Geochronology, Genesis and Redox Condition of the Lisong Granites in the Guposhan Region, Nanling Range: Constraints from Zircon U-Pb Dating, Whole-Rock Geochemistry, and Apatite Geochemistry

The Guposhan ore field, located in the Nanling metallogenic belt, is well known for large-scale Sn-W mineralization genetically linked to the Late Jurassic Guposhan pluton. The Lisong pluton, a product of regional magmatism, occurs in the central part of the Guposhan ore field. However, the critical factors responsible for the absence of intensive Sn polymetallic mineralization in the Lisong pluton remain poorly understood. Our geochronological results show that the coarse-grained hornblende-bearing and hornblende-free biotite monzogranites of the Lisong pluton were emplaced at 162.9 ± 1.5 Ma and 162.2 ± 2.3 Ma, respectively, which are contemporaneous with the Guposhan pluton. Geochemically, these intrusions are characterized by high SiO2, Al2O3, and total alkalis (K2O + Na2O), high Ga/Al ratios (3.09–3.69), and peraluminous compositions (A/CNK = 1.15–1.23), consistent with high K calc-alkaline A-type granites. Similar to the adjacent Guposhan pluton, the Lisong granites yield variable εHf(t) values from −3.0 to 5.7, apatite 87Sr/86Sr ratios of 0.69747–0.71190, and old two-stage Hf model ages (TDM2) of 0.85–1.40 Ga. These features suggest that the Lisong and Guposhan granites may share a common magma source involving mixing of crustal and mantle-derived melts. Apatite grains from the Lisong granites display negative Eu anomalies (δEu = 0.03–0.22) and near-normal to positive Ce anomalies (δCe = 0.99–1.07), which we interpret to reflect plagioclase fractional crystallization and reduced melt conditions, respectively. Bulk rock geochemistry and multi-element systematics of the Lisong granites indicate that they represent early-stage magmatic products. Their relatively low differentiation signatures were unfavorable for Sn enrichment and mineralization in the melt, which likely explains the lack of intensive Sn polymetallic mineralization in the Lisong pluton.