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 mi- croscopic scale is crucial for understanding the mineralization processes. We integrated structural analysis, microstructural observa- tions, whole-rock geochemistry, and thermo- dynamic 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 mineral- ization. The presence of deformed slaty fo- liation and hydrothermal sericite S-C fabrics indicates that the east-west–striking orebod- ies 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 bound- aries, suggesting that grain-scale enhanced permeability and fluid flow during miner- alization 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 mineraliza- tion efficiency depends on the degree of reac- tion between the reactive fluid and Fe-bear- ing 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 in- terplay between structural deformation and geochemical reactivity fundamentally con- trols disseminated mineralization in slate- hosted orogenic gold systems.