It is all about grams of gold per ton of dirt. And, it can be assayed relatively quickly after excavation - minimizing our wait. The goal is 200 grams of gold per ton of dirt. That is very possible and would be a motherload. Determining if the dirt has diamonds is a much longer process, and more expensive.
No drilling that I know of, this is open pit mining. The gold and diamonds are not on the top layer. They remove the top layer of dirt. IDK how much or how big an area. It could be 10 to 20 feet of topsoil on a hundred acres. That takes does take awhile. Find a bolder half the size of a house and your spending the day blowing it up. Fun, YES, but time consuming. LoL Hope this helps