Denison Announces Successful Completion of Neutralization Phase of Phoenix ISR Feasibility Field Test

Denison Mines Corp. 

1100 – 40 University Ave 

Toronto, ON  M5J 1T1 

www.denisonmines.com 

PRESS RELEASE

Denison Announces Successful Completion of Neutralization Phase

of Phoenix ISR Feasibility Field Test

Toronto, ON – December 12, 2022. Denison Mines Corp. (“Denison” or the “Company”) (TSX: DML;

NYSE American: DNN) is pleased to announce the successful completion of the neutralization phase of the

Phoenix in-situ recovery (“ISR”) Feasibility Field Test (“FFT”) at the Company’s 95% owned Wheeler River

project (“Wheeler River” or the “Project”). Sampling of monitoring wells around the FFT site has confirmed

the successful restoration of t he Leaching Zone (defined below) to environmentally acceptable pH

conditions, as outlined in the applicable regulatory approvals for the FFT.

The neutralization phase was initiated in mid-October 2022, following the highly successful completion of

the leaching phase of the FFT (see news releases dated October 17, 2022 and November 22, 2022), and

was designed to confirm certain environmental asse ssment assumptions and verify the efficiency and

effectiveness of the neutralization process planned for ISR mining at Phoenix.

David Cates, Denison’s President & CEO, commented, “The completion of the neutralization phase of

the FFT marks the end of our 2022 evaluation field act ivities at Wheeler River. During the year we

successfully constructed and co mmissioned the FFT facilities, and carried out both the leaching

and neutralization phases of the FFT. Our recovery of uranium bearing solution (“UBS”) with the

use of the ISR mining method is a first in the hi story of the Athabasca Basin region, and now we

have achieved another landmark accomplishment with the restoration of the test area to

environmentally acceptable pH conditions. The work was done on schedule and without any

recordable safety incidents – which is a testament to the hard work and professionalism of our

dedicated Saskatchewan-based staff of geoscientists, engineers, metallurgists, process operators,

well field operators, and contractors.”

Kevin Himbeault, Denison’s Vice President of Pl ant Operations & Regulatory Affairs, added, “The

Company embarked on the FFT to confirm the practical application of the ISR mining method within

the high-grade Phoenix uranium deposit. The results from the leaching and neutralization phases

of the FFT have confirmed our ability to leach UBS from the deposit and neutralize the pH conditions

within the test area in accordance with our ex pectations – providing significant support for the

processes utilized in defining the parameters for the Project’s Feasibility Study (‘FS’) and draft

Environmental Impact Statement.”

This press release constitutes a “designated news release” for the purposes of the Company’s prospectus

supplement dated September 28, 2021 to its short form base shelf prospectus dated September 16, 2021.

Completion of FFT Leaching & Neutralization Phases

The leaching phase of the FFT commenced in Sept ember 2022 (see news release dated September 26,

2022) and was completed in October 2022 (see news release dated October 17, 2022, and November 22,

2022), with the objective of assessing the effectivene ss and efficiency of the leaching process in the ore

zone located approximately 400m below the surface. The leaching phase consisted of the controlled

injection of an acidic mining solution into a portion of the existing Test Pattern (defined below) within the

ore zone (the “Leaching Zone”) and the recovery of the solution back to the surface using existing test wells.

Throughout the leaching phase, both vertical and horiz ontal containment of the mining solution was

maintained, with no migration of the mining solution observed above, below or outside of the designed FFT

test area along the Leaching Zone horizon. These resu lts were consistent with the findings from the 2021

tracer test (see news release dated October 28, 2021).

Following the process executed for the 2021 tracer test, the neutralization phase commenced after

completion of the leaching phase and included the initial recovery of additional leached mineralized solution

and injected lixiviant from the Leaching Zone. Following th is initial stage of neutralization, a mild alkaline

(basic) solution was injected into the Leaching Zone to further neutralize the area and reverse the residual

effects of remaining acidic solution injected dur ing the leaching phase. Overall, the results of the

neutralization phase achieved the ke y pH restoration parameter outlined in the applicable regulatory

approvals for the FFT, and verified the efficiency and effectiveness of the process for returning the Leaching

Zone to environmentally acceptable pH condition s. Regular monitoring of the FFT’s environmental

performance will continue into 2023.

The recovered solution from the neutralization phase is being stored temporarily on surface in tanks in

accordance with approved containment measures and will be further processed as part of the recovered

solution management phase of the FFT.

Feasibility Field Test Background

The FFT is designed to use the existing commercial-sca le ISR test pattern (“Test Pattern”), installed at

Phoenix in 2021 (see news releases dated July 29, 2 021, and October 28, 2021), to facilitate a combined

assessment of the Phoenix deposit’s hydraulic flow properties with the leaching characteristics that have

been assessed through the metallurgical core-leach testing program.

The FFT is fully permitted, having been authorized by both the Saskatchewan Minister of Environment (see

news release dated July 12, 2022) and the Canadian Nuclear Safety Commission (see news release dated

August 8, 2022).

Overall, the FFT is intended to provide further verification of the permeability, leachability, and containment

parameters needed for the successful application of the ISR mining method at Phoenix and is expected to

validate and inform various FS design elements – in cluding the expected production and remediation

profiles. The operation of the FFT is planned to occur in three phases: (1) the leaching phase, (2) the

neutralization phase, and (3) the recovered solution management phase.

As described above, the leaching phase and neutralization phase are now completed.

The recovered solution management phase is expected to commence in the spring of 2023, and involves

separating the solution recovered from both the le aching phase and the neutralization phase into (i)

mineralized precipitates and (ii) a neutralized trea ted solution. The mineralized precipitate will be

temporarily stored on surface in storage tanks and the neutralized treated solution will be re-injected into a

designated subsurface area.

About Wheeler River

Wheeler River is the largest undeveloped uranium projec t 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% U 3O8), 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 Gryp hon uranium deposits, discovered by Denison in 2008

and 2014, respectively, and is a joint venture betwe en Denison (operator) and JCU (Canada) Exploration

Company Limited (“JCU”). Denison has an effective 95% ownership interest in Wheeler River (90% directly,

and 5% indirectly through a 50% ownership in JCU).

A Pre-Feasibility Study (“PFS”) wa s completed for Wheeler River in 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

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 operati on 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 intere st, 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 c opy of this report is

available on Denison's website and under its prof ile 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 re lying 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 its effective 95% interest in the Wheeler River

project, Denison's interests in the Athabasca Basin include a 22.5% ownership interest in the McClean

Lake joint venture, which includes several uraniu m deposits and the McClean Lake uranium mill that is

contracted to process the ore fr om the Cigar Lake mine under a to ll milling agreement, plus a 25.17%

interest in the Midwest Main and Midwest A deposits, and a 67.01% interest in the Tthe Heldeth Túé (“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% ownership of 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%). Denis on's exploration portfolio includes further interests in properties

covering ~300,000 hectares in the Athabasca Basin region.

Denison is also engaged in post-closure mine care and maintenance services through its Closed Mines

group, which manages Denison's reclaimed mine site s in the Elliot Lake region and provides related

services to certain third-party projects.

For more information, please contact

David Cates (416) 979-1991 ext 362

President and Chief Executive Officer

Mac McDonald (416) 979-1991 ext 242

Executive Vice President and Chief Financial Officer

Follow Denison on Twitter @DenisonMinesCo

Qualified Persons

The disclosure of scientific or technical informatio n related to the FFT or Wheeler River project contained

in this release has been reviewed and approved, as applicable, by Mr. David Bronkhorst, P.Eng, Denison's

Vice President, Operations or Mr. Andrew Yackulic, P. Geo., Denison's Director, Exploration, who are

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 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 the following: expectations with respect to the FFT

program, scope, timing and the anticipated results thereof; the inte rpretation of the results of the FFT obtained to-date; scop e,

objectives and interpretations of the FS process for the proposed ISR operation for the Phoenix deposit; the results and interpretations

of the PFS and expectations regarding its joint venture ownership interests and the continuity of its agreements with its partn ers 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 modelling and assumptions upon which the work plans for the Wheeler River Project are based may

not be maintained after further work is completed. In additi on, Denison may decide or otherwi se be required to discontinue tes ting,

evaluation and development work if it is unable to maintain or ot herwise secure the necessary re sources (such as testing facili ties,

capital funding, regulatory approvals, etc.). Denison believes that the expectations re flected in this forward-looking informa tion 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 factor s discussed in Denison’s Annual Informati on Form dated March 25, 2022 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 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.

Cautionary Note to United States Investors Concerning Estimates of Mineral Resources and Mineral Reserves : This news

release may use the terms 'measured', 'indicated' and 'inferred' mineral resources. United States investors are advised that such terms

have been prepared in accordance with the definition standards on mi neral reserves of the Canadian Institute of Mining, Metallu rgy

and Petroleum referred to in Canadian National Instrument 43- 101 Mineral Disclosure Standards (‘NI 43-101’) and are recognized

and required by Canadian regulations. 'Inferred mineral resources' have a great amount of uncertainty as to their existence, and as to

their economic and legal feasibility. It cannot be assumed that all or any part of an inferred mineral resource will ever be upgraded to

a higher category. Under Canadian rules, estimates of inferred mi neral resources may not form the basis of feasibility or other

economic studies. United States investors ar e cautioned not to assume that all or any part of an inferred mineral resource exis ts, or

is economically or legally mineable. Unit ed States investors are also cautioned not to assume that all or any part of measure d or

indicated mineral resources will ever be converted into mineral reserves.

Effective February 2019, the United States Securities and Exchange Commission (‘SEC’) adopted amendments to its disclosure rules

to modernize the mineral property disclosure requirements for issuers whose securities are registered with the SEC under the

Exchange Act and as a result, the SEC now recognizes estimates of “measured mineral resources”, “indicated mineral resources”

and “inferred mineral resources”. In addition, the SEC has amended its definitions of “proven mineral reserves” and “probable mineral

reserves” to be “substantially similar” to the corresponding definitions under the CI M Standards, as required under NI 43-101.

However, information regarding mineral resources or mineral rese rves in Denison’s disclosure may not be comparable to similar

information made public by United States companies.