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 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 Mesoproterozoic Athabasca Group, between 410 and 450 metres below surface. It has the shape of a flat, elongated lense, approximately 1,950 metres in total length, 20 to 100 metres in width, and ranges up to 13.5 metres thick, with an average thickness of about 5.4 metres. It shows longitudinal and lateral geological continuity. It has a crescent-shaped cross-sectional outline that closely reflects the topography of the unconformity. The deposit is subdivided into the eastern Phase 1 and western Phase 2 zones. Phase 1 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 Manitou Falls Formation is 420 to 445 metres thick. The basement lithological domains consist of: • a variably graphitic pelite unit located directly below the deposit; • a calc-silicate rich unit labeled as “Meta-Arkose”; • a biotite pelite unit located to the south of the deposit area within which most of the mine access infrastructure is located. 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 Phase 1 area is dominated by an east-west trending protomylonitic to locally mylonitic zone containing numerous steeply dipping, east-striking fault zones. Directly below the Phase 1 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. Several steeply dipping northwest- and northeast- striking fault zones are located in this area and intersect the east-striking fault corridor in the central area of the Phase 1 mineralization. This area of intersecting faults controls the most extensive clay alteration observed within the Phase 1 area, both at the mineralized horizon and down to the 480 metre mining level. The Phase 1 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. Mineralization Two distinct styles of mineralization occur within the Cigar Lake deposit: • high-grade mineralization at the unconformity (“unconformity” mineralization), which includes all of the mineral resources and mineral reserves; • 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 at 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 Phase 1 area, 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 relatively lower grade Phase 2 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 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 black, red and/or green in colour. Uranium grades of the unconformity mineralization range up to 82% U3O8 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 and arsenic, 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.

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 below each frozen panel and the three JBS machines required are currently in operation. Two machines actively mine at any given time while the third is moving, setting up, or undergoing maintenance.

Mine development
Mine development for construction and operation uses two basic approaches: drill and blast with conventional ground support is applied in areas with a competent rock mass. 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 using the New Austrian Tunnelling Method (NATM). NATM was adopted as the primary method of developing new production cross- cuts, replacing the former Mine Development System (MDS).

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 approximately circular in profile.

Mine access
There are two main levels in the mine: the 480 and 500 metre levels. Both levels are in the basement rocks below the unconformity. Mining is conducted from the 480-metre level which is located approximately 40 metres below the ore zone. The main underground processing and infrastructure facilities are located on this level. The 500-metre level is accessed via a ramp from the 480-metre level. The 500-metre level provides for the main ventilation exhaust drift for the mine, the mine dewatering sump and additional processing facilities. All construction required for production has been completed.

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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 solution through a series of mixer and settler cells, the uranium is selectively extracted from the solution with an organic solvent. This stripping process increases the uranium’s concentration by five to ten times. The remaining solution, stripped of its uranium and containing waste metals, is sent to the Tailings Neutralization circuit.

Precipitation converts the uranium from a solution to 60% solid after going through a centrifuge wash. The molybdenum, present as an impurity in the solution, is removed by passing the solution through a series of carbon columns before precipitating the dissolved uranium by adding ammonia. This form of uranium concentrate is yellow, giving it the term “yellowcake.”

Calcining dries the yellowcake at high temperature to a black powder called uranium oxide concentrate, or more commonly, calcined yellowcake. The yellowcake from the Precipitation circuit is fed to a centrifuge, which removes 60% of the moisture. The remaining product is then completely dried in a furnace with multiple hearths, known as the calciner. This occurs at a high temperature of about 800ºC. The dry calcined yellowcake is then placed in storage bins. The final product contains about 85% uranium with less than 0.5% moisture. Although it is now powder black in colour, it is still referred to as yellowcake.

Packaging transfers the calcined yellowcake powder from the bin into steel drums. The loaded drums are trucked off site in truck-trailers and sea containers for domestic and overseas shipments. Each drum contains about 400 kilograms of yellowcake.