The Irwinton district is in the central part of Georgia at the inner margin
of the Coastal Plain province. The oldest rocks exposed in the district are
crystalline rocks of the Piedmont province. They are unconformably overlain
by nonmarine sedimentary strata of Late Cretaceous age, including gravel,
micaceous sand, and lenses of kaolin.
Bauxite has been found in a few of the kaolin lenses near the top of the
sequence of these strata. During a long period prior to deposition of the over-
lying marine beds of the Claiborne and Jackson Groups (middle and upper
Eocene), the Upper Cretaceous strata were subjected to subaerial erosion.
The bauxite deposits are considered to have formed during this period. They
range in thickness from a few inches to more than 10 feet and occupy areas
ranging from a few square feet to more than 5 acres. Most of the known
bauxite deposits lie along the valleys of Commissioners Creek and Big Sandy
Creek in Wilkinson County. The kaolin lenses are much larger than the
bauxite deposits; some of the lenses underlie more than 200 acres and are
more than 20 feet thick.
Bauxite was discovered in the district in 1907 and was mined from 1910 to
1928. A few additional carloads of ore were shipped in 1941 and 1942, but
no ore has been mined since that time. Reserves of high-grade bauxite are
very small. Reserves of all grades of bauxite plus bauxitic clay may be about
400,000 long tons.
The Irwinton district is the principal source of high-grade kaolin in the
United States. The presence of kaolin here has been known since early colo-
nial time, and it has been mined continuously since 1897. Production in 1959
was 1,940,279 short tons. The reserves of kaolin are very large but have never
been adequately measured. Reserves of first and second grade kaolin may be
67 to 84 million short tons. Kaolin of lower grade is present in larger quantity.
