Boron concentration and isotopic composition of halite from experiments and salt lakes in the Qaidam Basin

The concentration and isotopic abundance of boron in salt can he used to tr ace paleosalinities and depositional environments for marine and non marine evaporites. However, the mechanism of incorporating boron into halite duri ng evaporation of salt lake brines is subject to dispute, and there have be en few studies of boron concentrations and isotopic compositions during thi s process due to the low boron concentration in halite. A group of evaporat ion experiments from artificial solutions and salt lake brines have been an alyzed in this study. The results of boron concentration and isotopic analy ses demonstrate that the boron in halite comes mainly from fluid inclusions , with a lesser amount from coprecipitation. The isotopic fractionation fac tors between the brine and halite are from 0.9857 to 1.0000 for the evapora tion experiments, and 0.9945 to 1.0009 for natural samples from the salt la ke. The delta B-11 values of halite from the Qaidam Basin salt lakes vary f rom -4.7 to 25.8 parts per thousand, compared to -4.7 to 31.4 parts per tho usand in the salt lake brines. These values are controlled by the boron iso topic composition of the boron sources, pH values and Na/Ca ratios in the s alt lake brines. The variation of boron isotopes in halite map be used to t race the hydrochemical evolution and paleoevaporation environment in salt l akes. Copyright (C) 2000 Elsevier Science Ltd.