This sounds right. @Snuskpelle
320,000,000 tons x ~55,000,000 $/ton = $17,600,000,000,000,000 ($18 QUADRILLION) which is not the value claimed. So, he can't mean 320,000,000 tons of pure gold and must mean 320,000,000 tons of material prior to refining.
Dividing 18 quadrillion by ~1000 gives...