Chapter 13 Mineral and Soil Resources
Objectives of chapter 13
What are the major geologic processes occurring on and in the earth?
How does the rock cycle recycle earth materials and concentrate mineral
How fast are nonfuel mineral supplies being used up and how can we increase
supplies of key minerals?
What are the environmental effects of extracting and using mineral resources?
What is soil and what types are best for growing crops?
Why should we worry about soil erosion?
How can we control erosion and reduce the loss of nutrients form topsoil?
Structure of the Earth:
crust - outermost, thinnest layer; continental crust containing
silica rich rocks of 2.7 g/cm3 density, about 30 km thick, oceanic
crust containing rocks rich in iron and magnesium of 3.0 g/cm3,
about 5 km thick
mantle - thickest layer, most volume; rocks very rich in silicates
high in iron and magnesium, with a density about 3.3 g/cm3.
Contains the asthenosphere, a plastic layer within which is a low
velocity layer of partially melted rock.
core - a liquid outer core, and solid inner core made up of mostly
iron and nickel with a density of about 10 g/cm3
Lithosphere is the crust and solid part of the upper mantle, that
portion that lies above the asthenosphere.
The earth's lithosphere is broken up into 7 major plates, with a total
of about 21 plates. Fig. 13.3 b.
Plate tectonic theory explains the movement of the plates and the
processes that occur at the plate boundaries. The plates move as solid
blocks "floating" on the plastic asthenosphere.
Lithospheric plate boundaries:
Plate tectonics grew out of an earlier hypothesis known as
drift first proposed in 1912 by Alfred Wegener.
Plate motion produces: mountain belts, oceanic ridge system, metamorphic
rocks, volcanoes and earthquakes. Fig. 13.3 a
subduction zones with trenches are found at convergent plate
boundaries fig. 13.2
divergent plate boundaries - plates pull apart
convergent plate boundaries - plates push together
transform plate boundaries - plates slide past each other
The Rock Cycle and Mineral Resources
How are mineral deposits discovered and removed?
mineral - a naturally occurring, inorganic solid with a definite
crystalline structure, composition and physical properties
rock - an aggregate of one or more minerals
igneous rocks - rocks formed from a melt. Magma forms deep within the earth
and may harden there to form e.g. granite. It may rise to the surface as
lava and may harden to from e.g. basalt.
sedimentary rock - rocks formed from the particles derived from other rocks
and precipitates from solution. These particles and solutions are derived
from the weathering and erosion of previously existing rocks. Examples
are sandstone, limestone.
metamorphic rocks - rocks that have been subjected to heat and pressure
and or chemically active fluids from within the earth. E.g. marble, gneiss
rock cycle - any rock can be formed from any other rock. Fig. 13.6
mineral resources - a useful earth material that can be extracted
for reasonable cost. These are nonrenewable resources.
Energy resources - coal, oil
Metallic mineral resources - aluminum, iron
Non metallic mineral resources - salt, sand, gypsum
ore - a metal that can be profitably extracted
reserves - identified resources that can be economically extracted; increases
when new resources are discovered
other resources - identified and undiscovered resources not classified
Use of fossil fuels:
Geological studies conducted by direct and remote sensing methods
removal by surface or subsurface mining fig. 13-8. 13-9
What are Fossil Fuels?
In 1989 0.5 billion motor vehicles in the world. 34%, or 190 million, in
Each day we use 11.4 million barrels of oil
The U.S. has 2.3% of worlds oil, but uses 30% of the total world's oil
extracted each year; 68% of consumption for transportation
80% of U.S. oil fields are depleted.
U.S. imports 55% of its oil, in 1977 only 36%
Some estimates predict that at current rates of consumption oil reserves
will last at least 44 years.
In order to keep on using oil at the current rate and not run out, we must
add the equivalent of a new Saudi Arabian supply every 10 yrs. U.S.G.S
states new discoveries of oil peaked in 1962
Air pollution is significant: 60% of the 170 million tons of air pollutants
annually emitted into the atm in the U.S. is from autos. Gasoline accounts
for 25% of the CO2 emissions from fossil fuel, each gallon of
gas ads 19 lbs of CO2 to the air.
Burning releases heat trapping gasses. Drilling and recovery operations
Analysts project that if all harmful effects were included in the market
price for fossil fuels, (this applies to other mineral deposits as well)
and no gov't subsidies, then the price of these fuels would rise. This
would spur use of renewable energy sources, and improve energy efficiency.
Fossil fuels - term used for oil gas and coal. Produced by the
decomposition of deeply buried dead organic matter from plants (coal) and
animals under high temperatures and pressures over millions of years.
Provide 90% of energy consumed in world
Oil shale and tar sands relatively untapped fossil fuel
How are crude oil and natural gas formed and how do they accumulate
within the Earth?
Accumulation of minute sea creatures
Burial and heat and pressure to transform organic material to oil and
Oil and gas traps
anticline- up arching sedimentary strata
fault- a break in the rock along which movement has taken place
salt dome- dome shaped structures composed of salt, less dense
than most rocks, traps oil, gas
cap rock- impervious rock that keeps oil from moving through
source rock- the rock from which the oil is believed to have
reservoir rock- porous, permeable limestones or sandstones that
hold the oil and will release it when pumped
How are crude oil and natural gas extracted?
Wells are drilled in places that are believed to have commercial supplies.
Primary production- pumping from wells under natural pressure.
Secondary recovery- water, steam, chemicals are injected into
well to force oil toward wells. Recovery increased to 60%
Oil reserves approximate 1000 billion barrels (bl). Most of it in Middle
Natural gas accumulates above oil and is extracted along with
oil. Mostly methane CH2 some ethane, propane and butane.
How is oil refined?
It can be directly transported by pipelines as LNG liquid natural gas.
Much is wastefully burned off in the refinement of crude oil.
Only 125 years supply is believed to be left at current consumption.
Easier to process than oil, cheaper to transport than coal or oil.
Burns cleanly and efficiently.
Fractional distillation method used in oil refineries. (Fig. from Miller
2000). Crude oil is heated, the various components are driven off at certain
temperatures. Products range from gas to asphalt, including plastics and
various organic chemicals.
Use of oil shales and tar sands- synfuels - extract
hydrocarbons by heating to 500oC yield 14 gal/ton. May be considered
when supplies of oil and gas are depleted.
What are the environmental effects of the use of oil and gas?
How is coal formed?
Clear land to build well platforms, storage tanks, pipelines, roads etc.
Pollution of surface water, groundwater by runoff, infiltration, leakage,
wastewater, upwelling of brines
air pollutants both during well drilling, refinement and use
damage of ecosystems
oil seepage, pipe rupture accidents
release of toxic drill muds
unsightly oil platforms
transportation accidents both marine and on land
Coal is formed from the partially decomposed remains of vegetation that
collected in swamps, bogs and marshes millions of years ago.
Buried under many layers of sedimentary rocks the vegetation compressed
into the many forms of coal in use today.
Three forms of coal - lignite, bituminous and anthracite.
Coal classified as a fuel according to its carbon and sulfur content.
How is coal mined?
Reclamation - process of restoring land, reform surface and replant
vegetation. Rarely is it successful.
40 million metric tons accessible to strip mining. 90 billion metric tons
are within 165 ft of the surface.
Cheaper and higher yield than underground mining.
Tailings and spoils banks leave rocks, usually high in sulfides, in contact
with rainwater especially in temperate climates. Forms sulfuric acid that
percolates into groundwater and streams.
How is coal transported and what are the uses and problems associated
40% of coal is mined this way
dangerous: collapse, respiratory illness, explosion, fire
environmental problems: acid mine drainage, land subsidence, coal fires
Train is cheapest method to transport coal to power plants near population
Heat energy from burned coal is used to heat water to produce electricity.
Cannot easily be used for trucks, cars etc.
Coal is most abundant and dirtiest fuel.
Several options are being used or developed to clean coal use
coal produces 64% of world's electricity, 25% of total energy consumed
in U.S., 75% of world's steel
90% of our fossil fuel reserves; enough for several 100's of yrs.
very polluting: 70% of total sulfur dioxide, 30% of nitrogen dioxide, 35%
of carbon dioxide, and radioactive particles
threat to human health; kills several thousand people per year, many of
respiratory problems; several billion dollars in property damage
Clean Air Act amendments are requiring these emissions to be cut in half
if coals harmful environmental costs were included in its market price,
and subsidies were phased out, then coal would be expensive. Then it is
believed that more efficient, cheaper and environmentally safe renewable
sources would be used.
What is the environmental impact of using mineral resources?
clean prior to combustion
efficient boiler designs
scrubbing- the gases from coal burning are mixed with calcium carbonate,
calcium sulfate is produced. This material can be used for wallboard.
disruption of land surface
collapse or subsidence above underground mines
water & wind erosion of spoil heaps and tailings
acid mine drainage - carries H2SO4, contaminates
water, destroys aquatic life
soil - mixture of rock and mineral particles with decaying organic
matter, water, air and living organisms. It is produced slowly by rock
weathering, deposition of sediments and decay of organisms.
soil profile: fig. 13-14. Fig. 13-15 soil food web
soils with roughly equal mixtures of clay, sand, silt and humus are called
loams - the best soil for plant growth
O horizon - surface litter of fallen leaves, organic material
A horizon - topsoil layer or humus of decomposed leaves etc. zone of
B horizon - subsoil, zone of accumulation
C horizon - broken parent rock material
clay soils compact to much, not permeable
sandy soils drain and dry out too much.
Wind and water erosion main causes of soil removal.
Under normal conditions soil forms faster than it erodes. Roots hold soil
Mans activities: logging, farming, off road vehicles, construction, over-grazing
speed up erosion.
Stream erosion in steps- sheet, rills and gullies.
If topsoil is lost, soil is less fertile, and less able to hold water.
Sediment, the largest source of water pollution, fills up channels, reservoirs
and lakes, kills fish, increases flood risk.
soil is eroding faster than it forms - 16x faster in U.S.
productive potential of arid or semiarid land drops by 10% or more. Area
becomes more arid.
U.N. states the 40% of land is suffering from desertification
deforestation without reforestation
surface mining without reclamation
some irrigation methods
farming on marginal land
compaction by farm machinery and animals
How can desertification be slowed:
declining living standards
reduction of the destructive farming and logging methods.
Accumulation of salts in the topsoil as a result of irrigation.
Reduces crop growth hence yields.
Can be reversed by taking land out of production
By applying a large amount of water to flush salts - wasteful
To reduce soil erosion and restore fertility.
Conventional-tillage farming leaves fields plowed before winter exposing
them to erosion.
Conservation-tillage farming is minimum tillage or no-tillage
farming - fields are tilled as little as possible, no overturning.
Terracing: reduces erosion on steep slopes
holds more soil water
multiple crops are possible
Contour farming: planting crops in rows across the contour of
Strip cropping: alternate crops in strips with other crops,
trap soil, reduce runoff, prevents spread of pests and diseases. Use of
nitrogenous legumes increase nitrogen to soil
Alley cropping or agroforestry, or intercropping. Several crops
planted in strips along with trees or shrubs
Gully reclamation: plant fast growing shrubs, vines to stabilize
Windbreaks or shelterbelts: rows of trees are planted
to block wind.
How can soil fertility be maintained?
Fertilization by organic or inorganic mineral fertilizers
organic fertilizers: animal manure, green manure (plant derived) and
compost. Adds microorganisms, helps retain water, aerates soil.
Inorganic fertilizers: nitrogen, potassium and phosphorus are added
to soil as minerals which do not add to the structure or water holding
capacity of soil.
Can runoff into streams causing eutrofication of lakes