PLATINUM-GROUP MINERALS IN THE SELUKWE SUBCHAMBER, GREAT DYKE, ZIMBABWE - IMPLICATIONS FOR PGE COLLECTION MECHANISMS AND POST-FORMATIONAL REDISTRIBUTION

This paper presents the results of microprobe investigations of the Pl atinum-Group Elements (PGE) of the Serukwe Subchamber, Great Dyke, Zim babwe. The PGE are associated with base metal sulphides in the uppermo st pyroxenites of the Ultramafic Sequence of the Great Dyke. The follo wing minerals have been indentified: bismuthotellurides (moncheite, ma skovite, michenerite, kotulskite and polarite); arsenides (sperrylite) ; and sulphides and sulpharsenides (cooperite, laurite, braggite and h ollingworthite). Platinum Group Minerals (PGM) occur in three distinct textural environments: (I) at the boundary of sulphides and silicates /hydrosilicates, (2) entirely enclosed within sulphides, and (3) entir ely enclosed within silicate or hydrosilicate minerals. The stratigrap hic distribution, environments and textures of the PGM have important genetic implications, and cannot be explained by a single process. A m ulti-process model for the petrogenesis of the PGE mineralisation in t erms of complexation and intermediate compound formation is proposed. The primary mineralising events were due to orthomagmatic processes, b ut the observed textures are the result of microscale remobilisation o f PGM components by trapped interstitial fluids (hydromagmatic process es).