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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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