The Au|SiO-2 and Sn|SiO-2 complexes have been experimentally calibrated at varying temperature, silica concentration and pH: Au+++H-3SiO+--4AuH-3SiO-4lgK=-1.65436+9611.21/T Sn+{4+}+4H-3SiO+--4Sn(H-3SiO-4)-4lgK-{200℃}=42.73Compared with Au|Cl, Au|HS and Sn|OH complexes, AuH-3SiO-4 and Sn(H-3SiO-4)-4 complexes can be recognized as the dominant transport forms in Si|bearing solutions under pH and Eh conditions of general interest. The decrease of SiO-2 concentration and oxygen fugacity would reverse the direction of dissolution|complexing reactions, resulting in the precipitation of gold and silica, as well as cassiterite and silica. This study illustrates the significance of SiO-2|complexation in hydrothermal solutions for gold, tin and other metallizations.
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