Osisko Intersects 611 g/t Au Over 2.0 Metres at Windfall

TORONTO, ONTARIO--(Marketwired - Sep 20, 2017) - Osisko Mining Inc. (TSX:OSK) ("Osisko" or the "Corporation") is pleased to provide new results from the ongoing drill program at its 100% owned Windfall Lake gold project located in Urban Township, Abitibi, Québec. The recently expanded 800,000 metre drill program combines definition, expansion and exploration drilling in and around the main Windfall gold deposit and in the adjacent Lynx deposit (located immediately NE of Windfall). Significant new analytical results from 42 intercepts in 28 drill holes and wedges focused on infill and expansion drilling in the Underdog, Caribou, Zone 27 and Mallard corridors of the Windfall deposit are presented below.

Highlights from the new results include: 611 g/t Au over 2.0 metres (15.4 g/t Au over 2.0 metres cut) in OSK-W-17-913; 297 g/t Au over 2.1 metres (14.5 g/t Au over 2.1 metres cut) in OSK-W-17-862-W1; 120 g/t Au over 2.0 metres (28.7 g/t Au over 2.0 metres cut) in OSK-W-17-871-W1; 60.5 g/t Au over 2.4 metres in OSK-W-17-973; 65.5 g/t Au over 2.0 metres in OSK-W-17-978; and 47.0 g/t Au over 2.3 metres in OSK-W-17-820-W1. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

Underdog Corridor

OSK-OBM-16-601 intersected 16.2 g/t Au over 2.0 metres. Mineralization is composed of 5% pyrite stringers and ptygmatic tourmaline veins and disseminated pyrite hosted in a strongly sericitized andesite. The interval extends the FW3 upper 40 metres north-east of OSK-OBM-16-609 (63.2 g/t Au over 7.7 metres previously reported August 1, 2017).

OSK-W-17-820-W1 returned two intersections in the FW0 Footwall Zone: 5.78 g/t Au over 2.0 metres (including 11.3 g/t Au over 1.0 metre) and 9.02 g/t Au over 2.0 metres (including 12.0 g/t Au over 1.0 metre). Mineralization is composed of 1% disseminated pyrite or pyrite stringers within a fragmental felsic intrusion. The two intersections are 50 metres up-plunge and south-west of OSK-W-17-820 (5.79 g/t Au over 6.3 metres previously reported July 19, 2017). OSK-W-17-820-W1 also intersected the FW3 Zone returning 31.7 g/t Au over 2.2 meters, (including 115 g/t Au over 0.6 metres) (27.7 g/t Au over 2.2 metres cut) and the Z14 Zone, 47.0 g/t Au over 2.3 metres (including 266 g/t Au over 0.4 metres) (18.1 g/t Au over 2.3 metres cut). Both intersections are similar and associated with felsic porphyritic dikes with up to 2% pyrite stringers and local quartz veins. The interval in FW3 is 40 metres south-west of OSK-W-17-821 (9.27 g/t Au over 3.3 metres previously reported May 30, 2017).

OSK-W-17-847 intersected two intervals: 6.87 g/t Au over 2.0 metres and 8.85 g/t Au over 3.9 metres in the Underdog corridor. In the first interval, mineralization is within the fragmental felsic dike and composed of 1% pyrite stringers, and correlates with the FW0 hanging wall. In the second interval mineralization is composed of up to 20% pyrite stringers and pyrite-tourmaline stringers hosted in a strongly silicified felsic porphyritic intrusion. The interval correlates to the FW2 Zone 50 metres north-east of OBM-15-560 (11.0 g/t Au over 6.1 metres previously reported January 28, 2016).

OSK-W-17-855-W1 intersected 21.0 metres over 2.0 metres (including 41.2 g/t Au over 1.0 metre). Mineralization is composed of up to 30% pyrite in a fragmental felsic dike. The interval correlates to the FW1 Zone.

OSK-W-17-855-W2 intersected 26.1 g/t Au over 3.5 metres (including 66.2 g/t Au over 0.4 metres, 33.5 g/t over 0.7 metres and 31.5 g/t Au over 1.3 metres) in the FW3 Zone. Mineralization is composed of up to 7% pyrite stringers, traces of tourmaline-pyrite stringers, up to 5% disseminated pyrite, and local decimeter scale pyrite massive bands. It is hosted in a porphyritic felsic dike with quartz-eyes and strong silica alteration. This intersection is 50 metres north-east of OSK-W-17-807-W2 (32. 9 g/t Au over 2.0 metres previously reported August 14, 2017). OSK-W-17-855-W2 also intersected 9.2 g/t over 2.2 metres (including 18.6 g/t Au over 1.0 metre) in the Z14 Zone. Mineralization is composed of 1% disseminated pyrite associated to large quartz-eyes porphyritic dike. It is 70 metres north-east of OSK-W-17-807-W2 (4.29 g/t Au over 2.0 metres previously reported June 20, 2017).

OSK-W-17-864 intersected 14.0 g/t Au over 2.7 metres (including 28.6 g/t Au over 1.0 metre) in the FW3 Upper Zone. Mineralization is composed of up to 3% disseminated pyrite and up to 1% pyrite stringers hosted in the andesite. It is 25 metres south-west of OSK-W-17-854-W2 (18.6 /t Au over 3.5 metres previously reported August 1, 2017) and 15 metres north-east of OSK-W-17-871-W1 (120 g/t Au over 2.0 metres, this press release).

OSK-W-17-871-W1 intersected 120 g/t Au over 2.0 metres, (including 557 g/t Au over 0.4 metres) (28.7 g/t Au over 2.0 metres cut). Mineralization is composed of local visible gold, up to 10% disseminated pyrite, up to 10% pyrite tourmaline stringers and 2% pyrite stringers in a sericitized and chloritized rhyolite. The intersection is related to the FW3 Upper Zone and is 40 metres south-west of OSK-W-17-854-W2 (18.6 /t Au over 3.5 metres previously reported August 1, 2017).

OSK-W-17-885 returned two intersections: 6.69 g/t Au over 8.0 metres (including 22.3 g/t Au over 1.0 metre) and 6.55 g/t Au over 2.6 metres (including 18.2 g/t au over 0.8 metres). The first interval consists of a strongly sericitized and moderately silicified felsic intrusion with 2-5% disseminated pyrite and 1-2 % pyrite stringers in the FW0 Footwall Zone and is 100 metres north-east of OSK-17-780-W1 (5.97 g/t Au over 17.0 metres previously reported April 11, 2017). The second interval is a silica-rich zone with 3-5% tourmaline-pyrite stringers and 2% disseminated pyrite. This intersection is in the FW3 Zone and is 50 metres south-west of OSK-W-17-780 (9.38 g/t Au over 4.0 metres previously reported April 6, 2017).

OSK-W-17-889 intersected 4.35 g/t Au over 3.5 metres in the Wolf 2 Zone. Mineralization contains up to 20% pyrite stringers within a bleached andesite. It is 40 metres west-south-west of OSK-W-17-844 (8.14 g/t Au over 2.5 metres previously reported August 1, 2017).

OSK-W-17-1051 intersected 5.36 g/t Au over 2.7 metres. The strongly sericitized felsic dike hosts 3% pyrite stringers and trace tourmaline stringers. The interval correlates to Z14 Zone, a division of the FW3 Zone, 30 metres north-east of OSK-W-16-708-W1 (3.74 g/t Au over 3.0 metres previously reported August 31, 2016).

Caribou Corridor

OSK-EAG-13-494 intersected two intervals in Wolf: 6.52 g/t Au over 2.1 metres (including 19.6 g/t Au over 0.6 metres) and 4.56 g/t Au over 2.0 metres. Both intersectiions follow a contact between the andesite and a large quartz-eye porphyritic intrusion, with mineralization comprising up to 2% disseminated pyrite and pyrite stringers and associated with strong sericite alteration. The intersections infill 35 meters north-east of OSK-W-16-708-W1, and 25 meters south-west of OSK-16-708-W2 (12.5 g/t Au over 3.8 metres and 4.47 g/t Au over 2.8 metres, previously reported August 31 and September 12, 2016).

OSK-W-17-842 intersected the CS1 Zone within the Caribou Corridor and returned 14.5 g/t Au over 5.5 metres (including 182 g/t Au over 0.4 metres) (8.90 g/t Au over 5.5 metres cut). Mineralization is composed of 10% pyrite stringers and tourmaline-pyrite veins hosted in a fragmental andesite strongly sericitized, and is 50 metres north-east of OSK-W-16-749 (12.7 g/t Au over 5.4 metres previously reported January 23, 2017).

OSK-W-17-858-W2 intersected three intervals: 8.51 g/t Au over 2.3 metres; 32.6 g/t Au over 2.4 metres (including 76.6 g/t Au over 0.9 metres) and 9.50 g/t Au over 2.0 metres (including 34.5 g/t Au over 0.5 metre). The first interval correlates to the Wolf Zone and is composed of 2% pyrite and carbonate veins in a strongly sericitized felsic dike. The second and third intervals consists of a crustiform quartz carbonate vein in the Red Dog intrusion and in the andesite. Local visible gold, 5% pyrite stringers and tourmaline-pyrite stringers are also observed. The deepest vein is within the FW3 Upper Zone, 25 metres north-east of OSK-OBM-16-697 (29.1 g/t Au over 2.6 metres previously reported May 30, 2017).

OSK-W-17-862 intersected 17.4 g/t Au over 2.9 metres (including 30.8 g/t Au over 1.5 metres). Mineralization is at a contact between a gabbro and rhyolite with up to 4% disseminated pyrite in the silica altered zone. The interval is 30 metres above OSK-W-17-889 (16.2 g/t Au over 2.0 metres in this press release).

OSK-W-17-871 was previously reported on August 1,2017 with a cut value of 13.4 g/t Au over 4.8 metres. Additional analysis was done on the samples greater than 100 g/t and the interval has been recalculated to 17.9 g/t Au over 4.8 metres (including 143 g/t Au over 0.5 metres). The cut value remains unchanged. The mineralized zone is in a bleached to strongly sericitized large quartz-eye felsic intrusion containing 7% pyrite stringers. The intersection is 25 metres north-east of OSK-W-17-901 (16.2 g/t Au over 2.1 metres previously reported August 1, 2017) within the Caribou Corridor.

OSK-W-17-889 intersected 16.2 g/t Au over 2.0 metres (including 58.0 g/t Au over 0.5 metres) in the main Caribou Zone. Mineralization is at a contact between the gabbro and the rhyolite. The 1% pyrite stringers are associated with strong sericite alteration and a quartz-tourmaline vein. The interval is 30 metres below OSK-W-17-862 (17.4 g/t over 2.9 metres in this press release).

OSK-W-17-901 intersected two intervals: 13.8 g/t Au over 2.0 metres and 7.12 g/t Au over 2.0 metres (including 13.3 g/t Au over 1.0 metre). In both intervals, mineralization is composed of up to 1% disseminated pyrite and 1% pyrite stringers. The host rhyolite is strongly alterated in silica, sericite and carbonates. The first interval correlates to Caribou Main Zone and the second interval to Caribou footwall, 65 metres below OBM-16-660 (7.25 g/t Au over 6.9 metres previously published July 11, 2016).

OSK-W-17-913 intersected 611 g/t Au over 2.0 metres (including 4070 g/t Au over 0.3 metres) (15.4 g/t Au over 2.0 metres cut). The high-grade zone contains local visible gold and 1% pyrite stringers associated with pervasive silica flooding within a felsic dike. The host rock is strongly sericitized. The intersection correlates to the Wolf 2 Zone, 50 metres east-north-east of OSK W-16-718 (8.5 g/t Au over 4.7 metres previously reported September 19, 2016). The hole also intersected 13.6 g/t Au over 2.0 metres (including 26.5 g/t Au over 1.0 metre) in the Wolf footwall. Mineralization is associated with a large quartz-eyes porphyritic dike and composed of disseminated pyrite and trace of pyrite stringers. The interval is 40 metres north-east of OSK-W-16-718 (4.78 g/t Au over 2.6 metres previously reported September 19, 2016).

OSK-W-17-989-W1 intersected two proximate intervals in Caribou South 1 Zone: 3.59 g/t Au over 7.0 metres and 7.74 g/t Au over 3.0 metres (including 20.5 g/t Au over 1.0 metre). Mineralization is associated to a porphyritic felsic intrusion crosscutting a strongly sericitized and silicified andesite. Up to 20% pyrite stringers are observed. The interval is 65 metres south-west of OSK-W-16-709 (4.90 g/t Au over 3.7 metres previously reported August 23, 2016).

Zone 27

OSK-W-17-862-W2 intersected 297 g/t Au over 2.1 metres (including 2080 g/t Au over 0.3 metres) (14.5 g/t Au over 2.1 metres cut). The mineralization correlates to Zone 27 along the Red Dog intrusion contact, with visible gold associated with disseminated pyrite and pervasive silica alteration in a strongly silicified andesite.

OSK W-17-903 intersected 10.7 g/t Au over 2.0 metres (including 37.7 g/t Au over 0.5 metres). Mineralization consists of 2% pyrite stringers, 3% pyrite-tourmaline stringers and 5% disseminated pyrite hosted in silica and sericite altered andesite. The intersection correlates to Zone 27, 45 metres above OSK-W-16-746 (16.5 g/t Au over 3.7 metres previously reported January 5, 2017).

OSK-W-17-968 intersected 5.77 g/t Au over 2.4 meters in Zone 27. Mineralization consists of 3% quartz-tourmaline veins and 5% pyrite stringers in a strongly sericitized felsic dike. This intersection is 15 meters above OBM-16-600 (12.9 g/t Au over 4.2 metres previously reported March 16, 2016).

OSK-W-17-973 intersected two intervals in Zone 27: 60.5 g/t Au over 2.4 metres (including 122 g/t Au over 1.0 metre) (51.6 g/t Au over 2.4 metres cut) and 5.12 g/t Au over 2.1 metres (including 25.2 g/t Au over 0.4 metres). The first interval is composed of semi-massive pyrite in a silica altered porpyritic felsic dike. The second interval is at the contact between two felsic dikes and is composed of 1% pyrite in clusters or stringers.

OSK-W-17-880-W1 intersected 4.57 g/t Au over 2.5 metres (including 12.1 g/t Au over 0.5 metres) in Zone 27. Mineralization is composed of up to 4% disseminated pyrite and 3% pyrite stringers within a strongly sericitized andesite. The interval is 25 metres west of OSK-W-17-871 (3.18 g/t Au over 2.7 metres previously reported August 14, 2017).

OSK-W-17-1026 intersected 4.57 g/t Au over 2.3 metres (including 16.5 g/t Au over 0.6 metres). Mineralization occurs along a strongly sericitized felsic pophyritic dike as trace disseminated pyrite and pyrite stringers, and ptygmatic tourmaline veins. The interval is 15 metres above OBM-16-677.

Mallard Corridor

OSK-W-17-977 intersected 12.0 g/t Au over 2.2 metres (including 25.4 g/t Au over 0.9 metres). Mineralization contains local visible gold, up to 20% pyrite stringers, and 2-5% disseminated pyrite within a bleached andesite. The intersection extends the Mallard Zone 125 metres from the eastern limit (line 2300E), or 200 metres in the down plunge.

Other

OSK-W-17-855 intersected 3.93 g/t Au over 2.8 metres. Mineralization is composed of 5% disseminated pyrite in a quartz vein hosted in the andesite. This interval is not related to any known mineralized zone and is 100 metres south-east of the Caribou Corridor.

OSK-W-17-937 intersected 5.58 g/t Au over 3.0 metres (including 11.8 g/t Au over 1.0 metre). The mineralization is composed of disseminated pyrite and local crustiform quartz veins hosted in a moderately sericitized andesite. The intersection is 200 metres south-west of the main Caribou Corridor.

OSK-W-17-978 intersected two intervals: a crustiform vein, 65.5 g/t Au over 2.0 metres (including 327 g/t Au over 0.4 metres) (20.1 g/t Au over 2.0 metres cut) and 14.0 g/t Au over 2.0 metres (including 92.2 g/t Au over 0.3 metres). In the first interval, visible gold forms a millimeter-thick veinlet inside the crustiform vein. The mineralization is hosted in a sericitized porphyritic intrusion. The second interval contains 3% disseminated pyrite, 2% sphalerite and trace chalcopyrite associated with pervasive silica alteration. These intersections are 100 meters south-east of the Caribou Corridor and do not correlate with any of the currently defined mineralized zones.

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 ("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 ALS Laboratories in Val d'Or, Québec, Thunder Bay and Sudbury, Ontario or Vancouver, British Colombia or 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 the previous operator comprises 2,762,000 tonnes at 8.42 g/t Au (748.000 ounces) in the indicated category and 3,512,000 tonnes at 7.62 g/t Au (860,000 ounces) in the inferred category (sourced from a technical report dated June 10, 2015 entitled "Preliminary Economic Assessment of the Windfall Lake Gold Property, Québec, Canada" with an effective date of April 28, 2015, prepared in accordance with NI 43-101). The Windfall Lake gold deposit is currently one of the highest grade resource-stage gold projects in Canada. The bulk of the mineralization occurs in the Main Zone, a southwest/northeast trending zone of stacked mineralized lenses, measuring approximately 600 metres wide and at least 1.400 metres long. The deposit is well defined from surface to a depth of 500 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 870 metres in others, with significant potential to extend mineralization up and 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 Quebec and Ontario. Osisko continues to be well financed with approximately $190 million in cash and investments.

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 800,000 metre drill program; the significance of new results from the ongoing drill program at the Windfall Lake gold project; the significance of assay results presented in this press release; the type of drilling included in the drill program (definition drilling, expansion drilling to the NE of the main deposit and adjacent Lynx deposit, and exploration drilling on the greater deposit and Urban-Barry project area); additional high grade results from Caribou, Wolf, Zone 27 and Underdog; 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.

Contact

John Burzynski
President and Chief Executive Officer
(416) 363-8653