In Situ Trace Element Composition of Sphalerite and Its Geological Significance: A Case Study from the Huize Ge-Rich Pb-Zn Deposit, NE Yunnan

The Huize Ge-rich Pb-Zn deposit is an important part of the Sichuan–Yunnan–Guizhou carbonate-hosted Pb-Zn metallogenic area and is one of the most representative super-large deposits in the northeastern Yunnan Pb-Zn ore concentration area. The orebodies mainly occur in NE-trending interlayer fault zones. The Pb-Zn mineralization process of this deposit can be divided into the dolomite stage (I), sphalerite-galena stage (II), galena-sphalerite stage (III), and pyrite-calcite stage (IV). Based on a study of the deposit geology, we utilized LA-ICP-MS for in situ microanalysis of trace element compositions and element mapping of sphalerite from different stages to reveal the characteristics of the sphalerite trace element composition and occurrence mechanisms, understand the mineralization process, and constrain the genetic type of the deposit. This research shows that sphalerite color variations result from the multi-factor coupling of multiple trace element contents, element associations, and isomorphic substitutions among elements. Trace elements such as Mn, Fe, Cu, Ga, Ge, Ag, Cd, In, Sn, Sb, and Hg occur in the sphalerite lattice in the form of isomorphic substitutions or nanoscale mineral inclusions, whereas Pb occurs mainly as microscopic mineral inclusions (galena) in sphalerite. From the early to late stages of mineralization (SpI → SpII → SpIII), the mineralization temperature (132–205 °C) and sulfur fugacity (log10 fS2 = −15.29 to −19.89) both show a gradual decrease. During sphalerite crystallization in different stages, multiple trace elements exhibit coupled multi-element substitutions at the microscale: SpI: Zn2+ ↔ (Fe2+, Mn2+, Cd2+), 2Zn2+ ↔ 2Ag+ + Ge2+; SpII: Zn2+ ↔ (Fe2+, Cd2+), 2Zn2+ ↔ 2Ag+ + Ge2+, 3Zn2+ ↔ 2Cu2+ + Ge2+, 3Zn2+ ↔ 2(Cu, Ag)2+ + Ge2+, 2Zn2+ ↔ Ga3+ + Cu+, 2Zn2+ ↔ Ga3+ + (Cu, Ag)+; and SpIII: Zn2+ ↔ (Fe2+, Mn2+), 3Zn2+ ↔ 2Cu2+ + Ge2+, 3Zn2+ ↔ 2(Cu, Ag)2+ + Ge2+). Mn, Fe, and Ge are mainly enriched in SpI; Ga and Ag are mainly enriched in SpII; and Cd is mainly enriched in both SpI and SpII. By comparing the sphalerite trace elements signature of the Huize Ge-rich deposit with those of global typical MVT, SEDEX, VMS, epithermal, and skarn-type Pb-Zn deposits, and considering the deposit’s geological and geochemical characteristics, we suggest that the Huize Pb-Zn deposit is best classified as a medium- to low-temperature, carbonate-hosted Pb-Zn deposit.