Geological environment of the Cigar Lake uranium deposit

The Cigar Lake uranium deposit occurs within the Athabasca Basin of northern Saskatchewan, Canada. Like other major uranium deposits of the basin, it is located at the unconformity separating Helikian sandstones of the Athabasca Group from Aphebian metasediments and plutonic rocks of the Wollaston Group. The Athabasca Group was deposited in an intra-continental sedimentary basin that was filled by fluviatile terrestrial quartz sandstones and conglomerates. The group appears undeformed, and its actual maximum thickness is about 1500 m. On the eastern side of the basin, the detrital units correspond to the Manitou Falls Formations where most of the uranium deposits are located. The lower Pelitic unit of the Wollaston Group, which lies directly on the Archaean basement, is considered to be the most favourable horizon for uranium mineralization. On the Waterbury Lake property, the Manitou Falls formation is 250-500 m thick and corresponds to units MFd, MFc, and MFb. The conglomeratic MFb unit hosts the Cigar Lake deposit. However, the basal conglomerate is absent at the deposit, wedging out against an east-west, 20 m high, pre-Athabasca basement ridge, on top of which is located the orebody. Despite the presence of the orebody, large areas of the Waterbury lake property remain totally unexplored and open for new discoveries. 45 refs., 23 figs., 4 tabs