Brecciation, alteration, and mineralization at the Copper Flat porphyry copper deposit, Hillsboro, New Mexico Item Type text; Thesis-Reproduction (electronic); maps Authors Fowler, Linda Leigh 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 02/10/2021 11:45:33 Link to Item http://hdl.handle.net/10150/557922 BKECCIATION, ALTERATION, AND MINERALIZATION AT THE COPPER FLAT PORPHYRY COPPER DEPOSIT, HILLSBORO, NEW MEXICO by Linda Leigh Fowler A Thesis Submitted to the Faculty of the DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 1 9 - 8 2 STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of re­ quirements 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 thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction 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 judg­ ment the proposed use of the material is in the interests of scholar­ ship. In all other instances, however, permission must be obtained from the author. SIGNED: APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below: Date ACKNOWLEDGMENTS I recognize that this thesis could not have been written without the help and encouragement of many different individuals. X am thankful for the knowledge which I gained through taking courses under the facul­ ty of the Department of Geosciences at The University of Arizona. I would especially like to thank Dr. John Guilbert and Dr. Spencer Titley for the knowledge I gained in their economic geology courses and for serving on my thesis committee. I am thankful to Pete Dunn for his help in setting up this thesis and his advice all along the way. I would like to thank both the Tucson office and the Hillsboro office of Quin­ tana Minerals Corporation for their financial, technical,, and moral support throughout the research and writing of this thesis. Although many people were involvedI would especially like to thank Bob Donegan, Milt Hood, J. Avelar, Jeff Smith, Ivan Pupulidy, And Barbara Hutchison. I am thankful for the talks I had with fellow students and fellow em­ ployees on. my summer jobs who helped in their areas of expertise. Lastly, I am thankful"for my parents, brother "and sisters fer- "their continual encouragement and for the wisdom and strength that God has provided forme throughout this whole project. lit TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS............. vi LIST OF TABLES . ................. .................. .. x ABSTRACT .......... xi 1. INTRODUCTION ........ .. ........ .. 1 2. FIELD STUDIES. Regional Geology oo io Lithology. District-Wide Mineralization ..... ........ ...... 15 Structural Setting ................ .... 19 Summary of Field Evidence.......... 20 3. WHOLE ROCK ANALYTICAL DATA ........................... .. 23 Summary of the Whole Rock Analytical Data. 34 4. DRILL CORE STUDIES ............ .. ........ 35 General Characteristics of the Breccia Pipe. ........ 36 Descriptions of the Breccia Types Based on Matrix Mineralogy ................ ....... 39 Textural Variations in the. Quartz Monzonite.......... .. 49 Mineralization at Copper Flat. ............................. 49 Summary of Drill Core Observations.......... 51 5. THIN SECTION STUDIES.............. .. ............. .. 55 Petrologic Descriptions of the Rock Types........ .......... 55 Andesite . ........ ^ . 55 Quartz Monzonite ................... .......... 56 Latitic Dikes. ........ ..... 56 Alteration Assemblages .................................. 57 Supergene Effects. ..... .............. 65 Mineral Paragenesis. ..... ............ 65 Summary of Thin Section Data ............................. 67 iv V TABLE OF CONTENTS— Continued Page 6. ELECTRON MICROPROBE DATA . 69 Plagioclase Feldspar Compositions. 69 Potassium Feldspar Compositions. .; . .. ... » . 71 Biotite Compositions . .... ... 73 Chlorite Compositions. .... 75 Sericite Compositions. ...... .. ... ., . 75 Summary of Microprobe Data . 75 7. FLUID INCLUSION DATA . ... .. .... 82 Procedure. * . * . .. * 83 Fluid. Inclusions at Copper Flat. ... .............. 85 Summary of Fluid Inclusion Data. .. < . 98 8. THEORIES OF BRECCIATION. ... .. 102 Brecciation at the Copper Flat Deposit . 106 Summary and Conclusions. .. ... ., . 112 APPENDIX: A: LOCATIONS OF WHOLE ROCK ANALYSIS SAMPLES . 113 APPENDIX B: ELECTRON MICROPROBE ANALYSES . .. 114 APPENDIX C: SOURCES OF INFORMATION FOR CROSS SECTION DRILL HOLES . 128 APPENDIX D: COPPER FLAT ROCKS COMPARED WITH THE CLASSIFICATION OF KEITH (1978) .... :. .... 129 SELECTED BIBLIOGRAPHY. .... ... 130 LIST OF ILLUSTRATIONS Figure Page 1. Location map of the Copper Flat porphyry copper deposit . 2 2. The mine area, September, 1981, looking north . ........ .5 3. Regional Geologic Map . ......................... In Tube 4. Geologic Map of Copper F l a t ........ .................... In Tube 5. Cross section A—A ’ showing regional geologic relationships. A-A* are located on the plan map of Fig. 3 .............. 7 6. An outcrop of breccia showing the pegmatitic nature of the breccia matrix.; note the pen in the upper right of the photo for scale . .. .......... .. 9 7. Highly fractured quartz monzonite near the contact with the breccia ... ... .. .. .. .: . 10 8. Porphyritic andesite, with white plagioclase phenocrysts and black hornblende and biotite phenocrysts in a 1imonite­ st am e d groundmass« . @ . ... 12 9. Quartz monzonite veined with biotite, potassium feldspar, quartz,"and magnetite veins. ............... 13 10. Latite with plagioclase, orthoclase, hornblende, and biotite phenocrysts in a limonite-stained fine-grained ground- mass. ... .......................................... 14 11. A latite porphyry dike which cuts through andesite.......... 16 12. Typical vein structure of fissure veins in the andesite- based on Harley (1934) ...............................'. 18 13. An alkali-lime ternary diagram for Copper Flat rocks com­ pared with other copper porphyry rocks data from Titley and Beane (1981). ............... .............. .. 25 14. An AFM plot for the Copper Flat rocks as compared with the calc-alkaline versus the Thingmuli tholeiitic trend - based on Titley and Beane (1981).............. .. 27 vi vii LIST OF ILLUSTRATIONS— Continued Figure Page 15. An alkali-silica variation diagram for Copper Flat rocks in comparison, with other copper porphyry rocks - data from Titley and Beane (1981) ..... ............ 28 : 16. A Barker variation diagram for major oxides in the Copper Flat r o c k s . ........................................... .. 29 17. A. Barker variation diagram for the minor elements in Copper Flat rocks............................................... 30 18. A plot of Rb versus K and Sr versus Ca for the Copper Flat rocks . ............... ............. 32 19. Cross Section Location Map.............. ................ In Tube . t 20. Geologic Cross Section B -B * . ; . In Tube 21. Geologic Cross Section C-C* . .. .. ... ... .; . .. In Tube 22. Geologic Cross Section D-D' . .. ... .. .... ... In Tube. 23. Geologic Cross Section E-E' ... ...... ............ In Tube 24. Geologic Cross Section F-F* . ...... ....... In Tube 25. Geologic Cross Section G-G* ............... In Tube 26. Biotite Breccia with distinct breccia textures and fragment rotation — 75-10-635.......... ...................... .. 41 27. Biotite breccia with less well-defined, partially marginally replaced fragments - 75-5-694 . .... ........ 42 28. Biotite breccia with replacement of fragments - 75-46-342 . 43 29. Biotite breccia with two rock types: quartz latite and quartz monzonite - 75-42-463 ............ .......... 44 30. Feldspar breccia - 75-98-1151 ................ 46 31. Feldspar breccia with greenish sericite and calcite - 75-98-1431. .............................................. 47 32. Quartz breccia - 75-98-272 48 viii LIST OF ILLUSTRATIONS— Continued Figure • Page 33. Porphyritic quartz monzonite in an interval of biotite breccia - 75-9. •„ . ... 50 34. Photomicrograph of potassium feldspar rimming plagioclase in quartz monzonite - 74-2-200. ..... .......... .. 58 35. Photomicrograph of biotite breccia matrix in which biotite has been altered to chlorite - 75-12-229 - crossed niCO1S . ... e . o . .-. e e e e e . • . 60 36. Photomicrograph of biotite breccia matrix in which biotite has been altered to sericite and calcite with magnetite - 75-44-588 - crossed nicols. ...... ................ 61 37. Photomicrograph of potassium feldspar altered to sericite in feldspar breccia - 75-98-1431 - crossed nicols. .. 6.2 38. Photomicrograph of biotite "flooding" in a quartz monzonite fragment - 75-8-219 — crossed nicols. .... ... .. „ . 63 39. Reflected light photomicrograph of biotite (dark brown), pyrite and chalcopyrite with sphalerite exsolution stars — 75—12—210 . ..... .... 64 40. Mineral paragenetic sequence at Copper Flat ......... 66 f' - 41. Plagioclase feldspar