Other
Scientific paper
Sep 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011gecoa..75.5140z&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 75, Issue 18, p. 5140-5153.
Other
1
Scientific paper
This experimental study sheds light on the complexation of gold in reduced sulphur-bearing vapour, specifically, in H 2 O-H 2 S gas mixtures. The solubility of gold was determined in experiments at temperatures of 300, 350 and 365 °C and reached 2.2, 6.6 and 6.3 μg/kg, respectively. The density of the vapour varied from 0.02 to 0.22 g/cm 3 , the mole fraction of H 2 S varied from 0.03 to 0.96, and the pressure in the cell reached 263 bar. Statistically significant correlations of the amount of gold dissolved in the fluid with the fugacity of H 2 O and H 2 S permit the experimental data to be fitted to a solvation/hydration model. According to this model, the solubility of gold in H 2 O-H 2 S gas mixtures is controlled by the formation of sulphide or bisulphide species solvated by H 2 S or H 2 O molecules. Formation of gold sulphide species is favoured statistically over gold bisulphide species and thus the gold is interpreted to dissolve according to reactions of the form: Au(s) + ( n + 1 ) H S ( g ) = AuS · ( H S ) n ( g ) + H ( g ) Au(s) + H S ( g ) + m H O ( g ) = AuS · ( H O ) m ( g ) + H ( g ) Equilibrium constants for Reaction (A1) and the corresponding solvation numbers ( K A 1 and n ) were evaluated from the study of Zezin et al. (2007) . The equilibrium constants as well as the hydration numbers for Reaction (A2) ( K A 2 and m ) were adjusted simultaneously by a custom-designed optimization algorithm and were tested statistically. The resulting values of log K A 2 and m are -15.3 and 2.3 at 300 and 350 °C and -15.1 and 2.2 at 365 °C, respectively. Using the calculated stoichiometry and stability of Reactions (A1) and (A2) , it is now possible to quantitatively evaluate the contribution of reduced sulphur species to the transport of gold in aqueous vapour at temperatures up to 365 °C. This information will find application in modelling gold ore-forming processes in vapour-bearing magmatic hydrothermal systems, notably those of epithermal environments.
Migdisov Artashes A.
Williams-Jones Anthony E.
Zezin Denis Yu.
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