Experimental determination of the stabilities of Au2S(cr) at 25°C and at 25–250°C

A spectrophotometric study of aqueous Au(III) halide–hydroxide complexes at 25–80°C

“…Au(I) has a 5d 10 electronic configuration and in aqueous solution prefers linear complexes with two unidentate ligands; chloride and bisulfide Au(I) complexes account for Au transport in most hydrothermal fluids (e.g., Huheey et al, 1993;Seward, 2003a, 2004;Tagirov et al, 2005Tagirov et al, , 2006. [AuCl 2 ] À disproportionates at low chloride concentrations, especially at low temperatures (e.g., 10 À4 m at 25°C and increasing with increasing temperature; Gammons et al, 1997).…”

“…[Au(HS) 2 ] À is the best known Au(I) bisulfide complex (e.g., Tagirov et al, 2006), and this complex is likely to account of Au transport in many hydrothermal fluids and in reduced sulfur-bearing groundwaters. Other ligands can be important for mobilizing and transporting gold, in particular nitrogen and other sulfur-bearing ones, e.g., cyanide, thiocyanide, amines/ammines, thiosulfate and polythionate intermediates (e.g., Gray, 1998;Aylmore and Muir, 2001;Druschel et al, 2003), thiourea (e.g., Zhang et al, 2004) and thiocyanate (e.g., Broadhurst and du Preez, 1993;Kholmogorov et al, 2002).…”

Gold Behavior in Supergene Profiles Under Changing Redox Conditions: The Example of the Las Cruces Deposit, Iberian Pyrite Belt

“…Au 1+ -thiosulfates are highly stable in neutral and slightly reducing conditions, as well as in the presence of carbonates (Webster and Mann, 1984;Renders and Seward, 1989;Benedetti and Bouleguè, 1991;Gray et al, 1992;Freyssinet et al, 2005;Tagirov et al, 2006). The pH-Eh condition suggested by the precipitation of siderite and calcite at this stage in the Las Cruces gossan enhances the stability of precious metal thiosulfate complexes (Yesares et al, 2014(Yesares et al, , 2015.…”

“…This mineral paragenesis (siderite ± galena within the gossan, and cinnabar + Ag-sulfosalts within fault breccias in the cementation zone) involves a reducing solution and (bio)sulfur reduction, which constrains the role of thiosulfate complexes as the only mobilization mechanism throughout the supergene profile. In zones where solutions were more reducing, thiosulfate complexes could have been reduced to bisulfide complexes due to their high solubility under low oxygen fugacity and near neutral conditions, as well as in equilibrium with pyrite (Stroffegen, 1986;Webster, 1986;Huston and Large, 1989;Renders and Seward, 1989;Vlassopoulos and Wood 1990;Benedetti and Boulegue, 1991;Gray et al, 1992;Tagirov et al, 2006). Furthermore, late-vertical fault systems acted as high permeability conduits driving the Au-Ag-enriched basinal fluids, with precious metals thiosulfate and/or bisulfide complexes as stable compounds in solution, until reaching the cementation zone (Fig.…”

“…Secondary Au ores occur mainly as a result of dissolution and redistribution of Au during the weathering of primary sulfides. Supergene Au mobility occurs via complexation with organic-, halide-, hydroxide-, halide-hydroxide and sulfur ligands, which are dependent on weathering conditions (Boyle et al, 1975;Mann, 1984;Webster, 1986, Groen et al, 1990Benedetti and Bouleguè, 1991;Freyssinet et al, 2005;Tagirov et al, 2006;Usher et al, 2009;Ta et al, 2014). In addition, biological activity can contribute to dissolution-precipitation processes of Au during weathering in the near-surface environment (Reith et al, , 2007Southam et al, 2005Southam et al, , 2009Hough et al, 2008;Fairbrother et al, 2012).…”