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

The targeted feasibility study surface drilling campaign was completed at the end of September 2022. In the past 6 months, over 55,000 metres additional have been drilled by 9 underground rigs focused on expansion and infill work in the Lynx segment of the deposit.

Significant new analytical results are presented below and include 81 intercepts from 45 drill holes and 3 wedges. The infill intercepts are all located inside the defined mineral resource estimate blocks as described in Osisko’s feasibility study on Windfall (see FS Technical Report (as defined herein), a copy of which is available on SEDAR under Osisko’s issuer profile), and have targeted upgrading inferred mineral resources to measured or inferred mineral resources, as applicable. The expansion intercepts are all located outside the MRE blocks, and either expand resource wireframes or are located in a defined zone or corridor not yet correlated to a specific wireframe.

Select expansion intercepts extending wireframes include: 12.4 g/t Au over 6.6 metres in WST-22-1296, a 100-metre down plunge extension of Lynx Main wireframe 3388 and 20.5 g/t Au over 2.1 metres in WST-22-1294, a 60-metre down plunge extension of the same wireframe; 286 g/t Au over 2.1 metres in WST-22-1218, a 30-metre extension below Triple Lynx wireframe 3188; 120 g/t Au over 2.1 metres in WST-22-1218, a 40-metre extension above Triple Lynx wireframe 3162; 29.6 g/t Au over 8.4 metres from hole WST-22-1182A-W1, a 20-metre extension below Triple Lynx wireframe 3172; 69.7 g/t Au over 2.1 metres, a 60-meter extension east of Triple Lynx wireframe 3121.

Osisko Chief Executive Officer John Burzynski commented: “While Windfall has commenced the permitting process with the recent submission of our Environmental Impact Assessment (see Osisko news release dated March 29, 2023 and entitled “Osisko submits Windfall environmental impact assessment”), we have continued our work to improve our understanding of the continuity and extent of the MRE with drills on infill and expansion holes in the deposit. Today’s expansion results add good potential to increase the scale of defined areas of mineralization, and have also served well to identify additional areas to target new extensions of Windfall. The infill holes’ grade and lengths remain consistent with respect to the currently defined resources and continue to confirm our high-grade models.”

Select infill high-grade intercepts include: 204 g/t Au over 2.0 metres in WST-22-1249A, 101 g/t Au over 3.8 metres in WST-22-1286; 42.9 g/t Au over 7.9 metres in WST-22-1232; 106 g/t Au over 2.1 metres in WST-22-1116; 99.3 g/t Au over 2.0 metres in WST-22-1182A and 34.0 g/t Au over 5.0 metres in WST-22-1107. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

Maps: Long-Section_Expan-20230405_EN, Long-Sections_lens3388-20230405_EN, PR_EN_20230405_Surface, PR_EN_20230405_UG, Long-Section-_Infill-20230405_EN

Expansion Drilling

Notes: True widths are estimated at 55 – 80% of the reported core length interval. See “Quality Control and Reporting Protocols” below., BCT = Bob Cat, LHW = Lynx Hangingwall, LSW = Lynx South West, LXM = Lynx Main, LX4 = Lynx 4 and TLX = Triple Lynx.

Infill Drilling

Notes: True widths are estimated at 55 – 80% of the reported core length interval. See “Quality Control and Reporting Protocols” below., F11 = F-11 Zone, LXM = Lynx Main, LX4 = Lynx 4 and TLX = Triple Lynx.

Drill hole location

Bobcat

Mineralization most commonly occurs in gold-bearing quartz-pyrite veins controlled by northeast trending faults and shears and to a lesser extent in minor crustiform quartz-tourmaline-ankerite-pyrite veins and pyrite replacement zones and stockwork. Mineralization is hosted in sheared mafic volcanics, rhyolites near faults, or at the contact with felsic porphyritic intrusions.

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.

F-Zones

Mineralization is hosted in sheared andesites with carbonate replacement or quartz veining and occurs as quartz ± ankerite veinlets or as replacement type in shear zones and is characterised by trace to 10% pyrite with local visible gold. Alteration is dominated by sericite-fuchsite-tourmaline-pyrite.

Qualified Person

The scientific and technical content of this news release has been reviewed, prepared, and approved by Ms. Isabelle Roy, P.Geo. (OGQ 535), Director of Technical Services for Osisko’s Windfall gold project, who is a “qualified person” as defined by 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 (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 mineral resource estimate on Windfall (with an effective date of June 7, 2022 ) (the “Windfall Resource Estimate”) and the mineral reserve estimate on Windfall (with an effective date of November 25, 2022) (the “Windfall Reserve Estimate”) are described in the technical report entitled “Feasibility Study for the Windfall Project, Eeyou Istchee James Bay, Québec, Canada” (the “FS Technical Report”) and dated January 10, 2023 (with an effective date of November 25, 2022). The Windfall Resource Estimate, 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 Windfall Reserve Estimate, assuming 3.5 g/t operating, 2.5 g/t incremental, and 1.7 g/t development cut-off grade, comprises 12,183,000 tonnes at 8.06 g/t Au (3,159,000 ounces) in the probable mineral reserves category. The key assumptions, parameters, limitations and methods used in the Feasibility Study for Windfall, including the related Windfall Resource Estimate and Windfall Reserve Estimate, are described in a technical report (the “FS Technical Report”), which was prepared in accordance with NI 43-101. The FS Technical Report 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 reserves are defined from surface to a depth of 1,100 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).