RE: Question - digging dirt... Well, say they want to go 300 feet down (100 yards)
And they want to have one square mile like that (probably too big, but...)
so that is 1.6K yards x 1.6K yards, which is 2.56M sq yards, x 100 yards down
that comes to 256 million cubic yards of dirt.....which might even have gold in it...and they have to dig it up, truck it somewhere, and dump it....