Lecture OutlinesPhysical Geology, 10/e

Plummer, McGeary & Carlson

Steve Kadel, Glendale Community College

Geologic Resources

Physical Geology 10/e, Chapter 21

Geologic Resources and Earth’s Systems

• Geologic resources are valuable materials of geologic origin that can be extracted from the Earth– Many geologic resources originate in the hydrosphere

• Petroleum and coal come from organisms that lived and died in water

• Halite (salt) and other evaporite minerals come from dry lake beds

– Weathering interactions between geosphere, atmosphere and hydrosphere produce metal oxide ores

– Humans (biosphere) interact directly with the geosphere, the hydrosphere, and the atmosphere when extracting and utilizing resources

– Even water, when found beneath the Earth’s surface, is a geologic resource (renewable)

Types of Geologic Resources

• Geologic resources can be grouped into three major categories:– Energy resources - petroleum (oil and natural gas),

coal, uranium, geothermal resources– Metals - iron, copper, aluminum, lead, zinc, gold,

silver, platinum, etc.– Non-metallic resources - sand and gravel, limestone,

building stone, salt, sulfur, gems, gypsum, phosphates, etc.

• Groundwater is included in this category

Resources and Reserves

• Resources - the total amount of a valuable geologic material in all deposits, discovered and undiscovered

• Reserves - discovered deposits of geologic resources that can be extracted economically and legally under present conditions– The short-term supply of a geologic

materials

Energy Resources

• Fossil fuels (oil, natural gas, and coal) account for nearly 90% of U.S. energy

• Petroleum - oil and natural gas - occurs in oil pools (valuable underground accumulations)

• Occurrence of oil pools requires:– A source rock (rich in organic matter)– A reservoir rock in which it can be stored and

transmitted (e.g., sandstone)– An oil trap (set of conditions holding rock in reservoir

rock and preventing migration)– Deep enough burial (and sufficient time) to “cook”

the oil and gas out of the organic matter

Oil trapsOil traps

Petroleum Recovery

• Oil fields are regions underlain by one or more oil pools – Largest in U.S. are in Texas and Alaska

• Oil and natural gas are removed from the ground through wells that are drilled down into a reservoir rock within a trap

• Negative environmental effects resulting directly or indirectly from oil recovery and transport include oil spills, brine contamination of surface water, and ground subsidence

Petroleum Reserves

• At current rate of use, worldwide oil reserves should last about 35 to 40 years, and natural gas reserves somewhat longer

• As petroleum prices rise, alternate petroleum sources, such as heavy crude, oil shale and oil sand, will be increasingly exploited– Heavy crude is dense, viscous petroleum

– Oil shale is a black or brown shale with a high solid organic matter content from which oil can be extracted by distillation

– Oil sands (or tar sands) are asphalt-cemented sand or sandstone deposits

Coal

• Coal is a sedimentary rock that forms from the compaction of plant material that has not completely decayed– Forms from shallow burial and

compaction of peat

– Occurs in beds ranging from a few centimeters to thirty meters thick

– Primary use in U.S. is for generating electricity

Coal

• Four varieties of coal are lignite, sub-bituminous, bituminous, and anthracite– Lignite (brown coal) is soft and crumbly– Sub-bituminous and bituminous coal (soft coal) are

black and dusty; burn with a smoky flame• Often strip-mined

– Anthracite (hard coal) is shiny and dust-free; burns with a smokeless flame; low-level metamorphic rock

• Burning of high-sulfur coal can produce acid rain; strip mines can scar landscape

• U.S. has coal reserves than could last for centuries

Other Energy Resources

• The metal uranium is used to power nuclear power generators– Typically found in association with organic matter in sedimentary rocks– Accounts for 10% of U.S. energy production– Leaves radioactive waste as by-product

• Hydroelectric power provides about 4% of the energy needs of the United States– Renewable and non-polluting

• Geothermal power provides about 0.2% of U.S. energy needs, but could be greatly expanded with new techniques

• Other renewable and non-polluting sources include wave/current power, solar power, wind power, and hydrogen fuel cells– As fossil fuel supplies dwindle, these sources will become more important

Metals and Ores

• Metal ores are naturally occurring materials that can be profitably mined

• Whether or not a mineral deposit is considered an ore depends on its chemical composition, percentage of extractable metal, and the current market value of the metal

• Metallic ore deposits can originate by crystal settling in igneous intrusions, from hydrothermal fluids cooling in pores and factures, by chemical precipitation in surface or groundwater, or by river sedimentation (placers)

Mining and Metals

• Mining can be carried out on Earth’s surface (strip mines, open-pit mines, and placer mines) or underground– Metals mined using these techniques include

iron, copper, aluminum, lead, zinc, silver, gold and many others

• With care, negative environmental effects of mining, including unsightly tailings piles, surface scars, land subsidence, and acid mine drainage can be minimized

Non-metallic Resources

• Non-metallic resources are those that are not mined to extract a metal or as a source of energy– Such resources are used for construction

materials (sand, gravel, limestone, and gypsum), agriculture (phosphate, nitrate and potassium compounds), industrial uses (rock salt, sulfur, asbestos), gemstones (diamonds, rubies), and for manufacture of household and business products (glass sand, fluorite, diatomite, graphite)

• If it can’t be grown, it must be mined

End of Chapter 21