辽宁赛马碱性岩体两种稀有锆矿物的发现及其指示意义
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1.东华理工大学 核资源与环境国家重点实验室;2.辽宁省核工业地质二四一大队有限责任公司;3.江西省地质局第三地质大队

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国家自然科学基金项目(编号42272087, 42063006)、江西省自然科学基金(编号20224ACB213012, 20212BAB203003)和赣鄱俊才支持计划(编号20232BCJ23003)联合资助的成果。


The discovery of two rare zirconosilicates in the Saima alkaline complex, Liaoning Province, China, and its implications for Zr-REE mineralization
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1.State Key Laboratory of Nuclear Resources and Environment, East China University of Technology;2.No. 241 Group Co., Ltd., Liaoning Geological Exploration and Mining Group;3.The Third Geological Brigade of Jiangxi Geological Bureau

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    摘要:

    辽宁赛马碱性岩体首次发现两种稀有锆硅酸盐矿物——赵氏碱锆石和水硼锶钠锆石,为岩浆期异性石的热液蚀变产物。本文通过详细的岩相学、矿物学、地球化学以及同位素年代学研究,揭示了赵氏碱锆石和水硼锶钠锆石的产出特征、晶体结构、化学成分以及锆和稀土的岩浆富集-热液蚀变年龄,进而探讨岩浆期后交代流体与成矿元素迁移-沉淀的关系。赵氏碱锆石为早期蚀变产物,多呈它形,与残余异性石、次生斜方钠锆石、钠沸石和铈硅磷灰石等共生。其为斜方晶系, a = 11.8325(5) ?, b = 12.9141(3) ?, c = 6.7292(1) ?, V = 1028.25(4) ?3,晶体化学式为(Na0.97K0.78Ca0.06Pb0.01Sr0.01)Σ1.83(Zr0.98Ti0.01Hf0.01)Σ1.00Si3.02O9·2H2O。水硼锶钠锆石形成晚于赵氏碱锆石,呈它形粒状或集合体,与次生钠沸石、锆石、菱锶矿、方解石和铈硅磷灰石等蚀变矿物共生于异性石假晶,假晶中异性石残余、斜方钠锆石和赵氏碱锆石均较少。水硼锶钠锆石为三方晶系, a = 19.6634(3) ?, c = 9.9581(3) ?, V = 3334.45(1) ?3,晶体化学式为(Na7.10Ca2.55K0.01¨3.34)Σ13.00(Sr10.42Ba0.01Pb0.01¨0.56)Σ11.00(Zr12.85Ti0.49Hf0.13Al0.08Nb0.06¨0.39)Σ14.00Si42.01B5.99O132(OH)12·12H2O。赵氏碱锆石和水硼锶钠锆石为岩浆期异性石(218 ± 5 Ma)经历不同期次流体交代的蚀变产物,其中赵氏碱锆石与赛马岩浆分异的富碱自交代流体有关,而水硼锶钠锆石(107 ± 5 Ma)可能与古太平洋板块俯冲引起的外来富Sr、Ca和B碳酸盐化流体有关。赛马岩体异性石中稀土元素经流体交代,大量进入流体相而发生迁移,少量在赵氏碱锆石等蚀变锆矿物中保留。两种稀有锆矿物的发现对揭示热液流体性质、热液活动期次及锆等关键金属迁移-沉淀机制具有重要意义。

    Abstract:

    Georgechaoite and bobtraillite are rare zirconosilicates first discovered as secondary products after eudialyte alteration in the Saima alkaline complex, Liaoning Province. An integrated study of petrography, mineralogy, geochemistry and isotopic geochronology on these two minerals has been carried out, to reveal their occurrence, crystal structure, and chemical composition information, then to constrain the ages for magmatic enrichment and hydrothermal alteration of Zr-REE-bearing minerals, and eventually to discuss the relationship between post-magmatic fluid events and the mobilization-precipitation of ore-forming elements. Anhedral georgechaoite commonly occurs as the early alteration mineral after eudialyte, associated with secondary gaidonnayite, natrolite, britholite-(Ce) and other alteration minerals. It is orthorhombic with a = 11.8325(5) ?, b = 12.9141(3) ?, c = 6.7292(1) ?, V = 1028.25(4) ?3 and an empirical formula of (Na0.97K0.78Ca0.06Pb0.01Sr0.01)Σ1.83(Zr0.98Ti0.01Hf0.01)Σ1.00Si3.02O9·2H2O. In contrast, bobtraillite is the late alteration mineral posterior to georgechaoite. It occurs as anhedral crystals or mineral aggregates in close association with secondary natrolite, zircon, strontianite, calcite, britholite-(Ce) and other alteration minerals in the pseudomorph after eudialyte, but with few eudialyte relics, gaidonnayite or georgechaoite. Bobtraillite is trigonal with a = 19.6634(3) ?, c = 9.9581(3) ?, V = 3334.45(1) ?3 and an empirical formula of (Na7.10Ca2.55K0.01¨3.34)Σ13.00(Sr10.42Ba0.01Pb0.01¨0.56)Σ11.00(Zr12.85Ti0.49Hf0.13Al0.08Nb0.06¨0.39)Σ14.00Si42.01B5.99O132(OH)12·12H2O. Georgechaoite and bobtraillite represent secondary products crystallized from different episodes after magmatic eudialyte alteration, which formed around 218 ± 5 Ma. Georgechaoite results from alkali-rich auto-metasomatism fluids which evolved from the Saima alkaline magmas, whereas bobtraillite (107 ± Ma) is probably related to the external carbonate fluids raised by the subduction of the ancient Pacific plate. During the hydrothermal alteration, a large number of REEs were released from precursor eudialyte into fluid system and only the minorities were preserved in secondary minerals (e.g., georgechaoite and bobtraillite). The discovery of georgechaoite and bobtraillite is of great significance in deciphering the nature and episodes of post-magmatic fluids, and exploring the remobilization-precipitation mechanism of critical metals (e.g., Zr and REEs) in hydrothermal conditions.

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  • 收稿日期:2023-12-22
  • 最后修改日期:2024-04-26
  • 录用日期:2024-04-28
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