Epilogue - Thanatia: The Destiny of the Earth's Mineral Resources - page 509

iron ore reserves are larger than those of aluminium, the greater concentration of
the latter deposits with respect to Thanatia, make these “more valuable” from an
exergy perspective.
Exergy replacement costs can also provide a measure of the annual depletion
caused “down the rainbow” through raw material extraction. In a case study in-
volving 37 minerals, the authors examined the “down the rainbow” costs and the
“over the rainbow” ones, i.e. the embodied exergy required in the mining, benefi-
ciation and refining stages of mineral production. The “down the rainbow” figures
obtained show that the degradation of the non-fuel mineral endowment in 2008 was
equivalent to more than 5,000 Mtoe and around 4,000 Mtoe if recycling was taken
into account. The “over the rainbow” costs meanwhile, amounted to around 1,100
Gtoe. Such numbers highlight the elevated weight of mineral dispersion and the
need to account for it in order to improve raw material management on a global
scale.
17.3.3 The exergy evolution of mineral endowment
So as to provide a dynamic vision of mineral endowment, variable “time” was in-
cluded in the analysis. Specifically the authors considered the following research
questions in two case studies, Australia and the world as a whole: 1) how and at
what rate mineral commodities have been depleted over time and 2) how would
resources under a “business as usual scenario” be affected. This was carried out us-
ing the well-known Hubbert bell-shaped curves employing exergy replacement costs
instead of tonnage. This was done because exergy as a unit of measure has two ad-
vantages. First it accounts for the quality of the assessed commodity and second all
Hubbert Peak models can be placed into a single diagram, given that all curves are
comparable in size. This diagram has been coined by the authors as “exergy count-
down” and provides a snapshot of past, present and forecasted extraction rates,
together with the available fuel and non-fuel mineral reserves.
17.3.3.1 Case study: Australia
Australia, which apart from being one of the most important mineral exporting
nations in the world, is also unique in having registered ore grade trends for its
main minerals. The evolution of the extraction and depletion of Australia's gold,
copper, nickel, silver, lead, zinc, iron, coal, oil and natural gas deposits throughout
its mining history was analysed in terms of exergy replacement costs. The results
show a degradation of 2.4 Gtoe (some 5 times its 2010 oil reserves). The Hubbert
Peak Model revealed that the theoretical peak has been already reached for zinc
(2010), silver (2009), gold (2007), oil (1996) and lead (1994). Copper was forecasted
to reach its peak in 2026, natural gas in 2029, iron in 2030, nickel in 2039 and finally
coal in 2048. It should be noted however that the fit of the lead-zinc-silver group
was somewhat unsatisfactory.