Osisko Development : Cariboo Feasibility Study (April 2025)

ODV.V

APRIL 2025

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CARIBOO GOLD PROJECT - 2025 OPTIMIZED FEASIBILITY STUDY

SHOVEL READY PROJECT IN A TIER 11 MINING JURISDICTION

Limited universe of permitted development stage gold assets of scale in safe jurisdictions

SCALABLE ASSET WITH MEANINGFUL UPSIDE

Multi-million-ounce deposit at an average depth ~350 meters & open at depth; processing facilities

designed to accommodate expansion options assuming future resource conversions

DEVELOPING A DISTRICT MINING CAMP

Untapped exploration potential along two ~83 km mineralized trends on a ~1,900 km2 property-

larger than the entire Val d'Or camp-with numerous prospective targets

RESPONSIBLE STAKEHOLDER ENGAGEMENT

Focused on fostering and developing long-term partnerships and positive stakeholder relations

including with principal First Nations partners

1. Based on the Investment Attractive Index as outlined in the Fraser Institute Annual Survey of Mining Companies (2023).

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CARIBOO GOLD PROJECT - 2025 OPTIMIZED FEASIBILITY STUDY

All $ figures in CAD, unless otherwise noted (USDCAD 1.35 base case)

202 koz/yr in the first 5 years

Based on current reserves only

2028 first full year of production

US$1,157/OZ AISC*

US$947/oz total cash cost*

~US$652M initial capex1

92.6% total recovery rate LOM

BASE $2,400/oz | SPOT $3,300/oz

After-tax NPV5%2

BASE $2,400/oz | SPOT $3,300/oz

After-tax IRR2

M&I Resources | Inferred3

Significant conversion potential

Source: Refer to the 2025 FS for the assumptions, qualifications and limitations relating to disclosure about the 2025 Feasibility Study on the Cariboo Gold Project.

1. Based on base case USDCAD 1.35 exchange rate. 2. Based on USDCAD exchange rate of 1.35 under base case and 1.40 under spot case. 3. Mineral reserves include probable reserves 2.071 Moz Au (17.815 Mt grading 3.62 g/t Au). Mineral resources include in the measured category, 8 koz Au (47 kt grading 5.06 g/t Au); in Indicated, 1.604 Moz Au (17.332 Mt grading 2.88 g/t Au); in Inferred, 1.864 Moz Au (18.774 Mt grading 3.09 g/t Au). M&I resources are exclusive of mineral reserves.

*Non-IFRS Measure. See Cautionary Statements - Non-IFRS Measures.

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Accelerated Development Sequence

​ $296 million Free Cash Flow* in the first 5 years vs. -$63 million under the 2023 FS

​ Single-phase construction and ramp up directly to 4,900 tpd

​ +16% increase in annual gold production to 190 koz (LOM avg.); 202 koz in the first 5 years

Streamlined

Processing Operations consolidated into a single location at the mine site

​ Removes the need to transport flotation concentrate 116 km to the QR Mill (as previously contemplated)

Improved Flowsheet Design

​ Added gravity circuit expected to recover ~46% of gold in doré at site

​ Higher grade concentrate averaging 133 g/t Au (vs. 28 g/t previously) 80% reduction in transport trucks

​ Overall project recovery 92.6% over the LOM

Underground Mine Design

​ +60% increase in average stope size to ~5,600 t (~3,500 t previously) significantly reduces total number of stopes required to achieve average daily throughput

​ Allows for more operational flexibility of underground operations

Mineral

Reserves Probable Mineral Reserves largely unchanged - 2,071 koz (17.82 Mt at 3.62 g/t)

− Previously 2,031 koz (16.70 Mt at 3.78 g/t) in 2023 FS

Fully

Permitted

​ Mines Act and Environmental Management Act (British Columbia) permits secured in Q4 2024

​ 2025 FS design and sequencing aligned with obtained permits

− Transmission line permit work ongoing, expected in H2 2025

Source: Refer to the 2025 FS for the assumptions, qualifications and limitations relating to disclosure about the 2025 Feasibility Study on the Cariboo Gold Project. The 2023 Feasibility Study is based on the technical report titled "NI 43-101 Technical Report, Feasibility Study for the Cariboo Gold Project, District of Wells, British Columbia" (as amended) dated January 12, 2023 (with an effective date of December 30, 2022), a copy of which is available on SEDAR (https://www.sedarplus.ca) under the Company's issuer profile ("2023 FS").

*Non-IFRS Measure. See Cautionary Statements - Non-IFRS Measures.

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CARIBOO GOLD PROJECT - 2025 OPTIMIZED FEASIBILITY STUDY

Disclaimer

Osisko Development Corp. published this content on April 28, 2025, and is solely responsible for the information contained herein. Distributed via Public Technologies (PUBT), unedited and unaltered, on April 28, 2025 at 12:49 UTC.