Osisko Intersects 37.0 g/t Au Over 5.4 Metres at Osborne-Bell

NOT FOR DISTRIBUTION TO UNITED STATES NEWSWIRE SERVICES OR FOR DISSEMINATION IN THE UNITED STATES

TORONTO, Sept. 28, 2018 - Osisko Mining Inc. (TSX:OSK) ("Osisko" or the "Corporation") is pleased to provide new results from the ongoing infill drilling program at its 100% owned Osborne-Bell gold deposit located 15 kilometres northwest of the town of Lebel-sur-Quévillon, Québec. The 50,000-metre program combines definition and expansion drilling at Osborne-Bell and the surrounding Quévillon property area. The Osborne-Bell deposit remains open at depth. To date approximately 24,100 metres of infill drilling have been completed over the main Osborne-Bell deposit.

Significant new analytical results from 22 intercepts in 18 drill holes are presented below. Highlights from the new results include: 37.0 g/t Au over 5.4 metres in OSK-OB-18-051; 38.6 g/t Au over 2.5 metres in OSK-OB-18-011; 41.1 g/t Au over 2.4 metres in OSK-OB-18-086 and 26.6 g/t Au over 4.6 metres in OSK-OB-18-010. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

OSK-OB-18-010 intersected zone 2-650 averaging 26.6 g/t Au over 4.6 metres. Mineralization consists of local visible gold, up to 5% finely disseminated pyrite and trace pyrrhotite in an andesite with weak carbonate alteration.

OSK-OB-18-011 intersected 5.25 g/t Au over 5.3 metres and 38.6 g/t Au over 2.5 metres in zone 2-650. Mineralization consist of up to 10% clustered pyrite in a fragmented andesite with irregular felsic fragments.

OSK-OB-18-019 intersected 15.2 g/t Au over 3.0 metres in zone 2-652. The interval contains 2% disseminated pyrite in a felsic volcanic rock with moderate sericite and potassic alteration.

OSK-OB-18-023 intersected 13.0 g/t Au over 2.0 metres in zone 2-651. Mineralization consists of 5% disseminated pyrite and up to 3% pyrrhotite in a silica-biotite-sericite altered andesite.

OSK-OB-18-043 intersected 10.9 g/t Au over 6.3 metres in zone 2-650. Mineralization consists of local visible gold on the margin of quartz-carbonate-chlorite veins, up to 7% disseminated pyrite, trace chalcopyrite and sphalerite in an andesite with a penetrative silica and potassic alteration.

OSK-OB-18-051 intersected 37.0 g/t Au over 5.4 metres in zone 2-652. Mineralization consists of 2% pyrite stringers and trace chalcopyrite stringers in a strongly sericitized porphyritic rhyodacite with weak chloritization.

OSK-OB-18-055 intersected 11.8 g/t Au over 3.0 metres in zone 2-651. Mineralization includes up to 5% pyrite clusters in association with dismembered quartz-chlorite-carbonate veinlets, 2% pyrite stringers, 2% pyrrhotite clusters and trace chalcopyrite in an andesite with moderate sericitization and carbonatation.

OSK-OB-18-057 intersected 26.4 g/t Au over 2.1 metres in zone 2-650. Mineralization consists of up to 6% disseminated pyrite in an andesite strongly altered in sericite, biotite and chlorite.

OSK-OB-18-064 intersected 7.26 g/t Au over 3.4 metres in zone 2-651. Mineralization consists of up to 4% pyrite and 1% pyrrhotite in clusters and stringers and trace pyrite associated with dismembered quartz-chlorite-carbonates veinlets in a strongly sericitized andesite.

OSK-OB-18-069 intersected 6.18 g/t Au over 9.0 metres in zone 2-652. Mineralization consists of 3% pyrite, trace pyrrhotite and trace chalcopyrite as clusters and in association with quartz-carbonate veins. Mineralization is hosted in silica and sericite altered quartz-phyric rhyodacite.

OSK-OB-18-070 intersected 14.2 g/t Au over 3.3 metres and 38.0 g/t Au over 2.1 metres in zone 2-652. Mineralization consists of 2% pyrite dissemination, 1% sphalerite at the margin of quartz-carbonate veins in a moderately sericitized rhyodacite.

OSK-OB-18-073 intersected two intervals: 8.20 g/t Au over 4.1 metres and 29.4 g/t Au over 2.6 metres in zone 2-652. The first interval contains 5% of interstitial pyrite, locally trace to 20% chalcopyrite at the contact between a sericitized rhyodacite and a chloritized andesite. The second interval contains local visible gold associated with 2% pyrite and 1% chalcopyrite in stringers and clusters in a quartz-phyric rhyodacite with sericite and biotite alteration.

OSK-OB-18-075 intersected 19.6 g/t Au over 3.0 metres in zone 2-652. Mineralization consists of local visible gold, 8% pyrite, 1% sphalerite and trace disseminated chalcopyrite in a strongly sericitized and silicified porphyritic rhyodacite.

OSK-OB-18-077 intersected 8.28 g/t Au over 2.3 metres in zone 3-653. Mineralization consists of 5% chalcopyrite, 2% pyrite and trace sphalerite in a sericitized andesite.

OSK-OB-18-082 intersected 3.32 g/t Au over 6.0 metres in zone 3-653. Mineralization consists of 3% pyrite stringers and clusters, trace chalcopyrite in stringers hosted in quartz porphyritic rhyodacite.

OSK-OB-18-086 intersected 41.1 g/t Au over 2.4 metres in zone 3-551. Mineralization consists of up to 5% pyrite stringers, 1% disseminated chalcopyrite and trace sphalerite in a strongly sericitized quartz-phyric rhyodacite.

OSK-OB-18-088 intersected 3.90 g/t Au over 6.7 metres in zone 3-654 and 11.0 g/t Au over 3.1 metres in zone 3-653. The first interval contains up to 6% pyrite and 2% chalcopyrite in stringers hosted in an andesite altered in biotite and sericite. The second interval contains local visible gold, 2% pyrite stringers and 1% sphalerite in chlorite-carbonate veinlets. Mineralization is hosted in a strongly sericitized and silicified porphyritic rhyodacite.

OSK-OB-18-098 intersected 13.4 g/t Au over 2.4 metres in zone 3-652. Mineralization consists of 1% disseminated pyrite and stringers in sericite and chlorite altered quartz-phyric rhyodacite.

Qualified Person
The scientific and technical content of this news release has been reviewed, prepared and approved by Mr. Pascal Simard, P.Eng. (OIQ 5002937), Director of Northern Exploration for projects in Quebec, 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 currently unknown but is estimated at 65-80% 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 Columbia. 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. All samples are also analyzed for multi-elements, 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.

About the Osborne-Bell Gold Deposit
The Osborne-Bell gold deposit is located 15 kilometres northwest of the town of Lebel-sur-Quevillon in the Abitibi region of Québec, Canada. The mineral resource defined by Osisko, as disclosed in the Osborne-Bell Technical Report (as defined below), comprises 2,587,000 tonnes at 6.13 g/t Au (510,000 ounces) in the inferred mineral resource. Mineralization occurs in nine (9) individuals mineralized zones:1-551, 1-651, 1-653, 2-650, 2-652, 3-551, 3-552, 3-652, 3-653. All zones comprise sub-vertical lenses following intermediate and felsic volcanic rocks plunging to the northeast. The deposit is well defined from surface to a depth of 300 metres. For details regarding the key assumptions, parameters and methods used to estimate the mineral resources presented in respect of the Osborne-Bell gold project, please see the technical report entitled "Technical Report and Mineral Resource Estimate – Osborne-Bell deposit, Quévillon property " and dated April 23, 2018 (effective date of March 2, 2018), which has been prepared by InnovExplo Inc. from Val-d'Or, Québec (the "Osborne-Bell Technical Report"). The Osborne-Bell Technical Report is available on Osisko's website at www.osiskomining.com and on SEDAR under Osisko's issuer profile at www.sedar.com. For details regarding the PEA refer to "Preliminary Economic Assessment of the Windfall Lake Project, Lebel-sur-Quévillon, Québec, Canada” and dated August 1, 2018 (effective date of July 12, 2018), has been prepared for Osisko by BBA Inc., InnovExplo Inc., Golder Associates Ltd., WSP Canada Inc. and SNC-Lavalin Stavibel Inc. (the Windfall PEA). The Windfall PEA which includes the Osborne Bell Deposit is available on SEDAR (www.sedar.com) under Osisko’s issuer profile.

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 Quévillon 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 Québec and Ontario.

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. 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 news release contains the forward-looking information pertaining to, among other things, the timing and ability of Osisko to file a technical report in respect of this resource estimate; the prospects of the Osborne-Bell gold deposit; the potential for the Osborne-Bell gold deposit being a significant deposit; the potential future mill site for the Windfall Lake gold deposit; the timing and ability of Osisko, if at all, to publish a resource update for Windfall-Lynx; the projected capital expenditures of mining activities at the Osborne-Bell gold deposit; upgrading a inferred mineral resource to a measured mineral resource or indicated mineral resource categories; the significance of historic exploration activities and results. 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 Quévillon project and the Osborne-Bell Gold Deposit; the ability of the Corporation to obtain required approvals; 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