BORON ISOTOPE GEOCHEMISTRY AS A TRACER FOR THE EVOLUTION OF BRINES AND ASSOCIATED HOT-SPRINGS FROM THE DEAD-SEA, ISRAEL

A boron isotope study combined with analyses of elemental boron, lithium, and chlorine is used to suggest that brines from the Dead Sea and on-shore hypersaline thermal springs (Hamme Yesha, Hamme Zohar, and Hamme Mazor) are the products of interaction of evaporated seawater with detrital sediments. The high delta-B-11 values of the Dead Sea brines (55.7 to 57.4 parts per thousand versus NBS-951) and the hot springs (52.2 to 55.7 parts per thousand), and low B/Li ratios (2.0 to 2.3 and 2.5 to 2.7, respectively), relative to seawater, indicate preferential removal of B-10 from the brines and hence boron adsorption onto clay minerals. The brackish 'En Feshcha springs and the freshwater 'En Dawid and Nahal Arugot springs yield lower B contents and delta-B-11 values (37.7 to 40.6 parts per thousand and 33.8 to 36.9 parts per thousand, respectively). The delta-B-11 values and B contents of diluted Dead Sea brines lie on calculated mixing lines between the composition of the brackish and freshwater springs with the composition of the Dead Sea. The delta-B-11 values of the hot springs, however, given their boron content, are significantly lower than those of the mixing lines. Thus, waters from the hot springs cannot be a mixing product of the Dead Sea brine with freshwater. Instead, the Dead Sea brine has evolved from the brines of the hot springs through further isotopic fractionation and boron adsorption onto detrital sediments.