Granites and rare metal pegmatites of the Mufushan granitic batholith form a continuous magmatic sequence linked by fractional crystallization. Tourmaline is present in muscovite leucogranites and all types of pegmatites, including highly evolved Li-rich pegmatites. We utilized major element, trace element and in-situ B isotope analyses of tourmaline to investigate the effects of magmatic fractional crystallization and magmatic volatile phase (MVP) exsolution on Li migration and exceptional Li enrichment. Eight types of tourmaline are identified across three rock units: (i) Isolated (Tur Ia) and nodular (Tur Ib) tourmaline within muscovite leucogranites; (ii) black tourmaline in veins and/or clusters (Tur IIa), as isolated crystals (Tur IIb) and in tourmaline-quartz segregations (Tur IIc) within Li-poor pegmatites; and (iii) tourmaline as isolated pink crystals with zoning patterns (Tur IIIa), as isolated pink crystals and/or radiating clusters (Tur IIIb), and as isolated crystals enclosed in quartz block (Tur IIIc) within Li-rich pegmatites. Tourmaline in Mufushan muscovite leucogranites and Li-poor pegmatites belongs to the alkali-group and schorl series with Mg/(Mg + Fe) ratios of 0.10–0.31 and 0.12–0.48, respectively, containing almost no Li* and F (apfu, based on X + Y + Z = 15). In contrast, tourmaline in Li-rich pegmatites exhibits schorl-elbaite and elbaite-rossmanite compositions with low Mg/(Mg + Fe) ratio (avg. = 0.01), and evolved Li* (0.01–0.90 apfu, avg. = 0.41 apfu) and F (0.00–0.91 apfu, avg. = 0.36 apfu) contents. A pronounced increase in YAl, (Li* + Mn) contents, and Y[Al/(Al + Fe)] ratio is observed across the transition from Li-poor to Li-rich pegmatites, consistent with the anticipated pattern of fractional crystallization. The concentration of Li exhibits a sharp increase in Li-rich pegmatites (avg. Li = 6786 ppm) compared to Li-poor pegmatites (avg. Li = 114 ppm) and leucogranites (avg. Li = 469 ppm). Lithium contents increase and reach a peak during the crystallization of Tur IIIb (6686–11,667 ppm), and have lower peak contents during the precipitation of Tur IIIc (8261–9160 ppm), indicating that the incorporation of Li is influenced by MVP accumulation and exsolution. MVP exsolution significantly reduces the solubility of Nb, Ta, and Be in the residual melt, promoting the precipitation of beryl and columbite group minerals and facilitating the migration of fluid-mobile elements such as Li, Rb, Cs, and Ga to form lepidolite. The B isotope compositions of tourmaline range from −14.8 ‰ ∼ −12.6 ‰ in Li-poor pegmatites to −17.1 ‰ ∼ −14.0 ‰ in Li-rich pegmatites. Rayleigh fractionation modeling reveals that MVP saturation occurs after approximately 60 % B was removed from the pegmatite melt. The compositional variation of tourmaline demonstrates that Li enrichment is not only governed by continuous fractional crystallization, but also by MVP-related accumulation and exsolution mechanism.

中文翻译：

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使用碧玺追踪华南 Mufushan 花岗岩浴岩中的锂矿化


Mufushan 花岗岩浴岩的花岗岩和稀有金属伟晶岩形成一个连续的岩浆序列，由分数结晶连接。碧玺存在于白云母白花岗岩和所有类型的伟晶岩中，包括高度进化的富锂伟晶岩。我们利用电气石的主元素、微量元素和原位 B 同位素分析来研究岩浆分馏结晶和岩浆挥发相 （MVP） 溶出对 Li 迁移和异常 Li 富集的影响。在三个岩石单元中鉴定出八种类型的碧玺：（i） 白云母中的孤立 （Tur Ia） 和结节状 （Tur Ib） 碧玺;（ii） 矿脉和/或簇状中的黑色碧玺 （Tur IIa），作为孤立的晶体 （Tur IIb） 和贫锂伟晶岩内的电气石-石英偏析 （Tur IIc）;（iii） 碧玺为具有分区图案的孤立粉红色晶体 （Tur IIIa），孤立的粉红色晶体和/或辐射簇 （Tur IIIb），以及封闭在富锂伟晶岩内的石英块中的孤立晶体 （Tur IIIc）。木浮山白云母中的碧玺和贫锂伟晶岩属于碱族和贫锂伟晶岩，Mg/（Mg + Fe） 比分别为 0.10–0.31 和 0.12–0.48，几乎不含 Li* 和 F（apfu，基于 X + Y + Z = 15）。相比之下，富锂伟晶岩中的碧玺表现出钙镁-钠锂铁矿和钠锂铁矿-红铜矿成分，具有低 Mg/（Mg + Fe） 比率（平均 = 0.01），并进化出 Li*（0.01-0.90 apfu，平均 = 0.41 apfu）和 F（0.00-0.91 apfu，平均 = 0.36 apfu）含量。在从贫锂伟晶岩到富锂伟晶岩的转变中观察到 YAl、（Li* + Mn） 含量和 Y[Al/（Al + Fe）] 比率的显着增加，这与预期的分数结晶模式一致。 与贫锂伟晶岩（平均 Li = 114 ppm）和白花岩（平均 Li = 469 ppm）相比，富锂伟晶岩（平均 Li = 6786 ppm）的浓度急剧增加。锂含量在 Tur IIIb 结晶过程中增加并达到峰值 （6686–11,667 ppm），而在 Tur IIIc 沉淀过程中 （8261–9160 ppm） 具有较低的峰含量，表明 Li 的掺入受 MVP 积累和溶解的影响。MVP 溶出显著降低了 Nb、Ta 和 Be 在残余熔体中的溶解度，促进了绿柱石和铌岩族矿物的沉淀，促进了 Li、Rb、Cs 和 Ga 等流体移动元素的迁移形成锂云母。碧玺的 B 同位素组成范围从贫锂伟晶岩的 -14.8 ‰ ∼ -12.6 ‰ 到富锂伟晶岩的 -17.1 ‰ ∼ -14.0 ‰。Rayleigh 分馏模型显示，MVP 饱和发生在从伟晶岩熔体中去除约 60% 的 B 后。电气石的成分变化表明，锂富集不仅受连续分数结晶的控制，还受 MVP 相关的积累和溶出机制的控制。