Mining giant Rio Tinto (ASX:RIO,NYSE:RIO,LSE:RIO) said in a press release on Thursday, October 3, that it has completed the development and construction of Phase 1 of the A21 underground mine at its 100 percent-owned Diavik diamond mine.

The company detailed the construction process, which involved over 1,800 meters of underground tunnel development.

The Diavik diamond mine is located at the bottom of Lac de Gras in Canada's Northwest Territories. A21 is the fourth diamond pipe of the project and was opened by Rio Tinto in 2018. The company made the decision to go ahead with Phase 1 in February 2023, investing US$40 million.

Phase 1 of mining at A21 is expected to produce 1.4 million carats of diamonds.

“While re-examining the feasibility of underground mining at A21, the Diavik team developed a plan that resulted in the approval of the first phase of a 2-phase expansion project. This created an extension of the mine’s life until the first quarter of 2026,” Rio Tinto shared on its website.

Phase 2 was approved earlier this year with an additional investment of US$17 million. It is expected to produce an additional 800,000 carats.

“The A21 underground operation is positive news for our employees, partners, suppliers and local communities in the Northwest Territories, as it will enable operations to continue through to closure,” said Matt Breen, chief operating officer of Diavik.

Rio Tinto is also actively preparing for the eventual closure and remediation of the mine site with progressive reclamation activities.

Rio Tinto installed a wind farm that generates enough renewable energy to power the mine in 2012, saving 118,000 tonnes of carbon dioxide emissions, and is also constructing the largest solar panel project in Northern Canada, according to its website.

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Securities Disclosure: I, Gabrielle de la Cruz, hold no direct investment interest in any company mentioned in this article.