Q2 Highlights

• Gold production of 92,003 ounces, a new quarterly record;
• Operating cash flow of $55.7 million;
• Record mill throughput and mined tonnage.

Mine operating profits during the second quarter totaled $41.0 million compared to $1.6 million in the corresponding period in 2011. The Canadian Malartic mine commenced commercial production on May 19, 2011 and prior to that date results were capitalized. Record gold production of 92,003 ounces was achieved despite a fire at the mill processing facility, which affected mill throughput during a 10-day period in May 2012.

During the first half of 2012, the Canadian Malartic mine generated a profit of $111.5 million and Osisko generated a net profit of $42.6 million ($0.11 per share). In the corresponding period of 2011, the mine generated a profit of $1.6 million in its first 43 days of commercial production while the Company incurred a loss of $29.1 million ($0.08 per share).

Sean Roosen, President and Chief Executive Officer of Osisko, commenting on the second quarter performance: “We made good progress on the various ramp up issues during the quarter, including the improved performance of our first FLSmidth XL2000 cone crusher. Mine productivity was affected by inefficiencies in blasting cycles, which led to lower excavation rates and an increase in wear on equipment. The issue was due to faulty boosters, which resulted in a number of misfired blast holes. The problem has since been mitigated, however the company is in discussion with the explosive contractor and Osisko has indicated the intent to file a claim to be reimbursed for the increased costs incurred and production losses. With the completion of the secondary crusher installation, we expect to see a significant increase in throughput and gold production in Q3, coupled with a significant decrease in costs.”

Operating cash flow amounted to $55.7 million for the quarter and $134.4 million for the first half, compared to $15.0 million in the second quarter of 2011 and a shortfall of $5.6 million in the first six months of 2011. Investments in mining assets totaled $131.6 million for the first half.

The mine operating statement for the production period is as follows:

The increased costs in the second quarter are attributable to:

1. Higher tonnage milled (9.1% compared to Quarter 1, 2012);
2. Continued ramp-up costs with respect to the first unit of the secondary cone crusher;
3. Inefficiencies in the blasting cycle which impacted mining productivity; and
4. Higher than anticipated utilization of contractors.

Key operating results

(in thousands of Canadian dollars, unless otherwise noted)

The production statistics since commencement of commercial production on May 19, 2011 are as follows:

Mill operating statistics continue to show progress.

Osisko’s focus for the balance of 2012 will be:

1. Complete planned mill modifications with the installation of the second pebble crusher;
2. Stabilize the operating circuit to reach throughput design capacity of 55,000 tonnes per day;
3. Improve productivity of the mine;
4. Focus on optimization of operations and unit cost reduction.

Net earnings for the quarter amounted to $13.3 million compared to a loss of $23.8 million in 2011. The variance is attributable to higher gold sales as the mine is continuing its ramp up process since commencing operations on May 19, 2011, lower general and administration costs which were offset by higher financing costs as in 2011 the interest costs were capitalized and higher tax charges due to earnings. The 2011 results also included a write-down of $10.9 million following the abandonment of the Duparquet project.

The higher year-to-date profit of $42.6 million compared to a loss of $29.1 million in 2011 is mainly attributable to a full six months of operations at Canadian Malartic in 2012 and improved gold price.

Improved Financial Flexibility

During the quarter, the Company amended its $150 million credit facility with CPPIB Credit Investments Inc. (“CPPIB”), a wholly-owned subsidiary of the CPP Investment Board, with CPPIB making available to the Company an additional $100 million delayed draw term loan. The key terms of the amendment are as follows:

• The initial cash repayment schedule has been extended by one year to June 30, 2013. The reimbursements are based on 50% of free cash flow up to $60 million per annum.
• CPPIB will make available a delayed draw term loan of $100 million for working capital and general corporate purposes. Osisko may draw funds under this facility in $20 million increments, and any funds outstanding are reimbursable by December 31, 2013. There are no standby fees related to this tranche.

As part of the agreement, Osisko has agreed to reduce the strike price of share purchase warrants to $10 for Tranche A (was previously $10.75) and Tranche B (was previously $19.25). Of the total 12.5 million of warrants, 5.5 million Tranche B warrants can be accelerated at Osisko’s discretion if the share price trades at a 50% premium to the exercise price for a period of 15 days. Tranche A warrants expire on September 24, 2014 and Tranche B warrants are set to expire on December 31, 2015.

A summary of the Company’s financial position is as follows:

Exploration and Development

The Company continues to conduct exploration work on a regional basis around the Canadian Malartic infrastructure for additional resources and reserves, and is pursuing definition drilling at its Hammond Reef development project. At Hammond Reef, the Company has initiated various studies necessary for the Project Feasibility Study, which is expected to be completed in late 2012. The Minister of Environment of Ontario has approved the Terms of Reference for the Environmental Impact Assessment.

Osisko continues to aggressively pursue growth in its reserve and resource base, with some 81,000 meters drilled on its various projects during the quarter.

Osisko also entered into various agreements in 2012 to add to its project base:

• An option agreement with Global Geoscience Ltd. whereby Osisko can acquire an initial 45% interest in five Nevada gold properties by expending US$8 million in exploration over a four year period and subscribing for 14.2 million shares at an issue price of $0.06 per share for a total of $912,000. Osisko can acquire an additional interest of 25% in any property (for a total interest of 70%) by completing a bankable feasibility study on such property.
• An option agreement with Tri Origin Exploration Ltd. whereby Osisko can acquire an initial 51% interest in the Red Lake Extension property located in NW Ontario, by expending $5 million in exploration over a four year period, by paying Tri Origin a total of $800,000 in cash during the period and by subscribing for 5 million ordinary shares in Tri Origin at an issue price of $0.07 per share for a total of $350,000. Osisko can acquire an additional interest of 14% in any property (for a total interest of 65%) by completing a bankable feasibility study.

The Company has opened a regional exploration office in Denver, Colorado in order to enhance its activities in the USA.

The Company is also pursuing various initiatives to build its project base in Latin America.

Non-IFRS Financial Performance Measures

The Company has included certain non-IFRS measures including “cash cost per ounce” and “cash margin per ounce” to supplement its financial statements, which are presented in accordance with International Financial Reporting Standards (“IFRS”). Refer to the Company’s Management Discussion and Analysis for the three months ended June 30, 2012.

Q2 Conference Call Information

Osisko will host a conference call on Friday, August 10^th at 8:00am EDT, where senior management will discuss the financial results and provide an update of the Company’s activities. Those interested in participating in the conference call should dial in at (416) 981-9012 (Toronto local and international), or 1-800-909-4792 (North American toll free). An operator will direct participants to the call.

The conference call replay will be available from 10:00 a.m. EDT on August 10, 2012 until 11:59 p.m. EDT on August 25, 2012 with the following dial in number: (416) 626-4100 or Toll-free 1-800-558-5253, access code 21599128.

About Osisko Mining Corporation

Osisko Mining Corporation operates the Canadian Malartic gold mine in Malartic, Quebec and is pursuing exploration on a number of properties, including the Hammond Reef Gold Project in Northern Ontario.

Mr. Luc Lessard, Eng., Senior Vice-President and Chief Operating Officer of Osisko, is the Qualified Person who has reviewed this news release and is responsible for the technical information reported herein, including verification of the data disclosed.

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.

For further information in relation to the Hammond Reef project, please refer to the “Technical Report on the Hammond Reef Gold Property Atikokan area, Ontario” dated December 20, 2011. For further information in relation to the Canadian Malartic project, please refer to the “Feasibility Study – Canadian Malartic Project (Malartic, Quebec)”, dated December 2008. Both of these reports are available under the Osisko profile atwww.sedar.com.

Note Regarding Certain Measures of Performance

This press release contains certain non-IFRS measures, including “cash cost per ounce” and “cash margin per ounce”. The Company believes that these measures, together with measures determined in accordance with IFRS, provides investors with an improved ability to evaluate the underlying performance of the Company. Non-IFRS measures do not have any standardized meaning prescribed under IFRS, and therefore they may not be comparable to similar measures employed by other companies. The data is intended to provide additional information and should not be considered in isolation or as a substitute for measures of performance prepared in accordance with IFRS.

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, timely and successful completion of the planned mill modifications with the installation of the second pebble crusher, stabilization of the operating circuit to reach throughput design capacity of 55,000 tonnes per day, improvement of mine productivity, the optimization of the plant and the reduction of cost, positive outcome of any exploration work conducted around the Canadian Malartic infrastructure or at the Hammond Reef project, further development of its Hammond Reef project including timely completion of various studies necessary for the project feasibility study, and positive outcome of any claim to be filed with the Company’s explosive contractor.

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 achieve such events qualified by the foregoing cautionary note regarding forward looking statements, 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 and construction personnel, results of exploration and development activities, Osisko’s limited experience with production and mining operations, uninsured risks, regulatory framework and 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 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.