Description and Evolution of the Escondida Porphyry Copper
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Description and Evolution of the Escondida Porphyry Copper Deposit, Antofagasta Region, Northern Chile Ruben Agustin Padilla-Garza 2003 Description and Evolution of the Escondida Porphyry Copper Deposit, Antofagasta Region, Northern Chile by Ruben Agustin Padilla-Garza ____________________ A Dissertation Submitted to the Faculty of the DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 2003 2 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE As members of the Final Examination Committee, we certify that we have read the dissertation prepared by Ruben Agustin Padilla-Garza entitled Description and Evolution of the Escondida Porphyry Copper Deposit, Antofagasta Region, Northern Chile And recommend that it be accepted as fulfilling the dissertation requirement for the Degree of Doctor of Philosophy ___________________________________________ ___________________ Spencer R. Titley Date ___________________________________________ ___________________ Joaquin Ruiz Date ___________________________________________ ___________________ Christopher Eastoe Date ___________________________________________ ___________________ George Gehrels Date ___________________________________________ ___________________ DeVerle Harris Date Final approval and acceptance of this dissertation is contingent upon the candidate’s submission of the final copy of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement. ___________________________________________ ___________________ Dissertation Director: Spencer R. Titley Date 3 STATEMENT BY THE AUTHOR This dissertation has been submitted in partial fulfillment of requirements 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 University. Brief quotations from this dissertation 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 or her judgment the proposed use of the material is in the interest of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED:___________________ 4 Acknowledgments I am extremely grateful to BHP Billiton and Minera Escondida Ltda for providing financial support and permission to carry on this research. Hugo Dummett, former Vice President of the Discovery Group of BHP Minerals, deserves special recognition for initiating and supporting the development of this study. I also acknowledge Manuel Duran and Francisco Pimentel former, chief geologists of Escondida, for their important support to this study. The geological and technical staff of Minera Escondida also provided excellent support, particularly Nicolas Cruz, Carlos Alcayaga, Jonathan Gilligan, Guillermo Segovia and Luis Luengo. Jim Bratt from BHP and Hector Veliz, Eduardo Medina and Hans Niemeyer of the Universidad del Norte also deserve special credit for their contributions during the time I conducted my field work. The separation of intrusive phases from the deposit was considerably aided by the excellent mapping work carried out by Barry Quiroz. I am indebted to James Reynolds, Robert Kamilli, and Chris Eastoe for their unselfish guidance on the study of fluid inclusions. My friend Sergio Castro was always there to support me with the petrographic work. I also need to thank a large group of excellent scientists that assisted me with laboratory analysis, their names have been included throughout this thesis. The manuscript benefited from the comments of Mark Barton, Pepe Perellό, Lukas Zurcher, Denis Hall, Ryan Mathur, Eric Braun, and Eric Seedorff. My thanks to Virginia Braun whose editing added the final touches to this dissertation. My appreciation goes out to all my professors and my deep gratitude to my advisors, particularly Drs. Spencer Titley, Joaquin Ruiz and Chris Eastoe. 5 Dedico mi trabajo al trabajo de los otros, Al amor que es mi compañia y guia, Al bello planeta azul, A mi tierra natal: Latino America A los antepasados de mis padres que siempre me recuerdan mis orígenes, A Marcela y Rafael…porque cada acción mia tiene una pincelada suya, A mis hermanos y sus familias que siempre me recuerdan quien soy, A mis amigos, vivos y muertos, gracias por ese huequito de sus corazones…salud, Dedico y agradezco a Rocio, la bella compañera de mi vida, …ella lo sabe todo…, A ella la descubrí sin buscarla y la aprendí a amar sin estudiar nada, desde entonces ahí está en el centro de mi vida… a ti que mis ojos siempre ven y que mis manos siempre tocan aun cuando esperas, …y por supuesto…a mi Sol de Julio Tucsonense…y a mi Sol de Abril Andino para ellas siempre mi amor…, Y a todo aquello que la vida traiga y se acomode como parte de mi ser. 6 TABLE OF CONTENTS LIST OF FIGURES…………………………………………………………………….10 LIST OF TABLES……………………………………………………………………...14 ABSTRACT……………..………………………………………………………………15 INTRODUCTION…………………………………………………………………...….18 CHAPTER 1: REGIONAL GEOLOGY……………………………………………..22 Regional Structure…………………………………………………….…25 Summary and Interpretation of the Regional Geologic Setting…….……29 CHAPTER 2: DISTRICT GEOLOGY.......................................…………………….32 CHAPTER 3: GEOLOGY OF THE ESCONDIDA DEPOSIT…………………….36 Lithology…………………………………………………………………36 Faults..………………………………………………………………….. 40 NNW Fault System………………………………………………43 NE Discrete Faults……………………………………………….44 NW Discrete Fault Systems………………………..…………….44 The Enargite System……………………………………..44 The Cerrito System………………………………………45 Interpretation and Discussion……………………………………46 Paragnesis and Zoning of Hydrothermal Minerals, and Distribution of Supergene Minerals ………………...…………………………………...51 Hydrothermal Alteration…………………………………………52 Introduction………………………………………………52 Detailed Description of Hydrothermal Alteration…....….58 Stage A—Potassic………………………………..58 Stage A—Propylitic……………………………...59 Stage A—Silicification Shell ……………………60 Stage A—Early Veins………………………...….60 Stage B—Chlorite+Sericite±Quartz…………..…63 Stage B—Quartz-Sericite……………..…………65 Stage C—Advanced Argillic……….……………67 Mineralization……………………………………………………70 Introduction………………………………………………70 Detailed Description of Mineralization ……...….............72 Hypogene Ore………………………………........72 Sulfide Enrichment Blanket…………...................76 Leached Capping Zone…………………..............77 Copper Oxides……………………………...........78 7 CHAPTER 4: GEOCHRONOLOGY………...........................................................…79 Escondida District and Regional Geochronology ……………………….79 Escondida Deposit Geochronology……………...………………………81 Introduction…………………………………………………........81 U-Pb Ages ………....................………………………………….85 40Ar/36Ar Ages……………………………...................…………90 Biotite...................................................................................……..91 Igneous Biotite ……………………..................................91 Igneous Biotite from Phase 1 and Phase 2 of the Escondida Stock.....................................................91 Igneous Biotite from Cerro-Sureste Rhyolite........92 Hydrothermal Biotite…………….…................................92 Sericite………………………………………........……………...94 Alunite………………………………………........……………...95 Re-Os Age of Molybdenites………………………….......……...99 Interpretation and Discussion ……………………………………...…..100 CHAPTER 5: GEOCHEMISTRY OF HYDROTHERMAL FLUIDS …………..105 Fluid Inclusion Study…………………………………………………...105 Goal……………………………………………………………..105 Equipment………………………………………………………106 Methods………………………………………………………...106 Types of Fluid Inclusions...……...……………………………..108 Fluid Composition......................……………………………….109 Conditions of Pressure and Depth of Trapping...........................111 Distribution of Fluid Inclusions, Temperatures of Homogenization, and Depth of Trapping of the Different Hydrothermal Stages…112 Fluid Inclusions Within Igneous Quartz “Eyes”.....…….112 Description and Temperatures of Homogenization………………………………...112 Pressure Estimates……………………………...113 Fluid Inclusions Associated with Hydrothermal Stage A………………………………………………….114 Description……………………………………...114 Temperatures of Homogenization………………114 Pressure Estimates……………………………...115 Fluid Inclusions Associated with Hydrothermal Stage B……………………………………….................117 Description………………………………….…..117 Temperatures of Homogenization………………118 Pressure Estimates……………………………...118 Fluid Inclusions Associated with Hydrothermal Stage C…………………………………………........….120 Description…………………………….………..120 Temperatures of Homogenization ……………...120 8 Pressure Estimates……………………………...120 Secondary Late Liquid-Rich-Only Linear Arrays of Fluid Inclusions……………………………..…………..121 Description……………………………………...121 Temperatures of Homogenization………………121 Pressure Estimates……………………..……….121 Summary……………………..……………………....................121 Interpretation……..........…………………………………….….123 Sources and Evolution of Sulfur and Hydrothermal Fluids.......………..127 Introduction……………………………………………………..127 Evolution of Sulfide and Sulfate Species…………………........128 Sulfur Isotope Data…………………….....…………………….131 Oxygen-Hydrogen Isotope Data……………………....………..135 Discussion and Interpretation of Hydrothermal Evolution……………..139 CHAPTER 6: GEOCHEMISTRY OF IGNEOUS