MONTREAL, QUEBEC--(Marketwire - Feb. 19, 2013) - Osisko Mining Corporation (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 at US$1475 gold, combines the reserves and resources of the main Canadian Malartic (CM) and South Barnat deposits with those defined from satellite deposits. This update reports reserves as well as global resources in all categories as of January 1, 2013.

The open pit Proven & Probable gold reserves (using US$1475 gold) now stand at 10.1 million (M) ounces at a fully diluted average gold grade of 1.01 g/t Au, following total production of 588,615 ounces of gold since beginning of operations in 2011. Global Measured and Indicated (M&I) resources above a cut-off grade of 0.31 (Barnat) to 0.34 g/t Au (Canadian Malartic and satellites) stand at 11.70 M ounces gold, and global Inferred resources stand at 1.20 M ounces gold. The global in situ resources include reserves but exclude production.

Reserve estimates using base case US$1475 engineered pit design with 0.31 g/t Au (Barnat) to 0.34 g/t Au (Canadian Malartic and satellites) lower cut-off grade

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. Optimization parameters included:

The strip ratio in the main pit is estimated at 2.27 with average diluted grade of 1.03 g/t Au based on a calculated dilution of 8%. The quoted mineral reserve is exclusive of estimated historical stope crown pillar losses, estimated at less than 150,000 ounces gold. The Charlie zone has also been removed from the reserve statement as it will not be mined due to environmental restrictions.

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

Updated Global Resource Estimates

The global Measured and Indicated ("M&I") resource is 11.70 million ounces of gold at an average undiluted grade of 1.05 g/t Au, with an additional 1.20 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 0.31 to 0.34 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 Estimates

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

• The database comprised a total of 800,252 metres of drilling completed and assayed by Osisko as of the end of November 2012 (core and in-pit RC drilling) on a maximum 25 m x 25 metre grid, as well as 347,352 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 50 g fire assaying-AA finish or gravimetric finish at ALS Chemex laboratories in Val d'Or, Quebec.
• The database also comprised a total of 696,220 assays with an average of 1.38 metre per sample for a total of 961,755 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 10 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 thirty-seven different domains (sixteen in Canadian Malartic, thirteen in South-Barnat and eight in Gouldie).
• 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. 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 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.
• The US$1475 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 Director at Canadian Malartic, and Mr. Robert Wares, Hon. D.Sc., P. Geo. and Chief Geologist of Osisko, 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.

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, 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, access to skilled consultants, mining development and construction personnel, results of exploration and development activities, 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.