Classification, Distribution and Uses of Ores and Ore Deposits - Metals and Society: An Introduction to Economic Geology - page 33

exothermic and this increases the amount of energy required by the smelter.
Hydrous ore and gangue minerals have high water contents which is removed
by drying and roasting in large high-temperature kilns. The nickel oxide is
then smelted in furnaces that run at 1,360 C-1,610 C, the high temperatures
being required to accommodate the high magnesium content. Most laterite
smelters produce a ferronickel alloy that is sold directly steel manufacturers.

the placers, including the huge early Proterozoic example of the Witwatersrand in
South Africa and the more modern placers of California, Victoria, the Klondike and
the Yukon.
The final mineral in our short selection of commodities is uranium (Fig. 2.1e ).
An important class of deposits groups those localized at unconformities at the base
of Proterozoic sedimentary basins on Archean cratons in northern Canada and
northern Australia. Hydrothermal deposits in the USA and through central Asia
occur in younger sedimentary basins. Two notable examples where uranium is
produced in multi-element deposits are Olympic Dam in Australia (Fig. 2.1a ) and
the Witwatersrand conglomerates of South Africa. The R ossing deposit in Namibia

is magmatic, Randstad in Sweden occurs in black shales, and the Yeelirrie deposit
of Australia is hosted by surficial sediments (calcretes).
Most major iron deposits (not shown in Fig. 2.1 ) formed in a very specific
geological setting during a unique period of Earth history. About 90% of iron ore
is mined from “banded iron formations” or BIF, a type of chemical sediment that
precipitated from seawater on shallow continental platforms during the early
Proterozoic. As explained in Chap. 5, this period in Earth history saw a marked
increase in the oxygen content of the atmosphere and oceans, a process that
triggered the precipitation of iron oxide that had been dissolved in seawater. Most
of the world's great iron deposits are therefore found in sedimentary sequences
overlying Archean cratons; in Brazil, Australia, Canada and Russia.
Titanium is mined in two very different types of deposit. The most common ore
is ilmenite, a mineral that occurs as an accessory phase in a wide variety of igneous
and metamorphic rocks but also in much higher abundances in a special type of rock
called anorthosite. This rock consists essentially of calcic plagioclase with a few
percent of ferromagnesian minerals and a variable amount of Fe-Ti oxide.
A specific type called “massif anorthosite” was emplaced in continental crust
during the middle Proterozoic and this type commonly contains mineable
concentrations of ilmenite. Large deposits of this type are found in a belt that
extends from Quebec in Canada through to Norway.
When igneous or metamorphic rocks are subjected to chemical weathering and
erosion, ilmenite, which is stable under these conditions, is released, transported in
rivers and re-deposited at the coastline. When the continental crust is stable and
subjected to protracted periods of weathering, and when the coastline is a stable

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