A stream sediment geochemical re-investigation of the discovery of the platiniferous Merensky Reef, Bushveld Complex

The platiniferous Merensky Reef was discovered on the farm Maandagshoek in the Bushveld Complex in August 1924. A historical review of these events is presented, based partly on an unpublished report and a map by Dr Hans Merensky. It has been supposed that Merensky first traced the platinum to discordant ultramafic pipes. However, a re-examination of the topography and river systems in the area shows that this was not possible. A stream sediment study from this area has been undertaken to determine the source of the platinum originally panned at the discovery site. Determination of the Pt:Pd:Au ratio in these samples indicates a strong similarity with ratios in the Merensky Reef, and is completely different from the ratio found in the pipes, which are deficient in Pd and Au. These ratios also suggest that weathering and transportation has occurred predominantly due to physical rather than chemical processes. Two platinum-group element anomalies in the stream sediments are found upstream from the Merensky Reef outcrops. This results from a change in the fluvial system due to Pliocene to recent up warping with a reversal in flow direction.