Osisko Intersects 34.3 g/t Au Over 4.5 Metres at Windfall

High-Grade Infill Hits in Underdog and Zone 27 Continue

TORONTO, ONTARIO--(Marketwired - May 1, 2018) - 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 the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec. The 800,000 metre drill program combines definition, expansion and exploration drilling in and around the main Windfall gold deposit and the adjacent Lynx deposit (located immediately NE of Windfall).

Significant new analytical results from 24 intercepts in 12 drill holes and 5 wedges focused on infill drilling in the Windfall deposit are presented below. Today's infill drilling results will not be included in the pending mineral resource scheduled for release in May 2018.

Highlights from the new results include: 34.3 g/t Au over 4.5 metres in OSK-W-17-1172; 13.0 g/t Au over 5.7 metres in OSK-W-18-1336-W2; 27.7 g/t Au over 2.1 metres in OSK-W-17-778, 25.5 g/t Au over 2.1 metres in OSK-W-17-1380. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

Hole No. From
Au (g/t)
Au (g/t)
cut to
100 g/t
Zone Corridor
OSK-EAG-12-427 918.0 920.0 2.0 13.0 Underdog Underdog
including 918.9 920.0 1.1 23.6
OSK-EAG-13-513 1050.0 1054.0 4.0 10.6 FW4 Underdog
including 1050.0 1052.0 2.0 18.0
OSK-W-16-762 1253.0 1255.0 2.0 4.66 FW4 Underdog
OSK-W-17-778 917.0 919.2 2.2 11.6 FW0 Underdog
1095.4 1098.4 3.0 10.6 FW1 Underdog
1114.6 1117.1 2.5 9.24 FW1 Underdog
1132.0 1134.1 2.1 27.7 19.1 FW2 Underdog
including 1132.0 1132.4 0.4 145 100
1158.0 1160.0 2.0 4.49 FW2 Underdog
OSK-W-17-1172 136.5 141.0 4.5 34.3 27.4 Z27 Zone 27
including 136.5 137.0 0.5 44.1
including 140.0 141.0 1.0 131 100
OSK-W-17-1336-W1 723.0 725.0 2.0 9.44 Vein Red Dog
including 723.7 724.0 0.3 62.8
OSK-W-18-1336-W2 831.9 835.3 3.4 4.62 FW0 Underdog
849.7 852.3 2.6 3.53 FW0 Underdog
950.0 952.3 2.3 3.92 FW1 Underdog
964.0 969.7 5.7 13.0 FW1 Underdog
including 967.3 967.8 0.5 92.2
OSK-W-17-1380 361.1 363.2 2.1 25.5 25.3 Underdog Underdog
including 361.9 362.4 0.5 101 100
OSK-W-17-1394 902.7 904.8 2.1 13.0 Caribou Ext. Caribou
including 904.0 904.8 0.8 33.0
OSK-W-18-1402-W1 683.5 686.0 2.5 3.57 Vein Red Dog
including 684.5 685.0 0.5 17.6
OSK-W-18-1418 893.0 896.4 3.4 6.72 QTV Caribou
including 893.0 893.5 0.5 39.0
OSK-W-18-1423 268.4 271.0 2.6 3.07 Bobcat Bobcat
OSK-W-18-1431-W1 922.1 924.6 2.5 4.25 FW3 Underdog
OSK-W-18-1431-W2 765.0 767.0 2.0 3.55 FW1 Underdog
OSK-W-18-1435 555.5 558.0 2.5 16.7 Caribou Ext. Caribou
including 555.5 556.5 1.0 40.7
OSK-W-18-1457 52.7 55.0 2.3 10.5 Bobcat Bobcat
including 54.0 54.3 0.3 66.0
OSK-W-18-1459 256.0 258.0 2.0 9.52 Bobcat Bobcat
including 257.5 258.0 0.5 36.4
Notes: True widths are estimated at 65 - 80% of the reported core length interval. See "Quality Control" below.
Definitions: Ext. = Extension; FW = Footwall; QTV = Quartz-Tourmaline Vein.
Hole Number Azimuth
UTM E UTM N Section
OSK-EAG-12-427 330 51 1215 452701 5434438 2675
OSK-EAG-13-513 330 -55 1131 452629 5434514 2650
OSK-W-16-762 332 -56 1311 452730 5434409 2675
OSK-W-17-778 331 -58 1362 452689 5434338 2600
OSK-W-17-1172 144 -49 207 452022 5434797 2250
OSK-W-17-1336-W1 335 -61 1335 452616 5434449 2600
OSK-W-18-1336-W2 335 -61 1193 452616 5434449 2600
OSK-W-17-1380 335 -45 624 451895 5434473 1975
OSK-W-17-1394 335 -49 1165 453146 5434512 3100
OSK-W-18-1402-W1 330 -59 1224 452616 5434449 2600
OSK-W-18-1418 334 -45 1077 453288 5434531 3225
OSK-W-18-1423 327 -61 792 453025 5434853 3150
OSK-W-18-1431-W1 337 -62 1092 452287 5434336 2250
OSK-W-18-1431-W2 337 -62 1140 452287 5434336 2250
OSK-W-18-1435 331 -65 801 453028 5434848 3150
OSK-W-18-1457 137 -57 318 452982 5435148 3275
OSK-W-18-1459 132 -50 621 452860 5435186 3175

OSK-EAG-12-427 intersected 13.0 g/t Au over 2.0 metres in Underdog. Mineralization contains 5% pyrite stringers within an enclave of foliated andesite in a porphyric felsic dike.

OSK-EAG-13-513 intersected FW4 with 10.6 g/t Au over 4.0 metres in Underdog. Mineralization contains up to 5% pyrite stringers and 3% disseminated pyrite within a moderately sericitized felsic dike.

OSK-W-16-762 intersected FW4 with 4.66 g/t Au over 2.0 metres in Underdog. Mineralization contains 5% semi-massive pyrite and 2% pyrite stringers within a bleached andesite with moderate silica and sericite alteration.

OSK-W-17-778 intersected five intervals in Underdog: 11.6 g/t Au over 2.2 metres in FW0, 10.6 g/t Au over 3.0 metres and 9.24 g/t Au over 2.5 metres in FW1, and 27.7 g/t Au over 2.1 metres and 4.49 g/t Au over 2.0 metres in FW2. The first interval contains local visible gold with 15% pyrite-silica flooding in a sericitized and bleached felsic porphyritic intrusion. The second and third intervals contain up to 5% pyrite and pyrite-tourmaline stringers and up to 12% disseminated and cluster pyrite with patchy silica hosted in a strongly bleached to sericitized and silicified felsic porphyritic dike. The fourth interval is similar to the previous ones and contains local visible gold.

OSK-W-17-1172 intersected 34.3 g/t Au over 4.5 metres in Zone 27. Mineralization contains up 1% disseminated pyrite, 5% pyrite and pyrite-tourmaline stringers in a moderately silicified porphyritic felsic dike.

OSK-W-17-1336-W1 intersected 9.44 g/t Au over 2.0 metres in a vein in the Red Dog intrusive (hematized monzonite). Mineralization contains local visible gold within a centimetre-thick pyrite stringer.

OSK-W-17-1336-W2 intersected four intervals: 4.62 g/t Au over 3.4 metres and 3.53 g/t Au over 2.6 metres in FW0, 3.92 g/t Au over 2.3 metres and 13.0 g/t Au over 5.7 metres in FW1. The first interval contains local visible gold in a ptygmatic tourmaline vein hosted in a porphyritic felsic dike with up to 3% pyrite-tourmaline stringers and pyrite clusters in pervasive silica flooding. The second interval contains 2 to 5% semi-massive pyrite clusters, 1 to 3% pyrite stringers with smoky quartz-chlorite-tourmaline, local pervasive silica flooding, ptygmatic tourmaline veinlets, 2% semi-massive to massive pyrite associated with mafic fuchsitized fragments and 2% disseminated pyrite all hosted in a sericitized porphyritic felsic unit. The third interval contains up to 15% pyrite-tourmaline stringers hosted in a silicified and sericitized porphyritic felsic dike. The last interval contains local visible gold with up to 20% pyrite-silica flooding and 2% pyrite-tourmaline stringers within a silicified and sericitized felsic dike.

OSK-W-17-1380 intersected 25.5 g/t Au over 2.1 metres in Underdog. Mineralization contains semi-massive to massive pyrite, up to 7% pyrite-tourmaline and pyrite stringers and 3% disseminated pyrite within a sericitized porphyritic felsic dike. It is located 50 metres west of OSK-EAG-13-505 (8.37 g/t Au over 4.8 metres, previously released January 16, 2018).

OSK-W-17-1394 intersected 13.0 g/t Au over 2.1 metres in Caribou Extension. Mineralization contains 1% disseminated pyrite and traces of pyrite stringers within a chloritized andesite with moderate carbonate alteration.

OSK-W-18-1402-W1 intersected a mineralized vein in Red Dog intrusion returning 3.57 g/t Au over 2.5 metres. Mineralization is composed of 20-centimetre wide quartz vein with traces of pyrite.

OSK-W-18-1418 intersected 6.72 g/t Au over 3.4 metres in Caribou. Mineralization contains up to 5% pyrite and quartz-tourmaline veins at the chloritized contact between an andesite and a porphyric felsic dike.

OSK-W-18-1423 intersected 3.07 g/t Au over 2.6 metres in Bobcat. Mineralization corresponds with quartz-carbonates veins with 5% pyrite in a moderately sericitized andesite with fuschite and up to 2% disseminated pyrite.

OSK-W-18-1431-W1 intersected FW3 with 4.25 g/t Au over 2.5 metres in Underdog. Mineralization is composed of two decimetre-scale pyrite stringers within a sericitized and silicified porphyritic felsic dike.

OSK-W-18-1431-W2 intersected FW1 with 3.55 g/t Au over 2.0 metres in Underdog. Mineralization contains up to 5% fragments of pyrite-stringers and 3% disseminated pyrite in a foliated and sericitized porphyritic felsic dike with fuchsite.

OSK-W-18-1435 intersected 16.7 g/t Au over 2.5 metres related to Caribou Extension. Mineralization contains 1% disseminated pyrite and 3% pyrite-quartz clusters within a gabbro with moderate carbonate alteration.

OSK-W-18-1457 intersected 10.5 g/t Au over 2.3 metres in Bobcat. Mineralization contains up to 4% pyrite stringers associated with a tourmaline breccia hosted in a sericitized felsic porphyritic intrusion.

OSK-W-18-1459 intersected 9.52 g/t Au over 2.0 metres in Bobcat. Mineralization contains 8% pyrite stringer, 3% pyrite stringers and clusters and 2% pyrite in a crustiform vein in a silicified and chloritized gabbro with strong fuchsite alteration.

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 as of December 31, 2017.

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, 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.

Contact Information:

Osisko Mining Inc.
John Burzynski
President and Chief Executive Officer
(416) 363-8653