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<p>The albite–lepidolite–topaz Beauvoir granite of the Western European Variscan Belt hosts economic concentrations of rare metals (Li, Sn, Nb, Ta, and Be) associated with magmatic–hydrothermal processes, particularly in unit B1 at the top of the intrusion. The phosphate mineral assemblage indicates that amblygonite-group minerals (AGMs) constitute a subordinate Li-bearing phase in addition to lepidolite, whereas Be-phosphates (beryllonite and hurlbutite) represent the main host for beryllium. Magmatic apatite in exceptionally rare in the B1 unit, suggesting very low Ca activity in the melt. Compared with other peraluminous and perphosphorous granites and pegmatites, the crystallization of Be-phosphates together with the absence of beryl indicates persistently high phosphorus activity during advanced fractional crystallization. LA-ICP-MS analyses of AGMs indicate high but heterogeneous Li, Na, and F contents reflecting solid-solution between montebrasite and amblygonite, as well as AGM replacement by lacroixite. During subsequent hydrothermal stage, both primary Li- and Be-phosphates are progressively replaced by Ca-rich phosphates: morinite and crandallite-group minerals replace AGMs, whereas herderite, loomisite, and secondary apatite successively overprint Be-phosphates. These mineral sequences record significant Ca and Sr inputs from external fluids during early subsolidus evolution of the granite, a process also reflected in the whole-rock geochemical signatures. During muscovitization of albite and lepidolite, dissolution of Be-phosphates by circulating fluids induces significant Be loss, whereas AGM breakdown also releases some lithium. The evolution of the phosphate assemblages, therefore records the transition from highly fractionated magmatic conditions to hydrothermal alteration associated with muscovitization. Overall, the Beauvoir granite represents a distinctive rare-metal system characterized by a lepidolite–Be-phosphate association and the absence of beryl, indicating that the Li–Be endowment was essentially established during the magmatic stage and subsequently modified by hydrothermal redistribution.</p>

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The contrasted behaviour of Li and Be during the magmatic-hydrothermal transition: the example of the phosphate sequence in the Beauvoir granite (France)

  • 期刊论文

  • 发表日期：

    2026年5月27日

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  • Zia Steven Kahou,
  • Michel Cathelineau,
  • Marie-Christine Boiron,
  • Lucas Serin,
  • Naïla Mezoued,
  • Andreï Lecomte,
  • Chantal Peiffert,
  • Patrick Fullenwarth

摘要

The albite–lepidolite–topaz Beauvoir granite of the Western European Variscan Belt hosts economic concentrations of rare metals (Li, Sn, Nb, Ta, and Be) associated with magmatic–hydrothermal processes, particularly in unit B1 at the top of the intrusion. The phosphate mineral assemblage indicates that amblygonite-group minerals (AGMs) constitute a subordinate Li-bearing phase in addition to lepidolite, whereas Be-phosphates (beryllonite and hurlbutite) represent the main host for beryllium. Magmatic apatite in exceptionally rare in the B1 unit, suggesting very low Ca activity in the melt. Compared with other peraluminous and perphosphorous granites and pegmatites, the crystallization of Be-phosphates together with the absence of beryl indicates persistently high phosphorus activity during advanced fractional crystallization. LA-ICP-MS analyses of AGMs indicate high but heterogeneous Li, Na, and F contents reflecting solid-solution between montebrasite and amblygonite, as well as AGM replacement by lacroixite. During subsequent hydrothermal stage, both primary Li- and Be-phosphates are progressively replaced by Ca-rich phosphates: morinite and crandallite-group minerals replace AGMs, whereas herderite, loomisite, and secondary apatite successively overprint Be-phosphates. These mineral sequences record significant Ca and Sr inputs from external fluids during early subsolidus evolution of the granite, a process also reflected in the whole-rock geochemical signatures. During muscovitization of albite and lepidolite, dissolution of Be-phosphates by circulating fluids induces significant Be loss, whereas AGM breakdown also releases some lithium. The evolution of the phosphate assemblages, therefore records the transition from highly fractionated magmatic conditions to hydrothermal alteration associated with muscovitization. Overall, the Beauvoir granite represents a distinctive rare-metal system characterized by a lepidolite–Be-phosphate association and the absence of beryl, indicating that the Li–Be endowment was essentially established during the magmatic stage and subsequently modified by hydrothermal redistribution.