Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Distal alteration in the carbonate-hosted replacement and skarn systems at Yauricocha, central Peru Carrasco, Julio Jurado 2006

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-ubc_2006-0516.pdf [ 21.63MB ]
Metadata
JSON: 831-1.0052439.json
JSON-LD: 831-1.0052439-ld.json
RDF/XML (Pretty): 831-1.0052439-rdf.xml
RDF/JSON: 831-1.0052439-rdf.json
Turtle: 831-1.0052439-turtle.txt
N-Triples: 831-1.0052439-rdf-ntriples.txt
Original Record: 831-1.0052439-source.json
Full Text
831-1.0052439-fulltext.txt
Citation
831-1.0052439.ris

Full Text

D I S T A L A L T E R A T I O N IN T H E C A R B O N A T E - H O S T E D R E P L A C E M E N T A N D S K A R N S Y S T E M S A T Y A U R I C O C H A , C E N T R A L P E R U by JULIO JURADO C A R R A S C O Ingeniero Geologo, Universidad Nacional De San Antonio Abad Del Cusco, 1994 A THESIS SUBMITTED IN PARTIAL F U L F I L L M E N T OF THE REQUIREMENTS FOR THE D E G R E E OF M A S T E R OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES (Geological Sciences) THE UNIVERSITY OF BRITISH C O L U M B I A April 2006 © Julio Jurado Carrasco, 2006 ABSTRACT Despite numerous reviews of carbonate-replacement (CRD) and skarn deposits, there have been few exhaustive studies into the details of distal alteration features lateral and above to the mineralized centres at these deposits. These features record the passage of exhausted hydrothermal fluids and provide important guides for mineral exploration. Yauricocha, central Peru, is a Zn-Pb-Cu-Ag magmatic-hydrothermal system zoned around a late Miocene quartz monzonite-quartz diorite stock, which intruded limestone and marl of the Cretaceous Jumasha and Santonian Celendin formations. Northwesterly-trending folds controlled the emplacement of the stock, sulfide carbonate-replacement deposits at M i n a Central, skarn deposits at Cachi Cachi, and 'Carlin-style' A u mineralization at Purisima Conception. Low-grade porphyry-Cu, A u , and Ag-Cu-base metal veins lie within the stock. C R D and skarn are fringed by a visible zonal arrangement of bleached and grey marble, dolomite, calsilicates-, orange brown- to white carbonates-, and Mn-oxides minerals, quartz and sulfide veins, and local jasperoid. Thermal aureole surrounding the intrusion contains an inner zone of bleached marble and an outer zone of grey marble. Cryptic geochemical halos are defined by trace element abundance and oxygen and carbon isotope composition. In M i n a Central and Cachi Cachi, visible and cryptic alteration sequences extend up to 800m laterally from intrusive contact into Jumasha and Celendin formations, and over a similar vertical distance in proximity to the ores zones. A t M i n a Central, visible alteration is mainly structural controlled. Garnet skams occur locally associated with quartz diorite sills. Bleached versus gray marble units extend up to 430m from intrusive contact. Mn-carbonate veinlets, decreasing in abundance with distance, are present in marbles and limestone, and are spatially associated with sulfide orebodies. A t Cachi Cachi, alteration consists of andradite-grossular skarn, surrounded by bleached and grey marble. Pervasive bleaching characterizes rocks within 150m of the intrusive contact, while narrow bedding controlled zones of bleaching extend up to 450m away. Calcsilicate and carbonate vein networks are developed adjacent to ores, and decrease in abundance with distance away from intrusion. Visible and cryptic alteration halbs can be used as a model to explore carbonate-hosted replacement and skarn orebodies in other areas with geological features similar to Yauricocha. i i TABLE OF CONTENTS Abstract •••• u Table of Contents i i i List o f Tables , v i i List o f Figures ix Acknowledgments x i Dedication x i i CHAPTER ONE G E N E R A L INTRODUCTION 1.1. Distal Alteration at Carbonate-hosted Replacement Deposits 1 1.2. Carbonate-hosted Replacement Deposits: A n Overview 3 1.3. Objectives and Scope of the Thesis • • • 5 1.4. Historical Background 6 1.5. Previous Studies 7 1.6. Methods of Study 8 1.7. Thesis Organization 9 Chapters.. 9 Appendices ••• 10 References 11 CHAPTER TWO G E O L O G I C A L F R A M E W O R K 2.1. Introduction 18 2.2. Tectonic Setting : 21 2.3. Stratigraphic Framework 24 2.4. Intrusive Rocks 27 i i i 2.5. Contact Metamorphism and Metasomatism 28 2.6. Mineralization in the Yauricocha Min ing District 29 2.6.1. M i n a Central and Cachi Cachi 29 2.6.2. Purisima Conception 41 2.6.3. Base Metal Veins 41 2.6.4. L o w Grade Porphyry Copper and Gold Anomalous Zones 41 2.6.5. M i n a E x i t o 42 References -43 CHAPTER THREE DISTAL VISIBLE AND C R Y P T I C A L T E R A T I O N C H A R A C T E R I S T I C S A R O U N D T H E C A R B O N A T E - H O S T E D P O L Y M E T A L L I C R E P L A C E M E N T A N D S K A R N SYSTEMS A T MINA C E N T R A L AND C A C H I C A C H I , Y A U R I C O C H A 3.1. Introduction 45 3.2. Host Rocks and Alteration at M i n a Central and Cachi Cachi 48 3.3. Zones of Distal Alteration at M i n a Central .: 52 3.3.1. Host rocks in the Distal Alteration Zones at M i n a Central 53 3.3.2. Veins in the Distal Alteration Zones at M i n a Central 55 3.4. Zones o f Distal Alteration at Cachi Cachi .64 3.4.1. Host Rocks in the Distal Alteration Zones at Cachi Cachi 65 3.4.2. Veins in the Distal Alteration Zones at Cachi Cachi 68 3.5. Paragenesis of Distal Veins at M i n a Central and Cachi Cachi 82 3.6. Bu lk Chemical Analysis at M i n a Central and Cachi Cachi. 86 3.6.1. Trace Elements Geochemistry 86 3.6.1.1. Correlation Coefficients. 95 3.6.2. Oxygen and Carbon Stable Isotopes at M i n a Central and Cachi 102 3.7. Distal Visible and Cryptic Alteration Characteristics at Yauricocha 105 References I l l iv CHAPTER FOUR CONCLUSIONS, I N T E R P R E T A T I O N , S Y S T E M A T I C V I E W O F A L T E R A T I O N P A T T E R N S , A N D E X P L O R A T I O N CONSIDERATIONS A N D P O T E N T I A L 4.1. General Conclusions, Interpretation and Exploration Considerations 114 4.1.1. Thermal Aureole and Alteration Distribution 114 4.1.2. Host Rock Alteration 115 4.1.3. Proximal and Distal Veins 115 4.1.4. Metal Content. 116 4.1.5. Metal Zoning. 117 4.1.6. Stable Isotope Halo . . . . 118 4.2. Systematic V i e w of Alteration Patterns 118 4.3. Exploration Implications 121 References 122 APPENDICES Appendix A : Sampling Procedure and Samples Description •. 123 (Tables included in appendices A 1 - A 4 as Excel worksheet on attached C D ) Appendix A l : M i n a Central: Sample description. Appendix A 2 : Cachi Cachi: Sample description. Appendix A 3 : List of used abbreviations for sample description. Appendix A 4 : M i n a Central and Cachi: M D R U Peru Project 2002: Rock sample description. Appendix B : Mineral Identification B y Pima. 124 Appendix C: Mineral Identification B y X R D . 126 (Tables and graphs included in Appendices C1-C3 as Excel worksheets and Word files on attached C D ) Appendix C 1 : M i n a Central Pima and X R D mineralogy. Appendix C2: Cachi Cachi Pima and X R D mineralogy. Appendix C3 : M i n a Central and Cachi Cachi X R D diffractograms. Appendix D : Trace Elements Analytical Methods and Results 128 (Tables and graphs included in Appendices D1-D4 as Excel worksheets and Word files on attached C D ) . v Appendix D l : Trace Elements analytes, ranges, and methods Appendix D2: M i n a Central: Trace element geochemistry (include representative graphs). Appendix D2.1: M i n a Central: Host rocks and vein types correlation tables. Appendix D2.2: M i n a Central: Host rocks and vein types correlation coefficients. Appendix D2.3: M i n a Central: Statistical threshold without high erratic values. Appendix D3: Cachi Cachi Trace element geochemistry (include representative graphs). Appendix D3.1: Cachi Cachi: Host rocks and vein types correlation tables. Appendix D3.2: Cachi Cachi: Host rocks and vein types correlation coefficients. Appendix D3.3: Cachi Cachi: Statistical threshold without high erratic values. Appendix D4: M D R U Peru Project geochemistry samples for M i n a Central and Cachi Cachi. Appendix E : Oxygen and Carbon Stable Isotopes Analysis and Results. 131 (Tables and graphs included in Appendices E1-E5 as Excel worksheets attached on C D . Appendix E l : M i n a Central: Stable oxygen and carbon isotopes samples. Appendix E2 : Cachi Cachi: Stable oxygen and carbon isotopes samples. Appendix E3 : M i n a Central and Cachi Cachi: Stable oxygen and carbon isotopes results and raw data. Appendix E4: M D R U Peru Project: Stable oxygen and carbon isotopes samples description and results for M i n a Central and Cachi Cachi. Appendix F: Plates 1-3 133 v i LIST OF TABLES C H A P T E R T W O Table 2.1: Characteristics of sulfide orebodies and veins at M i n a Central, Yauricocha Mine , central Peru. Data summarized from Rodriguez (2002, 2004) 33 Table 2.2: Characteristics of sulfide orebodies and veins at Cachi Cachi, Yauricocha Mine , central Peru. Data summarized from Rodriguez (2002, 2004 40 C H A P T E R T H R E E Table 3.1: Host rock and distal vein types X R D mineralogy at M i n a Central 50 Table 3.2: Host rock and distal vein types X R D mineralogy at Cachi Cachi 51 Table 3.3: V e i n types found distally to sulfide orebodies at M i n a Central and Cachi Cachi 55 Table 3.4: Summary o f the distal alteration characteristic of zone A in M i n a Central 60 Table 3.5: Summary of the distal alteration characteristic of zone B in M i n a Central 61 Table 3.6: Summary of the distal alteration characteristic of zone C in M i n a Central 63 Table 3.7: Summary of the distal alteration characteristic of zone B , Celendin Formation, M i n a Central ; 63 Table 3.8: Summary o f the distal alteration characteristic of zone A in Cachi Cachi grid 75 Table 3.9: Summary o f the distal alteration characteristic of zone B in Cachi Cachi grid 76 Table 3.10.1: Summary of the distal alteration characteristic of zone A in Cachi Cachi regional 79 Tab le 3.10.2: Summary of the distal alteration characteristic of zone B in Cachi Cachi regional 79 Table 3.10.3: Summary of the distal alteration characteristic of zone C in Cachi Cachi regional 81 Table 3.11: Paragenetic and cross-cutting relationships among the distal alteration vein types in M i n a Central 83 Table 3.12: Paragenetic and cross-cutting relationships among the distal alteration vein types in Cachi Cachi : 83 Table 3.13: Threshold values for defining trace elements alteration halos 87 Table 3.14: Distribution of anomalous elements in the bleached/gray marble in the distal veins at Mina Central and Cachi Cachi 88 Table 3.15.1: M i n a Central trace element correlation (host rocks and vein types) 96 v i i Table 3.15.2: Mina Central trace element correlation (vein types 2 and 3) 97 Table 3.16.1: Cachi Cachi trace element correlation (host rocks and vein types) 98 Table 3.16.2: Cachi Cachi trace element correlation (vein types 1-4) 99 viii LIST OF FIGURES C H A P T E R O N E Figure 1.1: M a i n physiographic provinces of the South American Andes 2 Figure 1.2: Idealized cross section of the distribution of skarn, carbonate replacement (CRD) , Ag-base metal vein, and A u sediment hosted deposits in a generalized model for C u - M o porphyry deposit.. 3 C H A P T E R T W O Figure 2.1: Copper belts of the Andes 19 Figure 2.2: Miocene to early Pliocene copper belt of the Andes 20 Figure 2.3: Carbonate hosted deposits and prospects in central Peru 21 Figure 2.4:. Late Jurassic - Upper Cretaceous paleogeographic map o f Peru. 22 Figure 2.5: Geology map of central Peru 23 Figure 2.6: Simplified geology map of the Yauricocha mining district of central Peru 23 Figure 2.7: Generalized geological and alteration map of the Yauricocha minining district, central Peru 25 Figure 2.8: Schematic cross section through the Yauricocha mine of central Peru 26 Figure 2.9: Stratigraphic cross section of the Yauricocha mining district of central Peru 28 Figure 2.10: Schematic mineralogical zoning of the Yauricocha carbonate-hosted massive replacement ore bodies of central Peru 31 Figure 2.11: Mineralogical paragenetic relationships in the Yauricocha mining district of central Peru.. . ; — 32 C H A P T E R T H R E E Figure 3.1: Detailed geological and alteration map of the Yauricocha mining district, central Peru 47 Figure 3.2: Geological and alteration map of the surface outcrops around M i n a Central, Yauricocha mining district, central Peru 53 Figure 3.3: Distribution of alteration and veins at M i n a Central, Yauricocha, central Peru.. . 54 Figure 3.4: Alteration and vein types at M i n a Central, Yauricocha, central Peru 58 Figure 3.5: V e i n types and alteration at Mina Central, Yauricocha, central Peru 59 ix Figure 3.6: Geological and alteration map of the surface outcrops around Cachi Cachi, Yauricocha mining district, central Peru 67 Figure 3.7: Distribution of alteration and veins at Cachi Cachi, Yauricocha, central Peru 69 Figure 3.8: Alteration and vein types at Cachi Cachi, Yauricocha, central Peru. 71 Figure 3.9: V e i n types and alteration at Cachi Cachi, Yauricocha, central Peru 72 Figure 3.10: Distal vein types and alteration at Cachi Cachi, Yauricocha, central Peru. . . . . . . . . . . 74 Figure 3.11: Crosscutting relationships among vein types at Yauricocha, central Peru 84 Figure 3.12: Rose diagrams showing the orientation by vein types at M i n a Central and Cachi Cachi, Yauricocha, central Peru 85 Figure 3.13: Distribution of Zn , A s , M n and Sb laterally from intrusive contact with the host Jumasha Formation limestone at Cachi Cachi, Yauricocha, central Peru 91 Figure 3.14: Distribution of Zn, A s , M n and Sb laterally from intrusive contact with the host Jumasha Formation limestone at M i n a Central, Yauricocha, central Peru. 93 Figure 3.15: Oxygen and carbon isotopic compositions of rocks and high-temperature type 1 veins and types 2 and 3 veins at M i n a Central and Cachi Cachi, Yauricocha, central Peru.. . 104 C H A P T E R F O U R Figure 4.1: Systematic view of visible and cryptic alteration patterns at M i n a Central and Cachi Cachi, Yauricocha, Central Peru 119 x Acknowledgments This thesis has benefited from the help of many people. First and foremost, I would like to extend my gratitude to my supervisors Richard Tosdal and Gregory Dipple for their guidance, continuous patience and encouragement, and input. Many of their suggestions have been incorporated into the thesis. Shane Ebert is also gratefully acknowledged for his guidance and helpful discussions during the field season and for his prompt reviews of the first drafts of this study. Thanks to J im Mortensen for serving on my committee and for his input. I would particularly like to thank Richard Tosdal for accepting me to The University o f British Columbia in the first place and for putting at my disposal the valuable resources that made this thesis possible. Very special thanks to Arne Toma for always be in there for me, and for helping solve my software crises. Elisabetta Pani and Janet Gabites, from The Department of Earth and Ocean Sciences, generously provided technical assistance in the X R D and stable isotopes analyses. Thanks to Alex Al l en for her help with just about everything related to the paper work. I would also like to thank my friends and fellow graduate students at U . B . C . who created a nice environment in which to work, provided a source of fun and distraction, and made U B C an enjoyable place to spend this phase of my life. M y eternal gratitude to Anglo American Exploration, B H P Bil l i ton, C i a de Minas Buenaventura, C ia Minera Antamina, Noranda, Teck Cominco, Phelps Dodge, Sociedad Minera Corona, and the Natural Sciences and Engineering Research Council o f Canada for the financial and logistical support. Carlos Villanueva, from Sociedad Minera Corona is appreciatively recognized for granting access to the zone of study, and for providing all of the administrative and logistical support required. Gervasio Rodriguez from Sociedad Minera Corona is also thankfully acknowledged for his assistance and valuable discussions of the mine geology. Last but by no means least, I want to express my deeper gratitude to my beloved wife Paola and to little Julito, the most precious jewel that I w i l l ever have, for their understanding and permanent and unconditional emotional support from Peru during the course of my thesis. This thesis is dedicated to you guys! M y loving father; my gracious mother and older sister; wherever they are up in the sky, and all my family are also thanked for their love and support. x i CHAPTER ONE General Introduction 1.1. Distal Alteration at Carbonate-hosted Replacement Deposits A large number of hydrothermal mineral deposits of various styles o f precious- and base-metal mineralization, ranging from porphyry and associated proximal skarn deposits to polymetallic, and precious metal and mercury deposits (Vidal and Noble, 1994) form the prolific metallogenic belt of central Peru (Peterson, 1965; M c K e e and Noble, 1990; Nobel and M c K e e , 1999), which extends along the Western Cordillera and the adjacent high plateaus provinces (Fig. 1.1). The mineral deposits are mainly hosted by carbonate and other sedimentary rocks of Mesozoic age, and by volcanic and intrusive rocks mainly of Neogene age. Mineralization is thought to be spatially and temporally, and by inference probably also genetically, associated with several episodes of late Eocene (Quicay) to late Miocene (Uchucchacua, Alpamarca, Yauricocha) calc-alkalic intrusions of intermediate composition. Many of the classic base-metal deposits of central Peru are within zoned polymetallic districts, and some or them have one or more porphyry centers, and have replacement bodies or veins containing enargite in the central parts (Nobel and McKee , 1999). The Yauricocha district, centred near latitude 12°18'S, longitude 7 5 ° 4 5 ' W at an elevation of 4600 m.a.s.l., contains a Zn-Pb-Cu-Ag magmatic-hydrothermal system zoned around a late Miocene equigranular quartz diorite to quartz monzonite intrusion, which intruded Cretaceous limestone, marl, and shale. The district contains several different styles of mineralization including carbonate replacement deposits (CRD) at M i n a Central, also defined as "Cordilleran base metal lode and replacement-" (e.g. Einaudi, 1994; Bendezii et al., 2003) or enargite-bearing replacement- (Sillitoe and Perello, 2005) deposits; skarn orebodies at Cachi Cachi and 'Carlin-style' A u at Purisima Conception (Alvares and Noble, 1988 and 1990). Low-grade porphyry-Cu arid A u bearing veins occur within the late Miocene intrusion, and base metal or polymetallic veins occur within the intrusion and extend into the surrounding country rocks (Rodriguez, 2002). The term carbonate replacement deposit is used for zones of sulfides that lack appreciable calcsilicate minerals. The term skarn refers to zones containing sulfides associated with calcsilicate minerals. In the Yauricocha districts, both C R D and skarn deposits are closely associated within the same mineralizing systems. 1 Despite the numerous reviews of the polymetallic veins (Cox, 1986; Lefebure and Church, 1996) and replacement deposits (Morris, 1986; Nelson, 1996) class and the skarn deposits class (Meinert, 1993; Meinert et al, 2005), there have been few exhaustive studies into the details o f the distal alteration features above and lateral to the mineralized centres at these carbonate hosted base metal deposits, except locally (Megaw, 1987; Meinert et al., 2005). These features record the passage o f the exhausted hydrothermal fluids and provide important guides for mineral exploration. Figure 1.1: Main physiographic provinces of the South American Andes, showing the location of the Yauricocha mining district. Modified after Sillitoe and Perello (2005). 2 1.2. Carbonate-hosted Replacement Deposits: A n Overview Carbonate-hosted massive sulfides (Pb-Zn-Ag-Cu-Au) replacement deposits (CRDs) are quite well understood, characterized, and classified (Morris, 1986; Titley, 1993; Nelson, 1996; Megaw, 1998 and 2001; Bendezii et al., 2003; Sillitoe and Perello, 2005). They are epigenetic, polyphase intrusion-related, high-temperature (250°-500°C) (Titley, 1996; Megaw 1998), sulfide-dominant deposit rich in Pb-Zn-Ag-Cu rich subordinate A u , A s , Sb, B i , B a (Morris, 1986; Titley, 1996). They are associated with base metal skarn and porphyry copper deposits (Fig. 1.2; Sillitoe and Bonham, 1990), porphyry molybdenum (Cu) deposits (Titley 1993, Nelson, 1996) or un-mineralized porphyry bodies (Rubright and Hart, 1968). Many C R D s lie in fold-thrust belts on major structural domes, arches, anticlines, synclines or homoclines and have structural grains controlled by fault and fracture related to regional deformation (Prescott, 1926; Titley and Megaw, 1985; Megaw et al., 1988; Titley 1993). 0 km 1 2 3 4 km I 1 1 I I Figure 1.2: Idealized cross section of the distribution of skarn, carbonate replacement (CRD), Ag-base metal vein, and A u sediment hosted deposits in a generalized model for Cu-Mo porphyry deposit. (Sillitoe and Bonham, 1990). 3 Limestone, dolomite (dolostone) and dolomitized limestone are the major hosts rocks of C R D s , with minor deposits in other calcareous sedimentary rocks like shale (Megaw, 1998). The carbonate rocks are intruded by granite, quartz monzonite and other intermediate to felsic hypabyssal, porphyritic lithologies. C R D s typically form lenses or elongated to elongated-tabular bodies know as mantos where they are stratabound within the host stratigraphic sequence and as chimneys where they cut across the host stratigraphy (Nelson, 1996; Megaw, 1998). The lateral development of mantos for hundreds o f meters within "favourable" beds is one of the most significant characteristics of C R D s (Prescott, 1916 and 1926; Hewitt, 1968; Morris , 1968; Lovering et al., 1978). C R D s have distinctive deposit and district scale zonation along the stratigraphic and structurally controlled fluid flow pathways. Changes include ore and gangue mineralogy and metal zoning (Prescott, 1916; Morris, 1968; Newell , 1974; Meinert, 1992 and 1998; Megaw, 1990; Titley, 1993 and 1996; Megaw et al., 1996), orebody geometry (Megaw, 1998), intrusive geometry and composition (Einaudi et al., 1981; Megaw, 1990; Megaw et al., 1988; Meinert, 1992 and 1998; Graff, 1997), structural and bedding controls on mineralization (Prescott, 1916 and 1926; Morris , 1968; Hewit, 1968; Lovering et al., 1978; Thompson et al., 1983; Megaw, 1988 and 1990; Titley and Megaw, 1985; Megaw et al., 1988; Titley 1993), alteration (Prescott, 1916 and 1926; Hewett,T928; Hewit, 1968; Wanless, 1979; Titley and Megaw, 1985; Meinert, 1987; Megaw, 1986 and 1990; Megaw et al., 1988; Beaty and Thompson, 1988; Beaty et al., 1990a and 1990; Horton and DeVoto, 1990; Bendezii et al., 2003), and isotopic characteristics of wall rocks (Engel et al., 1958; Pinckney and Rye, 1972; Ohmoto, 1986; Diaz-Unsueta, 1986; Sweeney, 1987; Megaw, 1987 and 1990; Kesler et al., 1995, Vasquez et al., 1998; Freihauf and Pareja, 1998; Pareja and Friehauf, 1998). The deposits are usually zoned outward from a C u -rich central part through a wide Pb -Ag zone, to a Zn- and Mn-r ich fringe (Morris, 1986). Zoned alteration of carbonate rocks surrounding C R D and skarn deposits includes dolomitization, calcite precipitation, silicification, and minor calcic or ferroan silicates. On a larger scale, carbonate rocks are recrystallized to marble and dolomite, decarbonated or sanded, silicified or converted to jasperoid depending upon the composition of the sedimentary strata as wel l as the location within the alteration halo. Calcite and argentiferous manganese oxide minerals are common in veins, with ankeritic or dolomitic carbonate minerals forming veins closer to the sulfide bodies (Morris, 1968; Beaty et al., 1990; Megaw, 1998 and 2001; Megaw et al., 1988 and 1996; Titley, 1993 and 1996; Freihauf and Pareja, 1998; Bendezu et al., 2003). Water-rock exchange also alters the stable isotopic signature of carbonate host rocks over much broader 4 areas in limestone-dominated terranes (Beaty et al., 1990; Kesler et al., 1995) than in dolomite-dominated ones (Freihauf and Pareja, 1998). C R D s are generally smaller on a world scale than giant syngenetic polymetallic deposits such S E D E X or V M S ; they are nonetheless attractive mining targets because of their size (up to 100 mil l ion tons of ore; average 10-13 mil l ion tons), high precious metal contents (2-12% Pb, 2-18% Zn, 60-600 g/T A g , Tr-2% C u , and Tr-6 g/T Au) , continuity and typically metallurgically straightforward nature of the orebodies which makes them amenable to low-cost mining methods (Nelson, 1996; Megaw, 1998). C R D s also have important geographic, geologic and geochemical overlap with other carbonate-hosted deposits including Mississippi Val ley type deposits ( M V T ) and Irish type deposits (Titley and Megaw, 1995; Titley, 1996), and also with porphyry C u and M o deposits (Titley, 1993; Barton et al., 1995; Titley and Megaw, 1995), and epithermal veins (Fletcher 1929; Grant and Ruiz , 1988). Metal content, trace-element geochemistry, mineralogy, intrusion associations, and temperatures of ore deposition can be used to distinguish them and identify hybrids (Megaw et al., 1996; Meinert, 2000). 1.3. Objectives and Scope of the Study This thesis is part of The Sources and Exhausts in Polymetallic Carbonate Rock-hosted Ore Deposits: Miocene Magmatism and Alteration in Central Peru project (Bissig et al., 2005). The three-year duration project (started in June 2002 and finished in 2005) was focused in the prolific Miocene polymetallic belt of central Peru (Peterson, 1965; Nobel and M c K e e , 1999) between Antamina, the largest Cu-Zn skarn deposit in the world, on the north and Yauricocha on the south (Fig. 2.3). The project was undertaken by the Mineral Deposit Research Unit at the University o f British Columbia and supported by seven international mining companies (Anglo American Exploration, B H P Bil l i ton, C ia de Minas Buenaventura, C i a Minera Antamina, Noranda, Teck Cominco, and Phelps Dodge) and the Natural Sciences and Engineering Research Council o f Canada (Cooperative Research and Development program). Sociedad Minera Corona and Volcan Compania Minera provided additional logistical support in the field. The project aimed to develop a set of criteria to distinguish magmatic driven fluid flow from fluid flow driven by other processes and to develop a coherent view of alteration patterns in the spectrum of deposits. The first part was concentrated on the geologic, geochronologic, geochemical, mineralogic, and petrologic character and framework of plutonic complexes associated with carbonate-hosted polymetallic replacement or skarn deposits, whereas the 5 second part characterized the geochemical, isotopic, and mineralogic changes in carbonate rocks lateral and vertical to sulfide replacement or skarn bodies genetically and spatially associated with Miocene magmatic complexes. Detailed deposit- or district-scale studies were undertaken at Antamina, Uchucchacua and Yauricocha, plus detailed mapping o f a section o f the distal alteration around the giant Cerro de Pasco. This thesis reports on the study of Yauricocha, where the variety of Pb-Zn-Cu-Ag carbonate and intrusive-hosted deposit styles is ideal for studying distal alteration because it contains excellent surface and underground exposures. The main objective of this study was to define and quantify the mineralogical and geochemical characteristics of the distal alteration in carbonates rocks and vein types surrounding mineralized zones at .Mina Central and Cachi Cachi. This has been accomplished by mapping outcrops on the district scale, detailed local scale, and subtle hand sample scale alteration features, and by characterizing the petrological, trace elements and isotopical changes. A major focus of the research was to develop a coherent (systematic) view of alteration patterns in the spectrum of the Yauricocha deposit and to develop practical field and visual exploration guides that enhance exploration efforts for deposits similar to Yauricocha that may be partially or completely buried. 1.4. Historical Background The Incas did not pay much attention to Yauricocha. The first recorded exploitation of the Yauricocha mining district was by the Spaniards in the middle of the 16 t h century when gold and silver was mined from oxidized zones at M i n a Central. In 1927, the Cerro de Pasco Corporation bought the mining rights and eventually put the mine in production in 1948. In 1974, the Peruvian government nationalized the corporation, and the Mine became a part of C E N T R O M T N Peru S.A. (Empresa Minera del Centro del Peru S.A.). Economic mineralization in Cachi Cachi was discovered through a diamond drilling exploration program in 1978, was open-pit mined until 1986. The sulfide orebodies are currently mined through underground workings. In 1997, C E N T R O M I N Peru S.A. optioned the Yauricocha mine to Compam'a San Ignacio de Morococha (S IMSA) who conducted some exploration then returned the property. In March 2002, Sociedad Minera Corona S.A. purchased the Yauricocha mine in an auction. B y December 2004, mines in the Yauricocha mining district had produced 15,638,330 dry short tons (DST) of ore at average grades of around 4.75% Zn, 2.45% Pb, 1.01% C u , and 4.17 6 ounces per ton A g . The district currently has reserves o f 1,373,864 dry metric tons ( D M T ) at 5.04% Zn , 2.90% Pb, 1.05% C u , and 4.05 ounces per tonne A g (Rodriguez, 2004). 1.5. Previous Studies The first published study in the Yauricocha mining district was by Lacy (1949a) who described the oxide ores. Ward (1959) suggested, based on the spatial distribution o f the different types of pyrite, that the replaced sedimentary structures observed at Yauricocha orebodies could have been developed in an organic reef environment rather than in limestone caves. Thompson (1960) provided the first detailed geological background of the district, and described the tectonic arid stratigraphic setting, and the alteration, mineralization and mineralogy characteristics of the orebodies and country rocks. Through microscopic studies he distinguished five types of pyrite, continuous one to another in time and space. Type I is the oldest and the most distant from the orebodies, in contrast with type V , which is the youngest and is found in the orebody cores. Alvarez and Noble (1988, 1990) described the Carlin-style sedimentary rock-hosted precious metal mineralization at Purisima Conception. They suggest a spatial and temporal association of the deposit with a porphyry system and important polymetallic limestone replacement orebodies supplying insights into the origin of the deposit. Finally, they suggest that analogous deposits can be anticipated elsewhere in the Western Cordillera of central and northern Peru where hydrothermal fluids associated with Neogene stocks intersect impure carbonaceous limestone beds. Valdiv ia (1996) investigated the controls of the Cu-Pb-Zn-Ag mineralization of the district through field, petrographic and lead isotope studies. He concludes that in the eastern portion of the Western Cordillera in the central Andes, where the Yauricocha mining district is located, Paleozoic and Mesozoic rocks are cut by N W - S E longitudinal regional faults and by N - N E transversal faults, which controlled the emplacement of granodioritic intrusive rocks o f Cenozoic age. The Yauricocha Fault, its secondary fractures and the intrusive-derived fluids were responsible for the orebodies geometry, mainly with pipe-like forms. These pipes are located at the intersection of secondary fractures and present a clear structural zoning, apparently controlled by the fluid-pressure. His lead isotope data from galena indicate a magmatic source for the orebodies, derived from the stocks and their apophyses, with restricted contribution from the sediments. Other references for Yauricocha include Lacy (1949), Sigrist (1951), Ward (1959), Thompson (1960), Kobe (1961), Petersen (1965), Wright (1965), Cerro de Pasco Corporation (1970), Rado (1977), Centromin Peru (1980), Megaw (1987), Alvarez and Noble (1988 and 1990), Alvarez et al. (1989), Petersen et al. (1990), Valdivia (1996), Rado et al. (1996), Rado (1997), Noble and M c K e e (1999), Huanqui Lupa (1999), Arroyo Aguilar (2002), Lavado (2002), Rodriguez (2002 and 2004), Bissig et al. (2004), and Jurado et al. (2004). 1.6. Methods of Study A combination of detailed geological mapping, petrography, geochemistry of trace elements and oxygen and carbon isotopes were integrated to understand the characteristic and distribution of the distal alteration in carbonates rocks and vein types surrounding mineralized zones in the M i n a Central and Cachi Cachi areas within the Yauricocha district. Fieldwork during 2003 largely focused on detailed geological mapping characterizing the altered carbonate rocks and distal veins, defining the paragenetic relationships between distal veins, and determining the field relationship between mineralization and intrusive rocks. Samples were collected specially for petrographic, trace element and oxygen and carbon isotope studies. Petrographic and P I M A and X R D optical mineralogy techniques determined the mineral content in representative samples of each type o f lithology, vein and alteration assemblage. Mineral identification and examination of textures were performed at The University of British Columbia by using a transmitted and reflected light polarizing Nikon OPTEPHOT 2 - P O L microscope, a P I M A II infrared spectrometer, and a Siemens Diffraktometer D5000 X-ray powder diffractometer. The author made P I M A measurements, whereas Elisabetta Pani performed the measurements of the X R D samples. Detailed description of the techniques and procedures utilized in this study are included in the Appendices B and C. Rock chip samples were collected, prepared, and analyzed for trace element geochemistry at A L S Chemex. Sample preparation was conducted at their facilities in L ima , and all the geochemical analyses where done in North Vancouver, B . C . A l l the samples were analyzed for A u by fire assay, 47 elements by a combination of I C P - M S and I C P - A E S , H g by conventional cold vapour atomic absorption spectroscopy, and over limits for A g , Pb, Zn , C u and M n by A A S or I C P A E S just in the case of Cu . Trace element geochemistry defined an elemental distribution that reflects the alteration and vein-types identified in the field. Sample procedure, 8 sample preparation and analytical methods utilized in this study as well as tables and showing sample descriptions and geochemical results are attached in the appendices. Eighty-seven samples have been analyzed for 8 1 8 0 and 5 1 3 C isotopic compositions in limestone, marbles, carbonate-, and calcsilicates minerals. Measurements were made by Janet Gabites at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) lab at the University of British Columbia. The oxygen and carbon isotope patterns in carbonate rocks surrounding mineralized zones, in mineralized zones, and in distal veins enabled us to better understand district scale fluid flow, fluid-rock interaction, sources of oxygen and carbon, and the links between the different mineralization styles. Tables and graphics showing the results of the oxygen and carbon isotopes studies are included in the appendices. 1.7. Thesis Organization This thesis is presented in traditional format, in accordance with the University of British Columbia guidelines. Results are presented in Chapter 3. Supplementary information is provided in the appendices. Chapters Chapter one introduces the Yauricocha mining district on a geological context as well as summarizes the geological characteristics of carbonate replacement deposits (CRDs), the objectives and scope of the study, the history and previous studies conducted in the district, and the methodology applied in this study. Chapter two describes in detail the regional and district geologic framework of the district, the local geologic characteristic of the mineralized zones of Mina Central and Cachi Cachi, including lithologic and structural controls of mineralization, sulfide and gangue mineral characteristics, and alteration patterns and distribution. At the end, this chapter provides a brief local geological setting of the different mineralized centres within the Yauricocha mining district. Chapter three describes and characterizes in detail the distal visible and cryptic alteration, the mineral content as well as the mineralogical, trace element and oxygen and carbonate isotope geochemical characteristics in carbonates host rocks and veins surrounding the Mina Central and Cachi Cachi zones. Chapter four outlines the overall conclusions and interpretation of the study. A coherent (systematic) view of alteration patterns in the spectrum of the Yauricocha deposit and a practical field and visual exploration guide for deposits similar to Yauricocha are provided. 9 Appendices Appendix A provides sample location and sample descriptions of rocks and veins used in this study as well as the sampling procedure. Summary tables are included as Excel worksheets on attached C D . Appendix B provides a brief description of the sort-wave infrared reflectance spectrometry (SWIR) and its application for the identification of minerals. Sample were analysed in the University of British Columbia. Appendix C also provides a brief description of the qualitative powder X-ray diffraction and explains how was used to identify constituents of mixtures of crystalline phases in minerals. Samples were analysed at the University of British Columbia by Elisabetta Pani. Summary tables providing macroscopic description, observations and results of the P I M A and X R D studies and X R D diffractrograms are included as Excel worksheets and Word file on attached C D . Appendix D discusses the sample preparation and chemical analytical processes of trace elements geochemistry used in this study. Sample preparation process was conducted at A L S Chemex in L ima and the geochemical analysis at their facilities in Vancouver B . C . Summary and detailed tables and graphs showing the trace elements results are included as Excel worksheets and Word files on attached C D . Appendix E explains the procedure used in this study to obtain the calcite and dolomite 8 1 8 0 and 8 1 3 C isotopic composition of samples. Samples were analysed at the Pacific Centre for Isotopic and Geochemical Research at the University of British Columbia by Janet Gabites. Detailed description of isotope samples, results, and representative graphs are included as Excel worksheets on attached C D . Appendix F includes the Plate 1, Plate 2 and Plate 3 in pocket. 10 References Alvarez, A.A., and Noble, D.C, 1988, Sedimentary rock-hosted disseminated precious-metal mineralization at Purisima Conception, Yauricocha District, central Peru: Economic Geology, v. 83, no. 7, p. 1368-1378. Alvarez, A.A., Bonelli, A., and Noble, D.C, 1989, Sedimentary rock-hosted disseminated precious-metal deposits of the Yauricocha district, central Peru [abs.]: 28th International Geological Congress, Washington D.C, p-37-38. Alvarez, A.A., Noble, D.C, 1990, Mineralization de metales preciosos diseminados alojados en yacimientos de Purisima Conception, distrito de Yauricocha, centro del Peru: Centro de estudios y promotion de la tierra, Lima (CEPECT), El oro, Lima, p. 106-119. Arroyo Aguilar, A.A., 2002, Plan estrategico, operativo y resultados afio 2001, Centromin Peru S.A, Informe profesional para optar grado de ingeniero de minas, Facultad de Ingenieria Geologica, Minera, Metalurgica y GeografTa. EAP de Ingenieria de Minas: Universidad National Mayor de San Marcos, 141 p. Barton, M.D., Staude, J.M.G., Zurcher, L., and Megaw, P.K.M., 1995, Porphyry Copper and other intrusion-related mineralization in Mexico, in Pierce, F.W., and Bolm, J.G. eds., Porphyry Copper Deposits of the America Cordillera: Arizona Geological Society Digest 20, p. 487-524. Beaty, D.W., and Thompson, T.B., 1988, Carbonate-rich alteration assemblages in porphyry around manto-type orebodies in central Colorado, and their exploration significance: Geological Society of America, Program Abstracts 20, 45p. Beaty, D.W., Landis, G.P., and Thompson, T.B, eds., 1990, Carbonate-hosted sulfide deposits of the central Colorado Mineral Belt: Society of Economic Geologists Monograph 7,424 p. Beaty, D.W., Landis, G.P., and Thompson, T.B, 1990b, Carbonate-hosted sulfide deposits of the central Colorado Mineral Belt: Introduction, general discussion and summary, in Beaty, D.W., Landis, G.P., and Thompson, T.B., eds., Carbonate hosted sulfide deposits of the central Colorado mineral belt: Economic Geology Monograph 7, p. 1-18. Beaty, D.W, Merchand, J.S., O'Neill, T.F., Titley, S.R., Naeser, C.W., Cunningham, C.G., Landis, G.P., Wendlandt, R.F., and Harrison, W.J., 1990a, Origin of the ore deposits at Gilman, Colorado (6 Parts), in Beaty, D.W., Landis, G.P., and Thompson, T.B., eds., Carbonate hosted sulfide deposits of the central Colorado mineral belt: Economic Geology Monograph 7, p. 193-265. Bendezii, R., Fontbote, L., and Costa, M., 2003, Relative age of Cordilleran base metal lode and replacement deposits, and high sulfidation Au-(Ag) epithermal mineralization in the Colquijirca mining district, central Peru: Mineralium Deposita, v. 38, p. 683.694. Bissig, T., Escalante, A., Dipple, G., Ebert, S., Jurado, J., and Tosdal, R., 2005, Sources and exhausts in polymetallic carbonate rock-hosted ore deposits: Miocene magmatism and alteration in central Peru: Mineral Deposit Research Unit, University of British Columbia. 11 Centromin Peru S.A., 1980, Yauricocha, in Samame Boggio, M , ed.: E l Peru Minero, L ima , Editorial Peru, tomo 4, v. 2, p. 838-854. Cox, D.P. , 1986, Descriptive model of polymetallic veins, in Cox, D.P. , and Singer, D . A . , eds., Mineral deposit models: U .S . Geological Survey Bulletin 1693, p. 125. Cox, D.P. , 1986, Descriptive model of porphyry C u deposits, in Cox, D.P. , and Singer, D . A . , eds., Mineral deposit models: U .S . Geological Survey Bulletin 1693, p. 99-100. Cox, D.P. , and Singer, D . A . , eds., 1986, Mineral deposit models: U . S . Geological Survey Bulletin 1693, 379 p. Diaz-Unzueta, R., 1986, Geology and mineralization of L a Encantada silver-lead district, Coahuila, Mexico , in Clark, F.F. , Megaw, P . K . M . , and Ruiz , J. , eds., Lead-Zinc-Silver carbonate-hosted deposits of Northern Mexico: Society of Economic Geologist Guidebook, Nov. 13-17, p. 305-310. Einaudi M T , 1994, High sulfidation and low sulfidation porphyry copper/skarn systems: characteristics, cbntinua, and causes: Society of Economic Geologists, International exchange lecture. W E B link: http://pangea.stanford.edu7research/ODEX/marco-hilosulf.html. Engel, A . E . J . , Clayton, R . N . , Epstein, S., 1958, Variations in isotopic composition of oxygen and carbon in Leadville limestone (Mississippian, Colorado) and in its hydrothermal and metamorphic phases: Journal o f Geology, v. 66 (4), p. 374-393 Fletcher, A . R . , 1929, Mexico ' s silver lead manto deposits and their origin: Engineering and Min ing Journal, v. 127, p. 509-513. Friehauf, K . C , and Pareja, G . A , 1998, Can Oxygen isotopic haloes be produced around high-temperature dolostone-hosted ore deposits? - Evidence from the Superior District, Arizona: Economic Geology, v.93, p. 639-650. Graf, A . , 1997, Geology of the porphyry-style mineralization o f the Cerro Gloria stock associated with high-T, carbonate hosted Zn-Cu-Ag (Pb) skarn mineralization, San Martin district, Zacatecas, Mexico, M . S c . thesis: University of Arizona, Tucson, Arizona. Grant, G.J . , and Ruiz, J., 1988, The Pb-Zn-Cu-Ag deposits of Granadena mine, San Francisco del Oro - Santa Barbara district, Chihuahua, Mexico: Economic Geology, v. 83, p. 1683-1702. Hewett, D .F . , 1928, Dolomitization and ore deposition: Economic Geology, v. 23, p. 821-863. Hewitt, W.P . , 1968, Geology and mineralization o f the main mineral zone of the Santa Eulal ia district, Chihuahua, Mexico: Society of Min ing Engineers, Transactions, v. 241, p. 228-260. 12 Huanqui Lupa, T .B . , 1999, Controles de mineralization y perforation diamantina en el cuerpo Catas del distrito minero de Yauricocha, Yauyos Lima: Universidad Nacional San Agustin, Escuela Profesional de Ingenieria Geologica, Arequipa, Peru, 81 p. Jurado, J., Dipple, G . , Ebert, E . , and Tosdal, R . M . , 2004, Distal alteration around the carbonate-hosted polymetallic replacement and skarn system at Yauricocha, central Peru [abs.]: X I I Congreso Peruano de Geologia. Kesler, S.E., Vennemann, T .W. , and Vazquez, R., Stegner, D.P. , and Frederickson, G . C . , 1995, Application of large-scale oxygen isotope haloes to exploration for chimney-manto Pb-Zn-C u - A g deposits, in Coyner, A lan R., and Fahey, Patrick L . , eds., Geology and Ore Deposits of the American Cordillera: Geological Society of Nevada, Symposium Proceedings, Reno/Sparks, Nevada, p. 1383-1396. Kobe, H . W . , 1961, Idaita, mineral de cobre en Yauricocha: Sociedad Geologica del Peru. II Congreso Nacional de Geologia, Lima, tomo 36, anales, parte 1, p. 103-114. Lacy, W . C , 1949, Oxidation processes and formation of oxides ore at Yauricocha, L a Oroya: Sociedad Geologica del Peru, Volumen Jubilar 25 t h Anniversary, pt 2, fasc. 12, p. 1-15. Lavado, M . , 2002, E l metalotecto Jumasha y su analisis estratigrafico, Minas representativas: Hualgayoc, Raura, Uchucchacua, Yauricocha: Sociedad Geologica del Peru, X I Congreso Peruano de Geologia, L ima, p. 32. Lefebure, D . V . , and Hoy, T., 1996, Selected British Columbia Mineral Deposit Profiles, Volume II - More Metallic Deposits: British Columbia Ministry o f Energy, Mines, and Petroleum Resources, Open File 1996-13, 172 p. Lefebure, D . V . , and Church, B . N . , 1996, Polymetallic veins Ag-Pb-Zn±Au, in Lefebure, D . V . , and Hoy, T., eds., Selected British Columbia Mineral Deposit Profiles, Volume II - More Metallic Deposits: British Columbia Ministry of Energy, Mines, and Petroleum Resources, Open File 1996-13, p. 67-70. Lovering, T.S., Tweto, O., and Lovering, T .G. , 1978, Ore deposits o f the Gi lman district, Eagle County, Colorado: U . S . Geological Survey Professional Paper 1017, 90 p. M c K e e , E . H . , and Noble, D , 1990, Cenozoic tectonics events, magmatic pulses, and base- and precious-metal mineralization in the central Andes, in Ericksen, G .E . , Cafias Pinochet, M . T . , and Reinemund, J .A. , eds., Geology of the Andes and its relation to hydrocarbon and mineral resources: Houston, Texas, U . S . A . : Circum Pacific Counceil for Energy and Mineral Resources Earth Sciences Series, v. 11, p. 189-194. Megaw, P . K . M . , 1986, Argentiferous manganese-oxide alteration in wall and capping rocks of Santa Eulalia district, Chihuahua Mexico, Geological Society o f America, Programs, Abstracts, 18, p. 93. Megaw, P . K . M . , 1987, Oxygen and carbon isotopic shifts between altered and unaltered limestone in peripheries of the Santa Eulalia Min ing District, Chihuahua, Mexico: Geological Society of America, Program Abstracts 19, p. 769. 13 Megaw, P . K . M . , 1988, Tectonic localization and controls on high-temperature, carbonate-hosted Ag-Pb-Zn deposits of Northern Mexico, in Kisvarsanyi, G . , and Grant, S.K. , eds.: North American conference on tectonic control and the vertical and horizontal extent o f ore systems. Proceedings volume: Rol la , Univ . of Missouri Press, p. 92-103. Megaw, P . K . M . , 1990, Geology and geochemistry of the Santa Eulalia mining district, Chihuahua, Mexico: Unpublished Ph.D. Thesis, Univ. of Arizona, Tucson, Arizona, 463 p. Megaw, P . K . M . , 1998, Carbonate-hosted Pb-Zn-Ag-Cu-Au replacement deposits: A n exploration perspective, in Lentz D .R . ed., Mineralized intrusion-related skarn systems: Mineralogical Association of Canada. Short course series 26, chapter 10, p. 337-358. Megaw, P . K . M . , 2001, Carbonate-hosted Pb-Zn-Ag-Cu-Au replacement deposits: an exploration perspective: Proceedings of the ProExplo Meeting, L i m a Peru. Megaw, P . K . M . , Ruiz , J., and Titley, S.R., 1988, High-temperature, carbonate-hosted Ag-Pb-Zn(Cu) deposits of northern Mexico: Economic Geology, 83, 1856-1885. Megaw, P . K . M . , Barton, M . D . , and Islas-Falce, J. , 1996, Carbonate-hosted Lead-Zinc (Ag, C u , Au) deposits of Northern Chihuahua, Mexico, in Sangster, D.F. , ed.: Society o f Economic Geologists, Special Publication No . 4, p. 277-289. Meinert, L . D . , 1987, Skarn zonation and fluid evolution in the Groundhog Mine , Central Min ing District, New Mexico: Economic Geology, v. 82, p. 523-545. Meinert, L . D . , 1992, Skams and skarn deposits: Geoscience Canada, v. 19, p. 145-162. Meinert, L . D . , 1993, Metamorphism, metasomatism, and fluid flow in skarn deposits - the basis for genetic distinctions: Geological Society of America, Abstracts with Programs, v. 25, p. A110. Meinert, L . D . , 1998, Skarns and skarn deposits, summary and web links: Skarn Website http ://www. wsu.edu:8080/~meinert/skarnHP.html Meinert, L . D . , 2000, The role of magmatic fluids in skarn and porphyry systems: Australian Geological Congress, Abstracts with Programs, v. 59, p. 343. Meinert, L . D . , Dipple, G . M . , and Nicolescu, S., 2005, World skarn deposits, in Hedenquist, J.W., Thompson, J .F .H. , Goldfarb, R.J . , and Richards, J.P., eds.: Economic Geology 100 t h Anniversary Volume, p. 845-890. Morris , H.T. , 1968, The main Tintic mining district, Utah, in Ridge, J .D., ed, Ore deposits of the United States, 1933-1967 (Graton-Sales Volume): New York , American Institute of Min ing and Metallurgical Engineers, p. 1043-1073. Morris , H.T. , 1986, Descriptive model o f polymetallic replacement deposits, in Cox, D.P . , and Singer, D . A . , eds., Mineral deposit models: U . S . Geological Survey Bulletin 1693, p. 99-100. 14 Naito, K . , Fukahori, Y . , Peiming, FL, Sakurai, W. , Shimazaki, H . and Matsuhisa, Y . , 1995, Oxygen and carbon isotope zonations of wall rocks around the Kamioka Pb-Zn skarn deposits, central Japan - application to prospecting: Journal of Geochemical Exploration, v. 54, p. 199-211. Nelson, J .L. , 1996, Polymetallic manto Ag-Pb-Zn, in Lefebure, D . V . , and Hoy, T., eds., Selected British Columbia Mineral Deposit Profiles, Volume II - More Metallic Deposits: British Columbia Ministry of Energy, Mines, and Petroleum Resources, Open File 1996-13, p.101-103. Newel l , R . A . , 1974, Exploration geology and geochemistry of the Tombstone-Charleston area, Conchise Co , Arizona, Ph.D. thesis: Stanford University, California. Noble, D . C , and M c K e e , E . H . , 1999, The Miocene metallogenic belt of central and northern Peru, in Skinner, B . J . ed., Geology and ore deposits of the central Andes: Society o f Economic Geologist, Special Publication N o 7, chapter 5, p. 155-193. Ohmoto, H . , 1986, Stable isotope geochemistry of ore deposits, in Valley, J .W., Taylor, H.P . Jr., and OT^eil, J.R., eds., Stable Isotopes in High Temperature Geological Processes: Mineralogical Society of America, Reviews in Mineralogy, v. 16, p. 491-560. Pareja, G . A . , and Friehauf, K . C . , 1998, Conditions determining the utility o f oxygen isotopes as an exploration tool for carbonate-hosted deposits: Exploration Roundup '98, Vancouver, B . C . , January 27-30, Abstracts with Programs, 5 p. Petersen, U . , 1965, Regional geology and major ore deposits of central Peru: Economic Geology, v. 60, p. 407-416. Petersen, U . , V ida l , C . E . , and Noble, D . C , 1990, A special issue devoted to the mineral deposits of Peru, Preface: Economic Geology, v. 85, p. 1287-1295. Pinckney, D . M . , and Rye, R.O. , 1972, Variation of 0 1 8 / 0 1 6 , C 1 3 / C 1 2 , texture and mineralogy in altered limestone in the H i l l mine, Cave-in-Rock district, Illinois: Economic Geology, v. 67, p. 1-18. Prescott, B . , 1916, The main mineral zone of the Santa Eulalia district: American Institute o f Min ing Engineers Transactions, v. 51, p. 57-99. Prescott, B . , 1926, The underlying principles of the limestone replacement deposits of the Mexican Province: Engineering and Min ing Journal, v. 122, p. 246-296. Rado, E . G . , 1977, Potencial aurifero de la mina Yauricocha: Instituto de ingenieros de minas del Peru, X X I I I Convention de ingenieros de minas del Peru, Arequipa, Trabajos tecnicos, tomo l , p . 15-22. Rado, E . G . , 1997, Controles de mineralization en el distrito minero de Yauricocha: Sociedad Geologica del Peru, LX Congreso Peruano de Geologia, Lima, Resumenes extendidos, capitulo I: Metalogenia y yacimientos de minerales, p. 161-165. 15 Rado, E . G . , Cuba, O., Cema, J. , and Toledo, W. , 1996, Inventario de reservas de mineral, M i n a Yauricocha: Unpublished report, Lima, Centromin Peru, 333 p. Rodriguez, G . , 2002, Interin Annual Report: Sociedad Minera Corona S.A. , Unpublished internal report. Rodriguez, G . , 2004, Interin Annual Report: Sociedad Minera Corona S.A., Unpublished internal report. Rubright, R .D . , and Hart, O.J., 1968, Non-porphyry ores of the Bingham district, Utah, in Ridge, J.D., ed., Ore deposits of the United States, 1933-1967 [Graton-Sales volume]: N e w York: American Institute of Min ing and Metallurgical and Petroleum Engineers, v. 1, p. 886-907. Segura Perez, W.F . , 1993, Estudio geologico del stock Exito y sus posibilidades de desarrollo minero, mina Yauricocha, provincia Yauyos, departamento Lima: Universidad Nacional Mayor de San Marcos L ima , tesis para optar titulo ingeniero geologo, 118 p. Sigrist, K . F . , 1951, Yauricocha surface map, Unpublished report, L a Oroya: Cerro de Pasco Corporation, scale, 1:2000. Sillitoe, R. H . , Bonham Jr., H.F . , 1990, Sediment-hosted gold deposits: Distal products of magmatic-hydrothermal systems: Geology, v. 18, p. 157-161. Sillitoe, R . H . , Perello, J, 2005, Andean Copper Province: Tectonomagmatic settings, deposit types, metallogeny, exploration, and discovery, in Hedenquist, J .W., Thompson, J .F .H. , Goldfarb, R.J . , and Richards, J.P., eds.: Economic Geology 100 t h Anniversary Volume, p. 845-890. Sweeney, R . L . , 1987, Stable isotope geochemistry of calcite and limestone at Naica, Chihuahua, Mexico, M . S c . pre-publication: University of Arizona, Tucson, Arizona, 51 p. Thompson, D.S.R. 1960. The Yauricocha sulfide deposits, central Peru: London* England, Imperial College, University o f London, unpublished Ph.D. dissertation, 154 p. Titley, S.R., 1993, Characteristics of high-temperature, carbonate-hosted massive sulfide ores in the United States, Mexico , and Peru, in Kirkham, R . V . , Sinclair, W . D . , Thorpe, R . L , and Duke, J . M . , eds., Mineral Deposit Modeling: Geological Association of Canada Special Paper, v. 40, p. 585-614. Titley, S.R., 1996, Characteristics of high temperature, carbonate-hosted replacement ores and some comparisons with Mississippi Valley-type ores, in Sangster, D.F . , ed., Carbonate-hosted lead-zinc deposits: Society of Economic Geologists, Special Publication Number 4, p. 244-254. -Titley, S.R., and Megaw, P . K . M . , 1985, Carbonate-hosted ores of the Western Cordillera, an overview: A . I . M . E . , Preprint #85-115, 17 p. 16 Titley, S.R., and Megaw, P . K . M . , 1995, The setting and genesis of high-temperature, massive, carbonate-hosted replacement ores. Society of Economic Geologists International Field Conference on Carbonate-hosted Lead-Zinc Deposits, St. Louis Missouri , June 3-6, Extended Abstracts, p. 314-316. Valdivia , V . A . , 1996, Geology and metallogeny of the Yauricocha mine (Cu-Pb-Zn-Ag), central Peru, M . S c . thesis: Instituto de Geociencias, Universidade de Brasilia, Brasil . Web link: http://www.unb.br/ig/posg/mest/mestl06.htm Vazquez, R., Vennemann, T .W. , Kesler, S.E. and Russell, N . , 1998, Carbon and oxygen isotope halos in the host limestone, E l Mochito Zn-Pb-(Ag) skarn massive sulfide-oxide deposit, Honduras: Economic Geology, v. 93, p. 15-32. V ida l C . E . , and Noble, D . C , 1994, Yacimientos hidrotermales controlados por magmatismo y estructura en la region central del Peru: Sociedad Geologica del Peru, VIII Congreso Peruano de Geologia, L ima, Resumenes extendidos, p. 48-52. Wanless, H . , 1979, Limestone response to stress: pressure-solution and dolomitization, Journal of Sedimentology Petrology, v. 49, p. 437-462. Ward, H.J . , 1959, Sulfide orebodies at Yauricocha, central Peru - replacements o f organic reefs?: Economic Geology, v. 54: p. 1365-1379. Weigel, D . A . , and Kobe, H . W , 1992, Idaita, nukundamita y faces relacionadas, su ocurrencia y genesis en yacimientos minerales (Sintesis de investigaciones recientes respecto de aspectos mineralogicos, fisico-quimicos, parageneticos y metalogeneticos con referenda particular a Yauricocha, Peru y las islas del Pacifico SW): Boletin de la Sociedad Geologica del Peru, Lima, v. 83, p. 21-33. Wright, C M . , 1965, Geochemical and geological studies on barren and productive plutons in the Yauricocha area, central Peru, Unpublished report, L ima: Cerro de Pasco Corporation, 60 p. plus addendum! 17 CHAPTER TWO Geological Framework 2.1. Introduction The Yauricocha mining district is located within the Miocene to early Pliocene belt of the central Andes, which is one of the three economically fertile Cenozoic belts of the Andean Copper Province (Sillitoe and Perello, 2005). The belt semi-continuously extends for about 6000 km from northern Colombia to central Chile and adjoining west-central Argentina (Fig. 2.1). The section of the belt from northern Peru to central Chile, contains the most varied C u rhetallogeny of the entire Andes, with porphyry, skarn, breccia, enargite bearing carbonate replacement, high sulfidation epithermal enargite veins, red-bed and exotic oxide C u deposits (Fig. 2.2; Sillitoe and Perello, 2005). Complex polymetallic enargite-bearing veins and carbonate and associated rocks replacement deposits, as Cerro de Pasco, Marcapunta (Colquijirca), Yauricocha, Ucchuchacua, Huanzala, and Morococha, and prospects, are located in the northern and central Peru segment o f the belt (Fig. 2.3; Peterson, 1965; Noble and McKee , 1999; Tumialan De L a Cruz, 2002). This segment extends for about 1000 km along the Western Cordillera between latitudes 6° and 13° S, where it is centered east of the Mesozoic and early Paleogene coastal batholith and formed in stratigraphically and structurally complex Paleozoic to Cenozoic rocks dominated by marine-carbonate sequences (Fig. 2.2; Sillitoe and Perello, 2005). Late Cretaceous- (Peruvian), middle Eocene- (Incaic), early Miocene- (Quechua I), middle to late Miocene- (Quechua II and III), and Pliocene- to early Pleistocene multiple widespread episodes of contractional tectonism affected the rock units (Megard 1984; Sebrier et al., 1988; Sebrier and Soler, 1991; Benavides-Caceres, 1999; and Noble and M c K e e , 1999). The Zn-Pb-Cu-Ag magmatic-hydrothermal system at Yauricocha is zoned around a late Miocene equigranular quartz diorite to quartz monzonite pluton known as the Yauricocha-Exito Stock. The Yauricocha-Exito Stock intrudes Cretaceous limestone and shale, which host the polymetallic replacement deposits and skarn orebodies that form the mining district (e.g., Valdivia , 1996). "Carlin-style" A u mineralization at Purisima Conception (Alvarez and Noble, 1988; Alvarez et al., 1990; Noble et al., 2000) and base metal veins and low-grade porphyry C u and A u mineralization within the intrusion have also been recognized, but these are of lesser economic significance. Base metal veins have only been mined on a local scale. 18 her PANTANOS-PtGADORCl TO (43) „ PIEDRASFNT ADA (17) TAMBOGRANDE 02 1001 rANACOCHAl 12-10) MICHIQUILLAY (20) 10" 20° 30° MAIN Cu BELTS . j Miocene-early Pliocene I 1 Middle Eocene-early Oligocene B B Paleocene-early Eocene Late Cretaceous Fe oxide-Cu-Au E££9 Early Cretaceous Earty Cretaceous ESB Jurassic 1 i Middle-Late Jurassic i''M Late Paleozoic-early Mesozoic RAUL-CONDESl ABLE (lib) CERflO LtNOO Y A U R I C O C H A (7.47) DEPOSIT TYPES Porphyry Cu-(Mo, Au) Porphyry-related skarn Cu-(Mo, Au, Zn) Skarn Tourmaline breccia Enargite vein Enargite-bearing replacement Fe oxide-Cu-Au Volcanogenic massive sulfide Red bedCu Group of manto-typeCu deposits Group of red bed Cu deposits Major tectonic discontinuity EL ABRA (391 CHUQUICAMATA (35-31) TOKI (37) SAN BARTOLO PANCMO ARIAS (16) L OS PEL.AMRRES-EL PACHON (11 HtO BLANCO-LOS BRONCES (7-4) -SANTIAGO) FL TENIENTE (7-4) TACA TACA BAJO (34-33) ERHO SAMENTA (255) J&AJO OE L A ALUMBRERA (8- 7) fW— AQUA RICA (5) 4- CERRO CASALfc I14| LA FORT UNA (35-32) « FAMATINA (5-4) EL INDIO rtw SAN FRANCISCO DE LOS ANDES LOS BAGflES SUR 191 ^ EL ALTAR —4- SAN JORGE (263-257) 1" N DIENTE VERDE (10-91 ~* SAN PEDRO ARGENTINA GALL ETUE (73) -f CAMPANA MAHUIDA (76) LA VOLUNTAD (287) 60° Figure 2.1: Copper belts of the Andes showing selected deposits and prospects and their genetic types. Also shown are the three main traverse discontinuities in the Andes. Numbers in parentheses after deposits names are approximated deposits isotopic ages taken from compilation by many authors. The Yauricocha-Exito stock has a 4 0 A r - 3 9 A r age of 7.47+0.06 M a (Bissig et al., 2004). (After Sillitoe and Perello, 2005). 19 hp_° f'lf DRASENT ADA (17) QUITO JUNIN(6I ECUADOR CHAUCHA (11) |^ OABY|19). r\ if POOUO [161 H DEPOSIT TYPES • Porphyry Cu-Mo • Porphyry Cu-Au • Porphyry-related sKarn w Enargite-beaiing replacement Enargite vein \ Tourmaline breccia mm Exotic Cu Red bed Cu Major tectonic discontinuity CANARIACO LA GRANJA (14) YANACOCHA M2-10}' Et. GALENO PACKAGON (18) PAHAO(13) NORTHERN-CENTRAL PERU SEGMENT — - RIO BLANCO TURMALINA CERRO CORONA 113) MINAS CONGA (161 LACARPA MICHIQUILLAY (20) f MAGISTRAL (1S) ( PASHPAP(15) \ ANTAMINA 110) \ ' RAURA(10-8) L. P E R U BRAZIL """""""I I A iCERRO Dt PASCO (12-11)/ ) tk ' MARCAPUNTA (1110) 500 km YAURICOCHA OAT) 20° 30° DAMIANA FARALLON NEGRO DISTRICT MARICUNGA-ELINDIO SUB-BELT CERRO CASALE (14) . NEMESIS . REGALITO (18) . ELPOTRO(15) -RIO HURTAOO (COIPI TAl LOS AZULE S LOS PFLAMBRES 111-10) AMOS-ANDRFS VI2CACHITAS (17-10) PIMENION WEST WALL RIO BLANCO-LOS BRONCES |7 4) Juan Fernandez Ridge CENTRAL CHILE SUB-BELT CONCEPCIONt CHILE BOLIVIA ;<-,LAPAZ ' 'Hf „.COROCOHO cri , LAURANI (81 „J5y>ARAC0YA(17) =-—\CHACARILLA TK3NAMAR linrj . SAN BARfOLO _ L I N D E R O I • I INCAVIEJO (15) AQUA. RICA (5 fLA ALUMBRE RA 18-IVICUNITA \ t)FAMATlNA |5 EL INDIO (3-6) \ ARROVO 0HHA(12 LOS BAGRES SUR (9 'EL ALTAR-PHJOLIF» S ' E L P A C H O N | EHRO MERCEDAHi I • PARAMILLOS 118) MEgOOZA m DIENTE VERDE lie 9 (RIO D E L A S VACAS (9 / ELTENIENTE (6-41 / I BOSAHIO DE RENGO (7) ARGENTINA 8 0 i Figure 2.2: Miocene to early Pliocene copper belt of the Andes, showing the Yauricocha mining district and the main deposits and prospects and their genetic type. Also shown are the three main transverse discontinuities in the Andes. Numbers in parentheses after deposits names are approximated deposit isotopic ages taken from compilation by many authors. The Yauricocha-Exito stock has a 4 0 A r -3 9 A r age of 7.47±0.06 Ma (Bissig et al., 2004). Figure after Sillitoe and Perello (2005). 20 Prior to examining the characteristics of the distal alterations around the polymetallic carbonate hosted and skarn deposits, it is important to summarize the stratigraphy and structural architecture of the district, as these controlled the intrusion of the Yauricocha-Exito Stock as well as played a crucial role in the formation of the sulfide deposits. Figure 2.3: Carbonate hosted deposits and prospects in central Peru showing location of Yauricocha. 2.2. Tectonic Setting The polymetallic district of Yauricocha is located near the crest of a portion of the Western Cordillera of central Peru (Fig. 2.4.) at elevations between 4500 and 4700 meters above sea level (m.a.s.l.). The district is located within an older fold-and-thrust belt that formed during the middle Eocene Incaic orogeny (Megard et al., 1996). The sedimentary rocks, dominantly of Cretaceous age, have been folded into northwesterly trending anticlines and synclines and cut by parallel thrust faults (Fig. 2.5; Megard et al., 1996). The contractional structures have been subsequently cut by steeply dipping (75° - 90°) northwesterly, northeasterly, and easterly trending faults and fracture systems (Megard, 1968; Megard et al., 1996). The Yauricocha-Exito Stock intruded into the northwesterly trending anticlines and synclines along the northwest trending Yauricocha Fault (Fig. 2.6). The outcrop pattern o f the stock reflects the influence of these fabrics during pluton emplacement. The same folds and fault also exerts a control on the location of the sulfide-bearing carbonate-replacement deposits (CRD) and skarn deposits (see below and Figs. 2.6 and 2.8; Plate 1). 21 Figure 2.4: Late Jurassic - Upper Cretaceous paleogeographic map of Peru (adapted from Benavides-Caceres, 1999). Pre-mineral folds are the main structural features in the study area (Figs. 2.6 and 2.8; Plate 1). These include the Purisima Conception anticline and France Chert syncline in the M i n a Central area, Cachi Cachi anticline and Huamanrripa syncline in the Cachi Cachi area, and the Quimpara syncline north of the San Vicente mine, ca 10 km southeast o f Yauricocha (Fig. 2.7; Plate 1). The Purisima Conception anticline lies along the southwestern margin of the Yauricocha mining district. This tight fold generally trends N 5 0 ° W and plunges southeast. It is well defined by a folded 17-meter thick basaltic s i l l . Carlin-type disseminated gold has been described in decalcified and silicified, impure limestone located at the east flank of the basaltic s i l l in the core of the steeply plunging anticline (Alvarez and Noble, 1988; Noble et al., 2000). The France Chert syncline, lying northeast of Mina Central, is another tight fold with an axial trend varying from N 3 5 ° W in the south to N65°W in the north. The Zn-Pb-Cu-Ag C R D orebodies in M i n a Central are located in the western flank of this fold (Figs. 2.6 and 2.8; Plate 1). The N80°W to N 7 0 ° W trending Cachi Cachi-Prometida anticline, 2 kilometers north of M i n a Central, controlled emplacement of the Cachi Cachi skarn orebodies in this area. This fold plunges to the north in Prometida and to the south in Cachi Cachi. 22 —I I Quaternary Tertiary Volcanics Tertiary Peruvian Coastal Batholith Cretaceous Jurassic - Cretaceous Jurassic Triassic - Jurassic Carboniferous - Permian Precambrian - Devonian Figure 2.5: Geology map of central Peru after Megard (1996), Institute Geologico Minero y Metaliirgico ( INGEMMET). m Quartz monzonlte intrusive 4 Pb-Zn-Ag mineralization • H Celandine Formation QuarU-sphalerite-pyrite-galena-enargite vein m Jumasha Formation limestone 0 Km 1 Figure 2.6: Simplified geology map of the Yauricocha mining district of central Peru after the Centromin Peru compilation map with information from Stone, J.B., and Osborne, H . (1928), Snively, N . (1947), Sigrist, K .F . (1951), and Auilar Rios, F. (1970). 23 The axis of the Huamanrripa fold (west of Figure 2.6), S W of Cachi Cachi, and 1 km N of M i n a Central, is the northern prolongation of the France Chert syncline. To the east, where it trends N 4 5 ° W dipping 80°W, it is composed of calcareous recrystallized beds, and pipe-like breccia bodies. A basaltic si l l occurs to the west, and its axis dips 75-80°E. Approximately 10 k m SE of M i n a Central, the N45°W trending Quimpara syncline overlies the intrusive and it is composed of dark gray recrystallized calcareous beds. The N W trending Yauricocha Fault and associated subparallel brittle shear zones developed before and during the emplacement of the Yauricocha-Exito Stock. It is parallel to the regional trend of bedding, and follows the contact between limestone o f Jumasha Formation and calcareous shales of the overlying Celendin Formation. The fault extends along Silacocha Lake, from Ipillo mine in the south toward the northern slope of Huamanrripa H i l l (Fig. 2.7). A t Yauricocha, the C R D orebodies are spatially associated with the Yauricocha Fault, and form pipe-like breccia bodies in highly fractured rocks. The C R D orebodies are aligned along the fracture mesh, and commonly are located in limestone along contacts or at intersections of faults and bedding. Collapse or tectonically controlled pipe-like breccias are one of the most important hosts of high-grade orebodies (Fig. 2.8; Rodriguez, 2002). 2.3. Stratigraphic Framework Sedimentary rocks occurring within the Yauricocha mining district belong to the Goyllarisquisga, Jumasha, Celendin, and Casacalpa Formations. Limestone of the Jumasha Formation is the dominant host rock to the sulfide orebodies. The regional stratigraphy is summarized in Figure 2.9 (Thompson, 1960; Rodriguez, 2002, 2004). The Early Cretaceous Goyllarisquisga Formation is the oldest sedimentary unit in the region but does not crop out within the district. It does occur around the Exito Mine , located 5.5 km south-southeast of Yauricocha. There, the Formation only occurs in cores of anticline. Regionally the formation is composed of approximately 300 meters of white to gray coarse-grained sandstone, locally banded with carbonaceous shales, thin beds of impure coal, and clays. Near Chauca (approximately 14 km N E of Yauricocha mine), the sandstones are inter-bedded with red shales near the base of the formation. Conformably above the Goyllarisquisga Formation is the Cretaceous Jumasha Formation, which is the principal host rock in the Yauricocha mining district (Fig. 2.6; Plate 1). It consists of over 700 meters of light gray massive limestone. The base of the formation includes inter-bedded carbonaceous shales overlain by discontinuous brown-gray limestone lenses with local 24 422000 mE Figure 2.7: Generalized geological and alteration map of the Yauricocha mining district, central Peru. Black line insets shows area of detailed map at Mina Central and Cachi Cachi. 25 shale and siliceous beds up to 6 meters wide. Sedimentary breccias and a basaltic s i l l up to 17 meters wide are lesser rock types (Fig. 2.9). Intrusion of the Yauricocha-Exito stock has converted the limestone to marble and to 10 to 50 meter wide dolomitic zones along the intrusive contact, where the rocks host C u , Pb, Zn and A g mineralization. Figure 2.8: Schematic cross section through the Yauricocha mine of central Peru after Rodriguez (2004). View to the northwest. The late Cretaceous (Santonian) Celendin Formation conformably overlies the limestone of the Jumasha Formation. In the Yauricocha mining district, it consists of about 400 meters of fine-bedded silicified shales (chert) (Fig. 2.9) and recrystallized limestone along the western edge of the quartz diorite to quartz monzonite intrusion. Small epidote-, chlorite-rich garnet skarn bodies with pyrite dissemination associated with copper mineralization are also present (Rado, 1997). The Celendin Formation at Yauricocha has been previously mapped as part of the lower beds of the Casapalca Formation (Petersen, 1965; Centromin Peru S.A., 1980), and is locally known as France Chert (Wilson, 1963, Petersen 1965; Centromin Peru S.A., 1980). Throughout the Yauricocha region but not within the mining district, the Upper Cretaceous to lower Tertiary Casapalca Formation conformably overlies the Celendin Formation along a 26 gradational contact. The Formation is composed of red calcareous shales, pure limestone, and red sandy limestone with local lava and tuff beds. The Jumasha limestone-Celendin shale, Jumasha limestone-intrusive, and Celendin shale-intrusive contacts exert a strong control localizing the orebodies (Figs. 2.7 and 2.8). The largest orebodies are particularly located in the contact of the lithological units with the Celendin shale, which acting as a permeability barrier to the ore-bearing hydrothermal fluids helped to concentrate the lodes (Thompson, 1960; Rado, 1997). Grain size and fracture permeability at the sedimentary rocks also influence the mineralized bodies. Orebodies are emplaced in coarser grained limestone rather than in finer grained shale, and in areas with intense fracturing (i.e., in or close to faulted and folded zones) (Rodriguez, 2002). In M i n a Central, orebodies typically occur in limestone near or at the contact with the thermally metamorphosed Celendin Formation shale (France Chert) and also next to the stocks or dikes, whereas in Cachi Cachi, they are present along the Jumasha limestone-intrusive contact. 2.4. Intrusive Rocks The Yauricocha-Exito Stock is a composite intrusive elongated in a northwest direction parallel and largely concordant with stratigraphy in the fold-and-thrust belt (Fig. 2.7 and 2.8). A 4 0 A r - 3 9 A r age of 7.47 ± 0.06 M a has been determined on biotite (Bissig et al., 2004). The Yauricocha-Exito Stock intruded limestone of the Cretaceous Jumasha Formation and marls of the Santonian Celendin Formation. The stock has steeply dipping contacts with country rocks, and is elongate parallel to the regional structural trends. In M i n a Central, it occurs along the NW-trending France Chert and Purisima Conception folds whereas in Cachi Cachi along the WNW-trending Cachi Cachi and France Chert folds (Fig. 2.7; Plate 1). Satellite intrusives occur in clusters of small bodies with a surface area of a few hundred square meters to large bodies that cover several square kilometers. Small apophyses and dikes or sills are common along the edges of the larger bodies. The main intrusive body is locally zoned from quartz diorite-granodiorite in the center to quartz-monzonite on the margin (Rodriguez, 2002). Plagioclase, orthoclase, biotite, hornblende and quartz are the main minerals. Plagioclase varies from oligoclase to andesine, and commonly displays porphyritic textures. Quartz veins are commonly found in small zones o f silicification on the intrusive. 27 CASAPALCA FORMATION CELENDIN FORMATION JUMASHA FORMATION GOYLLARISQUISGA FORMATION EXPLANATION COVER C°<f< INTRUSIVE VOLCANIC \> " SHALE MARL LIMESTONE SANDY LIMESTONE SHALE LIMESTONE BASALTIC SILL |->—«•) MARL SANDSTONE Figure 2.9: Stratigraphic cross section of the Yauricocha mining district of central Peru after the Centromin Peru compilation map and Rodriguez (2004). 2.5. Contact Metamorphism and Metasomatism A l l the intrusions are bordered by contact metamorphic aureoles composed o f quartzites, hornfels, and recrystallized limestone in the country rocks. The extent, type, and degree of thermal metamorphism vary with sedimentary rock types. Thermal aureoles up to 0.6 km-wide form in limestone and marls along the western side of the main stock (Fig. 2.7; Plates 1, 2 and 3). A l l known skarn and carbonate replacement Pb-Zn-Ag orebodies formed within the thermal aureole. Small zones of endoskarn, up to 3 m wide, containing epidote, zoisite, tremolite, wollastonite, phlogopite, garnet, diopside and chlorite occur within intrusive rocks. Skarn bodies, up to 50 m wide, occur very locally (Fig. 2.7; Plate 1). 28 2.6. Mineralization in the Yauricocha Min ing District The Yauricocha mining district contains several different styles of mineralization including carbonate replacement deposits (CRD) at M i n a Central, skarn deposits at Cachi Cachi, Carl in-style A u at Purisima Conception, base metal veins in the surrounding country rocks and within the late Miocene intrusion, and low-grade porphyry-Cu and A u mineralization (Figs. 2.6 and 2.7; Petersen, 1965; Rado, 1977, 1997; Alvarez and Noble, 1988, Valdivia , 1996; Lavado, 2002; Rodriguez, 2004). The C R D and skarn deposits are the focus o f this study (Plate 1). 2.6.1. M i n a Central and Cachi Cachi The main sulfide mineralized zone is accessed via the workings at M i n a Central. There, Pb-Z n - C u - A g sulfides form irregular orebodies as C R D replacement deposits. They form mantos, lenses and vertical chimneys, and f i l l faults and fracture networks in limestone and within the intrusive (Table 2.1). Mineralized bodies typically lie near or at the contact with the Celendin Formation (France Chert) and along contacts with stocks and dikes. Some orebodies contain pipe-like breccia and tectonic breccia zones spatially related to lithological contacts or structural intersections. The vertical dimensions of orebodies are usually greater than in the horizontal with some bodies extending for more than 650 m vertically with variable widths only from 10 m to 40 m (Fig. 2.8; Table 2.1; Rodriguez, 2002). The distribution of orebodies composing M i n a Central is irregular. Some form interconnected extensive mineralized zones (i.e., Catas-Contacto Oriental-Antacaca), whereas others appear only partly interconnected over relatively large areas (i.e., Butz-Pozo Rico-Violeta-Erika). Sti l l other sulfide bodies form small individual and disconnected bodies (i.e., Cuye, Mascota, Sasacaca, Sur Medio, Contacto Occidental, Amoeba, Maritza, Carmencita, and Cuye Norte (Fig. 2.7). Orebodies hosted in Jumasha limestone at M i n a Central include Amoeba, Antacaca, Butz, Catas, Contacto Occidental, Contacto Oriental, " A " , Cuye, Cuye Norte, Erika, Gallito, Juliana (Veta), Juliana I, Juliana II, Katty, Marita, Mascota, Olguita, Pozo Rico, Sasacaca, Contacto Sur Medio, Violeta, Violeta - 329 and Jacqueline. Poderosa, Felicidad and E l Norte occur in rocks of the Celendin Formation (Table 2.1). Discontinuous mineralized veins are best developed in the main intrusive but are also present in Jumasha limestone. The horizontal and vertical dimensions of veins are variable and to date are not very well constrained in depth. Some sulfide-bearing veins in carbonate rocks may have variable widths ranging between 0.50 m and 2.50 m in M i n a Central and between 6 29 m and 8 m in Ipillo. Surface and underground mining and exploitation in M i n a Central, Cachi Cachi, Victoria, Exito and Ipillo, demonstrate three mineralized vein systems; the older system is E-striking, dipping N or S; the intermediate age system is 100-110° striking, dipping 60°-80°SW or N E ; and the youngest system is 070°-080° striking, dipping 65°-80°NW (Rodriguez, 2002, this study). Mineralized veins in Mina Central include Vetas " A " , " C " , " D " , "F" and " G " , Veta Cuye Sur, Veta Mascota and Veta Cuye. Detailed description of orebodies and veins at M i n a Central is presented in Table 2.1. In contrast to M i n a Central, the Cachi Cachi area, 1.5 km north, Pb-Zn sulfides are associated with massive pyrite replacement of limestone, local jasperoidal silicification, and minor wollastonite and diopside. A t deeper levels in the Cachi-Cachi deposit, skarn-style replacement predominates. A vertical zonation is evident with silicification, wollastonite content, and gold grades increasing at higher levels, and pyroxene content increasing with depth. Irregular individual mineralized bodies, mostly lenticular, occur individually in Cachi Cachi within Jumasha limestone along the N - S trending intrusive contact and adjacent to stocks or dikes. Mineralized veins are also present mainly in Jumasha limestone near skarn or intrusive bodies. The size of the orebodies at Cachi Cachi is variable; most of them are relatively small. Some may extend at least up to 100 m wide x 150 m long in size. Orebodies have been recognized up to 150 m depths in Level 410 (4,494 m.a.s.l.). U p to 3-15 m wide, irregular-shaped, breccia-pipe bodies are also present. Min ing and exploration activities suggest that economic mineralization at Cachi Cachi lies to depth of 450 m beneath the present surface (Rodriguez, 2004). In the Cachi Cachi area, three main orebodies, Privatizadora, Caprichosa and Rossy, are hosted in Jumasha limestone near the main intrusive (Table 2.2). The NW-str iking orebodies dip 65°S, 60°N and 80°S, respectively. Caprichosa and Rossy consist of calcareous breccia, whereas Privatizadora is a mixed breccia composed of intrusive and limestone fragments. Orebodies are 8 m wide x 18 m long for Privatizadora, and 2 to 5 m wide x 25 m long for Caprichosa. Unlike the Other two orebodies, Privatizadora also outcrops. Three NW-str iking veins, steeply dipping S, also have been recognized in Cachi Cachi: Veta Carmencita, Veta Dianita and Veta Virginia. Carmencita is mainly emplaced within calcareous breccias, Dianita is located in the skarn-Jumasha limestone contact, and Virg in ia outcrops in the intrusive-Jumasha limestone contact (Table 2.2). A l l three are recognized in Level 410 (4,494 m.a.s.l), and Carmencita has also been recognized on surface (2 to 6 m wide x 30 55 m long). In the intrusive, E-trending, dipping S, narrow polymetallic veins are also present. Detailed description of orebodies and veins at Cachi Cachi is presented in Table 2.2 below. Mineralogical zoning at the Yauricocha mining district is distinctive (Fig. 2.10). Orebodies replacing Jumasha limestone located close to the contact with the France Chert (thermally metamorphosed Celendin Formation) contain a nucleus of enargite. To the west, bornite-, chalcopyrite-, and enargite-rich orebodies predominate with Pb-Zn, Ag-, and Au-sulfide rich orebodies lying at the fringe. The broad scale zonation is observed on a small scale within individual orebodies. W E EXPLANATION — — Mineral zone boundaries 5sx3 F: galena-sphalerite-polybasite HSES quartz>trace reaigar/oropiment E: galena-sphalerite»chalcopyrite, pynte. hematite, siderite, calcite D: chalcopyrite, tenantite, sphalerite, galena, pyrite, quartz, fluonte. tennanite-chalcopyrite tennantite dominant locally replaced by enargite C: enargite, chalcopyrite, bornite, digenite, covelite, tennantite, chalcocite, tetrahedrite, idaite, late sphalerite B: enargite>tennantite>bismuth covelite, chalcocite, bornite. chalcopyrite A. enargite>covelite-bismuth, pyrite-quartz, zunyite LITHOLOGICAL UNITS Mlo-gd Granodiorite K-C Celendin Formation K-J Jumasha Formation F i g u r e 2 . 1 0 : S c h e m a t i c m i n e r a l o g i c a l z o n i n g o f t h e Y a u r i c o c h a c a r b o n a t e - h o s t e d m a s s i v e r e p l a c e m e n t o r e b o d i e s o f c e n t r a l P e r u b a s e d o n d e s c r i p t i o n o f t h e C e r r o D e P a s c o C o r p o r a t i o n r e p o r t ( 1 9 7 0 ) . Friable and massive pyrite is the most common sulfide in the Yauricocha mining district. Thompson (1960) has distinguished up to 5 different types based on the different stages of formation. An upward increase of pyrite is associated with increase of Pb-Zn and decrease of Cu-Au. The main Cu-sulfide is enargite, which is present in irregular masses associated with quartz and pyrite. Chalcopyrite is less abundant, and replaces brecciated limestone, cements quartz and friable pyrite or fills small cavities. Chalcopyrite is associated with native gold and electrum. Bornite is associated with chalcopyrite and in lesser amount with enargite. Covellite and idaite are present as inclusions in bornite. Small grains of tetrahedrite and tennantite are 3 1 abundant in the edges of enargite masses. Galena is disseminated in pyrite and skarn bodies where it is always associated with chalcopyrite and sphalerite. Sphalerite is associated with pyrite, galena and clays, generally on the edges of orebodies. Geocronite [Pbi4(Sb, As)6S23] is associated with galena, sphalerite, tetrahedrite and quartz, fi l l ing fractures and sphalerite cleavages. The most abundant gangue mineral is quartz. Calcite veinlets are associated with quartz and sphalerite. Fluorite is contemporaneous with galena and sphalerite. Specularite and siderite are present in limestone and veins at the Exito and Ipillo mines. Mineralogical paragenetic relationships in the Yauricocha mining district, after Thompson (1960) and Rodriguez (2004), are shown in Figure 2.11. MINERALS FIRST PHASE SECOND PHASE THIRD PHASE PYRITE QUARTZ GAUTE """ SERICITE • • • • • • MARCASITE mmm HEMATITE mmM mmm CALCITE mm SIDERITE mm BARITE SPHALERITE GALENA LUZONITE mm ENARGITE POLIBASITE TETRAHEDRITE mm TENNANTITE GOLD BISMUTITE — FLUORITE CHALCOPYRITE mmmM BORNITE ORANGE BORNITE mmm COVELITE mm* mmmm CHALCOCITE DIGENITE mmmmt mmm IDAITE ————— REALGAR mmm OROPIMENT _ PrrviraeiuA J U H I IIJIIJ JLI I I I I I il nf minora l iyat inn w - ~ i i c i^vo rri i I ^ J I O ^ V I i rai IL \M I I III id Giucauvi i ~^m m m^m m m^m^m Figure 2.11: Mineralogical paragenetic relationships in the Yauricocha raining district of central Peru after Thompson (1960) and Rodriguez (2004). The oxidation of orebodies at Yauricocha is partial to complete, and covers from the surface (around 4645 m.a.s.l.) to the level 720 (4182 m.a.s.l.) reaching at least 460 m. Supergene covellite, chalcosite, and digenite coexist with the oxides minerals. Goethite, jarosite, hematite, anglesite, kaolinite, gypsum, quartz, gold and silver are present in the residual oxidation zone, whereas cuprite, native cooper, malachite, azurite, brochantite, jarosite, cerusite, chrysocolla, and manganese oxide are mobile. 32 Table 2.1: Characteristics of sulfide orebodies and veins at Mina Central, Yauricocha Mine, central Peru. Surface elevation is 4,645 m.a.s.l. at Pique Central (Fig. 2.8)'. Main orebodies and veins in Figure 2.7 and Plate 1. Data summarized from Rodriguez (2002, 2004). OREBODY LOCATION HOST ROCK F O R M ORIENTATION SIZE Depth SULFIDE & GANGUE MINERALS OBSERVATIONS Amoeba S of Mina Central Jumasha limestone-Yauricocha intrusive contact irregular & rounded lens in limestone; veins in intrusive fusiform lenses & breccias Lens oriented 120785°NE; E-W trending fractures & veins from surface to level 520: plunge to the S. Below level 575: plunge to theN 10-16m wide surface to level 410 galena, sphalerite & pyrite, minor enargite, chalcopyrite & covellite friable & massive pyrite, galena, sphalerite, enargite & chalcopyrite. At central zone: pyrite & quartz core persistent from level 520 to below level 720. Galena & sphalerite at breccias Antacaca S of Catas 1 Jumasha orebody \ limestone-i Celendin shales & j Jumasha | limestone-I intrusive contacts surface to level 820 Antacaca & Catas form a large, almost continuous, ore body, only separated by limestone lenses. Mineralized breccia occurs towards the W edge of orebodies Ramal W of Antacaca j orebody j i fusiform lenses plunge from S to N 45m between levels 520 & 575, gradually diminishing with depth level 520 to level 670 friable pyrite, chalcopyrite, ; Part of Antacaca enargite, minor galena & j orebody; connected to sphalerite 1 Sasacaca orebody i through a zone of strong i oxidation Butz Butz W branch N of Pozo Rico orebody Jumasha limestone & Jumasha limestone-Central stock contact connected massive orebodies & brecciated structures intercepted by narrow EW trending veins dipping N surface to level 620 galena, sphalerite & massive/friable pyrite at EW trending veins E-W trending normal faulting also control mineralization friable pyrite, enargite, chalcopyrite, galena & sphalerite at level 520: well-defined orebody forming vein-like branches towards surface; up to level 620: partially oxidized narrow structure Butz Central branch level 465 to level 575 massive orebody: argentiferous galena, sphalerite, friable pyrite & chalcopyrite in quartz & fluorite gangue. Breccia: galena, sphalerite & pyrite. Mineralization decreases with depth massive orebody surrounded by mineralized breccia Butz E branch level 520 to level 620 friable pyrite, galena, sphalerite, enargite & chalcopyrite residual limonites at partially oxidized E border Table 2.1 (cont.): Characteristics of sulfide orebodies and veins at Mina Central, Yauricocha Mine, central Peru. Data summarized from Rodriguez (2002,2004). OREBODY Catas Principal Contacto 'Occidental Contacto Oriental Erika LOCATION SE of Cuye orebody NW of Catas orebody HOST ROCK Jumasha limestone-Celendin shales & Jumasha limestone-main intrusive contacts, following bedding. Limestone strongly brecciated & fractured along NW-SE & E-W trending systems FORM fusiform lenses ORIENTATION NW-SE pipe-like breccia LTumasha limestone-jfusiform lenses in Pique.Central stock limestone & parallel !SW contact veins in intrusive W of Catas orebody iveins parallel to 100°-110°/80°NE SIZE maximum width at level 520 Depth surface to level 720 Jumasha limestone proximal to Pique j Central stock fusiform lenses tendency to Levels 410, narrow toward 465, 520, surface. 575,620, I _ _ • _ 670 & 720 I greater extension \ level 360 to in level 520; width diminished from levels 575 to 670 level 720 elongated brecciated structure with recrystallized [limestone fragments parallel to bedding level 410 to level 520 SULFIDE & GANGUE MINERALS friable/massive pyrite, sphalerite, galena, minor chalcopyrite & bornite. Massive/brecciated pyrite with enargite at the core; loose masses of friable pyrite, galena, sphalerite & minor chalcopyrite, in limestone gangue, form an irregular cover around the core. Cu-Au rich orebody persists in depth with chalcopyrite, pyrite, hematite & magnetite; transported oxides: limonites, cuprite & native cooper. In the E border, oxidation very sallow. In the N edge, oxidation deepens even bellow level 410 abundant sphalerite, argentiferous galena, pyrite & sparks of chalcopyrite sphalerite & argentiferous galena in pyrite, fluorite & quartz gangue OBSERVATIONS largest orebody at Yauricocha. Limestone lenses & barren pyrite very common parallel to main orebody orientation. At E edge, mineralization limited by Celendin shales; at W border, intersected with Contacto Oriental orebody & at S margin, connected with Antacaca orebody apparently extension of Catas orebody, but different mineralogy Richest Ag-bearing 'orebody two types: (1) massive with enargite, chalcopyrite, pyrite, sphalerite & galena; (2) brecciated with limestone fragments & matrix with sphalerite, galena & pyrite •matrix of sphalerite, galena, argentiferous galena, pyrite & minor fluorite linked with Pozo Rico orebody in level 465, Butz orebody in levels 520 & 575 & Catas orebody in levels 465 & I 520 branch of Contacto Oriental orebody. To the ;N: both became one lorebody below level 520. To the S: width decrease Table 2.1 (cont.): Characteristics of sulfide orebodies and veins at Mina Central, Yauricocha Mine, central Peru. Data summarized from Rodriguez (2002,2004). OREBODY Contacto Sur Medio LOCATION NW of Sur Medio intrusive HOST ROCK Jumasha limestone-Sur Medio intrusive contact FORM calcareous breccia ORIENTATION E-W/80°N SIZE 100m long x 4m wide Depth surface to level 720 SULFIDE & GANGUE MINERALS sphalerite, galena, argentiferous galena & geocronite. Locally dissemination of red/ruby silver (proustite & pyrargyrite), native Ag, tetrahedrite in pyrite, calcite, rhodocrosite, realgar & orpiment gangue; garnet, sericite & sporadic limonites close to the contact OBSERVATIONS Cuye N edge of mineralized zone of Yauricocha mine Jumasha limestone located between Mascota stock & Celendin shales tubular & irregular orebody, locally winding narrow brecciated zones above level 465 E-W, dip varies from S to N largest length at level 575 decreases towards surface 1 surface to | level 720 Cu-Pb & Zn in the upper part grading to Cu in depth. Slight supergene enrichment up to level 360. Mineralization cover by banded residual silica rich in Au & Ag. Pyrite-quartz & pyrite with enargite & tetrahedrite at the core with peripheral galena, chalcopyrite, sphalerite & pyrite. Chalcopyrite, hematite, magnetite & gold increase below level 720 banded mineralization along original bedding & E-W trending fractures. Winding contact with limestone above level 465. evidence of more mineralization below level 720 Cuye Norte N of Cuye orebody Jumasha limestone-Mascota intrusive E contact lenses I levels 410, 1 575 & 620 argentiferous galena, galena, . sphalerite in pyrite, quartz, calcite & fluorite gangue. E-W trending galena & sphalerite veins in intrusive; oxidized zones close to intrusive: limonites, hematite, pyrolusite, jarosite, cerussite & gypsum closely related to Mascota intrusion. Apparently northern continuation of the Cuye orebody, but different mineralogy. Gallito N edge of Yauricocha mine Jumasha limestone close to Celendin shales contact calcareous breccia with fine-grained dark gray limestone fragments NW border: E-W trending structures. Jumasha-Celendin formations contact: 130765°-70°NE at level 300: 60m long x 4m wide ! level 245 to 1 level 575 matrix of fine-grained black clay with fine pyrite, sphalerite, galena & calcite. Cu-rich S border with bornite, tetrahedrite & enargite core with peripheral Pb & Zn-rich sulfides apparent increase in sulfide minerals and width wkh depth Table 2.1 (cont.): Characteristics of sulfide orebodies and veins at Mina Central, Yauricocha Mine, central Peru. Data summarized from Rodriguez (2002, 2004). OREBODY LOCATION HOST ROCK FORM ORIENTATIO N SIZE Depth \ SULFIDE & GANGUE i MINERALS OBSERVATIONS Jaqueline W of Catas orebody Jumasha limestone calcareous oval breccia with recrystallized limestone fragments 120° 28m long x 12m wide level 410 to level 465 sphalerite, argentiferous galena & pyrite contains barren central zone Juliana (V eta) NW of Cuye Norte intrusive Jumasha limestone in contact with Celendin shales in zone of calcareous breccia with marbleized limestone fragments in a calcareous crushed matrix with organic material content fusiform brecciated lenses & E-W trending veinlets at level 360 E-W trending structures dipping 85°N structure: 0.20 to 5m wide surface to level 620 fine pyrite, sphalerite, argentiferous galena, galena, marcasite & anomalous gold values in hyaline quartz, green and violet fluorite & Ca & Mn carbonates gangue Juliana I S of Juliana orebody Jumasha limestone. Calcareous breccia: close to N border of Cuye intrusion levels 245 & 360: slightly oval irregular calcareous breccia. Level 620: elongated structure calcareous breccia: dipping NE elongated structure: 5-7m wide level 245 to level 620 calcareous breccia: similar to Juliana orebody. Elongated structure: massive galena, sphalerite & pyrite Juliana II NW of Juliana orebody Jumasha limestone-Celendin shales contact calcareous breccia with recrystallized limestone fragments to the S: 130770°NE. To the N: E-W trending tensional jointing level 300: 110m long x variable width. SE of contact: 2.50m wide. W of levels 245, 300, 360, 410, 520, 575 & 620 similar to Juliana orebody. Levels 360,410 & 520: matrix of chalcopyrite, enargite, pyrite, sphalerite & argentiferous galena some sections connected with Juliana orebody Katty Jumasha limestone-Pique Central intrusive S contact contact breccia orebody with limestone & intrusive fragments, structures structures: 100°- ! 110775°N levels 465, 520, 575, 620, 670 &720 sphalerite & argentiferous galena in gangue of pyrite, fluorite & quartz massive sulfides, disseminations & breccias spread into endoskarn Table 2.1 (cont.): Characteristics of sulfide orebodies and veins at Mina Central, Yauricocha Mine, central Peru. Data summarized from Rodriguez (2002, 2004). OREBODY | LOCATION Marita Masco ta N of Mascota intrusive WofCuye orebody HOST ROCK Jumasha limestone-Celendin shales contact FORM Pozo Rico I N of Pique i Central stock Jumasha limestone above level 465 & Jumasha limestone-Mascota stock W contact bellow level 465 Jumasha limestone elongated structure that above level 360 is divided into three branches ORIENTATI ON 100°/80°-85°NW, plunge 60°S E-W, dipping steeply N. W branch dips S at level 230 funnel-shaped orebody. Branches above level 360 SIZE 90m long x 0.20-3.0m wide 135m long in level 360 Depth levels 465, 520, 575, 620 & 720 surface to level 670 surface to level 575 SULFIDE & GANGUE MINERALS argentiferous galena, sphalerite & pyrite small orebodies with high grade Pb-Zn throughout limestone-intrusive contact; Ag-Au & silica rich residual oxides from level 360 to level 670. Barren oxides above level 230. Transported oxides at three branches: malachite, cuprite, tenorite, Hmonites, argentojarosite, plumbojarosite & native cooper sulfides located at the NW zone, extended from level 360 to level 575 & separated from oxidized zone by barren Hmonites zone: Au-rich chalcopyrite & enargite; residual & transported oxides divided in two zones of Cu separated by barren Hmonites above level 410. Transported oxides: azurite, malachite, cuprite & tenorite plus bornite OBSERVATIONS main oxidized orebodies at Yauricocha mainly composed of oxides correlated with barren oxides of level 720. Primary sulfides zone joined with Catas orebody at level 410 Sasacaca W of Antacaca orebody Violeta Jumasha limestone surrounding Sur intrusive calcareous breccia NW-SE level 465 to level 670 elongated & brecciated small orebodies/structures with recrystallized limestone fragments 150° level 410 to level 720 friable/massive pyrite with enargite & chalcopyrite core and peripheral loose masses of friable pyrite, galena & sphalerite in calcareous breccia matrix of: sphalerite, argentiferous galena, pyrite & minor chalcopyrite connected to Antacaca orebody between levels 520 & 575 through oxidized zone; 10-15m wide skarn zone between orebody & intrusive Connected to Antacaca orebody on southern margin Table 2.1 (cont): Characteristics of sulfide orebodies and veins at Mina Central, Yauricocha Mine, central Peru. Data summarized from Rodriguez (2002,2004). OREBODY Violeta 329 Poderosa Felicidad El Norte Veta A LOCATION 20m SE of Central intrusive footwall of Veta A NW of Catas orebody HOST ROCK Jumasha limestone Jumasha limestone FORM Celendin formation Jumasha limestone massive pipe-like orebody surrounded by calcareous breccia with recrystallized limestone fragments lenticular sandy massive orebody | E-W lenticular narrow ! structures cutting j others of NE-SW I trending 'several irregular lenticular lenses 'controlled by 2 shear •zones caused by 'regional folding lenticular lenses sigmoid-like structure with local branches, connected to Catas (N edge) & Cuye (S edge) orebodies ORIENTATI ON E-W/81°N 155762°SW-NE-vertical. Very noticeable horizontal & vertical echelon structures. Some E-W trending narrow & superficial lenticular structures seem to cut NE-SW trending lenses 110773°-78°S SIZE up to lm in diameter Depth level 575 to level 620 level 620 up to 300m long x 2.5m wide above level 360 up to 2.5m wide 30m long x 3m wide. Size variable & apparently decrease with depth. surface to level 290 70m long x 0.20-1:50m wide levels 520, 575,620 & 670 SULFIDE & GANGUE MINERALS massive orebody: abundant sphalerite, argentiferous galena, pyrite & rhodocrosite. Argillic & calcareous breccia brittle matrix: pyrite, sphalerite & argentiferous galena sandy pyrite & chalcopyrite Cu-rich connected to other orebodies by pyrite veinlets. Cu-Pb-Zn rich EW trending lenticular structures sandy pyrite, enargite, quartz small scale horizontal & vertical zoning: Cu-rich core with peripheral Pb-Zn at the edges. Above level 240: massive pyrite with chalcopyrite, secondary bornite & covellite. Below level 240 massive pyrite with chalcopyrite spots, enargite, hematite, minor bomite & covellite filling up small fractures. friable/massive pyrite loose masses, galena & sphalerite in limestone gangue OBSERVATIONS connected at depth with southern part of; Central intrusive located in reverse faults cutting shales beds of along the Celendin & Jumasha formation contact cluster of veins in the NW extreme of Yauricocha mine; represents oldest veins developed in mine Table 2.1 (cont.): Characteristics of sulfide orebodies and veins at Mina Central, Yauricocha Mine, central Peru. Data summarized from Rodriguez (2002,2004), OREBODY 1 LOCATION HOST ROCK FORM ORIENTATION SIZE ! Depth 1 SULFIDE & GANGUE i MINERALS | OBSERVATIONS VetaC ;NW of Catas Orebody & S of Veta A Jumasha limestone structure apparently connecting Catas (middle zone) & Butz Central orebodies • 100775°S-subvertical 120m long x i levels 465, | sulfide zone: towards Catas & 0.20-1.50m j 520 & 575 j Butz orebodies; friable pyrite wide | loose masses, galena, sphalerite & minor chalcopyrite in ! limestone, clay & quartz gangue; | residual oxide zone: central | zone; goethite, hematite, quartz j & kaolinite VetaD NE of Contacto Oriental orebody structure apparently connecting Contacto Oriental (N edge) & Catas orebodies. Locally occurs in breccia 105780°S 130m long x j levels 520, 1 friable/massive pyrite loose 0.20-2.50m [ 575 & 620 j masses, galena, sphalerite & wide . | minor chalcopyrite in limestone | gangue VetaF NW of Catas orebody vein (second system) 30m long x 3m \ levels 465 ; friable/massive pyrite masses, wide | & 520 j galena, sphalerite & minor j- chalcopyrite in limestone gangue ; second vein system ] developed VetaG SW of Yauricocha mine Jumasha limestone-intrusive contact vein at fault breccia displacing Sasacaca orebody 090770°N (third system) 1.50m wide j level 520 j pyrite, sphalerite & minor j chalcopyrite ] third vein system I developed Veta Cuye S of Cuye orebody Jumasha limestone lenticular-like elongated brecciated structure brecciated vein 075°-100785°N-vertical 080778o-80oS ' 28m long (level j levels 360 j brecciated/brittle material 410) 40m long 1 & 410 I composed of pyrite, sphalerite & (level 360) x 1 argentiferous galena. Zoned 2.5-6m wide . • j ] chalcopyrite at central part Veta Cuye Sur 5 of Cuye orebody & N of Catas orebody 6 Veta A 30m long x ! level 620 toj pyrite, enargite, sphalerite, 0.20-3.0m wide i level 670 j galena Veta Mascota NW of Mascota orebody 115780°SW 60m long x j levels 360, j sphalerite, galena, pyrite & 6.80-4.50m 410, 465 & j rhodOcrosite in limestone gangue wide • . : 520 Table 2.2: Characteristics of sulfide orebodies and veins at Cachi Cachi, Yauricocha Mine, central Peru, surface elevation is 4,650 m.a.s.l. at Cachi Cachi open pit (Plate 1). Data summarized from Rodriguez (2002, 2004). OREBODY j LOCATION HOST ROCK I FORM ORIENTATION SIZE DEPTH SULFIDE & GANGUE MINERALS Privatizadora SW of Caprichosa Jumasha limestone- j mixed breccia with intrusive i limestone & I intrusive fragments 150765°SW, plunge 52° 18m long x 8m wide surface to level 410 galena, sphalerite & friable pyrite Caprichosa SW of Carmencita 1 calcareous breccia ! with abundant sandy j pyrite 130°/60°NE, plunge 57°NE 25m long x 2-5m wide level 410 galena, sphalerite & massive/sandy pyrite. 20m long calcareous footwall with abundant sandy pyrite Rossy S of Caprichosa intersects with | calcareous breccia Caprichosa orebody j at 4572m.a.s.l. • j NW-SE/80°S, plunge 55°-60°NE sphalerite, galena, pyrite & minor quartz Veta Carmencita S of Veta Dianita Jumasha limestone- 1 calcareous breccia intrusive 100°/75°S 55m long x 2-6m wide surface to level 410 sphalerite, galena, sandy pyrite & chalcopyrite Veta Dianita S of Veta Virginia skarn-Jumasha j vein limestone contact 105°/85°S, plunge 60°NE level 410 sphalerite, galena, pyrite & chalcopyrite Veta Virginia I N of Cachi Cachi mine Jumasha limestone- j vein intrusive NW-SE/S 50m long level 410 2.6.2. Purisima Conception Purisima Conception is located approximately 550 m east of the old open pit in the M i n a Central area (Figs. 2.6 and 2.7). It lies in the outer zone of thermal recrystallization of the host Cretaceous Jumasha Formation and Cu-Zn-Pb-Ag mineralization of M i n a Central, and within the hinge of the tight southeastwardly plunging Purisima Conception anticline. Weak gold mineralization is present in very thin quartz-pyrite veinlets, in general <l-3 mm wide, that f i l l planar brittle fractures in adularia and sericite-bearing metasomatized l imy siltstone, pyrite-rich jasperoid, and in thin layers of pyrite-rich argillic rock containing carbonaceous material in recrystallized limestone (Noble et al; 2000). The presence of jasperoid with anomalous A u , A s , Sb, Hg , T l and Te, and very low A g , Cu , Pb and B i concentrations led Alvarez and Noble (1988) to compare Purisima Conception to Carlin-style gold deposits such as those found in the Great Basin of the U S A (Alvarez et al., 1989 and 1990; Alvarez and Noble, 1990). This prospect was mapped during this study, but no detailed analysis was undertaken. 2.6.3. Base Metal Veins Superficial and underground exploration and detailed work in areas o f M i n a Central, Cachi Cachi, Victoria, Exito and Ipillo recognized three main systems o f base metal veins. The first one trends N75°W and dips 60°-80°SW or N E . A second one trends N70°E dipping 65°-80°NW, and the third one trends E W and is sub-vertical. The horizontal and vertical dimensions of the veins are relatively short, whereas the width is very variable, from 0.50 m to 2.50 m in the Yauricocha area, and from 6 to 8 m in Ipillo (Rodriguez, 2000). Pyrite-sphalerite-galena-quartz-chalcopyrite veins are located northwest of the mines in the district within the Jumasha limestone. Other numerous narrow pyrite-quartz-enargite-galena-sphalerite-covellite-fluorite-hematite-electrum veins cut the main intrusion (Figs. 2.6 and 2.7). 2.6.4. L o w Grade Porphyry Copper and Gold Anomalous Zones Low-grade porphyry-like disseminated copper and gold zones, located northeast o f M i n a Central, lie within the Yauricocha-Exito Stock (Figs. 2.6 and 2.7). The host equigranular, fine-to coarse-grained granodiorite is cut by up to 4 cm wide milky, locally drusy, quartz veins mainly along easterly and northerly trending vein systems. Locally, the vein sets form a very dense network of parallel veinlets. Zones of abundant pyrite veinlets and dissemination, goethite boxwork after pyrite, with moderate argillic, and very local and weak potassium alterations occur. 41 2.6.5. M i n a E x i t o The Exito mine is located at about 5.45 km south of M i n a Central, occurs at the contact o f Jumasha limestone with the granodioritic Yauricocha-Exito Stock, and lies at about 4600 m.a.s.l., the same elevation as the sulfide orebodies within M i n a Central and Cachi Cachi. Min ing operations are temporarily suspended (2005). Mineralized breccias and veins at Exito represent two different phases of mineralization. Breccia orebodies consist of sub-angular to sub-rounded fragments of sulfides, intrusive rock, and skarn in a sandy matrix. Exito and Bonanza are the most sulfide-enriched breccias orebodies. Minerals consist of galena, sphalerite, chalcopyrite, and coarse pyrite. Gangue consists of quartz, fluorite, calcite, serpentine, garnet, and secondary specularite (Rodriguez, 2002). 42 References Alvarez, A . A . , and Noble, D . C , 1988, Sedimentary rock-hosted disseminated precious -metal mineralization at Purisima Conception, Yauricocha District, central Peru: Economic Geology, v. 83, no. 7, p. 1368-1378. Alvarez, A . A . , Bonell i , A . , x a n d Noble, D . C , 1989, Sedimentary rock-hosted disseminated precious-metal deposits of the Yauricocha district, central Peru [abs.]: 28 t h International Geological Congress, Washington D . C , p. 37-38. Alvarez, A . A . , Noble, D . C , 1990, Mineralization de metales preciosos diseminados alojados en yacimientos de Purisima Conception, distrito de Yauricocha, centro del Peru: Centro de estudios y promotion de la tierra, L i m a ( C E P E C T ) , E l oro, L ima, p. 106-119. Benavides-Caceres, V . , 1999, Orogenic evolution of the Peruvian Andes: The Andean cycle: Society of Economic Geologists, Special Publication 7, p. 61-107. Bissig, T., Ul l r ich , T .D. , Tosdal, R . M . , and Ebert, S., 2004, The late Eocene to late Miocene magmatic arc of central Peru: New 4 0 A r / 3 9 A r age constraints from Yauricocha to Cerro de Pasco: Sociedad Geologica del Peru, X I I Congreso Peruano de Geologia, L ima. Centromin Peru S.A., 1980, Yauricocha, in Samame Boggio, M , ed.: E l Peru Minero, L ima, Editorial Peru, tomo 4, v. 2, p. 838-854. Cerro de Pasco Corporation, 1970, Geologia de los yacimientos minerales operados por la Cerro de Pasco Corporation, Geologia de las minas: Casapalca, Cobriza, Morococha, San Cristobal, Yauricocha, Geologia del distrito minero de Cerro de Pasco: Cerro de Pasco Corporation, L a Oroya, 155 p. Lavado, M . , 2002, E l metalotecto Jumasha y su analisis estratigrafico, Minas representativas: Hualgayoc, Raura, Uchucchacua, Yauricocha: Sociedad Geologica del Peru, X I Congreso Peruano de Geologia, L ima , p. 32. Megard, F. , 1968, Geologia del cuadrangulo de Huancayo, Boletin: Servicio de Geologia y Mineria, L ima, 18, 123 p. Megard, F. , 1984, The Andean orogeny period and its major structures in central and northern Peru: Journal of the Geological Society, London, v. 141, p. 893-900. Megard, F. , Caldas, J., Paredes, J. and De L a Cruz, N . 1996, Geologia de los cuadrangulos de Tarma (23-1), L a Oroya (24-1) y Yauyos (25-1): Instituto Geologico Minero y Metalurgico del Peru, Carta Geologica Nacional, series A , v. 69: 279 p. Noble, D . C , and M c K e e , E . H . , 1999, The Miocene metallogenic belt of central and northern Peru, in Skinner, B . J . ed., Geology and ore deposits of the central Andes: Society o f Economic Geologist, Special Publication N o 7, p. 155-193. Noble, D . , Campbell, A . , Ressel, M . , and Kamali , C , 2000, Gold-rich quartz-pyrite veinlets and jasperoid with "Carlin-type" geochemical characteristic at Purisima Conception, 43 Yauricocha district, central Peru: Sociedad Geologica del Peru, X Congreso Peruano de Geologia, L ima, Trabajos tecnicos, tomo 2, p. 489-496. Petersen, U . , 1965, Regional geology and major ore deposits of central Peru: Economic Geology, v. 60, p. 407-416. Rado, E . G . , 1977, Potential aurifero de la mina Yauricocha: Instituto de Ingenieros de Minas del Peni, X X I I I Convention de ingenieros de minas del Peru, Arequipa, Trabajos tecnicos, tomo 1, p. 15-22. Rado, E . G . , 1997, Controles de mineralization en el distrito minero de Yauricocha: Sociedad Geologica del Peni, I X Congreso Peruano de Geologia, L ima, Resumenes extendidos, capitulo I: Metalogenia y yacimientos de minerales, p. 161-165. Rodriguez, G . , 2002, Interin Annual Report: Sociedad Minera Corona S.A. , Unpublished internal report. Rodriguez, G . , 2004, Interin Annual Report: Sociedad Minera Corona S.A. , Unpublished internal report. Sebrier, M . , Lavenu, A . , Fornari, M . , and Soulas, J. , 1988, Tectonics and uplift in the central Andes (Peru, Bol iv ia , and northern Chile), from Eocene to present: Geodynamique, v. 3, p. 139-161. Sebrier, M . , and Soler, P., 1991, Tectonics and magmatism in the Peruvian Andes from late Oligocene time to Present: Geological Society of America, Special Paper 265, p. 259-278. Sillitoe, R . H . , Perello, J, 2005, Andean Copper Province: Tectonomagmatic settings, deposit types, metallogeny, exploration, and discovery, in Hedenquist, J .W., Thompson, J .F .H. , Goldfarb, R.J . , and Richards, J.P., eds.: Economic Geology 100 t h Anniversary Volume, p. 845-890. Thompson, D.S.R. 1960. The Yauricocha sulfide deposits, central Peru: London, England, Imperial College, University o f London, unpublished Ph.D. dissertation, 154 p. Tumialan De L a Cruz, P .H . , 2002. Yacimientos de reemplazamiento y rellenp en calizas en el Peni: Sociedad Geologica del Peni, X I Congreso Peruano de Geologia, L ima , Geologia de los yacimientos minerales, tomo 1, p. 597-606. Valdivia , V . A . , 1996, Geology and metallogeny of the Yauricocha mine (Cu-Pb-Zn-Ag), central Peru, M . S c . thesis: Instituto de Geociencias, Universidade de Brasilia, Brasil . Web link: http://www.unb.br/ig/posg/mest/mestl06.htm Wilson, J., 1963, Cretaceous stratigraphy of central Andes of Peru: Bulletin o f the American Association of Petroleum Geologists, v. 47, p. 1-34. 44 CHAPTER THREE Distal Visible and Cryptic Alteration Characteristics around the Carbonate-hosted Polymetallic Replacement and Skarn Systems at Mina Central and Cachi Cachi, Yauricocha 3.1. Introduction Alteration and mineralization of carbonate rocks surrounding carbonate-hosted replacement and skarn deposits are zoned away from the magmatic sources along stratigraphic and structurally controlled fluid flow pathways (Morris, 1968; Beaty et al., 1990; Meinert et al., 1997; Megaw, 1998 and 2001; Megaw et al., 1988 and 1996; Friehauf and Pareja, 1998; Bendezii et al., 2003; Titley, 1993 and 1996). Dip of host carbonate strata, composition of the host carbonate rock, and the geometry of igneous rocks also exert an essential control in the distribution of the distal alteration and the sulfide orebodies (Meinert et al., 1997; Megaw, 1998). Dolomitization, calcite precipitation, and silicification are common and ubiquitous. This alteration forms exterior to the deposit in response to thermally driven circulation of a combination of meteoric water, non-metalliferous connate brines derived from various sources, and magmatic-derived but metal-depleted hydrothermal fluids. In carbonate rocks that contain significant silicate minerals, an early phase of silification or jasperoid formation may predate sulfide deposition. On a large scale as the low temperature hydrothermal fluids leave the sulfide-deposition environment, carbonate rocks are varyingly recrystallized to marble and dolomite, decarbonated or sanded, silicified and converted to jasperoid or hornfels depending upon the composition of the sedimentary strata as well as the location within the alteration halo. Dolomite and jasperoid alteration are commonly found in the shallow level systems (Cerro de Pasco, Izcaycruz, Colquijirca). Most CRD-skarn deposits formed at deeper levels mainly lie within the thermal aureole of the nearby igneous rock (Antamina, Yauricocha, Mi lpo) . The size of the alteration halo depends in part on the size of the mineralized zone and the size of the associated intrusions. Calcite, quartz, calcsilicate minerals with pyrite and base-metal sulfides, and argentiferous manganese oxide minerals are common in veinlet networks or swarm of thin wavy-planar veinlets, with ankeritic or dolomitic carbonate minerals forming veins closer to the sulfide bodies. These veinlets represent fluid escape and fluid flow pathways for the fluids responsible for the mineralization. In carbonate-poor rocks, veins with argillized or silicified margins define the distal fringes of the magmatic-hydrothermal systems, and some can carry 45 gold resources (e.g. Theodore et a l . , 1998; Alvarez and Noble, 1988). Pervasive alteration effects may extend as little as 1 meter away from a massive sulfide bodies in primary dolomitic sedimentary rocks, but may extend tens to hundreds of meters away in calcitic limestone, with localized alteration extending kilometers along highly channelized fluid pathways (Beaty et a l . , 1990; Friehauf and Pareja, 1998). This chapter presents a description of the visible alteration and geochemical halos that can be mapped at the current outcrop outside the carbonate replacement orebodies at M i n a Central (Figs 3.1 and 3.2) and the skarn orebody at Cachi Cachi (Figs. 3.1 and 3.6). Both provide excellent sites to document the horizontal and vertical extent of fluid flow escape features. The visible alteration halo is viewed proximal to distal, that is from the border of the main intrusive toward the mineralized zones and altered or unaltered host rocks. Horizontal distances are referred to the contact of the mineralized zones and host rocks with the main intrusive on surface. Vertical distances correspond to the lateral upright extension of the alteration over the level 820 (4,082.892 m.a.s.l.), currently the deepest zone at Yauricocha with known mineralization (Figs. 2.6 and 2.8). District-scale (Fig. 3.1 and Plate 1) and detailed local-scale (Figs. 3.2 and 3.6; Plates 2 and 3) surface mapping and sampling of the thermal halo were conducted in the west side of the district, covering mineralized and altered zones from south of M i n a Central to the northern edge of Cachi Cachi. Mapping largely focused on the distribution and character of the distinctive distal alteration features genetically related to the mineralization, including the characterization of the alteration zones in the host rocks and the different types of distal vein meshes occurring around the mineralized zones. Limestone and marble bleaching, dolomitization, silicification, calcite veining (calcite precipitation) and other carbonates were fully identified, including their horizontal and vertical distributions. Furthermore, stratigraphic versus structural (fractures or diaclase) control of bleaching was established. Mapping also defined the cross-cutting relationships between different distal veins systems to establish the paragenetic relationships. Samples were collected for petrographic studies, trace elements geochemistry, oxygen and carbon stable isotope studies to trace the hydrothermal solutions. P I M A and X R D optical mineralogy techniques plus the use of a petrographic microscope were applied at the University of British Columbia to determine mineral content in representative samples o f each type of lithology, vein and alteration assemblage found at both M i n a Central and Cachi Cachi. Some of the analyzed samples display a degree of contamination either from the host rock or from the vein (Appendices C I and C2). Integration 46 of field observations with the results obtained with the optical and petrographic techniques essential for complete evaluation (Thompson et al., 1999). Figure 3.1: Detailed geological and alteration map of the Yauricocha mining district, central Peru. A larger version of the figure is included in Plate 1 also in the appendices. Area of detailed geological and alteration map at Mina Central (Plate 2) and Cachi Cachi (Plate 3) are enclosed in black line insets. 47 Detailed descriptions of the experimental methods used in this study are included in Appendices B and C . A summary of mineral content of all samples and X-ray diffractrograms are given in Tables 3.1 and 3.2 and in Appendices C1-C3. 3.2. Host Rocks and Alteration at M i n a Central and Cachi Cachi Lithologic units and distal veins identified and mapped in M i n a Central and Cachi Cachi were classified based on individual lithological and vein types found in the field. The description of the units starts with the altered/replaced rocks, followed by the relatively unaltered rocks (limestone), and finishes with the distal veins (Tables 3.1 and 3.2; Appendices C1-C3). Refer to Figures 3.1, 3.2, and 3.6 as well as Plates 1-3 for location throughout following discussion. Marble forms the closest alteration halo to the carbonate-replacement and skarn orebodies in M i n a Central and Cachi Cachi and is particularly common to the west o f the main intrusion within the Cretaceous Jumasha Formation where is zoned from white bleached marble near the contact with the mineralized orebodies or main intrusive to gray marble distal to the contact. Colour variation within marble is related to the presence or absence of calcsilicate minerals, graphite, and sulfide minerals. Bleached marble occurs pervasively up to 150 m from main intrusive or known mineralization in Cachi Cachi, and along with gray marble as structure or bedding-controlled units at up to 430 m in M i n a Central and 500 m in Cachi Cachi over 640 m and 670 m, respectively, above known mineralization. Both pervasive bleached marble and structural or bedded bleached marble contain very locally irregular garnet, calcsilicate, and orange brown and white or gray carbonate veins and lenses. Bleached marble contains more than 90 vol % of coarse- to medium-grained calcite with K -feldspar (orthoclase, microcline), plagioclase (anorthite), phlogopite, calcsilicate (augite), graphite, muscovite, brushite (Tables 3.1 and 3.2; Appendices C1-C3), and dissemination and traces of pyrite. Irregular calcsilicates minerals (augite) veins and lenses impart a greenish tint to bleached marble. Sharp boundaries between bleached and gray marble correspond to changes in graphite abundance. Organic carbon is nearly lacking in bleached marble and disseminated in gray marble. Gray to bleached marble zonation is largely controlled by pre-existing fold and thrust geometry at M i n a Central and broadly parallel to sedimentary bedding at Cachi Cachi. Gray marble, occurring up to 550 m from main intrusive and extending up to 720 m over known mineralization, usually contains fewer calcsilicate (augite) and sulfide veins (sparse to absent) than bleached marble. It consists of medium-grained to fine-grained calcite with 48 plagioclase (albite), K-feldspar (orthoclase), phlogopite, muscovite and minor quartz and pyrite. Trace amounts of disseminated graphite impart a gray colour to these rocks (Tables 3.1 and 3.2; Appendices C1-C3). Layers of gray marble commonly contain bleached marble as cm-scale halos to sulfide veins and locally as lenses or pods. Brown marble is very locally interbedded with bleached and gray marble in the Cachi Cachi area. They consist of fine to medium-grained calcite with quartz, phlogopite, fluorapatite, and graphite with pyrite (Tables 3.1 and 3.2; Appendices C1-C3). In the north part of zone B at M i n a Central, up to 1.2 m wide Celendin Formation gray hornfels beds occur locally up to 250 m laterally from main intrusive; beds extend up to 730 m over known mineralization. They are interbedded with weakly silicified, fine-grained dark gray limestone and a thin bed of bleached marble (Fig. 3.2). Hornfels contains calcite, dolomite, quartz, plagioclase (albite), amphibole (ferro-actinolite), phlogopite, augite, talc, clinochlore, and abundant pyrite veinlets (Table 3.1). Limestone is the predominant rock type in the Cretaceous Jumasha Formation, and unaltered limestone is not present below 4675 m.a.s.l. in Cachi Cachi. Massive limestone is dark gray in colour and contains fine- to medium-grained calcite with traces and veinlets of pyrite, which also appears as parallel veins. Limestone occurs in thick layers exhibiting lapiaz texture developed by weathering. Particularly in zone C , limestone has a fossiliferous content supported in a micritic calcite groundmass showing also presence o f trace amounts of quartz, K-feldspar (orthoclase), phlogopite, hydrotalcite, and muscovite (Tables 3.1 and 3.2). Graphite is present in minor amounts lending the gray colouration to limestone. A l l known skarn bodies are formed within the thermal aureole. Exoskarn consists o f andradite-grossular (~100 x 150 m in map view irregular body). Endoskarn consist of small zones of up to 3 m wide containing epidote, zoisite, tremolite, wollastonite, phlogopite, garnet, diopside and chlorite. Because the focus of this thesis is the study of the distal alteration around the carbonate-hosted and skarn orebodies and not the orebodies themselves, no more detail on skarn w i l l be provided. A t Yauricocha, four types of veins, 1-4, are recognized in the distal alteration zones (Table 3.3). Types 1-4 are found distributed sequentially outward at Cachi Cachi, whereas only types 2-4 are present at M i n a Central. They are found up to 780 m and 790 m laterally from the intrusive contact and up to 765 m and 760 m over known mineralization at M i n a Central and Cachi Cachi, respectively. The, syn-mineralization millimetre- to centimetre-scale veins, uncommon in limestone, display systematic horizontal and vertical zonation. In general, they 49 comprise garnet (Type la), calcsilicates minerals (Type lc ) , wollastonite (Type lb) , orange brown carbonate minerals (Type 2a), M n oxides-quartz-pyrite (Type 3 c), and late-stage dark gray- (Type 4a), light gray- (Type 4b), arid white- (Type 4c) calcite. Minor M n oxides- (Type 2b) or M n oxides-rich (Type 3a) bearing orange brown carbonate minerals and M n oxides-orange brown carbonate (Type 3b) minerals flooding the bleached and gray marbles near the C R D s lodes are also present. Additionally, variable calcite, quartz, pyrite, goethite, jarosite, and M n oxides minerals are present in syn-mineralization vein types, in most cases near the sulfide orebodies (Table 3.3). Pre- to syntectonic white calcite (Type 4d) veinlets formed during regional deformation; therefore not related to mineralization or alteration, occur largely in zone C . Table 3.1: Host rock and distal vein types X R D mineralogy at Mina Central. | HOST ROCK & VEIN TYPES i XRD results j limestone i calcite*, quartz, K-feldspar (orthoclase), phlogopite,! ! hydrotalcite, muscovite, ±gypsum, ±kaolinite, \ ±graphite j bleached | marble | calcite*, K-feldspar | gray marble calcite*, K-feldspar, phlogopite, muscovite,, +graphite, ±kaolinite, +gypsum | hornfels calcite*, dolomite, quartz, plagioclase (albite), augite, phlogopite, talc, amphibole (ferro-! actinolite), clinochlore a | orange brown | calcite*, goethite, quartz, ±siderite (magnesian I carboriate±calcite±quartz±pyritej calsian) b! orange brown ! carbonate±calcite±quartz±pyrite| calcite*, goethite, birnessite, zussmanite, ±quartz : ±MnOx a: MnOx±orange brown . j calcite*, quartz*, goethite, birnessite, zussmanite, i carbonate±calcite±quartz±pyrite; lepidocrocite b I pervasive MnOx-orange brown i , . m x , . . . i g a r b o n a t e I calcite*, quartz, birnessite, pyrolusite c! MnOx±quartz±pyrite Major phase* Type 1 veins comprise grossular, andradite, wollastonite, diopside (ferroan), and augite (calcite + quartz ± sjogrenite ± plagioclase ± sphalerite ± chalcocite± johannsenite) representing the high temperature veins associated with the formation of the skarn orebodies. The garnet and calcsilicate are found closer to the sulfide orebody, whereas wollastonite is a distal manifestation of the skarn system (Tables 3.1 and 3.2). Types 2 and 3 veins consist of calcite, siderite, ankerite and goethite (quartz + andradite + K-feldspar ± augite ± rhodonite ± rhodocrosite ± birnessite ± zussmanite ± pyrolusite ± 50 lepidocrosite ± hydrocerussite ± celsian ± pyrite ± sphalerite) representing an intermediate stage both temporal and distal (Tables 3.1 and 3.2). Weathering o f carbonate ± sulfide veins yields orange brown Fe-oxide coatings that mix with variable amounts of M n oxide minerals. Type 4a-4c veins, late-stage calcite veins consist of white to light-dark gray planar, millimetre wide veinlets locally associated with trace amounts of sulfides mainly pyrite, that clearly crosscut mineralization at M i n a Central and Cachi Cachi. They consist o f calcite (quartz ± graphite ± diopside ± pyrite) (Tables 3.1 and 3.2). Pre- to syntectonic Type 4d veins predate mineralization. They occur as white ptygrriatic, millimetre- to centimetre- scale, discontinuous and locally fibrous calcite associated with low angle faults. Tab le 3.2: H o s t r ock and distal v e i n types X R D minera logy at C a c h i C a c h i . X R D results calcite*, quartz, K-feldspar (orthoclase), ikalsillite, ±pseudo-eucryptite I H O S T R O C K & V E I N T Y P E S jlimestone .bleached marble calcite*, phlogopite, K-feldspar (orthoclase, imicrocline), plagioclase (anorthite), augite, muscovite, brushite, graphite, ±talc, ±kalsillite, ±pseudo-eucryptite jgray marble calcite*, K-feldspar (orthoclase), augite, plagioclase (albite), graphite, muscovite, +talc, l ±graphite jbrown marble calcite*, quartz, phlogopite, fluorapatite, +graphite grossular wollastonite calcsilicate±calcite±pyrite±MnOx Icalcite*, quartz*, diopside*, sjoegrenite, iplagioclase (albite), sphalerite, chalcocite, johannsenite Oalcsilicate±orange brown !carbonate±calcite Icalcite*, quartz*, diopside* (ferroan), plagioclase (albite), sjoegrenite, augite orange brown ;carbonate±calcite±quartz±pyrite orange brown icarbonate±calcite±quartz±pyrite± MnOx calcite*, quartz, ankerite, augite calcite*, quartz, ankerite, hydrocerussite, siderite (magnesian calsian) MnOx±orange brown carbonate±calcite±quarte±pyrite a n d r a d i t e * (ferroan), ankerite*, K-feldspar* pervasive MnOx-orange brown (orthoclase), celsian, sphalerite, pyrite, rhodonite, carbonate rhodocrosite c iMnOx±quartz±pyrite a dark gray calcite±pyrite±MnOx calcite*, diopside (ferroan), quartz b light gray calcite±pyrite±MnOx calcite*, quartz, pyrite c white calcite±pyrite (late-stage)±MnOx calcite*, ±graphite 4d white calcite (syntectonic) M a j o r phase" 51 3.3. Zones o f Distal Alteration at M i n a Central A t M i n a Central, zones of bleached marble, gray marble and limestone, and vein swarm systems and distal veinlets in host rocks adjacent to orebodies are distributed laterally and sequentially outward from the intrusive contact (Fig. 3.3). Distal alteration on the surface above M i n a Central has been separated in three zones based on the intensity and distribution of veinlets rich in M n , orange-brown carbonate minerals versus gray and white carbonate minerals and the presence of bleached limestone or marble versus unbleached or gray limestone or marble (Tables 3.4-3.7). The zones are irregular in size and in horizontal and vertical distances with respect to the intrusive contact. The halo of bleached marble versus gray marble and the distribution of the different vein types are mainly controlled by three NW-striking faults and associated shear zones. The strike of the fault systems varies from 110° to 160° and is sub-vertical. Local ly E-(080°-095°), N -(170°-020°), and NE-(035°-070°) striking fracture systems and very locally the bedding (striking with 130°-140° with sub-vertical dips), exert minor control on the distribution o f the distal alteration (Table 3.11). Contacts between the alteration zones are diffuse and irregular, and pods of one zone can be found within the mapped limits of another zone. The zones of distal alteration and their dominant characteristics are: Zone A : Veinlets, nodules, and lenses rich in M n oxides predominate. Zone varies from 0 to 400 m away from the intrusive contact. Zone B : Veinlets and distal lenses rich in brown carbonates predominate. Zone varies from approximately 260 m up to 700 m away from the intrusive contact. Zone C: Veinlets rich in white or gray carbonates predominate. The zone varies approximately from 350 m to 800 m away from the intrusive contact. Bleaching of limestone or bleached marble versus gray marble, and the abundance and density of the networks of veinlets, locally rich in sulfide minerals, decreases with distance away from the intrusion (Figs. 3.2-3.5). 52 Figure 3.2: Geological and alteration map of the surface outcrops around Mina Central, Yauricocha mining district, central Peru. Included on the map are the sample location and sample numbers that correspond to analysis presented in the appendices. A larger version of the figure is included in Plate 3 in the appendices. Sample numbers can be seen more clearly on the plate. 3.3.1. Host Rocks in the Distal Alteration Zones at M i n a Central Bleaching of limestone or bleached marble versus gray marble reaches horizontal distances o f at least 430 m S W from the M i n a Central pit and from the contact o f mineralized zones and host rocks with the main intrusive. In a vertical profile, the bleached limestone extends to elevations of at least 4,725 m.a.s.l., approaching at least 640 m over known mineralization 53 (level 820) (Fig. 2.8). The contact between the bleached or gray marble with the unaltered limestone is irregular. Near the intrusive contact, bleaching is pervasive (Fig. 3.3). DISTAL ALTERATION SCHEMATIC FIGURE - JUMASHA FORMATION - MINA CENTRAL H O S T R O C K S ZONE A D I S T A N C E F R O M M A I N I N T R U S I V E IN M E T E R S ZONE B ZONE C 2001 250l 3001 3501 400| 4501 5001 5501 6001 6501 7001 7501 800 limestone A_ B C „ „ , ' F l N T G R A I N E D D k G V SSTCROP B ? L C B X ! M A L F I N E G R A I N E D D A R K G R E Y Q F I N E G R A I N E D D K G Y I S P O T S L 0 C M H R N B X L O C B X bleached marble A J3 C C O A R S E G R A I N E D C R Y S T A L L I N E M E D I U M G R A J N E D L O C LT B W ! • : " L O C A L L Y grey marble A J3 C C O A R S E T O M E D I U M G R A I N E D V E H X F I N E G R A I N E D L O C BID MRB • F I N E G R A I N E D P A T C H E S . ! ' V E I N T Y P E S V N L T S ; 2a or bw carb ± ca ± qz A B C M G M D D E N S E N T W K O F V N L T S , C G N T W K O F V N L T S M I N O R V N L T S : N T W K V F W L T T 3 6 . C A H A L O i p p p p R A N n m '• L O C F L O O D I N G W / C A J A R I R R E G B A N D E D , N O D S / V N L T S 2b or bw carb ± qz ± MnOx A 13 C M D D E N S E N T W K O F V N L T S V N L T S < N O D S L O C V N V N L T S V E R Y D E N S E N T W K OF V N L T S C A S T R I N G S / S P O T S C A S T R I N G S / S P O T S , V N L T S L O C B X L O C W A V Y J A R > G O E H M 3a MnOx - or bw carb i ca A B C VNS / V N L T S / N O D S D I F F U S E N T W K ! V N L T S / L E N S E S V N L T S . V N L T S i O F V N L T S L E N S E S / V N L T S ' H M - G O E i V E R Y L O C V N L T S 3t perv MnOx -or bw carb A J3 C* F L O O D I N G N O D V N L T S / / V E R Y L O C V N L T S / ' ' L E N S E S 3c MnOx A B C a i H i N o s V N L T S N O D S V N L T S V N L T S / S T R I N G S @ C A V N 4 white calcite A C V N L T S F G V N L T S .• S P O T S @ (3) V N L T S V N L T S C G V N L T S / N O D S V N L T S F G SYN + V N L T S C G N O D ,• C G NOD / V N L T S / S T R I N G S C G M G S T R I N G S / S P O T S @ (4) V N L T S L O C @ (1) F L O O D I N G O R W I T H (5) S T R I N G S 200 [ 250 [ 3001 3501 4001 4501 5001 5501 6001 6501 7001 7501 B O O DISTAL ALTERATION SCHEMATIC FIGURE - CELENDIN FORMATION - MINA CENTRAL H O S T R O C K S D I S T A N C E F R O M M A I N I N T R U S I V E IN M E T E R S 2001 2501 300| 3501 4001 4501 5001 5501 5001 6501 7001 7501 800 limestone B" C W K ? M D N ! | L ! T ' N E 0 J U M A S H A F O R M A T I O N D I S S P Y hornfels A B_ C bleached marble A J3 C F I N E G R A I N E D V E I N T Y P E S 2a or bw carb ¥ C L O C V N L T S 4 white calcite A B_ C C G T O M G L A T E S T A G E 2001 2501 300| 3501 4001 4501 5001 5501 6001 6501 7001 7301 800 Figure 3.3: Distribution of alteration and veins at Mina Central, Yauricocha, central Peru. Distance is from intrusive contact just off the east edge of the geologic map shown in Figure 3.1. In zone A , bleached marble, locally brownish in colour, is saccharoidal, crystalline, and commonly coarse to very coarse-grained (1 to 2 mm). Grain size decreases with distance from the intrusive and mineralized orebodies, until in zone B , it is generally medium-grained (0.5 to 1 mm). Bleached marble it is not present in zone C. Gray marble occurring in zones A and B is similar texturally to beached marble. Grain size decreases outwards from coarse- to medium-grained to fine-grained away from contact. Gray marble locally contains isolated lenses of 54 bleached marble (Fig. 3.3; Tables 3.4 and 3.5). In the outer part of zone B , up to 2 m thick fine-grained bleached marble and medium-grained gray marble layers are controlled locally by bedding. Fine-grained, dark gray, unaltered Jumasha limestone occurs in the outer limit o f zone B and widely in zone C. In zone B , it is strongly fractured and locally is either weakly hornfelsic or presents isolated lenses of gray marble (Fig. 3.3; Tables 3.4-3.6). Celendin Formation rocks occur up to 250 m laterally from main intrusive and up to 730 m (4810 m.a.s.l.) over know mineralization in the northern portion of zone B , where a thin bed o f fine-grained bleached marble and some thin beds of hornfels are interbedded with weakly silicified fine- to very fine-grained limestone (Fig. 3.3; Table 3.7). 3.3.2. Veins in the Distal Alteration Zones at M i n a Central A t M i n a Central, three types of veins, 2-4, can be found as much as 780 m laterally from the intrusive contact largely along the sides o f the intrusion and polymetallic deposits. They furthermore extend over a vertical distance approaching 765 m over known mineralization. The abundance and density o f the lenses and networks, clusters, and swarms of veinlets, locally rich in sulfide minerals, decrease away from the main intrusive contact (Figs. 3.2-3.5; Table 3.3). T a b l e 3.3: V e i n types found d is ta l ly to su l f ide orebodies at M i n a Cent ra l and C a c h i C a c h i . | V e i n type Compos i t ion 1 1 .Calcs i l icate 1 i a. b. c. Garnet (grossular/andradite) Wollastonite Calcsilicate(diopside/augite) ± calcite/orange-brown carbonate ± pyrite ± Mn-oxides i 2. Orange-brown carbonate a. b. Orange-brown carbonate ± calcite±quartz ± pyrite -j j Orange-brown carbonate ± calcite±quartz ± pyrite ± Mn-ox ides j | 3. Mn- r ich veins i | 4. Calcite a. Mn-ox ide ± orange-brown carbonate ± calcite ± quartz ± pyrite b. ! Pervasive Mn-ox ide - orange brown carbonate ] c. M n oxide ± quartz ± pyrite j a. 1 Dark gray calcite ± pyrite ± M n oxide b. 1 Light gray calcite ± pyrite ± M n oxide c. 1 White calcite ± pyrite (late) ± M n oxide 1 d. \ White calcite (syntectonic) Type 2 veins and veinlets are composed of orange brown carbonate minerals (Type 2a), occasionally containing minor M n oxides minerals (Type 2b). Type 2 veins are found immediately fringing the carbonate replacement orebodies, they lie largely in zone B and extend into the inner part of zone C decreasing rapidly in density (Fig. 3.3; Tables 3.3-3.7). In 55 addition, pale-gray carbonate minerals, quartz, locally up to 3 vol % of pyrite, and occasionally poorly developed swarm of calcsilicates veinlets plus minor dissemination (<1 vol %) and traces of goethite and jarosite are present in Type 2 veins, in most cases near the sulfide orebodies. Distinctive orange-brown carbonate veinlets extend up to at least 780 m from the intrusive contact, and up to 4,850 m.a.s.l. in fine-grained unaltered limestone (Figs. 3.4c and 3.4d), reaching at least 765 m over known mineralization (level 820) (Fig. 2.6). In zone A , orange brown carbonate-quartz-Mn oxides (Type 2b) f i l l veins in moderately dense networks. In zone B , vein networks are very dense and locally veins are up to 7 cm wide and locally contain white calcite spots or strong jarosite>goethite or hematite dissemination. In zone C, veinlet swarms are more diffuse and are located mainly in proximity to the Jumasha Formation-Celendin Formation contact, or in the inner western boundary of the zone. Orange brown carbonate-Mn oxides broadly cut fine-grained dark gray Jumasha unaltered limestone, which is locally moderately brecciated. In zones A and B , very dense to weak networks of up to 1.4 cm wide veins, veinlets and nodules of orange brown carbonate (Type 2a) are present in fine-grained unaltered limestone. Veinlets are wavy, parallel or locally brecciated with unaltered and silicified limestone fragments. Sometimes Type 2a veins contain calcite, jarosite-rich medium-grained white calcite halos, or minor Mn-oxides minerals. They are commonly cut by M n oxide-bearing orange brown carbonate veinlets (Type 2b). In zones A and B , up to 10 vol % of M n oxides nodules are locally present. In zone C , local flooding of vein wall and very dense to generally weak to moderately developed networks of up to 3.5 cm wide veinlets of orange brown carbonate (Type 2a) occur in fine-grained dark gray unaltered limestone. Sometimes, orange brown carbonate veins contain abundant nodules and veinlets of coarse-grained crystalline calcite, minor M n oxide minerals or are locally brecciated containing up to 2.5 cm unaltered and silicified limestone rounded fragments. Limestone is locally brecciated. Type 3 veins and veinlets consist of orange brown carbonate minerals rich in M n oxide minerals (Type 3 a). Near the C R D lodes and in proximity to the intrusive contact, M n oxides minerals flood the bleached limestone (Type 3b veins) (Fig. 3.4a). In addition, quartz and pyrite are present (Type 3c) (Fig. 3.3; Tables 3.3-3.6). Manganese oxides-rich nodules and veinlets of orange brown carbonate occur along bedding and f i l l fracture meshes in marbles and limestone (Figs. 3.4 and 3.5a). They are spatially associated with the sulfide-rich orebodies and reach horizontal distances of up to at least 750 m from the intrusion. In a vertical profile, they occur at an altitude of up to 4,825 m.a.s.l. extending over a vertical distance of at least 740 m above 56 known mineralization (level 820) (Fig. 2.8). In general the carbonate veinlet networks rich in M n (Type 3) lie below meshes of orange-brown carbonate veinlets rich in Fe (Type 2). However, Type 3 veins can locally occur above Type 2 veins, in proximity to the regional N W -striking structures. Pervasive Mn-oxide bearing orange brown carbonate (Type 3b) flooding, nodules and veinlets basically define zone A . They occur widely in crystalline coarse- to medium-grained marbles. Marbles occasionally contains up to 10 vol % o f irregular "patches" of bleached or gray marbles and irregular and discontinuous veinlets of very fine-grained hydrothermal white calcite (Type 4). In zone C , Type 3b fill irregular and disperse veinlets and lenses in fine-grained dark gray limestone. In zone A , Mn-oxides bearing orange brown carbonate (Type 3a) fills wavy veinlets in crystalline medium-grained gray marble or veinlets and lenses in fine-grained dark gray limestone. Veinlets locally contain crystalline coarse-grained white calcite spots. In zone B , Type 3a is present in veinlets and up to 0.50 m wide lenses in gray marble and in veins, veinlets, nodules, and occasionally up to 8 cm wide irregular lenses in fine-grained dark gray limestone. Local ly networks of veinlets are diffuse (10 vol %), dense or are hematite- and goethite-rich containing veinlets and pods of white calcite especially in proximity to small orebodies and quartz-monzonite intrusives. Nodules may contain irregularly banded crystalline coarse-grained calcite veinlets. Local ly limestone is strongly fractured and brecciated and contains abundant Mn-oxides bearing orange brown carbonate (Type 3 a) and white calcite (Type 4). In zone C , Type 3a veins are irregular and locally parallel in fine-grained dark gray limestone. Type 4 veins and veinlets consist of late-stage dark gray- (Type 4a), light gray- (Type 4b), and white- (Type 4c) calcite, and occur up to 780 m from the intrusive and up to 765 m over ores in all three zones (Fig. 3.3; Tables 3.3-3.7). Additionally, minor disseminated pyrite (<1 vol %), M n oxides minerals, weak dissemination and boxwork o f goethite, and minor jarosite clots are present in the Type 4 veins, in most cases near the sulfide orebodies. Late-stage calcite veins form the distal fringe and also cut all the other vein types in alteration zones. In zone B , crystalline white calcite (Type 4c) is coarse-grained and fills lenses, or is medium-grained, locally drusy, and fills veins. Locally, veins contain orange brown carbonate-minor M n oxide or goethite halos. Calcite crystals usually contain graphite clots. Very locally Mn-oxides bearing orange brown carbonate (Type 3a) nodules contain crystalline coarse-grained calcite (Type 4c) in fine-grained dark gray limestone. In zone C , nodules and up to 1 57 cm wide veinlets of Type 4c composition are present in fine-grained dark gray limestone. They are locally brecciated containing unaltered and silicified limestone fragments. Type 4c veins are irregular, medium-grained, contain M n oxide veinlets or are fine-grained in abundant veinlets. Figure 3.4: Alteration and vein types at Mina Central, Yauricocha, central Peru, a) Pervasive sulfide-bearing manganese-orange brown carbonate nodules and vein networks (vein Type 3b) replacing recrystallized gray medium- to coarse-grained gray marble in the proximity of Mina Central main orebody. Gray marble includes bleached marble patches (-10% of total rock volume). (Sample site 252239) (Zone A , 275m SW of Exito stock), b) Fluid escape structures formed by veinlet networks of sulfide-bearing manganese-orange brown carbonate veins (vein Type 3a) in recrystallized medium-grained gray marbles (Sample site 252238) (Zone A , 280m SW of Exito stock), c) Close up of replacement of recrystallized bleached limestone by manganiferous carbonate minerals veins and pods (vein Type 3a) (Sample site 246405) (Zone B, 430m SW of Exito stock), d) Network of, up to 7cm wide, orange brown carbonate-quartz and minor manganese veinlets (vein Type 2b) mainly fracture controlled in pure dark gray limestone beds. Decrease of manganiferous carbonate is consistent with distance (Sample site 252208) (Zone B, 425m SW of Exito stock). In all three zones, crystalline generally fine-grained to locally coarse-grained white calcite syntectonic (Type 4d) veinlets are present in fine-grained dark gray unaltered limestone. Type 4d veins are very locally brecciated. 58 F i g u r e 3.5: V e i n types and alteration at M i n a Central, Yaur icocha, central Peru. C lockwise from left bottom, a) Dense vein swarm o f manganese-orange brown carbonate veinlets (vein Type 3a) and Mn-cemented breccia (vein Type 3c) in slightly recrystall ized limestone (Zone B, 470m S W of Exi to stock), b) Fracture controlled dense network o f orange brown carbonate veinlets (vein Type 2a) in limestone at about 380m from the Ex i to stock (Zone B). c) Fractured controlled orange brown carbonate veinlet f i l l ing f luid escape conduits in limestone at about 600 meters away from Ex i to stock (Zone B). d) Thin white calcite syntectonic veinlets (vein Type 4d) in pure limestone bed. Syntectonic veins have no relation with mineralization associated to hydrothermal activity (Zone C , 400m S W o f Exi to stock). 59 Table 3.4: Summary of the distal alteration characteristic of zone A in Mina Central. HOST ROCKS DISTANCE FROM INTRUSIVE 235 to 400m limestone Fine-grained dark gray limestone. General bedding 130767°S 235 to 290m ; 305 to 400m (287m) 055° locally cut by 000° & 155° 1 085°, 005782°W&020°, trending fractures \ 150780°SW, 035° & I 050775°NW trending fractures bleached marble (235, 270m) coarse-grained bleached marble (400m) locally bleached marble (locally light brown) gray marble (243, 274m) coarse to (280m) medium- (305 to 400) very fine-grained grained crystalline gray marble locally with 1 gray marble bleached marble patches (10%) • (280m) 065° trending fracture locally cut by | (305 to 400) 065770°SE trending 090787°S & 040787°S trending faults | fault control distribution of gray | marble VEIN TYPES 2 a orange brown | \ carbonate j (345m) veinlets along 020° trending fracture in limestone ! b i orange brown ! carbonate±quartz± | MnOx (287m) moderately dense network of veinlets along bedding, 000° & 155° trending fractures in limestone 3 ! a i MnOx-orange i brown carbonate±-j calcite (280m) wavy veinlets along bedding & 065° i trending fracture in gray marble i (345m) (coarse-grained calcite) veinlets & lenses along 085°, 005° & 050° trending fractures in limestone (400m) veinlets with white calcite spots along 035° trending fracture in limestone b pervasive MnOx-| i orange brown ! i carbonate (243,274m) very abundant flooding, nodules & veinlets in gray marble along 080°&090°, 020°, 130°&160o)040o&065° • | c MnOx (345m) locally abundant veinlets in gray marble 4 \ c | white calcite (late-i stage (235m) veinlets in bleached marble (305m) minor veinlets in gray marble I (243, 274m) very fine-grained; irregular & discontinuous veinlets in gray marble (400m) spots in MnOx-<orange brown carbonate veinlets ] d white calcite 1 (287m) coarse-grained crystalline; | ! (syntectonic) { syntectonic veinlets along 055° trending I fractures in limestone (345m) abundant fine-grained; syntectonic veinlets in limestone 60 Table 3.5: Summary of the distal alteration characteristic of zone B in Mina Central. DISTANCE FROM INTRUSION HOST ROCKS limestone 237 to 685m fine-grained dark gray limestone, (279, 333m) locally very strong fractured, (237, 321, 333, 657, 665m) locally brecciated, (400m) locally with malachite spots (2%) & | (530m) locally weakly hornfelsed. General bedding 140772°N 237 to 380m 400 to 685m 0807sub-vertical,090770°S& 105° (spacing: 10cm), 020°, 140755°SW,150777°NE&160°, 040°-050765°NW-subv, 060°&070° trending fractures & 050744°NW trending sinistral fault. 150766°NE trending sinistral fault/fractures (spacing: 45cm) 085°&095765°N, 000782°W(spacing: 5, 10 & 13cm), 135782°E-subv, 140°&160774°E-subv, 040774°SE, 050°, 070774°NW &075759°S (337m) 150775°NE , 050764°SE & j (400m) 020° locally cuts 135° & 075° 010°(locally cuts 150°) trending fractures j trending fractures (380m) 095764°N trending fault dextrally locally cuts 170°/sub-vertical trending fracture (4-5cm displacement) ! (429m) 065° locally cut by 090° & 000° \ \ trending fractures \ bleached I marble I (560m) locally bleached gray marble i patches in limestone & (650m) very ! locally medium-grained bleached marble i | gray marble 1 (685m) very locally gray marble. | 140760°NE trending fault i VEIN TYPES i 2 a orange brown carbonate±calcit e±quartz (267m) (jarosite-rich) veinlets with medium-grained white calcite halo in limestone ! (470m) irregularly banded coarse-grained i I crystalline (icalcite); veinlets along 1 bedding & 070° trending fractures in i limestone • (279m) (iquartz) network of veinlets in limestone 1 (530m) (iquartz) network of veinlets in ! limestone | (279m) (iquartz) minor veinlets in bleached gray marble patches i (560m) (iquartz) minor veinlets in i bleached gray marble patches > . (321m) (±calcite) moderately developed network veinlets along 160° trending fracture in brecciated limestone | (615m) (icalciteiMnOx) parallel veinlets j i along 000° trending fracture in limestone j i i i (337m) up to 1.4cm vein along 150° cut by orange brown carbonate-MnOx veinlets along 050° & 010°(locally cuts 150°) in limestone ! (650m) (iquartz) minor veinlets in i bleached marble b orange brown carbonate-MnOx (237m) veinlets along bedding & 080° trending fracture in limestone ; (400m) veinlets & nodules with white . ! calcite pods in veinlets along 020° i trending fracture in limestone j (272m) very dense network of veinlets along bedding & 160° trending fracture in light gray limestone | (413m) veinlets along 050°, 085°& 160° | ; trending fractures in limestone I (335m) very well developed network of up to 1cm wide, locally brecciated, veinlets along 150° trending sinistral fault & fractures in limestone \ (426m) up to 7cm wide vein with white i calcite veinlet/spots & disseminated | jarosite>goethite along 135° trending : fracture in limestone \ (337m) locally wavy, veinlets along 090°, 050°& 070° & 010°(locally cuts 150°) trending fractures in limestone. • 050° & 010° contain more Mn ! (625m) (hematite-rich reddish) vein with \ i white calcite veinlets & spots along 040° j I trending fracture in limestone 61 Table 3.5 (cont.): Summary of the distal alteration characteristic of zone B in Mina Central. ! DISTANCE FROM INTRUSION ! VEIN TYPES | 237 to 380m 400 to 685m 3 a | MnOx-orange i brown i carbonate±calcit I e (267m) veinlets along 080° & 045°-050° trending fractures & lenses along 140° trending fracture in limestone (429m) (hematite & goethite-rich) veins & veinlets with white calcite pods outcropping close to small orebodies & quartz-monzonite i (333m) abundant veinlets along 130° in brecciated limestone (429m) veins, veinlets & nodules along 065°(locally cut by 090°& 000°), 090° & | 000° in limestone (380m) fine-grained; diffuse network of veinlets along 095° trending fault, dextrally cutting 170° trending fracture with similar veinlets in limestone (470m) poor developed (10% of total rock; volume) network of veinlets/nodules along bedding & 070° trending fractures ! in limestone (657m) (icalcite) lenses mainly along 140° trending bedding in limestone I (665m) up to 8cm wide veinlets & lenses 1 i along 160° trending fracture in gray i limestone (685m) up to 0.50m wide lenses & veinlets along 140° trending fault in"gray j marble c | MnOx (279m) abundant veinlets along 150° & 050° trending fractures in limestone (400m) veinlets along 000°&040° trending fractures in limestone • (321m) locally nodules (10%) in brecciated limestone. (413m) locally veinlets along 160° trending fractures in limestone • [ (470m) veinlets along bedding & 070° ! trending fracture in limestone 4 c | white calcite j (late-stage) (237m) coarse-grained late-stage j (426m) veinlet/spots in orange brown crystalline; veinlets cutting orange brown; carbonate-MnOx vein carbonate±MnOx veinlets in limestone i (279m) minor veinlets in limestone (429m) coarse-grained crystalline; nodules in limestone (321m) veinlets & crystals with graphite stains in brecciated limestone (530m) minor veinlets in limestone (333m) veinlets in brecciated limestone (615m) coarse-grained dark gray; veinlets j along 000° trending fracture in limestone ; | (335m) medium-grained crystalline; vein with orange brown carbonate-MnOx halo along 050° trending sinistral fault in limestone i . (337m) medium-grained drussy crystalline; vein with goethite halo in limestone ; d i white calcite I (syntectonic) (665m) coarse-grained; nodules & syntectonic veinlets along 160° trending fracture in gray limestone 62 Table 3.6: Summary of the distal alteration characteristic of zone C in Mina Central. HOST ROCKS DISTANCE FROM INTRUSION 680 to 753m limestone up to 3.5m wide fine-grained dark gray limestone bed, (680, 700m) locally brecciated with fresh & silicified limestone fragments. General bedding 135°/83N° 080780°S, 000° & 020773°W, 110°, 115°, 130° & 140°, 035778°SE, 050°, 055776°SE & 065772°NW (spacing: 15-20cm) trending fractures VEIN TYPES 2 a orange brown carbonate (680m) very dense network of veinlets & flooding of vein along 115° & 130°, 035° & 065° trending fractures in limestone (717m) weak to moderately developed network of veinlets & flooding of vein wall with coarse-grained crystalline white calcite abundant nodules/veinlets & up to 2.5cm rounded limestone fragments along 065° trending fractures in limestone ! b orange brown carbonate-\ MnOx (700m) up to 3.5cm wide veinlets along 020° trending fractures in limestone 3 a MnOx-orange brown I ! carbonate (753m) very locally dendritic psylomelane-<orange brown carbonate locally very irregular parallel veinlets along 055° trending fractures in limestone j b; pervasive MnOx-orange 1 ! brown carbonate (75 lm) very locally very abundant veinlets/lenses along 080° trending fracture in limestone I c! MnOx (no carbonate) 4 c white calcite (late-stage) (751m) veinlets in white calcite vein (680m) (±MnOx) coarse-grained; nodules & veinlets along 115° & 130°, 035° & 065° trending! fractures in limestone (700m) coarse-grained; up to 1cm wide veinlets & fine-grained abundant veinlets in limestone (717m) coarse-grained crystalline; abundant nodules & veinlets in orange brown carbonate flooding of vein wall (751 m) medium-grained; vein with MnOx veinlets along 080° trending fracture in limestone 1 di white calcite | ! (syntectonic) (717m) coarse-grained crystalline; syntectonic veinlets along 000° & 050° trending fractures in! limestone Table 3.7: Summary of the distal alteration characteristic of zone B, Celendin Formation, Mina Central. ! DISTANCE FROM INTRUSION HOST ROCKS limestone 160 to 206m | (160, 206m) very fine-to-fine-grained, weak to moderate silicified limestone with ] disseminated pyrite (3-4%). Locally strongly silicified with abundant light green carbonate- j I pyrite parallel veinlets. General bedding 140°/83°N hornfels (191m) hornfels. 070773°Ntrending fractures j bleached ' marble (217m) fine-grained bleached marble thin bed with dark gray quartz veinlets with abundanti pyrite parallels to bedding & interbedded with limestone. 055765°NW trending fracture VEIN TYPES 2 ; a orange brown carbonate j (191m) veinlets along bedding & 070° trending fractures in hornfels 4 j c| white calcite (late-stage) j (191m) medium-grained dark gray late-stage; veinlets irregularly cutting orange brown i carbonate veinlets in hornfels ! (191m) veinlets in hornfels ! (217m) fine-grained late-stage; vein along 055° trending fracture cutting dark gray quartz I veinlets in bleached marble 63 In summary, the rocks adjacent to the carbonate replacement bodies at M i n a Central are flooded with manganese oxides (Type 3b veins) (Fig. 3.4a). Outward, there is increasing content of orange brown carbonate minerals in the veins (Type 3a) and a decreasing content o f M n oxide minerals (Type 2b) (Figs. 3.4b-d and 3.5a) and finally the veins are orange brown carbonate (Type 2a) only. Orange-brown carbonate (Type 2a) veins extend farther than Type 2b veins (Figs. 3.5b and 3.5c). Orange-brown carbonate veinlets and less common nodules (Type 2), locally rich in manganese (Type 3), are the distinctive distal manifestation of the hydro thermal systems. White calcite veins (Type 4) form the distal fringe (Fig. 3.5d) and also cut all the other vein types in alteration zones closer to the sulfide orebodies. In a general vertical profile, the carbonate veinlet networks rich in M n (Type 3) lie beneath networks of orange-brown carbonate veinlets rich in Fe (Type 2). Beyond the Mn-bearing and orange-brown carbonate veins are white calcite veins (Type 4), which can either be syntectonic veins (Type 4d) that predated the hydrothermal system or represent the distal exhausted hydrothermal fluids (Types 4a-4c) (Fig. 3.5d). 3.4. Zones of Distal Alteration at Cachi Cachi A s at M i n a Central, in Cachi Cachi, zones of bleached marble, gray marble and limestone (zones of dolomitization), and vein swarms and distal veinlets in host rocks adjacent to orebodies are distributed laterally outward from the intrusive contact (Fig. 3.3). In outcrops above Cachi Cachi, the distal alteration has also been divided in three zones. Divis ion is essentially based on the intensity and distribution of veinlets rich in calcsilicates minerals, orange-brown carbonate minerals versus gray and white carbonate minerals, Mn-oxides and the presence of bleached limestone or marble versus unbleached or gray limestone or marble (Tables 3.8-3.10). The zones are also irregular in size and horizontal and vertical distances with respect to the intrusive contact. The halo of bleached marble versus gray marble and the distribution of the different vein types are widely controlled by the E-striking bedding (070° to 095°). Local ly N E - . . N W - , N - , and E-trending fracture systems exert minor control on the distribution of the distal alteration (Table 3.12). Contacts between the alteration zones are less diffuse than near M i n a Central, and pods of one zone can be found within the mapped limits of another zone. The zones of distal alteration and their dominant characteristics are: Zone A : Pervasive limestone and marble bleaching, located in the east end o f the Cachi Cachi pit nearest to the principal intrusive. 64 Zone B : Limestone bleaching is widely controlled by the stratigraphy resulting in a stripped outcrop appearance. This zone is located in the west end of the Cachi Cachi pit and toward the west of the contact of the main intrusive with the mineralized zones and host rocks. Zone C: Discontinuous regional limestone bleaching controlled by the bedding most distal to the main intrusive. Bleaching of limestone or bleached marble versus gray marble, and the abundance and density of the networks of veinlets, locally rich in sulfide minerals, decreases with the distance away from the intrusion and from the Cachi Cachi pit (Figs. 3.6-3.10). 3.4.1. Host Rocks in the Distal Alteration Zones at Cachi Cachi Pervasively bleached marble (zone A ) , interlayered bleached limestone and bleached marble versus gray marble (zone B) , and diffuse but penetrative bleaching of limestone (not marble) (zone C) extend to approximately 150 m, 450-500 m, and 250-550 m, respectively from the contact of the mineralized zones and host rocks with the main intrusive. However, north of the Cachi Cachi pit, bleaching of limestone versus gray marble locally reaches around 700 m from the intrusive contact. West of the Cachi Cachi pit, unaltered Jumasha limestone occurs not closer to 430-450 m from the main intrusive contact. In a vertical profile, bleached marble occurs up to 4,750 m.a.s.l., while gray marble is noticeable at least up to 4,800 m.a.s.l., approaching no less than 670 and 720 m over known mineralization, respectively. However, north of the Cachi Cachi pit, bleached limestone and gray marble, locally reaches 4,840 m.a.s.l. extending up at least 760 m over known mineralization. West of the Cachi Cachi pit, unaltered limestone does not occur below 4,675 m.a.s.l. Pervasively bleached marble defines zone A that extends up to approximately 150 m from the contact of the mineralized zones and/or host rocks with the main intrusive (Figs. 3.7, 3.8a, and 3.8b; Table 3.8). The bleached marble is saccharoidal, crystalline, and generally coarse to very coarse-grained (1 to 2 mm). However, medium-grained (0.5 to 1 mm) bleached marble is also locally present. Near the outer limit of zone A , very coarse-grained bleached marble contains graphite clots as well as isolated lenses of pyrite-bearing, coarse-grained gray marble, similar to that in zone B . Locally, small granodiorite to quartz-monzonite porphyry intrusive dykes intrude some bleached marble beds. In zone B , bleaching of limestone and marble versus gray marble reaches horizontal distances of 450 to 500 m from the contact of the mineralized zones and/or host rocks with the main intrusive (Figs. 3.7, 3.8a, and 3.8b; Table 3.9). The bleaching of marble is widely 65 confined to bedding and extends into the outer zone of gray marble. Outcrops consist of bedding-controlled stripes of white and gray marble. The confinement to and flow of hydrothermal fluids along bedding is enhanced as the bedding strikes generally 075° to 095° and dips S from 045° to sub-vertical directly into the contact with the intrusive rocks. Distal alteration is very locally controlled by the fracture system. The marble is saccharoidal, crystalline, mainly medium- to coarse-grained, and generally finer grained than in zone A . Locally, grain size of marble is variable. Similarly, gray marble is generally finer grained than bleached marble. Saccharoidal, crystalline, very coarse-grained brownish bleached marble, containing less than 2 vol % of disseminated jarosite, is not common. The host rock locally contains up to 40 vol % of "patches" or "veins" of bleached or gray marble, as an evidence of irregular oxidation of the graphite within the host rock. The abundance of clots and traces of graphite in marbles is greater than in zone A . Near the outer limit of zone B , fine-grained dark gray limestone contains halos of bleached marble or bleached limestone. Zone C lies outside zones A and B . It is characterized by diffuse but penetrative bleaching of limestone (not marble) occurs some 250 to 550 m from the contact o f the mineralized zones and/or host rocks with the main intrusive (Tables 3.10.1-3.10.3). There, the distal alteration is generally confined to bedding (Fig. 3.10a), and as in zones A and B , the fracture systems exert lesser control. North of the Cachi Cachi pit, bleaching of limestone versus gray marble is locally controlled by a northerly trending steepy west dipping fault about 700 m from the intrusive contact (Tables 3.10). Bleaching is inferred to be due to the oxidation o f the graphite within the limestone, but it is not accompanied by recrystallization of limestone to marble. The contact between the fine- to medium-grained white or gray limestone with the fine-grained dark gray unaltered limestone is irregular with bleached and gray limestone layers present as fingers within the otherwise dark gray limestone of the Cretaceous Jumasha Formation (Fig. 3.10a). In zone C, carbonate rocks are noticeably finer grained than in zone A and B (Fig. 3.7). Bleached limestone is crystalline, commonly medium-grained, and locally weakly silicified. Saccharoidal, very coarse-grained (1.5 mm) bleached limestone is also locally present containing up to 8 cm wide, texturally similar (2 mm), gray marble "veins" with graphite clots. Lenses of very crystalline, very coarse-grained bleached limestone are locally enclosed in dark gray limestone. Gray marble is mostly medium-grained and contains up to 10 vol % of coarse-grained bleached limestone. 66 Figure 3.6: Geological and alteration map of the surface outcrops around Cachi Cachi, Yauricocha mining district, central Peru. Included on the map are the sample location and sample numbers that correspond to analysis present in the appendices. A larger version of the figure is included in Plate 3 in the appendices. Sample number can be seen more clearly on the Plate. 67 Locally, gray marble is fine-grained and silicified. Near the outer limit of zone B , some 430-450 m N W of the Cachi Cachi pit, very fine-grained dark gray unaltered limestone is present intercalated with medium-grained bleached limestone layers, l o c a l l y . M n oxides veinlets f i l l micro-fractures. 3.4.2. Veins in the Distal Alteration Zones at Cachi Cachi A t Cachi Cachi, four types of veins, 1-4, are recognized in the distal alteration zones. They are distributed sequentially outward within the zones, can occur up to at least 790 m laterally from the intrusive contact largely along the W side of the intrusion (Fig. 3.7; Table 3.3), and furthermore extend over a vertical distance approaching 750 m over known mineralization. The abundance and density of the lenses and networks, clusters, and swarms of veinlets, locally rich in sulfide minerals, decrease with the distance of the main intrusive (Figs. 3.6-3.10; Table 3.3). Type 1 veins and veinlets consist of grossular/andradite garnet (Type la), calcsilicates minerals (mainly diopside and augite) (Type lc) , and wollastonite (Type lb) (Fig. 3.7; Tables 3.3 and 3.8). In addition, orange brown carbonate and dolomite, quartz and pyrite are present in the Type 1 veins near the sulfide orebodies. Veins and isolated clusters of garnet, calcsilicate minerals, and wollastonite are present, laterally from the intrusive contact, at least up to 180, 400 and 450 m, respectively, in marble and limestone. In vertical section, garnet occurs up to 4,600 m.a.s.L, calcsilicate minerals up to at least 4,650 m.a.s.l., and wollastonite at up to at least 4,700 m.a.s.l. extending up to 520, 570, and 620 m over known mineralization. Near the intrusion, particularly north and west of the Cachi Cachi pit within zones A and B , lenses and veinlets of yellow brown garnet (grossularitic) (Type la) are more abundant in coarse-grained bleached or gray marble (Fig. 3.8c). Lenses are up to 0.90 x 1.60 m in size and contain up to 13 mm long crystals. Marble is occasionally locally silicified. In zone A , dense to diffuse network o f up to 3 mm wide, locally wavy, veinlets (10-60 vol %), irregular lenses, nodules, dissemination and traces o f pale green to pale yellow calcsilicate (diopside and augite) (Type lc ) (Fig. 3.8d) extend farther from the intrusive contact into zone B in marble and limestone. Calcsilicates are locally present in a moderate silicified white carbonate matrix with pyrite dissemination and veinlets (Figs. 3.7 and 3.9b). In zone C , calcsilicate minerals are also occasionally present in very dense networks of veinlets containing 30 vol % of M n oxides. 68 DISTAL ALTERATION SCHEMATIC FIGURE - CACHI CACHI GRID HOST ROCKS DISTANCE FROM MAIN INTRUSIVE IN METERS 5I)| 1001 150| 200| 250 | 300| 350 | 400| 450| 500| 560 | 600| 650 | 700| 7S0| 800 limestone FINE GRAINED DK GY - INTERBEDDED W/BLD % GY MRB bleached marble COARSE GRAINED COARSEGRAINED GREY MARBLE PATHCES / "VEINS" (20 - 30%) PY DISS, GRAPHITE TRACES COARSE TO MEDIUM GRAINED grey marble COARSE GRAINED PY DISS & STRINGS DISS GOE AFTER PY PYTR BLEACHED MARBLE PATCHES (15 - 40%) MEDIUM GRAINED FINE GRAINED VEIN TYPES PYDISS/VNLTS 1a grossular VNLTS/TRACES 1b wollastonite SWARM OF VNLTS 1c calc silicic ± or bw carb ± ca ± py ± MnOx VNLTS/LENSES PY DISS HEM / GOE DISS AFTER PY PYDISS VERY DENSE NTWKS OF VNLTS PYDISS 2 or bw carb ± ca ± qz ± py ± MnOx VERY DENSE / POOR NTWKS OF VNLTS PY DISS HEM STAINING TPY, ABUND GOE 3 MnOx ± or bw carb ± ca ± qz ± py LOCALLY BLD MRB HALOES MD DENSE / POOR NTWK OFVNLTS + LENSES, LOCAL NODULES PYDISS/VNLTS GOE / HEM DISS 4 dk/lt gy &wl ca COARSE GRAINED PYDISS VNS / LENSES COARSE TO MEDIUM GRAINED VNLTS NOO / LENSES PYDISS LOCALLY BLD. LOC BX GOE > JAR DISS 501 100| 150| 2001 2501 3001 3501 4001 4501 5001 5501 6001 6501 7001 7501 800 DISTAL ALTERATION SCHEMATIC FIGURE - CACHI CACHI REGIONAL MAPPING HOST ROCKS DISTANCE FROM MAIN INTRUSIVE IN METERS so I 1001 150| 2001 2501 3001 3501 4001 4501 5001 5501 600| 6501 7001 7501 800 limestone MEDIUM GRAINED. WK SIL'D FINE GRAINED DK GY LOC BX MnOx STRINGS bleached marble ABUND JAR. GOE, MnOx PYDISS FINE TO COARSE GRAINED , COARSE GRAINED ABUND DISS GOE 4 JAR MnOx STRINGS grey marble MEDIUM TO FINE GRAINED FINE TO COARSE GRAINED JAKbHUIij ' LOCAL WK SIL'D FINE TO COARSE GRAINED PYDISS/VNLTS PY STRINGS PY DISS. MnOx STRINGS BX WK GOE AFTER PY GRAPHITE TR VEIN TYPES 1a grossular LENSES/VNLTS 1b wollastonite DIFFUSE SWARM OF VNLTS PYDISS Ic calc silicic ± or bw carb ± ca ± py ± MnOx VNLTS / NODULES PY VNLTS /DISS SWARM OF VNLTS PY DISS 2 or bw carb ± ca ± qz ± py ± MnOx DENSE NTWK OF VNLTS ' SWARM OF VNLTS / LENSES VNLTS* LENSES/VNLTS 3 MnOx ± or bw carb ± ca ± qz ± py VNLTS/LENSES CALCITE HALO POOR DENSE & IRREG NTWK OF VNLTS 4 dk/lt gy &wt ca VNLTS / LENSES COARSE GRAINED PYDISS. BXWK AFTER PY FINE TO COARSE GRAINED LOC BX G A L ' C P Y COARSE LOC GRAPHITE VERY COARSE GRAINED GRAINED TR DISS GAL, MAL STAINS sol 1001 150| 200| 250| 3001 3501 4001 4501 5001 ssol 6001 esol 7001 7501 800 Figure 3.7: Distribution of alteration and veins at Cachi Cachi, Yauricocha, central Peru. Distance is from intrusive contact just off the east edge of geological map shown in Figure 3.1. zone B and in the most inner part of zone C, some 180 m and 450 m W of the Cachi pit, very dense swarms and networks of veinlets of light green-grayish wollastonite lb) are present in bleached marble, bleached limestone, and gray marble. Wollastonite 69 generally floods a matrix of pale-grayish carbonate minerals, quartz, up to 3 vol % of disseminated pyrite, locally disseminated goethite (<1 vol %), boxwork o f goethite after pyrite, and hematite and epidote clots (Figs. 3.7 and 3.9a). The mineral assemblages of vein Type 1 represents the high temperature veins associated with the formation of the skarn. The garnet (Type la) and calcsilicate (Type l c ) veins are found closer to the sulfide orebody, whereas the wollastonite (Typelb) veins are the distal manifestation o f the skarn system. Type 2 veins consist of orange brown carbonate minerals (Type 2a), irregularly containing minor M n oxides minerals (Type 2b). A t Cachi Cachi, Type 2 veins lie largely within zone B , decreasing rapidly in density toward zone C (Fig. 3.7; Tables 3.3, 3.9 and 3.10). Additionally, pale-gray carbonate, quartz, pyrite, irregular swarm of calcsilicate veinlets, and minor dissemination and traces of goethite and jarosite are present in the Type 2 veins close to sulfide orebodies. Outward, there is decreasing content of orange brown carbonate minerals in the veins (Type 3a) and a slight increasing content of M n oxide minerals (Type 2b). Flooding of vein walls, networks and swarms of veins, and pods of orange-brown carbonate and minor M n oxides-bearing orange brown carbonate outcrop reaches lateral distances from the main intrusive contact o f up to 610 m in gray marble and 670 m in unaltered limestone. Vertically, Type 2 veins reach some 720 m at around 4,800 m.a.s.l. in gray marble, and 745 m at around 4,830 m.a.s.l. over known mineralization in unaltered Cretaceous Jumasha limestone. In zone B , weathered resistant dense to very dense and diffuse networks and swarms o f up to 8 mm wide commonly wavy veins and lenses in marble are filled by orange-brown carbonates (Type 2a), irregularly with Mn-oxides (Type 2b) (Figs. 3.7, 3.9c and 3.9d). The vein networks and swarms decrease in density and in pyrite content with the distance from the intrusive contact. They frequently occupy around 60 vol % of the host rock, rarely flooding them. Occasional and locally, (4-5 vol %) pyrite-rich Type 2 veinlets have a thin halo of bleached limestone/marble or white calcite and f i l l stylolites (10 vol %). In zone C , irregular veinlets or pods, incipient networks of veinlets, and locally up to 3 cm wide lenses o f minor Mn-oxides bearing orange brown carbonate minerals (Type 2b) are present in marble or fine-grained gray limestone near the outer limit of zone B . 70 Figure 3.8: Alteration and vein types at Cachi Cachi, Yauricocha, central Peru, a) East view of zones A and B at Cachi Cachi grid displaying pervasive to bedded controlled bleaching (white bands) and bedding controlled vein swarm (dark bands). Note in the background the main intrusive (dark gray) in contact with the bleached marbles, b) Pervasive (left) to bedded (right) controlled bleaching. Sharp contact, between zones A and B, occurs at about 150 m from sulfide bearing rock, c) Close up of up to 1.60x0.90m in size grossular pods (vein Type la) in very coarse-grained recrystallized and bleached marble bed (Sample site 251239) (Zone A, 170m W of main intrusive), d) Fluid escape structures formed by veinlet networks of light green wollastonite-quartz (vein Type lb) cutting dolomite flooded, medium-grained pervasively bleached marble (Sample site 251208) (Zone B, 415m W of main intrusive). Type 3 veins and veinlets are composed of orange brown carbonate minerals rich in Mn oxide minerals (Type 3 a) or in quartz and pyrite (Type 3 c). In the Cachi Cachi area, the presence of Mn oxides minerals is considerably less than in Mina Central, where they flood the carbonate replacement bodies (Type 3b veins) (Fig. 3.7; Tables 3.3, 3.9, and 3.10). At Cachi Cachi, nodules, lenses, and network of veinlets of orange-brown carbonate mineral rich in Mn oxide are present in marble and limestone at least up to 790 m laterally from intrusive contact, extending up to 750 m vertically over known mineralization, at around 4,830 m.a.s.l. 71 F i g u r e 3 . 9 : V e i n t y p e s a n d a l t e r a t i o n at C a c h i C a c h i , Y a u r i c o c h a , c e n t r a l P e r u , a) C l o s e u p o f v e i n s w a r m c o m p o s e d o f l i g h t g r e e n w o l l a s t o n i t e - q u a r t z ( v e i n T y p e l b ) i n d o l o m i t e ( ? ) f l o o d e d f i n e - g r a i n e d g r a y m a r b l e ( S a m p l e s i t e 2 4 6 4 0 9 ) ( Z o n e B , 4 2 2 m W o f m a i n i n t r u s i v e ) , b ) V e r y d e n s e n e t w o r k o f c a l c s i l i c a t e ( d i o p s i d e ) - o r a n g e b r o w n c a r b o n a t e - q u a r t z v e i n l e t s ( v e i n T y p e l c ) f o r m i n g f l u i d e s c a p e s t r u c t u r e s i n a b l e a c h e d m a r b l e b e d ( S a m p l e s i t e 2 4 6 4 1 4 ) ( Z o n e B , 2 9 8 m W o f m a i n i n t r u s i v e ) , c) N e t w o r k o f u p to 6 m m , o r a n g e b r o w n c a r b o n a t e - c a l c i t e - q u a r t z v e i n l e t s ( v e i n T y p e 2 ) f o r m i n g f l u i d e s c a p e s t r u c t u r e s i n f i n e - g r a i n e d g r a y m a r b l e . ( S a m p l e s i t e 2 4 6 4 1 2 ) ( Z o n e B , 2 9 8 m W o f m a i n i n t r u s i v e ) , d) C l o s e u p o f v e i n s w a r m c o m p o s e d o f o r a n g e b r o w n c a r b o n a t e - q u a r t z ( v e i n T y p e 2 ) i n c o a r s e - g r a i n e d m a r b l e ( S a m p l e s i te 2 4 8 4 8 8 ) ( Z o n e B , 2 5 9 m o f m a i n i n t r u s i v e ) . I n z o n e B , u p t o 5 c m w i d e n o d u l e s , l e n s e s a n d w e a t h e r i n g r e s i s t a n t d e n s e t o d i f f u s e n e t w o r k s v e i n l e t s o f M n o x i d e s - b e a r i n g q u a r t z - b a n d e d p y r i t e ( T y p e 3 c ) , l o c a l l y rich i n w h i t e a n d o r a n g e - b r o w n c a r b o n a t e s ( T y p e 3 a ) , o c c u r a l o n g b e d d i n g a n d f i l l i n g f r a c t u r e s y s t e m s i n m e d i u m - g r a i n e d m a r b l e s , l o c a l l y r e p r e s e n t i n g 1 0 t o 2 0 v o l % o f t h e r o c k ( F i g . 3 . 1 0 b ) . V e r y l o c a l l y , t h e v e i n l e t s a n d n o d u l e s c o n t a i n m i n o r c o v e l l i t e , g a l e n a , g o e t h i t e , a n d h e m a t i t e d i s s e m i n a t i o n . I n z o n e C , n e t w o r k s o f T y p e 3 a v e i n s a r e d i f f u s e , i r r e g u l a r , a n d p o o r l y d e v e l o p e d i n f i n e - g r a i n e d g r a y m a r b l e a n d fine-grained g r a y l i m e s t o n e ; l o c a l l y u p t o 3 c m w i d e l e n s e s a r e a l s o p r e s e n t . T y p e 3 v e i n l e t s c r o s s - c u t o r a n g e b r o w n c a r b o n a t e m i n e r a l s ( T y p e 2 a ) v e i n l e t s . 72 Type 4 veins and veinlets are composed of late-stage dark gray- (Type 4a), light gray-(Type 4b), and white- (Type 4c) carbonate minerals (Tables 3.3 and 3.9-3.10). Near sulfide orebodies, they also contain minor pyrite, Mn oxides, minor goethite and jarosite. As in Mina Central, late-stage calcite veins are present in all three zones and form the distal fringe cutting all the other vein types in alteration zones. Veins and lenses of late-stage calcite are present in marble and limestone at least up to 790 m laterally from the intrusive contact. In a vertical profile, late-stage calcite occurs at 4,840 m.a.s.l. extending up to 760 m over known mineralization. Pyrite-bearing late-stage calcite (Types 4a, 4b, and 4c) fills up to 10 cm wide lenses, nodules, patches and up to 2.5 cm wide veins in bleached marble, bleached limestone, gray marble, and in minor quantity unaltered limestone in all the three zones cutting, locally wavy and irregularly, calcsilicates and carbonate vein networks or swarms (Fig. 3.10c). Particularly in zone A, late-stage calcite is coarse-grained (up to 12 mm in size crystals), even where medium and fine-grained textures are also locally present. Type 4 veins locally contain graphite clots and minor Mn-oxide veinlets. In zone B, pyrite-rich late-stage calcite veins have very narrow bleached marble halo, locally contain sub-angular limestone fragments or locally consist of at least two generations of calcite. Sometimes calcite is banded and drusy. Locally up to 5 mm wide Type 4 veins include dissemination of up to 4 mm long pyrite crystals, goethite boxwork after pyrite, galena, covellite and malachite clots in fine-grained gray marble. In zone C, the abundance of late-stage calcite veinlets in fine-grained unaltered Jumasha limestone is less than found in zones A and B. Up to 1 mm wide syntectonic white calcite (Type 4d) veinlets formed during regional deformation, thus not related to mineralization or alteration. There, Type 4d veinlets are also present in marble and unaltered limestone largely in zone C. In zone A, pyrite is common in the pervasively bleached limestone or marble. Dissemination or veining is generally less than 1 vol % of the rock; nevertheless, it reaches up to 5 vol % in proximity to the main intrusive. Disseminated pyrite is also present in all the calcsilicate and late-stage calcite veins. Hematite dissemination and veinlets occur in strongly goethite stained bleached marble. In zone B, locally abundant pyrite dissemination and veinlets (<3. vol %), locally with goethite and minor jarosite (after pyrite), occur regularly in marbles filling micro-fractures or in all the calcsilicates and late-stage calcite veins. Moderate goethite dissemination (<2 vol %) and traces, as well as minor hematite clots occur in orange-brown carbonate network of veins. In zone C, pyrite veinlets (2 vol %) and disseminations occur in 73 bleached limestone and gray marble, locally in unaltered limestone particularly near the outer limit o f zone B , and in all distal veins. Up to 3 cm wide veinlets o f M n oxides-rich quartz-pyrite occur filling fractures in marbles, occasionally veins are rich in orange-brown carbonates or contain minor galena dissemination. Locally moderate to abundant goethite and jarosite dissemination/clots, boxwork o f goethite after pyrite, and hematite spots occur in bleached limestone, gray marbles, orange-brown carbonate veins, and rarely in calcite veinlets. Boxworks of goethite after pyrite occurs also locally in gray marbles. Figure 3.10: Distal vein types and alteration at Cachi Cachi, Yauricocha, central Peru, a) Interfmgered, recrystallized bleached (white) and gray marbles (left) in contact with dark gray fine-grained limestone (right) at about 450 meters (zones B and C) from sulfide bearing rock. Bedding controls bleaching of beds, b) Mn-rich sulfide replacement of favorable calcareous horizon (foreground). Fracture controlled MnOx-orange brown carbonate-quartz veins (vein Type 3) extend beyond sulfide into medium-grained bleached and gray marble beds (Sample site 251206) (Zone B, 415m W of main intrusive), c) Up to 2.5cm wide, sub-parallel late-stage coarsely crystalline white calcite-pyrite veinlets (vein Type 4) cutting very coarse-grained saccharoidal pervasive bleached marble (Sample site 246481) (Zone A , 145mW of main intrusive). In summary at Cachi Cachi, the garnet (Type la) and calcsilicate veins (Type l c ) are found closer to the sulfide orebody, whereas the wollastonite veins (Type lb) are the distal manifestation o f the skarn system. The orange brown carbonate veins (Type 2) lie broadly within zone B . Manganese oxide-rich veins (Type 3) are present in lesser amounts than in Mina 74 Central. Irregular networks of veins, isolated lenses and traces of orange brown- (Type 2 ) and white-carbonate minerals (Type 4 ) , and Mn oxide-rich minerals ( T y p e 3 ) are less frequent in marbles and limestone particularly in zone C, as their abundance and density decrease broadly with the distance from main intrusive. Orange-brown carbonate veinlets (Type 2 ) , locally rich in manganese (Type 3 ) , are the distinctive distal manifestation of the hydrothermal systems. Similarly to Mina Central, white calcite veins cut all the other vein types in alteration zones closer to the sulfide orebodies, therefore they represent the distal or final exhausted hydrothermal fluids (Types 4 a - 4 c ) . In addition, white calcite veins can also be syntectonic veins (Type 4 d ) that predated the hydrothermal system. Table 3.8: Summary of the distal alteration characteristic of zone A in Cachi Cachi grid. DISTANCE FROM MAIN INTRUSION HOST ROCK 0 to 150m bleached marble mainly coarse-grained (1 to 2mm) to locally very coarse (>2mm) & medium-grained (0.5 to 1mm) saccharoidal crystalline bleached marble, locally with graphite traces. Pyrite dissemination j (<1 %) & traces common, dissemination locally greater (<5%) near main intrusive. Close to limit \ with zone B: coarse-grained with graphite traces, strong goethite, hematite veinlets & dissemination & locally pyrite traces. Locally as dissolution breccias. Bedding 084°/54°S (128m) i257subverticai, 015o-0207subvertical ! (143m) up to 4m wide stratum. 0757subvert, 0207subv (sp 6, 7, 12, 15cms) trending fractures ! (145m) 125772°S-subvertical, 0757subvertical & 0207subvertical trending fractures Gray marble (115m) very locally coarse-grained gray marble with pyrite traces (143m) halos of coarse-grained gray marble in bleached marble close to limit with zone B VEIN TYPES 1 A grossular (80m) yellow brown grossular traces in bleached marble, close to main intrusive j Cj calcsilicateipyrite (128m) light green or pale yellow calcsilicate-±pyrite veinlets/irregular lenses in white carbonate ! matrix/scab with diss pyrite (<1%) mainly along 125° trending fract in bleached marble. Dense or j diffuse network of veinlets (~60 to 10% of total volume of rock) & locally as <diss or traces 4j A dark gray 1 ! calcitcstpyrite i (128m) up to 5mm wide, coarse-grained late stage dark gray calcite-±pyrite(<l%) veinlets along j 015°-020° trending fractures in bleached marble. Veinlets cut irregular, sometimes undulately, calcsilicate veinlets B | light gray 1 (126m) up to 8mm wide, very coarse-grained late stage light gray calcite veins & veinlets with \ calcite±pyrite±MnOx j graphite traces, disseminated pyrite (<!%)& MnOx (1%) in bleached marble 1 i (128m) fine-grained light gray calcite veinlets & nodules of crystals with graphite traces & disseminated pyrite in bleached marble 1 C i white calcite±pyrite (145m) up to 2.5cm wide, coarse-grained late stage white calcite veinlets with <disseminated pyrite (<1%) mainly along 020° trending fracture seem to cut similar but irregular veinlets along i 075° trending fracture in bleached marble i i (145m) locally up to 10cm wide very coarse-grained white calcite veins & lenses with up to 12mm in size crystals & <diss py (<1%) along 125° trending fract & strings in bleached marble 75 Table 3.9: Summary of the distal alteration characteristic of zone B in Cachi Cachi grid. I DISTANCE FROM MAIN INTRUSION HOST ROCK limestone . 168 to 181m 205 to 298m 415 to 422m bleached marble O N gray marble VEIN TYPES 1! b! wollastonite very coarse grained, locally fine-grained (168m), crystalline bleached marble with abundant pyrite strings with disseminated jarosite(<l%) along 040° trending fractures. Average bedding/dip 078767°S 0307subvertical 040765°S, 155°-1607 75°-78°W, 105782°N (spacing: 10-20cm) trending fractures & 165775°-82°E trending dextral fault & fractures very coarse grained, locally fine grained (168m), crystalline gray marble with disseminated pyrite very coarse grained saccharoidal crystalline, with jarosite dissemination(<2%) & strings, to locally fine to medium grained bleached marble, locally enclosing texturally similar gray marble (20-30%) patches. Patches locally enclose bleached marble "veins" with disseminated pyrite(2%) (298m). Locally brown-grayish with abundant pyrite dissemination(3%) (257m). Average bedding/dip 085773°S 045° & 125785°NE, 140°-150782°NE, 070°, 020775°E & 105780°N trending fractures medium grained, to locally fine grained (205m), crystalline gray marble with pyrite dissemination & veinlets(l-3%) along 020775°E.trending fractures; locally with graphite traces, stylolites filled up with bitumen & texturally similar bleached marble patches (15-40%) (259m). Locally strongly fractured along 125° trending fracture (298m) 125°-130° & 140° trending fractures fine grained gray limestone interlayered with! bleached & gray marble & locally with halos; of bleached marble up to 0.90cm wide strata of saccharoidal \ very coarse-grained white, medium grained j It gy-browish & medium grained brown-yellowish bleached marble. Rock encloses gray marble (-30%) with disseminated goethite after pyrite in carbonate & MnOx veinlets along 020°. Goethite less abundant j along 040°, 055°, 125° & 150° trending fractures. Average bedding/dip 095772°S 040°-0557 65°N, 125° trending fractures 140°-150°&020° Fine-grained gray marble, locally enclosing bleached marble (10%) (422m) 125°-130° & 140°& 153° trending fractures green wollastonite crystals & swarm of veinlets in moderately silicified white carbonate (dolomite?) scab (flooding of veinlet wall) with disseminated pyrite (3%), along bedding, 045° & 125° trending fractures in bleached marble. Very similar swarm of veinlets in 415 & 422m grayish-light green wollastonite crystals & swarm of veinlets in moderately silicified i white carbonate (dolomite) scab (flooding of j veinlet wall) with disseminated pyrite(3%) along bedding, 125°-130° & 140° trending ; fractures. Locally with hematite & epidote spots in bleached marble (415m) & with j goethite dissemination(<l%) & boxwork with relictic pyrite in gray marble (422m). Very similar swarm of veinlets in 259m Table 3.9 (cont): Summary of the distal alteration characteristic of zone B in Cachi Cachi grid. DISTANCE F R O M MAIN INTRUSION VEIN TYPES 3i a calcsilicate±calcite ±pyrite calcsilicate±orange brown carbonate±calcite 168 to 181m (168m) up to 3mm wide calcsilicate±pyrite veinlets & lenses mainly along 130° trending fractures in white carbonate matrix/scab with disseminated pyrite in bleached marble 205 to 298m (205 to 254m) very dense network of wavy veinlets of weak-moderate silicified light gray calcite-diopsideipyrite (<1%) along bedding, 125° & 140° trending fractures in bleached marble orange brown carbonate±quartz±pyrite orange brown carbonate±calcite±quart z±pyrite±MnOx MnOxiorange brown carbonate±calcite±quart z±pyrite j (254m) calcsilicate traces in gray marble | moderate to poor (205m) dense network of orange j brown carbonate veinlets with abundant j calcsilicateicalcite along 125° & 150° trending I fractures (298m) in bleached marble j dense & poor networks of weathering resistant wavy | veinlets of orange brown carbonate-quartzipyrite I along bedding, 125°-128° & 140°-150° in gray I marble strata I (257-298m) very to poor dense networks of up to ] 6mm wide weathering resistant wavy veinlets of I orange brown carbonate-quartz-very coarse-grained calcite, with moderate disseminated goethite (traces-2%) & <hematite stains, along bedding, 125° & 150° trending fractures in gray marble strata. Veinlets locally with abundant pyrite(4-5%) & bleached marble halo (257m) dense networks of weathering resistant orange brown carbonate-quartz-pyrite(2-3%)-MnOx veinlets along bedding & 130° & 140°-150° trending fractures in gray marble strata 415 to 422m up to 8mm wide medium grained greenish-orange brown carbonate±pyrite (strong goethite) veinlets along bedding, 125°, 140c & 020° trending fractures in bleached marble; veinlets locally discontinuous (422m) & with white calcite halo (415m) moderate dense networks of up to 1cm wide weathering resistant MnOx-quartz-pyrite±calcite veinlets along bedding, 045° & 125° trending fractures. Locally up to 2.20cm wide lenses in top-last 30cm gray marble strata moderate to poor dense networks of weathering resistant wavy veinlets of orange brown carbonate-quartz-calcite±pyrite & locally flooding of veinlet wall along bedding, 130°, 140° & 153° trending fractures in gray marble & limestone; veinlets locally with bleached marble halos & filling stylolites (415m) dense network (60% of total rock volume) of up to 1mm wide weathering resistant wavy veinlets of orange brown carbonate-quartz-MnOx±pyrite along bedding, 125° & 140° trending fractures in gray marble (415m) poor developed network of MnOx-quartz-orange brown carbonate±pyrite strings & veinlets along bedding, 125° & 140° trending fractures in gray marble Table 3.9 (cont.): Sumrnary of the distal alteration characteristic of zone B. in Cachi Cachi grid. I DISTANCE FROM MAIN INTRUSION VEIN TYPE 168 to 181m 205 to 298m 415 to 422m bj MnOx±quartz±pyrite (415m) MnOx-quartz-pyrite veinlets & lenses along 040° & 020° trending fractures, locally with <goethite/hematite,<covelite stains dissemination in brown-yellowish bleached marble. Locally up to 5cm wide nodules & scattered veinlets along bedding, 055° & 150° trending fractures a | dark gray calciteipyrite (177m) up to 9mm wide very coarse grained (up to 6mm) crystalline late stage dark gray calcite veins & veinlets! mainly along 155°-160° trending fractures, sometimes wavy & locally with graphite traces & <disseminated pyrite in bleached & gray marbles (257,259m) up to 1mm wide gray calciteipyrite veinlets cut orange brown carbonate wavy veinlets in gray marble (257m) & sub-parallel veinlets along in 140°-150° trending fractures cut by very coarse grained light gray calcite±pyrite veinlets in bleached marble b! light gray calciteipyrite (168m) medium grained light gray calciteipyrite (<1%) veinlets, locally with bleached marble halos, along bedding & 105° trending fractures in gray marble. Veinlets irregularly cut wavy pyrite strings, similar but fine grained strings in bleached marble (205,254m) medium grained to very coarse grained light gray calcite±pyrite(<l%) veinlets along bedding, 125° & 140° trending fractures in bleached marble & gray marble (422m) light gray calcite pods in limestone c! white calciteipyrite (168m) up to 1mm wide white calciteipyrite (<1%) veinlets with dendritic psylomelane stains along 105° trending fracture & 165° trending dextral fault. Veinlets cut calcsilicate veinlets & lenses (205,254,298m) dense network of late stage coarse j grained brecciated crystalline white calcite veinlet, j locally patches & strings (254m), with graphite j traces along bedding, 125° & 140° trending fractures j in gray marble. Very coarse grained & up to 0.7cm j wide veinlets in bleached marble (257m, 298m) up to 1mm wide white calciteipyrite veinlets cut orange brown carbonate wavy veinlets in gray marble (259,298m) up to 8mm wide veinlets & up to 2cm wide pods of white calcite along bedding & fine grained calcite veinlets along 140°-150° in gray marble (415,422m) up to 8mm wide, nodules/lenses, veinlets & strings of brecciated white calcite with goethite dissemination & <jarosite in gray marble. Abundant strings in bleached marble (415m), gray marble & limestone (422m) (422m) white calcite-pyrite veinlet along bedding in gray marble d! white calcite (257,259m) fine grained white calcite syntectonic veinlets & discontinuous strings in gray marble (422m) up to lrhm wide white calcite syntectonic veinlets in gray marble Table 3.10.1: Summary of the distal alteration characteristic of zone A in Cachi Cachi regional. HOST ROCK bleached marble DISTANCE FROM MAIN INTRUSION 126 to 148m weakly to locally moderate (140m) silicified medium-grained bleached marble locally with disseminated pyrite, abundant jarosite, goethite, hematite spots (<1%), dendritic MnOx, pink smectite & epidote spots (136m) I gray marble 040°, 000°, 080782°S & 140° & 020°(t6) trending fracture (148m) up to 2.5m wide medium-grained crystalline gray marble strata. 125° & 140° trending fractures VEIN TYPES 1 c calcsilicate±pyrite±MnOx green lemon calcsilicate crystals, veinlets (sometimes diffuse) & nodules in moderate silicified white carbonate matrix/scab with pyrite veinlets (2%) & dissemination, along bedding, 000°, 140°, 020°(t6) trending fractures in bleached marble very dense network of calcsilicate±MnOx veinlets (30%) & nodules along 040° trending fracture in bleached marble 2 b orange brown I carbonate±calcite±quartz±pyrite: o r a " g e b r o w n carbonate-calcite±MnOx±quartz veinlets along 082° & very ±MnOx i l ° c a l ly along 040° & 080° trending fractures in bleached marble 41 c (148m) very dense network of calcite-orange brown carbonate-quartz±pyrite±MnOx along bedding, 125° & 140° trending fractures in gray j marble white calciteipyrite (148m) coarse-grained crystalline late stage white calcite (locally brecciated) veinlets with oxidized pyrite in gray marble Table 3.10.2: Summary of the distal alteration characteristic of zone B in Cachi Cachi regional. HOST ROCK limestone bleached marble gray marble DISTANCE FROM MAIN INTRUSION 172,300 to380m 400 to 453m fine-grained dark gray limestone, locally with Knox strings (440m) & locally interbedded with bleached (430m) & gray (450m) marbles 040787°S (fault), 125°- 130780°S, 170°-000°, 090°-095766°N, 140° (dextral fault), 070°, 020° (spacing: 20-25cm) & 110° trending fractures (172, 380m) locally moderate silicified (173m) fine-grained bleached marble (430 to 442m) very coarse-grained to locally medium-grained (430m) saccharoidal crystalline bleached marble with, locally abundant goethite & jarosite patines & dissemination (172,380m) 130°, 170°, 175° & 005780°E , 150°& 165°(t9) trending fractures (437,440m) up to 0.60cm wide, very coarse- j grained crystalline bleached marble lenses (10%) with abundant goethite (437m) & up to j 3cm wide very strong jarositic bleached marble "vein" along 120° (440m) in limestone j (172m) very coarse-grained, locally moderate silicified medium to fine-grained, crystalline gray marble with bleached marble (10%) patches, pyrite dissemination & veinlets(2%). (450,453m) coarse-grained to locally fine-grained gray marble with disseminated pyrite & abundant Knox strings filling stylolites & fractures. Interbedded with limestone (300, 380m) fine-grained gray marble with black pyrite strings along 130°, 150° & 110° trending fractures & interbedded with bleached marble (380m) 79 Table 3.10.2 (cont.): Summary of the distal alteration characteristic of zone B in Cachi Cachi regional. DISTANCE FROM MAIN INTRUSION i VEIN TYPES | 172, 300 to380m j 400 to 453m 1 a grossular (172m) It green to brown-yellowish grossular lenses (up to 13mm in size crystals) & veinlets along bedding, 170° & 150° trending fractures in moderate silicified bleached marble & up to 0.90mxl .60m in size lenses & scabs in gray marble c calcsilicate-calcite-pyrite (380m) swarms of calcite-calcsilicate-pyrite veinlets in bleached marble (400m) swarms of calcite-calcsilicate-pyrite veinlet, along 130°, 175° & 090° trending fractures, locally lenses with disseminated pyrite in gray marble 2 a orange brown carbonate±calcite±quartz (380m) up to 1.8m x 0.30cm of size, orange brown carbonate lenses & swarms of veinlets along 130°, 005780°E & 175° & 165°(t9) trending fractures in gray marble (442m) orange brown carbonate-calcite-quartz; veinlets along 140°, 070°, 020° cut by 055° in ; limestone i b 3 orange brown carbonate±calcite±MnOx (436m) up to 5mm wide, fine-grained orange j brown carbonate-light gray calcite±MnOx veinlets along 140° trending dextral fault in bleached marble ! -(442m) fine-grained orange brown carbonate-Knox along 020° trending fracture in bleached \ marble 3i : a 1 MnOx-orange brown carbonate±calcite±quartz (448m) Knox-orange brown carbonate vein along 130° in limestone \ (453m) up to 3cm wide black-greenish quartz- j Knox-orange brown carbonate veinlets & lenses with coarse-grained calcite crystals & veinlets along bedding, 140° & 170° trending i fractures in gray marble 41 b j light gray calcite±pyrite (173m) up to 2cm wide very coarse-grained (1cm) light gray crystalline calcite vein with up to 4mm disseminated pyrite crystal & goethite boxwork after pyrite in silicified bleached marble ' 1 c white calciteipyrite (172m) coarse-grained fibrous white calcite veinlets & lenses in gray marble with bleached marble (10%) (436m) up to 3 cm wide, very coarse-grained j brecciated white calcite vein with limestone fragments along 000° in limestone i i (173m) up to 2cm wide, late stage white calcite veinlets locally with epidote spots along 170° trending system in silicified gray marble (442m) very fine-grained banded colloform & j drussy white calcite veinlet along 020° trending fracture in bleached marble (448m) up to 8mm very coarse-grained late stage white calcite vein locally with graphite | specs, along 170°, cuts slightly sinistrally Knox-orange brown carbonate vein in limestone j i. (450m) coarse-grained white calcite veinlets along 020° trending fracture in limestone i (453m) coarse-grained calcite crystals & veinlets in quartz-Knox-orange brown carbonate lenses in gray marble ! j d white calcite (442m) up to 1.6cm, very coarse-grained white calcite syntectonic vein mainly along 040° & 005° in limestone 80 Table 3.10.3: Summary of the distal alteration characteristic of zone C in Cachi Cachi regional. I DISTANCE FROM MAIN INTRUSION HOST ROCK j 516 to 613m j 700,790m limestone I fine to very fine (516,606,613m) grained dark . , .. ••. ,• I , ,, 1 u J n i (790m) fine-grained gray limestone, : gray limestone, locally with abundant MnOx , ,, u • * J j strings (535, 606, 613m) locally brecc.ated I f l n e - 8 r a i n e d l i m e s t o n e l o c a l | y w i t h M n ° x ! 130°, 000° & 170° trending fractures j strings I 040°/subvertical, 120768°S & 130°/subvertical, j 000° (spacing: 23cm), 095°, 140° & 020° trending | | fracture cut by 115° trending sinistral fault bleached marble \ \ (700m) coarse-grained (1.5mm) | • i saccharoidal crystalline bleached marble j I with MnOx (1-2%) strings & jarosite .1 spots ! 177°/84°W trending fractures parallel to | . ' i regional fault gray marble i (700m) locally, up to 8cm wide, coarse (1.5mm) to very coarse-grained (>2mm) i \ (606-608m) fine-grained gray marble locally with j saccharoidal crystalline brown to gray I boxwork of goethite after pyrite (606m). (608m) i marble "veins" with graphite traces, white I I 051738°N trending fracture | calcite crystals & MnOx (1-2%) spots : along 177° trending fractures in bleached j | \ marble VEIN TYPES 2 a orange brown j (586m) orange brown carbonate veinlets along 040° i carbonate | & 130° & 095° trending fractures in limestone ! (606m) orange brown carbonate veinlets with white \ I calcite halo in limestone • ! b orange brown I V, , , . , , . ! (790m) orange brown carbonate-, " ^ , . , j (516m) banded calcite-orange brown carbonate- i v . .. - f , . . . . . „ : carbonate±calcite± i v „ , 1 1 £ - 0 i calcite±MnOx±quartz veinlets, locally ^ , » « / - v i quartz±MnOx lenses & veinlets along 115° . . . . , , n 0 m o , n n o quartz±MnOx : ,• . . i brecciated, along 130°, 000° & 170° i- trending fracture in limestone I ; . • j . i trending fractures in limestone I (608m) orange brown carbonate±MnOx veinlets in j gray marble 31 a | MnOx-orange (535m) diffuse & poorly developed network of j brown \ MnOx-orange brown carbonate veinlets along j carbonate±calcite± j bedding & 140° trending fracture in limestone i quartzipyrite !••- I-i (606m) weathering resistant MnOx-orange brown ! carbonate-quartz-calcite-<galena-±pyrite veinlets & j I very poorly developed network of MnOx-orange ! brown carbonate veinlets in gray marble (613m) weathering resistant MnOx-quartz irregular I veinlets with banded calcite along 120° trending | fracture cutting orange brown carbonate-quartz-i calcite strings in limestone 81 Table 3.10.3 (cont.): Summary of the distal alteration characteristic of zone C in Cachi Cachi regional. DISTANCE FROM MAIN INTRUSION VEIN TYPES light gray calcite veinlets i white | calciteipyrite i veinlets 516 to 613m (516m) very coarse-grained light gray crystalline calcite sub-parallel veinlets in limestone (535m) up to 1.5cm wide very coarse-grained crystalline white calcite irregular & discontinuous veinlets with goethite & graphite traces along bedding + white calcite veinlets along 000° & strings along bedding & 140° trending fracture in limestone (606m) up to 5mm wide, very coarse-grained crystalline white calcite veinlets with disseminated galena & malachite stains irregularly cut & dextrally moved by medium-grained white calcite (locally brecciated) & orange brown carbonate veinlets with white calcite halo in limestone (608m) 5mm wide, very coarse-grained crystalline white calcite veinlets with brown garnet inclusions & disseminated pyrite, galena, covelite & malachite stains along 051°/38°N trending fracture cutting orange brown carbonate wavy veinlets in gray marble 700,790m (790m) coarse-grained crystalline late stage white calcite veinlets in limestone 3.5. Paragenesis of Distal Veins at M i n a Central and Cachi Cachi Cross-cutting relations indicate at least a three-stage chronology o f veining at M i n a Central (Table 3.11) and at least four-stage chronology of veining at Cachi Cachi (Table 3.12). Pre-to syn-tectonic calcite veins predate mineralization, and represent a fifth vein stage that is unrelated. In general, vein Type 1 is oldest, vein Types 2 and 3 mutually cross cut each other and represent an intermediate stage both temporally and distally. V e i n Types 4a-4c cut all other type veins throughout alteration zones at M i n a Central and Cachi Cachi and are also found the most distal from the sulfide orebodies (Fig. 3.11). Ve in Type 1 are controlled by the regional fracture mesh that dominates the fold and thrust belt in the region (Fig 3.12), where as the younger vein types become more random, reflecting fracturing o f the thermal aureole during hydrothermal circulation. Ve in Type 1 does not occur in M i n a Central. In a local scale, cross-cutting relationship among distal veins filling fracture meshes are quite complex. In general at M i n a Central, the youngest E-striking structures are consecutively cut by N -striking, NW-striking, and by the oldest NE-stxiking structures (Table 3.11). 82 Table 3.11: Paragenetic and cross-cutting relationships among the distal alteration vein types in Mina Central. TIMING STRIKE j VARIATION VEINS, VEINLETS & LENSES TYPES j N E - S W L A T E 035°-070° 4c I white calcite (late-stage) i N W - S E I N T E R M E D I A T E 110°-160° 3c M n O x 2^ pervasive MnOx-orange brown ! carbonate 2 a \ MnOx-orange brown carbonate±white | calcite N-S j • 170°-020° 2b | orange brown carbonate±quartz±MnOx 1 E - W i E A R L Y 080°-095° 2 a orange brown carbonate±white 1 calcite±quartz A t Cachi Cachi, cross-cutting relationship among distal veins fill ing fracture meshes are more complex than in M i n a Central, due to the complex overlapping structural history of the district. Detailed field mapping defined four sets of structures on terms of timing (Table 3.12). Table 3.12: Paragenetic and cross-cutting relationships among the distal alteration vein types in Cachi Cachi. I TIMING STRIKE VARIATION VEINS, VEINLETS & LENSES TYPES 1 N W - S E L A T Q 165°-110° 4 white calci te±pyri te±MnOx ! E S E - W N W I N T E R M E D I A T E 105°-110° 3 MnOx±calcite±quartz±pyrite ! N N E - S S W - 015°-020° ; MnOx±orange brown j carbonate±calcite±quartz±pyrite { N E - S W 070°-075° 2 | orange brown carbonate±calcite±quartz±pyrite 1 N W - S E E A R L Y 140°-150° 1 calcsil icate, grossular, wollastonite, orange brown carbonate±quartz±pyrite | E - W 085°-095° grossular, wollastonite, calcsil icate, \ orange brown carbonate±quartz±pyrite j N -S 170°-005° | grossular, wollastonite, ; calcsilicate±quartz±pyrite 1 N W - S E 125°-130° 1 wollastonite, calcsilicate±quartz±pyrite 1 N E - S W 040°-055° wollastonite, calcsilicate±quartz±pyrite 83 Figure 3.11: Cross-cutting relationships among vein types at Yauricocha, central Peru, a, b) Mn-rich orange brown carbonate veins (type 3) along 020° and 110° trending fractures cutting wavy networks of orange brown carbonate (type 2) veinlets in dark gray fine-grained limestone at Mina Central (Sample site 252233). c, d) Up to 9 mm wide, very coarse-grained, late-stage, dark and white calcite veins (type 4a-c) along 155°-170° trending fractures cutting orange brown carbonate (type 2) swarm of veinlets in bleached marble and unaltered fine-grained limestones at zones B and C in Cachi Cachi (Sample sites 246425 and 246496, respectively), e) Pre- to syntectonic calcite (type 4d) veinlets formed during regional deformation are cut by orange brown carbonate (type 2) veinlets in dark gray fine-grained limestone. They are not related to the mineralization or alteration. They occur largely in zone C. 8 4 Cachi Cachi Mina Central Type 1 ? 180 180 Figure 3.12: Rose diagrams showing the orientation by vein types at Mina Central and Cachi Cachi, Yauricocha, central Peru. 85 3.6. Bu lk Chemical Analysis at M i n a Central and Cachi Cachi 3.6.1. Trace Element Geochemistry A total of 109 rock and vein chip samples from M i n a Central and Cachi Cachi were analyzed for trace elements. Samples were collected over a traverse of approximately 800 m W of the intrusive contact with the mineralized zones and host carbonate rocks. One samples o f unaltered limestone from the Jumasha Formation taken at Purisima Conception (approximately 800 m west o f M i n a Central pit) was also analysed to characterize background values for the district. Chip samples were prepared and analyzed for trace element geochemistry at A L S Chemex. Sample preparation was conducted at their facilities in Lima, and all the geochemical analyses were completed at the A L S Chemex laboratory in North Vancouver, B . C . Detailed description of the analyses, range of values, experimental methods, descriptive and correlation tables and representative graphs showing geochemical results are included in Appendices D and D1-D4. The purpose of the study was to define an elemental distribution that reflects the alteration and vein-types identified in the field. A s such, examination of the elements is in context of their distance from the intrusive contact. Trace element data therefore focuses on alteration halos within transects and sampling localities. Alteration halos are generally defined by a combination of trace element abundances significantly in excess of background values with visually calculated threshold values (Table 3.13). Representative elemental graphs illustrating the major conclusions to be drawn from the data are shown herein (Figs. 3.13 and 3.14). In this study, A u , A g , A s , Ba , B i , C d , C u , Hg , In, M n , M o , Pb, Sb, T l , W and Z n define halos around the hydrothermal orebodies at M i n a Central and Cachi Cachi (see also Rose etal . , 1979). Threshold values were both statistically and visually calculated. They were statistically calculated using the mean and the standard deviation values for sets of type o f samples following Govett (1983) (Appendices D2.1 and D3.1) (Table 3.13), and visually examining the statistic threshold values, without taking in account high erratic values (Appendices D2.3 and D3.3), with accepted thresholds values used in exploration. The last section of the table lists the thresholds values, which in combination with trace element abundances significantly in excess o f background values, used for halo definition. 86 Table 3.13: Threshold values for defining trace elements alteration halos. Statistically calculated (MEAN + 2STDEV; Govett, 1983) Mina Central Element Threshold (pp m) Element Threshold (ppm) Element Threshold (ppm) Element Threshold (ppm) Host rocks Au 0.07 Ag 3.8 As 590.1 Ba 513.71 Bi 0.47 Cd 6.04 Cu 67.41 Hg 0.64 In 0.14 Mn 8726.51 Mo 16.38 Pb 803.71 Sb 23.13 Tl 18.6 W 4.95 Zn 1078.27 Vein types Au 0.93 Ag 126.25 As 3956.23 Ba 4831.71 Bi 6.56 Cd 114.77 Cu 1144.87 Hg 2.06 In 9.8 Mn 17139.51 Mo 40.84 Pb 6513.99 Sb 598.91 Tl 135.88 W 90.28 Zn 65638.2 Cachi Cachi Element Threshold (ppm) Element Threshold (ppm) Element Threshold (ppm) Element Threshold (ppm) Host rocks Au 0.005 Ag 0.27 As, 868.16 Ba 898.85 Bi 0.74 Cd 1.89 Cu 22.9 Hg 0.03 In 0.04 Mn 4664.55 Mo 11.66 Pb 153.91 Sb 5.36 Tl 16.92 W 23.19 Zn 296.12 Vein types Au 0.09 Ag 28.82 As 567.49 Ba 2327.9 Bi 11.7 Cd 20.05 Cu 201.64 Hg 0.35 In 0.12 Mn 7138.83 Mo 19.42 Pb 842.85 Sb 47.22 Tl 183.67 W 4.86 Zn 5791.74 Visually calculated Element Threshold (ppm) Element Threshold (ppm) Element Threshold (ppm) Element Threshold (ppm) Au 0.01 Ag 0.2 As 20 Ba 150 Bi 0.2 Cd 1 Cu 15 Hg 0.02 In 0.03 Mn 400 Mo 2 Pb 30 Sb 2 T l ' 2 W 1 Zn 50 On a district-scale basis, polymetallic replacement deposits commonly are zoned outward from a Cu-rich central zone though a wide Pb -Ag zone, to a Zn- and Mn-fringe. Local ly A u , A g , A s , B i , Sb, and Te, are also enriched. Jasperoid, i f present, may be related to high B a and trace A g content. These elements plus Be, Co, Sn, and W may be present proximal to Zn-Pb skarn deposits (Govett, 1983; Morris, 1986). In Cu-rich deposits, metals are also vertically zoned, so that M o and Co may have their highest concentrations and widest halos along the fluid channels beneath the deposit. Copper w i l l have the widest halo at the level of the deposit, Z n and Pb just above the deposit, and A s , Sb, and B a completely above the deposits. In many districts Te appears to mark zone many hundred of meters above productive Pb-Zn deposits. Similarly high values of Cd , Hg , and M n are also indicative of ore at depth (Rose et al., 1979) 87 Table 3.14: Distribution of anomalous elements in the bleached/gray marble in the distal veins at Mina Central and Cachi Cachi. See Table 3.3 for vein types. Chemical data is presented in the Appendices D1-D3. W, weak; M , moderate; and S, strong. Bleached/gray marble Mina Central Vein type 2 Vein type 3 i Zones A 1 B ; c A i B ; c [ A B ' c i Zn s M j - s 1 • s M | S s M ! Pb w W S S M 1 s s W As w M s s S s s S i B i - ' ; ' - ! - 1 - 1 - i - 1 - 1 ! Ba - - - - - w s ~ 1 Mn s M s s M i s s s Sb w M s s M j s s s ! Tl w - M | w | •- M s s 1 A g | - - s M I W | S s M \u w - s M w 1 s s S Cu - ' I - M W w i - w W \ Mo | - • - 1 W i - w ' - -Hg - ]. - 1 - - M | M s M s Cd - - - w j - w - -i w _ - - M | _ _ _ Cachi Cachi I Vein type 2 Mo Bleached/gray marble Vein type 1 Vein type 3 Vein type 4 i Zones! A | B C A ; B c A B c A B ! c A B C i / n s I S - s i s' i - - - s - s w • - - ! I'b - - - W 1 s i - - s ! - - w - -As w ! S - s 1 s ! - - s i s - ! s s W j - - i Bi - s i s I - s ! - | - 1 • -1 - j - I - i - - 1 | Ba - - * - j - ; - - - - - - - -; Mn W ! - S w 1 - - - - s -- - s - - - ! i ' ' Sb w w - w ! i W - - - w - - s - -: Tl - w [ A g _]_ - - - - i - s - - s - - " 1 A u - - - w | w - - w I w S 1 s Cu - ! W j - - - I w ! w - - | - - i - . i - ! Hg - ! - I Cd - ; - i W: weak anomaly M : moderate anomaly S: strong anomaly w w w W 88 The best way to visualize the distribution of elements is through examining the element distribution with respect to bleaching and recrystallization of the limestone to marble and by vein type (Table 3.14). W (weak), M (moderate), and S (strong) symbols in table 3.14 are referred to levels of anomaly for each element (i.e., Zn: W [50-100 ppm], M [100-200 ppm], and S [>200 ppm]). The bleached rocks represent pervasive fluid flow, and the rocks wilfhave interacted completely with the hydrothermal fluid. Examination of these rocks w i l l be by the alteration zones. The veins and veinlet swarms represent the fluid escape, and their mineralogy obviously represents very different physiochemical conditions of formation. Zinc±arsenic are enriched in rocks near the intrusive contact in zone A at Cachi Cachi and M i n a Central. Zinc decreases toward the edge of bleached marble in Cachi Cachi and to the edge of bleached marble versus gray marble in M i n a Central, defining a 150 m wide halo at Cachi Cachi and a 400 m wide halo at M i n a Central. Zinc (<100 ppm) and A s (>50 ppm) are also elevated almost up to 650 m distal from the intrusive contact in zone B at both localities. Furthermore, up to 700m away from the intrusive in zone C at Cachi Cachi, Z n is also elevated (Figs 3.13a, 3.13c, 3.14a, and 3.14c). In rocks, M n defines very similar but broader halo at both deposits, where it is enriched in zones A and B . Manganese decreases toward the outer limits of both zones, defining a 400 m wide subtle halo in Cachi Cachi and a 650 m wide notable halo at M i n a Central. Similarly to Zn , M n also is elevated 700 m distal from the intrusive contact in zone C at Cachi Cachi (Figs 3.13e and 3.14e). Antimony (Figs 3.13g and 3.14g) and locally T l and A u accompany the base metals in the rocks, and are strongest near the sulfide orebodies at both localities. Weakly anomalous Pb is also present at M i n a Central. In summary at Cachi Cachi, bleached marble nearest the intrusion in zone A . i s enriched in Z n with weakly anomalous A s , M n , and Sb. In zone B , the bleached marble is enriched in Z n and A s , with weakly anomalous Sb and T l . In zone C , only M n shows any strong enrichment. A similar pattern is evident at M i n a Central, where Z n and M n are enriched in zone A with weakly anomalous Pb, A s , Sb, T l , and A u . In zone B , the bleached marble is only moderately enriched in Zn , A s , M n , and Sb and weakly enriched in Pb. N o element is enriched in the rocks of zone C at M i n a Central. In vein Types 1-3 at both mineralized centres, Z n and A s are also enriched in zone A , close to the intrusive, and well into zone B , decreasing from the intrusive contact. They define a 300 m wide halo at Cachi Cachi and at least a 530 m wide halo at M i n a Central. Furthermore, up to 800 m distal from the intrusive contact in zone C at Cachi Cachi and M i n a Central, Z n and A s are also elevated (>100 ppm). Zinc and A s are more enriched in vein Types 2 and 3 than in vein 89 Type 1 (Figs 3.13b, 3.13d, 3.14b, and 3.14d). A 300 m wide halo of enriched M n and Sb are defined by vein Type 1 at Cachi Cachi and at least a 530 m wide halo defined by vein Types 2 and 3 at M i n a Central; in general their abundance decreases away from the intrusive contact in zones A and B . Manganese (>800 pmm) and Sb (>10 ppm) are also elevated toward zone C in both localities. A t M i n a Central, the M n halo is probably larger than 530 m, because M n values exceed the upper limit of detection limit; therefore the M n trend was not completely constrained (Figs 3.13f, 3.13h, 3.14f, and 3.14h). In summary, the high temperature Type 1 veins, where present, are anomalous in Zn-Pb-As-B i and weakly anomalous in Mn-Sb-Au±Cu-Cd. The Type 2 carbonate and Type 3 Mn-r ich veins are rich in Zn-Pb-As-Mn-Sb. Around M i n a Central, the Type 3 veins carry strongly anomalous values of As -Mn-Sb-T l -Au-Ba and moderate to weakly anomalous Pb-Ag-Cu-Hg in zone B , more than 400 meters from the intrusive contact and sulfide orebodies. A t Cachi Cachi, Type 2 orange brown carbonate veins in Zone A near the intrusion are strongly anomalous in B i but in Zone C are depleted in B i but strongly anomalous in Z n - P b - A g - A s - M n and weakly anomalous in Sb-Au-Cu-Hg-Cd. Type 3 Mn-r ich veins at Cachi Cachi show a similar distribution of elements. Late Type 4 calcite veins only contain weakly anomalous Z n -Pb-As where found in Zone A at Cachi Cachi near to the skarn and intrusive contact (Figs 3.13 and 3.14). In conclusion, combining the two mineralized centers, Zinc±As is enriched in the rocks nearest the intrusion with M n forming a strong dispersion halo on the distal fringes. The remainder of the "epithermal" suite of Sb-Tl±Au accompanies the base metal in the rocks and is strongest near the sulfide orebodies (Figs 3.13 and 3.14). The veins present a comparable elemental halo that is much more systematic and indicative of an evolving hydrothermal fluid with ±Au±As±Bi±Cd±Hg±Sb, and ±T1 accompany Zn±Pb±Ag±Cu±Mn in veins strongly near sulfides orebodies 90 | eg' 0 o s- W •—I ^ S o 3 o 1 o 5 N he] 3 o ^ to a* § " > — CA 5 3 3 SB g * Cachi Cachi ro 05 5.5 o j? 3 3 a . o Zone C Zone B Zone A a • Rocks - Zn D • . • tj • x • • 11 • Bleached marble • Gray marble X Limestone A Limestone (background) i • B • • m )0 700 600 500 distance Zone C 400 300 200 from intrusive (m) Zone B 100 0 Halo Zone A c • Rocks - As 1 r"X~~" T l • Bleached marble • Gray marble A X Limestone A Limestone (background) i 1000 100 10 E a a 10000 1000 100 10 1 800 700 600 500 400 300 200 distance from intrusive (m) 100 Zone C Zone B Zone A b Veins - Zn t + • Vein types A la. lb 4-3 • Ic X 4 ^ 2 A Limestor 4 t (oackground) X X Threshold 100000 10000 1000 100 10 1 E a a 800 700 600 500 400 300 distance from intrusive (m) 200 100 Halo ZoneC Zone B Zone A d Veins - As • w 0 X * 0 t JL tot Vein types 0 A la. lb 4 3 • lc X 4 ^ ^ A Limestone ( o • • wckground) • Threshold i i i X 10000 1000 100 10 1 800 700 600 500 400 300 200 100 distance from intrusive (m) < C D CD C D CD CD C D CD CD CD i u d d CD C D C D u i d d Zone A Veins - Mn • _ _ i*t5 Threshold *> CO o 1 (punoj (backjji o Limestone] u -t + < 0 j + x Zone 0 Vein ty; o ro O C D O CD O CNI CD C O 8 1 C D C D in C D o o CD CO C D O O C D C D C D .O C D CD CJ 1+ •*> .•.44.. X X j | !+x s F I bf .S.s C D O O C D C D O C O C D C D O O L O CD CD C O C D C D r— C D C D C O E o o d ra O ro O u i d d i u d d u 0) c o 0 2 u £ I f : oa o -J 'JJ o o o CD eg CD CD CO C D C D C D o C D O C O O o X 8 c <2 JD o o or O) 1* I i l l ! u g E E CO tS 'j J O x 4 CD CD CO CD O CD CD CO CD CD r— C D CD CO E o c TO Figure 3.13 (cont.): Distribution of Zn (a, b), As (c. d), M n (e, f) and Sb (g, h) laterally from intrusive contact with the host Jumasha Formation limestone at Cachi Cachi, Yauricocha, central Peru. 92 8 a ja s 0 ri (-»• I? 2 §-§. OB g-5 O to O - r » ) £ N 0 1 3 3 /—s I c r 5 ^ 3 > I" a o to • o o> s i II IS g era Q o E-a ^  % 3 3 B-Mina Central Zone C Zone B Zone A a Rocks - Zn • • • • • • • • • • Bleached, marble • Grey mafble • Limestone • Limestone (regional) — Threshold 10000 1000 loo EL 10 750 Zone C 650 550 450 350 distance from intrusive (m) 250 Halo 150 Zone B ® Bleached marble • Grey mafble • • Limestoije • Limestone (regional) Threshold Zone A Rocks - As 1000 100 p. c 10 750 650 550 450 350 distance from intrusive (m) 250 150 ZoneC Zone B Zone A b o Veins - Zn + + X o o + o X 4 < ° + 0 < o Vein types A Limestone O -a + ia (regional; O 2b X 3b t—• i — • , , — Threshold 750 650 550 450 350 250 distance from intrusive (m) Halo 750 650 550 450 350 distance from intrusive (m) 250 1000000 100000 10000 1000 | 100 10 150 Zone C Zone B Zone A d • X o o o Veins - As x + + + + + + X + o o + X k A Lime (regie Vein types tone O 2a + 3a nai) O 2b X 3b Threshold 10000 1000 ioo i . 10 150 < a B' a < o o 3 _ S3 O o o •a ~ I-s § 3 o CO. - , ps a I' > 3 CO f ^  i 3 g i t B O pj CT p. o> cr i i (a gL O ^ 3 3s q o — — • Bleachei • Grey ma • Limesto • Limesto marble © rble le (regional) Rocks- Mn • • • • • * • i Threshold 750 650 Mina Central 100000 10000 1000 100 550 450 " 350 distance from intrusive (m) 250 Halo 150 Zone C i Zone B Zone A 9 • • _ Rocks - Sb • • 1 • • • • • Bleached tnarble • • Grey marble • Limestone • Limestone! (regional) Threshold • 100 B a. 0.1 750 650 550 450 350 distance from intrusive (m) 250 150 Zone C i Zone B Zone A f * ; ++ O X + + ! Veins - Mn + ++ cm- x x • 1 O O ; • ; o • 0 0 t-o o o Vein types A Limestonl (regional! k O 2b X 3b 750 650 550 450 350 250 15 distance from intrusive (m) Halo Zone C Zone B Zone A h Y Veins - Sb H O 1 o + + * 1 x — o i o ! + X + | J&o ° L i * * 1 ? c x o [ A Limestone (regional) Vein types | O 2a + 3a j O 2b X 3b 100000 10000 D. 1000 100 10000 1000 100 10 B c c 0.1 750 650 550 450 350 distance from intrusive (m) 250 150 3.6.1.1. Correlation Coefficients Statistical correlation among 49 elements was evaluated for M i n a Central (Appendices D2.1-D2.3) and Cachi Cachi (Appendices D3.1-D3.3). Tables 3.15 and 3.16 show the range of values and correlations for 16 elements typically used in the exploration for base metal deposits. In host rocks at M i n a Central, A g has good correlation (>0.7) with Cd , M n , W , and Z n and moderate correlation (0.5-0.7) with A u , A s , and Ba; whereas at Cachi Cachi, it displays good correlation only with M o and moderate correlation with N i and Pb. In both zones, no correlation with C u has been observed because of its low abundance. A t M i n a Central, A g do not correlates with Pb. Arsenic has a good correlation with M n and W at M i n a Central, strong correlation with W and Zn, and moderate correlation with Cu , N i , and Te at Cachi Cachi. Copper presents a good correlation with C d and Co, moderate correlation with A s , Fe, T l , W , and Z n at Cachi Cachi. In general, most of the base metal element suite correlates in both zones, especially A g , A l , A s , Cr, B i , M n , W , Z n and M o , N i , Pb, and moderately C u in Cachi Cachi. L o w values of A u have a good to moderate correlation with the "epithermal" suite o f elements in host rocks, especially Ba , Hg , In, and T l at M i n a Central and with C d , Sb, Te and T l in Cachi Cachi. Similarly to the case of the base metal element suite, the "epithermal" element suite also has a general good correlation with the other elements. L o w correlation values found between the base metal element suite with Hg , Sb, and T l at M i n a Central are l ikely related to the depth of the system because these elements are mainly associated with the suite of "epithermal" mineral deposits. In contrast, low to relatively moderate correlation of the base metal element suite with some "epithermal" element suite like Ba , Hg , and Sb at Cachi Cachi l ikely indicate a deeper origin for skarn orebodies formation, relative to the carbonate-hosted replacements ores at M i n a Central. These metal relationships are consistent with medium to high temperature for mineral deposition at the Yauricocha district. In vein types at M i n a Central and Cachi Cachi, practically the entire base metal element suite (Ag, A s , Be, B i , Cr, C u , M o , N i , Pb, Sn, W , Zn, and U ) presents a very consistent good to moderate correlation with each other. Moreover, the base metal element suite has a low to moderate correlation with A u , Ba , Cd , Hg , In, M n , Hg , Sb, and T l . Clearly, the statistical correlation values between trace elements for vein types at the Yauricocha district establish a genetic association of the distal vein types with the orebodies at depth. The general moderate correlation among the "epithermal" element suite likely represents a later and shallower influence in the composition of the vein types. 95 Table 3.15.1: Mina Central trace element correlation (host rocks and vein types). Element Range Background High correlation Moderate correlation ppm ppm >0.7 0.5-0.7 HOST ROCKS Au 0.0025-0.087 0.0025 Ba, Hg, In, Tl Ag, Ga, K, Mn, Rb, Sn, Th, W, Zn, Zr Ag 0.01-4.96 0.001 Cd, Mn, W, Zn Au, As, Ba As 2.5-937 2.5 Mn, W Ag Ba 31.5-520 37.5 Au, Bi, Ce, Ga, Ge, In, K, La, Rb, Ta, Ag, Al , Be, Co, Cr, Fe, Hf, Hg, Li , Mn, Th Nb, Ni, Sn, Ti, Tl, V, W, Y, Zn, Zr Moderate to high negative correlation (<-0.5) with Ca Bi 0.005-0.57 0.02 Al , Ba, Be, Ce, Co, Cr, Cs, Fe, Ga, Ge, In, Se, U Hf, K, La, Li , Na, Nb, Ni, Rb, Sn, Ta, Th, Ti, V, Y, Zr Moderate to high negative correlation (<-0.5) with Ca Cd 0.1-8.21 0.02 Ag, Pb, Zn Mn Cu 3.2-92.1 3.6 Hg 0.005-1.03 0.005 Au, In, Tl Ba, Cr, Ga, Hf, Ni, Rb, Sn, Ta, Th, V, Y, 7-. In 0.0025-0.182 0.0025 Au, Ba, Ce, Ga, Ge, Hf, Hg, K, Nb, Ni, Al , Be, Bi, Co, Cr, Fe, La, Ti, W Rb, Sn, Ta, Th, T l , , V, Y, Zr V Moderate to high negative correlation (<-0.5) with Ca Mn 249-> 12000 130 Ag, As, W, Zn Au, Ba, Cd Mo 0.05-25.2 0.4 Co, Cs, Ge, K, Na Pb 2.5-1265 3.5 Cd Mg Sb 0.45-33.1 0.8 Tl 0.22-29.2 0.76 Au, Hg, In, Rb, Sn, Th, V, Zr Al , Ba, Be, Ce, Co, Cr, Ga, Hf, K, La, Nb, Ni, Ta, Ti, Y W 0.05-7.2 0.3 Ag, As, Mn Au, Ba, In, Zn Zn 34-1590 1 Ag, Cd, Mn Au, Ba, W VEIN TYPES Au 0.0025-2.14 0.0025 Ba, Cs, Ga, Re, Sr, U Ag 0.21-261 0.001 Cu, Li Bi, Cr, Sb As 81-5320 .2.5 Be Ba 50-7750 37.5 Au, Na, Re, Sr Bi 0.04-15.85 0.02 Mg, S, Sn, Te Ag, Al . L i , Na, Pb, Ti Cd 0.17-223 0.02 Y, Zn Ce, Fe Moderate to high negative correlation (<-0.5) with Ca Cu 4-2780 3.6 Ag, Sb Cr, Li Hg 0.03-2.88 0.005 Na, Te In 0.008-24.2 0.0025 V Fe, Ga, Hf, Re Mn 1085-> 12000 130 Mo 0.27-60.3 0.4 Co, Ni, Tl Pb 21.1-9340 3.5 Bi, Ga, Mg, S, Sn, Ti Sb 4.24-1100 0.8 Cr, Cu Ag. Li Tl 0.73-254 0.76 Co, Mo, Ni W 0.1-150.5 0.3 Zn 182-153500 1 Cd Ce, Fe, Ge, U Moderate to high negative correlation (<-0.5) with Ca 96 Table 3.15.2: Mina Central trace element correlation (vein Types 2 and 3). Element Range Background High correlation Moderate correlation ppm ppm >0.7 0.5-0.7 VEIN TYPE 2 Au 0.0025-0.209 0.0025 Ag, Bi, Cu, In, Pb Hg. L i , Mg, Na, S, Sn, Te, V Ag 0.21-147 0.001 Au, Bi, Ga, Hg, In, Li , Mg, Na, Pb, S, Al . Cr. Cu, Hf, K, La, Nb, Se, Th Sn,Te,Ti,V As 113-5160 2.5 Be W Moderate to high negative correlation (<-0.5) with La Ba 50-1260 37.5 Cs Co, Ni, P, Ta, Tl Bi 0.07-15.85 0.02 Au, Ag, Ga, Hg, In, Li, Mg, Na, Pb, S, Al , Cr, Hf, K, La, Nb, Se Sn, Te, Th, Ti, V Cd 0.17-223 0.02 Ce, Cr, Fe, Se, U, Y, Zn Ge, Mn Moderate to high negative correlation (<-0.5) with Ca Cu 7.2-651 3.6 Au Ag, Pb Hg 0.03-2.71 0.005 Ag, Bi, Cr, Ga, In, Li , Mg, Na, Pb, S, Au, A l , Ce, La, Mn, Nb, Th Se, Sn, Te, Ti, V In 0.024-5.96 0.0025 Au, Ag, Bi, Ga, Hg, Li , Mg, Na, Pb, Al , Cr, Hf, K, La, Nb, Se S, Sn, Te, Th, Ti, V Mn 1085-> 12000 130 Ga, Se Cd, Ce, Co, Cr, Hg, Li , Na, Nb, Ni, S, Sn, Ta, Ti, Tl, U, Y, Zn Moderate to high negative correlation (<-0.5) with Ca Mo 2.05-60.3 0.4 Ta, Tl Co.Ni.Sr Pb 35-9340 3.5 Au. Ag, Bi, Ga, Hg, In, Li , Mg, Na, S, Cu, Se, Te, Ti, V Sn Sb 4.24-475 0.8 Tl 1.62-254 0.76 Co, Mo, Ni, Sr, Ta Ba, Mn W 0.1-150.5 0.3 Be As, Re Zn 182-153500 1 Cd, Ce, Cr, Fe, Ge, Se, U, Y Mn Moderate to high negative correlation (<-0.5) with Ca VEIN TYPE 3 Au 0.015-2.14 0.0025 As, Sr Ba, Cs, Na, Re, U Moderate to high negative correlation (<-0.5) with Ca Ag 0.87-261 0,001 Bi, Cu, Sb Cr, Li As 81-5320 2.5 Au,Ba, Na, Sr Cs, Re, U, Zn Ba 80-7750 37.5 As, Na, Sr Au, Re, Zn Bi 0.04-3.78 0.02 Ag, Cu, Sb Cr .L i Cd 0.81-71.3 0.02 Pb Ga, Na, Ta, W, Zn Cu 4-2780 3.6 Ag, Bi, L i , Sb Cr Hg 0.04-2.88. 0.005 Re,Te In 0.008-24.2 0.0025 Fe, V Ga, Ge, Hf, Re, Tl, U Moderate to high negative correlation (<-0.5) with Ca, Mn Mn 3810->12000 130 Moderate to high negative correlation (<-0.5) with Fe, Ga, In, Re, Tl. V Mo 0.27-51.3 0.4 Se, Zn Co, Ni, U Pb 21.1-7090 3.5 Cd Fe, Ga, Ge, Ta, Th, Ti, W Sb 4.33-1100 0.8 Ag,Bi ,Cr ,Cu Li Tl 0.73-139 . 0.76 Fe, In, Se, U, V Moderate to high negative correlation (<-0.5) with Ca, Mn W 0.3-7.8 0.3 Cd, Ni, Pb, Rb, Ta Zn 868-29200 1 Mo, U As, Ba, Cd, Ga, Ge, Na, Ni, Se 97 Table 3.16.1: Cachi Cachi trace element correlation (host rocks and vein types). Element Range Background High correlation Moderate correlation ppm ppm >0.7 0.5-0.7 HOST ROCKS Au 0.0025-0.06 0.0025 As, Be, Cd, Ge, Mn, Sb, Te, Tl. W. Zn Co, Fe, Ni Ag 0.01-0.21 0.001 Mo Ni. Pb As 2.5-1475 2.5 Au, Be, Cd, Co, Fe, Mn, Sb, Tl, W, Zn Cu,Ni,Te Moderate to high negative correlation (<-0.5) with Sr Ba 21.5-1026 37.5 Ga, K, Rb Al , Ge, Nb, Ni, Ta, Th, U, Y Moderate to high negative correlation (<-0.5) with Ca Bi 0.005-0.93 0.02 Mo Ge, In, Mn, Nb, Ni, Pb, Te, U, V Cd 0.04-2.48 0.02 Au, As, Be, Co, Cu, Mn, Tl, W, Zn Fe, Sb, Te Cu 2.4-23.4 3.6 Cd, Co As, Fe, Tl, W, Zn Hg 0.005-0.04 0.005 In 0.0025-0.015 0.0025 V Bi, Ce, Ga,Nb Mn 55-6420 130 Au, As, Be, Cd, Ge, Ni, Sb, Te, Tl, W, Zn Bi, Co, Fe, Mo Mo 0.2-16.3 0.4 Ag, Bi, Ni, Te, U Ge, Mn, Pb Pb 0.25-206 3.5 Ag, Bi, Mo Moderate to high negative correlation (<-0.5) with S Sb 0.2-7.67 0.8 Au, As, Be, Mn, Tl. W Cd, Co, Fe, Ni, Te, Zn Moderate to high negative correlation (<-0.5) with Ce Tl 0.28-27.3 0.76 Au, As, Be, Cd, Co, Fe, Mn, Sb, Te, W, Zn Cu, Ge, Ni Moderate to high negative correlation (<-0.5) with Sr W 0.05-38.9 0.3 Au, As, Be, Cd, Co, Fe, Mn, Sb, Tl, Zn Cu, Ni, Te Moderate to high negative correlation (<-0.5) with Sr Zn 1-382 1 Au, As, Be, Cd, Mn, Tl, W Co, Cu, Fe, Sb, Te VEIN TYPES Au 0.0025-0.172 0.0025 Ag 0.02-63 0.001 Cd,Cu As 2.5-1220 2.5 Sb, Tl.Zn Ce, Fe, La, Mn. Mo Moderate to high negative correlation (<-0.5) with Ca Ba 30-3690 . 37.5 Mn Bi 0.04-28.6 0.02. Na, Pb Cd 0.05-45.6 0.02 Ag,Cu Pb Cu 4-516 3.6 Ag, Cd Pb Hg 0.005-0.61 0.005 Cs In 0.0025-0.216 0.0025 Cr, Re, Sn, V, Zr A l , Be, Ga, Hf, Nb, P, Ta, Th, Ti Mri 76->12000 130 Ba As, Sb, Tl, Zn Mo 0.38-35.6 0.4 Fe, Ni, U As, Co, Te Pb 3.2-1665 3.5 Bi Cd, Cu, Na Sb 0.08-105.5 0.8 As, Tl, Zn Mn Tl 0.39-501 0.76 As, Sb, Zn La, Mn W 0.05-10.6 0.3 Be Zn 7-15400 1 As, Sb, Tl La, Mn 98 Table 3.16.2: Cachi Cachi trace element correlation (vein Types 1-4). Element Range Background High correlation Moderate correlation ppm ppm >0.7 0.5-0.7 VEIN TYPE 1 Au 0.0025-0.02 0.0025 Be, Co, Cr, Fe, Ga, In, Mo, Ni, Se, Sn, Ti, U, A l , As, Ce, Hf, La, Mn, Nb, P, Re, V, W, Y Sb, Th, Tl, Zn, Zr Ag 0.07-2.16 0.001 Bi, Cu, Na, Ni, P, Pb Be, Cd, Co, Cr, Cs, In, Mo, Re, Se, Sn ,Ti ,U,V As 2.5-1220 2.5 Ba, Cd, Ce, Co, Fe, Hg, La, Mn, Sb, Tl, W, Y, Au, Be, Ga, Sr, Th Zn Moderate to high negative correlation (<-0.5) with Ca Ba 40-2540 37.5 As, Hg, Mn, Rb, Sb, Tl, W, Zn Cd, Ce, Co, Fe, Ga, K, La, Sr, Y Moderate to high negative correlation (<-0.5) with Ca Bi 0.13-28.6 0.02 Ag, Cs, Cu, Mg,Na, Pb Cd,P,Te Cd 0.11-15.9 0.02 As, Co, Cs, Cu, Hg, Mn, Sb, Tl, Zn Ag, Ba, Be, Bi, Ce, Fe, La, Na, P, Pb,Th,Y Moderate to high negative correlation (<-0.5) with Ta Cu 4-60.8 3.6 Ag, Be, Bi , Cd, Co, Cs, Na, P, Pb Ce, Fe, Ga, Hg, La, Mn, Mo, Ni, Se, Th, Ti, U, V, W, Zn Hg 0.005-0.61 0.005 As, Ba, Cd, Ce, Co, Fe, La, Mn, Sb, Tl, W, Zn Be, Cu, Ga, Sr, Y In 0.015-0.216 0.0025 Au, Be, Cr, Mo, Ni, P, Re, Se, Sn, Ti, U, V, Zr Ag, A l , Co, Ga, Hf, Nb, Pb Mn 138->12000 130 As, Ba, Cd, Ce, Co, Fe, Hg, Sb, Tl, W, Zn Au, Be, Cu, Ga, Sr, Th, Y Moderate to high negative correlation (<-0.5) with Ca Mo 0.5-21.6 0.4 Ag, Be, Co, Cr, Ga, In, Ni, P, Re, Se, Sn, U, V Ag, A l , Ce, Cu, Fe, Ti, W, Y Pb 6-1665 3.5 Ag, Bi, Cs, Cu, Na Cd, In, Mg, Ni, P, Te Sb 0.62-105.5 0.8 As, Ba, Cd, Ce, Co, Fe, Hg, La, Mn, Tl, W, Y, Au, Be, Ga, Sr, Th Zn Tl 0.67-501 0.76 As, Ba, Cd, Ce, Co, Fe, Hg, La, Mn, Sb, W, Zn Au, Be, Ga, Sr, Y W 0.3-3.3 0.3 Au, As, Ba, Be, Ce, Co, Fe, Hg, La, Mn, Sb, Tl, Cu, Ga, Mo, Ni, Se, Th, Ti, U, V, Y z.n Moderate to high negative correlation (<-0.5) with Mg Zn 29-15400 1 As, Ba, Cd, Ce, Co, Fe, Hg, La, Mn, Sb, Tl, W Au, Be, Cu, Ga, Sr, Th, Y . VEIN TYPE 2 Au 0.0025-0.41 0.0025 Ba Ag 0.12-63 0.001 Cd, Cu, Pb, Zn Sb As 5-725 2.5 . Ce, Co, Fe, Ge, La, Mo, Ni, Sb, Se, Te, U, Y P, Tl, Zn Moderate to high negative correlation (<-0.5) with Ca, Mg, Sr Ba 30-3690 37.5 Au Mn Bi 0.12-5.85 0.02 Cd 0.32-45.6 0.02 Ag, Cu, Pb, Sb, Zn Moderate to high negative correlation (<-0.5) with Na Cu 8.9-516 3.6 Ag, Cd, Pb, Zn Sb Hg 0.005-0.61 0.005 Cs Hf, Zr In 0.0025-0.0097 0.0025 A l , Cr, Ga, Hf, K, Nb, Rb, S, Sn, Ta, Th, Ti, V, Cs, Li , Mg, P, Sr Zr Moderate to high negative correlation (<-0.5) with Mn Mn 76-5600 130 Tl Ba,W Moderate to high negative correlation (<-0.5) with A l , Ga, In, K, Mg, Nb, Rb, Sn, Sr,Th,Ti,V Mo 0.45-35.6 0.4 As, Ce, Co, Fe, Ge, La, Ni, Se, Te, U, Y Be, P, Sb, Tl, Zn Moderate to high negative correlation (<-0.5) with Ca, Sr 99 Table 3.16.2 (cont.): Cachi Cachi trace element correlation (vein Types 1-4). Element Range Background High correlation Moderate correlation ppm ppm >0.7 0.5-0.7 VEIN TYPE 2 Pb 10.8-1020 3.5 Ag, Cd, Cu,Zn Sb Sb 1.04-16.7 0.8 As, Cd, Te, Zn Ag, Ce, Co, Cu, Fe, Ge, La, Mo. Ni, Pb, Se,U,Y Moderate to high negative correlation (<-0.5) with Ca, K, Mg, Na, Sr Tl 1.04-20.3 0.76 Mn, W As, Be, Mo Moderate to high negative correlation (<-0.5) with K, Li , Mg, Sr W 0.05-10.6 0.3 Be, Tl Mn Zn 33-1935 1 Ag, Cd, Cu, Pb, Sb As, Ge, Mo, Te Moderate to high negative correlation (<-0.5) with K, Mg, Na, Nb, Sr VEIN TYPE 3 Element Range Background High correlation Moderate correlation ppm ppm >0.7 0.5-0.7 Au 0.0025-0.172 . 0.0025 Pb,Te Moderate to high negative correlation (<-0.5) with Hf, K, Mg, Na, Nb, Rb, Sr, Ta, Ti,Zr Ag 0.25-44.4 0.001 Hg, Pb, Sb Moderate to high negative correlation (<-0.5) with A l , Ga, Hf, K, Nb, Ni, Rb, Sn, Sr, Ta, Th, Ti, W, Zr As 16-170 2.5 Ce, Cs, Cu, Fe, Ga, La, Mo, P, Se, Te, U, V, Y Co, Cr, Ni, Re Moderate to high negative correlation (<-0.5) with Ca Ba 100-3620 37.5 Mn Tl Moderate to high negative correlation (<-0.5) with Ce, Cr, Cs, Cu, Fe, Ga, Ge, K, La, Nb, Ni, P, Rb, Sn, Ta, Th, Ti, U, V, Y, Zr Bi 0.39-3.33 0.02 Al , Ce, Cr, Ga, La, Li , Mo, Na, P. Re, Se, V, Y A l , Co, Cs, Cu, K, Ni, Rb, U, W , Moderate to high negative correlation (<-0.5) with Ca Cd 0.54-5.25 0.02 In, S, Zn Ce, Co, Fe, Ni, U Cu 10.4-26.6 3.6 A l , As, Ce, Cr, Cs, Fe, Ga, Ge, La, Mo, P, Rb, 1 Bi , Co, K, Li , Nb, Ni, Re, Sn, Ta, Se, Te, Ti, U. V, W, Y Th, Zr Moderate to high negative correlation (<-0.5) with Ba, Ca, Hg, Mn Hg 0.01-0.43 0.005 Ag,Sb Pb, Tl Moderate to high negative correlation (<-0.5) with Al , Cu, Ga, Ge, Hf, K, Mg, Na, Nb, Rb, Sn, Sr, Ta, Th, Ti, W, Zr In 0.029-0.096 0.0025 Ca, Ce, Co, Fe, Ni, S, Zn La, Se. U Mn 182-> 12000 130 Ba, Tl Moderate to high negative correlation (<-0.5) with A l , Cu, Ga, Ge, Hf, K, La, Mg, Nb, Ni, Rb, Sn, Ta, Th, Ti, U, V, Zr Mo 1.38-10.15 0.4 Al , As, Bi , Ce, Co, Cr, Cs, Cu, Fe, Ga, La, Li , Ge, K, Na, Rb, Ti, W Ni, P, Re, Se, U, V, Y Moderate to high negative correlation (<-0.5) with Ca Pb 36.9-100.5 3.5 Ag, Sb Au, Hg Moderate to high negative correlation (<-0.5) with Na, Sr Sb 0.84-57.4 0.8 Ag,Hg,Pb Moderate to high negative correlation (<-0.5) with A l , Ga, Hf, K, Mg, Nb, Ni, Rb, Sn, Sr, Ta, Th, Ti, W, Zr Tl 1.32-11.7 0.76 Mn Ba, Hg Moderate to high negative correlation (<-0.5) with Ge, Hf, Mg, Nb, Sn, Sr, Ta, Th, Ti, Zr W 0.1-1.5 0.3 Al , Cr, Cu, Ga, K, La, Nb, P, Rb, Sn, Ta, Th, Be, Bi , Ce, Co, Cs, Ge, Hf, Mg, Ti, V, Zr Mo, Na, Ni, Re, Se, Y Moderate to high negative correlation (<-0.5) with Ag, Ca, Hg, Sb Zn 40-966 1 Cd, Co, Fe, In, Ni, S Ce, La, Se, U 100 Table 3.16.2 (cont.): Cachi Cachi trace element correlation (vein Types 1-4). Element Range ppm Background ppm High correlation Moderate correlation >0.7 0.5-0.7 VEIN TYPE 4 Au 0.0025-0.0025 0.0025 Ag 0.02-0.71 0.001 As, Be, Bi, Cd, Cs, Cu, Fe, Hf, Hg, In. Mn. Mo, Ce, La, P, Re, Te Pb, S, Sb, Sn, Ta, Tl, U, V, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr As 6-225 2.5 Ag, Be, Cd, Cs, Cu, Fe, Hf, Hg, In,. Mn. Mo, Pb, S, Sb, Sn, Ta, Te, Tl. U. W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ca, Te Ba 30-150 37.5 A l , Bi , Ce, Co, Cr, Ga, K, La, Li , Mg, Nb, Ni, Fe, V P. Rb, Re, Se, Th, Ti, Y Moderate to high negative correlation (<-0.5) with Ca, Te Bi 0.04-0.5 0.02 Ag, A l , Be, Ce, Co, Cr, Cs, S, Fe, Ga, In, K, La, As, Cd, Hf, Hg, Mg, Mn, Mo, Pb, Li , Nb, Ni, P, Re, S, Ta, Th, Ti, U, V, Y Rb, Sb, Se, Sn, Tl, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ca. Ge, Sr Cd 0.05-1.32 0.02 Ag, As, Be, Cs, Cu, Fe, Hf, Hg, In, Mn. Mo, Bi Pb, S, Sb, Sn, Ta, Te, Tl, U, V, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr Cu 8.9-22.8 3.6 Ag, As, Cd, Hf, Hg, In, Mn, Mo, Pb, Sb, Sn, Tl, Be, Cs, S, Ta, U, Zr W, Zn Moderate to high negative correlation (<-0.5) with Ge, Sr Hg 0.005-0.06 0.005 Ag, As, Be, Cd, Cs, Cu, Fe, Hf, In. Mn, Mo, Bi , V Pb, S, Sb, Sn, Ta, Te, Tl, U, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr In 0.005-0.023 0.0025 Ag, As, Be, Bi, Cd, Cs, Cu, Fe, Hf, Hg, La, A l , Ce, Ga, Ni, P, Re Mn, Mo, Pb, S, Sb, Sn, Ta, Tl, U, V, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr Mn 93-493 130 Ag, As, Be, Cd, Cs, Cu, Fe, Hf, Hg, In, Mo, Pb, Bi , La S, Sb, Sn, Ta, Te, Tl, U, V, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr Mo 0.38-21 0.4 Ag, As, Be, Cd, Cs, Cu, Fe, Hf, Hg, In, Mn, Pb, Bi, V S, Sb, Sn, Ta, Te, Tl, U, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr Pb 3.2-255 Ag, As, Be, Cd, Cs, Cu, Fe, Hf, Hg, In, Mn, Bi, La Mo, S, Sb, Sn, Ta, Te, Tl, U, V, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr Sb 0.08-2.01 3.5 Ag, As, Be, Cd, Cs, Cu, Fe, Hf, Hg, In, Mn, Bi Mo, Pb, S, Sn, Ta, Te, Tl, U, V, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr Tl 0.39-8.15 0.8 Ag, As, Be, Cd, Cs, Cu, Fe, Hf, Hg, In, Mn, ; Bi , V Mo, Pb, S, Sb, Sn, Ta, Te, U, W, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr W 0.1-3.2 0.3 Ag, As, Be, Cd, Cs, Cu, Fe, Hf, Hg, In, Mn, B i . V . Y Mo, Pb, S, Sb, Sn, Ta, Te, Tl, U, Zn, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr Zn 7-604 1 Ag, As, Be, Cd, Cs, Cu, Fe, Hf, Hg, In, Mn, Bi Mo, Pb, S, Sb, Sn, Ta, Te, Tl, U, V, W, Zr Moderate to high negative correlation (<-0.5) with Ge, Sr 101 3.6.2. Oxygen and Carbon Stable Isotopes at M i n a Central and Cachi Cachi Depletion halos of 8 1 8 0 and 5 1 3 C relative to the host marine carbonate rocks are well documented around carbonate-hosted polymetallic and skarn deposits (Beaty et al., 1990; Kesler et al., 1995; Friehauf and Pareja, 1998). Large oxygen isotope halos are mapped in carbonate rocks especially in the upper parts above ore zones (Kesler et al., 1995; Nesbitt, 1996). Such halos are found at Yauricocha and correspond to the marble front that separates the mineralized zones from the fine-grained gray "unaltered" limestone. Calcite and dolomite 8 1 8 0 and 8 1 3 C isotopic compositions were measured in seventy-two samples of limestone, marble, hornfels and vein Types 1 through 4. Measurements were made at the Pacific Centre for Isotopic and Geochemical Research at the University of British Columbia. Detailed description of the experimental method, isotope samples description, and results are attached in Appendices E a n d E l - E 4 . Oxygen and carbon isotope studies on marble, limestone and carbonate vein were undertaken to trace hydrothermal fluid circulation outside the carbonate-hosted and skarn orebodies to obtain better understanding of fluid flow and permeability around M i n a Central and Cachi Cachi, sources of O and C , and links between both deposits. A t Yauricocha, the link between the carbonate-hosted replacement and skarn orebodies is constrained from field relationships and supported by using oxygen isotope data. Plots of representative samples are included in Figure 3.15 Data from M i n a Central include 7 analyses of limestone, marble or hornfels, 6 analyses of the orebody, 14 analyses of Type 2 veins (with host rock contamination of 5 to 50 vol %), and 16 analyses of Type 3 veins. Cachi Cachi data include four analyses of limestone and marble, 11 analyses of Type 1 veins, 9 analyses of Type 2 veins, three analyses of Type 3 veins, and three analyses of Type 4 veins. V e i n samples from both M i n a Central and Cachi Cachi include host rock contamination from 50 to 0 vol %. The first year of the project a reconnaissance sampling survey was conducted around the Antamina Cu-Zn skarn deposits on carbonate rocks of the Jumasha Formation, which also hosts the M i n a Central and Cachi Cachi orebodies. It was observe that isotopic compositions of limestone and gray marble cluster near normal marine carbonate compositions in 8 1 8 0 and 8 I 3 C . It was defined a range o f 21 to 25 8 1 8 0 per m i l V S M O W and 1 to 3 per m i l 8 1 3 C V P D B for most gray marbles within 800 m of the plutonic system there. This range was interpreted as the isotopic composition of the protolith limestone (Escalante and Dipple, 2005a). On this basis 102 limestone and marble from the Jumasha Formation and hornfels from the Celendin Formation with 8 1 8 0 values less than 20 %o and with 8 1 3 C values less than 1 % o , are considered depleted. Sedimentary oxygen isotope composition of the Celendin and Jumasha Formations are notably sparse within the Cachi Cachi and M i n a Central areas. Four of 43 samples from M i n a Central and 12 of 30 samples from Cachi Cachi have 8 1 8 0 values greater than 20 per m i l V S M O W (Appendix E3). The widespread and consistent depletion in 8 1 8 0 reflects the pervasive percolation of magmatic fluids through the study areas (Fig. 3.15). A s with the other study areas throughout central Peru (Bissig et al., 2005), 8 1 3 C depletions generally correlate with 8 1 8 0 depletion in the high temperature calcsilicate systems. The 8 l s O depletion zone extends well into alteration zone C at M i n a Central and Cachi Cachi (Figs. 3.15; Appendix E3). Only two samples of host rock record 8 1 8 0 values greater than 20 per mi l , and both of these come from the Celendin Formation, which is generally less altered than the Jumasha Formation at this locality. In addition, two samples of Type 2 veins, one from alteration zone B and one from alteration zone C , have 8 1 8 0 greater than 20 per mi l . Both of these samples are hosted within the Jumasha Formation limestone, and both samples have approximately 50 vol % of contamination of host limestone. Type 2 vein samples with less contamination consistently have 8 1 8 0 values less than 20 per mi l ; the purest samples have values that cluster near 8 1 8 0 values of 14 per mi l . These data are consistent with precipitation of Type 2 veins from magmatic fluids ( 8 1 8 0 of 9 to 11 per mil) at temperatures of about 400°C (O 'Ne i l etal. , 1969). Limestone and gray marble samples from alteration zone C of Cachi Cachi are also depleted in 8 I 8 0 (Appendix E3). A single sample of limestone from alteration zone B is the only host rock sample to retain 8 1 8 0 values greater than 20 per mi l . V e i n samples are more variably depleted. Type 1,2, and 3 veins with 40 vol % or greater wall rock contamination generally have 8 1 8 0 values greater than 20 per mi l . The isotope data from Cachi Cachi and M i n a Central are generally similar (Fig 3.15). The 8 1 8 0 depletion halo within limestone and gray marble extends into zone C ; the farthest depleted sample is located at about 700 m away from the intrusive contact (Appendix E3). In limestone, marble, hornfels, and vein Type 1 at Cachi Cachi, there is a high temperature shift in 8 1 8 0 and 8 1 3 C to magmatic values (10 per m i l and -10 per mi l , respectively), therefore depletions in 8 1 3 C correlates with 8 1 8 0 . Ore samples and vein Type 1 samples display a similar trend (Fig. 3.15a). 103 W a l l rock selvedges to Type 1,2, and 3 veins appear to be variably depleted. Type 2 and 3 veins also have low 8 1 8 0 values, but do not have depleted 5 1 3 C values (Fig. 3.15b). " L o w " temperature veins (Types 2, 3, and 4) are shifted toward magmatic 5 1 8 0 but not in 8 1 3 C . Depleted 8 1 8 0 values of <20 per mi l for vein Type 2 are consistent with precipitation of veins from magmatic fluids ( 8 1 8 0 of 9 to 11 per mil) at temperatures o f about 400 C (O 'Ne i l et al., 1969). 8 1 8 0 depletion halo within vein Type 2 extends up to 790 m in Cachi Cachi and 720 m in M i n a Central, laterally away from the intrusive contact into zone C (Appendix E3). 4.0 2.0 £ 0.0 Q a. > U to -2.0 -4.0 -6.0 -8.0 -10.0 y y y * y •X X y N • Cachi Cachi rocks o Mina Central rocks • Mina Central ore x Cachi Cachi Type I veins 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0. 26.0 5I80(VSM0W) 4.0 2.0 £ o.o Q > w 0 -4.0 -6.0 -8.0 -10.0 b * o < > • / < > • y A-\ o y A y •* y / o / J x ^-1 y j Field for rocks ^ ^ y 1 y y .1 ' Vein types * Cachi Cachi Type 2 A Mina Central Type2 • Cachi Cachi Type 3 oMina Central Type 3 « Cachi Cachi Type 4 10.0 12.0 14.0 24.0 26.0 16.0 18.0 20.0 22:0 6180(VSM0W) Figure 3.15: Oxygen and carbon isotopic compositions of (a) rocks and high-temperature Type 1 veins and (b) Types 2 and 3 veins at Mina Central and Cachi Cachi, Yauricocha, central Peru. 104 8 1 8 0 values of orebodies from Yauricocha fall within a range of 4 to 17 %o with the majority between 10 and 14 %o. This range of magmatic 8 1 8 0 values is consistent with previous studies that give a range o f 8 1 8 0 of 8 to 14 %o for magmatic-related mineralizing fluids in central Peru (e.g., Rye and Sawkins, 1974). C R D and skarn related vein Types 1, 2, and 3 from M i n a Central and Cachi Cachi all have 8 1 8 0 values that overlap the range of magmatic-hydrothermal values from associated orebodies (Appendix E3). This provides additional evidence for a link between the proximal skarn orebodies of Cachi Cachi, the carbonate-hosted orebodies of M i n a Central, and the distal veins found outside the sulfide ores. In conclusion, 8 1 3 C and 8 1 8 0 depletions recording the fluid escape at M i n a Central and Cachi Cachi are consistent with a magmatic fluid source. Oxygen depletion cryptic halos are wider than visible alteration halos and can be traced at least up to 700 m in carbonate rocks and up to 790 m in carbonate veins laterally away from the intrusive contact. Oxygen isotope zonation in carbonate rocks extends beyond the visible alteration zones at shallow levels indicating that fluid escape through carbonate rocks was mainly controlled by sedimentary layering in Cachi Cachi and by fracture meshes in M i n a Central. 3.7. Distal Visible and Cryptic Alteration Characteristic at Yauricocha Carbonate-hosted replacement orebodies at M i n a Central and skarn and carbonate-hosted replacement orebodies at Cachi Cachi lie within thermal aureole along intrusive contact that shows distinct zonal patterns at the district scale, and locally at M i n a Central and Cachi Cachi, proximal to distal visible alteration surrounding the sulfide deposits is divided in three zones, based on the intensity and distribution of hydrothermal alteration. In general, contacts between zones are diffuse and irregular. Zone A , inner and adjacent to the stock, is characterized by pervasive bleached marble at Cachi Cachi and by Mn-flooding of marbles and sulfide-bearing M n in veins at M i n a Central. Bedding-controlled stripes of bleached and gray marble and early calcsilicate veins at Cachi Cachi and younger pervasive orange brown carbonate minerals veins, containing variable amounts of M n oxide minerals, at M i n a Central characterize the intermediate zone B . Zone C, most distal to the stock, is characterized by unaltered limestone with discontinuous and diffuse regional limestone bleaching close to the outer limit o f zone B and by the predominance of white-gray carbonates minerals. The bleached marble, bleached limestone, gray marble, very local gray hornfels, and proximal to distal vein swarm systems that define the zones of the visible hydrothermal alteration and the thermal metamorphism are 105 better developed in proximity to mineralized zones and are irregular and laterally distributed outward from intrusive contacts. Ve in abundance and density decrease with distance from intrusives. Bleached lithologies, largely of the Cretaceous Jumasha Formation, reflect complete interaction with hydrothermal fluids. Color change corresponds to the loss of organic carbon and to the presence or absence of calcsilicate and sulfide minerals. Diopside and augite cause slight greenish tint to bleached units. Three scales of bleaching are recognized: decametre-scale pervasive massive bleaching, metre-scale bedding- or structural-controlled bleaching and centimetre-scale bleaching halos to veins. Bleaching of limestone is inferred to be due to the oxidation of the graphite within the limestone, but it is not accompanied by recrystallization of limestone to marble. Gray marble and gray hornfels reflects thermal metamorphisnr of dark gray Jumasha limestone or of marly limestone of Santonian Celendin Formation. Grain size o f altered rocks decrease outward from intrusive contact, gray marble is generally finer than bleached marble. In Zone C, carbonate rocks are noticeably finer grained than in Zones B and A . Sharp boundaries between bleached and gray marble correspond to changes in graphite abundance. A sequence of vein types from high to low temperature and proximal to distal veinlet swarms is evident. Veins of calcsilicate minerals (Type 1), orange brown carbonates (Type 2), Mn-r ich veins (Type 3), and white- to gray carbonates (Type 4a-c) represent fluid escape pathways. Manganese oxide rich veins (lower T) are nearest the C R D ores and forms strong dispersion halo on distal fringes, whereas calcsilicate-rich veins (high T) are nearest the skarn. Horizontal and vertical zonation of alteration is evident. Jumasha Formation limestone is the predominant host rock at the Yauricocha district. Unaltered limestone occurs not below 4675 m.a.s.l. at Cachi Cachi. A t M i n a Central, bleached units versus gray marble extend up to 43G m from intrusive contact and up to at least 640 m above known mineralization. Gray hornfels beds occur locally up to 250 m laterally and over 730 m from main intrusive and known mineralization. Manganese-rich orange brown carbonate veins extend up to 750 m, orange brown carbonate veins, and white- or gray-carbonate veins up to 780 m laterally from the intrusive over 740 m, and 765, respectively, over mineralized zones. Manganese-rich orange brown carbonate minerals are found immediately fringing the carbonate replacement orebodies, and are spatially associated with the sulfide-rich orebodies. They flood carbonate rocks in proximity to the ores. Outwards, there is increasing content o f orange brown carbonate minerals in veins and M n oxides minerals diminish away from ores; therefore, in general, 106 carbonate veinlet networks rich in M n lie below meshes of orange brown carbonate veinlets rich in Fe, which lie largely within zone B , decreasing in density toward zone C. Weathering o f carbonate ± sulfide veins yields orange brown Fe-oxide coatings that mix with variable amounts of M n oxide minerals. A t Cachi Cachi, pervasive massive bleaching predominates up to 150 m and bedding-controlled stripes of bleached and gray marble up to 500 m from intrusive, at least up to 540 m and 670 m over known mineralization. Gray marble and bleaching of limestone (not marble) is noticeable at least up to 550 m from intrusive and up to 720 m over orebodies. Garnet (grossular and andradite) veins are recognized up to 180 m, calcsilicate (diopside and augite) veins up to 400 m, and wollastonite veins up to 450 m from the intrusive over vertical distances of 520 m, 570 m, and 620 m from mineralized zones. They represent the high temperature veins associated with the formation of the skarn orebodies. The garnet and calcsilicate are found closer to the sulfide ores, whereas wollastonite is a distal manifestation of the skarn system. Orange brown carbonate minerals, occasionally containing minor M n oxides minerals, persist laterally over 610 m in gray marble and 670 m in unaltered limestone from main intrusive; vertically, they reach some 720 m in gray marble and 745 m in unaltered limestone. They lie broadly in zone B . Manganese-rich orange brown carbonates veins are considerably less common than in M i n a Central, A t Cachi Cachi, they reach at least 790 m laterally and over 750 m vertically. Orange brown carbonate veins, containing variable amount o f Mn-oxide minerals, represents an intermediate stage both in time and distance. Outward, there is decreasing content of orange brown carbonate minerals in the veins and a slight increasing content of M n oxide minerals. Late-stage white and gray carbonate veinlets occur in al three zones forming the most distal fringe representing the distal exhausted hydrothermal fluids. They extend over 790 m laterally and 760 m vertically and clearly crosscut all the other vein types. Syntectonic white calcite (Type 4d) veinlets formed during regional deformation, therefore not related to mineralization or alteration, occur in marble and unaltered limestone largely in Zone C at both localities. Pyrite is common in pervasively bleached limestone or marble, especially in proximity to main stock, and locally in gray marbles and unaltered limestone particularly near the outer limit of zone B . Minor pyrite is also present in all calcsilicate, orange brown carbonate and late-stage calcite veins. Cross-cutting relations indicate at least a three-stage chronology o f veining at M i n a Central and at least four-stage chronology of veining at Cachi Cachi. Pre-to syn-tectonic calcite veins predate mineralization. In general, calcsilicate veins are the oldest, orange brown carbonate 107 with variable amounts of M n oxide minerals mutually cross cut each other and represent an intermediate stage both temporally and distally. Late-stage white- to gray-carbonate veins cut all other type veins throughout alteration zones in both mineralized zones Regionally, at district scale, and locally at M i n a Central and Cachi Cachi, proximal to distal cryptic alteration surrounding the sulfide deposits is characterized in halos, based on the intensity and distribution of trace element and stable oxygen and carbon isotope anomalies of rocks and vein types characterized on the three visible alteration zones. In rocks, Zn±As defines in zone A a 150 m wide halo at Cachi Cachi and a 400 m wide halo at M i n a Central. Zinc and A s are elevated up to 650 m from the intrusion in zone B at both localities. Zinc is also elevated up to 700m from the intrusive in zone C at Cachi Cachi. In zones A and B , M n defines a 400 m wide subtle halo in Cachi Cachi and a 650 m wide remarkable halo at M i n a Central. Manganese also is elevated 700 m from the intrusive contact in zone C at Cachi Cachi. Antimony ±T1, and ±Au accompany the base metals in the rocks and are strongest near the sulfide orebodies at both localities. In zone A at M i n a Central, sporadic Pb is present. Combining the two mineralized centers, Z n ± A s is enriched in rocks nearest the intrusion with M n forming a strong dispersion halo on the distal fringes. "Epithermal" suite of Sb-Tl±Au accompanies the base metal in the rocks and is strongest near the sulfide orebodies. In vein Types 1-3, Z n and A s define a 300 m wide halo at Cachi Cachi and at least a 530 m wide halo at M i n a Central in zones A and B . Zinc and A s are elevated up to 800 m from the intrusive in zone C at both localities. Zinc and A s are more enriched in vein types 2 and 3 than in vein type 1. In vein type 1 at Cachi Cachi and in vein types 2 and 3 at M i n a Central, M n and Sb define two halos o f 300 m and 530 m wide, respectively, in zones A and B . Manganese and Sb are elevated in zone C in both localities. A t M i n a Central, the M n halo is probably larger than 530 m, because M n values exceed the upper limit of detection limit; therefore the M n trend was not completely constrained. Combining the studied areas, veins present comparable elemental halo that is much more systematic and indicative of an evolving hydrothermal fluid with elevated Zn±Pb±Ag±Cu±Mn and anomalous Au±As±Bi±Cd±Hg±Sb, and ±T1 accompany in veins near sulfides orebodies. In host rocks, metal relationships are consistent with medium to high temperature for mineral deposition at M i n a Central and Cachi Cachi. Base metal element suite (Ag, A l , A s , Cr , B i , M n , W , Z n and M o , N i , Pb, and C u in Cachi Cachi) and "epithermal" element suite (Au, Ba , Hg , In, Cd , Sb, Te, Tl) correlate with each other. L o w correlation values of the base metal element suite with Hg , Sb, and T l at M i n a Central are likely related to the depth o f the system. 108 L o w to relatively moderate correlation of the base metal element suite with Ba , Hg , and Sb at Cachi Cachi are likely indicating a relative deeper origin for the skarn orebodies formation relative to the carbonate-hosted replacements ores at M i n a Central. Base metal element suite (Ag, A s , Be, B i , Cr, C u , M o , N i , Pb, Sn, W , Zn , and U) consistently correlates (good to moderate correlation) with each other in vein types. A u , Ba , C d , Hg , In, M n , Hg , Sb, and T l correlate with the base metal element suite. Statistical correlation values for vein types clearly establish a genetic association of the distal vein types with the orebodies at depth. General moderate correlation among "epithermal" element suite likely represents a later and shallower influence in the composition of the vein types. Isotope data from M i n a Central and Cachi Cachi is generally similar. 8 1 3 C and 8 1 8 0 depletions tracking fluid escape are consistent with a magmatic fluid source. Oxygen depletion cryptic halos are wider at shallow levels than visible alteration halos, where they are recorded well into zone C and can be traced at least up to 700 m in carbonate rocks and up to 720 m, in Cachi Cachi, and up to 790 m, in M i n a Central, in carbonate veins laterally from the stock. Widespread and consistent depletion in 8 , 8 0 reflects pervasive percolation o f magmatic fluids. 8 1 3 C depletions generally correlate with 8 1 8 0 depletions in high temperature calcsilicate systems. Oxygen isotope zonation in carbonate rocks indicates that fluid escape through carbonate rocks was mainly controlled by sedimentary layering in Cachi Cachi and by fracture meshes in M i n a Central. In carbonate rocks and vein Type 1 at Cachi Cachi, there is a high temperature shift in 8 1 8 0 and 8 1 3 C to magmatic values (10 per mi l and -10 per mi l , respectively), depletions in 8 1 3 C correlates with 8 1 8 0 . Ore samples and vein Type 1 show similar trend. " L o w " temperature veins (Types 2, 3, and 4) are shifted toward magmatic 8 1 8 0 but not in 8 , 3 C . Depleted 8 1 8 0 values of near 14 per m i l for vein Type 2 are consistent with precipitation of veins from magmatic fluids ( 8 1 8 0 of 9 to 11 per mil) at temperatures of about 400 C. A range of 4 to 17 %o for 8 1 8 0 values of orebodies is consistent with previous studies that give a range of 8 1 8 0 of 8 to 14 %o for magmatic-related mineralizing fluids in central Peru. V e i n Types 1, 2, and 3 all have 8 1 8 0 values overlapping that range of values from associated orebodies, providing additional evidence for a link between the proximal skarn orebodies of Cachi Cachi, the C R D s orebodies of M i n a Central, and the distal veins found outside the sulfide ores. 109 In summary, there is a visible alteration sequence in M i n a Central and Cachi Cachi that is accompanied by systematic cryptic variations in whole rock and vein types and chemistry that extends up to 800 m laterally from the intrusive contact, and over a similar vertical distance. 110 References Alvarez, A . A . , and Noble, D . C , 1988, Sedimentary rock-hosted disseminated precious-metal mineralization at Purisima Conception, Yauricocha District, central Peru: Economic Geology, v. 83, no. 7, p. 1368-1378. Beaty, D . W . , Landis, G.P. , and Thompson, T .B , eds., 1990, Carbonate-hosted sulfide deposits o f the central Colorado Mineral Belt: Society of Economic Geologists Monograph 7, 424 p. Bendezu, R., Fontbote, L . , and Costa, M . , 2003, Relative age o f Cordilleran base metal lode and replacement deposits, and high sulfidation Au-(Ag) epithermal mineralization in the Colquijirca mining district, central Peru: Mineralium Deposita, v. 38, p. 683.694. Bissig, T., Escalante, A . , Dipple, G . , Ebert, S., Jurado, J . , and Tosdal, R. , 2005, Sources and exhausts in polymetallic carbonate rock-hosted ore deposits: Miocene magmatism and alteration in central Peru: Mineral Deposit Research Unit, University of British Columbia. Escalante, A . , and Dipple, G . , 2005a, Geology, alteration and fluid escape in the Antamina C u -Z n skarn deposit, Peru, in Bissig, T., Escalante, A . , Dipple, G . , Ebert, S., Jurado, J., and Tosdal, R., Sources and exhausts in polymetallic carbonate rock-hosted ore deposits: Miocene magmatism and alteration in central Peru: Mineral Deposit Research Unit, University o f British Columbia, Chapter 3. Friehauf, K . C , and Pareja, G . A , 1998, Can oxygen isotopic haloes be produced around high-temperature dolostone-hosted ore deposits? - Evidence from the Superior District, Arizona: Economic Geology, v.93, p. 639-650. Govett, G.J.S., ed., 1983, Handbook of Exploration Geochemistry Volume 3: Rock Geochemistry in Mineral Exploration, Elsevier Scientific Publishing Company, 461 p. Kesler, S.E., Vennemann, T .W. , and Vazquez, R., Stegner, D.P. , and Frederickson, G . C . , 1995, Application of large-scale oxygen isotope haloes to exploration for chimney-manto Pb-Zn-C u - A g deposits, in Coyner, A l a n R., and Fahey, Patrick L . , eds., Geology and Ore Deposits of the American Cordillera: Geological Society of Nevada, Symposium Proceedings, Reno/Sparks, Nevada, p. 1383-1396. Megaw, P . K . M . , 1998, Carbonate-hosted Pb-Zn-Ag-Cu-Au replacement deposits: A n exploration perspective, in Lentz D.R. ed., Mineralized intrusion-related skarn systems: Mineralogical Association of Canada. Short course series 26, chapter 10, p. 337-358. Megaw, P . K . M . , 2001, Carbonate-hosted Pb-Zn-Ag-Cu-Au replacement deposits: an exploration perspective: Proceedings of the ProExplo Meeting, L i m a Peru. Megaw, P . K . M . , Ruiz , J., and Titley, S.R., 1988, High-temperature, carbonate-hosted Ag-Pb-Zn(Cu) deposits of northern Mexico: Economic Geology, v. 83, 1856-1885. Megaw, P . K . M . , Barton, M . D . , and Islas-Falce, J., 1996, Carbonate-hosted Lead-Zinc (Ag, C u , Au) deposits of Northern Chihuahua, Mexico, in Sangster, D.F . , ed.: Society of Economic Geologists, Special Publication No . 4, p. 277-289. I l l Meinert, L . D . , Hefton, K . K . , Mayes, D . , and Tasiran, I., 1997, Geology, zonation, and fluid evolution o f the B i g Gossan C u - A u skarn deposit, Ertsberg district, Irian Jaya: Economic Geology, v. 92, p. 509-526. Morris , H.T. , 1968, The main Tintic mining district, Utah, in Ridge, J.D., ed, Ore deposits of the United States, 1933-1967 (Graton-Sales Volume): New York, American Institute of Min ing and Metallurgical Engineers, p. 1043-1073. Morris , H.T. , 1986, Descriptive model of polymetallic replacement deposits, in Cox, D.P. , and Singer, D . A . , eds., Mineral deposit models: U . S . Geological Survey Bulletin 1693, p. 99-100. Nesbitt, B . E . , 1996, Applications of oxygen and hydrogen isotopes to exploration for hydrothermal mineralization: Society of Economic Geologists Newsletter, v. 27, p. 1-13. Noble, D . C , and M c K e e , E . H . , 1999, The Miocene metallogenic belt of central and northern Peru, in Skinner, B . J . ed., Geology and ore deposits of the central Andes: Society o f Economic Geologist, Special Publication N o 7, chapter 5, p. 155-193. 0"Neil , J.R.; Clayton, R . N . ; and Mayeda, T . K . , 1969, Oxygen isotope fractionation in divalent metal carbonates; J. Chem. Phys. 51(12), p. 5547-5558. Petersen, U . , 1965, Regional geology and major ore deposits o f central Peru: Economic Geology, v. 60, p. 407-416. Rose, A . W . , Hawkes, H . E . , and Webb, J.S., 1979, Geochemistry in Mineral Exploration, 2 n d edition, Academic Press, 657 p. Rye, R .O. , and Sawkins, F.J. , 1974, Fluid inclusion and stable isotope studies on the Casapalca Ag-Pb-Zn-Cu deposit, Central Andes, Peru: Economic Geology, vol . 69, pp. 181-205. Theodore, T .G . , 1998, Geology of pluton-related gold mineralization at Battle Mountain, Nevada, Tucson, Arizona: University of Arizona and U . S . Geological Survey Center for Mineral Resources Monograph 2, 270 p. Titley, S.R., 1993, Characteristics of high-temperature, carbonate-hosted massive sulfide ores in the United States, Mexico, and Peru, in Kirkham, R . V . , Sinclair, W . D . , Thorpe, R.I. , and Duke, J . M . , eds., Mineral Deposit Modeling: Geological Association of Canada Special Paper, v. 40, p. 585-614. Titley, S.R., 1996, Characteristics of high temperature, carbonate-hosted replacement ores and some comparisons with Mississippi Valley-type ores, in Sangster, D.F . , ed., Carbonate-hosted lead-zinc deposits: Society of Economic Geologists, Special Publication Number 4, p. 244-254. Thompson, A . J . B . , Hauff, P .L , and Robitaille, A . J . , 1999, Alteration mapping in exploration: Application of short-wave infrared (SWIR) spectrometry, in S E G Newsletter: Society of Economic Geologist, No . 39, p. 16-27. 112 Tumialan De L a Cruz, P .H . , 2002. Yacimientos de reemplazamiento y relleno en calizas en el Peru: Sociedad Geologica del Peru, X I Congreso Peruano de Geologia, L ima , Geologia de los yacimientos minerales, tomo 1, p. 597-606. Valdivia , V . A . , 1996, Geology and metallogeny of the Yauricocha mine (Cu-Pb-Zn-Ag), central Peru, M . S c . thesis: Instituto de Geociencias, Universidade de Brasilia, Brasi l . Web link: ht^://vvww.unb.br/ig/posg/mest/mestl06.htm. 113 CHAPTER FOUR Conclusions, Interpretation, Systematic View of Alteration Patterns, and Exploration Considerations and Potential 4.1. General Conclusions, Interpretation, and Exploration Considerations 4.1.1. Thermal Aureole and Alteration Distribution The size of distal alteration zones in carbonate-hosted replacement and skarn deposits is dependent in part upon the size of the mineralized zones and the geometry o f the intrusion with respect to the host stratigraphy and structural fabric in those rocks. In most carbonate rock-hosted deposits and prospects of central Peru (Fig. 2.3; Bissig et al., 2005) either thermal aureoles and/or zone of veins form much larger exploration targets than the mineralized zones themselves. Yauricocha lies within the thermal aureole of the adjacent intrusion, similarly as most CRD-skarn deposits formed at deeper levels. A t the Yauricocha district, the main zones of mineralization lie within an area roughly 2 km long by 1 km wide (Fig. 2.6) and over a vertical depth of at least 600 m (Fig. 2.8), the quartz diorite to quartz monzonite intrusion occupies an area approximately 4.5 km long by 1.5 km wide (Fig. 2.7), and the thermal aureole lies within an area roughly 3.5 km long by 1 km wide (Fig 2.7) and over a vertical depth of at least 790 m. A t Yauricocha, the most pronounced visible alteration features are thermal metamorphism and fluid flow effects surrounding the quartz diorite to quartz monzonite Yauricocha-Exito intrusion. These include recrystallization, bleaching, and minor conversion of calcareous rocks to hornfels. Yauricocha contains an inner zone of bedding and structurally controlled bleached marble that extends as much as 500 m laterally from the main intrusive (Fig 3.4; Plate 3) and 670 m over known mineralization and an outer zone of gray marble that extends at least 550 m laterally (Fig 3.1; Plate 1) and 720 m vertically over know mineralization into the carbonate rocks. Limestone and marble widely correspond to the Jumasha Formation. Locally, thin interbedded Celendin Formation hornfels and weakly silicified limestone strata extend up to some 250 m laterally from the main intrusive over 730 m above known mineralization (Fig. 3.2; Plate 2). Thermal metamorphism is reflected by the presence of gray marble and gray hornfels. Proximal and distal calcsilicates, orange brown- to white carbonates, and M n oxides minerals, quartz and sulfide veins contiguous to carbonate-hosted and skarn orebodies are found up to 790 m laterally and 765 m vertically from the intrusive. 114 Summarizing, the polymetallic carbonate-hosted replacement deposit at M i n a Central and the skarn and carbonate-hosted replacement deposit at Cachi Cachi share similar alteration halos that extend over the entire vertical extent of the mineralized system, and up to about 800 meters laterally from the sulfide orebodies and/or from the intrusive. Older fold and thrust geometry at M i n a Central and sedimentary layering at Cachi Cachi control alteration. Where the stratigraphy or a structural fabric is at high angles to the contact, the visible alteration halo is much wider than where the stratigraphy or structural fabric is sub parallel to the contact. 4.1.2. Host Rock Alteration Bleaching and conversion of the host limestone to marble occurs closest to the intrusion. The effects of the bleaching in the host carbonate rocks extend well away from the intrusion and affect otherwise non-recrystallized limestone 500+ meters from the contact. Pervasive massive bleaching is the combined result of temperature due to intrusion and fluid circulation of volatiles through fracture permeability or fluid escape conduits controlled by the geometry of intrusive emplacements and by the structural fabric at M i n a Central and by the bedding in Cachi Cachi. Bedding-controlled limestone and bleached marble are present in fluid flow pathways that are more pervasive near orebodies and are thinner and controlled by sedimentary layering distal to them. Massive- and bedding-controlled bleached marble and limestone was probably produced at the same time in M i n a Central and Cachi Cachi. The extension of both units was controlled by the proximity to the pluton and the fracture-permeability of the rocks. The bleaching of limestone and marble is interpreted to reflect the oxidation of the graphite or loss of organic carbon in the carbonate rocks by oxidation. Bleaching reveals carbon destruction by fluid leakage and/or diffusion from veins. The colour change in the carbonate rocks corresponds to a loss of organic carbon and to the presence or absence of calcsilicate and sulfide minerals. Centimetre-scale diffusional bleaching represents limited leakage from planar hairline pyrite ± sulfides veins. Gray marble and gray hornfels reflects thermal metamorphism of limestone or of marly limestone. 4.1.3. Proximal and Distal Veins A t Yauricocha, within the alteration halo there is a consistent arrangement of distal and proximal veinlet networks or swarms of thin (hairline to 2 cm) wavy-planar veins-veinlets that surround the carbonate-hosted replacement and skarn ore zones. The veinlets also connected 115 different mineralized zones in the mine and are concentrated along favorable beds, therefore forming an asymmetrical halo extending up to 790 m laterally from the intrusive and mineralized zones (Plates 1-3), over 765 m above known mineralization. The halo extends outward from mineralized zones and diminishes in intensity away from mineralization. The veinlets contain variable amounts of carbonate (calcite, siderite, ankerite, rhodocrosite, or dolomite), calcsilicate (grossular, andradite, wollastonite, diopside, or augite) minerals ± quartz with pyrite and base-metal sulfides (sphalerite, galena, or chalcocite). Veins with higher temperature green calcsilicate minerals such as diopside, augite or garnet (grossular, andradite) are found near the intrusive source, closer to the sulfides orebodies, representing an association with the formation of the skarn. In contrast, wollastonite veinlets are found far from the intrusion and mineralized system, representing the distal manifestation o f the skarn system. The presence of calcsilicate veins and lenses in massive- and bedding-controlled bleached marble suggests that in both cases, permeability was fracture controlled. Calcsilicate veins are sparse to absent in gray marble. Orange-brown carbonate veins, containing variable amounts of M n oxides minerals, are the most ubiquitous distal veins and found throughout the alteration halo. They are also remarkably similar to the orange brown carbonate veinlet noted at other deeper C R D or skarn deposits in central Peru (Tosdal et al., 2005). Late-stage white- to gray carbonate veins occur are found throughout the thermal aureole forming the most distal fringe, representing the distal exhausted hydrothermal fluids. The veinlet networks or swarms o f veins-veinlets are important exploration guides. They are interpreted to represent the fracture permeability of rock units, therefore fluid escape and fluid flow pathways for the fluids responsible for mineralization and alteration. 4.1.4. Metal Content Geochemically the carbonate host rocks at Yauricocha contain elevated to weak base metals (especially Z n and Pb) and M n values accompanied by elevated to weak anomalous values of the "epithermal" suite of A s , Sb, T l ±Au, which are particularly strongest near sulfide orebodies. Summarizing, host rocks at M i n a Central and Cachi Cachi are enriched in Z n ± A s nearest the intrusion with M n forming a strong dispersion halo on the distal fringes. In rocks, cryptic Z n halos are as much as 150 m wide in Cachi Cachi and 400 m wide in M i n a Central from intrusive. Manganese defines a 400 m wide halo in Cachi Cachi and a 650 m wide halo at M i n a Central. In host rocks, statistical correlation values between base metal- and "epithermal-116 element" suites are consistent with medium to high temperature for mineral deposition, are related to the depth of the system, and are likely indicating a high temperature origin for the skarn orebodies formation of Cachi Cachi relative to the carbonate-hosted replacements ores at M i n a Central. The proximal and distal veins present a comparable elemental halo that is much more systematic and indicative of an evolving hydrothermal fluid. They carry trace amounts of sulfide, usually pyrite, and near the sulfide bodies are intimately associated with Mn-oxides. Near the sulfide bodies, the carbonate and Mn-r ich veins are rich in Zn-Pb-As-Mn-Sb±Tl±Au. More than 400 meters from the intrusive contact and sulfide orebodies, these veins are also moderate to weakly anomalous in Pb-Ag-Cu. A t Cachi Cachi, orange brown carbonate veins near the intrusion are strongly anomalous in B i but away from the intrusion, they are depleted in B i but strongly anomalous in Zn-Pb-As-Mn and weakly anomalous in Sb-Au-Cu-Hg-Cd. The veins also contain elevated to weak base metals (especially Zn , Pb, and Cu) and M n with or without elevated A g as well as elevated to weak of the "epithermal" suite o f A s , B i , Sb, T l , H g ±Au. In veins, Z n and A s define a 300 m wide halo at Cachi Cachi and a 530 m wide halo at M i n a Central. Manganese and Sb, respectively, define halos of 300 m and 530 m wide at Cachi Cachi and M i n a Central. Statistical correlation values between base metal- and "epithermal-element" suites clearly establish a genetic association of distal veins with base metal-rich orebodies. Geochemical studies around Yauricocha permit some generalization to be made applicable to exploration. Dispersion halos in carbonate veins forming the distal fringes and rising up to 800 m laterally and up to 790 m over carbonate-hosted and skarn orebodies are variable, broadest at depth and narrow at shallower levels in the hydrothermal system along the fluid escape channels. A t Yauricocha dolomitic rocks, are not abundant and are broadly restricted to the Celendin Formation. The "epithermal" suite o f elements (As, Sb, T l , H g and perhaps Cs) is also associated with low-grade distal A u in the Purisima Conception prospect, hosted in marls of the Celendin Formation (Alvarez and Noble, 1988; Noble et al., 2000). 4.1.5. Metal Zoning Lateral metal zoning is evident in Yauricocha. Low-grade porphyry style C u ± A u mineralization occurs at the core of the district. Proximal to the porphyry-carbonate intrusive contacts are Cu-rich zones (locally with high sulfidation mineralogy) grading outward to more 117 Zn-rich zones. Outward of the porphyry-carbonate contacts are Zn-Pb-Ag dominated zones lacking high sulfidation mineral assemblages. The most distal mineralization occurs as larger Ag-base metal (Pb-Zn) veins of potential economic interest, lying distal to the carbonate-hosted and skarn orebodies at Yauricocha and extending up to 3 km laterally from the center o f the district. These Ag-base metal veins provide a significantly larger exploration target than the main mineralized CRD-skarn bodies or the proximal veins. 4.1.6. Stable Isotope Halo Large oxygen isotope cryptic halos are mapped in carbonate rocks especially in the upper parts above ore zones (Kesler et al., 1995; Nesbitt, 1996). A t Yauricocha, widespread and consistent depletion in 8 1 8 0 reflects the pervasive percolation of magmatic driven fluids through the carbonate rocks and proximal and distal veins in the study areas at M i n a Central and Cachi Cachi. Oxygen isotope zonation in carbonate rocks and vein types extends beyond the visible alteration zones at shallow levels reaching at least up to 700 m and up to 790 m, respectively. Oxygen isotope depletions mark major fluid escape paths. Large negative 5 1 3 C is commonly attributed to organic C sources or to microbial activity. One potential source of organic carbon is the graphite oxidized and volatilized during bleaching of marble. A s with the other study areas throughout central Peru, 8 1 3 C depletions generally correlate with 8 1 8 0 depletion in the high temperature calcsilicate systems. 8 1 3 C and 8 1 8 0 depletions record the fluid escape at M i n a Central and Cachi Cachi and they are consistent with a magmatic fluid source. Depletion in 8 1 8 0 furthermore provides additional evidence for a link between skarn orebodies of Cachi Cachi, C R D s ores of M i n a Central and the distal veins found outside the sulfide ores. 4.2. Systematic V i e w o f Alteration Patterns A generalized model of the distal alteration surrounding the carbonate-hosted replacement and skarn orebodies at M i n a Central and Cachi Cachi within the Yauricocha district includes the distribution of bleached and unbleached limestone, marble, and minor hornfels, the distribution of millimeter to meter size proximal to distal veins surrounding mineralized zones, the metal content and stable oxygen and carbon isotope signature of rocks and proximal and distal veins, and the zonation of metals outward from the Yauricocha-Exito intrusion as summarized in the text above and graphically presented in Figure 4.1. 118 The systematic zoning visible at Yauricocha provides a view of a dynamic hydrothermal system that initially involved pervasive fluid flow along the structural and stratigraphic permeability that collapsed and became focused along the open fluid channels. The distribution of elements and minerals in these channels are controlled by the fluid rock interactions coupled with the temperature of the fluid and the composition of that spent fluid as it evolved moving away from the sites of sulfide deposition. The spatial distribution of distal alteration assemblages and veins emphasizes the importance of permeability in the form o f fracture and fault meshes as well as bedding in controlling the lateral extent of alteration and fluid escape from the C R D and skarn deposits at M i n a Central and Cachi Cachi. Where thepermeability is well developed at high angles to an intrusive contact, which appears to be the case at Yauricocha, hydrothermal fluids can alter the rocks at great distances. Geochemical dispersion halos are developed along the fluid escape channels, and are stronger near sulfide orebodies. Metal relationships are consistent with medium to high temperature for mineral deposition. Comparable elemental dispersion halos are systematic and indicative of an evolving hydrothermal fluid with elements typical o f high temperature environment, such as Zn , Pb, and C u accompany with elements of typical low temperature environment, such as A s , Cd , M n , Hg , Sb, and T l in rock and veins. Large oxygen isotopic depletion anomalies are found in the zone of marble within the thermal aureole of the intrusion, and are best developed within the zone o f bleached marble. Massive bleached marble is typically isotopically depleted and records percolation of substantial amounts o f magmatic fluid along major fluid escape structures such as bedding, fracture meshes, or faults. Visible and cryptic distal alteration is particularly well illustrated at M i n a Central and Cachi Cachi, where outcrop exposures allow distal veins to be traced above the sulfide orebodies, wel l above the extent of pervasive alteration. Alteration types that have been developed in halos include the following bleaching and associated recrystallization, laterally developed orange brown or gray carbonate minerals-sulfide veins, which are locally rich in M n oxides. Statistical correlations values between base metal and "epithermal" element suites are related to the depth of the system. They indicate a relative deeper origin for skarn ores relative to carbonate-hosted replacement ores and in conjunction with stable isotopic evidence indicate that magmatic-hydrothermal fluids dominate the vein systems at all levels. 120 4.3. Exploration Implications In summary, distal alteration patterns around M i n a Central and Cachi Cachi orebodies at the Yauricocha mining district indicate that fracture permeability dominate al l major fluid conducts at shallowest levels. The dominant fluid escape structures are sedimentary layering at Cachi Cachi and structural meshes at M i n a Central. Visible alteration is defined by marble halos, as well as by centimetre-scale calcsilicates-, orange brown- to white carbonates-, and M n oxides minerals, quartz and sulfide veins. Cryptic geochemical halos are defined by trace element abundance and oxygen and carbon isotope composition. In M i n a Central and Cachi Cachi, visible and cryptic alteration sequences extend up to almost 800 meters laterally from the intrusive contact, into the Jumasha and Celendin formations, and over a similar vertical distance. Visible and cryptic alteration halos can be used as a model to explore carbonate-hosted replacement and skarn orebodies in other areas with geological features similar to Yauricocha. Distal alteration features surrounding the carbonate-hosted and skarn orebodies of M i n a Central and Cachi Cachi within the Yauricocha mining district can provide valuable exploration guides. The same criterion is applied to the carbonate-hosted base and precious metal deposits in central Peru. The thermal aureoles surrounding porphyry related intrusions are an important place to focus exploration for C R D and skarn. Proximal veinlet networks or swarms surround and overlie mineralized zones providing a larger yet still relatively focused area in which to conduct exploration. Distal Ag-base metal veins extend the furthest, laterally and vertically, from mineralized zones. These veins provide the largest exploration target and can be useful district scale exploration guides. 121 References Alvarez, A . A . , and Noble, D . C , 1988, Sedimentary rock-hosted disseminated precious -metal mineralization at Purisima Concepcion, Yauricocha District, central Peru: Economic Geology, v. 83, no. 7, p. 1368-1378. Bissig, T., Escalante, A . , Dipple, G . , Ebert, S., Jurado, J., and Tosdal, R. , 2005, Sources and exhausts in polymetallic carbonate rock-hosted ore deposits: Miocene magmatism and alteration in central Peru: Mineral Deposit Research Unit, University of British Columbia. Jurado, 3., Dipple, G . , Ebert, E . , and Tosdal, R . M . , 2004, Distal alteration around the carbonate-hosted polymetallic replacement and skarn system at Yauricocha, central Peru [abs.]: X I I Congreso Peruano de Geologia. Jurado, J., Tosdal, R., and Dipple, G . , 2005, Geology and distal alteration at Cachi Cachi and M i n a Central, Yauricocha, Peru, in Bissig, T., Escalante, A . , Dipple, G . , Ebert, S., Jurado, J. , and Tosdal, R., Sources and exhausts in polymetallic carbonate rock-hosted ore deposits: Miocene magmatism and alteration in central Peru: Mineral Deposit Research Unit, University of British Columbia, Chapter 5. Kesler, S.E., Vennemann, T .W. , and Vazquez, R , Stegner, D.P. , and Frederickson, G . C , 1995, Application of large-scale oxygen isotope haloes to exploration for chimney-manto Pb-Zn-C u - A g deposits, in Coyner, A lan R., and Fahey, Patrick L . , eds., Geology and Ore Deposits of the American Cordillera: Geological Society of Nevada, Symposium Proceedings, Reno/Sparks, Nevada, p. 1383-1396. Nesbitt, B . E . , 1996, Applications of oxygen and hydrogen isotopes to exploration for hydrothermal mineralization: Society of Economic Geologists Newsletter, v. 27, p. 1-13. Noble, D . , Campbell, A . , Ressel, M . , and Kamali , C , 2000, Gold-rich quartz-pyrite veinlets and jasperoid with "Carlin-type" geochemical characteristic at Purisima Concepcion, Yauricocha district, central Peru: Sociedad Geologica del Peru, X Congreso Peruano de Geologia, L ima, Trabajos tecnicos, tomo 2, p. 489-496. Tosdal, R., and Bissig, T., 2005, Distal alteration around carbonate replacement deposits formed at shallow crustal levels: Matagente zone of Cerro de Pasco, central Peru, in Bissig, T., Escalante, A . , Dipple, G . , Ebert, S., Jurado, J., and Tosdal, R., Sources and exhausts in polymetallic carbonate rock-hosted ore deposits: Miocene magmatism and alteration in central Peru: Mineral Deposit Research Unit, University of British Columbia, Chapter 6. Tosdal, R., Dipple, G . , Ebert, S., Escalante, A . , Jurado, J., Bissig, T., and Pariguana, P., 2005, Atlas of distal alteration features found around carbonate-hosted polymetallic deposits, central Peru, in Bissig, T., Escalante, A . , Dipple, G . , Ebert, S., Jurado, J., and Tosdal, R. , Sources and exhausts in polymetallic carbonate rock-hosted ore deposits: Miocene magmatism and alteration in central Peru: Mineral Deposit Research Unit, University of British Columbia, Chapter 8. . 122 APPENDIX A Sampling Procedure and Samples Description A total of 173 samples were used in this study. Samples were collected using a rock hammer from wall rocks and major and minor fluid escape structures. Sampling method consisted in collecting in plastic bags about 1.5 to 2 kilograms of chip samples and about 15 x 15 cm in size hand samples of all the various host rocks and proximal and distal veins outcropping on surface at M i n a Central and Cachi Cachi. Some samples taken by Shane Ebert in the first year of the project (2002) are also included in the study. Sampling was based on grain size, texture or the distinctive color of the lithological unit and veins. Field observations included volume percentage of fractures, veinlets and sulfides, as well as the geometric and structural relationships between them. Systematic sampling transects were meant to capture the complete range of alteration styles outcropping within the district. Summary tables describing all the samples taken at both zones, M i n a Central and Cachi Cachi, between 2002 and 2003 and the abbreviations used on the descriptions are included in appendices A 1 - A 4 as Excel worksheets on attached C D . In Appendices A l and A 2 , unaltered rocks, altered host rocks, and vein types are described sequentially according to their distribution in each zone of alteration away from the intrusive or orebodies contacts (proximal to distal). A color code is also provided. Samples are geographically located based on their location on Plates 1 to 3. Two projections were needed due to the use of modern and old U T M system-based base maps provided by the Yauricocha mine personal. They are: U T M Zone 18S, P S A D 5 6 for samples located on Plates 1 and 3, and U T M Zone 18, Southern Hemisphere (WGS 84) for samples on Plate 2. Appendix A 3 lists all the abbreviations used in Appendices A l and A 2 . Samples taken by Shane Ebert on the first year of the project are described in Appendix A 4 . The first section of the appendix includes samples from M i n a Central (Main zone) and the second section, the ones from Cachi Cachi. 123 APPENDIX B Mineral Identification by P I M A One hundred and fifty five slabs and rough samples (seventy two for M i n a Central and eighty four for Cachi Cachi) were scanned using a portable short-wave infrared reflectance (SWIR) spectrometer ( P I M A II) at the University of British Columbia. The P I M A is commonly used in exploration of hydrothermal ore deposits for qualitative identification o f the mineralogy of altered rocks to define important compositional variation (mineral assemblages) and hence assist in identifying alteration patterns, classifying ore systems, and locating ore (Thompson et al, 1999). Typically, geologists have difficulty making identifications of these commonly fine-grained mineral species, their crystallinity, and composition. In this study, this technique was used to gather qualitative identification of the mineralogy of the altered rocks and veins types from proximal to distal phases of each zone o f alteration defined at M i n a Central and Cachi Cachi. The instrument can be operated in a lab or in a field setting. Pima requires no sample preparation and the analysis is totally non-destructive leaving no radiation damage. Measurements can be made on hole or partial rock chips, powders or soil samples (Pima Project, 2001-2003). Analysis of data requires the use of spectral reference libraries from different geological environments. Integration of results with field observations, petrography, and X-ray diffraction analysis is necessary for complete evaluation (Thompson et al., 1999). The P I M A II (Portable Infrared Mineral Analyzer) spectrometer operates in the wavelength region from 1300 to 2500 nm. In this wavelength region, minerals that contain hydroxyl (such as clays, amphiboles, some sulphates) and carbonate radicals absorb incident radiation, at specific wavelengths, in relative amounts that are diagnostic of the mineral species. Diagnostic spectra are produced. The hydroxyl and carbonate minerals are important components of alteration surrounding mineralization. Borates, phosphates, vanadates, ammonium minerals and some others also produce diagnostic spectra. The minerals absorb wavelengths o f incident radiation according to the energies of the stretching and bending vibrations of the carbonate and hydroxyl radicals in the mineral. These energies of vibration depend on the cation to which the radical is bonded (e.g. A l , Fe, Mg) and the structure, energies o f bonding and degree of ordering of the crystal lattice. The P I M A instrument produces reflectance spectra that were saved as individual binary files using Pima V i e w 3.1, a Windows 95/98/NT based program. It 124 allows easy viewing, analysis, plotting and printing of spectra acquired by the instrument. The spectra are measured on a sample area of about 10 mm by 2 mm (Pima II Operation Manual, 1994). References P I M A II operation manual (5 t h Edition), 1994: Integrated Spectronics, Document ref. N o . I S P L P 2 0 M - 5 , 2 6 p. Web page: http://www.intspec.com/PDFs/pimaII_manual.pdf. Pima Project, Pima Spectrometry, 2001-2003, Midcontinental Archaeometry Working Group ( M A W G ) : University of Illinois at Urbana-Champaign. Web page: http://www2.uiuc.edu/unit/ATAM/mawg/pima/home.html. Thompson, A . J . B . , Hauff, P .L , and Robitaille, A . J . , 1999, Alteration mapping in exploration: Application of short-wave infrared (SWIR) spectrometry, in S E G Newsletter: Society of Economic Geologist, No . 39, p. 16-27. 125 APPENDIX C Mineral Identification by X R D Twenty reference samples, denoted as " M D R U 80 to 99", were analyzed by qualitative powder X-ray diffraction using a Siemens Diffraktometer D5000 X-ray powder diffractometer at the University of British Columbia. X-ray crystallography is one of the most useful methods for exploring the nature of matter. X-ray diffractometry ( X R D ) is used to determine the phase content in many minerals and materials. A s a result, researchers in a wide range o f disciplines use it as an adjunct to chemical analysis in the identification of the constituents of mixtures of crystalline phases, e.g., in minerals, cements and alloys (C.A.S.T.I) . In this study, this technique was used to confirm P I M A and to help determine the phase contents of minerals. The samples were ground to a fine powder in an agate mortar and smeared on to a glass slide with ethanol. Step-scan X-ray powder-diffraction data were collected over a range 3-7O°20 with C u K a radiation on a standard Siemens (Bruker) D5000 Bragg-Brentano diffractometer equipped with a diffracted-beam graphite monochromator crystal, 2 mm (1°) divergence and antiscatter slits, 0.6 mm receiving slit and incident-beam Soller slit. The long fine-focus C u X-ray tube was operated at 40 kV and 40 mA, using a take-off angle o f 6°. The mineral identification process involved the drawing of the basal spacing of peaks (d in A) following the Bragg equation (nfc=2dsin6; n = first order Bragg diffraction peak, X -wavelength for the K radiation of C u (1.5418 A), d = interatomic or interplanar spacing between the atoms in the crystal, 29 = angle of diffraction => d = nX/2sin9). Mineral identification was done analyzing the X-ray diffractograms with automated search/match software supplied by Siemens (Bruker) using the complete International Centre for Diffraction Data ( ICDD) database PDF-4 (Raudsepp and Pani, 2005). In addition, twelve polished thin sections were prepared for M i n a Central and Cachi Cachi and analysed using a transmitted and reflected light polarizing Nikon O P T I P H O T 2-POL microscope. Summary tables providing macroscopic description, observations and results o f the P I M A and X R D studies of sample from both zones, M i n a Central and Cachi Cachi are included in Appendices C I and C2 as Excel worksheets on attached C D . Appendix C3 includes, as a Word file attached in C D , the X R D diffractrograms obtained with the automated search/match tool of the utilized software. 126 References Raudsepp, M . R , and Pani, E . , 2005, X-ray diffraction analysis of twenty samples, C R D project, l p . X R D diffractrometry: Centro per l'Assistenza Scientifica e Tecnologica alle Imprese (Center for Scientific and Technological Transfer Towards Companies) (C.A.S.T.I) . Web page: http://www.aquila.inma 127 APPENDIX D Trace Elements Analytical Methods and Results A total of 109 samples collected over traverses of up to 800 m W of the intrusive contact with mineralized zones and host carbonate rocks at M i n a Central and Cachi Cachi were prepared and analyzed for trace element geochemistry at A L S Chemex. Sample preparation process was conducted at their facilities in L ima and the geochemical analyses in Vancouver, B . C . Samples were dried and then fine crushed to better than 70% less than 2 mm. Next, a split off up to 250 grams was taken and pulverize to better than 85% passing 75 microns ( A L S Chemex schedule code PREP-31) . A l l the samples were analyzed for A u in parts per bi l l ion (pbb) by Fire Assay Fusion, lead pellet collection, with an Atomic Absorption Spectrometry ( A A S ) finish on a 30 gram sample ( A L S Chemex schedule code A u - A A 2 3 ) . This technique is used in exploration to detect low-level gold anomalies. The A A S provides an excellent resolution (0.005-10 ppm) for samples with a nominal weight of 30g. The process involves fire assay, cupellation, dissolution o f the lead-precious-metal-pill, pre-concentration solvent extraction, then flame atomic absorption. A l l o f the samples were also analyzed for 47 elements by HF-HNO3-HCIO4 acid digestion, HC1 leach and a combination of I C P - M S and I C P - A E S ( A L S Chemex schedule code M E -MS61) . The technique combines a strong 4-acid "near total" digestion that dissolves most minerals with a combination of I C P - M S and I C P - A E S analysis. The method provides highly cost-effective near total determination with low to very low detection limits. A 0.25 g split is heated in FINO3-HCIO4-HF to fuming and taking to dryness. Then the residue is dissolved in HC1 and solutions are analyzed by a combination of I C P - M S and I C P - A E S . Therefore the technique tests for the greatest number of trace elements with the fewest partial digestion or volatilization o f elements o f interest. Mercury was analyzed by conventional cold vapor atomic absorption spectroscopy ( A L S Chemex schedule code Hg-CV41) with a resolution of (0.01 -100 ppm). Over limits in A g , Pb, Zn , C u and M n O were analyzed by HF-HNO3-HCIO4 acid digestion, H C l leach and A A S or I C P A E S (for Cu) finish ( A L S Chemex schedule codes A g - , Pb-, Zn- , Cu- , M n - A A 6 2 ) . Trace elements are reported in parts per mil l ion (ppm) with the exclusion of M n O , Ca, M g , Fe, A l , K , Na , S, T i , and M n O that are reported as weight percent (wt %). 128 Correlation Coefficient The correlation coefficient measures the relationship between two data sets that are scaled to be independent of the unit of measurement. The population correlation calculation returns the covariance of two data sets divided by the product of their standard deviations: p x y = cov (x,y)/a x . o y c x 2 = l / n Z ( X i - | i x ) 2 oy2 = 1/n ECxi-riy) 2 The correlation is used to determine whether two ranges of data move together— that is, whether large values of one set are associated with large values of the other (positive correlation), whether small values of one set are associated with large values of the other (negative correlation), or whether values in both sets are unrelated (correlation near zero). Summary and detailed tables and graphs showing the trace elements results for M i n a Central and Cachi Cachi are included in Appendices D1-D4 as Excel worksheets and Word files on attached C D . Appendix D l lists the analytes, range of values, and experimental methods for each element. The first section of Appendix D2 and D3 include a summarized description and location of the samples, tables, and graphs showing geochemical results for all 49 elements for M i n a Central and Cachi Cachi, respectively. Samples are listed according to their distribution, in terms of distance, away from the intrusive contact. A s in appendices A l and A 2 , samples are geographically located using two projections: U T M Zone 18S, P S A D 5 6 for samples located on Plates 1 and 3, and U T M Zone 18, Southern Hemisphere ( W G S 84) for samples on Plate 2. For the plots (graphs in Appendices D2 and D3 , and Figures 3.7 and 3.8), concentrations below trace level are arbitrary assigned a concentration of 50% the detection limit. The second section of Appendix D2 and D3 lists the samples and geochemical results organized sequentially in terms of unaltered rocks, altered host rocks, and vein types. Appendices D2.1 and D.3.1 include correlation tables of host rocks, vein types (overall and by vein type), and orebodies for M i n a Central and Cachi Cachi, respectively. Correlation tables include statistical calculations for every single element, such as M i n and M a x (smallest and largest values), Mean, Median, Standard Deviation, 95 t h percentile (threshold), Mean + 129 Standard Deviation (statistical background), and 2Mean + Standard Deviation (statistical threshold) of sets of data, as well as detection limits. Appendices D2.2 and D3.2 include correlation coefficients plots o f host rocks, vein types (overall and by vein type), and orebodies for M i n a Central and Cachi Cachi, respectively. Appendices D2.3 and D3.3 include statistical thresholds values for the suit of elements: A u , A g , A s , Ba , B i , C d , C u , Hg , In, M n , M o , Pb, Sb, Te, T l , W and Z n that define halos around hydrothermal orebodies (Rose et al, 1979) at M i n a Central and Cachi Cachi, without considering high erratic values. Reference A L S Chemex, 2004: Canadian schedule of services & fee, p. 3, 8, 11, 13, 17-20. Web page: htt^://www.alschemex.conVseirices/services-feeschedule.htm. 130 APPENDIX E Oxygen and Carbon Stable Isotopes Analysis and Results Oxygen and carbon isotope studies on marble, limestone and carbonate vein were undertaken to obtain better understanding of fluid flow and permeability around M i n a Central and Cachi Cachi, fluid-rock interaction, sources of O and C , and links between both deposits. Calcite and dolomite 8 1 8 0 and 8 1 3 C isotopic compositions were measured in seventy-three samples from M i n a Central and Cachi at the Pacific Centre for Isotopic and Geochemical Research at the University of British Columbia. Powdered carbonate samples analyses were completed on a dual inlet/continuous flow Deltapius X L L S - I R M S mass spectrometer employing a Thermo Finnigan gas bench, T C / E A and Flash E A interfaces for high-precision measurement of the relative isotope abundances of 1 8 0 and 1 3 C . This mass spectrometer uses a thermochemical analyzer and automated carbonate mineral digestion system that permits the measurement of O isotopes from carbonate minerals, gases and liquids, and C isotopes in graphite, liquids, and gases. Between 200mg and 500mg of each sample or rock standard is weighed into a glass exetainer and sealed with a cap with a pierceable septum. The gas bench is loaded with samples interspersed with rock standards. The gas bench is at a constant temperature o f 32°C. The autosampler is set up to flush the closed exetainers with He for 5 minutes, to displace air in the headspace. Each exetainer is then acidified with 100% phosphoric acid to liberate CO2 gas, and allowed to equilibrate for an hour before analysis. The autosampler is loaded with both the acidifying needle and sampling needle, and is programmed to acidify the exetainer in the next row while measuring each sample. This keeps a constant reaction time for all samples. During the analyses, 10 aliquots of the sample CO2 are bracketed by 6 aliquots of a reference CO2 gas to provide internal calibration. External calibration is monitored using the carbonate standard N B S 18 and N B S 19. The values obtained for these two standards are used to calculate a fractionation correction that is applied to the sample results. 8 1 8 0 values are referred to V S M O W and hold uncertainty of about ± 0.45 %o, and 8 1 3 C values are with reference to V P D B with uncertainty of about ± 0 . 2 0 %o. After correction for fractionation, repeat analyses of N B S 18 give an average 8 1 3 C value of-5 .009 +/- 0.07%o and 131 5 1 8 0 value of 7.225 +/- 0.0827oo, N B S 19 give an average 8 1 3 C value o f 1.927 +/- 0.08%o and 8 , 8 0 value of 28.742+/-0.18. Detailed description of isotope samples, results, and representative graphs are included in Appendices E l - E 4 as Excel worksheets attached on C D . Appendices E l and E2 contain a summarized description and location o f the samples utilized in the stable oxygen and carbon isotope studies for M i n a Central and Cachi Cachi, respectively. Samples are listed in numerical order. Description of samples includes their location in terms of zones and distance from the intrusive contact, as wel l as field and laboratory estimated abundance of calcite, dolomite or orange brown carbonate. A s in appendices A and D , samples are geographically located using two projections: U T M Zone 18S, P S A D 5 6 for samples located on Plates 1 and 3, and U T M Zone 18, Southern Hemisphere (WGS 84) for samples on Plate 2. Appendix E3 includes the stable oxygen and carbon isotopes results, representative graphs, and raw data of M i n a Central and Cachi Cachi. Samples are grouped according to their location in zones as follow: Cachi Cachi Regional, Cachi Cachi grid, and M i n a Central. Distance from the intrusive for each sample is also included. Description and results of oxygen and carbon isotope studies for samples taken by Shane Ebert on the first year of the project are included in Appendix E4. The first section o f the appendix includes samples from M i n a Central (Main zone) and the second section, the ones from Cachi Cachi. 132 APPENDIX F Plates in Pockets Plate 1: Detailed geological and alteration map of the Yauricocha Min ing District, central Peru. Area of detailed geologic and alteration map at M i n a Central (Plate 2) and Cachi Cachi (Plate 3) are enclosed in black line insets. Plate 2: Geological and alteration map of the surface outcrops around M i n a Central, Yauricocha Min ing District, central Peru. Included on the map are the sample location and sample numbers that correspond to analysis presented in the appendices Plate 3: Geological and alteration map of the surface outcrops around Cachi Cachi, Yauricocha Min ing District, central Peru. Included on the map are the sample location and sample numbers that correspond to analysis presented in the appendices. 133 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0052439/manifest

Comment

Related Items