REVIEW OF MINERALOGY OF MERENSKY REEF, WITH SPECIFIC REFERENCE TO NEW DATA ON PRECIOUS METAL MINERALOGY

The precious minerals are predominantly associated with the base metal sulfides. Idiomorphic braggite, cooperite, and laurite, with minor sperrylite, are the major discrete platinoid minerals. Another main platinoid constituent, Pt-Fe alloy, most commonly occurs as complex intergrowths with other minerals, principally base metal sulfides. Studies of relationships of the precious minerals with the silicate-oxide gangue indicate a clear preference for their occurrence at the contact of the base metal sulfides with the gangue. Precious mineral grains are significantly smaller in chromite-rich ore compared with silicate-rich ore, while early minerals are demonstrably coarser than late-formed minerals.