Osisko Intersects 20.0 g/t Au Over 8.7 Metres at Windfall

TORONTO, June 12, 2018 (GLOBE NEWSWIRE) -- Osisko Mining Inc. (OSK:TSX) ("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 the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec. The 800,000 metre drill program commenced in late 2015 is now focussed on infill drilling within the main Windfall gold deposit and the adjacent Lynx deposit (located immediately NE of Windfall). Exploration and expansion drilling is also continuing at Windfall with several deep holes in progress to investigate the down-plunge areas in and around the Underdog and Lynx zones.

Today’s results include significant new analytical results from 74 intercepts in 35 drill holes and 8 wedges focused on infill drilling in the Windfall deposit are presented below.

Highlights from the new results include: 20.0 g/t Au over 8.7 metres and 22.5 g/t Au over 4.6 metres in OSK-W-18-747-W1; 14.4 g/t Au over 11.1 metres in OSK-W-18-1472; 69.6 g/t Au over 2.0 metres in OSK-W-17-903; 19.3 g/t Au over 5.9 metres in OSK-W-18-1532; 19.0 g/t Au over 5.9 metres in OSK-W-17-1184; 10.8 g/t Au over 9.1 metres in OSK-W-17-1125-W3; 19.6 g/t Au over 4.0 metres in OSK-W-18-1336-W2. 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" below.

OSK-EAG-12-314 intersected 4.60 g/t Au over 2.1 metres in Underdog. Mineralization contains 5% pyrite and a clustered quartz vein with local visible gold within a fragmental porphyritic felsic unit with moderate sericitization.

OSK-EAG-13-477 intersected 9.19 g/t Au over 2.1 metres and 9.31 g/t Au over 8.0 metres in Underdog. The first interval is composed of 40% pyrite in pervasive silica flooding with tourmaline in a porphyritic felsic dike. The second interval is composed of up to 5% pyrite tourmaline stringers with 1% chalcopyrite at a sericitized and silicified contact between two porphyritic felsic dikes.

OSK-W-17-778 intersected 4.52 g/t Au over 2.8 metres, 11.3 g/t Au over 2.5 metres and 9.61 g/t Au over 2.3 metres in Underdog. Mineralization contains up to 3% pyrite stringers,10% pyrite in pervasive silica flooding and local visible gold. The host is a porphyritic felsic dike with moderate silica and sericite alteration.

OSK-W-17-903 intersected 69.6 g/t Au over 2.0 metres in Zone 27. Mineralization contains up to 10% pyrite stringers and 5% disseminated pyrite in a bleached andesite with moderate silica and sericite alteration.

OSK-W-17-1056 intersected 35.5 g/t Au over 2.0 metres in Zone 27. Mineralization contains 1% disseminated pyrite and quartz tourmaline veins in a slightly sericitized and silicified rhyolite.

OSK-W-17-1125-W3 intersected 10.8 g/t Au over 9.1 metres in Caribou. Mineralization contains 5% pyrite stringers and 10% pyrite with pervasive silica flooding in a bleached felsic dike.

OSK-W-17-1184 intersected 19.0 g/t Au over 5.9 metres in Zone 27. Mineralization contains up to 13% pyrite stringers and clusters at the contact between a gabbro with strong fuchsite alteration and a sericitized porphyritic felsic dike.

OSK-W-17-1202 intersected 10.1 g/t Au over 5.7 metres in Zone 27. Mineralization contains up to 15% pyrite in pervasive silica flooding, 10% pyrite-tourmaline stringers, 2% disseminated pyrite and traces of chalcopyrite within a porphyritic felsic dike with silica and sericite alteration.

OSK-W-17-1239 intersected 33.2 g/t Au over 2.0 metres in Zone 27. Mineralization contains up to 30% pyrite stringers and 2% pyrite-tourmaline stringers hosted in a bleached andesite.

OSK-W-18-747-W1 intersected six intervals in Underdog: 4.75 g/t Au over 3.6 metres, 12.2 g/t Au over 2.0 metres, 7.64 g/t Au over 2.2 metres, 20.0 g/t Au over 8.7 metres , 11.9 g/t Au over 2.0 metres and 22.5 g/t Au over 4.6 metres. Mineralization of all the intervals contains up to 20% disseminated pyrite or in stringers with pervasive silica flooding and local visible gold within strongly silicified and sericitized porphyritic felsic dikes.

OSK-W-18-762-W1 intersected 8.70 g/t Au over 2.5 metres in Underdog. Mineralization contains trace disseminated and clustered pyrite hosted in a porphyritic felsic dike with moderate sericitization and weak silicification.

OSK-W-18-1066-W1 intersected 26.0 g/t Au over 1.9 metres, 6.6 g/t Au over 2.0 metres and 4.79 g/t Au over 5.0 metres in Underdog. Mineralization of all three intervals is composed of 1% disseminated and stringer pyrite in moderately sericitized porphyritic felsic dikes.

OSK-W-18-1336-W2 intersected 19.6 g/t Au over 4.0 metres in Underdog. Mineralization is composed of up to 5% pyrite in pervasive silica flooding and 1% pyrite stringers in a porphyritic felsic dike with moderate sericite, silica and chlorite alteration.

OSK-W-18-1402-W3 intersected 4.03 g/t Au over 2.0 metres and 6.57 g/t Au over 2.0 metres in Underdog. The first interval contains up to 5% pyrite-stringers and 1% disseminated pyrite in a bleached porphyritic felsic dike with moderate sericitization and chloritization and weak silicification. The second interval contains 1% pyrite stringers, 2% disseminated pyrite, and local visible gold in pervasive silica flooding at the contact with carbonate veinlets. The host is porphyritic felsic dike with moderate sericite and silica alteration.

OSK-W-18-1430-W1 intersected 26.0 g/t Au over 2.0 metres in Underdog. Mineralization contains 5% disseminated pyrite and trace disseminated chalcopyrite in a strongly chloritized andesite with weak sericitization and silicification.

OSK-W-18-1431-W2 intersected 11.3 g/t Au over 2.1 metres in Underdog. Mineralization contains up to 3% pyrite stringers, 1% pyrite in ptygmatic tourmaline veins, and local visible gold in a porphyritic felsic dike with moderate sericite, silica and carbonate and fuchsite alteration.

OSK-W-18-1434 intersected 4.76 g/t Au over 2.0 metres in Underdog. Mineralization contains up to 2% disseminated pyrite, traces of chalcopyrite, 2% pyrite in pervasive silica flooding, 1% pyrite in carbonate veinlets, and 1% pyrite tourmaline stringers. The host is a fragmental felsic dike with strong silica and sericite alteration.

OSK-W-18-1448 intersected 6.89 g/t Au over 2.0 metres in Caribou extension. Mineralization contains 1% pyrite in tourmaline ptygmatic veins in a rhyolite with moderate sericite and fuchsite alteration and weak silicification.

OSK-W-18-1449 intersected 3.71 g/t Au over 2.8 metres in Bobcat. Mineralization contains 1% pyrite clusters with quartz-tourmaline veins at a sericitized contact between a porphyritic felsic dike and a fragmental felsic dike.

OSK-W-18-1463 intersected 14.6 g/t Au over 2.0 metres and 3.24 g/t Au over 10.4 metres in Zone 27. The first interval contains up to 2% pyrite-tourmaline stringers and 5% pyrite in pervasive silica flooding hosted in foliated porphyritic felsic dike with strong sericite and moderate silica alteration. The second interval is composed of 1% pyrite-tourmaline stringers and 2% pyrite clusters in a sericitized and chloritized porphyritic felsic dike.

OSK-W-18-1465 intersected 3.24 g/t Au over 2.3 metres in Bobcat. Mineralization contains up to 7% pyrite with pervasive silica flooding hosted in a moderately silicified and sericitized rhyolite.

OSK-W-18-1466 intersected 4.26 g/t Au over 2.0 metres in Zone 27. Mineralization contains two 30-centimetre massive pyrite bands within a porphyritic felsic intrusion with moderate sericitization and patchy silica alteration.

OSK-W-18-1468 intersected 10.3 g/t Au over 3.3 metres in Caribou. Mineralization contains 3% pyrite stringers and a 30-centimetre wide massive pyrite zone hosted in a silicified and sericitized rhyolite.

OSK-W-18-1471 intersected 14.9 g/t Au over 2.0 metres not related to any known zone. Mineralization contains 3% pyrite clusters and trace pyrite-tourmaline stringers in a chloritized and slightly sericitized rhyolite.

OSK-W-18-1472 intersected 14.4 g/t Au over 11.1 metres in Bobcat. Mineralization contains 5% pyrite associated with 10-centimetre crustiform veins, 1% pyrite-tourmaline stringers and local visible gold in a moderately sericitized and silicified rhyolite in contact with a felsic porphyritic intrusion with moderate silica and sericite alteration.

OSK-W-18-1473 intersected 11.9 g/t Au over 2.9 metres in Caribou and 3.87 g/t Au over 2.3 metres in Zone 27. The first interval contains 10% pyrite stringers, one 15-centimetre-wide zone of massive pyrite, and one 7-centimetre wide pyrite-tourmaline stringer hosted in a silicified and sericitized rhyolite near a fault. The second interval contains up to 5% ptygmatic pyrite-tourmaline stringers hosted in a sericitized felsic porphyritic intrusion and a fuchsitized gabbro.

OSK-W-18-1476 intersected 3.05 g/t Au over 2.3 metres and 6.38 g/t Au over 2.0 metres in Zone 27. Mineralization contains up to 5% pyrite stringers and trace sphalerite in quartz veins hosted in a moderately sericitized and silicified rhyolite injected by a felsic porphyritic dike. The second interval contains 5% pyrite stringers in a moderately sericitized felsic porphyritic dike.

OSK-W-18-1490 intersected 7.34 g/t Au over 2.6 metres in Bobcat. Mineralization contains up to 10% interstitial pyrite and pyrite stringers, 3% pyrite in tourmaline ptygmatic veinlets, and 1% disseminated pyrite hosted within a sericitized and bleached gabbro in contact with a sericitized felsic porphyritic dike.

OSK-W-18-1494 intersected 14.8 g/t Au over 2.0 metres and 5.71 g/t Au over 2.2 metres in Bobcat. Mineralization contains local visible gold and 3% pyrite associated with folded and massive crustiform veins, 5% pyrite stringers and 5% disseminated pyrite within a strongly sericitized and bleached gabbro.

OSK-W-18-1497 intersected 10.0 g/t Au over 7.0 metres and 8.53 g/t Au over 6.0 metres in Zone 27. The first interval contains up to 3% pyrite stringers in a bleached andesite at the contact with a felsic porphyritic dike with 7% pyrite, 3% sphalerite and trace chalcopyrite in pervasive silica flooding. The second interval contains up to 5% disseminated pyrite and 3% pyrite stringers at the contact between a strongly sericitized felsic porphyritic intrusion and andesite.

OSK-W-18-1498 intersected 5.91 g/t Au over 2.0 metres and 3.58 g/t Au over 2.0 metres in Zone 27. Mineralization contains up to 10% pyrite stringers in a porphyritic felsic dike with moderate sericite and chlorite alteration and weak silicification.

OSK-W-18-1499 intersected 10.8 g/t Au over 2.5 metres in Caribou and 7.38 g/t Au over 5.0 metres and 3.02 g/t Au over 2.1 metres in Zone 27. The first interval in Caribou contains 2% disseminated pyrite in a foliated rhyolite with moderate sericite, chlorite and carbonate alteration and weak silicification. The second and third intervals in Zone 27 contain up to 25% disseminated pyrite, 15% pyrite-tourmaline stringers and clusters within smoky silica-tourmaline-chlorite and sericitized felsic porphyritic intrusion.

OSK-W-18-1501 intersected 37.4 g/t Au over 1.9 metres in Bobcat. Mineralization contains local visible gold, 1% pyrite in crustiform veins, 10% pyrite clusters and trace disseminated pyrite in a sericitized rhyolite.

OSK-W-18-1505 intersected 17.0 g/t Au over 2.1 metres and 4.5 g/t Au over 2.4 metres in Caribou. Mineralization contains up to 10% pyrite stringers with 30% pervasive silica flooding within a rhyolite with moderate sericite alteration.

OSK-W-18-1506 intersected 6.11 g/t Au over 2.1 metres in Caribou. Mineralization contains up to 30% pyrite in a 10 centimetres-wide stringer hosted in a sericitized and silicified rhyolite.

OSK-W-18-1509 intersected 4.27 g/t Au over 5.6 metres and 5.05 g/t Au over 2.2 metres in Bobcat. The first interval contains 5% interstitial pyrite within chlorite-silica hydrothermal breccia, 40% dismembered crustiform veins and fuchsite fragments hosted in a sericitized rhyolite. The second interval contains up to 5% pyrite within a dismembered quartz-carbonate vein and 3% pyrite stringers hosted in a weakly sheared, fuchsite and sericite altered gabbro.

OSK-W-18-1510 intersected 4.81 g/t Au over 2.2 metres in Zone 27. Mineralization contains massive pyrite over 1.5 metres with trace tourmaline in ptygmatic veinlets including 8% disseminated pyrite and stringers hosted in bleached and silicified andesite.

OSK-W-18-1517 intersected 3.60 g/t Au over 2.4 metres in Caribou, and 4.34 g/t Au over 2.6 metres and 5.72 g/t Au over 2.0 metres in Zone 27. The first interval in Caribou contains up to 10% pyrite stringers, 1% pyrite clusters, trace tourmaline stringers with pervasive silica flooding within a sericitized and silicified porphyritic felsic dike. The second and third intervals in Zone 27 contain up to 25% semi-massive pyrite, 10% pyrite stringers with traces of tourmaline hosted in a sericitized porphyritic felsic dike.

OSK-W-18-1518 intersected 3.57 g/t Au over 2.6 metres, 6.95 g/t Au over 4.0 metres, 20.6 g/t Au over 2.6 metres in Caribou and 5.87 g/t au over 2.0 metres in Zone 27. Intervals form Caribou contain 3% pyrite stringers and up to 50% semi-massive pyrite associated with tourmaline ptygmatic and quartz-tourmaline veinlets in a sericitized porphyritic felsic dike or a sericitized andesite. The interval in Zone 27 contains 3% pyrite stringers or clusters within a bleached andesite injected by a felsic dike.

OSK-W-18-1526 intersected 7.32 g/t Au over 2.0 metres and 3.15 g/t Au over 2.0 metres in Zone 27. Mineralization contains up to 2% pyrite stringers and local visible gold hosted in a bleached fragmental andesite.

OSK-W-18-1532 intersected 15.7 g/t Au over 2.0 metres, 19.7 g/t Au over 2.4 metres and 3.19 g/t Au over 2.1 metres in Caribou and 19.3 g/t Au over 5.9 metres in Zone 27. The first and second intervals contain local visible gold, traces pyrite stringers and clusters, locally up to 40% pyrite and 3% chalcopyrite with ptygmatic tourmaline veinlets hosted in a rhyolite. The third interval is composed of 2% pyrite-chalcopyrite stringers in a bleached andesite at the contact with silicified porphyritic dike with 20% pyrite-tourmaline centimetric bands and local visible gold. The interval form Zone 27 contains up to 7% pyrite and 5% pyrite with ptygmatic tourmaline vein hosted in a sericitized andesite.

OSK-W-18-1543 intersected 4.97 g/t Au over 3.2 metres in Zone 27. Mineralization contains up to 4% pyrite stringers, 15% semi-massive pyrite over two 30-centimetres interval, trace tourmaline ptygmatic veinlet and trace chalcopyrite hosted in a sericitized and silicified felsic porphyritic intrusion.

OSK-W-18-1552 intersected 7.31 g/t Au over 2.0 metres and 6.29 g/t Au over 4.5 metres in Zone 27. The first interval contains up to 4% pyrite clusters in an andesite with moderate silica, sericite and carbonate alteration. The second interval contains 1% pyrite in folded smoky quartz veins and 10% pyrite stringers hosted in a moderate sericitized and silicified porphyritic dike with locally 15% semi-massive pyrite (two 30-centimetres intervals), trace tourmaline ptygmatic veinlet and trace chalcopyrite.

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 (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 a press release disseminated by the Corporation on May 14, 2018, 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 (see press release entitled "Osisko Releases Its First Mineral Resource Estimate for Windfall Gold Deposit" dated May 14, 2018, which 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. Osisko continues to be well financed with approximately $150 million in cash and investments as of March 31, 2018.

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 the mineral resource estimate published by the Corporation on May 14, 2018 in respect of the Windfall Lake gold deposit; the significance of new results from the ongoing drill program at the Windfall Lake gold project, including in respect of the Lynx deposit; the significance of assay results presented in this press 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, and exploration drilling on the greater deposit and Urban-Barry project area); 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