Geochemical process of arsenic source and fate in water environment of karst gold mining region, Southwestern China

This study investigated the hydrogeochemical characteristics, sources, distribution and rapid release mechanisms of potentially toxic elements (PTEs) in a typical Carlin-type gold mining area, characterised by intense hydrological cycles in a karst region. A total of 65 samples, including mine water, groundwater, surface water, and rainwater, were analyzed for hydrochemistry, trace elements, and stable isotopes. Results show that multi-scale hydraulic pathways accelerate the vertical transport of oxygen and water, promoting the oxidative dissolution of gold-bearing sulfides and leading to the activation and migration of PTEs. Notably, arsenic (As) release is particularly significant, with peak concentrations reaching 9.97 mg/L. The study reveals that As pollution mainly originates from the oxidative dissolution of arsenopyrite, pyrite, and realgar, while the contribution of silicate mineral weathering to As release is relatively limited. Mineralogical analysis of sediments reveals that secondary mineral (Yukonite) is the primary host for As, with As predominantly existing in adsorbed and poorly crystalline iron-bound forms. This demonstrates that surface adsorption and co-precipitation by iron oxides are key factors controlling As mobility and fate. The findings provide new insights into the migration mechanisms of As and other PTEs in karst gold mining areas and offer important references for global Carlin-type gold deposit environmental geochemical research. • Arsenic from arsenopyrite, pyrite, realgar. • Yukonite regulates fate. • Adsorption, co-precipitation control mobility.