Large quartzite and chert clasts in the Archean gold-bearing reefs of South Africa have distinctive δ18O values that fall within a restricted range, 8.8‰ to 13.1‰. These values are thought to reflect the sources of the clasts and are not the result of oxygen isotopic reequilibration during postdepositional processes. Although the clasts are isotopically similar to several quartzite and chert source rocks, most potential provenance materials examined appear to be isotopically homogeneous on a centimetre scale, whereas many clasts are not. This difference indicates that several proposed sources may not be important provenance sites, as previously thought.

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