Whole-rock geochemistry, zircon U-Pb dating, and apatite volatiles compositions of granite porphyry from Secuo region, Yulong belt: Implications for ore-forming processes and potential

The Eocene Yulong Porphyry Copper Belt in eastern Tibet hosts >10 Mt of copper reserves and is genetically linked to subvolcanic-volcanic porphyry systems. Nevertheless, distinct magmatic-hydrothermal age discrepancies exist between the southern and northern portions of the Yulong Porphyry Copper Belt, implying possibly differential deep crustal processes. This study investigates the Secuo porphyry copper deposit in the southern Yulong Porphyry Copper Belt to elucidate its metallogenesis and formation mechanisms. Whole-rock geochemical data reveals that all samples belong to the high-K calc-alkaline to shoshonitic series, characterized by enrichment in light rare earth elements and large-ion lithophile elements coupled with depletion in high field strength elements. Whole-rock rare earth element modeling suggests that the ore-forming magma of the Secuo porphyry deposit underwent high-pressure, water-rich fractional crystallization dominated by amphibole with minor garnet. These features suggest derivation from a juvenile mafic lower crust, with geochemical affinities to adakitic rocks originating from delaminated lower crust and suggest that the deposit experienced multi-stage magmatic processes. Zircon U-Pb dating of the granite porphyry constrains the emplacement age of the Secuo at 38.31 ± 0.26 Ma. Sr-Nd isotopic compositions indicate a mixed source involving juvenile and ancient crustal components, consistent with other major deposits in the Yulong Porphyry Copper Belt (e.g., Yulong, Baomai, Malasongduo, Duoxiasomngduo, and Seli). Volatile components (F, Cl, OH) in apatite from mineralized porphyries provide critical insights into magmatic fertility. Thermodynamic modeling of volatiles demonstrates that the Secuo magma was water-saturated. During magma evolution, apatite records increasing XF/XCl and XF/XOH ratios but decreasing XCl/XOH ratios. Notably, the volatile evolution trends differ between apatite entrapped in zircon/amphibole and that hosted in plagioclase/biotite, suggesting an influx of F-, Cl-, and S-enriched melt or fluid during amphibole crystallization. This process enhances the potential for metal-Cl complexation, facilitating metal transport. Zircon oxygen fugacity (fO2) and apatite SO3 data reveal that the Secuo magma evolved under highly oxidized conditions, stabilizing sulfate (S6+) as the dominant sulfur phase and suppressing sulfide segregation. Such conditions are conducive to mineralization. Collectively, these petrological and geochemical signatures indicate that integrated petrological and geochemical signatures indicate that the Secuo porphyry shares key fertility indicators with large to giant deposits in the Yulong Porphyry Copper Belt (e.g., Yulong), highlighting its significant mineralization potential.