Osisko Lynx Bulk Sample Returns 17.8 g/t Au Reconciled Head Grade

89% Higher Grade than Predicted in Resource Block Model

TORONTO, Dec. 11, 2019 (GLOBE NEWSWIRE) -- Osisko Mining Inc. (OSK:TSX "Osisko" or the "Corporation") is pleased to provide new results from the ongoing exploration program at its 100% owned Windfall Lake gold project located in the Abitibi greenstone belt, Urban Township, Eeyou Istchee James Bay, Québec.  Results from processing 5,716 tonnes mined from Lynx (the “bulk sample”) have exceeded expectations, returning an average grade of 17.8 g/t Au. The bulk sample average grade is 89% higher than the 9.40 g/t Au predicted by infill drilling on the Lynx zone 311 resource block model wireframe. Mining of the bulk sample successfully confirmed the presence of mineralization predicted in the resource model, and the analytical results have confirmed the visual mineralization encountered along the stope. Highlights and full results are presented below.

Highlights

• Average grade of 17.8 g/t Au for the bulk sample is 89% higher than predicted in the 12.5 metre infill drilling block model
• Higher than anticipated average Au recovery of 97.2% achieved
• 66.7% of the gold was recovered in the gravity concentrate
• The sample contained 3,271 ounces Au and 2,176 ounces of Ag

President and Chief Executive Officer John Burzynski commented: “We are highly encouraged with the excellent results from this second bulk sample completed from the Windfall deposit.  The average grade greatly exceeded our expectations based on the infill drilling, returning 89% higher grade than anticipated.   The significant grade increase from the block model appears to correspond well with the very regular visible gold observed in Lynx drilling. The bulk sampling work is greatly helping to build our confidence in the continuity, grade, recoveries and the predictability of the mineralized zones at Windfall.”

Geology
The Lynx zone 311 bulk sample is characterized by an East-North-East sub vertical silica altered corridor with an average width of approximately 2.5 meters. Banded grey quartz veins contain 3 to 15% disseminated pyrite and local visible gold, cross-cutting foliated rhyolite and granodiorite with strong sericite and local fuchsite alteration. The continuous vein system was mapped along sills over three levels.

Processing
A total of 5,716 tonnes were processed in November 2019. The bulk sample test was performed at the Northern Sun Redstone concentrator. Processing produced gravity and flotation concentrates. Ore transportation trucks were sampled for moisture and weighed on a calibrated weight scale. The sample material was crushed and milled to a particle size favorable to the flotation recovery process. Gravity and flotation concentrates produced will be sent to a local smelter for sale. Day and night shift daily composite samples of streams for the reconciliation process were prepared and analyzed by an external independent lab. Concentrate production tonnage and assays were used to reconcile the bulk sample mass balance process in the concentrator. The reconciliation was performed by an external independent consultant using Bilmat (a reconciliation software) on a dry tonnes basis.