Tectonic-magmatic setting for Early Cretaceous low-sulfidation epithermal gold deposits in the Xing–Meng Orogenic Belt: Constraints from zircon U–Pb and Hf isotopic data of wulaga deposit, NE China

Abstract

The Xing–Meng Orogenic Belt hosts an amount of low-sulfidation epithermal gold deposits. However, the tectonic-magmatic setting remains problematic, which hinders understanding the factors that control the gold endowment in the region. Wulaga deposit is the largest low-sulfidation epithermal gold deposit in the northeastern Xing–Meng Orogenic Belt. Gold mineralization occurs in the crypto-explosive breccia zone of subvolcanic granodiorite porphyry. Zircon U–Pb ages of three granodiorite apophyses and previous pyrite Rb–Sr dating (113.8 ± 4.4 Ma) indicate granodiorite porphyry and gold mineralization was coeval. The ore-related granodiorite porphyry is moderate SiO2, high-K calc-alkaline, and metaluminous, suggesting an I-type granite. Moreover, Wulaga granodiorite porphyry displays low initial 87Sr/86Sr ratios and positive εNd(t) values with TDM2(Nd) of 799.7–897.4 Ma and εHf(t) values with TDM2(Hf) of 652–785 Ma, indicating that it was derived from partial melting of the Neoproterozoic juvenile mafic lower crust. Ti-in-zircon thermometry, medium–high Sr/Y ratio, high Ba/La, and fO2 value indicate that Wulaga granodiorite porphyry formed at relatively low temperatures (∼700 °C), rich water, and high fugacity within the stability field of garnet in the juvenile lower crust. Combined with ore-related tectonic-magmatic activities in the Wulaga, Dong'an, and Sandaowanzi gold deposits, the Early Cretaceous low-sulfidation epithermal gold deposits in the Xing–Meng Orogenic Belt were formed from magmatic-hydrothermal events triggered by mutual interaction between post-orogenic lithospheric extension related to the closure of the Mongol-Okhotsk Ocean and arc-back extension associated with rollback of the Paleo-Pacific Ocean plate. These data indicate the potential existence of the Early Cretaceous epithermal gold deposits that are related to the contemporaneous igneous activity.