Kevin L. Brown, 1989. "Kinetics of Gold Precipitation from Experimental Hydrothermal Sulfide Solutions", The Geology of Gold Deposits: The Perspective in 1988, Reid R. Keays, W. R. H. Ramsay, David I. Groves
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The rate of change in the solubility of gold and, in one case, silver has been measured as a function of changes in fo2, fH2, pH, and pressure. The experiments were carried out in a quartz-lined, stirred autoclave containing an aqueous H2S-HS− solution. Acidification of the solution causes a rapid decrease in gold solubility, an increase in fo2 and depressurization cause a slower decrease, and an increase in fH2 gives the slowest decrease in gold solubility. Increases in fo2 as well as depressurization give initial increases in gold solubility. A large depressurization causes a net increase in silver solubility. The interpretation is that loss of the HS" ligand is the main kinetic control on gold concentrations. The implications for ore deposition from geothermal fluid are that boiling, mixing with acid sulfate fluid, and mixing with oxygenated meteoric water could all be mechanisms for gold deposition. Acidification of silver and aqueous sulfide solutions results in rapid deposition of silver.