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Osisko Development Completes 13,000-Meter Infill Drilling Program at Cariboo Gold Project and Provides Update on Ongoing Lowhee Underground Drilling; Intercepts Include 44.68 g/t Gold Over 1.5 Meters From 27.9 Meters Downhole, Including 133.62 g/t Gold Over 0.5 Meters From 28.4 Meters Downhole

Press Release

HIGHLIGHTS

  • 13,684 m of grid infill drilling completed (2,659 m new results) on 10-m drill spacing in 142 drill holes from August 2025 representing the entirety of the planned Appian infill program
  • Highlight intercepts include: 44.68 g/t Au over 1.5 m from 27.9 m downhole (including 133.62 g/t Au over 0.5 m from 28.4 m downhole), and 25.78 g/t Au over 2.5 m from 41.3 m downhole (including 103.47 g/t Au over 0.5 m from 42.8 m downhole, and 12.51 g/t Au over 1.0 m from 41.8 m downhole)
  • 2,995 m of additional infill and near mine exploration drilling completed as part of ongoing Lowhee zone underground diamond drilling
  • Highlight intercepts include: 31.64 g/t Au over 2.0 m from 50.0 m downhole (including 125.24 g/t over 0.5 m from 50.5 m downhole), and 11.21 g/t Au over 4.9 m from 63.3 m downhole (including 58.19 g/t Au over 0.7 m from 65.0 m downhole, and 17.57 g/t Au over 0.7 m from 63.3 m downhole).
  • Results to date continue to contribute to a more detailed understanding of spatial controls and local variability within Lowhee Zone and give positive indications for near mine potential

MONTREAL, June 09, 2026 (GLOBE NEWSWIRE) — Osisko Development Corp. (NYSE: ODV, TSXV: ODV) (“Osisko Development” or the “Company”) is pleased to announce new infill drilling results from its completed 13,000-meter program on 10 meter drill spacing, as well as new results from additional infill and near mine exploration activities in the Lowhee Zone of the Company’s permitted, 100%-owned Cariboo Gold Project (the “Project”), located in central British Columbia (“B.C.”), Canada. Three of the six drill hole fans reported herein comprise the final 2,659 meters (“m”) of the 13,000 m underground infill program, bringing the final tally of drilling with full results to 13,684 m. The remaining three fans comprise an additional 2,995 m of infill and near mine exploration drilling at the L1290-ORE-000 and L1260-ORE-002 levels. Reconciliation work is underway on an updated localized block model, with final results anticipated in the second quarter of 2026.

Chris Lodder, President, stated, “The completion of the tighter infill drill spacing gives us a better understanding of vein corridor spatial geometries and local variability specific to this part of the Lowhee deposit, and gives us confidence going forward to help refine infill drill requirements, production designs and sequencing in the Lowhee deposit of the Cariboo Gold Project. The additional infill and near mine exploration intercepts reinforce the importance of continued drilling in underexplored zones.”

DRILL ASSAY HIGHLIGHTS

This news release includes assays from fifty-five (55) underground infill and near mine exploration HQ diamond drill (“DD”) holes (63.5-millimeter diameter) totaling 5,654 m with depths ranging from 76.5 to 138 m (see Table 1 and Figure 2). Select photon and fire assay highlights include:

  • 44.68 grams per tonne (“g/t”) gold (“Au”) over 1.5 m in BMU-25-176 from 27.9 downhole, including:
    • 133.62 g/t Au over 0.5 m from 28.4 m downhole
  • 25.78 g/t Au over 2.5 m in BMU-26-055 from 41.3 m downhole, including:
    • 103.47 g/t Au over 0.5 m from 42.8 downhole, and
    • 12.51 g/t Au over 1.0 m from 41.8 downhole
  • 31.64 g/t Au over 2 m in BMU-26-034 from 50.0 m downhole, including:
    • 125.24 g/t Au over 0.5 m from 50.5 m downhole, and
  • 11.21 g/t Au over 4.9 m in BMU-26-031 from 63.3 m downhole, including:
    • 58.19 g/t Au over 0.7 m from 65.0 m downhole, and
    • 17.57 g/t Au over 0.7 m from 63.3 m downhole
  • 21.84 g/t Au over 2.5 m in BMU-26-008 from 79.7 m downhole, including:
    • 91.3 g/t Au over 0.5 m from 79.7 m downhole, and
    • 6.79 g/t Au over 0.5 m from 81.2 m downhole, and
    • 5.97 g/t Au over 0.5 m from 80.7 m downhole, and
    • 2.66 g/t Au over 0.5 m from 80.2 m downhole, and
    • 2.47 g/t Au over 0.5 m from 81.7 m downhole
  • 91.99 g/t Au over 0.5 m in BMU-26-013 from 73.75 m downhole
  • 18.59 g/t Au over 2.65 m in BMU-26-006 from 43.35 m downhole, including:
    • 48.93 g/t Au over 1.0 m from 43.85 m downhole
  • 4.76 g/t Au over 6.05 m in BMU-26-037 from 85.0 m downhole, including:
    • 44.79 g/t Au over 0.5 m from 88.5 m downhole, and
    • 6.13 g/t Au over 0.5 m from 88.0 m downhole, and
    • 4.02 g/t Au over 0.5 m from 87.0 m downhole
  • 3.28 g/t Au over 7.3 m in BMU-25-179 from 81.7 m downhole, including:
    • 12.73 g/t Au over 0.95 m from 84.85 m downhole, and
    • 9.68 g/t Au over 0.9 m from 85.8 m downhole
  • 46.37 g/t Au over 0.5 m in BMU-26-022 from 14.0 m downhole

Complete assay highlights, including true width estimates, are presented in Table 1 and drill hole locations and orientations are listed in Table 2. Intervals not recovered were assigned zero grade. Top cuts have not been applied to high grade assays.

DISCUSSION OF RESULTS

  • Figures 4-6 (1260 level): Cut-off assay composites completing the planned 13,000 m systematic grid infill program. These last three fans were testing areas peripheral to reserve stopes, and outside the modeled vein corridors. Intercepts received to date suggest possible extensions of vein corridors, with potential for resource conversion and upside mineralization.
  • Figures 7-8 (1290 Level): Cut-off assay composites from additional infill drilling at the 1290 levels show a degree of spatial correlation with the modelled reserve stopes with intercepts outside these areas suggesting potential for resource conversion and upside mineralization.
  • Figure 9 (1260 Level): Cut-off assay composites from infill and near mine exploration drilling to the southeast at the 1260 level include several new intercepts outside the current vein corridors and resource footprint.
  • All intercepts will be incorporated in the planned remodelling and mineral resource calculation process to determine their implications on an updated local block model and any potential adjustments to planned reserve stopes. In certain areas, this may support the addition of new planned reserve stopes, subject to the final estimation process outcome.

Figure 1: Cariboo Gold Project deposit map with Location of Lowhee Zone and Cow Portal underground access.

Figure 2: Location and overview of ongoing Lowhee Zone underground definition infill and near mine exploration diamond drilling

Figure 3: Lowhee Zone select underground drilling highlights (plan view).

Figure 4: L1260-ORE-003 Lowhee Zone grid infill select underground drill assay highlights (this release) with previously released surface and underground diamond drilling results in cross section by fan. Results from immediately adjacent fans within slice omitted for visual clarity (20 m slice looking 048°).

Figure 5: L1260-ORE-003 Lowhee Zone grid infill select underground drill assay highlights (this release) with previously released surface and underground diamond drilling results in cross section by fan. Results from immediately adjacent fans within slice omitted for visual clarity (20 m slice looking 060°).

Figure 6: L1260-ORE-003 Lowhee Zone grid infill select underground drill assay highlights (this release) with previously released surface and underground diamond drilling results in cross section by fan. Results from immediately adjacent fans within slice omitted for visual clarity (20 m slice looking 073°).

Figure 7: L1290-ORE-000 Lowhee Zone infill select underground drill assay highlights (this release) with previously released surface and underground diamond drilling results in cross section by fan. Results from immediately adjacent fans within slice omitted for visual clarity (20 m slice looking 017°).

Figure 8: L1290-ORE-000 Lowhee Zone infill select underground drill assay highlights (this release) with previously released surface and underground diamond drilling results in cross section by fan. Results from immediately adjacent fans within slice omitted for visual clarity (20 m slice looking 025°).

Figure 9: L1260-ORE-002 Lowhee Zone infill and near mine exploration select underground drill assay highlights (this release) with previously released surface and underground diamond drilling results in cross section by fan. Results from immediately adjacent fans within slice omitted for visual clarity (20 m slice looking 051°).

Table 1: Length weighted assay composites and individual samples>=1.8 g/t for Lowhee Zone underground DD.

Drillhole ID   From (m) To (m) Length (m) Au (g/t) Est. True Width (m)
BMU-25-167   14.8 15.8 1 2.11 0.89
Including 14.8 15.3 0.5 3.23
49.4 50.4 1 2.23 0.77
Including 49.4 49.9 0.5 3.84
BMU-25-170 4 4.5 0.5 10.57 0.43
13.55 14.55 1 4.00 0.82
Including 14.05 14.55 0.5 7.86
41.5 42 0.5 5.45 0.43
58.5 59.5 1 2.84 0.91
Including 58.5 59 0.5 5.40
80.5 82 1.5 3.18 1.36
Including 80.5 81.5 1 4.69
BMU-25-173 17 17.5 0.5 2.53 0.43
BMU-25-176 3 3.55 0.55 2.46 0.28
27.9 29.4 1.5 44.68 1.36
Including 28.4 28.9 0.5 133.62
BMU-25-179   81.7 89 7.3 3.28 6.96
Including 84.85 85.8 0.95 12.73
and 85.8 86.7 0.9 9.68
90.5 92.4 1.9 2.01 1.87
Including 90.5 91 0.5 7.02
BMU-26-001   44.7 46.2 1.5 1.86 1.36
Including 45.2 45.7 0.5 4.78
BMU-26-002   31.7 34.2 2.5 7.08 2.27
Including 32.2 32.7 0.5 32.31
and 33.2 33.7 0.5 2.30
48.2 50.3 2.1 10.09 1.90
Including 48.9 49.8 0.9 23.31
65.8 68.1 2.3 9.52 2.08
Including 65.8 66.4 0.6 5.02
and 66.4 67.1 0.7 26.38
74 78.7 4.7 1.96 4.26
Including 78.2 78.7 0.5 16.64
BMU-26-003   1.5 3.1 1.6 2.47 1.45
Including 2 2.6 0.6 6.09
35.5 39 3.5 2.12 3.45
Including 35.5 36 0.5 12.60
73.35 75.85 2.5 7.30 2.46
Including 73.85 74.6 0.75 5.39
and 74.6 75.35 0.75 18.36
BMU-26-004 58.5 59 0.5 3.11 0.41
66.5 67 0.5 2.85 0.43
BMU-26-005   1 3.25 2.25 4.70 1.59
Including 1 1.5 0.5 12.10
and 2.75 3.25 0.5 8.91
14 16 2 5.28 1.41
Including 14 15 1 10.40
17.5 18.5 1 12.24 0.77
Including 18 18.5 0.5 23.47
30.9 31.9 1 7.13 0.82
Including 30.9 31.4 0.5 14.12
37 38 1 2.34 0.71
Including 37.5 38 0.5 4.52
40 41.5 1.5 4.13 0.86
Including 40 40.5 0.5 10.91
58 64 6 2.10 4.12
Including 62 62.5 0.5 10.88
and 62.5 63 0.5 10.99
76.25 78.8 2.55 5.92 1.18
Including 76.75 77.25 0.5 23.10
and 78.3 78.8 0.5 6.86
80.05 81.1 1.05 4.98 0.60
Including 80.05 80.55 0.5 7.50
and 80.55 81.1 0.55 2.68
90 91 1 2.18 0.64
Including 90 90.5 0.5 4.22
104.5 105 0.5 2.97 0.32
117.05 119.05 2 6.06 1.15
Including 117.55 118.05 0.5 4.97
and 118.05 118.55 0.5 17.27
128 129 1 1.96 0.71
137.4 138 0.6 9.22 0.42
BMU-26-006   2.95 3.95 1 12.53 0.71
Including 3.45 3.95 0.5 24.91
33.9 35.9 2 3.79 1.64
Including 34.9 35.4 0.5 11.52
and 35.4 35.9 0.5 2.63
43.35 46 2.65 18.59 1.70
Including 43.85 44.85 1 48.93
55.85 56.35 0.5 2.28 0.32
BMU-26-007 No Significant Assays
BMU-26-008 5.5 6 0.5 2.74 0.41
11.9 12.4 0.5 1.90 0.41
23 23.5 0.5 4.72 0.38
25 25.5 0.5 3.09 0.50
29 29.5 0.5 3.04 0.50
79.7 82.2 2.5 21.84 1.92
Including 79.7 80.2 0.5 91.30
and 80.2 80.7 0.5 2.66
and 80.7 81.2 0.5 5.97
and 81.2 81.7 0.5 6.79
and 81.7 82.2 0.5 2.47
98.1 99.1 1 4.33 0.64
Including 98.1 98.6 0.5 2.79
and 98.6 99.1 0.5 5.87
BMU-26-009 No Significant Assays
BMU-26-010   47.5 52.45 4.95 1.88 4.39
Including 47.5 48 0.5 6.10
and 48.5 49 0.5 7.42
and 51.45 51.95 0.5 2.77
63.45 65.6 2.15 2.53 2.08
Including 63.45 64 0.55 8.41
69 69.5 0.5 2.58 0.43
111.95 115 3.05 2.10 2.87
Including 111.95 112.5 0.55 8.80
BMU-26-011 31.9 32.4 0.5 16.65 0.41
35 36 1 2.61 0.91
Including 35 35.5 0.5 3.61
37.5 38 0.5 4.43 0.50
49 52 3 5.81 2.82
Including 49 49.5 0.5 8.54
and 51 51.5 0.5 24.00
55.2 55.7 0.5 7.31 0.45
66.45 69 2.55 6.93 2.02
Including 66.45 66.95 0.5 30.60
and 66.95 67.45 0.5 4.21
73 73.5 0.5 2.29 0.45
79 79.5 0.5 2.33 0.41
BMU-26-012 15.5 16 0.5 3.66 0.38
BMU-26-013 46 46.5 0.5 2.45 0.38
62 66.5 4.5 3.09 4.03
Including 63.25 63.75 0.5 2.15
and 63.75 64.25 0.5 6.20
and 64.25 64.75 0.5 17.14
68 71.5 3.5 2.05 3.29
Including 70.5 71 0.5 12.14
73.75 74.25 0.5 91.99 0.45
BMU-26-014 2 2.5 0.5 8.09 0.41
4.5 5 0.5 3.22 0.49
35 39.2 4.2 4.24 3.22
Including 35 35.5 0.5 2.42
and 37 37.7 0.7 22.40
51 52.15 1.15 4.98 1.00
Including 51 51.4 0.4 9.32
and 51.4 51.8 0.4 2.21
and 51.8 52.15 0.35 3.20
59.8 60.3 0.5 9.92 0.41
61.8 62.3 0.5 8.69 0.45
65.1 66.3 1.2 10.35 1.09
Including 65.8 66.3 0.5 24.70
76.7 78.2 1.5 2.17 1.30
Including 76.7 77.2 0.5 5.16
86.5 87 0.5 6.19 0.47
92 95 3 1.94 2.66
Including 93.6 94.5 0.9 5.52
BMU-26-015 4 4.5 0.5 3.37 0.49
13.75 14.75 1 2.87 0.82
Including 13.75 14.25 0.5 5.47
82 82.5 0.5 5.39 0.43
BMU-26-016 39 39.5 0.5 2.67 0.47
44.6 47.6 3 1.90 2.86
Including 45.1 45.6 0.5 10.11
65.5 71.3 5.8 3.11 5.65
Including 66.5 67 0.5 3.53
and 67 67.5 0.5 2.64
and 69.1 69.6 0.5 12.06
and 70.2 70.7 0.5 15.87
86 86.5 0.5 2.78 0.43
88.8 89.3 0.5 1.92 0.43
92.9 93.4 0.5 2.23 0.47
BMU-26-017 4.7 5.3 0.6 4.98 0.58
40.1 40.6 0.5 6.76 0.32
51 51.5 0.5 2.23 0.47
67.5 68 0.5 3.21 0.50
88 94 6 3.40 4.24
Including 89.15 89.8 0.65 26.50
BMU-26-018   27.5 32.35 4.85 4.39 4.40
Including 29.6 30.35 0.75 25.33
34.9 35.4 0.5 3.08 0.47
49.1 50.6 1.5 1.81 1.36
Including 49.6 50.1 0.5 4.72
74.25 75.75 1.5 2.19 1.30
Including 75.25 75.75 0.5 6.32
BMU-26-019 14.2 14.7 0.5 24.53 0.48
21.2 21.7 0.5 19.65 0.47
42.5 47.2 4.7 3.71 4.17
Including 43 43.5 0.5 11.11
and 44 44.5 0.5 9.14
and 44.5 45 0.5 7.40
and 45 45.5 0.5 2.85
and 46.6 47.2 0.6 2.63
70.4 70.9 0.5 5.95 0.47
BMU-26-020 45.5 46.1 0.6 3.47 0.56
BMU-26-021 1.95 2.45 0.5 3.04 0.50
27.7 28.2 0.5 4.33 0.50
32.45 32.95 0.5 6.50 0.43
38 38.5 0.5 2.44 0.50
70.2 70.7 0.5 2.75 0.48
BMU-26-022 14 14.5 0.5 46.37 0.45
62.1 63.1 1 2.17 0.92
Including 62.6 63.1 0.5 3.09
BMU-26-023 47.7 48.2 0.5 1.89 0.47
51.7 52.2 0.5 2.51 0.47
BMU-26-024   10.5 14.5 4 3.16 3.86
Including 11.55 12.15 0.6 19.60
96 97.7 1.7 2.92 1.60
Including 97.1 97.7 0.6 8.02
99.5 100 0.5 2.02 0.47
BMU-26-025 14.5 15 0.5 22.27 0.49
43 47.5 4.5 2.25 4.33
Including 43 43.5 0.5 5.52
and 45.5 46 0.5 8.60
and 46 46.5 0.5 4.24
49.75 51.75 2 2.89 1.93
Including 49.75 50.25 0.5 5.78
and 51.25 51.75 0.5 5.69
63 67.5 4.5 1.80 3.99
Including 63.5 64 0.5 4.49
and 66.5 67 0.5 8.63
BMU-26-026   1.2 2.2 1 2.20 1.00
Including 1.2 1.7 0.5 4.17
40 40.5 0.5 3.08 0.38
54.05 55.7 1.65 4.67 1.55
Including 54.55 55.2 0.65 11.08
60 63.9 3.9 2.16 3.66
Including 62.4 63.4 1 3.08
and 63.4 63.9 0.5 9.10
BMU-26-027 2.45 3.2 0.75 10.30 0.68
97.5 98.1 0.6 5.07 0.56
104.9 105.4 0.5 3.17 0.45
109.6 111.8 2.2 2.34 1.91
Including 109.6 110.1 0.5 5.28
and 110.8 111.3 0.5 4.47
BMU-26-028   3.2 5.6 2.4 9.40 1.77
Including 4.9 5.6 0.7 30.77
15.2 15.7 0.5 7.48 0.47
22 24 2 5.86 1.73
Including 23 23.5 0.5 19.10
and 23.5 24 0.5 3.98
45.5 46 0.5 2.16 0.43
59 59.5 0.5 3.20 0.43
64 66 2 3.84 1.64
Including 64 64.5 0.5 11.15
and 65 65.5 0.5 4.06
69.5 70 0.5 2.83 0.41
BMU-26-029   1.6 3.1 1.5 1.83 1.23
Including 2.1 2.6 0.5 4.70
33.4 33.9 0.5 2.02 0.35
39.6 41.3 1.7 4.17 1.39
Including 39.6 40.3 0.7 2.19
and 40.8 41.3 0.5 11.02
BMU-26-030 54.85 55.35 0.5 1.96 0.35
BMU-26-031   4.2 6.55 2.35 5.65 0.80
Including 5.5 6 0.5 24.39
18.85 20.35 1.5 3.00 1.15
Including 19.35 19.85 0.5 7.01
23.1 26.4 3.3 2.65 2.86
Including 23.1 23.6 0.5 4.89
and 24.5 25 0.5 11.61
55 55.5 0.5 3.99 0.43
63.3 68.2 4.9 11.21 4.09
Including 63.3 64 0.7 17.57
and 65 65.7 0.7 58.19
70.2 72.7 2.5 1.84 2.05
Including 71.2 71.7 0.5 3.73
and 72.2 72.7 0.5 4.85
79.1 82.5 3.4 4.29 2.40
Including 79.1 79.6 0.5 8.30
and 80.6 81.25 0.65 14.69
BMU-26-032   36.5 37.5 1 1.87 0.94
Including 36.5 37 0.5 2.05
BMU-26-033 40.5 41 0.5 2.39 0.43
BMU-26-034   50 52 2 31.64 1.73
Including 50.5 51 0.5 125.24
BMU-26-035 10.5 11 0.5 2.01 0.48
48.5 49.5 1 2.53 0.94
Including 48.5 49 0.5 4.64
BMU-26-036 5.5 6 0.5 3.61 0.45
45 46.5 1.5 2.68 1.30
Including 45.5 46 0.5 7.63
60.5 62 1.5 2.14 1.50
Including 61 61.5 0.5 5.40
63.5 64.7 1.2 1.82 0.95
Including 63.5 64 0.5 2.86
87.5 93 5.5 1.85 5.08
Including 87.5 88 0.5 3.00
and 89.15 89.9 0.75 6.01
and 92.35 93 0.65 4.19
102.5 104 1.5 2.37 1.41
Including 102.5 103 0.5 5.79
105 106.5 1.5 2.95 1.41
Including 105 105.5 0.5 4.76
and 105.5 106 0.5 3.86
BMU-26-037 64.5 65 0.5 5.26 0.45
66.5 67 0.5 15.57 0.47
85 91.05 6.05 4.76 5.69
Including 87 87.5 0.5 4.02
and 88 88.5 0.5 6.13
and 88.5 89 0.5 44.79
92 95 3 4.39 2.12
Including 93.5 94.45 0.95 13.13
98.55 99.4 0.85 2.97 0.77
BMU-26-038   32.5 34.5 2 2.36 1.69
Including 32.5 33 0.5 8.33
46.4 46.9 0.5 1.86 0.47
54.8 55.8 1 10.33 0.97
Including 54.8 55.3 0.5 17.57
and 55.3 55.8 0.5 3.09
85.9 90 4.1 3.28 3.87
Including 87.4 87.9 0.5 22.07
BMU-26-039   13 14.5 1.5 3.12 1.49
Including 14 14.5 0.5 7.43
39.65 42 2.35 6.58 2.31
Including 39.65 40.15 0.5 21.76
and 40.15 40.65 0.5 8.54
43 45 2 2.54 1.97
Including 44.5 45 0.5 9.77
64 65 1 4.63 0.82
Including 64.5 65 0.5 8.87
72.55 73.55 1 9.28 0.74
Including 73.05 73.55 0.5 18.45
78.9 79.4 0.5 2.73 0.38
86.9 87.4 0.5 2.38 0.38
BMU-26-040 0 0.5 0.5 3.20 0.47
13.8 14.3 0.5 3.81 0.47
40 46.5 6.5 2.01 6.14
Including 40.5 41 0.5 2.30
and 41 41.5 0.5 3.43
and 41.5 42 0.5 12.82
and 45.5 46 0.5 3.70
65.4 65.9 0.5 2.20 0.45
BMU-26-041 No Significant Assays
BMU-26-042   3.8 5.1 1.3 1.88 1.00
Including 4.5 5.1 0.6 3.39
16.75 17.25 0.5 1.85 0.38
69.3 71.2 1.9 1.82 1.56
Including 70.7 71.2 0.5 5.67
74 76.6 2.6 2.97 2.19
Including 74.5 75 0.5 4.17
and 75.6 76.1 0.5 9.43
BMU-26-043 No Significant Assays
BMU-26-044   56 58 2 6.57 1.53
Including 56.5 57 0.5 25.36
BMU-26-046 20 20.5 0.5 1.98 0.38
44.75 45.25 0.5 3.57 0.47
46.25 47.75 1.5 1.86 1.27
Including 46.25 46.75 0.5 4.67
57.5 58 0.5 2.20 0.38
BMU-26-049   43.95 46 2.05 8.96 1.63
Including 44.45 44.95 0.5 30.06
and 44.95 45.45 0.5 6.30
BMU-26-052   42.4 44.15 1.75 10.26 1.59
Including 42.9 43.65 0.75 20.54
and 43.65 44.15 0.5 4.09
BMU-26-055 2.5 3 0.5 7.29 0.35
  36 37.5 1.5 2.19 1.15
Including 36.5 37 0.5 5.66
41.3 43.8 2.5 25.78 2.38
Including 41.8 42.8 1 12.51
and 42.8 43.3 0.5 103.47
55.25 57.5 2.25 6.11 2.11
Including 55.25 55.75 0.5 9.88
and 56.75 57.5 0.75 11.41
59.6 62.55 2.95 2.84 2.77
Including 61.1 61.65 0.55 13.04
BMU-26-058   59.5 60.8 1.3 2.80 1.18
Including 59.5 60 0.5 4.27
and 60 60.8 0.8 1.89
BMU-26-061 No Significant Assays

Table 2: Underground DD collar locations, drillhole orientations, and max depths. Negative dips point down.

Hole ID Mine Location Easting
(UTM z12N)		 Northing
(UTM z 12N)		 Elevation
(m)		 Dip Azimuth Depth
(m)
BMU-25-167 L1260-ORE-003-DBY-013 596440.667 5882727.084 1264.922 35 137 117
BMU-25-170 L1260-ORE-003-DBY-013 596440.802 5882727.027 1264.291 25 137 105
BMU-25-173 L1260-ORE-003-DBY-013 596440.66 5882727.032 1263.529 15 137 99
BMU-25-176 L1260-ORE-003-DBY-013 596440.812 5882726.873 1262.956 5 137 99
BMU-25-179 L1260-ORE-003-DBY-013 596440.699 5882727.017 1262.574 -5 137 102
BMU-26-001 L1260-ORE-003-DBY-013 596440.714 5882727.075 1262.279 -15 137 84
BMU-26-002 L1260-ORE-003-DBY-013 596440.754 5882727.063 1261.746 -25 137 87
BMU-26-003 L1260-ORE-003-DBY-013 596440.777 5882727.016 1261.3 -35 137 96
BMU-26-004 L1290-ORE-000 596488.88 5882889.094 1291.795 33 288 125
BMU-26-005 L1260-ORE-002 596554.802 5882795.203 1261.637 45 137 138
BMU-26-006 L1260-ORE-003-DBY-013 596440.392 5882727.397 1260.969 -45 137 111
BMU-26-007 L1290-ORE-000 596488.713 5882889.197 1291.557 28 288 120
BMU-26-008 L1260-ORE-002 596554.834 5882795.201 1260.942 35 137 117
BMU-26-009 L1260-ORE-003-DBY-013 596440.323 5882726.661 1264.825 35 148 123
BMU-26-010 L1290-ORE-000 596488.786 5882889.128 1291.264 22 288 117
BMU-26-011 L1260-ORE-002 596554.76 5882795.183 1260.473 25 137 105
BMU-26-012 L1260-ORE-003-DBY-013 596440.504 5882726.526 1264.199 25 148 111
BMU-26-013 L1290-ORE-000 596488.721 5882889.189 1290.955 16 288 105
BMU-26-014 L1260-ORE-002 596554.95 5882795.104 1259.779 15 137 102
BMU-26-015 L1260-ORE-003-DBY-013 596440.553 5882726.416 1263.795 15 148 102
BMU-26-016 L1290-ORE-000 596488.578 5882889.235 1290.552 10 288 105.4
BMU-26-017 L1260-ORE-002 596555.101 5882795 1258.765 -5 137 96
BMU-26-018 L1260-ORE-003-DBY-013 596440.564 5882726.392 1263.097 5 148 87
BMU-26-019 L1290-ORE-000 596488.462 5882889.317 1290.282 3 288 90
BMU-26-020 L1260-ORE-003-DBY-013 596440.478 5882726.537 1262.567 -5 148 87.2
BMU-26-021 L1260-ORE-002 596555.086 5882795.087 1258.291 -15 137 99.3
BMU-26-022 L1290-ORE-000 596488.243 5882889.355 1289.961 -4 288 84
BMU-26-023 L1260-ORE-003-DBY-013 596440.504 5882726.495 1262.255 -15 148 90.2
BMU-26-024 L1260-ORE-002 596555.074 5882795.187 1257.876 -25 137 105.3
BMU-26-025 L1290-ORE-000 596488.511 5882889.253 1289.607 -16 288 76.5
BMU-26-026 L1260-ORE-003-DBY-013 596440.349 5882726.668 1261.96 -25 148 96
BMU-26-027 L1260-ORE-002 596555.006 5882795.284 1257.568 -35 137 117.3
BMU-26-028 L1290-ORE-000 596488.36 5882889.291 1289.247 -27 288 79.5
BMU-26-029 L1260-ORE-003-DBY-013 596440.35 5882726.533 1261.577 -35 148 104.9
BMU-26-030 L1260-ORE-002 596554.952 5882795.513 1257.503 -45 137 135.1
BMU-26-031 L1290-ORE-000 596488.513 5882889.25 1288.896 -38 288 82.5
BMU-26-032 L1260-ORE-003-DBY-013 596440.443 5882726.579 1261.192 -45 148 120.05
BMU-26-033 L1290-ORE-000 596489.052 5882889.305 1291.855 33 295 121.5
BMU-26-034 L1290-ORE-000 596489.035 5882889.3 1291.52 28 295 118.5
BMU-26-035 L1290-ORE-000 596488.946 5882889.367 1291.212 22 295 117
BMU-26-036 L1290-ORE-000 596488.915 5882889.401 1290.933 16 295 108
BMU-26-037 L1290-ORE-000 596488.765 5882889.295 1290.633 10 295 103.9
BMU-26-038 L1290-ORE-000 596488.897 5882889.482 1290.252 3 295 91.9
BMU-26-039 L1290-ORE-000 596488.63 5882889.607 1289.969 -4 295 87.4
BMU-26-040 L1290-ORE-000 596488.793 5882889.502 1289.5 -16 295 78.4
BMU-26-041 L1290-ORE-000 596488.716 5882889.586 1289.204 -27 295 81.2
BMU-26-042 L1290-ORE-000 596488.723 5882889.578 1288.881 -38 295 87.2
BMU-26-043 L1260-ORE-003-DBY-013 596439.884 5882725.792 1264.875 35 162 119.9
BMU-26-044 L1260-ORE-003-DBY-013 596439.995 5882725.451 1264.639 25 162 108
BMU-26-046 L1260-ORE-003-DBY-013 596440.054 5882725.434 1263.698 15 162 99.3
BMU-26-049 L1260-ORE-003-DBY-013 596439.882 5882725.752 1263.024 5 162 96
BMU-26-052 L1260-ORE-003-DBY-013 596439.997 5882725.694 1262.501 -5 162 96.3
BMU-26-055 L1260-ORE-003-DBY-013 596440.021 5882725.703 1262.192 -15 162 99.1
BMU-26-058 L1260-ORE-003-DBY-013 596439.965 5882725.858 1261.959 -25 162 105.3
BMU-26-061 L1260-ORE-003-DBY-013 596439.991 5882725.801 1261.52 -35 162 114.2

ABOUT LOWHEE ZONE

Geological mapping and geochemical sampling were carried out on Barkerville Mountain from 2017-2018, with the Lowhee Zone identified as a high-priority drill target. From 2019 to 2022, a total of 167 surface drill holes were completed, totaling 54,494.5 m.

Lowhee zone access is through Cow portal on the northwestern flank of Barkerville Mountain (Figure 1 and Figure 2) Cow portal construction was completed in Q4 2024 and development of the underground ramp into the Lowhee zone commenced in Q1 2025. The probable mineral reserves estimate for the Lowhee Zone includes 104,491 ounces of contained Au (923,162 tonnes grading 3.52 g/t Au) and represents approximately 5% of the total contained gold in the estimated probable mineral reserves for the Cariboo Gold Project.

ABOUT CARIBOO GOLD PROJECT

The Cariboo Gold Project is a permitted, 100%-owned feasibility-stage project located in the historic Wells-Barkerville mining camp of central British Columbia, Canada. Spanning approximately 186,740 hectares, the Company’s land package includes 443 mineral titles and covers a ~83-kilometre strike of highly prospective exploration targets extending northwest to southeast. In late 2024, the Project was granted the Mines Act and Environmental Management Act (British Columbia) permits, marking the successful completion of the permitting process for key approvals, solidifying the Project’s shovel-ready status.

The Cariboo Gold Project hosts probable mineral reserves of 2.071 million ounces of contained Au (17,815 kt grading 3.62 g/t Au); measured mineral resources of 8,000 ounces of contained Au (47 kt grading 5.06 g/t Au); indicated mineral resources of 1.604 million ounces of contained Au (17,332 kt grading 2.88 g/t Au); and inferred mineral resources of 1.864 million ounces of contained Au (18,774 kt grading 3.09 g/t Au). Mineral resources are reported exclusive of mineral reserves.

Technical Reports

Scientific and technical information relating to the Cariboo Gold Project and the 2025 feasibility study on the Cariboo Gold Project is supported by the technical report, titled “NI 43-101 Technical Report, Feasibility Study for the Cariboo Gold Project, District of Wells, British Columbia, Canada” and dated June 11, 2025 (with an effective date of April 25, 2025) (the “Cariboo Technical Report”).

For readers to fully understand the information in the Cariboo Technical Report, reference should be made to the full text of the Cariboo Technical Report in its entirety, including all assumptions, parameters, qualifications, limitations and methods therein. The Cariboo Technical Report is intended to be read as a whole, and sections should not be read or relied upon out of context. The Cariboo Technical Report was prepared in accordance with National Instrument 43-101 – Standards of Disclosure for Mineral Projects (“NI 43-101”) and is available electronically on SEDAR+ (www.sedarplus.ca) and on EDGAR (www.sec.gov) under Osisko Development’s issuer profile and on the Company’s website at www.osiskodev.com.

Qualified Persons

The scientific and technical information contained in this news release has been reviewed, verified and approved by Scott Smith, P. Geo., Vice President, Exploration of Osisko Development, a “qualified person” within the meaning of NI 43-101. Verification includes core photo and three-dimensional review of logged drillhole data and assays consistent with the Company’s standard operating procedures.

Quality Assurance (QA) – Quality Control (QC)

Whole core sampling was used for all definition infill HQ core completed in the logging facilities following daily QAQC checks for logging and sampling errors. Quality control (QC) samples are inserted at regular intervals in the sample stream, including blanks and reference materials with all sample shipments to monitor laboratory performance. Samples are bagged, labeled, sealed with numbered security tags.

Samples are taken by expeditor from the logging facilities direct to MSALABS’s analytical facility in Prince George, B.C., Canada, for preparation and analysis. The MSALABS facility is accredited to the ISO/IEC 17025 standard for gold assays and all analytical methods include quality control materials at set frequencies with established data acceptance criteria. The entire sample is dried, crushed, and split into sealed containers. Analysis for gold is by gamma ray analysis using the Chrysos PhotonAssay (PA1408X). Samples are bombarded with gamma rays and the resulting signal is sent to the detectors.

Near mine exploration infill HQ drill core samples are cut on site and submitted to ALS Geochemistry’s analytical facility in North Vancouver, British Columbia for preparation and analysis. The ALS facility is accredited to the ISO/IEC 17025 standard for gold assays and all analytical methods include quality control materials at set frequencies with established data acceptance criteria. The entire sample is crushed, and 250 grams is pulverized. Analysis for gold is by 50 gram fire assay fusion with atomic absorption (AAS) finish with a lower limit of 0.01 ppm and upper limit of 100 ppm. Samples with gold assays greater than 100 ppm are re-analyzed using a 1,000-gram screen metallic fire assay. A selected number of samples are also analyzed using a 48 multi-elemental geochemical package by a 4-acid digestion, followed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS).

ABOUT OSISKO DEVELOPMENT CORP.

Osisko Development Corp. is a continental North American gold development company focused on past producing mining camps with district scale potential. The Company’s objective is to become an intermediate gold producer through the development of its flagship, fully permitted, 100%-owned Cariboo Gold Project, located in central British Columbia, Canada. Its project pipeline is complemented by the Tintic Project located in the historic East Tintic mining district in Utah, U.S.A., a brownfield property with significant exploration potential, extensive historical mining data, and access to established infrastructure. Osisko Development is focused on developing long-life mining assets in mining-friendly jurisdictions while maintaining a disciplined approach to capital allocation, development risk management, and mineral inventory growth.

For further information, visit our website at www.osiskodev.com or contact:

Sean Roosen Philip Rabenok
Chairman and CEO Vice President, Investor Relations
Email: sroosen@osiskodev.com Email: prabenok@osiskodev.com
Tel: +1 (514) 940-0685 Tel: +1 (437) 423-3644

IBF4

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