Yaochong Mo deposit, a low-F porphyry Mo deposit from the Qinling-Dabie orogenic belt

Abstract

The Qinling-Dabie orogenic belt is the largest Mo mineralization belt in the world. The Yaochong porphyry Mo deposit is located in the northwest Dabie Mountains, with a proven reserve of 51kt Mo metal at an average grade of 0.058%. Here we report geochronology and geochemistry results of the Yaochong porphyry Mo deposit. Zircon U-Pb LA-ICP-MS dating shows that the Yaochong porphyry dykes and a hidden intrusion formed at 135Ma and 140Ma, respectively, which are consistent with Early Cretaceous Mo mineralization events in the Qinling-Dabie orogenic belt. Zircon grains from the Yaochong porphyry dikes (2–1788) and the hidden intrusion from drill holes (41–1940) have highly variable Ce4+/Ce3+ values. It is very likely that both the intrusion and the dikes have experienced high oxygen fugacity, but was partially reduced through assimilation. Apatite grains from the Yaochong porphyry and the intrusion are characterized by high but variable F concentrations and low Cl concentrations, suggesting that they formed in an F-enriched environment with high F/Cl components in the magma source. The Ti-in zircon temperatures of the porphyry dikes range from 700 to 710°C, whereas the average temperature of the buried intrusion nearby is 675°C. Yaochong porphyry shows geochemical and petrologic characteristics similar to those of low F stockwork type porphyry Mo deposit in North America, which may be inherited from the Dabie suture zone.