Osisko Intersects 489 g/t Au Over 3.7 Metres at Windfall

TORONTO, April 25, 2019 - Osisko Mining Inc. (OSK:TSX "Osisko" or the "Corporation") is pleased to provide new infill drilling results from the ongoing definition and expansion program at its 100% owned Windfall gold project located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec. The program is currently focused on infill drilling within the main Windfall gold deposit and the adjacent Lynx deposit (located immediately NE of Windfall), exploration and expansion drilling on the main mineralized zones, and deep exploration in the central areas of the intrusive system. Significant new analytical results from 58 intercepts in 21 drill holes and 14 wedges focused on infill drilling from surface and underground are presented below.

Highlights from new results include: 489 g/t Au over 3.7 metres in OSK-W-19-934-W1; 200 g/t Au over 2.1 metres in OSK-W-19-1414-W6; 130 g/t Au over 2.5 metres in WST-19-0066; 139 g/t Au over 2.0 metres in WST-19-058; 94.7 g/t Au over 2.5 metres in OSK-W-17-934; 21.3 g/t Au over 11.0 metres in OSK-W-19-1426-W2; 86.0 g/t Au over 2.1 metres in OSK-W-19-1848-W2; 72.2 g/t Au over 2.5 metres in OSK-W-19-934-W2; 57.9 g/t Au over 2.3 metres in OSK-W-19-909-W12; 48.8 g/t Au over 2.1 metres in OSK-W-19-1878; and 18.2 g/t Au over 5.6 metres in OSK-W-19-909-W9. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

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

Note: WST series drill holes were completed from underground drill stations.

OSK-W-17-934 intersected 94.7 g/t Au over 2.5 metres and 42.7 g/t Au over 2.0 metres in Lynx. The first interval contains local visible gold, 4% pyrite stringers, 2% pyrite clusters, sphalerite and quartz-carbonates veins within a moderate sericite and weak fuchsite altered gabbro. The second interval contains 3% pyrite stringers and quartz-carbonates veins hosted in a weak sericite altered rhyolite.

OSK-W-17-993 intersected 5.18 g/t Au over 2.1 metres in Lynx. Mineralization is composed of 7% disseminated pyrite and trace sphalerite within a strong pervasive silica altered rhyolite.

OSK-W-18-1608 intersected 10.2 g/t Au over 4.5 metres in Lynx. Mineralization consists of up to 5% pyrite clusters, quartz-tourmaline veins and local visible gold with strong silica flooding and strong sericite alteration. Mineralization is hosted at the contact between a strong sericite altered rhyolite with an andesite.

OSK-W-19-1414-W4 intersected 3.24 g/t Au over 2.5 metres in Lynx. Mineralization consists of up to 5% pyrite in dismembered stringers or clusters, and quartz-tourmaline veins at the contact between a moderate chlorite altered gabbro and a moderate sericite altered fragmental felsic volcanic.

OSK-W-19-1414-W5 intersected three intervals in Lynx: 9.43 g/t Au over 2.4 metres, 4.20 g/t Au over 3.5 metres and 4.31 g/t Au over 2.8 metres. The first interval contains up to 15% stringers in stockwork with strong pervasive silica flooding and quartz-tourmaline veins at the contact between a strong sericite altered gabbro and a strong silica altered rhyolite. The second interval contains 10% quartz-tourmaline veins within a strong silica altered rhyolite. The last interval contains 3% pyrite clusters and 2% pyrites stringers hosted in moderate sericite and silica altered rhyolite.

OSK-W-19-1414-W6 intersected 200 g/t Au over 2.1 metres in Lynx. Mineralization includes local visible gold, up to 4% fine disseminated pyrite and trace sphalerite within a strong silica and weak sericite altered porphyritic felsic dike.

OSK-W-19-1426-W2 intersected 21.3 g/t Au over 11.0 metres in Lynx. Mineralization consists of up to 3% pyrite stringers and clusters hosted at the contact between a moderate sericite and silica altered gabbro and a rhyolite.

OSK-W-19-1426-W3 intersected 23.8 g/t Au over 2.2 metres in Lynx. Mineralization consists of local visible gold and electrum, up to 3% pyrite stringers, sphalerite and chalcopyrite with quartz-tourmaline veins hosted in a moderate silica and fuchsite altered gabbro.

OSK-W-19-1835 intersect three intervals in Underdog: 11.8 g/t Au over 2.3 metres, 14.9 g/t Au over 2.0 metres and 13.7 g/t Au over 4.8 metres. The first interval contains up to 10% disseminated pyrite, clusters and stringers hosted in a strong sericite and moderate silica altered andesite. The second interval contains local visible gold, up to 7% pyrite stringers with pervasive silica flooding and trace chalcopyrite hosted in a moderate sericite altered felsic intrusion. The last interval contains local visible gold, disseminated pyrite and chalcopyrite, a massive quartz vein hosted in a weak sericite altered porphyritic felsic dike.

OSK-W-19-1848 intersected three interval in Lynx: 4.44 g/t Au over 2.6 metres, 7.46 g/t Au over 2.8 metres and 5.14 g/t Au over 2.0 metres. The first interval contains up to 5% disseminated pyrite, 3% pyrite stringers and pyrite-tourmaline veins hosted at the contact between a strong silica and sericite altered felsic intrusion and a gabbro. The second interval contains 3% pyrite stringers within a moderate sericite and silica altered rhyolite. The last interval is a quartz vein with 2% pyrite clusters hosted in a fragmental felsic intrusion.

OSK-W-19-1848-W1 intersected 13.2 g/t Au over 2.3 metres in Lynx. Mineralization consists of 2% disseminated pyrite and stringers, trace chalcopyrite and quartz-tourmaline veins hosted at the contact between a moderate sericite altered rhyolite and a weak sericite altered felsic intrusion.

OSK-W-19-1848-W2 intersected two intervals in Lynx: 48.1 g/t Au over 2.0 metres and 86.0 g/t Au over 2.1 metres. The first interval contains 3% pyrite stringers and clusters hosted at the contact between a moderate sericite altered intrusion and a bleached gabbro. The second interval contains local visible gold, 2% pyrite stringers and clusters and trace chalcopyrite with pervasive silica flooding hosted in a moderate sericite and fuchsite altered gabbro.

OSK-W-19-1859 intersected two intervals in Caribou: 19.4 g/t Au over 2.4 metres and 6.30 g/t Au over 2.2 metres. The first interval contains up to 3% disseminated pyrite and stringers within a moderated sericite, silica and chlorite altered rhyolite. The second interval contains 5% pyrite stringers and 1% disseminated pyrite with quartz veins hosted in a moderate sericite, carbonate and silica altered porphyritic felsic intrusion.

OSK-W-19-1871 intersected three intervals in Caribou: 3.71 g/t Au over 2.0 metres, 8.78 g/t Au over 2.5 metres and 20.5 g/t Au over 2.0 metres. The first interval contains 30% semi-massive pyrite, stringers and trace chalcopyrite hosted in a moderate sericite and silica altered porphyritic felsic dike. The second interval contains 15% semi-massive pyrite and stringers and clusters within a strong sericite altered porphyritic intrusion. The last interval contains up to 1% disseminated pyrite within a weak sericite and moderate silica altered andesite.

OSK-W-19-1874 intersected two intervals in Caribou: 3.11 g/t Au over 2.1 metres and 5.49 g/t Au over 12.9 metres. Both intervals are composed of up to 10% pyrite stringers hosted in a strong silica altered rhyolite.

OSK-W-19-1878 intersected three intervals in Lynx: 48.8 g/t Au over 2.1 metres, 3.63 g/t Au over 2.4 metres and 6.98 g/t Au over 2.0 metres. The first interval contains local visible gold and native silver, 2% pyrite stringers, 3% pyrite clusters and chalcopyrite with quartz-tourmaline veins hosted in a moderate sericite and fuchsite altered gabbro. The second interval contains 1% pyrite stringers within a moderate sericite and weak fuchsite altered fragmental felsic intrusion. The last interval contains 3% pyrite stringers and clusters with 1% quartz-tourmaline veins hosted in a moderate sericite altered rhyolite.

OSK-W-19-1882 intersected 3.74 g/t Au over 2.4 metres in Caribou. The mineralization consists of up to 60% massive pyrite and stringers within a strongly bleached andesite.

OSK-W-19-1886 intersected 3.30 g/t Au over 10.4 metres in Caribou. The mineralization includes 5% pyrite stringers and 2% ptygmatic tourmaline veins within a moderate sericite and silica altered rhyolite.

OSK-W-19-1900 intersected 6.65 g/t Au over 4.4 metres in Caribou. The mineralization is composed of up to 30% pyrites stringers and trace chalcopyrite with quartz veins within a string silica and a moderate sericite altered andesite.

OSK-W-19-909-W9 intersected 18.2 g/t Au over 5.6 metres in Lynx. The mineralization includes local visible gold with smoky quartz veins and up to 20% pyrite stringers hosted in weak sericite and silica altered porphyritic felsic intrusion.

OSK-W-19-909-W10 intersected 6.40 g/t Au over 2.6 metres in Lynx. The mineralization includes up to 2% finely disseminated pyrite within a strong silica altered porphyritic felsic intrusion.

OSK-W-19-909-W11 intersected 15.5 g/t Au over 2.2 metres in Lynx. The mineralization consists of local visible gold, 5% pyrite and 2% chalcopyrite with quartz-tourmaline veins hosted in a moderate fuchsite altered gabbro.

OSK-W-19-909-W12 intersected two intervals in Lynx: 57.9 g/t Au over 2.3 metres and 14.2 g/t Au over 4.5 metres. The first interval contains 3% pyrite clusters and stringers, quartz-tourmaline crustiform veins within a moderate sericite, fuchsite and chlorite altered gabbro. The second interval contains 1% finely disseminated pyrite and clusters hosted in a moderate sericite and silica altered rhyolite.

OSK-W-19-934-W1 intersected 489 g/t Au over 3.7 metres in Lynx. Mineralization consists of local visible gold with pyrite-tourmaline stringers and up to 4% pyrite clusters hosted at the contact between a moderated sericite altered rhyolite and a weak sericite altered andesite.

OSK-W-19-934-W2 intersected three intervals in Lynx: 9.75 g/t Au over 4.7 metres, 6.79 g/t Au over 2.0 metres and 72.2 g/t Au over 2.5 metres. The first interval contains 5% pyrite and 2% sphalerite with a quartz-tourmaline vein hosted at the contact between a strong silica altered rhyolite and a strong silica altered gabbro. The second interval contains 3% pyrite stringers and clusters in a strong silica, fuchsite and sericite altered gabbro. The last interval contains local visible gold, up to 15% pyrite with quartz-tourmaline veins and quartz crustiform veins hosted in a strong sericite altered rhyolite.

OSK-W-19-934-W3 intersected 10.4 g/t Au over 2.3 metres in Lynx. Mineralization consists of 1% pyrite stringers and quartz-tourmaline veins hosted in a weak sericite altered rhyolite.

WST-19-0058 intersected 139 g/t Au over 2.0 metres in Zone 27. Mineralization consists of local visible gold with a quartz crustiform vein hosted in a moderate chlorite and weak sericite altered felsic intrusion. WST-19-0058 was drilled from underground drill station BM-150-960-S located 150 metres below surface on section 2175E.

WST-19-0062 intersected 21.1 g/t Au over 2.0 metres in Zone 27. Mineralization consists of 2% pyrite clusters and 1% quartz-tourmaline veins within a moderate sericite, chlorite and weak fuchsite altered gabbro. WST-18-0062 was drilled from underground drill station BM-150-960-S located 150 metres below surface on section 2175E.

WST-19-0064 intersected 12.8 g/t Au over 5.2 metres in Zone 27. Mineralization consists of disseminated pyrite and quartz-tourmaline veins within a weak fuchsite altered gabbro. WST-19-0064 was drilled from underground drill station BM-150-960-S located 150 metres below surface on section 2175E.

WST-19-0065A intersected two intervals in Zone 27 4.02 g/t Au over 3.5 metres and 13.1 g/t Au over 2.0 metres. The first interval contains 5% pyrite clusters, 1% pyrite-tourmaline veins with quartz-carbonate veins hosted in a moderate sericite altered andesite. The second interval contains 2% semi-massive pyrite and 3% pyrite-tourmaline veins hosted in a moderate sericite porphyritic felsic intrusion. WST-19-0065A was drilled from underground drill station BM-150-960-S located 150 metres below surface on section 2175E.

WST-19-0066 intersected two intervals in Zone 27: 13.1 g/t Au over 2.0 metres and 130 g/t Au over 2.5 metres. The first interval contains 2% pyrite stringers and 1% ptygmatic tourmaline veins within a moderate chlorite and carbonates altered dacite. The second interval contains trace disseminated pyrite hosted in a moderate chlorite and carbonate altered gabbro. WST-19-0066 was drilled from underground drill station BM-150-960-S located 150 metres below surface on section 2175E.

WST-19-0068 intersected three intervals in Zone 27: 7.19 g/t Au over 2.4 metres, 5.59 g/t Au over 2.0 metres and 5.83 g/t Au over 7.8 metres. The first interval contains up to 10% disseminated pyrite and ptygmatic quartz-tourmaline veins within a moderate silica and sericite altered porphyritic felsic intrusion. The second interval contains 7% pyrite-tourmaline stringers hosted in a moderate sericite altered porphyritic felsic dike. The last interval contains up to 7% pyrite stringers hosted in a moderate silica, sericite and fuchsite altered porphyritic intrusion. WST-19-0068 was drilled from underground drill station BM-150-960-S located 150 metres below surface on section 2175E.

WST-19-0069 intersected two intervals in Zone 27: 4.68 g/t Au over 2.5 metres and 15.0 g/t Au over 2.1 metres. Both intervals contain 1% pyrite-tourmaline stringers, 5% finely disseminated pyrite and clusters in a moderate sericite altered porphyritic felsic intrusion. WST-19-0069 was drilled from underground drill station BM-150-960-S located 150 metres below surface on section 2175E.

WST-19-0080 intersected 3.78 g/t Au over 2.0 metres in Zone 27. Mineralization consists of up to 10% pyrite with quartz-tourmaline stringers and ptygmatic tourmaline veins hosted in a moderate sericite altered porphyritic felsic intrusion. WST-19-0080 was drilled from underground drill station AN-190-155-N located 190 metres below surface on section 2300E.

WST-19-085 intersected two intervals in Zone 27: 29.0 g/t Au over 2.0 metres and 3.62 g/t Au over 2.3 metres. The first interval contains local visible gold with pervasive silica flooding, up to 25% pyrite stringers and 1% chalcopyrite and sphalerite hosted in moderate sericite altered felsic intrusion. The last interval contains up to 20% semi-massive pyrite and stringers hosted in a strong sericite altered porphyritic felsic dike. WST-19-0085 was drilled from underground drill station AN-190-155-N located 190 metres below surface on section 2300E.

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 Lake Gold Deposit
The Windfall Lake gold deposit is located between Val-d'Or and Chibougamau in the Abitibi region of Québec, Canada. The mineral resource defined by Osisko, as disclosed in the Windfall Lake Technical Report (as defined below) and November 27, 2018 Lynx resource update, comprises 2,874,000 tonnes at 8.17 g/t Au (754,000 ounces) in the indicated mineral resource category and 10,352,000 tonnes at 7.11 g/t Au (2,366,000 ounces) in the inferred mineral resource category. For details regarding the key assumptions, parameters and methods used to estimate the mineral resources presented in respect of the Windfall Lake gold project, please see the technical report entitled "Technical Report and Mineral Resource Estimate for the Windfall Lake Project, Windfall Lake and Urban-Barry Properties" and dated June 12, 2018 (effective date of May 14, 2018), which has been prepared by InnovExplo Inc. from Val-d'Or, Québec (the "Windfall Lake Technical Report") and the press release “Osisko Releases Mineral Resource Update for Lynx” dated November 27, 2018, which has been prepared by Osisko and reviewed and approved by Micon International, Ltd. from Toronto, Ontario. The Windfall Lake Technical Report and press release are available on Osisko's website at www.osiskomining.com and on SEDAR under Osisko's issuer profile at www.sedar.com. The Windfall Lake gold deposit is currently one of the highest grade resource-stage gold projects in Canada. Mineralization occurs in four principal zones: Lynx, Zone 27, Caribou and Underdog. All zones comprise sub-vertical lenses following intrusive porphyry contacts plunging to the northeast. The deposit is well defined from surface to a depth of 900 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 Lake 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 Quevillon area (over 3,500 square kilometres).

Cautionary Note Regarding Forward-Looking Information
This news release contains "forward-looking information" within the meaning of the applicable Canadian securities legislation that is based on expectations, estimates, projections and interpretations as at the date of this news release. The information in this news release about the Windfall Lake gold deposit being one of the highest grade resource-stage gold projects in Canada; the significance of results from the new infill drilling and ongoing drill definition and expansion program at the Windfall Lake gold project; the significance of assay results presented in this news release; the deposit remaining open along strike and at depth; potential depth extensions of the mineralized zones down-plunge and at depth; the actual mineralization of local visible gold; the current 800,000 metre drill program; the type of drilling included in the drill program; potential mineralization; the potential to extend mineralization up and down-plunge and at depth at the Windfall Lake gold deposit; the ability to realize upon any mineralization in a manner that is economic; the ability to complete any proposed exploration activities and the results of such activities, including the continuity or extension of any mineralization; and any other information herein that is not a historical fact may be "forward-looking information". Any statement that involves discussions with respect to predictions, expectations, interpretations, beliefs, plans, projections, objectives, assumptions, future events or performance (often but not always using phrases such as "expects", or "does not expect", "is expected", "interpreted", "management's view", "anticipates" or "does not anticipate", "plans", "budget", "scheduled", "forecasts", "estimates", "believes" or "intends" or variations of such words and phrases or stating that certain actions, events or results "may" or "could", "would", "might" or "will" be taken to occur or be achieved) are not statements of historical fact and may be forward-looking information and are intended to identify forward-looking information. This forward-looking information is based on reasonable assumptions and estimates of management of the Corporation at the time such assumptions and estimates were made, and involves known and unknown risks, uncertainties and other factors which may cause the actual results, performance or achievements of Osisko to be materially different from any future results, performance or achievements expressed or implied by such forward-looking information. Such factors 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 Osisko to complete further exploration activities, including drilling; property interests in the Windfall Lake gold project; the ability of the Corporation to obtain required approvals and complete transactions on terms announced; 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. Although the forward-looking information contained in this news release is based upon what management believes, or believed at the time, to be reasonable assumptions. Osisko cannot assure shareholders and prospective purchasers of securities of the Corporation that actual results will be consistent with such forward-looking information, as there may be other factors that cause results not to be as anticipated, estimated or intended, and neither Osisko nor any other person assumes responsibility for the accuracy and completeness of any such forward-looking information, Osisko does not undertake, and assumes no obligation, to update or revise any such forward-looking statements or forward-looking information contained herein to reflect new events or circumstances, except as may be required by law.

For further information please contact:
John Burzynski
President and Chief Executive Officer
Telephone: (416) 363-8653