Placer formation by fluvial degradation of an alluvial fan sequence: the Proterozoic Carbon Leader placer, Witwatersrand Supergroup, South Africa

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Abstract
The Carbon Leader placer is one of a sequence of placers formed in the Carletonville goldfield, South Africa, in response to periodic fluvial degradation of a series of alluvial (fluvial) fans spreading southward into the Witwatersrand Basin. The Carbon Leader placer consists of broad, interconnecting, low-sinuosity ribbon bodies of conglomeratic and arenaceous sediments, which occur in two palaeodrainage systems, initially centred some 12 km apart. Ribbon bodies range to 500 m in width and 2 m in thickness, and accumulated from extensive migration of belts of small braided streams. Lithofacies and placer mineral distributions imply that fluvial current velocities were generally greater in the central parts of the palaeodrainage systems, decreasing towards the margins.
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