Petrogenesis and porphyry metallogenic potential of the Jinmen pluton in the Nanling Range, South China: Insights from whole-rock geochemistry, zircon trace elements, and U-Pb-Hf isotopes

The Jinmen pluton is situated on the southern margin of the Nanling metallogenic belt, where a skarn-type Cu-Fe-Mo-Au polymetallic deposit has been discovered in its proximity. Skarn-type deposits are widely recognized as an important component of porphyry metallogenic systems; however, systematic studies on the emplacement age, petrological classification, genetic relationship with skarn mineralization, and porphyry metallogenic potential of this pluton remain lacking. This study presents an integrated dataset of whole-rock geochemistry, zircon U-Pb-Hf isotopes, and molybdenite Re Os geochronology for the Jinmen pluton, which consists of biotite monzogranite with subordinate granite dikes and mafic microgranular enclaves (MMEs). Zircon LA-ICP-MS U Pb dating yields weighted mean ages of 161.6 ± 0.6 Ma to 158.7 ± 0.6 Ma for biotite monzogranite, 161.1 ± 0.8 Ma for granite dike, and 161.0 ± 0.6 Ma for MMEs, indicating coeval emplacement. Four molybdenite samples yield a weighted average Re Os age of 162.0 ± 0.4 Ma, confirming synchronous magmatism and mineralization during the Late Jurassic. All zircons yield negative Hf isotopic compositions (ε Hf ( t ) = −7.17 to −1.69), with two-stage model ages corresponding to the Paleoproterozoic (1.32–1.66 Ga). Proterozoic (1680 ± 30 Ma) and Silurian (438 ± 13 Ma) inherited zircons were identified in the biotite monzogranite, suggesting possible partial melting of ancient crustal materials. The development of acicular apatite in MMEs and oscillatory zoning in plagioclase within the host granite indicates magma mixing. Combined with whole-rock geochemical constraints, these characteristics demonstrate that the Jinmen pluton is an I-type granite originating from crustal anatexis modified by mantle material input; the MMEs are interpreted as the products of magma mixing between enriched mantle and ancient crustal melts. The biotite monzogranite additionally exhibits high oxygen fugacity (ΔFMQ = +0.9 to +3.4) and elevated V/Sc ratios (an indicator of a water-rich magma), which favors the exsolution of ore-forming fluids. Furthermore, a negative correlation between ΔFMQ and log[10 4 × (Eu/Eu*)/Yb N ] reflects magmatic oxidation during ascent, a process that enhances copper mobility and enrichment. These geochemical fingerprints are comparable to those of major porphyry Cu deposits worldwide, indirectly indicating the porphyry Cu exploration potential of the Jinmen pluton.