Aeroradioactivity Survey and Areal Geology of the Savannah River Plant Area, South Carolina and Georgia (ARMS-I) Page: 29

                                
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having been derived from the older formations .

6.   DETAILED DISTRIBUTION OF AERORADIOACTIVITY
A large range in the gamma aeroradioactivity, from 150 to 2100
cps, was found in the Savannah River Plant area. Although some of the
radiation may be due to a uniform blanket of fallout, the great range
described here and shown on the 1:250,000 map is almost certainly due
to natural variations in the surficial materials and the radiation
measured is regarded as derived from natural sources. The aeroradio-
activity within the Savannah River Plant reservation is shown in Fig.
12 and discussed in Sec. 6.3.
The highest natural radiation measured occurred in the Piedmont
Province, and the Piedmont is generally more radioactive than the
Coastal Plain, but the total range in aeroradioactivity is great in
each, 250 to 2100 cps over the Piedmont and 150 to 1300 cps over the
Coastal Plain. In the southeastern Coastal Plain there are many areas
of wooded swampland in which the shielding effect of standing water
under the trees reduced the measured radiation to 50 or 100 cps.
6.1 Distribution of Radioactivity Relative to Geology in the Piedmont
The areas of lowest aeroradioactivity in the Piedmont are under-
lain by rocks of the Carolina slate belt and of the highest aeroradio-
activity by granites and highly metamorphosed sedimentary rocks. The
aeroradioactivity of the slate is generally low, and locally, where
the slate is bounded by a granite or other more radioactive rock, the
line of radioactivity change is an accurate trace of the geologic
contact. The slate belt-granite contact in an area in Lexington
County, S. C., is shown in Fig. 7. In this same illustration the
radioactivity measured over the granite also contrasts with that mea-
sured over the Coastal Plain. Although the sinuous contact between
the granite and the overlapping Tuscaloosa formation could not be
delineated with data from flight lines spaced 1 mile apart, a good
break in level appears on many profiles where the contact is crossed.
In Saluda and Edgefield Counties, S. C., a large area of the
Carolina slate belt was covered by the survey. The slate was found in
the field reconnaissance to be of generally uniform composition and
metamorphic grade but the aeroradioactivity survey indicates a zoning
that parallels the regional strike of the slate belt. Fig. 8 shows
part of this area divided into three general zones. Zone 1 ()00 to
550 and 400 to 600 cps) occurs in two main belts. Zone 2 (300 to 400
cps) is roughly 3 miles wide and lies between the belts of zone I.
The large southward bulge in the zone 1-zone 2 boundary near the cen-
ter of Fig. 8 is controlled by the data of only one flight line (there
is another similar bulge just outside the area of Fig. 8 on the west).
As the radiation measured in zone 1 is not greatly different from that

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