Metamorphic temperature variations among Witwatersrand goldfields: Evidence from the pyrophyllite-chloritoid-chlorite mineral assemblage

Abstract

The assemblage pyrophyllite-chloritoid-chlorite-quartz has been recorded in most Witwatersrand goldfields. Combinations of these minerals are common in pelitic rocks, and also found in most other rock types in the upper Witwatersrand succession including conglomerates, quartzes, and metabasalts. Chlorite occurs in several different morphological forms including bundles, veins, coarse fibrous and granular aggregates, fine-grained aggregates, pressure shadow filings, nodules, and in massive form. Individual chlorite grains are compositionally homogeneous, and chlorite is generally of constant composition on a thin-section scale. In the whole Witwatersrand Basin, there is a wide range of 100 x ..