Denison Mines Corp.(“Denison” or the “Company”) (TSX: DML) (NYSE American: DNN) is pleased to announce the discovery of additional high-grademineralization approximately 40 metres outside of the previously estimated mineralized domain associated with the D1 lens of the Gryphon uranium deposit (“Gryphon”).Drillhole WR-837AD2intersected 2.3metres at 1.69% eU3O8including 0.5metres at 5.48% eU3O8 in the down plunge direction from the previously defined D1 lens. This area remains open down-plunge and along strike to the northeast for further expansion.Gryphon is situated approximately 3 km northwest of the Company's flagship Phoenix In-Situ Recovery (“ISR”) uranium mine development project, on Denison's 95%-owned Wheeler River property in northern Saskatchewan (see Figure 1). View PDF version.
The discovery was made as part of a highly successful delineationdrill programcarried out at Gryphonduring the first half of 2025. Results from the delineation drillingare expected to add confidence to the previously estimated mineral resources for Gryphon, having confirmed the current geological interpretation of the deposit and intersecting uranium grades in line with expected values.
Denison's President and CEO, David Cates, commented, “Our 2025 Gryphon delineationprogram was highly successful and achieved each of the program's key objectives – including (a) increasing the density of drill testing within the A1 high-grade domain and confirming the geologicalmodel, (b) collecting additional geotechnical, metallurgical and hydrogeological samples and information to support future project evaluation efforts, and (c) initial testing of areas identified for possible expansion of mineral resources that are outside of the mine design outlined in the 2023 Pre-Feasibility Study (“PFS”).
The delineationresults demonstrate thatGryphon is an excellent high-gradebasement-hosteduraniumdepositthat justifiesfurther project development evaluation and de-risking.With a focus on confirming the mineralizationin the A-series of lenses, a limited number ofdrillholes were designed to test for possible expansion ofthe estimatedmineral resource. As a result, we are excited that drillhole WR-837AD2encountered high-grade mineralization outside of the existing mineralized domain in an area that remains wide open for further expansion down-plunge and along strike. We are currently developing plansto follow-up this resultandtestother expansion targets.”
Gryphon Uranium Deposit
Gryphon was discovered by Denison in 2014 and is estimated to contain Indicated Mineral Resources of 61.9 million pounds U3O8(1,643,000 tonnes an average grade of 1.7% U3O8), plus Indicated Mineral Resources of 1.9 million pounds U3O8(73,000 tonnes at an average grade of 1.2%U3O8), with an effective date of August 7, 2018.
Gryphon is comprised of 24 primarily basement-hosted stacked lensesreferred to as the A-series, B-series, C-series, D-series and E-series lenses, which are interpreted to be stacked to form a zone of mineralization measuring approximately 280 metres long by 113 metres wide, with each lens having variable thicknesses and generally plunging to the northeast and dipping to the southeast (See Figure 2). Four high-grade domains have been established within the A1 and D1 lenses. The A1 high-grade domain represents 40% of the total Indicated Mineral Resources estimated for the deposit; whereas the combination of the three D1 high-grade domains represent approximately 10% of the total Indicated Mineral Resources.
Potential future development of the Gryphon deposit has been assessed as an underground mining operation at a PFSlevelin 2018 witha cost update completed in 2023. The outcomes of the study highlight robust economics with an estimated after-tax base-case Net Present Value(“NPV”)of $864.2 millionand internal rate of return (“IRR”) of 37.6%,based on estimated Probable Reserves of 49.7 million pounds U3O8(1,275,000 tonnes at 1.8% U3O8), a uranium selling price of USD$75/lbU3O8($101.25/lbU3O8),and an 8% discount rate. Gryphon's cash operating costs are estimated to be USD$12.75/lb U3O8, and its all-in cost of production (including initial capital costs of CAD$737.4million) isestimated to be US$25.47/lb U3O8. Accordingly, Gryphon has the potential to be competitive with the lowest cost uranium mining operations in the world.
Discovery of Additional High-Grade Mineralization Associated with the D1 lens
The D series lenses were targeted for potential mineral resource expansion in 2025 given theirhigh-grade,structurally controlled nature,and that previousdrilling left the mineralizationpartiallyopen in the down-plunge and along-strike directions.Prior to this program, no significant expansion drilling has occurred proximal to Gryphon since 2018.
The last drillhole of the2025program (WR-837AD2)encountered high-grade uranium mineralization, which is interpreted to expand the extentof the D1 zone by ~40 metres in the down-plunge direction. This drillhole tested a 100-metre gap in the previous drillhole spacing(see Figure 3)and justifies further follow-up drilling to test to additional down-plunge extension as well as the potential for along strike continuation.Drillhole WR-836 was also completed in the expansion area and also encounterednotable uranium mineralization, which indicates the system is open along strike to the north.
Denison reports its initial drillingresults as radiometric equivalent uranium (“%eU3O8”) from a calibrated, triplegamma, down-hole probe. All mineralized intersections have been sampled for chemical U3O8 assay and final results will be compiledfollowingreceipt of the data.
Table 1: Drillholeintercepts by lens for WR-836 and WR-837AD2.1
2025Delineation Drill Program Highlights
A total of ~12,500 metres of diamond drilling was completed in seventeen drillholes and multiple off cuts during the 2025 delineation programat Gryphon.Overall, the delineationprogram confirmed the current geological interpretation of the deposit and supported the grade-thickness (GT) assumptions in the resource block model.
The A1 lenswas the primary focus of the drill program asthe high-grade and low-grade domains containapproximately50% of the estimated IndicatedMineral Resourcefor Gryphon. Several drill holes intersected the A1 high-grade domain and established additional continuity within the A-series lenses.
The B and C series lenses are located below the A series within the center of the deposit and were also intersected as part of the 2025 delineation program. Together the B and C series lenses account for approximately 20% of the total estimated Indicated Mineral Resources.
Several drillholes encountered significant results, demonstrating the high-grade nature of Gryphon, including the following results from WR-831D1D2, which tested the primary lenses and returned the best mineralized intercepts from the delineation program:
Table 2: Drillholeintercepts by lens for WR-831D1D2.1
Additional Data Collected for Future De-risking and Study Work
Approximately 250kg of whole-core sampleswere collectedfor metallurgical test work. Metallurgical test programs are being developed to assess uranium recoveries toadvance the evaluation work completed to support the 2018 and 2023 PFS.
Geotechnical logging was completed on all drillholes and hydrogeological information was collected from two of the drillholeswhichwere outfitted withvibrating wire piezometers (VWPs). The information collected from these exercises is expected to increasethe understanding of different hydrogeological zones to support future mine-design planning.
This workadds to the extensive database of geological, hydrogeological, geotechnical, and metallurgical data forGryphon. This site-specific data is expectedtobe used to validatecertain key assumptions inpotential future technical studies further evaluating the Gryphon deposit for underground mining.
About Wheeler River
Wheeler River is the largest undeveloped uranium project in the infrastructure-rich eastern portion of the Athabasca Basin region, in northern Saskatchewan. The project is host to the high-grade Phoenix and Gryphon uranium deposits, discovered by Denison in 2008 and 2014, respectively, and is a joint venture between Denison (90% and operator) and JCU (Canada) Exploration Company Limited (“JCU”, 10%). In August 2023, Denison filed a technical report summarizing the results of (i) the feasibility study completed for ISR mining of the high-grade Phoenix uranium deposit and (ii) a cost update to the 2018 Pre-Feasibility Study for conventional underground mining of the basement-hosted Gryphon uranium deposit. More information on the studies is available in the technical report titled “NI 43-101 Technical Report on the Wheeler River Project Athabasca Basin, Saskatchewan, Canada” dated August 8, 2023,with an effective date of June 23, 2023, a copy of which is available on Denison's website and under its profile on SEDAR+ at www.sedarplus.ca and on EDGAR at www.sec.gov/edgar.shtml.
Based on the respective studies, both deposits have the potential to be competitive with the lowest cost uranium mining operations in the world. Permitting efforts for the planned PhoenixISR operation commenced in 2019 and several notable milestones were achieved in 2024 with the submission of federal licensing documents and the acceptance of the final form of the project's Environmental Impact Statement by the Province of Saskatchewan and the Canadian Nuclear Safety Commission.
About Denison
Denison is a uranium mining, exploration and development company with interests focused in the Athabasca Basin region of northern Saskatchewan, Canada. In addition to Denison's effective 95% interest in its flagship Wheeler River Project, Denison's interests in Saskatchewan also include a 22.5% ownership interest in the McClean Lake Joint Venture (“MLJV”), which includes unmined uranium deposits (planned for extraction via the MLJV's SABRE mining method starting in 2025) and the McClean Lake uranium mill (currently utilizing a portion of its licensed capacity to process the ore from the Cigar Lake mine under a toll milling agreement), plus a 25.17% interest in the Midwest Joint Venture's Midwest Main and Midwest A deposits, and a 70.55% interest in the Tthe Heldeth Túé (“THT”) and Huskie deposits on the Waterbury Lake Property. The Midwest Main, Midwest A, THT and Huskie deposits are located within 20 kilometres of the McClean Lake mill. Taken together, Denison has direct ownership interests in properties covering ~384,000 hectares in the Athabasca Basin region.
Additionally, through its 50% ownership of JCU (Canada) Exploration Company, Limited (“JCU”), Denison holds additional interests in various uranium project joint ventures in Canada, including the Millennium project (JCU, 30.099%), the Kiggavik project (JCU, 33.8118%), and Christie Lake (JCU, 34.4508%).
In 2024, Denison celebrated its 70th year in uranium mining, exploration, and development, which began in 1954 with Denison's first acquisition of mining claims in the Elliot Lake region of northern Ontario.
Qualified Persons
The technical information contained in this press release has been reviewed and approved byChad Sorba, P.Geo., Denison's Vice President Technical Services & Project Evaluation, who is a Qualified Persons in accordance with the requirements of NI 43-101.
Cautionary Statement Regarding Forward-Looking Statements
Certain information contained in this news release constitutes 'forward-looking information', within the meaning of the applicable United States and Canadian legislation, concerning the business, operations and financial performance and condition of Denison. Generally, these forward-looking statements can be identified by the use of forward-looking terminology such as 'potential', 'plans', 'expects', 'budget', 'scheduled', 'estimates', 'forecasts', 'intends', 'anticipates', or 'believes', or the negatives and/or variations of such words and phrases, or state that certain actions, events or results 'may', 'could', 'would', 'might' or 'will''be taken', 'occur' or 'be achieved'.
In particular, this news release contains forward-looking information pertaining to the following: scope, objectives and interpreted results of the Gryphon delineationprogram; future plans, includingpotential futureexploration potential and metallurgical test programs; and expectations regarding its joint venture ownership interests and the continuity of its agreements with its partners and third parties. Statements relating to 'mineral reserves' or 'mineral resources' are deemed to be forward-looking information, as they involve the implied assessment, based on certain estimates and assumptions that the mineral reserves and mineral resources described can be profitably produced in the future.
Forward looking statements are based on the opinions and estimates of management as of the date such statements are made, and they are subject to known and unknown risks, uncertainties and other factors that may cause the actual results, level of activity, performance or achievements of Denison to be materially different from those expressed or implied by such forward-looking statements. For example, the modelling and assumptions upon which the plans for Wheeler River are based may not be maintained after further work is completed. In addition, Denison may decide or otherwise be required to discontinuetesting, evaluation and otherwork if it is unable to maintain or otherwise secure the necessary resources (such as testing facilities, capital funding, regulatory approvals, etc.). Denison believes that the expectations reflected in this forward-looking information are reasonable but no assurance can be given that these expectations will prove to be accurate and results may differ materially from those anticipated in this forward-looking information. For a discussion in respect of risks and other factors that could influence forward-looking events, please refer to the factors discussed in Denison's Annual Information Form dated March 28, 2025 or subsequent quarterly financial reports under the heading 'Risk Factors'. These factors are not, and should not be construed as being exhaustive.
Accordingly, readers should not place undue reliance on forward-looking statements. The forward-looking information contained in this news release is expressly qualified by this cautionary statement. Any forward-looking information and the assumptions made with respect thereto speaks only as of the date of this news release. Denison does not undertake any obligation to publicly update or revise any forward-looking information after the date of this news release to conform such information to actual results or to changes in Denison's expectations except as otherwise required by applicable legislation
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