Annex 6

Uranuim Mine and Mill Facilities

6.1 Background

Owned by Eldorado Gold Mines (a private company), the first radium mine in Canada began operating in 1933 at Port Radium in the Northwest Territories. Uranium ore concentrate was sent to Port Hope, Ontario where radium was extracted. At that time, uranium had little or no commercial value, and the focus was on the ore's radium-226 content. The Port Radium Mine produced ore for radium until 1940, and reopened in 1942 to supply the demand for uranium from defence programs in the United Kingdom and the United States.

In 1943, Canada, the United Kingdom and the United States instituted a ban on private exploration and development of mines to extract radioactive materials. The Government of Canada also nationalized Eldorado Gold Mines in 1943, and established the federal Crown Corporation Eldorado Mining and Refining, which had a monopoly on all uranium prospecting and development. Canada subsequently lifted the ban on private exploration in 1948.

In 1949, Eldorado Mining and Refining began the development of a uranium mine in the Beaverlodge area of northern Saskatchewan, and in 1953, milling the ore on site commenced. The Gunnar and Lorado uranium mines and mills began operating in the same area in 1955 and 1957, respectively. Several other small satellite mines also opened in the area in the 1950s, sending ore for processing to either Eldorado or the Lorado mills.

In Ontario, 15 uranium mines began production between 1955 and 1960 in the Elliot Lake and Bancroft areas. Ten of the production centres in the Elliot Lake area, and three in the Bancroft area, produced tailings. The last of these mines ceased operations and was decommissioned in the 1990s. (These former mining and milling sites are discussed in Annex 8.)

At present, all active uranium mines are located in Saskatchewan. Uranium mining is ongoing at Rabbit Lake, McClean Lake and McArthur River, with Cluff Lake currently carrying out decommissioning activities (see Annex 7.6). Cigar Lake is currently under construction, and the Midwest Project is currently at the environmental assessment stage, at which the CNSC personnel are compiling technical review comments. Uranium mills and operational tailings management facilities exist at McClean Lake and Rabbit Lake, as well as at Key Lake, where on site deposits were mined out in 1997. Tailings deposition continues at Key Lake, since all the McArthur River ore is being processed there. Non-operational tailings management areas are located at Rabbit Lake, Key Lake and Cluff Lake. (The locations of operating and inactive uranium mining and milling sites in Canada are shown in Figure B.3.)

6.2 Province of Saskatchewan

Saskatchewan is the only province in Canada with operating uranium mines. In the past, mine and mill operators have requested harmonization in areas such as inspections and reporting requirements, involving Saskatchewan Ministry of Environment, Saskatchewan Ministry of Advanced Education, Employment and Labour and the CNSC. An agreement currently exists between the CNSC and the Province of Saskatchewan to encourage greater administrative efficiency in regulating the uranium industry. The agreement lays the groundwork for the two groups to coordinate and harmonize their respective regulatory regimes.

6.3 Operational tailings and waste rock management strategy

6.3.1 Overview

About one-quarter of the world's primary uranium production comes from uranium deposits in the Athabasca Basin in northern Saskatchewan. These deposits include:

• the current production sites of Rabbit Lake, Key Lake, McClean Lake and McArthur River,
• the Cluff Lake site, where production was terminated at the end of 2002, and
• sites of planned future production at Cigar Lake and Midwest.

The newer sites include the highest grade uranium ore bodies in the world (at McArthur River and Cigar Lake), averaging about 20 percent uranium. Some of these ores in the Athabasca Basin have high nickel and arsenic content (up to five and one percent, respectively), which introduces additional considerations into the management of tailings and waste rock resulting from the mining and milling of these ores.

6.3.2 Tailings management strategy

Mills with tailings management facilities (TMFs) are located at Rabbit Lake, Key Lake and McClean Lake. There is no mill at the McArthur River mine, because the ore is transported to Key Lake for processing. Similarly, mills are not planned at either Cigar Lake or Midwest. Ores will be transported to McClean Lake for initial processing, with final processing activities for Cigar Lake uranium solution to be divided between McClean Lake and Rabbit Lake.

All three sites currently use the same basic approach: previously mined open pits have been converted to engineered disposal systems for tailings. Although there are certain differences in detail, two basic principles underlie the containment of the tailings and their potential radionuclide and heavy metal contaminants:

• Hydraulic containment during the operational phase: As a result of dewatering during mining, the water level in the pit at the start of tailings placement is well below the natural groundwater level in the area. This dewatering creates a cone of depression in the groundwater system, resulting in the natural flow being directed toward the pit from every direction. This hydraulic containment feature is maintained throughout the operational life of the tailings facility by maintaining the pit in a partially dewatered state. Since water has to be pumped continuously from the pit, current water treatment technology results in high-quality effluent suitable for discharge to surface water.
• Passive long-term containment, using the hydraulic conductivity contrast between the tailings and their surrounding geologic materials: Long-term environmental protection is achieved through control of the tailings' geochemical and geotechnical characteristics during tailings preparation and placement. This control creates future passive physical controls for groundwater movement in the system, which will exist after the decommissioning of operational facilities.

The tailings contain a significant fraction of fine-grained materials (chemical precipitates formed during the ore processing reactions). Tailings consolidation occurs during operation, and will be completed during the initial decommissioning steps. The outcome is that the consolidated tailings have a very low hydraulic conductivity. When surrounded by a material with a much higher hydraulic conductivity, the natural groundwater path is around the impermeable plug of tailings.

Potential contaminant transport from the tailings is controlled by diffusion from the outer surface of the tailing mass; this is a slow process, with minimal advective contaminant flux, and a consequently high level of groundwater protection. Potential contaminant transport is further minimized by the geochemical properties of the tailings. Reagents are added during tailings preparation to precipitate dissolved elements such as radium, nickel and arsenic to stable insoluble forms, which enables long-term concentrations in the tailings' pore water to remain low.

A constructed permeable zone around the tailings may be installed (in the form of sand and gravel) while the tailings are placed, as is done at Rabbit Lake. Alternatively, the permeable zone may exist naturally, as is the case at McClean Lake and Key Lake. This natural permeable zone allows for subaqueous placement of tailings, which has advantages in terms of radiation protection and prevention of ice formation with the tailing mass. At McClean Lake, the sandstone formation surrounding the tailings has a hydraulic conductivity contrast of more than a factor of 100 relative to the tailings.

Extensive characterizations of the natural geologic formations and groundwater system, as well as the tailings' properties, are used to acquire reliable data for the computer models used to predict long-term environmental performance based on the fundamental principles governing the system. This performance will be confirmed by post-decommissioning monitoring, which will be continued until stable conditions are achieved and for as long as desired thereafter.

Section 6.4 of this Annex provides site-specific details for the Athabasca Basin tailings facilities. The development of these facilities began nearly 30 years ago, and their favourable operational experience and design evolutions - based on that experience - provide confidence in their performance, both now and in the future.

6.3.3vWaste rock management strategy

In addition to tailings from the milling process, uranium production results in large volumes of waste rock being removed before miners can access and mine the ore. The segregation of these materials according to their future management requirements is now a core management strategy. Material excavated from open pits is classified into three main categories: clean waste (both overburden and waste rock), special waste (containing sub-economic mineralization) and ore.

Clean waste

This term refers to waste materials that are benign with respect to future environmental impact, and that can be disposed in surface stockpiles or used on-site for construction purposes. These different types of materials are:

• Surficial soils with high organic content: When practical depths are present, a thin layer of surface soil is stripped, and separately stockpiled for replacement as the future surface soil layer during site reclamation activities.
• Overburden soils: A few metres of glacial till (typically around 10 metres) are present before the underlying sandstone rock is encountered. This material is either stockpiled separately for future use as fill during reclamation or used as the base for clean waste rock stockpiles.
• Waste rock: The Athabasca Basin is a sandstone basin that overlies the Precambrian Shield basement rock. The sandstone depth is shallow around the Basin perimeter, and increases to as much as 1,200 metres toward the centre of the Basin. Depths up to about 200 metres are practical for open pit mining, so that the sites at and near the Basin perimeter primarily feature this mining method.
• Large volumes (depending on the depth) of unmineralized sandstone are mined to reach the ore body. This material is stockpiled on the surface near the pit, and the stockpiles, minus whatever amount has been used for construction purposes, is subsequently reclaimed and vegetated. As mining approaches the ore body, a zone of altered (partially mineralized) rock is present. Both this halo of altered rock, and the basement rock below it, may contain small amounts of uneconomic uranium, and/or various metals such as nickel or arsenic.
• In some instances, because it contains sulphide, there is the potential for acidic leachate when the rock is exposed to moisture and oxygen from the atmosphere. This phenomenon of acid rock drainage (ARD) is common to many types of mining. Sophisticated methods are now available to segregate those amounts of waste rock, which represent a potential environmental risk - due to either ARD and/or dissolved contaminants in leachate - if left on the surface for the long term.
• This material, referred to as special waste, is managed differently from the environmentally benign waste rock. The segregation methods include borehole logging, collection and analyses of borehole samples prior to mining, and analyses of samples during mining. In addition to a retrospective laboratory analysis, real time analyses are made with an ore radiometric scanner to segregate each truckload - according to uranium content - as ore, special waste or waste rock, and direct it to the appropriate stockpile.
• Since uranium ore deposits are in secular equilibrium with its progeny, good correlations can be made between radioactivity of the ore and its uranium content. The latest technical development is the application of a handheld, portable scanner that uses x-ray fluorescence to perform field characterization for arsenic. This method has recently been tested at McClean Lake, and became operational for the mining of the most recent open pit there.
• Volumes of waste rock are much smaller for underground mining, but the same general considerations apply. Clean waste materials are stockpiled and used for construction or reclamation purposes. Any surplus amounts can be stockpiled, and the stockpiles reclaimed and vegetated. Special waste is either used as aggregate and underground backfill, or is returned underground to other mined areas or transferred to sites with mills or mined out open pits.

Special waste

As noted above, waste rock near ore bodies is potentially problematic, because it has some halo mineralization around the ore deposit, and is therefore potentially acid-generating in some instances and/or a source of contaminated leachates when exposed to an atmosphere containing oxygen. The disposal of this special waste in mined out pits and flooding, to cut off the oxygen supply from the atmosphere and stop oxidation reactions, is now a widely recognized solution. The special waste is segregated as it is mined, and temporarily stored on the surface on lined pads, with drainage collection systems for collection and treatment of runoff water. Following the completion of mining, the special waste is backhauled into the mined-out pit (see Figure 6.4.3.2). At a large pit with two or more zones, the direct transfer of special waste from the mining zone to a mined out zone is practical. Typically, any waste material with uranium content greater than either 300ppm U₃O₈ or 0.025 percent (250ppm) uranium is classed as special waste.

Similar to tailings facilities, extensive characterizations of natural geologic formations, groundwater system and waste rock properties are used to acquire reliable data for the computer models used to predict long-term performance. This performance is confirmed by post-decommissioning monitoring, which will be continued until stable conditions are achieved, and for as long as desired thereafter.

Ore

Typically, all material grading greater than 0.085 percent U has been classified as ore, and stockpiled to be fed to the mill. The cut-off grade for the mill may vary depending on market conditions for uranium.

6.3.4 Waste water treatment and effluent discharge

All mine and mill facilities provide water treatment systems to manage contaminated water collected from their tailings disposal facilities, as well as water inflows collected during open pit or underground mining, and problematic seepages from waste rock piles. The treatment processes vary from flow through to batch discharge systems, and largely rely on conventional physical settling and chemical precipitation methods found in the general metal mining industry. Typically, these sites have a single point of final discharge into the receiving environment; however, Key Lake operation has two discharge points. Uranium mines and mills also treat for radionuclides. Specifically, focus is placed on treatment for radium 226, using barium chloride precipitation. In the case of Rabbit Lake, additional treatment has been incorporated to reduce uranium levels in effluent discharge. The quality of effluent is controlled by regulatory approved codes of practice, as well as by effluent quality regulation.

In Northern Saskatchewan, effluent quality regulation ensures that Saskatchewan Water Quality Objectives (SSWQQ) are maintained at the final point of discharge for the various facilities. If the effluent is found acceptable (i.e., in compliance with regulatory limits), it is released to the environment. Otherwise, the effluent is recycled to the water treatment plants or mill for reprocessing. In 2007, the total volume of treated wastewater that met SSWQO requirements and was subsequently discharged to the receiving environment was 10,304,840 cubic metres from five active uranium mining and or milling sites in northern Saskatchewan.

To reduce the impact of effluent discharges to the receiving environment, the uranium mining and milling facilities have developed ecological risk models to evaluate the impacts of treated effluent discharges. The prime concerns resulting from this work are chronic not acute, and relate to control of metals not radionuclides. The control of nickel and arsenic loading has been a core focus; however, more recently, attention has turned to molybdenum and selenium loadings. This broader spectrum of contaminants of concern has led to efforts to develop and install the next generation of treatment technology based on the use of membrane technology.

As such, a large reverse osmosis plant has been installed at the Key Lake facility. Additional application of this technology is expected at other northern Saskatchewan facilities, particularly for mining as opposed to milling effluent components, in which the low ionic content of the effluent makes membrane technology less difficult.

6.4 Waste management facilities

6.4.1 Key Lake

6.4.1.1 Tailings management

The purpose of tailings management at Key Lake is to isolate and store the waste residue from the milling process so that the public and the environment are protected from any future impact. Conceptually, this effort involves containing the solids and treating the water to quality standards acceptable for release to the environment. The waste metal precipitates removed during water treatment are disposed of as solids in the tailings management facility (TMF).

From 1983 to 1996, waste from the Key Lake mill was deposited in an aboveground TMF (AGTMF) that covered an area 600 metres by 600 metres (36 hectares) and 15 metres deep. The TMF was constructed five metres above the groundwater table by using engineered dikes for perimeter containment and a modified bentonite liner to seal the bottom and isolate the tailings from the surrounding soil infrastructure.

Since 1996, the mined-out Deilmann open pit has been used as the TMF. Commissioned in January 1996, it is used to store tailings produced by milling a blend of McArthur River ore and special waste from McArthur River and Key Lake. The TMF has a bottom drainage layer constructed on top of the basement rock at the bottom of the mined-out pit. Tailings are deposited on top of this drainage layer, and water is continually pumped out to promote solids consolidation of overlying tailings.

Tailings were initially deposited into the pit by sub-aerial deposition, with the water being extracted from the tailings mass through the bottom drain layer and the raise well pumping system. The facility was later changed to sub-aqueous deposition by allowing the pit to partially flood.

Through the use of a tremie pipe system, tailings are deposited under the water cover, providing benefits in terms of placement and attenuation of radon emissions. In this system, tailings are placed in the mined-out pit by using what is termed “a natural surround” containment strategy. Tailings and residual water on the surface are removed during tailings placement, both by the drainage blanket and by surrounding groundwater wells. The residual water extracted from the tailings mass is collected for treatment. The consolidated tailings form a low-permeability mass relative to the higher permeability area surrounding the tailings.

After decommissioning, groundwater will follow the path of least resistance (i.e., around the tailings rather than through them), which minimizes environmental impacts. At the end of 2007, the Deilmann TMF contained 3,090,000 tonnes (dry weight) of tailings.

Figure 6.1 - Deilmann Tailings Management Facility at Key Lake

6.4.1.2 Waste rock management

Waste rock management facilities include two special waste storage facilities and three waste rock storage areas. The waste rock disposal areas comprise primarily benign rock and, therefore, do not have containment or seepage collection systems. The special waste contains low (uneconomic) levels of uranium and other potential contaminants, so this material is contained in engineered facilities that consist of underliners and seepage collection systems. Material from one of the special waste areas is being reclaimed for blending with high-grade McArthur River ore for the Key Lake mill feed. All other waste rock and special waste areas are inactive.

To reduce the decommissioning liability associated with the Deilmann North waste rock pile, approximately 1,300,000 cubic metres of nickel-rich waste rock were excavated and disposed of in the Gaertner pit.

6.4.1.3 Contaminated industrial wastes

Contaminated industrial wastes are either recycled or landfilled in the aboveground tailings management facility (AGTMF). Leachates from these materials are collected by the AGTMF's seepage collection system, and returned to the mill for process make-up water or treated and released to the environment. Typically, 5,000 cubic metres of industrial wastes are disposed of annually in this facility.

6.4.2 Rabbit Lake

6.4.2.1 Tailings management

The Rabbit Lake Above-Ground Tailings management Facility (RLAGTMF) is about 53 hectares in area, and contains approximately 6.5 million tonnes of tailings, which were deposited between 1975 and 1985. These tailings were all derived from the processing of the original Rabbit Lake ore deposit. The tailings within the AGTMF are confined by earth-filled dams at the north and south ends, and natural bedrock ridges along the east and west sides. The AGTMF is currently undergoing long-term stabilization and progressive reclamation.

The original Rabbit Lake open-pit mine was converted to a tailings management facility in 1986 by using pervious surround technology. Since its commissioning, the Rabbit Lake in-pit tailings management facility (RLITMF) has been used as a tailings repository for ore from the Rabbit Lake, B-zone, D-zone, A-zone and Eagle Point mines. At the end of 2007, the RLITMF contained 6,750,000 tonnes (dry weight) of tailings.

The pervious surround, consisting of sand and crushed rock, is placed on the pit floor and walls in advance of the tailings deposition. The pervious material allows drainage of the excess water contained in the tailings to an internal seepage collection system, and also allows the water contained in the surrounding host rock to be collected, which maintains a hydraulic gradient toward the facility during operations. The collected water is treated prior to its release into the environment. Upon final decommissioning and return to normal hydro-geologic conditions, groundwater will flow preferentially through the pervious surround rather than the low permeability tailings. Discharge of contaminants will be limited to diffusion across the tailings/pervious surround interface.

Figure 6.2 (a) - Rabbit Lake In-pit Tailings Management Facility

Figure 6.2 (b) - Rabbit Lake In-pit Tailings Management Facility

6.4.2.2 Waste rock management

The Rabbit Lake site contains a number of clean and mineralized stockpiles of waste rock, produced over the course of mining various local deposits since 1974. Some of the waste rock has been used for construction material. For example, waste rock was used to construct the road and pervious surround for the RLITMF. Eagle Point special waste is stockpiled on a lined storage pad until it is returned underground as backfill. Some waste rock piles were used as backfill and cover material in their respective pits. One rock pile, consisting primarily of Rabbit Lake sediments, has been contoured and vegetated.

Current projections are that no waste rock will remain on surface at Eagle Point after the mining and backfilling of mined-out stopes is complete. The D-zone waste rock pile consists of 0.2 million cubic metres of primarily lake-bottom sediments and organics. This material may eventually be used as cover material for the B-zone waste rock pile. The A-zone waste-rock pile (28,307 cubic metres of clean waste) has been flattened and contoured. The B-zone waste pile contains an estimated 5.6 cubic metres of waste material stored on a pile covering an area of 25 hectares. Contaminated runoff and seepage from this pile is collected and treated prior to release into the environment. All the special waste from the A-zone (69,749 cubic metres), B-zone (100,000 cubic metres) and D-zone (131,000 cubic metres) open-pit mines was returned to the pits and covered with layers of waste rock and/or clean till before the mined-out pits were allowed to flood.

There are approximately 6.7 million cubic metres of predominantly sandstone, with some basement rock and overburden tills, stored on the West #5 waste rock pile adjacent to the RLITMF. Mineralized waste is stored on four piles (1.8 million cubic metres) adjacent to the Rabbit Lake Mill. Runoff and seepage from these areas are collected in the RLITMF.

6.4.2.3 Contaminated industrial wastes

Radioactive and other contaminated materials from the Eagle Point Mine and Rabbit Lake Mill are disposed of in the contaminated landfill site located on the west side of the RLAGTMF. It is estimated that 6,178 cubic metres of uncompacted waste were placed at this site in 2007.

6.4.3 McClean Lake

6.4.3.1 Tailings management

McClean Lake was the first new uranium mill built in North America in 15 years. The mill and TMF are state-of-the-art efforts in worker and environmental protection for processing high-grade uranium ore. Open-pit mining of the initial ore body (JEB) began in 1995. After the ore was removed and stockpiled, the pit was developed as a TMF. The design of the TMF has been optimized for performance, both during operation and in the long-term, by employing key features such as:

• Production of thickened tailings within the mill process (addition of lime, barium chloride and ferric sulphate) to remove potential environmental contaminants from solution and yield geotechnically and geochemically stable tailings.
• Transport of the tailings from the mill to the TMF through a continuously monitored pipe-in-pipe containment system.
• Final sub-aqueous tailings placement within the mined-out JEB pit for long-term, secure containment in a belowground facility.
• Use of natural surround as the optimum approach for long-term ground water diversion around the consolidated tailings plug.
• Subaqueous tremie placement of the thickened tailings below a water cover in the pit from a floating barge. This method minimizes segregation of fine and coarse material, prevents the freezing of the tailings and enhances radiation protection due to the attenuation of radon emissions by the water cover.
• Use of dewatering wells around the entire pit perimeter to minimize clean groundwater inflow while maintaining hydraulic containment during operations - that is, the water levels are maintained such that groundwater flow is toward the pit.
• A bottom filter drain feeding a dewatering drift and raise wells to allow collection and treatment of discharged pore water during tailings consolidation.
• Recycling of pit water by a floating barge and a pipe-in-pipe handling system.
• Complete backfilling of the pit, upon decommissioning, with clean waste rock and a till cap.

At the end of 2007, 1,246,800 tonnes (dry weight) of tailings were contained in the JEB TMF.

Figure 6.3 (a) - JEB Tailings Management Facility at McClean Lake

Figure 6.3 (b) - JEB Tailings Management Facility at McClean Lake

6.4.3.2 Waste rock management

Open-pit mining at McClean Lake has progressed from one pit to the next (JEB, Sue C, Sue A, Sue E), with Sue B now in progress (Figure 6.4 (a)).

Figure 6.4 (a) - Sue Mining Area at McClean Lake

The majority of the wastes removed from the JEB and Sue C open pits were overburden material or sandstone. The overburden and clean waste rock stockpiles are located near the pits. The pad for the waste rock stockpile has been constructed using overburden. Special waste, stockpiled while mining the Sue C and JEB pits, has been back-hauled into the Sue C pit (Figure 6.4(b)).

Figure 6.4 (b) - Special Waste Backhaul to Sue C Pit at McClean Lake

All wastes (exclusive of the overburden) from the Sue A pit were also deposited into the mined-out Sue C pit. This approach was conservative, due to the uncertainty regarding segregating special waste based on its arsenic content. An XRF method, which was successfully tested during Sue A mining, provides the capability to segregate special waste based on acid generating potential (using a simple laboratory test), radiological content (using the ore scanner) and a key non-radiological contaminant (arsenic, using an XRF scanner). Special waste from Sue E was also placed into the mined-out Sue C pit, while clean waste was placed into a separate Sue E waste rock stockpile. The total waste rock inventory at McClean Lake at the end of 2007 was 51.7 million tonnes of clean material (primarily waste rock) and 5.9 million tonnes of mineralized waste rock (special waste).

6.4.3.3 Contaminated industrial wastes

Chemically or radiologically contaminated waste materials originate from the mining, milling and water treatment areas of McClean Lake operation. All the contaminated material is collected in yellow dumpsters, distributed around the site and deposited in the landfill for chemically and radiologically materials at the perimeter of the TMF. This landfill is within the hydraulic containment area of the JEB TMF. During final site decommissioning, these materials will be excavated and deposited into the JEB TMF. Approximately 1,040 cubic metres of waste has been landfilled in recent years.

6.4.4 Cigar Lake

6.4.4.1 Tailings management

Cigar Lake does not have a mill and does not produce tailings.

6.4.4.2 Waste rock management

There are five waste rock storage pads in operation at Cigar Lake. The current inventories result from test mining activities conducted at the site. Waste rock volumes are expected to increase substantially over the next few years as the construction of the operating mine is completed.

The first stockpile (stockpile A) has an unlined pad without seepage collection used for the storage of clean or benign waste rock. When possible, this rock is used as fill or construction material on site. The current stockpile contains approximately 40,863 cubic metres of clean waste rock.

A second stockpile (stockpile B) is used to store potentially acid reactive waste rock. Containment is provided by an impermeable liner and all drainage and decant waters are collected for treatment in the mine water treatment plant. The current stockpile contains approximately 2,080 cubic metres of waste rock.

The third stockpile (stockpile C) is used to store potentially acid reactive waste rock from underground. Containment is provided by an impermeable liner and all drainage and decant waters are collected for treatment in the mine water treatment plant. The current inventory for this waste rock stockpile is approximately 101,610 cubic metres.

The fourth stockpile (stockpile A-1) is used for storage of clean waste rock from shaft excavation. At the end of 2007, this stockpile contained approximately 20,208 cubic metres of clean waste rock. The overburden pile is the last waste rock stockpile. The current inventory for this waste rock stockpile is approximately 77,119 cubic metres. While some potentially acid reactive waste rock may be used as backfill in the mine, the majority of this material is eventually expected to be transported to the McClean Lake mine site for disposal in a mined-out pit.

6.4.4.3 Contaminated industrial wastes

This waste rock storage pile has already being addressed in stockpile B.

6.4.5 McArthur River

6.4.5.1 Tailings management

McArthur River does not have a mill and does not produce tailings.

6.4.5.2 Waste rock management

The McArthur River operation generates waste rock from production mining, development mining and exploration drilling. The waste rock is classified as either clean waste rock, potentially acid generating (PAG) waste rock or mineralized waste rock. The potentially acid generating and mineralized waste rock are temporarily stored on engineered lined containment storage pads. Leachate from these pads is contained and pumped to effluent treatment facilities. The segregated clean waste rock is disposed of on a pile that does not include the leachate containment and control systems.

The mineralized waste rock is shipped to the Key Lake operation and used as blend material for the ore feed to the Key Lake mill. The potentially acid-generating waste is crushed and screened, and the coarse material is used as aggregate for underground concrete backfilling operations. The clean waste is used for general road maintenance, both on site and on the haul road between McArthur River and Key Lake.

6.4.5.3 Contaminated industrial wastes

A transfer area, located adjacent to the mine headframe, is used to sort and temporarily store contaminated material. The contaminated material is shipped to the Key Lake operation, where it is disposed of in the AGTMF.

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