Geochemistry and environmental effect of cadmium in the super-large Jinding Pb-Zn deposit,Yunnan Province,China

The Jinding Pb-Zn deposit in Yunnan Province is the representative of a Cd-enriched area and mining activities lead to the release of Cd into the hypergenic ecosystem, resulting in Cd pollution. The concentrations of Cd vary greatly from one type to another type of rocks in the mining district. In the host rock, Cd concentrations range from 50×10⁻⁶ to 650×10⁻⁶ with an average of 310×10⁻⁶. In primary ores, Cd concentrations range from 14×10⁻⁶ to 2800×10⁻⁶ with an average of 767×10⁻⁶. However, in oxidized ores, Cd concentrations are highest, varying within the range of 110×10⁻⁶ to 8200×10⁻⁶, averaging 1661×10⁻⁶. It is shown that the oxidized ores are the main carrier and environmental source of Cd. Leaching test showed that Pb/Zn ores are easy to oxidize and thereafter release Cd and other harmful elements. These leached elements in the leachate may be precipitated rapidly in the order of Zn>Pb>Cd. As for the concentration distribution of Cd in the Bijiang River, it is estimated to be 15.7 μg/L Cd in water, 49.3 mg/L in suspended substances, and 203.7 mg/L in sediments. The average value of Cd in soil from the polluted area is 83.0 mg/kg. Natural weathering of Cd-rich rocks and minerals imposes a potential environmental risk on the aquatic ecosystem of the Bijiang catchment.