Denison Announces Closing of Transaction with Skyharbour and Formation of Four Prospective Exploration Joint Ventures Proximal to Wheeler River

TORONTO, Dec. 17, 2025 – Denison Mines Corp. (“Denison” or the “Company”) (TSX: DML; NYSE American: DNN) is pleased to announce that it has closed the previously announced transaction (the “Transaction”) with Skyharbour Resources Ltd. (“Skyharbour”) (TSX-V:SYH) (OTCQX: SYHBF), (Frankfurt:SC1P) and the formation of four joint ventures consisting of claims previously comprising Skyharbour’s Russell Lake Uranium Project (“Russell”), which is located directly adjacent to Denison’s flagship Wheeler River Project (“Wheeler River”). View PDF Version.

The new joint ventures are designed to drive collaboration between Denison and Skyharbour’s technical teams and to accelerate the evaluation of the prospective exploration ground adjacent to and proximal to Wheeler River.  Denison will serve as the operator for the Wheeler North and Wheeler River Inliers joint ventures, with ownership interests of 49% and 70% respectively.  Skyharbour will serve as the operator for the Russell Lake (or “RL”) and Getty East joint ventures, with Denison having ownership interests of 20% and 30%, respectively.

In addition, Denison and Skyharbour have entered into option agreements (the “Earn-In Option Agreements”), which allow Denison to increase its ownership interest in each of the Wheeler North and Getty East joint ventures to up to 70%.

About Denison

Denison is a leading uranium mining, development, and exploration company with interests focused in the Athabasca Basin region of northern Saskatchewan, Canada. Denison has an effective 95% interest in its flagship Wheeler River Uranium Project, which is the largest undeveloped uranium project in the infrastructure rich eastern portion of the Athabasca Basin region of northern Saskatchewan.

In mid-2023, the Phoenix feasibility study was completed for the Phoenix deposit as an ISR mining operation, and an update to the previously prepared 2018 Pre-Feasibility Study (‘PFS’) was completed for Wheeler River’s Gryphon deposit as a conventional underground mining operation. 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 Phoenix ISR operation commenced in 2019 and are nearing completion with approval in July 2025 of the project’s EA by the Province of Saskatchewan and conclusion in December 2025 of the Canadian Nuclear Safety Commission Public Hearing for Federal approval of the EA and project construction license.

Denison’s interests in Saskatchewan also include a 22.5% ownership interest in the McClean Lake Joint Venture (‘MLJV’), which includes unmined uranium deposits (with mining at McClean North deposit via the MLJV’s SABRE mining method having commenced in July 2025 using the MLJV’s SABRE mining method) 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 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 ~457,000 hectares in the Athabasca Basin region.

Additionally, through its 50% ownership of JCU (Canada) Exploration Company, Limited (‘JCU’), Denison holds 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.

About Skyharbour

Skyharbour holds an extensive portfolio of uranium exploration projects in Canada’s Athabasca Basin and is well positioned to benefit from improving uranium market fundamentals with interest in thirty-seven projects covering over 616,000 hectares (over 1.5 million acres) of land. Skyharbour has acquired from Denison, a large strategic shareholder of Skyharbour, a 100% interest in the Moore Uranium Project, which is located 15 kilometres east of Denison’s Wheeler River project and 39 kilometres south of Cameco’s McArthur River uranium mine. Moore is an advanced-stage uranium exploration property with high-grade uranium mineralization in several zones at the Maverick Corridor. Adjacent to the Moore Project is the Russell Lake Uranium Project, which hosts widespread uranium mineralization in drill intercepts over a large property area with exploration upside potential. Skyharbour is actively advancing these projects through exploration and drilling programs.

Skyharbour also has joint ventures with industry leaders Denison, Orano Canada Inc., Azincourt Energy, and Thunderbird Resources at the Russell, Preston, East Preston, and Hook Lake Projects, respectively. Skyharbour also has several active earn-in option partners, including CSE-listed Basin Uranium Corp. at the Mann Lake Uranium Project; TSX-V listed North Shore Uranium at the Falcon Project; UraEx Resources at the South Dufferin and Bolt Projects; Hatchet Uranium at the Highway Project; CSE-listed Mustang Energy at the 914W Project; and TSX-V listed Terra Clean Energy at the South Falcon East Project.

For more information, please contact: David Cates, President and Chief Executive Officer, (416) 979-1991 ext. 362; Geoff Smith, Vice President Corporate Development & Commercial, (416) 979-1991 ext. 358; Follow Denison on X (formerly Twitter), @DenisonMinesCo

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