Osisko Caribou Extension Increases to 1.2 Kilometres at Windfall

Notes:

1. True widths are estimated at 65 - 80% of the reported core length interval. See "Quality Control" below.
2. Definitions: FW = Foot Wall, HW = Hanging Wall, QTV = Quartz-Tourmaline Vein, VNCR = Crustiform Vein, Ext. = Extension

OSK-OBM-16-660 intersected 14.1 g/t Au over 2.9 metres in FW3U. Mineralization is composed of up to 5% pyrite stringers and disseminated pyrite hosted in sericitized andesite.

OSK-W-17-833-W1 intersected 8.24 g/t Au over 2.9 metres in FW3. Mineralization is composed of up to 10% pyrite stringers hosted in a strongly sericitized fragmental felsic dike.

OSK-W-17-833-W2 intersected 43.9 g/t Au over 3.0 metres in FW2. Mineralization is composed of up to 15% pyrite stringers, 5% disseminated pyrite and local visible gold. The host rock is a fragmental felsic dike cross-cut by a large quartz eyes porphyritic felsic dike, is strongly silicified and moderately sericitized. The interval extends FW2 25 metres east of OSK-W-16-706-W1 (7.10 g/t Au over 5.0 metres previously reported September 19, 2016).

OSK-W-17-847-W2 intersected 10.7 g/t Au over 2.1 metres within the Underdog Corridor. Mineralization corresponds with decimetres scale quartz-tourmaline veins hosted in a sericitized felsic dike with 3% pyrite, disseminated or in stringers.

OSK-W-17-866-W2 intersected five intervals in the Underdog Corridor: 11.6 g/t Au over 3.0 metres in FW0, 13.0 g/t Au over 2.4 metres in FW0 FW, 4.21 g/t Au over 6.0 metres in FW1; 5.4 g/t Au over 2.2 metres related to FW1 and 87.0 g/t Au over 2.4 metres related to FW3. Mineralization in the first interval is at a sericitized and silicified contact between two felsic intrusions, and is composed of 5% pyrite stringers and 1 % disseminated pyrite. The second and third intervals are composed of 1% disseminated pyrite and pyrite stringers in a sericitized and slightly silicified porphyritic felsic intrusion. The fourth and fifth intervals are composed of 3% disseminated pyrite and 2% pyrite stringers associated with intense pervasive silica flooding hosted within a porphyritic felsic intrusion. Local visible gold is observed in the FW3 zone.

OSK-W-17-885 intersected two intervals: 21.4 g/t Au over 2.0 metres and 7.81 g/t Au over 2.0 metres in FW0. The first interval is 100 m south-east of the Caribou Corridor and composed of local visible gold associated with pyrite-chalcopyrite-tourmaline stringers hosted in the rhyolite. The FW0 interval is composed of 2% disseminated pyrite associated with quartz-pyrite-carbonate veinlets.

OSK-W-17-885-W1 intersected three intervals in the Underdog Corridor: 5.24 g/t Au over 4.6 metres in FW0 HW, 5.95 g/t Au over 2.0 metres in FW1 HW and 5.19 g/t Au over 5.8 metres in FW1. Mineralization is composed of up 3% pyrite stringers and 1% disseminated pyrite in a sericitized and silicified felsic porphyritic dike. The third interval contains trace pyrite stringers with intense silica and sericite alteration. This hole extends FW1 HW to the north-east, 135 metres down plunge of OSK-W-17-821-W1 (4.63 g/t Au over 5.0 metres previously reported August 24, 2017).

OSK-W-17-903 returned 36.1 g/t Au over 4.0 metres in Zone 27. Mineralization is composed of up to 10% pyrite stringers and 5% disseminated pyrite in a moderately sericitized andesite.

OSK-W-17-903-W2 intersected 3.22 /t Au over 2.5 metres in FW3U. Mineralization is composed of 3% pyrite stringers with centimetre scale crustiform veins and quartz-tourmaline veins hosted in a sericitized andesite.

OSK-W-17-936-W1 intersected multiple mineralized zones in the Caribou Corridor: 12.6 g/t Au over 2.0 metres in Wolf HW, 14.2 g/t Au over 2.2 metres and 3.55 g/t Au over 2.1 metres in Wolf, and 204 g/t Au over 2.0 metres and 14.8 g/t over 2.0 metres in Wolf FW. The first two intervals are hosted in a sericitized andesite and composed of up to 10% pyrite stringers and 2% disseminated pyrite. The third interval includes 20% quartz-tourmaline veins associated with a hydrothermal breccia. The fourth and fifth intervals are composed of up to 1% pyrite stringers and 1% disseminated pyrite within a strongly silicified large quartz eyes porphyritic felsic intrusion.

OSK-W-17-936-W2 intersected four intervals in the Caribou Corridor: 3.36 g/t Au over 3.4 metres in Wolf 2, 27.7 g/t Au over 2.0 metres in a crustiform vein, 5.8 g/t Au over 2.0 metres in Wolf, and 6.41 g/t Au over 3.3 metres in Wolf FW. Wolf 2 mineralization and the crustiform vein are hosted in a strongly sericitized andesite and contain up to 8% pyrite stringers in stockwork texture. The Wolf interval contains local visible gold and 1% disseminated pyrite within a large quartz eyes porphyritic felsic intrusion. The last interval, the Wolf FW, is composed of 1% disseminated pyrite and 1% pyrite clusters in a silicified felsic dike.

OSK-W-17-937-W1 returned 14.6 g/t Au over 2.6 metres in CS1 HW. The mineralization is composed of 2% quartz-tourmaline veins and traces of disseminated pyrite. The interval is hosted in a strongly sericitized rhyolite.

OSK-W-17-975 returned 4.05 g/t Au over 2.5 metres in the extension of the Caribou Corridor. The mineralization is composed of trace disseminated pyrite and pyrite stringers in a chloritized andesite near the porphyritic felsic intrusion contact.

OSK-W-17-977 intersected 3.39 g/t Au over 2.8 metres in the Underdog Corridor. Mineralization is composed of trace disseminated and stringer pyrite associated with weak sericite and silica alteration within porphyritic felsic intrusion. This new zone is located just under the Red Dog intrusion, 60 metres north of the Mallard zone. The exact geometry and relationship with the Mallard zone is yet to be determined.

OSK-W-17-1009 returned 3.16 g/t Au over 2.1 metres in Zone 27. Traces of disseminated pyrite and pyrite stringers are associated with sericitized rhyolite.

OSK-W-17-1051 intersected three intervals all in the FW1 zone in the Underdog Corridor. The intervals returned 5.22 g/t Au over 2.3 metres, 7.09 g/t Au over 2.4 metres and 6.82 g/t Au over 3.5 metres in a strongly silicified and moderately sericitized large quartz eyes porphyritic felsic intrusion. The mineralization is composed of up to 25% pyrite stringers and 2% pyrite in silica flooding and up to 2% chalcopyrite. The second interval contains local visible gold.

OSK-W-17-1051-W2 intersected two intervals in the Underdog Corridor: 11.8 g/t Au over 4.0 metres in FW1 and 7.19 g/t Au over 2.2 metres in FW1 FW. The first interval is composed of 10% pyrite stringers and 1% disseminated pyrite associated with a strong silica alteration and hosted in fragmental felsic dike. The second interval is composed of up to 20% pyrite stringers and local visible electrum.

OSK-W-17-1081 returned 10.4 g/t Au over 2.4 metres in Zone 27. Mineralization is hosted in a strongly silicified and weakly sericitized porphyritic felsic dike and composed of up to 5% disseminated pyrite and quartz-tourmaline veins.

OSK-W-17-1087 returned 3.28 g/t Au over 2.0 metres in Drake. Mineralization is composed of 5% pyrite stringers within a sericitized porphyritic felsic dike.

OSK-W-17-1088 returned 7.73 g/t Au over 2.2 metres in Zone 27. Mineralization is composed of up to 10% pyrite within pervasive silica flooding hosted in a porphyritic felsic dike.

OSK-W-17-1105 intersected four intervals in the Caribou Corridor: 8.85 g/t Au over 2.0 metres, 4.94 g/t Au over 4.7 metres and 4.21 g/t Au over 2.3 metres in the extension of Caribou and 11.0 g/t Au over 11.2 metres, in the Wolf FW. The first two intervals are associated with large quartz eyes porphyritic felsic dikes and the mineralization is composed of up to 2% pyrite stringers and clusters. The sulphides content increases up to 15% pyrite stringers in the third interval with the mineralization hosted in a sericitized andesite. The last interval contains 15% pyrite stringers, 5% pyrite clusters and local visible gold associated with a strong sericitized andesite. This interval extends the Wolf FW zone 200m north-east and down plunge of OSK-W-17-913 (13.6 g/t Au over 2.0 metres previously reported September 20, 2017).

OSK-W-17-1110 intersected 4.39 g/t Au over 4.7 metres in the Caribou Corridor. Mineralization is composed of up to 10% pyrite clusters and up to 5% ptygmatic tourmaline veins in pervasive silica flooding. The mineralization is at the contact between an andesite and a porphyritic felsic intrusion.

OSK-W-17-1115 intersected a new zone returning 13.7 g/t Au over 2.8 metres. Mineralization is within a sericitized rhyolite and includes 4% disseminated pyrite, 2% pyrite clusters and disseminated tourmaline. This intersection is near a felsic intrusion and highlights a potential area between the main Caribou and the Lynx down plunge trends.

OSK-W-17-1116 returned 9.13 g/t Au over 3.0 metres in Zone 27. The mineralization is associated to a large quartz eyes porphyritic dike and composed of up to 10% pyrite and tourmaline veins.

OSK-W-17-1125-W3 returned 11.5 g/t Au 2.0 metres in the Wolf FW. Mineralization includes up to 30% pyrite stringers in a strongly sericitized fragmental felsic intrusion.

OSK-W-17-1137 intersected 3.01 g/t Au over 2.0 metres in Zone 27. Mineralization is composed of up to 8% pyrite stringers and up to 10% pyrite clusters within a strongly silicified rhyolite.

OSK-W-17-1138 returned 6.3 g/t Au over 16.0 metres in the Caribou Corridor. The mineralization is composed of 3% pyrite clusters, up to 10% pyrite stringers and disseminated chalcopyrite hosted in fragmental felsic dike and crustiform veins. Strong silica and fuchsite alteration are observed.

OSK-W-17-1145 intersected three intervals in Zone 27: 12.5 g/t Au over 2.4 metres, 9.93 g/t Au over 4.8 metres and 7.25 g/t Au over 5.9 metres. The mineralization is similar in the three intervals including up to 20% pyrite stringers in a strong silica flooding. The mineralization is hosted at the contact between a porphyritic felsic dike and the rhyolite.

OSK-W-17-1177 intersected 7.86 g/t Au over 3.4 metres in the extension of the Caribou Corridor. The mineralization is composed of 5% pyrite stringers associated with strong silica alteration zone within the andesite. This interval extends the Caribou Corridor 975 metres down plunge to the north-east from OSK-W-17-787 (7.21 g/t Au over 6.5 metres previously reported March 22, 2017). With this new hole, the Caribou Extension has now been traced to section 4075E, 1.2 kilometres north-east from the previous operator's 2015 resource envelope.

OSK-W-17-1224 returned 3.12 g/t Au over 2.4 metres in Mallard. Mineralization is in strongly sericitized and silicified andesite and composed of 30% quartz-carbonate veins with crustiform textures. The sulphides contain up to 2% disseminated pyrite and up to 7% pyrite stringers.

OSK-W-17-1226 intersected a new zone in the Caribou Corridor. The zone is located under a gabbro intrusion, which has the same orientation as the Red Dog, but above the main Caribou down plunge trend. The interval returned 8.29 g/t Au over 4.6 metres in a sericitized and silicified rhyolite cross-cut by felsic intrusions. The mineralization is composed of 10% pyrite stringers and locally semi-massive pyrite (10 cm wide). This new zone is located 150 metres down plunge of OSK-W-17-838 (731 g/t Au over 2.0 metres and 4.55 g/t Au over 3.0 metres previously reported August 24).

OSK-W-17-1232 returned 27.2 g/t Au over 2.0 metres in Zone 27. The mineralization is composed of 2% disseminated pyrite, 3% pyrite stringers and tourmaline veins in a strongly sericitized rhyolite.

OSK-W-17-1241 intersected 8.11 g/t Au over 3.5 metres in the upper part of the Caribou extension. Mineralization is composed of 5% pyrite stringers within a strongly sericitized fragmental intrusion. The geometry of this interval is yet to be determined.

OSK-W-17-1252 intersected 8.38 g/t Au over 2.0 metres in a new zone located 100 metres north-west of the Mallard Corridor. The mineralization is composed of 3% pyrite stringers and locally 20 centimetres scale pyrite veins within a moderately sericitized andesite.

OSK-W-17-1257 intersected three intervals in Zone 27: 7.69 g/t Au over 2.1 metres, 3.15 g/t Au over 2.3 metres and 15.4 g/t Au over 2.0 metres. The mineralization is at the contact between two porphyritic felsic dikes and is composed of up to 1% pyrite stringers, trace of pyrite clusters and one massive pyrite vein of 20 centimetres.

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 $220 million in cash and investments.

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.