Metal Deposits in Relation to Plate Tectonics

337 Pages·1984·13.827 MB·English

by  Dr. Frederick J. Sawkins (auth.)

Minerals and Rocks 17
Editor in Chief
P.J.Wyllie, Chicago, IL
Editors
A. El Goresy, Heidelberg
W von Engelhardt, Tubingen . T. Hahn, Aachen
£1. Sawkins
Metal Deposits
in Relation to
Plate Tectonics
With 173 Figures
Springer-Verlag
Berlin Heidelberg New York Tokyo 1984
Dr. FREDERICK J. SAWKINS
Department of Geology and Geophysics
University of Minnesota
108 Pillsbury Hall
310 Pillsbury Drive S.E.
Minneapolis, MN 55455, USA
Volumes I to 9 in this series appeared under the title
Minerals, Rocks and Inorganic Materials
ISBN-13: 978-3-642-96787-0 e-ISBN-13: 978-3-642-96785-6
DOl: 10.1007/978-3-642-96785-6
Library of Congress Cataloging in Publication Data. Sawkins, Frederick J. Metal
deposits in relation to plate tectonics. (Minerals and rocks; 17) Includes index.
\. Ore-deposits. 2. Plate tectonics. 1. Title. II. Series. TN263.S27 1983 553.4
83-16890
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© by Springer-Verlag Berlin Heidelberg 1984
Softcover reprint of the hardcover 1st edition 1984
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Media conversion, printing and binding: Briihlsche Universitiitsdruckerei, Giessen
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Preface
I attempt this volume with no small degree of trepidation, for
despite the near universal acceptance of plate tectonic theory,
and the undeniable sweep and power of the concepts in
volved, points of controversy and uncertainty still abound.
This is especially true with regard to the limited extent to
which many ancient geologic terrains, however well studied,
lend themselves to plate tectonic interpretation. There is also
considerable controversy regarding the genesis of many metal
deposits, and this impacts upon the degree to which such
deposits can be meaningfully related to the tectonic settings
in which they occur.
It is relatively simple matter to point out that certain types
of ore deposits exhibit impressive time-space associations
with certain kinds of more recent plate boundary environ
ments. It is also all too easy to possible plate tectonic-ore
deposit relationships in ancient geologic terrains. What is
more challenging is the recognition of the boundaries beyond
which speculation is idle, but within which useful new insights
regarding the relationship of certain ores to their lithologic
and tectonic environments may emerge.
My interest in plate tectonic-metal deposit relationships
was initially motivated by a desire to find a suitable frame
work within which students could be introduced to the wide
variety of distinctive metal deposit types. Somewhat later it
was fostered by the desire to investigate the degree to which
such concepts could be used in creative planning of explora
tion programs. However, I have encountered a certain degree
of confusion about metal deposits and their divergent types
amongst students, exploration geologists, and geochemists
interested in ore genesis problems. We all have much to learn
regarding these matters, but an attempt as synthesis seems
warranted at this time, especially in view of our increasing
dependence on earth resources. I make no claim that applica
tion of plate tectonic concepts can pinpoint new metal depo
sits. The main tool available to the exploration geologist is
VI Preface
that of analogy with respect to other deposits and to their
lithologic settings, i.e., certain types of metal deposits occur
in association with certain types of rocks. The importance of
plate tectonics is simply that plate interactions spawn various
types of lithologic assemblages and, thus, such concepts can
considerably sharpen our perceptions and interpretations of
geologic terrains. As such, they can aid the exploration geo
logist in his(her) evaluation of various lithologic sequences
and the types of metal deposits that might have been gener
ated within them.
The study of metal deposits has accelerated a great deal in
the last two decades, in particular through geochemical study.
The application of fluid inclusion, stable isotope, and various
experimental techniques to the study of metal deposits has
broadened our insights into the chemical and hydrodynamic
aspects of ore formation. These advances have, in turn,
allowed the formation of more realistic conceptual models for
various types of ore generating systems. Such models are of
considerable aid to the exploration and mining geologist in
areas of known mineralization, but are of more limited utility
in terms of the search for new mineral districts.
The problem of the geographic distribution of metal
deposits must be addressed initially in terms of geologic and
tectonic environments rather than the nuances of ore solution
geochemistry. Endeavors in this field, it seems, have not kept
pace with those of a more geochemical nature (e.g. Barnes,
1979). In part, this is because geochemical research tends to
be more 'tidy' and amenable to institutional funding and
publication that the rather less rigorous and more empirical
aspects of regional synthesis and compilation. The latter have
to be based on some combination of personal experience and
literature research. An important point in this regard is that
metal deposits and the systems that generate them need to be
viewed not as geochemical accidents, but rather as fortunate
culminations of normal geologic and geochemical processes.
No one has made this point with more eloquence than
Wyllie (1981), who states that metal deposits are not "the
illegitimate offspring from random couplings of rocks and
fluids from intermediate sources," but "have respectable
... family lineages, with ancestors deep within the continental
crust, or below it."
The extent to which ore generating systems can proceed to
fruition and where they develop depends on a host of local
factors, but the broad environmental controls in each case
Preface VII
will be tectonic. It follows that if these tectonic controls result
in the main from plate interactions, and if plate tectonics have
operated throughout much of earth history, then a variety of
environments favorable for ore generation must have re
peated themselves through geologic time. A consequence of
these observations, if correct, is that major irregularities in
the time distribution of various metal deposit types require
explanation.
Ore deposits can be broadly divided into those generated
by endogenetic processes and those generated by exogenic
processes. The former are invariably associated with thermal
processes and, in general, can be related more readily to
magnetic and tectonic events instigated by plate activity.
Deposits formed by surficial processes such as weathering or
shallow marine sedimentation will have relationships to their
tectonic environment that are more tenuous.
This volume represents an attempt to provide a rational
basis for the observed time-space distribution of metal
deposits, at least those of endogenous type. Such deposits can
form by a wide variety of mechanisms in a highly diverse
spectrum of geologic environments, and it follows that their
relationships to plate tectonics will vary from significant in
some instances to more tenuous in others. In fact, it is
important to realize that even in cases where an impressive
association between plate tectonics and certain ore types is
manifest, plate interactions merely provide the master control
for the particular geologic environments within which such
deposits tend to form.
What I propose to do in the chapters that follow is deal
with specific plate tectonic environments and cover the ore
deposits that can be associated with each. Descriptions of
individual type examples for which abundant data exist are
provided to add substance to the volume. Additional exam
ples are catalogued, where feasible, but any exhaustive
compilation of world metal deposits is early beyond the scope
of this book. Certain of my interpretations of distant ore
deposits garnered from the literature will inevitably be in
error, and possibly enrage some of those with first-hand local
knowledge. To such people I can only offer an advance
apology and an exhortation to publish and set the record
straight. The line between creative synthesis and idle specula
tion is an extremely fuzzy one. I have included, wherever
feasible, some thoughts on how the relationship between
tectonics, geologic terrains, and metal deposits can be used
VIII Preface
in the context of exploration planning. Inevitably, such
thoughts will be of a speculative nature, but the literature on
ore deposits is notably lacking in attempts to do this. A
concerted attempt has been made to include up to date
references and to avoid references pertaining to obscure
sources or unpublished material, so that the interested reader
with access to a good geological library can backtrack on any
particular subject.
It is hoped that this book will prove useful to students at
the advanced undergraduate and graduate levels, and to
mining and exploration geologists. lowe no small debt of
gratitude to various company geologists around the world for
their willingness to share freely of their time and local ex
pertise with an itinerant academic. Without their enormous,
and sometimes unheralded, contributions, the science of eco
nomic geology would be sad shape indeed, and in recognition
of this, I dedicate this volume to them. I am also indebted to
the front line troops such as Richard Sillitoe, who, not only
have covered vast amounts of territory, but have written
lucidly and imaginatively about their observations.
Finally, it is hoped that we will be able eventually to
use "fundamental ore deposit geology to elucidate plate
tectonics, not (only) the reverse" (Guilbert, 1981).
Acknowledgments. The initial typescript of this book was produced by Kathy
Ohler, for whose competent, patient, and always cheerful help I am most
grateful. The figures were draftet by Roxann Cioper and Jim Kiehne, and
I thank them for their timely aid.
lowe a special debt of gratitude to Richard Sillitoe who reviewed nearly
all stages of the manuscript and corrected a number of my misconceptions.
Discussions with my colleagues at the University of Minnesota were also
most helpful. Finally, my thanks to Peter Wyllie for initially suggesting the
project and for encouragement during its evolution.
Frederick J. Sawkins
Contents
Introduction: Plate Tectonics and Geology . . . . .
Part I Convergent Plate Boundary Environments
Chapter 1 Principal Arcs and Their Associated Metal
Deposits . . . . . 14
1.1 Porphyry-Type Deposits. 14
1.1.1 Associated Igneous Rocks . 16
1.1.2 Mineralization and Alteration Patterns 17
1.1.3 Fluid Inclusions and Stable Isotopes . 18
1.1.4 The EI Salvador Porphyry Copper Deposit, Chile 19
1.1.5 Genetic Models for Porphyry Copper Deposits 21
1.1.6 Suggestions for Exploration . 22
1.2 Copper-Bearing Breccia Pipes . . . . . . 23
1.2.1 Distribution and Associated Igneous Rocks 23
1.2.2 Mineralization and Alteration . . . . . . 23
1.2.3 Formation and Mineralization of Breccia Pipes 24
1.2.4 The Cumobabi Breccia Pipe Deposits, Mexico 26
1.2.5 Suggestions of Exploration 29
1.3 Skarn Deposits. . . . . . . . . . . . . 30
1.3.1 Distribution and Associated Igneous Rocks 30
1.3.2 Mineralization. . . . . . . . . . . . . 31
1.3.3 Genesis of Contact Metasomatic Skarn Deposits 34
1.3.4 Discussion and Suggestions for Exploration 36
1.4 Vein Deposits . . . . . . . . . . . . . 38
1.4.1 Distribution and Associated Igneous Rocks 38
1.4.2 Mineralization and Alteration . . . . . . 39
1.4.3 The Baguio, Philippines and Tayoltita, Mexico
Vein Systems . . . . . . . . . . . . . 39
1.4.4 Discussion and Suggestions for Exploration . . 46
x Contents
1.5 Precious Metal Deposits of the Western United
States. . . . . . . . . . . . . . . 46
1.5.1 Vein Deposits .......... . 46
1.5.2 Carbonate-Replacement Gold Deposits 49
1.5.3 Hot Spring-Type Gold Deposits . . . 53
1.5.4 Discussion. . . . . . . . . . . . . 55
1.6 Additional Deposits of Principal Arcs . 55
1.6.1 Massive Magnetite Deposits . 55
1.6.2 Manto-Type Copper Deposits 56
1. 7 Discussion......... 58
Chapter 2 Metal Deposits on the Inner Sides
of Principal Arcs . . . . 61
2.1 Contact Metasomatic Deposits. 62
2.1.1 Mineralization. . . . . . . . 62
2.1.2 The Providencia Ag-Pb-Zn-Cu Deposit,
Zacatecas, Mexico . . . . . . . . . . 66
2.1.3 Discussion and Suggestions for Exploration 68
2.2 Polymetallic Vein Systems. . . . . . . . 69
2.2.1 The Casapalca Ag-Pb-Zn-Cu Deposit, Peru . 70
2.2.2 Discussion and Suggestions for Exploration 72
2.3 Tin-Tungsten Deposits . . . . . . . . .. 74
2.3.1 Mineralization. . . . . . . . . . . . .. 77
2.3.2 The Llallagua Tin Porphyry Deposits, Bolivia 78
2.3.3 Discussion and Suggestions for Exploration 81
Chapter 3 Metal Deposits of Arc-Related Rifts .. 82
3.1 Climax-Type Porphyry Molybdenum Deposits 83
3.1.1 Mineralization and Alteration Patterns . . 85
3.1.2 Discussion and Suggestions for Exploration 88
3.2 Additional Lithophile Suite Deposits
in Arc-Related Rifts . . . . . . . . 91
3.3 Kuroko-Type Massive Sulfide Deposits 92
3.3.1 Mineralization and Alteration Patterns 96
3.3.2 Fluid Inclusion and Stable Isotope Data. 99
Contents XI
3.3.3 Buchans Polymetallic Sulfide Deposit,
Newfoundland. . . . . . . . . . . 101
3.3.4 Discussion and Suggestions for Exploration 105
3.4 Base and Precious Metal Vein Deposits 106
Chapter 4 Additional Aspects of Arc-Related
Metallogeny . . . . . . . . . .. 109
4.1 Metal Deposits Related to Fore-Arc Felsic
Magmatism . . . . . . . . . . . . .. 109
4.2 Paleozoic and Older Porphyry Copper Deposits 110
4.3 Massive Sulfide Deposits of the Caledonides,
Scandinavia . 112
4.3.1 Similar Massive Sulfide Deposits Elsewhere 115
4.4 Massive Sulfide Deposits in Greenstone Belts 118
4.4.1 The Kidd Creek Massive Sulfide Deposit, Ontario 121
4.4.2 Discussion and Suggestions for Exploration 123
4.5 Additional Aspects of Greenstone Belt
Metallogeny . 124
4.6 Gold Deposits in Greenstone Belts 128
4.6.1 The Homestake Gold Mine, South Dakota 129
4.6.2 Discussion and Suggestions for Exploration 132
4.7 Overview of Arc-Related Metallogeny. 132
4.7.1 Relation of Arc Metallogeny to Subduction Style 132
Part II Divergent Plate Boundary Environments
Chapter 5 Metallogeny of Oceanic-Type Crust 138
5.1 Generation of Oceanic-Type Crust 138
5.2 Contemporary Mineralization at Oceanic
Spreading Ridges. 141
5.2.1 The Salton Sea Geothermal System . 143
5.3 Massive Sulfide Deposits of the Troodos
Ophiolite, Cyprus 144
5.4 Additional Examples of Cyprus-Type Massive
Sulfide Deposits 147