California State Stuff – The Mineral

How appropriate that our state mineral is gold. California, like
gold, has long been the symbol of wealth and power. The image of
our state however is becoming tarnished, but gold never fades. The
glorious mask of King Tutankhamen is as fresh and lustrous today as
on the day it was made over three thousand years ago. One of the
unique properties of gold is that it does not combine readily with
other elements including oxygen, the great corroder. Gold is easily
to work, one gram can be hammered into a six foot square with a
thickness of only 1000 atoms. Heavier than lead and much rarer,
gold is scattered all over the world in small amounts and has been
treasured since antiquity.

The human quest for gold has caused massive shifts in population,
washed mountains to the sea, created instant cities and empires,
enslaved human beings, caused parents to sell their children
destroyed civilizations, and condemned vast numbers of people to a
squalid existence. The state motto is not “surf’s up ” as some
cynics have suggested but it’s “Eureka!” — I found it. But for
every one who has struck it rich, thousands have toiled in poverty.

To understand the full history of gold we must travel back in time,
and I do mean back, back to the beginning of the universe. After
the big bang (which astronomers think started the whole thing) the
only matter in the universe was hydrogen and helium, the simplest
elements. Clouds of hydrogen gas swirling and eddying throughout
space randomly converged. Under gravitational attraction the
molecules fell in toward one another. As more and more gas was
attracted, the molecules became excited and gave off visible light.
As the hydrogen atoms fell in together they became denser and
denser and hotter and hotter. When the temperature reached 20
million degrees Fahrenheit a nuclear reaction spontaneously began.
A star was born.

This nuclear reaction is called fusion; it is a simple event. Two
hydrogen atoms are forced together and form helium. In
the process a tiny bit of energy is released. A star lives its life
in a precarious balance– gravity pulling all of the atoms together
and fusion driving them all apart.

From the death and decay of these first stars came the other
elements of our universe, including gold. Stars begin to die when
all of the nuclear fuel is exhausted and they collapse violently in
cataclysmic explosions known as supernova. In the star’s center under tremendous gravitational pressure, helium is fused into carbon and oxygen, the first new elements to be made. Under continued and increased pressure silicon, sulphur, argon and calcium appeare. Eventually the very center becomes pure iron. Iron is very stable and cannot be changed under pressure. It actually absorbs energy from the rest of the star, causing a violent implosion and then an explosion.

The star’s center contracts into a pure ball of neutrons. The remaining star has a mass comparable to our sun but with a diameter of ten miles! A matchbox full of these pure neutrons weighs several tons. From the remnants of the star blasting out into space, under tremendous pressure and heat, the rest of the heavier elements are created, among them are uranium, lead and gold.

It was the death of these very first stars that began the mix of
elements that now make up the interstellar dust. The generations of
stars that followed, including our sun, were spawned from this dust
— that rich mixture of particles from blown-up stars coalesced
into our sun and the planet Earth over five billion years ago.
Carbon, oxygen, nitrogen, hydrogen and helium make up 99% of
living matter. Just like Joni Mitchell sang long ago about the
children of Woodstock, we are all literally “star dust.”

Next the gold got from the hot interior of the Earth to
the jewelry counter at Macy’s.

In my last column we began a review of California’s State mineral,
gold. Gold, like all the other elements except hydrogen and helium,
is formed during the violent death of a star. In this cataclysmic
explosion known as a supernova, very high temperature and pressure
creates the environment necessary for the formation of new elements. Stellar debris hurtles out into space and from this material new stars and planets are made. Five billion years ago gold was accreted into the Earth along with all the other elements and is now found scattered throughout our plantet in very small amounts.

And so how do these tiny bits of gold get concentrated enough so
that we can efficiently recover them? The earth is covered by
gigantic chunks of rock called plates that float over the hot, liquid magma. Think of the continents like the thin, skim of milk that forms on top of hot chocolate.

As we all know too well, California is a geologically active area.
About 100 million years ago Pacific Plate began grinding against
the North American Plate and began being subducted (geologic terms
have always seemed so erotic to me- subduction, orogeny, thrust
fault). The sea floor plunged under the North American plate. Some
of the material was scraped off and became the Coast Range but the
majority descended into the heat of the Earth. The entire mass of
rocks including the small amounts of gold melted. This old, melted
seafloor became the Sierra Nevada batholith (means deep rock).

Later this mass of rock began uplifting and intruding on the
overlying rocks. As the batholith got closer to the surface
superheated water flowed through it and dissolved gold and quartz
out of the mass of the rock. This super-rich stream was lighter
than the rest of the rock material and it forced its way upward and
filled the cracks and crevices of the overlying rock. Gold and
quartz come out of solution at about the same temperature so they
are often found together in distinct veins. These are the so-called
Mother Lode deposits that miners seek.

As the rock mass continued to uplift it was eventually exposed and
began to erode. Veins of gold and quartz washed out into streams.
Since gold is very heavy it was naturally deposited when the
velocity of streams slowed down. These deposits are known as placer
deposits and often occur near a sand bar or bend in the river. The
first gold miners in California had it made, they only had to go
and pick the gold out of the quartz veins or gather it up from
creeks and rivers.

The discovery of gold in California is a well-known story. At John
Sutters mill on the American River, James W. Marshall, found gold
concentrated at the base of the waterwheel. They attempted to keep
it a secret but failed. The world literally rushed into California. The native peoples already suffering at the hands of the Spanish were overwhelmed by the onslaught of gold-fevered settlers.

Soon, the easy to get gold was gotten and it became much difficult
to extract. Eventually the clever miners developed powerful water
cannons that duplicated the work of nature, except a billion times
faster. They literally washed mountainsides down and ran the debris
through collection boxes to extract the flakes of gold. The scale
of this destruction is almost unbelievable. Tremendous volumes of
sediment, debris, cobblestones, rocks washed down into creeks,
rivers and out into flood plains. Thousands of acres of very
productive farmland were ruined. The San Francisco Bay actually
turned brown with sediment. The Anti-Debris Association was formed
to fight this destructive practice. In 1884 a Circuit Court banned
the flushing of debris into streams thereby effectively stopping
hydraulic mining forever in California.

Over 75% of the gold ever mined in the US came out of the Sierra
Nevada and most of this was mined within sight of Highway 49, the
so-called gold country. To quote from Roadside Geology of Northern
California “Now that the passage of many years has enabled the
ravaged streams to clean their channels and a growth of trees to
start in the yawning earth wounds opened by hydraulic mining, it is
easy to cast a romantic spell over the memory of placer gold mining
in California. It is hard to remember in the stillness of a ghost
town that it was the site of a squalid industry driven by greed and
economic desperation and producing a commodity useful mainly for
storage at Fort Knox.”

Well not quite. Gold remains one of the most popular forms of body
adornment. Many humans like to pierce holes in their skin and slide
pieces of metal through them. And a ring of gold continues to be
the visible sign to the world that a male and a female are coupled
and unavailable to other members of their tribe. Eureka.



Posted on

August 22, 2009