Magmatic-hydrothermal evolution of the Dangba rare-metal granitic pegmatites in the Songpan–Ganzê orogenic belt, Eastern Tibet: Insights from muscovite and columbite-group minerals

IF 3.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Journal of Geochemical Exploration Pub Date : 2024-07-26 DOI:10.1016/j.gexplo.2024.107559
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Abstract

Rare-metal granitic pegmatites are commonly considered to be the results of a combination of magmatic and hydrothermal processes. Although magmatic crystallization and fractionation, and magmatic-hydrothermal transition have been extensively investigated, the processes related economically valuable mineralization of rare-metals and strong fractionation of geochemical twins remain controversial. This study presents a comprehensive analysis of the geochemical evolution of rare-metal mineralized pegmatites, focusing on the mineral chemistry of muscovite and columbite-group minerals (CGM) from the Dangba rare-metal granitic pegmatites in the Songpan–Ganzê orogenic belt. Our findings suggest that the random orientation growth of spodumene crystals and widespread distribution of disordered columbite-group minerals crystals are indicative of lithium saturation in the initial melt at the Dangba No. VII dike. Magmatic fractionation is indicated by gradually increasing ratios of alkali metals (K/Rb ratios) and Ta# (Ta/(Ta + Nb)) in muscovite and CGM, and is proposed to be an important factor for enrichment of rare-metals. During the magmatic-hydrothermal transition, muscovite from metasomatism of spodumene exhibits similar or slightly higher levels of Li, Rb, and Cs, compared to primary muscovite, but shows strong depletion of Ta, Nb, Sn, and W. Alteration of primary minerals (e.g., spodumene, alkali feldspar, and columbite-group minerals) results in the release of these elements into the reactive media (melt/fluid) during the metasomatism. This process ultimately leads to the depletion of rare metals in the early crystallized minerals. However, this process is advantageous for the subsequent mineralization of Ta and Nb, as well as their fractionation. The chemical compositions of exsolved aqueous fluid are influenced by the mineralogy of pegmatites and the partitioning behavior between melt and fluid. Furthermore, pervasive albitization serves as an exploration criterion for Li–Ta–Nb in the Ke'eryin Orefield.

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西藏东部松潘-甘孜造山带当巴稀有金属花岗伟晶岩的岩浆-热液演化:从黝帘石和铌铁矿族矿物中获得的启示
稀有金属花岗伟晶岩通常被认为是岩浆和热液过程相结合的结果。尽管岩浆结晶和分馏以及岩浆-热液转变过程已得到广泛研究,但与稀有金属有经济价值的成矿过程和地球化学孪晶的强烈分馏有关的过程仍存在争议。本研究对稀有金属成矿伟晶岩的地球化学演化进行了全面分析,重点研究了松潘-甘孜造山带党坝稀有金属花岗岩伟晶岩中的黝帘石和铌铁矿族矿物(CGM)的矿物化学。我们的研究结果表明,黝帘石晶体的随机取向生长和无序铌铁矿族矿物晶体的广泛分布表明了党坝七号堤坝初始熔体的锂饱和度。岩浆分馏作用表现在云英岩和 CGM 中碱金属(K/Rb 比)和 Ta# (Ta/(Ta + Nb))的比例逐渐增大,并被认为是稀有金属富集的一个重要因素。在岩浆-热液转变过程中,与原生黝帘石相比,来自闪长岩变质作用的黝帘石显示出相似或稍高的 Li、Rb 和 Cs 含量,但却显示出严重的 Ta、Nb、Sn 和 W 贫化。这一过程最终导致早期结晶矿物中稀有金属的耗竭。不过,这一过程对随后的钽和铌矿化及其分馏是有利的。外溶水流体的化学成分受伟晶岩矿物学以及熔体和流体之间的分配行为的影响。此外,普遍的白化现象也是 Ke'eryin 矿田锂辉石-钽-铌矿的勘探标准。
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来源期刊
Journal of Geochemical Exploration
Journal of Geochemical Exploration 地学-地球化学与地球物理
CiteScore
7.40
自引率
7.70%
发文量
148
审稿时长
8.1 months
期刊介绍: Journal of Geochemical Exploration is mostly dedicated to publication of original studies in exploration and environmental geochemistry and related topics. Contributions considered of prevalent interest for the journal include researches based on the application of innovative methods to: define the genesis and the evolution of mineral deposits including transfer of elements in large-scale mineralized areas. analyze complex systems at the boundaries between bio-geochemistry, metal transport and mineral accumulation. evaluate effects of historical mining activities on the surface environment. trace pollutant sources and define their fate and transport models in the near-surface and surface environments involving solid, fluid and aerial matrices. assess and quantify natural and technogenic radioactivity in the environment. determine geochemical anomalies and set baseline reference values using compositional data analysis, multivariate statistics and geo-spatial analysis. assess the impacts of anthropogenic contamination on ecosystems and human health at local and regional scale to prioritize and classify risks through deterministic and stochastic approaches. Papers dedicated to the presentation of newly developed methods in analytical geochemistry to be applied in the field or in laboratory are also within the topics of interest for the journal.
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