Osisko Intersects Bonanza Grades at Lynx Extension and Triple Lynx

TORONTO, Sept. 09, 2019 - Osisko Mining Inc. (OSK:TSX. "Osisko" or the "Corporation") is pleased to provide new drilling results from the ongoing definition and expansion drill program at its 100% owned Windfall gold project located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec.

The program is currently focused on infill drilling at the Lynx deposit, exploration and expansion drilling on the main mineralized zones, and deep exploration in the central areas of the mineralized intrusive system. Sixteen drills are active at Lynx and Triple Lynx, with another seven drills conducting infill and exploration drilling on other areas of the deposit.

Osisko President and Chief Executive Officer John Burzynski commented: “The continued flow of strong results from Lynx is making us rethink our approach to the Windfall deposit. We continue to see good continuity of high-grade mineralization at Lynx and now Triple Lynx, and both zones remain open for expansion down-plunge. The Lynx Extension and Triple Lynx are adding important ounces and these two recent discoveries are once again demonstrating the importance of the Lynx corridor in the Windfall mineralized system.”

Significant new analytical results from 14 intercepts in 2 drill holes and 10 wedges from surface focused on Lynx Extension and Triple Lynx drilling are presented below. Maps showing hole locations and full analytical results are available at www.osiskomining.com.

Notes: True widths are estimated at 55 – 80% of the reported core length interval. See "Quality Control and Reporting Protocols" below.

OSK-W-19-991-W3 intersected 9.00 g/t Au over 2.6 metres. Mineralization consists of up to 6% disseminated and stringer pyrite in a weakly bleached and carbonate altered rhyolite close to the contact with a bleached gabbro.

OSK-W-19-991-W4 intersected 29.3 g/t Au over 4.8 metres. Mineralization consists of up to 15% disseminated and stringer pyrite, trace molybdenite and sphalerite, and smoky quartz veins hosted in a moderate silica and carbonate altered rhyolite.

OSK-W-19-1272-W1 intersected 72.3 g/t Au over 12.7 metres. Mineralization consists of trace to 1% local visible gold in clusters and stringers, 7% disseminated and clustered pyrite, 2% pyrite stringers and 1% disseminated sphalerite with pervasive silica flooding and ptygmatic tourmaline veins hosted in strongly fuchsitized, silicified and sericitized rhyolite and gabbro.

OSK-W-19-1272-W2 intersected 5.62 g/t Au over 5.6 metres and 52.0 g/t Au over 12.4 metres. The first interval contains trace of pyrite stringers in a moderate silica altered rhyolite. The second interval contains local visible gold clusters, 10% disseminated pyrite and traces of chalcopyrite with pervasive silica flooding, 2% pyrite stringers within an alternation of moderate to strongly silica and sericite altered rhyolite and gabbro.

OSK-W-19-1367-W4 intersected 46.7 g/t Au over 3.9 metres. Mineralization consists of local visible gold and up to 10% pyrite stringers associated to silica flooding hosted in a moderate fuchsite and sericite altered rhyolite.

OSK-W-19-1857-W2 intersected 3.99 g/t Au over 3.0 metres. Mineralization consists of trace disseminated pyrite hosted in a moderate sericite altered rhyolite.

OSK-W-19-1857-W4 intersected 145 g/t Au over 3.5 metres. Mineralization consists of local visible gold and trace disseminated pyrite hosted in a strong sericite and moderate carbonate altered rhyolite.

OSK-W-19-1857-W5 intersected 8.12 g/t Au over 2.0 metres. Mineralization consists of 5% pyrite clusters and 1% chalcopyrite clusters with pervasive silica flooding hosted in a strongly silica and sericite altered rhyolite.

OSK-W-19-1963-W1 intersected 56.9 g/t Au over 2.4 metres. Mineralization consists of trace of visible gold and electrum, and 5% pyrite tourmaline clusters in a moderate silica and strong sericite altered rhyolite with breccia texture showing a sericite matrix with quartz fragments, tourmaline ptygmatic veins, quartz carbonate veins and trace fuchsite.

OSK-W-19-1975 intersected 7.98 g/t Au over 2.0 metres. Mineralization consists of 5% disseminated pyrite, 3% pyrite-tourmaline stringers and ptygmatic tourmaline veins hosted in moderate silica altered dacite.

OSK-W-19-1991 intersected 5.82 g/t Au over 2.6 metres. Mineralization consists of up to 5% pyrite and 2% sphalerite stringers with smoky quartz veins hosted in a strong silica altered rhyolite at the contact with a felsic porphyritic intrusion.

OSK-W-19-1992-W2 intersected 10.2 g/t Au over 3.5 metres and 16.3 g/t Au over 3.3 metres. Mineralization in both intervals consists of up to 7% pyrite in crustiform quartz-carbonate veins, 10% pyrite stringers, 5% disseminated pyrite, 3% pyrite cluster and trace chalcopyrite hosted in a moderate sericite-fuchsite and weakly silicified gabbro.

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 Osisko's 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 width determination is estimated at 55-80% of the reported core length interval for the zone. 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 the Windfall Lake Technical Report (as defined below) and November 27, 2018 Lynx resource update, comprises 2,874,000 tonnes at 8.17 g/t Au (754,000 ounces) in the indicated mineral resource category and 10,352,000 tonnes at 7.11 g/t Au (2,366,000 ounces) in the inferred mineral resource category. For details regarding the key assumptions, parameters and methods used to estimate the mineral resources presented in respect of the Windfall Lake gold project, please 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 by InnovExplo Inc. from Val-d'Or, Québec (the "Windfall Lake Technical Report") and the press release “Osisko Releases Mineral Resource Update for Lynx” dated November 27, 2018, which has been prepared by Osisko and reviewed and approved by Micon International, Ltd. from Toronto, Ontario. The Windfall Lake Technical Report and press release are 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 30 metres from surface in some areas and as deep as 2,000 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% interest 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 the Urban Barry area and nearby Quévillon area (over 2,700 square kilometres).

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 significance of results from the new infill drilling and ongoing drill definition and expansion program at the Windfall Lake gold project; the significance of assay results presented in this news release; the deposit remaining open along strike and at depth; potential depth extensions of the mineralized zones down-plunge and at depth; the actual mineralization of local visible gold; the current 800,000 metre drill program; the type of drilling included in the drill program; 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 such assumptions and estimates were made, and 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