Assessments of the economic, environmental and social consequences of mining have usually produced an estimate of the commercial benefits that mining in the area would generate, with environmental costs being examined in physical terms only. A theoretical framework for calculating the threshold environmental value of an area (the minimum size of the environmental cost of mining required to make conservation the socially optimal choice) is developed, where both the potential mining benefits and the rate of biological regrowth following mine rehabilitation are known. Including the rate of biological regrowth allows for the calculation of a more meaningful figure, as the benefits generated by rehabilitation are explicitly considered.