Geologic Resources - Poudre School District 5- Geologic...9/3/2014 MindTap - Cengage Learning 4/55 We use two types of geologic resources: mineral resources (Economically valuable

9/3/2014 MindTap - Cengage Learning

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Chapter 5: Geologic Resources Chapter Contents

Book Title: Earth

Printed By: Kevin Murray ([email protected])

© 2015, 2011 Cengage Learning, Cengage Learning

5

Geologic Resources

Chapter Introduction

5-1 Mineral Resources

5-2 Ore and Ore Deposits

5-2a Magmatic Processes

5-2b Hydrothermal Processes

5-2c Sedimentary Processes

5-2d Weathering Processes

5-3 Mineral Reserves vs. Mineral Resources

5-3a The Geopolitics of Metal Resources

5-4 Mines and Mining

5-5 Energy Resources: Coal, Petroleum, and Natural Gas

5-5a Coal

5-5b Petroleum

5-5c Natural Gas

5-6 Unconventional Petroleum and Gas Reservoirs

5-6a Coal Bed Methane

5-6b Tar Sands

5-6c Oil Shale

5-7 Energy Resources: Nuclear Fuels and Reactors

5-8 Energy Resources: Renewable Energy

5-8a Solar Energy

5-8b Wind Energy

5-8c Geothermal Energy

5-8d Hydroelectric Energy

5-8e Biomass Energy



5-8f The Future of Renewable Energy Resources

5-9 Conservation as an Alternative Energy Resource

5-9a Technical Solutions

5-9b Social Solutions

5-10 Energy for the st Century

Chapter Review

Key Terms

Chapter Review

Review Questions

Chapter 5: Geologic Resources Chapter Introduction

Book Title: Earth



Chapter Introduction

The Maersk Developer, a semisubmersible deepwater drilling platform on its

maiden voyage from Singapore. This platform is capable of drilling in water depths

of kilometers and is currently deployed in the Gulf of Mexico.



COURTESY OF MAERSK DRILLING

Fertile soil, level plains, easy passage across the mountains, coal, iron, and other metals

imbedded in the rocks, and a stimulating climate, all shower their blessings upon man.

Ellsworth Huntington

Since humanlike creatures emerged to million years ago, our use of geologic resources

has become increasingly sophisticated. Early hominids used sticks and rocks as simple

weapons and tools. Later prehistoric people used flint and obsidian to make more-effective

weapons and tools, and they used natural pigments to create elegant art on cave walls.

About 8000 BCE (Before Common Era), people learned to shape and fire clay to make

pottery. Archaeologists have found copper ornaments in Turkey dating from 6500 BCE;

years later, Mesopotamian farmers used copper farm implements. Today, geologic

resources provide iron for steel, silicon for making computer chips, and gasoline that

powers most cars.



We use two types of geologic resources: mineral resources (Economically valuable

geological materials including both metal ore and nonmetallic minerals.) and energy

resources (Geologic resources—including petroleum, coal, natural gas, and nuclear fuels—

used for heat, light, work, and communication) Mineral resources include all useful rocks

and minerals. As we will see in the sections that follow, many mineral resources are

naturally concentrated by processes that involve interactions among rock of the geosphere,

atmospheric gases, and water from the hydrosphere. Humans have mined and refined

these resources further to create the industrial world that has altered our planet. The

primary energy resources of the early st century are coal, petroleum, and natural gas—

all formed from the decayed remains of prehistoric plants and animals that have been

altered by Earth systems processes.

Chapter 5: Geologic Resources: 5-1 Mineral Resources

Book Title: Earth



5-1 Mineral Resources

Mineral resources include both metal ore and nonmetallic minerals. Recall from Chapter 2

that ore is rock sufficiently enriched in one or more minerals to be mined profitably.

Geologists usually use the term to refer to metallic mineral deposits, and it is commonly

accompanied by the name of the metal—for example, iron ore or silver ore.

Nonmetallic mineral resources (Economically useful rocks or minerals that are not

metals; examples include salt, building stone, sand, and gravel) refers to the useful rocks or

minerals that are not metals—such as salt, building stone, sand, and gravel. When we think

about “striking it rich” from mining, we usually think of gold. However, despite the recent

historically high price of gold, more money was made in the United States in the year 2010

from mining and selling sand, gravel, and crushed stone ($ billion in estimated

revenue) than from gold ($ billion in estimated revenue). Sand and gravel are mined

from stream and glacial deposits, sand dunes, and beaches, whereas crushed stone is

quarried from nonweathered igneous, metamorphic, or sedimentary bedrock. These

nonmetallic resources are mixed with portland cement—a material produced by heating a

mixture of crushed limestone and clay—to make concrete. Reinforced with steel, concrete is

used to build roads, bridges, and buildings. Thus, reinforced concrete is one of the basic

building materials of the modern world. In addition, many buildings are faced with stone—

usually granite or limestone. Marble, slate, sandstone, and other rocks used for building are

also mined from quarries cut into bedrock (Figure 5.1).

Figure 5.1

A quarryman in China splits a large granite block with a sledgehammer. After he

splits the rock, the circular saws in the background will cut it into thin slabs for

floors and walls.



COURTESY OF GRAHAM R. THOMPSON/JONATHAN TURK

There are many important metals and other elements that are fundamental parts of our

lives and of the industries that produce a range of products in daily use. Some of these

metals are familiar to us, such as iron, lead, copper, aluminum, silver, and gold. Others are

less well known, such as molybdenum (rifle barrels), tungsten (lightbulb filaments), and

borax (soaps, antiseptics).

All mineral resources are nonrenewable: we use them up at a much faster rate than

natural processes create them, although many can be recycled.

Chapter 5: Geologic Resources: 5-2 Ore and Ore Deposits

Book Title: Earth



5-2 Ore and Ore Deposits

If you pick up any rock and send it to a laboratory for analysis, the report will probably

show that the rock contains measurable amounts of iron, gold, silver, aluminum, and other

valuable metals. However, the concentrations of these metals are so low in most rocks that

the extraction cost would be much greater than the income gained by selling the refined

metals. In certain locations, however, natural geologic processes have enriched metals

many times above their normal concentrations. Table 5.1 shows that the concentration of a

metal in ore may exceed its average abundance in ordinary rock by a factor—called the

enrichment factor—of more than .

Table 5.1

Comparison of Concentrations of Specific Elements in Earth’s Crust with



Concentrations Needed to Operate a Commercial Mine

Element Natural

Concentration

in Crust (% by

Weight)

Concentration

Required to Operate a

Commercial Mine (%

by Weight)

Enrichment Factor

Aluminum to to

Iron to

Copper to to

Nickel

Zinc

Uranium

Lead

Gold

Mercury

© Cengage Learning

Successful exploration for new ore deposits requires an understanding of the processes that

concentrate metals to form ore. For example, platinum concentrates in certain types of

igneous rocks. Therefore, if you were exploring for platinum, you would focus on those

rocks rather than on sandstone or limestone.

With the exception of magmatic processes, which occur deep within the crust, the natural

processes that concentrate ore minerals all involve interactions of rocks and minerals of the

geosphere with water from the hydrosphere. The more common ore-forming processes are

described below.

Chapter 5: Geologic Resources: 5-2a Magmatic Processes

Book Title: Earth



5-2a Magmatic Processes



Magmatic processes (Geologic processes that form ore deposits as liquid magma solidifies

into igneous rock.) form mineral deposits as liquid magma solidifies to form an igneous

rock. These processes create metal ores as well as some gems and nonmetallic mineral

deposits including sulfur deposits and building stone.

Some large bodies of plutonic igneous rock, particularly those of mafic (high in magnesium

and iron) composition, solidify in layers (Figure 5.2). Each layer contains different minerals

and is of a different chemical composition than adjacent layers. Some of the layers may

contain rich ore deposits. The layering can develop by at least two processes:

1. Cooling magma does not solidify all at once. Instead, higher-temperature minerals

crystallize first, and lower-temperature minerals form later as the magma cools and

the temperature drops. Most minerals are denser than magma. Consequently, early-

formed crystals may sink to the bottom of a magma chamber in a process called

crystal settling (A process in which the crystals that solidify first from a cooling

magma settle to the bottom of the magma chamber because the minerals are more

dense than magma; the ultimate result is a layered body of igneous rock, each layer

containing different minerals.) . In some instances, ore minerals crystallize with

other early-formed minerals and accumulate in layers near the bottom of a pluton.

2. Some large bodies of mafic magma crystallize from the bottom upward. Thus, early-

formed ore minerals become concentrated near the base of the pluton.

Figure 5.2

An outcrop of layered mafic igneous rock from the Bushveld intrusion in South

Africa. The dark layers are made of chromite crystals that settled to the bottom of

the magma chamber more rapidly than the lower-density feldspar, making up the

lighter-colored layers. The layering itself is interpreted to reflect multiple injections

of magma into the magma chamber.



PHOTOGRAPH COURTESY OF JOHN DILLES

The largest ore deposits found in layered mafic plutons are the rich chromium and

platinum reserves of South Africa’s Bushveld intrusion. The pluton is about by

kilometers in area—roughly the size of the state of Maine—and about kilometers thick.

The Bushveld deposits contain more than billion tons of chromium and more than

billion grams of platinum, the greatest reserves in any known deposit on Earth. The

platinum alone is worth over $ billion at 2013 prices.

Chapter 5: Geologic Resources: 5-2b Hydrothermal Processes

Book Title: Earth



5-2b Hydrothermal Processes

Hydrothermal processes (Geologic processes in which hot water or steam dissolves

metals and minerals from rocks or magma; the solutions then seep through cracks before

cooling, to create ore deposits.) —hydro for “water” and thermal for “heat,” involving

interactions between hot water or steam and rocks or minerals—are probably responsible

for the formation of more ore deposits, and a larger total quantity of ore, than all other

processes combined. To form a hydrothermal ore deposit, hot water dissolves metals from

rock or magma. The metal-bearing solutions then seep through cracks or through

permeable rock, where they precipitate to form an ore deposit.



Although water by itself is capable of dissolving minerals, most hydrothermal waters also

contain dissolved salts. The presence of the salts greatly increases the water’s ability to

dissolve minerals. Therefore, hot, salty, hydrothermal water is a very powerful solvent,

capable of dissolving and transporting metals.

Hydrothermal water comes from three sources—granitic magma, groundwater, and the

oceans:

1. Granitic magma contains more dissolved water than solid granite rock. Thus, the

magma gives off hydrothermal water as it solidifies. Because many ore metals do not

fit neatly into the crystal structure of silicate minerals that form from a cooling

granitic magma, these elements become concentrated in the hydrothermal waters.

2. Groundwater can seep into Earth’s crust, where it is heated and forms a

hydrothermal solution. The solution circulates through rock in the crust and dissolves

ore metals, which later precipitate in concentrated form elsewhere. This scenario is

common in volcanic areas where hot rock or magma heat groundwater at shallow

depths.

3. In the oceans, hot, young basalt at a mid-oceanic ridge heats seawater as it seeps into

cracks in the seafloor.

Refer again to Table 5.1, which shows that tiny amounts of all metals are found in average

rocks of the Earth’s crust. For example, gold makes up percent of the crust,

while copper makes up percent and lead percent. Although the metals are

present in very low concentrations in country rock, hydrothermal solutions percolate

through vast volumes of rock, dissolving or scavenging (The process by which

hydrothermal fluids sweep through large volumes of country rock and dissolve low

concentrations of metals, concentrating them elsewhere as an ore deposit.) the metals and

carrying them in solution. Where they encounter changes in temperature, pressure, or

chemical environment, the solutions then can deposit the metals to form a local ore deposit,

(Figure 5.3).

Figure 5.3

Hot water scavenges metals from crystallizing igneous rock and the country rock

that surrounds it. The hydrothermal water then deposits metallic minerals in ore-

rich veins that fill fractures in bedrock. It also deposits low-grade disseminated

metal ore in large volumes of rock surrounding the veins.



© Cengage Learning

A hydrothermal vein deposit (A rich, sheetlike mineral deposit that forms when

economically-valuable minerals precipitate from hot water solutions along a fault or other

fracture.) forms when dissolved metals precipitate in a fracture in rock. Ore veins range

from less than a millimeter to several meters in width. A single vein can yield several

million dollars worth of gold or silver. The same hydrothermal solutions may also soak into

pores in country rock near the vein to create a large but much less concentrated

disseminated ore deposit (A large, low-grade hydrothermal deposit in which metal-

bearing minerals are widely scattered throughout a rock body; not as concentrated as a

hydrothermal vein.) . Because they commonly form from the same solutions, rich ore veins

and disseminated deposits are often found together. The history of many mining districts is

one in which early miners dug shafts and tunnels to follow the rich veins. After the veins

were exhausted, later miners used huge power shovels to extract low-grade ore from

disseminated deposits surrounding the veins.

In volcanically active regions of the seafloor, near a mid-ocean ridge and submarine

volcanoes, seawater circulates through the hot, fractured oceanic crust. The hot seawater

dissolves metals from the rocks and then, as it rises through the upper layers of oceanic

crust, cools and precipitates the metals to form submarine hydrothermal ore deposits

(Ore deposits that form when hot seawater dissolves metals from seafloor rocks and then,

as it rises through the upper layers of oceanic crust, cools and precipitates the metals.) .

The metal-bearing solutions can be seen today as jets of black water, called black smokers

(A jet of black water spouting from a fracture or vent in the seafloor, commonly near a

mid-oceanic ridge. The black color is caused by precipitation of fine-grained metal sulfide

minerals as the hydrothermal solutions cool on contact with seawater.) , spouting from



fractures and vents in the Mid-Oceanic Ridge. The black color is caused by precipitation of

fine-grained metal sulfide minerals as the solutions cool upon contact with seawater. The

precipitating metals accumulate as chimneylike structures near the hot-water vent. Rich

ore deposits form in such environments, but the cost to operate machinery in such great

water depths is prohibitive.

Chapter 5: Geologic Resources: 5-2c Sedimentary Processes

Book Title: Earth



5-2c Sedimentary Processes

Placer Deposits

Gold is denser than any other mineral. Therefore, if you swirl a mixture of water, gold dust,

and sand in a gold pan, the gold sinks to the bottom fastest. Differential settling also occurs

in nature. Many streams carry silt, sand, and gravel with an uncommon small grain of

gold. The gold settles fastest when the current slows down. Over years, currents agitate the

sediment and the dense gold works its way into cracks and crevices in the streambed. Thus,

grains of gold concentrate in gravel as well as in cracks and potholes eroded into the

bedrock of the streambed, forming a placer deposit (A surface mineral deposit formed

along stream beds, beneath waterfalls, or on beaches when water currents slow down and

deposit high-density minerals.) (Figure 5.4). The prospectors who rushed to California in the

Gold Rush of 1849, for example, mined placer deposits in conglomerate of Eocene age there.

Figure 5.4

Placer deposits form where water currents slow down and deposit high-density

minerals.



© Cengage Learning

Precipitates

Groundwater dissolves minerals as it seeps through soil and bedrock. In most

environments, groundwater eventually flows into streams and then to the sea. Some of the

dissolved ions, such as sodium and chloride, make seawater salty. In deserts, however,

playa lakes develop with no outlet to the ocean. Water flows into the lakes but can escape

only by evaporation. As the water evaporates, the dissolved salts concentrate until they

precipitate to form evaporite deposits (see Chapter 3). The composition of the salt and

specific salt minerals that form depend on the composition of dissolved ions transported to

the basin, which in turn depend upon the bedrock in the region. Evaporite deposits in desert



lakes include sodium chloride (table salt), borax, sodium sulfate, and sodium carbonate.

These salts are used in the production of paper, soap, and medicines and for the tanning of

leather.

Several times during the past million years, shallow seas covered large regions of North

America and all other continents. At times, those seas were so weakly connected to the open

oceans that water did not circulate freely between seas and the oceans. Consequently,

evaporation concentrated the dissolved salts until they precipitated as marine evaporites.

Periodically, new seawater from the open ocean would replenish the shallow seas,

providing a new supply of salt. Thick marine evaporite beds, formed in this way, underlie

nearly percent of North America. Table salt, gypsum (used to manufacture plaster and

sheetrock), and potassium salts (used in fertilizer) are mined extensively from these

deposits.

Most of the world’s supply of iron is mined from sedimentary rocks called banded iron

formations (Iron-rich sedimentary rocks composed of alternating iron-rich and silica-rich

layers; source of most of the world’s supply of iron.) , which are deposits composed of

alternating iron-rich and silica-rich layers (Figure 5.7). These iron-rich rocks precipitated

from the seas between and billion years ago, as a result of rising atmospheric

oxygen concentrations.

Figure 5.7

Banded iron formations from Michigan. The iron is concentrated as iron oxide in

the metallic gray layers; the red layers are chert.

COPYRIGHT AND PHOTOGRAPH BY DR. PARVINDER S. SETHI



Chapter 5: Geologic Resources: 5-2d W eathering Processes

Book Title: Earth



5-2d Weathering Processes

In environments with high rainfall, the abundant water dissolves and removes most of the

soluble ions from soil and rock near Earth’s surface. This process leaves the relatively

insoluble ions in the soil to form residual ore deposits (A mineral deposit formed from

relatively insoluble ions left in the soil near Earth’s surface after most of the soluble ions

were dissolved and removed by abundant water.) . Both aluminum and iron have very low

solubilities in water. Bauxite (A gray, yellow, or reddish-brown rock, composed of a

mixture of aluminum oxides and hydroxides, that formed as a residual deposit; the

principle source of aluminum.) , the principal source of aluminum, forms as a residual

deposit, and in some instances iron also concentrates enough to become ore. Most bauxite

deposits form in warm and rainy tropical or subtropical environments where chemical

weathering occurs rapidly. Thus, bauxite ores are common in Jamaica, Cuba, Guinea,

Australia, and parts of the southeastern United States (Figure 5.8).

Figure 5.8

This spheroidal texture is typical of bauxite, which is aluminum ore formed as a

residual soil deposit by intense tropical weathering of aluminum-rich rocks. This

bauxite is from northern Queensland in Australia. The pencil tip is pointing to

concentric layering within a spheroid that has been broken.

COPYRIGHT AND PHOTOGRAPH BY MARC S. HENDRIX



Box 5.1

DiggingDeeper

Manganese Nodules

A rich source of strategically important metals rests on the deep-ocean floor

Much of the Pacific Ocean floor is covered with golf ball– to bowling ball–sized

manganese nodules (A potato-shaped rock found on the ocean floor and rich in

manganese and other metals precipitated from seawater through

biomineralization) (Figures 5.5 and 5.6). A typical nodule contains to percent

manganese, percent iron, about percent each of copper and nickel, and lesser

percentages of other metals such as cobalt, zinc, and lead. At least different

elements have been reported from manganese nodules, several of which are metals

with significant commercial and military applications. The metals are probably

introduced into seawater by volcanic activity at mid-oceanic ridges, perhaps by

black smokers. Certain specialized bacteria and algae on the seafloor are able to

precipitate or biomineralize (The process by which living organisms produce

minerals.) the metals, effectively forming a nodule seed that continues to grow as

more metals are added to its outer layers.

Figure 5.5

Manganese nodules cover large portions of the seafloor. These are from the

central North Pacific Ocean at a depth of meters.



K.L. SMITH JR (MBARI) AND S.E. BEAULIEU (WHOI)

Figure 5.6

Close-up of a manganese nodule from the South Pacific Ocean Penny for

scale.


Hundreds of billions of tons of manganese nodules lie on the seafloor, with the

densest accumulations occurring in the Pacific Ocean. Most nodules occur at depths

of around kilometers, although some occur in water over kilometers deep and

some have been reported at less than kilometers.



Since the 1970s, large-scale mining of the nodules has been discussed, although it

has never been undertaken because the costs of recovering the nodules from these

depths is prohibitive. However, the economics of mining nodules from the seafloor

is changing because of recent increases in most metals prices and the strategic

importance of the so-called rare earth elements that occur in manganese nodules.

Rare earth elements are a suite of different metals that are used in an ever-

increasing array of high-tech equipment, including lasers, fiber optics, computer

disk drives and memory chips, rechargeable batteries, X-ray tubes, certain

superconductors, and liquid crystal displays.

Because of their chemical properties, rare earth elements do not commonly

concentrate in ore bodies, are expensive to refine, and create environmental

problems when they are mined. Over the past years, mining of rare earth

elements has largely shifted to China because of lower labor costs and less

restrictive environmental regulations. As a result, China now controls the vast

majority of rare earth element production, with some estimates as high as

percent.

In 2010, China temporarily halted exports of rare earth elements to Japan.

Although the embargo was short-lived, it set off political alarms around the world.

U.S. Secretary of State Hillary Rodham Clinton called the move a “wake up call,”

because it underscored the vulnerability of the U.S. economy to disruptions in the

supply of rare earth elements.

Among the alternatives to diversifying the source of rare earth elements is large-

scale mining of manganese nodules from the deep seafloor. As a result, detailed

maps of the distribution of manganese nodules are now being rapidly developed, as

are various systems for recovering nodules profitably from the deep seafloor. One

can imagine robotic undersea video cameras locating the nodules and giant

vacuums sucking them up and lifting them to a ship. But, because the seafloor is a

difficult environment in which to operate complex machinery and the

environmental consequences of such large-scale mining are not well understood,

the question as to when the profitable harvest of manganese nodules will begin

remains unanswered.

Chapter 5: Geologic Resources: 5-3 Mineral Reserves vs. Mineral Resources

Book Title: Earth



5-3 Mineral Reserves vs. Mineral Resources

Mineral reserves (A term to describe the known supply of ore in the ground; can be used

on a local, national, or global scale.) are the known amount of ore in the ground that can

be mined profitably. Reserves represent a working inventory of an economically extractable

mineral commodity in a particular mine or on a national or global scale. Mineral

resources, described at the beginning of this chapter, are all occurrences of a mineral



commodity, including those only surmised to exist, that have present or anticipated future

value.

Mining depletes mineral reserves by decreasing the amount of ore remaining in the ground,

but reserves may also increase in two ways. First, geologists may discover new mineral

deposits, thereby adding to the known amount of ore. Second, subeconomic mineral deposits

—those in which the metal is not sufficiently concentrated to be mined at a profit—can

become profitable if the price of that metal increases or if improvements in mining or

refining technology reduce extraction costs.

For example, in 1970, world copper resources, including all identified and undiscovered

sources, were estimated at billion metric tons. World reserves of copper—that portion of

copper resources that could be profitably extracted—were estimated at only million

metric tons. Between 1970 and 2010, however, improved mining techniques and rising

copper prices resulted in the production of about million metric tons of copper, nearly

percent more than the 1970 global reserve estimate. Moreover, these factors and the

discovery of new copper deposits have caused the 2010 global estimated reserve to be

million metric tons, more than double the 1970 estimate despite the past years of mining

and production.

Chapter 5: Geologic Resources: 5-3a The Geopolitics of Metal Resources

Book Title: Earth



5-3a The Geopolitics of Metal Resources

Earth’s mineral resources are unevenly distributed, and no single nation is self-sufficient in

all minerals. Moreover, as technology evolves, the value of mineral and energy resources

can change drastically. For example, salt was once used as currency. It drove the

establishment of trade routes, caused armed conflicts between the Vatican and its subjects

in Perugia (part of modern Italy) in 1540, and was at the source of a -year-long armed

struggle along the Texas-Mexican border in the 1860s and s. The discovery of large salt

deposits and development of refrigeration since then has significantly reduced the strategic

value of salt. Similarly, the discovery and refinement of large petroleum reserves has

eliminated the strategic value of whale oil.

Historically, five nations—the United States, Russia, South Africa, Canada, and Australia—

have supplied most of the mineral resources used by modern societies. However, today,

China is the world’s leading producer of many mineral resources, including aluminum,

gold, iron, lead, phosphate rock (used mainly for fertilizer), tin, tungsten and zinc. China is

also the world’s leading exporter of several mineral resources, including antimony, barite

(used in drilling muds), graphite, tungsten, and rare earth metals critical to defense and

other high-tech industries.

Although it is the lead producer and exporter of many mineral resources, China is also the

world’s largest consumer of many mineral commodities and has embarked on a strategic

policy of purchasing the rights to many large mineral deposits around the world. Today,

China’s domestic supply and demand for various mineral commodities is high enough to



directly affect the world mineral markets.

Many other nations have few mineral resources. For example, Japan has almost no metal

or fuel reserves; despite its modern economy and high productivity, it relies entirely on

imports for metals and fuel.

Currently, the United States depends on dozens of other countries for the majority of its

mineral consumption. In 2010, the United States was percent dependent on imports for

as many as different mineral commodities, because we have no geologic supply of our

own. Many of these commodities are important in the high-tech, communications, and

defense industries. Examples include yttrium, essential for microwave communications

equipment; cobalt, a critical metal alloy; and vanadium, essential for the manufacture of

supercomputers. The U.S. dependence on many mineral and metal imports has caused

some politicians to seek the establishment of a strategic reserve of these commodities.

Chapter 5: Geologic Resources: 5-4 Mines and Mining

Book Title: Earth



5-4 Mines and Mining

Miners extract both ore and coal (described in the following section) from underground

mines and surface mines. A large underground mine (A mine consisting of subterranean

passages that commonly follow ore veins or coal seams.) may consist of tens of kilometers

of interconnected passages that commonly follow ore veins or coal seams (Figure 5.9). The

lowest levels may be several kilometers deep. In contrast, a surface mine (A hole excavated

into Earth’s surface for the purpose of recovering mineral or fuel resources.) is a hole

excavated into Earth’s surface. The largest human-created excavation on Earth is the open-

pit copper mine at Bingham Canyon, Utah (Figure 5.10). It is kilometers in diameter and

kilometers deep and can be seen with the unaided eye from space. Since its beginning in

1873, the mine has produced about million tons of copper, along with significant

amounts of gold, silver, and molybdenum. Most modern coal mining is done by large power

shovels that extract coal from huge surface mines (Figure 5.11).

Figure 5.9

Machinery extracts coal from an underground coal mine.



Cultura Creative (RF)/Alamy

Figure 5.10

The Bingham Canyon, Utah, open-pit copper mine is the largest human-created

excavation on Earth. It is over kilometers in diameter and kilometer deep.

AGRICULTURAL STABILIZATION AND CONSERVATION SERVICE/USDA

Figure 5.11

Lignite (brown coal) being mined in Germany as a source of power.



MIK LAV/ SHUTTERSTOCK.COM

In the United States, the Surface Mining Control and Reclamation Act of 1977 requires

mining companies to restore mined land so that it can be used for the same purposes for

which it was used before mining began. In addition, a tax is levied to make it possible to

reclaim land that was mined before the law was enacted. Enforcement and compliance of

environmental laws waxes and wanes with the political climate in Washington. Yet

environmental awareness has increased dramatically over the past generation, and,

overall, mining operations pollute much less today than they did years ago. One of the

big challenges for the future is to clean up old mines that were operated under lax or

nonexistent environmental regulations of the past. In the United States, more than

unrestored coal and metal surface mines cover an area of about square kilometers,

almost as large as the state of Virginia. This figure does not include abandoned sand and

gravel mines and rock quarries.

Although underground mines do not directly disturb the land surface, some abandoned

mines collapse, and occasionally buildings have sunken into the resulting holes (Figure

5.12). Over hectares ( million acres) of land in central Appalachia have settled into

underground coal mine shafts.

Figure 5.12

This house tilted and broke in half as it sank into an abandoned underground coal

mine.

http://shutterstock.com/



CHUCK MEYERS/U.S. DEPT. OF THE INTERIOR

Mining of both metal ores and coal also creates huge piles of waste rock—rock that must be

removed to get at the ore or coal or that is left over after the refining of the ore. If the

waste piles are not treated properly, rain erodes the loose rock and leaches toxic elements

such as arsenic, sulfur, and heavy metals from the piles, choking the streams with sediment

and polluting both stream water and groundwater.

Chapter 5: Geologic Resources: 5-5 Energy Resources: Coal, Petroleum, and Natural Gas

Book Title: Earth



5-5 Energy Resources: Coal, Petroleum, and Natural Gas

Coal, petroleum, and natural gas are called fossil fuels (Energy resources including

petroleum, coal, and natural gas, which formed from the partially decayed remains of

plants and animals; they are nonrenewable and unrecyclable.) because they formed from

the remains of plants and animals. Fossil fuels are not only nonrenewable, but also

unrecyclable. When a lump of coal or a liter of oil (petroleum) is burned, the energy

dissipates and is, for all practical purposes, lost. Thus, our fossil fuel supply inexorably

diminishes.

Chapter 5: Geologic Resources: 5-5a Coal

Book Title: Earth





5-5a Coal

Coal (Figure 5.13) is a sedimentary rock made mostly of organic carbon—enough that the

rock will burn without refining. Coal-fired electric generating plants burn about percent

of the coal consumed in the United States and produce slightly less than percent of the

nation’s electricity. Although it is easily mined and abundant in many parts of the world,

coal emits air pollutants that can be removed only with expensive control devices. Mercury,

in particular, is released into the atmosphere mainly through coal-fired power plants.

Despite these drawbacks, coal is an abundant resource, with widespread availability

projected to last beyond the st century.

Figure 5.13

Anthracite is a hard, compact variety of coal with the highest carbon count and

lowest level of impurities of all coals.

ABUTYRIN/ SHUTTERSTOCK.COM

In North America, large quantities of coal formed during the Carboniferous Period,

between and million years ago, and later in Cretaceous and Paleocene times, when

warm, humid swamps covered broad areas of low-lying land. When plants die in forests

and grasslands, organisms consume some of the plant litter, and chemical reactions with

oxygen and water decompose the remainder. As a result, little organic matter accumulates,

except in the topsoil. In some swamps and bogs, however, plants grow and die so rapidly

that newly fallen vegetation quickly buries older plant remains. The new layers prevent

atmospheric oxygen from penetrating into the deeper layers, and decomposition stops

before it is complete, leaving brown, partially decayed plant matter called peat.




Plant matter is composed mainly of carbon, hydrogen, and oxygen and contains large

amounts of water. During burial, rising pressure expels the water and chemical reactions

release most of the hydrogen and oxygen. As a result, the proportion of carbon increases

until coal forms (Figure 5.14). The grade of coal and the heat that can be recovered by

burning coal can vary considerably depending on the carbon content (Table 5.2).

Figure 5.14

Peat, lignite, and coal form as organic litter accumulates rapidly in a swamp and

does not undergo complete decay. With subsequent burial, the organic litter

compacts, expels water, and transforms to peat. With further burial and the

addition of heat, peat will transform to lignite, then bituminous coal, and finally

anthracite.

Source: Cite Stephen Greb, the Kentucky Geological Survey at The University of Kentucky.

Table 5.2

Classification of Coal by Grade, Heat Value, and Carbon Content

Type Color Water

(%)

Other Volatiles

and

Noncombustible

Compounds (%)

Carbon

(%)

Heat

Value

(BTU/lb)

Peat Brown –

Lignite Dark brown

Bituminous

(soft coal)

Black – – –



Anthracite

(hard coal)

Black

© Cengage Learning

Chapter 5: Geologic Resources: 5-5b Petroleum

Book Title: Earth



5-5b Petroleum

The word petroleum (A complex liquid mixture of hydrocarbons, formed from decayed

plant and animal matter, that can be extracted from sedimentary strata and refined to

produce propane, gasoline, and other fuels. Also called crude oil or simply oil.) comes from

the Latin for “rock oil” or “oil from the earth.” Some natural oil seeps in Asia were used at

least as long ago as Alexander the Great, and oil wells in China were hand dug with bamboo

poles in 347 CE. In North America, the first commercial oil well was drilled in Titusville,

Pennsylvania, in 1859, ushering in a new energy age. Crude oil, as it is called when pumped

from the ground, is made up of thousands of different chemical compounds and ranges

widely in consistency and color. Some petroleums are brown, waxy substances that are

solid at room temperature but liquid at higher temperatures that exist within the Earth’s

crust. Some petroleums are yellowish or nearly clear liquids that resemble refined gasoline.

Most are rather thick and dark colored. Once recovered from a well, crude oil is refined to

produce propane, gasoline, heating oil, and other fuels (Figure 5.15). Petroleum also is used

to manufacture plastics, nylon, and other useful materials.

Figure 5.15

An oil refinery converts crude oil into useful products such as gasoline.




Formation of Petroleum

Petroleum forms from the accumulation of large quantities of organic matter in muddy

sediment deposited in swamps, lakes, and marine waters. Most of the organic matter comes

from algae, plant remains, and bacteria. Over millions of years, younger sediment buries

this organic-rich mud to depths of a few kilometers, where rising temperature and pressure

convert the mud to shale. At the same time, the elevated temperature and pressure cause

the organic matter to convert to a solid organic substance called kerogen (The waxy, solid

organic material in oil shales that yields oil when the shale is heated; the precursor of liquid

petroleum.) . At temperatures ranging from to about , the kerogen breaks

down chemically, liberating small organic molecules. These organic molecules form

petroleum.

The shale or other sedimentary rock from which oil originally forms is called the

petroleum source rock (The shale or other sedimentary rock from which oil or natural

gas originates.) . With time, some of the organic molecules in the source rock are expelled

as liquid petroleum that seeps into the pore spaces in adjacent rock layers. Because

petroleum is less dense than water in the pore spaces, the petroleum rises towards the

surface through the network of pores in the rock. If it is not trapped along the way, the oil

will migrate all the way to the surface, forming a natural oil seep. The La Brea Tar Pits in

downtown Los Angeles is perhaps the most famous example of a natural oil seep. Between

and years ago, over years ago species of organisms became trapped in tar

formed from the La Brea oil seeps, died, and were preserved.

In many circumstances, migrating petroleum will not reach the surface but rather will

become trapped in a conventional petroleum reservoir (A porous, permeable

sedimentary rock that is saturated with trapped oil.) . A conventional reservoir consists of



oil-saturated porous rock that is like an oil-soaked sponge (Figure 5.16). It is not an

underground pool or lake of oil. Many conventional reservoirs form when the rising oil is

trapped by an overlying layer of impermeable rock—that is, rock through which liquids do

not pass quickly because the pore spaces are too small or are otherwise big enough but not

interconnected, as with the isolated holes in Swiss cheese.

Figure 5.16

(A) Organic-rich mud accumulates in swamps, lakes, and some parts of the ocean

where low oxygen conditions prevent it from decaying quickly. (B) Younger

sediment buries the organic-rich mud. Rising temperature and pressure converts

the mud to shale, and the organic matter in it to kerogen. (C) With continued heat,

the kerogen breaks down, liberating petroleum that migrates out of the organic-

rich source rock and into adjacent layers. Once there, the petroleum rises towards

the surface until it is trapped. In this illustration, the oil is trapped where it

encounters an impermeable cap rock in the crest of a dome-like fold in the rock

layers.



© Cengage Learning 2015

To extract petroleum from a conventional reservoir, an oil company drills a well into it.

After the hole has been bored, the expensive drill rig is removed and replaced by a smaller

rig that sets pipe in the borehole and perforates the pipe adjacent to oil-bearing layers so

that the oil can flow from the rock into the pipe. Following, a pump jack (The above-

ground portion of a reciprocating piston pump on an oil well.) is installed to draw the

petroleum up the pipe (Figure 5.17). Fifty years ago, many conventional reservoirs lay near

the surface and oil was easily pumped from shallow wells. But these reserves have been

largely depleted, causing many modern oil companies to seek deeper reservoir targets,

sometimes below the seafloor in water up to kilometers deep.

Figure 5.17

A pump jack extracts oil from a conventional reservoir in Alberta, Canada. This

pump jack is situated in a field of canola, a plant used to make biofuel (see



“Biomass Energy” in Section 5-8).

KARL NAUNDORF/ SHUTTERSTOCK.COM

Primary recovery techniques utilize the pressure in a conventional reservoir to push oil into

the wellbore. As oil is removed, however, this pressure decreases to the point at which the

remaining oil cannot be drawn into the well bore. On average more than half of the oil in a

reservoir is too viscous to be pumped to the surface by conventional techniques and is left

behind when the oil field has “gone dry.” Additional oil can be extracted by secondary and

tertiary recovery techniques (Methods of extracting oil or natural gas by artificially

augmenting the reservoir energy or fluid composition, as by injection of water, pressurized

gas, solvents, or other fluids.) involving the injection of water, detergent, pressurized gas, or

other fluids into the reservoir. Secondary methods are employed first, and when those are

exhausted, tertiary methods are used. In one simple secondary process, water is pumped

into one well, called the “injection well.” The pressurized water floods the reservoir, driving

oil to nearby wells, where both the water and oil are extracted. At the surface, the water is

separated from the oil and reused, while the oil is sent to the refinery. One tertiary process

pumps detergent into the reservoir. The detergent dissolves the remaining oil and carries it

to an adjacent well, where the petroleum is then recovered and the detergent recycled.

Because an oil well location occupies only a few hundred square meters of land, most cause

relatively little environmental damage. However, oil companies are now extracting

petroleum from fragile environments such as the ocean floor and the Arctic tundra. To

obtain oil from the seafloor, engineers build platforms on pilings driven into the ocean floor

and mount drill rigs on these steel islands or use a drilling platform that floats but

maintains its position through powerful stabilizing motors controlled by a precise GPS

system (Figure 5.18).




Figure 5.18

An offshore oil-drilling platform extracts oil from below the seafloor.

PHOTOBANK.KIEV.UA/ SHUTTERSTOCK.COM

Despite great care, accidents occur during the drilling and extraction of oil. In 2010, the

largest accidental marine oil spill in the history of the petroleum industry took place in the

Gulf of Mexico when a blowout occurred on the seafloor below the Deepwater Horizon oil

platform. The seafloor blowout caused an explosion on the drilling platform that killed

workers and injured others. For three months, oil gushed uncontrollably from the

seafloor before the well was finally capped and declared dead. By then, however, an

estimated million barrels of oil had been released into the environment. The oil spread

throughout much of the Gulf of Mexico, poisoning marine life and disrupting marine and

coastal ecosystems.

Chapter 5: Geologic Resources: 5-5c Natural Gas

Book Title: Earth



5-5c Natural Gas

Natural gas (A mixture of naturally occurring light hydrocarbons composed mainly of

methane, , that is used for home heating and cooking and to fuel large electric




generation plants.) is an energy resource that forms in source rock or an oil reservoir when

crude oil is heated above during burial and causes the organic molecules to break

down to methane, , an organic molecule consisting of a single carbon atom bonded to

four hydrogen atoms. Many conventional petroleum reservoirs contain a layer of oil-

saturated rock, with a layer of gas-saturated rock above the heavier liquid petroleum. Other

conventional reservoirs are saturated only by gas.

Natural gas is used without refining for home heating and cooking and for fueling large

electrical generating plants. Because natural gas contains few impurities, it releases little

sulfur or other pollutants when it burns, although, as with all fossil fuels, combustion of

natural gas releases carbon dioxide, a greenhouse gas. This fuel has a higher net energy

yield, produces fewer pollutants, and is less expensive to produce than petroleum. At

current consumption rates, global natural gas supplies are projected to last between and

years.

Chapter 5: Geologic Resources: 5-6 Unconventional Petroleum and Gas Reservoirs

Book Title: Earth



5-6 Unconventional Petroleum and Gas Reservoirs

Today, roughly percent of energy used in the United States comes from petroleum, coal,

and natural gas, which traditionally have been the cheapest fuels. However, the price of

crude petroleum is subject to very large swings. For example, in inflation-adjusted 2011

dollars, crude oil rose from a low of $ in 1998 to a high of $ in 2008 before crashing

to $ per barrel that same year. Less than years later, in 2011, the price again had

climbed to more than $ per barrel. As of this writing (September, 2013), the price of

crude oil remains over $ per barrel.

In the past, many alternative forms of energy have been more expensive to develop than

coal or oil and gas produced from conventional reservoirs. However, the cost of producing

these alternative forms of energy has been decreasing, while the cost of producing

traditional fuels has been increasing. As a result, a major restructuring of the global energy

economy presently is underway. Many fuel sources that were uneconomical even a year

ago are now economic, particularly given the development of new technologies.

Among the biggest of the new changes in the energy economy is the production of oil and

gas from unconventional reservoir (A sedimentary rock that is capable of producing oil

with the application of special techniques, such as hydraulic fracturing.) . For example,

over the past few years in the United States, much of the exploration for oil and natural gas

has shifted towards the direct drilling of organic-rich petroleum source rocks. Previously,

these organic-rich shales were not drilled and produced directly because they are relatively

impermeable, and neither liquid hydrocarbons nor natural gas could migrate from the

rock into the wellbore quickly enough for production to be economic. Today, however,

technologic advances allow drilling rig operators to drill vertically down to near the top of

the source rock layer, then curve the wellbore degrees so that it passes horizontally

within it. After drilling a horizontal borehole for up to kilometers within the source rock



layer, the drill is removed from the borehole and the source rock is hydraulic fracturing

(The process of fracturing an unconventional reservoir—usually an organic-rich shale—by

forcing large volumes of pressurized fluid into it.) , or “fracked,” by forcing large volumes

of water mixed with sand down the borehole. The water pressure fractures the source rock,

while the sand is forced into the newly created fractures, propping them open. The network

of sand-filled fractures creates a permeable system of pores that allows the petroleum in the

source rock to migrate to the wellbore, where it is pumped to the surface.

Today, many organic-rich shale units in the United States, including the Marcellus Shale in

New York and Pennsylvania, the Eagleford and Barnett Shales in Texas, and the Bakken

Shale in Montana and North Dakota are developed by direct horizontal drilling and

hydraulic fracturing. Moreover, according to the U.S. Geological Survey, roughly half of the

industrial-grade sand that is quarried in the United States today is used for hydraulic

fracturing process, providing some indication of the magnitude of this recent shift in

exploration techniques.

Chapter 5: Geologic Resources: 5-6a Coal Bed Methane

Book Title: Earth



5-6a Coal Bed Methane

Although most commercial natural gas is produced from conventional reservoirs or

through direct drilling and hydraulic fracturing of source rocks, about percent of

current U.S. gas production comes from coal seams. There, natural Earth heat and

microbial activity slowly convert buried coal to coal bed methane (Methane that is

chemically bonded to coal. The methane can be recovered by removing the groundwater

from a coal bed, which decreases the pressure and allows the methane to separate from the

coal as a gas.) , methane that is chemically bonded to coal. Coal bed methane reserves in the

United States are estimated to be more than trillion cubic feet (Tcf), roughly a -year

supply at current rates of consumption.

Most coal beds have a high capacity to store water in small voids in the coal itself. As

natural processes convert coal to methane, the gas dissolves in the groundwater within the

coal. There, the gas is kept in solution by the pressure of overlying groundwater. Natural

gas companies drill thousands of wells into the coal beds and pump the groundwater to the

surface, decreasing the pressure on the water remaining in the coal bed. The decreased

pressure allows the methane to separate from the water. It is then piped to the surface,

where it is compressed and sent to market.

Because they store so much water, coal beds are important groundwater reservoirs for

farmers and ranchers, especially in the arid and semiarid western United States, where

extensive coal bed methane development is now occurring. However, coal bed methane

development has two serious impacts on regional agriculture and ecosystems. The

extraction of so much water from the coal beds has depleted essential aquifers and lowered

the water table over large areas. Secondly, coal bed water is commonly salty. After it is

pumped to the surface, the salt water can poison streams and soils, rendering them useless

for agriculture and wildlife. State and federal regulations on water extraction and disposal



methods attempt to minimize these impacts.

Chapter 5: Geologic Resources: 5-6b Tar Sands

Book Title: Earth



5-6b Tar Sands

In some regions, large sand deposits called tar sands (Sand deposits saturated with heavy

oil and an oil-like substance called bitumen.) are permeated with heavy oil and bitumen (A

thick, sticky, oil-like substance that permeates tar sands and can be converted to crude oil.) ,

a sticky, tar-like hydrocarbon. Crude oil can be obtained from both substances, but these

are too thick to be pumped and therefore require other methods of extraction.

The richest tar sands exist in Alberta (Canada), Utah, and Venezuela. In Alberta alone, tar

sands contain an estimated trillion barrels of petroleum, roughly years of U.S.

consumption at the 2010 rate. About percent of this fuel is shallow enough to be surface

mined. Tar sands are dug up and heated with steam to make the heavy oil and bitumen

fluid enough to separate from the sand. The oil and bitumen are then treated chemically

and heated to convert them to crude oil. At present, several companies mine the Alberta tar

sands profitably. Once those reserves are depleted, a portion of the deeper deposits,

comprising the remaining percent of the reserve, can be extracted using subsurface

techniques similar to those discussed for secondary and tertiary recovery.

Despite its great size, much controversy has surrounded the development of the Alberta tar

sands, because the refinement process uses water in very large volumes, which is then

expensive to clean prior to being released back into the environment. This controversy has

spilled over into the United States, where a major debate is ongoing regarding the

construction of the Keystone XL Pipeline that would connect the Alberta Tar Sands, the

currently booming oil fields in eastern Montana and western North Dakota, and refineries

on the Gulf Coast.

Chapter 5: Geologic Resources: 5-6c Oil Shale

Book Title: Earth



5-6c Oil Shale

In many parts of the world, including the United States, large quantities of organic-rich

shale exist that have not been heated enough to break down the kerogen contained in the

rock, to form petroleum. Such rock is called oil shale (A kerogen-bearing shale or fine-

grained limestone that yields liquid or gaseous hydrocarbons when heated.) (Figure 5.19). If

oil shale is mined, mixed with water, and then heated, the kerogen converts to petroleum.

In the United States, shale deposits contain the energy equivalent of up to six trillion barrels

of petroleum, enough to fuel the nation for more than years at the 2010 consumption

rate. However, with currently available technology, more energy is required to mine and

convert the kerogen in oil shale to petroleum than is generated by burning the oil, so it will



be necessary for a combination of world oil price increases and technological advances in

oil shale recovery techniques to make oil shale a viable source of energy in the future.

Figure 5.19

Oil shale is an organic-rich, fine-grained sedimentary rock containing significant

amounts of kerogen. This sample is from the Eocene Green River Formation near

Rock Springs, Wyoming. Penny for scale.


Water consumption also is a serious problem in oil shale development. Approximately two

barrels of water are needed to produce each barrel of oil from shale. Oil shale occurs most

abundantly in the semiarid western United States. In this region, scarce water is also needed

for agriculture, domestic use, and industry.

Chapter 5: Geologic Resources: 5-7 Energy Resources: Nuclear Fuels and Reactors

Book Title: Earth



5-7 Energy Resources: Nuclear Fuels and Reactors

Nuclear fuels (Radioactive isotopes, such as those of uranium, used to generate electricity

in nuclear reactors.) are radioactive isotopes that produce heat through nuclear reactions;

the heat is used, in turn, to generate electricity in nuclear reactors. Uranium is the most

commonly used nuclear fuel. These energy resources, like mineral resources, are

nonrenewable, although uranium is abundant.

Every step in the mining, processing, and use of nuclear fuel produces radioactive wastes.

The mine waste discarded during mining is radioactive. Enrichment of the ore produces

additional radioactive waste. When a uranium nucleus undergoes fission in a reactor, it

splits into two useless radioactive nuclei that must be discarded. After several months in a

reactor, the concentration of useful uranium in the fuel rods drops until the fuel pellets are



no longer viable. In some countries, these pellets are reprocessed to recover useful uranium

fuel, but in the United States this process is not economical, so the pellets are discarded as

radioactive waste.

In the early 1970s, the nuclear industry in the United States was growing rapidly, and

many energy experts predicted that nuclear energy would dominate the generation of the

country’s electric energy. These predictions have not been realized. Four factors have led to

the decline of the nuclear power industry:

1. Construction of new reactors in the United States has become so costly, in part

because of increased regulation, that electricity generated by nuclear power is more

expensive than that generated by coal-fired power plants.

2. After major accidents at Three Mile Island in the United States (1979), Chernobyl in

Ukraine (1986), and Fukushima Daiichi in Japan (2011), many people have become

concerned about safety.

3. Serious concerns remain about the safe disposal of nuclear wastes.

4. The demand for electricity has risen less than expected during the past three decades.

After the 1979 Three Mile Island nuclear accident (Figure 5.20), many plans for the

construction of new nuclear power plants were cancelled or suspended, and for years no

permits were issued for the construction of new reactors by the U.S. Nuclear Regulatory

Commission. Finally, in 2012 the Commission approved permits for four new reactors, two

at an existing nuclear power plant in Georgia and two at an existing plant in South

Carolina. Currently, the Commission is reviewing applications for new reactors at eight

existing nuclear power plants and two new locations.

Figure 5.20

The nuclear power plant at Three Mile Island in central Pennsylvania. The two

cooling towers and smaller dome-covered reactor (partly hidden from view) on the

left were permanently shut down following the 1979 accident. The reactor and

cooling towers on the right continue to operate.



DOBRESUM/ SHUTTERSTOCK.COM

Elsewhere in the world, nuclear power production has risen rapidly, and the International

Atomic Energy Agency in 2010 predicted a global increase of gigawatts, or percent

more capacity, by 2020. The agency additionally predicted that worldwide, by 2020, roughly

percent of electricity would come from nuclear generation. Much of this new growth is

anticipated to be in Asia. Thus, although policymakers in the United States have largely been

reconsidering the role of nuclear power as an energy source, the overall capacity for

nuclear-generated power worldwide is likely to increase.

Chapter 5: Geologic Resources: 5-8 Energy Resources: Renewable Energy

Book Title: Earth



5-8 Energy Resources: Renewable Energy

Solar, wind, geothermal, hydroelectric, and wood and other biomass fuels are renewable—

natural processes replenish them as we use them. Although the amount of energy produced

today by renewable sources is small compared to that provided by fossil and nuclear fuels,

renewable resources have the potential to supply all of our energy needs. As the prices of

conventional fossil fuels have risen along with worldwide energy demand, some renewables

have become economical. Except for biomass fuels, renewable energy sources emit no

carbon dioxide and therefore do not contribute to global warming.

Chapter 5: Geologic Resources: 5-8a Solar Energy

Book Title: Earth






5-8a Solar Energy

Current technologies allow us to use solar energy in three ways: passive solar heating,

active solar heating, and electricity production by solar cells.

A passive solar house is built to absorb and store the Sun’s heat directly. In active solar

heating systems, solar thermal collectors absorb the Sun’s energy and use it to heat water.

Pumps then circulate the hot water through radiators to heat a building, or the inhabitants

use the hot water directly for washing and bathing.

A solar cell (A device that produces electricity directly from sunlight; also sometimes called

a photovoltaic (PV) cell.) , or photovoltaic (PV) cell, produces electricity directly from

sunlight. A modern solar cell is a semiconductor, a device that can conduct electrical

current under some conditions but not others. Sunlight energizes electrons in the

semiconductor, producing an electric current.

Figure 5.21 shows an installation of solar panels. Although solar power still accounts for

less than percent of world energy demand, solar energy is our most abundant resource,

and PV cell production is the fastest-growing segment of the energy industry. Photovoltaic

arrays are now competitive with electricity costs during peak demand times in many desert

areas, especially those installed for single-family units. PVs are also cost-effective for

electricity needs far from existing power lines.

Figure 5.21

A Solar Farm in Germany.



ANYAIVANOVA/ SHUTTERSTOCK.COM

Chapter 5: Geologic Resources: 5-8b W ind Energy

Book Title: Earth



5-8b Wind Energy

In the United States, wind energy grew percent—a ten-fold increase—in the decade

between 2001 and 2011, and now accounts for about percent of the country’s total

electricity production. The total U.S. capacity for wind-generated electricity is the second

largest in the world at about gigawatts, enough to supply electricity to about million

average U.S. households. China’s capacity at gigawatts is highest in the world, and the

average household electricity use there is much lower, so many more average households

are served by China’s wind-generated electricity than in the United States.

Wind energy production is growing rapidly because construction of wind generators is

cheaper than building new fossil fuel–fired power plants. Wind energy is also clean and

virtually limitless. Gigantic wind farms now generate electricity in Texas, California, and

other states, and wind farms are now commonplace in many parts of Europe and

elsewhere (Figure 5.22). In the United States, a huge, untapped potential for wind

generation exists in several midwestern and western states, where winds blow strongly and

almost continuously. The main drawbacks to wind energy include its inconsistency, the

conspicuous nature of the wind turbines (which some people view as unsightly), the death

of birds and bats that collide with the turbine blades, and the noise generated by the blades.

Figure 5.22

Wind turbines generate electricity in Hesse, Germany.

ANKIRO/SHUTTERSTOCK.COM




Chapter 5: Geologic Resources: 5-8c Geothermal Energy

Book Title: Earth



5-8c Geothermal Energy

Energy extracted from Earth’s internal heat is called geothermal energy (Figure 5.23).

Geothermal plants typically collect underground steam from geysers, volcanoes, and hot

springs and use the steam to spin turbines, which generate electricity. Naturally hot

groundwater also can be pumped to the surface to generate electricity, or it can be used

directly to heat homes and other buildings. Alternatively, cool surface water can be pumped

deep into the ground, to be heated by subterranean rock, and then circulated to the surface

for use. The United States is the largest producer of geothermal electricity in the world, with

a production capacity of just over gigawatts.

Figure 5.23

The Wairakei geothermal power plant in New Zealand.

N.MINTON/ SHUTTERSTOCK.COM

In the United States, most geothermal plants are located in the western states, because the

region is more tectonically active and the geothermal gradient is higher. We will learn

about tectonics in Chapter 6. The oldest, and also presently the largest, steam-driven

geothermal plant in the United States is located at The Geysers, about miles north of San

Francisco. That plant alone is capable of generating gigawatts of electricity, enough for

about average U.S. households.




Relative to other renewables such as wind and solar, geothermal energy can be used

hours a day, days a week, so it has a larger capacity factor (A measure of the actual to

total potential output of an energy source over a period of time) —a measure of the amount

of the actual output of energy to the total possible output over some period of time. Because

the wind does not blow all the time and the Sun does not shine all the time, these energy

sources have a lower capacity factor.

Chapter 5: Geologic Resources: 5-8d Hydroelectric Energy

Book Title: Earth



5-8d Hydroelectric Energy

If a river is dammed, the energy of water dropping downward through the dam can be

harnessed to turn turbines that produce electricity. Hydroelectric generators supply

roughly percent of the world’s electricity. In the United States, about percent of our

electricity comes from hydroelectric power.

Although hydroelectricity is renewable, it is entirely dependent on adequate runoff, and

recent climate change has caused many of the large reservoirs in the western United States

to be drawn down significantly. Inadequate runoff lowers the capacity factor of

hydroelectric generating facilities. In addition, the construction of dams and formation of

reservoirs destroys wildlife habitats, agricultural land, towns, and migratory fish

populations. For example, the dams on the Columbia River and its tributaries are largely

responsible for the demise of salmon populations in the Pacific Northwest. Undammed wild

rivers and their canyons are prized for their aesthetic and recreational value. Large dams

also are expensive to build, and few suitable sites remain.

For these reasons, the United States is unlikely to increase its production of hydroelectric

energy. In fact, many historic dams—including some with hydroelectric power–generating

capabilities—are being removed.

Chapter 5: Geologic Resources: 5-8e Biomass Energy

Book Title: Earth



5-8e Biomass Energy

Biomass (plant based) fuels provide many sources of energy. The burning of wood as a

source of heat is familiar to all of us. Today, wood and agricultural products also are

burned for the generation of steam and electricity at the industrial level. Additionally,

biomass from oil-rich plants such as canola is converted to liquid form for use as a

transportation fuel. Much research currently is being directed towards the production of

liquid fuels and other chemicals from biomass.

Biomass energy can be produced domestically in most countries, thereby creating local jobs

and reducing foreign oil imports. However, production of biofuels is not always a net



energy gain; in some cases, more energy is used in the production and processing of these

fuels than can be extracted from them. In addition, burning of biomass produces carbon

dioxide, a greenhouse gas, and releases particulates and other pollutants into the

atmosphere.

Chapter 5: Geologic Resources: 5-8f The Future of Renewable Energy Resources

Book Title: Earth



5-8f The Future of Renewable Energy Resources

Aside from biofuels, none of the renewable resources discussed here can be used directly to

power cars and trucks. Several methods are available, however, to convert these energy

sources for use in transportation.

Perhaps the easiest way to use electricity to transport people and goods is the old-fashioned

electric train. Electric streetcars, commuter trains, and subways have been used for

decades. If we build more electric mass transit systems, and if people use them, we could

shift away from our dependence on the internal-combustion engine and on petroleum.

Eventually, the required electricity consumption could be supplied by renewable energy

sources.

Another solution is the electric car. Battery-only and gasoline-electric hybrid cars have seen

a recent increase in popularity and availability. If that trend continues, perhaps we can

further reduce the cost of and dependence on petroleum.

Energy planners also envision a hydrogen economy (An energy economy in which

hydrogen is used as a fuel.) , using a process in which elemental hydrogen is used as fuel. A

necessary part of this process is an electrochemical device called a fuel cell (An

electrochemical energy-conversion device that produces electricity from an external supply

of fuel, such as hydrogen.) , which uses the chemical energy of hydrogen to produce

electricity cleanly and efficiently, with water and heat as by-products. One type of fuel cell

separates hydrogen’s negatively charged electron from the hydrogen nucleus, which then

consists of a single positively charged proton. The electrons, in turn, combine with oxygen,

which then reacts with the hydrogen proton to form water and heat energy. In other types

of fuel cells, the electrons travel through an electrical circuit to reach the other side of the

cell, thereby producing an electrical current. Fuel cells can provide energy for systems as

large as a power station and as small as a laptop computer. They can also power cars,

trucks, trains, and other vehicles. Because they emit only water vapor, fuel cells release no

pollutants that create smog and cause health problems. However, fuel cells require a

reservoir of hydrogen, an extremely flammable gas, and there currently exists little

infrastructure for the refilling of fuel cells with hydrogen.

Chapter 5: Geologic Resources: 5-9 Conservation as an Alternative Energy Resource

Book Title: Earth





5-9 Conservation as an Alternative Energy Resource

The single quickest and most effective way to decrease energy consumption and to prolong

the availability of fossil fuels is to conserve energy (see Figure 5.24). Policies to improve

energy efficiency are more cost-effective than building new power plants. Such policies help

to reduce air pollution and dependence on oil imports while saving money for consumers

and industry.

Figure 5.24

The end-use efficiencies of common energy-consuming systems. Home heating

represents the only energy-consumption system that is even remotely efficient—

and even there, percent is wasted. Energy to produce incandescent lighting is

percent wasted; automobile transportation energy is percent wasted.

© Cengage Learning

Energy conservation has helped to produced dramatic results in the United States, where

expenditures for energy as a percentage of gross domestic product (GDP) fell from about

percent of GDP in 1980 to about percent of GDP in 2000. Higher global energy prices

since 2000 have caused expenditures for energy to rise again, to over percent of GDP,

despite the fact that the amount of energy used per person in the United States has fallen by

about percent over the same time period. Clearly, conservation is a critical component of



keeping the total expenditure for energy in the country from continuing to rise. Some

energy experts have suggested that if people in industrialized nations use more efficient

equipment and develop more efficient habits, these nations could conserve as much as half

of the energy they consume.

Energy use in the United States falls under three categories: buildings, industry, and

transportation. Two types of conservation strategies can be applied in each of those

categories. Technical solutions involve switching to more efficient implements. Social

solutions involve decisions to use existing energy systems more efficiently.

Chapter 5: Geologic Resources: 5-9a Technical Solutions

Book Title: Earth



5-9a Technical Solutions

Buildings

In 2010, residential and commercial buildings consumed about percent of all the energy

produced in the United States. Most of that energy was used for heating, air-conditioning,

and lighting.

Significant energy savings are possible in all aspects of energy consumption in buildings. As

one example, lighting accounts for about percent of the average U.S. home’s electricity

bill. Because incandescent lighting is about percent inefficient in energy consumption,

savings in that area alone are potentially great. A fluorescent bulb consumes one-fourth as

much energy as a comparable incandescent bulb and can last times longer. In addition,

new solid-state technology promises further advances in energy-efficient lighting. For

example, light-emitting diodes (LED) are lights that are illuminated by the movement of

electrons through a semiconductor (Figure 5.25). There is no filament as with incandescent

lights, and LEDs release almost no heat, so they are much more efficient, last much longer,

and use far less energy. Today, LEDs are used to in clock radios, jumbo TVs, and many

other applications. According to the U.S. Department of Energy, widespread switching to

LED lighting technologies over the next years could save the equivalent annual electrical

output of years by large electrical power plants.

Figure 5.25

A bank of light-emitting diodes (LEDs).



IGOR STEPOVIK/SHUTTERSTOCK.COM

Industry

Industry consumes about percent of the energy used in the United States. In general,

conservation practices are cost-effective, and many companies are taking advantage of the

fact that saving energy is profitable, although industry still wastes great amounts of energy.

For example, about two-thirds of the electricity consumed by industry drives electric

motors for machinery and tools. Most motors are inefficient because they run only at full

speed and are slowed by brakes to operate at the proper speeds to perform their tasks. This

approach is like driving your car with the gas pedal pressed to the floor and controlling

your speed with the brakes. Replacing older electric motors with variable-speed motors

would save vast amounts of electricity, but such replacement has been slow.

Transportation

About percent of all energy, more than percent of the oil usage in the United States,

and one-third of the nation’s carbon emissions are consumed transporting people and

goods.

The efficiency of standard gasoline-powered auto and truck engines is about percent

(Figure 5.24). Thus, we can save much energy by using more-efficient cars and trucks. Over

the past few decades, automobile manufacturers have offered vehicles with increasingly

efficient internal-combustion engines. Other avenues that auto companies are exploring



include electricity and hydrogen power.

A hybrid car uses a small, fuel-efficient gasoline engine combined with an electric motor

that assists the engine when accelerating. Hybrids consume less gas and produce less

pollution per mile than conventional gasoline engines. Current models of hybrid cars

achieve fuel efficiencies ranging from (traffic/highway) to miles per gallon,

depending on make and model, and they produce as much as percent fewer harmful

emissions than a comparable gasoline engine. Using hybrids and other energy-efficient

vehicles, American motorists could achieve a percent or greater increase in fuel

economy, the equivalent of about one-third of current oil imports.

Chapter 5: Geologic Resources: 5-9b Social Solutions

Book Title: Earth



5-9b Social Solutions

Social solutions involve altering human behavior to conserve energy. Energy-conserving

actions can be used in buildings, in industry, and in transportation. Some result in

inconvenience to individuals. For example, if you choose to carpool rather than drive your

own car, you save fuel but inconvenience yourself by coordinating your schedule with your

carpool companions. High-mileage cars are on the market, but they will make an impact

only if people make the social decision to use them. People argue that this social decision

comes at a cost because light vehicles make the driver and passengers more vulnerable in

case of an accident; but studies have shown that lighter, more agile vehicles, with better

turning capacity and more effective braking, are actually safer than heavier SUVs.

At home and in the workplace, wearing a sweater and lowering the thermostat in winter

and using less air-conditioning in summer might reduce the comfort margin but can save

considerable energy. Many other social solutions, however, are cost-free in terms of

inconvenience. When practiced by everyone, simply turning off the lights, the television set,

and other appliances when you leave a room will conserve large amounts of energy.

Chapter 5: Geologic Resources: 5-10 Energy for the st Century

Book Title: Earth



5-10 Energy for the st Century

The United States consumes roughly percent of the world’s oil yet owns only percent of

the known conventional oil reserves. In 2011, fossil fuels supplied percent of all energy

used in the United States; oil alone accounted for percent, natural gas for percent,

and coal for percent (Figure 5.26). Thus, oil is our major source of energy. In addition,

oil is the only portable energy resource currently in popular use, and thus is the main

energy resource for transportation in the United States. At current rates of consumption

and production, many estimates indicate that we have up to years of domestic coal

reserves, and at least several decades of natural gas reserves, although the increased



production of shale gas from hydraulic fracturing is extending that supply. Oil, however,

may be another story.

Figure 5.26

In the year 2011, fossil fuels supplied percent of all energy used in the United

States; oil alone accounted for percent, natural gas for percent, and coal for

percent.

Energy Information Administration/Annual Energy Review 2012

http://www.eia.gov/totalenergy/data/annual/perspectives.cfm

In 1956, M. King Hubbert, a geologist, was working at the Shell research lab in Houston,

Texas. Hubbert compared U.S. domestic oil reserves with current and predicted rates of oil

consumption. He then forecast that U.S. oil production would peak in the early 1970s and

would thereafter decline continuously. He predicted that Americans would have to make up

an ever-increasing difference between domestic oil supply and consumption by relying on

larger and larger imports, or they would have to turn to other energy resources. Other

experts and economists ridiculed his prediction, but in 1970 the U.S. domestic oil production

reached its maximum. It declined steadily until 2005, when nonconventional sources of oil,

deepwater discoveries, and the addition of domestically produced biofuels (along with

greater conservation) helped to reverse the downward trend (Figure 5.27). Since 2010, the

United States imports less petroleum than it produces domestically.

Figure 5.27

U.S. oil imports, production, and consumption since 1949. Until very recently, U.S.

reliance on oil imports had been rising, as predicted by M. K. Hubbert. However,

that trend is now heading downward, while U.S. domestic production of petroleum

is increasing. In 2010, the United States produced more than it imported for the first

time since 1997. These trend reversals are due to new U.S. production from

http://www.eia.gov/totalenergy/data/annual/perspectives.cfm



unconventional reservoirs, particularly through hydraulic fracturing.

Energy Information Administration/Annual Energy Review 2012 © Cengage Learning 2015

In 2008, oil prices rose to nearly $ a barrel, a price that many hoped would spur

producers to respond to demand by increasing production. However, some large oil

producers—such as Mexico, Russia, and Saudi Arabia—actually cut back their oil

production, citing cost and expense. At the same time, oil production by OPEC

(Organization of the Petroleum Exporting Countries) was lower than projected because of

turmoil in Iran and Iraq, further contributing to the increase in oil prices. The global

economic downturn in late 2008 and 2009 caused both the demand and the global price to

decrease to about $ per barrel. That decrease was short-lived, however, and by early 2011

world oil prices had climbed back to over $ per barrel, due largely to increased demand

from rapidly industrializing countries such as China and India. Because oil remains the

biggest single source of U.S. energy and the country continues to import nearly half its

supply, it is a virtual certainty that the U.S. energy future will continue to be intimately

linked with the global one.

So what will happen when global oil production drops below demand? First of all,

petroleum will not just “run out” one day, with all the wells suddenly going dry. The world

will run out of “cheap oil” before it runs out of oil. As supply dwindles and demand

increases, the price of fuel will rise and production of petroleum from unconventional oil

sources, including the direct drilling of shale source rocks and the development of oil shales

and tar sands, will likely increase. The production of biofuels also is likely to increase. Some

economists and geologists have suggested that the fluctuations in gasoline prices seen in

recent years are the first wave of disruptions resulting from declining global oil reserves

and that much greater disturbances are imminent.

People will not be able to afford as much fuel as they would like, so social and technical

conservation strategies—previously rejected—will be implemented. As a result, demand will

decrease. But if this decrease is not sufficient, petroleum prices will continue to rise. Many

economists predict that the price increase could be dramatic. This is an example of an

economic threshold effect. As long as potential supply is greater than demand, the price of

oil reflects mainly the cost of drilling, shipping, and refining. But the moment we cross the

threshold where demand is greater than supply, then an auction occurs where the rich can

outbid the poor.



Is it possible to alter global energy production from a fossil fuel economy to an economy of

renewable energy resources? In 2001, the UN’s Intergovernmental Panel on Climate

Change (IPCC) concluded that significant reduction of fossil fuel use is possible with

renewable “technologies that exist in operation or pilot-plant stage today . . . without any

drastic technological breakthroughs.” In other words, they suggested that if we

vigorously develop all the renewable energy resources listed in Section 5-7, the global

economic system could absorb a drastic decline in petroleum production without massive

disruptions. A year later, prominent energy experts published a rebuttal in Science,

proposing the exact opposite conclusion. Using almost the same phrases, with the simple

addition of the word not, they argued that “energy resources that can produce to

percent of present world power consumption without fossil fuels and greenhouse emissions

do not exist operationally or as pilot plants.” Their basic counterargument is that global

energy consumption is huge and renewable sources have low power densities. Thus, we do

not have the available land, nor could we quickly build, the required infrastructure to

replace fossil fuels. Most recently, in 2011, the IPCC again argued that close to percent of

world energy supplies could be met by the continued growth of renewable energy, provided

they are backed by policies that enable their development. This debate continues, as does

continued development and research into renewable resources.

When experts disagree, it is difficult for laypersons to evaluate the merits of the

contradictory arguments. But whoever is right, it is clear that if global energy demand

significantly exceeds supply, the world will fall into unprecedented economic chaos.

Commerce will slip into unimaginable depression. Food supplies will diminish, and food

distribution will become expensive. Poor people, who are already on the edge of

malnourishment, will starve. We can only hope that human ingenuity will combine with

economic and political commitment to develop alternative energy resources before these

catastrophes become reality.

Chapter 5: Geologic Resources Chapter Review

Book Title: Earth



Chapter Review

Key Terms

banded iron formations (Iron-rich sedimentary rocks composed of alternating iron-

rich and silica-rich layers; source of most of the world’s supply of iron.)

bauxite (A gray, yellow, or reddish-brown rock, composed of a mixture of aluminum

oxides and hydroxides, that formed as a residual deposit; the principle source of

aluminum.)

biomineralize (The process by which living organisms produce minerals.)

bitumen (A thick, sticky, oil-like substance that permeates tar sands and can be

converted to crude oil.)



black smokers (A jet of black water spouting from a fracture or vent in the seafloor,

commonly near a mid-oceanic ridge. The black color is caused by precipitation of fine-

grained metal sulfide minerals as the hydrothermal solutions cool on contact with

seawater.)

capacity factor (A measure of the actual to total potential output of an energy

source over a period of time)

coal bed methane (Methane that is chemically bonded to coal. The methane can be

recovered by removing the groundwater from a coal bed, which decreases the

pressure and allows the methane to separate from the coal as a gas.)

conventional petroleum reservoir (A porous, permeable sedimentary rock that is

saturated with trapped oil.)

crystal settling (A process in which the crystals that solidify first from a cooling

magma settle to the bottom of the magma chamber because the minerals are more

dense than magma; the ultimate result is a layered body of igneous rock, each layer

containing different minerals.)

disseminated ore deposit (A large, low-grade hydrothermal deposit in which metal-

bearing minerals are widely scattered throughout a rock body; not as concentrated as

a hydrothermal vein.)

energy resources (Geologic resources—including petroleum, coal, natural gas, and

nuclear fuels—used for heat, light, work, and communication)

fossil fuels (Energy resources including petroleum, coal, and natural gas, which

formed from the partially decayed remains of plants and animals; they are

nonrenewable and unrecyclable.)

fuel cell (An electrochemical energy-conversion device that produces electricity from

an external supply of fuel, such as hydrogen.)

hydraulic fracturing (The process of fracturing an unconventional reservoir—

usually an organic-rich shale—by forcing large volumes of pressurized fluid into it.)

hydrogen economy (An energy economy in which hydrogen is used as a fuel.)

hydrothermal processes (Geologic processes in which hot water or steam dissolves

metals and minerals from rocks or magma; the solutions then seep through cracks

before cooling, to create ore deposits.)

hydrothermal vein deposit (A rich, sheetlike mineral deposit that forms when

economically-valuable minerals precipitate from hot water solutions along a fault or

other fracture.)

kerogen (The waxy, solid organic material in oil shales that yields oil when the shale



is heated; the precursor of liquid petroleum.)

magmatic processes (Geologic processes that form ore deposits as liquid magma

solidifies into igneous rock.)

manganese nodules (A potato-shaped rock found on the ocean floor and rich in

manganese and other metals precipitated from seawater through biomineralization)

mineral reserves (A term to describe the known supply of ore in the ground; can be

used on a local, national, or global scale.)

mineral resources (Economically valuable geological materials including both metal

ore and nonmetallic minerals.)

natural gas (A mixture of naturally occurring light hydrocarbons composed mainly

of methane, , that is used for home heating and cooking and to fuel large electric

generation plants.)

nonmetallic mineral resources (Economically useful rocks or minerals that are not

metals; examples include salt, building stone, sand, and gravel)

nuclear fuels (Radioactive isotopes, such as those of uranium, used to generate

electricity in nuclear reactors.)

oil shale (A kerogen-bearing shale or fine-grained limestone that yields liquid or

gaseous hydrocarbons when heated.)

petroleum (A complex liquid mixture of hydrocarbons, formed from decayed plant

and animal matter, that can be extracted from sedimentary strata and refined to

produce propane, gasoline, and other fuels. Also called crude oil or simply oil.)

petroleum source rock (The shale or other sedimentary rock from which oil or

natural gas originates.)

placer deposit (A surface mineral deposit formed along stream beds, beneath

waterfalls, or on beaches when water currents slow down and deposit high-density

minerals.)

pump jack (The above-ground portion of a reciprocating piston pump on an oil well.)

residual ore deposits (A mineral deposit formed from relatively insoluble ions left in

the soil near Earth’s surface after most of the soluble ions were dissolved and

removed by abundant water.)

scavenging (The process by which hydrothermal fluids sweep through large volumes

of country rock and dissolve low concentrations of metals, concentrating them

elsewhere as an ore deposit.)

secondary and tertiary recovery techniques (Methods of extracting oil or natural



gas by artificially augmenting the reservoir energy or fluid composition, as by

injection of water, pressurized gas, solvents, or other fluids.)

solar cell (A device that produces electricity directly from sunlight; also sometimes

called a photovoltaic (PV) cell.)

submarine hydrothermal ore deposits (Ore deposits that form when hot seawater

dissolves metals from seafloor rocks and then, as it rises through the upper layers of

oceanic crust, cools and precipitates the metals.)

surface mine (A hole excavated into Earth’s surface for the purpose of recovering

mineral or fuel resources.)

tar sands (Sand deposits saturated with heavy oil and an oil-like substance called

bitumen.)

unconventional reservoir (A sedimentary rock that is capable of producing oil with

the application of special techniques, such as hydraulic fracturing.)

underground mine (A mine consisting of subterranean passages that commonly

follow ore veins or coal seams.)

Chapter 5: Geologic Resources Chapter Review

Book Title: Earth



Chapter Review

Chapter Review

5-1

Mineral Resources

Useful rocks and minerals are called mineral resources; they include both

nonmetallic mineral resources and metals. All mineral resources are

nonrenewable. Ore is rock sufficiently enriched in one or more minerals to be

mined profitably; geologists usually use the term to refer to metallic mineral

deposits.

5-2

Ore and Ore Deposits

Four types of geologic processes concentrate elements to form ore.



1. Magmatic processes form ore as magma solidifies.

2. Hydrothermal processes transport and precipitate metals from hot

water.

3. Sedimentary processes form placer deposits, evaporite deposits, and

banded iron formations.

4. Weathering removes easily dissolved elements from rocks and

minerals, leaving behind residual ore deposits such as bauxite.

Figure 5.3

Hot water scavenges metals from crystallizing igneous rock and

the country rock that surrounds it. The hydrothermal water then

deposits metallic minerals in ore-rich veins that fill fractures in

bedrock. It also deposits low-grade disseminated metal ore in

large volumes of rock surrounding the veins.

© Cengage Learning

5-3

Mineral Reserves vs. Mineral Resources

Mineral reserves are the known amount of ore in the ground.

5-4

Mines and Mining

Metal ores and coal are extracted from underground mines and surface

mines.



5-5

Energy Resources: Coal, Petroleum, and Natural Gas

One important energy resource is fossil fuels: coal, oil, and natural gas. Fossil

fuels are nonrenewable and unrecyclable. Plant matter decays to form peat.

Peat converts to coal when it is buried and subjected to elevated temperature

and pressure. Petroleum forms from the remains of organisms that settle to

the ocean floor or lake bed and are incorporated into source rock. The

organic matter converts to liquid oil when it is buried and heated. The

petroleum then migrates to a reservoir, where an oil trap retains it. Natural

gas forms in source rock or in an oil reservoir subjected to high temperature,

and consequently many oil fields contain a mixture of oil with natural gas

floating above the heavier liquid petroleum.

Figure 5.10

The Bingham Canyon, Utah, open-pit copper mine is the largest

human-created excavation on Earth. It is over kilometers in diameter

and kilometer deep.

AGRICULTURAL STABILIZATION AND CONSERVATION SERVICE/USDA

5-6

Unconventional Petroleum and Gas Reservoirs

Secondary and tertiary recovery can extract additional supplies of petroleum

from old wells, tar sands, and oil shale.



5-7

Energy Resources: Nuclear Fuels and Reactors

Nuclear power is expensive, and questions about the safety and disposal of

nuclear wastes have diminished its future in the United States. Nuclear fuels,

like mineral resources, are nonrenewable, although uranium is abundant.

Inexpensive uranium ore will be available for a century or more.

5-8

Energy Resources: Renewable Energy

Solar, wind, geothermal, hydroelectric, and biomass fuels are renewable

sources of energy.

5-9

Conservation as an Alternative Energy Resource

The single quickest and most effective way to decrease energy consumption

and to prolong the availability of fossil fuels is to conserve energy.

5-10

Energy for the 21st Century

Alternative energy resources currently supply a small fraction of our energy

needs but have the potential to provide abundant renewable energy.

Chapter 5: Geologic Resources Review Questions

Book Title: Earth



Chapter Review

Review Questions

1. Describe the two major categories of geologic resources.

2. Describe the differences between nonrenewable and renewable resources. List



one example of each.

3. Discuss the formation of hydrothermal ore deposits.

4. Describe the unique advantages of hydrogen fuel.

5. What is ore? What are mineral reserves? Describe three factors that can

change estimates of mineral reserves.

Chapter 5: Geologic Resources Review Questions

Book Title: Earth



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Geologic Resources - Poudre School District 5- Geologic...9/3/2014 MindTap - Cengage Learning 4/55 We use two types of geologic resources: mineral resources (Economically valuable