DETERMINATIONS OF WATER, HYDRATES AND PH IN FLUID INCLUSIONS BY MICRO-RAMAN SPECTROMETRY

This paper demonstrates four new possibilities in the analysis of fluid inclusions by micro-Raman spectroscopy. 1) Very low water contents, around 1 mol%, can be detected in fluid inclusions with no visible water coating the wall of the cavity, using a molecular symmetric stretching vibration at 3636 cm-1. With increasing water content, the Raman spectrum broadens and shifts towards lower wavenumbers, indicating H2O-H2O interactions which prevent any quantification if X(H2O) > 0.1. 2) The Raman spectrum Of H2S clathrate hydrate shows two bands at 2595 and 2605 cm-1 which are assigned to the stretching vibrations of the H2S molecule; it is compared with the spectrum of vapour, liquid and aqueous H2S. 3) The Raman spectrum of the LiCl.5H2O hydrate exhibits a stretching vibration band centred around 3400 cm-1, with an unusual large half peak width (300 cm-1) compared to other stochiometric salt hydrates at -160-degrees-C. The succession of phase melting above -160-degrees-C in a natural fluid inclusion was identified owing to the Raman spectrum of salt hydrates including LiCl.5H2O. 4) Very acidic solutions (pH between 1 and -0.5) were documented from the identification of HSO4- and SO4-- by Raman spectroscopy and the calibration of their intensity as a function of pH.