Osisko Intersects 265 g/t Au Over 2.4 Metres at Windfall

Highlights from the new results include: 265 g/t Au over 2.4 metres in OSK-W-17-1168; 191 g/t Au over 2.6 metres in OSK-W-17-1087; 198 g/t Au over 2.3 metres and 116 g/t Au over 2.1 metres in OSK-EAG-12-333; 173 g/t Au over 2.3 metres in OSK-W-17-1383; 47.7 g/t Au over 2.2 metres in OSK-W-17-1402, 42.7 g/t Au over 2.0 metres in OSK-W-17-1391 and 9.53 g/t over 8.9 metres in OSK-W-18-823-W2. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

OSK-EAG-12-333 intersected FW3 returning 3.07 g/t au over 4.8 metres and 116 g/t Au over 2.1 metres, and FW3U with 198 g /t Au over 2.3 metres in Underdog Corridor. The first interval is composed of up to 10% pyrite within pervasive silica flooding and 1% disseminated pyrite hosted in a porphyritic felsic dike with moderate chlorite, silica and sericite alteration. The second interval contains up to 20% pyrite and local visible gold within intense silica alteration. The third interval is composed of 3% pyrite stringers and local visible gold within a strongly sericitized and silicified felsic porphyritic dike.

OSK-EAG-12-427 intersected crustiform veins in FW4 returning 4.29 g/t Au over 2.2 metres in the Underdog Corridor. Mineralization is composed of 30% pyrite and 1% chalcopyrite in quartz-tourmaline-sericite veins.

OSK-EAG-13-480 intersected a vein in the Red Dog intrusion returning 37.1 g/t Au over 2.0 metres and FW1 FW with 6.68 g/t au over 2.0 metres. The first interval is composed of local visible gold in a quartz-carbonate vein with up to 3% pyrite and 1 % chalcopyrite. The second interval is composed of 1% pyrite stringers within porphyritic felsic dikes with moderate sericite, chlorite and fuchsite alteration.

OSK-W-17-762 intersected FW3 with 6.59 g/t Au over 2.5 metres in Underdog. Mineralization is composed of local visible gold within 10 centimetre silica flooding bands and 10% pyrite hosted in a porphyritic felsic intrusion.

OSK-W-17-795 intersected FW1 with 5.53 g/t Au over 3.4 metres in Underdog. Mineralization is composed of up to 10% pyrite stringers in silica flooding alteration hosted in a sericite altered felsic porphyritic dike.

OSK-W-17-866-W2 intersected FW0 with 4.92 g/t Au over 2.2 metres and FW3 with 7.59 g/t Au over 2.0 metres in Underdog Corridor. Mineralization from FW0 corresponds with 70% massive pyrite over 30 centimetres hosted within a felsic porphyritic dike with strong sericitization. The second interval is composed of up to 15% pyrite stringers and 1% disseminated pyrite hosted in a porphyritic felsic dike with moderate silica and sericite alteration.

OSK-W-17-901 intersected 8.27 g/t Au over 2.5 metres in FW3U. Mineralization is composed of a 10 centimetres silica flooding zone with 55% pyrite, 1% pyrite stringers and 7% disseminated pyrite in a bleached andesite.

OSK-W-17-903-W2 intersected 3.72 g/t Au over 4.9 metres in Zone 27 and 8.52 g/t Au over 2.0 metres in Z27 FW. The first interval is composed of disseminated and stringer pyrite at the contact between a silicified and weakly sericitized porphyritic dike and a weak chlorite, sericite altered andesite. The second interval is composed of pyrite traces hosted in an andesite with strong chlorite and carbonates alteration.

OSK-W-17-937-W1 intersected 26.6 g/t Au over 2.4 metres in Wolf 2. Mineralization is composed of up to 9% disseminated pyrite and 5% tourmaline-pyrite stringers at the contact between a bleached and strongly sericitized andesite and a small sericitized porphyritic felsic dike.

OSK-W-17-943 intersected 3.00 g/t Au over 2.0 metres in Caribou, and 4.51 g/t Au over 2.0 metres and 4.96 g/t Au over 2.0 metres in Wolf. The first interval is composed of up to 10% pyrite stringers and 2% disseminated pyrite hosted in a sericitized rhyolite and a sericitized porphyritic felsic dike. The second interval is composed of 3% pyrite stringers within a sericitized and chloritized porphyritic felsic dike. The third interval is composed of disseminated pyrite within an andesite with chlorite and carbonate alteration.

OSK-W-17-1025 intersected FW0 with 3.13 g/t Au over 2.3 metres. Mineralization is composed of 3% pyrite in silica flooding and 1% pyrite stringers in weakly sericitized porphyritic felsic dike.

OSK-W-17-1051 intersected FW3 with 7.6 g/t Au over 2.4 metres in Underdog Corridor. Mineralization is composed of up to 1% pyrite clusters and disseminated pyrite within a weak sericite and silica altered felsic porphyritic dike.

OSK-W-17-1087 intersected Mallard with 191 g/t Au over 2.6 metres. Mineralization is composed of 5% pyrite stringers and 1% disseminated pyrite within a sericite altered andesite.

OSK-W-17-1168 intersected 265 g/t Au over 2.4 metres in Caribou Corridor. Mineralization is composed of a crustiform vein with local visible gold and 1% pyrite clusters with tourmaline and fuchsite hosted in a gabbro with moderate chlorite alteration. The interval is 150 metres East of OSK-W-17-787 (7.21 g/t Au over 6.5 metres previously reported March 21, 2017).

OSK-W-17-1221 intersected 4.61 g /t Au over 2.0 metres in Wolf corridor. Mineralization is composed of a centimetre scale quartz carbonate vein in a chloritized and slightly silicified porphyritic felsic dike with traces of pyrite stringer.

OSK-W-17-1226 intersected 11.5 g/t Au over 2.0 metres, 10.4 g/t Au over 2.0 metres and 6.57 g/t Au over 2.2 metres in Caribou Extension. First and second intervals are composed of up to 10% pyrite-tourmaline stringers and disseminated pyrite in a sericitized rhyolite. The third interval is composed of 1% pyrite stringers hosted in porphyritic felsic dike with sericite alteration.

OSK-W-17-1232 intersected a vein returning 4.70 g/t Au over 2.0 metres in Caribou Corridor. Mineralization is composed of 3% disseminated pyrite and 7% ptygmatic tourmaline veins within a weak sericite altered rhyolite.

OSK-W-17-1275 intersected 4.49 g/t Au over 3.0 metres in Zone 27. Mineralization is composed of traces of pyrite stringers within a sericitized porphyritic felsic dike.

OSK-W-17-1293 intersected 6.54 g/t Au over 2.3 metres. Mineralization is composed of 1% pyrite and 1% chalcopyrite in quartz veins within a silicified, chloritized and carbonate altered monzonite (Red Dog intrusion).

OSK-W-17-1295 intersected FW3 with 3.36 g/t Au over 2.0 metres in Underdog. Mineralization is composed of 2% pyrite clusters in a sericitized and weakly silicified porphyritic felsic dike.

OSK-W-17-1310 intersected 3.61 g/t Au over 3.0 metres in Caribou and 3.37 g/t Au over 3.0 metres in Drake. The first interval is composed of 1% pyrite stingers within a chloritized and sericitized rhyolite. The second interval is composed of chloritized and sericitized andesite with 5% quartz-carbonate veins.

OSK-W-17-1319 intersected 5.80 g/t Au over 3.0 metres in Zone 27. Mineralization is composed of traces of disseminated pyrite within a sericitized porphyritic felsic dike.

OSK-W-17-1320 intersected 3.46 g/t Au over 3.3 metres in Caribou Extension. Mineralization is composed of disseminated pyrite and quartz-pyrite clusters in a chloritized, sericitized and silicified andesite.

OSK-W-17-1334 intersected 4.05 g/t Au over 2.0 metres in Bobcat. Mineralization is composed of disseminated pyrite and crustiform quartz-carbonate veins in a chloritized, silicified and carbonate altered gabbro.

OSK-W-17-1336 intersected three intervals: 4.16 g/t Au over 2.05 metres in a vein, 17.0 g/t Au over 3.0 metres in FW0 and 4.10 g/t Au over 2.0 metres in FW2, Underdog Corridor. The first interval is composed of 1% disseminated pyrite in a quartz vein within a strongly chloritized gabbro. The second interval is composed of up to 2% disseminated pyrite and 1% pyrite stringers in a sericitized porphyritic felsic dike. The third interval is composed of 1% pyrite stringers and 1% pyrite in quartz-carbonate veins within a moderate sericite and silica altered felsic porphyritic dike.

OSK-W-17-1337 intersected 3.39 g/t Au over 2.5 metres in Mallard. Mineralization is composed of up to 20% pyrite stringers within a sericitized, silicified and bleached andesite.

OSK-W-17-1342 intersected Mallard HW with 8.19 g/t Au over 2.1 metres. Mineralization is composed of traces of disseminated and clustered pyrite within a chloritized andesite.

OSK-W-17-1347 intersected 4.64 g/t Au over 2.0 metres in a vein and 11.1 g/t Au over 2.8 metres in Mallard FW. The first interval is composed of a five centimetre quartz vein with 15% pyrite clusters hosted in a chloritized, silicified and weakly sericitized andesite. The second interval is at the contact between a strongly chlorite, fuchsite altered andesite and a porphyritic felsic dike. Mineralization is composed of 10% pyrite clusters and 3% pyrite stringers. The vein is located 100 metres north-west of Mallard corridor and is not related to any known zones.

OSK-W-17-1350 intersected Caribou Extension with 4.16 g/t Au over 2.0 metres. The mineralization is composed of up to 2% pyrite stringers within a sericitized, chloritized and carbonate altered large quartz eyes felsic porphyritic dike.

OSK-W-17-1376 intersected a vein returning 10.2 g/t Au over 2.3 metres and FW2 with 33.6 g/t Au over 2.1 metres. The first interval is composed of 5-10% quartz-carbonate veining with 5% disseminated pyrite in an andesite with chlorite, carbonate, sericite and silica alteration. Mineralization in FW2 is composed of a silica and sericite altered porphyritic dike with up to 5%, locally 80%, pyrite-tourmaline stringers.

OSK-W-17-1383 intersected 173 g/t Au over 2.3 metres in Bobcat. Mineralization is composed of local visible gold, 3% pyrite stringers with pervasive silica flooding within a gabbro with silica, carbonate and sericite alteration.

OSK-W-17-1391 intersected 42.7 g/t Au over 2.0 metres in Caribou Extension. Mineralization is composed of up to 10% pyrite stringers and 1% chalcopyrite, local visible gold, tourmaline ptygmatic veins, quartz-tourmaline veins and crustiform veins hosted in a silicified and bleached andesite.

OSK-W-17-1399 intersected 3.72 g/t Au over 2.0 metres in Caribou Extension. Mineralization is composed of up to 10% pyrite-tourmaline stringers within a strongly silicified rhyolite.

OSK-W-17-1402 intersected Caribou with 3.39 g/t Au over 2.3 metres and multiples intervals in Underdog corridor: FW1 with 47.7 g/t Au over 2.2 metres, FW1 FW with 3.48 g/t Au over 2.0 metres and 3.35 g/t Au over 2.8 metres, and FW2 with 4.27 g/t au over 2.0 metres. The first interval is composed of 3% pyrite stringers, 5% pyrite clusters within a sericitized andesite with weak silica and fuchsite alteration. The second interval is composed of local visible gold, 2% disseminated pyrite and 1% pyrite clusters, hosted in a moderately sericitized porphyritic dike. The third and fourth intervals are composed of 3% pyrite stringers and 1% disseminated pyrite in pervasive silica flooding within a sericitized porphyritic felsic dike. The last interval is composed of 2% pyrite stringers and 1% pyrite-silica flooding within a sericite, silica and fuchsite altered felsic porphyritic dike.

OSK-W-18-823-W2 intersected CS1 with 9.53 g/t Au over 8.9 metres and 5.22 g/t Au over 2.0 metres in Caribou. Mineralization is composed of 10% semi-massive pyrite bands, 10% pyrite stringers, up to 10% disseminated pyrite and up to 2% ptygmatic tourmaline veinlets hosted in a sericitized, chloritized and bleached andesite.

OSK-W-18-1402-W1 intersected 5.79 g/t Au over 2.3 metres in FW0. The mineralization is composed of 3% pyrite in a ptygmatic tourmaline vein at low core angle within a silicified and sericitized fragmental felsic intrusion.

OSK-W-18-1418 intersected 4.78 g/t Au over 5.0 metres,5.95 g/t Au over 7.0 metres and 5.85 g/t Au over 2.0 metres in Caribou Extension. The first interval is composed of up to 5% pyrite stringers within a silicified and sericitized felsic porphyritic dike. The second interval is composed of up to 15% pyrite-tourmaline stringers hosted in a silicified and sericitized rhyolite. The third interval is composed of up to 10% pyrite-silica flooding within a silica altered andesite.

OSK-W-18-1421 intersected CW2 with 17.7 g/t Au over 2.9 metres in Caribou Corridor. Mineralization is composed of up to 8% pyrite stringers, 1% chalcopyrite, 1% sphalerite, ptygmatic tourmaline veins and local visible gold within a strongly silica altered rhyolite.

OSK-W-18-1423 intersected 6.04 g/t Au over 2.3 metres and 3.97 g/t Au over 3.0 metres in Caribou Extension. The first interval is composed of 7% disseminated pyrite within a bleached andesite. The second interval is composed of 4% disseminated pyrite, 2% pyrite stringers at a bleached andesite contact with a felsic porphyritic dike.

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.