Michelle Rogers is an English major from Lee County, Georgia
Du Pont has been involved in the
mining of various minerals in Florida in such places as the Trail
Ridge. Minerals which have been mined are titanium minerals such
as ilmenite, leucoxene, and rutile.
Since the turn of the century,
eight companies have mined heavy minerals in the United States.
Heavy minerals are the weathering-resistant minerals with specific
gravities of three or greater which are usually associated with
fossil beach sands, alluvial flood plains, and recent shorelines.
Major heavy mineral deposits are located along the eastern coastal
plain in New Jersey, the Carolinas, Georgia, Florida, and the
Mississippi embayment of Tennessee.
The Trail Ridge deposit was discovered
by Du Pont geologists in cooperation with the U.S. Bureau of Mines
and the Florida Geological Survey. The Trail Ridge orebody is
the largest known deposit of heavy minerals in the Atlantic-Gulf
Coastal Plain. The minerals occur under the southwest portion
of the ridge in a narrow band about one mile wide and eighteen
miles long along the Clay-Bradford County line. This deposit
is believed to have formed at the height of a transgressing sea.
The part of the Trail Ridge deposit being worked by Du Pont ranges
from twenty-five to seventy feet deep and the heavy minerals compose
about four percent of the sands. Other known deposits of heavy
minerals are near Yulee, north and south of Brunswick, Georgia,
Cumberland Island, and the Sea Island Chain. However, it is not
possible to mine the Georgia islands because they are either too
populated or they are not mineable for ecological reasons.
During World War I, Henry H. Buckman
and George A. Pritchard discovered ilmenite and other heavy minerals
along the northeastern coast of Florida. Production began in
1916 by a company named Buckman and Pritchard, Incorporated.
In the beginning, only ilmenite was recovered from the sands,
but later when zircon and rutile began to be used these minerals
were also recovered. Production from this mining expedition reached
a peak in 1927 and was discontinued completely in 1929. There
were no U.S. companies mining heavy minerals between 1929 and
1939 due to the depression.
After World War II, Du Pont geologists
began explorations to find a domestic source of ilmenite so the
Du Pont Pigments Department would not have to rely on foreign
ore supplies. In December, 1947, Du Pont began a long-term lease
agreement with the State of Florida Armory Board to mine and separate
heavy minerals from the Trail Ridge deposit within the boundaries
of Camp Blanding, Clay County, Florida. The plant was constructed
in 1948, was started in 1949, and was taken over by Du Pont in
1958. Du Pont designed and built a second plant just northeast
of Lawtey, Florida, on the Trail Ridge deposit and only fifteen
miles away from the first plant. This new plant, known as the
Highland Plant, started up in 1956. The first titanium metal
was produced by Du Pont in 1948 and the publicity of this interested
others, therefore increasing the demand for new deposits of high
grade titanium ores.
Yulee is also a great focus for
heavy mineral mining. These heavy mineral sand deposits are located
a few miles east, northeast, and north of the town of Yulee in
northeastern Florida. The deposits cover around five thousand
acres and are on the southern side of the St. Marys River, which
divides Georgia and Florida. These heavy mineral sand deposits
where supposedly first discovered in the early 1950s by Joseph
L. Gillson during his heavy mineral studies of the Coastal Plain.
The Yulee concentrations of heavy minerals occur in low ridges
composed mainly of quartz sand. The most abundant heavy minerals
in the deposits are ilmenite, zircon, epidote, rutile, sillimanite,
stautolite, leucoxene, tourmaline, kyanite, and hornblende. Of
these ilmenite, leucoxene, rutile, and zircon are the most important
ore minerals.
All of the heavy mineral orebodies
which have been mined in northern Florida have been parts of ridges
formed along shorelines. For example, Trail Ridge can be cited
as an example of a beach ridge built at the crest of an eroding
transgressing sea. The Yulee ridges formed as part of the Pamlico
barrier island of the Pleistocene age. These heavy mineral concentrations
in the ridges of the Pamlico barrier island accumulated in a downdrift
direction from a point where the St. Marys River entered the Atlantic
Ocean.
In the mining process, dredges
are used to mine the ore and gravity concentrates are then used
to separate out the heavy minerals and reject the quartz tailing.
Du Pont and Green Cove Springs wet mills float on the same pond
as the dredge, but the ASARCO wet mill is on permanent land.
Heavy mineral concentrates are pumped to the dry mills. The sands
often contain grains which are coated with other materials and
these impurities are removed through attrition scrubbing with
caustic just before dry milling. The gravity concentrates are
mixtures of titanium minerals, quartz, and heavy mineral silicates.
The concentrate is then dried and the conducting titanium minerals
are separated from the other products by high tension separators.
Next the titanium minerals are separated from each other through
magnetic means. After the titanium minerals are removed, the
remaining particles must be further treated to produce staurolite,
zircon, aluminum silicates, and monazite. The titanium minerals
are removed first. Then, at Du Pont, the remaining heavy minerals
are fed to high intensity electromagnets that remove staurolite.
This is the magnetic product. The nonmagnetic materials are
then pumped to spirals that concentrate the zircon and aluminum
silicates. The zircon concentrate is heated to 1100 degrees Fahrenheit
and then cleaned by high tension and electromagnetic separation.
The aluminum silicates are treated much the same way.
Garner, Thomas E. "Heavy
Minerals Industry of North America." International Congress:
29-42.
Pirkle, E. C. "The Yulee
Heavy Mineral Sand Deposits of Northeastern Florida."
725-737. |