OT3Key government approvals for the expansion of Mongolia’s Oyu Tolgoi copper and gold mine will allow Rio Tinto Group and its partners to advance talks with lenders, according to the state-owned company that holds a stake in the project.

Government agencies have agreed to accept a feasibility study on proposals to develop an underground mine at the site, one of the world’s largest copper deposits, and provided guarantees to the World Bank’s Multilateral Investment Guarantee Agency, state-owned Erdenes Oyu Tolgoi LLC said Monday in a statement.

The approvals show Mongolia’s “resolve to rapidly bring this world-class resource into production and on a broader level further demonstrates that Mongolia is open for business” said Davaadorj Ganbold, executive director of Erdenes Oyu Tolgoi. It holds Mongolia’s 34 percent stake in the mine and Rio-controlled Turquoise Hill Resources Ltd. holds the remaining 66 percent.

The partners will seek to raise as much as $6 billion of external funding for the underground mine, including third-party project financing and sales accords, according to a development plan published by Turquoise Hill in May. Rio is seeking to target 15 to 20 banks to raise more than $4 billion, Jean-Sebastien Jacques, head of its copper and coal business, said in May.