The reconstruction of the entrapment conditions of geological fluids requires determining the volumetric and composition properties of the inclusions containing these fluids. In some cases, the analytical data necessary for PVTX determination cannot be obtained from microthermometry. The quantification of the dissolved gases in aqueous fluid inclusions by Raman spectroscopy, following proper calibration of the instrument and methodology, can provide alternative data. In the present study, the intensity of the Raman signal of the symmetric stretching vibrational mode of methane was calibrated in order to (1) determine CH4 concentration in pure and saline water and (2) quantify the molar fractions of H2O and CH4 in the gas phase. High-pressure optical cell (HPOC), i.e. a pressurization system connected to a silica microcapillary heated on a customized heating-cooling stage, reveals to be much more convenient and accurate than synthetic fluid inclusions. Moreover, a wide range of pressure, temperature, and salinity can be covered by this methodology. Over than 1,000 measurements were produced to define the calibration curves, covering the ranges in temperature, pressure and salinity of 60-180 °C, 30-1000 bar, and 0-4 mol.kg-1 NaCl, respectively, which corresponds to a CH4 molality up to 0.6 mol.kg-1. The CH4 solubility vs. CH4/H2O Raman peak area ratio was fitted by a second-order polynomial curve (R² = 0.996). In the gas phase, the molar fraction of H2O vs. Raman peak area ratio is fitted by a straight line (R² = 0.990). The calibration was applied to a set of natural fluid inclusions trapped within late quartz Alpine fissure of the external part of the Central Alps (Switzerland). The determination of CH4 2 concentration in the studied fluids provided valuable insight on conditions of trapping and on the pressure regimes prevailing in this low-grade metamorphic setting.

Unconformity-related uranium deposits, which represent a significant high-grade uranium resource, are systematically surrounded by a host-rock alteration halo enriched in clay minerals. Illite is often the major clay mineral component of the halo and it displays a variable crystal structure. New data are provided on the crystal structure and the chemistry of illite encountered within and outside of the alteration halo surrounding the Shea Creek deposit. Two illite populations were distinguished using textural and structural criteria: samples rich in the tv-1M polytype display thin (sub-micrometer) and ‘hairy’ shapes, while samples richer in the cv-1M polytype contain illites with rigid lath-like shapes several micrometers wide. In barren ‘regional’ sandstone, the trends with depth of the textural and microstructural properties of illite particles are: (1) an increase of particle size, (2) an evolution to a more isometric form, and (3) a dominance of the cv-1M polytype over the tv-1M polytype. These trends record diagenetic processes under conditions of deep burial and differ from those observed in altered sandstone around the uranium mineralization. The altered sandstone is characterized by enrichment in the tv-1M polytype near the unconformity and/or brittle structural features. This tv-1M illitization took place in response to structurally-controlled infiltration of basement rocks by diagenetic brines which were further recycled after interaction into the overlying basin. Variations of the illite structural and textural properties may result from nucleation/growth kinetics and may be indicative of a change in the flow regime, and/or a change of saturation state of the fluid vs. illite. The tv-1M illite may be favored in environments characterized by a high fluid/rock ratio and a high supersaturation state of the fluids in proximity to mineralization.

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The distribution of primary minerals in a peat profile was investigated in a dated core ( 210 Pb, 14 C) taken from the upper part of an ombrotrophic bog. Using XRD, the most abundant minerals present in the peat were those of the local granite, suggesting that the dust entering the bog is mainly of local origin. Apatite and calcite are restricted to the top 8 cm of the profile, which suggests rapid dissolution. The release of P by apatite dissolution is possibly the main source of plant-available P to the oligotrophic waters. In contrast, quartz and feldspars appear to be preserved for thousands of years despite the low pH and abundance of organic acids. This study suggests that ombrotrophic peat bogs could be valuable archives of aluminosilicate deposition since the Late Glacial.

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