OSISKO WINDFALL DRILLING UPDATE: MORE HIGH-GRADE IN EXPANSION AND INFILL

Including 203 g/t Au over 5.2 metres and 93.9 g/t Au over 7.6 metres

(Toronto, September 15, 2022) Osisko Mining Inc. (OSK:TSX. “Osisko” or the “Corporation”) 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.

Significant new analytical results presented below include 103 intercepts in 46 drill holes (4 from surface, 42 from underground) and 6 wedges. The infill intercepts are located inside defined mineral resource estimate (“MRE”) blocks (see Osisko news release dated August 30, 2022). The expansion intercepts are located outside the MRE blocks and either expand resource wireframes or are in a defined zone or corridor not yet correlated to a specific wireframe.

A new Lynx 4 zone announced earlier this year (see Osisko news release dated March 23, 2022) was included in the recent MRE as Lynx 4 wireframe 3466. Two expansion holes confirmed the growth potential of this wireframe with intercepts 56.9 g/t Au over 2.4 metres and 14.0 g/t Au over 2.9 metres, 170 metres and 80 metres below the current MRE blocks, respectively.

Expansion intercepts extending wireframes include: 29.1 g/t Au over 5.8 metres, a 231-meter extension of Triple Lynx wireframe 3155 below the MRE blocks, 203 g/t Au over 5.2 metres, a 33-meter extension of Triple Lynx wireframe 3120 to the west, and 51.4 g/t Au over 2.1 meters, a 39-meter extension of Triple Lynx wireframe 3161 to the east.

Infill results in this release were received after the June 7, 2022 database closed for use in the recently released MRE, and were not included. These infill results will be used in future mine planning.

Osisko Chief Executive Officer John Burzynski commented: “Our drill program continues to deliver significant high-grade results. The expansion holes continue to clearly demonstrate additional potential growth of the resource base at Windfall. As the focus shifts to engineering and the pending feasibility study, we are reducing the number of active drills at site, however we will maintain exploration work on high-potential expansion areas as well as drilling on key infill areas for mine planning.”

Select infill high-grade intercepts include: 93.9 g/t Au over 7.6 metres in WST-22-1040, 127 g/t Au over 5.7 metres in WST-22-1032; 112 g/t Au over 5.9 metres in WST-22-1033; 57.0 g/t Au over 9.3 metres in OSK-W-22-2601-W7; 53.4 g/t Au over 8.2 metres in WST-22-1026; 214 g/t Au over 2.0 metres in WST-22-1029; 176 g/t Au over 2.1 metres in WST-22-1048; 151 g/t Au over 2.2 metres in WST-22-1068 and 155 g/t Au over 2.0 metres in WST-22-1071A. Maps showing hole locations and full analytical results are available at www.osiskomining.com. Maps: Long Section_Infill EN 20220915, Long Section_LX4-3466 EN 20220915, Long Section_Expan EN 20220915, PR_EN_20220915_Surface, PR_EN_20220915_UG.

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., LHW = Lynx Hangingwall, LSW = Lynx South West, 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.

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” as defined by National Instrument 43-101 – Standards of Disclosure for Mineral Projects (“NI 43-101”).

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 (“QA/QC”) 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 (“MRE“) defined by Osisko, as disclosed in the news release dated August 30, 2022, will be further described, including the key assumptions, parameters and methods used to estimate the mineral resource estimate disclosed in the August 30, 2022, news release, in the full technical report being prepared for this updated mineral resource estimate in accordance with NI 43-101, and will be available on SEDAR (www.sedar.com) under the Corporation’s issuer profile within 45 days, and assumes 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 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).

Cautionary Note Regarding Forward-Looking Information

This news release contains “forward-looking information” within the meaning of the applicable Canadian securities legislation that is based on expectations, estimates, projections and interpretations as at the date of this news release. Any statement that involves predictions, expectations, interpretations, beliefs, plans, projections, objectives, assumptions, future events or performance (often, but not always, using phrases such as “expects”, or “does not expect”, “is expected”, “interpreted”, “management’s view”, “anticipates” or “does not anticipate”, “plans”, “budget”, “scheduled”, “forecasts”, “estimates”, “potential”, “feasibility”, “believes” or “intends” or variations of such words and phrases or stating that certain actions, events or results “may”, “could”, “would”, “might” or “will” be taken to occur or be achieved) are not statements of historical fact and may be forward-looking information and are intended to identify forward-looking information. This news release contains the forward-looking information pertaining to, among other things: the Windfall gold deposit being one of the highest-grade resource-stage gold projects in Canada and having world-class scale; the key assumptions, parameters and methods used to estimate the mineral resource estimate disclosed in this news release; the prospects, if any, of the Windfall gold deposit; the timing and ability of Osisko to file a technical report for the mineral resource estimate disclosed in this news release; the timing and ability of Osisko, if at all, to publish a feasibility study for the Windfall gold deposit; upgrading an inferred mineral resource to a measured mineral resource or indicated mineral resource category; future exploration activities, including drilling, at the Windfall gold deposit; the deposit remaining open along strike and at depth; the plunge potential of the Lynx and Underdog zones; expected grade and resource growth; cut-off grade and sensitivity analysis; and the significance of historic exploration activities and results. Although the forward-looking information contained in this news release is based upon what management believes, or believed at the time, to be reasonable assumptions, Osisko cannot assure shareholders and prospective purchasers of securities of the Corporation that actual results will be consistent with such forward-looking information, as there may be other factors that cause results not to be as anticipated, estimated or intended, and neither Osisko nor any other person assumes responsibility for the accuracy and completeness of any such forward-looking information. Such factors include, among others, risks relating to the ability of exploration activities (including drill results) to accurately predict mineralization; errors in management’s geological modelling; the ability of Osisko to complete further exploration activities, including drilling; property and royalty interests in the Windfall gold deposit; the ability of the Corporation to obtain required approvals; the results of exploration activities; risks relating to mining activities; the global economic climate; metal prices; dilution; environmental risks; and community and non-governmental actions. Osisko does not undertake, and assumes no obligation, to update or revise any such forward-looking statements or forward-looking information contained herein to reflect new events or circumstances, except as may be required by law.

CONTACT INFORMATION:

John Burzynski
Chief Executive Officer
Telephone (416) 363-8653