Magmatic to aqueous phase transition in Li-pegmatite: microtextural and geochemical study of muscovite–lepidolite from Boam mine area, Uljin, South Korea

IF 4.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Mineralium Deposita Pub Date : 2024-06-14 DOI:10.1007/s00126-024-01286-z
Woohyun Choi, Changyun Park, Chul-Ho Heo, Seok-Jun Yang, Il-Hwan Oh, Kyung Su Park, Sung Hwa Choi
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Abstract

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 (Aliv + 2Alvi ↔ 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.

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锂辉石中从岩浆到水相的转变:韩国蔚珍 Boam 矿区麝香石-鳞片岩的显微质构和地球化学研究
这项研究利用含锂云母对位于韩国的著名锂辉石矿床 Boam 矿区进行了调查,以确定稀有元素伟晶岩形成过程中的岩浆-水转变。层状伟晶岩中的麝香石-鳞片岩系列云母表现出六种质地,根据主要元素和微量元素的组成分为三个阶段(早期、中期和晚期)。黝帘石-鳞片岩系列云母的置换机制遵循锂固定(Si ↔ Li + Al)和辉石置换(Aliv + 2Alvi ↔ Li + (Fe2+, Mg2+, Mn2+) + Si)矢量。早期阶段的云母由于低过冷度导致晶体快速增长而显示出较大的晶粒尺寸。与后期的鳞片岩相比,这些云母的扩散带具有较高的铌-钽浓度和较低的锂浓度,表明其分馏程度较低。这些特征表明早期云母起源于硅质熔体。中期云母与早期云母截然不同,边界不稳定,锂含量较高。硼的富集降低了熔体的粘度,增加了H2O的溶解度,导致生长速度加快,矿化速度减慢。B 对 HFSE 分配的抑制导致 Nb-Ta 浓度低于硅质熔体,这表明存在水熔体。细粒晚期云母与微晶石英共存,其特征是铯富集和铌钽贫化,而这只发生在通量丰富的水成岩流体中。K-Rb-Cs 的非瑞利行为表明,与熔融相不同,它偏离了部分结晶,这表明晚期云母起源于水流。因此,矿床中锂辉石的形成主要受控于硅熔体-水熔体-水液的不溶性以及每种介质中的分部结晶。
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来源期刊
Mineralium Deposita
Mineralium Deposita 地学-地球化学与地球物理
CiteScore
11.00
自引率
6.20%
发文量
61
审稿时长
6 months
期刊介绍: The journal Mineralium Deposita introduces new observations, principles, and interpretations from the field of economic geology, including nonmetallic mineral deposits, experimental and applied geochemistry, with emphasis on mineral deposits. It offers short and comprehensive articles, review papers, brief original papers, scientific discussions and news, as well as reports on meetings of importance to mineral research. The emphasis is on high-quality content and form for all articles and on international coverage of subject matter.
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