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of essentially unmetamorphosed arkose, conglomerates and siltstone with mafic flows and
sills of alkaline affinity (Morelli et al., 2009). The fault-controlled basin is confined to a
broad open syncline centered on Martin Lake (Ramaekers, 1981; Ashton et al., 2001).
Locally, extensive suites of east- to southeast striking mafic dikes, dated at 1818±4 Ma,
are interpreted as feeders to the Martin Lake Basin mafic flows and sills (Morelli et al.,
2009). The Martin Lake Basin formed during a period of active tectonism related to backarc
extension (Dieng et al., 2011) following the peak Trans-Hudson Orogeny (Hoffman,
1989, 1990; Corrigan, 2009) and can be therefore classified as a successor basin
(Clendenin et al., 1988).
Overlying the Martin Lake Basin are outliers of the Paleoproterozoic to
Mesoproterozoic Athabasca Formation (Rainbird et al., 2007). These occur south of the
Beaverlodge area and consist of generally flat-lying, undeformed quartz sandstone with
minor shale, conglomerate, and greywacke (Sibbald, 1983).
3.2.2. Uranium mineralization
The Beaverlodge area hosts a multitude of U deposits (Fig. 3.2), which were
actively mined between 1953 and 1963 from 284 deposits. Ore grades were generally in
the range of 0.15 to 0.25 per cent U but in places, up to 0.4 per cent U (Robinson, 1955;
Beck, 1969). About 25,000 t U was mined (Sibbald and Quirt, 1987), which is the
equivalent of the Millennium deposit in the Athabasca Basin (Roy et al., 2005). Some
previous investigators of the Beaverlodge U deposits reported a single event of U
mineralization (Dudar, 1960; Sassano, 1972), but others described two mineralizing
events (Turek, 1962). However, Tortosa (1983) identified five stages of U mineralization
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