Earth Science Frontiers ›› 2023, Vol. 30 ›› Issue (2): 415-425.DOI: 10.13745/j.esf.sf.2022.2.79

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Relationship between the large scale fenitization and REE mineralization on the border between Zhejiang and Fujian provinces: A review of recent research progress

CHEN Shizhong1,2(), ZHOU Yan1, XING Guangfu1, XU Mincheng1,*(), FAN Feipeng1, XI Wanwan1, ZHU Xiaoting1, GUO Weimin1   

  1. 1. Nanjing Center, China Geological Survey, Nanjing 210016, China
    2. ürümqi Comprehensive Survey Center on Natural Resources, China Geological Survey, ürümqi 830026, China
  • Received:2021-01-05 Revised:2022-05-09 Online:2023-03-25 Published:2023-01-05
  • Contact: XU Mincheng

Abstract:

Fenitization is considered to be a typical post magmatic alkaline metasomatic process usually associated with REE mineralization. The typical super large REE deposits related to fenitization include the Bayan Obo REE deposit in Inner Mongolia and the Maoniuping REE deposit in western Sichuan as respectively the first and second largest LREE deposits in China. The Tieshan metasomatic rock (TMR), located on the northeastern side of the Zhenghe-Dapu fault zone on the border between Zhejiang and Fujian Provinces, is the largest potassic metasomatite in southeastern China. Its prospective rare earth oxide (REO) resource is expected to reach ~62 million tonnes, with porphyry copper and apatite deposits showing prospects for critical metals such as REEs. The widely occurring fenites in TMR are closely related to the mineralization of P, REE, Ti and Ga. The fenite belt is about 1-2 km long and hundreds of meters wide, where ~40 REE-rich apatite orebodies were discovered. The fenites are composed of feldspar, pyroxene, amphibole, biotite and melanite, etc. Among them, potassic feldspars occur in four modes: (1) in facial alkali alteration or in alkali alteration with melanites, (2) in light or (3) dark alkali feldspar veins, or (4) in association with black garnet. Pyroxenes has three occurrence modes: in breccias or feldspar, or in association with amphiboles. Aegirine pyroxene displays obvious girdle structure under the microscope, with a light-green core and dark green crust, indicating there are higher diopside components at the core and higher aegirine content at the edge. The fenite was formed in the second magmatic stage of the Yanshanian Movement (157-156 Ma) and probably related to the intrusion of the Tongpeng’an potassic feldspar granite to the east, as REEs were enriched during the magmatic-hydrothermal activity. In the third stage of the Yanshannian Movement (118-114 Ma), the Tieshan metasomatic rock was altered by alkaline hydrothermal fluid from the porphyries and polymetallic mineralization occurred.

Key words: border between Zhejiang and Fujian provinces, alkaline metasomatism, fenite, REE deposits

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