Windfall Updated Mineral Resource Estimate

TORONTO - Osisko Mining Inc. reported on updated mineral resource estimate (MRE) for the Windfall gold deposit, located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec.

This MRE reflects the results of approximately 1.7 million meters of drilling, with 1.5 million meters completed by Osisko since October 2015, and includes all drilling completed as of September 2021 and all analytical results received as of October 20, 2021.

An additional 70,000 meters of infill and expansion drilling has been completed since September 2021. This additional drilling and outstanding analytical results, together with ongoing surface and underground drilling, will be integrated into the database for the pending feasibility study expected to be completed in Q4 2022.

Highlights include: 3.2 M oz measured & indicated ("M&I") resource avg. 10.5 g/t Au; M&I resource increase of 73% with avg. grade increased by 14%; Lynx contains 60% of MRE total gold.

Additional Lynx resource highlights: M&I 2.3 M oz avg. 12g/t Au; Inferred 1.8 M oz avg. 10.9 g/t Au; 3.6 M oz inferred resource avg. 8.6 g/t Au, reflecting a grade increase of 8%; 50% of the MRE is hosted in 30 wireframes; 98% of MRE is located from surface to 1200 m vertical depth; Exploration ramp access currently at >600 m vertical depth in Lynx; Lynx 600 bulk sample (Triple Lynx at level 600) work in progress; prior Lynx 311 bulk sample returned 189% positive grade reconciliation (see Osisko news release dated December 11, 2019); and strong open potential for expansion of high-grade zones in Lynx to the East and down plunge.

Chief Executive Officer, John Burzynski, said, "The world-class Windfall deposit continues to impress with grade and scale. Infill drilling has again exceeded our expectations, with excellent conversion, and the M&I resource increasing by 73% with average gold grade moving past double digits to 10.5 g/t. This MRE forms a strong foundation for the upcoming feasibility study. We are confident that as we complete the remaining infill work in the coming months, the resource will continue to grow and we should again see incremental increase in what is already a strong average grade.

Windfall is an outstanding, well-defined deposit which still has demonstrable strong upside potential to grow. The consistent trend over the past five years of drilling, as we completed our extensive and detailed surface and underground work programs, has been steady growth of ounces and increasing high-grade. We are confident that Windfall will grow significantly in the future with continued work. We would like very much to thank our employees and contractors for their tremendous efforts to advance our project, our Cree First Nation hosts and partners, the local and provincial governments, and our stakeholders and shareholders for their strong support."