My estimate for the cash they paid for the mining rights is ballpark, at best. I just know that when you have a big expense like that you would normally account for it in parts over the life of the asset.
You wouldn't pay a nickel for a billion in profits, but you also wouldn't pay a billion for a billion either.
Considering that Aurus intends to devote at least 10 years to these mines, a reasonable price paid for the mining rights might be 50 cents for every dollar potential.
Don't forget too that even if they planned on breaking even (which is a misinterpretation anyway), they would still have hundreds of millions more now that precious metal prices went up.