2Geology & Mineral Resources Chapter 15Geology & Mineral Resources
3GEOLOGIC PROCESSESThe earth is made up of a core, mantle, and crust and is constantly changing as a result of processes taking place on and below its surface.The earth’s interior consists of:Core: innermost zone with solid inner core and molten outer core that is extremely hot.Mantle: Thickest zone: a rigid outer part, but underneath is asthenosphere that is melted pliable rock that flows in convection currentsCrust: Outermost zone which underlies the continents and oceansLithosphere: combination of crust and outer part of mantle
4The Earth’s CrustThe Earth’s crust is relatively thin relative to the rest of the planet.25-70 km thick below the continentsaround 10 km thick below the oceans.The crust is rich in oxygen and other lighter minerals such as silicon, calcium and aluminum and is less dense than the mantle. The crust rides over the mantle causing the formation of oceans, mountains and volcanoes.Oceanic crustMore than two thirds of the Earth’s surface is composed of oceanic crust. Oceanic crust is continually formed from mantle material and so is relatively young. Even the oldest parts of the ocean floor are no more than 200 million years old.Continental crustThe continental crust is made up of igneous, metamorphic, and sedimentary rocks. It is not recycled within the Earth as often as oceanic crust, so some continental rocks are up to 4 billion years old.LithosphereAsthenosphere
5The LithosphereThe lithosphere comprises the crust and the upper most region of the mantle.The lithosphere carries the outer rock layer of the Earth, which is broken up into seven large, continent-sized tectonic plates and about a dozen smaller platesThe lithosphere overlies the hotter, more fluid lower part of the mantle, the asthenosphere.ContinentalCrustOceanic CrustMohorovicicdiscontinuityLithosphereMantleApprox. 70kmAsthenosphereApprox. 250km
6GEOLOGIC PROCESSESHuge volumes of heated and molten rack moving around the earth’s interior form massive solid plates that move extremely slowly across the earth’s surface.Tectonic plates: huge rigid plates that are moved with convection cells or currents by floating on magma or molten rock.
7Tectonic plate Inner core Spreading centerCollision between two continentsOceanic tectonic plateOcean trenchOceanic tectonic platePlate movementPlate movementTectonic plateOceanic crustOceanic crustSubduction zoneContinental crustContinental crustMaterial cools as it reaches the outer mantleCold dense material falls back through mantleHot material rising through the mantleMantle convection cellFigure 15.3Natural capital: the earth’s crust is made up of a mosaic of huge rigid plates, called tectonic plates, which move around in response to forces in the mantle.MantleTwo plates move towards each other. One is subducted back into the mantle on a falling convection current.Hot outer coreInner coreFig. 15-3, p. 337
8Plate tectonics is the theory explaining the movement of the plates and the processes that occur at their boundaries.
9Plate MovementHeat from the mantle drives two kinds of asthenospheric movement:convectionmantle plumesPlate motion is also partly driven by the weight of cold, dense plates sinking into the mantle at trenches.This heavier, cooler material sinking under the influence of gravity displaces heated material that rises as mantle plumes.Crust cools and sinks into mantleunder the influence of gravityNew crust createdat spreading ridgeCrust melts as itdescends into mantleHeating andcooling causesconvectionMantle plume of hotter material rising from near the coreIRON-NICKELCORE
10Oceanic crust (lithosphere) Abyssal plain Continental slope Folded mountain beltVolcanoesAbyssal plainAbyssal floorOceanic ridgeAbyssal floorAbyssal hillsTrenchCratonOceanic crust (lithosphere)Abyssal plainContinental slopeContinental shelfContinental riseMantle (lithosphere)Continental crust (lithosphere)Mantle (lithosphere)Figure 15.2Natural capital: major features of the earth’s crust and upper mantle. The lithosphere, composed of the crust and outermost mantle, is rigid and brittle. The asthenosphere, a zone in the mantle, can be deformed by heat and pressure.Mantle (asthenosphere)Fig. 15-2, p. 336
11INDIA-AUSTRALIAN PLATE Earth’s Major Tectonic PlatesEURASIAN PLATENORTH AMERICAN PLATEANATOLIAN PLATEJUAN DE FUCA PLATECARIBBEAN PLATECHINA SUBPLATEARABIAN PLATEAFRICAN PLATEPHILIPPINE PLATEPACIFIC PLATESOUTH AMERICAN PLATENAZCA PLATEINDIA-AUSTRALIAN PLATESOMALIAN SUBPLATEFigure 15.4Natural capital: the earth’s major tectonic plates. The extremely slow movements of these plates cause them to grind into one another at convergent plate boundaries, move apart from one another at divergent plate boundaries, and slide past one another at transform plate boundaries. QUESTION: What plate are you floating on?ANTARCTIC PLATEDivergent plate boundariesConvergent plate boundariesTransform faultsFig. 15-4a, p. 338
12Pacific PlateThe Pacific plate is off the coast of California. Lots of volcanoes and earthquakes occur here.“California will fall into the ocean” idea.It is the largest plate and the location of the ring of fire.
14Plate BoundariesVolcanic island arcCratonTrenchLithosphereSubduction zoneLithosphereLithosphereRising magmaAsthenosphereAsthenosphereAsthenosphereDivergent plate boundariesConvergent plate boundariesTransform faultsThe extremely slow movements of these plates cause them to:1. grind into one another at convergent plate boundaries2. move apart at divergent plate boundaries3. slide past at transform plate boundaries.Huge pressures created are released by earthquakes & volcanoesFigure 15.4Natural capital: the earth’s major tectonic plates. The extremely slow movements of these plates cause them to grind into one another at convergent plate boundaries, move apart from one another at divergent plate boundaries, and slide past one another at transform plate boundaries. QUESTION: What plate are you floating on?
15Convergent – the plates push together by internal forces Convergent – the plates push together by internal forces. At most convergent plate boundaries, the oceanic lithosphere is carried downward under the island or continent (subduction zone.) Earthquakes are common here. It also forms an ocean trench or a mountain range.
16Convergent Plates: push together Plate attrition occurs at convergent boundaries marked by deep ocean trenches and subduction zones. The Pacific plate is a convergent plate.Convergent plate boundaryDivergent plate boundaryDeep sea trenchMountain rangeActive volcanoWhen an oceanic plate collides with a continental plate, it sinks in to the mantle and eventually melts.Oceanic crustSubducting plateContinental crustMantle
17BoundariesDivergent – the plates move apart in opposite directions. Creates oceanic ridges
18Divergent PlatesThe size of the plates is constantly changing, with some expanding and some getting smaller.These changes occur along plate boundaries, which are marked by well-defined zones of seismic and volcanic activity.Plate growth occurs at divergent boundaries along sea floor spreading ridges such as the Mid-Atlantic Ridge and the Red Sea.Divergent plate boundaryDivergent plate boundaryContinental rift zoneMagma upwellings through fractures cause plates to diverge.The changing convection currents inside the Earth can cause new boundaries to form and old ones to disappear.
19Sea floor SpreadingSea floor spreading occurs as magma wells up from the mantle below, forcing the plates apart.As the new rock cools and solidifies it picks up and preserves the direction of the Earth’s magnetic field.On average the Earth’s magnetic field reverses once every million years. This leaves magnetic bands in the crust.New rock on either side of the ridge has the same magnetic information.This shows clear evidence of sea floor spreading and plates tectonics.
20Plate BoundariesThe Earth’s major earthquake and volcanic zones occur along plate boundaries.The movements of plates puts crustal rocks under strain.Faults are created where rocks fracture and slip past each other.Earthquakes are caused by the energy released during rapid slippage along faults.New Zealand’s alpine fault is visible from space, marking a transform boundary between the Indo-Australian plate and the Pacific plate.
21Continental Boundaries Where continental plates meet, the land may buckle and fold into mountain ranges.The highest mountains on Earth, the Himalayas, were formed in this way as the subcontinent of India collided with continental Asia.Few volcanoes form in these areas because the continental crust is so thick.
22BoundariesTransform – plates slide next or past each other in opposite directions along a fracture.California will not fall into the ocean!
23Faultline movement after an earthquake Transform BoundariesImage: NASAPlates may slide past each other at transform boundariesPlate size is not affected because there is no construction or destruction of material at these boundaries. However, they are responsible for large earthquakes.Pressure from the plates causes the boundary to lock in position and earthquakes occur when the rock gives way to release the pressure.San Andreas faultPhoto: Wiki commonsFaultline movement after an earthquake
24GEOLOGIC PROCESSESThe San Andreas Fault is an example of a transform fault.Figure 15-5
25ImportancePlate movement adds new land at boundaries, produces mountains, trenches, earthquakes and volcanoes.Important part of recycling earth’s crust, forming mineral deposits
26Changing Earth’s surface Internal processes – rely on heat from earth’s interior – tend to build up earth’s surfaceExternal processes – rely on energy from sun and earth’s gravity – tend to wear down earth’s surfaceErosion: Wind, water, glaciers, human activities especially deforestation (roots hold soil in place)Weathering: break down rocks, forms soilsPhysical – wind, rain, water freezing & expandingChemical – reactions with water, acids, gasesBiological – tree roots, lichen
27The Earth’s CrustWater, as rain, drains to rivers and lakes, which flow back to the ocean eroding the landscape in the process.Sediments eroded from continents and compressed into sedimentary rock can be later lifted and exposed in mountainsThe Earth's persistent oceans of liquid water cycle moisture through the atmosphere to the land and back again.Igneous rocks, such as basalt, form a major component of the crust and are essentially unchanged since their formation.
28The Rock CycleThe interaction of physical and chemical processes that turn 1 type of rock into another The slowest of the earth’s cycles; takes millions of years
29Erosion Transportation Heat, pressure, stress Magma (molten rock) WeatheringDepositionIgneous rock Granite, pumice, basaltSedimentary rock Sandstone, limestoneHeat, pressureCoolingHeat, pressure, stressMagma (molten rock)Figure 15.8Natural capital: the rock cycle is the slowest of the earth’s cyclic processes. The earth’s materials are recycled over millions of years by three processes: melting, erosion, and metamorphism, which produce igneous, sedimentary, and metamorphic rocks. Rock from any of these classes can be converted to rock of either of the other two classes, or can be recycled within its own class. QUESTION: List three ways that the rock cycle benefits your lifestyle.MeltingMetamorphic rock Slate, marble, gneiss, quartziteFig. 15-8, p. 343
30The Rock Cycle LAND SEA Extrusive igneous rock Sedimentary rock The rock cycle constantly redistributes material within and at the Earth's surface over millions of years by melting, erosion, and metamorphism. It is the slowest of the Earth's cycles and is responsible for concentrating the mineral resources on which humans depend.Extrusiveigneous rockcooling andcrystallizationweathering, exposure, andtransport, followed by burialSURFACELANDuplift anderosionSEAROCKS FORMED AT THE EARTH'S SURFACEuplift anderosionSedimentaryrockburial andrecrystallizationCRUSTIntrusiveigneous rockburial andrecrystallizationcooling andcrystallizationdeep burialmetamorphic rockMetamorphicrockROCKS FORMED IN THE EARTH'S INTERIORdeep burialmetamorphic rockMagmameltingMANTLE
32The Rock CycleThe Earth's rocks are grouped together according to the way they formed as:igneousmetamorphicsedimentary rocksIgneous rocks are created by volcanism and may form above the surface as volcanic rocks or below the surface as plutonic rocks.Heat and pressure within the Earth can transform pre-existing rocks to form metamorphic rocks.When rocks are exposed at the surface, they are subjected to weathering and erosion and form sediments.
33Types of RockThe Earth's crust is made up of solid, naturally occurring assemblages of minerals called rocks.The huge diversity of the Earth's rocks has developed over thousands of millions of years through:igneous activity (volcanism) main source of mineral resourcesmetamorphism (changes in form)sedimentation (formation of sediments and sedimentary rocks)Igneous rocksSedimentary rocksMetamorphic rocks
34Types of Rock Obsidian Marble Conglomerate Igneous rocks solidify from volcanic magma They vary in composition from basalt to granite and in texture from rapidly cooled glasses, such as obsidian, to slowly cooled coarse grains, such as granite.Metamorphic rocks result when pre-existing rock is transformed by heat and pressure. Metamorphic rocks are classified by texture and composition. Examples include gneiss, slate, marble and schist.Sedimentary rocks form when sediments accumulate in different depositional environments and then become compressed into brittle, layered rocks, e.g. shale, sandstone, limestone, and conglomerate.GraniteSchistSandstone
35Rock Classification Igneous Classification – Description – forms the bulk of the earth’s crust. It is the main source of many non-fuel mineral resources.Classification –Intrusive Igneous Rocks – formed from the solidification of magma below groundExtrusive Igneous Rocks – formed from the solidification of lava above ground
37SedimentaryDescription – rock formed from sediments. Most form when rocks are weathered and eroded into small pieces, transported, and deposited in a body of surface water.
38Clastic – pieces that are cemented together by quartz and calcium carbonate (Calcite). Examples: sandstone (sand stuck together), Conglomerate (rounded & concrete-looking) and Breccia (like conglomerate but w/ angular pieces)
39Sedimentary (Continued) Nonclastic –Chemical Precipitates – limestone precipitates out and oozes to the bottom of the ocean (this is why there is a lot of limestone in S.A.)Biochemical Sediments – like peat & coalPetrified wood & opalized wood
40MetamorphicDescription – when preexisting rock is subjected to high temperatures (which may cause it to partially melt), high pressures, chemically active fluids, or a combination of theseLocation – deep within the earth
41Dynamic Metamorphism – earth movement crushes & breaks rocks along a fault. Rocks may be brittle- (rock and mineral grains are broken and crushed) or it may be ductile- (plastic behavior occurs.)Rocks formed along fault zones are called mylonites.
42Examples: Contact Metamorphism- rock that is next to a body of magma Ex. limestone under heat becomes marble through crystallizationLimestone -> marblesandstone -> quartziteshale -> hornfelds (slate)
43Metamorphic (Continued) Regional Metamorphism – during mountain building; great quantities of rock are subject to intense stresses and heatEx. cont. shelves ram together
44Progressive Metamorphism – One form of rock changing into another shale->slate->schist->gneisscoal->graphitegranite->gneiss
45MineralsMineral: element or compound occurs naturally Mineral resource: concentration that can be extracted Considered Nonrenewable Essential for modern life Metallic: Aluminum, gold, copper Nonmetallic: sand, gravel, limestone Distribution of mineral resources is uneven 4 strategic metal resources: Manganese, Cobalt, Chromium, and platinum are critical and come from unstable countries in Africa – must stockpile Eventually will run out
46ResourcesMany resources are extracted from the different layers of the Earth and some minerals are mined for their uses economically:Coal, oil, and natural gas are all a mined resourceUranium is mined for nuclear reactionsGold, silver, platinum are precious metals and are used commerciallyBauxite is used for aluminum production and are used commerciallyMany precious metals are mined: Manganese, chromium, and platinum from S. Africa, Silver from Peru and Mexico, Uranium from Canada.Mining for precious metals like gold or silver results in the contamination with cyanide because the metals are sprayed with cyanide.
47OxygenThe most abundant element in Earth’s crustNitrogen:The most abundant element in Earth’s atmosphereIron:The most abundant element in the Earth’s core. Core also contain nickel.
48Specific Resources & Their Uses Limestone – abundant locally, formed from layers of seashells and organisms under pressure as they were covered; used in sidewalks, fertilizers, plastics, carpets, and moreLead – used in batteries and carsClay – used to make books, magazines, bricks, and linoleumGold – besides being used as money and for jewelry, gold is used in medicine (lasers, cauterizing agents) and in electronics (circuits in computers, etc.)
50United States Central – diamonds (Arkansas), bituminous coal West – bituminous and subbituminous coal, gold, silver, copperEast – anthracite coal, bituminous coalSouth – some gold (SC), bituminous coalNorth – bituminous coal, some gold (SD, WI)
51ENVIRONMENTAL EFFECTS OF USING MINERAL RESOURCES The extraction, processing, and use of mineral resources has a large environmental impact.Figure 15-9
52Natural Capital Degradation Extracting, Processing, and Using Nonrenewable Mineral and Energy ResourcesStepsEnvironmental effectsMiningDisturbed land; mining accidents; health hazards, mine waste dumping, oil spills and blowouts; noise; ugliness; heatExploration, extractionProcessingTransportation, purification, manufacturingSolid wastes; radioactive material; air, water, and soil pollution; noise; safety and health hazards; ugliness; heatUseFigure 15.10Natural capital degradation: some harmful environmental effects of extracting, processing, and using nonrenewable mineral and energy resources. The energy required to carry out each step causes additional pollution and environmental degradation.Transportation or transmission to individual user, eventual use, and discardingNoise; ugliness; thermal water pollution; pollution of air, water, and soil; solid and radioactive wastes; safety and health hazards; heat
53ENVIRONMENTAL EFFECTS OF USING MINERAL RESOURCES Minerals are removed through a variety of methods that vary widely in their costs, safety factors, and levels of environmental harm.A variety of methods are used based on mineral depth.Surface mining: shallow deposits are removed.Subsurface mining: deep deposits are removed.
54Methods Surface Mining Description – if resource is <200 ft. from the surface: Machines and explosives are used to break up & remove the topsoil and rocks. This is called the overburden. Remove the resource, reclamation followsBenefits – cheap, easy, efficientCosts – tears up the land, byproducts produce an acid that can accumulate in rivers and lakes
55Surface MiningResource that is near the surface can be economically extracted using open cuts in the earth.The alteration of the land and production of acid mine drainage can lead to pollution of waterways and aquifers. Abandoned mines can also leach acid drainage by rainwater.Coal seams exposedLand provides economic and technical difficultiesHighly erodible highwall remains
56Open-pit MiningMachines dig holes and remove ores, sand, gravel, and stone.Toxic groundwater can accumulate at the bottom.Figure 15-11
57Area Strip MiningEarth movers strips away overburden, and giant shovels removes mineral deposit.Often leaves highly erodible hills of rubble called spoil banks.Regrowth of vegetation is slowFigure 15-12
58Contour Strip Mining Used on hilly or mountainous terrain. Unless the land is restored, a wall of dirt is left in front of a highly erodible bank called a highwall.Figure 15-13
59Mountaintop RemovalMachinery & explosives remove the tops of mountains to expose coal.The resulting waste rock and dirt are dumped into the streams and valleys below.Causes extensive environmental damageFigure 15-14
60Surface Mining Control & Reclamation Act of 1977 Requires mining companies to reclaim (restore) surface-mined landMost cases only partly successful & take decadesReclamationDescription – returning the rock layer (overburden) and the topsoil to a surface mine, grading, fertilizing and planting itBenefits – restores land to good conditionCosts – expensive, time-consuming
61Methods (Continued) Underground Mining Description – digging a shaft down to the resource, using machinery (and people) to tear off and remove the resourceBenefits – can get to resources far underground, disturbs less land, creates less wasteCosts – leaves much of the resource in the ground, more expensive, more time-consuming, more dangerous
62Underground Mining Two main methods: room and pillar mining long wall miningRoom and pillar mining removes blocks of the coal seam while leaving others to act as pillars to keep the roof stable.Long wall mining uses machines that move along the length of the coal face. The removed coal falls onto a conveyor that takes it to the surface.As the machine moves forward the tunnel behind it is allowed to collapse.Photo: Eickhoff Maschinenfabrik and Eisengießereihttp://www.eickhoff-bochum.de/de/
63Coal Mine Silo Processing plant Coal crusher Long wall mining Ventilation shaft and elevatorRoom and pillar miningCoal conveyorPillars
64Mining Impacts Scarring / disruption of land Collapse of land above underground mines (subsidence)PollutionProduces more toxic air emissions than any other industryAcid mine drainage pollutes water suppliesProcessing ore releases mercury & arsenic, cyanide: companies have declared bankruptcy & walked away leaving toxic superfund sitesProduced ¾ of all US solid waste: 3 tons of waste is generated to produce 1 gold ring
65Nonrenewable Resources Definition – things human use that have a limited supply; they cannot be regrown or replenished by manDepletion time: economically depleted when is costs more to obtain than worth.At that point, 5 choices:ReduceReuseRecycleFind a substituteDo without
66SustainabilityDefinition – prediction of how long specific resources will last; ex. we have a 200 year supply of coal in the U.S.Knowing this helps people make decisions in resource useProblems – these are only predictions; they may not be accurate
67Dealing with Nonrenewable Resources Conservation Definition – using less of a resource or reusing a resource, ex. refilling plastic laundry jugs, reusing plastic bags, etc.Part of the solutionProblems – this requires a change in our lifestyle and some people will resist.
68Recycling Examples – aluminum, glass, tin, steel, plastics, etc. Part of the solutionProblems – recycling a resource can costs more than using the raw material; we don’t have the technology to recycle everything, people are resistant, need a market for recycled material
69Sustainable Use of Nonrenewable Minerals SolutionsSustainable Use of Nonrenewable Minerals• Do not waste mineral resources.• Recycle and reuse 60–80% of mineral resources.• Include the harmful environmental costs of mining and processing minerals in the prices of items (full-cost pricing).• Reduce subsidies for mining mineral resources.• Increase subsidies for recycling, reuse, and finding less environmentally harmful substitutes.• Redesign manufacturing processes to use less mineral resources and to produce less pollution and waste.Figure 15.18Solutions: ways to achieve more sustainable use of nonrenewable mineral resources. QUESTION: Which two of the solutions do you think are the most important?• Have the mineral-based wastes of one manufacturing process become the raw materials for other processes.• Sell services instead of things.• Slow population growth.Fig , p. 351