McArthur River is world's largest, high-grade uranium deposit with proven and probable reserves of 335.2 million pounds U3O8, average ore grade of 19.5% U3O8.
McArthur River is operated by Cameco. Ore is milled at the Key Lake operation, 80-kilometres southwest by road. The McArthur River and Key Lake operations together employ approximately 750 people.
Production capacity of McArthur River is 18.7 million pounds U3O8 annually - ore from McArthur is blended for processing with low-grade ore in stockpile at Key Lake.
McArthur River achieved International Standards Organization (ISO 14001) Certification in 2003.
The McArthur River minesite is located near Toby Lake in northern Saskatchewan, approximately 620 km north of Saskatoon.
The McArthur River mine site is compact, occupying approximately an area of one kilometre in the north/south direction and half kilometre in the east/west direction. The site consists of an underground mine, one full service shaft and two ventilation shafts along with numerous surface facilities, including inert waste rock stockpiles, a large capacity mine water treatment plant, a pump hose, ponds, standby diesel generators as well as maintenance and warehousing facilities.
The means of access to the McArthur River property is by an all-weather road and by air. All supplies to the site and shipment of product are transported by truck year round.
An 80 km all weather gravel road runs between the mine site and the Key Lake milling operation.
Geology and Mineralization
The McArthur River deposit is located in the south-eastern portion of the Athabasca Basin, within the south-west part of the Churchill structural province of the Canadian Shield. The crystalline basement rocks underlying the deposit are members of the Aphebian Wollaston Domain, metasedimentary sequence. These rocks are overlain by flat lying sandstones and conglomerates of the Helikian Athabasca Group. These sediments are over 500 m thick in the deposit area.
High grade uranium mineralization has been delineated from surface drilling over a strike length of 1,700 m, occurring at depths ranging between 500 m to 640m below surface.
Underground drilling programs have covered approximately 750 m of the 1,700 m strike length delineated from surface. Ore widths are variable along strike but the most consistent, high grade mineralization occurs proximal to the main graphitic thrust fault around the "nose" of the upthrust basement rock. Less consistent and generally lower grade mineralization occurs down dip along this fault contact between basement rock and sandstone.
Four distinct mineralized zones, identified as Zones 1, 2, 3 and 4, have been defined to date. Two additional Zones, A and B, are on the northern portion of the deposit and are indicated through surface drill holes only.
In general, the high-grade mineralization, characterized by botryoidal uraninite masses and subhedral uraninite aggregates, constitutes the earliest phase of mineralization in the deposit. Pyrite, chalcopyrite, and galena were also deposited during this initial mineralizing event. Later stage, remobilized uraninite occurs as disseminations, veinlets, and fracture coatings within chlorite breccia zones and along the margins of silt beds in the Athabasca sandstone.
Three different mining methods will be used to mine the orebody - raiseboring, boxhole boring and remote box hole stoping. All three methods use remote-controlled equipment which allows the ore to be mined while minimizing employee exposure to radiation. Raiseboring is being used to mine the first part of the orebody.
After the ore is mined, it is crushed and processed underground. The ore is pumped to the surface as a slurry or mud where it is put in specially designed containers for transportation by truck.
Ore is trucked to the Key Lake operation for milling over an 80-kilometre all-weather road. Wastes from McArthur River ore, milled at Key Lake, are processed and managed at the Key Lake site.
Each major step in the milling process is contained in separate buildings, which are linked. Material is transported from plant to plant in pipelines as a solution or slurry.
The major steps in the process are grinding to break rocks into sand, leaching to dissolve uranium, separating uranium solution from waste solids, extracting solvent to produce a purified uranium solution, precipitating and calcining yellowcake (98% U3O8) to recover uranium as granular powder, crystallizating to recover ammonia reagent as ammonium sulphate fertilizer, and finally bulk neutralizing to treat waste from the solid-liquid separation and solvent extraction processes as well as water from the mine and tailings area.
Environment and Community
Cameco is committed to environmentally safe operations and is continually monitoring and sampling to ensure the environment is effectively protected. Areas no longer in use are landscaped and revegetated to return them as much as possible to their predevelopment state.
The McArthur River site will be decommissioned when all the ore reserves are exhausted. All buildings, equipment and chemicals will be removed and the area contoured and revegetated. Salvageable material will be removed from the underground areas and all surface openings will be sealed off. A monitoring program will be conducted to ensure the site remains in a non-polluting, stable state.