Petrographical, mineralogical and geochemical characterisation of the leinster deposit, Kalahari manganese field, South Africa

Abstract: The world-renowned Paleoproterozoic Kalahari Manganese Field (KMF) is host to the world’s largest land-based manganese (Mn) deposit. The KMF is hosted within the Hotazel Formation, which comprises three chemosedimentary manganese ore beds interbedded with four superiortype iron formation beds. The Leinster Deposit is one of five erosional relics of the Hotazel Formation, and the northernmost deposit of the KMF. As a relatively small deposit, comprising low manganese grades, little research has been conducted on the Leinster Deposit compared to the remaining four deposits that lie to the south of this deposit. This study provides a detailed geological investigation of the Leinster Deposit, from which samples were taken from five drill cores that were provided by Anglo American. The nature of the deposit, as well as post-depositional alteration has also been addressed. The samples were petrographically, mineralogically and geochemically characterised into one of four groups, namely: (1) high-grade Banded Iron Formation, (2) BIF, (3) Mn ore and (4) mafic intrusions. The high-grade BIF group exhibits the highest Fe2O3 content, linked to the highest abundance of magnetite. This group also shows clear evidence for fluid alteration, which has resulted in the development of secondary gangue phases, as well as the minor sulphide precipitation (both pyrite and chalcopyrite). Despite being in close proximity to several igneous intrusions within the area, mineralogical constraints within the high-grade BIF group indicate that this group did not experience temperatures exceeding 700oC. The Fe content (44 to 54 wt%), combined with the SiO2 content (up to 34 wt%), restricts these samples from being classified as iron ore, but rather represent slightly upgraded BIFs. Hydrothermal leaching of Si (from an alkaline fluid) resulted in moderate residual enrichment of iron and Rare Earth Elements (REE). Rare Earth Elements and Yttrium (REY) patterns show a high level of similarity to previously reported BIF samples from the Main Kalahari Manganese Deposit (MKMD), which include being Heavy Rare Earth Element (HREE) enriched, show positive Y and La anomalies, as well as having absent Ce anomalies. Together, these REY trends are indicative of a marine environment with a high temperature hydrothermal component. Of importance, is the consistent positive Eu anomaly that present in the samples from this study but is typically absent in Hotazel BIFs...M.Sc. (Geology