Physical Geonomics: A Cradle-Grave-Cradle Approach for Mineral Depletion Assessment - Thanatia: The Destiny of the Earth's Mineral Resources - page 98

Exergy

Natural
Bonus

Thermod.
Rarity

Mine to
market cost

x C

x M

x B

Ore grade

Fig. 4.3 The concept of thermodynamic rarity (x c , x m and x B represent ore grades in Thanatia,
the mines and post-refining, respectively)

In the technosphere rarefaction appears both at the mineral's beginning-of-life
(BoL) and at its end-of-life (EoL). At the EoL it occurs when a metal or mineral
loses its usefulness and becomes landfilled, incinerated and sooner or later dispersed
into Thanatia, i.e. it “rarefies”. Its irreversible loss is accounted for by its exergy
replacement cost. At the BoL, when the mineral is mined and beneficiated, what
remains in the mine also rarifies, given that the concentration decreases as the limit
of Thanatia approaches. As a consequence and as stated previously, the amount of
exergy needed to extract the next tonne of mineral in turn increases. The rarefaction
process therefore carries two costs, one at the BoL and the other at the EoL.
In the authors' view, rarity is not a closed question (i.e a simple yes or no) but
rather a continuous function. Furthermore, it is not only a matter of ore grade
or geological scarcity but of exergy costing. It has a bearing on global energy
consumption and the sustainability of planetary resources because the greater the
thermodynamic rarity, the more di cult it is to obtain a given commodity. In this
respect, the economy of mine exploitation is better understood. This is because
thermodynamic rarity might unify into a continuous indicator all the following con-
cepts usually found in geological surveys serving to identify resources and reserves
data: recoverable, unrecoverable, hypothetical, proved, indicated, inferred, etc. There
is not an alternative single index that provides this knowledge.
Moreover, thermodynamic rarity, as measured in energy terms, evidently relates
to global energy consumption and the impact on the environment. The depletion
problem thus becomes not an absence of materials but an insu cient provision of