Hydrochemical Characteristics and Evolution of Underground Brine in Lop Nur, Northwestern China

Abstract

Lop Nur is located in the eastmost end of the Tarim Basin in Xinjiang, Northwestern China. This study covers the hydrochemical characteristics and evolution of underground brine in Lop Nur based on analytical data of 429 water samples (mainly brine). It is found that in the NE‐SW direction, from the periphery to the Luobei sub‐depression, while the hydrochemical type varies from the sodium sulfate subtype (S) to the magnesium sulfate subtype (M), the corresponding brine in the phase diagram transfers from the thenardite phase (Then) area, through the bloedite phase (Blo), epsomite phase (Eps), picromerite phase (Picro), and finally to the sylvite phase (Syl) area. As for the evolution degree, the sequence is the periphery < Luobei horizontally and the overlying glauberite brine < the underlying clastic brine vertically. It is concluded that the oxygen and hydrogen isotopic compositions of the brine have been evidently affected by evaporation and altitude effect, as well as the changes in local water circulation in recent years. Boron and chloride isotopic compositions show that the glauberite brine is formed under more arid conditions than the clastic one. The strontium isotopic composition indicates that the Lop Nur brine mainly originates from surface water; however, deep recharge may also be involved in the evolution of brine according to previous noble gas study. It is confirmed that the brine in Lop Nur has become enriched with potassium before halite precipitates over the full course of the salt lake evolution. Based on chemical compositions of brine from Drillhole LDK01 and former lithological studies, the evolution of the salt lake is divided into three stages and it is inferred that the brine in Lop Nur may have undergone at least two significant concentration‐dilution periods.