The genesis of the granitic rocks associated with the Mo-mineralization at the Hongling deposit, eastern Tianshan, NW China: Constraints from geology, geochronology, geochemistry, and Sr-Nd-Hf isotopes

Abstract

The eastern Tianshan is an important molybdenum metallogenic belt in the southern margin of the Central Asian Orogenic Belt (CAOB). The newly discovered Hongling Mo deposit is located in the north–east margin of the Kanggur–Huangshan shear zone in eastern Tianshan, NW China. However, the genesis of the granitic rocks associated with the Mo-mineralization is unclear. The monzogranite, monzogranite porphyry and porphyritic granite from the Hongling deposit are high-K calc-alkaline series and characterized by high SiO2 and Al2O3 and low MgO, TiO2, and P2O5 concentrations. They are enriched in K, Rb, U and Pb, and depleted in Nb, Ba, P, and Ti, with negative Eu anomalies. Zircon LA–ICP–MS U–Pb dating yielded mean ages for the monzogranite of 238 ± 5 Ma and 234 ± 3 Ma, monzogranite porphyry of 234 ± 2 Ma, and porphyritic granite of 232 ± 3 Ma, respectively, which coincide with molybdenite Re–Os model ages ranging from 227 ± 4 to 228 ± 4 Ma. The zircons from the monzogranite, monzogranite porphyry and porphyritic granite yield εHf (t) of 8.3–15.4, 8.4–16.1, and 7.8–14.7, respectively, and TDMc (Hf) ages of 0.23–0.76 Ga. The Hongling granites show a centralized distribution toward lower (87Sr/86Sr)i values of 0.70387–0.70450, higher εNd(t) values of 2.6 to 3.7, and TDM2(Nd) ages of 0.71–0.80 Ga. The geochemical characteristics of granitoids from the Hongling deposit are practically the same as the fertile granitoids from the Donggebi and Baishan deposits. The geochemical and isotopic data indicate that the Hongling granitoids were likely derived from the partial melting of the juvenile lower crustal materials generated during Precambrian to Paleozoic, with involving minor mantle components and related to intraplate extensional setting.