Abstract
The iron ore deposit of the Sishen Mine, Griqualand West region, Northern Cape, South Africa has traditionally been considered to be of supergene origin. The age of iron mineralization is thought to be Post Transvaal Supergroup, but prior and during to Gamagara Formation deposition in the Griqualand West region at approximately 2200 Ma to 2000 Ma. BIF-hosted laminated, massive and breccia iron ores of the Manganore Formation occur below the basal Doornfontein Member hosting conglomeratic ore of the Gamagara Formation. Oxidized BIF and the Wolhaarkop breccia underlies the ore in karstic depression structures of the dolostone and limestone succession of the Campbellrand Subgroup. The ores thicken towards the middle of the depression structures. Outside of the karstic depressions the BIF-hosted iron ore and conglomeratic ore are not developed. A regional erosion surface known as pre-Gamagara unconformity occurs between the BIF-hosted iron ore and conglomeratic ores. The Doornfontein is suggested to have accumulated in sinkhole structures or either deposited in lower lying region in the Paleoproterozoic. The metallogenesis of the iron mineralization in the BIF-host iron ore and the succeeding deposition of the conglomeratic Gamagara ores are put within in a regional geological context by this study...
M.Sc. (Geology)