The Kalahari manganese field: an enigmatic association of iron and manganese.

Proposed models of the giant Mn deposits in the Transvaal cover a diverse spectrum of genetic processes, from large-scale epigenetic replacement mechanisms and submarine volcanogenic-exhalative activity to purely chemical sedimentation whereby the influence of volcanism is of reduced significance. Discussion is presented of the potential metallogenic importance of glacial processes which occurred prior to the development of the Kalahari deposits, as manifested by the occurrence of an older diamictite unit. The snow-ball earth scenario proposed for Neoproterozoic Fe-Mn formations may provide an attractive explanation for the required levels of dissolved Mn in the anoxic parts of the Kalahari deposits. Factors which have yet to be addressed, however, are the primary source of Mn, the processes leading to the characteristic cyclic development of iron formation and Mn sediment, and the likely influence of a postulated sudden oxygenation during the deposition of the ores.
Proposed models of the giant Mn deposits in the Transvaal cover a diverse spectrum of genetic processes, from large-scale epigenetic replacement mechanisms and submarine volcanogenic-exhalative activity to purely chemical sedimentation whereby the influence of volcanism is of reduced significance. Discussion is presented of the potential metallogenic importance of glacial processes which occurred prior to the development of the Kalahari deposits, as manifested by the occurrence of an older diamictite unit. The snow-ball earth scenario proposed for Neoproterozoic Fe-Mn formations may provide an attractive explanation for the required levels of dissolved Mn in the anoxic parts of the Kalahari deposits. Factors which have yet to be addressed, however, are the primary source of Mn, the processes leading to the characteristic cyclic development of iron formation and Mn sediment, and the likely influence of a postulated sudden oxygenation during the deposition of the ores.