Quartz vein formation, metamorphism, and fluid inclusions associated with thrusting and bedding-parallel shear in Witwatersrand quartzites, South Africa

A second thrust event, associated with bedding-parallel shear along the northern margin of the Witwatersrand Basin, has been identified and characterized by means of an integrated metamorphic and fluid inclusion study of data obtained from syn-tectonic vein quartz. The regional metamorphic and accompanying hydrothermal event that affected the Witwatersrand rocks clearly pre-dates this shear-zone metamorphism, which suggests that the redistribution of gold due to hydrothermal activity, as suggested by other authors, must also be pre-Transvaal in age. Peak P-T conditions of ± 390°C at ± 3 kbar inferred for the shear zone event (the second thrust event) along the northern margin of the Witwatersrand Basin are indicative of an abnormally high geothermal gradient. -from Authors