Abstract

Detailed mineralogic examinations of core from a series of boreholes show that in the immediate vicinity of the Driekop dunite pipe the platinum-group mineralogy of the UG-2 chromitite has been influenced extensively. Statistical evaluations pertaining to 1,327 discrete precious metal mineral particles indicate a progressive change from a Pt-Fe and Pt-Pd-As-Sb type, i.e., precious metal alloy type of mineralization, to a normal Rustenburg-Merensky Reef Pt-Pd sulfide type away from the pipe. Laurite was found to be the predominant platinum-group mineral in one of the boreholes. The size of the platinum-group minerals and that of their base metal sulfide hosts in the UG-2 layer decreases away from the dunitc pipe. Primary millerite and eutecticlike intergrowths of pentlanditc, pyrite, and chalcopyrite were noted in some boreholes. The changes found could possibly be due to emanations of relatively large amounts of CO 2 and other volatiles originating from the locality of the dunite pipe.

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