On April 30th, 1538, during the era of Spanish conquistadors, a man named Blas del Castillo
travelled with a group of workers to the Masaya volcano in what is now Nicaragua due to rumors
that its lava lake contained molten gold.
Over the span of several months, they extracted molten material from its active lava lake,
thinking that they were rich.
However, they were disappointed when no gold or silver was found upon analyzing the samples
they obtained.
Although this story is an amusing anecdote, there in fact is a volcano that erupts molten
gold which is erupting right now.
This gold does not flow out of the volcano in question as tons of material each day,
but rather through releasing millions of tiny solid gold crystals into the air.
The volcano which produces this gold is known as Mount Erebus, which emits approximately
80 grams of gold each day.
Mount Erebus is located far south of New Zealand in Antarctica, where it is centered 37 kilometers
north of McMurdo Station.
This volcano is unusual for a number of reasons.
Not only is it the tallest active volcano in Antarctica, but it also is one of the coldest.
Yet, at its summit is an active lava lake, of which only 7 other volcanoes out of more
than 1300 contain.
Erebus is the tallest volcano to contain an active lava lake, and the rapid cooling due
to the frigid temperatures might explain why it is the only volcano known to emit solified
gold particles.
Gold is relatively common in deep magma chambers, where it occurs in the range of typically
less than 1 part per million in the molten material.
Some of this gold is then concentrated and brought to the surface through heated water,
where it is emplaced at depth in the conduit the water takes right above where the water
boils.
Thus, many gold deposits formed beneath ancient active volcanoes on what used to be a series
of hot springs.
Gold can also be precipitated around volcanic fumaroles, or even around the active volcanic
crater of an erupting volcano.
For example, the Galeras volcano in Colombia produces 56 grams of gold each day which is
emplaced around its highly active vent.
The deposition of gold at Mount Erebus is relatively similar, except in the case of
this volcano microscopic particles of gold crystallize on the cooler crust of its lava
lake.
For a period of several minutes to hours, additional gold particles grow around a piece
of material.
Then, volcanic gas lofts particles of the recently deposited gold into the air, where
it falls within a 2 meter radius of the lava lake.
These particles are quite small, ranging from 0.1 to 80 micrometers, where a micrometer
is one millionth of a meter.
Other elements are also emplaced around the crater walls, including zinc and copper, which
solidify as the respective minerals sphalerite and chalcopyrite.
A second reason why the emplacement of solid gold does not occur at other volcanoes relates
to the eruptive style at Mount Erebus.
Its eruptions typically consist of a persistent lava lake which refills and drains over time,
but also on occasion produces volcanic explosions in either strombolian or phreatomagmatic eruptions.
During the peaceful portion of the eruption when a simple lava lake is present, very little
gas is emitted which allows for the crystals to grow.
At other volcanoes which frequently contain lava lakes such as Kilauea in Hawaii or Ambrym
in Vanuatu, higher amounts of gas are emitted which do not allow time for crystals of gold
to grow.
You might wonder if the 80 grams of gold produced a day could be commercially mined, as at current
prices that would be worth $5,421 US Dollars each day.
The quick answer is no, as not only would it be too dangerous to mine due to the threat
of random volcanic explosions, but would not be cost effective given the extreme remoteness
of Mount Erebus.
Regardless, this scenic volcano produces 29.2 kilograms or 64.4 pounds of gold each year
which is worth a total of about 2 million US dollars.
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