Between defects and inclusions: the fate of tellurium in pyrite

Abstract Tellurium (Te) is a critical commodity, essential for renewable energies and high-tech applications. Most Te is currently recovered from copper smelters, but rising demand requires sourcing from alternative supplies. However, the mineralogy of Te-rich ores is poorly understood and hinders their economic potential. Here, we investigate the distribution of Te in pyrite from a high-grade Au-Ag-Te epithermal-type ore to inform metallurgical extraction methods, and secure future Te supply. We identified three distinct modes of Te incorporation in this pyrite, which challenge previous solubility models. (1) Te solid-solution, at concentrations (up to 285 ppma) that significantly exceed previous solubility limits. (2) Nano-telluride inclusions along cracks that formed by intra-grain remobilization. (3) Crystal defects, enriched in Te through pipe diffusion hosting up to 0.5 at.% Te. Our results therefore provide new fundamental insights into the chemical and structural coordination of Te in pyrite, which may guide future efforts for its direct recovery.