Browsing by Author "De Villiers, Johan"
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- ItemRestrictedThe mineralogy and crystallography of pyrrhotite from selected nickel and PGE ore deposits.(Society of Economic Geologists, 2010) Becker, Megan; De Villiers, Johan; Bradshaw, DeeThe nonstoichiometric sulfide pyrrhotite (Fe(1–x)S) common to many ore deposits occurs in a variety of crystallographic forms and compositions and occasionally is also intergrown with stoichiometric troilite (FeS). In this study, the mineralogy of pyrrhotite derived from several different nickel and PGE ore deposits in South Africa, Botswana, and Canada was examined in detail in terms of pyrrhotite association, crystallography, and mineral chemistry. Pyrrhotite samples were subdivided into two-phase 6C Fe11S12 pyrrhotite intergrown with 2C FeS troilite, two-phase 4C Fe7S8 pyrrhotite intergrown with 5C Fe9S10 pyrrhotite, single-phase 5C Fe9S10 pyrrhotite and single-phase 4C Fe7S8 pyrrhotite. None of the pyrrhotite samples analyzed were classified as two-phase 4C pyrrhotite intergrown with pyrite due to the scarcity of pyrite in these samples. Average solid solution Ni contents of NC pyrrhotite (0.75 ± 0.10 wt % Ni) in this study were found to be greater than in 4C pyrrhotite (0.43 ± 0.10 wt % Ni), but only when the pyrrhotite occurred as two-phase 4C pyrrhotite intergrown with NC pyrrhotite. For single-phase pyrrhotite occurrences in this study, 4C pyrrhotite was more Ni rich (up to 2 wt % Ni) than NC pyrrhotite (0.75 ± 0.19 wt % Ni). The average atomic metal/S ratios obtained for 4C Fe7S8 pyrrhotite was 0.869 ± 0.013 (n = 699), for 5C Fe9S10 pyrrhotite was 0.895 ± 0.013 (n = 316) and for 6C Fe11S12 pyrrhotite was 0.918 ± 0.017 (n = 101). The histogram comparing metal/S ratios of all the pyrrhotite samples analyzed showed a continuum of metal/S ratios, although with frequency maxima corresponding to the ideal compositions of 4C, 5C, and 6C pyrrhotite. The presence of the continuum however, was interpreted to be representative of nonstoichiometry in the pyrrhotite structure.
- ItemOpen AccessSimulation-based valuation of project finance investments in sub-Saharan Africa and its effects on net present value and default probabilities(2015) De Villiers, Johan; Biekpe, NicholasThis paper addresses the issue surrounding the valuation of valuing large-scale infrastructure projects located in emerging and frontier market countries. These are economies which, traditionally, have been characterised as having high levels of risk and uncertainty, thus presenting a significant challenge to capital allocation decisions and the associated theme of narrowing the finance gap. In light of this, a case study is used to investigate the impact that simulation has on the valuation of an actual infrastructure project located in a sub-Saharan African economy. Specifically, a Monte Carlo simulation-based cash flow model is presented of an investment into a renewable energy project located in South Africa. Results of the simulation process indicate the degree to which certain variables affect the output factors, juxtaposed with an initial base case. A clear need is established for a more sophisticated valuation method in order to accurately judge the investment opportunity and Monte Carlo simulation is presented as a viable solution.