|How is gold taken out of the ground?|
Gold (Au) is mined. Most gold deposits are
hydrothermal. This means that solutions deep in
the crust move from depth towards the surface.
These fluids are not pure water but have dissolved
ions such as Au ions. These atoms of Gold are
carried in solution mainly as chloride complexes
AuCl (aqueous). When the solutions ascend they
cool down and flakes of gold are precipitated from
solution. Geologists find these hydrothermal gold
deposits and then excavate the rocks, crush them
and separate the gold flakes from the waste.
Another source of gold is called a PLACER
deposit. These are sedimentary deposits in which
gold flakes and nuggets are concentrated by
fluvial processes (i.e. streams transport of bed
load). Eventually the heavy minerals like native
gold end up concentrated in the gravel deposits.
Gold is mined.
Gold is one of the few metals that can be found
as actual gold and not as gold ore (ore is
minerals containing the metal that need to be
smelted). Unfortunately, the process of extracting
gold ore is really bad for the environment,
because it uses mercury, which is very poisonous.
Taking gold out of the ground is called,
"mining". There are two main types of mining:
placer and vein. Placer mining is when the gold is
found with other products of dirt and sand and
then is separated out. Usually this is done with a
pan and water where the sand and dirt float to the
top of the bottom and the gold stays at the
bottom. Vein mining is the most important where
gold is obtained from processing thousands of
ounces of ore. The method is more extensive and
requires a lot of refining. Gold was discovered
right here in a Northern California river in 1848
by James Marshall; this is when the gold rush
started. If you go to Sacramento, California,
there are places where you can go mine for gold
yourself, and you get to keep the gold you find!
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