Sphalerite Chemistry, Niujiaotang Cd-Rich Zinc Deposit, Guizhou, Southwest China

Sphalerite in the Niujiaotang Cd rich zinc deposit, Duyun, Guizhou is characteristically light yellow in color with significant enrichment of cadmium which ranges from 0.83% to 1.97% (averaging 1.38%) in concentration in the mineral, corresponding to an enrichment coefficient as high as 30.47 to 72.96. In comparison with other major Pb Zn deposits in the world (the Mississippi Valley deposits, and the Fankou and Jinding deposits in China) the Niujiaotang deposit is n-n×10 times richer in cadmium. Sphalerite in the deposit is also rich in Ga and Ge, but poor in In, Mn and Fe, suggesting some special mechanisms that govern the geochemical behavior of these trace elements. Except for a minor amount of independent minerals like greenockite, cadmium occurs mainly as isomorphous impurity in the crystal lattice of sphalerite. During weathering and leaching under supergene condition, cadmium was separated from Zn, resulting in some secondary minerals of Cd, including oxides and otavite.