Age of the Yongxin Au deposit in the Lesser Xing'an Range: Implications for an Early Cretaceous geodynamic setting for gold mineralization in NE China

Abstract

The newly discovered Yongxin Au deposit in the Lesser Xing'an Range of north‐eastern Heilongjiang Province, NE China, has a resource of ~20 t with a grade of 4.1 g/t Au. The deposit is hosted by Carboniferous syenogranite and mylonite, and Cretaceous diorite porphyry and granite porphyry. The syenogranite has a LA‐ICP‐MS 206Pb/238U zircon age of 316 ± 2 Ma, and both the granite porphyry and diorite porphyry yield an age of 119 ± 1 Ma. The Rb–Sr isochron age of Au‐bearing pyrite from hydrothermal breccia‐type ore is 107 ± 4 Ma, and this is interpreted as the mineralization age of the Yongxin deposit. In combination with published geochronological data, we argue that epithermal Au mineralization in NE China formed during the period ca. 124 to 107 Ma and was produced during rollback of Palaeo‐Pacific oceanic slab. The Cretaceous epithermal Au deposits are distributed in the Erguna Massif, Lesser Xing'an Range, Zhangguangcai Range, and Jiamusi and Nadanhada terranes. In combination with the coeval porphyry Mo deposits present in these areas, we propose that the Erguna Massif, Lesser Xing'an Range, north‐eastern Great Xing'an Range, and eastern Jiamusi and Nadanhada terranes, where only epithermal gold deposits were discovered up to date, might be prospective for concealed porphyry Cu or Mo deposits.