As companies step back, the world's wealthy are piling in. This month, a company owned by New Zealand's Todd family backed construction of a railroad to transport iron ore from an Australian mine proposed by Flinders Mines Ltd. FMS.AU -3.57% They hope to emulate Australian mining entrepreneur Andrew Forrest, who built a $5.2 billion fortune in a decade by transforming Fortescue Metals Group Ltd. FMG.AU +1.81% from a tiny explorer into the world's fourth-largest iron-ore producer.