Observations on the geochemistry of indium

Abstract

Spectrographic observations are recorded on the occurrence of indium in sulphide minerals, largely of Australian origin, with a view to determining 1. (a) how traces of indium have been partitioned between primary sulphides; 2. (b) the influence of temperature etc. in partition equilibria; 3. (c) the subsequent behaviour of indium in unmixing processes and secondary mineral formation. Comparison of minerals from the same sources shows indium to be absent or low in primary iron sulphides, chalcopyrites etc., but preferentially incorporated in blende and, in lesser degree, galena. In minerals of thio-salt type, indium may be highly enriched in enargite and stannite, but virtually absent from tetrahedrite. In any one mineral field, indium is present in higher concentration in blendes or galenas deposited at higher temperatures. Except for galena, minerals preferentially incorporating indium as sulphides are based on tetrahedral coordination. The selectivity exhibited, and the fate of indium in ex-solution processes, are considered in the light of the structure of indium sulphide and the constitution of quasi-metallic sulphides. The association of indium with tin in cassiterites from Tasmania and New South Wales is considered. Recorded concentrations give some evidence of geochemical zoning.