The 40% was acquired following approval from the Court of Queen's Bench of Alberta's approval.
The transaction comes after a 19-month process triggered in April 2020 by former partner Dominion Diamond Mines filing for insolvency protection under the Canadian Companies' Creditors Arrangement Act.
Under the terms of the transaction, Rio has acquired all remaining Diavik assets held by Dominion, including unsold Diavik production and cash collateral held as security for Diavik's future closure costs.
In return, Rio has released Dominion and its lenders from all outstanding liabilities and obligations to fund the operations or closure of the joint venture.
Diavik's mine life extends to 2025.
"Diavik will now move forward with certainty to continue supplying customers with high quality, responsibly sourced Canadian diamonds and making a significant contribution to the Northwest Territories of Canada and local communities," Rio Tinto Minerals CEO Sinead Kaufman said.
"As owner and operator, Rio Tinto is committed to delivering Diavik's eventual closure safely and responsibly, to leave a positive legacy in consultation with our community and government partners."
Rio has operated Diavik since production started in 2003. In 2020, it produced 6.2 million carats of rough diamonds.
Located about 300 km north-east of Yellowknife, the mine employs over 1100 people, of which 17% are Northern Indigenous people.
