Osisko Deposits the First Tranche of Its Financial Guarantee Covering the Entire Cost of Rehabilitating the Canadian Malartic Site A first in the Quebec mining industry

MONTREAL, QUEBEC -- (Marketwire) -- 10/17/11 -- Osisko Mining Corporation ('Osisko' or the 'Company') (TSX: OSK)(FRANKFURT: EWX) is proud to announce it has deposited the amount of $22.1 million with the Quebec Government, representing 50 % of the financial guarantee of $44.2 million, to cover the entire future cost of rehabilitating its new Canadian Malartic mine site in the Abitibi region of Quebec. The balance of the guarantee will be remitted as two subsequent payments of $11.05 million each, to be made on or around September 1, 2012 and September 1, 2013.

A first in Quebec

For the first time in the history of Quebec mining, and even though it is not yet required by law, the financial guarantee will cover 100% of the estimated costs of rehabilitating the future mine site instead of the 70% currently required by law. Osisko originally announced its commitment to provide the entire amount back in 2009.

'Since the beginning of our project, we understood and accepted that such a commitment would constitute a moral obligation, even though it is not yet a legal obligation', commented Jean-Sebastien David, Vice-President Sustainable Development of Osisko. 'Not only does this new way of doing things reflect our socially responsible attitude as a corporate citizen, we also feel it is quite simply the most sensible thing to do.'

The payment schedule ensures that from this point forward, the financial guarantee deposited will cover any future liabilities incurred by an unforeseen closure of the mine, regardless of the reason. For example, it is estimated that if the mine were to close today, the rehabilitation costs would be approximately $8 million, which is more than covered by the current $22.1 million deposit.

Financial guarantee to be frequently re-assessed

The amount of the guarantee was determined using a rehabilitation plan approved by the Quebec ministries of Sustainable Development and Parks ('MDDEP') and Natural Resources and Wildlife ('MRNF'). This plan has already been submitted to the Canadian Malartic Mine Monitoring Committee and will be presented to the citizens of Malartic.

The guarantee will be re-assessed every three years, or more often if necessary; for example, in the case where adjustments to the mining operations justify changes to the rehabilitation plan. 'This frequency allows us, among other things, to improve our rehabilitation plan and take advantage of emerging technological innovations,' explained Jean-Sebastien David, 'and it also means we can adjust our financial guarantee to keep pace with inflation.'

'This new approach ensures that, regardless of the scenario, the entire cost of rehabilitating the site will be assumed by Osisko and never by Quebec taxpayers,' added Jean-Sebastien David. 'No matter what happens, neither the government of Quebec nor its taxpayers will be required to foot the bill for rehabilitating our site'.

About Osisko

Founded in 1998, Osisko is headquartered in Montreal, Quebec. Devoted primarily to mineral exploration at the onset, the Company later transitioned into a producer, with the development of the Canadian Malartic Mine. Osisko continues exploration activities in the Abitibi area of Quebec, and elsewhere in Canada and around the world.

Osisko employs more than 700 individuals.

Contacts:

Helene Thibault

Director of communications

(819) 856-9143
www.osisko.com


Sylvie Prud'homme

Director of Investor Relations

(514) 735-7131

Toll free: 1-888-674-7563