Introduction
A core drilled near Wolhaarkop in Griqualand West, South Africa intersected a highly oxidized Kuruman Iron Formation below red beds of the Gamagara Formation. The lateral equivalents of the Kuruman Iron Formation in this drill hole consist largely of siderite, ankerite, magnetite, greenalite and quartz. The Oxidation of the Kuruman Iron Formation in the borehole occurred almost certainly during weathering episode bracketed between about 2.2 Ma by the age of the Ongeluk lavas in the Transvaal sequence below the unconformity and by the age of Hartley lavas in the Olifantshoek Group above the unconformity.
Location
The manganese project is situated in the Northern Cape Province in South Africa, approximately 40 kilometres north-west of the town of Kuruman. Located at latitude 27°13'30.081"S and longitude 23°5'58.241"E, the site is accessed via the national N14 route between Johannesburg and Kuruman, and the provincial R31 road.
History
In 1940, various large mining companies acquired a manganese ore outcrop on a small hillock known as Black Rock. Several large properties underlain by ore were subsequently found and acquired. Today the Black Rock area is considered to be the largest and richest manganese deposit in the world. Manganese ore operations were extended and today include the eastern belt of the basin where the operations in discussion are found. Manganese ore is supplied locally owned smelters, but is mainly exported through Port Elizabeth to Japanese, Chinese and German and Indian customers.
Geology
The manganese ores of the Kalahari Manganese field are contained within sediments of the Hotazel Formation of the Griqualand West Sequence, a subdivision of the Proterozoic Transvaal Supergroup. The eastern part of the basin is known as the Hotazel Formation and the Langdon Formation, the average thickness of the Hotazel Formation is approximately 40 metres.
The manganese ore-bodies exhibit a complex mineralogy and more than 200 mineral species have been identified to date. The hydrothermal upgrading has resulted in a zoning of the ore-body with regard to fault positions. Distal areas exhibit more original and low-grade kutnohorite and braunite assemblages, while areas immediately adjacent to faults exhibit a very high-grade hausmannite ore. The intermediate areas exhibit a very complex mineralogy, which includes bixbyite, braunite and jacobsite amongst a host of other manganese-bearing minerals. A similar type of zoning also exists in the vertical sense. At the top and bottom contacts it is common to have high iron (Fe) and low manganese (Mn) contents while the reverse is true towards the centre of the seam. This vertical zoning has given rise to a mining practice where only the centre 3,5-metre high portion of the seam is being mined.
Two manganese seams are present. The No 1 seam is up to 6 metres in thickness, of which 3, 5 metres are studied. There is, therefore, minimum dilution. No mining is presently undertaken on No 2 seam.
