Osisko Declares Commercial Production at Canadian Malartic

MONTREAL, QUEBEC--(Marketwire - June 21, 2011) - Osisko Mining Corporation (TSX:OSK)(FRANKFURT:EWX), the Board of Directors, management and staff are very proud to announce the declaration of commercial production at their flagship Canadian Malartic Mine located in Malartic, Quebec.

Sean Roosen, President and Chief Executive Officer, commented on reaching this major milestone: "It is our great pleasure to report that our gold milling plant has processed an average of 33,300 tonnes per day during the 30-day period ending June 17, 2011. Our operating team has been successful in ramping up production rapidly and we are seeing steady progress on a daily basis in all facets of our operations. The rapid development of the Canadian Malartic Project from exploration to commercial production is a tribute to the hard work, dedication and expertise of our employees and contractors. With great pride we present Canada's newest and largest commercial gold mine".

Commercial production is determined within the gold industry as the first continuous 30 day period of plant operation at a rate of 60% of design capacity, which is 33,000 tonnes per day for the Canadian Malartic Mine. Accordingly, the first day of commercial production was May 19, 2011.

Milling Operations

Construction of the mill was completed in the first quarter. Following a water and waste rock testing period, ore was introduced into the mill in late March 2011. The first gold pour occurred on April 13, 2011.

Production statistics since introducing ore at the mill are as follows:

* Estimated partial month figures.

Production ramp up is progressing on a steady basis at the milling plant with an average throughput so far in June of 38,913 tonnes, including an average daily rate of 40,800 tonnes within the last ten days. The highest throughput day so far in the month of June was 45,143 tonnes.

Recovery rates are currently higher than anticipated, mainly due to higher retention time in the leach circuit and a better size fraction as the mill has not yet been brought up to full throughput capacity. The mill is being fed from a combination of stockpiles and run-of-mine ore. To date, the grade of ore being introduced into the mill has been below the overall reserve grade of the deposit; this was intentional as commissioning protocols were being completed and also reflected contour mining in lower grade areas of the deposit to set the first bench of the pit. To date, the ore mined corresponds very well with the reserve block model.

During the next six months, the operating focus will be on various operational functions to achieve the full design capacity of 55,000 tonnes per day and optimizing the operating performance.

Mr. Roosen added: "Achieving commercial production ahead of schedule (initially planned for August) is another great accomplishment for our team, and we are now focused on continuing to maximize both our operations and shareholder value."

Key project milestones to date:

Second Quarter Release

Osisko is expected to release its financial results for the second quarter on August 12, 2011.

About Osisko Mining Corporation

Osisko Mining Corporation operates the Canadian Malartic Gold Mine in Malartic, Quebec and is pursuing exploration on a number of properties, including the Hammond Reef Gold Project in Northern Ontario. Canadian Malartic's production is 100% unhedged.

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 including, without limitation, increasing of throughput at the mill to achieve design capacity, improving mill feed grade, maintaining recovery rates and increasing gold production. Although the Corporation believes the expectations expressed in such forward-looking statements are based on reasonable assumptions, including, without limitation that the diligent ongoing optimizing of its operations will be achieved and will, accordingly, improve its operating performance, 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, the Corporation's limited experience with production and development stage mining operations, uninsured risks, regulatory changes or sanctions, defects in titles, 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.