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黔西晚二叠世煤系基底凝灰岩中稀土元素的富集机制OA北大核心CSTPCD

Enrichment mechanism of rare earth elements in the tuffs from Late Permian coal-bearing basement in western Guizhou

中文摘要英文摘要

我国西南地区晚二叠世含煤岩系基底蚀变凝灰岩中高度富集稀土元素等多种关键金属.低温热液作用通常对煤和煤系中稀土元素的富集成矿有重要贡献,黔西地区位于世界著名的大范围低温热液作用区内,是研究低温热液作用下煤系稀土元素富集机理的良好对象.蚀变凝灰岩的地球化学和矿物学组成可以提供凝灰岩蚀变过程中流体演化、热演化和成矿过程等信息,但以前的研究对凝灰岩中蚀变矿物组成以及矿物的共伴生关系还缺乏深入探讨,限制了对关键金属富集过程的认识.研究结果表明:凝灰岩具有与高钛玄武岩一致的地球化学组成;火山玻璃以及由长石、辉石等交代蚀变形成的次生矿物,可能形成于表生风化或早期成岩阶段.稀土元素主要赋存在后期热液成因的脉状独居石中.本文提出了西南地区晚二叠世煤系基底凝灰岩中稀土元素富集的模式:降落后火山灰经历了表生风化作用,地表水和周期性海水的作用导致凝灰岩层顶部样品中的稀土元素发生淋滤而向下迁移,后期出渗型热液流体与凝灰岩发生的水岩作用,导致下部凝灰岩中的稀土元素被析出并随热液流体迁移到凝灰岩层上部而富集.

The altered tuffs in the Late Permian coal-bearing basement of the southwest region exhibit significant enrichment in rare earth elements and other critical metals. Low-temperature hydrothermal fluids have made an important contribution in this enrichment and mineralization. Western Guizhou,located in a globally significant region of low-temperature hydrothermal activity,provides an exceptional natural laboratory to unravel the mechanisms driving REE enrichment in coal-bearing strata under such conditions. The geochemical and mineralogical composition of altered tuffs can provide insights into fluid evolution,thermal history,and mineralization processes during alteration. However,a lack of under standing persists regarding the composition of altered mineral assemblages and their coexistence in the tuffs,which limits our comprehension of critical metal enrichment processes. This study reveals that the tuffs have geochemical properties consistent with high-titanium basalts;volcanic glass and secondary minerals formed by metasomatic alteration,such as feldspar and pyroxene,may have formed in the supergene weathering or early diagenetic stage;the vein-like distribution of monazite indicates the origin of late hydrothermal fluids. The proposed enrichment pattern of REEs in these tuffs is as follows:shortly after volcanic ash deposition,the tuff underwent supergene weathering. Surface water and periodic seawater incursions leached REEs from the upper tuff layers,causing downward migration. Subsequently,exfiltration hydrothermal fluids interacted with the tuff,leaching REEs from the lower layers and transporting them upwards,ultimately leading to enrichment in the overlying rock strata.

代世峰;沈明联;刘桂建;赵蕾

中国矿业大学(北京)地球科学与测绘工程学院,北京,100083中国矿业大学(北京)地球科学与测绘工程学院,北京,100083||中国科学技术大学地球和空间科学学院,安徽合肥,230026中国科学技术大学地球和空间科学学院,安徽合肥,230026

晚二叠世煤系基性凝灰岩稀土元素富集机制

Late Permiancoal-bearing stratamafic tuffrare earth elementsenrichment mechanism

《地质学报》 2024 (008)

2281-2298 / 18

本文为国家自然科学基金创新研究群体项目(编号42321002)和国家重点研发计划项目(编号2021YFC2902001)联合资助的成果.

10.19762/j.cnki.dizhixuebao.2024367

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