Summary

Deposit type

• Unconformity related

Summary:

ormed 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 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 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 Mesoproteroz

Mining

• Jet Boring

Summary:

nding soil will be frozen. Cameco use a reactive drilling system for ore extraction.

Cameco use the JBS method to mine the Cigar Lake deposit.

Bulk ground freezing
The permeable sandstone that overlays the deposit and basement rocks contains large volumes of water under significant pressure. From surface, Cameco freeze the ore zone and surrounding ground in the area to be mined to prevent water from entering the mine, to help stabilize weak rock formations, and meet our production schedule. This system freezes the deposit and underlying basement rock in two to four years, depending on water content and geological conditions. Cameco have identified greater variation of the freeze rates of different geological formations encountered in the mine, based on information obtained through surface freeze drilling. To manage our risks and to meet our production schedule, the area being mined must meet specific ground freezing requirements before we begin jet boring. Bulk freezing reduces but does not eliminate the risk of water inflows.

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 warm brine returning from each hole is chilled to a temperature of approximately -30ºC at the surface freeze plant and recirculated.

JBS mining
After many years of test mining, Cameco selected jet boring, a non-entry mining method, which was developed and adapted specifically for this deposit. This method involves:

- drilling a pilot hole into the frozen orebody, inserting a high pressure water jet and cutting a cavity out of the frozen ore;
- collecting the ore and water mixture (slurry) from the cavity and pumping it to storage (sump storage), allowing it to settle;
- using a clamshell, transporting the ore from sump storage to an underground grinding and processing circuit;
- once mining is complete, filling each cavity in the orebody with concrete; and
- starting the process again with the next cavity.

This is a non-entry method, which means mining is carried out from headings in the basement rock below the deposit, so employees are not exposed to the ore. This mining approach is highly effective at managing worker exposure to radiation levels. Combined with ground freezing and the cuttings collection and hydraulic conveyance system, jet boring reduces radiation exposure to acceptable levels that are below regulatory limits.

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 production requirements for the remainder of the mine life.

Cameco has divided the orebody into production panels. At least three production panels need to be frozen at one time to achieve the full annual production rate of 18 million pounds. One JBS machine will be located belo

Comminution

Crushers and Mills

Summary:

nal yellowcake production and packaging occurs at the McClean Lake mill.

Cigar Lake flowsheet
Mined ore and drill cuttings are piped into local pump boxes as a slurry for transfer to run of mine ore storage sumps. Partially dewatered ore is reclaimed from the sumps by an overhead crane mounted clamshell and fed by a screw feeder through a water flush cone crusher. Crusher discharge reports mostly to a ball mill operating in closed circuit with classification cyclones. Grinding circuit product is dewatered in an underground thickener and then reports to an underground ore slurry storage pachuca tank. From there, the ore slurry is pumped by positive displacement pumps through slurry pipelines up Shaft No. 2 to ore storage pachucas located on the surface. Thickened ore slurry is loaded into 5 m3 containers (four containers per truck) for shipment by road to the McClean Lake mill.

Beneficiation

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

Summary:

ounds U3O8 per year;
- process and package all of Cigar Lake’s current mineral reserves.

Cigar Lake ore slurry is processed in two locations:

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 like the ones used at McArthur River.

Water from this process, including water from underground operations, is treated on the surface. Any excess treated water is released into the environment.

McClean Lake – Containers of ore slurry are trucked to Orano’s McClean Lake mill, 69 kilometres to the northeast for further processing (Leaching to Yellowcake Packaging).

The McClean Lake mill is the only facility in the world capable of processing high-grade uranium ore without dilution. It can process uranium ore grades over 100 times the world’s average grade.

The mill has an annual production capacity of 24 million pounds of uranium concentrate, and it can receive and process uranium ore from conventional mining and high-grade ore slurry obtained through advanced remote mining techniques. The mill currently processes the high-grade ore slurry it receives from the Cigar Lake mine, the world’s second-largest and highest-grade uranium mine.

Ore Slurry arrives in specially designed containers on heavy transport trucks from the Cigar Lake mine located about 80km south of McClean Lake. The slurry, containing high-grade uranium, is unloaded using a specifically designed vacuum and container wash system. The slurry and wash water are put through a thickener. The thickened slurry is then pumped into pachucas.

Leaching involves extracting uranium from the ore by dissolving it into a sulphuric acid solution. Ferric sulphate and hydrogen peroxide are used to oxidize the uranium into a soluble form. This is a non-selective process, meaning that other naturally occurring elements are also dissolved, such as iron, arsenic, molybdenum, nickel, cobalt, selenium, etc.

Counter-Current Decantation (CCD) washes the uranium solution from the waste solids in the leached residue. The CCD wash solution flows in one direction and the leached residue flows in the opposite direction. The slurry is fed through a series of thickeners where the solids are separated from the liquids. The waste solids, containing a very small amount of soluble uranium, are sent to the Tailings Neutralization circuit.

Clarification removes suspended solids from the uranium solution after CCD, using a clarifier and sand filters. This is necessary to ensure the efficiency of the Solvent Extraction (SX) circuit downstream.

Solvent Extraction (SX) creates a purified and more concentrated uranium solution. By passing the uranium sol

Water Supply

Summary:

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

Grinding circuit product is dewatered in an underground thickener and then reports to an underground ore slurry storage pachuca tank. From there, the ore slurry is pumped by positive displacement pumps through slurry pipelines up Shaft No. 2 to ore storage pachucas located on the surface.

Cameco are currently 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.

Commodity Production

Operational metrics

Personnel

Job Title	Name	Profile	Ref. Date
General Manager	Lloyd Rowson		Feb 29, 2024
HSE & Quality Manager	Trent Hamilton		Feb 29, 2024