April 3, 2012

osiskoRobert Mailhot, Vice-President of Human Resources with Osisko and MNO
President Gary Lipinski shake hands after signing MOU

MNO President Gary Lipinski looks on as MNO Atikokan & Surrounding Area Métis
Council President Marlene Davidson signs the Memorandum of Agreement between
the MNO and Osisko

Participants in the MOU signing: Top left: Bud Dickson; Top left-centre: Martin Griffin,
Osisko Manager of Aboriginal Affairs; Top right-centre: Melanie Paradis, MNO Director
of Lands, Resources & Consultations; Top right: Joe Daze, MNO Coordinator of Lands,
Resources & Consultations
Bottom left: Jerome Girard, Osisko Project Director; Bottom left-centre: Robert Mailhot,
Osisko Vice-president of Human Resources; Bottom right-centre: Gary Lipinski,
MNO President; Bottom right: Marlene Davidson, President of MNO Atikokan
and Area Métis Council

Osisko Mining Corporation (“Osisko” or the “Company”) (OSK:TSX, EWX: Deutsche Boerse) is pleased to announce that its wholly-owned subsidiary, Osisko Hammond Reef Gold Ltd., and the Métis Nation of Ontario (“MNO”) have formally signed a Memorandum of Understanding (“MOU”) to guide their working relationship in regard to the development of the Hammond Reef gold project in northwestern Ontario.

The MOU sets out the way in which the local Métis community, as represented by MNO’s Treaty #3/Lake of the Woods/Lac Seul/Rainy River/Rainy Lake Consultation Committee and the Community Councils that are a part of the Committee, will be consulted regarding the development of the project and commits the parties to working together to address any potential impacts the project may have on Métis rights, interests and way of life. The Consultation Committee is made up of Joel Henley (President, Kenora Métis Council), Alvina Cimon (President, Northwest Métis Council), Marlene Davidson (President, Atikokan Métis Council), the President of Sunset Country Métis Council, the Region One Captain of the Hunt, and Regional Councillor Theresa Stenlund as Chair.

“This agreement is an important step in building a mutually respectful and sustainable relationship between the Métis community and Osisko Hammond Reef Gold Ltd. in relation to the Hammond Reef gold project. It sets out a consultation process through which Osisko Hammond Reef Gold Ltd. can engage with the Métis Community at the local and regional levels in order to better understand Métis rights and interests that may be impacted in the local area around the project, through, amongst other things, completing a traditional knowledge study and a technical review of the project”, said MNO President Gary Lipinski.

Sean Roosen, President and Chief Executive Officer of Osisko added: “The signing of this MOU is the result of a respectful consultation process between the signatories. This agreement represents a milestone in our continuing working relationship with all the local communities in the region and underscores Osisko’s commitment to continue developing a strong relationship with Aboriginal people”.

MNO Regional Councilor Theresa Stenlund, commented, “Our community looks forward to continuing to work with Osisko Hammond Reef Gold Ltd. in a positive and productive manner. The MNO has worked hard with Osisko Hammond Reef Gold Ltd. and we are happy to move forward and are proud of our positive relationship and successful negotiations. There is a real need for economic development in the northwest, and we see MNO’s involvement with Osisko Hammond Reef Gold Ltd. as an opportunity to foster opportunities for Métis businesses and citizens, while protecting our traditional values and way of life.”

Subject to the project impacts on Métis rights and interests (if identified through the consultation process), the parties also agreed to negotiate an IBA based on the goals and objectives of the MOU.

About MNO
The MNO represents the Métis people and Métis communities within Ontario through a province-wide governance structure at the local, regional and provincial levels. For more information on the MNO as well as its framework for government and companies to consult with Métis communities in Ontario visit www.metisnation.org.

About Osisko Mining Corporation
Osisko Mining Corporation operates the Canadian Malartic Mine in Malartic, Québec and is pursuing exploration on a number of properties, including the Hammond Reef gold project in Northern Ontario. On August 13, 2010, Osisko completed its acquisition of Brett Resources Inc.,following a friendly takeover offer announced on March 22, 2010 (Brett then became a wholly-owned subsidiary of Osisko and was renamed “Osisko Hammond Reef Gold Ltd.”). Osisko Hammond Reef Gold Ltd.’s main asset is the Hammond Reef gold project located near Atikokan, Ontario.

Forward-Looking Information
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 including, without limitation, the development of the Hammond Reef project. Although the Corporation believes the expectations expressed in such forward-looking statements are based on reasonable assumptions, including, without limitation that the development of the Hammond Reef project will be achieved, 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, the Corporation’s limited experience with production and development stage mining operations, uninsured risks, regulatory changes or sanctions, defects in titles, 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.