Trace element compositions of sulfides from Pb-Zn deposits in the Northeast Yunnan and northwest Guizhou Provinces, SW China: Insights from LA-ICP-MS analyses of sphalerite and pyrite
Qing Yang, Xiaojun Zhang, Thomas Ulrich, Jun Zhang, Jian Wang
Abstract
Trace elements in sphalerite and pyrite from six deposits at the Sichuan-Yunnan-Guizhou lead–zinc metallogenic province were analysed to constrain the composition, distribution characteristics and substitution mechanisms of trace elements by LA-ICP-MS analyses. The results show that the sphalerites are characterized by high Fe, Ge, Cd and low Bi, Ni, Co and Tl contents, while pyrites characteristically have high contents of Ni, Co, As and low contents of Ge, Ga, Tl, Bi and In. Iron, Ga, Mn, Cd and Ge in sphalerite and Co, Ni and Tl in pyrite are generally lattice-bound, while Ag, Cu, As and Sb are usually present in both micro-inclusions and solid solution. Significant correlations between some elements in sphalerite suggest the substitution mechanisms: 2Zn2+ ↔ (Ag+, Cu+) + (Ga3+, As3+) and 3Zn2+ ↔ 2(Cu+, Ag+) + Ge4+, and the existence of negative correlation between Fe and Mn implies a competition between both elements. The correlation trends between trace elements in pyrite demonstrate the coupled substitution mechanism of 2Fe2+ ↔ (Tl+, Cu+, Ag+) + Sb3+. Generally, darker sphalerite is relatively rich in Fe and Ge compared to light-color sphalerite, and is deficient in Ga, In and Sn. Regionally, the Cu in sphalerite tends to gradually increase from southeast to northwest, and pyrite from Maoping has significantly higher Co and Ti concentrations and Co/Ni ratios than that from the deposits in northwestern Guizhou. The variation of the Co/Ni ratio in pyrite at the scale of these deposits may provide vectors for the geochemical exploration of Pb-Zn mineralization and the Co/Ni ratios close to 0.1 are more prospective for a larger deposit.