PREFACE 



The work on this volume began in January 1972, 

 but in a broader sense its production began many 

 years ago. The chapters were written by geologists 

 most of whom have had many years of experience 

 studying the geology of mineral deposits, and more 

 particularly the commodities about which they have 

 written here. A total of nearly 2,300 man-years of 

 professional experience in the geology of mineral 

 resources is represented by the authors of the vol- 

 ume, and about 30 man-years went directly into its 

 preparation. Each chapter contains not only a syn- 

 thesis of the state of knowledge of the geology of 

 the commodity, but also an appraisal of the known 

 resources, and an examination of the geologic possi- 

 bilities for finding additional deposits. 



In January 1972, responsibility for the prepara- 

 tion of the volume was assigned to us as co-editors, 

 and we were given a tentative list of commodities 

 and authors. We provided each author with a sug- 

 gested outline of general topics to be covered, and 

 some guidelines as to scope and philosophy of ap- 

 proach, but beyond that we avoided any attempt to 

 fit each chapter into a stereotype. Moreover, the 

 types of commodities range from the major metals 

 and industrial minerals such as copper, silver, and 

 fluorspar, which have been the subject of geologic 

 research for years, to other commodities that are of 

 such varied geologic nature (such as pigments or 

 gemstones) or of such minor present importance 

 (such as scandium or thallium) that they cannot be 

 treated from the same viewpoint as the major min- 

 erals. The chapters range, therefore, from compre- 

 hensive summary reports to general essays that 

 reflect the individuality of the authors as well as 

 the variation among commodities. 



Throughout the book the emphasis is on geology, 

 but each chapter contains some summary informa- 

 tion on uses, technology, and economics. These sum- 

 maries are not meant to be exhaustive, however, and 

 additional details are in the 1970 edition of "Min- 

 eral Facts and Problems" (Bulletin 650 of the U.S. 

 Bureau of Mines) ; indeed, we regard that book and 

 the present volume as being complementary. 



In the examination of the geologic possibilities for 

 finding new deposits — in many respects the princi- 

 pal innovative contributions of this volume — we 

 asked the authors to frankly apply the limits of their 



ingenuity and not only to summarize current 

 theories but also to express their own intuitive ideas, 

 however speculative and unconventional they may 

 seem, that have come from years of study devoted 

 to the origin of mineral deposits. Readers will see 

 that some authors have speculated more coura- 

 geously than others. In any case, we believe readers 

 will find all the chapters interesting, and many 

 stimulating; and a few we believe can be frankly 

 characterized as intellectually exciting. 



Most chapters include a section on prospecting 

 techniques, and a summary of geologic or related 

 problems on which the authors believe research 

 might be most fruitful in the continuing efforts to 

 find new resources. 



An integral part of the book is the bibliographic 

 material cited at the conclusion of each chapter, in 

 lieu of repetition of detailed descriptions already in 

 print. Index and "spot" maps are not included in 

 most chapters because they are available elsewhere, 

 and in many cases with more detail than could pos- 

 sibly be included here. Maps showing the distribu- 

 tion of known deposits of many commodities in the 

 United States are available in the Mineral Resource 

 (MR) map series of the U.S. Geological Survey and 

 in the National Atlas of the United States. 



The first three chapters deal not with resources 

 of specific commodities but with general informa- 

 tion that is pertinent to the study of mineral re- 

 sources. In the introductory chapter we discuss the 

 purposes of the book, the distinctions between re- 

 serves and various categories of resources, and some 

 general conclusions drawn from our view of the book 

 in its entirety. In the second chapter V. E. McKelvey 

 discusses the problems of mineral-resource estimates 

 and public policy. In the third chapter, R. L. Erick- 

 son discusses some new points of view on the relation 

 of reserves and resources to the crustal abundance 

 of elements. 



We acknowledge with thanks the cooperation of 

 our colleagues in all phases of the preparation of 

 this volume. Whatever success the book may attain 

 is due entirely to a total effort. A paragraph of 

 acknowledgment originally submitted as a part of 

 the chapter on "Nuclear fuels" is given here instead 

 because we feel it applied to all chapters: "The 

 writers have drawn freely from published informa- 



