Paleoenvironmental Controls on the Texture and Chemical Composition of Pyrite From Non-Conglomeratic Sedimentary Rocks of the Mesoarchean Witwatersrand Supergroup, South Africa

Research Article| September 01, 2010 PALEOENVIRONMENTAL CONTROLS ON THE TEXTURE AND CHEMICAL COMPOSITION OF PYRITE FROM NON-CONGLOMERATIC SEDIMENTARY ROCKS OF THE MESOARCHEAN WITWATERSRAND SUPERGROUP, SOUTH AFRICA B.M. GUY; B.M. GUY Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, Auckland Park, 2006, South Africa, e-mail: bradguy5@gmail.com; nbeukes@uj.ac.za Search for other works by this author on: GSW Google Scholar N.J. BEUKES; N.J. BEUKES Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, Auckland Park, 2006, South Africa, e-mail: bradguy5@gmail.com; nbeukes@uj.ac.za Search for other works by this author on: GSW Google Scholar J. GUTZMER J. GUTZMER Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, Auckland Park, 2006, South Africa, Department of Mineralogy, Technische Universitat Bergakademie Freiberg, Brennhausgasse 14, D-09596, Freiberg, Germany, e-mail: jens.gutzmer@mineral.tu-freiberg.de Search for other works by this author on: GSW Google Scholar Author and Article Information B.M. GUY Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, Auckland Park, 2006, South Africa, e-mail: bradguy5@gmail.com; nbeukes@uj.ac.za N.J. BEUKES Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, Auckland Park, 2006, South Africa, e-mail: bradguy5@gmail.com; nbeukes@uj.ac.za J. GUTZMER Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, Auckland Park, 2006, South Africa, Department of Mineralogy, Technische Universitat Bergakademie Freiberg, Brennhausgasse 14, D-09596, Freiberg, Germany, e-mail: jens.gutzmer@mineral.tu-freiberg.de Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2010 Geological Society of South Africa South African Journal of Geology (2010) 113 (2): 195–228. https://doi.org/10.2113/gssajg.113.2.195 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation B.M. GUY, N.J. BEUKES, J. GUTZMER; PALEOENVIRONMENTAL CONTROLS ON THE TEXTURE AND CHEMICAL COMPOSITION OF PYRITE FROM NON-CONGLOMERATIC SEDIMENTARY ROCKS OF THE MESOARCHEAN WITWATERSRAND SUPERGROUP, SOUTH AFRICA. South African Journal of Geology 2010;; 113 (2): 195–228. doi: https://doi.org/10.2113/gssajg.113.2.195 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract 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 petrographic analyses revealed the presence of three paragenetic associations, namely detrital, diagenetic and epigenetic pyrite. Detrital pyrite is commonly observed in sandstone and diamictite from proximal shelf deposits. The mineral chemistry of large (0.1 to 0.5 mm in size) and small (<0.05 mm in size) detrital pyrite grains, based on Co, Ni and As contents, suggests a metamorphic and diagenetic origin, respectively. Significantly, a variety of early diagenetic pyrite forms has survived greenschist facies metamorphism; these occur exclusively in carbonaceous mudstones intercalated with fluvial inner shelf sandstones. The high Ni content of early diagenetic pyrite and the occurrence of early diagenetic Cu-Pb sulfides highlight the importance of organic matter and host rock composition. However, in distal to starved outer shelf depositional settings, detrital pyrite is absent and diagenetic pyrite is scarce. Nevertheless, the composition of diagenetic pyrite in distal magnetite-rich lithologies is similarly affected by host rock composition and possibly Fe-Mn reduction (elevated Co and As concentrations). Epigenetic pyrite, pyrrhotite and base-metal sulfides are prevalent in sandstone intercalations near diabase sills and fault zones. The composition of epigenetic pyrite is influenced by the temperature of the fluids and the interaction of the fluids with the host rock, as well as with precursor and associated iron sulfides.This study finds that local depositional and tectonic settings are instrumental in dictating the distribution, morphology and composition of diagenetic pyrite. In this regard, the formation of metal-rich early diagenetic pyrite is favored in carbonaceous mudstones associated with fluvial regimes in the upper Hospital Hill, Government, Jeppestown, Johannesburg and Turffontein Subgroups, where continental runoff would have supplied nutrients and sulfur species to the shallow water environment. In contrast, the scarcity of diagenetic pyrite in marine-dominated environments of the lower Hospital Hill Subgroup (of which some are carbonaceous) and distal portions of the Government and Jeppestown Subgroups, is consistent with a lack of sulfate in the Archean ocean. 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