Die ontwikkeling van 'n eksplorasiemodel vir ystererts in die penge-formasie by Thabazimbi

Abstract

The Thabazimbi mining area is underlain by rocks of the Transvaal Sequence. The Frisco and Penge Formations of the Chuniespoort Group are described with the aim of identifying marker beds within the formations and to investigate the formation of the carbonate and talc-rich hematite rocks, as well as the iron ore itself. The Penge Formation is subdivided into six zones and comprises mainly thick units of ferythmite which alternate with thin units of felutite; the Frisco Formation is comprised of chert-poor dolomite. Thrust faulting of the post-Waterberg tectonic period has tripled the sequence and three prominent mountain ranges have arisen as a result of differential erosion. The tectonism has thermodynamically metamorphosed the banded ironstone and metasomatised dolomite and banded ironstone, causing the formation of carbonate and talc-rich hematite rocks at depth in zones 2 and 3 of the Penge Formation. Leaching of the uppermost portions of the Frisco Formation has led to sagging, brecciation and collapse of zones 1 to 3 of the Penge Formation. The area has thus served as an ideal zone for supergene processes and the ensueing formation of iron ore. During the post-Karroo tectonic period, normal and reversed faults preferentially developed in the weak zones associated with collapse structures. In these areas a second period of ferruginisation by supergene processes took place, during the post-Karoo erosion cycle. Martite-hematite ore, which is the last phase of ferruginisation of banded ironstones, carbonate and talc-hematite rocks, can therefore be regarded as a product of chemical sedimentation, metamorphism and supergene processes. Areas in which brecciation of zones 2 and 3 has occurred and where collapse has taken place, as well as where mudstones, and dolerite dykes have served as barriers, are ferruginised. Post-Karoo faults which have subsequently affected the brecciated zones or collapse structures, or a combination thereof, have also been ferruginised. Areas in which the abovementioned elements or a combination thereof have occurred, should be regarded as a target for future exploration.