Geology and mineral resources of the Bethesda Church area, Greene County, Georgia

IC 35
GEORGIA STATE DIVISION OF CONSERVATION
DEPARTMENT OF MINES, MINING AND GEOLOGY A. S. FURCRON, Director
THE GEOLOGICAL SURVEY Information Circular 35
GEOLOGY AND MINERAL RESOURCES OF THE
BETHESDA CHURCH AREA, GREENE COUNTY, GEORGIA
by Jack H. Medlin
and Vernon J. Hurst
ATLANTA
1967

TABLE OF CONTENTS

INTRODUCTION ------------------------------------------ -------------- ------ ___ _

3

Purpose of the investigation __________---- -------- ________ ----

Location and size of area ____ ______ _ _ _ . _ . --- __ _

3

Topography __ ---------------------------- ______ . ___________________ _ ____ .

3

Drainage

____ . . ___ . __ ----- _____

Previous work _____ ----- ___ _____ _____ ___ _ __ ... ------------- _ _

3

Procedure

_ -- _ ...... _____ _ - - __ ------- __ _ ___ ___ 3

Field _ _ --- ----------- _ . __ _ ___ - ____ ----------- ______ __ .... --- . ___ 3

Laboratory ------------------- _________ ------------ --- . ---------- ________ 3

PETROLOGY ______ ----- __ ----------- --------------------- ______ ---- ________ -

_ 4

General statement ------------ ___ ------------------- ------------------------- 4 Petrography _______----------------------____________________________-----------------------------------------_______ _____ __________________________________ 4

Schist _____________________________ ----- ------ ______ ___________________ ___________________________ _________--------------- 4

Quartz-mica schist __ _------------------------------------------------------------------------------------__________________--------- 4

Mica-quartz schist _____

------- -------- ------------------------ 4

Mica schist ------------ ---------- ----- -

---- -----

5

Quartzite ._______..----------------------------------- .______________________------------------------------------------- - ---------_ _ _____ 5

Biotite gneiss . ------------------- ---------------------------------- 5

Biotite gneiss I - - - - ------- -------

---------- - - - - - - -------------- 5

Biotite-quartz-oligoclase gneiss ----------------

__ ----------- - - - - - - 6

Biotite gneiss II -----------------

-- - - - - -- -- -

-------- 7

Hornblende gneiss ___ ----------------- ---

____ ____

10

Hornblende gneiss I __

- ----------------- ------- _______ 10

Hornblende gneiss II ____________________________________ --------------------------------------- -------------------------- _____________ 11

Hornblende gneiss HI ---------------- ----

-------------------------------- 12

Hornblende gneiss IV ---------------------------------- ________________ --------------------------- --------- ------ . 14

Amphibolite ~-- ------------------------------------------------- 14

Coarse-grained amphibolite --------------------------

-------------- - 14

Amphibolite with quartz megacrysts --------------------------------------------------------- --------------------------------------- 18

Porphyritic amphibo1ite _________________________________________------------------------------________--------------------------------------- 20

Metapyroxenite ----- ------ - - - -------- -------- - - - - --- - - -- - - - - -- -- 21 Granite _ -------- ----- _____ ------------- ------- ---------- _____ _ ____ 22

Quartz veins and pegmatites ------------- ----------------- -------------- 23

Rhyolite dikes _______ ___----------------------------------------------------------

_________ 23

Diabase dikes -------------------------------------------------------------------------------------------------------- ------------ - - - 23

STRUCTURE _---- ----------

--------------------------~---------------- 25

GE 0 LOGIC HISTORY ------------------------------------------------------------------ --------------------------------------------------------------------- 25 Metamorphic history _______________ ______________________________________________________________________________ -------------------------------- ____ 25

Post-crystallization alteration

----- ------

------ - - - - - - - - --- 26

E pidotization __________________________________-------------------------------------- _______________________________ _______________________________________ 26

Saussuritization __ .

____ ____

---- - - - - - - - --- - - - - - 26

Significance of post-crystallization alteration ____________________ ____ _________________________ ________________ ____________________ 26

Summary ------ ------------ _____ ---------- ________ - - - - - - - - - - - - - - - 26

SAPROLITE MINERALOGY ------------------------------------- ___ -------------------------------------------- 26

ECONOMIC GEOLOGY ___________ --------- - ----------------- ---- ------------- - _ 27

Copper ____ ------ __ ____ --- -------------- ----------- ---------------- ------ _ 27
Gold ______ ---- _ ---------------- _____ __ ------- _ --------------------- -- --- ---------- 27 Iron and manganese ___ ----------- . _ _____ . ___ _ _________ -------------------- 27

Kaolin

.. --- -- ______ -- ______ _____ --- _ -------------- - - - - - 27

Pegmatite __ ___________ ---------- ----------- _ ---- --------

___ ------ ---

------------ - - - - 27

Talc ----- -- ----------- -----~----------- ----- - - ------- - - - - - 28

SUMMARY AND CONCLUSIONS - ------- --

------------------------~- 28

SELECTED REFERENCES ______ _______ ---------------------------------_------------------------------------------------------------------------------- 29

1

LIST OF TABLES

Table

1. Biotite Gneiss I ___ __

6

2. Biotite-Quartz-Oligoclase Gneiss

-------------------- -------------- 7

3. Biotite Gneiss II ---------------------------------------------------------------------------------------------------------- ____------ 8-9

4. Point-Count Analyses of Biotite Gneiss I, BiotiteQuartz-Oligoclase Gneiss and Biotite Gneiss II ---------------------- 10

5. Hornblende Gneiss I _____

---------- - - - - -- 11-12

6. Hornblende Gneiss II ___

------------------ 13

7. Point-Count Analysis of Hornblende Gneisses - - - - - - -------------- - - - 13

8. Hornblende Gneiss III - - - -- -- -- -----

14

9. Hornblende Gneiss IV ___

15

10. Coarse-Grained Amphibolite ----- - -------------------------------- -------------------------------------- _______________ 16-17

11. Point-Count Analyses of Coarse-Grained Amphibolite - -- -- ----------- --- 18

12. Amphibolite with Quartz Megacrysts - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19-20 13. Porphyritic Amphibolite ----------------------------- __________________________ --------------------------------------______________ 21

14. Point-Count Analyses of Porphyritic Amphibolite -- - - - ---- --- - - - - - - 21

15. Metapyroxenite - ---- - - - - - -- - ----------------- ___

22

16. Rhyolite Dikes ------

------~-- 24

17. Diabase Dikes - - - - - - - - - - - - -- - - - -- - - - - - - - - - - - -

25

LIST OF FIGURES

Figure

1. Location of Area. ----------------------------------------- _____ 3

2. Physiographic Divisions of Midland, Georgia. -----------

3

3. Characteristic Texture of Biotite Gneiss. ________________-----------------------------------------------_________ _____ 6

4. Epidote Boudin. - - - -- - - - -- - -- -----------

- -- -- - - - - - - ----- 12

5. Photomicrograph of Quartz Megacryst. __ .. ------------------------------------------------------------- ______________ 19

6. Euhedral Microcline in Rhyolite Dike,______ -----------------------------------------------------------------_______________ 24

7. Euhedral Quartz Grain with Beta-Quartz Shape. - - --------- - --------- 24

2

INTRODUCTION

Purpose of the Investigation

The Bethesda Church area in Greene County, Georgia, is on the eastern flank of the northeastsouthwest trending metamorphic belt, where the metamorphic grade declines.
This area was chosen for investigation because (1) its relict textures, lithologies and structural relations can shed light on the geologic history of a little-known pmt of the state and (2) in the area are hydrothermal alteration r.one of the type often associated with ore deposits.

The plateau is trenched by numerous streams
which flow generally southeast to the Coastal Plain. Dendritic drainage usually prevails with streams commonly entrenched 50-75 feet below the surrounding area.

By detailed geologic mapping the distribution of the different rocl< type has been traced out. By the outcrop pattetn , the observed field relations, and petrographic study an attempt has been made to deduce the origin of the r cks and to unravel at least the outlines of the geologic history of this part of the state.
Location and Size of Area
The Bethesda Church area (Fig. 1) is 55 miles southeast of Athens, 75 miles east of Atlanta, in Greene County, Georgia, and comprise about 40 . quare miles. It is mostly northeast of Union Point, Georgia, but includes a part of the city. It lie ea t of Georgia Highway 77 which coru1ects Union Point and Lexington north of Geor ia Highway 44 which connect Union Point and Wa hington, and we t of Georgia Highway 22.

' i
' i
' I
I
I
I I
\

ATLANTA



MADISON

S.C .

N

t

0

20 40

I

I

I

MILES

Figu1e 1. Location of the area.

Sf A
N
0 20 40
I MILES
Figme 2. Physiognuphic divisions of Midland GeO?gia.
Drainage
South Fork Cl'Osses the area in an ea t-west direction. Its principal tributary is Mitchell Hill Creek which drain the southeastern part of the area. The northeastern part is drained principally by the outhea t-flowing North Fork and it main tributary, White Creek The North Fork and
outb Fork join to the outhea t to form the Little River which in turn flow eastward into the Savannah River.
Previous Work
Watson (1902, p. 182) reported the occurrence of porphyritic granites jn Greene County. Hopkin (1914, p. 293) briefly mentioned that the Union Point area is composed of hornblende gneiss and gabbro-diorite. The state geologic map published in 1939 shows the rocks underlying the Bethesda Church area a hornblende gneiss, dioritic gneiss gabbro and injection gneiss of probable Pre-cambrian age. Crickmay (1952) included these rocks in the Wacoochee belt.

Topography
The area is within the physiographic area called the Washington Plateau (Fig. 2) by LaForge (LaForge, Cooke, Keith, and Campbe11 1925). The plateau comprises the eastern and southeastern portion of Midland Georgia, bordered on the west and northwest by the Midland Slope and southwest by the Coastal Plain. Generally the plateau is a smooth upland whose surface descends gently to the southeast from 800 feet above sea level at its northwestern margin to about 500 feet at its southeastern margin.

Procedure
Field. Field data were plotted on aerial photographs at a scale of 1:7,920. Foot traverses were first done along the roads and streams which provided most of the outcrops. Contacts were walked out.
Field work was done during 10 weeks of the summer 1963 and 2 weeks during December 1963.
Laboratory. Laboratory work was done during 1963-64 at the University of Georgia.

3

'Ihe petlograpnic study involved 105 thin ection . M.inel'als were identified by their optical propertie , measured partly with a U-stage. Fifteen sections were stained (Baily and Stevens, 1960) to facilitate identification of K-feldspar. A Norelco X-ray diffractometer was used to identify the micas, garnets, and clay minerals.
PETROLOGY
General Statement
Schist quartzite, biotite gneis es, hornblende gneisses, amphibolites and granites com;titute the older rock found in the a1ea. Quartz veins, mu covite pegmatites, quartz feJdspar rocks, diabase diJ<es and rhyolite dikes are younger and less e}..'i;ensive rock types. The older rocks, with the exception of the amphibolites, have a distinct foliation and trend to the northeast with predominantly vertical dips. The amphibolite , while not having a eli tinct foliation, do confo1m to the general trend of the surrotmding rocks. These older rocks, especially the basic types, are probably derived from the metamorphism of mafic intrusive or extrusive rock . The biotite gneisses probably re ulted from the metamorphism of ediments or intermediate intrusive igneous rocks. The schist conceivably resulted from the metamorphism of sediments or possibly extrusive igneous rocks.
The younger muscovite pegmatites and quartz veins me generally parallel or perpendicular to the foliation of the surroundi11g rocks and commonly show evidence of baking the ul'l'ounding rocks.
Diabase dikes everywhere transect the regional trend of older rocks. Trends range from N20 W to N40W with 10-15 variation along the strike of any one dike.
The rhyolite dikes trend from N55 W to N70W across the regional trend. They exhibit apparent bleaching effects on the surrounding rocks and are slightly metamorphosed.
' he rocks are described below on the basis of lithology and in a chro11ological sequence, the oldest rocl<s being those which exhibit a distinct foliation, the younger being those which exhibit no foliation (amphibolites), a11d the youngest being the muscovite pegmatites, quartz vein , rhy lite dikes and diabase dikes.
Under the terminology of this 1eport an amphibolite and hornblende gneis are metamorphic rocks which contain hornblende and p]agiocla e a major constituents with varying amounts of quartz. The distinction between the two i. made on the basis of the presence or absence of foliation. A hornblende gneiss possesses a distinct foliation; whereas, an amphibolite does not.
PETROGRAPHY
Schist
Three schist bands are present in the area. These include quartz-mica schist, mica-quartz schist and mica schist.

Quartz-utica Schi. t. In the southwe~ten1 part of the area (Plate 1) the quartz-mica schist crops out as aprolite and a weathered protuberences in road cuts near the Greene-Taliaf erro County line. The rock extends northeast into Taliaferro County, but its extent to the southwest is unknown. Hornblende gneiss borders it on the northwest; the contact is apparently conformable.
Cropping out within the quartz-mica schist are small bodies of chloritized talcose amphibolite whose relationship to the schist is unclear because of poor exposure. Found also within the schist is a ferruginous-manganiferous zone that is four feet wide. The zone trends N70E and dips 65 northwest parallel to the schistosity of the enclosing rock.
MegascopicaUy the schist is composed of coarse white mica and qna.rtz. In most pecimens pyrite and grayish-black splotches of iron oxide and visible. The latter are especially prevalent in weathered specimens. X-ray difflaction patterns show the schist to be composed essentially of paragonite, muscovite and quartz.
Mica-quartz Schist. On the northwest side of hornblende gnei s 1 (Plate 1) i a fine- to mediumgrained mica-quartz schist. Thi rock type oc ur intermittently along strilce. However, conspicuous outcrop are 400 yard ea t of the Mitchell Hill Gold Mine where attitude mea urements give a N65 E trend with vertkal dips. Where present, the schist is bordered on the southeast by hornblende gneiss I and on the northwe t by biotite gneis I. The apparent thickness of the unit is 75-100 feet.
East of the Mitchell Hill Gold Mine the rock is a grayish orange-pink (5YR7/2), fine- to mediumgrained mica-quartz schist which has crinkled foliation. This rock contains abundant magnetite which is unevenly distributed. The largest grains are found in veinlets of quartz, 1 mm. wide, which are bent and contorted.
Flakes of mica, 1 mm. in length, and aligned parallel to the foliation are strikingly visible as well as the quartz, which constitutes the remainder of the rock.
Along strike to the northeast the rock becomes coarser grained and pyritic. The pyrite occurs as splotches 1 mm. or ]e aero , and as distinct 0.5 mm. octahedra which exhibit striations. Some of the pyrite has been oxidized and occurs as splotches throughout the rock. The pyrite splotches are mainly along schistosity planes. The cubes are randomly distributed.
Microscopically the rock is composed of 60-65 percent quartz, 10-12 percent coarse muscovite and 20-25 percent very fine mica.
'l'he quartz is present as fractured, granulated and strained grains, a fraction of a millimeter across, which contain inclusions of mica.
Muscovite is in colorless flakes 1 mm. or less across, which are somewhat bent in places. The muscovite commonly has splotches and minute

4

granular grains of opaque material around or dusted within them, or reddish-brown irregularshaped masses of iron oxide. Commonly the muscovite is cross-cutting and surrounded by sworls of fine mica.
Sheafs of very fine mica, irregular in shape and ranging from 2 mm. to a fraction of a millimeter in size, are conspicuously present. These sworls are commonly wrapped around grains of quartz or are along grain boundaries. Commonly, irregular grains of black opaque magnetite are scattered around and within the very fine aggregates of mica.
Mica Schist. In the road cuts 800 yards west of the Anderson residence, are spotted outcrops of a silvery-gray, very fine-grained, mica schist. This schist is also found 2000 feet east of the Anderson residence along a sawmill road.
The rock trends N 72-80 E and dips 60-65 northwest. In a road cut 1000 yards west of Anderson's residence is a saprolite contact between the schist and a dark red, clayey saprolite which contains only a very small amount of very fine quartz. Relict hornblende boxworks were observed in the saprolite. Rough trend of the contact between the two rocks is N70-80 E.
The origin of the quartz-mica schist and mica schist are not considered in detail; however, the origin of the mica-quartz schist is discussed below.
The field data suggest that the mica-quartz schist occurs intermittently, and that it is related to biotite gneiss I which borders the schist on the northwest or to the quartzite which underlies the Mitchell Hill Gold Mine along strike to the southwest. Two things suggest the former: first, although outcropping in a top soil pit as a 75+ foot band, the schist is not present 700 feet east of the soil pit. Instead, contorted biotite gneiss I is present. Secondly, near the irregular contact between the gneiss and schist there is an increase in the contortion of the biotite gneiss. The schist displays the same type of contortion along with abundant quartz veinlets. Away from the contact the biotite gneiss shows no contortion.
Microscopically biotite gneiss I shows evidence of granulation of quartz, oligoclase and micas (see microscopic description of biotite gneiss I). The schist displays the same cataclastic effects on the quartz and micas suggesting that both rocks were affected by the same movement.
Mineralogically the two rocks are different. This implies that these differences were original or that there has been removal or addition of material, possibly concurrent with the deformational episode. If the two rocks were originally the same, then the movement causing the cataclastic effects could have been accompanied by silicification, forming the schist. Alternate1y, if the mineralogical differences were original, then the quartzitic schist could be related mineralogically to the quartzite which underlies Mitchell Hill Gold Mine. The latter explanation seems more plausible since their mineralogy is very similar.

The presence of the rock as an intermittent band suggests that the schist was probably a sediment or a felsic volcanic rock. Three assay samples from the schist were collected (see Economic Geology section).
Quartzite
Mitchell Hill Gold Mine is underlain by a quartzite. It composes a hill which rises 100 feet, rather steeply, above the creek at its base. This quartzite could be related to the mica-qu&rtz schist and biotite gneiss I, since the quartzite lies west along the strike of the biotite gneiss and micaquartz schist.
According to Jones (1909) a shaft passes several hundred feet through the quartzite and for a few feet beyond into a gneiss or mica schist. This could be the gneiss or schist found east of the gold mine. The shaft is now partially filled and the quartzite cannot be traced due to scarcity of exposures. However, the quartzite at the gold mine and the schist east of the ridge are probably related.
Megascopically the rock is a white, fine-grained quartzite which contains numerous veins of quartz and minute octahedra of pyrite abundantly scattered throughout.
Microscopically the rock is composed predominantly of irregularly shaped, slightly sutured, undulose grains of quartz, 0.5 mm. or less in diameter. Lesser amounts of microcline and plagioclase are present, and minor amounts of clinozoisite and epidote pseudomorph the plagioclase. Shreds of white mica, magnetite/ ilmenite, and sphene are scattered through the rock.
Within the rock there is a fluctuation in grain size from coarse to fine and back to coarse, resembling graded bedding. No secondary overgrowths were observed. Also present are roughly spherical aggregates, 3-4 mm. in diameter, of quartz and feldspar which appear to have once formed larger grains.
Jones (1909) suggested that the rock might be either a light-colored igneous rock of granitic composition which had been sheared, silicified and impregnated with pyrite; or that it might represent a clastic rock that had been silicified and sheared. The latter is the more plausible because there is a vague banding which might be bedding, the grains are more or less rounded, and there are spherical aggregates of quartz and feldspar which might represent clastic particles.
Biotite Gneiss
The area is underlain by three biotite gneisses. Specifically these are biotite gneiss I, biotitequartz-oligoclase gneiss and biotite gneiss II. The first two could be synonymous since they have essentially the same mineralogy, with few exceptions, and lie along strike of each other.
Biotite Gneiss I. Biotite gneiss I crops out immediately south of Mitchell Hill Creek. Ex-

5

posures are in the small streams which traverse it and eventually join Mitchell Hill Creek. The best outcrops are 400 yards east of Mitchell Hill Gold Mine in a topsoil pit. The biotite gnei s i 150 feet thick at this outcrop. Another outcrop is five hundred feet east of the pit in a. small tream. This outcrop is characterized by contorted bands.
Trend of the foliation of the biotite gneiss ranges from N60 E to N70 E; the dips are vertical. Pods of mica pegmatite traverse it in places, with 2 to 3 inch pieces of muscovite found as float.
Megascopically the biotite gneiss is light gray, coarse- to fine-grained, well foliated and crinkled in places. Mineral constituents are biotite, muscovite, quartz, and feldspar. Bands of biotite alternate with quartz-feldspathic layers. These bands of biotite range from 1/ 8 mm. to 1/ 4 mm. in width and are crinkled. Muscovite in the biotite bands is sometimes parallel with the biotite, sometimes crosscutting. The quartz-feldspathic bands range from 1/8 mm. to 1 em. in width depending upon the grain size of the rock. In the crinkled biotite gneiss the biotitic bands may be broken or stretched apart and V-shaped. This crinkling occurs predominantly in the region 500 yards east of Mitchell Hill Gold Mine.
Microscopic data and a modal analysis are given in Tables 1 and 4 respectively.
Biotite-Quartz-Oligoclase Gneiss. Cropping out 1800 yards northeast of Mitchell Hill Gold Mine, along Mitchell Hill Creek, is a band 100 feet wide of fine- to medium-grained, biotite-quartz-oligoclase gneis . It crops out as car-size boulders and crumbly saprolite in Mitchell Hill Creek, 400 yards east of its confluence with the South Fork. The gneiss is bordered on each side by coarse-grained amphibolite in Mitchell Hill Creek. Because of the rapidity of weathering of the gneiss, its contact relations with the amphibolite are obscure.

Megascopically the gneiss is grayish-white, fineto medium-grained, granoblastic and composed predominantly of biotite, quartz, and feldspar (Fig. 3). Conspicuous in some specimens are megacrysts of feldspar, 3-4 mm. in diameter, in a matrix of biotite, quartz, and feldspar. The rock is faintly foliated. Samples found 400 yards east of the Mitchell Hill Creek and South Fork confluence
Figwe 3. Characteristic texture of biotite gneiss I. Quartz (q), oligoclase (o), muscovite (m), and biotite (b). Crossed nicols, X 20.
have a coarser matrix and larger feldspar megacrysts, 5-10 mm. in diameter.
Optical data and mineral descriptions are given in Table 2 and a point count analysis in Table 4.
The relation between this rock type and biotite gneiss I east of Mitchell Hill Gold Mine is un-

Mineral

Shape

TABLE 1

BIOTITE GNEISS I

Size

Optic Sign Twinning

2V

Extinction Pleochroism

Oligoclase

anhedral equant

3/ 4-1 mm. biax. (-)

albite pericline

9-11 ..LX

Biotite

books

3-4 mm. in biax. (-) length

none

parallel

X=mod. yellow (5Y7/ 6)

Quartz

irregular, somewhat rounded

3/ 4 mm.

uni.(+)

Approximately 95% of the oligoclase is fresh and the remainder is slightly saussuritized (Fig. 3).

Products are epidote and sericite. Oligoclase displays fracturing and straining effects near zone of

shearing. Numerous minute prismatic inclusions of apatite are present.

Interleaving of biotite with muscovite and biotite with apatite is very common. Muscovite also

cross-cuts some biotite flakes. Where biotite and muscovite are interleaved, fine streaks of granular

magnetite are present along cleavages and edges of muscovite. Minute grains of rutile are scattered

around the edges of biotite and parallel with cleavages. Biotite flakes are bent in rocks collected from

the zone of shearing. Biotite commonly has inclusions of quartz and a minute mineral enclosed by a

pleochroic halo.

'

Quartz is found as inclusions in biotite, muscovite and as irregularly distributed grains in oli-

goclase; commonly displays cataclastic effects in specimens near zone of shearing.

6

certain. The two differ in several ways. First, biotite gneiss I east of Mitchell Hill has a distinct foliation due to parallel alignment of the biotite flakes, whereas, the biotite-quartz-oligoclase gneiss has only a sub-parallel alignment of biotite and no visible foliation. Secondly, biotite gneiss I contains no allanite, whereas, the biotite-quartz-oligoclase gneiss does. Thirdly, they differ in amount of modal biotite. The two rock types are similar in that they are along strike, that neither shows any K-feldspar when stained with sodium cobaltinitrite, and both contain approximately the same amounts of oligoclase and quartz. Probably the two rocks are the same. They both are shown as biotite gneiss on Plate 1.
Biotite Gneiss II. One mile east of the Union Point city limits, along Georgia Highway 44,

biotite gneiss II crops out as a 6 X 8 foot weathered protuberance in a cut on the south side of the road. From this point to the southeast and northwest the outcrops are few. The gneiss trends N50 E and dips vertically.
The best outcrops of biotite gneiss II are along the stream between the William Poss residence and the Bethesda Church. This unnamed stream will hereafter be referred to as Poss's Creek. Good outcrops also occur in South Fork to the northwest and southeast of the South Fork and Poss's Creek junction. Other outcrops are present in streams west of Bethesda Church.
Conspicuous outcrops of an interlayered hornblende gneiss which contains epidote boudins are found 300 feet west of the South Fork and Poss's

TABLE 2

BIOTITE-QUARTZ-OLIGOCLASE GNEISS

Mineral

Shape

Size

Optic Sign

2V

Twinning

Extinction Pleochroism

Oligoclase

equant to elongate;
boundaries irregular, slightly
sutured

3/4-1 1/4 mm.

biax. (-)

albite, pericline

9-11 _iX

Quartz

equant; irregular boundaries

3/4-1 mm.

uni. (+)

Biotite

ragged flakes

1/ 2-3/4

biax. (-)

mm. across

parallel

X=grayish yellow
(58/4) to mod. yellow
(5Y7/6) Z=light olive
brown (5Y5/6)

Epidote

majority skeletal,
some euhedral

1mm.

biax. (-) 2V=75a

polysyn-
thetic 30-40% grains

slightly inclined

Accessory: Rutile, magnetite and/or ilmenite, muscovite. Slight saussuritization of the oligoclase has produced sericite and epidote mainly along cleavage and
twin planes. Sericite ranges in grain size from very fine aggregates to individual flakes 1/16 to 1/8 mm. across, which are ragged, sieved and surrounded by finer flakes. Epidote is generally present as ragged patches in the oligoclase which seems to alter more in the center of the grains than randomly.
Quartz grains exhibit undulose extinction and are fractured. Fine quartz inclusions are in the epidote and oligoclase.
The biotite occurs as sub-parallel ragged flakes which are abundantly dusted with magnetite around the edges of books and along cleavages. Where biotite is altering to epidote and is within a fraction of a millimeter of altering oligoclase, in a majority of cases, no epidote is in the oligoclase; if biotite is not near, the epidote is frequently in the oligoclase.
The epidote grains are spottily distributed. Zoned and twinned euhedral grains of moderate yellow (5Y7/6) allanite surrounded by epidote grains are frequent. A prevalent relationship is subhedral epidote surrounded by grains of magnetite with the magnetite surrounded by biotite. The epidote with fair crystal shapes tend to cross-cut the biotite or to surround it. The first stage of alteration of the biotite to epidote is marked by the appearance of minute grains of epidote along the biotite cleavages. Commonly associated with this reaction are rounded minute grains of rutile. Both epidote and rutile surround each other. The epidote grains contain inclusions of quartz and oligoclase.

7

Creek junction along the Pass's Creek steam bed, and in the small stream flowing into Pass's Creek, 1500 yards west of where the South Fork and Pass's Creek join. The contacts are conformable.
Saprolite of the gneiss can be observed in road uts. crhe biotite gneiss IT sapl'Olite is a light yellowish-red clay containing f ine-grained g rayi hwhite flakes of mica and angular quartz grail1s. In road cuts, where the gneiss protrude 6 to 8 inches above the aprolite, it exhibit a blocky pheroidal type weathering pattern.
The character of the biotite gneis i varied. Grain size ranges from very fine- to coar e-grained and even megacrystic type . These grain size variations are along and aero. stril<e. Pronounced change in grain ize occur near the junction of South Fork and Pos 's Creek. Here the gneis takes on a foliated megacrystic texttue with !Jlagioclase being the megacryst. The l'Ock is almost a fine-grained quartzite 800 feet ea t of the contact with the coarse-grained amphibolite along
eorgia Highway '14. In the streams west of Bethesda Church the gneiss is extremely coarsegrained and well foliated.
The biotite gneiss has quartz veins, muscovitehearing pegmatite,, diabase dikes and rhyolite dikes within it. The diaba e dikes and rhyolite dikes always transect the foliation, wherea , the quartz veins and mu. covite pegmatites and sometimes aplites are roughly parallel and perpendicular to the foliation.
Diabase dikes ranging in width from 2 feet to 30 feet cut the biotite gneiss (Plate 1). No visible evidence of alteration is observed in the field, however microscopically one section of the biotite gneiss in contact with the diabase shows alteration (see microscopic description).
Three rhyolite dikes are present in the biotite gneiss, but no field evidence of alteration was observed due to poorness of outcrops.
The contact between the biotite gneiss and the amphibolite containing quartz megacrysts, lying on the northwest side of the gnei , is pre ent in two localities. One of the contacts is in a stream, 1200 yru:ds south of the Old Copper Mine on the

south side of South Fork This contact displays an intrusive relationship of amphibolite within the biotite gneiss. A similar relation is also present in another stream outcrop 1300 yards to the west. Contact relations between the gneiss and the coarse-grained amphibolite on the southeast side are seemingly regular, but uncertain in many places.
Megascopically the biotite gneiss is a grayishwhite, fine- to coarse-grained, muscovite-biotitequartz-feldspar, crystalloblastic gneiss. Locally the rock is an augen gneiss, and along Highway 44 it is noticeably quartzitic.
The silvery muscovite occurs as flecks 1/2 mm. in length to flakes 5 mm. in length. It is present within biotite flakes parallel to the biotite bands and as randomly oriented flakes. In the augen gneiss the muscovite and biotite seemingly wrap around the augens.
Black biotite is present as flecks a fraction of a millimeter in length and as books, 1 to 1/2 mm. in length, aligned to give the rock its gneissic texture. These folia or bands of biotite and muscovite are 1/8 mm. wide.
Quartz grains, 1 to 3 mm. in diameter, occur along with feldspar in the lighter part of the gneiss. The light-colored bands are 4-5 mm. in width. Commonly, grains of quartz, 1 em. in diameter, are evenly distributed through the rock.
Feldspar is present as grains, 1 to 4 mm. in diameter, and a augen 2 mm. wide and up to 1 em. in length. Together with quartz, the feldspar constitute greater than 80 percent of the gueiss. The feldspar and quartz grains are vaguely elongated parallel to the foliation.
Partly weathered pyrite is sparingly present in some specimens.
Tables 3 and 4 give the optical properties and microscopic description, and modal analyses of the biotite gneiss, respectively.
Shape, contact relations and overall mineral composition should be considered in suggesting an origin for the biotite gneisses. The shape of each rock body is generally tabular and conforms to the surrounding rocks. Contacts between the

Mineral Oligoclase

Shape anhedral

Quartz Biotite

irregular sutured
slender flakes

'fABLE 3 BIOTITE GNEISS (II)

Optic Sign

Size

2V

Twinning

2X1 mm. augen &
1 mm.
2-3 mm. & 1/2-3/4 mm.

biax.(- ) 2V= 'i8-
86
uni. C+)

albite & pericline

4/5X1/2 mm. biax. (-) & one
3/4mm.

Extinction 13-16 .lX
parallel

(Table 3 continued on next page.)

Pleochroism
X=pale yellowish orange (10YR8/6) to grayish yellow (5Y8/4)
Z=grayish brown (5YR3/2) to grayish olive (10YR4/2)

8

Mineral

Shape

Microcline anhedral

Muscovite Epidote

slender flakes & books
skeletal euhedral

Clinozoisite skeletal euhedral

TABLE 3-(Continued)

Size

Optic Sign Twinning

2V

3 mm. &

biax. (-)

one 1 mm.

gridiron

1-6 mm.

biax.(-}

Extinction Pleochroism

parallel

colorless

1mm. 1mm.

biax.(-) biax. (+)

polysynthetic
rarely
polysynthetic
rarely

parallel
slightly inclined

Accessory: zircon, sphene, red iron oxide, rutile, apatite, pyrite, magnetite/ ilmenite.
Oligoclase shows evidence of cataclastic deformation. Commonly, formerly equant oligocla e grah1 , 3 mm. X 2 mm., ate fractured and granulated into smaller grains. The majority of the grain how marked undulose extinct ion. Twinning lamellae are parallel to the gneissic texture in 90 percent of the cases.
Saussuritization of oligoclase is not as extensive in some sections as in others. The alteration occurs preferentially in small grains, and they are almost completely covered with very fine, white mica and fine-grained epidote-clinozoisite. Alteration also occurs along the edges in some of the larger grains. Sau uritization i along cleavages and twin planes and around the borders in other specimens.
Inclusions of oligoclase dusted with minute black opaque materials commonly occur in microcline.
The biotite gneiss altered by the diabase dike show that 95 percent of the oligoclase grains are covered by a low birefringent, medium relief, turbid material. In places this material is fluffy and cotton te>.."tured and radiates fTom the center of the oligoclase gr~t.i11s . Within this f luffy material are small, high relief, high birefringent, reddi h grains which resemble rutile. 'urrotmding most of the oligoclase grains, and closely associated with the turbid material, are flakes of a light green, moderate relief, low birefringent, slightly pleochroic miner al which resembles chlorite.
Most of the quartz grain are elongated parallel to the gneissic banding. A mortar texture is prevalent. The quartz grains with abundant undulo e extinction are fractured and granulated into smaller g'l'ains. Inclusions in the quartz are cut by f ractures. Vermicular or myrmekitic quartz is common near t he c011tact between oligocla e and microcline.
Epidote and clino?ioisite are commonly associated with biotite and muscovite and less commonly with plagioclase. Zoning between epidote and clinozoisite is common. Occasionally zoning between a pleochroic yellow epidote (piedmontite ?) and common epidote is present.
Euhedral epidote both cross-cuts and patallels the biotite cleavage trace . Epidote and clinozoisite are commonly found along twilming and cleavage planes in oligoclase. Clinozoisjte is predominant in this respect. Commonly where epidote replace;~ biotite, rutile and sphene are found between epidote and biotite grains.
Biotite is scattered through the gnei . in bands, giving a distinct foliation, or wrapped a1ound oligoclase augen. In all ections biotite i dusted with grains of black opaque material or has opaque matter closely a sociated with it, especially when muscovite and epidote are present. A common textural relation hip is epidote either cross-cutting or parallel to the cleavage of biotite, surrounded by magnetite, biotite and muscovite.
Rounded grains of rutile are found around the edges and along cleavage traces of the biotite. In the biotite are occasional minute, highly berefringent inclusions surrounded by halos. Euhedral sphene, transects a biotite flake occasionally.
Muscovite is present in varying amounts in all sections. It is colorless and highly birefringent. It may be interleaved with the biotite or cross-cut it. Where muscovite surrounds biotite, the borders of the biotite are lighter in color and small splotches and grains of opaque material are scattered around the muscovite.
Twinned microcline is present in varying amounts. Its boundaries with quartz may be sutured and may show undulose extinction and fracturing. Large grains of microcline are surrounded by grains of oligoclase. The microcline is unaltered in all sections and contains minute reddish needle inclusions. When microcline and oligoclase are in contact a myrmekitic texture is present 50 percent of the time.

9

TABLE 4. POINT-COUNT ANALYSES OF BIOTITE GNEISS I, BIOTITE-QUARTZOLIGOCLASE GNEISS AND BIOTITE GNEISS II IN VOLUMETRIC PERCENT

Oligoclase Quartz K-feldspar
Biotite Muscovite Epidote-
clinozoisite Sauss. Mica Rutile, Sphene
& Apatite Red Iron Oxide
& Opaque

Biotite Gneiss I
91-70 46.99 19.70
26.84 6.08

Biotite-Quartz Oligoclase Gneiss 91-35 55.48 22.57
14.93 .44

91-56 58.61 24.73 6.31 3.36
3.02

4.20

2.02

1.56

.67

present

.38

.87

.39 100.00

.44 100.00

.41 100.00

Biotite Gneiss II

109-70 57.59 27.31 4.72 3.03 4.38

207-11 65.44 20.21 1.84 9.61

89-26 47.59 24.86 21.93 2.54 1.47

2.26

2.30

1.14

.21

.46

.21

.14

.34

.29 100.00

.00 100.00

.13 100.00

109-79 57.32 25.59 4.32 5.08 2.71
2.90 1.35
.53
.20 100.00

91-70 91-35 91-56
109-70 207-11
89-26 109-79

Collected 500 yards east of Mitchell Hill Gold Mine. Collected 1800 yards northeast of Mitchell Hill Gold Mine. Collected 1500 yards northeast of Proctor residence, near biotite gneiss-coarse-grained amphibolite contact. Collected in Pass's Creek, 300 feet west of South Fork. Collected 1 mile northeast of the Bethesda Community Center. Collected in stream bed of White Creek. Collected along South Fork, 1500 yards northeast of the Bethesda Church.

biotite gneiss I and the mica-quartz schist are somewhat irregular due to movement that has deformed each and at times appear to be gradational. The contact between biotite gneiss I and the coarse-grained amphibolite on the northwest is irregular and unpredictable with the amphibolite probably intruding the gneiss. Contact relations between biotite gneiss II and hornblende gneiss II are conformable. However, an intrusive relation between the gneiss and the coarse-grained amphibolite on the southeast and the amphibolite with quartz megacrysts on the northwest is evident from the irregular nature of the contacts and occurrence of inclusions within the amphibolites.
Compositionally the gneisses differ (Table 4), but their occurrence as narrow bands suggest they could have all formed from sediments which were subsequently metamorphosed.
Hornblende Gneiss
Four hornblende gneiss bands underlie parts of the area. For the sake of simplicity and lack of sufficient evidence to correlate these bands with each other, they are discussed individually below.

Each has been as igned a number, thu g1vmg hornblende gneiss I, hornblende gneiss II hornblende gneiss III and hornblende gneiss IV. All have been studied in some detail.
Hornblende Gneiss I. Hornblende gneiss I crops out south of the Mitchell Hill Gold Mine as a band at least 600 feet wide. Fresh outcrops are in a small stream which joins Mitchell Hill Creek 600 feet west of its intersection with South Fork, and in a road cut approximately two miles southeast of the Harris residence. The remaining outcrops are saprolite. The hornblende gneiss trends N70EN600E and dips vertically. The gneiss is bordered on the southeast by a light-colored quartz-mica schist. The contact is not exposed, but appears to be regular and conformable. Contacts between purplish mica-quartz schist and biotite gneiss on the northwest appear to be conformable also, but the actual contact, again, is not observed.
The hornblende gneiss contains abundant coarse quartz-feldspar bands, 1-2 inches wide, which are parallel to the gneissic banding. Alteration along the margins of the bands has changed hornblende to biotite and chlorite for a distance of 1/4-1/ 2 inch from the band margins. Within the quartz-

10

feldspar bands are scattered coarser prismatic hornblende grains.
Fresh exposures display epidote boudins within the hornblende gneiss. The boudins range from 1/ 2 inch to 2 feet in width and 2 inches to 3 feet in length, and their long dimensions parallel the foliation. They contain veins of white quartz, 1/ 4 to 1/2 inch wide, generally parallel to the long dimension, but some quartz veins randomly traverse the boudins. In one outcrop a vein, ptygmatically folded and offset, continues completely through a boudin. Some of the boudins have been bent into "U" shapes. The hornblende gneiss thickens and thins around the boudins. Contacts between gneiss and boudins are gradational.
Megascopically the rock is a light to dark green, fine- to medium-grained, crystalloblastic, hornblende-plagioclase gneiss. Its variable appearance is caused by the light green, fine-grained, dense zones (boudins) of epidote, which are irregularly

distributed through the rock type. Microscopic data for the gneiss are given in Table 5.
Hornblende Gneiss II. Hornblende gneiss II enters the area 800 feet west of the contact between biotite gneiss II and the coarse-grained amphibolite along Georgia highway 44. The gneiss has a N53 E trend and continues through the area in this direction, outcropping in road cuts as a dark-red-brown clay containing a small percentage of quartz and in streams which traverse or parallel it.
It occurs as a four foot wide band surrounded by biotite gneiss in the road cut of Georgia highway 44. Further to the northeast, especially 300 feet west of the South Fork and Poss's Creek junction along Poss's Creek stream bed, and in the small stream flowing into Poss's Creek 1500 yards west of the South Fork and Foss's Creek join, the gneiss is present in at least four bands. These bands range in thickness from five feet to over 100 feet and are separated by 20 to 50 foot bands of biotite

Mineral

Shape

Hornblende subhedral to
anhedral

Andesine anhedral

TABLE 5

HORNBLENDE GNEISS I

Size

Optic Sign Twinning Extinction

2V

1/ 2 mm. in (-)

length

2V= 82

occasion- Z A C=20 o ally

1/ 2 mm. in (+) diam.

rarely 16-18 albitic l.X

Pleochroism Approx. %
X=light 45-50 greenish gray (5GY8; 1) Y=light olive gray (5Y5/ 2) Z=grayish yellow green (5GY5/ 2) X<Z<Y
45- 50

Epidote in Hbn. gneiss
Epidote in boudins
Quartz

patchy skeletal anhedral
mosaics of subhedral to euhedral
irregular

1mm.

(-)
2V= 7580

3/4 mm. to (-) 4 mm. across 2V= 75-
80

1 mm.

uni.( +)

none none

parallel parallel

slightly

5-8

slightly

95 % of boudin

Accessory: rutile, apatite, zircon, pyrite, magnetite and/or ilmenite.
Microscopically hornblende occurs in both the gneiss and boudins. Within the gneis epidotization of hornblende is rare and only minute granular grains of epidote locally occur within and around hornblende. Minute rounded grains of rutile are commonly f ound along hornblende clea vage a nd part ially surrounding hornblende. 'fhis phenomena is generally associated with the epidotization of hornblende. Very few hornblende grains are in the epidote bouclins ; tho e present are f ound either as inclusions in epidote or around the edges of epidote grains. The intermediat e zone between the hornblende gneiss and the epidote zone contains prismatic grains of hornblende, but with epidote predominating over hornblende. Inclusions of quartz, plagioclase, apatite and a black opaque mineral fr!:!auentlv occur in the hornblende.
(Table 5 continued on next page.)
11

'l'ABLE 5-(Continued)
Andesine is slightly saussuritized along the edges and along twinning planes in the hornblende gneiss. In the epidotic zones saussuritization is strong. Small inclusions of quartz are in the andesine. They are most noticeable in the lath-shaped plagioclase grains which are 2 to 4 mm. in length, but they also occur in grains less than 1 mm. Other inclusions are hornblende, rutile and minute prismatic grains of apatite.
The epidote is derived from alteration of hornblende and andesine. The majority is skeletal and patchy in appearance and contains sinuous inclusions of quartz. Epidote comprises 95 percent of the boudins and the remainder is quartz (Fig. 4 illustrates the texture of the boudins.), saussuritized andesine and epidotized hornblende.
Rutile is a secondary alteration product of hornblende. Within the centers of the rutile grains as well as along the partings, there is commonly a black opaque material, which is probably magnetite and/or ilmenite. Less commonly the rutile is partially surrounded by the opaque material.
All other accessories occur as inclusions in the major minerals. The rocks exhibit a micro-banding or layering in some sections, the layering due to differences in grain size. In the coarser "layers" the andesine occurs as twinned laths 4 to 5 mm. across.

The diabase dikes range in width from 2 feet to 30 feet, cut the hornblende gneiss with no visible evidence of alteration observed due to poorness of exposure.
Three rhyolite dikes are present in the gneiss but again field evidence is insufficient to ascertain any alteration effects.
Megascopically the hornblende gneiss is a grayish-black, fine- to medium-grained, erystalloblastic rock. The visible hornblende is fine pri matic grain aligned parallel, giving the ~ock it distinct foliation . Gn~yi h plagioclase i the only other major constituent. It occurs as fine equant grains distributed in bands between paper-thin prismatic grai11s of hornblende.

F'igttre 4. Photomicrograph of epidote boudin. Epidote (e) and quartz ( q). 0.5 mile east of Mitchell Hill Gold Mine. Unc1ossed nicols, X 20.
gneiss. Observations at three localities in partially weathered l'ock indicate that the inter-layering of the gneisses i conformable with the surrounding biotite gneiss.
Conspicuously present in these bands are epidote boudins. Northeast of South Fork, boudins of epidote from 1 inch to 6 inches in width and 2 inches to 1 foot in length are within the hornblende gneiss. Some of the boudins are not separated, but thicken and thin. The boudins of epidote are continuous along and across strike and increase to the northeast.
The bands of hornblende gneiss are indistinguishable megascopically and microscopically.
Present withil1 hornblende gneiss TI are quartz veins, muscovite-bearing pegmatites, diabase dikes and rhyolite dikes. The diabase dikes and rhyolite dikes always transect foliation, whereas, the quartz veins and muscovite pegmatites, and sometimes aplite are roughly parallel and perpendicular to the foliation.

Veinlets of epidote 1/16 mm. to 1/2 mm. wide traverse the rock in some specimens, not necessarily parallel to the foliation. Some transect earlier veinlets of epidote. Occasional fine quartz grains are present. Minute (less than 1 mm.) veinlets of quartz are found parallel to gneissic banding in some specimens.
Tables 6 and 7 give microscopic data and a point count analysis of hornblende gneiss II, respectively.
Hornblende Gneiss III. Exposed in the road cut west of Flint Lake and along a drainage ditch on the west side of the lake are hornblende gneiss III and a megacrystic amphibolite. The best outcrops of the two rocks are in the South Fork, both northeast and southwest of the road. The hornblende gneiss extends in a northeasterly direction in the area to at least the Old Copper Mine, where inadequate exposure prevents further delineation. The foliation strikes N53E and dips vertically.
The hornblende gneiss contains epidote-quartz veins, 2 inches or less in width, and epidote boudins, 11/ 2 to 3 inches thick and 6 to 9 inches long. The latter are aligned parallel to the foliation.
The porphyritic amphibolite intrudes the hornblende gneiss. Intrusive relations include irregular contacts, inclusions of the gneiss in the amphibolite, and amphibolite truncating the epidote-quartz veins in the gneiss.
In the road cut west of Flint Lake are two sets of fractures: N40E and N50W. Both sets are

12

TABLE 6 HORNBLENDE GNEISS II

Mineral

Shape

Size

Optic Sign

2V

Twinning

Extinction Pleochroism

Hornblende prismatic

1 mm. or less

(-)
2V=78o

ZAC= 17-19

X=moderate greenish yel-
low (10Y7I 4) Y=mod. olive
brown (5Y4/4) Z=dusty yellow green
(5GY5/2) Absorption
X<Z<Y

Andesine

elongate anhedral

1/ 2 mm. diam.

(+)
2V=78o

albite pericline

16-18 _l_X

Chlorite

feathery

1 mm.

(-)

rosettes

parallel

a=grayish yellow (5Y8/4)
y=grayish yellow green (5GY7/ 2)

Epidote

anhedral; patchy

1/2 mm. in (-)

diam.

2V=78

parallel

a= very pale orange (10YR8/2) ,8=pale greenish yellow (10Y8/2)

Accessory: Rutile, quartz, apatite and magnetite and/or ilmenite.
The prismatic grains of hornblende are aligned in planer units giving gneissic foliation. Most of the hornblende is unaltered, but parts of it have altered to epidote or to chlorite along the edges.
The majority of the andesine grains are unaltered, but a few have been saussuritized, yielding small grains of epidote. Inclusions of euhedral apatite and inegularly haped quartz grains ate present.
Most of the epidote forms from the alteration of hornblende to epidote and chlorite; thi alteration is spotted throughout the sections. In places epidote and low birefringent rosettes of chlorite are
associated. Rutile, quartz, apatite and magnetite and/ or ilmenite are scattered accessory minerals. Opaque
minerals are associated with the alteration of hornblende to chlorite, epidote and rutile. Apatite commonly occurs as pri matic inclusions in andesine.

Table 7. Point-Count Analysis of Hornblende Gneisses in Volumetric Percent.

Hornblende Hornblende

Gneiss I Gneiss III

109-74

225-1

Andesine

53.59

42.46

Hornblende

29.60

50.29

Epidote

6.91

1.97

Quartz

4.54

1.71

Sauss. Mica

.50

.32

Rutile & Apatite

3.15

Chlorite

1.57

Red Iron Oxide

.07

Opaque (magnetite,

-

-i-l-m-e-n-it-e-

-& -

-p-y-ri-t-e)--

-

--

-

--3-.-2-2--
100.00

--

-----.1-0----
100.00

109-74 Fine-grained hornblende gneiss collected

in Poss's Creek, 300 feet west of South

Fork.

225-1 Fine-grained hornblende gneiss collected

in road cut west of Flint Lake.

13

offset 2 to 3 inches. A quartz vein 1/2 inch wide is offset 4 inches in the N50W direction.
Also present in the road cut is a mica pegmatite 2 to 4 inches wide trending N30W, which intersects a dark-green, fine-grained, amphibolitic dike, 4 inches wide, which has a general trend of N45E. The two dikes are in both gneiss and amphibolite. The mica pegmatite behaves in a regular manner, whereas, the amphibolite dike is sinuous in character. North of the intersection of the two, the amphibolite dike is offset in a N5060"W direction for 4 feet in several places. The mica pegmatite cuts the amphibolite dike. Near the contact the amphibolitic dike is offset 1 to 2 inches in at least seven places by the N50W fracture system. The mica pegmatite is not offset by this set. Nearby, the N40E set offsets the N50W set 2 inches in a northeast direction. The mica pegmatite is not offset by this fracture set.
The following sequence of events is based on the preceding observations:
1) Formation of the hornblende gneiss with

development of foliation, followed by probable intrusions of porphyritic amphibolite.
2) Emplacement of amphibolitic dikes.
3) Development of northwest fracture set, offsetting amphibolite dike in northwest direction.
4) Formation of northeast fracture set and offset of the northwest set.
5) Emplacement of the pegmatitic dike.
Megascopically the hornblende gneiss is a darkgray to black, hard, heavy, fine- to mediumgrained, foliated rock which commonly has minute epidote veinlets traversing it. Linear rows of pyrite are parallel to the foliation.
The epidote boudins are light green, hard and very fine-grained. They frequently have veins of clear quartz, 1/4 inch wide, parallel to the long direction of the boudin.
Optical and mineral descriptions of hornblende gneiss III are given in Table 8 and a model analysis in Table 7.
Hornblende Gneiss IV. Hornblende gneiss IV enters the area 600 feet southeast of the Anderson residence. The gneiss continues to the northeast, cropping out conspicuously in road cuts near the Battle residence and Randolph Church. It trends northeasterly with foliation dipping steeply to the southeast.
Conspicuously present are epidote-quartz veins and boudins of epidote, which contain numerous veins of quartz, within the hornblende gneiss. These boudins vary from 1/4 inch to 4 inches in width and 6 to 9 inches long. The boudins are from

2 inches to 2 feet apart and decrease in amount to the northeast. Some of the epidote zones are not boudinaged.
Near the Battle residence pink zeolite veins occur frequently in the epidotic zones.
The contacts between the gneiss and the amphibolite are irregular but regionally conformable.
Contacts between the mica schist to the northwest and the gneiss appear conformable.
Megascopically the rock is a light-gray-green,
fine-grained, crystalloblastic hornblende gneiss. The microscopic description of the gneiss is
given in Table 9. The distribution, relation to surrounding rock,
mineralogy and texture of the hornblende gneisses aid in deciphering their origin. All the gneisses occur as distinct bands which are conformable in trend to all the other foliated rocks in the area. None show any intrusive relationships. All have epidote boudins within them. Mineralogically all the gneisses are fine- to medium-grained and composed predominantly of basic minerals. Microscopically there is no evidence of large metasomatic changes, thus the assumption that very little chemical change has occurred during metamorphism seems valid. If this is the case, then the hornblende gneisses probably represent metamorphosed basaltic flows. The epidote boudins within the gneisses could represent the segregation of epidote into bands during metamorphism or could be original chemical differences within
the basaltic rock.
Amphibolite Coarse-Grained Amphibolite. The coarse-grained amphibolite, gabbro according to Hopkins (1914), first appears in the area along Georgia Highway

TABLE 8 HORNBLENDE GNEISS III

Mineral

Shape

Size

Optic Sign

2V

Twinning

Extinction Pleochroism

Hornblende subhedral; 1/2 mm. anhedral

(-) 2V = 82

X=light greenish gray
(5GY8/1) Y=light olive
gray (5Y5/2) Z=grayish
yellow green
(5GY7/2)
X<Z<Y

Andesine An 38-42*

anhedral

1/8-1/4

(+)

mm. laths

albite

18-22 _iX

Accessory: Quartz, rutile, apatite Epidote from hornblende and andesine, saussuritized mica, magnetite/ilmenite, and pyrite are pres-
ent in all sections.
The hornblende is altered very little. Occasional minute grains of epidote are found around the edges of the hornblende. Commonly granular masses of rutile are present around prismatic hornblende grains.
Saussuritization of andesine is slight. Minute prismatic grains of apatite are included in the andesine. Highly birefringent epidote grains less than 1/16 mm. in diameter are scattered sparsely through the gneiss.
Rounded granular grains and masses of rutile, 1/2 mm. in diameter, are mainly around the hornblende. The rutile frequently has a black opaque mass of magnetite and/or ilmenite in the center and around the edges of the granular masses.
Quartz is present as irregularly shaped grains, a fraction of a millimeter across, scattered throughout the rock.

14

Mineral

Shape

Hornblende splintery

Andesine
Quartz Epidote

irregular equant
irregular
patchy; anhedral

TABLE 9

HORNBLENDE GNEISS IV

Optic Sign

Size

2V Twinning Extinction

3 mm. to (-) 1mm.

occasional ZAC= 15-19

1 mm. (+) 1-2 mm.

rarely albitic

15-17 l_X

1/ 2 mm. uni. (+)

l/2 mm. (-)

occasional polysynthetic

parallel

Pleochroism Approx.%
very light 50-60 green
40-50

none

5-10
frac. to 5

The pleochroism, though not measured, of hornblende in this rock is a lighter green than in the other hornblende bearing rocks. Epidotization along the cleavages and edges of the hornblende grains accompanied by rutile is common. This reaction is more prevalent in finer-grained specimens. Sieved inclusions of quartz are in the hornblende grains.
The equant grains of andesine have poikiloblastic inclusions of irregularly shaped quartz which composes 30 percent of the andesine grains. Prismatic hornblende and apatite are the remaining inclusion. The largel" andesine grains have prismatic grains of hornblende forming a circular pattern around them. Bluish granular and needle- haped clinozoisite occurs sparingly in the andesine grains.
Quartz commonly occurs as poikiloblastic inclusions, as minute veinlets traversing randomly through the gneiss and as scattered grains throughout the rock.
Epidote-clinozoisite are strewn throughout the rock. Commonly hornblende is surrounded by epidote and epidote is in turn surrounded by reddish-brown, opaque splotches of iron oxide. The boudins are predominantly epidote.

44, approximately 0.8 mile east of Bethesda Community Center. It continues through the area in a northeasterly direction and leaves the area at the Taliaferro-Greene County line, along Georgia Highway 44.
The best road outcr0ps are along Georgia Highway 44, 500 yards east of Bethesda Community Center. Here, and for 0.3 mile east, the rock is talcose and chloritic and contains scattered pyrite cubes, 2 to 3 mm. across. At outcrops east of Bethesda Community Center pod-shaped mica zones are scattered within the rock. They are aligned northeast-southwest. In places, notably on the old Asbury property and 300 feet east of Poss' dairy barn, the rock is extremely coarse grained and very talcose and chloritic (see Talc, Economic Geology section) .
The outcrop 500 yards east of South Fork on Georgia Highway 44 displays chloritization and vermiculization of the amphibolite, which is crumbly, hummocky and riblike in this cut. Within the cut are numerous quartz-feldspar dikes, muscovite pegmatites, a rhyolite dike and a dike marked by graphic intergrowths of quartz and feldspar. The width of the dikes varies from less than one inch to 15 feet. The muscovite pegmatites have small "offshoots" into the amphibolite. The quartz-feldspar dikes alter the amphibolite marginally to brown, crenulated, vermiculitic schist 1 to 4 inches wide, depending upon the size of the dike. Not all the dikes are bounded by crenulated schist. Near the east end of the cut there are 1/ 2 inch veinlets of epidote-quartz. The white, very fine-grained, rhyolite dike is 12 feet

wide and trends N55W. Along its margins the amphibolite appears bleached.
The amphibolite contains two retrograde zones to the northeast. The first is 700 yards east of the Greene-Taliaferro County line along Georgia Highway 44. It is 100 feet wide, composed of a darkgray, extremely coarse-grained, talcose-chloritic rock which has conspicuous 2 mm. cubes of pyrite. This zone is bounded on each side by coarsegrained amphibolite. Both rocks contain veins of quartz and muscovite pegmatites.
The second zone is 1200 yards due north of the Proctor residence. Boulders of a light gray-green, medium-grained, chloritic rock, 2 feet square or less, are found as float and protuberances on a hillside on the west side of a small stream. This rock has cubes of pyrite, 2 to 3 mm. in diameter, throughout. The float zone is approximately 300 feet wide and 400 feet long. Poor exposures elsewhere prevent tracing of the zone.
Fresh outcrops of the amphibolite are in the stream bed of Mitchell Hill Creek and north of Highway 44 along South Fork. Exposed in stream beds are randomly oriented veinlets of epidote, 1/ 8 mm. to 1 em. wide, which are abundantly present and stand out in relief from the amphibolite. The epidote veinlets increase to the northeast. Veinlets two inches wide with clusters of euhedral epidote crystals are near North Fork. Veins of white quartz traverse through the epidote clusters.
Contact of the amphibolite with the biotite gneiss, on the northwest side, is generally parallel

15

to the foliation of the biotite gneiss. The contacts in South Fork show an increase in grain size within the biotite gneiss, and a trace of foliation in the amphibolite, which is finer grained here than elsewhere. Contacts with the biotite gneiss to the southeast are irregular and not parallel to the regional trend.

Megascopically the fresh rock is a dark-green,

heavy, crystalloblastic, medium- to coarse-grained

amphibolite. The principal minerals are horn-

blende and plagioclase. The hornblende occurs as

equidimensional to slightly elongate interlocking

grains exceeding 6 mm. in length in the coarser

rocks. In finer grained rocks the hornblende (1

to 2 mm. across) is more equidimensional and is

the main constituent. The plagioclase is irregular

in shape to slightly elongated, being 4 to 5 mm.

across in the coarser rocks and 3/ 4 to 1 mm. across

in the finer grained rocks; it is more lath-shaped

in the finer grained rocks.

'

Pyrite and magnetite are the only other visible constituents in the rock and they occur as irregularly shaped splotches and minute octahedra which have reddish iron-oxide rims.

In the retrograded rocks, chlorite, hornblende and light-greenish epidotic minerals are the only visible constituents.

In weathered crumbly rocks, which are lighter in color, several constituents are visible. The light

color is caused by the weathering of plagioclase which takes on a "waxy" appearance. Hornblende alteration to chlorite in fresh rock becomes clearly visible in slightly weathered rock. Greenish casts of epidote also become more visible, occurring within plagioclase and around the hornblende.
Microscopic and optical data are given in Table 10; modal analyses in Table 11.
In considering the origin of the amphibolite, its overall bulk chemical composition, relation to the surrounding rocks, and the shape and texture of the rock should be considered.
Modal analyses of four representative amphibolites show that hornblende and andesine are approximately equal in the rock (Table 11). Though the rock type varies in grain size throughout the area, this mineralogic relationship is fairly constant.
The contact relations were not observed with the surrounding rock types. The amphibolite does conform to the regional trend, but its irregular shape and size suggest that it originated as an intrusive. The overall coarse-grained nature of the rock, the absence of distinct foliation, the mineral assemblage and the predominance of lath-shaped plagioclase grains all suggest that the rock could have originally been a basic intrusive, probably a gabbro, that has been slightly metamorphosed. The presence of abundant epidote veins, the prev-

TABLE 10 COARSE-GRAINED AMPHIBOLITE

Mineral

Shape

Size

Optic Sign 2V

Twinning

Extinction Pleochroism

Hornblende

irregular prismatic grains

1/ 8 to 6mm.

(-) 2V= 78-84

occasional

ZAC= 17-25

Andesine An 37-42*
Epidote
Clinozoisite
Chlorite

equant to lath-shaped irregular grains
rarely euhedral; mostly skeletals & spindles
Euhedral rhombs; rarely skeletals & spindles
feathery rosettes

5mm. lmm. 1 mm. or less
1 mm. or less
2 mm. or less

(+) 2V= 81-85"

albite pericline

( - ) 2V= polysyn-

70-83 ''

thetic

(+)

polysyn-

thetic

(-)
low 2V

22-27 1. X parallel
slightly inclined
parallel

Accessory: Saussurite mica, apatite, rutile, sphene, pyrite and other opaques. (Table 10 continued on next page.)

X=light greenish gray (5GY8/ 1)
Y=light olive gray (5Y5/2)
Z=grayish yellow green (5GY5/2)
X<Z<Y
none
none
yellowish gray (5Y8/ 1) to light green (5G8/ 1)

16

TABLE 10-(Continued)
Hornblende is evenly distributed throughout the rock. Epidotization of the hornblende is common with the products being epidote, biotite, chlorite, rutile and sphene. This alteration is along cleavages, fractures, grain boundaries and patches within the hornblende.
Commonly where hornblende has altered to chlorite, and epidote is not associated with the change, there is an increase in the amount of black opaque magnetite around the hornblende grains. The hornblende in some sections has numerous rodlike inclusions, with high relief, parallel to cleavage directions. In hornblende grains which have altered almost completely, these inclusions increase in size and begin to cluster into larger grains which can be identified as epidote and rutile. The biotite flakes are sparingly found along hornblende cleavages, and within the biotite flakes are flakes of feathery chlorite which parallel the biotite cleavage traces.
Euhedral apatite grains, 1 mm. in length, with opaque needlelike inclusions cross-cut the hornblende grains locally. Poikiloblastic inclusions of quartz, apatite, andesine, and sphene are commonly in the hornblende. Often there are inclusions of a fine-grained mineral with a halo.
Andesine is evenly distributed through the rock. Saussuritization of the andesine ranges up to 75 percent in some sections. Alteration is along cleavages, twin planes, edges, fractures and patches within the mineral, and is most readily visible in grains cut at oblique angles to cleavage and twinning planes. The products are fine-grained sericite and clinozoisite. In places the clinozoisite and epidote are zoned, whereas in other sections the bluish birefringent clinozoisite is confined to andesine and the highly birefringent epidote to hornblende. The sericite is in 1/16 mm. flakes surrounded by very fine sericite aggregates, Extensive saussuritization causes the andesine grains to assume a grayish-black cloudy appearance with marked undulose extinction.
The andesine laths commonly have minute needlelike inclusions which are both reddish to black and light green in polarized light. They are randomly distributed in andesine grains. Minute, rounded, liquid inclusions are also common, as are apatite and quartz inclusions. The larger apatite grains, 1 mm. in length, are commonly euhedral and parallel to andesine with lamellae. Quartz occurs as minute, irreguarly shaped inclusions and rarely as veinlets along albite twin planes, crossing from one lamellae to another.
Two epidote minerals, epidote and clinozoisite, are dispersed through the rock. They are commonly zoned. Epidote has formed from the epidotization of hornblende and saussuritization of andesine. It replaces hornblende along cleavage edges and also occurs as patches within hornblende. Commonly, epidote occurs around the edges, cleavages and twinning lamellae, and as patches within andesine grains. The majority of epidote is from andesine.
Euhedral rhombic-shaped epidote and spindle-shaped epidote are commonly surrounded by chlorite, with the spindles parallel to cleavage traces in the chlorite. In rare cases the euhedral epidote cuts the chlorite flakes in half. Commonly epidote is present within chlorite, which is in turn partly surrounded by hornblende grains. Associated grains of rutile are scattered around and within the epidote.
Veinlets of epidote, 1/8 mm. to 3/4 mm. in width, show differences depending upon the size of the veinlet. Where the smaller veinlets of epidote cross hornblende, the hornblende is readily altered to epidote. However, where the veinlets cross andesine, only small scattered grains of epidote are present. This suggests that plagioclase is not as susceptible to alteration along the epidote veinlets as is hornblende. Epidote reaction rims surrounded by chlorite and small rounded grains of rutile, are common. Secondary iron-oxide spots are present in epidote. Larger veinlets, 3/4 mm. or greater in width, have a thicker selvage of epidote and chlorite bordering the veinlet. Andesine laths, next to the veinlets, have embayments of epidote. The andesine twinning becomes patchy and absent near veinlets, and the twinning lamellae are slightly bent. Near the vein there is an increase in colorless mica. Most of the epidote grains have euhedral to subhedral shapes near the veinlets and also increase in grain size.
Chlorite commonly replaces hornblende and epidote with very little opaque matter associated with either transformation. The chlorite is typically found as feathery rosettes and as slender flakes either surrounding hornblende or occurring as patches in hornblende and as flakes parallel to hornblende cleavages. Epidote and rutile are found either as spindle-shaped inclusions parallel to the chlorite cleavage traces and edges or as epidote surrounding chlorite with rutile partially surrounding epidote.
Accessory apatite and zircon are scattered rarely throughout the section as inclusions in the major minerals. Opaque magnetite and/or ilmenite and pyrite are present in small amounts.
17

TABLE 11. POINT-COUNT ANALYSES OF COARSE-GRAINED AMPHIBOLITE EXPRESSED IN VOLUME PERCENT

109-12 109-89 91-54 91-45

Andesine Hornblende Epidote and
Clinozoisite
Sauss. Mica Chlorite Apatite
Rutile and Sphene Quartz Opaque

42.98 42.64
4.92 .67 .20 .87
.73 1.60 5.39

32.58 47.43
7.32 5.21 6.21
.54
.25 .46

40.49 40.68
4.46 9.60 2.79
.74
.56 .68

32.08 38.58
10.00 5.83
10.56 .77
2.12 .06

100.00 100.00 100.00 100.00

109-12 109-89
91-54
91-45

400 yards east of Bethesda Community Center along Georgia Highway 44.
3/4 mile northeast of Mitchell Hill Mine, along Mitchell Hill Creek.
3/ 4 mile northwest of where South Fork crosses Georgia Highway 44, along South
Fork. 200 yards east of South Fork Bridge in stream 100 feet south of Georgia High-
way 44.

alence of retrograde effects on the major minerals, along with the same retrograde effects on all surrounding rocks, the presence of the slightly metamorphosed rhyolite dikes and the alteration of the rock by the quartz-feldspar dikes all suggest that the rock has been slightly metamorphosed.
Amphibolite with Quartz Megacrysts. Actual outcrops of the amphibolite with quartz megacrysts are found 500 feet northeast of Durham's Lake and 2500 feet northwest of the Durham residence. Both outcrops are in former soil pits. A prominent north-northeast trending ridge, locally called "Rattlesnake Ridge", 1 mile east of the C. Durham residence, is underlain by this amphibolite.
Saprolite with abundant rounded megacrysts of quartz is present in most of the road cuts that pass over the amphibolite. Sawmill roads and many of the fields underlain by the rock are completely covered with 4 mm. to 1 em. in diameter quartz megacrysts. The quartz megacrysts in the saprolite increase to the northeast. Nevertheless, certain problems cause difficulty in mapping this rock type.
The lack of adequate exposure of this rock type, along with the presence of bands of biotite gneiss whose extent was not decipherable within the amphibolite, and the irregular distribution of quartz megacrysts in the saprolite suggest that either more than one rock type underlies this portion of the area or that the rock has a variable mineral assemblage (probably a combination of both). Further division could be made on the basis that the amphibolite in places does not contain visible but microscopic quartz. The presence of characteristic euhedral hornblende, microcline,
18

and the yellow pleochroic epidote are useful microscopic indicators.
Biotite mica occurs in the saprolite in varying amounts. This further complicates mapping of the saprolite. Typically mica is not found in amphibolites. Some saprolite outcrops contain an abundance of mica, whereas, at other places the saprolite contains only small amounts. The amount of biotite may vary in one saprolite outcrop.
Quartz is absent from the saprolite in road cuts along the dirt road that passes on the western side of the Bethesda Church. Outcrops of the amphibolite, 300 feet southeast of South Fork, are notably void of any visible quartz. Quartz is generally absent in the road cut 300 feet northwest of South Fork; however, there the saprolite has zones that contain quartz megacrysts.
Found cropping out in three places within the amphibolite is a grayish-white, coar se-grained, biotite-quartz-feldspru: gneiss. rumbly and weathered outcrops are fo und 1200 yar ds northwest of the M. Durham residence along the fork of a stream. Another outcrop is found 1 1/ 2 miles due east of the C. Durham residence along a sawmill road on C. Durham's property. The gneiss at this locality is composed of fine-grained quartz and white chalky feldspar separated by bands of biotite. The latter two localities are areas in which the saprolite contains abundant megacrysts of quartz.
Amphibolite in the road cuts between the Bethesda Church and the South Fork is altered. Here dark-green, coarse-grained crumbly rock is composed of biotite, vermiculite, hornblende and "waxy" plagioclase. The outcrops have abundant swarms of muscovite pegmatites throughout. The pegmatites range in size from less than 1 inch to 3 feet in width. Some are offshoots from larger pegmatites; others are pod-shaped and seemingly not connected. There is an increase in brown mica in small lenses and in parallel folia which trend N45E. The outcrops contain greenish veins of quartz and epidote, 1/ 4 to 1 inch wide, which trend N75W. There is no visible alteration around these veins.
Near the northern end of the road cut, 300 feet southeast of South Fork, a quartz-feldspar rock with euhedral hornblende grains, 4 to 6 mm. in diameter, is present. It contains rounded grains of quartz, 2 to 3 mm. in diameter and is relatively unaltered compared to the brownish micaceous rock type found elsewhere in the road cut.
The relation of the amphibolite to the biotite gneiss II to the southeast is uncertain, however, intrusions of amphibolite in the biotite gneiss are present 1200 yards south of the Old Copper Mine in small streams that run into South Fork. This suggests that the contact is somewhat irregular and possibly intrusive in nature. Inadequate exposures prevent the exact contact being located. To the northwest the contact between the hornblende gneiss and the amphibolite is somewhat irregular and not continuous. The contacts are based on the quartz content of the saprolite.

Megascopically the amphibolite is a light to dark green and is extremely variable in grain size and in mineral constituents. The amphibolite grain size ranges from fine to coarse grained.
Equant, euhedral grains of hornblende, less than 1 rnrn. to 8 rnrn. in diameter, are scattered through the rock in such a manner that they sometimes overlap. The large euhedral grains of hornblende are in a fine to medium-grained matrix of epidote, plagioclase and finer grained hornblende. In all specimens studied the hornblende occurs as euhedral grains as well as finer anhedral grains in the groundrnass. In some outcrops the groundmass of the rock has been weathered and leached leaving the large equant hornblende grains etched in relief. This gives the rock a rough surface texture.
In some samples hornblende displays a type of "graded bedding". In these samples the euhedral hornblende grains are 1 to 2 rnrn. in size and increase in size up to 6 to 8 mrn. toward a single row of grains, 1 ern. in diameter, followed by a gradual decrease in grain size.
Megacrysts of quartz (Fig. 5), 4 rnrn. to 1 ern. in diameter, glass clear, oblate, spherical and elongate in any one specimen, occur in the amphibolite. Euhedral equant hornblende is present in specimens with quartz megacrysts, but it is seemingly finer grained than where quartz is absent. Three

prominent features can be observed about the megacrysts: in somewhat weathered specimens, 5 to 10 percent of the megacrysts turn to a
Figu1e 5. Microcline (m), hMnblende (h), epidote ( e), a1ound periphery of qua1tz ( q) megacryst. Crossed nicols, X 20.
"waxy" white clayey material; in weathered and fresh specimens, a brownish-green reaction rim

Mineral Hornblende
Andesine An 40-46*
Epidoteclinozoisite
Quartz Microcline

TABLE 12 AMPHIBOLITE WITH QUARTZ MEGACRYSTS

Shape

Size

Optic Sign

2V

Twinning

Extinction Pleochroism

equant, euhedral & anhedral prismatic

6 to 8 rnrn. & 1 rnrn. or less

(-) 2V= 82-84 ''

prismatic, 1 rnrn. or lath-shaped less

(+) 2V=85o

commonly twinned
albite & pericline

ZAC= 17-19
20-22 l_X

X=light greenish gray
(5GY8/l) Y =light olive
gray
(5Y5/2) Z=grayish yel-
low green (5GY5/2)
X<Z<Y

euhedral, subhedral, also patchy, skeletal
rounded to subrounded
anhedral, equant to subequant

2 rnrn. or less
4 rnrn.-1 ern. in diarn. 3/ 4 mrn. to 1 rnrn.

(- ) (+)
uni. (+) biax. (-)

polysyn-
thetic commonly

parailel

none

gridiron

Accessories: sphene, rutile and apatite (Table 12 continued on next page)
19

TABLE 12-(Continued)
Hornblende is present as large equant grains and as small splintery grains. The alteration of hornblende to epidote along cleavages, edges and fractures is prevalent. The small splintery grains of hornblende are preferentially altered more than are the larger more equant grains. Numerous rodlike epidote inclusions, 1/2 mm. in length, are found along the cleavages of the hornblende.
Andesine is generally almost completely sauss uritized to clinozoisite and a very fine flaky sericite. This alteration is best developed along grain edges, cleavages and twin planes, and as patches within the andesine. Andesine is almost completely obliterated, assumes a dark cloudy appearance and shows marked undulose extinction. It is abundantly dusted with a very fine-grained opaque matter. A few andesine grains found near euhedral hornblende are little altered. This is also true of andesine around megacrysts of quartz. Colorless inclusions of various shapes are abundant within the andesine.
Both epidote and clinozoisite are abundant. Zoning prevails, but anomalous clinozoisite commonly is associated with andesine; whereas, epidote occurs with hornblende. A third variety of epidote ( ?) is present, always as an inclusion in hornblende. This epidote is pleochroic in shades of yellow and is surrounded by yellowish-green (5Y8/1) common epidote.
Quartz occurs as large megacrysts which are fractured into 12 to 18 irregular shaped, somewhat sutured grains that exhibit undulose extinction (Fig. 5). The boundaries of the quartz megacrysts are irregular and in contact with andesine, hornblende, microcline. and epidote. Microcline composes 10 to 15 percent of some megacrysts and is found either within or rimming the quartz megacrysts. Hornblende and andesine are rarely present as inclusions.
Fresh grains of microcline are present in all sections (Fig. 5). It comprises less than 10 percent of the rock by volume. It occurs predominantly around or within quartz megacrysts and rarely as inclusions in hornblende.

(epidote) is present around the megacrysts; the megacrysts are abundantly fractured. In some speciments the quartz megacrysts compose 25 to 30 percent of the rock and in others not more than one percent.
The finer grained groundmass contains visible saussuritized lath-shaped plagioclase. Epidote is a most conspicuous component.
Quartz-feldspar veinlets, 1/4 to 2 inches wide, randomly traverse the rock. Near the margins of these veinlets, hornblende has been incorporated into the veinlets with a notable increase in its grain size.
In some float specimens zoning is common. This is an alteration of euhedral hornblende zones with little quartz surrounded by zones of the same material with abundant quartz. Milky quartz veins, 1/4 to 1/2 inch wide, are found in both masses. The quartz veins cut the quartz megacrysts and distort them.
Microscopically the amphibolite is composed predominantly of quartz megacrysts, euhedral hornblende, fine-grained plagioclase, epidote and hornblende. An ill-defined relict diabase texture is present. Table 12 gives optical data and microscopic descriptions of the rock components.
Relict diabase texture, spotty non-pleochroic relicts in hornblende (possibly pyroxene) and the general overall chemical composition all indicate that this was a basic igneous rock. The field distribution though not well defined, and the presence of quartz megacrysts in a rock, which usually contains only accessory quartz, suggest that a basaltic rock with silica-filled vesicles could have been metamorphosed to produce the amphibolite. Alternately, the absence of foliation, presence of
20

a relict diabase texture, coarse grain size, spotty non-pleochroic relicts in hornblende (possibly pyroxene) the presence of quartz and overall mineral composition, the "graded bedding" and zoning of the quartz (any large metamorphic effects would wipe these out), all could indicate that the rock was once a quartz gabbro which has undergone a slight metamorphism, producing an amphibolite. The latter seems more plausible.
Porphyritic Amphibolite. Exposed in the road cuts west of Flint Lake is a porphyritic amphibolite. Outcrops are also present in South Fork, both northeast and southwest of the road for a distance of 1/2 mile in each direction.
The amphibolite crops out in 10 to 15 foot wide irregular patches and as 1 to 2 foot wide stringers in contact with hornblende gneiss III. The contact between the two rocks is irregular and unpredictable. There are no clear-cut baking relations, but there is an apparent decrease in grain size of the megacrystic amphibolite near the contact of the two rocks. Inclusions of gneiss in the amphibolite and amphibolite truncating the epidote-quartz veins in the g n e i s s are further evidence of an intrusive relation. The amphibolite possesses no foliation.
Structural data concerning fracture sets, muscovite pegmatites and amphibolite dikes were previously discussed with hornblende gneiss III.
Contacts between the metapyroxenite and the porphyritic amphibolite are seemingly irregular though exposed only in the saprolite.
Megascopically the porphyritic amphibolite is a gray-black rock composed predominantly of hornblende and plagioclase in varying grain size. The plagioclase occurs as white laths 1 to 5 mm. in

length, as well as euhedral grains, 3 to 4 mm. in diameter, in a hornblende-plagioclase-epidote matrix. Hornblende is present primarily as prismatic grains, 1 to 2 mm. in length, without parallel alignment. In some specimens are conspicuous biotite flakes, 5 mm. in diameter.
Veinlets of quartz, epidote and calcite (0.5 mm. or less in width) randomly traverse some specimens. Microscopic descriptions and modal analyses of the porphyritic amphibolite are given in Tables 13 and 14 respectively.
An igneous origin for the amphibolite is indicated by its intrusive relations. The rock could be derived from a basic intrusive.
Metapy.roxenite
This rock crops out extensively in the spillway of Flint Lake and 500 feet east of the spillway. Outcrops are good along the road on the west side of the lake and south along the road to Georgia Highway 44. Prominent outcrops are found 500 feet north of the intersection toward Flint Lake.

TABLE 14. POINT-COUNT ANALYSES OF PORPHYRITIC AMPHIBOLITE EXPRESSED
IN VOLUME PERCENT

225-33

225-35

Hornblende Andesine
An 44-46*
EpidoteClinozoisite
Sauss. Mica Quartz Rutile, Apatite
& Sphene
Chlorite Opaque (includes
magnetite/ilmenite and pyrite)

32.88
41.01 21.42
1.76 .81 .34
1.62
.16

39.88
36.49 14.23
.13 .13 1.23 7.78
.13

100.00

100.00

225-33 Collected 400 yards northeast of Flint Lake.
225-35 Collected 600 yards northeast of Flint Lake, in South Fork stream.

TABLE 13

Mineral

Shape

PORPHYRITIC AMPHIBOLITE

Optic Sign

Size

2V

Twinning

Extinction Pleochroism

Hornblende

subhedral anhedral prismatic

2mm.

(-)

occasion-

2V= 80-82 ally

ZA C= 20-22 o

X=light greenish gray
(5GY8/1) Y=light olive gray
(5Y5/ 2) Z=grayish yellow-green
(5GY7/ 2)
X<Z<Y

Andesine An
44-46*

euhedral megacrysts
& anhedral grains

5 mm. in diam.
1 mm.

(-)

albite &

2V= 82-84 o perieline

21-23
l_X

Epidote-

elongate

lmm.

(- )

Clinozosite euhedral

(+ )

grains

parallel slightly inclined

non-pleochoric

Chlorite

feathery

lmm.

(-)

parallel light green

Accessory: apatite, rutile, magnetite and/or ilmenite and pyrite.
Hornblende occurs as grains, irregular in shape, with ragged edges and as prismatic grains. Both are sieved. Chloritization and epidotization is evident along the edges of hornblende. Opaque grains of magnetite are closely associated with these reactions. Prismatic grains of hornblende thicken and thin around the megacrysts of andesine, suggesting that the prismatic grains may have been pushed apart by growing megacrysts.
All of the andesine is saussuritized along cleavages, twinning planes and around margins, and completely altered in places. In specimens containing megacrysts of andesine and finer grains of andesine in the matrix, the larger megacrysts are preferentially saussuritized. The products of saussuritization are euhedral elongate epidote and clinozoisite and very fine-grained sericite. Numerous minute needle inclusions are in the andesine.
Epidote and clinozoisite are associated 90 percent of the time with plagioclase and about 10 percent with hornblende.
The chlorite is associated with hornblende.

21

Mineral Hornblende

Shape
euhedral to anhedral patchy grains
subhedral
to anhedral,

Size 1 mm.

TABLE 15

META PYROXENITE

Optic Sign

2V

Twinning

commonly

11/ 2 em. or less (-)

""'uidote- anhedral, 2mm. (- )

Clinozoisite patchy,

or less (+ )

skeletal

Extinction
ZAC=
43-45

Pleochroism Approx o/o

non-

10-15

pleochroic

light bluish green to olive green

60-65 20-25

Accessories: apatite, rutile and opaques.
Augite is commonly surrounded by fibrous hornblende or occurs as felted non-pleochroic patches within hornblende.
Hornblende occurs as feathery and fibrous grains, but mostly as patchy anhedral grains with ragged edges. Commonly it contains irregular shaped, high birefringent, deep-yellow pleochroic grains, 1 mm. or less in diameter, of epidote (piedmontite). There are also deep-yellow pleochroic patches scattered through some hornblende grains. The epidote grains commonly have black opaque patches within them. All are then surrounded by hornblende. Rodlike inclusions of a high birefringent mineral are common in hornblende. Commonly rounded "knobby" grains of rutile, 1/ 8 mm. across, occur within and around hornblende crystals.
Both epidote and clinozoisite occur within the metapyroxenite, but epidote predominates. The epidote rarely replaces hornblende, although it does occur along the cleavages and edges of hornblende.

In the outcrops around Flint Lake, the metapyroxenite contains abundant, randomly oriented, veinlets of quartz and feldspar, 1/ 2 inch or less in width. In the Flint Lake spillway the rock is intensely sheared and faulted, but possesses no distinct foliation. The lack of adequate exposures prevented an accurate delineation of the rock's extent.
The irregular contacts between the metapyroxenite and the hornblende gneiss and porphyritic amphibolite, which are northwest of the metapyroxenite, can be traced west of Flint Lake to the road. In the road cut at the intersection of Georgia Highway 44 and the road west of Flint Lake, a 2 X 3 foot outcrop of amphibolite is present. This rock is medium in grain size and does not show any visible retrograde effects as does the extremely coarse-grained metapyroxenite. Outcrops of this amphibolite can be found 1200 yards to the northeast. Whether this amphibolite is the same as the Flint Lake metapyroxenite is unknown.
Megascopically the metapyroxenite is a darkgreen, heavy, extremely coarse-grained rock. It contains grains of hornblende, 1 em. or less in diameter, separated by light-greenish mediumgrained epidote.
Table 15 gives optical properties and mineral descriptions of this rock.

The presence of relict pyroxene, coarse-grained nature of the rock and the overall mineral assemblage indicate that this rock was an ultrabasic, intrusive, igneous rock. The absence of foliation indicates a younger age than the foliated rocks.
Granite
Granite saprolite exposures are present within the Woodville city limits and extending 3000 feet east of the city limits along the bituminous-surfaced road. No actual outcrops were observed, but a light-yellowish-red, medium- to coarse-grained, clayey saprolite containing fairly abundant amounts of quartz, gray-to-black fine mica and relict feldspar grains is present.
The saprolite changes in texture 3000 feet east of Woodville to a dark-red, fine-grained saprolite which is composed predominantly of clay with very small amounts of quartz and mica. The clayey saprolite exhibits relict boxwork or "honeycomb" structures along with a faint foliation which could be hornblende gneiss. Contact relations between the two rocks are obscure. The granite saprolite is continuous along the dirt road which trends north after it forks off from the bituminous road 3000 feet east of Woodville.
Granite is also found 300 feet west of Union Point city limits on Georgia Highway 44, along the north-flowing tributary of the South Fork. Outcrops in this stream are of a white-gray, mediumto coarse-grained, biotite-quartz-feldspar granite. The biotite is randomly scattered 1 to 2 mm. flakes

22

in medium- to coarse-grained interlocking quartz and feldspar. Possible saprolite of the rock is found 600 yards east of Union Point city limits, 150 feet north of Georgia Highway 44 intersection with the bituminous-surfaced road. The saprolite is in contact with metapyroxenite saprolite.
Quartz Veins and Pegmatites
Quartz veins and muscovite pegmaties are abundant. The quartz veins are 1/ 2 foot wide to a fraction of an inch in width. The majority are either parallel or perpendicular to the foliation of the rocks. Some pinch out within 18 inches, others can be traced 25 to 30 feet. Commonly they are along fracture sets when they are parallel or perpendicular to the foliation of the rocks. The quartz veins commonly are offset along a northwest-southeast set of fractures from 1 inch to 1.5 feet.
Locally, where quartz veins traverse epidote boudins, there is a noticeable increase in the grain size of the epidote. In some boudins there are very coarse-grained clusters of epidote within the quartz veins.
Muscovite pegmatites, like the quartz veins, are abundant. Like the veins, they are, in the majority of cases, roughly parallel or perpendicular to the foliation of the surrounding rocks if the rocks have a foliation. The pegmatitic rocks vary in grain size from fine grained to extremely coarse grained, containing in addition to quartz, feldspar and muscovite, biotite, magnetite and epidote in varying amounts. One pegmatite, to be discussed in another section, is being mined. Some of the larger ones are found east of the Poss residence along Georgia Highway 44 in road cuts.
In the country rocks the medium- to coarsegrained muscovite pegmatites and aplites range in size from 6 inches to 2 feet in width. They are continuous in all outcrops observed. A slight thickening and thinning is commonly present. In dirt road cuts, 200 feet to the north of North Fork, there are numerous pegmatites. At this locality hornblende gneiss is the country rock and locally it has been biotitized and chloritized by the pegmatites. There are numerous grains of hornblende within the pegmatitic material. The pegmatitic bands are 1/ 4 to 3 inches wide and are parallel to the gneiss foliation. These pegmatitic bands alternate with brownish biotitized and chloritized hornblende bands which range from 1/ 2 to 6 inches wide. Parallel hornblende laths within the quartz-feldspar groundmass increase in grain size. The biotitized and chloritized bands of hornblende gneiss are around the margins of the muscovite bearing pegmatitic material and grade laterally into less altered hornblende gneiss.
The alteration of the surrounding rocks by the quartz veins and especially the pegmatites, indicates that they are younger than the enclosing rocks.
Rhyolite Dikes
Rhyolite dikes are found in four places. The most accessible one is in a road cut west of South Fork of the Little River along Georgia Highway 44. In this road cut the dike is 12 feet wide and trends N55W in coarse-grained amphibolite. A

second dike is 900 yards northeast of the Poss residence along Poss's Creek. It is 15-18 feet wide and trends N78W.
Cropping out 1000 yards west of M. Durham's residence is a third rhyolite dike. It is 15+ feet wide and trends N70 W. It can be traced for 500 feet in a northwest direction to the stream crossing. Because of poor exposure the only relationships between the rhyolite and surrounding rock types that can be obtained are in the Georgia Highway 44 road cut west of South Fork of the Little River. Here, apparent bleaching ( ?) of the surrounding crumbly chlorite-vermiculite amphibolite is apparent for 1 1/ 2 feet from the contact. At the contact there is a change in color, grain size, and mineral type. Near the contact the crumbly saprolite is brownish, fine-grained and clayey, with abundant mica. Six to eight inches away from the contact there is a gradual change in color toward a greenish black and an increase in grain size. One and one-half feet away from the contact a greenish-black clayey saprolite with mica still exists, but relict hornblende grains can be seen as well as "waxy" feldspar grains.
Megascopically the rhyolite is whitish gray and porphyritic. It contains colorless, 1 to 3 mm., euhedral quartz grains with the characteristic betaquartz shapes, and 1 to 3 mm., pinkish, euhedral microcline grains. Both are found in a fine groundmass composed of quartz, feldspar, biotite and muscovite. In places, notably west of M. Durham's residence, pyrite cubes, 1 mm. or less in diameter, are sparingly scattered through the rock.
The microscopic description and optical data of the rock is given in Table 16.
The presence of these slightly metamorphosed rhyolite dikes in rocks that have been metamorphosed as high as the amphibolite facies shows that they are younger than the surrounding rocks. The fine grain size and the presence of morphological beta quartz indicates that the dikes were formed near the surface and cooled rapidly. Possibly the dikes were "feeder" dikes to surface flows near the end of the metamorphism. Possibly they are even younger and are concurrent with evidence of vulcanism on the Coastal Plain.
Diabase Dikes
Eight previously unreported diabase dikes are in the area (see Plate 1). They cut all the other rocks. They range in width from 2 feet up to 50 feet. Some can be traced for 3 miles. Their trend ranges from N20W to N40W with variations in any one dike; the dip is mostly vertical. The width of the dikes varies by 2 to 5 feet from one outcrop to another. Best exposures are in road cuts that cross the dikes. The largest dike in the area is in front of the Proctor residence along Georgia Highway 44. The dike here has split into two parts. The larger dike 40 feet wide, the smaller apophysis is 2 feet wide and 10 to 15 feet west of the larger dike.
In the same outcrop the dike cuts a white, extremely coarse-grained pegmatite. The pegmatite is bent and contorted on both sides of the diabase. The majority of the dikes are partially weathered,

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Mineral

Shape

Micro line
Quartz
Oligoclase An 29-33*
Muscovite Biotite

euhedral phenocryst
bipyramida!(?) & anhedral
equant laths
shreds

Size
1 mm. to 3 mm.
3 mm. in diam. to 1mm.
2 mm. or less

TABLE 16 RHYOLITE DIKES

Optic Sign Twinning 2V

(-)
2V = 78

gridiron

uni. (+)

(+)
2V = 82

albite

1/ 2 mm. or less

Extinction
10-13 l. X

Comments
N = 1.5240
f3
Characteristic beta-quartz morphology

Part of the microcline occurs as euhedral aggregates 1 to 2mm. across which are abundantly fractured. The edges of the larger grains of microcline commonly have irregular embayments filled by the finer matrix minerals and in places there are apparent inclusions of the matrix minerals. The gridiron twinning of the microcline is very close, giving a felted or quilted appearance (Fig. 6). Some microcline grains display a vague zoning optically. Irregular, minute fractures filled by quartz are in a few microcline grains.
Quartz occurs as phenocrysts (Fig. 7), and a fine-grained matrix constituent. The phenocrysts of quartz, like the microcline, have embayments around the grain margins and the finer grained matrix minerals fill the embayments. This gives the quartz a resorbed appearance.
Oligoclase has abundant fine-grained inclusions of mica and is commonly dusted with irregular brown to black opaque masses.
Muscovite and biotite occur as shreds, 1/ 2 mm. across or less, and commonly interleaved. Black opaque material parallel to cleavage traces are common, as well as around the shreds of mica.

Figur e 6. Euhedral microcline in 1hyolite dike. Cross ed nicols, X 20.

Figtl?'e 7. Euhedral qua1tz g7ain with characteristic betaquartz shape. Crossed nicols, X 20.

forming spheroidal boulders in streams and road cuts and a dark red-brown clay with relict diabase fragments. Float of the diabase can be traced readily by its resistance to weathering and the spheroidal shape of the residual boulders.
Megascopically the diabase is a dark greenishblack, hard, heavy fine- to medium-grained rock with diabasic texture. Dark-gray microlites of
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plagioclase can be seen randomly oriented with the spaces between microlites filled by light-green grains of pyroxene.
Optical data and the microscopic description of the diabase is given in Table 17.
The origin and age of the diabase dikes of Georgia have been considered by Lester and Allen (1950). They related the origin to post-Paleozoic

Mineral Augite

Shape anhedral

Size 1mm.

Labradorite subhedral

An

micro lites

62-69*

1 mm. length

TABLE 17

DIABASE DIKES

Optic Sign

2V

Twinning

(+)

(+) 2V = 84-86

occasional

Extinction ZAC=
48
36-40 .lX

Pleochroism
non-pleochroic pale greenbrown

Olivine

anhedral

1 mm.

Accessories: magnetite and pyrite.
Augite is unaltered.
Labradorite is relatively unaltered, but some grains are cloudy. The microlites are separated from each other by anhedral augite.
Colorless olivine grains are scattered through the rock. Some grains are half olivine and half augite, suggesting an augite replacement of olivine. Very fine, transparent, acicular grains with parallel extinction and index of refraction greater than balsam radiate from some olivine grains.
Minute scattered, subhedral to anhedral grains of magnetite and pyrite are disseminated sparingly. The magnetite is commonly found along the edges of the augite.

downwarps which opened fissures in the crystalline rocks. They suggested that the source was a relatively deep magmatic basin and that all the dikes in the Georgia Piedmont came from the same magma source.
Darton (1880), Roberts (1923) and others dated the dikes that occur from Virginia to Connecticut as Triassic in age on the basis of stratigraphic position. Lester and Allen concluded also that the unmetamorphosed character of the dikes indicate a post-Paleozoic age. Their wide distribution in rocks older than Cretaceous and absence from Cretaceous and younger rocks implies either a Triassic or Jurassic age.
STRUCTURE
A strong regional schistosity and foliation is impressed on most of the rocks. The trend is northeast-southwest with mostly vertical dips.
Fracture sets in the rocks are predominantly parallel and perpendicular to the foliation. They become more conspicuous to the northeast. Sets range from N28E to N50E and from N40W to N62W. The quartz veins, quartz-feldspar dikes and muscovite pegmatites are commonly parallel to one of these directions. Quartz-feldspar "dikes", muscovite pegmatites, and quartz veins which trend parallel to the gneissic banding are locally offset by the N50 to 62W trending set of fractures. This offset is for 1 to 2.5 feet in the northwest-southeast direction. They are fractured along the N38 to 40 E direction but not offset. In places, notably in the road cut west of Flint Lake, the northeast fracture set offsets the northwest set 1 to 2 inches in the northeast direction.
Possible shear zones are at Flint Lake within the metapyroxenite and near the Mitchell Hill Gold Mine. The extent of these zones is not known.
Epidote boudins are abundant in all the horn-

blende gneisses in the area, whereas, the amphibolites do not exhibit any boudinaging, which would indicate that their history began after the most intense folding and deformation had subsided.
A glance at the attitude measurements plotted on Plate 1 reveals that there are two distinct trends present. One is N60 to 70E and the other is N40 to 45E, both with predominantly vertical dips. By projecting these two distinct attitude trends to the southwest, it becomes obvious that they would intersect at some point outside the area to the southwest.
Two obvious explanations are present. Either a regional reorientation of the stress fields has occurred or a deflection of the foliated rocks occurred when the emplacement of the gabbro took place. This gabbro is now the coarse-grained amphibolite described previously. The latter explanation seems more plausible. If this explanation is true, then this is further evidence that the amphibolite was originally an intrusive rock and post dates the metamorphism which impressed a foliation on the surrounding rocks.
GEOLOGIC HISTORY
Metamorphic History
The earliest decipherable episodes are the deposition of sedimentary and pyroclastic ( ?) rocks, intercalated with basaltic flows, followed by the intrusion of gabbro, granite and pyroxenite. The rocks were then metamorphosed to the amphibolite facies. Synchronous with the metamorphism was the development of the foliation, folding, boudinaging, and emplacement of quartz veins and pegmatites. The amphibolites, granite and metapyroxenite do not exhibit foliation and therefore, are probably subsequent to this first metamorphism.

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A second period of less intense metamorphism caused cataclastic and retrograde effects on the hornblende, biotite and plagioclase. This retrograding effect increases to the northeast within the hornblende-bearing rocks. The biotite gneiss near Mitchell Hill Gold Mine and the hornblende gneiss west of Flint Lake show very little retrograde effects. Fracturing parallel and perpendicular to foliation, followed by offsetting of the quartz veins and pegmatites in a northwest-southeast direction also occurred during this period.

temperature and the availability of a transporting agent. An example in which little exchange occurred is the presence of epidote and clinozoisite in the same rock. These minerals represent a possible disequilibrium within the rock, since clinozoisite and epidote could easily combine and form an epidote intermediate in composition if certain physical and chemical conditions are met. In places, the conditions were met and exchange of chemical constituents did occur, and common epidote is the predominate epidotic mineral.

The zones of shearing between the biotite gneiss and mica-quartz schist east of Mitchell Hill Gold Mine and within the metapyroxenite took place during this period. The crinkling of primary foliation and the cataclastic textures present in both the gneiss and schist attest to this fact. Since the metapyroxenite exhibits no foliation and if it was emplaced subsequent to the first metamorphism, then the shearing occurred either concurrent with or in waning stages of the second metamorphism.
Postdating the pegmatites are the rhyolite dikes which alter and transect the regional trend of the surrounding rocks. The dikes display slight metamorphic effects, implying either their emplacement during the waning stages of the second metamorphism or later intrusion and subjection to a possible third metamorphism.
The diabase dikes are subsequent to the rhyolite dikes and pegmatites. Evidence for this includes the cutting of the pegmatites by the diabase dikes, chilling effects on country rock and no evidence of metamorphic effects. They cut across the regional trend.
Post-Crystallization Alteration
Epidotization. Epidotization affects hornblende along cleavages and grain edges. This process seems to increase to the northeast within the hornblende-bearing rocks. The epidotization is closely associated with veinlets of epidote and is commonly accompanied by flakes and rosettes of chlorite, grains of rutile and rarely biotite. Within the biotite-bearing rocks epidote commonly replaces biotite. Accompanying this change is muscovite.
Saussuritization. The plagioclase feldspars are commonly saussuritized along cleavages and margins. The principal products are epidote and clinozoisite and saussurite mica. The epidote minerals predominate. Common epidote is confined to hornblende and clinozoisite prevails within and around plagioclase. In some rocks the two epidotes are zoned. Epidote predominates in the zoning cases. This occurrence is notable to the northeast.
Significance of Post-Crystallization Alteration
The reactions and the products of the above cannot be listed as balanced chemical equations. Instead they were all occurring synchronously. Whether interaction and exchange of the chemical components between the different minerals occur depends upon the minerals involved and pressure,

The formation of epidote, biotite, chlorite and talc from hornblende and the saussuritization of plagioclase represent volume changes. The changes could have been accomplished by the introduction of water.
Summary
The mineral assemblage of the hornblende and biotite gneisses and their distribution as continuous conformable bands suggest that they were originally interlayered sediments and basaltic flows. The irregular shape, basic mineral assemblages, and grain size of the amphibolites and metapyroxenite indicate they originated as intrusive rocks. The ubiquity of hornblende and its subhederal shape in the layered mafic rocks indicate that the rocks were metamorphosed to the amphibolite facies.
Cataclastic textures, crinkled foliation, offset of quartz veins and pegmatites, baking by pegmatites, and hydrothermal alteration suggest a second, less intense, metamorphism. The hydrothermal alteration is evidenced by breakdown of hornblende to epidote, chlorite and rutile. These products are found predominantly as patchy, irregular-shaped grains along cleavages and grain boundaries.
The slight metamorphic effects, present in an area metamorphosed to the amphibolite facies, and the cross-cutting relations connote the emplacement of the rhyolite dikes in waning stages of the second metamorphism or possibly during a third metamorphism.
The unmetamorphosed nature, cross-cutting relations, and chilling effects on bordering rocks indicate that the diabase dikes are subsequent to the rhyolite dikes and are post-metamorphic.
It is not certain whether the two periods of metamorphism can be separated by a long time interval or whether they are successive stages in one main event.
SAPROLITE MINERALOGY
Saprolite samples of the biotite gneisses, hornblende gneisses and amphibolites were collected to determine the mineral constitutents in weathered residuum of these rocks. Care was taken not to collect soil samples. The samples were analyzed for bulk mineral constituents and then for clay size fraction of the saprolite.
The biotite gneiss saprolite is a light-red, clayey, powdery type which contains very fine quartz

26

and silvery-gray mica. X-ray diffraction patterns from 5 different localities showed that kaolinite, lOA o mica and an abundant amount of quartz are present. This substantiates the petrographic study in that abundant quartz and feldspar and mica are present in the thin sections. In the weathering processes the quartz and mica remain essentially the same, although the mica is slightly hydrated and decomposed. The feldspar decomposes to kaolinite.
The hornblende gneiss saprolite is generally a dark-red to brown, clayey type which contains minute grains of quartz. X-ray patterns show that the saprolite is mostly kaolinite with low intensity peaks of lOA o mica in some samples. A little quartz is in all samples.
The occurrence of kaolinite only and little or no montmorillonite suggests that both the plagioclase and hornblende decompose to kaolinite. The appearance of lOA o mica can be related to saussuritization which is observed in the petrographic work.
Typical saprolite of the amphibolites is a dark brown-red clay with a minor amount of quartz. A few samples contain grayish-white flakes of mica. X-ray diffraction patterns of bulk saprolite without mica show the clay to be kaolinite and minor quartz. Patterns of samples with mica show chlorite, vermiculite, kaolinite and quartz. This agrees with the petrographic study with one exception; vermicullte was not recognized in the thin sections.
ECONOMIC GEOLOGY
This section is a brief description of minerals and rocks which have been mined or prospected in the area.
Copper
Reynolds Prospect-This prospect is located on the Malcolm Durham property. The workings include an old shaft 100+ feet deep and four newly excavated trenches around the shaft. These trenches resulted from a drilling program carried out by the Tennessee Copper Company in 1960. According to Mr. Owen Kingman and Mr. Otis Gibson, geologists for the Tennessee Copper Company (personal communication), the methods used and the results obtained from the prospecting program are as follows:
1) A total of 2000 feet of superdip magnetic traverse was run over the prospect without locating an anomaly.
2) A sum of 4,650 feet of self-potential traverses was run over the prospect area without finding an anomaly.
3) Three holes were drilled on the property to a depth of 280 feet below the surface and 400 feet along strike. No mineralization of value was found.
4) The rock intersected by the drill holes consisted of amphibolite or hornblende gneiss with occasional alternate bands of granite gneiss. The general strike of the rock is

N20E with an approximate dip of 75NW. A few grains of pyrite are observed in the core; calcite is common as a fracture filling.
5) Each hole intersected a fault which is estimated to strike N12E.
Surficially the country rock is a dark green, extremely chloritized amphibolite or hornblende gneiss, abundantly peppered with pyrite cubes, and with abundant blue and green stains of the secondary copper minerals, malachite and azurite.
Gold
Mitchell Hill Gold Mine-Jones (1909) reported that gold had been mined in commercial quantities from here. It was exploited as early as 1852 and in 1875 by Mr. William Smith. Mr. Smith reportedly obtained nine to fifteen dollars worth of gold per week. Subsequent to Mr. Smith's operation, a mining company drove a tunnel several hundred feet into a ridge and ran several crossdrifts. There is no record of gold removed by this operation.
The auriferous rock is the quartzite described in a previous section. Jones reported an assay value of $1.24 per ton. Three assay samples collected by the writers yielded values of $1.75, $0.87 and $0.70 per ton. Although these values are below ore grade, the prospect warrants further investigation, especially east along the schist band which lies along strike of this auriferous locality.
Iron and Manganese
Deposits of iron and manganese are found in the southeastern part of the area (see Plate 1). The deposit is in a 3.5 to 4 foot zone of quartz, garnet and magnetite, striking N70E and dipping 65 northwest, parallel to the schistosity of the mica-schist which encloses it.
A vertical shaft was sunk in 1916 or 1917 to a depth of 80 feet and drifts 30 and 28 feet were extended to the northeast and southwest respectively. Hard and soft ore 23 inches between a hanging wall of micaceous schist and a footwall of quartz, kaolin and a little mica, was present in the northeast drift (Hull, LaForge and Crane 1919).
Float of the zone can be traced 1/2 mile.
Kaolin
On the Hester property 0.3 mile east of the Poss residence a weathered pegmatite has been mined for kaolin. According to Veatch (1908), the kaolin formed from the weathering of a 15 to 20 foot wide northwest-southeast trending pegmatite. A shaft 40 feet deep was dug and two drifts run longitudinally for 50 feet. Part of the open pit workings of the pegmatite are now covered by road fill. No exposures of the weathered pegmatite were observed by the writers.
Pegmatite
Old Sunshine Mine-This property is presently owned by Mr. William Poss. The mine workings

27

are in a cut about 150 feet long by 75 feet wide and 20 feet deep. The mine was originally opened about 1944 for scrap mica. Subsequent to 1944, the mining of feldspar was begun by B. P. Tuggle. The operation stopped about 1954, but Mr. W. F. Stuckey reopened the mine in 1963 to produce quartz.
The pegmatite has a 6 to 8 foot wide clear quartz core surrounded by feldspar with silvery-gray herringbone mica within fractures in the feldspar and in pockets scattered randomly through the rock. Clusters of spessartite garnet 4 to 8 inches wide are found randomly in the feldspathic portion of the pegmatite. Some of the garnets are golf-ball size. Also within the feldspar are brownish-black splotches of radioactive minerals. Furcron (1955), described these as occurring in veinlets and aggregations in the feldspar. A spectrographic analysis reported by Furcron shows niobium to be the major element with U, T, Y, Ca, Si, Fe and Ta as minor elements. An X-ray analysis by Vernon J. Hurst showed the radioactive mineral to be metamict.
Minable amounts of scrap mica and feldspar and quartz remain.
Talc
Talc is found in at least three places. The first locality is 0.5 mile west of Bethesda Community Center on the old Asbury property. Hopkins (1914) briefly described this occurrence. According to Mr. Hackney, a local resident in the area, this locality is called the "old lead prospect". The actual outcrop is on a small knoll 500 feet south of Georgia Highway 44, now completely covered by vegetation; however, numerous prospecting pits are visible. The country rock was an amphibolite or gabbro, which is now extremely talcose and chloritic in places. Two-inch veins of bladed talc are in some float boulders. To the southwest scattered float contains pyrite cubes 4 mm. in diameter.
Talcose amphibolite is also 0.5 mile east of the Poss residence in a pasture. This outcrop is on the south side of Georgia Highway 44. The outcrops are in a drainage ditch within the pasture, 500 yards east of the dairy barn. No vein talc was found.
Talcose outcrops of a basic rock are found 1200 yards southeast of Mitchell Hill Gold Mine in the southeast portion of Plate 1. These outcrops are 2 X 4 foot protuberances in a road cut. The rock is a chloritized-talcose basic rock similiar to the two noted above. No vein talc was found.

SUMMARY AND CONCLUSIONS
This investigation was undertaken to determine the geologic history of the Bethesda Church area. The study began by detailed field work and subsequently followed by a petrographic study. The nature of the various lithologies was first delineated and their distribution plotted to produce a geologic map. The rocks were then studied petrographically for mineralogy, texture, and alteration effects. Both the petrographic study and the distribution of the rocks were used in an attempt to outline the metamorphic history and origin of the rocks.
The saprolite mineralogy of the prevalent rock types was investigated, as was the economic mineral potential of the area.
The following conclusions result from this study:
1. The principal rock types in the Bethesda Church area are amphibolite and hornblende gneiss, with lesser amounts of biotite gneiss, schist, metapyroxenite, quartzite and granite. Three different types of amphibolite are present. One contains megacryst of quartz, possibly a metamorphosed vesicular basalt or quartz gabbro. Another is a coarse-grained variety, likely a metamorphosed gabbro. The third is a porphyritic variety. The hornblende and biotite gneisses likely represent originally intercalated basalt flows and graywacke sediments.
2. Two periods of metamorphism, separated by intrusive activity, are present. During the first period the rocks were metamorphosed to the amphibolite facies. The development of foliation and folding were concurrent with this period. This was followed by intrusions of gabbro and pyroxenite. Cataclastic effects accompanied by shearing and subsequent hydrothermal alteration occurred during the second period of metamorphism.
3. Slightly metamorphosed rhyolite dikes crosscut the regional trend and indicate a period of vulcanism subsequent to or during the waning stages of the latter metamorphism.
4. Late cross-cutting diabase dikes are unmetamorphosed and their chilled contact suggests that they are post-rhyolite.
5. The saprolite mineralogy varies distinctly and predictably for each rock type.
6. Possible economic deposits of feldspar, iron ore, mica, quartz and gold are present.

*Plagiocla se comp ositions determined with th e Fe dor ow -Nikitin ty pe stereo g r a m plot. See Em m ons, R.C., 19 43 , The U niv el'sal Sta g e, Geo]ogical Society of A merica , M emoir 8. 205 p p .

28

SELECTED REFERENCES

Bailey, E. H. and Stevens, R. C. (1960), Selective staining of K-feldspar and plagioclase on rock slabs and thin sections: American Mineralogist, Vol. 45, Nos. 9 & 10, pp. 1020-1025.
Cloos, Ernst (1947), Boudinage: Transactions American Geophysical Union, Vol. 28, pp. 626-632.
Cloos, Ernst (1946), Lineation, a critical review and annotated bibliography: Geological Society of America Memoir 18, 122 p.
Crickmay, Geoffrey W. (1952), Geology of the crystalline rocks of Georgia: Georgia Geological Survey Bulletin 58, 54 p.
Darton, N. H. (1880), Relationship of the trap rocks of Newark system in the New Jersey region: U. S. Geological Survey Bulletin 67, pp. 70-74.
Engle, A. E. J., and Engle, C. G. (1951), Origin and evolution of hornblende andesine amphibolites and kindred facies (abstract): Geological Society of America Bulletin 62, pp. 1435-1436.
Fairbairn, H. W. (1949), Structural petrology of deformed rocks: Addison-Wesley Press Inc., Cambridge, Mass., 344 p.
Furcron, A. S. (1955), Prospecting for Uranium in Georgia, Part I: Georgia Mineral Newsletter, Vol. 8, p. 42.
Galpin, S. L. (1915), Feldspar and mica deposits of Georgia: Georgia Geological Survey Bulletin 30, pp. 65-66.
Gates, R. M. (1958), Syntectonic amphibolites: Geological Soeiety of America Bulletin, Vol. 69, No. 12, pt. 2, p. 1570.
Grout, F. F. (1932), Petrography and pertology: McGrawHill Book Co., New York, 522 p.
Grim, Ralph E. (1953), Clay mineralogy: McGraw-Hill Book Company, Inc., New York, 384 p.
Haseltine, R. H. (1924), Iron ore deposits of Georgia: Georgia Geological Survey Bulletin 41, 222 p.
Hatch, F. H., Wells, A. K. and Wells, M. K. (1961), Petrology of the igneous rocks: Thomas Murphy and Co., London, 515 p.
Hopkins, 0. G. ( 1914), Asbestos, talc and soapstone deposits of Georgia: Georgia Geological Survey Bulletin 29, p. 293-294.
Hull, J.P.D., LaForge, Laurence. and Crane, W. R. (1919), Report on the manganese deposits of Georgia: Georgia Geological Survey Bulletin 35, p. 212-214.
Hurst, Vernon J. (1955), Stratigraphy, structure and mineral resources of Mineral Bluff quadrangle: Georgia Geological Survey Bulletin 63, p. 137 p.
Hurst, Vernon J. (1959), The geology and mineralogy of Graves Mountain, Georgia: Georgia Geological Survey Bulletin 68, 33 p.

Jones, S. P. (1909), Gold deposits of Georgia: Georgia Geological Survey Bulletin 19, pp. 264-265.
Kerr, P. F. (1959), Optical mineralogy: McGraw-Hill Book Co., New York, 442 p.
Kesler, T. L. (1942), Correlation of some metamorphic rocks in the central Carolina Piedmont: Geological Society of America Bulletin, Vol. 55, pp. 775-782.
Lester, J. G. and Allen, A. T. (1950), Diabase of Georgia Piedmont: Geological Society of America Bulletin, Vol. 61, pp. 1217-1224.
Long, Leon, Kulp, J. Laurence and Echelmann, F. Donald (1959), Chronology of major metamorphic events in the southeastern U. S.: American Journal of Science, Vol. 257, No. 8, pp. 585-603.
McCallie, S. W. (1910), Mineral resources of Georgia: Georgia Geological Survey Bulletin 23, 208 p.
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Ramberg, Hans (1952), The origin of metamorphic and metasomatic rocks: The University of Chicago Press, 317 p.
Roberts, J. K. (1928), The geology of the Virginia Triassic: Virginia Geological Survey Bulletin 29, p. 163.
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Silver, Leon T. and Grunenfelder, M. (1957), Alteration of accessory allanite in granites of the Elberton Area, Georgia: Geological Society of America Bulletin, Vol. 68, No. 12, pt. 2, p. 1796.
Smith, L. L. (1931), Magnetite deposits of French Creek, Pennsylvania: Pennsylvania Geological Survey, 4th series, M-14, pp. 32-52.
Turner, F. J. and Verhoogen, J. (1960), Igneous and metamorphic petrology: McGraw-Hill Book Co., New York, 694 p.
Veatch, Otto (1909), Clay deposits of Georgia: Georgia Geological Survey Bulletin 18, pp. 256-257.
Watson, Thomas L. \ 1902), Granites and gneisses of Georgia: Georgia Geological Survey Bulletin 9-A & 10-A, p. 182-187.
Winchell, A. N. and Winchell, H. (1951), Elements of optical mineralogy: John Wiley and Sons, New York, 551 p.

29

GEOLOGIC MAP ot the
BETHESDA CHURCH AREA GREENE COUNTY, GEORGIA
by
Jack H. Medlin
1967
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Plate 1
Information Circular 35 Georgia Department of Mines, Mining, and Geology A. S. Furcron, Director

N

EXPLANATION

D

Quartz muscovite paragonite schist

i1iliJ Mica quartz schist

il ~G ';ii:::X:

Quartzite

Biotite gneiss

Hornblende gneiss I, II, Ill, IV

Coarse grained amphibolite

-
~
E1
(~ a ol

Amphibolite with quartz megacrysts Porphyritic amphibolite
Meta pyroxenite
Granite
Ferruginous manganiferous zone

Rhyolite dikes

Zones of hydrothermal alteration
lZJ Diabase dikes

SYMBOLS

Inferred contacts

Probable contacts

Contacts

Str ike and dip of foliation



Foliation vertical

Old mines and prospects

G

Sample for gold assay