Abstract
Gold is present only in trace amounts in normal rock but is concentrated in large gold deposits after hydrothermal leaching from the parent rock, followed by localized precipitation when the pressure and temperature are reduced. Kerrich (page 2101) shows how laboratory results by Loucks and Mavrogenes (page 2159) shed light on the aqueous gold complex that acts as the gold shuttle. This complex is only stable within a clearly defined window of pressure and temperature, explaining why most gold deposits form within a specific window of hydrothermal conditions.