The Discovery of lithium-boron large scale deposit in Zetso salt lake, Ngali District of Tibet and its prospects for development and utilization

During 2016-2018, aiming at the Zetso Salt Lake in the western of Qiangtang Basin, Tibet Autonomous Region, Tianjin Center of China Geological Survey joined The No.5 Geological Survey Party of Tibet Autonomous Region Geological and Mineral Exploration and Development Bureau to form a team to carry out the geological survey and assessment, eventually found it is a large scale brine-lithium-Boron deposit. Zetso Salt Lake, with a length of 16.3 km, width within 3.3-11.3 km, has an area of 113.8 km², also, it has a larger range in it depth, with shallow water around it but gradually becoming deeper and deeper to the middle of the lake with the deepest part of 44 m, average water depth of 24 m and the altitude of it is 4940 m. Zetso is located within the Qiangtang-Sanjiang Composite Plates. The Quaternary strata around Zetso can be divided into Pleistocene lacustrine sediments, Holocene alluviation, Holocene alluvial-diluvial, Holocene lacustrine sediments and Holocene surface brine. Lake basin can be divided into four hydrogeological units of bedrock fissure water, subsandy pore aquifer, subclayey pore aquifer and lake brine. By the authors statistics and calculation, the atmospheric precipitation adding into the Zetso directly is 1.081×10⁷ m³/a, the supplies of the surface water into it is 8.262×10⁷ m³/a, the supplies of the underground water into it is 2.052×10⁷ m³/a, as a result, the total watersupply amount per year into Zetso is about 11.395×10⁷ m³/a. Natural evaporation is the main discharge mode in Zetso lake. Its annual evaporation amount is 12.745×10⁷ m³/a, annual average amount value is 1.35×10⁷ m³/a, the total salt amount from surface water supplies into it is 7.8×10⁴ t/a. The main salt brine elements within Zetso are Cl^-, Na⁺, SO₄^2-, K⁺, CO₃^2-, HCO₃^-, B₂O₃, Mg²⁺, Li⁺, etc. The salt lake has an average salinity of 41.57 g/L, pH 9.31, therefore, the brine belongs to high salinity one and its water chemical type is due to sodium sulfate subtypes. The average grade of LiCl is 376.02 mg/L, its resources is 102.68×10⁴ t, thus, it has been proved to be a large scale brine-lithium deposit; in the meantime, the average grade of B₂O₃ is 840 mg/L, its resources is 229.38×10⁴ t, it also has been proved to be a large scale brine-boron deposit. On the foundation of the comprehensive analysis of lithium, boron resource requirements, extracting lithium technology, construction of salt field, and climatic conditions as well as economic value etc., the authors make a prospection of exploitation and utilization to Zetso salt lake in the future.