Kiggavik (Lone Gull): An unconformity related uranium deposit in the Thelon basin, northwest territories, Canada

Among several uranium prospects in the Baker Lake area, located at the northeastern rim of the Thelon Basin, the Kiggavik (Lone Gull) deposit is at an advanced exploration stage. Two ore zones, the Main and Centre Zones have been explored by drilling spaced 30mx15m and reserves of over 40 million lbs U3O8 with an average grade of 0,6% U3O8 are indicated. The Kiggavik mineralization is basement hosted in mica rich quartz-feldspathic metasediments of probably Aphebian age and in a late Hudsonian granite. The level of erosion reached in the area of the deposit below the Middle Proterozoic Thelon Sandstone, has removed traces of the Aphebian paleo-surface and parts of the deposit, leaving the closest outcrops of the unconformity approximately 2 km to the north. A post-ore diabase dyke has intruded the Main Zone with the effect that some ore was redistributed. Parallel, cigar-shaped ore lenses and the surrounding alteration halos are defined by sets of crosscutting structures. The strike of the lenses in the Main Zone is ENE and they plunge at 25 deg. in the same direction. In the Centre Zone, located on strike approximately 600 m ENE of the Main Zone, the mineralization occurs in meta-arkoses and schists. A barren orthoquartzite horizon controls the form and separates two ore lenses. Graphitic series are not known in the vicinity of the deposit but organic matter is found in all ore zones. Kiggavik is a monometallic deposit with pitchblende and coffinite as the main ore minerals. Common features with uranium deposits in the Athabasca basin such as a general relation to the unconformity, similar alteration, structural control, presence of diabase dykes and chronology of the deposit etc., emerged in the course of exploration. However, Kiggavik possesses some features such as the particular form of the ore lenses in the basement and in the granite, the uncertain extent of these mineralized lenses towards the unconformity and the absence of graphitic horizons, which are not as generally known in these types of deposits and make in combination a unique setting. (author). 4 refs, 12 figs, 3 tabs