Geological and geochemical features and significance of travertine in travertine-island from Zhabuye salt lake , Tibet，China

The Zhabuye salt lake is a unique salt lake, which naturally produces lithium carbonate and is rich in Cs. From east to west, there are 3 suites of the travertine, respectively 25~30m, 15~25m, 0~15m above the lake surface. There are several fabric patterns of travertine, such as bedded structure, alveolate structure, oolitic structure, block structure, miarolite structure, radial structure, crustose structure and so on. Textural patterns are made up of granular texture, acicular texture, inclusion texture, solution texture, hollow texture and organic texture. The major minerals in the travertine are aragonite and calcite, which aragonite shows in solid or hollow acicular texture, calcite appears in rhombic granular texture, parcel structure or corrosion structure. The content of CaO are almost accordant in the 3 suites of travertine and the average value is 49.49%~51.16%.The NASC normalized REE patterns are also accordant nearly, and all of their HREE is rich. The average value of Cs are 4.54μg/g→6.68μg/g→5.34μg/g from east to west, and the average of Li appears in an increasing trend: 109.9μg/g→116.5μg/g→136.9μg/g. It releases CO2 when spring seeps from underground. Then spring meets with lake water, due to rapid growth of the spring's pH value, calcium carbonate deposits then forms travertine .The source area of Li,Cs,B in Zhabuye salt lake is deep re-melting magma, and spring is the carrier of the mineralization. Some of the elements such as Cs, Li preserve in travertine, others converge in salt lake. Because of sustained evaporation, the content of rare alkali metal is increasing in salt lake.