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the metamorphic complex could be found. The highest natural gamma radioactivity measured in the airborne survey was 2100 cps which was recorded over the complex in western Columbia County, Ga. A nearby area of 1900 cps was checked on the ground with a hand counter which showed a range of 0.03 to 0.1 mr/hr, averaging about 0.05 mr/hr. The Coastal Plain is generally less radioactive than the Piedmont but a great range in aeroradioactivity was recorded. The older Coastal Plain formations (those farthest from the ocean, the Upper Cretaceous and Eocene) are the most radioactive and generally range from 400 to 800 cps. Many areas in Lexington and eastern Aiken Counties, S. C., mostly containing Upper Cretaceous rocks, are much higher in radioactivity and range from 700 to 1300 cps. The younger Coastal Plain formations, Miocene through Pleistocene, are the least radioactive in the Savannah River Plant area and generally range from 300 to 600 cps. 4. GEOLOGY OF THE PIEDMONT The metamorphic complex occurs in two parts of the area studied, in the northernmost corner of the area north of Lake Murray (Fig. 6), and in a belt trending nearly parallel to the Fall Line. A small part of the southern belt is covered by overlapping younger Coastal Plain rocks in Georgia, but in South Carolina it is largely covered by these rocks. The southeast edge of this belt of the metamorphic complex is exposed where larger stream valleys have been cut through the Coastal Plain. The metamorphic complex consists mostly of schist and gneiss with many small bodies of granite and gneissic granite. There are in- clusions of argillacous rock similar to that of the Carolina slate belt and earlier reports have mentioned occurrences of quartzites. Dark mafic rocks occur in many places and two prominent hills in northeastern Columbia County, Ga., are underlain by serpentine. No attempt was made to subdivide the complex because the units of which it consists (schist, gneiss, and intrusive granite) all occur inti- mately associated over the entire area in which the complex is found. Several areas formerly mapped as granite plutons in the complex10 were found to include large amounts of schist and paragneiss and are here considered part of the complex. Some of the highly metamorphosed rock has probably been derived by metamorphism of the Carolina slate belt, although some of the complex is probably older than the Carolina slate belt. The slate, schist, and part of the gneiss of the metamorphic complex are steeply inclined, intensely folded, and intruded by small masses of igneous rock, particularly granite. Rocks of the Carolina slate belt occur in two major zones which extend across the entire Savannah River Plant area. One is between the two areas of the metamorphic complex described above and is ex- tensively exposed from Lake Murray to Clark Hill Reservoir and the
Map with graded color shading to show levels of naturally-occurring gamma aeroradioactivity within the Savannah River Plant Area, South Carolina and Georgia, along with explanatory text. Scale 1:250,000.
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Schmidt, Robert G.Aeroradioactivity Survey and Areal Geology of the Savannah River Plant Area, South Carolina and Georgia (ARMS-I),
report,
December 1960;
Washington D.C..
(https://digital.library.unt.edu/ark:/67531/metadc13012/m1/24/:
accessed May 24, 2024),
University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu;
crediting UNT Libraries Government Documents Department.