Calculation of the thermodynamic properties of aqueous silica and the solubility of quartz and its polymorphs at high pressures and temperatures

Oxygen diffusion studies. I. A preliminary ion microprobe investigation of oxygen diffusion in some rock-forming minerals

“…However, in hydrothermal exchange experiments (under suitable P,T conditions) the effect of dissolution on the majority of silicates should be minimal, provided the material is of good quality and unstrained, and the pH of the fluid is close to 7. In this context it is interesting to note that problems of solution-reprecipitation were anticipated with the quartz experiments because of the relatively high solubility of SiO2 in H20 at 600-700 ~ at 1 kbar (Walther and Helgeson, 1977). Since the diffusion profiles showed little or no evidence of such problems, it would appear that the faster dissolution of the sawn cut-back surfaces of the specimen buffered the system and preserved the finish on the (more stable) polished faces (Vig et al, 1977;Suda et al, 1978;Kennedy et al, 1962).…”

Contrôles structuraux de la minéralisation aurifère de la veine Consuelo, Pataz, La Libertad, Pérou /

“…Le pompage par succion consiste quant à lui au pompage de fluides hydrostatiques dans des environnements peu profonds associés à des zones en extension ou en décrochement (Gaboury et Daigneault 2000). Les changements abrupts de pression ainsi créés jouent un rôle important dans la précipitation du quartz, de l'or et des sulfures dont la solubilité varie, entre autre, en fonction de la pression et de la température (Fyfe et al 1978;Walther et Helgeson 1977;Helgeson et Lichtner 1987) bien que d'autres mécanismes comme l'interaction fluideroche, le pH, le degré d'oxydation du milieu et des fluides, la séparation de phase et le mélange de fluides aient aussi été documentés (Helgeson et Garrels 1968;Seward et al 1979;Mikucki 1998). …”

Qualification of Thermodynamic Data for Geochemical Modeling of Mineral-Water Interactions in Dilute Systems

“…In particular for the silicate minerals, such results depend on the assumed thermodynamic properties of aqueous silica [SiO 2 (aq)]. These properties have long been somewhat controversial, particularly at temperatures near 25°C (Walther and Helgeson 1977[DIRS 133240], pp. 1324-1328.…”