Genesis and characteristics of the Wolhaarkop breccia and associated manganore iron formation

M.A.Hematized iron formation known as the Manganore iron formation is slumped into sinkhole structures in the Campbellrand Subgroup, Transvaal Supergroup, on the Maremane dome. These iron deposits are underlain by manganiferous breccias known as the Wolhaarkop Breccia. Known iron and manganese deposits of this type occur in an arc from Sishen in the north to Postmasburg in the south. The area is not being mined for manganese at the moment due to the relatively high grade of the Kalahari manganese field situated to the north of this area. The iron deposits, though, are some of the richest in the world. The aim is to establish the mode of origin for the Wolhaarkop Breccia. The Wolhaarkop Breccia is interpreted as being a residual ancient manganese wad from a karst environment in manganese rich dolostones of the Campbellrand Subgroup. This siliceous breccia contains authigenic megaquartz and angular poorly sorted clasts of chalcedony and quartz, set in a braunite-hematite matrix. Fluid inclusions in the authigenic quartz of the Wolhaarkop Breccia have been studied to establish the source of the fluid responsible for quartz precipitation in the Wolhaarkop Breccia, and indirectly, for the formation of the Wolhaarkop Breccia. Thermometric data was used to determine the maximum possible pT and depth conditions under which the quartz might have been precipitated. Fluid chemistry was determined using the bulk crush-leach method to shed some light on the fluid origin. It was established that the fluid responsible for chert recrystallization and precipitation of authigenic quartz and chalcedony had a meteoric source. Considering the results of the above-mentioned analysis, it was concluded that the iron and manganese deposits were formed during a cycle of uplift followed by subsidence. During the period of uplift, erosion in a karst environment and enrichment of iron formation in a supergene environment concentrated manganese as a manganese wad, and iron as a residual iron-oxide laterite. Meteoric water was the main fluid present during this period. Later, during a stage of subsidence, the Wolhaarkop Breccia underwent diagenesis and later lower greenschist-facies metamorphism. During a final stage of uplift the deposit was exposed to the atmosphere again, the dolostones were weathered away and the residual Manganore iron formation and Wolhaarkop Breccia were exposed to supergene alteration