Mr. Chris Lodder reports

OSISKO DEVELOPMENT ANNOUNCES MINERAL RESOURCE UPDATE FOR THE TRIXIE DEPOSIT, TINTIC PROJECT

Osisko Development Corp. has released an updated mineral resource estimate (MRE) for its 100-per-cent-owned underground Trixie deposit, within the company's wider Tintic project, located in the historic East Tintic mining district in central Utah, United States. The 2024 Trixie MRE incorporated an additional 1,674 underground chip samples over 1,678 metres (5,507 feet) of underground development, and 7,385 m of drilling (24,229 ft) in 122 holes completed by the company since the release of the initial Trixie MRE, with an effective date of Jan. 10, 2023.

Relative to the 2023 Trixie MRE, contained gold ounces in measured and indicated resources decreased by 29 per cent and inferred resources decreased by 79 per cent primarily due to lower estimated grades that incorporated an updated geologic model interpretation and conversion of inferred resources. Drill results and underground mapping from the 2023 exploration program improved the knowledge of the extent and distribution of mineralization, resulting in modelling improvements to both mineralization and the historical mine shape model.

Chris Lodder, president, stated: "The 2024 Trixie MRE incorporates changes to our interpretation of the main mineralized structures and reflects better understanding of the structural controls of the deposit and realistic mining parameters following our exploration and test mining work in 2023. To date exploration and mining occurred on less than 10 per cent of known mineralized structures in the West Tintic district and thus, we see significant precious metal potential at depth, on parallel structures to Trixie, along the Trixie and Sioux Ajax faults to the north and south, as well as around all historic high-grade gold mines in the West Tintic district. These high-grade gold targets, combined with the copper-gold porphyry potential where drilling is under way, and a large area of polymetallic carbonate replacement potential, illustrate that we have only scratched the surface in understanding the overall metal endowment potential of the Tintic district."

Trixie mineral resource estimate:

• The 2024 Trixie MRE comprises six mineralized zones within the greater Trixie deposit, including T2, T3, T4, Wild Cat, 40 fault and 75-85 over a strike length of 530 metres, a maximum width of 105 m and to a maximum depth of 195 m for the deposit, and is 350 m from surface. These dimensions are for the overall size of the mineralized zone structures, with the 2024 Trixie MRE blocks contained within a smaller 440 m strike length, 60 m total width and 195 m depth footprint.
• Gold mineralization is associated with high-sulphidation epithermal mineralization, structurally controlled and hosted within the quartzites. Mineralization consists of native gold, and rare gold-silver-rich telluride minerals with quartz and quartz-barite-sulphosalt stockwork veining.
• The T2 zone is the highest-grade structure within the overall deposit. In 2023, a total of 4,637 ounces were recovered from processing mineralized material with an overall feed grade of 35.61 grams per tonne Au. The 2023 drill program also converted ounces from inferred to indicated, and drilling at depth indicated a transition from high-grade gold to anomalous copper, which prompted the testing of the deep porphyry target at Trixie West.
• The T4 zone envelops the T2, 40 fault and Wild Cat domains. Within the T4 domain, there are discrete subvertical high-grade gold structures, defined on multiple levels and sections. However, these structures appear to be more discontinuous and less disseminated in the broader area than had been previously estimated. In 2023, mapping and modelling modified the interpretation from a stockwork to distinct high-grade structures. As a result, the model now incorporates tight search parameters around these structures, increasing confidence within the zone, while also including the quartz-barite-sulphosalt disseminated stockwork mineralization.
• • A mineralized fault structure, known as the 40 fault, is mapped over 230 m strike length and 80 m at depth and is about one m wide. This fault is a mineralized domain within the T4 and offsets vertically dipping epithermal Au-Ag structures;
  • The Wildcat domain, a discrete structure within the T4, is steeply dipping to the east and strikes for 237 m and terminates at the 40 fault;
  • The T1 zone, previously described in the 2023 Trixie MRE, has been incorporated into the T4 zone. The T1 zone was previously an envelope on the contacts of both the 75-85 and T2 zones. The T1 zone had similar high-grade fissure zones as described in the T4 zone, that are constrained within the T4 envelope. Additional drilling in this area also reduced the estimated contained gold above cut-off.
• The 75-85 zone is a moderately west-dipping silica sulphide cemented breccia zone. Drilling along strike to the south suggests that the 75-85 zone truncates both the T2 structure and T4 zone. Mine development in 2023 intersected previously unknown stopes within the modelled 75-85 zone and high-grade assays were less continuous at depth, although increasing down plunge.

Trixie and greater Tintic conclusions and recommendations:

• In 2023, the company completed a total of 6,028 m (19,776 ft) of underground drilling in 73 diamond drill holes at Trixie. Assays were finalized up to hole TRXU-DD-23-069 and were included in the 2024 Trixie MRE.
• The new drilling, mapping and historical data compilation improved the interpretation and revealed that there is significant potential for parallel high-grade gold fissure zones similar to T2 and adjacent to the existing mine development. Much of the Trixie area remains unexplored.
• At Trixie, exploration potential remains highly prospective at depth near historical stopes that ceased mining at the water table. The Trixie deposit remains open to the north, along strike of T2, down dip below the historical 756, down plunge to the Survey vein and additional, parallel structures are highly possible within the epithermal system.
• The company continues to explore for additional high-sulphidation epithermal Au and Ag targets along the four-kilometre strike length of historical mines and has identified at least a dozen new drill-ready targets from extensive data compilation and regional fieldwork in 2023. Further work is recommended to test these targets.

Porphyry target drilling:

• Copper-gold-molybdenum porphyry potential remains an exploration priority for the company. One diamond drill rig is currently active at surface testing a porphyry target at Big Hill and is at a current depth of 1,180 m (3,872 ft). Assays are pending for this drill hole.
• One drill hole tested a copper-gold-porphyry target below Trixie and was drilled to a depth of 759.6 m (2,492 ft) when it crossed the Eureka Lily fault to the east and out of the prospective alteration zone. Further drill testing of a copper-gold porphyry target at depth below the Trixie deposit is recommended to the west.
• The development of the 1,390 m decline ramp at Trixie, completed in September, 2023, significantly improving access to the underground workings for exploration development and drilling beyond the 625 level.
• The company has advanced rehabilitation at the 750 level to allow for further underground diamond drilling to test for the down-dip extent of the 756 zone and the porphyry target below Trixie.

The cut-off grade for the 2024 Trixie MRE is 4.32 g/t Au compared with 4.85 g/t Au in the 2023 Trixie MRE primarily due to the difference in the estimated cost of heap leach processing ($41/ST) relative to the previously estimated mill processing scenario ($89/ST).

Qualified persons

The scientific and technical information contained in this news release has been reviewed and approved by Maggie Layman, PGeo, vice-president, exploration, of Osisko Development, and a qualified person within the meaning of National Instrument 43-101.

The independent QPs for the 2024 Trixie MRE, within the meaning of NI 43-101, are William Lewis, PGeo, and Alan J. San Martin, MAusIMM (CP), of Micon International Ltd. Each QP is independent of Osisko Development within the meaning of NI 43-101 and has reviewed and approved the content in this news release.

Quality assurance/quality control

All drill core and exploration samples are dispatched to ALS Geochemistry or SGS Canada for off-site sample preparation and analysis. Both labs are ISO/IEC 17025 certified, and ALS Geochemistry is also ISO 9001 certified. Samples are assigned a unique sample ID. All geological and sampling information is entered into a Datamine Fusion database. Core is sawn in half and half is sampled. Certified standards and blanks are inserted into all sample dispatches. Samples are collected by Old Dominion Transportation and dispatched to SGS Canada's laboratory in Burnaby, B.C., or ALS Geochemistry's laboratories in Elko, Nev., or Twin Falls, Idaho. Sample submission forms accompany the samples, and digital copies are e-mailed to the destination lab.

Core sample preparation is completed by ALS Geochemistry or SGS Canada, including drying, crushing and pulverizing of samples. Analytical assays include gold by 30-gram fire assay with atomic absorption spectroscopy finish, and gold overlimits by fire assay with gravimetric finish. Screen metallic analyses are performed on selected samples. Multielement analysis (including silver) is by four-acid digest with inductively coupled plasma atomic emission spectroscopy/inductively coupled plasma mass spectrometry finish. The pulps are returned to Osisko Development and coarse rejects are disposed after 90 days. Assays are reported to Osisko Development and then loaded into Datamine Fusion. Quality assurance/quality control samples are checked, and assays are merged with sample information for future reporting.

Underground face samples are collected by company geologists from each of the active mining faces, with samples transported by the geologists from Trixie to the on-site company laboratory located at the Burgin administrative complex. Underground samples are dried, crushed to less than 10 millimetres and a 250-gram split is taken. The split is pulverized, and a 30-gram fire assay with gravimetric finish is completed to determine gold and silver grades, reported in oz/short ton and g/t.

The company's Burgin laboratory is not a certified analytical laboratory, but the facility is managed by a qualified laboratory manager with annual auditing by technical staff. The laboratory has been independently audited by Qualitica Consulting and Micon International's QP with recommendations implemented. Interlaboratory check assays using ALS Geochemistry as a third party independent analysis of samples is routinely carried out as part of continuing QA/QC work. Certified OREAS QC standards and blanks are inserted at regular intervals in the sample stream to monitor laboratory performance.

True width is estimated to be approximately 0.5 m to three m (1.6 to 10 ft) for all fissure veins and discrete structures (T2, T3, 75-85, Wildcat and 40 fault) and the T4 zone is modelled at an average width of 90 m (300 ft) and encompasses disseminated mineralization and discontinuous veins ranging from several centimetres to one m (three ft).

About Osisko Development Corp.

Osisko Development is a North American gold development company focused on past-producing mining camps located in mining friendly jurisdictions with district-scale potential. The company's objective is to become an intermediate gold producer by advancing its 100-per-cent-owned Cariboo gold project, located in central British Columbia, Canada, the Tintic project in the historic East Tintic mining district in Utah, United States, and the San Antonio gold project in Sonora, Mexico. In addition to considerable brownfield exploration potential of these properties, that benefit from significant historical mining data, existing infrastructure and access to skilled labour, the company's project pipeline is complemented by other prospective exploration properties. The company's strategy is to develop attractive, long-life, socially and environmentally sustainable mining assets, while minimizing exposure to development risk and growing mineral resources.

We seek Safe Harbor.