Alexandre Tarantola

Fused-silica capillary capsules (FSCCs) as reference synthetic aqueous fluid inclusions to determine chlorinity by Raman spectroscopy

Microthermometry is the most common technique used to determine the salinity of aqueous fluid inclusions but, in some cases, this technique cannot be applied. The Raman analysis of water is a good alternative. Instead of preparing fluid inclusions within minerals by the crack-and-heal method, fused-silica capillary capsules (FSCCs) were used as synthetic fluid inclusions to calibrate the Raman signal of water toward chlorinity. The preparation of FSCCs is convenient in the preparation of synthetic fluid inclusions, and the composition of the standard solutions is well controlled all along the preparation procedure. Standard fluid compositions made in FSCCs are stable over time. The treatment of Raman data is reduced to the subtraction of a straight baseline and the measurement of Raman intensity at two wavenumbers, such that it is simple and independent from the operator. The method has been tested by comparison of the results obtained from Raman spectroscopy and with phase transitions observed in microthermometry from natural and synthetic fluid inclusions hosted in quartz. The polarisation effects, due to the birefringence of quartz, are treated by positioning the crystal at the extinction angle or by using an unpolarised laser radiation. The results obtained from Raman spectroscopy are in good agreement with microthermometry, over a wide salinity range (3.3 to 22.8 mass% NaCl eq ), with a similar precision.

Water redistribution in experimentally deformed natural milky quartz single crystals – implications for H2O-weakening processes

Natural quartz single crystals were experimentally deformed in two orientations: (1) ⊥ to one prism plane and (2) in O + orientation at 900 and 1000°C, 1.0 and 1.5 GPa, and strain rates of ~1 × 10 A6 s A1. In addition, hydrostatic and annealing experiments were performed. The starting material was milky quartz, which consisted of dry quartz with a large number of fluid inclusions of variable size up to several 100 μm. During pressurization fluid inclusions decrepitated producing much smaller fluid inclusions. Deformation on the sample scale is anisotropic due to dislocation glide on selected slip systems and inhomogeneous due to an inhomogeneous distribution of fluid inclusions. Dislocation glide is accompanied by minor dynamic recovery. Strongly deformed regions show a pointed broad absorption band in the ~3400 cm A1 region consisting of a superposition of bands of molecular H 2 O and three discrete absorption bands (at 3367, 3400, and 3434 cm A1). In addition, there is a discrete absorption band at 3585 cm A1 , which only occurs in deformed regions and reduces or disappears after annealing, so that this band appears to be associated with dislocations. H 2 O weakening in inclusion-bearing natural quartz crystals is assigned to the H 2 O-assisted dislocation generation and multiplication. Processes in these crystals represent recycling of H 2 O between fluid inclusions, cracking and crack healing, incorporation of structurally bound H in dislocations, release of H 2 O from dislocations during recovery, and dislocation generation at very small fluid inclusions. The H 2 O weakening by this process is of disequilibrium nature because it depends on the amount of H 2 O available.

Evaluation of the Potential of the Pegmatitic Quartz Veins of the Sierra de Comechigones (Argentina) as a Source of High Purity Quartz by a Combination of LA-ICP-MS, ICP, Cathodoluminescence, Gas Chromatography, Fluid Inclusion Analysis, Raman and FTIR spectroscopy

Due to the increasing demand for high purity quartz the pegmatitic quartz veins of the Guacha Corral shear zone (Sierra de Comechigones, Sierras Pampeanas, Argentina) get increasing economic interest. The presented combination of accurate field work backed by transmitted light microscopy, cathodoluminescence, LA-ICP-MS spot chemical analyses and analyses of solutes and gases liberated from fluid inclusions was developed in order to produce a robust exploration tool able to select in an early stage of prospection quartz veins that are promising for the production of high purity quartz. One of the important results of this combination of methods is the possibility to define the amount of lattice bound impurities. Such lattice bound impurities are difficult to eliminate by mineral preparation techniques whereas solid and fluid inclusions are amenable to a mineral preparation. In the present case the combination of methods produced a positive evaluation of the studied quartz veins as an excellent source for the production of high purity quartz.