Sulphur Isotopes in Metamorphosed Precambrian Fe-Pb-Zn-Cu Sulphides and Baryte at Aggeneys and Gamsberg, South Africa

K. von Gehlen, H. Nielsen, I. Chunnett and A. Rozendaal
Institut für Geochemie, Petrologic und Lagerstättenkunde, University of Frankfurt, Senckenberg-Anlage 28, D-6000 Frankfurt, FR Germany
Stable Isotope Laboratory, Geochemisches Institut, University of Göttingen, Goldschmidt-Str. 1, D-3400 Göttingen, FR Germany
Black Mountain Mineral Development Company (Pty) Ltd., Private Bag XO1, Aggeneys, CP 8893, Rep. of South Africa
O'okiep Copper Company Ltd., PO Box 17, Nababeep, CP 8265, Rep. of South Africa

Abstract: Sulphur isotope ratios in sulphides and baryte from stratabound and stratiform orebodies in a metavolcanic-sedimentary sequence in Namaqualand were found, in part, to be extreme for Precambrian sulphur. Black Mountain, Aggeneys, in the west gave an average for the sulphides of δ34S = +8.9±3.7‰ (9 samples), an average for barytes of +20.6±4.3‰ (3 samples). Broken Hill, Aggeneys, in the centre gave an average for the sulphides of δ34S = +19.8±3.1‰ (19 samples). Gamsberg, in the east, gave an average for the sulphides of δ34S = +29.2±1.8‰ (24 samples), and an average for barytes of +35.4±0.2‰ (2 samples). The δ34S values increase eastward. Their range is strongly on the positive side and does not centre around zero. The Gamsberg barytes and most Gamsberg sulphides have more positive δ34S values than those reported for other Precambrian sulphides and sulphates. We interpret the above sulphur isotope range as being mainly due to the varying contributions of submarine-exhalative sulphide sulphur with δ34S close to zero and bacterially(?) reduced sulphate with strongly positive δ34S, apparently from evaporites in the east. Metamorphism of amphibolite facies grade has partly isotopically re-equilibrated the ore minerals, as indicated by galena-pyrrhotine and sulphide-baryte isotope temperatures from single specimens, but has not destroyed the primary sulphur isotope range indicating pre-existing sulphate concentrations.

Mineralogical Magazine; December 1983 v. 47; no. 345; p. 481-486; DOI: 10.1180/minmag.1983.047.345.09
© 1983, The Mineralogical Society
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