Chlorine substitution in natural sphalerites

Abstract

Reports of chloride substitution in common natural sulphides are lacking but are predictably influenced by key variables in hydrothermal systems including T, pH, Eh aCl-, and aHS-. Materials scientists have long recognized that "II-VI compounds" (e.g. sphalerite) may accommodate halogens with charge balance maintained by cation deficiencies (e.g. Zn1- 0.5xS1-xClx). The majority of around 200 analyses of sphalerite from the Century Zinc mine (NW Queensland) reveal chlorine above electron microprobe detection limits with a maximum of ca 2200 ppm. The analyses support the Zn deficiency substitution although a small subset reveal a 1:1 (molar) correlation of Cl with the highest (Cu+Ag) implying an additional coupled substitution mechanism. Colloform sphalerite from the Galmoy mine (Ireland) has variable concentrations of Cl up to 6000 ppm in growth zones also displaying variations of Fe and Cd. The chlorine content of sphalerite may therefore provide a new tool to characterize the evolution of conditions in hydrothermal ore deposits.