There are many variables, it is not a simple thing to design an optimum pit, or to decide when to go to a decline or underground.
Some mines operate at a stripping ration of 20 to 1 - for tonne of ore you get 20 tonnes of waste have to moved. That is why surface deposits are highly prized, especially of good grade, as there is less waste to remove before you get to the good stuff and income comes earlier.
