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

The Council for Geoscience has been conducting a high-density regional geoc hemical mapping program since 1973. A total area of 295,000 km(2) (25% of t he 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-orde r stream sediments or representative soil samples. The minus 75 mu m fracti on of samples is routinely analysed for 24 elements by simultaneous XRF. Th e results show an excellent correlation between soil chemistry and underlyi ng geological formations. Background values of elements in soils are determ ined over different lithological units for the identification of anomalous values relative to these. The database can be used in exploration, the chem ical characterisation of different geological units, as well as application s 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 proces sing revealed large Cu, Ni, Co and Au anomalies, indicating anthropogenic c ontamination. Soil geochemistry has also been used, in conjunction with vet erinary information, to explain livestock illness related to rock and soil qualities. (C) 1999 Elsevier Science B.V. All rights reserved.