Mountaintop removal mining

Mountaintop removal mining (MTR), often referred to as mountaintop mining (MTM), is a form of surface mining that involves the mining of the summit or summit ridge of a mountain. It is most closely associated with coal mining in the Appalachian Mountains, located in the eastern United States, the most biologically diverse temperate hardwood forests in the world. The process involves blasting with explosives to remove up to 1,000 vertical feet (300 m) of mountain to expose underlying coal seams. Waste form mining in the form of excess rock and soil are often dumped into what are called a "holler fills" or "valley fills." After active mining has been completed all disturbed areas of the mining operation are required by Federal law contained in the Surface Mining Control and Reclamation Act of 1977 (SMCRA) to be reclaimed as one of several post-mining land use options.



History

Increased demand for coal in the United States, sparked by the 1973 and 1979 petroleum crises, created incentives for a more economical form of coal mining than the traditional underground mining methods involving hundreds of workers, triggering the first widespread use of MTR. Its prevalence expanded further in the 1990s to retrieve relatively low-sulfur coal, a cleaner-burning form, which became desirable as a result of amendments to the U.S. Clean Air Act that tightened emissions limits on high-sulfur coal processing. With an increasing call for energy independence in the U.S., as well as a growing call for Coal-To-Liquids and "clean coal technologies", MTR has continued to expand into the 2000s.

Occurrence

MTR in the United States is most often associated with the extraction of coal in the Appalachian Mountains, where the United States Environmental Protection Agency (EPA) estimates that 2,200 square miles (5,700 km2) of Appalachian forests will be cleared for MTR sites by the year 2012. It occurs most commonly in West Virginia and Eastern Kentucky, the top two coal producing states in Appalachia, with each state using approximately 1000 metric tons of explosives per day for the purposes of surface mining. At current rates, MTR in the U.S. will mine over 1.4 million acres (5,700 km²) by 2010, an amount of land area that exceeds that of the state of Delaware.

Process



Land is deforested prior to mining operations and the resultant lumber is either sold or burned. According to SMCRA, the topsoil is supposed to be removed and set aside for later reclamation. however, coal companies are often granted waivers and instead reclaim the mountain with "topsoil substitute." The waivers are granted if adequate amounts of topsoil are not naturally present on the rocky ridge top. Once the area is cleared, miners use explosives to blast away the overburden, the rock and subsoil, to expose coal seams beneath. The overburden is then moved by various mechanical means to areas of the ridge previously mined. These areas are the most economical area of storage as they are located close to the active pit of exposed coal. If the ridge topography is too steep to adequately handle the amount of spoil produced then additional storage is used in a nearby valley or hollow, creating what is known as a valley fill or “hollow fill.” A front-end loader or excavator then removes the coal, where it is transported to a processing plant. Once coal removal is completed, the mining operators back stack overburden from the next area to be mined into the now empty pit. After backstacking and grading of overburden has been completed topsoil (or a topsoil substitute) is layered over the overburden layer. Next grass seed is spread in a mixture of seed, fertilizer, and mulch made from recycled newspaper. Dependant on surface land owner wishes the land will then be further reclaimed by adding trees if the pre-approved post-mining land use is forest land or wildlife habitat. If the land owner has requested other post-mining land uses the land can reclaimed to be used as pasture land, economic development or other uses specified in SMCRA.

Because coal usually exists in multiple geologically stratified seams, miners can often repeat the blasting process to mine over a dozen seams on a single mountain, increasing the mine depth each time. This can result in a vertical descent of hundreds of extra feet into the earth. Many if not all of these seams mined in the MTR method are too thin to be mined using any other method of mining.

Economics

Just under half of the electricity generated in the United States is produced by coal-fired power plants. MTR accounted for less than 5% of U.S. coal production as of 2001. In some regions, however, the percentage is higher, for example MTR provided 30% of the coal mined in West Virginia in 2006.

Historically in the U.S. the prevalent method of coal acquisition was underground mining which is very labor-intensive. In MTR, through the use of explosives and large machinery, more than two and a half times as much coal can be extracted per worker per hour than in traditional underground mines, and thus greatly reducing the need for workers. The industry lost approximately 10,000 jobs from 1990 to 1997, as MTR and other more mechanized underground mining methods became more widely used. The coal industry asserts that surface mining techniques, such as mountaintop removal, are safer for miners than sending miners underground.

Proponents argue that in certain geologic areas, MTR and similar forms of surface mining allow the only access to thin seams of coal that traditional underground mining would not be able to mine. MTR is some times the most cost-effective method of extracting coal and provides high paying jobs. The counties that host MTR are often the poorest in Appalachia. For instance, in McDowell County, West Virginia, which produces the most coal in the state, over 37% of residents live below the poverty line. In Kentucky, counties with coal mining have economies no better than adjoining counties where no mining occurs.

Legislation in the United States

In the United States, MTR is allowed by section 515(c)(1) of SMCRA. Although most coal mining sites must be reclaimed to the land's pre-mining contour and use, regulatory agencies can issue waivers to allow MTR. In such cases, SMCRA dictates that reclamation must create "a level plateau or a gently rolling contour with no highwalls remaining."

Permits must be obtained to deposit valley fill into streams. On four occasions, federal courts have ruled that the US Army Corps of Engineers violated the Clean Water Act by issuing such permits. Massey Energy Company is currently appealing a 2007 ruling, but has been allowed to continue mining in the meantime because "most of the substantial harm has already occurred," according to the judge.

The Bush administration appealed one of these rulings in 2001 because the Act had not explicitly defined "fill material" that could legally be placed in a waterway. The EPA and Army Corps of Engineers changed a rule to include mining debris in the definition of fill material, and the ruling was overturned. However, if passed, the Clean Water Protection Act (H.R.1310), a bill in the House of Representatives, would revert this change by specifying that coal mining waste does not constitute fill material, in effect disallowing valley fills.

On December 2, 2008, the Bush Administration made a rule change to remove the Stream Buffer Zone protection provision from SMCRA allowing coal companies to place mining waste rock and dirt directly into headwater waterways.

A federal judge has also ruled that using settling ponds to remove mining waste from streams violates the Clean Water Act. He also declared that the Army Corps of Engineers has no authority to issue permits allowing discharge of pollutants into such in-stream settling ponds, which are often built just below valley fills.

On January 15, 2008, the environmental advocacy group Center for Biological Diversity petitioned the United States Fish and Wildlife Service to end a policy that waives detailed federal Endangered Species Act reviews for new mining permits. The current policy states that MTR can never damage endangered species or their habitat as long as mining operators comply with federal surface mining law, despite the complexities of species and ecosystems. Since 1996, this policy has exempted many strip mines from being subject to permit-specific reviews of impact on individual endangered species.

On May 25, 2008 North Carolina State Representative Pricey Harrison introduced a bill to ban the use of mountaintop removal coal from coal fired power plants within North Carolina. This proposed legislation would have been the only legislation of its kind in the United States, however the bill was defeated.

Criticism

Critics contend that MTR is a destructive and unsustainable practice that benefits a small number of corporations at the expense of local communities and the environment. Though the main issue has been over the physical alteration of the landscape, opponents to the practice have also criticized MTR for the damage done to the environment by massive transport trucks, and the environmental damage done by the burning of coal for power. Blasting at MTR sites can also expels fly-rock into the air, which can disturb or settle onto private property nearby.

Advocates of MTR claim that once the areas are reclaimed as mandated by law, the area provides flat land suitable for many uses in a region where flat land is at a premium. They also maintain that the new growth on reclaimed mountaintop mined areas is better suited to support populations of game animals. Many thin seams of coal can only be recovered by MTR mining as they are too small for man and machines to enter by underground mining methods. Critics are quick to show photographs of active mine sites but then rarely show the same area after mining and reclamation has been completed. They claim that because flat land is worth more than steep rocky mountain side, land value increases after completion of MTR for the local land owners. These mines employ many local residents and pay some of the highest wages in the region for equipment operators.

Some artists have been leaders in the fight against the process of mountaintop removal. Writers and musicians have been particularly active in Kentucky. In April 2005, respected writer and social critic Wendell Berry invited Kentucky writers on a tour of mountaintop removal sites that started a movement that continues to heat up. The attending writers have since contributed writing on the issue to national magazines and newspapers and even created a respected book called Missing Mountains, edited by Kristin Johnason, Bobbie Ann Mason, and Mary-Ann Taylor Hall. The book contains a foreword by Silas House and an afterword by Berry and is widely used in college courses.

2005 also saw the release of the album Songs For the Mountaintop, a collection of anti-MTR music. In 2007 the band Public Outcry (Silas House, Jason Howard, Jessie Lynne Keltner, Kate Larken, George Ella Lyon, and Anne Shelby) was formed to sing anti-MTR songs. They have performed at universities, festivals, and libraries throughout the region and in 2008 released their first, eponymous album.

Many personal interest stories of coalfield residents have been written; the first, Lost Mountain by Erik Reese,was released in 2005. In addition, Penny Loeb (Moving Mountains: How One Woman and Her Community Won Justice From Big Coal) and Michael Shnayerson (Coal River) have also contributed to the anti-mountaintop removal struggle with informative works. To date, Dr. Shirley Stewart Burns, a coalfield native, has written the only academic book on mountaintop removal, titled Bringing Down The Mountains (2007), which is loosely based on the 2005 Ph.D. dissertation of the same name. All of these books are critically acclaimed and their authors continue to make a collective effort to give voice to the people of the Appalachian coalfields.

In 2006, cultural historian, Jeff Biggers, published The United States of Appalachia, which chronicled the historical contributions of Appalachians and their impact on the nation, and examined the role of mountaintop removal in destroying Appalachia's history and cultural significance. Biggers continues to write extensively on the cultural and human costs of mountaintop removal, and the parallel connection between the devastation of the environment and the culture.

In 2006, Catherine Pancake released the first comprehensive feature-length documentary on mountaintop removal "Black Diamonds: Mountaintop Removal and the Search for Coalfield Justice." The film received critical acclaim and multiple awards including a selection in the Documentary Fortnight at Museum of Modern Art (MoMA.org.) The film features Julia Bonds who won the 2003 Goldman Prize.

In 2007 Ann Pancake released the novel Strange As This Weather Has Been, which has been hailed by critics and received several awards. The book is the first major fiction work about the subject of MTR and was highly critical of the mining practice.

In 2007, a feature documentary titled Mountain Top Removal was completed by Haw River Films. The film features Mountain Justice Summer activists, coal field residents, and coal industry officials. Included in the film are Former US President George W. Bush and West Virginia Governor Joe Manchin, among others. On April 18, 2008 the film received the Reel Current award selected and presented by Al Gore at the Nashville Film Festival.

In 2008, a second feature documentary titled Burning the Future: Coal in America was made by Director David Novack and produced by former Shooting Gallery executive, CJ Follini. The film examines the explosive conflict between the coal industry and residents of West Virginia. Confronted by emerging “clean coal” energy policies, local activists watch a world blind to the devastation caused by coal's extraction. The film was awarded The International Documentary Association's 2008 Pare Lorentz award for Best Documentary

Maria Gunnoe is a community organizer with the Ohio Valley Environmental Coalition who is concerned about the long-term effects of mountaintop removal coal mining. She is featured in the 2008 documentary film Burning the Future: Coal in America and the 2007 documentary film Mountain Top Removal. In 2006, Gunnoe received the Callaway Award for her organizing efforts in her southern West Virginia community.

Biodiversity

An EPA environmental impact statement finds that streams near valley fills from mountaintop removal contain high levels of minerals in the water and decreased aquatic biodiversity. The statement also estimates that 724 miles (1,165 km) of Appalachian streams were buried by valley fills between 1985 to 2001.

Although U.S. mountaintop removal sites by law must be reclaimed after mining is complete, reclamation has traditionally focused on stabilizing rock formations and controlling for erosion, and not on the reforestation of the affected area.Fast-growing, non-native grasses such as lespedeza sericea, planted to quickly provide vegetation on a site, compete with tree seedlings, and trees have difficulty establishing root systems in compacted backfill. Consequently, biodiversity suffers in a region of the United States with numerous endemic species. In addition, introduced species of elk on mountaintop removal sites in Kentucky are eating tree seedlings.

From http://en.wikipedia.org/

Mine reclamation

Mine reclamation is the process of creating useful landscapes that meet a variety of goals, typically creating productive ecosystems (or sometimes industrial or municipal land) from mined land. It includes all aspects of this work, including material placement, stabilizing, capping, regrading, placing cover soils, revegetation, and maintenance.

In the USA, Mine reclamation is a regular part of modern mining practice.[1]

From http://en.wikipedia.org/

Longwall mining

Longwall mining is a form of underground coal mining where a long wall (typically about 250-400 m long) of coal is mined in a single slice (typically 1-2 m thick). The longwall "panel" (the block of coal that is being mined) is typically 3-4 km long and 250-400 m wide.



History



The basic idea of longwall mining was developed in England in the late 17th century. Miners would undercut the coal along the width of the coal face, removing coal as it fell, and using wooden props to control the fall of the roof behind the face. this was known as the Shropshire method of mining. While the technology has changed considerably, the basic idea remains the same, to remove essentially all of the coal from a broad coal face and allow the roof and overlying rock to collapse into the void behind, while maintaining a safe working space along the face for the miners.

Starting around 1900, mechanization was applied to this method. By 1940, some referred to longwall mining as "the conveyor method" of mining, after the most prominent piece of machinery involved. Unlike earlier longwall mining, the use of a conveyor belt parallel to the coal face forced the face to be developed along a straight line. The only other machinery used were an electric cutter to undercut the coal face and electric drills for blasting to drop the face. Once dropped, manual labor was used to load coal onto the conveyor parallel to the face and to place wooden roof props to control the fall of the roof.

Such low-technology longwall mines continued in operation into the 1970's. The best known example of this was the New Gladstone Mine near Centerville, Iowa. This longwall mine did not even use a conveyor belt, but relied on ponies to haul coal tubs from the face to the slope where a hoist hauled the tubs to the surface.

Longwall mining has been extensively used as the final stage in mining old room and pillar mines. In this context, Longwall mining can be classified as a form of retreat mining.

Modern Methods



The gate road along one side of the block is called the maingate or headgate; the road on the other side is called the tailgate. Where the thickness of the coal allows, these gate roads have been previously developed by continuous miner units, as the longwall itself is not capable of the initial development. In thinner seams the advancing longwall mining method may be used. In this system the gate roads are formed as the coal face advances. Only the maingate road is formed in advance of the face. The tailgate road is formed behind the coal face by removing the stone above coal height to form a roadway that is high enough to travel in. The end of the block that includes the longwall equipment is called the face. The other end of the block is usually one of the main travel roads of the mine. The cavity behind the longwall is called the goaf, goff or gob.

Fresh air travels up the main gate, across the face, and then down the tail gate. Once past the face the air is no longer fresh air, but return air carrying away coal dust and mine gases such as methane, carbon dioxide, depending on the geology of the coal. Return air is extracted by ventilation fans mounted on the surface. A series of seals are erected as mining progresses to maintain goaf gas levels.

Typically to avoid coal in the goaf spontaneously combusting, goaf gases are allowed to build up so as to exclude oxygen from the goafed area. This means that there is an explosive goaf fringe between the face and the goaf at all times requiring constant monitoring.

The longwall equipment includes:

* A number of hydraulic jacks, called powered roof supports, chocks or shields, which are typically 1.75m wide and placed in a long line, side by side for up to 400 m in length in order to support the roof of the coalface. An individual chock can weigh 30-40 tonnes, extend to a maximum cutting height of up to 6 m and have yield rating of 1000-1250 tonnes each, and hydraulically advance itself 1m at a time.
* The coal is cut from the coalface by a machine called the shearer (power loader). This machine can weigh 75-120 tonnes typically and comprises a main body, housing the electrical functions, the tractive motive units to move the shearer along the coalface and pumping units (to power both hydraulic and water functions). At either end of the main body are fitted the ranging arms which can be ranged vertically up down by means of hydraulic rams, and onto which are mounted the shearer cutting drums which are fitted 40-60 cutting picks. Within the ranging arms are housed very powerful electric motors (typically up to 850 kW) which transfer their power through a series of lay gears within the body the arms to the drum mounting locations at the extreme ends of the ranging arms where the cutting drums are. The cutting drums are rotated at a speed of 20-50 revs/min to cut the mineral from coal seam.
* The shearer moves along the length of the face sat upon the AFC, driving through a chainless haulage system (which resembles a ruggedised rack and pinion system especially developed for mining),Previous to chainless haulage systems, a heavy duty chain was run the length of the coal face for the shearer to pull itself along the face. The shearer moves at a speed of 10-30m/min depending on cutting conditions. The AFC on which the shearer sits, is placed in front of the powered roof supports, and the shearing action of the rotating drums cutting into the coal seam, disintegrates the coal this being loaded onto the AFC. The coal is removed from the coal face by a scraper chain conveyor called the AFC to the main gate. Here it is loaded onto a conveyor belt and transported to the surface, usually via a network of conveyor belts.
* At the main gate the coal is usually reduced in size in a crusher, and loaded onto the first conveyor belt by the beam stage loader (BSL).

As the shearer removes the coal, the AFC is snaked over behind the shearer and the powered roof supports move forward into the newly created cavity. As mining progresses and the entire longwall progresses through the seam, the goaf increases. This goaf collapses under the weight of the overlying strata. The strata approximately 2.5 times the thickness of the coal seam removed collapses and the beds above settle onto the collapsed goaf. This collapsing can lower surface height considerably, causing serious problems like changing the course of rivers and severely damage building foundations.

The advantages of longwall mining include:

* better resource recovery (about 80% compared with about 60 percent for Room and pillar method)
* less roof support consumables needed
* higher volume coal clearance systems
* minimal manual handling
* subsidence is largely immediate, allowing for better planning and more accountability by the mining company.
* safety of the miners is enhanced by the fact that they are always under the hydraulic roof supports when they are extracting coal

The disadvantages of longwall mining include:

* surface subsidence, which may considerably alter the landscape above the mine which can damage natural or man-made structures or features.

From http://en.wikipedia.org/

Landfill mining

Landfill mining and reclamation (LFMR) is a process whereby solid wastes which have previously been landfilled are excavated and processed. The function of landfill mining is to reduce the amount of landfill mass encapsulated within the closed landfill and/or temporarily remove hazardous material to allow protective measures to be taken before the landfill mass is replaced. In the process, mining recovers valuable recyclable materials, a combustible fraction, soil, and landfill space. The aeration of the landfill soil is a secondary benefit regrading the landfill's future use. The combustible fraction is useful for the generation of power. The overall appearance of the landfill mining procedure is a sequence of processing machines laid out in a functional conveyor system. The operating principle is to excavate, sieve and sort the landfill material.

The concept of landfill mining was introduced as early as 1953 at the Hiriya landfill operated by the Dan Region Authority next to the city of Tel Aviv, Israel. Waste contains many resources with high value, the most notable of which are non-ferrous metals such as aluminium cans and scrap metal. The concentration of aluminium in many landfills is higher than the concentration of aluminum in bauxite from which the metal is derived.

Practical applications

Landfill mining is also possible in countries where land is not available for new landfill sites. In this instance landfill space can be reclaimed by the extraction of biodegradable waste and other substances then refilled with wastes requiring disposal.

Mining construction landfill sites is the simplest form of landfill mining. Construction landfills contain three basic components, wood, scrap metal and gypsum, or drywall, along with a minimal amount of other construction materials. The wood collected can be used as fuel in coal burning power plants and the scrap metal reprocessed.

Mining of municipal landfills is more complicated and has to be based on the expected content of the landfill. Older landfills, in the United States before 1994, were often capped and closed, essentially entombing the waste. This can be beneficial for waste recovery. It can also create a higher risk for toxic waste and leachate exposure as the landfill has not fully processed the stewing wastes. Mining of bioreactor landfills and properly stabilized modern sanitary landfills provides its own benefits. The biodegradable wastes are more easily sieved out, leaving the non biodegradable materials readily accessible. The quality of these materials for recycling and reprocessing purposes is not as high as initially recycled materials, however materials such as aluminum and steel are usually excluded from this.

Landfill mining is most useful as a method to remediate hazardous landfills. Landfills that were established before landfill liner technology was well established often leak their unprocessed leachate into underlying aquifers. This is both an environmental hazard and also a legal liability. In the US, Environmental Protection Agency fines can tax the local economy up to 30 years after the site has closed. Mining the landfill simply to lay a safe liner is a last, but sometimes necessary resort.

Tools and machinery

The parts of the mining process are the different mining machines. Depending on the complexity of the process more or fewer machines can be used. Machinery is easily transported on trucks from site to site, mounted on trailers. The following machines are added in order in increase of mining complexity:

* Excavators
* Moving floor and elevator conveyor belts
* A coarse rotating trommel screen
* A fine rotating trommel screen
* A magnet
* Front end loader
* Odor control sprayer

The mechanics of mining

An excavator or front end loader uncovers the landfilled materials and places them on a moving floor conveyor belt to be taken to the sorting machinery. A trommel is used to separate materials by size. First, a large trommel separates materials like appliances and fabrics. A smaller trommel then allows the biodegraded soil fraction to pass through leaving non-biodegradable, recyclable materials on the screen to be collected.

An electromagnet is used to remove the ferrous material from the waste mass as it passes along the conveyor belt.

A front end loader is used to move sorted materials to trucks for further processing.

Odour control sprayers are wheeled tractors with a cab and movable spray arm mounted on a rotating platform. A large reservoir tank mounted behind the cab holds neutralising agents, usually in liquid form, to reduce the smell of exposed wastes.

Operational flow

Excavators dig up waste mass and transport it, with the help of front end loaders, onto elevator and moving floor conveyor belts. The conveyor belts empty into a coarse, rotating trommel. The large holes in the screen allow most wastes to pass through, leaving behind the over-sized, non-processable materials. The over-sized wastes are removed from inside the screen. The coarse trommel empties into the fine rotating trommel. The fine rotating trommel allows the soil fraction to pass through, leaving mid-sized, non-biodegradable, mostly recyclable materials. The materials are removed from the screen. These materials are put on a second conveyor belt where an electromagnet removes any metal debris. Depending on the level of resource recovery, material can be put through an air classifier which separates light organic material from heavy organic material. The separate streams are then loaded, by front end loaders, onto trucks either for further processing or for sale. Further manual processing can be done on site if processing facilities are too far away to justify the transportation costs.

From http://en.wikipedia.org/

In-situ leach

In-situ leaching (ISL), also called in-situ recovery (ISR) or solution mining, is a process of recovering minerals such as copper and uranium through boreholes drilled into the deposit. The process initially involves drilling of holes into the ore deposit. Explosive or hydraulic fracturing may be used to create open pathways in the deposit for solution to penetrate. Leaching solution is pumped into the deposit where it makes contact with the ore. The solution bearing the dissolved ore content is then pumped to the surface and processed. This process allows the extraction of metals and salts from an ore body without the need for conventional mining involving drill-and-blast, open-cut or underground mining.

Process

In-situ leach mining involves pumping of a leachate solution into the ore body via a borehole, which circulates through the porous rock dissolving the ore and is extracted via a second borehole.

The leachate solution varies according to the ore deposit - for salt deposits the leachate can be fresh water into which salts can readily dissolve. For copper, acids are generally needed to enhance solubility of the ore minerals within the solution. For uranium ores, the leachate may be acid or sodium bicarbonate.

Soluble salts

In-situ leach is widely used to extract deposits of water-soluble salts such as sylvite (potash), halite (rock salt, sodium chloride), and sodium sulfate. It has been used in the US state of Colorado to extract nahcolite (sodium bicarbonate). In-situ leaching is often used when the deposits are too deep, or the beds too thin for conventional underground mining.

Uranium

Solutions used to dissolve uranium are either acid (sulfuric acid or less commonly nitric acid) or carbonate (sodium bicarbonate, ammonium carbonate, or dissolved carbon dioxide). Dissolved oxygen is sometimes added to the water to mobilize the uranium. ISL of uranium ores started in the United States and the Soviet Union in the early 1960s. The first uranium ISL in the US was in the Shirley Basin in the state of Wyoming, which operated from 1961-1970 using sulfuric acid. Since 1970, all commercial-scale ISL mines in the US have used carbonate solutions.

At the end of 2008 there were four in-situ leaching uranium mines operating in the United States, operated by Cameco, Mestena and Uranium Resources Company, all using sodium bicarbonate. ISL produces 90% of the uranium mined in the US. Two more ISL projects are in licensing and proposal stages in the US, and two in reclamation in 2006.

Significant ISL mines are operating in Kazakhstan and Australia. The Beverley uranium mine in Australia uses in-situ leaching. ISL mining produces around 21% of the world's uranium production.

Examples of in-situ uranium mines

* The Beverley Uranium Mine, South Australia, is an operating ISL uranium mine and Australia's first such mine.
* The Honeymoon Uranium Mine, South Australia, due 2008, will be Australia's second ISL uranium mine.
* Crow Butte (operating), Smith Ranch-Highland (operating), Christensen Ranch (reclamation), Irigaray (reclamation), Churchrock (proposed), Crownpoint (proposed), Alta Mesa (operating), Hobson (standby), La Palangana (development), Kingsville Dome (operating), Rosita (standby) and Vasquez (restoration) are ISL uranium operations in the United States. See Uranium mining in the United States

Copper

In-situ leaching of copper was done by the Chinese by 977 AD, and perhaps as early as 177 BC. Copper is usually leached using acid (sulfuric acid or hydrochloric acid), then recovered from solution by solvent extraction electrowinning (SX-EW) or by chemical precipitation.

Ores most amenable to leaching include the copper carbonates malachite and azurite, the oxide tenorite, and the silicate chrysocolla. Other copper minerals, such as the oxide cuprite and the sulfide chalcocite may require addition of oxidizing agents such as ferric sulfate and oxygen to the leachate before the minerals are dissolved. The ores with the highest sulfide contents, such as bornite and chalcopyrite will require more oxidants and will dissolve more slowly. Sometimes oxidation is speeded by the bacteria Thiobacillus ferrooxidans, which feeds on sulfide compounds.

Copper ISL is often done by stope leaching, in which broken low-grade ore is leached in a current or former conventional underground mine. The leaching may take place in backfilled stopes or caved areas. In 1994, stope leaching of copper was reported at 16 mines in the US. At the San Manuel mine in the US state of Arizona, ISL, underground mining, and open-pit mining were being done simultaneously in different parts of the same ore body.

Gold

In-situ leaching has not been used on a commercial scale for gold mining. A three-year pilot program was undertaken in the 1970s to in-situ leach gold ore at the Ajax mine in the Cripple Creek district in the US, using a chloride and iodide solution. After obtaining poor results, perhaps because of the complex telluride ore, the test was halted.

Controversies



In-situ leach techniques are often controversial, sometimes because of acid leachate solution.

The concerns of environmental groups and landholders centre around;

* Acidification of groundwaters
* Mobilisation of potentially hazardous heavy metals and, in the case of uranium, radioactive heavy metals.
* Disturbance of the groundwater table, mixing of groundwater aquifers and general disturbance of the land atop the ore body
* Destruction of habitat for stygofauna and other rock-inhabiting organisms, bacteria, et cetera.
* Potential spills of acidic and metal-bearing or salt-bearing leachates upon the surface

From http://en.wikipedia.org/

Hydraulic mining

Hydraulic mining, or hydraulicking, is a form of mining that employs water to dislodge rock material or move sediment. Previously, the use of a large volume of water had been developed by the Romans to remove overburden and then gold-bearing debris as in Las Médulas of Spain, and Dolaucothi in Britain. The method was also used in Elizabethan Britain for developing lead, tin and copper mines, and became known as hushing.

The modern form of hydraulicking, using jets of water directed under very high pressure through hoses and nozzles at gold-bearing upland paleogravels, was first used by Edward Matteson near Nevada City, California in 1853. Matteson used canvas hose which was later replaced with crinoline hose by the 1860s. In California, hydraulic mining often brought water from higher locations for long distances to holding ponds several hundred feet above the area to be mined. Insofar as California hydraulic mining exploited primarily river gravels, it was one form of placer mining, that is, working of alluvium (river sediments).

Ancient development



Water was used on a large scale by Roman engineers in the first centuries BC and AD when the Roman empire was expanding rapidly in Europe. Using a process later known as hushing, the Romans stored a large volume of water in a reservoir immediately above the area to be mined; the water was then quickly released. The resulting wave of water removed overburden and exposed bedrock. Gold veins in the bedrock were then worked using a number of techniques, and water power was used again to remove debris. The remains at Las Medulas and in surrounding areas show badland scenery on a gigantic scale owing to hydraulicking of the rich alluvial gold deposits. Las Medulas is now a UNESCO World Heritage site. The site shows the remains of at least seven large aqueducts of up to 30 miles in length feeding large supplies of water into the site. The gold-mining operations were described in vivid terms by Pliny the Elder in his Naturalis Historia published in the first century AD. Pliny was a procurator in Hispania Terraconensis in the 70's and must have witnessed for himself the operations. The use of hushing has been confirmed by field survey and archaeology at Dolaucothi in South Wales, the only known Roman gold mine in Britain.

Modern process



Early placer miners in California discovered that the more gravel they could process, the more gold they were likely to find. Instead of working with pans, sluice boxes, long toms, and rockers, miners collaborated to find ways to process larger quantities of gravel more rapidly. Hydraulic mining became the largest-scale, and most devastating, form of placer mining. Water was redirected into an ever-narrowing channel, through a large canvas hose, and out a giant iron nozzle, called a "monitor." The extremely high pressure stream was used to wash entire hillsides through enormous sluices. By the early 1860s, while hydraulic mining was at its height, small-scale placer mining was a thing of the past. The vast majority of lone prospectors could not sustain themselves, and the mining industry was taken over by large companies, most of which found hard rock gold mining (or quartz mining) more profitable. By the mid-1880s, it is estimated that 11 million ounces of gold (worth approximately US$7.5 billion at mid-2006 prices) had been recovered by hydraulic mining in the California Gold Rush.

Environmental effects

While generating millions of dollars in tax revenues for the state and supporting a large population of miners in the mountains, hydraulic mining had a devastating effect on riparian environments and agricultural systems in California. Millions of tons of earth and water were delivered to mountain streams that fed rivers flowing into the Sacramento Valley. Once the rivers reached the relatively flat valley, the water slowed, the rivers widened, and the sediment was deposited in the floodplains and river beds causing them to rise, shift to new channels, and overflow their banks, causing major flooding, especially during the spring melt.

Cities and towns in the Sacramento Valley experienced an increasing number of devastating floods, while the rising riverbeds made navigation on the rivers increasingly difficult. Perhaps no other city experienced the boon and the bane of gold mining as much as Marysville. Situated at the confluence of the Yuba and Feather rivers, Marysville was the final "jumping off" point for miners heading to the northern foothills to seek their fortune. Steamboats from San Francisco, carrying miners and supplies, navigated up the Sacramento River, then the Feather River to Marysville where they would unload their passengers and cargo. Marysville eventually constructed a complex levee system to protect the city from floods and sediment. Hydraulic mining greatly excerbated the problem of flooding in Marysville and shoaled the waters of the Feather River so severely that few steamboats could navigate from Sacramento to the Marysville docks.

The spectacular eroded landscape left at the site of hydraulic mining can be viewed at Malakoff Diggins State Historic Park in Nevada County, California. A similar landscape can be seen at Las Médulas in northern Spain, where Roman engineers hydrauliced the rich gold alluvial deposits of the river Sil. Pliny the Elder mentions in his Naturalis Historia that Spain had encroached on the sea and local lakes as a result of hydraulic operations.

Legal ramifications

Vast areas of farmland in the Sacramento Valley were deeply buried by the mining sediment. Frequently devastated by flood waters, farmers demanded an end to hydraulic mining. In the most renowned legal fight of farmers against miners, the farmers sued the hydraulic mining operations and the landmark case of Edwards Woodruff v. North Bloomfield Mining and Gravel Company made its way to the United States District Court in San Francisco where Judge Lorenzo Sawyer decided in favor of the farmers in 1884, declaring that hydraulic mining was “a public and private nuisance” and enjoining its operation in areas tributary to navigable streams and rivers. Hydraulic mining was recommenced after 1893 when the United States Congress passed the Camminetti Act which allowed such mining if sediment detention structures were constructed. This led to a number of operations above brush dams and log crib dams. Most of the water-delivery infrastructure had been destroyed by an 1891 flood, so this later stage of mining was carried on at a much smaller scale in California.

Beyond California

Although often associated with California due to its adoption and widespread use there, the technology was exported widely, to Oregon (Jacksonville in 1856), Colorado (Clear Creek, Central City and Breckenridge in 1860), Montana (Bannack in 1865), Arizona (Lynx Creek in 1868), Idaho (Idaho City in 1863), South Dakota (Deadwood in 1876), Alaska, British Columbia (Canada), and overseas. It was used extensively in Dahlonega, Georgia and continues to be used in developing nations, often with devastating environmental consequences. The devastation caused by this method of mining caused one miner Edwin Carter Log Cabin Naturalist to switch from mining to collecting wildlife specimens from 1875-1900 in Breckenridge . His unique 12 foot high ceiling log cabin exists today and has been recently renovated.

Hydraulic mining was used extensively in the Central Otago Gold Rush that took place in the 1860s in the South Island of New Zealand, where it was known as sluicing. In addition to its use in true mining, hydraulic mining can be used as an excavation technique, principally to demolish hills. For example, the Denny Regrade in Seattle was largely accomplished by hydraulic mining. Hydraulic mining is the principal way that kaolinite clay is mined in Cornwall, in South-West England.

Popular Culture

The battle between the old method of pan mining and hydraulic mining is the central theme of the 1985 western film Pale Rider.

From http://en.wikipedia.org/

Heap leaching

Heap leaching is an industrial mining process to extract precious metals and copper compounds from ore.

Process

The mined ore is crushed into small chunks and heaped on an impermeable plastic and/or clay lined leach pad where it can be irrigated with a leach solution to dissolve the valuable metals. Either sprinklers, or often drip irrigation, are used to minimize evaporation. The solution then percolates through the heap and leaches out the precious metal. This can take several weeks. The leach solution containing the dissolved metals is then collected.

Precious metals method

The crushed ore is irrigated with a dilute cyanide solution. The solution percolates through the heap and leaches out the precious metal. This can take several weeks.

The solution containing the precious metals ("pregnant solution") continues percolating through the crushed ore until it reaches the liner at the bottom of the heap where it drains into a storage (pregnant solution) pond. After separating the precious metals from the pregnant solution, the dilute cyanide solution (now called "barren solution") is normally re-used in the heap-leach-process or occasionally sent to an industrial water treatment facility where the residual cyanide is treated and residual metals are removed. The water is then discharged to the environment, posing possible water pollution.

During the extraction phase, the gold ions form complex ions with the cyanide:



Recuperation of the gold is readily achieved with a redox-reaction:



Copper method

The method is similar to the cyanide method, above, except sulfuric acid is used to dissolve copper from its ores. The acid is recycled from the solvent extraction circuit (see solvent extraction-electrowinning, SX/EW) and reused on the leach pad. A byproduct is iron(II) sulfate, jarosite, which is produced as a byproduct of leaching pyrite, and sometimes even the same sulfuric acid that is needed for the process.

Although the heap leaching is a low cost-process, it normally has recovery rates of 60-70%, although there are exceptions. It is normally most profitable with low-grade ores. Higher-grade ores are usually put through more complex milling processes where higher recoveries justify the extra cost. The process chosen depends on the properties of the ore.

Sulfuric acid heap leaching of nickel

The method is an acid heap leaching method like that of the copper method in that it utilises sulfuric acid instead of cyanide solution to dissolve the target minerals from crushed ore. The method has been developed by European Nickel PLC for the rock laterite deposits of Turkey and the Balkans.

From http://en.wikipedia.org/

Glory hole (petroleum production)

A glory hole in the context of the offshore petroleum industry is an excavation into the sea floor designed to protect the wellhead equipment installed at the surface of a petroleum well from icebergs or pack ice. An economically attractive alternative for exploiting offshore petroleum resources is a floating platform; however, ice can pose a serious hazard to this solution. While floating platforms can be built to withstand ice loading up to a design threshold, for the largest icebergs or the thickest pack ice the only sensible alternative is to move out of the way. Floating platforms can be disconnected from the wellheads in order to allow them to be moved away from threatening ice, but the wellhead equipment is fixed in place and hence vulnerable.

The keel of an iceberg or pack ice can extend far below the surface of the water. If this keel extends deep enough to make contact with the sea floor, it will scour the sea floor as the ice moves with the current. To protect the wellhead equipment from possible scouring, a glory hole is excavated into the sea floor. This excavation must be deep enough to allow adequate clearance between the top of the wellhead equipment and the surrounding sea floor. The resulting glory hole can be either open or cased. A cased glory hole utilizes steel casing as a retaining wall while an open glory hole is simply an excavation.

Due to the cost of excavating individual glory holes, typically each glory hole will contain several wellheads. Locating multiple wellheads within a single glory hole is made possible by the use of directional drilling.

Etymology

The usage of the term glory hole in this context almost certainly is taken from its historical usage in the mining industry to refer to excavations.

From http://en.wikipedia.org/

Fire-setting

Fire-setting is a method of mining used mostly in antiquity. Fires were set against a rock face to heat the stone, which was then doused with water causing the stone to fracture by thermal shock. This technique was best performed in opencast mines where the smoke and fumes could dissipate safely. The technique was very dangerous in underground workings without adequate ventilation. The method became redundant with the growth in use of explosives.

History



The method is first described by Diodorus Siculus in his Bibliotheca historica written about 60 BC, about methods of mining used in ancient Egyptian gold mines. It is also mentioned in greater detail by Pliny the Elder in his Naturalis Historia published in the first century AD. In Book XXXIII, he describes mining methods for gold, and the pursuit of the gold-bearing veins underground using tunnels and stopes. He mentions the use of vinegar to quench the hot rock, but water would have been just as effective as vinegar was expensive at the time for regular use in a mine. The reference to vinegar may come from a description by Livy of Hannibal's crossing of the Alps, when it was said that the soldiers used vinegar in fire-setting to remove large rocks in the path of his army.



Pliny also says that the method was used both in opencast and deep mining. That the method was used in practice is confirmed by remains found at the Roman gold mine of Dolaucothi in west Wales, when modern miners broke into much older workings during the 1930s where they found wood ashes near worked rock faces. In another part of the mine, there are three adits at different heights which have been driven through barren rock to the gold-bearing veins for some considerable distance, and they would have not only provided drainage but also ventilation to remove the smoke and hot gases during a fire-setting operation. They were certainly much larger in section than was normal for access galleries, and the draught of air through them would have been considerable.

Fire-setting would have been used extensively during opencast mining, and is also described by Pliny in connection with the use of another mining technique known as hushing. Aqueducts were built to supply copious amounts of water to the minehead, where they were used to fill tanks and cisterns. The water was unleashed to scour the hillside below, both soil in the case of prospecting for metal veins, and then rock debris after a vein had been found. Fire-setting was used to break up the hard rocks of the vein itself and surrounding barren rock, and was much safer than use in underground workings since the smoke and fumes would be dissipated much more easily than in a confined space underground. Pliny also describes undermining methods were used to facilitate attack of the hard rocks, and probably the softer alluvial deposits too.

Agricola



The method continued in use in the medieval period, and is described by Georg Agricola in his treatise on mining and mineral extraction, De Re Metallica. He warns about the problem of the "foetid vapours" and the need to evacuate the workings while the fires are lit, and presumably for some time afterwards until the gases and smoke had cleared. The problem raises the question of ventilation means in the mines, a problem often solved by ensuring that there was a continuous path for escape of the noxious fumes, perhaps aided by artificial ventilation. Agricola mentions the use of large water-powered bellows to create a draught, and continuity of workings to the surface were essential for a stream of air to run through them.

In later times, a fire at the base of a shaft was used to create an updraught, but just like fire-setting, it was a hazardous and dangerous procedure, especially in collieries. As the number and complexity of the underground workings increased, care was needed to channel the air draught to all parts of the tunnels and faces. It was usually achieved by installing doors at key points. Most of the deaths in coal mine disasters were caused by inhalation of the toxic gases produced by firedamp explosions.



The method continued in use for many years afterwards until finally made redundant by the use of explosives. However, they also produce toxic gases and care is needed to ensure good ventilation to remove those gases, like carbon monoxide, as well as choice of the explosive itself to minimise their emission.

From http://en.wikipedia.org/

Drift mining

Drift mining is a method of accessing valuable geological material, such as coal, by cutting into the side of the earth, rather than tunneling straight downwards (see shaft mine). Drift mines have horizontal entries, called adits, into the mineral deposit from a hillside. Drift mines are distinct from slope mines, which have an inclined entrance from the surface to the mineral deposit. If possible, though, drifts are driven at just a slight incline so that removal of material can be assisted by gravity.

Nome Alaska
Drift mining methods were used extensively during the gold rush, around the turn of the last century, in Nome, Alaska. The technique, slightly different than that described above, was ingeniously adapted to the challenges faced in the region. Gold was abundant around the turn of the century in Nome. During the warm summer months gold could be easily recovered using gravity separation techniques; these techniques required water.

It didn't take long for miners to discover and recover all of the "easy" gold. During the winter time, when the sun disappears for months and everything including the ocean freezes, miners found themselves sitting around in bars doing nothing, or drinking and getting in trouble. Most of the ground in Nome, called permafrost, has been frozen solid for centuries. By "drift mining" miners were able to recover much of the gold buried under the permafrost, as described below.



Gold is not everywhere, over time nature causes it to be concentrated in specific places. In Nome these places included three ancient beach lines, now inshore, above sea level, and buried under roughly fifty feet of permafrost with two feet of tundra (a mossy layer of vegetation that acts like a blanket to keep the permafrost frozen during the summer) on top of it. The miners that drifted these buried deposits got rich beyond your wildest dreams!

The first step in mining is, of course, finding the gold. This is called prospecting. Drift miners, knowing roughly where to look, still had to find exactly where the gold was deep under the frozen ground. This was done by building a fire on top of the permafrost and, each day as it melted, shoveling away the mud. The process would be continued until reaching either a "pay streak" or bedrock. Not all prospecting shafts paid off. Even the luckiest miners prospected many a barren hole before striking it rich. When the gold was found the true "drift mining" began.

Gold, when it was finally found in these places, occurred on top of either bedrock or "false bedrock" (a layer of clay that the gold was not able to sink through). Drift miners, once they had found a "pay streak," would tunnel horizontally from the bottom of their prospecting shaft and follow the gold across the surface of the bedrock. This was a very efficient mining method. The fifty feet or more of frozen dirt above them did not need to be removed. The tunnels, because the ground was frozen, would not cave in. Miners would discover old underground beaches and rivers rich with gold and follow the gold until it was depleted. One drift miner, on "Little Creek" in Nome, having sunk five unproductive holes, almost out of money, and working on his sixth, struck what turned out to be the richest pay dirt ever found on the face of the planet; two hundred ounces of gold per pan (a small shovel full of dirt). Around the year 1900 the population of Nome was more than twenty thousand; it's a bit less than four thousand today. Many of those people were drift miners. Nome's gold fields, appearing untouched from the surface, are honeycombed with tunnels left by the gold rush drift miners. Today's miners, as they prospect for gold using modern drilling equipment, almost expect as they follow promising underground signs of gold to find, right when they think they're going to strike it rich, that a gold rush era drift miner has beat them to it! Their drill, grinding through the permafrost, suddenly hits an air pocket... a drift miner's tunnel.

Today's miners use heavy equipment to remove all of the dirt, or "overburden" from on top of the pay streak. With all of the "easy" gold long gone, this takes a lot of digging. A personal friend, after spending two years digging a huge pit with excavators, was dismayed to find a drift miner had been there first; there was other gold, but the drift miner had gotten the best of it. This form of drift mining proved to be an efficient and safe way for turn of the century miners to recover gold from deep beneath the frozen ground in Nome Alaska. It could be done during the winter. A hot fire, some shovels, and a few hearty souls were all that was needed. To their credit, for their hard work and persistence, many a drift miner left Nome with pockets full of gold.

From http://en.wikipedia.org/

Quartz reef mining

Primary gold typically occurs in quartz veins. The extraction of gold ore from these hard quartz veins was historically referred to as quartz reef mining.

A Prussian engineer, Jacob Brache was the first to think that quartz reefs might have even more gold than alluvial fields.

The new mining companies had to sink very deep shafts to get quartz from the reefs deep underground. Horizontal tunnels called drives were dug out from the shaft at different levels to find the gold-bearing rock.

All rock dug out had to be hoisted to the surface. So did lots of water and even the workers at the end of the day. Big engines were installed to hoist lifts and buckets up the shafts.

On the surface above the shaft stands a building known as the poppet head or pit head. The poppet head contained a wheel called a gin wheel which lifted buckets of rock up to a raised platform called a Brace. Wheeled buckets then carried the rock along elevated tracks to waste dumps or processing works. The steel cable that hoisted the bucket passed over the gin wheel.

The gold was brought to the surface as small particles embedded in lumps of quartz. The quartz was then crushed into a fine dust by stamping batteries.

A battery contained a row of stampers. There was a heavy piece of steel on the bottom of each stamper. Each stamper was connected to the cam shaft which was turned by a water wheel. The steel shoes went up and down between wooden guides and pounded the quartz which had been fed into steel boxes underneath the stampers. Many of the stamping batteries worked 24 hours a day.

After crushing, the quartz dust was mixed with water to make sloppy mud which then ran down sloping tables, called Wilfey tables. On top of these tables were copper sheets coated with mercury, which attracts gold. The gold particles stuck to the mercury, and could be collected from there.

Quartz mines

* Victoria Quartz mine, Bendigo: In Australia, the deepest shaft used to mine a quartz reef was almost a kilometre and a half deep.
* Central Deborah gold mine, Bendigo: The mine still stands today. It started mining in 1851 and was mined continuously for 157 years. It was a deep reef quartz goldmine. During the working life of the mine 60,000 tonnes of quartz was brought to the surface but only 1 tonne of gold extracted.
* Gold Hill (Nevada County, California), USA: Site of one of the first discoveries of quartz gold in California, and now California Historical Landmark No. 297: "...this discovery created the great excitement that started the development of quartz mining into a great industry.

From http://en.wikipedia.org/

Quarry

A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often colocated with concrete and asphalt plants due to the requirement for large amounts of aggregate in those materials.



Problems

Quarries in level areas with shallow groundwater or which are located close to surface water often have engineering problems with drainage. Generally the water is removed by pumping while the quarry is operational, but for high inflows more complex approaches may be required. For example, the Coquina quarry is excavated to more than 60 feet (18 m) below sea level. To reduce surface leakage, a moat lined with clay was constructed around the entire quarry. Ground water entering the pit is pumped up into the moat. As a quarry becomes deeper water inflows generally increase and it also becomes more expensive to lift the water higher during removal - this can become the limiting factor in quarry depth. Some water-filled quarries are worked from beneath the water, by dredging.

Many people and municipalities consider quarries to be eyesores and require various abatement methods to address problems with noise, dust, and appearance. One of the more effective and famous examples of successful quarry restoration is Butchart Gardens in Victoria.

Many quarries naturally fill with water after abandonment and become lakes. Others are made into landfills.

Types of rock



Types of rock extracted from quarries include:

* Cinder
* Chalk
* China Clay
* Clay
* Coal
* Coquina
* Construction aggregate (sand and gravel)
* Globigerina Limestone (Malta)
* Granite
* Gritstone
* Gypsum
* Limestone
* Marble
* Ores
* Phosphate rock
* Sandstone
* Slate

From http://en.wikipedia.org/

Placer mining

Placer mining (usually /'plæsɜ(r)/, also /'pleɪsɜ(r)/) is the mining of alluvial deposits for minerals. This may be done by open-pit (also called open-cast mining) or by various forms of tunneling into ancient riverbeds. Excavation may be accomplished using water pressure (hydraulic mining), surface excavating equipment or tunneling equipment.

The name derives from Spanish, placer, meaning "sandbank." It refers to mining the precious metal deposits (particularly gold and gemstones) found in alluvial deposits—deposits of sand and gravel in modern or ancient stream beds. The metal or gemstones, having been moved by stream flow from an original source such as a vein, is typically only a minuscule portion of the total deposit. The containing material may be too loose to safely mine by tunneling. Where water under pressure is available, water under pressure may be used to mine, move, and separate the precious material from the deposit.

History



Placers supplied most of the gold for a large part of the ancient world. Hydraulic mining methods such as hushing were used widely by the Romans across their empire, but especially in the gold fields of northern Spain after its conquest by Augustus in 25 BC. One of the largest sites was at Las Médulas, where seven 30 mile long aqueducts were used to work the alluvial gold deposits through the first century AD. (Inclusions of platinum-group metals in a very large proportion of gold items indicate that the gold was largely derived from placer or alluvial deposits. Platinum group metals are seldom found with gold in hardrock reef or vein deposits.) In North America, placer mining was famous in the context of several gold rushes, particularly the California Gold Rush, the Fraser Canyon Gold Rush and the Klondike Gold Rush. Placer mining continues in many areas of the world as a source of diamonds, industrial minerals and metals, gems (in Myanmar and Sri Lanka), platinum, and of gold (in the Yukon, Alaska and British Columbia).

Methods

The simplest technique to extract gold from placer ore is panning. In panning, some mined ore is placed in a large metal or plastic pan, combined with a generous amount of water, and agitated so that the gold particles, being of higher density than the other material, settle to the bottom of the pan. The lighter gangue material such as sand, mud and gravel are then washed over the side of the pan, leaving the gold behind. Once a placer deposit is located by gold panning, the miner usually shifts to equipment that can treat volumes of sand and gravel more quickly and efficiently.



The same principle may be employed on a larger scale by constructing a short sluice box, with barriers along the bottom to trap the heavier gold particles as water washes them and the other material along the box. This method better suits excavation with shovels or similar implements to feed ore into the device. Similar in principle to a sluice is a rocker, a cradle-like piece of equipment that could be rocked like a cradle to sift sands through screens, which was introduced by Chinese miners in British Columbia and Australia, where the practice was referred to as "rocking the golden baby". Another Chinese technique was the use of blankets to filter sand and gravels, catching fine gold in the fabric's weave, then burning the blankets to smelt the gold. Chinese were noted for the thoroughness of their placer extraction techniques, which included hand-washing of individual rocks as well as the complete displacement of streambeds and advanced flume and ditching techniques which became copied by other miners.



A trommel is composed of a slightly-inclined rotating metal tube (the 'scrubber section') with a screen at its discharge end. Lifter bars, sometimes in the form of bolted in angle iron, are attached to the interior of the scrubber section. The ore is fed into the elevated end of the trommel. Water (often under pressure) is provided to the scrubber and screen sections and the combination of water and mechanical action frees the valuable minerals from the ore. The mineral containing ore that passes through the screen is then further concentrated in smaller devices such as sluices and jigs. The larger pieces of ore that do not pass through the screen can be carried to a waste stack by a conveyor.

Environmental effects

Although not required, the process water may be continuously recycled and the ore from which the sought after minerals have been extracted ("the tailings") can be reclaimed. While these recycling and reclamation processes are more common in modern placer mining operations they are still not universally done.



In earlier times the process water was not generally recycled and the spent ore was not reclaimed. The remains of a Roman alluvial gold mine at Las Médulas are so spectacular as to justify the site being designated UNESCO World Heritage status. The methods used by the Roman miners are fully described by Pliny the Elder in his work Naturalis Historia published in about 77 AD. The author was a Procurator in the region and so probably witnessed large-scale hydraulic mining of the placer deposits there. He also added that the local lake Curacado had been heavily silted by the mining methods.



Environmental activists describe the hydraulic mining form of placer mining as environmentally destructive because of the large amounts of silt that it adds to previously clear running streams. Most placer mines today use settling ponds, if only to ensure that they have sufficient water to run their sluicing operations.



In California, from 1853 to 1884, "hydraulicking" of placers removed an enormous amount of material from the gold fields, material that was carried downstream and raised the level of the Central Valley by some seven feet in some areas and settled in a huge layer at the bottom of San Francisco Bay. The process raised an opposition calling themselves the "Anti-Debris Association". In January of 1884, a United States District Court banned the flushing of debris into streams, and the hydraulic mining mania in California's gold country came to an end.

From http://en.wikipedia.org/

Open-pit mining

Open-pit mining, also known as open-cast mining, open-cut mining, and strip 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 that produce building materials and dimension stone are commonly referred to as quarries. People are unlikely to make a distinction between an open-pit mine and other types of open-cast mines, such as quarries, borrows, placers, and strip mines.

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.



Extraction

Open-pit mines are dug on benches, which describe vertical levels of the hole. These benches are usually on four metre to sixty metre 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 perm. 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 pit. This is known as the waste dump. The waste dump is also tiered and stepped, to minimise degradation.

Ore which has been processed is known as tailings, and is generally a slurry. This is pumped to a tailings dam or settling pond, where the water evaporates. Tailings dams can often be toxic due to the presence of unextracted sulfide minerals, some forms of toxic minerals in the gangue, and often cyanide which is used to treat gold ore via the cyanide leach process.



Rehabilitation

After mining finishes, the mine area must undergo rehabilitation. Waste dumps are contoured to flatten them out, to further stabilise them. If the ore contains sulfides it is usually covered with a layer of clay to prevent access of rain and oxygen from the air, which can oxidise the sulfides to produce sulfuric acid, a phenomenon known as acid mine drainage. This is then generally covered with soil, and vegetation is planted to help consolidate the material. Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals. There are no long term studies on the success of these covers due to the relatively short time in which large scale open pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become "acid neutral" and stop leaching to the environment. The dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with a fence, to prevent access, and it generally eventually fills up with ground water. In arid areas it may not fill due to the deep groundwater levels.'

Typical open cut grades

Gold is generally extracted in open-pit mines at 1 to 2 ppm (grams per ton) but in certain cases, 0.75ppm gold is economic. This was achieved by bulk heap leaching at Alkane Minerals Ltd. Peak Hill mine in western New South Wales, near Dubbo, Australia.

Nickel, generally as laterite, is extracted via open-pit down to 0.2%. Copper is extracted at grades as low as 0.15% to 0.2%, generally in massive open-pit mines in Chile, where the size of the resources and favorable metallurgy allows economies of scale.

Materials typically extracted from open-pit mines include:

* Clay
* Coal
* Coquina
* Diamonds
* Gravel and stone (stone refers to bedrock, while gravel is unconsolidated material, as found in glacial or fluvial deposits)
* Granite
* Gritstone
* Gypsum
* Limestone
* Marble
* Metal ores, such as copper, iron, gold, and molybdenum

Open-pit mines



This list includes only those large open-pit mines for which an article exists in Wikipedia.

Australia

* Super Pit – gold mine near Kalgoorlie, Western Australia.
* Cadia mine; gold and copper mine located near Orange, New South Wales.

Bulgaria

* Maritsa Iztok Mines – coal mine near Radnevo, Stara Zagora Province, Bulgaria.

Canada

* Adams Mine – controversial abandoned mine in Kirkland Lake, Ontario.
* Colomac Mine – gold mine in Northwest Territories, Canada.
* Diavik Diamond Mine – diamond mine in Northwest Territories, Canada.
* Ekati Diamond Mine – diamond mine in Northwest Territories, Canada.
* Pine Point Mine – lead and zinc mine in Northwest Territories, Canada.

Chile

* Chuquicamata – copper mine;
* Escondida copper mine
* Pascua Lama – gold and silver mine in Atacama, Chile (in project)
* Radomiro Tomic copper mine
* El Abra copper mine
* Spence Copper Mine

Colombia

* Cerrejón – coal mine in Guajira Department.

Indonesia

* Batu Hijau mine – copper and gold mine on the island of Sumbawa.
* Grasberg mine – located in the mountains of the Papua province.

Kyrgyzstan

* Kumtor Gold Mine – gold mine in Tian Shan Mountains at 4,000-4,400 m (14,000 ft) above sea level.

Mongolia

* Boroo Gold Mine – gold mine 110 km (70 mi) WNW of the capital Ulan Bator.

Namibia

* Rossing – uranium mine.



Peru

* Yanacocha – gold mine

Portugal

* Sao Domingos Mine – copper mine.

Russia



* Mirny Mine − diamond mine in Mirny, Eastern Siberia
* Udachnaya pipe − diamond mine in Yakutia, Russia.

South Africa

* The Big Hole, former diamond mine in Kimberley, more than 1,000 m (3,300 ft) deep; now a museum
* The Jagersfontein Mine

United Kingdom

* Penrhyn Quarry – slate quarry in Wales.

United States



* Berkeley Pit - former copper mine in Butte, Montana; now a toxic lake and tourist attraction.
* El Chino Mine – copper mine in Grant County, New Mexico.
* Hull-Rust-Mahoning Mine – largest open pit iron mine in the world near Hibbing, Minnesota.
* Bingham Canyon Mine – copper mine in Salt Lake County, Utah.
* Lavender Pit – copper mine in Cochise County, Arizona.

Zambia

* Nchanga Open Pit Mine, Chingola. The second largest open cast mine in the world, covering nearly 30 km² and up to 400m deep.

From http://en.wikipedia.org/

Omega Hydraulic Diggings

The Omega Hydraulic Diggings are located one mile north of what was the town of Omega, California during the California Gold Rush. The site is southeast of the unincorporated town of Washington, California. From SR 20, the diggins are reachable via the gravel Omega Road which merges with Forest Route 29 in small sections.

The hydraulic diggings became a registered California Historical Landmark (No. 629) on 1958-01-29. The plaque's inscription reads:

ALPHA AND OMEGA

One mile north of here were the towns of Alpha and Omega, named by gold miners in the early 1850s. The tremendous hydraulic diggings, visible from near this point, engulfed most of the original townsites. Alpha was the birthplace of famed opera singer Emma Nevada. Mining at Omega continued until 1949, and lumbering operations are carried on there today (1958).

California Registered Historical Landmarks Nos. 628-629

From http://en.wikipedia.org/

Mountaintop removal mining

Mountaintop removal mining (MTR), often referred to as mountaintop mining/valley fills (MTM/VF), is a form of surface mining that involves extreme topographic destruction and deforestation of the summit or summit ridge of a mountain. It is most closely associated with coal mining in the Appalachian Mountains, located in the eastern United States, the most biologically diverse temperate hardwood forests in the world. The process involves blasting with explosives to remove up to 1,000 vertical feet (300 m) of densely-forested mountain to expose underlying coal seams. The mountaintop is is often dumped into mountain streams in what is called a valley fill.

Because of its destructive nature, MTR is controversial and is opposed by environmentalists, local residents, and others. Controversy over the practice stems from both the extreme topographical and ecological changes that the mining site undergoes, as well as from the storage of waste material generated from the mining and processing of the coal. Coal industry proponents of MTR point to its efficiency and profitability, and the increase of flat land. However, less than 5 percent of the flattened mountains in West Virginia have any kind of economic development after mining. Typical post-mine land use includes prisons, solid waste landfills, pasture, and two golf courses. Mountaintop removal operations are highly mechanized and employ far fewer people than traditional underground mining.

History

Increased demand for coal in the United States, sparked by the 1973 and 1979 petroleum crises, created incentives for a more economical form of coal mining than the traditional underground mining methods involving hundreds of workers, triggering the first widespread use of MTR. Its prevalence expanded further in the 1990s to retrieve relatively low-sulfur coal, a cleaner burning form, which became desirable as a result of amendments to the U.S. Clean Air Act that tightened emissions limits on high-sulfur coal processing. With an increasing call for energy independence in the U.S., as well as a growing call for Coal-To-Liquids and "clean coal technologies", MTR has continued to expand into the 2000s.

Occurrence

MTR in the United States is most often associated with the extraction of coal in the Appalachian Mountains, where the United States Environmental Protection Agency (EPA) estimates that 2,200 square miles (5,700 km2) of Appalachian forests will be cleared for MTR sites by the year 2012. It occurs most commonly in West Virginia and Eastern Kentucky, the top two coal producing states in Appalachia, with each state using approximately 1000 metric tons of explosives per day for the purposes of surface mining. At current rates, MTR in the U.S. will mine over 1.4 million acres (5,700 km²) by 2010, an amount of land area that exceeds that of the state of Delaware.

Process



No vegetation survives MTR, so the land is deforested prior to mining operations and the resultant lumber is either sold or burned. According to the federal surface mining law SMCRA, the topsoil is supposed to be removed and set aside for later reclamation., however, coal companies are often granted waivers and instead reclaim the mountain with "topsoil substitute." Once the area is cleared, miners use explosives to blast away the overburden, the rock and subsoil, to expose coal seams beneath. Often, the overburden is then pushed into a nearby valley or hollow, creating what is known as a valley fill. A dragline excavator then removes the coal, where it is transported to an often on-site processing plant and washed. Millions of gallons of by-product from this coal processing, called coal sludge or slurry, are often stored nearby in open-air pools isolated from natural waterways by earthen dams. This procedure allows any useable coal particles to separate from the water and settle to the bottom. Once coal removal is completed, the mining operators replace the topsoil (or a topsoil substitute) on the site and seed it for revegetation. Dependant on mostly geologic factors the land can sometimes be used afterward for different purposes, such as forestry.

Because coal usually exists in multiple geologically stratified seams, miners can often repeat the blasting process to mine over a dozen seams on a single mountain, increasing the mine depth each time. This can result in a vertical descent of hundreds of extra feet into the earth.

Economics

Just under half of the electricity generated in the United States is produced by coal-fired power plants. MTR accounted for less than 5% of U.S. coal production as of 2001. In some regions, however, the percentage is higher, for example MTR provided 30% of the coal mined in West Virginia in 2006.

Historically in the U.S. the prevalent method of coal acquisition was underground mining which is very labor-intensive. In MTR, through the use of explosives and large machinery, more than two and a half times as much coal can be extracted per worker per hour than in traditional underground mines, and thus greatly reducing the need for workers. The industry lost approximately 10,000 jobs from 1990 to 1997, as MTR and other more mechanized mining methods became more widely used. The United Mine Workers of America has called for additional legal measures to protect communities from the degradation and destruction that results from nearby blasting. The coal industry asserts that surface mining techniques, such as mountaintop removal, are safer for miners than sending miners underground.

Proponents argue that in certain geologic areas, MTR and similar forms of surface mining allow easier access to coal than traditional underground mining, and that it is the most cost-effective method of extracting coal. However, the counties that host MTR are often the poorest in Appalachia. For instance, in McDowell County, West Virginia, which produces the most coal in the state, over 37% of residents live below the poverty line. In Kentucky, counties with coal mining have economies no better than adjoining counties where no mining occurs.

A 2008 study from environmental consulting firm Downstream Strategies LLC concluded that wind farm development is a more economic land-use option than mountaintop removal coal mining in West Virginia. The study was commissioned by Coal River Mountain Watch, a group that works to stop mountaintop mining and which encourages the development of wind projects instead. The study calculated that a wind farm consisting of 164 wind turbines and generating 328 megawatts of electricity, would provide over $1.74 million in annual property taxes to Raleigh County. By comparison, the coal severance taxes related to the mountaintop removal mining would provide the county with $36,000 per year.

Legislation in the United States

In the United States, MTR is allowed by section 515(c)(1) of the Surface Mining Control and Reclamation Act (SMCRA). Although most coal mining sites must be reclaimed to the land's pre-mining contour and use, regulatory agencies can issue waivers to allow MTR. In such cases, SMCRA dictates that reclamation must create "a level plateau or a gently rolling contour with no highwalls remaining."

Permits must be obtained to deposit valley fill into streams. On four occasions, federal courts have ruled that the US Army Corps of Engineers violated the Clean Water Act by issuing such permits. Massey Energy Company is currently appealing a 2007 ruling, but has been allowed to continue mining in the meantime because "most of the substantial harm has already occurred," according to the judge.

The Bush administration appealed one of these rulings in 2001 because the Act had not explicitly defined "fill material" that could legally be placed in a waterway. The EPA and Army Corps of Engineers changed a rule to include mining debris in the definition of fill material, and the ruling was overturned. However, if passed, the Clean Water Protection Act (H.R.1310), a bill in the House of Representatives, would revert this change by specifying that coal mining waste does not constitute fill material, in effect disallowing valley fills.

On December 2, 2008, the Bush Administration made a rule change to remove the Stream Buffer Zone protection provision from SMCRA allowing coal companies to place mining waste rock and dirt directly into headwater waterways thereby affecting downriver areas.

A federal judge has also ruled that using settling ponds to remove mining waste from streams violates the Clean Water Act. He also declared that the Army Corps of Engineers has no authority to issue permits allowing discharge of pollutants into such in-stream settling ponds, which are often built just below valley fills.

Additionally, a September 2007 survey conducted by the Civil Society Institute found that 65% of Americans oppose the Bush Administration's proposal "to ease environmental regulations to permit wider use of 'mountain top removal' coal mining in the U.S." The study also found that 74% of Americans are opposed to the expansion of MTR coal mining in general, and that 90% of Americans agree that more mining should be permitted only after the United States government has assessed its impacts on safety and the environment.

On January 15, 2008, the environmental advocacy group Center for Biological Diversity petitioned the United States Fish and Wildlife Service to end a policy that waives detailed federal Endangered Species Act reviews for new mining permits. The current policy states that MTR can never damage endangered species or their habitat as long as mining operators comply with federal surface mining law, despite the complexities of species and ecosystems. Since 1996, this policy has exempted many strip mines from being subject to permit-specific reviews of impact on individual endangered species.

On May 25, 2008 North Carolina State Representative Pricey Harrison introduced a bill to ban the use of mountaintop removal coal from coal fired power plants within North Carolina. This proposed legislation would be the first of its kind in the United States.

Criticism

Critics contend that MTR is a destructive and unsustainable practice that benefits a small number of corporations at the expense of local communities and the environment. Though the main issue has been over the physical alteration of the landscape, opponents to the practice have also criticized MTR for the damage done to the environment by massive transport trucks, and the environmental damage done by the burning of coal for power. Blasting at MTR sites also expels coal dust and fly-rock into the air, which can disturb or settle onto private property nearby. This dust contains sulfur compounds, which corrodes structures and is a health hazard.

Advocates of MTR claim that once the areas are reclaimed as mandated by law, the area provides flat land suitable for many uses in a region where flat land is at a premium. They also maintain that the new growth on reclaimed mountaintop mined areas is better suited to support populations of game animals.



Artists have been leaders in the fight against the process of mountaintop removal. Writers and musicians have been particularly active in Kentucky. In April 2005, respected writer and social critic Wendell Berry invited Kentucky writers on a tour of mountaintop removal sites that started a movement that continues to heat up. The attending writers have since contributed writing on the issue to national magazines and newspapers and even created a respected book called Missing Mountains, edited by Kristin Johnason, Bobbie Ann Mason, and Mary-Ann Taylor Hall. The book contains a foreword by Silas House and an afterword by Berry and is widely used in college courses.

2005 also saw the release of the album Songs For the Mountaintop, a collection of anti-MTR music. In 2007 the band Public Outcry (Silas House, Jason Howard, Jessie Lynne Keltner, Kate Larken, George Ella Lyon, and Anne Shelby) was formed to sing anti-MTR songs. They have performed at universities, festivals, and libraries throughout the region and in 2008 released their first, eponymous album.

Many personal interest stories of coalfield residents have been written; the first, Lost Mountain by Erik Reese,was released in 2005. In addition, Penny Loeb (Moving Mountains: How One Woman and Her Community Won Justice From Big Coal) and Michael Shnayerson (Coal River) have also contributed to the anti-mountaintop removal struggle with informative works. To date, Dr. Shirley Stewart Burns, a coalfield native, has written the only academic book on mountaintop removal, titled Bringing Down The Mountains (2007), which is loosely based on the 2005 Ph.D. dissertation of the same name. All of these books are critically acclaimed and their authors continue to make a collective effort to give voice to the people of the Appalachian coalfields.

In 2006, cultural historian, Jeff Biggers, published The United States of Appalachia, which chronicled the historical contributions of Appalachians and their impact on the nation, and examined the role of mountaintop removal in destroying Appalachia's history and cultural significance. Biggers continues to write extensively on the cultural and human costs of mountaintop removal, and the parallel connection between the devastation of the environment and the culture.

In 2006, Catherine Pancake released the first comprehensive feature-length documentary on mountaintop removal ["Black Diamonds: Mountaintop Removal and the Search for Coalfield Justice."] The film received critical acclaim and multiple awards including a selection in the Documentary Fortnight at Museum of Modern Art (MoMA.org.) The film features Julia Bonds who won the .

In 2007 Ann Pancake released the novel Strange As This Weather Has Been, which has been hailed by critics and received several awards. The book is the first major fiction work about the subject of MTR and was highly critical of the mining practice.

In 2007, a feature documentary titled Mountain Top Removal was completed by Haw River Films. The film features Mountain Justice Summer activists, coal field residents, and coal industry officials. Included in the film are Former US President George W. Bush and West Virginia Governor Joe Manchin, among others. On April 18 2008 the film received the Reel Current award selected and presented by Al Gore at the Nashville Film Festival.

In 2008, a second feature documentary titled Burning the Future: Coal in America was made by Director David Novack and produced by former Shooting Gallery executive, CJ Follini. The film examines the explosive conflict between the coal industry and residents of West Virginia. Confronted by emerging “clean coal” energy policies, local activists watch a world blind to the devastation caused by coal's extraction. The film was awarded The International Documentary Association's 2008 Pare Lorentz award for Best Documentary

Maria Gunnoe is a community organizer with the Ohio Valley Environmental Coalition who is concerned about the long-term effects of mountaintop removal coal mining. She is featured in the 2008 documentary film Burning the Future: Coal in America and the 2007 documentary film Mountain Top Removal. In 2006, Gunnoe received the Callaway Award for her organizing efforts in her southern West Virginia community.

Biodiversity

An EPA environmental impact statement finds that streams near valley fills from mountaintop removal contain high levels of minerals in the water and decreased aquatic biodiversity. The statement also estimates that 724 miles (1,165 km) of Appalachian streams were buried by valley fills between 1985 to 2001.

Although U.S. mountaintop removal sites by law must be reclaimed after mining is complete, reclamation has traditionally focused on stabilizing rock formations and controlling for erosion, and not on the reforestation of the affected area. Fast-growing, non-native grasses such as lespedeza sericea, planted to quickly provide vegetation on a site, compete with tree seedlings, and trees have difficulty establishing root systems in compacted backfill. Consequently, biodiversity suffers in a region of the United States with numerous endemic species.In addition, introduced species of elk on mountaintop removal sites in Kentucky are eating tree seedlings. Erosion also increases, and the lack of trees contributes to flooding. In the Eastern United States, the Appalachian Regional Reforestation Initiative works to promote the use of trees in mining reclamation.

Sludge ponds

As with other methods of coal mining, processing of the coal mined generates waste slurry (also called coal sludge), which is usually stored in large sludge ponds impounded by an on-site dam. Many coal slurry impoundments in West Virginia exceed 500 million gallons in volume, and can be larger than 7 billion gallons. Such impoundments can be hundreds of feet high and sometimes have close proximity to schools or private residences.

The most controversial sludge dam at present sits 400 yards (400 m) above Marsh Fork Elementary School. On May 31, 2005, 16 people were arrested at Governor Manchin's office for protesting the Governor's refusal to fund the relocation of the school. The leaking (according to CorpWatch) sludge pond is permitted to hold 2.8 billion gallons of coal sludge, and is 21 times larger than the pond which killed 125 people in the Buffalo Creek Flood in 1972.



Kentucky's Martin County Sludge Spill occurred after midnight on October 11, 2000, when a coal sludge impoundment broke through into an underground mine below, propelling 306 million gallons of sludge down two tributaries of the Tug Fork River. The spill polluted hundreds of miles of waterways, contaminated the water supply for over 27,000 residents, and killed all aquatic life in Coldwater Fork and Wolf Creek.

From http://en.wikipedia.org/