Introduction: Natural Resources AndHuman History (1) Over one hundred sixty thousand years ago, ourancestors probably began to use flint, chert, andobsidian 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 copperby smelting. Before another thousand years had passed, they haddiscovered how to smelt lead, tin, zinc, silver, andother metals.
Introduction: Natural Resources AndHuman History (2) The technique of mixing metals to make alloys camenext.– Bronze was composed of copper and tin.– Pewter was composed of tin, lead, and copper. The smelting of iron came much later—about 3300years ago. The first people to use oil instead of wood for fuelwere the Babylonians, about 4500 years ago. The first people to mine and use coal were theChinese, about 3100 years ago.
Mineral Resources (1) Mineral deposits are any volume of rock containingan enrichment of one or more minerals. Mineral resources have three distinctivecharacteristics: Occurrences of usable minerals are limited inabundance and localized at places within the Earth’scrust. The quantity of a given mineral available in any onecountry is rarely known with accuracy. Deposits of minerals are depleted by mining andeventually exhausted.
Mineral Resources (2) Ore is an aggregate of minerals from which one ormore minerals can be extracted profitably. “Ore” is an economic term, whereas “mineraldeposit” is a geologic term. The economic challenges of ore are to find it, mineit, and refine it as cheaply as possible. The lowest-grade ores ever mined—about 0.5percent copper—were worked only at a time of highmetal prices.
Mineral Resources (3) In 2002, lowest grade of of mineable copperore is closer to 1 percent. Over production of copper around the world,combined with economic recession, has resultedin the closing of many mines, particularly thoseexploiting the lowest grades of ores.
Mineral Resources (4) Sphalerite, galena, and chalcopyrite are ore mineralsfrom which zinc, lead, and copper respectively canbe extracted. Ore minerals rarely occur alone. They are mixed with other nonvaluable minerals,collectively termed gangue.– Gangue may include quartz, feldspar, mica, calcite, ordolomite.
Origin Of Mineral Deposits (1) All ores are mineral deposits because each of themis a local enrichment of one or more minerals ormineraloids. Not all minerals deposits are ores. In order for a deposit to form, processes must bringabout a localized enrichment of one or moreminerals.
Origin Of Mineral Deposits (2) Minerals become concentrated in five ways: 1. Concentration by hot, aqueous solutions flowingthrough fractures and pore spaces in crustal rock to formhydrothermal mineral deposits. 2. Concentration by magmatic processes within a body ofigneous rock to form magmatic mineral deposits.
Origin Of Mineral Deposits (3) 3. Concentration by precipitation from lake water or seawater to form sedimentary mineral deposits. 4. Concentration by flowing surface water in streams oralong the shore, to form placers. 5. Concentration by weathering processes to formresidual mineral deposits.
Hydrothermal Mineral Deposits (1) Some solutions originate when water dissolved inmagma is released as the magma rises and cools. Other solutions are formed from rainwater orseawater that circulates deep in the crust. Mineral deposits formed from midocean ridgevolcanism are called volcanogenic massive sulfidedeposits.
Hydrothermal Mineral Deposits (2) The pyroxene-rich rocks of the oceanic crust yieldsolutions charged with copper and zinc. As a result, volcanogenic massive sulfide deposits arerich in copper and zinc. In black smokers, the rising hydrothermal fluidappears black due to fine particles of iron sulfideand other minerals precipitated from solution as theplume is cooled by contact with cold seawater. The chimney-like structure is composed of pyrite,chalcopyrite, and other ore minerals deposited byhydrothermal solution.
Hydrothermal Mineral Deposits (3) When a hydrothermal solution moves slowlyupward, as with groundwater percolating through anaquifer, the solution cools very slowly. If dissolved minerals were precipitated from such aslow-moving solution, they would be spread over alarge volume of rock and would not be sufficientlyconcentrated to form an ore.
Hydrothermal Mineral Deposits (4) When a solution flows rapidly, as in an openfracture, or through a mass of shattered rocks, orthrough a layer of porous tephra where flow is lessrestricted, cooling can be sudden and can occur overshort distances. Rapid precipitation and a concentrated mineral depositare the result. Veins formed when hydrothermal solutions depositminerals in open fractures. Many such veins are found in regions of volcanicactivity.
Hydrothermal Mineral Deposits (5) The famous gold deposits at Cripple Creek,Colorado, were formed in fractures associated witha small caldera. The huge tin and silver deposits in Bolivia are infractures that are localized in and aroundstratovolcanoes. Many famous ore bodies are associated withintrusive 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 fractionalcrystallization are two ways of separating someminerals from other. The processes involved are entirely magmatic, andso such deposits are referred to as magmaticmineral deposits.
Magmatic Mineral Deposits (2) Pegmatites formed by fractional crystallization ofgranitic magma commonly contain richconcentrations of such elements as: Lithium. Beryllium. Cesium. Niobium.
Magmatic Mineral Deposits (3) Much of the world’s lithium is mined frompegmatites such as those at King’s Mountain, NorthCarolina, and Bikita in Zimbabwe. The great Tanco pegmatite in Manitoba, Canada,produces much of the world’s cesium, andpegmatites in many countries yield beryl, one of themain ore minerals of beryllium.
Magmatic Mineral Deposits (4) Crystal settling, another process of fractionalcrystallization, is especially important in low-viscosity basaltic magma. One of the first minerals to form is chromite, themain ore mineral of chromium. The dense chromite crystals settle to the bottom ofthe magma, producing almost pure layers ofchromite. The world’s principal deposits of chromite are in theBushveld igneous complex in South Africa and the GreatDike of Zimbabwe.
Sedimentary Mineral Deposits The term sedimentary mineral deposits is appliedto any local concentration of minerals formedthrough processes of sedimentation. One form of sedimentation is the precipitation ofsubstances carried in solution. There are three types of sedimentary mineraldeposits: Evaporite deposits. Iron deposits. Stratabound deposits.
Evaporite Deposits (1) Evaporite deposits are formed by evaporation oflake water or seawater. The layers of salts precipitate as a consequence ofevaporation. Salts that precipitate from lake water of suitablecomposition include sodium carbonate (Na2CO3), sodiumsulfate (Na2SO4), and borax (Na2B4O7.1OH2O).
Evaporite Deposits (2) Huge evaporite deposits of sodium carbonate werelaid down in the Green River basin of Wyomingduring the Eocene Epoch. Oil shales were also deposited in the basin. Borax and other boron-containing minerals aremined from evaporite lake deposits in Death Valleyand Searled and Borax Lakes, all in California; andin Argentina, Bolivia, Turkey, and China.
Evaporite Deposits (3) Much more common and important than lake waterevaporites are the marine evaporites formed byevaporation of seawater. The most important salts that precipitate fromseawater are: Gypsum (CaSO4.2H2O). Halite (NaCl). Carnallite (KCl.MgCl2.6H2O).
Evaporite Deposits (4) Low-grade metamorphism of marine evaporitedeposits causes another important mineral, sylvite(KCl), to form from carnallite. Marine evaporite deposits are widespread. In North America, for example, strata of marineevaporites underlie as much as 30 percent of the landarea.
Evaporite Deposits (5) 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 arewidespread, but the amount of iron in averageseawater is so small that such deposits cannot haveformed from seawater that is the same as today’sseawater.
Iron Deposits (2) All sedimentary iron deposits are tiny bycomparison with the class of deposits characterizedby the Lake Superior-type iron deposits. These remarkable deposits, mined principally inMichigan and Minnesota, were long the mainstayof the U.S. steel industry. They are declining in importance todaybecauseimported ore is replacing them. They are of early Proterozoic age (about 2 billionyears or older).
Iron Deposits (3) They are found in sedimentary basins on every craton(Labrador, Venezuela, Brazil, Russia, India, SouthAfrica, and Australia). They appear to be the product of chemical precipitation. They are interbedded layers of chert and several differentkinds of iron minerals. The cause of precipitation remains uncertain.
Iron Deposits (4) Many experts suspect these evaporites formed fromseawater of a different composition than today’sseawater. The grade of the deposits ranges from 15 to 30percent Fe by weight.
Iron Deposits (5) Two additional processes can form iron ore: First, leaching of silica during weathering can lead tosecondary enrichment and can produce ores containing asmuch as 66 percent Fe. The second way a Lake Superior-type iron can become an oreis through metamorphism.– First, grain sizes increase so that separating ore minerals fromthe gangue becomes easier and cheaper.– Second, new mineral assemblages form, and iron silicate andiron carbonate minerals originally present can be replaced bymagnetite 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 thesedimentary rock into an ore. Iron ores formed as a result of metamorphism arecalled taconites, and they are now the main kind ofore 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 thatthey look like sediments. The sulfide mineral layers are enclosed by andparallel to the sedimentary strata in which theyoccur. For this reason, they are called stratabound mineraldeposits.
Stratabound Deposits (2) Most stratabound deposits are diagenetic in origin. Stratabound deposits form when a hydrothermalsolution 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 arealso stratabound:– Broken Hill, Australia.– Mount Isa in Australia.– Kimberley in British Columbia.
Placers (1) A mineral with a high specific gravity will becomeconcentrated by flowing water. Deposits of minerals having high specific gravitiesare placers. Most placers are found in stream gravels that aregeologically young.
Placers (2) The most important minerals concentrated in placersare gold, platinum, cassiterite (SnO2), and diamond. More than half of the gold recovered throughout allof human history has come from placers.
Placers (3) The South African fossil placers are a series of gold-bearingconglomerates. They were laid down 2.7 billion years ago as gravels in theshallow marginal waters of a marine basin. Associated with the gold are grains of pyrite and uraniumminerals. Nothing like the deposits in the Witwatersrand basin has beendiscovered 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 concentrationthrough the removal of soluble materials and theconcentration of a less soluble residue. A common example of a deposit formed throughresidual concentration is bauxite.
Residual Mineral Deposits (2) Bauxites are: The source of the world’s aluminum. Concentrated in the tropics because that is wherelateritic weathering occurs. Found in present-day temperate conditions, such asFrance, China, Hungary, and Arkansas, where theclimate 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 depositsformed during the last 60 million years, All of the very large bauxite deposits formed lessthan 25 million years ago.
Residual Mineral Deposits (4) Many of the world’s manganese deposits have beenformed by secondary enrichment of low-gradeprimary deposits, particularly in tropical regions.Secondary enrichment zones are produced bydeposition of soluble minerals near the groundwatertable, leached from mineral deposits present nearthe surface. One of the largest nickel deposits ever found, inNew Caledonia, was formed by secondaryenrichment.
Residual Mineral Deposits (5) Secondary enrichment has led to large deposits inthe arid southwestern United States and desertregions of northern Chile of: Pyrite (FeS2). Chalcopyrite (CuFeS2). Chalcocite (CuS2).
Useful Mineral Substances (1) Excluding substances used for energy, there are twobroad 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 (3) Geochemically scarce metals represent less than0.1 percent by weight of the crust. They are present exclusively as a result of atomicsubstitution. Atoms of the scarce metals (such as nickel,cobalt, and copper) can readily substitute formore common atoms (such as magnesium andcalcium).
Useful Mineral Substances (4) Most ore minerals of the scarce metals aresulfides. A few, such as the ore minerals of tin and tungsten,are oxides; Most scarce metal deposits form ashydrothermal or magmatic mineral deposits.
Energy Resources (1) The uses of energy can be grouped into threecategories: Transportation. Domestic use. Industry (meaning all manufacturing and raw materialprocessing plus the growing of foodstuffs).
Energy Resources (2) Most energy used by humans is drawn annuallyfrom major fuels: Coal. Oil. Natural gas. Nuclear power. Wood and animal dung.
Fossil Fuels (1) The term fossil fuels refers to the remains of plantsand animals trapped in sediment that can be used forfuel. The kind of sediment, the kind of organic matter,and the processes that take place as a result of burialand diagenesis, determine the kind of fossil fuel thatforms.
Fossil Fuels (2) In the ocean, microscopic phytoplankton andbacteria are the principal sources of trapped organicmatter that are transformed (mainly by heat) to oiland gas. On land, trees, bushes, and grasses contribute mostof the trapped organic matter, forming coal ratherthan oil or natural gas.
Fossil Fuels (3) In many marine and lakes shales, burialtemperatures never reach the levels at which theoriginal organic molecules are converted into oiland natural gas. Instead, an alteration process occurs in which wax-likesubstances 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 thesame surface area as the swamp in which itoriginally accumulated. Coal seams are found in Utah, Montana, Wyoming,and the Dakotas. Peat formation has been widespread and more orless continuous from the time land plants firstappeared about 450 million years ago, during theSilurian Period.
Coal (3) The greatest period of coal swamp formationoccurred during the Carboniferous and Permianperiods, when Pangaea existed. These periods produced the great coal bed of Europe andthe eastern United States. The second great period of coal deposition peakedduring the Cretaceous period but commenced in theearly Jurassic and continued until the mid-Tertiary.
Petroleum: Oil and Natural Gas The major use of oil really started about 1847, when amerchant in Pittsburgh, Pennsylvania, started bottling andselling rock oil as a lubricant. In 1852, a Canadian chemist discovered kerosene, aliquid that could be used in lamps. In Romania in 1856, workers were producing 2000barrels a year. In 1859, the first oil well was drilled in TitusvillePennsylvania; Modern use of gas started in the early seventeenth century inEurope, where gas made from wood and coal was used forillumination.
Origin of Petroleum (1) Petroleum is a product of the decomposition oforganic matter trapped in sediment. Nearly 60 percent of all the oil and gas discoveredso far has been found in strata of Cenozoic age. Petroleum migration is analogous to groundwatermigration. When oil and gas are squeezed out of theshale in which they originated and enter a body asandstone or limestone, they can migrate easily. Because it is lighter than water, the oil tends to glideupward, 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 of5000 km2and reaches a thickness of 60 m. Similar deposits, almost as large, are known in Venezuelaand in Russia.
Oil Shale The world’s largest deposit of rich oil shale is inColorado, Wyoming, and Utah. Only oil shale that produces 40 liters of oil perton 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 ofoil shales in all countries unattractive bycomparison to oil and gas.
Other Sources of Energy (1) Biomass energy: Wood and animal dung. Hydroelectric power. Nuclear energy. Heat energy is produced during controlledtransformation (fission) of suitable radioactiveisotopes. Three of the radioactive atoms that keep the Earthhot by spontaneous decay—238U, 235U, and 232Th—can bemined and used to obtain nuclear energy.
Other Sources of Energy (2) Geothermal power. Geothermal power is produced by tapping the Earth’s internalheat flux (Zealand, Italy, Iceland and the United States). Energy from winds, waves, tides, and sunlight: Winds and waves are both secondary expressions of solarenergy. Winds have been used as an energy source for thousands ofyears through sails on ships and windmills. Steady surface winds have only about 10 percent of the energythe human race now uses.
Other Sources of Energy (3) Tides arise from the gravitational forces exerted on theEarth by the Moon and the Sun.– If a dam is put across the mouth of a bay so that water canbe trapped at high tide, the outward flowing water at lowtide can drive a turbine.
Consumption Rates In North America, each person uses approximately20 tons of crushed rock, cement, sand and gravel,fertilizer, oil, gas, coal, metals, and othercommodities per year. For the world as a whole, the consumption rate isabout 9 tons per person per year. About 54 billion tons of material is dug up and usedeach year.