Geology, Alteration, Mineralization and Hydrothermal ...

Geology, Alteration, Mineralization and Hydrothermal Evolution of the La Bodega-La Mascota deposits, California-Vetas Mining District, Eastern Cordillera of Colombia, Northern Andes

by Alfonso Luis Rodríguez Madrid Geologist, Universidad Industrial de Santander, 2005

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in The Faculty of Graduate and Postdoctoral Studies (Geological Sciences) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) February, 2014 © Alfonso Luis Rodríguez Madrid

Abstract

La Bodega (LB) and La Mascota (LM) deposits (inferred resources in 2010 of 3.47 Moz Au, 19.2 Moz Ag and 84.4 Mlbs Cu at 2 g/t Au cut off) are located in the California-Vetas Mining District, 35 km NE of Bucaramanga, in the Eastern Cordillera of Colombia within the Santander Massif. Mineralization exhibits NE-trending, NW-dipping structural control associated with the right lateral strike-slip La Baja fault. Mineralization at LB is composed of veins networks and tectonichydrothermal breccias while LM mineralization is largely contained in hydrothermal breccias with adjacent narrow veining zones. Mineralization is hosted in Proterozoic Bucaramanga (gneiss) Complex and Triassic-Jurassic leucogranites. Hydrothermal alteration and mineralization occur in six stages. An early porphyry-style phase comprises stages 1 and 2. Stage 1 is characterized by propylitic alteration with epidote, chlorite, calcite, specularite veins, minor pyrite and chalcopyrite, probably associated in time with Mo-Cu mineralization (Re/Os on molybdenite ~10 Ma) and porphyritic granodiorites (U/Pb in zircon ~10-8.4 40 39 Ma) cropping out in the district. Stage 2 ( Ar/ Ar on muscovite ~3.4 Ma) is characterized by phyllic alteration (muscovite/sericite – illite, quartz, pyrite) associated with quartz+pyrite veins. Epithermal phase (stages 3-6) is related to multi-phase hydrothermal breccia development and advanced 40 39 argillic (quartz-alunite) alteration which based on alunite Ar/ Ar geochronology took place between ~2.6 and ~1.3 Ma. Stage 3 is characterized by copper sulfide deposition. Stage 4 is characterized by wolframite deposition in veins/breccias. Stage 5 is characterized by enargite deposition. Stage 6 is characterized by minor porous quartz deposition followed by sphalerite with alunite+quartz. Pyrite is common to all these stages. Gold-silver mineralization took place in stages 2-5 associated with sulfides, sulfosalts, tellurides, as electrum and native gold. Hydrothermal events were by followed by near surface supergene alteration and fault reactivation that created intensely fractured/gouge-rich fault zones. At LM, stages 4-5 quartz primary fluid inclusions assemblages indicate boiling and they have homogenization temperatures of ~143-238°C and salinities of 0.5-5.6 wt% NaCl equiv. LM and LB 34 pyrite exhibit light δ S signatures: -16.9‰ to –11.3‰ at LM and -8.3‰ and –6.1‰ at LB. Alunite 18 δ O and δD data indicate that it was precipitated largely from magmatic fluids.

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Preface

This research thesis is part of the Colombia Porphyry and Epithermal Gold Project, developed by the Mineral Deposit Research Unit (MDRU) with the initiative of mineral exploration companies, including Ventana Gold Corp. (taken over by AUX Colombia Ltda.) and EcoOro Minerals (former Greystar Resources) working at the California-Vetas Mining District area in Colombia. Researchers for this project in the California-Vetas Mining District area include PhD. Thomas Bissig (Research Associate and Project leader), PhD. Craig Hart (MDRU Director), PhD. Luis C. Mantilla Figueroa (Universidad Industrial de Santander, Geology Department professor) and the author of this thesis. Some analytical work provided in this thesis was conducted by other people, specifically:   

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Ar/ Ar geochronology was carried out by analyses by Janet Gabites in the Pacific Center for Isotopic Research (PCIGR) at The University of British Columbia. U/Pb geochronology on zircons was carried out by Richard Friedman in the Pacific Center for Isotopic Research (PCIGR) at The University of British Columbia. Stable isotope analysis on pyrite and alunite was carried out by April Vuletich and Kristen Feige at Queen’s University.

Location maps in Chapter 1 Figure 1.1 are based on Google Earth 2013 information from Colombia. The conceptual framework of this thesis, presented in Chapter 2 includes figures and tables taken, adapted and/or modified from several publications as referred in the text, including: Corbett and Leach (1998), Corbett (2002), Einaudi et al. (2003), Sillitoe and Hendenquist (2003), Simmons et al. (2005), Sillitoe (2010), Moncada et al. (2012). Tectonic context related figures presented in Chapter 3 includes Figure 3.1, modified after Restrepo et al. (2011), Cediel et al. (2003), Ward et al. (1973); Royero and Higuera (1999); Wolff et al. (2005); and Figure 3.2, modified after Taboada et al. (2000); Prieto et al. (2012); Vargas and Mann (2013). The geological maps presented in Figures 3.3, 3.4 and 3.17 are based on previous geological maps by Ward et al. (1973), Mendoza and Jaramillo (1979), Polania (1980), Ventana Gold Corp. La Bodega project geological map by A. Bernasconi and geology team (that included the author of this thesis) provided by the company in 2010; collaborations by L. C. Mantilla Figueroa and T. Bissig and the author of this thesis for presented MDRU Colombia Porphyry and Epithermal Gold Project (this study). Maps presented in these figures were edited by Sara Jenkins (MDRU GIS expert) and the author of this thesis. Figure 3.15 summarizes field structural data collected by Parra (2007) and Pratt (2009). Figure 5.19 in Chapter 5 is modified after Einaudi et al. (2003) and adapted in the context of La Bodega and La Mascota deposits. 40

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Ar/ Ar geochronology results in Chapter 6 and Appendix 3 includes samples collected by T. Bissig (2011). Stable isotopic data includes samples collected by T. Bissig (2011) and one sulfur sample collected by M. Mendoza (2011) for which analytical result was provided by L. C. Mantilla Figueroa (2012). Appendix A3 includes one sample (ALR035) collected by the author for this project. U/Pb geochronoly on zircons results from this sample were presented in Bissig et al. (2012) and published on Mantilla Figueroa et al. (2013). None of the other text, figures, or data in this thesis is taken directly from previously published articles.

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Table of Contents

Abstract ................................................................................................................................................ ii Preface ................................................................................................................................................ iii Table of Contents ................................................................................................................................ iv List of Tables ....................................................................................................................................... xi List of Figures ..................................................................................................................................... xii List of Abbreviations ........................................................................................................................... xv Acknowledgements ........................................................................................................................... xvi Dedication........................................................................................................................................ xviii Chapter 1. Introduction ......................................................................................................................... I

1.1 General location of the study area ............................................................................. I 1.2 Climate and physiography ........................................................................................ 2 1.3 Mining history ........................................................................................................... 3 1.4 Previous studies ....................................................................................................... 4 1.5 Colombia porphyry and epithermal gold project ........................................................ 6 1.6 Project justification and objectives ............................................................................ 6 1.6.1 Specific objectives ............................................................................................. 7 1.7 General methodology ............................................................................................... 8 1.8 Thesis organization .................................................................................................. 9 Chapter 2. Hydrothermal Systems Conceptual Framework: Porphyry Copper and Epithermal Systems ............................................................................................................................................. 11

2.1 Introduction ............................................................................................................ 11 2.2 Porphyry copper systems ....................................................................................... 11 2.2.1 Alteration and mineralization in porphyry copper systems ................................ 15 2.3 Faults and fracture networks and their role in hydrothermal.................................... 18

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2.4 Sulfidation state ...................................................................................................... 22 2.5 Epithermal systems (high-sulfidation and low-sulfidation). ...................................... 24 2.5.1 High-sulfidation deposits .................................................................................. 29 2.5.2 Low-sulfidation deposits ................................................................................... 31 2.5.3 Summary of genetic factors related to epithermal deposits .............................. 34 Chapter 3. Tectonic, Geological and Structural Context of The California-Vetas Mining District and The La Bodega - La Mascota Gold Deposits .................................................................................... 36

3.1 Tectonic setting and location of the California-Vetas Mining district ........................ 36 3.2 Lithology of the California Vetas Mining District and its expression within La Bodega - La Mascota deposits. ................................................................................................. 42 3.2.1 Bucaramanga (Gneiss) Complex ..................................................................... 46 3.2.2 Santander Plutonic Group (Late Triassic to Early Jurassic) .............................. 50 3.2.3 Sedimentary rocks (Late Cretaceous) .............................................................. 55 3.2.4 Porphyritic bodies and related rocks (Late Miocene) ........................................ 56 3.2.5 Hydrothermal breccias (Plio-Pleistoscene) ....................................................... 58 3.3 Structural context ................................................................................................... 64 3.3.1 Main regional structures ................................................................................... 64 3.3.2 Main structures within La Bodega – La Mascota .............................................. 66 3.4 Structural relationships, hydrothermal breccias and mineralization ......................... 70 Chapter 4. Alteration at La Bodega and La Mascota: Characteristics, Mineral Assemblages and Distribution......................................................................................................................................... 72

4.1 Introduction ............................................................................................................ 72 4.2 Methods of identification of alteration minerals ....................................................... 72 4.3 Alteration minerals assemblage and zonation at La Bodega and La Mascota ........ 73 v

4.3.1 Propylitic alteration: chlorite and chlorite-epidote alteration zones characteristic minerals .................................................................................................................... 77 4.3.2 Phyllic alteration: muscovite and Illite alteration zones ..................................... 81 4.3.3 Advanced argillic alteration: alunite-quartz alteration, kaolinite-alunite alteration, silicification and related textures ............................................................................... 85 4.4 Discussion of alteration assemblages..................................................................... 93 Chapter 5. Ore Mineralogy, Mineralization Styles and Paragenetic Evolution at La Bodega and La Mascota ............................................................................................................................................. 96

5.1 Introduction ............................................................................................................ 96 5.2 Methodology........................................................................................................... 97 5.3 Mineralization stages, veins and ore related mineral distribution at La Bodega and La Mascota .................................................................................................................. 99 5.3.1 Stage 1: pre-mineralization, specularite bearing veins ................................... 101 5.3.2 Stage 2: early mineralization, pyrite ± quartz veins ........................................ 103 5.3.3 Stage 3: mineralization stage, copper sulfide bearing structures .................... 105 5.3.4 Stage 4: mineralization stage, wolframite bearing veins and breccias ............ 113 5.3.5 Stage 5: late mineralization, enargite bearing veins ....................................... 116 5.3.6 Stage 6: Post- mineralization stage, sphalerite bearing structures ................. 120 5.3.7 Stage 7: supergene features related to mineralization, late faulting and iron oxides bearing structures. ....................................................................................... 124 5.4 Mineral zonation and gold grade distribution at La Bodega and La Mascota ........ 126 5.5 Paragenetic sequence of events at La Bodega and La Mascota .......................... 131 Chapter 6. Geochronological Constraints of Alteration and Mineralization Events at La Mascota and La Bodega ....................................................................................................................................... 136

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6.1 Introduction .......................................................................................................... 136 6.2 Methodology......................................................................................................... 138 6.2.1 Sample collection ........................................................................................... 139 6.2.2 Analytical procedures ..................................................................................... 140 6.3 Results ................................................................................................................. 143 6.4 Alunite and muscovite alteration geochronology, relationship to the CVMD geological history and paragenetic sequence of mineralizing events at La Bodega and La Mascota ................................................................................................................................... 147 Chapter 7. Fluid Inclusion Microthermometry from Epithermal Quartz at La Bodega and La Mascota ......................................................................................................................................................... 150

7.1 Introduction .......................................................................................................... 150 7.2 Previous fluid inclusion studies in the California-Vetas Mining District .................. 151 7.3 Methodology......................................................................................................... 153 7.3.1 Sample preparation, equipment configuration and data collection .................. 153 7.3.2 Salinity, pressure and depth calculation procedures ...................................... 155 7.4 Petrography of fluid Inclusions in this study .......................................................... 156 7.4.1. La Mascota sample petrography and fluid inclusion petrography summary ... 157 7.4.2 La Bodega sample petrography and fluid inclusion petrography summary ..... 162 7.5 Microthermometry results ..................................................................................... 165 7.5.1 La Mascota, sample ALR189 ......................................................................... 167 7.5.2 La Bodega, sample ALR260F ........................................................................ 168 7.6 Discussion ............................................................................................................ 170 7.6.1 Enargite related quartz fluid inclusions at La Mascota (ALR189) .................... 170 vii

7.6.2 Wolframite related quartz fluid inclusions at La Mascota (ALR189) ................ 170 7.6.3 La Bodega, enargite quartz related fluid inclusions (ALR260) ........................ 172 7.6.4 Implication of fluid inclusions microthermometry results and boiling ............... 173 7.6.5. Estimation of depth of emplacement based on primary fluid inclusion analysis ............................................................................................................................... 174 7.6.6 Comparison to other fluid inclusion studies within the California Vetas Mining District and hydrothermal environment implications ................................................ 176 Chapter 8. Origin of Mineralizing Fluids at La Bodega and La Mascota: Insights from Oxygen, Deuterium and Sulfur Stable Isotopes ............................................................................................ 180

8.1 Introduction .......................................................................................................... 180 8.2 Methodology......................................................................................................... 184 8.2.1 Sample selection and separation ....................................................................... 184 8.2.2 Analytical methods ......................................................................................... 186 8.3 Results ................................................................................................................. 188 8.3.1 Pyrite sulfur isotopes ...................................................................................... 188 8.3.2 Alunite sulfur isotopes .................................................................................... 193 8.3.3 Geothermometry using the Δ34S between alunite – pyrite pairs...................... 193 8.3.4 δD and δ18O isotopes. .................................................................................... 195 8.4 Discussion ............................................................................................................ 197 8.4.1 Pyrite δ34S signatures .................................................................................... 197 8.4.2 δ34S of alunite – pyrite pairs and geothermometry constraints at La Bodega, La Mascota and La Plata ............................................................................................ 200 8.4.3 Origin of the hydrothermal mineralizing fluids ................................................. 200

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Chapter 9. Evolution of La Bodega and La Mascota Deposits: A Discussion and Comparison to Other Epithermal Deposits .............................................................................................................. 202

9.1 Late Miocene history ............................................................................................ 202 9.2 Porphyry phases at La Bodega and La Mascota: early stages 1 and 2 in the context of the CVMD............................................................................................................... 203 Stage 1 ................................................................................................................... 203 Stage 2 ................................................................................................................... 205 9.3 Epithermal phase: stages 3, 4, 5 and 6. ............................................................... 207 Stage 3 ................................................................................................................... 207 Stage 4 ................................................................................................................... 208 Stage 5 ................................................................................................................... 209 Stage 6 ................................................................................................................... 210 9.4 Oxidation state of the hydrothermal and mineralizing fluids. ................................. 213 9.5 Depth of emplacement of the mineralization and surface processes. ................... 214 9.6 Summary of mineralization characteristics at La Bodega/La Mascota and comparison to other similar epithermal and porphyry systems ................................... 218 Chapter 10. Conclusions, Exploration Implications and Recommendations for Future Work ........ 222

10.1 Conclusions ........................................................................................................ 222 10.2 Exploration implications ...................................................................................... 224 10.3 Recommendations ............................................................................................. 225 References ...................................................................................................................................... 227 Appendix A1. Drill Hole Locations. .................................................................................................. 241 Appendix A2. Sample Location within Drill Holes, Brief Descriptions, Notes and Analysis Carried out ......................................................................................................................................................... 243 Appendix A3. Gold Relationships to element concentrations at La Bodega and La Mascota. ....... 271 Appendix A4. Alteration Minerals Identification Methods at La Bodega - La Mascota Deposits. ... 278

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Apppendix A5. Sulfides and Paragenetic Sequence Related Support Data. X-Ray Difraction Analysis on Selected Samples and Energy Dispersion X-Ray Spectrum of Seleced Samples. .... 296 Appendix A6. Geochronological Data for Samples Presented in Chapter 6. La Bodega, La Mascota, El Cuatro.......................................................................................................................................... 302 Appendix A7. Fluid Inclusion Study Microthermometry and Data. .................................................. 318 Appendix A8. Thin Section Petrography of Selected Samples from La Bodega, La Mascota and El Cuatro .............................................................................................................................................. 326

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List of Tables Chapter 2 Table 2.1. Characteristics of Principal Alteration-Mineralization Types in Porphyry Cu Systems¹ (from Sillitoe, 2010) ........................................................................................................................... 17 Table 2.2. Features of principal Hydrothermal Breccia Types in Porphyry Cu Systems (Sillitoe, 2010) ................................................................................................................................................. 21 Table 2.3. Examples of buffer reactions and association to sulfidation state or environment (after Einaudi et al. 2003) ........................................................................................................................... 22 Table 2.4. Summary of Hydrothermal Alteration Assemblages Forming in Epithermal Environments (Simmons et al., 2005) ...................................................................................................................... 26 Table 2.5. Principal field-oriented characteristics of epithermal types and subtypes (from Sillitoe and Hedenquist, 2003) ............................................................................................................................. 28

Chapter 4 Table 4.1. Comparison and correspondence of alteration assemblages at La Bodega and La Mascota to alteration assemblages described for epithermal environment by Simmons et al. (2005) and for porphyry environment according to Sillitoe (2010). .............................................................. 76

Chapter 5 Table 5.1. Summary of ore related minerals observed at La Bodega and La Mascota (this study except where indicated) and their relationship to alteration zones defined in Chapter 4 and mode of occurrence. ...................................................................................................................................... 100 Table 5.2 Correlation matrix for sixteen elements at La Bodega (DDH LB251 and LB327) and La Mascota (DDH LB 202 and LB205). ................................................................................................ 128

Chapter 6 40

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Table 6.1. Summary of results of ArK/ Ar geochronology at La Bodega, La Mascota and El Cuatro. ............................................................................................................................................. 144

Chapter 7 Table 7.1. Fluid inclusions characterization and associated codes. ............................................... 156 Table 7.2 Summary of results from 62 fluid inclusions microthermometry analysis at La Mascota and La Bodega grouped based on common characteristics, mainly location within quartz crystal. 166

Chapter 8 Table 8.1. Natural abundance and reference standards for light stable isotopes (Adapted from Hoefs, 1997 in Campbel and Larson 1998) .................................................................................... 180 Table 8.2. Stable Isotope terminology (Campbel and Larson, 1998) .............................................. 181 34 Table 8.3. Stable isotope results of δ S, O and D (‰) in the California-Vetas Mining district. 189

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List of Figures Chapter 1 Figure 1.1. Geographic location and physiography of the project area.. ............................................ 2

Chapter 2 Figure 2.1. Worldwide locations of porphyry Cu systems cited as examples of features discussed in the text along with five additional giant examples. ............................................................................ 12 Figure 2.2. Telescoped porphyry Cu system (after Sillitoe, 2010). ................................................... 14 Figure 2.3. Common alteration mineralogy in hydrothermal systems in their relative pH and temperature stability range (after Corbett and Leach, 1998) ............................................................ 16 Figure 2.4. Dilational structures. A. Dilational veins and related structures. B. Extension mineralization styles at different crustal levels (after Corbett and Leach, 1998). ............................. 20 Figure 2.5. Log fS2 – 1000/T diagram, contoured for Rs, illustrating fluid environments in porphyry copper, porphyry copper related base-metal veins, and epithermal Au-Ag deposits in terms of a series of possible cooling paths (from Einaudi et al., 2003). ............................................................. 23 Figure 2.6. Location of epithermal deposits in the world (modified after Simmons et al., 2005).. .... 25 Figure 2.7. Low Sulfidation and High sulfidation model and related ore textures examples. (Adapted and modified after Corbett, 2002)...................................................................................................... 27 Figure 2.8. Summary of the various silica and calcite textures observed in the epithermal environment (from Moncada et al., 2012) ......................................................................................... 33

Chapter 3 Figure 3.1 (next page). Location of California-Vetas Mining District (CVMD) within Colombia, South America; in relation to the Chibcha Terrane (Ch) (Restrepo et al., 2011) and the Maracaibo Subplate Realm triangular tectonic block (MSP) (Cediel et al., 2003). The map shows the major fault systems that divide these tectonic blocks and terranes.. .......................................................... 38 Figure 3.2 Schematic 3D model based on seismic tomography showing Bucaramanga seismic nest and relationship to interaction between the Caribbean, Nazca and South American Plates (Modified after Taboada et al., 2000; Prieto et al., 2012; Vargas and Mann, 2013) ......................................... 41 Figure 3.3 California-Vetas Mining District Geological Map. (After Polania 1980, Evans, 1976, Ward, 1973; Mantilla et al., 2012, MDRU Colombia Gold Project). ............................................................. 43 Figure 3.4. La Mascota and La Bodega area geological map showing location for geological drill holes that were sampled and studied geological sections ................................................................ 44 Figure 3.5. N-S geological cross-section B-B’ at La Bodega, looking west ...................................... 45 Figure 3.6. N-S geological cross section M-M’ at La Mascota, looking west. ................................... 46 Figure 3.7. Examples of the Bucaramanga Complex at La Bodega and La Mascota.. .................... 49 Figure 3.8. Jurassic intrusive rocks (leucogranites) from La Mascota and La Bodega.. .................. 52 Figure 3.9. Pegmatite rocks at La Bodega. ....................................................................................... 54 Figure 3.10. Late Cretaceous rocks (Tambor Formation). Outcrop to the west of California town. . 55 Figure 3.11 Miocene porphyritic granidiorites at the CVMD. ............................................................ 57 Figure 3.12. La Bodega typical hydrothermal breccias.. ................................................................... 60 Figure 3.13. Breccia types at La Mascota based on physical components and arrange. ................. 62 Figure 3.14. Tectonic-hydrothermal breccia (THBX) at different scales. .......................................... 63 Figure 3.15. Structural data representing main trends within La Bodega and La Mascota. ............. 68 Figure 3.16. Common examples of fractured rocks and faults and fault breccias filled with gouge at La Bodega and La Mascota. ............................................................................................................. 69 Figure 3.17. Geological map of the California Vetas Mining district showing prospective areas for the development of dilational structures along La Baja Trend (yellow ovals) where mining takes place. ................................................................................................................................................. 71

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Chapter 4 Figure 4.1. B-B’ North - South geological section looking west. Alteration at La Bodega. Relationship to protholith and gold (Au) mineralization. .................................................................... 74 Figure 4.2. M-M’ North - South geological section looking west. Alteration at La Mascota. Relationship to protholith and gold (Au) mineralization. .................................................................... 74 Figure 4.3. Chlorite and chlorite-epidote alteration assemblages developed in amphibolite lenses at La Bodega.. ....................................................................................................................................... 79 Figure 4.4. Chlorite and chlorite-epidote alteration mineral assemblages, examples from La Mascota. ............................................................................................................................................ 80 Figure 4.5. Muscovite (sericite) and illite alteration assemblages at La Bodega. ............................. 83 Figure 4.6. Muscovite (sericite) and illite alteration assemblages at La Mascota ............................. 84 Figure 4.7. Alunite, occurrence at La Bodega related to quartz (silicification) and kaolinite. ........... 87 Figure 4.8. Alunite occurrence related to quartz and kaolinite alteration at La Mascota.. ................ 88 Figure 4.9. Macroscopic textures related to silicification-advanced argillic alteration and hydrothermal breccias at La Mascota and La Bodega. ..................................................................... 91 Figure 4.10. Microphotographs of main textures related to La Mascota Hydrothermal Breccias ..... 92

Chapter 5 Figure 5.1. Specularite veins and related minerals related to stage 1 at La Bodega and La Mascota. ......................................................................................................................................................... 102 Figure 5.2. Quartz + pyrite veins at La Bodega and La Mascota, stage 2. ..................................... 104 Figure 5.3. La Bodega. Copper sulfides bearing veins and associated alteration.. ........................ 106 Figure 5.4. La Mascota, copper sulfides and gold, stage 3. Figure 5.5. Relationship of copper sulfides, pyrite and silver sulfosalts in stage 3 ......................... 109 Figure 5.6 Gold (electrum) bearing quartz vein with minor sphalerite and chalcopyrite cross cutting quartz + cubic pyrite + hematite vein in muscovite alteration zone. ................................................ 111 Figure 5.7. Molybdenite occurrence at La Bodega and La Mascota (pre-stage 2? and early stage 3?). .................................................................................................................................................. 112 Figure 5.8. Hydrothermal breccia with quartz cement exhibiting tectonic foliation (THBX) at La Bodega. ........................................................................................................................................... 114 Figure 5.9. Wolframite (hübnerite) occurrence at La Mascota.. ...................................................... 115 Figure 5.10. Enargite occurrence at La Bodega. ............................................................................ 117 Figure 5.11. Enargite at La Mascota. .............................................................................................. 118 Figure 5.12. Tennantite-tetrahedrite at La Mascota in relation to stages 4 and 5 and associated silver mineralization.. ....................................................................................................................... 119 Figure 5.13. Sphalerite and marcasite at La Bodega. ..................................................................... 122 Figure 5.14. Sphalerite, marcasite and sulfur at La Mascota. ......................................................... 123 Figure 5.15. Supergene alteration minerals at La Bodega and La Mascota. .................................. 125 Figure 5.16. N-S Section B-B’, looking west. Mineralization style at La Bodega based on predominant ore mineral association. ............................................................................................. 129 Figure 5.17. N-S Section M-M’ looking west. Mineralization style at La Mascota based on predominant ore mineral association. ............................................................................................. 130 Figure 5.18. Paragenetic sequence for La Bodega and La Mascota. ............................................. 132 Figure 5.19. Log f S2 – 1000/T diagram, showing sulfidation state of magmas and mineral sulfidation reactions at 1 bar (Einaudi and Hedenquist, 2003). In blue, it is represented the range of minerals within La Bodega and La Mascota deposits paragenetic sequence and the evolution path of the hydrothermal fluids is schematically shown .................................................................................... 135

Chapter 6 Figure 6.1 Recent geochronological data shown on the geological map of the California Vetas district. Map based on this study and MDRU Colombia Porphyry and Epithermal Gold Project.. .. 141 40 39 Figure 6.2 Samples selected for ArK/ Ar geochronology ............................................................ 142

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Figure 6.3. Alunite and muscovite (sericite) ArK/ Ar age spectra at La Macota, La Bodega and El Cuatro.. ............................................................................................................................................ 146 40 39 Figure 6.4. ArK/ Ar geochronology ages on alunite and muscovite within La Bodega and La Mascota in relation to the stages of paragenetic sequence of hydrothermal events at La Mascota and La Bodega; hydrothermal events at La Perezosa and El Cuatro and magmatic events at the CVMD. ............................................................................................................................................. 149

Chapter 7 Figure 7.1. La Mascota, sample ALR189; DDH LB 202 at 203.m; approximate depth from surface: 100 m (Figure 3.6). Polymictic clast to cement supported multiple phases hydrothermal breccia. 158 Figure 7.2. La Mascota, ALR189F. FIs in enargite related quartz. ................................................. 160 Figure 7.3. La Mascota, ALR189F. FIs in wolframite related quartz. .............................................. 161 Figure 7.4. La Bodega, ALR260F. Fluid inclusions in enargite related quartz.. .............................. 164 Figure 7.5. Fluid inclusion data compiled for La Mascota and La Bodega in enargite related quartz and wolframite related quartz within this study. Total of 62 measurements. .................................. 169 Figure 7.6. Fluid inclusion trends from fluid inclusion data. Salinity vs Homogenization temperature. ......................................................................................................................................................... 171 Figure 7.7. Depth of emplacement estimate based on fluid inclusion microthermometry of hydrothermal quartz at La Mascota from sample ALR189. ............................................................. 177 Figure 7.8. Salinity (wt%NaCl equiv.) vs Homogenization temperature of FIs in quartz from different paragenetic stages with California-Vetas Mining district ................................................................. 179

Chapter 8 Figure 8.1. Selected samples for isotopic analysis from La Bodega and La Mascota.. .................. 185 34 Figure 8.2 δ S values obtained at the California-Vetas Mining District compared to classic deposits types around the world including several high sulfidation deposits ................................................ 191 34 Figure 8.3. δ S values obtained at the California-Vetas Mining District compared to the sample 40 39 ages obtained by Ar/ Ar geochronology on alunite related to pyrite and the presumable age based on mineralization stages. ...................................................................................................... 192 34 34 Figure 8.4. δ Salunite vs. δ Spyrite plot showing data from La Mascota, La Bodega and La Plata from different paragenetic stages (colored markers). ..................................................................... 196 18 18 Figure 8.5. δD vs δ O plot (reported relative to VSMOW). δ O from alunite (SO4) isotopic compositions is calculated in equilibrium with hydrothermal fluids at a temperature of 251 °C. .... 197

Chapter 9 Figure 9.1. Schematic block diagram of the CVMD at La Baja Trend, at ~10 Ma-8 Ma over current surface. Late Miocene rocks (porphyry dikes, breccia, tuff (?) volcanic rocks) and probable volcano at Cerro Violetal are indicated. An inferred mid crustal magma chamber from which porphyries, volatiles and metals are derived is indicated. Geology adapted from (Ward et al., 1973; Mendoza and Jaramillo, 1973; Polania, 1980; Galvis, 1998; Felder et al., 2005; Bernasconi et al., 2010; MDRU Epithermal and Porphyry Gold Project, 2013).. ................................................................... 204 Figure 9.2. Schematic block diagram of the CVMD at La Baja Trend showing distribution of alteration and mineralization developed during the Pliocene (~4-3.25 Ma). ................................... 206 Figure 9.3. Schematic block diagram of the CVMD at La Baja Trend showing distribution of alteration and mineralization developed during the Pliocene-Pleistocene (~2.5-1 km in thickness if unaffected by significant erosion. Low sulfidation-state chalcopyrite ± bornite assemblages are characteristic of potassic zones, whereas higher sulfidation-state sulfides are generated progressively upward in concert with temperature decline and the concomitant greater degrees of hydrolytic alteration, culminating in pyrite ± enargite ± covellite in the shallow parts of the lithocaps. The porphyry Cu mineralization occurs in a distinctive sequence of quartz-bearing veinlets as well as in disseminated form in the altered rock between them”. Relevant characteristics of alteration envelopes and veins relationships within porphyry systems are compiled in Table 2.1(Sillitoe, 2010). Overprinting of late, shallow, generally epithermal styles of precious- and basemetal mineralization over early, deep mineralization of porphyry type is a common characteristic of porphyry copper systems (Figure 2.4) widely known as telescoping (Sillitoe, 1994). Crosscutting relationships, including offset veins,

15

provide definitive evidence for the relative ages of hydrothermal events at a particular location (Seedorff et al., 2005). Duration of hydrothermal activity of 50.000 yr to 500.000 yr are common, but several large porphyry Cu deposits include multiple events span several million years (Seedorff et al., 2005).

Figure 2.3. Common alteration mineralogy in hydrothermal systems in their relative pH and temperature stability range (after Corbett and Leach, 1998)

16

Table 2.1. Characteristics of principal alteration-mineralization types in Porphyry Cu Systems¹ (after Sillitoe, 2010) Alteration type² (alternative name) Sodic-calcic

Position in system (abundance)

Key minerals

Potassic (K-silicate)

Core zones of porphyry Cu deposits (ubiquitous)

Biotite, K-feldspar

Propylitic

Marginal parts of systems, below lithocaps (ubiquitous)

Chlorite-sericite (sericite-claychlorite [SCC])

Possible ancillary minerals

Principal sulfide assemblages (minor) Typically absent

Contemporaneous veintels³ (designation)

Veinlet selvages

Economic potencial

Magnetite + actinolite (M-type)

Albite/oligoclase

Actinolite, epidote, sericite andalusite, albite, carbonate, tourmaline, magnetite

Pyrite-chalcopyrite, chacolpyrite + bornite, bornite + degenite + chalcocite

Biotite (EB-type), K-feldspar, quartz-biotite-sericiteK-fedspar-andalusitesulfides (EDM/T4-type), quartz-sulfides + magnetite (A-type), quartz-molybdenite + pyrite + chalcopyrite (central suture; B-type)

EDM-type with sericite + biotite + K-feldspar + andalusite + disseminated chalcopyrite + bornite; others none, except locally K-feldespar around A- and B-types

Normally barren, but locally ore bearing Main ore contributor

Chlorite, epidote, albite, carbonate

Actinolite, hematite, magnetite

Pyrite (+ sphalerite, galena)

Pyrite, epidote

Upper parts of porphyry Cu core zones (common, particularly in Aurich deposits)

Chlorite, sericite/illite, hematite (martite, specularite)

Carbonate, epidote, smectite

Pyrite-chalcopyrite

Chlorite + sericite + sulfides

Chlorite, sericite/illite

Common ore contributor

Sericitic (phyllic)

Upper parts of porphyry Cu deposits (ubiquitous, except with alkaline intrusions)

Quartz, sericite

Pyrophyllite, carbonate, tourmaline, specularite

Pyrite + chalcopyrite (pyrite-enargite + tennantite, pyritebornite + chalcocite, pyrite-sphalerite)

Quartz-pyrite + other sulfides (D-type)

Quartz-sericite

Commonly barren, but may constitute ore

Advanced argillic

Above porphyry Cu deposits, constitutes lithocaps (common)

Quartz (partly residual vuggy), alunite⁴, pyrophyllite, dickite, kaolinite

Diaspore, andalusite, Pyrite-enargite, zunyite, corundum, pyrite-chalcocite, dumortierite, topaz, pyrite-covellite specularite

Pyrite-enargite + Cu sulfides (includes veins)

Quartz-alunite, quartzpyrophyllite/dickite, quartz-kaolinite

Locally constitutes ore in lithocaps and their roots

Deep, including Albite/oligoclase, Diopside, below porphyry Cu actinolite, epidote, garnet deposits (uncommon) magnetite

Barren, except for subephitermal veins

¹ Excluding those developed in carbonate-rich rocks. ² Arranged from probable oldest (top) to youngest (bottom), except for propylitic that is lateral equivalent of potassic; advanced argillic also forms above potassic early in systems. ³ Many veinlets in potassic, chlorite-sericite, and sericitic alteration contain anhydrite, which also occurs as late, largely monomineralic veinlets. ⁴ Alunite commonly intergrown with aluminum-phosphate-sulfate (APS) minerals (see Stoffregen and Alpers, 1987)

17

2.3 Faults and fracture networks and their role in hydrothermal. Successful development of hydrothermal ore systems requires an appropriate dynamic setting to generate metal fertile fluid reservoirs; second, it requires the generation of permeable fluid pathways to drain fluids from potentially largevolume fluid reservoirs and transport them to volumetrically much smaller ore deposition sites (Cox, 2005). According to Candela and Piccoli (2005); in porphyry systems, dilational tectonic features may accommodate some high level plutons, as well as their associated cupolas and apophyses. The large scale through-going fractures that host these local zones of dilations can extent to lower crust and control magmatism (Cox, 2005). Deformation is required to regenerate permeability and facilitate the high fluid flux necessary to produce hydrothermal ore systems (Cox, 2005). Episodic fluid redistribution from breached, overpressured (i.e., suprahydrostatic) reservoirs has the potential to generate large fluid discharge and high fluid/rock ratios around the downstream parts of fault systems after large rupture events (Cox, 2005). Hydrothermal selfsealing of faults, together with drainage of the hydraulically accessible parts of reservoirs between earthquakes, progressively shuts off flow along fault ruptures (Cox, 2005). According to Corbett and Leach (1998); different styles of dilational ore environments can be distinguished associated with different levels of the hydrothermal systems (Figure 2.4) including: tension fracture/veins, jogs (Sibson, 1989, 1992 In Corbett and Leach, 1998), flexures (Sibson, 1989 In Corbett and Leach, 1998), hanging (foot) wall splits (splays), domes and ore shoots

18

(McKinstry, 1948 In Corbett and Leach, 1998). These features may have become filled by hydrothermal minerals originating veins and veins networks (Corbett and Leach, 1998). Intense fluid activity can be indicated by abundant veins, hydrothermal alteration around veins and fracture networks, and disturbance to isotopic systems (Cox, 2005). Dilatant features mentioned here are distinguished from, and locally transitional to, breccias (Corbett and Leach, 1998). According to Corbett and Leach (1998), practically all magmatic arc gold-copper systems contain breccias, and processes of breccia formation are intimately related (e. g. El Indio Pascua, Deyell et al. 2005; Lagunas Norte, Cerpa et al., 2013). Components of a breccia include fragments or broken rock clasts, that become milled with increase deformation – brecciation); matrix, which comprises minerals (including ore) deposited from hydrothermal fluids as well as locallyderived and introduced rock material of a finer grain size than the fragments; cement, formed by minerals precipitated from hydrothermal fluid and so occurs within the matrix; open space or cavities develop between fragments which may become filled by hydrothermal minerals including ore during or following brecciation (Corbett and Leach, 1998). Hydrothermal fluids may partially or totally replace matrix grains and this can make it hard to distinguish between these two elements (matrix and cement). Cement precipitated from aqueous fluids is a diagnostic component of most hydrothermal breccias (Davies et al., 2008). According to Sillitoe (2010), hydrothermal breccias associated with porphyry systems include magmatic-hydrothermal, phreatic at the porphyry Cu level, phreatic at the epithermal level and phreato-magmatic (Table 2.2). 19

On the other hand, tectonic breccias are formed by mechanical disruption of rocks in response to tectonic stress and tend to occur in identifiable, usually steeply dipping, fault planes (Lawless and White, 1990). Tectonic breccias on fault zones within active hydrothermal system form highly permeable channels for the passage of fluids (Lawless and White, 1990). Dike-like tectonic breccias cemented by hydrothermal fluids are referred as tectonic-hydrothermal breccias i.e. Owl Creek calcite-cemented breccias, Wyoming-Montana, US (Kats et al., 2006).

Figure 2.4. Dilational structures. A. Dilational veins and related structures. B. Extension mineralization styles at different crustal levels (after Corbett and Leach, 1998).

20

Table 2.2. Features of principal Hydrothermal Breccia Types in Porphyry Cu Systems (Sillitoe, 2010)

Type

Position in system (abundance)

Within porphyry Cu Magmatic deposits, locally around Hydrothermal them (ubiquitous)

Form

Irregular, pipelike bodies (10s-100s m in diameter)

Phreatic (porphyry Cu level)

Within and around porphyry Cu deposits (relatively common)

Dikes uncommonly sills and irregular bodies

Phreatic (epithermal level)

Within lithocaps, local surface manifestations as eruption breccia (relatively common)

Phreatomagmatic

Diatremes span porphyry Cu and epithermal environments; surface manifestations as maar volcanoes (present in ~20% of systems)

Relative Timing

Typically intermineral

Clast Features

Matrix/Cement

Commonly monomictic

Quartz-magnetitebiotite-sulfides/ quartz-muscovitetourmaline-sulfides + rock flour + igneous rock (i. e. igneous breccia)

Clast/matrix proportions

Alteration Types

Main Cubearing mineral(s)

Economic Potential

Clast or matrix supported

Potassic + chloritesericite + sericitec, uncommonly advanced argillic

Chalcopyrite, uncommonly bornite

May constitute ore, commonly high grade

Generally none

Barren unless rich in preexisting mineralization (e.g., Bisbee; Bryant, 1987)

Enargite, Luzonite

May constitute high sulfidation Cu/Au/Ag ore

Locally enargite

Commonly barren, but may host porphyry Cu or high-sulfidation ore types

Polymict, rounded to subrounded

Muddy rock flour

Matrix supported

Typically intermineral Irregular bodies relative to (10s-100s m in lithocap diameter) development

Chalcedony, quartz, alunite, barite, sulfides, native S



Kilometerscale, downwardnarrowing conduits

Polymictic, centimeter-sized, rounded, and polished; juvenile (magma blob, pumice) clasts locally

Rock flour with juvenile tuff or magma blob component; early examples cut by porphyry Cu mineralization

Matrix dominated; accretionary lapilli in matrixdominated layers

Late

Commonly late, but early examples known

21

Sericitic, advanced argillic, or none

Advanced argillic None advanced argillig, but early examples with any alteration type depending on the exposure level

2.4 Sulfidation state The terms "sulfur content" and "sulfidation state" denote the relative values of the chemical potential of sulfur implied by sulfide mineral assemblages in ore deposits (McKinstry, 1959, 1963 and Barton, 1970 in Einaudi, 1994). The sulfidation state is used by Einaudi et al. (2003) as defined by Barton (1970) and in a manner analogous to oxidation state, where the frame of reference is temperature and the fugacity of S2 and O2 gas, respectively. The difference between the oxygen or sulfur fugacity implied by a natural mineral assemblage compares with that of a buffer reaction (e.g., table 2.3) and forms the basis for assigning relative oxidation or sulfidation states (Einaudi et al., 2003). Table 2.3. Examples of buffer reactions and association to sulfidation state or environment (after Einaudi et al. 2003) Reactions (Buffer) Environment Limit Reactants

=

Fe3O4

+ O2 =

Fe2O3

Magnetite

+ O2 =

hematite

2 FeS

+ S2 =

2 FeS2

Pyrrhotite

+ S2 =

pyrite

5 CuFeS2

+ S2 =

Cu5FeS4

+

4 FeS2

chalcopyrite

+ S2 =

bornite

+

pyrite

0.67Cu12As4S13 + S2 = tennantite

0.47 FeAsS +

Arsenopyrite

Products

1.41CuFeS2 chalcopyrite

+ S2 =

2.67 Cu3AsS4 enargite

+ S2 = 0.12Cu12As4S13 + 1.88 FeS2 + S2 =

tennantite

22

+

pyrite

Lower limit of intermediate sulfidation states Boundary between intermediate and high sulfidation states Transition between porphyry copper deposits (sensu stricto) and porphyry related base-metal veins Lower limit to sulfidation state in intermediate Sulfidation epithermal deposits

Terminology based on sulfidation reactions among minerals in the system Cu-FeAs-S common to porphyry copper deposits, porphyry-related veins, and epithermal precious-metal deposits has been introduced in order to easily compare the sulfidation state between different fluids and between fluids and mineral assemblages: "very low", "low", "intermediate", "high", and "very high" sulfidation states (Einaudi et al., 2003). Each sulfidation state has an upper thermal limit (Einaudi et al., 2003; Figure 2.5).

Figure 2.5. Log fS2 – 1000/T diagram, contoured for Rs, illustrating fluid environments in porphyry copper, porphyry copper related base-metal veins, and epithermal Au-Ag deposits in terms of a series of possible cooling paths. Mineral symbols: asp: arsenopyrite, bn: bornite, cc: chalcocite, ch: chalcopyrite; cv: covellite, dg: digenite, en: enargite; hm: hematite, lo: loellingite, ln: luzonite, mt: magnetite, py=pyrite, po: pyrrhotite (from Einaudi et al., 2003).

23

2.5 Epithermal systems (high-sulfidation and low-sulfidation). The term “epithermal” is derived from Lindgren’s (1933) classification of ore deposits and refers to those that formed at shallow crustal levels (Robb, 2005). Epithermal systems are an important source of precious and base metals (as gold, silver, copper and zinc); they are associated with convergent margins and commonly related to known porphyry systems (Figure 2.6): Tertiary and younger examples are found around the Pacific Rim, in the Mediterranean and Carpathian regions of Europe, older are within Tethyan arc from Europe to Asia and volcanic arcs of all ages with rare examples as old as Archean (Simmons et al., 2005). Epithermal ore deposits form over the temperature range of >>0.01mm) with few individuals of up to 0.1 mm (possibly primary, up to 0.1%). Veins: Pyrite (cubic and dodecahedric) vein with minor chalcocite and bornite on pyrite wall; cutting fine pyrite+quartz vein (qz2 in veins)

Thin section

Hand sample photograph

XPL

1 cm Microphotographs Magnification

qz1

2X

XPL+RL

py

qz1

mus (ser), minor qz py vnlet qz+alu

qz1 2 mm

qz2

386

Sample (cont') Zone DDH Depth [m] ALR126 La Bodega LB251 300.8 Code Rock Type Leucogranite INT Alteration Phyllic (muscovite-quartz); apparently minor alunite (?) cont… Microphotograph Zoom Magnification 20X RL

cc

bn py

cpy

Au 15 μm

387

Sample ALR128 Rock Type Alteration

Zone La Bodega Leucogranite Phyllic (muscovite-illite, quartz)

DDH LB251 Code

Depth [m] 318.3 INT

Description, Notes Granite. Main Minerals: Quartz1: Primary Quartz (32%) Random individuals of up to 2 mm in diameter. Anhedral habit. Feld spars (55%): Mostly altered to sericite (fine grained muscovite) and silica (Microcrystaline Quartz) Muscovite: Primary (?) (10%) Random individuals and adjacent to quartz crystals. Quartz (2): Secondary (microcrystalline Quartz or silica) (15%): Aggregates of Crystals of 0.01 to 0.05 mm in diameter. Anhedral habit to semicircular shape. Related to muscovite alteration. Muscovite (sericite) (40%): Fine grained making a groundmass intergrained with silica in some cases. Product of feldspars (possibly plagioclase) alteration. Pyrite (3%): random cubic crystals related to sericite up (1-2 mm in width) Veins: Qz+Py vein with minor cpy cuting Qz+Py microvein. Chalcopyrite microinclusions in pyrite and possibly gold microinclusions in pyrite and pyrite fractures.

Thin section


XPL

1 cm

Microphotograph Magnification

5X

XPL

mus

ser

qz1

py

qz 2 (fine grained)

388

Sample (cont') Zone ALR128 La Bodega Rock Type Leucogranite Alteration Phyllic (muscovite-illite, quartz) Microphotograph Magnification 2X

DDH LB251 Code

Depth [m] 318.3 INT

RL+XPL

qz (comb) mus

qz1 ser

py

mus

2 mm Microphotograph Magnification

20X

RL

150 μm

Au cpy py

Au

389


Zone La Bodega Leucogranite Phyllic (muscovite, quartz)

DDH LB251 Code

Depth [m] 331.9 INT

Description, Notes Granite. Coarse grained. Quartz+pyrite+chacocite+borniten+covellite (+Au?) vein cutting and displacing. Quartz+pyrite veinlet. Au inclusions in Py. Quartz 1 (40%): Anhedral, weakly strained, undulose extinction, up to 0.5 mm. Feldspars (45%): Altered to sericite. Muscovite (10%): tabular random individuals up to 0.01 mm. Pyrite (5%): Subhedral disseminated fine grained cubic habit (1% up to 0.1mm) and in quartz vein subhedral cubic habit (4%, up to 0.4 mm). Veins: Quartz+pyrite+chalcopyrite+chalcocite+bornite+-covellite (?) and minor Au (in borders?) vein cutting Quartz+pyrite veinlet with Au inclusions (?).

Thin section


1 cm Microphotograph Magnification

2X

RL+XPL

py +CuS

qz1

ser py (disseminated) mus

2 mm

390

XPL

Sample (cont') Zone ALR130 La Bodega Rock Type Leucogranite Alteration Phyllic (muscovite, quartz) Microphotograph Magnification 20X

DDH LB251 Code

Depth [m] 331.9 INT

150 μm

cpy

py


50X

RL

Au? cc

cv

py

cc cpy

50 μm

391


Zone La Bodega

DDH LB114

Depth [m] 207.9 Code Gneiss BG Propylitic (chlorite, titanite, pyrite), minor sericite on feldspars

Description, Notes Feldspar-quartz Gneiss with biotite. Granoblastic-granolepidoblastic texture. Chlorite alteration on mafics and biotite. Chlorite+pyite vein cut by Quartz+Pyrite (coarse) vein. Quartz 1 (30%): subidiomorphic elonged porphyroblasts up to 1.5 mm with undulose extinction. Quartz subgrains ~ 0.2mm. Fekdspars (40%): Subidiomorfic-elonged in some cases. Plagioclase (20%), moderately altered to sericite (?) and replaced by quartz subgrains (?); K-felspar (20%), not clearly seen in thin section,altered to sericite (?). Mafics and Biotite (30%): Biotite (20%) is up to 2 mm, subidiomorphic, tabular, altered to chlorite, and replaced also by titanite and pyrite; Hornblende (10%) is up to 2 mm, subidiomorphic, tabular, altered to chlorite and replaced also by titanite and pyrite. Veins: Chlorite+pyrite veins cut by quartz=pyrite vei(coarse) vein with sericite alteration halo (?)

Thin section


XPL


2X

RL+XPL subgrains

fds (ser?)

py

hb?

chl?

fds (ser?)

qz subgrains

2 mm

qz1

392

py

Sample (cont') Zone DDH Depth [m] ALR137 La Bodega LB114 207.9 Code Rock Type Gneiss BG Alteration Propylitic (chlorite, titanite, pyrite), minor sericite on feldspars Microphotograph Magnification 2X RL+XPL

py (after hb?bt?)

ttn (after hb?bt?)

chl (after hb?bt?)

qz1

subgrains

qz (strained) subgrains

fds

qz1


10X

PPL

py (after hb?) ttn, rt (after hb?bt?)

chl (after hb?bt?)

250 μm

393


Zone La Mascota

DDH LB114 Code

Hydrothermal breccia (Quartz cemented breccia)

Depth [m] 296.9 HYBX

Advanced argillic (quartz alunite, silicification)

Description, Notes Clast to cement supported breccia. Quartz clasts, pyrite clasts, quartz replaced clasts with pyrite. Clasts (gneiss) with sericite alteration, also replaced by titanite and rutile (probably after mafics). Minor sericite (?) replaced by alunite (?) Quartz cement (fine grained) with alunite and minor pyrite all around clasts. Quartz clast with quartz cement overgrown around it in one side of the clast. Quartz shows undulose extinction. Clasts: 40% Quartz, gneiss, quartz replaced clasts, pyrite. Matrix: 25%. Finer grained groundmass (all replaced by quartz and alunite). Cement: 35%. Quartz veins and Quarzt overgrowing clasts and veins. Very fine grain. Massive texture that may alteranate with comb texture forming colloform texture. Plumose texture in quartz veins. Quartz veins are cutting breccia and are crosscut by later finer grained quartz veins.

Thin section


PPL

1 cm

Microphotographs Magnification

clast

qz clast ser

0.5 mm

alu+qz

qz rimming clast

394

zr

rt/ttn

py

Sample (cont') Zone DDH ALR147 La Mascota LB114 Rock Type Hydrothermal breccia (Quartz cemented breccia) ..cont.. Microphotographs Magnification 10X PPL

Code


ttn

py

gneiss clasts replaced by, ser, ttn/rt, py.

rt

25 μm

395


Zone La Mascota

DDH LB114 Code

Gneiss Advcanced argillic (alunite>quartz)

Depth [m] 300.4 BG

Description, Notes Rock: Gneiss (Qz-Fd gneiss). Granoblastic texture. Quartz (30%): individuals and aggregates (2-4mm) with suture contacts sometimes exhibiting intragrains and always exhibiting undulose extinction. Feldspar (63%): Background mass replaced by fine grained quartz (silica, 40%), and alunite (33%). Sphene (3%): up to 1 mm individuals, possibly after biotite?. Arrow shaped crystals with high relief. Also at quartz borders aligned aggregates. Pyrite (2%): Disseminated individuals (0.01 mm) within alunite-Quartz. Zircon (0.01%): Rounded shape individuals of (0.01mm).. High relief . Veins: Pyrite (90%)+Quartz (10%) vein with quartz halo (1-2 mm width); cut by fine grained alunite (80%) vein with quartz halo (silica).

Thin section


XPL


qz 2 (silica)

5X

RL+XPL

qz 1 (gneiss)

qz 2 (silica)

alu py

ttn

0.5 mm

396


Zone La Mascota

DDH LB114 Code

Gneiss Advanced argilic (quartz, alunite)

Depth [m] 302.5 BG

Description, Notes Quartz feldspar gneiss. Intensely silicide and alunitizied. Quartz 1 (29%): Commonly aligned aggregates (gneiss fabric) with sutured contacts of individuals up to 3 mm. Undulose extinction and some subgrains. Cross cut by micrystaline quartz veins and other veins. Feldspars (64%) are obliterated, altered to microcrystalline quartz 2 (35%), alunite 1(27%) and illite (?) (2%) Pyrite (1%): Disseminated cubic-pyritohedric individuals up to 3-10 µm related to microcrystalline quartz and alunite. Quartz 2 (35%): Microcrystalline quartz (silica). 10-5 µm. replacing feldspars mainly (?) Alunite 1 (30%): Fibrous-tabular intercrossed habit aggregates . Veins: Vein 1: Quartz+Coarse grained pyrite vein. Pyrite (uo to 5mmdiameter. Rounded Au (2-3 µm) inclusions in Pyrite. Vein2: Quartz+Pyrite+Chalcocite (?) vein. Vein 3: Cuts vein 1 and 2. Alunite-Quartz vein with platty alunite texture, minor pyrite intergrained with Chalcocite and or chalcopyrite (?)

Thin section


XPL Gneissosity (?)


2X

RL+XPL

qz 1 microfault

py

qz 2 (silica)

2 mm

alu

397

Sample (cont') Zone DDH ALR149 La Mascota LB114 Rock Type Gneiss Alteration Advanced argilic (quartz, alunite) Microphotograph Zoom Magnification 50X RL

Code

Depth [m] 302.5 BG

Au inclusion

py 5 μm

398


Zone DDH La Mascota LB114 Code Hydrothermal breccia Advanced argillic (quartz-alunite, silicification)


Description, Notes Clasts supported breccia with Quartz>Alunite cement, and quartz and alunite replacing matrix and clasts. Clast of mx sup fine grained BX. Qz+w cement. crustiform cavities with qz+w filling and later sph+alu at center. Clasts (40%): Up to 7 mm (?) Gneiss; altered to alunite and quartz, few clasts altered to illite ? (1%), quartz and quartz replaced clasts (breccia). Matrix (25%): Fine grained milled material, replaced by silica. Cement (35%): Quartz, microcrystalline quartz (5µm typically) (15%) coloform quartz rimming clasts and in quartz veins (1mm) (10%) and alunite (fibrous crystals, 10 µm inrelated to fine grained quartz cement and 1-2 mm in coarse grained quartz). Veins and cavities fillings: Vein 1: Quartz+pyrite vein. Comb quartz with coarse pyrite (1-3 mm py). Vein and Py within vein seems broken. Quartz with ondulating texture. Pyrite is weakly tarnished. Vein 2: Alunite, quartz, crosscutting vein 1 refractions of vein 2 within intersection of veins. Minor Wolframite in quartz vein walls. Vein 3: Quartz+Wolframite, minor Pyrite. Cavity filling: Alunite+sphalerite/wurtzite (?)


Thin section

PPL


2X

RL+XPL

sph/ wrt

qz (comb)

py

w

py alu

2 mm

qz

qz (silica)

399


Zone La Mascota

DDH LB114 Code

Gneiss Advanced argillic (quartz-alunite)

Depth [m] 322.9 BG

Description, Notes Gneiss. Granolepidoblastic texture ?),. Quartz (25%): Individual and pairs of blasts with sutured contacts, undulose extinction. Feldspars (69%): Altered to Alunite (40%) and Microcrystaline quartz (29%). Accessories: Sphene (4%) (euhedral crystals (up to 2mm possibly after alteration of mafic minerals), Zircon (alunite) superimposed to phyllic (mus-ill)

Description, Notes Gneiss. Granolepidoblastic texture (?), intense quartz veining and illite-muscovite alteration overprinted bysiulicification and alunite alteration. Quartz veins make locally cock ade texture around clasts. Quartz (1) (up to 13%): Aggregates and individuals up to 0.5mm. Undulose extinction and subgrain domains. Alteration "groundmass" (83%): Illite+Muscovite, mucrocrystaline quartz, Alunite, Rutile-sphene. Illite (20%) and Muscovite (25%): After alteration of feldspars and possibly micas. Fine grained ground mass (0.01 mm) mixed with microcrystalline quartz and alunite (0,01 mm). Deformation shadows Quartz 2 (microcrystalline) (20%): Massive texture aggregate up to 0.01mm crystals. Alunite (15%): Partially overprinting Illite and muscovite (?): Sacaroidal texture aggregate mixed with quartz 2 . Rutile-titanite aggregate (3%): individuals up to 0.01 mm cubic and rhombohedra shape with arrow shaped tips. Pyrite 1 (4%): Pyrite in ground mass, cubic up to 0.2 mmm. Au inclusions (4µm) and chalcocite inclusions. Vein 1: Pyrite+Quartz (undulatory extinction) Au inclusions (up to 10µm). Vein 2: Quartz+pyrite, minor wolframite, Au and cc (?) inclusions in pyrite. Vein 3: quartz (flamboyant) cross cutting vein 2. Au in Quartz in vein 2. Vein 4: Quartz+py+en (Au inclusions in en), minor W in qz walls; cut by Vein 5: Quartz+Alunite (platty)

Thin section


XPL

1

2 1 cm Microphotograph Magnification

1 2X

RL+XPL

qz2+alu

2 mm

408

Sample (cont') ALR193 Rock Type Gneiss Microphotograph Magnification

Zone La Mascota

DDH LB202

Depth [m] 219.1 BG

Code 2 2x

RL+XPL

2.1 qz+alu (sacaroidal text)

py


qz (colloform, flamboyant, comb)

2.1 10X

RL+PPL

py

alu

en w qz+alu vn5

250 μm

en

409


Zone La Mascota

DDH LB202

Depth [m] 230.6 Code Gneiss BG Phyllic (muscovite-illite) with superimposed advanced argillic (quartz-alunite)

Description, Notes Gneiss: feldspar-quartz gneiss with granoledidoblastic texture, augen-texture; phyllic alteration with superimposed advanced argillic (quartz-alunite) alteration cross cut by wolframite bearing quartz veins. Quartz 1 (25%): quartz augens up to 0.2 mm, subidomorphic, augen-shaped and elonged shaped, undulose extinction. Felspars (50%): Fine grained, gray groundmass, altered to sericite-illite, quartz and minor alunite. Mafics (20%?): Fine grained, shows around quartz augens altered to rutile/titanite/pyrite, muscovite, sericite and alunite. Pyrite1 (5%?): disseminated fine grained subhedral, 0.01 mm. Veins: quartz wolframite vein: Banded quartz with mosaic texture and zoned quartz; wolframite blades (sticks) reddish brown in PPL (with high relief) and gray in RL. Cross cut by quartz+ pyrite vein, fminos=r wolframite crystals (few of them fractured), fractured pyrite with chalcocite (?) in fractures and partially in borders.

Thin section



2X

qz (zoned)

2 mm

410

XPL

Sample (cont') Zone DDH Depth [m] ALR199 La Mascota LB202 230.6 Code Rock Type Gneiss BG Alteration Phyllic (muscovite-illite) with superimposed advanced argillic (quartz-alunite) Microphotograph Magnification 10X RL

w

alu

qz (mosaic)

w

py

250 μm


10X

PPL

w

qz (mosaic)

w

250 μm

rt/ttn

411


Zone La Mascota

DDH LB202 Code

Gneiss Propylitic (Epidote-chlorite)

Depth [m] 327.9 BG

Description, Notes Gneiss, banded with predominatnly leucosomes and mesosomes. Intyenses Epidote-Chlorite and rutile alteration. Quartz (11% in mesosomes to 30% in leucosomes): Undulatory extinction with chess board pattern) Feldspar (Plagioclase)(12% in mesosomes to 40% in leucosomes): Weak evidence on polysynthetic twinning. Intensely altered (epidote, clay?). Epidote up to 45% in mesosome and 8% in leucosomes: alteration product Chlorite in microveins and as alteration product of mainly mafics (15%) and 5% in leucosomes. Rutile (15%) Product of alteration of mafic, but also found as alteration of feldspars (?) Speculartite microveins (?) (2%)

Thin section


XPL

epi+chl+rt/ttn


10X

XPL rt/ttn

epi

chl

spc

plg

250 μm

412


Zone DDH Depth [m] La Bodega LB258 233.2 Code Amphibolite A Propylitic (chlorite, epidote, rutile/titanite, carbonate, specularite, pyrite)

Description, Notes Amphibolite. Propylitic alteration, chlorite mainly on amphiboles and biotite (?)Epi veins cut by spc+epi veinlets, cut by spc+carbonate vein with minor py. Horblende (65%): subidiomorphic tabular (?) altered to chlorite, epidote, titanite. Biotite (20%?): subidiomorphic tabular altered to chlorite and titanite (?). Feldspars (20%): Plagioclase?. Fine grained, altered to sericite, calcite (?) and epidote (?). quartz 1 (5%): subidiomorphic, elonged, fine grained. Alteration. Epidote, adjacent to veins, titanite (after hornblende and biotite). Pyrite (after biotite?). Veins: Calcite+-pyrite with epidote halo cut by specularite+calcite+pyrite and chalcopyrite.

Thin section


XPL


2X epi

chl? ca

qz

2 mm

413

Sample (cont') Zone DDH Depth [m] ALR234 La Bodega LB258 233.2 Code Rock Type Amphibolite A Alteration Propylitic (chlorite, epidote, rutile/titanite, carbonate, specularite, pyrite) Microphotograph Magnification 2X RL+PPL

epi

chl?

ttn

ca

spc

py, cpy


20X

RL+XPL

cpy

spc

py

spc

150 μm

414


Zone DDH La Bodega LB258 Code Granodiorite-granite Chlorite with superimposed weak sericite alteration

Depth [m] 277.5 INT

Description, Notes Granodiorite (?), weakly deformed. Quartz (33%): Aggregates with undulose extinction of crystals up to 3-4 mm wide. Some grains have subgrains and dislocation evidence (parallel subgrains in within one crystals and ondulating extinction). Also some grains have recrystallization around them with individulas around 0.1 mm in diameter. Plagioclase (30%): Random aggregates with polysynthetic twinning. Altered to sericite (?) alteration sometimes surrounding some plagioclase core relict. Orthoclase (?) (25%). Random individuals with euhedral to subhedarl habit. Minor kaolin (?) and sericite alteration. Quartz inclusions. Chlorite (8%).: Randomly distrituted crystals up to 0,2 mm long with no particular orientation after alteration of biotite (?) . Rutile (2%) and Titanite (1%): Aggregates product of alteration of biotite and closely related to chlorite. Pyrite (illite, quartz), minor superimposed alunite. Microphotograph Magnification 50X RL

py cpy

5 μm Microphotograph Magnification

50X

RL

py en

5 μm

425


Zone DDH La Bodega LB013 Code Qz-Fd Gneiss Phyllic (muscovite-illite) with superimposed alunite.

Depth [m] 150.6 BG

Description, Notes Quartz feldspar gneiss??? Intensely altered and deformed. Quartz (30%): Aggregates of 2 to 4 grains with sutured contacts. 1-2 mm grain size of each blast. Ondulating extinction. Fedspars (70%): Completely obliterated aggregates of feldspars to sericite mainly. Veins 1: Quartz+Coarse greaind Pyrite (Au? Inclusions) Pyrite (1%): Disseminated Pyrite (0,5mm) related to sericite alteration. Cut by Vein 2: Quartz+py+en vein parallel to shear bands Vein 3. Microvein, minor Quartz+pyrite restricted to microvein parallel to shear bands. Feathery structure showing undulose extinction. Quartz (shear band) with apparent dextral orientation.

Thin section



qz

ser

25 μm

426

XPL

Sample Zone ALR275 La Bodega Rock Type Qz-Fd Gneiss Microphotograph Magnification 2X

DDH LB013

Depth [m] 150.6 BG

Code RL+XPL Quartz subgrains

py

en

fine py

Micro crystalline Quartz

2 cm


5X

XPL

Microshear band (?)

ser

qz1

0.5 mm

427


Zone DDH La Bodega LB013 Tectonic Hydrothermal breccia Advanced argillic (quartz, alunite)

Code

Depth [m] 230.75 THBX

Description, Notes Tectonic breccia, silicified. Matrix supported, but matrix is replaced by quartz. Clast (15%): Angular subspherical clasts of mainly Quartz (up to 3 mm) (10%) and Pyrite (up to 2mm) (5%). Matrix (85%): replaced by microcrystalline quartz (55%) and Alunite (30%), very fine grained (5µm). Cross cut by Quartz+Py cross cutting Quartz+Py veinsy vein with Minor alunite mainly in Vein walls. Quartz from veins, clasts and matrix exhibits undulose extinction.

Thin section


XPL


2X

RL+XPL

qz clast py qz (vn)

py

qz+alu mx

qz clast

2 mm

428


Zone La Bodega Tectonic hydrothermal breccia Advanced argillic (alunite quartz)

DDH LB013 Code

Depth [m] 231.8 THBX

Description, Notes Clast to cement supported breccia. Clasts: Subrounded to subangular clasts with sericitic alteration superimposed by quartz alteration. Cement: Alunite>>quartz. Pyrite in cement (cubic) Quartz (1) (30%): Sacaroidal texture, very fine grained replacing clasts. Sericite (10%): Mixed with quartz (1) in altered clasts, replaced by silica. Quartz 2 (10%). Mainly in veins, open space and related to alunite-quartz cement. Comb texture. Alunite (30%). Main cement of breccia. Sacaroidal texture. Pyrite (10%): Cubic Pyrite in Alunite-Quartz cements. Ranges from less than 10 µm to 2-3 mm in diameter.. chalcocite (?) inclusions in pyrite (up to 0.03 mm). Chalcopyrite in Pyrite border. Cavities (10%)

Thin section


XPL


2X

RL+XPL

alu

qz (silica) py

qz (silica)

2 mm

429


Zone La Mascota

DDH LB221

Depth [m] 315.1 Code Gneiss BG Propylitoic alteration (chlorite, carbonate) with superimposed pargillic (illite)

Description, Notes Gneiss: Feldspar-Quartz gneiss with minor biotite. Quartz (38%): Aggregates with sutured contact intergrained with plagioclase (up to 3mm). Undulose extinction and subgrains (very common; 5-10%). May be replacing alred feldspars. Feldspars (43%): up to 3 mm. mainly plagioclase; polysynthetic twinning of albite, 12ͼ angle of extinction. Moderatley altered (clay, illite-sericite, minor calcite (?) also to minor alteration to sphene (1%) and epidote?. Undulatory extinction and deformed (twinning lamellae are dextrally displaced) Biotite (15%): Mainly at quartz and plagioclase borders. Up to 2 mm. Mainly altered to chlorite (10%) and Rutile-titanite (5%): Hornblende (4%): Possibly hornblende altered to epidote and chlorite?. Zircon (