Ch21

Chapter 21: Resources of Minerals
and Energy

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.

 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.

 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.

 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.

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.

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.

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.

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.

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).

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.

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.

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—238
U, 235
U, and 232
Th—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.

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