The Longmala and Mengya’a skarn Pb–Zn deposits, Gangdese region, Tibet: evidence from U–Pb and Re–Os geochronology for formation during early India–Asia collision

Abstract

The Longmala and Mengya’a deposits are two representative skarn Pb–Zn deposits of the Nyainqêntanglha Pb–Zn–(Cu–Mo–Ag) polymetallic belt in the Gangdese region, Tibet, China. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating of the mineralization-related biotite monzogranite from the Longmala deposit yielded a weighted mean age of 55.7 Ma, which can be interpreted as the emplacement age of the pluton. Re–Os dating of three molybdenite samples from the Longmala deposit yielded model ages of 51.8–54.3 Ma, with a weighted mean age of 53.3 Ma, which is interpreted as the mineralization age of the deposit and overlaps the age of the causative intrusion. The Re–Os dating of four molybdenite samples from the Mengya’a deposit yielded model ages of 60.4–65.8 Ma, with a weighted mean age of 63.6 Ma, which represents the mineralization age of this deposit. Our new precise age data for these two deposits are consistent with the existing ages of ca. 65–51 Ma for other skarn polymetallic deposits in the Nyainqêntanglha metallogenic belt. In addition, these new age data, combined with existing information on the geological evolution history of the Lhasa terrane, indicate that the belt of skarn deposits is closely related to initial collision between India and the Asian continents.

Keywords:

• geochronology
• India–Asia collision
• Longmala deposit
• Mengya’a deposit
• Nyainqêntanglha metallogenic belt
• Gangdese

Acknowledgements

We are grateful to Jianzhen Geng for his help in zircon U–Pb isotopic dating and Chao Li for the Re–Os isotope analyses. We thank Huaping Zhang for his assistance in the fieldwork. We thank Professor Leon Bagas, Dr Liujun, and the anonymous reviewer for their constructive reviews. Special thanks to Dr Robert J. Stern, Professor Richard J Goldfarb, and Hegen Ouyang for their constructive suggestions.

Additional information

Funding

This research project was financially supported jointly by the Scientific Research Fund of the China Central Non-Commercial Institute [grant number K14l6]; the National Basic Research program of China (973) [grant number 2011CB403103]; and the Geological Survey Programme of the mineral resources potential evaluation [grant number 12120113036200].