Dios Exploration

OSISKO AND DIOS DISCOVER NEW GOLD SHOWINGS

ON THE AU33 WEST PROJECT

(Montreal, December 22, 2011) Osisko Mining Corporation (the Company or Osisko) (OSK: TSX, EWX: Deutsche Boerse) and Dios Exploration Ltd (Dios, DOS: TSX-V) 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).