Earth Science Frontiers ›› 2023, Vol. 30 ›› Issue (5): 93-105.DOI: 10.13745/j.esf.sf.2023.5.3

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Coupling relationship between the stability of Li/Be complexes and Li/Be differential enrichment in granitic pegmatites—an experimental study

HONG Tao1,2(), ZHAI Mingguo3,4,5,*(), WANG Yuejun1,2, LIU Xingcheng5,6, XU Xingwang3,4,5, GAO Jun3,4,5, HU Mingxi1,2, MA Jing1,2   

  1. 1. Guangdong Provincial Key Laboratory of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China
    2. Guangdong Southern Marine Science and Engineering Laboratory (Zhuhai), Zhuhai 519082, China
    3. University of Chinese Academy of Sciences, Beijing 100049, China
    4. CAS Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
    5. Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing 100029, China
    6. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
  • Received:2022-12-15 Revised:2023-01-31 Online:2023-09-25 Published:2023-10-20
  • Contact: ZHAI Mingguo

Abstract:

Pegmatite lithium (Li)-beryllium (Be) deposits are an important type of strategic Li-Be deposit. However, anatexis, on one hand, only produces a small amount of pegmatite-forming melts while Li/Be extraction efficiency for anatectic pegmatites is low; on the other hand, it is still controversial whether magmatic fractional crystallization results in high Li/Be enrichment in pegmatites and increased extraction efficiency. With the observation of fluid immiscibility in Li/Be-rich silica melt, it suggested that melt-fluid immiscibility may also lead to pegmatite formation. Current studies on the pegmatite Li-Be mineralization processes during the melt-fluid phase mainly focus on the whole-rock geochemical characteristics of granitic pegmatites, the in-situ geochemical changes of the rock-forming minerals (mica, quartz, feldspar, etc.) and ore minerals (beryl, etc.), and the mineralogical and geochemical characteristics of melt/fluid inclusions in petrogenic minerals, ore minerals, and accessory minerals (garnet, etc.). So far no obvious correlation has been found between the depositional age and the types of melt/fluid inclusions. To understand the mechanism of abnormal Li/Be enrichments in pegmatites it is key to study the distribution and stability of Li/Be complexes during the melt-fluid phase, however, the former study is scarce and the latter non-existent. In this study we investigated the effects of pH and calcium/aluminum additions on the stability of Li/Be complexes. We found that (1) the stability of Be complex was more affected by pH compared to Li complex; (2) under constant pH, the addition of aluminum promoted Be but hindered Li precipitations; and (3) the addition of calcium had less effect on Li than on Be precipitations. Future high-temperature, high-pressure experimental simulation studies should further enhance our understanding of the Li/Be enrichment processes and provide a geochemical basis for new Li/Be mineralization models based on the stability of Li/Be complexes.

Key words: Li-Be deposits, melt/fluid inclusions, stability of Li/Be complexes, episodic metallogenic process

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