In the Athabasca Basin, northern Saskatchewan, Canada, Proterozoic sandstones unconformably overlie Archean and Aphebian metasedimentary rocks. Multiple fluid events, involving isotopically- and chemically-distinct fluids, have produced a paragenetically-identifiable assemblage of clay, silicate and oxide minerals in permeable sandstone aquifers and along fault zones.

Proximal to faults, $\sp{87}$Sr/$\sp{86}$Sr ratios of chlorite and dravite and $\delta$ D values of illite, chlorite and dravite indicate mixing of the basinal and basement fluids as a result of focused fluid flow. Rb-Sr isochron and model ages of 1477+/$-$57 and 952 Ma for the crystalline 2M/3T illites indicate the timing of the high-temperature, basinal fluid events associated with fluid mixing.

$\delta\sp{18}$O and $\delta$ D values of late-formed kaolinite in reactivated fault zones in sandstones and metasedimentary rocks indicate formation from late-Precambrian to post-Cretaceous meteoric waters at temperatures of 50$\sp\circ$C and less. Along these faults, previously formed illite, sudoite and dravite, have aberrantly low $\delta$ D values and variable Fe, Mg, K and H$\sb2$O contents with no concurrent shifts in their $\delta\sp{18}$O values and uranium oxides have anomalously low $\delta\sp{18}$O values with varying U, Pb, Si and Ca contents. Rb-Sr and K-Ar ages in illites with the lowest $\delta$ D values have been reset to as young as 300 Ma and are similar to discordant U/Pb ages in $\sp{18}$O-depleted uranium oxides. Combined, the isotopic and chemical data indicate substantial interactions between the clay, silicate and oxide minerals and relatively modern meteoric waters at high integrated water/rock ratios in close proximity to reactivated faults. Distal to faults, regional movements of the basinal fluids during early and high-temperature diagenesis have been identified from paleomagnetic data on diagenetic hematites that indicate formation of magnetically- and isotopically-distinct generations of hematite and suggest pulsing of the high temperature basinal fluids within the sandstone aquifers over considerable periods of time.

The isotopic, chemical, paleomagnetic and petrologic data indicate that the Athabasca Basin has had a long and protracted fluid history similar to that documented for more modern sedimentary basins. The data show that the major sandstone aquifers within the basin have been affected by widespread lateral fluid flow of diagenetic fluids over distances of hundreds of kilometers and also that these fluid migration paths have been modified by cross-formational fluid flow near active fault zones. The results show that studies of pervasive fluid events in large sedimentary basins must take an integrated petrologic-isotopic-geochemical approach in order to assess the mechanisms which control the local and regional fluid movements in sedimentary sequences. (Abstract shortened by UMI.)