The origin of A-type granites and W-Sn-REE-Nb-Ta mineralization: Insights from geochronology, geochemistry, and Sr-Nd-Pb-Hf-O isotopes of Xiaonanshan granitoids in Guangdong Province, South China

The Xiaonanshan W deposit, located in Guangdong Province, South China, is a quartz vein−type deposit that is linked to medium- to fine-grained granite. The ore bodies primarily occur as quartz veins, sulfide-quartz veins, and greisen veins. Zircon U-Pb dating of the fine-grained granite yields an age of 80.04 ± 0.37 Ma, and muscovite from the W-bearing greisen vein provides a 40Ar-39Ar plateau age of 81.01 ± 0.41 Ma. Precise Re-Os dating of molybdenite coexisting with wolframite yields Re-Os model ages for four samples ranging from 81.17 ± 0.92 Ma to 79.27 ± 0.9 Ma, with a weighted mean age of 80.1 ± 1.3 Ma and an Re-Os isochron age of 78.3 ± 2.7 Ma. These geochronological results indicate that both the granite and the associated W mineralization formed simultaneously during the Late Cretaceous. The granite is characterized by high SiO2 contents (72.18−73.45 wt%), elevated total alkalis (Na2O + K2O = 11.35−12.18 wt%), and enriched rare earth elements (REEs; ΣREE = 247.9−294.1 ppm), as well as high Ga/Al ratios (10,000 × Ga/Al = 3.39−3.63). These characteristics classify it as an A-type granite with an A2-subtype affinity. Sr-Nd isotope analyses yield initial 87Sr/86Sr values ranging from 0.7065 to 0.7082, and εNd(t) values from −5.8 to −4.5. Pb isotope compositions show little variation, with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values ranging from 18.524 to 18.821, 15.704−15.719, and 38.799−39.000, respectively. In situ Hf-O isotope analyses reveal εHf(t) values ranging from −7.16 to +0.88, and uniform δ18O values of 6.2‰ to 7.3‰, suggesting a mixed mantle-crust source. The calculated oxygen fugacity (fO2) values range from FMQ −0.41 to FMQ +1.21. Zircon grains exhibit relatively low Eu/Eu*(0.06−0.12) and Ce/Ce* ratios (2.33−22.87), indicative of low oxygen fugacity. The visible tetrad effect (0.78−0.80), coupled with the presence of abundant Nb-Ta minerals and enriched REEs, suggests strong fractionation and significant W-Sn-Nb-Ta-REE mineralization potential. Additionally, garnet U-Pb dating of the Cu-Pb-Zn−bearing skarn in the deposit’s periphery yields an age of 81.2 ± 2.7 Ma, consistent with the emplacement of the Xiaonanshan granite and associated W-Sn mineralization. This correlation underscores the potential for skarn Cu-Pb-Zn-Sn polymetallic deposits and peripheral vein Pb-Zn-Ag mineralization. The large-scale Cretaceous granitoid magmatism and W-Sn polymetallic mineralization in the region are attributed to lithospheric extension. Further evaluation of the W-Sn, Nb-Ta-REE, and Pb-Zn-Ag mineralization potential of Cretaceous A-type granites in eastern China remains crucial.