Recent innovative applications of geophysics to new uranium discoveries in the Athabasca Basin

The history of exploration for uranium in the Athabasca Basin of northern Saskatchewan, Canada, has evolved from early airborne radiometric surveys and ground prospecting in the 1960's to resistivity, gravity and horizontal loop electromagnetic (HLEM) surveys plus drilling in the 1970's, to a predominance of deep penetrating airborne and ground time domain electromagnetic (TDEM) surveys since then, accompanied by systematic drilling of graphitic conductors at regular intervals. While other types of geophysical surveys have been and are still employed to supplement EM techniques, exploration remains very much a conductor-focused exercise. The eastern Athabasca basin has seen most of the historic exploration work and is becoming very much a mature uranium play. There is a limited amount of remaining conductor length to be tested for conventional unconformity-type deposits, and there is evidence of a diminishing return on this methodology. While discoveries of less than 30,000 tonnes (U3O8) have been made, it has been seventeen years since the discovery of the world class McArthur River deposit in 1988. This has led to the realization that a paradigm shift is required to improve the discovery rate and sustain uranium production from the basin. At Cameco, a new defining principle is a greater emphasis on employing geophysical techniques to remotely map the ore system geology at all scales, both the geological conditions that favor uranium deposition/preservation and the subtle manifestations of the presence of a uranium deposit. This means greater attention to attempting to understand the lithostructural setting and the ore-fluid processes involved. Innovative thinking and integration in the last five years have significantly improved Cameco's rate of discovery and identification of new uranium occurrences in the Athabasca Basin of northern Saskatchewan, Canada. Some recent discoveries which will be discussed, in order of advancement, are 1) the O2 North Extension (Next) zone, Eagle Point mine area, 2) Zone A, McArthur River Mine area, 3) the Millennium deposit, midway between the McArthur River and Key Lake mines, and 4) a very recent discovery at the Virgin River project, in the south-central part of the basin. These recent successes are related to a variety of themes, notably 1) brownfields - a renewed focus on brownfields to mine-scale exploration and careful use of orientation surveys to characterize and predict deposit response, 2) basement-hosted - a new focus on lower-cost, lower-risk production from basement-hosted uranium to supplement production from the classic unconformity deposits, 3) grid format surveys - a focus on defining the ore system geology in three dimensions through the use of grid format surveys, 4) integration - more integration of the disciplines through 3D visualization, notably through the use of downhole geological, geochemical and geophysical data, and 5) innovation - employing new uses of existing geophysical techniques for faster, better, cheaper exploration. The significance of the Millenium and O2 Next discoveries relates to the presence of a relatively undertested target type in the Athabasca basin located at depths of 50 to 350 m below the unconformity. The off-conductor position of O2 Next bears similarities to Zone O2 which lies 200 m southeast of the Collins Bay fault, as well as the original basement-hosted discovery by Gulf Minerals in 1968 of the Rabbit Lake deposit which is located 200 m into the hanging wall of the graphitic Rabbit Lake fault. Millenium constitutes a potentially different style of basement-hosted mineralization which is footwall to the dominant graphitic structure. The significance of Zone A at the McArthur River mine relates to the recognition that considerable potential remains in this area for both unconformity and basement-hosted styles of mineralization. The message of the Virgin River greenfields discovery is that considerable efficiencies are achievable by taking a more selective approach to systematic drilling of conductors using more refined geophysi cal coverage, particularly under deep sandstone cover