Zircon U-Pb-Hf-O Isotopic Characteristics and Geological Significance of Nannihu and Shibaogou Rock Mass in Luanchuan Ore Concentration Area, Western Henan Province

The Luanchuan mining area is located at the southern edge of the North China Craton, which is rich in mineral resources and has produced a number of large-sized and super-large porphyry-silica type molybdenum and tungsten deposits. There are frequent magmatic activities in Late Mesozoic, forming several ore-bearing granite bodies and porphyry rock strains, and the controlling factors of their mineralization differences and potentials are still unclear. In this paper, we take the Mo-rich granite body of Nannihu and the ore-poor granite body of Shibaogou in the Luanchuan mining concentration area as the research objects, and based on zircon U-Pb dating and Hf-O isotope study, we reveal the age of their diagenesis and metallogeny, magma source area, and metallogeny indication significance. The zircon U-Pb ages of the Shibaogou rock and the Nannihu rock are (147.5±2.2) Ma and (139.5±1.8) Ma, respectively, and both are the products of Yanshan-age magmatism. The zircon εHf(t) values of the Shibaogou body range from −27.40～−14.51, and the two-stage mode age T_DM2 values range from 2.15～2.93 Ga, with δ¹⁸O values of 5.42‰ to 6.77‰. The zircon εHf(t) values of the Nannihu body range from −16.84～−8.04, with second-stage mode age T_DM2 values ranging from 1.70～2.26 Ga and δ¹⁸O values of 5.88‰～8.27‰. The zircon U-Pb ages and Hf-O isotope results indicate that the source area of the Shibaogou ore-poor magma originated from partial melting of the thickened lower crust of the Qinling orogenic belt in the context of localized extensional downstretching of post-collisional orogeny; and that the Mo-rich porphyry magma of the Nannihu is characterized by crust-mantle mixing.