Thesis (M.Sc.)--Memorial University of Newfoundland, 2001. / Includes bibliographical references. Also available online.

Undergraduate honors paper--Mount Holyoke College, 2006. Dept. of Astronomy. / Includes bibliographical references (leaves 80-87).

The Summitville high-sulfidation gold deposit is hosted by a volcanic dome consisting of the South Mountain Quartz Latite that was erupted 23 Ma ago during formation of the Platoro Caldera complex in the San Juan volcanic field of south central Colorado. Alteration and mineralization developed during or shortly after dome emplacement as a result of metal-rich magmatic fluids and vapor emanating from a crystallizing intrusion at depth. Copper, arsenic, silver and gold are enriched in the deposit with two of the last paragenetic stages, the barite-base metal sulfide and goethite stages, containing the highest gold grades. Barite contains magmatic sulfur with a range of δ34S values (19.3 – 31.8 ‰) that reflects SO42– – H2S isotopic equilibration over a temperature range of 115 to 180 °C, which is consistent a calculated temperature of 147 °C based on the sulfur isotopic fractionation between intergrown barite and galena. Barite δ18O values (19.3 – 31.8 ‰) indicate the barite fluids contained a minor component of meteoric water. Barite growth zones with acicular crystals (wires) of emplectite (CuBiS2), a mineral not previously reported from Summitville, contained primary fluid inclusions that yielded a wide range of vapor to liquid homogenization temperatures as a result of stretching but consistent freezing point depressions that infer an average salinity of 5.1 wt. % NaCl equivalent. These data indicate that the barite fluids were modestly enriched in magmatic sulfur and metals (Cu, As, Bi, Pb, Zn, Au, Ag) and that barite precipitation was likely triggered by cooling during mixing with meteoric waters. The goethite stage developed during weathering of the deposit that likely occurred during uplift and exposure around 9 to 7.7 Ma ago based on 40Ar/39Ar dates on jarosite. The assemblage goethite + hematite ± jarosite ± scorodite ± gold filled open spaces and coated barite of the barite-base metal sulfide stage. Inclusions of barite and bladed alunite in the iron oxide/hydroxide (FeOx) matrix have the texture, composition and isotopic values of their earlier formed counterparts in the deposit and therefore represent residual material that survived the weathering event. Three 40Ar/39Ar dates on the bladed alunite ranged from 23.15 to 22.88 Ma, confirming their origin as magmatic hydrothermal alteration alunite. Layers of compositionally zoned, small rhombohedral crystals of alunite were also discovered in the FeOx matrix. Although these could not be successfully dated, they had a distinct texture, chemistry and isotopic composition (δ34S = 0.8 ‰ δ18O = 4.7 ‰) that indicated they formed during the weathering event. The acidic, oxidizing supergene fluids remobilized and broadly enriched the top of the deposit in Cu and Ag and locally in native gold (5 wt. % Ag).

Mollies Nipple is a butte located in Kane County, Utah and is part of Grand Staircase-Escalante National Monument (GSENM). Mollies Nipple is now of particular interest to the Mars research community because of the presence of unusual diagenetic alunite and jarosite minerals. These minerals are present in sedimentary environments on Mars and have been used to interpret the diagenetic and depositional environments as acidic and/or arid. On Earth, these minerals are present in modern acid saline lakes, fumaroles, or acid mine drainage, but not commonly as diagenetic cements. The butte was mapped as Navajo Sandstone via photogeologic mapping, but the apex is 200 m higher than the surrounding upper extent of that unit in adjacent areas and there are some lithological inconsistencies that suggest the caprock may be a different overlying formation. Correctly understanding the diagenetic and depositional history of Mollies Nipple will inform future studies on Mars and has the potential to change the paradigm of these interpreted jarosite-bearing Martian environments. Stratigraphic sections were measured in the field and samples were collected for laboratory analysis. The dominant lithofacies is a cross-bedded quartz arenite. Structureless quartz arenite to wacke with lenticular green-gray quartz wacke (ash) is also present. Jarosite cement is common in upper sections of Mollies Nipple and is present, but sparse, in lower section of Mollies Nipple. Alunite is present in the upper section of Mollies Nipple. ANOVA conducted on point count data from samples collected from Nipple and representative samples of potential formations at Mollies Nipple do not differentiate between the possible formation candidate and Navajo Sandstone. Based on distribution of lithofacies, comparison with adjacent outcrops of Temple Cap Formation, Page Sandstone, and Carmel Formation, we conclude that the caprock at Mollies Nipple is most likely the Temple Cap Formation.

While Andosols have a proven capacity to buffer acid inputs, their long-term chemical response to elevated acid deposition remains poorly known. In this respect, the high anion retention capacity of Andosols constitutes a key parameter. Yet, the mechanisms involved in anion retention, especially sulphate, are still a matter of scientific debate. In this study, we report on the impacts of volcanogenic S and acid depositions on (i) the sulphate distribution and (ii) the processes involved in the neutralisation of the acid inputs, in two distinct soil series located downwind from Masaya volcano (Nicaragua), one of the world's largest natural source of SO2. The first series corresponds to weathered Eutric Andosols rich in allophanic constituents and the second series to weakly developed Vitric Andosols rich in volcanic glass. Long-term acid gas emission by Masaya volcano has led to important changes in the chemistry of the Andosols downwind. Sustained acid inputs have decreased the pH and exchangeable base cations contents in both Vitric and Eutric soils. These soils also show substantial S enrichment (up to 5470 mg S kg-1). However, these changes do not affect the soil acid neutralising capacity of the solid phase (ANCs) in a significant way. Despite the larger ANCs of the Vitric comparatively to the Eutric Andosols, soil pH was less in the Vitric than in the Eutric Andosols. This is related to the naturally and kinetically different mechanisms involved in the regulation of the volcanogenic acid fluxes: mineral weathering (slow kinetics) is the dominant process in Vitric Andosols, whereas cation exchange and sulphate sorption (rapid kinetics) significantly contribute to regulate proton consumption in Eutric Andosols. Formation of basic aluminium sulphate (BAS) [(K,Na)nAlx(OH)y(SO4)z] minerals in soils exposed to volcanogenic S-rich acid inputs was inferred from the results of selective extraction experiments (NH4F, KH2PO4 and oxalate). Precipitation of BAS probably constitutes the most effective inorganic SO42- retention mechanism (9-51% of total S), SO42- adsorption onto soil constituents (1-36% of total S) and occlusion into short-range ordered minerals (0-22% of total S), probably governed by ferrihydrite, constituted additional effective inorganic SO42- retention processes. Using transmission electron microscopy coupled with energy-dispersive analysis, we provide the first direct evidence of BAS minerals in soils. BAS minerals can form in these Andosols, because of the large inputs of H+ and SO2 and the availability of readily weatherable volcanic glass, which acts as an effective source of Al. Surface precipitation, i.e. two-dimensional chemisorption followed by three-dimensional nucleation and precipitation, rather than direct precipitation from solution, is likely the formation pathway of BAS particles in these soils. / Malgré une capacité importante à neutraliser les apports acides, le fonctionnement à long terme des Andosols est aussi susceptible d'être affecté par les dépôts acides. A cet égard, la capacité de rétention anionique élevée des Andosols constitue un paramètre clef. Or, les mécanismes de rétention des anions, en particulier du sulfate, demeurent un sujet controversé.Nous étudions ici les effets de dépôts acides et soufrés d'origine volcanique sur (i) la distribution du sulfate et (ii) les processus impliqués dans la neutralisation des apports acides, dans deux séries d'Andosol contrastées exposées aux émissions du volcan Masaya (Nicaragua), une des principales sources naturelles de SO2 atmosphérique. La première série comprend des Andosols Vitriques possèdant une réserve importante de minéraux altérables de nature vitreuse et la seconde est constituée d'Andosols Eutriques, plus évolués, possèdant des teneurs élevées en minéraux secondaires à organisation cristalline à courte distance. Les émissions prolongées de gaz acides provenant du volcan Masaya modifient fortement la chimie des sols exposés à ces apports. Ainsi, le pH et les teneurs en cations échangeables des Andosols Vitriques et Eutriques diminuent alors que la concentration totale en S augmente (jusqu'à 5470 mg S kg-1) en réponse aux apports d'acides. Par contre, la capacité de la phase solide de ces sols à neutraliser l'acidité (ANCs) n'est pas significativement affectée. Malgré une ANCs plus élevée dans les Andosols Vitriques comparativement aux Andosols Eutriques, le pH de ces sols est plus faible parce que les mécanismes impliqués dans la régulation des flux de protons sont différents: ceux-ci s'opèrent principalement par des réactions lentes d'altération minérale dans les Andosols Vitriques et par des réactions rapides impliquant l'échange ionique et la sorption d'anions sulfates dans les Andosols Eutriques. Sur base d'extractions sélectives (NH4F, KH2PO4 et oxalate), l'immobilisation sous forme de minéraux hydroxy-alumino-sulfatés [(K,Na)nAlx(OH)y(SO4)z] apparaît comme le mécanisme de rétention du SO42- inorganique le plus important (9-51% du S total), l'adsorption du SO42- à la surface de constituants du sol (1-36% du S total) et le piégeage du SO42- (0-22% du S total), vraisemblablement au sein d'oxydes de fer mal cristallisés, constituent également des processus efficaces de rétention du sulfate inorganique. Nous mettons en évidence par observation directe, pour la première fois, la présence de minéraux hydroxy-alumino-sulfatés dans des sols par microscopie électronique à transmission couplée à une sonde analytique EDS. La formation de ces minéraux est elle-même favorisée par l'apport considérable de sulfate d'origine volcanique et l'hydrolyse intense des verres qui libère l'aluminium en solution. La précipitation à la surface des phases adsorbantes plutôt que la précipitation directe en solution semble être le mécanisme de formation des minéraux hydroxy-alumino-sulfatés dans ces sols.