Mr. John Burzynski reports

OSISKO WINDFALL 2023 DRILLING UPDATE REGIONAL EXPLORATION TO RESUME

Osisko Mining Inc. has provided an update from the continuing drill program at its 50-per-cent-owned Windfall gold project, located in the Abitibi greenstone belt, Urban township, Eeyou Istchee James Bay, Quebec.

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

Highlights from the 2023 drill program are presented herein and include 320 intercepts from 248 drill holes and one wedge. These highlights are intercepts with a metal factor (grams times metres) 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, 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 10 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-kilometre 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.

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 plus or minus silica alteration and contains 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 plus or minus tourmaline alteration and contains disseminated pyrite from trace to 80 per cent with local visible gold. Pyrite stockworks can form envelopes that reach several tens of metres in thickness. 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 Isabelle Roy, PGeo (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 per cent to 80 per cent 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 one-kilogram screen fire assay or standard 50-gram fire assay/AA finish or gravimetric finish at: (i) ALS Laboratories in Val d'Or, Que., Vancouver, B.C., Lima, Peru, or Vientiane, Laos; (ii) Bureau Veritas in Timmins, Ont. The one-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 multielements, including silver, using a four-acid digestion/ICP-MS method at ALS Laboratories. Drill program design, quality assurance/quality control and interpretation of results are performed by qualified persons employing a quality assurance/quality control program consistent with NI 43-101 and industry best practices. Standards and blanks are included with every 20 samples for quality assurance/quality control purposes by the corporation as well as the lab. Approximately 5 per cent of sample pulps are sent to secondary laboratories for check assay.

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-per-cent interest in the high-grade Windfall gold deposit, located between Val d'Or and Chibougamau in Quebec, and holds a 50-per-cent interest in a large area of claims in the surrounding Urban Barry area and nearby Quevillon area (over 2,300 square kilometres).

We seek Safe Harbor.