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.

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

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).

ABOUTOSISKODEVELOPMENTCORP.

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:

CAUTION REGARDING FORWARD LOOKING STATEMENTS

This news release contains "forward-looking information" (within the meaning of applicable Canadian securities laws) and "forward-looking statements" (within the meaning of the U.S. Private Securities Litigation Reform Act of 1995, as amended) (collectively, "forward-looking statements"). Such forward-looking statements are identified with words such as "may", "will", "would", "could", "anticipate", "believe", "expect", "plan", "intend", "potential", "estimate", "propose", "project", "outlook", "foresee", "objective", "strategy", variants of these words or the negative or comparable terminology, as well as terms usually used in the future and the conditional. Information contained in forward-looking statements is based upon certain material assumptions that were applied in drawing a conclusion or making a forecast or projection, including the assumptions, qualifications, limitations or statements pertaining to: the utility and significance of results to contribute to a more detailed understanding of spatial controls and local variability within the Lowhee Zone and its ability and significance in providing positive indication (if any) for near mine potential; the results, timing, utility and significance of the infill drill program and its impacts on the localized block model and/or future production stope designs and sequencing (if any); the tighter infill drilling spacing providing better understanding of vein corridor spatial geometries and local variability within Lowhee; the ability of results (if any) to help refine infill drill requirements, production designs and sequencing in the Lowhee deposit; the significance of continued drilling in underexplored zones; the interpretation and accuracy of intercepts to suggest possible extensions of vein corridors, with potential for resource conversion and upside mineralization; the interpretation and accuracy of assay composites showing a degree of spatial correlation with the modelled reserve stopes with intercepts outside these areas suggesting potential for resource conversion and upside mineralization; the prospectivity of exploration in the Lowhee Zone and targets outside of currently defined mineral reserves and/or mineral resources; the consistency of results with modelled reserve stopes (if at all); the interpretation and accuracy of spatial geometries, geological structure and local variability modeling and assumptions in regard to potential reserve or resource revisions (if at all); the ability and timing (if at all) to complete planned remodelling and mineral resource calculation process; the significance of implications (if any) on an updated local block model and any potential adjustments to planned reserve stopes; the ability of estimation results (if any) to support the addition of new planned reserve stopes; the results (if any) of further exploration work and ability of the Company to define and expand mineral resources beyond current mineral resource estimates; the ability and utility of exploration work (including drilling) to inform resource modeling, mine planning, production stope design procedures and parameters, refinement of infill drill requirements, and the appropriate drill spacing for future infill drilling (if at all); assumptions, qualifications and parameters underlying the Cariboo Technical Report (including, but not limited to, the mineral resources, mineral reserves, production profile, mine design and project economics); the results of the Cariboo Technical Report as an indicator of quality and robustness of the Cariboo Gold Project, as well as other considerations that are believed to be appropriate in the circumstances; the ability of the Company to achieve the estimates outlined in the Cariboo Technical Report in the timing contemplated (if at all); mineral resource category conversion; the future development and operations at the Cariboo Gold Project; management's perceptions of historical trends, current conditions and expected future developments; the utility and significance of historic data, including the significance of the district hosting past producing mines; the ability of exploration work (including drilling and sampling) to accurately predict mineralization; the ability of the Company to complete its exploration and development objectives for its projects in the timing contemplated and within expected costs (if at all); the ability to adapt to changes in gold prices, estimates of costs, estimates of planned exploration and development expenditures; the Company's strategy and objectives relating to the Cariboo Gold Project as well as its other projects; the assumptions, qualifications and limitations relating to the Cariboo Gold Project being permitted; the exploration potential and prospectivity (if any) of its properties; regulatory framework remaining defined and understood as well as other considerations that are believed to be appropriate in the circumstances, and any other information herein that is not a historical fact may be "forward looking information". Actual results could differ materially due to a number of factors, including, without limitation: risks relating to third-party approvals, including the issuance of permits by governments, capital market conditions and the Company's ability to access capital on terms acceptable to the Company for the contemplated exploration and development at the Company's properties; risks related to the exploration, development and operation of the Cariboo Gold Project; risks related to geological modeling and resource estimation; health, safety and security incidents; regulatory delays or changes in regulatory framework and applicable laws; labour shortages or disputes; general economic and market conditions and business conditions in the mining industry; fluctuations in commodity and currency exchange rates; changes in regulatory framework and applicable laws, as well as those risks and factors disclosed in the Company's most recent annual information form, financial statements and management's discussion and analysis as well as other public filings on SEDAR+ (www.sedarplus.ca) and on EDGAR (www.sec.gov). Although the Company believes the expectations conveyed by the forward-looking statements are reasonable based on information available as of the date hereof, no assurances can be given as to future results, levels of activity and achievements. The Company disclaims any obligation to update any forward-looking statements, whether as a result of new information, future events or results or otherwise, except as required by law. Forward-looking statements are not guarantees of performance and there can be no assurance that these forward-looking statements will prove to be accurate, as actual results and future events could differ materially from those anticipated in such statements. Accordingly, readers should not place undue reliance on forward-looking statements.

Neither the TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this news release. No stock exchange, securities commission or other regulatory authority has approved or disapproved the information contained herein.

Photos accompanying this announcement are available at:

https://www.globenewswire.com/NewsRoom/AttachmentNg/c95dd822-2dbf-4ceb-81d4-4cc026b1ce7a

https://www.globenewswire.com/NewsRoom/AttachmentNg/ff7153e1-c044-4a80-a130-da29b9095147

https://www.globenewswire.com/NewsRoom/AttachmentNg/f8ca8a7f-087e-449d-be05-40a1e2cfd4a3

https://www.globenewswire.com/NewsRoom/AttachmentNg/1524082c-2bc4-40b3-b223-e8b576d4c8e4

https://www.globenewswire.com/NewsRoom/AttachmentNg/1d1b5350-23ac-4a6f-86ab-5edf96284305

https://www.globenewswire.com/NewsRoom/AttachmentNg/475d36ae-85f3-4274-8588-8ccf4e0d07ac

https://www.globenewswire.com/NewsRoom/AttachmentNg/74e1fcae-2495-4feb-a1c3-28ec1e120682

https://www.globenewswire.com/NewsRoom/AttachmentNg/a823b3a5-ae02-4c1f-95cf-e3c59a1ada8f

https://www.globenewswire.com/NewsRoom/AttachmentNg/dfe31f11-5f8f-4bab-ad16-371a0f72b809

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°).

© 2026 Canjex Publishing Ltd. All rights reserved.