TY - JOUR
T1 - The activity-composition relationship of oxygen and hydrogen isotopes in aqueous salt solutions
T2 - II. Vapor-liquid water equilibration of mixed salt solutions from 50 to 100°C and geochemical implications
AU - Horita, Juske
AU - Cole, David R.
AU - Wesolowski, David J.
PY - 1993/10
Y1 - 1993/10
N2 - The difference between oxygen and hydrogen isotope activity and composition ratios of water in mixed salt solutions in the system Na-K-Mg-Ca-Cl-SO4-H2O was determined by means of a vaporliquid water equilibration method over the temperature range of 50 to 100°C. The observed isotope salt effects in complex mixed salt solutions to very high ionic strengths agree quantitatively with calculations based on the assumption of a simple additive property of the isotope salt effects of the individual salts in the solutions. Sofer and Gat (1972, 1975) and Horita and Gat (1989) also observed that this simple mixing rule applies to synthetic and natural chloride-mixed salt solutions at room temperature. Equations to convert between the isotope activity and composition scales for brines and fractionation factors between brines and other substances are presented. For most geochemical interactions between brines and other phases (vapor, gases, minerals) such as evaporation/boiling, mineral precipitation, and mineral/rock alteration, the isotope activity scale should be used. The isotope composition scale, on the other hand, is most useful for studies of mixing of different brines and formation of brines by mineral dissolution. Misusage of the two isotopic scales of brines will, and probably in the literature has, lead to incorrect conclusions in many isotopic studies of brine-dominated systems (origin of brines, temperature of mineral formation, isotope ratios of fossil fluids).
AB - The difference between oxygen and hydrogen isotope activity and composition ratios of water in mixed salt solutions in the system Na-K-Mg-Ca-Cl-SO4-H2O was determined by means of a vaporliquid water equilibration method over the temperature range of 50 to 100°C. The observed isotope salt effects in complex mixed salt solutions to very high ionic strengths agree quantitatively with calculations based on the assumption of a simple additive property of the isotope salt effects of the individual salts in the solutions. Sofer and Gat (1972, 1975) and Horita and Gat (1989) also observed that this simple mixing rule applies to synthetic and natural chloride-mixed salt solutions at room temperature. Equations to convert between the isotope activity and composition scales for brines and fractionation factors between brines and other substances are presented. For most geochemical interactions between brines and other phases (vapor, gases, minerals) such as evaporation/boiling, mineral precipitation, and mineral/rock alteration, the isotope activity scale should be used. The isotope composition scale, on the other hand, is most useful for studies of mixing of different brines and formation of brines by mineral dissolution. Misusage of the two isotopic scales of brines will, and probably in the literature has, lead to incorrect conclusions in many isotopic studies of brine-dominated systems (origin of brines, temperature of mineral formation, isotope ratios of fossil fluids).
UR - http://www.scopus.com/inward/record.url?scp=0027803789&partnerID=8YFLogxK
U2 - 10.1016/0016-7037(93)90194-2
DO - 10.1016/0016-7037(93)90194-2
M3 - Article
AN - SCOPUS:0027803789
SN - 0016-7037
VL - 57
SP - 4703
EP - 4711
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 19
ER -