Stratigraphy, structure, and seismicity in slate belt rocks along the Savannah River

STRATIGRAPHY, STRUCTURE, AND SEISMICITY IN SLATE BELT ROCKS ALONG THE SAVANNAH RIVER
compiled by T. M. Chowns


~

~

GGS

1881

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Printed by the Georgia Geological Survey for the Georgia Geological Society's 11th Annual Meeting and Field Trip
GUIDEBOOK 16
Atlanta 1976

For convenience in selecting our reports from your bookshelves, they wilJ be color-keyed across the spine by subject as follows:

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Valley & Ridge mapping and structural geology Piedmont & Blue Ridge mapping and struc-
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Colors have been selected at random, and will be augmented as new subjects are published.

STRATIGRAPHY, STRUCTURE, AND SEISMICITY IN SLATE BELT ROCKS ALONG THE SAVANNAH RIVER
compiled by X, M. Chowns ------
Printed by the Georgia Geological Survey for the Georgia Geological Society's 11th Annual Meeting and Field Trip
Atlanta 1976

Georgia Geological Society Atlanta, Georgia

Officers 1975-76

President President-Elect Secretary Treasurer

- Sam Pickering - Tim Chowns - Bruce O'Connor - Eric Eslinger

Officers 1976-77

President

- Tim Chowns

Field Trip Committee
Tim Chowns - Chairman Bob Carpenter Eric Eslinger Bruce O'Connor Charlotte Abrams Barbara Rassmann

CONTENTS Page

INTRODUCTION by T.M. Chowns

2

GENERAL GEOLOGY OF THE CAROLINA SLATE BELT ALONG THE

GEORGIA-SOUTH CAROLINA BORDER by R.H. Carpenter

9

THE LINCOLNTON METADACITE by Travis A. Paris . . .

13

GEOLOGIC SECTION ACROSS THE MODOC FAULT ZONE, MODOC,

SOUTH CAROLINA by David E. Howell and William A. Pirkle . . . . .

16

THE GEOLOGY OF THE BELAIR FAULT ZONE AND BASEMENT ROCKS OF THE AUGUSTA, GEORGIA AREA by Bruce J. O'Connor and David C. Prowell . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . 21

GRAVITY AND SEISMIC STUDIES IN THE CLARK HILL RESERVOIR AREA

by Leland T. Long, Harry E. Deman, Helmut Y. Hsiao, and George E. Marion.

33

GRAVES MOUNTAIN by M. Eugene Hartley, III

42

ROAD LOG, FIRST DAY .

54

ROAD LOG, SECOND DAY

71

ii

ILLUSTRATIONS Page

Figure 1. Portion of the geologic map of Georgia

1

Figure 2. Geologic belts along the Savannah River north of Augusta . . . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 3. Geologic cross section along the Savannah River north of Augusta . . . . . . . . . . . . . . . . . . . 5

Figure 4. Generalized geologic map of the eastern Piedmont along the Savannah River, South Carolina and Georgia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 5. Metamorphic facies across the Modoc Fault zone in South Carolina east of the Clark Hill Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 6. Regional geologic map of the area west of Augusta, Georgia showing the extent of Coastal Plain and Piedmont rocks, and the Belair Fault zone . . . . . . . . . . . . . 22

Figure 7. Geologic map of the Belair clay pit area showing Coastal Plain rock, the Belair Fault zone, peat deposit and trench location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 8. Northeast view across Belair Fault exposed in a gulley at north end of Belair clay pits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 9. Generalized view of the trench acros:; the Belair Fault zone at the south end of the Belair clay pits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 10. Simple Bouguer anomaly map of the Clark Hill Reservoir area . . . . . . . . . . . . . . . . . . . . . 34

Figure 11. Regional Bouguer gravity anomalies of Georgia and South Carolina . . . . . . . . . . . . . . . . . 35

Figure 12. Index map showing relation of gravity to seismic recording sites, epicenters, and modeled profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 13. Profile AA' showing model used to explain Bouguer anomalies and hypothetical geological structure based on gravity model . . . . . . . . . . . . . . . . . . . . . . . . . 38

Figure 14. Portion of topographic map showing Graves Mountain and vicinity . . . . . . . . . . . . . . . . . 42

Figure 15. Oblique aerial photograph of Graves Mountain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Figure 16. Schematic cross sections illustrating proposed origin of the Graves Mountain kyanite quartzite deposit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Figure 17. View of West Mountain pit showing benches characteristic of open pit mining methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Figure 18. Photograph showing crusher belt, conical mill stockpile, and belt to surge bin at the mill. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Figure 19. Location map showing field trip route and numbered stop locations . . . . . . . . . . . . . . . . . 53

Figure 20. Fault in argillite showing rotation of bedding and axial plane cleavage . . . . . . . . . . . . . . . . 57

iii

Page Figure 21. Small thrust fault in argillite showing rotation of bedding and cleavage . . . . . . . . . . . . . . . 58
Figure 22. Photo of outcrop on NE side of cloverleaf at junction of I-20 and Bobby Jones Freeway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Figure 23. Areal photo of the Belair clay pits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Table 1. Table 2.

TABLES Page
Radiocarbon dates from peat lens and carbonaceous grey clay lenses . . . . . . . . . . . . . . . . . 26
Microearthquakes in the southern part of the Clark Hill Reservoir area . . . . . . . . . . . . . . . 40

iv

BLUE RIDGE AND PIEDMONT CRYSTALLINE ROCKS

MAFIC TO INTERMEDIATE

vl

METAVOLCANIC ROCKS

METADA CITE

. . .,. .--',. I] v3 FELS I C META VOLCANI CS

UNDIFFERENTIATED

1 METAVOLCANICS/ SERICITE

v4

PHYLLITE/ META-ARGILLITE /

QUARTZ MICA SCHIST

META-ARGILLITE /SERICITE
I ____:____ PHYLLITE / META VOLCANICS

AMPHIBOLITE/ GABBRO

mp2 GABBRO
DIABASE
GRANITE UNDIFFERENTIATED
GRANITE/ GNEISSIC BIOTITE GRANITE

POI-tPHYRITIC GRANITE

GRANITE GNEISS / AMPHIBOLITE

GRANITE GNEISS/ GRANITE

~ ~

BIOTITE GNEISS/ FELDSPATHIC BIOTITE GNEISS

BIOTITE GRANITE GNEISS/ FELDSPATHIC BIOTITE
GNEISS /AMPHIBOLITEHORNBLENDE GNEISS

~ BIOTITIC GNEISS/MICA
~ SCHIST I AMPHIBOLITE
BlOTITIC GNEISS/ AMPHIBOLITE: .
BIOTITE GNEISS
HORNBLENDE GNEISS / AMPHIBOLITE
HORNBLENDE GNEISS/ AMPHIBOLITE/ GRANI'rE GNEISS
AMPHIBOLITE/EPIDOTE QUARTZITE/ GRANITE GNEISS
AMPHIBOLITE/ BIOTITIC GNEISS/ QUARTZ SERICITE SCHIST
META-ARGILLITE/ PHYLLITE
SILLIMANITE SCHIST /GNEISS

E

GRAPHITE SCHIST SERICITE SCHIST

SERICITE SCHIST /MICACEOUS QUARTZITE /SERICITE PHYLLITE
QUARTZ MICA SCHIST I HORNBLENDE SCHIST/ BIOTITIC GNEISS
~ QUARTZITE/MICA SCHIST

Figure 1. Portion of the geologic map of Georgia (Georgia Geological Survey, 1976).

INTRODUCTION

T. M. Chowns Department of Geology
West Georgia College Carrollton, Georgia 30117

Ten years have elapsed since Crawford, Hurst and Ramspott led the Southeastern Section of the Geological Society of America on a field trip to examine extrusive volcanics and associated dike swarms in central-east Georgia (Crawford, et al., 1966). The trip came as the culmination of three years of mapping in the central Savannah River area, the first detailed mapping to be carried out in that part of the state (Hurst, et al., 1966), and a major contribution towards the new Geologic Map of Georgia (Georgia Geol. Surv., 1976). This year the Georgia Geological Society returns to the same area to r~-~xamine this southeastern-most portion of the Georgia Piedmont, and to review some recent work which has followed in the wake of the original work of Hurst and associates. The papers which follow provide complementary information to that published in the original guidebook.
Regional Settin_g_

The field trip will examine Piedmont rocks on both sides of the Savannah River, in Georgia and South Carolina, between Lincolnton and McCormick in the north and Augusta in the south. This entire area is predominantly a metamorphic terrane but with rocks belonging to two different suites:
1. Low grade metasediments and metavolcanics of the Carolina slate belt. 2. High grade schists and gneisses of the Charlotte belt. These represent the most southeasterly components of the southern part of the exposed Appalachian orogen and are overlapped at the Fall Line by sedimentary rocks of the Coastal Plain Province (see table).

Geologic belts of the Carolina and Georgia Piedmont southeast of the Brevard zone with correlations as proposed by Hatcher, 1972.

Carolinas

Georgia

INNER PIEDMONT Kings Mountain CHARLOTTE Carolina slate belt

DADEVILLE Wacoochee UCHEE, KIOKEE Little River, Belair belts

High grade migmatitic belts are indicated by UPPER CASE, low grade non-migmatitic belts by lower case.

Slate Belt Rocks
The majority of stops on the field trip will be in rocks of the Carolina slate belt or Little River Sequence I, as they are referred to in Georgia (Crickmay, 1952). These rocks consisted of felsic to mafic. volcanics and volcaniclastics with associated terrigenous sediments, which were generally metamorphosed to greenschist facies, although in places they reached the lower amphibolite facies.
Crickmay (1952) originally recognized three separate parallel belts occupied by the Little River Sequence, and these show up clearly on the new state geologic map (F!g. 1). Proceeding from north to south, these are the northern Little River belt, southern Little River belt and Belair belt (Fig. 2). Each

1 The term Sequence is used in preference to Crickmay's "Series" because of the time-stratigraphic

connotation of the latter.

2

UCHEE

SOUTH CAROLINA

KIOKEE

0
I
0

j

. ' tp Mllea
'10 ICII_.,.

~ Slate belt rocks
D Coastal Plain

~. Porphyritic granite

/

Fault

Figure 2. Geologic belts along the Savannah River north of Augusta. 3

of these belts may be traced into South Carolina from the generalized geologic map of Overstreet and Bell (1965 ), although there is poor agreement in the case of the northern belt. At first, it appears that this northern belt may be equated with the Kings Mountain belt of the Carolinas, but recent work by Griffin (1972) indicates that the latter is sheared out at the Georgia Line.
Charlotte Eili...H&cl_{L
In Georgia, the rocks of the Charlotte belt were referred to as the Uchee and Kiokee belts by Crickmay (1952). They consist of high grade schists, gneisses and migmatites of amphibolite facies. Although only one stop is scheduled in these rocks, they are important to an understanding of the overall regional setting.
The precise relationship between these rocks and the slate belt rocks is uncertain. There are several possibilities.
1. They may be stratigraphically equivalent rocks of higher metamorphic grade. 2. They may be stratigraphically older rocks occupying the centers of regional anticlinoria, in which
case the difference in metamorphic grade suggests an unconformity at the contact. 3. Where major faults or shear zones occur it is possible that the rocks on either side belong to
totally different tectonic units und urc therefore unrelated stratigraphically or structurally. 4. Since the slate belt-Charlotte belt boundary is poorly defined, it is possible that a combination of
relationships is involved. The consensus of opinion favors possibility four, although it appears that rocks of the Uchee belt in southeast Georgia may be in large part stratigraphically equivalent to the slate belt while the Kiokee rocks are probably older and may be part of a different tectonic element since they are bounded on both the north and south by shear zones. It is important to remember that until such a time that geologic mapping has proceeded to the extent where it is possible to distinguish stratigraphic, metamorphic facies and tectonic boundaries, the belts of the Piedmont are of descriptive convenience only.
The Itinerary
The first day of the field trip will consist of a traverse across the southern part of the Little River belt, the Kiokee and Belair belts (Fig. 3 and 4). There Will be opportunity to see a variety of slate belt lithologies, including metamorphosed volcanics, volcaniclastics and terrigenous clastics of greenschist facies as well as equivalent rocks of amphibolite facies close to the boundary with the Kiokee belt. Special attention will be given to a discussion of faulting and seismicity in these rocks.
Most important of the faults in the area is the Modoc Fault, a zone of intense shearing and cataclasis which occurs at the boundary between the Little River and Kiokee belts. According to Howell and Pirkle, who will lead this part of the trip, this fault is continuous from Alabama, where it is known as the Goat Rock Fault, into North Carolina, and is thus one of the major structural features of the southern Piedmont. Further south, in the vicinity of Augusta, O'Connor and Prowell will demonstrate spectacular evidence of Cenozoic faulting where Piedmont Rocks are thrust over Coastal Plain sediments along the Belair Fault.
Recent work at Belair indicates that part of the movement on this fault has occurred within the last 2000 years and thus raises the question of whether this and other faults in the area may not be seismically active at the present. A number of macroseismic and microseismic events have been recorded further north in the Clark Hill Reservoir area, but Long and co-workers conclude in this guidebook that there is insufficient evidence to positively connect this activity with any known fault. Dr. Long will be on hand during the field trip to discuss the evidence of historic seismicity.
The second day's trip will be centered around Lincolnton, where Carpenter and Paris will demonstrate a stratigraphic succession in the type area of the Little River Sequence. The area is especii:tlly significant for the rare insight it allows into volcanism and sedimentation in a Paleozoic island arc in the southern Piedmont. Because of the low metamorphic grade, original sedimentary and volcanic textures and structures are well preserved.
Associated with these volcanic rocks are a number of economic deposits, particularly gold, sulphides, and kyanite. Most important of these is the kyanite quartzite at Graves Mountain which will be visited at the conclusion of the trip. According to Hartley, the origin of this body may be explained by exhalative volcanic reactions within the island arc pile.
4

LITTLE RIVER BELT

MODOC

~

FAULT

..J
1&.1

ZONE

m

KIOKEE BELT

BELAIR BELT
8) (1

01
NW
EXPLANATION

I~/ ' I-::_\ / ....,
"'J,.,. /,
~

Upper Sedimentary Sequence
Felsic Pyroclastic Sequence
Lincolnton Metadacite

')( )C
,..X )( )(

0 M//u

3

Cataclastlc Schists & Gneisses
Belair Phyllites

::::::::?)/-

.. ... . ~

~ 0 ~

lJI ,.
.. " )( )(

Coastal Plain Sediments Granite
High Grade Charlotte Rocks

Figure 3. Schematic cross section along the Savannah River. Numbers refer to field trip stops at the end of this guidebook. Belt boundaries are after Figure 2. Geology is modified from Figure 4.

Slate Belt Rocks Little River Belt
Upper sedimentary sequence with local mafic volcanic zones

Felsic pyroclastic sequence

Lincolnton metadacite

Modoc Fault Zone

W

Cataclastic sericite and muscovite schists with local mafic zones

Subdivided in South Carolina into

Sericite Schist

Mylonite gneiss

Muscovite button schist

Belair Belt
~ Undifferentiated metasediments and metavolcanics

Charlotte and Kiokee Belt Rocks
Biotite granite gneiss and other high grade metamorphic rocks
Granite - massive and gneissic
Coastal Plain sediments undifferentiated
Amphibolite and hornblende gneiss (on west) ultramafic rocks (on east)

Figure 4. Generalized geologic map of the eastern Piedmont along the Savannah River, South Carolina and Georgia. Geology by R. H. Carpenter, D. E. Howell, W. A. Pirkle, B. J. O'Connor, and D. C. Prowell modified after the Geologic Map of Georgia (Georgia Geological Survey, 1976) .
6

I
At

0

I ' '

0

5 Kilometers

7

In the pages which follow, the field trip leaders develop the variousthemesof stratigraphy, structure and seismicity in the field trip area at greater length.
REFERENCES
Crawford, T.J., Hurst, V.J., and Ramspott, L.D., 1966, Extrusive volcanics and associated dike swarms in central-east Georgia: Guidebook for field trip 2, Southeastern Section, Geol. Soc. Amer., 1966, 53 p.
Crickmay, G.W., 1952, Geology of the crystalline rocks of Georgia: Georgia Geol. Surv., Bull. 58, 56 p. Georgia Geological Survey, 1976, Geologic map of Georgia: Dept. of Natural Resources; Atlanta,
Georgia. Griffin, V.S., Jr., 1972, Progress report on a geologic study in Abbeville and McCormick Counties,
South Carolina, South Carolina Div. Geol., Geology Notes, v. 16, p. 59-78. Hatcher, R.D., Jr., 1972, Developmental model for the southern Appalachians: Geol. Soc. Amer. Bull.,
v. 83, p. 2735-2760. Hurst, V.J., Crawford, T.J., and Sandy, J., 1966, Mineral resources of the central Savannah River area,
v. I: Central Savannah River Area Planning and Development Commission, Augusta, Georgia, 467 p. Overstreet, W.C., and Bell, H., III, 1965, The crystalline rocks of South Carolina: U.S. Geol. Surv. Bull.
1183, 126 p.
8

GENERAL GEOLOGY OF THE CAROLINA SLATE BELT
ALONG THE GEORGIA- SOUTH CAROLINA BORDER
R. H. Carpenter Department of Geology University of Georgia Athens, Georgia 30602
Introduction
This section briefly summarizes the status of the geologic knowledge of a portion of the Carolina slate belt along the South Carolina-Georgia boundary. Termed the Little River belt in Georgia, this sequence consists mainly of volcanic and volcaniclastic rocks with an aggregate thickness which is probably in excess of 15,000 feet. The area is of geologic interest for several reasons.
Since the 1800's, a number of earthquakes have been recorded, including one near Lincolnton, Georgia in 1875 with an intensity of VI (Modified Mercalli Scale). Several earthquakes of lesser magnitude have occurred since 1970, and these are currently being studied by seismologists at the Georgia Institute of Technology and the University of South Carolina (see Long, L.T., et al., in this guidebook). In recent years several important faults have been delineated, and the possible relationships between these various faults and the earthquake activity is of considerable interest. Most important is the Modoc Fault located at the southeastern boundary of the slate belt (see Howell, D. E., and Pirkle, W.A. in this guidebook).
Because of the complex structure of the area, stratigraphic relationships had not been previously determined, but in the past three years, detailed mapping has provided a stratigraphic framework that serves as a basis for interpreting the geologic history of a portion of the island-arc system that existed in the area in the early Paleozoic. It now appears that the Lincolnton, Georgia - McCormick, South Carolina area was one of the principal centers of felsic volcanism in the ancient volcanic belt and served as a source of pyroclastic sediments for hundreds and possibly several thousands of square miles.
The area is also of interest because of the various metallic and non-metallic mineral deposits which have been mined from this section of the slate belt. The principal mineral commodity currently being produced is kyanite from Graves Mountain in Lincoln County, Georgia, the second largest kyanite mine in the world (see Hartley, M.E., in this guidebook). In the late 1800's and early 1900's, gold and copper were mined from the area, the most productive mines being the Magruder mine in Wilkes County, Georgia, the Dom Mine in McCormick, South Carolina, and several mines in the Columbia-Parks district in Georgia near the head of the Little River embayment. Small deposits of manganese were also mined from the area during World Wars I and II.
Previous Work
Prior to 1965, published geologic accounts of the area were mainly restricted to descriptions of mines and mineral localities. Regional maps, such as the "Geologic Map of Georgia" (Georgia Geological Survey, 1939) and "The Crystalline Rocks of South Carolina" (Overstreet and Bell, 1965 a,b) generally categorized the area in "belts", but structural, stratigraphic, metamorphic, and intrusive relationships within the belts were not indicated. More detailed geologic mapping and mineral surveys under the direction of V.J. Hurst were initiated in Georgia in the early 1960's through a government-funded grant to the University of Georgia from the Central Savannah River Area Planning and Development Commission (Hurst and others, 1966). In Lincoln and Wilkes Counties, Fouts (1966) and Crawford (1968 a,b) delineated several important rock units including the Lincol~ton metadacite, while Henry Bell of the U.S. Geological Survey conducted geological and geochemical surveys in McCormick County, South Carolina in the late 1960's. His mapping includes a general map of the McCormick area (Bell, 1973) and unpublished maps of McCormick and Edgefield Counties which are on open-file at the South Carolina Geological Survey.
More recently, Travis Paris (1976) has completed a M.S. thesis at the University of Georgia on the geology of the Lincolnton 71f2 minute quadrangle. His work is particularly significant since he determined the general stratigraphic succession, the style of folding, petrology and petrochemistry of volcanic units,
9

and certain metamorphic isograd relationships. The Woodlawn quadrangle, located immediately south of the Lincolnton quadrangle, is currently being investigated by Tim Pope in his M.S. thesis research at the University of Georgia. Some of this mapping has been incorporated into the new "Geologic Map of Georgia (Georgia Geological Survey, 1976). (Fig. 1)
In addition to the work cited above, the summary of the geological relationships which follows includes information obtained from unpublished studies by Gene Hartley, Susan Fallis, and Jack Knorr, as well as those of the author.
This section briefly summarizes our present knowledge of the stratigraphy, igneous intrusives, metamorphism, and structure of the slate belt along the South Carolina- Georgia boundary.
STRATIGRAPHY
Three sequences of volcanic and volcaniclastic rocks comprise the slate belt in the McCormickLincolnton area. From oldest to youngest these are: 1. Lincolnton metadacite; 2. felsic pyroclastic sequence; and 3. upper sedimentary sequence. Lincolnton Metadacite: This unit is one of the more unique volcanic lithologies in the entire slate belt. It is typically a quartz porphyry, consisting of large phenocrysts of blue, opalescent quartz in a creamcolored matrix of finely crystalline quartz and plagioclase (see Paris, T.A., this guidebook). It is considered to represent a sequence of flows and tuffs which probably exceed 5,000 feet in thickness.
A geochronological study of the Lincolnton metadacite is in progress (Carpenter, Odom, and Hartley). Rb-Sr whole rock analyses and U-Pb analyses of zircon have been completed, and both provide ages between 560-570 million years (Cambrian). Felsic Pyroclastic Sequence: This unit is interpreted to be a time-transgressive sequence of pyroclastic debris derived mainly from the volcanic center represented by the Lincolnton metadacite. The most abundant lithologies are vitric and vitric-crystal tuffs, but other common lithologies include lithic, and lithic lapilli tuffs, agglomerates, welded tuffs, and mafic tuffs. Also present are some felsic and mafic flows, and intercalated sedimentary lithologies which include tuffaceous graywackes, argillites, and cherts. Although felsic rocks predominate, prominent mafic units are also recognized. The average thickness measured in several sections is approximately 3500 feet. Upper Sedimentary Sequence: This sequence consists mainly of banded argillite and thin, interbedded, mafic volcanics, with some graywacke and is the youngest stratigraphic unit recognized in the study area. It occurs most extensively in the large synclinorium that lies immediately west of the Modoc Fault but is also exposed along other synclinal axes to the west. The upper portion of the unit has been removed by erosion so that the total thickness is not known. An estimated minimum thickness is about 5,000 feet.
INTRUSIVE ROCKS
Intrusive rocks within the study area are mainly comprised of dikes and sills. Those exhibiting a distinct metamorphic overprint include metagabbro (sills), metabasalt, meta-andesite, and metarhyodacite. These intrusives tend to be more concentrated in the Lincolnton metadacite and become less abundant in younger sequences, suggesting that they were actually "feeder dikes" to higher level volcanics. The dikes show a pronounced tendency to occur as "swarms", with a dominant trend between N 20W and N 60W. In some areas where extensive exposures are present, up to 40% of the exposure may consist of an intricate network of these intrusives, most less than 15 feet in thickness.
Post-metamorphic dikes include the Triassic-Jurassic diabases which are common throughout the Piedmont province and, in addition, severallamprophyre dikes.
Numerous granitic and gabbroic stocks have been mapped in the high-grade Charlotte belt rocks immediately flanking the study area to the northwest (Uchee belt) and southeast (Kiokee belt). In general, they appear to be post-metamorphic, and geochronological studies of selected plutons indicate ages in the 250-400 m.y. range which are clearly younger than the early Paleozoic volcanics in the slate belt.
10

METAMORPHISM
The slate belt rocks in the study area have been only weakly metamorphosed (greenschist facies) except along the northwestern and southeastern margins where marked metamorphic gradients are recognized. The northwestern margin of the Lincolnton metadacite lies within the abrupt transition from greenschist to amphibolite-grade metamorphism which is the traditional Charlotte belt-slate belt boundary. It is characterized by the recrystallization of the groundmass, development of biotite, and a transition from albite to oligoclase. Immediately northwest of the Lincolnton metadacite, kyanite, cordierite, and sillimanite have been recognized. If the Lincolnton metadacite occupies the core of an anticlinorium, which most recent workers tend to accept, then gneisses and schists occurring to the northwest may actually represent the same volcanic rocks which are present in the slate belt. The rapid increase in metamorphic grade in the southwestern part of the area is superimposed on the Modoc Fault zone and. the rocks immediately southeast of this zone.
Within the Lincolnton Quadrangle, Paris (1976) has defined an axis of low-grade metamorphism between two flanking albite-oligoclase isograds. In this area, it is possible to recognize delicate volcanic features such as shards, amygdules, spherulites, pumice, and devitrified obsidian. In this section, various volcanic lithologies, which are chemically and mineralogically quite similar, can be differentiated on the basis of textures.
STRUCTURE
The low-grade rocks of the slate belt are interpreted by a number of investigators to represent a complex synclinorium flanked by adjacent anticlinoria (the Charlotte belt and Kiokee belt). Within the slate belt, a single generation of vertical isoclinal folds with a gentle plunge to the northeast represents the predominant fold style. In general the folding is tight but becomes more open in the southeastern portion of the belt (Fig. 3 and 4). Along the boundaries of the slate belt in the more intensely metamorphosed rocks, some superimposed folds are evident, but these lose their prominence in the central portion.
The most important fault in the area is the Modoc Fault zone located near the southeastern boundary of the slate belt. It appears that this fault is part of the GDat Rock Fault system which can be traced through the Central Piedmont of Georgia into Alabama. There is also some indication that this fault continues to the northeast into North Carolinaandpossibly Virginia (Howell, 1976), so that it may prove to be one of the major tectonic features of the southern Appalachians.
In addition, the isoclinal folds are transected by a series of northwest trending faults, the greatest concentration of which has been delineated south and west of Lincolnton. One of these faults has been traced for a distance of five miles and displacements in excess of 2500 feet have been determined in certain cases. There are also some local low angle thrust faults with displacements generally less than a few feet.
References
Bell, H., III, 1973, Some results of geochemical sampling in McCormick County, South Carolina: U.S. Geol. Survey Bull. 1376, 22 p.
Crawford, T.J., 1968a, Geologic map of Lincoln County, Georgia: Central Savannah River Area Planning and Development Commission, Augusta, Georgia.
_ _ _ _ _ _ , 1968b, Geologic map of Wilkes County, Georgia: Central Savannah River Area Planning and Development Commission, Augusta, Georgia.
Fouts, J.A., 1966, The geology of the Metasville area, Wilkes and Lincoln Counties, Georgia: unpublished M.S. thesis, University of Georgia, 61 p.
Georgia Geological Survey, 1936, Geologic map of Georgia: Dept. of Natural Resources, Atlanta, Georgia.
1976, Geologic map of Georgia: Dept. of Natural Resources, Atlanta, Georgia.
11

Howell, D.E., 1976, Major structural features of South Carolina; Northeast-Southeast Section Annual Meetings, Abstract with programs, v. 8, no. 2, p. 200.
Hurst, V.J., Crawford, T.J., and Sandy, J., 1966, Mineral resources of the Central Savannah River Area, v. 1-2: Central Savannah River Area Planning and Development Commission, Augusta, Georgia.
Overstreet, W.C., and Bell, H., III, 1965a, The crystalline rocks of South Carolina: U.S. Geol. Survey Bull. 1183, 126 p.
- - - -- - - - - -- -- ' 1965b, Geologic map of the crystalline rocks of South Carolina: U.S. Geol. Survey Misc. Geol. Inv. Map I-413.
Paris, T.A., 1976, The geology of the Lincolnton 7% Quadrangle, Georgia-South Carolina: unpublished M.S. thesis, University of Georgia, 191 p.
12

THE LINCOLNTON METADACITE
Travis A. Paris 5604 Malmsbury Road Knoxville, Tennessee 37921
Introduction
Within the Carolina slate belt of South Carolina arrlGeorgia is a unit of metavolcanic rocks termed the Lincolnton Metadacite. This ellipsoid body of felsic quartz porphyry occurs in central Lincoln County, Georgia, and extends eastward into western McCormick County, South Carolina. Its outcrop area is approximately 17 miles long, stretching from about one-mile southeast of Metasville, Georgia, to about one-half mile west of McCormick, South Carolina. A maximum outcrop width of four and threefourths miles occurs in central Lincoln County near Lincolnton, Georgia.
Earlier workers describe this body as a granite porphyry (Jones, 1909) and as a soda-granite (Peyton and Cofer, 1950). Mapping in the Metasville, Georgia, 7112' quadrangle by Fouts (1966); in Lincoln and Wilkes Counties, Georgia, by Crawford (1968a,b); and in McCormick County, South Carolina, by Bell (1973) outlined the contacts of the body. Concurrent petrographic studies indicated that the major rock type was metadacite (Fouts, 1966). Mapping and further petrologic studies in the Lincolnton, Georgia- South Carolina 7W quadrangle by the author have refined the contacts of the metadacite body and recognized four petrographic subtypes of this metadacite.
1. Porphyritic Coarse-grained Metadacite 2. Porphyritic Fine-grained, Metadacite 3. Fine-grained Metadacite and Granophyric Metadacite (not distinguishable in the field) 4. Gneissic Metadacite
Metadacite Subtypes
PORPHYRITIC METADACITE, FINE GRAINED AND COARSE GRAINED
The major rock type in the Lincolnton metadacite sequence is porphyritic metadacite. Intercalated with it are fine-grained non-porphyritic dacites, minor mafic tuffs, mafic lava flows, and sediments. These rocks, which are metamorphosed from the upper greenschist to lower amphibolite facies, are intruded by metamorphosed mafic and felsic dikes and gabbro sills. These latter rocks are intruded, in turn, by unmetamorphosed lamprophyre, basalt, rhyolite, and Triassic diabase dikes.
The porphyritic metadacites are white to light-pink in overall color and are characterized by elliptical (8-10mm long) blue-gray quartz phenocrysts and saussuritized, blocky plagioclase (An 0 to An 20-25) phenocrysts in a fine to coarse-grained quartz-feldspar matrix. The phenocrysts commonly exhibit a preferred orientation with long axes parallel to the strike of the foliation . This parallelism may represent original flow orientation. Biotite, chlorite, or hornblende are the common mafic accessory minerals and occur in clots. Pseudomorphs of epidote, and biotite or chlorite after a blocky mineral (possibly a pyroxene) are seen in some thin sections. Muscovite and magnetite/ilmenite are additional accessory minerals. The porphyritic metadacites, as well as the fine-grained and granophyric metadacites, exhibit poor foliation.
The porphyritic metadacites yield a tan to red-brown sandy-clay saprolite with a concentration of blue-gray quartz pebbles at the surface. A siliceous hardpan is usually present within and above the saprolite (C Horiz.on). Where possible, float fragments should be used in conjunction with the saprolite because certain siliceous tuffs in overlying formations yield a very similar saprolite.
FINE GRAINED METADACITES
The fine-grained metadacites are characterized by equi-dimensional (1-2mm) grains of quartz and plagioclase in an even finer matrix of quartz, plagioclase, and some muscovite. In some samples of this fine-grained metadacite and a few samples of the porphyritic metadacite, the feldspars are almost completely replaced by epidote, yielding a fine-grained green epidosite with or without quartz phenocrysts.
13

GRANOPHYRIC METADACITES
The granophyric metadacites are white, fine-grained rocks similar to fine-grained dacite in hand specimen. In thin section the rocks are composed of granophyric intergrowths of quartz and plagioclase. In some samples, single grains are granophyric while in others, the granophyric intergrowth has nucleated around a phenocryst, usually quartz.
GNEISSIC METADACITES
The gneissic metadacites are comprised of the above described varieties of metadacite metamorphosed to the amphibolite facies. The rocks are white to tan-colored and exhibit distinct mineral elongations and lineations. Quartz phenocrysts are elongated and smeared. Plagioclase phenocrysts are altered exhibiting hazy borders and biotite is smeared out in black streaks. Hornblende needles, where present, are parallel to foliation. Perthitic microcline occurs only in the gneissic metadacites.
Summary
It is probable that the porphyritic metadacites represent porphyritic lava flows and ash flows, while the fine-grained metadacites are quickly cooled flows or ash flows lacking phenocrysts. The granophyric dacites probably represent shallow sills or recrystallized glassy flows. The gneissic metadacites are the previously mentioned varieties metamorphosed to amphibolite grade.
Chemical analyses of the metadacites have been made by the author; Bell (1973); and Crickmay
(1952). The rocks are soda metarhyolites with Na2o present in greater amounts than K2o. The rocks
are similar petrographically and chemically to the quartz keratophyres of Gilluly (1935). The term metadacite is retained on the basis of petrography and precedence, however, even though it is in conflict with the chemical name.
The sequence of metadacites and subordinate volcanics and sediments has been given informal formational status by the author and called the Lincolnton Metadacite after the town of Lincolnton, Georgia, which is situated within the formation . The type area for the Lincolnton Metadacite is immediately north of Stop 12 along Georgia Highway 220, from the U.S. Highway 378-Georgia Highway 220 intersection (lat. 33 48' 20"N; long 82 24'12"W). Additional reference areas for the formation are: 1. along Aycock Farm Road, from the south bank of Curry Creek (Stop 11) to the north bank of Soap Creek; and 2. along Rowland Road east from Georgia Power Company's high tension lines for 0.7 miles to the creek which flows under the road (Stop 10).
References
Bell, H., III, 1973, Some results of geochemical sampling in McCormick County, South Carolina: U.S. Geol. Survey Bull. 1376, 22 p.
Crawford, T.J., 1968a, Geologic map of Lincoln County, Georgia: Central Savannah River Area Planning and Development Commission, Augusta, Georgia.
1968b, Geologic map of Wilkes County, Georgia: Central Savannah River Area Planning and Development Commission, Augusta, Georgia.
Crickmay, G.W., 1952, Geology of the crystalline rocks of Georgia: Georgia Geol. Survey Bull. 58, 54 p.
Fouts, J.A., 1966, The geology of the Metasville area, Wilkes and Lincoln Counties, Georgia: unpublished M.S. thesis, Univ. Georgia.
Gilluly, J., 1935, Keratophyres of eastern Oregon and the spilite problem, part 2: Am. Jour. Sci. 5th ser., v. 29, no. 1?2, p. 336-352.
14

Jones, S.P., 1909, Second report on the gold deposits of Georgia: Georgia Geol. Survey Bull. 19, p. 59-63; p. 80-102.
Paris, T.A., 1976, The geology of the Lincolnton 7~' quadrangle, Georgia-South Carolina: unpublished M.S. thesis, Univ. Georgia, 191 p.
Peyton, A.L., and Cofer, H.E., Jr., 1950, Magruder and Chambers copper deposits, Lincoln and Wilkes Counties, Georgia: U.S. Bur. Mines, Rept. Inv. 4655.
15

GEOLOGIC SECTION ACROSS THE MODOC FAULT ZONE,
MODOC, SOUTH CAROLINA
David E. Howeli Division of Geology South Carolina State Development Board Columbia, South Carolina
William A. Pirkle University of South Carolina
Aiken Campus Aiken, South Carolina
Introduction
This section presents preliminary results of work currently being conducted by William A. Pirkle and David E. Howell along the South Carolina side of the Clark Hill Reservoir. Pirkle has been conducting detailed mapping in the Carolina slate belt, and Howell has been engaged in regional studies concerning major geologic structures in South Carolina. Earlier work in the area includes generalized geologic mapping in McCormick County (Bell, 1966; Johnson, 1970) and geochemical sampling (Bell, 1973).
The cross-section displayed on this part of the trip begins near Parksville, South Carolina (in argillite of the Carolina slate belt) extends southward across the Modoc Fault zone, and ends in granitic gneisses of the Kiokee belt exposed near the Clark Hill dam. The authors interpret the traverse to lie on the southeast limb of a northeast trending regional synclinorium immediately northwest of the Kiokee anticlinorium so that the rock units increase in age downsection towards the southeast. The Kiokee belt has been interpreted by Overstreet and Bell (1965) to represent a zone of Charlotte belt rocks flanked on both sides by slate belt rocks; in the northwest the Little River belt (specifically the Lincolnton metadacite sequence, See Paris, T.L., this guidebook) and in the southeast the Belair belt.
The boundary between the Little River belt and the Kiokee belt coincides with the Modoc Fault zone (Overstreet and Bell, 1965; Johnson, 1970) which may be traced northeastwards from Modoc, South Carolina to Lake Murray near Columbia, South Carolina. Recently, Daniels (1974) has shown on the basis of geophysical data that the fault extends southwestwards at least 20 miles (32 km) into Georgia, and Howell (1976) believes it may be contiguous with the Goat Rock Fault in the west Georgia Piedmont.
The Modoc Fault zone coincides with a rapid increase in metamorphic grade which is evident along the traverse; north of Modoc, the slate belt rocks belong to the lower greenschist facies while to the south they are of the amphibolite facies (Fig. 5).
Major rock types to be s~en along the traverse include argillite, quartz-sericite schist, mylonite gneiss button schist, and granitic gneiss (Fig. 4).
Rock Types
ARGILLITE
Argillite outcrops in a belt roughly 5 miles (8 km) in width that trends approximately N 65E. The most common rock types within the unit are argillite, tuffaceous argillite, tuff, and siltstone. The rocks of the argillite unit are almost always laminated, even in outcrops that appear massive on casual observation. Laminations are commonly graded and indicate that the unit is upright. Several thin graphitic phyllite zones ranging from less than one foot to several feet in thickness are also present. Within the argillites are a number of tabular, mafic hypabyssal or extrusive igneous bodies. Some of these are amygdaloidal suggesting lava flows; others are non-amygdaloidal and may be dikes, sills or flows. All have been metamorphosed. These metamorphosed mafic igneous rocks suggest a possible correlation of this argillite unit with the Wildhorse Branch Formation mapped by Secor and Wagener (1968) and the lower slate belt unit mapped by Bell and others (1974) to the northeast.
16

. ..
\

\(/)
10
I~

I

I

~~,o<

~ CLARK

\ ...-:

HILL

,

RESERVOIR ' \

CAROLINA

........... .. .. LOWER
GREENSCHIST FACIES

SLATE

BELT
....... .:.





::. ~ ..... .....

.......! ...
! .,. UPPER
_:: "' GREENSCHIST
FACIES _ ..... -

-,.

MODOC
FAULT
ZONE

-- ,.

AMPHIBOLITE FACIES










KIOKEE BELT

1
N

0

2

3

4 Miles

----

Metamorphic Facies Boundaries Boundary of Modoc Fault Zone

Figure 5. Metamorphic facies across the Modoc Fault zone in South Carolina east of the Clark Hill Reservoir.
17

QUARTZ-SERICITE SCHIST
The argillite is underlain to the southeast by a sericite-rich schist. The contact between these units is gradational, and boundaries must be determined using arbitrary criteria. We have marked the boundary based on the predominance of quartz-sericite schist over argillite. The major rock types of this unit are quartz-sericite schist, argillite, sericite schist, and metaquartzite.
The unit displays pronounced compositional banding. Thin to thick argillite layers (up to 1m) interlayered with sericite-rich schist are present in the northwest part of the unit, but they become less abundant to the southeast where increasing metamorphic grade (to upper greenschist facies) has altered the argillite to sericite schist.
This quartz-sericite schist unit marks the beginning of the cataclasis associated with the Modoc Fault zone in this area,and cataclastic textures become increasingly prominent towards the southeast. Button schist, possibly cataclastic in origin, first appears in the northwest part of this unit in the less competent, thin argillite layers, while cataclastic porphyroclasts first appear in the argillite unit near the boundary of the quartz-sericite units. These porphyroclasts increase in abundance to the southeast.
MYLONITE GNEISS
The quartz-sericite schist grades downsection into a mylonite gneiss (terminology of Higgins, 1971), characterized by strong compositional banding. Cataclastic textures are dominant, and evidence of increased recrystallization of mineral grains can be seen. Cataclastic evidence includes the presense of protomylonite, fluxion structure, and cataclastic "tails" on porphyroclasts. Interlayered porphyroblastic felsic gneiss and mica schist, which sometimes displays buttons, are two of the important rock types.
Biotite and garnet are present and increase in abundance to the southeast. The transition from upper greenschist metamorphic grade to amphibolite metamorphic grade takes place within the mylonite gneiss.
BUTTON SCHIST
Two button schist zones occur in the mylonite gneisses in the southern part of the Modoc Fault zone. These are interpreted as phyllonitic (cataclastic) schists. The buttons which dominate the rock are generally muscovite throughout and range up to 4 em in diameter. Other minerals include small flakes of biotite (to 3mm), parallel to foliation, very small quartz grains (tolmm) and small euhedral garnets (to1mm) which cross-cut foliation.
The angles of the ends of the buttons at stop 5 outline two intersecting cleavages or foliations. These cleavages or foliations may have been responsible for the button development. Conversely, the button development may have given rise to the appearance of the cleavage or foliation. These cleavage planes strike at about N 30 - 35E and N 70 - 75E respectively, with button elongation trending at about N 45 - 50 E.
Phyllonitic schists in the Brevard zone similar to the type found here were interpreted by Roper (1972) as related to" ... intense cataclasis, shearing and partial recrystallization." Hatcher (1969, p. 120) concluded that button structure in the Brevard zone was due to shearing and extension.
GRANITIC GNEISS
Kiokee belt rocks observed in the Clark Hill area consist of polyphase folded biotite-granite gneisses with small amounts of amphibole gneiss and biotite schist. Other rock types in the Kiokee belt in South Carolina include metaquartzites, amphibolites, granite, metagranite, mafic and ultramafic intrusives, and a wide range of metasedimentary and possibly metavolcanic rocks (Overstreet and Bell, 1965). The Kiokee belt in this area is a 15-mile wide (25 km) anticlinoria! feature that extends at least as far northeast as Columbia, South Carolina, and is bounded to the northwest and southeast by rocks of the Carolina slate belt (Overstreet and Bell, 1965).
18

Metamorphism_
Detailed study of the metamorphism along this metamorphic front is far from complete. Observations based on current work indicate that a steep metamorphic gradient from lower greenschist facies to upper amphibolite facies exists in a 1 mile wide (1.6km) zone near Modoc, South Carolina, (Fig. 5).
Northwest of Modoc, as at Parksville, rocks of the Carolina slate belt belong to the lower greenschist metamorphic facies, while rocks of the Kiokee belt to the southeast belong to the almandineamphibolite metamorphic facies ranging to the kyanite subfacies. At Modoc, evidence of increasing metamorphic grade is seen in the presence of the upper greenschist facies quartz-plagioclase-biotitemuscovite mineral assemblage near the picnic area (stop 3). At this same locality, rocks containing the assemblage chlorite, albite, and actinolite occur in narrow concordant zones of apparent basaltic composition. Metamorphic grade increases from this point to a point 0.7 miles (l km) to the southeast where the rocks contain an assemblage typical of almandine-amphibolite metamorphic facies (biotite, almandine, hornblende, and plagioclase). Within the button schist unit, small (to 3 mm) euhedral garnets are seen along with small (to 3 mm) flecks of biotite. In the fault zone, metamorphic grade is found to increase directly with an increase in cataclastic texture.
Structure
The rocks of the Kiokee belt underlie the rocks of the Carolina slate belt stratigraphically. Topbottom evidence is common in the slate belt and indicates that at least from Parksville to Modoc the rocks are part of a limb of a syncline with its axis northwest of Parksville, trending about N 50E and plunging at about l0N. The rocks of the Carolina slate belt are apparently folded over the Kiokee anticlinorium and are found bordering the Kiokee belt on the southeast in the Belair belt.
Fold styles within the fault zone at Modoc include isoclinal folds, some with sheared out noses. Drag folds in the fault zone are common and are invariably "Z" folds when viewed from the southwest.
Rocks of the Kiokee belt display polyphase folding of at least 2 and possibly 3 phases, but these rocks do not display the cataclastic textures of the Modoc Fault zone, nor the cleavage characteristics of the Carolina slate belt as at Parksville, South Carolina.
The cataclastic zone is approximately 3 miles wide (5 km) and forms the boundary between rocks of the Carolina slate belt to the northwest .:md rocks of the Kiokee belt to the southeast (Fig. 5 ). Howell (1976) correlated this zone with the Go .t Rock Fault of Alabama and Georgia (Crickmay, 1933) and extended the fault through South Caroli 'a. The Geologic Map of Georgia (Georgia Geological Survey, 1976) does not show this fault zone as b. ing continuous between the Modoc segment and the Goat Rock Fault. We feel however, that shear zones .md other anomalies indicate a continuous zone which likely will be determined by more detailed mapping. The cataclasis appears to be of Paleozoic age and may be related to ductile flattening in the formation of the Kiokee anticlinorium. Here cataclastic textures dip steeply to the northwest subparallel to compositional layering and foliation.
Small vertical faults which are younger than the Modoc Fault are common in the area. These faults lie principally in two planes and cross cut the cataclastic textures of the Modoc Fault zone. One system is commonly found at about N 40W, and the oth~r at about N 20E, roughly parallel with the Belair Fault of Prowell and others (1976). (See O'Connor, B., and Prowell, D., in this guidebook).
References
Bell, H.,III, 1966, Geologic map of portions of McCormick County, South Carolina: South Carolina Div. Geology open file report.
___ _ 1973, Some results of geochemical sampling in McCormick County, South Carolina: U.S. Geol.
Surve'y Bull. 1376, 22 p.
Bell, H., III; Butler, J.R.; Howell, D.E.; and Wheeler, W.H., 1974, Geology of the Piedmont and Coastal Plain near Pageland, South Carolina and Wadesboro, North Carolina: Carolina Geol. Soc. Field Trip Guidebook, 23 p.
19

Crickmay, G.W., 1933, The occurrence of mylonites in the crystalline rocks of Georgia: Am. Jour. Sci., v. 226, p. 161-177.
Daniels, D.L., 1974, Geologic interpretation of geophysical maps, central Savannah River area, South Carolina and Georgia: U.SGeol. Survey, Geophys. Inv. map 68-893, scale 1/250,000.
Hatcher, R.D., Jr., 1969, Stratigraphy, petrology, and structure of the low rank belt and part of the Blue Ridge of northwesternmost South Carolina: South Carolina Div. Geology Geol. Notes, v. 13, p. 105-141.
Higgins, M.W., 1971, Cataclastic rocks: U.S. Geol. Survey Prof. Paper 687, 97 p. Howell, D.E., 1976, Major structural features of South Carolina: Geol. Soc. America,Abs. with Programs,
v. 8, no. 2, p. 200-201. Johnson, H.S., 1970, Preliminary geologic map of McCormick County, South Carolina: South Carolina
Div. Geology open file report, scale 1/125,000. Overstreet, W.C., and Bell, H., III, 1965, The crystalline rocks of South Carolina: U.S. Geol. Survey Bull.
1183, 126 p. Pickering, S.M., Jr., 1976, Geologic map of Georgia: Georgia Geol. Survey, scale 1/500,000. Prowell, IJ.C., O'Connor, B.J., and Rubin, M., 1976, Preliminary evidence for Holocene movement along
the Belair Fault zone near Augusta, Georgia: U.S. Geol. Survey Open File Rept. 75-680, 8 p. Roper, P.J., 1972, Structural significance of "button" or "fish scale" texture in phyllonitic schist of
the Brevard Zone, northwestern South Carolina: Geol. Soc. America, v. 83, p. 853-859. Secor, D.T., Jr., and Wagener, H.D., 1968, Stratigraphy, structure, and petrology of the Piedmont in
central South Carolina: South Carolina Div. Geology Geol. Notes, v. 12, p. 67-84.
20

THE GEOLOGY OF THE BELAIR FAULT ZONE AND BASEMENT ROCKS OF THE AUGUSTA, GEORGIA AREA
Bruce J. 0 'Connor Georgia State University Department of Geology
University Plaza Atlanta, Georgia 30303
David C. Prowell U.S. Geological Survey Reston, Virginia 22092
Introduction
The Belair Fault zone is located in eastern Georgia a few miles west of Augusta (see Fig. 6). It was discovered in July, 1973, by O'Connor (O'Connor and others, 1974) at the Belair clay pits of the Georgia Vitrified Brick and Clay Company (locality "A", Fig. 6) during reconnaissance mapping for the Geologic Map of Georgia (Ga. Geol. Survey, 1976). Since that time, detailed mapping and extensive subsurface inv stigations (including augering, core drilling, and backhoe trenching) have been done by the U.S. Geological Survey and the Georgia Geological Survey (O'Connor and Prowell, 1976; Prowell and others, 1975).
This review and the field trip stops (numbers 7, 8, and 9) are designed to acquaint the reader with the "basement" rocks of the Augusta area and the geology of the fault zone. They also provide an opportunity to compare the "basement" rocks of the Little River Series, as used by Crickmay (1952), of the Augusta area with those to the north which will be seen on other portions of this field trip. The Coastal Plain strata are briefly describ d be ause they relate directly to the faulting.
Several workers hav reported on various g ologic aspects of th 1egion. These include regional studies of g:r und water and Pi d.mont and oastal Plain geology by LeGrand and Furcron (1956); regional and conomi geology of the Piedmont and Coastal Plain by Hurst and others (1966) and geologic maps of the area by Crawford (1968) and Sandy (1968). Aspects of Tertiary stTatigraphy hav been covered in guidebooks by Crawford and thers (1966), Sandy and others (1966) and Herriclt and Counts (1968). Economic clay deposits of the region have been described by Smith (1929 1931).
Regional Lithology and Stratigraphy
PIEDMONT ROCKS - KIOKEE BELT
"Basement" rock types in the Augusta area fall into two broad categories: 1. gneisses and granites, 2. phyllites and greenstones (Fig. 4). North of the Fall Line granites and high grad gneisses are the predominant rock types of the Kiokee belt of Crickmay (1952). The metamorphic rocks include biotite granite gneiss (most abundant), biotite gneiss, hornblende gneiss, and migmatite. Foliation in the Augusta area generally strikes east-northeast and dips southeast although this may vary locally because of shearing and intense folding. The gneisses are highly metamorphosed (locally sillimanite grade) and are intruded by a variety of pegmatites and by massive to foliated granitic bodies which range from medium-grained to coarsely porphyritic. Similar lithologies have also been observed in the subsurface south of the Fall Line.
21

0

5 Miles

0

5 Kilometers

Figure 6. Regional geologic map of the area west of Augusta, Ga., showing the extent of Coastal Plain (unpatterned) and Piedmont (patterned) rocks, and the Belair fault zone (heavy lines). Letters A, B, and C show localities mentioned in text. Base from U.S. Army Map Service, Athens, Ga., S.C. sheet, 1:250,000, 1953.
22

The Kiokee belt gneisses are in general similar to, but contain more abundant felsic varieties, than the Charlotte belt gneisses to the north in Georgia and South Carolina. Some lithologies probably represent older metamorphosed igneous plutonic rocks whereas others may be metamorphosed sedimentary and/or volcanic deposits. Although their age is unknown, they are thought to be late Precambrian and/or early Paleozoic in age.
The southern margin of the Kiokee belt is marked by an abrupt change in metamorphic grade along a previously unrecognized shear zone which is particularly well exposed at the Martin-Marietta (Dan) quarry north of Augusta on the Richmond-Columbia County line (locality "C", Fig. 6). Here, fine-grained banded and laminated pink, red, grey and green feldspathic mylonitic gneisses are intimately interlayered with minor amphibolites which are locally altered to chlorite schists. Preliminary studies suggest that the fine-grained, banded mylonitic gneisses which predominate at the southeastern side of the quarry grade to coarser, more massive gneiss on the north. South of the quarry are the fine grained sericitic phyllites of the Belair belt, but their contact with the fine-grained gneisses is not exposed.
PIEDMONT ROCKS- BELAIR BELT
The Belair belt "basement" rocks are various phyllites and greenstones which are found along the northern edge of the Fall Line at Augusta and as erosional inliers surrounded by Coastal Plain sediments. These are the only "basement" rocks known to be in fault contact with Coastal Plain sediments along the Belair Fault. Crickmay (1952) referred to these as the Belair belt of his Little River Series (equivalent to Carolina slate belt lithologies). They include a wide variety of fine-grained sedimentary and volcanic rocks which have been metamorphosed to the lower greenschist facies. The most common varieties in the Augusta area are laminated blue-gray to green chlorite-sericite phyllite ("meta-argillite") as seen at the Belair Pits (Stop 9); gray and red-mottled sericite phyllite (meta-tuff) (Stop 'i); and chlorite-albiteepidote greenstone (probably metabasalt) which are best exposed on Ras Creek west of Lake Olmstead on the north side of Augusta.
Most "basement" rock exposures are weathered to white, orange, red, gray, or green saprolite which locally extends to a depth of 100 feet. Saprolites along the fault and immediately beneath the Coastal Plain-Piedmont unconformity are commonly leached white regardless of the original rock type.
Although their age is unknown, the Belair belt rocks are believed to be late PreCambrian to early Paleozoic in age; and, although they physically overlie the Kiokee belt gneisses, the exact stratigraphic relations between the two is uncertain. Previous workers (LeGrand and Furcron, 1956; Hurst and others, 1966) suggested that the Kiokee belt forms the core of a large anticlinorium flanked on the north and south by the low grade (and therefore presumably younger) rocks of the Little River and Belair belts respectively (Fig. 2). This structural picture, however, is probably too simple because both margins of the Kiokee belt are now known to be marked by zones of cataclasis, the Modoc Fault on the north (Howell and Pirkle, this guidebook) and the previously mentioned zone of mylonitic gneiss on the south. This suggests that the Kiokee belt is at least in part fault controlled. However, this does not necessarily negate the anticlinorium structure because the relative magnitude and direction of movement along the shear zones is unknown.
COASTAL PLAIN SEDIMENTARY ROCKS
Coastal Plain units consist of a variety of sands and clays deposited in fluvial and shallow marine environments. These deposits range in age from Holocene to possibly as old as Late Cretaceous and they unconformably overlie the Piedmont rocks.
The basal unit in the area, the Tuscaloosa Formation, is a sequence of fluvial, kaolinitic sends and gravels containing lenticular kaolin deposits which are locally of commercial value. In the Augusta area, the Tuscaloosa is less than 60 meters (200 feet) thick and is typically white or buff to pink; but weathered outcrops are commonly stain d red, orange, tan oT purple.
The age of the Tuscaloosa Formation is a crjtical question because these are the oldest Coastal Plain deposits cut by the Belair Fault. Traditionally this unlL has n correlated with the Tuscaloosa Formation (Upper Cretaceous) of w stern Georgia and Alabama on the basis of gross overall lithologic similarity and stratigraphic position. However a defmite correlation is rufficult because of th general lack of fossils in the east Georgia section. ln addition, palynological studies by Ts hudy and Patterson (1975) indicate that in east Georgia some clays mapped as Tuscaloosa are as yonng as middle Eocene. The name ' Tuscaloosa Formation" is, therefore, in question: we retain it here only for convenience. To the east in
23

South Carolina similar strata are called the Middendorf Formation which Scrundato and Bond (1972) have correlated with the east Georgia Tuscaloosa. However, we prefer not to assign the east Georgia beds to the Middendorf until stratigraphic continuity can be established.
In most places where the unconformity at the base of the Tuscaloosa is exposed, it is a reasonably flat, planar erosion surface having only minor irregularities. Mapping and drilling have shown that this planar nature is quite persistent so that the unconformity forms a smooth surface gently dipping to the southeast at 4 to 6 meters per kilometer (20 to 30 feet per mile). Local relief on the unconformity is less than 5 meters (15 feet). This is extremely important, for although the Belair Fault zone is rarely exposed, it can be located on the basis of abrupt and consistent changes in the elvation of the unconformity.
Eocene sediments which unconformably overlie the Tuscaloosa Formation are composed of plastic clays, fullers earth, and fine-grained sands. These include a locally well-developed basal sequence of spiculitic claystone and sandstone (including the Albion Member of Sandy and others, 1966) which are at least in part as old as middle Eocene (Claibornian). More important, however, are the widespread upper Eocene (Jacksonian) deposits formerly designated as the Barnwell Formation. These include a lower clay-rich unit (the Twiggs Clay Member) and an upper unit of fine clayey quartz sand containing thin clay laminae (the Irwinton Sand Member, LaMoreaux, 1946). These grade northward, updip into ferrugineous, pebbly, crossbedded sands. Fresh exposures commonly show Ophiomoroha burrows suggestive of a shallow marine environment of deposition. All of the sandy units typically weather to massive or mottled red and brown argillaceous sands considered diagnostic of the Barnwell Formation.
The unconformity at the base of the Eocene sediments is quite irregular and has local relief of more than 6 meters (20 feet). Because of poor exposure, deep weathering and the lack of persistent marker horizons, this unconformity has not been mapped in detail. Also, because of poor exposure, we have not documented faults in the Eocene sediments.
SURFICIAL DEPOSITS
In the Augusta area, minor accumulations of eolian(?) sand are composed of fine-grained, well-sorted, red to brown quartz sand, locally containing minor amounts of dark organic matter with faint to massive bedding. The sand is rarely more than 6 meters (20 feet) thick and although it is found overlying all rock types (including basement saprolites), it is thickest on high ridges underlain by Eocene sediments. The sand is considered Pleistocene although its actual age is unknown.
Other surficial deposits include alluvial and colluvial debris locally containing lenses of Holocene organic material. Recent mining operations at the south end of the Belair clay pits (Fig. 7) exposed a lens of peat as much as 2 meters (6 feet) thick and 15 meters (50 feet) long containing numerous well preserved logs and stumps' (mainly pine, cypress, and northern white cedar) as much as 30 centimeters (1 foot) in diameter and 6 meters (20 feet) in length. In some places at the base of the lens, the stumps were found in growth position. The lens overlay approximately 0.3 meters (1 foot) of Tuscaloosa sands and graded laterally into and was overlain by reworked Coastal Plain deposits. Radiocarbon dates on wood yielded ages of 2390 ... 200 years B.P. (before present) at the base of the lens and 1540 .._ 200 years B.P. at the top of the lens (Table 1). Subsequent mining has removed this peat lens.
Description of the Belair Fault Zone
The Belair Fault zone is composed of a series of at least seven en echelon east-dipping reverse faults and is known to extend a distance of 21 kilometers(13 miles) from Fort Gordon Military Reservation on the south to just west of the Savannah River on the north (Fig. 6). Individual fault segments are 1.5 to 5 kilometers (1 to 3 miles) in length. Their en echelon nature is indicated by the fact that surface exposures show that the segments are straight, identical in orientation (strike N 25E, dip 50SE) and are essentially parallel to cleavage in the adjacent phyllites. However, because they are en echelon, the fault zone taken as a whole varies in trend from N 20E toN 50E.
The fault zone has been delineated by detailed surface mapping and extensive drilling using the unconformity at the base of the Tuscaloosa Formation as a marker horizon. As much as 30 meters (100 feet) of vertical separation of the unconformity has been determined on the northern end (locality B, Fig. 6), and separation decrea&es toward the south where the zone includes fewer individual faults. At the southernmost control point, near the southeastern margin of the Fort Gordon reservation, we found a separation of only 4.5 meters (15 feet) (at the limit of resolution of our technique because of relief on
24

0

1000

2000 Feet

Figure 7. Geologic map of the Belair clay pit area south of U.S. Highway 78-278, showing Coastal Plain (unpattemed) rock, the Belair fault zone (heavy line), peat deposit and trench location. Base from U.S. Geological Survey Augusta West and Grovetown quadrangles, 1957. This is locality A of the text (Fig. 6).
25

TABLE 1

Radiocarbon dates from peat lens and carbonaceous grey clay lenses.

Peat Lens Samples

Lab No. W-3212 W-3211

Description Wood from top of peat lens Wood from base of peat lens

W-3208

Peat and wood from top of peat lens

W-3209

Alkali soluble fraction residue of W-3208

W-3210

Peat and wood from base of peat lens

Age (years B.P .) 1540 ._ 200 2390 ... 200 750 ... 200 1020 ... 200 2020 ... 200

Carbonaceous grey clay lenses (Fig. 9)

W-3452

Composite of 4 samples from zone in down block

W-3447

Composite from upblock lens and gouge in fault. Points a, b, c, and d

470 ... 300 1900 ... 1000

Organic material from drill holes in shear zone

W-3432

Carbonaceous clay

W-3446

Carbonaceous clay

1710 ... 600 1490 ... 700

Note: The above analyses were made at the U.S.G.S. Radiocarbon lab in Reston, Va., by Meyer Rubin. See Prowell and others (1975) for description of method and discussion of date reliability. Exact ages may have changed since the aforementioned report because of radon decay before final C-14 analysis was made.

26

the unconformity). However, the increasing thickness of Coastal Plain cover and the possibility of other en echelon faults make it difficult to be certain whether or not the vertical separation completely dies out here.
Data gathered so far indicates that the southward dip of the unconformity on the eastern (upthrown) block is more than twice that on the western (downthrown) block. This suggests that the eastern block was moving up and tilting southward relative to the western block during faulting. Also, slickensides found in the fault plane plunge southeast suggesting that the eastern block has moved northward as well as upward.
The fault zone does not show any topographic expression along its known length. It is exposed at only two localities south of the Fall Line (localities A and B, Fig. 6) . The best and most extensive exposures are at the Belair clay pits of the Georgia Vitrified Brick and Clay Company (Fig. 7) described as Stop 9. As shown in Figure 8, Little River phyllites (now leached saprolites) have been thrust over kaolinitic and gravelly Tuscaloosa sands along a fault which can be seen at several places along the west side of the pits for a distance of approximately 365 meters (2500 feet).
Similar relations may be seen at In terstate High way 20 just east of the Bobby Jones Expressway (Ga. Hwy. 232) (locality B, Fig. 6 , described as Stop 8). Here , two fault segments have been exposed by road grading (com-tesy of t he Ga. Dept. of Transportation) at two separate places (approx. 365m or 1200 feet apart) north and south of I-20. This locality is unique in that it is the only place where we have been able to observe the Coastal Plain-Piedmont unconformity on the downthrown (west) block in contact with the fault.
Recency of Faulting
Holocene faulting is indicated by radiocarbon ages and structural-stratigraphic relations exposed in a backhoe trench across the fault zone at the south end of the Belair pits where previous drilling had indicated 16.5 meters (55 feet) of separation on the Coastal Plain-Piedmont unconformity (Fig. 7). Results from the trench were reported by Prowell and others (1975) and a sketch of the relations found in this trend is shown in Figure 9.
In the following paragraphs, we only present a general summary of our findings, and for more information the reader should refer to the original report (Prowell and others, 1975).
The trench showed that the fault cuts both the Tuscaloosa and the overlying reworked sediments. The latter are poorly stratified clayey sands containing numerous small phyllite chips and a zone of carbonaceous grey clayey lenses all of which are interpreted as having been derived from the phyllites and Coastal Plain sediments exposed by earlier faulting. Offset of the zone of grey lenses indicates about 1 meter (3 feet) of dip slip since their deposition.
The unconformity at the base of the colluvial debris overlying the reworked sediments (Fig. 9) is not a well defined boundary and we could not ascertain if this boundary was offset by the faulting. However, the slope of the boundary between the reworked sediments and the colluvial debris does have a marked deflection in the vicinity of the fault.
Radiocarbon dates on four samples from the trench and drill holes (Table 1) range from 1900 ...1000 to 1490 ...700 years B.P. and have one anomalously low and apparently spurious age of 470 ...300 years. Unfortunately the dates show a great amount of uncertainty because the samples did not contain sufficient organic material for a standard analysis. In spite of this uncertainty we believe that the dates are approximately correct suggesting a maximum depositional age of 1500 to 2000 years B.P. for the reworked sediments and thus a maximum age for late movement on the fault. This is supported by dates of 1540 to 2390 years B.P. from wood in the peat lens (described earlier) about 150 meters (500 feet) to the east of the trenches. Whereas the peat lens cannot be traced directly into the zone of grey lenses in the trench, the fact that they both are found at similar elevations and are contained within the same type of reworked sediment suggests they are probably contemporaneous. In addition, the presence of this peat lens (swamp) deposit on a hillside on the upthrown block is highly suggestive of uplift and draining by movement on the fault about 1500 years ago.
Since their initial release (Prowell and others, 1975) , the radiocarbon dates from the grey clay lenses have been the subject of much private discussion. Could the carbon have been introduced later by ground water after deposition? Microscopic examination of the organic material shows that it does indeed consist of plant debris of sufficient quantity to account for the carbon obtained for dating. No staining indicative of soluble carbon was seen and alkali extracts contained little or no carbon. This information, coupled with the fact that the carbon is in particulate form, makes it unlikely that the
27

00 C'l
Figure 8. Northeast view across Belair fault (right hammer) exposed in a gulley at north end of Belair clay pits (Ga. Vitrified Brick and Clay Co.) approximately 180 meters (200 yards) south of U.S. Highway 78-278 (see Fig. 7). White, leached, kaolinitic saprolites of "Little River" phyllites are thrust over "Tuscaloosa" kaolinitic sands and gravels. The fault strikes N25E and dips 50SE. Bedding in the sediments dips steeply to the northwest because of drag by the overriding fault block. Note the fault at the lower left within the Tuscaloosa sediments and parallel to the main fault.

w

A-SOIL HORIZON
---- ------------------ -

E
.GROUND SURFACE
COLLUVIAL ------- ------------- -::::::::::=-- :::::::.:-DEBRIS

REWORKED SEDIMENTS

- - - - ------

1:-.:l
~

GREZYONLEE_OFN~ {

- -- - -

--REWORKED SEDIMENTS -

0

"> FEET

0

1 METRE

Figure 9. Generalized view of the trench across the Belair fault zone at the south end of the Belair clay pits (see Fig. 7). Points "a", "b", "c" and "d" are grey lense material described in text.

dated carbon was a result of intrusion or infiltration from some external source. We believe that the carbon flakes in the grey lenses were deposited at the same time as the sands of the reworked sediments, and that the radiocarbon ages determined are therefore approximate depositional ages.
The different amounts of separation of the unconformities (16.5 m for the base of the Tuscaloosa, 1m for the base of the reworked sediments) indicates more than one episode of movement on the Belair Fault. Correspondingly, the lack of a fault scarp along the fault zone suggests that the rate of vertical displacement was such that the local erosion could remove any surficial expression.
Significance and Geologic Hazard
Although the eastern United States has much less seismic activity and fewer known young faults than the western United States, we now know that there has been much more post-Cretaceous faulting than was previously realized (Prowell, 1976, York and Oliver, 1976). Of the approximately 30 known Cretaceous and younger faults, the Belair Fault zone has the youngest documented movement in the eastern United States and it is the only fault in the east for which a Holocene movement has been documented.' Whereas the Belair Fault zone is not known to be seismically active, it is not far from areas of known activity such as Charleston, S.C. and Lincoln Co., Ga. (Long and others, this guidebook). In addition, the lack of seismic activity in the Augusta area may be only apparent, as no monitoring has been done there. In order to determine the potential for earthquake activity on the Belair Fault zone, we will need a much better understanding of its movement history.
Summary
"Basement" rock of the ENE-trending Kiokee belt in the Augusta area consists of high grade gneisses (mainly granite gneiss) which are intruded by a variety of granites. On the south the Kiokee belt is in contact with low grade phyllites and related metavolcanic and metasedimentary rocks of the Belair belt of the "Little River Series" as used by Crickmay (1952). the two belts are separated by a zone of mylonitic gneiss which is best exposed in the Martin-Marietta (Dan) quarry north of Augusta.
The Belair Fault zone has been traced 21 kilometers (13 miles) by means of detailed surface mapping and extensive drilling. It trends NNE and has as much as 30 meters (100 feet) of vertical separation of the unconformity at the base of the Tuscaloosa Formation. Surface exposures of the fault at two localities show that the basement phyllites have been thrust westward over Coastal Plain sediments with at least two episodes of movement; one in the last few thousand years.
Future investigations on the Belair Fault zone should be directed toward further documentation of its Holocene movement as well as determining its pre-Holocene history. An attempt should be made to trace the zone further to the north and south in order to more clearly define its regional setting and relationship to the mylonite zone between the Kiokee and Belair belts. Arrl finally, further studies are needed to unravel the complex Coastal Plain stratigraphy and to determined what effects the faulting has had on these rocks.
Acknowledgements
We would like to express our appreciation to Mr. Karl Kline, President, and Mr. Jack Hatten of the Georgia Vitrified Brick and Clay Company; Mr. H.V. Barnett, Chief Forester, and Mr. G.S. Lewis, Forester, of the (U.S. Army) Fort Gordon Military Reservation for their help in the many phases of this project at their facilities. Road-grader excavation w9.s provided by Appling maintenance facility of the Georgia Department of Transportation, Mr. John Pierce, supervisor. The core drilling by Mr. M.P. Crowell, Mr. D.M. Cannon, and Mr. Samual Sanford (GGS) and the assistance of Mr. J.P. Minard, Jr. and Mr. J.S. Rankin (USGS) are gratefully acknowledge. The writers have greatly benefitted from discussions with G.S. Grainger (Ga. Power Co.), D.E. Howell (S.C. Devel. Bd.), R.H. Carpenter (Univ. of Ga.), Earl Titcombe (U.S. Army Corps of Engineers) and Tom Watson, C.E. Abrams, J.H. Hetrick, P.F. Huddlestun, and S.M. Pickering, Jr. (Georgia Geological Survey). T.M. Chowns and W.A. Thomas read early versions of this manuscript. We would like to acknowledge Meyer Rubin, USGS, for his efforts in the radiocarbon dating of samples.
This research has been in part supported by a grant to the Georgia Geological Survey by the U.S. Geological Survey (Grant No. 14-08-0001-G-165).
30

References
Crawford, T.J., 1968, Geologic map, Columbia County, Ga.: Central Savannah River Area Planning and Development Commission, and Geology Department, University of Georgia, Athens, Ga.
Crawford, T.J., Hurst, V.J. and Ramspott, L.D., 1966, Extrusive volcanics and associated dike swarms in central east Georgia: Geol. Soc. Amer., SE Section Guidebook, Field Trip No. 2, 53 p.
Crickmay, G.W., 1952, Geology of the crystalline rocks of Georgia: Ga. Geol. Survey Bull. 58, 56 p.
Georgia Geological Survey, 1976, Geologic map of Georgia: Dept. of Natural Resources, Atlanta, Georgia.
Herrick, S.M. and Counts, H.B., 1968, Late Tertiary stratigraphy of eastern Ga.: Ga. Geol. Society Guidebook No.7, 88 p.
Hurst, V.J., Crawford, T.J. and Sandy, J., 1966, Mineral resources of the central Savannah River area, Georgia: Univ. of Georgia, Dept. of Geol., U.S. Dept. Commerce, v. 1, 467 p.
LaMoreaux, P.E., 1946, Geology and ground water resources of the Coastal Plain of east-central Georgia: Ga. Geol. Survey Bull. 52, 173 p.
LeGrand, H.E. and Furcron, A.S., 1956, Geology and ground water resources of central-east Georgia: Ga. Geol. Survey Bull. 64, 17 4 p.
Marine, I.W., and Siple, G.F., 1974, Buried Triassic Basin in the central Savannah River area, South Carolina and Georgia: Geol. Soc. Amer. Bull., v. 85, pp 311-320.
O'Connor, B.J., Carpenter, R.H., Paris, T.A., Hartley, M.E., and Denman, Jr., H.E., 1974, Recently discovered faults in the central Savannah River area: [abs.] Ga. Acad. Sci. Bull., v. 32, p. 15.
O'Connor, B.J., and Prowell, D.C., 1976, Post-Cretaceous faulting along the Belair Fault Zone near Augusta, Ga.: [abs.] in Geol. Soc. Amer. Abstracts with Programs, v. 8, pp. 236-237.
Prowell, D.C., 1976, Implications of Cretaceous and Post-Cretaceous faults in the eastern United States; in Geol. Soc. Amer. Abstracts with Programs, v. 8, pp. 249-250.
Prowell, D.C., O'Connor, B.J., and Rubin, M., 1975, Preliminary evidence for Holocene movement along the Belair Fault Zone near Augusta, Georgia: U.S. Geol. Survey open-file rept. 75-680, 12 p.
Sandy, John, 1968, Geologic map, Richmond County, Georgia: Central Savannah River Area Planning and Development Commission, and Geology Dept., Univ. of Ga., Athens, Ga.
Sandy, John, Carver, R.E., and Crawford, T.J., 1966, Stratigraphy and economic geology of the Coastal Plain of the central Savannah River area, Georgia: Geol. Soc. A mer. SE Section, Guidebook Field Trip No. 3, 30 p.
Scrundato, R.J., and Bond, T.A., 1972, Cretaceous-Tertiary boundary of east-central Georgia and westcentral South Caroiina: Southeastern Geology, v. 14, pp. 233-239.
Smith, R.W., 1929, Sedimentary kaolins of the Coastal Plain of Georgia: Ga. Geol. Survey Bull. 44, 482 p.
- - - -- , 1931, Shales and brick clays of Georgia: Ga. Geol. Survey Bull. 45, 362 p .
Tschudy, R.H., and Patterson, S.H., 1975, Palynological evidence for Late Cretaceous, Paleocene and Early and Middle Eocene ages for strata in the kaolin belt, central Georgia: U.S. Geol. Survey, Jour. Research, v. 3, pp. 437-445.
31

York, J.E., and Oliver, J.E., 1976, Cretaceous and Cenozoic faulting in eastern North America: Geol. Soc. Amer. Bull., v. 87, pp. 1105-1114.
32

GRAVITY AND SEISMIC STUDIES IN THE CLARK HILL RESERVOIR AREA
Leland Timothy Long Harry Edward Denman Helmut Yang-An Hsiao George Eugene Marion
School of Geophysical Sciences Georgia Institute of Technology
Atlanta, Georgia
Introduction
The earthquake at 21:55 UT, on November 1, 1875, near Lincolnton, Georgia, was one of the two largest in Georgia based on its epicentral intensity of VI. Earthquake activity has continued in the Clark Hill Reservoir Area (CHRA) as indicated by ATL (Atlanta) seismograms (Long, 1974) and by other microearthquake monitoring studies (Denman, 1974). On August 2, 1974, in the northern part of the CHRA, an earthquake with an extended aftershock sequence occtuTed (Bridg s, 1975 Talwani, et al., 1975) . Thes('! events make th CHRA one of the most active areas in or near Georgia.
In 1974, the School o Geophysical Sciences at the Georgia Institute of Technology expanded the geophysical investigation of the CHRA initiated by Denman (1974). The new study included an analysis of gravity and geologic and seismic refraction data as well as monitoring for natural seismic activity in the area. The object of the g ophysical investigation has been to find, if possible, the relation between the structures of the earth's crust, and them chanism of earthquakes in the CHRA. In particular, the research is being addressed to the problem of associating these earthquakes with geologic structures which could include mapped or hypothesized faults, and also to the question of whether there exists a relation between earthquakes and any of the observed faults in the CHRA.
The object o.f this contribution is limited to a pres ntation of the Bouguer anomaly map of the CHRA to an explanation of the relation of the geology to observed Bouguer anomalies, and to a discussion of the seismic aetivity observed to dat in the southern portion of the resexvoir. This seismic activity in the southern portion of the reservoir and its explanation pertain directly to the question of the hypothesized active status assigned to the Modoc Fault by Talwani and Howell (1976).
Bouguer Anomaly Map
Denman (1974) compiled 311 gravity values on the Georgia side of the CHRA. From September 1974 to June 1976 the survey area was extended and station separation reduced by obtaining approximately 1400 new gravity values. The grav'ty data now cover the nine 7lh. minute quadrangles extending from latitudes 33 37.5' to 34Q and longitudes 82 15' to 8237.5' (see Fig. 10). The average station density is one obsenation per square kilometer with 2 to 3 observations per kilometer along selected lines. Because of difficulties with access by road, many points were obtained by boat.
Standard reduction methods were applied, and a density of 2.67 gmjcm3 was used for computation of Bouguer anomalies. The international gravity formula of 1931 was used in the reduction. The combined error in the total redu tion process is considered to be less than 0.45 mGal. Reoccupation
of selected stations indicates a maximum error range of . 0.28 mGal. In some areas, however, the
gravity da a showed an apparent scatter on the order of.. 1.0 mGal. This apparent scatter can be explained by the density variations of the near-surfac geologic units. For exampl , mafic units which may b in the form of sheets no thieker than 0.1 km can produce an anomaly which is 1.5 mGal greater
on its outcrop than at a distance of about 0.5 km. Hence, the 2.0 mGal contour interval implies a map
accuracy of about.. 1.0 mGal for interpolated values, The CHRA Bouguer map is located within a band of positive Bouguer anomalies. This band trends
about N 45E and is slightly convex to the northwest (s e Fig. 11). In tb CHRA' map, tbe positives of this band take the form of elongated, sharp or broad highs in the central and southeastern quadrangles.
A number of circular negative anomalies which correspond to granitic intrusions of episode C (Overstreet
an<;l Bell, 1965) occur within the band. One of these, the Danburg granite, occurs in the northwest
33

3337.5'L__ _L.____::._~c......-~=-....IL-=--..,;:_-_.::..J__..L__c......___.t._ _ ___, 8237.5'
0 2 4 6 8 10 (kilometers)
SIMPLE BOUGUER ANOMALY MAP OF THE CLARK HILL RESERVOIR AREA
by
Leland Timothy Long Harry Edward Denman Helmut Yung-An Hsiao George Eugene Marion
( 1976)
GEORGIA INSTITUTE OF TECHNOLOGY research supported by
Nuclear Regulatory Commission, Office of Nuclear Regulatory Research
Figure 10. The contour interval is 2.0 mGal.
34

Figure 11. Regional Bouguer gravity anomalies of Georgia and South Carolina (after Long et al., 1972, and Long et al., 1976). Shaded areas are positive Bouguer anomalies. 'The CHRA map boundary is shown as the central rectangle.
35

quadrangle of the CHRA map. Sharp positive anomalies,which correspond to gabbroic intrusives, also occur throughout the band. Three such intrusives occur along a NE strike in the northeast quandrangle. To the northwest but outside the CHRA map, the Bouguer anomalies rapidly become more negative in response to the increase in elevation and associated isostatic compensation. To the southeast and in the southeast quadrangle of the CHRA map, the Bouguer anomalies are moderately negative and generally correspond to granitic and gneissic rocks of the Kiokee belt. The band of positive anomalies, which covers most of the CHRA map, corresponds largely to the metamorphosed sedimentary and igneous rocks of the Carolina slate belt in South Carolina or the Little River belt in Georgia (Crickmay, 1952). The environment of deposition of these rocks is generally assumed to be analogous to that of an island arc system.
The CHRA Bouguer anomaly map (Fig. 10) shows the influence of almost all the major geologic units. The geologic data used for comparison with the Bouguer anomalies were obtained largely from the Geologic Map of Georgia (Georgia Geological Survey, 1976) and Overstreet and Bell (1965). These maps were supplemented and/or updated from the maps or investigations of Paris (1976), Daniels (1974) and Bell (1973). More recent geological data can be found elsewhere in this field trip guidebook. Because they are the same scale, the gravity map (Fig. 10) can be compared directly with the geologic map attached
to this field trip guidebook for location of units discussed below.
The large -16 mGal negative anomaly is caused by the Danburg granite in the northwest quadrangle. The contour lines enclosing the Danburg granite are distorted according to the relative density of the surrounding rock units. On the northwest edge of the Danburg granite the more dense mafic metavolcanic rocks and phyllites cause the gradient to steepen. The phyllite is also responsible for a positive anomaly in the northeast corner of the north quadrangle. The east to northeast extension of the negative contours about the Danburg granite are related to undifferentiated granites or schists. South of the Danburg granite a sequence of granites and granite gneisses yields similar negative contours. The negative anomalies in the southwestern quadrangle are caused by a granite. The Goshen granite in the northwest comer of the central quadrangle causes an isolated negative anomaly. The negative anomalies in the southeast comer of the CHRA map are related to granite gneisses.
The sharp positive anomalies in the northeast part of the CHRA map are caused by gabbros. The gabbro just north of the central positive (within Hickory Knob State Park, South Carolina) extends at least 4 km into the crust and may have been the source for some of the more recent mafic units to the south. A gabbro in the northeast corner of the CHRA map has an 18 mGal high, and the contours indicate a possible relation to a sharp linear high which extends S 60W across the upper part of the southeast quadrangle. In both zones these units are associated with magnetic highs. These two sharp positive anomalies appear to merge to a single gravity high in the southwest quadrangle. The Lincolnton metadacite in the central quadrangle does not produce the same magnitude of gravity anomalies as do the gabbro units and the mafic metavolcanics. The flanks of the metadacite indicate an interlayering of felsic and mafic flows and tuffs. The more felsic members would tend to decrease the average density. Careful examination of the details in the gravity data show 0.5 to 1.0 mGal anomalies corresponding to density irregularities throughout the metadacite. Many other minor structures of the geologic units, such as the faults in the metadacite, appear to influence the gravity anomalies.
The Modoc Fault which is mapped in the southeast corner of the CHRA map, does not have a significant gravity expression of its own but occurs in a zone of steep gravity gradient between a mafic unit to the north and granite gneisses to the south.
A zone of structures which extends S 30 E from the Danburg granite, appears to involve all structures in the area down to the southern boundary of the Carolina slate belt. These features include the placement of granite gneisses south of the Danburg granite, the truncation of the metadacite, the convergence of the sharp linear positive anomalies, and irregularities in gravity and magnetic (Daniels, 1974) contours in the southwest comer of the southeast quadrangle.
In order to help evaluate the structural significance of the various geologic units a profile (see Fig. 12) was drawn from the Danburg granite southeast across the Modoc Fault. Profile AA' (Fig. 13) exhibits the different geological units which are responsible for the most prominent anomalies in the area. About 15 km from the NW end of the profile, the gravity anomalies show a steep gravity gradient of -1.8 mGal per kilometer. The source of the gravity gradient is the Danburg granite which is a low density material. In the model, a density contrast of -0.06 gm/cm3 (implied density of 2.67 gm/cm3) and a depth of about 8 km were used. The top layer of a large anticline composed of metadacite crosses central Lincoln County. The metadacite is the source of a positive 6.5 mGal anomaly, which can be
36

3337.5''-------"---.......:::._ _.ac;:;::__~:...__.-==--~-~_.c_~~___:...L_-L-~:::1..,__..J

8237.5'

8230'

0 2 4 6 8 10 ( kilometers)

Figure 12. Index map showing relation of gravity to seismic recording sites, epicenters and modeled profiles. The solid line in the southeast quadrangle denotes the Kiokee belt- Carolina slate belt boundary (Daniels, 1974). The saw tooth line denotes the Modoc Fault(?) as shown on geologic map of Georgia (1976).
37

A B
-40
5
-40 10

5

10 15 B' 20 25

A'
45 50 fjp:-0.03 60
60
A' 50

-
-
>-
...J
<l
:E
0 z
<l

a::

~ -8
C)

.. .

:>

m 0

12

...
A'
.. .

-rs



I. 9, -20

II

.'?.

I5 20 25 30

I I 1 I I

I III

II II

I III

I

35
II ' I

40

I ' I

I

DISTANCE ( km)

Figure 13. Profile AA' showing model used to explain Bouguer anomalies and hypothetical geological structure based on gravity model.
38

modeled by a density contrast of 0.05 gmjcm3 and a depth of 3 km. From 25 km to 43 km away from the northwest end of profile AA' there are two peaks of positive anomalies which are caused by mafic rocks. The first peak, which occurs at about 30 km, is associated with a compact syncline. The second and larger positive anomaly, is also associated with a synclinal axis, but it was modeled by a structure with a density contrast of 0.3 gm/cm3 , a width of 2.5 km and a depth of 6 km. These units may be manifestations of compositional variations in the metavolcanics. The southeast end of the profile is modeled as a low density granite or granite gneiss with thickness increasing to the southeast.
The available intensity data from the November 1, 1875 earthquake indicate a macroseismic epicenter near Lincolnton, Georgia. However, the intensity data were sparse, particularly to the north, and the actual epicenter could have been north of Lincolnton. More recent events recorded at ATL between 1963 and 1973 were generally located north of Lincolnton when data from other stations were available.
In an attempt to find the source of these events, Denman (1974) conducted a microearthquake survey by seismic monitoring in the CHRA from September, 1973 through April1974. A total of 85 low-noise days of recording were o.btained and on the basis of amplitude and character, nine events, all within 20 km of the southern part of the reservoir, were interpreted to be of natural origin (Table 2). In particular, a January 4, 1974 microearthquake recorded by three stations was computed to have occurred at 33 39.63' N, 82 24.12' Won the Little River arm of the Clark Hill Reservoir (Fig. 12). The precision of the epicenter computation was about ._ 0.1 km, but the accuracy may be no better than. 2.0 km because of uncertainty in the shear wave velocity. A near-surface depth was indicated for the hypocenter. This is perhaps the first microearthquake to be recorded in Georgia by portable recorders.
On August 2, 1974 in the northern part of the reservoir a magnitude mb = 4.3 event occurred
which was not compatible with any of the microearthquake epicenters recorded by Denman (1974). During the following year, most of the recording efforts in the CHRA were directed toward the study of the aftershocks of this earthquake. Seismic monitoring in the southern part of the reservoir was renewed in December 1975 near Double Branches (CH5, Fig. 12) and has continued to date by telephone telemetry of seismic data to Georgia Institute of Technology. A listing of local events recorded at CH5 is given in Table 2. Many appear to be very close to the recording station; in particular the last eight appear to be within 0.75 km of CH5. The sequence shows a b-value_of about 1.0 computed directly from amplitudes, and a few events exhibit a ringing character which can probably be attributed to propagation in a medium with high velocity layers.
All but two of the events in Table 2 were recorded at only one station. Consequently, non-seismic sources or very small near-by explosions can not be entirely ruled out. However, confusion of these events with quarry explosions is unlikely because their size, S-P time, and P-wave to S-wave amplitude ratio generally rule out locations of known quarries. The station locations and known epicenters are shown on (Figure 12). The trace of the Modoc Fault (see Howell, D.E., and Pirkle; W.A., in this guidebook) and Carolina slate belt- Kiokee belt boundary as identified by Daniels (1974) from magnetic data are shown for comparison. While many events could have been located on these structures, the data to date are inconclusive or circumstantial at best, and conclusions with respect to the hypothesized active status of these faults in the CHRA are premature.
Acknowledgments
We wish to express appreciation to the many students in the School of Geophysical Sciences who assisted in the field work. Dr. Robert Carpenter, University of Georgia provided valuable discussions concerning the geology. This research was supported by the U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research under grant number AT (49- 24) - 0210.
39

Table 2 _
MICROEARTHQUAKES IN THE SOUTHERN PART OF THE CLARK HILL RESERVOIR AREA

Date mo day yr
09 22 73 10 12 73 10 13 73 10 16 73 10 16 73 10 16 73 11 16 73 01 03 74
01 04 74

Time (UT} hr min sec
01:57 11:11 11:02 13:20 13:41 15:34 12:48 01:30
18:30

{S-P} sec
1.8 2.73 0.79 1.96 1.96 1.96 1.63 1.77 0.53 1.24 0.40

Station
DBR DBR DBR DBR DBR DBR DBR ESP
CLY
NHC MSP

Distance or Location km
13.5 20.5
5.9 11.8 11.8 11.8
9.9 10.6 33 ::HJ.63' N 0.1 km
82 24.12' w. 0.1 km
depth near surface

*

12 30 75

09:30:24.

3.o ;=

CH5

01 05 76

18:43:57.

0.2

CH5

01 16 76

16:13:56.

0.4

CH5

01 22 76

05:46:38.8

0.8

CH5

01 25 76

06:16:43.5

0.3

CH5

01 26 76

15:41:45.

0.2

CH5

03 26 76

22:35:31.4

0.4

CH5

03 26 76

22:35:59.9

0.4

CH5

04 15 76

03:51:48.3

2.0

CH5

05 26 76

08:55 ~~:~

2.7 4.2

CH5 CH6

06 03 76

21:37:04.

0.1

CH5

06 04 76

04:59:36.8

0.1

CH5

06 05 76

11:31:52.3

0.1

CH5

06 06 76

08:06:50.5

0 .1

CH5

06 06 76

04:39:16.0

0.1

CH5

06 07 76

02:15:25.9

0.1

CH5

06 07 76

05:54:09.4

0 .1

CH5

06 08 76

16:40:47.1

0.1

CH5

22.4 01.5 03.0 06.0 02.2 01.5 03.0 03.0 15.0
8212" w
3353" N 00.75 00.75 00.75 0 0 .7 5 00.75 00.75 00.75 00.75

* Many events which occurred in the northern part of reservoir were recorded following the event of
August 2, 1974. Events from that epicenter area are excluded from this list.
;= Precision estimated at .0.1 sec.

40

References Bell, H., III, 1973, Geochemical studies near McCormick, South Carolina: U.S. Geol. Survey Bull.
1376, p. 369-382. Bridges, S.R., 1975, Evaluation of stress drop of the August 2, 1974 Georgia-South Carolina earthquake
and aftershock sequence: M.S. thesis, Georgia Institute of Technology, 103 p. Crickmay, G.W., 1952, Geology of the crystalline rocks of Georgai: Georgia Geol. Survey Bull. No. 58,
54 p. Daniels, D.L., 1974, Geologic interpretation of geophysical maps, central Savannah River area,
South Carolina and Georgia: Geophysical investigations of the U.S. Geol. Survey, Map GP-893. Denman, H.E., 1974, Implications of seismic activity at the Clark Hill Reservoir: M.S. Thesis, Georgia
Institute of Technology, 103 p. Georgia Geological Survey, 1976, Geologic map of Georgia: Dept. of Nat. Resources; Atlanta, Georgia. Long, L.T., 1974, Earthquake sequences and b-values in the southeast United States: Bull. Seis. Soc. Am.
64, p. 267-273. Long, L.T., Talwani, P., and Bridges, S.R., 1976, Simple Bouguer gravity map of South Carolina:
South Carolina Division of Geology. Long, L.T., Bridges, S.R., and Dorman, L., 1972, Simple Bouguer Anomaly map of Georgia: Ga. Geol.
Survey. Overstreet, W.C. and Bell, H., III, 1965, The crystalline rocks of South Carolina: U.S. Geol. Survey
Bull. 1186, 126 p. Paris, T.A., 1976, The geology of the Lincolnton 7l!z' Quadrangle, Georgia-South Carolina: M.S. Thesis,
University of Georgia, 191 p. Talwani, P. and Howell, D.E., 1976, Crustal structure of South Carolina, some speculations: (abstract)
Geol. Soc. Am. Abstracts with Programs, 8, No. 2, p. 234. Talwani, P., Secor, D.T., and Scheffler, P., 1975, Preliminary results of aftershock studies following the
2.August 1974, South Carolina earthquake, E:arthquake Notes, 46, No.4, p. 21-28.
41

GRAVES MOUNTAIN M. Eugene Hartley, III, Geologist C-E Minerals, Div. of Combustion Engineering, Inc.
Exploration Office 4020 Lexington Road Athens, Georgia 30601
Introduction This paper briefly presents the geology of Graves Mountain, a proposed origin, a summary of the mineralogy, the mining and milling methods, the uses of kyanite, some information about the company, and an outline of the development of the deposit. Graves Mountain is located about 5 miles southwest of Lincolnton, Georgia, in Lincoln County on U.S. Highway 378 (Fig. 14). The mountain actually consists of three hills, two of which have a relief of uver 400 feet over the surrounding countryside. Of these two, West Mountain isnow 200 feet lower as a result of mining and is now termed the West Mountain Pit. East Mountain, now the tallest, will be mined next. Plans have not been finalized for South Mountain which is actually the easternmost hill.
Figure 14. Portion of topographic map showing Graves Mountain and vicinity (Aonia 7%' quadrangle, USGS; contour interval is 10 feet).
42

Previous Work
The first paper on the minerals at Graves Mountain was published by Shepard in 1859. Mineralogical investigations mainly on rutile and lazulite by mineralogists, (mostly German) continued until the end of the century. A few papers followed, but the first detailed geologic mapping and petrographic investigation was presented by Hurst in Georgia Geological Survey Bulletin 68 (1959). His paper may be consulted for a list of references of the previous work. Espenshade and Potter also list the previous work and present a map in U.S.G.S. Professional Paper 336 (1960). They also discuss the origins that have been suggested for Graves Mountain.
Development of the Kyanite Deposit
Commercial interest in kyanite at the mountain was initiated in 1940 by Joel Watkins of Virginia. A group of businessmen acquired the property from Watkins in 1947 but were unsuccessful due to the limited market for kyanite at the time. Paul Bennett acquired the deposit in 1961 and placed the operation into production in 1963 as Aluminum Silicates, Inc. Combustion Engineering, Inc. acquired the deposit in 1965 and enlarged it to a 60,000 tpy (ton per year) operation which gave it the capacity to produce over half of the U.S. consumption of kyanite (Fig. 15).
C-E Minerals, Inc.
Graves Mountain is currently the only operating kyanite mine forC-E Minerals, Inc., a division of Combustion Engineering, Inc. of Stamford, Connecticut. Combustion Engineering is an international industrial complex with more than 45,000 employees that designs, produces, and constructs nuclear power plants, fossil fuel generating systems, petrochemical plants, offshore oil producing equipment, heavy water systems, glass, refractories, and other products mainly for the industrial rather than private sector. More familiar to geologists, perhaps, C-E produces Tyler sieves, Ro-Tap, and Raymond coal grinding mills. C-E Minerals is headquartered in King of Prussia, Pennsylvania, and mines, processes, or imports about 20 industrial minerals. These are used, in part, to make processed mineral mixtures and synthetic minerals for industry. The company specialized in producing refractory mineral products for various companies including the C-E Refractories Division. The company's Exploration Office, located in Athens, Georgia, due to the proximity of the University of Georgia Science Library, is involved in a search for a variety of industrial minerals and assists current mining operations.
The Graves Mountain operation produces kyanite and "glass makers' grade" pyrite. The pyrite is used as the coloring agent in amber and brown glass, for example, beer bottles. Although the locality is well known for rutile, none is produced; instead, the C-E rutile product is imported from Australia. E.E. Pasco, a mining engineer, is both Vice President of Mining and Exploration forC-E Minerals and manager of the Graves Mountain operation which includes the calcining and shipping plant near Washington, Georgia. John Strohl, a mining engineer based at the plant, is mainly involved in the exploration and mining of other industrial minerals.
General Geology and Origin of Graves Mountain
The Graves Mountain lithologies are interbedded among a thick volcanic sequence, mostly tuffs, that was deposited in the Cambrian around a volcanic island interpreted to be part of an island arc chain. These rocks are now represented by the Carolina slate belt. The Cambrian data is based on the 560-570 million year date obtained on the associated Lincolnton metadacite (Carpenter, Odum, and Hartley, in progress).
Occurring gradationally, the main rock units on Graves Mountain are kyanite quartzite, sericite schist, and metamorphosed quartz-crystal tuff. The sericite schists are interpreted to be metamorphosed felsic vitric tuffs (volcanic ash probably of rhyolitic composition) and felsic crystal-vitric tuffs which are similar but contain quartz and feldspar phenoclasts (crystals ejected with the ash). The sericite schists grade into a metamorphosed crystal tuff (containing quartz phenoclasts) with a felsic to intermediate matrix (rhyolitic to andesitic). Cleavage is not well-developed in this unit due to the abundant phenoclasts; however, in thin section the sericite, chlorite, and biotite alignment is more obvious. Subrounded opalescent blue quartz phenoclasts 4 to 10 mm in diameter characterize this tuff. This subrounding is interpreted to be due to resorption in a magma during upward transport towards the volcanic vent.
43

Figure 15. Oblique aerial photograph of Graves Mountain with labeled index.
44

-

f:\].1.e<l taiJ.in!IS

~
CJl
-parking
to High~aY )78
.t

shO'P
Vie~ is to the southeast

Bipyramidal quartz outlines, indicative of their volcanic origin, are visible of the phenoclasts in thin sections.
The crystal tuff with quartz phenoclasts is the dominant crystal tuff at Graves Mountain; however, it is suspected, from previous experience in nearby areas, that all gradations of a less resistant crystal tuff with feldspar phenoclasts and a lithic tuff occur interbedded. Fresh samples of the crystal tuffs containing quartz phenoclasts have the appearance of a blue-gray conglomerate at Graves Mountain. Boulders beneath the old cut on the north side of East Mountain and outcrops further downhill provide the best specimens.
Kyanite quartzite is the main kyanite, rutile, and lazulite bearing unit. It is also the most resistant unit and supports all three hills at Graves Mountain. Although most of the unit contains less than 80% SiOz the name quartzite is preferred over previous names. The rock is dominantly composed of recrystallized interlocking quartz grains, and the added term kyanite qualified the SiOz content which is lower than for typical quartzites.
Although it is now accepted that kyanite does not necessarily imply intense metamorphic conditions, the origin is still debated. It should be noted that the kyanite quartzite appears to be an irregular lensoid structure in a sericite schist series. It has been suggested by some that this originated as a kaolin-sand lens, but the occurrence of bipyramidal quartz phenoclasts in the unit favors a tuffaceous origin. In addition, the fine grained nature of this quartzite appears to rule out an arenaceous urigin. It has also been suggested that the unit could have originated as a weathered tuff. This is more reasonable, however, requires local rather than widespread weathering in order to explain the presence of feldspar phenoclasts in some laterally equivalent sericite schists. It is proposed here, instead, that the kyanite quartzite represents a portion of a vitric tuff that was intensely leached by ascending volcanic solutions. Similar solutions are a main feature in the volcanic exhalative model now widely accepted by geologists involved in modern base metals exploration. In this proposal, such hot ascending solutions passed through and along a portion of the vitric tuff intensely leaching it and depositing silica, resulting in a cherty, clay-rich mixture. This high silica arrd alumina material was subsequently transformed into a kyan'ite quartzit upon regional greenschist metamorphism . Leaching was probably more intense along soluti n passag ways whi h may have foDowed irregular networks as well as bedding. This may explain the ccurren e of kyanite stringers that cut parall Llcyanite-ricb bands. Leaching of soft material between the passageways may have caused the dissemination of kyanite elsewhere in the deposit.
Other elements which were mobilized by the exhalative solutions include potassium, titanium and iron. Potassium was partially removed, ircn, as pyrite was added while titanium was probably locally redistributed. Where the potassium was not completely removed sericite formed rather than kyanite during metamorphism. Figure 16 is a generalized cross section that illustrates this possible origin.
The structure of the units at Graves Mountain is not well understood. Overall, the kyanite quartzite dips to the northwest at about 60-70 and trends N 50-70E. The West Mountain pit is along this trend. Work on minor folding and cleavage(s) is lacking. Several faults have been noted.
Weathering
One of the important but commonly overlooked features at Graves Mountain is the three weathering zones developed on the quartzite. This zoning can be seen in large broken boulders and in the overall view of the pit. The outer zone of the boulders and the top of the mountain, now largely removed, is highly weathered and leached of iron and several other elements. The weathering of pyrite probably produced acidic water that facilitated this leaching during weathering. This zone is a white, fine-sandy, locally friable kyanite quartzite that has the appearance of a very fine grained sandstone. This is considered good ore because it is easily crushed and free of iron. The iron oxides from the outer zone appear to have been deposited in a middle zone coloring it tan to reddish brown. Unfortunately, much of the kyanite is iron stained in this zone. The iron oxides also apparently migrated deeper into boulders and into the mountain itself along joints, fractures, schistose zones and faults where present. Only the center of the same boulders and the lowermost sections of the pit show the unweathered, light bluish gray kyanite quartzite that represents the third zone. This rock is hard to crush but provides good ore with blue kyanite and fresh pyrite.
46

Step 1. Volcanic island, explosive andesite-rhyolite-

-~0- -

-

~

.. J

0

.. .

.





'

basalt type. Locus of Graves Mountain is shown shaded and enlarged in the following sections. --------::::oo~

tuffs

sea
~-- level

crystal tuff-
Step 2. Formation of tuffaceous layers from ash and other volcaniclastic material.

...,...
" I '\ft
. ' . ... . -.-, --~-~-r, ~--~~~~, ~~: ~------~. ----lseevael . \ '
tuff

crystal tuff

sea ------------------------------------ level
Step 3. Intense leaching of a portion of the vitric tuff bed by ascending exhalitive-like solutions depositing silica and leaving a cherty-clay rich section in the vitric tuff.
-

Figure 16. Schematic cross sections illustrating proposed origin of the Graves Mountain kyanite quartzite deposit.
47

Step 4. View of the irregular lensoid chertyclay rich area before metamorphism.

----------------------------

Step 5. Regional metamorphism at the Greenschist Facies. The lensoid mass is transformed into kyanite quartzite.
Step 6. Weathering and erosion to the present level that leaves the resistant kyanite quartzite as the supporting unit for the hill.
48

Mineralogy and Chemistry
KYANITE
Kyanite, Al203Si02 or Al2Si05, occurs mainly in the kyanite quartzite unit as subhedral to euhedral bladed crystals, commonly less than 20 mm in length. Some blades show alteration to pyrophyllite along margins and cleavage. The color of the kyanite varies from white to shades of tan and brown, to light-blue depending upon the weathering zone in which it occurs. Theoretical kyanite contains 63% Al203 and 37% Si02. The commercial product contains about 57% Al203, 40% Si02, 1% Fe203, and 1% Ti02.
RUTILE
Specimens of Graves Mountain rutile are displayed in mineral museums throughout the world and illustrated in many mineralogy books. It was mainly this interest in rutile that accounted for the earliest collecting trips and publications by German mineralogists over a centl\ry ago. Collecting is now only allowed durin!~: authorized field trips.
Now specimens of rutile are difficult to find. Crys,tals over about 10 mm are uncommon, and specimens over about 50 mm or 2 inches are rare. Open vugs in the central quartzite unit provide the brightest specimens, but removal without damage is difficult. In most vugs, the quartz crystal lining, if present, is coated with iron oxides, some of which iridescent. Likewise, the rutile, if present, may be coated. The worker who occasionally finds such a crystal removes the coating with fairly sharp blows from an ice pick or nail. The very rare uncoated crystals are magnificent. Most rutile crystals found at the mountain occur as residuum in the soil or around waste rock.
Fine rutile is more common than collector sized crystals, though it is not abundant enough for recovery at the mill. Most of the fine rutile occurs as red-brown prisms less than %mm in diameter and in quantities of less than 112% of the rock.
LAZULITE
Lazulite, (Mg, Fe) Al2(P04)2(0H)2, is not the same as !azurite or lapis lazuli, but it is desired for slabbing by lapidaries. Graves Mountain samples have been illustrated in several mineral books. Lazulite usually occurs as light dusky to azure blue pyramidal crystals less than 10 mm in length within a quartzite matrix.
PYRITE
Pyrite occurs in the fresh bluish gray kyanite quartzite as aggregates and small cubes usually less than 3 mm in diameter. Quantities vary, but it may locally account for as much as 10% of the rock. Cube shaped voids are evidence that the pyrite occurred in the overlying weathered zones of kyanite quartzite.
OTHER MINERALS
Pyrophyllite, Al2Si401o(OH)2, occurs locally as white to iron-stained radiating clusters 10-25 mm in diameter. White clusters with a dark-brown to black iron oxide matrix have been collected. Ilmenite, FeTi03, occurs as tabular to platy crystals usually less than 10 mm in diameter. Specimens are probably best found in rain washed ditches on the northwest side of the saddle between East and West Mountains. Iridescent, botryoidal masses of iron oxides are found in vugs and weathered schistose "zones in the kyanite quartzite.
Mining and Milling at Graves Mountain
The kyanite quartzite unit at Graves Mountain is mined by open pit methods utilizing 20-foot benches (Fig. 17). The ore is drilled and blasted, loaded onto trucks with a diesel shovel, and hauled to the crusher stockpile. The ore is then fed into a jaw crusher and reduced to minus 1% inches and transferred by belt through a tunnel underneath the stockpile to a surge bin at the side of the mill (Fig. 18). From there it goes to a rod mill where it is wet-crushed to form a minus 28 mesh sluny.
49

Figure 17. View of West Mountain pit showing benches characteristic of open pit mining methods. 50

Figure 18. Photograph showing crusher belt, conical mill stockpile, and belt to surge bin at the mill. 51

The resulting material is deslimed to prepare it for concentration by flotation methods. One of the most commonly asked questions is about the principle of flotation, the more generally
used method of mineral concentration. In short, it is based upon differences in the surface chemistry of various minerals. Upon addition of certain chemicals, particles of some minerals are rendered wettable whereas others are not. Air blown through the agitated slurry floats the non-wettable mineral particles on bubbles to the surface where they concentrate as a froth. This is scraped off with paddle wheels and collected in a trough. Recycling upgrades the concentrate. The mill superintendent, Bob Mauney, is better qualified to answer more questions.
After the desliming step at the Graves Mountain mill, the kyanite ore slurry is conditioned with pine oil and xanthate using an amine collector. After passing through flotation cells to remove pyrite and sericite, the slurry is reconditioned with sulfuric acid and petroleum sulfonate. Kyanite is floated in rougher cells and then recycled through several cells that upgrade it. The kyanite is partially dried by drainage from a stockpile and then kiln dried. Then it is passed through high intensity magnetic separators to removed ilmenite and iron stained kyanite, providing a product with a maximum of 1% FezOs. This resultant product is termed raw kyanite and is minus 35 mesh.
The kyanite product is trucked to the company's Little River Shipping Plant located on rail near Washington, Georgia. Here the kyanite is bagged or loaded in bulk for shipment. Some of the kyanite is first ground to other sizes, mainly minus 48, 100, 200 and 325 mesh. Some of the kyanite is also calcined. The high purity pyrite ("glass makers grade") produced at the mill is also bagged here. In addition, this plant serves as a custom grinding operation for several minerals, including zircon, produced elsewhere.
Kyanite is mainly used as a refractory; a material able to maintain certain physical and chemical identities at high temperatures. Desirable properties of the high alumina refractories made from kyanite include the ability to withstand high temperatures, abrasion, pressure, chemical attack, spalling, and thermal shock. Kyanite is blended with other materials to form castables, mortars, and ramming mixes. Upon firing (calcining) to 1100-1480C kyanite converts to silica and, dominantly, mullite, a stable refractory compound or pynthetic mineral. Calcining other minerals such as sillimanite, andalusite, topaz, dumortierite, and certain kaolin-bauxite mixtures also forms mullite. Kyanite, however, expands upon firing, a very desirable property to compensate for the shrinkage of other materials such as binding clay. These properties make kyanite based refractories suitable for furnace linings, kiln construction, and heavy duty kiln ware. The steel industry consumes nearly half of the kyanite produced. Some kyanite is also used in brake shoes, and welding rods, as well as in certain metal foundary molds, wall tile, sanitary porcelains, and special purpose ceramics.
Calcined kyanite is produced at the company's Little River Shipping Plant near Washington, Georgia. Mullite refractories are also produced from calcined kaolin-bauxite mixtures at the C-E Mulcoa Plant near Andersonville, Georgia. These dimensionally stable products are used where compensating expansion is not needed.
52

Figure 19. Location map showing field trip route and numbered stop locations (see Figs. 2 and 4 for the geology of the region). Base from U.S. Army Map Service, Athens, Ga., S.C. sheet, 1:250,000, 1953. Contour interval is 100 feet.
53

ROAD LOG FIRST DAY

Mileage Between points Cumulative

0.0

0.0

Remarks
Leave parking lot in front of lodge at Hickory Knob, State Resort Park, near McCormick, South Carolina driving towards park entrance. Hickory Knob State Park sits on outcrops of an unmapped gabbro stock (see Long, this guidebook). Exposures of this body and bouldery float may be seen in numerous places along the drive from the lodge towards the entrance.

3.7

3.7

Park entrance, tum right on county roadS 33-7.

1.6

5.3

Junction with U.S. 378, tum left.

2.2

7.5

Entrance to Baker Creek State Park, tum left.

0.7

8.2

Stop beside Baker Creek and walk upstream and then along the first

tributary on the right hand side.

54

STOP ONE BAKER CREEK Bob Carpenter

Fresh outcrops of the Lincolnton metadacite and cross-cutting mafic dikes are exposed in the stream. This exposure is an excellent example of the Lincolnton metadacite in a fresh, relatively unmetamorphosed state. The most striking features of the rock are the abundance of blue, opalescent quartz phenocrysts and the massive nature of the outcrop.
Return to paved road and examine saprolite exposures showing the same relationships observed in the stream.

Mileage Between points Cumulative

0.7

8.9

Return to U.S. 378, turn left and proceed eastwards.

1.1

10.0

R & D shopping center on right.

0.9

10.9

Junction with county road S 33-44, turn right toward Plumb Branch.

3.5

14.4

Junction with country road S 33-30, turn right.

5.5

16.4

Junction with U.S. 221, SC 28, turn right.

5.1

21.5

Parksville, city limit; continue 0.1 miles and stop. Walk across railroad

tracks to outcrops east of road.

55

STOP TWO- PARKSVILLE
Bill Pirkle and David Howell
This exposure is typical of the badly weathered, banded argillites of the Carolina slate belt in this area. When fresh, the rock is blue-gray to gray-green but weathers to shades of tan, brown, and red, as here. Metamorphism is very slight (lower greenschist facies), and bedding laminations, 1 mm1 em thick, sometimes graded, are still readily apparent.
Beds generally strike about N 65 E and dip at about 50 northwest in this area, but a gentle mesoscopic fold with hinge trending approximately N 50 E and plunging 25 N is present in this outcrop. They are cut by an axial plane cleavage to the regional folding which strikes about N 45 E and is approximately vertical. Cleavage bedding intersections and graded bedding, when found, indicate that the rocks are right side up and lie on the southeast flank of a syncline.
Near the center of the outcrop, a small, deeply weathered, tabular mafic igneous body is exposed.
As an alternative to this stop, there is a better exposure 3lfz miles to the east, but this may be destroyed as a result of impending road construction. To reach Stop 2a, continue 0.3 miles on U.S. 221 to junction with county roadS 33-138 and turn left over railroad crossing. Cross Stephens Creek with water mill on right (1.5 mls) and continue another 1.9 miles to stop. Outcrop is in banks on left hand side of road.
The banded argillite at this stop is similar to that at Stop 2 but is less weathered. It shows clear graded laminations consisting of alternating light quartzo-feldspathic, and dark chlorite-sericite rich, layers.
Both axial plane and bedding plane cleavage are well developed. Axial plane cleavage in the argillite in this vicinity generally trends about N 48 E and dips at almost 90, but is interrupted in this outcrop by faulting.
The main fault trends N 32 E, and from slight bending of beds adjacent to the fault plane, appears to be upthrown on the southeast side. Graded bedding is right side up on both sides, suggesting that this may be a fracture in the center of a small, tightly folded anticline. The axial plane cleavage on the north (left) side of the fault strikes N 50 E and dips 51o SW (rougl;lly parallel with the outcrop face in Fig. 20) while on the south (right) side, it strikes N 80 E and dips 25 W.
56

The fact that the cleavage is rotated in this way indicates that this is one of the latest faults in the area, and the trend is roughly parallel with the Belair Fault near Augusta, Georgia, which has been shown to have Cenozoic movement (Prowell, et al., 1976). Similar rotations have been noted on a number of argillite outcrops in the area but, due primarily to, weathering and vegetation, this is one of the few instances where faulting can be clearly demonstrated.
About 50 feet southeast of the main fault, a smaller thrust fault, which also rotates cleavage, is present (Fig. 21).
Figure 20. Fault in argillite showing rotation of bedding and axial plane cleavage. A: fault zone. B: bedding- N 44 E 40NW; cleavage- N 50 E 51o SE (roughly parallel to outcrop face). C: bedding- N 25 E 75 SE; cleavage- N 80 E 25 NW.
57

Figure 21. Small thrust fault in argillite showing rotation of bedding and cleavage.

Mileage Between points Cumulative

Return to U.S. 221 in Parksville and resume log.

Continue southwards on U.S. 221.

4.0

25.5

Modoc, city limit.

0.8

26.3

Entrance to Modoc Park No. 6 (U.S. Corps of Engineers Clark Hill Resv.),

turn right.

0.7

27.0

Road junction by park theatre and restrooms, turn sharp right.

0.5

27.5

Stop beside road and walk westwards along lakeshore on north side of road.

58

STOP THREE- MODOC FAULT ZONE Bill Pirkle and David Howell
Lithologies within the Modoc Fault zone in this area resemble those in the slate belt except that metamorphic grade increases sharply to upper greenschist facies, and cataclastic textures become prominent.
This exposure illustrates the transition from argillite-like rocks to quartz-sericite schists which is indicative of the increasing metamorphic grade. Argillite-like rocks occur mainly at the northeastern end of the exposure, while quartz sericite schists with occasional thin, nearly pure, metaquartzites and discontinuous quartz veins are well exposed on the western point. Button schist fabrics believed to be of cataclastic origin are well displayed. The buttons which are small (up to 1.5 em) are developed parallel to the foliation in phyllitic layers of low quartz content in both the schists and argillite-like rocks. Other cataclastic textures which may be seen in hand specimens of the schist include fluxion structure, mylonite zones, and flattened quartz lenses. Foliations trend dominantly N 70E and dip steeply northwest but are sometimes distorted by small drag folds developed along the boundaries between competent and incompetent layers (best observed when the lake level is below 330 feet).
At the northeast end of the exposure is a small fault with associated drag folds, which appears to be younger than all other textural and structural features of the rock and, again, trends approximately parallel to the Belair Fault.
Returning along the lakeshore on the north side of the promontory, about 800 feet east of this exposure, is an exposure of argillite-like rocks containing concordant layers of greenish chlorite, actinolite, and plagioclase rock of apparent basaltic composition.
Cataclasis is only incipent in this exposure, and cataclastic textures are difficult to detect but, in particular, the plagioclase grains, which are probably porphyroblasts, appear to display cataclastic tails.
The chlorite-rich zone is cut by a small fault which trends N 75E and dips steeply to the north, and there is also some folding. The axial plane to one small fold strikes N 60E and dips at 65N. There are also several small drag folds in this outcrop. Northwest trending fractures with small offsets may be seen cross-cutting all other textures and structures.
59

Mileage Between points Cumulative

0.5

28.0

Return to park theatre and turn right

0.5

28.5

Proceed to parking area near boat ramp and stop. Cross road and walk to

outcrop about 300' to north on lakeshore.

STOP FOUR- MODOC FAULT ZONE Bill Pirkle and David Howell

At this stop we are about 1,000 feet southeast of Stop 3 and quartz-sericite schists have passed gradationally into mylonite gneisses containing the first traces of biotite. Penetrative deformation fabrics are now dominant, and porphyroblastic textures are better developed. Evidence of cataclasis includes protomylonite, porphyroblasts with cataclastic tails, flattened quartz lenses, and some button schists of possible cataclastic origin. Sheared out isoclinal folds with axial planes closely paralleling compositional layering (N 70E) are present, and slickensides, which plunge northwest at intermediate angles, are sometimes observed when the lake level is low.

1.2

29.7

Return to entrance of Modoc Park 6 and turn right on U.S. 221.

2.0

31.7

Dirt road to Bel Ridge Baptist Church and Grace Methodist Church,

turn right.

0.5

32.2

Stop at gate to Bel Ridge Church and walk westwards along track to

lakeshore on north side of promontory.

60

STOP FIVE- MODOC FAULT ZONE Bill Pirkle and David Howell

0

..

The muscovite button schists at this outcrop represent the southernmost rock unit of the Carolina slate belt on the north side of the Kiokee anticlinorium in this area. The unit is interpreted as a cataclastic or phyllonitic schist. The buttons, up to 4 em in diameter, are mainly muscovite, although some contain quartz-rich cores. Other minerals which occur outside the buttons include small euhedral garnets and flakes of biotite. The dominant foliations producing the buttons are N 30 35E and N 70 - 50E, with buttons elongated at N 45 - 50E.
Notice that the small pocket beach west of the outcrop is almost entirely composed of buttons derived from this unit.
Mileage Between points Cumulative

0.5

32.7

Return to U.S. 221, tum right and continue southwards.

2.3

35.0

Junction of U.S. 221 and SC 28. Stop at intersection.

61

STOP SIX - CLARKS HILL Bill Pirkle and David Howell

Exposed here are interlayered granite gneisses and biotite schists of amphibolite facies which belong to the Kiokee belt. Although these rocks have been subject to polyphase folding (not evident at this exposure), there is no evidence of cataclasis.
Note the distinctive "sawdust" residuum which characterized the weathered granite gneisses. This is typical of these rocks throughout the Kiokee and Charlotte belts of South Carolina.

Mileage Between points Cumulative

Continue southwards on SC 28 towards Augusta.

7.2

42.2

Savannah River; South Carolina-Georgia state line. Road becomes Ga. 28.

4.9

47.1

Fall line unconformity; the hill tops are capped by the Tuscaloosa Formation

(Cretaceous?) while the valleys are cut into Piedmont rocks.

2.3

49.4

Red light at junction between Ga. 28 and Washington Rd., turn left.

0.5

49.9

Junction between Washington Rd. and Stelling Rd., tum left.

0.4

50.3

Stop in parking lot at Westside High School and examine outcrops on the

north side of school.

62

STOP SEVEN - WESTSIDE HIGH SCHOOL Bruce O'Connor and Dave Prowell
Radio Tow-er
'

::.\~

Fresh outcrops of grey to pink phyllite on north side of school building are composed of an aggregate of black, grey, pink, red, brown, tan and buff lenticular patches of fine sericite with scattered fragments of quartz, feldspar and rock particles. The rock color usually ranges from grey to pink, but varies depending on the proportions of the component fragments. The different colored sericite patches are aligned parallel to the foliation and tend to be elongate parallel to a strike trending N 35 SE, typical of the regional trend in the area. Locally a few small kink bands and folds can be seen.
The outcrop is interpreted as a deposit of fragmental volcanic debris predominantly composed of ash and pumice (now as colored patches) with minor crystal and rock fragments. The various colors probably reflect either different degrees of oxidation of the orignal fragments or original differences in rock composition.
One interesting question is whether or not this might be a welded tuff. That is, do the flattened fragments owe their shape to original flattening during welding immediately following eruption? This would of course indicate a subaerial environment of deposition. However, in order for this to be true, it is necessary that the later metamorphic cleavage has formed exactly parallel to the original plane of pumice compaction (i.e. original bedding). While this is not impossible, one would expect to see some discordance between bedding and cleavage at least locally. Unfortunately, bedding is not apparent at this locality and there are not enough other exposures of the unit to adequately test the idea.
On the other hand, it is equally possible that the rock was originally deposited as a pumice tuff and that the fragments have subsequently been tectonically flattened during metamorphism.
The same rock unit also outcrops along strike approximately % mile to the southwest in the vicinity of the shopping center at the intersection of Ga. Highways 28 and 104. However, due to poor exposure and Coastal Plain cover we have not yet been able to trace it any great distance. It would, however, make an excellent marker unit.

Mileage Between points Cumulative

0.4

50.7

Return to Washington Rd. and turn left.

0.4

51.1

Junction with 1-20, turn right onto ramp and proceed on 1-20 west.

2.6

53.7

Stop on shoulder beneath overpass immediately before exit to Ga. 232 W

(Bobby Jones Expressway).

63

STOP EIGHT- BELAIR FAULT
Bruce 0 'Connor and Dave Prowell
Two segments of the Belair Fault Zone are exposed in excavations at the cloverleaf intersection of U.S. Interstate Highway 20 and the Bobby Jones Expressway (Ga. Hwy. 232). The first of these (location A of index map) is located at the west end of the cut bank on the north side of 1-20 at the north-bound exit ramp for the Bobby Jones Expressway. The fault strikes N 27E, dips 50SE and is best seen in the middle of the clearing where white phyllite saprolite of the up-block (on the right) abuts against the basal Tuscaloosa unconformity (also resting on white phyllite saprolite) on the down-block (Fig. 22). The unconformity has been tilted 30 degrees to the west by drag along the fault. This is the only place where the unconformity on the down block has been observed in contact with the fault.
Unfortunately the fault is difficult to see on casual examination since in the lower half of the exposure (about 10 feet) it is bounded on either side by white phyllite saprolite and is not readily visible. In the upper half of the exposure the fault is obscured by intense weathering and by fill which was spread over the entire cut during landscaping of the right-of-way. To make matters worse, the fault appears to have the "wrong" orientation (i.e. appears to dip west) because the exposure makes an acute angle with the fault and because of the prominence of the west-dipping unconformity on the down-block.
Phyllites on the up-block are blue-grey in color and commonly are deformed by southeast plunging (32) minor folds and crinkles. Foliation in the phyllite strikes N 25E and dips 42SE subparallel to the fault plane. The Tuscaloosa sediments are predominantly cream to buff colored kaolinitic sands which are deeply stained and mottled in various shades of purple, red and yellow. The base of the Tuscaloosa on the down-block is marked by a thin bed of conglomerate 3 to 13 centimeters (1 to 5 inches) thick and composed of subrounded, bluish grey pebbles and cobbles of quartz resting directly on the up-turned edges of white, laminated phyllite saprolite.
To the south another fault segment is exposed within the southeast quadrant of the clover leaf approximately 365 meters (1200 feet) SSW from the locality A described above (see "B" of index map). The fault lies east of the Bobby Jones (north-bound) about 30 meters (100 feet) west of the north-bound rarnp from Bobby Jones to 1-20 (east). Here the fault thrusts phyllite over Tuscaloosa sands and is exposed for approximately 76 meters (250 feet) along strike. A shallow trench exposes the fault in cross-section midway along the clearing. The fault strikes N 32 E, dips 50-60 SE and is essentially straight throughout its length with only minor irregularities.
Fresh blue-grey phyllite on the up-block is warped and crinkled along minor folds plunging 16SSE. They appear to post-date a well-developed mineral lineation which plunges eastward down the dip of the foliation (which strikes N 33E and dips 28SE) subparallel to the fault. Locally the phyllite contains several narrow (1-2 em wide) irregular white kaolinitic veins(?) subparallel to the foliation. They are of unknown origin.
64

0')
01
Figure 22. Photo of outcrop on NE side of cloverleaf at junction of I-20 and Bobby Jones Freeway. Fault strikes N27E and dips 50SE and drags up downblock unconformity about 2 meters (5 feet). Photo was taken looking northeast.

Tuscaloosa sands on the down-block are typical white and cream colored kaolinitic sands in which bedding dips 35 degrees to the north-west due to drag along the fault. Yellow, red and orange Liesegang bands giving the appearance of east-dipping bedding planes are developed parallel to and within 0.5 meter (1-2 feet) of the fault plane.
Drilling between A, B and the southwest side of the clover leaf indicates that at least one additional en echelon fault segment lies west of locality B within a zone several hundred feet wide. This drilling indicates that the base of the Tuscaloosa lies between 270 and 285 feet elevation on the western side of the zone (the down-block) while on the east side (the up-block) the unconformity outcrops at the 380 foot elevation. These relations indicate up to 30 meters (100 feet) of total vertical separation of the unconformity across the entire zone.
Both localities were found by tracing the unconformity through surface mapping and drilling along strike from the exposures at the Belair pits. The exposures were cleared specifically for this study by the Georgia Department of Transportation in August of 1975.
Mileage Between points Cumulative

0.2

53.9

Continue on I-20 and exit on Ga. 232 E (Bobby Jones Expressway).

Continue southwards.

3.3

.57.2

Exit on U.S . 78,278 (Fort Gordon Hwy.) and proceed westwards.

2.7

59.9

Entrance to Fort Gordon.

0.3

60.2

Turn left on dirt road into pits of the Georgia Vitrified Brick and Clay Co.

(NOTE: Access to the Belair Pits is allowed only for authorized field trips. Contact the Georgia Vitrified Brick and Clay Company, Box 8, Harlem, Ga. 30814, for authorization).

STOP NINE - BELAIR FAULT AND CLAY PITS Bruce O'Connor and David Prowell

66

General Description: The Belair1 clay pits have been owned and operated since 1902 by the Georgia Vitrified Brick and Clay Company (Mr. Karl Klein, president). Phyllites and their saprolites are hauled 34 kilometers (21 miles) by truck to the Campania plant near Harlem in Columbia County. They are then blended with Coastal Plain clays and formed into sewer pipe (from green phyllite) and fire brick (from white phyllite). A further discussion of the pits and their clays may be found in Smith (1931).
The Belair locality is of interest because it provides the best and most extensive exposures of the Belair Fault zone and of the Belair belt phyllites anywhere in the area. It was at this locality that the fault was discovered by 0 'Connor in 1973 during reconnaissance mapping for the Geologic Map of Georgia (Georgia Geological Survey, 1976).
At Belair, the fault plane strikes N 25- 30E, dips 50SE and can be traced for approximately 760 meters (2,5000 feet) along the west side of the pits (Fig. 7). It marks the western limit of mining because the phyllite (saprolite) has been juxtaposed with Tuscaloosa sediments which are not suitable for mining. A narrow gouge zone (up to 2 inches wide) of quartz sand and pebbles in a clay matrix is commonly developed along the fault plane between phyllite and sediments. In addition, the phyllite (saprolite) is commonly sheared along a wider zone (up to .6 meter (2 feet) in width) adjacent to the main fault contact. In many places slickensides within the sheared phyllite occur in two sets: one plunging down dip and the other plunging 50 to 60 SW.
Where green chloritic phyllites occur in the up-block, they are leached to tan and white kaolinitic saprolite (similar in color to the kaolinitic Coastal Plain sands) for about 1 meter (1 to 4 feet) away from the fault.plane. This leached zone is generally accompanied by a 15 to 30 centimeter (6 to 12 inch) zone of resistant dark brown to red-brown ferrugineous, sheared phyllite. This brown phyllite is easily recognized and serves as a convenient fault marker where the fault contact may be obscure .
In many cases small subsidiary faults and shears are present in both the hanging wall and the foot wall (Fig. 8). Minor fault splays within the Tuscaloosa dip more gently than the main fault and converge with it down dip. Occasionally, west-dipping conjugate shears are seen. Within the phyllites of the hanging wall there are numerous faults of diverse orientation. However, in most cases they cannot be directly related to the Belair system. Although there are local variations, the cleavage in the phyllite is sub-parallel to-the fault plane.
Tuscaloosa sediments at Belair are typical tan, cream, and buff colored kaolinitic sands with numerous gravel layers and local kaolin beds. Detritus is predominately white to milky quartz with some smokey (vein) quartz clasts. Bedding is subhorizontal, but locally well developed cross-bedding is present. However, due to drag along the fault, dips of 30 to 60 degrees (to the northwest) are commonly observed up to 6 meters (20 feet) away from the fault plane (Fig. 8). Drilling and surface mapping indicates 17.5 meters ('55 to 60 feet) of vertical s~paration of the base of the Tuscaloosa across the fault.
Traverse Along Fault Trace
The following paragraphs and the accompanying aerial photo of the pit area (Fig. 23) outline a traverse from north to south along the fault.
Locality 9- A
Start traverse at northern-most gulley exposure of fault (location A, Fig. 23). This is where the fault was first discovered and where all of its typical fej:ltures (described above) can be seen. The fault can be traced along the ground surface to the north approximately 550 meters (1800 feet) and to the south for about 485 meters (1600 feet).
Augering on the down-block west of the fault shows that approximately 10 meters (34 feet) of Tuscaloosa sediments overlie basement rocks. Combined with surface mapping of the unconformity on the up-block west of the fault, this indicates at least 18 meters (60 feet) of vertical separation.
It should be noted that the white material on the tree-lined bench above the 'phyllite on the north bank of the pit is not Tuscaloosa but is mostly mine waste and asphalt pavement of an abandoned coal yard. However, at a few places a 0.6 meter (1-2 foot) layer of argillaceous, limonitic quartz gravel rests directly on the phyllite below the mine debris. These gravels are probably young (Pliocene?) stream sediments deposited after faulting and erosion had exposed the phyllite.
1 The name Belair comes from the water tower and railroad siding which formerly served the clay pits.
67

CIJ <:.0
Figure 23. Areal photo of the Belair clay pits taken by the U.S.G.S. in 1971. The sol-id line running NE-SW is the fault trace. Points A, B, and Care explained in text. Refer to Figure 7 for approximate scale.

Little River phyllites fn this "north side" pit (terminology after Smith, 1931) are typical laminated dark greyish green to bluish grey sericite-chlorite phyllites ("meta-argellite") mined for sewer tile (pipe) fabrication. Fresh exposures locally show well developed, small scale tight to isoclinal folds which plunge gently to the NNE and SSW. Upon exposure, however, the rock decrepitates rapidly into small flakes and chips while on prolonged weathering it decays to a rusty brown to orange saprolite.
Continue south along the fault trace following the east bank of the pit.
A small exposure of the fault (dipping 70- 80SE) outcrops in the bank and gulley on south side of a small access road into the "north side" pit. Here brown ferrugineous phyllite at the fault grades east into white phyllite which in turn grades 1nto green phyllite over a distance of 20 feet. South from here the fault is buried under mine debris beyond the fence.
Walk through gate and continue south on dirt mine road which begins to angle across the fault onto the up-block beyond this point.
Cross bridge over Butler Creek, bear to the right (west) (fork to left leads to pits east of pond). Continue along the northwest side of pond which marks the flooded remnant of the "main" pit where mining first began in 1902 but was stopped in the early 1940's. Up stream on the right (west) are the timbers of an abandoned railroad spur bridge which formerly served the "main" pit. The bridge lies just west of and parallel to the fault trace.
Continue south along the west side of the pond. Fresh "pavement" of green phyllite on the up-block crops out on the left (east) near a fork in the road and near the edge of the pond.
Locality 9-B
The cut bank near the shore of the pond shows typical Tuscaloosa kaolinitic sand with thin irregular kaolin beds. Bedding dips 15 degrees to the west due to drag along the fault which lies along the west shore of the pond. Drilling here shows 7.5 meters (25 feet) of Tuscaloosa overlying the unconformity on the down-block,.which indicates 18 meters (60 f~et) of offset relative to the elevation of the unconformity exposed on the up-block east of the pond.
The bank on the east side of the pond is underlain by red and green phyllite and saprolite. The basal Tuscaloosa unconformity lies further east beyond the bank approximately 12 meters (40 feet) above the level of the pond. A low angle fault forms the subhorizontallight colored zone midway up the bank. This light zone dips east and separates green phyllite (below) from red ferrugineous phyllite (above) and is marked by large discontinuous lenses of vein quartz with decomposed iron sulfide stringers.
Leave the road and continue south along the edge of the pond for approximately 9 meters (30 feet) to recent gulley exposures of the fault. Here, brown and white phyllites are thrust over Tuscaloosa sands. The fault plane trends N 25E and dips 44SE and shows down-dip slickensides.
Ascend gulley and continue south along dirt road and examine small exposures of the fault in ditch on east side of road. Beyond here the road curves to the southeast and angles across the fault onto the up-block.
Continue south. The gulli-ed dirt road on the left (south of pond) leads to pit exposures in red phyllite east of pond. Outcrops of green phyllite occur in the woods on right.
Further south the road bends sharply to right and enters loading area for the "south" or "fire clay" pit. Local distortion along shears (trending N-S, and dipping 35 W) were exposed in yellow-brown phyllite at the bend but have since been removed by road widening.
Locality 9-C
Good exposures in "south" or "fire clay" clay pit (locality C, Fig. 23) in white to tan (leached?) kaolinitic phyllite saprolite which is mined for fire brick fabrication. The fault trace passes through the drainage ditch on the west side of the pit.
Typical Tuscaloosa sediments and the basal unconformity above the phyllite are best exposed on the up-block on the southeast side of the pit. The Tuscaloosa is usually overlain by several feet of light colored, poorly stratified, poorly sorted clayey sands with small chips of phyllite and angular quartz fragments (up to 13 em (5 inches) across) . We interpret this material as being reworked from Coastal Plain sediments and phyllite exposed on the up-thrown block.
69

A lens of peat up to 1.5 meters (5 feet) thick and 15 meters (50 feet) wide with numerous tree

trunks and stumps was observed at the center of the south wall of the pit. Although the lens has since

been removed by mining operations some of the tree trunks may still be seen lying about (many of them

have been burned for firewood). This peat lens was enclosed in reworked sediments and yielded radio-

carbon dates (on wood) of 1,540 to 2,390 . 200 years B.P. from top and bottom respectively (see

Table 1). Although the area is considerably disturbed by mine activity the general setting of the lens

indicates that it was exposed on a north-facing hill slope on the up-block. We interpret the deposit as

a fault-line swamp that was uplifted and drained by renewed movement along the fault.

A backhoe trench across the fault south of the drainage ditch on the west side of the pit has exposed

several critical age relations. However, because of the extremely unstable nature of the ground the trench

has since been filled in. Drilling to the base of the Tuscaloosa on the down-block indicates 16.5 meters

(55 feet) of offset. The trench shows that extensive erosion took place after this faulting since almost

all of the Tuscaloosa on the up-block has been striped off and is overlain by a meter of reworked

sediment. .

.

Grey lenses of sandy clay within these reworked sediments have been offset up to 1 meter (3 feet).

Colluvial debris with a pronounced A soil horizon unconformably overlies the reworked sediments. The

unconformity at the base of the colluvium showG a marked deflection in tho vicinity of tho fault, but it

is not clear if it has been cut by the fault.

These relations indicate 1 meter (3 feet) of movement since the deposition of the reworked sediments

about 2,000 years ago. Evide'nce of this age comes from radiocarbon dates (Table 1) on the weakly car-

bonaceous sandy clay lenses within the reworked sediments. Unfortunately, the ages have a high degree

of uncertainty (. 1000) due to the low carbon content of the samples. However, most of the ages cluster

in the 1,500'- 2,000 year range except for one very young age of 470 years.

The peat lens to the east which was at the same elevation as the ground surface at the trenches also

yielded similar ages. While the exact relation between the peat lens and grey lenses cut by the fault in

the trenches is uncertain, they may well be either contemporaneous or the organic material in the grey

lenses may have been derived from the peat lens.

This is the southern-most end of the traverse. Return north along the dirt mine road to the point of

beginning and U.S. 78-278. If time allows turn right on the gullied dirt road at south end of pond and walk

along the bench to the east side of the pond. Here the unconformity at the base of the Tuscaloosa is

exposed above deep red laminated phyllites which show numerous minor faults and small scale folds. Large

lenses of vein quartz with weathered sulfide stringers can be seen at the northeast corner of the pond at

the north end of the high bank. This zone of veins and accompanying white (leached?) phyllite lies along

a low angle, east dipping fault mentioned earlier in the traverse.

Mileage Between points Cumulative

10.9 1.3
38.9

71.1 72.4
111.3

Return to U.S. 78, 278 and continue westwards.
Entrance to Georgia Vitrified Brie~ and Clay Co. brickworks on right.
Junction of U.S. 78, 278 with U.S. 22'1, Ga. 47 in Harlem, turn right. Fall-line unconformity is on the north side of town.
Return to Hickory Knob State Park via Ga. 47, Ga. 220 and U.S. 378 through Appling (8.5 mls), Phinizy (4.6 mls), Leah (3.2 mls) New Hope (7.0 mls), and Kenna (Martins Crossroads) (1.7 mls).

70

ROAD LOG- SECOND DAY

Mileage Between points Cumulative

Remarks

0.0

0.0

Leave parking lot in front of lodge at Hickory Knob State Park and drive

to entrance.

3.7

3.7

Park entrance, turn right on county road S. 33-7.

1.6

5.3

Junction with U.S. 378, turn right.

1.2

6.5

Clark Hill Resv.; South Carolina-Georgia state line.

0.6

7.1

Elijah Clark State Park on right.

1.1

8.2

Turn right (west) on paved road (to Bethany Church).

2.3

10.5

Turn left on paved road and proceed southwestwards; view of Graves

Mountain ahead on skyline (access road to Murry Creek Campsite to

the right).

0.9

11.4

Stop beside road.

STOP TEN - SOAP CREEK EMBAYMENT Bob Carpenter and Travis Paris

Creek 71

This stop reveals some interesting dike-sill relationships in the Lincolnton metadacite. Two porphyritic meta-andesite dikes with chilled margins are present in the saprolite exposure, while at the north end of the cut, a metabasalt dike is exposed. West of the road, another cut through the same section occurs along an abandoned road, and there is an additional thin rhyodacite dike. All of the dikes strike between N 35W and N 70W and have steep dips.
On the west bank of the abandoned road, a coarse crystalline metagabbro is exposed. The unit appears to be concordant with the Lincolnton metadacite and is probably a sill.
The metadacite has a massive, homogeneous character in these outcrops and locally contains small amphibole-plagioclase-biotite inclusions. A prominant foliation in the metadacite trends N 50 E and dips steeply to the northwest. Silica hardpan, a gray amorphous precipitate of silica formed by the weathering of plagioclase, occurs in the upper portion of the saprolite (C-horizon).

Mileage Between points Cumulative

Continue southwestwards on paved road.

0.9

12.3

Junction with Ga. 79, turn right.

1.0

13.3

Turn left (west) on paved road to Curry Hill (access road to Murry Creek

Campsite to the right).

1.5

14.8

Turn left on paved road and drive south.

1.5

16.3

Stop on south side of Curry Creek.

STOP ELEVEN - CURRY CREEK Bob Carpenter and Travis Paris

72

This stop exposes the Lincolnton metadacite near- its western contact, where it shows affects of higher metamorphic grade and greater structural complexity than normal. The groundmass of quartz and plagioclase is markedly coarser, and coarse crystalline biotite is also conspicuous.
Interlayered with the metadacite is a mafic, metasedimentary unit consisting of the mineral assemblage amphibole-biotite-plagioclase, locally with thin epidote-quartz pods. Alternating plagioclaserich and amphibole-rich layers, and locally thin layers of metadacite, define compositional layering which is parallel to the dominant foliation direction ( N 60E). Additional evidence for a sedimentary origin for the unit is the absence of cross-cutting relationships with the metadacite. Thus, the metadacite here is not likely a hypabyssal intrusive, but rather a series of felsic flows and/or tuffs with interbedded mafic tuffaceous material probably of andesitic composition.
Within the less resistant mafic units, epidote-quartz pods reveal tight internal folding, and boudinage is locally conspicuous where the more massive epidote-rich rocks have been pulled apart. The axial planes of these small folds trend east to northeast, and the plunge is nearly vertical.
Several prominant thrust faults are exposed in the cut. These strike about N 65E and dip 25 - 35 to the southeast. A displacement of approximately six feet is indicated along one of the faults.

Mileage Between points Cumulative

Retrace route back to U.S. 378.

8.1

24.4

Junction with U.S. 378, turn left and drive northeastwards.

0.3

24.7

Junction with Ga. 220 W to Kenna (Martins OlOBsroads), turn right.

1.0

25.7

Outcrops of metadacite on left with well developed silica hardpan.

0.4

26.1

Soap Creek Embayment

0.5

26.6

Metadacite saprolite on left.

1.1

27.7

Road junction, turn right and then left immediately.

0.1

27.8

Stop beside road and begin walking traverse.

73

STOP TWELVE Bob Carpenter and Travis Paris
74

This stop involves a walk of about a mile across the first syncline east of the Lincolnton

metadacite. The group will depart from the buses at point A and walk to point B along the paved

road. (See location map). Units encountered along the traverse include:

1. Lincolnton metadacite.

Although the outcrop is weathered, the occurrence. of quartz phenocrysts in a dacitic matrix

is evident. Silica hardpan is well-developed in the saprolite. 2. Lower unit, felsic pyroclastic sequence. (Estimated thickness 2060 ft.).

I

This unit consists mainly of vitric quartz crystal tuffs. The matrix is dominantly sericite and

'

finely crystalline quartz, with chlorite abundant locally. At the upper contact on the south

side of the road is an outcrop of vitric lithic tuff.

3. Upper unit, felsic pyroclastic sequence. (Estimated thickness 870ft.).

Most outcrops of this unit consist of feldspar, feldspar-quartz tuffs, and tuffaceous graywackes._

The matrix is dominantly finely crystalline quartz and feldspar, rather than quartz and sericite.

At the base is a zone devoid of outcrop that is believed to represent a mafic volcanic rock. Thin

mafic zones are interbedded throughout this unit.

4. Upper sedimentary sequence. (Estimated thickness greater than 750ft.).

This sequence, exposed in the axis of the syncline, consists mainly of argillite and graywacke,

with well-developed sedimentary layering. Graded bedding is common and serves to indicate

top-bottom relationships. Thin mafic zones are interbedded with this sequence.

5. Upper unit, felsic pyroclastic sequence. (Estimated thickness 800 ft.).

This unit is equivalent to interval 3 above. On the south side of the road near the ea;tern contact,

a mafic zone consisting of lithic tuffs and metabasalt is exposed.

6. Lower unit, felsic pyroclastic sequence.

These outcrops are equivalent to those observed in interval 2 and consist of lithic lapilli tuffs

(welded?) with a matrix of sericite and quartz. Small kink-type folds are present.

Mileage Between points Cumulative

2.4

30.2

Continue southwards to intersection and bear right.

0.3

30.5

Junction with Ga. 47, turn right and drive west into Lincolnton.

4.3

34.8

Junction with U.S. 378, tum left.

4.5

39.3

Entrance to Graves Mountain, turn left.

0.1

39.4

Park in front of mine office.

(NOTE: Access to Graves Mountain is allowed only for authorized field

trips. Contact C.E. Minerals, 4020 Lexington Road, Athens, Ga. 30601

for authorization).

75

STOP THIRTEEN- GRAVES MOUNTAIN Gene Hartley

Graves Mountain consists of a lensoid kyanite quartzite body which occurs within the felsic

pyroclastic sequence seen at Stop 12. It is the second largest producer of kyanite in the world, and

a famous mineral locality, well known for kyanite, pyrophyllite, lazulite and rutile. The mineralization

is believed to be synvolcanic in origin, although modified by subsequent metamorphism. Further details

may be found in the foregoing article by Hartley.

,

The group will assemble in front of the mine office (where restrooms are available) and walk along

the haulage road by the mill and jaw crusher to examine the West Mountain Pit.

Subsequently, interested persons are invited to gather in small groups (less than 20) for a tour of

the mill.

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