Returning to the US Ballen studied for a PhD at the Colorado School of Mines in Golden , Colorado .
Returning to the US Ballen travelled to Johannesburg in 1982 where he found work as a geologist and mining entrepreneur .
Returning to the US Ballen studied for a PhD at the Colorado School of Mines in Golden , Colorado , and travelled to Johannesburg in 1982 where he found work as a geologist and mining entrepreneur .