If farm incomes in B or C begin to rise, mill or mine wages will look less attractive to potential recruits, who will become less willing to leave their villages.

The mill or mine owners (or labor recruiters) can look elsewhere for job candidates or raise wages to encourage more volunteers from the customary locations.

The South Korean mill earlier this year agreed to buy as much as 15 percent of the Roy Hill iron ore project in Australia and a 7.8 percent stake in a coal mine in Mozambique.