Indium (In) is an element that has recently gained great economic importance due to its application in strategic energy and information technologies. Future In shortages projected by the EC Joint Research Council are due to insufficient exploration for In resources, reflecting the poor understanding of the hydrothermal ore-forming processes that result in economic enrichment of In. Key questions are the relative importance of different geologically relevant ligands for hydrothermal In complexation and the efficiency of different ore-deposition mechanisms for formation of economic deposits. Quantitative understanding of the solubility and transport of metals in hydrothermal fluids is central for process models of fluid-rock interaction and for predicting the formation of hydrothermal ore deposits. Predictive models based on experimental laboratory studies at elevated temperatures and pressures and numerical computer simulations are particularly powerful tools for understanding geochemical processes of hydrothermal ore-forming systems. Quantitative high-temperature data for the solubility and complexation of some ore metals such as Cu, Zn, Pb, Ag and Au have been obtained during the last two decades, but many important rare-metals (e.g. In, Ga, Ge, Sc, Rare Earth Elements, Nb, Ta) have not been experimentally studied and their behavior in hydrothermal systems can currently not be modeled. With the new solubility and spectroscopy experiments on fluoride and chloride complexes of indium generated by this project, we provide the relevant input data that make it possible to create predictive In distribution models in ore deposits. The strong differences in complexation behavior across the hydrothermal temperature range of 200-400 °C relevant for such systems explains the large variability of different In deposit styles. The new data will help secure economically feasible In supply in the future for high tech applications such as smart phone displays and solar panels.
