Gold, a chemical element with the symbol Au, is a highly sought-after precious metal, having been used as money, in jewelry, in sculpture, and for ornamentation since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold mining consists of the processes and techniques employed in the removal of gold from the ground. There are several techniques by which gold may be extracted from the Earth. Since the 1880s, South Africa has been the source for a large proportion of the world’s gold supply, with about 50% of all gold ever produced having come from South Africa. Other major producers are the United States, Australia, China, Russia and Peru. The world's oceans also hold a vast amount of gold, but in very low concentrations. At current consumption rates, the supply of gold is believed to last 45 years. This book will present current research on gold mining including methodologies for discovering new deposits of gold as well as economic and environmental issues. <...>

The term Rock Minerals is sufficiently indefinite to permit of considerable latitude in the choice of minerals to be included by it. Besides those that constitute the mass of any rock there are the less abundant though common kinds, as well as occasional, exceptional, ones. In any case the mineral may be an original constituent of the rock or one that has been developed in it subsequent to its formation. Rock Minerals, therefore, embrace not only all primary minerals, but all those of secondary origin produced by any manner of alteration of previously existing minerals.

In this, the first attempt to give in English a comprehensive review of petrographic methods, it cannot be otherwise than that there should be many omissions—it is to be hoped not many errors. If any is found the author will be extremely glad to have his attention called to it, as he will also be for criticisms, or suggestions for additional material that should be included.

The present work was carried out in partial fulfillment of the requirements for the degree of Doctor ol Philosophy at the University of Cincinnati. The author Blends his sincere thanks to the members of the Departments of Biological Sciences and Geology at the University fur generously giving of their time and knowledge during the preparation of the manuscript. Especial thanks is extended to Dr. К. Е. Caster, under whose direction the manuscript was prepared. I le was a source ol help and en-tonragement, and his invaluable library made many rare «inks readily available to me. 1 am indebted to Dr. Norman П. Newell for reviewing the manuscript and offering many helpful suggestions. To my "wife continuing thanks for proofreading and typing the greater bulk of the manu-Mtipt.

Miners and geologists have always known that the value of minerals in a given volume of ore depends heavily on the position of the ore in the orebody and on the value of the ground surrounding it. Thus, traditional methods of ore reserve estimation have attempted to combine data, on the position of the sample with an intuitive notion of "area of influence" to produce usable results. Polygonal and triangular weighting, rectangular zones of influence, and inverse distance methods were all developed so that both characteristics—spatial position and value of surrounding ground-would be included in the estimation. However, there is no objective way to measure the reliability of these estimating techniques.

Emphasis in this book has been placed on principles, methods, and technique. The structure of specific areas is not discussed, except for the purpose of illustrating principles. The writer has intentionally refrained from a treatment of the more speculative phases of geotectonics because he believes that such subjects can be intelligently studied only by geologists with a broad background in many fields of geology.

The indecisiveness of some of the criteria used in structural geology may cause dismay to some students. It is better, however, for the reader to realize the difficulties of structural geology and to understand at the outset that such a subject can never be treated with mathematical precision. The structural geologist must be proficient in weighing and balancing the evidence.

Structural geology records colossal work done by natural forces on the visible and invisible rocks of every continent. The energy expended in this work has been chiefly of two kinds—solar and terrestrial. Geologists of the nineteenth century paid particular attention to the part played by solar radiation in governing the dynamical history of the outer earth. A leading project of the twentieth century is to learn how the conditions of the planet's deep interior have also controlled the same history.

One purpose of this book is to advance the idea that many minerals are not fixed and simple in composition. Some years ago Professor D. Jerome Fisher of the University of Chicago pointed out that the writer's Elements of Optical Mineralogy had made such a treatment available to advanced students for some years, but that no elementary textbook, in any language, presented the subject in a similar way. A result of Dr. Fisher's suggestion has been the preparation of this volume.

Foreword

To honor the name of Waldemar Lindgren by this dedication of a volume on western ore deposits is altogether a natural and fitting tribute. For 46 years Geologist Lindgren has contributed, and contributed largely, to what the world knows of the metalliferous wealth of the Rocky Mountain region. As a Government geologist for more than a quarter of a century, he became the leader in that field of research, so that his painstaking methods of thorough field and laboratory study were made an essential part of the equipment of another generation of workers, who, in turn, added their contributions to the world's store of knowledge and of metals. Later, as a teacher in a great scientific and technical institute, Professor Lindgren has continued this leadership with an ever increasing circle of intellectual influence. This volume is at once proof of that leadership and tribute to the leader.

Equally appropriate is the linking of the name of the Rocky Mountain Club with this volume. That famous institution did not limit its interest to a simple topographic or orographic province but rather represented the traditions of the advancing western frontier and its visions of economic exploration and industrial development. As its successor in interest, the American Institute of Mining and Metallurgical Engineers has made a grant from the Rocky Mountain Fund for the publication of this volume as a research "of especial interest to the Rocky Mountain region." This use of income derived from the assets of an honored organization, which in so many ways fostered and furthered the interests of the West, will serve to perpetuate both the name and the spirit of the Rocky Mountain Club.

Waldemar Lindgren himself well illustrates one of the best phases of western development. Coming to the Rocky Mountain region as a young man, fresh from the schools of a country which has contributed to the world so many scientists and engineers, he applied his best energies to the tasks of the frontier. Success attended his efforts—not the spectacular success of a mining executive, but the more lasting success in the steady laying of foundations for a better understanding of the mineral wealth of the country by sharing his observed facts with others and passing along the torch of scientific truth. As opportunity offered, Lindgren widened his field of exploration and broadened his knowledge of ore deposits by adding Australia and South America, Mexico and Canada to his roll of scientific conquests.

It is this inspiring record of broad experience and personal attainment, both as investigator and as instructor, that makes the name of Lindgren so appropriate in its present setting; yet the enthusiastic cooperation of so many contributors to this volume is an expression of something more. " Guide, philosopher, and friend " aptly describes Waldemar Lindgren to all who have enjoyed the high privilege of close association with him. His genius has won our admiration, but it is the sincerity of intellect and kindliness of spirit that have bound to him a host of friends, some of whom have joined in this comprehensive tribute to the man and his chosen field of endeavor.

Structural geology may be defined as a study of the framework of the earth's crust and the causes that are distorting it. However, in its broader phases, structural geology deals with deformation of the entire earth and is not limited merely to the crust. Although we see only a thin rind and although information about the greater bulk of the earth, the unseen vast interior, must of necessity be based on indirect evidence— yet it is to deep-seated adjustments that many of the surface crumplings arc attributed. The central theme of structural geology, then, is the deformation of the earth, its causes and effects. Unerring interpretation of observed rock structures is the goal sought.

At the outset, any idea of immobility of the earth should be dismissed from our minds. The crust oscillates to the rise and fall of the tides. Continual shifting of enormous sedimentary loads through the agencies of erosion, transportation, and deposition is attended by both deep-seated and surface adjustments. The shape of the earth itself is largely a response to the rate of axial spinning; modify the speed of rotation, and a corresponding change in the earth's shape, with attendant deformation of the crust, would inevitably follow. In short, the earth is not inert but is ceaselessly changing, and complete rigidity has no place in structural geology.

Beginning students of geology soon realize that the earth's crust has failed many times and in many places. Mountains of folded rock have been pushed up thousands of feet; enormous areas of relatively undisturbed formations have been gently tilted; beds once forming below ocean level have been raised several miles above their place of origin. All these and a host of other examples present a clear picture of tremendous masses moved great distances. The total forces involved in these distortions must have been stupendous, and we arc prone to think that this is all of the distant past — surely no major deformation of the earth is going on today or we should be able to see and measure it.

Indeed, there seems to be a rather general assumption that the earth is now passing through a stage of relative quiet, resting, as it were, after widespread recent deformations. Thus, the present is considered by many to be a poor key with which to unlock the structural mysteries of the past. <...>