Preliminary Economic Assessment for the J Zone Deposit Waterbury Lake Property

This report presents a preliminary economic assessment for the Tthe Heldeth Túé deposit, proposing the transport of uranium-bearing solution to the existing McClean Lake mill for final processing.

Report context

The Preliminary Economic Assessment (PEA) for the J Zone Deposit Waterbury Lake Property in Saskatchewan, Canada, considers the processing of uranium-bearing solution (UBS) from the Tthe Heldeth Túé deposit at the McClean Lake mill. The mill is owned by Orano (77.5%) and Denison Mines Inc (22.5%). The study assumes a production rate of 2.1 million lbs U₃O₈ per year from Tthe Heldeth Túé, representing approximately 10 to 15% of the total McClean Lake mill feed. Toll milling agreement terms have not been assessed as part of this study.

Processing route

Tthe Heldeth Túé UBS Production and Transport

The proposed mining method uses an in-situ recovery (ISR) approach within a freeze wall enclosure, creating a contained "bathtub" for lixiviant. Well spacing has been reduced to 7 metres compared to 10 metres in the Wheeler River prefeasibility study. Hydraulic gradient within each well pattern will be created by pump and injection, with the ability to reverse flows to maximise recovery. Metallurgical testing has confirmed achievement of a UBS head grade of 7 g/L.

UBS from the wellfield will be sent to a production storage facility large enough for several days of UBS and lixiviant at both the Tthe Heldeth Túé and McClean mill sites. Storage can be either in lined ponds or tanks with a retention time of seven days. Open pond storage will allow solids settling and provide open air for radon dissipation. UBS will then be trucked from the wellfield settling pond to the McClean mill reservoir storage.

McClean Lake Mill Integration

The McClean Lake mill was designed as a typical acid leach uranium mill and is currently configured to be fed from either the ore stockpile and grinding circuit or from the ore slurry receiving facility. Tthe Heldeth Túé UBS held in McClean storage will be pumped into the mill at one of two points: the low pH UBS could be added directly to the leach circuit (the preferred option), which should reduce acid addition rates for other ore(s) being co-milled, or the UBS could be piped directly to the counter-current decantation (CCD) circuit prior to the clarification circuit.

The CCD circuit consists of six thickeners in series and separates uranium-containing solution from barren residual solids. Wash water is added to minimise aqueous uranium in the final solids, which are directed to a tailings neutralisation circuit. Following CCD, the solution is clarified and passed through sand filters before being sent to two parallel solvent extraction circuits.

Solvent Extraction and Final Product

In solvent extraction, the solution is contacted with an organic solvent, whereby uranium is selectively transferred to the organic along with any molybdenum. Uranium and molybdenum are then stripped out of the organic phase using anhydrous ammonia into an ammonium sulphate solution, resulting in a purified and concentrated uranium solution. The pregnant strip solution passes through molybdenum removal carbon columns before advancing to the yellowcake precipitation circuit, where anhydrous ammonia precipitates ammonium diuranate (ADU). The ADU is thickened, densified, washed through a centrifuge, and advanced to a calciner producing high-purity U₃O₈ product for off-site shipment.

Final drummed yellowcake will be a blend of the entire feed stream through McClean. The Tthe Heldeth Túé is described as a relatively clean ore feed source compared to Cigar Lake or Midwest deposits, both of which have contaminants of concern that could result in penalties at the refinery. The scope of this study has not considered what other ores will be co-milled with Tthe Heldeth Túé UBS, and therefore the final product make-up cannot be determined.

Ancillary Circuits and Tailings Management

Ancillary circuits supporting the uranium recovery process include an acid plant, ferric sulphate plant, oxygen plant, ammonium sulphate crystallisation plant, tailings management facility (TMF), water treatment plant, and reagent receipt and storage facilities. The flowrate will increase to the tailings neutralisation circuit during Tthe Heldeth Túé processing, but no change to the tailings neutralisation tanks is expected. Modifications are not expected to be required for the solvent extraction circuits, with maximum sustained capacities to date indicating continuous operation of the two existing circuits for a combined rate of 24 million lbs/yr U₃O₈ should be possible.

The existing tailings management facility provides approximately 2.4 million m³ of tailings storage. Expected precipitates by-products generated during Tthe Heldeth Túé operation are Fe/Ra precipitates and gypsum precipitate. The volume of Fe/Ra precipitates assumed for this PEA to estimate TMF storage fees is 10,000 m³. The McClean Lake mill equipment and infrastructure is currently able to deposit gypsum in the TMF, with no capital or operating costs expected to be required to process gypsum precipitates.

Key reported parameters

Technical qualifications

The processing cost for Tthe Heldeth Túé could be significantly higher or lower compared to the current cost of processing Cigar Lake ore, depending on the status of other ore sources at the time of Tthe Heldeth Túé production. Toll milling agreement terms have not been assessed as part of this study. The scope has not considered what other ores will be co-milled with Tthe Heldeth Túé UBS, and therefore the final product make-up cannot be determined. Contaminant levels in the yellowcake could reach penalty levels at the refinery, and the toll milling agreement would need to take this into consideration.

*Source: Preliminary Economic Assessment for the J Zone Deposit Waterbury Lake Property, Saskatchewan, Canada, Recovery Methods sections.*