Hyperspectral cathodoluminescence study of indium-bearing sphalerite from the Mt Carlton high-sulphidation epithermal deposit, Queensland, Australia

Abstract

Sphalerite is the most important host mineral for the recovery of indium. New techniques to study the presence and distribution of this critical metal in sphalerite can therefore be of interest for scientific and technological purposes alike. In this study we use the emerging tool of hyperspectral cathodoluminescence (CL) mapping, combined with X-ray element mapping and spot analyses, to characterise the composition and CL properties of indium-bearing sphalerite from the Mt Carlton high-sulphidation epithermal deposit (NE Queensland, Australia). Mt Carlton sphalerite contains highly elevated concentrations of indium (up to 19.57 wt%) occurring within ∼1 μm thick colloform bands, which show an average composition of (Zn_0.63Cu_0.20In_0.15Ga_0.01)S_0.96. Indium, Cu and Ga are interpreted to have been incorporated via the coupled substitution 2Zn²⁺↔Cu⁺+(In,Ga)³⁺. Hyperspectral CL mapping reveals a high-intensity CL emission directly related to In–Cu–(Ga)-rich sphalerite, centred at wavelengths between ∼500 and ∼600 nm. The CL peak is shifted to the higher-wavelength positions when the proportion of In relative to Cu increases. Our study shows that hyperspectral CL mapping is a powerful and efficient technique to study the distribution of In in sphalerite.