Solubility of gold in oxidized, sulfur-bearing fluids at 500–850 °C and 200–230 MPa: A synthetic fluid inclusion study

Stability of AuCl2− from 25 to 1000 °C at Pressures to 5000 bar and Consequences for Hydrothermal Gold Mobilization

“…The ionic strength of experimental solutions was fixed at 1 M. In the present study, the data of [3] were corrected for ionic strength for the calculation of the thermodynamic value of Au solubility constant (Supplementary Material Section 2). Experimental Au solubility data reported by Ryabchikov and Orlova [7] (750 °С, 1500 bar, Supplementary Material Section 3.1), Guo et al [9] (800 °С, 2000 bar, Supplementary Material Section 3.2), and Zajacz et al [8] (1000 °С, 1500 bar, Supplementary Material Section 3.3) were Difference between Au solubilities calculated using Equation (5) and observed in the experiments vs. NaCl molality.…”

“…The ionic strength of experimental solutions was fixed at 1 M. In the present study, the data of [3] were corrected for ionic strength for the calculation of the thermodynamic value of Au solubility constant (Supplementary Material Section 2). Experimental Au solubility data reported by Ryabchikov and Orlova [7] (750 °С, 1500 bar, Supplementary Material Section 3.1), Guo et al [9] (800 °С, 2000 bar, Supplementary Material Section 3.2), and Zajacz et al [8] (1000 °С, 1500 bar, Supplementary Material Section 3.3) were The differences between the experimental and calculated Au solubility values (last two columns of Table 1) do not exceed 0.2 log units and are independent of NaCl concentration in the wide range of fluid salinities (from 0.1 to 3 mol·(kg H2O) −1 ), HCl concentrations, and redox conditions (Figure 3). This confirms the high accuracy of our method of the calculation of activity coefficients (in particular, the constant value of the ion size parameter o a = 4.5 Å), including the activity coefficient of H2°(aq), which was calculated ignoring the salting-out effect even in concentrated NaCl solutions.…”

“…The ionic strength of experimental solutions was fixed at 1 M. In the present study, the data of [3] were corrected for ionic strength for the calculation of the thermodynamic value of Au solubility constant (Supplementary Material Section 2). Experimental Au solubility data reported by Ryabchikov and Orlova [7] (750 • C, 1500 bar, Supplementary Material Section 3.1), Guo et al [9] (800 • C, 2000 bar, Supplementary Material Section 3.2), and Zajacz et al [8] [8] for sulfur-free NaCl-HCl-H 2 fluids were used in our calculations, because thermodynamic data for sulfur-bearing species are highly uncertain at the experimental T-P parameters. The Au solubility constant reported by Gammons and Willams-Jones [4] for 300 • C and P sat.…”

A new method to quantitatively control oxygen fugacity in externally heated pressure vessel experiments

“…For conducting such experiments, the method proposed here provides an alternative to experimentation in IHPV equipped with a Shaw membrane, a technique that is being applied only in a few laboratories worldwide (e.g., Schmidt et al, 1997;Scaillet and Evans, 1999;Gaillard et al, 2001;Botcharnikov et al, 2005;Klimm et al, 2012a;Pichavant et al, 2016). An additional application area where flexible f O 2 control is critically important is the investigation of the solubility of metals in silicate melts and magmatic fluids because these will always be f O 2 dependent as most dissolution reactions involve the oxidation of the metal (Bell et al, 2011;Brenan et al, 2016;Guo et al, 2018;Sullivan et al, 2018;Zajacz et al, 2010Zajacz et al, , 2011Zajacz et al, , 2012aZajacz et al, , 2013. Sulfur is a constituent of important ligands that form complexes with ore-forming metals, and it goes through a very sharp redox transition from S 2− to S 6+ oxidation state exactly in the characteristic f O 2 range of arc magmas (Jugo et al, 2005(Jugo et al, , 2010Klimm et al, 2012b;Richards, 2014).…”

“…The above equation is based on Fick's first law and on Sievert's law, which assume that diatomic molecules break down to atoms when they permeate through metals (Gupta, 2006;Sieverts, 1929). This latter assumption gives rise to the exponent of 0.5 on the f H 2 values in the formula instead of using an exponent of 1 as Fick's first law would require if hydrogen diffused in its molecular form.…”