Apatite fingerprints from the Dengfuxian Ore District and their implications for W–Sn mineralization in South China

Abstract Tungsten (W) and tin (Sn) are critical strategic metals for high-technology industries and for understanding the magmatic and hydrothermal processes that control W–Sn mineralization, essential for guiding exploration. The Dengfuxian ore district, a representative W–Sn deposit within the Nanling Metallogenic Belt that contains ∼90% of China’s W resources, hosts total resources of 68 kt Sn + WO3 and 10 kt Ta2O5 + Nb2O5, together with Pb, Zn, Cu, Mo, Au, and fluorite as valuable by-products. The district provides an ideal natural laboratory because it encompasses various lithologies. In this study, apatite samples were collected from the Dengfuxian ore district, including from W–Sn-bearing quartz veins, granite hosting the mineralized veins, barren granite, and lamprophyres, as well as apatite from W–Sn-bearing skarn in the Xitian ore district. These samples were investigated using cathodoluminescence imaging, U-Pb dating, major- and trace-element geochemistry, and Nd isotopic analyses, combined with partial least squares discriminant analysis (PLS-DA). We further extend the result of PLS-DA to apatite from W–Sn-bearing granites across South China, identifying key elemental signatures in apatite that serve as robust indicators of magmatic processes and ore-forming potential. Our results reveal three diagnostic features. First, magmatic and hydrothermal apatite can be clearly distinguished by texture and chemistry. Magmatic apatite typically shows oscillatory or homogeneous zoning in CL images and is enriched in Th and REE, whereas hydrothermal apatite displays dark CL, irregular textures, and enrichment in U but depletion in REE. Second, apatite Nd isotopes and trace elements provide a reliable means of discriminating magma sources. Apatite from Sn-bearing granites yields less negative εNd(t) values (peak around −7) and indicates stronger mantle contributions, whereas apatite from W-bearing granites shows more negative εNd(t) values (peak around −12) consistent with crustal derivation, and W–Sn-bearing granites define an intermediate field (peak around −9). These isotopic distinctions are further supported by trace-element patterns, with crust-derived apatite generally characterized by lower Sr, Ce, and La/Sm values compared to mantle-derived apatite. Third, apatite provides a sensitive record of granitoid fertility through signals of magmatic differentiation and redox state. In W–Sn-bearing fertile granites, apatite reflects a higher degree of fractionation, indicated by elevated REE contents, and low Mg and Sr/Y ratios, together with reduced conditions manifested by low Eu/Eu* values. In contrast, apatite from barren granites shows the opposite geochemical trends. Our PLS-DA results from Dengfuxian, supported by comparison with the Xitian ore field, demonstrate that apatite geochemistry and isotopes provide reliable criteria for distinguishing magmatic from hydrothermal apatite, constraining magma sources, and evaluating granitoid fertility, thereby offering a robust framework for understanding W–Sn metallogeny and guiding exploration across South China.