Overview

Deposit type

• Unconformity related

Summary:

Cigar Lake is an unconformity-related uranium deposit. Deposits of this type are believed to have formed through an oxidation-reduction reaction at a contact where oxygenated fluids meet with reducing fluids. That contact broadly coincides with the unconformity surface. The Cigar Lake deposit occurs at the unconformity contact between rock of the Athabasca Group and underlying Wollaston Group, an analogous setting to the Key Lake, McClean Lake, Collins Bay and McArthur River deposits. It shares many similarities with these deposits, including general structural setting. mineralogy, geochemistry, host rock association and the age of the mineralization; however, it is distinguished by its flat-lying geometry, size, the intensity of its alteration process, the high degree of associated hydrothermal clay alteration and the presence of massive, extremely rich, high-grade uranium mineralization.

The Cigar Lake deposit is similar to the McArthur River deposit in that the sandstone that overlies the basement rock contains large volumes of water at significant pressure. Unlike McArthur River, however, this deposit is flat-lying with the ore zone being overlain by variably developed clay alteration as opposed to silica enrichment.

Property geology
The Cigar Lake uranium deposit, which has no direct surface expression, is located at the unconformity between the middle Paleoproterozoic Wollaston Group metasediments and the late Paleoproterozoic to Mesoproterozoic Athabasca Group, between 410 and 450 metres below surface. It has the shape of a flat, elongated lens, approximately 1,950 metres in total length, 25 to 100 metres in width, and ranges up to 15.7 metres thick, with an average thickness of about 5.4 metres. It shows longitudinal and lateral geological continuity. It has a crescent-shaped crosssectional outline that closely reflects the topography of the unconformity. The deposit is subdivided into the eastern CL Main and the western CLEXT zones. CL Main is further divided into the East and West Pods.

The deposit and host rocks consist of three principal geological and geotechnical elements:
• the deposit itself
• the overlying sandstone
• the underlying metamorphic basement rocks

The MF Formation is 420 to 445 metres thick. The basement lithological domains consist of:
• a variably graphitic pelite unit located directly below the deposit
• a biotite pelite unit located to the south of the deposit area within which most of the mine access infrastructure is located
• a minor calc-silicate rich unit located near the boundary between the graphitic and biotite pelites.

The graphitic pelite unit has been further divided into two sub-domains, including a graphite and sulphide-rich portion located directly below the uranium mineralization that has undergone variable and locally significant shear deformation, and a lesser graphite-rich portion that contains significantly less sulphides and shows less shear deformation.

The structural framework in the Cigar Lake area is dominated by an east-west trending protomylonitic zone containing numerous steeply dipping, east-striking fault zones. Directly below the ore zone, these east-striking faults consist of graphitic breccia zones that are up to several metres wide and largely coincide with the 20-metre basement high, along which the uranium mineralization is located. This area of east-striking faults generally controls the most extensive clay alteration observed within the Cigar Lake area, both at the mineralized horizon and down to the 500L.

The deposit is surrounded by a strong alteration halo affecting both sandstone and basement rocks, characterized by extensive development of Mg-Al rich clay minerals (illite-chlorite). This alteration halo in the sandstone is centred on the deposit and reaches up to 200 metres in width and 250 metres in height, tapering with elevation. In the basement rocks, this zone extends in the range of 200 metres in width and as much as 100 metres in depth below the deposit. The mineralization is hosted principally by the Athabasca Group and consists mainly of uraninite and pitchblende along with nickel and cobalt arsenides (Bruneton, 1983).

Mineralization
Two distinct styles of mineralization occur within the Cigar Lake deposit:
- high-grade mineralization at or proximal to the unconformity ("unconformity" mineralization), which includes all of the mineral resources and mineral reserves.
- low-grade, fracture controlled, vein-like mineralization which is located either higher up in the sandstone ("perched" mineralization) or in the basement rock mass

The high-grade mineralization located in proximity to the unconformity contains the bulk of the total uranium metal in the deposit and currently represents the only economically viable style of mineralization, in the context of the selected mining method and ground conditions. It is characterized by the occurrence of massive clays and very high-grade uranium concentrations.

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 relatively higher grade eastern CL Main zone, 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 weakly mineralized contiguous clay cap 1 to 10 metres thick. In the western CLEXT zone, the proportion changes to approximately 20% clay, 60% quartz and 20% metallic minerals.

While pre- and post-mineralization faulting played major roles in creating preferential pathways for uranium-bearing fluids and, to some extent, in remobilizing uranium, the internal distribution of uranium within the unconformity mineralization has likely been largely controlled by geochemical. processes. This is reflected in the continuity and homogeneity of the mineralization and its geometry, particularly in the eastern part of the deposit. A very sharp demarcation exists between well mineralized and weakly mineralized rocks, both at the upper and particularly at the lower surface of the deposit.

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 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 black, red and/or green in colour.

Uranium grades of the unconformity mineralization range up to 86% U2Os for a 0.5 metre interval from a drillhole intersection within the mining area. Geochemically, the deposit contains quantities of the elements nickel, copper, cobalt, lead, zinc, molybdenum, arsenic and rare earth elements, but in non-economic concentrations. Higher concentrations of these elements are associated with massive pitchblende or massive sections of arseno-sulphides. Primary age of the unconformity mineralization has been estimated at 1.3 billion years.

The deposit has been subjected to faulting after its formation, which has contributed to the formation of vein-type mineralization that has been termed "perched" within the sandstone and vein-type mineralization within the basement. These mineralized bodies form, volumetrically, a very small part of the total mineralized rock and are currently of no economic significance.

Mining Methods

• Jet Boring

Summary:

The Cigar Lake deposit has historically been divided into two parts. The eastern portion, previously referred to as Phase 1, is now referred to as the Cigar Lake Main (CL Main) portion of the deposit, whereas the western portion, previously referred to as Phase 2, is now referred to as the Cigar Lake Extension (CLEXT). Cameco plans to produce first ore from CLEXT in 2030.

At Cigar Lake, the permeable sandstone which overlays the deposit and basement rocks, contains large volumes of water at significant pressure. Before we begin mining, Cameco freeze the ore zone and surrounding ground. Cameco use a jet boring system to mine the ore.

Production plan: the average mine production varies annually from 115 to 160 tonnes per day during peak production, depending on the grade of ore being mined.

Jet boring mining system (JBS) mining
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, and relatively thin, flat-lying mineralization.

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.

All of the mine equipment for mine operation is owned by Cameco, with the exception of diamond drilling equipment.

Mine development
Mine development for construction and operation uses two basic approaches: for good quality. competent rock mass, drill and blast with conventional ground support is applied; for poor quality, weak rock mass, the New Austrian Tunnelling Method (NATM) is applied. Most permanent areas of the mine, which contain the majority of the installed equipment and infrastructure, are hosted in competent rock mass and are excavated and supported conventionally. The production tunnels immediately below the orebody are primarily in poor, weak rock mass and are excavated and supported following NATM principles.

NATM, as applied at Cigar Lake, involves a multi-stage sequential mechanical excavation, extensive external ground support and a specialized shotcrete liner. The liner system incorporates yielding elements which permit controlled deformation required to accommodate additive pressure from mining and ground freezing activities. The production tunnels have an inside diameter of five metres and are circular in profile.

Cameco has successfully excavated nine NATM production tunnels on the east side of CL Main and two production tunnels on the west side of CL Main. All production tunnels are backfilled with low strength backfill after ore is depleted above these tunnels. NATM excavation techniques are expected to be used in 14 CLEXT production tunnels as well as in conventional headings in areas where poor ground conditions are expected.

Cameco plans its mine development to take place away from known groundwater sources whenever possible. In addition, Cameco assesses all planned mine development for relative risk and applies extensive additional technical and operating controls for all higher risk development.

Mine access
The main access to the mine is via Shaft No. 1, a circular concrete-lined shaft, 4.9 metres in diameter which extends to a depth of 500 metres below the surface and provides direct access to the working level on the 480L. Shaft No. 1 is used as the main access and services shaft, and as a route for delivery of fresh ventilation underground.

Shaft No. 2 is a circular lined shaft, 6.1 metres in diameter, also sunk to a depth of 500 metres. This shaft is located 90 metres south of Shaft No. 1 and provides access to 480L. It is divided into two compartments by a central airtight partition: one compartment serves as the main path for exhaust air from the mine; the second compartment is used to downcast additional fresh ventilation air, as well as provide secondary egress and a number of additional services. The primary ventilation system has been designed to supply a volume of up to 240 m3 /s of fresh air to the mine.

Mine Levels – 480L and 500L
There are two main levels in the mine: the 480L and the 500L. Both levels are located in the basement rocks below the unconformity. Mining is conducted from the 480L, which is located about 40 metres below the ore zone. The main underground processing and infrastructure facilities are also located on this level. The 500L is accessed via a ramp from the 480L. The main ventilation exhaust drift for the mine, the mine dewatering sump and additional processing facilities are located on 500L.

Artificial Ground Freezing
Cameco bulk freezes the ore zone and surrounding ground prior to mining an area. This system freezes the deposit and underlying basement rock in two to four years, depending on water content and geological conditions.

Freezing is key to the success of mining the deposit, and results in several enhancements to mining conditions, including: (1) increasing the stability of the area being mined; (2) minimizing the risk of water inflows into the mine from the water-bearing rock above the unconformity; and (3) reducing the radiation resulting from radon dissolved in the water In 2015, the CLJV decided to pursue a strategy of freezing exclusively from surface. This strategy has resulted in the following benefits:
• reducing risk to mine development
• allowing ground freezing to start before development of underground production tunnels
• simplifying mining operations, since ground freezing infrastructure and activities are located on surface.

Artificial ground freezing for mining of CLEXT mineral reserves will follow a similar strategy of freezing exclusively from surface.

Artificial ground freezing is accomplished by drilling a systematic grid of boreholes through the orebody from surface. A network of supply and return pipes on surface convey a calcium chloride brine to and from each hole. The warmed brine returning from each hole is chilled to a temperature of approximately -30ºC at the surface freeze plant and recirculated.

The Cigar Lake production schedule relies upon the ground being sufficiently frozen prior to the start of JBS mining.

Comminution

Crushers and Mills

Summary:

Cigar Lake ore from the JBS mining method is processed at two locations. Size reduction is conducted underground at Cigar Lake, while leaching, purification, concentration and final yellowcake production and packaging occurs at the McClean Lake mill. The ore is trucked as a slurry from Cigar Lake to the McClean Lake mill in purpose-built containers.

Cigar Lake flowsheet
Broken ore and pilot hole drill cuttings from the JBS units report to ROM ore storage sumps. Ore solids either settle in the ROM or report in the ROM overflow (fine solids) hydraulically to the underground thickeners, depending on particle size and settling velocity. Coarse ore is recovered by an overhead crane mounted clamshell and is fed by a screw feeder into a water flush cone crusher. Crusher discharge reports to a ball mill operating in closed circuit with classification hydrocyclones. Grinding circuit product reports to an underground thickener and the thickened slurry is pumped to an underground ore slurry storage pachuca tank. From there, the ore slurry is pumped by one of the positive displacement pumps through slurry pipelines up Shaft No. 2 to ore storage pachucas located on surface. The ore reports to a thickener and then is loaded into 5 m3 containers (four containers per truck) for shipment by road to the McClean Lake mill.

Cigar Lake Extension (CLEXT)
Other than the addition of booster pumps to assist in moving jetted ore from the CLEXT portion of the mine back to the process area, no significant changes to the process circuit are anticipated to process CLEXT ore.

Processing

• Solvent Extraction
• Calcining
• Sulfuric acid (reagent)
• Crush & Screen plant
• Agitated tank (VAT) leaching
• Counter current decantation (CCD)
• Dewatering

Summary:

Cigar Lake ore from the JBS mining method is processed at two locations. Size reduction is conducted underground at Cigar Lake, while leaching, purification, concentration and final yellowcake production and packaging occurs at Orano’s McClean Lake mill. The ore is trucked as a slurry from Cigar Lake to the McClean Lake mill, 69 kilometres to the northeast, in purpose-built containers.

Cigar Lake
The ore slurry produced by the JBS is pumped to Cigar Lake’s underground crushing, grinding and thickening facility. The resulting finely ground, high density ore slurry is pumped 500 meters to surface to one of the two slurry holding tanks. It is blended and thickened, removing excess water. The final slurry, at average grade of approximately 14%, is pumped into transport truck containers.

McClean Lake Mill
In accordance with the JEB Toll Milling Agreement, the McClean Lake mill was expanded to process and package all of Cigar Lake’s mineral reserves. Originally, the mill had a production capacity of 12 million pounds U3O8 per year. In order to process all of Cigar Lake’s mineral reserves and other ores at McClean Lake, projects were identified to increase the total production capacity at the mill to 24 million pounds U3O8 per year. Construction of the expanded facility began in 2012 and was completed in 2016. Further changes were completed in 2021 to increase the capacity in the front-end circuits (leaching, CCD) from a nominal 45 kt ore/year to 59 kt ore/year.

All of the 18 million pounds U3O8 annual output from Cigar Lake will be converted to yellowcake at the McClean Lake mill.

McClean Lake mill flowsheet
Finely ground ore slurry is trucked from Cigar Lake by B-trains carrying four 5 m3 slurry containers to the receiving facility located at McClean Lake. The receiving facility was based on the design of the Key Lake ore slurry receiving facility, inclusive of some revisions. The slurry is off-loaded by vacuum, thickened and pumped to storage pachuca tanks.

Leaching involves extracting uranium from the ore by dissolving it into a sulphuric acid solution.

The previous two-stage near-atmospheric pressure leach circuit was reconfigured to a one-stage atmospheric leach circuit to allow ore to be leached to the target leach extraction of 99.5%. Leach cooling and hydrogen gas concentration control have been added to address exothermic leaching reactions and the potential for hydrogen to be released from leaching Cigar Lake high-grade ore.

The leached slurry is fed to the CCD circuit, where it is washed with acidified wash water. Clarification and storage capacity is provided for the pregnant leach solution.

The clarified uranium solution is fed to two parallel SX plants. The original 12 million pound U3O8 per year SX circuit capacity is supplemented by a new 14 million pound U3O8 per year circuit to provide a total nominal capacity of 26 million pounds U3O8 per year.

The loaded strip solution from the SX circuits is fed to two parallel molybdenum removal carbon column circuits. Two precipitation reaction tanks are used to precipitate yellowcake with ammonia. Barren strip sand filters clarify the barren strip solution. A centrifuge provides yellowcake dewatering requirements prior to calcination of the yellowcake precipitate. The calcined product is directed to the packaging facilities where it is packaged in 210L steel drums for shipment. A new packaging system was installed in 2013 to accommodate increased production rates and enhance fugitive dust control.

A third ammonia reagent supply tank was added for solvent extraction and precipitation in 2014, and additional ferric sulphate production capacity was added in 2022. An additional ammonium sulphate crystallization plant similar in size to the original plant was installed as well. A new tailings neutralisation circuit was constructed to provide the retention times required for full production rates.

Cigar Lake Extension (CLEXT)
No additional changes are required to the McClean Lake circuit to process ore from the CLEXT mineral reserves.

Pipelines and Water Supply

Summary:

The Cigar Lake minesite has access to sufficient water from nearby Waterbury Lake for all planned industrial and residential activities.

Cameco is studying how even more of the water needed for the jet boring mining method at our Cigar Lake mine could be recycled and re-used. If Cameco can identify a viable technology, then would expect to see a reduction in the amount of surface water directly withdrawn for underground use by the Cigar Lake mine.

Process Water Management
As much as reasonably possible, process water (water that has been in contact with the ore during JBS mining and ore processing) is recirculated in the underground process circuit. Minor flows of fresh water used for washdowns in process sump areas ultimately report to a collection pond for treatment.

Process water not recycled in the process circuit is pumped to surface, collected in a surge pond and ultimately treated in a conventional two-stage water treatment plant.

Water generated from the mining operations is collected in a separate system and pumped from underground to a storage pond on surface. The mine water is treated separately from the process water in batches through the water treatment circuit.

A portion of the treated water is recycled into the mining and processing circuits where required. The remaining treated water is released to the environment via a monitoring pond batch release system.

Slurry pipeline
Shaft No. 2 is a 500 m deep vertical mine service shaft and includes transportation of ore in the form of two slurry pipelines.

Production

Operational metrics

Personnel

Job Title	Name	Profile	Ref. Date
Chief Metallurgist	Biman Bharadwaj		Feb 25, 2025
General Manager	Kirk Lamont		Feb 25, 2025
HSE & Quality Manager	Trent Hamilton		Feb 25, 2025
Operations Manager	Imre Bartha		Feb 25, 2025
Senior Maintenance Planner	John Lindberg		Feb 25, 2025
VP, Technical Services	Lloyd Rowson		Feb 25, 2025