Both the Phoenix and Gryphon deposits are classified as Athabasca Basin unconformity-associated uranium deposits. Phoenix straddles the unconformity contact between the Athabasca Sandstone and underlying basement, while Gryphon is entirely hosted in the basement rocks.

Uranium mineralization at the Phoenix deposit occurs at the unconformity between Athabasca sandstones and basement rocks, with the most intense mineralization adjacent to the WS fault. A minor amount is basement fracture hosted mineralization extending below the north part of Zone A.

Mineralization and alteration have been traced over a strike length of approximately one kilometre. Since discovery hole WR-249 was drilled in 2008, 253 drill holes have reached the target depth, delineating two distinct zones (A and B) of high-grade uranium mineralization.

Mineralization is in the form of the oxide uraninite/pitchblende (UO2).

Average trace metal concentrations for Phoenix assay samples greater than 0.2% U3O8 are as follows: 576 ppm Ni, 194 ppm Co, 319 ppm As, 2,092 ppm Zn, 18 ppm Ag, 7,176 ppm Cu, and 9,143 ppm Pb. Average concentrations of Ni, Co and As are at the low end of the range found in other uranium deposits in the Athabasca basin.

Mineralization at Gryphon occurs 720 m below surface and is centred approximately 220 m below the sub-Athabasca unconformity. It is within 80 m of the unconformity at its highest point and 370 m below the unconformity at its deepest point. The deposit consists of a set of parallel, stacked, elongate lenses that are broadly conformable with the basement geology and associated with a significant fault zone (G Fault) that separates a thin unit of quartzite (quartz-pegmatite) from an overlying graphitic pelite (upper graphite). The lenses dip moderately to the southeast and plunge moderately to the northeast. The deposit is approximately 450 m long in the plunge direction and 80 m wide across the plunge. Thickness is variable and is a function of the number of stacked lenses present, generally varying between 2 m and 20 m. To date, the majority of mineralization is hosted within two lenses associated with the upper and lower graphite units. Two predominant types of mineralization have been noted:
- Irregular Fracture Fill - Weak, dark black, low grade mineralization occurring as blebs and foliation-parallel fracture fill associated with breccias and centimetre-scale dravite veinlets in the Upper Graphite.
- Semi Massive - Black, high grade mineralization associated with hematite and secondary uranium minerals occurring as lenses and pods parallel to foliation. "Worm rock" textures are also observed.

Mineralization at Gryphon is dominated by uraninite/pitchblende, with very minor coffinite and trace carnotite, uranophane, and brannerite. Gangue mineralogy is dominated by alteration clays (illite, kaolinite, chlorite), dravite and hematite with minor relict quartz, biotite, graphite, zircon, and ilmenite. Only trace concentrations of pyrs are noted comprising galena, chalcopyrite, and pyrite.

Average trace metal concentrations for Gryphon assay samples greater than 0.2% U3O8 are as follows: 107 ppm Ni, 62 ppm Co, 30 ppm As, 18 ppm Zn, 14 ppm Ag, 301 ppm Cu, and 3,525 ppm Pb. These concentrations are lower than those recorded for the Phoenix deposit.

Denison plans to mine the Phoenix deposit using the ISR extraction method with a low pH lixiviant. Uranium ISR uses the native groundwater in the orebody, which is fortified with a low pH solution and in most cases an oxidant. Pumping the solution through the ore zone and allowing the solution to contact the ore requires sufficient permeability of the ground.

Physically ISR mining is conducted through drill holes from surface to the orebody, known as wells. Wellfields are the groups of wells, installed and completed in the mineralized zones that are designed to effectively target delineated mineralization and reach the desired production goals. The mineralized zones are the geological sandstone units where the leaching solutions are injected and recovered via wells in an ISR wellfield. At present, the drilling of individual wells will be carried out utilizing either air rotary or mud rotary methods. The wellfield at Phoenix has been designed using a standard hexagonal pattern with 10m spacing between wells.

The uranium ISR process will involve the dissolution of the water-soluble uranium compound from the mineralized host sandstones at low pH ranges using acidic solutions. The acidic solution will dissolve and mobilize the uranium, allowing the dissolved uranium to be pumped to the surface within the mining solution.

Containment of the solution is a requirement in ISR operations to ensure recovery of the uranium and to minimize regional groundwater infiltration into the ore zone and associated dilution of the
mining solution. In typical ISR operations, this is normally achieved through natural clay or other impermeable geological layers. At Phoenix, the basement rock below the orebody achieves this purpose but the sandstone formation which hosts and surrounds the ore zone is not impermeable and is hydraulically connected to the regional groundwater system throughout the Athabasca basin. As a result, in order to maintain containment, the entire orebody will be isolated by use of an artificial freeze wall that will cover all sides and above the orebody to create an impermeable dome to surround the deposit. This dome will be keyed into the impermeable basement rocks on all sides. The freeze wall will be established by drilling a series of cased holes from surface and across the orebody, and keyed into the basement rock. Circulation of a low temperature brine solution in the holes will remove heat from the ground, freezing the natural groundwater, and establishing an impermeable frozen wall encapsulating the deposit.

After the low pH solution has passed through the deposit, dissolving uranium, it will be pumped to a surface processing plant for uranium recovery.

The PFS mine plan allows for Gryphon to be accessed via two shafts from surface, the production shaft (full-service, 5 m diameter, 550 m deep) and the ventilation shaft (4.5 m diameter, 500 m deep), to support underground development and production. Heated fresh air will be delivered via the production shaft, with return air exhausted up the ventilation shaft. An emergency hoist/conveyance will be installed in the ventilation shaft.

Access from the production shaft to the mine workings will be via a single ramp (4.5 m wide x 5.0 m high at a typical gradient of -15 percent) to be developed from the 500 Level (Shaft Station) to the 815 Level. The main haulage ramp will be located on the hangingwall side of the deposit and will be used to provide access for personnel and materials from the shaft to the mine workings, for movement of mining equipment from level to level within the mine, and for ore/waste haulage to the rockbreaker station near the shaft.

Ore will be truck hauled to a rockbreaker/grizzly station on the 500 Level near the production shaft and hoisted to surface. The underground mine is expected to produce approximately 605 tonnes per day of ore and an average of 330 tonnes per day of waste rock during the steady state operating period.

Underground production will be from the longhole stoping mining method, primarily longitudinal retreat. Longitudinal retreat involves accessing the resource from a central access point on each sublevel, developing ore sills (overcut and undercut drifts) along strike to the extents of each zone, and mining stopes from the extents back to the initial access. Mined stopes will be backfilled using a combination of rockfill, cemented rockfill, and hydraulic fill. The hydraulic fill will be directed to the empty stopes by means of boreholes and pipelines. Waste rock and cemented rockfill will be directed to the stopes via underground haulage trucks and LHDs.

Phoenix Deposit Processing at Wheeler River.
The uranium recovery or precipitation plant will house most of the process equipment in a 46,500 square foot pre-fabricated metal building. The plant will have four major circuits: impurities removal, yellowcake precipitation, dewatering/drying and packaging.

Uranium bearing solution containing dissolved uranium from the wellfields will be pumped to the precipitation plant for beneficiation as described below:
- pH adjustment – The pH of the incoming solution to the plant is constantly monitored and maintained at a specific value to ensure the uranium is fully dissolved through the addition
of acid.
- Impurities Removal – the uranium bearing solution is pumped to a series of agitated tanks
where sodium hydroxide and barium chloride are progressively injected, along with a flocculant. The resulting increase in pH and the addition of barium chloride and flocculant promote the formation of metal hydroxides and radium precipitates. The solution flows by gravity to a decanter/settler, allowing the precipitates to sink to the bottom and the clear solution to rise to the top. Metal hydroxides and radium complex precipitates will be directed to a filter press, where 90% of the moisture containing uranium rich solution is recovered. The filtered cake with a 10% moisture content is disposed of in tote bags and stored on the special waste pile on surface in a lined area. The solution overflowing from the decanter/settler is filtered in a series of sand filters, where entrained precipitate is pumped back to the decanter/settler unit. The clear uranium bearing solution is forwarded to the next processing step.
- Yellowcake precipitation – Uranium oxide (U3O8), referred in the industry as “yellowcake”, is recovered from the solution following the iron/radium removal process. Hydrogen peroxide is injected in a 3-stage series of agitated tanks to precipitate uranium. Additional pH adjustment is provided, if required, by further addition of sodium hydroxide. A thickener provides time for growth of the uranium oxide crystals. The precipitate accumulates at the bottom of the thickener and the barren leach solution (BLS), depleted of uranium, rises to the top. The BLS is cleaned through a series of sand filters prior to refortification. The precipitated yellowcake product accumulated at the bottom of the thickener is withdrawn at the underflow of the thickener and pumped through a filter press, where excess liquid is removed and circulated back to the thickener.
- Yellowcake dewatering/drying and packaging – Entrained solid particles exiting the filter press are collected and packaged. Fresh water is sprayed on the surface of the cake displaying trapped BLS within the cake, reducing the entrainment of contaminants to the dryer. The remaining moisture is evaporated in a low-temperature dryer. The product drying activity is a batch process, where a specific volume of dewatered yellowcake product is accumulated in a vessel surrounded with a jacket of circulating oil from an oil bath heated at high temperature. The drying circuit is design with 6 dryers capable of producing 1 M lbs/a. Once the moisture is removed from the yellowcake product, the material is transferred into 400 L steel drums by gravity, where it is allowed to cool prior to the installation of covers.
- BLS refortification – The ISR recovery process circulates lixiviant through the mineralized zone and it is expected that, over time, some contaminants may accumulate in the recycled
solution. As described previously, it will be possible for a certain volume of BLS solution to be removed and replaced by fresh solution. Otherwise a groundwater well will provide fresh water to the process to offset any process consumption. Sulfuric acid and hydrogen peroxide are then added to the volume of make-up water. The solution is then mixed with the recycled BLS and re-injected in the wellfield.
- Reagents storage and preparation – Sulfuric acid, hydrogen peroxide, sodium hydroxide, and barium chloride are the main chemicals used in the uranium recovery plant. Acid and caustic serve to adjust pH, an oxidant enables the dissolution of uranium in the ground, and barium chloride co- precipitates radium generated during the uranium leaching process. Other chemicals, such as flocculants, are needed to settle precipitates at different stages of the process.

Gryphon Deposit Processing at McClean Lake Mill.
Mineral processing for Gryphon production is based on processing at the McClean Lake mill.

The mill is currently configured to be fed from either the ore stockpile and grinding circuit or from the ore slurry receiving facility, which is currently used to receive high-grade material from Cigar Lake.

The grinding circuit, consisting of a SAG and ball mill, is currently not in service, and is available to the Gryphon feed.

Currently, the leach circuit operates with only the seven secondary leach vessels in service, which advance to the CCD circuit. The primary leach tanks and the primary thickener are not currently in service. In leaching, sulphuric acid is used to leach the uranium from the ore into solution. Some uranium is not directly leachable and must first be oxidized. Hydrogen peroxide is added to oxidize the uranium to a soluble state and ferric sulphate is added to assist in the oxidation kinetics.

The CCD circuit consists of six thickeners in series and is utilized to separate the uranium containing solution from the barren residual solids. Wash water is added to minimize the aqueous uranium in the final solids from the circuit, which are directed to a tailings neutralization circuit.

The final solids from the CCD circuit, along with waste streams from the SX circuit and other sources throughout the mill, are directed to the tailings neutralization circuit. Ferric sulphate, barium chloride, and lime are added to stabilize any arsenic, molybdenum, radium, and other minor elements that have been solubilized in the process. The final tailings are thickened and pumped to the tailings management facility.

In order to improve SX performance, the uranium bearing solution from CCD is clarified and passed
though sand filters to remove any suspended solids from the solution. It is then sent to the two parallel solvent extraction circuits.

In SX, the solution is contacted with an organic solvent, whereby the uranium is selectively transferred to the organic along with any molybdenum. The uranium and molybdenum are then
stripped out of the organic phase using anhydrous ammonia into an ammonium sulphate solution, resulting in a purified (with the exception of molybdenum) and concentrated uranium solution.

The pregnant strip solution is passed though molybdenum removal carbon columns, used to remove any molybdenum, which is an impurity in the final uranium product. The further purified solution is then advanced to the yellowcake precipitation circuit, where anhydrous ammonia is used to precipitate ammonium di-urinate (ADU). The ADU is then thickened, densified, and washed though a centrifuge, where it is then advanced to a calciner. The calciner produces a high purity U3O8 product that is then packaged for off-site shipment and processing.