The Riou Lake Project is underlain by 250 to 800 metres of Proterozoic sandstone of the Athabasca Group that dips shallowly to the south. The sandstone unconformably overlies Archean-aged basement rocks of the Tantato Domain, which comprise metavolcanic units, graphite-bearing metasedimentary gneiss, mafic sills and granites that have been affected by amphibolite to granulite facies metamorphism. Extensive Archean mylonitic shear zones are developed in the region, including the Black Lake Shear Zone east of the project, which defines the boundary between the Tantato Domain and the Mudjatik Domain. Basement rocks trend mainly northeast, and are affected by tight, megascopic folds.
On the Riou Lake property, post-Athabasca faults strike mainly to the northeast, and include the southerly dipping Riou Lake reverse fault system. This structure varies in strike across the property, bending from a northeast trend in southwestern parts of the property, through to east-west in the central parts and then southeast-trending in the eastern parts of the property southeast of Riou Lake. This structure is associated with an extensive upthrust block of basement and sandstone, indicating apparent reverse displacement of at least 170 metres. This fault, and areas of faulting associated with conductive graphitic gneiss units beneath the Athabasca sandstone to the south of the Riou Lake Fault, comprise several of the principal exploration targets on the project. Electromagnetic ("EM") surveys and follow-up drilling have also confirmed the presence of curved, northeast to east-west trending, graphite-bearing conductive units to the south of the Riou Lake Fault. Graphite-rich lithologies, due to their chemical nature as a reductant and the common localization of faulting and consequent structural permeability along these units, are associated with many of the major uranium deposits in the eastern Athabasca Basin.
Exploration Activities and Results
Principal exploration activities conducted on the Riou Lake property by UEX and its predecessor, Pioneer, have comprised surface prospecting and lake sediment sampling, EM and magnetic surveys, and the drilling of widely spaced drill holes along conductive units and faults. In addition to local radioactive boulders in till, potential surface indicators of uranium mineralization include the presence of radioactive, phosphatic boulders along a west-northwest trending possible footwall fault to the Riou Lake Fault south of Riou Lake, anomalous uranium and associated pathfinder elements in lake sediments, and the presence of radioactive artesian springs in the southwestern portions of the property. The latter may reflect the upward migration of deep waters along faults, suggesting structural targets in areas where basinal waters may have tapped a radioactive source.
UEX has focused its drilling on areas where EM conductors have been defined by ground geophysical surveys, and known or interpreted positions of faults where they intersect or come close to intersecting the sub-Athabasca unconformity. Although drilling has been of a reconnaissance nature, and is widely spaced, several areas of anomalous alteration, low-grade uranium mineralization and associated faulting have been intersected near the sub-Athabasca unconformity, which form principal target areas for follow-up drilling.
In southeastern parts of the property along the PM conductor, three holes (RLG-D1, RLG-D10 and P2-H1) have intersected a broad area of bleaching, silicification and clay alteration in the Athabasca sandstone column that is comparable to the peripheral alteration halo to many uranium deposits. Narrow intervals of anomalous uranium mineralization were also locally intersected near the unconformity, containing up to 0.537% U3
over 0.07 m.
South of Riou Lake, drilling has intersected graphitic gneiss in several drill holes within basement rocks (e.g. holes RLG-D8, D9, D14, D20 and D25) that are also locally associated with disseminated pitchblende mineralization over narrow intervals near the unconformity. Holes RLG-D7 and RLG-D11 both intersected a major southwest-dipping fault that forms a southerly strand of the Riou Lake Fault system. A 60-metre wedge of basement is thrust over Athabasca sandstone in hole RLG-D7. Although no mineralization or significant alteration is associated with the fault here, the style and magnitude of faulting is similar to that associated with uranium deposits elsewhere in the Athabasca Basin.
In southwestern parts of the Riou Lake property, an area containing numerous radioactive springs has been tested by several drill holes. In addition to the springs, this area was deemed additionally prospective by the presence of EM conductors which run through the area, and by evidence of post-Athabasca faulting which affects topography and outcrop patterns. Drilling here has intersected wide intervals of faulting in the lower portions of the Athabasca sandstone column that are associated with areas of bleaching, sandstone bedding rotation, and vertical offset locally in excess of 30 metres of the Athabasca unconformity. Anomalous radioactivity, with associated elevated nickel and arsenic concentrations, occurs at and immediately adjacent to the sub-Athabasca unconformity in several drill holes. Drilling in hole RLD-20 also intersected a graphitic breccia in basement rocks, which may represent one of the principal fault strands. Follow-up drilling of this area in drill hole RLG-D21-2 in 2007 encountered a 60-metre wide zone of bleached, brecciated and faulted sandstone showing local tilted bedding and tectonic/hydrothermal breccias. In this drill hole, a 0.5-metre interval from limonitic sandstone containing pitchblende stringers just above the unconformity between 774.4 to 774.9 metres returned 0.448% U3
and anomalous nickel, arsenic, copper and lead. This represents the most significant uranium-bearing intersection to date on the property, and demonstrates the potential for unconformity-style mineralization associated with faulting on the property.