The Geochemical Study About Salt Lake Elements And Isotopes In Tengger Desert,Inner Mongolia

Tengger Desert is located in Alxa area where is the west of Inner Mongolia,as the important salt lakes of modern inland desert in our country.There is short of systematic research on the salt lake brine and recharge water in this area,especially on the source of the material and the geochemical process of the salt lakes.There are some disputes about the source of the recharge water of the salt lake brine in this area,and they are as following:?1?Mainly from leakage water of Tibetan Plateauin lakes and rivers,along the deep fault of the Tibetan Plateau and Alxa;?2?Mainly from the groundwater formed under the cold environment in Late Pleistocene,and the limited modern precipitation and rivers;?3?Mainly from modern precipitation and near groundwater.In order to analyse the evolution rule between the groundwater of Tengger Desert and salt lake brine,and discuss the source and control factors of the salt lake,we make use of elemental geochemistry and bor.on chlorine isotope geochemistry,to systematically study the evolution rule of groundwater in the area,the formation and evolution of salt lake brine,and the source of material.The research results will provide basic research information for the formation and evolution of Saline Lake in the region and the development of resources.On the basis of the existing research on the chemical characteristics of the salt lake brine water,we made systematic field investigation and sampling work in Tengger desert areas,and analysis experiments of elements and isotopes were carried out.Combined with the geological background,the following conclusions are obtained:?1?Na⁺is main supply water cations in the investigated area,the content relationship of cations is Na⁺>Mg²⁺>Ca²⁺>K⁺,the anions mainly are Cl^-and SO₄^2-,and the Cl^-content is slightly larger than that of SO4^2-.The major ions in the salt lake brine mainly are Na⁺,Cl^-and SO4^2-,and their content are more than 81%of the total amount of ions in this area,which is the primary factor of halogenesis and hydrochemical type of salt lake brine.?2?Most of groundwater in Tengger Desert is brackish water,while fresh water only exist in the southwest,east and the near of the fault F7.The change range of?¹¹B values in groundwater is slightly less than that of the salt lake brine,and same as the variation range of the?¹¹B values of the lacustrine sediments,non marine brines and non marine evaporate.It shows that the?¹¹B values of the brine in the salt lake is mainly related to the groundwater,and the groundwater also dissolved the salt substance in the surrounding rock.?3?Several salt lakes in the west and southwest of Tengger Desert are supplied by the Shiyang river,and the salt lakes in the northeast are mainly recharged by the groundwater from Helan mountain.Both lakes located in the eastern belong to the salt lake area distributed along the NE-SW direction and the lakes located in the central belong to the salt lake area distributed along the NNW-SSE direction have low?¹¹B values and high B/Cl ratio,which are similar to the groundwater from near the fault F7,indicating that these salt lakes are mainly supplied by groundwater controlled by fault F7.The three groups of lakes basin in southwest,central and eastern areas distribute in different directions which are related to the development of regional architectonic and the evolution of the desert.Meanwhile,it is also indicated that the tectonic activity in the area has great influence on the lake basin.?4?Whether the Qaidam basin or the research area,the?³⁷Cl values of sodium sulfate type brine are highest,those in the magnesium sulfate type brine are lower,and those in the chloride type brine are lowest.These changes are related to the history of the evolution of the hydrochemistry of the salt lakes.The evidences of the different salinization of groundwater,the?³⁷Cl values of salt lake brine and the ratios of Br/Cl indicated together that the salt lakes located in the eastern and northeastern may be supplied by saline water from the Tertiary stratum.?5?The?¹¹B values of northen Tengger Desert is higher than southern due to the adsorption of clay minerals,which is related to the increase of the?¹¹B value.The higher value of the?¹¹B of the Jilantai salt lake brine may be related to both the adsorption of a large number of clay minerals and the common deposition of a large number of calcite.The distribution characteristic of the?³⁷Cl values showed that the evolution of these salt lake brines may be affected by multiple factors such as tectonic activity-induced supplies of Tertiary deep waters and the water-rock interaction in Tengger desert region.