河海大学谭红兵教授团队报道了西藏富稀有金属元素地热温泉的来源、富集机制及资源效应。该研究于2024年9月10日发表在《中国科学：地球科学》杂志上。

据悉，锂(Li)、铷(Rb)、铯(Cs)等稀有金属是中国新兴产业发展的战略性重要矿产资源。确保这些资源的长期稳定供应至关重要。西藏地热系统发达，地热系统类型多样，分布广泛。西藏大部分高温地热系统中稀有金属元素(RMEs)异常丰富，有潜力成为稀有金属的新基地，以确保中国未来的战略性矿产资源供应。青藏高原特殊的盐湖资源与地热系统也有着密切的关系。地热泉在矿质岩石从深部向浅部迁移富集、内源矿化与外源矿化过渡、矿化向汇化过程中起着关键作用。然而，这些泉水中元素富集和演化的机制尚未被系统地揭示，许多理论问题仍有待研究。

本研究在总结分析前人研究成果的基础上，采用水化学和同位素地球化学方法对西藏地区典型地热泉进行了调查，探讨了RMEs的异常富集机制和地热泉的抗阻作用。综合分析表明，藏区地热温泉的总溶解固形物(TDS)和水化学类型与世界主要地热田相似，但藏区温泉异常富含Li(平均5.48mg/L)、Rb(平均0.75mg/L)和Cs(平均3.58mg/L)，富集程度是天然水体的数百至数万倍。这些富集地热温泉的分布受雅鲁藏布江缝合带和伸展的N-S向裂谷控制，特别是在两者的交汇带，地热温泉最为富集。从空间分布、同位素特征和元素地球化学特征等方面分析，西藏地泉中富集的RMEs主要来源于欧亚大陆下俯冲印度板块部分熔融形成的岩浆热液。这些流体不仅作为热源维持地热活动，而且作为物质源参与地热泉的物质循环。

在区域地壳富集RMEs的背景下，Li、Rb、Cs等不相容元素在岩浆—热液作用下的部分熔融、岩浆分异、热液流体析出等过程中逐渐富集，并通过深部高温水—岩相互作用进一步从围岩中提取成矿元素。最终，爆发发生，这些液体流到地表形成了富含RMEs的地热泉。在极度干旱的气候环境下，随着地热泉的排水，RMEs不断被地表径流输送到湖盆，并不断集中演化成盐湖盐水，构成了内源—外源叠加的富集盐湖成矿模式。研究结果强调，全面解释地热泉的成因、运移、富集机制和成矿作用，将加深对稀有金属成矿过程的认识，有助于建立青藏高原各地质体重点稀有金属矿产资源的理论模型，显著扩大勘探范围，准确评价稀有金属矿产的成矿潜力。

附：英文原文

Title: Sources, enrichment mechanisms, and resource effects of rare metal elements-enriched geothermal springs in Xizang, China

Author: Fei XUE, Hongbing TAN, Xiying ZHANG, Jinbao SU

Issue&Volume: 2024/09/10

Abstract: Rare metals such as lithium (Li), rubidium (Rb), and cesium (Cs) are strategically crucial mineral resources for the development of emerging industries in China. Ensuring a stable long-term supply of these resources is essential. The geothermal systems in Xizang, China are well-developed, with a wide distribution of various types. Most high-temperature geothermal systems in Xizang are exceptionally enriched in rare metal elements (RMEs) and have the potential to become a new source of rare metals to secure China’s strategic mineral resource supply in the future. A close relationship also exists between the geothermal system and the special salt lake resources on the Tibetan Plateau. Geothermal springs thus play a key role in the migration and enrichment of RMEs from deep to shallow parts of the crust, in the transition between endogenous and exogenous mineralization, and source-to-sink processes. However, the mechanisms of element enrichment and evolution in these springs have not been systematically discussed, and many theoretical issues remain to be investigated. Based on summarizing and analyzing previous research, this study employs hydrochemical and isotopic geochemistry methods to investigate typical geothermal springs across Xizang and explore the anomalous enrichment mechanism of RMEs, and the resource effects of geothermal springs. Comprehensive analysis shows that the total dissolved solids (TDS) and hydrochemical types of geothermal springs are similar to those of major geothermal fields worldwide, but the Tibetan springs are abnormally rich in Li (averaging 5.48mg/L), Rb (averaging 0.75mg/L), and Cs (averaging 3.58mg/L), which are hundreds to thousands of times more concentrated than natural waters. The distribution of these enriched geothermal springs is controlled by the Yarlung Zangbo suture zone and the extended N-S trending rifts, especially in the intersection zone of the two, where the geothermal springs are the most enriched. Based on the spatial distribution, isotopic, and elemental geochemistry, the RMEs enriched in Tibetan geothermal springs are mainly derived from the magmatic-hydrothermal fluids generated by the partial melting of the subducted Indian plate under the Eurasian continent. These fluids not only maintain geothermal activities as a heat source but also participate in the material cycle of the geothermal spring as a material source. Against the background of regional crustal enrichment in RMEs, incompatible elements such as Li, Rb, and Cs are gradually enriched in magmatic-hydrothermal processes including partial melting in the source, magmatic differentiation, and hydrothermal fluid exsolution, and some ore-forming elements are further extracted from surrounding rocks through deep high-temperature water-rock interactions. Eventually, an eruption occurs, and these fluids move to the surface to form a geothermal spring rich in RMEs. With the drainage of geothermal springs, the RMEs are continuously transported to the lake basin by surface runoff and continue to concentrate and evolve into salt lake brines under an extremely arid climate environment, constituting an endogenous source and exogenous accumulation salt lake metallogenic model. This comprehensive explanation of the sources, migration, enrichment mechanisms, and resource effects of geothermal springs will deepen the understanding of rare metal mineralization processes, and aid in the advancement of theoretical models for key rare metal mineral resources in various geological bodies of the Tibetan Plateau, significantly expanding exploration scopes and accurately assessing the resource potential of RMEs.

DOI: 10.1007/s11430-024-1413-0

Source: https://www.sciengine.com/SCES/doi/10.1007/s11430-024-1413-0