Detailed Assessment of Platinum-Group Minerals Associated With Chromitite Stringers in the Merensky Reef of the Eastern Bushveld Complex, South Africa

Noble metal nanoclusters and nanoparticles precede mineral formation in magmatic sulphide melts

“…Although this is only demonstrated for the element combination Pt–As and only in sulphide melts, no a priori reason is evident why the same principle should not also hold for all other noble metals in sulphide and metal melts, as well as for trace minerals crystallizing from silicate melts. In magmatic sulphide deposits, the platinum-group elements (PGE) are to a large extent organized as discrete arsenide, antimonide, bismutho–telluride and stannide minerals242526272829, although theoretically all noble elements could be accommodated by the lattices of the coexisting base metal sulphides. For us this does not come as a surprise: these mineral compositions reflect the preferred metal–ligand nano-associations in which the PGE occur in magmatic sulphide melts, present well before discrete (micron-sized) PGE minerals become stable.…”

PGE Production in Southern Africa, Part I: Production and Market Trends

“…The upper and lower chromitite seams differ in composition: The lower seam comprises more than 48% (by area) of Pt-Pd sulfides, whereas the upper seam is dominated by Pt-Fe alloys (>45%) [45]. The PGE concentration is highest in the upper part of the layer [65]. The occurrence of PGE elements is closely linked to the presence of Fe-Ni-Cu sulfides [44].…”

“…The UG2 layer contains primary magmatic PGE-bearing minerals and minerals that have been modified by secondary processes (e.g., metasomatic processes). In contrast to the Merensky reef, the UG2 layer exhibits the highest concentration of PGEs at the bottom [65]. The PGE-bearing minerals (mostly Pt sulfide, Pt-Pd sulfide, laurite, ferroplatinum, cooperite, braggite, and Pt-Rh-Cu) and discrete metals Pd, Os and Ir are heterogeneously distributed, resulting in varying concentrations of PGEs in the lateral extent [44,45].…”

“…The PGE-bearing minerals occur enclosed in base-metal sulfides, along grain boundaries and the contact zones of sulfides and silicates or oxides [44,63]: in 38% to 97% of occurrences, PGE-bearing minerals were found to be enclosed in or attached to base metal sulfides; the remainder are enclosed in silicates [64,66]. The most commonly occurring base metal sulfides are pyrrhotite, pentlandite and chalcopyrite, with~40%,~30% and~15%, respectively [65,66]. Orthopyroxene, plagioclase feldspar, clinopyroxene and phlogopite account for~60%,~20%,~15% and~5% of the silicate minerals, respectively.…”

An overview of the platinum-group element nanoparticles in mantle-hosted chromite deposits

“…This is one of the three deposits exploited for PGEs in the Bushveld Complex in South Africa (Campbell et al, 1983;Tredoux et al, 1995;Vermaak, 1995;Ballahus and Sylvester, 2000;Prichard et al, 2004;Naldrett, 2004;Godel et al, 2007;Mungall and Naldrett, 2008;Scoates and Fiedman, 2008;Woordouw et al, 2010;Rose et al, 2011). Wirth et al (2013) presented TEM observations on thinned BMS grain foils that were previously selected and retrieved using FIB-FESEM to avoid large PGM inclusions.…”