Hydrochemistry Of Lithium Ore In Mamico Salt Lake And Chronology And Geochemistry Of Travertine,Tibet

Mamicuo Salt Lake is located in Mami Township,Gize County,Tibet Autonomous Region.It is a comprehensive salt deposit with solid-liquid coexistence.The grade of lithium chloride in the lake surface brine is 5.6 g/L,and the resource amount is about 2.5 million tons.It is the best lithium salt lake in the same type of salt lakes in Tibet.Previous studies on the geological characteristics and brine resource development of Mamico Salt Lake have been carried out.In this paper,the’Mamicuo lithium boron enrichment model’and’Mamicuo regional tectonic background and the influence of climate change on the evolution of salt lake’are taken as scientific problems.The water samples,sediment samples and calcareous samples of the salt lake and its surrounding water system are analyzed by hydrochemical composition analysis,main and trace elements analysis,heavy sand analysis,uranium chronology analysis,carbon and oxygen isotope analysis.Get the following understanding:The hydrochemical characteristics were identified.The hydrochemical types of river runoff are mainly Ca·Na·Mg-HCO₃·Cl,Na·Ca-HCO₃·Cl and Ca·Na·Mg-HCO₃,and the hydrochemical types of river tributaries are mainly Ca-HCO₃ and Ca·Mg-SO₄·HCO₃.The chemical types of spring water are mainly Mg·Ca-HCO₃·SO₄ and Na·Mg-HCO₃·Cl;the chemical type of lake water is sodium sulfate subtype.Hydrochemical type is mainly controlled by rock weathering and evaporation crystallization.The average contents of Li and B₂O₃ in river runoff were 938.5μg/L and 14.7 mg/L,respectively.The average contents of Li and B₂O₃ in river tributaries were 19.8μg/L and 1.02 mg/L,respectively.The average contents of Li and B₂O₃ in spring water were 1091.5μg/L and 10.1 mg/L,respectively.The average contents of Li and B₂O₃ in lake water were 0.72 g/L and 1.3 g/L,respectively.The element content in river runoff is between tributary and spring water and close to spring water content,indicating that the exposed spring water in the region is an important source of river water.The average contents of water-soluble lithium（Li）and boron（B）in river sediment were 0.58μg/g and 3.53μg/g,respectively,and the average contents of Li and B in river suspension were 76.1μg/g and 59.4μg/g,respectively.River water supplies about 94.6×10~6 m~3 of lake water,the main supply source of Mamicuo Salt Lake.The annual total supply of Li Cl and B₂O₃ in river water was 409.21 tons and 979.80 tons,respectively,and the annual supply of Li Cl and B₂O₃ in river water was 7.6 tons and 6.3 tons,respectively.The material source of Mamicuo Salt Lake was identified,and the enrichment mechanism model of lithium and boron was established.The Na and K ions in the lake water are derived from the weathering of limestone strata and magmatic rocks in the Mamicuo area.The tourmaline granite veins in magmatic rocks show that magmatic differentiation or lithium-rich and boron-rich hydrothermal fluids have occurred in the area.The tourmaline granite veins are one of the sources of lithium and boron in salt lakes.Groundwater carries a large amount of lithium and boron to recharge salt lakes through deep water-rock reactions.Lithium and boron are first pre-concentrated in rocks during magmatic or hydrothermal activities.After rock weathering,they are leached in river water or/and enriched in spring water through water-rock reactions.After they are incorporated into the Mamicuo Salt Lake,they are super-concentrated under evaporation.The mineralogical and geochemical characteristics of newly discovered travertine rocks in this work were determined.The travertine platform is distributed in the terrace of the east bank of the river,and the sedimentary facies are divided into thick blocks and thin layers.Travertine texture types include granular structure,needle structure,honeycomb structure,radial structure and so on.The main mineral in the travertine is low magnesium calcite,and the average content of Ca O is45.01%.Trace elements enriched in U,Sr,depleted in Nb,Nd,Zr,enriched in light rare earth elements.The average contents of Li,B and Cs are 17.94μg/g,17.77μg/g and 55.27μg/g respectively,which are 0.8 times,1.6 times and 45.3 times of crustal abundance.Calcareous is thermogenic,and its sedimentary fluid is a mixture of surface fluid and deep fluidThe formation age of travertine deposits,the restoration of regional tectonic setting and the reconstruction of paleoclimate information were determined.Travertine formation occurs from late mid-updating to early and mid-updating,and can be divided into four stages:231.1-218.4 Ka BP,160.6-145.3 Ka BP,110.7-93.3 Ka BP,72.4-54 Ka BP.The formation time of travertine is highly coincident with the tectonic activity during the republican movement and the development time of the ancient Great Lakes in the Qinghai-Tibet Plateau,which plays an indicative role in regional tectonic activity and the ancient Great Lakes period.Travertine age showed a young trend with the decrease of altitude,indicating that the Mamicuo area was on the rise under the action of neotectonics movement.The climate of 110.7-54 Ka BP is dry and cold.The ratios of trace elements（Sr/Ca,Mg/Sr,Mg/Ca）and∑REE in travertine were positively correlated with rainfall and temperature.There may have been several paleo-lake periods before 145 Ka BP in the Qinghai-Tibet Plateau,and the separation of Mamicuo and paleo-lake began to evolve into salt lake around54 Ka BP.The influence of regional tectonic evolution and climate change on the evolution of Mamicuo Salt Lake was discussed.Mamico Salt Lake belongs to the ancient lake separation evolution metallogenic model.Mamicuo was separated from the ancient Great Lakes under the influence of regional tectonic uplift,and the climate change after separation had an important impact on its evolution process.Mamicuo experienced the evolution from freshwater lake to salt lake in late arid climate,and formed modern hydrochemical characteristics.The salt formation period is divided into carbonate type and sulfate type.Lithium element finally forms large liquid lithium ore through pre-concentration,enrichment and super-concentration.After boron enrichment,large solid boron deposits were deposited on the northwest side of the salt lake under the combined action of spring water doping,spring water doping,stable hydrodynamic conditions and low temperature conditions.