Economic analysis of changing the stone mining method from surface to underground- First part: Economic analysis (Case study: Dehbid stone mine)

Quarrying stands as a prevalent method in surface mining, instrumental for the extraction of a variety of building stones. However, the escalation in mining depth alongside environmental issues stemming from waste and dust production during quarry mining has necessitated a shift towards underground stone mining in various countries. Global experiences attest to the fact that underground mining of building stone not only mitigates or completely eradicates environmental issues associated with surface mining but also proves to be more economically viable. This is due to the entire relocation of mining operations underground and the consequent reduction in waste removal costs. Room and pillar, a method extensively employed for underground mining of building stone, has yet to find application in Iran for this specific purpose. Hence, this research endeavors to conduct an economic analysis of the transition from surface (quarry) to underground (room and pillar) mining methods. Utilizing data from the Dehbid marble mine, the economic feasibility of this transition was assessed with the aid of COMFAR software. The analysis encompassed a thorough evaluation of investment and operational costs, as well as revenue generation for both mining methods. All calculations were grounded in the price indices of Iran for the year 1402. The findings reveal that, with a discount rate of 25%, the net present value (NPV) accrued from the underground mining method (101,000,000,000,000 Rials) significantly surpasses that of surface mining (52,741,000,000,000 Rials). Additionally, the internal rate of return (IRR) for both mining methods exceeds the minimum absorption rate of 25%. However, the IRR for underground mining stands at a remarkable 158.57%, distinctly higher than the 43.92% noted in surface mining. These indicators collectively position underground mining as the more economically viable option for this particular mine. Furthermore, when comparing the capital return periods of both plans, surface mining exhibits a return period of 4 years for normal conditions and 6 years under dynamic conditions. In contrast, underground mining maintains a consistent return period of 3 years for both normal and dynamic conditions. Taking into account the time value of money, this analysis solidifies the economic advantage of opting for underground mining.