Osisko Reports Fire Damage at Canadian Malartic Mill Limited to Cyclone Number Four Area

MONTREAL, QUEBEC--(Marketwire - May 10, 2012) - Osisko Mining Corporation (the "Company" or "Osisko") (TSX:OSK)(FRANKFURT:EWX) follows up on the earlier report of a fire at the Canadian Malartic Mill, and provides the following information update. A full assessment is in progress, and further details will be disseminated as they become available.

Preliminary indications are that the fire at Canadian Malartic was started by welding in proximity to the number four cyclone area and spread to the mill roof of that sector. The fire began at 11:50 pm yesterday, and was extinguished at approximately 4:30 am this morning. Proper emergency procedures were followed and there were no injuries to staff or emergency workers during the incident. No industrial chemicals or toxic gases were released during the fire.

As of 7:30 am this morning, staff began assessing damage. All staff are currently back at work on site, and regular mining activities are continuing in the pit outside the mill area. Mining operations continue on a normal schedule today.

Initial reports from site indicate the fire was contained around the number four cyclone and immediate area. Preliminary observations are as follows: the mill utilizes four cyclone sets - the number four cyclone set is damaged; the overhead crane in the cyclone bay is damaged; there is limited damage to the overhead crane in the ball mill bay; there is damage to the structure of the roof area above the cyclone bay; there is some limited damage to the wall of that bay. There appears to have been no damage to the SAG or ball mills and other systems of the mill.

Preliminary assessment indicates that the mill will be shut down for a period of approximately two to three weeks as a result of the fire. Osisko will be using this downtime to advance maintenance operations at the Canadian Malartic mill. The Canadian Malartic operation is covered by property damage insurance subject to a $250,000 CAD deductible, and business interruption insurance subject to a 20-day equivalent deductible.

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.

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, consequences of this incident on operations at Canadian Malartic and resumption of operations. Although Osisko believes the expectations expressed in such forward-looking statements are based on reasonable assumptions, including, without limitation, that all technical conditions will be met in order to proceed diligently with resumption of milling activities at Canadian Malartic however 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 access to skilled consultants, mining development and construction personnel, Osisko's limited experience with production and development of operations, uninsured risks, regulatory framework and changes, availability of personnel, materials and equipment, actual performance of facilities, equipment and processes relative to specifications and expectations, 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.