Exergy as an Indicator for Resources Scarcity: The Exergy Loss of Australian Mineral Capital — A Case Study

Over the span of the 20th century, the global demand for metals and minerals has increased dramatically. This is associated with a general trend of declining ore grades from most commodities, meaning higher quantities of ore needed to be processed and thus more energy. Hence, quantifying the loss of mineral capital in terms of mass is not enough since it does not take into account the quality of the minerals in the mine. Exergy is a better indicator than mass because it measures at the same time the three features that describe any natural resource: quantity, composition and a particular concentration. For the sake of better understanding the exergy results, they are expressed in tons of Metal equivalent, tMe, which are analogously defined to tons of oil equivalent, toe. The aim of this paper is 1) to show the methodology for obtaining the exergy loss of mineral resources throughout a certain period of time and 2) to apply it to the Australian case. From the available data of production and ore grade trends of Australian mining history, the tons of Metal equivalent lost, the cumulative exergy consumption, the exergy decrease of the economic demonstrated reserves and the estimated years until depletion of the main base-precious metals are provided, namely: for gold, copper nickel, silver lead and zinc.