Zircon U–Pb and molybdenite Re–Os geochronology, Hf isotope analyses, and whole-rock geochemistry of the Donggebi Mo deposit, eastern Tianshan, Northwest China, and their geological significance

Abstract

The geodynamic setting of Mesozoic magmatic rocks and associated mineralization in eastern Tianshan, Northwest China, are attracting increasing attention. The newly discovered giant Donggebi molybdenum deposit (0.508 Mt at 0.115% Mo) is located in the central part of eastern Tianshan, Xinjiang. The molybdenum mineralization was genetically associated with the Donggebi stock, comprised of porphyritic granite and granite porphyry. Secondary ion mass spectrometry (SIMS) zircon U–Pb dating constrains that the porphyritic granite and granite porphyry emplacement occurred at 233.8 ± 2.5 Ma and 231.7 ± 2.6 Ma, respectively. The Re–Os model ages of six molybdenite samples range from 235.2 to 237.0 Ma, with a weighted mean age of 236.1 ± 1.4 Ma, which is roughly consistent within errors with the zircon U–Pb ages, suggesting a Middle Triassic magmatic–mineralization event at Donggebi. Geochemically, the Donggebi granitoids are characterized by high SiO₂ and K₂O contents, with low MgO contents, belonging to high-K calc-alkaline granites. These rocks show pronounced enrichment in K, Rb, U, and Pb, and depletion in Sr, Ba, P, and Ti, with negative Eu anomalies (Eu/Eu* = 0.20–0.38). In situ Hf isotopic analyses of zircon from the porphyritic granite and granite porphyry yielded ε_Hf(t) values ranging from +6.6 to +10.5, and from +5.5 to +10.1, respectively. The geochemical and isotopic data imply that the primary magmas of the Donggebi granitoids could have originated by partial melting of a juvenile lower crust that involved some mantle components. Combined with the regional geological history, geochemistry of the Donggebi granitoids, and new isotopic age data, we thus propose that the Donggebi molybdenum deposit was formed in the Middle Triassic, and occurred in an intracontinental extension setting in eastern Tianshan.

Keywords:

• SIMS zircon U–Pb dating
• molybdenite Re–Os dating
• Hf isotope
• geochemistry
• Donggebi Mo deposit
• eastern Tianshan

Acknowledgements

We are very grateful to Editor-in-chief, Robert J. Stern, and two anonymous reviewers for constructive comments and improvement of the manuscript. We thank Yaqing He, Senior Engineer of Xinjiang Luomu Mining Corporation, for great support and assistance for our fieldwork. We are very grateful to the Chinese Academician, Yusheng Zhai, of the China University of Geosciences (Beijing) for a helpful scientific review of an earlier version of the manuscript. Professor Xianhua Li of the Institute of Geology and Geophysics, Chinese Academy of Sciences, and Professor Li Su of the China University of Geosciences (Beijing) are also appreciated for their support for SIMS zircon U–Pb dating.

Additional information

Funding

This research was financially supported by the Program of the China Geological Survey [1212011085471 and 1212011220923], by the Key Program of the National Natural Science Foundation of China [41030423], by the Major Basic Research Program of People’s Republic of China [2014CB440903], and by the 111 Project under the Ministry of Education and the State Administration of Foreign Experts Affairs, China [B07011].