Osisko Discovers New High-Grade Extension in Step-Out Drilling at Hammond Reef DDH 368 intersects 9 metres averaging 17.3 g/t Au included within 84 metres averaging 2.78 g/t Au

MONTREAL, QUEBEC -- (Marketwire) -- 08/12/10 -- Osisko Mining Corporation ('Osisko')(TSX: OSK); (FRANKFURT: EWX) and Brett Resources Inc. ('Brett', BBR - TSX.V) are pleased to announce results from two exploratory step-out holes at the ongoing drilling program at Hammond Reef, located in western Ontario. Highlight drill hole BR-368 intersected 9 metres averaging 17.36 g/t Au, included in a larger intercept of 84 metres averaging 2.78 g/t Au. The Hammond Reef project is 100 percent owned by Brett, which is currently 77.2% held by Osisko and being fully acquired as a result of the recent all-stock bid.

Results from the two new holes are presented in the table below. These holes were designed to explore the down-dip extension of the deposit in an area formerly known as the Gap Zone between sections 2525E and 2725E.

STEP-OUT DRILL HOLES

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Hole No.             Section    From (m)      To (m)  Length (m)      Au g/t

BR-360                 2525E      315.38      329.00       13.62        0.91
And                               402.50      462.50       60.00        0.74

BR-368                 2725E      249.50      333.50       84.00        2.78
including                         306.50      315.50        9.00       17.36
including                         308.41      310.00        1.59       54.20

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Diamond drill hole BR-368 contains higher-grade mineralization between 306.5 and 315.5, which when a top cut of 30g/t gold is applied, averages 9 metres of 13.08 g/t Au (and 84.0 m at 2.32 g/t Au). This higher grade interval does not include 'pinch and swell' vein-type mineralization, but rather disseminated gold and pyrite in an area of strong carbonatization, which suggests potential exists for significant volumes of higher grade material.

These two step-out holes indicate the potential for a 200 to 250 metre-long down-dip extension to the known deposit, along a 200 metre strike length between sections 2525E and 2725E. When combined with recently reported extensions along sections 1320E to 1670E (see Aug. 9 2010 press release), these holes confirm the potential for down-dip extensions to the deposit for 200 to 400 metres (true length) beyond the known resource volume and along a minimum strike length of 1400 metres.

The current drill program at Hammond Reef comprises mostly definition drilling within the known resource volume as well as exploration/step-out holes in the immediate area of the deposit. Osisko is in the process of expanding the drill program, which will include definition drilling on 50 by 25 metre grid along the 2.5 kilometre strike length of the known deposit (sections 1050E to 3550 E), as well as larger scale step-out holes along strike and down-dip, designed to define the outer limits of the deposit.

About Hammond Reef

Osisko and Brett are presently focused on upgrading and expanding gold resources at the 100%-owned Hammond Reef Gold Deposit, located near Atikokan, Ontario. A Preliminary Assessment Study was completed on the Hammond Reef deposit on November 12, 2009 and filed on SEDAR, resulting in an Inferred Mineral Resource of 6.70 million ounces of gold (259.4 million tonnes grading 0.80 grams per tonne (g/t) gold at a cut-off grade of 0.30 g/t, which relates to the economic cut-off in the PA Study). The deposit remains open along strike and at depth and over 97% of this resource is within 300 metres of surface. For additional details of the resource estimates at Hammond Reef please refer to the November 12, 2009, July 23, 2009 and October 15, 2008 news releases of Brett Resources Inc.

All NQ core assays reported above were obtained by standard 30 g fire assaying-AA finish or gravimetric finish at ALS Chemex laboratories in Thunder Bay, Ont., and North Vancouver, B.C., ISO/IEC guideline 17025-accredited facilities. Reported drill core weighted averages were calculated using a minimum of 0.40 g/t Au over successive maximum intervals of 20 metres with an upper cut-off of 30 g/t Au where indicated. Lost core within mineralized intersections were incorporated as blank intervals and assigned a 0.001 g/t grade in all length weighted calculations.

Osisko follows strict QA-QC protocol measures in keeping with industry standards and regulatory reporting requirements. Mr. Sergio Cattalani, PGeo. and Vice-President Exploration of Osisko and Brett, and Mr. John Zbeetnoff, PGeo, 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.

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 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 Osisko and Brett (collectively the 'Parties') expect 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, the commencement of commercial production. Although the Parties believe 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 warrant further development of the Hammond Reef Project, 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 personnel, results of exploration and development activities, the Parties' 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 Osisko's most recent Annual Information Form and in Brett's most recent Management Discussion and Analysis filed on SEDAR, which also provide additional general assumptions in connection with these statements. The Parties caution that the foregoing list of important factors is not exhaustive. Investors and others who base themselves on the Parties' forward-looking statements should carefully consider the above factors as well as the uncertainties they represent and the risk they entail. The Parties believe 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


Osisko Mining Corporation

Sylvie Prud'homme

Investor Relations

514-735-7131

Toll Free: 1-888-674-7563
www.osisko.com