Osisko Provides Resource Update for Hammond Reef Project

MONTREAL, QUEBEC--(Marketwire - Jan. 28, 2013) - Osisko Mining Corporation (TSX:OSK)(FRANKFURT:EWX) is pleased to provide an updated resource estimate for its 100%-owned Hammond Reef gold project, located near Atikokan, Ontario. Additional drilling by Osisko has allowed for upgrading the bulk of the resource to the measured and indicated (M&I) categories, which will lead to conversion to reserves once the ongoing feasibility is completed. This update reports both global and in-pit resources in all categories.

Key points:

• Global M&I resources currently stand at 5.43 million ounces gold at an average grade of 0.86 g/t Au and the global inferred resource stands at 1.75 million ounces gold at an average grade of 0.72 g/t Au (based on 0.50 g/t Au lower cut-off; see table below).
  
  
• Global M&I resources currently stand at 7.47 million ounces gold at an average grade of 0.65 g/t Au and the global inferred resource stands at 3.12 million ounces gold at an average grade of 0.52 g/t Au, based on a 0.30 g/t Au lower cut-off; see table below).
  
  
• The in-pit M&I resource is now 5.31 million ounces at an undiluted grade of 0.72 g/t gold, based on a Whittle-optimized pit shell using a gold price of US$1,400 per ounce. The in-pit inferred resource adds 0.28 million ounces at an undiluted grade of 0.65 g/t Au. Overall pit parameters include an average lower cut-off grade of 0.32 grams per tonne gold and a low waste/ore strip ratio of 1.01.
  
  
• At US$2,000 per ounce gold, the in-pit M&I resource increases to 7.87 million ounces and the inferred resource increases to 2.12 million ounces at an average grade of 0.56 grams per tonne gold.
  
  
• The A (Main) and Mitta Zones form a contiguous deposit (west pit), while the 41 zone is separate (east pit). The system was modeled as two pits with a total strike length of 2500 metres (sections 870E to 3370E). Exploration drilling around the Mitta and A zones has been successful in extending the deposit in the down-dip (southeast) direction, to a maximum distance (along dip) of 850 metres.
  
  

Sean Roosen, President and CEO of Osisko, commented: "We are very pleased with Osisko's updated resource estimate for the Hammond Reef Project, which has achieved a significant increase with respect to the initial acquisition from Brett Resources estimate. It is important to note that the new in-pit resource for Hammond Reef has a low strip ratio of 1.01 and is quite robust, as it is based on current processing and mining costs at Canadian Malartic, adjusted for Ontario power rates. With over 625,000 metres of drilling completed, 76% of the in-pit resource is contained in the measured category, which is the highest achievable confidence level."

SGS Canada Inc. of Montreal, Quebec ("SGS") are the independent resource estimate consultants who have authorized the release of the following estimates. Global M&I resources currently stand at 5.43 million ounces gold at an average grade of 0.86 g/t Au and the global inferred resource stands at 1.75 million ounces gold at an average grade of 0.72 g/t Au. The table below summarizes the SGS estimates using variable lower cut-off grades:

Hammond Reef Global Resource Estimates

Category	Grade (g/t)	Tonnes (M)	Cut-off (g/t)	Oz (M)
Measured	0.67	212.9	0.2	4.60
Indicated	0.44	268.7	0.2	3.84
M+I	0.54	481.6	0.2	8.44
Inferred	0.44	271.8	0.2	3.80
Measured	0.74	184.7	0.3	4.38
Indicated	0.55	174.4	0.3	3.09
M+I	0.65	359.1	0.3	7.47
Inferred	0.52	185.2	0.3	3.12
Measured	0.90	123.5	0.5	3.59
Indicated	0.78	72.9	0.5	1.83
M+I	0.86	196.4	0.5	5.43
Inferred	0.72	75.7	0.5	1.75
Measured	1.09	76.8	0.7	2.70
Indicated	1.03	32.3	0.7	1.07
M+I	1.07	109.2	0.7	3.77
Inferred	0.96	27.4	0.7	0.84
Measured	1.29	46.8	0.9	1.94
Indicated	1.28	16.0	0.9	0.66
M+I	1.28	62.8	0.9	2.59
Inferred	1.22	11.0	0.9	0.43
Measured	1.39	36.2	1.0	1.61
Indicated	1.40	11.6	1.0	0.52
M+I	1.39	14.7	1.0	2.13
Inferred	1.35	7.5	1.0	0.32

G Mining Services Inc of Montreal, in collaboration with SGS, also estimated resources within a Whittle-optimized pit shell using a base case gold price of US$1,400 per ounce and pit limits that are unconstrained by lakeshores. The optimization yielded two distinct pits separated by approximately 200 metres with an average strip ratio of 1.01. The total in-pit M&I resource for the Hammond Reef gold deposit is 5.31 million ounces of gold at an average undiluted grade of 0.72 g/t Au, based on a derived lower cut-off grade of 0.31 g/t Au (west pit) and 0.33 g/t Au (east pit).

Hammond Reef Undiluted Resource Estimates within US$1,400 Whittle pit shell

PIT AREA	Category	Grade (g/t)	Tonnes (M)	Cut-off (g/t)	Oz (M)
West	Measured	0.75	151.2	0.31	3.63
West	Indicated	0.58	44.7	0.31	0.83
West	M+I	0.71	195.9	0.31	4.46
West	Inferred	0.65	13.1	0.31	0.27
East	Measured	0.80	24.1	0.33	0.62
East	Indicated	0.75	9.43	0.33	0.23
East	M+I	0.79	33.6	0.33	0.85
East	Inferred	0.50	0.27	0.33	0.01
All	Measured	0.75	175.3	0.32	4.25
All	Indicated	0.61	54.1	0.32	1.06
All	M+I	0.72	229.5	0.32	5.31
All	Inferred	0.65	13.3	0.32	0.28

Sensitivity of the undiluted in-pit resource (based on variable minimum cut-off grades) to gold price is as follows:

Sensitivity of Hammond Reef in-pit Resource Estimates to variable gold prices

Gold Price (US$)	Cut-off	Category	Grade (g/t)	Tonnes (M)	Oz (M)
$1,000	0.45	M&I	0.86	140.6	3.90
$1,000	0.45	Inferred	0.77	8.2	0.20
$1,200	0.37	M&I	0.78	183.5	4.61
$1,200	0.37	Inferred	0.70	11.0	0.25
$1,400	0.32	M&I	0.72	229.5	5.31
$1,400	0.32	Inferred	0.65	13.3	0.28
$1,600	0.28	M&I	0.66	313.1	6.66
$1,600	0.28	Inferred	0.60	29.9	0.57
$1,800	0.25	M&I	0.62	368.7	7.31
$1,800	0.25	Inferred	0.52	61.3	1.02
$2,000	0.23	M&I	0.58	419.7	7.87
$2,000	0.23	Inferred	0.49	136.1	2.12
$2,200	0.21	M&I	0.56	448.8	8.11
$2,200	0.21	Inferred	0.47	167.8	2.53

Details on the parameters of the resource estimates are as follows:

• The database comprised a total of 2,144 holes for 629,367 metres of drilling completed and assayed by Brett Resources and Osisko as of the end of April 2012 on a minimum 25 m x 25 m grid. (All NQ core assays reported by Osisko were obtained by standard 50 g fire assaying-AA finish or gravimetric finish at ALS Chemex laboratories.)
  
  
• The database also comprised a total of 413,412 assays with an average of 1.5 metre per sample for a total of 618,596 assayed metres.
  
  
• The estimates were done using Ordinary Kriging (OK) interpolation as the geostatistical method based on 5.0 metres analytical composites.
  
  
• All estimates are based on a block dimension of 10 metres E, 10 metres N and 12 metres height with estimation parameters determined by variography.
  
  
• Geological interpretation identified a Main domain and several smaller domains (that surround the Main domain. The Main domain is a tabular zone that dips to the southeast and includes the A, Mitta and 41 zones on surface. The RAB was recognized as a separate southern domain that was ignored for the purposes of the global and in-pit resource estimate.
  
  
• Calculations are based on original samples capped to a maximum of 15 g/t Au for the Main domain, resulting in 99 capped intervals with an overall gold loss of 2.0%. Capping for the smaller domains was at 10 g/t for variable gold losses between 0.8% and 2.2%. All 5-metres composites are calculated based on cut original data.
  
  
• Tonnage estimates are based on an average rock density of 2.74 tonnes/cubic metre for the altered tonalite host rock.
  
  
• The global resource estimates using the lower cut-off of 0.50 g/t Au is emphasized for reporting purposes, which is higher than the in-pit cut-off of 0.31-0.33 g/t Au estimated for the US$1,400 Whittle shell.
  
  
• With respect to the previously published in-pit inferred resource (see November 7, 2011 press release), although base-case gold price was increased from US$1,200/oz to US$1,400/oz, the increased unit processing cost (from US$6.66/t to US$8.75/t) and mining costs (from US$1.61/t to US$1.98/t) and decreased recovery (from 91% to 87-88%) have made the new pit shells slightly smaller than before.
  
  

The two US$1,400 Whittle shells have approximate maximum dimensions of 2,500 metres in total length, 1,050 metres in width and a vertical depth to 380 metres. Pit optimization parameters are summarized in the table below:

Parameter	Unit	Value
Gold price	US$/oz	1400
Royalties	%	2.0%
Refining cost	US$/oz	5.0
Processing cost	US$/t milled	8.75
Administration	US$/t milled	1.75
Rehabilitation	US$/t milled	0.25
Sustaining capital	US$/t milled	0.52
Total ore cost	US$/t milled	11.27
Recovery West Pit	%	88.0%
Recovery East Pit	%	87.0%
Mining dilution	%	0%
Mining loss	%	0%
Cut-off grade West Pit	g/tAu	0.31
Cut-off grade East Pit	g/tAu	0.33
Base mining cost rock	US$/t mined	1.98
Reference elevation	m	430
Cost per bench below	US$/bench/t mined	0.046
Mining cost overburden	US$/t mined	3.50
Max pit slope West Pit	degrees	From 41.3 to 50.3
Max pit slope East Pit	degrees	From 45.4 to 48.6
Density overburden	t/m3	2.0

About Hammond Reef

Osisko acquired the Hammond Reef project through the acquisition of Brett Resources in August 2010. To date, Osisko has drilled over 629,000 metres at Hammond Reef, is completing an EIA that will be filed in accordance with the accepted terms of reference and will table a feasibility study in the first half of 2013. The project is located approximately 20 kilometres from grid power, and is located 23 kilometres north of the town of Atikokan. Osisko signed a Resource Sharing Agreement with eight first nations groups in December 2010 as well as a Memorandum of Understanding with the Métis Nation of Ontario in April 2012.

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 and Upper Beaver projects in Northern Ontario.

Mr. Michel Dagbert, Eng. of SGS Canada Inc. (global resource estimate) and Mr. Louis-Pierre Gignac, Eng. of G Mining Services Inc. (Whittle-optimized in-pit resource estimate) are the Qualified Persons responsible for the technical information reported herein, including verification of the data disclosed. Ms. Anne Charland, P. Geo. and Vice-President of Exploration Canada for Osisko, has also reviewed and approved the technical contents of this news release.

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 further work on the stated resources will lead to mineral reserves that can be mined economically.

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, the commencement of commercial production. 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 warrant further development of the project, 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 personnel, results of exploration and development activities, Osisko's limited experience with production and development stage mining operations, uninsured risks, regulatory 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.