Lead Isotope Evidence on the Detrital Origin of Witwatersrand Pyrites and its Bearing on the Provenance of the Witwatersrand Gold

Detrital pyrite in the Witwatersrand gold fields of South Africa; evidence from truncated growth banding

“…Investigation of pyrite from in situ strata-bound and stratiform gold deposits (Fleet et al, 1989) revealed crates. Therefore, the compact rounded variety of pyrite in the Witwatersrand deposits most probably does represent allogenic detrital grains that survived diagenesis and low-grade metamorphism without significant compositional alteration, as previous workers have suggested (e.g., Ramdohr, 1958;Saager, 1970;Koppel and Saager, 1974;Hallbauer, 1986). The As content of these ores is probably of detrital origin as well.…”

“…We suggest that these may have developed from a colonial (framboidal-like) form of pyrite during lithification and diagenesis (cf. Koppel and Saager, 1974). have noted that the abundance and variety of Ni,Co,Pt sulfarsenides in the Witwatersrand sulfide assemblage is unusual.…”

“…Hydrothermalists point to the inferred secondary characteristics of the ore mineral suite, the virtual absence of detrital grains of iron oxides and ilmenite, greenschist facies metamorphism, and the two basinwide geochemical associations (Au-S-Fe-As in conglomerates and C-U-Au in carbon seams) that elsewhere are associated with hydrothermal processes. The interpretation of compact rounded pyrite grains associated with the gold ores as allogenic detrital (e.g., Ramdohr, 1958;Saager, 1970;Koppel and Saager, 1974;Hallbauer, 1986) has always been important (perhaps essential) evidence favoring a placer model. However, Phillips et al (1988a, p. 322) note that chemical rounding and pseudomorphous replacement of iron oxides and ilmenite have been invoked as explanations for some of this rounded pyrite (e.g., Ramdohr, 1958;Ramdohr, 1969, fig.…”

Alternative model for the derivation of gold in the Witwatersrand Supergroup

“…after their deposition. Koeppel & Saager (1974) found a similarity between the U/Pb-isotope ratios in allogenic pyrites of the Witwatersrand and pyrites from gold deposits in the Barberton schist belt. Trace element data on these pyrites do not support such similarities (Utter 1978).…”

The Nature of the Witwatersrand Gold-Uranium Deposits

“…Koppel and Saager (1973) reported that the isotopic composition of the lead in some of the detrital sulphides in the Witwatersrand reefs is similar to that of lead in galena from certain mines in the Barberton Mountain Land. Both of these ages are younger than the topmost rocks of the Archean greenstone sequence in the Barberton Mountain Land, which are older than 3250 m.y.…”