Osisko is a Canadian precious-metals mining company headquartered in Montreal, Quebec. It operates in Canada with a focus on gold mines in the Abitibi gold belt of Quebec. The company was known as Osisko Exploration LTD. before changing its name in May 2008. It owns at least 17.41 million troy ounces (1,194,000 lb; 542,000 kg) of gold reserves (including 10.71 in malartic and 6.7 at Hammond Reef, malartic reserves up 20% in March 2011 due to higher gold prices) and over 230 square kilometres (89 sq mi) of land in the Malartic-Cadillac area. Based on market capitalization, it is one of Canada's largest Canadian gold mining companies. The Canadian Malartic mine will be the biggest gold mine ever in Quebec and one of the biggest gold mines in Canada.
Commercial production at Canadian Malartic (its flagship gold mine) began May 19, 2011.
The company is named after Quebec's Osisko Lake because of its historical significance. The lake, located within Quebec's portion of the Abitibi gold belt in the region of Rouyn-Noranda is where, in 1920, Noranda founder Edmond Henry Horne made his first major mineral discovery, a deposit that became known as the Horne Mine.