Geochronology and Geochemical Characteristics of Granitic Porphyry from the Daweng Cu-Au Deposit in the Eastern Segment of the Bangong-Nujiang Metallogenic Belt and Their Geological Significance

The Daweng Cu-Au mineralization occurrence is located in the eastern segment of the Bangong Co-Nujiang metallogenic belt. The mining area mainly exposes granite porphyry, monzonite, and syenite porphyry, with granite porphyry as the ore-bearing rock. Sericitic alteration is widely developed, followed by argillic alteration; locally, carbonatization, potassic alteration, and silicification are also observed. The alteration shows a planar distribution concentrated around small intermediate-acidic intrusions. Metallic mineralization mainly includes pyritization, chalcopyritization, gold mineralization, sphaleritization, hematitization, and limonitization. LA-ICP-MS zircon U-Pb dating yields ²⁰⁶Pb/²³⁸U weighted mean ages of (116.64±0.68) Ma and (116.90±0.74) Ma for the granite porphyry, indicating an Early Cretaceous emplacement age. The granite porphyry is genetically classified as I-type granite, with an average aluminum saturation index (A/CNK) of 1.00. It is strongly enriched in large-ion lithophile elements (LILE) Rb and Ba, slightly depleted in high-field-strength elements (HFSE) Ta and Nb with pronounced Nb-Ta negative anomalies, and significantly enriched in Sr, showing weak Eu and Ce negative anomalies. These features indicate formation in a convergent plate subduction tectonic setting; the magma system was volatile-rich and characterized by active fluid circulation, representing a hydrous magma with typical geochemical signatures of arc magmatic rocks. The mineralization is closely related to magmatic-hydrothermal activity in a subduction orogenic setting. We infer that during southward subduction of the Bangong Co-Nujiang Tethys oceanic basin, high-oxygen-fugacity fluids rich in water and ore-forming materials, generated by dehydration of the oceanic slab, metasomatized the lower crust, forming ore-bearing magmas that ascended and emplaced. The mineralization belongs to a porphyry-epithermal metallogenic system.