Carbon dioxide as a proxy for orogenic gold source

Despite many decades of study, the genesis of orogenic gold deposits remains in debate. One aspect of this debate concerns the origin of the mineralising fluids. Two important constraints are that the fluids are sulphur and CO₂ bearing and that high fluid fluxes are maintained in a spatially localised environment for a relatively short period of time whereas crustal metamorphism/decarbonation operates over many millions of years, the source is not localised and is of regional extent. In this paper we explore the devolatilization of a subducting slab material using coupled petrological thermo-mechanical numerical approach that takes into account dehydration and decarbonation processes. Recent phase equilibria calculations show that decarbonisation of the slab requires much higher temperatures that normally occurs within subduction zones and the devolatilization site in the slab is spatially and temporally localised during slab roll-back or within a hot orogen when the slab material is incorporated into the overriding plate. We also investigate the plausibility of large gold sources in the collisional and back-arc environments.