High-density regional geochemical mapping of soils and stream sediments in South Africa

Abstract

The Council for Geoscience has been conducting a high-density regional geochemical mapping program since 1973. A total area of 295,000 km 2 (25% of the surface area of South Africa) has been covered at a sampling density of one sample per square kilometer. A helicopter is used to collect first-order stream sediments or representative soil samples. The minus 75 μm fraction of samples is routinely analysed for 24 elements by simultaneous XRF. The results show an excellent correlation between soil chemistry and underlying geological formations. Background values of elements in soils are determined over different lithological units for the identification of anomalous values relative to these. The database can be used in exploration, the chemical characterisation of different geological units, as well as applications in environmental and agricultural fields. Results of geochemical mapping of the Bushveld Complex, South Africa, show a distinct anomaly of platinum and palladium, apparently related to a stratiform platiniferous reef on the boundary between the Main and Upper Zones of the Rustenburg Layered Suite. Geochemical mapping in the vicinity of some areas of mining and ore processing revealed large Cu, Ni, Co and Au anomalies, indicating anthropogenic contamination. Soil geochemistry has also been used, in conjunction with veterinary information, to explain livestock illness related to rock and soil qualities.