Osisko and DIOS Discover New Gold Showings on the AU33 WEST Project

MONTREAL, QUEBEC -- (Marketwire) -- 12/22/11 -- Osisko Mining Corporation (the 'Company' or 'Osisko') (TSX: OSK)(FRANKFURT: EWX) and Dios Exploration Ltd ('Dios')(TSX VENTURE: DOS) are pleased to announce the results of the 2011 sampling program on the AU33 WEST property, situated south of Eastmain River in the James Bay region of Quebec. The work revealed outcropping gold showings in a felsic (tonalite-granodiorite) intrusive complex, with 34 of the mineralized outcrops concentrated in an 18-km2 area. All the showings yielded values above 100 ppb gold (0.1 g/t Au), and seven yielded between 1.58 g/t and 23.6 g/t Au. These anomalous values represent 13% of the 260 samples collected from this part of the property.

A two-month prospecting program was carried out on the AU33 WEST property in 2011, targeting the felsic (tonalite-granodiorite) igneous complex, the diorites and the volcanic belts found up-ice of gold-bearing till dispersal trains and boulders defined by DIOS' earlier work. In all, 807 outcrops from across the property were described, sampled and analyzed for gold.

The outcropping auriferous mineralization comprises 1-2% pyrite as disseminations and fracture fillings, locally accompanied by minor chalcopyrite and malachite, and is associated with potassic alteration. The gold-bearing outcrops were found up-ice of a NE-to-SW glacial dispersal train using historical data and DIOS' data for auriferous till and boulders.

The gold values are associated with silver grades and generally copper as well, in addition to bismuth and molybdenite, suggesting a porphyry-type deposit. The individual outcrops remain open laterally and at depth, and future work will focus on detailed prospecting, stripping, channelling and drilling to better define the nature and extent of the mineralization.

The style of mineralization (disseminated, not vein-hosted) and metal association suggest potential for a low-grade bulk tonnage porphyry gold deposit on the property.

Osisko has the option to acquire a 51% undivided interest in the AU33 WEST property by incurring $5,000,000 in exploration expenditures and making cash payments of $700,000 during a five-year period. Osisko has the option to acquire an additional 9% participating interest in exchange for $9,000,000 of additional exploration expenditures during an additional five-year period, each million dollars ($1,000,000) of additional expenditures increasing Osisko's interest by 1%. And finally, Osisko also has the option to acquire an additional 10% interest by solely funding a feasibility study pertaining to the AU33 WEST property within a time period equal to the lesser of: (i) the remaining time before expiry of the second option period, and (ii) a period of two years. Osisko will be Project Manager during the option period.

Osisko follows strict QA-QC protocol measures in keeping with industry standards and regulatory reporting requirements. All assays reported above were obtained by standard 50-g fire assay with AA or gravimetric finish (method Au-AA24) and a multi-element package applied to selected samples (method ME-ICP 41) at the ALS Chemex laboratories in Val-d'Or, Quebec. This news release was prepared by J. Berge, Jr. Eng., and approved by Louis Caron, P.Geo., the Qualified Person (43-101).

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, further development of the AU33 WEST project. Although Osisko 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 warrant further development of the AU33 WEST 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, results of exploration and development activities, uninsured risks, regulatory changes, defects in title, availability of personnel, materials and equipment, timeliness of government approvals, 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.

Contacts:

John Burzynski

Vice-President Corporate Development

(416) 363-8653
www.osisko.com


Sylvie Prud'homme

Director of Investor Relations

(514) 735-7131

Toll Free: 1-888-674-7563