Geochronology, geochemistry and Hf isotopes of andesites in the Sandaowanzi gold deposit (Great Xing'an Range, NE China): implications for petrogenesis, tectonic setting, and mineralization

The Sandaowanzi gold deposit is an extremely Au-rich deposit in the Northern Great Hinggan Range in recent years. Zircon U-Pb geochronology, Hf isotope analysis, and the geochemistry of andesites of the Longjiang Formation from the Sandaowanzi gold deposit were used to investigate the origin, magmatic evolution as well as mineralization and tectonic setting of the Early Cretaceous epithermal gold deposits in the northern Great Hinggan Range area. Zircon U-Pb dating reveals an emplacement age of 123.4 +/- 0.3 Ma, indicating that the andesites of the Sandaowanzi gold deposit was formed during the Early Cretaceous. The andesites are enriched in light rare earth elements relative to heavy rare earth elements and have weak negative Eu anomalies (delta Eu = 0.76-0.90). The rocks are also enriched in large-ion lithophile elements, such as Rb, Ba, Th, U, and K, and depleted in the high-field-strength elements, such as Nb, Ta, and P. These characteristics are typical of volcanic rocks related to subduction. Igneous zircons from the andesite samples have relatively homogeneous Hf isotope ratios, Hf-176/Hf-177 values of 0.282343-0.282502, epsilon Hf(t) values of - 12.58 to - 6.95, and two-stage model ages (T-DM2) of 1743-1431 Ma. The characteristics of the andesites of the Longjiang Formation are consistent with derivation from partial melting of enriched mantle wedge metasomatized by subducted-slab-derived fluids. These rocks formed in an extensional environment associated with the closure of the Mongol-Okhotsk Ocean and subduction of the Paleo-Pacific Plate. Mineralization occurred towards the end of volcanism, and the magmatic activity and mineralization are products of the same geodynamic setting.