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Josiah Edward Spurr.

Geology applied to mining; a concise summary of the chief geological principles, a knowledge of which is necessary to the understanding and proper exploitation of ore-deposits, for mining men and students online

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GEOLOGY APPLIED TO MINING



Published by the

Me G raw -Hill B oolc Comp any



>Succe^sons to the Book Departments of the

McGraw Publishing Company Hill Publishing Company

Publishers of books for

Electrical World The Engineering and Mining Journal

Engineering Record American Machinist

Electric RaiKvay Journal Coal Age 1

Metallurgical and Cnemical Engineering Power



GEOLOGY APPLIED TO
MINING



A CONCISE SUMMARY OF THE CHIEF GEOLOGICAL
PRINCIPLES, A KNOWLEDGE OF WHICH IS NECES-
SARY TO THE UNDERSTANDING AND PROPER
EXPLOITATION OF ORE DEPOSITS



FOR MINING MEN AND STUDENTS



BY
JOSIAH EDWARD SPURR, A M.

Geologist, United States Geological Survey ; Consulting Geologist and

Mining Engineer to the Sultan of Turkey ; Fellow of the Geological

Society of America; Member American Institute of Mining

Engineers, Member Washington Academy of Sciences, etc.



FIRST EDITION SIXTH IMPRESSION



McGRAW-HILL BOOK COMPANY
239 WEST 39TH STREET, NEW YORK

6 BOUVERIE STREET, LONDON, E.G.



COPYRIGHT, 1904,
BY

THE ENGINEERING AND MINING JOURNAL
COPYRIGHT, 1907,

BY THE

HILL PUBLISHING COMPANY



PREFACE.



The writer was led to attempt the present volume througn
the perception of how great a need there was, among
mining men and students, of some work stating concisely
those results of the science of geology which bear upon ore-
deposits. No work of this type exists, so far as the writer
is aware, in any language. The demand for such informa-
tion is great among men of the classes referred to; yet in
any of the available works on geology they find very little
of that for which they are searching, combined with a great
deal of that which, for the moment, is immaterial.

In preparing this work two points have been kept in
mind; first, to make statements as clear as possible, con-
sidering the technical nature of the subject; and, second,
to present the scientific facts accurately, and as fully as
absolutely necessary. Simplicity of language has been
constantly striven after, but it must be remembered that
it is impossible to discuss any technical matter without
using terms peculiar to it.

This book, as it goes forth, is far from meeting the
author's perfect approval. It is a beginning, and it is

359588



iv PREFACE.

believed that the demand is sufficient to warrant its imme-
diate publication. But it is the writer's purpose to work
steadily at its improvement and elaboration.

So sincere is his wish to furnish the desired information
to the large class for whom the book is intended, that he
asks for private communications from readers, stating
where they have not found the writing clear enough, or
asking information on questions not contained in this book.
Such suggestions will be a valuable aid to future enlarge-
ment and revision.

Although the writer addresses men who have had little to
do with geology as a science, or with the theory of that par-
ticular branch of geology with which the book deals
namely, the study of ore-deposits yet, before developing
his subject, he has deemed it necessary to anticipate a little.
With this purpose the first chapter has been inserted. For
a correct understanding of the science of ore-deposits, and
how the principles of geology may be practically applied to
economic advantage in finding and exploiting ore-bodies, it
is necessary, first of all, to have some ideas of what ore-
bodies are, and how they have formed. The study of the
processes of ore deposition has long been in a state of slow
growth; within the past twenty years, however, it has been
more rapid and steady than heretofore, and the writer feels
justified in laying down certain principles.

Suggestions and criticisms of the most helpful nature in
regard to this work have been made by friends, who have
read portions of the rough draft of the manuscript. For
such aid grateful acknowledgment is due to Messrs.



PREFACE. V

T. Wayiand Vaughan, A. H. Brooks, and Waldemar Lind-
gren, of the United States Geological Survey. Especial
thanks are due to Mr. T. A. Rickard, Editor of the
Engineering and Mining Journal, who carefully went over
the manuscript and made such trenchant suggestions as to
its revision that the general presentation was greatly alter-
ed and improved thereby.

J. E. SPURR.
Washington, D. C., Feb. 3, 1904.



CONTENTS.



CHAPTER I.

THE PROCESSES OF ORE-DEPOSITION.

Metamorphism, or Changes in the Earth's Crust 1

The Origin of Metamorphk Rocks 1

Transformation of Igneous and Metamorphic Rocks into

Sedimentary Rocks 6

Special Metamorphic Processes Connected with Ores . 7

Processes of Ore-Concentration 9

Concentration directly from Igneous Rocks, while Molten

or Cooling 9

Theory of Direct Concentration of the Basic Constit-
uents, During a State of Chiefly Igneous Fluidity

of the Rock 9

Theory of Concentration of the Silicious and other
Constituents, in a State of Aquaeo-Igneous

Fluidity . . 13

Extraction of Silicious and Other Constituents in
Solution in Waters Expelled from Cooling Rocks,
and Deposition in Foreign Rocks .... 15
Ore Deposits Formed Chiefly by Vapors .... 17

The Origin of Certain Hot Springs 18

Concentration by Underground Waters in General . . 19

Concentration by Surface Waters . . ' . . . .20

Relative Work of Underground and of Surface Waters 21

The Mode of Ore-Deposition . 22

CHAPTER II.

THE STUDY OF THE ARRANGEMENT OF THE STRATIFIED ROCKS AS
APPLIED TO MINING.

The Formation of Stratified Rocks 24

Formation of Sediments by Mechanical Agencies ... 24

Formation of Sediments by Chemical Agencies ... 25

Formation of Sediments by Organic Agencies .... 25

Transformation of Sediments to Hard Rocks .... 2(5

The Physical Characters of Sedimentary Rocks 26



VI 11 CONTENTS.

Page

The Chief Kinds of Sedimentary Rocks, Their Origin and Char-
acteristics 28

The Distinction between Bedding, Cleavage, Schistosity, and

Gneissic Structure 32

Different Geologic Periods during which Sedimentary Rocks

have Formed 35

Characteristics of the Different Fossils 43

The Order of Succession as Found in Actual Practice . . 52

Relation of Physical Characters to Geologic Age ... 53

Comparison and Correlation 56

Mode of Determining the Relative Age of Different

Strata 56

Mode of Correlating Similar Strata in Adjacent or

Separated Regions 57

The Association of Valuable Minerals with Certain Strata . . 58

General Relations of Stratified Ores 58

Preferential Association with Certain Geologic Periods . 62
Preferential Association with Certain Kinds of Sediment-
ary Rocks 68

Contemporaneous Deposition of Ores and Strata ... 69
Selection of Favorable Strata for the Subsequent Deposi-
tion of Ores 73

CHAPTER III.

THE STUDY OF IGNEOUS ROCKS AS APPLIED TO MINING.

Physical Characters of Igneous Rocks . . . . . . .79

The Different Kinds of Igneous Rocks 82

Classification of Igneous Rocks for Mining Men 83

Additional Definitions 88

Transitions between Different Kinds of Igneous Rocks . . 93

Forms of Igneous Rocks 95

General Relation between Igneous Rocks and Ore-Deposits . 99
Special Relation between Certain Igneous Rocks and Ore-
Deposits Ill

Advantages of Different Forms of Igneous Rocks . . .111

Advantages of Different Kinds of Igneous Rocks . . .112

Preferences of Certain Igneous Rocks for Certain Ores,

. Displayed During the Cooling Processes . . .112
Preferences of Certain Igneous Rocks for Certain Ores,
Displayed by Selective Precipitation of Metals
from Solution 115



CONTENTS. IX

Page

Ore-bodies in the Role of Igneous Intrusive Rocks .... 117
Igneous Rocks Intrusive Subsequent to Ore-Deposition . .118

CHAPTER IV.

THE STUDY OF DYNAMIC AND STRUCTURAL GEOLOGY AS APPLIED
TO MINING.

Part I. General Conceptions and Mapping 120

Definitions . ' 120

Folds and Faults 121

Effects of Erosion on Folded and Faulted Rocks . .126

The Surface Mantle of Debris 130

The Systematic Working out of Geologic Structure . .133

Strike and Dip 133

Recording Observations on Maps 136

Migration of Outcrops 139

Construction of Geologic Sections . .''-. . . . 142
Economic Results of Mapping and Cross-Sectioning . 145
Mapping and Sectioning of Igneous Rocks . . . 147
Part II. Rock Deformation and Dislocation, and Their Con-
nection with Mineral Veins 148

Measurement of Folds and Faults 148

Folds and Faults as Loci of Ore-Deposition . . . .164

Deposition of Ore in Folds 164

Deposition of Ore along Faults 169

Joints in Rocks 173

Ore-Deposition along Joints 175

Fractures and Fissures 177

Deposition of Ores along Fractures and Fissures . . 184
Shear-Zones or Crushed Zones, and Their Suitability for

Ore-Deposition 193

General Relations Between Rock Disturbances and Ore-
Deposits 194

The Intersection of Circulation Channels as Seats of

Mineralization 195

Rock Movements Subsequent to Ore-Deposition . . . 197
Dislocations Subsequent to Ore-Deposition as Seats

for Later Mineralization 198

Ribbon Structure 199

Faulted Faults and Their Relation to Ore-
Deposition 200

Rock Movements along Earlier-Formed Dikes . . . 203



X CONTENTS.

Page

Part III. Placers 205

The Concentration of Gold in Placers 205

Concentration by Chemical Water-Action . . . 206

Concentration by Mechanical Water-Action . . . 208

Effects of Glacial Action 211

Various Kinds of Stream Gold-Placers 214

Beach Placers 218

Bench Placers 221

Old Placers 222

Fossil Placers 226

Re-concentrated Placers 227

Placers Other Than Gold-Placers 229

Residual Deposits 233

CHAPTER V.

THE STUDY OF CHEMICAL GEOLOGY AS APPLIED TO MINING.

The Study of Ore-Concentration . . 235

The Shallow Underground Waters 237

The Work of Underground Waters in Dissolving Rocks . . 239

The Work of Underground Waters in Precipitating Minerals . 242

Manner of Deposition in the Deeper Underground Regions . 244

Special Chemical Processes of the Shallow Underground Waters 255

Zone of Weathering or Oxidation 256

Precipitation of Ores at the Surface 259

Precipitation of Ores in the Shallow Underground Zone . 265

Concentration According to Relative Solubilities . 265

Secondary Sulphide Enrichment 269

Features of the Process of Reconcentration of Pre-
existing Ores by Shallow Descending Waters . 272
Examples of Secondary Alteration by Surface Waters . 278
Manner in which Minerals are Precipitated by De-
scending Waters 285

Characteristics of Ore-Deposits Formed by Ascending and

by Descending Waters 289

Changes in Richness in Depth 293

Association of Minerals 299

Rock Alterations as Guide to the Prospector 301

CHAPTER VI.

THE RELATION OF PHYSIOGRAPHY TO MINING.



ILLUSTRATIONS.



Fig, Page

1. Map of Gap Nickel mine, Lancaster, Pennsylvania . . . 11

2. Ideal sketch to illustrate unconformities 53

3. Cliff on Kuskokwim River, Alaska, showing lateral tran-

sition between sandstones and shales 64

4. Occurrence of ore in a definite stratum, introduced subse-

quent to the stratum's formation. Rico, Colorado . . 75

5. Limestone beds of Derbyshire, with intruded igneous rock

traversed by veins 76

6. Dikes cutting granite, Cape Ann, Massachusetts ... 97

7. Primary pyrrhotite in augite 101

8. Conditions in a copper vein at Butte, Montana .... 116

9. Iron-ore bodies in Lola mine, Santiago, Cuba . . . .118

10. Folding of limestones and shales, Kuskokwim River, Alaska 122

11. Close folding of limy shales, on Yukon River, Alaska . .122

12. Overthrown folds 123

13. A monoclinal fold 123

14. Faults in strata near Forty Mile, Alaska 124

15. Reversed fault in Empire mine, Grass Valley, California . 124

16. Compensating faults, Omaha mine, Grass Valley, California 125

17. Eroded anticlinal range of deformation, Uinta Range, Utah 127

18. Simple fault-scarp at the Palisades, Yukon River . . . 129

19. Reversed erosion fault-scarp in the Lower Austrian Alps . 129

20. Bank of Glacial drift, Gloucester, Massachusetts . . .132

21. Figure illustrating strike and dip 134

22. Symbol for recording strike and dip 138

23. Diagram of a topographic base for geologic cross-sections . 144

24. Stereogram illustrating the total displacement of a fault . 154

25. Stereogram illustrating various functions of a fault . . . 155

26. Stereogram illustrating the computation of a fault move-

ment, where part of the data is concealed .... 157

27. Stereogram of fault, where the lateral and perpendicular

separations are zero 158

28. Stereogram illustrating a bedding fault 158

29. Ideal vertical section of faulted stratified rocks, illustrating

fault functions .... .161



Xll ILLUSTRATIONS.

Fig. Page

30. Diagram illustrating the relations of throw and vertical

separation, in the case of a reversed fault 161

31. Diagram illustrating the term off set as applied to a fault . 163

32. Auriferous saddle veins, Bendigo, Australia 164

33. Diagram showing occurrence of ore shoots in pitching arches

or folds of the strata, Elkhorn mine, Montana . . .166

34. Vein formation in the fractured apex of an anticline; New

Chum Railway mine, Bendigo, Australia .... 167

35. Deposition of ores in anticlinal folds, with barren synclinals,

West Side Vein, Tombstone District, Arizona . . .168

36. Ore-deposition along faults, Bushwhacker-Park Regent

mine, Aspen, Colorado 170

37. Ore-deposition in the fissure along a minor fault, Eureka

vein, Rico, Colorado 172

38. Columnar jointing of basalt on Koyukuk Mountain, Yukon

River, Alaska 174

39. Formation of ores along joints, Monte Cristo, Washington 176

40. Sheet of glass cracked by torsional strain 178

41. Open fissure cutting and deflected by calcite vein, Mercur,

Utah 180

42. Granite quarry, showing increase of fractures and fissures

near the surface, Rockport, Massachusetts 183

43. Veins formed by the successive selection of different frac-

tures by mineralizing solutions, Ajax mine, Tintic, Utah 187

44. Disappearance or deflection of veins on passing from sand-

stone into shale, Bendigo, Australia 188

45. Deflection of veins in passing through slate, Bendigo,

Australia 188

46. Linked veins, Pachuca, Mexico 192

47. Ore shoot, Annie Lee mine, Cripple Creek, Colorado . . .196

48. Ribbon structure in quartz vein, Grass Valley, California . 201

49. Successive stages of faulting, Aspen, Colorado .... 202

50. Vein following a pre-existing dike, De Lamar, Idaho . . 204

51. "False bottom" of clay in gold placer deposit, Seward Penin-

sula, Alaska 210

52. Glacier-scooped basin containing auriferous glacial gravels,

Otago district, New Zealand 213

53. Irregular glacier-scooped depressions, filled with auriferous

glacial gravels, Otago district, New Zealand .... 213

54. Gulch placer, Koyukuk district, Alaska 215

55. Ideal river, showing accumulation of auriferous bars . . 217



ILLUSTRATIONS. Xlll

Fig. Page

56. Section of beach placers, Nome, Alaska 220

57. Bench and valley placers, Blue Mountains, Oregon . . 221

58. Generalized section of an old placer 223

59. Contour map of Neocene bedrock surface, Grass Valley,

California . 225

60. Old auriferous gravels (Miocene), Otago district, New

Zealand 226

61. Platinum placers, River Iss, Ural Mountains, Russia . . 230

62. Section of tin placers, Siak district, Sumatra .... 231

63. Fossil in native silver as evidence of ore-deposition by re-

placement (of limestone) 249

64. Ore-deposition by replacement of schist along crushed zone,

Otago, New Zealand 249

65. Ore-deposition at the intersection of two circulation chan-

nels, Rico, Colorado . . 252

66. Deposition of iron ore by descending waters in joints and

pockets in limestone, Pennsylvania Furnace, Pennsyl-
vania 270

67. Close relation of galena zone to surface, evidence of depo-

sition of descending waters, Monte Cristo, Washington . 281

68. Ore in the roof formed by intersecting fractures, as evidence

of deposition by ascending waters, Bendigo, Australia . 291

69. Iron-ore deposit formed by descending waters, showing

constant relation to surface, Mesabi range, Minnesota . 292

70. Gold in pyrite and quartz. Thin section of ore magnified.

Grass Valley, California 300



CHAPTER I.
THE PROCESSES OF ORE DEPOSITION.



METAMORPHISM, OR CHANGES IN THE EARTH'S

CRUST.

THE ORIGIN OF METAMORPHIC ROCKS.

7s the earth's surface stable?

The seemingly stable crust of our earth undergoes slow
but stupendous alterations. In the course of our brief
lifetime we may not notice them; but, if we do, we marvel
at them. Such things as a river that has shifted its course,
a harbor that becomes choked with sand, or a mud island
that is washed away by the waves, interest us strongly.
Yet the researches of geology show that, during the long
succession of centuries, rivers which run from the uplands
to the sea may entirely remove mountains and spread them
out as sediments upon the ocean floor. In the course of
time these deposits may be lifted above the sea again to
form new land; for the crust of the earth is not quiet, but
is forever heaving up and down, expanding, contracting,
bending and breaking, converting sea-bottoms into dry
land, sinking mountains into the sea, and crumpling plains
into mountains. All this goes on with such undemon-



2 . GEOLOGY APPLIED TO MINING.

strati ve slowness that those who live on the earth are
hardly made aware of these changes and are rarely dis-
turbed by them.

Example: Modern history records upward and downward
movements of the land at various points. It has lately
been ascertained that the whole region of the Great Lakes
is undergoing a slow tilting to the south-southwest. Meas-
urements, extending over a number of years, of the distances
between certain marks and the level of the lakes render it
probable that the region is being lifted on one side or de-
pressed on the other, and that the rate of change is such that
the two ends of a line 100 miles long and lying in a south-
southwest direction are relatively displaced four-tenths of a
foot in 100 years. The waters of each lake are rising on the
southern and western shores, or falling on the northern and
eastern shores, or both. At Toledo and Sandusky, the
water advances 8 or 9 inches in depth in a century. A
tract of land near Sandusky on which hay was made in
1828 is now permanently under water. In 3,500 years the
Falls of Niagara will cease to flow, as a consequence of this
movement.*

How may sedimentary rocks become metamorphic ?

Regions which were once deeply buried may become part
of the surface by the removal of the overlying mass; and
study of the rock thus revealed gives an idea of what goes
on in the depths of the earth. Among the lessons thus
learned is the following : When sediments have accumulated
(as they may in the course of ages), to a depth of several
miles, the lower layeis may be affected by the weight of

* G. K. Gilbert, 18th Annual Report United States Geological Survey :
Part II, pp. 601-645.



THE PROCESSES OF ORE DEPOSITION. 3

those above, by the internal heat of the earth and other
causes, so that chemical changes take place. The materials
begin to recrystallize, new minerals grow from the debris of
those in the sediments; and finally the rock becomes quite
different in appearance.

Sometimes we find such a rock with the marks of its
sedimentary origin still visible. Other rocks may be so
perfectly recrystallized that there is no direct evidence in
their structure that they ever were sediments, and we can
only determine this point in roundabout ways, as by
tracing the much altered rock into some less altered portion.
Such rocks are metamorphic; and they are chiefly divided
into schist and gneiss.



Example: In the northwest highlands of Scotland, on Ben
More and on Sgonnan More, movements in Cambrian con-
glomerates, sandstones and shales have produced extraor-
dinary changes. The conglomerate in its unaltered form is
composed of rounded pebbles in a loose, gritty matrix.
Where subjected to movement the softer pebbles have been
crushed, flattened and elongated in the direction of move-
ment. In some cases they have been drawn out to such
an extent as to form thin lenticular bands of mica or horn-
blende-schist, flowing around the harder pebbles of quartz.
The original gritty matrix has been converted into a fine
micaceous or chloritic schist. Were it not for the presence
of the crushed schistose pebbles it would probably be
impossible to tell that this schist had a sedimentary origin.*



* B. N. Peach, J. Home, W. Gunn, C. T. Clough, L. Hinxman, and H. M.
Cadell, Quarterly Journal, Geological Society, Vol. XL1V, pp. 431-432.



4 GEOLOGY APPLIED TO MINING.

How are igneous rocks formedf

The metamorphic rocks are related to another class of
crystalline rocks the true igneous rocks. The igneous rock
has crystallized from a molten condition. At the surface
the formation of igneous rock is illustrated by lavas, but such
rocks are formed on a grander scale beneath the surface.
An igneous rock has generally a fairly constant texture,
and is composed throughout of the same minerals, which
are often about the same size, and lie in different attitudes.
These characteristics arise from the circumstances that the
mass has been fluid before cooling, so that all parts come to
have about the same composition ; and since all parts have
cooled under nearly the same conditions, the resulting
minerals and structure are the same.

Why are metamorphic rocks often banded?

A true metamorphic rock has not been really fluid, in the
generally accepted sense of that word. At the most, the
effect of pressure and heat have made it slightly plastic, so
that it has yielded and slipped a very little. Therefore,
when it recrystallized, the materials did not move far in the
rock. If there were in the original sediments successive
v ayers of different nature, (such as dark ferruginous mud
beneath clean quartz sand), the recrystallized rock will
often preserve the banding; the mud will appear as a dark
layer of crystalline ferruginous minerals and the sand bed
will be represented by crystalline quartz.

Banded structure in metamorphic rocks may also be pro-
duced by more active crystallization along slipping planes
than in the rest of the rock.



THE PROCESSES OF ORE DEPOSITION. 5

May a metamorphic rock assume the characters of an
igneous rvck?

The conditions which make a mass plastic and those
which make it fluid are not sharply separated. A rock
undergoing metamorphosis may become so plastic and so
thoroughly recrystallized that the result will be the same
as if the rock had slowly cooled from a molten state. Some
igneous rocks are known to have been thus formed, by slow
metamorphism, from sediments. When we can prove the
origin of such rocks, we often prefix the term metamorphic
to them thus, metamorphic granite but often we can-
not tell whether a granite is metamorphic or igneous, for
the characters are alike.



May an igneous rock assume the characters of a metamorphic
rock?

An igneous rock may, by becoming subject to conditions
of long-continued slight plasticity and pressure, acquire the
characters of a true metamorphic rock. A slight move-
ment takes place, generally along close-set parallel planes,
and here an active recrystallization and a re-arrangement
of the minerals occur, resulting in a banded structure. The
rock may lose all the traces of its essentially igneous
character, and become a gneiss or schist, indistinguishable
from one that has formed by the alteration of sediments.



Example: The crystalline schists and gneisses of the
Malvern Hills, in England, have been formed by the meta-



6 GEOLOGY APPLIED TO MINING.

morphism of igneous rocks. Shearing has taken place in
bands of varying breadth situated at irregular intervals.
The gneissic structure usually shades off on each side of the
zone into ordinary igneous masses (diorite, granite, etc.),
and within the zone itself the metamorphism varies in
intensity. Proofs of mechanical forces resulting in shear-
ing are numerous. Hornblende crystals are drawn out
into ribbons, and feldspars are bent and broken. Fre-
quently black mica is formed along the shear-planes, so
that the rock splits into thin leaves whose surfaces glisten
with mica, while the interior may be dioritic. The chief
mineral changes are the recrystallization of feldspar, and
the production of biotite, muscovite, quartz and actinolite.*



TRANSFORMATION OF IGNEOUS AND METAMORPHIC ROCKS
INTO SEDIMENTARY ROCKS.

Can igneous and metamorphic rocks be changed back to sedi-
mentary ones?

The earth's surface consists in part of igneous and meta-


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Online LibraryJosiah Edward SpurrGeology applied to mining; a concise summary of the chief geological principles, a knowledge of which is necessary to the understanding and proper exploitation of ore-deposits, for mining men and students → online text (page 1 of 21)