Processing of Wheeler River deposits is proposed under a custom milling agreement using existing northern Saskatchewan uranium mills, with site-specific handling designed for coarse Gryphon mineralization and high-grade Phoenix slurry.
Report context
This technical report, dated 2018, presents recovery methods for the Wheeler River Property based on the "Preliminary Economic Assessment for the Wheeler River Uranium Project, Saskatchewan, Canada," SRK Consulting (Canada) Inc., March 31, 2016. That PEA was based on mineral resource estimates for the Gryphon deposit effective September 25, 2015 and the Phoenix deposit effective May 28, 2014. The report section has been reviewed and there are no material changes in the opinion of the qualified person.
Processing route
Custom milling concept
The PEA study assumes Wheeler River project mill feed will be trucked to an existing uranium mill in northern Saskatchewan under a custom milling agreement. Three such facilities exist in northern Saskatchewan.
Key Lake operation, owned by Wheeler River joint venture partners Cameco (83%) and AREVA (17%), is about 30 km from the Wheeler River site by road. At present, the Key Lake mill is fully utilized for processing of McArthur River ores and is assumed to be not available for processing Wheeler River deposits.
Rabbit Lake operation, owned by Wheeler River joint venture partner Cameco (100%), has capacity to process low grade feed such as Gryphon but is nearing the end of its existing tailings storage capacity. It is uncertain if new capacity will be made available for future potential feed sources.
McClean Lake site's JEB mill, owned by AREVA 70%, 22.5% Denison, and 7.5% OURD Canada, is the preferred facility. Upon completion of upgrades in progress during 2015/2016, the JEB mill will have available capacity in both processing and tailings storage.
Gryphon deposit mineralization handling at Wheeler River (proposed design)
The design for handling Gryphon deposit production is similar to current practice at Cameco's Eagle Point mine. Coarse muck will be skipped to surface for storage on a plant feed pad. For the few stopes that could be exceptionally high grade, underground blending would likely be performed prior to loading the skip. On surface, the plant feed will be stockpiled and blended as required, and loaded onto tractor-trailer trucks for transport to the McClean Lake mill. The trailer design will match those used currently for hauling "special waste" (low grade material) from McArthur River to Key Lake mill. The regulatory limit for this style of shipping is approximately 2.4% U₃O₈. With the average run-of-mine grade from Gryphon predicted to be 1.90%, a moderate amount of blending of low grade with high grade during truck loading would be suitable to stay within this constraint. At the McClean Lake mill, the existing mill feed pad used for the grinding circuit feed has sufficient stockpile capacity to allow blending for a consistent feed grade.
Phoenix deposit processing at Wheeler River (proposed design)
The Phoenix deposit mine production will use a water jet bore system (JBS) mining method. It is assumed that the process design for Phoenix will closely follow that installed at Cigar Lake.
The first stage of processing Phoenix takes place underground at the Wheeler River site. The mineralized slurry from the JBS will be pumped to the underground crushing and grinding facilities and the resulting finely ground, high density slurry is pumped to surface storage tanks and thickened. It will then be loaded into truck mounted slurry containers, similar to those currently being used for the McArthur River and Cigar Lake mines.
Underground slurry handling (proposed design)
The high grade slurry exiting the JBS cavity will flush into the local pump box. The low density slurry will then be pumped to a run-of-mine (ROM) storage sump. Partially dewatered material will be reclaimed from the sumps by an overhead crane mounted clamshell and fed through a water flush cone crusher and on to a ball mill operating in closed circuit with cyclones. Thickened cyclone overflow will be pumped to a high grade slurry storage pachuca tank located underground. From there, the slurry will be pumped up to storage pachucas located on the surface.
As much as reasonably possible, untreated water will be recirculated underground in the process. Overflow water from the ROM storage sump is collected in the recycle water tank for recirculation to the JBS pump box. Overflow water from the underground thickener may be recirculated and filtered for medium and high pressure water supplies to the JBS. Excess water will be pumped to Gryphon and then pumped to the surface water management ponds at Gryphon. Treated water will be utilized in the mining and processing circuits where required.
Surface slurry handling (proposed design)
Slurry from the surface storage pachucas will be pumped to the mix tank and continuously feed the loadout thickener. The thickener will remove as much water as possible from the slurry prior to container loadout.
The container filling system for Phoenix will replicate the existing systems at Cigar Lake and McArthur River. The thickener underflow will be pumped to the container feed tank. From there, the slurry will be pumped into a loop that will feed the filling stations, located directly above the truck-mounted containers. The slurry containers for transport of Phoenix will be similar to those currently used for the transport from McArthur River to the Key Lake mill and Cigar Lake to the McClean Lake mill.
Transportation (proposed design)
Delivery of the mill feed to the McClean Lake mill will require construction of a 45 km section of haul road between the McArthur River mine and the Cigar Lake mine. The cost for this road has been included in the capital costs estimates. Wheeler River project mill feed will consist of both lower grade coarse dry muck and high grade slurry. Life-of-mine quantities to be trucked are estimated at:
- 975 kt (dry) of low grade coarse dry muck from Gryphon deposit, handled conventionally in covered trucks
- 240 kt (dry) from Phoenix deposit in a high grade slurry (50% solids by weight) in special containers
JEB mill process description (testwork basis)
The JEB mill process chemistry is typical of acid leach uranium milling, with design details tailored to high grade Saskatchewan ores. A simplified overview of the mill flowsheet as currently configured is provided in the report.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Gryphon average run-of-mine grade | % U₃O₈ | 1.90 | Predicted design |
| Regulatory shipping limit (coarse dry) | % U₃O₈ | 2.4 | Current regulatory |
| Gryphon life-of-mine trucked material | kt (dry) | 975 | Estimated design |
| Phoenix life-of-mine trucked material | kt (dry) | 240 | Estimated design |
| Phoenix slurry solids content | % by weight | 50 | Design assumption |
| Haul road construction length | km | 45 | Proposed design |
| Phoenix process design basis | – | Cigar Lake | Assumed design |
| Gryphon handling design basis | – | Eagle Point mine | Proposed design |
| Gryphon shipping container design basis | – | McArthur River to Key Lake | Proposed design |
| Phoenix shipping container design basis | – | McArthur River and Cigar Lake | Proposed design |
| Truck scale configuration | – | Dual, sufficient for B-train haulage | Proposed design |
Project website: https://denisonmines.com/projects/wheeler-river-project/
Technical qualifications
The recovery methods section has been reproduced from the Preliminary Economic Assessment dated March 31, 2016, which was based on mineral resource estimates for the Gryphon deposit effective September 25, 2015 and the Phoenix deposit effective May 28, 2014. Denison anticipates incorporating the updated mineral resource estimate for the Gryphon deposit disclosed in this report in the PFS for the Property, which was commenced in the third quarter of 2016.
The Key Lake mill is assumed to be not available for processing Wheeler River deposits because it is fully utilized for processing of McArthur River ores. Rabbit Lake has uncertain tailings storage capacity for future potential feed sources.
The haul road power line route has not been studied. The water treatment plant design will be refined as estimates of mine water chemistry and flow are refined in later phases of project development. Final disposal options for sludge will be evaluated as the project progresses.
The report states that the Wheeler River project does not include a ramp from surface to underground.
Source: "Wheeler River Property , 2018 Technical Report," Section 17 Recovery Methods, Section 18 Project Infrastructure, Denison Mines Corp.
