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The solubility of gold and quartz in 0. 01, 0.10 and 1. 00 mol/kg NaCl solutions with various pH was determined in the presence of the NNO oxygen buffer at 300℃and 50 MPa using a flexible gold cell hydrothermal apparatus. The Au speciation in the SiO2-NaCl-H2O system was inferred and the equilibrium constants for the following dissolution reactions were obtained:Au + H2O = AuOH0 + 1/2H2, logK(AuOH0) = - 7.92± 0.25;Au + Cl + H2O = AuOHCl- + 1/2H2, logK(AuOHCr) = - 7.56 ±0.65.The present study suggests that Au as AuOH0 and AuOHCl- is basically transported in ore-forming solutions under geologically realistic conditions of acidity, chloride molality and oxygen fugacity. The reason for the common association of Au with SiO2 in hydrothermal gold deposits is discussed.
The solubility of gold and quartz in 0.01, 0.10 and 1. 00 mol / kg NaCl solutions with various pH was determined in the presence of the NNO oxygen buffer at 300 ° C and 50 MPa using a flexible gold cell hydrothermal apparatus. The Au Speciation in the SiO 2-NaCl-H 2 O system was inferred and the equilibrium constants for the following dissolution reactions were obtained: Au + H 2 O = AuOH 0 + 1 / 2H 2, log K (AuOH 0) = -7.92 ± 0.25; Au + Cl + H 2 O = AuOHCl - + 1 / 2H2, logK (AuOHCr) = - 7.56 ± 0.65. The present study suggests that Au as AuOH0 and AuOHCl- essentially consisting in ore-forming solutions under geologically realistic conditions of acidity, chloride molality and oxygen fugacity. The reason for the common association of Au with SiO2 in hydrothermal gold deposits is discussed.