Geochronology, geochemical and isotopic constraints on petrogenesis of intrusive complex associated with Bianjiadayuan polymetallic deposit on the southern margin of the Greater Khingan, China

The Early Paleozoic Bianjiadayuan complex of monzodiorite and biotite-bearing monzogranite is located in the southern part of the Huanggangliang–Ganzhuermiao metallogenic belt, southern Greater Khingan, China. The 206Pb/238U ages of zircons from the monzodiorite and biotite-bearing monzogranite are 129.67 ± 0.4 and 143.20 ± 1.2 Ma, respectively. The total REE contents of the rocks are very high, especially LREEs, suggesting obvious LREE and HREE fractionation; the monzodiorite has weak negative Eu anomalies, the biotite-bearing monzogranite highly negative anomalies. These rocks are all rich in large ion lithophile elements (Rb and U) and relatively depleted in high-field-strength elements (Nb and Ta). The monzodiorites and biotite-bearing monzogranites have εHf(t) values of 1.39–5.69 and 0.86–2.46 and tDM2 ages of 0.82–1.09 and 1.04–1.24 Ga, respectively. In the εHf(t)–t diagram, the data plot between the chondrite and depleted mantle lines of Hf isotopic evolution, showing the rocks were derived mainly from new crustal material that had been derived by the differentiation of the mantle. We conclude that this area underwent an important episode of crustal growth in the Meso–Neoproterozoic. The relationship between the intrusive complex and the orebody was related to faulting; we infer that the Bianjiadayuan Pb–Zn polymetallic deposit is mainly related to Late Jurassic–Early Cretaceous (144–129 Ma) magmatic activity, and it represents large-scale mineralisation in the context of Paleo-Pacific plate subduction and regional extension.