Quantification of Solute Composition in H 2 O-NaCl-CaCl 2 Solutions Using Cryogenic 2D Raman Mapping.

Various analytical techniques have been developed to determine the solution composition of fluid inclusions, including destructive, non-destructive, single-inclusion, and bulk-inclusion methods. Cryogenic Raman spectroscopy, as a non-destructive and single-inclusion method, has emerged as a potentially powerful tool of quantitative analysis of fluid inclusion composition. A method of point analysis using cryogenic Raman spectroscopy has been previously proposed to quantitatively estimate the solute composition of H₂O-NaCl-CaCl₂ solutions, but there are uncertainties related to heterogeneity of frozen fluid inclusions and potential bias in the processing of Raman spectra. A new method of quantitative analysis of solute composition of H₂O-NaCl-CaCl₂ solutions using Raman mapping technology is proposed in this study, which can overcome the problems encountered in the point analysis. It is shown that the NaCl/(NaCl + CaCl₂) molar ratio of the solution, X(_{NaCl, m}), can be related to the area fraction of hydrohalite over hydrohalite plus antarcticite, F_hydrohalite, by the equation X(_{NaCl, m}) = 1.1435 F_hydrohalite − 0.0884, where F_hydrohalite = hydrohalite area/(hydrohalite area + antarcticite area). This equation suggests that the molar fraction of a salt component may be estimated from the fraction of the Raman peak area of the relevant hydrate. This study has established a new way of estimating solute composition of fluid inclusions using cryogenic Raman mapping technique, which may be extended to other solutions. [ABSTRACT FROM AUTHOR]