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.

Figure 21.1

Figure 21.2

Mineral Resources (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.

Mineral Resources (3)  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.

Mineral Resources (4)  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.

Origin Of Mineral Deposits (2)  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.

Origin Of Mineral Deposits (3)  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

Hydrothermal Mineral Deposits (2)  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.

Hydrothermal Mineral Deposits (3)  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.

Hydrothermal Mineral Deposits (4)  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

Hydrothermal Mineral Deposits (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.

Magmatic Mineral Deposits (2)  Pegmatites formed by fractional crystallization of granitic magma commonly contain rich concentrations of such elements as:  Lithium.  Beryllium.  Cesium.  Niobium.

Magmatic Mineral Deposits (3)  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.

Magmatic Mineral Deposits (4)  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 (Na 2 CO 3 ), sodium sulfate (Na 2 SO 4 ), and borax (Na 2 B 4 O 7.1OH 2 O).

Evaporite Deposits (2)  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.

Evaporite Deposits (3)  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 (CaSO 4.2H 2 O).  Halite (NaCl).  Carnallite (KCl.MgCl 2.6H 2 O).

Evaporite Deposits (4)  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.

Evaporite Deposits (5)  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, w ere 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 (SnO 2 ), 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.

Residual Mineral Deposits (2)  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.

Residual Mineral Deposits (3)  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.

Residual Mineral Deposits (4)  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.

Residual Mineral Deposits (5)  Secondary enrichment has led to large deposits in the arid southwestern United States and desert regions of northern Chile of:  Pyrite (FeS 2 ).  Chalcopyrite (CuFeS 2 ).  Chalcocite (CuS 2 ).

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.

Useful Mineral Substances (2)  Geochemically abundant metals include:  Iron.  Aluminum.  Manganese.  Magnesium.  Titanium.

Useful Mineral Substances (3)  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).

Useful Mineral Substances (4)  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, p eat 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 km 2 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.

Other Sources of Energy (2)  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.

Other Sources of Energy (3)  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