A Re-Examination of the Solubility of Indium in Hydrothermally Synthesized Galena and Sphalerite

Abstract Galena and sphalerite were synthesized in hydrothermal pressure vessels with In114m as a tracer in order to establish In solubility over a range of temperatures of geological interest. Previous experimental results were re-examined in the light of knowledge of the effects of Cu, Ag, and Fe in In-containing galena and sphalerite systems, improved analytical technique, and with recognition of problems with some experimental runs. The solubility of In in galena was determined as 16.85 ppm at 350 °C, 25.3 ppm at 400 °C, 40.12 ppm at 450 °C, and 98.18 ppm at 500 °C. The solubility at 550 °C as ≥ 72 ppm. Solubility of In in sphalerite was determined to be ≥32.68 ppm at 500 °C and 86.60 ppm at 550 °C by radiometric measurements. Luminescence measurements determined solubilities of 22 ppm at 500 °C and 72 ppm at 550 °C. A survey of the In-contents of galena and sphalerite in ore deposits is based on data from LA-ICP-MS analyses. The results for galena are higher than the range of In-contents in natural galena, possibly due to partitioning of indium to coexisting sphalerite and chalcopyrite. The low In-contents in sphalerite determined at relatively high temperatures are in marked disagreement with high In-contents in natural sphalerite. The coupled substitution In + Cu ⇌ 2Zn in sphalerite, and other coupled substitutions, is the likely explanation for this difference.