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The Geology and Geochemistry of the Summit Creek Molybdenum Prospect, Custer County, Idaho

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The Geology and Geochemistry of the Summit Creek Molybdenum Prospect, Custer County, Idaho Western Michigan University ScholarWorks at WMU Master's Theses Graduate College 4-1983 The Geology and Geochemistry of the Summit Creek Molybdenum Prospect, Custer County, Idaho Thomas Murray Hanna Follow this and additional works at: https://scholarworks.wmich.edu/masters_theses Part of the Geology Commons Recommended Citation Hanna, Thomas Murray, "The Geology and Geochemistry of the Summit Creek Molybdenum Prospect, Custer County, Idaho" (1983). Master's Theses. 1599. https://scholarworks.wmich.edu/masters_theses/1599 This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. THE GEOLOGY AND GEOCHEMISTRY OF THE SUMMIT CREEK MOLYBDENUM PROSPECT, CUSTER COUNTY, IDAHO by Thomas Murray Hanna A Thesis Submitted to the Faculty of The Graduate College in partial fulfillment of the requirements for the Degree of Master of Science Department of Geology Western Michigan University Kalamazoo, Michigan A pril 1983 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THE GEOLOGY AND GEOCHEMISTRY OF THE SUMMIT CREEK MOLYBDENUM PROSPECT, CUSTER COUNTY, IDAHO Thomas Murray Hanna, M.S. Western Michigan University, 1983 The Summit Creek stock, a molybdenum prospect located in the Pioneer Mountains of central Idaho, is a 46.7 m.y. old medium grained, slightly porphyritic quartz monzonite, which has intruded the late Ordovician Phi Kappa formation. Trend surface analysis shows that the stock is the product of one intrusive event. Perva­ sive mineral alteration usually associated with such porphyry (stockwork) molybdenum deposits is not present in this pluton, and the alteration that is present is confined to local faults and fractures. Geochemical and petrographic evidence suggest that the pluton is a fe ls ic d iffe re n tia te from a melt which originated at a depth of 220-260 kilometers along an east-dipping subduction zone. Whole rock major element geochemical analysis indicates that the stock is . a high potassium calc-alkaline in trusion . Trace element analysis shows sim ilarities to other stocks associated with economic molyb­ denum deposits. In addition, chemical analysis of a rg i11ic assem­ blages are sim ilar to those of porphyry molybdenum deposits. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS My thanks to Utah International for their financial and logistical support during the field work on this project. In particular, I would like to thank Richard J. Thompson who started me in economic geology and fo r his guidance and stim ulating discussion of the area. Also thanks to Miles G. Shaw for his support and help in the field. Additional thanks go to Chris Schmidt, Cynthia Wood fo r their review of the manuscript, and Ron Chase for his discussions in the field. I would like to thank John Grace for his critical review of this paper and his help with the laboratory procedures. Thomas Murray Hanna Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INFORMATION TO USERS This reproduction was made from a copy of a document sent to us for microfilming. While the most advanced technology has been used to photograph and reproduce this document, the quality of the reproduction is heavily dependent upon the quality of the material submitted. 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When a map, drawing or chart, etc., is part of the material being photographed, a definite method of “sectioning” the material has been followed. It is customary to begin filming at the upper left hand comer of a large sheet and to continue from left to right in equal sections with small overlaps. If necessary, sectioning is continued again—beginning below the first row and continuing on until complete. 4. For illustrations that cannot be satisfactorily reproduced by xerographic means, photographic prints can be purchased at additional cost and inserted into your xerographic copy. These prints are available upon request from the Dissertations Customer Services Department. 5. Some pages in any document may have indistinct print. In all cases the best available copy has been filmed. University Microfilms International 300 N. Zeeb Road Ann Arbor, Ml 48106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1320628 HANNA, THOMAS MURRAY THE GEOLOGY AND GEOCHEMISTRY OF THE SUMMIT CREEK MOLYBDENUM PROSPECT, CUSTER COUNTY, IDAHO WESTERN MICHIGAN UNIVERSITY M.S. 1983 University Microfilms International 300 N. Zeeb Road, Ann Arbor, MI 48106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE: In all cases this material has been filmed in the best possible way from the available copy. Problems encountered with this document have been identified here with a check mark V 1. Glossy photographs or pages. 2. Colored illustrations, paper or print 3. Photographs with dark background i / ' 4. Illustrations are poor copy _______ 5. Pages with black marks, not original copy. 6. Print shows through as there is text on both sides of page. 7. Indistinct, broken or small print on several pages ' i s ' ' . 8. Print exceeds margin requirements 9. Tightly bound copy with print lost in spine____ 10. Computer printout pages with indistinct print. 11. Page(s) ______lacking when material received, and not available from school or author. 12. Page(s) seem to be missing in numbering only as text follows. 13. Two pages numbered . Text follows. 14. Curling and wrinkled pages __ 15. O th e r . ■ _______________________________ University Microfilms International Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ACKNOWLEDGMENTS ........ .... ................... i i LIST OF FIGURES . ................. ..... ........ v LIST OF PLATES . .... vi LIST OF TABLES . ..... ........ v ii Chapter I. INTRODUCTION ......... ........ 1 Purpose o f Study . ........... 1 Location .................. 1 Description of Study Area . ........ 1 Geology o f the Pioneer Mountains ........... 3 Stratigraphy............... ... .................... 3 Igneous Units . 8 Structure .............. ............... 10 Regional Ore D e p o sits ................... ... .................... 11 Plate Subduction and Porphyry Molybdenum Deposits . 11 Porphyry Molybdenum Systems in North America ..... 14 Alteration .................... 15 Mineralization .................. 17 I I . ANALYTICAL PROCEDURES ................. 22 Sampling ....... .................. 22 Petrographic Analysis . .... 23 Geochemical Analysis .... ................... 23 iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chapter I I I . GEOLOGY OF THE SUMMIT CREEK AREA . 28 Sedimentary Rocks . ........... 28 Igneous Rocks ................ ........................31 Structure ........ ...................... 34 Breccia ................... .......................... 36 Mineralization .................. 36 Alteration . ...................... 38 IV. PETROGRAPHY . ........ ... ........ 40 Quartz Monzonite . 40 Altered Quartz Monzonite ..................... .... 42 Breccia ........................ 43 V. STATISTICAL ANALYSIS ............ 44 Discussion of Trend Surface Analysis Method and Presentation o f Data . .................... 44 VI. PETROGENESIS . ............... 52 Petrogenesis of the Summit Creek Stock . 52 Emplacement . .................. 52 V II. CHEMICAL ANALYSIS . ..... .... 55 Whole R o c k .................. 55 Trace Element . ............... 57 Geochemistry of Altered Rocks ............. 61 V III. CONCLUSION ................... 64 BIBLIOGRAPHY ......... ..... 67 iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES FIGURE 1. Location map o f the Pioneer Mountains and study area . ............... .... ... 2 2. General geologic map of Idaho and location of the Pioneer Mountains .................... 4 3. General s tra ti graphic column of the Pioneer Mountains . .................. 5 4. Depth to subducting slab for differentiated
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