The main aim of the contribution is to combine data on the consecutive stages of deformation, inflow and migration of palaeofluids and accumulation of mineral filling with uranium traces within the faulted-fractured environment at the Krasnokamensk Area, SE Transbaikalia, Russia. Object of examination is a framework of fault zones transecting the Proterozoic-Paleozoic granitic unit to the extent of northwestern part of uranium-bearing Streltsovskaya caldera of Mesozoic age. Considerations of stress- and permeability-time relationships in faulted-fractured zones were taken with account of stress and strain dependencies within fluid saturated rock massifs at crustal seismogenic level. Stress-time consecution of fault zone permeability was developed using set of fieldwork and lab tests including structural-geological survey, fault slip data analysis, mineral-chemical diagnostics, microstructural observations, and radiographic studies. Practical applications of obtained data for solving uranium mining and environmental issues are indicated in conclusion.
The different fluid percolations in the granitic complex of Saint-Sylvestre (Northwest French Massif Central) at the end of the Hercynian orogeny is relatively well described in the mining area, but their extension is unknown at the scale of the whole massif. Microthermometric and microstructural studies, outside any mineralized zone, show that different fluids circulated among three sets of microfissures: i) aqueous-carbonic fluids (N40 °E and N150 °E), ii) aqueous vapours and liquids (east-west) similar to those considered as linked to the granite episyenitisation, and iii) low temperature aqueous fluids (east-west). The first event is characterized by high temperatures at rather low pressures, indicating a high geothermal gradient (80–90 °C·km−1) similar to those observed in the proximity of intrusions in the present-day geothermal field. It confirms the close space-time relationships between the migration of these aqueous-carbonic fluids and the Late Hercynian granites intruding the Saint-Sylvestre massif some kilometers southwards. Other fluid events, attesting a cooling of more than 200 °C after the previous fluid stages, seem to be related to the incoming of meteoric fluids in the system, followed by local fluid immiscibility and cooling. These processes are common features of geothermal areas. La percolation de différents types de fluides dans le complexe de Saint-Sylvestre (Nord-Ouest du Massif central), à la fin de l'orogenèse Hercynienne, est assez bien décrite dans les secteurs minéralisés et/ou altérés, mais leur extension à l'échelle du massif reste peu connue. Les études microstructurales et microthermométriques, réalisées hors contexte minéralisé, montrent que différents fluides percolent selon trois orientations de microfissures : (i) fluides aquo-carboniques (N40 °E et N150 °E), (ii) fluides aqueux vapeurs et liquides (est-ouest) similaires à ceux responsables de l'épisyénitisation, (iii) fluides aqueux de faible température (également est-ouest). Le premier événement est caractérisé par des températures élevées (450 °C), pour des pressions relativement faibles, indiquant un fort gradient géothermique (80–90 °C·km−1), similaire à ceux observés à proximité d'intrusions dans les champs géothermiques actuels. Il confirme l'étroite relation espace-temps entre la migration de ces fluides aquo-carboniques et les granites tardifs intrudant le massif de Saint-Sylvestre. Les autres événements fluides, attestant un refroidissement de plus de 200 °C, semblent être liés à la venue de fluides météoriques dans le système, suivie par une immiscibilité locale des fluides, et à un refroidissement, processus commun des systèmes géothermiques.
