The company said the offer will involve a primary issue of 333mn shares.
A judge ruled that changing the status of the protected area in the Amazon rainforest requires a federal law.
The Australian operation is Rio Tinto's 16th iron ore mine and will produce low-phosphorous ore.
Latin America's top gold miner is undergoing significant changes under CEO David Garofalo, with non-core assets sold to help fund Chilean JV projects, while efficiency remains a key priority.
Brazilian President Michel Temer's decision to open up to exploration a Denmark-sized reserve, announced on August 23, is being heavily contested in Brazil and abroad.
The price of copper has climbed to over US$3/lb, the highest since October 2014.