“This is an exciting day for Rio Tinto and Riversdale,” Rio energy chief executive Doug Ritchie said.

“This is a great opportunity for our business to deliver on the development of a large-scale coking coal resource.”

Ritchie and Rio chief development officer for coal projects Matt Coulter, along with Rio managing director David Peever have been appointed to Riversdale’s board with more appointments from Rio expected to follow.

The company is aiming to develop Riversdale’s Mozambique coal assets “as quickly as possible”

“Our experience in delivering on major projects and infrastructure provides a strong

platform for us in developing Riversdale's asset base,” Ritchie said.

“Operating under our strong values framework, we have the expertise, resources and incentives to efficiently develop the projects to a world-class standard, delivering immense benefits to the people of Mozambique.

“Our long-term development strategy for Riversdale underlines Rio Tinto’s commitment to Africa, where our activities extend beyond our operating mines, including an extensive exploration program and numerous ongoing projects in the region.”

Rio’s chances of completing the acquisition of Riversdale became unlikely after Tata Steel and Brazilian steelmaker Cia Siderurgica Nacional both increased their stakes in Riversdale during earlier weeks of the offer.

Both steelmakers collectively hold 44.72% of the company.

Riversdale’s flagship Benga coking coal mine in Mozambique is a joint venture development, with Tata owning 35%.

At full production under stage-two development, the Benga mine is aiming to export 6 million tonnes per annum of prime hard coking coal and 4Mtpa of export thermal coal by 2013.

Riversdale is also advancing a prefeasibility study for its nearby and bigger $2 billion Zambeze hard coking coal project, which holds more than 9 billion tonnes of resources.

Last year the company started investigating the long-term possibility that Zambeze could become a 90Mtpa run-of-mine operation.

Riversdale closed up 1c to $16.52 on Friday while Rio shares were up 25c to $86.25.