Osisko Infill Drilling Confirming High-Grade Mineralization at Windfall

68.5 g/t Au Over 9.8 Metres in Underdog

494 g/t Au Over 2.8 Metres in Lynx

TORONTO, July 25, 2018 -- Osisko Mining Inc. (TSX:OSK) ("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 and with several deep holes in progress to investigate the down-plunge areas in and around the Underdog and Lynx zones.

Today's results focus on infill drilling and include significant new analytical results from 70 intercepts from 33 drill holes and 5 wedges in the Lynx deposit and Underdog zone and include one wireframe extension intercept (Hole OSK-W-18-1593), one extension intercept in a zone not currently included in wireframes (OSK-W-18-1555), and one new intercept not related to any known mineralized zone (OSK-W-18-1461).

Osisko President & CEO John Burzynski noted: "Today’s infill numbers on Lynx and Underdog show very positive and encouraging results as we continue to add drill holes and move more of our mineral resource from inferred to indicated. This is the positive trend that we expected as we work towards completing the second half of our major drill program. In context with last week’s Preliminary Economic Assessment (see Osisko news release dated July 17, 2018), we are confident that the work that we are doing today will only improve on the strength of the deposit as we move Windfall towards our anticipated feasibility study in 2019.”

Highlights from the new infill drilling results include 13 intervals with assays of >32 g/t Au (>1 oz/t Au) (uncut) including: 494 g/t Au over 2.8 metres in OSK-W-18-1593; 68.5 g/t Au over 9.8 metres in OSK-W-18-1066-W1; 273 g/t Au over 2.2 metres and 109 g/t Au over 2.0 metres in OSK-W-18-1546; 145 g/t Au over 2.2 metres in OSK-W-18-1504; 46.4 g/t Au over 5.2 metres in OSK-W-18-1613; 39.3 g/t Au over 5.6 metres in OSK-W-18-1557. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

Notes: True widths are estimated at 65 – 80% of the reported core length interval. See "Quality Control and Reporting Protocols" below.
Definitions: VNCR = Crustiform veins.

OSK-W-17-1039 intersected 11.4 g/t Au over 2.4 metres in Lynx. Mineralization consists of 5% pyrite and a quartz-tourmaline crustiform vein with local visible gold hosted in a moderately sericitized rhyolite.

OSK-W-18-909-W5 intersected 7.94 g/t Au over 2.1 metres in Lynx. Mineralization consists of trace disseminated pyrite with a crustiform vein hosted in a chlorite, silica, carbonate and fuchsite altered and foliated gabbro.

OSK-W-18-1066-W1 intersected 68.5 g/t Au over 9.8 metres and 39.6 g/t Au over 2.2 metres in Underdog. The first interval contains local visible gold, up to 15% pyrite and 1% chalcopyrite in pervasive silica flooding patches in a strongly silicified and sericitized porphyric felsic dike with local fuchsite. The second interval contains local visible gold, 2% pyrite in ptygmatic veins, trace chalcopyrite stringers and cluster with pervasive silica flooding, and trace disseminated pyrite in a sericitized and strongly silicified porphyritic dike.

OSK-W-18-1336-W2 intersected 4.36 g/t Au over 2.4 metres and 4.55 g/t Au over 2.0 metres in Underdog. The first interval contains 5% pyrite-tourmaline stringers, 3% pyrite clusters and 2% coarse grained pyrite in volcanic fragments in a sericitized fragmental felsic dike. The second interval contains trace disseminated pyrite and cluster in a sericite, chlorite, and carbonate altered porphyritic felsic dike.

OSK-W-18-1426 intersected 12.1 g/t Au over 2.0 metres and 5.64 g/t Au over 2.3 metres in Lynx. Mineralization is composed of up to 15% interstitial and disseminated pyrite with moderate silica flooding at the contact between a locally sericitized and fuchsitized gabbro and a porphyritic felsic intrusion.

OSK-W-18-1461 intersected 16.9 g/t Au over 2.3 metres in Lynx. Mineralization consists of local visible gold and up to 15% pyrite in silica flooding, hosted in a silicified and sericitized rhyolite at contact with a gabbro. This intersect is located 50 metres northwest of hole OSK-W-17-958 which returned 5.74 g/t Au over 5.0 metres (previously reported October 3^rd, 2017) and is outside the current Lynx resource wireframes.

OSK-W-18-1464 intersected 4.52 g/t Au over 2.7 metres and 42.3 g/t Au over 3.6 metres in Lynx. The first interval is composed of 3% disseminated pyrite, 3% pyrite stringers and local visible gold in a stockwork of smoky quartz veinlets in a sericitized fragmental felsic dike at the contact with a gabbro. The second interval contains local visible gold and up to 10% disseminated pyrite in a crustiform quartz-ankerite ± tourmaline veinlet in a strongly carbonate and chlorite altered gabbro.

OSK-W-18-1492 intersected 18.9 g/t Au over 3.1 metres in Lynx. Mineralization consists of local visible gold, 2% disseminated pyrite and trace sphalerite in silica flooding and trace pyrite stringers in quartz or carbonate-quartz veins hosted in a moderately sericitized and silicified felsic porphyritic intrusion.

OSK-W-18-1496 intersected 10.1 g/t Au over 2.2 metres in Lynx. Mineralization consists of 4% pyrite as stringers or in patches with quartz-carbonates veins hosted in a moderately sericitized, weak silica and fuchsite altered gabbro.

OSK-W-18-1503 intersected 62.1 g/t Au over 2.6 metres in Lynx. Mineralization consists of local visible gold and 2% disseminated pyrite with pervasive silica flooding in a foliated rhyolite with moderate silica and sericite alteration.

OSK-W-18-1504 intersected 145 g/t Au over 2.2 metres in Lynx. Mineralization consists of local visible gold in fracture filling in pervasive silica flooding hosted in a silicified, sericitized and slightly fuchsitized gabbro.

OSK-W-18-1516 intersected 13.5 g/t Au over 3.1 metres and 13.4 g/t Au over 2.9 metres in Lynx. The first interval contains local visible gold and up to 7% disseminated pyrite in a smoky quartz-carbonate vein hosted at a silicified contact between a rhyolite and a gabbro. The second interval contains up to 9% pyrite stringers and disseminated and local visible gold in pervasive silica flooding. Both intervals are hosted in a strongly silicified fragmental felsic intrusion with intrusive, volcanic, tourmaline and pyrite fragments.

OSK-W-18-1522 intersected 17.6 g/t Au over 3.2 metres in Lynx. Mineralization consists of trace visible gold with up 5% pyrite tourmaline stringers, trace pyrite-sphalerite stringer with pervasive silica flooding in a silicified and sericitized rhyolite.

OSK-W-18-1529 intersected 4.27 g/t Au over 2.7 metres in Lynx. Mineralization consists of 3% pyrite stringers and 2% pyrite in quartz-tourmaline veins hosted in a moderate chlorite, sericite, carbonate altered fragmental felsic dike.

OSK-W-18-1531 intersected 10.2 g/t Au over 2.3 metres, 27.9 g/t Au over 2.7 metres and 4.34 g/t Au over 4.3 metres in Lynx. Mineralization in the first two intervals consists of local visible gold and up to 20% pyrite in pervasive silica flooding hosted in a sericitized and silicified fragmental felsic dike. The last interval contains up to 10% pyrite in crustiform veins in pervasive silica flooding and a quartz-tourmaline vein hosted in a silicified and sericitized gabbro.

OSK-W-18-1536 intersected 3.25 g/t Au over 2.1 metres in Lynx. Mineralization consists of up to 10% disseminated pyrite with quartz veins in a sericite, silica, chlorite altered and bleached gabbro with local fuschite.

OSK-W-18-1536-W1 intersected 23.7 g/t Au over 2.5 metres, 34.1 g/t Au over 2.0 metres in Lynx and 5.86 g/t Au over 2.0 metres in a vein. The first and second intervals contain up to 10% disseminated pyrite and local visible gold in a strongly silicified porphyritic felsic intrusive or rhyolite. The vein contains 1% pyrite clusters, trace pyrite-tourmaline stringers and 20% quartz veining in a strongly chloritized, moderately sericitized and bleached gabbro.

OSK-W-18-1539 intersected 12.4 g/t Au over 2.5 metres in Lynx. Mineralization consists of local visible gold, up to 3% pyrite-tourmaline stringers and 4% disseminated or clustered pyrite at the silicified, sericitized and bleached contact between a porphyritic felsic dike and a rhyolite.

OSK-W-18-1540 intersected 7.07 g/t Au over 2.0 metres in Lynx. Mineralization consists of trace pyrite in a crustiform quartz-carbonate vein in a strongly silicified and sericitized porphyritic felsic dike.

OSK-W-18-1546 intersected multiple zones of mineralization in the Lynx Corridor: 4.13 g/t Au over 2.7 metres, 29.9 g/t Au over 2.8 metres, 10.4 g/t Au over 2.4 metres, 3.79 g/t Au over 2.1 metres, 19.0 g/t Au over 4.5 metres, 109 g/t Au over 2.0 metres, 273 g/t Au over 2.2 metres and 8.66 g/t Au over 2.6 metres. The first interval contains 2% disseminated pyrite in a silicified rhyolite at contact with a sheared and faulted gabbro. The second interval contains local visible gold and up to 10% disseminated pyrite at the contact between a silicified porphyritic dike and a rhyolite. The third and fourth intervals contain 3% disseminated pyrite in a strongly sericitized rhyolite. The fifth interval contains local visible gold, 3% disseminated pyrite and 2% pyrite-tourmaline stringers at a silicified contact between a rhyolite and a gabbro. The sixth interval contains 7% disseminated and stringer pyrite in a silicified gabbro with a crustiform vein. The seventh interval contains local visible gold, up to 5% disseminated pyrite and 3% pyrite stringers with crustiform veins hosted in a silicified gabbro. The eighth interval contains local visible gold and 2% disseminated pyrite in a chlorite, fuchsite and bleached altered gabbro with pervasive silica flooding.

OSK-W-18-1550 intersected 36.0 g/t Au over 3.6 metres in Lynx. The interval contains local visible gold, 10% pyrite and trace sphalerite in pervasive silica flooding and ptygmatic tourmaline veins within a sericite and fuchsite altered rhyolite.

OSK-W-18-1551 intersected 34.0 g/t Au over 2.4 metres in Lynx. Mineralization contains up to 1% pyrite stringers with quartz clusters in a silicified rhyolite.

OSK-W-18-1555 intersected 27.4 g/t Au over 2.0 metres in Lynx. Mineralization contains up to 15% disseminated and stringer pyrite in a crustiform quartz-carbonate vein hosted in a silicified and fuchsite altered gabbro. This hole extends a crustiform vein corridor 25 metres toward south-west from OSK-W-17-803, which returned 6.38 g/t Au over 2.3 metres (previously reported May, 24^th, 2017).

OSK-W-18-1557 intersected 39.3 g/t Au over 5.6 metres in Lynx. Mineralization is composed of up to 8% fine pyrite stringers and clusters and quartz-tourmaline veins at the silicified contact between a rhyolite and a fragmental felsic dike.

OSK-W-18-1560 intersected 11.9 g/t Au over 2.3 metres and 26.1 g/t Au over 2.4 metres. Mineralization is composed of local visible gold, up to 3% pyrite stringers, and 2% pyrite-tourmaline veinlets with strong pervasive silica alteration hosted in moderate bleached gabbro.

OSK-W-18-1565 intersected 16.4 g/t Au over 2.6 metres, 6.49 g/t Au over 6.2 metres and 9.63 g/t Au over 2.8 metres in Lynx. The first interval contains local visible gold and 3% disseminated pyrite at the strongly silicified contact between rhyolite and felsic dike. The second interval contains local visible gold and 3% disseminated pyrite in a strongly silicified rhyolite. The third interval contains up 5% disseminated pyrite with quartz-carbonate veins in a silicified gabbro.

OSK-W-18-1569 intersected 10.3 g/t Au over 2.4 metres in Lynx. Mineralization is composed of up to 5% pyrite stringers with pervasive silica flooding and moderate fuchsite alteration in a fragmental felsic unit.

OSK-W-18-1569-W1 intersected 20.9 g/t Au over 2.4 metres in Lynx. Mineralization is composed of local visible gold and 1% pyrite with dismembered quartz-carbonate veins, 2% pyrite stringers, 2% pyrite in pervasive silica flooding and ptygmatic tourmaline veins and 2% pyrite cluster in a sericitized and silicified rhyolite.

OSK-W-18-1570 intersected 24.5 g/t Au over 2.3 metres and 10.7 g/t Au over 2.0 metres in Lynx. The first interval contains local visible gold and 3% pyrite with pervasive silica flooding hosted in a sericitized and silicified porphyritic felsic dike. The second interval contains local visible gold with ptygmatic tourmaline veins and quartz clusters and 5% pyrite with pervasive silica flooding in a strongly silicified rhyolite.

OSK-W-18-1575 intersected 36.1 g/t Au over 2.4 metres and 7.35 g/t Au over 2.0 metres in Lynx. The first interval contains up to 2% disseminated pyrite and 1% chalcopyrite in breccia textured quartz veins hosted in a sericitized rhyolite. The second interval contains 2% pyrite stringers, 1% disseminated pyrite in a chloritized and moderately bleached gabbro.

OSK-W-18-1578 intersected 5.48 g/t Au over 5.1 metres, 3.59 g/t Au over 2.6 metres and 3.39 g/t Au over 2.2 metres in Lynx. Mineralization consists of up to 5% disseminated pyrite with pervasive silica alteration and moderate sericite alteration hosted in a fragmental felsic intrusive unit, porphyritic felsic dike or rhyolite.

OSK-W-18-1579 intersected 4.07 g/t Au over 2.0 metres and 4.09 g/t Au over 2.3 metres in Lynx. Mineralization consists of local visible gold, up to 1% disseminated pyrite in pervasive silica flooding and traces of pyrite fragments within in a sericitized fragmental dike.

OSK-W-18-1587 intersected 10.0 g/t Au over 2.0 metres, 13.2 g/t Au over 2.4 metre and 5.01 g/t Au over 6.0 metres in Lynx. The first interval contains 5% pyrite in pervasive silica flooding and quartz-tourmaline veins in a strongly sericitized and silicified gabbro. The second interval contains local visible gold and 10% disseminated pyrite is strongly silicified rhyolite.

OSK-W-18-1593 intersected multiple intercepts in Lynx: 3.33 g/t Au over 2.3 metres, 494 g/t Au over 2.8 metres, 6.63 g/t Au over 2.5 metres and 3.19 g/t Au over 2.4 metres. The first interval contains 1% pyrite cluster in pervasive chlorite-fuchsite altered gabbro injected by quartz veinlets. The second interval contains a 3 cm wide gold stringer within a silica altered band and pyrite stringers at the contact with a gabbro xenolith and fragmental felsic unit. This high-grade interval extends Lynx resource wireframe 305 approximately 10 meters vertically and is 30 metres vertically above OSK-W-17-1098 (42.8 g/t Au over 2.3 metres, previously reported June, 7^th, 2018). The third and fourth intervals are composed of 5% to locally 20% quartz-tourmaline veins, trace disseminated or stringer pyrite in a strongly silicified and moderately chloritized gabbro.

OSK-W-18-1608 intersected 7.2 g/t Au over 3.3 metres in Lynx. Mineralization consists of up to 3% disseminated pyrite and 10% disseminated pyrite in two quartz-tourmaline-ankerite veins in a gabbro with strong pervasive silica alteration and moderate sericite-fuchsite alteration.

OSK-W-18-1613 intersected 46.4 g/t Au over 5.2 metres and 6.58 g/t Au over 2.1 metres in Lynx. Mineralization consists of up to 7% pyrite and 2% sphalerite with pervasive silica flooding in a strongly silicified fragmental felsic dike with local fuchsite.

OSK-W-18-1615 intersected 18.0 g/t Au over 2.1 metres and 12.7 g/t Au over 2.1 metres in Lynx. The first interval contains local visible gold with 10% disseminated and stringer pyrite with pervasive silica flooding in a sericitized gabbro. The second interval contains 3% disseminated pyrite at the strongly sericitized and moderately silicified contact between a gabbro and porphyritic felsic dike.

OSK-W-18-1627 intersected 9.25 g/t Au over 2.4 metres and 11.8 g/t Au over 2.0 metres in Lynx. Mineralization consists of 3% disseminated or stringer pyrite in association with quartz-carbonate crustiform veins and up 1% ptygmatic tourmaline veinlets in slightly fuchsite-altered gabbro.

Qualified Person
The scientific and technical content of this news release has been reviewed 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 (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 current focus of the current 800,000 metre drill program; the significance of the Windfall Lake Technical Report; the significance and assumptions in the preliminary economic assessment prepared in respect of the Windfall and Osborne-Bell deposits as disclosed news release of Osisko dated July 17, 2018; the expectation that the mineral resource grade will be higher than the inferred resource grade; the expectation that the indicated mineral resource grade will be higher than the inferred mineral resource grade; the significance of new results from the ongoing drill program at the Windfall Lake gold project and the adjacent Lynx deposit, including the new infill drill results from the ongoing drill definition and expansion program at Windfall Lake; the significance of assay results presented in this news release; the type of drilling included in the drill program (definition, expansion and exploration drilling in and around the main Windfall Lake gold deposit and the adjacent Lynx deposit, with several deep holes in progress to investigate the down-plunge areas in and around the Underdog and Lynx zones); 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.

For further information please contact:
John Burzynski
President and Chief Executive Officer
Telephone: (416) 363-8653