Osisko Development Corp. (NYSE: ODV) (TSX-V: ODV) is pleased to announce underground infill and exploration diamond drilling results as part of the ongoing 2023 exploration program at the Company’s 100%-owned Trixie test mine, within the Company’s wider Tintic Project located in the historic East Tintic Mining District in central Utah, U.S.A.

Chris Lodder, President of Osisko Development, commented, “We are excited to announce the results of the most-recent phase of our Trixie exploration program, highlighting areas outside of our initial resource area, and the start of our porphyry drilling campaign with an initial hole from underground at Trixie. Based on our surface and underground geological and geochemical compilation, we have identified this as a high priority target as a potential magmatic source to known high-grade gold and silver epithermal systems and the surrounding anomalous copper in structures and hydrothermally altered host rocks. This target is one of several porphyry targets we will be testing in the coming year, with the target being a non-outcropping Bingham style porphyry copper-gold system.”

DRILL ASSAY HIGHLIGHTS

This news release includes assays from 17 DD holes (refer to Table 1). Select assay highlights include:

• 7.66 grams per tonne gold and 4.00 g/t silver over 7.32 meters in TRXU-DD-23-035 (0.22 troy ounce per short ton Au and 0.12 oz/t Ag over 24.00 feet) including
  • 38.03 g/t Au and 7.96 g/t Ag over 1.22 m in TRXU-DD-23-035 (1.11 oz/t Au and 0.23 oz/t Ag over 4.00 ft.)
• 14.85 g/t Au and 34.87 g/t Ag over 5.49 m in TRXU-DD-23-035 (0.43 oz/t Au and 1.02 oz/t Ag over 18.00 ft.) including
  • 27.02 g/t Au and 25.70 g/t Ag over 1.83 m in TRXU-DD-23-035 (0.79 oz/t Au and 0.75 oz/t Ag over 6.00 ft.)
• 22.54 g/t Au and 2,301.00 g/t Ag over 0.46 m in TRXU-DD-23-041 (0.66 oz/t Au and 67.11 oz/t Ag over 1.50 ft.)
• 54.95 g/t Au and 1,143.21 g/t Ag over 2.59 m in TRXU-DD-23-045 (1.60 oz/t Au and 33.34 oz/t Ag over 8.50 ft.) including
  • 130.00 g/t Au and 2,715.00 g/t Ag over 1.07 m in TRXU-DD-23-045 (3.79 oz/t Au and 79.19 oz/t Ag over 3.50 ft.)

DRILL RESULTS SUMMARY

• In 2023, the Company has drilled 72 holes for a total of 6,125 m (20,095 ft.) at Trixie. To date, assays have been received for 51 DD holes, with assays pending for the remaining holes. This portion of the 2023 exploration drill program is now complete.
• Approximately 25% of the drilling to date consists of delineation of domains within the area of the current Trixie MRE (as defined herein) and 75% is exploration drilling adjacent to the area of the Trixie MRE, including step outs down dip, down plunge and along strike testing for mineralized structures.
• The focus of these recent holes was to test for mineralization along one of the priority target areas south on strike from the known T2 domain, towards the Sioux Ajax fault (see Figure 2). A highlight from this area includes 54.95 g/t Au and 1,143.21 g/t Ag over 2.59 m in hole TRXU-DD-23-045 (1.60 oz/t Au and 33.34 oz/t Ag over 8.50 ft.).
• A down dip highlight in the T1 domain includes 7.66 g/t Au and 4.00 g/t Ag over 7.32 m in TRXU-DD-23-035 (0.22 oz/t Au and 0.12 oz/t Ag over 24.00 ft.). This intercept is approximately 25 m (75 ft.) from the known Trixie MRE deposit boundary.
• The 75-85 domain consists of a discrete, north-south striking, moderate to steeply west-dipping structure in the footwall of the T4domain that was historically mined prior to the discovery of the T2 domain. See Figure 3 for domain geometry and relationships.
• The T1 domain consists of Tintic quartzite-hosted disseminated mineralization interpreted as a halo to the T2 domain.
• These drilling results will provide valuable infill data to improve our understanding and the confidence level of the mineralized zones defined in the area of the Trixie MRE and to support a an updated mineral resource estimate in the future.
• The exploration results will assist with understanding the extent of mineralized structures and support future underground exploration.

TRIXIE PORPHYRY DRILLING

• The Company is pleased to announce that drilling of the Trixie West high-priority copper-gold-molybdenum potential porphyry target from underground at Trixie commenced in early October 2023 (see Figure 5).
• The Tintic District, located 65 km (40 miles) from Rio Tinto’s Bingham Canyon Mine, has historically been recognized as an area prospective for porphyry style copper-gold-molybdenum mineralization. Styles of mineralization and alteration present within the Tintic District support an interpretation of a classic porphyry-epithermal system with a high degree of rheologic and structural control on mineralization style and distribution (Figure 4).
• The objective of the drill program is to test a new area below the Trixie deposit for a potential porphyry style copper-gold-molybdenum mineral system that may have been the source of the significant high-grade gold and silver epithermal mineralization and past producing carbonate silver-lead-zinc replacement deposits.
• Two large lithocaps, presented as anomalous surface geochemical footprints, a type of high heat signature indicative of significant potential subsurface volcanic activity, have been identified within the Company’s Tintic Project property (Figure 5), namely in the Big Hill and Silver Pass areas. Drilling in these areas is expected to commence in Q4 2023 subject to permits.

About Trixie

The Trixie test mine is one of several gold and base metal targets within the larger Tintic Project consisting of >17,000 acres of patented mining claims and mineral leases within the historic East Tintic Mining District of Central Utah, U.S.A. The T2 and T4 structures at Trixie show multi-ounce gold grades associated with high sulphidation epithermal mineralization, structurally controlled and hosted within quartzites. The T2 structure mineralization consists of native Au, and rare Au-Ag rich telluride minerals with quartz. The T4 is a mineralized stockwork zone is located in the hanging wall of the T2 and is comprised of Au-Ag rich mineralization in host rock quartzite with quartz-barite-sulphosalt stockwork veining. Mineralization reports consistent multi-ounce gold grades along the entire strike length.

A 3D model and virtual site tour of Trixie and the wider Tintic Project is accessible on the Company’s VRIFY page at: https://vrify.com/decks/12801.

Information relating to the Tintic Project and the current MRE for the Trixie deposit is supported by the technical report entitled “NI 43-101 Technical Report, Initial Mineral Resource Estimate for the Trixie Deposit, Tintic Project, Utah, United States of America”, dated January 27, 2023 (with an effective date of January 10, 2023) prepared for the Company by independent representatives of Micon International Limited. Reference should be made to the full text of the Tintic Technical Report, which was prepared in accordance with National Instrument 43-101 – Standards of Disclosure for Mineral Projects 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.

Figure 1: Tintic Project – Trixie Area

Figure 2: Trixie Underground Long Section

Figure 3: Trixie Long Section Sample Highlights

Figure 4: Generalized Deposit Model of a high sulphidation epithermal porphyry system

Figure 5: Lithocap Highlights Porphyry Target Areas

Table 1: Drilling Length Weighted Assay Composites at Trixie

Qualified Persons

The scientific and technical information contained in this news release has been reviewed and approved by Maggie Layman, P.Geo., Vice President, Exploration of Osisko Development, and a “qualified person” within the meaning of NI 43-101.

Quality Assurance– Quality Control

All drill core and exploration samples are dispatched to SGS Canada’s laboratory in Burnaby, British Columbia for offsite sample preparation and analysis. Samples are assigned a unique sample ID. All geological and sampling information is entered into 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, British Columbia. Sample submission forms accompany the samples, and digital copies are emailed to SGS Canada.

All core sample preparation is completed by SGS Canada, including drying, crushing, and pulverizing of samples. Analytical assays include gold by 30 gram fire assay with AAS finish (GO_FAA30V10), and gold overlimits by fire assay with gravimetric finish (GO_FAG30V). Multielement analysis (including silver) is by four-acid digest with ICP-AES/ICP-MS finish (GE_ICM40Q12). 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.

True width determination is estimated to be approximately 0.3 m to 2.4 m (1 to 8 ft.) wide for the T2 structure, approximately 3 m to 25 m (10 to 80 ft.) for the T4 mineralized stockwork zone located in the hanging wall of the T2 structure and 1.5 m to 3 m (5 to 9 ft.) for the 75-85 structure.

About Osisko Development Corp.

Osisko Development Corp. is a premier North American gold development company focused on high-quality past-producing properties located in mining friendly jurisdictions with district scale potential. The Company’s objective is to become an intermediate gold producer by advancing its 100%-owned Cariboo Gold Project, located in central B.C., Canada, the Tintic Project in the historic East Tintic mining district in Utah, U.S.A., 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.