Origin of the Badaguan porphyry Cu[sbnd]Mo deposit, Inner Mongolia, northeast China: Constraints from geology, isotope geochemistry and geochronology

Abstract

The Badaguan porphyry CuMo deposit is located in the Derbugan metallogenic belt of northeastern Inner Mongolia, China. The host granodioritic porphyry and the wall rock granitic porphyry were emplaced at 230Ma and 238Ma, respectively. The granodioritic porphyry has (87Sr/86Sr)i values of 0.70535–0.70549, εNd(t) values of 0.41–1.17, εHf(t) values of 1.30–6.51, and two–stage model ages (TDM2) of 1131–848Ma. In contrast, the granitic porphyry is characterized by εHf(t) values from −0.75 to 7.28 that yield TDM2 model ages of 1355–816Ma. The geochemical and SrNdHf isotopic data for the magmatic rocks associated with the Badaguan porphyry CuMo deposit indicate that these intrusions were generated by the partial melting of juvenile lower crust. The δ18O values of ore fluids from different mineralizing stages are between −6.0‰ and +1.5‰, and the fluid δDwater values vary from −119.3‰ to −140.0‰, indicating a mixed fluid of magmatic and meteoric water, the SPb isotopes show that the metal was mostly derived from a deep-seated magma that involved some crustal materials, with a narrow δ34S range (−2.4‰ to +3.5‰). We infer that the Badaguan porphyry CuMo deposit formed during a period of southeast–directed subduction of the Mongol–Okhotsk oceanic plate beneath the Erguna Block.