KOmatiite METamorphic devolatilization and METal mobilization (KOMET²): Implications for orogenic gold deposit formation

Orogenic gold deposits are extensively studied as they account for more than 25% of the global gold supply. These deposits are found along a crustal continuum, from granulite to prehnite-pumpellyite facies rocks. The metamorphic devolatilization of metasedimentary and metavolcanic rocks at the greenschist-amphibolite facies transition is widely acknowledged as the primary source of fluids and metals for orogenic gold deposits up to amphibolite facies. At temperature above 600°C, however, this model is challenged as fluids may induce partial melting of quartz-feldspath-bearing rocks, consuming the fluids and preventing formation of deposits. Recent modelling suggests that komatiite — a significant but overlooked lithological unit in Precambrian greenstone belts — may generate auriferous metamorphic fluids up to the granulite facies and contribute to orogenic gold deposit formation.

The aims of KOMET² are to: 1) test the metamorphic devolatilization model applied to komatiite and investigate auriferous fluid production, 2) evaluate the contribution of komatiite devolatilization to orogenic gold deposit formation.

To achieve these aims, we will investigate metakomatiites in the Southern Cross and Kalgoorlie auriferous greenstone belts in the Yilgarn craton in Western Australia. By combining the mineralogy, whole rock geochemistry and thermodynamic P-T-X models of granulite to greenschist facies metakomatiite, we will characterize the behavior of metals, metalloids and ligands (e.g., As, Au, C, Co, Cu, Mo, Ni, Pt, S, Sb, Sn, Te) during prograde metamorphism and determine if an auriferous metamorphic fluid is produced. Orogenic gold deposits will be investigated to determine the link between metakomatiite devolatilization and ore formation.