Chapter 21: Resources of Minerals and Energyapsacwestridge.edu.pk/assets/admin/upload/notes/... · Mineral Resources (1) Mineral deposits are any volume of rock containing an enrichment

Chapter : Minerals and Energy Resources

Introduction: Natural Resources And Human History (1)

Over one hundred sixty thousand years ago, our ancestors probably began to use flint, chert, and obsidian to make tools.

Metals were first used more than 20,000 years ago.

Copper and gold were the earliest metals used.

By 6000 years ago, our ancestors extracted copper by smelting.

Before another thousand years had passed, they had discovered how to smelt lead, tin, zinc, silver, and other metals.

Introduction: Natural Resources And Human History (2)

The technique of mixing metals to make alloys came

next.

– Bronze was composed of copper and tin.

– Pewter was composed of tin, lead, and copper.

The smelting of iron came much later—about 3300

years ago.

The first people to use oil instead of wood for fuel

were the Babylonians, about 4500 years ago.

The first people to mine and use coal were the

Chinese, about 3100 years ago.

Mineral Resources (1)

Mineral deposits are any volume of rock containing an enrichment of one or more minerals.

Mineral resources have three distinctive characteristics:

Occurrences of usable minerals are limited in abundance and localized at places within the Earth’s crust.

The quantity of a given mineral available in any one country is rarely known with accuracy.

Deposits of minerals are depleted by mining and eventually exhausted.

Figure 21.1

Figure 21.2


Ore is an aggregate of minerals from which one or

more minerals can be extracted profitably.

“Ore” is an economic term, whereas “mineral

deposit” is a geologic term.

The economic challenges of ore are to find it, mine

it, and refine it as cheaply as possible.

The lowest-grade ores ever mined—about 0.5

percent copper—were worked only at a time of high

metal prices.


In 2002, lowest grade of of mineable copper

ore is closer to 1 percent.

Over production of copper around the world,

combined with economic recession, has resulted

in the closing of many mines, particularly those

exploiting the lowest grades of ores.


Sphalerite, galena, and chalcopyrite are ore minerals

from which zinc, lead, and copper respectively can

be extracted.

Ore minerals rarely occur alone.

They are mixed with other nonvaluable minerals,

collectively termed gangue.

– Gangue may include quartz, feldspar, mica, calcite, or

dolomite.

Origin Of Mineral Deposits (1)

All ores are mineral deposits because each of them

is a local enrichment of one or more minerals or

mineraloids.

Not all minerals deposits are ores.

In order for a deposit to form, processes must bring

about a localized enrichment of one or more

minerals.


Minerals become concentrated in five ways:

1. Concentration by hot, aqueous solutions flowing

through fractures and pore spaces in crustal rock to form

hydrothermal mineral deposits.

2. Concentration by magmatic processes within a body of

igneous rock to form magmatic mineral deposits.


3. Concentration by precipitation from lake water or sea

water to form sedimentary mineral deposits.

4. Concentration by flowing surface water in streams or

along the shore, to form placers.

5. Concentration by weathering processes to form

residual mineral deposits.

Hydrothermal Mineral Deposits (1)

Some solutions originate when water dissolved in

magma is released as the magma rises and cools.

Other solutions are formed from rainwater or

seawater that circulates deep in the crust.

Mineral deposits formed from midocean ridge

volcanism are called volcanogenic massive sulfide

deposits.

Figure 21.3


The pyroxene-rich rocks of the oceanic crust yield solutions charged with copper and zinc.

As a result, volcanogenic massive sulfide deposits are rich in copper and zinc.

In black smokers, the rising hydrothermal fluid appears black due to fine particles of iron sulfide and other minerals precipitated from solution as the plume is cooled by contact with cold seawater.

The chimney-like structure is composed of pyrite, chalcopyrite, and other ore minerals deposited by hydrothermal solution.


When a hydrothermal solution moves slowly

upward, as with groundwater percolating through an

aquifer, the solution cools very slowly.

If dissolved minerals were precipitated from such a

slow-moving solution, they would be spread over a

large volume of rock and would not be sufficiently

concentrated to form an ore.


When a solution flows rapidly, as in an open fracture, or through a mass of shattered rocks, or through a layer of porous tephra where flow is less restricted, cooling can be sudden and can occur over short distances.

Rapid precipitation and a concentrated mineral deposit are the result.

Veins formed when hydrothermal solutions deposit minerals in open fractures.

Many such veins are found in regions of volcanic activity.

Figure 21.5


The famous gold deposits at Cripple Creek, Colorado, were formed in fractures associated with a small caldera.

The huge tin and silver deposits in Bolivia are in fractures that are localized in and around stratovolcanoes.

Many famous ore bodies are associated with intrusive igneous rocks.

Tin in Cornwall, England,

Copper at Butte, Montana, Bingham, Utah, and Bisbee, Arizona.

Figure 21B1

Figure 21B2

Magmatic Mineral Deposits (1)

The processes of partial melting and fractional

crystallization are two ways of separating some

minerals from other.

The processes involved are entirely magmatic, and

so such deposits are referred to as magmatic

mineral deposits.


Pegmatites formed by fractional crystallization of

granitic magma commonly contain rich

concentrations of such elements as:

Lithium.

Beryllium.

Cesium.

Niobium.


Much of the world’s lithium is mined from

pegmatites such as those at King’s Mountain, North

Carolina, and Bikita in Zimbabwe.

The great Tanco pegmatite in Manitoba, Canada,

produces much of the world’s cesium, and

pegmatites in many countries yield beryl, one of the

main ore minerals of beryllium.


Crystal settling, another process of fractional crystallization, is especially important in low-viscosity basaltic magma.

One of the first minerals to form is chromite, the main ore mineral of chromium.

The dense chromite crystals settle to the bottom of the magma, producing almost pure layers of chromite.

The world’s principal deposits of chromite are in the Bushveld igneous complex in South Africa and the Great Dike of Zimbabwe.

Sedimentary Mineral Deposits

The term sedimentary mineral deposits is applied to any local concentration of minerals formed through processes of sedimentation.

One form of sedimentation is the precipitation of substances carried in solution.

There are three types of sedimentary mineral deposits:

Evaporite deposits.

Iron deposits.

Stratabound deposits.

Evaporite Deposits (1)

Evaporite deposits are formed by evaporation of

lake water or seawater.

The layers of salts precipitate as a consequence of

evaporation.

Salts that precipitate from lake water of suitable

composition include sodium carbonate (Na2CO3), sodium

sulfate (Na2SO4), and borax (Na2B4O7.1OH2O).


Huge evaporite deposits of sodium carbonate were

laid down in the Green River basin of Wyoming

during the Eocene Epoch.

Oil shales were also deposited in the basin.

Borax and other boron-containing minerals are

mined from evaporite lake deposits in Death Valley

and Searled and Borax Lakes, all in California; and

in Argentina, Bolivia, Turkey, and China.


Much more common and important than lake water

evaporites are the marine evaporites formed by

evaporation of seawater.

The most important salts that precipitate from

seawater are:

Gypsum (CaSO4.2H2O).

Halite (NaCl).

Carnallite (KCl.MgCl2.6H2O).


Low-grade metamorphism of marine evaporite

deposits causes another important mineral, sylvite

(KCl), to form from carnallite.

Marine evaporite deposits are widespread.

In North America, for example, strata of marine

evaporites underlie as much as 30 percent of the land

area.


Marine evaporites produce:

Most of the salt that we use.

The gypsum used for plaster.

The potassium used in plants fertilizers.

Figure 21.6

Iron Deposits (1)

Sedimentary deposits of iron minerals are

widespread, but the amount of iron in average

seawater is so small that such deposits cannot have

formed from seawater that is the same as today’s

seawater.

Iron Deposits (2)

All sedimentary iron deposits are tiny by comparison with the class of deposits characterized by the Lake Superior-type iron deposits.

These remarkable deposits, mined principally in

Michigan and Minnesota, were long the mainstay of the U.S. steel industry.

They are declining in importance todaybecause imported ore is replacing them.

They are of early Proterozoic age (about 2 billion years or older).

Iron Deposits (3)

They are found in sedimentary basins on every craton

(Labrador, Venezuela, Brazil, Russia, India, South

Africa, and Australia).

They appear to be the product of chemical precipitation.

They are interbedded layers of chert and several different

kinds of iron minerals.

The cause of precipitation remains uncertain.

Iron Deposits (4)

Many experts suspect these evaporites formed from

seawater of a different composition than today’s

seawater.

The grade of the deposits ranges from 15 to 30

percent Fe by weight.

Iron Deposits (5)

Two additional processes can form iron ore:

First, leaching of silica during weathering can lead to

secondary enrichment and can produce ores containing as

much as 66 percent Fe.

The second way a Lake Superior-type iron can become an ore

is through metamorphism.

– First, grain sizes increase so that separating ore minerals from the

gangue becomes easier and cheaper.

– Second, new mineral assemblages form, and iron silicate and iron

carbonate minerals originally present can be replaced by

magnetite or hematite, both of which are desirable ore minerals.

Figure 21.7

Iron Deposits (5)

Ore grade is not increase by metamorphism,

The changes in grain size and mineralogy transform the

sedimentary rock into an ore.

Iron ores formed as a result of metamorphism are

called taconites, and they are now the main kind of

ore mined in Lake Superior region.

Stratabound Deposits (1)

Some of the world’s most important ores of lead, zinc, and copper occur in sedimentary rock;

The ore minerals—galena, sphalerite, chalcopyrite, and pyrite—occur in such regular, fine layers that they look like sediments.

The sulfide mineral layers are enclosed by and parallel to the sedimentary strata in which they occur.

For this reason, they are called stratabound mineral deposits.

Figure 21.8

Stratabound Deposits (2)

Most stratabound deposits are diagenetic in origin.

Stratabound deposits form when a hydrothermal solution invades and reacts with a muddy sediment.

The famous copper deposits of Zambia, in central Africa, are stratabound deposits.

The world’s largest and richest lead and zinc deposits are also stratabound:

– Broken Hill, Australia.

– Mount Isa in Australia.

– Kimberley in British Columbia.

Placers (1)

A mineral with a high specific gravity will become

concentrated by flowing water.

Deposits of minerals having high specific gravities

are placers.

Most placers are found in stream gravels that are

geologically young.

Figure 21.9

Figure 21.10

Placers (2)

The most important minerals concentrated in placers

are gold, platinum, cassiterite (SnO2), and diamond.

More than half of the gold recovered throughout all

of human history has come from placers.

Placers (3)

The South African fossil placers are a series of gold-bearing

conglomerates.

They were laid down 2.7 billion years ago as gravels in the

shallow marginal waters of a marine basin.

Associated with the gold are grains of pyrite and uranium

minerals.

Nothing like the deposits in the Witwatersrand basin has been

discovered anywhere else.

– Mining the Witwatersrand basin has reached a depth of 3600 m

(11,800 ft).

– The deposits are running out of ore.

Residual Mineral Deposits (1)

Chemical weathering leads to mineral concentration

through the removal of soluble materials and the

concentration of a less soluble residue.

A common example of a deposit formed through

residual concentration is bauxite.


Bauxites are:

The source of the world’s aluminum.

Concentrated in the tropics because that is where lateritic weathering occurs.

Found in present-day temperate conditions, such as France, China, Hungary, and Arkansas, where the climate was tropical when the bauxites formed.

Not found in glacial regions.

– Glaciers scrape off the soft surface materials.


More than 90 percent of all known bauxite deposits

formed during the last 60 million years,

All of the very large bauxite deposits formed less

than 25 million years ago.


Many of the world’s manganese deposits have been formed by secondary enrichment of low-grade primary deposits, particularly in tropical regions. Secondary enrichment zones are produced by deposition of soluble minerals near the groundwater table, leached from mineral deposits present near the surface.

One of the largest nickel deposits ever found, in New Caledonia, was formed by secondary enrichment.


Secondary enrichment has led to large deposits in

the arid southwestern United States and desert

regions of northern Chile of:

Pyrite (FeS2).

Chalcopyrite (CuFeS2).

Chalcocite (CuS2).

Useful Mineral Substances (1)

Excluding substances used for energy, there are two

broad groups of useful minerals:

Metallic minerals, from which metals such as iron,

copper, and gold can be recovered.

Nonmetallic minerals, such as salts, gypsum, and clay.


Geochemically abundant metals include:

Iron.

Aluminum.

Manganese.

Magnesium.

Titanium.


Geochemically scarce metals represent less

than 0.1 percent by weight of the crust.

They are present exclusively as a result of atomic

substitution.

Atoms of the scarce metals (such as nickel,

cobalt, and copper) can readily substitute for

more common atoms (such as magnesium and

calcium).


Most ore minerals of the scarce metals are

sulfides.

A few, such as the ore minerals of tin and tungsten,

are oxides;

Most scarce metal deposits form as

hydrothermal or magmatic mineral deposits.

Energy Resources (1)

The uses of energy can be grouped into three

categories:

Transportation.

Domestic use.

Industry (meaning all manufacturing and raw material

processing plus the growing of foodstuffs).

Figure 21.12

Energy Resources (2)

Most energy used by humans is drawn annually

from major fuels:

Coal.

Oil.

Natural gas.

Nuclear power.

Wood and animal dung.

Fossil Fuels (1)

The term fossil fuels refers to the remains of plants

and animals trapped in sediment that can be used for

fuel.

The kind of sediment, the kind of organic matter,

and the processes that take place as a result of burial

and diagenesis, determine the kind of fossil fuel that

forms.

Fossil Fuels (2)

In the ocean, microscopic phytoplankton and

bacteria are the principal sources of trapped organic

matter that are transformed (mainly by heat) to oil

and gas.

On land, trees, bushes, and grasses contribute most

of the trapped organic matter, forming coal rather

than oil or natural gas.

Fossil Fuels (3)

In many marine and lakes shales, burial

temperatures never reach the levels at which the

original organic molecules are converted into oil

and natural gas.

Instead, an alteration process occurs in which wax-like

substances containing large molecules are formed.

This material, which remains solid, is called kerogen,

and it is the substance in so-called oil shale.

Coal (1)

Coal is the most abundant fossil fuel.

It is the raw material for nylon, many other plastics,

and a multitude of other organic chemicals.

Through coalification, peat is converted to lignite,

subbituminous coal, and bituminous coal.

Anthracite is a metamorphic rock.

Figure 21.13

Coal (2)

A coal seam is a flat, lens-shaped body having the

same surface area as the swamp in which it

originally accumulated.

Coal seams are found in Utah, Montana, Wyoming,

and the Dakotas.

Peat formation has been widespread and more or

less continuous from the time land plants first

appeared about 450 million years ago, during the

Silurian Period.

Coal (3)

The greatest period of coal swamp formation

occurred during the Carboniferous and Permian

periods, when Pangaea existed.

These periods produced the great coal bed of Europe and

the eastern United States.

The second great period of coal deposition peaked

during the Cretaceous period but commenced in the

early Jurassic and continued until the mid-Tertiary.

Petroleum: Oil and Natural Gas

The major use of oil really started about 1847, when a merchant in Pittsburgh, Pennsylvania, started bottling and selling rock oil as a lubricant.

In 1852, a Canadian chemist discovered kerosene, a liquid that could be used in lamps.

In Romania in 1856, workers were producing 2000 barrels a year.

In 1859, the first oil well was drilled in Titusville Pennsylvania;

Modern use of gas started in the early seventeenth century in Europe, where gas made from wood and coal was used for illumination.

Origin of Petroleum (1)

Petroleum is a product of the decomposition of organic matter trapped in sediment.

Nearly 60 percent of all the oil and gas discovered so far has been found in strata of Cenozoic age.

Petroleum migration is analogous to groundwater migration. When oil and gas are squeezed out of the shale in which they originated and enter a body a sandstone or limestone, they can migrate easily.

Because it is lighter than water, the oil tends to glide upward, until it encounters a trap.

Figure 21.14

Figure 21.15

Figure 21.16

Tars

Tar is made of oil that is exceedingly viscous;

The largest known occurrence of tar sand is in Alberta,

Canada, where the Athabasca Tar Sand covers an area of

5000 km2 and reaches a thickness of 60 m.

Similar deposits, almost as large, are known in Venezuela

and in Russia.

Oil Shale

The world’s largest deposit of rich oil shale is in

Colorado, Wyoming, and Utah.

Only oil shale that produces 40 liters of oil per

ton are worth mining.

The richest shales in the U.S. are in Colorado:

they produce as much as 240 liters of oil per ton.

Production expenses today make exploitation of

oil shales in all countries unattractive by

comparison to oil and gas.

Other Sources of Energy (1)

Biomass energy:

Wood and animal dung.

Hydroelectric power.

Nuclear energy.

Heat energy is produced during controlled transformation (fission) of suitable radioactive isotopes.

Three of the radioactive atoms that keep the Earth hot by spontaneous decay—238U, 235U, and 232Th—can be mined and used to obtain nuclear energy.


Geothermal power.

Geothermal power is produced by tapping the Earth’s internal

heat flux (Zealand, Italy, Iceland and the United States).

Energy from winds, waves, tides, and sunlight:

Winds and waves are both secondary expressions of solar

energy.

Winds have been used as an energy source for thousands of

years through sails on ships and windmills.

Steady surface winds have only about 10 percent of the energy

the human race now uses.


Tides arise from the gravitational forces exerted on the

Earth by the Moon and the Sun.

– If a dam is put across the mouth of a bay so that water can

be trapped at high tide, the outward flowing water at low

tide can drive a turbine.

Consumption Rates

In North America, each person uses approximately

20 tons of crushed rock, cement, sand and gravel,

fertilizer, oil, gas, coal, metals, and other

commodities per year.

For the world as a whole, the consumption rate is

about 9 tons per person per year.

About 54 billion tons of material is dug up and used

each year.

Figure 21.20

Chapter 21: Resources of Minerals and Energyapsacwestridge.edu.pk/assets/admin/upload/notes/... · Mineral Resources (1) Mineral deposits are any volume of rock containing an enrichment

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