The distribution of germanium in polymetallic sulphide assemblages: case studies from Kipushi and Tsumeb

Stewart, Caitlin Nesta
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Germanium (Ge) is considered a critical raw material within the EU and USA, as it is becoming more valuable and in demand as its technological uses increase. Ge is used to create solar panels, and is used in fibre optics, and infra-red optics. Two African deposits contain the highest known grades of Ge globally, Kipushi in the DRC and Tsumeb in Namibia. Both are Pb-Zn-Cu deposits that have been mined in the past. Both of these deposits are referred to as ‘Kipushi-type’ deposits; these are epigenetic, carbonate-hosted polymetallic pipe-like ore bodies. Most of the Ge in these deposits is hosted in the Ge-bearing sulphides, renierite and germanite; however, Ge has also been found to concentrate into some of the other sulphides. Past studies suggest that Ge concentrates into the sphalerite in various sulphide ore deposits, by substituting with the Zn, as these two elements have the same ionic radius and ionic charge. A Tescan Integrated Mineral Analyser (TIMA) was used to determine the distribution of the Ge within the Kipushi and Tsumeb deposits. Element maps show that the Ge is not concentrated in the sphalerite, but is rather concentrated in the galena and tennantite in both Kipushi and Tsumeb. This suggests that the Ge is substituting for Pb in the galena (Ge2+ ↔ Pb2+; Ge4+↔ Pb4+), as these two elements have the same ionic charge, but do not have the same ionic radius, this substitution is possible at high temperatures. The Ge has substituted for Cu in the tennantite (Ge2+↔ Cu2+) as these two elements have the same ionic radius and charge. Ge will concentrate into these mineral phases when the Ge-bearing sulphides are both present and absent in the sulphide assemblages. Knowing where the Ge is concentrated will assist in the best possible extraction of the element for the future mining of these deposits, making more Ge available to the electronics market
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science, 2020