Earth Science Frontiers ›› 2023, Vol. 30 ›› Issue (4): 283-298.DOI: 10.13745/j.esf.sf.2023.2.41

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Geochemistry, geochronology and Hf isotopic characteristics of rare earth-bearing quartz syenite in eastern Dashuigou, East Kunlun

WANG Tao(), LI Jiqing*(), HAN Jie, WANG Taishan, LI Yulong, YUAN Bowu   

  1. Key Laboratory of Geological Process and Mineral Resources in the Northern Part of Qinghai Tibet Plateau, Qinghai Geological Survey Institute, Xining 810012, China
  • Received:2022-05-23 Revised:2023-02-24 Online:2023-07-25 Published:2023-07-07

Abstract:

The discovery of the rare metal/rare earth-bearing alkaline complex in Dagele area, middle East Kunlun was a major breakthrough in the exploration of rare metal and rare earth deposits in East Kunlun. The subsequent discovery of rare earth-bearing quartz syenite in eastern Dashuigou further expanded the scope of exploration, which is of great significance to the strategic mineral exploration and scientific research in East Kunlun. This paper reports the geochronological, geochemical, and Hf isotope studies of the quartz syenite to reveal its petrogenesis, magma source area and tectonic setting. The quartz syenite has a mean zircon (Zr) U-Pb age of (400.2±3.7) Ma corresponding to the Early Devonian. It belongs to the quasi-aluminous alkaline series, characterized by high SiO2 content (64.11%-66.20%), enriched Al2O3 (15.98%-16.19%) and alkali (Na2O+K2O, 11.31%-11.85%), especially K2O (7.24%-8.18%), and low Ti2O (0.38%-0.44%), CaO (1.13%-1.86%), and MgO (0.13%-0.22%) contents, with a A/CNK value of 0.9-0.98. It is enriched in large ion lithophile elements (Rb, K, Ba, Th), and depleted in high field strength elements (Nb, Ta, Ti, P). Results of 10000Ga/Al value (2.8-3.4), Zr content ((751.30-1034.85)×10-6 ), (Zr+Nb+Ce+Y) content ((881.49-1210.16)×10-6), Zr saturation temperature (905.76-931.41 ℃), and Y/Nb ratio (1.87-2.45), along with tectonic discrimination diagrams, indicate the quartz syenite is A2-type granitoid. Combined with regional tectonic and magmatic evolution data, it is believed the quartz syenite was formed in post-collision extension environment; while the Zr εHf(t) value (-0.76-+1.41), and the second stage (tDM2) Hf model age (1303-1435 Ma) indicate the quartz syenite is derived from partial melting of Middle-Proterozoic felsic crust during mantle-derived, high-temperature basaltic magmatic underplating.

Key words: Dashuigou area, Early Devonian, A2 type granite, rare earth mineralization, geochemistry, Hf isotope

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