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Osisko Development Intercepts 361.93 G/T GOLD over 1.10 Meters (10.56 OZ/T GOLD over 3.60 Feet) IN Underground Sampling at Trixie, Tintic Project

Drill Results

NYSE: ODV TSXV: ODV NEWS RELEASE

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OSISKO DEVELOPMENT INTERCEPTS 361.93 G/T GOLD OVER 1.10 METERS (10.56 OZ/T

GOLD OVER 3.60 FEET) IN UNDERGROUND SAMPLING AT TRIXIE, TINTIC PROJECT

Montreal, Québec, September 1 3, 2023 – Osisko Development Corp. (NYSE: ODV, TSXV: ODV)

("Osisko Development " or the "Company") is pleased to announce chip sampling results from new

development areas as part of its ongoing exploration program at its 100%-owned Trixie test mine ("Trixie"),

within the Company's wider Tintic Project ("Tintic" or the "Tintic Project"), located in the historic East Tintic

Mining District in central Utah, U.S.A.

Chris Lodder, President of Osisko Development, commented, "The new developments at Trixie to the

north continue to show mineralization and high-grade gold samples within the T2 and T4 zones toward a

mineralizing fault structure, the Trixie Fault. We will continue to explore this area to the north toward the

historical 756 ore shoot. This area was previously developed over a 275-metre strike length down to vertical

depths of 300 meters and had an average grade of 6-8 g/t gold, while primarily mined for flux. This area

remains open in all directions. We are also pleased to announce the near completion of the new decline at

Trixie, which is expected to break through in the next few weeks. This is a milestone accomplishment for

our team that will improve access for deeper and nearby exploration as well as any future potential

production at Trixie or nearby target areas."

UNDERGROUND CHIP SAMPLE ASSAY HIGHLIGHTS

This news release includes assays from 41 underground exploration face, back and rib chip sample strings

in development at Trixie (refer to Table 1). Selected assay highlights include:

• 42.75 grams per tonne ("g/t") gold ("Au") and 25.23 g/t silver ("Ag") over 0.73 meters ("m") in

CH01539 (1.25 troy ounce per short ton ("oz/t") Au and 0.74 oz/t Ag over 2.4 feet ("ft."))

• 68.10 g/t Au and 39.10 g/t Ag over 1.68 m in CH01548 (1.99 oz/t Au and 1.14 oz/t Ag over 5.5 ft.)

including

o 422.49 g/t Au and 223.14 g/t Ag over 0.24 m (12.32 oz/t Au and 6.51 oz/t Ag over 0.80 ft.)

• 168.60 g/t Au and 161.33 g/t Ag over 1.06 m in CH01549 (4.92 oz/t Au and 4.71 oz/t Ag over 3.47

ft.) including

o 288.48 g/t Au and 262.50 g/t Ag over 0.61 m (8.41 oz/t Au and 7.66 oz/t Ag over 2.00 ft.)

• 361.93 g/t Au and 153.48 g/t Ag over 1.10 m in hole CH01561 (10.56 oz/t Au and 4.48 oz/t Ag over

3.60 ft.) including

o 590.81 g/t Au and 259.93 g/t Ag over 0.55 m (17.23 oz/t Au and 7.58 oz/t Ag over 1.80 ft.)

• 11.08 g/t Au and 12.02 g/t Ag over 3.17 m in CH01562 (0.32 oz/t Au and 0.35 oz/t Ag over 10.40

ft.)

• 40.35 g/t Au and 47.93 g/t Ag over 0.73 m in CH01566 (1.18 oz/t Au and 1.40 oz/t Ag over 2.40

ft.)

• 26.92 g/t Au and 271.51 g/t Ag over 1.52 m in CH01574 (0.79 oz/t Au and 7.92 oz/t Ag over 5.00

ft.) including

o 77.92 g/t Au and 769.73 g/t Ag over 0.37 m (2.27 oz/t Au and 22.45 oz/t Ag over 1.20 ft.)

CHIP SAMPLE RESULTS SUMMARY

• Chip samples were collected from the T2 structure and T4 stockwork on the 625 ft level and along

new development at the Trixie decline (See Figures 2 and 3).

• Sampling on the 625 ft-level focussed on development to the north towards the Trixie fault and the

756 vein.

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• Samples collected near the Trixie decline focussed on a new crosscut west towards the T2

structure at the 600 ft-level.

• Approximately 95% of the 1,390 m (4,550 ft.) Trixie portal and underground decline ramp has been

completed to date, with approximately 250 ft. remaining to breakthrough. The Company anticipates

completion of the decline ramp to the main 625 ft-level in Q3 2023.

• The sampling and drilling results provide support that our target areas to the north of Trixie and to

the south down plunge of the T2 structure are mineralized and warrant further follow-up exploration

drilling and sampling.

• These sampling results will provide valuable data to improve our understanding and the confidence

level of the mineralized zones defined in the area of the Trixie MRE (as defined herein) and support

a future mineral resource estimate ("MRE") update.

• The Company is currently working on an updated MRE for the Trixie deposit to incorporate the new

2023 drilling results and the remaining 2022 drilling that was not included in the Tintic Technical

Report (as defined herein) published on January 27, 2023 (with an effective date of January 10,

2023), due to assay lab delays. This new MRE is expected to be completed once the 2023 drilling

program has concluded and all assay results have been received.

Face Sampling Methodology

As most structures at Trixie are steeply dipping to the east or west, current sampling procedures are

designed to sample the structure. Chip samples are collected and do not exceed 1.0 m (3 ft.) in length.

The face is washed for safety, and for better identification of mineralization, alteration and structures. The

hanging wall and footwall of the structures are marked up on the face and back, samples intervals are

marked up and follow lithological contacts.

Samples are collected in feet and assays are reported in grams per tonne and troy ounce per short ton

gold and silver. Conversions to metric and imperial measurements are rounded to two decimal places.

About Trixie

The Trixie test mine is one of several gold and base metal targets within the larger Tintic Project consisting

of >17,000 acres of patented mining claims and mineral leases within the historic East Tintic Mining District

of Central Utah, U.S.A. The T2 and T4 structures at Trixie show multi -ounce gold grades associated with

high sulphidation epithermal mineralization, structurally controlled and hosted within quartzites. The T2

structure mineralization consists of native Au, and rare Au-Ag – rich telluride minerals with quartz. The T4

is a mineralized stockwork zone is located in the hanging wall of the T2 and is comprised of Au -Ag rich

mineralization in host rock quartzite with quartz-barite-sulphosalt stockwork veining. Mineralization reports

consistent multi-ounce gold grades along the entire strike length.

A 3D model and virtual site tour of Trixie and the wider Tintic Project is accessible on the Company's VRIFY

page at: https://vrify.com/decks/12801.

Information relating to the Tintic Project and the current MRE for the Trixie deposit (the "Trixie MRE") is

supported by the technical report entitled "NI 43-101 Technical Report, Initial Mineral Resource Estimate

for the Trixie Deposit, Tintic Project, Utah, United States of America ", dated January 27, 2023 (with an

effective date of January 10, 2023) prepared for the Company by independent representatives of Micon

International Limited (the "Tintic Technical Report"). Reference should be made to the full text of the Tintic

Technical Report, which was prepared in accordance with NI 43 -101 and is available electronically on

SEDAR+ (www.sedarplus.ca) and on EDGAR ( www.sec.gov) under Osisko Development 's issuer profile

and on the Company's website at www.osiskodev.com.

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Figure 1: Trixie Project Area

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Figure 2: Trixie Long Section

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Figure 3: Trixie Long Section Sample Highlights

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Table 1: Chip Sample Length Weighted Assay Composites at Trixie

METRIC IMPERIAL

Hole ID Depth

from (m)

Depth to

(m)

Length

(m) Au (g/t) Ag (g/t) Depth

from (ft.)

Depth to

(ft.)

Length

(ft.) Au (oz/t) Ag (oz/t) Target

CH01535 0.70 1.37 0.67 2.47 413.75 2.30 4.50 2.20 0.07 12.07 T4

CH01536 0.00 1.37 1.37 7.24 18.21 0.00 4.50 4.50 0.21 0.53 T4

CH01536 Including 0.00 0.49 0.49 17.24 42.27 0.00 1.60 1.60 0.50 1.23 T4

CH01537 0.61 1.68 1.07 12.25 60.28 2.00 5.50 3.50 0.36 1.76 T2

CH01538 No Significant Assays T2

CH01539 0.00 1.52 1.52 21.80 18.96 0.00 5.00 5.00 0.64 0.55 T2

CH01539 Including 0.79 1.52 0.73 42.75 25.23 2.60 5.00 2.40 1.25 0.74 T2

CH01540 0.00 1.52 1.52 0.34 373.02 0.00 5.00 5.00 0.01 10.88 T2

CH01541 No Significant Assays Trixie Decline

CH01543 0.00 1.04 1.04 5.92 17.84 0.00 3.40 3.40 0.17 0.52 T2

CH01543 Including 0.24 0.61 0.37 11.31 29.38 0.80 2.00 1.20 0.33 0.86 T2

CH01544 0.00 0.76 0.76 18.03 63.87 0.00 2.50 2.50 0.53 1.86 T2

CH01545 0.00 0.76 0.76 10.10 17.37 0.00 2.50 2.50 0.29 0.51 T2

CH01545 Including 0.37 0.76 0.40 13.44 18.41 1.20 2.50 1.30 0.39 0.54 T2

CH01546 0.00 1.58 1.58 5.06 3.85 0.00 5.20 5.20 0.15 0.11 T2

CH01546 Including 1.10 1.58 0.49 9.84 - 3.60 5.20 1.60 0.29 - T2

CH01548 0.00 1.68 1.68 68.10 39.10 0.00 5.50 5.50 1.99 1.14 T2

CH01548 Including 0.00 0.24 0.24 422.49 223.14 0.00 0.80 0.80 12.32 6.51 T2

CH01549 0.00 1.40 1.06 168.60 161.33 0.00 4.60 3.47 4.92 4.71 T2

CH01549 Including 0.00 0.61 0.61 288.48 262.50 0.00 2.00 2.00 8.41 7.66 T2

CH01550 0.00 1.04 1.04 7.95 38.51 0.00 3.40 3.40 0.23 1.12 T2

CH01550 Including 0.00 0.27 0.27 13.30 49.90 0.00 0.90 0.90 0.39 1.46 T2

CH01551 1.52 3.05 1.52 3.43 - 5.00 10.00 5.00 0.10 - T2

CH01552 0.94 1.34 0.40 3.43 - 3.10 4.40 1.30 0.10 - T2

CH01554 0.61 0.70 0.09 1.20 36.82 2.00 2.30 0.30 0.04 1.07 T2

CH01556 0.73 3.05 2.32 - 152.66 2.40 10.00 7.60 - 4.45 T2

CH01556 7.62 9.14 1.52 - 89.41 25.00 30.00 5.00 - 2.61 T2

CH01557 8.53 9.14 0.61 - 84.92 28.00 30.00 2.00 - 2.48 T2

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METRIC IMPERIAL

Hole ID Depth

from (m)

Depth to

(m)

Length

(m) Au (g/t) Ag (g/t) Depth

from (ft.)

Depth to

(ft.)

Length

(ft.) Au (oz/t) Ag (oz/t) Target

CH01558 0.00 0.15 0.15 - 110.39 0.00 0.50 0.50 - 3.22 T2

CH01559 No Significant Assays Trixie Decline

CH01560 4.82 5.49 0.67 - 46.76 15.80 18.00 2.20 - 1.36 T2

CH01561 0.00 1.10 1.10 361.93 153.48 0.00 3.60 3.60 10.56 4.48 T2

CH01561 Including 0.00 0.55 0.55 590.81 259.93 0.00 1.80 1.80 17.23 7.58 T2

CH01562 0.00 3.17 3.17 11.08 12.02 0.00 10.40 10.40 0.32 0.35 Trixie Decline

CH01562 Including 0.00 1.52 1.52 17.45 9.19 0.00 5.00 5.00 0.51 0.27

CH01563 No Significant Assays Trixie Decline

CH01564 0.00 0.82 0.82 30.07 91.36 0.00 2.70 2.70 0.88 2.66 T2

CH01565 3.05 4.57 1.52 12.96 45.63 10.00 15.00 5.00 0.38 1.33 T2

CH01566 0.00 0.73 0.73 40.35 47.93 0.00 2.40 2.40 1.18 1.40 T2

CH01567 0.00 1.07 1.07 14.58 242.42 0.00 3.50 3.50 0.43 7.07 T2

CH01567 Including 0.61 1.07 0.46 26.40 507.23 2.00 3.50 1.50 0.77 14.79 T2

CH01568 0.85 1.46 0.61 1.75 11.83 2.80 4.80 2.00 0.05 0.34 T2

CH01569 0.00 0.61 0.61 18.38 121.08 0.00 2.00 2.00 0.54 3.53 T2

CH01570 No Significant Assays Trixie Decline

CH01571 0.91 1.52 0.61 4.29 100.45 3.00 5.00 2.00 0.13 2.93 T2

CH01572 0.00 1.52 1.52 1.14 9.69 0.00 5.00 5.00 0.03 0.28 T2

CH01573 0.00 1.40 1.40 4.67 17.45 0.00 4.60 4.60 0.14 0.51 T2

CH01574 0.00 1.52 1.52 26.92 271.51 0.00 5.00 5.00 0.79 7.92 T2

CH01574 Including 0.34 0.70 0.37 77.92 769.73 1.10 2.30 1.20 2.27 22.45 T2

CH01574 and 0.98 1.37 0.40 18.07 273.06 3.20 4.50 1.30 0.53 7.96 T2

CH01575 0.00 0.91 0.91 15.43 31.35 0.00 3.00 3.00 0.45 0.91 T2

CH01576 0.00 1.52 1.52 16.25 21.32 0.00 5.00 5.00 0.47 0.62 T2

CH01577 0.00 1.52 1.52 3.77 118.44 0.00 5.00 5.00 0.11 3.45 T2

CH01578 0.00 1.13 1.13 12.92 36.20 0.00 3.70 3.70 0.38 1.06 T2

CH01578 Including 0.00 0.46 0.46 22.87 65.75 0.00 1.50 1.50 0.67 1.92 T2

CH01579 0.00 1.22 1.22 4.66 11.24 0.00 4.00 4.00 0.14 0.33 T2

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Qualified Persons

The scientific and technical information contained in this news release has been reviewed and approved

by Maggie Layman, P.Geo., Vice President, Exploration of Osisko Development, and a "qualified person"

within the meaning of NI 43-101.

Quality Assurance (QA) – Quality Control (QC)

Underground face samples are collected by Company geologists from each of the active mining faces, with

samples transported by the geologists from Trixie to the on-site Company laboratory located at the Burgin

administrative complex. Underground samples are dried, crushed to <10 mm and a 250 g split is taken.

The split is pulverized, and a 30 g Fire Assay with gravimetric finish is completed to determine gold and

silver grades, reported in oz/short ton and g/t.

The Company's Burgin laboratory is not a certified analytical laboratory, but the facility is managed by a

qualified laboratory manager with annual auditing by technical staff. Inter -laboratory check assays using

ALS Laboratory as a third-party independent analysis of samples is routinely carried out as part of ongoing

QA/QC work. Certified OREAS QC standards and blanks are inserted at regular intervals in the sample

stream to monitor laboratory performance.

True width determination is estimated to be approximately 0.3 m to 2.4 m (1 to 8 ft.) wide for the T2 structure

and approximately 3 m to 25 m (10 to 80 ft.) for the T4 mineralized stockwork zone located in the hanging

wall of the T2 structure.

About Osisko Development Corp.

Osisko Development Corp. is a premier North American gold development company focused on high-quality

past-producing properties located in mining friendly jurisdictions with district scale potential. The Company's

objective is to become an intermediate gold producer by advancing its 100%-owned Cariboo Gold Project,

located in central B.C., Canada, the Tintic Project in the historic East Tintic mining district in Utah, U.S.A.,

and the San Antonio Gold Project in Sonora, Mexico. In addition to considerable brownfield exploration

potential of these properties, that benefit from significant historical mining data, existing infrastructure and

access to skilled labour, the Company's project pipeline is complemented by other prospective exploration

properties. The Company 's strategy is to develop attractive, long -life, socially and environmentally

sustainable mining assets, while minimizing exposure to development risk and growing mineral resources.

For further information, please contact Osisko Development Corp.:

Sean Roosen Philip Rabenok

Chairman and CEO Director, Investor Relations

Email: [email protected] Email: [email protected]

Tel: +1 (514) 940-0685 Tel: +1 (437) 423-3644

CAUTIONARY STATEMENTS

Cautionary Statement Regarding Test Mining Without Feasibility Study

The Company cautions that its prior decision to commence small -scale underground mining activities and batch vat leaching at the

Trixie test mine was made without the benefit of a feasibility study, or reported mineral resources or mineral reserves, demo nstrating

economic and technical viability, and, as a result there may be increased uncertainty of achieving any particular level of recovery of

material or the cost of such recovery. The Company cautions that historically, such projects have a much higher risk of economic and

technical failure. Small scale test -mining at Tri xie was suspended in December 2022 and resumed in the second quarter of 2023.

Even with the resumption of small -scale test-mining at Trixie, there is no guarantee that production will continue as anticipated or at

all or that anticipated production costs will be achieved. The failure to continue production may have a material adverse impact on the

Company's ability to generate revenue and cash flow to fund operations. Failure to achieve the anticipated production costs may have

a material adverse impact on the Company 's cash flow and potential profitability. In continuing current operations at Trixie, the

Company has not based its decision to continue such operations on a feasibility study, or reported mineral resources or miner al

reserves demonstrating economic and technical viability.