Osisko Mining Inc. (TSX:OSK) is pleased to provide new results from the ongoing deep-hole program at its 100% owned Windfall Lake gold project located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec.

In May 2018, Osisko commenced two deep exploration drill holes (“Deep Underdog” and “Deep Lynx”) to investigate the potential for depth extensions of the Lynx and Underdog mineralized zones, as well as to further test the intrusion-related geological model for the Windfall deposit at depths of approximately 2000 metres to 2500 metres from surface.

New drilling has confirmed and expanded the Triple 8 discovery (see Osisko news release dated July 11^th, 2018). Wedge hole OSK-W-18-1603-W2 intersected a zone of sericite and silica alteration over 85 metres containing sulfides and zones of gold mineralization from approximately 1485 metres to approximately 1570 metres downhole.  This alteration zone includes two significant gold bearing intervals located between approximately 1510 to 1554 metres downhole. The new wedge extends the Triple 8 zone by 50 metres to the south from the discovery hole OSK-W18-1603.  Triple 8 geometry is still being interpreted, however the zone appears to remain open in all directions.  Previously drilled wedge OSK-W-18-1603-W1 intersected a fault zone and porphyritic intrusive in the anticipated Triple 8 area.  Maps and sections showing the location of the two new wedges and their relation to the Triple 8 discovery are provided on the Corporation’s website. The Triple 8 Zone falls well outside the area of the recently announced Windfall mineral resource estimate (see Osisko news release dated May 14^th, 2018).

Osisko President and CEO John Burzynski commented:  “Today’s follow-up results from the new wedge hole in the Triple 8 discovery are a great confirmation that there is significant high-grade gold at depth in the Windfall intrusive system.  What we find very exciting is that the Triple 8 alteration zone now extends over 85 metres wide, on a scale we haven’t seen before at Windfall, indicating that we may be approaching a main source of the mineralizing system.  We are confident that as we progress with drilling the deeper sections of the Windfall deposit we will continue to have discovery success.”

Sericite and silica alteration begins within the host andesite and gabbro package at approximately 1434 metres, increasing in intensity to a strongly altered zone between 1485 metres to 1570 metres. Alteration is found peripheral to a felsic stock dipping 40° to the north-east and shows the same chlorite – biotite +/- garnet alteration encountered in the Triple 8 discovery hole.  Exact geometries and relationships between the mineralization and the emplacement of the felsic stock have yet to be determined. The Triple 8 Zone appears to be sub-vertical with a 70 degree dip and is oriented NNE at 030 degrees. Mineralization consists of semi-massive and stringer pyrite with local visible gold and strong silica alteration. The zones contain minor sphalerite, chalcopyrite, pyrrhotite, and trace arsenopyrite. A number of minor mineralized intervals were encountered in the hanging wall and the footwall of the main mineralized corridor (assays pending).

Today’s results include the currently available significant analytical results from OSK-18-1603-W2.  Maps showing the drill hole location and analytical results are available at www.osiskomining.com.

OSK-W-18-1603-W2

Gold mineralization in the main alteration corridor (1485 metres to 1570 metres downhole) is hosted in a pervasive altered andesite and is subdivided into two intervals which correspond to the Triple 8 Zone. The first interval, from 1510.3 metres to 1524.0 metres is hosted in strong pervasive silica and moderate sericite alteration. Mineralization consists of up to 35% pyrite stringers, local semi-massive pyrite, trace chalcopyrite, sphalerite, arsenopyrite and local visible gold. The second interval extends from 1538.4 metres to 1550.9 metres and contains up to 30% pyrite stringers, up to 20% pyrite-tourmaline veins, trace sphalerite and local visible gold within a strong silica and moderate sericite altered 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.

Quality Control and Reporting Protocols

True width determination for the Triple 8 Zone is currently undetermined but is estimated at 65-80% of the reported core length intervals. Assays are uncut except where indicated. Intercepts occur within geological confines of a major zone but have not been correlated to individual vein domain at this time. 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 and interpretation of results are performed by a “qualified person” 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 comprises 2,382,000 tonnes at 7.85 g/t Au (601,000 ounces) in the indicated resource category and 10,605,000 tonnes at 6.70 g/t Au (2,284,000 ounces) in the inferred resource category. 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 for Osisko by InnovExplo Inc. from Vald’Or, Québec, and is available on SEDAR (www.sedar.com) under Osisko’s issuer profile. 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.