Osisko Intersects 39.4 g/t Au Over 2.4 Metres At Windfall

(Toronto, October 25, 2017)  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 Urban Township, Abitibi, 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 18 intercepts in 11 infill holes (at 15 metre spacings) between section 2150E – 2450E, and 4 infill/expansion holes in Zone 27 of the Windfall deposit are presented below.

Highlights from the new results include: 39.4 g/t Au over 2.4 metres in OSK-W-17-1186; 18.8 g/t Au over 4.2 metres in OSK-W-17-1154; 25.7 g/t Au over 2.6 metres in OSK-W-17-903-W1;  and 7.90 g/t Au over 8.0 metres. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

Osisko is performing definition drilling in Zone 27.  The definition program is focused on infilling a 200 metre wide by 200 metre deep area of Zone 27 with a 15 metres drill spacing.  The area is between section 2150E and 2350E.

Notes:

1. True widths are estimated at 65 – 80% of the reported core length interval.  See “Quality Control” below.
2. Definitions: FW = Foot Wall

OSK-W-17-864 intersected 7.9 g/t Au over 8.0 metres. Mineralization is composed of up to 20% pyrite stringers within strong pervasive silica alteration. The andesite host is also sericite and fuchsite altered. Traces of chalcopyrite are observed along the interval.

OSK-W-17-903-W1 intersected 25.7 g/t Au over 2.6 metres in the Zone 27 Footwall. The mineralization is hosted in a strongly sericitized andesite, cut by the Red Dog intrusion, and composed of 3% pyrite stringers. The interval is 30 metre south-west of OSK-W-17-903 (10.7 g/t Au over 2.0 metres previously reported September 20, 2017).

OSK-W-17-1009 intersected 5.73 g/t Au over 2.7 metres. Mineralisation is in a porphyritic felsic intrusion and composed of massive pyrite stringers and pyrite-tourmaline veins. The intrusion is strongly sericitized and silicified.

OSK-W-17-1018 intersected 3.93 g/t Au over 2.0 metres. Mineralisation is composed of 6% semi-massive pyrite and 8% pyrite stringers within a strong silica and sericite altered rhyolite. The interval is 45 metres north-west of the main Zone 27.

OSK-W-17-1023 intersected 4.00 g/t Au over 3.6 metres. Mineralization is at the contact between the felsic intrusion and the rhyolite. Up to 4% pyrite stringers and few quartz-tourmaline veins are within a strong silica and sericite alteration envelope.

OSK-W-17-1038 intersected 16.4 g/t Au over 2.3 metres. Mineralization is composed of up to 5% pyrite stringers in a silica altered felsic porphyritic intrusion.

OSK-W-17-1050 intersected 6.55 g/t Au over 3.5 metres. Mineralization is composed of up to 4% pyrite stringers, 5% pyrite clusters and 1% quartz-tourmaline veins within a strongly sericitized and silicified rhyolite.

OSK-W-17-1103 intersected 15.4 g/t Au over 2.2 metres. Mineralization is composed of 10% pyrite-silica flooding at the contact between the andesite and the felsic porphyritic intrusion.

OSK-W-17-1106 intersected 3.02 g/t Au over 2.2 metres. Mineralisation is composed of trace disseminated pyrite and trace pyrite stringers hosted in a strongly sericitized rhyolite.

OSK-W-17-1122 intersected 7.05 g/t Au over 2.2 metres. Mineralization is composed of up to 10% pyrite stringers hosted in a strongly silicified and sericitized felsic dike.

OSK-W-17-1129 intersected 8.2 g/t Au over 2.2 metres. Mineralization is composed of up to 30% pyrite-silica flooding within a strongly sericitized rhyolite.

OSK-W-17-1154 intersected 18.8 g/t Au over 4.2 metres. Mineralization is composed of 10% semi-massive pyrite and 10% pyrite stringers within a strongly silicified and sericitized felsic intrusion.

OSK-W-17-1164 intersected 7.12 g/t Au over 7.8 metres. Mineralization is composed of trace pyrite stringers and trace pyrite clusters hosted in a sericite altered large quarts eyes, porphyritic felsic dike.

OSK-W-17-1080 intersected four intervals: 5.04 g/t Au over 3.0 metres, 18.0 g/t Au over 5.0 metres, 3.98 g/t Au over 3.2 metres and 3.47 g/t Au over 2.2 metres. The mineralization is composed of up to 15% pyrite stringers, 5% pyrites clusters and disseminated pyrite. Mineralization correlates with felsic intrusions, fragmental or porphyritic textured, hosted in strongly sericitized and silicified rhyolite or andesite.

OSK-W-17-1186 intersected 39.4 g/t Au over 2.4 metres. Mineralization is composed of 5% pyrite stringers and 5-10% disseminated pyrite within a strongly sericitized and silicified andesite.

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 dOr, 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-dOr 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-dOr 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 Québecs 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 $250 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”, “managements 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 managements 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