Ore-forming processes of giant carbonate-hosted ZnPb deposit and Ge enrichment mechanism in Zhugongtang, Guizhou Province, China: Constraints from trace element and isotopic compositions of sulfides

Abstract

The Zhugongtang ZnPb deposit, with >3.27 million tons of Zn + Pb averaging 6.76 % Zn and 2.27 % Pb, along with 592 tons of Ge, is a newly discovered giant ZnPb deposit in northwest Guizhou Province of the Sichuan-Yunnan-Guizhou metallogenic region, Southwest China. This deposit is hosted in Devonian, Carboniferous, and Permian carbonate rocks. Three stages of hydrothermal mineralization were identified: (1) the pyrite-sphalerite-quartz stage, (2) the sphalerite-galena-pyrite-calcite stage, and (3) the carbonate stage, and three generations of sphalerite (Sp-1, Sp-2, and Sp-3) were identified. In this study, analyses of in situ trace element compositions in sphalerite and SPb isotopic compositions of sulfides were conducted to determine the origin and mineralization processes of the Zhugongtang deposit. Sphalerite is characterized by enrichment of Ge (mean = 109 ppm), Cd (mean = 875 ppm), and Ga (mean = 30 ppm) and depletion of In, Sn, and Co, with increasing Ge and Cu and decreasing Mn, Ag and Pb from the early to late stages. Ge incorporates into sphalerite via a coupled substitution of 3Cu⁺ + Sb³⁺ + Ge⁴⁺ ↔ 5Zn²⁺. The temperature and sulfur fugacity (fS₂) are estimated from the trace element concentrations in sphalerite, which indicate medium- to low-temperature and intermediate-sulfidation conditions with decreasing temperature and fS₂ from Sp-1 to Sp-3. The pyrite, sphalerite, and galena have δ³⁴S values ranging from 11.3 to 17.8 ‰, 10.2 to 17.3 ‰, and 8.4 to 14.7 ‰, respectively, indicating that the reduced sulfur likely originated from the thermochemical reduction of sulfate (TSR) with multiple sources. High-precision in situ Pb isotope ratios of ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁶Pb/²⁰⁴Pb range from 39.609 to 40.230, 15.860 to 16.042, and 18.768 to 18.984, respectively, which implies that the lead was sourced primarily from the host rock and basement strata. On the basis of a comprehensive analysis of ore geology and geochemical data, the Zhugongtang deposit is classified as an MVT deposit. With the gradual decrease in temperature and fS₂, sphalerite (Sp-2 and Sp-3) precipitated in large quantities with significant enrichment of Ge (mean 147 ppm).