The McArthur River Operation is an underground uranium mine operated by Cameco Corporation with a joint venture partnership with Areva Resources Canada. Accessing the exceptionally rich orebody has been challenging due to a weak host rock mass at depth, pervasive fault and joint systems, a high level of radioactivity, and the water pressure resulting from the 500m-thick water-bearing sandstone formation. Mining and geotechnical engineers at McArthur River Operation have leveraged past experiences in the Athabasca Basin, artificial ground freezing, a hybrid of mining and civil engineering excavation techniques, and a novel integrative design and construction process to successfully access very challenging ore zones. The most outstanding achievement was witnessed during the design and construction of the first raisebore chamber in the Zone 2 Panel 5 area. The safe completion of this development was a ‘game changer’ for future development, mining sequencing and ore recovery.
Located in the Athabasca Basin of Northern Saskatchewan, the McArthur River Operation is the world's largest high grade uranium mine, as it provides 15% of the world's uranium production with an average annual output of nearly 9,000 tonnes of uranium oxide in 2009 . The mine hosts enormous reserves of high grade ore (approximately 21%) occurring between 500m and 640m below surface . Controlled mostly by the P2 thrust fault, the unconformity-type orebodies at the McArthur River Operation are nestled between the crystalline basement rocks of the Aphebian Wollaston Domain, and the sandstones and conglomerates of the Helikian Athabasca Group . Around the ore zones, the radioactive nature of the deposits has created a halo of altered rock masses at various stages; clays, pervasive clay in fillings, and unconsolidated sands add to the complex fracture system. One solution to mitigate these challenges has been the use of the raisebore mining method to safely and economically extract the ore. Although innovative and effective, the method still requires raisebore chambers and extraction chambers to be excavated in complex geological and hydrogeological conditions. Geotechnical endeavours have always been carefully engineered at the McArthur River Operation to account for all the parameters. However, in the geotechnical design and execution of the new Zone 2 Panel 5 (Figure 1), a novel approach that integrated 10 years of experience in the Athabasca Basin was crafted and successfully implemented. This paper recounts a new geotechnical design procedure, construction, and monitoring that is considering by the author to be the best-practice for mining through the unconformity in the Athabasca Basin.
As described in previous papers [3–4], the McArthur River Operation has created and successfully implemented a novel geotechnical design procedure to account for geological and hydrogeological conditions, geotechnical analyses, radiation protection, artificial ground freezing, inflow preparedness, customized factors of safety, and regulatory requirements (Figure 2). The details about each of these aspects can be found in Yameogo . In the case of the first chamber of the Zone 2 Panel 5, three geomechanical domains were identified with a specific excavation sequence and design, timing, and installation of the ground support .