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

• Applicant: Dr. Simon Hector
• Subject Area: Mineralogy, Petrology and Geochemistry ; Geology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555064577

Orogenic gold deposits are extensively studied as they represent over 25% of the world's gold supply. These deposits can be found in a range of geological settings, from very high to low-grade metamorphic rocks, but they usually form between 1-3 kbar and 250-475°C, primarily in greenschist to lower amphibolite facies rocks. During metamorphism, the mineralogy of the rocks evolves to accommodate the increasing pressure and temperature conditions. The breakdown of hydrated minerals into new stable minerals releases metamorphic fluids that can leach metals from the rock. It is widely acknowledged that orogenic gold deposits form due to the release of fluids and metals from metasedimentary and metavolcanic rocks at the transition from greenschist to amphibolite facies. However, there is a puzzle concerning the formation of orogenic gold deposits at higher temperatures (500-700°C), known as hypozonal deposits, particularly in amphibolite to granulite facies rocks. Indeed, at temperatures above 600°C, fluids generated in a quartz-feldspar-bearing rock may trigger its partial melting, consuming the fluids and preventing the formation of ore deposits. Recent research suggests that the metamorphic devolatilizaton of komatiite, an ultramafic rock typical of the Archean period, could release significant amounts of gold-rich fluids even at temperatures as high as 800°C without causing partial melting. Such fluids could account for the formation of hypozonal orogenic gold deposits and fit with their frequent association with komatiites in Archean greenstone belts. However, this model needs to be tested. The aims of the KOMET² project are: 1) to test whether the metamorphic devolatilization of komatiite produces gold-rich fluids; 2) to evaluate the contribution of komatiite devolatilization to orogenic gold deposit formation. To achieve these goals, we have identified an ideal study area in the Southern Cross and Kalgoorlie greenstone belts in Western Australia. These areas host greenschist to granulite facies komatiite and numerous orogenic gold deposits, including the hypozonal type. By studying the mineralogy, geochemistry, and metamorphic history of komatiite, combined with thermodynamic modeling, 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. Furthermore, a detailed petrographic and isotopic study of the Marvel Loch deposit in the Southern Cross area, along with in-situ geochemistry and dating of hydrothermal minerals, will allow us to determine the link between komatiite devolatilization and hypozonal orogenic gold deposit formation.

• DFG Programme: Research Grants
• International Connection: Austria, Switzerland
• Co-Investigators: Dr. Antonin Bilau; Professor Dr. Jochen Kolb; Alexandre Peillod, Ph.D.
• Cooperation Partners: Privatdozent Dr. Massimo Chiaradia; Dr. Clifford Patten