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Osisko Development Intersects 13.32 G/T Au over 11.40 Meters and 115.5 G/T Au over 0.95 Meter at Valley Zone

Drill Results

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OSISKO DEVELOPMENT INTERSECTS 13.32 G/T AU OVER 11.40 METERS AND

115.5 G/T AU OVER 0.95 METER AT VALLEY ZONE

MONTREAL, October 5, 2021 – Osisko Development Corp. (“Osisko Development” or the “Company”)

(TSX.V-ODV) is pleased to announce drilling results from the 2021 exploration and category conversion

drill program campaign at its Cariboo Gold Project (“ Cariboo”) in central British Columbia. A total of 10

diamond drill rigs are currently active on the Project.

Summary

• A total of 138,000 meters have been drilled thus far in 2021. Of that, 46,000 meters have been

drilled in the Valley Zone.

• Recent assay results include holes CM-21-030 to CM-21-043 (Figure 1).

• CM-21-033 assayed 100.00 g/t Au over 0.50 meter, CM -21-041 assayed 112.50 g/t Au over

0.50 meter and 115.50 g/t Au over 0.95 meter (Figure 2).

• CM-21-038 intersected multiple mineralized vein corridors including 13.32 g/t Au over

11.40 meters with high-grade samples of 31.40 g/t Au over 0.50 meter, 27.40 g/t Au over 1.00

meter, 23.30 g/t Au over 1.40 meter, 47.40 g/t Au over 1.30 meters, and 20.10 g/t Au over 0.60

meter.

• CM-21-043 assayed 7.09 g/t Au over 12.70 meters including samples of 19.40 g/t Au over 1.30

meters, 10.45 g/t Au over 1.40 meters, 16.80 g/t Au over 0.60 meters, 14.50 g/t Au over 0.50

meter, 10.55 g/t Au over 0.60 meter and 14.05 g/t Au over 0.50 meter. This interval is open along

strike and at depth.

• Detailed drilling results and a drill hole location plan map are presented at the end of this release.

Chris Lodder, President of Osisko Development commented, “Each of these 14 drill holes returned highly

anomalous gold assays in the Valley Zone. The intervals reported are vein corridors comprised of many

individual mineralized quartz veins within the sandstone. The gold is associated with the quartz vein-hosted

pyrite. During production, these higher-grade samples will be separated using an ore sorter to improve the

overall grade of the pre-concentrate.”

Assay Highlights

• 13.05 g/t Au over 4.65 meters in hole CM-21-030 including

• 62.70 g/t Au over 0.90 meter

• 10.83 g/t Au over 3.90 meters in hole CM-21-030 including

• 71.90 g/t Au over 0.50 meter

• 63.90 g/t Au over 1.05 meters in hole CM-21-031

• 51.00 g/t Au over 0.50 meter in hole CM-21-031

• 16.63 g/t Au over 4.50 meters in hole CM-21-033 including

• 100.00 g/t Au over 0.50 meter

• 84.10 g/t Au over 1.10 meters in hole CM-21-034

• 13.10 g/t Au over 3.15 meters in hole CM-21-034

• 17.60 g/t Au over 2.90 meters in hole CM-21-035 including

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• 35.60 g/t Au over 0.80 meter

• 58.10 g/t Au over 0.50 meter in hole CM-21-037

• 4.44 g/t Au over 10.10 meters in hole CM-21-037

• 19.37 g/t Au over 2.60 meters in hole CM-21-038 including

• 55.00 g/t Au over 0.75 meter

• 13.32 g/t Au over 11.40 meters in hole CM-21-038 including

• 47.40 g/t Au over 1.30 meters

• 6.51 g/t Au over 17.90 meters in hole CM-21-039 including

• 31.90 g/t Au over 1.30 meters

• 61.50 g/t Au over 0.50 meter in hole CM-21-039

• 11.15 g/t Au over 3.00 meters in hole CM-21-039

• 10.23 g/t Au over 2.85 meters in hole CM-21-040

• 38.50 g/t Au over 0.65 meter in hole CM-21-041

• 112.50 g/t Au over 0.50 meter in hole CM-21-041

• 7.38 g/t Au over 11.35 meters in hole CM-21-041

• 115.50 g/t Au over 0.95 meter in hole CM-21-041

• 7.98 g/t Au over 8.10 meters in hole CM-21-042 including

• 92.30 g/t Au over 0.50 meter

• 11.99 g/t Au over 7.30 meters in hole CM-21-043

• 6.17 g/t Au over 7.00 meters in hole CM-21-043

• 7.09 g/t Au over 12.70 meters in hole CM-21-043

Mineralized quartz veins on Cariboo are overall sub- vertical dip and northeast strike. Vein corridors are

defined as a high- density network of mineralized quartz veins within the axis of the last folding event and

hosted within a brittle meta- sandstone or calcareous meta- sandstone. Vein corridors are modelled at a

minimum thickness of 2 meters and average about 4.5 meters true width. Individual mineralized veins within

these corridors have widths varying from centimeters to several meters and strike lengths from a few meters

to over 50 meters. These corridors have been defined from surface to a vertical depth averaging 300 meters

and remain open for expansion at depth and along strike. Gold grades are intimately associated with quartz

vein-hosted pyrite as well as pyritic, intensely silicified wall rock haloes in close proximity to the veins.

True widths are estimated to be 60% to 75% of reported core length intervals. Intervals not recovered by

drilling were assigned zero grade. Top cuts have not been applied to high grade assays. Complete assay

highlights are presented in Table 1, drill hole locations are listed in Table 2.

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Figure 1: Cariboo deposit areas overview map

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Figure 2: Valley Zone select drilling highlights

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Qualified Persons

Per National Instrument 43-101 Standards of Disclosure for Mineral Projects, Maggie Layman, P.Geo. Vice

President Exploration of Osisko Development Corp. , is a Qualified Person and has prepared, validated,

and approved the technical and scientific content of this news release.

Quality Assurance – Quality Control

Once received from the drill and processed, all drill core samples are sawn in half, labelled and bagged.

The remaining drill core is subsequently stored on site at a secured facility in Wells, BC. Numbered security

tags are applied to lab shipments for chain of custody requirements. Quality control (QC) samples are

inserted at regular intervals in the sample stream, including blanks and reference materials with all sample

shipments to monitor laboratory performance. The QAQC program was designed and approved by Lynda

Bloom, P.Geo. of Analytical Solutions Ltd.

Drill core samples are submitted to ALS Geochemistry’s analytical facility in North V ancouver, British

Columbia for preparation and analysis. The ALS facility is accredited to the ISO/IEC 17025 standard for

gold assays and all analytical methods include quality control materials at set frequencies with established

data acceptance criteria. The entire sample is crushed, and 250 grams is pulverized. Analysis for gold is

by 50g fire assay fusion with atomic absorption (AAS) finish with a lower limit of 0.01 ppm and upper limit

of 100 ppm. Samples with gold assays greater than 100 ppm are re-analyzed using a 1,000g screen metallic

fire assay. A selected number of samples are also analyzed using a 48 multi -elemental geochemical

package by a 4- acid digestion, followed by Inductively Coupled Plasma Atomic Emission Spectroscopy

(ICP-AES) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS).

About Osisko Development Corp.

Osisko Development Corp. is uniquely positioned as a premier gold development company in North

America to advance the Cariboo Gold Project and other Canadian and Mexican properties, with the

objective of becoming the next mid- tier gold producer. The Cariboo Gold Project, located in central British

Columbia, is Osisko Development's flagship asset with measured and indicated resources of 21.44 Mt at

4.6 Au g/t for a total of 3.2 million ounces of gold and inferred resource of 21.69 Mt at 3.9 Au g/t for a total

of 2.7 million ounces of gold (see NI 43- 101 Technical Report and mineral resource estimate effective

October 5th, 2020) . The considerable exploration potential at dept h and along strike distinguishes the

Cariboo Gold Project relative to other development assets as does the historically low, all-in discovery costs

of US $19 per ounce. The Cariboo Gold Project is advancing through permitting as a 4,750 tonnes per day

underground operation with a feasibility study on track for completion in the first half of 2022. Osisko

Development's project pipeline is complemented by potential near -term production targeted from the San

Antonio gold project, located in Sonora Mexico and early exploration stage properties including the Coulon

Project and James Bay Properties located in Québec as well as the Guerrero Properties located in Mexico.

Osisko Development began trading on the TSX Venture Exchange under the symbol “ ODV” on

December 2, 2020.

For further information, please contact Osisko Development Corp.:

Jean Francois Lemonde

VP Investor Relations

[email protected]

Tel: 514-299-4926

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Forward-looking Statements

Certain statements contained in this press release may be deemed “forward‐looking statements” within the

meaning of applicable Canadian and U.S. securities laws. These forward ‐looking statements, by their

nature, require Osisko Development to make certain assumptions and necessarily involve known and

unknown risks and uncertainties that could cause actual results to differ materially from those expressed or

implied in these forward ‐looking statements. Forward ‐looking statements are not guar antees of

performance. Words such as “may”, “will”, “would”, “could”, “expect”, “believe”, “plan”, “anticipate”, “intend”,

“estimate”, “continue”, or the negative or comparable terminology, as well as terms usually used in the

future and the conditional, are intended to identify forward ‐looking statements. Information contained in

forward‐looking statements is based upon certain material assumptions that were applied in drawing a

conclusion or making a forecast or projection, including management’s percept ions of historical trends,

current conditions and expected future developments, including with respect to results of further exploration

work to define and expand mineral resources, expected conclusions of optimization studies, that vein

corridors continue to be defined as a high- density network of mineralized quartz within the axis of the last

folding event and hosted within the sandstones and that the deposit remains open for expansion at depth

and down plunge, as well as other considerations that are believed to be appropriate in the circumstances.

Osisko Development considers its assumptions to be reasonable based on information currently available,

but cautions the reader that their assumptions regarding future events, many of which are beyond the

control of Osisko Development, may ultimately prove to be incorrect since they are subject to risks and

uncertainties that affect Osisko Development and its business. Such risks and uncertainties include, among

others, risks relating to the ability of explorati on activities (including drill results) to accurately predict

mineralization; errors in management’s geological modelling; the ability of to complete further exploration

activities, including drilling; property and royalty interests in the Cariboo gold deposit; the ability of the

Corporation to obtain required approvals; the results of exploration activities; risks relating to mining

activities; the global economic climate; metal prices; dilution; environmental risks; and community and non-

governmental acti ons and the responses of relevant governments to the COVID -19 outbreak and the

effectiveness of such responses.

For additional information with respect to these and other factors and assumptions underlying the forward ‐

looking statements made in this news r elease concerning Osisko Development, see the Filing Statement

available electronically on SEDAR (www.sedar.com) under Osisko Development's issuer profile. The

forward‐looking statements set forth herein concerning Osisko Development reflect management's

expectations as at the date of this news release and are subject to change after such date. Osisko

Development disclaims any intention or obligation to update or revise any forward- looking statements,

whether as a result of new information, future events or otherwise, other than as required by law.

Neither the TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in

the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of

this news release. No stock exchange, securities commission or other regulatory authority has

approved or disapproved the information contained herein.

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Table 1: Cariboo Gold Project 2021 Length Weighted Drill Hole Gold Composites

HOLE ID FROM M TO (M) LENGTH

(M) AU (G/T)

CM-21-030 82.50 83.00 0.50 10.20

127.50 128.70 1.20 6.31

181.85 183.95 2.10 3.75

194.10 194.70 0.60 4.21

201.75 206.40 4.65 13.05

Including 202.25 202.75 0.50 4.73

and 205.50 206.40 0.90 62.70

218.60 222.50 3.90 10.83

Including 218.60 219.10 0.50 71.90

and 222.00 222.50 0.50 9.46

294.65 296.75 2.10 6.10

Including 295.15 295.75 0.60 7.55

and 295.75 296.25 0.50 15.85

330.00 331.90 1.90 3.77

Including 330.00 330.90 0.90 6.19

420.60 421.10 0.50 5.38

CM-21-031 33.95 35.00 1.05 63.90

53.40 55.00 1.60 17.91

Including 53.40 54.00 0.60 5.04

and 54.50 55.00 0.50 51.00

CM-21-032 26.70 27.20 0.50 5.62

35.85 36.35 0.50 6.99

52.90 54.60 1.70 8.50

Including 53.90 54.60 0.70 17.25

89.50 90.00 0.50 6.32

339.05 341.75 2.70 4.51

Including 341.15 341.75 0.60 16.35

348.85 349.40 0.55 8.24

355.70 360.00 4.30 4.78

Including 359.05 360.00 0.95 14.65

407.50 408.10 0.60 4.46

418.95 422.10 3.15 4.95

Including 418.95 420.00 1.05 5.69

and 420.00 420.50 0.50 15.30

429.50 430.00 0.50 8.52

448.20 448.70 0.50 6.00

CM-21-033 109.00 113.50 4.50 16.63

Including 110.15 110.65 0.50 100.00

and 113.00 113.50 0.50 46.90

132.00 132.60 0.60 4.43

139.90 140.40 0.50 19.05

163.50 164.40 0.90 9.02

174.80 175.30 0.50 3.26

176.50 177.00 0.50 3.19

186.50 187.60 1.10 5.93

CM-21-034 137.40 138.45 1.05 28.30

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Including 137.95 138.45 0.50 45.80

153.20 154.30 1.10 84.10

159.25 160.15 0.90 21.80

172.40 175.95 3.55 3.06

Including 172.40 172.90 0.50 11.90

and 172.90 173.40 0.50 4.74

186.00 186.50 0.50 3.65

207.50 208.00 0.50 3.24

226.75 229.90 3.15 13.10

Including 226.75 227.25 0.50 23.90

and 228.80 229.90 1.10 25.90

241.50 243.60 2.10 4.35

Including 241.50 242.00 0.50 16.70

301.10 301.60 0.50 8.66

422.55 423.05 0.50 11.25

CM-21-035 27.70 28.20 0.50 12.55

36.30 36.80 0.50 7.23

60.50 64.50 4.00 1.78

Including 61.00 61.50 0.50 9.49

99.20 102.10 2.90 17.60

Including 99.20 100.00 0.80 35.60

and 100.00 101.00 1.00 15.10

and 101.00 101.60 0.60 11.75

CM-21-036 338.75 339.70 0.95 3.08

487.25 494.70 7.45 2.55

Including 487.25 488.05 0.80 4.12

and 489.75 491.05 1.30 5.04

and 491.05 491.65 0.60 6.99

and 491.65 492.15 0.50 6.15

507.50 508.25 0.75 5.88

CM-21-037 77.95 81.80 3.85 3.14

Including 79.60 80.15 0.55 7.37

and 80.15 81.00 0.85 4.23

93.75 94.25 0.50 4.25

115.55 116.05 0.50 3.30

190.65 191.15 0.50 3.54

195.65 196.15 0.50 5.57

200.00 200.50 0.50 4.81

249.65 250.80 1.15 7.22

Including 250.15 250.80 0.65 10.50

260.60 261.40 0.80 12.70

301.50 302.00 0.50 6.83

310.45 310.95 0.50 58.10

334.30 337.85 3.55 4.32

Including 335.30 335.80 0.50 21.50

362.50 363.00 0.50 9.99

375.60 376.10 0.50 11.20

472.95 474.00 1.05 8.32

578.70 588.80 10.10 4.44

Including 579.70 580.50 0.80 17.50