(IDEX Online) - Rio Tinto is to invest $40m to extend the life of Diavik, Canada's largest mine, on the edge of Arctic Circle.It says that underground mining below the existing A21 open pit operation should yield an additional 1.4m carats and extend the life of the deposit into the first quarter of 2026. It had been scheduled to close in 2025.Rio Tinto, the world's second-largest metals and mining corporation, said it was planning a further underground project for 2024, expected to contribute a further 0.8m carats.Sinead Kaufman, chief executive of Rio Tinto Minerals said: "Rio Tinto's decision to support the underground development of the A21 pipe was prefaced on compelling industry fundamentals, our proven capacity to safely develop diamond mines in extreme conditions and a track record in competing successfully in the global diamond industry. This is good news for our employees, partners, suppliers and local communities in the Northwest Territories."Rio Tinto became 100 per cent owner of the mine since November 2021, ending along legal battle with Dominion Diamond Mines over the mine's operating costs and production targets.Dominion went into administration in April 2020 and Rio Tinto bought its 40 per cent holding.Last April Rio Tinto warned that the forthcoming closure of the mine would have a significant impact on the local economy.The deposit, 300 km northeast of Yellowknife, is one of the largest employers in Northwestern Territories, providing 1,100 jobs, and contributing almost 10 per cent of its GDP.Diavik (pictured) opened in 2003 and produced 6.2 million carats of rough diamonds in 2020.