Frank, Mark R.
M.S. (Master of Science)
Department of Geology and Environmental Geosciences
Geology; Mineralogy; Geochemistry; Thermodynamics--Research; Sulfides--Research; Silicates--Research
Layered mafic intrusions are magmatic sulfide deposits that commonly contain platinum group element (PGE)-rich ore along with larger copper and nickel deposits. These magmatic systems are thought to form as a result of silicate-sulfide immiscibility triggered by magmatic processes such as magma mixing. This process can effectively segregate and concentrate PGEs into the sulfide phase to produce PGE-rich ore deposits. This study focused on determining the concentrations of Pt, Ni, Mo and Cr in sulfide and silicate melts at experimental conditions comparable to Ni-Cu-PGE-ore-forming magmatic sulfide systems. Experiments were conducted in a vertical tube furnace at 1100 °C and 1 atm with the oxygen fugacity buffered by Ni-NiO. EMPA analysis of run products yielded Pt and Ni partitioning values, D(sul/si/Pt) and D(sul/sil/Ni), between sulfide compositions within the Fe--Cu--Ni--S system and silicate melt: D(sul/si/Pt) = ∼3 to 1600 and D( sul/sil/Ni) = 5 +/- 5 to 1400 +/- 900.;Pyrrhotite-compositions were used to calculate the f( sys/S2) of the experiments. D( sul/si/Pt) was found to decrease with increasing f( sys/S2) while D(sul/sil/Ni) increased with increasing f(sys/S2). Ni concentrations in the sulfide run products have a variable influence on Pt partitioning. Additionally, Cr concentrations were only measurable in silicate run products suggesting that chromite layers in natural deposits likely form through magma mixing and fractional crystallization and do not require sulfide melt saturation. A Rayleigh fractionation model for Pt was created from data in this study and corresponds well with data from natural systems. Natural PGE deposits such as the Merensky Reef, in the Bushveld Complex and the J. M. Reef, in the Stillwater Complex likely formed through magma mixing processes involving the equilibration of silicate and immiscible sulfide melts.
Castillo, Marco Eduardo, "Platinum and nickel partitioning between sulfide and silicate melts as a function of sulfur fugacity" (2015). Graduate Research Theses & Dissertations. 4414.
Northern Illinois University
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