Speciation of aqueous tellurium(IV) in hydrothermal solutions and vapors, and the role of oxidized tellurium species in Te transport and gold deposition

Thermodynamic calculations show that slightly basic, mildly reduced fluids that can transport Au efficiently as Au(HS)2- can also carry significant Te (e.g., ∼100 ppb at 300 °C). The calculations also suggest that under magmatic hydrothermal conditions, large amounts of Te can be transported as Te(IV) complexes in oxidized fluids (coexisting with SO2(g)). Reduction of Te(IV) caused by processes such as fluid-rock interaction or fluid mixing will lead to a dramatic decrease in the solubilities of both Te and Au, and to the precipitation of telluride minerals.