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Mineral chemistry of sphalerite and galena from Pb-Zn mineralization hosted by the Transvaal Supergroup in Griqualand West, South Africa

Paleoproterozoic Mineralization Research Group, Department of Geology, RAU, P.O. Box 524, Auckland Park 2006, South Africa, e-mail: mschaefer{at}angloamerican.co.za; jg{at}na.rau.ac.za; njb{at}na.rau.ac.za;

L.N. Greyling

Paleoproterozoic Mineralization Research Group, Department of Geology, RAU, P.O. Box 524, Auckland Park 2006, South Africa, Present address: Economic Geology Research Institute, School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa, e-mail: greylin{at}science.pg.wits.ac.za

The relative and absolute abundance of minor and trace elements in ore-forming sphalerite and galena can yield important constraints regarding the metallogenesis of carbonate-hosted Pb-Zn deposits. This contribution presents an extensive set of mineral chemical data for sphalerite and galena from two deposits and several subeconomic occurrences of Pb-Zn mineralization in the Transvaal Supergroup on the Ghaap Plateau in Griqualand West. Significant differences are recognised between different localities and different styles of mineralization, but results obtained compare rather well with literature data of Phanerozoic Mississippi Valley-type deposits.

Fe and Cd constitute the two most important minor constituents in sphalerite from the Ghaap Plateau. Average concentrations vary between 0.54 weight % and 3.21 weight % for Fe and 0.13 weight % and 0.67 weight % for Cd. A first order correlation exists between average Fe/Mn ratios in sphalerite and host rock lithologies, while variations in concentrations of Co (7 to 177ppm), Ni (9 to 21ppm), Ga (2 to 99ppm) can only tentatively be attributed to differences in mineralization style, host rock, and metal source. Compared to sphalerite, trace element contents, in galena are very low with only Cd and Ag occurring in concentrations that consistently exceed 10ppm. Concentrations of more than 1000ppm Ag are reported for structurally-controlled Pd-rich subeconomic breccia runs close to the Griquatown fault zone.