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Multistage pyrites and association with uranium mineralization in the Yingqian granite-related uranium deposit, South China
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DOI：10.1016/j.oregeorev.2026.107406.png)
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Abstract
En 中文
Multi-stage pyrites commonly occur in hydrothermal uranium deposits, yet the genesis and association with uranium mineralization remain unclear. This study addresses these issues through integrated petrographic and geochemical analyses, combined with geochemical modeling, on the Yingqian granite-related uranium deposit in South China. Petrographic investigations reveal three major stages of pyrites in the Yingqian deposit, i.e., the pre-ore massive Py1 and syn-ore veinlet Py2 and Py3. All three generations of pyrites exhibit similar and narrow ranges of δ34S (−8.63 to − 11.71‰), δ56Fe (−1.37 to 0.84‰) and δ57Fe (−1.97 to 1.27‰) values, indicating a common source for sulfur and iron. Rayleigh fractionation modeling suggests that the limited sulfur isotopic variation in pyrites from the Yingqian deposit, as well as other hydrothermal uranium deposit worldwide, is attributed to the precipitation from H2S-bearing fluids, rather than via reduction of sulfate derived from oxidized U-bearing fluids. Based on petrographic characteristics, isotopic compositions and geochemical modeling, the pre-ore massive Py1 is interpreted to be formed by the flocculation of colloidal iron sulfides or the mixing of H2S-bearing fluids and iron-bearing fluids. In contrast, the deposition of Py2, Py3 and uraninite are produced by the interactions involving uranium-bearing fluids, H2S-bearing fluids and hosting granites. Some Py1 grains are extensively metasomatized by ore fluids with the enrichment of U, Co, As, Se, and Cu, similar to those enriched in the syn-ore Py2 and Py3, indicating the high concentration of these metals in the ore-forming fluids. The precipitation of Py1 immobilized the flowing reducing H2S and therefor enhance the reducing capacity for the ore-forming environment. In addition, pyrite is kinetically more efficient than the Fe-bearing silicates in the magmatic rocks. Consequently, the pre-ore massive Py1 constitutes ideal chemical traps, facilitating multiple episodes of metasomatism and superimposed mineralization by subsequent uranium-bearing fluids. Our findings highlight the critical role of H2S-bearing fluids in the formation of multistage pyrites and associated uranium enrichment, a process that may have broad application to other sulfide-bearing uranium polymetallic deposits worldwide.
Keywords:
Hydrothermal uranium deposits
Multi-stage pyrites
South China
Geochemical modeling
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