| Summary: | Fluid flow in the Athabasca Basin, situated in the Canadian Shield in northern Saskatchewan, has been episodic and basin-wide as a result of intermittent reactivation of faults. Periodic fluid events precipitated ferromagnetic minerals that recorded the inclination and polarity of the magnetic field at that time. Because the Canadian Shield has been continually changing with respect to latitude (inclination), owing to continental drift, and because of periodic reversals in polarity, these paleomagnetic signatures may serve to distinguish magnetic minerals as characteristic of a particular fluid event. Five main magnetic signatures (A, S, B, C, and incoherent D) have been recognized in the Athabasca Basin. The A- and S-magnetizations are present throughout the entire Athabasca Basin and are associated with extensive fluid flow during early (1700-1600 Ma) diagenesis. The B-magnetization is associated with uranium mineralization during peak burial diagenesis (1600-1450 Ma). Absence of uranium deposits in the west of the basin coincides with the lack of B-magnetization. The C-magnetization is associated with a late fluid event (~900 Ma), which is not as widespread as the previous fluid events. Permeability of the basin may have been restricted at this time, to a few horizons and reactivated fault zones. Late Phanerozoic to recent uplift, erosion, and fracturing resulted in the incursion of low temperature meteoric fluids. Incoherent D-magnetization is present in most of the upper sections of the Athabasca Group, in reactivated fault zones, and along the east edge of the basin, as a result of pervasive alteration of hematite to goethite and limonite by these meteoric fluids. The Thelon Basin in the Northwest Territories, is a Proterozoic intracratonic basin similar to the Athabasca Basin in tectonic setting, age, and deposition. Magnetizations in the Thelon Basin correspond to those observed in the Athabasca Basin. The A-magnetization is more prominent than its counterpart in the east of the Athabasca Basin, possibly due to less interaction with late fluids. The reverse polarity B-magnetization is very scarce in the Thelon Basin, except near uranium mineralization at the Kiggavik deposit. It also appears that A-, S-, B-, and C-magnetizations have been overprinted by a low temperature secondary magnetization, consistent with the present day magnetic field (
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