Integrating biotite and zircon geothermometry with halogen chemistry and oxygen fugacity constraints: implications for magmatic fluid evolution and gold mineralization in the northern margin of the North China craton

The Northern margin of the North China Craton (NNCC) hosts major gold deposits linked to Late Jurassic–Early Cretaceous granitic magmatism. Although spatial relationships between specific intrusions (e.g., Dahuabei, Haigou, Xitaizi–Jinchanggouliang granites and Duimiangou quartz monzodiorite) and mineralization are established, the roles of magmatic temperature, halogen chemistry, redox state, and fluid exsolution in ore formation remain debated. This study integrates zircon–biotite geothermometry, halogen fugacity proxies, and oxygen fugacity (fO₂) constraints to reconstruct magmatic–hydrothermal evolution in the Hadamengou, Jinchanggouliang–Erdaogou, and Haigou deposits. Field evidence, including pegmatite dikes, unidirectional solidification textures (UST), and quartz “eyes,” indicates volatile-rich residual melts (10–50% H₂O) and hydraulic fracturing during fluid release. Biotite Cl/F ratios reveal contrasting metallogenic affinities: Cl-rich systems at Jinchanggouliang–Erdaogou resemble porphyry Cu–Au environments, whereas F-rich magmas at Hadamengou and Dahuabei are comparable to porphyry Mo settings. Zircon and biotite geochemistry indicates moderately oxidized conditions near the Ni–NiO to magnetite–hematite buffers, favoring Au transport as chloride and sulfur complexes. Variations in halogen activity and redox state control deposit styles and emphasize localized physicochemical controls on gold fertility.