Osisko Updates Reserves at Canadian Malartic

12% Lower Gold Price Assumption Results in 2% Decrease in Reserves

2014 Gold Production Estimated at 525,000 - 575,000 Ounces

MONTREAL, QUEBEC--(Marketwired - Mar 12, 2014) - Osisko Mining Corp. (TSX:OSK)(FRANKFURT:EWX) is pleased to provide an updated reserve and resource estimate for its 100%-owned Canadian Malartic project. This new estimate, calculated using a price of US$1,300 per ounce of gold, combines the reserves and resources of the main Canadian Malartic (CM), the South Barnat deposit and the defined satellite deposits. This update reports reserves as well as global resources in all categories as of January 1, 2014.

The open pit Proven & Probable gold reserves now stand at 9.37 million (M) ounces at a fully diluted average gold grade of 1.04 grams per tonne ("g/t Au"), following total 2013 production of 475,277 ounces of gold. Total precious metal production from the beginning of operations in April 2011 to December 31, 2013 was 1,044,388 ounces gold and 753,776 ounces silver. Global Measured and Indicated (M&I) resources stand at 11.10 M ounces gold, and global Inferred resources stand at 1.16M ounces gold. The global in situ 2014 resources include reserves but exclude production.

Reserve estimates using base case US$1,300 engineered pit design with lower cut-off grade of 0.33 g/t Au

Outlook for 2014

Mill throughput is expected to stabilize at approximately 55,000 tonnes per day ("tpd") in 2014 with the completion of optimization programs currently in progress. Together with increased contribution from higher grade material in the now accessible northern pit wall, it is anticipated that gold production for the current year will increase to between 525,000 - 575,000 ounces (an increase of between 11% - 21% over record 2013 production of 475,277 ounces gold).

Sean Roosen, President and Chief Executive Officer, stated: "We are very pleased with this updated reserve estimate. Using a 12% lower gold price (US$1300 versus US$1475), the net difference from the 2013 estimate of 10.1 million ounces is only 235,000 fewer ounces (2%), once 2013 production (before recovery) is taken into account. We've always contended that Canadian Malartic is a superior, world class deposit, and these numbers once again prove our point. Even in a challenging gold price environment, the mine maintains its strong economics. Average reconciliation since the beginning of production has been plus 2% from the reserve model, further demonstrating the very robust nature of the reserves."

Commenting on the outlook for 2014, Mr. Roosen continued: "The Canadian Malartic mine is still on its upward production trajectory, with increasing grade and throughput, and decreasing costs. We've been setting record after record on throughput, gold production, and lower costs on an annual, quarterly and monthly basis. With our gold production outlook of 525,000 - 575,000 ounces for 2014 we are anticipating another record breaking year that should be highly profitable for our shareholders."

For the purpose of the reserve estimate, the optimal Whittle pit shell was used as a guideline for the manual design of the engineered pit, and only the in-pit measured and indicated resources were considered. Due to constraints on capital expenditures in 2013, no attempt was made to convert out-of-pit resources to additional reserves. The strip ratio in the main pit is estimated at 2.10 with average diluted grade of 1.05 g/t Au based on a calculated dilution of 8%. Optimization parameters included:

Sensitivity of the Proven and Probable reserves to gold price has been estimated using Whittle pit shells and lower cut-off grades (Jeffrey satellite pit excluded, 0.06% of total reserve):

Updated Global Resource Estimates

The global M&I resource is 11.10 million ounces of gold at an average undiluted grade of 1.06 g/t Au, with an additional 1.16 million ounces gold at an average grade of 0.75 g/t Au in the Inferred category, based on a lower cut-off grade of 0.263 to 0.332 g/t Au. The global resources include the above-stated reserves but exclude past production. The tables below summarize the estimates per deposit:

Canadian Malartic Updated Global Resource Estimate

Details on the parameters of the resource estimates are as follows:

• The database comprised a total of 1,030,888 metres of drilling completed and assayed by Osisko as of the end of December 2013 (core and in-pit RC drilling) on a maximum 25 m x 25 m grid, as well as 338,927 metres of historical drilling validated and retained from a larger database of historical drilling (Canadian Malartic Mines and Lac Minerals). All NQ or HQ core assays reported by Osisko were obtained by standard 50g fire assaying-AA finish or gravimetric finish at ALS Chemex laboratories in Val d'Or, Quebec.
• The database also comprised a total of 729,405 assays with an average of 1.40 metre per sample for a total of 1,020,919 assayed metres.
• The estimates were done using Ordinary Kriging (OK) as the geostatistical interpolation method based on 5.0 metre analytical composites. Resources were also estimated using Inverse Distance Squared (ID2) interpolation for testing and comparative purposes, which produced similar results, i.e. less than 2 percent difference in total ounces at all cut-offs.
• Calculations were based on original samples cut to a maximum of 5 g/t to 70 g/t Au depending on the domain. The apparent reduction in the gold content varies from 0 to 14.5% depending of the domains. All five metre composites were calculated based on cut original data.
• All estimates were based on a Parent Cell dimension of 20 metres E, 10 metres N and 10 metres height with estimation parameters determined by variography.
• Geological interpretation identified fifty-one different domains (sixteen in Canadian Malartic, fifteen in Barnat, eight in Gouldie, five in Jeffrey and seven in Western porphyry).
• Underground voids were modeled from historical mine plans and adjusted according to positions of drill intersections in stopes and drifts. Void volumes of stopes were increased by one metre along all edges to compensate for uncertainties. Some stopes have been investigated in detail during mining activities and re-modelled to replace the older voids. The void models were then used to deplete the resource estimate. All samples located within the voids were also removed from the estimate.
• Tonnage estimates in Canadian Malartic and Barnat area were based on rock densities of 2.69 tonnes/cubic metre for the porphyry, 2.75 for altered sediments and 2.83 for altered ultramafic rocks. Rock densities vary from 2.65 to 2.88 tonnes/cubic metre for other sector as Jeffrey, Gouldie and Western Porphyry.
• The US$1,300 engineered pit has approximate maximum dimensions of 3,560 metres in length, 1,265 metres in width and a vertical depth of 410 metres.

Mr. Donald Gervais, P.Geo., Technical Services Manager at Canadian Malartic, and Mr. Robert Wares, D.Sc., P.Geo., Senior Vice President, Exploration and Resource Development, are the Qualified Persons who have reviewed this news release and are responsible for the technical information reported herein, including verification of the data disclosed. All assays were obtained at ALS Chemex laboratories in Val d'Or, Quebec, an ISO/IEC guideline 17025-accredited facility. For further information on Canadian Malartic, please see at www.osisko.com or at www.sedar.com "Updated resource and reserve estimates for the Canadian Malartic Project Malartic, Quebec", dated May 10, 2011 and prepared by Belzile Solutions Inc. and G Mining Services Inc., as updated by press release dated February 19, 2013.

Reject the Inadequate Goldcorp Offer

As previously disclosed, the Osisko Board of Directors has unanimously recommended that Osisko shareholders reject the hostile take-over bid initiated by Goldcorp and not tender their Osisko shares to the Goldcorp offer. The Osisko Board determined that the Goldcorp offer fails to adequately compensate Osisko shareholders for, among others things, the strategic value of Osisko's world-class asset base, the significant upside potential of Osisko's Canadian Malartic Mine, or the increased risk inherent in Goldcorp common shares. The full basis for the Osisko Board's recommendation is available in a Directors' Circular, a copy of which is available online at www.osisko.com.

Shareholders who have questions or who may have already tendered their shares to the Goldcorp Offer and wish to withdraw them, may do so by contacting our Information Agent, Laurel Hill Advisory Group at:

North American Toll Free: 1-877-452-7184

Banks, Brokers or collect calls: 416-304-2011

Email: assistance@laurelhill.com

Cautionary Notes Concerning Estimates of Mineral Resources

This news release uses the terms measured, indicated and inferred resources as a relative measure of the level of confidence in the resource estimate. Readers are cautioned that mineral resources are not economic mineral reserves and that the economic viability of resources that are not mineral reserves has not been demonstrated. In addition, inferred resources are considered too geologically speculative to have any economic considerations applied to them. It cannot be assumed that all or any part of an inferred mineral resource will ever be upgraded to a higher category. Under Canadian rules, estimates of inferred mineral resources may not form the basis of feasibility or pre-feasibility studies or economic studies except for Preliminary Assessment as defined under NI 43-101. Readers are cautioned not to assume that further work on the stated resources will lead to mineral reserves that can be mined economically.

Forward-Looking Statements

Certain statements contained in this press release may be deemed "forward-looking statements". All statements in this release, other than statements of historical fact, that address events or developments that Osisko expects to occur, are forward looking statements. Forward looking statements are statements that are not historical facts and are generally, but not always, identified by the words "expects", "plans", "anticipates", "believes", "intends", "estimates", "projects", "potential", "scheduled" and similar expressions, or that events or conditions "will", "would", "may", "could" or "should" occur including, without limitation, the stabilization of mill throughput, the completion of optimization programs, the decrease of costs and increase of grade and gold production, the anticipation of a highly profitable record breaking year in 2014, the Corporation's view on the quality and the potential of its Canadian Malartic asset and on Goldcorp common shares, and that mining of the deposits identified in this press release will be executed fully and will return values identified in the foregoing estimate. Although Osisko believes the expectations expressed in such forward-looking statements are based on reasonable assumptions, including, without limitation, that all technical, political and financial conditions will be met in order to continue mining operations at Canadian Malartic to allow for the full extraction of the mining reserves, such statements are not guarantees of future performance and actual results may differ materially from those in forward looking statements. Factors that could cause the actual results to differ materially from those in forward-looking statements include gold prices, Osisko's limited experience with production and mining operations, uninsured risks, regulatory framework and changes, defects in title, availability of personnel, materials and equipment, timeliness of government approvals, actual performance of facilities, equipment and processes relative to specifications and expectations, unanticipated environmental impacts on operations market prices, continued availability of capital and financing and general economic, market or business conditions.

These factors are discussed in greater detail in Osisko's most recent Annual Information Form and in the most recent Management Discussion and Analysis filed on SEDAR, which also provide additional general assumptions in connection with these statements. Osisko cautions that the foregoing list of important factors is not exhaustive. Investors and others who base themselves on forward-looking statements should carefully consider the above factors as well as the uncertainties they represent and the risk they entail. Osisko believes that the expectations reflected in those forward-looking statements are reasonable, but no assurance can be given that these expectations will prove to be correct and such forward-looking statements included in this press release should not be unduly relied upon. These statements speak only as of the date of this press release.