The Exergy Evolution of Mineral Wealth - Thanatia: The Destiny of the Earth's Mineral Resources - page 380

Fig. 13.6 The Hubbert Peak applied to Australian copper reserves
been supported by the development of a new technology, namely “high pressure acid
leach” or HPAL (Sec. 8.7.2) which is capable of processing di cult to treat nickel
laterite ores 4 .
Fig. 13.7 shows that the ore grade of Ni mines has decreased from 4.57 to 1.17%
in the time period analysed. Accordingly, the natural bonus decreased from 1.6 to
1.4 toe/t.
Fig. 13.8 shows the Hubbert Peak Model applied to Australian nickel reserves.
Considering that the reserves of nickel were R 1967 = 112:3 Mtoe, the peak is set to
occur in 2039. The regression factor of the curve is RF = 0:80.
13.3.4 Silver
Silver is usually found in Australian mines also containing lead and zinc and hence
their production rates are highly connected. Silver can also be produced from gold
or copper mines but this is a minor contribution when compared to their lead-
zinc-silver counterparts. The Broken Hill silver-lead-zinc field in New South Wales,
responsible for the establishment of almost all major mining companies in Australia,
was discovered in 1883 and quickly proved very profitable.
Silver ore grades have since suffered a drastic reduction, passing from over 3,500
g/t in the initial years, to less than 800 g/t in only a decade. Since 1931, ore grades
have declined to less than 200 g/t, with the current ore grade around 105 g/t (see
Fig. 13.9). This loss of quality is reflected in the natural bonus: 342 toe/t in 1884
and dropped to 248 toe/t in 2007.
The Hubbert Peak Model applied to silver reserves generates a poor fit. The
4 The major mine at Murrin Murrin has been particularly instrumental in pioneering HPAL plants
(it should be noted that other similar and simultaneously occurring projects failed financially and
technically, namely Cawse and Bulong).