The mechanism of migration and precipitation of associated silver in the Shanhu tungsten-tin deposit, Guangxi

The Shanhu tungsten-tin deposit in Guangxi displays vertical inverse zoning:tin enrichment in the upper part, tungsten and tin enrichment in the middle part, and tungsten enrichment in the lower part of the deposit. The lower salinity and density of the ore-forming fluids suggest slightly reduction and acidic systems. The associated silver tends to be migrated as chlorine complexes and sulfur complexes. The migration and precipitation of silver complexes depend on the S^2- concentration in the hydrothermal solution. The S^2- concentration increases with the decrease of mineralization temperatures and the increase of Ca²⁺ concentration and pH values, resulting in the precipitation of abundant sulfides and silver-bearing sulfosalts. The associated silver tends to occur in the lower and middle parts of ore veins due to lower ore-forming temperatures in the deeper parts.