Behaviour of strontium in subsurface calcium chloride brines: Southern Israel and Dead Sea rift valley

Calcium chloride brines are, as a rule, relatively rich in strontium, but the enrichment is usually limited and is found to be related to the concentration of calcium. The limiting mechanisms were evaluated as a model which comprises simple interactions between minerals and solutions. Based on the known ranges of strontium concentration in minerals, mineral solubilities and partition coefficients of strontium (both poorly known in certain cases), six fields of Sr Ca molar ratios were defined in terms of participating minerals and processes: (a) 0.38-1.56 × 10^{- 3} by dolomitization of calcite; (b) 1.5-2.2 × 10^{- 2} due to dolomitization of aragonite; (c) 0.4-1.4 × 10^{- 2} as a result of solution-reprecipitation of calcite; (d)0.12-0.20 through transformation of aragonite to calcite; (e)0.10-0.60 through equilibrium of the pair calcite-strontianite; and (f)0.01-0.08 by equilibrium with gypsum and celestite. The model was applied to the analysis of two groups of brines from southern Israel which are originated in the coastal plain (group C) and in the rift valley (group R). The low Mg Ca ratios of both water groups point to dolomitization as the main subsurface modifying process. Sr Ca ratios of brines belonging to group C are consistent with dolomitization of aragonitic surface sediments at the beginning of their evolution. Brines of group R bear evidence to a similar pathway at the beginning of their evolution, but most of them were further affected by interaction with limestone.