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<p>The mechanism of lithium (Li) enrichment in pegmatites remains debated between fractional crystallization and magmatic fluid involvement. Here we investigate the world-class Jiajika Li deposit, the largest hard-rock Li deposit in Asia, using high-precision Rb isotope data from a 3000-m scientific drill core covering Li-rich pegmatites, Li-poor pegmatites, aplites, granites, and metasedimentary rocks. The results reveal systematic Rb isotope fractionation, with Li-rich pegmatites showing the highest δ⁸⁷Rb values (up to + 0.63‰) and Li contents (up to 6011&#xa0;µg/g), significantly exceeding both wall rocks (-1.24‰ to + 0.29‰) and the average upper continental crust (-0.14‰). These patterns cannot be explained by post mineralization alteration, wall-rock assimilation, or fractional crystallization. In contrast, melt-hydrothermal fluid mixing models reproduce the observed Rb isotope data and Li-Rb co-enrichment, demonstrating that magmatic fluids exsolved during phase separation efficiently transported and concentrated rare metals, driving Li enrichment by up to 15-fold. Integration of Rb isotopes with Li and Ba isotopes reveals a coherent magmatic-fluid signature, establishing a novel multi-isotope approach to trace fluid-mediated ore-forming processes. We conclude that δ⁸⁷Rb values primarily reflect fluid flux and interaction intensity, whereas Li concentrations record precipitation efficiency. This refined framework underscores the indispensable role of magmatic fluids in the mobilization, transport, and deposition of Li in pegmatite systems, advancing genetic models and guiding exploration for rare-metal resources.</p>

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Lithium enrichment in pegmatites driven by magmatic fluids: evidence from Rb stable isotopes

  • 期刊论文

  • 发表日期：

    2026年2月11日

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  • Xia Hu,
  • Guangwei Li,
  • Zhiqin Xu,
  • Fang Huang

摘要

The mechanism of lithium (Li) enrichment in pegmatites remains debated between fractional crystallization and magmatic fluid involvement. Here we investigate the world-class Jiajika Li deposit, the largest hard-rock Li deposit in Asia, using high-precision Rb isotope data from a 3000-m scientific drill core covering Li-rich pegmatites, Li-poor pegmatites, aplites, granites, and metasedimentary rocks. The results reveal systematic Rb isotope fractionation, with Li-rich pegmatites showing the highest δ⁸⁷Rb values (up to + 0.63‰) and Li contents (up to 6011 µg/g), significantly exceeding both wall rocks (-1.24‰ to + 0.29‰) and the average upper continental crust (-0.14‰). These patterns cannot be explained by post mineralization alteration, wall-rock assimilation, or fractional crystallization. In contrast, melt-hydrothermal fluid mixing models reproduce the observed Rb isotope data and Li-Rb co-enrichment, demonstrating that magmatic fluids exsolved during phase separation efficiently transported and concentrated rare metals, driving Li enrichment by up to 15-fold. Integration of Rb isotopes with Li and Ba isotopes reveals a coherent magmatic-fluid signature, establishing a novel multi-isotope approach to trace fluid-mediated ore-forming processes. We conclude that δ⁸⁷Rb values primarily reflect fluid flux and interaction intensity, whereas Li concentrations record precipitation efficiency. This refined framework underscores the indispensable role of magmatic fluids in the mobilization, transport, and deposition of Li in pegmatite systems, advancing genetic models and guiding exploration for rare-metal resources.