Like I’ve said on the last post, there are many mining methods and their use is defined by the nature of the mineral deposit:
Strip mining: Commonly used for coal, sand, gravel and oil sands. This method is used when the resources occur in shallow horizontal deposits near the surface. Consists on the removal of the soil and rocks layers -also called overburden, until the resources’ exposure. Afterwards, the resource is extracted by machinery and each strip is refilled with the overburden that had been removed.
The environmental impacts of strip mining are:
- Destruction of natural communities over large areas;
- Extensive soil erosion;
- Acid drainage, a process in which chemical runoff rans into waterways. Occurs when sulfide minerals in newly exposed rock surfaces react with oxygen and rainwater to produce sulfuric acid. The sulfuric acid runs off and leaches metals from the rocks. Acid drainage is actually a natural phenomenon, however, mining accelerates it by exposing many new rock surfaces at once;
- Water polution by sulfuric acid;
Subsurface mining: Commonly used for zinc, lead, nickel, tin, gold, copper, diamonds, phosphate, salt, coal and uranium. Is used when the resources occurs in concentrated pockets deep underground. The most dangerous form of mining, consists on deep excavation. Networks of tunnels are dug or blasted out to follow deposits of the mineral, removed by the miners. Subsurface mining can be mind-boggling, and the world’s deepest mines extend nearly 4 km (2.5 mí) undergroud, are found in South Africa.
The environmental impacts of the subsurface mining are:
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Acid drainage ;
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Toxic leachate can make it’s way down into groundwater;
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Abandoned mine sites can continue polluting groundwater long after mining has ceased;
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Subsurface mining often progresses below the water table, so water must be constantly pumped out of the mine in order to prevent flooding. When a mine is abandoned, the pumping ceases, and water floods the mine;
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Poisoned water might find an outlet, usually into streams and rivers where, in changing the pH level, the ambient life is killed;
The social impacts of subsurface mining are:
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One of society’s most dangerous occupations because if a mine collapse, there will be a massive sinking of the land above, like happened in Utah, in August 7th, 2008, resulting on the death of six miners;
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Injury and death from dynamite blasts and collapsed tunnels;
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Toxic fumes and coal dust can be fatal because they can lead to respiratory diseases, including fatal black lung disease.
Open pit mining: Commonly used for copper, iron, gold, diamonds and coal. Whenever the mineral to be exploited is gravel, sand, clay, and stone like limestone, granite, marble and slate, the pits are called quarries. Is used when the mineral is spread widely and evenly throughout a rock formation, or when the earth is unsuitable for tunneling. This process consists on digging a gigantic hole and removing the desired ore, along with waste rock that surrounds the ore. The pit is expanded until the resource runs out or becomes unprofitable; than the pit is abandoned. The world’s largest open pit mine is the Binghan Canyon Mine, near Salt Lake City, Utah, with 4km (2.5 mi) across and 1.2 km (o.75 mi) deep. The Binghan is also the world’s largest human made hole in the ground.
The open pits needs to be large because of the volume of waste rock needed to be removed in order to extract relatively small amounts of ore, which contains still smaller traces of mineral.
The environmental impacts of open pit mining are:
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Considerable degree of habitat loss and aesthetic degradation;
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Acid drainage, therefore chemical contamination;
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Abandoned pits generally fill up with groundwater because they’re far more deeper than water table. This groundwater soon becomes toxic as water and oxygen reacts with sulfides left in ore, in a way that sulfuric acid is produced.
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Acidic water from the pit can harm wildlife, percolate into groundwater supplies and spread through the region’s environment;
Curiosity:
Even though developed nations have regulations requiring waste heaps to be capped with clay, soil, and vegetation once the mines are closed, many dumps will leach acid for hundreds of thousand of years. The largest Superfund toxic waste cleanup site in the US is the Berkeley Pit. Closed in 1982, nowadays the huge hole is filled with groundwater and became so acidic (pH of 2.5) and concentrated with toxic metals that microbiologists discovered new species of microbes in the water. The impressive thing is that the harsh conditions were so rare in nature that scientists had never before encountered microbes adapted to them.
Placer mining: Commonly used for gold and gems, this method is used on riverbed deposits, whenever metals and gems accumulate, having been displaced from elsewhere and carried along by flowing water. In this process the miners sift through material in modern or ancient riverbed deposits, normally using running water to separate lightweight mud and gravel from heavier minerals of value. This method is used by Congo’s coltan miners. Today’s African miners are like the miners who ventured to California in the Gold Rush of 1849 and later to Alaska in the Klondike Gold Rush, areas where placer mining is still practiced.
The environmental impacts of placer mining are:
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Debris are washed into streams, in a way that they become uninhabitable for fish and other life for many miles downstream;
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The stream banks are disturbed, causing erosion and ecological harm to important riparian plant communities.
Mountaintop removal: Commonly used for coal in Appalachian Mountains. This method is used especially because it is economically efficient for companies to extract coal, in a way that it has expanded in recent years. This practise consists on the removal of the mountain’s fores by clear cut, than the topsoil is removed, and rocks are blasted away to expose the coal. Repeated cycles of blasting and extraction may remove hundreds of vertical feet of mountaintop. The environmental impacts of placer mining on stream and river ecosystems pale in comparison to the devastation wrought by mountaintop removal, no wonder why there are some environmental organizations like ILove Mountains and Appalachian Voices agains this type of mining.
Nowadays, there is a lot of pressure from civils, environmental organizations and governamental departments to forbit the mountaintop removal. Yesterday (3/31/09), a federal judge issued an injunction blocking the U.S. Army Corps of Engineers from authorizing new mountaintop removal mining operations through its streamlined Nationwide Permit procedure.
The environmental impacts of mountaintop removal are:
- Waste rocks dumped into valleys and streams degradates or destroys immense areas of habitat and pollutes and clogs streams and rivers;
- Intensified erosion because of the slopes deforestation and valleys filled with debris;
- Mudslides become frequent and flash floods ravage the lower valleys;
- Some critics argue that valley fillig violates the Clean Water Act.
The social impacts of mountaintop removal are:
- People living near the sites can be heartbreaking. Blasts from mines crack house foundations and wells;
- Floods tear through properties;
- Coal dust causes respiratory ailments;
- Contaminated water unleashes a variety of health problems;
- Loose rock tumbles down into yards and homes;
- Overloaded coal trucks speed down once-peaceful rural roads;
- Landowners are pressured to sell their land to coal companies;
- Coal industry touts the importance of mining jobs for the Appalachian economy. However, the efficiency of mountaintop removal means that fewer workers are needed. Therefore, in recent years, even though coal extraction has risen, employment has declined;
Because of the environmental impacts of mining, governments of the US, Canada, and other nations now require that mining companies restore, or “reclaim”, vegetation atop surface-mined sites following mining. However, there are still many nations like Congo that don’t have any regulation at al. In the US, the Surface Mining Control and Reclamation Act mandates restoration efforts, and requires companies to post bonds to cover reclamation before mining is approved. To restore a site, they have to remove buildings and other structures, replace overburden and fill in shafts, and replante the area with vegetation.
About replanted areas, some things still need to be reminded:
- Even restored sites might still suffer from mining impacts -such as soil and water impact from acid drainage for many years.
- Restored sites do not generally regain the natural biotic communities that were present before mining. That happens because the fast-growing grass anchor restoration efforts helping to control erosion, however, it doesn’t do anything to speed the establishment of forests, wetlands, or other complex natural communities;
- The grass used often outcompete slower growing native plants in the acidic, compacted, nutrient-poor soils that usually result from mining;
- Many vital symbioses that maintain ecosystems are eliminated by mining and are very difficult to restore. Specialized relationship between plants and fungi and plants and insects are examples.
It is still very important to remember that minerals are nonrenewable, they’re in finite supply, because they don’t regenerate fast enoughto provide us a new supply once we have mined all known reserves.
In 2008, geologists calculated that the world’s known reserves of tantalum will last us for about 129 more years at today’s rate of consumption; if the demand increases, it might run out faster. If everyone in the world consumed it at US rate, than it would last for 18 years, only.
However, there are reasons that make it very hard to know for sure how long the minerals reserves will last:
- As we discover new deposits of minerals, the amount of “known reserve” increases, as well as the years these minerals are available to us. That’s the main reason why some previously predicted shortages have not come to pass.
- New technologies can modivy demand for minerals in unpredictable ways. Just as cell phones and computer chips boosted demand for tantalum, fiber-optic cables decreased demand for copper as they replaced copper wiring in communications applications;
- Changing consumption patterns alter the speed with which we exploit mineral resources. Today China, India, and other nations are rapidly increasing their consumption, and as a result, global demand and market prices for many metals and other commodities are rising;
- Advances in recycling technologies could help us to extend the lifetimes of some mineral resources.
Despite these sources of uncertainty, it is also good to keep in mind that the Earth’s supplie of mineral resources are finite, nonrenewable, and therefore, it is wise to search for ways to use them more sustainably. Although recycling might not be the final step, it certainly helps.
