摘要: In this chapter, ancient placers refer to deposits of Archaean and early Proterozoic age. Because each deposit may cover hundreds square kilometres, they present economically attractive exploration targets. Individual placer like the Steyn/Basal in Welkom goldfield South Africa have produced excess 4500 t (metric tons) gold from heavy mineral concentrates distributed over a palaeosurface area 170 km2 (Minter et al., 1986). This amounts about 26 gold/km2. Another important deposit, Vaal placer, which lies adjacent Klerksdorp goldfield, extracts 32 Production figures well-known Witwatersrand Supergroup illustrate their productivity relative other types (Figure 9.1).
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