The company has had to tweak the mine design and development plan for the project in Ecuador, which has pushed back its already delayed pre-feasibility study to Q1 2021.
Iron ore's demand-driven price surge last year is increasingly looking like an aberration as supply factors once again start to weaken the price outlook.
Fresh bid is far better than the $2.55bn it offered earlier this month and considerably more than the $2.45bn offered by Yancoal, the Chinese-backed miner that is Rio’s preferred buyer.
Australia's Atlas Iron, which narrowly escaped collapse when iron or prices crashed in 2015, has deferred construction of a new mine, citing weak prices for the steelmaking commodity.