Denison Announces Discovery of Additional High-Grade Mineralization at Gryphon and Reports Results from Successful Delineation Program
Denison Mines Corp.
1100 – 40 University Ave
Toronto, ON M5J 1T1
www.denisonmines.com
PRESS RELEASE
Denison Announces Discovery of Additional High-Grade Mineralization
at Gryphon and Reports Results from Successful Delineation Program
Toronto, ON – July 16, 2025. Denison Mines Corp. (“Denison” or the “Company”) (DML: TSX, DNN:
NYSE American) is pleased to announce the discovery of additional high- grade mineralization
approximately 40 metres outside of the previously estimated mineralized domain associated with the D1
lens of the Gryphon uranium deposit (“Gryphon”). Drill hole WR-837AD2 intersected 2.3 metres at 1.69%
eU3O8 including 0.5 metres at 5.48% eU3O8 in the in the down plunge direction from the previously defined
D1 lens. This area remains open dow n-plunge and along strike to the northeast for further expansion.
Gryphon is situated approximately 3 km northwest of the Company’s flagship Phoenix In- Situ Recovery
(“ISR”) uranium mine development project, on Denison’s 95% -owned Wheeler River property in northern
Saskatchewan (see Figure 1).
The discovery was made as part of a highly successful delineation drill program carried out at Gryphon
during the first half of 2025. Results from the delineation drilling are expected to add confidence to the
previously estimated mineral resources for Gryphon, having confirmed the current geological interpretation
of the deposit and intersecting uranium grades in line with expected values.
Denison’s President and CEO, David Cates, commented, “Our 2025 Gryphon delineation program was
highly successful and achieved each of the program’s key objectives – including (a) increasing the
density of drill testing within the A1 high- grade domain and confirming the geological model, (b)
collecting additional geotechnical, metallurgical and hydrogeological samples and information to
support future project evaluation efforts, and (c) initial testing of areas identified for possible
expansion of mineral re sources that are outside of the mine design outlined in the 2023 Pre -
Feasibility Study (“PFS”).
The delineation results demonstrate that Gryphon is an excellent high -grade basement-hosted
uranium deposit that justifies further project development evaluation and de-risking. With a focus
on confirming the mineralization in the A -series of lenses, a limited number of drill holes were
designed to test for possible expansion of the estimated mineral resource. As a result, we are
excited that drill hole WR-837AD2 encountered high-grade mineralization outside of the existing
mineralized domain in an area that remains wide open for further expansion down-plunge and along
strike. We are currently developing plans to follow-up this result and test other expansion targets.”
Gryphon Uranium Deposit
Gryphon was discovered by Denison in 2014 and is estimated to contain Indicated Mineral Resources of
61.9 million pounds U 3O8 (1,643,000 tonnes an average grade of 1.7% U 3O8), plus Indicated Mi neral
Resources of 1.9 million pounds U3O8 (73,000 tonnes at an average grade of 1.2% U3O8), with an effective
date of August 7, 2018.
Gryphon is comprised of 24 primarily basement-hosted stacked lenses referred to as the A-series, B-series,
C-series, D-series and E-series lenses, which are interpreted to be stacked to form a zone of mineralization
measuring approximately 280 metres long by 113 metres wide, with each lens having variable thicknesses
and generally plunging to the northeast and dipping to the southeast (See Figure 2) . Four high- grade
domains have been established within the A1 and D1 lenses. The A1 high-grade domain represents 40%
of the total Indicated Mineral Resources estimated for the deposit; whereas the combination of the three
D1 high-grade domains represent approximately 10% of the total Indicated Mineral Resources.
Potential future development of the Gryphon deposit has been assessed as an underground mining
operation at a PFS level in 2018 with a cost update completed in 2023. The outcomes of the study highlight
robust economics with an estimated after -tax base-case Net Present Value (“NPV”) of $864.2 million and
internal rate of return (“IRR”) of 37.6%, based on estimated Probable Reserves of 49.7 million pounds U3O8
(1,275,000 tonnes at 1.8% U3O8), a uranium selling price of USD$75/lb U3O8 ($101.25/lb U3O8), and an 8%
discount rate. Gryphon’s cash operating costs are estimated to be USD$12.75/lb U3O8, and its all-in cost
of production (including initial capital costs of CAD$737 .4 million) is estimated to be US$25.47/lb U 3O8.
Accordingly, Gryphon has the potential to be competitive with the lowest cost uranium mining operations in
the world.
Discovery of Additional High-Grade Mineralization Associated with the D1 lens
The D series lenses were targeted for potential mineral resource expansion in 2025 given their high-grade,
structurally controlled nature, and that previous drilling left the mineralization partially open in the down-
plunge and along-strike directions. Prior to this program, no significant expansion drilling has occurred
proximal to Gryphon since 2018.
The last drill hole of the 2025 program (WR-837AD2) encountered high -grade uranium mineralization,
which is interpreted to expand the extent of the D1 zone by ~40 metres in the down-plunge direction. This
drill hole tested a 100-metre gap in the previous drill hole spacing (see Figure 3) and justifies further follow-
up drilling to test to additional down-plunge extension as well as the potential for along strike continuation.
Drill hole WR -836 was also completed in the expansion area and also encountered notable uranium
mineralization, which indicates the system is open along strike to the north.
Denison reports its initial drilling results as radiometric equivalent uranium (“%eU3O8") from a calibrated,
triple gamma, down-hole probe. All mineralized intersections have been sampled for chemical U3O8 assay
and final results will be compiled following receipt of the data.
Table 1: Drill hole intercepts by lens for WR-836 and WR-837AD2.1
Drill Hole Lens
From
(m)
To
(m)
Length
(m)5 %eU3O82
WR-8361 D13 800.3 800.8 0.5 0.40
WR-837AD21 D13 834.6 836.9 2.3 1.69
(includes)4 835.6 836.1 0.5 5.48
Notes:
1. Drill hole orientation (azimuth/dip) for WR-836 is 306.8o/-73.4o and for WR-837AD2 is 311.1o/-71.0o
2. eU3O8 is radiometric equivalent uranium from a calibrated total gamma down-hole probe. All intersections have been
sampled for chemical U3O8 assay
3. Intersection interval is composited above a cut-off grade of 0.05% eU3O8
4. Intersection interval is composited above a cut-off grade of 2.0% eU3O8
5. As most of the drill holes are oriented steeply toward the northwest and the basement mineralization is interpreted to
dip moderately to the southeast, the true thickness of the mineralization is expected to be approximately 85% of the
intersection lengths
2025 Delineation Drill Program Highlights
A total of ~12,500 metres of diamond drilling was completed in seventeen drill holes and multiple off cuts
during the 2025 delineation program at Gryphon. Overall, the delineation program confirmed the current
geological interpretation of the deposit and supported the grade-thickness (GT) assumptions in the resource
block model.
The A1 lens was the primary focus of the drill program as the high-grade and low-grade domains contain
approximately 50% of the estimated Indicated Mineral Resource for Gryphon. Several drill holes intersected
the A1 high-grade domain and established additional continuity within the A-series lenses.
The B and C series lenses are located below the A series within the center of the deposit and were also
intersected as part of the 2025 delineation program . Together the B and C series lenses account for
approximately 20% of the total estimated Indicated Mineral Resources.
Several drill holes encountered significant results , demonstrating the high- grade nature of Gryphon,
including the following results from WR-831D1D2, which tested the primary lenses and returned the best
mineralized intercepts from the delineation program:
Table 2: Drill hole intercepts by lens for WR-831D1D2.1
Lens
From
(m)
To
(m)
Length
(m)6 %eU3O82
A43 655.6 657.3 1.7 0.87
A33 664.9 667.3 2.4 0.20
A23 682.5 684.3 1.8 0.76
A13 689.3 700.3 11.0 1.76
(includes)4 692.6 694.4 1.8 3.85
(includes)4 695.3 697.2 1.9 5.28
B13 701.2 708.0 6.8 0.13
B23 713.0 717.4 4.4 0.14
B33 721.0 735.5 14.5 2.13
(includes)4 723.9 725.7 1.8 6.38
(includes)4 727.1 727.6 0.5 2.60
(includes)4 731.5 734.0 2.5 6.16
B3 (continued)3 737.5 743.8 6.3 0.91
(includes)4 740.1 740.7 0.6 3.42
Notes:
1. Drill hole orientation (azimuth/dip) 295.8o/-77.0o
2. eU3O8 is radiometric equivalent uranium from a calibrated total gamma down-hole probe. All intersections have been
sampled for chemical U3O8 assay
3. Intersection interval is composited above a cut-off grade of 0.05% eU3O8
4. Intersection interval is composited above a cut-off grade of 2.0% eU3O8
5. Intersections with less than 0.5 GT were left out of the table to simplify the results
6. As most of the drill holes are oriented steeply toward the northwest and the basement mineralization is interpreted to
dip moderately to the southeast, the true thickness of the mineralization is expected to be approximately 85% of the
intersection lengths
Additional Data Collected for Future De-risking and Study Work
Approximately 250 kg of whole-core samples were collected for metallurgical test work. Metallurgical test
programs are being developed to assess uranium recoveries to advance the evaluation work completed to
support the 2018 and 2023 PFS.
Geotechnical logging was completed on all drill holes and hydrogeological information was collected from
two of the drill holes which were outfitted with vibrating wire piezometers (VWPs). The information collected
from these exercises is expected to increase the understanding of different hydrogeological zones to
support future mine-design planning.
This work adds to the extensive database of geological, hydrogeological, geotechnical, and metallurgical
data for Gryphon. This site -specific data is expected to be used to validate certain key assumptions in
potential future technical studies further evaluating the Gryphon deposit for underground mining.
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. The project is host to the high- grade Phoenix and
Gryphon uranium deposits, discovered by Denison i n 2008 and 2014, respectively, and is a joint venture
between Denison (90% and operator) and JCU (Canada) Exploration Company Limited ("JCU", 10%). In
August 2023, Denison filed a technical report summarizing the results of (i) the feasibility study completed
for ISR mining of the high-grade Phoenix uranium deposit and (ii) a cost update to the 2018 Pre-Feasibility
Study for conventional underground mining of the basement -hosted Gryphon uranium deposit. More
information on the studies is available in the te chnical report titled "NI 43 -101 Technical Report on the
Wheeler River Project Athabasca Basin, Saskatchewan, Canada" dated August 8, 2023, with an effective
date of June 23, 2023, a copy of which is available on Denison's website and under its profile on SEDAR+
at www.sedarplus.ca and on EDGAR at www.sec.gov/edgar.shtml.
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 several notable milestones were achieved in 2024 with the submission of federal
licensing documents and the acceptance of the final form of the project's Environmental Impact Statement
by the Province of Saskatchewan and the Canadian Nuclear Safety Commission.
About Denison
Denison is a uranium mining, exploration and development company with interests focused in the
Athabasca Basin region of northern Saskatchewan, Canada. In addition to Denison's effective 95% interest
in its flagship Wheeler River Project, 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 Midwest Joint Venture's 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
~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 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.
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
Qualified Persons
The technical information contained in this press release has been reviewed and approved by Chad Sorba,
P.Geo., Denison's Vice President Technical Services & Project Evaluation, who is a 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 identified by the use of forward- looking terminology 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: scope, objectives and interpreted
results of the Gryphon delineation program; future plans, including potential future exploration potential and metallurgical test
programs; and expectations regarding its joint venture ownership interests and the continuity of its agreements with its partners and
third parties. Statements relating to ‘mineral reserves’ or ‘mineral resources’ are deemed to be forward- looking information, as they
involve the implied assessment, based on certain estimates and assumptions that the mineral reserves and mineral resources
described can be profitably produced in the future.
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, the modelling and assumptions upon which the plans for Wheeler River are based may not be maintained
after further work is completed. In addition, Denison may decide or otherwise be required to discontinue testing, evaluation and other
work if it is unable to maintain or otherwise secure the necessary resources (such as testing facilities, capital funding, 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 accurate and results may differ materially from 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, 2025 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
Figure 1: Wheeler River Property Map
Figure 2: Plan View of Gryphon Deposit
Figure 3: Location and Interpretation of Drill Holes WR-836 and WR-837AD2
Inclined Longitudinal Section (left) Isometric Cross-section (right)