(Toronto, April 29, 2020) Osisko Mining Inc. (OSK:TSX. “Osisko” or the “Corporation”) is pleased to provide new drilling results from the ongoing definition and expansion drill program at its 100% owned Windfall gold project located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec.

Operations remain temporarily suspended in respect of the Government of Québec’s closure of all non-essential business in effort to contain COVID-19. When drilling resumes, it will remain focused on the Lynx deposit, the main mineralized zones, and down plunge exploration in the central areas of the mineralized system.

Significant new analytical results from the definition drilling program on Lynx and Triple Lynx are presented below and include 44 intercepts in 16 drill holes, 2 extensions and 13 wedges.

Of note is drill hole OSK-W-20-2217-W2 which returned 35.3 g/t Au over 2.7 metres, confirming the up-plunge extension of the Triple Lynx zone 120 metres from nearest wireframe (see Osisko news release dated February 19, 2020). Also, drill hole OSK-W-19-2170 returned 40.2 g/t Au over 3.5 metres confirming high grade in the down plunge area of Triple Lynx.

Selected high-grade intercepts from new results include: 104 g/t Au over 2.0 metres in WST-20-0323; 76.5 g/t Au over 2.6 metres in OSK-W-18-1747-W1; 41.2 g/t Au over 4.2 metres in WST-20-0386; and 73.6 g/t Au over 2.3 metres in OSK-W-19-1193-W2.  Maps showing hole locations and full analytical results are available at www.osiskomining.com.

Infill Drilling

Notes: True widths are estimated at 55 – 80% of the reported core length interval. See “Quality Control and Reporting Protocols” below.

DRILL HOLE LOCATION

Lynx Zone

Mineralization in the Lynx zone is typically characterized by trace to 15% disseminated, clustered or stringer pyrite (locally up to 70%), local visible gold, trace to 3% sphalerite, chalcopyrite, and galena, local ptygmatic pyrite-tourmaline or tourmaline veinlets, quartz-carbonate veins (locally crustiform), smoky quartz veins and veinlets, and local chlorite-calcite or quartz-carbonate chlorite fracture filling. Alteration consists of weak to strong sericite, weak to strong silica with areas of local pervasive silica flooding, weak to moderate chlorite and carbonate, and locally weak to strong fuchsite. Mineralization is hosted in or at the contacts of felsic porphyritic or fragmental intrusions with rhyolites, andesites (locally bleached), or gabbros.

Triple Lynx Zone

Mineralization in the Triple Lynx zone is typically characterized by trace to 30% disseminated, clustered or stringer pyrite, local visible gold, trace sphalerite, chalcopyrite, and galena, local quartz-tourmaline veins (up to 20%), local ptygmatic tourmaline veins, and local smoky quartz and quartz-carbonate veins. Alteration consists of weak to strong sericite, weak to strong silica with areas of local pervasive silica flooding, weak to moderate chlorite and carbonate, and locally weak to strong fuchsite. Mineralization is hosted in or at the contacts of felsic porphyritic dikes with rhyolites (locally bleached) or gabbros.

Qualified Person

The scientific and technical content of this news release has been reviewed, prepared and approved by Mr. Louis Grenier, M.Sc.A., P.Geo. (OGQ 800), Project Manager of Osisko’s Windfall Lake gold project, who is a “qualified person” as defined by National Instrument 43-101 – Standards of Disclosure for Mineral Projects (“NI 43-101”).

Quality Control and Reporting Protocols

True width determination is estimated at 55-80% of the reported core length interval for the zone. Assays are uncut except where indicated. Intercepts occur within geological confines of major zones but have not been correlated to individual vein domains at this time. Reported intervals include minimum weighted averages of 3.0 g/t Au diluted over core lengths of at least 2.0 metres. All NQ core assays reported were obtained by either 1-kilogram screen fire assay or standard 50-gram fire-assaying-AA finish or gravimetric finish at (i) ALS Laboratories in Val d’Or, Québec, Thunder Bay, Ontario, Sudbury, Ontario or Vancouver, British Colombia, or (ii) Bureau Veritas in Timmins, Ontario. The 1-kilogram screen assay method is selected by the geologist when samples contain coarse gold or present a higher percentage of pyrite than surrounding intervals. Selected samples are also analyzed for multi-elements, including silver, using an Aqua Regia-ICP-AES method at ALS Laboratories. Drill program design, Quality Assurance/Quality Control (“QA/QC”) and interpretation of results is performed by qualified persons employing a QA/QC program consistent with NI 43-101 and industry best practices. Standards and blanks are included with every 20 samples for QA/QC purposes by the Corporation as well as the lab. Approximately 5% of sample pulps are sent to secondary laboratories for check assay.

About the Windfall Gold Deposit

The Windfall gold deposit is located between Val-d’Or and Chibougamau in Eeyou Istchee James Bay, Québec, Canada. The mineral resource defined by Osisko, as disclosed in the news release dated February 19, 2020 and supported by the technical report entitled “An updated mineral resource estimate for the Windfall Lake Project, Located in the Abitibi Greenstone Belt, Urban Township, Eeyou Istchee James Bay, Québec, Canada” and dated April 3, 2020 (with an effective date of January 3, 2020), and assuming a cut-off grade of 3.5 g/t, comprises 4,127,000 tonnes at 9.1 g/t Au (1,206,000 ounces) in the indicated mineral resource category and 14,532,000 tonnes at 8.40 g/t Au (3,938,000 ounces) in the inferred mineral resource category. The key assumptions, parameters and methods used to estimate the mineral resource estimate disclosed in the February 19,2020 news release are further described in the full technical report prepared by Micon International Limited (“Micon”) and BBA Inc (“BBA”), in accordance with NI 43-101 available on SEDAR (www.sedar.com) under the Corporation’s issuer profile. The Windfall gold deposit is currently one of the highest-grade resource-stage gold projects in Canada and has world-class scale. Mineralization occurs in three principal zones: Lynx, Main Zone, and Underdog.  Mineralization is generally comprised of sub-vertical zones following intrusive porphyry contacts plunging to the northeast. The deposit is well defined from surface to a depth of 1,200 metres and remains open along strike and at depth. Mineralization has been identified 30 metres from surface in some areas and as deep as 2,000 metres in others, with significant potential to extend mineralization down-plunge and at depth.

About Osisko Mining Inc.

Osisko is a mineral exploration company focused on the acquisition, exploration, and development of precious metal resource properties in Canada. Osisko holds a 100% interest in the high-grade Windfall gold deposit located between Val-d’Or and Chibougamau in Québec and holds a 100% undivided interest in a large area of claims in the surrounding Urban Barry area and nearby Quévillon area (over 2,700 square kilometres).