Volcanic Stratigraphy, Alteration Zoning, and Vein Paragenesis of the Sascha-Pelligrini Low- Sulphidation Epithermal System, Santa Cruz, Argentina

Queensland University of Technology School of Natural Resource Sciences

Quinn Eric Smith B. App. Sc. (QUT)

2009

Supervisor: Assoc. Prof David Gust

A Thesis submitted for the degree of Master of Applied Science (Queensland University of Technology)

KEYWORDS

Epithermal, Low-sulphidation, Gold-Silver, Vein Paragenesis, Deseado Massif, Chon Aike, Santa Cruz, Argentina

Abstract

The Sascha-Pelligrini low-sulphidation epithermal system is located on the western edge of the Deseado Massif, Santa Cruz Province, Argentina. Outcrop sampling has returned values of up to 160g/t gold and 796g/t silver, with Mirasol Resources and Coeur D‟Alene Mines currently exploring the property.

Detailed mapping of the volcanic stratigraphy has defined three units that comprise the middle Jurassic Chon Aike Formation and two units that comprise the upper Jurassic La Matilde Formation. The Chon Aike Formation consists of rhyodacite ignimbrites and tuffs, with the La Matilde Formation including rhyolite ash and lithic tuffs. The volcanic sequence is intruded by a large flow-banded rhyolite dome, with small, spatially restricted granodiorite dykes and sills cropping out across the study area.

ASTER multispectral mineral mapping, combined with PIMA (Portable Infra- red Mineral Analyser) and XRD (X-ray diffraction) analysis defines an alteration pattern that zones from laumontite-montmorillonite, to illite-pyrite- chlorite, followed by a quartz-illite-smectite-pyrite-adularia vein selvage. Supergene kaolinite and steam-heated acid-sulphate kaolinite-alunite-opal alteration horizons crop out along the Sascha Vein trend and Pelligrini respectively.

Paragenetically, epithermal veining varies from chalcedonic to saccharoidal with minor bladed textures, colloform/crustiform-banded with visible electrum and acanthite, crustiform-banded grey chalcedonic to jasperoidal with fine pyrite, and crystalline comb quartz. Geothermometry of mineralised veins constrains formation temperatures from 174.8 to 205.1°C and correlates with the stability field for the interstratified illite-smectite vein selvage.

associated with selenide-rich magmatic pulses, pressure release boiling and wall-rock silicate buffering.

The study of the Sascha-Pelligrini epithermal system will form the basis for a deposit-specific model helping to clarify the current understanding of epithermal deposits, and may serve as a template for exploration of similar epithermal deposits throughout Santa Cruz.

III

CONTENTS INTRODUCTION ...... 1

REGIONAL GEOLOGICAL SETTING ...... 3 SASCHA-PELLIGRINI EPITHERMAL SYSTEM ...... 7 METHODS ...... 9

FIELD INVESTIGATIONS ...... 9 SAMPLE PREPARATION AND ANALYTICAL TECHNIQUES ...... 10 Short Wave Infrared (SWIR) spectrometry ...... 10 X-ray Diffraction ...... 11 Microscopy ...... 12 Geochemistry ...... 13 Remote sensing ...... 14 RESULTS ...... 16

STRATIGRAPHY ...... 16 PETROGRAPHY ...... 21 Chon Aike Formation ...... 21 La Matilde Formation ...... 22 Other units ...... 23 GEOCHEMISTRY ...... 26 STRUCTURAL SETTING ...... 33 EPITHERMAL VEINING ...... 36 Quartz textures ...... 36 VEIN GEOCHEMISTRY AND MINERALOGY ...... 39 GEOTHERMOMETRY ...... 42 ALTERATION ...... 43 Regional Alteration – Multispectral Mineral Mapping ...... 43 Prospect Alteration – PIMA and XRD...... 46 ALTERATION GEOCHEMISTRY ...... 55 DISCUSSION ...... 61

VOLCANOLOGY ...... 61 Depositional setting ...... 61 Eruption styles ...... 63 Magma Petrogenesis...... 68 HOST ROCK CONTROL AND STRUCTURAL MODEL ...... 70 ALTERATION ZONING ...... 74 VEIN PARAGENESIS ...... 82 SUPERGENE OVERPRINT ...... 88 SUMMARY ...... 89 CONCLUSION ...... 93 REFERENCES ...... 96 APPENDIX 1...... 109 APPENDIX 2...... 115 APPENDIX 3...... 119 APPENDIX 4 (MAP) ...... 121 APPENDIX 5 (MAP) ...... 122

List of Figures

Figure 1. Conceptual models and genetic classifications of epithermal deposits ...... 3 Figure 2. Location of the Sascha-Pelligrini study area...... 6 Figure 3. Sample and prospect locations ...... 7 Figure 4. Comparison of accepted results for rock standard SEQG566 with returned analysis...... 14 Figure 4. Stratigraphy for the Sascha-Pelligrini study area...... 19 Figure 5. Interpretive geology, structure and mapped veining for the Sascha-Pelligrini study area...... 20 Figure 7. XRF major element results for Sascha-Pelligrini volcanic samples ...... 29 Figure 8. ICP-MS trace element results for Sascha-Pelligrini volcanic samples...... 30 Figure 9. REE spider diagrams for Sascha-Pelligrini volcanic samples...... 31 Figure 10. REE geochemistry normalised to upper crust, Bajo Pobre and lower crust xenoliths ...... 32 Figure 11. Vein trace orientation in Sascha Main indicating dextral oblique-slip movement...... 33 Figure 12. Sascha Main saccharoidal and chalcedonic vein phases ...... 35 Figure 13. Sascha Main ginguro vein phases ...... 35 Figure 14. Sascha Main pyritic-chalcedonic vein phases ...... 35 Figure 15. Backscattered SEM images of characteristic vein mineral assemblages...... 41 Figure 16. Backscattered SEM images of coexisting electrum-sphalerite grains ...... 42 Figure 17. Selected end-member spectra compared to known library spectra ...... 44 Figure 18. Aster mineral mapping results, simplified geology and gold geochemistry ...... 45 Figure 19. Selected end-member spectra used for mineral mapping and spectral unmixing ...... 47 Figure 20. PIMA and XRD profiles of individual vein phases from the Sascha Main vein zone ...... 50 Figure 21. PIMA and XRD profiles of individual vein phases from the Sascha Ginguro vein zone ...... 51 Figure 22. PIMA and XRD profiles of individual vein phases from the pyrite-chalcedony vein zone ...... 52 Figure 23. PIMA and XRD profiles of individual vein phases from the Sascha Sur vein zone ...... 53 Figure 24. ESEM images of alteration mineral morphologies ...... 54 Figure 25. Selected immobile elements and geochemical mass-changes for rhyolite crystal ash tuff alteration within Sascha Main...... 57 Figure 26. Selected immobile elements and geochemical mass-changes for rhyodacite ignimbrite alteration within Sascha Sur...... 58 Figure 27. Selected immobile elements and geochemical mass-changes for rhyolite ash tuff alteration within Pelligrini...... 59

Figure 28. Bar graph comparing net mass-changes for immobile elements Dy and Zr ...... 60 Figure 29. Styles of explosive eruptions ...... 67 Figure 30. Structural model for the Sascha-Pelligrini study area ...... 72 Figure 31. Riedel shear model for the Sascha – Pelligrini and Huevos Verdes systems ...... 72 Figure 32. Alteration zoning and mineral assemblage model ...... 75 Figure 33. Alteration zoning and mineral assemblages of the Hishikari epithermal system ...... 78 Figure 34. Vein paragenetic relationships for the Sascha-Pelligrini epithermal system ...... 82 Figure 35. Vein mineral paragenetic relationships for the Sascha-Pelligrini epithermal system ...... 83 Figure 36. Conceptual epithermal model for the Sascha-Pelligrini epithermal system...... 92

List of Tables

Table 1. End-member alteration mineral spectra locations ...... 14 Table 2. Representative whole-rock geochemical analysis...... 25 Table 3. Summary geochemical signatures of Sascha Main vein phases...... 39 Table 4. Calculated electrum-sphalerite formation temperatures...... 42 Table 5. PIMA and XRD results of characteristic alteration assemblages ...... 47 Table 6. Tabulated correlation coefficient values for immobile elements Dy, Sm and Y...... 60

List of Appendices

Appendix 1. Petrography ...... 110 Appendix 2. Quartz textures...... 116 Appendix 3. Digital Dataset...... CD Pocket Appendix 4. Sascha-Pelligrini Fact Geology Map...... Map Pocket Appendix 5. Sascha-Pelligrini Interpretive Geology Map...... Map Pocket

Statement of Original Authorship

The work contained in this Thesis has not been previously submitted for a degree of diploma at any other higher education institution. To the best of my knowledge, this contains no material previously published or written by another person except where due reference is made.

Signed: ______

Date: ______

VII

Acknowledgements

There have been numerous people who have provided invaluable assistance throughout the duration of my project who I would like to thank. Firstly, I would like to sincerely thank my supervisor Associate Professor David Gust for his time, work and commitment over the duration of the project.

I would also like to acknowledge the support and technical advice provided by Stephen Nano, Daryl Nunn and Mirasol Resources during field visits to Argentina. The project would not have been able to succeed without them.

Thank you to the QUT technical staff, in particular Luke Nothdurft, Loc Duong and Bill Kwiecien for their assistance and time on all the machines at QUT. Thanks to Peter Cole from the UQ rock prep lab for helping to process all the thin sections and samples.

Finally, special thanks must go to my family and friends for their support and encouragement along the way.

VIII

Introduction

Epithermal deposits provide significant gold for world reserves. Individual deposits can exceed 40 million ounces of contained gold (Lihir, Papua New Guinea), produce over 1 million ounces of gold per annum (Porgera, Papua New Guinea), and contain spectacular gold grades in excess of 100 ounces per ton (Midas, Nevada; Hishikari, Japan). Epithermal deposits vary significantly in size and form. They are often characterised by relatively small, banded quartz-chalcedony veins with spectacular visible gold, or large scale disseminated mineralisation associated with residual „vuggy‟ silica. Their importance provides impetus for understanding how they form.

Epithermal deposits are defined as being „formed by ascending hot waters near the surface in or near effusive rocks at relatively low temperature and pressure‟ (Lindgren, 1922) and are analogous to modern geothermal systems, with formation conditions of less than 200°c and less than 100 bars (Lindgren, 1933). Recent fluid inclusion studies suggest temperatures of ore deposition are less than 300°C, stable isotope analysis are consistent with a meteoric source of water and a magmatic volatile source for sulphur and carbon (Cooke and Simmons, 2000).

Initial classifications of epithermal deposits were based on geologic studies that summarise common features and formulate schematic or conceptual models. Conceptual models portray the anatomy of an epithermal deposit, showing the vertical and horizontal mineral and alteration zoning typically observed in epithermal districts (Buchanan, 1981). End-member models were formulated to incorporate deposit variability, and lead to classification based on depositional settings (Berger and Eimon, 1982). Detailed paragenetic studies outline variations in mineralogy, and indicate that epithermal deposits can be classified by observed mineral assemblages irrespective of depositional setting (Bonham, 1986; Heald et al, 1987; Berger and Henly, 1988).

Quinn Smith Master of Applied Science Thesis 1

Studies on phase relationships of observed mineral assemblages suggest that the variability of epithermal deposits is due principally to variations in fluid chemistry. Genetic classifications incorporate this observation and relate the deposit type to the oxidation state of the mineralising fluid (White and Hedenquist, 1990; Sillitoe, 1993; White and Hedenquist, 1995). Low- sulphidation (LS) epithermal mineralisation forms from reduced, near-neutral pH conditions, with H2S(aq) the predominant sulphur species. Temperatures of ore deposition are less than 300°C and salinities are usually less than 3.5 weight percent NaCl equivalent (Cooke and Simmons, 2000). High- sulphidation (HS) epithermal mineralisation forms from oxidised, acidic conditions, with SO2(g) formed from the disproportionation of magmatic gases. Temperatures of ore deposition vary from greater than 400°C to 100°C, with salinities generally less than 5 weight percent NaCl equivalent (Cooke and Simmons, 2000).

Current research in epithermal mineralisation indicates that HS and LS deposits are end-members of a transitional environment, with the existence of deposits characterised by mineral assemblages intermediate between HS and LS deposits (Hedenquist and Arribas, 2000). Genetic classifications of epithermal deposits are subject to continual debate. Corbett (2002, 2004, and 2005) suggests epithermal mineralisation forms largely from the same fluid source, with end-member deposits due to differing tectonic regime, host rocks, depth of formation, relation to intrusive bodies and dominance of circulating meteoric fluids (Figure 1).

Specific deposits often differ from the general model, with conceptual and genetic classifications of epithermal deposits continually evolving. Examination of individual deposits both test and refine the general model. This thesis aims to develop a deposit specific model for the geology, zoning of vein mineral textures, mineral assemblages and associated geochemistry, and alteration assemblages for the Sascha – Pelligrini LS epithermal system in Santa Cruz, Argentina. The deposit specific model will help to clarify the current understanding of epithermal deposits by providing a test of the genetic and conceptual classifications. The deposit specific model may also

Quinn Smith Master of Applied Science Thesis 2

serve as a template for exploration of similar epithermal deposits throughout Santa Cruz.

Figure 1. Conceptual models and genetic classifications of epithermal deposits showing end-member high- and low-sulphidation styles to be part of a broader range of hydrothermal systems. (Corbett, 2005).

Regional geological setting

The Sascha-Pelligrini epithermal system falls within the Deseado Massif - a large region of subdued upland physiography that is flanked by the Austral Basin to the south, the San Jorge Basin to the north, the Andean cordillera to the west and the Atlantic Ocean to the east. The Deseado Massif is host to thick sequences of Permo-Triassic rift sediments emplaced in north- to northwest-trending basins in Precambrian and Lower Palaeozoic rocks (Echavarria et al, 2005). Precambrian and Lower Palaeozoic upper greenschist to amphibolite facies metamorphic basement crops out within or near the valley of the Rio Deseado. Sedimentation occurred at the onset of widespread extensional tectonics that eventually resulted in the Gondwanaland break-up. The Middle Triassic El Tranquilo Formation represents the last traces of this phase of sedimentation as uplift commenced

Quinn Smith Master of Applied Science Thesis 3

in the Lower Jurassic. Calc-alkalic granitic stocks and dikes of the La Leona Formation, which are found in rare localities to the east, (Sanders, 2000) were emplaced during this uplift.

After the lower Jurassic uplift, widespread subsidence and deposition of a range of continental-fluvial sedimentary rocks occurred in the Deseado Massif.

Volcanic activity commenced in the Lower-Middle Jurassic. This activity was characterised by the extrusion of flood basalts and the intrusion of mafic dikes and sills that, together with minor clastic sedimentation, compose the Bajo Pobre Formation. The thickness of this sequence ranges from 200 to 1,000 meters and is controlled by northeast-trending half-graben structures of which the southern sides show the thickest accumulations (Sanders, 2000). These structures were created by a new kinematic regime that persisted through to the Neocomian that produced a structural fabric that is approximately normal to the Permo-Triassic graben trends.

Unconformably overlying the Bajo Pobre Formation is the Bahia Laura Group, which is comprised of the Middle Jurassic Chon Aike Formation and the Middle to Upper Jurassic La Matilde & Bajo Grande Formations. These rocks form a large ignimbritic plateau composed of lava flows, pyroclastic rocks, ash-flow tuffs and re-worked volcanic and non-volcanic epiclastic sequences. The volcanic rocks range in composition from basaltic-andesite lavas and rhyodacite to rhyolitic ash-flow tuffs. The sequence represents a marked increase in the volume and areal extent of volcanic deposition as magmatic activity migrated westward towards the Andean continental margin (Gust et al, 1985).

The Deseado Massif epithermal veins are contemporaneous with the waning stages of the volcanism represented by the Bahia Laura Group rocks. Dating of various mineral deposits (Echavarria et al, 2005) indicates that the volcanic host rocks are only several millions of years older than the hydrothermal systems responsible for the economic mineralisation.

Quinn Smith Master of Applied Science Thesis 4

Circular caldera structures, irregular partial-collapse features and linear fissures are identified within the Chon Aike Formation and are locally associated with mineralised hydrothermal alteration systems. A late-stage resurgent dome activity has emplaced the rhyolitic and dacitic intrusive rocks and ash-flow tuffs of the La Matilde and Bajo Grande Formations (Sanders, 2000). This period of hypabyssal volcanic activity is closely related to economic mineralisation throughout the Massif.

A series of rock formations have been deposited within the Deseado Massif subsequent to the Late Jurassic. These form cover sequences to the mineralisation and represent the end of subsidence and the establishment of „cratonic‟ stability across the Massif. These cover sequences include the continental sediments and pyroclastic rocks of the Middle Cretaceous Baqueró Formation and a series of back-arc, olivine basalt flows that inter- finger with continental and shallow marine volcano-clastic sediments of Upper Cretaceous to Upper Tertiary transgression-regression cycles (Gorring et al, 1997). The Andean stage of Late Cainozoic uplift resulted in further widespread eruption of olivine basalt flows and tuffs that form the dissected plateaus of the modern landscape (Panza and Franchi, 2002). The Deseado Massif is covered in the north and south by Late Pliocene to Recent coarse gravels known as the “Rodados Patagónicos”.

Quinn Smith Master of Applied Science Thesis 5

Figure 2. Location of the Sascha-Pelligrini study area, distribution of Chon Aike volcanics, operating mines and advanced exploration projects of Santa Cruz, Argentina.

Quinn Smith Master of Applied Science Thesis 6

Figure 3. Locations of samples used for whole-rock geochemistry, and alteration analysis. Also shown are the prospect locations across the study area. Sascha Main, Sascha Central and Sascha Sur comprise the Sascha Vein Zone (SVZ). Map projection WGS84 SUTM19.

Quinn Smith Master of Applied Science Thesis 7

Sascha-Pelligrini epithermal system

The Sascha-Pelligrini epithermal system comprises an area of approximately 70 square kilometers on the western edge of the Deseado Massif, north- central Santa Cruz Province, Argentina (Figure 2). The Sascha-Pelligrini epithermal system is expressed as intermittent outcropping epithermal veins and pervasive silicification, and consists of the Sascha Vein Zone (SVZ), Marcellina and Pelligrini prospects (Figure 3).

The SVZ was initially discovered during reconnaissance exploration for Orvana in 1997. Mirasol subsequently visited the area and staked the property in October 2003 during the inception of its Santa Cruz exploration program (Smith et al, 2006).

The SVZ is centered on a 4.4 kilometer long vein trend and encompasses the Sascha Main, Sascha Central and Sascha Sur zones. Sascha Main is a 1.7 kilometer-long, northwest-trending zone of intermittently outcropping, sub- parallel veins and structural splays that collectively define a corridor reaching 300m in width. Exposed veins are up to 2 meters wide, and display classic low-sulphidation crustiform-colloform quartz textures. Assay results from 50 vein samples average 14.23g/t gold and 89.8g/t silver, with values of up to 160g/t gold and 796 g/t silver.

Sascha Central is a continuation of the SVZ, and is expressed as small discontinuous veinlets and un-mineralised goethite-rich shears. Sascha Central encompasses a 1.2 kilometer long un-mineralised corridor between the Sascha Main to the north and Sascha Sur to the south.

Sascha Sur is a 1.2 kilometer long zone of semi-continuous multi-directional veinlets. Individual veinlet zones are up to 40 meters wide. Individual veinlets are typically 1 to 30 centimeters wide with rare veining up to 1.5 meters wide. Assay results from 120 composite veinlet samples average 0.2 g/t gold and 3.4 g/t silver with values of up to 1.6 g/t gold and 158 g/t silver.

Quinn Smith Master of Applied Science Thesis 8

The Marcellina prospect occurs on a parallel structure to the SVZ and crops out as a small veinlet and vein breccia zone. The veinlet zone reaches 20 meters in width, with individual veinlets typically being 1 to 20 centimetres wide. Vein sampling has returned assays of up to 0.25 g/t gold and 1.16 g/t silver.

The Pelligrini prospect forms a predominant topographic high within the study area and is manifest as a large zone of intense silica replacement, brecciation and minor veining. Assayed samples contain up to 1.47 g/t gold and 11 g/t silver from minor quartz veins located stratigraphically below the silica replacement horizon.

Methods

Field investigations Geologic mapping has been completed across the study area including detailed outcrop and vein facies mapping at 1:1000 and 1:2500 scales over the vein zones (Appendix 3). Prospect scale geologic mapping was completed at 1:5000 with regional mapping completed at 1:25,000 (Appendix 4 & 5). Detailed mapping was constrained by GPS-surveyed tape and compass grids, with prospect and regional mapping constrained with rectified air photo images and GPS. Spatial positioning of the air photo was achieved through the use of ER Mapper, using a cubic polynomial rectification constrained to ASTER satellite imagery with approximately 120 control points. Original detailed outcrop mapping was subsequently repositioned with differential GPS (DGPS) control.

Trench sections were mapped at 1:200 scale, with vein windows mapped at 1:50 scale. Trench start and end points were DGPS-positioned, with trench length, orientation and topography measured with tape, compass and clinometer. Survey data for individual sections were plotted on graph paper for field mapping. Vein windows were mapped on a measured tape grid, with

Quinn Smith Master of Applied Science Thesis 9

control at 50cm intervals. Trench floor and wall geology, veining, structure and alteration were mapped with tape and compass control along the trench floor. 39 trenches were mapped over 1485 meters (35 at Sascha Main, 4 at Sascha Sur)(Appendix 3). All trenches were photographed on 1 to 2 meter intervals, with photos combined into composite images for individual trenches.

Sample preparation and analytical techniques

Short Wave Infrared (SWIR) spectrometry Alteration sampling was conducted across the study area for analysis by a Portable Infrared Mineral Analyser (PIMA). Regional traverses perpendicular to the vein trend at 250 meter sample spacing were undertaken to determine the extent of the alteration halo and define background geological response. Detailed traverse lines perpendicular to the vein at 5 and 1 meter sample intervals were conducted to identify zonation within the alteration system. Vein wall rock and vein clay samples were collected to define individual vein phase assemblages. A total of 199 hand samples were collected across the study area for PIMA analysis (Appendix 3). PIMA hand samples were air dried for 48 hours, with PIMA sample surfaces cleaned of loose material prior to analysis.

Alteration samples were analysed using a PIMA II, operated by Integrated Spectronics control software version 3.4.0, at IAMGOLD in Mendoza, Argentina. The PIMA II cycle count was left at the standard 0.2409, with controller version of 1.58. An internal calibration was conducted on start-up, and then after every 10-20 samples. Calibration was performed on samples SP223, SP210, SP189, SP179, SP159, SP149, SP139, SP125, SP109, SP079, SP059, and SP039. Samples were held to the sight window for an analysis of approximately 30 seconds, with the internal reference sample following for another 30 seconds. The PIMA II operating temperature was maintained below 38ºC.

Quinn Smith Master of Applied Science Thesis 10

PIMA spectra were analysed with „The Spectral Geologist‟ (TSG) computer program. Raw PIMA II spectra were interpreted through „The Spectral Assistant‟ (TSA) within TSG. Output information included mineral 1, weight 1, mineral 2, weight 2, TSA Error, AlOH 2200nm Absorption Wavelength, and ALOH 2200nm Absorption Depth (Appendix 3).

X-ray Diffraction Samples were prepared for chemical analysis and x-ray diffraction at the University of Queensland (UQ) sample preparation laboratory. Samples were dried for three days at 60ºC, and then crushed using a hardened steel jaw crusher and disc mill. Rock chips were pulverised using a hardened steel swing mill, with approximately 100 grams of material pulverised for 45 seconds to obtain an ideal particle size of 100 microns.

Samples of vein and wall rock alteration were prepared for clay and mineral assemblage identification. Orientated clay samples were prepared by ultrasonic dispersion of approximately 2g of pulverized material in ten times its volume of distilled water. Material left in suspension after 5 minutes was separated by pipette, and spread over a glass slide. The samples were left to dry on top of a warm surface until the water had evaporated, leaving a gravimetrically separated clay fraction.

Randomly orientated powder samples for quantitative XRD analysis were prepared by micronisation. Approximately 3g of pulverized material and 12ml of alcohol were placed into the micronisation mill using agate cylinders and milled for 5 minutes. The slurry obtained is homogenous and the particle size is ideally 1-5 microns. The slurry was placed into pre-labeled glass beakers and left to dry in an oven at 60°c. Once dried, about 1.5-2g of sample was re- mixed and lightly packed into circular aluminum sample holders.

58 PIMA and hand samples of vein and wall rock alteration were analysed for clay and mineral assemblages by X-Ray Diffraction (XRD) at the X-Ray Analysis Facility (XAF) Queensland University of Technology (QUT). The

Quinn Smith Master of Applied Science Thesis 11

XRD analyses were carried out on a Philips wide-angle PW 1050/25 vertical goniometer using Co Kα radiation. The samples were measured with steps of 0.02° 2θ and a scan speed of 1.00° per minute from 3 to 75° 2θ. Spectra were analysed with the software packages TRACES and SIROQUANT for mineral identification (Appendix 3).

Microscopy Twenty-four cover slipped sections were prepared for petrographic analysis. Nineteen polished sections were made of vein samples for petrographic and microprobe analysis. Twelve alteration samples were prepared by breaking rock fragments to expose fresh surfaces, and mounting on aluminium stubs with carbon tape. Polished sections and mounted rock fragments were carbon coated prior to microprobe analysis.

Microprobe analyses were undertaken at the QUT Analytical Electron Microscopy Facility using a JEOL-JXA-840A Scanning Electron Microprobe with an Energy-Dispersive Spectrometry (EDS) detector. Operating conditions for the quantitative determination of mineral chemistry were: 20kV accelerating voltage, beam current of approximately 1.7nA, count time of 100 seconds, 38mm working distance, 40° take off angle for the EDS detector and a focused beam of <10μm in diameter. EDS spectra were collected and interpreted through Moran Scientific quantitative EDS software. Vein minerals were probed between 2 and 8 times from core to rim, with a total of 381 spectra collected from 8 sections (Appendix 3).

Clay morphology analyses were undertaken at the QUT Analytical Electron Microscopy Facility using a FEI Quanta Environmental Scanning Electron Microscope with an Energy-Dispersive Spectrometry (EDS) detector Samples were analysed in high vacuum with operating voltage between 15 and 20kV. Working distance was set to 10mm with a spot size of 3 to 4 angstroms (Appendix 3).

Quinn Smith Master of Applied Science Thesis 12

Geothermometry Formation temperatures are calculated from compositional relationships between coexisting electrum and sphalerite mineral grains. The equation derived by Shikazono (1985) uses the mole fraction of silver in electrum and the mole fraction of FeS in sphalerite to calculate a pressure independent temperature and is expressed as:

2 3 T = (28,765 + 22,600 x (1- NAg) – 6,400 x (1- NAg) ) /(49.008 – 9.152 log XFeS + 18.2961 log 2 NAg + 5.5 x (1- NAg) ),

Where NAg, XFeS, and T denote mole fraction of silver in electrum, mole fraction of FeS in sphalerite and absolute temperature in degree Kelvin (+/- 20º) respectively.

Geochemistry Twenty-four whole rock samples, including 2 quartz blanks, 1 standard and 1 duplicate were analysed for major, trace and rare-earth geochemistry. Rock sample SEQG566 (Moultrie, 1995), with known major and trace element geochemistry, was used as an internal standard for comparison (Figure 4) (Appendix 3). Major elements (Si, Al, Ca, Fe, K, Mg, Mn, Na, P, Ti, S, and Cr) were determined by X-ray fluorescence (XRF) Silicate Fusion at Ultra Trace Analytical Laboratories in Perth, Western Australia. Glass beads were prepared using a sample/flux ratio of 12:22.

Trace and rare earth elements (Ag, As, Ba, Ce, Co, Cs, Cu, Dy, Er, Eu, Ga, Gd, Hf, La, Li, Nb, Nd, Rb, Sb, Sm, Sr, Th, Y,Yb, and Zr) were determined by Inductively Coupled Mass Spectrometry (ICP-MS) at Ultra Trace Analytical Laboratories.

Samples were digested in hydrofluoric, nitric, hydrochloric and perchloric acids allowing a total digestion in most samples. Loss on ignition (LOI) was determined with samples heated between 105 and 1000 degrees Celsius. LOI results were determined gravimetrically and reported on a dry sample basis.

Quinn Smith Master of Applied Science Thesis 13

350 y = 1.0618x R2 = 0.9987 300

250

200

150

100

Trace Element Standard Standard (ppm)Element Trace 50

0 0 50 100 150 200 250 300 350 Trace Element Analysis (ppm) Figure 4. Comparison of accepted results for rock standard SEQG566 with returned analysis performed by Ultra Trace Laboratories, Perth.

Remote sensing

Image acquisition ASTER Level 1B data was acquired through NASA‟s data acquisition request (DAR) process. A formal research proposal was submitted to NASA for ASTER data acquisition. The proposal was submitted through; http://asterweb.jpl.nasa.gov/gettingdata/authorization/proposal.asp

The proposal was accepted by NASA, with Michael Abrams, ASTER Science Team Leader Jet propulsion laboratory, uploading two level 1B scenes to the asterweb.jpl.nasa.gov FTP site for download. The scenes were downloaded and contained the following image identification numbers;

AST_L1B_003_03122003143108_03272003165841.hdf And AST_L1B_00301192005143600_01312005113946.hdf

Quinn Smith Master of Applied Science Thesis 14

Image processing ASTER scene „AST_L1B_00301192005143600_01312005113946.hdf‟ was cloud-free over the entire study area and was subsequently chosen for multispectral image processing.

The level 1B ASTER scene was atmospherically corrected through the use of the computer software „FLASH‟, utilising a modified transform 5 process. The atmospherically corrected ASTER scene was processed in ENVI4.2 and registered from the ephemeral satellite information. Mineral spectra were identified through band rationing outlining the presence of kaolinite, illite and alunite. The most spectrally pure pixels were determined through the use of the „Pixel Purity Index‟ (Broadman et al, 1995), highlighting end-members of kaolinite, illite and alunite. End-member spectra were chosen from the image for comparison with the USGS spectral library and subsequently used as a standard for further processing.

The locations for each of the end-member mineral spectra are as follows;

Mineral Spectra Easting Northing Datum/Projection Alunite 415106E 4713855N WGS84/SUTM19 Illite 410096E 4705185N WGS84/SUTM19 Kaolinite 412646E 4705425N WGS84/SUTM19 Table 1. End-member mineral spectra locations used for ASTER image processing.

The ASTER scene was subset to the study area and transformed to „minimum noise fraction‟ (MNF) space to reduce background noise and spectral scatter (Broadman et al, 1995). Natural surfaces are rarely composed of a single uniform material and spectral mixture modelling is necessary to identify areas of mixed spectral signatures (Kruse and Hintington, 1996). The subset MNF image was processed with Global Ore Discovery‟s proprietary „mixture tuned matched filter‟ (MTMF) analysis to identify pixels containing variable amounts and mixtures of kaolinite, illite and alunite. The MTMF analysis produced information related to abundance, and infeasibility for the mineral within a given pixel. Pixels containing a low

Quinn Smith Master of Applied Science Thesis 15

infeasibility and high abundance for a given mineral were subjectively chosen by evaluating populations from a scatter plot of infeasibility versus abundance. The MTMF data was smoothed with a convolution median filter on a 3x3 pixel matrix.

Abundance grids for kaolinite and illite were exported as high resolution geotiff's and subsequently opened in MapInfo. The alunite shape files were opened in MapInfo and converted to vector data. The ASTER VNIR 231 image was compressed and exported to ecw format (Appendix 3).

Results

Stratigraphy The volcanic stratigraphy of the Sascha-Pelligrini area is divided into five units; of these, three units comprise the Chon Aike Formation and two comprise the La Matilde Formation (Figure 5). The Chon Aike Formation consists of a basal massive, biotite rhyodacite welded ignimbrite, a middle pumiceous, biotite rhyodacite welded tuff, and an upper clast-rich, welded rhyodacite crystal ash tuff. The La Matilde Formation comprises a basal lithic ash rhyolite tuff which grades into a crystal ash rhyolite tuff, and is overlain by a unit of finely laminated rhyolite ash tuffs with spherulitic and accretionary lapilli horizons. Unit thickness is highly variable and the thicknesses reported are representative of maximum exposed thickness. The Chon Aike Formation is 678 meters thick and the La Matilde Formation is 130 meters thick in the Sascha-Pelligrini area. Reported Chon Aike Formation and La Matilde thicknesses range from 300 to >900 meters and 15 to >175 meters respectively (Echavarria et al, 2005; Sanders, 2000).

The lower unit of the Chon Aike Formation crops out throughout the study area and is relatively homogenous in appearance (Figure 6; Appendix 4 & 5). Internal variations include variably welded horizons and the inclusion of small clasts of rare mica schist. Welding within the rhyodacite ignimbrite varies both vertically and horizontally, and forms composite welding horizons

Quinn Smith Master of Applied Science Thesis 16

preserved as topographic highs across the study area. The estimated thickness of the unit is 570 meters. The overlying unit is similar in composition, but contains pumice and occasional hematite-chlorite altered juvenile lava clasts. It is also welded with compaction ratios of fiamme of up to 10:1. The estimated maximum thickness of this unit is 100 meters. The top of the Chon Aike Formation is composed of a welded rhyodacite crystal ash tuff that contains juvenile and accidental clasts comprised of fine grained granite, hematite-chlorite, and mica schist. The unit also contains abundant large angular spherulitic devitrified volcanic glass and pumice fragments. The estimated thickness of the horizon is 8 meters.

The La Matilde Formation exhibits paraconformable contacts with the underlying sequence. The basal unit of the La Matilde Formation is a rhyolitic tuff that varies from a sparsely distributed lower lithic –rich horizon (~10 to 20 meters thickness) to a more geographically widespread upper ash-flow tuff (~75 meters thickness). The lithic-rich horizon contains accidental clasts of angular and rounded metamorphic rocks. Clast size and angularity increase towards the northwest with the unit becoming pumiceous towards the southeast. The upper ash-flow is a rhyolite tuff with occasional devitrification textures. Finely laminated rhyolite ash tuffs with locally developed spherulites and accretionary lapilli horizons crop out within the Pelligrini prospect (Figure 6; Appendix 4 & 5) and overlie the ash-flow tuff. The laminated ash tuff mantles the topography of the underlying unit, and attains a maximum exposed thickness of 55m. The La Matilde Formation exhibits extreme vertical and lateral variation.

A large flow-banded to spherulitic rhyolite dome with auto-brecciated margins crops out within the Pelligrini prospect and intrudes into the upper-most unit of the La Matilde Formation (Figure 5 & 6; Appendix 4 & 5). The volcanic tuff sequences are intruded by small, spatially restricted, biotite-albite porphyritic granodiorite dykes and sills.

The Jurassic volcanic sequence is unconformably overlain by a 15 meter thick Oligocene feldsarenite to sparry grainstone that is preserved in

Quinn Smith Master of Applied Science Thesis 17

topographic depressions. The unit has a conglomeritic base comprised of rounded tuff fragments to 10 centimeters in diameter, grading upward to a sandy feldsarenite intercalated with bivalve, gastropod and bryzoan fragments. Epiclastics and fine laminated rhyolitic ash surges with prominent cross stratification and carbonized plant fragments are locally developed at the top of the unit (Appendix 1, plate 12). The unit is best exposed to the west of the SVZ and intermittently crops out under overlying cover sequences (Figure 6; Appendix 4 & 5).

Pliocene olivine tholeiite basalt forms a large plateau that runs through the middle of the study area and also intermittently crops out as remnant plugs and dykes. Pleistocene gravels and recent sediments cover most of the low- lying areas, with gravels being best preserved as plateau caps to the Oligocene feldsarenite (Figure 6; Appendix 4 & 5).

Quinn Smith Master of Applied Science Thesis 18

Figure 5. Stratigraphy of the Sascha-Pelligrini study area showing correlated unit age, diagrammatic relationship of rock units, unit thicknesses and grain size.

Quinn Smith Master of Applied Science Thesis 19

Figure 6. Interpretive geology, structure and mapped veining of the Sascha-Pelligrini study area. Unit colours are the same as figure 5.

Quinn Smith Master of Applied Science Thesis 20

Petrography

Least altered samples from each lithology within the study area were selected for petrographic examination.

Chon Aike Formation The lower ignimbrite of Chon Aike Formation is crystal rich with subordinate lithic clasts. The phenocryst assemblage comprises sodic plagioclase (30%), sanidine (20%), quartz (30%), biotite (10%), muscovite (5%), ilmenite and magnetite (5%). Plagioclase and sanidine phenocrysts occur as moderately altered, subhedral to euhedral, broken fragments ranging up to ~4mm in length. Quartz phenocrysts are large, ranging up to ~5mm in size, and are significantly embayed. Biotite and rare muscovite occur as small plates and books ranging up to ~2mm in size, and are usually altered to chlorite and sericite respectively. Ilmenite and magnetite constitute minor phenocryst phases but are generally abundant in the less altered groundmass. Very small accessory phases including zircon and apatite rarely occur in the samples. Devitrified glass shards (<1mm) comprise the majority of the groundmass. The glass shards are intensely welded with no original texture preserved (Appendix 1, Plate 1).

The middle welded tuff of the Chon Aike Formation is pumice and ash rich with rare juvenile lava clasts. Strongly welded and deformed devitrified glass shards (<1mm) comprise the majority of the unit with no original x, y or cuspate shapes preserved. Pumice glass is totally altered, with rare axiolitic devitrification developed on pumice margins and spherulites developed within pumice interiors. Pumice clasts are strongly flattened, range in size of up to 12cm in length and define a strong eutaxitic texture. The phenocryst assemblage of the middle unit comprises albite (20%), sanidine (15%), quartz (30%), biotite (10%), pumice (20%), ilmenite and magnetite (5%). Albite and sanidine phenocrysts are subhedral, strongly sericitised, and range up to ~2mm in length. Biotite occurs as subhedral to euhedral plates and minor books ranging up to ~2mm in length, and is also strongly

Quinn Smith Master of Applied Science Thesis 21

sericitised. Quartz occurs as angular subhedral fragments ranging up to ~4mm in size (Appendix 1, Plate 2).

The upper crystal ash tuff of the Chon Aike Formation is crystal and ash rich with abundant accidental and juvenile lava clasts. The unit is comprised of abundant moderately welded and strongly deformed devitrified glass shards (<1mm). The horizon is unique with rare cuspate shapes preserved within the glass shards. Strong mantling and welded textures occur around larger lithic and juvenile clasts. Phenocryst are comprised of albite (20%), sanidine (25%), quartz (35%), biotite (15%), ilmenite and magnetite (5%). Albite and sanidine phenocrysts occur as moderately altered subhedral to euhedral broken fragments ranging up to ~3mm in length. Quartz phenocrysts range up to ~4mm in size, and are moderately embayed. Biotite and rare muscovite occur as small plates and books ranging up to ~2mm in size, and are usually altered to chlorite and sericite respectively. Ilmenite and magnetite constitute minor phenocryst phases and are generally abundant only in the lesser altered groundmass. Lithic clasts distinct to the horizon are comprised of rare mica schist and strongly altered fine-grained granitic fragments. Abundant juvenile lava clasts range up to 15mm in diameter and are strongly altered to chlorite and hematite. Angular volcanic glass fragments contain abundant spherulitic devitrification textures and range up to 10mm in size. Silicification replaces pumice glass with fine grained quartz, preserving devitrification textures (Appendix 1, Plate 3).

La Matilde Formation The basal unit of the La Matilde Formation is crystal rich with abundant lithic clasts. The phenocrysts comprises feldspar (35%), quartz (45%), muscovite (15%), ilmenite and magnetite (5%). Feldspars are subhedral broken fragments, completely sericitised, and range up to 5mm in size. Quartz phenocrysts are subhedral broken fragments and range up to 2mm in size. Muscovite occurs as small plates and is strongly sericitised. Weakly-welded devitrified glass shards (<1mm) comprise the groundmass, with no original shard textures preserved. Lithic clasts are comprised of distinct rounded muscovite schist and range up to 10cm in size (Appendix 1, Plate 4).

Quinn Smith Master of Applied Science Thesis 22

The lithic basal unit of the La Matilde Formation grades into an ash-rich crystal rhyolite tuff. The phenocryst assemblage of the crystal rhyolite tuff comprises sanidine (30%), quartz (50%), and muscovite (20%). Sanidine phenocrysts occur as large subhedral to euhedral broken fragments and range up to 3mm in size. Quartz phenocrysts occur as strongly embayed subhedral broken fragments and range up to 3mm in size. Muscovite phenocrysts range up to 1mm in length and occur as small plates. Poorly welded devitrified glass shards comprise the majority of the groundmass, with rare cuspate textures preserved. Rare axiolitic to bow-tie devitrification textures form around phenocrysts (Appendix 1, Plate 5).

The upper unit of the La Matilde Formation is comprised of abundant ash with minor phenocrysts. Broken, subhedral to euhedral sanidine crystals are the only phenocrysts phase in the unit. Intensely altered glass shards comprise the majority of the tuff, with no original shard textures preserved. Silicification is strong within the unit and replaces volcanic glass, preserving spherulitic devitrification and accretionary lapilli textures (Appendix 1, Plate 6).

Other units The flow-banded rhyolite contains euhedral phenocrysts within a finely crystalline groundmass. Euhedral sanidine crystals are the only phenocryst phase present. The strongly sericitised groundmass is comprised of very fine feldspar and quartz crystals. Flow-banded textures are distinguished by alternating quartz-rich and feldspar-rich layers. Large spherulitic devitrification textures (<5mm) develop within the unit in areas that are glass- rich and phenocryst-poor. Silicification is strong within the unit preserving flow-banded and spherulitic textures (Appendix 1, Plates 8 & 9). Auto-breccia is locally developed around the margins of the flow-banded rhyolite. Large angular clasts of flow-banded and spherulitic rhyolite up to 2 meters in diameter are hosted within a finely crystalline groundmass composed of euhedral sanidine and quartz crystals (Appendix 1, Plate 7).

Quinn Smith Master of Applied Science Thesis 23

Granodiorite dykes and sills intrude the tuff sequence and contain large euhedral phenocrysts within a crystalline groundmass. The phenocryst assemblage is composed of sodic plagioclase (50%), hornblende (20%), biotite (15%), quartz (10%), ilmenite and magnetite (5%). Plagioclase phenocrysts are moderately altered to sericite, occur as euhedral crystals, rarely show concentric zoning, and range up to ~4mm in size. Hornblende and biotite phenocrysts are strongly altered to chlorite, sericite and minor calcite and range up to ~3mm in size. Quartz occurs as small euhedral phenocrysts and range up to ~1mm in size. Ilmenite and magnetite constitute minor phenocryst phases and range up to ~0.5mm in size. Phenocrysts occur in a feldspar lath groundmass (Appendix 1, Plate 10).

The feldsarenite to sparry grainstone is well sorted with variably rounded clasts and high porosity. The clasts comprise feldspar (20%), quartz (35%), lithics (5%), echinoderm, gastropod and mollusc fragments (40%). Clasts are variably altered, mostly matrix supported, and cemented with sparry calcite. Quartz fragments range from euhedral crystals to well rounded and embayed clasts up to ~2mm in size. Lithic fragments are comprised of altered tuffs and angular chalcedonic quartz fragments (Appendix 1, Plates 11 & 12).

Basalts occur as remnant dykes, plugs and flows, and are aphanitic to slightly porphyritic. Basalt flows are vesicular, and comprised of fine grained- olivine and feldspar. Feldspars range in composition from oligoclase to labradorite, with minor zeolites infilling vesicles. Basalt dykes and plugs are slightly porphyritic and weakly chloritised. Euhedral feldspars are weakly albitised, range from oligoclase to labradorite, and are in a feldspar lath groundmass (Appendix 1, Plates 13 & 14).

Quinn Smith Master of Applied Science Thesis 24

Crystal Crystal Pumice Pumice Ash Flow- Rhyodacite Lithic Ash Rhyolite Rhyodacite Rhyodacite banded ignimbrite Rhyolite Rhyolite Ash Tuff Tuff tuff Rhyolite Tuff Tuff Sample QR25 QR05-27 QR1 QR23 QR05-26 QR05-21 QR05-37 SiO2 63.2 74.5 70.3 84.9 76.1 78.3 77.1 TiO2 0.6 0.28 0.23 0.17 0.07 0.18 0.15 Al2O3 15.4 14.8 13.6 8.28 13.1 10.6 12.6 Fe2O3 5.14 1.16 2.39 1.46 1.55 1.46 0.39 MnO 0.13 BDL 0.06 BDL 0.02 0.03 0.02 MgO 1.52 0.27 0.46 0.23 0.14 0.26 0.2 CaO 4.41 0.14 1.79 0.43 0.21 0.14 0.09 Na2O 2.63 1.38 2.9 0.1 0.22 1.5 0.99 K2O 3.23 4.36 4.45 0.94 5.41 3.24 4.9 P2O5 0.172 0.019 0.068 0.032 0.03 0.049 0.035 SO3 BDL 0.02 0.29 0.54 0.03 1.06 0.12 LOI 3.54 2.18 2.38 3.43 2.67 3.13 1.55 Total 99.97 99.11 98.92 100.51 99.55 99.95 98.15 Ag BDL BDL BDL BDL BDL BDL 2 As 1 2 14 127 248 3 4 Co 32 8 22 BDL 6 2 12 Cu 9 2 2 13 3 4 4 Mo 8.5 3 7 6.5 3.5 1.5 3.5 Ga 16.4 15.2 14.4 9.4 11.8 13.8 18.6 Sb 0.6 1 1 14.6 2.4 0.4 2 Rb 115 182 159 74.6 220 117 191 Sr 315 82.5 215 23 24.5 137 137 Y 20.9 15.6 19.3 11.3 18.6 6.7 11.7 Zr 60 67 70 43 87 100 86 Nb 6.5 4.5 7 5 10 9 10 Cs 4.9 8.6 8.2 4.1 5.6 2.4 4.3 Ba 902 943 996 81 889 830 1350 La 29.9 29.3 39.2 20.3 29.8 25.2 31.1 Ce 61.1 57.1 69.7 39.7 60.2 41.2 64.4 Nd 25.1 20.9 25.4 14.8 26.1 14.4 23.8 Sm 5.05 4 4.65 3 5.5 2.6 4.5 Eu 1.2 0.8 0.85 0.55 0.5 0.4 0.7 Gd 4.2 3 3.6 2.4 3.8 2 3 Dy 3.75 2.7 3.25 2.05 3.8 1.55 2.45 Er 2.2 1.65 1.95 1.25 2.35 0.8 1.35 Yb 2.15 1.9 2.1 1.3 2.8 0.85 1.5 Hf 1.8 2.4 2.6 1.4 3.6 4.8 3 Th 12.5 17.3 18.8 9.7 21.5 6.6 21.1

Table 2. Representative whole-rock geochemical analyses for Jurassic volcanic units of the Sascha-Pelligrini study area.

Quinn Smith Master of Applied Science Thesis 25

Geochemistry Least altered representative samples of each of the volcanic tuffs were analysed for both major and trace elements (Table 2). REE values for Bajo Pobre andesite (Pankhurst and Rapela, 1995) were used to test for fractional crystalisation trends within the volcanic suite, with REE values for the Sierra Los Chacays xenoliths (Pankhurst and Rapela, 1995) used to test for partial melting of the upper crust.

The volcanic rocks of the Sascha-Pelligrini area are high-K rhyodacites and rhyolites with K2O contents ranging from 3.2 to 5.4 weight percent. SiO2 contents vary from 63 to 78 weight percent, with most of the samples being greater than 70 weight percent SiO2. Na2O concentrations are low, and show and inverse correlation with K2O concentration (Figure 7). The Sascha-

Pelligrini volcanic tuffs have a broad range in Al2O3 content (8.28 to 15.4 weight percent), Fe2O3 content (1.16 to 5.14 weight percent) and CaO content (0.14 to 4.41 weight percent).

Groups identified on the basis of stratigraphy and petrography are easily discernable on most major and trace element graphs (Figures 7 and 8). Chon Aike Formation rhyodacites are distinguished primarily by their relatively low

SiO2 contents (63 to 74 weight percent). Abundances of all major elements except for K2O have correlations with SiO2, however Al2O3, TiO2, NaO and

K2O show decrease in concentrations above 70 weight percent SiO2. Trace elements Sr and Yb decrease with increasing SiO2, with Rb, Cs and Zr showing correlation with SiO2. Trace elements Ba, Ce, Hf, Nb and Th increase in concentration to 70 weight percent SiO2, with a marked decrease in concentration above 70 weight percent SiO2.

La Matilde Formation rhyolites are distinguished by their very high SiO2 contents. The rhyolites have a limited SiO2 content ranging from 76.1 to 78.3 weight percent. Abundances of Al2O3, Fe2O3, CaO and K2O decrease with increasing SiO2 content, while TiO2, MgO, NaO and P2O5 correlate with SiO2.

Trace elements Sr, Zr, and Hf correlate with SiO2, with Ba, Cs, Rb, Ce, Yb,

Nb and Th contents decreasing with increasing SiO2.

Quinn Smith Master of Applied Science Thesis 26

Chondrite-normalised REE patterns of the Sascha-Pelligrini samples are light-REE enriched (Figure 9). LREE concentrations range between 85 and 165 times chondritic levels, with Yb concentrations approximately 5.2 to 17.4 times chondritic levels. La/Yb ratios vary from 7.2 to 20.2. REE patterns shallow towards the heavy-REE, with La/Gd values from 5.9 to 10.6 and Gd/Yb values from 1.09 and 1.90. Chondrite-normalised REE patterns for the Chon Aike Formation are smooth and near parallel (Figure 9), with minor negative Eu anomalies. Chondrite-normalised REE patterns for the La Matilde Formation have a distinct negative Eu anomaly. La Matilde rhyolites diverge towards the heavy-REE, with Dy/Yb values between 0.88 and 1.19. Chondrite-normalised REE values for the flow-banded rhyolite are similar to the La Matilde rhyolite tuffs, and show a negative Eu anomaly.

The Rhyodacite suite REE pattern is relatively flat normalised against crustal abundances, with slight negative Nd and Y, and positive Yb anomalies (Figure 10). REE patterns show a decrease in total REE concentrations with increasing SiO2. The Rhyodacite suite of samples is slightly enriched relative to upper crust and shows a small positive Eu anomaly. La concentrations range from 0.9 to 1.3 times upper crust. Ce/Yb values range from 0.85 to

1.14. Increasing SiO2 and K2O in the rhyolite suite leads to a slight depletion in REE relative to upper crust, with Eu inverting to a small negative anomaly.

La concentrations in high SiO2 rhyolites range from 0.6 to 1.0 times upper crust, with Ce/Yb values from 0.73 to 1.66.

REEs for the Rhyodacite suite are slightly enriched, with small negative Eu and Y anomalies (Figure 10). La concentrations range between 2.0 and 2.7 times Bajo Pobre. Ce/Yb values range from 1.27 to 1.49. REE patterns show a progressive depletion in heavy REE‟s with increasing SiO2, with negative

Eu, Y and positive Yb anomalies becoming more pronounced. Highest SiO2 rhyolites are enriched in light, and depleted in heavy REE‟s relative to Bajo

Pobre andesite. High SiO2 rhyolites have La concentrations which range from 1.7 to 2.1 times Bajo Pobre. Ce/Yb values range from 0.96 to 2.18.

Quinn Smith Master of Applied Science Thesis 27

Sierra Los Chacays xenolith normalised REE patterns are light-REE enriched (Figure 10). The Rhyodacite suite show slight negative Eu, Y and positive Yb anomalies. La concentrations range between 13.7 and 18.3 times xenolith levels. Ce/Yb values range from 2.78 to 3.25. REE patterns shallow towards the heavy-REE, with Ce/Sm values from 2.53 to 3.14 and Sm/Yb values from 0.98 to 1.10. REE patterns show a progressive depletion in heavy REE‟s with increasing SiO2, with negative Eu, Y and positive Yb anomalies becoming more pronounced. High SiO2 rhyolites have La concentrations which range from 11.81 to 14.57 times Sierra Los Chacays xenoliths. Ce/Yb values range from 2.10 to 4.75. REE patterns of high SiO2 rhyolites shallow towards the heavy-REE, with Ce/Sm values from 2.29 to 3.32 and Sm/Yb values from 0.91 to 1.43.

Quinn Smith Master of Applied Science Thesis 28

18 0.8

16 0.6

Al2O3 TiO2 12 0.4

0.2

6 20 60 65 70 75 80 85 90 60 65 70 75 80 85 90

5 1.5 4

Fe2O3 MgO (total) 3 1

2 0.5 1

50 40 60 65 70 75 80 85 90 60 65 70 75 80 85 90

4 3

3 CaO NaO 2 2

1 1

06 0.20 60 65 70 75 80 85 90 60 65 70 75 Chon80 Aike 85 90 La Matilde 5 Flow Banded Rhyolite 0.15 Chon Aike Least Altered 4 La Matilde Least Altered

P2O5 K2O 3 0.1

0.05 1

0 0 60 65 70 75 80 85 90 60 65 70 75 80 85 90 SiO2 SiO2

Figure 7. XRF major element results for Sascha-Pelligrini volcanic samples in weight percent plotted against SiO2. Least altered samples for each of the stratigraphic units are shown in red.

Quinn Smith Master of Applied Science Thesis 29

1800

1600 300 1400

1200

200 Ba 1000 Sr 800

600 100 400

200

12 0 3000 60 65 70 75 80 85 90 60 65 70 75 80 85 90

10 250

Cs 8 200 Cs Rb 6 150

4 100

2 50

1000 03 60 65 70 75 80 85 90 60 65 70 75 80 85 90 90

Ce 80

70 2 60 Ce Yb 50 40 1 30

1200 60 60 65 70 75 80 85 90 60 65 70 75 80 85 90

5 Zr 100

4 Zr Hf 80 3

60 2

4012 251 60 65 70 75 80 85 90 60 65 70 75 80Chon Aike 85 90 Nb La Matilde Flow Banded Rhyolite 10 20 Chon Aike Least Altered La Matilde Least Altered

8 Nb Th 15

10 4

2 5 60 65 70 75 80 85 90 60 65 70 75 80 85 90 SiO2 SiO2

Figure 8. ICP-MS trace element results (Sr, Ba, Cs, Rb, Ce, Yb, Zr, Hf, Nb & Th) for Sascha-Pelligrini volcanic samples in parts per million (ppm) plotted against SiO2.

Quinn Smith Master of Applied Science Thesis 30

Rhyodacite Ignimbrite (Chon Aike) 1000 Rhyodacite Ash Tuff (QR1) Pumaceous Rhyodacite Tuff (QR05-27) Crystal Ash Rhyodacite Ignimbrite (QR25)

100

1 La Ce Nd Sm Eu Gd Dy Y Yb

Rhyolite Tuff (La Matilde) 1000 Rhyolite Ash Tuff (QR05-21) Crystal Ash Rhyolite Tuff (QR05-26) Lithic Rhyolite Tuff (QR23)

100

1 La Ce Nd Sm Eu Gd Dy Y Yb Rhyolite Intrusive (La Matilde) 1000 Flow Banded Rhyolite (QR05-37)

100

1 La Ce Nd Sm Eu Gd Dy Y Yb

Figure 9. Chondrite-normalised REE diagrams for least altered Sascha- Pelligrini volcanic stratigraphic units. Normalised to C1 chondrite of McDonough and Sun (1995). Quinn Smith Master of Applied Science Thesis 31

Sierra Los Chacays Xenolith Upper Crust Normalised REE Bajo Pobre Normalised REE Normalised REE (Rudnick & Gao, 2003) (Pankhurst & Rapela, 1995) (Pankhurst & Rapela, 1995)

Yb Yb Yb Y Y Y Dy Dy Dy Flow Banded Rhyolite (S007) Rhyolite Banded Flow Gd Gd Gd Eu Eu Eu

Sm Sm Sm

Nd Nd Nd Flow (La Matilde)Rhyolite Dome Ce Ce Ce

La La La

Yb Yb Yb Y Y Y Dy Dy Dy Laminated Rhyolite Ash Tuff Ash Rhyolite Laminated (S008) Tuff Rhyolite Ash Crystal (S018) Tuff Rhyolite Lithic Crystal Gd Gd Gd

Eu Eu Eu Sm Sm Sm Rhyolite Tuff (La Matilde) Tuff Rhyolite Nd Nd Nd Ce Ce Ce La La La

Yb Yb Yb Y Y Y

Dy Dy Dy

Gd Gd Gd

(S022) Tuff Rhyodacite Pumice Ash (S023) Tuff Rhyodacite Pumaceous Ignimbrite (S024) Rhyodacite Ash Crystal Eu

Eu Eu

Sm Sm Sm

Nd Nd Nd Rhyodacite Ignimbrite Rhyodacite (Chon Aike) Ce Ce Ce

La La La 1 1 1 10

10 10 0.1 0.1 0.1 100 Figure 10. REE geochemistry for least altered stratigraphic units from the Sascha- Pelligrini study area normalised to upper crust, Bajo Pobre andesite, and Sierra Los Chacays xenoliths with increasing primitive lower crustal signatures respectively. Quinn Smith Master of Applied Science Thesis 32

Structural setting The SVZ is hosted on a right-lateral, oblique-slip fault system termed the Sascha Fault (Figure 11). Sascha Main is hosted within a normal fault- bounded graben trending approximately 315°. Mineralised veins are developed at right-stepping structural splays along the southwesterly dipping 315° trend. North-trending left-lateral and east-trending right-lateral structures within the normal faulted block are often unmineralised and offset the vein trend. The graben is comprised of La Matilde rhyolite tuffs which are inferred to thicken to the southeast and thin towards the northwest. Structural studies, based on airphoto and satellite image interpretation, indicate the block is bound by regional northeast-trending left-lateral basement transfer structures. The 315° trending Sascha fault rotates through to a north-trending 360° orientation in Sascha Central. The orientation change of the Sascha fault is controlled by, and bounded by, northeast-trending left-lateral transfer structures. Epithermal veining is limited to small, unmineralised quartz veinlets, within the north-trending Sascha fault.

Figure 11. Mapped surface vein trace orientation in Sascha Main indicating dextral oblique-slip movement with mineralised veins forming on right-stepping structural splays to the main 315° trending Sascha fault.

Quinn Smith Master of Applied Science Thesis 33

The Sascha fault changes orientation from north-trending within the transfer structure corridor, back to 315°on the northern margin of Sascha Sur. Epithermal veining is hosted within the hanging-wall of a half-graben. The half-graben is bounded to the west by the northeast dipping, oblique-slip, normal Sascha fault. The strike extent of the veinlet zone is controlled by northeast-trending left-lateral transfer structures that offset the Sascha fault. North-trending left-lateral, and east-trending right-lateral structures offset the vein trend with the half-graben block.

The Marcellina veinlet zone parallels Sascha Sur, and is hosted within a 315º trending normal fault. Epithermal veining is hosted within the hanging wall of a half graben structure. The normal fault dips towards the northeast, extending under basalt cover to the north, and recent sediment to the south.

Pelligrini is hosted within a similar structural setting to Sascha Sur and Marcellina. Epithermal veining is hosted within the hanging wall blocks of 315º trending half grabens. Veining is controlled by northeast dipping oblique-slip normal structures, bounded to the north and south by northeast- trending right-lateral transfer structures.

Quinn Smith Master of Applied Science Thesis 34

A B

1 cm

Figure 12. Sascha Main saccharoidal vein phase (B) overprinting the earlier chalcedonic (A) vein phase.

A B C D E F G H

1 cm

A. Wall rock silicification B. Initial crustiform gold-silver ginguro band I (Ginguro Stage I) C. Pseudoacicular fine bladed quartz D. Colloform/crustiform chalcedony E. Colloform/crustiform chalcedony-ginguro bands with minor adularia (Ginguro Stage II) F. Secondary kaolinite G. Coarse lattice bladed quartz H. Saccharoidal and vuggy quartz 0.1 mm I. Photomicrograph of gold and acanthite within chalcedony-ginguro band (Reflected PPL x40) Figure 13. Sascha Main ginguro vein phase.

B 0.25 mm

A. Saccharoidal and vuggy quartz B. Crustiform banded chalcedonic quartz with disseminated pyrite infilling cavity within saccharoidal vein phase C. Photomicrograph of fine disseminated pyrite within chalcedonic quartz (Reflected PPL x10)

1 cm Figure 14. Pyritic chalcedonic vein phase overprinting saccharoidal vein phase. Quinn Smith Master of Applied Science Thesis 35

Epithermal veining

Quartz textures Veins in the Sascha Main prospect are subdivided into a series of vein-types with different textural and geochemical signatures. These veins vary from chalcedonic to crystalline comb quartz.

Chalcedonic veins are white-grey to brown, massive to finely-banded chaotic veins and veinlets; they generally occur on the western side of the vein trend (Figure 12). Angular leached clasts of argilllised wall rock that include strongly colloform-banded, fine saccharoidal silica define zones of single pulse tectonic breccia. These zones generally occur as large deflation surfaces with no outcrop expression and are considered equivalent to the chalcedonic phase (Appendix 2, Plate 1).

Saccharoidal veins with minor bladed textures are white and consist of medium- to coarse-grained saccharoidal and crystalline silica with prominent bladed carbonate pseudomorphs (Appendix 2, Plates 3 & 4). The saccharoidal veins consist of massive to weakly crustiform-banded quartz exhibiting local ghosted breccia textures. These veins overprint the chalcedonic veins (Figure 12), occur through the center of the vein trend, and are considered to be equivalent to the ginguro mineralization event (see below).

Fine-grained, strong colloform / crustiform-banded vein and vein breccia with bands of adularia, clay and bladed quartz textures supersede the saccharoidal veins. Dark grey to black, sulphide-rich bands with native gold and silver sulphides occur with colloform-banded chalcedonic silica. The sulphide bands are several millimeters in width and are similar in character to the „ginguro‟ bands described by Izawa et al (1990). This phase typically forms as an initial pulse of several repeated bands on the margin of vuggy saccharoidal and bladed quartz. Colloform / crustiform-banded chalcedonic quartz and ginguro deposition occurs prior to the formation of bladed quartz textures (Figure 13). Wall rock breccias proximal to the colloform / crustiform

Quinn Smith Master of Applied Science Thesis 36

veins contain ginguro-like bands encrusting wall rock fragments, followed by saccharoidal to crystalline silica fill (Appendix 2, Plate 2).

Crustiform-banded grey chalcedonic veins with fine pyrite and hematite typically occur as chaotic veins and breccia zones on vein margins (Appendix 2, Plate 5). Rare saccharoidal and cockade-textured quartz is present. Outcropping veins have strong iron oxide gossanous zones (Appendix 2, Plate 6). This phase is associated with pervasive kaolinite alteration and silica-pyrite flooding of the lithic tuff on the eastern side of the vein trend. The chalcedonic veins with fine pyrite and hematite are observed overprinting the saccharoidal with minor bladed texture quartz vein phase (Figure 14).

Jasperoidal veins are massive to moderately banded, contain disseminated pyrite and are distinguished by their unique cryptocrystalline matrix amongst vuggy quartz cavities (Appendix 2, Plate 7). The jasperoidal veins crop out along strike from the chalcedonic veins with fine pyrite.

Late stage veins of euhedral, axiolitic, clear to milky quartz crystals (comb quartz) are typically less than 5 cm wide and grow perpendicular to vein margin. The comb quartz veins overprint all other vein phases (Appendix 2, Plates 8 & 9). Silica-poor, limonite-rich, tectonic breccias and veins commonly occur within structural intersections associated with major faulting. Limonite-stained structures are observed cross-cutting veining.

Sascha Sur exhibits multiple quartz textures expressed as multiphase veinlets, veins and vein breccias. Grey-white chalcedonic quartz with patchy disseminated pyrite is associated with anomalous gold-silver values and occurs as a late infill to paragenetically earlier saccharoidal to crystalline quartz veins (Appendix 2, Plate 10). Amethystine quartz and euhedral axiolitic comb quartz veinlets cross-cut both chalcedonic with disseminated pyrite and saccharoidal vein phases (Appendix 2, Plates 8 & 9).

The Marcellina veinlet zone is expressed as multiphase veinlets which collectively define a stockwork. The veinlets form with an initial

Quinn Smith Master of Applied Science Thesis 37

crustiform/colloform phase, followed by axiolitic comb quartz growth, and are infilled with ladder-banded chalcedonic quartz with banding perpendicular to vein margin (Appendix 2, Plate 11).

The Pelligrini prospect forms a predominant topographic high within the study area, and is a large zone of intense silica replacement, brecciation and minor veining. A stratigraphically controlled zone of pervasive silica replacement forms within the rhyolite ash tuff. Silicification is texturally destructive, with minor rock textures locally preserved (Appendix 2, Plate 17). Massive chalcedonic to weakly banded chalcedonic veins and associated wall-rock breccias occur within the same stratigraphic level as the pervasive silicification. The chalcedonic veins have a distinctive red-black colour due to inclusions of hydrothermal hematite and pyrolusite (Appendix 2, Plate 13). Weakly banded chalcedonic to saccharoidal quartz veins with prominent bladed textures occur stratigraphically below the pervasive silicification and contain anomalous gold and silver values (Appendix 2, Plate 12). Multiple- pulse, milled-clast hydrothermal breccia veins occur directly below the pervasive silicification. Breccia veins contain rock, vein and earlier breccia clasts within a chalcedonic quartz matrix (Appendix 2, Plates 13 to 16). Zones of clast-supported, silica-flooded jigsaw breccias occur within all stratigraphic levels, and contain angular rock fragments with a hydrothermal quartz matrix (Appendix 2, Plate 16).

Vein morphology along the SVZ is found to be primarily controlled by host rock rheology. The least competent lithic rhyolite tuffs consistently host discontinuous, chaotic veining. Crystal-ash rhyolite tuffs host upward terminating veins with high grade ginguro bands that encompass the vein margins. Pumiceous rhyodacite tuffs at Sascha Sur and Marcellina host broad zones of discontinuous multi-directional veinlets, with ash tuffs at Pelligrini being pervasively silicified and brecciated.

Quinn Smith Master of Applied Science Thesis 38

Vein geochemistry and mineralogy The vein phases across the Sascha-Pelligrini area have distinct geochemical signatures (Table 3). Early phase comb and chalcedonic quartz veins are anomalous in gold and silver, and have elevated concentrations of arsenic, barium and manganese. The early phase comb and chalcedonic quartz veins average 0.52g/t gold and 3.2g/t silver. Colloform/crustiform and ginguro- banded veins exhibits high gold and silver values associated with low concentrations of arsenic, barium and antimony. Colloform/crustiform and ginguro-banded veins average 14.23g/t gold and 89.8g/t silver. The colloform/crustiform-banded vein phase is hosted on the margins of the more voluminous saccharoidal and bladed vein phase. The saccharoidal and bladed vein phase is anomalous in gold and silver, averaging 0.19g/t gold and 0.5g/t silver. The chalcedonic with disseminated pyrite phase is anomalous in gold and silver, averaging 0.76g/t gold and 9.5g/t silver, and also has high concentrations of antimony and arsenic. The jasperoidal phase is anomalous in silver with high concentrations of barium and moderate concentrations of arsenic. The flow-banded rhyolite and auto-breccia at Pelligrini is anomalous in silver, with vein samples characterised by local mercury values of up to 633ppb. On the basis of 639 rock chip samples (Appendix 3) collected from the SVZ, the generalized multi-element signature is strongly elevated in gold, silver and arsenic, moderately elevated in antimony and barium, weakly elevated in copper, lead and zinc, and locally anomalous in mercury.

Vein Phase Au Ag As Ba Cu Hg Mn Pb Sb Zn Au/Ag As/Au No. of Ratio Ratio Samples Comb & 0.52 3.2 409 201 11 1 236 56 8 28 6 786 408 chalcedonic Ginguro 14.23 89.8 186 107 12 1 133 20 7 17 6 2 50

saccharoidal 0.19 0.5 511 94 12 1 132 38 7 25 3 1022 123 & bladed chalcedonic 0.76 9.5 1124 97 17 1 135 30 41 21 13 118 44 & pyrite Jasperoidal 0.06 1.7 465 486 13 1 170 24 4 29 27 273 14 & pyrite

Table 3. Summary geochemical signatures of Sascha Main vein phases with key epithermal elements. Elements are reported as ppm.

Quinn Smith Master of Applied Science Thesis 39

Element ratios of exploration rockchip geochemistry indicate that the textural variants of the different veins are geochemically distinct. While their differences are evident in a range of elements, it is most pronounced in the arsenic:gold ratio (Table 3). The arsenic:gold ratio clearly differentiates the early phase chalcedonic, the colloform/crustiform ginguro-banded phase, and the jasperoidal and chalcedonic with disseminated pyrite phases. The arsenic:gold ratio shows a separation of three orders of magnitude between the ginguro and jasperoidal and chalcedonic with disseminated pyrite phases.

Individual vein phases are also characterised by unique mineral assemblages. The colloform/crustiform ginguro-banded veins are comprised of the ore minerals, acanthite and selenium-rich acanthite, electrum, silver halides, uytenbogaardtite, petrovskaite and jalpaite, with gangue minerals jamesonite, hematite, calcite, sphalerite, galena, chalcopyrite, dufrenoysite, barite, adularia and muscovite (Figure 15). The chalcedonic veins with disseminated pyrite contain ore minerals acanthite, selenium-rich acanthite and jalpaite, and gangue minerals, pyrite, arsenopyrite, hematite, barite, gypsum, muscovite and jarosite.

Electron microprobe analysis of individual mineral grains from samples from across the Sascha-Pelligrini area show geochemical zoning. Acanthite incorporates selenium contents ranging from 1.65 to 6.21 weight percent and has compositional ranges of Ag2S0.96Se0.04 to Ag2S0.83Se0.17. Iron content of sphalerite ranges from 0.71 to 2.75 weight percent with calculated compositional ranges from Zn0.95Fe0.05S to Zn0.99Fe0.01S . Sphalerite also incorporates manganese (<1.86 weight percent Mn) and copper (<3.08 weight percent Cu); calculated compositions range from Zn0.91Fe0.05Cu0.04S to

Zn0.93Fe0.04Mn0.03S. Silver content of electrum varies over the entire ginguro event, and ranges from 6.49 to 87.17 weight percent; electrum varies from

Ag0.05Au0.95 to Ag0.88Au0.12.

Quinn Smith Master of Applied Science Thesis 40

A B 5

3 4 1 3 2 2 4 1

C 1 D 3

2 1 2

E F 4

3 1

2 1 3 2

G H 2

2 1 4 3 1 5 4

Figure 15. Backscattered SEM images of characteristic vein mineral assemblages.

A. Ginguro Stage I (QR05-4A) 1-Se rich Acanthite, 2-Jamesonite, 3-Acanthite, 4-Barite, 5-Quartz B. Ginguro Stage I (QR05-4A) 1-Se Acanthite, 2-Iodoembolite, 3-Barite, 4-Quartz C. Ginguro Stage I (QR05-4A) 1-Ag rich electrum, 2-acanthite and uytenbogaardtite intergrowth D. Ginguro Stage II (QR05-4B) 1-Acanthite, 2-Iodoargyrite, 3-Barite E. Ginguro Stage II (QR05-4B) 1-Iodoargyrite, 2-Gold, 3-Quartz F. Ginguro Stage II (QR05-4B) 1-Iodoembolite, 2-Hematite, 3-Calcite, 4-Quartz G. Pyrite Chalcedony (QR05-6) 1-Pyrite, 2-Hematite, 3-Hematite & Gypsum, 4-Acanthite, Se Acanthite & Jalpaite, 5-Quartz H. Pyrite Chalcedony (QR05-6) 1-Pyrite (As zoning), 2-Hematite & Gypsum, 3-Acanthite, 4-Quartz

Quinn Smith Master of Applied Science Thesis 41

Geothermometry Shikazono (1985) proposed that formation temperatures can be calculated from coexisting electrum and sphalerite by combining the thermodynamic equations for electrum in equilibrium with argentite (Barton and Toulmin 1964), and equilibrium between FeS in sphalerite and pyrite (Barton and Skinner 1979).

In order to obtain reliable formation temperatures from coexisting electrum and sphalerite grains, Shikazono (1985) suggests that the grains must be in direct contact with each other without mutual replacement textures; that the FeS content of sphalerite and the Ag content of electrum have not changed during the post depositional period; and that trace element impurities in electrum and sphalerite are of low concentration.

E E E E S S S

Figure 16. Backscattered SEM images of coexisting electrum-sphalerite grains used for geothermometry calculations. E-electrum, S-sphalerite, J-jalpaite.

Ag content of Fe content of Electrum-sphalerite Sample Grain Site N X electrum sphalerite Ag Fes geothermometer Electrum- (Shikazono eq. 6, (atm fraction) (atm fraction) (mol fraction) (mol fraction) Sphalerite 1985) (°C)

4B-18 Core-Core 81.12 2.25 0.887 0.041 204.8 4B-18 Rim-Rim 79.45 2.54 0.876 0.040 205.1 4B-19 Core-Core 72.64 0.79 0.829 0.012 177.6 4B-19 Core-Rim 72.64 0.71 0.829 0.011 174.8 4B-20 Core-Core 87.15 3.05 0.925 0.047 204.2 4B-20 Rim-Rim 86.67 1.91 0.922 0.030 190.3

Table 4. Silver content of electrum, iron content of sphalerite, and calculated electrum-sphalerite formation temperatures from the Sascha ginguro vein phase.

Quinn Smith Master of Applied Science Thesis 42

Formation temperatures are estimated from compositional relationships between coexisting electrum and sphalerite mineral grains. Mineral grains considered to be in equilibrium are presented in figure 16, with calculated temperatures of formation presented in table 4. Coexisting electrum and sphalerite were found within the Sascha ginguro stage II mineralising phase. Electrum in equilibrium with sphalerite has a silver content which ranges from 72.64 to 87.15 weight percent, with calculated composition varying from

Ag0.829Au0.171 to Ag0.925Au0.075. The iron content of sphalerite in equilibrium with electrum ranges from 0.71 to 3.05 weight percent, with calculated composition varying from Zn0.953Fe0.047S to Zn0.998Fe0.018S. Calculated electrum-sphalerite formation temperatures range from 174.8°C to 205.1°C +/- 20°C, and vary less than 13.2°C from core to rim.

Alteration

Regional Alteration – Multispectral Mineral Mapping Using the spectral information recorded by the ASTER sensor, mineral maps for the remotely sensed alteration minerals kaolinite, illite and alunite are created for the entire study area (Figure 18). Surface cover across the study area includes localised woody shrubs and grasses, rock outcrop, gravels and recent alluvium, allowing good exposure of the alteration system. End- member spectra of minerals used for mineral mapping and spectral unmixing correlate well with known library spectra (Figure 17). Areas of mineralogically homogenous and mixed pixels are abundant over the prospect areas. ASTER-derived mineral maps readily define the regional extent of alteration over the known prospects.

Sascha Main is characterised by abundant, moderate intensity kaolinite, with small areas of mixed, moderate intensity illite and kaolinite (Figure 18). Pixels containing pure illite and alunite are located in small areas to the north and west of the area respectively. Vein distribution and associated anomalous gold values correlate with areas of mixed kaolinite and illite.

Quinn Smith Master of Applied Science Thesis 43

Sascha Sur is characterised by a broad zone of mixed illite and kaolinite, which is zoned outwardly to pure illite (Figure 18). Illite and kaolinite intensity is strong over the veinlet zone and is dominated by illite. Similar to Sascha Main, vein distribution and associated anomalous gold values correlate with areas of mixed kaolinite and illite.

The Marcellina veinlet zone is characterised by abundant kaolinite, with zones of mixed kaolinite and illite associated with veining and weakly anomalous gold values (Figure 18). The alteration at Pelligrini is a large area of mixed kaolinite and illite, in combination with zones of pure kaolinite or illite (Figure 18). The pervasive silicification correlates to areas of high abundance kaolinite, mixed kaolinite and illite, and scattered alunite. Mineral mapping has highlighted a zone of intense kaolinite and illite that corresponds to an outcropping chalcedonic vein and vein-breccia. In the western part of the Pelligrini prospect, and stratigraphically below the zone of pervasive silicification, the alteration assemblage is dominated by illite. ASTER Selected Endmember Spectra - Library Spectra Comparison

Illite (This Study) Kaolinite (This Study) Alunite (This Study) Illite IL101 Kaolinite CM92 Alunite GDS84

Reflectance

1.7 2.2 2.2 2.3 2.3 2.4 Wavelength μm

Figure 17. Selected end-member spectra compared to known library spectra.

Quinn Smith Master of Applied Science Thesis 44

Figure 18. ASTER mineral mapping results showing kaolinite, illite and alunite intensities and illite-kaolinite ratios. Simplified geology and gold assays are also presented from the Sascha-Pelligrini study area.

Quinn Smith Master of Applied Science Thesis 45

Prospect Alteration – PIMA and XRD In combination with the regional scale ASTER multi-spectral mineral mapping, detailed analysis of individual prospects reveal a variety of hydrothermal alteration minerals occur within the Sascha-Pelligrini epithermal system. PIMA spectral analysis across the study area identifies spectrally pure end-members of kaolinite, illite, muscovite and alunite (Figure 19). Mixtures of end-member spectra are common, and characterise distinct alteration assemblages at each prospect location. XRD analysis confirms PIMA results and identifies mixed-layered illite-smectite vein selvage assemblages (Table 5). Hydrothermal alteration across the Sascha-Pelligrini area is strong to intense. Hydrothermal minerals completely replace primary phenocrysts and glass in intensely altered wall-rocks, except for primary quartz and zircon. Strongly altered rocks contain relict plagioclase and mica, with primary rock textures preserved.

Montmorillonite and iron-chlorite alteration of the host ignimbrite unit can be detected several kilometers away from the outcropping veins at Sascha Main. Veins are hosted within a strong pervasive kaolinite +/- iron oxide alteration halo of several hundred meters. Individual vein phases have distinct alteration selvages at the vein/wall-rock margin, extending centimeters to meters into the host sequence. Silicification of the wall-rock occurs within the alteration selvage and becomes more pervasive and texturally destructive within 30 centimeters of the main vein.

Quinn Smith Master of Applied Science Thesis 46

Illite K-Alunite Kaolinite Muscovite

Reflectance

1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5

Wavelength (μm) Figure 19. End-member PIMA mineral spectra foriIllite, k-alunite, kaolinite and muscovite from the Sascha-Pelligrini area. Spectra presented across the short wave infrared (SWIR) band width of 1.3μm to 2.5μm. Sample PIMA XRD SP196 Kaolinite Quartz (37.3%), Kaolinite (44.8%), Illite (17.9%) SP197 Illite, Muscovite Quartz (59.9%), Illite (+illite-smectite mixed layer)(40.1%) SP198 Illite, Phengite Quartz (71.4%), Illite (+illite-smectite mixed layer)(25.6%), Kaolinite (2.9%) SP199 Muscovite Quartz (71.5%), Illite (28.5%) SP200 Kaolinite Quartz (40.8%), Kaolinite (44.5%), Illite (+illite-smectite mixed layer)(14.8%) SP054 Kaolinite Quartz (51.5%), Kaolinite (48.5%) SP216 Kaolinite, Halloysite Quartz (74.8%), Kaolinite (25.2%) SP053 Kaolinite Quartz (68.9%), Kaolinite (31.1%) SP103 Kaolinite Quartz (48.8%), Kaolinite (31.3%), Illite (19.9%) SP201 Kaolinite, Halloysite Quartz (40.7%), Kaolinite (44.1%), Illite (15.2%) SP104 Kaolinite Quartz (56.1%), Kaolinite (43.9%) SP202 Kaolinite Quartz (46.7%), Kaolinite (40.7%), Illite (12.6%) SP105 Kaolinite Quartz (44%), Kaolinite (52.7%), Illite (2.4%), Calcite (0.9%) SP160 K Alunite, Opal Quartz (74.3%), Alunite (16.5%), Jarosite (9.3%) SP159 Illite, NH Alunite Quartz (57.3%), Mica (24.9%), Orthoclase (12.6%), Albite (1.1%), Illite (2.6%), Jarosite (1.4%) SP158 Illite, NH Alunite Quartz (46.6%), Mica (24.5%), Orthoclase (12.3%), Albite (13.7%), Illite (1.7%), Jarosite (1.3%) SP157 Dickite, Nacrite Quartz (49.1%), Kaolinite (44.5%), Hematite (6.3%), Anatase (0.2%) QR05-23 NA Quartz (28.5%), Albite (26.8%), Orthoclase (17.2%), Mica (9.5%), Chlorite (8.8%), Calcite (4.6%), Sanidine (3%), Illite (1.7%) QR11 NA Quartz (27.9%), Albite (29.5%), Mica (14.9%), Orthoclase (13.6%), Chlorite (10.6%), Calcite (1.8%), Illite (1.7%) SP021 Illite, Kaolinite Quartz (56.7%), Mica (23.5%), Kaolinite (7.4%), Orthoclase (3.9%), Albite (3.9%), Illite (2.3%), Jarosite (2.3%) SP023 NA Quartz (56.8%), Mica (23.6%), Kaolinite (6.4%), Orthoclase (6.3%), Albite (3.3%), Illite (2%), Jarosite (1.2%), Calcite (0.3%)

Table 5. PIMA results compared to quantitative XRD results for samples containing characteristic alteration assemblages from individual prospect areas. Sample locations are shown on figures 3, 20, 21, 22 and 23.

Quinn Smith Master of Applied Science Thesis 47

At Sascha Main, PIMA and XRD analysis of alteration associated with the chalcedonic vein phase indicates the vein phase is hosted within the background kaolinite-dominated alteration halo. Alteration outside the zone of intense silicification on the margin of the saccharoidal to bladed and colloform / crustiform ginguro-banded vein phase is characterised by illite overprinted by kaolinite (Table 5, Figures 20, 21 & 24). Wall-rock alteration within the zone of intense silicification is characterised by illite-smectite mixed-layered clays, with the vein assemblage comprised of muscovite and Illite, with secondary kaolinite infilling vugs. The chalcedonic and jasperoidal vein phases are hosted within pervasive kaolinite, illite and halloysite alteration. Overprinting crystalline to comb quartz veins are associated with pervasive, texturally preserving halloysite (Table 5, Figures 22 & 24).

Sascha Sur is hosted within a background laumontite alteration halo of several kilometers. The alteration halo over the veinlet zone is characterised by illite (+/- mixed-layer illite-smectite) > kaolinite +/- laumontite, alunite and lesser gypsum. PIMA and XRD analysis of alteration assemblages of better developed veins indicates alteration outside the zone of intense silicification is characterised by illite, patchy laumontite and minor chlorite overprinted by kaolinite. Wall-rock alteration within the zone of intense silicification is characterised by illite>kaolinite/halloysite>gypsum. Vein assemblages are dominated by illite, with kaolinite overprinting illite and infilling vugs (Table 5, Figures 23 & 24).

A background alteration halo of kaolinite that overprints laumontite around the periphery of the pervasive silicification is characteristic of Pelligrini. The alteration assemblage proximal to the pervasive silicification is characterised by kaolinite, minor jarosite and alunite overprinting illite. Pervasive hematite alteration forms a small halo on the northern periphery of the kaolinite- jarosite-alunite alteration zone. Minor veins and veinlets cross-cutting the pervasive silicification are associated with potassium alunite, natroalunite, opal and dickite. (Table 5, Figure 24).

Quinn Smith Master of Applied Science Thesis 48

Detailed PIMA analysis of individual vein selvages along the SVZ indicate each alteration assemblage is associated with distinct Al-OH absorption wavelengths and absorption depths within the short wave infrared (SWIR) spectrum. PIMA results from samples taken along a traverse perpendicular to the saccharoidal and bladed vein phase shows the Al-OH spectra absorption wavelength increases towards the vein, with decreases in the Al-OH absorption depth in samples of silicified wall-rock (Figure 20). PIMA results from adjacent to the ginguro-banded vein shows the Al-OH spectra absorption wavelength and absorption depth increases on the vein selvage, and decreases in samples of silicified wall-rock (Figure 21). The Al-OH spectra absorption wavelength and absorption depth decrease in samples of silicified wall-rock for the pyrite-chalcedony PIMA traverse (Figure 22). PIMA sampling across gossanous chalcedonic veins at Sascha Sur shows the Al- OH spectra absorption depth increases towards the vein selvage, and the Al- OH spectra absorption wavelength decreases in samples of silicified wall- rock adjacent to the vein (Figure 23).

Quinn Smith Master of Applied Science Thesis 49

FeOx vein FeOx Tuff Rhyolite Saccharoidal quartz vein vein quartz Saccharoidal textures bladed with Analysis Vein location sample PIMA vein quartz Comb silicification Wall-rock AL(OH) Absorption Wavelength AL(OH) AbsorptionDepth

LEGEND LEGEND Depth Absorption

0.35 0.25 0.15 0.05 0 0.3 0.2 0.1

50cm 50cm 50cm 50cm 50cm 50cm 50cm 50cm 50cm SP113 SP113 SP113 SP113 SP113 SP113 SP113 SP113 SP113

SP113

SP200 SP200 SP200 SP200 SP200 SP200 SP200 SP200 SP200 SP200

SP199 SP199 SP199

SP199 SP199 SP199 SP199 SP199 SP199 0.8m @ 22.5g/t Au Au 22.5g/t 0.8m Au @ 22.5g/t 0.8m Au @ 22.5g/t 0.8m @ SP199 0.8m @ 22.5g/t Au Au 22.5g/t 0.8m Au @ 22.5g/t 0.8m Au @ 22.5g/t 0.8m @ Au 22.5g/t 0.8m Au @ 22.5g/t 0.8m Au @ 22.5g/t 0.8m @

Sample SP198 SP198 SP198 SP198 SP198 SP198 SP198 SP198 SP198 SP198

XRD Profile XRD

- SP197 SP197 SP197 SP197 SP197 SP197 SP197 SP197 SP197

SP197

SP196

SP196 SP196 SP196 SP196 SP196 SP196 SP196 SP196 SP196 PIMA Sascha Main 2211 2213 2212 2210 2209 2208 2207 2206

Wavelength Absorption Figure 20. PIMA and XRD profiles of individual vein phases from the Sascha Main vein zone showing sample location, geology and veining, gold/silver assays, and SWIR absorption wavelength and absorption depth.

Quinn Smith Master of Applied Science Thesis 50

Rhyodacite Crystal Tuff Crystal Rhyodacite Wall-rock silicification Wall-rock Ash Crystal Tuff Rhyolite Vein Analysis Vein location sample PIMA vein quartz Comb Tuff Pumice Rhyodacite Vein Analysis Vein location sample PIMA Quartz Comb Quartz-Ginguro Banded Au-Ag Wall-rock silicification Wall-rock FeOx stained chalcedonic chalcedonic stained FeOx pyrite disseminated with veins Saccharoidal & Bladed Quartz & Bladed Saccharoidal AL(OH) AL(OH) Absorption Wavelength AL(OH) Absorption Depth

AL(OH) Absorption Wavelength AL(OH) AbsorptionDepth

LEGEND LEGEND LEGEND

LEGEND

Absorption Depth Absorption Depth Absorption

0.25 0.15 0.05 0 0.3 0.2 0.1 0.19 0.18 0.17 0.16 0.2 0.205 0.195 0.185 0.175 0.165 SP103 SP103 SP103 SP103 SP103 SP103 SP103 SP103 SP103

50cm 50cm 50cm 50cm 50cm 50cm 50cm 50cm 50cm SP103 SP020 SP020 SP020 SP020 SP020 SP020 SP020 SP020 SP020

SP020

SP201 SP201 SP201 SP201 SP201 SP201 SP201 SP201 SP201

SP201 0.5m @ 0.5m @ 0.5m @ 0.5m @ 0.5m @ 0.5m @ 0.5m @ 0.5m @ 0.5m @ 70 70 70 70 70 70 70 70 70 48.51g/t Au / 796g/t Ag 796g/t Ag / 796g/t Ag / Au 796g/t 48.51g/t / Au 48.51g/t Au 48.51g/t 48.51g/t Au / 796g/t Ag 796g/t Ag / 796g/t Ag / Au 796g/t 48.51g/t / Au 48.51g/t Au 48.51g/t Ag 796g/t Ag / 796g/t Ag / Au 796g/t 48.51g/t / Au 48.51g/t Au 48.51g/t 1m @ 0.23g/t Au /Ag Au 1.8g/t /Ag Au 0.23g/t @ 1.8g/t 1m /Ag 0.23g/t Au @ 1.8g/t 1m 0.23g/t @ 1m 1m @ 0.23g/t Au /Ag Au 1.8g/t /Ag Au 0.23g/t @ 1.8g/t 1m /Ag 0.23g/t Au @ 1.8g/t 1m 0.23g/t @ 1m /Ag Au 1.8g/t /Ag Au 0.23g/t @ 1.8g/t 1m /Ag 0.23g/t Au @ 1.8g/t 1m 0.23g/t @ 1m 0.3m @ 0.3m @ 0.3m @ 0.3m @ 0.3m @ 0.3m @ 0.3m @ 0.3m @ 0.3m @ SP021 SP021 SP021

SP021 SP021 SP021 SP021 SP021 SP021 17.79g/t Au / 104.5g/t Ag 104.5g/t Ag / 104.5g/t Ag / 104.5g/tAu 17.79g/t / Au 17.79g/t Au 17.79g/t 17.79g/t Au / 104.5g/t Ag 104.5g/t Ag / 104.5g/t Ag / 104.5g/tAu 17.79g/t / Au 17.79g/t Au 17.79g/t 17.79g/t Au / 104.5g/t Ag 104.5g/t Ag / 104.5g/t Ag / 104.5g/tAu 17.79g/t / Au 17.79g/t Au 17.79g/t SP104 SP104 SP104 SP021 SP104 SP104 SP104 SP104 SP104 SP104 SP104 Sample

Sample

1m @ 1m @ 1m @ 1m @ 1m @ 1m @ 1m @ 1m @ 1m @

XRD Profile XRD 3.88g/t Au / 29.5g/t Ag 29.5g/t Ag / 29.5g/t Ag / 29.5g/t Au 3.88g/t / Au 3.88g/t Au 3.88g/t 3.88g/t Au / 29.5g/t Ag 29.5g/t Ag / 29.5g/t Ag / 29.5g/t Au 3.88g/t / Au 3.88g/t Au 3.88g/t 3.88g/t Au / 29.5g/t Ag 29.5g/t Ag / 29.5g/t Ag / 29.5g/t Au 3.88g/t / Au 3.88g/t Au 3.88g/t -

Profile XRD - SP202 SP202 SP202 SP202 SP202 SP202 SP202 SP202 SP202 SP202 2m 2m 2m 2m 2m 2m 2m 2m 2m

SP022 SP022 SP022 SP022 SP022 SP022 SP022 SP022 SP022 SP022

SP105 Sascha Sur PIMA Sascha Sur SP105 SP105 SP105 SP105 SP105 SP105 SP105 SP105 SP105

PIMA SaschaGinguro

2209 2208 2207

2209.5 2208.5 2207.5 2206.5

2211 2213 2212 2210 2209 2208 2207 2206 2205 Absorption Wavelength Absorption Wavelength Absorption

Figure 21. PIMA and XRD profiles of individual vein phases from the Sascha ginguro vein zone showing sample location, geology and veining, gold/silver assays, and SWIR absorption wavelength and absorption depth.

Quinn Smith Master of Applied Science Thesis 51

Rhyodacite Crystal Tuff Crystal Rhyodacite Vein Analysis Vein location sample PIMA vein quartz Comb Tuff Pumice Rhyodacite Vein Analysis Vein location sample PIMA vein quartz Comb silicification Wall-rock Lithic Rhyolite Tuff Lithic Rhyolite FeOx stained chalcedonic chalcedonic stained FeOx stockwork veins to opaline pyrite disseminated with Wall-rock silicification Wall-rock FeOx stained chalcedonic chalcedonic stained FeOx pyrite disseminated with veins Crystal Ash Rhyolite Tuff Ash Crystal Rhyolite AL(OH) Absorption Wavelength AL(OH) Absorption Depth AL(OH) Absorption Wavelength AL(OH) AbsorptionDepth LEGEND

LEGEND LEGEND

LEGEND Absorption Depth Absorption

Depth Absorption

0.38 0.36 0.34 0.32 0.28 0.26 0.24 0.22 0.3 0.2 0.19 0.18 0.17 0.16 0.2 0.205 0.195 0.185 0.175 0.165

50cm 50cm 50cm 50cm 50cm 50cm 50cm 50cm 50cm

SP053 SP053 SP053 SP020 SP020 SP020 SP020 SP020 SP020 SP053 SP053 SP053 SP020 SP020 SP020 SP053 SP053 SP053 SP053 SP020

70 70 70 70 70 70 70 70 70

1m @ 0.23g/t Au /Ag Au 1.8g/t /Ag Au 0.23g/t @ 1.8g/t 1m /Ag 0.23g/t Au @ 1.8g/t 1m 0.23g/t @ 1m 1m @ 0.23g/t Au /Ag Au 1.8g/t /Ag Au 0.23g/t @ 1.8g/t 1m /Ag 0.23g/t Au @ 1.8g/t 1m 0.23g/t @ 1m 1m @ 0.23g/t Au /Ag Au 1.8g/t /Ag Au 0.23g/t @ 1.8g/t 1m /Ag 0.23g/t Au @ 1.8g/t 1m 0.23g/t @ 1m

SP021 SP021 SP021 SP021 SP021 SP021 SP021 SP021 SP021 SP021 Sample XRD Profile XRD SP216 SP216 SP216 SP216 SP216 SP216 SP216 SP216 SP216 SP216 -

Sample

XRD Profile XRD - 2m 2m 2m

2m 2m 2m 2m 2m 2m Chalcedony PIMA Chalcedony

- 1m @ 1m 1.37g/t /@ Au g/t1m 12.4 1.37g/t /@ Au Ag g/t1m 1.37g/t12.4 /@ Au Ag g/t12.4 Ag 1m @ 1m 1.37g/t /@ Au g/t1m 12.4 1.37g/t /@ Au Ag g/t1m 1.37g/t12.4 /@ Au Ag g/t12.4 Ag 1m @ 1m 1.37g/t /@ Au g/t1m 12.4 1.37g/t /@ Au Ag g/t1m 1.37g/t12.4 /@ Au Ag g/t12.4 Ag SP022 SP022 SP022 SP022 SP022 SP022 SP022 SP022 SP022 SP022 SP054

SP054 SP054 SP054 SP054 SP054 SP054 SP054 SP054 SP054

PIMA Sascha Sur

SaschaPyrite 2209 2208 2207

2209.5 2208.5 2207.5 2206.5

2211 Wavelength Absorption 2212 2210 2209 2208 2207 2206 2205 Wavelength Absorption

Figure 22. PIMA and XRD profiles of individual vein phases from the Sascha pyrite- chalcedony vein zone showing sample location, geology and veining, gold/silver assays, and SWIR absorption wavelength and absorption depth.

Quinn Smith Master of Applied Science Thesis 52

Rhyodacite Crystal Tuff Crystal Rhyodacite

Rhyodacite Pumice Tuff Pumice Rhyodacite

Comb quartz vein quartz Comb

PIMA sample location sample PIMA

Vein Analysis Vein

Wall-rock silicification Wall-rock

veins with disseminated pyrite disseminated with veins FeOx stained chalcedonic chalcedonic stained FeOx Rhyodacite Crystal Tuff Crystal Rhyodacite Vein Analysis Vein location sample PIMA vein quartz Comb Tuff Pumice Rhyodacite Wall-rock silicification Wall-rock

FeOx stained chalcedonic chalcedonic stained FeOx pyrite disseminated with veins

AbsorptionDepth

AL(OH)

Wavelength

Absorption AL(OH)

AL(OH) Absorption Wavelength AL(OH) AbsorptionDepth

LEGEND

LEGEND LEGEND LEGEND

Absorption Depth Absorption Depth Absorption

0.16

0.17

0.18

0.19

0.2

0.165

0.175

0.185

0.195 0.205 0.19 0.18 0.17 0.16 0.2 0.205 0.195 0.185 0.175 0.165

SP020 SP020 SP020

SP020 SP020 SP020 SP020 SP020 SP020 SP020 SP020 SP020 SP020 SP020 SP020

SP020 SP020

70 70 70

70 70 70 70 70 70 70 70 70  70 70 70



1m @ 0.23g/t Au /Ag Au 1.8g/t 0.23g/t @ 1m 1m @ 0.23g/t Au /Ag Au 1.8g/t 0.23g/t @ 1m 1m @ 0.23g/t Au /Ag Au 1.8g/t 0.23g/t @ 1m

1m @ 0.23g/t Au /Ag Au 1.8g/t 0.23g/t @ 1m 1m @ 0.23g/t Au /Ag Au 1.8g/t 0.23g/t @ 1m 1m @ 0.23g/t Au /Ag Au 1.8g/t 0.23g/t @ 1m 1m @ 0.23g/t Au /Ag Au 1.8g/t /Ag Au 0.23g/t @ 1.8g/t 1m /Ag 0.23g/t Au @ 1.8g/t 1m 0.23g/t @ 1m 1m @ 0.23g/t Au /Ag Au 1.8g/t /Ag Au 0.23g/t @ 1.8g/t 1m /Ag 0.23g/t Au @ 1.8g/t 1m 0.23g/t @ 1m

/Ag Au 1.8g/t /Ag Au 0.23g/t @ 1.8g/t 1m /Ag 0.23g/t Au @ 1.8g/t 1m 0.23g/t @ 1m

SP021 SP021 SP021

SP021 SP021 SP021 SP021 SP021 SP021 SP021 SP021 SP021

SP021 SP021 SP021 SP021

SP021 Sample Sample

XRD Profile XRD XRD Profile XRD - -

2m 2m 2m

2m 2m 2m 2m 2m 2m 2m 2m 2m 2m 2m 2m

SP022

SP022 SP022 SP022

SP022

SP022 SP022 SP022

SP022 SP022 SP022 SP022 SP022 SP022 SP022 SP022 SP022

PIMA Sascha Sur Sascha Sur PIMA Sascha Sur

2207

2208 2209

2209 2208 2207

2206.5

2207.5

2208.5 2209.5 2209.5 2208.5 2207.5 2206.5

Absorption Wavelength Absorption Wavelength Absorption

Figure 23. PIMA and XRD profiles of individual vein phases from the Sascha Sur vein zone showing sample location, geology and veining, gold/silver assays, and SWIR absorption wavelength and absorption depth.

Quinn Smith Master of Applied Science Thesis 53

A B 1 2

5 μm 10 μm

C 1 D

10 μm 5 μm

2 E F E 3

5 μm 20 μm

G H

5 μm 10 μm

Figure 24. ESEM images of alteration mineral morphologies from individual alteration systems within the study area. A. Pelligrini (SP157) 1-Laumontite, 2-Kaolinite B. Pelligrini (SP158) 1-Illite, 2-Quartz C. Pelligrini (SP160) 1-Alunite, 2-Opal D. Sascha Main (SP196) Kaolinite E. Sascha Main (SP197) Illite F. Sascha Main (SP199) 1-Muscovite, 2-Illite, 3-Quartz G. Sascha Sur (SP021) Laumontite H. Sascha Sur (SP023) 1-Illite, 2-Gypsum

Quinn Smith Master of Applied Science Thesis 54

Alteration geochemistry Table XX. Selected PIMA and XRD results Mass balance alteration geochemistry is calculated for individual alteration zones, within stratigraphically homogeneous units using the methods of MacLean and Barret (1993). Least altered samples for each of the stratigraphic host units were chosen through petrographic and XRD examination. Least altered precursor samples for the rhyolite crystal ash tuff, rhyodacite ignimbrite, and rhyolite ash tuff are QR05-26, QR25 and QR05-21 respectively. Sample locations are shown in figure 3.

The Sascha Main alteration profile shows a general mass gain with increasing alteration intensity proximal to veining. Immobile element concentrations decrease with increasing alteration intensity and mass gain (Figure 25 A). Sample SP196 is located 160cm from the vein margin (Figure

19), and is characterised by moderate mass gains in SiO2 (16.5%), Al2O3

(14.5%), small mass gains in TiO2 (1%) and Fe2O3 (4.6%), and a small mass

loss in K2O (-2.2%) (Figure 25 B). SP197 and SP198 are located 90cm and 25cm from the vein respectively, and show the largest mass gains in the

profile. SP197 shows large mass gains in SiO2 (235.9%), Al2O3 (42.6%),

moderate mass gains in Fe2O3 (14.4%), K2O (10.2%), and small mass gains

in MgO (3.9%), TiO2 (2.1%), Na2O (0.9%) (Figure 25 B).

Similar to Sascha Main, the Sascha Sur alteration profile shows mass gains adjacent to epithermal veins. Increasing alteration intensity decreases immobile element concentrations associated with mass gains (Figure 26 A). Sample QR05-23 is located approximately 2.3km from the Sascha Sur

veinlet zone (Figure 3), and is characterised by small mass gains in Al2O3

(2.5%), Fe2O3 (2.6%), CaO (3.8%), Na2O (2.9%), and MgO (0.6%), with

small mass losses in SiO2 (-5.2%) and K2O (-1.5%) (Figure 26 B). The largest mass gains in the profile are observed in samples located directly on

the vein margin. SP023 shows large mass gains in SiO2 (163.3%), Al2O3

(22%), a moderate mass gain in K2O (6.2%), and small mass gains in Fe2O3

(1.6%), MgO (1.1%), and TiO2 (0.6%) (Figure 26 B).

Quinn Smith Master of Applied Science Thesis 55

The Pelligrini alteration profile is unique, with a mass loss in the kaolinite-illite peripheral alteration zone, and a mass gain in the zone of pervasive silicification with alunite and opal. Increasing alteration within the host lithology at Pelligrini causes immobile element concentrations to increase with mass losses, and decrease with mass gains (Figure 27 A). The alteration of the rhyolite ash tuff around the periphery of the silicified- alunite/opal zone is characterised by a large mass loss in SiO2 (-45.9%), small mass losses in Al2O3 (-3.7%), K2O (-3.2%), and Na2O (-1.4%), with a small mass gain in Fe2O3 (4.5%) (Figure 27 B). SP160 is located directly within the silicified-alunite/opal zone and shows the largest mass gain in the profile. SP160 shows large mass gains in SiO2 (63.3%), moderate mass gains in SO3 (16.2%), small mass gains in Al2O3 (5.4%), Fe2O3 (3.4%), and

K2O (1.3%), with a small mass loss in Na2O (0.6%) (Figure 27 B).

Quinn Smith Master of Applied Science Thesis 56

A Rhyolite Crystal Ash Tuff Immobile Elements 6 Sm vs Dy y = 1.4372x QR05-26 2 Linear (Sm vs Dy) R = 0.9792 5

SP196 4 SP199

SP198 Sm ppm Sm 2

1 SP197

0 0 0.5 1 1.5 2 2.5 3 3.5 4

Dy ppm

B Sascha Main Alteration 101 311.05 100 235.92 SP196 SP199 SP198 SP197

ChangeMass (g/100g)

-50 SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 SO3 NET

Figure 25. Selected immobile elements and geochemical mass-changes for rhyolite crystal ash tuff alteration within Sascha Main.

Selected immobile elements showing single precursor, highlighted by red circle, and altered samples along linear alteration trends for homogenous stratigraphic horizons. Bar graphs showing mass-changes of major elements in samples representing increasing alteration intensity for individual alteration systems.

A. Immobile elements Sm and Dy within the rhyolite crystal ash tuff which hosts Sascha Main. B. Mass changes for major elements within the Sascha Main alteration system based on the single precursor QR05-26

Quinn Smith Master of Applied Science Thesis 57

AC Rhyodacite Ignimbrite Immobile Elements 4 Dy vs Y y = 0.1788x QR25 2 QR05-23 3.5 Linear (Dy vs Y) R = 0.9951 QR11 3 SP021

2.5

Dyppm 1.5 SP023 1

0.5 0 0 5 10 15 20 25 Y ppm

B D Sascha Sur Alteration 100 163.3 QR05-23 QR11 SP021 SP023 196.16

(g/100g) Change Mass

-50 SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 SO3 NET

Figure 26. Selected immobile elements and geochemical mass-changes for rhyodacite ignimbrite alteration within Sascha Sur.

A. Immobile elements Dy and Y within the rhyodacite ignimbrite which hosts Sascha Sur B. Mass changes for major elements within the Sascha Sur alteration system based on the single precursor QR25

Quinn Smith Master of Applied Science Thesis 58

A E Rhyolite Ash Tuff Immobile Elements 3.5 Dy vs Y y = 0.193x 2 SP157 Linear (Dy vs Y) R = 0.9703 3

SP159 2.5 SP158 2 QR05-21

Dyppm 1.5

1 SP160 0.5

0 0 2 4 6 8 10 12 14 16 18 Y ppm

B F Pelligrini Alteration 100 SP160 SP158 SP159 SP160

ChangeMass (g/100g)

-50.87 -50 SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 SO3 NET

Figure 27. Selected immobile elements and geochemical mass-changes for rhyolite ash tuff alteration within Pelligrini.

A. Immobile elements Dy and Y within the rhyolite ash tuff which hosts Pelligrini B. Mass changes for major elements within the Pelligrini alteration system based on the single precursor QR05-21

Quinn Smith Master of Applied Science Thesis 59

The trace element Zr is generally considered as immobile in many alteration systems (Maclean and Kranidiots, 1987; Cail and Cline, 2001, Grant, 1986; Grant 2005). Comparisons of possible immobile elements Dy, Sm and Y with Zr show good correlations (Table 6). Mass change calculations using Zr show similar trends to mass-changes calculated from Dy, however absolute values differ by up to 58% (Figure 28).

Samples Outliers Dy vs Zr Sm vs Zr Y vs Zr R2 R2 R2 Rhyolite Crystal QR05-26, SP196, SP197 0.94 0.96 0.84 Ash Tuff SP198, SP199 Rhyodacite QR25, QR05- SP021, SP023 0.92 0.91 0.92 ignimbrite 23, QR11 Rhyolite Ash QR05-21, SP157, SP159 0.83 0.34 0.98 Tuff SP158, SP160

Table 6. Tabulated correlation coefficient values for immobile elements Dy, Sm, and Y plotted against Zr.

Dy vs Zr net mass change comparison 120 Zr net mass-change Dy net mass-change 100 80

Mass Change (g/100g) Change Mass -20

-40

-60 SP198 SP199 QR05-23 QR11 SP158 SP160

Figure 28. Bar graph comparing net mass changes for immobile elements Dy and Zr.

Quinn Smith Master of Applied Science Thesis 60

Discussion

Epithermal deposits are characteristically hosted within complex geological environments subject to multiple episodes of deformation (Begbie et al, 2007) and overprinting alteration (Mauk and Simpson 2007; Gemmel 2007; Warren et al,2007; Ducart et al, 2006). Host sequences exhibit strong controls on the type and nature of alteration and the morphology of veining. Understanding the local geology within the study area is vital in generating a realistic and accurate generic model of the epithermal system.

Volcanology

Depositional setting Large silicic volcanic environments have complex and diverse facies associations and stratigraphic relationships. Facies associations within the Sascha-Pelligrini area comprise two compositionally distinct volcanic sequences of rhyodacite and rhyolite ash-flows and minor air-fall deposits (Chon Aike and La Matilde Formations). The rhyolite sequence is deposited on a minor unconformity on the rhyodacite sequence and represents deposition of significantly less material. The rhyodacite sequence is very thick (~670m) strongly welded, and laterally continuous across the study area. The upper rhyolite sequence is relatively thin (~130m), poorly welded and spatially restricted within the study area.

Classification into broad facies models is achieved by the unique characteristics within the volcanic stratigraphy. Stratigraphic associations, or facies associations, can be used to reconstruct palaeogeological environments and depositional settings aiding in the interpretation of eruption styles. Continental silicic provinces are composed of rhyolite domes and flows of subdued topography rising above large ignimbrite shields (Cas and Wright, 1987). The focal element of a silicic province is the caldera, which may contain multiple eruption points and a basin for accumulation of volcanic material. The critical facies association within silicic volcanic terrains is the

Quinn Smith Master of Applied Science Thesis 61

recognition of volcanics formed in intracaldera or extracaldera environments (Cas and Wright, 1987). Intracaldera deposits are comprised of lavas and domes, thick crystal-rich ignimbrites and associated near vent co-ignimbrite breccias and intercalated epiclastics. Extracaldera successions are dominated by thin sheet-like outflow ignimbrites interspersed with pyroclastic fall and abundant epiclastic deposits.

The deposition of the homogenous and strongly welded rhyodacite ignimbrite of the Chon Aike formation within the study area requires the pre-existence of a large topographic depression proximal to an eruption source (Cas and Wright, 1987). The lithic concentration zone, or lag deposit, within the La Matilde rhyolite ash tuff would suggest eruption proximal to source vents and characteristically shows a decrease in maximum clast size away from the source (Sheriden, 1979). Resurgent rhyolitic flow domes, such as at Pelligrini, form within or at the margins of the caldera structure, however they may also be erupted outside the caldera margin (Cas and Wright, 1987). On the basis of facies models (Cas and Wright, 1987), the thick, homogenous and strongly welded nature of the rhyodacite ignimbrite, lithic concentration zones within the rhyolite sequence, and the resurgent flow dome at Pelligrini is consistent with an intracaldera depositional setting.

Although facies associations within the study area suggest an intra-caldera setting, Guido et al (2004) proposes that the distribution of the Jurassic volcanics of the Chon Aike and La Matilde formations are associated with intersections of regional east-northeast and west-northwest basement fractures. Regional east-northeast and west-northwest basement transfer structures traverse the study area, with spatially restricted rhyolite tuffs confined within grabens and half-grabens bound by the structures. Maximum size lithic clast vectors from the base of the rhyolite sequence suggest a source close to the intersection of the basement structures in the north-west of the study area. Echeveste et al (1999) and Guido et al (2004) propose the large volume of volcanic material that comprises the Chon Aike and La Matilde formations were produced through a complex system of Jurassic extensional graben-forming structures with only minor caldera formation.

Quinn Smith Master of Applied Science Thesis 62

Therefore the facies associations of the volcanics within the study area may closely represent an intra-caldera setting, with volcanics erupted from a complex series of graben-forming extensional fractures instead of a classic caldera margin.

Eruption styles Eruption styles depend strongly on the physical properties of magma. Magma properties are related to temperature, melt composition, proportion of crystals, amount of dissolved volatiles and the abundance of gas bubbles (Sparks et al, 1997). Explosive eruptions of dacitic-rhyolitic material usually occur through degassing of dissolved volatiles with decreasing lithostatic load (Sparks et al, 1997). Highly explosive dacitic-rhyolitic eruptions can produce tremendous amounts of pyroclastic material. Collapse of the giant La Garita caldera in the San Juan Volcanic Field erupted as much as 5000km3 of material in individual eruptions, producing the well studied Fish Canyon Tuff (Lipman, 2000).

Pyroclastic deposits can be classified into genetic groups of fall, flow and surge according to their mode of transport and deposition (Sparks and Walker, 1973) (Figure 29). Pyroclastic fall deposits are formed from material that has been explosively ejected from a vent (Sheriden, 1979) and usually mantle topography, with the geometry and size of the deposit controlled by eruption column height and wind conditions (Cas and Wright, 1987). Pyroclastic flows are formed by the collapse of a convective ash cloud, with a lateral deposition of pyroclastic material away from the eruptive centre (Sheriden, 1979). Pyroclastic flows are controlled by topography with material filling valleys and depressions; flows emplaced at extremely high velocities may mantle topography (Cas and Wright, 1987). Pyroclastic surges are deposited from directed blasts caused by plug explosions, phreatomagmatic eruptions or changing vent geometry (Sheriden, 1979).

The volcanic units of the Sascha-Pelligrini area record several distinct eruption styles. The rhyodacite crystal ignimbrite forms a thick, homogeneous

Quinn Smith Master of Applied Science Thesis 63

composite welded package with no clear lithological separation between welded horizons. Lithic clasts are rare and occur as small discrete fragments within a much finer-grained crystal-rich matrix. The rhyodacite unit may represent a composite flow formed by eruption column collapse from multiple vents or fissures. Alternatively, this unit may have been produced by multiple rapid eruptive events from a single vent or fissure. Both models imply a relatively synchronous and rapid deposition.

Welding within the rhyodacite ignimbrite varies both vertically and horizontally, and forms composite welded horizons preserved as topographic highs across the study area. Complex welding patterns develop in pyroclastic flows due to varying temperature and load stress and vary irregularly from proximal to distal vent facies (Christiansen, 1979; Wilson and Hildreth, 1997). The composite welding within the lower rhyodacite ignimbrite of the Chon Aike Formation suggests deposition originated from a succession of small eruptions that quickly deposited material at relatively hot temperatures. The lack of air-fall horizons within the ignimbrite package suggests that the pyroclastic flows were associated with low eruption columns (Guido et al, 2004), or alternatively, the volcanic ash was elutriated from the eruption column.

An increase in lithic and juvenile lava clasts towards the top of the rhyodacite ignimbrite coupled with the transition into a massive strongly welded pumice tuff represents a change in the vent geometry producing a more energetic eruption sequence. Thin air-fall ash horizons at the top of the pumiceous unit may indicate that buoyant lift-off occurred within the pyroclastic flow, producing a co-ignimbrite plume. Buoyant lift-off is thought to be the main mechanism for producing co-ignimbrite plumes, elutriating fine ash and preferentially enriching pyroclastic flows in crystal material (Sparks et al, 1997). Dilute gravity flows can form on the sides of an eruption column, and deposit thin ash layers proximal to eruption centres in a similar manner to co- ignimbrite plumes (Sparks et al, 1997).

Quinn Smith Master of Applied Science Thesis 64

The transition at the top of the Chon Aike from a massive welded pumice tuff to welded crystal ash rhyodacite tuff with abundant juvenile chlorite-hematite, granitic and lithic clasts represents renewed vent activity. Lithic clasts signal a possible change in vent geometry or vent clearing. Abundant deep-origin chlorite-hematite and granitic clasts represent a tapping of deeper parts of an exhausted magma chamber. The welded crystal ash rhyodacite tuff is the last eruptive unit of the Chon Aike sequence, and subsequently has the least amount of lithostatic load. Strong welding with abundant undeformed clasts and minimal lithostatic load suggests the crystal ash rhyodacite package was deposited at high temperatures proximal to source. Current exposure of highly welded ignimbrites and disconformable relationships with the overlying un-welded rhyolite ash package, represents a period of erosion and volcanic quiescence.

The spatially restricted La Matilde rhyolite ash tuffs show disconformable relationships with the underlying Chon Aike Formation, suggesting they were deposited after a brief period of volcanic quiescence. Stratigraphic relationships between the La Matilde and Chon Aike formations are debatable, with significant lateral and vertical facies changes within the units obscuring depositional contacts. The laminated tuffs of the La Matilde Formation often interdigit with the ignimbrites of the Chon Aike Formation, leading Sanders (2000) to suggest that the two units were deposited concurrently. Epiclastic deposits of the La Matilde show disconformable contacts with the underlying Chon Aike, however they do not represent a significant hiatus in volcanic activity, but rather reworking of pyroclastic material between eruptions (Pakhurst et al, 1998; Guido et al, 2004).

The massive rhyolite package of the La Matilde Formation formed from a single, violent eruption filling a pre-existing valley. The lithic rhyolite tuff at the base of the La Matilde represents a proximal lag breccia, sourced from a single vent following a transition from rhyodacite to rhyolite volcanism. Metamorphic muscovite schist clasts compose >95% of the total lithics and represent a deep vent source of pre-Jurassic basement. Lithic fragments in pyroclastic deposits result from conduit and vent erosion during explosive

Quinn Smith Master of Applied Science Thesis 65

eruptions, recording changes in mechanics and timing of caldera collapse (Suzuki-Kamata et al, 1993: Browne and Gardner, 2003). The lithic unit has extreme vertical and lateral geometry variations, with clast size vectors identifying a single vent in the north-west of the study area. The lithic lag breccia is contemporaneous with the massive valley-filling un-welded rhyolite crystal ash tuff.

Eruption column collapse after the initial explosion that deposited the lithic lag breccia produced a relatively cool pyroclastic flow that travelled along a pre-existing valley towards the southeast. The flow deposited the un-welded rhyolite crystal ash tuff, the most extensive unit of the La Matilde Formation. The overlying rhyolite ash unit at the top of the La Matilde sequence mantles topography and contains zones of accretionary lapilli. Mantled topography and accretionary lapilli indicate the rhyolite ash is an air-fall sequence deposited during a rain event. The planar-bedded rhyolite ash is contemporaneous with the air-fall ash, and represents the settling of the convecting cloud from the initial transitional eruption that produced both the lag breccia and the un-welded crystal ash rhyolite tuff.

Several distinct eruption styles are recorded within the volcanic sequence. The rhyodacite crystal ignimbrite exposed at the base of the sequence was rapidly deposited by eruption column collapse from multiple vents or fissures creating a composite welded unit. An increase in lithic and juvenile lava clasts towards the top of the unit, and the transition into a massive strongly welded pumice tuff represents a change to a more energetic eruption sequence. The transition at the top of the Chon Aike to welded crystal ash rhyodacite tuff with abundant undeformed juvenile and lithic clasts represents renewed vent activity, with deposition under minimal lithostatic load proximal to source. The spatially restricted La Matilde rhyolite sequence was deposited from a single violent eruption depositing the lag breccia proximal to the vent. The pyroclastic flow produced by the eruption column collapse deposited the un-welded rhyolite crystal ash tuff, with settling of the convective cloud depositing the planar-bedded rhyolite ash tuff.

Quinn Smith Master of Applied Science Thesis 66

Figure 29. Styles of explosive eruptions with vent development restricted to half-graben and graben forming regional basement structures.

A. Convective – Development of Plinian eruption column, fine grained pyroclastic fallout covers wide area. B. Transitional – Development of convective plume with some pyroclastic fallout, oscillating fountain feeds some pyroclastic flows with associated co-ignimbrite plumes. C. Collapsing – Sustained fountain of pyroclastic material feeds continual massive pyroclastic flows that develop large co-ignimbrite plumes. Small convecting cloud above collapsing fountain. (Modified from Purdy 2003, after Neri et al 2002)

Quinn Smith Master of Applied Science Thesis 67

Magma Petrogenesis Two petrographically and geochemically distinct groups (rhyodacite and rhyolite) compose the Sascha-Pelligrini suite of the study area. Hydrothermal alteration affects rocks throughout the majority of the study area and precludes quantitative petrochemical modeling the volcanic rock suite. Sorting, welding, post emplacement crystallisation and devitrification, as well as erosion prior to hydrothermal alteration contribute to the complexity of the suite‟s genesis.

The pyroclastic rocks of the study area belong to the Jurassic Chon Aike and La Matilde Formations which form a silicic large igneous province (LIP) with an estimated volume of 235,000km3 (Pankhurst et al, 1998). The generation of large volumes of silicic magma reflects large-scale crustal melting controlled by the water content and composition of the crust, and a large thermal (+/- mass) input from the mantle (Bryan, 2007). Jurassic rhyolites of the Chon Aike Formation were produced through anatexis of sedimentary source material, with silicic melts generated from heat input of mantle-derived basaltic melts ponding at the base of the crust (Gust et al, 1985). The Chon Aike silicic LIP is characterised by the absence of mantle-derived rocks (Pankhurst el at, 1998), with basaltic andesite of the Bajo Pobre Formation being the least evolved and restricted to only a few localities (Pankhurst and Rapela, 1995; Pankhurst et al, 1998; Sanders, 2000; Sharpe et al, 2002). Trace element similarities between the basaltic andesite of the Bajo Pobre and the rhyolites of the Chon Aike suggest the rhyolite formed from partial melting of the basaltic andesite (Storey and Alabaster, 1991; Pankhurst and Rapela, 1995; Pankhurst et al, 1998).

Pankhurst and Rapela (1995) demonstrate that the sequence from basaltic andesite (Bajo Pobre) to dacite/rhyodacite to rhyolite (Chon Aike) can be modeled by a combination of partial melting and fractional crystallisation. Batch partial melting of a depleted Bajo Pobre andesite produces Chon Aike equivalent dacite through 20% melt extraction, with a residual composition composed of orthopyroxene and plagioclase. Fractional crystallisation of dacite to rhyodacite is accomplished with the removal of 50% crystal

Quinn Smith Master of Applied Science Thesis 68

assemblage composed of 10% amphibole and 90% plagioclase. High-silica rhyolite is produced from fractional crystallisation of the rhyodacite, with the removal of 40% crystal assemblage composed of approximately 58% plagioclase, 40% hornblende, 1% apatite and trace allanite.

The exposed rhyodacite sequence of the Chon Aike Formation exhibits some variation in REE abundances. The last ash-flow unit of the sequence, the pumice ash welded rhyodacite tuff, is enriched in the LREE, depleted in the middle REE with a pronounced negative Eu anomaly relative to the first ash- flow rhyodacite. These REE differences are consistent with the proposed fractionation trends of Pankhurst and Rapela (1995).

The rhyolitic tuff sequence of the La Matilde Formation shows a general decrease in REEs from the massive crystal ash tuff to the planar bedded air- fall ash tuff. The REE pattern for the lag breccia lithic tuff deviates from the general rhyolite sequence patterns and may represent contamination from a variety of components. The lag breccia is considered to be deposited through the initial explosive eruption of the rhyolitic sequence, contains vent derived material, and outcrops within the intense alteration zone of Sascha Main. The discrepancies observed for the lag breccia REE trend may be a complex product of obscuring alteration and vent contamination. Similar to the rhyodacite package, the rhyolite sequence REE patterns show a negative Eu anomaly, decrease in REE concentrations with continued eruptive units, and depressed HREEs. The negative Eu anomaly may be controlled by the fractionation of sanidine, with the depletion of REEs controlled by the fractionation of hornblende. Compositional zoning observed in sequence suggests eruption of a zoned magma chamber.

Eruptive sequences commonly show an orderly progression from most evolved to least evolved magmatic ejecta, representing eruption from compositionally zoned magma chambers (Hildreth, 1979). Individual ash-flow sheets of the rhyodacite sequence within the study area have a limited compositional range. Large volume, phenocryst-rich ignimbrites such as the rhyodacite sequence rarely develop from zoned magma chambers, with the

Quinn Smith Master of Applied Science Thesis 69

fractionation process prematurely aborted by venting of the dominant magma volume (Hildreth, 1979). This may be the case for the rhyodacite sequence, however the volcanic stratigraphy below the ignimbrite is not observed, and a more evolved silicic unit may exist at the base of section below the rhyodacite.

The rhyodacite and rhyolite units form two distinct groups within the study area. Strong hydrothermal alteration, sorting, welding, post emplacement crystallisation and devitrification, as well as erosion throughout the majority of the study area precludes quantitative petrochemical modeling the volcanic rock suite. Variation in REE abundances across the rhyodacite and rhyolite sequences is consistent with the proposed fractionation trends of Pankhurst and Rapela (1995). Pankhurst and Rapela (1995) demonstrate that the sequence from basaltic andesite (Bajo Pobre) to dacite/rhyodacite to rhyolite (Chon Aike) can be modeled by a combination of partial melting and fractional crystallisation.

Host Rock Control and Structural Model Host rock rheology controls vein distribution and morphology within the Sascha-Pelligrini system and is a common control in many epithermal deposits (Brathwaite et al, 2001; Christie et al, 2007; Izawa et al, 1990). Outcrop distribution of ginguro-banded veins at Sascha Main is limited, with quartz veins and lenses hosted within poorly welded crystal ash rhyolite tuff. The heavily altered and relatively friable tuff restricts coherent vein development within the current stratigraphic exposure. Outcrop morphology of discontinuous quartz veins within the rhyolite tuff suggests that veins are upward terminating within a friable tuff that does not host continuous brittle fractures. The lithic rhyolite tuff hosts discontinuous and chaotic veining, with friability and high porosity favouring multiple discontinuous fractures and veinlets. Pumiceous rhyodacite tuffs at Sascha Sur and Marcellina host broad zones of discontinuous multi-directional veinlets, while the ash tuffs at Pelligrini are pervasively silicified and brecciated.

Quinn Smith Master of Applied Science Thesis 70

Lithological controls are well documented at numerous epithermal deposits, with coherent 2 to 3 meter wide veins in andesite at the Hauraki goldfield changing to stockwork veining in rhyolite with individual veins less than 10 centimeters in width (Christie et al, 2007). Well developed coherent epithermal veins are developed within crystalline and brittle Bajo Pobre andesite that underlies the Chon Aike Formation (Dietrich et al, 2008) as well as felsic intrusives within the Chon Aike Formation (Wallier and Tosdal, 2008). The rheologically brittle massive crystalline rhyodacite ignimbrite that stratigraphically underlies the current outcrop exposure at Sascha Main may host larger epithermal veins in more continuous fractures. The rhyodacite ignimbrite at Sascha-Pelligrini is analogous to the massive quartz-feldspar porphyritic, densely welded, pumiceous ignimbrite (Granosa) within the Chon Aike Formation that hosts the majority of veining within the Cerro Vanguardia epithermal deposit (Sharpe et al, 2002).

Epithermal veining at Sascha-Pelligrini was emplaced during a period of extensional tectonics that formed northwest-trending grabens. The extensional event was contemporaneous with the last stages of the Chon Aike (Echavarria et al, 2005) with the stratigraphically high La Matilde rhyolite filling the grabens and half-grabens. Maximum dilation and associated fluid flow formed at right-stepping structural spays along the right-lateral, oblique- slip, 315° trending normal Sascha Fault (Figure 30). The tension axis trended toward the northeast quadrant, producing left-lateral movement in north- and northeast-trending fault and shear zones, and right-lateral movement in structures oriented between 330° and 250°.

Quinn Smith Master of Applied Science Thesis 71

Figure 30. Structural model for the Sascha – Pelligrini study area showing vein styles and kinematic indicators for observed structural orientations.

San Jose District

Sascha Vein Zone

Figure 31. Riedel shear model for the San Jose district applied to the Sascha –

Pelligrini study area. Mineralised veins striking at 315° parallel to 1 represent extension fracture (T) in the model. Veins striking >315° are observed with a sinistral strike-slip component (San Jose), whereas veins striking <315° are observed to have a dextral strike-slip component (SVZ). (After Dietrich et al 2008).

Quinn Smith Master of Applied Science Thesis 72

Contrary to recent structural interpretations of the Desseado Massif that suggest right-lateral structures develop only narrow discontinuous and en echelon veins of no economic significance (Echavarria et al, 2005), detailed mapping of the SVZ indicates mineralised veins are hosted by right-lateral fault structures. A recent structural study of the Huevos Verdes veins within the San Jose district also supports the concept that economic significant epithermal veins are hosted on right-lateral fault structures. The structural model of the SVZ correlates well with the structural model of the San Jose district for the northwestern edge of the Desseado Massif. This structural model suggests right-lateral west-northwest-trending faults (280°) and left- lateral north-northwest-trending faults (350°) act as a conjugate shear pair.

The orientation of 1 is modelled as the acute bisector of the conjugate shear pair and is orientated at 315°. The majority of the veins at Huevos Verdes within the San Jose district are modelled as purely extensional, and similar to the SVZ, are orientated parallel to 1 at 315°. The trend of the Huevos Verdes and Sascha systems varies from 300° to 340° with an overall left- lateral strike-slip component observed for the Huevos Verdes veins striking at 325°(Dietrich et al, 2008), and an overall right-lateral strike-slip component observed for the Sascha veins striking at 315°. The Huevos Verdes model correlates with the observed structural pattern of the SVZ and fits well with the Riedel shear model (Figure 31). Left-lateral north-northwest-trending lineaments represent the main shear plane and north-northwest and west- northwest structures represent R and R‟ shears respectively (Dietrich et al, 2008).

Host rock rheology controls vein morphology and alteration patterns across the study area. The current exposure along the SVZ indicates the friable rhyolite tuffs of the La Matilde Formation do not host continuous brittle fractures or veins, and instead host upward terminating veins, stockwork vein zones, and pervasive silicification. Brittle fractures and more massive veining may be developed within the crystalline rhyodacite ignimbrite that stratigraphically lies below the current vein exposure. Structural analysis of the SVZ indicates the tension axis trended toward the northeast quadrant, producing right-lateral movement along the 315° trend. The structural pattern

Quinn Smith Master of Applied Science Thesis 73

of the SVZ conforms to the Riedel shear model, with 1 orientated at 315° and modelled as the acute bisector of the conjugate shear pair.

Alteration zoning Hydrothermal alteration within active geothermal fields is well documented (eg. Browne, 1978; White, 1981; Hedenquist and Henley, 1985; Spycher and Reed, 1989; Reyes, 1990; Fulignati et al, 1997; Cox and Browne, 1998; Ruggieri et al, 1999; Simmons and Browne, 2000; Patrier et al, 2003; and Bignall et al, 2004), with observed alteration assemblages and mineral zoning forming the basis of epithermal alteration models (Berger and Eimon, 1982; Heald et al, 1987; Berger and Henley, 1988 etc).

Hydrothermal alteration of the SVZ is characterised by quartz, adularia, illite, pyrite and minor calcite, and is overprinted by a late stage kaolinite- dominated assemblage. Throughout the Sascha-Pelligrini area, the common hydrothermal minerals define distinct alteration zones around epithermal veins (Figure 32). Each zone is characterised by a unique mineral assemblage and can be grouped into two major alteration types according to fluid chemistry. Clay abundance progressively increases above and towards the vein margins, with formation of alteration assemblages driven by reduced neutral or oxidized acid fluids.

Quinn Smith Master of Applied Science Thesis 74

Figure 32. Schematic cross section of alteration zoning and mineral assemblage observed for the Sascha-Pelligrini epithermal system.

Quinn Smith Master of Applied Science Thesis 75

The primary alteration assemblage along the SVZ formed from a near neutral to weakly alkaline chloride water, and is characteristic of the alteration found in many active geothermal systems (Simmons and Browne, 2000). Primary vein calcite, quartz pseudomorphs after bladed calcite and adularia occur within the saccharoidal vein phase at Sascha Main and form from gas loss and cooling associated with boiling (Browne and Ellis, 1970). Platy calcite scales, analogous to bladed calcite within epithermal veins, form in geothermal wells 100 to 300 meters above the point where the geothermal water first flashes to steam (Simmons and Browne, 2000). The weakly alkaline chloride-rich geothermal waters at Broadlands-Ohaaki contain approximately 1,300 mg/kg chloride and 1,900 mg/kg CO2 (Hedenquist and Henley, 1985), and produce a characteristic alteration assemblage dominated by quartz, adularia, illite, calcite, chlorite and pyrite (Simmons and Browne, 2000).

Abundant kaolinite, alunite and native sulphur are observed at many epithermal deposits, and occur overlying or towards the periphery of inferred fluid up-flow zones (Schoen et al, 1974; Love et al, 1998; Simpson et al, 2001). Steam-heated, acid-sulphate waters commonly occur in the vadose zone above boiling up-flow points, with alteration formed by leaching of rocks from fluids concentrated in H2SO4. Fluids concentrated in H2SO4 can be produced by atmospheric oxidation of sulphides, oxidation at the water table by H2S release via boiling, and the condensation of magmatic vapor (Rye et al, 1992). The acid-sulphate water reacts with the host-rock to produce kaolinite, cristobalite, alunite, pyrite and native sulfur (Scheon et al, 1974). Stable isotope studies of alunite from acid-sulphate alteration zones suggest precipitation from dominantly meteoric waters with magmatic SO2 (Rye et al, 1992; Love et al, 1998; Mykietiuk et al, 2004).

Calcium-rich zeolites that characterise the peripheral alteration halo of the Sascha-Pelligrini system form within the shallow and peripheral zones of geothermal systems (Simmons and Browne, 2000; Steiner, 1977).

Condensation of CO2 gas and absorption into cool ground waters produces

Quinn Smith Master of Applied Science Thesis 76

these zeolites as well as low-temperature clays and carbonates (Simpson et al, 2001). Country rock exposed to residual water after steam separation has a high H2S/H2 ratio and also favors pyrite formation (Browne and Ellis, 1970). The distal laumontite-montmorillonite alteration assemblage of the Sascha- Pelligrini system passes to illite-dominant alteration proximal to epithermal veins. The H2O content of calcium zeolites progressively decreases with increasing temperature, zoning from laumontite to wairakite (Steiner, 1977). Laumontite forms at temperatures above 110°C, passing to wairakite at 150°C, with illite forming above 200°C (Reed, 1994). The replacement of Ca- zeolites (laumontite) with calcite and illite proximal to epithermal veins within the Sascha-Pelligrini system indicates an increase in temperature and dissolved CO2 content towards fluid up flow points (Browne and Ellis, 1970; Cox and Browne, 1998).

The alteration assemblage of quartz, adularia, illite, calcite, chlorite and pyrite along the SVZ is in equilibrium with deep chloride-rich waters (Simmons and Browne, 2000). This alteration assemblage results from the recrystallisation of the original rock with uptake of variable amounts of H2O, CO2 and H2S. Mass balance geochemistry across the study areas shows hydrothermal fluids proximal to veins introduced variable amounts of SiO2, Al2O3, Fe2O3,

K2O, MgO, TiO2 and Na2O, and correlates well to the chemistry of the observed alteration assemblages.

PIMA alteration profiles adjacent to the SVZ show a decrease in the SWIR AlOH clay absorption feature towards the silicified vein selvages representing a decrease in total clay abundance (Pontual et al, 1997; Herrmann et al, 2001). Although total clay abundance decreases towards the vein, the increase in the absorption wavelength position corresponds to an increase in the amount of Fe and Mg in illite attributable to increasing temperature (Post and Noble, 1993). Compositional variations of white micas studied in various geothermal systems generally show an increase in K, Si, Fe and Mg and a decrease in Al with increasing temperature (Bishop and Bird, 1987; Cathelineau and Izquierdo, 1988; McDowell and Elders, 1983). Interstratified illite-smectite vein selvages at Sascha Main confine fluid temperature to

Quinn Smith Master of Applied Science Thesis 77

below 220°C (KRTA, 1990) with illite-smectite alteration located above mineralised veins at Golden Cross (Simpson et al, 1998) and Hishikari (Izawa et al, 1990; Ibaraki and Suzuki, 1993) (Figure 33). Interstratified illite- smectite usually occurs at the top of the gold mineralised interval (Hedenquist and White, 2005) and suggests the current exposure at Sascha Main is at a high level within the epithermal system.

The disassociation of aqueous CO2 during pressure release boiling within the SVZ provides H+ into solution. The subsequently acidic hydrothermal environment hydrolyzes feldspars within the host rock adjacent to the epithermal system, forming the dominant clay-illite alteration halo. Pressure release boiling, disassociation of aqueous CO2, and acidity buffering from wall-rock feldspars releases Ca+ into solution to form bladed calcite within the vein system. Calcite in equilibrium with adularia, illite and muscovite at Sascha Main results from the reduced acidity buffering of host-rock K- feldspar (sanidine) and K-mica (muscovite) with deep chloride waters (Browne and Ellis, 1970; Browne, 1978; Simmons and Browne, 2000).

Figure 33. Alteration zones and mineral assemblages of the Hishikari epithermal system showing alteration zoning from sericite and or kaolinite through to illite- smectite mixed layer clays above the gold-silver veins. The presence of chlorite- sericite-adularia and minor mixed layer clays marks the alteration within the gold mineralised interval.

Quinn Smith Master of Applied Science Thesis 78

The Sascha Main and Sur systems are characterised by abundant kaolinite associated with halloysite, hematite, goethite and very minor alunite and gypsum. This acid-sulphate alteration overprints illite assemblages and is spatially related to weathered pyritic veins and wall-rocks. Altered rocks with acid-sulphate assemblages contain abundant cubic voids after pyrite with mass-balance geochemistry indicating no introduction of sulphate. SWIR analysis of alteration adjacent to pyritic veins show a systematic increase in both absorption wavelength and absorption depth, attributed to an increase in overprinting kaolinite (Pontual et al, 1997). The Sascha Main acid-sulphate blanket represents a supergene alteration assemblage formed by oxidation of wall-rock pyrite above the palaeo-water table. During weathering of pyrite, iron released by carbonic acid-bearing rainwater precipitates almost immediately as ferric hydroxide due to the low pH and Eh (Schoen et al, 1974). Bright yellow-orange amorphous iron hydroxides, hematite and goethite characteristic of weathered pyrite are abundant throughout the kaolinite blanket over Sascha Main.

The Pelligrini acid-sulphate alteration characterised by abundant kaolinite, with lesser alunite, natroalunite and opal, forms a broad circular alteration halo around pervasive silicification. The acid-sulphate alteration passes vertically to illite-pyrite alteration, and represents overprinted alteration assemblages. The Pelligrini alteration system is similar to that formed above blind orebodies within the Fresnillo district (Simmons, 1991) and is most likely associated with H2S oxidation in a steam-heated environment. Base cation leaching and mass loss within the pervasively altered ash tuff at Pelligrini is indicative of steam-heated acid-sulphate leaching (Reyes, 1990; Rye et al, 1992), with large mass gains in sulphate corresponding to the introduction of alunite. The intense pervasive silicification is associated with potassium enrichment and is characteristic of ore-related hydrothermal silicification within the Desseado Massif (Echavarria et al, 2005). Intense silicification occurs within stratigraphically high La Matilde and Chon Aike units above epithermal veining at Manantial Espejo in Argentina (Wallier and Tosdal, 2008). Silicification within these units is interpreted to form at the

Quinn Smith Master of Applied Science Thesis 79

palaeo-water table that channeled lateral flow of the hydrothermal system and led to silica precipitation (Wallier and Tosdal, 2008). The stratigraphically high silicification associated with acid-sulphate alteration forming by oxidation of H2S within a steam-heated environment places the current exposure at Pelligrini above the water table with formation temperatures less than 100°C (Rye et al, 1992).

Hematite-rich rocks developed along the northern periphery of the kaolinite- alunite-jarosite alteration zone at Pelligrini suggest horizontal permeability with products of hydrolysis migrating laterally from the source. Steamboat Springs provides a modern analogue to the alteration at Pelligrini, with hematite-rich zones developed at the transition from acid-sulphate to montmorillonite alteration (Schoen et al, 1974). High temperature dickite in outcropping polymict vein breccias associated with pervasive illite-dominant alteration adjacent to low-temperature alunite-opal at Pelligrini suggest the acid-sulphate assemblage has encroached downward into hotter parts of the epithermal system. The complex alteration at Pelligrini represents a well preserved high-level epithermal alteration system at the palaeo-water table. Hematite-rich rocks along the northern periphery of the alteration system represent the location of the palaeo-water table, and the boundary between the downward migrating low-temperature alunite-opal assemblage with the higher temperature illite-dominant assemblage. The overprinting alteration assemblages may represent a descending water table in a waning geothermal system with low-temperature alunite-opal alteration forming in illite altered rocks. Oxidation of H2S vapors produce dilute, acid SO4 waters and acid-sulphate alteration above fluid up flow points (Pelligrini), with outflow of neutral Cl waters (Sascha) discharged at a considerable distance from up flow points (Giggenbach, 1992).

Hydrothermal minerals define distinct alteration zones across the study area. Formation of alteration assemblages is driven by fluid chemistry, and can be characterised on the basis of an assemblage in equilibrium with reduced neutral or oxidized acid fluids. The alteration system around the SVZ is characterised by a broad distal laumontite-montmorillonite alteration halo that

Quinn Smith Master of Applied Science Thesis 80

passes to illite-dominant alteration proximal to epithermal veins. Vein selvages are characterised by smectite and interstratified illite-smectite, with the alteration assemblage indicating a reduced neutral environment. The initially acidic hydrothermal fluid is buffered by wall-rock feldspars, forming the dominant clay-illite alteration halo. The Sascha Main acid-sulphate blanket represents a supergene alteration assemblage formed by oxidation of wall-rock pyrite above the palaeo-water table. The acid-sulphate alteration passes vertically to illite-pyrite alteration, and represents overprinted alteration assemblages. Base cation leaching and mass loss within the pervasively altered ash tuff at Pelligrini is indicative of steam-heated acid- sulphate leaching, with large mass gains in sulphate corresponding to the introduction of alunite. The overprinting alteration assemblages across the study area indicate a lowering of the water table during the waning stages of the epithermal system.

The study of alteration minerals through the use of field portable PIMA equipment has provided a qualitative estimate of alteration mineralogies. Based on the methodology employed through the use of PIMA equipment, potential errors can occur in mineral identification. PIMA alteration sampling is a useful field based tool for rapid identification of alteration mineralogies sufficient for a mineral exploration program. Where possible, ground truthing of PIMA data should be validated by quantitative XRD analysis of selected individual alteration assemblages. Depending on the use and need of alteration data, PIMA can be effectively used a quick field base tool for exploration programs dealing with strong clay alteration of host rocks. The comparison between PIMA and XRD data shows detailed clay mineralogies and mixed layer clay assemblages can only be identified through the use of XRD analysis. Detailed alteration studies must employ lab based XRD sampling to quantitatively outline the alteration mineralogies.

Quinn Smith Master of Applied Science Thesis 81

Vein Paragenesis Detailed trench and outcrop mapping identifies six temporally and texturally distinct vein phases along the SVZ. The paragenesis of the vein phases along the SVZ form six main stages: stage one, chalcedonic; stage two, colloform-crustiform +/- ginguro; stage three, saccharoidal; stage four, chalcedonic with disseminated pyrite; stage five, jasperoidal; and, stage six, crystalline and comb veins (Figure 34). The colloform- crustiform-banding of stage two forms as an initial mineralising phase on the margins of stage three saccharoidal veins. The main mineralising events are stage two, associated with two colloform-crustiform ginguro bands, and stages four and five, associated with chalcedonic and jasperoidal veins with disseminated pyrite. Individual mineralising events are comprised of complex mineral paragenetic sequences with mineral relationships giving insight into system evolution (Figure 35).

Vein Phase

Chalcedonic

Saccharoidal with minor bladed textures Colloform/Crustiform +/- ginguro Chalcedonic with patchy disseminated pyrite

Jasperoidal Vein Vein Phase Crystalline and Comb

> TIME >

Figure 34. Vein phases plotted against time outlining the vein paragenetic relationships for the Sascha-Pelligrini epithermal system.

Quinn Smith Master of Applied Science Thesis 82

Supergene

Chalcedony Pyrite

Supergene

Stage II Ginguro

Supergene

Stage I Ginguro

14 2

AsS

6 )2(OH)6

Al)O10(OH)

FeSb

(SO

(Si

AuS

SeS 2

KFe

Ag3CuS2

CaSO

AsFeS

FeS

(Sn,Fe)(O,OH)

AgI

Ag(Cl,Br)

Ag(Cl,Br,I)

KAl

KAlSi3O8

BaSO

Pb2As2S5

AgAu(SeS)

ZnS

PbS

CuFeS

CaCO

Pb(Ag)

AgAu Ag Formula

Jarosite

Jalpaite

Gypsum

Arsenopyrite

Pyrite

Varlamoffite

Iodoargyrite

Embolite

Iodoembolite

Muscovite

Adularia

Barite

Dufrenoysite

Petrovskaite

Sphalerite

Galena

Chalcopyrite

Calcite

Acanthite

Gold

Uytenbogaardtite

Hematite

Jamesonite

Electrum

Se Acanthite Mineral

Figure 35. Vein mineral paragenetic relationships for the Sascha-Pelligrini epithermal system.

Quinn Smith Master of Applied Science Thesis 83

Ginguro stage I mineralisation is characterised by the initial precipitation of selenium-rich acanthite. Mineral assemblages observed in selenide-bearing epithermal deposits suggests oxygen fugacities were below or very close to the hematite-magnetite buffer, ƒSe2(g)/ƒS2(g) ratios were lower than unity, and temperatures of formation were between 150° to 210°C (Simon et al, 1997). Under these conditions, selenium cannot be separated from sulphur; the early substitution of selenium in sulphide minerals prevents its concentration in hydrothermal fluids, and limits precipitation to silver selenides (Simon et al, 1997). Selenide-bearing minerals are often associated with gold and silver mineralisation (Simon et al, 1997) and commonly occurr in many epithermal deposits throughout Indonesia (Kieft and Oen, 1973), Japan (Shikazono, 1978), Kunashir Island (So et al, 1995), Nevada (Saunder et al, 1988), Mexico (Petruk and Owens, 1974), and New Zealand (Main et al, 1972). Selenium-rich acanthite is associated with gold and silver mineralisation across the SVZ, with silver selenide restricted to a single stage that predates, or is contemporaneous with gold and silver deposition. The presence of silver selenide in the ginguro stage I ore marks an acidic-oxidised magmatic- sourced fluid that rapidly hydrolyses feldspars.

Following the introduction of an acidic-oxidised magmatic-sourced fluid, the fluid pH increases during equilibration with wall-rocks associated with silicate- buffered dilution (Reed and Palandri, 2006). The solution pH increases as H+ ions are consumed in breaking down the primary rock silicates, resulting in an exchange of aqueous H+ for cation from the rock. The overall reaction changes the initially acidic aqueous phase (magmatic composition) to a composition in equilibrium with a propylitic assemblage. The H+ is exchanged for base cations, and sulphate is reduced to sulphide. The molar ratios of sulphate to sulphide change from 24.5 to 0.00018 and the concentration of aqueous H2 increases 3 orders of magnitude. Sulphate concentration decreases due to the combined effects of fractionation of early-formed sulphate minerals (barite, jarosite, gypsum, and alunite) and the reduction of sulphate to sulphide with reaction of ferrous iron to form hematite, magnetite or epidote. The high concentration of SO2 in magmatic gases renders them much more oxidising than equilibrium with ferrous iron in wall rocks allows

Quinn Smith Master of Applied Science Thesis 84

(Reed, 1994). The outward traverse of such fluids inevitably yields reduced fluids and a relatively more oxidised wall rock (Giggenbach, 1992; Reed, 1994).

The concentration of Ba2+ in the hydrothermal fluid increases as sulphate is reduced to sulphide through acid neutralisation from wall-rock buffering (Reed, 1994). The precipitation of barite within ginguro stage I indicates a reduced fluid that has mixed with shallow acid-sulphate waters above the water table. Following the increase in pH, hematite replaces pyrite (Spycher and Reed, 1989), with gold and silver precipitated as electrum (Reed and Palandri, 2006). Silver-rich electrum coexisting with intergrown uytenbogaardtite and acanthite represents disequilibrium cooling of a high- termperature gold-bearing argentite and electrum assemblage (Figure 14 A, B) (Barton, 1980). This disequilibrium assemblage may be associated with conduit sealing and system quiescence.

Vein filling associated with ginguro stage I mineralisation sealed the fluid conduit allowing fluid pressure to increase. Incremental structural dilation and associated fracturing resulted in rapid pressure release with isoenthalpic boiling of the hydrothermal fluid depositing fine pseudo-accicular bladed calcite prior to deposition of ginguro stage II (Figure 11). Calcite is a common soluble phase in epithermal veins (Dong et al, 1995), with the precipitation of vein calcite driven by the loss of CO2 due to boiling and the subsequent 2- generation of CO3 ions from the dissociation of HCO3 (Henley, 1985). Primary pseudo-acicular bladed calcite is replaced by quartz, preserving the original crystal morphology.

Mineralisation during Sascha ginguro stage II is characterised by the initial precipitation of hematite in association with barite. Electrum and acanthite are the first ore minerals to be depositied, followed by precipitation of gangue calcite (Figure 14 C, D). Gold and uytenbogaardtite are precipitated after calcite, followed by selenium rich acanthite. Base metal sulphides, chalcopyrite, sphalerite and galena, are deposited after uytenbogaardtite, with the lead sulphosalt dufrenoysite marking the end of ginguro stage II

Quinn Smith Master of Applied Science Thesis 85

mineralisation. Gangue minerals adularia and muscovite characterise the final stages of mineralisation. Quartz and barite are deposited throughout most of the ginguro mineralising event.

Ginguro stage II mineralisation followed isoenthalpic boiling from 280°C, decreasing pH and favoured the precipitation of acanthite instead of arsenic and antimony sulphosalts (Drummond and Ohmoto, 1985; Spycher and Reed, 1989). Continued wall-rock silicate buffering of the low pH fluid increases Ba2+ in solution as sulphate is reduced to sulphide through acid neutralisation (Reed, 1994). The occurrence of gangue barite throughout ginguro stage II indicates the continuation of fluid mixing between the reduced hydrothermal fluid and shallow acid-sulphate waters above the water table. Following an increase in pH, hematite replaces pyrite (Spycher and Reed, 1989), with gold and silver precipitating as electrum (Reed and Palandri, 2006). Calculated electrum-sphalerite formation temperatures range from 174°C to 205°C and indicate a decrease in fluid temperature from isoenthalpic boiling at 280°C associated with increasing pH. Chalcopyrite precipitates at pH 3.5-3.8, consuming bornite and pyrite, with sphalerite precipitating at pH 5.4, and galena precipitating at pH 5.7 (Reed and Palandri, 2006; Reed, 1994). The rise in pH associated with wall-rock buffering and acid neutralisation decreases metal concentrations by many orders of magnitudes as the fluid approaches neutral pH (Reed and Palandri, 2006). The sequential precipitation of chalcopyrite-sphalerite-galena in ginguro stage II is characteristic of an increase in fluid pH as wall-rock feldspars neutralise acidic metal-bearing fluids (Reed and Palandri, 2006). Neutral fluid is marked by the presence of adularia and muscovite precipitated as the last phases within the ginguro stage II event. Following fluid neutralisation and precipitation of ginguro bands, the fluid conduit may have sealed allowing fluid pressure to increase once again.

Ginguro stage II mineralisation is followed by coarse lattice bladed calcite pseudomorphs and saccharoidal quartz. Rapid pressure release boiling associated with structural dilation and/or hydrothermal eruptions deposited coarse bladed and crystalline calcite after the ginguro stage II event. The

Quinn Smith Master of Applied Science Thesis 86

current outcrop exposure suggests the epithermal system was sealed after deposition of coarse bladed and crystalline calcite.

Overprinting pyritic chalcedonic quartz veins represents renewed hydrothermal activity focused along parallel fractures to the preceding ginguro event. The presence of pyrite associated with chalcedonic and jasperoidal silica indicates meteoric incursion within the upper level of the epithermal system. Chaotic pyritic chalcedonic and jasperoidal quartz veins are hosted within silicified lithic rhyolite tuff in Sascha Main. Spatially restricted and laterally discontinuous lithic tuff concentration zones may have acted as a confined aquifer between underlying strongly welded tuff and overlying rhyolite crystal ash tuffs, introducing cool, oxygenated meteoric water at depth below the palaeosurface. Simultaneous dilution and cooling by cold water mixing yields substantial pyrite in association with acanthite below temperatures of 177°C (Reed and Palandri, 2006). Copper-rich acanthite inverts to jalpaite at temperatures below 117°C, and exists as a 2 phase region with acanthite limiting temperatures of formation to below 106°C (Skinner, 1966). Strong arsenic zoning in pyrite represents local disequilibrium during growth, representing local fluctuations in the S2/As2 ratio (Kretchmar and Scott, 1976).

Quinn Smith Master of Applied Science Thesis 87

sulfosalts Jamesonite and Dufrenoysite indicate a transgression from the typically low sulphur activity during the systems evolution, indicating brief intervals of intermediate sulphidation. Electrum-sphalerite formation temperatures indicate a decrease in fluid temperature associated with increasing pH. The sequential precipitation of chalcopyrite-sphalerite-galena in ginguro stage II indicates an increase in fluid pH, with adularia and muscovite marking the return to neutral conditions in equilibrium with a propylitic assemblage. The presence of pyrite associated with chalcedonic and jasperoidal silica indicates simultaneous dilution and cooling by cold water mixing above the water-table.The progression from deeper level veining exposed adjacent to shallow level veining correlates with the overprinting alteration at both Sascha and Pelligrini and represents the downward migration of the water table across the study area over the systems evolution.

Supergene Overprint Destabilisation of wall-rock pyrite by oxygenated ground water produces acid sulphate water associated with kaolinite. Acid sulphate groundwater destabilises pyrite within chalcedonic quartz mineralisation, with pyrite being replaced by hematite. Selenium-rich acanthite, acanthite and jalpaite persist as inclusions within supergene hematite and gypsum. The silver halide assemblage within outcropping veins at Sascha is uncharacteristic of silver chloride-rich supergene zones within many silver-rich deposits. Embolite, iodoembolite and iodoargyrite variably overprint acanthite, and in conjunction with free gold comprise the supergene assemblage of the Sascha Ginguro veins. Silver halides are common secondary minerals in supergene zones of silver rich mineral deposits, zoning from silver chloride to silver iodide with depth (Gammons and Yu, 1997). Silver iodides are uncommon in outcropping supergene-enriched veins with iodide rapidly oxidizing to iodate (Gammons and Yu, 1997), however silver iodide persists within the supergene zone at Sascha Main. Preservation of silver iodide within outcropping veins across the Sascha-Pelligrini area can be attributed to the dry, cold and arid climate of Patagonia.

Quinn Smith Master of Applied Science Thesis 88

Summary

Facies associations of the volcanics within the study area closely represent an intra-caldera setting, with volcancis erupted from a complex series of graben-forming extensional fractures instead of within a classic caldera margin. Several distinct eruption styles are recorded within the volcanic sequence. The rhyodacite sequence was rapidly deposited by eruption column collapse from multiple vents or fissures creating a composite welded unit. The spatially restricted La Matilde rhyolite sequence was deposited from a single violent eruption, and associated column collapse, with settling of the convective cloud.

Strong hydrothermal alteration, sorting, welding, post emplacement crystallisation and devitrification, as well as erosion throughout the majority of the study area precludes quantitative petrochemical modeling the volcanic rock suite. Variation in REE abundances across the rhyodacite and rhyolite sequences is consistent with the proposed fractionation trends of Pankhurst and Rapela (1995). Pankhurst and Rapela (1995) demonstrate that the sequence from basaltic andesite (Bajo Pobre) to dacite/rhyodacite to rhyolite (Chon Aike) can be modeled by a combination of partial melting and fractional crystalisation.

Host rock rheology controls vein morphology and alteration patterns across the study area. The current exposure along the SVZ indicates the friable rhyolite tuffs of the La Matilde Formation host upward terminating veins, stockwork vein zones, and pervasive silicification. Brittle fractures and more massive veining may be developed within the crystalline rhyodacite ignimbrite that stratigraphically lies below the current vein exposure. Structural analysis of the SVZ indicates the tension axis trended toward the northeast quadrant, producing right-lateral movement along the 315° trend.

The structural pattern of the SVZ conforms to the Riedel shear model, with 1 orientated at 315° and modelled as the acute bisector of the conjugate shear pair.

Quinn Smith Master of Applied Science Thesis 89

Hydrothermal minerals define distinct alteration zones across the study area. The alteration system around the SVZ is characterised by a broad distal laumontite-montmorillonite alteration halo that passes to illite-dominant alteration proximal to epithermal veins. Vein selvages are characterised by smectite and interstratified illite-smectite, with the alteration assemblage indicating a reduced neutral environment. The initially acidic hydrothermal fluid is buffered by wall-rock feldspars, forming the dominant clay-illite alteration halo. The Sascha Main acid-sulphate blanket represents a supergene alteration assemblage formed by oxidation of wall-rock pyrite above the palaeo-water table. Alteration assemblages at Pelligrini are indicative of steam-heated acid-sulphate leaching.

Individual mineralising events of ginguro-banded and pyritic chalcedonic and jasperoidal veins are comprised of complex mineral paragenetic sequences that give an insight into systems geochemical evolution. Ginguro stage I and II is characterised by an initially acidic fluid, with wall-rock buffering driving the fluid to equilibrium with a propylitic assemblage. The precipitation of barite indicates fluid mixing with shallow acid-sulphate waters above the water table. Electrum-sphalerite formation temperatures indicate a decrease in fluid temperature associated with increasing pH. The sequential precipitation of chalcopyrite-sphalerite-galena in ginguro stage II is characteristic of an increase in fluid pH, with adularia and muscovite marking the return to neutral conditions in equilibrium with a propylitic assemblage. The presence of pyrite associated with chalcedonic and jasperoidal silica indicates simultaneous dilution and cooling by cold water mixing above the water-table.The progression from deeper level veining exposed adjacent to shallow level veining correlates with the overprinting alteration at both Sascha and Pelligrini and represents the downward migration of the water table across the study area over the systems evolution. The unique supergene, silver iodide assemblage, preserved within outcropping veins across the Sascha-Pelligrini area can be attributed to the dry, cold and arid climate of Patagonia.

Quinn Smith Master of Applied Science Thesis 90

The Sascha-Pelligrini study area consists of a well preserved, high-level, Jurassic low-sulphidation epithermal system hosted within the Chon Aike Formation. The presence of lead sulfosalts Jamesonite and Dufrenoysite indicate intermittent intervals of higher sulfur fugacities, with the epithermal system progressing from typical low-sulphidation to intermediate-sulphidation assemblages. The transgression between sulphidation states supports the idea that end-member deposits form as part of a continuum between the two. The Sascha-Pelligrini epithermal system was produced by a complex interaction of pyroclastic volcanics, host-rock rheology and geochemistry, structural setting, paleo-water table and hydrothermal fluid evolution. The conceptual model for the Sascha-Pelligrini study area is presented in figure 36, with epithermal veining forming on graben and half-graben structures below the palaeo-water table. The model depicts the association between host rock, alteration zoning including vein selvages and depth of palaeo- water table. Each individual aspect plays an important role in the nature and occurrence of the systems evolution, of which each is essential in combining to form an epithermal deposit.

Quinn Smith Master of Applied Science Thesis 91

Pelligrini studyarea.

–

mal model mal for the Sascha

Figure36. Conceptual epither

relationships,rheological control, vein distribution and currenterosional surface. depicts Model alteration andvein selvage zoning, palaeo water table, structural and stratigraphic

Quinn Smith Master of Applied Science Thesis 92

Conclusions

The Chon Aike rhyodacite sequence shows an enrichment of LREE through the fractionation of hornblende, allanite and apatite, with the Eu anomaly and drepssion of the middle REE controlled by fractionation of plagioclase and hornblende respectively. Decreasing REE trends in the La Matilde rhyolite might be due to the eruption of a zoned magma chamber. Similar to the rhyodacite package, the rhyolite sequence REE patterns show a negative Eu anomaly, decrease in REE concentrations with continued eruptive units, and depressed HREE‟s. The negative Eu anomaly may be controlled by the fractionation of sanidine, with the depletion of REE‟s controlled by the fractionation of hornblende. High-silica rhyolite can be produced from fractional crystalisation of rhyodacite, with the removal of 40% crystal assemblage composed of 58.05% plagioclase, 40% hornblende, 1% apatite and 0.05 allanite (Pankhurst and Rapela, 1995).

XRD analysis in combination with PIMA and ASTER spectral analysis defines an alteration pattern that zones from laumontite-montmorillonite, to illite- pyrite-chlorite, followed by a quartz-illite-smectite-pyrite-adularia vein selvage. The alteration assemblage of quartz, K-feldspar, illite, calcite, chlorite and pyrite across the Sascha-Pelligrini area is commonly observed in geothermal systems and is in equilibrium with near neutral, deep chloride

Quinn Smith Master of Applied Science Thesis 93

waters (Simmons and Browne, 2000). Condensation of CO2 gas and absorption into cool ground waters within the periphery of the epithermal system has produces low-temperature clays, carbonates and calcium zeolites (Simpson et al, 2001).

The supergene kaolinite blanket over Sascha Main is charcterised by hematite, goethite and bright yellow-orange amorphous iron hydroxides, with the acid-sulphate assemblage formed through the weathering of pyrite. Base cation leaching and mass loss within the pervasively altered ash tuff at Pelligrini is indicative of steam-heated acid-sulphate leaching (Reyes, 1990; Rye et al, 1992), with large mass gains in sulphate corresponding to the introduction of alunite. The oxidation of H2S within a stream heated environment takes place above the water table at temperatures not exceeding 100°C (Rye et al, 1992), with opal at Pelligrini confining temperature of formation to less than 120°C (KRTA, 1990).

ASTER mineral mapping is an invaluable tool in rapidly identifying alteration systems across large mineral districts. PIMA spectral analysis enables rapid field identification of alteration minerals, however cannot identify interstratified clays. XRD analysis readily identifies and quantifies alteration minerals, however does not highlight end-member mineral compositions. Characterisation of epithermal alteration systems should incorporate ASTER, PIMA and subsequent XRD analysis. Individual methods can readily identify alteration minerals, however the realisation of the complete alteration assemblage and spatial distribution can effectively be compiled with all three tools.

Paragenetically, epithermal veining varies from chalcedonic to saccharoidal with minor bladed textures, colloform- crustiform-banded with visible electrum and acanthite, crustiform-banded grey chalcedonic to jasperoidal with fine pyrite, and crystalline comb quartz. Mineralisation during the ginguro events is controlled by fluctuating pH, driven by a combination of magmatic gases, pressure release boiling and silicate wall-rock buffering. Pyrite-rich chalcedonic veins formed through simultaneous dilution and cooling by cold

Quinn Smith Master of Applied Science Thesis 94

water mixing, yielding substantial pyrite in association with acanthite below temperatures of 177°C (Reed and Palandri, 2006). Electrum-sphalerite geothermometry of ginguro mineralised veins constrains formation temperatures from 174.8 to 205.1°C and correlates with the stability field for the interstratified illite-smectite vein selvage.

Vein morphology, mineralogy and associated alteration are controlled by host rock rheology, permeability, and depth of the palaeo-water table. Mineralisation within ginguro banded veins resulted from fluctuating fluid pH associated with selenide-rich magmatic pulses, pressure release boiling and wall-rock silicate buffering. The Sascha-Pelligrini epithermal system provides a deposit specific model helping to clarify the current understanding of epithermal deposits, and may serve as a template for exploration of similar epithermal deposits throughout Santa Cruz.

Quinn Smith Master of Applied Science Thesis 95

References

Barton M.D. (1980). “The Ag-Au-S system” Economic Geology 75: 303-316.

Barton P.B. Jr. and Skinner B.J. (1979). “Sulfide mineral stabilites” In: Barnes H.L. (ed) Geochemistry of Hydrothermal Ore Deposits New York, John Wiley and Sons: 278-403.

Barton P.B. Jr. and Toulmin P. (1964). “The electrum tarnish method for the determination of the fugacity of sulphur in laboratory sulphide systems” Geochimica et Cosmochimica Acta 28: 619-640.

Begbie M.J., Sporli K.B., Mauk J.L. (2007). “Structural Evolution of the Golden Cross Epithermal Au-Ag Deposit, New Zealand”. Economic Geology 102: 873-892

Berger B.R and Henley R.W. (1988). "Advances in the Understanding of Epithermal Gold-Silver Deposits, with Special Reference to the Western United States." Economic Geology monograph 6: 405-423.

Berger B.R. and Eimon P.I. (1982). “Conceputal models of Epithermal Precious Metal Deposits” Cameron symposium on unconventional mineral deposits, Dallas, Texas, Society of minning engineers of the american institute of mining, metallurgical and petroleum engineers.

Bignall G., Sekine K., Tsuchiya N. (2004). “Fluid-rock interaction processes in the Te Kopia geothermal field (New Zealand) revealed by SEM-CL imaging” Geothermics 33: 615-635.

Bishop B.P. and Bird K.B. (1987). “Variation in sericite compositions from fracture zones within the coso Hot Springs geothermal system” Geochimica et Cosmochimica Acta 51: 1245-1256.

Quinn Smith Master of Applied Science Thesis 96

Boardman J. W., Kruse F. A., Green, R. O. (1995) “Mapping target signatures via partial unmixing of AVIRIS data” In: Summaries of the Fifth Annual JPL Airborne Earth Science Workshop, Washington, D. C., JPL Publication 95-1 1: 23-26.

Bohnam H.R. Jr. (1986). “Models for volcanic-hosted epithermal precious metal deposits; a review”. Volcanism, Hydrothermal Systems and related Mineralisation, Auckland, International volcanological congress.

Brathwaite R.L., Cargill H.J., Christie A.B., Swain A. (2001). “Lithological and spatial controls on the distribution of quartz veins in andesite- and rhyolite- hosted epithermal Au-Ag deposits of the Hauraki Goldfield, New Zealand” Mineralium Deposita 36: 1-12.

Browne B.L., and Gardner J.E. (2003). “The nature and timing of caldera collapse as indicated by accidental lithic fragments from the AD ~1000 eruption of Volcan Ceboruco, Mexico” Journal of Volcanology and Geothermal Research 130: 93-105.

Browne P. R. L. (1978). "Hydrothermal Alteration in Active Geothermal Fields." Annual Reviews in Earth and Planetary Science 6: 229-250.

Browne P.R.L. and Ellis A.J. (1970). “The Ohaki-Broadlands hydrothermal area, New Zealand: Mineralogy and related geochemistry” America Journal of Science 269: 97-131.

Bryan S. (2007). “Silicic Large Igneous Provinces”. Episodes 30: 20-31

Buchanan L.J. (1981). "Precious metal deposits associated with volcanic environments in the Southwest." Arizona Geological Society Digest 14: 237- 262.

Quinn Smith Master of Applied Science Thesis 97

Cail T.L. and Cline J.S. (2001). “Alteration associated with gold deposition at the Getchell Carlin-type gold deposit, North-Central Nevada” Economic Geology 96: 1343-1359.

Cass R.A.F. and Wright J.V. (1987). “Volcanic successions: modern and ancient” Unwin Hyman, London.

Cathelineau M. and Izquierdo G. (1988). “Temperatire-composition relationships of authigenic micaceous minerals in the Los Azufres geothermal system” Contributions to mineralogy and Petrology 100: 418-428.

Christainsen R.L. (1979). “Cooling units and composite sheets in relation to caldera structure” Geological Society of America Special Paper 180: 29-42.

Christie A.B., Simpson M.P., Brathwaite R.L., Mauke J.L., Simmons S.F. (2007). “Epithermal Au-Ag and Related Deposits of the Hauraki Goldfield, Coromandel Volcanic Zone, New Zealand”. Economic Geology 102: 785-816.

Cooke D.R. and Simmons S.F. (2000). "Characteristics and Genesis of Epithermal Gold Deposits." SEG Reviews 13: 221-244.

Corbett G. (2002). "Epithermal Gold for Explorationists." AIG Journal paper 2002-01: 1-26.

Corbett G. (2004). "Epithermal and Porphyry Gold - Geological Models." The AusIMM Bulletin No.6 2004(Nov/Dec): 33-44.

Corbett G. (2005). “Epithermal Au-Ag deposit types – Implications for exploration” Proexplo Conference, Peru, May 2005.

Cox M.E. and Browne P. (1998). “Hydrothermal alteration mineralogy as an indicator of hydrology at the Ngawha geothermal field, New Zealand” Geothermics 27 (3): 259-270.

Quinn Smith Master of Applied Science Thesis 98

Dietrich A., Gutierrez R., Nelson E.P., Layer P.W. “Geology of the Epithermal Huevos Verdes Vein System and San Jose District, Deseado Massif, Patagonia, Argentina”. PACRIM Congress 24-26 November 2008.

Dong G., Morrison G., Jaireth S. (1995). "Quartz textures in epithermal veins, Queensland - classification, origin and implication." Economic Geology 90: 1841-1856.

Drummond S.E. and Ohmoto H. (1985). "Chemical Evolution and Mineral Deposition in Boiling Hydrothermal Systems." Economic Geology 80: 126- 147.

Ducart D.F., Crosta A.P., Souza Filho C.R. (2006). “Alteration Mineralogy at the Cerro La Mina Epithermal Prospect, Patagonia, Argentina: Field Mapping, Short-Wave Infrared Spectroscopy, and ASTER Images”. Economic Geology 101: 981-996.

Echavarria L.E., Schalamuk I.B., Etcheverry R.O. (2005). “Geologic and tectonic setting of Desseado Massif epithermal deposits, Argentina, based on El Dorado-Monserrat.” Journal of South American Earth Sciences 19: 415- 432.

Fulignati P., Malfitano G., Sbrana A. (1997). “The Pantelleria caldera geothermal system: Data from the hydrothermal minerals” Journal of Volcanology and Geothermal Research 75: 251-270.

Gammons C.H. and Yu Y. (1997). “The stability of aqueous silver bromide and iodide complexes at 25-300°C: Experiments, theory and geologic applications” Chemical Geology 137: 155-173.

Gemmell J.B. (2007). “Hydrothermal Alteration Associated with the Gosowong Epithermal Au-Ag Deposit, Halmahera, Indonesia: Mineralogy, Geochemistry, and Exploration Implications”. Economic Geology 102: 893- 922.

Quinn Smith Master of Applied Science Thesis 99

Giggenbach W.F. (1992). “Magma degassing and mineral deposition in hydrothermal systems along convergent plate boundaries”. Economic Geology 87: 1927-1944

Gorring M.L., Kay S.M., Zeitler P.K., Ramos V.A., Rubico D., Fernández I., Panza, J.L. (1997). “Neogene Patagonian plateau lavas: Continental magmas associated with ridge collision at the Chile triple junction”. Tectonics 16: 1-17.

Grant J.A. (1986). “The isocon diagram – A simple solution to Gresens‟ equation for metasomatic alteration” Economic Geology 81: 1976-1982.

Grant J.A. (2005). “Isocon analysis: A brief review of the method and applications” Physics and Chemistry of the Earth 30: 997-1004.

Guido D.M., Escayola M.P., Schalamuk I.B. (2004). The basement of the Deseado Massif at Bahia Laura, Patagonia, Argentina: a proposal for its evolution”. Journal of South American Earth Sciences 16: 567-577

Gust D. A., Biddle K. T., Phelps D.W., Uliana M.A. (1985). "Associated middle to late Jurassic volcanism and extension in southern South America." Tectonophysics 116: 223-253.

Heald P., Foley N.K., Hayba D.O. (1987). "Comparative Anatomy of Volcanic-Hosted Epithermal Deposits: Acid-Sulfate and Adularia-Sericite Types." Economic Geology 82(1): 1-26.

Hedenquist J. W., Arribas A., Gonzalez-Urien E. (2000). "Exploration for Epithermal Gold Deposits." SEG Reviews 13: 245-277.

Hedenquist J.W. and Henley R.W. (1985). "The Importance of CO2 on Freezing Point Measurements of Fluid Inclusions: Evidence from Active

Quinn Smith Master of Applied Science Thesis 100

Geothermal Systems and Implications for Epithermal Ore Deposition". Economic Geology 80: 1379-1406.

Hedenquist H.W. and White N.C. (2005). “Epithermal gold-silver ore deposits: Characteristics, interpretation, and exploration” Short course 5-6th March Toronto, Canada. Prospectors and Developers Association of Canada & Society of Economic Geologists.

Henley R.W. (1985). "The geothermal framework of epithermal deposits." Reviews in Economic Geology 2: 1-24.

Herrmann W., Blake M., Doyle M., Huston D., Kamprad J., Merry N., Pontual S. (2001). “Short Wavelength Infrared (SWIR) Spectral Analysis of Hydrothermal Alteration Zones Associated with Base Metal Sulfide Deposits at Rosebery and Western Tharsis, Tasmania, and Highway-Reward, Queensland” Economic Geology 96: 939-955.

Hildreth W. (1979) “The Bishop Tuff: Evidence for the origin of compositional zonation in silicic magma chambers” in Chapin C.E. and Elston W.E. eds., Ash flow tuffs: Geological Society of America Special Paper 180: 43-75.

Ibaraki K. and Suzuki R. (1993). “Gold-Silver Quartz-Adularia veins of the Main, Yamada and Sanjin deposits, Hishikari Gold Mine; A comparative study of their geology and ore deposits” Resource Geology Special Issue 14: 1-11.

Izawa E., Urashima Y., Ibaraki K., Suzuki R., Yokoyama T., Kawasaki K., Koga A., Taguchi S. (1990). “The Hishikari gold deposit: high-grade epithermal veins in Quaternary volcanics of southern Kyushu, Japan” Journal of Geochemical Exploration 36: 1-56.

Kieft C. and Oen I.S. (1973). “Ore minerals in telluride-bearing gold-silver ores of Salida, Indonesia, with special reference to the distribution of selenium” Mineralium Deposita 8: 312-320.

Quinn Smith Master of Applied Science Thesis 101

Kretschmar U. and Scott S.D. (1976). “Phase relations involving arsenopyrite in the system Fe-As-S and their application” Canadian Mineralogist 14: 364- 386.

Kruse, F. A. and Huntington J. H., (1996). “The 1995 Geology AVIRIS Group Shoot” In: Proceedings, 6th JPL Airborne Earth Science Workshop, JPL Publication 96-4 1: 155-166.

KRTA (1990). Important hydrothermal minerals and their significance. KRTA Limited Mineral Services Division, Brisbane, Australia.

Lindgren W. (1922). “A suggestion for the terminology of certain mineral deposits”. Economic Geology 17: 292-294.

Lindgren W. (1933). Mineral Deposits. New York, McGraw-Hill Book Company

Lipman P.W. (2000). “The central San Juan caldera cluster: Regional volcanic framework, in Bethke P.M. and Hay R.L. eds., Ancient Lake Creede: Its volcano-tectonic setting, history of sedimentation, and relation to mineralisation in the Creede mining district: Geological Society of America Special Paper 346: 9-69

Love D.A., Clark A.H., Hodgson C.J., Mortensen J.K., Archibald D.A., Farrar E. (1998). “The timing of adularia-sericite-type mineralisation and alunite- kaolinite-type alteration, Mount Skukum epithermal gold deposit, Yukon territory, Canada: 40Ar-39Ar and U-Pb geochronology” Economic Geology 93: 437-462.

MacLean W.H. and Barrett T.J. (1993). “Lithogeochemical techniques using immobile elements” Journal of Geochemical Exploration 48: 109-133.

Quinn Smith Master of Applied Science Thesis 102

MacLean W.H. and Kranidiotis P. (1987). “Immobile elements as monitors of mass transfer in hydrothermal alteration: Phelps Dodge massive sulphide deposit, Matagami, Quebec” Economic Geology 82: 951-962.

Main J.V., Rodgers K.A., Kobe H.W., Woods C.P. (1972). “Aguilarite from the Camoola Reef, Maratoto Valley, New Zealand” Mineralogical Magazine 38: 961-964.

Mauk J.L. and Simpson M.P. (2007). “Geochemistry and Stable Isotope Composition of Altered Rocks at Golden Cross Epithermal Au-Ag Deposit, New Zealand” Economic Geology 102: 841-871.

McDowell S.G. and Elders W.A. (1983). “Allogenic layer silicate minerals in borehole Elmore #1, Salton Sea geothermal field, California, USA” American Mineralogist 68: 1146-1159.

Moultrie J.M. (1995) “The Geology, petrology and geochemistry of the Neurum Tonalite and Bellthorpe Andesite”, unpub, Honours thesis, Queensland University of Technology.

Mykietiuk K., Lopez R., Fernandez R. (2004). “Stable isotope study of steam- heated low-sulphidation epithermal alteration, Deseado Massif, Argentina” Eugen Stumpfl Memorial Symposium, University of Western Australia publication 33.

Neri A., Di Muro A., Rosi M. (2002). “Mass partition during collapsing and transitional columns by using numerical simulations” Journal of Volcanology and Geothermal Research 115: 1-18

Pankhurst R.J. and Rapela C.R., (1995). “Production of Jurassic rhyolite by anatexis of the lower crust of Patagonia”. Earth and Planetary Science Letters 134: 23-36.

Quinn Smith Master of Applied Science Thesis 103

Pankhurst R.J., Leat P.T., Sruoga P., Rapela C.W., Marquez M., Storey B.C., Riley T.R. (1998). “The Chon Aike province of Patagonia and related rocks in West Antarctica: A silicic large igneous provice”. Journal of Volcanology and Geothermal Research 81 113-136.

Panza J.L. and Franchi M.R. (2002). “Magmatismo basaltico cenozoico extrandino”. In: Haller, M.J. (Ed.), Geología y Recursos Naturales de Santa Cruz, Relatorio del XV Congreso Geológico Argentino. Asociación Geológica Argentina, Buenos Aires, p. 201-236.

Patrier P., Beaufort D., Mas A., Traneau H. (2003). “Surficial clay assemblage associated with hydrothermal activity of Bouillante (Guadeloupe, French West Indiess)” Journal of Volcanology and Geothermal Research 126: 143-156.

Petruk W. and Owens D. (1974). “Some mineralogical characteristics of the sivler deposits in the Guanajuato mining distict, Mexico” Economic Geology 69: 1078-1085.

Pontual S., Merry N., Gamson P. (1997). “Spectral interpretation field manual” G-mex volume 1 Melbourne, Ausspec International Pty. Ltd.

Post J.L. and Noble P.N. (1993). “The near-infrared combination band frequencies of dioctahedral smectites, micas and illites” Clays and Clay Minerals 41 (6): 639-644.

Purdy D.J. (2003). “Volcanic stratigraphy and origin of the Wallangarra Volcanics, Wandsworth volcanic group, northern NSW, Australia”, unpub, Masters Thesis, Queensland University of Technology.

Reed M.H. (1994). “Hydrothermal alteration in active continental hydrothermal systems” In: Lentz, D.R., Alteration and Alteration Processes associated with Ore-Forming Systems, Geological Association of Canada, Short Course Notes 11: 315-337.

Quinn Smith Master of Applied Science Thesis 104

Reed M.H. and Palandri J. (2006). “Sulfide mineral precipitation from hydrothermal fluids” Reviews in Mineralogy and Geochemistry 61: 609-631.

Reyes A.G. (1990) “Petrology of Philippine geothermal systems and the application of alteration mineralogy to their assessment” Journal of Volcanology and Geothermal Research 43: 279-309.

R. L. Rudnick and S. Gao (2003) “Composition of the Continental Crust” In The Crust (ed. R. L. Rudnick) volume 3, pages 1-64 of Treatise on Geochemistry (eds. H. D. Holland and K. K. Turekian), Elsevier-Pergamon, Oxford

Ruggieri G., Cathelineau M., Boiron M-C., Marignac C. (1999). “Boiling and fluid mixing in the chlorite zone of the Larderello geothermal system” Chemical Geology 154: 237-256.

Rye R.O., Bethke P.M., Wasserman M.D. (1992). “The stable isotope geochemistry of acid sulphate alteration” Economic Geology 87: 225-262.

Sanders G. (2000). “Regional Geologic Setting of the Gold-Silver Veins of the Deseado Massif, Southern Patagonia, Argentina”. Argentina Mining 2000. Exploration, Geology, Mine Development Business Opportunities Conference, Mendoza, Engineering and Minning Journal, LatinoMinera.

Saunder J.A., Utterback W.C., Day W.C., Christian R. (1988). “Characteristics of bonanza epithermal gold mineralisation at the Sleeper deposits, Nevada, USA” Geological Society of Australia Extended Abstracts 23: 368-388.

Schoen R., White D.E., Hemley J.J. (1974). “Argillization by descending acid at Steamboat Springs, Nevada” Clays and Clay Minerals 22: 1-22.

Quinn Smith Master of Applied Science Thesis 105

Sharpe R., Riveros C., Scavuzzo V. (2002). “Stratigraphy of the Chon Aike Formation ignimbrite sequence in the Cerro Vanguardia Au-Ag epithermal vein district”. Actas Del XV Congreso Geologico Argentino, El Calafate.

Sheriden M.F. (1979). “Emplacement of pyroclastic flows: A review” Geological Society of America Special Paper 180: 125-136.

Shikazono N. (1978). “Selenium content of acanthite and chemical environments of Japanese vein-type deposits” Economic Geology 73: 524- 533.

Shikazono N. (1985). “A comparison of temperatures estimated from the electrum-sphalerite-pyrite-argentite assemblage and filling temperatures of fluid inclusions from epithermal Au-Ag vein type deposites in Japan” Economic Geology 80: 1415-1424.

Sillitoe R.H. (1993). “Epithermal Models: Genetic Types, Geometrical Controls and Shallow Features”. Ore Deposit models. Roberts R.G. and Sheahan P.A., Geoscience Canada. Reprint series 3: 403-417.

Simmons S.F. (1991). “Hydrologic implications of alteration and fluid inclusion studies in the Fresnillo District, Mexico: Evidence for a brine reservoir and a descending water table during the formation of hydrothermal Ag-Pb-Zn orbodies” Economic Geology 86: 1579-1601.

Simmons S.F. and Browne P.R.L. (2000). “Hydrothermal minerals and precious metals in the Broadlands-Ohaaki geothermal system: Implications for understanding low-sulphidation epithermal environments” Economic Geology 95: 971-999.

Simon G., Kesler S.E., Essene E.J. (1997). “Phase relations among selenides, sulfides, tellurides, and oxides: II. Applications to selenide-bearing ore deposits” Economic Geology 92: 468-484.

Quinn Smith Master of Applied Science Thesis 106

Simpson M.P., Maukl J.L., Simmons S.F. (1998). “The occurrence, distribution and XRD properties of hydrothermal clays at the Golden Cross epitherml Au-Ag deposit, New Zealand” Proceedings of the 20th New Zealand Geothermal Workshop, Geothermal Institute, The University of Auckland.

Simpson M.P., Mauk J.L., Simmons S.F. (2001). “Hydrothermal alteration and hydrologic evolution of the Golden Cross epithermal Au-Ag deposit, New Zealand” Economic Geology 96: 773-796.

Skinner B.J. (1966). “The system Cu-Ag-S”. Economic Geology 61: 1-26

Smith Q., Nano S., Heenan T., Moloney M. (2006). “Mirasol Resources Ltd. Summary Technical Report for the Sascha Project”. Unpublished report.

So C.-S., Dunchienko V.Y., Yun S.-T., Park M.-E., Choi S.-G., Shelton K.L. (1995). “Te- and Se- bearing epithermal Au-Ag mineralisation, Prasolovskoye, Kunashir Island, Kuril Iland Arc” Economic Geology 90: 105- 117.

Sparks R.S.J., Bursik M.I., Carey S.N., Gilbert J.S., Glaze L.S., Sigurdsson H., Woods A.W., Volcanic Plumes, 574pp, John Wiley, Hoboken N.J., 1997.

Sparks R.S.J. and Walker G.P.L. (1973). ”The ground surge deposit: A third type of pyroclastic rock” Nature, Physical Science 241: 62-64.

Spycher N.F. and Reed M.H. (1989). “Evolution of a Broadlands-type epithermal ore fluid along alternative P-T paths: Implications for the transport and deposition of base, precious and volatile metals” Economic Geology 84: 328-359.

Steiner A. (1977). The Wairakei Geothermal Area North Island, New Zealand. New Zealand Geological Survey bulletin 90.

Quinn Smith Master of Applied Science Thesis 107

Storey B.C. and Alabaster T. (1991). “Tectonomagmatic controls on Gondwana break-up models: evidence from the proto-pacific margin of Antartica”. Tectonics 10: 1274-1288

Suzuki-Kamata K., Kamata H., Bacon C.R. (1993). “Evolution of the Caldera- Forming Eruption at Crater Lake, Oregon, indicated by Component Analysis of Lithic Fragments” Journal of Geophysical Research 98 (8): 14,059-14,074.

Taylor S.R. and McLennan S.M. (1981). “The composition and evolution of the continental crust: rare earth element evidence from sedimentary rocks” Philosophical Transactions of the Royal Society of London, Series A: Mathematical and Physical Sciences 301 (1461): 381-399.

Wallier S. and Tosdal R.M. “The Manantial Espejo Epithermal Low- Sulphidation Silver (-Gold) Deposit, Deseado Massif, Argentina”. PACRIM Congress 24-26 November 2008.

Warren I., Simmons S.F., Mauk J.L. (2007). “Whole-Rock Geochemical Techniques for Evaluating Hydrothermal Alteration, Mass Changes, and Compositional Gradients Associated with Epithermal Au-Ag Mineralisation”. Economic Geology 102: 923-948.

Wilson C.J.N. and Hidreth W. (1997). “The Bishop Tuff: New Insights from Eruptive Stratigraphy” The Journal of Geology 105: 407-439.

White D.E. (1981). “Active geothermal systems and hydrothermal ore deposits” Economic Geology 75th Anniversary Volume: 392-423.

White N. C. and Hedenquist J. W. (1990). "Epithermal environments and styles of mineralization: variations and their causes, and guidelines for exploration" Journal of Geochemical Exploration 36(1-3): 445-474.

White N.C. and Hedenquist J. W. (1995). "Epithermal Gold Deposits: Styles, Characteristics and Exploration" SEG Newsletter 23: 9-13.

Quinn Smith Master of Applied Science Thesis 108

Appendix 1

Petrography

Quinn Smith Master of Applied Science Thesis 109

A B

Plate 1. Rhyodacite crystal ignimbrite with large albite, sanidine, biotite (chlorite after biotite) and embayed quartz phenocrysts in a quartz-feldspar-glass ash matrix. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

A B

Plate 2. Rhyodacite pumice ash tuff with sericitised albite, sanidine and biotite phenocrysts. Large, devitrified flattened pumice clasts and embayed quartz phenocrysts in a quartz-feldspar-glass ash matrix. Strong compaction textures. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

A B

Plate 3. Rhyodacite crystal ash tuff with albite, sanidine, biotite (chlorite after biotite) and embayed quartz phenocrysts in a quartz-feldspar-glass ash matrix. Large fine-grained quartz-feldspar-biotite juvenile clasts prominent. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

Quinn Smith Master of Applied Science Thesis 110

A B

Plate 4. Lithic rhyolite tuff with sericitised sanidine, minor muscovite and embayed quartz phenocrysts in a quartz-feldspar-glass ash matrix. Large mica schist lithic clasts prominent. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

A B

Plate 5. Rhyolite crystal ash tuff with sericitised sanidine, minor muscovite and embayed quartz phenocrysts in a quartz-feldspar-glass ash matrix. Rare devitrification textures in glassy matrix. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

A B

Plate 6. Rhyolite ash tuff with fine sanidine laths, quartz and glass shards. Rare spherulitic and accretionary lapilli layers. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

Quinn Smith Master of Applied Science Thesis 111

A B

Plate 7. Flow-dome auto-breccia fine sanidine-quartz crystalline matrix, with large clasts of flow-banded and spherulitic rhyolite to 2m in diameter. Photo A XPL x100. Photo B PPL x100. Field of view approximately 1mm.

A B

Plate 8. Flow-banded rhyolite with euhedral sanidine phenocrysts in a crystalline quartz-feldspar matrix. Photo A XPL x100. Photo B PPL x100. Field of view approximately 1mm.

A B

Plate 9. Spherulitic rhyolite with spherulites to 5mm in a quatz-feldspar-glass matrix. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

Quinn Smith Master of Applied Science Thesis 112

A B

Plate 10. Porphyritic granodiorite dyke with sanidine and sodic plagioclase phenocrysts. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

A B

Plate 11. Marine fossiliferous feldsarenite with bivalve, gastropod and bryzoan fragments with a micritic cement. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

A B

Plate 12. Epiclastic with mica, quartz, feldspar and calcite clasts. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

Quinn Smith Master of Applied Science Thesis 113

A B

Plate 13. Vesicular olivine tholeiite plateau basalt. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

A B

Plate 14. Basaltic dyke with microcline and oscilitory zoned anorthite phenocrysts in a feldspar lath ground-mass. Photo A XPL x50. Photo B PPL x50. Field of view approximately 2mm.

Quinn Smith Master of Applied Science Thesis 114

Appendix 2

Quartz Textures

Quinn Smith Master of Applied Science Thesis 115

Plate 1 Chalcedonic single pulse tectonic breccia. Angular leached clasts of argilllized wall rock, including strongly colliform banded fine saccharoidal to chalcedonic silica. Scale bar equals 10mm.

Plate 2 Single phase wall rock breccia proximal to main veins contain sulphide bands in matrix to wall rock fragments. Sulphide bands occur on clast edges, grading to late crystalline quartz lining inter clast voids. Scale bar equals 10mm. A – Wall rock clast A B B – Sulphide band

Plate 3 A White, fine-grained saccharoidal silica with fine, prismatic-bladed carbonate pseudomorphs. Scale bar equals 10mm. A – Quartz-clay wall rock alteration B B – Fine bladed pseudomorphs

Plate 4 White, fine-grained saccharoidal silica with vuggy cavities. Scale bar equals 10mm.

Plate 5 Chalcedonic with disseminated pyrite vein/vein breccia with supergene iron oxide gossanous zones. Scale bar equals 10mm.

Plate 6 Banded quartz-iron oxide gossanous crust on chalcedonic with disseminated pyrite vein. Scale bar equals 10mm.

Quinn Smith Master of Applied Science Thesis 116

Plate 7 B A Massive to banded jasperoidal silica with disseminated sulphides and a saccharoidal, moderately banded pyrite matrix. Scale bar equals 10mm. A – Jasperoidal silica B – Pyritic crystalline to saccharoidal quartz

Plate 8 C Amythestine to milky, euhedral axiolitic comb quartz crystals growing perpendicular to vein margins. Scale bar equals 10mm. B A – Silicified wall rock B – Amythestine quartz C – Large euhedral zoned quartz crustals

Plate 9 Euhedral axiolitic clear to milky comb quartz crystals growing perpendicular to vein margins. Scale bar equals 10mm.

Plate 10 Grey-white fluidised vein breccia with crustiform banded chalcedonic to crystalline quartz. Scale bar equals 10mm.

Plate 11 Chalcedonic vein breccia cross-cut by crustiform chalcedony, followed by milky comb quartz with iron oxide staining, and infilled with „ladder‟ banded cream chalcedonic quartz. Cream chalcedonic quartz preserves meniscus like texture. Horizontal vein slice in formation orientation with top of photo towards palaeosurface. Scale bar equals 10mm.

Quinn Smith Master of Applied Science Thesis 117

Plate 12 Crustiform chalcedonic, bladed and colloform banded quartz vein overprinted by axiolitic comb quartz. Scale bar equals 10mm.

Plate 13 Chalcedonic fluid streaming breccia with crystalline quartz overprint. Scale bar equals 10mm.

Plate 14 Matrix supported vein breccia with massive to banded chalcedonic vein fragments and silicified tuff fragments within chalcedonic silica. Scale bar equals 10mm.

Plate 15 Monomict vein breccia containing clasts of pervasively silicified wall-rock in chalcedonic to jasperoidal silica matrix. Scale bar equals 10mm.

Plate 16 Monomict chalcedonic quartz jigsaw breccia containing wall rock clasts Scale bar equals 10mm.

Plate 17 Intensely silicified tuff with relict rock textures preserved. Scale bar equals 10mm.

Quinn Smith Master of Applied Science Thesis 118

Appendix 3

Digital Dataset

Quinn Smith Master of Applied Science Thesis 119

DVD-ROM includes: ASTER raw scenes and processed images and alteration maps Geothermometry calculations and excel spreadsheet Mapinfo dataset including o Exploration geochemistry o Geological mapping o PIMA and XRD dataset o Remotesensing including rectified airphoto and ASTER products o Workspace folders of maps presented in the thesis Microprobe data including Jeol840 mineral probe data and Quanta ESEM alteration probe images PIMA data files and processed excel spreadsheet Scanned trench maps Whole rock data including tables and spreadsheets included within the thesis XRD raw data and processed excel spreadsheet

Quinn Smith Master of Applied Science Thesis 120

Appendix 4

Sascha-Pelligrini Fact Geology Map 1:10,000 WGS82 SUTM19

Quinn Smith Master of Applied Science Thesis 121 402,000 mE 404,000 mE 406,000 mE 408,000 mE 410,000 mE 412,000 mE SASCHA-PELLIGRINISASCHA-PELLIGRINISASCHA-PELLIGRINI FACTFACTFACT GEOLOGYGEOLOGYGEOLOGY

! !

! ! 4 , 7 0 6 m N !

! !

4 , 7 0 6 m N !

! !! !

! ! !

! !

! !! !

!! !

! !

! ! ! ! ! !

! ! ! !

! ! ! !! ! ! !

! ! ! !

!! ! ! !

! ! ! ! !

! ! !

STRATIGRAPHY 4 , 7 0 m N

Playa

! !

! ! ! ! 4 , 7 0 m N ! Recent alluvium %%

! !! ! ! ! Pliestocene gravel ! ! ! Pliocene olivine tholeite %% !! ! Lower Miocene feldsarenite

! ! ! ! ! Dacite-Andesite dykes and sills

! ! %% %% Sperulitic ash tuff with accretionary lapilli Flow-banded/spherulitic auto- breccia (Flow-Dome Complex) !! ! %% ! Flow-banded/spherulitic lavas (Flow-Dome Complex)

L a M t i l d e ( U p r J u s c ) Crystal ash rhyolite tuff ! !! ! !! ! Epiclastics and juvenile clast

!! ! ash rhyodacite tuff

! !! !! ! Biotite, pumice/juvenile

% clast rhyodacite tuff

! ! !

!! %%! ! ! ! Biotite rich rhyodacite ignimbrite ! !

! ! % C h o n A i k e ( L w r J u a s c )

! !

! ! STRUCTURE 4 , 7 0 2 m N ! ! %% !! ! !! Normal Fault %%

4 , 7 0 2 m N Mapped Structure !!

Major Airphoto Linearment

Minor Airphoto Linearment

%% % Flat lying stratigraphy

!15 Statigraphic/Structural Dip

VEIN CLASSIFICATION Crystalline and Comb quartz

Chalcedonic to opaline + diss. pyrite Jasperoidal + diss. pyrite

T I M E Colloform/crustiform +/- ginguro

Weakly banded and bladded saccharoidal quartz

Chalcedonic quartz and single pulse banded cockade breccia HYDROTHERMAL SILICA CLASSIFICATION Silica matrix phreatic breccia with metamorphic clasts Silica matrix phreatic jigsaw breccia

Pervasive silicification 4 , 7 0 m N

Structurally controlled silicification

Silica fill, banded 4 , 7 0 m N hydrothermal breccia

00 0.50.5 11 Sascha-Pelligrini Fact Geology * 1:10,000 WGS84 SUTM19 kilometerskilometerskilometers Quinn Smith 2006

402,000 mE 404,000 mE 406,000 mE 408,000 mE 410,000 mE 412,000 mE

Appendix 5

Sascha-Pelligrini Interpretive Geology Map 1:10,000 WGS82 SUTM19

Quinn Smith Master of Applied Science Thesis 122 402,000 mE 404,000 mE 406,000 mE 408,000 mE 410,000 mE 412,000 mE SASCHA-PELLIGRINISASCHA-PELLIGRINISASCHA-PELLIGRINI INTERPRETIVEINTERPRETIVEINTERPRETIVE GEOLOGYGEOLOGYGEOLOGY

! !

! ! 4 , 7 0 6 m N !

! !

4 , 7 0 6 m N !

! !! !

! ! !

! !

! !! !

!! !

! !

! ! ! ! ! !

! ! ! !

! ! ! !! ! ! !

! ! ! !

!! ! ! !

! ! ! ! !

! ! !

% 4 , 7 0 m N

! ! STRATIGRAPHY ! !

4 , 7 0 m N Playa ! % Recent alluvium ! ! ! !

! ! Pliestocene gravel % ! ! Pliocene olivine tholeite

! ! Lower Miocene feldsarenite ! !

% Dacite-Andesite dykes and sills ! % % Sperulitic ash tuff with accretionary lapilli ! ! Flow-banded/spherulitic auto- % ! breccia (Flow-Dome Complex)

Flow-banded/spherulitic lavas (Flow-Dome Complex) ! ! L a M t i l d e ( U p r J u s c ) ! Crystal ash rhyolite tuff ! !

! !

! !! Epiclastics and juvenile clast

! !% ash rhyodacite tuff

! ! ! ! Biotite, pumice/juvenile

! %%! ! ! ! ! clast rhyodacite tuff

! ! % ! Biotite rich rhyodacite ignimbrite

C h o n A i k e ( L w r J u a s c )

! ! ! 4 , 7 0 2 m N % ! ! ! ! ! STRUCTURE % Normal Fault 4 , 7 0 2 m N ! Mapped Structure

Major Airphoto Linearment

% Minor Airphoto Linearment

% Flat lying stratigraphy

!15 Statigraphic/Structural Dip

VEIN CLASSIFICATION Crystalline and Comb quartz

Chalcedonic to opaline + diss. pyrite Jasperoidal + diss. pyrite

Colloform/crustiform +/- ginguro T I M E

Weakly banded and bladded saccharoidal quartz

Chalcedonic quartz and single pulse banded cockade breccia HYDROTHERMAL SILICA CLASSIFICATION Silica matrix phreatic breccia with metamorphic clasts Silica matrix phreatic jigsaw breccia 4 , 7 0 m N Pervasive silicification

Structurally controlled

4 , 7 0 m N silicification

Silica fill, banded hydrothermal breccia

00 0.50.5 11 * Sascha-Pelligrini Interpretive Geology 1:10,000 WGS84 SUTM19 kilometerskilometerskilometers Quinn Smith 2006

402,000 mE 404,000 mE 406,000 mE 408,000 mE 410,000 mE 412,000 mE