Petrogenesis and tectonic setting of igneous rocks from the Dongbulage porphyry Mo deposit, Great Hinggan Range, NE China: Constraints from geology, geochronology, and isotope geochemistry

Abstract

The Dongbulage porphyry Mo deposit is a recently discovered deposit located in the Huanggang–Ganzhuermiao polymetallic metallogenic belt of Inner Mongolia, NE China. Here, we present zircon U–Pb ages and Hf isotopic compositions, and whole-rock geochemical and Sr–Nd–Pb isotopic data, for magmatic rocks associated with Mo mineralisation to constrain the age and petrogenesis of these rocks. The rocks are dominated by mineralised granite porphyries, quartz-monzonites, and rhyolite. Zircon U–Pb dating shows that the ore-bearing granite porphyries have ages of 154.4 ± 3.5, 155.4 ± 1.1, and 158.7 ± 0.6 Ma, the quartz-monzonites have ages of 157.8 ± 1.6 and 166.5 ± 1.3 Ma, and the rhyolite has an age of 172.9 ± 3.0 Ma. The granite porphyries and rhyolites are characterised by high K2O and SiO2 contents, enrichment in light rare-earth elements, strong negative Eu anomalies, and pronounced depletion in Ba, Nb, Ta, Sr, P, and Ti. The quartz-monzonites show enrichment in large-ion lithophile elements (Rb and K), are depleted in heavy rare-earth elements, Nb, Ta, Sr, P, and Ti, and exhibit weak negative Eu anomalies. All of the rocks have low initial 87Sr/86Sr (0.7022–0.7064) and εNd(t) values (−3.62 to + 3.99), positive εHf(t) values (+1.1 to + 13.8), and young two-stage Nd and Hf model ages (TC DM(Nd) = 623–1240 Ma and TC DM(Hf) = 305–1108 Ma, respectively). Whole-rock Pb isotopic compositions show a narrow range of values, with 206Pb/204Pb = 18.314–19.116, 207Pb/204Pb = 15.573–15.595, and 208Pb/204Pb = 38.731–39.296, which, together with their Sr–Nd–Hf isotopic compositions, indicate the dominance of a mantle source component. The isotopic data suggest that the Dongbulage magmatic rocks were derived from partial melting of juvenile lower crust. The granite porphyries are highly evolved I-type magmas with geochemical characteristics similar to those of porphyry granitoids associated with Mo mineralisation in the Great Hinggan Range. On the basis of the regional geology and geochemistry, we suggest that the Dongbulage porphyry Mo deposit formed in a subduction setting associated with southward subduction of the Mongol–Okhotsk oceanic plate.