Alternatively, there are companies like Mount Gibson Iron Ore ( ASX: MGX ) that have incredibly low cost mines, however the mine life is short so there is a risk that any future mine purchases will not be as low-cost and dilute shareholder returns. The next Rio Tinto? In my eyes, the best up-and-coming alternative to Rio Tinto is Fortescue Metals Group Limited ( ASX: FMG ). Fortescue has relatively high costs compared to Rio, at an estimated US$72 per tonne of iron ore, but is widely considered the third or fourth lowest cost listed global producer. In the past I had been concerned about the group's high debt load, however it is rapidly being paid down early in order to reduce interest payments and boost profitability even if the iron ore price falls over time.