An investigation into the 87Sr/86Sr radiogenic isotope geochemistry of the manganese ore of the Kalahari Manganese Field with a view on hydrothermal fluid flow and related rare earth element enrichments

Abstract

Abstract The Paleoproterozoic Kalahari Manganese Field is the largest known land-based manganese (Mn) deposit on Earth and comprises five erosional relics of the iron- and manganese-rich Hotazel Formation. A total of 19 manganese ore samples from the lower manganese ore horizon of the Hotazel Formation were selected for analysis based on their relative metasomatic alteration states. These samples range from primary diagenetic, classic supergene enriched, hydrothermally enriched (Wessels-type ore) and thrusted manganese ore. When normalised to Post-Archaean Australian shale composites, rare earth elemental analyses on the selected samples indicate significant relative enrichments within the thrusted manganese ore, an ore type that hasn’t been studied from a geochemical point of view, so far. A comparison between these respective enrichments and 87Sr/86Sr ratios indicates a distinct link between REE enrichments and associated alteration events, and a progressive increase in 87Sr/86Sr isotope values. An isotopic relationship between fluid infiltration events and REE redistribution within the Hotazel Formation has been established, highlighting unique isotope signatures necessary in better defining and characterising metasomatism within the Paleoproterozoic Kalahari Manganese Field.