伟晶岩锂同位素研究进展及其对锂成矿过程的指示
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自然资源部成矿作用与资源评价重点实验室,中国地质科学院矿产资源研究所

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国家自然科学基金重点项目(编号42330806)、中国地质科学基本业务费项目(编号JKYZD202315,JKYQN202327)和中国地质大调查项目(编号DD20243484,DD20230289)


Progress in lithium isotopic study of pegmatites and its application in lithium deposit
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1) MNR Key Laboratory of Metallogeny and Mineral Resource Assessment, Institute of Mineral Resource, Chinese Academy of Geological Sciences

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    摘要:

    花岗伟晶岩是最重要的硬岩型锂资源来源,近年来前人应用锂同位素对伟晶岩成岩成矿过程开展较多的研究工作。本文在综述伟晶岩锂同位素研究进展的基础上,重点分析了伟晶岩的锂同位素在指示伟晶岩熔体源区、指示伟晶岩熔体分离、结晶和流体出溶中的研究思路,为揭示伟晶岩的锂成矿过程提供了启示。前人研究表明,伟晶岩熔体结晶分异和流体出溶过程均会产生较明显的锂同位素分馏:① 结晶分异使残余伟晶岩熔体富集7Li;② 流体出溶使熔体富集6Li;③ 扩散分馏使快速迁移的6Li累积在熔体远端。全球伟晶岩(包括甲基卡伟晶岩)的Li含量与δ7Li之间均有明显的负相关关系,甲基卡伟晶岩分异程度的增高与δ7Li呈负相关关系。前人研究多认为,高分异伟晶岩体系中锂同位素变轻可能是云母和锂辉石等富6Li矿物的大量结晶、富7Li流体出溶丢失或动力分馏作用等原因造成的。另一方面,不平衡结晶分异作用会产生显著的动力分馏,热液蚀变作用会产生强烈的低温分馏,这些过程产生的同位素分馏效应会模糊锂的来源信息,给同位素示踪带来困难。因此,伟晶岩锂同位素组成可能对于指示锂的来源作用有限,但可以较好地指示熔体结晶分异和流体出溶等地质过程,有助于揭示伟晶岩熔体-流体的演化过程,指示锂矿化机制。

    Abstract:

    Granite pegmatites are the most important hard?rock type lithium resources. In recent years, many studies have been carried out on the diagenesis and mineralization of pegmatite using lithium isotopes. This article provides an analysis of the lithium application to trace the source region of pegmatite melts, indicate the separation, crystallization, and fluid exsolution of pegmatite melts, and provide insights into the lithium metallogenic process of pegmatites, based on the review of the advances of lithium isotopes in pegmatites. Researchers have shown that crystallization differentiation and fluid exsolution in pegmatite melts cause significant lithium isotope fractionation: ① crystallization increase δ7Limelt; ② fluid exsolution decreases δ7Limelt; ③ diffusion fractionation leads to the accumulation of 6Li at the melt''s far end. There''s a significant negative correlation between Li content and δ7Li in global pegmatites (including Jiajika pegmatite), and the increase of differentiation degree of Jiajika pegmatite is negatively correlated with δ7Li. The lightening of lithium isotopes in differentiated pegmatite systems may result from extensive crystallization of 6Li-rich minerals like mica and spodumene, fluid exsolution, or dynamic fractionation, as indicated by prior studies. In addition, unbalanced crystal differentiation and hydrothermal alteration can induce significant isotope fractionation, while the resultant isotope fractionation complicates lithium source identification, hampering isotope tracing efforts. The lithium isotopic composition in pegmatites may not reliably trace lithium sources but can elucidate geological processes like melt crystallization differentiation and fluid exsolution, aiding in understanding pegmatite''s melt-fluid evolution and lithium mineralization mechanisms.

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  • 收稿日期:2024-05-01
  • 最后修改日期:2024-05-23
  • 录用日期:2024-05-23
  • 在线发布日期: 2024-05-29
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