Wow. I had no idea that mining gold was so...chancy. I'd always imagined that a mining company would have some general idea of where a gold deposit would be, and that they'd simply dig down to where they needed to and find gold ore...which would of course need to be refined, but which would be in chunks & veins throughout a load of given rock.
Not so.
While they do indeed use geologists to take samples and determine (roughly) where the gold is, and while their engineers do work to remove as many inefficiencies as possible what's essentially happening is that once they find that general area they simply remove *all* of the rock and sift/sort the entire lode to get like a gram of gold per ton. The gold is so dispersed that you can't see it with the naked eye.
And this all somehow "economical" (yes, WILDLY destructive to the Earth but...worth it profit-wise). If you need a reminder on how rare gold is: All the gold ever mined in human history put together would make a cube that's about 68 ft on all sides. This amount can fit in an Olympic sized swimming pool.