Gold(I) Complexation in Chloride Hydrothermal Fluids

A critical assessment and processing of experimental data published in the literature on the stability of hydroxide and chloride complexes of Au(I) was carried out. Based on the obtained Gibbs energies of AuOH(aq), AuCl(aq), and AuCl2-, the standard thermodynamic properties and parameters of the Helgeson-Kirkham-Flowers model equation of state were determined for these species. The resulting set of parameters makes it possible to calculate the solubility of Au in chloride fluids up to 1000 degrees C, 5000 bar with the possibility of extrapolation to higher PT parameters. As a geological application of the obtained data, a model calculation of the deposition of native gold by cooling chloride-sulfide fluid was carried out with an assessment of changes in the composition of the fluid, the sequence of formation of solid phases, and changes in the fineness of gold.