The spatial distribution law of B, Li, Rb and Cs elements and supernormal enrichment mechanism in Tibet geothermal system

The Tibet Plateau hosts the very typical geothermal resources in the world, which belongs to the main part of the Mediterranean-himalayan geotropics. The most typical characteristic is that these geothermal springs show unusual enrichment of many rare and dispersed elements such as B, Li, Rb, and Cs. Correspondingly, large-scale travertine or silica sinters are widely deposited in almost all geothermal fields. Some of the silica sinters show an unusual enrichment of Cs that formed a new type of Cs deposit. However, the origin of those enriched elements and their enrichment mechanism in geothermal water has remained unclear. This study based on the long observation in the field as well as accumulated datasets, and previous literature summarized for the geothermal system in the Tibetan Plateau, is in an attempt to provide new insights into the origin and mechanism of the enrichment of these typical elements. Geochemical datasets show an unusual and coincident enrichment of B, Li, Rb and Cs in the high-temperature geothermal springs as well as silica sinters along Yaluzangbu Suture in Tibet. Depleted B isotope and elemental association, groundwater deep circulation as well as much geophysical evidence indicate the dominant source likely originates from residual magmatic fluids derived from crustal partial remelting while water-rock interaction itself seems difficult to develop so large-scale enrichment of these elements. It can thus be concluded that the plate collision and thrust, crustal partial remelting and magmatic fluids differentiation and evolution during the upwelling and groundwater deep circulation synergistically play effects on the unusual enrichment of typical elements. This study will strengthen a comprehensive understanding of the unique geothermal system for both water resources-energy-minerals in Tibet, in particular, help people focus on special minerals dissolved in geothermal water. In addition, the study will also instruct to well assess the values of mineral resources of geothermal water or deposits.