[en] Mineralogical, fluid inclusion homogenisation temperature and composition studies, and D/H, ¹³C/¹²C and ¹⁸O/¹⁶O isotope studies have been performed on the Cluff Lake and Rabbit Lake uranium deposits and their host rocks. The following aspects are emphasized: 1) Metamorphism of the basement in presence of an essentially carbonic fluid (granulite facies); 2) Evaporitic type of sedimentation with high Mg-Li-B- and organic matter at the beginning of the Athabasca basin sedimentation; 3) Presence of highly concentrated brines (approximately 30% eq. weight NaCl) during diagenesis of the sandstone; 4) Hydrothermal alteration (around 200⁰C), at the boundary between basement and cover. Solutions during at least one stage of uranium mobilization and deposition were very similar to these diagenetic brines from the point of view of temperature, pressure, salinity, Cl/Br and stable isotopes (D/H and ¹⁸O/¹⁶O). ¹³C/¹²C ratios on CO₂ are consistent with a derivation from organic matter by thermal degradation. However chloritization cannot be related to this stage and is not yet understood. Diagenesis of the Athabasca sandstone was an important step in the formation of economic uranium concentrations. (author)