Germanium, indium, gallium and cadmium in zinc ores: a mineral system approach.

Abstract\nKEY POINTSSphalerite is the main Zn ore mineral and is the primary source of Cd, Ge and In, and a minor source of Ga. Owing to a shift from fossil fuel to renewable energy sources, these four minor elements have progressively become more important to the economy. Despite this, resources of Cd, Ga, Ge and In are rarely reported, as these metals are not considered material to the economics of resource development. As a result, the distribution of these elements between and within deposits is poorly known, and national and international resources are largely unreported. Following previous studies, we have compiled analytical data for Cd, Ga, Ge and In from sphalerite and used global and local ore geochemical datasets to assess geochemical controls on the concentration of these elements in Zn deposits. Our results are similar to those of previous studies and suggest that lower-temperature deposits are enriched in Ge, whereas higher-temperature deposits are enriched in In. However, modelling of hydrothermal geochemistry indicates other factors are important in concentrating these metals. In particular, the oxidation state of the fluid (oxidised <italic>vs</italic> reduced) and the depositional mechanisms also have a strong influence in Ga, Ge and In enrichment. Reduction of oxidised fluids is particularly effective in depositing Ge, whereas cooling very effectively deposits In and, in some cases, Ge. As a consequence, some higher-temperature deposits (<italic>e.g.</italic> high sulfidation epithermal and some volcanic-hosted massive sulfide) can be Ge-enriched, and some lower-temperature deposits (<italic>e.g.</italic> siliciclastic–carbonate shale-hosted deposits) can be enriched in In. Using the existing ore geochemical data and calculated characteristic Ge/Zn and In/Zn ratios, indicative estimates have been made on the endowment of Australian Zn deposits of Ge and In. These estimates highlight the potential of the North Australian Zinc Belt for Ge and for VHMS deposits for In. Although there is a large amount of uncertainty in the estimates, they are indicative of the potential for these metals in Australia.The efficacy of metal leaching from regional alteration zones depends on the temperature of alteration and the alteration minerals. For example, low-temperature (<200 °C) chlorite-rich zones tend to sequester zinc, whereas zinc is leached from higher-temperature, chlorite-rich zones.The concentrations of Ga, Ge and In in sphalerite and zinc ores depend not only on temperature but also on the redox state of the ore fluids and sphalerite depositional mechanisms.The endowment of Ge, In and other critical minerals in zinc deposits can be/has been estimated using typical (median) ratios of these elements to zinc for individual deposits or deposit types and zinc endowments of individual deposits. [ABSTRACT FROM AUTHOR]