Mineralogy and Geochemistry of the Xiaotunxiang Fluorite Deposit in Guizhou Province, SW China, and Their Geological Significance

The Xiaotunxiang deposit, a newly discovered large-scale fluorite resource (1.28 Mt ore reserves) in southwestern Guizhou Province, China, provides a critical case study for understanding fluorite mineralization in the region. To constrain its genesis, this study integrates detailed ore deposit geology with mineralogy, trace element geochemistry, and strontium isotope analysis of fluorite. The ore mineral assemblage is dominated by fluorite, quartz, and calcite, with minor amounts of barite and pyrite. Trace element data reveal significant enrichment in Ti, Cr, Mo, and Sb relative to the upper continental crust. Fluorite exhibits moderate total REE contents (26.8–138 ppm), slight heavy REE enrichment (ΣLREE/ΣHREE = 0.17–1.88), pronounced negative Ce anomalies (δCe = 0.59–0.72), and negligible Eu anomalies (δEu = 0.95–1.14). These geochemical signatures are closely comparable to those of nearby fluorite deposits (Qinglong, Gaoling, and Getang), indicating a shared source of ore-forming materials. Strontium isotope ratios (87Sr/86Sr = 0.707468–0.707682) are consistent with local carbonate wall rocks, confirming their role as the primary source of calcium. We conclude that the Xiaotunxiang deposit formed from a low-temperature hydrothermal system where fluorine and associated metals were likely sourced from the Emeishan basalts, while calcium was derived from the interaction of acidic fluids with carbonate host rocks. Precipitation was ultimately triggered by fluid–rock (water/rock) interaction, classifying Xiaotunxiang as a carbonate-hosted hydrothermal deposit.