The geology of the country surrounding Loskop Dam, Transvaal

Abstract

The Loskop System in its type locality has been investigated. It consists predominantly of arenaceous sediments and minor shales, siltstones a.no. conglomerates·. Lithologically the components ·of this system are remarkably similar to those of the overlying Waterberg System. Heavy mineral concentrates from rocks of both systems were investigated to determine whether there were sufficient points of difference to demarcate the Loskop System from the Waterberg System on petrographical data. The similarity of these heavy mineral suites agrees with the close correspondence in nature of the sediments in which the minerals occur and is not corroborative of the grouping of the rocks on the Loskop System into a separate stratigraphical entity. Evidence of volcanicity contemporaneous with the deposition of a portion of the Waterberg System is present in the area mapped in the form of pyroclastic material intimately associated with intensely folded Waterberg beds. The latter are overlain by practically undisturbed strata of the same system. The intraformational and local folding in the Waterberg beds is thought to be due to subaqueous slumping at the time of eruption of the pyroclastic material. A description is given of the Rooiberg Felsite in particular its chemical composition is compared with that of Karroo Rhyolite and with felsite of the “Premier Mine Type” The latter type is distinctive in several respects but especially in its high mg content. When plotted on Smithson diagrams, the length breadth ratios of zircons obtained from the felsitic lava of the Bushveld Complex are found to be very much the same as those obtained for sediment of the Loskop System. Two new chemical analyses are reported.