Osisko Mining Corporation: Canadian Malartic Style Mineralization Discovered at the Jeffrey Zone

MONTREAL, QUEBEC--(Marketwire - Feb. 28, 2011) - Osisko Mining Corporation ("Osisko") (TSX:OSK)(FRANKFURT:EWX) and Golden Valley Mines Ltd. (TSX VENTURE:GZZ) are pleased to announce additional results from the 2010 drill program targeting the Jeffrey Zone on the Malartic CHL Property, currently under option from Abitibi Royalties Inc., a wholly-owned subsidiary of Golden Valley Mines Ltd., and located immediately east of Osisko's 100%-owned Canadian Malartic gold property.

Highlights from twenty-nine drill holes include 67.0 metres averaging 1.06 g/t Au (CHL10-2282) and 26.7 metres averaging 2.57 g/t Au (CHL10-2273) in the Jeffrey zone. This set of holes includes new Canadian Malartic style mineralization discovered in the Pontiac sediments immediately south of the Jeffrey Zone. Significant intersections include 41.0 metres averaging 2.50 g/t Au (CHL10-2275 uncut) and 24.0 metres averaging 3.36g/t Au (CHL10-2285). Asterisks in the assay table below indicate those holes which have encountered this new mineralization:

Hole No.	Section	From (m)	To (m)	Length (m)	Au g/t	Au g/t
					(uncut)	(cut)
CHL10-2270	7575E	64.0	91.0	27.0	1.00	---
CHL10-2271	7575E	72.0	123.0	51.0	0.59	---
CHL10-2272	7575E	92.1	130.5	38.4	0.70	---
CHL10-2273	7600E	82.5	109.2	26.7	2.57	---
including		85.5	87.0	1.5	23.80	---
CHL10-2274	7600E	104.0	125.3	21.3	0.67	---
CHL10-2275*	7350E	42.0	83.0	41.0	2.50	1.84
Including*		45.0	46.0	1.0	56.80	30.00
And		188.1	223.5	35.4	0.64	---
CHL10-2277	7625E	78.0	96.9	18.9	0.95	---
CHL10-2278	7625E	99.5	120.0	20.5	0.91	---
CHL10-2279	7500E	36.0	50.8	14.8	1.27	---

CHL10-2280	7375E	81.0	130.5	49.5	0.70	---
And		147.8	184.5	36.7	1.74	---
including		148.6	150.0	1.4	28.10	---
And		208.5	225.0	16.5	1.35	---
including		223.5	225.0	1.5	10.20	---
CHL10-2281*	7375E	108.2	118.5	10.3	2.57	---
And		183.7	215.5	31.8	0.53	---
CHL10-2282	7375E	202.5	269.5	67.0	1.06	---
including		209.2	210.5	1.3	10.90	---
including		257.5	259.0	1.5	11.03	---
CHL10-2285*	7325E	18.5	42.5	24.0	3.36	---
including		36.5	37.7	1.2	15.25	---
And		81.5	111.0	29.5	0.61	---
CHL10-2288	7375E	90.0	162.0	72.0	0.74	---
including		106.5	108.0	1.05	6.07	---
And		192.0	225.0	33.0	0.65	---
CHL10-2289	7325E	124.5	148.5	24.0	1.57	---
including		139.5	141.0	1.5	18.20	---
CHL10-2291	7225E	16.5	40.5	24.0	0.59	---
including		39.0	40.5	1.5	3.90	---
CHL10-2294	7325E	16.5	33.0	16.5	0.79	---
And		76.5	108.2	31.7	0.55	---
CHL10-2295	7375E	21.5	45.0	23.5	0.61	---
including		24.5	26.0	1.5	4.56	---
And		116.5	134.5	18.0	0.83	---
CHL10-2298	7325E	11.8	22.7	10.9	1.05	---
CHL10-2299	7300E	27.0	53.5	26.5	1.11	---
And		80.5	103.0	22.5	0.70	---
CHL10-2300	7300E	11.5	31.7	20.2	0.97	---

The new mineralization identified in the Pontiac metasediments is located 20m to 35m south of the contact with the Cadillac fault and the porphyry body hosting the Jeffrey zone. The zone appears to have a true width of approximately 7 to 10 metres and plunges steeply to the north toward the contact with a steep rake to the east. It is now traced over 75 m of strike from section 7325E to 7400E and remains untested to the west. The disseminated mineralization sits in altered greywacke and in porphyry, which is similar to that of the Canadian Malartic deposit.

Mineralization at the Jeffrey Zone is located along the southern limit of the Cadillac Break, where it consists of disseminated pyrite-gold in potassic-altered quartz-feldspar porphyry dikes, in contact with a predominately ultramafic flow sequence, and in subordinate diorite-gabbro and sedimentary units. Narrower, higher-grade mineralization is hosted in quartz veined (silicified) porphyry or talcose and chlorite-altered ultramafic schists.

Drill holes CHL10-2276, CHL10-2283, CHL10-2284, CHL10-2286, CHL10-2287, CHL10-2290 and CHL10-2301 did not intersect significant mineralization. Assays are pending for drill holes CHL10-2292, CHL10-2293, CHL10-2296 and CHL10-2297. Definition drilling on the Jeffrey Zone is based on a series of sections spaced at 25-metre intervals over an east-west strike length of 400-metres and north-south distance of 135 metres. The objective of the current program is to gather sufficient drill information along strike and to depth to complete an initial indicated resource calculation by the beginning of Q2 2011.

Continuity of steeply-dipping mineralization at Jeffrey is now well established along a strike length of 400 metres (sections 7200E to 7600E), with a true width of 30 to 60 metres. Mineralization is more sporadic further east between sections 7600E and 8100E. Mineralization has been traced to a depth of 200 metres on most sections, where it remains open at depth. The western extremity of the Jeffrey Zone (section 7200E) lies 1000 metres east of the eastern limit of the Barnat extension (see October 14, 2010 press release), and most of the intervening kilometre has yet to be drilled.

All NQ core assays reported above were obtained by standard 50 g fire assaying-AA finish or gravimetric finish at ALS Chemex laboratories in Val d'Or, Quebec. Reported drill core weighted averages were calculated using a minimum of 0.40 g/t Au over successive intervals of 20 metres. The lengths of mineralized intervals of less than 20 metres were minimized, and an upper cut-off of 30 g/t Au was applied to individual assays where indicated. Intervals containing individual assays that are greater than six times the average of the interval are included separately. Intersected drifts or lost core within mineralized intersections were incorporated as blank intervals.

Osisko follows strict QA-QC protocol measures in keeping with industry standards and regulatory reporting requirements. Mr. Robert Wares, P. Geo. and Executive Vice-President of Osisko, and Mr. François Bouchard, P. Geo., are the Qualified Persons who has reviewed this news release and are responsible for the technical information reported herein, including verification of the data disclosed including the sampling, analytical and test data underlying the technical information.

Osisko has the right to acquire a 70% interest in the Malartic CHL Property in consideration for $150,000 in cash payments over a four year period (total amount paid) and by completing a minimum $2,000,000 in exploration work over a four year period. Upon earning its 70% interest, Golden Valley will maintain a free-carried interest of 30% to production.

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 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.