Geochronology, geochemistry, and Sr–Nd–Pb–Hf isotopes of ore-related diorites in the Erdaohe Pb-Zn-Ag deposit, Great Hinggan Range, NE China: Constraints on timing, petrogenesis and tectonic setting

Abstract

The Erdaohe deposit is a newly discovered large-sized skarn Pb-Zn-Ag deposit located in the middle segment of the Great Hinggan Range, NE China. Geochronologic and geochemical data for the ore-related diorites in the deposit are presented here to explore the age, petrogenesis and geodynamic setting of these rocks. Zircon U–Pb LA-ICP-MS dating results show that the ore-related diorites were emplaced at 145–142 Ma. Geochemically, the ore-related diorites are generally characterized by high Y (22.5–32.7 ppm) and Yb (2.23–3.28 ppm) contents, low Sr/Y (14–40) ratios, light rare earth element (LREEs) and large ion lithophile element (LILE) (e.g., Rb and K) enrichments, and high field strength element (HFSE) (e.g., Nb, Ta, and Ti) depletions. These geochemical features are similar to those of arc magmas. Furthermore, the diorites have low (87Sr/86Sr)i compositions, fairly variable εNd(t) values and positive εHf(t) values, corresponding to 0.70604 to 0.70720, −7.8 to +2.6 and +4.5 to +8.0, respectively. These diorites have relatively young Sm–Nd and Hf model ages of 1564 to 721 Ma and 955 to 619 Ma, respectively. The whole-rock Pb isotopes show a narrow range. These isotopic data suggest that the parental magma was sourced mainly from juvenile crustal components, followed by assimilation and fractional crystallization in the crust with limited concomitant input of ancient crustal materials during magma ascent. In the Late Jurassic, the Great Hinggan Range was under compression due to the closure of the Mongol–Okhotsk Ocean, while in the Early Cretaceous, it was under extension related to the influence of the Paleo-Pacific plate. Based on the geochemical evidence and regional geodynamic evolution, we conclude that the formation of the Erdaohe deposit was associated with Paleo-Pacific plate subduction.