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Some Facts About Ore Deposits By G. Montague Butler 1935 Soft Cover
Some Facts About Ore Deposits By G. Montague Butler
Arizona Bureau Of Mines, Geological Series No. 8 August 15 1935
Bulletin No. 139
PUBLISHED BY University of Arizona
TUCSON, ARIZONA
PREFACE
This little book consists principally of a series of articles that appeared during 1919 and 1920 in the Arizona Mining Journal (now the Mining Journal) , published at Phoenix, Arizona.* Each chapter represents one article, and, in most instances, no material changes have been made in these articles, although the last two chapters and the appendices are new and some material has been added to each of the other chapters in order to bring them up to date.
The series was originally written for prospectors or miners who are interested in the theoretical aspects of their vocation, and who are honestly seeking to learn the truth. So many mining engineers, geologists, and students of these subjects have, however, commented favorably upon the articles and expressed a desire to obtain them in book form that it is hoped they will prove to have some value to a wider audience than that for which they were originally written.
The statements made are not original contributions to knowl-edge, and rarely represent merely the personal opinions and ideas of the writer. In most instances the convictions expressed are the common heritage of all students of geology and mining, and may be accepted unquestionably as representing the concensus of opinion of the great majority of such men. The assertions set forth cannot all be proven, and no attempt to prove them is made; they are the fruit of diligent and careful observations made by thousands of scientists and mining engineers scattered all over the world. While time may prove some of them to be incorrect, and will doubtless add much to our knowledge of several of the points discussed, most of the views presented may be accepted as having become so firmly established that there is small possibility that they will ever be successfully assailed. It has been necessary to indulge in broad generalizations, and it is admitted that numerous exceptions exist to specific rules given. It is believed, however, that it would prove confusing to discuss such exceptions.
Most of the chapters were originally published as part of a series entitled, "Some Common Mining Fallacies." It has been the aim of the writer, however, not so much to lay emphasis upon "Mining. Fallacies" formed, then, merely a pretext for the presentation of facts, or what the majority of mining geologists believe to be facts; and no apology seems necessary when comparatively little is said about fallacies and much about facts, as is the case in several of the chapters.
It is realized that some of the topics very briefly presented herewith might profitably be greatly expanded, but it was not the desire of the writer to trespass upon the field of several excellent and exhaustive treatises already in print, to which reference is made in the bibliography. It is hoped that many readers will be led to seek in these works further light on sub-jects of such interest and importance to our mineral industries.
While, as previously stated, almost every fact herein presented has already appeared in print, most of the chapters were written from memory without immediate reference to the literature of the subject, and it would require a vast amount of time and trouble to locate the sources of the data set forth. The writer sincerely regrets that he is not in a position to give proper credit for his ideas, and offers his apologies to anyone who may feel that his work has been slighted.
Doctor B. S. Butler and Doctor R. J. Leonard have read the manuscript critically, and the writer has adopted a number of suggestions made by them. His sincere thanks are extended to them for their invaluable assistance and encouragement.
G. M. BUTLER.
August 15, 1935.
TABLE OF CONTENTS
CHAPTER
PAGE
I.-The Higher Values with Increased Depth Myth 7
A Widespread, but Fallacious, Belief 7
The Deposition of Ore 7
Ore Deposits Usually Decrease in Value with Increasing Depth 9
Explanation of the Prevalence of the Fallacy 10
Conclusion 11
II.-The Change of Character of Ore with Increased Depth Myth 13
The Facts 13
The Primary Ore Zones 14
The Silver Zone 15
The Lead Zone 16
The Zinc Zone 16
The Arsenic Zone 16
The Copper Zone 16
The Iron-Gold Zone 17
The Rare Metals or Pegmatite Zone 17
Other Facts Relating to the Primary Ore Zones 17
Emmons' Table of Ore Zones 18
Arrangement of Deposits in Zones on the Surface 20
Examples 21
III.-Some Myths Relating to Leaching 23
Some False Ideas Stated 23
Veins and Similar Structures Do Not Always Contain Valuable
Minerals 23
Some Minerals Are Not Normally Subject to Leaching 23
Leaching or Mechanical Removal of Valueless Minerals May
Result in Enrichment 25
IV.-Some Myths Relating to Secondary Enrichment 28
Secondary Enrichment Defined 28
Enriching Processes 28
The Secondary Enrichment of Gold 29
The Secondary Enrichment of Sulphides 31
Some Fallacious Ideas 34
Important Influence of Carbonates 35
V.-The Phonolite Myth 37
The Title Explained 37
The Rocks Associated with Gold Deposits 38
The Rocks Associated with Silver Deposits 39
The Rocks Associated with Lead and Zinc Deposits 39
The Rocks Associated with Copper Deposits 40
The Rocks Associated with Mercury Deposits 40
The Rocks Associated with Chromium Deposits 40
The Rocks Associated with Tin Deposits 40
The Rocks Associated with Tungsten Deposits 41
The Rocks Associated with Platinum Deposits 41
CHAPTERPAGE
VI-Some Myths Relating to Outcrops 43
Introductory 43
Valuable Deposits Not Always Marked by Prominent Outcrops 43
Veins Do Not Always Widen Below Their Outcrops 45
No Fixed Relationship Exists Between Length of Outcrop and Depth to Which Development May Profitably be Carried 46
The Presence of Certain Species of Plants Not a Very Reliable
Indication of the Existence of an Outcrop 47
Additional Observations on Outcrops 48
VII.-The Blowout Myth 51
Foreword 51
A Blowout Defined 51
Few Mineral Deposits Were Originally Molten 51
"Burnt" Outcrops Not Necessarily Indicative of Volcanic Activity 52
Ore Deposits Not Invariably Precipitated from Water Solutions 53
The Facts About So-called Blowouts 54
VIII.-Some Fallacies Relating to Ore Shoots 58
An Ore Shoot Defined 58
The Nature of Ore Shoots 59
Conditions Favoring the Formation of Ore Shoots 59
Veins and Mineralized Structures Do Not Always Contain Ore
Shoots 61 Ore Shoots Not Always Found Where Conditions Seem Favorable 62 Conditions Favoring the Development of Ore Shoots in One Lo-
cality May Not Do So Elsewhere 63
No Fixed Relation Exists Between the Horizontal and Vertical
Dimensions of Ore Shoots 64
IX.-The Aluminum Myth 65
An Erroneous Idea 65
The Facts About Aluminum 65
Other Valuable Substances Unrecoverable from Some of their
Compounds 67
The Myth Illustrated 68
Remarks on Complete Analyses 69
X.-The Divining Rod Myth 71
An Ancient and Widely Held Idea 71
Nature of Instruments Used 71
Possibility that Divining Rods May Have Been Used Successfully 72
All Users Not Imposters 72
Facts Bearing on the Solution of the Problem 73
Theories Explaining the Action of Divining Rods 73
Divining Rods and Geophysical Instruments Differentiated 76
Classification of Geophysical Methods 76
Practical Value of Geophysics 77
Appendix A.-Brief Descriptions of Minerals Mentioned 79
Appendix B.-Rocks 94
Igneous Rocks 94
Clastic Rocks 94
Chemical Precipitate Rocks 95
Organic Rocks 95
Metamorphic Rocks 95
Description of Rock Species Mentioned 95
Selected Bibliography 99
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