Dec 6 (Reuters) - Rio Tinto said on Wednesday its share of capital expenditure to develop the Simandou iron ore project in Guinea and associated rail and port infrastructure would be about $6.2 billion.

Simandou, set to be the world's largest iron ore project, will add around 5% to global seaborne supply when it comes on line in 2025.

It will be key to Rio Tinto's ambitions to supply high-grade iron ore for decarbonisation of the steel industry and is expected to command a majority of the miner's capital investments in the next three years.

Rio Tinto owns two of four Simandou mining blocks as part of its Simfer joint venture with China's Chalco Iron Ore Holdings (CIOH) and the government of Guinea. Rio Tinto holds a 53% stake in the joint venture, while CIOH holds the rest.

Simandou has been the subject of prolonged negotiations due to its complex ownership structure, delays caused by legal wrangling, Guinea's political changes and difficulties around construction.

The total initial funding requirement to develop the Simandou iron ore project is estimated to be about $11.6 billion, Rio Tinto said in a statement.

"Simandou will deliver a significant new source of high-grade iron ore that will strengthen Rio Tinto's portfolio for the decarbonisation of the steel industry," division chief Bold Baatar said in a statement.

Rio Tinto's capital investment is expected to be around $10 billion per year from 2024 to 2026, with the majority on Simandou as spending winds down at the Oyu Tolgoi project in Mongolia beyond 2024.

First production from the two blocks co-owned by Rio Tinto is expected in 2025, ramping up over 30 months to an annualised capacity of 60 million tonnes per year. The company said its share of the production will be 27 million tonnes.

The other two blocks of Simandou are being developed by Winning Consortium Simandou (WCS), made up of Singapore-based Winning International Group, Weiqiao Aluminium - part of the China Hongqiao Group - and United Mining Suppliers. (Reporting by Sameer Manekar in Bengaluru and Melanie Burton in Melbourne; Editing by Shinjini Ganguli and Sam Holmes)