Osisko Announces Revised Mine Production Plan at Canadian Malartic

MONTREAL, QUEBEC--(Marketwire - April 28, 2011) - Osisko Mining Corporation (TSX:OSK)(FRANKFURT:EWX) ("Osisko") is pleased to provide a revised summary of the annual mine production plan for its 100%-owned Canadian Malartic project. This new plan is based on the $US1000 gold reserve estimate of 10.71M ounces gold that was recently disclosed (see March 31, 2011 press release). G Mining Services of Montreal are the independent consultants for Osisko who have authorized the release of the following plan. Highlights include:

• Gold production (which started this month) will total 1.02 M ounces over the next 18 months;

• Recoverable gold has increased by 1.46 M ounces to 9.18 M ounces (at 85.8% recovery) from the previously disclosed figure of 7.72 M ounces (at 86.1% recovery; see February 10, 2010 press release).

• Mine life has increased 31 percent (3.8 years) to 16.0 years, based on a 55,000 tonnes per day (tpd) milling rate that will increase to 60,000 tpd in mid-2012.

• Average of 625,000 oz. per year gold production during the first full five years (2012-2016);

• Average of 574,000 oz. per year gold production during 16-year life of mine.

Sean Roosen, President and CEO, noted: "We are very pleased to present our shareholders with this updated mine plan that is based on the latest engineered pit and new reserve estimates of 10.7 M ounces gold. The reserve and resultant mine schedule are based on $US 1000 oz. gold price, which is 33 percent less than current spot price. Start-up and commissioning are going very smoothly at Canadian Malartic and production has commenced on a 24-hour per day basis with six doré bars poured to date. Studies are under way to ramp up production to 65,000 tonnes per day in 2013, which will have the effect of boosting annual production. We are continuing our intensive drilling program on the Canadian Malartic property and expect to continue to bring in additional reserves in the coming years".

The updated summary of the annual mine production plan at the previously-established milling rate is outlined in the following table:

New Annual Mine Production Estimates based on 55,000 to 60,000 TPD Mill Rate*

Mine life is estimated at 16.0 years, based on a 55,000 tonnes per day (tpd) milling rate that will increase to 60,000 tpd in mid-2012. Mine production daily rate, including waste, is being estimated at an average of 194,000 tpd, an increase of 24,000 tpd over the previously disclosed figures (see February 10, 2010 press release). The deposit will be mined by conventional open pit mining methods using an initial fleet of twelve 227-tonne haul trucks, two electric hydraulic shovels, and various ancillary equipment to support the mining operations. The fleet will be ramped up in subsequent years according to the requirements of the mining plan. The waste to ore ratio is estimated at an average of 2.27 to 1.

Total gold production over life-of-mine is currently estimated at 9.18 million ounces gold, at an average production rate of 574,000 ounces per year. The first full five years of production would account for 3.13 million ounces of production at an average rate of 625,100 ounces per year. Economic parameters, including updated mining and processing costs over life-of-mine, will be disclosed in an upcoming press release toward the end of May 2011.

These reserve estimates and mine schedule assume that all necessary authorizations will be obtained in order to begin mining the South Barnat portion of the deposit by 2014. Permitting work is continuing to include the mining authorizations for South Barnat and the deviation of Highway 117 by 2012, with the goal of minimizing the section of the highway to be relocated and reducing the social impact on the community.

Mr. Louis-Pierre Gignac, Eng. of G Mining Services Inc. and Mr. Paul Johnson, Eng. and General Manager of Technical Services for 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.

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 the Corporation 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. Although the Corporation believes the expectations expressed in such forward-looking statements are based on reasonable assumptions, including, without limitation that all technical, economical and financial conditions will be met in order to put the Canadian Malartic Project into commercial production, 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 mill production personnel, results of exploration and development activities, the Corporation's limited experience with production and development stage mining operations, uninsured risks, regulatory 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 the Corporation's most recent Annual Information Form filed on SEDAR, which also provides additional general assumptions in connection with these statements. The Corporation cautions that the foregoing list of important factors is not exhaustive. Investors and others who base themselves on the Corporation's forward-looking statements should carefully consider the above factors as well as the uncertainties they represent and the risk they entail. The Corporation 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.