Abstract
Ph.D. (Geology)
The Paleoproterozoic Kalahari Manganese Field (KMF) is the largest known land-based manganese (Mn) deposit on Earth. Of the five erosional relics that the KMF comprises within the Hotazel Formation, the Kalahari Manganese Deposit (KMD) is the largest. The Mn ores within the KMD are hosted in three beds that alternate with banded iron-formation (BIF) and hematite lutite. The low-grade ore (<38 wt% Mn), is mostly quartz-free and carbonate-rich, whereas the high-grade ore (>44 wt% Mn), is a carbonate-free, Mn oxide-rich ore.
The drill cores analysed incorporate the Nchwaning (I, II and III), Belgravia and Gloria mines, as well as the Black Rock outcrop. This study provides a correlation of petrographical, mineralogical and geochemical data, in order to characterise and interpret the protolith, low-grade and high-grade ores of both the upper and lower Mn ore bodies. The source, transport, deposition, diagenesis, metamorphism, as well as hydrothermal alteration of the Mn ores have been addressed. The spatial distribution of the mineral assemblages, the mechanism of Mn enrichment, fluid characteristics and fluid-rock interactions, as well as the influence of epigenetic alteration processes and the erosional unconformity on the quality of the ore has been discussed. The fluid-rock interaction leads to the presence of boron (B), which is considered highly detrimental to the steel quality. Thus, the spatial distribution, location and the source of the B, as well as ways of dealing with its presence has been addressed. A regional model for the alteration of the Mn ores, based on the above results, has been produced.
Five distinct drill core groups, based on mineralogical associations, textural features and geochemical characteristics were distinguished. The diagenetic textural features are comprised of carbonate minerals, and generally preserved within the lower grade ores. The higher grade ores show replacement of the carbonates with oxides and ‘secondary’ carbonate minerals, whilst the highest grade ore is almost completely devoid of the textural features. The upper ore bodies display higher Fe and Si contents, whereas the lower ore bodies show enrichment in Mn and Ca. This suggests pervasive and incipient oxidation, as well as carbonate leaching from the upper to the lower bed. An increase in grade is characterised by enrichment in Mn, Fe, Cu, Pb, Zn, Ni and Co, and depletion in Ca, Mg and Si. The high-grade ores are enriched in Ba, Sr, Li and B, with the upper ore beds generally exhibiting higher abundances of these elements relative to the lower ore bodies.
Boron is mineralogically controlled and hosted by braunite, braunite-II, gaudefroyite, tephroite and the carbonate- and serpentine-group minerals. The trace elements were redistributed and locally concentrated