An Ecological Cost Accounting Model for Open-Pit Mining: Application to Ultimate Pit Limit Optimization and Slope Angle Optimization Potential Assessment

Ecological disturbance is rarely included as an internal factor in ultimate pit limit design. As a result, conventional methods based on profit maximization are limited in their ability to support green and efficient open-pit mine designing. In this study, an ecological cost accounting model for open-pit mining was developed based on the DPSIR framework. In the proposed model, land occupation and associated ecosystem degradation cost, carbon emission cost, environmental pollution control cost during the mining period, ecological monitoring and maintenance cost, and post-closure reclamation cost were monetized and integrated with economic profit. On this basis, an economic–ecological comprehensive benefit was defined as the difference between economic profit and total ecological cost. This comprehensive benefit was used to support ultimate pit limit scheme selection and the assessment of slope angle optimization potential. A set of candidate ultimate pit limit schemes was generated for a large open-pit iron mine under different combinations of zonal slope angles and open-pit scales. The ecological costs of the candidate schemes were mainly between USD 1160 million and USD 1350 million. In terms of cost composition, land occupation and associated ecosystem degradation cost accounted for approximately 67.3% of the total ecological cost. After ecological cost was included, the peak of the economic–ecological comprehensive benefit shifted toward a smaller open-pit scale, indicating that profit maximization alone may lead to excessive pit expansion. Zonal sensitivity analysis showed that the strongest responses on slope angle optimization potential were found in Zones 4# and 3#. For each 1° increase in slope angle, average increases of approximately USD 41.38 million and USD 35.32 million in pit profit were obtained in Zones 4# and 3#, respectively.