Petrography and geochemistry of the Hotazel Formation on Mukulu 265, Kalahari Manganese Field, Northern Cape Province

Abstract: With the need for steel ever increasing, the Kalahari Manganese Deposit is a resource of great economic importance and as such, the need for accurate data and comprehensive studies on the manganese and iron ores are vital. The Mukulu 265 project area is positioned along the border of the high (Wessels-type) to low (Mamatwan-type) grade manganese ore and like the neighbouring N’chwaning and Wessels mines, is subject to: intrusions by diabase dykes; thrusting and subsequent overlapping of strata; normal faulting and associated Wessels event enrichment; and erosion along two separate unconformities, namely the Mapedi/Gamagara and the Kalahari unconformities. As a result of these structural evolutionary events, both the iron and the manganese ores vary in grade, mineralogy and texture from north to south and east to west. This variation is the result of contact metamorphism and associated igneousrelated hydrothermal fluids; supergene alteration along the Mapedi/Gamagara unconformity; and metasomatic alteration along the reactivated north-south striking normal faults. The latter is responsible for the systematic residual enrichment in manganese content and the increase in high-grade minerals in the manganese ore, as well as the subsequent leaching of carbonates and silicates that is witnessed in the northern section of Mukulu 265. Based on varying degrees of alteration from south to north on Mukulu 265, the banded iron formation, hematite lutite and manganese ores have been broadly categorised into three classes, namely least altered (LA), partially altered (PA) and highly altered (HA). The LA rock-types are considered to be closest to the primary rock-types found on Mukulu 265 and show relatively little alteration compared to the PA and HA samples. From the LA to the HA manganese ore samples, there is a clear increase in manganese oxides such as hausmannite, predominantly at the expense of carbonates such and kutnohorite and dolomite, particularly within the ovoids. Sampling and analysing the manganese ore by visually distinguishing common subzones, reveals a distinct pattern within the lower manganese ore beds of the selected boreholes that shows a lateral geochemical trend. This geochemical trend exhibits higher concentrations in manganese with lower concentrations in undesired elements such as iron within the lowercentral portion of the lower manganese ore bed. The geochemical pattern exhibited by the ore zones forms the basis by which the ore grade changes with depth and thus underpins its importance for selective mining processes. An interpretation of the ore genesis based on geochemical and mineralogical results for the lower manganese ore bed, suggests that the...M.Sc. (Geology