Speciation distribution and phase partition laws of rare alkali metals in geothermal sinter deposits in southern Tibet: Implications for the cesium mineralisation in the geothermal system

The unusually enriched cesium (Cs) and associated some other rare alkali metals in large-scale geyserites in the geothermal system of southern Tibet, China as well as other places all over the world, has great potential for exploitation. In this paper, in order to reveal the mineralisation mechanism of Cs in geyserites, the speciation distribution and solid-liquid phase partition laws of rare alkali metals in various types of sinters at Gudui were systematically issued. It was found that Rb and Cs tend to be enriched in sinters, while Li tends to stay in geothermal springs. The speciation distribution of Cs in geyserites is that it mainly accumulates in the residual and reducible fractions, with a small amount of oxidisable fraction, suggesting that Cs is adsorbed by clay minerals and FeMn oxides, combined with organic matter reactive groups of microorganisms, and retained in the crystalline water of the silicate lattice. Therefore, it is concluded that the unusual enrichment and mineralisation of Cs in geyserites is mainly controlled by physical and chemical effects, with biological effects playing an auxiliary contributing role. If Cs mineral resources in geyserites are to be developed in the future, geyserites in the form of amorphous SiO₂ colloids should be preferentially selected and then clay minerals, FeMn oxides and microbial exploitation of the sedimentary layers in the geothermal deposits should be also considered.