The Qarhan Salt Lake (QSL) in the Qaidam Basin in western China is the lar
gest brine potash deposit in the world. The formation of M
gSO4-defificient evaporites in the QSL, whether from the evaporation of river waters with hi
gh Na+ and Cl− levels, bacterial sulfate reduction (BSR) in brines resultin
g in SO42− depletion, or the mixin
g of the river and sprin
g waters, remains controversial. The δ34S values of 33 intercrystalline brines and 10
gypsum samples from a sediment core (ISL1A) collected in the QSL were presented in this study. Combinin
g these results with previously reported major ionic concentrations, total dissolved solids (TDS) and δ34S values of difffferent waters, and 87Sr/86Sr ratios of sediments, it was concluded that (1) δ34S values of the intercrystalline brines (+6.7‰ to +12.1‰) and
gypsum (+8.1‰ to +10.1‰) su
ggested that the BSR was insi
gnifificant in the QSL. These values were dominated by those of inflflowin
g waters and the evaporation process; (2) river waters with hi
gh Na+ and Cl− levels were unable to form M
gSO4-defificient evaporites in the QSL. A stron
g positive correlation of Na and Cl equivalents coupled with hi
gh (Na+ + Cl−)/TDS ratios su
ggested that the lar
ge amount of solutes in Golmud River waters results from the dissolution of halite rather than the chemical weatherin
g of rocks; and (3) the flflowin
g system of the river and sprin
g in the past 50 kyr was similar to the modern supplyin
g
system, and mixing of river and spring waters was responsible for the precipitation of evaporites in the QSL.