Osisko Continues to Define and Expand Multiple High-Grade Vein Corridors at Valley Zone on Cariboo Gold Project

At Valley Zone, 24,000 meters were drilled in 74 holes in 2020. This news release discusses the assay results from holes CM-20-037 to CM-20-063 (Figure 1). Highlights include 9.33 g/t Au over 12.10 meters including 62.9 g/t Au over 0.60 meters in hole CM-20-046 (Figure 2). This Zone has not been drill tested since 2017, and significant potential exists to add both inferred and indicated resource to the deposit. The Company has commenced drilling on the 2021 drill program. A total of ten drill rigs will be active on the property by January 15^th.

Sean Roosen, CEO of Osisko Development commented, “The most recent high-grade results from the Valley Zone certainly go to the character of this project. We are still seeing many exciting new zones in this project that are within the current mine plan area. With the recent financing of over 200 million dollars completed, we will be increasing our rig count and intensifying our exploration efforts both in the current mine plan area and on the new targets that have been generated on along the 83km (50 mile) long mineralized trend.”

Further highlights from drilling at Valley are presented below.

Valley Zone Drilling Highlights:

• CM-20-041: 9.97 g/t Au over 4.75 meters
• CM-20-041: 64.8 g/t Au over 0.70 meters
• CM-20-041: 9.41 g/t Au over 3.85 meters
• CM-20-045: 38.5 g/t Au over 1.5 meters
• CM-20-045: 4.68 g/t Au over 7.35 meters
• CM-20-046: 16.57 g/t Au over 2.80 meters including 62.2 g/t Au over 0.50 meters
• CM-20-046: 9.33 g/t Au over 12.1 meters including 62.9 g/t Au over 0.60 meters
• CM-20-047: 7.44 g/t Au over 7.40 meters
• CM-20-048: 31.34 g/t Au over 1.30 meters including 52.40 g/t Au over 0.70 meters
• CM-20-049: 5.98 g/t Au over 8.40 meters
• CM-20-050: 8.93 g/t Au over 4.65 meters
• CM-20-051: 167 g/t Au over 0.50 meters
• CM-20-051: 4.95 g/t Au over 16.3 meters including 41.8 g/t Au over 0.70 meters
• CM-20-052: 30.68 g/t Au over 2.05 meters
• CM-20-053: 17.52 g/t Au over 2.15 meters
• CM-20-056: 43.9 g/t Au over 1.10 meters
• CM-20-057: 7.76 g/t Au over 15.60 meters (Core photos in Figure 3)
• CM-20-059: 5.50 g/t Au over 9.50 meters including 60.9 g/t Au over 0.80 meters

“Mineralized quartz veins on the Cariboo Gold Project 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 F3 fold and hosted within the sandstones. Vein corridors are modelled at a minimum thickness of 2 meters and individual veins within each corridor range in width from millimeter to several meters. The modelled vein corridors for the resource update includes the internal dilution of the subeconomic sandstone within these vein corridors. These corridors have been defined from surface to a vertical depth averaging 300 meters and remain open for expansion at depth and down plunge. Gold grades are intimately associated with vein-hosted pyrite as well as pyritic, intensely silicified wall rock haloes in close proximity to the veins. Photographs from the recently drilled vein corridor in hole CM-20-057 are presented in Figure 3.

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.

Figure 1 accompanying this announcement is available at
https://www.globenewswire.com/NewsRoom/AttachmentNg/349b798c-02fc-43a7-a203-3b3c84367401

Figure 2 accompanying this announcement is available at
https://www.globenewswire.com/NewsRoom/AttachmentNg/8b490ac3-ce5c-4efb-9691-d92e565b8aab

Figure 3 accompanying this announcement is available at
https://www.globenewswire.com/NewsRoom/AttachmentNg/bd212d1f-3c96-434b-a681-e13084eec877

Figure 3: Drill core photos from CM-20-057. This vein corridor assayed 5.98 g/t Au over 23.40 meters (core length) from 217.2 to 240 .6 meters depth including a higher grade corridor from 7.31 g/t Au over 15.6 meters from 225 to 240.6 meters. The individual quartz veins host the gold mineralization and are modelled as vein corridors, defined as a high-density network of mineralized quartz veins within the prospective sandstone unit (black). The vein corridors include both the mineralized quartz veins and the unmineralized sandstone unit, therefore the vein corridors include some internal dilution over the composited interval.

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 Vancouver, 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 well-capitalized and 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 resource 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. The considerable exploration potential at depth 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 second half of 2021. 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 Qu?bec as well as the Guerrero Properties located in Mexico. Osisko Development will begin trading on the TSX Venture Exchange under the symbol "ODV" on December 2, 2020.

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 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 guarantees 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 perceptions of historical trends, current conditions and expected future developments, 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 F3 fold 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 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, may ultimately prove to be incorrect since they are subject to risks and uncertainties that affect Osisko and its business. Such risks and uncertainties include, among others, risks relating to the ability of exploration 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 actions 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 press release, see the section entitled “Risk Factors” in the most recent Annual Information Form of Osisko which is filed with the Canadian securities commissions and available electronically under Osisko’s issuer profile on SEDAR at www.sedar.com and with the U.S. Securities and Exchange Commission and available electronically under Osisko’s issuer profile on EDGAR at www.sec.gov. The forward‐ looking statements set forth herein reflect Osisko’s expectations as at the date of this press release and are subject to change after such date. Osisko 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.

Table 1: Cariboo Gold Project 2020 Length Weighted Drill Hole Gold Composites

Table 2: Drill Hole Locations and Orientations