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Gregg Canyon Intrusive Center, Sonoma Range, Nevada: Magmastism and Porphyry-Style Alteration-Mineralization

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Gregg Canyon Intrusive Center, Sonoma Range, Nevada: Magmastism and Porphyry-Style Alteration-Mineralization Gregg Canyon Intrusive Center, Sonoma Range, Nevada: Magmastism and Porphyry-Style Alteration-Mineralization Item Type text; Electronic Thesis Authors Wallenberg, Alexandra 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, presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 04/10/2021 12:47:02 Link to Item http://hdl.handle.net/10150/642064 GREGG CANYON INTRUSIVE CENTER, SONOMA RANGE, NEVADA: MAGMASTISM AND PORPHYRY-STYLE ALTERATION-MINERALIZATION by Alexandra Leigh Wallenberg ____________________________ Copyright © Alexandra Leigh Wallenberg 2020 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 2020 1 2 Acknowledgments We extend our gratitude to organizations that funded this project, including an SEG Graduate Student Fellowship from the Society of Economic Geologists Foundation sponsored by AngloAmerican, a Courtright Scholarship from the Arizona Geological Society, summer research funding from the J. David Lowell Scholarship in the Department of Geosciences at the University of Arizona, a Geological Society of America Research Grant, and a Geological Society of Nevada Elko Chapter Scholarship. We thank Ralph Stegen of Freeport Exploration, Steve Shaver, Clancy Wendt, Odin Christensen, and Christin Lucas for providing previous reports and data from the Sonoma property. We acknowledge helpful scientific discussions with Carson Richardson, Mark Barton, Mihai Ducea, and Steve Shaver. We thank Roger and Nancy Johnson, nearby ranchers, for their tremendous hospitality, advice, knowledge, and assistance during field work. Jojo and Annemarie Wallenberg provided valued company and assistance during the field season. This work is a part of a M.S. thesis study at the University of Arizona. We appreciate reviews from Bob Thomas and Fleet Koutz. 3 Table of Contents ABSTRACT ................................................................................................................................ 7 INTRODUCTION ....................................................................................................................... 9 PREVIOUS WORK AND EXPLORATION HISTORY .............................................................................. 11 REGIONAL TECTONICS AND MAGMATISM ..................................................................................... 13 GEOLOGIC FRAMEWORK OF THE SONOMA RANGE AND ENVIORNS ...................................................... 16 STRUCTURE ........................................................................................................................... 18 MINERAL DEPOSITS ................................................................................................................. 21 METHODS .............................................................................................................................. 24 GEOLOGIC MAPPING ............................................................................................................... 24 PETROGRAPHY AND ELECTRON MICROPROBE ANALYSIS ..................................................................... 24 WHOLE-ROCK GEOCHEMISTRY AND ASSAYS ................................................................................... 24 ROCK TYPES ........................................................................................................................... 25 OVERVIEW OF THE GEOLOGY OF GREGG CANYON ........................................................................... 25 STRUCTURE ........................................................................................................................... 31 PRE-ORE STRUCTURES .............................................................................................................. 31 POST-ORE STRUCTURES ............................................................................................................ 31 HYPOGENE VEINS AND ALTERATION-MINERALIZATION ......................................................... 32 QUARTZ ± K-FELDSPAR AND BIOTITE VEINS AND ASSOCIATED POTASSIC ALTERATION ................................ 33 MUSCOVITE ± QUARTZ VEINS WITH GREISEN MUSCOVITE ALTERATION .................................................. 33 BARREN QUARTZ VEINS ............................................................................................................ 34 QUARTZ-SERICITE-PYRITE VEINS AND ASSOCIATED SERICITIC AND INTERMEDIATE ARGILLIC ALTERATION ......... 34 CHLORITE AND WEATHERED SULFIDE VEINS AND VEINLETS ................................................................ 34 HYDROTHERMAL BRECCIAS AND MASSIVE HYDROTHERMAL QUARTZ .................................................... 35 SKARN AND HORNFELS ............................................................................................................. 36 HYDROTHERMAL MINERAL COMPOSITIONS .................................................................................... 37 SUPERGENE ALTERATION-MINERALIZATION.......................................................................... 38 OVERVIEW ............................................................................................................................ 38 LEACHED CAPPING ................................................................................................................... 38 CHALCOCITE .......................................................................................................................... 38 DISTRIBUTION OF METAL GRADES AND TRACE ELEMENT CONTENTS .................................................... 38 INTERPRETATIONS ................................................................................................................. 40 SPATIAL RELATION AND TIMING OF FAULTING ................................................................................ 40 ECONOMIC RESOURCES AND EXPLORATION POTENTIAL OF THE SONOMA PROSPECT ................................. 40 4 DISCUSSION ........................................................................................................................... 41 COMPARISON TO OTHER QUARTZ MONZONITIC-GRANITIC PORPHYRY MO-CU SYSTEMS IN THE GREAT BASIN . 41 CONCLUSIONS ....................................................................................................................... 42 FIGURE CAPTIONS ................................................................................................................. 44 FIGURES................................................................................................................................. 46 TABLES .................................................................................................................................. 59 APPENDICES .......................................................................................................................... 70 REFERENCES .......................................................................................................................... 95 5 Gregg Canyon intrusive center, Sonoma Range, Nevada: Magmatism and porphyry-style alteration-mineralization Alexandra Leigh Wallenberg* and Eric Seedorff Lowell Institute for Mineral Resources, Department of Geosciences University of Arizona, 1040 East Fourth Street Tucson, Arizona 85721-0077 USA *Corresponding author: e-mail, [email protected] Published as: Wallenberg, A. L. and Seedorrf, E., 2020, Gregg Canyon intrusive center, Sonoma Range, Nevada: magmatism and porphyry-style alteration-mineralization, in Koutz, F.R., and Pennell, W. M., eds.: Vision for discovery: Geology and Ore Deposits of the Basin and Range, Reno, Nevada, in press. 6 Abstract The Gregg Canyon intrusive center is a Cretaceous quartz monzonitic to granitic porphyry Mo-Cu system located southeast of Winnemucca on the eastern side of the Sonoma Range, southwest of the Getchell trend. The area was explored for molybdenum during the 1960s and 1970s and subsequently for gold. This study builds on previous work and reports results of field mapping, petrography, whole-rock geochemical analyses, and compositions of igneous and hydrothermal minerals. Five Mesozoic intrusive centers, including Gregg Canyon, and three regional thrust faults crop out in the Sonoma Range, two of which crop out at Gregg Canyon. Whether mineralized or barren, none of the intrusions has geometries that suggest apparent control by the older thrust faults. Eugeoclinal rocks of the Ordovician Valmy Formation overlie the transitional facies rocks of the Cambrian Osgood Mountains Quartzite and Preble Formation along the Roberts Mountains thrust. In turn, those rocks are overlain by upper Paleozoic eugeoclinal rocks of the Havallah Sequence along the Golconda thrust. The Gregg Canyon intrusive center occurs near the confluence of the Roberts Mountains and Golconda thrusts and consists of six major intrusive phases. The earliest and largest intrusion (107 Ma K-Ar biotite, 94.1 Ma U-Pb zircon) is a barren, equigranular biotite-hornblende granodiorite (~67% SiO2) that hosts younger granodiorite porphyry (~70% SiO2) phases. Other Cretaceous intrusions include quartz monzonite porphyries (~74% SiO2), feldspar porphyries, granite porphyry stocks at depth, and biotite
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