Denison Announces Completion of Highly Successful Phoenix Isr Field Test Program
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Denison Mines Corp.
1100 – 40 University Ave
Toronto, ON M5J 1T1
www.denisonmines.com
PRESS RELEASE
DENISON ANNOUNCES COMPLETION OF HIGHLY SUCCESSFUL
PHOENIX ISR FIELD TEST PROGRAM
Toronto, ON – Oct. 28, 2021. Denison Mines Corp. (“Denison” or the “Company”) (TSX: DML, NYSE
American: DNN) is pleased to announce the initial resu lts of a highly successful In-Situ Recovery (“ISR”)
field test program (“2021 ISR Field Test”) completed within the commercial-scale ISR test pattern installed
in the Phase 1 area of the high-grade Phoenix uranium deposit (“Phoenix”) at the Company’s 95% owned
Wheeler River Uranium Project (“Wheeler River” or the “Project”) in northern Saskatchewan.
Achieved the commercial-scale production flow rate assumed in the Pre-Feasibility Study
(“PFS”) prepared for the Project in 2018.
Demonstrated hydraulic control of injected solution during ion tracer test – reporting no
elevated values of the tracer element in the monitoring wells surrounding the commercial-
scale test pattern.
Established breakthrough times between injection and recovery wells, spaced 5 to 10
meters apart, that are consistent with previous ‘Proof of Concept’ hydrogeological
modelling conducted by Petrotek Corporation ("Petrotek").
Completed ‘clean-up phase’ following tracer test demonstrating ability to remediate the test
pattern – reducing tracer concentrations to as low as 4% of peak test levels within eight
days of remediation.
David Cates, Denison’s President & CEO, commented, “We are pleased to have safely and successfully
completed another significant ISR field program at Phoenix. Our evaluation team and field staff have
worked diligently over an eight-month period to expertly carry out a complex project execution plan
that has delivered the data and results necessary for our Company to continue our industry-leading
efforts to further de-risk the application of the ISR mining method in the Athabasca Basin region.
While our previous test work has provided considerable support for the use of ISR at Phoenix, the
achievement of the targeted flowrate from the PFS in a commercial-scale well pattern located within
Phase 1 of Phoenix, and the tangible demonstration of our ability to control fluid flows during the
tracer test, together mark another highly significant de-risking milestone for the Project.
With the field test completed and the Company well capitalized, our technical team is moving full-
steam ahead with the development of our field plans for 2022 while also supporting the recent
launch of the formal feasibility study process.”
The 2021 ISR Field Test program was designed to further increase confidence and reduce risk in the
application of the ISR mining method at Phoenix – with the detailed results providing the necessary datasets
for the permitting and preparation of a planned lixiviant test in 2022, which is expected to support the
completion of the recently announced Feasibility Study (or “FS”) for the Project (see press release dated
September 22, 2021).
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.
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Test Pattern Installation
A test pattern consisting of five commercial-scale wells ("CSWs"), including GWR-038 to GWR-042, and
10 additional small diameter monitoring wells (“MW s”) (together described as the “Test Pattern”), was
successfully installed within t he Phase 1 area of the Phoenix deposit (see Figure 1) during the summer
months (see press release dated July 29, 2021).
Three methods of permeability enhancem ent were successfully evaluated on the five CSWs, with post
permeability enhancement testing resulting in observed improvement in hydraulic responses and inter-well
connectivity within the Test Pattern. These result s exhibit and confirm the ability to engineer additional
access to the natural permeability within the deposit. Permeability enhancement methods included the use
of the MaxPERF drilling tool as well as wireline-con veyed tools designed to per forate and stimulate well
production using a controlled propellant. The wireline tools can effectively “clean out” restricted pathways
within the well screen, well bore, and the geological formation and provide increased flow rates in the wells
by intersecting and connecting to the naturally occurring fractures within the ore zone.
Twenty single-well injection tests were completed on the Test Pattern to evaluate natural permeability and
the efficiency of permeability enhancement methods deployed in the CSWs. Nine single-well pump tests
were completed amongst the five CSWs and four of the MWs to evaluate permeability, sustainable pumping
rates, hydraulic connectivity, and baseline groundwat er conditions. Importantly, testing showed good
hydraulic connection between the CSWs in the ore zone horizon and no significant responses in any of the
MWs in overlying or underlying horizons (see Figure 2). One step-rate injection test was conducted on the
center CSW (GWR-040) to evaluate hydraulic conne ctivity, maximum injection rates and injection
pressures.
Full-Scale Well Pattern Pump and Injection Test
A full-scale well pattern injection and pumping test wa s conducted to determine hydraulic connectivity for
the Test Pattern as a whole, and to evaluate potential production rates for the pattern. The test was run as
a modified 4-spot pattern as there was an unanticipat ed failure of the submersible pump in GWR-042.
During the test, injection rates were matched to pumping extraction rates for balanced flow in the Test
Pattern. Pumped groundwater from each of the out er wells (GWR-038, GWR-039, and GWR-041) was
recycled for injection in the center well (GWR-040) to create a closed system. Production rates for the Test
Pattern achieved a sustainable rate of 45.3 litres per minute (“L/min”) injection in GWR-040 with minimal
pressure on surface balanced with 15.1 L/min extraction at each GWR-038, GWR-039 and GWR-041. This
test fundamentally achieved the 50 L/min flow rate assumed in the PFS for an operating well pattern.
Hydraulic control of the Test Pattern was confirmed by no significant hydrologic responses observed in any
of the overlying or underlying monitoring wells.
Ion Tracer Test
Following the full-scale injection and pumping test, an ion tracer test was completed using the 4 functional
CSWs in the Test Pattern. Flow rates were run at t he same levels as the full-scale well pattern test with
45.3 L/min injection at the center well and a balanced extraction flow of 15.1 L/min at each of the three
outer wells. The ion tracer, consisting of a 15% concentration of potassium chloride (KCl) by weight, was
injected as an initial slug into the Test Pattern at GWR-040, followed by a chase phase involving the
recirculation of water extracted from the three outer wells (closed system). The chase phase continued until
peak concentrations of the ion tracer, measured in to tal dissolved solids (“TDS”), were observed at the
three extraction wells (GWR-038, GWR-039 and GW R-041), followed by a decline in TDS prior to
commencement of a remediation test.
Breakthrough of the ion tracer, as observed by an incr ease in the TDS, occurred at the three extraction
wells within 9 hours (GWR-039), 12 hours (GWR- 041), and 14 hours (GWR-038). These breakthrough
times observed during the field test are consistent with previous hydrogeological modelling conducted by
Petrotek (see press release dated June 4, 2020).
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Remediation Test
After completion of the ion tracer test, a “clean-up” remediation test was conducted to simulate the ability
to remove injected fluid from the Test Pattern. For th is test, injection was halted at the center well (GWR-
040) and the three extraction wells were pumped to remove the remaining injected ion tracer. Tracer
concentrations measured during the eight-day cl ean-up simulation, as observed by field TDS
measurements, declined to as low as 13% of the peak TDS value in GWR-038, 11% of the peak TDS value
in GWR-041, and 4% of the peak TDS value in GWR-039.
Hydrogeological Monitoring
Monitoring during the ion tracer test and subsequent clean-up test included: 376 field measurements of
TDS from the CSW extraction wells to identify tracer concentrations; logging of water levels in each of the
CSWs along with all of the surrounding MWs at five-minute intervals; logging of TDS values at five-minute
intervals in the three overlying MWs to confirm the ab sence of any tracer concentrations in the overlying
horizons; and daily groundwater sampling to send for lab analysis to confirm TDS values measured in the
field and the exact concentration of the KCl tracer.
The ability to maintain hydraulic control was established by sampli ng the three overlying MWs for TDS
values before and after the ion tracer test. No elevated values in TDS were observed during the test, thus
confirming there was no migration of the tracer to overlying horizons.
Data collected as part of the 2021 field progra m will be utilized to update the Phoenix hydrogeological
model, and will provide the necessary data for the permitting and preparation of a lixiviant test planned for
the Test Pattern in 2022.
Ongoing Permeameter Analysis
In addition to the hydrogeological tests described above, over 1,000 drill core samples were collected from
historic holes, re-logged for hydrogeologic charac teristics, and analyzed for permeability utilizing the
permeameter on-site. Samples were selected to en sure the database of on -core permeability results
included representative samples from all of the planned mining phases at Phoenix.
COVID-19
The Company is committed to ensuring that the Wheeler River site is a safe operating environment for its
staff and contractors and that the Company's field activities do not compromise the health and safety of the
residents of northern Saskatchewan. In 2020, the Company's Occupational Health and Safety Committee
in Saskatoon developed a comprehensive guide for the sa fe resumption of work at Wheeler River. The
protocols consider the unique health and safety risks associated with operating a remote work camp amidst
the ongoing COVID-19 pandemic. Public health guidelines and best practices (including testing) have been
incorporated into the Company's protocols.
The 2021 ISR Field Test was completed over an eight-month period and involved the on-site support of
over 100 different staff and contract ors. COVID-19 rapid testing was comp leted regularly at the site, with
no positive cases reported during the entire program. These results demonstrate the effectiveness of the
Company’s COVID-19 protocols and helped to ensure that the extensive scope of the 2021 ISR Field Test
was completed on schedule.
Groundwater Measurement and Sampling Procedures
Individual wells are monitored and logged at five-m inute intervals utilizing In-Situ LevelTROLL 700 Data
Logger transducers installed on cabl es below the water table, providing water level, water pressure, and
temperature data based on factory calibrations. Man ual water level readings are recorded using a Heron
Instruments Inc. water level tape upon commence ment and completion of each log. Flow rates and
cumulative flow volumes are measured ‘in-line’ on injection and extraction hose lines and recorded at four-
hour minimum intervals, using Great Plains Industries Inc. FLOMEC Turbine Stainless Steel Flowmeters
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calibrated to factory specifications. TDS measurements from individual wells are monitored and logged at
five-minute intervals utilizing In-Situ AquaTROLL 200 Data Logger transducers installed on cables below
the water table and in flow cells on surface ‘in-line’ with the extraction hose lines. The AquaTROLLs provide
water level, water pressure, temperature, and con ductivity data based on factory calibration. TDS is
calculated from conductivity measurements via the AquaTROLLs based on factory calibration formulas as
well as field calibrations using standard solutions of known conductivity. T he data from LevelTROLL and
AquaTROLL transducers are downloaded using Win-Situ 5 software. Manual field measurements of TDS,
conductivity, pH, and dissolved oxygen are taken from samples collected from extraction wellhead sample
ports, at 4 hour intervals during active testing, using an YSI ProDSS Handheld Multiparameter Water
Quality Meter. The Water Quality Meter is field calibrated at a minimum of once per week, based on
manufacturer specifications, using solutions of know n pH and conductivity. Groundwater samples for lab
analysis are collected from wells following the Compan y’s standard Groundwater Sampling Procedure for
Wheeler River and are sent to Saskatchewan Resear ch Council ("SRC") Environmental Analytical
Laboratories located in Saskatoon. Samples are collected from the sample port of the wellhead for
extraction wells, during pumping of MWs and after wells are purged. Quality control groundwater samples
for lab analysis included the collection of field duplicate and field blank samples at a rate of 1 in 20, or a
minimum of 1 per month.
For a description of the data verification, assay procedures and the quality assurance program and quality
control measures applied by Denison, please see Denison's Annual Information Form dated March 26,
2021 filed under the Company's profile on SEDAR at www.sedar.com.
About Phoenix Phase 1
As outlined in the Company's news release dated De cember 1, 2020, Denison has decided to adapt its
plans for the Project to use a phased mining approach, which is expected to allow for the targeted extraction
of the least capital-intensive reserv es first, based on the grade and distribution of ore in various areas of
the deposit. The supporting trade-off study provides for mining to occur over 5 phases.
Phase 1 of the deposit is estimated to c ontain approximately 22.2 million pounds U 3O8 (37,242 tonnes at
27.1% U3O8, above a cut-off grade of 0.8% U3O8) in Probable mineral reserves. Based on current designs,
the Company estimates approximately 6.6 million pounds U3O8 (7,717 tonnes at 39.2% U3O8, above a cut-
off grade of 0.8% U3O8) in Probable mineral reserves are contained within the expected operating perimeter
of the CSWs in the Test Pattern (see Figure 1). Thes e estimates are derived as a direct subset of those
reported in the Technical Report titled "Pre-feasib ility Study for the Wheeler River Uranium Project,
Saskatchewan, Canada" dated October 30, 2018 with an effective date of September 24, 2018. The key
assumptions, parameters and methods used to estimate the mineral reserves herein remain unchanged.
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 Gryphon 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 PFS was completed for Wheeler River in 2018, cons idering the potential economic merit of developing
the Phoenix deposit as an ISR operat ion 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 U3O8
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
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 expendi tures 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.
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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 copy 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 66.90% 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 33.8123%)
and Christie Lake (JCU 34.4508%). Denis on’s exploration portfolio includes further interests in properties
covering ~280,000 hectares in the Athabasca Basin region.
Denison is also engaged in mine decommissioning and environmental services through its Closed Mines
group (formerly Denison Environmental Services), which mana ges Denison's Elliot Lake reclamation
projects and provides post-closure mine care and maintenance services to a variety of third-party clients.
For more information, please contact
David Cates (416) 979-1991 ext 362
President and Chief Executive Officer
Shae Frosst (416) 979-1991 ext 228
Investor Relations
Follow Denison on Twitter @DenisonMinesCo
Qualified Persons
The disclosure of scientific or technical inform ation related to certain hydrogeological results and
interpretations (including the hydrogeological investigations carried out as part of the 2021 ISR Field Test
and associated analysis) contained in this release has been reviewed and approved by Mr. David
Bronkhorst, P.Eng, Denison's Vice President, Operat ions and Mr. Andrew Yackul ic, 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 c an be identified by the use of forward-look ing terminology such as ‘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’, ‘be achieved’ or ‘has
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the potential to’.
In particular, this news release contains forward-looking information pertaining to the following: the interpretation of results of the ISR
field program, including expectations regarding further de-risking of the ISR mining method; Denison’s capitalization to enable further
studies; the initiation of the FS and the planned scope, elements, and objectives of the FS; other evaluation activities, objectives and
expectations, including the permeameter analysis and the ongoing EA and related processes; the results of the PFS and expectations
with respect thereto, including the mineral resource estimates and project designs disclosed to-date and the ability to maintain or build
upon such designs; other development and expa nsion plans and objectives; Denison’ s COVID-19 and other health and safety
protocols; and expectations regarding its join t venture ownership interests and the cont inuity 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 are based may not be maintained after further
testing or be representative of actual conditions within the Phoenix deposit. In addition, Denison may decide or otherwise be required
to discontinue its field test ac tivities or other testing, ev aluation and development work at W heeler River if it is unable to maintain or
otherwise secure the necessary resources (such as testing fac ilities, capital funding, regulatory approvals, etc.) or operation s are
otherwise affected by COVID-19 and its potent ially far-reaching impacts. Denison believe s that the expectations reflected in t his
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 fo rward-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 26, 2021 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 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 compar able to similar information made public by U.S. companies subject to the reportin g
and disclosure requirements under the United States federal securities laws and the rules and regulations thereunder. . United States
investors are cautioned not to assume that all or any part of m easured or indicated mineral res ources will ever be converted in to
mineral reserves. United States investors are also cautioned not to assume that all or any part of an inferred mineral resource exists,
or is economically or legally mineable.
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Figure 1: Plan Map Showing Location of Phoenix Deposit (Phase 1) – ISR Test Pattern
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Figure 2: Cross Section Showing Location of Test Pattern Wells at Phase 1