The Bolivian Altiplano is part of the inner arc Polymetallic Belt of the Andes, and is a Cretaceous-Cenozoic intermontane basin located between the Andean arc of the Western Cordillera and the Paleozoic fold belt of the Eastern Cordillera. Reconnaissance geological mapping shows that epithermal mineralisation in the NE Altiplano is related to silicic magmatism located on NW-trending Altiplano growth faults and intersections with NE and E-W lineaments. Magmatism was episodic and occurred during the Miocene arc broadening episode, which correlates with increased plate convergence rates. Most magmatism is mid Miocene (19-10 Ma), and formed flow-dome-sill-stock complexes. The upper (9-7.5 Ma) and late (6.5-4 Ma) Miocene episodes, in contrast, generally formed ash-flow calderas and strato-volcanoes. The three episodes are mainly dacites and rhyolites of the high-K calc-alkaline suite, with some shoshonites, and can only be distinguished isotopically, with progressively stronger crustal contamination in the younger episodes. Sr-Nd-O isotopes and trace elements show that the magmas evolved by variable fractionation and assimilation from subduction-related, mantle-derived magmas which were isotopically enriched by bulk contamination with Precambrian gneisses. Mapping, petrography and XRD show that the epithermal deposits have large areas of pervasive phyllic alteration with a propylitic halo. Tourmaline alteration occurs in the cores of Sn-bearing deposits. Argillic and silicic alteration in some deposits are subsurface features of hot spring systems. Mineralisation (Au-Ag-Cu-Pb-Zn) is disseminated and in sheeted veins and veinlets which have a NE-trend, related to the regional tectonic stress. Dating and O-H isotopes show that the mineralisation is genetically related to the dacitic magmatism and formed from a dominantly magmatic fluid, with meteoric mixing in the upper levels. Differences between the Polymetallic Belt and the Copper Belt are mainly a function of erosion level. Polymetallic deposits of the Eastern Cordillera contain important Sn and form the main part of the Tin Belt. Minor Sn also occurs in Altiplano deposits hosted by Paleozoic marine sediments, but not in those in Tertiary red beds. Tin was probably derived from the Paleozoic sediments, and is not related to deep subduction.

A fast pneumatic transfer facility was installed at the Nuclear Engineering Teaching Laboratory (NETL) of the University of Texas at Austin for the purpose of cyclic thermal and epithermal neutron activation analysis. In this work efforts were focused on the evaluation of cyclic epithermal neutron activation analysis (CENAA). Various NIST and CANMET certified materials were analyzed by the system. Experiment results showed 110Ag as one of the isotopes favored by the system. Thus, the system was put into practical application for identifying silver concentration in the Arctic atmospheres in air filters collected in 2009, and traces in metallic ores Comparison of silver concentrations via CENAA with the CANMET certified reference materials gave very good results. / text

The development of an open pit mine at the Endeavour 42 (E42) epithermal gold deposit, situated in the Junee-Narromine Volcanic Belt of the Ordovician Macquarie Arc, central New South Wales, has provided a 3D view of the structurally controlled deposit which was hitherto not available due to the paucity of outcrop in the region. Outcropping geological relationships present a complicated history of overprinting structural deformation and vein events, including the spatial characterization of the gold-mineralizing system. Host rocks consisting of interbedded sedimentary and resedimented volcaniclastic facies, trachyandesite and porphyritic andesite lavas and intrusions (coherent and autoclastic facies), intruded by a large diorite sill, were initially tilted and faulted, followed by the emplacement of multiple dyke phases along faults. Economic gold mineralization at E42 is restricted to faults, fault-hosted breccias, and veins, and was deposited over a period spanning two distinct structural regimes. Early gold-bearing veins are steeply dipping and interpreted as forming coevally along two sets of faults and dykes within a tensional stress regime. High grade fault-hosted, hydrothermally cemented breccia intervals are included temporally with early gold-bearing veins based on comparable mineralogy and steep, fault parallel orientations. Crosscutting the early steep gold-bearing vein sets are two populations of coeval inclined gold-bearing veins, dipping moderately to the southwest and northwest, respectively, which formed in a compressional stress regime with tension directed subvertically. The E42 epithermal deposit likely developed in the period of overall crustal extension, ca. 443-433 Ma, following Phase 1 of the Late Ordovician – Early Silurian Benambran Orogeny. The generation of permeability, styles of fracture propagation, and the reactivation of pre-existing planes of weakness in the rock package are key factors in the development and current geometry of the E42 gold deposit. High grade veins and faults are commonly flanked by sericite-quartz ± carbonate alteration haloes, which exhibit consistent geochemical patterns for metals and pathfinder elements, both laterally away from structures, and vertically within the deposit. Au, Ag, As, Hg, Sb, Tl, Cu, Pb, and Zn, all display increasing concentrations towards high-grade structures, as well as higher up in the epithermal system, with varying dispersion haloes.

The Pierina high-sulphidation epithermal Au-Ag deposit is located in the Cordillera Negra of north-central Perú, ~ 5km north of the coeval intermediate-sulphidation Ag–base metal Santo Toribio deposit, and in rocks of the Calipuy Supergroup. The deposit contains ~ 8 M oz Au, hosted in non-refractory iron oxides and, with heap-leach extraction, is one of the lowest-cost Au producers in the world. Stage Ia (15 Ma) and Ib (14.4 Ma) advanced-argillic alteration formed from mixed magmatic and meteoric waters. The main, 14.4 Ma event produced vuggy quartz alteration, focussed in a 16.9 Ma dacitic pumice-lithic tuff, and surrounded by quartz-alunite, quartz-dickite, and illite-montmorillonite alteration zones, the product of increased meteoric water contributions towards the periphery of the deposit. Stage II sulphide-barite mineralization introduced gold and silver, hosted submicroscopically in the disseminated high-sulphidation pyrite-enargite assemblage. Precipitation occurred from a low-to-medium - salinity magmatic fluid that mixed with meteoric waters at the site of ore deposition. A 14.1 Ma 40Ar/39Ar age for supergene alunite records the rapid incursion of meteoric waters into the deposit. The resulting oxidation of sulphides to schwertmannite, goethite, and hematite was facilitated by microbes, recorded by the stable-isotopic compositions of supergene barite+acanthite. Schwertmannite is enriched in Au and Ag and is the main precious-metal host. Regional pedimentation is inferred to have initiated retrograde boiling of the source magma chamber at 15 Ma, with renewed magma incursion triggering major alteration at 14.4 Ma. Both events involved the exsolution of an SO2-rich vapour and a more saline aqueous fluid. The latter migrated to Santo Toribio generating phyllic alteration and intermediate-sulphidation mineralization, whereas the SO2-rich vapours caused pyrite-bearing feldspar-destructive alteration along fluid pathways during ascent to Pierina. The subsequent single-phase, H2S-rich mineralizing fluid exsolved from the retracting magma at higher pressures. Vapour contraction during ascent along altered, unreactive pathways minimized the loss of S- and H+, optimizing the transport of Au as AuHS0. Watertable displacement resulting from pediment incision promoted the flow of groundwater into the epithermal environment where mixing with magmatic fluids precipitated gold. Supergene oxidation optimized conditions for microbial activity, a critical factor in the generation of economic mineralization. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2009-04-01 16:02:47.525

The development of an open pit mine at the Endeavour 42 (E42) epithermal gold deposit, situated in the Junee-Narromine Volcanic Belt of the Ordovician Macquarie Arc, central New South Wales, has provided a 3D view of the structurally controlled deposit which was hitherto not available due to the paucity of outcrop in the region. Outcropping geological relationships present a complicated history of overprinting structural deformation and vein events, including the spatial characterization of the gold-mineralizing system. Host rocks consisting of interbedded sedimentary and resedimented volcaniclastic facies, trachyandesite and porphyritic andesite lavas and intrusions (coherent and autoclastic facies), intruded by a large diorite sill, were initially tilted and faulted, followed by the emplacement of multiple dyke phases along faults. Economic gold mineralization at E42 is restricted to faults, fault-hosted breccias, and veins, and was deposited over a period spanning two distinct structural regimes. Early gold-bearing veins are steeply dipping and interpreted as forming coevally along two sets of faults and dykes within a tensional stress regime. High grade fault-hosted, hydrothermally cemented breccia intervals are included temporally with early gold-bearing veins based on comparable mineralogy and steep, fault parallel orientations. Crosscutting the early steep gold-bearing vein sets are two populations of coeval inclined gold-bearing veins, dipping moderately to the southwest and northwest, respectively, which formed in a compressional stress regime with tension directed subvertically. The E42 epithermal deposit likely developed in the period of overall crustal extension, ca. 443-433 Ma, following Phase 1 of the Late Ordovician – Early Silurian Benambran Orogeny. The generation of permeability, styles of fracture propagation, and the reactivation of pre-existing planes of weakness in the rock package are key factors in the development and current geometry of the E42 gold deposit. High grade veins and faults are commonly flanked by sericite-quartz ± carbonate alteration haloes, which exhibit consistent geochemical patterns for metals and pathfinder elements, both laterally away from structures, and vertically within the deposit. Au, Ag, As, Hg, Sb, Tl, Cu, Pb, and Zn, all display increasing concentrations towards high-grade structures, as well as higher up in the epithermal system, with varying dispersion haloes.

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The development of an open pit mine at the Endeavour 42 (E42) epithermal gold deposit, situated in the Junee-Narromine Volcanic Belt of the Ordovician Macquarie Arc, central New South Wales, has provided a 3D view of the structurally controlled deposit which was hitherto not available due to the paucity of outcrop in the region. Outcropping geological relationships present a complicated history of overprinting structural deformation and vein events, including the spatial characterization of the gold-mineralizing system. Host rocks consisting of interbedded sedimentary and resedimented volcaniclastic facies, trachyandesite and porphyritic andesite lavas and intrusions (coherent and autoclastic facies), intruded by a large diorite sill, were initially tilted and faulted, followed by the emplacement of multiple dyke phases along faults. Economic gold mineralization at E42 is restricted to faults, fault-hosted breccias, and veins, and was deposited over a period spanning two distinct structural regimes. Early gold-bearing veins are steeply dipping and interpreted as forming coevally along two sets of faults and dykes within a tensional stress regime. High grade fault-hosted, hydrothermally cemented breccia intervals are included temporally with early gold-bearing veins based on comparable mineralogy and steep, fault parallel orientations. Crosscutting the early steep gold-bearing vein sets are two populations of coeval inclined gold-bearing veins, dipping moderately to the southwest and northwest, respectively, which formed in a compressional stress regime with tension directed subvertically. The E42 epithermal deposit likely developed in the period of overall crustal extension, ca. 443-433 Ma, following Phase 1 of the Late Ordovician – Early Silurian Benambran Orogeny. The generation of permeability, styles of fracture propagation, and the reactivation of pre-existing planes of weakness in the rock package are key factors in the development and current geometry of the E42 gold deposit. High grade veins and faults are commonly flanked by sericite-quartz ± carbonate alteration haloes, which exhibit consistent geochemical patterns for metals and pathfinder elements, both laterally away from structures, and vertically within the deposit. Au, Ag, As, Hg, Sb, Tl, Cu, Pb, and Zn, all display increasing concentrations towards high-grade structures, as well as higher up in the epithermal system, with varying dispersion haloes. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Imaging spectrometry data or hyperspectral imagery acquired using airborne systems have been used in the geologic community since the early 1980&rsquo / s and represent a mature technology. The solar spectral range 0.4&ndash / 2.5 &amp / #956 / m provides abundant information about hydroxyl-bearing minerals, sulfates and carbonates common to many geologic units and hydrothermal alteration assemblages. Satellite based Hyperion image data is used to implement and test hyperspectral processing techniques to identify alteration minerals and associate the results with the geological setting. Sisorta gold prospect is characterized by porphyry related epithermal and mesothermal alteration zones that are mapped through field studies. Image specific corrections are applied to obtain error free image data. Extensive field mapping and spectroscopic survey are used to identify nine endmembers from the image. Partial unmixing techniques are applied and used to assess the endmembers. Finally the spectral correlation mapper is used to map the endmembers which are kaolinite, dickite, halloysite, illite, montmorillonite and alunite as clay group and hematite, goethite and jarosite as the iron oxide group. The clays and iron oxides are mapped with approximately eighty percent accuracy. The study introduces an image specific algorithm for alteration minerals identification and discusses the outcomes within the geological perspective.

White Island is a highly active volcano with an acidic, S-rich hydrothermal system in the Bay of Plenty, North Island, New Zealand. In this acidic environment a series of subsurface Fe-rich layers are ubiquitous in the crater sediments at shallow depth and are capable of modifying the flow and gas flux dynamics in the system. The mineralogy of the subsurface Fe-rich layer(s) and the processes leading to their formation are unknown. Here the mineralogy and formation of the subsurface Fe-rich layers in relation to the surface and subsurface environment(s) within the Main Crater at White Island are assessed. Based on geochemical analyses, subsurface Fe-rich crusts are composed of a mix of jarosite and goethite, cementing crater fill sediments into cohesive layers. Saturation index (SI) and Eh/pH assessments identify that fluids evolved at White Island are undersaturated with respect to the mineral phases present in the Fe-rich subsurface layers. Formation of the Fe-rich subsurface layers is most likely related to the transition between atmospheric gases and/or meteoric water mixing with hydrothermal fluids. This transition zone creates an environment conducive to forming jarosite and goethite forming in the same layer. Additionally, subsurface sediments including the Fe-rich layers show a consistent organic carbon isotopic signature of -23 ‰. Microscopic investigations confirm diatoms and microbes are present in the subsurface Fe-rich layers. The full extent of microbial activity in relation to the Fe-rich layers at White Island still requires further investigation. Based on chemical extractions for isotopic analyses, Fe-rich layers are shown to preserve δ¹³C signatures indicative of microbial life. Interface zones such as those identified in the hydrothermal environment at White Island can create metal-rich deposits and habitable/preservative microbial environments as well as affecting the macroscopic dynamics of volcanic and epithermal systems.