Denison Announces Agreement to Form Exploration Joint Ventures with Cosa Resources

Denison Mines Corp.

1100 – 40 University Ave

Toronto, ON M5J 1T1

www.denisonmines.com

PRESS RELEASE

Denison Announces Agreement to

Form Exploration Joint Ventures with Cosa Resources

Toronto, ON – November 27, 2024. Denison Mines Corp. (“Denison” or the “Company”) (TSX: DML;

NYSE American: DNN) is pleased to announce that is has executed an agreement (the “Agreement”) with

Cosa Resources Corp. (“Cosa”) (TSX-V: COSA) to form three uranium exploration joint ventures in the

eastern portion of the Athabasca Basin region in no rthern Saskatchewan. Pursuant to the Agreement,

Cosa will acquire a 70% in terest in Denison’s 100%-owned Murp hy Lake North, Darby, and Packrat

properties (the “Properties”) in exchange for approximately 14.2 million Cosa common shares, $2.25M in

deferred equity considerat ion, and a commitment to spend $6.5 million in expl oration expenditures at

Murphy Lake North and Darby (the “Transaction”).

David Cates, President & CEO of Denison, commented, “Denison is pleased to collaborate with Cosa

in a way that is mutually beneficial and enhances our exposure to the potential discovery of a

meaningful uranium deposit on the Properties and through Cosa’s existing uranium exploration

portfolio. With Denison focused on executing on our core mining and development-stage projects,

we believe Cosa is an excellent partner to advance exploration of the Properties. The entire Cosa

senior management team has worked with Denison previously, and have strong technical

capabilities, plus a unique familiarity with the Properties and nearby discoveries.”

Transaction Highlights:

 The transaction is structured to incentivize exploration activity, with Cosa required to invest a

minimum of $6.5 million in explorat ion expenditures to retain its operatorship and ownership level

of the Murphy Lake North and Darby properties.

 Denison to receive meaningful consideration in the form of an upfront payment of 14,195,506 Cosa

common shares (representing ~19.95% ownership in terest in Cosa post transaction), deferred

equity consideration of $2.25 million of additional Cosa common shares, and a royalty on each of

the Properties.

 Denison retains a minimum 30% di rect interest in the Properties and will become Cosa’s largest

shareholder, while also securing strategic pre- emptive rights and a buydown right to increase

Denison’s interest in the Darby property.

 Denison will have the right to nom inate one director to Cosa’s boar d of directors for so long as

Denison holds at least 5% of the issued and outstanding common shares and an additional director

to Cosa’s board of directors for so long as Denison holds at least 10% of the issued and outstanding

common shares.

Terms of the Transaction

Under the terms of the Acquisition Agreement, Cosa will acquire a 70% interest in each of the Properties

from Denison. See Figure 1 for the location of the Properties. Upon closing of the Transaction, the parties

will form a joint venture for eac h of the Propert ies (each, a “Joint Venture”) and Cosa will become the

project operator. Denison will retain a 30% interest in each of the Properties.

As consideration for the Transaction, Cosa will issue 14,195,506 common shares to Denison, equivalent to

19.95% of the outstanding common shares of Cosa following completion of the Transaction. Denison will

retain a 2% Net Smelter Royalty (“NSR”) on Darby and Packrat, and a 0.5% NSR on Murphy Lake North.

Cosa has been granted the right to reduce the NSR royalty rate on each of Darby and Packrat to 1% for a

cash payment of C$2,000,000 per project.

Additionally, Cosa will be required to:

 issue Denison a further C$2,250, 000 in deferred consideration shares within a five-year period

beginning at the closing date (the “Closing Date”) of the Transaction;

 fund 100% of the next C$1,500,000 in explor ation expenditures on Murphy Lake North by

December 31, 2027, otherwise Denison’s ownership interest in the property will increase to 51%

and Denison will become the operator; and

 fund 100% of the next C$5,000,000 in explor ation expenditures on Darby by June 30, 2029,

otherwise Denison’s ownership interest in the property will increase to 51% and Denison will

become the operator.

Darby is subject to a buydown right (the “Buydown”), which permits Denison to reclaim up to a 60% interest

in Darby until such time as Denison’s interest in the project falls below 10%, or commercial production of

500,000 lbs. of U3O8 is achieved from the applicable Darby claim.

Cosa is to appoint a technical advisor nominated by D enison for a period of five years from the Closing

Date or until all of Cosa’s obligations under the Acquisition Agreement have been fulfilled.

Completion of the Transaction is subject to a number of conditions precedent, including, but not limited to:

(i) acceptance by the TSX.V and receipt of other applicable regulatory approvals to be obtained by Cosa,

and (ii) certain other closing conditions customary for a transaction of this nature.

On closing, Denison and Cosa will enter into an Investor Rights Agreement, which will provide for, among

other things, a pre-emptive right and top-up rights ent itling Denison to maintain and/or acquire up to a

19.95% interest in Cosa, on the condition that Deni son holds at least 5% of the issued and outstanding

common shares. Additionally, Denison will have the right to nominate one director to Cosa’s board of

directors for so long as Denison hol ds at least 5% of the issued and outstanding common shares and an

additional director to Cosa’s board of directors for so long as Denison holds at least 10% of the issued and

outstanding common shares.

About Denison

Denison is a uranium mining, exploration and development company with interests focused in the

Athabasca Basin region of northern Saskatchewan, Canada. The Company 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,

a feasibility study was completed for the Phoenix deposi t as an in-situ recovery (“ISR”) mining operation,

and an update to the previously prepared 2018 Pre-Feasibility Study 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 lo west cost uranium mining operations in the world.

Permitting efforts for the planned Phoenix ISR operation commenced in 2019 and a several notable

milestones were achieved in 2024 with the submissi on of federal licensing documents and the proposed

final versions of the Environmental Impact Statement (“EIS”) to the Canadian Nuclear Safety Commission

and the Province of Saskatchewan.

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 MWJV’s Midwest Main and Midwest A deposits, and a 69.44% 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. Tak en 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 is celebrating 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.

For more information, please contact

David Cates (416) 979-1991 ext. 362

President and Chief Executive Officer

Geoff Smith (416) 979-1991 ext. 358

Vice President Corporate Development & Commercial

Follow Denison on X (formerly Twitter) @DenisonMinesCo

About Cosa Resources Corp.

Cosa Resources is a Canadian uranium exploration company operating in northern Saskatchewan. The

portfolio comprises roughly 237,000 ha across mu ltiple 100% owned and Cosa operated joint venture

projects in the Athabasca Basin region, all of which are underexplored, and the majority reside within or

adjacent to established uranium corridors.

Cosa’s award-winning management team has a long track record of success in Saskatchewan. In 2022,

members of the Cosa team were awarded the AME Colin Spence Award for their previous involvement in

discovering IsoEnergy’s Hurricane deposit. Prior to Hurricane, Cosa personnel led teams or had integral

roles in the discovery of Denison’s Gryphon deposit and 92 Energy's Gemini Zone and held key roles in

the founding of both NexGen and IsoEnergy.

Cosa’s primary focus through 2024 was initial drilling at the 100% owned Ursa Project, which captures over

60-kilometres of strike length of the Cable Bay Sh ear Zone, a regional structural corridor with known

mineralization and limited historical drilling. It potentially represents the last remaining eastern Athabasca

corridor to not yet yield a major discovery, which the Company believes is primarily due to a lack of modern

exploration. Modern geophysics completed by Cosa in 2023 identified multiple high-priority target areas

characterized by conductive basement stratigrap hy beneath or adjacent to broad zones of inferred

sandstone alteration – a setting that is typical of mo st eastern Athabasca uranium deposits. Guided by a

recently completed Ambient Nois e Tomography (ANT) survey, Cosa’s second and most recent drilling

campaign at Ursa intersected a significant zone of unconformity-style sandst one hosted structure and

alteration underlain by several intervals of anomalou s radioactivity in the bas ement rocks. Follow-up is

currently in planning for 2025.

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 identif ied by the use of forward-looking termi nology 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 Denison's current intentions and objectives with

respect to, and commitments set forth in, the Acquisition Agreement and ancillary agreements and the expected benefits thereof; the

assumption that the transactions set forth in the Acquisition Agreement will be complet ed as described; the Company’s exploration,

development and expansion plans and objectives for the Explorat ion Properties and other Company projects; and expectations

regarding its joint venture ownership interests and the continuity of its agreements with its partners and third parties.

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 c ause the actual results, level of activi ty,

performance or achievements of Denison to be materially different from those expre ssed or implied by such forward-looking

statements. For example, the parties to the Acquisition Agreement may not complete obligations as described therein and/or the

exploration objective for the Exploration Properties may not be achieved.

In addition, Denison may decide or otherwis e be required to discontinue testing, eval uation and other work on the Company’s other

properties if it is unable to maintain or otherwise secure the necessary resources (such as te sting facilities, capital funding , joint

venture approvals, 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 accu rate and results may differ materially fr om

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, 2024 under the heading

‘Risk Factors’ or in subsequent quarterly financial reports. These factors are not, and should not be construed as being, exhaustive.

Accordingly, readers should not place undue re liance on forward-looking statements. The forward-looking information contained i n

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 rel ease to conform such information to actual results or to changes in

Denison's expectations except as otherwise required by applicable legislation.

Figure 1: Detailed Map of Properties Subject to the Acquisition Agreement