2724 Geochemical and mineralogical characterisation and resource potential of the Namib Pb-Zn tailings (Erongo Region, Namibia)
DOI:
https://doi.org/10.17159/Abstract
In southern Africa, historic mining and mineral processing of base metal deposits have nearly exclusively focussed on the extraction of major metals, leading to the loss of remaining valuable raw materials into tailings dumps and waste rock piles. At the Namib Pb-Zn mine (Erongo Region, Namibia), historic base metal tailings deposits are present as unreclaimed, exposed waste piles. The tailings comprise silt- to sand-sized material and contain major concentrations of base metals (Pb av. 1.15 wt.%, Zn av. 3.20 wt.%), S (av. 9.95 wt.%), as well as lower values of other metals (Cu av. 490 µg/g, Cd av. 133 µg/g, Ag av. 22 µg/g), and critical elements like Sb (av. 14.7 µg/g) and In (14.3 µg/g). Former mineral processing targeted only the extraction of galena and sphalerite. As a consequence, the qualitative mineralogical composition of tailings is similar to that of the primary ore. Ca-Fe-Mg(-Mn) carbonates, quartz, micas, chlorite, minor graphite, magnetite, and rare parisite relate to the former host rock and gangue matrix, whereas Fe-rich sphalerite, galena, magnetite, pyrite with minor pyrrhotite, rare arsenopyrite, marcasite and cassiterite, and accessory scheelite are original constituents of the primary ore. Reprocessing of such a material would be challenging, but a mixed Pb-Zn concentrate enriched in Cd and Ag might be obtained. In future, possible reprocessing of Namib tailings and associated disposal of wastes into an appropriately designed repository would not only generate valuable metal commodities, but such activities would also eliminate a major metal pollution source from the local environment.
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