The economic pit limit is an important concept in the design and operation of a surface mine. The economic pit limit is the maximum boundary that a surface mine can extend to and still remain economically feasible to operate. Once the economic pit limit is exceeded, the cost of removing the waste rock (i.e., overburden and rock adjacent to the ore) exceeds that of the profits from the sale of the valuable mineral.

For a regularly shaped open pit, the economic pit limit can be determined relatively easily using the geometry of the orebody, the overburden volume, and the economic factors that dictate mining and processing costs and the value of the mineral resources. For irregularly shaped pits (i.e., for irregularly shaped orebodies, in areas with irregular topography or mining limitations), determining the pit limit becomes a more complex process and software packages are commonly used.

Figure: Note that although most of the mineral deposit is in the pit limit, portions are either too deep or require too much stripping to be economically mined at the current production costs and mineral price. Changes in costs and prices can adjust the pit limits.