If gold is $2,000/ounce and mining costs are $1,500/ounce, profit is $500/ounce. If gold doubles to $4,000/ounce, profit increases to $2,500/ounce (a fivefold increase).
"Let's just say that gold is at $2,000 an ounce, okay? And let's say that the cost to mine for gold... all the expenses, let's just say it cost a company $1,500 to pull an ounce of gold out of the ground. ... But if you sell it for $4,000 an ounce and it costs $1,500 an ounce, then that's a profit of $2,500."