The Geochemical Characteristics And Origin Of The Potassium-rich Brine From Kunteyi Salt Lake In The Qaidam Basin

The underground brine of Kunteyi Salt Lake in the western Qaidam Basin is rich,which has good prospects for development and utilization.The Dayantan mine is located in the sedimentary center of the Kunteyi Salt Lake and belongs to the sub-basin depression in the basin.It is the main storage area of the intercrystalline brine.Intercrystalline brine samples were taken from different depths?9.8m¹33m?of the Dayantan mine and oilfield brine samples were taken from the Lenghu structure.The chemical composition of the brines and there hydrogen and oxygen values,as well as the boron and chlorine isotopic values were analyzed.The results show that the intercrystalline brines are potassium-rich brines which is rich in K⁺?average 11.83g/L?and has a high degree of salinity?average 363.94g/L?.And the chemical type of intercrystalline brine is magnesium sulfate subtype.The chemical type of oilfield brine is chloride type and it is rich in Ca²⁺and Sr²⁺and has a low degree of salinity?average 39.02g/L?.According to the ion content and ion characteristic coefficient(r_Na/r_Cll and r_Br×10³/r_Cl),the shallow intercrystalline brine?9.8m to 11.5m?is mainly formed by the precipitation of atmospheric precipitation and leaching of salt rock by evaporation and condensation.The deep intercrystalline brine?30m to 133m?has the origin of the atmospheric precipitation salt rock leaching and is characterized by deep-source oil field water recharge.Hydrogen and oxygen isotopic composition shows that significant"oxygen isotopic positive deviation"phenomenon has occurred in intercrystalline brine and oil fieldbrine.It is inferred that the higher?¹⁸O and?D values of deep intercrystalline brines?30m to 133m?are related to shallow intercrystalline brines?9.8m to 11.5m?and the infiltration of atmospheric water-falling filter salt rocks along the fractures.Boron and chlorine isotopic composition shows that the shallow potassium-rich intercrystalline brine has a higher?³⁷Cl and a lower?¹¹B value,while the deep intercrystalline brine?30m to133m?has lower?³⁷Cl values and higher?¹¹B values.According to the chemical composition of the brines and there hydrogen and oxygen values,as well as the boron and chlorine isotopic values,the origin of shallow potassium-rich intercrystalline brines is the recharge of atmospheric precipitation leaching salt rocks.The deep potassium-rich intercrystalline brine?30m to 133m?comes from atmospheric precipitation and osmotic recharge of shallow intercrystalline brine?9.8m to11.5m?.And at the same time,the recharge of oilfield brine along deep structural faults leads to the similar geochemical characteristics between deep intercrystalline brines?30m to 133m?and oilfield brines.