<p>Layered igneous intrusions such as the Stillwater Complex in Montana contain the most economic concentrations of platinum-group elements (PGE) in the world, yet the processes involved in the enrichment of these PGE remain unclear. Some researchers propose that the PGE were enriched into sulfide phases through purely magmatic processes, while others postulate that late-stage, high-temperature fluids caused remobilization of the more soluble elements upwards from the base of the crystal pile. Although much work has been carried out on the economic PGE-enriched ore zone (J-M reef), the silicate mineralogy and the bulk geochemistry of the Complex, the detailed petrographic trends have not been investigated. This dissertation comprises a detailed petrographic study into the assemblages associated with sulfide and other trace minerals throughout the stratigraphy.</p><p>Sampling was carried out from both surface outcrops and drill cores over four consecutive field seasons. Polished thin sections were produced which were then examined by petrographic microscope and electron microprobe. In addition, bulk rock analysis was carried out by x-ray fluorescence spectrometry (XRF).</p><p>In brief, the sulfide and trace mineral assemblage studies described below reveal a number of interesting observations. An upwards trend from pentlandite-rich to pyrrhotite-rich to chalcopyrite + pyrite-rich assemblages is observed below the reef, and the same trend occurs above the reef with the transition occurring just below the reef, in upper GN-I. Trace element analysis shows that Cu levels are higher above the reef than below it, and that although Zn and Cu contents are correlated below the reef, a restricted range of Zn contents occurs above the reef, while Cu is highly variable. As all `low-temperature' assemblages (those associated with extensive silicate alteration or the presence of greenschist facies minerals such as chlorite, clinozoisite and epidote) were discounted, the majority of sulfide assemblages present were either pristine(multiphase, often globular in shape, with no associated silicate alteration) or high-temperature (multiphase, with high-temperature minerals such as biotite, hornblende, carbonates, etc, and with little associated silicate alteration) in occurrence. Some differences were observed between the hanging-wall and footwall rocks, including the presence of native copper, sphalerite in a calcite-hornblende vein, and high-temperature carbonates in footwall and not hanging-wall rocks. The high-temperature carbonates observed comprise dolomite with exsolved patches of calcite. The textural relationships and Fe-Mn compositions of the Stillwater carbonates are similar to those of mantle carbonates. High-temperature desulfidation is also observed both above and below the reef, in the form of pyrite being converted to magnetite, and chalcopyrite to a Cu-Fe-oxide (delafossite). Both sets of assemblages are associated with little to no silicate alteration. When taken together, the upwards increase in Cu and S, the variable Cu contents above the reef, the native copper, high-temperature carbonates and high-temperature sphalerite-bearing veins below the reef, and the evidence for desulfidation are all most readily explained by the remobilization of selected phases by a high-temperature fluid. This dissertation provides evidence that the fluid present in the latter stages of Stillwater formation had a carbonic as well as a Cl-rich component, and would therefore have been efficient in PGE remobilization.</p> / Dissertation

Thèse (M.Sc.)--Université Laval, 2005. / Titre de l'écran-titre (visionné le 23 février 2006). Bibliogr.

Thesis (Master of Science)--Miami University, Dept. of Geology, 2004. / Title from first page of PDF document. Document formatted into pages; contains [1], v, 76 p. : ill. Includes bibliographical references (p. 42-50).

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 217-260).

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-08-30T23:05:10Z No. of bitstreams: 1 CARLOS HENRICKSON BARBALHO DE MOURA – DISSERTAÇÃO (PPGEPM) 2018.pdf: 10493787 bytes, checksum: 063013097342f1433f86bc8ac8434722 (MD5) / Made available in DSpace on 2018-08-30T23:05:10Z (GMT). No. of bitstreams: 1 CARLOS HENRICKSON BARBALHO DE MOURA – DISSERTAÇÃO (PPGEPM) 2018.pdf: 10493787 bytes, checksum: 063013097342f1433f86bc8ac8434722 (MD5) Previous issue date: 2018-03-28 / Capes / A petrofísica computacional é uma técnica que vem sendo utilizada cada vez mais na indústria do petróleo para caracterizar reservatórios e simular computacionalmente o seu comportamento físico. Através dessa técnica é possível caracterizar um elevado número de amostras, sob diferentes condições ambientais, em um tempo relativamente curto. Este trabalho propõe um modelo de estimativa de permeabilidade que utiliza parâmetros petrofísicos retirados de imagens de microtomografia de raios x (µCT) e os compara com parâmetros petrofísicos medidos em laboratório. Foi analisado um conjunto de 19 amostras com características deposicionais, diagenéticas e texturais diferentes entre si, pertencentes às bacias do Araripe, Potiguar e Sergipe-Alagoas. Delas, 14 são de calcário, 2 de tufa calcária, 2 de caliche e 1 de dolomito. Em laboratório foi utilizado um permoporosímetro a gás para medir os parâmetros porosidade e permeabilidade. As amostras de µCT foram adquiridas com resolução em torno de 2,0 µm. O conjunto de imagens criado foi tratado no software Avizo Fire e foram extraídos os parâmetros porosidade, permeabilidade, conectividade e diâmetro equivalente de poros. Um modelo estatístico foi estabelecido para predição da permeabilidade a partir dos parâmetros do espaço poroso extraídos das imagens de µCT. Os resultados indicam que a conectividade dos microporos, inferida a partir do cálculo do Número de Euler em imagens 3D, é o parâmetro que exerce maior influência na estimativa da permeabilidade, seguida pela porosidade dos macroporos e pela conectividade dos macroporos. O modelo preditivo proposto apresentou um coeficiente de determinação de 0,994, mostrando-se bastante confiável para o grupo de amostras investigado. / Computational petrophysics is a technique that has been increasingly used in the petroleum industry to characterize reservoirs and to simulate computationally its physical behavior. Through this technique it is possible to characterize a big number of samples, under different environmental conditions, in a relatively short time. This work proposes a model of permeability estimation that uses petrophysical parameters taken from x - ray microtomography images (µCT) and compare them with petrophysical parameters measured in the laboratory. It was analyzed a set of 19 samples with different depositional, diagenetic and textural characteristics, belonging to the Araripe, Potiguar and Sergipe - Alagoas basins. Of these, 14 are limestones, 2 of tufa limestone, 2 of caliche and 1 of dolomite. In the laboratory a gas permoporosimeter was used to measure the porosity and permeability parameters. µCT samples were obtained with a resolution of about 2.0 μm. The set of images created was treated in Avizo Fire software and the porosity, permeability, connectivity and pore diameter parameters were extracted. A statistical model was established to predict permeability from pore space parameters extracted from µCT images. The results indicate that the connectivity of micropores, inferred from the calculation of the Euler Number in 3D images, is the parameter that exerts the greatest influence in the estimation of permeability, followed by the porosity of the macropores and the connectivity of the macropores. The proposed predictive model presented a coefficient of determination of 0.994, being very reliable for the group of samples investigated.

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abstract: Molybdenum and uranium isotope variations are potentially powerful tools for reconstructing the paleoredox history of seawater. Reliable application and interpretation of these proxies requires not only detailed knowledge about the fractionation factors that control the distribution of molybdenum and uranium isotopes in the marine system, but also a thorough understanding of the diagenetic processes that may affect molybdenum and uranium isotopes entering the rock record. Using samples from the Black Sea water column, the first water column profile of 238U/235U variations from a modern euxinic basin has been measured. This profile allows the direct determination of the 238U/235U fractionation factor in a euxinic marine setting. More importantly however, these data demonstrate the extent of Rayleigh fractionation of U isotopes that can occur in euxinic restricted basins. Because of this effect, the offset of 238U/235U between global average seawater and coeval black shales deposited in restricted basins is expected to depend on the degree of local uranium drawdown from the water column, potentially complicating the interpretation 238U/235U paleorecords. As an alternative to the black shales typically used for paleoredox reconstructions, molybdenum and uranium isotope variations in bulk carbonate sediments from the Bahamas are examined. The focus of this work was to determine what processes, if any, fractionate molybdenum and uranium isotopes during incorporation into bulk carbonate sediments and their subsequent diagenesis. The results demonstrate that authigenic accumulation of molybdenum and uranium from anoxic and sulfidic pore waters is a dominant process controlling the concentration and isotopic composition of these sediments during early diagenesis. Examination of ODP drill core samples from the Bahamas reveals similar behavior for sediments during the first ~780ka of burial, but provides important examples where isolated cores and samples occasionally demonstrate additional fractionation, the cause of which remains poorly understood. / Dissertation/Thesis / Ph.D. Geological Sciences 2012

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Cabonate-hosted hydrocarbon reservoirs will play an increasingly important role in the energy supply, as 60% of the world's remaining hydrocarbon resources are trapped within carbonate rocks. The properties of carbonates are controlled by deposition and diagenesis, which includes calcite cementation that begins immediately after deposition and may have a strong impact on subsequent diagenetic pathways. This thesis aims to understand the impact of early calcite cementation on reservoir properties through object-based modelling and Lattice Boltzmann ow simulation to obtain permeability. A Bayesian inference framework is also developed to quantify the ability of Lattice Boltzmann method to predict the permeability of porous media. Modelling focuses on the impact of carbonate grain type on properties of early cemented grainstones and on the examination of the theoretical changes to the morphology of the pore space. For that purpose process-based models of early cementation are developed in both 2D (Calcite2D) and 3D (Calcite3D, which also includes modelling of deposition). Both models assume the existence of two grain types: polycrystalline and monocrystalline, and two early calcite cement types specific to these grain types: isopachous and syntaxial, respectively. Of the many possible crystal forms that syntaxial cement can take, this thesis focuses on two common rhombohedral forms: a blocky form 01¯12 and an elongated form 40¯41. The results of the 2D and 3D modelling demonstrate the effect of competition of growing grains for the available pore space: the more monocrystalline grains present in the sample, the stronger this competition becomes and the lesser the impact of each individual grain on the resulting early calcite cement volume and porosity. The synthetic samples with syntaxial cements grown of the more elongated crystal form 40¯41 have lower porosity for the same monocrystalline grains content than synthetic samples grown following more blocky crystal form 01¯12. Moreover, permeability at a constant porosity is reduced for synthetic samples with the form 40¯41. Additionally, synthetic samples with form 40¯41 exhibit greater variability in the results as this rhombohedral form is more elongated and has the potential for producing a greater volume of cement. The results of the 2D study suggest that for samples at constant porosity the higher the proportion of monocrystalline grains are in the sample, the higher the permeability. The 3D study suggests that for samples with crystal form 01¯12 at constant porosity the permeability becomes lower as the proportion of monocrystalline grains increase, but this impact is relatively minor. In the case of samples with crystal form 40¯41 the results are inconclusive. This dependence of permeability on monocrystalline grains is weaker than in the 2D study, which is most probably a result of the bias of flow simulation in the 2D as well as of the treatment of the porous medium before the cement growth model is applied. The range of the permeability results in the 2D modelling may be artificially overly wide, which could lead to the dependence of permeability on sediment type being exaggerated. Poroperm results of the 2D modelling (10-8000mD) are in reasonable agreement with the data reported for grainstones in literature (0.1-5000mD) as well as for the plug data of the samples used in modelling (porosity 22 - 27%, permeability 200 - 3000mD), however permeability results at any given porosity have a wide range due to the bias inherent to the 2D flow modelling. Poroperm results in the 3D modelling (10 - 30, 000mD) exhibit permeabilities above the range of that reported in the literature or the plug data, but the reason for that is that the initial synthetic sediment deposit has very high permeability (58, 900mD). However, the trend in poroperm closely resembles those reported in carbonate rocks. As the modelling depends heavily on the use of Lattice Boltzmann method (flow simulation to obtain permeability results), a Bayesian inference framework is presented to quantify the predictive power of Lattice Boltzmann models. This calibration methodology is presented on the example of Fontainebleau sandstone. The framework enables a systematic parameter estimation of Lattice Boltzmann model parameters (in the scope of this work, the relaxation parameter τ ), for the currently used calibrations of Lattice Boltzmann based on Hagen-Poiseuille law. Our prediction of permeability using the Hagen-Poiseuille calibration suggests that this method for calibration is not optimal and in fact leads to substantial discrepancies with experimental measurements, especially for highly porous complex media such as carbonates. We proceed to recalibrate the Lattice Boltzmann model using permeability data from porous media, which results in a substantially different value of the optimal τ parameter than those used previously (0.654 here compared to 0.9). We augment our model introducing porosity-dependence, where we find that the optimal value for τ decreases for samples of higher porosity. In this new semi-empirical model one first identifies the porosity of the given medium, and on that basis chooses an appropriate Lattice Boltzmann relaxation parameter. These two approaches result in permeability predictions much closer to the experimental permeability data, with the porosity-dependent case being the better of the two. Validation of this calibration method with independent samples of the same rock type yields permeability predictions that fall close to the experimental data, and again the porosity-dependent model provides better results. We thus conclude that our calibration model is a powerful tool for accurate prediction of complex porous media permeability.

Trithiocarbonates (TTCs) with less than six carbon atoms per molecule historically have proved to be better bulk sulphide mineral collectors than conventional dithiocarbonates (DTCs). However, high vapor pressures of the short-chain mercaptan decomposition products prevented them from general industrial use. Impala’s commitment in TTC development changed in 2002 when the nC12-trithiocarbonate indicated strong synergism when added to their existing flotation suite. A concerted research effort at the University of Utah followed, and in particular on their surface chemistry. To compliment current research and development at Impala, fundamental work regarding the surface hydrophobicity of pyrrhotite under electrochemically controlled conditions was undertaken at Utah University. Controlled contact angle measurements showed that the surface hydrophobicity of pyrrhotite can be increased by small additions of nC12-trithiocarbonate to SIBX. It was also found that this improvement in the surface hydrophobicity with the SIBX-TTC mixture was more significant at lower oxidation potentials. Work at Utah University further showed that a C12 decomposition product may or may not be present with an adsorbed TTC molecule. External reflectance infrared spectroscopy in the mid infrared region suggested a “crowding” of the collectors at the surface when SIBX and TTC are combined. This was based on an increase in the absorbance of the -CH2- peaks in the mixed collector system. In bench scale flotation tests on PGM bearing samples from the Merensky reef, it was found that a 5 molar percent replacement of SIBX with nC12-trithiocarbonate improved the flotation activity relative to the standard SIBX-DTP mixture. Improvements were in the recoveries of PGMs, copper and nickel. The addition of TTC also increased the flotation rates of both slow and fast floating valuables as is predicted by the Kelsall equation. The optimum mixture for the pilot plant trials was thus a 5 molar percent replacement of the current collector suite with nC12-TTC. Based on the bench flotation results, research was extended to a pilot plant trial. At a depressant dosage of 100g/ton, the PGM concentrate grades from the first rougher cell improved from 120g/ton to 175g/ton when the TTC was introduced. This was achieved without any effect on the recovery from the first cell. This increase in concentrate grade is believed to arise from the nature of both: <ul> <li>The mineral-collector surface state, and</li> <li>The bubble surface interaction.</li> </ul> Overall, the standard SIBX-DTP collector combination and the new SIBX-DTP-TTC collector combination (both at 100g/ton depressant) was also compared to pilot plant tests with SIBX-DTP at high (350g/ton) depressant dosages. The latter suite forms the currents reagent suite at Impala Platinum. When comparing the first two trials, at 100g/ton depressant, the addition of TTC as a ternary collector resulted in a recovery improvement of approximately 2.2% with a simultaneous increase in final concentrate grade from 57g/ton to 73g/ton. The result was a reduction in solids recovery from 5.3% to 4.1%. When comparing the TTC trial to the standard collector suite at high depressant dosages, only a small reduction (3.6% vs. 4.1%) in solids recovery was achieved with a final concentrate grade of 85g/ton. The PGM recoveries were very similar. Based on current Merensky milling rates, depressant and TTC costs, and calculated replacements based on the pilot plant tests, a projected cost saving on chemicals is R9.6 million per annum. Financial impacts on processing, grade and kinetics have not been made. It was also concluded that the detrimental effect of mild steel milling on the flotation activity of SIBX-DTP was diminished with the addition of the long-chain TTC with SIBX and DTP. As part to this research, a preliminary plant trial on UG-2 underground material showed a reduced primary rougher chromite grade as well as a significant increase in PGM concentrate grade for the first two primary rougher cells. This is an important finding, especially for the melting process. In this final study a partial (5 molar percent) replacement of the standard collector used was also made. What was further realised was a significant increase in the final concentrate grade when compared to the standard conditions. / Dissertation (MEng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / MEng / unrestricted