Geology Reference
In-Depth Information
The estimation of learning curves using econometric techniques has some points
for consideration. Söderholm and Sundqvist (2007). For instance, the need to sur-
vey the effect of detaching single observations especially outliers that may affect the
learning rate estimate or the impact of using different variable definitions. Another
issue is related to the way in which technological learning is operationalised. Ad-
ditionally, it is important to investigate differences in learning rates across various
technologies.
Without a doubt, the main barrier in an analysis regarding the influence of
technology in the mining sector's energy consumption is the lack of data about
fuel use trends for most commodities. Nevertheless, Mudd's investigation into gold
suggests that although progress in technology has been made, in most cases energy
requirements are increasing, because the core issue is the ore grade (Mudd, 2007b;
Domínguez and Valero, 2013). Hence, the long-term decline in ore grades will most
likely involve an unavoidable long-term increase in energy requirements. There is
simply not enough evidence to suggest that technology can indefinitely, avert the
rising energy demand.
Based on the results of Domínguez and Valero (2013), the authors assume that
the state of technology in the mining and concentration stages will not change
significantly throughout time and thus, the unit exergy costs are solely influenced by
changes in ore grades. It should be stated however that this is still an approximation
which could be eventually refined by additional empirical data and the application
of the learning curve theory.
12.4 Energy consumption as a function of ore grade for some
important commodities
The first step in calculating the exergy replacement costs of minerals is to obtain the
current energy consumption as a function of the ore grade associated with the mining
industry. Ideally, this should be obtained from empirical data. In this section two
important commodities where this information is available are briefly described,
namely gold and copper. The reader is also referred to (Valero D. et al., 2013),
where in addition to gold and copper, nickel, cobalt and uranium were analysed.
For the remaining commodities (where only static information is available), the
authors refer to the data contained in Table 8.3.
12.4.1 Gold
Mudd (2007b) studied the global trend of gold extraction in detail (see Fig. 12.2)
finding a clear declining ore grade tendency in the countries reviewed, namely Brazil,
Australia, South Africa, Canada and the United States. In Australia for instance,
ore grades have declined from 37 g/t in 1859, to the current 2 g/t. Cox and Singer
(1992) report an average gold content in different deposits of 0.22 g/t, taking into
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