CHAPTER 12 - GEOLOGIC RESOURCES
Overview
Geologic resources, included in virtually every manufactured object, are
nonrenewable and occur in three main categories: energy, metals, nonmetallic
resources, including ground water. The term ‘resources’ encompasses the total
amount of a geologic material in all deposits, both discovered and
undiscovered. ‘Reserves’ are that part of resources that have been discovered
and can be extracted economically and legally under present conditions.
Canada’s energy needs are supplied from oil, natural gas, hydroelectricity,
coal, and nuclear sources (in decreasing order of contribution). Oil and gas
accumulations require a source rock, reservoir rock, trap, and the proper
thermal maturity provided by burial. Production from oil and gas fields is by
drilling. Petrochemicals are produced by refining. Exploitation involves drilling
offshore and can create environmental problems.
Global oil reserves will last 40 to 45 years at present consumption rates, but
the United States is running out of oil, with current domestic reserves of only 8
years, and currently imports 51% of its consumption. Recent discoveries of
gas hydrates off Canada’s coastlines will provide valuable fuel sources for the
future. Other sources of petroleum include heavy crude, oil sands, and oil
shale. About 30% of Canada’s oil production comes from the Athabasca Oil
Sands in northern Alberta.
Coal supplies about 20% of electricity used in Canada but 88% of electricity in
the United States. Varieties of coal (Table 12.1) include peat, lignite,
subbituminous, bituminous, and anthracite. Coal is extensively preserved in
the Appalachian, interior, and far western coal fields (Figure 12.12). Extraction
and use of coal creates environmental problems with air and water pollution.
Reserves suggest centuries of supply at present rates of production in North
America.
Uranium is used in nuclear reactors to produce 7% of Canada’s energy needs.
Canada produces about 1/3 of the world’s uranium; most is mined from high
grade reserves in Saskatchewan. Alternative sources of energy are renewable,
and include hydroelectric, geothermal, solar, and wind power. Processes
involving ocean currents also have potential, as do nuclear fusion and the
burning of hydrogen from dissociation of water.
Ores are naturally occurring materials that can be mined at a profit. Many
metallic ores associated with igneous rocks may result from crystal settling,
hydrothermal fluids, contact metamorphism, hydrothermal veins, disseminated
deposits, hot springs and pegmatites. Other metallic ores are formed by
surface processes such as chemical precipitation, concentration by weathering
(placers), and supergene enrichment.
There is a relationship between ores and plate tectonics. Hot springs at
diverging plate boundaries may precipitate metals. Ophiolites and volcanism at
island arcs may produce rich ore deposits at converging plate boundaries.
Subduction produces metallic deposits along continental margins.
Mining involves underground or surface activity (open-pit, strip, or placer), all
of which require attention to environmental problems, particularly waste rock,
subsidence and acid drainage.
The chapter concludes with a discussion of important metals (iron, copper,
aluminum, lead, zinc, silver, gold, and others; Table 12.2), nonmetallic
resources (construction materials, fertilizers, and evaporites, gemstones,
asbestos, talc, and others), observations on new areas and tools for
exploration that may increase reserves, and closes with a discussion of the
need for balance between extreme positions taken by exploiters,
environmentalists and conservationists.
Learning Objectives
1. The three main categories of geologic resources are: energy, metals and
nonmetallic resources. All are nonrenewable. Resources include discovered and
undiscovered deposits. Reserves are discovered deposits that can be extracted
economically and legally under current conditions.
2. Fossil fuels provide about 65% of Canada’s energy. About 32% of Canada’s
energy is from oil, 28% from hydroelectric, 25% from natural gas, 8% from
coal, and 7% from nuclear sources.
3. Petroleum includes crude oil and natural gas. Oil and natural gas originate
in sedimentary rocks, and underground oil and gas accumulations require
source rock, reservoir rock, a trap, and proper thermal maturity. Traps include
structures (anticlines, faults), stratigraphic traps, unconformities, reefs, and
salt domes. Oil fields are regions with one or more oil pools. Environmental
concerns involving petroleum include spills, natural seeps, subsidence, and air
pollution.
4. World oil reserves will last from 40 to 45 years at present rates of
consumption. The United States imports approximately 51% of the oil it uses,
and its domestic reserves are only 8 years at current rates of production.
Canada has substantial oil and natural gas reserves and recent finds of
methane hydrate offshore may provide important energy sources. Heavy
crude, oil sands, and oil shale will also provide significant sources of oil in the
future.
6. Coal provides only 8% of Canada’s energy but 24% of U.S. energy. Ranks
of coal from lowest to highest are: peat, lignite, subbituminous, bituminous,
and anthracite. The major bituminous coal producing areas in North America
are the Appalachian, interior and far western fields. North American coal
reserves are adequate for centuries at current rates of production.
7. Uranium is used in nuclear reactors, which supply about 7% of Canadian
electricity. Canada mines about 1/3 of the world’s uranium from high grade
deposits in Saskatchewan. Uranium is also mined from sandstones in the
western United States. Reserves are adequate for the foreseeable future, and
breeder reactors may extend the amount of uranium that can be used as fuel.
8. Renewable alternative sources of energy include hydroelectric power, and
power derived from other energy sources such as geothermal, solar, wind,
tidal, wave, ocean current and oceanic temperature differences, nuclear
fusion, and hydrogen dissociated from water.
9. Metallic ore deposits are created in igneous rocks by crystal settling,
hydrothermal fluids, contact metamorphism, hydrothermal veins, hot springs
and in pegmatites. Chemical precipitation of ores in sediment layers is a
common occurrence for iron and manganese. Concentration by weathering
produces placers. Supergene enrichment develops copper ores as a result of
leaching and redeposition by groundwater.
10. Metallic ore deposits are related to plate tectonics. Diverging plate
boundaries develop hydrothermal fluids that contain metallic ions and form hot
spring deposits in rift valleys along mid-oceanic ridges. Converging plate
boundaries may develop ores associated with ophiolites and island arcs.
11. Mining involves both underground and surface activity. Open-pit, strip and
placer mines are large surface operations that pose potential environmental
problems from waste rock, subsidence, and acid drainage.
12. Important metals for an industrialized economy include iron, copper,
aluminum, lead, zinc, silver, gold, chromium, nickel, cobalt, manganese,
molybdenum, tungsten, vanadium, tin, mercury, titanium, and platinum. Ores
of most of these metals are recovered by open pit mining, and those ores may
have several of these minerals in association.
13. Nonmetallic resources include sand and gravel, stone (cut or crushed),
fertilizers (phosphates, nitrates and potassium compounds), evaporites (rock
salt, gypsum, and sulfur), gemstones, asbestos, talc, mica, barite, borates,
fluorite, clays, diatomite, glass sand, and graphite.
14. Ocean mining will increase in the future to exploit manganese nodules,
and brine deposits. Better technology will also be applied to the search for
resources on land.
15. The future will require balancing three positions: 1) maintain or raise
standard of living worldwide; 2) maintain environmental quality; 3) conserve
resources for the future.
Boxes
12.1 – IN GREATER DEPTH – THE DEVELOPMENT OF CANADA’S OIL AND
GAS INDUSTRY – North America’s first commercial oil well was dug in 1858
at Oil Springs, Ontario; shallow reservoirs still produce oil and gas in southern
Ontario today. Oil was first discovered in Alberta at Pincher Creek in 1902 and
natural gas was found at Bow Island in 1908. The first significant oil find in
western Canada occurred in 1947 when the Leduc #1 well was drilled south of
Edmonton. Alberta’s oil industry grew in the 1950’s and 60’s as the Western
Canada Sedimentary Basin was extensively explored and developed. Alberta
now supplies 55% of Canada’s oil. Suncor Energy began development of the
first successful open-pit oil sands mining operation in 1964 and oil sands now
account for 30% of Canada’s oil production. Offshore exploration of Canada’s
east coast began in 1959 and resulted in discovery of the Hibernia, Terra
Nova, White Rose and Sable Island fields.
12.2 – IN GREATER DEPTH – OFFSHORE OIL – THE HIBERNIA PROJECT The Hibernia field lies on the Grand Banks off Canada’s east coast and consists
of two sandstone reservoirs that host light crude oil. Oil production from
Hibernia began in 1997 and an average 150,000 barrels of oil are extracted
per day. Severe environmental conditions, including high storm waves and
icebergs posed many challenges to the development of the Hibernia field and a
unique platform was designed that can be disconnected from its base in the
event of a potential iceberg collision. Specially designed tankers are also used
to transport oil to the mainland.
12.3 - ENVIRONMENTAL GEOLOGY - FLAMMABLE ICE. METHANE HYDRATE
DEPOSITS - SOLUTION TO ENERGY SHORTAGE OR MAJOR
CONTRIBUTOR TO GLOBAL WARMING? - Methane hydrates are methane
trapped in ice crystals, usually in permafrost areas and the deep ocean floor.
Vast amounts of methane hydrate fuel occur on the ocean floor; perhaps twice
the amount available from petroleum and coal combined. Large amounts of
methane hydrate have recently been discovered off the western coast of
Vancouver Island and a world research site for the study of these deposits has
been established at the Mallik field in the Mackenzie Delta of northwestern
Canada. Exploitation of methane hydrates is a challenge because the deposits
are deep, and any change in pressure or temperature releases the methane.
Since methane is a greenhouse gas, its release into the atmosphere from
disruption of the sea floor by any cause could increase global warming
12.4 - ENVIRONMENTAL GEOLOGY – THE SYDNEY TAR PONDS – CANADA’S
LARGEST TOXIC DUMP – The Sydney Tar Ponds in Nova Scotia contain toxic
coal-tar deposits produced as a by-product of the steel making industry and
dumped into a former tidal estuary between the early 1900’s and 1988.
Contaminants, including PAHs, PCBs, benzene, toluene, kerosene, naphthalene
and tar, are flushed from the ‘ponds’ into Sydney harbour with each tide.
Federal, provincial and municipal co-operation is required to remediate this
site – at a cost estimated at between $500 and $800 million or more.
12.5 – IN GREATER DEPTH – CANADA’S MINERAL WEALTH – Canada is one
of the world’s leading exporters of minerals and metals, producing copper,
gold, nickel, zinc, potash, uranium, asbestos, cadmium, titanium concentrate,
aluminum, platinum, salt, molybdenum, gypsum, cobalt and lead for world
markets. The mining industry contributes 4% of the Canadian gross domestic
product. Many Canadian settlements owe their origin to the mineral extraction
industry and newly developed diamond mines in the Northwest Territories
have strengthened future economic prospects for Canada’s northern
communities. It is predicted that Canada will supply 20% of the world’s
diamonds within the next ten years.
Short Discussion/Essay
1.
2.
3.
4.
5.
Why will recycling never replace the need for new materials?
What are methane hydrates? Where are they found?
Explain why most metallic ores are mined by open pit methods.
Why are most metallic ores of magmatic and/or hydrothermal origin?
Why are most nonmetallic ores associated with sedimentary deposits?
Longer Discussion/Essay
1. Why do reserve estimates constantly change?
2. Will population growth ultimately exceed resource availability on the earth;
why or why not?
3. Why do oil and natural gas commonly occur together?
4. Why is most electricity in Canada generated from oil and hydroelectric
sources?
5. What sources of energy would you predict Canada to be using 10 years, 20
years and 50 years in the future?
Selected Readings
Two recent issue of Scientific American (1990 v. 261, 11 papers; 1998, v. 278,
4 papers) have been devoted to energy issues.
The U.S. Geological Survey, Division of Energy and Mineral Resources
(formerly U.S. Bureau of Mines) publishes the Mineral commodity summaries
(previously call Minerals Yearbook) annually. It is available from
Superintendent of Documents, U.S. Government Printing Office, Washington,
D.C. 20402 or U.S. Geological Survey, Book and Open-File Report Sales, Box
25425, Denver CO 80225.
Ahearne, J. 1993."The future of nuclear power," American Scientist 81(1):2436.
Brimhall, G. 1991."The genesis of ores," Scientific American 264: 106-116.
Cocoran, E. 1991."Cleaning up coal," Scientific American 264: 106-116.
Draper, D., 1998. Our Environment - A Canadian Perspective
Gibbons, J.H., Blau, P.D., and Gwin, H.L. 1989."Strategies for energy use,"
Scientific American 261: 136-143.
Martinez, J.D. 1991."Salt domes," American Scientist 79 (5): 420-431