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The first part of this paper focuses on the analysis of fluid inclusions by micro-Raman spectrometry. S04 2and HS-are the only polyatomic anions identified by this technique. Na + , Ca 2+ , Mg 2+ , Fe 2+ cations can be identified by the Raman spectrum of the corresponding salt hydrate which nucleates on cooling. Gas analysis is the most fruitful field of application of micro-Raman spectrometry. Errors in the reconstruction of the bulk V-X properties of gas-bearing fluid inclusions, arising either from Raman analysis or from the quantitative interpretation of phase equilibria, are discussed. Geochemical constraints inferred from these analyses are considered in the second part. The V-X properties of fl uids in the CO -H-N-S sy stem are deduced mainly from room-temperature measurements. They are shown to be representative of the fluid V-X properties in the P-T conditions of trapping, and thus, to yield representative f0 2 and fS 2. The paleo-redox state of fluids associated with U, Sn, W, and Au deposits is shown partly to account for the contrasted behaviour of these metals at the hydrothermal stage. Gas concentration is a key parameter for control ling meta I transport and deposition properties of fluids. This is because it controls the static dielectric constant of the fluid, wh ich in turns constrains the ion-pair stability. It is shown that some Nrbearing fluids may be the end product of major redox reactions. Finally , the H 2-and 0 2-bearing fluid inclusions found in three uranium deposits provide evidence fo r water radiolysis by alpha particles.

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A new analytical method, based on the Raman spectroscopy of the ν(OH) stretching vibration of water, has been developed for the determination of the concentration of chloride in aqueous solutions with the goal of reconstructing the bulk ion content of fluid inclusions that are relics of paleo-fluid circulation in rocks. The method involves calibrating the area of one band of the spectrum difference between pure water and solutions of appropriate composition with respect to the chloride concentration. Calibration curves were constructed for the major geological chemical salts LiCl, NaCl, KCl, CaCl2, and MgCl2, and NaCl–CaCl2 systems. The application to fluid inclusions has been confirmed using synthetic fluid inclusions. For cubic minerals such as fluorite, the calibration curve for the NaCl system correctly estimates the chlorinity. For birefringent minerals, such as quartz, the Raman spectrum of the aqueous solution depends on the orientation of the host crystal. The crystal must be oriented in such a way that one axis of the ellipse of the indicatrix projects parallel to the spectrometer slit. This method complements micro-thermometric data and allows the determination of chlorinity when ice-melting temperature cannot be used.