In situ compositional and sulfur isotopic analyses of banded sphalerite from the Kangjiawan Pb-Zn deposit, South China: Insights into incorporation mechanisms of critical metals (Cd, Ga, In)

• Three zoning bands can be identified in Kangjiawan deposit with homogeneous Cd and distribution patterns of Ga and In. • The banded sphalerite should be formed by intrinsic, self-organized processes. • The skarn Pb-Zn deposits of South China are for not only Cd (and probably In) exploration, but also Ga exploration. The critical metals Cadmium (Cd), gallium (Ga), germanium (Ge) and indium (In) are essential to the development of the green technologies that are at the core of low-carbon societies. Although sphalerite is their principal host mineral in nature, high-temperature hydrothermal Pb-Zn deposits have seldom been the subject of focused studies on these metals. Using in situ measurements of major elements by EMPA and trace elements and sulfur isotopes by LA-ICP-MS, together with LA-ICP-MS elemental mapping, this study investigated the microscale critical elemental distributions and incorporation mechanisms in banded sphalerite from the Kangjiawan skarn Pb-Zn deposit, South China. Three typical optical zoning bands can be identified (bands R1 to R3 from dark to light). Different bands are characterized by different concentrations of minor/trace elements, with the darker bands displaying higher Fe, Mn and Cu concentrations. Spot concentrations for Cd, Ga and In range from 0.21 to 0.29 wt%, 1.03 to 41.40 ppm, and 0.12 to 10.14 ppm, respectively. Cd is homogeneously distributed within the sphalerite grains, whereas Ga is mainly concentrated in band 2. Rhythmic distribution of In concentrations notwithstanding, it does not correlate with the above colour banding. Moreover, elemental concentrations do not display any systematic increase/decrease from core to rim at the micrometer-scale, which indicates that microscale processes at or near the growing crystal edges account for the observed compositional zoning. The Kangjiawan sphalerite displays δ 34 S V-CDT values ranging from 1.98 to 5.18 ‰, typical of magmatic-derived ore-forming materials. Sulfur isotopes also do not display systematic variations from core to rim, further highlighting that the banded sphalerite should form by intrinsic, self-organized processes. The elemental correlation analyses suggest the isovalent substitution Cd 2+ ↔ Zn 2+ , and coupled substitution In 3+ + (Cu, Ag) + ↔ 2Zn 2+ . A strong correlation between Ga and Mn is manifested, probably suggesting a more complex mechanism Ga 3+ + Mn 2+ + (Cu, Ag) + ↔ 3Zn 2+ . Combined with published global sphalerite data, this study advocates the more promising of MVT deposits for Ga and Ge exploration whereas skarn deposits for In exploration. There is no distinction between low- and high-temperature hydrothermal deposits in forming economic Cd mineralization. Strikingly, the Kangjiawan sphalerites are characterized by high Ga contents, similar to those from MVT deposits. Collectively, our study highlights the potential of skarn Pb-Zn deposits, at least from South China, for not only Cd and In exploration, but also Ga exploration.