Denison Announces Successful Completion of Inaugural ISR Field Test Program at Tthe Heldeth Túé (THT)

Press Release

TORONTO, Nov. 6, 2023 – Denison Mines Corp. (“Denison” or the “Company”) (TSX: DML) (NYSE American: DNN) is pleased to announce the successful completion of the inaugural In-Situ Recovery (“ISR”) field test program within the Tthe Heldeth Túé uranium deposit (“THT”) at the Company’s 67.41% owned Waterbury Lake Uranium Project (“Waterbury”), which is located in northern Saskatchewan, Canada and is situated in close proximity to key regional infrastructure, including roads, the provincial power grid, and Denison’s 22.5%-owned McClean Lake mill (see Figure 1). View PDF version

The THT ISR field test involved the installation of an 8-well ISR test pattern (“Test Pattern”) designed to collect an extensive database of hydrogeological data, and the program successfully achieved each of its planned objectives, including:

• Confirmed Hydraulic Conductivity:  Pump and injection tests were successfully completed within the Test Pattern, validating hydraulic connectivity in 100% of the test wells within the ore zone, and achieving hydraulic conductivity values (a measure of permeability) consistent with the 2020 Preliminary Economic Assessment (“PEA”) for the project. Sufficient permeability within the ore zone is a key criteria for the successful deployment of the ISR mining method.
• Established 10-hour Breakthrough Time with Ion Tracer Test:  A subsequent tracer test significantly increased the confidence in the initial hydrogeological evaluations (pump and injection tests) within the Test Pattern. The tracer test demonstrated Denison’s ability to maintain hydraulic control of injected solutions and achieve breakthrough times consistent with expectations.
• Demonstrated the Effectiveness of Permeability Enhancement: One method of permeability enhancement was successfully deployed from multiple wells demonstrating the suitability of the method to the THT deposit.  Efficiency of permeability enhancement was verified by comparison of pre- and post-permeability enhancement hydraulic testing.

David Cates, Denison’s President and Chief Executive Officer, commented “Our recently completed ISR de-risking efforts at THT demonstrate the competitive advantage of our in-house Saskatoon-based technical team.  While there is no short-cut for the collection of key project-specific technical data, our team developed a program for THT that leveraged our experience and maximized the value of our time and efforts in the field.  The program was completed safely and delivered excellent results, confirming our previous expectations that THT can be amenable to ISR mining and should be considered as a potentially low-cost and highly prospective uranium development project.

Despite higher uranium prices, many potential projects in the uranium mining industry struggle to meaningfully advance towards a future development or restart decision.  We continue to meaningfully invest in our exploration and development pipeline projects, and the results from the ISR field test program support bringing THT forward for additional evaluation, and reinforce the project’s potential to become Denison’s second ISR uranium mine development asset in the Athabasca Basin”.

In November 2020, an independent PEA was completed for Waterbury evaluating the potential use of the ISR mining method at THT. The PEA demonstrated robust economics for a small-scale Athabasca Basin ISR mining project, highlighted by an estimated all-in cost per pound U3O8 of US$24.93 and a pre-tax internal rate of return estimated at 50.0% based on a uranium selling price of US$65.00 per pound U3O8 (see press release dated November 17, 2020).

The PEA included recommendations to further advance the technical de-risking of the project with the collection of site-specific data.  As the PEA is preliminary in nature, there is no certainty that the results of the PEA will be realized and mineral resources that are not mineral reserves do not have demonstrated economic viability.

2023 ISR Field Test Program

The 2023 ISR field test program was designed to validate the permeability of THT, and to collect a database of hydrogeological and metallurgical data to further evaluate the ISR mining conditions present at the deposit.  This data is expected to de-risk the ISR requirements related to permeability and is to be further incorporated into ISR mine planning efforts as part of the completion of a potential future Pre-Feasibility Study (“PFS”) for THT.

The Test Pattern consists of 8 small diameter wells in the Eastern Pod of THT (see Figure 2) – made up of four monitoring wells, two pump/injection wells, one Vibrating Wire Piezometer (“VWP”) and one recharge well.  Each test well was drilled to their target depths and, as applicable, outfitted with well screens and/or pressure monitoring devices.

Core collected from the test wells within the mineralized zone is also expected to allow Denison to verify and update the current mineral resource estimate for the deposit and support future wellfield design and mineral processing assessments.

Successful Completion of Hydrogeologic Test Work

The 2023 ISR field test program included preliminary hydrogeological tests completed by using the test wells to move water through the Test Pattern.  Measurements of the movement of water (hydraulic pressure changes) within the ore zone provide evidence of the hydraulic conditions present and are indicative of the potential movement of mining solution in an ISR mining operation.  Over 20 different pump, injection, or slug tests were completed during the program.

Results from the hydrogeological testing produced hydraulic conductivity values consistent with the PEA. Importantly, 100% of the wells located within the Test Pattern showed hydraulic connectivity with another test well.

Additional supportive test work completed during the program included permeability and porosity tests conducted either downhole or on mineralized drill core recovered during the test program.

Execution of Ion Tracer Test

Following hydrogeologic testing, a 2-hole ion tracer test was completed within the Test Pattern. The ion tracer was injected into GWA-003A (Injection well), with pumping occurring from the extraction well (GWA-002).  Water recovered from the extraction well was then recirculated until concentrations of the ion tracer stabilized.

After completion of the ion tracer test, remediation was then conducted to demonstrate the ability to remove injected tracer fluid from the Test Pattern. Injection was halted at the injection well and the extraction well continued to pump to remove the remaining injected ion tracer. Based upon tracer concentrations measured during the two-day clean-up period, 89% of the injected tracer mass was recovered in the extraction well.

Vertical hydraulic control during the tracer test was confirmed through monitoring of the VWP installed in GWA-004, which provided pressure recordings at 3 positions in the sandstone above the mineralized zone, 3 positions in the mineralized zone, and 2 positions in the basement horizons. Hydraulic control was also validated through sampling of the four perimeter monitoring wells for total dissolved solids (“TDS”) values before and after the ion tracer test. No elevated values in TDS were observed outside of the test area during the ion tracer test, confirming no migration of the tracer outside of the two-spot pattern.

Demonstration of the Effectiveness of Permeability Enhancement Method

One method of permeability enhancement was successfully evaluated on three test wells, with efficiency verified by comparison of pre- and post-permeability enhancement hydraulic conductivity tests.  Permeability enhancement has been proven to increase and normalize hydraulic conductivity in the area proximal to the wellbore.  This is important as it provides a useful tool for increasing contact of injected fluids with the ore zone to maximize uranium recoveries in an ISR mining environment.

Collection of Other Supporting ISR Datasets

In addition to the hydrogeological tests described above, samples will be collected from the drill core recovered from the test wells to facilitate (1) assessment of matrix permeability to inform an initial model of the hydrogeological variations of the deposit, (2) future column leach and core leach testing to investigate the uranium extraction curve, lixiviant requirements, reagent consumption and solution flow rates; and (3) characterization of hydrogeologic units and anticipated flow path distribution.

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