Osisko Windfall Infill Drilling Confirming Shallow Mineralized Zones

TORONTO, Aug. 08, 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 now focussed on infill drilling within the main Windfall gold deposit and the adjacent Lynx deposit (located immediately NE of Windfall), and exploration and expansion drilling on main mineralized zones with several deep holes in progress to investigate the down-plunge areas in and around the Underdog and Lynx zones.

Today’s results, presented in the table below, include significant new analytical results from 59 intercepts in 37 drill holes and extensions focused on shallow infill drilling in the Windfall deposit all above 400 metres vertical depth.

Highlights from the new results include: 34.8 g/t Au over 4.3 metres in OSK-W-18-1614; 12.6 g/t Au over 10.7 metres and 27.0 g/t Au over 4.2 metres in OSK-W-18-1547; 37.9 g/t Au over 3.2 metres in OSK-W-18-1586; and 34.6 g/t Au over 2.0 metres in OSK-W-18-1510. 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-OBM-16-662 intersected 4.25 g/t Au over 5.0 metres in Zone 27. Mineralization consists of up to 1% disseminated pyrite within a strong sericite altered andesite in contact with a felsic dike.

OSK-W-18-1466 intersected 3.81 g/t Au over 2.0 metres in Zone 27. Mineralization consists of 2% disseminated pyrite and stringers within a strong sericite and chlorite altered andesite in contact with a felsic porphyritic dike.

OSK-W-18-1481 intersected 12.7 g/t Au over 2.0 metres in Bobcat. Mineralization consists of up to 3% pyrite stringers and quartz-tourmaline veins within a strong silica and moderate sericite altered felsic porphyritic dike.

OSK-W-18-1487 intersected 3.62 g/t Au over 5.5 metres in Caribou. Mineralization consists of 2% pyrite stringers and trace sphalerite within a strong sericite and silica altered felsic porphyritic dike.

OSK-W-18-1497 intersected 5.45 g/t Au over 2.2 metres and 3.84 g/t Au over 2.7 metres in Caribou. Both intervals contain up to 10% pyrite stringers at the contact between a strong silica altered rhyolite and a felsic porphyritic intrusion.

OSK-W-18-1505 intersected 9.78 g/t Au over 3.0 metres in Caribou and 3.07 g/t Au over 2.0 metres in Zone 27. The first interval contains 10% pyrite stringers within a strong sericite altered felsic porphyritic dike. The last interval contains up to 5% pyrite stringers within a strong sericite altered rhyolite.

OSK-W-18-1506 intersected 6.66 g/t Au over 2.3 metres in Zone 27. Mineralization consists of up to 10% disseminated pyrite and 3% pyrite-tourmaline veins within a strong sericite and weak silica altered felsic porphyritic intrusion.

OSK-W-18-1509 intersected 6.23 g/t Au over 2.2 metres in Bobcat. Mineralization consists of 3% disseminated pyrite included in silica flooding hosted in a moderate silica and weak sericite altered felsic fragmental dike. The interval extends the Bobcat zone 25 metres north-east from OSK-W-17-1251 (8.89 g/t Au over 3.0 metres, reported January 25, 2018).

OSK-W-18-1510 intersected 34.6 g/t Au over 2.0 metres in Zone 27. Mineralization consists of up to 10% pyrite stringers, locally semi-massive, hosted in a weak sericite and fuchsite altered andesite.

OSK-W-18-1517 intersected 4.24 g/t Au over 6.3 metres in Caribou. Mineralization consists of 10% pyrite clusters at a faulted contact between a moderate sericite altered gabbro and a rhyolite.

OSK-W-18-1518 intersected a vein returning 5.39 g/t Au over 2.4 metres. Mineralization consists of disseminated pyrite within the monzonitic “Red Dog” dike.

OSK-W-18-1534 intersected 4.38 g/t Au over 2.0 metres in Zone 27. Mineralization consists of up to 7% quartz-tourmaline stringers, 1% pyrite clusters and ptygmatic tourmaline veins within a strong sericite altered felsic porphyritic dike.

OSK-W-18-1538 intersected 5.69 g/t Au over 2.0 metres and 6.60 g/t Au over 2.0 metres in Zone 27. The first interval contains 2% disseminated and stringer pyrite within a moderate sericite altered felsic porphyritic intrusion. The second interval contains up to 3% pyrite stringers and 1% disseminated pyrite and quartz-tourmaline veins at the contact between a strong silica and sericite altered felsic porphyritic dike and a chlorite altered andesite.

OSK-W-18-1543 intersected 8.15 g/t Au over 2.3 metres in Zone 27. Mineralization consists of local visible gold, up to 7% pyrite with quartz-tourmaline veins and trace chalcopyrite hosted at a strong sericite altered contact between a felsic porphyritic intrusion and a rhyolite.

OSK-W-18-1545 intersected 3.31 g/t Au over 6.7 metres and 5.33 g/t Au over 2.5 metres in Caribou. Both intervals contain up to 10% pyrite, disseminated or in clusters, and trace pyrite-tourmaline stringers hosted in a moderate sericite altered rhyolite.

OSK-W-18-1547 intersected six intervals: 4.86 g/t Au over 4.6 metres, 3.67 g/t Au over 2.4 metres and 3.60 g/t Au over 2.2 metres in Caribou and, 12.6 g/t Au over 10.7 metres, 27.0 g/t Au over 4.2 metres and 22.5 g/t Au over 2.5 metres in Zone 27. The first interval contains 15% pyrite stockwork within a moderate sericite altered rhyolite. The second and third intervals contain up to 7% pyrite stringers, locally semi-massive, and trace tourmaline stringers within a strong sericite altered felsic porphyritic dike. The three Zone 27 intervals contain up to 15% pyrite stringers, locally semi-massive, pyrite-silica flooding, local visible gold, trace sphalerite and chalcopyrite hosted in strong silica altered felsic dike.

OSK-W-18-1552 intersected 5.98 g/t Au over 2.3 metres in Caribou. Mineralization consists of up to 7% pyrite stringers at the contact between moderate sericite altered rhyolite and a felsic porphyritic dike.

OSK-W-18-1558 intersected three intervals: 11.4 g/t Au over 2.0 metres and 3.30 g/t Au over 2.4 metres in Caribou and 6.98 g/t Au over 7.1 metres in Zone 27. The first interval contains trace pyrite, disseminated and clustered, within a moderate sericite altered felsic dike. The second interval contains up to 15% stringer and disseminated pyrite within a strong silica altered and moderate sericite altered rhyolite. The last interval contains up to 10% pyrite stringers, 1% disseminated pyrite within a moderate silica and sericite altered felsic porphyritic dike.

OSK-W-18-1559 intersected 3.43 g/t Au over 2.0 metres in Zone 27. Mineralization consists of 1% pyrite stringers within a moderate sericite altered contact between an andesite and a felsic intrusion.

OSK-W-18-1563 intersected four intervals: 4.72 g/t Au over 2.8 metres and 4.52 g/t Au over 2.0 metres in Caribou and, 5.20 g/t Au over 2.9 metres and 4.67 g/t Au over 2.0 metres in Zone 27. The first interval contains 30% semi-massive pyrite hosted in a moderate sericite altered rhyolite. The second interval contains trace disseminated pyrite within a moderate chlorite altered rhyolite. The third interval contains 2% disseminated pyrite and 1% pyrite stringers within a moderate silica and carbonate altered felsic porphyritic intrusion. The last interval contains 1% pyrite, disseminated and stringers, within a moderate chlorite altered andesite.

OSK-W-18-1567 intersected 3.34 g/t Au over 2.0 metres and 8.56 g/t Au over 3.8 metres in Zone 27. The first interval contains trace disseminated pyrite and ptygmatic tourmaline veins hosted in a moderate sericite altered rhyolite. The second interval contains 5% pyrite-tourmaline veins and 1% pyrite stringers hosted in quartz-carbonate and moderate sericite altered felsic porphyritic intrusion.

OSK-W-18-1572 intersected 3.44 g/t Au over 2.0 metres in Caribou and 6.61 g/t Au over 2.0 metres in Zone 27. The first interval contains 2% pyrite-silica flooding and 1% pyrite stringers within a moderate sericite, chlorite and carbonate altered rhyolite. The second interval contains up to 2% pyrite, disseminated and stringers, hosted in a moderate chlorite and carbonate altered felsic dike.

OSK-W-18-1577 intersected 8.83 g/t Au over 2.4 metres in Zone 27. Mineralization consists of 40% semi-massive pyrite at a strong sericite altered contact between a gabbro and felsic porphyritic intrusion.

OSK-W-18-1580 intersected 6.47 g/t Au over 2.0 metres in Zone 27. Mineralization consists of 5% quartz-tourmaline veins and 5% semi-massive pyrite hosted in a weak sericite altered rhyolite.

OSK-W-18-1586 intersected 37.9 g/t Au over 3.2 metres in Zone 27. Mineralization contains 25% pyrite-tourmaline stringers and local visible gold within a strong silica and moderate sericite altered rhyolite.

OSK-W-18-1594 intersected 3.53 g/t Au over 2.4 metres in Zone 27. Mineralization consists of up to 15% pyrite stringers hosted in a moderate sericite altered felsic porphyritic dike.

OSK-W-18-1596 intersected 5.52 g/t Au over 2.1 metres in Zone 27. Mineralization consists of up to 3% pyrite, disseminated and stringers, hosted in moderate sericite altered rhyolite.

OSK-W-18-1597 intersected two intervals: 9.08 g/t Au over 2.1 metres in Caribou and 5.08 g/t Au over 2.5 metres in Zone 27. The first interval contains up to 1% pyrite, disseminated and clusters, hosted in moderate sericite and chlorite altered rhyolite. The second interval contains up to 20% pyrite-tourmaline stringers within a moderate sericite altered rhyolite.

OSK-W-18-1601 intersected 4.38 g/t Au over 2.0 metres in Caribou. Mineralization consists of 2% pyrite stringers, 1% sphalerite clusters and quartz veins hosted in a moderate sericite, moderate chlorite and weak fuchsite altered gabbro.

OSK-W-18-1602 intersected three intervals: 18.4 g/t Au over 2.0 metres, 7.94 g/t Au over 2.4 metres and 4.13 g/t Au over 2.0 metres in Caribou. The first interval contains trace disseminated and stringer pyrite within a moderate sericite altered rhyolite. The second interval contains 10% pyrite stringers, ptygmatic tourmaline veins and trace sphalerite and chalcopyrite hosted in a strong silica and moderate sericite altered felsic porphyritic intrusion.

OSK-W-18-1605 intersected 3.05 g/t Au over 2.0 metres in Zone 27. Mineralization contains up to 8% pyrite stringers and 1% disseminated pyrite at the contact between a sericite felsic porphyritic intrusion and a bleached andesite.

OSK-W-18-1607 intersected 3.89 g/t Au over 2.0 metres in Zone 27. Mineralization consists of 1% pyrite stringers within a moderate chlorite altered rhyolite.

OSK-W-18-1609 intersected two intervals: 5.54 g/t Au over 2.5 metres in Caribou and 4.69 g/t Au over 2.7 metres in Zone 27. The first interval contains up to 15% pyrite stockwork and 1% disseminated pyrite hosted in moderate sericite and weak silica altered rhyolite.

OSK-W-18-1611 intersected two intervals: 5.19 g/t Au over 2.1 metres in Caribou and 5.41 g/t Au over 2.1 metres in Zone 27. The first interval contains 80% massive pyrite and pyrite stockwork hosted in a strong sericite and silica altered felsic porphyritic intrusion. The second interval contains 2% pyrite clusters, 1% pyrite stringers and fine disseminated pyrite hosted in a moderate chlorite altered andesite.

OSK-W-18-1614 intersected two intervals: 6.47 g/t Au 2.1 metres and 34.8 g/t Au over 4.3 metres in Zone 27. The first interval contains pyrite stringers within a strong sericite and fuchsite altered contact between a gabbro and a fragmental andesite. The second interval contains 20% pyrite stringers and 2% disseminated pyrite within a strong sericite altered fragmental andesite.

OSK-W-18-1617 intersected 3.49 g/t Au over 2.6 metres in Caribou. Mineralization consists of 20% pyrite stringers, 10% sphalerite, pyrite-silica flooding and 1% pyrite-tourmaline veins hosted in moderate sericite and silica altered rhyolite.

OSK-W-18-1631 intersected 17.1 g/t Au over 2.0 metres in Zone 27. Mineralization consists of trace pyrite stringers and clusters within a strong sericite altered felsic 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 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 only 30 metres from surface in some areas and as deep as 1,200 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