Tracing the origin of salts in groundwater by Sr isotopic composition (the crystalline complex of the southern Sinai, Egypt).

Water sources (12) with salinity ranging 200-450 mg/litre were analysed. The salts are composed of approx 30% Na, (K) and Cl, and approx 70% Ca, (Sr), Mg, SO₄ and HCO₃. The ⁸⁷Sr/⁸⁶Sr ratio of the waters is in the range of 0.7087-0.7100 with an average of 0.7090 + or - 0.0003. The ⁸⁷Sr/⁸⁶Sr ratio in the basement rocks (acid igneous and metamorphic) is generally >0.71; even low Rb/Sr minerals have values of 0.72. Assuming that the Sr in the water genetically accompanies Ca, the major constituent of the carbonate fraction, the low ⁸⁷Sr/⁸⁶Sr ratio excludes the possibility that this fraction originated from the dissolution of country rock. It is suggested that the water composition is mainly controlled by aerosols originating from beach sands and sabkha sediments from the coastal plains of the Sinai. Under present conditions chemical weathering is negligible.-P.Br.