How to account for mineral depletion. The exergy and economic mineral balance of Spain as a case study

This paper describes a way to account for mineral depletion through exergy replacement costs, which are defined as the exergy required to replace minerals from a complete dispersed state back to the initial conditions of composition and concentration in which they were originally found and with the best available technologies. The advantage of using such an indicator is that the scarcity factor of each commodity together with the state of technology can be taken into account. Moreover, as exergy is fully additive, all kinds of resources can be compared. Conducting an exergy analysis of the production for 22 non-fuel minerals in Spain for the year 2009, we obtain that the exergy replacement costs are 41.67 Mtoe, this amount is equivalent to the average domestic coal consumption in Spain for 2 years. If we account for the imports and exports of the 22 substances and we calculate the material consumption, production plus imports minus exports, we have that the total exergy replacement cost increases to 98.97 Mtoe. In the case of fossil fuels, if we add the imports to the Spanish production, the total exergy replacement costs are 94.15 Mtoe, where 93% corresponds only to imports. Depending if the energy source chosen for replacing the domestic mineral capital is in form of coal or electricity, the monetary equivalent of mineral depletion by extraction would be 3272 to 13,518 M€ (between 0.31 and 1.28% of Spanish GDP). If we take into account the total mineral consumption (also including the net flows from the rest of the world), the monetary equivalent would be between 27,408 and 57,008 M€ (2.61 to 5.43% of GDP). We also propose another relevant estimation. If we account for the exergy replacement costs using a theoretical price estimated by applying the relationship between extraction/replacement costs to actual price, the monetary value of exergy replacement cost of extracted minerals would be 188,863 M€, 18.62% of Spanish GDP and 84 times higher than the value obtained with current resource prices (2323 M€). For the resource consumption, the monetary value would be 280,594 M€, which represents an equivalent of 26.77% of Spanish GDP and is 25 times higher than the value estimated with actual and current resource prices (11,137 M€).