Fluid transport and reaction during disseminated mineralization in orogenic gold systems

Disseminated mineralization is responsible for much of the production from orogenic gold deposits, and deciphering the nature of reactive fluid flow across the macro- to microscopic scale is crucial for understanding the mineralization processes. We integrated structural analysis, microstructural observations, whole-rock geochemistry, and thermodynamic modeling at the Liba orogenic gold deposit in the West Qinling orogen, central China, aiming to unravel the behavior of fluid in slate-hosted disseminated mineralization. The presence of deformed slaty foliation and hydrothermal sericite S-C fabrics indicates that the east-west−striking orebodies are hosted within sinistral brittle-ductile shear zones, which act as deposit-scale fluid migration conduits. The spatial distribution of pyrite within the mineralized slates closely aligns with pore networks and grain boundaries, suggesting that grain-scale enhanced permeability and fluid flow during mineralization were primarily accommodated by microcracking along grain boundaries. Combined with whole-rock geochemical data and thermodynamic modeling, we reveal that under conditions where rock permeability is sufficient for fluid transport, gold mineralization efficiency depends on the degree of reaction between the reactive fluid and Fe-bearing minerals. Compared to siliceous slate, the higher abundance of Fe-bearing minerals in argillaceous slate enhances reactivity at the fluid-mineral interface, promoting sulfide formation and gold precipitation. This study demonstrates that the physicochemical interplay between structural deformation and geochemical reactivity fundamentally controls disseminated mineralization in slate-hosted orogenic gold systems.