Denison Announces 2020 Phoenix Expansion Drilling Returns Best Results to Date at Zone C

Denison Mines Corp.

1100 – 40 University Ave

Toronto, ON M5J 1T1

www.denisonmines.com

PRESS RELEASE

DENISON ANNOUNCES 2020 PHOENIX EXPANSION DRILLING

RETURNS BEST RESULTS TO DATE AT ZONE C

Toronto, ON – Feb. 9, 2021. Denison Mines Corp. (“Denison” or the “Company”) (DML: TSX, DNN: NYSE

American) is pleased to report the results from the 2020 exploration and expansion drilling program focused

on the area proximal to the high-grade Phoenix uranium deposit (“Phoenix”) at the Company’s 90% owned

Wheeler River Uranium Project (“Wheeler River”). During the program, 19 drill holes were completed for a

total of approximately 7,400 metres – all of which w ere located outside of the extents of the mineral

resources currently defined at Phoenix. The results from the program were highlighted by the intersection

of high-grade uranium mineralization in Zone C, where no mineral resource is currently estimated:

• 5.69% U3O8 over 5.0 metres in WR-328D1, located approximately 22 metres northeast of historic

mineralized hole WR-368 (1.59% U3O8 over 2.0 metres); and

• 8.84% U3O8 over 2.5 metres in WR-767D1, located approximately 35 metres to the northea st of

WR-328D1.

The mineralization in WR-328D1 and WR-767D1 represent the best mineralized intersections returned to

date from exploration drilling at Phoenix Zone C.

Andy Yackulic, P. Geo. , Denison’s Director, Exploration, commented, “The grades and thicknesses of

the mineralized intersections from the 2020 Phoenix Zone C drilling represent a significant upgrade

compared to historical drilling at Zone C. With each successive hole at Zone C, Denison’s

exploration team becomes more optimistic about the prospect of de lineating a n additional

mineralized zone that could potentially be incorporated into future development plans for the

Phoenix In-situ recovery (“ISR”) operation.”

This press release constitutes a "designated news release" for the purposes of the Company's prospectus

supplement dated November 13, 2020 to its short form base shelf prospectus dated June 2, 2020.

Phoenix Zone C

Zone C is the southwestern -most mineralized zone at Phoenix (see Figure 1) . Prior to the 2020 drilling

program, Zone C was defined over a strike length of approximately 250 metres by only five mineralized

intersections. Historic exploration drilling at Phoenix was largely focused on the delineation of Zone A and

Zone B. As a result of the lack of historic al drilling at Zone C, no resource estimate exists for the

mineralization previously identified at Zone C.

The 2020 drilling program was designed to test the continuity and extents of known mineralization at Zone

C. Eleven drill holes were completed at Zone C in 2020 for a total of 4,600 metres. Three of these drill holes

returned uranium mineralization, successfully extending the mineralized zone's strike length by

approximately 20 metres to the southwest and delineating a potential high-grade mineralized “core.”

Mineralized intersections from 2020 drilling at Zone C are outlined in Table 1 and illustrated in Figure 2.

With Denison’s recent decision to adopt a freeze wall design and phased mining approach, as part of the

ISR mining operation planned for the Phoenix deposit (See Denison’s news release from Dec ember 1,

2020), it is possible that further exploration could result in the delineation of a mineral resource that could

become a future mining “phase” at Phoenix. Additional drilling will be required to determine the extent of

uranium mineralization at Zone C.

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Table 1 – Phoenix Zone C Mineralized Intersections

Hole-ID From (m) To (m) Length (m) U3O8(%)

WR-328D11,3,4 376.4 381.4 5.0 5.69

WR-767D11,3,4 382.0 384.5 2.5 8.84

WR-7712,3,4 376.5 377.5 1.0 0.89

Notes: (1) Intersection interval is composited above a cut-off grade of 1.0% U3O8;

(2) Intersection interval is composited above a cut-off grade of 0.1% U3O8;

(3) WR-328D1 was drilled at an azimuth of 333.7° and an inclination of -80.3°. WR-767D1 was

drilled at an azimuth of 310.4° and an inclination of -79.3°. WR-771 was drilled at an azimuth of

310.0° and an inclination of -79.5°.

(4) Lengths indicated are the down-hole length and do not represent the true thickness of

mineralization. True thickness is estimated to be approximately 98% of stated downhole length.

Phoenix Zone A and Zone B

Eight diamond drill holes totalling 3,796.0 m were completed to test the extents of known mineralization at

Zones A and B. While several drill holes intersected weak uranium mineralization, the only notable potential

extension of existing mineralization was reported in drill hole WR -765D1 in Zone B – which intersected

0.36% U3O8 over 3.5 metres (from 401.3 to 404.8 metres), drilled at an azimuth of 332.3° and an inclination

of -79.6°, approximately 15 metres east of WR -333 (which previously intersected 14.6% U 3O8 over 6.0

metres).

Sampling and Assay Procedures

Drill core with anomalous total gamma radioactivity (>300 counts per second using an RS-120 or RS-125

scintillometer) was sampled over 0.5 metre intervals. Sampling is undertaken on site by splitting the core

in half, with one half submitted for analysis and the other half retained in the core box for future reference.

Uranium chemical assays are performed by the Saskatchewan Research Council ("SRC") Geoanalytical

Laboratories located in Saskatoon. Sample preparation involves crushing and pulverizing core samples to

90% passing -106 microns. Splits of the resultant pulps are initially subm itted for multi -element ICP-MS

analysis following partial (HNO3:HCl) and total (HF:HNO3:HClO4) digestions. Samples with ≥ 1,000 ppm

U (partial digest) are re -assayed for U 3O8 using an ISO/IEC 17025:2005 accredited method for the

determination of U 3O8 weight percentage. Pulp splits are digested using aqua -regia, and the solution

analyzed for U3O8 weight percentage using ICP-OES. In addition to internal checks by SRC Geoanalytical

Laboratories, the Company has rigorous quality assurance and quality control ("QAQC") procedures ,

including the insertion of standard reference materials, blanks and field duplicates. The assay data is

subject to verification procedures by qualified persons employed by Denison prior to disclosure. For further

details on the assay, QAQC and data verification procedures , please see Denison's Annual Information

Form dated March 13, 2020, filed under the Company's profile on SEDAR (www.sedar.com).

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 – including combined Indicated Mineral Resources of

132.1 million pounds U3O8 (1,809,000 tonnes at an average grade of 3.3% U3O8), plus combined Inferred

Mineral Resources of 3.0 million pounds U 3O8 (82,000 tonnes at an average grade of 1.7% U 3O8). 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 (10%).

The Wheeler River P re-Feasibility Study (“PFS”) was completed in late 2018, considering the potential

economic merit of developing the Phoenix deposit as an ISR operation and the Gryphon deposit as a

conventional underground mining operation. Taken together, the project is estimated to have mine

production of 109.4 million pounds U 3O8 over a 14-year mine life, with a base case pre -tax NPV of $1.31

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billion (8% discount rate), Internal Rate of Return ("IRR") of 38.7%, and initial pre- production capital

expenditures of $322.5 million. The Phoenix ISR operation is estimated to have a stand- alone base case

pre-tax NPV of $930.4 million (8% discount rate), IRR of 43.3%, initial pre-production capital expenditures

of $322.5 million, and industry leading average operating costs of US$3.33/lb U3O8. The PFS is prepared

on a project (100% ownership) and pre-tax basis, as each of the partners to the Wheeler River Joint Venture

are subject to different tax and other obligations.

Further details regarding the PFS, including additional scientific and technical information, as well as after-

tax results attributable to Denison's ownership interest, are described in greater detail in the NI 43- 101

Technical Report titled "Pre- feasibility Study for the Wheeler River Uranium Project, Saskatchewan,

Canada" dated October 30, 2018 with an effective date of September 24, 2018. A copy of this report is

available on Denison's website and under its profile on SEDAR at www.sedar.com and on EDGAR at

www.sec.gov/edgar.shtml.

Denison suspended certain activities at Wheeler River during 2020, including the EA process, which is on

the critical path to achieving the project development schedule outlined in the PFS. While the EA process

has resumed, the Company is not currently able to estimate the impact to the project development schedule

outlined in the PFS, and users are cautioned against relying on the estimates provided therein regarding

the start of pre-production activities in 2021 and first production in 2024.

About Denison

Denison is a uranium exploration and development company with interests focused in the Athabasca Basin

region of northern Saskatchewan, Canada. In addition to the Wheeler River project, Denison's Athabasca

Basin exploration portfolio consists of numerous p rojects covering over 250,000 hectares. Denison's

interests in the Athabasca Basin also include a 22.5% ownership interest in the McClean Lake joint venture

("MLJV"), which includes several uranium deposits and the McClean Lake uranium mill, which is currently

processing ore from the Cigar Lake mine under a toll milling agreement, plus a 25.17% interest in the

Midwest and Midwest A deposits, and a 66.90% interest in the Tthe Heldeth Túé (“THT,” formerly J Zone)

and Huskie deposits on the Waterbury Lake pr operty. Each of Midwest, Midwest A, THT and Huskie are

located within 20 kilometres of the McClean Lake mill.

Denison is engaged in mine decommissioning and environmental services through its Closed Mines group

(formerly Denison Environmental Services), which manages Denison's Elliot Lake reclamation projects and

provides post-closure mine care and maintenance services to a variety of industry and government clients.

Denison is also the manager of Uranium Participation Corp., a publicly traded company which invests in

uranium oxide and uranium hexafluoride.

For more information, please contact

David Cates (416) 979-1991 ext 362

President and Chief Executive Officer

Sophia Shane (604) 689-7842

Investor Relations

Follow Denison on Twitter @DenisonMinesCo

Qualified Persons

The technical information contained in this release has been reviewed and approved by Mr. Andrew

Yackulic, P. Geo., Denison's Director, Exploration, who is a Qualified Person 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 ‘plans’, ‘expects’, ‘budget’,

‘scheduled’, ‘estimates’, ‘forecasts’, ‘intends’, ‘anticipates’, or ‘believes’, or the negatives and/or variations of such words and phrases,

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or state that certain actions, events or results ‘may’, ‘could’, ‘would’, ‘might’ or ‘will be taken’, ‘occur’, ‘be achieved’ or ‘has the potential

to’.

In particular, this news release contains forward-looking information pertaining: the interpretation of the results from the 2020 Phoenix

exploration program, underlying assumptions and the Company’s intentions with respect thereto; the results of the PFS and

expectations with respect thereto , including the duration and scope of impacts of the COVID -19 pandemic and affiliated operational

adjustments; development and expansion plans and objectives, including plans future mining phases for the pr oject described in the

PFS; and expectations regarding its joint venture ownership interests and the continuity of its agreements with its partners.

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 acti vity,

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

statements. For example, areas of interest for further exploration selected based on interpretation of current and historic exploration

may not result in findings of significance after further testing. 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 di ffer

materially from those anticipated in this forward -looking information. For a discussion i n 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 13, 20 20

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.

Cautionary Note to United States Investors Concerning Estimates of Mineral Resources an d Mineral Reserves: This press

release may use terms such as “measured”, “indicated” and/or “inferred” mineral resources and “proven” or “probable” mineral

reserves, which are terms defined with reference to the guidelines set out in the Canadian Institute of Mining, Metallurgy and Petroleum

(“CIM”) CIM Definition Standards on Mineral Resources and Mineral Reserves (“CIM Standards”). The Company’s descriptions of its

projects using CIM Standards may not be comparable to similar information made public by U.S. companies subject to the reporting

and disclosure requirements under the United States federal securities laws and the rules and regulations thereunder.

Figure 1 - Phoenix Deposit – 2020 Exploration Drilling

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Figure 2 - Phoenix Zone C – 2020 Exploration Drilling