Chemical controls on gold transport and deposition in orogenic lode-gold systems

Orogenic gold ore deposits are important indicators of crustal-scale hydrothermal fluid flow during the evolution of metamorphic belts and account for about 25% of the global gold production. They are structurally related to major transcrustal shear zones and form through advection of large volumes of low-salinity aqueous-carbonic geofluids. Despite considerable research, several key questions in the formation of orogenic gold deposits are still not resolved, such as the composition and source of the ore fluids, the relative role of different gold precipitation mechanisms, and the contribution of magmatic fluids to the hydrothermal systems. The project will address the chemical controls on formation of orogenic gold deposits through an integrated approach that links well-designed field-based research in the Ilomantsi greenstone belt (E Finland) with numerical geochemical modeling. The field-based studies will constrain the stable isotope signature of fluid tracers (B, S) that could discriminate magmatic and metamorphic fluid sources, and determine the composition of gold ore fluids (main cations, ore metals, ligands) using LA-ICPMS microanalysis of fluid inclusions. New thermodynamic models for gold solubility in aqueous-carbonic fluids will be developed and verified based on the field data, resulting in more realistic and predictive numerical simulations of key processes that control fluid production, gold transport and deposition in crustal-scale hydrothermal systems. The project involves international collaborations with leading research institutions in light stable isotope geochemistry (GFZ Potsdam, SUERC Glasgow) and fluid inclusion studies (ETH Zürich).