Osisko Mining Corporation

Osisko Exploration Ltée (OSK:TSX-V, EWX: Deutsche Boerse) ) is pleased to announce the updated National Instrument 43-101 compliant inferred resource estimate for its 100%-owned Canadian Malartic gold deposit, located in the Abitibi region of Quebec, Canada. RSG Global Consulting Pty Ltd. of Perth, Australia ("RSG Global"), independent resource estimate consultants for Osisko, has authorized the release of the updated resource estimate. Based on a lower cut-off grade of 0.4 g/t Au and using various geostatistical approaches, RSG Global has estimated an inferred resource between 8.37 and 8.47 million ounces gold. The tables below summarize results of the estimates using three different lower cut-off grades.

Sean Roosen, President of Osisko, commented: "We are very pleased with the new resource estimate, which has increased the size of the inferred resource by almost 30 percent. The increase is due to the expansion of the deposit towards the east as well as reducing the lower cut-off to 0.4 g/t Au, justified by preliminary scoping study numbers, comparison to analogous deposits currently in production and the increasing quality of our data base. The deposit remains open to the west and to the southeast towards the Gouldie Zone. Excellent potential for additional mineralization also exists in the Barnat South Zone, the Norrie zone which we are currently drilling, as well as on the recently acquired East Amphi property. We wish to remind our shareholders that our current drill programs cover less than 5 percent of our property holdings in the Malartic area. We are highly encouraged by our progress on the Canadian Malartic project and we feel that Osisko shareholders can look forward to a very positive year as the Company continues to explore and develop this exceptional mineralized system".

Osisko is currently carrying out a 150,000 metre definition drill program on the Canadian Malartic deposit with the objective of releasing an NI 43-101 compliant measured and indicated resource estimate on the main portion of the deposit by early 2008. An additional 20,000 metres of exploration drilling is also slated for 2007. The complete NI 43-101 compliant report related to this press release will be filed on SEDAR as soon as it is made available to Osisko by RSG Global.

Notes on the calculation of the inferred resource estimates (numbers in brackets indicate figures used in the December 2006 inferred resource calculation and are included for comparison):

• The database comprised a total of 330,813 metres of drilling (244,271 metres) obtained from historical drilling and from approximately 102,046 metres of drilling (41,720 metres) completed and assayed by Osisko as of the end of May 2007.
• The outer mineralized envelope was modeled into a wireframe solid using a 0.2 g/t Au cut-off grade. Approximate dimensions of the envelope were 1930 metres (1470 metres) in length, 400 to 800 metres (460 to 850 metres) in width, to a maximum vertical depth of 600 metres (620).
• Ordinary kriging estimates indicate that 97.4% of the resource occurs from surface to a depth of 375 metres, which is the assumed maximum depth of the eventual pit.
• All estimates are based on a Parent Cell dimension of 30 metres E, 20 metres N and 10 metres height (same) with estimation parameters determined by variography.
• Calculations are based on 3 metre composites cut to a maximum of 20 g/t Au (25 g/t Au), which resulted in an approximate 2 percent reduction in the mean grades of the composites.
• RSG Global has informed management that the preferred estimate for reporting at the present time was the ordinary kriging estimate. MIK and MIK+SMU estimates may be deemed more suitable in the future as the quality of the data base increases.
• The lowest cut-off used in the resource estimate is 0.4 g/t Au, compared to 0.5 g/t Au used in the December 2006 estimate. The current estimate using ordinary kriging at a 0.5 g/t Au lower cut-off indicates 221.2 Mt at an average grade of 1.05 g/t Au, equivalent to 7.50 Moz Au. This represents an increase of 15 percent over the December 2006 estimate. This new lower cut-off was selected based on preliminary scoping study figures and on economic cut-offs used in analogous deposits with similar proposed mining scenarios, such as Boddington in Western Australia (0.4 g/t Au lower cut-off) and Fort Knox, Alaska (0.39 g/t Au lower cut-off).
• Underground stopes, shafts and drifts (data supplied by Osisko) were modeled into a wireframe solid, were treated as voids and removed from the model.
• All composites touching underground stopes were discarded
• Tonnage estimates are based on rock densities of 2.68 tonnes/cubic metre for the porphyry and 2.75 tonnes/cubic metre for the sediments (same).
• Potential positive bias of approximately 12 percent (10 to 20 percent) exists in the historical Canadian Malartic Mines data base. The resource estimate was compensated for the potential bias by :
  
  
  • Modeling the high grade domains separately than the lower grade material, capturing the majority of the historic data;
  • Applying high grade distance restrictions to the grade estimate, i.e. data above 4g/t Au is restricted to a 30m x 30m x20m sample search;
  • Applying a density reduction of approximately 7% to account for any potential stopes or workings not defined, and also to allow for a potential metal over-call in the historic assay data.

Mr. Brett Gossage (MAusIMM) and Mr. David Slater (MAusIMM) of RSG Global are independent Qualified Persons in accordance with National Instrument 43-101 and are responsible for the technical information presented in this news release. RSG Global is an international mining and exploration consulting firm with operational experience throughout the world. RSG Global has contributed to a large number of feasibility studies, due diligence or technical reviews and audits. Particularly relevant to the Canadian Malartic audit is RSG Global's experience in resource estimation of large open pit gold deposits by non-linear methods such as uniform conditioning, conditional simulation and multiple indicator kriging. This includes estimation studies completed on Rosia Montana, Lero Gold, Hidden Valley, Essakan, Youga and other gold deposits.

The Canadian Malartic gold deposit and adjacent areas are being evaluated for a large-scale open pit, bulk-tonnage mining operation. The quantities and grades reported above are preliminary in nature and there has been insufficient work to date to define a NI 43-101 compliant measured/indicated mineral resource on the property. Furthermore, it is uncertain if additional work will result in the definition of an economic mineral reserve on the property. Mr. Robert Wares, P. Geo. and Executive Vice-President of Osisko, is the internal Qualified Person responsible for reviewing and approving the technical contents of this news release.