The UG2-Merensky Reef interval of the Bushveld Complex northwest of Pretoria

Abstract

Northwest of Pretoria, the UG2-MerenskyReef interval overlies a Critical Zone-Lower Zone sequence that contains numerous large blocks of floor material. Nevertheless, individual layers can be correlated with equivalent units at Crocodile River mine, the Rustenburg, hnpala, Union, and Amandelbult sections. Concentrations of platinum-group elements in two borehole intersections of the UG2 chromitite are 4 ppm over 1.2 m and 2.4ppm over 2.2 m. Therefore, bulk PGE levels appear to be only moderately lower than those at Western Platinum mine. This renders models explaining PGE enrichment by upward percolating melt or fluids problematic. The Merensky Reef, although containing sulphides, is only weakly mineralized with PGE (0.6ppm). The UG2 pyroxenite is separated from the UG2 chromitite by a 15 m noritic layer.

Petrogenesis of PGE mineralised intrusions in the floor of the northern Bushveld Complex

“…Rietfontein rocks have Mg# 0.87. These data overlap with those of the LZ and LCZ but are less evolved than those of the UCZ (e.g., Maier and Eales, 1997;Maier et al, 2013;McDonald and Holwell, 2011).…”

Geochemical evidence for multiphase emplacement in the southern Platreef

“…Serpentinites are compositionally variable from hole to hole and even within individual cores: Serpentinised harzburgites, with net-textured sulphides, have the highest Cr of all rock types (< 4000 ppm Cr). The Sr content in the lower serpentinite in core ATS27 is high for an ultramafic rock (< 374 ppm) compared with an average harzburgite of 70 ppm Sr, 26 which reflects the interstitial plagioclase content. They show evidence of reaction with adjacent country rocks, with occasionally high V values (e.g.…”

Platinum-group minerals in the Skouries Cu-Au (Pd, Pt, Te) porphyry deposit

“…PGE-enriched porphyry deposits globally have very similar Au/(Pd + Pt) of ∼90 and Pd/Pt of ∼10 (Fig. 7, Augé et al, 2005Augé et al, , 2002Eliopoulos et al, 2014;Eliopoulos and EconomouEliopoulos, 1991;Maier and Bowen, 1996;Steele, 1978;Thompson et al, 2001). However, it is worth noting that the company assay data provided in this study shows no correlation between Au and Pd + Pt (R 2 = 0.01), with an average Au/(Pd + Pt) of 310, meaning that Au grade should not be used as a proxy for PGE grade.…”