Geology Reference
In-Depth Information
17.2.6 Depletion should be measured on a grave-to-cradle basis
through exergy replacement costs
Humanity must consider depletion and dispersion as an inevitable part of a ma-
terial's life. This is what the authors refer to as “down the rainbow”. The reader
has seen that in all attempts to measure depletion “over the rainbow”, either in
monetary or physical terms, there exists a tension relating to the impossibility of
assigning an objective value to physical scarcity. The concept even though it is in
essence, imaginary, can aptly explain and measure the degree of depletion which
occurs as a direct result of Man's activities. In theory, a given mineral's price should
provide a good indication of depletion but in reality countries and mining compa-
nies always want to exchange their mineral endowment for quick cash. Thereby a
mineral's price is subject to market abundance, combined with political and finan-
cial uncertainties and conflicts of interests rather than diminution. In which case,
mankind is hardly going to hurry towards the goal of reaching a global accounting
consensus that takes a long hard look at the annual loss of value in mineral terms.
Regrettably therefore, raw material dispersion has not been su ciently considered
in economic analysis. It has instead simply been ignored as a material availability
loss; or considered as an environmental concern. As happens with heat and energy
balances, the effect of Man is likewise obtained in the difference:
Extracion + Recycling - Societal stock = Dispersion
An alternative measuring yardstick could be the annually extracted tonnes for
each and every mineral. Nevertheless this would entail an intricate accounting
system (as a tonne of indium will not have the same monetary or mineral value of a
tonne of iron). Tonnes extracted state nothing as to the value of that which could
be potentially exploited in the future.
In the authors' opinion, mineral endowment depletion must be measured on
a grave-to-cradle basis (Valero D. et al., 2013). There is however, as of yet, no
universal and systematic accounting of element cycles and there remains a need
to go further into the accounting of annual endowment loss. In light of this, the
authors propose a measurement of resource depletion through either the minimum
or actual physical cost of replacing minerals with the best available technology, from
a degraded state in Thanatia to the conditions in which they are currently present in
Nature. The two parameters with which to do so are replacement exergy and exergy
replacement cost. Whereas the “over the rainbow” component represents actual
consumption, “down the rainbow” symbolises the debt that this current generation
passes over to those of the future.
Exergy replacement costs can also explain the three types of entropic criticality
that a given commodity might present: First, “mine criticality” appears when the
element is not scarce per se but rather sparsely distributed in the crust rather than
concentrated in mines. An example of such would be the extraction of lithium in
oceans. The second relates to when the metal is found with others that show simi-
lar chemical behaviour, presenting thus “chemical criticality”. Rare earths exhibits
 
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