Osisko Intersects 1026 g/t Au Over 2.7 Metres at Lynx

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

TORONTO, Oct. 23, 2018 - Osisko Mining Inc. (OSK:TSX. "Osisko" or the "Corporation") is pleased to provide new infill drilling results from the ongoing drill definition and expansion 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 commenced in late 2015. The program is currently focussed on infill drilling within the main Windfall gold deposit and the adjacent Lynx deposit (located immediately NE of Windfall), exploration and expansion drilling on the main mineralized zones, and deep exploration in the central areas of the intrusive system. Significant new analytical results from 37 intercepts in 17 drill holes and 6 wedges focused on infill drilling are presented below.

Highlights from the new results include: 1026 g/t Au over 2.7 metres in OSK-W-18-1725; 48.7 g/t Au over 3.3 metres in OSK-W-18-1560-W2; 59.3 g/t Au over 2.0 metres in OSK-W-18-1503-W1; 39.3 g/t Au over 2.3 metres in OSK-W-18-1665; 33.3 g/t Au over 2.7 metres in OSK-W-18-1711-W2 and 9.01 g/t Au over 9.2 metres in OSK-W-18-1402-W3. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

Note: True widths are estimated at 65 – 80% of the reported core length interval. See "Quality Control and Reporting Protocols" below.

OSK-W-18-1402-W3 intersected 9.01 g/t Au over 9.2 metres in Underdog. Mineralization includes up to 15% pyrite stringers, 3% chalcopyrite, 2% quartz-tourmaline ptygmatic veins and local visible gold within a strong silica and sericite altered felsic porphyritic dike.

OSK-W-18-1475 intersected 8.09 g/t Au over 2.2 metres in Lynx. Mineralization includes 4% disseminated pyrite and stringers in a moderate chlorite, weak silica and sericite altered rhyolite.

OSK-W-18-1503-W1 intersected three intervals in Lynx: 5.09 g/t Au over 2.3 metres, 59.3 g/t Au over 2.0 metres and 29.7 g/t Au over 2.0 metres. The first interval contains 5% disseminated/cluster pyrite, and up 3% pyrite/pyrite-tourmaline stringers within a weak fuchsite and sericite altered gabbro. The second interval contains local visible gold in pyrite stringers and trace chalcopyrite within a moderate sericite altered rhyolite. The third interval has local visible gold and electrum within centimetre scale smoky quartz veins, hosted in a moderate sericite altered rhyolite.

OSK-W-18-1545 intersected 11.2 g/t Au over 2.9 metres in Zone 27. Mineralization consists of up to 40% pyrite as stringers, patches and semi-massive, ptygmatic tourmaline veinlets and quartz-carbonate veins hosted at the contact between a fuchsite, sericite, chlorite altered gabbro and moderate sericite altered fragmental felsic intrusion.

OSK-W-18-1557 intersected 3.72 g/t Au over 2.0 metres in Lynx. Mineralization consists of up to 40% pyrite as stringers and patches with ptygmatic tourmaline veinlets and breccia quartz-carbonate veins hosted at the contact between a fuchsite, sericite and chlorite altered gabbro and a moderate sericite altered fragmental felsic intrusion.

OSK-W-18-1560-W1 intersected three intervals in Lynx: 5.35 g/t Au over 2.3 metres, 9.89 g/t Au over 2.3 metres and 6.88 g/t Au over 3.9 metres. The first interval contains up to 7% pyrite stringers, 5% pyrite in smoky quartz veins, 2% pyrite in dismembered tourmaline ptygmatic veins, 10% disseminated and clustered pyrite in a sericitized and silicified rhyolite. The second interval contains 7% disseminated pyrite and 5% pyrite within quartz-carbonate veins hosted in a sericite, silica and fuchsite altered gabbro. The third interval contains up to 7% disseminated pyrite, 5% pyrite in quartz-carbonate veins hosted in a bleached, sericitized and silicified gabbro.

OSK-W-18-1560-W2 intersected two intervals in Lynx 5.28 g/t Au over 2.3 metres and 48.7 g/t Au over 3.3 metres. The first interval contains up to 10% pyrite stringers, 10% pyrite with pervasive silica flooding, 10% disseminated pyrite and 3% disseminated chalcopyrite. The mineralization is hosted in an alternation between bleached, sericitized and silicified gabbro and sericitized rhyolite. The second interval contains up to 20% disseminated pyrite, 20% pyrite stringers, 5% pyrite within quartz-tourmaline veins and 1% hosted in a silica, fuchsite and sericite altered gabbro.

OSK-W-18-1587 intersected 10.0 g/t Au over 2.0 metres in Lynx. Mineralization consists of 4% disseminated pyrite and ptygmatic quartz-tourmaline veins within a strong sericite and silica altered contact between a gabbro and a rhyolite.

OSK-W-18-1665 intersected 39.3 g/t Au over 2.3 metres in Zone 27. Mineralization consists of up to 15% pyrite-tourmaline and trace of ptygmatic tourmaline veinlets hosted in a moderate sericite altered porphyritic felsic intrusion.

OSK-W-18-1678 intersected 5.88 g/t Au over 2.1 metres in Zone 27. Mineralization includes local visible gold, 5% pyrite and 1% chalcopyrite in fragmented and dismembered quartz-carbonate veinlets, 3% disseminated pyrite and quartz-tourmaline stringers hosted in bleached and sericitized gabbro.

OSK-W-18-1691 intersected 4.25 g/t Au over 2.2 metres in Caribou. Mineralization includes traces disseminated pyrite in a strongly chloritized, moderately bleached and sericitized andesite.

OSK-W-18-1707 intersected four intervals: 3.95 g/t Au over 2.3 metres and 6.23 g/t Au over 2.0 metres in Caribou; 27.4 g/t Au over 2.4 metres and 6.81 g/t Au over 4.0 metres in Zone 27. The first interval includes 10% pyrite and 2% sphalerite within pervasive silica flooding, hosted in a silica and sericite altered rhyolite. The second interval contains up to 10 % pyrite stringers, locally semi-massive, wthin silicified and sericitized rhyolite. The third and fourth intervals include up to 15% pyrite stringers, 1% pyrite within smoky quartz veins, hosted in a bleached, strong silica and sericite altered felsic porphyritic intrusion.

OSK-W-18-1710 intersected 14.2 g/t Au over 2.3 metres in Bobcat. Mineralization consists of up to 40% crustiform veins with 2% pyrite, trace sphalerite and chalcopyrite hosted in a weak sericite and silica altered rhyolite.

OSK-W-18-1711 intersected 5.08 g/t Au over 2.6 metres in Lynx. Mineralization consists of 2% pyrite in quartz-tourmaline veins within a sericite and silica altered rhyolite; OSK-W-18-1711-W1 intersected 4.55 g/t Au over 2.0 metres, 12.5 g/t Au over 2.8 metres and 6.36 g/t Au over 2.0 metres. The first interval includes 1% pyrite stringers and clusters in a sericite, silica and carbonate altered rhyolite. The second interval contains 7% pyrite-tourmaline stringers, 5% pyrite clusters within a silica, sericite and fuchsite altered rhyolite. The third interval contains 1% pyrite stringers and clusters in a strong chlorite, weak sericite and carbonate altered rhyolite; OSK-W-18-1711-W2 intersected 33.3 g/t Au over 2.7 metres in Lynx. Mineralization consists of local visible gold, 5% disseminated pyrite and quartz-tourmaline veins hosted in a moderate silica and sericite altered gabbro.

OSK-W-18-1712 intersected 5.14 g/t Au over 2.2 metres in Lynx. Mineralization consists of 2% pyrite stringers, 2% pyrite clusters and ptygmatic tourmaline veins hosted at the contact between a strong silica altered rhyolite and a weak fuchsite altered gabbro.

OSK-W-18-1713 intersected 6.48 g/t Au over 2.1 metres in Zone 27. Mineralization consists of 40% semi-massive pyrite and trace chalcopyrite with quartz clusters and hosted in a silica altered porphyritic felsic dike.

OSK-W-18-1714 intersected 3.59 g/t Au over 2.4 metres. Mineralization consists of 4% pyrite stringers and clusters with 2% crustiform veins and 1% quartz-tourmaline veinlets hosted in a moderate silica and fuchsite altered gabbro.

OSK-W-18-1723 intersected two intervals in Lynx: 22.7 g/t Au over 2.2 metres and 4.06 g/t Au over 2.6 metres. The first interval includes up to 15% pyrite and trace sphalerite within pervasive silica flooding, trace disseminated pyrite clusters and stringers and ptygmatic tourmaline veinlets hosted a moderate sericite rhyolite. The second interval contains 5% pyrite stringers, 1% pyrite and traces of chalcopyrite in a laminated quartz-tourmaline veinlet hosted in a moderate sericite and weak fuchsite altered gabbro.

OSK-W-18-1725 intersected two intervals in Lynx: 1026 g/t Au over 2.7 metres and 13.9 g/t Au over 4.0 metres. The first interval contains local visible gold, up to 15% disseminated pyrite and stringers with pervasive silica flooding hosted in strong silica, weak fuchsite altered porphyritic felsic dike. The second interval contains local visible gold, up to 7% pyrite stringers within a weak fuchsite altered fragmental felsic dike.

OSK-W-18-1727 intersected 6.51 g/t Au over 2.0 metre in Lynx. Mineralization includes 1% pyrite stringers within a strong chlorite, moderate carbonate, weak sericite and fuchsite altered gabbro.

OSK-W-18-1729 intersected three intervals in Zone 27: 3.16 g/t Au over 5.0 metre, 7.00 g/t Au over 2.3 metres and 3.62 g/t Au over 3.1 metres. The first interval contains 10% pyrite stringers with local tourmaline ptygmatic veins hosted at the contact between a moderate sericite and weak silicified altered felsic porphyritic dike and a moderate sericite altered andesite. The second interval contains 7% pyrite stringers and up to 20% pyrite in pervasive silica flooding within a silicified and sericitized porphyritic felsic intrusion. The third interval contains up to 5% pyrite stringers, 3% pyrite with ptygmatic tourmaline veins and 3% disseminated pyrite within a moderate sericite and weak silica altered felsic porphyritic intrusion.

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 Osisko's 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 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 Colombia, or (ii) 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 Osisko, as disclosed in the Windfall Lake Technical Report (as defined below), comprises 2,382,000 tonnes at 7.85 g/t Au (601,000 ounces) in the indicated mineral resource category and 10,605,000 tonnes at 6.70 g/t Au (2,284,000 ounces) in the inferred mineral resource category. For details regarding the key assumptions, parameters and methods used to estimate the mineral resources presented in respect of the Windfall Lake gold project, please see the technical report entitled "Technical Report and Mineral Resource Estimate for the Windfall Lake Project, Windfall Lake and Urban-Barry Properties" and dated June 12, 2018 (effective date of May 14, 2018), which has been prepared by InnovExplo Inc. from Val-d'Or, Québec (the "Windfall Lake Technical Report"). The Windfall Lake Technical Report is available on Osisko's website at www.osiskomining.com and on SEDAR under Osisko's issuer profile at www.sedar.com). The Windfall Lake gold deposit is currently one of the highest grade resource-stage gold projects in Canada. Mineralization occurs in four principal zones: Lynx, Zone 27, Caribou and Underdog. All zones comprise sub-vertical lenses following intrusive porphyry contacts plunging to the northeast. The deposit is well defined from surface to a depth of 900 metres and remains open along strike and at depth. Mineralization has been identified 30 metres from surface in some areas and as deep as 2000 metres in others, with significant potential to extend mineralization 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 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. 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 Windfall Lake gold deposit being a world-class gold system; the significance of new results from the ongoing deep-hole drill/exploration program at the Windfall Lake gold project; the significance of assay results presented in this news release; potential depth extensions of the Lynx and Underdog mineralized zones; the potential, if any of the Deep Underdog and Deep Lynx zones; the type and extend of drilling on the Deep Underdog and Deep Lynx zones, including planned wedge holes; the success of Osisko's deep-hole drill/exploration program at the Windfall Lake gold project, if any; the down-plunge projection of the gold mineralized structures; the current 800,000 metre drill program; the type of drilling included in the drill program; 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 such assumptions and estimates were made, and 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