Manganese in South Africa: its mineral economics, geology and geometallurgy

Abstract Manganese (Mn) is a crucial metal for steelmaking and is increasingly being sought after for its use in the battery and clean-energy sectors. Through discovery of the Kalahari Manganese Field (KMF), the world’s largest land-based Mn resource, South Africa has positioned itself as a major player in the global Mn supply chain. However, only a fraction of this total Mn resource is currently being exploited, and opportunities for further exploitation in the KMF and at several other Mn deposits and occurrences throughout South Africa remain to be realised. To consolidate scientific and industrial interest in the entire South African Mn resource base, the present contribution provides a holistic overview of (1) global Mn mineral economics, (2) the processes that give rise to enrichment of Mn in crustal rocks, (3) the palaeoenvironmental implications of Mn enrichments, (4) the geology of domestic Mn deposits and occurrences, and (5) the geometallurgical and mineral processing paradigms applicable to full value realisation from these diverse ore types. South African Mn deposits are broadly subdivided into those formed from chemical sedimentary processes and subsequent diagenesis (e.g., the KMF, deep-sea Mn nodules and crusts); those formed as residual enrichments after chemical weathering of Mn-bearing protolith (e.g., North West Manganese Fields); and those formed through mobilisation by hydrothermal fluids and groundwater (e.g., vein and breccia-hosted deposits in fractured lithologies in the Cape Supergroup, Waterberg Group, etc.). Because of these differences in the mechanisms of Mn deposit formation, and because of the various valence and ligand bonding interactions associated with Mn, the resultant mineralogy of the individual deposit groups is widely varied. Primary chemical sediments typically comprise Mn2+ carbonates, braunite and occasionally Mn2+ silicates, which may be locally upgraded to Mn2+/3+ oxide minerals by subsequent hypogene enrichment. Low temperature deposits, including Mn nodules, groundwater-associated deposits, and residual accumulations are marked by Mn4+ mineral parageneses, which may subsequently be modified by regional metamorphism. Inasmuch as Mn grade is a primary variable governing economic Mn extraction, a growing body of geometallurgical work highlights that full value realisation will only be achieved through targeted exploitation of the Mn mineralogical diversity. This includes the realisation that Mn valence and ligand coordination impact the energy consumption and reagent utilisation during down-stream processing.