Geology Reference
In-Depth Information
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Metallic mineral resources, including tin, copper, gold,
and silver, are known from Late Paleozoic-age rocks, espe-
cially those deformed during mountain building. The host
rocks for deposits of lead and zinc in southeast Missouri
are Cambrian dolostones, although some Ordovician rocks
contain these metals as well. These deposits have been mined
since 1720, but have been largely depleted. Now most lead
and zinc mined in Missouri comes from Mississippian-age
sedimentary rocks.
The Silurian Clinton Formation crops out from Alabama
north to New York, and equivalent rocks are found in New-
foundland. This formation has been mined for iron in many
places. In the United States, the richest ores and most exten-
sive mining occurred near Birmingham, Alabama, but only a
small amount of ore is currently produced in that area.
Petroleum and natural gas are recovered in commer-
cial quantities from rocks ranging in age from the Devonian
through Permian. For example, Devonian rocks in the Michi-
gan Basin, Illinois Basin, and the Williston Basin of Montana,
South Dakota, and adjacent parts of Alberta, Canada, have
yielded considerable amounts of hydrocarbons. Permian reefs
and other strata in the western United States, particularly
Texas, have also been important producers.
Although Permian coal beds are known from several
areas, including Asia, Africa, and Australia, much of the
coal in North America and Europe comes from Pennsylva-
nian (Upper Carboniferous) deposits. Large areas in the
Appalachian region and the midwestern United States are
What Would You Do
You are the geology team leader for an international mining
company. Your company holds the mineral rights on large
blocks of acreage in various countries along the west coast of
Africa. The leases on these mineral rights will expire shortly,
and you've been given the task of evaluating which leases are
the most promising. How do you think your knowledge of Pa-
leozoic plate tectonics can help you in these evaluations?
underlain by vast coal deposits (
Figure 20.29). These coal
deposits formed from the lush vegetation that fl uorished in
Pennsylvanian coal-forming swamps (Figure 20.18).
Much of this coal is bituminous coal, which contains
about 80% carbon. It is a dense, black coal that has been so
thoroughly altered that plant remains can be seen only rarely.
Bituminous coal is used to make coke, a hard, gray substance
made up of the fused ash of bituminous coal. Coke is used to
fi re blast furnances for steel production.
Some Pennsylvanian coal from North America is
anthracite, a metamorphic type of coal containing up to
98% carbon. Most anthracite is in the Appalachian region
(Figure 20.29). It is especially desirable because it burns
with a smokeless flame and yields more heat per unit vol-
ume than other types of coal. Unfortunately, it is the least
common type—much of the coal used in the United States
is bituminous.
Figure 20.29 Distribution of Coal Deposits in the United
States The age of the coals in the midwestern states and the
Appalachian region are mostly Pennsylvanian, whereas those in
the West are mostly Cretaceous and Cenozoic.
 
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