Mineral Resources

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Types of Mining

Placer Mining

gold panning 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.

The 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. 

Coloma CA 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.
Coloma CA Coloma CA
aqueduct 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 canal.
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.
monitor for placer mining Large-scale commercial placer mining used huge water nozzles, or monitors to blast away gold-bearing gravels.
placer workings, CA 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.

Open-Pit Mining

copper mine, AZ 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.
copper mine, AZ A typical mining truck, capacity 50 tons or so. The capital costs of even a small mine are in the millions.
copper mine, Utah 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.
copper mine, Utah 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.
nickel mine, Ontario An open pit at Sudbury, Ontario.
nickel mine, 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.
iron ore plant, PA 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.
taconite pellets 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.
molding sand 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.
strip mines, KY The open areas among the wooded hills are coal strip mines in eastern Kentucky.

Underground Mining

Climax MIne, Colorado 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.
Climax Mine, Colorado 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.

The mine is sitting right on the Continental Divide at 11,000 feet elevation. This picture was taken in May.

Climax Mine, Colorado Later on, mining was carried on by surface mining. This is the mine in the summer of 1999.
sand mine, Wisconsin 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


ore crusher 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.
separation mill After crushing, the ore goes to a mill, such as this one near Sudbury, Ontario.
ball mills 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.
mill control room This large mill complex is operated by only about 100 workers and run from this control room.
ore flotation tanks 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.

Waste Disposal

tailings 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.
tailings Bingham Canyon, Utah, has a vast waste pile.
tailings 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.
tailings Some tailings present particular health problems, like these uranium mine tailings in New Mexico.
acid mine runoff 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 old mines.
mercury mine 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 - we hope.
runoff collection pond 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.


smelter, Sudbury, Ontario The smelter complex at Sudbury, Ontario. You are looking at well over a billion dollars worth of industrial facilities. The dark, medium-sized stack is nearly as tall as the Washington Monument. The tall stack is 1250 feet high - tallest in the world when it was built. The metal tubes leading to its base are almost 20 feet in diameter.

One of the facilities here is a shop for servicing rail equipment used in the mines. Given the variety of metals extracted from the ores here, this plant could literally build a locomotive from scratch. (They don't, but they could if they decided to.)

smelter, Sudbury, Ontario The Sudbury Superstack. This single stack emits one per cent of the entire planet's sulfur emissions - up to 40,000 tons per day.
smelter, Sudbury, Ontario Smelting separates metal ores from silicate slag. Here slag is being poured off a crucible. To tip it, someone has to attach a chain to the rear of the crucible. I talked to a retired smelter worker who told me of a friend who was attaching the chain when the shackle broke and dumped the contents of the crucible on him.
slag cars, Sudbury, Ontario Slag is poured into these cars and taken to the slag disposal area. The white material is lime to prevent slag from sticking to the metal of the cars.
slag dumping, Sudbury, Ontario The slag is dumped on a disposal heap.


energy use, CA 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!
energy use, CA 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.
energy use, CA Again in 1993. The pink car is still there - trying for a spot on the National Register of Historic Places, no doubt.
energy use, CA 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?
oil drilling bit oil drilling bit 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

tunnel, New York City 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.
tunnel, New York City 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 machine bits 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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