Depending on the strip ratio of a pit it will cost about 25-50% (e.g 10/t vs 40/t) of the cost of mining the ore as compared to going underground. The surface infastructure costs stay about the same. More importantly you can get mining much faster and cheaper (no shaft and stope development, a much simipler mining plan, no ventillation issue or back filling issues and less skill dependent mining).

... Been There