Chlorine isotopic geochemistry of salt lakes in the Qaidam Basin, China

Abstract

The isotopic compositions of chlorine in salt lake brine coexisting with halite, oil-field water and river water from the Qaidam Basin (Qinghai, China) have been examined using high-precision measurement of chlorine isotopes based on thermal ionization mass spectrometry of the Cs sub(2)Cl sup(+) ion. delta sup(37) Cl values vary from - 2.05 to + 2.94 ppt, with average values of +2.94 ppt for hot spring water, +1.35 ppt for river water, -0.38 ppt for oil-field brine, -0.40 ppt for saline water and -0.63 ppt for salt lake brine. The preliminary results show isotopic fractionation of chlorine in salt lake brine during salt precipitation. The variation of the delta sup(37) Cl value in these salt lakes is mainly associated with brine evaporation and halite precipitation and with the hydrochemistry of the input water. The chlorine isotopic composition may reflect the degree of evaporation of the salt lake brine and may be used to distinguish brine that are in equilibrium with precipitating salts and brines that have dissolved earlier evaporates