Sources and enrichment mechanisms of rare metals in hot springs in South Tibet: A case study of the Yangyi hot spring

In the context of rapid global technological and industrial advancement, the growing demand for rare metals underscores the need for their study. The South Tibet develops abundant geothermal resources which are rich in rare metal elements, serving as a unique platform for research into the origin and formation of rare metal elements within geothermal systems. This study focuses on the characteristics of rare metal elements in the geothermal system of the southern Tibetan Plateau, especially the extreme enrichment of Li, Rb, Cs and other elements. Although this phenomenon has attracted significant attention in the geological community, a comprehensive model explaining the sources and enrichment mechanisms of these rare metal elements is lacking. Consequently, this paper investigates the Yangyi hot spring located in the central part of the Yadong-Gulu rift and its adjacent magmatic rocks, aiming to explore its hydrochemical characteristics, determine the composition and evolution characteristics of magmatic source areas from various eras in the Yangyi region, and reveal the connection between hot spring development in South Tibet and enrichment of rare metal elements. Analysis of the hydrochemistry of Yangyi hot spring and geochemistry of adjacent magmatic rocks led to the following insights: (1) The hot spring shows exceptional enrichment in rare metal elements, with a notably higher of Cs over Rb, which is a rarity in geothermal systems; (2) Sr-Nd isotope analysis in various -aged magmatic rocks indicates a gradual enrichment of the magmatic source, implying increased contributions from the Indian continent; (3) The Sr element in hot springs primarily originates from water-rock interaction, while elements such as Li, Rb, Cs are more derived from the contribution of highly evolved magmatic fluids; (4) Rare metal elements were initially concentrated in felsic magma, derived from the partial melting of the Indian continental crust, and further enriched by evolved magmatic fluids, playing a pivotal role in enriching rare metal elements within hot springs across the South Tibet. This study concludes that most rare metal elements in hot springs across the South Tibet originate from magmatic fluid injections, and thus establishes a connection between the development of these hot springs and rare meta elements enrichment. This research not only offers fresh insights into rare metal elements enrichment in hot springs across South Tibet, but also provides essential references for grasping the enrichment mechanisms of rare metal elements in worldwide geothermal systems.