Sulfur sources of sedimentary “buckshot” pyrite in the Auriferous Conglomerates of the Mesoarchean Witwatersrand and Ventersdorp Supergroups, Kaapvaal Craton, South Africa

B. M. Guy, S. Ono, J. Gutzmer, Y. Lin, N. J. Beukes

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)

Abstract

Large rounded pyrite grains (>1 mm), commonly referred to as “buckshot” pyrite grains, are a characteristic feature of the auriferous conglomerates (reefs) in the Witwatersrand and Ventersdorp supergroups, Kaapvaal Craton, South Africa. Detailed petrographic analyses of the reefs indicated that the vast majority of the buckshot pyrite grains are of reworked sedimentary origin, i.e., that the pyrite grains originally formed in the sedimentary environment during sedimentation and diagenesis. Forty-one of these reworked sedimentary pyrite grains from the Main, Vaal, Basal, Kalkoenkrans, Beatrix, and Ventersdorp Contact reefs were analyzed for their multiple sulfur isotope compositions (δ34S, Δ33S, and Δ36S) to determine the source of the pyrite sulfur. In addition, five epigenetic pyrite samples (pyrite formed after sedimentation and lithification) from the Middelvlei and the Ventersdorp Contact reefs were measured for comparison. The δ34S, Δ33S, and Δ36S values of all 41 reworked sedimentary pyrite grains indicate clear signatures of mass-dependent and mass-independent fractionation and range from −6.8 to +13.8 ‰, −1.7 to+1.7‰, and−3.9 to+0.9‰, respectively. In contrast, the five epigenetic pyrite samples display a very limited range of δ34S, Δ33S, and Δ36 S values (+0.7 to +4.0‰, −0.3 to +0.0‰. and −0.3 to +0.1‰, respectively). Despite the clear signatures of mass-independent sulfur isotope fractionation, very few data points plot along the primary Archean photochemical array suggesting a weak photolytic control over the data set.

Original languageEnglish
Pages (from-to)751-775
Number of pages25
JournalMineralium Deposita
Volume49
Issue number6
DOIs
Publication statusPublished - Aug 2014

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Economic Geology

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