Encyclopedia of Global Resources part 96 pot

Open-pit mining is much more economical than underground mining, although there are some large underground mines.. Geological Survey Natural Bitumen Resources of the United States http:

of alternative energy schemes (Exxon, for example,

invested $5 billion in its oil-from-shale project in

Col-ony, Colorado) and the acquisition of holdings in

such other energy sectors as coal and uranium These

companies would do much the same vis-à-vis biofuels

in the high-cost-petroleum era that followed the U.S

invasion of Iraq in 2003

The downturn in the price of oil in the 1980’s

caused the majors to shut down most of their

alterna-tive energy projects and to seek means for surviving in

the lean years of the global recession As these

compa-nies would do in even more publicized ventures

dur-ing the 1990’s, when the price of oil remained in the

twenty-five-dollar-per-barrel range, many turned to

mergers in order to economize, beginning with the

1984 merger between SoCal and Gulf Oil that enabled

Gulf to sell off many of its subsidiaries and service

sta-tions and led SoCal to change its name to Chevron A

decade later, what had been exceptional in 1984

be-came, momentarily, almost commonplace The

pro-cess began in December, 1998, when British Petroleum

(BP) acquired Amoco (formerly the American Oil

Company or Standard Oil of Indiana) for more than

$50 billion The following year the combined

corpo-ration purchased ARCO (one of the major players in

the discovery of Alaskan oil) Combined with its

sub-sequent acquisition of Burmah Castrol, a lubricant

manufacturing company, BP was able to pare

approxi-mately twenty thousand jobs worldwide and become

temporarily the world’s largest oil company

BP held that distinction for only a few months, until

Exxon and Mobil merged in November, 1999, into the

largest corporation in the world The transaction

en-abled the combined corporation to sell off more than

seventeen hundred service stations (to Tosco) and

trim its payroll by nearly ten thousand employees The

merger mania did not end there, or on the United

States side of the Atlantic Ocean In 1999, two giant

Eu-ropean petroleum firms, France’s Total and Belgium’s

Petrofina, merged into TotalFina, and then acquired

France’s other major petroleum company, Elf, to make

TotalFina the fourth largest petroleum company in the

world Then, in 2001, another Sister-Sister marriage

occurred, this time involving Chevron and Texaco

In short, by the time oil prices began to rise

appre-ciably shortly after the terrorist attack on New York

and Washington, D.C., on September 11, 2001, and

especially following the U.S invasion of Iraq in 2003,

a new set of six “supermajors” had emerged in the

world of private oil companies: Exxon-Mobil,

BP-Amoco, Chevron-Texaco, TotalFina, Royal Dutch Shell, and Conoco-Phillips (whose two units com-pleted their merger in August, 2002) All are vertically integrated and, compared to the “independents,” they have a commanding share of the market Unlike that of the Seven Sisters, though, their power is rooted in sales, not the production of oil, in which they accounted for only approximately 10 percent of the oil produced in the early years of the twenty-first century, and cer-tainly not in ownership of oil and gas, for which their combined ownership accounts for less than 5 percent

of the world’s known oil and gas reserves

State-Owned Petroleum Industries Comparatively speaking, the real “supermajors” are not these private oil companies but the seven largest state-owned petroleum companies in the contempo-rary world, led by those of Saudi Arabia, Iran, Russia, and Venezuela, but also including the state-owned companies of China, Brazil, and Malaysia Collectively, these seven account for nearly one-third of the world’s gas and oil production and the majority of its known oil reserves More important, when combined with the production capacity and reserve holdings of other state-owned oil companies, these actors account for the overwhelming majority of the world’s oil and gas pro-duction and reserves In that sense they are more anal-ogous to the Seven Sisters than today’s “supermajor” private oil corporations However, unlike the Seven Sisters, they do not collaborate with one another Quite to the contrary, they sometimes compete with one another for influence inside OPEC (where only Saudi Arabia, Iran, and Venezuela are represented) and for profits in the world’s petroleum marketplace

Joseph R Rudolph, Jr.

Further Reading

Davis, David Howard Energy Politics 4th ed New York:

St Martin’s Press, 1993

Deffeyes, Kenneth Hubbert’s Peak: The Impending World Oil Shortage Rev ed Princeton, N.J.:

Prince-ton University Press, 2003

Falola, Toyin, and Ann Genova The Politics of the Global Oil Industry: An Introduction Westport, Conn.:

Praeger, 2005

Grace, Robert Oil: An Overview of the Petroleum Indus-try 6th ed Houston, Tex.: Gulf, 2007.

Paul, William Henry Future Energy: How the New Oil In-dustry Will Change People, Politics, and Portfolios.

Hoboken, N.J.: John Wiley and Sons, 2007

Priest, Tyler The Offshore Imperative: Shell Oil’s Search for

Petroleum in Postwar America College Station: Texas

A&M University Press, 2007

Rees, Judith, and Peter Odell, eds The International

Oil Industry: An Interdisciplinary Perspective New

York: St Martin’s Press, 1987

Sampson, Anthony The Seven Sisters: The Great Oil

Com-panies and the World They Shaped New York: Viking

Press, 1975

Simmons, Matthew B Twilight in the Desert: The Coming

Saudi Oil Shock and the World Economy Hoboken,

N.J.: John Wiley and Sons, 2005

Solberg, Carl Oil Power: The Rise and Imminent Fall of an

American Empire? New York: New American Library,

1976

Yeomans, Matthew Oil: Anatomy of an Industry New

York: New Press, 2004

Yergin, Daniel The Prize: The Epic Quest for Oil, Money,

and Power New ed New York: The Free Press, 2008.

See also: Energy politics; Getty, J Paul; Oil and

natu-ral gas exploration; Oil embargo and energy crises of

1973 and 1979; Organization of Petroleum Exporting

Countries; Peak oil; Resources as a medium of

eco-nomic exchange; Resources as a source of

interna-tional conflict; Rockefeller, John D.; Saudi Arabia;

United States; Venezuela

Oil shale and tar sands

Category: Energy resources

Oil shale and tar sands are sources of oil and gas fuel,

lubricants, and chemical feedstock Tar sands are

rocks with pore spaces filled by solid or semisolid

bitu-men Oil shale is any fine-grained sedimentary rock

containing kerogen and yielding petroleum when

heated in the absence of oxygen.

Background

Tar sands are most abundant in sandstone and

lime-stone Most large deposits occur near sedimentary

ba-sin margins in deltaic, estuarine, or freshwater rocks

Oil shale occurs in lacustrine (lake) sediments,

associ-ated with coal, or in marine shale

Kerogen is a waxy, insoluble organic compound

with a large molecular structure Almost all

sedimen-tary rocks contain some kerogen; those that both

con-tain kerogen and yield a few liters of oil per metric ton are considered oil shale About 45 liters per metric ton generally is the minimum figure used for calculat-ing reserves Ninety to 135 liters are required for de-velopment Some shales contain more than 225 liters per metric ton Worldwide shale oil resources have been estimated at 3 trillion barrels, of which the United States has 2 trillion

Origin of Oil Shale Oil shale forms in oxygen-deficient environments where organic debris accumulates more rapidly than

it is destroyed by oxidation, scavengers, or decay Deep, confined ocean basins with stagnant water or restricted water circulation may preserve organic de-bris Baltic and Manchurian oil shales are of this ori-gin Swamp lakes, with slow circulation and rapid ac-cumulation of plant debris, also may produce oil shale Oil shale accompanying coal in Scotland and North America are examples Lakes with noncircu-lating water at the bottom also may accumulate oil shale The gigantic Green River oil shale deposit of Wyoming and Colorado is of this type

Producing Oil Shale Very great amounts of shale are needed for economi-cally significant petroleum production Open-pit mining is much more economical than underground mining, although there are some large underground mines Pits 300 meters deep and 3 kilometers across have costs equal to those of underground mining in the Green River deposit Further expansion reduces expense, making gigantic pits the most economical mining option Heating shale in the absence of oxy-gen (retorting) converts kerooxy-gen (solid organic mate-rial that is insoluble in petroleum solvents) to liquids The liquid then requires hydrogenation to make pe-troleum

Retorted shale is saline and/or alkalic powder Open pits are ready disposal sites for waste material, and underground mines may be backfilled The re-maining 10 percent or more of retort waste, however, requires disposal elsewhere Finally, the waste must be isolated from surface water and groundwater to pre-vent contamination In situ processing solves some disposal problems In this method large blocks of oil shale are undermined and collapsed, creating an un-derground porous rubble Gas introduced to the top

of the rubble is ignited, after which the shale burns on its own Gas and oil “cooked” from the rock are

drawn from the base of the rubble, leaving the spent

shale underground

Shale Oil History

Shale oil for medicinal purposes was produced in

1350 at Seefeld, Austria The manufacture of

illumi-nating oil and lubricants from oil shale began in

France around 1830 and quickly spread through

Eu-rope and North America Petroleum almost entirely

supplanted shale oil during the late nineteenth

cen-tury Afterward, shale oil production was largely

lim-ited to periods of oil shortage or of military or

eco-nomic blockade Flammable oil shale, rich in kerogen,

has been burned to generate steam in Latvia

Scot-land, the former Soviet Union, Manchuria, Sweden,

France, Germany, South Africa, the United States,

Brazil, and Australia all have produced shale oil, but

total world production through 1961 was only about

400 million barrels

Tar Sand Occurrence

Tar sand bitumens are larger, heavier, and more

com-plex hydrocarbon compounds than those in liquid

petroleum, and they include substantial nitrogen and

sulfur (“Bitumen” is a term for a very thick, natural

semisolid material such as asphalt or tar.) Deposits are

most abundant in sandstone or limestone Most large

deposits are in deltaic, estuarine, or freshwater

sand-stone The largest occur at depths of less than 1,000

meters on sedimentary basin margins where inclined

layers of petroliferous rocks approach the surface

Here, upward migrating petroleum could lose

vola-tiles and, with oxygenation and biodegradation, leave

asphalt-impregnated rock Some solid bitumens may

be hydrocarbons not yet sufficiently altered to form

liquids rather than residues of once liquid material

United States reserves, although large, are

insignif-icant compared to those of Canada and Venezuela

Additional deposits are known in Albania, Siberia,

Madagascar, Azerbaijan, the Philippines, and

Bul-garia

Tar Sand History

Tar sands have been used since ancient times for

sur-facing roads, laying masonry, and waterproofing The

Athabasca tar sand deposit of northern Alberta,

Can-ada, was discovered in 1778 when Peter Pond, a fur

trader, waterproofed his canoes with tar Geologic

ex-ploration began in the 1890’s, and by 1915 tar sand

was being shipped to Edmonton, Alberta, to pave

streets Pilot plant extraction of oil began in 1927 Af-terward, exploitation continued with provincial and federal subsidies and support By the end of the twen-tieth century, operations were self-supporting

Tar Sand Exploitation Canadian tar sand is mined in large open pits and transported to processing plants where steam treat-ment produces bitumen froth and sand slurry Naph-tha steam removes the remaining sand, leaving viscous bitumen Raw bitumen then is “cracked,” a chemical process by which the large organic mole-cules in the bitumen are broken into smaller, more liquid molecules, gas, and coke Finally, cracked oil is hydrogenated to produce synthetic crude oil Sulfur

is a salable by-product Sand ultimately is returned

to the pit, overburden is replaced, and the site is re-forested

Open-pit production, however, is feasible only at the shallow periphery of the deposit, so in situ extrac-tion will be required for about 90 percent of the Cana-dian deposit In one system, wells drilled into the de-posit are injected with steam to liquefy the bitumen Bitumen then is pumped until flow ceases, after which the well is again steamed In another system wells sunk into the tar sand are ignited Heat then cracks the bi-tumen, producing liquid and gas that flow to produc-tion wells

Ralph L Langenheim, Jr.

Further Reading

Bartis, James T., et al Oil Shale Development in the United States: Prospects and Policy Issues Santa Monica,

Calif.: Rand Institute, 2005

Chastko, Paul Developing Alberta’s Oil Sands: From Karl Clark to Kyoto Calgary, Alta.: University of Calgary

Press, 2004

Clarke, Tony Tar Sands Showdown: Canada and the New Politics of Oil in an Age of Climate Change Toronto:

J Lorimer, 2008

Meyer, Richard F., ed Exploration for Heavy Crude Oil and Natural Bitumen: Research Conference Tulsa,

Okla.: American Association of Petroleum Geolo-gists, 1987

Nikiforuk, Andrew Tar Sands: Dirty Oil and the Future

of a Continent Vancouver, B.C.: Greystone Books,

2009

Rühl, Walter Tar (Extra Heavy Oil) Sands and Oil Shales.

Stuttgart, Germany: Enke, 1982

Russell, Paul L Oil Shales of the World: Their Origin,

currence, and Exploitation New York: Pergamon

Press, 1990

Selley, Richard C Elements of Petroleum Geology 2d ed.

San Diego, Calif.: Academic Press, 1998

Welles, Chris The Elusive Bonanza: The Story of Oil

Shale—America’s Richest and Most Neglected Natural

Resource New York: Dutton, 1970.

Web Sites

U.S Department of the Interior, Bureau of

Land Management

About Oil Shale

http://ostseis.anl.gov/guide/oilshale/index.cfm

U.S Department of the Interior, Bureau of

Land Management

About Tar Sands

http://ostseis.anl.gov/guide/tarsands/index.cfm

U.S Geological Survey

Heavy Oil and Natural Bitumen: Strategic

Petroleum Reserves

http://pubs.usgs.gov/fs/fs070-03/fs070-03.pdf

U.S Geological Survey

Natural Bitumen Resources of the United States

http://pubs.usgs.gov/fs/2006/3133/pdf/FS2006-3133_508.pdf

See also: Athabasca oil sands; Energy economics;

Mining wastes and mine reclamation; Oil and natural

gas formation; Open-pit mining; Strip mining

Oil spills

Category: Pollution and waste disposal

Major oil spills can be environmentally devastating.

Not all spills are catastrophic, however, and a number

of techniques have been developed to contain and clean

up the oil; a spill’s location is the single most important

factor in the amount of damage it causes.

Background

The world’s oil reserves are developed by drilling, a

process that brings oil to the surface, where it can be

stored temporarily in tanks until transportation by

pipeline or oil tanker The oil is then transported:

Pipelines move oil long distances across land, while

tankers carry oil across the oceans Transported oil

is delivered to refineries, where it is separated into various useful components, including gasoline, jet fuel, home heating oil, diesel fuel, and lubricants These refined products are shipped to storage facili-ties where they await delivery

The drilling, storage, and transportation of oil sometimes result in the accidental release of oil into the natural environment Even with improvements in technology and safety, accidental spills are inevitable because of the unpredictable natures of human error, faulty equipment, and weather During the drilling of

a well, oil can surge upward to the surface and spill out into the environment, an event referred to as a “blow-out.” Oil storage tanks can leak oil through a faulty valve or through a valve accidentally left open Oil transported by pipeline can escape into the environ-ment if the pipeline is accidentally ruptured Oil tank-ers can spill oil into the ocean after grounding during severe weather

The Fate of Spilled Oil Oil spilled onto the ground generally soaks into the soil and does not spread far from the source of the spill Large populations of soil bacteria eventually de-grade most of the oil Oil spilled into water, however, spreads over the surface into a thin film After spread-ing, the oil covers a large area far away from the source

of the spill

Once on the water’s surface, oil is subjected to a se-quence of weathering processes Volatile components

in the oil are rapidly lost to the atmosphere Ultravio-let radiation in sunlight breaks down some oil com-ponents in a process called photooxidation Water-soluble components of oil dissolve into the water Oil remaining on the surface begins to break up into small droplets that enter the water, a process aided by high winds and waves Water turbulence at the surface can mix oil and water together into a mixture called a mousse In the water, oil collects suspended particles, and this mixture eventually sinks to the bottom Bot-tom oil is rolled along by water currents while collect-ing more oil and particles Eventually, bottom oil is buried or washed ashore

Oil that remains in the natural environment for any length of time is subjected to the natural process

of biodegradation The bacteria that carry out this process are widespread in the environment These or-ganisms use the oil as a nutrient source to grow In the process, they degrade the chemical components of

the oil into harmless end products This process, if

given sufficient time, can remove the majority of

spilled oil from the natural environment

Oil Cleanup Techniques

Oil spilled on the ground can be soaked up with straw

or commercially available oil sorbents The oil-soaked

materials can then be disposed of by burning or

burial Oil spilled into water presents a far greater

challenge to clean up, since it can quickly spread over

a large area Since spilled oil spreads quickly, a rapid

response is essential The flow of oil into the

environ-ment must be stopped, and the spread of spilled oil

must be minimized Oil containment booms are often

used to stop the spread of oil across water Booms are

placed around the source of the spill in an effort to

re-strict oil to a small area where it can be picked up by

skimmers Skimmers dip a belt into the water to pick

up oil from the surface and then scrape the belt across

a roller to remove the oil The oil scraped off the belt

falls into a storage tank

Oil that has escaped to cover large areas of water

surface can be removed by the use of chemical

disper-sants Dispersants break up the oil into tiny droplets that

readily mix into the water Oil that has been mixed into

the water is less likely to strand along the shoreline

Oil that strands on the shoreline can be difficult to

remove Shoreline cleanup of sandy beaches is often

labor-intensive and employs rakes, shovels, and

sorbents to remove oil Rocky shorelines can

some-times be cleaned safely by low-pressure water

spray-ing, but high-pressure spraying can be harmful

Cer-tain shoreline types, like marshes, are particularly

sensitive to disturbance and should be left alone

One of the more effective tools to emerge for the

cleanup of oiled shorelines is bioremediation This

method relies on the natural ability of bacteria in the

environment to break down oil In bioremediation,

natural breakdown is stimulated by the addition of a

fertilizer to the shoreline because the natural process

is often limited by a lack of nutrients With the

addi-tion of nutrients to the fertilizer, oil biodegradaaddi-tion

occurs at an accelerated rate This technique was

used successfully on the shorelines of Prince William

Sound after the Exxon Valdez oil spill.

Environmental Effects of Oil Spills

Pictures of dead and dying animals are often used

to depict the biological damage that oil spills can

cause The effects of major spills are indeed

devastat-ing The effects of smaller spills—or of spills in the open ocean—are significantly less severe The degree

of damage varies with a number of factors, including the type of oil spilled, the amount of oil spilled, and the location of the spill Spill location is perhaps the single most important factor Spills that occur in open water areas, such as coastal seas, typically have less bio-logical impact than those that occur in enclosed water areas, such as bays and sounds A comparison of the biological damage after the 1969 Santa Barbara oil

spill and the 1989 Exxon Valdez oil spill will illustrate

this point

The Santa Barbara oil spill occurred in the Santa Barbara Channel off the coast of California A total of 69,000 barrels of oil was released as a result of a well blowout The oil spread over a large area of coastal seas and weathered for a period of seven days before portions began to strand on shorelines Only a frac-tion of the spilled oil eventually came ashore along beaches and rocky shores The oil caused the death of shore animals, seabirds, and marine mammals, but mortality was neither widespread nor extensive be-cause of the prior weathering and dispersal of the oil

The Exxon Valdez oil spill occurred in Prince Wil-liam Sound, Alaska, in 1989 The tanker Exxon Valdez

ruptured its oil storage tanks after grounding on Bligh Reef Ruptured tanks released a total of 264,200 barrels of oil into the enclosed waters of Prince Wil-liam Sound The spilled oil did not weather or disperse prior to its spread across 28,500 square kilometers

of enclosed water and 1,900 kilometers of adjacent shoreline Therefore, the death of shoreline animals was widespread and extensive, as was the death of sea-birds and marine mammals An estimated 250,000 to 500,000 seabirds died as a result of the spill, in addi-tion to an estimated 4,000 to 6,000 marine mammals Oil was still found buried beneath the surface of some shorelines four years after the spill

Steve K Alexander

Further Reading

Easton, Robert Black Tide: The Santa Barbara Oil Spill and Its Consequences New York: Delacorte Press,

1972

El-Nemr, Ahmed Petroleum Contamination in Warm and Cold Marine Environments New York: Novinka

Books, 2006

Fingas, Merv The Basics of Oil Spill Cleanup 2d ed.

Edited by Jennifer Charles Boca Raton, Fla.: Lewis, 2001

Holleman, Marybeth The Heart of the Sound: An

Alas-kan Paradise Found and Nearly Lost Salt Lake City:

University of Utah Press, 2004

Loughlin, Thomas R., ed Marine Mammals and the

Ex-xon Valdez San Diego, Calif.: Academic Press, 1994.

National Research Council Oil in the Sea III: Inputs,

Fates, and Effects Washington, D.C.: National

Acad-emy Press, 2003

_ Oil Spill Dispersants: Efficacy and Effects

Wash-ington, D.C.: National Academies Press, 2005

Ott, Riki Not One Drop: Betrayal and Courage in the Wake

of the Exxon Valdez Oil Spill White River Junction,

Vt.: Chelsea Green, 2008

Web Site

National Oceanic and Atmospheric

Administration, National Ocean Service,

Office of Response and Restoration

Exxon Valdez Oil Spill

http://response.restoration.noaa.gov/exxonvaldez

See also: Alaska pipeline; American Petroleum

Insti-tute; Biotechnology; Environmental biotechnology;

Exxon Valdez oil spill; Oil and natural gas drilling and

wells; Oil industry; Petroleum refining and

process-ing; Water pollution and water pollution control

Olivine

Category: Mineral and other nonliving resources

Where Found

Olivine is common in the Earth’s crust Large

depos-its of olivine are often associated with certain

volca-noes

Primary Uses

The main use of olivine is the use of peridot as a

gem-stone, which is found in Arizona and on the Red Sea

island of Zebirget Through chemical reaction, it is

also an energy source

Technical Definition

Olivine generally appears in a variety of

yellowish-green and yellowish-brown colors, depending on its

specific chemical composition It has a hardness of 6.5

to 7 on the Mohs scale The name olivine refers to a

se-ries of high-temperature minerals that have the end

members forsterite (Mg2SiO4) and fayalite (Fe2SiO4) When the two are chemically combined they form the magnesium iron silicate that is commonly called oliv-ine The higher-temperature member, forsterite, is rich in the element magnesium

Description, Distribution, and Forms Olivine is the group name for a series of minerals that have the end members forsterite and fayalite The ol-ivine group of minerals is one of the more important rock-forming minerals that make up the Earth’s crust

It is a high-temperature mineral group that is often associated with the volcanic rock basalt It is a com-mon mineral in the rocks that constitute the Earth’s lower crust and upper mantle Olivine is also one of the essential minerals found in the stony variety of meteorites

Olivine often occurs as attractive crystals In color, olivine can appear with differing shades of yellowish-green Depending upon its specific chemical compo-sition, olivine can also appear in shades of yellowish-brown to an almost reddish color

History Forsterite was named after Johann R Forster, an eigh-teenth century German naturalist who sailed with the English explorer Captain James Cook Fayalite, the lower-temperature end member of the series, is rich

in iron It was named after the island Fayal in the Azores, where it is abundant

Obtaining Olivine Since olivine is a high-temperature mineral, it is usu-ally absent from the Earth’s surface Large deposits

of olivine are often associated with certain volcanoes

An unusually explosive volcano can rapidly transport olivine up from great depths and then expel it as

it erupts Lavas produced by such volcanoes often have numerous individual olivine crystals scattered throughout; the crystals may also clump together and form as nodules In both cases these crystals were forming within the magma at depth and were then transported upward with the rising magma When the magma eventually flowed out of the volcano as lava, it contained the olivine that originally formed at great depth Associated with these eruptions are other rocks called xenoliths, which also formed at depth; they contain olivine as one of their principal minerals This kind of rock is called periodite

Uses of Olivine

Peridot is the variety of olivine that is used as a

gem-stone It is somewhat transparent and ranges in color

from a yellowish-green to olive green The dark

yellow-green stones are considered to be the most valuable

Flawless peridot is common, and it can be faceted in

many different ways Fine-quality peridot comes from

the San Carlos Indian Reservation in Arizona The

most sought-after stones come from the island of

Zebirget in the Red Sea Peridot is the birthstone for

the month of August

Paul P Sipiera

Web Sites

Natural Resources Canada

Canadian Minerals Yearbook, 2005: Magnesium

http://www.nrcan.gc.ca/smm-mms/busi-indu/cmy-amc/content/2005/36.pdf

U.S Geological Survey

Mineral Information: Magnesium Statistics and

Information

http://minerals.usgs.gov/minerals/pubs/

commodity/magnesium/

See also: Gems; Igneous processes, rocks, and

min-eral deposits; Iron; Magma crystallization;

Magne-sium; Minerals, structure and physical properties of;

Mohs hardness scale; Silicates; Silicon; Volcanoes

Open-pit mining

Category: Obtaining and using resources

Open-pit mining refers to the removal of mineral

re-sources from the Earth without the use of either tunnels

or wells A gravel pit represents the simplest example of

an open-pit mine Although some mining engineers

distinguish between strip mining and open-pit

min-ing, the methods employed in both are similar The

ma-jor difference is that strip mines are generally shallow,

while a pit may eventually descend to hundreds of

me-ters below the original surface of the Earth.

Background

Open-pit mining is the method mine owners prefer to

use when the mineral body lies close enough to the

surface of the Earth to allow the removal of the ore in

continuous layers It is both the safest and most eco-nomical method of extracting mineral resources from

a site It has been estimated that worldwide 70 percent

of all minerals mined are obtained through open-pit mining processes There is a strong economic incen-tive for mine operators to use the open-pit method Mining by the open-pit method allows the mining company to extract 100 percent of the ore-bearing rock In underground mines using tunnels and shaft-ing, the recovery rate of ore-bearing rock is generally

60 percent or less Open-pit mining is also consider-ably safer than underground mining, as the ore is re-moved with power shovels and large trucks Although underground mining also uses mechanized equip-ment, the workers are still exposed to risks such as cave-ins and explosions not present in open pits

Methods

A few minerals are soft enough to be mined without the use of explosives More commonly, mining pro-ceeds through a series of drilling holes, placing explo-sive charges in the holes and blasting, and then re-moving the shattered rock with extremely large power shovels and trucks Most equipment used in open-pit mining is gargantuan in size Power shovels, excava-tors, and draglines are custom-assembled at the mine since they are too large to transport other than in pieces In the past, when a mine closed, this equip-ment was abandoned at the site Today it is more likely

to be salvaged as scrap metal In a few former mining districts, specialized equipment has been left in place and preserved as part of historic landmarks

In some cases the ore body lies close enough to the surface that mining begins directly More often, a layer of waste material known as the overburden must

be removed before the ore itself is exposed The over-burden consists of the topsoil and underlying dirt and rock that contains no extractable ore When mining begins, the layer of topsoil will be removed carefully and piled separately from other waste material, as the topsoil will be needed for use in the restoration pro-cess when the mine site is exhausted

Depending on the mine site, the type of ore mined, and other factors, the mining may proceed in parallel strips or may be done in a circular pattern that gradu-ally expands in diameter Coal is often mined in strips,

as the mineral frequently occurs in layers that can cover a wide area but are only a meter or so in thick-ness The mine operator removes the overburden from a strip of coal, excavates the coal, and then

peats the process in a strip running next to the first

strip When the ore body is exhausted, the

overbur-den will be backfilled into the stripped area as part of

the restoration process In the past, before legislation

required mine operators to practice restoration, a

strip-mined area often consisted of a devastated

land-scape dominated by alternating trenches and ridges,

with the land left unusable for either agriculture or

wildlife habitat Beginning with the passage of

envi-ronmental regulations in the 1960’s, in the United

States, strip-mined areas have been backfilled,

lev-eled, and seeded with grass and trees

Metals such as iron are generally mined in pits that

become both deeper and wider over time The

min-ing operation will commence as closely as possible to

the known center of the site and expand both out and

down as ore is removed As time passes, the pit may

be-come surrounded by large piles of tailings, or waste rock The final depth of the pit will be determined by factors such as the thickness of the ore body and the stability of the surrounding walls of the pit A pit devel-oped to excavate material such as gravel often has walls composed of soft materials, such as a mixture of sand and gravel, and at risk of collapsing into the pit Gravel pits therefore are generally quite shallow Even

a pit mine for hard minerals, such as copper or iron, where the mineral is found in rock, may eventually reach a depth where the height of the walls makes it unsafe to dig the pit any deeper If the ore is suffi-ciently valuable, mining of the remaining ore body may continue using shaft mining

In the past, large open-pit mines often operated next to or within communities, such as Butte, Mon-tana, and Bisbee, Arizona, both of which had

An open-pit mine in Kazakhstan (Time & Life Pictures/Getty Images)

mous copper mines At one time the Anaconda

opera-tion at Butte was reputed to be the largest open-pit

mine in the world As the mines expanded, homes and

businesses were forced to relocate to accommodate the

mine’s operation By the end of the twentieth century,

however, the general public had grown less tolerant of

mining Property owners have sued mining

compa-nies over quality-of-life issues such as noise pollution

and dust Developers now generally try to avoid

open-ing new open-pit mines close to towns or suburbs

Environmental Issues

Open-pit mining raises a number of obvious

environ-mental protection questions Even at its most

innocu-ous, the mining process tends to be both noisy and

dusty Truck or rail traffic to and from the mine can

create a nuisance as well as a safety hazard for area

res-idents As the pit is deepened, it may affect the local

water table Water can seep into the pit, lowering the

water table for the surrounding area, and can then

present a hazard to local streams as it is pumped out

loaded with sediment Strip mining on hillsides can

lead to erosion and contamination by mine spillage of

the local streams

Depending on the ore being mined, the open-pit

mine may present potentially life-threatening

prob-lems in addition to dust and noise The mine itself

may be relatively harmless, but processing plants built

next to the mine to remove the ore from waste rock may involve the use of dangerous chemicals and pro-duce toxic by-products Precious-metals mining can

be particularly hazardous In gold mining, for exam-ple, the ore often occurs in such small amounts within the ore body that remarkably large amounts of ore must be processed to obtain the precious metal using

a method that employs cyanide and mercury If these substances leak into the environment, they can poi-son streams and kill wildlife kilometers away from the mine itself Iron ore mining can release sulfides into the environment, as can mining coal Although not as toxic as cyanide and mercury, sulfides raise the acidity

of water and can make lakes and streams uninhabit-able by aquatic life

In the United States, Canada, and many other na-tions, mine owners are now required by law to restore

an open-pit mining site as closely as possible to its orig-inal condition Toxic wastes must be removed or neu-tralized and the pit filled in Restoration efforts at strip-mining sites in eastern states that enjoy a rela-tively wet climate, such as Tennessee and Ohio, have been successful Phosphate mining areas in Tennes-see, for example, have been restored for use in agri-culture Gravel pits and limestone quarries may be used as small wetlands Water has always been prone

to build up in abandoned pit mines Engineering con-sulting firms exist that specialize in preparing

U.S Bureau of Economic Analysis, , May, 2008.

$121.3

$225.7

$262.4

$275.8

Billions of Dollars

300 250

200 150

100 50

2006

2000

2005

2007

Note: Includes oil and gas extraction, other mining, and support activities for mining.

U.S Gross Domestic Product in Mining, 2000-2007

doned pits to become wetlands and ponds These

firms clean up the site, slope the walls to make the pit

safer, remove any potentially dangerous mining

de-bris, and plant the species of vegetation most

benefi-cial to wildlife native to the region Restoration efforts

in arid climates have been less successful Lack of rain

makes restoring native vegetation difficult and, even

if tailings dumps and mine pits are bulldozed to less

artificial contours, the scars from mining will be

visi-ble for centuries

Nancy Farm Männikkö

Further Reading

Bell, Fred J., and Laurance J Donnelly “Quarrying

and Surface Mining.” In Mining and Its Impact on the

Environment New York: Taylor & Francis, 2006.

Cameron, Eugene N At the Crossroads: The Mineral

Problems of the United States New York: Wiley, 1986.

Chinese Organizing Committee of the Fourteenth

World Mining Congress, ed Mining for the Future:

Trends and Expectations New York: Pergamon Press,

1990

Hartman, Howard L., and Jan M Mutmansky

Intro-ductory Mining Engineering 2d ed Hoboken, N.J.:

J Wiley, 2002

Hustrulid, William, and Mark Kuchta Open Pit Mine

Planning and Design 2d ed New York: Taylor and

Francis, 2006

Institution of Mining and Metallurgy Surface Mining

and Quarrying: Papers Presented at the Second

Interna-tional Surface Mining and Quarrying Symposium

Lon-don: Author, 1983

Smith, Duane A Mining America: The Industry and the

Environment, 1800-1980 Lawrence: University Press

of Kansas, 1987 Reprint Niwot: University Press of

Colorado, 1993

Tatiya, Ratan Raj Surface and Underground Excavations:

Methods, Techniques, and Equipment London: A A.

Balkema, 2005

Twitty, Eric “The Technology of Open Pit Mining and

Blasting.” In Blown to Bits in the Mine: A History of

Mining and Explosives in the United States Ouray,

Colo.: Western Reflections, 2001

Web Sites

Mine-Engineer.Com

Open Pit Surface Mine

http://www.mine-engineer.com/mining/

open_pit.htm

U.S Geological Survey Mining and Quarrying http://minerals.usgs.gov/minerals/pubs/

commodity/m&q See also: Mining wastes and mine reclamation; Quarrying; Strip mining; Underground mining

Ophiolites

Category: Geological processes and formations

Ophiolites are pieces of oceanic crust and upper mantle that have been thrust up on continental crust They contain a wide range of minerals.

Definition The process that forms ophiolites occurs where conti-nental crust is bent down and slips under oceanic crust, generally in a subduction zone Ophiolites con-sist of a vertical sequence of (from bottom to top) mantle rocks, gabbro, sheeted dykes, and pillowed lavas Ophiolites are remnants of ancient ocean bas-ins, demonstrating that an ocean basin once existed

in the area and that plate convergence has destroyed the ocean basin Ophiolites generally define and dec-orate suture zones, places where once-separated con-tinental blocks have collided Ophiolites host a wide range of minerals, including chromite, platinum-group elements, and gold Ophiolites are also impor-tant from a natural resources perspective because the tectonic forces that have put them in place often also form sedimentary basins that can contain fossil fuel deposits (oil, gas, and coal)

Overview The term “ophiolite” comes from the Greek word

ophis, meaning snake or serpent; the term’s origin is

similar to that of the rock called “serpentinite.” Both terms refer to the mottled green (reptilian) appear-ance of these rocks Ophiolites are sequences of oce-anic crust and upper mantle that have been emplaced

on continental crust by a process known as obduction Obduction often faults, folds, and otherwise disrupts the original sequence of rocks Nevertheless, ophio-lites provide the best-known example of the structure

of oceanic crust

The typical ophiolite sequence is on the order of