Role of CO₂ in the formation of gold deposits

G. N. Phillips & K. A. Evans
NATURE, VOL 429, 24 JUNE 2004, P. 860-863

Much of global gold production has come from deposits with uneconomic concentrations of base metals, such as copper, lead and zinc. These gold-only deposits are thought to have formed from hot, aqueous fluids rich in carbon dioxide, but only minor significance has been attached to the role of the CO₂ in the process of gold transport. This is because chemical bonding between gold ions and CO₂ species is not strong, and so it is unlikely that CO₂ has a direct role in gold transport. An alternative indirect role for CO₂ as a weak acid that buffers pH has also appeared unlikely, because previously inferred pH values for such gold-bearing fluids are variable. Here we show that such calculated pH values are unlikely to record conditions of gold transport, and propose that CO₂ may play a critical role during gold transport by buffering the fluid in a pH range where elevated gold concentration can be maintained by complexation with reduced sulphur. Our conclusions, which are supported by geochemical modelling, may provide a platform for new gold exploration methods.

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Role of CO2 in the formation of gold deposits

Role of CO₂ in the formation of gold deposits