Gold-bearing reefs of the Witwatersrand Basin: A model of synsedimentation hydrothermal formation

The current concepts concerning the genesis of the unique ore-bearing reefs of the Witwatersrand Basin and its gold resource potential are considered. The results of microscopic examination of ore from the Black, Ventersdorp Contact, Carbon Leader, and Vaal reefs, as well as of thermobarometric study of quartz, are presented. A model of synsedimentation hydrothermal origin of the reefs in the process of evolution of primary colloidal-disperse systems is substantiated on the basis of these results and the data published by other authors. The formation of these systems is related to the periodic gain of deep ore-bearing gas-saturated fluids. The gold mineralization was formed under conditions of partially closed systems, where various mineral-forming processes developed (metasomatism, crystallization of true solutions and gels, gel metasomatism, dispersion of crystalline phases, segregation of mineral particles, formation of early minerals, etc.). New data on REE specialization of ore-bearing fluids are discussed. The specific features of the gold, carbonic, and uranium mineralization of the intracratonic basin are emphasized.