Osisko Discovers New Mineralized Zone Adjacent to South Barnat

MONTREAL, QUEBEC -- May 21, 2009 - Osisko Mining Corporation ("Osisko") (TSX: OSK) (FRANKFURT: EWX) is pleased to announce the discovery of a new mineralized zone adjacent to the South Barnat deposit. The new zone has thus far been intersected in three holes that yielded the following results:

Hole No.	Section	From (m)	To (m)	Length (m)	Au g/t
BA09-3581	550E	18.9	39.0	20.1	6.17
including		27.0	28.5	1.5	25.60
BA08-3426	575E	16.0	57.6	41.6	8.36
including		30.0	34.2	4.2	41.40
BA09-3594	600E	59.5	122.0	62.5	7.70
including		86.5	91.0	4.5	49.20

The new zone is located approximately 50 metres north of South Barnat between sections 550E and 600 E. The discovery contains a new style of mineralization not previously observed at either Canadian Malartic or South Barnat, consisting of high-grade quartz-pyrite breccias replacing ultramafic rocks with abundant fine visible gold. Orientation and geometry of the new zone are presently unknown, however, it is open at depth and appears to be plunging to the southeast. Assuming a subvertical dip, the true width of this zone may range between 15 and 28 metres.

This discovery is the result of definition drilling in peripheral areas of the South Barnat deposit, designed to test material immediately around the known deposit that would be included in a potential open pit engineered to mine the deposit. The definition drill program on South Barnat has been completed and was focused on an 850 metre-long grid oriented northwest-southeast with drill sections spaced 25 metres apart. The grid was extended an additional 250 metres east for this program, and this extension was drilled along sections spaced 50 metres apart. A NI 43-101 compliant inferred resource estimate of 2.0 million ounces for South Barnat was released on January 26, 2009 and the technical report was filed on SEDAR on February 17, 2009. The current definition drill program will lead to a NI 43-101 compliant Measured and Indicated resource estimate for South Barnat, to be released in May 2009, with a pit-constrained estimate to be released in June 2009.

Drilling to date suggests that the minimum strike length of the South Barnat Zone is 1050 metres with an average true width between 20 and 120 metres. The mineralized zone is open along strike to the east, where it merges with the former East Malartic Mine and where recent drilling has indicated a possible extension over an additional 150 metres. South Barnat extends to depths of 250 to 400 metres in the central portion, where the system is still open at depth. Estimated depth in the northwestern third of the deposit is 130 to 200 metres.

All NQ or HQ core assays reported above were obtained by standard 50 g fire assaying-AA finish or gravimetric finish at ALS Chemex laboratories in Val d'Or, Quebec. Reported weighted averages were calculated using a minimum of 0.50 g/t Au over successive maximum intervals of 20 metres with no upper cut-off of individual assays. Intersected drifts or lost core within mineralized intersections were incorporated as blank intervals.

Osisko Mining Corp. is currently developing the Canadian Malartic gold deposit and adjacent mineralized zones into a large-scale open pit, bulk-tonnage mining operation. The Company is well-funded and is carrying out an aggressive definition drilling, exploration and development campaign. A NI 43-101 compliant, 7.7 million ounce gold Measured and Indicated global resource on the main Canadian Malartic gold deposit was released on September 8, 2008 and the technical report has been filed on SEDAR. This includes a NI 43-101 compliant, 6.3 million ounce gold Reserve estimate released in the Feasibility Study on the main Canadian Malartic gold deposit on November 25, 2008, for which the technical report has been filed on SEDAR. These estimates did not include the South Barnat Zone or any other mineralized zone located outside the main deposit that is currently being evaluated by Osisko.

Mr. Robert Wares, P. Geo. and Executive Vice-President of Osisko, is the Qualified Person who has reviewed this news release and is responsible for the technical information reported herein, including verification of the data disclosed including the sampling, analytical and test data underlying the technical information.

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 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 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.

CONTACT INFORMATION:

Osisko Mining Corporation
John Burzynski
Vice-President Corporate Development
514-735-7131
www.osisko.com

or

Osisko Mining Corporation
Daniel Boase
Investor Relations
416-742-5600
Toll Free: 1-866-580-8891

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Renmark Financial Communications Inc.
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