MadSci Network: Earth Sciences

Re: How do people find gold? Is there a special device that locates it?

Date: Thu Jan 3 16:42:49 2002
Posted By: David Kopaska-Merkel, Staff Hydrogeology Division, Geological Survey of Alabama
Area of science: Earth Sciences
ID: 1004835086.Es

There is no special gold-finding device, like there is for radioactive
materials. However, there are many ways of prospecting for gold, some of
which include the use of sophisticated devices that can also be used for
other purposes.

One of the oldest methods is still a good first step: panning. Gold is
refractory, which means that it is not easily destroyed. Therefore, when
gold-bearing rocks weather, the gold particles are transported more or less
intact and end up in streams. Because gold is heavy it is concentrated with
other heavy particles in places where light particles cannot settle.
Panning carries this process a step further and allows gold to be
concentrated in a pan from which lighter materials have been winnowed
(washed out). If you find gold in a stream, you have already located one
gold deposit, but you do not know the size and shape of the area in which
gold can be found. Also, the gold in the stream bed must have a source, and
the particles of gold in the stream are a clue to this unknown source,
which could be more valuable than the auriferous (gold-bearing) stream
sediments. You can follow the gold downstream until it is so rare that it
is not worth seeking, and you can follow it upstream, towards the source.
When the gold in the stream vanishes, you have passed the source.

The gold in a stream is commonly derived from rocks formed by hydrothermal
(hot water) activity. Hydrothermal quartz crystals fill fractures in rock
(forming quartz veins) and sometimes gold is deposited with the quartz.
This is not the only kind of rock that contains gold, but it is one of the
most common. If you know from panning that there is a source of gold in a
certain region, you can search for it in several ways. Wandering around
with a burro and a hammer can work, but some modern methods are more
effective. You can look for hydrothermal rocks, or the other kinds of rocks
that may harbor gold. When you find them, collect samples and have them
analyzed chemically. In this way, you can find concentrations of tiny gold
particles that you might never see with the naked eye. If you find that the
gold is indeed in a hydrothermal deposit, then knowledge of how and where
that deposit formed gives you more clues about where to find the gold.
Generally, the geologic history of a region dictates that a given type of
deposit (for example, hydrothermal quartz veins) can form only in certain
places. Thus, you can prospect for gold using a geologic map.  Modern
prospectors may use a variety of methods: knowledge of historical
discoveries, chemical analyses of rocks that could host gold, geologic
mapping, and so on. After the gold deposit is located, additional chemical
analyses are needed to determine how much gold is present and the
concentration of gold in the ore. If the deposit is small, or the ore of
low grade, it might cost more to mine the gold than the metal is worth.

I hope this brief summary helps. I urge you to go online and look for other
sources of information about gold.  Here is a link to a list of
earth-science education web sites
( There is a
section listing web sites that give minerals information where you can
learn a lot more about gold and about mining.

David Kopaska-Merkel
Geological Survey of Alabama
PO Box 869999
Tuscaloosa AL 35486-6999
(205) 349-2852
fax (205) 349-2861

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