University of Nevada Reno omparative Geology and Geochemistry With Respect to \/PPrecious Metal Mineralization of Selected California Coast Range Mercury Mining Districts A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science by Hilbert Nathaniel Shields Mines Library University of Nevada - Reno Reno, Nevada 89557 May, 1982 MINES UMRAJUT I s 17 5A The thesis of Kilbert N. Shields is approved: Thesis Advisor University of Nevada Reno May 1983 11 TABLE OF CONTENTS Page Acknowledgement...................................... vii A b s t r a c t ............................................ viii Introduction ......................................... 1 Purpose of Study ............................... 1 Selection of Areas of Study .................. 2 Method of S tudy ................................. 4 Geology of Areas of Study ............................. 7 Coast Range Regional Geology..................... 7 General Geologic Setting..................... 7 Mineralogy of Mercury Deposits.............. 12 Sulphur B a n k .................................. 14 Introduction............................... 14 Regional Geology ......................... 17 Stratigraphy............................... 17 Mineralization............................. 19 Results of Sampling........................ 22 Syar Quarry-St. John's Mine Area ............... 25 Introduction ............................. 25 Regional Geology ............................ 27 Stratigraphy ............................. 28 Mineralization ........................... 30 Results of Sampling........................ 31 Mt. Diablo Mine A r e a ........................... 35 Introduction ............................. 35 Regional Geology ......................... 37 Stratigraphy............................... 37 Mineralization............................. 39 Results of Sampling........................ 41 Guadalupe Mine A r e a ........................... 44 Introduction............................... 44 Regional Geology ......................... 46 Stratigraphy ............................. 47 Mineralization............................. 49 Results of Sampling........................ 50 Ill page Ambrose Comstock Mine Area......................54 Introduction...............................54 Regional Geology...........................56 Stratigraphy................................57 Mineralization.............................61 Results of Sampling........................ 64 New Idria Mine Area............................ 69 Introduction...............................69 Regional Geology .......................... 7 0 Stratigraphy................................ 72 Mineralization..............................74 Results of Sampling........................ 76 Rinconada Mine Area ........................... 79 Introduction................................79 Regional Geology ........................ 81 Stratigraphy...............................81 Mineralization.............................. 83 Results of Sampling........................ 83 Discussions and Interpretations...................... 8(5 Geochemistry .................................. 86 Introduction............................... 86 Cluster Analyses on an n x m Data Matrix. 90 Cluster Analyses on an n x n Data Matrix. -103 Silica-Carbonate Rocks ........................ 106 Conclusions.................................... 109 Bibliography........................................ Ill Appendix............................................ 114 IV ILLUSTRATIONS (Plates are in Pocket) Plate 1. Geologic and Sample Location Map, Sulphur Bank Mine Area, Clear Lake County, California 2. Geologic and Sample Location Map, Syar Quarry - St. John's Mine Area, Solano County, California 3. Geologic and Sample Location Map, Mt. Diablo Mine Area, Contra Costa County, California 4. Geologic and Sample Location Map, Guadalupe Mine Area, Santa Clara County, California 5. Geologic and Sample Location Map, Ambrose-Comstock Mine Area, San Benito County, California 6. Geologic and Sample Location Map, New Idria Mine Area, San Benito County, California 7. Geologic and Sample Location Map, Rinconada Mine Area, San Luis Obispo County, California GRAPHS Page Graph 1. Bar Graph Showing Distribution of Elements Found at Sulphur Bank Mine Area . 23 2. Bar Graph Showing Distribution of Elements Found at Syar Quarry-St. John's Mine A r e a ................................ 33 3. Bar Graph Showing Distribution of Elements Found at Mt. Diablo Mine Area. .42 4. Bar Graph Showing Distribution of Elements Found at Guadalupe Mine Area . .51 5. Bar Graph Showing Distribution of Elements Found at Ambrose-Comstock Mine A r e a .................................... 65 6. Bar Graph Showing Distribution of Elements Found at New Idria Mine Area . .77 V 7. Bar Graph Showing Distribution of Elements Found at Rinconada Mine Area. 8 4 FIGURES Figure 1. Index Map of California Showing Location of Mine Areas Studied...................... 3 2. Simplified Tectonic Map of California. .8 3. Location and Access Map of the Sulphur Bank Mine A r e a ............ ..............15 4. Photograph Showing the Contact Between Bleached and Boulder Zones................ 20 5. Location and Access Map of the St. John's Mine - Syar Quarry Area.................. 26 6. Field Sketch Map of Geology with Sample Locations, Syar Quarry Area.............. 29 7. Location and Access Map of the Mt. Diablo Mine A r e a ................................ 36 8. Location and Access Map of the Guadalupe Mine A r e a ........................ .. .45 9. Location and Access Map of the Ambrose- Comstock Mine Area and the New Idria Area..55 10. Geologic Map of the No.Stayton District. 58 11. Photograph Showing Acicular Stibnite and Silicified Breccia at Vein Margin ........ 63 12. Geologic Map of the New Idria District . 71 13. Location and Access Map of the Rinconada Mine A r e a ................................ 80 14. Correlation Matrix and Dendrogram from a Cluster Analysis of 43 Soil Samples. 91 15. Correlation Matrix and Dendrogram from a Cluster Analysis of 21 Serpentinite Outcrop Samples.......................... 9 3 16. Correlation Matrix and Dendrogram from a Cluster Analysis of 72 Silica-Carbonate Rock Samples ............................ 94 VI 17. Correlation Matrix and Dendrogram from a Cluster Analysis of 78 Sedimentary Rock Samples............................ 95 18. Correlation Matrix and Dendrogram from a Cluster Analysis of 94 Igneous Rock S a m p l e s .................................. 97 19. Correlation Matrix and Dendrogram from a Cluster Analysis of 47 Retort Tailing S a m p l e s ................................... 9 8 20. Correlation Matrix and Dendrogram from a Cluster Analysis of All Rocks That Contained Either Au or Ag (46)............ 100 21. Correlation Matrix and Dendrogram from a Cluster Analysis of 80 Stream Sediment S a m p l e s ................................. 101 22. Correlation Matrix and Dendrogram from a Cluster Analysis of 32 Knoxville Stream Sediment Samples......................... 1°2 23. Correlation Matrix and Dendrogram from a Cluster Analysis of 51 Silica-Carbonate Rocks. (Samples were clustered on the basis of similarity between the elements in each sample).................................. 105 24. Diagram Showing Gains and Losses by Weight of Principal Oxides During Alteration of Serpentinite to Silica-Carbonate Rock..107 TABLES Table 1. Summary of Analytical Results ............. 87 2. The distribution of samples by rock type from each district, used to derive rock sample correlation matrices............... 89 3. Chemical analysis showing change from serpentinite to silica-carbonate rock at New Almaden..............................107 4. Elemental abundance in common rocks and rock forming minerals.................... 118 ACKNOWLEDGEMENTS Vll This project evolved from work with Gulf Mineral Resources Co. (GMRC), assisting Mr. C. N. Upchurch on a gold reconnaissance exploration project in California. The metals exploration manager of GMRC, Mr. T. Heidrick, was instrumental in securing funding for this project. I would like to acknowledge his assistance, and the help of GMRC's staff both in Denver and Reno. I would like to thank Mr. Upchurch for his many suggestions and for the stimulating and often argumentative discussions that surrounded them. Also, C. Bonds for her imaginative and creative drafting and D. Kennedy for her patience and cooperation in typing this manuscript. This study was undertaken under the chairmanship of Dr. L. C. Hsu and the supervision of Dr. L. T. Larson and Dr. H. LeMay of the University of Nevada, Reno. I would like to extend my thanks to these gentlemen and to all the other staff and fellow students who helped me during my period of residence at the above institution. I would especially like to thank W. Crone for his help with the computer statistics. Finally, I would like to acknowledge the landowners that gave us permission to repeatedly go on their property. Also, the -various laboratories for their help and cooperation with all the analytical work. Vlll ABSTRACT The geochemical relationship between mercury deposits and precious metal occurrences was studied in seven Calif­ ornia mercury mining districts. Four hundred thirty-four rock, stream sediment, soil and mercury retort tailings samples from seven districts were analysed for Au, Ag, Hg, Sb, As, and Te. The study confirmed that gold and silver are associated with the Coast Range mercury districts. The mineralization appears to be more strongly controlled