THE AGE OF UNCONFORMITY-RELATED URANIUM MINERALIZATION IN THE ATHABASCA BASIN, NORTHERN SASKATCHEWAN

Age data are presented for major Athabasca Basin uranium deposits at Cigar Lake, Cluff Lake, Collins Bay, Dawn Lake, Eagle Point, McArthur River, Midwest, and Rabbit Lake, as well as for several minor or undeveloped deposits, including Hughes Lake and Nisto. The best constrained data indicate that almost all the deposits formed in a restricted time interval between about 1330 and 1380 Ma. This range of ages is believed to be real and not the result of uncertainties in the calculation of ages based on discordant data. The one major exception is the recently discovered NiAs-free deposit at McArthur River, for which a well-determined age of 1514 +/- 18 Ma (2sigma) has been obtained. Even this deposit yields an age in the 1330-1380 Ma range for some material. Periods of reworking-redeposition occurred at approximately 1280, approximately 1000, approximately 575, and approximately 225 Ma. These may be basin-wide, affecting to some degree all the deposits that we have studied. Other times of redeposition are less well determined, but may be present as well. No ages that approach the approximately 1700 Ma age of the Athabasca Group have been found to date for unconformity-related deposits, and the Athabasca Basin mineralization is unrelated to the approximately 1750 Ma pitchblende vein deposits in the Beaverlodge Lake area.