Deshui Yu , Haibo Yan , Shoujing Wang , Deru Xu , Zhilin Wang , Chi Ma , Fushuai Wei
{"title":"西藏东部柯伊林稀有金属矿区伟晶岩中电气石的化学成分和硼同位素组成:伟晶岩演化的意义","authors":"Deshui Yu , Haibo Yan , Shoujing Wang , Deru Xu , Zhilin Wang , Chi Ma , Fushuai Wei","doi":"10.1016/j.gexplo.2024.107475","DOIUrl":null,"url":null,"abstract":"<div><p>Pegmatites occur widely in the Ke'eryin rare metal orefield. The genesis and evolution of the Ke'eryin pegmatites are still in dispute, and morphological and geochemical studies on tourmalines from the Ke'eryin pegmatites are limited. In this study, in-situ analyses of major and trace elements and B isotope were conducted to uncover the origin of tourmaline and the evolution of related pegmatites. Three types of tourmaline from the Ke'eryin barren pegmatite were identified: elongated columnar or needle-columnar tourmaline (Tur-1 type), isolated, disseminated, irregular, and massive tourmaline (Tur-2 type), and long columnar tourmaline (Tur-3 type). Petrographically, the Tur-1 type crystallized at the early stage of pegmatitic crystallization sequence, the Tur-2 type possibly formed at the early- and/or <em>syn</em>-pegmatitic crystallization sequence, whereas the Tur-3 type likely formed at the relatively late crystallization sequence. Compositionally, most tourmalines belong to the alkali group with a few falling in the vacancy group. All the tourmalines show a schorl composition and are of magmatic origin. Chemical variations from the Tur-1 to Tur-3 tourmalines are controlled by magma fractionation and melt compositions rather than crystal chemical effects. Most tourmalines follow the (Na, Mg)(X<sub>vac</sub>, Al)<sub>−1</sub>, (Mg, OH)(Al, O)<sub>−1</sub>, and (Ca, Mg<sub>2</sub>)(X<sub>vac</sub>, Al<sub>2</sub>)<sub>−1</sub> exchange vectors. The higher contents of Zn, Sn, Li, Be, Nb, and Ta and negative Eu anomalies in the Tur-3 type indicate that it was likely crystallized at a more evolved stage. In combination with textural evidence and tourmaline chemistry, we suggest that the Tur-1 and Tur-2 types were formed at the relatively earlier stage of pegmatite-forming magma and the Tur-3 type was likely formed closer to the end-stage of barren pegmatite crystallization. The B isotopic compositions are relatively homogeneous and display slightly higher in the Tur-3 type, which were likely caused by fractional crystallization during B-rich magma evolution. It can be inferred that the tourmaline in more evolved and/or Li-mineralized pegmatite with magma evolution should have higher Li, Be, Nb, Ta, and Sn contents, implying that tourmaline chemistry may be used as a potential exploration indicator for rare metal mineralization.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"262 ","pages":"Article 107475"},"PeriodicalIF":3.4000,"publicationDate":"2024-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Chemical and boron isotopic compositions of tourmaline from the pegmatite in Ke'eryin rare metal orefield, Eastern Tibet: Implications for pegmatitic evolution\",\"authors\":\"Deshui Yu , Haibo Yan , Shoujing Wang , Deru Xu , Zhilin Wang , Chi Ma , Fushuai Wei\",\"doi\":\"10.1016/j.gexplo.2024.107475\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>Pegmatites occur widely in the Ke'eryin rare metal orefield. The genesis and evolution of the Ke'eryin pegmatites are still in dispute, and morphological and geochemical studies on tourmalines from the Ke'eryin pegmatites are limited. In this study, in-situ analyses of major and trace elements and B isotope were conducted to uncover the origin of tourmaline and the evolution of related pegmatites. Three types of tourmaline from the Ke'eryin barren pegmatite were identified: elongated columnar or needle-columnar tourmaline (Tur-1 type), isolated, disseminated, irregular, and massive tourmaline (Tur-2 type), and long columnar tourmaline (Tur-3 type). Petrographically, the Tur-1 type crystallized at the early stage of pegmatitic crystallization sequence, the Tur-2 type possibly formed at the early- and/or <em>syn</em>-pegmatitic crystallization sequence, whereas the Tur-3 type likely formed at the relatively late crystallization sequence. Compositionally, most tourmalines belong to the alkali group with a few falling in the vacancy group. All the tourmalines show a schorl composition and are of magmatic origin. Chemical variations from the Tur-1 to Tur-3 tourmalines are controlled by magma fractionation and melt compositions rather than crystal chemical effects. Most tourmalines follow the (Na, Mg)(X<sub>vac</sub>, Al)<sub>−1</sub>, (Mg, OH)(Al, O)<sub>−1</sub>, and (Ca, Mg<sub>2</sub>)(X<sub>vac</sub>, Al<sub>2</sub>)<sub>−1</sub> exchange vectors. The higher contents of Zn, Sn, Li, Be, Nb, and Ta and negative Eu anomalies in the Tur-3 type indicate that it was likely crystallized at a more evolved stage. In combination with textural evidence and tourmaline chemistry, we suggest that the Tur-1 and Tur-2 types were formed at the relatively earlier stage of pegmatite-forming magma and the Tur-3 type was likely formed closer to the end-stage of barren pegmatite crystallization. The B isotopic compositions are relatively homogeneous and display slightly higher in the Tur-3 type, which were likely caused by fractional crystallization during B-rich magma evolution. It can be inferred that the tourmaline in more evolved and/or Li-mineralized pegmatite with magma evolution should have higher Li, Be, Nb, Ta, and Sn contents, implying that tourmaline chemistry may be used as a potential exploration indicator for rare metal mineralization.</p></div>\",\"PeriodicalId\":16336,\"journal\":{\"name\":\"Journal of Geochemical Exploration\",\"volume\":\"262 \",\"pages\":\"Article 107475\"},\"PeriodicalIF\":3.4000,\"publicationDate\":\"2024-04-06\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of Geochemical Exploration\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0375674224000918\",\"RegionNum\":2,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Geochemical Exploration","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0375674224000918","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
摘要
伟晶岩广泛出现在柯伊林稀有金属矿区。克厄林伟晶岩的成因和演化仍存在争议,对克厄林伟晶岩中碧玺的形态和地球化学研究也很有限。本研究進行了主要和微量元素及硼同位素的原位分析,以揭示電氣石的起源和相關偉晶岩的演變。研究人員從 Ke'erin 瘠薄偉晶岩中鑑定了三類電氣石:細長柱狀或針柱狀電氣石(Tur-1 型)、孤立、散佈、不規則和塊狀電氣石(Tur-2 型),以及長柱狀電氣石(Tur-3 型)。在岩相學上,Tur-1型電氣石結晶於偉晶岩結晶序列的早期階段,Tur-2型電氣石可能形成於早期及/或同時期偉晶岩結晶序列,而Tur-3型電氣石可能形成於相對較晚的結晶序列。在成分上,大部分電氣石屬於鹼性組,只有少數屬於空位組。所有電氣石都顯示出雪卡爾成分,並源自岩漿。Tur-1至Tur-3碧璽的化學變化是受岩漿分馏和熔融成分所控制,而非晶體化學影響。大部分電氣石遵循(Na, Mg)(Xvac, Al)-1、(Mg, OH)(Al, O)-1 和(Ca, Mg2)(Xvac, Al2)-1 的交換向量。Tur-3 型中较高的 Zn、Sn、Li、Be、Nb 和 Ta 含量以及负的 Eu 异常表明,它很可能是在更为演化的阶段结晶的。结合纹理证据和电气石化学成分,我们认为 Tur-1 和 Tur-2 型是在伟晶岩形成岩浆的相对较早阶段形成的,而 Tur-3 型可能是在更接近贫瘠伟晶岩结晶的末期形成的。Tur-3 型的 B 同位素组成相对均匀,显示略高,这很可能是在富 B 岩浆演化过程中的碎裂结晶造成的。由此推論,在岩漿演化過程中,演化程度較高及/或鋰礦化程度較高的偉晶岩中的電氣石,應具有較高的鋰、鈹、鈮、鉭和錫含量,這意味著電氣石的化學作用可作為稀有金屬礦化的潛在勘探指標。
Chemical and boron isotopic compositions of tourmaline from the pegmatite in Ke'eryin rare metal orefield, Eastern Tibet: Implications for pegmatitic evolution
Pegmatites occur widely in the Ke'eryin rare metal orefield. The genesis and evolution of the Ke'eryin pegmatites are still in dispute, and morphological and geochemical studies on tourmalines from the Ke'eryin pegmatites are limited. In this study, in-situ analyses of major and trace elements and B isotope were conducted to uncover the origin of tourmaline and the evolution of related pegmatites. Three types of tourmaline from the Ke'eryin barren pegmatite were identified: elongated columnar or needle-columnar tourmaline (Tur-1 type), isolated, disseminated, irregular, and massive tourmaline (Tur-2 type), and long columnar tourmaline (Tur-3 type). Petrographically, the Tur-1 type crystallized at the early stage of pegmatitic crystallization sequence, the Tur-2 type possibly formed at the early- and/or syn-pegmatitic crystallization sequence, whereas the Tur-3 type likely formed at the relatively late crystallization sequence. Compositionally, most tourmalines belong to the alkali group with a few falling in the vacancy group. All the tourmalines show a schorl composition and are of magmatic origin. Chemical variations from the Tur-1 to Tur-3 tourmalines are controlled by magma fractionation and melt compositions rather than crystal chemical effects. Most tourmalines follow the (Na, Mg)(Xvac, Al)−1, (Mg, OH)(Al, O)−1, and (Ca, Mg2)(Xvac, Al2)−1 exchange vectors. The higher contents of Zn, Sn, Li, Be, Nb, and Ta and negative Eu anomalies in the Tur-3 type indicate that it was likely crystallized at a more evolved stage. In combination with textural evidence and tourmaline chemistry, we suggest that the Tur-1 and Tur-2 types were formed at the relatively earlier stage of pegmatite-forming magma and the Tur-3 type was likely formed closer to the end-stage of barren pegmatite crystallization. The B isotopic compositions are relatively homogeneous and display slightly higher in the Tur-3 type, which were likely caused by fractional crystallization during B-rich magma evolution. It can be inferred that the tourmaline in more evolved and/or Li-mineralized pegmatite with magma evolution should have higher Li, Be, Nb, Ta, and Sn contents, implying that tourmaline chemistry may be used as a potential exploration indicator for rare metal mineralization.
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.