Structure and mineralization of the Oro Blanco Mining District, Santa Cruz County, Arizona Item Type text; Dissertation-Reproduction (electronic) Authors Knight, Louis Harold, 1943- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 27/09/2021 20:13:55 Link to Item http://hdl.handle.net/10150/565224 STRUCTURE AND MINERALIZATION OF THE ORO BLANCO MINING DISTRICT, SANTA CRUZ COUNTY, ARIZONA by * Louis Harold Knight, Jr. A Dissertation Submitted to the Faculty of the DEPARTMENT OF GEOLOGY In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 1 9 7 0 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE I hereby recommend that this dissertation prepared under my direction by Louis Harold Knight, Jr._______________________ entitled Structure and Mineralization of the Pro Blanco______ Mining District, Santa Cruz County, Arizona_________ be accepted as fulfilling the dissertation requirement of the degree of Doctor of Philosophy________________________________ a/akt/Z). m date ' After inspection of the final copy of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:* SUtzo. /16? QJr zd /rtf C e f i, r --------- 7-------- /?S? This approval and acceptance is contingent on the candidate1s adequate performance and defense of this dissertation at the final oral examination. The inclusion of this sheet bound into the library copy of the dissertation is evidence of satisfactory performance at the final examination. STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduc­ tion of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED: c y ACKNOWLEDGMENTS I wish to express my gratitude to The Anaconda Company for their support of this dissertation in the form of The Anaconda Company Scholarship. This award permitted the author to devote his full time to the study of the Oro Blanco mining district. Many individuals have aided me throughout the course of the study. I would especially like to thank Mr. G. A. Barber of The Anaconda Company for generously offering the drafting and laboratory facilities of his office. In addition Mr. Barber spent a day in the field with the author and has offered many helpful suggestions through­ out the course of the study. I have likewise profited from many dis­ cussions with Dr. R. C. Baker, also of The Anaconda Company. I wish to thank Dr. Evans B. Mayo and Dr. Willard C. Lacy of The University of Arizona who each spent a day in the field with the author and who reviewed this manuscript. Thanks also go to Dr. John W. Anthony, Dr. John M. Guilbert, and Dr. William C. Peters, all of The University of Arizona, for reviewing the manuscript. Mr; Fred Noon, rancher and historian, of Arivaca, Arizona, kindly supplied the author with history, shipping records, and assay data from various properties in the Oro Blanco mining district. I am also indebted to numerous property owners in the district for permission to examine the prospects and mines. iii XV The figures contained in this report arc the skillful work of Mr. W. D. Kaderli, draftsman for The Anaconda Company. Thanks also go to my wife Carol who assisted in the final stages of preparation of the manuscript. TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS viii LIST OF T A B L E S .................................................. % A B S T R A C T ...................................................... %i INTRODUCTION ......................... 1 Purpose and Scope ....................... 1 Location andAccessibility ................. 1 Summary of Physical Features ^ ^ to Field and Laboratory Work . 4 Previous Investigations . tn GENERAL GEOLOGY .................................................. 7 SEDIMENTARY AND VOLCANIC ROCKS 11 Jurassic (?) R o c k s .......... 11 Cobre Ridge Tuff .... 11 Cretaceous (?) R o c k s ........ 19 Oro Blanco Formation . 19 Age of Mesozoic Rocks . ... 27 Tertiary Rocks ............ 29 Montana Peak Formation . 29 Atascosa Formation . 37 Tertiary Gravels and Tuffs 41 Quaternary Rocks .......... 41 Gravels ................. 41 Regional Correlation .... 42 Las Guijas Mountains . 43 Pajarito Mountains . 44 Baboquivari Mountains . 47 Sierrita Mountains . 50 Patagonia Mountains . 53 Cerro Colorado Mountains 55 Summary . ............... 57 INTRUSIVE IGNEOUS ROCKS 58 Jurassic (?) Rocks . 58 Warsaw Quartz Monzonite 58 v vi TABLE OF CONTENTS— Continued Page Cretaceous (?) Rocks ................................. .. 62 Ruby Diorite ................ ........ 62 Tertiary Rocks .............................................. 64 Sidewinder Quartz Monzonite .... ................... < 64 Blue Ribbon Andesite ............... .. .............. 67 Rhyolite Dikes . ............... ................ .. 68 STRUCTURE.................................... 74 District Structure ................... .. ............. .. 74 North-northeast F a u l t s ......................... 74 Northeast Faults ................................ 75 Northwest Faults ..... ............................... 76 F o l d s ..................................... 79 Recent Structure ..................... .............. .. 80 Regional Structure . ................................. 81 Fraguita Peak Area, Oro Blanco M o u n t a i n s .......... .. 81 Las Guijas Mountains . ................................... 83 Pajarito Mountains ....... ........................ 84 Cerro Colorado Mountains ...... .................... 86 Sicrrita Mountains ......... .................... 86 Baboquivari Mountains . ................... ....... 88 Discussion of Regional Structure ......................... 88 Origin of District and Regional Structure .......... 91 Importance of Crustal Tension .................... 91 Evidence for Doming and Collapse ....................... 92 Mechanism for the Formation of the Structural P a t t e r n ......................... 93 Age of the Collapse Structure ........................... 102 . Relationship of Lineaments to Southern . Arizona Structure .......... .......... .... 103 Origin of Southern Arizona Basin and Range Structure .................................. 104 ECONOMIC G E O L O G Y ................................... 107 History and Production ........... ................ 108 Mineralization Types ........................... .. 110 Quartz-Sulfide V e i n s .................. 110 Silicificd Zones , ....................... 128 Breccia V e i n s .................. 139 Miscellaneous Mineralization ................... .... 144 Placers .......................................... 145 vii TABLE OF CONTENTS— Continued Page Alteration.................... 145 District Zoning ....... ........ .......... 147 Origin of the Mineral Deposits ............... 150 Discussion of Mineralization ..... ..................... 152 Economic Potential of the District ....... .......... 155 Influence of the Collapse Structure Upon Localization of Mineralized Districts ................. 157 GEOLOGIC H I S TORY................ 3,59 CONCLUSIONS .................................................... i66 REFERENCES C I T E D .......... I69 LIST OF ILLUSTRATIONS Figure Page 1. Index M a p .......... 2 2. Stratigraphic Column ....................................... 8 3. Geologic Map, Oro Blanco Mining District, Santa Cruz County, Arizona ............................... in pocket 4. Oro Blanco Conglomerate Member ............................. 22 5. Interbeddcd Pebbly Sandstone and Sandstone ................ 26 6 . Mule Ridge, Showing Members of Montana Peak Formation.................................... 36 7. Tuff Member of the Atascosa Formation ....................... 40 8. Regional Correlation C h a r t ............ ............ .. in pocket 9. Mountain Ranges of Southern Arizona ......................... 45 10. Geologic Map of the Fresnal Canyon Area, Baboquivari Mountains ................................. 49 11. Volcanic Neck Composed of Tertiary Rhyolite ................ 72 12. Interpretative Geologic Cross Sections, Oro Blanco Mining District, Santa Cruz County, Arizona .................. in pocket 13. Regional Geologic Map, Oro Blanco Area, Pima and Santa Cruz Counties, Arizona ....................... in pocket 14. Geologic Map of the Tascuela Area, Sierrita Mountains 87 15. Regional Structure Map ................................. in pocket 16. Formation of Collapse Structure.............. 98 17. Metal Occurrence Map, Oro Blanco and Pajarito Mining Districts ................................... in pocket viii ix LIST OF ILLUSTRATIONS— -Continued Figure Page 18. Surface Geology, Austerlitz Mine ....................... in pocket 19. Geologic