A Geological Mapping and Geochemical Sampling programme has been carried out in three separate prospects, total area about 30 sq. miles, over gneisses and granulites of the Namaqualand Shield, Cape Province, South Africa. The rocks are divided according to content of mafic minerals, grain size and presence of certain other diagnostic minerals. Particular attention is paid to the "noritoid" or biotite pyroxene granulite, which crops out in irregular pods, lenses and occasionally dyke-like bodies of widely differing size. This rock-type is almost certainly of the type in which the O'okiep copper deposit occurs and in the prospects mapped at least one body is known to contain copper. The origin of this rock is the subject of some argument but evidence is presented here to suggest that the rock was emplaced before the regional metamorphism. There is a possibility that copper sulphides are to be found in the outcrop mentioned above but the origin of the malachite staining at the surface is thought to be the retrograde metamorphism of the rock whereby waters at temperatures in the Greenschist facies range carried copper up from below and deposited it, along with epidote and chlorite
The Geochemical Sampling of the prospects establishes that the distribution of values of Cu, Ni, Zn and Pb in stream sediment is neither perfectly Gaussian or Log-Gaussian, but the population is not large enough for any real significance to be attached to this. The highest value of copper in stream sediment in the regional sampling is less than a quarter of that immediately below the copper mineralisation described above.
An orientation survey carried out in the stream-bed immediately below the mineralisation shows that, on minus 80 mesh samples, copper content decays to background in about 810 feet. The implication of this conclusion is that under the present sampling scheme there is only about a 20% probability that an anomaly will be noted.
The regional data are also expressed in the form of Geochemical Maps,
of both raw and smoothed values.