This study investigated the Boam mine area, a prominent Li-pegmatite deposits located in South Korea, using Li-bearing micas to determine the magmatic–aqueous transition involved in rare-element pegmatite formation. Muscovite–lepidolite series micas from the layered pegmatite exhibited six textures, classified into three stages (early, intermediate, and late) based on compositions of major and trace elements. The substitution mechanisms of muscovite–lepidolite series micas follow lithium fixation (Si ↔ Li + Al) and phengitic substitution (Al^iv + 2Al^vi ↔ Li + (Fe²⁺, Mg²⁺, Mn²⁺) + Si) vectors. Early-stage micas displayed a large grain size due to rapid crystal growth due from low undercooling. Diffusional zonation of these micas with the higher Nb–Ta and lower Li concentrations compared with later-stage lepidolite indicate a lower degree of fractionation. These features suggest a silicic melt origin for early-stage micas. Intermediate-stage micas are distinctly separated from the early-stage type and feature erratic boundaries with higher Li composition. B enrichment reduced the melt viscosity and increased the H₂O solubility, resulting in an increase in growth rate and retardation of mineralization. The inhibition of HFSE partitioning by B lead to a lower Nb–Ta concentration than the silicic melt, suggesting the existence of an aqueous melt. Fine-grained late-stage mica coexists with microcrystalline quartz, and is characterized by Cs enrichment and Nb–Ta depletion that exclusively occur in flux-rich aqueous fluids. Non-Rayleigh behavior of K-Rb-Cs indicates a deviation from fractional crystallization unlike melt phases, suggesting an aqueous fluid origin for late-stage micas. Consequently, the formation of Li-pegmatite in the deposit was predominantly controlled by the immiscibility of silicic melt–aqueous melt–aqueous fluid and fractional crystallization within each medium.

本研究调查了位于韩国的著名锂伟晶岩矿床 Boam 矿区，利用含锂云母来确定稀有元素伟晶岩形成过程中涉及的岩浆-水相转变。层状伟晶岩中的白云母-锂云母系云母具有六种结构，根据主量元素和微量元素的组成分为早期、中期和晚期三个阶段。白云母-锂云母系列云母的取代机制遵循锂固定(Si ↔ Li + Al)和多硅取代(Al ^iv + 2Al ^vi ↔ Li + (Fe ²⁺ 、 Mn ²⁺ ) + Si) 向量。由于低过冷度导致晶体快速生长，早期云母表现出较大的晶粒尺寸。与后期锂云母相比，这些具有较高 Nb-Ta 浓度和较低 Li 浓度的云母的扩散分带表明分馏程度较低。这些特征表明早期云母的硅熔体起源。中间阶段的云母与早期阶段的云母明显分离，并且具有不稳定的边界和较高的锂成分。 B富集降低了熔体粘度并增加了H ₂ O溶解度，导致矿化生长速率增加并延迟。 B 对 HFSE 分配的抑制导致 Nb-Ta 浓度低于硅熔体，表明存在水熔体。细粒晚期云母与微晶石英共存，其特征是 Cs 富集和 Nb-Ta 贫化，仅发生在富含通量的水相流体中。 K-Rb-Cs 的非瑞利行为表明与熔融相不同的是分步结晶的偏差，表明后期云母的水性流体起源。 因此，矿床中锂伟晶岩的形成主要受硅熔体-水熔体-水流体的不混溶性以及每种介质内的分步结晶的控制。