Banded iron formation (BIF) is the most commonly mined source of iron ore, but the details of its genesis are poorly defined. Algoma-Type BIF is a predominantly chemical sedimentary rock comprising iron-rich phases (hematite, magnetite, chlorite) and chert as distinct laminae associated with deep marine lithologies, especially volcanic rocks and black shales. The iron minerals are thought to be direct chemical precipitates from Fe-enriched bottom waters or formation waters, most probably related to proximal volcanic activity. Key questions examined in this study are the paragenetic relationships and origins of mineralogically distinct layers in the Temagami BIF and the possible mechanism of replacement of primary hematitic layers by magnetite. The latter is a fundamental process in generating ore-grade BIF. The mineralogical and geochemical fingerprints of the different components of the BIF are also examined as clues to their likely sources (i.e., from upflowing hydrothermal fluids, contemporaneous volcaniclastic material, or precipitation from the local bottom water). Field observations indicate three separate depositional horizons for BIF in the area and exclude previous suggestions of fold repetition. Documented relationships between different types of layers and different facies of BIF in outcrop and in samples of the ore material, including petrographic features and aspects of the mineral chemistry and whole rock geochemistry, were used to construct a detailed paragenesis of the Temagami BIF. Two paragenetically distinct types of hematite and three types of magnetite are distinguished by different habits, grain size, cross-cutting relationships and growth features. Whole rock geochemical data confirm that the different facies of BIF were mainly products of redox-driven precipitation, combined with local hydrothermal and clastic input.

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En Afrique du Sud, le supergroupe Pongola s’est déposé sur le craton du Kaapvaal à environ 3 milliards d’années. Le groupe Mozaan repose sur le groupe basal Nsuze et contient des pélites, des arénites quartziques, des grès et des conglomérats. Dans ce type de conglomérat, des gisements d’uranium et des minéralisations d’or ont été reconnus dans le monde, au Canada, au Brésil, en Australie et en Afrique du Sud. Des petites minéralisations ont été avérées dans le groupe Mozaan, très différentes de celles qui ont été exploitées dans le bassin voisin du Witwatersrand. Ce travail pétrographique, minéralogique et géochimique concerne les formations conglomératiques et gréseuses basales du Mozaan Group dans le Denny Dalton. Il est fondé sur l’étude de deux carottes dans lesquelles des minéralisations en uranium ont été reconnues. Une attention particulière a été portée sur le matériel détritique car, dans ces conglomérats, les gisements sont de type placer avec des remobilisations plus ou moins marquées. Les grains détritiques identifiés associés à la pyrite détritique, sont la monazite fréquente, les oxydes de titane, les minéraux d’uranium thorium (coffinite, thorite, thorianite), le zircon, l’apatite, la chromite ainsi que d’autres sulfures (chalcopyrite, arsénopyrite). La roche source est vraisemblablement de matériel acide avec un faible apport basique ainsi que métamorphique. La morphologie des minéraux suggère un transport court de la source vers le bassin de Pongola. Les analyses pétrographiques et chimiques mettent en évidence les différentes minéralisations qui caractérisent les processus diagénétiques et hydrothermaux qui ont affecté le groupe Mozaan. Des observations nouvelles ont été réalisées sur les minéraux d’uranium avec la mise en évidence de phospho-coffinite, de phosphates alumineux hydratés de terres rares et des altérations très développées qui affectent les grains de monazite. Ces assemblages minéralogiques révèlent une diagenèse avec la circulation de fluides acides comme l’atteste la présence de pyrite et des APS dans la porosité secondaire des roches. Aucun grain d’uraninite détritique ni d’uraninite authigène n’a été observé dans cette étude. L’hypothèse la plus vraisemblable est que l’uranium des zones minéralisées provient de l’altération des grains de monazite à 2.54 Ga par des fluides acides. La remobilisation se fait en milieu ouvert et l’uranium cristallise essentiellement en bordures des grains de pyrite sous forme de phospho-coffinite. / In South Africa, the Pongola Supergroup was deposited on the craton Kaapvaal about 3 Ga years. The Mozaan group based on the basal Nsuze group and contains mudstones, arenites, sandstones and conglomerates. In this type of conglomerate, uranium and gold mineralization deposits have been recognized in the world, Canada, Brazil, Australia and South Africa. Small mineralization have been proved to in the Mozaan group, very different from those that have been exploited in the the neighbor of the Witwatersrand Basin. The petrographic, mineralogical and geochemical work concerns basal conglomerate and sandstone formations of Mozaan Group in Denny Dalton. It is based on the study of two cores where uranium mineralizations have been recognized. Particular attention was focused on the detrital material, because in these conglomerates, the deposits are placer type with the remobilizations more or less marked. The detrital grains identified associated with the detrital pyrite are frequent monazite, titanium oxides, thorium uranium minerals (coffinite, thorite, and thorianite), zircon, apatite, chromite and other sulphides (chalcopyrite, arsenopyrite). The source rock is likely acidic material with low basic contribution and metamorphic.The mineral morphology suggests a short transport the source to the Pongola basin. Petrographic and chemical analyzes show that characterize the different diagenetic mineralization and hydrothermal processes that have affected the Mozaan group. New observations were made on uranium minerals with the detection of phospho-coffinite, aluminous hydrated rare earth phosphates and highly developed alterations affecting monazite grains. These mineral assemblages reveal a diagenesis with the flow of acidic fluids as evidenced by the presence of pyrite and APS in the secondary porosity of the rocks. Detrital and authigène uraninite grains were not observed in this study. The most likely hypothesis is that the uranium mineralized zones comes from the weathering of monazite grains to 2.54 Ga by acidic fluids. Remobilization is done in open and uranium mainly crystallizes edges of pyrite grains in the form of phospho-coffinite.

The Batopilas Mining District was a major silver producer, with estimated historic production of more than 300 million ounces. Orebodies consist of high-grade silver in the forms of native silver, acanthite and proustite hosted dominantly in calcite veins. Recent exploration has facilitated the reexamination of the geologic features and origin of the enigmatic native silver district. Sulfur, lead, and strontium isotopic studies have been conducted to constrain the fluid and metal sourcing. [delta]³⁴SvCDT isotope signatures for galena, sphalerite and pyrite range from -8 to -2, -6 to 0, and -5 to 3°/₀₀, respectively. A fractionation temperature of 227±25 °C can be obtained using average sulfur isotope values for galena and sphalerite. Galena lead isotopic values show two distinct signatures. Samples of massive-replacement style mineralization have ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb values of 18.742 and 18.747, 15.611 and 15.618, and 38.512 and 38.535, respectively. For vein samples, the corresponding values range from 18.799 to 18.817, 15.623 to 15.639, and 38.603 to 38.655. The lead isotopic signatures for vein galena have lower thorogenic lead content than other ore deposits in the Sierra Madre Occidental, suggesting a different source of metals. Vein calcite samples have ⁸⁷Sr/⁸⁶Sr isotopic compositions ranging from 0.707551 to 0.70590 (±0.000009) and Sr concentrations ranging from 51 to 246 ppm. These vein components may reflect mixed deep-marine sedimentary and Precambrian basement sources. A reconnaissance fluid inclusion study was conducted to better constrain fluid temperature and composition. The minerals studied included quartz, fluorite, and two types of sphalerite. The average eutectic temperatures obtained are -38°C, -31°C, and -43°C, respectively, indicating a complex mineralizing brine. Homogenization temperatures averaged 143°C, 165°C, and 174°C, and the NaCl equivalent weight percents averaged 4, 7, and 17, respectively. Fluids involved in vein mineralization are different from those typical of epithermal vein Ag-Au deposits, and may represent sedimentary brines that have circulated through the underlying basement. / text

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Thesis (M.Sc.)--Memorial University of Newfoundland, 2006. / Restricted until October 2007. Bibliography: leaves 182-200. Also available online.

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Although mining is essential to life in our modern society, it generates huge amounts of waste that can lead to acid mine drainage (AMD). Most of these mine wastes occur as large piles that are open to the atmosphere so that air and water vapor can circulate through them. This study addresses the reactions and transformations of the minerals that occur in humid air in the pore spaces in the waste piles. The rate of pyrite oxidation in moist air was determined by measuring over time the change in pressure between a sealed chamber containing pyrite plus oxygen and a control. The experiments carried out at 25?C, 96.8% fixed relative humidity, and oxygen partial pressures of 0.21, 0.61, and 1.00 showed that the rate of oxygen consumption is a function of oxygen partial pressure and time. The rates of oxygen consumption fit the expression (dn/dt=(3.31x10^-7)(P^0.5)(t^-0.5) It appears that the rate slows with time because a thin layer of ferrous sulfate + sulfuric acid solution grows on pyrite and retards oxygen transport to the pyrite surface. The transformation of efflorescent sulfate minerals (the reaction products of iron sulfide oxidation) from a pyrrhotite-rich massive sulfide is explained using a systematic analysis of their stoichiometry and thermodynamics. Their stabilities are controlled by oxygen partial pressure, relative humidity, and activity of sulfuric acid and can be visualized using log activity of oxygen-log activity of water and log acitvity of sulfuric acid-log activity of water diagrams developed during this study. Samples from the field site were analyzed in the laboratory to determine mineralogy, equilibrium relative humidity, chemical composition, and acid generation potential. Dissolution experiments showed that fibroferrite-rich samples had the highest acid producing potential, followed by copiapite-rich samples and then halotrichite-rich samples. The most abundant metals in solutions produced by dissolving the salts were magnesium, aluminum, zinc, copper, calcium, and lead. The molar concentrations of the metals varied with mineralogy. However, all of these minerals release metals and acid when they dissolve and therefore represent a significant environmental threat. / Ph. D.

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