WINDFALL PROPERTY

The Windfall property is 100% owned by Osisko Mining Inc. and consists of 286 individual claims covering an aggregate area of 12,523 hectares. The Windfall project, located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec, Canada is 700 kilometres north-northwest of Montréal, 200 kilometres northeast of Val-d’Or and 115 kilometres east of Lebel-sur-Quévillon. The Windfall project falls within the traditional territory of the Cree First Nation of Waswanipi.

Figure 1: Map showing the location of the Windfall project.

KEY FACTS

Windfall is a world-class gold deposit located in the Eeyou-Itschee James Bay territory of Quebec, Canada.

1,86 M oz Au6,023 MT AT 9.6 G/T AU (MEASURED AND INDICATED) MINERAL RESOURCE ESTIMATE

4.24 M oz Au16,401 MT AT 8.0 G/T AU (INFERRED) MINERAL RESOURCE ESTIMATE

125 km²PROJECT AREA

26%ZONE 27 POSITIVELY RECONCILED BULK SAMPLE

89%LYNX ZONE POSITIVELY RECONCILED BULK SAMPLE

1,224,453 mCURRENT DRILLING PROGRAM

3,467 mLONGEST DRILLHOLE IN CANADA

PEA HIGHLIGHTS

• First 7 years of full production: 300,000 oz Au per year average, 8.1 g/t Au average diluted grade
• Peak recovery of 328,000 oz Au in year 6; average production over 18 year life of mine (“LOM”) of 238,000 oz Au per year (based on MRE database as of November 2020)*
• 50.6% Pre-Tax Internal Rate of Return (“IRR”), 39.3% After-Tax IRR; C$2.6 Billion Pre-Tax Net Present Value (“NPV”), C$1.5 Billion After-Tax NPV; After-Tax Payback Period 2.2 years from start of production
• Average annual after-tax free cash flow of C$253 Million in the first seven years of full production (C$1.8 Billion cumulative), cumulative LOM after-tax free cash flow of C$2.6 Billion
• AISC of US$610/oz Au
• Capital expenditure (“Capex”) of C$544 Million (includes power line construction and C$55 Million as contingency in direct and indirect costs), NPV/Capex ratio of 2.7
• PEA assumes 3,100 tonnes per day (“tpd”) milling operation
• Average gold recovery of 94.8%; total operating cost of C$122/tonne
• Windfall will generate over C$8.2 Billion of gross revenue and C$1.7 Billion in taxes
• Creation of approximately 400 direct jobs and 200 indirect jobs during operation, over 500 jobs during construction

*Cautionary Statement – The reader is advised that the PEA summarized in the website is intended to provide only an initial, high-level review of the project potential and design options. The PEA mine plan and economic model include numerous assumptions and the use of inferred mineral resources. Inferred mineral resources are considered to be too speculative to be used in an economic analysis except as allowed for by NI 43-101 in PEA studies. There is no guarantee that inferred mineral resources can be converted to indicated or measured mineral resources, and as such, there is no guarantee the project economics described herein will be achieved.

Key results, assumptions and estimates contained in the technical report, entitled “Preliminary Economic Assessment Update for the Windfall Project” (the “Windfall PEA”) and dated April 23, 2021 (effective date of April 6, 2021), that has been prepared for Osisko by BBA Inc. with the assistance of a number of specialized consultants, including Andrieux & Associates Geomechanics Consulting LP, Entech Mining Ltd., GCM Consultants, Golder Associates Ltd., and WSP Canada Inc. The Windfall PEA is available on SEDAR (www.sedar.com) under Osisko’s issuer profile.

LATEST NEWS — WINDFALL

July 20, 2021

OSISKO DRILLING RETURNS HIGH-GRADE AT WINDFALL

July 7, 2021

OSISKO WINDFALL INFILL AND EXPANSION DRILLING CONTINUES TO ADD HIGH-GRADE

June 29, 2021

OSISKO WINDFALL INFILL AND EXPANSION DRILLING ADDS HIGH-GRADE