Grand Canyon of the North
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The biggest operating open pit iron ore mine in the world, more than three miles long, two miles wide and 535 feet deep. It was the first strip mine on the Mesabi Iron Range.
The amazing view continues to grow as the present mining operation expands.
Visitor information center on-site with area brochures. Open mid-May through September, Monday through Saturday, 9 a.m. to 5 p.m., Sunday 1-5 p.m.
Open-pit mining, also known as opencast mining and open-cut mining, refers to a method of extracting rock or minerals from the earth by their removal from an open pit or borrow.
The term is used to differentiate this form of mining from extractive methods that require tunneling into the earth. Open-pit mines are used when deposits of commercially useful minerals or rock are found near the surface; that is, where the overburden (surface material covering the valuable deposit) is relatively thin or the material of interest is structurally unsuitable for tunneling (as would be the case for sand, cinder, and gravel). For minerals that occur deep below the surface—where the overburden is thick or the mineral occurs as veins in hard rock— underground mining methods extract the valued material.
Open-pit mines are typically enlarged until either the mineral resource is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic. When this occurs, the exhausted mines are sometimes converted to landfills for disposal of solid wastes. However, some form of water control is usually required to keep the mine pit from becoming a lake.Open Cut mines are dug on benches, which describe vertical levels of the hole. These benches are usually on four meter to sixty meter intervals, depending on the size of the machinery that is being used. Many quarries do not use benches, as they are usually shallow.
Most walls of the pit are generally dug on an angle less than vertical, to prevent and minimise damage and danger from rock falls. This depends on how weathered the rocks are, and the type of rock, and also how many structural weaknesses occur within the rocks, such as a fault, shears, joints or foliations.
The walls are stepped. The inclined section of the wall is known as the batter, and the flat part of the step is known as the bench or berm. The steps in the walls help prevent rock falls continuing down the entire face of the wall. In some instances additional ground support is required and rock bolts, cable bolts and shotcrete are used. De-watering bores may be used to relieve water pressure by drilling horizontally into the wall, which is often enough to cause failures in the wall by itself.
A haul road is situated at the side of the pit, forming a ramp up which trucks can drive, carrying ore and waste rock.
Waste rock is piled up at the surface, near the edge of the open cut.
Minnesota's iron ore was actually discovered while miners were on their way to seek gold. Since their aim was gold, the iron was ignored. As it turned out, the iron would become more valuable to northern Minnesota than the gold.
Iron ore was discovered on the three iron ranges at different times. The first ore shipped from the Vermilion Range was in 1884, the Mesabi Range in 1892, and the Cuyuna Range in 1911.
The mines were operated through the hard work of the miners. They used shovels and pickaxes to take the ore out of the rock. Horses and mules hauled the ore out of the mine. Later, steam shovels and engine powered tools were used. Mining was dangerous work. Many miners were killed in mine accidents. The worst mining disaster in Minnesota happened in 1924 on the Cuyuna Range. Forty-one miners drowned in the Milford mine when a nearby lake broke through the underground mine, flooding the tunnels.
The mines attracted immigrants from almost every nation in Europe. Thousands of immigrants were arriving in America at the same time as the mines were opened. The Minnesota mines provided jobs for many immigrants. Most of the jobs were for unskilled, manual labor that required great physical strength.
Towns were built around the mines. As the mines were expanded, many towns were moved to new locations because they were built on top of iron ore. Part of the city of Hibbing, known as the "North Forty", was moved to make way for mine expansion. The move started in 1919 and took two years to complete at a cost of $16,000,000. 185 houses and 20 businesses were moved, and some of the larger buildings had to be cut in half for the move. Only a few uninhabited remnants of the original townsite are left. If you visit Hibbing today, you can see remains of sidewalks, house foundations and street lights near the Hull Rust Mahoning Mine overlook.
Since ore shipping began in 1895, more than 1.9 billion tons of earth has been removed to form this "Man-Made" Grand Canyon. At peak production in the 1940's, as much as one quarter of the ore mined in the United States came from the Hull Rust Mine. The present Hull Rust (about 2,291 acres) embraces more than 30 individual mines which had been opened between 1895 and 1957.
Most high grade iron ore has been removed from the site. However, the site continues operating extracting taconite.
Taconite is a low-grade iron ore. When the high-grade natural iron ore was plentiful, taconite was considered a waste rock and not used. But as the supply of high-grade natural ore decreased, industry began to view taconite as a resource. Dr. E.W. Davis of the University of Minnesota, along with other scientists and engineers, conducted years of laboratory tests and experiments to find a way to take the iron ore out of the taconite rock. After many years of hard work, a process was developed to create taconite pellets.
1. Blasting
Taconite is a very hard rock. Using explosives, the taconite is blasted into small pieces.
2. Transportation
The taconite pieces are scooped up by electric shovels. Each shovel can hold up to 85 tons of rock! The shovels place the taconite into giant dump trucks. These trucks are as big as a house and hold up to 240 tons of taconite. The trucks take the taconite directly to the processing plant, if it is nearby, or to train cars if it is far away.
3. Crushing
At the processing plant, the taconite is crushed into very small pieces by rock crushing machines. The crushers keep crushing the rock until it is the size of a marble. The rock is mixed with water and ground in rotating mills until it is as fine as powder.
4. Separation
The iron ore is separated from the taconite using magnetism. The remaining rock is waste material and is dumped into tailings basins. The taconite powder with the iron in it is called concentrate.
5. Pellets
The concentrate (the wet taconite powder) is rolled with clay inside large rotating cylinders. The cylinders cause the powder to roll into marble-sized balls. (This is like rolling wet, sticky snow into balls to make a snowman). The balls are then dried and heated until they are white hot. The balls become hard as they cool.
6. Steel
The taconite is loaded into ore ships. These ships sail on the Great Lakes to Gary, Indiana, Cleveland, Ohio and other steel-making towns. The taconite is brought to the steel mills to be melted down into steel.
In conclusion:
The Hull Rust Mahoning Mine in Hibbing, Minnesota
* World's largest open pit iron ore mine
* First ore shipments in 1895 (still being mined today, 100 years later)
* Originally 30 separate mines
* Total area: 1,591 acres
* Total length: 3 1/2 miles
* Greatest width: 1 1/2 miles
* Greatest depth: 535 feet
* Total ore shipped: About 1 billion tons Total rock removed: About 2 billion tons (that's 4 trillion pounds!)
To claim this cache, please email me the following:
1)The name the "locals" use for the piles of overburden.
2)The estimated height of the dump truck.
3)The estimate of how many cubic yards of rock that would fill the shovel.
4)The name given to processed taconite.
5) The name of the popular sport now played on the site of Old North Hibbing.
6) How far was that section of the city moved.
Optional.
a) Post a picture of your group inside the bucket or with the truck.
b) Post a picture of your group with the cut-outs at GZ.
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