GOLD
Gold (Au), a metallic, element of characteristic, golden
colour most often occurs as the native metal alloyed in varying
amounts,with silver. Less frequently it is found in chemical
combination with tellurium principally as sylvanite(( Au, Ag)
Te2) or calaverite (AuTe2). Gold crystallises in the isometric
system, but crystals are usually distorted into dendritic or
leaf-like aggregates. More often, gold shows no crystallinity
but is found finely disseminated through its ores. The metal
is soft, malleable (grains will flatten instead of breaking when
struck with a hammer), ductile, and very heavy (sp.gr. 19.3
when pure). It is not affected by any single acid. Colour
intensity depends upon the amount of silver present. Placer
gold is often associated.with other heavy minerals such as
magnetite, ilmenite, rutile, zircon, and titanite
in " black
sand."
Calaverite (AuTe2) is pale yellow to, yellowish silvery
white in colour. Crystals are small, striated and lath shaped,
and belong to the monoclinic system. Calaverite has a hardness
of 2.5 and sp. gr. of 9.O. The gold content of the pure mineral
is 44 per cent.
S.ylyanite ((AuAg) Te2) is the most abundant telluride
of gold. It is silvery white to steel grey.in colour with bright
metallic lustre and prominent cleavage. Hardness (1.5-2) and
sp. gr. (7.9-8.3) are somewhat less than for calaverite. The
gold content of sylvanite is 24.2 per cent.
Gold mining. methods have been many.and varied. Early.
workings were exploited by pan and sluice box. Later,
hydraulicking and dredging became common placer practice.
With development.of lodes and underground placers, under-
ground methods became increasingly important and most of
the known techniques have been used.
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