DML.TO · 2017-05-26 12:00:00

Denison Reports Assays Increase Grades BY 45% and Deliver Most Meaningful Gryphon D-Lens Result to Date at Wheeler River

Drill Results

Denison Mines Corp.

1100 – 40 University Ave

Toronto, ON M5J 1T1

www.denisonmines.com

@DenisonMinesCo

PRESS RELEASE

DENISON REPORTS ASSAYS INCREASE GRADES BY 45%

AND DELIVER MOST MEANINGFUL GRYPHON D-LENS RESULT

TO DATE AT WHEELER RIVER

Toronto, ON – May 26, 2017 Denison Mines Corp. (“Denison” or the “Company”) (DML: TSX, DNN: NYSE

MKT) is pleased to report a significant increase in uranium grades from previously released preliminary

radiometric probe results, following the receipt of uranium assays from the Company’s winter 2017 drilling

program on the 60% owned Wheeler River project. The winter 2017 explorat ion program involved a

combination of infill drilling at the Gryphon deposit and resource expansion exploration drilling to the

northwest of the Gryphon deposit. The Wheeler River project is host to the high-grade Gryphon and

Phoenix uranium deposits, and is the largest undeveloped high-grade uranium project in the infrastructure

rich eastern portion of the Athabasca Basin region in northern Saskatchewan.

The Company currently reports prelimi nary radiometric equivalent grades ("eU 3O8"), derived from a

calibrated downhole total gamma probe, during its exploration programs and subsequently reports definitive

assay grades following sampling and geochemical analysis of the mineralized drill core.

Highlights

 As has been the case in past years, assays returned higher grades of U 3O8 than the preliminary

eU3O8 reported during the drilling program. For the winter 2017 results, assay grades greater than

0.5% U3O8 were on average 45% higher than their corresponding radiometric equivalent grades;

 Drill hole WR-633D3 returned assay results of 3.3% U 3O8 over 13.5 metres, 6.2% U 3O8 over 2.5

metres and 1.3% U3O8 over 3.0 metres within the D series lenses. This result represents the best

hole drilled to date, in terms of combined grade s and thicknesses of mineralization, from the

mineralized zone identified to the northwest of t he current resources estimated for the Gryphon

deposit.

In November 2015, the Company estimated the Gry phon deposit to contain inferred resources of 43.0

million pounds U3O8 (above a cut-off grade of 0.2% U3O8) based on 834,000 tonnes of mineralization at an

average grade of 2.3% U 3O8, occurring as a series of stacked lenses on various stratigraphic, fault-

controlled planes within the basement rocks – termed the A, B, and C series lenses. Since then, a

significant zone of new mineralization has been discovered and partially delineated to the northwest, termed

the D series of lenses, in combination with the discovery of additional mineralization on the A and B planes.

Taken together, results from exploration drilling si nce the beginning of 2016, has defined a mineralized

zone that comprises multiple lenses spanning over 300 metres in strike length and remains open.

Dale Verran, Denison’s Vice President of Exploration, commented, “This set of Gryphon assay results have

exceeded expectations – particularly for drill hole WR -633D3, which now ranks as the best hole to date

in the D series of lenses. These results re-emphasi ze the potential of the D series lenses to add

meaningful resources to the Gryphon deposit, ahead of a planned update to the resource estimate for

the project. This summer, in addition to the ongoing infill drilling at Gryphon, we are planning to continue

to explore the D lenses with the objective of defini ng high-grade zones and maximizing the indicated

resources that will be included in the upcoming PFS”

The Company is also pleased to re port the assay results from its in fill drilling program at the Gryphon

deposit, including the results of a further 17 drill hol es, totaling 8,402 metres. The results confirm the

continuity and high-grades of Gryphon’s A, B and C series inferred resources and indicate potential for

resource growth with higher than expected assay grades compared to the inferred grade model in certain

portions of the deposit. A further 18 drill holes are planned to be completed during the summer 2017

program to complete the infill program at Gryphon.

Technical Highlights From Assay Results

Winter 2017 assay results for ex ploration drilling are provided in Table 1. Nine holes totalling 6,330

metres were completed outside of the current infe rred resources estimated for the Gryphon deposit,

including four holes targeting the Gryphon D seri es lenses, and five holes down-dip of the A and B

series lenses. The highlights from these result s illustrate the potential for meaningful resource

expansion at Gryphon:

 3.3% U3O8 over 13.5 m (including 11.8% U3O8 over 3.5 m) D series mineralization in WR-633D3

 6.2% U3O8 over 2.5 m D series mineralization in WR-633D3

 1.3% U3O8 over 3.0 m (including 3.8% U3O8 over 1.0 m) D series mineralization in WR-633D3

 2.9% U3O8 over 3.0 m (including 8.5% U3O8 over 1.0 m) B series mineralization in WR-689

 8.6% U3O8 over 1.0 m D series mineralization in WR-689

 15.1% U3O8 over 1.0 m D series mineralization in WR-689

In addition to exploration drilling to expand mineralization outside of the current Gryphon resource, the

2017 winter drilling program continued with infill and delineation drilling with the objective of increasing

the level of confidence of the current inferred resources to an indicated level. Winter 2017 assay results

from infill and delineation drilling are provided in Table 2, and represent an overall increase in grade

and thicknesses of mineralization in comparison to the previously reported radiometric equivalent

grade results (see Denison’s press releases dated March 29, 2017 and April 20, 2017). Highlights

from the infill results include the following results:

 7.3% U3O8 over 6.0 m (including 10.9% U3O8 over 4.0 m) A series mineralization in WR-567D2

 1.9% U3O8 over 6.6 m (including 3.4% U3O8 over 3.0 m) B series mineralization in WR-567D2

 5.1% U3O8 over 7.0 m (including 7.6% U3O8 over 4.5 m) A series mineralization in WR-567D1

 5.5% U3O8 over 3.5 m B series mineralization in WR-567D1

 4.0% U3O8 over 9.0 m A series mineralization in WR-687D2

 4.3% U3O8 over 6.0 m (including 8.2% U3O8 over 3.0 m) A series mineralization in WR-582D2

 3.1% U3O8 over 5.5 m (including 8.0% U3O8 over 2.0 m) A series mineralization in WR-606D2

 2.8% U3O8 over 5.5 m (including 14.2% U3O8 over 1.0 m) A series mineralization in WR-688D3

 1.6% U3O8 over 8.0 m (including 11.6% U3O8 over 1.0 m) A series mineralization in WR-688D2

Illustrative Figures & Further Details

A plan map of the Gryphon A, B, C and D series lenses is provided in Figure 1. The inset on Figure 1 shows

a schematic cross section of the A, B, C and D series lenses and their respective inclined longitudinal

section windows (as shaded rectangles). Figures 2 to 5 provide inclined longitudinal sections of the Gryphon

A, B, C and D series lenses respectively. The modelled mineralized lenses shown in Figures 1 to 5 are

defined using a 0.05% U 3O8 or eU 3O8 grade shell and minimum thickness of two metres. There is no

certainty that the modelled mineralized lenses shown will constitute future mineral resources and they may

be subject to modifications as further drilling data becomes available.

Further details regarding the Gryphon deposit and the current mineral resource estimates are provided in

the NI 43-101 Technical Report for the Wheeler River project titled “Preliminary Economic Assessment for

the Wheeler River Uranium Project, Saskatchewan, Canada" dated April 8, 2016 with an effective date of

March 31, 2016. A copy of this report is avail able on Denison’s website and under its profile on SEDAR

at www.sedar.com and on EDGAR at www.sec.gov/edgar.shtml.

Sampling and Assay Procedures

Drill core with anomalous total gamma radioactivity (>500 counts per second) 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 assays are performed by the

Saskatchewan Research Counc il ("SRC") Geoanalytical Laborat ories using an ISO/IEC 17025:2005

accredited method for the determination of U 3O8 weight %. Sample preparation involves crushing and

pulverizing core samples to 90% passing -106 microns. The resultant pulp is digested using aqua-regia and

the solution analyzed for U3O8 weight % using ICP-OES. Core recovery at Gryphon is typically 100% and

therefore radiometric equivalent U 3O8 grades ("eU 3O8") are not required as a substitute for chemical

U3O8 assays. In addition to internal checks by SRC Geoanalytical Laboratories, the Company has rigorous

quality assurance and quality control ("QAQC") procedur es 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 23, 2017 filed under

the Company's profile on SEDAR (www.sedar.com).

Detailed Assay Results

The following tables provide the detailed assay results from the drill holes completed during the winter 2017

exploration program at Wheeler River. The assay results are shown next to the previously reported

radiometric equivalent results, and have been assigned a lens designat ion based on the stratigraphic

position of the mineralized interval.

Table 1: Winter 2017 assay results for exploration drilling outside of the Gryphon resource

Previously reported

Downhole Total Gamma Probe4,8 Final Assay 5,8

Lens

Section Hole

Number

From

(m)

Length9

(m)

eU3O8

(%)2

From

(m)

Length9

(m)

U3O8

(wt%)3

5175GP

WR-689D1 560.5 561.5 1.0 0.22 560.8 562.8 2.0 0.07 B

and 566.3 567.3 1.0 0.11 Below cut-off grade of 0.05% U3O8 B

and 570.4 571.4 1.0 0.18 571.2 572.2 1.0 0.23 B

and 668.4 669.4 1.0 0.13 668.8 669.8 1.0 0.09 D

and 675.7 676.7 1.0 0.13 673.7 674.7 1.0 0.12 D

and1 Below cut-off grade of 0.1% eU3O8 676.2 677.2 1.0 0.15 D

and 679.7 680.7 1.0 1.6 680.2 681.2 1.0 1.5 D

and 692.3 693.7 1.4 0.23 692.9 694.4 1.5 0.16 D

5200GP

WR-689 557.2 558.6 1.4 0.54 Navigational drilling - no core recovery A

and 561.0 562.0 1.0 0.13 Navigational drilling - no core recovery B

and 564.9 566.8 1.9 2.74 564.0 567.0 3.0 2.9 B

including6,7 565.6 566.6 1.0 5.08 566.0 567.0 1.0 8.5 B

and 573.2 574.2 1.0 0.60 573.0 574.0 1.0 0.95 B

and 584.1 585.1 1.0 0.32 584.0 585.0 1.0 0.19 B

and1 Below cut-off grade of 0.1% eU3O8 666.6 667.6 1.0 0.05 D

and 679.6 680.6 1.0 0.50 680.4 681.4 1.0 0.20 D

and 684.6 685.6 1.0 0.15 685.2 686.2 1.0 0.23 D

and 711.1 712.8 1.7 2.86 712.0 713.0 1.0 8.6 D

and 718.4 719.6 1.2 7.5 719.7 720.7 1.0 15.1 D

WR-633D3 674.6 675.6 1.0 0.12 675.3 676.3 1.0 0.09 B

and 742.8 743.8 1.0 0.11 743.5 744.5 1.0 0.09 D

and 753.3 756.4 3.1 0.75 753.9 756.9 3.0 1.3 D

including6,7 755.3 756.3 1.0 2.0 755.9 756.9 1.0 3.8 D

and 758.6 771.8 13.2 2.5 759.2 772.7 13.5 3.3 D

including6,7 764.3 768.1 3.8 7.8 765.2 768.7 3.5 11.8 D

including1,6,7 Below cut-off grade of 1.0% eU3O8 771.7 772.7 1.0 1.0 D

and 774.6 777.4 2.8 3.7 775.4 777.9 2.5 6.2 D

5225GP

WR-690 585.9 587.0 1.1 0.18 586.9 587.9 1.0 0.21 B

and 593.0 594.0 1.0 0.74 594.0 595.0 1.0 0.62 B

and 654.5 655.5 1.0 0.70 655.6 656.6 1.0 0.66 C

and 722.3 723.3 1.0 0.23 723.4 724.4 1.0 0.16 D

and 726.1 727.1 1.0 0.18 727.4 728.4 1.0 0.16 D

Notes:

1. Result not reported previously

2. eU 3O8 is the radiometric equivalent U3O8 derived from a calibrated total gamma downhole probe

3. U 3O8 is the chemical assay of mineralized split core samples

4. Downhole probe result composited above a cut-off grade of 0.1% eU 3O8 unless otherwise indicated

5. Assay result composited above a cut-off grade of 0.05% U 3O8 unless otherwise indicated

6. Downhole probe result composited above a cut-off grade of 1.0% eU 3O8

7. Assay result composited above a cut-off grade of 1.0% U 3O8

8. Composites compiled using 1.0 metre minimum mi neralization thickness and 2.0 metres maximum waste

9. As the drill holes are oriented steeply toward the nort hwest and the basement mineralization is interpreted to dip

moderately to the southeast, the true thickness of the mineralization is expected to be approximately 75% of the

intersection lengths

Table 2: Winter 2017 assay results for Gryphon resource infill and delineation holes

Downhole Total Gamma Probe4,8 Assay 5,8

Section Hole

Number

From

(m)

Length9

(m)

eU3O8

(%)2

From

(m)

Length9

(m)

U3O8

(wt%)3

Lens

4775GP

WR-584BD1 624.8 627.8 3.0 2.0 626.3 628.3 2.0 4.0 A

including6,7 626.0 627.6 1.6 3.7 626.3 627.8 1.5 5.0 A

and1 Below cut-off grade of 0.1% eU3O8 631.8 632.8 1.0 0.05 B

and 637.6 638.6 1.0 0.11 638.2 639.2 1.0 0.08 B

4825GP

WR-683 No significant mineralization No significant mineralization

WR-683D1 635.8 638.9 3.1 1.8 635.5 639.0 3.5 1.3 A

including6,7 636.2 638.2 2.0 3.5 637.0 639.0 2.0 2.1 A

and 645.2 646.2 1.0 0.31 645.5 646.5 1.0 0.73 B

and 657.5 658.5 1.0 0.46 658.0 659.0 1.0 0.12 B

WR-687D11 Below cut-off grade of 0.1% eU3O8 664.5 665.5 1.0 0.09 A

and 672.0 673.0 1.0 0.40 667.0 674.0 7.0 0.06 A

and 673.4 674.4 1.0 0.10 Merged with interval above A

and 676.6 678.0 1.4 1.6 677.0 678.5 1.5 2.9 B

including6,7 676.8 677.8 1.0 2.2 677.5 678.5 1.0 4.1 B

and 682.7 683.7 1.0 0.55 683.0 684.0 1.0 0.64 B

WR-575D1 626.2 625.9 1.5 0.36 624.0 627.0 3.0 0.28 A

and1 Below cut-off grade of 0.1% eU3O8 648.0 650.5 2.5 0.15 B

and1 Below cut-off grade of 0.1% eU3O8 652.5 653.5 1.0 0.05 B

4900GP

WR-6871 Below cut-off grade of 0.1% eU3O8 666.0 667.0 1.0 0.07 A

and 681.4 682.4 1.0 0.14 Below cut-off grade of 0.05% U3O8 A

and 685.0 686.5 1.5 0.88 685.2 686.7 1.5 0.47 A

and 690.8 691.8 1.0 0.12 Below cut-off grade of 0.05% U3O8 B

WR-687D21 Below cut-off grade of 0.1% eU3O8 537.0 538.0 1.0 0.05 A

and 648.9 649.9 1.0 1.8 649.8 650.8 1.0 2.8 A

and 652.8 661.9 9.1 2.5 653.4 662.4 9.0 4.0 A

and1 Below cut-off grade of 0.1% eU3O8 670.0 672.0 2.0 0.09 B

and 676.3 677.3 1.0 0.10 Below cut-off grade of 0.05% U3O8 B

and 686.2 687.4 1.2 0.15 687.2 688.2 1.0 0.24 B

4950GP

WR-567D1 674.3 675.9 1.6 0.33 675.0 676.5 1.5 0.51 A

and 689.8 690.8 1.0 0.66 691.0 693.0 2.0 0.49 A

and 694.9 696.9 2.0 1.3 695.5 696.5 1.0 3.1 A

and 700.0 707.1 7.1 3.9 701.0 708.0 7.0 5.1 A

including6,7 701.1 705.5 4.4 6.1 702.0 706.5 4.5 7.6 A

and 723.1 727.1 4.0 3.8 724.0 727.5 3.5 5.5 B

4975GP

WR-567D21 Below cut-off grade of 0.1% eU3O8 585.8 586.8 1.0 0.06 A

and1 Below cut-off grade of 0.1% eU3O8 663.1 664.1 1.0 0.05 A

and 664.5 665.6 1.1 0.42 664.6 665.6 1.0 0.09 A

and 670.1 671.1 1.0 0.89 670.1 671.1 1.0 1.2 A

and 691.2 692.2 1.0 1.2 691.7 692.7 1.0 0.66 A

and 694.3 695.7 1.4 0.71 695.0 696.0 1.0 0.61 A

and 698.4 704.6 6.2 5.9 698.8 704.8 6.0 7.3 A

including6,7 700.2 704.3 4.1 8.7 700.8 704.8 4.0 10.9 A

and1 Below cut-off grade of 0.1% eU3O8 711.5 712.5 1.0 0.07 B

and 713.5 714.9 1.4 0.22 714.0 716.0 2.0 0.15 B

and 732.8 736.4 3.6 2.1 733.4 740.0 6.6 1.9 B

including6,7 733.0 735.8 2.8 2.6 733.4 736.4 3.0 3.4 B

including1,6,7 Below cut-off grade of 1.0% eU3O8 739.0 740.0 1.0 2.1 B

and 739.0 740.0 1.0 0.40 Merged with interval above B

and 744.8 747.4 2.6 0.28 745.5 748.0 2.5 0.29 B

5100GP

WR-606D21 Below cut-off grade of 0.1% eU3O8 747.5 748.5 1.0 0.09 A

and 764.3 765.3 1.0 0.11 765.0 766.0 1.0 0.05 A

and1 Below cut-off grade of 0.1% eU3O8 770.5 771.5 1.0 0.06 A

and1 Below cut-off grade of 0.1% eU3O8 777.7 778.7 1.0 0.09 A

and 785.4 786.4 1.0 0.15 785.9 786.9 1.0 0.13 A

and 792.4 793.4 1.0 0.11 Merged with interval below A

and 794.2 798.8 4.6 2.0 793.6 799.1 5.5 3.1 A

including6,7 795.9 797.8 1.9 4.1 796.6 798.6 2.0 8.0 A

and 803.5 808.1 4.6 0.45 805.1 808.6 3.5 0.34 B

including6,7 804.6 805.6 1.0 1.5 805.1 806.1 1.0 1.0 B

WR-688D3 758.1 759.1 1.0 0.24 758.5 759.5 1.0 0.38 A

and 762.4 767.7 5.3 2.7 763.0 768.5 5.5 2.8 A

including6,7 764.4 765.7 1.3 9.4 765.0 766.0 1.0 14.2 A

and1 Below cut-off grade of 0.1% eU3O8 770.5 772.5 2.0 0.07 B

and 775.2 776.2 1.0 0.12 Merged with interval below B

and 779.1 780.1 1.0 0.11 Merged with interval below B

and 780.4 781.4 1.0 0.10 Merged with interval below B

and 782.2 785.1 2.9 0.71 775.5 785.5 10.0 0.26 B

including6,7 783.5 784.5 1.0 1.6 784.0 785.0 1.0 1.6 B

and 793.1 794.2 1.1 5.4 793.7 794.7 1.0 9.2 C

5125GP

WR-6881 Below cut-off grade of 0.1% eU3O8 520.6 521.6 1.0 0.09 A

and 774.1 778.9 4.8 0.51 774.5 783.5 9.0 0.30 A

WR-688D2 756.5 757.5 1.0 0.33 757.5 758.5 1.0 0.95 A

and 761.2 762.7 1.5 3.0 762.3 770.3 8.0 1.6 A/B

including6,7 761.3 762.3 1.0 4.3 762.3 763.3 1.0 11.6 A

and 767.5 769.2 1.7 0.47 Merged with interval above B

5150GP

WR-582D2 741.6 742.6 1.0 0.72 741.5 743.0 1.5 0.34 A

and 746.2 752.0 5.8 4.1 746.5 752.5 6.0 4.3 A

including1,6,7 Below cut-off grade of 1.0 % eU3O8 747.5 748.5 1.0 1.0 A

including6,7 748.8 751.6 2.8 8.1 749.0 752.0 3.0 8.2 A

WR-684 796.1 797.1 1.0 0.11 797.6 798.6 1.0 0.14 A

and 813.7 827.9 14.2 0.39 815.1 829.6 14.5 0.46 A

including6,7 813.7 814.7 1.0 1.2 815.1 816.1 1.0 2.1 A

including1,6,7 Below cut-off grade of 1.0 % eU3O8 817.1 818.1 1.0 1.2 A

and 830.5 835.1 4.6 2.5 832.2 836.2 4.0 1.9 B

including6,7 831.0 832.2 1.2 8.3 832.7 833.7 1.0 6.8 B

WR-688D1 766.5 768.9 2.4 0.72 767.5 770.0 2.5 0.32 A

and 775.5 776.5 1.0 0.16 776.5 778.0 1.5 0.15 A

5175GP

WR-684D11 Below cut-off grade of 0.1% eU3O8 794.4 795.4 1.0 0.06 A

and 803.6 805.2 1.6 0.18 805.5 812.5 7.0 0.15 A

and 806.4 807.4 1.0 0.13 Merged with interval above A

and 808.3 810.2 1.9 0.18 Merged with interval above A

and 813.6 815.5 1.9 0.18 815.5 817.5 2.0 0.19 A

and 831.5 832.5 1.0 0.12 833.5 834.5 1.0 0.17 B