Mn Types
Manganese ores occur in four main types in southern Africa.
(1) Primary (e.g. Mamatwan carbonates)
(2) Hydrothermally altered (e.g. Wessels)
(3) Supergene enriched (e.g. oxide ores at Mamatwan)
(4) Karstic (e.g. Postmasburg)
Mamatwan-type ore is by far the most extensive. Mineralogically it is dominated by kutnahorite and braunite.
Wessels-type ore is a higher grade ore produced by hydrothermal alteration, but is now largely mined out. Most common minerals are hausmannite and bixbyite.
Supergene enriched sections occur commonly with Mn carbonate ores, which is the case iwth the Mamatwan deposits. Here common minerals are manganomelane and todorokite.
Karst-type Mn develops by weathering of Mn-bearing dolomites. Because of low oxygen levels in the early part of the Precambrian, Mn was abundant in seawater and dolomites of that age have high Mn levels. Green-schist level metamporphism has produced partridgeite, braunite, and bixbyite from poorly crystaline protores.