Mr. David Cates of Denison reports

DENISON ANNOUNCES DISCOVERY OF HIGH-GRADE URANIUM MINERALIZATION AT MOON LAKE SOUTH

Denison Mines Corp.'s drill hole MS-23-10A intersected 1.38 per cent eU3O8 (equivalent triuranium octoxide) over 8.7 metres (0.05 per cent eU3O8 cut-off), including a subinterval grading 2.88 per cent eU3O8 over 3.1 metres, intersected approximately 30 metres above the unconformity in the Athabasca sandstone, as part of the recently completed winter exploration program at the Moon Lake South property.

Uranium mineralization was encountered in four of the six drill holes completed during the 2023 winter exploration program, which was designed to evaluate the strike length of low-grade mineralized occurrences identified in the 2021 and 2016 drill programs.

Andy Yackulic, PGeo, Denison's director, exploration, commented: "The discovery of high-grade uranium mineralization at Moon Lake South gives further proof that the CR-3 trend has the potential to host a large, high-grade unconformity-associated uranium deposit. The fact that this high-grade material lies approximately 30 metres above the unconformity contact is very encouraging -- as perched mineralization like this is typically only found proximal to high-grade unconformity-hosted deposits."

David Cates, Denison's president and chief executive officer, added, "The discovery of high-grade sandstone-hosted uranium mineralization at Moon Lake South is a very exciting development for Denison as our company's recent field testing at the nearby 95-per-cent-owned Wheeler River project has illustrated the potential viability of mining high-grade Athabasca basin sandstone-hosted uranium deposits via in situ recovery (ISR) mining."

2023 Moon South winter exploration program highlights

The 2023 winter exploration program consisted of six completed diamond drill holes totalling 3,301 metres, designed to evaluate the potential to expand the footprint of known mineralization discovered in 2016 and 2021 by testing conductivity anomalies identified from the 2022 stepwise moving-loop electromagnetic (SWML EM) survey.

Uranium mineralization was encountered in four of the six drill holes completed during the winter exploration program. The mineralized intersections are summarized in the attached table.

The most significant mineralization was returned from hole MS-23-10A, which intersected a broad zone of high-grade mineralization grading 1.38 per cent eU3O8 over 8.7 metres, associated with strong grey alteration, located approximately 30 metres above the sub-Athabasca unconformity. Given the limited number of drill holes completed during the winter program, the mineralization discovered in MS-23-10A remains open in multiple directions for future follow-up.

Radiometric equivalent grades, sampling, analysis and data verification

Following the completion of a drill hole, the hole is radiometrically logged using a downhole gamma probe, which collects continuous readings of radioactivity along the length of the drill hole. Probe results are then calibrated using an algorithm calculated from the comparison of probe results against geochemical analyses in the area. The gamma-log results provide an immediate radiometric equivalent uranium value (eU3O8 per cent) for the hole, which, except in very high-grade zones, is reasonably accurate. The company typically reports eU3O8 as a preliminary result and subsequently reports definitive assay grades following sampling and chemical analysis of the mineralized drill core.

Assay sample intervals are generally 50 centimetres long, except where higher-grade or lower-grade mineralization boundaries fall within the interval. In that case, two 25-centimetre samples are collected. Flank samples of 1.0 metre are always collected where mineralization is located. Systematic geochemistry samples are collected every 10 metres down the hole.

All assayed core is split in half, with one-half retained and the other sent to the Saskatchewan Research Council geoanalytical laboratory in Saskatoon for analysis. Control samples are routinely assayed with each batch of core samples analyzed.

About Moon Lake South

The Moon Lake South project is a joint venture between Denison Mines, which holds a 75-per-cent interest in the property, and Canalaska Uranium Ltd., which holds the remaining 25-per-cent interest. Denison acts as the project operator.

The project lands are located in the southeastern part of the Athabasca basin, approximately 12 kilometres southwest of Denison's Phoenix deposit and 30 kilometres northwest of Cameco's Key Lake operation. The property is accessible year-round through the Fox Lake tote road, allowing Denison's exploration team to use the nearby Wheeler River camp as a base of operations.

About Denison Mines Corp.

Denison is a uranium exploration and development company with interests focused in the Athabasca basin region of Northern Saskatchewan, Canada. The company has an effective 95-per-cent 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. Denison's interests in Saskatchewan also include a 22.5-per-cent ownership interest in the McClean Lake joint venture, which includes several uranium deposits and the McClean Lake uranium mill that is contracted to process the ore from the Cigar Lake mine under a toll milling agreement, plus a 25.17-per-cent interest in the Midwest Main and Midwest A deposits, and a 67.41-per-cent interest in the Tthe Heldeth Tue (THT, formerly J zone) and Huskie deposits on the Waterbury Lake property. The Midwest Main, Midwest A, THT and Huskie deposits are each located within 20 kilometres of the McClean Lake mill.

Through its 50-per-cent ownership of JCU, Denison holds additional interests in various uranium project joint ventures in Canada, including the Millennium project (JCU: 30.099 per cent), the Kiggavik project (JCU: 33.8118 per cent) and Christie Lake (JCU: 34.4508 per cent). Denison's exploration portfolio includes further interests in properties covering approximately 300,000 hectares in the Athabasca basin region.

Denison is also engaged in postclosure mine care and maintenance services through its Closed Mines group, which manages Denison's reclaimed mine sites in the Elliot Lake region and provides related services to certain third party projects.

Qualified person

The technical information contained in this release has been reviewed and approved by Andrew Yackulic, PGeo, Denison's director, exploration, who is a qualified person in accordance with the requirements of National Instrument 43-101.

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