OSISKO INTERSECTS 41.2 g/t Au OVER 3.5 METRES AT WINDFALL

Additional High-Grade Infill Holes in Caribou, Underdog and Bobcat

(Toronto, April 19, 2018)  Osisko Mining Inc. (OSK:TSX. “Osisko” or the “Corporation”) is pleased to provide new results from the ongoing drill program at its 100% owned Windfall Lake gold project located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec. The 800,000 metre drill program combines definition, expansion and exploration drilling in and around the main Windfall gold deposit and the adjacent Lynx deposit (located immediately NE of Windfall).

Significant new analytical results from 46 intercepts in 23 drill holes and 5 wedges focused on infill drilling in the Main Windfall lake deposit are presented below. Today’s infill drilling results will not be included in the pending mineral resource scheduled for release in May 2018.

Highlights from the new results include: 82.5 g/t Au over 2.0 metres in OSK-W-17-1391; 41.2 g/t Au over 3.5 metres in OSK-W-18-1402-W3; 34.3 g/t Au over 2.6 metres in OSK-W-18-1435; 31.4 g/t Au over 2.7 metres in OSK-W-18-1440; 5.53 g/t Au over 11.9 metres in OSK-W-17-801; and 24.0 g/t Au over 2.4 metres in OSK-W-17-1409. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

Notes:

1. True widths are estimated at 65 – 80% of the reported core length interval. See “Quality Control”
2. Definitions: Ext = extension, FW = Footwall, QTV = Quartz-Tourmaline Vein, U = Upper, VNCR = Crustiform Vein

OSK-EAG-12-333 intersected 5.38 g/t Au over 2.0 metres in FW3. Mineralization is composed of 7% pyrite-silica flooding and up to 1% pyrite stringers within a strong silica, weak sericite altered felsic porphyritic dike.

OSK-EAG-12-424 intersected 6.72 g/t Au over 2.5 metres in FW3. Mineralization is composed of up to 5% pyrite stringers, 1% pyrite clusters and quartz veins within a moderate sericitized felsic porphyritic dike.

OSK-W-17-801 intersected four intervals in Caribou Extension: 7.75 g/t Au over 2.9 metres, 3.70 g/t Au over 2.4 metres, 5.53 g/t Au over 11.9 metres and 3.92 g/t Au over 4.4 metres. The first and second intervals are composed of up to 5% pyrite stringers and semi-massive pyrite within a strong sericite altered andesite. In the third and fourth intervals, mineralization is composed of up to 3% pyrite stringers, 3% pyrite clusters and 1% disseminated pyrite at the contact between a strong chlorite altered andesite and a strong sericite altered felsic porphyritic dike. These two intervals are 100 metres down plunge of OSK-W-17-1351 (3.65 g/t Au over 2.2 metres and 3.64 g/t Au over 2.3 metres previously reported January 18, 2018).

OSK-W-17-1371 intersected 3.96 g/t Au over 2.5 metres in Wolf. Mineralization is hosted in a quartz vein and composed of up to 2% disseminated pyrite within a strong chlorite altered andesite.

OSK-W-17-1378 intersected two intervals in Caribou: 4.41 g/t Au over 2.1 metres and 5.36 g/t Au over 2.5 metres. The first interval is composed of 1% pyrite stringers within strong chlorite, and weak fuchsite altered felsic porphyritic dike. The second interval is composed of trace disseminated or stringer pyrite  and quartz-tourmaline veins within a strong chlorite altered andesite.

OSK-W-17-1379 intersected 3.03 g/t Au over 2.3 metres in Caribou Extension. Mineralization is composed of trace pyrite stringer and chalcopyrite within a felsic porphyritic dike.

OSK-W-17-1391 intersected 82.5 g/t Au over 2.0 metres in Caribou. Mineralization is composed of 1% pyrite stringers and quartz vein within a chloritized andesite.

OSK-W-17-1394 intersected 4.25 g/t Au over 2.1 metres in Caribou Extension. Mineralization is composed of 2% pyrite stringers, 1% disseminated pyrite within a strong sericite altered rhyolite.

OSK-W-17-1397 intersected two veins in Caribou returning 3.53 g/t Au over 2.0 metre and 3.69 g/t Au over 2.2 metres. Both intersects are composed of up to 15% disseminated pyrite hosted in quartz veins within a strong silica, strong sericite and moderate chlorite altered rhyolite.

OSK-W-17-1399 intersected 4.45 g/t Au over 2.5 metres in Caribou Extension. Mineralization is composed of 2% pyrite clusters and quartz veins within a weak sericite altered rhyolite layered with gabbro.

OSK-W-17-1406 intersected two intervals in Bobcat: 7.28 g/t Au over 2.0 metres and 6.91 g/t Au over 2.0 metres. Both intersects are composed of up to 4% disseminated pyrite and quartz-tourmaline crustiform veins within a weak sericite altered gabbro.

OSK-W-17-1409 intersected three intervals: 24.0 g/t Au over 2.4 metres and 6.11 g/t Au over 2.0 metres in Bobcat and 7.17 g/t Au over 2.4 metres in Caribou Extension. The first two intervals are composed of trace disseminated and stringer pyrite and quartz-tourmaline veins within a strong sericite and silica altered rhyolite. The last interval is composed of trace disseminated pyrite and quartz-tourmaline veins within a strong chlorite and weak sericite altered rhyolite.

OSK-W-18-1066-W1 intersected two intervals: 12.9 g/t Au over 2.0 metres in FW3 and 21.0 g/t Au over 2.2 metres in FW3 Footwall. The first interval is composed of 35% semi-massive pyrite within a strong sericite altered felsic porphyritic dike. The second interval is composed of 10% pyrite stringers and pyrite-silica flooding within a moderate sericite altered felsic porphyritic dike.

OSK-W-18-1402-W1 intersected 4.07 g/t Au over 6.6 metres in FW1. Mineralization is composed of up to 2% pyrite in stockwork and stringers within a strong sericite altered felsic porphyritic dike.

OSK-W-18-1402-W3 intersected five intervals: 8.11 g/t Au over 2.3 metres in FW0, 6.21 g/t Au over 3.5 metres in FW1, 4.98 g/t Au over 2.0 metres and 41.2 g/t Au over 3.5 metres in FW1 FW, and 9.36 g/t Au over 4.7 metres in FW3. The first interval is composed of up to 15% pyrite in pyrite-silica flooding, stringers and disseminated within a strong sericite altered felsic porphyritic dike. The second interval is composed of up to 3% pyrite-silica flooding, 1% chalcopyrite and quartz veins within a strong silica and sericite altered felsic porphyritic dike. The third and fourth intervals are composed of up to 20% pyrite-silica flooding, up to 2% chalcopyrite, 1% quartz-tourmaline veins and local visible gold within strong silica and strong sericite altered felsic porphyritic dikes. The last interval is composed of 10% pyrite stringers, 2% disseminated pyrite and local visible gold within a strong sericite and strong silica altered felsic porphyritic dike.

OSK-W-18-1423 intersected 5.63 g/t Au over 2.2 metres in Caribou Extension. Mineralization is composed of 1% stringer and disseminated pyrite within a strong sericite altered andesite.

OSK-W-18-1430 intersected 7.91 g/t Au over 2.0 metres in FW1. Mineralization is composed of up to 30% semi-massive pyrite in stringers or pyrite-silica flooding and 5% disseminated pyrite within a moderate sericite altered felsic porphyritic dike.

OSK-W-18-1430-W1 intersected 4.95 g/t Au over 3.0 metres in FW2. Mineralization is composed of low core angle quartz-tourmaline veins with 2 % disseminated pyrite within a felsic porphyritic dike.

OSK-W-18-1431 intersected 5.73 g/t Au over 2.0 metres in FW4. Mineralization is composed of 2% pyrite stringers, 1% pyrite clusters within a strong sericite altered felsic porphyritic dike.

OSK-W-18-1431-W1 intersected two intervals: 3.06 g/t Au over 2.3 metres in FW1 and 13.5 g/t Au over 2.1 metres in FW3 FW. Both intersects are composed of up to 3% pyrite stringers, 2% disseminated pyrite and 1% pyrite clusters within strong sericite altered felsic porphyritic dikes.

OSK-W-18-1434 intersected two intervals: 11.6 g/t Au over 4.7 metres in FW3 and 16.0 g/t Au over 2.4 metres in FW3U. The first interval is composed of up to 15% pyrite stringers, pyrite-silica flooding, and local visible gold within a strong sericite and strong silica altered felsic porphyritic dike. The second interval is composed of 15% semi-massive pyrite, pyrite-tourmaline veins within a strong sericite altered felsic porphyritic dike.

OSK-W-18-1435 intersected two intervals in Caribou Extension: 34.3 g/t Au over 2.6 metres and 4.38 g/t Au over 2.0 metres. The first interval is composed of 80% massive pyrite veins and quartz-tourmaline veins within a strong chlorite, weak sericite and weak carbonate altered andesite. The second interval is composed of 15% pyrite stringers within a strong carbonate altered andesite.

OSK-W-18-1440 intersected 31.4 g/t Au over 2.7 metres in FW1. Mineralization is composed of up to 25% semi-massive pyrite, 5% pyrite-tourmaline veins, and local visible gold within a strong sericite and strong silica altered felsic porphyritic dike.

OSK-W-18-1441 intersected 8.06 g/t Au over 6.6 metres in Bobcat. Mineralization is composed of 7% disseminated pyrite and 3% pyrite-tourmaline stringers within a strong fuchsite and silica altered gabbro.

OSK-W-18-1445 intersected 5.75 g/t Au over 3.5 metres in Caribou Extension. Mineralization is composed of local visible gold and up to 35% pyrite in stringers, pyrite-tourmaline veins and clusters within a strong sericite and silica altered felsic porphyritic dike.

OSK-W-18-1446 intersected three intervals: 10.8 g/t Au over 3.2 metres in FW1, 4.27 g/t Au over 2.0 metres in FW2 and 4.05 g/t Au over 2.2 metres in FW3. The first interval is composed of up to 5% disseminated pyrite and pyrite-tourmaline veins and local visible gold within a strong silica and sericite altered felsic porphyritic dike. The second interval is composed of 3% disseminated pyrite in quartz-tourmaline veins within a moderate sericite altered felsic porphyritic dike. The last interval is composed of local visible gold, up to 5% pyrite stringers and pyrite-silica flooding within a strong silica altered felsic porphyritic dike.

OSK-W-18-1448 intersected 6.02 g/t Au over 2.0 metres in Caribou. Mineralization is composed of 9% pyrite stringers within a moderate silica and sericite altered felsic porphyritic dike.

OSK-W-18-1459 intersected 8.26 g/t Au over 2.0 metres in Bobcat. Mineralization is in a crustiform vein and composed of up to 3% disseminated pyrite within a strong silica and moderate fuchsite altered gabbro.

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 the 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 widths determinations are estimated at 65-80% of the reported core length intervals for most of the zones. 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 ALS Laboratories in Val d’Or, Québec, Thunder Bay and Sudbury, Ontario or Vancouver, British Colombia or 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 the previous operator comprises 2,762,000 tonnes at 8.42 g/t Au (748.000 ounces) in the indicated category and 3,512,000 tonnes at 7.62 g/t Au (860,000 ounces) in the inferred category (sourced from a technical report dated June 10, 2015 entitled “Preliminary Economic Assessment of the Windfall Lake Gold Property, Québec, Canada” with an effective date of April 28, 2015, prepared in accordance with NI 43-101). The Windfall Lake gold deposit is currently one of the highest grade resource-stage gold projects in Canada. The bulk of the mineralization occurs in the Main Zone, a southwest/northeast trending zone of stacked mineralized lenses, measuring approximately 600 metres wide and at least 1,400 metres long. The deposit is well defined from surface to a depth of 500 metres and remains open along strike and at depth. Mineralization has been identified only 30 metres from surface in some areas and as deep as 870 metres in others, with significant potential to extend mineralization up and 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% 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 3,300 square kilometres), a 100% interest in the Marban project located in the heart of Québec’s prolific Abitibi gold mining district, and properties in the Larder Lake Mining Division in northeast Ontario, including the Jonpol and Garrcon deposits on the Garrison property, the Buffonta past producing mine and the Gold Pike mine property. The Corporation also holds interests and options in a number of additional properties in northern Quebec and Ontario.  Osisko continues to be well financed with approximately $190 million in cash and investments as of December 31, 2017.

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 current 800,000 metre drill program; the significance of new results from the ongoing drill program at the Windfall Lake gold project; the significance of assay results presented in this press release; the type of drilling included in the drill program (definition drilling, expansion drilling to the NE of the main deposit and adjacent Lynx deposit, and exploration drilling on the greater deposit and Urban-Barry project area); 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 it was made, 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