Geological Society of America

246 Economic Geology (Posters)

Wednesday, 3 November 2010
8:00 AM - 6:00 PM
Hall D

SULFUR ISOTOPES OF BASE-METAL SULFIDE AND BARITE PAIRS FROM THE AGGENEYS-GAMSBERG BHT DISTRICT, SOUTH AFRICA

Paper number: 246-1
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Craig R. McClung Presenting Author
University of Johannesburg, Auckland Park, N/A
Jens Gutzmer
TU Bergakademie, Freiberg, N/A
Ellen Gertloff
University of Johannesburg, Auckland Park, N/A
Nicholas J. Beukes
University of Johannesburg, Auckland Park
Harald Strauss
Westfalische Wilhelms-Universitat Munster, Munster, N/A

Abstract

Stratiform and stratabound base metal deposits of the Aggeneys-Gamsberg BHT district of South Africa, occur in amphibolite-facies metasedimentary rocks of the Mesoproterozoic Bushmanland Group. Sulfur isotope ratios from the district are distinctly enriched in ³⁴S when compared to contemporaneous Mesoproterozoic seawater. All deposits exhibit a bimodal distribution in δ³⁴S_sulfide values and a systematic increase in δ³⁴S from the west to the east across the district. At the Swartberg deposit δ³⁴S_sulfidevalues average -0.6‰ and +16‰, while δ³⁴S_barite values average +23.8‰. The central portion of the district is occupied by the Broken Hill and Big Syncline deposits. The δ³⁴S_sulfidevalues for the Broken Hill deposit average +1.9-10.4‰ and +17.5‰, while the Big Syncline deposit exhibits average δ³⁴S_sulfidevalues of +11.1‰ and +19.7‰, with barites averaging +29.8‰.

The heavy δ³⁴S values of primary sulfides are consistent with the values of the stratabound barites from throughout the district. In contrast, petrographic evaluations of the samples that display lower values indicate remobilization and reflect the influx of isotopically lighter magmatic sulfur. The heavier values fall within the range of coeval seawater, indicating a seawater sulfur source; however, the heavier values of the Big Syncline and Gamsberg can only be explained by deposition in a restricted basin. We suggest that the high δ³⁴S values at Gamsberg and Big Syncline resulted from the preferential removal of ³²S from the initial S-reservoir, via BSR, and precipitated as early diagenetic pyrite thereby enriching the sulfur reservoir in ³⁴S.