24.96 | 15.69
East Indies | 2.58 | 2.51 | 7.00
Roumania, Galicia, and | | |
western Europe | 2.79 | 4.07 | 2.64
India | 1.55 | 1.41 | 2.31
Persia and Mesopotamia | 1.40 | .19 | 13.52
Japan and Formosa | .48 | .51 | 2.87
Egypt and Algeria | .40 | .07 | 2.15
Germany | .14 | .22 | --
Canada | .06 | .33 | 2.31
Northern South America, | | |
including Peru, | | |
Trinidad and Venezuela | .93 | .43 | 13.31
Southern South America, | | |
including Bolivia and | | |
Argentina | .26 | .06 | 8.24
China | -- | -- | 3.19
Italy | } | |
Cuba | } | .02 |
Other countries | } | |
| ------ | ------ | ------
World total | 100.00 | 100.00 | 100.00
-------------------------+--------------+--------------+-------------
Looking forward to the future, it is clear that there will be
considerable shifts in the centers of principal production of petroleum
in the directions indicated by the reserve figures. In particular,
conspicuous development of production may be expected in the immediate
future in the countries bordering the Caribbean Sea and the Gulf of
Mexico. In the eastern hemisphere production is rapidly increasing in
Persia and Mesopotamia; and Russia, with the stabilization of political
conditions, may become ultimately the world's leading oil producer. At
the now indicated rate of production, world reserves now estimated would
be exhausted in eighty-six years and the peak of production would be
passed earlier. With continuing acceleration of production, total
reserves would be exhausted in considerably less time,--providing
physical conditions would allow the oil to be pumped from the ground at
the necessary speed, which they probably will not. These figures taken
at face value are alarming; but the earth offers such huge possibilities
for further discoveries that the life of oil reserves above indicated is
likely to be considerably extended. At many times in the history of the
mineral industry the end has apparently been in sight for certain
products; but with the increased demand for these products has come
increased activity in exploration, with the result that as yet no
definite end has been approached for any one of them. The more immediate
problems of the petroleum industry seem to the writer to be of rather
different nature: first, whether the discovery and winning of the oil
can be made to keep pace with the enormous acceleration of demand; and
second, the adjustment of political and financial control of oil
resources, the possession of which is becoming so increasingly vital to
national prosperity.
In regard to the first question, it is a much more difficult problem
today to locate and develop a supply of oil to replace the annual world
production (recently half a billion barrels), than it was twenty years
ago, when it was necessary for this purpose to find only one-fifth this
amount; and if the demand is unchecked, it will be still more difficult
to replace the three-quarters of a billion barrels of oil which will
doubtless be required in a very few years. Regardless of the amount of
oil actually in the ground, it is entirely possible that physical
limitations on its rate of discovery and recovery will prevent its being
made available as fast as necessary to meet the increasing demand. This
fact is likely to make itself felt through increase of price. Other
natural results should be the development of substitutes, such as
alcohol or benzol for gasoline; the larger recovery of oil from oil
shales; and the general speeding up of conservational measures of
various kinds. These are all palliatives and not essential remedies. To
make enough alcohol to substitute for the gasoline now coming from oil
would use a very considerable fraction of the world's food supply. To
make enough benzol (a by-product of coke) to replace gasoline would
necessitate the manufacture of many times the amount of coke now
required by the world's industries. To develop the oil shale industry to
a point where it could supply anything like the amount of oil now
derived from oil pools would mean the building of great plants,
including towns, railroads, and other equipment, equivalent to the
plants of the coal mining industry. To apply any one of the various
conservational measures discussed on later pages would only temporarily
alleviate the situation.
The question of political and financial control of oil supplies may be
illustrated by particular reference to the United States. On present
figures it appears that within three to five years the peak of
production in this country will be passed; and at the present rate of
production the life of the reserves may not be over seventeen to twenty
years. Of course production could not continue to the end at this rate,
and the actual life will necessarily be longer. Again the doubtful
factor is the possibility for further discoveries. Many favorable
structures have been mapped which have not yet been drilled, and there
are considerable unexplored areas where the outcrops are so few that
there is no clue at the surface to the location of favorable structures.
The future is likely to see a considerable amount of shallow drilling
for the sole purpose of geological reconnaissance. For upwards of ten
years important parts of the public domain have not been available for
exploration, but Congress has now enacted legislation which opens up
vast territories for this purpose.
Even with large allowance for these possibilities, it seems unlikely
that production in the United States can increase very long at the
accelerating rate of the domestic demand, which is already in excess of
domestic production. The supplies of Mexico are in a large part
controlled by American capital and are thus made available to the
United States (subject, of course, to political conditions); but even
with these added, the United States is in a somewhat unfavorable
situation as compared with certain other countries. This situation is
directing attention to the possibility of curtailment of oil exports,
and to the possibility of acquiring additional oil supplies in foreign
countries. In this quest the United States is peculiarly handicapped in
that most foreign countries, in recognition of the vital national
importance of the oil resource, have imposed severe restrictions on
exploration by outsiders. Nationals of the United States are excluded
from acquiring oil concessions, or permitted to do so only under
conditions which invalidate control, in the British Empire, France,
Japan, Netherlands, and elsewhere, and the current is still moving
strong in the direction of further exclusion. As the United States
fields are yet open to all comers, it has been suggested that some
restriction by the United States might be necessary for purposes of
self-protection, or as an aid in securing access to foreign fields. The
activity of England during and since the war has increased the amount of
oil controlled by that country from an insignificant quantity to
potentially over half of the world's oil reserves. The problem of future
oil supplies for the United States presents an acute phase of the
general question of government coöperation or participation in mineral
industries, which is further discussed in Chapter XVIII.
The following table summarizes the distribution of the oil production in
the United States, together with the salient features of its geologic
distribution and character.
This table, in conjunction with Fig. 8 below, shows clearly that the
bulk of the United States production of oil comes from two great
sources--the Pennsylvanian sandstones of the Mid-Continent field in
Kansas and Oklahoma, and the Cretaceous and Tertiary sediments of the
southern half of California. Phenomenal development of the Central and
North Texas field in 1919 increased its yield to about one-sixth of the
country's total. The older Appalachian oil field, extending from New
York to West Virginia and Tennessee, was the earliest area discovered;
it is still one of the more productive fields, though it has long since
passed its maximum production. The other principal sources of oil are
the Gulf Coast field in Louisiana and Texas, the North Louisiana field,
the southern Illinois field, and the Rocky Mountain region. This last
region, containing large amounts of government land recently opened to
exploration, bids fair to produce increasing quantities of oil for some
time.
PAST PRODUCTION OF PETROLEUM IN THE UNITED STATES. (FIGURES FROM U. S.
GEOLOGICAL SURVEY)
-------------+-----------------+----------+-----------+---------------
| | | | _Total
| _Age of | |_Production| production
| containing | | for 1918 |including 1918
_State_ | rocks_ | _Base_ |(barrels)_ |(barrels)_
-------------+-----------------+----------+-----------+---------------
Alaska |East-Low. |Paraffin | (a) | (a)
| Tertiary | | |
| West-Jurassic | | |
California |Cretaceous: | | |
| Tertiary |Asphalt | 97,531,997| 1,110,226,576
Colorado |Pierre-Cretaceous|Paraffin | 143,286| 11,319,370
Illinois |Mississippian- |Paraffin | 13,365,974| 298,225,380
| Pennsylvanian | | |
Indiana |East-Ordovician |Paraffin | 877,558| 106,105,584
| (Trenton) West-| | |
| Pennsylvanian | | |
Kansas |Pennsylvanian |Par.-Asph.| 45,451,017| 148,450,298
Kentucky, |Mississippian |Paraffin | 4,376,342| 18,213,188
Tennessee | | | |
Louisiana |Cretaceous-Quat. |Paraffin | 16,042,600| 150,769,911
| Cretaceous- | | |
| Eocene | | |
Michigan, |Carboniferous |Paraffin | (a) | (a)
Missouri | | | |
Montana | -- | -- | 69,323| 213,639
New Mexico |Carboniferous- | -- | (a) | (a)
| Cretaceous | | |
New York, |Devonian- |Paraffin | 8,216,655| 788,202,717
Pennsylvania| Carboniferous | | |
Ohio, East |Ordovician- |Paraffin | 7,285,005| 463,367,386
and West | Carboniferous | | |
Oklahoma |Pennsylvanian |Paraffin |103,347,070| 851,320,457
Texas |Pennsylvanian, |Asph.-Par.| 38,750,031| 327,550,005
| Cretaceous-Quat.| | |
Utah | -- | -- | (b) | (b)
West |Devonian- | -- | 7,866,628| 294,474,710
Virginia | Carboniferous | | |
Wyoming |Carboniferous- |Asph.-Par.| 12,596,287| 40,019,573
| Cretaceous | | |
Other | -- | -- | 7,943| 112,925
| | |-----------| -------------
| | |355,927,716| 4,608,571,719
-------------+-----------------+----------+-----------+---------------
(a) Included in "Other."
(b) Included in Wyoming.
[Illustration: FIG. 7. Chart showing the present tendency of
the United States in respect to its unmined reserve of petroleum. Data
from U.S. Geological Survey. After Gilbert and Pogue.]
=Methods of estimating reserves.= It may be of interest to inquire into
the basis on which predictions are made of the life of an oil pool. The
process is essentially a matter of platting curves of production, and of
projecting them into the future with the approximate slopes exhibited in
districts which are already approaching exhaustion.[21] While no two
wells or two districts act exactly alike, these curves have group
characteristics which are used as a rough basis for interpreting the
future.
[Illustration: FIG. 8. The annual output of the principal oil
fields of the United States for the last twenty years. Data from U.S.
Geological Survey.]
A less reliable method is to calculate from geologic data the volume and
porosity of the oil-bearing reservoirs, and to estimate the percentage
of recovery on the basis of current practices and conditions. Complete
data for this method are often not available; but in the early years of
a field, before production curves are established, this method may serve
for a rough approximation.
[Illustration: FIG. 9. Curve showing the usual decline in oil
field production after the period of maximum output is reached. After
Ralph Arnold. The Petroleum Resources of the United States, Smithsonian
report for 1916, p. 283. Compare this theoretical curve of final
decrease with the production curve shown in Fig. 8.]
=Classes of oils.= When crude petroleum is distilled, it gives off in
succession various substances and gradually thickens until it leaves a
solid residue, which may be largely either paraffin wax or asphalt. The
two main classes of oils are determined by the nature of this solid
residual. The products given off are natural gas and then liquid
hydrocarbons of various kinds, which evaporate in the order of their
lightness. Petroleum is thus a mixture or mutual solution of different
liquids, gases, and solids. Nearly one-fifth of the domestic consumption
of crude petroleum is burned directly as fuel, and four-fifths are
refined. The several principal primary products of refinement are
gasoline, kerosene, fuel oil, and lubricating oil; but these may be
broken up into other substances, each the starting point of further
refinements, with the result that present commercial practice yields
several hundred substances of commercial value. With increasing chemical
and technical knowledge these products are being multiplied. The rapidly
increasing demand for gasoline has led to the use of processes which
extract a large proportion of this substance from the raw material, by
"cracking" or breaking up other substances; but while, under the stress
of necessity, there is possibility of slight modification of the
proportions of principal substances extracted from the crude oil, it is
not possible to change these proportions essentially. It is, therefore,
a problem to adjust relative demands to supplies of the different
products. The domestic demand for gasoline is greater than the supply.
On the other hand, the demand for kerosene, which must be produced at
the same time, is much less than the domestic supply. Hence the
importance of maintaining export markets for kerosene.
The nature or grade of the oil of various fields is an important matter
in considering reserves for the future. Perhaps half of the United
States reserves consist of the asphalt-base oils of the California and
certain of the Gulf fields, which yield comparatively small amounts of
gasoline and other valuable light products, though they are very
satisfactory for fuel purposes. Similarly the large reserve tonnages of
oil in Mexico and the Caribbean countries, in Peru, and probably in
Russia, are essentially of the heavier, lower grade oils. The oils of
the Mid-Continental and eastern fields of the United States, of Ontario,
of the Dutch East Indies, of Burma, and of Persia and Mesopotamia are
reported to be largely of the paraffin base type, which, because of its
larger yield of gasoline and light oils, is at present considerably more
valuable. These generalizations are of course subject to qualifications,
in that the oils of a given region may vary considerably, and that some
oils are intermediate in character, containing both asphalt and paraffin
wax.
=Conservation of oil.= The rapid increase in demand for oil as compared
with discovery of new sources is leading naturally to a more intensive
study of the conservational aspects of the industry. This is a complex
and difficult subject which we shall not take up in detail, but we may
point out some of the phases of the problem which are receiving especial
attention.
[Illustration: FIG. 10. Chart showing the relative values of
the principal petroleum products manufactured in the United States from
1899 to 1914. After Gilbert and Pogue. Note the decreasing importance of
kerosene in sustaining the cost of refining, and the necessity of
exports for maintaining a balanced outlet of products. Data from Story
B. Ladd, Petroleum Refining. Census of Manufactures: 1914, Bureau of
Census, Washington, 1917, p. 10.]
About 50 per cent of the oil in the porous strata, of oil pools is
ordinarily not recovered, because it clings to the rock. Efforts are
being made along various lines to increase the percentage of
recovery,--as, for instance, in preventing infiltration of water to the
oil beds and in the use of artificial pressures and better pumping.
"Casing-head gasoline" is being recovered to an increasing extent from
the natural gas which was formerly allowed to dissipate in the air.
Minute division of the ownership of a pool, with consequent
multiplication of wells and unrestricted competition, tends to gross
over-production and highly wasteful methods. The more rapid exhaustion
of one well than the others may result in the flooding of the oil sands
by salt waters coming in from below. Various efforts have been made
toward a more systematic and coördinated development of oil fields.
In general, the organization and technique involved in the development
of an oil field are improving in the direction of extracting a greater
percentage of the total available oil.
Better methods of refining the oil, and the refining of a larger
percentage of the crude oil, make the oil more available for a greater
variety of purposes and therefore more valuable. Great advances have
been made along these lines, particularly in the application of the
"cracking" method for a greater recovery of the more valuable light oils
at the expense of the less valuable heavy oils. Similarly, modifications
of internal combustion engines will probably permit the use, in an
increasing number of cases, of products of lower volatility than
gasoline.
One of the conservational advances in coming years will probably be a
restriction in the amount of crude oil used directly for fuel and road
purposes without refining. These crude uses cut down the output of much
desired products from the distillation of the oil. Various other
restrictions in the use of oil have been proposed, such as the
curtailment of the use of gasoline in pleasure cars. The gasless Sundays
during the war represented an attempt of this kind. In general, it seems
likely that such restrictions will come mainly through increase in the
price of oil products.
The substitution of oil from oil shales, and of alcohol for gasolene,
already mentioned, will be conservational so far as the oil is
concerned, though perhaps not so in regard to other elements of the
problem.
GEOLOGIC FEATURES
=Organic theory of origin.= According to this theory, accumulations of
organic materials in sedimentary beds, usually muds or marls, have been
slowly altered and distilled during geologic ages; the products of
distillation have migrated chiefly upward to porous strata like
sandstones or cavernous limestones, where, under suitable conditions,
they have become trapped.
The original organic material is believed to have been plants of low
order and animal organisms (such as foraminifera) which were deposited
as organic detritus with mud and marl in the bottoms of ponds, lakes,
estuaries, and on the sea bottom,--in both salt and fresh waters.
Bacteria are supposed to have played a part in the early stage of
alteration, sometimes called the biochemical stage. When the organic
matter was buried under later sediments and subjected to pressure,
physical conditions were responsible for further volatilization or
distillation. This stage is called the geochemical stage. There is much
in common as to origin between coal, oil shales, and petroleum.
According to White,[22]
whether the ingredient organic matter, be it plant or animal,
will be in part transformed to coal of the ordinary type, to
cannel, to oil shale, to the organic residues in so-called
bituminous shales and carbonaceous shales, or to petroleum and
natural gas, is dependent upon the composition of the
ingredient organic débris, the conditions of its accumulation
or deposition, and the extent of the microbian action.
White has further developed the important principle that, in the
geochemical stage of development, both coal and oil react to physical
influences in much the same way; and that therefore when both are found
in the same geologic series, the degree of concentration of the coal,
measured by its percentage of carbon, may be an indication of the stage
of development of the oil. More specifically where the coal contains
more than 65 to 70 per cent of fixed carbon, chances for finding oil in
the vicinity are not good (though commercial gaspools may be found),
probably for the reason that the geochemical processes of distillation
have gone so far as to volatilize the oils, leaving the solid residues
in the rock. White also finds that the lowest rank oils, with
considerable asphalt, are found in regions and formations where the
coal deposits are the least altered, and the lighter, higher rank oils,
on the whole, where the coal has been brought to the correspondingly
higher ranks; in other words, up to the point of complete elimination of
the oil, improvement in quality of the oil accompanies increased
carbonization of the coal. The principle, therefore, becomes useful in
exploration in geologic series where oil is associated with coal. Where
the coal is in one series and the oil in another, separated by
unconformity (indicating different conditions of development), the
principle may not hold, even though there is close geographical
association.
The oil and gas distillates migrate upward under gas pressure and under
pressure of the ground-water. If there are no overlying impervious beds
to furnish suitable trapping conditions, or conditions to retard the
flow, the oil may be lost. The conditions favorable for trapping are
overlying impervious beds bowed into anticlines, or other structural
irregularities, due either to secondary deformation or to original
deposition, which may arrest the oil in its upward course. A dome-like
structure or anticline may be due to stresses which have buckled up the
beds, or to unequal settling of sediments varying in character or
thickness; thus some of the anticlinal structures of the Mid-Continent
field may be due to settling of shaley sediments around less
compressible lenses of sandstone which may act as oil reservoirs, or
around islands which stood above the seas in which the oil-bearing
sediments were deposited and on the shores of which sands capable of
acting as oil reservoirs were laid down. Favorable conditions for
trapping the oil may be furnished by impervious clay "gouges" along
fault planes, or by dikes of igneous rock. Favorable conditions may also
be merely differences in porosity of beds in irregular zones, determined
by differences either in original deposition or in later cementation.
The thickness of oil-producing strata may vary between 2 or 3 feet and
200 feet. The porosity varies between 5 and 50 per cent. In sandstones
the average is from 5 to 15 per cent. In shales and clays, which are
commonly the impervious "cap-rocks," porosity may be equally high, but
the pores are too small and discontinuous to permit movement.
When the impervious capping is punctured by a drill hole, gas is likely
to be first encountered, then oil, and then water, which is usually
salty. The gas pressure is often released with almost explosive
violence, which has suggested that this is an important cause of the
underground pressures. It has been supposed also that the pressures are
partly those of artesian flows. The vertical arrangement of oil, gas,
and water under the impervious capping is the result of the lighter
materials rising to the top. In certain fields, oil and gas have been
found in the tops of anticlines in water-saturated rocks, and farther
down the flanks of folds or in synclines in unsaturated rocks.
The localization of oil pools is evidently determined partly by original
organic deposition, often in alignment with old shore lines, and partly
by the structural, textural, and other conditions which trap the oil in
its migration from the source.
=Effect of differential pressures and folding on oil genesis and
migration.= Another organic hypothesis proposed somewhat recently[23] is
that oil is formed by differential movement or shearing in bituminous
shales, which are often in close relationship with the producing sand of
an oil field, and that the movement of oil to the adjacent sands is
accomplished by capillary pressure of water and not by ordinary free
circulation of water under gravity. The capillary forces have been shown
to be strong enough to hold the oil in the larger pores against the
influence of gravity and circulation. The accumulation of the oil into
commercial pools is supposed to take place in local areas where the
oil-soaked shale, due to jointing or faulting, is in direct contact with
the water of the reservoir rock. This suggests lack of wide migration.
This hypothesis is based on experimental work with bituminous shales.
The general association of oil pools with anticlinal areas is explained
on the assumption that anticlines on the whole are areas of maximum
differential movement, resulting in oil distillation, and that they are
ordinarily accompanied by tension joints or faults, affording the
conditions for oil migration. Data are insufficient, however, to
indicate the extent to which the anticlinal areas are really areas of
maximum shearing. As regards the exact nature of the process, it is not
clear to what extent differential movement may involve increase in
temperature which may be the controlling factor in distillation,--although
in McCoy's experiment oil was formed when no appreciable amount of heat
was generated.
The development of petroleum by pressure alone acting on unaltered
shale, as shown by these experiments, has been taken by White[24] to
have a significant bearing on the geochemical processes of oil
formation. Under differential stresses acting on fine-grained
carbonaceous strata under sufficient load, there is considerable
molecular rearrangement, as well as actual movement of the rock
grains,--thus promoting the distillation of oil and gas from the organic
matter in the rocks, and the squeezing out of the oil, gas, and water
into adjacent rocks, such as coarse round-grained sandstones and porous
limestones, which are more resistant to change of volume under pressure.
Migration, concentration and segregation of the oil, gas, and water is
supposed to be brought about, partly through the effect of capillary
forces--the water, by reason of its greater capillary tension, tending
to seize and hold the smaller voids, and thus driving the oil and gas
into the larger ones--and partly through the action of gravity.
White also suggests that the process may go further where the parent
carbonaceous strata are of such thickness and under such load of
overlying rocks that they undergo considerable interior adjustment and
volume change before yielding to stress by anticlinal buckling,--than
where the strata yield quickly. It is not clear to the writer that the
interior adjustment assumed under this hypothesis is necessarily slowed
up or stopped by anticlinal buckling. Interior stresses are inherent in
any sedimentary formation, when settling and consolidating and
recrystallizing under gravity, and these may be independent of regional
thrusts from without.
The first oils evolved by pressure from the organic mother substance are
probably heavy, the later oils lighter, and the oils from formations and
regions where the alteration is approaching the carbonization limit are
characteristically of the highest grade. This is the reverse of the
order of products obtained by heat distillation. Whether there is also a
natural fractionation and improvement of the first heavy oils as they
undergo repeated migrations is not known.
=Inorganic theory of origin.= Another theory of the source of oil has
had some supporters, although they are much in the minority. This is the
so-called "inorganic" theory, that oil comes from magmas and volcanic
exhalations. In support of this theory attention is called to the fact
that igneous rocks and the gases associated with them frequently carry
carbides or hydrocarbons; that many oil fields have a suggestive
geographic relationship with volcanic rocks; and that certain of the oil
domes, as for instance in Mexico, are caused by plugs of igneous rocks
from below. It has been suggested that deep within the earth carbon is
combined with iron in the form of an iron carbide, and that from the
iron carbide are generated the hydrocarbons of the oil, either by or
without the agency of water. Iron carbide is magnetic, and significance
has been attached to the general correspondence between the locations of
oil in the western United States and regions of magnetic disturbance.
It seems not unlikely that some inorganic theory of this sort is
necessary to explain the ultimate source of oil or of the substances
which become oil, but the evidence is overwhelming that organic agencies
have been mainly responsible for the principal oil pools now known.
=Oil exploration.= A simple geographic basis for oil exploration is the
fact that the major oil fields of the world are situated between 20° and
50° north latitude, and that thus far there are no major oil areas
within the tropics or within the southern hemisphere. This broad
generalization may have little value when exploration is carried
further. It has also been suggested that the geographic distribution of
oil corresponds roughly with the average annual temperatures, or
isotherms, between 40° and 70.°[25] It is thought that this present
distribution of temperatures may indicate roughly the temperatures of
the past when the oil was accumulated; and the inference is drawn that
there was some sort of limitation of areal deposition within these
temperature limits. If this be true, the only reasons why the southern
hemisphere is not productive are the relatively small size of the land
areas and the lack of exploration to date.
In approaching broadly the problem of oil exploration, the geologist
considers in a general way the kinds and conditions of rocks which are
likely to be petroliferous or non-petroliferous. Schuchert[26]
summarizes these conditions for North America as follows:
1. The impossible areas for petroliferous rocks.
(_a_) The more extensive areas of igneous rocks and especially
those of the ancient shields; exception, the smaller dikes.
(_b_) All pre-Cambrian strata.
(_c_) All decidedly folded mountainous tracts older than the
Cretaceous; exceptions, domed and block-faulted
mountains.
(_d_) All regionally metamorphosed strata.
(_e_) Practically all continental or fresh-water deposits; relic
seas, so long as they are partly salty, and saline lakes are
excluded from this classification.
(_f_) Practically all marine formations that are thick and uniform
in rock character and that are devoid of interbedded dark
shales, thin-bedded dark impure limestones, dark marls, or
thin-bedded limy and fossiliferous sandstones.
(_g_) Practically all oceanic abyssal deposits; these, however, are
but rarely present on the continents.
2. Possible petroliferous areas.
(_a_) Highly folded marine and brackish water strata younger than
the Jurassic, but more especially those of Cenozoic time.
(_b_) Cambrian and Ordovician unfolded strata.
(_c_) Lake deposits formed under arid climates that cause the
waters to become saline; it appears that only in salty
waters (not over 4 per cent?) are the bituminous materials
made and preserved in the form of kerogen, the source of
petroleum; some of the Green River (Eocene) continental
deposits (the oil shales of Utah and Colorado) may be of
saline lakes.
3. Petroliferous areas.
(_a_) All marine and brackish water strata younger than the
Ordovician and but slightly warped, faulted, or folded; here
are included also the marine and brackish deposits of relic
seas like the Caspian, formed during the later Cenozoic. The
more certain oil-bearing strata are the porous thin-bedded
sandstones, limestones, and dolomites that are interbedded
with black, brown, blue, or green shales. Coal-bearing strata
of fresh-water origin are excluded. Series of strata with
disconformities may also be petroliferous, because beneath
former erosional surfaces the top strata have induced
porosity and therefore are possible reservoir rocks.
(_b_) All marine strata that are, roughly, within 100 miles of
former lands; here are more apt to occur the alternating
series of thin and thick-bedded sandstones and limestones
interbedded with shale zones.
The extent to which marine or brackish water conditions of sedimentation
are requisite to the later formation of oil, as is suggested in the
above quotation, has long been a debatable question. It may be noted
that certain oil shales formed in fresh water basins contain abundant
organic matter which is undoubtedly suitable for the generation of oil
and gas, and that these shales on distillation yield oil essentially
like that obtained from oil shales of marine origin; that certain
important oil-bearing sands of the younger Appalachian formations were
laid down in waters which are believed to have been only slightly
saline; that natural gas is present in fresh water basins; and that it
has not been demonstrated that salt in appreciable amounts is necessary
for the geologic, any more than for the artificial, distillation of oil.
Most of the great oil fields have been in regions of marine or other
saline water deposits, but it has not been proved that this is a
necessary condition. White[27] says: "At the present stage of our
knowledge, fresh-water basins appearing otherwise to meet the
requirements should be wildcatted without prejudice."
The principal oil-bearing horizons in any locality are comparatively
few, and it is ordinarily easy to determine by stratigraphic methods the
presence or absence of a favorable geologic horizon. By knowing the
succession and thicknesses of the beds in a given region it is possible
to infer from surface outcrops the approximate depth below the surface
at which the desired horizon can be found. To do this, however, the
conditions of sedimentation, the initial irregularities of the beds, the
structural conditions, including unconformities, and other factors must
be studied.
In exploration for oil the determination of the existence and location
of the proper horizon is but an initial step. For instance, the oil of
the Midcontinent field of the United States is in the beds of the
Pennsylvanian, which are known to occupy an enormous area extending from
Illinois and Wyoming south to the Gulf of Mexico. This information is
clearly not sufficiently specific to limit the location of drill holes.
Sometimes seepages of oil or showings of gas near the surface are
sufficient basis for localizing the drill holes.[28] Commonly, however,
it is necessary to find some structural feature in the nature of a dome
or anticline which suggests proper trapping conditions for an oil pool.
This is accomplished by geologic and topographic mapping of the surface.
Levels and contours are run and outcrops are platted. As the outcrops
are usually of different geologic horizons, it is necessary to select
some one or more identifiable beds as horizon markers, and to map their
elevations at different points as a means of determining the structural
contours of the beds. When several key horizons are thus used, their
elevations must be reduced to the elevations of one common horizon by
the addition or subtraction of the intervals between them. For instance,
knowing the succession, an outcrop of a certain sandstone may indicate
that the marking horizon is 200 feet below, and the structural contour
is then drawn accordingly. Observations of strike and dip at the surface
are helpful; but where the beds are but slightly flexed, small
irregularities in deposition may make strike and dip observations
useless in determining major structures. It is then necessary to have
recourse to the elevations of the marking horizons.
In the selection of key horizons, knowledge of the conditions of
sedimentation is very important. For example, some of the oil fields
occur in great delta deposits, where successive advances and retreats of
the sea have resulted in the interleaving of marine and land deposits.
The land-deposited sediments usually show great variations in character
and thickness laterally and vertically; and a given bed is likely to
thin out and disappear when traced for a short distance, rendering
futile its use as a marker. The marine sediments, on the either hand,
show a much greater degree of uniformity and continuity, and a bed of
marine limestone may extend over a large area and be very useful as a
key horizon.
Over large areas outcrops and records of previously drilled water and
oil wells may not be sufficient to give an indication of structure; it
then becomes necessary to secure cross sections by drilling shallow
holes to some identifiable bed, and to determine the structure from
these cross sections, in advance of deeper drilling through a favorable
structure thus located. The coöperative effort of the Illinois State
Survey and private interests, cited on page 306, is a good illustration
of this procedure. This method is only in its infancy, because
well-drilling has not yet exhausted the possibilities of structures
located from surface outcrops.
The so-called anticlinal structures, which have been found by experience
to be so favorable to the accumulation of oil, are by no means
symmetrical in shape or uniform in size. They may be elongated arches
with equal dip on the two sides, or one side may dip and the other be
nearly flat. In a territory with a general dip in one direction, a
slight change in the angle, though not in the direction of dip,
sometimes called an arrested dip, may cause sufficient irregularity to
produce the necessary trapping conditions. In other cases the anticline
may be of nearly equidimensional dome form. The largest anticlines which
have been found to act as specific reservoirs are rarely more than a few
miles in extent, and in many cases only a mile or two. The "closure" of
an anticline is the difference between the height of a given stratum at
the highest point and at the edges of the structure. A considerable
number of productive anticlines are known in which the beds dip so
gently as to give a closure of 20 feet or less.
After the structural outlines of beds near the surface have been
determined, all possible information should be used in projecting these
structures downward to the oil-producing horizons. Where a number of
wells have been previously drilled in the vicinity, examination of their
records may indicate certain lateral variations in the thickness of the
beds between the horizon which has been mapped and the producing
horizon. The effect of such lateral variations may be either to
accentuate the surface structure, or to cause it to disappear entirely
and thus to indicate lack of favorable trapping conditions. The
possibility of several oil-producing beds, at different depths--a not
uncommon condition in many fields--should also be kept in mind.
As already indicated, anticlines are not always essential to make the
necessary trapping conditions. In the Beaumont field of Texas, for
instance, it has been shown that irregular primary deposition of
sediments differing in porosity both vertically and horizontally allowed
the oil to migrate upward irregularly along the porous beds and parts
of beds, and to be trapped between the more impervious portions of the
beds.
Further questions to be considered in the exploration of an area are the
content of organic matter in the sediments which may have served as a
source of oil, the presence of impervious cap-rocks or of variations in
porosity sufficient to retain the oil, the thickness of sediments and
the extent to which they have undergone differential stresses, the
amount of erosion and the possibilities that oil, if formed, has escaped
from the eroded edges of porous strata, and, where carbonaceous beds are
present, their degree of carbonization, and many other similar matters.
Each field in fact has its own "habit," determined by the interaction of
several geologic factors. This habit may be learned empirically.
Geologists have often gone wrong in applying to a new district certain
principles determined elsewhere, without sufficient consideration of the
complexity and relative importance of the sundry geologic factors which
in the aggregate determine the local habit of oil occurrence.
Geographically associated fields characterized by similarity of oil
occurrence, age, and origin, are known as _petroliferous provinces_. The
factors entering into the classification of fields are so numerous that
more precise definition of a petroliferous province is hardly yet agreed
upon.
The part played by the economic geologist in oil exploration and
development is a large one for the obvious reasons given above. Probably
no other single division of economic geology now employs so large a
number of geologists. Practically no large oil company, or large piece
of oil exploration and development, is now handled without geologic
advice. Quoting from Arnold:[29]
It ought to be as obvious that exploration with the drill
should be preceded by careful geologic studies as it is that
railroad construction should be based on surveys. These
studies should include such subjects as topography,
stratigraphy, structure, and surface evidence of petroleum in
the regions to be tested. The work divides itself into two
stages--preliminary reconnaissances and detailed surveys.
The preliminary reconnaissance should consist in procuring all
the available published and hearsay evidence regarding the
occurrence of oil or gas seepages or hydrocarbon deposits in
the region; in making preliminary geologic surveys to
determine from which formations the oil is to come and the
areal distribution of these formations; in determining those
general regions in which the surface evidence is supposed to
be most favorable for the accumulation of hydrocarbons; and in
determining the best routes and methods of transportation.
The second stage includes detailed geologic surveys of those
regions where the surface evidence indicates that petroleum is
most likely to be found and the location of test holes at
favorable points. By working out the surface distribution and
structure of the formations it is usually possible to select
the areas offering the best chances of success. Geology should
always be the dominant factor in determining the location of
test holes, although modifications to meet natural conditions
must sometimes be made.
OIL SHALES
One of the sources of oil which is likely to become important in the
future is oil shales,--that is, shales from which oil product can be
extracted by distillation. These have already been referred to on
previous pages. Such shales are now mined only in Scotland and in France
to a relatively small extent, but there are immense reserves of these
shales in various parts of the world which are likely to be drawn upon
when commercial conditions require it. In the United States alone it is
estimated that the oil shales are a potential source of oil in amounts
far greater than all the natural petroleum of this hemisphere.[30] The
solution of the problem of extraction of oil from shales is fairly well
advanced technically, and the problem has now become principally one of
cost. In order to recover any large amount of oil from this source,
operations of stupendous magnitude, approximately on the scale of the
coal industry, must be established. As long as there are sufficient
supplies of oil concentrated by nature to be drawn upon, it is unlikely
that oil shale will furnish any considerable percentage of the world's
oil requirements. With the great increase in world demand for oil,
however, which may very possibly outstrip the available annual supply in
the future, and particularly with the increase in the United States
demand relative to domestic supplies, exhaustive surveys of the
situation are being made with a view to development of oil shales when
warranted by market conditions.
Oil shales are sedimentary strata containing decomposed products of
plants and animals. Locally they grade into cannel coal, with which they
are genetically related. They may be regarded as representing the kinds
of sediments from which the oil of oil pools has in the main originated.
The most extensive of the oil shales of the United States are found in
the Eocene beds of northwestern Colorado, northeastern Utah, and
southwestern Wyoming, and in the Miocene beds of northern Nevada. The
largest known foreign deposits occur in Brazil and Russia.
NATURAL GAS
ECONOMIC FEATURES
Natural gas is used both for lighting and for fuel purposes. In the
United States it has become the basis of a great industry, the value of
the product ranging above that of lead and zinc. The United States is
the largest producer of natural gas. Other producers are Canada, Dutch
East Indies, Mexico, Hungary, Japan, and Italy. Nearly all producing oil
fields furnish also some natural gas.
In the United States nearly 40 per cent of the total production of
natural gas comes from West Virginia, about 17 per cent from
Pennsylvania, about 17 per cent from Oklahoma, and less than 10 per cent
from each of Ohio, California, Louisiana, Kansas, Texas, and several
other states.
One of the recent interesting developments in this industry is the
recovery of gasoline from the natural gas. This is obtained by
compression and condensation of the casing-head gas from oil wells, and
also, more recently, by an absorption process which is applied not only
to "wet" gas from oil wells but also to so-called "dry" gas occurring
independently of oil. It is a high-grade product which in recent years
has amounted to about 10 per cent of the total output of gasoline for
the United States.
GEOLOGIC FEATURES
Natural gas, like oil, originates in the distillation of organic
substances in sediments, and migrates to reservoirs capped by impervious
strata. It is commonly, though not always, associated with oil and coal.
The geologic features of its occurrence have so much in common with oil
that a description would essentially duplicate the above account of the
geologic features of oil.
ASPHALT AND BITUMEN
ECONOMIC FEATURES
Asphalt and bitumen are not used as energy resources, but they have so
much in common with oil in occurrence and origin that they are included
in this chapter.
Asphalt and bitumen find their main use in paving. Other important uses
are in paints and varnishes, in the manufacture of prepared roofing, for
various insulating purposes, and in substitutes for rubber.
Nearly the entire world's supply of natural asphalt comes from the
British Island of Trinidad and from Venezuela. Both of these deposits
are under United States commercial control probably affiliated with
Dutch-English interests. Prior to the war about half the product went to
Europe and half to the United States. Large amounts of asphaltic and
bituminous rock, used mainly in paving, are normally produced in Alsace,
France, and in Italy. Prior to the war both the Alsatian and Italian
deposits were under German commercial control. Their output is
practically all consumed in Europe.
The United States takes a large part in the world's trade in natural
asphalt, by importation from Trinidad and Venezuela, and by some
reëxportation chiefly to Canada and Mexico. The United States also
produces some natural asphalt and bituminous rock for domestic
consumption. Deposits of natural asphaltic material are widely
distributed through the United States, but commercial production is
limited to a few localities in Kentucky, Texas, Utah, Colorado,
Oklahoma, and California.
The asphalt manufactured from petroleum constitutes a much larger
tonnage than natural asphalt though it does not enter so largely into
world trade. The manufactured product is largely but not exclusively in
American control. Large amounts are made in this country and will no
doubt be made for the next decade, from oil produced in the southwestern
states and in Mexico. At the present time as much or more asphalt is
made in the United States from Mexican as from domestic crude oil. The
refineries are located near the Gulf coast so that exports can avoid
overland shipments. The relative merits of natural asphalt and asphalt
manufactured from oil may be subject to some discussion; but it is
perfectly clear that the manufactured material is sufficient, both in
quantity and variety, to make the United States entirely independent and
have an exportable surplus.
GEOLOGIC FEATURES
Natural asphalt and similar products are in the main merely the
residuals of oil and gas distillation accumulated by nature under
certain conditions already described in connection with oil (pp.
140-144). In some cases the asphaltic material is found as impregnations
of sediments, and appears to have remained in place while the lighter
organic materials were volatilized and migrated upward. In other cases
it occurs in distinct fissure veins; the fissures and cavities
apparently were once filled with liquid petroleum, which has
subsequently undergone further distillation. The original liquid
character of some of these bitumens is shown by occasional fragments of
unworn "country rock" imbedded in the veins. The effect of surface
waters, carrying oxidizing materials and sulphuric acid, is believed to
have contributed to the drying out and hardening of these veins or
dikes.
Asphalts and bitumens include a wide variety of hydrocarbon materials,
such as gilsonite, grahamite, elaterite, ozokerite, etc., which are used
for somewhat different purposes. The deposits of the United States show
much variety in form, composition, age, and geologic associations. The
important Kentucky deposits occur as impregnations of Carboniferous
sandstones at the base of the Coal Measures of that state.
The Trinidad asphalt comes from the famous "pitch lake," which is a
nearly circular deposit covering about a hundred acres 150 feet above
sea level, and which is believed to fill the crater of an old mud
volcano. The so-called pitch consists of a mixture of bitumen, water,
mineral and vegetable matter, the whole inflated with gas, which escapes
to some extent and keeps the mass in a state of constant ebullition. The
surface of the lake is hard, and yet the mass as a whole is plastic and
tends to refill the excavations. The lake is believed to be on the
outcrop of a petroleum-bearing stratum, and the pitch to represent the
unevaporated residue of millions of tons of petroleum which have exuded
from the oil-sands. The pitch is refined by melting,--the heat expelling
the water, the wood and other light impurities rising, and the heavy
mineral matter sinking to the bottom.
The asphalt of Venezuela is similar in nature, but the pitch "lake" is
here covered with vegetation and the soft pitch wells up at certain
points as if from subterranean springs.
FOOTNOTES:
[17] For more detailed treatment of international coal movements before
the war and of coal movements within the United States, see the U. S.
Geological Survey's _World Atlas of Commercial Geology_, Pt. 1, 1921,
pp. 11-16.
[18] Campbell, Marius R., The coal fields of the United States: _Prof.
Paper 100-A, U. S. Geol. Survey_, 1917, pp. 5, 6, 7.
[19] Compiled from tables quoted by White, David, The petroleum
resources of the world: _Annals Am. Acad. Social and Political Sci._,
vol. 89, 1920, pp. 123 and 126.
[20] White, David, _loc. cit._, p. 113.
[21] See Arnold, Ralph, Petroleum resources of the United States: _Econ.
Geol._, vol. 10, 1915, p. 707.
[22] White, David, Late theories regarding the origin of oil: _Bull.
Geol. Soc. Am._, vol. 28, 1917, p. 732.
[23] McCoy, A. W., Notes on principles of oil accumulation: _Jour.
Geol._, vol. 27, 1919, pp. 252-262.
[24] White, David, Genetic problems affecting search for new oil
regions: _Mining and Metallurgy_, _Am. Inst. of Min. Engrs._, No. 158,
Sec. 21, Feb., 1920.
[25] Mehl, M. G., Some factors in the geographic distribution of
petroleum: _Bull. Sci. Lab._, _Denison Univ._, vol. 19, 1919, pp. 55-63.
[26] Schuchert, Charles, Petroliferous provinces: _Bull. 155_, _Am.
Inst. Mining and Metallurgical Engrs._, 1919, pp. 3059-3060.
[27] Loc. cit., p. 20.
[28] Seepages or residual bituminous matter near the surface may be due
to upward escape of oil material through joints in the rocks capping a
reservoir, and productive pools may be found directly below such
showings. In other regions similar surface indications may mean that the
stratum in the outcrop of which they are found is oil-bearing; but
accumulations of oil, if present, may be several miles down the dip, at
places where the structural conditions have been favorable. In still
other cases the seepage may have been in existence for such a long time
as to exhaust the reservoir. It must also be remembered that gas seeps
are common in sloughs and marshes where vegetation is decaying, and may
be of no significance in the search for petroleum.
[29] Arnold, Ralph, Conservation of the oil and gas resources of the
Americas: _Econ. Geol._, vol. 11, 1916, pp. 321-322.
[30] Oil shales may also be made to yield large quantities of fuel and
illuminating gas, and of ammonia (see pp. 101-102).
CHAPTER IX
MINERALS USED IN THE PRODUCTION OF IRON AND STEEL (THE FERRO-ALLOY
GROUP)
GENERAL FEATURES
Iron and steel and their alloys are the most generally used of the
metals. The raw materials necessary for their manufacture include a wide
variety of minerals.
Iron is the principal element in this group; but in the manufacture of
iron and steel, manganese, chromium, nickel, tungsten, molybdenum,
vanadium, zirconium, titanium, aluminum, uranium, magnesium, fluorine,
silicon, and other substances play important parts, either as
accessories in the furnace reactions or as ingredients introduced to
give certain qualities to the products.
Nearly all parts of the world are plentifully supplied with iron ores
for an indefinite period in the future, but their abundant use has thus
far been confined mainly to the countries bordering the North
Atlantic,--the United States, Germany, and England,--which, possessing
ample coal supplies, have had the initiative to develop great iron and
steel industries. China has abundant coal, moderate quantities of iron
ore, and a large population, but a low per capita consumption of iron
and steel products. Development of its iron and steel industry is just
beginning. Japan has neither coal nor iron in sufficient quantities, and
hence the Japanese effort in recent years to control the mineral
resources of China and other countries. As a result of the war Germany
has been largely deprived of its iron ores, and France may assume
somewhat the rank in iron ore production once held by Germany. Sweden
and Spain have been considerable producers of iron ore, but both lack
coal, with the result that their ores have been largely exported to
England and Germany. With increase of per capita consumption in outlying
parts of the world, iron and steel industries are beginning to develop
locally on a small scale, as in India, South Africa, and Australia.
Russia has had sufficient supplies of coal and iron, but the stage of
industrial development in that country has not called for great
expansion of its iron and steel industry.
There has been a tendency for iron and steel manufacture to become
concentrated at a comparatively few places on the globe favored by the
proper combinations of coal, iron, transportation, proximity to
consuming populations, initiative and capacity to take advantage of a
situation, and other factors. Even though on paper conditions may seem
to be favorable in outlying territories for the development of
additional plants, this development is often held back by competition
from the established centers. On the west coast of the United States,
there are raw materials for an iron and steel industry and there has
been discussion for years as to the possibilities of starting a
successful large scale steel industry. The consuming power of the local
population for all kinds of iron and steel would seem to be great enough
to warrant such action. However, the demand is for an extremely varied
assortment of iron and steel products; and to start an industry, making
only a few of the cruder products such as pig iron and semi-finished
forms, would not meet this demand. All varieties of finishing plants and
associated factories would also need to be started in order to meet the
situation. This would require large capital. Furthermore the local
demand for some of the accessory finished products might not warrant the
establishment of the accessory plants.
Throughout the history of the iron and steel business there has been a
marked tendency for the iron ore to move to regions of coal production
rather than for the coal to move to the iron ore regions. The coal or
energy factor seems ultimately to control. This is due in considerable
part to the fact that coal furnishes the basis of a great variety of
industries for which iron ore is only one of the feeders, and which are
so interrelated that it is not always easy to move the iron and steel
industry to a spot near the sources of iron ore where iron and steel
alone could be produced.
In regard to iron ore supplies of proper grade and quantity, the United
States is more nearly self-sufficing than any of its competitors. It
imports minor amounts of ore from Cuba and Canada, and even from Chile
and Sweden, to border points, in the main merely because these imported
ores can compete on a price basis with the domestic ores. The entire
exclusion of these ores, however, would make comparatively little
difference in the total volume of our iron and steel industry; though it
would probably make some difference in distribution, to the disadvantage
of plants along the coast. There is only one kind of iron ore in which
the United States has anything approaching deficiency, and that is ore
extremely low in phosphorus, adapted to making the so-called
low-phosphorus pig which is needed for certain special steels. Ordnance
requirements during the war put a premium on these steels. While some of
these extremely low-phosphorus ores are mined in the United States,
additional quantities have been required from Spain and Canada and to a
lesser extent from North Africa and Sweden. Also the Spanish pyrite,
imported ordinarily for its sulphur content, on roasting leaves a
residue of iron oxide extremely low in phosphorus which is similarly
used. The elimination of pyrite imports from Spain during the war,
therefore, was a considerable contributing factor to the stringency in
low-phosphorus iron ores. War experience showed that the United States
was dependent on foreign sources for 40 per cent or upwards of its needs
in this regard. Certain developments in progress, notably the project
for concentration of siliceous eastern Mesabi Range ores, make it likely
that future domestic production will more nearly be able to meet the
requirements.
The equivalent of 15 per cent of the iron ore mined in the United States
is exported as ore to Canadian ports on the Great Lakes and in the form
of crude iron and steel products to many parts of the world. England and
Germany are almost the sole competitors in the export trade.
When we turn to the minerals used for making the alloys of iron and as
accessories in the manufacture of iron, it appears that no one of the
principal iron and steel producing countries of the world is
self-supporting, but that these "sweeteners" must be drawn in from the
far corners of the earth. The importance of these minor constituents is
altogether out of proportion to their volume. For instance, only
fourteen pounds of manganese are necessary in the making of a ton of
steel, yet a ton of steel cannot be made without manganese. The
increasing specialization in iron and steel products, and the rapidly
widening knowledge of the qualities of the different alloys, are
constantly shifting the demand from one to the other of the ferro-alloy
minerals. Each one of the ferro-alloy minerals may be regarded as being
in the nature of a key mineral for the iron and steel industry, and the
control of deposits of these minerals is a matter of international
concern. Control is not a difficult matter, in view of the fact that the
principal supplies of practically every one of the alloy minerals are
concentrated in comparatively few spots on the globe,--as indicated on
succeeding pages.
Nature has not endowed the United States, nor in fact the North American
continent, with adequate high-grade supplies of the principal
ferro-alloy minerals,--with the exception of molybdenum, and with the
exception of silica, magnesite, and fluorspar, which are used as
accessories in the process of steel making. With plenty of iron ore and
coal, and with an iron and steel capacity amounting to over 50 per cent
of the world's total, the United States is very largely dependent on
other countries for its supplies of the ferro-alloy minerals. The war
brought this fact home. With the closing of foreign sources of supplies,
it looked at one time as if our steel industry was to be very greatly
hampered; and extraordinary efforts were made to keep channels of
importation open until something could be done in the way of
development, even at excessive cost, of domestic supplies. The result of
war efforts was a very large development of domestic supplies of
practically all the ferro-alloy minerals; but in no case, with the
exceptions noted above, did these prove sufficient to meet the total
requirements. This development was at great cost and at some sacrifice
to metallurgical efficiency, due to the low and variable grades of the
raw materials. With the post-war reopening of importation much of the
domestic production has necessarily ceased, and large amounts of money
patriotically spent in the effort to meet the domestic requirements have
been lost. These circumstances have resulted in the demand in Congress
from producers for direct financial relief and in demand for protective
tariffs, in order to enable the new struggling industries to exist, and
to permit of development of adequate home supplies. Such tariffs might
be beneficial to these particular domestic industries if wisely planned;
but also, in view of the limited amounts of these particular ores in
this country, their general low grade, and the high cost of mining,
tariffs might very probably hasten exhaustion of our limited supplies
and might handicap our metallurgical industries both in efficiency and
cost (see pp. 365-366, 393-394).
IRON ORES
ECONOMIC FEATURES
=Technical and commercial factors determining use of iron ore minerals.=
Popularly, an iron ore is an iron ore, and there is little realization
of its really great complexity of composition and the difficulty of
determining what is or is not a commercial ore. Percentage of iron is of
course an important factor; but an ore in which the iron is in the
mineral hematite is more valuable than one with an equivalent percentage
of iron which is in the form of magnetite. Substances present in the ore
in minor quantities, such as phosphorus, sulphur, and titanium, have a
tendency to make the iron product brittle, either when it is cold or
when it is being made, so that excessive amounts of these substances may
disqualify an ore. Excessive quantities of silica, lime, or magnesia may
make the ore undesirable. Where an acid substance, like silica, is
balanced by basic constituents like lime and magnesia, considerable
amounts of both may be used. Excessive moisture content may spoil an ore
because of the amount of heat necessary to eliminate it in smelting.
The metallurgical processes of the iron and steel industry are
essentially adapted to the principal grades of ore available. The
cheapest of the steel-making processes, called the acid Bessemer
process, requires a very low-phosphorus ore (usually below .050 per cent
in the United States and below .030 per cent in England.) The basic
open-hearth processes, making two-thirds of the steel in the United
States, allow higher percentages of phosphorus, but not unlimited
amounts. The basic Bessemer (Thomas) process, used for the "minette"
ores of western Europe and the Swedish magnetites, may use an ore with
any amount of phosphorus over 1.5 per cent. The phosphatic slag from
this process is used as fertilizer. The supply of low-phosphorus
Bessemer ore in the United States is at present limited as compared with
that of the non-Bessemer ores, with the result that steel-plant
construction for many years past has been largely open-hearth. The
open-hearth process is favored also because it allows closer control of
phosphorus content in the steel.
Small but increasing amounts of steel are also made in the electric
furnace; for the most part, however, this process is more expensive than
the others, and it is used principally for special alloy steels.
Iron ores are seldom so uniform in quality that they can be shipped
without careful attention to sampling and grade. In the Lake Superior
region the ores are sampled daily as mined, and the utmost care is taken
to mix and load the ore in such a way that the desired grades can be
obtained. Ordinarily a single deposit produces several grades of ore.
When ores are put into the furnace for smelting the mixtures are
selected with great care for the particular purpose for which the
product is to be used. The mixture is compounded as carefully as a
druggist's prescription. An ore salesman, after ascertaining the nature
of the iron and steel products of a plant, has to use great skill in
offering particular ores for sale which not only will meet the desired
grade in regard to all elements, but also will meet competition in
price. In some respects, the marketing of different grades of iron ore
is as complex as the marketing of a miscellaneous stock of merchandise.
With ores, as with merchandise, custom and sentiment play their
part,--with the result that two ores of identical grade mineralogically
and chemically may have quite a different vogue and price, simply
because of the fact that furnace men are used to one and not to the
other and are not willing to experiment.
The geologist is ordinarily concerned merely with finding an ore of as
good a general grade as possible; but he often finds to his surprise
that his efforts have been directed toward the discovery of something
which, due to some minor defect in texture, in mineralogical
composition, or in chemical composition, is difficult to introduce on
the market. There is here a promising field, intermediate between
geology (or mineralogy) and metallurgy, for the application of
principles of chemistry, metallurgy, and mineralogy, which is occupied
at the present time mainly by the ore salesman. Both the mineralogist
and metallurgist touch the problem but they do not cover it. With
increasingly precise and rapidly changing metallurgical requirements,
this field calls for scientific development.
=Geographic distribution of iron ore production.= Iron ores are widely
distributed over the world, but are produced and smelted on a large
scale only in a few places where there is a fortunate conjunction of
high grades, large quantity, proximity of coal, cheap transportation to
markets, and manufacturing enterprise. Over 90 per cent of the iron ore
production of the world is in countries bordering the North Atlantic
basin. The United States produces about 40 per cent, France about 12 per
cent, England about 10 per cent, Germany before the war 15 to 20 per
cent, and Spain, Russia, and Sweden each about 5 per cent. Lesser
producing countries are Luxemburg, Austria-Hungary, Cuba, Newfoundland,
and Algeria; and insignificant amounts are produced in many other parts
of the world. Of the world's iron and steel manufacturing capacity, the
United States has about 53 per cent, Germany 16 per cent, England 14 per
cent, France 10 per cent, the remainder of Europe (chiefly Russia,
Austria-Hungary, and Belgium) 7 per cent. The absence of important iron
ore production and of iron and steel manufacture either in the southern
hemisphere or in any of the countries bordering the Pacific is a
significant feature, when we remember what part iron plays in modern
civilization. Japan, however, is beginning to develop a considerable
iron and steel industry, which promises to use a large amount of ore
from China, Manchuria, and Korea, and possibly to compete in American
Pacific Coast markets.
In the United States about 85 per cent of the production, or one-third
of the world's production, comes from the Lake Superior region, a large
part of the remainder from the Birmingham district, Alabama, and smaller
quantities from the Adirondacks. For the rest of the North American
continent, the only largely producing deposit is that at Belle Isle,
Newfoundland, which is the basis of the iron industry of eastern Canada.
Cuba supplies some ore to the east coast of the United States.
In Europe there are only three large sources of high-grade iron ore
which have heretofore been drawn on largely,--the magnetite deposits of
northern Sweden, the hematites and siderites of the Bilbao and adjacent
districts of northern Spain, and the magnetite-hematite deposits of
southern Russia. The first two of these ores have been used to raise the
percentage of iron in the low-grade ores which are the principal
reliance of western Europe. The Swedish ores have also been necessary
in order to raise the percentage of phosphorus and thus make the ores
suitable for the Thomas process; on the other hand the Spanish ores and
a small part of the Swedish material have been desired because of their
low phosphorus content, adapted to the acid Bessemer process and to the
manufacture of low-phosphorus pig. The Russian ores have largely been
smelted in that country.
The largest of the western European low-grade deposits is a geographic
and geologic unit spreading over parts of Lorraine, Luxemburg, and the
immediately adjacent Briey, Longwy, and Nancy districts of France. The
ores of this region are called "minette" ores. This unit produces about
a fourth of the world's iron ore. Low-grade deposits of a somewhat
similar nature in the Cleveland, Lincolnshire, and adjacent districts of
England form the main basis for the British industry. There is minor
production of iron ores in other parts of France and Germany, in
Austria-Hungary, and in North Africa (these last being important because
of their low phosphorus content).
Comparison of figures of consumption and production of iron ores
indicates that the United States, France, Russia, and Austria-Hungary
are self-supporting so far as quantity of materials is concerned.
Certain ores of special grades, and ores of other minerals of the
ferro-alloy group required in steel making, however, must be imported
from foreign sources; this matter has been discussed above. Great
Britain and Germany appear to be dependent on foreign sources, even
under pre-war conditions, for part of the material for their furnaces.
During the war there was considerable development of the low-grade
English ores, but this does not eliminate the necessity for importing
high-grade ores for mixture. Belgium produces a very small percentage of
her ore requirements and is practically dependent on the
Lorraine-Luxemburg field.
The principal effect of the war on iron ore production was the
occupation of the great French mining and smelting field by the Germans,
thereby depriving the French of their largest source of iron ore. Since
the war the situation has been reversed, France now possessing the
Lorraine field, which formerly supplied Germany with 70 per cent of its
iron ore. As the German industrial life is largely based on iron and
steel manufacture, the problem of ore supplies for Germany is now a
critical one. It has led to German activity in Chile and may lead to
German developments in eastern Europe and western Asia, particularly in
the large and favorably located reserves of southern Russia. It seems
likely, however, that arrangements will also be made to continue the
export of ore from the Lorraine field down the Rhine to the principal
German smelting centers. France needs the German coal for coking as
badly as Germany needs the French iron ore. The Rhine valley is the
connecting channel for a balanced movement of commodities determined by
the natural conditions. These basic conditions are likely in the long
run to override political considerations.
The Lake Superior deposits, the Swedish magnetites, the Spanish
hematites, and the Russian ores carry 50 to 65 per cent of metallic
iron. The Birmingham deposits of southeastern United States, the main
British supplies, and the main French and German supplies contain about
35 per cent or less. It is only where ores are fortunately located with
reference to consuming centers that the low-grade deposits can be used.
For outlying territories only the higher-grade deposits are likely to be
developed, and even there many high-grade deposits are known which are
not mined. The largest single group not yet drawn on is in Brazil.
Others in a very early stage of development are in North Africa and
Chile.
=World reserves and future production of iron ore.= The average rate of
consumption of iron ore for the world in recent years has been about 170
million tons per year. At this rate the proved ore reserves would last
about 180 years. If it be assumed that consumption in the future will
increase at about the same rate as it has in the past, the total
measured reserve would still last about a century. These calculations of
life, however, are based only on the known reserves; and when potential
reserves are included the life is greatly increased. And this is not
all; for beyond the total reported reserves (both actual and potential),
there are known additional large quantities of lower-grade ores, at
present not commercially available, but which will be available in the
future,--to say nothing of expected future discoveries of ores of all
grades in unexplored territories. Both geological inference and the
history of iron ore exploration seem to make such future discoveries
practically certain. Iron ore constitutes about 4 per cent of the
earth's shell and it shows all stages of concentration up to 70 per
cent. Only those rocks are called "iron ores" which have a sufficiently
high percentage of iron to be adapted to present processes for the
extraction of iron. When economic conditions demand it, it may be
assumed that iron-bearing rocks not now ordinarily regarded as ores may
be used to commercial advantage, and therefore will become ores.
Not only is an indefinitely long life assured for iron ore reserves as a
whole, but the same is true of many of the principal groups of deposits.
The question of practical concern to us, therefore, is not one of total
iron ore reserves, but one of degrees of _availability_ of different
ores to the markets which focus our requirements for iron.
The annual production of ore from a given district is roughly a measure
of that ore's ability to meet the competitive market, and therefore, of
its actual immediate or past availability. Annual production is the net
result of the interaction of all of the factors bearing on availability.
It may be argued that there are ores known and not yet mined which are
also immediately available. On the whole, they seem to be less available
than ores actually being produced; otherwise general economic pressure
would require their use and actual production.
In considering the future availability of iron ores, it is obvious that
tables of past production afford only a partial basis for prediction.
Presumably districts which have produced largely in the past may be
expected to continue as important factors. In these cases production has
demonstrated availability. Continued heavy production may thus be
expected from the ores of the Lake Superior region, from the Clinton
hematites of Alabama, from the ores of the Lorraine-Luxemburg-Briey
district, from the Cleveland ores of England, from the Bilbao ores of
Spain, from the high-grade magnetites of northern Sweden, and (assuming
political stability) from the ores of southern Russia.
Similarly, also, recent increases in production from certain districts
are probably significant of increased use of such ores in the future.
Among these developments are the increasing production of Swedish ores
and their importation into England and Germany, and the increasing use
of Clinton hematites and Adirondack magnetites in the United States.
Low-grade ores from the great reserves of Cuba are being mined and
brought to the east coast of the United States in increasing amounts,
and it is highly probable that they will take a larger share of the
market. A similar project in Chile, which lay dormant during the war
because of restricted shipping facilities, is expected in the near
future to yield important shipments to the United States. In none of
these cases will production be limited in the near future by ore
reserves. Increased production and use of iron ores are also to be
looked for in Newfoundland, North Africa, China, India, Australia, and
South Africa.
On the commercial horizon are ores of still newer districts, the
availability of which may not be read from tables of production. Their
availability must be determined by analysis and measurement of the
factors entering into availability. Availability of iron ore is
determined by percentage of iron, percentages of impurities, percentages
of advantageous or deleterious minor constituents, physical texture,
conditions for profitable mining, adaptability to present furnace
practice, distance from consuming centers, conditions and costs of
transportation, geographical and transportational relation to the coal
and fluxes necessary for smelting, trade relations, tariffs and taxes,
inertia of invested capital, and other considerations. All of these
factors are variable. A comparison of ores on the basis of any one of
these factors or of any two or three of them is likely to be misleading.
A comparison based on the quantitative consideration of all of the
several factors seems to be made practically impossible by the
difficulty of ascertaining accurately the quantitative range and
importance of each factor, and by the difficulty of integrating all of
the factors even if they should be determined. However, their combined
effect is expressed in the cost of bringing the product to market; and
comparison of costs furnishes a means of comparing availability of ores.
A high-grade ore, cheaply mined and favorably located with reference to
the points of demand, will command a relatively high price at the point
of production. The same ore so located that its transportation costs are
higher will command a lower price; or it may be so located that the
costs of mining and bringing it to places where it can be used are so
high that there is no profit in the operation. There are known
high-grade iron ores which, because of cost, are not available under
present conditions.
The availability of an ore, then, depends on its relation to a
market,--whether, after meeting the cost of transportation, it can be
sold at prevailing market prices at the consuming centers, and can still
leave a fair margin of profit for the mining operation. The price
equilibrium between consuming centers affords a reasonably uniform basis
against which to measure availability of ores.
Figures of cost are obtainable as a basis for comparison of availability
of iron ores of certain of the districts, but not enough are at hand for
comparison of the ores of all districts. Careful study of costs has
demonstrated the availability in the near future of the Brazilian
high-grade Bessemer hematites; and projects which are now under way for
exportation to England and the United States will doubtless make this
enormous reserve play an important part in the iron industry. Iron ore
is known but not yet mined in many parts of the western United States
and western Canada. With the increasing population along the west coast
of North America, projects for smelting the ore there are becoming more
definite. Establishment of smelters on the west coast would make
available a large reserve of ore (see also, however, p. 155).
The list of changes now under way or highly probable for the future
might be largely extended. The use of iron and steel is rapidly
spreading through populous parts of the world which have heretofore
demanded little of these products. This increased use is favoring the
development of local centers of smelting, which will make available
other large reserves of iron ore. The growth of smelting in India, China
and Australia illustrates this tendency.
Iron ore reserves are so large, so varied, and so widely distributed
over the globe, that they will supply demands upon them to the remote
future. Reserves become available and valuable only by the expenditure
of effort and money. Ores are the multiplicand and man the multiplier in
the product which represents value or availability. Iron ore can be made
available, when needed, almost to any extent, but at highly varying cost
and degree of effort. The highest grade ores, requiring minimum
expenditure to make them available, are distinctly limited as compared
to total reserves. Any waste in their utilization will lead more quickly
to the use of less available ores at higher cost. One of the significant
consequences of the exhaustion of the highest grade reserves will be an
increased draft upon fuel resources for the smelting of the lower grade
ores. Availability of iron ores is limited, not by total reserves, but
by economic conditions.
GEOLOGIC FEATURES
Iron rarely exists in nature as a separate element. It occurs mainly in
minerals which represent combinations of iron, oxygen, and water, the
substances which make up iron rust. Very broadly, most of the iron ores
might be crudely classified as iron rust. In detail this group is
represented by several mineral varieties, principal among which are
hematite (Fe_{2}O_{3}), magnetite (Fe_{3}O_{4}), and limonite (hydrated
ferric oxide). Iron likewise combines with a considerable variety of
substances other than oxygen; and some of these compounds, as for
instance iron carbonate (siderite), iron silicate (chamosite,
glauconite, etc.), and iron sulphide (pyrite), are locally mined as iron
ores. While an ore of iron may consist dominantly of some one of the
iron minerals, in few cases does it consist exclusively of one mineral.
Most ores are mixtures of iron minerals.
Fully nine-tenths of the iron production of the world comes from the
so-called hematite ores, meaning ores in which hematite is the dominant
mineral, though most of them contain other iron minerals in smaller
quantities. About 5 per cent of the world's iron ores are magnetites,
and the remainder are limonites and iron carbonates.
Iron ores are represented in nearly all phases of the metamorphic cycle,
but the principal commercial values have been produced by processes of
weathering and sedimentation at and near the surface.
=Sedimentary iron ores.= Over 90 per cent of the world's production of
iron ore is from sedimentary rocks. The deposits consist in the main
either of beds of iron ore which were originally deposited as such and
have undergone little subsequent alteration, or of those altered
portions of lean ferruginous beds which since their deposition have been
enriched or concentrated sufficiently to form ores. A minor class of
iron ores in sediments consists of deposits formed by secondary
replacement of limestones by surface waters carrying iron in solution.
1. Deposits of the first class,--originally laid down in much their
present form,--are usually either oölitic, _i. e._, containing great
numbers of flat rounded grains of iron minerals like flaxseeds, or
consist in large part of fossil fragments of sea shells, replaced by
iron minerals. The Clinton ores of the Birmingham district, the Wabana
ores of Newfoundland, the minette ores of the Lorraine district in
central Europe, and the oölitic ores of northern England are all of
these types. Their principal iron mineral is hematite, although the
English ores also contain considerable iron carbonate or siderite. The
cementing or gangue materials are chiefly calcite and quartz, in
variable proportions.
The large reserves of high-grade hematite in the Minas Geraes district
of Brazil are also original sediments, but lack the oölitic texture.
An insignificant proportion of the world's iron is obtained from "bog
ores," which are sedimentary deposits of hydrated iron oxide in swamps
and lakes. These ores have been used only on a small scale and chiefly
in relatively undeveloped countries. They are of particular interest
from a genetic standpoint in that they show the nature of some of the
processes of iron ore deposition as it is actually going on today.
None of the ores of this class, with the exception of the iron
carbonates, have undergone any considerable surface enrichment since
their primary deposition. Neither, with the exception of the Brazilian
ores, have they undergone any deep-seated metamorphism. The shapes,
sizes, and distribution of the deposits may be traced back to the
conditions of original deposition. In England and western Europe the
principal deposits have been only slightly tilted by folding. In the
United States the Clinton ores have partaken in the Appalachian folding.
In Brazil, the ores have undergone close folding and anamorphism.
2. Deposits of the second class, which owe much of their value to
further enrichment since deposition, are represented by the hematite
ores of the Lake Superior district. These may be thought of as the
locally rusted and leached portions of extensive "iron formations," in
which oxidation of the iron, and the leaching of silica and other
substances by circulating waters, have left the less soluble iron
minerals concentrated as ores. The Lake Superior iron formations now
consist near the surface mainly of interbanded quartz (or chert) and
hematite, called _jasper_ or _ferruginous chert_ or _taconite_. These
are similar in composition to the leaner iron ores of Brazil, called
_itabirite_, but differ in that the silica is in the form of chemically
deposited chert, rather than fragmental quartz grains.
[Illustration: FIG. 11. Alteration of Lake Superior iron
formation to iron ore by the leaching of silica.]
When originally deposited the iron was partly hematite (perhaps some
magnetite) and largely in the form of iron carbonate (siderite) and
iron silicate (greenalite), interbanded with chert. The original
condition is indicated by the facts that deep below the surface, in
zones protected from weathering solutions, siderite and greenalite are
abundant, and that they show complete gradation to hematite in
approaching the surface. The ore has been concentrated in the iron
formation almost solely by the process of leaching of silica by surface
or meteoric waters, leaving the hematite in a porous mass. Figure 11
illustrates this change as calculated from analyses and measurements of
pore space. During this process a very minor amount of iron has been
transported and redeposited. In short, the Lake Superior iron ores are
residual deposits formed by exactly the same weathering processes as
cause the accumulation of clays, bauxites, and the oxide zones of
sulphide deposits. The development of an iron ore rather than of other
materials as an end-product is due merely to the peculiar composition of
the parent rock. The solution of silica on such an immense scale as is
indicated by these deposits has sometimes been questioned on the general
ground that silica minerals are insoluble. However, there is plenty of
evidence that such minerals _are_ soluble in nature; and the assumption
of insolubility, so often made in geologic discussions, is based on the
fact that most other minerals are _more_ soluble than silica minerals,
and that in the end-products of weathering silica minerals therefore
usually remain as important constituents. Iron oxide, on the other hand,
is _less_ soluble even than silica,--with the result that when the two
occur together, the evidence of leaching of silica from the mixture
becomes conspicuous.
The fact that these deposits are almost exclusively residual deposits
formed by the leaching of silica has an important bearing on
exploration. If they have been formed by the transportation and
deposition of iron from the surrounding rocks, there is no reason why
they should not occasionally be found in veins and dikes outside of the
iron formation. As a matter of fact they do not transgress a foot beyond
the limits of the iron formation. Failure to recognize the true nature
of the concentration of these ores has sometimes led to their erroneous
classification as ores derived from the leaching and redeposition of
iron from the surrounding rocks.
The distribution and shapes of ore deposits of this class are far more
irregular and capricious than those of the primary sediments, as would
be expected from the fact that their concentration has taken place
through the agency of percolating waters from the surface, which worked
along devious channels determined by a vast variety of structural and
lithological conditions. The working out of the structural conditions
for the different mines and districts constitutes one of the principal
geologic problems in exploration. These conditions have been fully
discussed in the United States Geological Survey reports, and are so
various that no attempt will be made to summarize them here.
One of the interesting features of the concentration of Lake Superior
iron ores is the fact that it took place long ago in the Keweenawan
period, preceding the deposition of the flat-lying Cambrian formations,
at a time when the topography was mountainous and the climate was arid
or semi-arid. These conditions made it possible for the oxidizing and
leaching solutions to penetrate very deeply, how deeply is not yet
known, but certainly to a depth below the present surface of 2,500 feet.
At present the water level is ordinarily within 100 feet of the surface,
and oxidizing solutions are not going much below this depth. This
region, therefore, furnishes a good illustration of the intermittent and
cyclic character of ore concentration which is now coming to be
recognized in many ore deposits.
Subsequent changes far beneath the surface have folded, faulted, and
metamorphosed some of the Lake Superior iron ores but have not enriched
them. The same processes have recrystallized and locked together the
minerals of some of the lean iron formations, making them hard and
resistant, so that subsequent exposure and weathering have had little
effect in enriching them to form commercial ores.
The weathering of limestones containing minor percentages of iron
minerals originally deposited with the limestones may result in the
residual concentration of bodies of limonite or "brown ores" associated
with clays near the surface. This process is similar in all essential
respects to the concentration of the Lake Superior ores. Such limonitic
ores are found rather widely distributed through the Appalachian region
and in many other parts of the world. Because of the ease with which
they can be mined and smelted on a small scale they have been used since
early times, but have furnished only a very small fraction of the
world's iron.
3. In a third class of sedimentary ores, the iron minerals are supposed
to have been introduced as replacements of limestones subsequent to
sedimentation. Such ores are not always easy to discriminate from ores
resulting primarily from sedimentation. This class is represented by the
high-grade deposits of Bilbao, Spain, Austrian deposits, and by smaller
deposits in other countries. The Bilbao ores consist mainly of siderite,
which near the surface has altered to large bodies of oxide minerals.
They occur in limestones and shales and are not associated with igneous
rocks. The deposits are believed to have been formed by ordinary surface
waters carrying iron in solution, and depositing it in the form of iron
carbonate as replacements of the limestones. The original source of the
iron is believed to have been small quantities of iron minerals
disseminated through the ordinary country rocks of the district. The
action of surface waters, in thus concentrating the iron in certain
localities which are favorable for precipitation, is similar to the
formation of the lead and zinc ores of the Mississippi valley, referred
to in the next chapter. Deposits formed in this manner may be roughly
tabular and resemble bedded deposits, or they may be of very irregular
shapes.
The sedimentary iron ores in general evidently represent an advanced
stage of katamorphism, and illustrate the tendency of this phase of the
metamorphic cycle toward simplification and segregation of certain
materials. The exact conditions of original sedimentation present one
of the great unsolved problems of geology, referred to in Chapter III.
=Iron ores associated with igneous rocks.= About five per cent of the
world's production of iron ore is from bodies of magnetite formed in
association with igneous rocks. These are dense, highly crystalline
ores, in which the iron minerals are tightly locked up with silicates,
quartz, and other minerals, suggestive of high temperature origin. The
largest of these deposits is at Kiruna in northern Sweden; in fact this
is the largest single deposit of high-grade ore of any kind yet known in
the world. Here the magnetite forms a great tabular vertical body lying
between porphyry and syenite. In the Adirondack Mountains of New York
and in the highlands of New Jersey, magnetites are interbedded and
infolded with gneisses, granites, and metamorphic limestones. In the
western United States there are many magnetite deposits, not yet mined,
at contacts between igneous intrusives and sedimentary rocks,
particularly limestones (so-called "contact-metamorphic" deposits). The
ores of the Cornwall district of Pennsylvania and some of the Chilean,
Chinese, and Japanese ores are of the same type.
Magnetites containing titanium, which prevents their use at the present
time, are known in many parts of the world as segregations in basic
igneous rocks. They are actually parts of the igneous rock itself (p.
34). Among the large deposits of this nature are certain titaniferous
ores of the Adirondacks, of Wyoming, and of the Scandinavian peninsula.
In all of these cases, it is clear that the origin of the ores is in
some way related to igneous processes, and presumably most of the ores
are deposited from the primary hot solutions accompanying and following
the intrusion of the igneous rocks; but thus far it has been difficult
to find definite and positive evidence as to the precise processes
involved. None of these deposits have undergone any important secondary
enrichment at the surface. Their sizes, shapes, and distribution are
governed by conditions of igneous intrusion, more or less modified, as
in the Adirondacks, by later deformation.
=Iron ores due to weathering of igneous rocks.= A small part of the
world's iron ores, less than 1 per cent of the total production, are the
result of surface alteration of serpentine rocks. These ores are mined
principally in Cuba (Fig. 12). Here they have been developed on a
plateau-like area on which erosion is sluggish. The process of formation
has been one of oxidation of the iron minerals and leaching of most of
the other constituents, leaving the iron concentrated near the surface
in blanket-like deposits. The minerals of the original rock contained
alumina, which, like the iron, is insoluble under weathering conditions,
and hence the Cuban iron ores are high in alumina. They also contain
small quantities of nickel and chromium which have been concentrated
with the iron. A large part of the iron minerals, especially where close
to the surface, have been gathered into small shot-like nodules called
_pisolites_. It is thought that the solution and redeposition of the
iron by organic acids from plant roots may be at least a contributing
cause in the formation of this pisolitic texture.
[Illustration: FIG. 12. Representing in terms of weight the
mineralogical changes in the katamorphism of serpentine rock to iron
ore, on the assumption that alumina has remained constant, eastern
Cuba.]
The Cuban iron ores are similar in their origin to _laterites_, which
are surface accumulations of clay, bauxite, and iron oxide minerals,
resulting from the weathering of iron-bearing, commonly igneous, rocks.
The typical laterites carry more clay and bauxite than the Cuban iron
ores, but this is due merely to the fact that the original rocks
commonly carry more materials which weather to clay. In fact the Cuban
iron ores are themselves, broadly speaking, laterites.
=Iron ores due to weathering of sulphide ores.= A relatively minute
portion of the world's iron ore comes from the "gossans" or "iron caps"
over deposits of iron sulphides. The gossans are formed by oxidation and
leaching of other minerals from the deposits, leaving limonite or
hematite in concentrated masses (see pp. 46-47).
MANGANESE ORES
ECONOMIC FEATURES
Manganese ores are used mainly in the manufacture of steel, the alloys
spiegeleisen and ferromanganese being added to the molten steel after
treatment in the Bessemer converter and open-hearth furnace in order to
recarburize and purify the metal. The alloy ferromanganese is also used
in the production of special manganese steels. Manganese ore is used in
relatively small amounts in dry batteries, in the manufacture of
manganese chemicals, in glass making, and in pigments. Steel uses 95 per
cent of the total manganese consumed, batteries and chemicals 5 per
cent. On an average each ton of steel in the United States requires 14
pounds of metallic manganese, equivalent to 40 pounds of manganese ore.
With manganese ores, as with iron ores, the percentage of minor
constituents,--phosphorus, silica, sulphur, etc.,--determines to a large
extent the manner of use. Low-grade manganese ores, ranging from 10 to
35 per cent in manganese, 20 to 35 per cent in iron, and containing less
than 20 per cent of silica, are used mainly in the production of the
low-grade iron-manganese alloy called _spiegeleisen_ or _spiegel_ (16 to
32 per cent manganese). The higher-grade ores, ranging from 35 to 55 per
cent in manganese, are used mainly in the production of the high-grade
alloy called _ferromanganese_ or _ferro_, in which the manganese
constitutes 65 to 80 per cent of the total. To a very limited extent
manganese is smelted directly with iron ores, thus lessening the amount
to be introduced in the form of alloys; this, however, is regarded as
wasteful use of manganese, since its effectiveness as so used is not
very great. Steel makers usually prefer to introduce manganese in the
form of ferromanganese rather than as spiegel. On the other hand, the
ores of the United States as a whole are better adapted to the
manufacture of spiegel. With the shutting off of foreign high-grade
supplies during the war, resulting in the increased use of local ores,
it became necessary to use larger amounts of the spiegel which could be
made from these ores. Metallurgists stated that it was theoretically
possible to substitute spiegel for the higher grade alloy up to 70 per
cent of the total manganese requirement, but in actual practice this
substitution did not get much beyond 18 per cent.
The principal manganese ore-producing countries in normal times are
Russia, India, and Brazil. Relatively little ore is used in these
countries, most of it being sent to the consuming countries of Europe
and to the United States. The Indian ore has been used largely by
British steel plants, but much of it also has gone to the United States,
Belgium, France, and Germany. The Russian ore has been used by all five
of these countries, Germany having a considerable degree of commercial
control and receiving the largest part; a small quantity is also used in
Russia. Brazilian ore has gone mainly to the United States, and in part
to France, Germany, and England.
Smaller amounts of manganese ore have been produced in Germany,
Austria-Hungary, Spain, and Japan. This production has had little effect
on the world situation. That produced in Austria-Hungary and Germany is
used in the domestic industry. That from Spain and Japan is in large
part exported.
The highest grade of manganese ore comes from the Russian mines,
especially those in the Caucasus region. Most of the ore used for the
manufacture of dry batteries and in the chemical industry, where
high-grade ores are required, has come from Russia. By far the larger
part of the Russian production, however, has gone into steel
manufacture. Indian and Brazilian ores have likewise been used mainly in
the steel industry. Some Japanese ore also is of high grade and is used
for chemical and battery purposes.
Nature has not endowed the United States very abundantly with manganese
ores, and such as are known are widely scattered, of relatively small
tonnage, and of a wide range of grade. The principal producing districts
are the Philipsburg district of Montana and the Cuyuna Range of
Minnesota; there are also scattering supplies in Virginia, Arizona,
California, and many other states. The use of domestic ores has
sometimes been unsatisfactory, because of frequent failure of domestic
producers to deliver amounts and grades contracted for. It has been, on
the whole, cheaper, easier, and more satisfactory for the large
consumers to purchase the imported ore, which is delivered in any
desired amount and in uniform grades, rather than to try to assemble
usable mixtures from various parts of the country.
Before the European War, the United States produced only 1 to 2 per cent
of its needed supply of manganese, the rest being imported mainly from
India, Russia, and Brazil, in the form of ore, and from England in the
form of ferromanganese (about half of the total requirement). The
partial closing of the first two and the fourth of these sources of
supply under war conditions made it necessary to turn for ore to Brazil
and also to Cuba, where American interests developed a considerable
industry in medium-grade ores. At the same time steps were taken to
develop domestic resources; and with the high prices imposed by war
conditions, the domestic production, both of high- and low-grade ore,
was increased largely, but still was able to supply only 35 per cent of
the total requirements of manganese.
At the close of the war sufficient progress had been made--in the
discovery of many new deposits in the United States, in the use of
low-grade domestic ores, which before had not been able to compete with
imported ores, and in the increased use of spiegel, allowing wider use
of low-grade ores,--to demonstrate that, if absolutely necessary, and at
high cost, the United States in another year or two could have been
nearly self-sufficing in regard to its manganese requirements. The
release of shipping from war demands resulted immediately in larger
offerings of foreign manganese ore and of ferromanganese from England,
at prices which would not allow of competition from much of the domestic
or Cuban ore production or from the domestic manufacture of alloys. The
result was a rather dramatic closing down of the manganese industry,
with much financial loss, the passage of a bill for reimbursement of
producers, and a demand on the part of the producers, though not of
consumers, for a protective tariff. In the questions thus raised it is
desirable that geologists and engineers professionally connected with
the industry thoroughly understand the basic facts; for they are liable
to be called upon for advice, not only on questions relating to domestic
supplies affected by possible future foreign policies, but on the
formulation of the policies themselves. Conservation, cheaper steel, and
future trade relations of the United States all require consideration,
before action is taken to protect this one of several similarly situated
mineral industries, in the effort to make the country self-supporting.
These questions are further dealt with in Chapters XVII and XVIII.
Manganese production was also developed during the war in the Gold Coast
of West Africa, in Costa Rica, in Panama, in Java, and elsewhere; but
with the possible exception of Java and Chile, none of these sources are
likely to be factors in the world situation. The war-developed manganese
production of Italy, France, Sweden, and United Kingdom is also unlikely
to continue on any important scale.
GEOLOGIC FEATURES
Like iron ores, manganese ores consist principally of the oxides of
manganese (pyrolusite, psilomelane, manganite, wad, and others), and
rarely the carbonate of manganese (rhodochrosite). They are similar in
their geologic occurrence to many of the iron ores and are often mixed
with iron ores as manganiferous iron ores and ferruginous manganese
ores.
The higher grade manganese ores are of two general types. Those of the
Caucasus district in Russia are sedimentary beds, oölitic in texture,
which were originally deposited as rather pure manganese oxides, and
which have undergone little secondary concentration. They are mined in
many places in much the same manner as coal. Those of India and Brazil
are chiefly surface concentrations of the manganese oxides, formed by
the weathering of underlying rocks which contain manganese carbonates
and silicates. The origin of the primary manganese minerals in the
Indian and in some of the Brazilian deposits is obscure. In others of
the Brazilian ores, the manganese was deposited in sedimentary layers
interbedded with siliceous "iron formations," and the whole series has
subsequently been altered and recrystallized.
The manganese ores of Philipsburg, Montana, the principal large
high-grade deposits mined in the United States, were derived by surface
weathering from manganese carbonates which form replacements in
limestone near the contact with a great batholith of granodiorite. The
primary manganese minerals probably owe their origin to hot magmatic
solutions, as suggested by the close association of the ores with the
igneous rock, the presence of minerals containing chlorine, fluorine,
and boron, and the development in the limestone of dense silicates and
mineral associations characteristic of hot-water alteration. The
manganese ores are mined principally in the oxidized zone. Rich silver
ores are found below the water table, but mainly in veins independent of
the manganese deposits.
At Butte, Montana, a little high-grade manganese material has been
obtained from the unoxidized pink manganese carbonate, which is a common
mineral in some of the veins. It is associated with quartz and metallic
sulphides and is similar in origin to the copper ores of the same
district (pp. 201-202).
The lower-grade and the more ferruginous manganese ores are of a
somewhat similar origin to the principal high-grade ores, in that they
represent surface concentrations of the oxides from smaller percentages
of the carbonates and silicates in the rocks below. Deposits of this
nature have been derived from a wide variety of parent rocks--from
contact zones around igneous intrusions, from fissure veins of various
origins, from calcareous and clayey sediments, and from slates and
schists. The manganese and manganiferous iron ores of the Cuyuna
district of Minnesota, the largest source of low-grade ores in this
country, were formed by the action of weathering processes on
sedimentary beds of manganese and iron carbonates constituting "iron
formations." The process is the same as the concentration of Lake
Superior iron ores described elsewhere.
Manganese, like iron, is less soluble than most of the rock
constituents, and tends to remain in the outcrop under weathering
conditions. To some extent also it is dissolved and reprecipitated, and
is thus gathered into concretions and irregular nodular deposits in the
residual clays. In some cases it is closely associated with iron
minerals; in others, due to its slightly greater solubility, it has been
separated from the iron and segregated into relatively pure masses. With
manganese, as with iron, katamorphic processes are responsible for the
concentration of most of the ores. The ores are in general surface
products, and rarely extend to depths of over a hundred feet.
CHROME (OR CHROMITE) ORES
ECONOMIC FEATURES
The principal use of chrome ores is in the making of the alloy
ferrochrome (60 to 70 per cent chromium), used for the manufacture of
chrome, chrome-nickel, and other steels. These steels have great
toughness and hardness, and are used for armor-plate, projectiles,
high-speed cutting tools, automobile frames, safe-deposit vaults, and
other purposes. Chrome ore is used also both in the crude form and in
the form of bricks for refractory linings in furnaces, chiefly
open-hearth steel furnaces; and as the raw material for bichromates and
other chemicals, which are used in paints and in tanning of leather. In
the United States in normal times about 35 per cent of the total
chromite consumed is used in the manufacture of ferrochrome, and about
35 per cent for bichromate manufacture, leaving 30 per cent for
refractory and other purposes.
In the higher commercial grades of chrome ore the percentage of chromic
oxide is 45 to 55 per cent, but under war conditions ore as low as 30
per cent in Cr_{2}O_{3} was mined. Recovery of chrome from slags
resulting from the smelting of chromiferous iron ores was one of the
war-time developments.
The principal chromite-producing countries in normal times are New
Caledonia, and Rhodesia (controlled by French and British interests),
and to a somewhat lesser extent Russia and Turkey (Asia Minor). Small
amounts of chromite are mined in Greece, India, Japan, and other
countries. The Indian deposits in particular are large and high-grade
but have been handicapped by inadequate transportation. The production
of chrome ore in New Caledonia, Rhodesia, Russia, and Turkey has usually
amounted to more than 90 per cent of the total world's production. The
ore from New Caledonia has been used by France, Germany, England, and to
some extent by the United States. Rhodesian ore has been used by the
United States and the principal European consumers. Latterly more
Rhodesian ore has gone to Europe and more Caledonian ore to the United
States. The Russian ore has been in part used in Russia and in part
exported, probably going mainly to France and Germany. The Turkish ore
has been exported to the United States, England, and Germany; it
probably supplied most of Germany's chromite requirements during the
war.
During the war the United States was temporarily an important producer,
as were also Canada, Brazil, Cuba, and to a minor degree Guatemala.
The richest chrome ore mined at present comes from Guatemala, but the
mines are relatively inaccessible. The New Caledonian, Rhodesian,
Russian, Turkish, and Indian ores are also of high grade. The ores mined
in the United States, Canada, Brazil, Cuba, Greece, and Japan are of
lower grade.
The use of domestic chromite supplies in the United States presents much
the same problem as does manganese. The ore bodies are small, scattered,
and of a generally law grade. War-time experience showed that they could
be made to meet a large part of the United States requirements, but at
high cost and at the risk of early exhaustion of reserves. California
and Oregon are the principal sources, and incidental amounts have been
produced in Washington, Wyoming, and some of the Atlantic states. With
the resumption of competition from foreign high-grade ores at the close
of the war, the domestic mining industry was practically wiped out; the
consequences being financial distress, partial direct relief from
Congress, and consideration of the possibilities of a protective
tariff,--which in this case would have to be a large one to accomplish
the desired results (see Chapters XVII and XVIII).
GEOLOGIC FEATURES
The principal chrome mineral is chromite, an oxide of chromium and iron.
Chromite is a common minor constituent of basic igneous rocks of the
peridotite and pyroxenite type. In these rocks it occurs both as
disseminated grains, and as stringers, and large irregular masses which
probably represent magmatic segregations. Alteration, and weathering of
the parent rock, forming first serpentine and then residual clays, make
the chromite bodies progressively richer and more available, by leaching
out the soluble constituents of the rock leaving the chromite as
residual concentrates. All the important chromite deposits of the world
are associated in somewhat this manner with serpentine or related
rocks. They are formed in the same way as the lateritic iron ores of
Cuba, and from the same sort of rocks (pp. 171-173). Chromite is very
insoluble, and the mechanical breaking down of deposits and
transportation by streams frequently forms placers of chrome sands and
gravels. Such placers have not been worked to any extent.
Katamorphic processes give the important values to chromite deposits.
NICKEL ORES
ECONOMIC FEATURES
The principal use of nickel is in the manufacture of nickel steel, the
most important of all alloy steels. Ordinary nickel steels carry about
3-1/2 per cent nickel. Nickel is used in all gun and armor-plate steels,
and in practically all other good steels except tool steels. It is also
extensively alloyed with other metals, particularly with copper to form
the strong non-corrosive metal (monel metal) used for ship propellers
and like purposes. Nickel is also used for electroplating, for nickel
coins, for chemicals, etc. Of the total production about 60 per cent is
used in steels, 20 per cent in non-ferrous alloys and 20 per cent in
miscellaneous uses. The ores mined range from 2 to 6 per cent in
metallic nickel.
Canada (Sudbury, Ontario) produces over three-fourths of the world's
nickel and is likely to have an even greater share of the future
production. The French supply from New Caledonia is second in
importance, and minor amounts are produced in Norway and in several
other countries. The control and movement of the Canadian and New
Caledonian supplies are the salient features of the world nickel
situation. Nickel leaves the producing countries mostly as matte.
Canadian matte has been refined mainly in the United States, but the
tendency is toward refining a larger proportion in Canada. In Europe
there are refineries in France, England, Belgium, Germany, and Norway,
which normally treat the bulk of the New Caledonian and some of the
Canadian production. Small quantities of New Caledonian matte or ore are
also refined in Japan, and during the war considerable amounts came to
the United States.
The United States now produces perhaps 10 per cent of its normal
requirements of nickel from domestic sources, principally as a
by-product of copper refining. However, the United States has a large
financial interest in the Canadian deposits, and refines most of the
matte produced from Sudbury ores in a New Jersey refinery. Shipments to
Europe of Canadian nickel refined in the United States have been a
feature of the world's trade in the past.
The nickel-bearing iron ores of Cuba, consumed in the United States,
constitute a potential nickel supply of some importance, if processes of
preparation become commercially perfected.
Known supplies of nickel in Canada and New Caledonia are ample for a
considerable future, and geologic conditions promise additional
discoveries at least in the former field. The probable reserves of the
Sudbury district have been estimated to be fully 100,000,000 tons, which
would supply the world's normal pre-war requirements for about a hundred
years.
In recent years the British and Canadian governments have taken an
active interest in the nickel industry. They organized a joint
commission for its investigation, the report[31] of which furnishes the
most comprehensive view of the world nickel situation yet available. The
British government has directly invested in shares of the
British-American Nickel Company, and has negotiated European contracts
for sale of nickel for this company. The Canadian government has exerted
some pressure toward larger refining of nickel matte in Canada.
GEOLOGIC FEATURES
The principal ore minerals are the nickel sulphides and arsenides
(particularly pentlandite, but also millerite, niccolite, and others),
which are found at Sudbury intergrown with the iron and copper
sulphides, pyrrhotite and chalcopyrite; and the hydrated
nickel-magnesium silicates (garnierite and genthite), which are products
of weathering. The richer ores of Canada contain about 5 or 6 per cent
of nickel, the New Caledonian ores less than 2 per cent. The Sudbury
ores carry also an average of about 1.5 per cent of copper.
Nickel, while present in the average igneous rock in greater amounts
than copper, lead, or zinc, is apparently not so readily concentrated in
nature as the other metals and is rarely found in workable deposits. The
few ore bodies known have been formed as the result of unusual
segregation of the nickel in highly magnesian igneous rock of the norite
or gabbro type, at the time of its solidification or soon after; and in
some cases, in order to produce the nickel ore, still further
concentration by the agency of weathering has been necessary. Thus there
are two main types of deposits.
The first, the sulphide type, is represented by the great ore bodies of
the Sudbury district. These are situated in the basal portions of a
great norite intrusive, and are ascribed to segregation of the sulphides
as the rock solidified. To some extent the segregation was aided by
mineralizing solutions following the crystallization of the magma, but
in general there is little evidence that the ores were deposited from
vagrant solutions of this kind (see pp. 34-35). These ores owe their
value to primary concentration; secondary transportation and
reprecipitation by surface waters has not been important. A small amount
of the green arsenate, annabergite or "nickel bloom," has been developed
by oxidation at the surface.
The second, the garnierite or "lateritic" type of nickel ores, is
somewhat more common and is represented by the deposits of New
Caledonia. In this locality the original rock is a peridotite,
relatively low in nickel, which has been altered to serpentine.
Weathering has concentrated the more resistant nickel at the expense of
the more soluble minerals, and has produced extensive blanket deposits
of clay, which in their lower portions contain nickel in profitable
amounts. Similar processes, working on material of a somewhat different
original composition, have produced the nickel-bearing and
chrome-bearing iron ores of Cuba (pp. 171-173).
TUNGSTEN (WOLFRAM) ORES
ECONOMIC FEATURES
The principal use of tungsten is in the making of high speed tool
steels. It is added either as the powdered metal or in the form of
ferrotungsten, an alloy containing 70 to 90 per cent of tungsten.
Tungsten is also used for filaments in incandescent lamps, and in
contacts for internal combustion engines, being a substitute for
platinum in the latter use. Of late years tungsten alloys have also been
used in valves of airplane and automobile engines.
The average grade of tungsten ores mined in the United States is less
than 3 per cent of the metal; before smelting they are concentrated to
an average grade of 60 per cent tungsten oxide.
Germany through its smelting interests controlled the foreign tungsten
situation prior to the war; two-thirds of its excess output of
ferrotungsten was consumed by England and the balance principally by the
United States and France. Other consumers in the main satisfied their
requirements by imports of tool steel from these four countries.
The bulk of the tungsten ore consumed in Europe prior to 1914 came from
British possessions; these were principally the Federated Malay States,
Burma, Australia, and New Zealand. The United States, Portugal, Bolivia,
Japan, Siam, Argentina, and Peru were also producers. The great demand
for tungsten created by the war added China to the list of important
producers and greatly increased the production from Burma and Bolivia.
Smelting works were established in England and those of the United
States and France were greatly enlarged. England is at present in a
position to dominate the world tungsten situation. The question of
control of the ores obtainable in China, Korea, Siam, Portugal, and
western South America is likely to be an important one for the future.
Of the annual pre-war world production, the United States used about
one-fifth. Three-fourths of this requirement was met by domestic
production. The balance was obtained by importation, chiefly from
Germany, from Portugal and Spain, and from England, both of concentrates
and of ferrotungsten.
To the considerable demand for high speed tool steels occasioned by
munitions manufacture, production in the United States responded
quickly. Supplies of tungsten came chiefly from California, Colorado,
Arizona, Nevada, and South Dakota. At the same time importation largely
increased, chiefly from the west coast of South America and the Orient.
Consumption reached a half of the world's total. Considerable amounts of
ferrotungsten were exported to the Allies.
The end of the war created a possible tungsten shortage in this country
into a tungsten surplus. In so far as actual domestic consumption is
concerned there has been a return to something like pre-war conditions,
as the only known new use to which tungsten may be put--the manufacture
of die steel--does not involve the use of any large amount of
ferrotungsten. The richer mines of the two chief tungsten-producing
districts in the United States have shown impoverishment and at present
no important new deposits are known. The grade of the producing deposits
is on an average low. The domestic production of tungsten ore will
doubtless decrease, owing to the importation of cheaper foreign ores,
unless a high tariff wall is erected. Importation from the Orient and
the west coast of South America should continue in reduced amounts,
depending upon the ability of domestic manufacturers to obtain and hold
foreign markets for ferrotungsten and high speed tool steel. In the
commercial control of tungsten ores the United States has at present a
strong position, second only to that of England.
GEOLOGIC FEATURES
Tungsten ores contain tungsten principally in the form of the minerals
scheelite (calcium tungstate), ferberite (iron tungstate), hübnerite
(manganese tungstate), and wolframite (iron-manganese tungstate). All
these minerals are relatively insoluble and have high specific gravity,
and as a consequence they are frequently accumulated in placers, along
with cassiterite and other stable, heavy minerals. A large part of the
world's tungsten production in the past has been won from such deposits.
Placers are still important producers in China, Siam, and Bolivia,
although in these countries vein deposits are also worked.
With the exhaustion of the more easily worked placer deposits,
increasing amounts of tungsten are being obtained from the primary or
fixed deposits. These are found almost exclusively in association with
granitic rocks, and have a variety of forms. The most productive
deposits are in the form of veins, cutting the granites and the
surrounding rocks into which the granites were intruded, and containing
quartz, metallic sulphides, and in some cases minerals of tin, gold, and
silver. The deposits of the two most important districts in the United
States, in Boulder County, Colorado, and at Atolia, California, are of
this general nature. The close association of such deposits with
plutonic igneous rocks, and the characteristic mineral associations (see
pp. 37-41) suggest strongly that the deposits were formed by hot
solutions deriving their material from a magmatic source.
Other tungsten deposits, which only recently became of importance, are
of the contact-metamorphic type--in limestones which have been invaded
by hot aqueous and gaseous solutions near the borders of granitic
intrusions. In these occurrences the tungsten mineral is almost
invariably scheelite, and is associated with calcite, garnet, pyroxene,
and other silicates. A magmatic origin of the tungsten is probable. Some
of the deposits of the Great Basin area and of Japan are of this nature,
and it is believed that important deposits of this type may be
discovered in many other countries.
Tungsten is likewise found in original segregations in igneous rocks and
in pegmatite dikes, but these deposits are of comparatively small
commercial importance.
In some tungsten deposits a hydrated oxide called tungstite has been
formed as a canary-yellow coating at the surface. On the whole, however,
tungsten minerals are very resistant to weathering, and in all their
deposits secondary concentration by chemical action at the surface has
not played any appreciable part. The disappearance of tungsten minerals
from alluvial materials which are undergoing laterization, which has
been described in Burma,[32] seems to indicate that the tungsten is
dissolved in surface waters to some extent; but in the main it is
probably carried completely out of the vicinity and not reprecipitated
below.
MOLYBDENUM ORES
ECONOMIC FEATURES
The main use of molybdenum is in the manufacture of high-speed tool
steels, in which it has been used as a partial or complete substitute
for tungsten. Its steel-hardening qualities are more effective than
those of tungsten, but it is more difficult to control metallurgically.
It has been used in piston rods and crank shafts for American
airplanes. Its use in tool steel is mainly confined to Europe, where its
metallurgical application is in a more advanced stage than in the United
States. Molybdenum is added to steel either as powdered molybdenum or in
the form of ferromolybdenum, an alloy containing 60 to 70 per cent of
the metal. Molybdenum chemicals are essential reagents in iron and steel
analysis and other analytical work; they are also used as pigments.
Molybdenum metal has been used to a small extent in incandescent lamps
and as a substitute for platinum in electric contacts and resistances.
Molybdenum ores range from considerably less than 1 per cent to about 5
per cent in molybdenum.
The world's principal sources of molybdenum ores in approximate order of
importance are the United States, Canada, Norway, Australia, Korea,
Austria, Peru, and Mexico.
About half of the world's supply is produced in the United States.
Production of molybdenum in this country practically began in 1914. Most
of the production has come from Colorado and Arizona. It is believed
that the United States contains reserves more than sufficient to meet
any possible future demand. Thus far the demand has not kept up with
capacity for production. The principal consuming countries are England,
France, and Germany.
GEOLOGIC FEATURES
The chief ore minerals are molybdenite (molybdenum sulphide) and
wulfenite (lead molybdate). The larger part of the world's production is
from the molybdenite ores. Molybdenite occurs principally in association
with granitic rocks,--in pegmatite dikes, in veins, and in
contact-metamorphic deposits,--in all of which associations its origin
is traced to hot solutions from the magma. It is frequently present as
an accessory mineral in sulphide deposits containing ores of gold,
copper, silver, lead, and zinc. At Empire, Colorado, one of the
principal producing localities, it is found in veins, associated with
pyrite, and filling the interstices between brecciated fragments of a
wall rock composed of alaskite (an acid igneous rock). In molybdenite
deposits secondary concentration has not been important.
Wulfenite is rather common in the upper oxidized zone of deposits which
contain lead minerals and molybdenite. It is probably always secondary.
Deposits of wulfenite have been worked on a small scale in Arizona.
VANADIUM ORES
ECONOMIC FEATURES
Vanadium is used mainly in steel, to which it gives great toughness and
torsional strength. Vanadium steels are used in locomotive tires,
frames, and springs, in those parts of automobiles that must withstand
special bending strains, in transmission shafts, and in general in
forgings which must stand heavy wear and tear. Vanadium is also used in
high-speed tool steels, its use materially reducing the amount of
tungsten necessary. It is added in the form of ferrovanadium, carrying
35 to 40 per cent of vanadium. Another use of vanadium is in
chrome-vanadium steels for armor-plate and automobiles. Minor amounts
are used in making bronzes, in medicine, and in dyeing.
The low-grade ores of the United States range from 1 to 8 per cent of
vanadium oxide, the general mean being nearer the lower figure. The
high-grade ores of Peru contain from about 10 to as high as 50 per cent
of the oxide; the roasted ore as shipped averages about 35 to 40 per
cent.
Two-thirds of the world's supply of vanadium comes from Peru, where the
mines are under American control. The concentrates are all shipped to
the United States and some of the ferrovanadium is exported from this
country to Europe. The Germans during the war supplied their needs for
vanadium from the minette iron ores in the Briey district in France, and
presumably the French will in the future utilize this source. An
unrecorded but small quantity is obtained by the English from
lead-vanadate mines in South Africa. There are some fairly large
deposits of vanadium minerals in Asiatic Russia, which may ultimately
become an important source.
The United States supplies less than one-half of its normal needs of
vanadium, from southwestern Colorado and southeastern Utah. The grade of
these deposits is low and the quantity in sight does not seem to promise
a long future. Through its commercial control of the Peruvian deposits,
the United States dominates the world's vanadium situation.
GEOLOGIC FEATURES
The Minasragra vanadium deposit of Peru contains patronite (vanadium
sulphide) associated with a peculiar nickel-bearing sulphide and a black
carbonaceous mineral called "quisqueite," in a lens-shaped body of
unknown depth, enclosed by red shales and porphyry dikes. The origin is
unknown. The patronite has altered at the surface to red and brown
hydrated vanadium oxides.
The deposits of Colorado and Utah are large lens-shaped bodies
containing roscoelite (a vanadium-bearing mica) in fissures and
brecciated zones and replacing the cementing materials of flat-lying
sandstones. Locally the sandstones contain as much as 20 per cent of the
roscoelite. The deposits contain small amounts of fossil wood which may
have been an agent in the precipitation of the vanadium. There is
considerable doubt as to their origin, but it is generally supposed that
they represent concentrations by surface waters of minute quantities of
material originally scattered through the surrounding sediments; it has
also been suggested that certain igneous dikes in this region may have
had some connection with the mineralization. Deposits of carnotite, a
potassium-uranium vanadate, which have been worked for their content of
uranium and radium and from which vanadium has been obtained as a
by-product, are found as impregnations of the sandstone in these same
localities (p. 265).
There are other deposits containing small amounts of vanadium which are
not at present available as ores. Vanadinite, a lead-vanadate, and
descloizite, a vanadate of copper or lead, are found in the oxide zones
of a number of lead and copper deposits in the southwestern United
States and Mexico. Titaniferous iron ores, extensive deposits of which
are known in many places, usually contain a small percentage of
vanadium.
Outside of the Peruvian deposit, the affiliations of which are doubtful,
the vanadium deposits of economic importance owe their positions and
values mainly to the action of surface processes, rather than to igneous
activity.
ZIRCONIUM ORES
ECONOMIC FEATURES
The oxides of zirconium have high refractory properties which make them
useful for refractory bricks and shapes for furnace linings, for
chemical ware, and for other heat, acid, and alkali resisting articles.
For these purposes they find a limited market. Experimental work seems
to show possibilities of a very considerable use of zirconium as a steel
alloy; indeed, results are so suggestive that during the war the
government conducted an active campaign of investigation with a view to
using it in ordnance and armor steel. For such purposes the alloy
ferrozirconium is used, which carries 25 to 35 per cent zirconium metal.
The principal known deposits of zirconium ores, in order of commercial
importance, are in Brazil, in India, and in the United States (Pablo
Beach, Florida). The Brazilian and Indian deposits are also the
principal sources of monazite (pp. 288-289). The United States controls
one of the important Brazilian deposits. Germany before the war
controlled the Indian deposits, and is reported to have taken much
interest in the development of zirconium steels. During the war German
influence in India was effectively broken up. The use of zirconium has
been in an experimental state, and known sources of supply have been
ample for all requirements.
GEOLOGIC FEATURES
The zirconium silicate, zircon, is a fairly common accessory constituent
of granitic rocks and pegmatite veins. From these rocks it is separated
by weathering, disintegration, and stream transportation, and, having a
high specific gravity, it becomes concentrated in placers. The deposits
of southern India, of the coast of Brazil, and of Pablo Beach, Florida,
all contain zircon along with ilmenite, garnet, rutile, monazite, and
other insoluble, heavy minerals, in the sands of the ocean beaches.
Smaller deposits of zircon-bearing sands exist in rivers and beaches in
other parts of the United States and in other countries, but none of
these deposits has thus far proved to be of commercial importance.
The largest and most important zirconium deposits are on a mountainous
plateau in eastern Brazil and are of a unique type, entirely different
from those just described. They contain the natural zirconium oxide,
baddeleyite or brazilite, mixed with the silicate, the ore as produced
carrying about 80 per cent zirconia (ZrO_{2}). The ores consist both of
alluvial pebbles and of extensive deposits in place. The latter are
associated with phonolite (igneous) rocks, and seem to owe their origin
to the agency of hot mineralizing solutions from the igneous rocks.
TITANIUM ORES
ECONOMIC FEATURES
Titanium is sometimes used in steel manufacture to take out occluded
gases and thus to increase the strength and wearing qualities. Its
effect is to cure certain evils in the hardening of the molten steel,
and it is not ordinarily added in amounts sufficient to form a definite
steel alloy. Aluminum is frequently used in place of titanium. Titanium
is added in the form of ferrotitanium, containing either about 15 per
cent titanium and 6 to 8 per cent carbon, or about 25 per cent titanium
and no carbon. Titanium compounds are also used in pigments, as
electrodes for arc-lights, and by the army and navy for making
smoke-clouds.
The United States has domestic supplies of titanium sufficient for all
requirements. Production has come chiefly from Virginia. Additional
quantities have been imported from Canada and Norway. The recently
developed deposits of Pablo Beach, Florida, may produce important
amounts of titanium minerals along with the output of zircon and
monazite.
GEOLOGIC FEATURES
The principal titanium minerals are rutile (titanium oxide) and ilmenite
(iron titanate). These minerals are formed mainly under high
temperatures, either during the original solidification of igneous
rocks, or as constituents of the pegmatites which follow the
crystallization of the main igneous masses. The Virginia production
comes from pegmatite dikes cutting through gabbros, syenites, and
gneisses. The deposits contain rutile in amounts as high as 30 per cent
of the mass, but averaging 4 or 5 per cent, in addition to varying
amounts of ilmenite. Titaniferous magnetites, formed in many basic
igneous rocks by the segregation of certain iron-bearing materials into
irregular masses, contain large quantities of ilmenite which are not
commercially available under present metallurgical processes.
Rutile and ilmenite both have high specific gravity and are little
affected by weathering. Consequently they are not decomposed at the
surface, but when carried away and subjected to the sorting action of
streams and waves, they form placer deposits. Both of these minerals are
recovered from the sands at Pablo Beach, Florida.
MAGNESITE
ECONOMIC FEATURES
The most important use of magnesite is as a refractory material for
lining furnaces and converters. It is also used in the manufacture of
Sorel cement for stucco and flooring, in making paper, in fire-resisting
paint, in heat insulation, and as a source for carbon dioxide. Small
amounts are used in Epsom salts and other chemicals.
As taken from the ground the ore consists principally of the mineral
magnesite or magnesium carbonate, with minor impurities (1 to 12 per
cent) of lime, iron, silica, and alumina. In making magnesite bricks, it
is calcined or "dead-burned" to drive out the carbon dioxide.
Austria-Hungary and Greece are the large European producers of magnesite
and Scotland supplies a little. Most of the European production is
consumed in England and the Central European countries, but part has
been sent to America. Outside the United States there are American
supplies in Canada, and recent developments in Venezuela and Mexico
(Lower California).
Magnesite is produced in considerable quantities in the United States,
in California and Washington. Some material is imported from Canada, and
a small amount comes from Scotland as return cargo for ballast purposes.
Before the war only about 5 per cent of the United States requirements
of magnesite were met by domestic production. The country was
practically dependent on imports from various European countries;
chiefly from Austria-Hungary and Greece The Austrian magnesite
(controlled in large part by American capital) was considered especially
desirable for lining open-hearth steel furnaces, because of the presence
of a small percentage of iron which made the material slightly more
fusible than the pure mineral. When the shipments from this source were
discontinued during the war and prices rose to a high figure,
experiments were made with American magnesite, and the deposits on the
Pacific Coast were developed on a large scale. A process of treatment
was perfected by which the Washington magnesite was made as desirable
for lining furnaces as the Austrian material. At the same time large
amounts were imported from Canada and Venezuela and lesser amounts from
Lower California.
Under the high prices which prevailed during the war, dolomite was to
some extent substituted for magnesite. Dolomite, which may be thought of
as a magnesite rock high in lime, occurs in large quantities close to
many points of consumption. It is cheaper but less satisfactory than
magnesite, and is not likely to be used on any large scale.
While the United States has undoubtedly sufficient reserves of magnesite
to supply the domestic demands for many years, the mines are far from
the centers of consumption and it is expensive to transport the
material. Since the war, magnesite shipped from Canada and overseas has
again replaced the American product in the eastern market to some
extent. The Canadian magnesite is of lower grade than the domestic and
European magnesite and is consequently less desirable. Deposits in
Venezuela are also expected to furnish some material for the eastern
furnaces, in competition with those of Austria and Greece. Austrian
magnesite, however, will be likely to dominate the market in the future
if delivered at anything like pre-war prices. This situation has led to
agitation for a protective tariff on magnesite.
GEOLOGIC FEATURES
Magnesite, as noted above, is the name of a mineral, the composition of
which is magnesium carbonate. The principal magnesite deposits are of
two types, of different modes of origin and of somewhat different
physical characteristics.
The large magnesite deposits of Austria and of Washington, as well as
those of Quebec, occur as lenses in beds of dolomite (calcium-magnesium
carbonate). They are in fairly close proximity to igneous rocks, and
magnesia-bearing solutions issuing from these rocks are believed to have
dissolved out the calcium carbonate of the dolomite and replaced it with
magnesium carbonate. In these deposits the material is coarsely
crystalline and forms fairly large, continuous bodies, which are worked
by quarrying. The Washington deposits closely resemble marble, and had
sometimes been mistaken for that rock until war-time needs resulted in
their more thorough investigation.
The commoner type of magnesite deposits is represented by those of
Greece, California, Venezuela, and many other countries. These consist
of veins and replacements in serpentine. The original rock was a highly
magnesian igneous rock of the peridotite type, which is very unstable
under weathering conditions, and rapidly alters to serpentine. Magnesite
is formed both by this process and by the further breaking down of the
serpentine itself. The processes are those of katamorphism. Under these
circumstances the magnesite is characteristically fine-grained or
massive, and occurs in veins, lenses, and irregular bodies in cavities
and fractured zones. It is usually worked by open cuts.
Magnesite is also reported to occur in sedimentary beds in which it was
primarily deposited in its present form and has not undergone later
alteration. Such deposits are not important commercially.
FLUORSPAR
ECONOMIC FEATURES
The chief use of fluorspar is as a flux in the manufacture of
open-hearth steel. Minor uses are in chemical and enameling industries,
in the smelting of copper, lead, and iron, and in the manufacture of the
ferro-alloys in the electric furnace.
In order to be used in steel-making, the fluorspar after being
concentrated should contain at least 85 per cent calcium fluoride and
less than 4 per cent silica. Chemical and enameling industries require
material with 95 to 98 per cent calcium fluoride and less than 1 per
cent silica.
The chief foreign producer of fluorspar is Great Britain, and much of
this product comes to the United States. Canada produces a small
amount, some of which also comes to the United States. Several thousand
tons are produced yearly in Germany and France, and are largely consumed
there.
The production of fluorspar in the United States is several times that
of any other country. The ore mined comes principally from the southern
Illinois and western Kentucky field, and is used largely for fluxing
purposes in open-hearth steel furnaces. Minor amounts are produced in
Colorado, New Mexico, and other states.
The United States has sufficient supplies of fluorspar to meet all its
own demands for this material. Small amounts, however, are imported for
use in eastern furnaces because the material can be brought over from
England very cheaply. The domestic fluorspar is suitable for practically
all purposes for which fluorspar is used except for lenses in optical
instruments. For this use very small quantities of material imported
from Japan have been used, but recently fluorspar of a grade suitable
for optical purposes has been found in Illinois, Kentucky, New
Hampshire, and other states. For fluxing purposes domestic fluorspar is
superior to the foreign product.
GEOLOGIC FEATURES
Fluorspar is the trade name for the mineral fluorite, which is composed
of calcium fluoride. This is a common mineral in veins and replacements
which carry ores of zinc, lead, silver, gold, copper, and tin. It is
formed under a variety of conditions, but is always ascribed to
solutions coming from nearby igneous rocks.
The large fluorspar deposits of Illinois and Kentucky contain fluorite
with calcite, barite, and metallic sulphides, in wide veins filling
fissures in limestones and sandstones and replacing the fissure walls.
Into these sediments there are intruded certain peridotite dikes. The
fluorite and associated minerals were probably deposited by hot
solutions bringing the material from some large underlying igneous mass
of which the dikes are off-shoots.
In the western United States many metalliferous deposits carry large
amounts of fluorite, which is treated as a gangue or waste mineral, but
which could be profitably extracted if there were local markets. In
England, fluorite is obtained in this manner as a by-product from lead
and zinc mines.
SILICA
ECONOMIC FEATURES
Silicon and its oxide, silica, find important applications in the
manufacture of iron and steel. Silicon, like manganese, is an important
constituent of many steels, the alloy ferrosilicon being added to
deoxidize and purify the metal and thus to increase its tensile
strength. Like titanium, it is added chiefly for its curative effect
rather than as a useful ingredient. On an average 4 pounds of 50 to 55
per cent ferrosilicon are used in the United States for each ton of
steel produced. A higher grade of ferrosilicon (80 to 85 per cent) is
used for certain special steels, and during the war considerable
quantities were used in making hydrogen gas for balloons. Lower grades
(10 to 15 per cent silicon) are practically a high silicon pig iron.
Silica has an important use in the form of silica brick or "ganister"
for lining furnaces and converters in which acid slags are formed. For
this purpose siliceous rocks, chiefly quartzites and sandstones, are
ground up, mixed with lime as a binder, and fused and pressed into
bricks and shapes. For the most satisfactory results the rock should
contain 96 per cent or more of silica, and very little of the alkali
materials, which increase the fusibility.
In addition to its applications to the iron and steel industry, silica
finds an almost universal use in a wide variety of structural and
manufacturing operations. The extensive use of sand and gravel--composed
chiefly of silica--for road materials and railway ballast is well known.
In construction work silica is used in the form of stone, sand-lime
brick, cement, mortar, concrete, etc. Large quantities of sand, or
silica, are used for molds in foundries, for abrasives, for the
manufacture of glass, for filters, and for a great variety of other
purposes which readily suggest themselves (see pp. 84, 267).
For most uses of silica there are local supplies available. For certain
purposes requiring material of a particular chemical composition or
texture, however, satisfactory deposits are known in only a few places.
For example, the material for silica refractories is obtained in the
United States chiefly from certain regions in Pennsylvania, Missouri,
and Wisconsin. The United States has ample domestic supplies of silica
for practically all requirements.
Ferrosilicon of the higher grades is manufactured principally in
electric furnaces at Niagara Falls. The capacity is ample to meet all
demands, but cheap ferrosilicon from Canada also enters United States
markets.
GEOLOGIC FEATURES
Silicon and oxygen, making up the compound silica, are the two most
abundant elements in the earth's crust, and quartz (SiO_2) is a very
abundant mineral. The processes of weathering and transportation
everywhere operative on the surface of the earth tend to separate quartz
from other materials, and to concentrate it into deposits of sand.
Katamorphism is primarily responsible for most of the deposits of silica
which are commercially used. Anamorphism--cementing and hardening the
sands into sandstones and quartzites--has created additional value for
certain uses, as in refractories, building stones, and abrasives (see
pp. 84, 267).
FOOTNOTES:
[31] Report of the Royal Ontario Nickel Commission. Printed by order of
the Legislative Assembly of Ontario, Toronto, 1917.
[32] Campbell, J. Morrow, Tungsten deposits of Burma and their origin,
_Econ. Geol._, vol. 15, 1920, p. 511.
CHAPTER X
COPPER, LEAD, AND ZINC MINERALS
COPPER ORES
ECONOMIC FEATURES
The electrical industry is the largest consumer of copper. The
manufacture of brass, bronze, and other copper alloys constitutes
another chief use for the metal. Considerable quantities of copper
sheets, tubes, and other wares are used outside of the electrical
industry, as for instance in roofing, plumbing, and ship bottoms. Copper
is also used in coinage, particularly in China, where it is the money
standard of the working population.
The average grade of all copper ores mined in the United States in
recent years has been about 1.7 per cent metallic copper. Ores
containing as low as 0.6 per cent have been mined in the Lake Superior
country, and bonanza deposits containing 20 to 60 per cent have been
found and worked in some places, notably in Alaska and Wyoming. The
lower-grade ores, carrying 1 to 3 per cent copper, are usually
concentrated before smelting, while the richer ores, carrying 3 to 5 per
cent or more, are generally smelted direct. Many of the ores contain
values in gold and silver, and also in lead and zinc. An average of
about 40c. worth of gold and silver per ton is obtained from all the
copper ores of the United States.
In other countries the average grade of copper ores mined is somewhat
higher than in the United States,--where large scale operations,
particularly the use of steam-shovel methods on extensive bodies of
disseminated or "porphyry" copper ores, as well as improvements in
concentrating and metallurgical processes, have made possible the use of
low-grade ore.
The principal sources of copper are the North American continent, Chile
and Peru, Japan, south and central Africa, Australia, and Spain and
Portugal. Smaller quantities are produced in Russia, Germany, Norway,
Cuba, Serbia, and a number of other countries.
The United States normally produces nearly two-thirds of the world's
copper and consumes only about one-third. In addition the great bulk of
the South American, Mexican, and Canadian crude copper comes to the
United States for refining. Through financial interests abroad and by
means of refining facilities, the United States controls a quantity of
foreign production which, together with the domestic production, gives
it control of about 70 per cent of the world's copper. No other country
produces one-sixth as much copper as the United States.
England, because of production in the British Empire (mainly Africa and
Australia) and British financial control of production in various
foreign countries, is not dependent upon the United States for supplies
of raw copper. Japan, Spain, Portugal, and Norway are able to produce
from local mines enough copper for their own needs and for export. But
France, Italy, Russia, Germany, and the rest of Europe normally are
dependent upon foreign sources, chiefly the United States. South
America, Mexico, Canada, Africa, and Australia are exporters of copper.
The control of these countries over their production in each case is
political and not financial, except in the case of Canada, where about
half the financial control is also Canadian. It is in these countries
and in Spain that the United States and England have financial control
of a large copper supply.
Before the war German interests had a considerable control over the
American copper industry through close working arrangements with
electrolytic refineries. Germany was the largest foreign consumer of
copper, and German companies bought large quantities of the raw copper
in the United States, Canada, Mexico, and South America, had it refined,
and sold the finished material in both the American and foreign markets.
During the war this control was broken up.
In view of the importance of copper metal as a raw material,
particularly in the electrical industry, the strength of the United
States in copper as a key resource ranks even above its control of
petroleum.
In the United States in recent years about 40 per cent of the annual
production of copper has come from Arizona, chiefly from the Bisbee,
Globe, Ray-Miami, Jerome, and Morenci-Metcalf districts; about 18 per
cent has come from the Butte district of Montana; about 12 to 15 per
cent from Keweenaw Point, Michigan; and about 12 per cent from Bingham,
Utah. From 3 to 5 per cent of the country's output comes from each of
the states of New Mexico, Nevada, Alaska, and California. All other
states together produce only a little over 2 per cent of the total.
The so-called "porphyry" coppers in Utah, Arizona, Nevada, and New
Mexico, described below, are the source of about 35 per cent of the
present production of the United States. The deep mines of Butte and
Michigan are responsible for about 30 per cent of the production, and
the ore bodies of Arizona (other than porphyry) and of Alaska produce
about 25 per cent.
Reserves of copper ore are such as to give no immediate concern about
shortage, nor to indicate any large shift in the distribution of
production in the near future. Development is on the whole considerably
in advance of present demands. The principal measured reserves are in
the so-called porphyry coppers of the United States and Chile. In the
United States the life of these reserves now estimated is approximately
25 years. The reserves of the Chile Copper Company are the largest of
any known copper deposit in the world, and the Braden copper reserve
(also in Chile) is among the largest. For the deep mines of the United
States, the developed reserves have a life of perhaps only five years,
but for most of these mines the life will be greatly extended by further
and deeper development. The porphyry coppers, because of their
occurrence near the surface and the ease with which they may be explored
by drilling, disclose their reserves far in advance. The deep mines are
ordinarily developed for only a few years in advance of production.
GEOLOGIC FEATURES
The principal copper minerals may be classified into the sulphide group,
the oxide group, and native copper. Native copper, mined in the Lake
Superior region, is the source of 8 to 10 per cent of the world's copper
supply. The oxide group of minerals--including the copper carbonates,
azurite and malachite; the silicate, chrysocolla; the oxide, cuprite;
the sulphates, chalcanthite and brochantite; and some native copper
associated with these minerals--probably supplies another 5 per cent.
The remaining 85 per cent is derived from the sulphide group. Of the
sulphide group by far the most important mineral is chalcocite (cuprous
sulphide), which supplies the bulk of the values in the majority of the
mining camps of the western hemisphere. Locally, as at Butte, enargite
(copper-arsenic sulphide) is of great value. Other minerals of
considerable importance in some districts are chalcopyrite and bornite
(copper-iron sulphides), tetrahedrite (copper-antimony sulphide), and
covellite (cupric sulphide). Very commonly the copper sulphides are
associated with large quantities of the iron sulphide, pyrite, as well
as with varying amounts of lead and zinc sulphides and gold and silver
minerals.
The principal copper ores originate in the earlier stages of the
metamorphic cycle, in close association with igneous activity.
Katamorphism or weathering, in place, has played an important part in
enriching them. The processes of transportation and sedimentary
deposition, which have done so much toward making valuable iron ore
deposits, have contributed little to the formation of copper ores.
=Copper deposits associated with igneous flows.= The copper ores of the
Lake Superior district, and of a few small deposits in the eastern
United States, contain small percentages of native copper in
pre-Cambrian volcanic flows or in sediments between the flows. The ore
bodies have the form of long sheets parallel to the bedding, the copper
and associated minerals filling amygdaloidal openings and small fissures
in the flows, and replacing conglomeratic sediments which lie between
the flows. The copper was probably deposited by hot solutions related to
the igneous rocks, either issuing from the magmas or deriving heat and
dissolved material from them. Secondary concentration has not been
important. There is practically none of it near the present erosion
surface; but it appears in one part of the district near an older
erosion surface covered by Cambrian sediments, suggesting a different
climatic condition at that time.
The Kennecott copper deposits of Alaska have a number of resemblances to
the Lake Superior copper deposits, suggesting similarity in origin. The
Kennecott deposits occur exclusively in limestone, which rests
conformably on a tilted surface of igneous flows ("greenstones") not
unlike those of Lake Superior. The flows carry native copper and copper
sulphides in minutely disseminated form and in amygdules, but apparently
not in quantities sufficiently concentrated to mine. The flows are
supposed to be the original source of the copper now in the limestone.
The primary copper mineral in the limestone is chalcocite, in
exceptionally rich and solid masses, showing no evidence of having
replaced earlier sulphides. It is regarded as a product of primary
deposition, under the influence of hot solutions related in some way to
the igneous flows; but whether the solutions were magmatic, originating
in the lavas or below, or whether they were meteoric waters rendered hot
by contact with the extrusives, and thereby made effective in leaching
copper from them, is not clear. The oxidation of the Kennecott copper
ores is not extensive. It presents an interesting feature, in that since
glacial time the ground has been frozen and the moisture is now present
in the form of ice. The oxidation clearly took place before glacial
time. Abundant fragments of both the oxide and the sulphide ores are
mined from the lateral moraine of a nearby glacier. This is a good
illustration of the cyclic nature of secondary concentration which is
coming to be recognized in so many camps.
The Boleo copper deposits of Lower California occur in volcanic tuffs
and associated conglomerates of Tertiary age. They have certain peculiar
mineralogic associations--the ores containing large quantities of all
the common copper oxide minerals, and a number of rare oxide minerals of
copper, lead, silver, and cobalt, together with gypsum, sulphur, and
much iron and manganese oxide. The copper oxides and carbonates are in
places gathered into rounded concretions called "boleos" (balls).
Sulphides are present in the lowest beds and may represent the form in
which the copper was originally deposited. The copper-bearing beds have
been much silicified, and it has been suggested that mineralization was
accomplished by hot-spring waters, probably of igneous origin. These
deposits have a few marked similarities to the Lake Superior copper
ores.
=Copper veins in igneous rocks.= A second group of copper ores in
igneous rocks is made up of deposits in distinct fissure veins and as
replacements along such veins. The chief deposits of this type are at
Butte, Montana--which is, from the standpoint of both past and present
production, the greatest single copper district in the world. Here a
large batholith of Tertiary granite was intruded by porphyry dikes; and
faulting, accompanying and following the intrusions of the dikes,
developed numerous fissures. The fissures were mineralized with copper
sulphides and arsenides, iron sulphides, and locally with zinc sulphide
and manganese carbonate,--all in a matrix of quartz. At the same time
the wall rocks were extensively mineralized and altered; the fissure
veins grade off into the wall rock, and in fact the larger part of the
ore is simply altered granite with disseminated sulphides. The solutions
which deposited the ores are inferred to have been hot from the nature
of the wall-rock alterations, from the presence of hot-water minerals
like fluorite, cassiterite, and others, and from the general association
of the ores in time and place with the porphyry intrusions. The
solutions are believed to have originated from the porphyry and possibly
from other intrusives.
In the Butte district, and in the great majority of copper sulphide vein
ores throughout the world, secondary concentration by surface waters has
played a considerable part in developing ores of commercial value. Near
the surface the copper is leached out and carried down by waters
containing various solvents, particularly sulphuric acid from the
oxidation of pyrite. A leached zone is formed containing the ordinary
products of rock weathering,--rusty quartz and clay, sometimes black
with manganese oxides. A small part of the copper remains in this zone
as oxides, carbonates, and silicates. Below the oxidized and leached
zone there is evidence of deposition of a large amount of secondary
copper sulphide in the form of chalcocite. This is supposed to have been
formed by the leaching of copper from above as soluble copper sulphate,
and its precipitation below by iron and other sulphide minerals which
the solutions meet on their downward course--a reaction which has been
demonstrated experimentally. It was formerly supposed that most of the
chalcocite was of this origin; but as chalcocite is found in important
amounts with enargite and chalcopyrite to great depths (now 3,500 feet),
where the veins are still rich and strong, it begins to appear that much
of the chalcocite is of primary origin.
The fissures along which the Butte ores occur are in three main sets,
which in order of age strike roughly east-west, northwest-southeast, and
northeast-southwest. Two-thirds of the ore is in the first set, about 30
per cent in the second, and the remainder in the third. The
mineralization of the several vein systems cannot be discriminated, and
it is thought that it was accomplished as a more or less continuous and
progressive process. There is some evidence, also, that the fracturing
in the several fracture systems was likewise a nearly continuous
progressive process, contemporaneous with the ore deposition, and
perhaps developing under a single great shear which caused more or less
simultaneous and overlapping systems of fractures in the various
directions.
="Porphyry coppers."= Another type of copper deposits in igneous rocks
is the disseminated or "porphyry" deposits. The term "porphyry" as
commonly used includes true porphyries, monzonites, granites, and other
igneous rocks. Ores of this type are represented by the great deposits
of Bingham, Utah; Ray, Miami, and the New Cornelia mine of Arizona; Ely,
Nevada; Santa Rita, New Mexico; Cananea, Sonora, Mexico; northern Chile;
and many other districts of importance. They form the greatest known
reserves of copper ore. These deposits contain copper minerals, usually
in the marginal portions of acid porphyries, in many irregular, closely
spaced veins, and in minute seams and spots disseminated through the
mass of the rock. In the Ray and Miami and other districts the
mineralization has spread largely through adjacent schists, but these
deposits are included with the porphyry copper deposits in commercial
parlance. The porphyry deposits are of an undulating blanket form of
considerable areal extent and shallow depth. At the surface is a leached
and weathered zone, often containing more or less of the oxides,
carbonates, and silicates of copper, ranging in thickness up to 1,000
feet, but averaging 200 feet or less. Below this is a zone carrying
copper in the form of chalcopyrite, enriched by chalcocite deposition
from above, ranging in thickness up to 400 feet. The ore in this zone
varies from one-half of 1 per cent to 6 per cent of copper and
ordinarily averages between 1 and 2 per cent. The use of ore of this
grade is made possible by the large quantities and by the cheap and
efficient mining and metallurgical practices. The ore body grades below
into a zone characterized by lean chalcopyrite, which is supposed to
represent original or primary deposition from hot waters associated with
the porphyry intrusion. This primary ore, or protore, was clearly formed
after the solidification of the igneous rocks, though soon after, by
solutions from igneous sources which followed fractured and shattered
zones.
=Copper in limestone near igneous contacts.= Another great group of
copper deposits occurs as replacements of limestone adjacent to porphyry
or granitic intrusives. This type is illustrated by some of the deposits
at Bingham, Utah, and at Bisbee, Arizona. The primary deposition was of
chalcopyrite and other copper sulphides, together with garnet, diopside,
and other minerals known to have required high temperature in their
formation. The ore fills fissures and replaces extensive masses of the
limestone. It is likely to show a fairly sharp contact on the side
toward the intrusive, and to grade off into the country rock on the
other side with numerous embayments and irregularities. These deposits
have been enriched by weathering in the same manner as indicated above
for the porphyry coppers, but to highly varying degrees. In the Bisbee
deposits large values were found in the weathered zone, and secondary
sulphide enrichment below this zone is also important. In the Bingham
camp, on the other hand, the weathered zone is insignificant and most of
the ore beneath is primary. The weathering of the silicated limestone
gangue results in great masses of clay which are characteristic features
of the oxide zones of these deposits.
=Copper deposits in schists.= Other copper deposits, as at Jerome,
Arizona, in the Foothill and Shasta County districts of California, at
Ducktown, Tennessee, etc., are irregular lenticular bodies in schists
and other rocks, but all show relationship to igneous rocks. The Rio
Tinto ores of Spain and Portugal, which belong in this group, have been
referred to on page 108.
In the Jerome or Verde district of central Arizona, folded pre-Cambrian
greenstones and sediments were invaded by masses of quartz-porphyry, and
after further deformation, rendering many of the rocks schistose, were
intruded by an augite-diorite. Contact metamorphism along both the
quartz-porphyry and the diorite contacts was practically lacking. The
ore bodies were formed as irregular pipe-like replacements of the
schists, being localized in one case by a steeply pitching inverted
trough of impervious diorite, and in other cases by shear zones which
favored vigorous circulation. A later series of small diorite or
andesite dikes cut the ore bodies. The primary ores consist of pyrite,
chalcopyrite, and other sulphides, with large amounts of jaspery quartz
and some calcite and dolomite. They were clearly formed by replacement
of the schists particle by particle, as shown by the frequent
preservation of the schist structure in a banding of the sulphide
minerals, the residual shreds of unreplaced schist material in the ores,
and the usual gradual transition from unreplaced schists to those
completely replaced by massive sulphides. The localization of the most
important mineralization in an inverted trough is good evidence that the
solutions came from below, and the nature of the mineral associations
suggests an origin through the work of hot waters associated with
igneous intrusives. The diorite, being most closely related in time and
space with the ore bodies, seems the most logical source of the ore
materials.
Secondary concentration of the Jerome ores has proceeded along the
general lines previously outlined (pp. 46-50, 202). Here again the
evidence is clear that the ores were concentrated in an earlier period,
in this case in pre-Cambrian times, probably during the long interval
required for the base-leveling of the pre-Cambrian mountains. Since
Cambrian times the deposits have been for the most part buried by later
sediments. Some of the deposits are still protected by this overlying
blanket and mining has not yet reached the zone of altogether primary
sulphides. Others have been faulted up and again exposed by erosion; but
since being uncovered, steep slopes and rapid erosion have apparently
favored the scattering of the copper rather than its concentration and
enrichment. In the United Verde Mine, oxidizing conditions at present
prevail to the bottom of the chalcocite zone.
The very large reserves of the Katanga copper belt of the Belgian Congo
are in the form of tabular masses in schistose and highly metamorphosed
Paleozoic sediments. The ore bodies are roughly parallel to the bedding,
but in instances follow the schistosity which cuts across the bedding.
They consist dominantly of the oxide minerals, though in several ore
bodies sulphides have been shown by diamond-drilling. The ores have a
high content of cobalt and also carry precious metals. The origin of the
deposits is not known, but has been ascribed to granitic masses
intrusive into the schists.
=Sedimentary copper deposits.= In the later phases of the metamorphic
cycle, the agencies of transportation (in solution) and sedimentary
deposition have resulted in some low-grade deposits of copper sulphides
in sedimentary rocks. Deposits of this type are found in the Rocky
Mountain region, where they are referred to as the "Red Beds" coppers,
but are of no commercial importance. Similar deposits in Germany, the
Mansfield copper-bearing shales, have been worked for some time, and
during the war were Germany's main source of copper. On Keweenaw Point,
Michigan, deposits of native copper formed in this manner in the
"Nonesuch" beds have been worked on a commercial scale. Other copper
ores on Keweenaw Point are replacements of conglomerate beds between
igneous flows, and are of a different origin already described (p. 200).
While much of the copper of sedimentary beds gives evidence that it was
deposited from solution in cracks and as replacements of the wall rocks,
often through the agency of abundant organic material in the beds, and
while also comparatively little of this copper can be identified as
having been deposited in detrital flakes or fragments along with the
other mineral fragments, there is, nevertheless, considerable evidence
that some of these deposits were formed essentially during the
sedimentation of the enclosing beds and as incidents to this process.
Such evidence consists of a close limitation of the copper to certain
beds, its wide and uniform distribution within these beds, its absence
in similar beds near at hand, the absence of evidence of feeding and
escape channels of the kind which would be necessary in case the
solutions were introduced long afterward, and often a minute
participation of the copper minerals in the minor structures of bedding,
false-bedding, and ripple-marks, which would be difficult to explain as
due to secondary concentration.
The Corocoro copper deposits of Bolivia occur in beds of sandstone with
no igneous rocks in the vicinity. However, they are all closely
associated with a fault plane, igneous rocks occur at distances of a few
miles, and the general mineralization is coextensive with the belt of
igneous rocks; the deposits are therefore ascribed to a magmatic source
rather than to sedimentary processes. Toward the surface the copper is
in part in the form of sulphides, somewhat altered to oxide minerals,
and farther down it is entirely native copper, associated with gypsum.
This is the only district outside of Lake Superior where native copper
has been mined on an important scale.
=General comments.= In general, the commercially prominent copper
deposits show a close relationship to igneous rocks in place, time, and
origin. Seldom do the ores extend more than 1,000 feet away from the
igneous rock.
The common downward order in sulphide deposits is: first, a weathered
zone, originally formed mainly above the water table, consisting above
of a leached portion and below of oxides and carbonates of copper in a
gangue of quartz or clay; second, a zone of secondary sulphide
enrichment, characterized by chalcocite coatings, chalcopyrite, and
pyrite, with a gangue of quartz and igneous rock or limestone; and
third, a zone of primary deposition with similar gangue, characterized
by chalcopyrite, and at Butte by enargite and chalcocite. The oxide zone
as a whole may be rich or lean in values, depending on the nature of the
associated gangue material and country rock. When these are more soluble
than the copper--as is commonly the case in limestone--the copper may be
residually concentrated, notwithstanding the fact that much copper
originally present has been carried off in solution. When the associated
gangue and country rock are less soluble than the copper--as is common
with quartz and igneous rocks--the oxide zone is likely to be depleted
of values.
The zones formed by weathering and secondary enrichment are extremely
irregular, both in distribution and depth, in any one deposit, and they
overlap and grade into one another in a very complex fashion. In many
places the primary zone is too lean to be mined to commercial advantage;
but in other places, as at Butte, and in the limestone deposits of
Bingham, the primary ores are of considerable importance.
When evidence of secondary sulphide enrichment was first recognized
there was a tendency to magnify its effectiveness, and to assume that in
most cases the values were due to this process; that the primary zones
would be found to be valueless. In recent years the emphasis is being
somewhat changed because of the recognizing in many camps of rich
primary zones. While some chalcocite is clearly the result of secondary
enrichment from above, other chalcocite seems to have been related
closely to the primary deposition. The quantitative discrimination of
the two is a matter of great difficulty.
It has come to be recognized that the zonal arrangement caused by
enrichment from the surface has been imposed usually on a zonal
arrangement caused by the primary hot solutions and not related to the
surface but to the source of the solutions. In some districts, as
illustrated by Butte and Bingham, the copper-bearing minerals seem to
have been deposited nearest the igneous source, while the lead, zinc,
gold, and silver minerals have been deposited farther away,--suggesting
the cooling of the solutions with increasing distance from the igneous
source. The further investigation of this primary zonal arrangement
promises interesting results with a practical bearing on exploration and
development.
One of the newer features of the investigation of copper deposits has
been the recognition of the cyclic nature of the secondary
concentration. This process has been related not only to the present
erosion surface, but to older surfaces now partly buried under later
rocks. Ransome's[33] summary of conditions at the Ray-Miami camp has a
somewhat general application.
Supergene enrichment has generally been treated as a
continuously progressive process. There is considerable
probability, however, that it is essentially cyclic, although
the cyclic character may not be patent in all deposits. A full
development of the cycle can take place only under a certain
equilibrium of a number of factors, including climate,
erosion, topography, and character of rock. The essential fact
appears to be that as enrichment progresses and chalcocite
increases the process of enrichment becomes slower in action,
and erosion may, in some circumstances, overtake it. With the
removal of some of the protecting zone of chalcocite the
protore is again exposed to oxidation and a second cycle of
enrichment begins.
Although much of the enriched ore is now below ground-water
level, it probably was once above that level, and enrichment
is believed to have taken place mainly in the zone of rock
above any general water table.
Where the old erosion surface roughly coincides with the present erosion
surface, the deposits follow more or less the topography. Where the old
erosion surface pitches below later sediments, the ores pitch with it,
and therefore do not follow the present topography. The recognition of
the cyclic nature of secondary concentration is obviously of great
significance in exploration and development.
Although a vast amount of study has been devoted to the origin and
enrichment of copper deposits, and although the general conditions and
processes are pretty well understood, the results thus far have been
largely qualitative rather than quantitative.
LEAD ORES
ECONOMIC FEATURES
The most prominent uses of lead are in the manufacture of alloys, such
as type-metal, bearing metal, shot, solder, and casting metal; as the
oxide, red lead, and the basic carbonate, white lead, in paints; for
lead pipe, cable coverings, and containers of acid active material; and
in lead compounds for various chemical and medical uses. Of the lead
consumed in the United States before the war about 38 per cent was
utilized in pigments, 30 per cent in alloys other than shot, 15 per cent
in pipe, 10 per cent in shot, and 7 per cent in all other uses. During
the war much larger quantities were used in munitions, such as shot and
shrapnel.
The lead content of commercial ores varies widely. It ranges from as low
as .25 per cent in the Joplin district of Missouri, to about 15 per cent
in the Broken Hill deposits of Australia, and over 20 per cent in the
Bawdwin mines of Burma. In the Coeur d'Alene district of Idaho and the
southeastern district of Missouri, the two greatest lead producers in
the United States, the average grades are about 10 per cent and about
3-1/2 per cent respectively. The grade of ore which may be profitably
worked depends not only upon the economic factors,--such as nearness to
consuming centers, and the price of lead,--but also upon the amenability
of the ore to concentration, the content of other valuable metals, and
the fact that lead is very useful in smelting as a collector of gold and
silver.
Most lead ores contain more or less zinc, and lead is obtained as a
by-product of most zinc ores. Argentiferous lead ores form one of the
principal sources of silver, and also yield some gold. Lead and copper
are produced together from certain ores. Thus the separation of many
ores into hard and fast classes, as lead, or zinc, or copper, or silver,
or gold ores, cannot be made; in some of the mineral resource reports of
the United States Geological Survey the statistics of these five metals
are published together.
The main sources of lead ore, named in order of their importance, are
the United States, Australia, Spain, Germany, and Mexico, which account
for over 80 per cent of the world's production. Most of the countries of
Europe outside of Spain and Germany produce small amounts of lead, but
are largely dependent on imports. Spain exports argentiferous lead and
pig lead mainly to England and France, with minor quantities to other
countries of Europe and to Argentina. Before the war Germany, which was
the largest European consumer, utilized all its own production of lead
ores and imported an additional 10 per cent of the world's ores for
smelting, as well as considerable amounts of pig lead. Its principal
deposits were those of Silesia; under the Peace Treaty they may possibly
be lost to Poland, leaving German smelters largely dependent on imports.
Australia before the war normally shipped lead concentrates and pig lead
to England and also to Belgium, Germany, and Japan. England, the second
largest European consumer, before the war had insufficient smelting
capacity within the British Empire and was partly dependent on
foreign-smelted lead. During the war, however, England contracted for
the entire Australian output, and enlarged its smelting capacity
accordingly. This may mean permanent loss to Belgium, which had depended
mainly on the Australian ores for its smelting industry before the war.
In North Africa there is a small but steady production of lead, most of
which goes to France. Recent developments in Burma have shown large
reserves of high-grade lead-zinc-silver-copper ores, and this region may
be expected to become an important producer. There are also large
reserves of lead in the Altai Mountains of southwestern Siberia and in
the Andes Mountains of South America.
England, through control of Australian and Burman lead mines and
smelters, domestic smelting facilities, and some financial control in
Spain, Mexico, and elsewhere, and France, through financial control of
Spanish and North African mines and Spanish, Belgian, and domestic
smelters, have adequate supplies of lead.
The United States produces about a third of the world's lead and twice
as much as any other country. Normally the domestic production is almost
entirely consumed in this country. Mexico sends large quantities of
bullion and ore to the United States to be smelted and refined in bond.
Mexican lead refined and exported by the United States equals in amount
one-sixth of the domestic production. Small quantities of ore or bullion
from Canada, Africa, and South America are also brought into the United
States for treatment.
Through domestic production, smelting facilities for Mexican ore, and
commercial ownership in Mexico and elsewhere, the United States controls
over 45 per cent of the world's lead production. Before the war Germany,
through the "Lead Convention" or International Sales Association, and
through smelting and selling contracts with large producing mines,
practically controlled the European lead market as well as exports from
Mexico and the United States and from Australia. During the war German
foreign influence was practically destroyed.
In the United States about a third of the production of lead comes from
southeastern Missouri and about a fourth from the Coeur d'Alene
district of Idaho. The five states, Missouri, Idaho, Utah, Colorado and
Oklahoma, produce about nine-tenths of the country's total output.
Reserves of lead ore are not large in proportion to demand, contrasting
in this regard with zinc ore.
GEOLOGIC FEATURES
The principal lead mineral is the sulphide, galena, from which the great
bulk of the world's lead is derived. Cerussite (lead carbonate) and
anglesite (lead sulphate) are mined in some places in the upper part of
sulphide deposits, and supply a small fraction of the world's output.
The ores of lead are of two general classes:
The first class, the so-called "soft" lead ores, nearly free from copper
and precious metals, and commonly associated with zinc ores, are found
in sedimentary beds independent of igneous intrusion. They are of
world-wide distribution, were the first to be extensively exploited,
were at one time the dominant factor in world production of lead, and at
present produce about 30 per cent of the world's total. They are
represented by the deposits of the Mississippi Valley, of Silesia, and
some of the Spanish deposits. The general description of the origin of
the zinc ores of the Mississippi Valley on pp. 216-218 applies to this
class of lead ores. It should be noted, however, that in the principal
United States lead-producing district, that of southeastern Missouri,
the lead ores occur almost to the exclusion of the zinc ores, and are
more disseminated through the limestone than is characteristic of the
zinc ores. Ores of this type have been found extending only to shallow
depths (not over a few hundred feet), and because of the absence of
precious metals their treatment is comparatively simple.
The second class consists of ores more complex in nature, which are
found in association with igneous rocks, and which usually contain some
or all of the metals, zinc, silver, gold, copper, iron, manganese,
antimony, bismuth, and rare metals, with various gangue minerals among
which quartz, siderite, and silicates are important. Today these ores
are the source of about 70 per cent of the world's lead. They are
represented by the lead deposits of the Rocky Mountain region (Coeur
d'Alene, Idaho; Leadville, Colorado; Bingham, Utah; etc.); of Broken
Hill, New South Wales; of Burma; and of many other places. They are all
related to the earlier stages of the metamorphic cycle and occur in
close genetic association with igneous activity. They include deposits
in the body of igneous rocks,--in the form of well-defined veins,
replacements along zones of fissuring and shearing, and disseminated
masses,--as well as veins and replacements in the rocks, particularly in
limestones, adjoining igneous intrusions. The deposits present a wide
variety of shapes depending on the courses of the solutions by which
they were formed. The materials of the ore minerals are believed to have
been derived from the igneous rocks and to have been deposited by hot
solutions. The source of the solutions--whether magmatic or
meteoric--presents the same problems which have been discussed elsewhere
(pp. 41-42). The ores are frequently mined to great depths. Because of
their complexity they require involved processes of treatment to
separate out the values.
Ores of this nature have already been referred to in the discussion of
the copper ores of Bingham and Butte, and will be referred to in
connection with the zinc-lead-silver ores of Leadville, Colorado.
Special reference may be made here to the Coeur d'Alene district of
Idaho, which is the second largest producer of lead in the United
States.
The Coeur d'Alene deposits are almost unique in that they contain
galena as vein-fillings and replacements in quartzite, with a gangue of
siderite (iron carbonate). Quartzite (instead of limestone) is an
unusual locus of replacement ores, and siderite is an unusual gangue.
These ores are believed to owe their origin to acid igneous intrusives,
because of the close association of the ores with some of these
intrusives, and because of the content of high-temperature minerals.
Some of the ore bodies are found far from intrusives, but it is supposed
that in such cases further underground development may disclose the
intrusives below the surface. Secondary concentration has been
insignificant.
In general, weathering of lead ores at the surface and secondary
sulphide enrichment below are not so extensive as in the case of copper
and zinc. Galena is fairly stable in the oxide zone, and even in moist
climates it is found in the outcrop of many veins. Weathering removes
the more soluble materials and concentrates the lead sulphide with the
residual clay and other gangue. In some districts cerussite and a little
anglesite are also found in the oxide zone. The carrying down of lead in
solution and its deposition below the water table as a secondary
sulphide is not proved on any extensive scale. In this respect it
contrasts with zinc; and when the two minerals occur together, lead is
likely to be more abundant in the oxide zone, and zinc in the sulphide
zone below. Such a change in composition with depth is also found in
some cases as the result of primary vertical variations in the
mineralization.
ZINC ORES
ECONOMIC FEATURES
Zinc metal has commonly gone under the name of "spelter." Brass and
galvanized iron contain zinc as an essential ingredient. Of the total
United States zinc consumption in normal times, about 60 per cent is
used in galvanizing iron and steel objects to protect them from rust, 20
per cent is used in the manufacture of brass and other alloys, 11 per
cent goes into the form of rolled sheets for roofing, plumbing, etc., 1
per cent is employed in desilverizing lead bullion, and the remaining 8
per cent is used for pigments, electrodes, and other miscellaneous
purposes. During the war the use in brass-making was greatly increased.
The zinc content of the ores mined today ranges from a little over
1-1/2 per cent in the Joplin district of Missouri, to 25 per cent and
higher in some of the deposits of the Coeur d'Alene and other western
camps, and over 40 per cent in certain bonanzas in British Columbia and
Russia. The ores usually contain both zinc and lead in varying
proportions, and sometimes gold, silver, and copper are present. Of the
zinc produced in the United States, about 73 per cent is obtained from
ores containing zinc as the principal element of value, about 25 per
cent from zinc-lead ores, and 2 per cent from copper-zinc and other
ores. The average grade of the straight zinc ores is about 2-1/2 per
cent.
Of the world's zinc ore, the United States produces in normal times
about one-third, Germany about one-fifth, Australia about 15 per cent,
Italy, North Africa and Spain each about 5 per cent. The remaining 15 to
20 per cent comes from a large number of scattered sources, including
Japan, East Asia, Norway and Sweden, Canada, Mexico, Austria, France,
Greece, Siberia, and Russia. In the near future the Bawdwin mines of
Burma will probably be increasingly important producers. Large reserves
of zinc also exist in the Altai Mountains of southwestern Siberia, and
in the Cordilleran region of South America. In short, zinc is one of the
most widely distributed of metallic resources; there is consequently
less necessity for great international movements than in the case of
many other commodities.
The smelting of zinc concentrates is in general carried on close to the
points of consumption and where skilled labor is available, rather than
at the mines,--although smelters to handle part of the output have
recently been built in Australia and in Burma. In Europe the great
smelting countries have been Germany and Belgium, and to a lesser extent
England and France. Before the war these four countries with the United
States produced over nine-tenths of the world's spelter. Belgium did
principally a custom business, and a large part of its exports went to
England. Australian and Tasmanian zinc ores were the basis of the
Belgian and English smelting industries, and also supplied about
one-third of the German requirements. Since the war England has
contracted to take practically the entire Australian output. This fact,
in connection with war-time destruction of Belgian smelters, leaves the
future of the Belgian zinc industry in some doubt. Germany may possibly
lose to Poland its richest zinc mines, those of Silesia. German
activity in the rich deposits of Mexico is to be expected. France
controls the deposits of North Africa and satisfies a considerable part
of its requirements from that source. Smaller movements of zinc include
exports from Italy to England, and a complex interchange among the
lesser producers of Europe. English and French zinc-smelting capacity
was expanded during the war, and the industry in these countries is in a
strong position. Japan also developed a considerable smelting industry
during the war, importing ores from eastern Asia and Australia.
The United States normally smelts and consumes all its large production
of zinc ores and does not enter foreign markets to any extent. Small
amounts of zinc concentrates are brought in from Mexico and Canada to be
smelted in bond. During the war,--when the Allies were cut off by enemy
operations from the customary Belgian and German supplies of spelter,
and by shortage of ships from Australian zinc ores,--Australian,
Spanish, Italian, and other ores were imported into the United States,
and large quantities of spelter were exported from this country to
Europe. Mine and smelter capacities were greatly increased,
over-production ensued, and with the cessation of hostilities many
plants were obliged to curtail or cease operations. The United States
has now about 40 per cent of the zinc-smelting capacity of the world.
For the present at least the capacity is far in excess of the domestic
requirements.
Before the war German control of the international zinc market was even
stronger than in the case of lead. The German Zinc Syndicate, through
its affiliations, joint share-holdings, ownership of mines and smelters,
and especially through smelting and selling contracts, controlled
directly one-half of the world's output of zinc and three-fourths of the
European production. It regulated the Australian exports by means of
long-term contracts, and had considerable influence in the United
States. To some extent it was able to so manipulate the market that zinc
outside the syndicate was also indirectly controlled. During the war
political jurisdiction was used by the Allied countries to destroy this
German influence.
In the United States the principal zinc-producing regions are the Joplin
and adjacent districts of Missouri, Oklahoma, Kansas, and Arkansas,
furnishing about one-third of the country's output; the Franklin Furnace
district of New Jersey, and the Butte district of Montana, each
yielding about one-sixth of the total supply; and the Upper Mississippi
Valley district of Wisconsin, Iowa, and Illinois, the Leadville district
of Colorado, and the Coeur d'Alene district of Idaho, each producing
between one-tenth and one-twentieth of the total. Smaller quantities are
produced in Tennessee, New Mexico, Nevada, and several other states.
Reserves of zinc are ample for the future. They are now developed
considerably in advance of probable requirements, a fact which causes
keen competition for markets and renders zinc-mining more or less
sensitive to market changes.
GEOLOGIC FEATURES
The most important mineral of zinc is the sulphide, sphalerite or "zinc
blende." The minerals of the oxide zone are smithsonite (zinc carbonate)
and calamine (hydrous zinc silicate), which yield minor amounts of zinc
and are especially productive at Leadville, Colorado. Zincite (zinc
oxide) and willemite (zinc silicate) are the important minerals in the
deposits of Franklin Furnace, New Jersey. The association of most
deposits of zinc with more or less lead has been noted.
The ores of zinc are of two general classes, corresponding to the two
classes of lead ores (pp. 211-212). Zinc ores of the first type are in
veins and replacements in sedimentary rocks at shallow depths,
independent of igneous association, and are supposed to have been formed
by cold solutions. They are found in the Mississippi Valley, in Silesia,
and in many of the smaller European deposits. They were formerly the
leading zinc-producers, and now produce about 45 per cent of the world's
total. Zinc ores of the second type consist of veins and replacements
related to intrusive rocks, sometimes extending to considerable depths,
and of more complex composition. They include most of the deposits of
the American Cordilleran region (Butte, Coeur d'Alene, Leadville,
etc.), of Franklin Furnace, of Australia, of Burma, and of many other
places.
The zinc-lead ores of the type found in the Mississippi Valley are of
special interest, in that they are sulphide ores of an origin apparently
independent of igneous agencies. These ores occur as fissure-fillings
and replacements, mainly in nearly flat-lying Paleozoic limestones and
dolomites--the Bonne Terre dolomitic limestone of southeastern Missouri,
the Boone formation of southwestern Missouri and Oklahoma, the Galena
dolomite of Wisconsin and Illinois. They are variously associated with a
gangue of dolomite, calcite, quartz, iron pyrite, barite, and chert. Not
infrequently they are spread out both in sheets and in disseminated form
along carbonaceous layers within or at the base of the limestone.
The source of the primary sulphides has been a subject of much
discussion. All are agreed that they were first deposited with the
sediments in minutely dispersed form, through the agency of the organic
contents of the sediments, and that such deposition was somewhat
generally localized by estuarine conditions which favored the
accumulation of organic remains. Many years ago, before the evidence of
estuarine deposition was recognized, Chamberlin suggested an ingenious
hypothesis for the northern Mississippi Valley,--that the organic
material had been localized by ocean's currents forming something in the
nature of a Sargasso sea. Differences of opinion become acute, however,
when the attempt is made to name the precise sedimentary horizon, out of
several available horizons, in which for the most part this primary
concentration occurred. Judging from the organic contents of the several
beds, the primary source may have been below, within, or above the
present ore-bearing horizons. If the ore came from the lower horizons,
it was introduced into its present situation by an artesian circulation,
for which the structural conditions are favorable. If the ore was
derived from overlying horizons, downward moving solutions accompanying
erosion did the work. If the primary source was within the horizon of
present occurrence of the ores, both upward and downward moving waters
may have modified and transported them locally. For each of these
hypotheses a plausible case can be made; but much of the evidence can be
used interchangeably for any one of them. In spite of the wealth of data
available, it is astonishingly difficult to arrive at a conclusion which
is exclusive of other possibilities. Without attempting to argue the
matter in detail the writer merely records his view, based on some
familiarity with these districts, that, on the whole, the evidence
favors the accumulation of these deposits by downward moving meteoric
solutions during the weathering of overlying strata; but that it is by
no means certain that a part of the ores has not been derived from lower
horizons. The great area of the producing districts in comparison with
their depth, the uniform association of the ore-bearing zone with the
surface regardless of geologic horizon uncovered by erosion, the failure
of the ores to extend in quantity under cappings of later formations,
and the known efficacy of oxidizing waters in local downward transfers
of zinc and lead, seem to suggest concentrating agencies which are
clearly related to surface conditions.
It is of interest to note that in many places in the limestones of
Missouri and Virginia, and elsewhere in the Paleozoic rocks, there are
sinks of limonite and clay near the surface, which are likewise believed
to have originated through downward movement of waters deriving their
mineral contents from the erosion and stripping of overlying sediments.
Still further, the primary deposition of Clinton iron ores in many parts
of the Mississippi Valley and eastward to the Appalachians took place in
stratigraphic horizons not far removed from the horizons of lead and
zinc deposition. When the peculiar conditions controlling the deposition
of the Clinton ores are understood (see pp. 52-53) it is entirely
possible that they may throw some light on the genesis of the lead and
zinc ores.
Since the ores were introduced into essentially their present locations,
secondary concentration has produced an oxide zone of clay, chert, and
iron oxide, with varying amounts of zinc carbonate, zinc silicate, lead
sulphide, and rarely lead carbonate. This zone is obviously developed
above water level, and is seldom as much as 100 feet thick. Zinc, and to
a less extent lead, have been taken into solution as sulphates, with the
aid of sulphuric acid resulting from the oxidation of the associated
pyrite. Zinc has been carried away from the weathered zone in solution
faster than lead, leaving the lead more or less concentrated near the
surface. Some of the zinc carried down has been redeposited secondarily
as zinc sulphide. Evidences of this secondary sulphide enrichment can be
seen in many places; yet certain broad quantitative considerations raise
a doubt as to whether this process has been responsible for the main
portion of the values of the sulphide zone. If downward secondary
enrichment had been a dominant process, it might be expected that the
ores would be richer in places where erosion had cut away more than
half the limestone formation carrying the ore, than in places where it
had barely cut into the formation. This is not the fact,--which suggests
that erosion in its downward progress has carried a large part of the
zinc completely out of the vicinity.
Zinc ores of this same general character are also found in Paleozoic
rocks (Knox dolomite) in Virginia and Tennessee. Their manner of
occurrence suggests the same problem of origin as in Missouri and
Wisconsin, but no decisive evidence of their source has been discovered.
Of the zinc ores associated with igneous intrusions, those of the Butte
and Coeur d'Alene districts are described in connection with copper
and lead ores on pp. 201-203, 208, and 212-213.
Zinc constitutes about 75 per cent by weight of the recoverable metals
of the Leadville district of Colorado. About two-thirds of the zinc
occurs as the sulphide and about one-third as the carbonate resulting
from weathering of the sulphide. The zinc sulphide is associated with
lead, iron, and copper sulphides and gold and silver minerals. In the
oxide zone the zinc carbonate is associated with oxides and carbonates
of various metals, including those of lead, copper, iron, and manganese.
The iron and manganese oxides are mined in considerable tonnage as a
flux. It is an interesting fact that, although mining has been carried
on in this district for upwards of forty years, only within the last
decade has the existence of zinc ores in the oxide zone been recognized.
This has been due largely to the fact that the iron and manganese oxides
effectively stain and mask the zinc carbonate.
The Leadville ores occur as replacements and vein-fillings in a gently
faulted and folded Carboniferous limestone, in deposits of a general
tabular shape, parallel to the bedding but with very irregular lower
surfaces. The limestone is intruded by numerous sheets of porphyry,
mainly parallel to the bedding but sometimes cutting across it, against
the under sides of which most of the ore occurs. The primary sulphides
are believed to be genetically related in some fashion to these
porphyries. The older view was that the agents of deposition were
aqueous solutions from the surface above, which derived their mineral
content chiefly from the porphyries. Later views favor solutions coming
directly from the porphyries or deeper igneous sources. While in form
and association these ores are characteristic igneous contact deposits,
they lack the high-temperature silicates which are so distinctive of
many ores of this type.
The zinc ores of Franklin Furnace, New Jersey, belong in the group
associated with igneous agencies, but have certain unique features. They
consist of willemite and zincite, together with large amounts of
franklinite (an iron-manganese oxide) and silicates, in a pre-Cambrian
white crystalline limestone near its contact with a coarse-grained
granite-gneiss. The origin of the ores is obscured by later shearing and
metamorphism, but it seems best explained by replacement of the
limestone by heated solutions coming from the granitic mass. The view
has also been advanced that the ores originated in the limestone before
the advent of the igneous rocks. Secondary concentration is not
apparent.
FOOTNOTES:
[33] Ransome, Frederick Leslie, The copper deposits of Ray and Miami,
Arizona: _Prof. Paper 115, U.S. Geol. Survey_, 1919, pp. 12-13.
CHAPTER XI
GOLD, SILVER, AND PLATINUM MINERALS
GOLD ORES
ECONOMIC FEATURES
The principal and most essential use of gold is as a standard of value
and a medium of exchange. Gold has been prized since the earliest times
because of its luster, color, malleability, and indestructibility, and
has long been used as a trading medium. At present little of the metal
is actually circulated from hand to hand. Stocks of gold, however,
accumulated by governments and banking interests, form the essential
foundation of paper currency and of the vast modern system of credit
relations. In the settlement of international trade balances
considerable quantities of gold frequently move from debtor to creditor
nations. Although the amounts thus shipped are frequently great in
value, they are very small in volume. It is interesting to note that the
entire accumulated gold stocks of the world's governments--about nine
billion dollars--cast in a solid block, with the horizontal dimensions
of the Washington monument, would be only about 12 feet high.
Other uses of gold are in dentistry, and in the arts for jewelry,
gilding, and other forms of ornamentation. Consumption for these
purposes has been increasing of late years and now takes a third or more
of the world's annual production. In the United States, before war-time
restrictions were adopted, the consumption for jewelry and similar uses
exceeded the consumption in coinage. Since the war it has exceeded the
total domestic production of gold. An interesting problem for the future
is how an adequate supply of gold is to be distributed between monetary
uses and the arts. The curve of increase in the requirements of the arts
indicates that, unless there is greatly increased production, all the
world's gold will be necessary for the arts in a comparatively few
years. To retain it for monetary purposes would require government
restrictions.
Of all the mineral commodities, gold has played perhaps the most
important and certainly the most romantic part in the world's history.
The "lure of gold" has taken men to the remotest corners of the globe.
It has been the moving force in the settlement and colonization of new
countries, in numerous wars, and in many other strenuous activities of
the human race.
About two-thirds of the annual gold production of the world comes from
the British Empire--from South and West Africa, Australasia, Canada, and
India. A single colony, the Transvaal, produces about 40 per cent of the
world's total. British capital, which seems to have a particular
affinity for investments in gold mines, controls not only the larger
part of the output from the colonies, but also important mines in
Siberia, Mexico, South America, and the United States.
Russia, Mexico, and Japan have small gold production. The chief deposits
of Russia are those of Siberia, which have had an important output and
have apparent great possibilities of increase. Other foreign districts
are numerous and widely scattered, but, with the exception of Colombia
and Korea, no one of them yields 1 per cent of the world's gold.
French interests control about a tenth of the production of the
Transvaal, and minor supplies in Mexico and South America--in all about
6 per cent of the world's production. Germany and Austria control less
than 1 per cent of the total gold production. German interests formerly
had extensive holdings in South Africa and Australia, but during the war
this control was eliminated.
The United States, the second largest gold-producing country, supplies
about 20 per cent of the world's total. Commercially it controls
production of another 5 per cent in foreign countries, chiefly in
Canada, Mexico, South America, and Korea. About one-fourth of the United
States production comes from California. Other producing states in order
of importance are Colorado, Alaska, South Dakota, Nevada, Arizona,
Montana, and Utah. These eight states supply 95 per cent of the
country's output, and most of the remainder is obtained from other
western states.
International movements of gold depend chiefly upon its use in the
settlement of trade balances, and are not governed by the considerations
which control ordinary mineral commodities. Imports and exports vary
with changing foreign trade balances. Large amounts of gold normally go
to London, because Great Britain requires all gold produced in the
colonies to be sent to England; but since England ordinarily has an
unfavorable balance of trade, much of this gold is reëxported. The
United States up to a few years ago was also a debtor nation, and more
gold was exported than was imported. During the war, however, this
country became the greatest of the creditor nations and imports of gold,
chiefly from Europe, were several times the exports.
The total world's gold production up to 1920 has been upwards of 19
billions of dollars, of which about 10 billions have gone into the arts
or been hidden and lost, leaving 9 billions in monetary reserve.
At the present writing the United States government holds an unusually
large fraction of the world's gold reserve, about 28 per cent or 2
billion dollars,--an amount equal to two-thirds of the aggregate
production of the United States to date. Other large stocks of gold are
held, in order, by Great Britain, France, and Russia, these three with
the United States holding over a half of the world's total gold reserve.
Germany has about 1-1/2 per cent of the total reserve, and, with its
tremendous debt and no sources of new production, is of course in a
particularly unfavorable position.
The total amount of gold now (1920) accounted for by governments as
money is not more than 10 per cent of the value of the notes and
currency issued against this gold. Before the war it was 60 per cent. In
the United States the pre-war percentage was 99-1/2 per cent. Since the
war it has been 45 per cent. The ratio of gold to currency is now so
small that the gold standard is hardly a physical fact, but is to be
regarded rather more as a profession of faith. Notwithstanding the
recent falling off in gold production, an increment of approximately 350
million dollars is potentially available each year to be added to the
gold reserves. Whether this increment, or a larger increment which may
come from new discoveries, is sufficient to maintain a reasonable
proportion between gold stocks and the necessary normal increase in
paper currency, has been, and doubtless will continue to be, a subject
of vigorous discussion and speculation.
During and immediately following the war, the gold production of the
world showed rather an alarming progressive decrease. About 1915 the
group of three greatest producers--South Africa, United States, and
Australia,--reached the acme of its production, and output then fell
off. Simultaneously there was a marked decrease of production in many of
the less important districts. This general decline was due in
considerable part to the fact that during the war the price of gold was
fixed and its use restricted to monetary purposes. The price of gold,
which is itself the standard of value, could not rise to offset growing
mining costs and to maintain profits, as was the case with iron, copper,
and the other metals,--with the result that the margin of profit in gold
mining became so small as materially to affect exploration and
production. Another important cause of decreased production was the
actual exhaustion of certain mines, and the lowering of the grades of
ore available in many others. New discoveries did not supply these
deficiencies. In the United States, for instance, physical conditions of
one kind or another were responsible for lessening of production from
Alaska, Cripple Creek, and California. Minor causes included conflicts
in California between agricultural and mining interests over water
rights, and a succession of dry seasons which did not afford enough
water for the working of placers; and in Alaska difficulties due to
litigation over the oil-flotation process of recovering gold from its
ores. As a result of all these conditions, many of the smaller mines
were closed down, others continued operations only by curtailing
exploration and by mining solely the richest and most accessible ore
bodies, and there was a general discouragement and lack of inducement to
engage in gold mining.
The gold situation has become a matter of great concern to the various
governments, since national financial stability and the confidence of
the public in the national credit are based largely upon the acquirement
of an adequate gold reserve. Both in England and in the United States,
committees of experts have been appointed to make exhaustive
investigations and present recommendations for measures to stimulate
production. The report of the joint committee from the United States
Bureau of Mines and Geological Survey gives a comprehensive review of
the conditions in the gold-mining industry.[34]
During the war there was vigorous demand by gold miners both in the
United States and South Africa for a bonus on gold. These demands
received serious consideration on the part of the governments, but were
denied on the general ground of the doubtful adequacy of such a measure
to meet the situation, and the danger of upsetting the gold standard of
value. In the United States, for instance, a bonus of $10 per ounce was
asked for. It did not appear likely that this could increase the annual
production from the United States by more than 10 per cent, in face of
the physical conditions being met in gold mining. The bonus would have
had to be paid on all the gold mined, which would make the increment of
production very expensive; to secure an added production of ten million
dollars would have cost in the neighborhood of forty millions. Ten
millions is only one-third of 1 per cent of the gold reserve already
held by this country, and it would obviously have taken a long time for
this small increase in annual production to make itself felt in the size
of the gold reserves.
Since the war gold has gone to a considerable premium in England, due to
the action of the British government in establishing a "free"
market,--that is, abandoning the restriction that gold marketed in
London should be offered to the government or the Bank of England at the
fixed statutory price for monetary purposes. With the pound sterling at
a considerable discount outside of England, other countries could afford
to bid, in terms of British currency, far above the British mint price.
The result is that the South African miner of gold receives a premium
due to depreciation of sterling exchange, while the American miner still
receives the regular mint price. The agitation for a bonus therefore
continues in the United States. However, with the removal of war-time
restrictions gold has been allowed to go to the arts, the demand from
which is already equal to one-third of the world's gold production, is
rapidly increasing, and is temporarily acute due to the accumulation of
requirements resulting from war restrictions. This situation has a
general tendency to improve the position of the gold miner, though the
outlook is still far from bright.
It is an interesting fact that India is absorbing a good half of the
free gold. India, in regard to its demand for precious metals and
stones, has been described as "an abyss from which there is no return."
This is an important contributing cause of the shortage of gold in the
rest of the world.
Looking forward to the future, it seems that increased exploration,
which is resulting from the present premium on gold, is likely to bring
in new reserves to increase production. Because of lack of important
discoveries in recent years, there is pessimism in some quarters as to
the possibilities of large increase of production; but, considering the
history of gold discoveries, and the amount of ground still to be
explored both areally and vertically, this pessimism does not seem to be
wholly justified from the geologic standpoint. Curves representing the
world's gold production in past years show periods of increasing annual
production as new fields are discovered, followed by periods of
decreasing production when no new ore bodies are coming in to replace
dwindling reserves. It is entirely possible that in recent years the
gold-mining industry has been merely in one of these temporary stagnant
periods. There are many regions, both in the vicinity of worked-out
lodes and in unsettled and poorly explored countries, where gold may
still be discovered; there may be far greater resources of this metal
still covered up than all those which man has thus far uncovered. A
single new deposit or district may make a great difference in the
world's production, as suggested by the experience of the past. Regions
which are especially attractive for exploration and the discovery of new
deposits are in Siberia and South America, which in the opinion of many
engineers may eventually rival South Africa. Mexico, with the
establishment of a stable government, should also have a greatly
increased production.
GEOLOGIC FEATURES
The principal gold mineral is native or metallic gold. This occurs in
nature in small scales, crystals, and irregular masses, and also in
microscopic particles mechanically mixed with pyrite and other
sulphides. Chemically, gold is very inactive and combines with but few
other elements. A small part of the world's supply is obtained from the
gold-silver tellurides--calaverite, sylvanite, krennerite, and petzite.
Gold deposits are of two general classes--placers, and veins or lodes.
Placers, which are in general the more easily discovered and more easily
worked deposits, have in the past been the chief source of the world's
gold supply. It is estimated that in the first twenty-seven years of the
modern era of gold-mining, beginning with the discovery of gold in
California in 1848, 87 per cent of the world's production was obtained
from placers. At present the placers of recent geologic age supply a
tenth to a fifth of the gold, and ancient or fossil placers in the
Transvaal supply another two-fifths. In the United States about a fourth
of the gold production comes from placers, mainly from California and
Alaska.
Placers are detrital or fragmental sediments containing the ore in
mechanical fragments, which are derived from the erosion and
transportation of solid-rock veins or lodes, sometimes called the
"mother lode." During the process of transportation and deposition there
is more or less sorting, because of differing density of the mineral
fragments, resulting in the segregation or concentration of the ore
minerals in certain layers or channels. Gold, because of its weight,
tends to work down toward bedrock, or into scoured or excavated portions
of stream channels. In a few cases it is carried in some quantity to the
sea and concentrated in beach sands. The processes are not unlike the
mechanical concentration of ores by crushing and water sorting. Seldom,
however, do the processes go far enough in nature to produce an ore
which can be used directly without some further mechanical sorting. Ore
minerals concentrated in placers are those which resist abrasion and
chemical solution during the processes of weathering and transportation,
and which have a density sufficiently high so that they are partially
sorted out and concentrated from the accompanying quartz and other
minerals. To warrant their recovery they must also be of such high
intrinsic value that it pays to mine small quantities. The most
important of such minerals are gold, tin, platinum, and the precious
stones. Iron, copper, lead, and zinc minerals are often somewhat
concentrated as placers, but their intrinsic value is not high enough to
warrant the attempt to recover them in the large amounts necessary to
make them commercially available.
Placers are forming now and have formed at all stages of the earth's
history. Early placers may be reworked and further concentrated by
renewal of the proper erosional and transportational conditions. Old
placers may be buried beneath younger rocks, cemented, and more or less
recrystallized. "Fossil" placers of this kind are best represented by
deposits in the Black Hills of South Dakota and probably by the South
African gold deposits.
In the Witwatersrand deposits of South Africa, the gold is concentrated
in the lower parts of large conglomerate and quartz sand layers of great
areal extent. Pebbles of the conglomerate are mainly quartz and
quartzite. The gold, in particles hardly visible to the eye, is in a
sandy matrix and is associated with chloritoid, sericite, calcite,
graphite, and other minerals. The origin of the gold deposits of this
district is not entirely agreed on, but the evidence seems on the whole
to favor their placer origin. Some investigators of these ores believe
them to have been introduced into the conglomerate and sand by later
solutions, possibly by hot solutions related to certain diabase
intrusions that cut the beds.
In the vein or lode or hard-rock deposits, the gold is mainly metallic
gold, and to a minor extent is in the form of gold tellurides. It is
usually closely associated with iron pyrite in a matrix or gangue of
quartz. Seldom is a gold deposit free from important values in other
minerals. About 84 per cent of the gold mined in vein or lode deposits
of the United States is associated with silver minerals, the combined
value averaging about $6 per ton; about 13 per cent comes from copper
ores which have an average yield of gold and silver of 50c. per ton; and
3 per cent comes from zinc and lead ores, with an average gold and
silver yield ranging from $1 to $6 per ton. The geologic occurrence of
gold in the copper, lead, and zinc ores has already been referred to in
the discussions of these ores.
Reference will be made here only to the vein deposits in which gold,
with silver, constitutes the principal values. Because of their common
gangue of quartz these are often called "dry" or "siliceous" ores. Their
principal occurrence is in distinct fissure veins in igneous rocks, with
more or less replacement of the wall rock. The igneous rocks are
commonly acid intrusives of a granite or porphyry type, less commonly
intrusives of gabbro and diabase and surface lavas of rhyolite and
basalt. In a few cases the ores are contact-metamorphic deposits of the
type described under copper ores. In still rarer cases they are in
pegmatites. Gold is commonly associated with minerals and wall-rock
alterations indicating deposition by hot solutions, which are inferred
to have come from the igneous rocks.
Because of the resistant nature both of ore minerals and gangue,
weathering and secondary concentration have had little effect in
enriching gold deposits. So far as there has been any noticeable effect
on the gold content of the ores, it has been due to the leaching out of
other constituents, principally pyrite and other sulphides, leaving the
gold present in slightly larger proportions. Locally there is evidence
of solution of gold in weathered zones and its deposition in the
sulphide zones below. Solution is believed to be accomplished by
chloride solutions, and is favored by the presence of manganese which
delays precipitation. The precipitating agent below may be ferrous
sulphate, various sulphides, native metals, or organic matter.
Of the vein or lode gold ores in the United States some of the most
productive and best known have the following geologic features:
The California gold belt extends north and south along the west slope of
the Sierra Nevada Mountains. The ore is in a series of parallel and
overlapping veins striking with the trend of the range, associated with
granodiorite intrusives in schist and slate. There is no pronounced
secondary concentration. These deposits are the source of most of the
great placer deposits of California, hence the name "Mother Lode"
applied to a part of them. The principal ore deposits are somewhat
removed from the main mass of intrusive which forms the crest of the
Sierra Nevada range, and are more closely related to the smaller similar
intrusive masses farther down the slope. The gangue is mainly quartz.
At Juneau, Alaska, great dikes of albite-diorite intrude greenstones and
schists, and low-grade gold ores occur in shattered portions of the
diorite. These ores were mined on a great scale at the Treadwell Mine.
Another famous low-grade deposit is the Homestake Mine in the Black
Hills of South Dakota, where pre-Cambrian slates and schists of
sedimentary origin are impregnated with gold, associated with quartz,
dolomite, calcite, pyrite, and other minerals. The origin is supposed to
have some connection with intrusives into the schists; but the relations
of the ores to intrusives, both in age and in place, present many
puzzling questions which make conclusion as to origin very difficult.
In the Cripple Creek district of Colorado, a volcanic neck two or three
miles in diameter breaks through pre-Cambrian granites, gneisses, and
schists. The volcanic rocks consist mainly of tuffs and breccias cut by
basic dikes. The ore bodies are in fissures and sheeted zones,
principally in the granitic rocks, but associated with these dikes. The
ore is mainly gold telluride, in a gangue of quartz together with pyrite
and a variety of minerals characteristic of hot-water solutions. Also
the wall rocks have the characteristic hot-water alterations. There is
slight enrichment near the surface.
At Goldfield, Nevada, native gold is found in surface igneous flows of a
dacite type, which have undergone extensive hydrothermal alterations
characterized by the development of alunite (a potassium-aluminum
sulphate), quartz, and pyrite. The ore fills fissures to some extent,
but is mainly a replacement of the wall rock. Association with typical
hot-water minerals and hydrothermal alterations of the wall rock are
again believed to indicate the origin of the ores through ascending hot
solutions from a deep source.
One of the interesting features of this occurrence is the abundance of
alunite. Sulphate minerals are commonly formed by oxidizing solutions.
The abundant presence, therefore, of a sulphate mineral with minerals of
a primary deep-seated source has led to much discussion of origin. The
hypothesis was developed that these minerals result from the interaction
of deep-seated sulphide-bearing solutions with surface oxidizing
solutions.[35] It may be noted that in recent years other sulphate
minerals have been occasionally regarded as primary, including gypsum,
anhydrite, barite, and others. It has been suggested that if igneous
emanations contain free oxygen and sulphur, or sulphur dioxide, it would
be expected that as they become cool sulphur trioxide would be formed
which would result in the sulphate at suitable temperature.[36]
Other deposits containing gold are discussed in connection with silver
on following pages.
SILVER ORES
ECONOMIC FEATURES
Silver has two important uses--in money and in the arts. As money, it is
used in the United States and Europe for subsidiary coinage,--silver
coins normally circulating at more than their intrinsic value,--but its
greatest monetary use is in India and China, where it has been the basis
for the settlement of foreign exchange balances. In China also it is the
money standard of the country. In the arts, silver is employed chiefly
in the making of articles of luxury, such as jewelry and tableware. In
the Orient this use is closely related to its use as money, since the
natives invest their savings both in silver jewelry and silver coins.
There is some consumption of silver by certain chemical industries, and
quantities of increasing importance are used in the form of silver salts
by the photographic and moving picture industries. It has been estimated
that before 1914 about two-thirds of the new silver produced went into
the arts and one-third into money. During the war, however, increasing
amounts were used in coinage, and less than one-fifth of the output was
used in the arts. Demands for silver for monetary purposes will probably
continue to take the larger part of the world's production for some
time. In this connection it may be noted that India has adopted a gold
standard, but that the conservative habits of the population will
doubtless continue to call for large amounts of silver.
About half of the silver production of the world comes from the dry or
siliceous silver ores, which are mined solely for that metal and the
associated gold; and about half of the production is obtained as a
by-product in the mining of other metals, principally copper and lead.
The average grades of these ores, in combined values of gold and silver,
were referred to on p. 228. While the aggregate amount of silver
obtained as a by-product of other ores is large, the percentage of
silver in the copper or lead in any mine is ordinarily very small.
Consequently the world output of silver depends to a considerable extent
upon conditions in the copper- and lead-mining industries.
Of the total world output of silver, normally about 75 per cent comes
from North America. Of this the United States and Mexico each produce
about two-fifths and Canada one-fifth, and minor amounts are produced in
Central America. In late years, political disturbances in Mexico reduced
that country's production to less than half the normal figure, and the
United States took the place which Mexico had held for many years as the
leading silver producer. The United States and Mexican supply is
obtained from the Rocky Mountain belt, and the Canadian production comes
chiefly from the Cobalt, Ontario, district. Outside of North America the
principal producing areas are Australia, South America (Peru and to a
less extent Bolivia and Chile), Europe (chiefly from Spain, Germany, and
Austria-Hungary, but with smaller amounts from all the other countries),
and Japan. Thus, while there are sources of silver in many places, the
great bulk of the world's output comes from North America. In the
financial ownership of mines, including ownership in other countries,
the United States controls over half the world's silver, Great Britain
about a third, and Germany about a tenth (principally in Mexico).
All the silver mined in the United States is smelted and refined by
domestic plants; and in addition much of the Canadian, Mexican, and
South and Central American silver is exported to the United States as
ore and base bullion, to be treated in this country. The United States
is therefore the great silver-selling country of the world.
The great silver-consuming countries are India and China, and normally
about a half of the world's output goes to these two countries. This
major movement of silver, from America to the Far East, takes place
through the London market, since England has been the chief nation
trading in the Orient. The balance of the world's silver consumption is
widely distributed among the countries of Europe and South America and
the United States (which consumes about one-tenth of the total). For the
European trade most of the silver also goes through London, which is the
great clearing-house and the market where prices are fixed.
In the later years of the war and immediately after, the demands for
silver were probably twice the world's output. The resulting rise in
price was unprecedented. Silver actually became worth more as bullion
than as currency, and in Europe much trouble was experienced because of
its withdrawal from currency to be melted up. This condition was later
followed by an equally striking drop in price as supply caught up with
demand.
In the United States, as in many other countries, it was desired during
the war to accumulate large stocks of gold as a basis of credit for the
flotation of government loans, and the export of gold was prohibited.
Consequently in the settlement of foreign trade balances, particularly
with the nations of the Orient, very large amounts of silver bullion had
to be used. Current production proved inadequate, and it was necessary
to utilize the stocks of silver dollars in the United States Treasury.
To this end the Pittman Silver Act, passed in April, 1918, authorized
the melting down and conversion into bullion of 350,000,000 dollars out
of the Treasury stock, and the retirement of a corresponding number of
silver certificates and the issue of Federal Reserve bank notes. In this
manner old stocks of silver, Manila dollars, etc., were called into
service--though the stage was not reached, as it was in Germany, where
it became necessary to melt down silver plate and ornaments. The silver
used for exchange and export was to be replaced by the purchase of
bullion from American producers at $1 per ounce, and its coining into
new dollars. A minimum price of $1 per ounce was thus established for
silver bullion.
The immediate result was to increase the price of silver at the mine;
but with the continued rise in demands for silver, the price in the open
market went far above this figure, the maximum being reached in 1920
when the price of silver went to $1.39 per ounce. Naturally, but little
silver was then offered to the government at the fixed price of $1 under
the Pittman Act. With the more recent slump in the general market for
silver to a price below $1, offers to the government under the Pittman
Act have been renewed.
That part of the silver production which is a by-product of copper
production has been low since the war, because of the stagnation in the
copper industry. The production from lead ores, on the other hand, was
not handicapped by lack of demand for lead. With the restoration of
order in Mexico, a presumption of large silver production in that
country may be expected. Increases may probably be expected also from
new mines in Burma and from Bolivia. On the whole, no large increase in
world production can be assumed from present known resources. New
discoveries will be necessary to make any considerable change.
Of the mine production of silver in the United States, about two-thirds
of the total comes from the states of Montana, Utah, Idaho, and Nevada.
Other considerable producers are Colorado, Arizona, California, Alaska,
and New Mexico. All the other states together produce less than 5 per
cent of the total. The most important single districts are the Butte
district of Montana, the Coeur d'Alene district of Idaho, and the
Tonopah district of Nevada, supplying respectively about one-fifth,
one-eighth, and one-tenth of the country's total silver output.
GEOLOGIC FEATURES
The most important mineral of silver is the sulphide, argentite or
"silver glance." Other minerals which yield a minor percentage of the
total silver produced are the silver-antimony sulphides, pyrargyrite or
"ruby silver," stephanite or "black silver," and polybasite; the
silver-arsenic sulphides, proustite or "light ruby silver" and pearcite;
and the silver antimonide, dyscrasite. In the oxide zone the most
abundant minerals are cerargyrite (silver chloride) and native or "horn"
silver. In addition to these definite mineral forms, silver is present
in many ores in an undetermined form in other sulphides, notably in
galena, sphalerite, and pyrite. Silver differs from gold in that it is
chemically active and forms many stable compounds, of which only the
more important have been mentioned.
The fact that half the world's silver is obtained as a by-product in the
mining of other metals has been referred to. In the United States about
a third of the production comes from dry or siliceous ores, over a third
from lead and zinc ores, and a fourth to a third from copper ores. A
fraction of 1 per cent of the total is obtained as a by-product of gold
placers, and all the remainder is won from lode or hard-rock deposits.
The general geologic features of the silver-bearing copper and lead
ores, and of the dry or siliceous gold and silver ores, have been
described on previous pages. The Philipsburg district has been referred
to in connection with manganese ores, and the Bolivian tin-silver ores
will be described in connection with tin. We shall consider here only a
few of the more prominent districts which have been primarily silver
producers.
The Cobalt district of northern Ontario is the most productive silver
district in North America. The ores are found in numerous short, narrow
veins, principally in pre-Cambrian sediments near a thick quartz-diabase
sill. Locally they penetrate the sill. Native silver and various silver
sulphides, arsenides, and antimonides are associated with minerals of
cobalt, nickel, bismuth, lead, and zinc, in a gangue of calcite and some
quartz. The ore is of very high grade. The ore minerals are believed to
have been deposited by hot solutions emanating from deep magmatic
sources after the intrusion of the diabase. The present oxidized zone is
very shallow, but may have been deeper before being stripped off by
glaciation; it is characterized by native silver and arsenates of nickel
and cobalt in the form of the green "nickel bloom" and the pink "cobalt
bloom." The silver minerals are distinctly later in origin than the
cobalt and nickel in the unoxidized zone, as evidenced by the relations
of the mineral individuals when seen under the microscope. This fact,
together with the abundance of native silver in the oxide zone, has
suggested downward concentration of the silver by surface waters; but
recent studies have indicated the probability that some of the silver at
least was deposited by the later ascending solutions of magmatic origin.
In the Tintic district of central Utah, Paleozoic limestones have been
intruded by monzonite (an acid granitic or porphyritic igneous rock),
and covered by surface flows, the flows for the most part having been
removed by subsequent erosion. The sediments have been much folded and
faulted, and the ore bodies occur as fissure veins which locally widen
into chimneys or pipes in fracture zones, accompanied by much
replacement of limestone. There is a rough zonal arrangement of the ore
minerals around the intrusive, gold and copper minerals (chiefly
enargite and chalcopyrite) being more prominent near the intrusive, and
argentiferous galena and zinc blende richer at greater distances. Silver
constitutes the principal value. The gangue is mainly fine-grained
quartz or jasperoid, and barite. The water table is at unusually great
depths (2,400 feet) and there is a correspondingly deep oxidized zone,
which is characterized by lead and zinc oxide minerals much as at
Leadville (p. 219).
The Comstock Lode at Virginia City, Nevada, on the east slope of the
Sierra Nevadas, was one of the most famous bonanza deposits of gold and
silver in the world. While the richer ore has all been extracted,
lower-grade material is still being mined and the fissure is still being
followed, in the hope of some day striking another fabulously rich ore
body. The lode occupies a fault fissure parallel to the trend of the
range and dipping about 40 degrees to the east, which can be traced
about two and a half miles along the strike, with igneous rocks forming
both hanging and foot walls. There are no sedimentary rocks in the
district. The high-grade part of the vein is several hundred feet in
thickness, with many irregular branches; the great thickness has been
thought to be at least in part due to the tremendous pressure exerted by
growing quartz crystals. The wall rocks have undergone a "propylitic"
alteration, with development of chlorite, epidote, and probably
sericite, much as at Butte. The ore contains rich silver sulphide
minerals and native gold, in a gangue composed almost entirely of
quartz. The ore was doubtless formed by hot solutions, but the exact
nature of these solutions, whether magmatic or meteoric, has not been
proven. The hypothesis was early developed that the ores were deposited
by surface waters,--which are supposed to have fallen on the summits of
the Sierra Nevadas, to have sunk to great depths where they were heated,
enabling them to pick up metallic constituents from the diabase forming
one wall of the ore body, and to have risen under artesian pressure
along the fault plane, where loss of heat and pressure resulted in
deposition. Later studies have emphasized the similarity of the
ore-depositing conditions with those in other districts where the ores
are believed to have come directly from magmatic sources, and this
origin is now generally favored for the Comstock Lode. However, the
earlier theory has not been disproved.
The Tonopah, Nevada, district is very similar to the Goldfield district
(p. 230). Silver and gold are found in veins and replacements in a
series of Tertiary volcanic flows and tuffs, all of which have been
complexly faulted. Silver is the dominant constituent of value. The
formation of fissures and faults accompanying and caused by the
intrusion and cooling of lavas was first clearly shown in this district.
Evidences of origin through the work of hot solutions, probably
magmatic, are the close association of the ores in place and in time
with the igneous rocks--ore deposition in most of the flows having taken
place before the next overlying flows were put down,--the presence of
fluorine, the nature of the wall-rock alterations, the fact that both
hot and cold springs are found close together underground (indicating
unusual sources for the hot springs), the contrast in composition
between the ores and the country rock, and the general relation of these
ores to a large number of similar occurrences in Tertiary lavas in the
same general area.
Under weathering conditions, the silver sulphide minerals in general are
oxidized to form native silver and cerargyrite, which are relatively
insoluble and remain for the most part in the oxide zone. Silver is less
soluble than copper and zinc, but more soluble than gold; and to some
extent it is removed in solution, particularly where the oxidation of
pyrite forms ferric sulphate. Farther down it may be reprecipitated as
native silver, argentite, and the sulpho-salts, by organic matter or by
various sulphides. The secondarily enriched ores are in a few districts,
as at Philipsburg, Montana, the most valuable portions of the deposits.
In other cases, sulphide enrichment does not appear to have contributed
greatly to the values. The zones of oxide ores, secondary sulphide ores,
and primary or protores are in most silver deposits much less regular
and much less definitely marked than in the case of copper ores.
PLATINUM ORES
ECONOMIC FEATURES
The principal uses of platinum are: as a catalytic agent in the contact
process for the manufacture of sulphuric acid, and in the making of
nitric acid from ammonia; for chemical laboratory utensils that must be
resistant to heat and acids; for electrical contacts for certain
telephone, telegraph, and electrical control instruments, and for
internal combustion engines; in dental work; and for jewelry. In normal
times before the war, it is estimated that in the United States the
jewelry and dental industries used 75 per cent of the platinum metals
consumed, the electrical industry 20 per cent, and the chemical industry
5 per cent. During the war, with the extraordinary expansion of
sulphuric and nitric acid plants, these proportions were reversed and
the chemical and electrical industries consumed about two-thirds of the
platinum. Substitutes have been developed, particularly for the
electrical uses, and the demand from this quarter may be expected to
decrease.
About 90 per cent of the world's crude platinum produced annually comes
from the Ural Mountains in Russia. The deposits next in importance are
those of Colombia. Small amounts are produced in New South Wales,
Tasmania, New Zealand, Borneo, British Columbia, United States, India,
and Spain; and as a by-product in the electrolytic refining of the
Sudbury, Canada, nickel ores. The extension of this method of refining
to all of the Sudbury ores would create an important supply of platinum.
The Colombian output has been increasing rapidly since 1911. Meanwhile
the Russian production has declined; and from the best information
available, it is not likely that Russia will be able to maintain
production for many more years. Estimates of the life of the Russian
fields are from 12 to 20 years at the pre-war rate of production.
The platinum situation is commercially controlled by buying and
mine-operating agencies,--the French having, before the war, practically
dominated the Russian industry, while American interests controlled in
Colombia. The situation is further influenced by four large refineries,
in England, Germany, United States, and France.
Before the war the United States produced less than 1 per cent of the
new platinum it consumed annually. Production comes principally from
California, with smaller amounts from Oregon, Alaska, and Nevada. The
many efforts which have been made to develop an adequate domestic supply
of this metal do not indicate that the United States can ever hope to
become independent of foreign sources for its future supplies of
platinum.
There is little reason to doubt that the Colombia field, commercially
dominated by the United States, holds great promise for the future. The
output has come largely from native hand labor, and with the
installation of dredges can probably be greatly increased.
During the war, the need for platinum for war manufactures was so urgent
and the production so reduced, that restrictions against its use in
jewelry were put into force in all the allied countries. The United
States government secured quantities of platinum which would have been
sufficient for several years' use if war had continued. With the
cessation of hostilities restrictions on the use of platinum were
removed, and the accumulated metal was released by the government from
time to time in small quantities; but the demands for platinum in the
arts were so great that prices for a time tended to even higher levels
than during the war. More recently supply is again approaching demand.
GEOLOGIC FEATURES
Platinum, like gold, occurs chiefly as the native metal. This is usually
found alloyed with iron and with other metals of the platinum group,
especially iridium, rhodium, and palladium. Most of the platinum as used
in jewelry and for electrical purposes contains iridium, which serves to
harden it. Paladium-gold alloys are a substitute for platinum, chiefly
in dental uses.
The original home of platinum is in basic igneous rocks, such as
peridotites, pyroxenites, and dunites, where it has been found in small,
scattered crystals intergrown with olivine, pyroxene, and chromite.
Platinum is very dense and highly resistant to oxidation and solution.
In the breaking up and washing away of the rocks, therefore, it is
concentrated in small grains and scales in stream and beach placers. Of
the world production of platinum over 99 per cent has been derived from
placers.
The Ural Mountain deposits of Russia are gold- and platinum-bearing
placers, in streams which drain areas of dunite rock containing minute
quantities of native platinum. The deposits of Colombia and Australasia
are placers of a similar character. In the United States small
quantities of platinum are recovered from the gold-bearing gravels of
California and Oregon, where the streams have come from areas of
serpentine and peridotite.
A platinum arsenide, called sperrylite, is sometimes found associated
with sulphide minerals in basic igneous rocks. At Sudbury, Ontario, this
mineral, together with palladium arsenide, is found in the nickel ores,
especially in the weathered zone where it is concentrated by removal of
more soluble materials. It has also been found in the copper mines of
Rambler, Wyoming. In the Yellow Pine district of southern Nevada,
metallic gold-platinum-palladium ore shoots are found in association
with copper and lead ores, in a fine-grained quartz mass which replaces
beds of limestone near a granitic dike. No basic intrusives are known
in the district. The deposit is unusual in that it has a comparatively
high content of platinum (nearly an ounce to the ton), and is probably
genetically related to acid intrusives. From all these deposits, only
small quantities of platinum are mined.
FOOTNOTES:
[34] Report of a joint committee appointed from the Bureau of Mines and
the United States Geological Survey by the Secretary of the Interior to
study the gold situation: _Bull. 144, U. S. Bureau of Mines_, 1919. See
also Report of Special Gold Committee to Secretary of the Treasury,
February 11, 1919.
[35] Ransome, F. L., The geology and ore deposits of Goldfield, Nevada:
_Prof. Paper 66, U.S. Geol. Survey_, 1909, p. 193.
[36] Butler, B. S., Loughlin, G. F., Heikes, V. C., and others, The ore
deposits of Utah: _Prof. Paper 111, U.S. Geol. Survey_, 1920, p. 195.
CHAPTER XII
MISCELLANEOUS METALLIC MINERALS
ALUMINUM ORES
ECONOMIC FEATURES
Bauxite (hydrated aluminum oxide) is the principal ore of aluminum. Over
three-fourths of the world's bauxite production and 65 per cent of the
United States production is used for the manufacture of aluminum. On an
average six tons of bauxite are required to make one ton of metallic
aluminum. Other important uses of bauxite are in the manufacture of
artificial abrasives in the electric furnace, and in the preparation of
alum, aluminum sulphate, and other chemicals which are used for
water-purification, tanning, and dyeing. Relatively small but
increasingly important quantities are used in making bauxite brick or
high alumina refractories for furnace-linings.
Aluminum is used principally in castings and drawn and pressed ware, for
purposes in which lightness, malleability, and unalterability under
ordinary chemical reagents are desired. Thus it is used in parts of
airplane and automobile engines, in household utensils, and recently in
the framework of airplanes. Aluminum wire has been used as a substitute
for copper wire as an electrical conductor. Aluminum is used in
metallurgy to remove oxygen from iron and steel, and also in the
manufacture of alloys. Powdered aluminum is used for the production of
high temperatures in the Thermite process, and is a constituent of the
explosive, ammonal, and of aluminum paints.
Deposits of bauxite usually contain as impurities silica (in the form of
kaolin or hydrous aluminum silicate), iron oxide, and titanium minerals,
in varying proportions. Bauxites to be of commercial grade should carry
at least 50 per cent alumina, and for the making of aluminum should be
low in silica though the content of iron may be fairly high. For
aluminum chemicals materials low in iron and titanium are preferred; and
for refractories which must withstand high temperatures, low iron
content seems to be necessary. The abrasive trade in general uses
low-silica high-iron bauxites.
The only large producers of bauxite are the United States and France,
which supplied in normal times before the war over 95 per cent of the
world's total. Small amounts are produced in Ireland, Italy, India, and
British Guiana. During the war a great deal of low-grade bauxite was
mined in Austria-Hungary and possibly in Germany; but on account of the
large reserves of high-grade material in other parts of the world, it is
doubtful whether these deposits will be utilized in the future. Bauxites
of good grade have been reported from Africa, Australia, and many
localities in India. From geologic considerations it is practically
certain that there are very large quantities available for the future in
some of these regions.
The international movements and the consumption of bauxite are largely
determined by the manufacture of aluminum, and to a lesser extent by the
manufacture of abrasives and chemicals. The principal foreign producers
of aluminum are France, Switzerland (works partly German-owned), Norway
(works controlled by English and French capital), England, Canada,
Italy, Germany, and Austria. French bauxite has normally supplied the
entire European demands,--with the exceptions that Italy procures part
of her requirements at home, and that the Irish deposits furnish a small
fraction of the English demand.
The deposits of southern France, controlled largely by French but in
part by British capital, have large reserves and will probably continue
to meet the bulk of European requirements. France also has important
reserves of bauxite in French Guiana.
The United States produces about half of the aluminum of the world, and
is the largest manufacturer of artificial abrasives and probably of
aluminum chemicals. Most of these are made from domestic bauxite. Prior
to the war, the United States imported about 10 per cent of the bauxite
consumed, but these imports were mainly high-grade French bauxite which
certain makers of chemicals preferred to the domestic material. The
small production of Guiana is also imported into the United States.
Bauxite is exported to Canadian makers of aluminum and abrasives.
During the war period domestic deposits were entirely capable of
supplying all the domestic as well as Canadian demands for bauxite,
although these demands increased to two and one-half times their
previous figure. At the same time considerable amounts of manufactured
aluminum products were exported to Europe, whereas aluminum had
previously been imported from several European countries.
The United States production of bauxite comes mainly from Arkansas, with
smaller amounts from Tennessee, Alabama, and Georgia. The reserves are
large but are not inexhaustible. Most of the important deposits are
controlled by the large consumers of bauxite, principally the Aluminum
Company of America and its subsidiaries, though certain chemical and
abrasive companies own some deposits. The Aluminum Company of America
also controls immense deposits of high-grade bauxite in Dutch and
British Guiana, and further exploration by American interests is under
way.
With the return to normal conditions since the war, some of the domestic
bauxite deposits probably can not be worked at a profit, a situation
which is likely to require the development of the tropical American
deposits.
GEOLOGIC FEATURES
Aluminum is the third most abundant element in the common rocks and is
an important constituent of most rock minerals; but in its usual
occurrence it is so closely locked up in chemical combinations that the
metal cannot be extracted on a commercial scale. In the crystalline form
aluminum oxide constitutes some of the most valuable gem stones. Many
ordinary clays and shales contain 25 to 35 per cent alumina
(Al_{2}O_{3}), and the perfection of a process for their utilization
would make available almost unlimited aluminum supplies. The principal
minerals from which aluminum is recovered today are hydrous aluminum
oxides, the most prominent of which are bauxite, gibbsite, and
diaspore--the aggregate of all these minerals going commercially under
the name of bauxite.
Prior to the discovery of bauxite ores, cryolite, a sodium-aluminum
fluoride obtained from pegmatites in Greenland, was the chief source of
aluminum. It is only within about the last thirty-five years that
bauxite has been used and that aluminum has become an important material
of modern industry. Cryolite is used today to form a molten bath in
which the bauxite is electrolytically reduced to aluminum.
Bauxite deposits in general are formed by the ordinary katamorphic
processes of surface weathering, when acting on the right kind of rocks
and carried to an extreme. In the weathering of ordinary rocks the bases
are leached out and carried away, leaving a porous mass of clay (hydrous
aluminum silicates), quartz, and iron oxide. In the weathering of rocks
high in alumina, and low in iron minerals and quartz, deposits of
residual clay or kaolin nearly free from iron oxide and quartz are
formed. Under ordinary weathering conditions the kaolin is stable; but
under favorable conditions, such as obtain in the weathered zones of
tropical climates, it is broken up, the silica is taken into solution
and carried away, and hydrous aluminum oxides remain as bauxite ores.
This extreme type of weathering is sometimes called lateritic alteration
(see pp. 172-173). Impurities of the bauxite ores are the small
quantities of iron and titanium present in the original rocks, together
with the kaolin which has not been broken up. The deposits usually form
shallow blankets over considerable areas, with irregular lower surfaces
determined by the action of surface waters--which work most effectively
where joints or other conditions favor the maximum circulation and
alteration. A certain degree of porosity in the original rock is also
known to favor the alteration. A complete gradation from the unaltered
rock through clay to the high-grade bauxite, with progressive decrease
in bases and silica, concentration of alumina and iron oxide, and
increase of moisture and pore space, is frequently evident (see Fig.
13). The bauxite is earthy, and usually shows a concretionary or
pisolitic structure similar to that observed in residual iron ores (p.
172). Near the surface there may be an increase in silica,--probably due
to a reversal of the usual conditions by a slight leaching of alumina,
thus concentrating the denser masses of kaolin which have not been
decomposed.
The Arkansas bauxite deposits, the most important in the United States,
are surface deposits overlying nepheline-syenite, an igneous rock with
a high ratio of alumina to iron content. The most valuable deposits are
residual, and some parts have preserved the texture of the original
rock, though with great increase in pore space; most of the ore,
however, has the typical pisolitic structure. Near the surface the
pisolites are sometimes loosened by weathering, yielding a gravel ore,
and some of the material has been transported a short distance to form
detrital ores interstratified with sands and gravels. The complete
gradation from syenite to bauxite has been shown.
[Illustration: FIG. 13. Diagram showing gradation from syenite
to bauxite in terms of volume. The columns represent a series of samples
from a single locality in Arkansas. After Mead.]
In the Appalachian region of Tennessee, Alabama, and Georgia, bauxite
occurs as pockets in residual clays above sedimentary rocks, chiefly
above shales and dolomites. Its origin has probably been similar to that
described.
The bauxite deposits of southern France occur in folded limestones, and
have been ascribed by French writers to the work of ascending hot waters
carrying aluminum sulphate. They present some unusual features, and
evidence as to their origin is not conclusive.
At the present time bauxite is doubtless forming in tropical climates,
where conditions are favorable for deep and extreme weathering of the
lateritic type. The breaking up of kaolin accompanied by the removal of
silica is not characteristic of temperate climates, though many clays in
these climates show some bauxite. It is possible that, at the time when
the bauxite deposits of Arkansas and other temperate regions were
formed, the climate of these places was warmer than it is today.
In studying the origin of bauxites, it should not be overlooked that
they have much in common with clays, certain iron ores, and many other
deposits formed by weathering.
ANTIMONY ORES
ECONOMIC FEATURES
Antimony is used mainly for alloying with other metals. Over one-third
of the antimony consumed in the United States is alloyed with tin and
copper in the manufacture of babbitt or bearing-metal. Other important
alloys include type-metal (lead, antimony, and tin), which has the
property of expanding on solidification; "hard lead," a lead-antimony
alloy used in making acid-resisting valves; Britannia or white metal
(antimony, tin, copper, zinc), utilized for cheap domestic tableware;
and some brasses and bronzes, solders, aluminum alloys, pattern metals,
and materials for battery plates and cable coverings. Antimony finds a
very large use in war times in the making of shrapnel bullets from
antimonial lead. Antimony oxides are used in white enameling of metal
surfaces, as coloring agents in the manufacture of glass, and as paint
pigments; the red sulphides are used in vulcanizing and coloring rubber,
as paint pigments, in percussion caps, and in safety matches; and other
salts find a wide variety of minor uses in chemical industries and in
medicine.
Antimony ores vary greatly in grade, the Chinese ores carrying from 20
to 64 per cent of the metal. The presence of arsenic and copper in the
ores is undesirable. Several of the more important antimony districts
owe their economical production of that metal to the presence of
recoverable values in gold. Some lead-silver ores contain small
quantities of antimony, and "antimonial lead," containing 12 to 18 per
cent antimony, is recovered in their smelting.
China is by far the most important antimony-producing country in the
world, and normally supplies over half the world's total. Chinese
antimony is exported in part as antimony crude (lumps of needle-like
antimony sulphide), and in part as antimony regulus, which is about 99
per cent pure metal. France was the only other important source of
antimony before the war (25 to 30 per cent of the world production), and
Mexico and Hungary produced small amounts. The large demand for antimony
occasioned by the war, besides stimulating production in these
countries, brought forth important amounts of antimony ore from Algeria
(French control) and from Bolivia and Australia (British control), as
well as smaller quantities from several other countries. Of the
war-developed sources, only Algeria and perhaps Australia are expected
to continue production under normal conditions.
Before the war, antimony was smelted chiefly in China, England, and
France, and to a lesser extent in Germany. British and French commercial
and smelting interests dominated to a considerable extent the world
situation, and London was the principal antimony market of the world.
During the war Chinese antimony interests were greatly strengthened, and
facilities for treating the ore in that country were increased. Japan
also became important as a smelter and marketer of Chinese ore, and
increasing quantities of antimony were exported from China and Japan
directly to the United States. English exports ceased entirely and were
replaced in this country by Chinese and Japanese brands.
The United States normally consumes about one-third of the world's
antimony. Before the war the entire amount was secured by importation,
two-thirds from Great Britain and the rest from the Orient, France, and
other European countries. Domestic production of ore and smelting of
foreign ores were negligible. (These statements refer only to the purer
forms of antimony; the United States normally produces considerable
amounts of antimonial lead, equivalent to somewhat less than 5 per cent
of the country's total lead production, but this material cannot be
substituted for antimony regulus in most of its uses.)
During the war, under the stimulus of rising prices, mining of antimony
was undertaken in the United States and several thousand tons of metal
were produced--principally from Nevada, with smaller amounts from
Alaska, California, and other western states. The great demands for
antimony, however, were met chiefly by increased importation. Imports
were mainly of regulus from Chinese and Japanese smelters of Chinese
antimony; but about a third was contained in ores, including most of the
production of Mexico which had formerly gone to England, and about 15
per cent of the Bolivian output. Antimony smelters were developed in the
United States to handle these ores.
At the close of hostilities there had accumulated in the United States
large surplus stocks of antimony and antimonial materials. With a very
dull market and low prices, domestic mines and smelters were obliged to
close down. The dependence of the United States on foreign sources of
antimony and the importance of the metal for war purposes led to some
agitation for a protective tariff--in addition to the present import
duty of 10 per cent on antimony metal--in order to encourage home
production (see pp. 365-366, 393-394).
In summary, the United States is almost entirely dependent upon outside
sources for its antimony, although there are inadequately known reserves
in this country which might be exploited if prices were maintained at a
high level. The future of United States smelters is problematical.
China, the world's chief source of antimony, at present dominates the
market in this country, largely due to the low cost of production and
favorable Japanese freight rates.
GEOLOGIC FEATURES
The antimony sulphide, stibnite, is the source of most of the world's
production of this metal. Antimony oxides, including senarmontite,
cervantite, and others, are formed near the surface, and in some of the
deposits of Mexico and Algeria they supply a large part of the values
recovered. Jamesonite, bournonite, and tetrahedrite (sulphantimonides of
lead and copper), when found in lead-silver deposits, are to some extent
a source of antimony in the form of antimonial lead.
Stibnite is found in a variety of associations and is present in small
quantities in many types of deposits. In the commercial antimony
deposits, it is in most cases accompanied by minor quantities of other
metallic sulphides--pyrite, cinnabar, sphalerite, galena, arsenopyrite,
etc.--in a gangue of quartz and sometimes calcite. Many of the deposits
contain recoverable amounts of gold and silver.
The deposits of the Hunan Province of southern China occur as seams,
pockets, and bunches of stibnite ore in gently undulating beds of
faulted and fissured dolomitic limestone. In the vicinity of the most
important mines no igneous rocks have been observed, and the origin of
the ores has not been worked out.
In the Central Plateau of France the numerous antimony deposits are
stibnite veins cutting granites and the surrounding schists and
sediments. An origin related in some way to hot ascending solutions
seems probable.
The deposits of the National district of western Nevada, the most
important war-developed antimony deposits of the United States, consist
of stibnite veins with a gangue of fine-grained drusy quartz, cutting
through flows of rhyolite and basalt. They are intimately related to
certain gold- and silver-bearing veins, and all are closely associated
with dikes of rhyolite, which were the feeders to the latest extrusion
in the district. The wall rocks have undergone alteration of the
propylitic type. These relations, and the presence of the mercury
sulphide, cinnabar, in some of the ores (see pp. 258-259), suggest an
origin through the work of ascending hot waters or hot springs. These
waters probably derived their dissolved matter from a magmatic source,
and worked up along vents near the rhyolite dikes soon after the
eruption of this rock.
In the weathering of antimony deposits, the stibnite usually alters to
form insoluble white or yellowish oxides, which are sometimes called
"antimony ocher." These tend to accumulate in the oxide zone through the
removal of the more soluble accompanying minerals. Secondary sulphide
enrichment of antimony deposits, if it occurs at all, is negligible.
ARSENIC ORES
ECONOMIC FEATURES
About two-thirds of the arsenic consumed in recent years has been used
in agriculture, where various arsenic compounds--arsenic trioxide or
"white arsenic," Paris green, lead arsenate, etc.--are used as
insecticides and weed killers. Arsenic compounds are also used in
"cattle-dips" for killing vermin. The only other large use of arsenic is
in the glass industry, arsenic trioxide being added to the molten glass
to purify and decolorize the product. Small quantities of arsenic
compounds are used in the preparation of drugs and dyeing materials, and
metallic arsenic is used for hardening lead in shot-making.
The principal arsenic-producing countries are the United States,
Germany, France, Great Britain, Canada, and Mexico. Spain, Portugal,
Japan, and China are also producers, and recent trouble with the
"prickly-pear" pest in Queensland, Australia, has led to local
development of arsenic mining in that country. For the most part,
European production has been used in Europe and American production in
the United States.
Arsenic is recovered almost wholly as a by-product of smelting ores for
the metals. The potential supply is ample in most countries where
smelting is conducted, but owing to the elaborate plant required to
recover the arsenic, apparatus is not usually installed much in advance
of the demand for production. Rapid expansion is not possible.
Before the war the arsenic needs of the United States (chiefly
agricultural) were supplied by a few recovery plants in the United
States, Mexico, and Canada. Several large smelters had not found it
profitable to install recovery plants, as the market might have been
oversupplied and prices were low. During the war, with the extensive
demand for insecticides for gardening, there was a considerable
deficiency of arsenic supplies. With rising prices production was
stimulated, but was still unable to meet the increased demand. This
situation resulted in regulation of the prices of white arsenic by the
Food Administration.
Production of arsenic in the United States comes chiefly from smelters
in Colorado, Washington, Utah, Montana, and New Jersey. Small amounts
are produced by arsenic mines in Virginia and New York. A Mexican plant
at Mapimi has been shipping important quantities to the United States.
The plant at Anaconda, Montana, is expected to produce an ample supply
in the future.
The United States is entirely independent in arsenic supplies and will
probably soon have an exportable surplus. Export trade, after the
reconstruction period, will probably meet competition from France and
Germany where production was formerly large.
GEOLOGIC FEATURES
Arsenic-bearing minerals are numerous and rather widely distributed, but
only a few of them are mined primarily for their content of arsenic.
Arsenopyrite or "mispickle" (iron-arsenic sulphide) has been used
intermittently as a source of white arsenic in various places,--notably
at Brinton, Virginia, and near Carmel, New York. The former deposits
contain arsenopyrite and copper-bearing pyrite impregnating a
mica-quartz-schist, adjacent to and in apparent genetic relation with
aplite or pegmatite intrusives. In the latter locality arsenopyrite is
found associated with pyrite in a gangue of quartz, forming a series of
parallel stringers in gneiss close to a basic dike.
The orange-red sulphides of arsenic, orpiment and realgar, are formed
both as primary minerals of igneous source and as secondary products of
weathering. They are rather characteristic of the oxide zones of certain
arsenical metallic ores, and are believed in many cases to have formed
from arsenopyrite. They are mined on a commercial scale in China.
The great bulk of the world's arsenic, as previously stated, is obtained
as a by-product of smelting operations. The enargite of the Butte copper
ores (pp. 201-203) contains a considerable amount of arsenic, a large
part of which will be recovered from the smelter fumes by new processes
which are being installed. The gold-silver ores of the Tintic district
(pp. 235) also yield important amounts, the arsenic-bearing minerals
being enargite and tennantite (copper-arsenic sulphides) and others. The
silver ores of the Cobalt district of Ontario (pp. 234-235), containing
nickel and cobalt arsenides, produce considerable arsenic. Many other
metallic ores contain notable amounts of arsenic, which are at present
allowed to escape through smelter flues, but which could be recovered
under market conditions which would repay the cost of installing the
necessary apparatus.
BISMUTH ORES
ECONOMIC FEATURES
Bismuth metal is used in alloys, to which it gives low fusibility
combined with hardness and sharp definition. Bismuth alloys are employed
in automatic fire sprinklers, in safety plugs for boilers, in electric
fuses, in solders and dental amalgams, and in some type and bearing
metals. Bismuth salts find a considerable application for pharmaceutical
purposes, especially in connection with intestinal disorders, and the
best grades of bismuth materials are used for this purpose. The salts
are also used in porcelain painting and enameling and in staining glass.
Bolivia is the most important producer of bismuth ore. The output is
controlled entirely by British smelting interests. An important deposit
exists in Peru, the output of which is limited by the same British
syndicate. Considerable bismuth is produced in Australia, Tasmania, and
New Zealand, all of which likewise goes to England. Germany before the
war had three smelters which produced bismuth from native ores in
Saxony; bismuth was one of the few metals of which Germany had an
adequate domestic supply. Recently southern China is reported to be
mining increasing amounts of bismuth.
The United States produces the larger part of its bismuth requirements,
chiefly from plants installed at two lead refineries. A further
installation would make this country entirely independent of foreign
supplies if occasion required. Imports, from England and South America,
have been steadily declining, but during the war were somewhat
increased. The United States does not export bismuth so far as known.
GEOLOGIC FEATURES
The principal minerals of bismuth are bismuthinite (bismuth sulphide),
bismutite (hydrated carbonate), bismite or bismuth ocher (hydrated
oxide), and native bismuth.
The native metal and the sulphide are believed to be formed mainly as
primary minerals of igneous origin. In the deposits of New South Wales
they are found associated with molybdenite in quartz gangue, in
pipe-like deposits in granite. The oxide and the carbonate are probably
products of surface weathering. The Bolivian deposits contain the native
metal, the oxide, and the carbonate, associated with gold, silver, and
tin minerals, in one locality in slates and in another locality in
porphyry. The origin is not well known.
In the United States, the sulphide, bismuthinite, is found in the
siliceous ores of Goldfield, Nevada (p. 230), and in minor amounts in a
great number of the sulphide ores of the Cordilleran region. The ores of
the Leadville and Tintic districts (pp. 219 and 235) yield the larger
part of the United States production, the bismuth being recovered as
by-product from the electrolytic refining of the lead bullion. Large
amounts of bismuth pass out of the stacks of smelters treating other
western ores, and while it would not be cheap nor easy to save the
bismuth thus lost, it could probably be done in case of necessity.
CADMIUM ORES
ECONOMIC FEATURES
Cadmium is used in low melting-point alloys--as, for example, those
employed in automatic fire-extinguishers and electric fuses,--in the
manufacture of silverware, and in dental amalgams. During the war the
critical scarcity of tin led to experiments in the substitution of
cadmium for tin in solders and anti-friction metals. Results of some of
these experiments were promising, but the war ceased and demands for tin
decreased before the cadmium materials became widely used. Future
developments in this direction seem not unlikely. Cadmium compounds are
used as pigments, particularly as the sulphide "cadmium yellow," and to
give color and luster to glass and porcelain. Cadmium salts are also
variously used in the arts, in medicine, and in electroplating.
Practically the entire cadmium output of the world comes from Germany
and the United States. In addition, England produces a very small
quantity. Before the war Germany produced about two-thirds of the
world's total, and supplied the European as well as a considerable part
of the United States consumption. During the war the United States
production increased three to four fold, imports ceased, and
considerable quantities were exported to the allied nations in Europe
and to Japan. At present the United States is entirely independent as
regards cadmium supplies. Production is sufficient to supply all the
home demand and to permit exports of one-third of the total output. A
considerable number of possible cadmium sources are not being used, and
the production is capable of extension should the need arise.
GEOLOGIC FEATURES
Nearly the only cadmium mineral known is the sulphide, greenockite, but
no deposits of this mineral have been found of sufficient volume to be
called cadmium ores. Sphalerite almost always contains a little cadmium,
probably as the sulphide; and in zinc deposits crystals of sphalerite in
cavities are frequently covered with a greenish-yellow film or coating
of greenockite. These coatings have probably been formed by the
decomposition of cadmium-bearing zinc sulphide in the oxide zone, the
carrying down of the cadmium in solution, and its precipitation as
secondary cadmium sulphide. The zinc oxide minerals in the surficial
zone also are sometimes colored yellow by small amounts of greenockite.
In the zinc ores of the Joplin district of Missouri, cadmium is present
in amounts ranging from a trace to 1 per cent and averaging 0.3 per
cent.
Germany's cadmium is produced by fractional distillation of the Silesian
zinc ores, which contain at most 0.3 per cent cadmium. In the United
States there are large potential sources in the zinc ores of the
Mississippi valley, and considerable cadmium is recovered in roasting
them. Much of the American cadmium is also obtained from bag-house dusts
at lead smelters.
The general geologic conditions of the cadmium-bearing ores are
indicated in the discussion of lead and zinc deposits in an earlier
chapter.
COBALT ORES
ECONOMIC FEATURES
Cobalt finds its largest use in the form of cobalt salts, employed in
coloring pottery and glass and in insect poisons. Cobalt is also used in
some of the best high-speed tool steels. "Stellite," which is used to a
limited extent in non-rusting tools of various sorts, and in
considerable quantity to replace high-speed tool steels, is an alloy of
cobalt, chromium, and small quantities of other metals. Considerable
experimental work has been done on the properties and uses of cobalt
alloys, and their consumption is rapidly on the increase.
Cobalt is an item of commerce of insignificant tonnage. There are only
two countries, Canada (Ontario) and the Belgian Congo, which produce
noteworthy amounts. The Katanga district in the Congo produces blister
copper that contains as much as 4 per cent of cobalt, though usually
less than 2 per cent. This product formerly went to Germany, and now
goes entirely to Great Britain. Just how much cobalt is saved is
unknown, but probably several hundred tons annually. It is probable that
most of the cobalt in these ores will be lost on the installation of a
leaching process for recovery of the copper. Canada exports most of its
product to the United States, though the amount is small. Domestic
production in this country has been too small to record. The United
States has been dependent on imports from Canada.
GEOLOGIC FEATURES
The principal cobalt minerals are smaltite (cobalt arsenide), cobaltite
(cobalt-arsenic sulphide), and linnæite (cobalt-nickel sulphide). Under
weathering conditions these minerals oxidize readily to form asbolite, a
mixture of cobalt and manganese oxides, and the pink arsenate, erythrite
or "cobalt bloom."
Cobalt minerals are found principally in small quantities disseminated
through ores of silver, nickel, and copper. The production of Canada is
obtained mainly as a by-product of the silver ores of the Cobalt
district (described on pp. 234-235), and smaller amounts are recovered
from the Sudbury nickel ores (pp. 180-182). The cobalt of Belgian Congo
is obtained from rich oxidized copper ores which impregnate folded
sediments (p. 205).
MERCURY (QUICKSILVER) ORES
ECONOMIC FEATURES
Uses of mercury are characterized by their wide variety and their
application to very many different phases of modern industry; they will
be named here in general order of decreasing importance. About one-third
of the mercury consumed in this country goes into the manufacture of
drugs and chemicals, such as corrosive sublimate, calomel, and glacial
acetic acid. Mercury fulminate is used as a detonator for high
explosives and to some extent for small-arms ammunition--a use which was
exceedingly important during the war, but is probably of minor
consequence in normal times. Mercuric sulphide forms the brilliant red
pigment, vermilion, and mercuric oxide is becoming increasingly
important in anti-fouling marine paint for ship-bottoms. Either as the
metal or the oxide, mercury is employed in the manufacture of electrical
apparatus (batteries, electrolyzers, rectifiers, etc.), and in the
making of thermostats, gas governors, automatic sprinklers, and other
mechanical appliances. Mercuric nitrate is used in the fabrication of
felt hats from rabbits' fur. In the extraction of gold and silver from
their ores by amalgamation, large amounts of metallic mercury have been
utilized, but of late years the wide application of the cyanide process
has decreased this use. Minor uses include the making of certain
compounds for preventing boiler-scale, of cosmetics, and of dental
amalgam.
The ores of mercury vary greatly in grade. Spanish ores yield an average
in the neighborhood of 7 per cent, Italian ores 0.9 per cent, and
Austrian ores 0.65 per cent of metallic mercury. In the United States
the ores of California yield about 0.4 per cent and those of Texas range
from about 0.5 to 4 per cent. In almost all cases the ores are treated
in the immediate vicinity of the mines, and fairly pure metal is
obtained by a process of sublimation and condensation. This is usually
marketed in iron bottles or flasks containing 75 pounds each.
The large producers of mercury are, in order of normal importance,
Spain, Italy, Austria, and United States. Mexico, Russia, and all other
countries produce somewhat less than 5 per cent of the world's total.
The largest quicksilver mines of the world are those of Almaden in
central Spain, which are owned and operated by the Spanish government.
This government, after reserving a small amount for domestic use, sells
all the balance of the production through the Rothschilds of London. In
addition British capital controls some smaller mines in northern Spain.
England thus largely controls the European commercial situation in this
commodity, and London is the world's great quicksilver market, where
prices are fixed and whence supplies go to all corners of the globe.
Reserves of the Almaden ore bodies are very large. Sufficient ore is
reported to have been developed to insure a future production of at
least 40,000 metric tons--an amount equivalent to the entire world
requirements at pre-war rates of consumption for 100 years.
The mercury deposits of the Monte Amiata district of central Italy were
in large part dominated by German capital, but during the war were
seized by the Italian government. The mines of Idria, Austria-Hungary,
were owned by the Austrian government and their ultimate control is at
present uncertain. Reserves are very large, being estimated at about
one-half those of Almaden. Although England has had a considerable
control over the prices and the market for mercury, the Italian and
Austrian deposits have provided a sufficient amount to prevent any
absolute monopoly. English interests have now secured control of the
Italian production, and it is expected that they will also control the
Austrian production--thus giving England control of something over
three-fourths of the world's mercury.
In the United States about two-thirds of the mercury is produced in the
Coast Range district of California, and most of the remainder in the
Terlingua district of Texas. Smaller quantities come from Nevada,
Oregon, and a few other states. The output before the war was normally
slightly in excess of domestic demand and some mercury was exported to
various countries. Due to the exhaustion of the richer and more easily
worked deposits, however, production was declining. During the war, with
increased demands and higher prices, production was stimulated, the
United States became the largest mercury-producing country in the world,
and large quantities were exported to help meet the military needs of
England and France.
With the end of war prices and with high costs of labor and supplies,
production in the United States has again declined. Many of the mines
have passed their greatest yield, and though discovery of new ore bodies
might revive the industry, production is probably on the down grade.
Future needs of this country will probably in some part be met by
imports from Spain, Italy, and Austria, where the deposits are richer
and labor is cheaper. This situation has caused much agitation for a
tariff on imports. The present tariff of 10 per cent is not sufficient
to keep out foreign mercury.
Outside of the United States large changes in distribution of production
of quicksilver are not expected for some time. The reserves of the
European producers are all large and are ample to sustain present output
for a considerable number of years. It is reported that there will be a
resumption of mining in the once very productive Huancavelica District
of Peru and in Asia Minor, and with restoration of political order there
may be an increase in output from Mexico and Russia,--but these
districts will be subordinate factors in the world situation. On
geologic grounds, new areas of mercury ores may be looked for in regions
of recent volcanic activity, such as the east coast of Asia, some
islands of Oceania, the shores of the Mediterranean, and the Cordilleras
of North and South America,--but no such areas which are likely to be
producers on a large scale are now known.
GEOLOGIC FEATURES
The chief mineral of mercury, from which probably over 95 per cent of
the world's mercury comes, is the brilliant red sulphide, cinnabar.
Minor sources include the black or gray sulphide, metacinnabar, the
native metal, and the white mercurous chloride, calomel. The ores are
commonly associated with more or less iron sulphide, and frequently with
the sulphides of antimony and arsenic, in a gangue consisting largely of
quartz and carbonates (of calcium, magnesium, and iron). The precious
metals and the sulphides of the base metals are rare.
Mercury deposits are in general related to igneous rocks, and have
associations which indicate a particular type of igneous activity. They
are not found in magmatic segregations, in pegmatites, nor in veins
which have been formed at great depths and under very high temperatures.
On the contrary, the occurrence of many deposits in recent flows which
have not been eroded, their general shallow depth (large numbers
extending down only a few hundred feet), and the association of some
deposits with active hot springs now carrying mercury in solution,
suggest an origin through the work of ascending hot waters near the
surface. The mercury minerals are believed to have been carried in
alkaline sulphide solutions. Precipitation from such solutions may be
effected by oxidation, by dilution, by cooling, or by the presence of
organic matter. Being near the surface, it is a natural assumption that
the waters doing the work were not intensely hot. At Sulphur Bank
Springs, in the California quicksilver belt, deposition of cinnabar by
moderately hot waters is actually taking place at present; also these
waters are bleaching the rock in a manner often observed about mercury
deposits.
The Coast Ranges of California contain a great number of mercury
deposits extending over a belt about 400 miles long. The ore bodies are
in fissured zones in serpentine and Jurassic sediments, and are related
in general to recent volcanic flows. A considerable amount of bituminous
matter is found in the ores, and is believed to have been an agent in
their precipitation.
The Terlingua ores of Texas are found in similar fractured zones in
Cretaceous shales and limestones associated with surface igneous flows.
The occurrence of a few ore bodies in vertical shoots in limestone,
apparently terminating upward at the base of an impervious shale,
furnishes an additional argument for their formation by ascending
waters.
In the few deposits (_e. g._, those of Almaden, Spain, and of the deep
mines of New Almaden and New Idria, California,) where there is no such
clear relation to volcanic rocks as generally observed, but where the
ores contain the same characteristic set of minerals, it is concluded
that practically the same processes outlined above have been active in
their formation; and that the volcanic source of the hot solutions
either failed to reach the surface or has been removed by erosion. The
same line of reasoning is carried a step further, and in many
gold-quartz veins in volcanic rocks, where cinnabar and its associated
minerals are present, it is believed that waters of a hot-spring nature
have again been effective. Thus cinnabar, when taken with its customary
associations, is regarded as a sort of geologic thermometer.
In the weathering of mercury deposits, cinnabar behaves somewhat like
the corresponding silver sulphide, argentite. In the oxide zone, native
mercury and the chloride, calomel, are formed. In the Texas deposits a
red oxide and a number of oxychlorides are also present. The carrying
down of the mercury and its precipitation as secondary sulphide may
have taken place in some deposits, but this process is unimportant in
forming values.
TIN ORES
ECONOMIC FEATURES
The largest use of tin is in the manufacture of tin-plate, which is
employed in containers for food, oil, and other materials. Next in
importance is its use in the making of solder and of babbitt or bearing
metal. Tin is also a constituent of certain kinds of brass, bronze, and
other alloys, such as white metal and type metal. Minor uses include the
making of tinfoil, collapsible tubes, wire, rubber, and various
chemicals. Tin oxide is used to some extent in white enameling of metal
surfaces. Roughly a third of the tin consumed within the United States
goes into tin-plate, a third into solder and babbitt metal, and a third
into miscellaneous uses.
The ores of tin in general contain only small quantities of the metal.
Tin has sufficient value to warrant the working of certain placers
containing only a half-pound to the cubic yard, although the usual run
is somewhat higher. The tin content of the vein deposits ranges from
about 1 per cent to 40 per cent, and the average grade is much closer to
the lower figure.
Great Britain has long controlled the world's tin ores, producing about
half of the total and controlling additional supplies in other
countries. The production is in small part in Cornwall, but largely in
several British colonies--the Malay States, central and south Africa,
Australia, and others. The Malay States furnish about a third of the
world's total. Another third is produced in immediately adjacent
districts of the Dutch East Indies, Siam (British control), and China,
and some of the concentrates of these countries are handled by British
smelters, especially at Singapore.
Tin is easily reduced from its ores and most of the tin is smelted close
to the sources of production. Considerable quantities, however, have
gone to England for treatment. London has been the chief tin market of
the world, and before the war the larger portion of the tin entering
international trade went through this port. During the war a good deal
of the export tin from Straits Settlements was shipped direct to
consumers rather than via London, but it is not certain how future
shipments may be made.
Significant features of the tin situation in recent years have been a
decline of production in the Malay States, and a large and growing
production in Bolivia. Malayan output has decreased because of the
exhaustion of some of the richer and more accessible deposits; certain
governmental measures have also had a restrictive effect. Bolivian
production now amounts to over a fifth of the world's total and bids
fair to increase. About half the output is controlled by Chilean, and
small amounts by American, French, and German interests. A large portion
of the Bolivian concentrates formerly went to Germany for smelting, but
during the war American smelters were developed to handle part of this
material; large quantities are also smelted in England.
The United States produces a small fraction of 1 per cent of the world's
tin, and consumes a third to a half of the total. The production is
mainly from the Seward Peninsula of northwestern Alaska. For American
tin smelters, Bolivia is about the only available source of supplies;
metallic tin can be obtained from British possessions, but no ore,
except by paying a 33-1/3 per cent export tax. The United States exports
tin-plate in large amounts, and in this trade has met strong competition
from English and German tin-plate makers.
A world shortage of tin during the war required a division of available
supplies through a central international committee. Somewhat later, with
the removal of certain restrictions on the distribution of tin,
considerable quantities which had accumulated in the Orient found their
way into Europe and precipitated a sensational slump in the tin market.
GEOLOGIC FEATURES
The principal mineral of tin is cassiterite (tin oxide). Stannite, a
sulphide of copper, iron, and tin, is found in some of the Bolivian
deposits but is rare elsewhere.
About two-thirds of the world's tin is obtained from placers and
one-third from vein or "lode" deposits. Over 90 per cent of the tin of
southeastern Asia and Oceania is obtained from placers. Tin placers,
like placers of gold, platinum, and tungsten, represent concentrations
in stream beds and ocean beaches of heavy, insoluble minerals--in this
case chiefly cassiterite--which were present in the parent rocks in
much smaller quantities, but which have been sorted out by the
classifying action of running water.
The original home of cassiterite is in veins closely related to granitic
rocks. It is occasionally found in pegmatites, as in certain small
deposits of the Southern Appalachians and the Black Hills of South
Dakota, or is present in a typical contact-metamorphic silicated zone in
limestone, as in some of the deposits of the Seward Peninsula of Alaska.
In general, however, it is found in well-defined fissure veins in the
outer parts of granitic intrusions and extending out into the
surrounding rocks. With the cassiterite are often found minerals of
tungsten, molybdenum, and bismuth, as well as sulphides of iron, copper,
lead, and zinc, and in some cases there is evidence of a rough zonal
arrangement. The deposits of Cornwall and of Saxony show transitions
from cassiterite veins close to the intrusions into lead-silver veins at
a greater distance. The gangue is usually quartz, containing smaller
amounts of a number of less common minerals--including lithium mica,
fluorite, topaz, tourmaline, and apatite. The wall rocks are usually
strongly altered and in part are replaced by some of the above minerals,
forming coarse-grained rocks which are called "greisen."
The origin of cassiterite veins, in view of their universal association
with granitic rocks, is evidently related to igneous intrusions. The
occurrence of the veins in distinct fissures in the granite and in the
surrounding contact-metamorphic zone indicates that the granite had
consolidated before their formation, and that they represent a late
stage in the cooling. The association with minerals containing fluorine
and boron, and the intense alteration of the wall rocks, indicate that
the temperature must have been very high. It is probable that the
temperature was so high as to cause the solutions to be gaseous rather
than liquid, and that what have been called "pneumatolytic" conditions
prevailed; but evidence to decide this question is not at present
available.
The most important deposits of tin in veins are those of Bolivia, some
of which are exceptionally rich. These are found in granitic rocks
forming the core of the high Cordillera Real and in the adjacent
intruded sediments, in narrow fissure veins and broader brecciated zones
containing the typical ore and gangue minerals described above, and
also, in many cases, silver-bearing sulphides (chiefly tetrahedrite).
There appear to be all gradations in type from silver-free tin ores to
tin-free silver ores, although the extremes are now believed to be rare.
In the main the tin ores, with abundant tourmaline, appear to be more
closely related to the coarse-grained granites, and to indicate intense
conditions of heat and pressure, while the more argentiferous ores, with
very little or no tourmaline, are found in relation to finer-grained
quartz porphyries and even rhyolites, and seem to indicate less intense
conditions at the time of deposition. The ores of the whole area, which
is a few hundred miles long, have been supposed to represent a single
genetic unit, and the sundry variations are believed to be local facies
of a general mineralization. Processes of secondary enrichment have in
places yielded large quantities of oxidized silver minerals and wood tin
near the surface, with accumulations of ruby silver ores at greater
depths.
The only other vein deposits which are at present of consequence are
those of Cornwall. Here batholiths of granite have been intruded into
Paleozoic slates and sandstones, and tin ores occur in fissures and
stockworks in the marginal zones. With the exhaustion of the more easily
mined placers, the lode deposits will doubtless be of increasing
importance.
Cassiterite is practically insoluble and is very resistant to
decomposition by weathering. Oxide zones of tin deposits are therefore
enriched by removal of the more soluble minerals. Stannite probably
alters to "wood tin," a fibrous variety of cassiterite. Secondary
enrichment of tin deposits by redeposition of tin minerals is
negligible.
URANIUM AND RADIUM ORES
ECONOMIC FEATURES
Radium salts are used in various medical treatments--especially for
cancer, internal tumors, lupus, and birth marks--and in luminous paints.
During the latter part of the war it is estimated that over nine-tenths
of the radium produced was used in luminous paints for the dials of
watches and other instruments. In addition part of the material owned by
physicians was devoted to this purpose, and it is probable that the
accumulated stocks held by the medical profession were in this way
reduced by one-half. The greatly extended use of radium, together with
the distinctly limited character of the world's known radium supplies,
has led to some concern; and considerable investigation has been made of
the possibilities of mesothorium as a substitute for radium in luminous
paints. Low-grade radium residues are used to some extent as
fertilizers.
Uranium has been used as a steel alloy, but has not as yet gained wide
favor. Uranium salts have a limited use as yellow coloring agents in
pottery and glass. The principal use of uranium, however, is as a source
of radium, with which it is always associated.
European countries first developed the processes of reduction of radium
salts from their ores. Most of the European ores are obtained from
Austria, where the mines are owned and operated by the Austrian
government, and small quantities are mined in Cornwall, England, and in
Germany. Production is decreasing. The European hospitals and
municipalities have acquired nearly all of the production.
The United States has the largest reserves of radium ore in the world,
and the American market has in recent years been supplied from domestic
plants. Before the war, radium ores were shipped to Europe for treatment
in Germany, France, and England, and radium salts were imported from
these countries. There are now radium plants in the United States
capable of producing annually from domestic ores an amount several times
as large as the entire production of the rest of the world. Practically
all the production has come from Colorado and Utah. Known reserves are
not believed to be sufficient for more than a comparatively few years'
production, but it is not unlikely that additional deposits will be
found in the same area.
GEOLOGIC FEATURES
Uranium is one of the rarer metals. Radium is found only in uranium ores
and only in exceedingly small quantities. The maximum amount which can
be present in a state of equilibrium is about one part of radium in
3,000,000 parts of uranium. The principal sources of uranium and radium
are the minerals carnotite (hydrous potassium-uranium vanadate) and
pitchblende or uraninite (uranium oxide).
The deposits of Joachimsthal, Bohemia, contain pitchblende, along with
silver, nickel, and cobalt minerals and other metallic sulphides, in
veins associated with igneous intrusions.
The important commercial deposits of Colorado and Utah contain
carnotite, together with roscoelite (a vanadium mica) and small amounts
of chromium, copper, and molybdenum minerals, as impregnations of
flat-lying Jurassic sandstones. The ores carry up to 35 per cent uranium
oxide (though largely below 2 per cent), and from one-third as much to
an equal amount of vanadium oxide. The ore minerals are supposed to have
been derived from a thick series of clays and impure sandstones a few
hundred feet above, containing uranium and vanadium minerals widely
disseminated, and to have been carried downward by surface waters
containing sulphates. The ore bodies vary from very small pockets to
deposits yielding a thousand tons or so, and are found irregularly
throughout certain particular beds without any special relation to
present topography or to faults. The association of many of the deposits
with fossil wood and other carbonaceous material suggests that organic
matter was an agent in their precipitation, but the exact nature of the
process is not clear. In a few places in Utah the beds dip at steep
angles, and the carnotite appears in spots along the outcrops and
generally disappears as the outcrops are followed into the hillsides;
this suggests that the carnotite may be locally redissolved and carried
to the surface by capillary action, forming rich efflorescences. Because
of the nature of the deposits no large amount of ore is developed in
advance of actual mining; but estimates based on past experience
indicate great potentialities of this region for future production.
In eastern Wyoming is a unique deposit of uranium ore in a quartzite
which lies between mica-schist and granite. The principal ore mineral is
uranophane, a hydrated calcium-uranium silicate, which is believed to be
an oxidation product of pitchblende. Some of the ore runs as high as 4
per cent uranium oxide, and the ore carries appreciable amounts of
copper but very little vanadium.
Very recently radium ores have been discovered in the White Signal
mining district of New Mexico, which was formerly worked for gold,
silver, copper, and lead. The radium-bearing minerals are torbernite and
autunite (hydrous copper-uranium and calcium-uranium phosphates), and
are found in dark felsite dikes near their intersections with east-west
gold-silver-quartz veins. The possibilities of this district have not
yet been determined.
Pitchblende has been found in gold-bearing veins in Gilpin County,
eastern Colorado, and in pegmatite dikes in the Appalachians, but these
deposits are of no commercial importance. Pitchblende is grayish-black,
opaque, and so lacking in distinctive characteristics that it may
readily be overlooked; hence future discoveries in various regions would
not be surprising.
CHAPTER XIII
MISCELLANEOUS NON-METALLIC MINERALS
NATURAL ABRASIVES
ECONOMIC FEATURES
Natural abrasives are less important commercially in the United States
than artificial abrasives, but a considerable industry is based on the
natural abrasives.
Silica or quartz in its various crystalline forms constitutes over
three-fourths of the tonnage of natural abrasives used in the United
States. It is the chief ingredient of sand, sandstone, quartzite, chert,
diatomaceous earth, and tripoli. From the sand and sandstone are made
millstones, buhrstones, grindstones, pulpstones, hones, oilstones, and
whetstones. Sand, sandstone, and quartzite are also ground up and used
in sand-blasts, sandpaper, and for other abrasive purposes. Chert or
flint constitutes grinding pebbles and tube-mill linings, and is also
ground up for abrasives. Diatomaceous (infusorial) earth is used as a
polishing agent and also as a filtering medium, an absorbent, and for
heat insulation. Tripoli (and rottenstone) are used in polishing powders
and scouring soaps as well as for filter blocks and many other purposes.
Other important abrasives are emery and corundum, garnet, pumice,
diamond dust and bort, and feldspar.
Imports of abrasive materials into the United States have about
one-third of the value of those locally produced. While all of the
various abrasives are represented in these imports, the United States is
dependent on foreign sources for important parts of its needs only of
emery and corundum, garnet, pumice, diamond dust and bort, and grinding
pebbles.
Emery and corundum are used in various forms for the grinding and
polishing of hard materials--steel, glass, stone, etc. The principal
foreign sources of emery have been Turkey (Smyrna) and Greece (Naxos)
where reserves are large and production cheap. Production of corundum
has come from Canada, South Africa, Madagascar, and India. The domestic
production of emery is mainly from New York and Virginia, and corundum
comes from North Carolina. Domestic supplies are insufficient to meet
requirements, and cannot be substituted for the foreign material for the
polishing of fine glass and other special purposes. Curtailment of
imports during the war greatly stimulated the development of artificial
abrasives and their substitution for emery and corundum.
Garnet is used chiefly in the form of garnet paper for working leather,
wood, and brass. Garnet is produced mainly in the United States and
Spain. The United States is the only country using large amounts of this
mineral and imports most of the Spanish output. The domestic supply
comes mainly from New York, New Hampshire, and North Carolina.
Pumice is used in fine finishing and polishing of varnished and enameled
surfaces, and in cleaning powders. The world's principal source for
pumice is the Lipari Islands, Italy. There is a large domestic supply of
somewhat lower-grade material (volcanic ash) in the Great Plains region,
and there are high-grade materials in California and Arizona. Under war
conditions these supplies were drawn on, but normally the high-quality
Italian pumice can be placed in American markets more cheaply.
Diamond dust is used for cutting gem stones and other very hard
materials, and borts or carbonadoes (black diamonds) for
diamond-drilling in exploration. Most of the black diamonds come from
Brazil, and diamond dust comes from South Africa, Brazil, Borneo, and
India.
Chert or flint pebbles for tube-mills are supplied mainly from the
extensive deposits on the French and Danish coasts. The domestic
production has been small, consisting principally of flint pebbles from
the California beaches, and artificial pebbles made from rhyolite in
Nevada and quartzite in Iowa. War experience demonstrated the
possibility of using the domestic supply in larger proportion, but the
grade is such that in normal times this supply will not compete with
importations.
Feldspar as an abrasive is used mainly in scouring soaps and
window-wash. Domestic supplies are ample. The principal use of feldspar
is in the ceramic industry and the mineral is discussed at greater
length in the chapter on common rocks (p. 86).
For the large number of abrasives produced from silica, outside of flint
pebbles, domestic sources of production are ample. Siliceous rocks are
available almost everywhere. For particular purposes, however, rocks
possessing the exact combinations of qualities which make them most
suitable are in many cases distinctly localized. _Millstones and
buhrstones_, used for grinding cereals, paint ores, cement rock,
fertilizers, etc., are produced chiefly in New York and Virginia; partly
because of trade prejudice and tradition, about a third of the American
requirements are imported from France, Belgium, and Germany.
_Grindstones and pulpstones_, used for sharpening tools, grinding
wood-pulp, etc., come mainly from Ohio and to a lesser extent from
Michigan and West Virginia; about 5 per cent of the consumption is
imported from Canada and Great Britain. _Hones_, _oilstones_, and
_whetstones_ are produced largely from a rock called "novaculite" in
Arkansas, and also in Indiana, Ohio, and New England; imports are
negligible. _Flint linings_ for tube-mills were formerly imported from
Belgium, but American products, developed during the war in
Pennsylvania, Tennessee, and Iowa, appear to be wholly satisfactory
substitutes. _Diatomaceous earth_ is produced in California, Nevada,
Connecticut, and Maryland, and _tripoli and rottenstone_ in Illinois,
Missouri, and Oklahoma; domestic sources are sufficient for all needs,
but due to questions of back-haul and cost of rail transportation there
has been some importation from England and Germany.
GEOLOGIC FEATURES
The geologic features of silica (quartz), feldspar, and diamonds are
sufficiently indicated elsewhere (Chapter II; pp. 84, 196, 86, 291-292).
Diatomaceous earth is made up of remains of minute aquatic plants. It
may be loose and powdery, or coherent like chalk. It is of sedimentary
origin, accumulated originally at the bottoms of ponds, lakes, and in
the sea.
Tripoli and rottenstone are light, porous, siliceous rocks which have
resulted from the leaching of calcareous materials from various
siliceous limestones or calcareous cherts in the process of weathering.
Grinding pebbles are derived from the erosion of limestone or chalk
formations which contain concretions of extremely fine-grained and dense
chert. Under stream and wave action they are rounded and polished. The
principal sources are ocean beaches.
Corundum as an abrasive is the mineral of this name--made up of
anhydrous aluminum oxide. Emery is an intimate mechanical mixture of
corundum, magnetite, and sometimes spinel. Corundum is a product of
contact metamorphism and also a result of direct crystallization from
molten magma. Canadian corundum occurs as a constituent of syenite and
nepheline-syenite in Lower Ontario. In North Carolina and Georgia, the
corundum occurs in vein-like bodies at the contact of peridotite with
gneisses and schists, and also in part in the peridotite itself. In New
York the emery deposits are segregations of aluminum and iron oxides in
norite (a basic igneous rock). The emery of Greece and Turkey occurs as
lenses or pockets in crystalline limestones, and is the result of
contact metamorphism by intrusive granites.
Garnets result mainly from contact metamorphism, and commonly occur
either in schists and gneisses or in marble. The principal American
occurrences are of this type. Being heavy and resistant to weathering,
they are also concentrated in placers. The Spanish garnets are reported
to be obtained by washing the sands of certain streams.
Pumice is solidified rock froth formed by escape of gases from molten
igneous rocks at the surface. It is often closely associated with
volcanic ash, which is also used for abrasive purposes.
In general, the geologic processes entering into the formation of
abrasives cover almost the full range from primary igneous processes to
surface alterations and sedimentation.
ASBESTOS
ECONOMIC FEATURES
The principal uses of asbestos are in high-pressure packing in heat
engines, in thermal and electrical insulation, in fire-proofing, and in
brake-band linings.
The largest producers of asbestos are Canada (Quebec) and, to a
considerably less extent, Russia. United States interests have financial
control of about a fourth of the Canadian production, and practically
the entire export trade of Canada goes to the United States. Russia
exports nearly all her product to Germany, Austria, United Kingdom,
Belgium, and the Netherlands. Previous to the war the output was largely
controlled by a German syndicate. There is a considerable recent
production in South Africa, which is taken by England and the United
States, and small amounts are produced in Italy, Cyprus, and Australia.
The United States has been a large importer of asbestos, from Canada and
some other sources. Domestic production is relatively insignificant, and
exports depend chiefly on an excess of import. Georgia is the principal
local source. Arizona and California are also producers, their product
being of a higher grade. The United States is the largest manufacturer
of asbestos goods, and exports go to nearly all parts of the world.
So long as the abundant Canadian material is accessible on reasonable
conditions, the United States is about as well situated as if
independent. Some Canadian proposals of restriction during the war led
to a study of other supplies and showed that several deposits, such as
those in Russia and Africa, might compete with the Canadian asbestos.
GEOLOGIC FEATURES
Asbestos consists mostly of magnesium silicate minerals--chrysotile,
anthophyllite, and crocidolite. The term asbestos covers all fibrous
minerals with some tensile strength which are poor conductors and can be
used for heat-protection. Like talc, they are derived principally from
the alteration of olivine, pyroxene, and amphibole,--or more commonly
from serpentine, which itself results from the alteration of these
minerals. Chrysotile is the most common, and because of the length,
fineness, and flexibility of its fibers, enabling it to be spun into
asbestos ropes and fabrics, it is the most valuable. Anthophyllite
fibers, on the other hand, are short, coarse, and brittle, and can be
used only for lower-grade purposes. Crocidolite or blue asbestos is
similar to chrysotile but somewhat inferior in fire-resisting qualities.
Asbestos deposits occur chiefly as veinlets in serpentine rock, which is
itself the alteration of some earlier rock like peridotite. They are
clearly formed in cracks and fissures through the agency of water, but
whether the waters are hot or cold is not apparent. The veinlets have
sometimes been interpreted as fillings of contraction cracks, but more
probably are due to recrystallization of the serpentine, proceeding
inward from the cracks. In Quebec the chrysotile asbestos (which is
partly of spinning and partly of non-spinning grade) forms irregular
veins of this nature in serpentine, the fiber making up 2 to 6 per cent
of the rock.
In Georgia the asbestos, which is anthophyllite, occurs in lenticular
masses in peridotite associated with gneiss. It is supposed to have
formed by the alteration of olivine and pyroxene in the igneous rocks.
In Arizona chrysotile is found in veins in cherty limestone, associated
with diabase intrusives. Here it is believed to be an alteration product
of diopside (lime-magnesia pyroxene) in a contact-metamorphic silicated
zone.
Crocidolite is mined on a commercial scale only in Cape Colony, South
Africa. The deposits occur in thin sedimentary layers interbedded with
jaspers and ironstones. Their origin has not been worked out in detail.
The deposits of Russia, the Transvaal, Rhodesia, and Australia are of
high-grade chrysotile, probably similar in origin to the Quebec
deposits. The asbestos of Italy and Cyprus is anthophyllite, more like
the Georgia material.
BARITE (BARYTES)
ECONOMIC FEATURES
Barite is used chiefly as a material for paints. For this purpose it is
employed both in the ground form and in the manufacture of lithopone, a
widely used white paint consisting of barium sulphate and zinc sulphide.
Ground barite is also used in certain kinds of rubber goods and in the
making of heavy glazed paper. Lesser amounts go into the manufacture of
barium chemicals, which are used in the preparation of hydrogen
peroxide, in softening water, in tanning leather, and in a wide variety
of other applications.
Germany is the world's principal producer of barite and has large
reserves of high grade. Great Britain also has extensive deposits and
produces perhaps one-fourth as much as Germany. France, Italy, Belgium,
Austria-Hungary, and Spain produce smaller but significant amounts.
Before the war the United States imported from Germany nearly half the
barite consumed in this country, and produced the remainder. Under the
necessities of war times, adequate domestic supplies were developed and
took care of nearly all the greatly increased demands. Production has
come from fourteen states, the large producers being Georgia, Missouri,
and Tennessee. During the war, also, an important movement of
barite-consuming industries to the middle west took place, in order to
utilize more readily and cheaply the domestic product. For this reason
it is not expected that German barite will play as important a part as
formerly in American markets,--although it can undoubtedly be put down
on the Atlantic seaboard much more cheaply than domestic barite, which
requires long rail hauls from southern and middle-western states.
GEOLOGIC FEATURES
The mineral barite is a heavy white sulphate of barium, frequently
called "barytes" or "heavy spar." Witherite, the barium carbonate, is a
much rarer mineral but is found with barite in some veins.
All igneous rocks contain at least a trace of barium, which is probably
present in the silicates, and these small quantities are the ultimate
source of the more concentrated deposits. Barite itself is not found as
an original constituent of igneous rocks or pegmatites, but is
apparently always formed by deposition from aqueous solutions. It is a
common gangue mineral in many deposits of metallic sulphides, both those
formed in relation to igneous activity and those which are independent
of such activity, but in these occurrences it is of little or no
commercial importance.
The principal deposits of barite are found in sedimentary rocks, and
especially in limestones and dolomites. In these rocks it occurs in
veins and lenses very similar in nature to the lead and zinc deposits of
the Mississippi valley (p. 211 _et seq._), and, like them, probably
deposited by cold solutions which gathered together small quantities of
material from the overlying or surrounding rocks. The Missouri deposits
are found in limestones in a region not far from the great southeastern
Missouri lead district, and vary from the lead deposits in relative
proportions rather than in kind of minerals; the veins consist chiefly
of barite, with minor quantities of silica, iron sulphide, galena, and
sphalerite. The deposits of the southern Appalachians occur as lenses in
limestones and schists.
Barite is little affected by surface weathering, and tends to remain
behind while the more soluble minerals of the associated rock are
dissolved out and carried away. A limited amount of solution and
redeposition of the barite takes place, however, resulting in its
segregation into nodules in the residual clays. Most of the barite
actually mined comes from these residual deposits, which owe their
present positions and values to katamorphic processes. The accompanying
clay and iron oxide are removed by washing and mechanical concentration.
Certain investigators of the deposits of the Mississippi valley are
extremely reluctant to accept the idea that the ores are formed by
surface waters of ordinary temperatures, and are inclined to appeal to
heated waters from a hypothetical underlying magmatic source. The fact
that barite is a characteristic mineral of many igneous veins, and the
fact that in this same general region it is found in the
Kentucky-Illinois fluorspar deposits,--where a magmatic source is
generally accepted,--together with doubts as to the theoretical efficacy
of meteoric waters to transport the minerals found in the barite
deposits, have led certain writers to ascribe to these barite deposits a
magmatic origin. The magmatic theory has not been disproved; but on the
whole the balance of evidence seems strongly to indicate that the barite
deposits as well as the lead and zinc ores, which are essentially the
same in nature though differing in mineral proportions, have been
concentrated from the adjacent sediments by ordinary surface waters.
BORAX
ECONOMIC FEATURES
Borax-bearing minerals are used almost entirely in the manufacture of
borax and boric acid. Fully a third of the borax consumed in the United
States is used in the manufacture of enamels or porcelain-like coatings
for such objects as bathtubs, kitchen sinks, and cooking utensils. Other
uses of borax or of boric acid are as a flux in the melting and
purification of the precious metals, in decomposing chromite, in making
glass, as a preservative, as an antiseptic, and as a cleansing agent.
Recent developments indicate that the metal, boron, may play an
important part in the metallurgy of various metals. It has been used in
making very pure copper castings for electrical purposes, in aluminum
bronzes, and in hardening aluminum castings; and an alloy, ferroboron,
has been shown experimentally to act on steel somewhat like
ferrovanadium.
The bulk of the world's borax comes from the Western Hemisphere, the
United States and Chile being the two principal producers. There are
additional large deposits in northern Argentina, southern Peru, and
southern Bolivia, which have thus far been little drawn on because of
their inaccessibility. English financial interests control most of these
South American deposits.
The only large European producer of borax is Turkey. Italy and Germany
produce small amounts. There has also been small production of borax in
Thibet, brought out from the mountains on sheep-back.
The United States supplies of borax are sufficient for all domestic
requirements and probably for export. Small quantities of boric acid are
imported, but no borax in recent years. The domestic production comes
entirely from California, though in the past deposits in Nevada and
Oregon have also been worked.
GEOLOGIC FEATURES
The element boron is present in various complex boro-silicates, such as
datolite and tourmaline, the latter of which is used as a precious stone
(pp. 290, 293). None of these are commercial sources of borax. The
principal boron minerals are borax or "tincal" (hydrated sodium borate),
colemanite (hydrated calcium borate), ulexite (hydrated calcium-sodium
borate), and boracite (magnesium chloro-borate). Commercially the term
borax is sometimes applied to all these materials. These minerals appear
in nature under rather widely differing modes of origin.
The borax production of Italy is obtained from the famous "soffioni" or
"fumaroles" of Tuscany. These are volcanic exhalations, in which jets of
steam carrying boric acid and various borates, together with ammonium
compounds, emerge from vents in the ground. The boric acid material is
recovered by a process of condensation.
Borates, principally in the form of borax, occur in hot springs and in
lakes of volcanic regions. The Thibet deposits, and those formerly
worked at Borax Lake, California, are of this type. Certain of the
hot-spring waters of the California coast ranges and of Nevada carry
considerable quantities of boron, together with ammoniacal salts, and in
some places they deposit borax along with sulphur and cinnabar. It seems
probable (see p. 40) that these waters may come from an igneous source
not far beneath.
Most of the borax deposits of California, Nevada, and Oregon, though not
at present the largely producing ones, and probably most of the Chilean
and adjacent South American deposits, are formed by the evaporation of
desert lakes. They are products of desiccation, and in Chile are
associated with the great nitrate deposits (pp. 102-104), which are of
similar origin. The salts contained in these deposits are mainly borax,
ulexite, and colemanite. The sources of these materials are perhaps
deposits of the type mentioned in the last paragraph, or, in California,
certain Tertiary borate deposits described below. Whatever their source,
the borates are carried in solution by the waters of occasional rains to
shallow basins, which become covered with temporary thin sheets of water
or "playa lakes." Evaporation of these lakes leaves broad flats covered
with the white salts. These may subsequently be covered with drifting
sands and capillary action may cause the borates to work up through the
sands, becoming mixed with them and efflorescing at the surface. One of
the largest of the California deposits of this general class is that at
Searles Lake, from which it has been proposed to recover borax along
with the potash (pp. 113-114).
The deposits which at present constitute the principal source of
domestic borax are not the playa deposits just described, but are masses
of colemanite in Tertiary clays and limestones with interbedded basaltic
flows. The principal deposits are in Death Valley and adjacent parts of
California. The colemanite occurs in irregular milky-white layers or
nodules, mingled with more or less gypsum. The deposits are believed to
be of the replacement type, rather than ones formed contemporaneously
with the sediments. Whether they are due to magmatic solutions carrying
boric acid from the associated flows, or to surface waters carrying
materials leached from other sediments, is not clear. The crude
colemanite as mined carries an average of about 25 per cent B_2O_3; it
is treated with soda in the manufacture of borax, or with sulphuric acid
in making boric acid.
Boron is present in minute quantities in sea water. When such water
evaporates, it becomes concentrated, along with the magnesium and
potassium salts, in the "mother liquor"; and upon complete evaporation,
it crystallizes out as boracite and other rarer minerals. Thus the
Stassfurt salts of Germany (p. 113) contain borates of this type in the
carnallite zone of the upper part of the deposits. This is the only
important case known of borate deposits of marine origin.
BROMINE
ECONOMIC FEATURES
Bromine finds a considerable use in chemistry as an oxidizing agent, in
separating gold from other metals, and in manufacturing disinfectants,
bromine salts, and aniline colors. The best known and most widely used
bromine salts are the silver bromide, used in photography, and the
potassium bromide, used in medicine to depress the nervous system.
During the war, large quantities of bromine were used in asphyxiating
and lachrymating gases.
The chief center of the bromine industry in Europe prior to 1914 was
Stassfurt, Germany. No other important commercial source in foreign
countries is known, though small quantities have been obtained from the
mother liquors of Chile saltpeter and from the seaweed, kelp, in various
countries. India has been mentioned as a possible large producer in the
future.
The United States is independent of foreign sources for bromine. The
entire domestic tonnage is produced from brines pumped in Michigan,
Ohio, West Virginia, and Pennsylvania. A large part of the output is not
actually marketed as bromine, but in the form of potassium and sodium
bromides and other salts. During the war considerable quantities of
bromine materials were exported to Great Britain, France, and Italy.
GEOLOGIC FEATURES
Bromine is very similar chemically to chlorine, and is found under much
the same conditions, though usually in smaller quantities. The natural
silver bromide (bromyrite) and the combined silver chloride and bromide
(embolite) are fairly common in the oxide zones of silver ores, but are
not commercial sources of bromine.
Bromine occurs in sea water in appreciable amounts, as well as in some
spring waters and many natural brines. When natural salt waters
evaporate, bromine is one of the last materials to be precipitated, and
the residual "mother liquors" or bitterns frequently show a considerable
concentration of the bromine. Where complete evaporation takes place, as
in the case of the Stassfurt salt deposits (p. 113), the bromine salts
are crystallized out in the final stages along with the salts of sodium,
magnesium, and potassium. The larger part of the world's bromine has
come from the mother liquor resulting from the solution and fractional
evaporation of these Stassfurt salts.
The bromine obtained from salt deposits in the eastern United States is
doubtless of a similar origin. It is produced as a by-product of the
salt industry, the natural or artificial brines being pumped from the
rocks (p. 295), and the bromides being extracted either from the mother
liquors or directly from the unconcentrated brines.
FULLER'S EARTH
ECONOMIC FEATURES
Fuller's earth is used chiefly for bleaching, clarifying, or filtering
mineral and vegetable oils, fats, and greases. The petroleum industry is
the largest consumer. Minor uses are in the manufacture of pigments for
printing wall papers, in detecting coloring matters in certain
food-products, and as a substitute for talcum powder.
Fuller's earths are in general rather widely distributed. The principal
producers are the United States, England, and the other large consuming
countries of Europe. The only important international trade in this
commodity consists of exports from the United States to various
countries for treating mineral oils, and exports from England for
treating vegetable oils.
There is a large surplus production in the United States of fuller's
earth of a grade suitable for refining mineral oils, but an inadequate
production of material for use in refining edible oils, at least by
methods and equipment now in most general use. However, the imports
needed from England are more than offset by our exports to Europe of
domestic earth particularly adapted to the petroleum industry.
Production in the United States comes almost entirely from the southern
states; Florida produces over three-fourths of the total and other
considerable producers are Texas, Georgia, California, and Arkansas.
Imports from England are normally equivalent to about a third of the
domestic production.
GEOLOGIC FEATURES
Fuller's earth is essentially a variety of clay having a high absorptive
power which makes it useful for decolorizing and purifying purposes.
Fuller's earths are in general higher in water content and have less
plasticity than most clays, but they vary widely in physical and
chemical properties. Chemical analyses are of little value in
determining whether a given clay will serve as fuller's earth, and an
actual test is the only trustworthy criterion.
Deposits of fuller's earth may occur under the same variety of
conditions as deposits of other clays. The deposits of Florida and
Georgia consist of beds in slightly consolidated flat-lying Tertiary
sediments, which are worked by open cuts. The Arkansas deposits are
residual clays derived from the weathering of basic igneous rocks, and
are worked through shafts.
GRAPHITE (PLUMBAGO)
ECONOMIC FEATURES
_Crystalline graphite_ is used principally in the manufacture of
crucibles for the melting of brass, bronze, crucible steel, and
aluminum. About 45 per cent of the quantity and 70 per cent of the value
of all the graphite consumed in the United States is employed in this
manner. Both _crystalline_ and _amorphous graphite_ are used in
lubricants, pencils, foundry facings, boiler mixtures, stove-polishes
and paint, electrodes, and fillers or adulterants for fertilizers. The
most important use of amorphous graphite is for foundry facings, this
application accounting for about 25 per cent of the total United States
consumption of graphite of all kinds. _Artificial graphite_ is not
suitable for crucibles or pencils but is adapted to meet other uses to
which natural graphite is put. It is particularly adapted to the
manufacture of electrodes.
The grade of graphite deposits varies widely, their utilization being
largely dependent on the size of the grains and the ease of
concentration. Some of the richest deposits, those of Madagascar,
contain 20 per cent or more of graphite. The United States deposits
contain only 3 to 10 per cent. The graphite situation is complicated by
the differences in the quality of different supplies. Crucibles require
coarsely crystalline graphite, but pencils, lubricants, and foundry
facings may use amorphous and finely crystalline material.
The largest production of high-grade crucible graphite has come from
Ceylon, under British control, and about two-thirds of the output has
come to the United States. The mines are now worked down to water-level
and costs are increasing.
In later years a rival supply has come from the French island of
Madagascar, where conditions are more favorable to cheap production, and
where reserves are very large. French, British, and Belgian interests
are concerned in the development of these deposits. The quality of
graphite is different from the Ceylon product; it has not found favor in
the United States but is apparently satisfactory to crucible makers in
Europe. Most of the output is exported to Great Britain and France, and
smaller amounts to Germany and Belgium.
Less satisfactory supplies of crystalline graphite are available in many
countries, including Bavaria, Canada, and Japan. Large deposits of
crystalline material have been reported in Greenland, Brazil, and
Roumania, but as yet have assumed no commercial importance.
Amorphous graphite is widely distributed, being produced in about twenty
countries,--chiefly in Austria, Italy, Korea, and Mexico. Certain
deposits have been found to be best for special uses, but most countries
could get along with nearby supplies.
A large part of the world's needs of crucible graphite will probably
continue to be met from Ceylon and Madagascar, while a large part of
the amorphous graphite will come from the four sources mentioned.
The United States has been largely dependent upon importations from
Ceylon for crucible graphite. Domestic supplies are large and capable of
further development, but for the most part the flake is of such quality
that it is not desired for crucible manufacture without large admixture
of the Ceylon material. Restrictions during the war required crucible
makers to use at least 20 per cent of domestic or Canadian graphite in
their mixtures, with 80 per cent of foreign graphite. This created a
demand for domestic graphite which caused an increased domestic output.
Most of the production in the United States comes from the Appalachians,
particularly from Alabama, New York, and Pennsylvania, and smaller
amounts are obtained from California, Montana, and Texas. One of the
permanently beneficial effects of the war was the improvement of
concentrating practice and the standardization of output, to enable the
domestic product to compete more effectively with the well-standardized
imported grades. Whether the domestic production will hold its own with
foreign competition under peace conditions remains to be seen. Domestic
reserves are large but of low grade.
The Madagascar graphite, in the shape and size of the flakes, is more
like the American domestic graphite than the Ceylon product. Small
amounts have been used in this country, but American consumers appear in
general to prefer the Ceylon graphite in spite of its greater cost. The
Madagascar product can be produced and supplied to eastern United States
markets much more cheaply than any other large supply; and, in view of
the possible exhaustion of the Ceylon deposits, it may be desirable for
American users to adapt crucible manufacture to the use of Madagascar
material as has already apparently been done in Europe.
Expansion of the American graphite industry during the war, and its
subsequent collapse, have resulted in agitation for a duty on imports of
foreign graphite.
Amorphous graphite is produced from some deposits in the United States
(Colorado, Nevada, and Rhode Island), but the high quality of Mexican
graphite, which is controlled by a company in the United States, makes
it likely that imports from this source will continue. Since the war the
Mexican material has practically replaced the Austrian graphite in
American markets. The output of Korea is divided between the United
States and England.
Artificial graphite, in amounts about equal to the domestic production
of amorphous graphite, is produced from anthracite or petroleum coke at
Niagara Falls.
GEOLOGIC FEATURES
The mineral graphite is a soft, steel-gray, crystalline form of carbon.
Ceylon graphite occurs in veins and lenses cutting gneisses and
limestones. Usually the veins consist almost entirely of graphite, but
sometimes other minerals occur in important amounts, especially pyrite
and quartz. The association of graphite with these minerals, and also
with feldspar, pyroxene, apatite, and other minerals, suggests that the
veins are of igneous origin, like some of the pegmatite veins in the
Adirondacks of New York. The graphite is mined from open pits and
shafts, and sorted by hand and mechanically. The product consists of
angular lumps or chips with a relatively small amount of surface in
proportion to their volume.
In Madagascar the graphite is mainly disseminated in a graphitic schist,
though to some extent it is present in the form of veins and in gneiss.
Most of the graphite is mined from a weathered zone near the surface,
and the material is therefore soft and easily concentrated. The product
is made up of flakes or scales, and in the making of crucibles requires
the use of larger amounts of clay binder than the Ceylon graphite.
The flake graphite of the United States, principally in the Appalachian
region, occurs in crystalline graphitic schists, resulting from the
anamorphism of sedimentary rocks containing organic matter. Certain beds
or zones of comparatively narrow width carry from 3 to 10 per cent of
disseminated graphite. The graphite is recovered by mechanical processes
of sorting. The graphite is believed to be of organic origin, the change
from organic carbon to graphite having been effected by heat and
pressure accompanying mountain-building stresses. Some of the graphite
also occurs in pegmatite intrusives and adjacent wall rocks. This
graphite is considered to be of inorganic origin, formed by the breaking
up of gaseous oxides of carbon in the original magma of the pegmatites.
The Montana graphite is similar in origin. This inorganic graphite in
pegmatite veins resembles Ceylon graphite, in breaking into large lumps
and chips, but supplies are very limited.
Amorphous graphite is formed in many places where coal and other
carbonaceous materials have undergone extreme metamorphism. It
represents simply a continuation in the processes by which high grade
coals are formed from plant matter (pp. 123-127). The Mexican deposits
are of this type, and occur in beds up to 24 feet in thickness
interbedded with metamorphosed sandstones.
In general, graphite is primarily concentrated both by igneous processes
in dikes, and by sedimentary processes in beds. In the latter case
anamorphism is necessary to recrystallize the carbon into the form of
graphite.
GYPSUM
ECONOMIC FEATURES
The principal use of gypsum is in structural materials. About two-thirds
of the gypsum produced in the United States is used in the manufacture
of various plasters--wall plaster, plaster of Paris, and Keene's cement
(for statuary and decorative purposes),--and about a fifth is used as a
retarder in Portland cement. Another important structural use is in the
manufacture of plaster boards, blocks, and tile for interior
construction. Gypsum is used as a fertilizer under the name of "land
plaster," and with the growing recognition of the lack of sulphur in
various soils an extension of its application is not unlikely. Minor
uses are in the polishing of plate glass, in the manufacture of dental
plaster, in white pigments, in steampipe coverings, and as a filler in
cotton goods.
The world's gypsum deposits are widely distributed. Of foreign
countries, France, Canada, and the United Kingdom are the principal
producers. Germany, Algeria, and India produce comparatively meager
amounts. The United States is the largest producer of gypsum in the
world. In spite of its large production, the United States normally
imports quantities equivalent to between one-fifteenth and one-tenth of
the domestic production, mainly in the crude form from Nova Scotia and
New Brunswick for consumption by the mills in the vicinity of New York.
This material is of a better grade than the eastern domestic supply,
and is cheaper than the western supply for eastern consumption. During
the war this importation was practically stopped because of governmental
requisition of the carrying barges for the coal-carrying trade, but with
the return of normal conditions it was resumed. There is no prospect of
importation of any considerable amount from any other sources. The
domestic supply is ample for all demands.
Production of gypsum in the United States comes from eighteen states.
Four-fifths of the total comes from New York, Iowa, Michigan, Ohio,
Texas, and Oklahoma. There are extensive deposits in some of the western
states, the known reserves in Wyoming alone being sufficient for the
entire world demands for many decades.
The United States exports a small amount of crude gypsum to Canada,
principally for use in Portland cement manufacture. This exportation is
due to geographic location. The United States is the largest
manufacturer of plaster boards, insulating materials, and tile, and
exports large quantities of these products to Cuba, Australia, Japan,
and South America.
GEOLOGIC FEATURES
Gypsum is a hydrated calcium sulphate. It is frequently associated with
minor quantities of anhydrite, which is calcium sulphate without water,
and under the proper natural conditions either of these materials may be
changed into the other.
Common impurities in gypsum deposits include clay and lime carbonate,
and also magnesia, silica, and iron oxide. In the material as extracted,
impurities may range from a trace to about 25 per cent. _Gypsite_, or
gypsum dirt, is an impure mixture of gypsum with clay or sand found in
Kansas and some of the western states; it is believed to have been
produced in the soil or in shallow lakes, by spring waters carrying
calcium sulphate which was leached from gypsum deposits or from other
rocks.
Gypsum deposits, like deposits of common salt, occur in beds which are
the result of evaporation of salt water. Calcium makes up a small
percentage of the dissolved material in the sea, and when sea waters are
about 37 per cent evaporated it begins to be precipitated as calcium
sulphate. Conditions for precipitation are especially favorable in arid
climates, in arms of the sea or in enclosed basins which may or may not
once have been connected with the sea. Simultaneously with the
deposition of gypsum, there may be occasional inwashings of clay and
sand, and with slight changes of conditions organic materials of a limey
nature may be deposited. Further evaporation of the waters may result in
the deposition of common salt. Thus gypsum beds are found interbedded
with shales, sandstones, and limestones, and frequently, but not always,
they are associated with salt beds. The nature of these processes is
further discussed under the heading of salt (pp. 295-298).
The anhydrite found in gypsum deposits is formed both by direct
precipitation from salt water and by subsequent alteration of the
gypsum. The latter process involves a reduction of volume, and
consequently a shrinkage and settling of the sediments. The hydration of
anhydrite to form gypsum, on the other hand, involves an increase of
volume and may result in the doming up and shattering of the overlying
sediments.
Gypsum is fairly soluble in ground-water, and sink-holes and solution
cavities are often developed in gypsum deposits. These may allow the
inwash of surface dirt and also may interfere with the mining.
All the important commercial gypsum deposits are believed to have been
formed by evaporation of salt water in the manner indicated. Small
quantities of gypsum are formed also when pyrite and other sulphides
oxidize to sulphuric acid and this acid acts on limestone. Thus gypsum
is found in the oxide zones of some ore bodies. These occurrences are of
no commercial significance.
MICA
ECONOMIC FEATURES
The principal use of sheet mica is for insulating purposes in the
manufacture of a large variety of electrical equipment. The highest
grades are employed particularly in making condensers for magnetos of
automobile and airplane engines and for radio equipment, and in the
manufacture of spark plugs for high tension gas engines. Sheet mica is
also used in considerable amounts for glazing, for heat insulation, and
as phonograph diaphragms. Ground mica is used in pipe and boiler
coverings, as an insulator, in patent roofing, and for lubricating and
decorative purposes.
India, Canada, and the United States are the important sheet
mica-producing countries, before the war accounting for 98 per cent of
the world's total. India has long dominated the sheet mica markets of
the world, and will probably continue to supply the standard of quality
for many years. The bulk of the Indian mica is consumed in the United
States, Great Britain, and Germany. The mica of India and the United
States is chiefly muscovite. Canada is the chief source of amber mica
(phlogopite), though other deposits of potential importance are known in
Ceylon and South Africa. Canadian mica is produced chiefly in Quebec and
Ontario, and is exported principally to the United States.
Important deposits of mica (principally muscovite) are also known in
Brazil, Argentina, and German East Africa. Large shipments were made
from the two former countries during the war, both to Europe and the
United States, and Brazil particularly should become of increasing
importance as a producer of mica. The deposits in German East Africa
were being quite extensively developed immediately before the war and
large shipments were made to Germany in 1913.
The United States is the largest consumer of sheet mica and mica
splittings, absorbing normally nearly one-half of the world's
production. Approximately three-fifths of this consumption is in the
form of mica splittings, most of which are made from muscovite in India
and part from amber mica in Canada. Due to the cheapness of labor in
India and the amenability of Indian mica to the splitting process, India
splittings should continue to dominate the market in this country. Amber
mica is a variety peculiarly adapted to certain electrical uses. There
are no known commercial deposits of this mica in the United States, but
American interests own the largest producing mines in Canada. Shipments
of Brazilian mica are not of such uniformly high quality as the Indian
material, but promise to become of increasing importance in American
markets.
Of the sheet mica consumed annually, the United States normally produces
about one-third. War conditions, although stimulating the production of
domestic mica very considerably, did not materially change the
situation in this country as regards the dependence of the United States
on foreign supplies for sheet mica.
About 70 per cent of the domestic mica comes from North Carolina and 25
per cent from New Hampshire. The deposits are small and irregular, and
mining operations are small and scattered. These conditions are largely
responsible for the heterogeneous nature of the American product. It is
hardly possible for any one mine to standardize and classify its
product, although progress was made in this direction during the war by
the organization of associations of mica producers. This lack of
standardization and classification is a serious handicap in competition
with the standard grades and sizes which are available in any desired
amounts from foreign sources.
For ground mica, the domestic production exceeds in tonnage the total
world production of sheet mica, and is adequate for all demands.
GEOLOGIC FEATURES
Mica is a common rock mineral, but is available for commerce only in
igneous dikes of a pegmatite nature, where the crystallization is so
coarse that the mica crystals are exceptionally large. Muscovite mica
occurs principally in the granitic pegmatite dikes. The phlogopite mica
of Canada occurs in pyroxenite dikes. The distribution of mica within
the dikes is very erratic, making predictions as to reserves hazardous.
The associated minerals, mainly quartz and feldspar, are ordinarily
present in amounts greater than the mica. Also, individual deposits are
likely to be small. For these reasons mining operations cannot be
organized on a large scale, but are ordinarily hand-to-mouth operations
near the surface. A large amount of hand labor is involved, and the
Indian deposits are favored by the cheapness of native labor. The output
of a district is from many small mines rather than from any single large
one.
Pegmatites which have been subjected to dynamic metamorphism are often
not available as a source of mica, because of the distortion of the mica
sheets.
The mining of a mica is facilitated by weathering, which softens the
associated feldspar, making it an easier task to take out the mica
blocks. On the other hand, iron staining by surface solutions during
weathering may make the mica unfit for electrical and certain other
uses.
Scrap or ground mica is obtained as a by-product of sheet mica and from
deposits where the crystals are not so well developed. Black mica
(biotite) and chlorite minerals, which are soft and flexible but not
elastic and are found extensively developed in certain schists, have
been used to a limited extent for the same purposes.
MONAZITE (THORIUM AND CERIUM ORES)
ECONOMIC FEATURES
The mineral monazite is the source of the thorium and cerium compounds
which, glowing intensely when heated, form the light-giving material of
incandescent gas mantles. Welsbach mantles consist of about 99 per cent
thorium oxide and 1 per cent cerium oxide. Cerium metal, alloyed with
iron and other metals, forms the spark-producing alloys used in various
forms of gas lighters and for lighting cigars, cigarettes, etc.
Mesothorium, a by-product of the manufacture of thorium nitrate for gas
mantles, is used as a substitute for radium in luminous paints and for
therapeutic purposes. The alloy ferrocerium is used to a small extent in
iron and steel.
The world's supply of monazite is obtained mainly from Brazilian and
Indian properties. Before the war German commercial interests controlled
most of the production, as well as the manufacture of the thorium
products. During the war German control was broken up.
The United States has a supply of domestic monazite of lower grade than
the imports, but is dependent under normal conditions on supplies from
Brazil and India. The American deposits are chiefly in North and South
Carolina, and have been worked only during periods of abnormally high
prices or of restriction of imports. Known reserves are small and the
deposits will probably never be important producers. During the war,
however, the United States became the largest manufacturer of thorium
nitrate and gas mantles and exported these products in considerable
quantity. An effort is now being made to secure protective legislation
against German thorium products.
GEOLOGIC FEATURES
Monazite is a mineral consisting of phosphates of cerium, lanthanum,
thorium, and other rare earths in varying proportions. The content of
thorium oxide varies from a trace up to 30 per cent, and commercial
monazite sands are usually mixed so as to bring the grade up to at least
5 per cent.
Yellowish-brown crystals of monazite have been found scattered through
granites, gneisses, and pegmatites, but in quantities ordinarily too
small to warrant mining. In general the mineral is recovered on a
commercial scale only from placers, where it has been concentrated along
with other dense, insoluble minerals such as zircon, garnet, ilmenite,
and sometimes gold. The Indian and Brazilian monazite is obtained
principally from the sands of ocean beaches, in the same localities from
which zircon is recovered (p. 189). The North and South Carolina
monazite has been obtained chiefly from stream beds, and to a slight
extent by mining and washing the rotted underlying rock, which is a
pegmatized gneiss. Monazite, together with a small amount of gold, is
also known in the stream gravels of the Boise Basin, Idaho, where a
large granitic batholith evidently carries the mineral sparsely
distributed throughout. These deposits have not been worked.
PRECIOUS STONES
ECONOMIC FEATURES
Precious stones range high in the world's annual production of mineral
values. A hundred or more minerals are used to some degree as precious
stones; but those most prized, representing upwards of 90 per cent of
the total production value, are diamond, pearl, ruby, sapphire, and
emerald. In total value the diamonds have an overwhelming dominance.
Over a ton of diamonds is mined annually.
Diamonds come mainly from South Africa, which produces over 99 per cent
of the total. Pearls come chiefly from the Indian and Pacific oceans.
Burma is the principal source of fine rubies. Siam is the principal
producer of sapphires. Colombia is the principal source of fine
emeralds.
The United States produces small amounts of sapphires (in Montana) and
pearls (from fresh-water molluscs). Diamonds, rubies, and emeralds are
practically absent on a commercial scale. Of other precious and
semi-precious gem stones produced in the United States, the principal
ones are quartz, tourmaline, and turquoise.
On the other hand, the United States absorbs by purchase over half of
the world's production of precious stones. It is estimated roughly that
there are now in the United States nearly one billion dollars' worth of
diamonds, or over one-half of the world's accumulated stock, and
probably the proportions for the other stones are not far different.
Value attaches to a precious stone because of its qualities of beauty,
coupled with endurance and rarity, or because of some combination of
these features which has caught the popular fancy. No one of these
qualities is sufficient to make a stone highly prized; neither does the
possession of all of them insure value. Some beautiful and enduring
stones are so rare that they are known only to collectors and have no
standard market value. Others fail to catch the popular fancy for
reasons not obvious to the layman. While the intrinsic qualities go far
in determining the desirability of a stone, it is clear that whim and
chance have been no small factors in determining the demand or lack of
demand for some stones. As in other minerals, value has both its
intrinsic and extrinsic elements.
For the leading precious stones above named, the values are more nearly
standard throughout the world than for any other minerals, with the
exception of gold and possibly platinum. Highly prized everywhere and
easily transported, the price levels show comparatively little variation
over the world when allowance is made for exchange and taxes. The
valuation of precious stones is a highly specialized art, involving the
appraisal not only of intrinsic qualities, but of the appeal which the
stone will make to the buying public. In marking a sale price for some
exceptional stone not commonly handled in the trade, experts in
different parts of the world often reach an almost uncanny uniformity of
opinion.
It is estimated that the world stock of precious stones approximates
three billion dollars, or a third of the world's monetary gold reserve.
Because of small bulk and standard value, this wealth may be easily
secreted, carried, and exchanged. When the economic fabric of
civilization is disturbed by war or other conditions, precious stones
become a medium of transfer and exchange of wealth of no inconsiderable
importance.
The beauty of a stone may arise from its color or lack of color, from
its translucency or opaqueness, from its high refraction of light, and
from the manner of cutting and polishing to bring out these qualities.
Hardness and durability are desirable qualities. The diamond is the
hardest known mineral and the sapphire, ruby, and emerald rank high in
this regard. On the other hand the pearl is soft and fragile and yet
highly prized.
GEOLOGIC FEATURES
The principal precious stones above named are of simple composition.
Diamond is made of carbon; the pearl is calcium carbonate; ruby and
sapphire are aluminum oxide--varieties of the mineral corundum; the
emerald is silica and alumina, with a minor amount of beryllia. Minute
percentages of chromite, iron, manganese, and other substances are often
responsible for the colors in these stones. Carbon also constitutes
graphite and is the principal element in coal. Lime carbonate is the
principal constituent of limestone and marble. Alumina is the principal
constituent of bauxite, the ore of aluminum, and of the natural
abrasives, emery and corundum. Silica, the substance of common quartz,
also constitutes gem quartz, amethyst, opal, agate, onyx, etc.
Most of the world's diamonds come from the Kimberley and Transvaal
fields of South Africa, where they are found in a much decomposed
volcanic rock called "blue ground." This is a rock of dull, greasy
appearance consisting largely of serpentine. It was originally
peridotite, occurring in necks or plugs of old volcanoes penetrating
carbonaceous sediments. When the rock is mined and spread at the
surface, it decomposes in the course of six months or a year, allowing
it to be washed and mechanically sorted for its diamond content. The
amount of ground treated in one of the large mines is about equal to
that handled in operating the huge porphyry copper deposit of Bingham,
Utah; the annual production of diamonds from the same mine could be
carried in a large suit-case.
The diamonds were clearly formed at high temperatures and pressures
within the igneous rocks. It has been suggested that the igneous magma
may have secured the carbon by the melting of carbonaceous sediments
through which it penetrated, but proof of this is difficult to obtain.
Artificial diamonds of small size have been made in the electric furnace
under high-pressure conditions not unlike those assumed to have been
present in nature.
Weathering and transportation of rocks containing diamonds have resulted
in the development of diamond-bearing placers. The South African
diamonds were first found in stream placers, leading to a search for
their source and its ultimate discovery under a blanket of soil which
completely covered the parent rock. The proportion of diamonds now mined
from placers is very small.
The diamonds of Brazil come from placer deposits. This is the principal
source of the black diamond so largely used in diamond-drilling.
The United States produces no diamonds on a commercial scale. Small
diamonds have been found in peridotite masses in Pike County, Arkansas,
but these are of very little commercial value. A few diamonds have been
found in the glacial drift of Wisconsin and adjacent states, indicating
a possible diamond-bearing source somewhere to the north which has not
yet been located (p. 317).
Pearls are concretions of lime carbonate of organic origin, and are
found in the shells of certain species of molluscs. Their color or
luster is given by organic material or by the interior shell surface
against which the pearl is formed. The principal supply comes from the
Indian and Pacific Oceans, but some are found in the fresh water mussels
of North America, in the Caribbean, and on the western coast of Mexico
and Central America.
From the beginning of history the principal source of rubies has been
upper Burma, where the stones are found in limestone or marble near the
contact with igneous rocks, associated with high-temperature minerals.
The weathering of the rock has developed placers from which most of the
rubies are recovered. Siam is also an important producer. In the United
States rubies have been found in pegmatites in North Carolina, but these
gems are of little commercial importance.
Sapphires are of the same composition as rubies and are found in much
the same localities. Most of the sapphires of the best quality come from
Siam, where they are found in sandy clay of placer origin. In the United
States sapphires are recovered from alluvial deposits along the Missouri
River near Helena, Montana, where they are supposed to have been derived
from dikes of andesite rocks. In Fergus County, Montana, they are mined
from decomposed dikes of lamprophyre (a basic igneous rock). In North
Carolina sapphire has been found in pegmatite dikes.
The principal source of fine emeralds is in the Andes in Colombia. Their
occurrence here is in calcite veins in a bituminous limestone, but
little seems to be known of their origin. The only other emerald
locality of commercial importance is in the Ural Mountains of Siberia.
Emeralds have been found in pegmatite dikes in North Carolina and New
England, but the production is insignificant.
Tourmaline is a complex hydrous silicate of aluminum and boron, with
varying amounts of magnesium, iron, and alkalies. It is a rather common
mineral in silicated zones in limestones near igneous contacts, but gem
tourmalines are found principally in pegmatite dikes. They have a wide
variety of colors, the red and green gems being the most prized. Maine,
California, and Connecticut are the principal American producers.
Turquoise is a hydrated copper-aluminum phosphate. It is found in
veinlets near the surface in altered granites and other igneous rocks.
It is usually associated with kaolin and frequently with quartz, and is
believed to have been formed by surface alterations. In the United
States it is produced chiefly in Nevada, Arizona, and Colorado.
In general the principal gem minerals, except pearl and turquoise, occur
as original constituents in igneous intrusives, usually of a pegmatite
or peridotite nature. Sapphire, ruby, emerald, and tourmaline result
also from contact metamorphism of sediments in the vicinity of igneous
rocks. Weathering softens the primary rocks, making it possible to
separate the gem stones from the matrix. When eroded and transported the
gems are concentrated in placers.
SALT
ECONOMIC FEATURES
The principal uses of salt are in the preserving and seasoning of foods
and in chemical industries. Chemical industries require salt for the
manufacture of many sodium compounds, and also as a source of
hydrochloric acid and chlorine. A minor use of salt is in the making of
glazes and enamel on pottery and hardware.
Because of the wide distribution of salt in continental deposits and
because of the availability of ocean and salt-lake brines as other
sources, most countries of the world either possess domestic supplies of
salt adequate for the bulk of their needs, or are able to obtain
supplies from nearby foreign countries. Certain sea salts preferred by
fish packers and other users are, however, shipped to distant points.
About a fifth of all the salt consumed in the world annually is produced
in the United States, and other large producers are Great Britain,
Germany, Russia, China, India, and France.
The United States produces almost its entire consumption of salt, which
is increasing at a very rapid rate. Salt is produced in fourteen states,
but over 85 per cent of the total output comes from Michigan, New York,
Ohio, and Kansas. Reserves are practically inexhaustible.
Exports and imports of salt form a very minor part of the United States
industry, each being equivalent to less than 5 per cent of the domestic
production. A large part of the imported material is coarse
solar-evaporated sea salt, which is believed by fish and pork packers to
be almost essential to their industry. Imports of this salt come from
Spain, Italy, Portugal, and the British and Dutch West Indies; during
the war, on account of ship shortage, they were confined chiefly to the
West Indies. A considerable tonnage of specially prepared kiln-dried
salt, desired by butter-makers, is imported from Liverpool, England.
There are also some small imports from Canada, probably because of
geographic location. Exports of domestic salt go chiefly to Canada,
Cuba, and New Zealand, with smaller amounts to practically all parts of
the world.
Salt is recovered from salt beds in two ways. About a fourth of the
salt produced in the United States is mined through shafts in the same
manner as coal, the lumps of salt being broken and sized just as coal is
prepared for the market. The larger part of the United States
production, however, is derived by pumping water down to the beds to
dissolve the salt, and pumping the resulting brine to the surface where
it is then evaporated. A considerable amount of salt, also, is recovered
from natural brines--which represent the solution of rock salt by
ground-waters--and from the waters of salt lakes and the ocean.
GEOLOGIC FEATURES
Common salt constitutes the mineral halite, the composition of which is
sodium chloride. It is rarely found perfectly pure in nature, but is
commonly mixed with other saline materials, such as gypsum and
anhydrite, and occasionally with salts of potassium and magnesium. The
general grade of rock-salt deposits, where not admixed with clay, is
perhaps 96 to 99 per cent of sodium chloride.
The ultimate source of salt deposits is the sodium and chlorine of
igneous rocks. In the weathering of these rocks the soda, being one of
the more soluble materials, is leached out and carried off by
ground-waters, and in the end a large part of it reaches the sea. The
chlorine follows a similar course; however, the amount of chlorine in
ordinary igneous rocks is so extremely small that, in order to explain
the amount of chlorine present in the sea, it has been thought necessary
to appeal to volcanic emanations or to some similar agency. Ocean water
contains about 3.5 per cent by weight of dissolved matter, over
three-fourths of which consists of the constituents of common salt.
Chief among the other dissolved materials are magnesium, calcium,
potassium, and SO_4 (the sulphuric acid radical).
When sea water evaporates it becomes saturated with various salts,
according to the amounts of these salts present and their relative
solubilities. In a general way, after 37 per cent of the water has
evaporated gypsum begins to separate out, and after 93 per cent has
evaporated common salt begins to be deposited. After a large part of the
common salt has been precipitated, the residual liquid, called a
"bittern" or "mother liquid," contains chiefly a concentration of the
salts of magnesium and potassium. Still further evaporation will result
in their deposition, mainly as complex salts like those found in the
Stassfurt deposit (p. 113).
The actual processes of concentration and precipitation in sea water or
other salt waters are much more complex than is indicated by the above
simple outline. The solubility of each of the various salts present, and
consequently the rate at which each will crystallize out as evaporation
proceeds, depends upon the kinds and concentrations of all the other
salts in the solution. Temperature, pressure, mass-action, and the
crystallization of double salts are all factors which influence the
nature and rate of the processes and add to their complexity. During a
large part of the general process, several different salts may be
crystallizing out simultaneously. It is evident that gypsum may be
precipitated in some quantity, and that external conditions may then
change, so that evaporation ceases or so that the waters are freshened,
before any common salt is crystallized out. This fact may explain in
part why gypsum beds are more widely distributed than beds of common
salt. At the same time the much greater amount of sodium chloride than
of calcium sulphate in sea water may explain the greater thickness of
many individual salt beds.
The evaporation of salt waters, either from the ocean or from other
bodies of water, is believed to have been responsible for nearly all of
the important deposits of common salt. This process has been going on
from Cambrian time down through all the intervening geologic ages, and
can be observed to be actually operative today in various localities.
The beds of salt so formed are found interstratified with shales,
sandstones, and limestones, and are frequently associated with gypsum.
On a broad scale, they are always lens-shaped, though they vary greatly
in extent and thickness.
The necessary conditions for the formation of extensive salt beds
include arid climate and bodies of water which are essentially
enclosed--either as lakes, as lagoons, or as arms of the sea with
restricted outlets,--where evaporation exceeds the contributions of
fresh water from rivers, and where circulation from the sea is
insufficient to dilute the water and keep it at the same composition as
the sea water. Under such conditions the dissolved salts in the enclosed
body become concentrated, and precipitation may occur. A change of
conditions so that mud or sand is washed in or so that calcareous
materials are deposited, followed by a recurrence of salt-precipitation,
results in the interstratification of salt beds with shales, sandstones,
and limestones.
For the formation of very thick beds of salt, and especially of thick
beds of fairly pure composition, however, this simple explanation of
conditions is insufficient. The deposits of Michigan and New York occur
in beds as much as 21 feet in thickness, with a considerable number of
separate beds in a section a few hundred feet thick. Beneath the potash
salt deposits of Stassfurt, beds of common salt 300 to 500 feet in
thickness are found, and beds even thicker are known in other
localities. When we come to investigate the volume of salts deposited
from a given volume of sea water, we find it to be so small that for the
formation of 500 feet of salt over a given area, an equivalent area of
water 25,000 feet deep would be required. It has therefore been one of
the puzzling problems of geology to determine the exact physical
conditions under which deposition of these beds took place.
One of the most prominent theories, the "bar" theory, suggests that
deposition may have taken place in a bay separated from the sea by a
bar. Sea water is supposed to have been able to flow in over the bar or
through a narrow channel, so that evaporation in the bay was about
balanced by inflow of sea water. Thus the salts of a very large quantity
of sea water may have accumulated in a small bay. As the process went
on, the salts would become progressively more concentrated, and would be
precipitated in great thickness. A final complete separation of the
basin from the sea, for instance by the relative elevation of the land,
might result in complete desiccation, and deposition of
potassium-magnesium salts such as those found at Stassfurt (p. 113).
Another suggestion to explain the thickness of some salt beds is that
the salts in a very large basin of water may, as the water evaporated
and the basin shrank, have been deposited in great thickness in a few
small depressions of the basin.
Other writers believe that certain thick salt deposits were formed in
desert basins (with no necessary connection with the sea), through the
extensive leaching of small quantities of salt from previous sediments,
and its transportation by water to desert lakes, where it was
precipitated as the lakes evaporated. Over a long period of time large
amounts of salt could accumulate in the lakes, and thick deposits could
result. Such hypotheses also explain those cases where common salt beds
are unaccompanied by gypsum, since land streams can easily be conceived
to have been carrying sodium chloride without appreciable calcium
sulphate; in ocean waters, on the other hand, so far as known both
calcium sulphate and sodium chloride are always present, and gypsum
would be expected to accompany the common salt.
A partial explanation of some great thicknesses found in salt beds is
that these beds, especially when soaked with water, are highly plastic
and incompetent under pressure. In the deformation of the enclosing
rocks, the salt beds will flow somewhat like viscous liquids, and will
become thinned on the limbs of the folds and correspondingly thickened
on the crests and troughs.
The salt deposits of the Gulf Coast of Texas and Louisiana should be
referred to because of their exceptional features. They occur in low
domes in Tertiary and more recent sands, limestones, and clays. Vertical
thicknesses of a few thousand feet of salt have been found, but the
structure is known only from drilling. In some of these domes are also
found petroleum, gypsum, and sulphur (p. 110). No igneous rocks are
known in the vicinity. It has been thought by some that the deposits
were formed by hot waters ascending along fissures from underlying
igneous rocks, and the upbowing of the rocks has been variously
explained as due to the expanding force of growing crystals, to
hydrostatic pressure of the solutions, and to laccolithic intrusions. On
the other hand, the uniform association of other salt and gypsum
deposits with sedimentary rocks, and the absence of igneous rocks,
suggest that these deposits may have had essentially a sedimentary
origin, and that they have been modified by subsequent deformation and
alteration. The origin is still uncertain.
Other mineral deposits formed under much the same conditions as salt are
gypsum, potash, borax, nitrates, and minerals of bromine; and in a study
of the origin of salt deposits these minerals should also be
considered.
TALC AND SOAPSTONE
ECONOMIC FEATURES
Soapstone is a rock composed mainly of the mineral talc. Popularly the
terms _talc_ and _soapstone_ are often used synonymously. The softness,
greasy feel, ease of shaping, and resistance to heat and acids of this
material make it useful for many purposes. Soapstone is cut into slabs
for laundry tubs, laboratory table tops, and other structural purposes.
Finer grades are cut into slate pencils and acetylene burners. Ground
talc or soapstone is used as a filler for paper, paint, and rubber
goods, and in electrical insulation. Fine grades are used for toilet
powder.
Pyrophyllite (hydrated aluminum silicate) resembles talc in some of its
properties and is used in much the same way. Fine English clays (p. 85)
are sometimes used interchangeably with talc as paper filler.
The United States produces nearly two-thirds of the world's talc. The
other large producers are France, Italy, Austria, and Canada (Ontario).
The United States is independent of foreign markets for the bulk of its
talc consumption, but some carefully prepared talc of high quality is
imported from Canada, Italy, and France. Italy is our chief source of
talc for pharmaceutical purposes, though recently these needs have been
largely supplied by high-grade talc from California. In the United
States, Vermont and New York are the leading producers of talc and
Virginia of soapstone slabs. Reserves are large.
GEOLOGIC FEATURES
Talc is hydrated magnesium silicate, as is also serpentine, a mineral
with which talc is closely associated. Both are common alteration
products of magnesian silicate minerals such as olivine, pyroxene, and
amphibole. Talc is also derived from the recrystallization of magnesian
carbonates.
Talc deposits consist of lenses and bands in metamorphic limestones,
schists, and gneisses of ancient age. The talc itself is usually
schistose like the wall rocks, and is largely a product of mechanical
mashing. In some cases, also, talc results from the alteration of
igneous rocks without mashing--as in the case of the large talc and
soapstone deposits of Virginia, which are the result of rather complete
alteration of basic igneous rocks such as peridotites and pyroxenites.
Talc is known to result from the weathering of magnesian silicates under
surface conditions, but the common occurrence of the principal deposits,
in highly crystalline rocks which have undergone extensive deep-seated
metamorphism, is an indication that processes other than weathering have
been effective. It has been suggested that hot ascending solutions have
been responsible for the work, but without much proof. A more plausible
explanation for many deposits is that the talc results from the dynamic
metamorphism or shearing of impure magnesian carbonates (as in highly
magnesian limestones), the process resulting in elimination of the
carbon dioxide and recrystallization of the residue. Certain talc
deposits, such as those of Ontario, show clearly traces of the original
bedding planes of limestone crossing the cleavage of the talc, and the
rock bears all the evidence of having formed in the same manner as a
common slate. Talc and slate are almost the only mineral products which
owe their value principally to dynamic metamorphism.
CHAPTER XIV
EXPLORATION AND DEVELOPMENT
THE GENERAL RELATIONS OF THE GEOLOGIST TO EXPLORATION AND DEVELOPMENT
The economic geologist is more vitally concerned with exploration and
development than with any other phase of his work. This comes closest to
being his special field. Here is a fascinating element of adventure and
chance. Here is the opportunity to converge all his knowledge of geology
and economics to a practical end. The outcome is likely to be definite
one way or the other, thus giving a quantitative measure of the accuracy
of scientific thinking which puts a keen edge on his efforts. It is not
enough merely to present plausible generalizations; scientific
conclusions are followed swiftly either by proof or disproof. With this
check always in mind, the scientist feels the necessity for the most
rigid verification of his data, methods, and principles.
The general success of the application of geology to exploration and
development is indicated by the rapid increase in demand for such
service in recent years, and by the large part it plays in nearly all
systematic and large-scale operations. The argument is sometimes made
that many mineral deposits have been found without geologic assistance,
and that therefore the geologist is superfluous. The answer to this
argument is that there are often hundreds of "practical" explorers in
the field to one geologist, and that in proportion to numbers the story
is quite a different one. The very fact that many large mining
organizations, as a result of their experience, now leave these matters
of exploration and development largely in the hands of geologists, is a
tribute to the usefulness of the science. Also, it is to be remembered
that not all applications of geology are made by geologists. It is hard
to find a prospector or explorer who has not absorbed empirically some
of the elements of geology, and locally this may be enough. Very often
men who take pride in the title of "practical prospectors" are the ones
with the largest stock of self-made geological theories.
During a prospecting boom it is not uncommon for speculators and
promoters to attempt to discount geologic considerations where these run
counter to their plans. The catching phrase "bet against the geologist"
has a broad appeal to an instinctive preference for the practical as
opposed to the theoretical. If the public would stop to note the
character of the support behind the geologist, including as it does the
larger and more successful operators, it would not be so ready to accept
this implication.
Another aspect of this question might be mentioned. There is scarcely an
oil field or mining camp in the world without a cherished tradition to
the effect that, prior to discovery, the mineral possibilities had been
reported on unfavorably by the geologists,--again implying that success
has been due to the hard common sense of the horny-handed prospector.
These traditions persist in the face of favorable geological reports
published before discovery; they are natural expressions of the
instinctive distrust of any knowledge which is beyond the field of
empirical experience. In many cases the discoveries were made long
before geologists appeared on the scene. In others, possibly one or two
geologic reports were unfavorable, while many were favorable. In the
aggregate, there can be no question that, in proportion to the scale of
its use, geological advice has had more than its proportion of success.
Even under the most favorable conditions, the chances against the
success of an individual drill hole or underground development are
likely to be greater than the chances for it. The geologist may not
change this major balance; but if he can reduce the adverse chances by
only a few per cent, his employment is justified on purely commercial
grounds.
The above comments refer to sound geological work by competent
scientists. The geologic profession, like many others, is handicapped by
numbers of ill-trained men and by many who have assumed the title of
geologist without any real claim whatever,--who may do much to discredit
the profession. The very newness of the field makes it difficult to draw
a sharp line between qualified and unqualified men. With the further
development of the profession this condition is likely to be improved
(see pp. 427-428).
So new is the large-scale application of geology to exploration and
development, and so diverse are the scientific methods of approach, that
it is difficult to lay out a specific course for a student which will
prepare him for all the opportunities he may have later. In the writer's
experience, both in teaching and practice, the only safe course for the
student is to prepare broadly on purely scientific lines. With this
background he will be able later to adapt himself to most of the special
conditions met in field practice.
PARTLY EXPLORED VERSUS VIRGIN TERRITORIES
In selecting an area to work, the geologic explorer will naturally
consider various factors mentioned in succeeding paragraphs; but the
natural first impulse is to start for some place where no one else has
been, and to keep away from the older principal mining camps,--on the
assumption that such grounds have been thoroughly explored and that
their geological conditions bearing on exploration are fully understood.
It is safe to say that very few mineral districts are thoroughly
understood and explored. Numerous important discoveries of recent years
have been in the extensions of old mines and old districts; and when one
considers the scale of even the most extensive mine openings in
comparison with the vast body of rock available for exploration, it is
clear that this will continue to be the situation far into the future.
It is the writer's belief that the economic geologist stands at least as
good a chance of success in exploration in the older districts as he
does in new fields. Nature is exceedingly erratic and economical in
providing places favorable for mineral production; in a producing
district the geologic conditions have been proved to be right, and the
explorer starts here with this general pragmatic advantage. The explorer
here has another great advantage, that much essential information has
been gathered which can be built into his plan of operations. He can
start, scientifically and practically, where the other man left off. One
of the best-known economic geologists has maintained that the more
previous work done, the better, because it furnished him more tools to
work with. There is no such thing as "skimming the cream" from a
geologic problem; there is no end in sight in the search for more
knowledge.
This attitude toward the problem of exploration has also proved
advantageous on the business or financial side. A successful backer of
mineral enterprises once remarked that his best prospecting was done
from the rear platform of a private car,--meaning that this mode of
transportation had carried him to the center of important mining
activities, where the chances for large financial success showed a
better percentage than in more general and miscellaneous exploration.
THE USE OF ALL AVAILABLE INFORMATION
Effective scientific exploration requires the use of all available
information applying to the specific area. This might seem to be too
obvious to require mention, yet observance of the methods of explorers
seems to call for warning against the rather common tendency to go into
a field unprepared with a thorough knowledge of preceding work. It is
easy to forget or overlook some investigation made many years
previously; or to assume that such work is out of date, and of no
special consequence in the application of new thought and method which
is the basis of the faith and confidence of each new geologic explorer.
A study of the reports on an old camp shows how often the younger
generations have ignored the results of the older. Many of the same
elementary truths are rediscovered by successive generations, after
large efforts which could have been saved by means of proper care and
investigation of the previous literature and mapping.
In outlying parts of the world, the existing information bearing on
exploration may be at a minimum. In many of the older mining camps and
throughout most civilized countries, however, careful investigation will
usually disclose a considerable range of useful information bearing on
the territory to be explored. In the United States the natural course to
be pursued is to hunt carefully through the reports of the U. S.
Geological Survey, the Bureau of Mines, various state surveys,
universities, and private organizations (so far as these reports are
available), and through the technical journals and the reports of
technical societies, for something bearing on the district to be
explored. Even if no specific report or map is to be found, it is
usually possible to locate general maps or accounts which are likely to
be of use.
COÖPERATION IN EXPLORATION
Competition in exploration often develops an atmosphere of suspicion and
furtiveness which is highly unfavorable to coöperative efforts.
Individuals and companies may handicap themselves greatly by a desire to
play a lone hand, and by failure to take advantage of an exchange of
information. This action may be based, particularly on the part of
strong mining companies, on the assumption that they know all that is
necessary about the problem, and that an outsider has nothing to
contribute. Financial and other conditions may require this attitude;
but in large part it is a result of temperament, as clearly indicated by
the difference in methods followed by different groups and in different
mining districts. From the scientific point of view this attitude can
hardly be justified, in view of the extremely narrow limits of human
knowledge as compared with the scientific field to be explored. The sum
total of knowledge from all sources is only a small fraction of that
necessary for the most effective results. The mutual exchange of
information and discussion is usually justified on the basis of
self-interest alone, to say nothing of the larger interest to the
mineral district, to the country, or to science.
National and state survey organizations exercise considerable effort to
secure records of drilling. In some cases they have the legal power to
command this information, particularly in relation to appraisals for
taxation and "blue sky" laws. In a larger number of cases drill records
are secured through voluntary coöperation with explorers. A considerable
number of records are nevertheless not filed with public agencies and
some of these are permanently lost. Even where the records are turned in
to a public organization, they are in most cases not directly available
to explorers.
Public registration of all drilling records is a highly desirable
procedure in the interests of the development of the mineral industry as
a whole. A vast amount of unnecessary duplication can thus be avoided.
The record of a drill hole, even though barren, may be of vast
significance in the interpretation of future developments and should be
recorded as carefully as an abstract of land title. The property right
of the explorer in such information can be and usually is protected by
withholding the record from public inspection until sufficient time has
elapsed to give him full opportunity to use the information to his own
best advantage.
The opportunities for coöperation with specialists of public
organizations are almost unlimited. These organizations are likely to
have an accumulation of data and experience extending through long
periods and over large areas, which the private explorer ordinarily
cannot hope to duplicate. With proper restrictions this information may
be available for public use. A good illustration of current coöperative
effort of this kind is in the deep exploration for oil in the Trenton
limestone of Illinois. Outcrops and other specific indications are not
sufficient to localize this drilling; but the information along broad
geologic and structural lines which has been collected previously by the
Illinois Survey is sufficient so that, with a comparatively small amount
of shallow drilling, the locus of the more favorable structural
conditions may be determined. In this case the Survey is directing the
initial exploration, which is financed by private capital.
ECONOMIC FACTORS IN EXPLORATION
The approach to the problem of exploration is very often determined by
local requirements and conditions; but if one were to come at the
problem from a distance and to keep matters in broad perspective, the
first step would be a consideration of what might be called the
_economic factors_. Let us suppose that the geologist is free to choose
his field of exploration. An obvious preliminary step is to eliminate
from consideration mineral commodities which are not in steady or large
demand and are much at the mercy of market conditions, or which are
otherwise not well situated commercially. The underlying factors are
many and complex. They include the present nature and future
possibilities of foreign competition, the domestic competition, the
grades necessary to meet competition, the cost of transportation, the
cost of mining under local conditions--including considerations of labor
and climatic and topographic conditions,--the probability of increase or
decrease in demand for the product, the possible changes in
metallurgical or concentrating practice (such as those which made
possible the mining of low-grade porphyry copper ores), the size of
already available reserves, and the mining laws in relation to
ownership and regulation. Most of these factors are discussed at some
length on other pages. After looking into the economic conditions
limiting the chromite, nickel, or tin developments in the United States,
the explorer might hesitate to proceed in these directions,--for he
would find that past experience shows little promise of quantities and
grades equivalent to those available in other countries, and that there
is little likelihood of tariffs or other artificial measures to improve
the domestic situation. Before and during the war, commercial conditions
might have shown the desirability of hunting for pyrite, but more recent
developments in the situation cast some doubt on this procedure. To go
ahead blindly in such a case, on the assumption that the pyrite market
would in some fashion readjust itself, would not be reasoned
exploration. Again, in considering exploration for copper, account
should be taken in this country of the already large reserves developed
far in advance of probable demand, which require that any new
discoveries be very favorably situated for competition. In oil, on the
other hand, a very brief survey of the economic factors of the situation
indicates the desirability of exploration. The comparative shortage of
lead supplies at the present time suggests another favorable field for
exploration.
In short, before actual field exploration is begun, intelligent
consideration of the economic factors may go far toward narrowing the
field and toward converging efforts along profitable lines. Looked at
broadly, this result is usually accomplished by the natural working of
general laws of supply and demand; but there are many individual cases
of misdirected effort, under the spell of provincial conditions, which
might easily be avoided by a broader approach to the problem.
GEOLOGIC FACTORS IN EXPLORATION
Coming to the geological aspects of exploration, the procedure in its
early stages is again one of elimination. Oil and coal, for instance,
are found in certain sediments of certain ages, and one would not look
for them in an area of granite. For every mineral resource there are
broad geologic conditions of this sort, particularly the genetic,
structural, and metamorphic conditions, which make it possible to
eliminate vast areas from consideration and to concentrate on relatively
small areas.
After the elimination of unfavorable areas, there comes the hunt for
positively favorable geologic conditions--for a definite kind of
sediment or igneous rock, for a definite structure, for the right kind
of mineralogic and metamorphic conditions, or for the right combination
of these and other geologic elements. The geologic considerations used
in exploration for the various mineral deposits are so many and so
diverse, and they require so much adjustment and interpretation in their
local application, that one would be rash indeed to attempt anything in
the nature of an exhaustive discussion. It is hardly practicable to do
more than to outline, for illustrative purposes, a few of the geologic
factors most commonly used in exploration.
MINERAL PROVINCES AND EPOCHS
Mineral deposits may be similar in their mineralogic and geologic
characters and relations over a considerable area. They may give
evidence of having developed under the same general conditions of
origin; perhaps they may even be of the same geologic age. The
gold-silver deposits of Goldfield, of Tonopah, the Comstock Lode of
Virginia City, and many other deposits through the Great Basin area of
the southwestern United States and Mexico have group characteristics
which have led geologists to refer to this area as a "metallogenic" or
"metallographic" province. The gold-silver ores on the west slope of the
Sierra Nevadas, for nearly the entire length of California, likewise
constitute a metallogenic province. The Lake Superior copper ores on the
south shore of Lake Superior, the silver ores on the north shore,
miscellaneous small deposits of copper, silver, and gold ores to the
east of Lake Superior, the nickel ores of Sudbury, and the
silver-nickel-cobalt ores of the Cobalt district are all characterized
by similar groups of minerals (though in highly differing proportions),
by similar geologic associations, by similar age, and probably by
similar conditions of origin. This area is a metallogenic province. The
lead and zinc ores of the Mississippi Valley constitute another such
province. The oil pools of the principal fields are characterized by
common geologic conditions over great areas (p. 149), which may likewise
be considered as forming mineral provinces; for them the term
"petroliferous provinces" has been used. The list might be extended
indefinitely. Knowledge of such group distributions of minerals is a
valuable asset to the explorer, in that it tends to localize and direct
search for certain classes of ores in certain provinces; also, within a
province, it tells the explorer what is to be normally expected as
regards kinds and occurrences of mineral deposits. In searching for
minerals of sedimentary origin, the explorer will use stratigraphic
methods in following definite sedimentary horizons. In searching for
ores related to igneous intrusions he will naturally hunt for the
intrusions, and then follow the periphery of the intrusions for
evidences of mineralization, taking into account possible features of
zonal arrangement of minerals about the intrusives (see pp. 42-44), and
the preference of the ores for certain easily replaced horizons like
limestones, or for certain planes or zones of fracturing.
Just as minerals may be grouped by provinces, they may be grouped by
geologic ages. Such groupings are especially useful in the case of
minerals which are closely related to certain stratigraphic horizons,
such as coal, oil, and iron. The greater number of the productive coal
deposits of the United States are of Carboniferous age, and the
distribution of sediments of this age is pretty well understood from
general geologic mapping. The Clinton iron ores all follow one general
horizon in the lower-middle Paleozoic. The Lake Superior iron ores are
pre-Cambrian, and over three-fourths of them occur at one horizon in the
pre-Cambrian. Gold deposits of the United States were formed mainly in
the pre-Cambrian, the early Cretaceous, and the Tertiary. Copper
deposits of the United States were formed chiefly in pre-Cambrian,
Cretaceous, and Tertiary time. While there are many exceptions and
modifications to general classifications of this sort, they seem to
express essential geologic facts which can be made very useful in
localizing exploration.
CLASSIFICATION OF MINERAL LANDS
In recent years there has been considerable development of the practice
of classifying mineral lands in given areas for purposes of exploration
and valuation, or for purposes of formulation and administration of
government laws. This has been done both by private interests and by the
government. These classifications take into account all of the geologic
and economic factors ascertainable. The classes of mineral land
designated vary with the mineral, the district, and the purpose for
which the classification is made.
Common procedure for commercial exploration purposes is to divide the
lands of a given territory into three groups--(1) lands which are
definitely promising for mineral exploration, (2) lands of doubtful
possibilities, and (3) lands in which the mineral possibilities are so
slight that they may be excluded from practical consideration. Each of
these classes may be subdivided for special purposes. Another commonly
used classification is, (1) proved mineral lands, (2) probable mineral
lands, usually adjacent to producing mines, (3) possible mineral lands,
and (4) commercially unpromising mineral lands.
The classification of the public mineral lands by government agencies is
fully discussed by George Otis Smith and others in a bulletin of the
United States Geological Survey.[37] The purposes, methods, and results
of this classification should be familiar to every explorer. Nowhere
else is there available such a vast body of information of practical
value. Quoting from this report:
A study of the land laws shows the absolute necessity of some
form of segregation of the lands into classes as a
prerequisite to their disposition. Agricultural entry may not
be made on lands containing valuable minerals, nor coal entry
on lands containing gold, silver, or copper; lands included in
desert entries or selected under the Carey Act must be desert
lands; enlarged-homestead lands must not be susceptible of
successful irrigation; placer claims must not be taken for
their timber value or their control of watercourses; and lands
included in building-stone, petroleum, or salt placers must be
more valuable for those minerals than for any other purpose.
So through the whole scheme of American land laws runs the
necessity for determining the use for which each tract is best
fitted.
For this purpose the Geological Survey has made extensive classification
of coal lands, oil and gas lands, phosphate lands, lands bearing potash
and related salines, metalliferous mineral lands, miscellaneous
non-metalliferous mineral lands, and water resources. The scope of the
work may be indicated by the factors considered. For instance coal is
investigated in relation to its character and heat-giving qualities
(whence comes its value), quantity, thickness, depth, and other
conditions that effect the cost of its extraction. Metalliferous mineral
lands are considered in relation to general geology, country rock,
intrusions and metamorphism, structure, outcrops and float of lodes,
prospects and mines, samples, and history of the region.
Classifications of this kind have often proved useful to large holders
of land as a basis for intelligent handling of problems of sale,
taxation, and the granting of rights to explorers. Because of the lack
of this elementary information, there has been in some quarters timidity
about dealing with large holdings, for fear of parting with possible
future mineral wealth,--with the result that such tracts are carried at
large expense and practically removed from the field of exploration. To
the same cause may be attributed some of the long delays on the part of
the government in opening lands for mineral entry or in issuing patents
on land grants.
OUTCROPS OF MINERAL DEPOSITS
Many mineral deposits have been found because they outcrop at the
surface; the discoveries may have been by accident or they may have been
aided by consideration of geologic factors. There are still vast
unexplored areas in which mineral deposits are likely to be found
standing out at the surface. For much of the world, however, the surface
has been so thoroughly examined that the easy surface discoveries have
been made, and the future is likely to see a larger application of
scientific methods to ground where the outcrops do not tell an obvious
story. Mineral deposits may fail to outcrop because of covering by
weathered rock or soil, by glacial deposits, or by younger formations
(surface igneous flows or sediments), or the outcrop of a deposit may be
so altered by weathering as to give little clue to the uninitiated as to
what is beneath. Mineral deposits formed in older geologic periods have
in most cases been deeply covered by later sediments and igneous rocks.
Such deposits are in reach of exploration from the surface only in
places where erosion has partly or wholly removed the later covering. An
illustration of this condition is furnished in the Great Basin district
of Nevada, where ore bodies have been covered by later lava flows. The
ore-bearing districts are merely islands exposed by erosion in a vast
sea of lava and surface sediments. Beyond reasonable doubt many more
deposits are so covered than are exposed, and it is no exaggeration to
say that by far the greater part of the mineral wealth of the earth may
never be found. Where a mineral-bearing horizon is exposed by erosion at
the surface, underground operations may follow this horizon a long way
below the capping rocks; but, after all, such operations are
geographically small as compared with the vast areas over which the
covering rocks give no clue as to what is beneath. One of the principal
problems of economic geology for the future is to develop means for
exploration in territories of this sort. A beginning has been made in
various districts by the use of reconnaissance drilling, combined with
interpretation of all the geologic and structural features. The
discovery of one of the largest nickel deposits in the Sudbury district
of Canada was made by reconnaissance drilling to ascertain the general
geologic features, in an area so deeply covered as to give little
suggestion as to the proper location for attack.
SOME ILLUSTRATIVE CASES
The use of outcrops in oil exploration has been noted on other pages
(pp. 146-147).
Outcrops of coal seams may be found in folded or deeply eroded areas.
For the most part, however, and especially in areas of flat-lying rocks,
the presence of coal is inferred from stratigraphic evidence and from
the general nature of the geologic section--which has been determined by
outcrops of associated rocks or by information available at some distant
point. The structural mapping of coal beds on the basis of outcrops and
drill holes has been referred to (pp. 126-127).
Iron ores are very resistant to solution. Where hard and compact they
tend to form conspicuous outcrops, and where soft they may be pretty
well covered by clay and soil. In glaciated areas, like the Lake
Superior region, outcrops of iron ore are much less numerous because of
the drift covering. Certain of the harder iron ores of the Marquette,
Gogebic and Menominee districts of Michigan and of the Vermilion
district of Minnesota project in places through the glacial drift, and
these ores were the first and most easily found. Much the greater
number of iron ore deposits of Lake Superior, including the great soft
deposits of the Mesabi range of Minnesota, fail to outcrop. On the other
hand the _iron formation_, or mother rock of the ore, is hard and
resistant and outcrops are numerous. The hematite ores of Brazil have
many features in common with the Lake Superior ores in age and
occurrence, but they have not been covered with glacial deposits.
Outcrops of the iron ore are large and conspicuous, and the surface in
this territory gives one some idea of what the Lake Superior region may
have looked like before the glaciers came along. Certain of the soft
iron ores of the lateritic type, as in Cuba, outcrop over great areas
where their topographic situation is such that erosion has not swept
them off. On erosion slopes they are seldom found. The Clinton iron ores
of the southeastern United States outcrop freely.
Some of the lead and zinc deposits of the Mississippi Valley outcrop at
the grass roots as varying mixtures of iron oxide, galena, chert, and
clay, though they seldom project above the general surface. The old lead
ranges of Wisconsin and Illinois, found at the surface a century ago by
the early explorers and traders, have served as starting points for
deeper exploration which has located the zinc deposits. Erosion channels
have freely exposed these ore bodies, and in the Wisconsin-Illinois
deposits most of the ores thus far found are confined to the vicinity of
these channels. The greater number of the lead and zinc deposits of the
Mississippi Valley, however, are covered with weathered material or with
outliers of overlying sediments, with the result that underground
exploration is necessary to locate them.
Sulphide deposits in general, including those carrying gold, silver,
copper, lead, zinc, and other metals, have many common features of
outcrop. The iron sulphide commonly present in these ore bodies is
oxidized to limonite at the surface, with the result that prospectors
look for iron-stained rocks. These iron-stained rocks are variously
called the "gossan," the "iron capping," the "colorado," or the
"eiserner Hut" (iron hat). The gossan is likely to resist erosion and to
be conspicuous at the surface,--though this depends largely on the
relative resistance of the wall rocks, and on whether the gangue is a
hard material like quartz, or some material which weathers more rapidly
like limestone or igneous rock. The gossan does not often carry much
value, though it may show traces of minerals which suggest what may be
found below. Gold, silver, and lead are not easily leached out of the
surface outcrops. Copper and zinc are much more readily leached, and in
the outcrop may disclose their existence only by traces of staining. It
happens not infrequently, therefore, that copper and zinc deposits are
found through the downward exploitation of oxidized gold, silver, and
lead ores. The veins at Butte were first worked for silver, and the ore
bodies at Bingham, Utah, and Jerome, Arizona, were first mined for gold.
Exceptionally, copper ore in enriched, oxidized form outcrops, as at
Bisbee, Arizona.
It is not always true that valuable sulphide deposits have an
iron-stained outcrop, for in some of them iron sulphide or pyrite is so
scarce that the surface outcrops may be light-colored clayey and
siliceous rocks.
Silver is often represented in the outcrop by silver chloride or
cerargyrite, which may be easily identified. The prospecting for such
surface ores is sometimes called "chloriding."
The presence in the outcrop of dark manganese oxides associated with
vein quartz sometimes indicates the presence below of copper and zinc
and other minerals, as at Butte.
Extensive alterations of the country rock in the way of silicification
and sericitization, and the presence of minerals like garnet,
tourmaline, diopside, and others, known to be commonly deposited by the
same hot solutions which make many ore deposits, may furnish a clue for
exploration below. These characteristics of the country rock, however,
are likely to be masked at the outcrop by later weathering, which
superposes a kaolinic or clayey alteration.
TOPOGRAPHY AND CLIMATE AS AIDS IN SEARCHING FOR MINERAL OUTCROPS
The topographic expression of a mineral deposit depends upon its
hardness and resistance to erosion as compared with the adjacent rocks.
If more resistant it will stand out at the surface; if less resistant,
it will form a depression. The conditions determining resistance are
exceedingly variable, and no broad generalization can be made; but
within a local province a given group of mineral deposits may
characteristically form depressions or ridges, and thus topographic
criteria may be very useful in exploration. Even with such limitations,
the variations of the topographic factor may be so great as to require
much care in its use. Sulphide ores in quartzites are likely to develop
depressions under erosion. In limestones they are more likely to stand
out in relief, because of the softer character of the limestone, though
this does not always work out. Crystalline magnetite and hematite are
more resistant to erosion than almost any other type of rock, and stand
out at the surface with proportional frequency.
Climatic conditions may determine the locus of search for certain
surface minerals. Bauxite and lateritic iron ores, for instance, are
known to favor tropical climates. In exploration for these minerals, the
climatic factor must be applied in connection with the topographic
considerations already mentioned, and both, in turn, in connection with
the character of the country rock as determined by general geologic
surveys. A combination of climatic, topographic, and other physiographic
conditions may be used also in exploration for certain types of residual
clays.
SIZE AND DEPTH OF ORE BODIES AS DETERMINED FROM OUTCROP
Where the ore body is harder than the surrounding rock, it stands out in
conspicuous outcrops and is likely to show a narrowing below. Where it
is softer than the surrounding rocks, and outcrops in a topographic
depression, it is perhaps more likely to show widening below. These
features are due to the general facts that, where the ore body is hard
and resistant, the downward progress of erosion is likely to be arrested
where the adjacent rocks occupy the larger part of the surface, that is,
where the ore body is narrower. This principle is often vaguely
recognized in the assumption that an exceptionally large outcrop of an
ore vein may be "too good to last." Again, such a generalization must be
applied to a specific case with much caution.
Attempts to forecast the depth of veins from their extent at the surface
meet with only partial success. In a very general way great persistence
horizontally suggests persistence in depth, on the ground that the
section exposed on the surface is as likely to be a section of average
dimensions as one along vertical lines.
Faith is the first article of the prospector's creed, and it is hard to
shake his conviction that every ore outcrop must widen and improve
below. As expressed by the French-Canadian prospector in the Cobalt
district, the "vein calcite can't go up, she must go down." While the
scientist may have grounds to doubt this reasoning, he is not often in a
position to offer definite negative evidence.
THE USE OF PLACERS IN TRACING MINERAL OUTCROPS
Outcrops of ore-bearing rock may occasionally be located by tracing a
placer deposit back to its source, or by following up ore fragments in
the "wash" on mountain sides to the place of origin, or by noting ore
fragments in glacial deposits. The presence of an ore mineral in a
placer naturally raises the question as to whence it came. If it is a
recent placer, it may be comparatively easy to follow up the stream
channels to the head-water territory which is delivering the main mass
of sediment, and there to locate a vein in place. The problem is
complicated by multiplicity of tributaries and by large size of the
drainage areas. In such cases careful panning and testing of the gravels
at frequent intervals may show which of several tributaries are
contributing most of the values, and thus may further localize the area
of search. Many important mining districts, including Butte, Bisbee, the
Mother Lode region of southern California, the diamond fields of Africa,
and others, have been found by tracing up placers in this manner. In the
case of an older placer deposit, where the topography and drainage have
been much altered since its formation, or where the deposit has been
covered by later sediments, the problem is of course much more
difficult.
Much less than a commercially valuable placer deposit in unconsolidated
surface rocks may start a search for the mother lode. A single fragment
of ore in the "wash" naturally directs attention up the slope, and the
repetition of fragments in a certain direction may lead unerringly to
the source. The fragments may not even in themselves carry value, but
may consist of detrital material from the leached outcrop--such as iron
or manganese oxides, which, because of their red or black color, stand
out conspicuously in the rock débris.
In the Lake Superior region large angular fragments of iron ore or iron
formation in the glacial drift immediately raise question as to source.
If the fragments are rounded and small, they usually indicate a very
distant source. The general direction of glacial movement is known in
most places, and by tracing up the fragments in this direction the
outcrop may be found; or the chain of fragments may be traced to a point
where they stop, which point may serve to locate the parent bedrock
carrying the ore body, even though it does not outcrop.
An interesting suggestion was made some years ago with reference to the
diamonds found sporadically in the terminal moraines in Wisconsin and
other mid-west states. The diamonds are of such size and quality as to
indicate surely the existence of a real diamond field somewhere to the
north. The locations of these diamond finds were platted on a glacial
map, and lines were projected in a general northerly direction along the
known lines of the glacial movement. It was found that these lines
converged at a point near Hudson's Bay. The data were too meager and the
base line too short for this long projection, and the indicated source
of the diamonds can be regarded as the merest speculation. However, with
the finding of additional diamonds in the drift, as seems very likely,
the refinement of this method might conceivably bring results in time.
THE USE OF MAGNETIC SURVEYS IN TRACING MINERAL LEDGES
Magnetic surveys are often useful in tracing iron-bearing rocks beneath
the surface, in the discovery of outcrops of such rocks, and in working
out their lines of connection. This method is in general use for the
crystalline iron ores in the Lake Superior region, Canada, the
Adirondacks, and elsewhere in the glaciated portions of the United
States. It is not so useful for the brown ores and the Clinton ores of
the southeastern United States, which are only slightly magnetic and can
be commonly located by other methods.
Where the ore is strongly magnetic, and is associated with other rocks
which are non-magnetic, the nature of the magnetic field determined by a
surface survey with vertical and horizontal needles may tell something
about the shape and size of the ore body. Commonly, however, magnetic
ores are associated with leaner magnetic rocks,--with the result that
the magnetic survey, unless it happens to lead to an outcrop of ore,
indicates only the general area through which underground exploration
might be warranted. In the hematitic iron ores of Lake Superior,
magnetism is less pronounced than in the magnetites; and in the soft
hydrous hematites, like those of the Mesabi district, it may cause only
slight disturbance of the magnetic needle. This disturbance is usually
sufficient to locate the position of the iron-bearing formation, though
not the position of the ore.
Where the iron formation has been highly metamorphosed, and rendered
resistant to weathering and erosion so that it will not concentrate into
ore, it is likely to have higher magnetic attraction than the richer
ores. For this reason an area of strong magnetic attraction is
ordinarily regarded as not particularly favorable to the finding of
important hematite deposits. However, this attraction may be very useful
in tracing out the formation to a place where it is less metamorphic,
less resistant to erosion, less likely to outcrop, and yet more
promising for the discovery of iron ore. For instance, on the east end
of the Mesabi and on the east and west ends of the Gogebic district,
magnetic surveys trace the iron formation with great ease to points
where the attraction is low and the conditions for exploration more
favorable.
The magnetic needle has also been used in the search for nickel ore in
the Sudbury district of Ontario, but without great success, because of
the variety of rocks other than nickel which are more or less magnetic,
and because of the slight magnetic properties of the nickel ore itself.
In a large-scale exploration of this type, conducted some years ago, a
favorable magnetic belt was discovered, and a pit was sunk to water
level but not to bedrock. Years later, the extension of this pit by only
a few feet disclosed one of the great ore bodies of the district.
Experimental work on the use of the magnetic needle on copper deposits
has yielded some interesting and suggestive results, but this
investigation is still under way and the results have not been
published.
THE USE OF ELECTRICAL CONDUCTIVITY AND OTHER QUALITIES OF ROCKS IN
EXPLORATION
In addition to magnetism, rocks and ores have other properties
susceptible to observations made at a distance, such as electrical
conductivity, transparency to X-rays, specific induction, elasticity,
and density. All these qualities have been of interest to geologists in
some connection or another, but none of them have yet been used
effectively in exploration for mineral resources. The only one of these
properties that has thus far seemed to promise practical results is
electrical conductivity. The results yet obtained are slight, and this
kind of investigation has rested under something of a cloud, due to
extravagant claims of inventors. Nevertheless, there has been a
considerable amount of scientific work by physicists, geologists, and
engineers, supplemented by special war-time investigations of rock and
earth conductivity in connection with ground telephones and the tapping
of enemy conversations, which seems to indicate a distinct possibility
of practical results in the future,--perhaps not so much in locating
specific ore bodies as in locating general types of formation and
structures,--which may serve to supplement other methods of search.[38]
The transmission and reflection of sound waves in rocks have also been
more or less investigated with reference to their possible military use.
It seems not impossible that these phenomena may be of some geologic aid
in the future, but experimental work is yet in a very early stage.
THE USE OF STRUCTURE AND METAMORPHISM IN EXPLORATION
The necessity for careful use of structural data in exploration scarcely
requires discussion. References have been made to structural features in
connection with coal, oil, iron ore, and other minerals. This phase of
study can scarcely be too intensively followed. The tracing of a folded
or faulted vein, in a particularly complex system of veins, requires
application of all of the methods and principles of structural geology.
Similarly, the importance of applying the principles of metamorphism,
embodied in the _metamorphic cycle_ (pp. 27-28) is almost self-evident.
Certain kinds of metamorphism are suggestive of the nature of the
mineral deposits with which they are associated. One would not look for
minerals known to be caused mainly by surficial processes in rocks which
have been altered mainly by deep-seated processes. The presence of
metamorphism indicating high temperatures and pressures to some extent
limits the kinds of minerals which one may expect to find. On the other
hand, minerals known to be primarily formed at great depths, providing
they are resistant to surface weathering, may be found in deposits which
are the result of surficial alterations or katamorphic processes; that
is, they may become concentrated as residual materials in weathered
zones or as placers.
DRILLING IN EXPLORATION
In the absence of distinctive outcrops, as well as when outcrops are
found, drilling is a widely used method of underground exploration in
advance of the sinking of shafts or the driving of tunnels. Drilling is
more useful in the locating and proving of mineral deposits of large
bulk, like deposits of coal, iron, and oil, than mineral deposits of
small bulk and high value, like gold and silver deposits. However, it is
not always used in the exploration of the first class of deposits and is
not always eliminated in the exploration of the second class. With the
development of better mechanical devices, better methods of controlling
and ascertaining the direction of the drill hole, and more skillful
interpretation of drill samples, the use of drilling is rapidly
extending into mineral fields where it was formerly thought not
applicable.
The geologist takes an active part in drilling operations by locating
the drill holes, by determining the angle of the holes, by identifying
and interpreting the samples, by studying bedding, cleavage, and other
structures as shown in the samples, and determining the attitude of
these structures in the ground, by determining when the horizon is
reached which is most promising for mineral, and by determining when the
hole shall be stopped. With a given set of surface conditions, the
problem of locating and directing a drill hole to secure the maximum
possible results for the amount expended requires the careful
consideration of many geologic factors,--and, what is more important,
their arrangement in proper perspective and relationship. Faulty
reasoning from any one of the principal factors, or over-emphasis on any
one of them, or failure to develop an accurate three-dimensional
conception of the underground structural conditions, may lead to failure
or extra expense. Success or failure is swiftly and definitely
determined. The geologist is usually employed by the company financing
the drilling; but in recognition of the importance of his work, some of
the large contracting drill companies now employ their own geologists.
The technique of the geologic interpretation and direction of drilling
has become rather complicated and formidable, and has resulted in the
introduction of special college courses in these subjects.
The desirability of public registration of drilling records is discussed
on another page (pp. 305-306).
QUANTITATIVE ASPECTS OF GEOLOGIC EXPLORATION
In recent years there has been a tendency to reduce the geologic factors
in exploration to some kind of a quantitative basis. While these factors
may be very variable and very complex, their net effect frequently may
be expressed in terms of quantitative averages. In various mines and
mining districts where operations are of wide extent, local quantitative
factors have been worked out which are useful in predicting results from
proposed explorations in undeveloped portions. Figures of this sort may
be useful and practical guides in planning any given exploration, its
cost, and its probable outcome.
Quantitative methods are illustrated in the general account of Lake
Superior iron ore exploration in a later section.
Curves of production from oil wells and from oil districts have been
found to have certain characteristic features in common which are often
used in predicting the future output and life of a given well, property,
or district. Where associated with coal, the percentage of fixed carbon
in the coal may be a guide to the presence and nature of the oil (see
Chapter VIII).
The geological staff of the Netherlands East Indies estimated the tin
reserves of one of these islands by the use of a factor or coefficient,
based on the experience of another island.
In the Cobalt district of Canada a factor for future discoveries and
output, based on past experience, was similarly developed.
Hoover[39] made a statistical study of several hundred metal mines in
various parts of the world, and found that not 6 per cent of the mines
that yielded profits ever made them from ore mined below 2,000 feet; and
that of the mines that paid dividends, 80 per cent did not yield profit
below 1,500 feet, and most of them died above 500 feet.
Attempt has been made by a Swedish geologist to estimate the iron ore
resources of continents by the use of an iron coefficient. This
coefficient was obtained by dividing the known iron ore resources of the
comparatively well-investigated portions of the world by the number of
square miles in which they occurred, and was then multiplied into the
area of the continents whose resources were to be determined.
The application of quantitative methods of this kind has not yet become
very general, nor is it possible to use them in some cases; where
applied many of them have been very crude and others have been partly
disproved by experience. With increasing knowledge and experience, such
methods are becoming more accurate and useful, and are likely to have
wider use in the future.
ORIGIN OF MINERAL DEPOSITS AS A FACTOR IN EXPLORATION
In exploration, the geologist is keen to ascertain the origin of the
mineral deposit. This is often a source of wonder to the layman or
"practical" man, and the geologist may be charged with having let his
fondness for theory run away with him. A widespread fatalistic
conception is expressed in the Cornishman's dictum on ore, "Where it is,
there it is." Yet an understanding of the origin of any particular ore,
the "why" of it, is coming to be recognized as the most effective means
of reaching sound practical conclusions. By ascertaining the approximate
origin of the ore, it may be possible at once to infer a whole group of
practical considerations based on experience with ores of like origin in
other localities. The origin of the ore is the geologist's primary
interest, and it is this which gives him his most effective and
distinctive tool in exploration. Many other phases of exploration work
may be picked up empirically by any one familiar with the local
conditions; but when the man without sound geologic training attempts to
go into this particular field, his lack of background and perspective
often leads to fantastic hypotheses which may vitiate the inferences on
which he plans his exploration.
The scientific investigator, while not accepting the fanciful theories
of the local observer, will make a mistake if he fails to recognize the
residuum of solid fact on which they are built. Many practical explorers
are shrewd observers of empirical facts, even though their explanations
may show a lack of comprehension of the processes involved. Any
assumption of superiority, intolerance, or lack of sympathy, on the part
of the geologist, toward the inadequate explanations and descriptions
given him by the practical man, is likely to indicate a weakness or
limitation in his own mental processes. The geologist's business is to
sift out the fact from the inference, and not to throw over the whole
structure because some of the inferences are faulty.
LAKE SUPERIOR IRON ORE EXPLORATION AS AN ILLUSTRATION
To illustrate the application of some of the methods of exploration of
the kinds described in this chapter, the writer selects an example from
his own experience in the Lake Superior iron fields.[40]
In this region, consideration of the economic aspects of the problem may
eliminate from the best explorable field certain Canadian portions which
are far from water transportation, because the conditions in these
sections would prevent the use of anything but an exceptionally large
and rich deposit. Economic conditions determine in advance also that it
is not worth while looking for ores of certain grades, either because
they are not usable on account of deleterious constituents or low
content of iron, or because these particular grades have already been
developed in excess of requirements. Having determined what ore is
desired, whether Bessemer or non-Bessemer, whether open-hearth or
foundry, further elimination of area is possible on the basis of past
experience.
Coming to the geologic phases of the problem, the first step is to
eliminate great areas of rock which are known never to contain iron ore,
like the granite areas and the quartzite and limestone areas. Within the
remaining areas, by examination of the surface outcrops and with the aid
of magnetic surveys, iron formations are found which are the mother rock
of the ores. In Michigan, it has been possible to use certain percentage
expectations in the areal location of iron formations within certain
series of rocks extending over wide areas. Such percentage coefficients
have been useful, not only in exploration, but also in the valuation of
lands which are so covered with drift that no one knows whether they
carry an iron formation or not.
Examination of the iron formations results in elimination of large parts
of them, because their metamorphic condition is not favorable to ore
concentration. In the remaining areas more intensive methods are
followed. It is scarcely possible to summarize briefly all of the
structural and stratigraphic methods used in locating the ore bodies.
These have often been described in print.[41] Comparatively recent
advances in this phase of exploration work have been in the more
detailed application of stratigraphic methods to the iron formation. The
group characteristics of the iron formation are fairly uniform and
distinctive as compared with all other rocks; yet within the iron
formation there are so many different kinds of layers represented that
it is possible to use these variations with great effectiveness, in
correlating favorable horizons for ore deposition, in interpreting drill
records, and in other ways. Another method of approach, employed chiefly
on the Mesabi Range, relates to the slumping of the ore layers which
results from the leaching of silica during the concentration of the ore.
This slumping can be measured quantitatively, and has been used to much
advantage in exploration, in correlation of ore horizons, in preparation
of sections and ore estimates, etc.
Early geologic explorations in the Lake Superior country were based on
the assumption that the ores were concentrated by waters working down
from the present erosion surface; but recognition of the fact that the
waters which did the work were related to a far older and different
erosion surface, under conditions which allowed of a far deeper
penetration, has modified exploration plans for certain of the districts
like the Marquette and Gogebic.
Notwithstanding the complexity of the geologic factors involved, their
net result has been to concentrate iron ores in a surprisingly uniform
ratio to the mass of the formation in different parts of the
region,--with the result that on an average it may be predicted for any
district, in an exploration of sufficient magnitude, how much ore is
likely to be cut in either vertical or horizontal dimension. Thirteen
per cent of the productive area of the Mesabi iron formation is iron
ore. For the remainder of the Lake Superior region five or six per cent
is the factor. These figures mean that, if a person could explore a
broad enough area of iron formation, any miscellaneous group of drill
holes or underground openings would tend to yield these percentage
results. Such percentages are amply sufficient to pay a large profit on
the exploration. The question may be raised why the application of
geology is required, if such average results can be secured from
miscellaneous undirected work. The answer is that seldom is it possible
to conduct an exploration on a sufficiently large scale to be sure of
approximating this average, and that geologic study has made it possible
in many cases to secure a better percentage result. If the geologist is
able to raise the percentage ever so little, the expenditure is amply
justified. He is not expected to have 100 per cent success; but he is
expected to better the average returns, and in this on the whole he has
not failed.
Applying this method specifically to the Gogebic Range, it appears that
up to January 1, 1918, exploration and development had covered 3,650
acres of iron formation, measured along the dip in the plane of the
footwall, within the limits of the area in which the formation is in
such condition as to allow concentration of the ore. The total area of
the footwall to a depth of 3,000 feet is approximately 9,650 acres. The
range, therefore, was 38 per cent developed to this depth. In the
developed area, 160,000,000 tons of ore had been found, or approximately
one ton per square foot of footwall area, or 43,800 per acre of
footwall explored. The total area of ore measured on the footwall was
785 acres. The ratio of ore area to total explored area, measured in the
plane of the footwall, was 21-1/2 per cent. This may be taken in a rough
way to indicate the average exploring possibilities in new ground, where
local conditions to the contrary do not exist. This means that over the
whole range about one drill hole or cross-cut in five will strike ore on
an average. Or, looked at in another way, about 200 feet of drifting in
every 1,000 on the footwall will be in ore. Applying this factor to the
unexplored area, amounting to 6,000 acres, the range had an expectation
on January 1, 1918, to a depth of 3,000 feet, over and above ores
already discovered, of approximately 262,800,000 tons. This was
sufficient to extend the life of the range by about forty-four years.
Knowing the average cost of development of ore per foot in the past, and
knowing the annual output and its rate of acceleration, it is possible
to figure with some accuracy how much expenditure should be planned for
annually in the future in order to maintain a safe margin of reserves
against output.
Such quantitative considerations in the Lake Superior region serve not
only to guide the general conduct of the exploration and development
work, but in some cases as a basis for valuation both for commercial and
taxation purposes.
DEVELOPMENT AND EXPLOITATION OF MINERAL DEPOSITS
The search for new ore bodies is closely related to the development,
extension, and mining of ore bodies already found. In this field the
geologist finds wide application of his science. Here he may not be so
much concerned with the economic factors or with the broader methods of
geologic elimination; his study is more likely to be based mainly on the
local geologic conditions.
Some of the larger and more successful mining companies, perhaps the
greater number of them these days, have geologists whose business it is
to follow closely the underground operations, with a view to advising on
the conduct of the development work. This requires the most precise and
intensive study. For instance, the Anaconda Copper Mining Company has a
staff of several geologists, who follow the underground work in the
utmost detail and whose approval must be obtained by the operating
department in the formulation of any development plan. The complexity
and fault relations of the veins in this company's mines are such that
the application of these methods has abundantly justified itself on the
cost sheet.
Too often mining companies leave the planning and execution of the
underground development work to the local management, commonly to the
underground mining captain, without geologic consultation. This
procedure does not eliminate the economic geologist; for when the
development fails at any point, or new and unexpected conditions are
met, the geologist is likely to be called in. In such cases the practice
of a geologist is like that of the ordinary medical practitioner; he is
called in only when his patients are in trouble. The use of adequate
geologic advice in the planning stages is about as little advanced in
some localities as the practice of preventive medicine.
The work of the economic geologist may not be ended by the finding and
development of the ore; for the moment this is accomplished, he should
again consider the economic phases of the problem--the grade of his ore,
its probable amount, and other features, in relation to the general
economic setting. In his enthusiasm for physical results, he may be
carried into expenditures not justified by the economic factors in the
problem. Some one else may and usually does look out for the economic
elements, but the prudent geologist will at least see to it that someone
is on the job.
FOOTNOTES:
[37] Smith, George Otis, and others, The classification of the public
lands: _Bull. 537, U.S. Geol. Survey_, 1913.
[38] Schlumberger, C., _Study of underground electrical prospecting_:
Translated from the French by Sherwin F. Kelly, Paris, 1920.
Bergstrom, Gunnar, and Bergholm, Carl, "Teknisk Tidskrift, Kemi och
Bergvetenskap," 1918, Book 12.
[39] Hoover, Herbert C., _Principles of mining_: McGraw-Hill Book Co.,
New York, 1909, p. 32.
[40] Leith, C. K., Use of geology in iron ore exploration: _Econ.
Geol._, vol. 7, 1912, pp. 662-675.
[41] Van Hise, C. R., and Leith, C. K., Geology of the Lake Superior
region: _Mon. 52, U.S. Geol. Survey_, 1911.
CHAPTER XV
VALUATION AND TAXATION OF MINERAL RESOURCES
POPULAR CONCEPTION OF MINERAL VALUATION
The total returns from mining may not in the aggregate be far above the
expenditure for exploration, development, and extraction; yet the total
mineral wealth of the United States, on the basis of earning power and
aside from the industries based on it, cannot be far from sixty billions
of dollars, and this wealth has virtually come into existence since the
1849 gold rush to California. The mining industry supports a large
population. These facts are the solid basis for the widespread popular
interest in mineral investment--and mineral speculation. But there are
other reasons for this interest,--the gambler's chance for quick
returns, the "lure of gold," the possibility of "getting something for
nothing," the mushroom nature of certain branches of the industry, the
element of mystery related to nature's secrets, and the conception of
minerals as bonanzas with ready-made value, merely awaiting discovery
and requiring no effort to make them valuable. In the United States a
factor contributing to the popular interest is the large freedom allowed
by the laws to discover and acquire minerals on the public domain.
Perhaps no other field of industry comes so near being common ground for
all classes of people. The mineral industry is a field in which it is
easy to capitalize not only honest and skillful endeavor, but hopes,
guesses, and greed. It is not to be wondered at, therefore, that in the
popular mind the valuation of a mineral resource is little more than a
guess, and sometimes not even an honest one.
Nevertheless, the mineral industry has become second only to agriculture
in its capital value and in its earning capacity. In this industry it is
hardly possible to arrive at valuations as securely based as in many
other industries, but the elements of hazard are not so hopeless of
measurement as might be supposed. The great mineral and financial
organizations do not depend on mere guesses, but use well-tried methods.
If the general investor were to give more attention to these methods he
would doubtless save himself money, and the mineral industry would be
rid of a great incumbrance of parasites who live on the credulity of the
public. To anyone familiar with the mineral field, it is often
surprising to see the rashness with which a conservative business man,
who would not think of entering another industrial field without close
study of all the factors in the situation, will invest in minerals
without using ordinary methods of analysis of values.
In the following account of valuation of minerals in the ground, and the
closely related subject, taxation of such minerals, the attempt is made
to state some of the principles briefly and simply with a view to making
them intelligible to the layman. Values beyond the mine are concerned
with so many factors of a non-geologic nature that they are not here
discussed.
VALUATION AND TAXATION OF MINES
INTRINSIC AND EXTRINSIC FACTORS IN VALUATION
It is essential to recognize at the outset that the value of a mineral
deposit, like the value of any other commercial material, comprises two
main elements; an intrinsic element based on the qualities of the
material itself, and an extrinsic element based on its availability and
the nature of the demands for it. The two elements may not be sharply
separated, and neither exists without the other. A mineral deposit in
easy reach of a populous community, which has sufficiently advanced
methods and requirements to use it, may have high value; an exactly
similar deposit, if far removed from points of consumption, handicapped
by transportation, or available only to people without developed methods
for its use, may have little or no value. Intrinsically the deposits are
alike; but extrinsically they are far different, and their values are
correspondingly unlike. Even two adjacent properties, differently
managed and controlled, and with different relations to markets, may
have somewhat different values depending on the use made of them. The
value of a deposit may vary from year to year with changes in demand for
its output, or with changes in metallurgical and other processes which
make its use possible. Minerals of small bulk and high value, as for
instance gold, platinum, and diamonds, have a nearly standard value
related to their intrinsic properties, because they can be transported
so easily to any part of the world. On the other hand, materials of
large bulk and low unit value, such as coal, iron ore, and clay, may
have highly varying values independently of their physical
characteristics, because of their relative immobility. But the values
even of gold and precious stones represent a combination of intrinsic
qualities and of demand. A diamond is made of carbon but is more
valuable than coal or graphite because it appeals to the esthetic taste.
It is only because man introduces an element of demand that the diamond
takes on value. In short, man is the multiplier and the mineral
substance is the multiplicand in the product known as value.
Recognition of the two elements of value is vital to a clear
understanding of the methods and problems of valuation of minerals. It
is too often assumed that the physical properties constitute the sole
factor.
Looked at in a large way, the returns from the mineral industry are
commensurate with the effort put into discovery and development of
mineral resources, even though the returns to lucky individuals have
been excessive. In respect to the importance of the human energy
element, the mining of minerals is not unlike the cropping of soils.
Some interesting economic studies have been made of mining districts to
ascertain whether the total return has been equal to the total
investments by both successful and unsuccessful participants. The
results show that, even in some of the most successful districts, there
is not a large "social surplus,"--that is, a surplus of receipts over
total expenditures. It is difficult to generalize from such studies with
any degree of accuracy; but it seems likely that if we could measure the
vast amount of fruitless effort which has been expended in
non-productive territories, the result would tend to bear out the
general conclusion that the social surplus for the mineral industry as a
whole is a modest one, if it exists at all. Of course, it is to be
remembered that the total benefits from mineral resources are not to be
measured in terms of gain to the producers,--but that their measurement
must take into account the satisfying of all the complex demands of
modern civilization.
VALUES OF MINERAL DEPOSITS NOT OFTEN ESTABLISHED BY MARKET TRANSFERS
While minerals as extracted and used may have standard market values,
mineral deposits in the ground are not bought and sold on the open
market with sufficient frequency to establish standard market values. A
sale may establish a criterion of value for the particular deposit, but
not for the class of deposits,--for no two mineral deposits are exactly
alike. Stock quotations may establish a certain kind of market value,
but these are often vitiated by extraneous considerations. For these
reasons the valuation of a mineral deposit is in each case a special
problem.
THE AD VALOREM METHOD OF VALUATION
The ordinary commercial method of valuing mineral deposits recognizes
the two main elements of value above discussed. This method is sometimes
called the _rational_ or _ad valorem_ method. The profit per ton (or per
other unit) of the product is established, on the basis either of past
performance of the property or of experience with other similar
properties. This profit is multiplied by the total tonnage estimated in
the deposit, the estimate including known reserves, probable reserves,
and in some cases possible and prospective reserves. The product of the
profit per ton and the total tonnage gives the total net amount which
will be received; it does not, however, give the present value, because
the commodity cannot all be taken out and sold at once, but must be
mined and absorbed by the market through a considerable period of years.
The returns receivable some years in the future have obviously a lower
proportionate present worth than amounts to be received at once. The
interest rate comes into play, making it necessary to discount each
annual payment for the number of years which will elapse before it is
received. It is evident, therefore, that an estimate of the _life_ of
the property is necessary, involving not only knowledge of the reserves,
but also a forecast of the annual extraction or _rate of depletion_.
As a simple case of _ad valorem_ valuation for illustrative purposes, a
deposit containing 1,000,000 tons in reserve has an estimated output of
100,000 tons a year for ten years, on which the profit per ton has in
the past averaged $1 and is expected to average $1 in the future. Ten
annual instalments or dividends of $100,000 are to be received. The
present value of the total of these instalments is figured by an annuity
method. It is the value upon which the series of dividends will pay
interest at a predetermined rate, in addition to paying to a sinking
fund annual instalments which, safely invested each year at a low rate
of interest (usually 4%), will repay the present value at the end of the
ten years. In our hypothetical case, if an interest rate of 8% be taken,
the present value of $1,000,000, to be received through ten years in ten
equal instalments, is $612,000. In other words, the sum of $612,000 will
be replaced by the sinking fund at the end of ten years, and will pay 8%
interest during this period,--this requiring total receipts of
$1,000,000 in ten equal annual instalments. If the deposit here cited as
an illustration were to be worked out in three years, thus yielding
three annual instalments of $333,000, its value would be $833,000.
Each of the factors entering into this method of valuation covers a wide
range of variables, any one of which may be difficult to determine.
The profit per ton for a given deposit may have been extremely variable
in the past, making it difficult to determine whether the highest or
lowest figure should be projected into the future or whether some
average should be taken; and if an average, whether the time covered by
the average should be long or short. For a small, short-lived deposit
obviously the most recent conditions would be taken into account in
estimating future profits. For a long-lived property there would be more
tendency to consider the long-time average vicissitudes, as reflected in
the average profits of the past. For some mineral commodities there are
cycles of prices, costs, and profits, of more or less definite length,
established during the long past history of the industry; and in such
cases it is desirable in calculating averages to use a period covering
one or more of these cycles, rather than some shorter or longer period.
For many minerals, however, these cycles have been too irregular to
afford a sound basis for future estimates. If the experience of the
property itself is too short to afford a sufficient foundation for
forecasting profits, or if there has been no previous work on the
property, then it is necessary to use averages based on other
properties or other districts; or if there are none strictly
comparable, to build up a hypothetical figure from various estimated
costs of labor, supplies, and transportation, selling prices, etc. In
the estimate of the profit factor, the geologist is not primarily
concerned.
In estimating the total reserves in a mine, geological considerations
nearly always play a large part. An ore body may in some few cases be
completely blocked out by underground work or drilling, eliminating the
necessity for inferring conditions beyond those actually seen; but in
the huge majority of mineral deposits the reserves are not so definitely
known, and it becomes necessary for the geologist, through knowledge of
similar occurrences, through study of the structural features of the
deposit, its origin, and its history, to arrive at some sort of an
estimate of reserves.
In estimating the life of a mineral deposit it is necessary to start
with the figure of total reserves, and from a study of conditions of
mining and of markets to estimate the number of years necessary to
exhaust the deposit. This is a more nearly commercial phase of the
problem, in which the geologist takes only part of the responsibility.
Perhaps more estimates of value have gone wrong because of misjudgment
of this factor than for any other cause. If the physical conditions are
satisfactory, it is easy to assume a rate of extraction and life based
on hope, which experience will not substantiate.
The choice of the interest rate to be used in discounting future
receipts to present worth likewise is a financial and not a geologic
matter. Again, however, the geologist must give consideration to this
factor, in view of the fact that the interest rate must be varied to
cover the different degrees of hazard and doubt in the geologic factors.
For instance, to the extent to which the estimate of ore reserves is
doubtful, it is necessary to use a high rate of interest to allow for
this hazard. In a large, well-developed mineral deposit, with the
geological factors all well known and the demand and market well
established, it is reasonable to use a lower rate of interest. In
general, the mineral industry is regarded in financial circles as being
more hazardous than many other industrial lines; and money is put into
the industry with the expectation of a high rate of interest, no matter
how safe the investment may be. In actual practice interest rates used
in making valuations vary from 6 to 15 or 20 per cent.
It is clear that, where a property has long life, the interest will very
materially reduce the present value of the ores to be mined far in the
future. Reserves to be mined more than thirty years hence have
relatively little or no present value. Beyond a certain point,
therefore, the acquirement and holding of reserves for future use by
private companies has little commercial justification. This is a matter
which is too often not sufficiently well considered. Man's natural
acquisitiveness often leads him into investments which, because of the
time and interest factor, have little chance of successful outcome. Of
course a large corporation, anticipating an indefinitely long life, or
perhaps aiming at monopoly, may afford to hold reserves as a matter of
general insurance longer than a small company,--even though, because of
the interest rate, these reserves have no present value on their books.
It is likewise true that governments, looking forward to the future of
the nation, and without the necessity of paying so much attention to
interest and taxes, are not so limited by this consideration.
An illustration of the limiting effect of the interest rate on the
acquirement of long-lived coal deposits by private interests is
discussed in Chapter XVII on Conservation. Investments made many years
ago have so augmented, even at low interest rates, as to make it
practically impossible to count on a return of capital and interest; or
if the return were to be exacted from the public it would mean excessive
charges, which are not possible in competition with other mines not so
burdened.
In the commercial valuation of oil wells and pools, much the same method
is used as has been described for mineral resources in the solid form,
but the estimate of reserves or life is based on consideration of curves
of production of the sort mentioned on pages 134-136.
The essence of the _ad valorem_ method of valuation above described is
income-producing capacity. This method recognizes the fact that the
value of the mineral deposit depends, not only on its physical
constitution, but also on what performance can be expected from it.
Stock quotations on mineral properties in the standard markets are based
substantially on estimates of income capacity, more or less on the _ad
valorem_ basis. However, the quotations also reflect the hopes and fears
of the public, often resulting in valuations quite different from those
based on studies of the objective conditions.
The war introduced new considerations into the problems of _ad valorem_
valuation. Under peace conditions there is a tendency toward the
establishment of normal costs, selling prices, and markets, which can be
taken more or less for granted by anyone attempting to value mineral
deposits. Under war and post-war conditions, few of these elements can
be taken for granted; it becomes necessary to consider the entire world
situation in regard to a mineral commodity, the effects of the Peace
Treaty (which greatly concerns minerals), future international
relations, tariffs, and other matters of a similar sort. If a person
were today valuing a manganese deposit according to the method above
outlined, and were to confine himself solely to a narrow consideration
of past markets and profits on individual properties, he would be very
likely to go wrong,--for the world manganese situation has an immediate
and practical bearing on each local problem (see pp. 173-176).
OTHER METHODS OF MINERAL VALUATION AND TAXATION
We have discussed the _ad valorem_ method of valuation at some length
because it is the one in widest commercial use, and also because the
principles involved underlie practically all other methods of mineral
valuation. The _ad valorem_ method is used in appraisals for taxation in
some districts and for some commodities, as, for instance, the iron
mines of Michigan and Wisconsin. Its application, however, requires
skill and judgment if equitable results are to be secured. For taxation
purposes, therefore, it is not uncommon to adopt purely arbitrary or
empirical methods which eliminate the element of judgment, and which
often result in valuations quite different from those used commercially.
The state of Minnesota divides its iron ore deposits into a series of
classes, on each of which a more or less arbitrary flat value per ton is
placed, based on the spread between cost and selling price. The
adjustments of flat values on the several classes through a series of
years, however, as well as the assigning of specific ores to the
different classes, have been based on the same factors as are used in
_ad valorem_ valuations.
The state of Wisconsin uses a so-called "equated income" method of
valuation and taxation for the lead and zinc deposits of the
southwestern part of the state. Under this method the state puts such a
tax on the mine incomes for the preceding year as will yield
approximately the same total return as under the _ad valorem_
method,--the whole being based on the assumption that each deposit has
about the average life figured for the mines of the entire district. So
far as individual ore deposits vary from this average life, the value
fixed departs from the true or _ad valorem_ value.
Several states impose specific taxes based on the operations of the
mines for the preceding year or for some combination of preceding years,
as expressed in tonnage output or net profits or net proceeds,
regardless of life or reserves. So far as output or net proceeds for a
year are proportional to the real value of the property, a rough
approximation to equitable taxation as between mines is accomplished.
Often, however, the valuation thus obtained has little relation to the
true value, because it does not take into account the great differences
between properties in reserves, in life, and in capacity for future
profit.
Income taxes, national and state, are of course based on the profits of
the preceding year; but in the collection of these taxes from mineral
operations, it is recognized that mineral deposits are wasting assets,
and therefore a considerable part of the income may under the law be
regarded as a distribution of capital assets, and be deducted from
taxable income. The amount to be deducted obviously depends on the size
of the reserves and the life,--with the result that progressive
adjustment of income tax valuations tends to take into consideration
exactly the same factors as are used in the _ad valorem_ method. It is
obviously unjust, for instance, to collect the same proportion of tax
from the annual income of a mine which has a life of only two years as
from a mine which has a life of fifty years. Under the federal income
tax a capital value is placed on the mineral deposit as of March 1,
1913, which total capital value may be increased with subsequent
discoveries. As the ore is taken out of the ground and sold, income tax
is paid only on the difference between the assigned capital value per
unit and the selling profit. If, for instance, the capital value as of
March 1, 1913, is placed at 50c. per ton of mineral in the ground, and
ten years later a ton is sold for a profit of $1, income tax is paid on
50c. The figure of 50c. per ton as value in the ground is actually
obtained by estimating a profit, when the ore is ultimately mined and
sold, of $1 per ton, and discounting this dollar to present worth as of
March 1, 1913. Therefore the total amounts on which taxes are paid
during the life of the mine should represent approximately the total
accruals of interest from March 1, 1913. In this manner the proportion
of annual income to be taxed becomes larger with the length of the life
period. With a deposit having a life of thirty years the net result is
that about half of the aggregate income is taxed, though this figure of
course varies somewhat with the interest rate used.
In the collection of income taxes from coal mines in England, and in the
collection of certain state income taxes in the United States, a
considerably smaller allowance is made for the retirement of capital
value (or for _depletion_, as this is commonly called). In these cases
the deduction allowed is a small fixed percentage of the capital value,
regardless of the actual life of the property.
The treatment of mineral resources as wasting assets in the United
States income tax law meets one considerable practical difficulty--namely,
that the law really requires physical or _ad valorem_ valuation of
every mineral property by the government, as a check on the claims for
depletion allowance. This immense and expensive task is too much for the
tax collection agencies as now organized, and it may be questionable
whether it will ever be desirable to expand these agencies to the extent
required for such a purpose. This is the principal argument for the use
of arbitrary depletion factors such as those sometimes used abroad.
There are many advocates of the straight tonnage tax on mineral
deposits, on the ground that it is simple, definite, and easily applied.
The present tendency is to extend the application of this form of tax.
It is clear, however, that to assume the same value per ton for taxing
purposes on a property making a large profit, and on another property
which, because of physical conditions, is barely able to operate at a
profit, imposes a relative injustice. To meet this difficulty, it is
sometimes proposed that the tonnage tax should be graded in such a
manner as to allow for differences in physical conditions and in profit
at different mines. When one attempts to apply a graded tonnage tax,
however, it soon becomes apparent that, in order to make such a
valuation equitable as between properties, it is necessary to use all
of the factors of the _ad valorem_ method for each of the properties.
The wide appeal of arguments for a flat tonnage tax is based partly on
popular misconception of the complexity of elements entering into
mineral valuations.
There are many forms of more or less indirect tax which are substituted
in different parts of the world for direct taxes. For instance, certain
states in South America do not tax ores in the ground, but collect the
revenue in the form of mining licenses or export taxes.
GENERAL COMMENTS ON TAXATION OF MINERAL RESOURCES
There has been a noticeable tendency in recent years to regard mineral
resources as a heritage of the people, to be held in trust, rather than
as property to be acquired and managed solely for private interest. This
tendency has been indicated by the adoption in various parts of the
world of laws affecting rights to explore and acquire minerals on the
public domain; laws relating to the right of eminent domain over
minerals already alienated from the government; laws regulating the
exploitation of minerals in the interests of conservation; laws relating
to tariffs and other restrictions on the export of mineral commodities;
and laws relating to taxation.
The feeling that mineral resources really do not belong in private hands
has undoubtedly been an underlying factor in the imposition of heavy
taxes. Contributing to this action also are the popular belief in the
intrinsic bonanza values in mineral resources, the failure to recognize
the large element of value which is put into such resources by human
efforts, and the failure to realize that the social surplus in the
aggregate is small. To some tax officials an ore is an ore, more or less
regardless of situation, of conditions of mining, of the demand for the
product, and of the time when the demand will allow the ore to be
mined,--in short, more or less regardless of what the ore may be made to
yield as a going business. In this way heavy taxes are sometimes imposed
on mineral reserves, which are based on unwarrantably high appraisals of
future possibilities, and which cannot be paid out of earnings.
Ultimately, a tax must be adjusted to the capacity of the mine to pay
out of its earnings, and this capacity in turn is determined both by the
physical characters of the ore and by the success with which it may be
made available for consumption. This view of valuation for taxing
purposes is sometimes opposed by mining men on the grounds that it taxes
brains, skill, and initiative, and that it puts a premium on shiftless
management. The same argument might be applied to the valuing of any
business or profession. To the writer the argument is not sound, in that
it fails to recognize the element of human energy in resource values. If
value were to be confined solely to the intrinsic character of the ore
itself, there would be required an almost impossible degree of
discrimination on the part of taxing officials to dissociate this value
from other considerations; and there would be required further the
differentiation between efficient and inefficient management, which
involves so many considerations that the conclusion would be worthless.
In the application of income taxes to mining operations, there is
sometimes another tendency toward over-taxation in that the income is
regarded as more or less permanent, and insufficient allowance is made
for exhaustion of the mineral deposit. Under the United States income
tax, mineral deposits are definitely recognized as wasting assets and
this factor is allowed for; but in state income taxes and in England and
other parts of the world, allowances for this purpose are small.
There is wide belief that heavy taxation of mineral resources,
particularly on the _ad valorem_ basis, retards exploration and prevents
the development of the reserves which are necessary to stabilize the
mineral industry. High taxes have undoubtedly had this effect in some
cases, especially where taxes have been imposed on resources long prior
to development; but, in the writer's view, this tendency in general has
not yet passed the danger point, and is not likely to do so until taxes
become positively confiscatory of the industry. To argue that increase
of taxes may even have certain beneficial results on the mineral
industry may lead to suspicion of one's mental soundness; but it is hard
to escape the conclusion that the incidence of high taxes has led to a
much more careful study of the question of reserves, has eliminated in
some cases the expenditure of money for development of excessive
reserves to be used far in the future, and has tended to prevent
over-production.
Where mineral reserves are developed too far ahead of demand, the
interest on the investment piles up an economic loss to be charged
against the industry. It may be assumed that the urge for exploration
will continue as long as there is demand for mineral resources; and
that, to keep the industry on a sound basis, a certain amount should be
set aside and charged to cost for the purpose of keeping up reserves in
a proper ratio to production. Much remains to be learned about the most
desirable ratio between reserves and production. In many camps, before
the incidence of high taxes, this ratio was not properly determined; and
there was a tendency, due to natural acquisitiveness and in the absence
of anything to hinder it, to build up reserves indefinitely. The first
effect of high taxes in such camps has frequently been the curtailment
of exploration and development. Later, as production has begun to
approach the end of the reserves, exploration has been resumed, but only
on a scale necessary to insure production for a limited period in
advance.
The argument that high taxes inhibit exploration is good only beyond the
point where the industry itself becomes no longer profitable. If there
is sufficient demand for the resource, it is obvious that such a
condition cannot long continue; for, as production and the development
of reserves fall off, the resulting increase in the price received for
the product is likely to offset any effect of taxes, and to restimulate
production and exploration.
Nevertheless, in this period of high taxes following the war, there is
much discouragement in the matter of exploration, suggesting that the
danger point is being approached. Some relief has been afforded by
recent special provisions of the federal income tax law, recognizing
mineral resources as wasting assets, allowing recent discoveries to be
included with total assets for depletion purposes, and recognizing
special and peculiar circumstances with reference to each mine. Also a
certain amount of exploration goes on through the momentum gained from
past conditions, without sufficiently full recognition of the effect of
present high taxes. This is not surprising when it is remembered that
the people actively engaged in field exploration often do not think
sufficiently fully of the tax situation, until after a discovery or
development has brought them face to face with it.
Because of the vital importance of the reserve factor in mineral
valuation, geologic aid and advice are extensively sought by both public
and private organizations. Mining geologists are playing an important
part in the application of the national income tax. A larger number are
acting for private companies in appraisals required by this tax. Many
geologists are used in making valuations for state taxes, and in two
cases the state geological surveys have complete charge of appraisals.
These appraisals include not only examinations of specific properties,
but general surveys of large regions, to ascertain possible values of
undeveloped lands and to establish broad principles of valuation based
on a consideration of all the physical factors in the situation.
CHAPTER XVI
LAWS RELATING TO MINERAL RESOURCES
This heading is likely to suggest mining law and the vast literature
devoted to it. Mining law has mainly to do with questions of the
ownership and leasing of mineral deposits. In addition, there are laws
relating to the extraction of mineral products, including those having
to do with methods of mining and with safety and welfare measures. There
are laws affecting the distribution of mineral products, such as those
relating to tariffs, duties, international trade agreements, and many
other matters. There are laws relating to underground water, to shore
lines, and to various geologic engineering fields.
In the formulation of these laws, as well as in the litigation growing
out of their infraction, basic geologic principles are involved; and
thus it is that the geologist finds much practice in the application of
his science to legal questions. It will be convenient to consider some
of the laws relating to mineral resources under three headings: first,
ownership and control; second, extraction; and third, distribution.
I
LAWS RELATING TO OWNERSHIP AND CONTROL OF MINERAL RESOURCES
Large use of mineral resources is of comparatively recent date. Some of
the mineral industries are not more than a decade or two old and the
greater number of them are scarcely a century old. In the United States
the mineral industry dates mainly from the gold rush to California in
1849. The formulation of laws relating to the ownership of minerals has
on the whole followed rather than preceded the development of the
mineral industries; and hence mining laws relating to ownership are not
of great age, although historical precedent may be traced far back.
ON ALIENATED LANDS
Where lands came into private ownership, or were "alienated" from the
governments before the formulation of mining laws, varied procedures
have been followed in different countries.
In England and the United States, under the old régime in Russia, and to
a slight extent in other parts of the world, mineral titles remain with
the owner of the land and the government does not exercise the right of
eminent domain. But even in England, where private property rights have
been held peculiarly sacred, the discovery of oil during the later years
of the war led to an attempt to expropriate the oil rights for the
government. Because of the objection of landowners this attempt has not
reached the statute books, but the movement is today an extremely live
political question in England. A somewhat similar question is involved
also in the movement to nationalize the coal resources of England, now
being so vigorously urged by the labor party. In the United States, no
serious attempt has yet been made to take over mineral resources from
private ownership.
Other countries have gone farther in retroactive measures in regard to
alienated lands. Under the leadership of France, most of the countries
of western Europe have appropriated to their governments the
undiscovered mineral resources on private ground, particularly those
beneath the surface, except where previously they had been specifically
conveyed to the private owners, or with the exception of certain
designated areas and minerals which had been conveyed to private
ownership prior to certain dates. Some minerals occurring at the
surface, variously specified and defined in different countries, are
allowed to remain with the private owners, although often subject to
government regulation in regard to their development and use.
In varying degree this treatment of mineral resources on alienated lands
is followed in the British colonial laws--in South Africa, Australia,
New Zealand, and Canada--and in the Latin-American laws. The laws are
usually based on specified classifications of minerals. Those occurring
at or near the surface, and called "quarries," "placer deposits,"
"non-mines," or "surface deposits," usually remain with the surface
owners. Those beneath the surface, called "sub-surface deposits" or
"mines," in general belong to the government. In some of the countries
of South America the state exercises eminent domain even over the
surface deposits; and in others even sub-surface minerals remain in
private ownership, where specifically granted, or where the transfer of
property took place prior to certain dates.
Where the government has acquired mineral ownership of lands previously
alienated, the resources are open for development either by the owners
of the surface or by others, on a rental, lease, specific tax, labor, or
concession basis. The government holds the title, exacts tribute, and
more or less directs and controls the operation. Exceptionally, as in
Ontario, British Columbia, Quebec, and Newfoundland, the government
grants patents, that is, it disposes of its rights to purchasers.
ON THE PUBLIC DOMAIN
Where the development of mineral resources began before the lands had
passed from governmental ownership, special mining laws were enacted.
Looked at broadly, these laws may be regarded as based on two partly
conflicting considerations.
(1) The assumption that mineral resources, which are wasting assets,
accumulated through long geologic periods, are peculiarly public
property,--not to be allowed to go into private ownership, but to be
treated as a heritage for the people as a whole and to be transferred to
posterity in the best possible condition. Some of the early minerals to
be developed were used either for money or for war purposes, leading
naturally to the acceptance of the idea that these belonged to the
government or to the sovereign.
(2) The assumption that the discovery and development of mineral
resources requires a free field for individual initiative, and that the
fewest possible obstacles are to be put in the way of private ownership.
Governments have not as a rule been greatly interested nor particularly
successful in exploration. Therefore, in framing laws of ownership,
concessions have been made to encourage private initiative in
exploration and development. In the case of the United States this idea
was coupled with the broad doctrine that the government held public
lands only in the interest of the people, and that its people were
entitled to secure these lands for private ownership with the least
possible restriction.
A survey of the mining laws affecting the public domain or
non-alienated lands of different parts of the world, as well as the
history of changes in the mining laws, indicates a wide range of
relative emphasis on these two underlying considerations. In the United
States, at one extreme, the laws have been such as to give the maximum
possible freedom to private initiative, and to allow easy acquirement of
mineral resources from the government. At the other extreme, in South
Africa, Australia, and South America, it is impossible for the
individual to secure title in fee simple from the government; he must
develop the mineral resources on what amounts to a lease or rental
basis, the ownership remaining in the government.
The trend of events in mineral laws is toward the latter procedure. This
is evidenced in the United States by the withdrawal of large areas of
public lands from entry, and by the recent enactment substituting
leasing privileges for specified minerals for the outright ownership
which was allowed under the federal law before the lands were withdrawn
from entry. The withdrawal of oil lands from public entry in other parts
of the world is another illustration (see pp. 131-132).
NATIONALIZATION OF MINERAL RESOURCES
Nationalization, as this term is popularly understood, means financial
control and management of mineral resources by the government, either
through actual ownership or through measures of public control designed
to eliminate private interest from the active direction of the
resources. In a broader sense, it may be used to include a considerable
variety of restrictive and coercive measures adopted by the government
in the proposed interests of public welfare,--as illustrated by the
war-time measures instituted by the United States and other governments
relating to the mining and distribution of coal, and to coal prices. In
this broader sense various aspects of nationalization are indicated
under other headings in this and other chapters.
It is clear that other countries of the world have gone farther in the
direction of nationalization of mineral resources than the United
States. The tendency was manifest before the war, and has been strongly
emphasized during and since the war. In the United States,
notwithstanding war-time measures, the subject has not yet come
prominently forward, at least by name. On the other hand, there has been
growing recognition of the dependence of public welfare on the proper
handling of mineral resources--particularly of the energy resources,
coal and oil,--as evidenced by a variety of proposals and measures under
consideration in legislative and administrative branches of our national
and state governments. Even taxation, both local and national, has in
effect reached a stage where private interest has become considerably
minimized by the increasing burdens laid on the industry by government
requirements. The immediate purpose of taxation is to raise money for
the needs of the government; but in the formulation of tax measures
there is clearly to be discerned a growth of underlying sentiment that
natural resources belong in some fashion to the public, and that private
control is to be regarded not as a sacred property right but as a trust
held on sufferance of the public.
In view of the obvious trend toward nationalization in other parts of
the world and the significant tendencies in the United States, it seems
likely that the subject of nationalization of mineral resources will
come prominently to the front in this country in the comparatively near
future. If so, it is time that students of mineral resources should
recognize the comprehensiveness of this problem, and should attempt to
develop basic principles to serve as a guide in the direction and
formulation of the numerous and complex measures which are sure to be
proposed. At present there is no government or technical organization
related to the industry which is studying the problem in its broader
aspects and is in a position to advise wisely with public officials
interested in this problem.
It is beyond the scope of this book to discuss the pro and con of an
economic question of this magnitude. The writer would, however, record
his belief, which is implied also in discussions in other chapters, that
the discovery and intelligent management of mineral resources by their
very nature and infinite variety require private initiative, and that
the history of government efforts in this field in this and other
countries does not promise that nationalization can supply sufficient
advantages to counterbalance the loss of this element. With this view
the problem of nationalization becomes one of determining what steps, if
any, can be taken by a government to the advantage of public welfare,
which will at the same time preserve and foster private initiative,
exercised with the hope of reward, which seems alone to be capable of
meeting the variable, elastic, and complex problems inherent in the
development of a natural resource.
A first step toward a broad scientific attack on this problem would be
the recognition of the fact that tariffs, taxes, conservation,
international mineral questions, leasing laws, and various technical
investigations of minerals are but parts of a great unit problem. With
this recognition there should follow naturally an attempt to correlate
and direct the many government agencies, legislative and administrative,
now concerned with different aspects of the problem. Under present
conditions, the various elements of the problem are considered by
different groups of persons, without sufficient contacts or correlation
to promise the development of a broad, underlying policy.
EFFECT OF OWNERSHIP LAWS ON EXPLORATION
The nature and the progress of exploration (and development) in
different countries have been more or less related to the character of
the mining laws.
Where the mineral resource has passed from government control into
private ownership, exploration is a matter of commercial arrangement
between the explorer and the owner. There is often some lag in
exploration, especially where the lands are held in considerable blocks.
The owner is often not inclined, or unable, to institute effective
exploration himself; and even though he is willing to offer favorable
exploration terms to others, the inducement is often less attractive
than on government lands. For instance, it is stated that in England,
due to the many requirements of law and custom, it takes on an average
eight years, and in some cases even longer, to close a coal lease after
the terms have been agreed upon. The slowness of exploration and
development on the great land grants in the United States, and on the
tracts of the large timber companies, also illustrates the retarding
effect of private ownership. It is partly this situation that is making
governments increasingly careful about parting with mineral ownership,
and that is leading to the introduction of more or less coercive
measures, either to regain control or to make it easier for the public
to explore and develop minerals on privately owned lands. Under the
great land grants to railroads in the United States it is becoming
increasingly difficult to secure mineral patents from the government;
and there has been litigation between government and grantees, as in the
case of certain oil lands of the Southern Pacific Railway. The taxation
in some states of mineral rights which have been reserved by large
owners is indirectly resulting in appraisal of these rights by the
owners and in efforts to utilize them. As long as mineral rights were
not taxed independently of surface rights, they were often reserved in
selling surface rights on the mere chance that mineral might be found in
the future, and thereby general exploration and development were held
back.
In the United States, minerals on the public domain have been open to
exploration and acquirement with minimum restrictions, except for the
considerable areas later withdrawn from entry. After long delay a part
of these withdrawn lands are again open to private exploration, but not
to fee ownership. Specified minerals--coal, oil, phosphates, and
potash--may be explored for, and may be leased under certain
restrictions as to amount and time of development. The effect of this
act on exploration is yet to be proved; but since many of the lands have
now been shown to be favorable for minerals which are in great demand,
there is little doubt that exploration will be resumed on a large scale.
On the whole, under the federal mining laws of the United States the
individual prospector has maximum leeway,--and from the standpoint of
development of resources this procedure probably has been justified.
In other countries where the mineral resources are owned by the
government, there is in most cases considerable restriction, through
licenses and other regulative measures, upon the activities of
prospectors. This restriction, together with the fact that it is usually
not possible to secure title to the land, but only to secure rights
through rental or leasing, is to some extent a deterring influence on
the penniless prospector. It does not follow that under these conditions
exploration and development are absent. The charges imposed are light,
and in the early stages require comparatively small contributions as
evidence of good faith. It is to be remembered that exploration has
become concentrated more and more into the hands of persons financially
able to meet such conditions. Exploration is passing from the highly
hazardous stage of individual effort into a systematic business with
calculable returns.
USE OF GEOLOGY IN RELATION TO OWNERSHIP LAWS
The contacts between geology and laws relating to mineral ownership are
many and varied; a few illustrative examples are offered.
Many difficulties arise from the loose use of mineral names in these
laws. The laws governing location of mineral deposits in Cuba are so
framed that iron ores may be located and claimed from the government
either as "iron ores" or as "bog ores and yellow ochers." Some of the
important ores of eastern Cuba, now being extensively used in the United
States, came into litigation because rival claimants had overlapping
claims under the two classifications. The wording of the law is of
course ambiguous, and suggests that geologists did not have a hand in
its framing. To establish title to these claims it was necessary to show
whether these ores had been rightfully located as iron ores, or whether
they should have been located as bog ores and yellow ochers. This
involved an analysis of the geological conditions, to show that the ores
are the result of normal weathering and concentration in place of the
underlying rocks--an origin common to many iron ore deposits,--and that
they do not have the characteristic origin of bog ores. In short, the
question was settled on the scientific principles of origin of ores and
of metamorphic geology.
The efforts of our federal government to frame and apply mining laws to
public lands have involved extensive geological and mining surveys by
the United States Geological Survey and the Bureau of Mines. The land
classification work for this purpose by the Geological Survey has been
of wide scope. The recently enacted leasing law, which opens up
government lands for exploration of coal, oil, potash, and phosphate,
requires carefully prepared geologic data for its proper administration.
State governments also have initiated surveys of an exploring nature for
taxing and other public purposes (see pp. 306, 311).
In the United States there is a wide use of geologists as witnesses in
litigation affecting "extralateral rights." The federal mining law gives
the owner of the claim containing the "apex" or top of a mineral vein
or lode the right to follow the vein down the dip, with certain
limitations, even though this takes him on to adjacent properties under
other ownership. Where two branches of a vein are followed down from
separate claims, the owner of the oldest claim is entitled to the vein
below the point of junction. The law was framed to validate a procedure
more or less established by mining custom. It was obviously framed with
a very simple and precise conception in mind--namely, a simple vein
definitely and easily followed, without much interruption or contortion.
In nature, however, veins or lodes have a most astonishing variety of
form and occurrence, making it difficult to frame a definition that is
comprehensive and at the same time sufficiently precise for all cases. A
commonly used definition of a vein or lode is a mineralized mass of rock
which is followed for purposes of finding ore. The mineral matter may be
continuous or discontinuous. There may be one definite wall, or two
walls, or none at all. There may be associated gouges and altered or
mineralized rock. The vein may consist of almost any combination of the
elements of mineral matter, walls, gouges, and mineralized rock. Instead
of being a simple tabular sheet, a vein may have almost any conceivable
shape; it may consist of multiple strands of most complex relations; it
may have branches and cross-over connections. It may be a more or less
mineralized sedimentary formation with limits determined by original
deposition. It is very often bent or folded, and even more often
faulted; the faulting may be of great complexity, making it extremely
difficult to follow the vein. The vein may be cut by other veins of
different ages, which in places may be hard to distinguish one from
another. Erosion working down on a complex vein displaced by faulting
and folding may bring several parts of the same vein to the surface,
developing what seem to be separate vein apices. Where there are many
veins close together, it may be difficult to determine whether the
entire mass should be considered a unit vein or lode (a "broad lode"),
or whether each vein should be considered independently under the law.
The geologic aspects of these problems are obvious. There are few mining
districts where the vein conditions are so simple that no geological
problems are left to be solved with relation to extralateral rights. In
the early stages of the mining, separate operations may be carried on
for a considerable time in a district without mutual interference; but
as mining is carried down the dip, what seemed to be separate veins may
be found to be parts of the same vein or parts of a complex vein system,
and separate mining organizations are thus brought into conflict. It
then becomes necessary either to consolidate the ownerships or to go to
the courts to see which claim has the extralateral rights. In either
case, the geologist is called on to play a large part,--in the valuation
of rights for the purpose of combination, or in litigation to settle
apex rights. A geologic survey of the conditions is a prerequisite. In
order to get the needed information for the courtroom, it may be
necessary to go further, and to conduct extensive underground
exploration under geologic direction. Some of the most intensive and
complete geological surveys of mineral resources in existence have been
done for litigation purposes. The study in these cases is not empirical,
but goes into every conceivable scientific aspect of the situation which
may throw any light on the underground conditions--the source of the
ores, the nature and source of the solutions which deposited them, their
paths of travel, the structural and metamorphic conditions, the
mineralogical and chemical character of the ores and rocks, and even
broader questions of geologic age. The many volumes of testimony which
have accumulated during famous apex trials cover almost every phase of
geology, and are important primary sources for the student of economic
geology.
It is often argued that strictly scientific, impartial geologic work is
impossible in connection with one of these trials, because the viewpoint
is warped by the desire to win. The sharp contrast in the views of
experts on the two sides is cited in evidence.
There is no denying the fact that the conditions of a trial tend toward
a certain warp in scientific perspective. On the other hand, the very
existence of competitive and opposing interests leads to the most
intensive detailed study, and to complete disclosure of the facts. In
most cases there are no substantial differences in the statements of
scientific fact by reputable experts on the two sides, although there
may be wide differences in the inferences drawn from these facts. The
failure to note a fact, or any distortion or misstatement of a fact, is
followed so quickly by correction or criticism from the other side, that
the professional witness usually takes the utmost pains to make his
statement of fact scientific and precise as far as his ability goes. Few
scientific treatises in geology contain any more accurate accounts of
mineral deposits than testimony in cases of this sort. If every student
of geology, early in his career, could have a day on the witness stand
on a geologic problem, under both direct and cross examination, he would
learn once and for all the necessity for close and accurate thinking,
the difference between a fact and an inference, and the difference
between inductive study of facts and the subjective approach to a
problem.
It is a common assumption that a witness called to testify on scientific
matters is on a somewhat different basis from the eye-witness to an
event or transaction. We are not sure that this assumption is justified.
Seldom is it possible in mining operations to disclose the facts in
three dimensions so completely that they may be empirically observed and
platted by the layman. The grouping and presentation of the facts in
adequate perspective require an analysis of the origin of the ores and
rocks, the rock alterations, the structural systems, and other facts. No
one ever saw the vein or lode in the process of formation. The true
nature of the event and of its physical results must be inferred
inductively from circumstantial evidence. If it be conceded that it is
necessary and right to call an eye-witness to an event involved in
litigation, it is equally necessary where there are no eye-witnesses to
call the persons best qualified to interpret the circumstantial
evidence.
It is to be remembered that apex cases are only one kind of a vast
variety of cases affecting mineral resources. At one time or another,
and in some connection or another, practically every geologist of
considerable experience has found it necessary to testify on geologic
matters in court. The wide interest attaching to certain spectacular
apex cases has led in some quarters to hasty criticism of the
participation of geologists therein, without apparent recognition of the
fact that the criticism applies in principle to many other kinds of
litigation and to practically all economic geologists. This criticism
also fails to take cognizance of the fact that, for every case tried,
there are many settled out of court through the advice and coöperation
of geologists. While there may be in the geologic profession, as in
others, a very few men whose testimony can be bought outright, in
general it must be assumed that geologists will appear on the witness
stand only when, after careful examination, they are satisfied that
there is a legitimate point of view to be presented.
Geologists and engineers understand more clearly than almost any other
group the extent to which the complexities of nature vary from the
conditions indicated in the simple wording of the law of extralateral
rights. Almost to a man, they favor either modification or repeal of the
law. On the other hand, the law has been in force since 1872, it has
been repeatedly interpreted and confirmed by the courts, and a vast body
of property rights has been established under it. Lawyers see great
legal difficulties in the way of its repeal or serious modification.
Mining men for the most part are not primarily interested one way or
another, unless there is potential application of the extralateral-rights
provision to their particular properties. Of those who are thus interested,
some hope to gain and some fear they may lose in the application of the
law. The general public naturally has little direct interest in the
problem. There is thus no effective public sentiment favoring the repeal
or modification of the law. It seems likely that for some time to come the
law, in spite of its recognized defects, must be applied, and the best
geological effort must be directed toward reaching interpretations which
come most near to meeting its intent. To refuse to lend geologic science
to the aid of justice because the law was improperly framed is hardly a
defensible position. Presumably it will never be possible to frame laws
with such full knowledge of nature's facts as to eliminate the necessity
for scientific advice in their interpretation.
It has been suggested that the courts, and not the litigants, should
employ the geologists. The practical objection to this proposition lies
in the difficulty encountered by the judge in the proper selection of
geologists. On the assumption that the judge would select only men in
whom he had confidence, it is not likely that he would override their
conclusions. The outcome of the case, therefore, would be largely
predetermined at the moment the selection of experts was made. It is to
be doubted whether courts can have the knowledge of the scientific field
and of the requirements of the situation necessary to make the wisest
selection of men to interpret the given condition. The competitive
element would be eliminated. From a judicial standpoint, there seems to
be an equally good chance of getting at the best interpretation of the
facts by listening to presentations from different standpoints, with the
accompanying interplay of criticism and questioning.
Another practical objection to appointment of experts by the court is
the limitation of court costs, which would make it impossible to secure
the highest grade men. So far as these men are public employees, such as
members of the federal or state geological surveys, this might be
arranged. For others, it might be suggested that they should be willing
to sacrifice their energy and time in the interests of justice; but as
long as human nature and conditions are what they are, it is perhaps
futile to argue this question.
If it is right to apply science to practical affairs, in other words, if
the profession of economic geology is a legitimate one, it seems
inevitable that the application must be in some part directed by the
geologist himself, in order to avoid mistakes and confusion. The
contention that the scientist must isolate himself in a rarified
atmosphere to avoid contamination from a non-scientific, commercial, or
legal atmosphere, seems to the writer practically untenable, if we
recognize any obligation on the part of science to the practical conduct
of human affairs. The fact that the geologist in making these
applications may occasionally find himself in a non-scientific
atmosphere may be deplored from the standpoint of maximum creativeness
in science, and from this standpoint there may be reason for limitation
of time given to this kind of work,--but to stay out entirely on this
ground is to deny his obligation to make his science helpful to his
fellows. The problem cannot be solved by staying out. It calls rather
for an especial effort on the part of the scientist to establish and
maintain his standards of science and ethics in the applied fields. Some
doubtless fail in this effort. Others are strengthened scientifically
and ethically, and contribute important aid in raising general
standards. The principle of non-participation in such activities for
fear of lowering scientific standards may make the geologist's problem
easier, but at the expense of non-fulfillment of duties. Such a course
has for its logical consequence an abandonment of the application of his
science to untrained men without the ethical anchorage of scientific
achievement. In short, there may be legitimate criticism of individual
geologists for their methods and ethics in the applied field, and this
is desirable as an aid to maintaining and improving standards; but it
is not a logical step from this to the conclusion that, to avoid
unfortunate incidents, economic geologists must cloister themselves and
thus deny the very implication of their title.
II
LAWS RELATING TO EXTRACTION OF MINERAL RESOURCES
Under this heading come a wide variety of laws and
regulations,--national, state, and local,--affecting the manner in which
mineral resources shall be mined or quarried. Such laws may specify the
number of shafts or outlets, the use of safety and prevention devices,
miners' compensation and insurance, and many other features. Most of
these laws are framed for the purpose of conserving human life and
energy, but they directly affect the mining or extraction of the mineral
resources themselves. Geology plays but little part in relation to such
laws.
Where the government retains ownership and leases or rents the
resources, there are often provisions regarding the manner of mining and
the quality and quantity of the material to be mined, in the interests
of efficient operation and conservation. The geologist is often called
into consultation both in framing and in dealing with the infraction of
such provisions. It may be noted that the control thus exercised on the
operator by government ownership is very much the same as that often
exercised by the private fee owner. It is not unusual for fee owners of
mineral rights to maintain a geological staff in order to follow
intelligently underground developments, to see that the best methods of
exploration and mining are followed, and that ores are either extracted
or left in accordance with the best conservational practice.
III
LAWS RELATING TO DISTRIBUTION AND TRANSPORTATION OF MINERAL RESOURCES
Under this heading come governmental regulations affecting directly or
indirectly the transportation and the destination of mineral products.
Transportation rates, tariffs, zoning, duties, and international trade
agreements of all sorts have vital effects on distribution. In framing
any of these measures for a mineral resource, it is desirable to know
all about the character of the raw material, its physical occurrence and
distribution, and the possibilities for future development. In adjusting
the scientific naming and classification of mineral materials with the
crude names and classifications used commercially--as in tariffs, in
import and export laws, in reports of revenue collectors, in railway and
ship rates, etc.--the geologic information is likewise necessary.
Heretofore, the formulation of measures concerning mineral distribution
has often not been done on a scientific and impartial basis; but in
recent years geologists have been called on more frequently for aid and
advice, as a means of checking or verifying the special pleadings of the
different industries. The rude disturbance of trade routes during the
war brought home the necessity of basing control of distribution of
mineral products on fundamental facts of geology and geography; thus it
was that geologists had a considerable voice in the vast number of
special measures taken for war purposes by such organizations as the
Shipping Board, the War Trade Board, the War Industries Board, and other
public organizations. The same was true in relation to the mineral
resource questions at the Peace Conference. In the reconstructive
measures of the future, a still larger use of scientific considerations
may be looked for. Further suggestions as to the relation of geology to
laws affecting distribution appear in the chapter on International
Aspects (Chapter XVIII).
IV
OTHER RELATIONS OF GEOLOGY TO LAW
It is often assumed that the economic geologist is exclusively
interested in mineral resources. However, there are varied applications
of geology outside of the mineral resource field,--to many kinds of
engineering and construction operations, to soils, to water resources,
and to transportation,--any of which may develop legal problems
requiring geologic service. A few illustrative cases follow.
The classification of mineral materials in contracts presents many
difficulties. A contract for a railway cut, for a canal, or for any
other kind of excavation may specify different prices for removing
different mineral materials. Too often these are stated in extremely
crude and arbitrary terms, such as _rock_, _hard rock_, _hardpan_,
_earth_, _dirt_, etc., without regard to the actual variety of materials
to be dealt with. When, therefore, in the case of the Chicago drainage
canal, the contractor encountered a soft shale and claimed compensation
for rock excavation, geologists played a considerable part in the
extensive litigation that followed in the attempt to define the facts of
nature in terms of a contract which did not recognize them. In a railway
cut through glacial drift or till, a contractor came suddenly upon a
mass of till which had been so thoroughly cemented in place as to have
all the resistance of rock. Litigation was then necessary to decide
whether this should be classified as dirt or rock.
Rock and dirt slides of all kinds, met with in open-pit mining, canals,
and other excavations, present engineering problems with a geologic
basis. The kinds of rocks, their strength, porosity, and moisture
content, the effects of weathering, and the structural conditions must
be determined in order to ascertain the cause of the slides, and are
features which figure largely in litigation arising from troubles of
this sort.
Both federal and state laws give the right to lateral and vertical
support. When, therefore, adjacent or underlying excavations cause earth
movements in a neighbor's property, litigation is likely to ensue and
the geologist is likely to be called in. The long-wall method of coal
mining, extensively practiced in certain parts of the United States, is
slowly withdrawing support from the ground overlying the coal seams,
resulting in damages to surface structures and in some cases to
overlying mineral deposits. Extensive litigation has been the result,
and the future seems to promise more of it. In certain metal-mining
camps, where considerable amounts of materials have been mined to great
depths, caves and cracking in the surface are reaching over unexpectedly
wide areas, again threatening litigation.
The laws relating to the use of surface and underground waters touch the
geologic conditions in many ways. The permanent lowering or raising of a
water level through mining or damming may require a careful geological
analysis of the underground conditions affecting the movements of
ground-water. The use of streams for placer mining, as in California,
has resulted in formulation of laws and in extensive litigation, again
requiring analysis of geologic conditions.
In fact geologists, perhaps more than any other group, have come to
realize how many and how varied are the ways in which people get into
conflict in using the earth on which they live.
CHAPTER XVII
CONSERVATION OF MINERAL RESOURCES
THE PROBLEM
Conservation of mineral resources may be defined as an effort to strike
a proper balance between the present and the future in the use of
mineral raw materials.
Mineral resources have been used to some extent as far back as evidences
of man go, but great drafts on our resources have come in comparatively
recent years. The use of many minerals has started within only a few
years, and for others the acceleration of production within the past two
or three decades has been rapid (see pp. 63-64). In general, the use of
mineral resources on a large scale may be said to have started within
the lifetime of men still active in business. The wide use of power
necessary to an industrial age, the development of metallurgy, the
increasing size and complexity of demands for raw material, mean that
the intensive development and use of our mineral resources is in its
infancy, and is in many respects in an experimental stage.
As nations have awakened to their need of mineral raw materials and to
the recent rapid depletion of these materials, they have been naturally
led to inquire how long the reserves may last, and to consider
prevention of waste and the more efficient use of materials, with a view
to planning more prudently for future national supplies. The first
inquiries seemed to reveal such shortage of mineral supplies as to call
for immediate and almost drastic steps to prevent waste, and possibly
even to limit the use of certain minerals in the interests of posterity.
More careful study of the problem, as might be expected, revealed new
factors and greater complexity. The conservational idea has a wide
sentimental appeal, but the formulation and application of specific
plans meet many difficulties. In its practical aspects the problem is
now a live one, the solution of which is requiring the attention of
mining men, engineers, geologists, economists, and public officials. It
is a question which is coming more and more into the field of actual
professional practice of the economic geologist.
It is our purpose to indicate the general nature of the conservation
problem. We may assume agreement to the desirability of preventing
waste, of making a wise present use of mineral products, and of striking
a proper balance between the present and future in their use. Nature has
taken many long geologic periods to build up these reserves. We, of the
present generation, in a sense hold them in trust; they are entailed to
our successors. With this general thought in mind, how shall we proceed
to formulate definite plans for conservation?
An initial step is obviously a careful taking of stock. With increasing
knowledge of mineral resources, it is becoming apparent that early
estimates of supplies were too low. Many of these estimates failed to
take into account mining to great depths, and wide use of low-grade
ores, rendered possible by improved methods; and especially they failed
to put sufficient emphasis on the probabilities of new discoveries to
replace exhausted supplies. Early predictions have already been upset in
regard to a number of mineral resources. The recognition of the general
fact that the world is far from explored in two dimensions, to say
nothing of three, of the fact that known geologic conditions do not yet
indicate definite limits to the possibilities of exploration for most
mineral resources, and of the consequent fact that for a long time in
the future, as in the past, discoveries of new mineral deposits will be
roughly proportional to the effort and money spent in finding
them,--which means, also, proportional to the demand,--makes it
impossible, for most of the mineral resources, to set any definite
limits on reserves. It is comparatively easy to measure known reserves;
but a quantitative appraisal of the probable and possible reserves for
the future is extremely difficult. Successive revisions of estimates
have, with but few exceptions, progressively increased the total mineral
supplies available. The result is that the time of exhaustion has been
pushed far into the future for most of the important minerals, thus
minimizing the urge for immediate and drastic conservational action,
which followed naturally from early estimates of very limited supplies.
For both coal and iron, supplies are now known for hundreds or even
thousands of years. For oil and lead, on the other hand, the reserves
now known have a life of comparatively few years, but the possibilities
for successful exploration make it probable that their life will be
greatly extended. Notwithstanding this tendency to lengthen the
exhaustion period, the limits of mineral resource life are still small
as compared with the life of the nation or of civilization,--and the
fundamental desirability of conservation is not materially affected.
It is not easy to predict the rate of production for the future. At the
present rate of coal production in the United States, the supplies to a
depth of 6,000 feet might last 6,000 years; but if it be assumed that
the recent _acceleration_ of production will be continued indefinitely
into the future, the result would be exhaustion of these supplies in
less than 200 years. It is generally agreed that exhaustion will come
sooner than 6,000 years, but will require more time than 200 years. The
range between these figures offers wide opportunity for guessing. It is
supposed that per capita consumption may not increase as fast in the
future as in the past, that possibly an absorption point will be
reached, and that there will be limits to transportation and
distribution; but how to evaluate these factors no one knows. In the
case of some of the metallic resources, such as iron, the fact that the
world's stock on hand is constantly increasing--losses due to rusting,
ship-wrecks, etc., being only a small fraction of the annual
output--suggests that a point will be reached where new production will
cease to accelerate at the present rate and may even decline. But again,
the factors are so complex and many of them so little known, that no one
can say how soon this point will be reached.
For the immediate future, there is little to be feared from shortage of
mineral supplies in the ground. The difficulties are more likely to
arise from the failure of means to extract and distribute these supplies
fast enough to keep up with the startling acceleration in future demand
indicated by the figures of recent years. The speed and magnitude of
recent material developments in many lines cannot but raise question as
to whether we have the ability to understand and coödinate the many
huge, variable, and accelerating factors we have to deal with, or
whether some of the lines of development may not get so far ahead of
others as to cause serious disturbance of the whole material structure
of civilization. Coal alone, which now constitutes a third of our
railway tonnage, may with increased rate of production require
two-thirds of present railway capacity. Will railway development keep
up? It may be noted that national crises and failures in the past
history of the world have seldom, if ever, been due to shortage of raw
materials, or in fact to any failure of the material environment.
In its early stages the conservation movement in this country concerned
itself principally with the raw material. Later there came the
recognition of the fact that conservation of raw materials is closely
bound up with the question of conservation of human energy. The two
elements in the problem are much like the two major elements in mineral
resource valuation (see pages 329-330). If in saving a dollar's worth of
raw material, we spend two dollars worth of energy, it naturally raises
question as to the wisdom of our procedure. It might be wiser in some
cases to waste a certain amount of raw material because of the saving of
time and effort. It might be better for posterity to have the product of
our energy multiplied into raw material than to have the raw material
itself. The valuation of these two major elements of conservation is
again almost impossible of quantitative solution. We do not know what is
the best result to be aimed for. We cannot foresee the requirements of
the future nor the end toward which civilization is moving--or should
move. The extravagance of the United States is often contrasted
unfavorably with the thriftiness of Europe. When considered in relation
to raw materials alone, there seems to be basis for this charge. When
considered in relation to the product of human energy into raw
materials, the conclusion may be far different; for the output per man
in the industries related to mineral resources is far greater in the
United States than in Europe. In the case of iron, it has been estimated
that the output per man in the United States is two and one-half times
as great as in the rest of the world. Which is best in the true
interests of conservation, we are not yet able to see.
Our view of what is desirable in the way of conservation depends
somewhat on the limitations imposed by self-interest or location. By
devoting ourselves exclusively to one mineral resource, we might work
out a conservation program very disadvantageous to the best use of some
other mineral commodity. We might take steps to conserve chromite in the
United States which would have a disastrous effect on the iron and
steel industry. We might conserve coal by the substitution of oil, when
the procedure is hardly warranted by the supplies of oil available. We
might work out a program for the United States which would not be the
best conservational plan for the world as a whole, and which would
ultimately react to the disadvantage of the United States. The wisest
and most intelligent use of mineral resources seems to call
unquestionably for their consideration in their world relations, rather
than for a narrow interpretation of local requirements.
DIFFERENCES BETWEEN PRIVATE AND PUBLIC EFFORTS IN CONSERVATION
It appears that a wide range of effective conservational practices has
resulted solely from the effort to make more money through more
efficient operations, and this is likely to be true in the future. Many
improvements in mining, grading, sorting, concentration, and metallurgy
of minerals, to yield larger financial returns, are coming naturally
through private initiative, under the driving power of self-interest.
Another considerable group of conservational practices is possible only
to governments or other public agencies. This group of practices on the
whole requires some sacrifice of the immediate financial interest of the
individual, in the interests of the community as a whole, or in the
interests of posterity. In this group may be mentioned the compulsory
use of methods of mining, sorting, and metallurgy which tend to conserve
supplies but result in higher prices; the control of prices; the
elimination or lowering of the so-called resource or royalty value (p.
375); and the removal of restrictions on private combination or
coöperation, leading to more efficient methods, lessening of cost, and
better distribution of the product; or, what might amount to the same
thing, the acquirement by the government of the resources to be operated
on this larger scale.
The most effective conservation measures yet in effect are the ones
dictated by self-interest and instituted by private initiative.
Governmental measures are not yet in effective operation. Illustrations
of these two types of conservational effort are cited in relation to
coal on later pages.
THE INTEREST RATE AS A GUIDE IN CONSERVATION
In striking a balance between the present and the future, economists
have emphasized the importance of recognizing the interest rate as a
guiding, if not a controlling consideration. It is obviously difficult
for private capital to make investments of effort and money for the
purpose of conservation which will not be returned with interest some
time in the future. For the present, at least, this consideration
furnishes the best guide to procedure in the field of private endeavor.
So far as conservational measures, such as investment in an improved
process of concentrating low-grade ores, promise return of capital and
an adequate interest rate in the future, they are likely to be
undertaken.
It is clear that governments are not so closely bound by this economic
limitation. They can afford to carry their investments in raw materials
and processes at a lower interest rate than the private investor. Their
credit is better. Taxes do not figure so directly. They can balance
losses in one field against gains in another. As a matter of insurance
for the future of the nation, a government may feel justified in
inaugurating conservational measures for a particular resource without
hope of the interest return which would be necessary to the private
investor. In appraising the iron ores of Lorraine taken over by France
from Germany at the close of the war, the actual commercial value of
these ores, as figured by the ordinary _ad valorem_ method, was only
ninety millions of dollars. It is clear, however, that to France as a
nation the reserves were worth more. They could afford to pay more for
them, and could afford to spend more money on conservational practice
than under ordinary commercial limitations, because of the larger
intangible and more or less sentimental interest.
The valuation of this larger interest, as a means of determining the
limit to which conservational investments may be made, lies in the
political field. It may be suggested, however, that a desirable first
step in any governmental program of conservation is to ascertain the
cost and the possibility of an adequate return of capital and interest.
These determinations at least afford a definite point of departure, and
a means for measuring the cost to the people of measures which are not
directly self-supporting.
ANTI-CONSERVATIONAL EFFECTS OF WAR
Experience during the recent past indicates that the exploitation of
mineral resources for war purposes is on the whole anti-conservational.
It is true that the vast amount of war-time exploration and development,
as well as the thoroughgoing investigations of the utilization of
various minerals, have led to better knowledge of the mineral resources
and their possibilities. It is also true that the war required a much
more exhaustive census of mineral possibilities than ever before
attempted. The immediate and direct effect of the war, however, was the
intensive use of mineral resources without careful regard to cost,
grade, or many other factors which determine their use in peace times.
For instance, in ordinary times considerable quantities of
high-phosphorus iron ores are mined; but, because of the fact that such
ores require more time for conversion into steel, war-time practice
concentrated on the higher-grade, low-phosphorus ores, resulting in an
unbalanced production which in some cases amounted almost to robbing of
ore deposits. In the case of coal, quantity was almost the only
consideration; it was impossible to grade and distribute the coal to
meet the specialized demands of industry. The results were a general
lowering of the standards of metallurgical and other industrial
practices, and increased cost. High-grade coals were used where
lower-grade coals were desirable for the best results. In the making of
steel, it is the custom to select the coal and coke with great care in
regard to their content of phosphorus, sulphur, ash, and other
constituents which affect the composition of the steel product; but
during the war it became necessary to accept almost any kind of coal,
with a resulting net loss in quantity and in grade of output.
For a considerable number of mineral resources, such as the
ferro-alloys, foreign sources of supply were cut off during the war,
requiring the development and use, at high cost, of low-grade scattered
supplies in the United States. It was found possible to produce enough
chromite in the United States for domestic requirements, but at two or
three times the normal price of imported chromite. The grade was low and
the loss in efficiency to the consuming interests was a high one. The
extremely limited natural supplies were raided almost to the point of
exhaustion.
With the post-war resumption of importation of minerals of this kind,
producers naturally began a fight for a protective tariff, and the
question is yet unsettled. The tariff, if enacted, would in most cases
have to be a high one in order to permit the use of domestic supplies.
The results would be a large increase in cost to other industries,
decreased efficiency, and the early exhaustion of limited supplies in
this country. Most of the mineral resources have been concentrated by
nature in a comparatively few places in the world; and when the two
elements of conservation are considered--the materials themselves and
the human energy expended in obtaining and using them--it is clear that
any measure which interferes with the natural distribution of the
favored ores is anti-conservational from the world standpoint.
CONSERVATION OF COAL
In the sections on mineral resources, there are many casual references
to conservation of specific minerals. Here we shall not go further than
to introduce a brief discussion of the conservation of coal as
illustrative of the general problem of conservation of mineral
resources.
It has been estimated that the United States possesses, to a depth of
3,000 feet, in beds 14 inches or over, 3,538,554,000,000 tons of coal,
and an additional reserve between 3,000 and 6,000 feet of
666,600,000,000 tons.[42] If all the unmined coal to a depth of 3,000
feet could be placed in one great cubic pile, the pile would be 18 miles
long, 18 miles wide, and 18 miles high. Of the original amount of coal
to this depth only about 0.4 of 1 per cent has been mined or wasted in
mining. The wastage is estimated at about 50 per cent. If the annual
production of coal were to remain the same as in recent years, the total
life of the coal reserves (to a depth of 3,000 feet) would be between
4,000 and 6,000 years; but if the acceleration of production of recent
years were to be maintained in the future, the life would be but little
over 100 years, and the life of the highest-grade coal now being mined
might not be over 50 years. All agree that the acceleration of
production is not likely to continue indefinitely, which will mean that
the life of coal reserves to 3,000 feet will be somewhere between the
two extremes named. It seems clear that actual shortage of coal will not
be felt for some hundreds of years; but this period of years is short as
compared with the probable life of the race.
MEASURES INTRODUCED OR PROPOSED TO CONSERVE COAL
The following list of measures for conservation of coal is taken from
several sources. The exhaustive report of the British Coal
Commission,[43] published in 1905, contains a considerable number of
specific recommendations for conservation of the coal of Great Britain.
The reports of the National Conservation Commission[44] of the United
States, published in 1909, treat of the conservation of the coal of the
United States and naturally follow some of the recommendations of the
British report. The coal section of the National Conservation report was
prepared by M. R. Campbell and E. W. Parker of the U. S. Geological
Survey, and is contained in U. S. Geological Survey Bulletin 394. The
recommendations there given are amplified and developed by Van Hise[45]
in his book on Conservation, published in 1910. Since that time the
subject has been discussed by Smith, Chance, Burrows, Haas,[46] and
others, and certain additional conservational methods have been
proposed. A considerable number of men have also discussed the
sociologic and economic aspects of the question. The report of the
Conservation Commission of Canada,[47] published in 1915, treats rather
fully of the conservation of mineral resources.
It will suit our purpose, and avoid some repetition, if we group most
of these recommendations without regard to authorship. In general, these
recommendations can be grouped under the heads: (A) Methods of mining
and preparation of coal; (B) Improvement of labor and living conditions
at the mines; (C) Introduction or modification of laws to regulate or to
remove certain restrictions on the coal industry; (D) Distribution and
transportation of coal; (E) Utilization of coal; (F) Substitutes for
coal as a source of power.
=(A) Mining and preparation of coal.= Under this heading may be included
a large number of proposals which concern primarily the engineering
treatment of the coal underground and in the mine plants. Some of the
more important measures are:
1. Introduction of the long-wall system of mining in places where the
conditions allow it, in order to minimize the waste underground.
2. Modification of the room-and-pillar system of mining, by which larger
pillars are left while the mine advances, and are recovered in the
retreat,--thereby recovering a larger percentage of coal than under the
old system, where small, thin pillars were left, which failed and were
permanently lost.
It has been argued that the great loss of coal by leaving it in pillars
could be saved by using other material to support the roof; but an
elementary calculation of the cost of this procedure shows that it is
cheaper to use the coal. Chance[48] says:
The coal left as pillars to support the roof is thus utilized
and performs a necessary and useful function, yet the
principal part (perhaps two-thirds) of the 200,000,000 tons
our friends the conservationists claim is wilfully and
avoidably wasted every year is this coal that is left in
pillars to support the roof. I think we can safely claim that
this is not waste, but, on the contrary, is engineering
efficiency of the highest type, in that it utilizes the
cheapest and least valuable material available to support the
roof and saves the whole labor cost of building supports of
other materials. Investigation as to what becomes of that part
of the 200,000,000 tons claimed as wasted, which is not
utilized as pillars to support the roof, will disclose the
fact that a very large portion is coal that is left in mine
workings that are abandoned because the roof is unsafe and
because a continuance of operation would result in injuries or
loss of life. Coal left in the mines in order to conserve
human lives cannot be classed as avoidable waste. A small part
of the 200,000,000 tons is lost because it is intimately mixed
with refuse and because the labor cost of recovering it and
separating it from the refuse would be greater than its value.
3. Mining of shallow bituminous beds by means of the steam shovel.
Progress has been made along this line in the last few years, and
valuable deposits are thus mined which can be mined profitably by no
other method.
4. New methods of filling mined-out spaces with sand, and new methods of
mine survey and design. According to Haas[49]
the greatest advance in the question of method was the system
of mine survey and design perfected in both the anthracite and
bituminous fields. The relatively new method of filling old
spaces with sand, etc., has also achieved success.
5. Use of methods by which coal is not left in the roof for the support
where the roof is weak, and by which coal of inferior quality is not
left in the roof.
6. Wider use of coal-cutting machines by which the wasting of thinner
beds may be avoided.
7. Where conditions allow it, the working of the upper beds before the
lower, in order not to destroy the upper ones by caving. The mining of a
lower coal seam has often so broken up the overlying strata as to render
it impossible to recover the upper coal seams contained therein. There
are certain difficulties, however, in the way of this conservational
measure. In some localities the seams are under separate ownership, and
there is a resulting conflict of interests. Also, if the better coal
seam happens to be below and the poorer seams above, market conditions
may require that the lower seam be mined regardless of the destruction
of the upper ones.
8. Elimination of coal barriers to mark the limits between properties.
This involves more coöperation.
9. Improvement of mining machinery, power drills, etc.
10. Centralization of power stations, rather than the use of many small
units.
11. Elimination of the wasting of slack or fine coal, through more
careful methods of mining, through limitations on the excessive use of
powder and larger use of wedges, through the abolition of laws for the
payment of miners on a run-of-mine basis, and in the case of anthracite
through recovery of the "silt" or dust caused by mining and sorting. It
has been argued that the excessive use of powder ("shooting from the
solid") means loss of coal, owing to the fact that it shatters the coal
and makes a relatively large amount of slack, besides being accompanied
by increased danger from fire and explosion and from weakening of the
roof. Although the excessive use of powder makes a large amount of
slack, it does not necessarily result in waste, for this fine coal is
carefully saved and for certain purposes is as valuable as the lump
coal. So far as the procedure endangers life, it is of course
objectionable.
12. Better use of fine coal. It has been recommended that infirm and
finely broken coal be washed and compressed, thus avoiding the wasting
of slack coal, which was formerly thrown away or burned. However, in
recent years there has been comparatively little waste of this kind, for
slack coal in general finds nearly as ready a market as lump coal and
the use of slack is increasing. There has been much discussion also of
the possibilities of using the coal waste on the ground to make power
for electric transmission.
13. More careful attention to sorting and sizing of all grades of coal
coming from the mine and to preparation of coals for special uses. On
the other hand, some operators say that the ends of conservation will be
best met by limiting the sorting and sizing now practiced. The large
number of sizes now put on the market greatly increases the cost of
production.
14. Wider use of the lower-grade fuels of the west, particularly with
the aid of briquetting.
=Progress in above methods.= Methods of mining and preparation of coal
have been improved. Campbell and Parker state:[50]
A much greater proportion of the product hoisted is now being
sent to market in merchantable condition. Part of this is due
to better and more systematic methods of handling, and part to
the saving of small sizes which formerly went to the culm
banks. The higher prices of coal and the development of
methods for using these small sizes have also made it
possible, through washing processes, to rework the small coal
formerly thrown on the culm banks, and these are now
furnishing several millions of tons of marketable coal
annually.
In general there is increase in the percentage of recovery of coal.
Whereas in the past the loss in mining was said by Campbell and
Parker[51] to average 50 per cent, now an extraction of 70 to 90 per
cent may be looked for.
Quoting from Smith and Lesher:[52]
Observation of the advances made in mining methods in the last
decade or two affords slight warrant for belief in any charge
of wasteful operation. As consumers of coal we might do well
to imitate the economy now enforced by the producers in their
engineering practice. In the northern anthracite field machine
mining in extracting coal from 22- and 24-inch beds, and
throughout the anthracite region the average recovery of coal
in mining is 65 per cent., as against 40 per cent. only twenty
years ago. Nor are the bituminous operators any less
progressive in their conservation of the coal they mine.
In anthracite mining, powdered coal or "silt" has accumulated in
stockpiles and in stream channels to many tens of millions of tons. It
is estimated that this constitutes nearly 6 per cent of the coal mined.
Significant progress has been made recently in the recovery and use of
this silt as powdered fuel for local power purposes.
However, physical and commercial conditions do not in all cases allow of
the full application of these new methods. Once a mine has been opened
up on a certain plan, it is difficult to change it. As a whole the
longer and better organized companies are better able to change than the
smaller companies.
Conservation measures of the above kinds, as so far applied, have come
mainly from private initiative based on self-interest,--though the
coöperation of the government has been effective, particularly along
educational and publicity lines.
=(B) Improvement of labor and living conditions at the mines.= Under
this heading should be mentioned the improvement of housing, sanitation,
and living conditions; improvements in the efficiency of labor, through
making living conditions such as to attract a higher-grade labor supply
and through educational means; the introduction of safety methods; the
introduction of workmen's compensation and insurance; and other measures
of a similar nature. All these measures as a class are sometimes grouped
under the name of "welfare work."
Much thought and discussion have been devoted to the possibilities of
improvement of labor and living conditions from the standpoint of
conservation of human energy. In some quarters this subject has been
treated as being independent of the physical conservation of mineral
resources, and it has been the tendency to assume that conservation of
human energy might be more or less inimical to conservation of mineral
resources. Certain of the changes already introduced have undoubtedly
increased the cost of mining; and, until there was a general increase in
selling price, this increased cost may have had the effect of
eliminating certain practices of mineral conservation which might
otherwise have been possible. For instance, according to Smith and
Lesher:[53]
The increased safety in the coal mines that has come through
the combined efforts of the coal companies, the state
inspectors, and the Federal Bureau of Mines necessarily
involves some increase in cost of operation, but the few cents
per ton thus added to the cost is a small price to pay for the
satisfaction of having the stain of blood removed from the
coal we buy. That form of social insurance which is now
enforced through the workmen's compensation laws alone adds
from 2 to 5 cents a ton to the cost of coal.
On the other hand, there can be no doubt that large advances have been
made in welfare movements which were introduced for the purpose of
insuring a steadier, better, and larger supply of labor, and that the
general gain in efficiency of operation thereby obtained has absorbed a
large part of the increased cost.
In general, conservation measures of this class have been developed
coöperatively by private and public efforts, without important
sacrifice of private interest. There is obviously room for much wider
application of such measures, especially in some of the bituminous
fields where conditions are still far from satisfactory.
=(C) Introduction or modification of laws to regulate or to remove
certain restrictions on the coal industry.= It has been proposed:
1. To modify the laws so as to take care of situations where vertically
superposed beds are owned by different parties, preventing the proper
mining of the coal by either party.
2. To modify the laws so as to eliminate conflict in mining practice in
cases where the coal is associated with oil and gas pools.
3. To allow larger ownership by companies utilizing the coal (now only 3
per cent owned by such companies).
4. To place restrictions on over-capitalization, which leads to wasteful
mining in order to secure quick and large returns on large capital.
5. To remove restrictions on concentration of control. This means, as a
corollary proposition, virtual restriction of competition. Concentration
of control into comparatively few hands has undoubtedly favored
conservation. It is easy to see that the stronger financial condition of
the large companies makes it possible for them to take fuller advantage
of modern methods of extraction, distribution, and marketing.
This proposal was especially urged for the bituminous coal industry
before the war in order to avoid over-production and over-development.
The very wide distribution of the bituminous coals, their enormous
quantity, and their exceedingly diversified ownership had led to
over-development of coal properties. Quoting from Smith and Lesher:[54]
In estimating the aggregate losses incurred by society by
reason of the large number of mines not working at full
capacity, the facts to be considered are that the capital
invested in mine equipment asks a wage based on a year of 365
days of 24 hours, while labor's year averaged last year only
230 days in the anthracite mines and only 203 days in the
bituminous mines, with only five to eight hours to the day.
These conditions prevented in some cases even the most modest
introduction of better methods, or of changes that would enhance the
average profits through a relatively short period of ten or fifteen
years at the expense of the present year. It was necessary to get at the
best of the coal available in the cheapest possible way, regardless of
the losses of coal left in the ground.
To some extent the force of this argument was minimized by war and
post-war conditions, but even yet development of coal mines is ahead of
transportation and distribution.
6. To allow coöperation in the limitation of output, in the avoidance of
cross freights, in gauging the market in advance, and in division of
territory, all of which would allow cheaper mining and thus give larger
leeway to conservational measures. This necessarily would be accompanied
by government regulation. According to Van Hise,[55] who was active
before the war in advocating this conservational measure, such a
procedure
is neither regulated competition, nor regulated monopoly; but
the retention of competition, the prohibition of monopoly,
permission for coöperation and regulation of the latter. In
Chicago there cannot be one selling agency for the different
coal companies which operate in Illinois, but there must be
many selling agencies, and the coal of Pittsburgh must come
into Illinois and the Illinois coal go toward Pittsburgh;
every one of which things makes unnecessary costs, but all of
which are inevitable under the extreme competitive system.
Because of these facts it is necessary to waste the coal. If
at the very same prices the different mines could coöperate in
the limitation of the output, avoidance of cross freights,
gauging the market in advance, and division of territory, they
could mine their coal more cheaply, have a greater profit for
themselves and conserve our resources.
To some extent the plan here advocated was put into effect during the
war by the United States Coal Administration; but the conditions of this
trial were so complicated by special war requirements, that the
conservational advantages of unified control were not demonstrated.
7. To reduce the excessive royalties paid to fee owners. Smith and
Lesher[56] have recently called attention to the relatively high
resource cost in some of the coal fields, represented by the payment of
royalties to fee owners. In the case of anthracite the payment averages
32 to 35 cents per ton, and exceptionally runs as high as a dollar per
ton. For the bituminous coal the average resource cost is probably not
much over five cents a ton. They suggest the possibility of lowering
this cost by governmental regulation; and make an especially strong
argument for not allowing the government-owned coal lands to go to
private owners, who in the future, with the accumulation of interest on
the investment, will feel justified in asking for a large "resource"
return in the way of royalty.
If the resource cost could be lowered, further introduction of
conservational methods by the operators would be possible without
greatly increasing the cost to the public.
8. To require or allow, by government regulation, a raising of the price
of coal to the consumer, thereby allowing wider application of
conservational practices. Some of the increased recoveries of coal above
noted have been made possible only by increase in the market price. If
coöperation were permitted in the manner described in paragraph 6, the
same results might be accomplished without increasing the price. Recent
high prices caused by the war situation are reflected in the
introduction of many conservational changes which were not before
possible. However, in some cases the demand for quick results under
present conditions has an opposite effect, because of the desire to
realize quick profits regardless of conservation.
9. The local conservation of coal at the expense of heavier drafts on
coal of other parts of the world, by imposition of export taxes and
preferential duties, has been discussed. While the effect of such a
measure would doubtless be conservational from the standpoint of the
United States, it is doubtful if it could be so regarded from the
broader standpoint of world civilization. Under present world conditions
such a step would be disastrous.
10. Government ownership has been proposed as a means of facilitating
the introduction of conservation measures. In the United States there is
yet no major movement in this direction. In England the question of
nationalization of coal mines is an extremely live political problem
(see pp. 343, 345-347).
Little progress has been made in conservation measures which involve
legal enactments of the kinds above listed.
=(D) Distribution, and transportation of coal.= It has been argued that
conservational results would ensue from:
1. Cheaper transportation.
2. Larger use of waterways.
3. Improvement in distribution of the product by partition of the market
and by larger use of local coals. For effectiveness this proposition
would have to include control of the agencies of distribution, in order
to minimize excessive profits of middlemen.
4. Purchasing and storage of coal by consumers during the spring and
summer months in anticipation of the winter requirements, in order to
equalize the present highly fluctuating seasonal demands on the mines
and railroads, and to eliminate the recurring shortages of coal in the
winter months. This was particularly recommended by the United States
Bituminous Coal Commission in a recent report.[57]
5. Where conditions allow it, conversion of coal into power at the mine
and delivery of power rather than coal to consuming centers. This type
of conservation is being put into practice on a large scale above
Wheeling, on the Ohio River, where there has recently been built a two
hundred thousand kilowatt installation for steam-generated electric
power. Some of the power will be delivered to Canton, Ohio, over fifty
miles away. This plant uses local coal and the cost of coal is figured
at two mills per kilowatt-hour.
Under this heading of distribution and transportation of coal, might be
considered certain international relations. The international movements
of coal are summarized in another place (pp. 115-117). Anything in the
way of tariffs or trade agreements which would tend to interfere with or
to limit the great natural international movements of coal--which in a
free field are based on suitability of grade, cost, location,
transportation, etc.--would be anti-conservational from the world's
standpoint, although they might be of local and temporary advantage. For
instance, the coal exported from England, which has heretofore
dominated the international trade of the world, is of a high grade.
American coal available for export is on the whole of considerably lower
grade, being higher in volatile matter. Unless this coal is beneficiated
at home, it can replace the English coal in the export field only at
increased cost of transportation and lower efficiency in use. The time
may come when it will be desirable to ship lower-grade coals long
distances; but when the two factors of conservation are considered--the
intrinsic qualities of the coal, and the efforts necessary to utilize
it--it would seem to be conservational at this stage to ship to long
distances only the coal which nature seems specially to have prepared
for this purpose.
=(E) Utilization of coal.= Conservational proposals of this kind are:
1. Substitution of retort coke-ovens for beehive ovens, to save not only
a larger quantity of coke but also valuable by-products (see pp.
118-119). Additional improvements in coking ovens may make possible the
manufacture of some sort of coke from a much wider range of bituminous
coals than can be used at present.
2. Larger use of smoke consumers and mechanical stokers.
3. Larger use of central heating plants, with higher efficiency than
many local plants.
4. Substitution of gas engines for steam engines, and improvement of the
steam engine.
5. Improvement in methods of smelting, leading to larger output of metal
per ton of coke used. Also the development of electric smelting for
certain metals.
6. More careful study and classification of the qualities of coals, in
order to avoid use of higher-grade coals where inferior coals would
serve the purpose.
7. More consumption at the collieries.
8. Larger use of powdered coal as fuel.
9. Improvement of force-draft furnaces.
10. Larger use of gas, a by-product of coal mining, and extraction of
other by-products.
11. More efficient transformation of peat and coal into power and light.
12. The possible use of oil flotation to eliminate foreign mineral
matter.
Most of the conservation measures above proposed have already been
applied with good results, and with promise of large results for the
future. The stimulus has come largely from self-interest. War conditions
in some ways aided and in others hindered these developments. One of the
conspicuous gains was the building of many by-product coke plants, under
the necessity of securing the nitrates and hydrocarbons for munition and
other purposes.
=(F) Substitutes for coal as a source of power.= Some of the more
prominent measures along this line which have been discussed are:
1. Larger use of water power. This has sometimes been popularly assumed
to be, at least potentially, a complete solution of the problem; but
nevertheless it has its distinct limitations.
Water power has the advantages that its sources are not exhausted by
use, and that the relatively greater initial cost of a hydro-electric
plant is frequently more than compensated for by the saving in man power
required and by the lower operating expense. However, the total amount
of water power which can be developed on a commercial basis is rather
closely limited, and much of the available power is so distributed
geographically that it cannot be economically supplied to the industries
which need it. Of the total water-power resources of the United States
which have been estimated by the Geological Survey to be available for
ultimate development, over 70 per cent is west of the Mississippi,--whereas
over 70 per cent of the horse-power now installed in prime movers is east
of the Mississippi. Electric power cannot at present be economically
transmitted more than a few hundred miles. Furthermore, for many uses of
coal, as in metallurgical and chemical processes which require the heat
or reducing action of burning coal, and in its use as fuel for ships,
hydro-electric power cannot be substituted. It seems clear that while
the use of water power will increase, particularly as rising prices of
coal make possible the development of new sites, it can never take the
place of the mineral fuels in any large proportion.
For the immediate future, measures which have been suggested to extend
the use of water power include: the more complete utilization of water
powers already in use through more efficient machinery and methods; a
certain degree of redistribution of industries, so that those requiring
large amounts of power may be located in areas where water power is
cheap and abundant; and the interconnection of hydro-electric plants so
that their full capacity may be used. Some water powers which have been
developed are not being fully utilized because the plants are not
connected with distribution systems large enough to use all the power.
During the war the United States Geological Survey, in coöperation with
the Fuel Administration and the War Industries Board, collected the
information required to prepare maps showing the locations and relations
of power stations and transmission lines throughout the country. This
survey of the situation showed many possibilities, which had before been
but vaguely realized, of interconnections which would increase the
efficiency of the plants.
2. Substitution of lower-grade coals--of bituminous for anthracite, and
of low-grade bituminous for high-grade bituminous coals. Larger use of
low-grade western coals. War and post-war conditions have shown Germany
the way to a wide and effective use of its lignites. This has been
accomplished by coöperation of the government and private interests.
This vast improvement in methods of treatment and recovery of heating
elements and by-products will doubtless have a widespread effect on
utilization of lignites in other parts of the world.
3. Substitution of alcohol and natural gas, oil, oil shales, peats,
etc., as a source of power. This merely concentrates the conservation
problem more largely on these minerals, in some of which, at least, it
is already considerably more acute than in the case of coal; it is not a
solution of the problem, but merely a shifting of emphasis.
Business conditions have limited private enterprise in this class of
measures, but some progress has been made. More rapid introduction of
these measures would require sacrifice of private interest and probably
may be accomplished only by application of public power.
DIVISION OF RESPONSIBILITY BETWEEN GOVERNMENT AND PRIVATE INTERESTS
IN THE CONSERVATION OF COAL
A review of the conservation measures above listed indicates that many
of them are already in operation, and that the initiative for such
measures has been largely supplied by private ownership endeavoring to
advance its own interest. In this category are to be included most of
the improvements in physical methods of mining, preparation, and
utilization of coal, the use of substitutes for coal, the concentration
of control into larger groups better able to introduce new methods, and
the improvement of labor and living conditions; also, under recent
conditions, the increase in selling price, allowing for a wider
application of these measures. Another group of conservation proposals,
which have not yet been put into substantial effect, are obviously
beyond the power of private interests; and must be introduced, if at
all, by the application of government power. These include the
elimination of resource or royalty costs, the control of
over-capitalization, the removal of restrictions on concentration of
control, the granting of permission for coöperation among competitive
units, the regulation of selling price minimums in order to insure
during normal times the use of better physical practices, and the
control of distribution. In short, it appears that there are two great
spheres of conservational activity--one within the field of private
endeavor, and the other possible only by collective action through the
government. The principal advances thus far made have been in the field
of private endeavor.
The government has aided greatly in the advancement of conservation
measures arising within the field of private endeavor. One need only
refer to many governmental investigations, to the spreading of
information as to best methods, and to local compulsory requirements
that the best practices be made uniform and that backward interests
thereby be brought into line.
Recognition of the fact that there is a large body of sound
conservational practice in the coal industry which falls within the
range of self-interest seems essential in planning further changes in
the direction of conservation. Conservational measures do not all
require sacrifice of the individual to the public, nor of the present to
the future generations. An exercise of public power is not in all cases
essential to the advancement of conservation. The respective limits of
the fields of public and private endeavor are not sharply defined, and
vary from place to place and time to time, depending upon local
conditions and special requirements.
In general, the sphere of private interest includes measures which will
bring adequate commercial return. The interest rate is the limiting and
controlling factor. When it is possible--by improvement of methods of
mining, better planning, better preparation of coal, better
transportation and distribution, or better utilization--to secure a
larger average return on the investment, or to insure return through a
longer period of years, self-interest naturally requires the
introduction of such methods as rapidly as financial conditions allow.
Even some of the improvements in labor and welfare conditions have been
introduced in this way, with a view to securing a more permanent and
more efficient labor supply, and thereby aiding the enterprise from the
commercial standpoint.
Within the sphere of government activity lie the removal of unnecessary
restrictions on private initiative, and such conservation measures as
involve some sacrifice of individual returns--in other words, a
reduction of the normal interest rate. Exercise of government power may
be directly helpful within the field of private endeavor without
materially sacrificing private interests; but beyond this point there
are additional large possibilities of conservational activity which are
clearly beyond the control of private interests. The introduction of any
of these latter changes would evidently be so far-reaching in effect,
and would require such broad readjustments not only within but without
the mineral industry, that the necessity or desirability is not in all
cases so clear as in the case of measures already introduced for private
interest.
The most obviously helpful step possible to the government in the
immediate future is to permit coöperative arrangements under private
ownership,--which would make it possible to use common selling agencies,
thereby reducing the cost of selling; to divide the territory to be
served, thereby avoiding excessive cross freights; and to allot the
output in proportion to the demand from various territories, thus
eliminating excessive competition and over-production. All of these
measures could be accomplished without detriment to the public if
properly regulated by the government. The very large saving possible by
this means would allow the introduction of conservational methods at the
mines without raising the cost to the public.
War conditions required even more immediate and sweeping application of
government power than above indicated, but conservational purposes were
quite overshadowed by other considerations.
Where the mineral resources are already owned by the government, or can
be acquired by the government, some of the troublesome factors in the
problem are removed. In such cases it is possible to work out an
intelligent plan for government control without the difficulties which
arise in dealing with private ownership,--although, of course, new
difficulties are introduced (see also pp. 345-347.)
The fact that there are conservational measures possible only to
governments has been widely used as an argument for introducing
government ownership or control. Recent vigorous demands for the
nationalization of natural resources in Europe, and the increasing
discussion of the subject in this country, may be regarded as phases of
the conservation problem. It is not the purpose here to argue either for
or against the drastic exercise of government power in the conservation
of natural resources, but merely to call attention to the measures which
are being discussed.
CONSERVATION OF MINERALS OTHER THAN COAL
The discussion of conservation as applied to specific minerals might be
extended almost indefinitely; but perhaps enough has been said to
indicate the general nature of the field. Before the war careful
estimates of world supplies had been made for comparatively few
minerals, although these included some of the most important, such as
coal, oil, and iron. War conditions required a hasty estimate of world
reserves of most of the mineral products. The reader interested in the
problem will find an extremely interesting body of literature issued by
the various governments on this subject. Of especial interest to the
American reader will be the reports of the U. S. Geological Survey and
of the Bureau of Mines.
In recent years there has been increasing recognition of the
possibilities of conservational saving by concentration, refinement, and
even manufacture of mineral commodities at or near the point of
origin,--thus lessening the tonnage involved in transportation of the
crude products. Limitations of fuel and other conditions often make this
procedure difficult; but considerable progress is being made both
through private initiative and, especially in international trade,
through governmental regulations of great variety.
FOOTNOTES:
[42] Campbell, M. R., The coal fields of the United States: _Prof. Paper
100-A_, _U. S. Geol. Survey_, 1917, p. 24.
[43] Final report of the Royal Commission on coal supplies: House of
Commons, London, vol. 16, 1905.
[44] Report of the National Conservation Commission: Senate Document No.
676, 60th Congress, 2d session, Govt. Printing Office, Washington, 1909.
[45] Van Hise, C. R., _The conservation of natural resources in the
United States_: Macmillan Co., New York, 1910.
[46] Haas, Frank, The conservation of coal through the employment of
better methods of mining: Abstract of paper presented to Pan-American
Scientific Congress, Washington, Dec., 1915-Jan., 1916.
[47] Adams, Frank D., Our mineral resources and the problem of their
proper conservation: _6th Ann. Rept., Commission of Conservation_,
_Canada_, 1915, pp. 52-69.
[48] Chance, H. M., Address before the mine engineering class of the
Pennsylvania State College, Quoted by F. W. Gray, The conservation of
coal: _Bull. 47_, _Can. Mining Inst._, 1916, p. 201.
[49] _Loc. cit._
[50] Campbell, M. R., and Parker, E. W., Coal fields of the United
States, Papers on the conservation of mineral resources: _Bull. 394, U.
S. Geol. Survey_, 1909, p. 12.
[51] _Loc. cit._ p. 12.
[52] Smith, George Otis, and Lesher, C. E., The cost of coal: _Science_,
vol. 44, 1916, p. 768.
[53] _Loc cit._, pp. 768-769.
[54] _Loc. cit._, p. 771.
[55] Van Hise, Charles R., _Coöperation in industry_, pp. 7-8, Address
given before annual meeting of the National Lumber Manufacturers'
Association, Chicago, Illinois, May 31, 1916.
[56] _Loc. cit._, p. 767.
[57] Stabilization of the bituminous coal industry, Extracts from the
award and recommendations of the United States Bituminous Coal
Commission, Government Printing Office, Washington, 1920.
CHAPTER XVIII
INTERNATIONAL ASPECTS OF MINERAL RESOURCES
WORLD MOVEMENT OF MINERALS
Of the annual world production of minerals about two-thirds are used
within the countries where the minerals are produced and one-third is
shipped to other countries. In this chapter we are concerned primarily
with the part which moves between countries. It may be assumed that the
consumption within the countries of origin is a matter of national
rather than international concern.
In pre-war times minerals constituted about 33 per cent[58] of the value
of the total foreign trade of the United States, and 28 per cent of the
foreign trade of Germany. Figures are not available to show the
proportion of mineral tonnage to that of other commodities.
One of the several interesting facts in this world movement of minerals
is that the movement of most of them shows a rather remarkable
concentration. For instance, manganese moves from three principal
sources to four or five consuming centers. Chromite moves from two
principal sources; tungsten also from two. Even for certain commodities
which are widely distributed and move in large amounts, the
concentration of movement is rather marked; for instance, the world
movement of coal is controlled by England, the United States, and
Germany. In other words, although the world movement of mineral
commodities is widespread and exhibits many complex features, most of
the individual minerals follow two or three salient lines of movement.
This means in general that for each mineral there are certain sources of
limited geographic extent, which, because of location, grade, relation
to transportation, cost--in short, all the factors that enter into
availability--are drawn upon heavily for the world's chief demands. The
convergence of these materials toward a few consuming centers indicates
generally concentration of coal production necessary to smelting, high
development of manufacturing, large per capita use, concentration of
facilities, strong financial control, and, not least, a large element of
enterprise which has taken advantage of more or less favorable
conditions.
If a nation were fully supplied with mineral resources, without excess,
the mineral problem might be almost exclusively domestic in its nature.
But no country is so situated. For most of the mineral products the
dominant supply is likely to be controlled by one or two nations, the
other nations being correspondingly deficient and dependent. Even the
United States, which is more nearly self-sustaining in mineral resources
than any other country, is almost wholly dependent on other countries
for certain mineral supplies; and in the case of minerals of which it
has an excess it is dependent on other countries for markets. The view
that the mineral resource problem is solely a local and national one, of
no concern to outsiders, ignores this fundamental fact of distribution
of raw materials.
Control of smelting facilities makes it possible for certain countries
to exercise considerable influence over the production and distribution
of minerals in other countries, and thus presents many difficult
international questions. Even more difficult are the international
problems created by the commercial ownership and control of minerals in
the ground by nationals of other countries.
The national and international aspects of mineral resources are
difficult to separate, so intimately do they react on each other. To
some extent there may be conflict of interest between the two, but in
the main the international questions may be logically approached from
the standpoint of national self-interest; for, in the conduct of the
national industry along broad and enlightened lines, world conditions
must necessarily be considered. A clearer comprehension of the world
mineral relations, and an understanding of our own opportunities and
limitations in comparison with those of our neighbors, cannot but
eliminate some of the unnecessary handicaps to the best use of the world
mineral resources, and result in a lessening of causes of international
discord.
A brief survey of the mineral conditions preceding, during, and
following the war may serve as a convenient means of approach to a study
of the present international aspects of the mineral problem.
MOVEMENT OF MINERALS UNDER PRE-WAR CONDITIONS OF INTERNATIONAL TRADE
If the world pre-war movement of minerals is considered broadly, it may
be regarded as conforming essentially to normal trade conditions of
supply and demand. There have been barriers to overcome, such as tariffs
and trade controls and monopolies of various kinds, but these barriers
have not prevented the major movements between the best sources of
supply and the principal consuming centers. These movements may be
regarded as a more or less spontaneous internationalization of mineral
resources by private enterprise. The aim of free trade or unrestricted
commerce was equality of trade opportunities; but such conditions of
unrestricted competition tended to concentrate trade in the hands of the
strongest interests and to prevent equality of opportunity.
The efforts made to promote or hinder international mineral movements by
tariffs, bonuses, embargoes, subsidies, transport control, patents,
government management, financial pressure, and other means have been
incited mainly by national or imperial self-interest, and have thus been
to some extent inimical to an internationalization based on the
principle of the greatest good to the greatest number. It may be
supposed that, in any effort to attain supernational or international
control, motives and measures based on national self-interest of the
sort here mentioned will continue to play an important part.
CHANGES DURING THE WAR
The war wrought fundamental changes in the world movement of minerals.
The character and distribution of the demands changed. Customary sources
of supply were cut off. Financial disturbances and ship shortage
profoundly modified the nature, distribution, and extent of the world
movement. Our domestic mineral industry was abruptly brought to a
realization of its vital relations with international trade. To
illustrate, the large movement of manganese from India and Russia to the
United States was abruptly stopped, and we had to develop a source of
supply in Brazil. The stoppage of pyrite importations from Spain as a
means of saving ships required the development of pyrite and sulphur
supplies in the United States. The export of oil from the United States
to European countries was greatly stimulated, and the export to other
countries was correspondingly decreased. The world movements of coal
were vitally affected, principally by the limitation of the coal
shipments from England and the United States to South America and the
concentration of shipments to European countries. The closing of German
coal supplies to nearby countries also had far-reaching consequences.
The cutting off of the German potash left the world for the time being
almost unsupplied with this vital fertilizing ingredient. The Chilean
nitrates, on which the world had relied for fertilizer purposes, were
diverted almost exclusively to the manufacture of powder. The total
annual imports of mineral commodities into the United States were
reduced by 1,200,000 tons. Our exports, though they continued in large
volume, were mainly concentrated in Europe. The story of these
disturbances in the world movement of minerals, though highly
interesting, is too long to be told here.
Out of these sweeping and rapid changes in the world movement of mineral
commodities there arose, partly as cause and partly as effect,
international agreements for the allocation of minerals, as a means of
insuring the proper proportions of supplies to the different countries
for the most effective prosecution of the war. Inter-Allied purchasing
committees in London and in Paris found it necessary to make an
inter-Allied allocation of the output of Chilean nitrate, because the
sum of the demands exceeded the total supply by a considerable fraction,
and to agree on the distribution and prices of the world's supplies of
tin, tungsten, and platinum. For many other commodities agreements of
various sorts were made. For instance, the United States entered into an
agreement with England and France for the purchase of iron ore and
molybdenum from Scandinavia to keep it out of Germany. The United States
and England agreed as to supplying Canada with ferromanganese. New
problems of world allocation came up almost daily.
Another war change in mineral conditions, of a more permanent nature,
was the liquidation of German ownership and control of minerals in
allied countries, and in some cases even in neutral countries.
POST-WAR CONDITION OF THE MINERAL TRADE
The mineral industry has by no means reverted to its pre-war condition.
The old movements have been only partially resumed, and new elements
have entered. Shipping is still disturbed. Governments have been
coöperating in various ways in the liquidation of government stocks of
minerals. The German commercial control of minerals outside of its
boundaries, as noted above, has been much weakened. The Reparations
Committee created by the Peace Treaty has enormous powers over the use
and distribution of the mineral resources of Germany, which directly and
indirectly affect the mineral supplies of Europe and all the world. The
terms of the Peace Treaty changed in fundamental ways the international
channels of mineral movement.
The mineral situation of Europe is in such a state of chaos that the
combined efforts of governments will be necessary for many years to
bring order. This will be accomplished partly through the Reparations
Committee, but may require other forms of coöperation. An international
coal commission has already been formed to look after the distribution
of coal through Europe. International coöperation in mineral
distribution is not merely a theoretical possibility for the future,--it
is now the outstanding fact with reference to the European situation.
The recognition of their dependence on neighbors for important mineral
resources has led to earnest efforts on the part of nations to supply
deficiencies. The great activity of the British government in acquiring
oil is one example. The falling off of gold production the world over,
together with the increased disparity between gold reserves and the
currency issued against them, is causing serious consideration of
government action to encourage the gold industry by financial measures
tending to increase the profit of the miners (see pp. 224-225).
Before and since the war most countries of the globe, outside of England
and the United States, have gone far in the exercise of the right of
eminent domain over mineral resources within their own boundaries. Even
in England the recent movement to nationalize the coal and oil resources
is an indication of the general tendency. In the United States the
movement has manifested itself thus far only in the increasing
reluctance on the part of the government to part with mineral resources
on the public domain,--as is clear from the terms of its new leasing law
to cover oil, coal, gas, potash, and phosphates on public lands.
Before the war only the German government was clearly identified with
private interests in international trade and in the acquirement of
mineral reserves. Since the war all governments except that of the
United States are taking an active part in these fields, both directly
and in coöperation with private capital. The British government has
taken a direct financial interest in certain companies, such for
instance as the Anglo-Persian and Shell Oil Companies, and in some cases
is actively interested in the acquirement of selling contracts. In
England there is a wider use of voting trusts in controlling private
companies, with the purpose of preventing the control from falling into
alien hands. Government control of shipping in certain countries is
involving various degrees of control of mineral movements. Also, through
loans and bonds, mineral resources in certain countries have been tied
up by the loaning governments. There has been wide extension of
government control of minerals in mandatory territories and elsewhere
through many new loans and regulations. These steps are in effect
closing important parts of the world to private initiative, and
particularly to nationals of other countries. Whether these activities
of governments are economically desirable or not, they are the actual
conditions, not theories.
If this situation continues, it raises the question whether our
government will not be forced, in protection of its own mineral
industries, also to take a direct part; for under present conditions,
our importers and exporters find themselves dealing single-handed with
governments or with private groups so closely identified with
governments as to have much the same power. In matters of shipping,
credits, exchange, tariffs, embargoes, and opportunity to acquire
foreign reserves, the actual and potential disadvantage to American
interests is obvious.
TENDENCIES TOWARD INTERNATIONAL COÖPERATION AND POSSIBILITY OF
INTERNATIONAL CONTROL[59] OF MINERALS
Under the pre-war conditions, unrestricted competition in world trade by
private enterprise had led to a certain kind of internationalization of
mineral deposits based on natural conditions of availability. There is a
natural tendency to work back as quickly as possible to this condition,
but new elements have entered which seem to make it difficult for
governments to keep their hands off. The participation of governments in
world mineral trade, when not modified by international coöperation or
some other higher form of control, seems to be having a tendency in the
opposite direction--to be closing the doors of equal opportunity and
preventing the natural world use of the world's resources.
These new conditions, together with others outlined in the preceding
section, have made it necessary to pay more attention to the
possibilities of international coöperation than ever before,--not as a
restrictive measure, except temporarily in regard to the Central
European powers,--but as a means of insuring open channels of movement
for raw materials, and of insuring equal economic opportunities to all.
Many of our mineral industries have already appealed to our government
for coöperation and aid in their international dealings. Further,
mineral industries in private hands in the various Allied countries have
attempted to get together to arrange for private coöperation, and
appealed to the Peace Conference for authority to do so. In certain
cases the necessity for coöperative action became so apparent that
pressure was brought to bear on the Peace Conference for the forming of
some sort of international economic body which would make possible some
of these steps. These movements were all dictated by considerations of
self-interest, but self-interest broadened and educated by a knowledge
of the world's situation.
Just as the increasing size of the units engaged in the mineral trade
within national boundaries has led to discussion of the possibilities of
government control in the interest of the public, so the increasing size
of the units in the international mineral trade, the units in many cases
being governments, is leading to discussion of the possibility of some
international or supernational control in the interest of the world
good. Just as national interest is the lengthened shadow of individual
interest, so international interest may be regarded in some aspects as
the lengthened shadow of national interest.
The general purpose of the suggested control is to minimize
international friction; but more specifically it has been suggested that
some sort of international coöperation is necessary in order to insure
equality of opportunity among nations, both in supplies and in markets,
and thereby to prevent the crowding of the weaker by the stronger
nations. This is the gist of one of the famous fourteen points. The
purpose might be accomplished by direct allocation of supplies or by
control of tariffs and exchange.
One of the conditions which seems to require international coöperation
is the exploitation of mineral deposits in backward countries.
Unrestricted competition among nations in such exploitation has been an
important cause of international controversy. It was planned at Peace
Conference that the mineral resources in countries taken over by the
great powers under mandatories should be developed and used in the
interest of the group of nations, rather than for the special interest
of the nation taking the mandatory. One of the natural functions of any
international or supernational organization would be the adjustment and
settlement of difficulties arising from this provision.
This topic brings up the question as to the right of any nation or group
of nations to exert any force on weaker nations in the exploitation of
mineral resources. On the principal of self-determination and of the
complete freedom of action of nations, this procedure seems unjustified.
On the other hand, whether rightly or wrongly, civilization has created
great material demands which must be satisfied. The individuals,
companies, and governments which use force to exploit resources in
weaker countries are merely the agents in supplying the demand created
by all of us. While their methods are often indefensible, the exploiters
cannot be regarded merely as irresponsible buccaneers who are
projecting themselves unnecessarily into somebody else's business.
Whatever the sentimental and ethical aspects of the question, it seems
almost inevitable that the demands of civilization will continue to
require the exploitation of weaker countries; and in proportion as these
countries are backward in coöperating, they must feel the world
pressure. An agreement for international coöperation in such matters,
therefore, is not to be regarded as merely a cold-blooded attempt to rob
weaker nations,--but rather as a means of improving methods in
satisfying the actually existing material demands of civilization. For
illustration, the criticism of England's attempt to develop the oil
industry of Mesopotamia and Persia has to a large extent confused the
methods with the aim sought for. It is the writer's view that
development of these resources is inevitable, and that criticism should
not be directed toward nations and groups attempting to attain these
results, but rather to the methods applied. For the purposes of this
discussion, it is not necessary to go beyond the acceptance of the fact
of demand, nor to argue the question as to whether the material demands
of civilization should be curbed and progress restricted to matters of
mind and human happiness.
METHODS OF INTERNATIONAL COÖPERATION
The first step in international consideration of minerals is obviously
one of fact-finding. This became painfully evident during the great war,
when the sudden cutting off of outside supplies and markets brought home
the fact that the mineral question is only in part a domestic one. The
average mining man had come to take the established marketing and
commercial conditions more or less for granted, and had not looked into
the underlying factors. There had been a tendency to assume that a kind
Providence was in some manner looking after these elements in the
situation. The nearest approach to Providence, as a matter of fact, was
a small group of importers and exporters, possessing special knowledge
of the international movements of certain commodities,--which knowledge
was of unsuspected importance to the mineral industry. War conditions
showed that neither the general public nor the mineral industry as a
whole, much less the government, had even an elementary grasp of the
important elements of the world mineral situation. The mobilizing of
this information under high pressure, through the coöperation of
government and private agencies, was an interesting and important
feature in the complex activities back of the firing line. It is vastly
to the credit of the men interested in the mineral industry in this
country, and presumably also in other countries, that almost without
exception they contributed their bits of knowledge to the common pool,
even though these bits had been in a sense their private capital.
Certain importers, who by their knowledge of international phases of the
mineral situation had been able to exercise a profound influence on
domestic markets, voluntarily sacrificed their own interest for the
common cause and pointed out ways in which reductions of imports could
be made.
The problems of the Peace Conference, and of other international
agreements now pending, have required a still further systematizing of
international information. One of the results has been the establishment
of organizations of an international fact-finding character in our own
and in certain other governments. In the chapters on the several
minerals in this book, are summarized some of the salient features of
the international situation developed by study of the kind indicated.
Knowledge of the physical facts of the world mineral situation is only a
first step. Their interpretation and correlation, the study of the
underlying principles, the formulation of the necessary international
agreements and regulations, constitute even more difficult problems,
which are far from solved.
There always has been some coöperation of governments in the mineral
trade through the ordinary diplomatic channels. The question is now
prominent whether, in view of the new conditions, it may not be
necessary to develop better machinery--in the form of some international
or supernational organization, possibly patterned on war procedure--in
order to expedite the negotiations and to minimize possibilities of
friction.
During the war, when the world demand exceeded the total world supply of
certain commodities, such as nitrate and tin, international commissions
were formed in order to make an equitable distribution of these minerals
and prevent favored strong nations from taking too large a proportion of
the total. This procedure presented no insurmountable difficulties. A
canvass of the total supplies available and of the demands of the
various countries ordinarily led to voluntary compromise in the
allocation of supplies. Most of the regulations of these commissions
were applied to mineral industries which were unable to meet the total
demand. They were not tried out in cases where there were excess
supplies; this process obviously would have been much more difficult,
though perhaps not impossible.
The general success of international attempts to allocate mineral
supplies during the war suggests the lines along which results might be
accomplished during peace. The process is essentially a matter of
getting at the facts, and then discussing the situation around a
table,--thus eliminating the long delays and misunderstandings arising
from the procedure through the older established diplomatic channels.
How far such a procedure might be possible without the compelling common
interest of war is debatable.
The great powers of the Reparations Committee, previously noted, and of
the recently formed European coal commission, already indicate the
general nature of the machinery for international control which might be
exercised through a league of nations. It is not our purpose to argue
for international control or for any specific plan of control, but
rather to outline the problem. The question is not an academic one.
Various kinds of international control are present facts, and the
problem relates to the possibilities of more effective organization of
existing agencies.
CONSERVATION IN ITS INTERNATIONAL RELATIONS
The interests of conservation, considering both its physical and its
human energy phases (p. 362), seem to call for an international
understanding in the use of mineral resources which will result in the
minimum hindrance to their free movements along natural channels of
trade. The essential fact of the concentration of mineral supplies in
comparatively few world localities, and the fact that no nation is
supplied with enough of all varieties of minerals, mean that artificial
barriers to their distribution cannot but impose unnecessary handicaps
on certain localities, which may be anti-conservational from a world
standpoint. If the few countries possessing adequate supplies of
high-grade ferro-alloy minerals, for instance, were to restrict their
distribution by tariffs or other measures, the resulting cost to
civilization through the handicapping of the steel industry would be a
large one. Or if, for the general purpose of making the United States
entirely self-supporting in regard to mineral supplies, sufficiently
high import tariffs were imposed on these minerals to permit the use of
the low-grade deposits in the United States, earlier exhaustion of the
limited domestic supplies would follow, and in the meantime the cost to
the domestic steel industry would be serious. Cost may be taken to
represent the net result of human energy multiplied into raw material.
The movement would therefore be anti-conservational. If each state in
the United States were to start out to become entirely self-sustaining
in regard to minerals, and by various regulations were able to prohibit
the use of minerals brought in from without, or the export of its excess
of minerals, the waste in effort and materials would be obvious. Nature
has clearly marked out fields of specialization for different
localities, and the effective use of mineral supplies is just as much a
matter of specialization as the effective use of man's talents. If the
United States, because of its vast copper deposits, is in a position to
specialize in this line and to aid the world thereby, this should
involve recognition of the fact that other countries are better able to
specialize in other commodities,--thereby forming a basis for mutual
exchange, which is desirable and necessary for world development.
This conservational argument against artificial barriers does not
necessarily imply complete elimination of tariffs or other restricting
or fostering measures. Within limits these may be necessary or desirable
in order to maintain differences in the standard of living, or in order
to permit the growth of infant industries; but to carry these measures
to a point where they interfere with essential mineral movements
determined by nature is obviously anti-conservational.
For some mineral commodities, international coöperation may prevent
duplication in efforts and the development of excessive supplies in
advance of the capacity of the world to use them. Partly because of lack
of such coöperation, certain mineral commodities have been developed in
such large quantities in various parts of the world that it may be many
years before demand catches up with development. In the meantime, large
and unnecessary interest charges are piling up. This financial loss
measures the loss in effectiveness of collective human effort.
In the above discussion, little reference has been made to shortage of
total world supplies as an argument for international coöperation. This
is an argument often cited, and with some effectiveness during the war.
It is the writer's view that this phase of the problem has been much
exaggerated. Except for certain periods during the war, in considering
the world as a whole adequate supplies of all mineral commodities have
been available at all times. They have been developed as rapidly as
needed, in some cases more rapidly; and geological conditions seem to
indicate that this condition will continue for some time in the future,
through national and individual effort. Combined efforts of governments
seem hardly necessary as yet to accomplish this purpose. In fact, there
is rather more danger of over-development, without due regard to the
working of the interest rate, which might be prevented by international
coöperation. The main problem now is not one of total supplies, but of
their effective and equitable distribution.
EXPLORATION IN ITS INTERNATIONAL RELATIONS
When an explorer or prospector leaves his own country to discover and
acquire minerals in other countries, with a view to exportation, it is
reasonably obvious that he must first acquire a sound knowledge of at
least some of the elements of international trade in minerals,--such as
shipping facilities, rates, tariffs, attitude of the government toward
ownership, toward export, etc. For example, the prospector for oil in
foreign countries will not get very far without considering the recent
steps taken by foreign governments, and mentioned on pp. 131-132.
The necessity of study of the international situation in conducting
domestic exploration is not so generally recognized; and yet anyone
today who confines his attention solely to the local physical facts of
the situation, and who ignores international considerations, may find
himself in difficulties. The investigation of international questions is
not merely desirable from the standpoint of general information, but may
be vital to the business or professional success of the explorer. For
instance, he might take up the exploration and development in the United
States of fertilizers and ferro-alloy minerals which are ordinarily
imported; and without understanding the severe limitations imposed by
the foreign situation, he might find himself with a property, sound from
a physical standpoint, but financially a failure. It is comparatively
easy, by running over the long list of mineral commodities used in the
United States, to eliminate, on international grounds, a considerable
number from the field inviting financial success, and to concentrate on
others whose economic relations are sound. In the rapid changes during
and since the war, the necessity for consideration of world conditions
has been brought home at heavy expense to many business and professional
men engaged in the mineral industry.
VALUATION IN ITS INTERNATIONAL RELATIONS
For mineral commodities of limited supply and steady demand, market
conditions may be more or less taken for granted, and valuation may be
based on local considerations. For a large number of mineral resources,
however, the competitive market conditions are anything but stable,
because of foreign competition. It is necessary not only to know the
basis for this competition, but also to be able to follow intelligently
its various changes. The value of many of our mineral deposits in recent
years has varied widely with changes in the foreign situation.
RELATIVE POSITION OF THE UNITED STATES IN REGARD TO SUPPLIES OF MINERALS
The United States is more nearly self-sustaining in regard to mineral
commodities as a whole than any other country on the globe. The
following statement summarizes qualitatively our position:
1. Minerals of which our exportable surplus dominates the world
situation:
Copper.
Petroleum has belonged in this class until recently. In
the future imports will be required (see 5 following).
2. Minerals of which our exportable surplus constitutes an important but
not a dominant factor in the world trade:
Cement.
Coal.
Iron and steel.
Phosphates.
Silver.
Sulphur.
Uranium and radium.
3. Minerals of which our exportable surplus is not an important factor
in world trade. Small amounts of most of these minerals have been and
will doubtless continue to be imported because of special grades,
back-haul, or cheaper sources of foreign supply, but these imports are
for the most part not essential as a source of supply:
Aluminum and bauxite.
Arsenic.
Artificial abrasives and emery (except Naxos emery).
Asphalt and bitumen.
Barite.
Bismuth.
Borax.
Bromine.
Building stone (except Italian marble).
Cadmium.
Feldspar.
Fluorspar.
Fuller's earth.
Gold.
Gypsum.
Lead.
Lime.
Magnesite.
Mineral paints (except umber, sienna, and ocher from France and Spain).
Molybdenum.
Pyrite.
Salt (except special classes).
Talc.
Titanium.
Tripoli and diatomaceous earth.
Zinc.
4. Minerals for which the United States must depend almost entirely on
other countries:
Cobalt.
Nickel.
Platinum and metals of the platinum group.
Tin.
5. Minerals for which the United States will depend on foreign sources
for a considerable fraction of the supply:
Antimony.
Asbestos.
Ball clay and kaolin.
Chalk.
Chromite.
Corundum.
Diamond dust and bort.
Garnet.
Graphite.
Grinding pebbles.
Manganese.
Mercury.
Mica.
Monazite.
Naxos emery.
Nitrates.
Petroleum (see below).
Potash.
Precious stones.
Pumice.
Tungsten.
Vanadium.
Zirconium.
In the past the production of petroleum in the United States has
dominated the world petroleum situation; but domestic consumption has
now overtaken production, and unless discoveries of oil come along at a
rapid rate the domestic deficiency seems likely to increase, with
corresponding increase in our dependence on foreign sources (see pp.
128-132).
Some of the minerals of this last class, such as potash, manganese, and
chromite were developed under war conditions in the United States to
such an extent as to materially lessen the demand for importation; but
in normal times domestic sources can supply a considerable fraction of
the demand only at high cost and with the aid of a protective tariff.
No attempt will be made here to present the detailed figures on which
the above generalizations are based. In view of the present disturbed
conditions of production and consumption, any judgment as to future
demands or available surplus must take into account several factors
which cannot be accurately measured,--such as financial control in
foreign countries, possible tariffs, and foreign competition. For this
reason the above statement should be regarded as only tentative, though
it is the result of a rather exhaustive study of conditions in relation
to the world control of shipping. The classes named overlap to some
extent, and it is to be expected that some of the commodities placed in
one class may in the near future be transferred to another.
In terms of value, the United States has a potential export surplus of
minerals about twice as large as that of all the rest of the world put
together. Countries which were neutral during the war have the remaining
export surplus. Great Britain, France, and Italy have net import
requirements considerably in excess of their exports. Germany has almost
as large a deficit of minerals as the United States has a surplus.
From the above facts it is clear that, in any scheme of international
control or coöperation, the United States would have by far the heaviest
stake, and perhaps the most to lose by restriction. It seems equally
clear that the preponderance of exportable surplus of minerals over
necessary imports justifies the United States in taking a broad and
liberal view of the importation of needed minerals. The war-time
necessity of making our country as nearly self-sustaining as possible
does not seem to obtain in peace times. To carry that principle to an
extreme means not only the expensive use of low-grade domestic supplies,
but the elimination of the imports which are so necessary to balance our
export trade.
These facts also raise the question as to how far the United States is
justified in exploiting the rest of the world to add to its already
great preponderance of control,--as, for instance, in copper. Any
further aggrandizement of our position in regard to such minerals may be
directly at the expense of neighbors who are already far less well
supplied than ourselves, and is to be justified only on the basis of
adding to the world's supply for common use, and of lending our expert
assistance to neighbors to make them more nearly self-supporting. To
carry out our campaign in these cases without regard to the needs of
other countries will obviously not hasten the ideal of a democratic
world with equal opportunity for all. On the other hand, the great
freedom allowed by our laws in regard to foreign commercial control of
our minerals, as compared to the restriction on such control in other
countries, suggests the desirability of exerting our pressure for the
open door policy in all parts of the world, in the interest of desirable
reciprocal relations.
In this connection there has been a tendency to criticise England's
post-war activity in securing oil reserves for the future. Self-interest
has clearly dictated the necessity for improving England's weak position
in regard to this vital energy resource. The success of this movement
obviously means a lessening of the future preponderance of the United
States in the oil industry, and calls for increased activity on the part
of the United States in maintaining the desirable leading position it
has long held. From the writer's viewpoint, however, the fair success of
a rival does not call for criticism of motives. If there is any just
criticism, it applies to methods (see pp. 390-391).
Whatever action may be taken by the United States in regard to
international mineral questions, it is clear that the war has brought
this country into such world relations that it has become imperative for
us to study and understand the world mineral situation much more
comprehensively than before,--in the interest not only of intelligent
management of our own industries, but of far-sighted handling of
international relations. Under the stress of war the government,
especially through the Geological Survey, the Bureau of Mines, and the
several war boards, found it necessary to use extraordinary efforts to
obtain even elementary information on the international features of
mineral trade. Much progress has been made, but only a start. The
geologist or engineer who fails to follow these investigations may be
caught napping in the economic phases of his work.
THE COAL AND IRON SITUATION OF WESTERN EUROPE UNDER THE TERMS OF THE
PEACE TREATY
A mineral problem of special international importance at the present
time relates to the disposition of the coal and iron resources of
Germany. Germany's coal and iron have been the basis for its commanding
position in industry and commerce. In fact, its development of these
resources has been probably the most vital element in the European
economic situation. The terms of the Peace Treaty in regard to these
commodities have far-reaching consequences, not only for Germany but for
all Europe, and indirectly, for the world.
Germany (Westphalia) outclasses all other European sources in grades of
metallurgical coal, in quantities produced, and in cheapness of
production. Both France and Belgium must continue to be dependent on
this source for important parts of the coking coal for metallurgical
purposes, notwithstanding France's acquisition of the Saar Basin, which
produces mainly non-coking coal, and the development of new reserves in
Belgium. Germany's command of coal is wrecked in several ways. The
French take over full and absolute possession of the coal of the Saar
Basin, though Germany has the right to repurchase it at the end of
fifteen years, in case this territory then elects for union with
Germany. The coal of Upper Silesia, with a production of about 23 per
cent of the total of all German hard coal, is to be ceded to Poland,
subject, however, to plebiscite. Germany undertakes to deliver to France
each year, for not to exceed ten years, an amount of coal equal to the
difference between the annual pre-war production of the French coal
mines destroyed as a result of the war, and the production of the mines
of the same area during the years in question,--such delivery not to
exceed 20,000,000 tons in any one year of the first five, nor 8,000,000
in any one year of the succeeding five years. In addition, Germany
agrees to deliver coal, or its equivalent in coke, as follows: to France
7,000,000 tons annually for ten years; to Belgium 8,000,000 tons
annually for ten years; to Italy an annual quantity rising by annual
increments from 4,500,000 tons in 1919-20 to 8,500,000 tons in each of
the six years 1923-24 to 1928-29; and to Luxemburg, if required, a
quantity of coal equal to the pre-war annual consumption of German coal
in Luxemburg.
The total pre-war coal production of Germany in 1913 was 191,500,000
tons. The diminution of production due to loss of territory in
Alsace-Lorraine, in the Saar Basin, and in Upper Silesia amounts to
about 61,000,000 tons. The further required annual distribution of coal
to France, Italy, Belgium, and Luxemburg amounts to about 40,000,000
tons. This leaves about 90,000,000 tons for Germany's domestic use, as
compared with a pre-war domestic use of 139,000,000 tons. Even then,
these calculations make no allowance for coal to be used in export trade
to neutrals or other countries, some part of which seems vital to
Germany's trade. They make no allowance for the deterioration of plant
and machinery in the mines, which will delay resumption of coal
production. They make no allowance for the diminution in working hours
and the lack of transportation. In short, unless there is a miraculous
recovery and development of Germany's coal industry, impossible
conditions have been imposed. Some recognition of this fact appears in
the great powers to adjust terms which have been vested in the
Reparations Committee. Successive revisions of requirements by the
Reparations Committee have already reduced the direct contributions of
coal from Germany nearly fifty per cent. The entire European coal
situation is in a state of chaos. It was found necessary in 1918 to
appoint a Coal Commission under international control, to attempt to
allocate and distribute supplies. It seems inevitable that the physical
facts of the situation will prevail, and that the control of the Allies
will resolve itself into efforts to distribute and coördinate supplies
so as to keep the European machinery going, more or less regardless of
the terms of the Peace Treaty.
One of the important outcomes of this situation has been the recent
rapid development of German lignite production, based on newly
worked-out methods of treatment and utilization.
By taking over Alsace-Lorraine, France acquires about 70 per cent of the
iron ore reserves and annual production of Germany. This production was
in minor part smelted locally,--the larger part moving down the Rhine to
the vicinity of the Ruhr coal fields, and Ruhr coal coming back for the
smelting in Lorraine. This great channel of balanced exchange of
commodities has been determined by nature, and is not likely to be
permanently affected by political changes. For the time being, however,
the drawing of a political boundary across this trade route hinders the
full resumption of the trade. Self-interest will require both Germany
and France to keep these routes open. France requires German coal to
supply the local smelters near the iron fields, and German markets for
the excess production of iron ore. On the other hand, Germany's great
smelting district in the Ruhr Basin is largely dependent on the
Lorraine iron ore, and the movement of this iron ore requires coal from
down the Rhine as a balance.
The intelligent handling of this great coal and iron problem is of
far-reaching consequence to the mineral industries of the world.
CONCLUSION
In the foregoing discussion it is not our purpose to argue for any
specific national or international plan or procedure, but rather to show
something of the nature of the problem,--and particularly to show that
intelligent and broadened self-interest requires a definite national
policy in regard to world mineral questions. Realization of this fact is
a long step toward the solution of the international problems. No
geologist, engineer, or business man is safe, in the normal conduct of
his affairs, without some attention to these matters.
It is our purpose further to bring home the fact that international
coöperation in the mineral field is not merely an academic possibility,
but that in many important ways it is actually in existence. The terms
of the Peace Treaty alone have far-reaching consequences to the explorer
or mining man in all parts of the world. The modifications of these
terms, which are inevitable in the future, will not be of less
consequence. It is necessary not only to know what these are, but to aid
in their intelligent formulation.
LITERATURE
A vast new literature on the subject of international mineral relations
has sprung into existence during and following the war, and anyone may
easily familiarize himself with the essentials of the situation. Some of
the international features are noted in the discussion of mineral
resources in this book. For fuller discussion, the reader is especially
referred to the following sources:
The reports of the United States Geological Survey. Note especially
_World Atlas of Commercial Geology_, 1921.
The reports of the United States Bureau of Mines.
_Political and commercial geology_, edited by J. E. Spurr, McGraw-Hill
Book Co., New York, 1920.
_Strategy of minerals_, edited by George Otis Smith, D. Appleton and
Co., New York, 1919.
_Coal, iron and war_, by E. C. Eckel, Henry Holt and Company, New York,
1920.
_The iron and associated industries of Lorraine, the Sarre district,
Luxemburg, and Belgium_, by Alfred H. Brooks and Morris F. LaCroix,
Bull. 703 U. S. Geological Survey, 1920.
_The Lorraine iron field and the war_, by Alfred H. Brooks, Eng. and
Min. Journ., vol. 109, 1920, pp. 1065-1069.
Munitions Resources Commission of Canada, final report, 1920.
FOOTNOTES:
[58] Umpleby, Joseph B., _Strategy of minerals--The position of the
United States among the nations_: D. Appleton and Co., New York, 1919,
p. 286.
[59] Control is here used in a very general sense to cover activities
ranging from regulation to management and ownership. The context will
indicate in most cases that the word is used in the sense of regulation
when referring to governmental relationships.
CHAPTER XIX
GEOLOGY AND WAR
GEOLOGY BEHIND THE FRONT
The experience of the great war disclosed many military applications of
geology. The acquirement and mobilization of mineral resources for
military purposes was a vital necessity. In view of the many references
to this application of geology in other parts of this volume, we shall
go into the subject in this chapter no further than to summarize some of
the larger results.
As a consequence of the war-time breakdown in international commercial
exchange, the actual and potential mineral reserves of nations were more
intensively studied and appraised than ever before, with the view of
making nations and belligerent groups self-sustaining. This work
involved a comprehensive investigation of the requirements and uses for
minerals, and thus led to a clearer understanding of the human relations
of mineral resources. It required also, almost for the first time, a
recognition of the nature and magnitude of international movements of
minerals, of the underlying reasons for such movements, and of the vital
inter-relation between domestic and foreign mineral production. The
domestic mineral industries learned that market requirements are based
on ascertainable factors and that they do not just happen. Large new
mineral reserves were developed. Metallurgical practices were adapted to
domestic supplies, thus adding to available resources. Better ways were
found to use the products. Some of these developments ceased at the end
of the war, but important advances had been made which were not lost.
One of the advances of permanent value was the increased attention to
better sampling and standardization of mineral products, as a means of
competition with standardized foreign products. For instance, the
organization of the Southern Graphite Association made it possible to
guarantee much more uniform supplies from this field, and thereby to
insure a broader and more stable market. Such movements allow the use
of heterogeneous mineral supplies in a manner which is distinctly
conservational, both in regard to mineral reserves and to the human
energy factors involved. In another war the possibilities and methods of
meeting requirements for war minerals will be better understood.
In these activities, geologists had a not inconsiderable part. The U. S.
Bureau of Mines, the U. S. Geological Survey, state geological surveys,
and many other technical organizations, public and private, turned their
attention to these questions. One of the special developments was the
organization by the Shipping Board of a geologic and engineering
committee whose duty it was to study and recommend changes in the
imports and exports of mineral commodities, with a view to releasing
much-needed ship tonnage. This committee was also officially connected
with the War Industries Board and the War Trade Board. It utilized the
existing government and state mineral organizations in collecting its
information. Over a million tons of mineral shipping not necessary for
war purposes were eliminated. This work involved also a close study of
the possibilities of domestic production to supply the deficiencies
caused by reduction of foreign imports.
Other special geological committees were created for a variety of war
purposes. In the early stages of the war a War Minerals Committee, made
up of representatives of government and state organizations and of the
American Institute of Mining Engineers, made an excellent preliminary
survey of mineral conditions. A Joint Mineral Information Board[60] was
created at Washington, composed of representatives of more than twenty
government departments which were in one way or another concerned with
minerals. It was surprising, even to those more or less familiar with
the situation, to find how widely mineral questions ramified through
government departments. For instance, the Department of Agriculture had
men specially engaged in relation to mineral fertilizers and arsenic.
Sulphur and other mineral supplies were occupying the attention of the
War Department. Mica and other minerals received special attention from
the Navy Department. The Tariff Board, the Federal Trade Commission, the
Commerce Department, even the Department of State, had men who were
specializing on certain mineral questions. All these departments had
delegates on the Joint Mineral Information Board, in which connection
they met weekly to exchange information for the purpose of getting
better coördination and less duplication.
The National Academy of Sciences established a geologic committee, with
representatives from the U. S. Geological Survey, the state geological
surveys, the Geological Society of America, and other organizations.
This committee did useful work in correlating geological activities,
mainly outside of Washington, and in coöperation with the War Department
kept in touch with the geologic work being done at the front.
While the activities of geologists for government, state, and private
organizations were for the most part in relation to mineral resource
questions, this was by no means the total contribution. The U. S.
Geological Survey and other organizations, in coöperation with the War
Department, did a large amount of topographic and geologic mapping of
the eastern areas for coast-defense purposes. This work involved
consideration of the topography for strategic purposes, as well as the
stock-taking of mineral resources--including road materials and water
supplies. The revision of Geological Survey folios, with these
requirements in mind, brought results which should be of practical use
in peace time. Studies were likewise made of cantonment areas, with
reference to water supplies and to surface and sub-surface conditions.
Many geologists were engaged in the military camps at home and abroad,
and in connection with the Student Army Training Corps at the
universities, in teaching the elements of map making, map
interpretation, water supply, rock and soil conditions in relation to
trenching, and other phases of geology in their relation to military
operations. The textbook on Military Geology,[61] prepared in
coöperation by a dozen or more geologists for use in the courses of the
Student Army Training Corps, is an admirable text on several phases of
applied geology. The name of the book is perhaps now unfortunate,
because most of it is quite as well adapted to peace conditions as to
those of war. There is no textbook of applied geology which covers
certain phases of the work in a more effective and modern way. The
topics treated in this book are rocks, rock weathering, streams, lakes
and swamps, water supply, land forms, map reading and map
interpretation, and economic relations and economic uses of minerals.
Another book,[62] on land forms in France, prepared from a physiographic
standpoint, was a highly useful general survey of topographic features
and was widely used by officers and others.
GEOLOGY AT THE FRONT[63]
Perhaps the most spectacular and the best known use of geology in the
war was at and near the front. This use reached its earliest and highest
development in the German army, but later was applied effectively by the
British and British Colonial armies, and by the American Expeditionary
Force.
One of the first intimations to the American public of the use of
geology at the front appeared in the publication of German censorship
rules in 1918,--when, among the prohibitions, there was one forbidding
public reference to the use of earth sciences in military operations. A
leading American paper noted this item and speculated at some length
editorially as to what it meant.
It was discovered that geologists to the number of perhaps a hundred and
fifty were used by the Germans to prepare and interpret maps of the
front for the use of officers. Features represented on these maps
included topography; the kinds of rocks and their distribution; their
usefulness as road and cement materials; their adaptability for trench
digging, and the kinds and shapes of trenches possible in the different
rocks; the manner in which material thrown out in trenching would lie
under weathering; the ground-water conditions, and particularly the
depth below the surface of the water table at different times of the
year and in different rocks and soils; the relation of the ground-water
to possibilities of trench digging; water supplies for drinking
purposes; the behavior of the rocks under explosives, and the resistance
of the ground to shell-penetration; the underground geological
conditions bearing on tunnelling and underground mines; and the
electrical conductivity of rocks of different types, presumably in
connection with sound-detection devices and groundings of electric
circuits. Some of the captured German maps were models of applied
geology. They contained condensed summaries of most of the features
above named, together with appropriate sketches and sections. During the
Argonne offensive by the American army the captured German lines
disclosed geologic stations at frequent intervals, each with a full
equipment of maps relating to that part of the front. From these
stations schools of instruction had been conducted for the officers in
the adjacent parts of the front.
The British efforts were along similar lines, although they came late in
the war, under the leadership of an Australian geologist. Their efforts
were especially useful in connection with the large amount of tunnelling
and mining done on the British front. Among the many unexpected and
special uses of geology might be cited the microscopical identification
of raw materials used in the German cement. It became necessary for
certain purposes to know where these came from. The microscope disclosed
a certain volcanic rock known to be found in only one locality. In the
Palestine campaign, the knowledge of sources of road material and water
supply based on geologic data was an important element in the advance
over this arid region. Wells were drilled and water pipes laid in
accordance with prearranged plans.
In spite of the fact that the usefulness of geology had been clearly
indicated by the experience of the German and British armies, the
American Expeditionary Force was slow to avail itself in large measure
of this tool; but after some delay a geologic service was started on
somewhat similar lines under the efficient leadership of
Lieutenant-Colonel Alfred H. Brooks, Director of the Division of Alaskan
Resources in the U. S. Geological Survey. The work was organized in
September, 1917, and during the succeeding ten months included only two
officers and one clerk. For the last two months preceding the armistice
there was an average of four geologic officers on the General Staff, in
addition to geologists attached to engineering units engaged in road
building and cement making, and plans had been approved for a
considerable enlargement of the geologic force. The work was devoted to
the collection and presentation of geologic data relating to (1) field
works; (2) water supply; and (3) road material. Of these the first two
received the most attention. Maps were prepared, based somewhat on the
German model, for the French defenses of the Vosges and Lorraine
sectors, and for the German defenses of the St. Mihiel, Pont-a-Mousson,
and Vosges sectors. Water supply reports covered nearly 15,000 square
kilometers. The following description of the formations, taken from the
legend of one of the geologic maps, shows the nature of the data
collected:
_Silt, clay and mud, with some limestone gravel_, usually more
or less saturated, except during dry season (June to
September), in many places subject to flooding. Surface
usually soft except during Summer. These deposits are 1/2 to 2
meters thick in the small valleys, and 2 to 3 meters in the
---- Valleys. Unfavorable to all field works on account of
ground-water and floods, and not thick enough for cave
shelters.
_Silts with some clay and fine sands and locally some fine
gravel and rock débris._ These deposits occur principally on
summits and slopes, and are probably from 1 to 2 meters thick.
Even during dry season (June to September) they retain
moisture and afford rather soft ground. In wet season the
formation is very soft and often muddy. In many places water
occurs along bottom of these deposits. Favorable for trenches,
but which require complete revetment, and ample provision for
drainage, not thick enough for cave shelters; cut and cover
most practical type of shelter.
_Clay at surface with clay shales below._ This deposit occurs
in flats and is usually saturated for a depth of 1 to 2-1/2
meters, during wet season, for most of the year the surface is
soft, but in part dries out in Summer. Deep trenches usually
impossible, and even shallow trenches likely to be filled with
water; defensive works will be principally parapets revetted
on both sides. Cave shelter construction usually
impracticable, unless means be provided for sinking through
saturated surface zone into the dry ground underneath. Cut and
cover usually the most practical type of shelter in this
formation.
_Clay at surface with calcareous clay shale and some thin
limestone layers below._ This formation occurs in low rounded
hills; surface saturated during wet weather, but terrain
permits of natural drainage, and dries out during Summer;
during wet season (October to May) the surface zone is more or
less saturated, and ground may be muddy to a depth of a meter
or more, ground-water level usually within two or three meters
of surface. Trench construction easy, but requires complete
revetment, and ample provision for surface drainage. Cave
shelters can be constructed in this formation where the slope
is sufficient to permit of drainage tunnels. The depth to
ground-water level should always be determined by test shafts
or bore holes in advance of dugout construction.
_Surface formation usually clay 1 to 2 meters in depth; below
this is soft clay shales or soft limestone._ Surface usually
fairly well drained, and fairly hard ground. In general,
favorable for trenches and locally favorable for cave
shelters. In some localities underground water prevents cave
shelter construction. The presence or absence of underground
water should always be determined by test shafts or bore holes
in advance of dugout construction.
_Surface formation consisting of weathered zone 1/2 to 1-1/2
meters thick, made up of clay with limestone fragments and
broken rock. Below is compact limestone formation._ The
surface of this formation is usually fairly hard, and well
drained except in wettest season. Trenches built in it require
little revetting; very favorable for cave shelters, but
requires hard rock excavation. Some thin beds of clay occur in
some of the limestone, and at these a water bearing horizon
will be found. Where a limestone formation rests on clay as
near ---- a line of springs or seepages is usually found. Such
localities should be avoided, or the field works placed above
the line of springs or seepages. This formation is best
developed in the plateau west of ----. Here it is covered by
only a thin layer of soil, hard rock being close to the
surface.
The limestones afford the only rock within the quadrangle
which can be used for road metal.
_Quarries_ (in part abandoned).
_Limestone gravel pits._
_Locus of springs and seepages._ These should be avoided as
far as possible in the location of field works, especially of
dugouts. Field works should be placed above the lines of
springs.
The water supply maps with accompanying engineer field notes are models
of concise description of water supply conditions, with specific
directions for procedure under different conditions. A few paragraphs
taken from these notes are as follows:
Ground overlying rock, such as limestone, compact sandstone,
granites, etc., which are usually fractured, is from the
standpoint of underground water, most favorable for siting of
field works. Clay shales and clay hold both surface and
underground water, and are, therefore, unfavorable for field
works. The contact between hard rocks resting on clay or clay
shales is almost invariably water bearing, and should be
avoided in locating field works.
At localities where impervious formations (clay, etc.) occur
at or near the surface, they hold the water and form a
superficial zone of saturation. This condition makes trench
construction and maintenance difficult, and cave shelters can
usually only be made by providing means of sinking through the
saturated zone. The surface saturated zone often dries out in
summer.
In pervious, or almost pervious rocks, the zone of saturation,
or ground-water level, lies at much lower depth, and may
permit of the construction of field works as well as cave
shelters above it.
Underground water bearing horizons and water bearing faults
should be avoided in locating field works.
Wherever there is any uncertainty about the underground water
conditions, test shafts or bore holes should always be made in
advance of the construction of extensive deep works.
EFFECT OF THE WAR ON THE SCIENCE OF ECONOMIC GEOLOGY
In general, the war required an intensive application of geology along
lines already pretty well established under peace conditions. Much was
done to make the application more direct and effective, and a vast
amount of geologic information was mobilized. The general result was a
quickened appreciation of the possibilities of the use of geology for
practical purposes. Perhaps the most important single result was a wider
recognition of the real relations of mineral resources to human
activities, and of the international phases of the problem. More
specifically, there was a most careful stock-taking of mineral resources
and a consideration of the "why" of their commercial use. Many new
resources were found, as well as new ways to utilize them.
FOOTNOTES:
[60] Now known as Economic Liaison Committee.
[61] _Military geology and topography_, Herbert E. Gregory, Editor.
Prepared and issued under the auspices of Division of Geology and
Geography, National Research Council, Yale Univ. Press, New Haven, 1918.
[62] Davis, W. M., _Handbook of Northern France_, Harvard Univ. Press,
Cambridge, 1918.
[63] For more detailed description of this subject the reader is
referred to The use of geology on the Western Front, by Alfred H.
Brooks, _Prof. Paper 128-D_, _U. S. Geol. Survey_, 1920.
CHAPTER XX
GEOLOGY AND ENGINEERING CONSTRUCTION
Economic applications of geology are by no means confined to mineral
resources (including water and soils). The earth is used by the human
race in many other ways. Human habitations and constructions rest on it
and penetrate it. It is the basis for transportation, both by land and
water. Its water powers are used. In these various relations the
applications of geology are too numerous to classify, much less to
describe. While only a few of these activities have in the past required
the participation of geologists, the growing size of the operations and
increasing efficiency in their planning and execution are multiplying
the calls for geologic advice. The nature of such applications of
geology may be briefly indicated.[64]
FOUNDATIONS
The foundations of modern structures such as heavy buildings, especially
in untried localities, require much more careful consideration of the
substrata than was necessary for lighter structures. In planning such
foundations, it is necessary to know the kinds of rocks to be excavated,
their supporting strength, their structures, the difficulties which are
likely to be caused by water, and other geologic features. Failure to
give proper attention to these factors has led to some disastrous
results.
The planning of foundations and abutments of bridges requires similar
geologic knowledge. In addition, there must be considered certain
physiographic factors affecting the nature and variation of stream flow
and the migration of shore lines.
SURFACE WATERS
Construction of great modern dams is preceded by a careful analysis of
sub-surface conditions, in regard to both the rocks and the water. It is
necessary to know the supporting strength of the rocks in relation to
the weight of the dam; to know whether the rocks will allow leakage
around or beneath the dam; and to know whether there are any zones of
weakness in the rocks which will allow shearing of foundations under the
weight of the dam in combination with the pressure of the ponded water.
It is necessary to know whether the valley is a rock valley or whether
it is partially filled with rock débris; if the latter, how deep this
débris is, and its behavior under load and in a saturated condition.
Here again physiographic factors are of vital importance, both in
relation to the history of development of the valley, and to questions
of stream flow and reservoir storage.[65]
Construction of dams is only an item in the long list of engineering
activities related to surface waters. River and harbor improvements of a
vast range likewise involve geologic factors. Problems of wave action,
shore currents, shifting of shores, erosion, and sedimentation, which
are of great importance in such operations, have long occupied the
attention of the geologist. They belong especially in the branch of the
science known as physiography.
Geology in relation to underground water supplies is discussed in
Chapter V.
TUNNELS
The digging of tunnels for transportation purposes, for aqueducts, and
for sewage disposal requires careful analysis of geologic conditions in
regard to both the rocks and the underground water. Knowledge of these
conditions is necessary in planning the work, in inviting bids, and in
making bids. It is necessary during the progress of the work. Too often
in the past disastrous consequences, both physical and financial, have
resulted from lack of consideration of elemental geologic conditions.
The building of the great New York aqueducts and subways through highly
complex crystalline rocks has been under the closest geological advice
and supervision. The detailed study of the geology of Manhattan Island
through a long series of years has resulted in an understanding of the
rocks and their structures which has been of great practical use. In the
aqueduct construction the kinds of rock to be encountered in the
different sections, their water content, their hardness, their joints
and faults, were all platted and planned for, and actual excavation
proved the accuracy of the forecasts. An interesting phase of this work
was the tunneling under the Hudson at points where the pre-glacial rock
channel was buried to a depth of nearly a thousand feet by glacial and
river deposits,--this work requiring a close study of the physiographic
history of the river.
SLIDES
Slides of earth and rock materials, both of the creeping and sudden
types, have often been regarded as acts of Providence,--but studies of
the geologic factors have in many cases disclosed preventable causes. A
considerable geologic literature has sprung up with reference to rock
slides, which is of practical use in excavation work of many kinds.
The cause of such movements is gravity. The softer, unconsolidated rock
materials yield of course more readily than the harder ones, but even
strong rocks are often unable to withstand the pull of gravity. The
relative weakness of rock masses on a large scale was graphically shown
by Chamberlin and Salisbury,[66] in a calculation indicating that a mass
of average hard rock a mile thick, domed to the curvature of the earth,
can support a layer of only about ten feet of its own material. The
structural geologist, through his study of folds, faults, and rock
flowage, comes to regard rocks essentially as failing structures.
Disturbances of equilibrium, resulting in rock movements under gravity,
may be caused by local loading, either natural or artificial. Natural
loading may be due to unusual rainfall, or raising of water level, or
increased barometric pressure. Artificial loading may come from
construction of heavy buildings or dams. Movement may also result from
excavation, which takes away lateral support--and such excavation again
may be caused by natural processes of erosion or by artificial processes
involved in construction. Movement may be caused by mere change in the
moisture content of rocks, or by alterations of their mineral and
chemical character, affecting their resistance to gravity. In still
other cases, earthquakes are the initiating cause of movement.
In unconsolidated rocks, a frequent cause of movement is the presence of
wet and slippery clay layers. The identification and draining of these
clay layers may eliminate this cause. In certain sands, on the other
hand, water may actually act as a cement and tend to increase the
strength of the rock. Planes of weakness in the rock, such as bedding,
joints, and cleavage, are also likely to localize movement.
Earth materials, and even fairly hard rocks, may creep under gravity at
an astonishingly low angle. The angle from the horizontal at which loose
material will stand on a horizontal base without sliding is called the
angle of rest or repose. It is often between 30° and 35°, but there is
wide variation from this figure, depending on the shapes and sizes of
the particles and on other conditions. It has been suggested that even
the slight differences in elevation of continents and sea bottoms may,
during long geologic eras, have caused a creep of continental masses in
a seaward direction.
In problems relating to slides, the geologist is concerned in
determining the kinds of rocks, their space relations, their structures
and textures, their metamorphic changes, their water content and the
nature of the water movement, their strength, both under tension and
compression, and other factors.
In the digging of the Panama Canal, a geological staff was employed in
the study of the rock and earth formations to be met. However, had more
attention been paid to geologic questions in the planning stages, this
great undertaking, so thoroughly worked out from a purely engineering
standpoint, would have avoided certain mistakes due to lack of
understanding of the geological conditions. It is a curious fact that in
these early stages no strength tests of rocks were made, and that no
thorough detailed study was made of the geologic factors affecting
slides and their prevention. It was only after the slides had become
serious that the geological aspects of the subject were intensively
considered. The results of the geologic study, therefore, are useful
only for preventive measures for the future and for other undertakings.
One of the interesting features of this investigation was the discovery
that certain soft rock formations were rendered weaker rather than
stronger by the draining off of the water. It had been more or less
assumed that the water had acted as a lubricant rather than as a cement.
SUBSIDENCE
Not the least important application of geology to slides is in relation
to deep mining operations. While the mining geologist has been
principally engaged in exploration and development of ores, he is now
beginning to be called in to interpret the great earth movements caused
by the sinking of the ground over mining openings. For instance, the
long-wall method of coal mining has resulted in a slow progressive
subsidence of the overlying rock, affecting overlying mineral beds and
surface structures over great areas. Detailed studies have been made of
this movement, in order to ascertain its relation to the strength and
structure of the rocks, its relation to the nature of the excavation,
its speed of transmission, and the possible methods of prevention.
German scientists have perhaps gone further with this kind of study than
anyone else. In an elaborate investigation of subsidence over a coal
mine in Illinois,[67] unusually complete data were obtained as to the
nature, direction, and speed of the transmission of strains through
large rock masses, and as to their effect in producing secondary rock
structures.
RAILWAY BUILDING
In railway building, the planning and estimation of cuts and fills is
now receiving geologic consideration, in order to make sure that no
geologic condition has been overlooked which will affect costs, the
stability of the road, or the accurate formulation of contracts. The
location of best sources of supply for ballast is also a geologic
problem (see pp. 90-91).
The physiographic phases of geology also are finding important
applications to railroad building. The physiographer studies the surface
forms with a trained eye, which sees them not as lawless or
heterogeneous units but as parts of a topographic system, and he is able
to eliminate much unnecessary work in the location of trial routes.
Further study of some of the older railroads from this standpoint has
led to considerable improvements. Physiographic study has also been
applied to railway bridge construction, in the appraisal of the
difficulties in surmounting stream barriers. A still broader use of
physiography or geography, not popularly understood, is illustrated in
the case of certain transcontinental railroads, in the study of the
probable future development of the territory to be served--many features
of which can be predicted with some accuracy from a study of the rocks,
soils, topography, conditions of transportation, and natural conditions
favoring localization of cities. The location of new towns in some cases
has been based on this kind of preliminary study.
In locating an Alaskan railway close to the end of a momentarily
quiescent glacier, troubles were not long in appearing, due to the fact
that the glacier was really not as stable as it seemed to the layman. A
specialist on glaciers, knowing their behavior, their relations to
precipitation, their relations to earthquakes, the speed of their
movement, and the periodicity of their movement, was ultimately called
into consultation on the location of the railroad.
ROAD BUILDING
Road building in recent years has become a stupendous engineering
undertaking, which is requiring geologic aid to locate nearby sources of
supply for road materials. A considerable number of geologists are now
devoting their attention to this work. It relates not only to the
hard-rock geology but to the gravel and surface geology. Certain
northern states are using specialists in glacial geology to aid in
locating proper supplies of sand and gravel.
GEOLOGY IN ENGINEERING COURSES
Many engineering courses include elementary geologic studies, in
recognition of the close relationship between geology and engineering.
Men so trained, though not geologists, have been responsible for many
applications of geology to engineering. With the increasing size and
importance of operations, calling for more specialization, the
professional geologist is now being called in to a larger extent than
formerly. A logical trend also is the acquirement of more engineering
training on the part of the geologist, for the purpose of pursuing these
applications of his science.
FOOTNOTES:
[64] Excellent texts on this subject may be found in _Military Geology
and Topography_, Herbert E. Gregory, Editor, prepared and issued under
the auspices of Division of Geology and Geography, National Research
Council, Yale Univ. Press, New Haven, 1918, and _Engineering Geology_,
by H. Ries and T. L. Watson, Wiley and Sons, New York, 2d ed., 1915.
[65] Atwood, W. W., Relation of landslides and glacial deposits to
reservoir sites in the San Juan mountains, Colorado: _Bull. 685_, _U. S.
Geol. Survey_, 1918.
[66] Chamberlin, T. C., and Salisbury, R. D., _Geology_, vol. 1, 1904,
pp. 555-556.
[67] Schultz, Robert S., Jr., _Bull. Am. Inst. Mining and Metallurgical
Engrs._ In preparation.
CHAPTER XXI
THE TRAINING, OPPORTUNITIES, AND ETHICS OF THE ECONOMIC GEOLOGIST
Economic geology is now an established and well-recognized profession,
but there is yet nothing approaching a standardized course of study
leading to a degree in economic geology. There are as many different
kinds of training as there are institutions in which geology is taught.
Within an institution, also, it is seldom that any two persons take
exactly the same groups of geologic studies. This situation allows wide
latitude of training to meet ever changing requirements, but in other
respects it is not so desirable.
PURE VERSUS APPLIED SCIENCE
In no institution are all the applied branches of geology taught. There
is constant pressure for the introduction of more applied courses; this
seems to be the tendency of the times. The economic geologist, fresh
from vivid experiences in his special field, is often insistent that a
new course be introduced to cover his particular specialty. Any attempt,
however, to put into a college course a considerable fraction of the
applied phases of geology would mean the crowding out of more essential
basic studies. To yield wholly to such pressure would in fact soon
develop an impossible situation; for, on the basis of time alone, it
would be quite impossible to give courses on all of the applied subjects
in a training period of reasonable length.
On the other hand, the failure to introduce a fair proportion of applied
geology, on the ground that the function of the college is to teach pure
science and that in some way economic applications are non-scientific,
seems to the writer an equally objectionable procedure,--because it does
not take into account the unavoidable human relations of the science,
which vivify and give point and direction to scientific work. The
development of science in economic directions does not necessarily mean
incursion into less scientific or non-scientific fields. It is true
that many of the economic applications of geology are so new and so
constantly changing that they are not yet fully organized on a
scientific basis; but this fact is merely an indication of the lag of
science, and not of the absence of possibilities of developing science
in such directions. There is today a considerable tendency among
geologists of an academic type, whose lives have been spent in purely
scientific investigation and teaching, to assume that anything different
from the field of their activities is in some manner non-scientific, and
therefore less worthy. Many economic geologists have been made to feel
this criticism, even though seldom expressed openly. For the good of
geologic science, this tendency seems to the writer extremely
unfortunate. The young man entering the field of economic geology should
be made to understand that his is the highest scientific opportunity;
and that if parts of his field are not yet fully organized, the greater
is his own opportunity to participate in the constructive work to be
done.
Under war requirements many geologists were called upon to extend their
efforts to bordering fields of endeavor. In some quarters these
activities were regarded as non-scientific, and as subtracting from
efficiency in purely geological work,--and yet out of this combined
effort came a wider comprehension of new scientific fields, between the
established sciences and between sciences and human needs. It is
inevitable that in the future these fields, now imperfectly charted,
will be occupied and developed, perhaps not by the men who are already
well established in their particular fields of endeavor, but by coming
scientists. In this light, it was a privilege for geologists to
participate in the discovery and charting activities of the war.
Still another attempt to discriminate between scientific and
non-scientific phases of geologic effort has been the assumption by
certain scientific organizations with reference to standards of
admission,--that work done for practical purposes may be regarded as
scientific only if it leads to advancement of the science through the
publication of the results. There is by no means any general agreement
as to the validity of this distinction. On this basis, some of the most
effective scientific work which is translated directly into use for the
benefit of civilization is ruled out as science, because it is
expressed on a typewritten rather than on a printed page.
While applied phases of the geologist's work may be truly scientific in
the broader sense, it is undoubtedly easy in this field to drift into
empirical methods, and to emphasize facility and skill at the expense of
original scientific thought. The practice of geology then becomes an art
rather than a science. This remark is pertinent also to much of
non-applied geologic work in recent years. A considerable proportion of
this empirical facility is desirable and necessary in the routine
collection of data and in their description; but where, as is often the
case, the geologist's absorption in such work minimizes the use of his
constructive faculties, it does not aid greatly in the advancement of
science.
Geology is by no means the only science in which there has been
controversy as to the relative merits of the so-called pure and applied
phases; but as one of the youngest sciences, which heretofore has been
pursued mainly from the standpoint of "pure science," it is now, perhaps
more than any other science, in the transition stage to a wider
viewpoint. In the past there was doubt about the extension of chemistry
toward the fields of physics and engineering, and of physics toward the
fields of chemistry and engineering, and of both physics and chemistry
toward purely economic applications; but out of these fields have grown
the great sciences of physical chemistry, chemical engineering, and
others,--and few would be rash enough to attempt to draw a line between
the pure and applied science, or between the scientific and
non-scientific phases of this work. This general tendency means a
broadening of science and not its deterioration.
COURSE OF STUDY SUGGESTED
There are almost as many opinions on desirable training for economic
geology as there are geologists, and the writer's view cannot be taken
as representing any widely accepted standard. On the basis of his own
experience, however, both in teaching and in field practice, he would
lay emphasis on the fundamental branches both of geology and of the
allied sciences,--general geology, stratigraphy, paleontology,
physiography, sedimentation, mineralogy, petrology, structural and
metamorphic geology, physics, chemistry, mathematics, and biology.
After these are covered, as much attention should be given to economic
applications as time permits. The time allowance for training, at a
maximum, is not sufficient to cover both pure and applied science.
Subsequent experience will supply the deficiencies in applied knowledge,
but will not make up for lack of study of basic principles.
It is safe advice to a student wishing to prepare for economic geology
that there is no royal road to success; that his best chance lies in the
effort to make himself a scientist, even though he cover only a narrow
field; that if he is successful in this, opportunities for economic
applications will almost inevitably follow. To devote attention from the
start merely to practical and commercial features, rather than to
scientific principles, brings the student at once into competition with
mining engineers, business men, accountants, and others, who are often
able to handle the purely empirical features of an economic or practical
kind better than the geologist. In the long run the economic geologist
succeeds because he knows the fundamentals of his science, and not
because he has mere facility in the empirical economic phases of his
work. Of course there are exceptions to this statement,--there are men
with a highly developed business sense who are successful in spite of
inadequate scientific training, but such success should be regarded as a
business and not a professional success.
Geology is sometimes described as the application of other sciences to
the earth. This statement might be made even broader, and geology
described as the application of all knowledge to the earth. In the
writer's experience, the best results on the whole have been obtained
from students who, before entering geology, have had a broad general
education or have followed intensively some other line of study. Whether
this study has been the ancient languages, law, engineering, economics,
or other sciences, the results have usually been good if the early
training has been sound. To start in geology without some such
background, and without the resulting power of a well-trained mind, is
to start with a handicap in the long race to the highest professional
success. It follows, then, that intensive study of geology should in
most cases not begin until late in the undergraduate course, and
preferably not until the graduate years. Two or three years of graduate
work may then suffice to launch the geologist on his career, but so
great is the field, and so rapid the growth of knowledge within it, that
there is no termination to his study. It is not enough to settle back
comfortably on empirical practice based solely on previously acquired
knowledge. Each problem develops new scientific aspects. It is this ever
renewing interest which is one of the great charms of the science.
However, whether the student has a general training in geology, a
specialized knowledge of certain branches, or takes it up incidentally
in connection with engineering and other sciences, he will find
opportunities for economic applications. The frequent success of the
mining engineer in the geological phases of his work is an indication
that even a comparatively small amount of geological knowledge is
useful.
The writer is inclined to emphasize also the desirability of what might
be called the quantitative approach to the subject,--that is, of
training in mathematics and laboratory practice, which gives the student
facility in treating geologic problems concretely and in quantitative
terms. Geology is passing from the descriptive and qualitative stages to
a more precise basis. For this reason the combination of geology with
engineering often proves a desirable one. It is not uncommon for the
student trained solely in the humanities and other non-quantitative
subjects to have difficulty in acquiring habits of mind which lead to
sufficient precision in the application of his science. He may have a
good grasp of general principles and be able to express himself well,
but he is handicapped in securing definite results. This does not
necessarily mean that a large amount of time should be given to study of
quantitative methods; exact habit of mind is more important in the early
stages than expert facility with methods.
The teacher of economic geology finds his data so voluminous that it is
difficult to present all the essential facts and yet leave sufficient
time for discussion of general principles or for drill in their
constructive application. It is difficult to lay down any rule as a
guide to the proper division of effort; but from the writer's point of
view, it is a mistake to attempt to crowd into a course too many facts.
At best they cannot all be given; and in the attempt to do so, the
student is brought into a passive and receptive attitude, requiring
maximum use of his memory and minimum use of his reasoning power.
Presentation of a few fundamental facts, combined with vigorous
discussion tending to develop the student's ability to use these facts,
and particularly tending to develop a constructive habit of
investigation, seems to be the most profitable use of time during the
course of training. The acquirement of facts and details will come fast
enough in actual practice.
The variety, amount, and complexity of the data available in geology
tend in themselves toward generalizations in teaching--toward the
deductive rather than the inductive method. A certain amount of
generalization is desirable, but its over-emphasis develops bad habits
of mind on the part of the student, and requires radical readjustment of
his ideas in subsequent field investigations. To retain a proper
emphasis on inductive methods, it is necessary to limit the amount of
data presented. Good results have been obtained by using the "case
system," now common in the teaching of law--that is, by starting with a
specific fact or situation as a basis for developing principles.
Another advantage in the restriction of data is the opportunity thus
afforded for spending more time in the study of original reports rather
than of the short textbook summaries. The student thus learns where the
best primary sources of information are, how to find them, and how to
extract essentials from them.
FIELD WORK
Field work is an essential part of any course of geologic training. Not
only should it be taken at every opportunity during the regular school
year, but no summer should be allowed to pass without geologic practice
in the field. Opportunities for such work are offered in the summer
field courses given by various institutions. In recent years it has
usually been possible, also, for the student with elementary training to
take part in summer geological survey work for state, national, or
private organizations. In fact, after two or three years of geologic
training, it is comparatively easy for the student to earn at such
intervals during the year a fair fraction of his year's expenses.
The ideal arrangement, from the writer's viewpoint, would be about an
equal division of time between indoor and outdoor study. The
alternation from one to the other supplies a much needed corrective to
clear thinking. It is impossible to bring all the subject materials into
the classroom and laboratory; such study must inevitably be more or less
deductive and generalized. If the student at frequent intervals is not
able to acquire and renew a mental picture of field conditions, there is
likely to be a faulty perspective even in regard to principles, and a
considerable gap between the theoretical and applied phases of his
knowledge. It may be possible in the classroom, for instance, to discuss
faults in great detail with the aid of maps, diagrams, and pictures; and
yet it is extremely difficult to get a real three-dimensional conception
of the problems without actually standing on the ground.
SPECIALIZATION IN STUDIES
With the increasing size and efficiency of human operations has come an
inevitable tendency to specialization. Where, in the past, the necessary
geologic work might be passably done by the mining engineer, the local
superintendent or operator, it is now being intrusted to specialists.
Even within the more strictly engineering phases of the mining
engineer's work, there is the same tendency toward specialization; his
work is being divided up among the electrical engineers, the mechanical
engineers, the hydraulic engineers, and others. The opportunities for
geologic work, therefore, are distinctly in the direction of
specialization. The student in determining the field he shall enter
needs to take this fact into account and to prepare accordingly, but not
at the sacrifice of the broad basal training. Only a small part of the
specialization can be accomplished in college. The remainder will come
with experience.
In the future there is likely to be increasing specialization among the
different educational institutions in the phases of applied geology
which are taught. Geographic location has a good deal to do with this
tendency. Where an institution is located near a coal or oil field, it
is likely, as a matter of course, to specialize to some extent in the
application of geology to these resources. Or, the specialization may
arise from the fact that the teachers have had special training in
certain phases of applied geology, and such training naturally and
properly determines the emphasis to be placed. Courses in engineering
geology are finding a natural development in the leading engineering
colleges.
In view of the fact that it is impossible for any one institution to
cover all phases of applied geology, because of lack of time, and in
view of the fact that even if this were attempted the results would be
very unequal, because of the varied experience of teachers or because of
geographic location, it would seem wise definitely to recognize these
limitations and for each institution to play up the work it can do best.
With freedom of migration among universities, a student by moving from
place to place can thus secure any combination of specialized courses
which best fits his requirements.
A DEGREE OF ECONOMIC GEOLOGY
There has been some agitation in recent years for standardization of
courses in economic geology, and for the granting of a special degree in
evidence of the completion of such a course. The principal argument for
this procedure is that it would tend to insure a better average of
training and would draw a line between worthy geologists and a host of
ill-trained pseudo-geologists. The earth is so accessible, and its use
so varied, that geology is handicapped perhaps more than any other
science by persons who really have no valid claim to a scientific title.
The writer doubts whether a special degree in economic geology would go
far toward improving this situation. Even if the courses were the same
in different institutions, the manner of treatment and the ability of
the teachers would be so varied that in the future, as in the past,
anyone inquiring into the real standing of a geologist would be likely
to consider his individual training rather than the degree attached to
his name. There would be no guarantee that institutions not qualified to
give the degree might not do so. However, the principal objection in the
writer's mind to a degree of economic geology is the assumption that it
is possible for anybody, in the present stage of knowledge, to formulate
a standardized course adequate or best to meet the varied requirements.
Considering the breadth and the variety of the field, any such attempt
at standardization would have to be highly arbitrary. Once established,
it would be a hindrance to the natural development of new courses to
meet the ever changing requirements. When, if ever, the science of
economic geology becomes fully organized, a standardized course may be
possible. In the present stage of the science, more elasticity is
required than seems to be possible in any of the courses proposed.
One of the purposes of the introduction of a degree of economic geology,
to separate the sheep from the goats, may be accomplished in another
way,--namely, by the establishment and maintenance of high standards of
admission and high aims on the part of the various professional
societies having to do with geology and mining. If this is done,
membership in such societies may be regarded as evidence of sound
training and achievement. To some extent this procedure may relieve the
pressure on universities for uniformity of courses and degrees, leaving
them free to develop in such manner as seems best. Scientific
organizations, overlooking the entire field, are in a position to take
into account the greatest variety of factors of training and experience
in selecting their members. Failure of any university course to make men
eligible for such recognition will obviously react on the course in a
desirable way.
THE OPPORTUNITIES OF THE ECONOMIC GEOLOGIST
It has been the aim in this book to present a general view of the fields
of activity of the economic geologist; and the list of chapter headings
in itself summarizes the variety of his opportunities. The rapidly
increasing use of earth materials promises far greater calls for
geologic aid in the future than in the past. The profession is in its
infancy.
Opportunities for employment are ordinarily found in three main
directions--in educational institutions, in the federal and state
geological surveys, and in private organizations. Connection with the
United States Geological Survey excludes participation in private work,
and in recent years even in teaching. In the state surveys there is
ordinarily more latitude in this regard. In the educational
institutions, it is rather the common procedure for the instructor to
secure his field practice and experience through private agencies, or
through part time connection with state surveys,--an arrangement with
advantages to all concerned. The educational institution secures the
benefit of the field experience which it cannot afford to provide, and
is enabled to hold geologists at salaries far below their earning
capacity. The geologist gains by the opportunity to alternate between
office and field study, and to correct his perspective by the constant
checking of theory with field conditions. The combination tends to keep
the clearly scientific and the applied phases in a proper relative
proportion; it minimizes the danger of drifting into purely empirical
field methods on the one hand, and of losing touch with actualities on
the other. Geologists devoting their attention solely to field work
often complain that they do not have time to digest and correlate their
results, nor to keep up with what others are doing. On the other hand,
geologists without current field practice are likely to develop too
strongly along subjective, deductive, and theoretical lines. The teacher
gains in freshness and force in the presentation of his subject in the
classroom, and the very effort necessary for presentation requires
better analysis and coördination of his field observations. The private
or state organization gains in this combination by drawing on the
general and varied knowledge which has necessarily been accumulated for
teaching and investigative purposes.
Temperament and circumstances will determine in which of these
directions the student will turn. However, in view of the present
natural tendency to be attracted by the large financial rewards in the
commercial field, it may not be out of place to emphasize the fact that
these rewards are perhaps more likely to be gained through perfected
training and experience in state and national surveys and in educational
institutions, than through early concentration in the commercial field.
In any case, the financial side will take care of itself when sufficient
knowledge and proficiency have been attained in any branch of the
science.
The world is the geologist's laboratory; it is the only limit to his
activities. The frontiers are near at hand, both physically and
intellectually. There are few fields so attractive from the scientific
standpoint. There are few in which the successful prosecution of the
science can be of so much direct benefit to civilization and can yield
such large financial rewards. If, in addition, the opportunities for
travel and adventure are taken into account, what profession promises a
more interesting and useful life?
So far we have discussed geology as a profession. It has proved its
value also as a training for administrative and other public careers.
The profession contributes its full share of men to these activities.
The practice of geology deals with a wide variety of factors, and
requires the constant exercise of judgment in balancing, correlating,
and integrating these factors in order to reach sound conclusions. This
objective treatment of complex situations is valuable training for the
handling of human affairs.
ETHICS OF THE ECONOMIC GEOLOGIST
Ethical questions involved in the practice of economic geology have
called out much discussion, and, in some cases, marked differences of
opinion among men equally desirous of doing the right thing. In the
plain choice between right and wrong, there is of course no difference
of opinion. Unfortunately in many of the questions which arise the
alternatives are not so clearly labeled.
The lure of discovery and quick returns always has, and doubtless always
will, draw into the field large numbers of persons without sound ethical
anchorage or standards. Fortunately, these are not the persons in
control of the mineral industries; they are mere incidents in the great
and stable business built up by legitimate demands for raw materials.
The view is sometimes expressed that the geologist should hold himself
aloof from the business or applied phases of his profession, because of
the danger of being tainted with commercialism. This argument would
apply to the engineer as well as to the geologist. To carry such a
procedure through to its logical conclusion would mean substantially the
withdrawal of scientific aid from industry,--which, to the writer, is
hardly a debatable question. Circumstances are trending inevitably to
the larger use of geologic science in the commercial field. The problems
of ethics cannot be solved by staying out. The economic geologist is
rather called upon to do his part in raising the standards of ethics in
that part of the field in which he has influence. This he can do by
careful appraisal of all the conditions relating to a problem which he
is asked to take up, and by refusing to act where questionable ethical
standards are apparent or suspected. He must understand fully the
purposes for which his report is to be used; merely as a matter of
professional self-interest, there is no other course open to him. In a
field in which there is so much danger from loose ethical conceptions,
the premium on rigid honesty and nice appreciation of professional
ethics is proportionately higher. The extreme care taken in this matter
by acknowledged leaders in the profession of economic geology should be
carefully considered by the young man entering the profession. There is
a reason.
In other chapters reference is made to certain special ethical
questions, such as the use of geology in mining litigation (pp.
349-355), and the necessity of the geologist's recognizing his own
limitations (pp. 92-94), but no attempt has been made to cover the
variety of such questions that may come up. It is safe to assume that no
special ethical code can be made sufficiently comprehensive, detailed,
and elastic to cover all the contingencies which are likely to be met in
the practice of economic geology; nor is it likely that any such code,
if attempted, would be any improvement on the spirit of the Golden Rule.
Simple decency and common sense in their broader implications are
essential to the practice of the profession.
INDEX
Abrasives, 267-270, 397
Abyssinia, potash, 112
Adams, Frank D., 367
Adirondacks, New York, graphite, 282
iron ores, 160, 162, 163, 171
phosphate from magnetic ores, 105-106
use of magnetic surveys in tracing iron rocks, 317
Ad valorem method of valuation of mineral deposits, 331-335
Africa, bauxite, 242
coal, 116
cobalt, 255
copper, 197-198, 205
tin, 260
_See also_ South Africa; North Africa; East Africa; West Africa.
Alabama, bauxite, 243, 245
graphite, 281
iron, 52-53, 160, 162, 163, 166-167
Alaska, antimony, 248
copper, 36, 41, 47, 49, 199, 200-201
gold, 222, 224, 229
silver, 234
tin, 261, 262
Algeria, antimony, 247, 248
gypsum, 283
iron, 156, 160, 161, 194
petroleum, 128
phosphates, 104, 105, 106
_See also_ North Africa.
Almaden, Spain, mercury ores, 256-257, 259
Alsace, potash, 111-113
Alsace-Lorraine, coal and iron of, under Peace Treaty, 401-402
Aluminum Company of America, 243
Aluminum ores, 241-246, 397
_See also_ Bauxite.
Alunite, 39, 41-42, 112, 114, 230
Anaconda, Montana, arsenic production, 250
Anaconda Copper Mining Company, manufacture of phosphate, 105
use of geology in development and exploration, 326-327
Anamorphism, defined, 27, 57
Anamorphism of mineral deposits, 26, 57-58
Anhydrite, occurrence in gypsum deposits, 284-285
Anticlines, occurrence of oil in, 141-142, 147-148
Antimonial lead, 246
Antimony ores, 246-249, 398
Apex law, 349-350, 353
Aplites, 35
Appalachians, barite, 274
bauxite, 245
graphite, 282-283
petroleum, 132, 135
pitchblende, 266
pyrite, 108
tin, 262
_See also_ under individual states.
Argentina, borax, 275
mica, 286
petroleum, 128
tungsten, 183
Arizona, asbestos, 271, 272
copper, 33, 38, 41, 47, 48, 198-199, 203, 204-205, 208, 314, 316
gold, 222
manganese, 175
molybdenum, 186,187
silver, 234
tungsten, 183
turquoise, 293
Arkansas, bauxite, 96, 243, 244-245, 246
diamonds, 292
fuller's earth, 279
hones, oilstones and whetstones, 269
phosphates, 105
zinc, 215
Arnold, Ralph, 134, 136, 149-150
Arsenic ores, 249-251, 397
Artesian wells, 73
Asbestos, 270-272, 398
Asphalt and bitumen, 56, 151-153, 397
Atolia, California, tungsten ores, 185
Atwood, W. W., 414
Australasia, cement, 87
coal, 116
gold, 222
Australia, antimony, 247
arsenic, 250
asbestos, 271, 272
bauxite, 242
bismuth, 252
coal, 115
copper, 197-198
gold, 41, 222, 224
iron, 154, 164, 165
lead, 210-211, 212
molybdenum, 186
phosphates, 105
silver, 232
tin, 260
tungsten, 183
zinc, 214-215, 216
Australia, laws relating to ownership of mineral resources, 343, 345
Austria, cement, 87
graphite, 280
mercury, 256, 257
molybdenum, 186
talc, 299
uranium and radium, 264
zinc, 214
Austria-Hungary, barite, 272
coal, 115, 116
iron, 160, 161
magnesite, 191-193
manganese, 174
silver, 232
_See also_ Hungary.
Austria-Hungary, commercial and political control of various
minerals, 64
Ball clay, 85, 398
"Bar" theory of formation of thick salt beds, 297
Baraboo, Wisconsin, quartzites of, 82
Barite, 272-274, 397
Basalt, 17, 19, 82, 90
Bauxite, 9, 50, 96, 241-246, 397
Bavaria, graphite, 280
Bawdwin Mines, Burma, lead and zinc, 209, 214
Beaumont Field, Texas, occurrence of oil, 148
Belgian Congo, cobalt, 255
copper, 205
Belgium, barite, 272
cement, 87
coal, 115-117, 127, 401
flint linings, 269
iron, 160-161
lead, 54-55, 210
millstones and buhrstones, 269
phosphates, 104
zinc, 54-55, 214
Belgium, commercial and political control of various minerals, 64, 280
Belle Isle, Newfoundland, iron ores, 52-53, 160, 166
Bergholm, Carl, 319
Bergstrom, Gunnar, 319
Bessemer processes of steel making, 158, 161
Bilbao, Spain; iron ores, 160, 170
Billingsley, Paul, and Grimes, J. A., 44
Bingham, Utah, copper and lead ores, 37, 42, 47, 199, 203, 204, 207,
208, 212, 314
Birmingham, Alabama, iron ores, 160, 162, 163, 166-167
_See also_ Clinton iron ores.
Bisbee, Arizona, copper ores, 47, 198, 204, 314, 316
Bismuth ores, 252-253, 397
Bitumen and asphalt, 56, 151-153, 397
Black Hills, South Dakota, gold ores, 228, 229
tin ores, 262
"Blue ground," occurrence of diamonds in, 291
"Bluestone," 84
Bohemia, uranium and radium ores, 265
Boise Basin, Idaho, monazite deposits, 289
Boleo, Lower California, copper ores, 201
Bolivia, antimony, 247
bismuth, 252, 253
borax, 275
copper, 206
nitrates, 103
petroleum, 128
silver, 232
tin, 261, 262-263
tungsten, 183, 184
Bolivia, commercial and political control of various minerals, 64
Bonne Terre limestone, Missouri, zinc ores, 217
Boone formation, Missouri, zinc ores, 217
Borax, 274-277, 397
Borax Lake, California, borax deposits, 276
Borneo, diamond dust, 268
platinum, 238
Bort, 267, 268, 398
Boulder batholith, Montana, ore-deposits of, 44
Boulder County, Colorado, tungsten ores, 184
Braden copper ores, Chile, 199
Brazil, chromite, 179
coal, 116
diamonds and diamond dust, 268, 292
graphite, 280
iron, 52-53, 162, 165, 167, 313
manganese, 174-175, 176
mica, 286
monazite, 288, 289
oil shales, 151
zirconium, 189-190
Brazil, commercial and political control of various minerals, 64
Briey district, France, iron ores, 161, 163
vanadium, 187
Brinton, Virginia, arsenic ores, 251
British Coal Commission, 367
British Columbia, laws relating to mineral resources, 344
British Empire. _See_ Great Britain.
British Guiana, bauxite, 242, 243
British South Africa, coal, 116
Broken Hill, New South Wales, lead and zinc ores, 209, 212
Bromine, 277-278, 397
Brooks, Alfred H., 404, 408
Brooks, Alfred H., and LaCroix, Morris F., 404
Buhrstones, 269
Building stone, 80-84, 88-90, 397
Bureau of Mines, 403, 406
Burma, lead, 209, 210, 212
rubies, 289, 292
silver, 233
tungsten, 183, 185
zinc, 214, 216
Burrows, J. S., 367
Butler, B. S., Loughlin, G. F., and Heikes, V. C., 44, 55, 230
Butte, Montana, arsenic in copper ores, 251
copper ores, 40, 47, 49, 198-199, 201-203, 207, 208
manganese ores, 177, 314
silver ores, 234, 314
use of placers in locating ores, 316
zinc ores, 215-216
zonal arrangement of minerals, 42, 44
Cadmium ores, 253-254, 397
California, antimony, 248
asbestos, 271
asphalt and bitumen, 152
basalt, 82
borax, 275, 276-277
chromite, 179
copper, 199, 204
diatomaceous earth, 269
fuller's earth, 279
gold, 222, 224, 227, 229, 308, 316, 342
granite, 82
graphite, 281
grinding pebbles, 268
magnesite, 191-193
manganese, 175
mercury, 40, 256, 257, 259
natural gas, 151
petroleum, 132, 133, 135, 137
potash, 112, 113-114
pyrite, 108
serpentine, 83
silver, 234, 308
tourmaline, 293
tungsten, 183
Campbell, J. Morrow, 185
Campbell, M. R., 121, 122, 366
Campbell, M. R., and Parker, E. W., 367, 370-371
Canada, arsenic, 250
asbestos, 270-271, 272
cement, 87
chromite, 179
coal, 115, 116
cobalt, 255
copper, 197-198
corundum, 268, 270
feldspar, 86
fluorspar, 193, 194
gold, 222
graphite, 280-281
grindstones and pulpstones, 269
gypsum, 283-284
iron, 52-53, 155, 156, 160, 165
magnesite, 191-193
mica, 286, 287
molybdenum, 186
natural gas, 151
nickel, 180-182
petroleum, 128
phosphates, 105, 106
platinum, 238
pyrite, 107-108
salt, 294
silver, 232, 234-235
talc, 299, 300
titanium, 190
zinc, 214, 215
Canada, laws relating to ownership to mineral resources, 343
use of magnetic surveys in tracing iron rocks, 317
Cananea, Sonora, Mexico, copper ores, 203
Cannel coal, 125
Cape Colony, South Africa, asbestos, 272
Capillarity, effect on ground-water level, 70
effect on petroleum migration, 142-143
Capital value of mineral resources, 64, 328
"Capping," of copper ores, 47
Carbonado, 268
Carey Act, classification of public lands under, 310
Carmel, New York, arsenic ores, 251
Casing-head gasoline, 139, 151
Caucasus region, Russia, manganese ores, 174, 176
Cement, 86-88, 397
Cementation, mineral products resulting from, 24
Cementing materials, source of, 25
Central America, cement, 87, 88
silver, 232
_See also_ Costa Rica, Guatemala, Panama.
Central Powers. _See_ Germany, Austria-Hungary.
Cerium ores, _See_ Monazite.
Ceylon, graphite, 280-283 mica, 286
Chalk, 83, 398
Chamberlin, T. C., 217
Chamberlin, T. C., and Salisbury, R. D., 415
Chance, H. M., 367, 368
Chert, use for abrasives, 267, 268, 270
Chile, borax, 275, 276
bromine, 277
coal, 116
copper, 197-199, 203
iron, 155, 161, 162, 164, 171
manganese, 176
nitrates, 100, 101-104
phosphates, 105, 106
potash, 112
silver, 232
sulphur, 109-110
Chile, commercial and political control of various minerals, 64, 261
China, antimony, 247-248, 249
arsenic, 250, 251
bismuth, 252
coal, 115, 116, 127, 154
iron, 154, 160, 164, 165, 171
petroleum, 128
salt, 294
silver, 232
tin, 260
tungsten, 183, 184
China, commercial and political control of various minerals, 64
"Chloriding" for silver ores, 314
Chrome (or chromite) ores, 178-180, 307, 365-366, 398
Clarke, F. W., 13, 17, 18
Classification of mineral deposits, 27-59
of mineral lands, 309-311
of mineral materials, adjustment of scientific to commercial names,
356
Clays, 18, 85, 91-92, 398
Cle Elum, Washington, iron ores, 58
Cleavage, 26
Cleveland district, England, iron ores, 161
Clifton-Morenci district, Arizona, copper ores, 38, 198
Climate, as a factor in exploration, 315
effect of in formation of bauxites, 246
Clinton iron ores, 9, 52-53, 163, 166-167, 218, 313, 317
Coal, conservation of, 365, 366-382
European international situation, 116-117, 386, 387, 393, 400-403
general economic and geologic features, 56, 115-127, 309, 397
reserves, 116, 360-361, 366-367
Cobalt district, Ontario, arsenic, 251
cobalt, 255
silver ores, 232, 234-235, 308, 316
use of coefficient to estimate future output, 322
Cobalt ores, 254-255, 398
Coeur d'Alene district, Idaho, lead-silver ores, 39, 45, 211, 212-213,
216, 234
Coke, 118-119
Colloids, content of in clays, 92
Colombia, coal, 116
emeralds, 289, 293
gold, 222
platinum, 238
Colombia, commercial and political control of various minerals, 64
"Colorado," 313
Colorado, arsenic, 250
asphalt and bitumen, 152
bismuth, 253
coal, 117
fluorspar, 194
gold, 222, 230
graphite, 281
lead, 211, 212
molybdenum, 186
oil shales, 150
petroleum, 133
silver, 234
tungsten, 183, 184
turquoise, 293
uranium and radium, 264-265, 266
vanadium, 187-188
zinc, 216, 219-220
Commercial and political control of mineral resources, 65, 387, 388
_See also_ under individual resources.
Common rocks, as mineral resources, 80-94
Comstock Lode, Nevada, silver ores, 235-236, 308
Congo. See Belgian Congo
Connecticut, basalt, 82
diatomaceous earth, 269
tourmaline, 293
Conover, Julian D., 12
Conservation, 359-382, 393-395
application of economic geology to, 1-2
of coal, 366-382
of common rocks, 81
of human energy, 362
international aspects, 362-363, 375, 376-377, 393-395
of petroleum, 137-139
Conservation Commission of Canada, 367
Contact metamorphism, 20, 24, 25-27, 36-37
_See also_ Igneous after-effects.
Contracts, classification of earth materials in, 356-357
Copper ores, 9, 36-50, 51-52, 55, 197, 209, 307, 308-309, 313-314, 318,
396
Cornwall, England, tin ores, 42, 260, 262, 263
uranium and radium ores, 264
Corocoro, Bolivia, copper ores, 206
Corundum, 267-268, 270, 398
Costa Rica, manganese, 176
"Cracking" processes for refining petroleum, 137, 139
Cripple Creek district, Colorado, gold ores, 230
Cuba, chromite, 179
copper, 197
iron, 8-9, 50, 58, 96, 155, 160, 163, 171-173, 313, 349
manganese, 175
nickel, 181
petroleum, 128
Cuyuna Range, Minnesota, manganese ores, 175, 177
Cycle, erosion or topographic, 6-7
Cyclic nature of ore concentration, 7-8, 47-48, 56, 169, 201, 205, 208,
325
Cyprus, asbestos, 271, 272
Dams, geologic problems involved in construction, 414
Davis, W. M., 408
Death Valley, California, borax deposits, 276
Degree of economic geology, 427-428
Denmark, cement, 87
chalk, 83
grinding pebbles, 268
Depletion of mineral deposits, as factor in valuation and taxation,
331, 337, 339
Depth as a factor in mineral deposition, 43, 49, 58-59
Diamond dust, 267, 268, 398
Diamonds, 289-292, 316, 317
Diatomaceous earth, 267, 269, 398
Diorite, 82
Dolomite, 23, 192
Domes, occurrence of oil in. _See_ Anticlines.
Domes, salt and sulphur, Gulf Coast, 110, 298
Drilling, exploration of mineral deposits by, 320-321
Drilling records, public registration of, 305-306
Ducktown, Tennessee, copper ores, 204
Dutch East Indies, natural gas, 151
petroleum, 128, 129
tin, 260
use of coefficient to estimate tin reserves, 322
Dutch Guiana, bauxite, 243
Dutch West Indies, phosphates, 105, 106
Dynamic metamorphism, 25-26
East Africa, mica, 286
East Indies. See Dutch East Indies.
Eckel, E. C., 404
Economic Liaison Committee, 406
Egypt, petroleum, 128
phosphates, 104
Eiserner Hut, 313
Electrical conductivity, use in exploration of mineral deposits, 319
Ely, Nevada, copper ores, 41, 203
Emeralds, 289, 291, 293
Emery, 267-268, 270, 397, 398
Emmons, W. H., 43
Empire, Colorado, molybdenum ores, 186
Energy resources, 115-153
accelerating production of, 64, 130-131, 361, 366-367
Engineering, application of economic geology to, 2, 413-419
England. _See_ Great Britain
Enrichment, secondary, 7-8, 25, 46-50.
_See also_ under Copper ores, silver ores, etc.
Epigenetic ore deposits, use of term, 32, 36
"Equated Income" method of taxation, 335-336
Erosion, relation to oxide zones, 47-48
Erosion cycle, description of, 6-7
Ethics, questions of, 430-431
Europe, coal and iron situation under terms of Peace Treaty, 400-403
Expert witnesses, use of geologists as, 349-355, 357-358
Exploitation of mineral deposits, functions of geologist, 326-327
Exploration of mineral deposits, 301-327
effect of ownership laws on, 347-349
effect of taxation on, 339-341
quantitative aspects of, 321-322, 324-326
relation to international conditions, 395-396
Extralateral rights, litigation affecting, 349-355
Extrusive rocks, formation of, 19
Federated Malay States. _See_ Malay States.
Feldspar, 16, 86, 268-269, 397
Ferro-alloy minerals, 156-158, 173-196, 307, 362-363, 365-366, 393-394,
397-398
Ferroboron, 275
Ferrocerium, 288
Ferrochrome, 178
Ferromanganese, 173-174
Ferromolybdenum, 186
Ferrosilicon, 195
Ferrotitanium, 190
Ferrotungsten, 182-183
Ferrovanadium, 187
Ferrozirconium, 189
Ferruginous chert, 167
Fertilizer minerals, 99-114
Field work for students of economic geology, 425-426
Flint linings for tube mills, 269
Florida, fuller's earth, 279
phosphates, 105, 107
titanium, 190, 191
zirconium, 189
Flowage, rock, 25, 26
Fluorspar, 193-194, 397
Foothill district, California, copper ores, 204
Formosa, petroleum, 128
Foundations, application of geology to, 413
France, antimony, 247, 249
arsenic, 250-251
asphalt and bitumen, 152
barite, 272
bauxite, 242, 245
cement, 87
chalk, 83
coal, 115-117, 127
coal and iron situation under Peace Treaty, 400-403
fluorspar, 194
grinding pebbles, 268
gypsum, 283
iron, 154, 160-162, 163, 166-167, 402-403
manganese, 176
millstones and buhrstones, 269
molding sand, 84
oil shales, 150
phosphates, 104, 105
potash, 111-113
salt, 294
talc, 299
vanadium, 187
zinc, 214
France, control of various minerals in other countries, 64, 104-105,
178, 180, 210, 215, 222, 238, 247, 261, 280
laws relating to ownership of mineral resources, 343
relative position in regard to supplies of minerals, 399
Franklin Furnace, New Jersey, zinc ores, 215-216, 220
"Freestone," 84
French Guiana, bauxite, 242
Fuel ratio of coal, defined, 120
Fuller's earth, 278-279, 397
Gabbro, 19, 82
Gale, Hoyt S., 111
Galena dolomite, Wisconsin, zinc ores, 217
Galicia, petroleum, 128, 129
potash, 112
Ganister, 84, 91, 195
Garnet, 267, 268, 270, 398
Gas, natural, 57, 151
Georgia, asbestos, 271, 272
barite, 273
bauxite, 243, 245
corundum, 270
fuller's earth, 279
marble, 83
Georgia granite, volume change in weathering of, 21
Germany, arsenic, 250-251
barite, 272-273
bismuth, 252
borax, 275, 277
bromine, 277, 278
cadmium, 253, 254
cement, 87
coal, 115-117, 127, 400-403
copper, 9, 52, 197-198, 206
fluorspar, 194
gypsum, 283
iron, 154, 160-162, 402-403
lead, 54-55, 210-211
lignites, 379, 402
millstones and buhrstones, 269
nitrates, manufactured, 101-102
petroleum, 128
potash, 111-112
salt, 294, 297
silver, 232
tripoli and rottenstone, 269
uranium and radium, 264
zinc, 54-55, 214-215, 216
zirconium, 189
Germany, control of various minerals in other countries, 64, 174, 183,
189, 198, 211, 215, 222, 232, 257, 261, 271, 288, 387
participation of government in mineral trade, 388
relative position in regard to supplies of minerals, 399
Geysers, 72
Gilbert, Chester G., 123
Gilbert, Chester G., and Pogue, Joseph E., 119, 134, 138
Gilpin County, Colorado, uranium ores, 266
Glacial geology, application to railroad building, 418
application to road materials, 91, 418
Glacial soils, 95
Globe, Arizona, copper ores, 198
Gneissic structure, 26
Gogebic district, Michigan, iron ores, 312, 318, 325-326
Gold, monetary reserves, 223
Gold Coast, West Africa, manganese, 176
Gold ores, 36-50, 51, 221-230, 308-309, 313-314, 397
Goldfield, Nevada, alunite, 41-42, 114
bismuth, 253
gold-silver ores, 36, 39, 230, 308
Gossan, 47, 109, 173, 313
Government ownership and control. _See_ Nationalization.
Governments, participation in mineral ownership and international
trade, 388-390
Granite, 17, 19, 82, 90
Graphite, 279-283, 398
Graphite Association, Southern, 405
Gravel, sand and, 84-85
Gray, F. W., 368
Great Basin, Nevada, covering of mineral deposits by lavas, 311-312
gold-silver ores, occurrence in a metallogenic province, 308
tungsten ores, 185
Great Britain, arsenic, 250
barite, 272
cadmium, 253
cement, 78
chalk, 83
clay, 85
coal, 115-117, 126, 127
fluorspar, 193-194
fuller's earth, 278-279
grindstones and pulpstones, 269
gypsum, 283
iron, 154, 160-161, 163
manganese, 176
salt, 294
tripoli and rottenstone, 269
uranium and radium, 264
Great Britain, control of various minerals outside of British Isles,
64, 101, 104-105, 132, 152, 165, 178, 181, 183, 198, 210, 214,
222, 225, 232, 242, 247, 252, 256-257, 260, 275, 280
income taxes on mineral properties, 337, 339
laws relating to ownership of mineral resources, 343
participation of government in mineral trade, 388
relative position, in regard to supplies of minerals, 399
tendencies toward nationalization, 346
Great Plains, lignite, 118
pumice, 268
Greece, chromite, 178-179
emery, 268, 270
magnesite, 191-193
zinc, 214
Greenland, graphite, 280
Gregory, Herbert, 407, 413
Grimes, J. A., and Billingsley, Paul, 44
Grinding pebbles, 267, 268, 270, 398
Grindstones, 269
Ground-waters, composition of and relation to commercial use, 73-75
distribution and movement of, 68-72
influence in deposition of ore deposits, 41-42
relation to military operations, 78-79, 408, 410-411
relation to rock slides, 78, 416-417
source of, 68
Ground-water level, description of, 70
relation to oxide zone, 48
relation to zone of weathering, 22
Ground-water supply, relation of geology to, 75-76
Guano, 104, 106
Guatemala, chromite, 179
Guiana, bauxite, 242-243
Gulf Coast region, lignite, 118
petroleum, 132, 135, 137
salt, 298
sulphur, 110
_See also_ Louisiana, Texas, etc.
Gypsum, 100, 283-285, 397
Haas, Frank, 367, 369
"Head" of underground water, 71-73
Heikes, V. C., Butler, B. S., and Loughlin, G. F., 44, 55, 230
Highway building, application of geology to, 90-91
Holland, cement, 87
commercial and political control of various minerals, 64
_See also_ Dutch East Indies, etc.
Homestake Mine, South Dakota, gold ores, 229
Hones, 269
Hoover, Herbert C., 322
Hot springs, relation to ore-deposits, 40, 258-259
Hot waters, evidence of formation of ores by, 37-41
Huancavelica district, Peru, mercury ores, 258
Hudson River, physiographic problems in tunneling under, 415
Hudson's Bay, possible diamond field, 317
Humus, 94
Hunan Province, China, antimony ores, 249
Hungary, antimony, 247
natural gas, 151
_See also_ Austria-Hungary.
Hydrosphere, 18
Hypogene ores, use of term, 32-33
Idaho, coal, 117
lead, 39, 45, 209, 211, 212-213
monazite, 289
phosphates, 105
silver, 234
zinc, 214, 216
Idria, Austria-Hungary, mercury ores, 257
Igneous after-effects, ore-deposits formed as, 19-20, 36-46
Igneous rocks, formation of, 19
mineral deposits associated with, 19-20, 34-46
principal minerals of, 14-16
proportions of principal types, 17
relative abundance of, 17
weathering of, 20
Illinois, clay, 85
coal, 115, 117, 126
fluorspar, 194
limestone, 83
petroleum, 132, 133, 135
pyrite, 109
sand and gravel, 85
tripoli and rottenstone, 269
zinc, 216
Illinois Geological Survey, coöperative exploration for oil, 147, 306
Income tax, application to mineral properties, 336-339
India, bauxite, 242
India, bromine, 277
chromite, 178-179
coal, 115, 116
corundum, 268
diamond dust, 268
gypsum, 283
iron, 154, 164, 165
manganese, 174-176
mica, 286
monazite, 288, 289
petroleum, 128, 129
platinum, 238
salt, 294
zirconium, 189
Indiana, coal, 117, 126
hones, oilstones and whetstones, 269
limestones, 83
petroleum, 133, 135
Interest rate, as a guide in conservation, 364
choice of for valuation purposes, 233
limiting effect on acquirement of reserves, 334
International aspects of mineral resources, 2, 383-404
International Coal Commission, 387, 393, 402
International trade, in common rocks, 80
in minerals, 383-388
participation of governments, 388-390
Intrusive rocks, formation of, 19
Iowa, flint linings, 269
grinding pebbles, 268
gypsum, 284
zinc, 216
Ireland, bauxite, 242
Iron and coal, situation of western Europe under terms of Peace
Treaty, 400-403
Iron and steel, metallurgical processes, 158-159
Iron and steel industry, possible establishment on west coast of
United States, 155, 165
Iron cap, of sulphide deposits, 47, 109, 313
Iron ores, anti-conservational effect of war, 365
attempt to estimate reserves of continents, 322
exploration of in Lake Superior region, 323-326
general geologic and economic features, 8-9, 28, 34, 36, 47, 50,
52-53, 55-56, 58, 96, 153-156, 158-173, 397
litigation concerning Cuban, 349
metallogenic provinces and epochs, 308-309
outcrops, 312-313
taxation of in Lake Superior region, 335
use of magnetic surveys, 317-318
world reserves, 162-165, 360-361
Itabirite, 167
Italy, asbestos, 271, 272
asphalt and bitumen, 152
barite, 272
bauxite, 242
borax, 275
cement, 87
graphite, 280
manganese, 176
marble, 83
mercury, 256-257
natural gas, 151
petroleum, 128
pumice, 268
salt, 294
sulphur, 109-110
talc, 299
zinc, 214-215
Italy, coal situation under Peace Treaty, 401
commercial and political control of various minerals, 64
relative position in regard to supplies of minerals, 399
Japan, arsenic, 250
cement, 87
chromite, 178-179
coal, 115, 117
copper, 197-198
gold, 222
graphite, 280
iron, 154, 160
manganese, 174
natural gas, 151
petroleum, 128
silver, 232
sulphur, 109-110
tungsten, 183, 185
zinc, 214
Japan, control of various minerals in other countries, 64, 105, 154, 247
Jasper, 167
Java, manganese, 176
Jerome, Arizona, copper ores, 41, 47, 198, 204-205, 314
Joachimsthal, Bohemia, uranium and radium ores, 265
Joint Mineral Information Board, 406
Joplin district, Missouri, cadmium, 254
lead and zinc ores, 54-55, 209, 211, 214, 215, 216-219
Juneau, Alaska, gold ores, 229
Kansas, gypsite, 284
natural gas, 151
petroleum, 132, 133, 135
salt, 294
zinc, 215
Kaolin, 85, 398
Katamorphism, defined, 27, 57
Katanga, Belgian Congo, cobalt, 255
copper ores, 205
Kennecott, Alaska, copper ores, 36, 41, 47, 49, 200-201
Kentucky, asphalt and bitumen, 152, 153
coal, 117
fluorspar, 194
marble, 83
petroleum, 133
sandstone, 84
Kimberley, South Africa, diamonds, 291-292
Knox dolomite, Tennessee, zinc ores, 219
Korea, gold, 222
graphite, 280, 282
iron, 160
molybdenum, 186
tungsten, 183
Lacroix, Morris F., and Brooks, Alfred H., 404
Lake Superior copper ores, 36, 52, 200, 206
Lake Superior copper, silver, gold ores, occurrence in a metallogenic
province, 308
Lake Superior iron ores, 8, 47, 55-56, 160, 162, 163, 167-170, 309,
312-313
Lake Superior region, iron ore exploration in, 317-318, 323-326
Land grants in United States, retarding effect on exploration, 349
"Land-plaster", 100
Laterites, 172-173
Laws relating to mineral resources, 342-358
Lawton region, Pennsylvania, coal, 117
Lead and zinc, Wisconsin, equated income method of taxation, 335-336
Lead ores, 36-50, 54-55, 209-213, 307, 308, 313-314, 361, 397
Leadville, Colorado, bismuth, 253
lead and zinc ores, 212, 216, 219-220
Leasing law, on public lands in western United States, 348
Leith, C. K., 323
Leith, C. K., and Mead, W. J., 45
Leith, C. K., and Van Hise, C. R., 56, 324
Lesher, C. E., and Smith, George Otis, 371, 372, 373, 375
Lignite, 118, 120, 122, 124
German development of, 379, 402
Lime, 82, 99-100, 397
Limestone, 15, 17, 23, 82-83, 89-90, 91
Lincolnshire district, England, iron ores, 161
Lindgren, W., 43
Lipari Islands, Italy, pumice, 268
Lithosphere, principal elements of, 13
principal minerals of, 14-16
principal rocks of, 16-17
Litigation, use of geologists in, 349-355, 357-358
Lode, application of legal term to diverse mineral deposits, 350
Long-wall system of coal mining, conservational aspect, 368
subsidence of overlying ground and resulting litigation, 357, 417
Longwy, France, iron ores, 161
Lorraine, iron ores, 52-53, 161-162, 163, 166, 364, 402-403
phosphate from Thomas slag, 104
Loughlin, G. F., Butler, B. S., and Heikes, V. C., 44, 55, 230
Louisiana, natural gas, 151
petroleum, 132, 133, 135
salt, 298
sulphur, 110
Lower California, copper, 201
magnesite, 191-192
Luxemburg, coal situation under Peace Treaty, 401
iron ores, 160-162, 163
_See also_ under Lorraine, iron ores
Madagascar, corundum, 268
graphite, 280-282
Magmatic segregation, mineral deposits thus formed, 34-35, 59
Magmatic waters, evidence of formation of ores by, 37-41
Magnesite, 191-193, 397
Magnetic surveys in tracing mineral ledges, 317-318
Magnetite deposits, 34, 171, 191, 317-318
Maine, feldspar, 86
granite, 82
tourmaline, 293
Malay States, tin, 260-261
tungsten, 183
Manchuria, iron, 160
Mandatory countries, exploitation of minerals in, 390-391
Manganese ores, 47, 55, 173-178, 314, 386, 398
Mansfield shales, Germany, copper ores, 9, 52, 206
Mantle rock, 22
Mapimi, Mexico, arsenic production, 250
Marble, 83, 89-90
Marbut, Curtis F., 95
Marl, 83
Marquette district, Michigan, iron ore outcrops, 312
Maryland, diatomaceous earth, 269
serpentine, 83
Marysville, Utah, alunite deposits, 114
Mashing, 25-26
Massachusetts, granite, 82
serpentine, 83
McCoy, A. W., 142
Mead, Daniel W., 69, 77-78
Mead, W. J., 245
Mead, W. J., and Leith, C. K., 45
Mehl, M. G., 144
Menominee district, Michigan, iron ore outcrops, 312
Mercury ores, 40, 255-260, 398
Mesabi district, Minnesota, concentration of siliceous iron ores, 156
exploration for iron ores, 313, 318, 324, 325
Mesopotamia, petroleum, 128-130, 137, 391
Mesothorium, 288
Metallogenic provinces and epochs, 308-309
Metamorphic cycle and its relation to classification of mineral
deposits, 27-28
"Metamorphic rocks," defined, 27
Metamorphism, relation to economic geology, 10
use of principles of in exploration
for mineral deposits, 319-320
_See also_ Katamorphism, Anamorphism, Contact metamorphism,
Dynamic metamorphism, Weathering, etc.
Metasomatic replacement, 24
Metcalf-Morenci district, Arizona, copper ores, 38, 198
Meteoric waters, influence of in deposition of ore deposits, 25, 41-42
Mexico,
antimony, 247-248
arsenic, 250
cement, 87
copper, 197-198, 201, 203
gold, 222
graphite, 280-282, 283
lead, 210-211
magnesite, 191-192
mercury, 256, 258
molybdenum, 186
natural gas, 151
petroleum, 128, 129, 137, 144
silver, 231-232, 233
vanadium, 188
zinc, 214-215
Mexico, commercial and political control of various minerals, 64
Miami, Arizona, copper ores, 33, 47, 48, 198, 203, 208
Mica, 285-288, 398
Michigan,
bromine, 277
copper, 199
grindstones and pulpstones, 269
gypsum, 284
iron. _See_ Lake Superior iron ores, Gogebic district, etc.
limestone, 83
salt, 294, 297
Michigan, taxation of iron ores, 335
Midcontinent field, petroleum, 132, 135, 137, 141, 146
Military geology, preparation of textbook, 407
Military operations, relation of ground-waters to, 78-79
Millstones, 269
Minas Geraes, Brazil, iron ores, 52-53, 162, 165, 167, 313
Mineral deposits,
classification and general features of origin, 27-59
exploration and development, 301-327
origin as a factor in economic problems, 29-31, 322-323
outcrops, 311-317
secondary concentration, 46-50, 54-57
_See also_ under Iron ores, Copper ores, etc.
zonal arrangement, 42-45
Mineral industry,
basis for popular interest in, 328
"social surplus" of, 330
Mineral lands, classification, 309-311
Mineral paints, relative position of United States, 397
Mineral provinces and epochs, 308-309
Mineral resources,
conservation, 359-382
general quantitative considerations, 60-66
international aspects, 383-404
laws relating to, 342-358
nationalization, 345-347, 375-376, 377-378, 382
political and commercial control, 65
relative position of the United States in regard to supplies, 396-400
valuation and taxation, 328-341
world movement, 383-388
world reserves, 65-66
Mineralogy, relation to economic geology, 3
"Minette" iron ores, 158, 161, 166
Mining law, 342-358
Mining methods, control of by government or owners in interests of
conservation, 355
Minnesota,
granite, 82
iron. _See_ Lake Superior iron ores, Mesabi district, etc.
manganese, 175, 177
Minnesota, taxation of iron ores, 335
Mississippi Valley, cadmium, 254
lead and zinc ores, 54-55, 108, 211-212, 214, 215-219, 308, 313
Missouri, barite, 273-274
cadmium, 254
lead, 209, 211
silica for refractories, 195
tripoli and rottenstone, 269
zinc, 214, 215, 217-218
Molybdenum ores, 185-187, 397
Monazite, 288-289, 398
Montana, arsenic, 250-251
copper, 40, 42, 47, 49, 198-199, 201-203, 207, 208
gold, 222
graphite, 281, 283
manganese, 175, 176-177
petroleum, 133
phosphates, 105
sapphires, 293
silver, 42, 234, 237, 314
zinc, 42, 216, 219
Monte Amiata district, Italy, mercury ores, 257
Morenci-Metcalf district, Arizona, copper ores, 38, 198
Mother Lode district, California, gold ores, 229, 308, 316
Munitions Resources Commission of Canada, 404
Nancy, France, iron ores, 161
National Academy of Sciences, 407
National Conservation Commission, 367
National district, Nevada, antimony ores, 249
Nationalization of mineral resources 345-347, 375-376, 377-378, 382, 388
Natural abrasives, 267-270, 397
Natural gas, 57, 151
Nebraska, potash, 112, 114
Netherlands. _See_ Holland, Dutch East Indies, etc.
Nevada, alunite, 39, 41-42, 114
antimony, 247, 249
bismuth, 253
borax, 275, 276
copper, 41, 199, 203
diatomaceous earth, 269
gold, 36, 222, 230, 308, 311-312
graphite, 281
grinding pebbles, 268
mercury, 357
oil shales, 151
platinum, 239-240
silver, 36, 38, 234, 235-237, 308, 311-312
tungsten, 183
turquoise, 293
zinc, 216
New Almaden, California, mercury ores, 259
New Brunswick, gypsum, 283-284
New Caledonia, chromite, 178-179 nickel, 180-182
New Cornelia, Arizona, copper ores, 203
Newfoundland, iron ores, 52-53, 160, 166
laws relating to ownership of mineral resources, 344
New Hampshire, fluorspar, 194
garnet, 268
mica, 287
New Idria, California, mercury ores, 259
New Jersey, arsenic, 250
basalt, 82
clay, 85
iron, 171
sand and gravel, 85
zinc, 215, 220
New Mexico, copper, 199, 203
fluorspar, 194
silver, 234
uranium and radium, 265-266
zinc, 216
New South Wales, Australia, bismuth, 252-253
coal, 115, 116
lead, 209, 210, 212
platinum, 238
zinc, 214, 216
New York,
arsenic, 250, 251
emery, 268, 270
garnet, 268
graphite, 281, 282
gypsum, 284
iron, 160, 162, 163, 171
limestone, 83
millstones and buhrstones, 269
petroleum, 132, 133
pyrite, 108
salt, 294, 297
sandstone, 84
talc, 299
New Zealand,
bismuth, 252
phosphates, 105
platinum, 238
tungsten, 183
New Zealand, laws relating to ownership of mineral resources, 343
Nickel ores, 34-35, 180-182, 307, 308, 318, 398
Nitrates, 99-100, 101-104, 386, 392, 398
Nonesuch beds, Michigan, copper ores, 52, 206
North Africa,
iron, 156, 160, 161, 164
lead, 210
phosphates, 104, 105, 106
potash, 112
zinc, 214-215
North Carolina,
coal, 117
corundum, 268, 270
emeralds, 293
feldspar, 86
garnet, 268
granite, 82
mica, 287
monazite, 288, 289
rubies, 292
sand and gravel, 85
sapphires, 293
Northern Plains, coal, 118
Norway,
copper, 197-198
molybdenum, 186
nickel, 180
titanium, 190
zinc, 214
_See also_ Scandinavia.
Nova Scotia,
gypsum, 283-284
saddle-reef gold ores, 41
Oceania,
mercury, 258
phosphates, 105, 106
tin, 261
Ohio,
bromine, 277
clay, 85
coal, 117
grindstones and pulpstones, 269
gypsum, 284
hones, oilstones and whetstones, 269
limestone, 83
natural gas, 151
petroleum, 133
salt, 294
sand and gravel, 85
sandstone, 84
Oil. _See_ Petroleum.
Oil shales, 56, 139, 150-151
Oilstones, 269
Oklahoma,
asphalt, and bitumen, 152
gypsum, 284
lead, 211
natural gas, 151
petroleum, 132, 133, 135
tripoli and rottenstone, 269
zinc, 215
Ontario, Canada,
arsenic, 251
cobalt, 255
corundum, 270
mica, 286
nickel, 34-35, 180-182, 308, 312, 318
platinum, 238, 239
silver, 232, 234-235, 308, 316
talc, 299, 300
Ontario, Canada, laws relating to ownership of mineral resources, 344
Onyx marble, 83
Open-hearth process of steel making, 158-159
Ore deposits. _See_ Mineral deposits.
Oregon, borax, 275, 276
chromite, 179
mercury, 257
Origin of mineral deposits, as a factor in economic problems, 29-31,
322-323
Outcrops of mineral deposits, 311-316
Ownership laws, effect on exploration of mineral deposits, 347-349
relation of geology to, 349-355
Oxide zones, 22, 46-50, 313-314
_See also_ under Copper ores, Silver ores, etc.
Pablo Beach, Florida, titanium ores, 190-191
zirconium ores, 189
Pacific coast, possible establishment of iron and steel industry, 155,
165
Pacific coast province, coal, 117
Palegeography, relation to economic geology, 4
Paleontology, relation to economic geology, 4
Palestine campaign, use of geologic data, 409
Panama, manganese, 176
Panama Canal, slides, 416-417
Parker, E. W., and Campbell, M. R., 367, 370-371
Peace Conference, use of geologists in advisory capacity, 356, 406
Peace Treaty, coal and iron situation of western Europe under terms of,
117, 400-403
effect of terms on valuation problems, 335
Silesian lead and zinc ores, 210, 214
Pearls, 289-292
Peat, formation of, 123-124
Pegmatites, 19-20, 35, 39
Peneplains, formation of, 6
Pennsylvania, basalt, 82
clay, 85
coal, 115, 117, 126
flint linings, 269
graphite, 281
iron, 171
limestone, 83
natural gas, 151
petroleum, 133
sand and gravel, 85
sandstone, 84
serpentine, 83
silica for refractories, 195
slate, 85
Persia, petroleum 128-130, 137, 391
Peru, bismuth, 252
borax, 275
coal, 116
copper, 197-198
mercury, 258
molybdenum, 186
nitrates, 103
petroleum, 128, 137
phosphates, 106
silver, 232
tungsten, 183
vanadium, 187, 188
Petroleum, 57, 127-150, 307, 310, 386, 396, 398
Petroliferous provinces, 149, 308
Petrology, relation to economic geology, 3
Philipsburg, Montana, manganese and silver ores, 37, 175, 176-177, 237
Phosphates, 99-100, 104-107, 397
Physiography, general discussion and relations to economic geology, 6-10
_See also_ Topography.
Physiography, relation to bridge building, 413
relation to Hudson River tunnels, 415
relation to railway construction, 418
relation to river and harbor improvements, 414
Pisolites, 172
Pitch. _See_ Asphalt.
Pittman Silver Act, 233
Placers, formation of, 51
gold deposits in, 227
_See also_ Monazite, Platinum, Tin, Tungsten, and other minerals.
use in tracing mineral outcrops, 316-317
Plasticity of clay, 92
Platinum ores, 51, 237-240, 386, 398
Plumbago. _See_ Graphite.
Pogue, Joseph E., 100
Pogue, Joseph E., and Gilbert, Chester G., 119, 134, 138
Poland, lead and zinc, 210, 214
Political and commercial control of mineral resources, 65, 387-388
_See also_ under individual resources.
Porosity of rocks, 69, 141
Porphyry copper ores, 197, 199, 203
Portland cement. See Cement.
Portugal, arsenic, 250
copper, 197-198, 204
pyrite, 107-108
salt, 294
tungsten, 183
Potash, 86, 99-100, 111-114, 386, 398
Precious stones, 289-293, 398
Primary ore deposits, use of term, 32
Primary ores, relation to depth, 49
Propylitic alteration, 39, 236
Protore, use of term, 33, 48
"Proximate" analyses of coal, 120
Public domain, laws relating to ownership of mineral resources on,
343-344
Pulpstones, 269
Pumice, 267, 268, 270, 398
Puzzolan cement. See Cement.
Pyrite, 100, 107-109, 307, 386, 397
Pyrophyllite, 299
Quartz, as geologic thermometer, 38
geologic occurrence, 16, 38-39, 43, 45, 47, 168-169, 196
production and use, 84, 267, 269
Quartzite, 84, 91
Quebec, Canada, asbestos, 270-272
magnesite, 193
mica, 286
Quebec, laws relating to ownership of mineral resources, 344
Queensland, Australia, arsenic, 250
Quicksilver ores. _See_ Mercury ores.
Radium ores, 55, 263-266, 397
Railway construction, application of geology to, 417-418
Rambler, Wyoming, occurrence of platinum, 239
Ransome, F. L., 33, 208, 230
Ray, Arizona, copper ores, 33, 47, 48, 198, 203, 208
"Red Beds" copper ores, 9, 206
Registration, public, of drilling records, 305-306
Regulus, 247
Reparations Committee, 387, 393, 402
Replacement, metasomatic, 24
Reserves of mineral resources, 65-66, 359-363, 393-395
_See also_ under individual resources.
"Resource cost" of coal, reduction of in interests of conservation,
334, 375
Rhode Island, coal, 117
graphite, 281
Rhodesia, asbestos, 272
chromite, 178-179
Ries, H., and Watson, T. L., 413
Rio Tinto, Spain, copper ores, 204
pyrite, 108
Road building, application of geology to, 90-91, 418
"Rock flour," defined, 95
Rock slides, 78, 415-417
Rocks, common, as mineral resources, 80-84
Rocky Mountain region, coal, 117
petroleum, 132, 135
Room-and-pillar system of coal mining, modification for conservational
purposes, 368-369
Rottenstone, 267, 269
Roumania, graphite, 280
petroleum, 128, 129
Royal Ontario Nickel Commission, 181
Royalties on coal, reduction of in interests of conservation, 334, 375
Rubies, 289, 291-292
Russia, asbestos, 270-271, 272
cement, 87
chromite, 178-179
coal, 115, 127
copper, 197-198
gold, 222
iron, 155, 160-161, 163
manganese, 174-176
mercury, 256, 258
oil shales, 151
petroleum, 128-120, 137
phosphates, 104, 106
platinum, 238, 239
potash, 112
salt, 294
zinc, 214
Russia, commercial and political control of various minerals, 64
laws relating to ownership of mineral resources, 343
Russia, Asiatic, vanadium, 187
_See also_ Siberia.
Saar Basin, coal of, under Peace Treaty, 401
Salisbury, R. D., and Chamberlin, T. C., 415
Salt, 294-298, 397
Salt domes of Gulf Coast, 298
Sand, 15, 84, 267
Sand and gravel, 84-85
Sandstone, 15, 17, 23, 84, 90, 267, 269
Santa Rita, New Mexico, copper ores, 203
Sapphires, 289, 291, 293
Sargasso Sea theory, of deposition of lead and zinc sulphides, 217
Saxony, bismuth, 252
tin, 262
Scandinavia, molybdenum, 386
nitrogen-fixation plants, 102
Schistose structure, 26
Schlumberger, C., 319
Schuchert, Charles, 144
Schultz, Robert S., Jr., 417
Scotland, magnesite, 191
oil shales, 150
Searles Lake California, borax deposits, 276
potash deposits, 112, 113-114
Secondary enrichment, 7-8, 25, 46-50
_See also_ under Copper ores, Silver ores, etc.
Secondary ore deposits, use of term, 32
Sedigenetic deposits, use of term, 51
Sedimentary mineral deposits, unsolved problems, 9, 53, 56
Sedimentary rocks, formation of, 22-24, 96
mineral deposits associated with, 23, 51-57
principal minerals of, 15-16
proportions of principal types, 17
relative abundance of, 16
weathering of, 23
Sedimentation, relation to economic geology, 2
Segregation, magmatic, 34-35, 59
Sericitic alteration, 39
Serpentine, 83
Seward Peninsula, Alaska, tin ores, 261, 262
Shale, 15, 17, 23, 85, 90
Shasta County, California, copper ores, 204
Shipping Board, 356, 406
Siam, sapphires, 289, 293
tin, 260
tungsten, 183, 184
Siberia, emeralds, 293
gold, 222, 226
lead, 210
vanadium, 187
zinc, 214
Silesia, cadmium, 254
coal, under Peace Treaty, 401
lead and zinc ores, 54-55, 210, 211-212, 214-215, 216-218
Silica, 195-196, 267, 269
_See also_ Quartz, Quartzite, Sand, Sandstone, etc.
"Silt" (fine coal), use of, 370, 371
Silver ores, 36-50, 55, 231-237, 308, 313-314, 397
Silver Reef, Utah, deposits, 55
Slate, 85, 89
Slides, earth and rock, 78, 357, 415-417
Smelting capacity of world, 61
Smith, George Otis, 310, 367, 403
Smith, George Otis and Lesher, C. E., 371, 373, 373, 375
Smyrna, Turkey, emery, 268
Soapstone, 299-300
Societies, professional, standards of admission, 421-422, 428
Soils, classification, 97
composition, 96-97, 99
origin, 94-96
use of fertilizer minerals on, 99-101
use of geology in study of, 95-98
Sound waves, possible use in exploration, 319
South Africa, asbestos, 271, 272
cement, 87
coal, 116
cobalt, 255
copper, 197-198, 205
corundum, 268
diamond dust, 268
diamonds, 289, 291-292, 316
gold, 222-226, 228
iron, 154,164
mica, 286
tin, 260
vanadium, 187
South Africa, laws relating to ownership of mineral resources, 343, 345
South America, cement, 87-88
coal, 116
lead, 210, 211
mercury, 258
zinc, 214
_See also_ under individual countries.
South America, laws relating to ownership of mineral resources,
343-344, 345
South Carolina, coal, 117
monazite, 288, 289
phosphates, 105, 107
South Dakota, gold, 222, 228, 229
quartzite, 84
tin, 262
tungsten, 183
Southern Graphite Association, 405
Southern Pacific Railway, litigation in regard to oil lands, 348
Spain, arsenic, 250
barite, 272
cement, 87
copper, 197-198, 204
garnet, 268, 270
iron, 154, 156, 160-161, 162, 163
lead, 210, 211-212
manganese, 174
mercury, 256-257, 259
phosphates, 104, 106
platinum, 238
potash, 111-113
pyrite, 107-108
salt, 294
silver, 232
sulphur, 109-110
zinc, 214-215
Spain, commercial and political control of various minerals, 64
Spiegeleisen, 173-174
Springs, 72
Spurr, J. E., 43, 64, 403
Stassfurt, Germany, borax, 277
bromine, 278
potash, 111-112, 113, 296-297
salt, common, 296-297
Steel. _See_ Iron and steel
Stone. _See_ Building stone, Common rocks.
Storage of coal, 376
Stratigraphy, relation to economic geology, 4
Structural geology, relation to economic geology, 5
use of principles of in exploration for mineral deposits, 319-320
Structures of rocks, relation to earth stresses, 5
relation to topography, 7
Subsidence of ground over mining operations, geologic study of, 357, 417
Sudbury, Ontario, cobalt, 255
nickel ores, 34-35, 180-182, 308, 312, 318
platinum, 238, 239
Sulphide enrichment. _See_ Secondary enrichment.
Sulphur, 99-100, 109-111, 397
Sulphur Bank Springs, California, deposition of mercury by hot waters,
259
Supergene ores, use of term, 32, 33, 48
Surface water supplies, 76-78
Surface waters, application of geology to use of, 414
relation to excavation and construction, 78-79
Sweden, cement, 87
iron, 154, 155, 156, 158, 160, 162, 163, 171
manganese, 176
phosphate from Thomas slag, 104
zinc, 214
_See also_ Scandinavia.
Switzerland, cement, 87
nitrogen fixation plants, 102
Syngenetic ore deposits, use of term, 32, 34, 51
Taconite, 167
Talc and soapstone, 299-300, 397
Tankage, use of phosphate content, 104
Tariffs, proposed, on mineral resources, 175-176, 179, 184, 192, 248,
257-258
Tariffs and duties, anti-conservational effect of, 362-363, 366, 375,
376, 393-394
Tasmania, bismuth, 252
platinum, 238
zinc, 214
Taxation of mineral resources, 1, 335-341
Tennessee, barite, 273
bauxite, 243, 245
copper, 204
flint linings, 269
marble, 83
petroleum, 132, 133
phosphates, 105, 107
zinc, 54-55, 216, 219
Terlingua district, Texas, mercury, 257, 259
Texas, asphalt and bitumen, 152
coal, 117
fuller's earth, 279
graphite, 281
gypsum, 284
mercury, 256, 257, 259
natural gas, 151
petroleum, 132, 133, 135, 148
salt, 298
sulphur, 110
Thermal metamorphism. _See_ Contact metamorphism.
Thermal waters, 72
Thibet, borax, 275, 276
Thomas process of steel making, 158, 161
use of slag for phosphate content, 104, 106
Tin ores, 36-50, 51, 260-263, 307, 322, 386, 392, 398
Tintic, Utah, silver ores, 39, 42, 235, 251, 253
Titaniferous magnetites, 34, 171, 191
Titanium ores, 190-191, 398
Tonopah, Nevada, gold silver ores, 38, 234, 236-237, 308
Topographic cycle, description of, 6
Topography, relation to mineral deposits, 7-9, 314-315
relation to rock structures, 7
Tourmaline, 290, 293
Training in economic geology, 420-428
Transvaal, Africa, asbestos, 272
diamonds, 291
gold, 222, 223-225, 228
Trap-rock, 82
Travertine, 83
Treadwell Mine, Alaska, gold ores, 229
Trenches, military, application of geology to, 408, 410-411
Trinidad, asphalt, 152, 153
petroleum, 128
Tripoli, 267, 269, 398
Tungsten ores, 51, 182-185, 386, 398
Tunis, phosphates, 104-106
potash, 112
_See also_ North Africa.
Tunnels, application of geology to construction, 414-415
Turkey, borax, 275
chromite, 178-179
emery, 268, 270
Turquoise, 290, 293
Tuscany, Italy, borax deposits, 275
Umpleby, Joseph B., 383
Underground waters. See Ground-waters.
United Kingdom. See Great Britain.
United States, abrasives, natural, 267-270, 397, 398
aluminum, 242-245, 397
antimony, 247-248, 249, 398
arsenic, 250-251, 397
asbestos, 270-272, 398
asphalt and bitumen, 152, 397
barite, 273-274, 397
bauxite, 242-245, 397
bismuth, 252-253, 397
borax, 275, 276, 397
bromine, 277, 278, 397
cadmium, 253-254, 397
cement, 87-88, 397
chalk, 83, 398
chromite, 179, 398
coal, 115-118, 126, 127, 366-367, 397
common rocks, 82-88, 397
copper, 197-208, 396
corundum, 267-268, 270, 398
diatomaceous earth, 269, 398
emery, 267-268, 270, 397
feldspar, 86, 397
ferro-alloy minerals, general, 154-158
fertilizers, general, 100-101
fluorspar, 194, 397
fuller's earth, 278-279, 397
garnet, 268, 260, 398
gold, 222-230, 397
graphite, 279-283, 398
grinding pebbles, 268, 398
gypsum, 283-284, 397
iron, 158-163, 166-171, 397
lead, 209-213, 397
lime, 82-83, 397
magnesite, 191-193, 397
manganese, 174-177, 398
mercury, 256-259, 398
mica, 286-287, 398
mineral paints, 397
molybdenum ores, 186-187, 397
monazite, 288, 289, 398
natural abrasives, 267-270, 397, 398
natural gas, 151
nickel, 181, 398
nitrates, 102, 398
oil shales, 150-151
petroleum, 128-150, 396, 398
phosphates, 104-107, 397
platinum, 238-240, 398
potash, 112-114, 398
precious stones, 290, 292-293, 398
pumice, 268, 398
pyrite, 107-109, 397
salt, 294-298, 397
silica, 195-196
silver, 231-237, 397
stone, 82-88, 397
sulphur, 109-111, 397
talc, 299, 300, 397
tin, 261, 262, 398
titanium, 190-191, 398
tripoli, 269, 398
tungsten, 183-185, 398
uranium and radium, 264-266, 397
vanadium, 18, 188, 398
zinc, 214-220, 398
zirconium, 189, 398
United States, control of various minerals in other countries, 64, 102,
129, 152, 163-164, 165, 175, 180-181, 184, 187, 189, 191, 198,
222, 232, 238, 243, 261
laws relating to ownership of mineral resources, 343-345
quantitative feature of mineral production, 60-66
relative position in regard to supplies of minerals, 396-400
tendencies toward nationalization of mineral resources, 345-346
United States Bituminous Coal Commission, 376
United States Bureau of Mines, activities in the war, 406
literature or international mineral relations, 403
United States Geological Survey, activities in the war, 406, 407
classification of mineral lands, 310-311
employment by, 428
literature on international mineral relations, 403
United States Shipping Board, 356, 406
Uranium ores, 55, 263-264, 397
Utah, arsenic, 250, 251
asphalt and bitumen, 152
bismuth, 253
copper, 37, 42, 47, 55, 199, 203, 204, 207, 208, 314
gold, 222, 314
lead, 42, 211, 212
manganese, 55
oil shales, 151
phosphates, 105
potash, 112, 114
silver, 42, 55, 234, 235
uranium and radium, 55, 264, 265
vanadium, 55, 187-188
Utah, ore deposits, relation to intrusive stocks, 44
Vadose zone, 70
Valuation of Lorraine iron ores at Peace Conference, 364
Valuation of mineral resources, 81, 328-341, 396
Value, capital, of mineral resources, 64, 328
Value of United States mineral production and imports, 62
Value of world mineral production, 62-63
Vanadium ores, 55, 187-188, 398
Van Hise, C. R., 367, 374
Van Hise, C. R., and Leith, C. K., 56, 324
Vein, application of legal term to diverse mineral deposits, 350
Venezuela, asphalt, 152, 153
magnesite, 191-193
petroleum, 128
phosphates, 105
Verde district, Arizona. _See_ Jerome district.
Vermilion district, Minnesota, iron ore outcrops, 312
Vermont, granite, 82
marble, 83
serpentine, 83
slate, 85
talc, 299
Virginia, arsenic, 250, 251
emery, 268
manganese, 175
millstones and buhrstones, 269
pyrite, 108
talc and soapstone, 299, 300
titanium, 190
zinc, 54-55, 219
Virginia City, Nevada. _See_ Comstock Lode
Volcanic ash, use as abrasive, 270
Wabana, Newfoundland, iron ores, 52-53, 160, 166
Wales, coal, 126
War, anti-conservational effects of, 365-366
application of geology to, 405-412
effect on ad valorem valuations, 335
War Industries Board, 356, 406
War Minerals Committee, 406
War Trade Board, 356, 406
"Wash," use in tracing mineral outcrops, 316-317
Washington, arsenic, 250
chromite, 179
magnesite, 191-193
Water, applications of economic geology to, 68
as a mineral resource, 61, 62, 67-79
general geologic relations, 67-68
hygroscopic, defined, 68
of constitution, defined, 68
quantity absorbed by soils and rocks, 69
relative abundance of, 18
source of, 67
use of, litigation arising from, 357-358
_See also_ Ground-waters, Surface waters, Hot waters, Meteoric
waters, Magmatic waters.
Water power, possibilities of substituting for coal, 378-379
Water supplies, 72-78
Water supply maps for military use, 411-412
Water table, defined, 70
_See also_ Ground-water level.
Waters, thermal, 72
Watson, T. L., and Ries, H., 413
Weathering, of igneous rocks and veins, 20-22
of igneous rocks, formation of mineral deposits by, 50
of mineral deposits, 46-50
of sedimentary rocks, 23-24
production of clay by, 91
production of soils by, 94-96
zone of, 70
Welfare work, in interests of conservation, 372-373
Wells, 72-73
West Africa, gold, 222
manganese, 176
West Indies, cement, 87
phosphates, 105, 106
salt, 294
West Virginia, bromine, 277
coal, 117
grindstones and pulpstones, 269
natural gas, 151
petroleum, 132, 133
Whetstones, 269
White, David, 128, 129, 140, 143, 146
White Signal district, New Mexico, uranium and radium ores, 265-266
Wisconsin, artesian wells, 73
diamonds in glacial drift, 292, 317
granite, 82
iron. _See_ Lake Superior iron ores, Gogebic district, etc.
quartzite, 82, 84, 195
zinc, 216
Wisconsin, equated income method of taxation, 335-336
taxation of iron ores, 335
Witwatersrand, South Africa, gold ores, 228
Wolfram ores. _See_ Tungsten ores.
Woodward, H. B., 69
Wyoming, chromite, 179
oil shales, 151
petroleum, 133
phosphates, 105
platinum, 239
potash, 112
uranium and radium ores, 265
Yellow Pine district, Nevada, platinum ores, 239-240
Yellowstone Park, springs and geysers of, 72
Zinc and lead ores, Wisconsin, equated income method of taxation, 335-336
Zinc ores, 36-50, 54-55, 213-220, 308, 313-314, 398
Zinc Syndicate, German, 215
Zirconium ores, 189-190, 398
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| Transcriber's Note |
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| Some inconsistent spelling in the text has |
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| Page 15 In the symbol FeCO_{3} the _{3} is |
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| Page x DEVELOPMNET changed to DEVELOPMENT |
| Page 87 Unites changed to United |
| Page 89 heterogenous changed to heterogeneous |
| Page 179 Guatemela changed to Guatemala |
| Paqe 329 familar changed to familiar |
| Page 433 Afrcia changed to Africa |
| Page 434 Winconsin changed to Wisconsin |
| Page 444 westtern changed to western |
| Page 450 ownnership changed to ownership |
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