Osisko Announces Revised Mine Production Plan at Canadian Malartic Gold Production Forecast at 1.02M ounces over next 18 months

MONTREAL, QUEBEC -- (Marketwire) -- 04/28/11 -- 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 dore 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(i)

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            Ore   Waste           Ore  Grade Processed  Recovery Recovered
          Mined   Mined Strip  Milled  (g/t)      Gold       (%)      Gold
Period     (Kt)    (Kt) Ratio    (Kt)             (oz)                (oz)
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2011     11,676  27,592  2.36  13,305   0.99   423,703      84.8   359,477
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2012     29,494  63,649  2.16  21,050   1.15   778,379      85.1   662,137
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2013     27,853  65,214  2.34  21,900   1.06   749,025      84.4   632,357
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2014     26,134  56,394  2.16  21,900   1.01   707,738      83.9   593,953
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2015     21,793  58,021  2.66  21,900   1.01   712,033      85.4   608,378
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2016     18,498  60,913  3.29  21,900   1.02   718,105      87.6   628,725
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2017     23,699  55,873  2.36  21,900   0.97   682,535      85.2   581,822
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2018     21,843  57,507  2.63  21,900   1.03   724,880      87.5   634,386
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2019     18,739  60,881  3.25  21,900   0.97   685,867      88.3   605,948
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2020     19,787  60,079  3.04  21,900   0.90   632,701      87.0   550,677
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2021     20,331  59,391  2.92  21,900   0.91   643,088      87.3   561,212
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2022     21,704  58,157  2.68  21,900   0.65   460,168      83.5   384,441
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2023     18,713  39,188  2.09  21,900   0.96   675,349      87.2   588,972
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2024     21,473  28,816  1.34  21,900   0.96   678,610      86.1   584,183
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2025     21,154  14,430  0.68  21,900   0.96   673,329      84.7   569,977
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2026     18,146  10,676  0.59  21,900   0.99   697,368      84.0   585,675
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2027        569     182  0.32   2,736   0.71    62,550      82.3    51,502
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Total/a
 vg.    341,606 776,963  2.27 343,691   0.9710,705,428      85.8 9,183,822
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(i)Mill feed in a given year may include stockpiled ore.

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.

Contacts:

Osisko Mining Corporation

John Burzynski

Vice-President Corporate Development

(416) 363-8653
www.osisko.com


Osisko Mining Corporation

Sylvie Prud'homme

Investor Relations

(514) 735-7131

Toll Free: 1-888-674-7563