mining is a kind of surface,
open-pit mining. When you think of
this kind of mining, you usually think of early
prospectors. Click here to visit our Prospecting page.
Prospectors, another name for miners, were looking for
They might find it in flakes, nuggets, or gold dust. Gold is
veins like the ones in the palm of your hand. The gold
had to be separated from the rock around it. Sometimes water
erosion helped it along by wearing away the rock so that the
gold flowed with the water into the nearby rivers. When this
happened, it would travel with the water until it reached parts
of the river where the water slowed down—like bends in the
river. Because gold is heavier, it would drop to the bottom. This was a terrific thing for the early prospectors
because it took an underground mineral and made it into a
surface mineral. Surface minerals are easier and cheaper to
reach. Prospectors would travel around until they found their
claim, or land that they wanted to mine.
Placer mining was done in rivers, creeks, and streams. The
great thing about placer mining was that you didn’t actually
have to know too much about mining to do it. Simply said,
placer mining was where the miner scooped dirt into a pan from
the bottom of a stream, river, or creek. He swirled the
dirt and water and then poured
the water out of the pan [panning]. Since gold was heavier, it would
be left in the pan. That’s why miners used to say that they hit
“pay dirt” when they found lots of gold in one place.
If the prospector found a stream where there were lots of
gold nuggets, he used a rocker. Rockers were long boxes that
the prospector shoveled the dirt and water into. He would rock
this box [like panning], combining the water and dirt, and this
poured out the end of the box leaving the gold behind. Sometimes placer miners would work
together because this made the job easier. It was not an easy
job. Miners stood in cold, deep
water for hours and hours and the work was really hard.
picture on the right shows a
sluice taking the water,
dirt, and gold downhill. A geological
engineer, named Rafal Swiecki, says that even expensive new
tools for dredging gold don’t work as well as the sluice. He
says that the sluice doesn’t clog up as much as the newer
equipment does, it is cheaper, and actually collects more gold
the first time through. It is interesting to see that placer
mining is still going on all over the world.
After awhile, prospectors found all the surface gold and had to
start digging deeper to find it. Sometimes a hundred foot deep holes were dug in
order to find a vein of gold.
The dirt from the bottom of the hole was put into a
bucket which was pulled out of the hole by other miners.
Then it was mixed with water like they did with placer
mining. Gold would sink to the bottom and the dirt
would be poured off with the water.
Amy Green | Agency:
placer mining has its drawbacks, though. The streams and
rivers that are being mined have their bottom layers removed.
This wrecks the habitats that were down there. The
environment is hurt by the sandy silt that flows down into other
streams from the mine. This changes the level of the
streams and makes them muddy so that the sun doesn’t reach the
fish and underwater life.
that prospecting was over with the Gold Rush. We were
surprised to find out that it isn’t true. Nowadays, prospectors
are usually looking for underground minerals because—like in the
Gold Rush days—surface mining has already found the minerals
that are on, or close to, the surface. Satellite photos are
used to find places where minerals might be located. The gold rush
prospectors went from river to river until they found
gold. This took a lot of time and was
unsuccessful. Now we use scientific tools to test
the ground above areas that might be mined. Scientists look for
something called ‘trace elements’ which are really small pieces
of rocks or ore that tell the scientists that the mineral might
be there. For example, when we visited the
zinc mine, we
were told that it was originally found by people who saw
ore on the top of the mountain.
Geologists knew what kind
of rock would be found around zinc ore so they probably looked
for that, too. With the high cost of
scientists are sure to locate a mineral, find out how much is
there, and test the quality of it before they ever begin to mine
Minerals Mined using Placer
Prospecting tools today:
Gravimeter: Gravity meters measure
the pull of gravity.
This meter will show the kind of rock or mineral that is
underground by how much pull they have. It helps the
scientist to understand what is underground.
Magnetometers: help find certain kinds of iron ores and
Ultraviolet Lamps: used to find fluorescent minerals.
We went in a
zinc mine and saw how the light made different minerals glow
in different colors.
counters: measure radiation to find uranium and other