Canada is the largest uranium producer in the world. One quarter of the total world uranium production comes from uniquely rich deposits in the Proterozoic Athabasca Basin in Saskatchewan. Recently, renewed interest in nuclear energy caused a worldwide boom in uranium exploration. In Alberta, extensive staking took place in the Athabasca Basin and adjacent basement, as well as in central and southern Alberta.Alberta Geological Survey has initiated a re-evaluation of Alberta's uranium potential to
The Athabasca Basin, which straddles the Alberta-Saskatchewan border, contains some of the greatest uranium resources in the world. Athabasca-type, unconformity-related uranium deposits are unique in size and grade compared to similar deposits elsewhere. These deposits have uranium oxide pods, veins and disseminations at or close to the unconformity at the base of the Athabasca Group.
The flat-lying Athabasca strata are mainly fluvial, pervasively altered, red to pale tan quartzose conglomerate, sandstone, siltstone and mudstone and are about 1.7 to 1.8 billion years old. The underlying crystalline basement is made of reworked Archean and Early Proterozoic crust. The mines in the eastern part of the basin in Saskatchewan contain the richest uranium deposits in the world. The potential exists for similar unconformity-associated uranium deposits in the western part of the Athabasca Basin.
The Alberta portion of the basin was intensely explored in the 1970s and early 1980s, and uranium occurrences have been documented in drillcore along the Maybelle structural trend south of Lake Athabasca and in a few outcrops north of the lake. Northeastern Alberta is favourable for uranium exploration because
In the Dragon Lake area, along the Maybelle River shear zone, steep, brittle fractures in the sandstone have disseminated to high-grade uraninite within a chlorite and illite-altered halo at the base of the Fair Point Formation of the Athabasca Group.
One intersection has 21% U3O8 over 5 metres, with thin intervals of pure uraninite. In 2006, Areva reported intersections of up to 54.5% U3O8. The alteration halo has numerous other metals, including nickel, arsenic, lead, molybdenum and cobalt. This halo of complex mineralization and alteration extends at least 200 metres along the zone. This means the reactivated shear zone is permeable and was the main path for the upwelling of mineralizing fluids. Paragenetic and textural relationships indicate several phases of this mineralization and remobilization.
The northern rim of the Athabasca Basin is exposed on the north shore of Lake Athabasca. Exploration for uranium has documented several uraniferous outcrops with 10,000 counts per second and uraniferous boulder trails or individual boulders with up to 16,000 counts per second. This was done with scintillometer traverses, geological mapping, airborne and ground geophysics and drilling. Near the Alberta-Saskatchewan border, uraniferous boulders showed geochemical characteristics consistent with a Saskatchewan source, whereas to the west, boulders have a distinct geochemical signal that suggests a local source in Alberta.
Southern Alberta has recently re-emerged as having potential for sandstone-hosted
epigenetic uranium deposits.
Mesozoic to Tertiary formations in the Western Canada Sedimentary Basin are of similar age and lithological characteristics to formations in Wyoming, Colorado, Utah, New Mexico and south Texas, which host many important sandstone-hosted uranium deposits.
In the U.S., roll-front and peneconcordant tabular-type uranium deposits are hosted in organic-rich, reduced, porous fluvial and shallow-marine sandstones near regional oxidation/reduction fronts. Individual deposits commonly contain up to 50,000 t U3O8 at average grades of 0.2% U3O8, and occur in districts that contain up to 300,000 t U3O8 or more. Sandstone-hosted uranium deposits in the U.S. have been producing since the 1950s using conventional mining and in situ leach (ISL) methods.
In 2006, Alberta Geological Survey started to evaluate the regional potential for sandstone-hosted uranium in Alberta. Studing the stratigraphy, lithology, alteration, structure, geochemistry and anomalous radioactivity of and within favourable formations will help us better understand the potential for sandstone-hosted uranium deposits.
During the last uranium boom in the 1970s and early 1980s, exploration for sediment-hosted uranium deposits was conducted sporadically in Alberta. Several radioactive occurrences were discovered, but there was reportedly little detailed follow-up exploration. However, the recent interest in uranium as fuel for nuclear energy, together with advances in ISL technology, have rekindled exploration interest for uranium in Mesozoic and Tertiary fluvial to shallow-marine sandstones in southern Alberta.
Below is an overview of some of the formations with potential for sandstone-hosted uranium deposits in Alberta.
Sandy, clastic sediments of the Campanian (81 million years ago) age in the Milk River Formation in southeastern Alberta contain a weakly anomalous (up to 200 counts per second) radioactive occurrence, associated with rusty, altered sandstone, within the massive sandstone unit in the banks of Police Creek. The radioactivity is caused by elevated Thorium content (69ppm). The sandstone has elevated content of well-rounded monazite grains.
The dominantly fluvial Campanian (80-75 million years ago) Belly River clastic wedge includes Foremost, Oldman and Dinosaur Park formations that were deposited as the Laramide Orogeny began. In the Basal Belly River wedge, conglomeratic fluvial sandstone channel complexes reach thicknesses up to 30 metres and some exceed 1 km in width in at least one area.
Fluvial sandstone channels of Campanian-Maastrichtian age (72-66 million years ago) St. Mary River Formation are generally reduced, friable and sometimes contain abundant organic material. The upper part of the St. Mary River Formation, called Whitemud member, is represented by a regional oxidation of the upper beds that formed during a significant break in sedimentation, before deposition of the organic-rich Battle shale and Kneehills tuff zone. A radioactive occurrence (up to 350 cps) is associated with folded and faulted beds of St. Mary River Formation near the village of Kimball. At this occurrence organic-rich black shale contain 67ppm uranium.
Reduced, friable fluvial sandstones of Maastrichtian–Paleocene (66-64 Ma) Willow Creek Formation (some with abundant organic material) were reported in the 1994 AGS Metallogenic Report to host “...four radioactive occurrences (with maximum radioactivity of 2000, 900, 300 and 200 cps…) along the Waterton River over about 7 km.” More recently, industry reported a rock grab sample with 0.9% U3O8 in Willow Creek Formation (U-Bone occurrence (see Map)). Recently, radioactive occurrence was discovered in grey siltsones of Willow Creek Formation near Fort McLeod (photo). Airborne resistivity survey, drilling and radon cup sampling results are now available to review through released assessment reports.
Massive cross-bedded fluvial sandstones of Paleocene (64-60 Ma) Porcupine Hills Formation in southwestern and central Alberta were staked for uranium in 2005. Airborne Radiometric Survey, outcrop sampling, soil and water sampling results are now available to public through assessment reports.
Paleocene (65-62 Ma) Ravenscrag Formation comprises fluvial and estuarine immature sandstones, mudstones and lignites, and reportedly is being explored for uranium in both southwestern Saskatchewan and southeastern Alberta. It has been suggested that uranium was mobilized by groundwaters and deposited under reducing conditions, particularly by coals lower in the stratigraphic sequence. Concentrations up to 0.2% U3O8 have been reported from previous exploration.