The Athabasca Basin in northern Saskatchewan contains some of the world’s highest-grade unconformity-related uranium deposits, the genesis of which has been extensively explored in the literature. Constraints on the temperature, pressure, and composition of diagenetic fluids within the Athabasca Basin have mainly come from research conducted in uranium-mineralised areas, however, research conducted distally from known uranium mineralisation is relatively scarce. This study aims to provide a detailed data set on the temperature, pressure, and composition of diagenetic fluids using petrographic, fluid inclusion, and illite geothermometric methods on samples from the Rumpel Lake drill core, and to compare the results with other barren areas in the Athabasca Basin. The Rumpel Lake drill core contains five formations from within the Athabasca Group (from oldest to youngest): the Read, Manitou Falls, Lazenby Lake, Wolverine Point, and Locker Lake formations. The Read, Manitou Falls, Lazenby Lake, and Locker Lake formations are mainly comprised of sandstone (quartz arenite to quartz wacke), whereas the Wolverine Point Formation is comprised of fine-grained sandstone in addition to several layers of siltstone and shale. Fluid inclusion homogenisation temperatures obtained from syntaxial quartz overgrowths range from 51°C to 253°C, with no discernable trend of temperatures with depth. Illite formation temperatures are also consistent throughout the stratigraphy of the Rumpel Lake drill core, and range mainly from 220°C to 230°C, with one outlying temperature at 251°C. Three types of fluids are recorded within the Rumpel Lake drill core: (1) a low to moderate salinity (3.4 – 13.6 wt. % NaCl) NaCl-dominated fluid that is present in minor quantities; (2) a high salinity (21.1 – 24.4 wt. % NaCl) NaCl-dominated fluid that is abundant throughout the Rumpel Lake drill core and (3) a high salinity (24.9 – 31.0 wt. % NaCl + CaCl2) CaCl2-dominated fluid that is abundant throughout the Rumpel Lake drill core. The consistency of temperatures, as well as salinities, throughout the Rumpel Lake drill core indicates that fluid convection was the dominant fluid flow regime during part of the diagenetic history of the Athabasca Group sandstones. It is suggested that convection cells within the Athabasca Basin were dynamic during diagenesis, and may have moved laterally through the Athabasca Group or grown in size during prolonged sedimentation. The low salinity fluids are interpreted to represent different mixing ratios between freshwater (deposited with the fluvial units in the Athabasca Group) and evaporated seawater (the high salinity NaCl-dominated fluid, deposited with the marine units in the Athabasca Group), which implies that fluid convection was likely in place before the evaporated seawater percolated down into the large sandstone aquifer below the Wolverine Point Formation. The acquisition of calcium by the original Na-rich evaporated seawater may have come from a number of sources (e.g. the alteration of detrital plagioclase, alteration of the Wolverine Point Formation, or the basement rocks below the unconformity). It is suggested that one discrete source of calcium is not necessary to explain the formation of the CaCl2-dominated fluids, as convection serves as a giant linkage between the Athabasca Group and the basement rocks below the unconformity, which may acquire calcium from various sources. The results of this study also imply that, like the source of calcium, the source of uranium need not come from one discrete source, as there is evidence to suggest that the diagenetic fluids generated within the Athabasca Group have interacted with both basement lithologies and the Athabasca Group, and mixed during prolonged fluid convection within the Athabasca Group sandstones.