Intercepts Confirm Potential for Significant Expansion of Windfall

81.8 g/t Au over 3.5 metres; 22.3 g/t Au over 4.1 metres

Osisko Mining Inc. (TSX:OSK) is pleased to provide new exploration results from its 100% owned Windfall gold project located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec.

Hole OSK-22-1109-W2 targeted the projected down plunge extension of Lynx 4 at a vertical depth from surface of 1,670 metres. The hole successfully intercepted significant widths of high-grade gold mineralization, including 81.8 g/t Au over 3.5 metres (2.39 ounces per ton over 11.5 feet) and 22.3 g/t Au over 4.1 metres (0.65 ounces per ton over 13.4 feet). These intercepts confirm potential for a major down-plunge extension of the Lynx 4 high-grade zone, which could have significant implications for the future potential expansion of the Windfall deposit.

The new intercepts are 625 metres (2,050 feet) down plunge from the nearest resource block (Lynx 4 wireframe 3449) included in the most recent Mineral Resource Estimate for Windfall (see Windfall MRE (2022) (as defined herein). The technical report was filed on SEDAR (www.sedar.com) under Osisko’s issuer profile on September 14, 2022). The new mineralization is typical of Lynx 4 wireframe 3449, including disseminated pyrite associated with strong pervasive silica alteration hosted in a sericitized gabbro, with local visible gold.

Osisko Chief Executive Officer John Burzynski commented: “Windfall has scale and grade unparalleled in the global near-term development category. With the recent on-time delivery of our Windfall MRE (based on approximately 1.7 million metres of drilling since 2015), we have now focused on completion of the definitive feasibility study which is on schedule for delivery before the end of the year. Today’s down-plunge results are a strong indication of a much larger deposit, underscoring the consistency and predictability of the geology model we have developed for Windfall over the past six years. The addition of 625 metres length to one of our highest-grade Lynx 4 zones shows there is great potential for Windfall to move to the top of the class, when compared to other significant Canadian long-life, high-grade gold deposits.”

Maps showing hole locations and full analytical results are available at www.osiskomining.com. Maps: 20220927_Lynx 4_EXT_EN MRE, 20220927_Lynx 4_EXT_EN plan, 20220927_Lynx 4_EXT_EN long section, PR_EN_20220927_Surface.

Exploration drilling

Notes: True widths are estimated at 55 – 80% of the reported core length interval. See “Quality Control and Reporting Protocols” below. * See Osisko news released dated October 21, 2019, ** see Osisko news release dated January 11, 2021.

Drill hole location

Lynx Zone

Mineralization occurs as grey to translucent quartz-carbonate-pyrite-tourmaline veins and pyrite replacement zones and stockworks. Vein-type mineralization is associated with haloes of pervasive sericite-pyrite ± silica alteration and contain sulphides (predominantly pyrite with minor amounts of chalcopyrite, sphalerite, galena, arsenopyrite, and pyrrhotite) and local visible gold. Replacement mineralization is associated with strong pervasive silica-sericite-ankerite ± tourmaline alteration and contains disseminated pyrite from trace to 80% with local visible gold. Pyrite stockworks can form envelopes that reach several tens of metres thick. Fuchsite alteration is common and is spatially constrained to near the gabbros. Mineralization occurs at or near geological contacts between felsic porphyritic or fragmental intrusions and the host rhyolites or gabbros and locally can be hosted along the gabbro-rhyolite contact.

Qualified Person

The scientific and technical content of this news release has been reviewed, prepared and approved by Mr. Louis Grenier, M.Sc.A., P.Geo. (OGQ 800), Director of Exploration for Osisko’s Windfall gold project, who is a “qualified person” within the meaning of National Instrument 43-101 – Standards of Disclosure for Mineral Projects.

Quality Control and Reporting Protocols

True width determination is estimated at 55-80% of the reported core length interval for the zone. Assays are uncut except where indicated. Intercepts occur within geological confines of major zones but have not been correlated to individual vein domains at this time. Reported intervals include minimum weighted averages of 3.5 g/t Au diluted over core lengths of at least 2.0 metres. NQ core assays were obtained by either 1-kilogram screen fire assay or standard 50-gram fire-assaying-AA finish or gravimetric finish at: (i) ALS Laboratories in Val d’Or, Québec, Vancouver, British Colombia, Lima, Peru or Vientiane, Laos; and (ii) Bureau Veritas in Timmins, Ontario. The 1-kilogram screen assay method is selected by the geologist when samples contain coarse gold or present a higher percentage of pyrite than surrounding intervals. Selected samples are also analyzed for multi-elements, including silver, using a Four Acid Digestion-ICP-MS method at ALS Laboratories. Drill program design, Quality Assurance/Quality Control and interpretation of results is performed by qualified persons employing a QA/QC program consistent with NI 43-101 and industry best practices. Standards and blanks are included with every 20 samples for QA/QC purposes by the Corporation as well as the lab. Approximately 5% of sample pulps are sent to secondary laboratories for check assay.

About the Windfall Gold Deposit

The Windfall gold deposit is located between Val-d’Or and Chibougamau in the Abitibi region of Québec, Canada. The MRE for Windfall is supported by the technical report entitled “Mineral Resource Estimate Update for the Windfall Project” dated September 14, 2022 (with an effective date  of June 7, 2022) (the “Windfall MRE (2022)”), and assuming a cut-off grade of 3.50 g/t Au, comprises 811,000 tonnes at 11.4 g/t Au (297,000 ounces) in the measured mineral resource category, 10,250,000 tonnes at 11.4 g/t Au (3,754,000 ounces) in the indicated mineral resource category and 12,287,000 tonnes at 8.4 g/t Au (3,337,000 ounces) in the inferred mineral resource category. The key assumptions, parameters and methods used to estimate the MRE for Windfall are further described in the Windfall MRE (2022), being the full technical report for this updated MRE prepared in accordance with NI 43-101, and is available on SEDAR (www.sedar.com) under Osisko’s issuer profile. The Windfall gold deposit is currently one of the highest-grade resource-stage gold projects in Canada and has world-class scale. Mineralization occurs in three principal areas: Lynx, Main, and Underdog. Mineralization is generally comprised of sub-vertical lenses following intrusive porphyry contacts plunging to the northeast. The resources are defined from surface to a depth of 1,600 metres, including the Triple 8 (TP8) zone. The resources excluding TP8 are defined from surface to a depth of 1,200 metres. The deposit remains open along strike and at depth. Mineralization has been identified at surface in some areas and as deep as 2,625 metres in others with significant potential to extend mineralization down-plunge and at depth.

About Osisko Mining Inc.

Osisko is a mineral exploration company focused on the acquisition, exploration, and development of precious metal resource properties in Canada. Osisko holds a 100% interest in the high-grade Windfall gold deposit located between Val-d’Or and Chibougamau in Québec and holds a 100% undivided interest in a large area of claims in the surrounding the Urban Barry area and nearby Quévillon area (over 2,400 square kilometres).