A REVIEW OF THE TRANSVAAL SEQUENCE, SOUTH-AFRICA

The 2500-2100 Ma Transvaal Sequence of South Africa comprises 15,000 m of relatively unmetamorphosed volcanic, clastic and chemical sedimentary rocks. Protobasinal clastic sediments and basaltic to rhyolitic volcanics are ascribed to fluvial deposition and subaerial extrusion. These units grade into the dolomites of the Chuniespoort Group, which are interpreted as having been laid down within a widespread epeiric sea; associated iron formations probably represent deposition within a distal, deeper basinal facies. The resurgent Chuniespoort depository expanded towards the northeast, and was the fourth component of a successor basin sequence, initiated in preceding Witwatersrand and Ventersdorp Supergroup times. Following extensive chemical weathering, the clastic sedimentary rocks of the Pretoria Group were laid down within a series of smaller, linked, fault-bounded basins, reflecting reactivation of Ventersdorp rift zones. A megacyclic alternation of fan/fan-delta/lacustrine delta and lake basin/lake margin sedimentation with subordinate, largely subaerial, volcanism is inferred. These rocks are unconformably succeeded by the voluminous Rooiberg Group felsites and associated basic-intermediate lavas and immature fluvial sediments, which terminated the Transvaal Sequence. The sequence is noted for epigenetic gold, lead-zinc, fluorite, manganese, iron, asbestos, andalusite and tin mineralization. © 1990.