Witwatersrand, Republic of South Africa

The Witwatersrand banker gold-uranium placer of the Kaapvaal Craton is perhaps the most famous example of a fossil placer. There has been much speculation on the origin of the deposit and two main arguments have been proposed: either that it is a fossil placer, with detrital native gold, uraninite and pyrite grains mechanically introduced into a basin followed by redistribution of elements (notably uranium) by metamorphism, or that the gold, uranium-bearing minerals and pyrite are epigenetic and hydrothermal in origin. The host rock is an oligomictic conglomerate of vein quartz, chert, jasper, banded iron formation and quartzite pebbles in a matrix of secondary quartz and phyllosilicates. It contains detrital, abraded pyrite, chromite, zircon, uraninite, gold and other heavy minerals. Locally, gold and uranium are found within narrow carbonaceous-rich horizons. Over seventy minerals have been recorded.

Major Minerals:

Pyrite, native gold, uraninite, thorian uraninite, carbonaceous material, uraniferous carbon (called thucholite), brannerite

Minor Minerals:

Arsenopyrite, cobaltite, galena, gersdorffite, pyrrhotite, bravoite, rutile, anatase, sphalerite, chromite, zircon

Trace Minerals:

Include Ir-Os-Ru alloys, iron-platinum alloys, monazite, xenotime, tennantite, stromeyerite


Detrital minerals include zircon, chromite, ilmenite, magnetite, pyrite, arsenopyrite and gersdorffite; authigenic minerals include rutile, anatase, gersdorffite and bravoite. Pyrite occurs as rounded grains enclosing native gold, pyrrhotite and chalcopyrite. Thorian uraninite forms rounded to euhedral grains in conglomerates, uraninite occurs as euhedral crystals in hydrocarbons, elsewhere uranium occurs as coffinite and as uranium-titanium oxide intergrowths (uranium-leucoxene) comprising leucoxene, anatase and brannerite. Native gold forms small rounded grains associated with pyrite or 1-2µm grains associated with hydrocarbons where it is perhaps biogenic in origin. Remobilized gold is more abundant than detrital gold, but has not traveled far.


Feather and Keen 1975; Feather, 1976; Hallbauer and Utter, 1977; Simpson and Bowles, 1977; Thiel et al., 1979; Clemmey, 1981; Saager et al., 1982; Smits, 1987