Characteristics and Dating of Brine in Paleo-Salt Lakes of the Western Qaidam Basin

Abstract

Abstract The brine in paleo-salt lakes in the Qaidam Basin is a very important resource of potassium and lithium salts. There has been little research on the formation mechanism of the brine according to noble gases and their isotopic characteristics, let alone research on the formation age of the brine. For this reason, this paper studies the formation mechanism and formation age of the brine in paleo-salt lakes in the Qaidam Basin according to the test data of the samples of noble gas elements and their isotopes collected in the latest deep boreholes in the Qaidam Basin. In the study area, the He content in the brine ranges from 12.2×10− 6 to 1,326.9×10− 6, the Ne content from 1.253×10− 6 to 19.1×10− 6, and the Ar content from 3,046.5×10− 6 to 5,023.1×10− 6; the ratio of 3He/4He ranges from 2.00 ×10− 8 to 2.30×10− 7, R/Ra from 0.01 to 0.16Ra, 20Ne/22Ne from 9.2 to 10.6, 21Ne/22Ne from 0.024 to 0.032, and 40Ar/36Ar from 298.7 to 352. In combination with the correlations between 20Ne/22Ne and 21Ne/22Ne, and 3He/4He and 40Ar/36Ar, and in accordance with the special physical properties of noble gases He, Ne, and Ar (such as lower solubility in groundwater and higher solubility with the increase of ion radius), the following can be inferred: The brine in paleo-salt lakes in the Qaidam Basin has two sources: deep crust and atmospheric precipitation; the reservoirs of the brine in paleo-salt lakes in the Qaidam Basin are Quaternary - Paleogene strata; the brine was formed from Triassic to Ordovician, earlier than the reservoir age according to the calculation of 3He/4He in the brine based on the age accumulation effect.