Genesis of Glauberite Sedimentation in Lop Nur Salt Lake - Constraints from Thermodynamic Simulation of the Shallow Groundwater in the Tarim River Basin, China

This study was carried out in Lop Nur Salt Lake, which is one of the largest closed playa in the world and is located in the lowest part of the Tarim Basin at its east end. The objective of this study was to further reveal the genesis of the giant glauberite sedimentation in Lop Nur Salt Lake by thermodynamic simulation of the shallow groundwater in the Tarim River basin with the Equilibrium and Evaporation (EQL/EVP) program, as the shallow groundwater of the Tarim River basin may represent the recharging water body into Lop Nur. The shallow groundwater of the Tarim River basin is of the sodium sulfate subtype and the magnesium sulfate subtype and is dominated by the sodium sulfate subtype. The shallow groundwater is poor in Ca2+ but is rich in So(4)(2-). We( )use the EQL/EVP program, an equilibrium model that simulates the evaporation of dilute waters as well as of concentrated brines, to simulate the evaporation of the shallow groundwater, and got the results showing good agreement between predicted and observed mineral sequences and assemblages. The simulation results clearly showed that a small amount of glauberite can be formed under an open system, a large amount of glauberite can be precipitated under a closed system, and that the amount of glauberite precipitated under the closed system is approximately 100 times higher than that under open system, indicating that a closed system is more conducive to the formation of glauberite. However, even in the closed system, the amount of glauberite precipitated by simulated evaporation is much less than the observed amount that is deposited in Lop Nur. Therefore, it is inferred that Lop Nur must also be recharged by deep calcium-rich waters. With the Tarim River basin and deep calcium-rich waters as the recharge sources and under arid climate conditions, the water of Lop Nur was concentrated by evaporation, minerals began to accumulate over a long period of time, and a large amount of glauberite was formed, which provides storage space for potassium-rich brine in Lop Nur.