Fluid Inclusions and Trace Element Content of Quartz and Pyrite Pebbles from Witwatersrand Conglomerates: Their Significance with Respect to the Genesis of Primary Deposits

Abstract

Mineral-inclusion, trace-element, and fluid-inclusion studies were made on the Witwatersrand (South Africa) allogenic detrital pyrite [7782-50-5] and quartz [7440-09-7] pebbles to provide information about their primary origin. Mineral inclusions showed that granitic pegmatites were important as primary deposits for the Basal Reef and B-Reef, whereas rocks of the Dominion Reef volcanic sequence were possibly a source of detritus for the Klerksdorp Au field. For portions of the Ventersdrop Contact Reef, quartz-tourmaline-Au-bearing veins were a likely source. Inclusion studies and Co-Ni contents suggest that differences exist between the pyrites from Barberton deposits and Witwatersrand localities. The trace element distribution in quartz pebbles provides evidence of geochem. different source areas. The Th/U ratios in detrital pyrite, uraninite, and carbonaceous matter are of the same magnitude (0.1-0.4), suggesting a similar type source. Quartz pebbles have similar ratios to those mentioned, as well as ratios representative of granitic rocks (av. 3.5-4), which emphasizes the presence of different genetic types of quartz in the Witwatersrand conglomerate. [on SciFinder(R)]