3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item The role of sulphur in siderophile and chalcophile element enrichment of the lithospheric mantle: constraints from Kaapvaal mantle xenoliths and high-pressure partial melting experiments of S±C-bearing eclogite(2019) Burness, SaraSulphur- and carbon-bearing melts play an important role as metasomatic agents within the cratonic mantle lithosphere. While carbon-bearing melt metasomatism has been linked to various lithosphere enrichment processes including, diamond formation and kimberlite magmatism as part of the deep carbon cycle, information about the behaviour of sulphur during metasomatism and partial melting is less well constrained. Sulphide minerals predominantly host the mantle platinum group element (PGE), siderophile and chalcophile element budgets, and their behaviour during melting controls the movement of these economically important metals. Here I present a case study of eclogite and peridotite metasomatism by sulphur±carbon-bearing fluids/melts by comparing new experimental work with geochemical, stable isotopic and petrologic investigations of sulphide-bearing eclogite and peridotite xenoliths from several key kimberlite occurrences on the Kaapvaal craton, South Africa. The experiments conducted from 2 to 3.5 GPa and 1050 to 1300 ºC on sulphur±carbon-bearing eclogite compositions demonstrate that the critical factors concerning the mobility of sulphur in upper mantle eclogite are the degree of partial melting and the compositions of the resulting melts. Pure sulphide melt is shown to be largely immobile within the MORB-like eclogite system unless aided by more fluid-mobile carbonate±silicate melts at these upper mantle conditions. Sulphur is effectively mobilised as immiscible sulphide liquid melt pools within CO2-free basaltic-andesite melts and as dissolved elemental sulphur within intermediate carbonate-silicate melts at >15 % partial melting of the mixed volatile-bearing eclogite compositions. Comparative investigations of eclogite and peridotite xenoliths show that the metasomatic precipitation of secondary sulphide is intimately linked to metasomatism of the host silicate assemblage. The sulphide minerals are exceptionally redox sensitive and contain variable PGE contents with characteristic I-PGE/P-PGE fractionations, which are controlled by the compositional character of the metasomatic melt/fluid. Specifically, the xenoliths investigated here show evidence for several contrasting depth-dependent, and sometimes location-specific, metasomatic events which may have affected both the Kaapvaal cratonic lithosphere as well as the craton above. Moreover, this study demonstrates that metasomatic enrichment of the cratonic lithosphere by sulphur±carbon-bearing fluids/melts has resulted in isotopic heterogeneities and the addition of new minerals such as sulphide and potentially also diamond since the Archean.Item Efficiency of degrading packed bed bioreactors(2016) Botes, Anthin JohnIn South Africa, the need for water treatment is increasing, especially in the mining sector. As active water treatment technologies are expensive, the mining sector has an increasing need for passive water treatment technology, with low maintenance and operating costs, yet efficient water treatment ability. Literature on passive water treatment suggests that these systems only offer a narrow range of treatment capabilities. Therefore, hybrid water treatment systems could be a solution to low-cost water treatment in South Africa. The Degrading Packed Bed Reactor (DPBR) is one of the units comprising the hybrid treatment group. The DPBR’s main action is to convert sulfates into sulfides and alkalinity. In practice, the main drawback of the DPBR is clogging. Clogging lessens the amount of Acid Mine Drainage (AMD) that comes into contact with Sulfur Reducing Bacteria (SRB) in the DPBR, thereby reducing the efficiency of the bioreactor. In this study, six small-scale DPBRs were constructed. Each was classified according to its unique organic source (manure, straw, vegetable food processing waste, wood shavings, chicken litter and a combined sample with layers of all the carbon sources). Synthetic AMD was fed through the six bioreactors for a period of three months. From the small-scale DPBRs, the permeability, sulfate, iron and pH of the exit samples were measured. On average, the carbon sources removed 50 % of the sulfates and 98 % of the iron from the fed AMD. The different carbon sources showed no significant difference between each other in terms their sulfate and iron removal. The range between the best performing carbon source and the poorest performing carbon source, in terms of sulfate removal, was 17%. For iron removal, the range between the best and poorest performing carbon sources was only 2%. It was found that the permeability of the carbon sources played a larger role in the efficiency of the DPBR than the type of carbon source used. Manure is highly effective in terms of pH improvement, sulfate and iron removal. However, this is at the expense of permeability, as its packing clogs very rapidly. Compost and straw have excellent permeabilities which do not change significantly over long timeframes. This is, however, at the expense of the remedial ability of the packing materials. The combined reactor, in every instance, offers a good compromise between these different behaviours.