The Exergy Replacement Costs of Mineral Wealth - Thanatia: The Destiny of the Earth's Mineral Resources - page 358

account that gold is also extracted as a byproduct in ores of other major metals
such as NiCu, CuMo or ZnPb.
The average ore grade of the gold deposits studied by Mudd (2007b) is 2.244
g/t. The average energy consumption of mines worldwide meanwhile is reported
at 143,000 GJ/t. The latter value includes all the processes of gold production:
mining, beneficiating, smelting, converting and refining. The authors are however
only interested in the first two steps. Kennecott Utah Copper (2006a) reports an
energy share for gold production of 27% for mining, 54% for concentrating, 12%
for smelting, 6% for refining and 1% for tailings. Hence, it is assumed that 81%
of the energy use in gold production is used for those steps directly relating to
mining and concentrating. Furthermore, the same company reports that 1 kg of
gold is obtained from 2,180 kg of blister copper, which in turn is produced from
concentrated copper after the beneficiating process at around 30% Cu-purity. In
the absence of other sources of information, it is assumed that after beneficiation,
gold has a concentration of x r = 1:38E 04.

1200000

Real data set
Concentration Energy [GJ/t]

1000000

y = 135,664x -0,285

800000

600000

400000

200000

0

0 10 20 30 40 50 60 70 80 90

Ore Grade [g/t]

Fig. 12.2 Energy requirements for gold production in function of ore grade. Adapted from Mudd
(2007b)

12.4.2 Copper

Data sets for energy requirements as a function of the copper ore grade are ob-
tained from the study of Mudd (2010a) of sulphidic ores which contain also cobalt
and nickel. Mudd allocates energy among minerals according to tonnage. It is
assumed that 60% of the whole energy recorded is used for the mining and con-
centration processes 1 . Kennecott Utah Copper (2004) reports an average grade for
Cu after beneficiation of x r =28%. For the smelting and refining stages, the authors
assume the value given by the ecoinvent database (Classen et al., 2007) (21.4 GJ/t).

1 See in Sec. 8.4 the data related to copper energy consumption from Chapman and Roberts
(1983) and Kennecott Utah Copper (2004).