The gold sulfate, AuSO4, is a very common and useful precipitate. It is used in the production of Au(II) sulfide and for the extraction of gold from cyanide leachates. It is also used in the purification of gold and in some alloys, including amalgam. The gold sulfate is easily soluble in most acids and is dissolved readily by solutions of cyanide. It is also soluble in iodic acid, but this action is much slower than that of aqua regia. It is soluble in the thiosulphites of calcium, sodium and potassium. It is also soluble in some alkaline sulphides and the thiocyanates of copper, nickel and zinc. Gold is soluble in solution of the cyanides of the simple cyanides, such as sulphocyanides and ferrocyanides, but the action is slow unless the aqueous solutions are heated.

The long-held paradigm that only hydrogen sulfide and chloride act as ligands to mobilise and concentrate gold by fluids across the lithosphere, has been challenged by recent in situ X-ray absorption spectroscopy, solubility measurements and molecular dynamics and thermodynamic calculations (1-4, 9-13). The results show that the trisulfur ion S-3S3- forms stable, soluble complexes with Au+ at elevated temperatures and pressures in fluids derived from magmatic hydrothermal sources (1-5, 13-16).

These new data show that, above 300 degC, H2S-SO2-rich fluids containing the trisulfur ion are capable of extracting and transporting gold from magmas and rocks to sites of ore deposit in shallow orogenic and epithermal Cu-Au-Mo and Carlin gold deposits. This capacity is enhanced by the ability of S-3S3- to concentrate gold at hot stages of metamorphism, particularly in the amphibolite facies (17-19).