Osisko Reports Preliminary Metallurgical Results on Barnat

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MONTREAL, QUEBEC--(Marketwire - Feb. 26, 2009) - Osisko Mining Corp. (TSX:OSK)(FRANKFURT:EWX) is pleased to report the following preliminary results from the metallurgical program on the South Barnat deposit, located northeast of its 100% owned Canadian Malartic gold deposit.  A NI 43-101 compliant inferred resource of 2.03 million ounces of gold (36.3 Mt grading 1.74 g/t Au) was recently announced for South Barnat (see January 26, 2009 press release).

Overall recovery from 42 individual leach tests of the direct whole ore cyanidation process is confirmed at an average of 92% (range of 86.6% to 97.2%) from composite samples representing the main lithologies of the deposit at an average head grade of 1.92 g/t Au (range of 0.74 to 7.64 g/t Au) and prepared to 80% minus 60 microns grind size.  The table below summarizes the results for the various lithological composites (averages for 6 composites per lithology):


Composite             Consumption          Average 
type                     kg/tonne    Au Extraction      Residue       Head
(Avg. 6 composites)   NaCN    CaO                %       Au g/t     Au g/t
Piche porphyry 1      0.37   0.21             89.4         0.19       1.80
Piche porphyry 2      0.42   0.21             91.3         0.08       0.98
Piche porphyry 3      0.25   0.23             93.6         0.23       4.24
Piche mixed           0.50   0.16             94.5         0.12       2.16
Piche ultramafic 1    0.40   0.38             93.9         0.09       1.41
Piche ultramafic 2    0.19   0.26             93.9         0.06       0.95
Pontiac mixed         0.49   0.28             87.0         0.25       1.90


The Piche composites refer to mineralized porphyry and serpentinized ultramafics located within the Cadillac fault zone; the mixed composites consisted of 35% porphyry and 65% ultramafics. The Pontiac mixed composites refer to 70% mineralized metasediments and 30% porphyry, all located south of the fault.  Overall recoveries are thus far superior to those obtained in the Canadian Malartic deposit (average of 84% for head grade of 1.0 g/t Au), which was anticipated since pyrite-gold mineralization appears coarser grained at Barnat.  Petrographic studies have been initiated on mineralized samples to establish specifics of gold mineralization at South Barnat and confirm the preliminary metallurgical results that indicate South Barnat ore will be compatible with the processing circuit at Canadian Malartic.

Preliminary grinding tests on Barnat composites indicate a Bond Working Index (BWI) of 16.6 kwh/t for Pontiac mineralized metasediments and a BWI of 14.4 kwh/t for Piche mineralized porphyry (average BWI of 15.0).  This compares well with an average BWI of 15.7 kwh/t for Canadian Malartic ore, as reported in the published Feasibility Study.

Additional metallurgical test work will focus on Pontiac mineralized metasediments, especially silicified sediments, as these are now known to contain a significant proportion of the inferred resource at South Barnat.

Sean Roosen, President and CEO of Osisko, commented:  "These encouraging metallurgical test results at South Barnat are the foundation for another significant milestone in the development of the Canadian Malartic project. The results to date indicate that South Barnat mineralization would yield satisfactory, if not superior, recoveries if blended into the processing circuit designed for the Canadian Malartic deposit. Additional definition work is ongoing at South Barnat, both on the resource front and the metallurgical front, with the objective of establishing a Measured and Indicated resource as well as definitive gold recoveries at South Barnat by mid-Q2 2009."

All metallurgical and grinding test work is being carried out by SGS Lakefield Research on composite samples prepared from fresh NQ core taken throughout the deposit to provide representative combination of all ore types and lithologies that will be encountered in the actual mining operation.

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 and exploration campaign. Eight drills are currently working on the property, with five dedicated to completing the 130,000 metre infill drilling on the South Barnat Zone by the end of February.

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. The NI 43-101 compliant inferred resource estimate for South Barnat was released on January 26, 2009 and the technical report has been filed on SEDAR on February 17, 2009.

Mr. Denis Cimon, Eng. M.Sc. and Manager of Mineral Processing for Osisko, and Mr. Robert Wares, P. Geo. and Executive Vice-President of 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 including the sampling, analytical and test data underlying the technical information.

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.

Osisko Mining Corporation
John Burzynski
Vice-President Corporate Development
Osisko Mining Corporation
Daniel Boase
Investor Relations
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