The Cigar Lake deposit is located 40 km inside the margin of the eastern part of the Athabasca Basin. It is an unconformity related uranium deposit.

The unconformity mineralization consists primarily of three dominant rock and mineral facies occurring in varying proportions. These are quartz, clay (primarily chlorite with lesser illite) and metallic minerals (oxides, arsenides, sulphides). In the two higher grade eastern pods (Phase 1), the ore consists of approximately 50% clay matrix, 20% quartz and 30% metallic minerals, visually estimated by volume. In this area, the unconformity mineralization is overlain by a very weakly mineralized contiguous clay cap one to five metres thick. In the lower grade western lens (Phase 2), the proportion changes to approximately 20% clay, 60% quartz and 20% metallic minerals.

Uranium oxide in the form of uraninite and pitchblende occurs in both a sooty form and as botryoidal, metallic masses. It occurs as disseminated grains in aggregates ranging in size from millimetres to decimetres, and as massive metallic lenses up to a few metres thick floating in a matrix of sandstone and clay. Coffinite (uranium silicate) is estimated to form less than 3% of the total uranium mineralization. The mineralized rock is variably green, red and/or black in colour.

Uranium grades of the unconformity mineralization range up to 82% U3O8 for a 0.5 m interval from a single drillhole intersection within the mining area.

Geochemically, the deposit contains quantities of the elements Ni, Cu, Co, Pb, Zn, Mo and As, but in non-economic concentrations. Higher concentrations of these elements are associated with massive pitchblende or massive sections of arseno-sulphides.

The jet boring mining system, a non-entry mining method, has been selected to mine the Cigar Lake deposit because of the challenges associated with mining the deposit, including control of groundwater, weak rock formations, radiation protection, water inflow and relatively thin, flat-lying mineralization. This method was selected after many years of exploration and test mining activities following the discovery of the deposit in 1981.

The JBS mining method consists of cutting cavities out of frozen ore using a high-pressure water jet. Access to the orebody is achieved by drilling boreholes upwards from the production crosscuts below and then inserting specialized jetting tools to the ore horizon. Jetting begins at the top of a cavity and retreats vertically downward in thin slices, resulting in a cylindrical void with a height corresponding to the thickness of the orebody (up to 13.5 metres) and a diameter of 4.5 to 6 metres. The resulting void is tightly backfilled with concrete, and the cycle is repeated to recover adjacent ore.

This non-entry method was developed and adapted specifically for the Cigar Lake deposit, and does not directly expose personnel to the ore. The mining process is controlled from headings located in barren basement rock below the orebody, where the levels of radiation exposure to workers are very low. Radiation protection is further enhanced through the containment of the ore cuttings within cuttings collection and hydraulic conveyance systems, and via the application of ground freezing which limits the mobility of potentially radon-bearing water. These unique properties of the mining method have proven very effective at minimizing workers’ exposure to radiation.

The mine equipment fleet is currently comprised of three JBS units, plus other equipment to support mine development, drilling and other services, and is sufficient to meet the needs of the mine plan for the next few years. The current mine plan, with its underlying productivity assumptions, assumes that a fourth JBS unit is required later in the mine life. Cameco is currently investigating if productivity improvements could negate the need for the fourth JBS unit.

All of Cigar Lake’s ore slurry will be processed at the McClean Lake mill.

The existing two stage near atmospheric pressure leach circuit will be reconfigured to two parallel low pressure circuits to allow ore to be leached separately from other ore feeds to McClean Lake. Leach cooling and hydrogen gas concentration control have been added to deal with the exothermic reaction and potential for hydrogen evolution from leaching the high grade ore. An oxygen plant was constructed to provide the leach oxidizing agent. The existing hydrogen peroxide system will be available as an alternative. The leached solution will be fed to the existing primary thickener. The overflow will report directly to the clarification area, and the underflow will be washed with the leach residues from other McClean Lake ores in the Counter Current Decantation (CCD) circuit. Additional wash capacity is available in the new Counter Current Cyclone (CCC) circuit, and can be implemented if required. Additional clarification and storage capacity will be provided for pregnant leach solution. The washed and clarified uranium solution will be fed to two parallel Solvent Extraction (SX) plants. The existing 10 Mlbs U3O8/year circuit capacity will be supplemented by a new 17 Mlbs U3O8/year SX circuit to provide a total capacity of 27 Mlbs U3O8/yr. The pregnant strip solution from the SX circuit will be fed to two parallel molybdenum removal carbon column circuits comprised of two new columns in addition to the existing six. Additional capacity will be installed in the precipitation circuit to increase retention times and improve barren strip clarification. A new centrifuge will provide yellowcake dewatering requirements with the existing centrifuge providing additional capacity if required. Existing calciner and packaging facilities will be used to provide the packaged, calcined product.