Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Types of Mining
||Everybody's mental picture of mining - gold panning.
Actually panning was used mostly in prospecting as a
quick way to determine whether or not stream sediments
contained gold. If gold turned up, the miner worked his
way upstream and eventually uphill to find the source.
material in the pan is noticeably darker than the
surrounding gravels. It consists largely of "black
sand" - magnetite, which is actually the most common
mineral found in panning.
||Here's where it all began, Coloma, California. A
workman at John Sutter's sawmill (reconstructed at left)
noticed flecks of gold in a sluice leading to the mill.
The gold had weathered out of rocks upstream. Below are
views looking up and down the American River here.
||Placer mining requires large amounts of water. Some
of the engineering feats by early miners were marvels of
pick-and-shovel engineering. This aqueduct spans a valley
near Grass Valley, CA. In some gold-rush areas of
California, nearly every back road is flanked by a small
||This old canal near Sonora, CA still carries water.
Well maintained canals like this are now used for local
water supplies, stock watering, and so on. Note that it's
following the contour line and definitely not flowing
straight downhill like a natural stream would.
||Large-scale commercial placer mining used huge water
nozzles, or monitors to blast away gold-bearing
||The Malakoff Diggings over a century after mining
ceased. The flat upland surface is an old erosion surface
covered by Tertiary lava flows. Many of these flows moved
down ancient valleys and buried ancient stream gravels
that were also gold-bearing. After attacking modern
gravels, gold miners went after the ancient gravels as
well. Note that these diggings are high above the valley
bottom. Gravels washed downstream covered large areas
near the base of the mountains. Siltation filled channels
in the Sacramento Valley and caused flooding. It took
about 30 years for the silt to move down the valley. The
big loser was San Francisco Bay, which lost much of its
shallows and wetlands.
||A typical open pit mine near Tuscon, Arizona. The
benches are about 20 feet high. Note the red zone
parallel to the land surface, showing the depth of
weathering, and the bluish tint of the fresh rock. This
is a porphyry copper deposit: copper minerals
disseminated in a fine-grained granitic rock. The fresh
rock is not economically minable, but weathering leaches
copper from the surface and concentrates the ores at
deeper levels, making the deposit rich enough to mine.
||A typical mining truck, capacity 50 tons or so. The
capital costs of even a small mine are in the millions.
||As Crocodile Dundee would put it: "That's not a
mine. This is a mine." This is the Bingham
Canyon copper mine west of Salt Lake City. From bottom to
top the mine reaches 2,500 vertical feet and has its own
climate zones. Note the haze in the bottom and the snow
on the higher levels.
||Everything at Bingham Canyon is on a grand scale. The
shovel cab is the size of a house - it fills a rail car
with one scoop. Tires for the earth movers are twelve
feet in diameter and cost $20,000.
||An open pit at Sudbury, Ontario.
||Where do you go from here? The bottom of the pit is
700 feet below. The pit can't be deepened without
widening it, and can't be widened without beginning to
move huge amounts of barren rock. Solution: start
underground mining from the bottom, linking to existing
tunnels from other mines.
||The device here revolutionized iron mining. In the
1950's, we only had a century or so of iron ore reserves.
Low-grade ore (called taconite)was abundant, but
too finely mixed with silicate rock. It could be
separated, but the resulting ore was too fine-grained -
it would blow right out of a blast furnace.
||This is how the problem was solved. The ground ore is
mixed with clay and sprayed onto a rotating conical drum,
where it rolls up into balls. When the balls reach a
certain size they roll off the drum onto a conveyor belt.
The result is the familiar gray pellets found along every
railroad track in the country. Thanks to this process
taconite can be mined readily and our iron reserves, for
all practical purposes, are unlimited.
||The perfect tread impressions in this sand near Ripon,
Wisconsin give some clue as to its use. Most of the sand
from this pit (in the St. Peter Sandstone) is exported to
Mexico for sand casting automobile engine blocks.
Any time you see a metal part with rounded corners and a
pebbly finish, it was probably sand-cast. The sand can be
re-used, of course, but eventually the grains become too
rounded to hold impressions well.
||The open areas among the wooded hills are coal strip
mines in eastern Kentucky.
||Everyone's mental picture of a mine: the molybdenum
mine at Climax, Colorado. Although the scene is 2,000
feet underground, it's still 10,000 feet above sea level.
Older mines had rails, but modern mines tend to use
diesel earth movers. To do that, you need adequate
ventilation, and most large mines have a noticeable wind
blowing through them. Some mines move more air, pound for
pound, than they do ore.
||All mining is like a military retreat - you pull back
with careful planning all the way. The mining at Climax
was once done by stoping - caving in the ore from
below. By 1969 the mine had collapsed the top of the
mountain to produce this "glory hole", looking
quite a bit like the crater of Mount Saint Helens.
mine is sitting right on the Continental Divide at 11,000
feet elevation. This picture was taken in May.
||Later on, mining was carried on by surface mining.
This is the mine in the summer of 1999.
||One of the most unusual mines in the United States -
an underground sand mine near Pepin Wisconsin. The
mine produces fracturing sand used in oil drilling
to hold fractures open to speed oil flow. Such sand has
to be coarse, very hard (to withstand enormous pressure),
and very round (so it can penetrate deep into fractures
without sticking). The coarse and poorly-cemented
Cambrian sandstone here is ideal.
From Mine to Metal
||The first stage in processing ore is to crush it to
roughly head-sized chunks. This zinc mine near Knoxville,
Tennessee has its crusher underground in the mine itself.
||After crushing, the ore goes to a mill, such as this
one near Sudbury, Ontario.
||Big chunks of ore are ground to sand size in ball
mills like these, filled with ore and large steel
balls. Yes, they do make a racket! They are not spinning
as fast as they appear - this is a long exposure in dim
light. The stationary mill shows the studs that help keep
the ore from slipping as the mill rotates.
||This large mill complex is operated by only about 100
workers and run from this control room.
||Once milled, the ore is separated from the silicate
residue by flotation. Surprisingly, it's the dense
ore that floats. Legend has it a miner's wife noted that
ore particles stuck to her soapsuds while washing her
husband's clothes. The milled ore is mixed with a
surfactant (fancy name for suds) sticks to the foam and
is skimmed off while the barren silicate rock sinks.
||Pulverized silicate residue from the flotation
process is called tailings. Tailings at Sudbury,
Ontario are deposited here. In places the tailings are
over 200 feet deep.
||Bingham Canyon, Utah, has a vast waste pile.
||Writers of the "ancient mysteries" school
claim that even today we could not build the Great
Pyramid. At peak production, Bingham Canyon moved the
volume of the Great Pyramid every month. To get an
idea of the scale of the waste piles, look at the
buildings at the base of the pile, bottom center.
||Some tailings present particular health problems,
like these uranium mine tailings in New Mexico.
||A common environmental hazard of mining is iron
contamination, leached out of the mine itself or mining
wastes. A little iron is essential to life; too much is
toxic. The rocks in the bottom of this stream near
Boulder, Colorado have been colored orange by iron from
||Small but very deadly. The mine here on the slopes of
Mount Diablo, near San Francisco, CA, is barely the size
of a football field but produced mercury. Associated
minerals in the deposit contain arsenic, antimony, and
other delectables. The pond catches the polluted runoff -
||The mine at Climax, Colorado, sends its waste water
over the Continental Divide to the Colorado River, with a
long chain of settling and filtration ponds extending
down-valley. Note the iron staining around this pond, the
highest in the chain.
||A typical street in the San Francisco Bay Area in
1972, just before the first oil embargo. This is looking
from the front yard of my former home. Don't even think
of trying to ban overnight on-street parking here!
||Same street in 1979; the cars look less crowded only
because a lot of residents are at work. Note the pink car
on the right edge of the photo.
||Again in 1993. The pink car is still there - trying
for a spot on the National Register of Historic Places,
||And 1994. The pink car has finally been painted and
moved after a mere 15 years. Have we learned anything
from the energy crunch of the 1970's?
||The business end of an oil drill. The three conical
wheels have studs impregnated with diamonds. They roll on
the rock as the drill turns and chip it away. The
fragments are flushed up the drill hole.
If the bit had
conventional pipe threads, imagine how hard it would be
to remove after being twisted by thousands of pounds of
force. That's why the threads taper so sharply. A turn of
only a few degrees is enough to loosen the threads.
Modern Tunneling Technology
||Some of the largest underground mining operations in
the U.S. are happening beneath Manhattan. This tunnel is
part of a massive sewage project, and the section here
was excavated using old-fashioned drilling and blasting.
||Once a long enough tunnel was excavated, a rotary
tunneling machine was installed. It cut the tunnel here.
The machine is guided by laser; a laser beam is oriented
in the direction the tunnel is to follow and the machine
operator keeps the laser beam cetntered on a target. This
tunnel is bare rock, not lined in any way.
||Tunneling machines have dozens of studded bits like
these pressing into the rock to grind it away. Very
similar (but bigger and more advanced) machines bored the
English Channel Tunnel. These are scaled up versions of
the wheels on the oil drill above.
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Created 18 September 1998, Last Update 28 May 2003
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