The principles of economic geology / Принципы экономической геологии

Since the first edition of the "Principles of Economic Geology" appeared in 1918, great progress has been made in the subject. In the preparation of this, the second edition, it was desired to bring the general treatment and the descriptions of mining districts up to date and at the same time not to increase greatly the size of the book. To do this the descriptions have been cut down where possible and the number of maps and other illustrations has been increased considerably. It is believed that this is desirable because most geologists find maps and sections easier to read and often more illuminating than long descriptions. The number of footnote references has been greatly increased.

The text has been completely reset and rewritten. A few illustrations appearing in the first edition have been retained, but nearly all those appearing in the second edition are new. The number of illustrations is increased from 210 to 329.

In the first edition the subjects most emphasized were genesis and enrichment. In the present edition the subject of structural control of the deposits is given equal weight. This has been made possible because of the very great increase in the number, and often in the quality, of the maps and sections of reports that have appeared in the past twenty-two years.

Since the first edition appeared, there have been many changes in terminology. The terms "hypogene," "supergene," "pyrometasoma-tic," "hypothermal," "mesothermal," "epithermal," and many others have been widely accepted and are in general use. These are used in this text, but frequent reference is made to their earlier synonyms. Undoubtedly the use of these terms improves the terminology of the science, yet in order to use the earlier literature of the subject, the student should know the older, widely used synonyms. In general the older synonyms or both terms are used in the first ten chapters of the text.

In the past twenty-five years the great contributions to economic geology have been made possible by the detailed mapping of areas that contain ore deposits. As a result the relations of ore deposits to their geologic environments have become better known. Hypogene zoning, the position of deposits with respect to igneous intrusions, particularly with respect to the roofs of batholiths, have become apparent. These subjects and related hypotheses have greatly interested the writer, and they have been rather fully treated in "Gold Deposits of the World, issued in 1937. That seemed permissible since the book mentioned is not a text. In a textbook such hypotheses, which perhaps are not sufficiently "aged" and which are not everywhere accepted may be stated, but not with an air of finality, and they are not given great prominence herein. Perhaps it is the duty of the writer of a text to present the subject as it is accepted by a majority of those active in the investigation of the subject. At least he should not become an enthusiastic advocate of insufficiently tried and debatable theories. Important working hypotheses, however, should be presented and discussed.

The treatment of the subject of supergene sulphide enrichment has been abridged somewhat. That seemed desirable in order to gain space for the descriptions of a very considerable number of the great sulphide deposits developed since 1918 that are chiefly or entirely hypogene. Most of the newer chemical data pertaining to supergene enrichment are introduced although the treatment of the details of the processes has been abridged. Other chapters of the general treatment have been shortened to make space for maps, sections, and short descriptions of deposits outside the United States, hundreds of which have appeared for the first time in the past twenty-two years.

As in the first edition, the book is divided into two parts: (1) a general treatment of the subject and (2) a treatment separately of metals and nonmetals, except fuels. Extensive rearrangements of chapters of the first part have been made: the chief one of these is the treatment of structural control of epigenetic deposits as a separate unit. This chapter is the last one of those (I to XVI) treating the general subject. Placing this chapter after the one treating the general subject of genesis (XV) may seem illogical, but it has the advantage of giving emphasis to structural control, and Chapter XVI is written so that it may, with advantage, be reviewed after the last chapter (XXIV) of the text has been read.

I acknowledge my indebtedness to Professors F. F. Grout, C. R. Stauffer, G. M. Schwartz, J. W. Gruner, G. A. Thiel, and to Mr. F. B. Hanley of the Department of Geology and Mineralogy of the University of Minnesota; and to Dr. D. M. Davidson, who has read critically the section of African copper deposits; to Dr. Т. М. Broderick, who has read sections on Lake Superior copper and iron deposits; and to Dr. Т. Т. Quirke, who read the section on Sudbury. The chapters on genesis were read by Dr. M. H. Frohberg. Other contributions are acknowledged where they appear. Most of the drawings were made by, W. I. Gardner, L. K. Lancaster, H. S. Norman, W. C. Lawson, Reino Ranta, K. C. Silgen, H. J. Maiers, and Mrs. Louise Bush, all of whose services are gratefully acknowledged.