Low-temperature mineralization of Sb-Au polymetallic ores in the Badu area, Youjiang Basin: constraints from minerals trace elements and sulfur isotopes

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Introduction The dynamic mechanisms of Youjiang Basin low-temperature mineralization and the source of ore-forming fluids remain controversial, particularly regarding Indosinian versus Yanshanian tectonic driving forces and deep crustal versus sedimentary fluid origins. Methods This study focuses on the Badu Sb-Au deposit and conducts LA-ICP-MS in-situ trace-element and sulfur-isotope analyses of pyrite, sphalerite, stibnite, and ankerite to constrain ore-forming processes and resolve key regional metallogenic debates. Results Two generations of pyrite are recognized: supergene-altered Py Ⅰ developed within quartz-sulfide veins (δ 34 S = 17.93‰–19.53‰, avg. 18.70‰), and hydrothermal euhedral disseminated Py Ⅱ (δ 34 S = 17.73‰–18.68‰, avg. 18.12‰), representing early hydrothermal mineralization. Sphalerite exhibits Cd enrichment, In-Sn-Co depletion, and Ga/In ratios <1, indicating typical Mississippi Valley-type (MVT) fluid characteristics. Trace-element evidence confirms that ankerite precipitated under sedimentary-hydrothermal transitional conditions (La = 514.08–514.98 ppm; Eu = 73.60–93.64 ppm), while stibnite formed during subsequent dominant hydrothermal stages (La = 183.05–223.89 ppm; Eu = 12.51–13.93 ppm). The significantly elevated Eu concentrations in stibnite represent primary geochemical signals of reducing, Eu 2+ -rich hydrothermal fluids. Stratigraphically ordered hydrothermal minerals yield averaged δ 34 S values of 14.58‰ (ankerite), 14.66‰ (sphalerite), and 13.98‰ (stibnite). The overall sulfur-isotope variation, coupled with trace-element redox indicators, records fluid mixing and progressive hydrothermal evolution rather than a simple monotonic trend. Discussion and Conclusion Integrated mineral paragenesis and geochemical fingerprints demonstrate that ore-forming fluids were dominated by modified sedimentary pore fluids with minor deep-source contributions, and mineralization was driven by Yanshanian asthenosphere upwelling and lithospheric extension, overprinting early Indosinian tectonic frameworks. This study establishes a clear data-driven genetic model for Sb-Au mineralization in the Badu deposit, clarifies long-standing dynamic and fluid-source controversies in the South China LTMD, and supplements the regional low-temperature metallogenic theory.