Geology Reference
In-Depth Information
Gold's ore grade has followed a general declining trend, even though there have
been various intermediate peaks coinciding with new discoveries. Ore grades have
descended from 50 g/t in 1857, to 1.94 g/t in 2007.
With this information, the authors have calculated gold's natural exergy bonus
(exergy replacement cost) which has decreased from 13 to 7 toe/kg in the period
analysed. They have also produced a Hubbert Peak Model for all post-1943 Aus-
tralian gold deposits. Previous years have been discarded due to the fluctuation
of production rates, caused by the discovery of new gold fields. It was assumed
that by 1943 most of the reserves had been already discovered. The value of R for
1943 was calculated as the sum of the exergy replacement cost reserves in 2007,
plus the cumulated exergy replacement cost of production between 1943 and 2007
(R 1943 = 90:9 Mtoe). Accordingly, the theoretical peak in production occurs in 2007
(see Fig. 13.4) with a regression factor of RF = 0:87. It should however be noted
that empirical data suggests that the peak occurred some ten years earlier. The
authors believe that the discrepancy between the real and modelled peak may have
been caused by external factors, which include for example, corporate strategies
rather than resource scarcity per se.
Fig. 13.4 The Hubbert peak applied to Australian gold reserves
13.3.2 Copper
Copper has also been an important contributor to the country's wealth, given that
Australia is a major world copper producer. Copper deposits were discovered and
have been worked on a significant and profitable scale since 1842. Ore grades have
however declined from over 27% to 1.01%. Exergy replacement costs have decreased
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