Osisko Windfall 2023 Drilling Update Regional Exploration to Resume

The 2023 drilling campaign primarily targeted infill areas. Since the start of the year, over 95,000 metres have been drilled by 8 underground rigs focused on the Lynx segment of the deposit.

Highlights from the 2023 drill program are presented below and include 320 intercepts from 248 drill holes and 1 wedge. These highlights are intercepts with a metal factor (grams*meters) greater than 20. The intercepts are all located within the defined mineral resource estimate ("MRE") 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 indicated mineral resources or indicated minerals resources to measured mineral resources as applicable.

Osisko Chief Executive Officer John Burzynski commented: "Infill drilling at the Windfall deposit is progressing well and confirming our models. High-grade gold continues to be intercepted in the Lynx areas including Triple Lynx, once again highlighting the world-class nature of the deposit. Of note, we have more than ten intervals in this set of numbers that returned values over one kilogram per tonne of gold. Infill drilling will continue into next year. We and our joint venture partner are very much looking forward to resuming exploration on our greater than 2,300 square kilometer land package around Windfall in the coming months."

Regional exploration in the Urban Barry area will recommence on near-deposit and regional grassroots targets. Exploration will include ground geophysics and diamond drilling of various targets.

Maps showing Windfall hole locations are available at www.osiskomining.com.
Maps: Top_Intersect_2023, PR_Longsections_ 20231026_EN.

2023 Drilling

Notes: True widths are estimated at 55 - 80% of the reported core length interval. See "Quality Control and Reporting Protocols" below. LXM = Lynx Main, LHW = Lynx Hanging Wall, and TLX = Triple Lynx. *0.5 meters of core not recovered in this interval.

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 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 ("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 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 Mineral Reserve, 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 the FS Technical Report, which was prepared in accordance with National Instrument 43-101 - Standards of Disclosure for Mineral Projects ("NI 43-101"). The FS Technical Report is available on SEDAR+ (www.sedarplus.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 50% interest in the high-grade Windfall gold deposit located between Val-d'Or and Chibougamau in Québec and holds a 50% interest in a large area of claims in the surrounding Urban Barry area and nearby Quévillon area (over 2,300 square kilometers).

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" or "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 expected timing (if at all) to hook-up the power line; the expected allocation of power under the power allocation agreement being realized (if any); the expected power demand for Windfall; the assumptions limitations and qualifications in the FS Technical Report, including relating to the Windfall Resource Estimate and Windfall Reserve Estimate; reliance on third-parties for infrastructure, including power lines, with reference to the agreement with Miyuukaa for the transmission of hydroelectric power to the Windfall site; the results of the FS Technical Report, including NPV, IRR, production, tax-free cash flows, capex, AISC, milling operations, average recovery, job creation; the Lynx zone remaining open to expansion down plunge. Such factors include, among others, risks relating to the ability of exploration activities (including drill results) to accurately predict mineralization; reliance on third-parties, including governmental entities, for mining activities, including for infrastructure; the timing and ability, if at all, to obtain permits; the reliance on third-parties for infrastructure critical to build and operate the Windfall project, including power lines; our ability to obtain power for the Windfall project, if at all or on terms economic to the Corporation; the status of third-party approvals or consents; errors in management's geological modelling; the ability of Osisko to complete further exploration activities, including (infill) 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 Canadian/United States dollar exchange rate; the global economic climate; metal (including gold) prices; dilution; environmental risks; and community and non-governmental actions. For additional information with respect to these and other factors and assumptions underlying the forward-looking information in this news release, please see the section entitled "Risk Factors" in the most recent annual information form of Osisko for the year ended December 31, 2022, a copy of which is available on SEDAR+ (www.sedarplus.com) under Osisko's issuer profile. 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. 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