Osisko Intersects 7.14 g/t Au Over 12.7 Metres at Garrison

TORONTO, ONTARIO--(Marketwired - Oct. 5, 2017) - Osisko Mining Inc. (TSX:OSK) ("Osisko" or the "Corporation") is pleased to announce new results from the ongoing drill program at its 100% owned Garrison gold project located in Garrison Township, Ontario. Over 70,000 metres of new drilling have been conducted by Osisko on the Garrison Project to date. A total of seventeen new intercepts in sixteen holes are reported in this release, with significant assay results presented in the table below.

Significant new results include: 7.14 g/t Au over 12.7 metres in OSK-G17-420; 5.18g/t Au over 17.0 metres and 1.62 g/t Au over 16.1 metres in OSK-G17-412; 1.37g/t Au over 30.2 metres in OSK-G17-408; 2.84 g/t over 7.1 metres in OSK-G17-415.

The new results continue to demonstrate the potential to expand the extent of known mineralization in the 903 Zone. The 2017 drill program will continue to explore extensions of the mineralized zones within the Garrcon, Jonpol and 903 zones. Maps and sections showing hole locations and complete drilling 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-G17-367 was drilled in the central section of the 903 Zone targeting extensions of the main 903 syenite body to depth. Two intervals in the 903 syenite intersected 1.20 g/t Au over 15.3 metres and 2.03 g/t Au over 11.0 metres. The two broad zones are hosted in syenite showing a porphyritic texture and significant fracturing containing specular hematite and pyrite mineralization.

OSK-G17-370 targeted the eastern extension of the main 903 Zone and 903 South Zone along strike. The hole intersected a new shallow mineralized zone along the flow contact between an ultramafic volcanic and mafic volcanic. This horizon contains limited syenite surrounded by a broad quartz carbonate veining over 10 metres and averaging 2.65 g/t Au over 9.1 metres. A second mineralized zone was intersected along the eastern extension of the 903 South Zone horizon characterized by intense quartz and iron carbonate fracturing adjacent to diabase and hosted within ultramafic volcanic. This interval reported a average of 1.33 g/t Au over 12.0 metres.

OSK-G17-371A, 374A and 382 were drilled southwest of the main 903 syenite, targeting a linear magnetic low that may represent a fault offset extension of the main 903 Zone extending west. All three holes intersected a zone of mariposite alteration ranging from 50 to 75 metres in width containing syenite coincident with the magnetic low. Anomalous gold grades were reported from holes 374A and 382. OSK-G17-371A intersected two separate syenite dykes ranging in width from 15 to 40 metres. The first syenite dyke showed a brick red hematite alteration and limited quartz veining which averaged 1.65 g/t Au over 13.0 metres. The second broader syenite contained considerable quartz - iron carbonate veining up to 1 metre in width a long with minor hematite alteration and disseminated pyrite; this interval averaged 2.00 g/t Au over 11.4 metres.

OSK-G17-379, 396, 406 were drilled along section 3000W in the western section of the main 903 Zone. Each of the holes intersected syenite within the 903 Zone. A strong interval of quartz - iron carbonate veining and hematite alteration was found in OSK-G17-396 reporting a shallow intercept averaging 1.03 g/t Au over 16.0 metres. Drilling 55 metres below this intercept hole OSK-G17-406 also intersected syenite containing significant iron - carbonate veining along with a moderate hematite alteration believed to be the extension of the zone found in OSK-G17-396. Within the syenite dykes two mineralized zones averaged 2.44 g/t Au over 8.0 metres and 1.43 g/t Au over 15.1 metres. Below this interval (110 metres) OSK-G17-379 intersected syenite dykes hosted within mariposite schist. An interval within the dyke assayed 5.37 g/t Au over 2.0 metres also coincident with veining and hematite alteration.

OSK-G17-400, 412 were drilled along section 2950W within the main 903 Zone. Drill hole OSK-G17-400 was drilled north of the main syenite body and did not intersected any significant dykes; drilling into the footwall metasediment the hole intersected a 5 cm quartz-iron carbonate vein and surrounding fracturing that averaged 6.44 g/t Au over 2.0 metres. Testing 120 metres below OSK-G17-400,OSK-G17-412 intersected a broad zone of syenite along the main trend of the 903 Zone. Within the syenite was quartz-iron carbonate veining with moderate hematite alteration of the syenite as well as along fractures and showing disseminated pyrite within the syenite; this interval averaged 1.62 g/t Au over 16.1 metres. This hole also intersected the footwall metasediment within which a broad chlorite alteration zone containing quartz and iron carbonate veining from 2-40 cm in width and showing disseminated pyrite within the metasediment, averaging 5.18 g/t Au over 17.0 metres. A second interval within the metasediment showing only limited quartz-iron carbonate fracturing to 1 cm width averaged 10.4 g/t Au over 2.0 metres.

OSK-G17-408 was drilled along the eastern strike extension of the 903 Zone targeting the up dip extension of syenite intersected in OSK-G17-332 (1.09 g/t Au over 17.0 metres, March 15, 2017). The hole intersected syenite 35 metres up dip of OSK-G17-332. The syenite contained moderate quartz - iron carbonate veins from 10 to 20 cm in width along with hematite alteration and disseminated pyrite. This shallow interval averaged 1.37 g/t Au over 30.2 metres.

OSK-G17-415, 420 were drilled along section 2800W in the central 903 Zone. OSK-G17-415 was drilled 50 metres down dip of OSK-G17-335 (1.57g/t Au over 10.0 metres and 1.49 g/t Au over 9.0 metres, March 15, 2017). The hole successfully intersected the main 903 syenite dyke at a vertical depth of 185 metres but reported limited mineralization. The upper part of hole OSK-G17-415 intersected the southern 903 Zone within highly altered metasediment containing sericite and iron carbonate alteration. Very fine disseminated pyrite along with 1-2 cm quartz - iron carbonate veins contained within the metasediment averaged 2.84 g/t Au over 7.1 metres. OSK-G17-420 was drilled 50 metres up dip from OSK-G17-335, intersecting a 75 metre wide syenite body. Within the upper contact of the syenite there is considerable strong hematite alteration along with limited quartz - iron carbonate veining and 2-3% coarse disseminated pyrite; this interval returned 7.14 g/t Au over 12.7 metres.

OSK-G17-345, -404, -411 did not intersect significant mineralization.

Qualified Person

The scientific and technical content of this press release has been reviewed, prepared and approved by Mr. Greg Matheson, P.Geo. Senior Project Manager of the Garrison 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

True widths of the new exploration intercepts reported in this press release have yet to be determined, but are typically 65 - 90% of reported core lengths. Additional drilling is planned for the immediate area which will enable the true width determination. Assays are uncut except where indicated, and calculated intervals are reported over a minimum length of 2 metres using a lower cutoff of 1.0 g/t Au. All HQ core assays reported were obtained by either whole sample rock metallic screen/fire assay or standard 30 gram fire-assaying with ICP finish at SGS Minerals Services in Cochrane, Ontario. The whole sample metallic screen assay method is selected by the geologist when samples contain coarse gold or any samples displaying gold initial fire assay values greater than 4g/t. Drill program design, Quality Assurance/Quality Control and interpretation of results is performed by qualified persons employing a Quality Assurance/Quality Control program consistent with NI 43-101 and industry best practices. Standards and blanks are included with every 20 samples for Quality Assurance/Quality Control purposes by the Corporation as well as the lab. Approximately 5% of sample pulps are sent to secondary laboratories for check assays.

About the Garrison Project

The Garrison Project area is comprised of 214 mineral claims, 25 mining leases, and 87 patent claims encompassing approximately 8,000 hectares. Both Garrcon and Jonpol have resource estimates that are described in a technical report prepared in accordance with NI 43-101, which was completed by a previous operator Northern Gold Mining Inc. (entitled "Technical Report on the Golden Bear Project - Garrison Property: Larder Lake Mining Division, Garrison Township, Ontario, Canada") dated December 30, 2013, with an effective date of December 30, 2013 (the "Garrison Technical Report"). The Garrison Technical Report was prepared by A.C.A. Howe International Limited for Northern Gold Mining Inc. (a wholly-owned subsidiary of Osisko) and is available on Osisko's website at www.osiskomining.com and on SEDAR under Northern Gold Mining Inc.'s issuer profile at www.sedar.com.

Resource estimates were conducted by A.C.A. Howe International Limited according to CIM standards. The Garrcon Zone estimates showed 15.1 million tonnes with an average grade of 1.07 g/t Au (521,000 oz) in measured resources; 14.1 million tonnes averaging 1.16 g/t Au (526,000 oz) in indicated resources; and 1.7 million tonnes averaging 0.72 g/t Au (39,000 oz) in inferred resources. Potential underground resources of 5.1 million tonnes averaging 3.49 g/t Au (577,000 oz) in the inferred category were also outlined. Resources were reported at a cut-off grade of 0.4 g/t Au for open pit extraction and 1.5 g/t in a bulk underground mining scenario using a gold price of US$1,250/oz.

At the Jonpol Zone, resources were estimated as 0.87 million tonnes averaging 5.34 g/t Au (150,000 oz) in the indicated category; and 1.07 million tonnes averaging 5.56 g/t Au (192,000 oz) in inferred resources. Resources were reported at a cut-off grade of 3.0 g/t Au and assume an underground extraction scenario using a gold price of US$1,250/oz.

Readers are cautioned that inferred resources have a great amount of uncertainty as to their existence and as to whether they can be mined economically. It cannot be assumed that all or any part of the inferred resources will ever be upgraded to a higher category. Mineral resources are not mineral reserves and do not have demonstrated economic viability.

Garrcon Zone

The Garrcon Zone has a shallow plunge eastward along the footwall of the Destor-Porcupine Fault Zone with the bulk of the resource in the western, more densely drilled area. The zone is exposed at surface and has potential for open pit bulk mining at an estimated overall stripping ratio of 1.8:1. There is potential for additional underground resources below the pit and along the easterly plunge of the zone, which is open for further exploration down dip and along strike.

The Garrcon shaft was sunk in 1935 and 1936 by the Consolidated Mining and Smelting Co. of Canada ("Cominco") and the Shaft and South Zones were tested for high grade gold mineralization. Cominco drove approximately 1,430 metres of drifts and cross cuts, mining underground veins. Diamond drilling by Cominco and Lac Minerals Ltd. in the mid-to-late 1980s identified broad sections of low grade mineralization. In 2006-2007, ValGold Resources Ltd. conducted additional drilling confirming these zones. From 2009-2013 Northern Gold Mining Inc. conducted 97,000 metres of diamond drilling which delineated the current resource.

In 2014, Northern Gold Mining Inc. was granted a trial mining permit allowing the extraction of up to 150,000 tonnes. Northern Gold Mining Inc. mined 73,534 dry tonnes which was processed at the nearby Holt mill facility recovering 3,516 oz at an average head grade of 1.55 g/t and recovery of 95.9%. The trial production permit remains active.

Jonpol Zone

Jonpol is situated in the Munro Fault Zone, a west striking splay off the north side of the Destor-Porcupine Fault. Hosted in a shear zone tens of metres wide in altered mafic volcanic rocks, the deposit consists of four high grade gold mineralized zones (JP, JD, RP and East) over a strike length of 1.7 kilometers. Gold mineralization is hosted in quartz carbonate veins, in mafic and ultramafic host rocks, and is associated with intense albite and/or sericite alteration and pyrite mineralization.

In 1997, a 49,087 tonne bulk sample was extracted from the central part of the JP zone by Hillsborough Resources Limited with an average grade of 6.7 g/t which produced 9,476 ounces Au. From 1985-2013, over 130,000 metres of drilling was completed on the property by previous operators. Development work on the JP zone included the sinking of a 184 metre shaft as well as development of a ramp to the 150 metre level with mining on six sublevels. The Jonpol infrastructure underwent reclamation in the late 1990s and was closed out in 2001, but the existing ramp and shaft are preserved.

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 Qu?(C)bec and holds a 100% undivided interest in a large area of claims in the surrounding Urban Barry area (82,400 hectares), a 100% interest in the Marban project located in the heart of Qu?(C)bec's prolific Abitibi gold mining district, and properties in the Larder Lake Mining Division in northeast Ontario, including the Garrcon and Jonpol zones 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 Ontario. Osisko continues to be well financed and has approximately $246 million in cash and equity investment.

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 ongoing drill program at the Garrison gold project; results of the current drill program; the significance of new drill results reported in this press release; the ability of new drill results to demonstrate potential for expansion of the previously defined Garrcon, Jonpol and 903 mineralized zones at the Garrison project; the scope of the 2017 drill program; that the 2017 drill program will follow new extensions of these mineralized zones to further define the scale of mineralization at the Garrison project; potential mineralization; 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; 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; 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.