Introduction - Metals and Society: An Introduction to Economic Geology - page 16

Fig. 1.7 Three types of Pb-Zn sulfide ore distinguished by different grain size. Top left Very fine-
grained unmetamorphosed ore from the McArthur River deposit. The pale yellow banded material
is fine-grained Zn-Fe sulfides and clay minerals. The detrital grains of quarts and lithic fragments
deform these bands; Right Fine-grained and deformed, slightly metamorphosed ore from Mt Isa.
Bottom left. Coarse-grained galena and bustamite (Mn-Ca silicate) from Broken Hill where
granulite-facies metamorphism has produced in large, easily processed ore (Photo (a) from Ross
Large, photo (b) from Peter Muhling, photo c from Chris Arndt)
contribute significantly to the viability of the operation. Common examples of such
“bonus metals” include gold or silver in copper ores, and platinum metals in Ni
ores. Another topical example is the rare- earth elements which were initially
recovered as a by-product during mining of the Bayan Obo iron deposit in China
(see Chap. 6). In contrast, the presence of small amounts of other metals can
complicate the extraction process and decrease the value of the ore. Examples of
“toxic” or unwanted metals include phosphorous in iron ore and arsenic in base-
metal sulfide ores.
1.5.3 Location of the Deposit
In Box 1.4 we also saw the influence of the location of a deposit. Its value, and its
very viability, decreases if it is far from centres of industry or population, or in a
harsh climate, or in a politically unstable region. All these factors increase the cost
of mining or of bringing the metals to market; or they render the operation of a mine
too dangerous or risky.