This excerpt taken from the RIO 20-F filed May 16, 2007.
Distribution iron ore and pellets
Our ownership and operation of transportation systems designed for the efficient transportation of iron ore products complement our iron ore mining business in the Northern and Southeastern Systems where we operate an integrated railroad and terminal network in each of them. These networks transport our iron ore
products from interior mining locations to maritime terminals and Brazilian customers. For a more detailed description of the networks, see Logistics, below.
We do not own or operate an integrated transportation system for our Southern System. Instead, we enter into freight contracts with our affiliated company, MRS, to transport our iron ore products at market rates from MBRs mines and Oeste mines to our Guaíba Island and Itaguaí maritime terminals.