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MONTREAL, Sept. 08, 2025 (GLOBE NEWSWIRE) -- Osisko Development Corp. (NYSE: ODV, TSXV: ODV) ("Osisko Development" or the "Company") is pleased to announce results from its infill and exploration diamond drill, and development sampling campaigns in the Lowhee Zone within the Company's permitted, 100%-owned Cariboo Gold Project ("Cariboo" or the "Project"), located in central British Columbia ("B.C."), Canada. The program to date has consisted of approximately 6,471 meters ("m") of underground infill drilling and approximately 398 m of chip and rock saw channel sampling.

Chris Lodder, President, stated, "The recent underground infill drilling at Lowhee Zone was conducted to analyze how grade holds up under tighter drilling and to investigate optimal drill hole spacing for future mining. We're highly encouraged that underground exploration drilling in the Lowhee Zone and across the deposit completed to date continues to indicate that veins remain open at depth, highlighting the strong potential for future resource expansion through additional exploration programs leveraging existing underground infrastructure. A comprehensive 13,000-meter infill drill program is already underway, designed to deliver important data for local resource modeling, mine planning, and optimization of production stope design. We anticipate providing regular progress updates on this program in the coming months."

DRILL ASSAY HIGHLIGHTS

This news release includes assays from sixty-eight (68) underground infill and exploration diamond drill ("DD") holes totaling approximately 6,471 m completed from November 2024 through early August 2025 (see Table 1) and for which assays were received by a cut off date of August 16, 2025. Select fire and photon assay highlights include:

• 625.95 grams per tonne ("g/t") gold ("Au") over 0.5 m in hole BMU-25-040
• 57.29 g/t Au over 3.05 m in hole BMU-25-032, including:
  • 238.20 g/t Au over 0.5 m
  • 52.57 g/t Au over 0.6 m
    • 23.77 g/t Au over 1.0 m
• 15.26 g/t Au over 4.4 m in hole BMU-25-004, including:
  • 83.40 g/t au over 0.5 m
  • 46.80 g/t Au over 0.5 m
• 26.23 g/t Au over 2.4 m in hole BMU-25-025 including:
  • 55.96 g/t Au over 0.8 m
  • 29.45 g/t Au over 0.55 m
    • 3.39 g/t Au over 0.5 m
• 55.74 g/t Au over 1.0 m in hole BMU-25-034, including:
  • 57.15 g/t Au over 0.5 m
    • 54.34 g/t Au over 0.5 m
• 8.37 g/t Au over 5.9 m in hole BMU-25-014, including:
  • 50.24 g/t Au over 0.5 m
  • 15.97 g/t Au over 0.5 m
  • 10.02 g/t Au over 0.55 m
  • 6.88 g/t Au over 0.5 m
  • 6.41 g/t Au over 0.5 m
    • 5.74 g/t Au over 0.5 m
• 7.06 g/t Au over 6.4 m in hole BMU-25-026, including:
  • 75.61 g/t Au over 0.5 m
    • 8.53 g/t Au over 0.5 m
• 12.44 g/t Au over 3.45 m in hole BMU-25-017, including:
  • 79.17 g/t Au over 0.5 m
    • 4.93 g/t Au over 0.5 m
• 7.23 g/t Au over 5.75 m in hole BMU-25-019, including:
  • 61.18 g/t Au over 0.5 m
  • 13.32 g/t Au over 0.5 m
    • 3.31 g/t Au over 0.5 m
• 28.55 g/t Au over 1.45 m in hole BMU-25-045, including:
  • 80.20 g/t Au over 0.5 m

True widths are estimated to be between 50% and 90% of reported core length intervals. Intervals not recovered by drilling were assigned zero grade. Top cuts have not been applied to high grade assays. Complete assay highlights are presented in Table 1 and drill hole locations and orientations are listed in Table 3.

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

Figure 2: Lowhee Zone select underground drilling highlights.

INFILL AND EXPLORATION PROGRAM SUMMARY

• 14 NQ (47.6-millimeter diameter) diamond drill holes (BMU-25-008 to 021) with depth ranging from 42 to 48 m focused on infilling a 25 m long section of planned ore drive.
• 4 NQ diamond drill holes (BMU-25-001, 003, 004, 007) with an average depth of 290 m were drilled to explore zones adjacent to the existing Lowhee Zone mineral resources.
• 22 NQ diamond drill holes (BMU-25-032 to 053) with an average depth of 90 m conducting systematic grid infill on a set of mineral reserve blocks, mineral inferred resources, and non-DSO resources.
• 8 NQ diamond drill holes (BMU-24-001 to 008) with an average depth of 118 m were drilled infilling areas within existing mineral reserves and resources.

NEXT STEPS

• A 13,000-meter systematic grid infill program is underway within the Lowhee Zone targeting mineral reserve blocks, inferred mineral resources, and non-DSO resources in an approximate 100 m swath transecting approximately the full width of the Lowhee Zone (Figure 3). Drilling at 10 m centers from new development at the 1,260 elevation level, the program is expected to provide a comprehensive data set that will inform resource modeling, mine planning, production stope design procedures and parameters, and the appropriate grid spacing for future infill drilling. Additional systematic grid infill drill programs are planned in step with future underground development progress into other areas of the deposit.
• Structural modelling suggests that the sandstone rock package, the primary host rock for the Cariboo deposit, remains open well beyond depths tested to date. Positive results from deeper drilling across the deposit highlight strong potential for extensions at depth, below the currently defined mineral reserves and resources (Figure 4).

Figure 3: Location of the ongoing 13,000-meter infill drilling campaign.

Figure 4: Northeast facing long section of the Cow Mountain and Lowhee Zone deposit areas with select three-meter composite highlights illustrating exploration potential at depth and along strike to the southeast.

UNDERGROUND CHIP/CHANNEL SAMPLING HIGHLIGHTS

This news release contains assays from eighty-nine (89) underground face and wall rock chip and rock saw channels ("CH") totaling approximately 398 m completed in ore and access development from October 2024 through July 2025 (see Table 2) and for which assays were received by a cut off date of July 31, 2025. Select fire and photon assay highlights include:

• 22.01 g/t Au over 3.8 m in chip channel UGCH00189, including:
  • 104.37 g/t Au over 0.8 m
• 12.23 g/t Au over 4.6 m in chip channel UGCH00183, including:
  • 69.95 g/t Au over 0.8 m
• 6.25 g/t Au over 4.2 m in rock saw channel UGCH00236, including:
  • 12.64 g/t Au over 1.0 m
    • 13.62 g/t Au over 0.9 m
• 5.81 g/t Au over 4.2 m in face chip channel UGCH00193, including:
  • 20.66 g/t Au over 1.1 m
• 3.32 g/t Au over 6.5 m in face chip channel UGCH00213, including:
  • 13.52 g/t Au over 1.0 m
    • 7.77 g/t Au over 1.0 m
• 4.82 g/t Au over 4.2 m in rock saw channel UGCH00246, including:
  • 25.22 g/t Au over 0.8 m
• 4.22 g/t Au over 4.2 m in rock saw channel UGCH00245, including:
  • 7.51 g/t Au over 1.2 m
    • 4.86 g/t Au over 1.5 m
• 3.61 g/t Au over 4.4 m in chip channel UGCH00176, including:
  • 22.20 g/t Au over 0.7 m
• 3.02 g/t Au over 5.2 m in chip channel UGCH00210, including:
  • 9.87 g/t Au over 1.0 m
    • 3.13 g/t Au over 1.2 m
• 4.14 g/t Au over 3.7 m in rock saw channel UGCH00243, including:
  • 7.65 g/t Au over 1.0 m
    • 6.07 g/t Au over 1.2 m
      

True widths are estimated to be between 85% and 100% of reported sample intervals for all face sampling in ore drives and wall sampling in crosscuts. Wall samples in ore drives (along the vein) are excluded from the above list and indicated as select (Table 4). Top cuts have not been applied to high grade assays. Complete assay highlights are presented in Table 2 and sample locations are listed in Table 4.

Figure 5: Lowhee Zone face and wall rock chip and rock saw channel samples with select assay highlights.

Table 1: Length weighted assay composites and individual samples>=3.0 g/t for Lowhee Zone underground diamond drillholes completed November 2024 – August 16, 2025.

Drillhole ID		From (m)			To (m)	Length (m)		Au (g/t)
BMU-24-001		77.8			78.3	0.5		6.28
		83.4			85.25	1.85		9.64
	Including	84.25			84.75	0.5		33.54
		92.5			93	0.5		3.25
		102			105	3		7.89
	Including	103.9			104.5	0.6		25.93
	and	104.5			105	0.5		15.25
BMU-24-002		92.2			92.9	0.7		5.09
		98			98.5	0.5		22.89
BMU-24-003		83			83.5	0.5		36.82
BMU-24-004		92.9			98	5.1		3.60
	Including	92.9			93.4	0.5		6.10
	and	95.6			96.1	0.5		24.06
BMU-24-005		117			117.5	1		4.28
		123.75			124.25	0.5		17.85
BMU-24-006		80.4			82	1.6		3.72
	Including	81			82	1		5.39
BMU-24-007		15.6			17.5	1.9		4.04
	Including	17			17.5	0.5		12.51
		34.9			35.5	0.6		3.81
		39.2			39.7	0.5		17.30
		47.8			48.3	0.5		6.92
		87			87.55	0.55		3.05
		94.1			94.6	0.5		19.34
		100.5			104.05	3.55		3.40
	Including	100.5			101.4	0.9		7.53
	and	102			102.5	0.5		3.16
	and	103.4			104.05	0.65		3.94
		106.9			107.7	0.8		3.70
		111.45			113.2	1.75		12.18
	Including	111.45			111.95	0.5		23.82
	and	111.95			112.65	0.7		12.03
BMU-24-008		20.75			22	1.25		3.70
	Including	20.75			21.25	0.5		8.48
		53.5			55.25	1.75		3.76
	Including	53.5			54.05	0.55		10.15
		100.55			101.6	1.05		25.19
		104.6			105.1	0.5		23.47
		109.4			112.5	3.1		3.85
	Including	109.9			110.5	0.6		6.62
	and	112			112.5	0.5		12.14
		118.8			119.4	0.6		5.59
BMU-25-001		130.5			133.65	3.15		7.29
	Including	132.5			133.65	1.15		18.45
BMU-25-002	No significant assays
BMU-25-003		273			273.5	0.5		7.64
BMU-25-004		15			15.5	0.5		3.22
		24.75			25.3	0.55		3.87
		46.2			47.25	1.05		4.09
	Including	46.75			47.25	0.5		7.89
		64.75			67.45	2.7		5.51
	Including	64.75			65.25	0.5		19.35
	and	66.85			67.45	0.6		8.53
		84.45			85.35	0.9		17.90
		95.5			96.5	1		10.94
	Including	96			96.5	0.5		21.10
		116.5			120.2	3.7		8.00
	Including	118			118.6	0.6		6.82
	and	119.6			120.2	0.6		40.80
		125.3			126	0.7		18.05
		139.1			141.8	2.7		3.51
	Including	139.6			140.15	0.55		3.44
	and	141.25			141.8	0.55		11.85
		144			148.4	4.4		15.26
	Including	144			144.5	0.5		83.40
	and	147.9			148.4	0.5		46.80
		152.9			153.6	0.7		7.71
		158.45			159	0.55		7.81
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