ABSTRACT
Most world-class high-grade iron ore deposits are the product of enrichment of Precambrian iron formations but processes responsible for enrichment are still unclear. Different models, ranging from syngenetic and diagenetic, deep-seated hydrothermal and ancient supergene to modern supergene, are at present being under investigation. The existing controversy is furthered by lack of preservation of geological or textural evidence and the monomineralic composition of the ores that are almost exclusively composed of hematite, a mineral with a wide field of stability and very simple chemical composition that reveals little about its origin. To explore new avenues to distinguish ancient supergene from hydrothermal high-grade hematite ore deposits, we are conducting detailed studies of the Beeshoek, Sishen, and Thabazimbi iron ore deposits, all hosted by Superior-type iron-formations of the Transvaal Supergroup, South Africa. Results illustrate that the most reliable way to distinguish deposits of ancient supergene origin from hydrothermal deposits may be a detailed analyses of their geological setting, most notably their association with erosional unconformities and geological structures.
