The production of sand and gravel from its deposits may be a relatively
simple operation or one of considerable complexity. Gravel for surfacing
a road may be dug from a conveniently located pit and loaded
mechanically into trucks that haul it to the road. A large sand- and
gravel-producing operation, however, may include not only mechanical
equipment to load and transport the material but also a processing plant
where it can be washed if necessary and screened to various sizes.
In a “dry pit” operation, mechanical cranes or shovels pick up the
gravel and sand and load it into trucks, railroad cars, or conveyor
belts to be transferred to the processing plant. There clay and dirt may
be washed out and the sand and gravel is sized by screens. Conveyor
belts carry sand and gravel to the various processing operations and to
storage bins or piles on the ground.
A “wet pit” operation produces sand and gravel from an artificial pond
or lake. In some operations the sand and gravel is mined by a dredge
that floats on the water (fig. 19). In some pits, a stream of water is
directed from the dredge against the bank of gravel to wash the gravel
into the lake. A large metal pipe at the front of the dredge slants down
into the water and sucks up the sand and gravel from the underwater part
of the deposit. The gravel, sand, and water is then pumped through a
pipe at the rear of the dredge to the processing plant on the shore.
In some types of wet pit operations a large scoop or bucket operated
from a crane on the shore, or by cables fastened to the shore, is used
to dig sand and gravel from beneath the water.
Dredges are used to pump up sand and gravel from the beds of Illinois
rivers, especially the Mississippi, Ohio, and Wabash.
The sand and gravel resources of many parts of the state have been
mapped and studied by the Illinois Geological Survey, and work of this
kind is continuing.
SILICA (TRIPOLI) AND OTHER MINERAL MATERIALS OF EXTREME SOUTHERN
ILLINOIS
The hills of extreme southern Illinois contain several mineral materials
that are entirely or largely restricted, in important quantities, to
that part of the state. Some of them, such as silica and novaculite,
come directly from bedrock deposits of great age; others, such as some
of the sands and gravels, are of more recent origin.