Abstract
The Hashitu Mo deposit located in the southern part of the Great Hinggan Range (GHR) is a newly-discovered Mo deposit. The orebodies mainly occur as quartz-sulfide veins in monzogranite and granite porphyry. Besides, minor quartz porphyry is located in the orefield. The zircon U-Pb ages, ore-forming elements, and whole-rock geochemical and Sr-Nd-Pb isotopic data were obtained from granitic rocks associated with Mo mineralization to constrain their age, petrogenesis, metallogenic and tectonic significance. The ore-bearing monzogranite and granite porphyry have zircon U-Pb ages of 149.3 ± 0.7 Ma and 149.5 ± 1.1 Ma, respectively, and the quartz porphyry has an age of 153.2 ± 1.1 Ma. All rocks have similar geochemical characteristics, with high contents of K2O and SiO2, enrichment in Rb, Th, U, K, Nd, Zr, and Hf, depletion in Ba, Nb, Sr, and Ti, and strong negative Eu anomalies. The rocks have low initial 87Sr/86Sr (0.7049–0.7069) and εNd(t) values (2.29–3.47) and young two-stage Nd model ages (TDM2 = 656–752 Ma). The whole-rock Pb isotopic compositions show a wide range, i.e., (206Pb/204Pb)t = 18.93–19.79, (207Pb/204Pb)t = 15.51–15.59, and (208Pb/204Pb)t = 37.21–38.18. The granites are significantly enriched in Mo (concentration coefficient (K) = 19.94). The factor analysis result shows that the factor F1(As-Bi-Zn-Pb-Ag-Sb-B) represents regional background information of Pb-Zn-Ag polymetallic mineralization in the southern GHR, whereas the factor F3(Mo-F) represents the local metallogenic factor. The geochemical and isotopic data suggest that the Hashitu granitic rocks were derived from partial melting of the juvenile lower crust, possibly the Neoproterozoic crust. Based on the geology and geochemistry, we propose that the Hashitu Mo deposit formed in a post-orogenic extensional tectonic setting associated with the southward subduction of the Mongol-Okhotsk oceanic plate.
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