矿床地球化学国家重点实验室知识库

Zinc (Zn)-Lead (Pb) deposits are generally rich in cadmium (Cd), and the weathering of sulfide minerals in such deposits results in large releases of Cd into the environment. From an environmental and public health standpoint, understanding Cd sources and cycling is critical to identifying potential hazards to humans. In this study, the Cd isotope compositions (expressed as delta Cd-114/110) of secondary minerals such as anglesite (-0.57 +/- 0.03 parts per thousand; 2 S.D.), granular smithsonite (0.04 +/- 0.14 parts per thousand; 2 S.D.), layered smithsonite (0.15 +/- 0.40 parts per thousand; 2 S.D.), hydrozincite (0.26 +/- 0.01 parts per thousand; 2 S.D.) and clay minerals (-0.01 +/- 0.06 parts per thousand; 2 S.D.) from the Fule Zn-Pb-Cd deposit, Southwest China, are investigated to better understand the Cd sources and cycling in this area. Combined with our previous study (Zhu et al., 2017), the work herein elucidates the patterns of Cd isotopic fractionation during the formation processes of such secondary minerals and traces the weathering of these minerals into the ecosystem. The delta Cd-114/110 values of secondary minerals exhibit the following decreasing trend: hydrozincite > large granular smithsonite > small granular smithsonite > anglesite. Although different amounts of Cd were lost during the formation of equally sized samples, no or minor variations in Cd isotopic composition were observed. However, significant isotopic differences were observed between different size fractions. These results demonstrate that the particle size of secondary minerals and weathering products of sulfide significantly influence Cd isotope composition and fractionation during natural weathering. This systematic fractionation provides an initial foundation for the use of Cd isotopes as environmental tracers in ecosystems and in the global Cd isotope budget.