PALEOENVIRONMENTAL CONTROLS ON THE TEXTURE AND CHEMICAL COMPOSITION OF PYRITE FROM NON-CONGLOMERATIC SEDIMENTARY ROCKS OF THE MESOARCHEAN WITWATERSRAND SUPERGROUP, SOUTH AFRICA

摘要: A petrographic and mineral chemical study was conducted on pyrite from non-conglomeratic sedimentary rocks of the 3.0 to 2.8 Ga Witwatersrand Supergroup. Detailed analyses revealed presence three paragenetic associations, namely detrital, diagenetic epigenetic pyrite. Detrital is commonly observed in sandstone diamictite proximal shelf deposits. The chemistry large (0.1 0.5 mm size) small (<0.05 detrital grains, based Co, Ni As contents, suggests a metamorphic origin, respectively. Significantly, variety early forms has survived greenschist facies metamorphism; these occur exclusively carbonaceous mudstones intercalated with fluvial inner sandstones. high content occurrence Cu-Pb sulfides highlight importance organic matter host rock composition. However, distal starved outer depositional settings, absent scarce. Nevertheless, composition magnetite-rich lithologies similarly affected by possibly Fe-Mn reduction (elevated Co concentrations). Epigenetic pyrite, pyrrhotite base-metal are prevalent intercalations near diabase sills fault zones. influenced temperature fluids interaction rock, as well precursor associated iron sulfides. This finds that local tectonic settings instrumental dictating distribution, morphology In this regard, formation metal-rich favored regimes upper Hospital Hill, Government, Jeppestown, Johannesburg Turffontein Subgroups, where continental runoff would have supplied nutrients sulfur species shallow water environment. contrast, scarcity marine-dominated environments lower Hill Subgroup (of which some carbonaceous) portions Government Jeppestown consistent lack sulfate Archean ocean.