Advances in C-O-H-N-S fluid geochemistry based on micro-Raman spectrometric analysis of fluid inclusions
Dubessy, Jean; Poty, Bernard; Ramboz, Claire
European Journal of Mineralogy Volume 1 Number 4 (1989), p. 517 - 534
published: Aug 31, 1989
manuscript accepted: Feb 8, 1989
manuscript received: Jun 16, 1988
ArtNo. ESP147050104004, Price: 29.00 €
Abstract The first part of this paper focuses on the analysis of fluid inclusions by micro-Raman spectrometry. SO42-and HS- are the only polyatomic anions identified by this technique. Na+, Ca2+, Mg2+, Fe2+ 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 fluids in the C-O-H-N-S system 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 fO2 and fS2. 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 controlling metal transport and deposition properties of fluids. This is because it controls the static dielectric constant of the fluid, which in turns constrains the ion-pair stability. It is shown that some N2-bearing fluids may be the end product of major redox reactions. Finally, the H2- and O2-bearing fluid inclusions found in three uranium deposits provide evidence for water radiolysis by alpha particles.