Measurement of the hydrogen and oxygen isotopic compositions of concentrated chloride brines and brines from fluid inclusions in halite

Koehler, G.D., Chipley, D. and Kyser, T.K., 1991. Measurement of the hydrogen and oxygen isotopic compositions of concentrated chloride brines and brines from fluid inclusions in halite. Chem. Geol. (Isot. Geosci. Sect.), 94: 45-54. Solutions of l-5 m NaCI, KCl, CaC12 and MgC12, and synthetic brines were analyzed for hydrogen and oxygen isotopic compositions by vacuum distillation-microequilibration techniques. No effect on the hydrogen isotopic composition was observed for any of the solutions within the precision of the technique of It Sob determined from analyses of distilled water. Oxygen isotopic compositions of solutions measured by vacuum distillation-microequilibration indicate that oxygen isotopes are not fractionated during analysis in NaCl, KC1 and CaCl, solutions. Vacuum distillation-microequilibration analyses of MgC12 solutions show depletions in “0 relative to pure water that can be related to the concentration of Mg’+ in the solution. The greatest depletion in IgO occurs in the 4 m MgC12 solutions which have 6”O-values 6Oh lower than that measured for pure water. Corrections based on the measurement of the 6’80-values of the pure MgC12 solutions can also be applied to mixed chloride brines. Both melting and crushing of halite grown in solutions of known isotopic composition followed by microequilibration to determine the stable isotopic composition of fluid inclusions give results within the precision determined from analyses of distilled water.