XAS evidence for the stability of polytellurides in hydrothermal fluids up to 599  C, 800 bar

Although the crustal abundance of tellurium (Te) is about half of that of gold (Au), several classes of Au deposits are highly enriched in Te. Our understanding of the nature of this Au-Te association is hampered by the lack of experimental studies of Te geochemistry at elevated temperature. We characterized the structure of polytelluride solutions from room temperature to 599ºC at 800 bar using in situ X-ray absorption spectroscopy. Both ab-initio XANES and EXAFS fits show that polytellurides are stable up to the highest temperature with planar structures (four-or threefold coordination of Te) giving way to linear chaines (e.g. Te2-ion) at temperatures above --200ºC. This is the first experimental confirmation of the thermal stability of polytelluride species. The data shows that polytellurides play an important role in Te transport in reduced S-rich or CO2-rich solutions and vapors.