Zircon U–Pb dating and Sr–Nd–Pb–Hf isotopes of the ore-associated porphyry at the giant Donggebi Mo deposit, Eastern Tianshan, NW China.

The giant Donggebi porphyry Mo deposit is located in the Jueluotage metallogenic belt of Eastern Tianshan, Xinjiang, Northwest China. Mo mineralization mainly occurs as numerous veinlets in the altered sandstone wall-rocks, with the development of potassic, phyllic, argillic and propylitic alteration assemblages outward from a buried porphyritic granite stock. Zircon crystals from the buried porphyritic granite yield a weighted average 206 Pb/ 238 U age of 236 ± 2.2 Ma (MSWD = 1.2, 1σ, n = 17), slightly older than the molybdenite Re–Os isotope ages of 231–234 Ma, suggesting that the Donggebi porphyry Mo deposit was formed in the Triassic, post-collisional tectonism subsequent to termination of the Paleo-Asia Ocean. The samples from porphyritic granite show high contents of SiO 2 , K 2 O and Al 2 O 3 , low contents of TiO 2 , MgO and CaO, and peraluminous high-K calc-alkaline to shoshonite affinity, with obvious LREE enrichment and negative Eu anomalies. They have high initial 87 Sr/ 86 Sr ratios of 0.70618 to 0.70821, ε Nd( t ) values of 0.60 to 1.62, and T DM2 (Nd) ages of 0.88 to 0.96 Ga. Their ( 206 Pb/ 204 Pb)t, ( 207 Pb/ 204 Pb)t and ( 208 Pb/ 204 Pb)t values are 17.122–18.577, 15.493–15.574, and 37.887–38.006, respectively. Zircons from the porphyritic granite yield εHf(t) values of − 1.58 to 4.82, and T DM2 (Hf) ages of 0.96–1.36 Ga. These geochemical and isotopic data imply that the Donggebi porphyritic granite originated mainly from partial melting of lower continental crust derived from a depleted mantle. The Donggebi Mo deposit is unique based upon the crustal source for the causative porphyry, the distal position of mineralization, and the previously revealed CO 2 -rich ore-forming fluids, and thus belongs to the collisional- or Dabie-type porphyry deposits as exemplified by the Qiane'chong and Yaochong deposits in Dabie Shan, the Donggou deposit in Qinling Orogen, China. [ABSTRACT FROM AUTHOR]