Abstract

Gold particles in systematically collected ore samples from the Proterozoic Carbon Leader Reef paleoplacer were studied by ore microscopy and analyzed for their silver and mercury contents. Most of the gold was mobilized and reconstituted forming irregular jagged grains often intimately intergrown with authigenic sulfide minerals, whereas gold particles of detrital appearance are extremely rare. Mobilization and reconstitution took place as a result of compaction and metamorphic overprint. Original sedimentary distribution patterns were not altered significantly suggesting that element migration occurred only over short distances.Individual gold grains as well as gold grain concentrates obtained from individual ore samples possess uniform fineness values (silver contents). These uniform fineness values are considered to result from metamorphic homogenization processes. The assumption is made, therefore, that the silver contents found in Witwatersrand gold particles are not those inherited from primary gold sources and provide, at best, limited information on the types of mineralization which existed in the provenance terrane of the sediments.On a regional scale, the fineness values of the gold particles exhibit distribution patterns which cannot be correlated with sedimentological facies outlined by heavy mineral distributions. Consequently, studies of regional fineness distributions are of questionable value for grade evaluation during exploitation and exploration.Mercury was found to be present in appreciable amounts in Witwatersrand gold particles (1.2-5.9%; x = 3.1%). It is suggested that the major source of the mercury is the surrounding sediments from which the element was mobilized and subsequently amalgamated with gold as a result of metamorphism. The mercury contents of Witwatersrand gold particles, as with the silver contents (fineness), yield little information on the geochemistry of primary gold mineralization.

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