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Mercury Contamination
Before the invention of the cyanide heap leaching method of extracting gold from ore in the
1890s, the mercury amalgamation method was used. With mercury amalgamation, crushed gold
and silver ore was mixed with liquid mercury. The mercury leached the gold and silver out into a
sometimes doughy solution called amalgam. The amalgam was commonly heated in retorts to
vaporize the mercury and leave the gold and silver behind. Mercury was sometimes recycled
through the process and sometimes not. However, in the 19th century, both the apparatus and
the process was "leaky" even when the mercury was carefully recycled. Steam engines to run
milling machinery were expensive to acquire and maintain, so many if not most of the mills using
the mercury amalgamation method were located along streams and rivers to take advantage of
cheap water power. This has resulted mercury contamination in the soils and watersheds of
some areas of the state.
The worst area for mercury contamination is the Carson River downstream of New Empire and
the main drainages such as Six Mile Canyon and Gold Canyon leading into it. During the Com-
stock
Era (1859-1880), about 7 million pounds of mercury are believed to have been lost through
this
drainage area, most of which went out into the Carson Sink. This is considered a Superfund
Site. NBMG studied the Carson River and has reports available on our website. The USGS has
both general and specific site information on mercury contamination.
It is important to note that not all areas of potential mercury contamination in Nevada have been studied or even identified. If you have concerns about a particular site, you should hire a consulting geologist or an engineering firm to do a study. It is also important to note that you may be held liable for the clean-up of any land you acquire or stake that has a mercury contamination problem.
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