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Sodium Metasomatism and Magnesio-Riebeckite Mineralization in the Wilson Ridge Pluton

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Sodium Metasomatism and Magnesio-Riebeckite Mineralization in the Wilson Ridge Pluton UNLV Retrospective Theses & Dissertations 1-1-2000 Sodium metasomatism and magnesio-riebeckite mineralization in the Wilson Ridge pluton Deborah Ann Potts University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/rtds Repository Citation Potts, Deborah Ann, "Sodium metasomatism and magnesio-riebeckite mineralization in the Wilson Ridge pluton" (2000). UNLV Retrospective Theses & Dissertations. 1155. http://dx.doi.org/10.25669/vxk6-khfc This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in UNLV Retrospective Theses & Dissertations by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis arxJ dissertation copies are in typewriter face, while others may t>e from any type of computer printer. The quality of this reproduction is dependent upon tfie quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print t)leedthrough, substarxlard margins, and improper alignment can adversely affect reproduction. 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Further reproduction prohibited without permission. SODIUM METASOMATISM AND MAGNESIO-RIEBECKITE MINER.ALIZATION IN THE WILSON RIDGE PLUTON by Deborah Ann Potts Bachelor of Science University o f Nevada, Las Vegas 1993 A thesis submitted in partial fulfillment of the requirements for the Master of Science Degree Department of Geoscience College of Sciences Graduate College University of Nevada, Las Vegas May 2000 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number 1399928 Copyright 2000 by Potts, Deborah Ann Alt rights reserved. UMI UMI Microform 1399928 Copyright 2000 by Bell & Howell Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. Bell & Howell Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Copyright by Deborah A. Potts 2000 All Rights Reserved Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thesis Approval UNIV The Graduate College University of Nevada, Las Vegas March 29 2 0 ^ 0 The Thesis prepared by Deborah Ann P o tts Entitled Sodium Metasomatism and Magneslo-R iebeckite M ineralization in the Wilson Ridge Pluton is approved in partial fulfillment of the requirements for the degree of Master of Science in Geology Exantmation Committee Chair Dean of the Graduate College Examination Committee Member Examination Committee Member GraduéeradiÆe CollegeCollei Faculty Representative PR/1017-53/l-«) u Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Sodium Metasomatism and Magnesio-Riebecidte Mineralization in the Wilson Ridge Pluton by Deborah A. Potts Dr. Rodney V. Metcalf, Examination Committee Chair Associate Professor of Geoscience University of Nevada, Las Vegas The Wilson Ridge pluton contains a rare occurrence of hydrothermal sodic amphibole. Hydrothermal amphibole occurs as fracture coatings, veinlets, dense stockwork-type networks, and diffusive alteration fronts. Electron microprobe analyses of the hydrothermal amphibole reveal a range of Na-rich compositions, most notably magnesio-riebeckite. Magnesio-riebeckite in the Wilson Ridge pluton formed by Na- metasomatism related to subsolidus hydrothermal alteration involving Na-rich fluids of meteoric origin. Whole-rock geochemistry of samples from zones of hydrothermal amphibole show enrichment ofNaiO (> 9 .6 wt. %) and depletion of K 2O (0 .1 5 wt. %) and CaO (2.4 wt. %) relative to unaltered host rock. Secondary fluid inclusions associated with zones of hydrothermal amphibole contain daughter crystals of halite and up to three other unknown crystals. Oxygen isotope studies suggest that granitoid rocks containing hydrothermal amphiboles have lower S ‘* 0 values (+3.68% o to + 6.97% o) than unaltered granitoid rocks ( 5 ‘* 0 values +6.04% o to + 9.23% o). Ill Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ABSTRACT.......................................................................................................................iii LIST OF FIGURES.......................................................................................................... vi LIST OF TABLES..........................................................................................................viii ACKNOWLEDGEMENTS............................................................................................. ix CHAPTER! INTRODUCTION.................................................................................. I Purpose .........................................................................................................................2 Study Design and Instrumental Techniques .............................................................3 CHAPTER 2 GEOLOGY AND GEOLOGIC HISTORY OF THE WILSON RIDGE PLUTON.................................................................................7 CHAPTER 3 FIELD OCCURRENCES AND PETROGRAPHY OF AMPHIBOLE ALTERATION IN THE WILSON RIDGE PLUTON.....................................11 Field Occurrences - Kingman W ash ........................................................................ 11 Petrography of Kingman Wash - Dike Rocks .......................................................... 12 Petrography o f Kingman Wash - Granitoid Host Rocks .........................................13 Field Occurrences - Horsethief Canyon ....................................................................17 Petrography of Horsethief Canyon-Dike Rocks ...................................................... 18 Petrography of Horsethief Canyon-Granitoid Host Rocks ..................................... 19 Additional Occurrences of Blue Amphibole in the Wilson Ridge Pluton .............19 Relationship of Blue Amphibole Mineralization to Structures ..............................20 Saline Fluid Inclusions ...............................................................................................25 CHAPTER 4 COMPOSITION OF BLUE AMPHIBOLE IN THE WILSON RIDGE PLUTON............................................................................... 29 X-ray diffractometry.................................................................................................. 29 Electron Microprobe Analyses of Blue Amphiboles .............................................. 29 Structural Formula Calculation ................................................................................. 32 Amphibole Classification and Compositional Variability ..................................... 33 CHAPTER 5 WHOLE-ROCK COMPOSITIONS.................................................... 40 Whole-rock Geochemistry .........................................................................................40 IV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Whole-rock Oxygen Isotope Analyses .....................................................................40 CHAPTER 6 DISCUSSION: ORIGIN OF BLUE AMPHIBOLE IN THE WILSON RIDGE PLUTON................................................................................46 Evidence of Subsolidus Hydrothermal Origin .........................................................46 Discussion of the Timing of Mineralization ............................................................ 46 Evidence of Na-metasomatism ................................................................................. 47 Origin of Hydrothermal Water - Interpretation of Oxygen Isotope Data .............48 Source of Sodium ......................................................................................................
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