Characterisation of manganese occurrences in the Kalahari Manganese Field: Constraints from high-resolution 2D seismic surveys

Manganese is an important industrial metal and has a variety of applications in the steel manufacturing, industrial and biological sectors. Most manganese deposits are sedimentary in origin and the sedimentary type comprise more than 95% of high-grade world-class manganese deposits. The Palaeoproterozoic Kalahari Manganese Field in South Africa is composed of sedimentary-hosted manganese interbedded with banded iron formation and is host to the world’s largest known land-based manganese resources. High-resolution 2D reflection seismic surveys were conducted to characterise the subsurface geology of the Kalahari Manganese Field in the Severn area to delineate the manganese mineralisation and associated structures in the northern section of the Kalahari Manganese Field. The contacts between the various lithologies of the: (1) Ventersdorp and Transvaal supergroups, (2) Campbellrand and Schmidtsdrif subgroups and Koegas and Asbestos Hills subgroups, (3) Ghaap and Postmasburg groups, (4) the Makganyene and Ongeluk formations, (5) Ongeluk and Hotazel formations, (6) Hotazel and Mooidraai formations, (7) Transvaal and Keis supergroups (the pre-Gamagara unconformity), (8) Keis and Karoo supergroups, and (9) Karoo Supergroup and Kalahari Group has been imaged. The results indicate that the manganese mineralisation occurs at a depth of ~1.5 km, with the thickness of the Hotazel Formation on the seismic profiles being approximately 150 m. Several structures are observed on the seismic sections and strike north-south, northeast-southwest and northwest-southeast. The north-south striking structures are interpreted as dolerite dykes as they exhibit high seismic amplitude attenuation. Determining the location of dykes beneath the surface is important for exploration drilling and production in mining. The northeast-southwest and northwest-southeast striking structures are interpreted as reactivated normal faults and shallow dipping listric thrust faults that “stacked” or “duplicated” the lithologies. The reactivated normal faults served as pathways for mineral-rich fluid migration. The northeast-southwest and northwest-southeast striking structures are significant as these structures are associated with structurally-controlled manganese mineralisation. The pre-Gamagara and Kalahari unconformities also have supergene ore enrichment events associated with them. Reflection seismics is effective in mapping the subsurface geology and structures within the Kalahari Manganese Field.