Geology and geochemistry of altered serpentinites in the Burks Mountain complex, Columbia County, Georgia

GEOLOGY AND GEOCHEMISTRY OF ALTERED SERPENTINITES IN THE
BURKS MOUNTAIN COMPLEX, COLUMBIA COUNTY, GEORGIA
Mark D. Cocker
GEORGIA DEPARTMENT OF NATURAL RESOURCES ENVIRONMENTAL PROTECTION DIVISION GEORGIA GEOLOGIC SURVEY

Cover Photo: Fractured clast of serpentinite, altered to talc along fractures and rim of clast. Small divisions on scale are centimeters. Outcrop along Old Petersburg Road.

GEOLOGY AND GEOCHEMISTRY OF ALTERED SERPENTINITES IN THE BURKS MOUNTAIN COMPLEX,
COLUMBIA COUNTY, GEORGIA
Mark D. Cocker
Georgia Department of Natural Resources Joe D. Tanner, Commissioner
Environmental Protection Division Harold F. Reheis, Director Georgia Geologic Survey
William H. McLemore, State Geologist Atlanta 1991
Bulletin 124

TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS .......................................................................................................................................... v LIST OF TABLES ........................................................................................................................................................... vi ABSTRACT ..................................................................................................................................................................... 1 INTRODUCTION.......................................................................................................................................................... 1
Purpose .......................................... .. ................................................................................................................. 1 Location ............................................................................................................................ ...................... .......... 1 Topography...................................................................................................................................................... 2 Exposure ........................................................................................................................................................... 2 Vegetation ........................................................................................................................................................ 2 Previous studies .............................................................................................................. .. .............................. 2 Burks Mountain Complex.............................................................................................................................. 2 Field and laboratory techniques ................................................................................................................... 4 Acknowledgements ........................................................................................................................................ 5 REGIONAL GEOLOGY ................................................................................................................................................ 5 LOCAL GEOLOGY....................................................................................................................................................... 7 Rock Types ......................................................................................................... .. .................... .. .. ............... .. ... 7
General ............................................................................................................................................... 7 Felsic lithologies ................................................................................................................................ 7 Mafic lithologies ................................................................................................................................ 11 Ultramafic lithologies .................. ............................................................................................ .. ....... 11 Multilithic breccia ............................................................................................................................. 24 Weathering of serpentini.te and talc ............................................................................................... 24 Coastal Plain sedimentary rocks .................................................................................................... 30 Structural Geology .......................................................................................................................................... 32 Ductile deformation ......................................................................................................................... 32 Brittle deformation ........................................................................................................................... 32
Talc veins and chlorite fractures ........................................................................................ 35 Carbonate veins .................................................................................................................... 35 Quartz veins ........................................................................................................................... 35 Multilithic breccia ................................................................................................................. 35 "Dry" brittle fracturing ......................................................... .. ............................................. 35 Summary of fractures and vein distribution ............................................................................................... 37 Topographic lineaments ................................................................................................................................. 37 METAMORPHISM AND ALTERATION ........................................ ................. ......................................................... 37 Felsic and mafic rocks of the Kiokee belt ..................................................................................................... 37 Ultramafic rocks .............................................................................................................................................. 40 Prograde metamorphism ............................................................................................................... 40 Serpentinization ................................................................................................................................ 43 Alteration of serpentinite ................................................................... .. ........................ ..... ............... 46 Talc .......................................................................................................................................... 49 Carbonate ............................................................................................................................... 49 Chlorite ................................................................................................................................... 49 Silicification ........................................................................................................................... 49 Alteration of country rocks ............................................................................................................................ 49 Secondary biotite ............................................................................ .................................................. 51 Secondary albite ................................................................................................................................ 51 Ti-bearing phases .............................................................................................................................. 51
iii

TABLE OF CONTENTS (cont.)

Page

PETROCHEMISTRY ..................................................................................................................................................... 51

Felsic and mafic rocks ............................................................................... .......................... .... .......... .............. 54

Ultramafic rocks .............................................................................................................................................. 54

Magmatic trends ............................................................................................................................... 54

Effects of serpentinization ............................................................................................................... 59

Effects of metasomatism .................................................................................................................. 64

Effects of silicification ................... ................................................................................................... 70

Chemical effects of weathering ..................................................................................................................... 70

GEOPHYSICS ................................................................................................................................................................ 75

Gravity .... .......................................................................................................................................................... 75

Magnetics ......................................................................................................................................................... 75

DISCUSSION AND CONCLUSIONS ........................................................................................................................ 77

Physical conditions during prograde metamorphism ............................................................................... 77

Physical conditions during serpentinization .............................................................. ................................ 77

Physical conditions during serpentinite alteration .................................................................................... 81

PARAGENESIS AND ORIGIN ................................................................................................................................... 86

Paragenesis ................................................................................................................ ....................................... 86

Geochronology of metamorphism and alteration ..................... .............. .. ................................................. 86

Origin of the Burks Mountain ultramafic rocks ......................................................................................... 89

REFERENCES CITED ................................................................................................................................................... 92

APPENDICES ................................................................................................................................................................ 97

I.

Whole Rock Chemistry- Mafic and Felsic Rocks ......................................................................... 99

II.

Whole Rock Chemistry- Ultramafic Rocks .................................................................................. 101

III. Norms- Felsic and Mafic Rocks .................................................................................................... 103

IV. Norms- Ultramafic Rocks .............................................................................................................. 105

V.

Modal Analyses- Mafic and Felsic Rocks .................................................................................... 107

VI. Modal Analyses- Ultramafic Rocks .. .. ........................................................................................... 108

iv

Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9.
Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25.
Figure26. Figure 27. Figure28. Figure 29. Figure30.
Figure 31. Figure 32. Figure 33. Figure 34. Figure 35. Figure 36. Figure 37. Figure 38. Figure39. Figure40. Figure 41. Figure42. Figure 43. Figure44. Figure 45. Figure 46.

LIST OF ILLUSTRATIONS
Page
Location map of the Burks Mountain complex and project area............................................... 3 Generalized geologic map of the Pollards Comer area............................................................... 6 Geologic map of the talc prospect ....................... ........................................................................... 8 Photomicrograph of quartzo-feldspathic gneiss ............................ ..................................... .. ....... 10 Granite in contact with talc and coarse-grained chlorite in drill core ....................................... 10 Photomicrograph of metagabbro (amphibolite) ............................................. .............................. 12
o Ca0-Al2 3 diagram of mafic lithologies ........................................................... ........................ ... 13
Photomicrograph of metabasalt (amphibolite) ............................................................................. 14 Banded amphibolite gneiss (metabasalt) in contact with talc and coarse-grained chlorite in drill core .......................................................................................................................... 14 Ground magnetic map of the talc prospect (contour interval 200 gammas) ............................ 15 Photomicrograph of lizardite .......................................................................................................... 17 Photomicrograph of Fe-Cr spinel, lizardite and chlorite ............................................................ 17 Photomicrograph of Fe-Cr spinel (reflected light) ................................................................... .... 18 Photomicrograph of lizardite pseudomorphs after olivine and enstatite ................................ 18 Position of analyses relative to normalized base of serpentinite ................ ........................ ....... 19 Normative olivine and enstatite versus height above base of the serpentinite ....................... 20 Ti-magnetite and ilmeno-hematite concentrations ...................................................................... 21 Millimeter-scale layering in contact with massive serpentinite ................................................. 22 Photomicrograph of millimeter-scale layering ............................................................................. 23 Cross section B-B' .............................................................................................................................. 25 Long section A-A' ............................................................................................................................. 26 Detailed geology of Old Petersburg Road outcrop ...................................................................... 27 Multilithic breccia ............................................................................................................................. 28 Closeup view of multilithic breccia ....... ......................................................................................... 28 Chlorite, foliated talc and massive talc alteration envelope around serpentinite clast in multilithic breccia ................................................................................... ............................. 29 Massive talc clast with fibrous talc rim in coarse-chlorite from multilithic breccia ................ 29 Talc boulder field .............................................................................................................................. 31 Outcrop of Coastal Plain sandstones ...................................................................................... .. ..... 31 Histogram of foliation dips (core and surface) ......................................................................... .... 33 Histogram of strikes of foliation, igneous layering, metamorphic contacts, granite contacts (surface) ................................................................................................................. 34 Histogram of dips of talc, chlorite and carbonate veins and fracture fillings (core) ............... 36 Histogram of brittle structure orientations (surface) ................................................................... 38 Histogram of stream orientations ................................................................................................... 39 Photomicrograph of acicular tremolite partially replaced by lizardite and carbonate .......... 41 Talc pseudomorphs after enstatite porphyroblasts ..................................................................... 41 Disseminated patchy talc in serpentinite ...................................................................................... 42 Cr-Al-Fe+3 diagram .......................................................................................................................... 44 Photomicrograph of magnetite destruction in talc ....... .. ...................................... ...................... . 47 Modal magnetite- talc diagram ....................................................... .............. .......... .. .. ..... .. ..... ....... 48 Modal talc-lizardite diagram ........................................................................................................... 50 Photomicrograph of secondary biotite cutting and replacing hornblende .............................. 52 Photomicrograph of secondary biotite cutting and replacing plagioclase .. ............................. 52 Photomicrograph of secondary albite ............................................................................................ 53 Niggli mg-c-(al-alk) triangular diagram ................. .. .... ................................................................. 55 Ca0-Na2o-K20 triangular diagram ...................................................... ........................................ 56 AFM triangular diagram ....................................................................... ........ .. .. ........................ ....... 57

v

Figure47. Figure48. Figure49. Figure 50. Figure 51. Figure 52. Figure 53. Figure 54. Figure 55. Figure 56. Figure 57. Figure 58. Figure 59. Figure 60. Figure 61. Figure 62. Figure 63. Figure 64. Figure 65. Figure 66. Figure67. Figure 68. Figure 69. Figure 70. Figure 71. Figure 72. Figure 73.

LIST OF ILLUSTRATIONS (cont.)

Page

Normative Ab-An-Q diagram ....................................................................................................... .. 58

Si02 and MgO versus height above base in the serpentinite ..................................................... 60 CaO versus height above base in the serpentinite ....................................................................... 61

C02 versus height above base in the serpentinite ....... ............................................................ .... 62 Co versus Ni ...................................................................................................................................... 63

Co versus height above base in the serpentinite .......................................................................... 63

RO' versus Si02-H2o ....................................................................................................................... 65

RO' /Si02 versus height above base in the serpentinite ............................................................. 66

H 20 / Si02 versus height above base in the serpentinite ............................................................ 66

Oxidation ratio versusH20/Si02.................................................... ............................. .. ............... 67

Al20 3 versus height above base in the serpentinite .................................................................... 67

Na20 and K20 versus height above base in the serpentinite .................................................... 68

SFei0O2vaenrdsuMs HgO20, F/eS2io032

r a tio .......................... ....... ........................................................................... and FeO versus serpentinite alteration type ........................................

69 71

o Al20 3 and CaO versus serpentinite alteration type .................................................................... 72
Na2 and K20, and Ti02 versus serpentinite alteration type .................................................. 73

Ground magnetic survey line ................................................................................. ......................... 76

Time-temperature diagram for Alleghanian metamorphism .................................................... 78

P-T phase diagram for MSH system .............................................................................................. 79

P-T phase diagram for MASH system ........................................................................................... 80

Temperature-silica phase diagram for MSH system ................................................................... 83

T-XC02 phase diagram ........................................................................................... ......................... 84 Chlorite Al20 3 content versus distance from igneous contact .................................................. 85 Chlorite Al20 3 content versus metamorphic grade .................................................................... 87 Paragenesis of Burks Mountain complex ...................................................................................... 88

Frequency versus Mg/CMg+Fc) in selected u.Jtramafites ............................................................ 91

Sample location rnaps .......................... ............................................................................................. 110

Table 1. Table 2. Table 3.

LIST OFTABLES
Page Typical prograde metamorphic assemblage of serpentinites ................................................... 45 Average whole rock analyses: serpentinite, talc,chlorite ............................................................ 74 Chemistry of fresh and weathered serpentinite ........................................................................... 74

vi

GEOLOGY AND GEOCHEMISTRY OF ALTERED SERPENTINITES IN THE BURKS MOUNTAIN COMPLEX,
COLUMBIA COUNTY, GEORGIA
by
Mark D. Cocker

ABSTRACT
Ultramafite bodies, hosting potentially economic talc, nickel, chromium, vanadium, titanium, and rare earth element mineralization, occur within metamorphic rocks of the Kiokee belt in Columbia County, Georgia. The ultrarnafites are fragments of the elongate Burks Mountain igneous complex. This complex is conformably enclosed within gently to moderately dipping, middle to upper amphibolite facies gneisses and schists.
The Burks Mountain complex near Pollards Corner, Georgia consists principally of serpentinites derived from differentiated, layered cumulate metaharzburgites. The serpentinite is vertically zoned from olivine-normative rich at the base to enstatitenormative rich at the top. Rhythmic, fine-scale silicate banding is developed near the upper part of the exposed complex. Associated with the silicate banding are layers of massive magnetite and ilmeno-hematite, enriched in V, P, Ti02 and rare earth elements. Textures suggest separation of an immiscible Fe-rich melt from the silicate melt, perhaps related to anlnjection of new magma, and slow cooling at deep crustal levels.
Remnants of an olivine+ I-enstatite+ I- tremolite +I- anthophyllite+ chlorite assemblage, preserved in
the metaharzburgite is indicative of upper amphibolite facies metamorphism and peak metamorphic conditions near 700C and 3-5 kb. Later, retrograde greenschist facies metamorphism of the metaharzburgite to a lizardite serpentinite indicates that conditions during serpentinization were probably below 250C and 500 bars pressure with less than 300 bars fluid pressure.
Subsequent fracturing of the serpentinites opened channelways for hydrous, siliceous, and COTbearing fluids to form talc selvages around serpentinite clasts and along fractures in the serpentinite. In one of the serpentinites, which was studied in detail, extensive fracturing occurred alongits upper contact. The resulting multilithic breccia consists mainly of talc clasts

with minor amounts of Kiokee gneiss and kaolinized granite clasts in a matrix of chlorite. Chlorite formed at the expense of lizardite and talc during the influx of alumina-bearing solutions. Also at that time, chloritization of the adjacent country rock led to development ofsecondary albiteand biotite, and remobilized CaO and Ti02 to form titanite and ilmenite. Widespread quartz veining and silicification affected large portions of some of the other serpentinite bodies.
It is suggested that the mafic-ultramafic Burks Mountain complex was intruded at deep crustal levels into the Kiokee belt rocks that may represent a continental margin or a transitional continental-island arc setting. During the Alleghanian orogeny, this complex was dismembered and emplaced into its present structural position. The metamorphism, fracturing and alteration of the ultramafites is probably related to the Alleghanian orogeny and events during or immediately following its waning stages. Peak metamorphism and deformation in the Kiokee belt is dated at 315 to 268 Ma (Dallmeyer and others, 1986).
INTRODUCTION
PURPOSE
The geology and geochemistry of talc-bearing ultramafites and of the enclosingcountry rocks located approximately 3.5 km ESE of Pollards Corner in Columbia County, Georgia is described and interpreted in this report. A description of the talc mineralization, its origin, and its economic significance is documented in an accompanying publication (Cocker, in press (b)). The economic potential for nickel, chromium, titanium, vanadium and rare earth elements are also discussed in the accompanying publication.
LOCATION
The area covered by the current investigation is located 3.5 km ESE of Pollards Corner in Columbia

1

County, Georgia (Fig. 1). The northwestern corner of the project area is approximately 8215'W and 3337'30"N in the northwestern comer of the Evans 7.5' quadrangle. Reconnaissance studies to the west overlapped into the northeast comer of the Appling 7.5' quadrangle.
Access to the area is via Georgia Highway #304/ U.S. Highway #221 or Georgia Highway #-104. to Pollards Corner and via the paved Old Petersburg Road or the graded dirt Old Middleton Road to the village of Rosemont at the western end of Burks Mountain.
TOPOGRAPHY
Elevation of the project area generally ranges from 250 to 350 feet (76 to 108 m). The surface is gently rolling to flat and is cut by a few steep-sided gullies, 3 to 7feet (1 to 2m) deep. Along the northern edge of the project area, the western end of Burks Mountain rises 180 feet (55 m) above the surrounding area to a maximum elevation of 535 feet (163 m). This east-west trending ridge consists of a series of elongate hills, which gradually decrease in altitude to the east, and terminates at the Savannah River. Pervasively silicified scrpentinites underlying Burks Mountain are significantly more resistant to weathering than surrounding lithologies.
Earlier studies (Hopkins, 1914; LeGrand and Furcron, 1956; McLemore, 1965; Worthington, 1964; and Hurst and others, 1966) refer to the western end of Burks Mountain as Burte (or Burt) Mountain and to the eastern end as Dixie Mountain. Recent studies (Secor, 1987; Sacks and others, 1987; Sacks and others, 1989; Vincent, and others, 1990) refer to the ridge as Burks Mountain because it is named as such on the Evans 7.5' topographic quadrangle. In this report, this ridge will be referred to as Burks Mountain, with references to Dixie and Burte Mountain as used in earlier studies.
EXPOSURE
Rocks in the project area are exposed along: three major roadcuts on Old Petersburg Road; steep-sided gullies and creeks; and on the upper slopes of Burks Mountain. In addition, outcrops of resistant rocks are scattered in fields and forested areas. The high annual rainfall averaging 48.5 inches (LeGrand and Furcron, 1956) and warm temperatures are typical of subtropical conditions leading to extensive weathering of bedrock.
VEGETATION
Forests of pine and mixed hardwood, the South-

em Pinelands, cover approximately 50 percent of the project area with the remainder of this area consisting of open pasture. The vegetation patterns reflect, to a certain extent, the character of the underlying lithologies.
Serpentinite, talc and silicified serpentinite tend to form poor soils, which are generally rocky and well drained. Such soils arc drier than the more deeply weathered soil and saprolite developed over the surrounding rocks. Soils developed from serpentinites arc generally enriched in Mg and Fe, but very low in vital nutrients such asK, Na, P, AI and various trace elements associated with less basic rocks. This unusual soil composition is commonly reflected in unusual vegetation communities. Within this study area, oaks, sweetgum and hickory are prevalent in areas with outcrop or float from the serpentinite.
Deeply weathered gneisses, granites and schists or coastal plain sandstones tend to form the better soils. Pastures or pines are more prevalent in these areas of more felsic substrate.
PREVIOUS STUDIES
The earliest geologic studies of the Pollards Corner area were generally regional in scope (Hopkins, 1914; Crickmay, 1952; LeGrand and Furcron, 1956). These studies first noted the occurrence of mafic and ultramafic rocks in this part of the Piedmont.
During the 1960's a number of studies were concerned with the economic evaluation of the Pollard's Corner area (Worthington, 1964; McLemore, 1965; Hurst and others, 1966). In the early 1960's, the J.M. Huber Corporation tested the nickel and chrome potential in four core holes in the vicinity of Dixie Mountain and in one core hole approximately 1/2 mile southeast of Pollard's Comer.
More recent studies include a brief description of the "Burks Mountain suite" ofultramafic rocks (Vincent and others, 1990) and regional studies of stratigraphy, petrology, structure and tectonic evolution of the southeasternmost Piedmont in Georgia and South Carolina (Maher, 1978; Secor and others, 1986a and 1986b; Sacks and others, 1987; Sacks and others, 1989). A regional synthesis of the stratigraphy, structure, and tectonostratigraphy of the southernmost part of the Appalachian orogen has also been recently compiled (Higgins and others, 1988).
"BURKS MOUNTAIN COMPLEX"
The mafic/ultramafic bodies in the vicinity of Pollards Corner remained unnamed (Hopkins, 1914; LeGrand and Furcron, 1956; McLemore, 1965) until

2

Burks Mountain Complex

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Figure 1. Location map of the Burks Mountain complex and project area. 3

they were defined as the Burks Mountain complex by Sacks and others (1987) and the Burks Mountain suite by Vincent and others (1990). In order to establish some consistency and simplicity in terminology, this report will refer to the mafic/ultramafic bodies as the Burks Mountain complex. The Burks Mountain suite oflithologies as described by Vincent and others (1990) are actually alteration phases of the same protolith (Cocker, 1989a).
FIELD AND LABORATORY TECHNIQUES
The present investigation focussed on a small area which was mapped in detail on a scale of 1"=200 feet (1 :2400) using an enlarged topographic base. Roadcu ts containing exposures of the serpentinite or important metamorphic, intrusive and structural relations were mapped in greater detail at a scale of 1"=50 feet (1 :600). As an aid in 1:2400 scale mapping and to establish stations for a detailed ground magnetic survey, a grid was established using tape and Brunton compass. A baseline (the ON line in Fig. 10) was established along a N73E line with stations every 200 feet along that line. From those baseline stations, secondary lines were run perpendicular to the baseline with additionaI stations established every 100 feet along these secondary lines. An initial ground magnetic survey orientation line (the ODE line in Fig. 10) was run along the Old Petersburg Road with stations every 50 feet. The grid was oriented parallel to the Old Petersburg Road so as to avoid barbed wire fences and power lines and to be perpendicular to the anticipated strike of the serpentinites and local structure. These procedures were designed to maximize anticipated geologic effects and to minimize cultural effects on the ground magnetic survey.
Ten drill holes were cored in 1987 and 1988 to obtain subsurface lithologic, structural, alteration, and veining data. Drill core was logged in detail (1"=10 feet) and then sampled for geochemical analysis, thin section and x-ray diffraction studies.
Rock-chip geochemical samples were collected during the field mapping phase from selected outcrops and float. Float was sampled when outcrops were lacking and after it was determined by field relations that the float was essentially in place. Rockchip samples were collected by taking 20 to 301/2 inch chips from an area of approximately 5 to 10 feet in diameter to minimize single sample variations. Channel samples were taken to obtain an average composition of certain lithologies. Occasionally, the sampling area was restricted to a particular portion of an outcrop, or single samples were taken because of sample availability.

Whole-rock analyses of core and surface samples
included analysis for Si02, AI2o3, Fe203, FeO, MgO,
CaO, Na20, K20, LOI, Ti02, P20 5, and MnO. Selected samples were analyzed for Au, Ag, Cu, Pb, Zn, As, Hg,

Pt, Pd, Co, Ni, Cr, Sr, V and Ba.Jnduced coupled argon

plasma (ICAP) techniques were used for 5102, Al203,

MgO, CaO, Na20, ~0, Ti02, P20y an and Ba. Dichromatic titration was used

d MnO, Sr, V for Fe+2 and

Fe+3. Loss-on-ignition (LOl) was determined bygravi-

metric analysis. Ni, Cr, Co, Rb, Cu, Pb, Zn, Ag, Au and

As were determined by atomic absorption (AA). Fire

assay and ICP were used for Pt and Pd analysis.

Samples were sent to Skyline Labs., Inc.(Wheat Ridge,

CO) for standard whole-rock analyses and for trace-

element analyses. In addition, selected samples were

analyzed for rare earth elements (REE) by instrumen-

tal neutron activation analysis (lNAA) and by x-ray

fluoresence (XRF) by Bondar-Oegg, lnc. (Lakew od,

CO).

X-ray diffraction analysis (XRD) was used to de-

termine the mineralogy of the serpentinite, because

optical and chemical methods are not suitable for

distinguishing the various serpentine minerals:

antigorite, lizardite and chrysotile. Because the ser-

pentine minerals have different structures, diffraction

methods can distinguish the different types of serpen-

tine. The 330 reflection at 1.56-1.57 Angstroms, which

is unique to antigorite (Bailey, 1969; Wicks and

O'Hanley,1988),distinguishes an tigori tefrom Jizardi te.

The chrysotile structure is composed of two layers and

is distinguished on the basis of 20l reflections. The one-

layer nature oflizardite lT (in contrast to the two-layer

structure of chrysotile) is clearly indicated by the 111

series of reflections (Wicks and O'Hanley, 1988). Other

minerals: talc, chlorite, calcite, dolomite and magne-

site, were identified by XRD.

Petrographic studies consisted of optical mineral

identification and textural relations descriptions using

standard transmitted- and reflected-light microscopy.

Twenty-three standard thin-sections and 6 polished

thin-sections of fresh, unweathered drill core samples

collected during this study plus 12 standard thin-

sections of surface samples collected by Vincent and

others (1990) were examined. These samples represent

11 separate serpentinite bodies which together extend

over 12 km along strike. Modes of mineral abundances

were determined from pointcountsof300 to350grains

per thin-section. For counts of 300-350 points, a two

standard deviation error ranges from <1 to 5 percent

with a 95 percent confidence level (Van der Plas and

Tobi, 1965). The lower error level (<1) is for low per-

centage minerals, and the higher error level is for

mineral percentages in the 25-75 percent range.

4

ACKNOWLEDGEMENTS
The author gratefully acknowledges Mr. J. Dan Smith of Augusta, Georgia for his permisssion to conduct the investigation on his property and for his continued interest in the work. The author wishes to express thanks to all the reviewers for their criticisms and comments of earlier versions of this document. These include Drs. Gilles 0. Allard and James A. Whitney of the University of Georgia and Dr. Paul E. Sacks of the United States Geological Survey.
REGIONAL GEOLOGY
A series of serpentinitebodiesoccurring southeast ofPollards Corner in Columbia County, Georgia form part of an elongate group of mafic/ultramafic rocks defined as the Burks Mountain complex (Sacks and others, 1989). The Burks Mountain complex (Fig. 2) extends from Columbia County in Georgia into South Carolina for a total strike length of over 20 miles (33 km). A second belt of small pods and lenses of ultramafic rock and amphibolite, located 2.5-3 miles (4-5 km) north of and roughly parallel to the Burks Mountain complex, may be part of the Burks Mountain complex which was folded over on the northwest limb of the Kiokee antiform (Sacks and others, 1989). The Burks Mountain complex mainly consists of serpentinite, metagabbro, talc and several types of amphibolite interpreted as a suite of metamorphosed and locally altered harzburgite, cumulate wherlite or olivine clinopyroxenite, cumulategabbro and anorthositic gabbro, rodingite and possibly mafic volcanic rocks (Sacks and others, 1989).
The Burks Mountain complex is roughly parallel to the regional strike (Fig. 2) and concordant with regional foliation of gently to moderately dipping, middle to upper amphibolite grade, migmatitic metamorphic rocks of the Kiokee belt (part of the Macon melange of Higgins and others, 1988) in the southeastem part of the Piedmont Province of Georgia. The Kiokee belt is a northeast-trending, lithostratigraphic belt extending from eastern Georgia into South Carolina. It consists of a sequence of migmatitic micaceous quartzo-feldspathic gneiss, locally interlayered with amphibole-biotite schist, and biotite-muscovite schist. Migrnatitic gneiss and sillimanite schist indicate that middle to upper amphibolite facies metamorphism was attained in the Kiokee belt (Secor and others, 1986a; Secor, 1987; Maher, 1978 and 1987; Snoke and Frost, 1988; Sacks and others, 1989). The Kiokee belt is separated on the north (Fig. 2) from lower-grade, greenschist facies, metamorphic rocks of the Carolina slate belt by a 4-5 km wide zone of cataclastic rocks

referred to as the Modoc fault zone (Secor and others, 1986a; Sacks and Dennis, 1987). On the south, the Kiokee belt is separated from similar, lower-grade, greenschist facies, metamorphic rocks of the Belair belt by the Augusta fault zone (O'Connor and Prowell, 1976; Maher, 1978 and 1987).
Metamorphism and emplacement of the Kiokee belt into its present position occurred during the Alleghanian orogeny, the last recognized major episode in the development of the Appalachian orogen (Secor and others, 1986a and 1986b; Dallmeyer and others, 1986; and Secor, 1987). In Georgia and South Carolina, the Alleghanian orogen is divided into three stages of deformation lasting from 315-268 Ma (Secor and others, 1986a and 1986b; Dallmeyer and others, 1986; and Secor, 1987). The Lake Murray deformation, accompanied by extensive felsic magmatic activity, produced amphibolite grade regional metamorphism in the Kiokee belt. Intense shearing along the Modoc fault zone juxtaposed migmatites of the Kiokee belt against lower-grade greenschist facies rocks of the Carolina slate belt. Regional-scale folding during the Clark Hill deformation produced the Kiokee antiform (Secor and others, 1986a, Maher, 1978). The northwest limb of the Kiokee antiform was steeply folded and then cut by the Modoc fault zone. Shearing along the Irmo shear zone, which lies within the Modoc fault zone in Georgia and South Carolina, occurred during the Irmo deformation.
Current evidence suggests that the Appalachian orogen is a tectonic collage of numerous lithotectonic blocks added to the North American craton by collision or by transform faulting throughout the Paleozoic Era (Cook and others, 1979; Williams and Hatcher, 1982; Higgins and others, 1988). The Kiokee belt and the adjacent Carolina slate belt to the north and Belair belt to the south may have accumulated in association with one or more subduction-related, Cambrian-age volcanic arcs (530-580 Ma) developed adjacent to the African continent (Whitney and others, 1978; Feiss, 1982; Rogers, 1982; Secor and others, 1983 and 1986b; Shelley and others, 1988; Higgins and others, 1988). These lithotectonic blocks were accreted to North America by the Late Ordovician (Kish and others, 1979; Vick and others, 1987; Sacks and others, 1989), and metamorphosed and emplaced into their present position during the Alleghanian orogeny (Secor and others, 1986a and 1986b; Dallmeyer and others, 1986; and Secor, 1987).
During northwestward translation of the crystalline thrust sheet above an Appalachian decollement over relatively unmetamorphosed strata (Cook and others, 1979), a ramp antiform developed with the Kiokee belt in its core (Secor, 1987). Fluids released

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EXPLANATION

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Serpentinite) Burks Mountain Amphibolite Complex

-""34 Strike and dip of foliation

Figure 2. Generalized geologic map of the Polards Corner area. (Modified from Georgia Geologic Survey, 1976; Sacks and others, 1989).

from the overriden rocks probably helped lubricate the thrust faulting and may have produced retrograde metamorphism in the overthrust sheet (Armstrong and Dick, 1974; Tull, 1978; Frazier and Schwimmer, 1987).
Subsequent to the Alleghanian penetrative deformation and the accompanying regional metamorphism, brittle faulting developed in the eastern Piedmont. One fault set is composed of northeast-trending, steeply dipping, generally silicified faults. Geologic relations bracket the age of these faults between 268 Ma and 195 Ma (Secor and others, 1986a) suggesting that they may be related to Mesozoic rifting associated with the opening of the Atlantic Ocean. Two other sets, consisting of small vertical faults, commonly cross-cut thecataclastic textures of the Modoc fault zone and strike at about N40W and N20E (Howell and Pirkle, 1976). The latter fault set may be similar in age to that of the Cenozoic Belair fault located along the southeastern edge of the Kiokee belt near Augusta (O'Connor and Prowell, 1976; Howell and Pirkle, 1976).
LOCAL GEOLOGY
ROCK TYPES
General
In the Savannah River area, rocks of the Kiokee belt consist of a migmatitic, two-mica gneiss, with subordinate layers of amphibolite, schist and muscovite gneiss. The gneiss is fine- to medium-grained and contains biotite with lesser amounts of muscovite. Included within the two-mica gneiss are: homogeneous, muscovite gneiss; migmatitic, sillimanite-bearing, two-mica schist; metaqua rtzi te; biotite gneiss; and leucocratic granite. These rocks are intruded by numerous concordant and discordant pegmatite and aplite dikes (Maher, 1978). A pronounced layering and foliation formed during the Lake Murray deformation event are characterized by: compositional banding, layers of different grain size, and preferred orientation of inequant minerals (Maher, 1978).
Within the area of investigation, the Kiokee belt rocks consist mainly of an interlayered sequence of migmatitic, micaceous quartzo-feldspathic gneiss plus hornblende-biotite gneiss and schist with minor metaquartzite (mg in Fig. 3). Additional lithologies include granitic gneiss, biotite-quartz-feldspar gneiss, granite, metagabbro, metabasalt and serpentinite. Layering and foliation strike northeast and dip between 10-30SE(Fig. 3). Abundant, medium-grained, quartzfeldspar granite dikes (Pmg in Fig. 3) intrude the

metamorphic rocks and are cut in tum by numerous, generally narrow, quartz-feldspar pegmatites.
Felsic Lithologies
Quartzo-feldspathic or granitic gneiss consists of 23-33 percent quartz, 19-30 percent microcline, 29-45 percent plagioclase (An15_25), 2-8 percent biotite, 0-2 percent muscovite, 0-1.6 percent blue-green hornblende, trace to 1 percent titanite, trace opaques, and 01 percent apatite. Myrmekite is common and is composed of quartz and plagioclase. Coarse-grained (0.44.5 mm), strained quartz and feldspar are elongated (Fig. 4) parallel to a foliation defined by thin layers of biotite and considerably smaller (0.02-1 mm) quartz and feldspar grains. Elongation of the quartz and feldspar grains is commonly up to a 4:1length to width ratio. Rounded and embayed biotite suggests dissolution and remobilization of components during metamorphism. Muscovite occurs as well-formed grains that appear to replace feldspar and as patchy, nonaligned, embayed remnants. Anhedral to euhedral titanite appears to be secondary as it commonly rims an opaque mineral tentatively identified as ilmenite.
Biotite-quartz-feldspar gneiss is composed of alternating biotite and quartz + feldspar-rich layers. Overall, thin section-scale composition is 25 percent biotite, 30 percent quartz, 23 percent plagioclase, 21 percent orthoclase, <1 percent apatite, <1 percent titanite, <1 percent zircon, and a trace amount of opaques. Although the banding has been folded, biotite crystals are not bent or otherwise stressed, and a small number of biotites are oriented across the banding. This indicates recrystallization of biotite and growth of post-kinematic biotite. Grain size averages between 0.2-1 mm. Quartz commonly displays a mylonitic texture with coarse-grained, strained quartz and plagioclase (An22_31) occurring in layers separated by fine-grained quartz and feldspar. Anhedral and elongate secondary(?) titanite (<1 percent) commonly is concentrated with zircon in biotite-rich layers, and commonly rims opaque minerals (ilmenite?).
Granitic rocks are exposed as numerous small outcrops aligned as a northeast trending dike, and they occur in the large roadcut south of the multilithic breccia (Fig. 3). Granitic dikes were intercepted in the drill core (Fig. 5). Granitic clasts occur in the multilithic breccia in the Old Petersburg Road roadcut and in drill core. A thin-section of sample PC 2-88, from DDH 872, reveals no penetrative texture and only minor strain visible in the silicates. Biotite occurs in random orientation in this thin-section. These relationships suggest that these granitic rocks are mainly post-kinematic. This rock consists of 36 percent quartz, 34 percent

7

r -__ , _,_, ..;. .::-

- .. ' \ . . .
f :...-:-:

~

~- .

. ~

~ \ I

"""' ...,;,..

...:, . --~,

\ . ..... .-~~ . -;-. + .:.. _I

22 (roadcut) 87-3
0
10

Af"

18

0

500

I

I

Scale

(in feet)

Figure 3. Geologic map of the talc prospect (Cocker, 1991b). Map shows the locations of drill holes and sections A-A' and B-B'.

8

EXPLANATION
.1~ ~ Cretaceous/Tertiary undifferentiated
~ Multilithic breccia ~ Serpentinite ~ Permo-Carboniferous granite
c==J Migmatitic biotite amphibole gneiss
- - - ..... Contact (dashed where uncertain; dotted where concealed) Fault (inferred from ground magnetic data and drill holes)
.,._ ?..- Low angle fault (thrust ?)
~ 25 strike and dip of foliation y 10 Strike and dip of centimeter-scale igneous layering
0 87-1 Diamond drill hole
A ~A Line of section Roadcut
9

Figure 4. Photomicrograph of quartzo-feldspathic gneiss. Note the elongation of quartz (Q) and microcline (M). Sample is from DOH 87-1, 208 feet. Width of field of view is 2.65 mm.
Figure 5. Granite in contact with talc and coarse-grained chlorite in drill core. Rocks include granite (G), talc (T), and chlorite (C). Contact is shown by arrow. DOH 88-2 from 200-212 feet. Top of core is in upper right and bottom is in lower left. Width of photo is approximately 2 feet.
10

microcline, 27percent plagioclase, 3 percent biotite, <1 percent opaques, and a trace amount of zircon. Myrrnekite, consisting of plagioclase and quartz, is abundant.
Mafic Lithologies
The mafic rocks of the Burks Mountain complex are dominantly amphibolite and epidote amphibolite with garnet amphibolite, garnet-epidote amphibolite, metagabbro and a northositic gabbro also present (Sacks and others, 1989). Coarse-grained amphibolites with relictcumulate texturesare interpreted as metagabbros. Two types of metagabbros in the Burks Mountain complex are distinguished on the basis of their mineralogy and geochemistry. Pyroxene metagabbros contain approximately equal amounts of plagioclase and hornblende, whereas the anorthositic metagabbros contain only minor interstitial hornblende and have higher CaO and AI20 3 contents (Sacks and others, 1989). Epidote-rich metagabbroic amphibolites, spatially associated with serpentinite, are interpreted to be rodingites because they are enriched in CaO (18-23 weight percent) and Sr (700-3500 ppm), relative to A1 20 3 (12-18 weight percent) (Sacks and others, 1989). Rodi ngi tes are calc-silicate rocks formed from metasomatism of mafic to felsic rocks associated with serpentinized ultramafic rocks.
Amph.ibolites not associated with serpentinite in the Burks Mountain complex are relatively fine-grained and lack cumulate textures. They contain blue-green hornblende, plagioclase, and quartz with minor epidote, biotite, chlorite, garnet, titanite and opaques. Basaltic protoliths fortheseamphibolitesaresuggested by their chemistry: MgO + CaO <22 weight percent
and Ti02 =0.8 to 2.0 weight percent (Sacks and others,
1989). b1 the present study, two amphibolites were en-
counter d: a metagabbro and a metabasalt. The metagabbrooccursasdasts in thcmultilith.icbreccia in DOH PC87-1 at a depth of approximately 43 feet. 1t consists of 50 percent blue-green homblende, 18 percent plagioclase, 25 percent epido~e, 5 percent opaque minerals (magnetite ?), 1 percent olivine, and trace amounts of titanite and apatite. Olivine is rare and occurs as remnants rimmed by hornblende. Epidote principally replaces plagioclase but also commonly replaces hornblende (Fig. 6). Titanite occasionally rims the magnetite(?}. Average grain size of this amphibolite is 0.1-0.2 mm .This amphibolite is interpreted to be a metagabbro intermediate in composition (Fig. 7) to the rod ingi tcs and anorthosi lic gabbros no ted by Sacks
and othcrs(l989). This amphibolite is similar in AJ 2o3
content (17.2 weight percent) but lower in CaO (14.5

weight percent) compared to the rodingite samples
o containing AI2 3 (12-18 weight percent) and CaO (18-
23 weight percent) (Sacks and others, 1989). The drill core intercepts (this study) into fresh
Kiokee rocks suggest that the metabasalts are the most abundantamphibolitesoccurring the Kiokee belt rocks that host the Burks Mountain complex. They consist of 44-47 percent plagioclase, 33-43 percent hornblende, 68 percent biotite, 2-4 percent ilmenite(?) + magnetite(?), 0.3-1 percent apatite, 0-3 percent quartz, and trace amounts of titanite (Fig. 8). Plagioclase ranges
from ~4 to An36. Average grain size of this amphi-
bolite ranges from 0.4-2 nun. Hornblende occurs as small, euhedral grains up to large, anhedral masses. Quartz is anhedral and relatively fh1e-grained (about 0.2 mm). Opaques are anhedral to euhedral with no app<uent concentration. The presence 0f secondary titanite as rims on some opaque minerals suggests these opaques may be ilmenite. Apatite is anhedral to euhedral. Preferred orientation of biotite ranges from none in sample PC 1-175 to strongly parallel layered concentrations defining foliation/banding as seen above the 96 foot mark in DOH 88-2 in Fig. 9.
Ultramafic Lithologies
Within the project area, two major serpentinite masses of the Burks Mountain complex are referred to as the northern and southern serpentinites (Fig. 3). The pervasively silicified northern serpentini teisrclatively well-exposed as the western end of the Burks Mountain ridge. It is considerably mor resistant to weathering than adjacent gneisses and granites. The southern serpentinite is not exposed but is overlain by a mu1tilithic breccia, containing mainly ultramaficclasts. This breccia is exposed in a long roadcut on the Old Petersburg Road approximately 1400 feet south of the Old Middleton Ferry Road. Talc boulders derived by weathering of the multilithk breccia were used to define the areal extent of the multilithic breccia. Drill data and a ground magnetic survey (Fig. 10) define the subsurface aspect of the southern serpentinite which appears concordant or nearly concordant to tl1e enclosing regional foliation. The magnetics indicate thnt the southern serpentinite strikes N 64E.
Kiokce gneisses and amphibolites underlie the southern serpentinite in all drill holes and overlie this serpentinite in DOH PC 88-2 (Fig. 21 and 22). Ln the other drill holes, the serpentinite is overlain by the multilithic breccia. Most of the clasts in the multilithic breccia are ultramafites similar to the underlying serpentinite, suggesting that a large portion of this breccia was probably derived from the serpentinite. Drilled intercepts show the southern serpentinite to

11

Figure 6. Photomicrograph of metagabbro (amphibolite). Minerals include hornblende (H), plagioclase (P) and epidote (E). The epidote has formed during a reaction between hornblende and plagioclase. Sample is from DDH 871, 43 feet. Width of field of view is 2.65 mm.
12

24

22

- 20
~

~ G)

18

0

~

cG.). 16

~
..c::

14

t:Tt

rol

Q) 12

)

10
0
uttl 8

6

4

24
Al2o3 (weight percent)

Explanation:
gab 1 = gabbro (1) an gab= anorthositic gabbro (1) rod= rodingite (1) gab 2 = gabbro (2) amp = amphibolite (2)
Sources: (1). Sacks and others (1989) (2). Cocker (this report)
Figure 7. Ca0-Al20 3 diagram of mafic lithologies.

13

Figure 8. Photomicrograph of metabasalt (amphibolite). Minerals include hornblende (H), plagioclase (P), and biotite (B). Sample is from DDH 87-4, 225 feet. Width of field of view is 2.65 mm.
Figure 9. Banded amphibolite gneiss (metabasalt) in contact with talc and coarse-grained chlorite in drill core. Rocks include amphibolite (A), talc (T), and chlorite (C). DDH 88-2 from 94-112 feet. Contact is shown by arrow. Top of core is at upper right and bottom is at lower left. Width of photo is approximately 2 feet.
14

scale

Cln feet)

0

500

I

I

N

t

Figure 10. Ground magnetic map of the talc prospect. Contour interval is 200 gammas (Cocker, 1991 (b)). The ground
magnetic readings greater than 2200 gammas are shaded. These areas are underlain at or near the surface by magnetite-bearing serpentinite.

15

range from 95-145 feet (29-44 m) thick with an average of 117 feet (36 m). Where the lower contact of the southern serpentinite was recovered, it consists of a relatively narrow zone of steatized serpentinite with local intervals of coarse-grained chlorite. The upper and lower contacts of the serpentinite in DDH PC 882 are similar.
The principal ultramafic lithology of the Burks Mountain complex is a dark green to black, homogeneously textured serpentinite. The typical, least altered serpentinite is composed of 65-85 percent, coarse (0.1-1 mm), mesh-textured, lizardite serpentine (Fig. 11). Disseminated, ubiquitous (1-5 percent), primary "chromite" occurs as large (0.5-6 mm), pitted, deeply cmbayed and corroded masses (Fig. 12 and 13) and smaller (0.05-0.1 mm), subhedral to euhcdral grains. Alkhromite, except for one sample collected by Vincent and others (1990), is altered to fenitchromite and/or Cr-magnetite (see section on metamorphism). Local concentrations of disseminated to layered and massive Ti-magnctite and ilmeno-hematite occur in the northern serpentinit on the western end of Burks Mountain. Abundant (0-4 percent), very fine-grained (0.1-0.2 mm), s condary magnetite "dust'' is concentrated along and commonly fonns elongate masses amund mesh-texture rims in lizardite (Fig. 11 and 14). This magnetite formed by the release of F during serpentinization ofFe-Mgsilicates-principallyolivine and pyroxene (Fig. 14). The least altered serpentinite commonly contains 5-25 percent secondary carbonate, talc, chlorite, and quartz. Secondary magnetite is absent in talc fonned during alteration of the lizardite.
The mineralogy of the serpentinite is divided into thr e categori s: 1) pdrnary igneous minerals which are relicts from th originc 1ultramaficbody(Cr-spinels - altered to magnetite);2) metamorphic minerals which formed during regional metamorphism (an thophyllite, tremoli te, lizardite, cnsta tit (altered to talc or lizardite), olivine (altered to lizardite and magnetite), talc, chlorite, Fe-Cr spinel, and magnetite); and 3) secondary minerals which are alteration products, fonned after regional m tam rphism of ptimary and metamorphic minerals (talc, chlorite, m. gnetite, carbonates, and quartz).
The original composition of the serpentinite is inferred to be a peridoUte/harzburgite based on preserved primary texturcsand whole-rock geochemistry of the least altered serpentinite. Mesh-textured lizardite (Fig. 11 and 14) pseudomorphic after olivine and orthopyroxene (basti te} indica tc aharzburgite protoli th (Sacks and others, 1989). Other, relatively uncommon, ultramafic rocks in the Burks Mountain complex are interpreted as having olivine-clinopyroxcnite cumulates (wehrlites) as a protolith with possible relict

igneous layering (Sacks and others, 1989). From normative analyses of anhydrous
serpentinite whole-rock chemical analyses, original compositions are inferred to range from 53 percent enstatite, 37 percent forsterite, and 0 percent diopside to 17 percent enstatite, 67 percent forsterite, and 3 percent diopside. (The CaO used to make diopside in the nonnative calculations occurs as carbonate in the serpentinite and may reflect influx of CaO-bearing solutions). A steady, progressive change in the abundance of normative mafic minerals with depth suggests an igneous differentiation trend in the serpentinized harzburgite (Fig. 15 and 16). Normative enstatite demonstrates a continual enrichment from 17 percent at the base to 53 percent near the top, normative forsterite declines from 67 percent to 37 percent, and normative diopside declines from 13 percent to 0 percent. Two analyses collected 10 feet above the base of the serpentinite are off of these trends and may represent the original composition of the ultramafic magma (a chilled average composition) or contamination from more siliceous fluids (metamorphic oral teration) near the lower contact. The clustering of normative forsterite and enstatite pairs from different drill holes at similar heights above the base strongly suggests that the basal contact of the serpentinite with the underlying gneiss is more or less intact and unchanged following its emplacement. If this serpentinite is a fault slice of a larger ultramafic body, then additional ultramafites may have existed stratigraphically below the present base.
Relict igneous layering occurs as: layered concentrations of Cr-magnetite; layered concentrations of high-Ti02 magnetite; and fine to coarser scale silicate banding. Thick, >8 em, layers containing coarse, veinlike segregations of high-Ti02 magnetite, hematite and ilmenite (Fig. 17) are associated with the silicate banding on Burks Mountain (Cocker, 1989c}. Concentrations of Cr-magnetite in layers dipping approximately at the same angle to local and regional gneissic banding are locally present in the drill core. Fine, millimeter-scale (Fig. 18) and coarser- (>10 em) scale primary silicate banding is exposed on the western end of Burks Mountain. This layering dips at steep angles to the northwest (perhaps due to rotation following emplacement). The fine-scale layering displays warping which is similar to load cast deformation in sedimentary rocks. Similar warping is noted in the pyroxenites of a layered ophiolite complex in Papua New Guinea (Jaques, 1981). Despite extensive alteration, the millimeter-scale layers consisted of cyclic cumulate olivine + intercumulate enstatite (?), now altered to quartz and talc respectively, and cumulate enstatite(?) altered to talc (Fig. 19).

16

Figure 11. Photomicrograph oflizardite.Magnetite (M) released during serpentinization is concentrated along the mesh texture rims. Sample is from DDH 87-1, 88 feet. Width of field of view is 1.13 mm.
Figure 12. Photomicrograph of Fe-Cr spinel, lizardite and chlorite. Large, rectangular opague (black) grain is Fe-Cr spinel (magnetite) which is rimmed and slightly embayed with chlorite (C) and surrounded by mesh-textured lizardite. Sample is from DOH 87-4, 185 feet. Width of field of view is 2.65 mm.
17

Figure 13. Photomicrograph of Fe-Cr spinel (reflected light). Surrounding mineral (gray) is chlorite. Sample is from DDH 87-4, 225 feet. Width of field of view is 1.13 mm.
Figure 14. Photomicrograph of lizardite pseudomorphs after olivine and enstatite. Magnetite (M) is concentrated along rims of the mesh-texture and outlil1es lizardite pseudomorphs of olivine (0) and enstatite (E) and is also concentrated along cleavages in the enstatite. Areas of hjgher relief are magnesite which has partially replaced lizardite in the core o.f the mesh-texture. Sample is from DDH 87-4,140 feet. Width of field of view is 2.65 mm.
18

88-2
Southwest

87-5

Drill Holes

87-4

87-1

88-1

Northeast

~~~;I Multllithlc Breccia
R Serpentinite

Vertical Scale (in feet) 40 30 20
10 0
Level

Figure 15. Position of analyses relative to normalized base of serpentinite. The positions of analyses are indicated by the larger, bolder numbers (feet above base). The relative differences in height between analyses with nearly similar norms are shown by the smaller, lighter numbers (0', 3', 24').

19

70 ~----~------------------------------------------------------~

0~--~--~----.---.----.---.---.----.---.---,----.---.---.~~
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 Height Above Base (in feet)

.Figure 16.Normative olivine and enstatite versus height above base of the serpentinite.Trend lines suggest a continual change in composition from

the base towards the top of the serpentinite and are inferred to represent igneous differentiation. Samples are from DOH's 87-1,87-4,87-5 and 88-2.

Closely spaced pairs are from different drill holes and reinforce the concept of changing composition at similar horizons during coolingof the magma.

The samples at 10 and 26 feet lie off from the main trends. These may contain some talc which has a higher Si02 content than the serpentinite. With

a higher Si02 content, normative enstatite would appear more abundant and normative olivine less abundant than whatthey really were prior to the

addition of Si02.

\

Figure 17. Ti-magnetite and ilmenohematite concentrations. Note curvature of contact (shown by arrow) between Fe-Ti oxide rich layer and lower layer. Veinlets of Fe-Ti oxides (black) do not penetrate lower layer. Sample B-850 from western end of Burks Mountain. Scale on left is in centimeters.
21

Figure 18. Millimeter-scale layering in contact with massive serpentinite. Layering is composed of olivine plus enstatite and enstatite. The enstalite is altered l talc (light layers), and the olivine is altered to quartz (dark layers). t:Jpward curvingo(!ayering (shown by arrows) on both sides of the dark planarfeatureand thefactthatthese features do not extend into the underlying massive serpentinite indicate that this is not a fault. This lanarfeature may represent a minor amount of late-stage magma injected upward into the layered part of the sample. This sample (B-825) is from the western end of Burks Mountain. Scale on left is in centimeters.
22

Figure 19. Photomicrograph of millimeter-scale layering. Layering is composed of olivine plus enstatite and enstatite. The enstatite is altered to talc (T), and the olivine is altered to quartz (Q). Outlines of the former olivine and enstatite grains enhanced by magnetite (black). Sample B-825 from western end of Burks Mountain. Width of field of view is 2.65 mm.
23

Alteration of the serpentinite produced talc, chlorite, carbonate, and quartz. Small (0.05-2 em) patches of talc, chlorite and carbonate (not necessarily together) are disseminated throughout the serpentinite. Coarse, platy talc forming a cross-fiber texture with an average width of 1 em, occurs along fractures and edges of ultramafic clasts in the multilithic breccia. This talc may be a pseudomorph after chrysotile or amphibole, but no trace of a previous mineral was found by XRD or petrographic analyses. Massive talc extends from the fibrous talc or from fractures or clast rims into the serpentinite. Coarse-grained chlorite (derived from the alteration of talc and/or crushed serpentinite?) occurs in fractures, as the matrix in a multilithic breccia, and along the country rockserpentinite contact.
The northern serpentinite is pervasively silicified and cut by stockwork and multistage quartz veining in many parts of the Burks Mountain complex. Petrographic examination of silicified serpentinites indicates that lizardite mesh-texture is preserved but silicification completely replaced alllizardite leaving only the igneous/metamorphic and secondary magnetite. Fibrous foliated talc is overprinted and replaced by silicification. In outcrop, the silicified mafic rocks have a distinct, fine-grained, flinty appearance due to the fine grain size (0.25 to 0.5 mm) of the secondary quartz.
Multilithic breccia
Multilithic breccia is a mappable lithology (mbx in Fig. 3) which overlies the southern serpentinite (Figs. 20 and 21). This breccia is exposed in a roadcut (location shown in Fig. 3) beside the Old Petersburg Road (Fig. 22, 23, 24,25 and 26) and is penetrated in at least four of the drill holes. In DOH's PC 87-5,-4, and -1, the multilithic breccia overlies the main serpentinite body. In DDH PC 88-1, the breccia directly overlies gneiss, and the main serpentinite mass is missing. Traces of talc and chlorite in DDH PC 87-2, poor recovery in the upper part of DOH's PC 87-3 and 87-2, plus talc boulders on the surface suggest the breccia is present in the drilled section but was not recovered. Additional occurrencesofmultilithicbreccia represented by rounded talc boulders occur to the north at various points around the base of Burks Mountain and to the west overlyinga suspected serpentinite massapproximate!y 0.8 km south of Phinizy on Georgia State Highway 47.
Themultilithicbreccia principallyconsists ofsmall (<0.5 m), subrounded to rounded, ultramafic clasts with minor (<20 percent) Kiokee gneiss and kaolinized granite clasts enclosed in and supported by a matrix of coarsely crystalline chlorite (Fig. 23, 24, 25 and 26). Ultramafic clasts are rimmed by foliated talc. Com-

plete replacement of the smaller serpentinite clasts by talc is conunon (Fig. 26), although serpentinite-cored clasts are also present (Fig. 24 and 25).
The breccia matrix, composed of coarse-grained (05-1 em) chlorite, is friable and poorly consolidated (Fig. 24, 25 and 26). During core driJling, the drilling fluids generally wash out and remove the friable chlorite lea ving a chaotic mixture of lithologies. Surface weathering removes the chlorite and decomposes gneiss and granite clasts and serpentine leaving the inert talc clasts as a surface residuum of subrounded to rounded pebbles, cobbles and boulders (Fig. 27). Much of the area covered by the talc boulder fields is probably underlain by multilithic breccia.
Drill intercepts of the multilithic breccia indicate a maximum thickness of 137 feet (42 m) in DDH PC 875 and a minimum thickness of 85 feet (26m) in DDH PC 88-1 (Fig. 20 and 21). Potentially thinner breccia interceptsof20-30feet (6-9 m)aresuggested in DDHPC872 and DDH PC 87-3 because of suspect lithologies and poor recovery. Average thickness in the confirmed intercepts is 76 feet (23m). The breccia thickens to the west but disappears between DDH PC 87-5 and DOH PC 88-2. Talc boulders several hundred feet west of DDH PC 87-5 indicate the breccia probably extends under that area. The down-dip extent of the breccia was not tested. A three-point solution on the basal contact of the breccia with the serpentinite defines a plane with a strike of N390W dipping 10SW.
The breccia provides important vidence concerning the timing of serpentinite brecciation, aIteration to talc and formation of chlorite. The presence of Kiokee gneiss and kaolinized granite as clasts (Fig. 23 and 24) within the breccia conclusively indicates that the high grade regional metamorphism and felsic igneous activity that produced the Kiokee gneiss and granite, respectively, occurred prior to brittl deformation and brecciation of the serpentinite. Low temperature and pressure retrograde m !amorphism resulting in th formation of the serpentinite also occurred prior to brecciation. Alt ration of the serpentinil to talc, carbonate and chlorite aJ ng fractures and in breccia clasts occurred subsequent to brecciation and hence after regional high-grade and retrograde metamorphism.
Weathering of serpentinite and talc
Weathering affected the northern and southern serpentinites indistinctly different manners. The northem mass is less affected by weathering principally because f its silicification. Weathering of partially silicified serpcntinitcproduced a type fpseudogossan boxwork consisting of resistant quartz veins, silicified

24

NW

SE

B

343"

B'

Line of Section A.-A'

Old Middletown Road

l

Surface Elevation 350'

\"' ~?

mg

Kt

G ~ Pmg

mg

Gneiss

r

1

Gneiss

l
DOH 87-1 DOH 87-4

I

I

mg Gneiss

N U1

""
I

?

200

Scale Un feet>
200 100

100 0

Figure 20. Cross section B-B'. This section was constructed from the surface geology and the geology projected from DDH's 87-1 and 87-4 into the section. This section is oriented at 90 to the long section A-A'. The existence of the fault on the north side of the serpentinite is inferred from the ground magnetic sections (Cocker, unpublished data).

sw
A
88-2

73

Old Petersburg Road

NE

l

Line of Section B-B'

A'

1en\) Gneiss

EXPLANATION
r Talc (in serpentinite) Diamond drill hole

200 scale !In feet)
100
..------.---""0 200 100

Figure 21. Long section A-A'. This section shows the distribution of the multilithic breccia relative to the underlying southern serpentinite as determined from drill hole data. DDH's 87-4,87-5, and 88-2 are projected into the section. The existence and attitude of the fault between DDH's 875 and 88-2 is inferred from the ground magnetics and the apparent displacement of the serpentinite in this section.

N

0

20

40 Feet

I

I

I

scale

t

mafic gneiss (deeply weathered)

Figure
0
0.
Figure
':D 0
~ Figure 23 Figure 26_
Figure 24

large serpentinite clasts
2' strong silicification serpentinite biotite quartz feldspar gneiss

Figure 22. Detailed geology of Old Petersburg Road outcrop. Outcrop map shows the distribution and relative size of clasts in the multilithic breccia (mbx in Fig. 3). Clasts are principally serpentinite although no attempt is made to distinguish the serpentinite clasts from clasts of Kiokee rocks except for those clasts which are of mappable size. Contact with the overlying Kiokee gneiss is at approximately 220 feet. Small faults are indicated by heavy black lines. The numbers along the west side of the outcrop indicate the distance in feet from the northern end of the outcrop. Approximate positions of photographs in the text are shown as small bars alongside of the road. Location of this roadcut is shown in Fig. 3.
27

Figure 23. Multilithic breccia. View is of the multilithic breccia with formation of coarse-grained chlorite and talc. Clasts include: kaolinized granite (G), Kiokee gneiss and amphibolite (K), serpentinite with talc rims (S), and talc (T). View is along Old Petersburg Road from 170 to 182 feet south of north end of roadcut (Fig. 22). Scale, located in center of photograph, is 10 em (4 inches). Figure 24 is a closeup of the area to the upper right of the scale.
Figure 24. Closeup view ofmultilithic breccia. Clasts include: Kiokee gneiss (G), serpentinite with talc rims (8), and talc (T). Matrix is coarse-grained chlorite (C). Clast in left center is pictured in Figure 48. Scale is 10 em (4 inches). View is along Old Petersburg Road at about 177 feet south ofnorth end ofroadcut (Fig. 22).
28

Figure 25. Chlorite, foliated talc and massive talc alteration envelope around serpentinite clast in multilithic breccia. Closeup view of alteration adjacent to edge of serpentinite clast in multilithic breccia, Old Petersburg Road, with coarse-grained chlorite (C); foliated talc rim (T); massive talc+ carbonate (TC); and serpentinite with patchy talc (5). Scale is 10 em (4 inches). View is along the Old Petersburg Road at about 140 feet south of the north end of the roadcut (Fig. 22).
Figure 26. Massive talc clast with foliated talc rim in coarse-chlorite from multilithic breccia. Massive talc (MT) in core of clast with a foliated talc (FT) rim. Other clasts to the left, upper left and lower right also have similar foliated talc (FT) rims. Matrix is coarse-grained chlorite (C). View is along Old Petersburg Road at about 177 feet south of north end of roadcut (Fig. 22). Scale is 10 em (4 inches).
29

layers, and oxidized, pitted serpentinite. The lack of significant weathering of a silicified rock produces an organically poor, thin soil which does not retain as much moisture as a thicker, organic rich soil. As a ridge former, there is no drainage onto or over the silicified serpentinite. Weathering is inhibited by the physical nature of the bedrock. Fracturing of the relatively brittle, silicified rock produced numerous open fractures and cavities and greatly enhances subsurface drainage off the ridge. The loss ofcirculation in numerous cavities and fractured rock during attempts to drill on the western and eastern ends of Burks Mountain by the Georgia Geologic Survey and the J.M. Huber Corporation respectively, is a direct effect of the fractured bedrock.
Clasts derived from the southern serpentinite are exposed in the multilithic breccia in the Old Petersburg Road roadcut (Fig. 23 and 25). This outcrop illustrates the strong degree of weathering typical of a serpentinite in the Georgia Piedmont. Weathering is facilitated by the physical character of the bedrock. The multilithic breccia contains numerous passages, as evidenced by coarse chlorite which surrounds clasts and the numerous through- going fractures, for groundwater movement and retention.
Although serpentinite is strongly affected by weathering, talc appears to be stable under the same conditions. Talc appears fresh in outcrop and forms a surficial residual deposit in certain parts of the project area. The surficial deposit consists of subangular to rounded pebbles, cobbles and boulders commonly so abundant as to form a pavement (Fig. 27). Although the density of surficial talc suggests a similar concentration might occur in the subsurface, drilling indicates considerably less talc. Drilling within the area of surficial talc provided the following results: 1) poor recovery, 2) recovery of a mixture of talc and gneiss clasts, and 3) occasional recovery of coarse-grained chlorite in addition to the talc and gneiss clasts. These results suggest that multilithic breccia similar to that exposed on the surface underlies the surficial talc deposits.
The concentration of talc boulders at the surface depended on development of the multilithic breccia. Brecciation of the serpentinite produced numerous clasts which were subjected to replacement by talc and the development of a chlorite-rich matrix. Rapid decomposition and removal of this breccia matrix and non-talc clasts freed and concentrated the resistant talc clasts.
Talc which formed during metamorphism appears to be stable under intense tropical weathering conditions in Nigeria (Akpanika and others, 1987) and under subtropical conditions in Winterboro, Alabama

(Blount and Vassiliou, 1980). Deep weathering of a dolomite-hosted talc deposit at Winterboro produced yellow, red and brown clays from theilliteplusquartzbearingdolorniteand left thetalcessentially untouched except for a possible reduction in grain size. Evans and Guggenheim(1988)suggestthatdeepsaproliticweathering of serpentinites may produce nickel- and ferric iron-rich talc and the Ni-analog of talc, willemsite; these were not recognized in this study, but they may be present.
Coastal Plain sedimentary rocks
Numerous outcrops of arkosic sandstones and conglomeratic sandstones occur unconformably overlying gneisses, schists and granites over much of the mapped area (Kt in Fig. 3). Most outcrops occur along creeks and gullies, but outcrops are also present in shallow roadcutsand drainage ditches (Fig. 28). Gravelrich layers dip at a shallow angle to the south. The maximum observed thickness in outcrop is about 8 feet (2.5 m). The sandstones are typically massive, light-gray, yellow and pinkish-white, micaceous arkosic and kaolinitic sands with locally crossbedded sands. The gravel consists mainly of subrounded to subangular quartz pebbles with a small percentage of weathered gneiss and granite pebbles.
These clastic rocks are similar to those described by Eargle (1955), LeGrand and Furcron (1956), and O'Connor and Prowell (1976) as belonging to the Cretaceous-age Tuscaloosa Formation. O'Connor and Prowell (1986) question the age and correlation of "Tuscaloosa" sedimentary rocks in eastern Georgia because of palynological studies by Tschudy and Patterson (1975) which suggest some clays may be as young as middle Eocene. Frazier and Schwimmer (1987) indicate that the Tuscaloosa is present in westem Georgia but is overstepped in central Georgia by Cenozoic strata. Huddleston (personal communication, 1991) suggests that, in light of recent field work in the Coastal Plain rocks, the sedimentary rocks exposed within thepresentstudyarea maybepartofthe Upper Cretaceous Gaillard Formation.
The nearest, previously identified occurrences of the "Tuscaloosa Formation" in Columbia Co. are about 8 miles (12.8 km) down dip to the south near the border with Richmond Co. (LeGrand and Furcron, 1956). In neighboring McDuffie Co., the "Tuscaloosa Formation" extends up to the western end of Greenbriar Creek, about three miles (5 km) south of the project area but approximately along strike. Undifferentiated Cretaceous and Tertiary sands in South Carolina extend to an area approximately 18 miles (30 km) northeast of the Savannah River along strike with the Pol-

30

Figure 27. Talc boulder field. Talc boulders are rounded clasts weathered out of the underlying multilithic breccia. Location is approximately 600 feet east of the multilithic breccia roadcut on the Old Petersburg Road (Fig. 22). Approximate location is shown in Fig. 3. Hammer in center of picture is about 1 foot long.
Figure 28. Outcrop of Coastal Plain sandstones. Note white clasts are kaolinite. Outcrop is along drainage ditch on east side of Old Petersburg Road 200 feet south of the intersection with Old Middleton Road (Fig. 3). Scale is 10 em (4 inches).
31

lards Corner study area (Secor and others, 1986a). Thickness of the "Tuscaloosa Formation" (Gaillard
Formation ?) ranges from 20 feet (6 m) near Thomson to 190 to 220 feet (58 to 67 m) near the sou them edge of McDuffie and Columbia Counties. Average dip of the basal contact is approximately 45 feet per mile (8.6 m per km) (LeGrand and Furcron, 1956). In the study area, maximum elevation of the basal contact with the underlying crystalline rocks, as observed in outcrop, is 320 feet (98 m) above sea level. The highest exposure of the ''Tuscaloosa" (Gaillard Formation ?) in the study area is at 350 feet (107 m) suggesting a maximum thickness of 30 feet (9 m) for this unit. Clastic-appearing material recovered from 0 to 100 feet (30m) in DOH PC87-6 suggests local thicknesses up to 100 feet (30m). The sharp increase in thickness may be due to latestage (Cenozoic?) faulting. The elevation of the basal contact at 320 feet (98 m) is similar to that of the Tuscaloosa Formation near Columbus, Georgia at 310 feet (94 m), but considerably lower than the 502 feet (153m) in Talbott Co., the 545 feet (166m) in Crawford Co. and the 550 feet (168 m) in McDuffie Co. (Eargle, 1955).
STRUCTURAL GEOLOGY
Structural data were obtained from geologic mapping, core logging, geophysical data, and topographic map lineament analysis. Lineations were compiled for the area from portions of four U.S.G.S. 7.5 minute quadrangle maps: the Appling, Evans, Clarks Hill and Leah quadrangles.
Ductile deformation
The project area is located on the gently dipping southeast limb of the Kiokee antiform. The axis of the Kiokee antiform is located approximately 2 miles (3 km) north of the study area trending in a N60-6~E direction (Fig. 2). Measurements of 62"foliation/bandi.ng dips in nine core holes and 32 dips from outcrops within the project area indicate that 55 percent of the foliations dip 10-30SE with 22 percent dipping 30550SE (Fig. 29). Dips measured in outcrops along the Old Petersburg Road tend to steepen adjacent to late, high angle faults. Foliations in surface outcrops generally (50 percent) strike N60-75E (Fig. 30) which is approximately parallel to the axial strike of the Kiokee antiform. Most structural features originating prior to or associated with this Alleghanian deformation (foliations, stratigraphic contacts, igneous layering in the ultramafic bodies, and strike of gncissic granite) are parallel to this northeast trend (Fig. 30).

Mineral banding is best developed in amphibolites, gneisses and schists and is discernible in older granites (granitic gneisses). The banding is defined by
alternating layers of quartz+ feldspar and biotite+ I-
hornblende. Microscopic textures indicate that microscale folding in the gneisses is pre-biotite. Intermediate, outcrop-scale folding was not observed in the project area.
Mylonitization of Kiokee felsic gneisses observed in this study area is manifested as elongated, stressed and broken quartz. Large quartz grains are elongate parallel to the biotite foliation and arc extensivc.ly strained; abundant fine-grained quartz occurs adjacent to the larger quartz grains (Fig. 4). These features contrast with the relatively non-deformed Kiokee belt rocks to the south of the Burks Mountain area and immediately north of the Augusta fault (Maher, 1987).
In contrast with the felsic and rna ftc rocks, nearly all of the ultramafic rocks examined during this study and by Vincent and others (1990> show no megascopic or microscopic mineral alignment. Sacks and others (1989) interpret thin, discontinuous layers of chromite grains as a foliation parallel with the regional foliation and suggest that these rocks were penetratively deformed and foliated prior to serpentinization. The present study found magnetite rather than chromite to be the predominant spinel; in addition, this magnetite occurs as disseminated, intricately embayed grains and as primary, layered, magmatic segregations. Elongated blebs of metamorphic magnetite and serpentine in one serpentinite sample collected by Vincent and others (1990) are probably due to localized ductile deformation. An absence of penetrative deformation is indicated also in the preservation of numerous preserpentinization textures. Such textures include millimeter-scale primary layering, delicate sprays of acicular tremolite and anthophyllite, intricately embayed
primaryI metamorphic magnetite, and pseudomor-
phs of Iizardite after olivine and enstatite.
Brittle deformation
In this part of the Kiokee belt, brittle deformation is complex and multi-stage. Brittle deformation occurs as faults, multilithic breccias, and open-space quartz veining. Some older, brittle structures are preserved by younger granite and pegmatite dikes.
The paucity of outcrops inhibits observations of brittle structures, particularly those structures larger than outcrop scale. Recognition and measurement of the orientation of topographic lineaments (elongate stream segments and ridge crests) may suggest geologic control (brittle structures, resistant and nonresistant rock units, etc.) of these lineaments.

32

18 -
16 -
- Ill 14
..0......
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r::
6 -
4 -
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s
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etc

I

10 20

30 40

50 60

T

s c

c lsl

IT

I

I

70

80

90

Inclination (in degrees)
c = Core S = Surface

Figure 29. Histogram of foliation dips (core and surface). Angles of veins measured relative to core axis were
recalculated to dips from horizontal. Note the concentration of dips from 10-300. Total number of strikes measured is 101.

33

7 -

- Ul 6
(l)
..!<
- r,-..1..
+J 5
Ul

11-1

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(l)

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60

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40 20 North 20

40

60

Orientation (degrees from North)

80 East

F = Foliation

C = Metamorphic contacts

G = Granite contacts I = Igneous layering

Figure 30. Histogram of strikes of surface foliation, igneous layering, metamorphic contacts, and granite (intrusive) contacts. Note the concentration of strikes from N55-75E. Total number of strikes is 37.

34

Talc veins and chlorite fractures
Talc "veins", developed as alteration envelopes adjacent to microscopic fractures, are common in outcrop and in drill core. The talc alteration products include carbonate, principally dolomite and magnesite. These veins are moderately to steeply dipping with 90 percent of the 41 veins in drill core dipping 30850 (Fig. 31). (Dip azimuths in drill core are unmeasurable without oriented core). One group of veins, dipping 60-65, contains 22 percent of the veins; this group may represent a major fracture set. Dips of fractures containing coarse-grained chlorite are concentrated (49 percent of the 37 fractures) in the range 40-60 (Fig. 31).
Carbonate veins
White to cream colored carbonate veins in serpentinite are locally abundant in drill core but are virtually absent in surface exposures. Petrographic and geochemical studies indicate that carbonates are completely absent in surface samples probably due to weathering. Carbonate veins appear to show a preferred orientation with 55 percent of the 33 measured veins dipping from 50-65 (Fig. 31). XRD analyses indicate that dolomite is generally more abundant than magnesite and calcite. At least three different stages of carbonate veining and associated alteration observed in thin sectionsmay reflect a temporal change in carbonate mineralogy. Cross-cutting relations indicate that some carbonate veins are younger than the talc and quartz veins.
Quartz veins
Quartz veining is common in the northern serpentinite, but it is uncommon torarcin the southern serpentinite. Dips of 26 quartz veins in six drill holes do not show any preferred orientation.Dips of5 quartz veins in the northern serpcntini te range from 60 to 90, but this represents too small a sample size to characterize the population. The quartz veins range from small, simple veins, 1-3 mm wid e, to large, composite veins, up to 15 em wide. Cross-cutting relationships, grain size variations, degree of crystallinity, and alteration envelopes suggest a complex period of fracturing and veining; at least 10distinct episodesofvein fill ing have been observed.
Multilithic breccia
The multilithic breccia strikes N39W (based on a 3-pointsolutionon the baseofthemultilithic breccia in

drill holes) and this is essentially parallel to a major group of stream lineaments that strike N30-45W and to a fracture system that strikes N40W (Howell and Pirkle, 1976).
The occurrence of the breccia principally along the upper edge of the serpentinite and the mixture of lithologies within the breccia suggests a tectonic origin. The breccia may mark a thrust contactbetween the serpentinite and the overlying I<iokee metamorphic rocks. The lack of breccia or fracturing in DOH 88-2 suggests that the thrust may extend to greater depths than those drilled.
The presence of multiliU1ic breccia around the base of the serpentinite at Bu_rks Mountain suggests that the northern serpentinite may be underlain by mul tili thicbreccia. The sharp boUlldaries ofthe ground magnetic anomaJy of tha t serpentinite (Fig. 10) indicates that the northern serpentinite does not dip beneath the surface between Burks MowHain and the southern serpentinite. Theseobservationssuggestthat the multili thic breccia may represent a low-angle, brittle deformation zone which broke up a once continuous serpentinite mass into two units moving the upper serpentinite to the north relative to the lower serpentinite.
The absence of this multilithic breccia along the basal contact of the southern serpentinite suggests that the multilithic breccia is not related to emplacement of the Burks Mountain serpcntinitcs. The multilithic breccia was apparently formed after emplacement and appears to represent a low-angle, brittle deformation event which resulted in a relatively minor displacement of approximately several hundred meters.
"Dry" brittle fracturing
Brecciated drill core not accompanied by alteration or mineralization is referred here as brittle fracturing. It is commonly observed in and adjacent to the southern serpentinite and in th e northern serpc nti11ite. Measurable frac ture surfaces are rare to absent. This fracturing must be younger than all the other brittle deformation, because there is no associated alteration or mineralization and it affects all other brittle features. Long interva Is of fractured core suggest that this fracturing is more extensive than surface geologic mapping indicates. Topographic expression of thisfracturingmay occur as lineamen t trends as discussed below.
Faults depicted on the geologic map (Fig.3) and in sections A-A' (Fig. 21) and B-B' (Fig. 20) are interpreted principally from ground magnetic anomalies (Fig. 10) and from abrupt truncation of mapped gcol gicunits. The dry brittle fracturing may be r lated to development of these inferred faults.

35

18

1-
-

--

~

c

-

c

-
- - 10 8

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Q)

6

::l

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Q)
l-1

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r 0

0

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-c

-

~
~

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,_

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~
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c
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10 20

30

40

50

60

70

Inclination (in degrees)

r-----
c.
I--
T

T Ch ~

80

90

c = Carbonate Ch = Chlorite Q = Quartz T = Talc

Figure 31. Histogram of dips of talc, carbonate, and chlorite veins and fracture fillings (core). Angles of veins measured relative to core axis were recalculated to dips from horizontal. The strongest concentrations of dips of talc veins is from 60-65. Chlorite fractures tend to dip from 40-60. The strongest concentration of carbonate veins dip from 50-65. The number of each type is 41 talc, 34 carbonate, and 37 chlorite structures. The strongest overall concentration is from 50-650.

36

Summary of fracture and vein distribution
The composite distribution ofdips measured from 137 veins of carbonate, chlorite, and talc shows a crude bell-shaped distribution with 35 percent of the veins forming an apex in the 50 to 65 range (Fig. 31). The composite distribution of orientations of brittle structures (dikes, faults, veins and abrupt breaks in magnetic anomalies) show concentrations between N25700W, N25-40E and N60-75E (Fig. 32).
Development of fractures, veins and breccias in the serpentinite with various vein, fracture and breccia fillings and alteration envelopes indicates a prolonged period or several periods of brittle fracturing. Brittle fracturing occurred after serpentinization was completed. This fracturing was accompanied by an influx of "metamorphic/hydrothermal" solutions which altered serpentinite adjacent to the fractures and deposited various minerals in the fractures. Lizardite formation is a volume-for-volume replacement and does not involve expansion of the ultramafite. Also, if the fractures were present at the time of formation of the lizardite, chrysotile would have formed in those fractures. Because no chrysotile is developed, fracturing had to occur after serpentinization.
Geologic relations indicate the following sequence of brittle deformation:
1) mylonitization during the waning stages of the Alleghanian orogen;
2) brittle fracturing and brecciation of the serpentinite with development of talc and carbonate along fractures and rimming breccia clasts; talc occurs with chlorite within the fractures;
3) multistage fracturing occurring with introduction of silica- probably at a lower temperature;
4) multistage fracturing accompanied by carbonate veining;
5) faulting and fracturing with little or no associated veining or alteration.
Topographic lineaments
In northern Columbia County, structural control of topography is not pronounced due a low to moderate topographic relief and deep weathering of the bedrock. No significant ridges are present except for Burks Mountain.
Because streams commonly are controlled by geology, their orientations were measured and plotted to determine whether patterns of structural controls are evident. A total of 370 streams and creeks, in addition

to the Savannah River, provide a large database for topographic lineament analysis. Stream orientations were measured in a 30,000 foot x 60,000 foot area centered on the project area. This area is elongate eastwest subparallel to regional strike. The size of the area was constrained to the north by the presence of Clark Hill Lake and to the east and west by large granitic intrusions. In an area of such low relief, the orientations of some of the streams may be controlled by bedrock factors such as lithology or fractures.
A visual inspection ofstreamorientation distributions (Fig. 33) suggests that 30 percent of the population is background (2 to 8 streams per 5 interval). An additional 30 percent appear to be erratically distributed and could be regarded as statistically random clusters. A major duster, containing 30 percent of the streams, strikes fromN25-55W with the greatest concentration, up to 22 streams per 5 interval, between N35-50W. The major populations of brittle structures (Fig. 32) and stream lineations (Fig. 33) are roughly coincident suggesting a possible influence of these structures on stream lineations. Small vertical faults, striking at about N40W and N20E, are common and cross-cut the cataclastic textures of the Modoc fault zone approximately parallel to the Belair fault (Howell and Pirkle, 1976). It suggests the N40W faults are controlling stream orientations in this portion of the Kiokee belt. There is no clustering of stream orientations in the N20E direction. Isolated and unexplained orientations of stream segments are seen at N0-5W, N40-45E, and N80-85E (Fig. 33).
METAMORPHISM AND ALTERATION
FELSIC AND MAFIC ROCKS OF THE KIOKEE BELT
The Kiokee belt consists of metamorphosed igneous and sedimentary rocks with a minor component of syn- or post-metamorphic felsic intrusions. Alleghanian-age, upper amphibolite facies regional metamorphism is predominantly prograde with a minor retrograde overprint. Metamorphic assemblages observed in the present study developed mainly subsequent to penetrative, ductile deformation and prior to development of cataclastic textures.
In the immediate vicinity of the Burks Mountain complex, metamorphic assemblages include:
1) quartz-microcline-plagioclase (oligoclaseandesine)-bio ti te-muscovi te-(epidote) (McLemore, 1965)
2) homblende-plagioclase(andesine)almandine-epidote-(quartz-biotite) (McLemore, 1965)

37

6 -

....

1-

r-1 l
Ill~
~Q)Q) .~ -1 c+J +J".-1
lllQ)
~Q) 0~
tTl
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,-.,
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--

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D MD D

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v

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0
w 80 60 40

20

I

N

20 40

60

80 E

Orientation (in degrees from North)

D =Dikes

F =Faults

V =Veins

M = Magnetic data

Figure 32. Histogram of surface brittle structure orientations. Structures are concentrated from N25-700W, N25400E and N60-75E. The northwest trend overlaps the stream orientation trend in Fig. 33. Orientations are from unpublished field data (Cocker, 1989a) and abrupt breaks in magnetic anomalies from the ground magnetic survey (Fig 10). Total number of orientations is 63.

38

- 22

- 1""'4
IU

20

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Orientation (in degrees from North)

Figure 33. Histogram of stream orientations. Orientations were compiled from all stream segments (total= 371) at
least 1000 feet long within an area 30,000 feet east to west and 10,000 feet north to south centered on the project area
(Cocker, 1991b). The concentration of orientations from N25W to N55W may be influenced by N25W to N40W brittle fractures.

39

3) hornblende-plagioclase (oligoclase)-epidote(quartz-biotite) (McLemore, 1965)
4) biotite-almandine-hornblende-plagioclase (Howell and Pirkle, 1976).
5) hornblende-plagioclase (oligoclase-andesine)biotite-ilmenite-titanite (this study)
6) hornblende-plagioclase(oligoclase-andesine)epidote-magnetite-olivine (this study)
7) biotite-quartz-plagioclase (oligoclase)-orthoclase-titanite (this study)
8) biotite-quartz-plagioclase (oligoclase)-microcline-hornblende-titanite-muscovite (minor) (this study)
The high-grade metamorphism is recorded as muscovite + sillimanite-bearing schists and gneisses and migmatitic gneisses (Maher, 1978, 1987; Secor and others, 1986a, Dallmeyer and others, 1986, Secor and others, 1986b, Secor, 1987; Sacks and others, 1989). The presence of sillimanite schist and gneiss adjacent to some felsic intrusions (McLemore, 1965; Hurst and others, 1966) suggest local heating above lhc kyanitestaurolite subfacies f the amphibolite facies (McLemore, 1965, and Howell and Pirkle, 1976). More detailed studies are required to determine the overall metamorphic grade and the potential for metamorphic zonation developed during Alleghanian (or older) metamorphism in the Kiokee belt rocks.
The presence of blue-green hornblende, Na-rich plagioclase (An14_24>and epidote in Kiokee belt rocks (this study and Sacks and others, 1989) indicate at least locally developed retrograde metamorphism to the epidote-amphibolite facies (McLemore, 1965). Retrograde metamorphism could result from release of fluids during thrusting of the Kiokee belt rocks onto the North American craton as discussed earlier. A younger, lower-grade metamorphism is suggested by the presence of zeolites in fractures (McLemore, 1965).
ULTRAMAFIC ROCKS
Prograde Metamorphism
Most of the ultramafites belonging to the Burks Mountain complex in Georgia are serpentinized or are altered from a serpentinite. The serpentinization generally conceals the original character of the ultramafic protolith and older metamorphic assemblages. Relicts of prograde metamorphic assemblages in the form of textures and mineral phases providea pictureofevents preceding serpentinization. Serpentinization occurred after peak Alleghanian metamorphism. Textural and mineralogical criteria favorretrogradc serpentinization in astatic environment. Several episodesofserpentinite alteration and fracturing added further complexities

to the metamorphic development (Cocker, 1989a). Evidence of a prograde metamorphic assemblage
earlier than the serpentinite is preserved in the form of: 1) earlier metamorphic minerals, 2) pseudomorphs of these minerals, and 3) reactant phases. Sprays of acicular tremolite (Fig. 34) and anthophyllite (up to 5 mm in length) are cut and partially pseudomorphed by lizardite indicating that these amphiboles were formed prior to serpentinization. Elongate, prismatic talc pseudomorphs cross cut and are superimposed on the primary igneous layering (Fig. 35); they are interpreted to beretrogradereplacementsofporphyroblastic enstatite. Pitted, embayed and corroded, coarse-grained magnetite enclosed in chlorite (Fig. 12 and 13) is interpreted to be the product of a prograde reaction between magmatic chromitel spinel and adjacent serpentine or olivine. Patchy, disseminated talc (Fig. 36) in serpentine is distinct from fracture-related talc (Fig. 24, 25 and 26) and may be a prograde (or retrograde) metamorphic remnant; textural relations with lizardite are inconclusive regarding this relationship.
Lizardite pseudomorphs after primary(?) olivine and pyroxene (Sacks and others, 1989; this study) indicate that olivine and pyroxene were stable phases prior to serpentinization (Fig. 14). The formation of enstatite porphyroblasts (noted above) that cross cut the primary igneous layering and mineralogy indicates that temperature and pressure conditions were sufficiently favorable for local recrystallization of enstatite. This evidence suggests that olivine and enstatite were stable up to and including conditions favorable for the partial recrystallization of enstatite. An assemblage containing olivine- enstatite- tremolite - chlorite - magnetite (spinel group) is approximately equivalent to the sillimanite-muscovite facies (upper amphibolite facies in Table 1). Anthophyllite, a Ca-poor amphibole, is present (this study) in samples from the eastern end of the Burks Mountain complex near the Savannah River.
Kyanite to sillimanite facies prograde metamorphism should have caused there-equilibration of the ultramafic assemblage existing prior to this metamorphism and formed a high-grade assemblage that would
have included olivine+ tremolite, +I-talc,+ I-enstatite, +I- Ca-pooramphibole,+I- spinel. Olivine, pyroxene,
trcmolite and anthophyllite arc preserved as pseudomorphs and unaltered porphyroblasts (Fig. 14, 19,34 and 35). Lack of preserved antigorite or chrysotile textures in theserpcntinitessuggests that these minerals did not develop, or that they reacted completely at a higher grade during progressive metamorphism to form olivine+ tremolite +additional phases. Because antigorite is non-pseudomorphic, its development would have obliterated igneous textures. The preser-

40

Figure 34. Photomicrograph of acicular tremolite partially replaced by lizardite and calcite. Minerals are tremolite (T}, lizardite (L), and calcite (C). Sample is from DOH 87-1, 78 feet. Width of field of view is 1.13 mm.

0 Ill II II II II

1

0 z

Figure 35. Talc pseudomorphs after enstatite porphyroblasts. Note porphyroblasts crosscut millimeter scale layering. Sample is from west end of Burks Mountain. Scale is 10 em.

41

Figure 36. Disseminated patchy talc in serpentinite. Lighter areas are talc. Remainder of rock is weathered serpentinite. View is along Old Petersburg Road at 95 feet south of north end of roadcut (Fig. 22). Scale is 10 em (4 inches).
42

vation of these textures indicates that antigorite did not develop. Thelack ofantigorite suggests that water, which is necessary to form serpentine from an anhydrous phase such as olivine, was not available to the metaharzburgHes during prograde metamorphism.
Metamorphism of primary spinel/chromite in alpine-type serpentinites commonly results in the formation of chlorite+ ferritchromite +/- Cr-magnetite
+I-magnetite(Goldingand Bayliss, 1968;0nyeagocha,
1974; Springer, 1974; Bliss and MacLean, 1975; Frost, 1975; Evans and Frost, 1975; Pinsent and Hirst, 1977; Lipin, 1984). The corroded disseminated magnetite in the Burks Mountain serpentinite is remarkably similar to metamorphic chromite in dunites in the Blue Ridge of North Carolina (Lipin, 1984). The reaction to form magnetite in the Burks Mountain serpentinite is probably similar to the following: chromite + olivine1 +fluid= ferritchromite + olivine2 +chlorite. Duringprogrademetamorphism, primary spinel is progressively oxidized from the rim to the core to formlerri tchromi te and ma~eti te through the substitution of Fe+3 for AI, and Fe 2 for Mg. Increasing metamorphic grade causes further oxidation with. additional replacement of Cr by Fe+3 pushing the spineJ composition towards that of magnetite (Bliss and McLean, 1975; Pinscnt and Hirst, 1977; Lipin, 1984). Primary spinels with a high AI content have a lower stabiH ty than high Cr-spineJs and are oxidized at lowermetamorphicgrades than Cr-rich spinels (Pinsent and Hirst, 1977).
The average composition of the Burks Mountain spinels are estimated from whole-rock analyses by assuming the following: 1) spineJ is the only phase in this ultramafic rock accommodatinfu appreciable amounts of Cr and Fe+3; 2) the Cr/Fe ratio is controlled primarily by the content of Cr and Fe+3 (and hence the fugacity of 0 2>in the rock; 3) a secondary control is exerted by the modal amounts of serpentine mineralsand chlorite which can accommodate modest amounts of Cr and small amounts of Fe+3 and by the modal amounts of talc which is virtually free of these elements. Increase in the Cr/Fe+3 ratio with increasing grade is interpreted as due to an increase in modal amounts of phases that cannot accommodate Cr. The
AI2o3 content of spinel is controlled by the coexist-
ence of chlorite, spinel and two magnesium silicates at given P, T and H20 fugacity. In the Burks Mountain scrpentinites, only one magnesium silicate, lizardite, can accommodate appreciable amounts of AI.
Lacking direct analyses of the phases involved, an admittedly indirect and somewhat tenuous path may be used to arrive at an estimate of the original spinel com:rositions. If one assumes that all the Cr, AI and Fe+ in the ultramafic rock occurs in spinels plus

chlorite altering from the spinels and that no Cr, AI and Fe+3 has been added to or removed from the rock during metamorphism, the original com:fosition of the spinel can be estimated on a Cr-Al-Fe+ triangular diagram (Fig. 37). Most samples of "fresh" and silicified serpentinite plot in a small area above 86 percent Fe+3, below6 percent AI and 9 percent Cr. Serpentinite altered to talc contains more AI (approximately 8 per-
cent~. The Fe+3:Cr:Al ratios of serpentinite include
Fe+ in secondary magnetite as a product of serpentinization. If these ratios are compared with those in talc where the secondary magnetite is absent, there is ~nly a difference of approximately 5 percent less Fe+ .
Evans and Frost (1975) suggest that spinel compositions in metamorphosed ultramafic rocks show a progressive change with increasing progressivemetamorphic grade from Fe+3-rich to more Cr-rich with a sharp increase in AI content in upper amphibolite facies rocks. Thejr study focusses on the non-reacting or more stable spinels instead of the reactant spinels (zoned spinels). The shift in composition reflects only the compositions of the progressively more stable spinels noted in other metamorphosed serpentinites (Bliss and McLean, 1975;Pinsent and Hirst, 1977; Lipin, 1984). The sharp increase in Al-content of spinels during upper amphibolite metamorphism is due to the formation of metamorphic spinels (Frost, 1975).
Chlorite is an ubiquitous phase adjacent to the corroded magnetite except where the chlorite is replaced by younger alteration phases (carbonate and talc). The anomalous birefringence of this chlorite is zoned from brown to medium blue distal to the magnetite. The ratio (Fetotal+Mn+Cr)/ (Fetotal+Mn+Cr+Mg) estimated from the birefringence (Laird, 1988) indicates the chlorite is zoned from Mgpoor to Mg-rich with increasing distance from the magnetite. The chlorite is a reaction product reflecting an Fe and AI contribution from the spinel, and a Mg and Si02 contribution from olivine/serpentine. Chlorite adjacent to magnetites in the Burks Mountain serpentinHes suggests that the original spinels were Al-rich. Studies by Golding and Bayliss (1968) note tha~ chlorite developed only where the affected chromite is Al-rich, and chlorite is absent where the chromite is Cr-rich. Also, with increasing grade of metamorphism, the Al-content of chlorites increases as a result of the increasing oxidation of spinel and release of AI to form the chlorite (Frost, 1975; Pinsent and Hirst, 1977).
Serpentinization
Based on preserved textures and geochemistry,

43

Fe3

serpentinite 0 talc o silicified serpentinite A steatlzed layered ultramafic magnetite-rich gabbro
* weathered serpentinite

~ ~

Cr

AI

Spinel Composltlons-Burks Mountain Complex

Figure 37. Cr-AI-Fe+3 Diagram. Analyses cluster near the high Fe+3 comer.

Table 1.

Typical prograde metamorphic assemblages of serpentinites (modified from Evans and Frost, 1975).

Metamorphic Assemblages

Metamorphic Facies

chrysotile/lizardite + brucite + diopside antigorite + brucite + diopside antigorite + olivine + diopside antigorite + olivine + tremolite talc+ olivine + tremolite Ca-poor amphibole + olivine + tremolite enstatite + olivine + tremolite enstatite+ olivine+ tremolite +spinel enstatite + olivine + diopside + spinel

Prehnite-pumpellyite Greenschist (lower)
(upper) Amphibolite (lower)
(to)
Amphibolite (upper) Granulite

45

the typical Burks Mountain complex serpentinite is inferred to have formed from a harzburgite (Cocker, 1989a and 1989b). Mesh-textured lizardite is pseudomorphic after olivine, orthopyroxene (bastite) (Sacks and others, 1989; this study), anthophyllite, and tremolite and is the only serpentine mineral identified in thin-sections or in XRD analyses of core samples. In silicified serpentinites, quartz forms mesh-texture pseudomorphs (outlined by secondary magnetite) which are identical to those in unaltered lizardite. Olivine and orthopyroxene pseudomorphs, which are preserved as quartz and talc, may be remnants of primary igneous olivines and pyroxenes or metamorphic recrystallization products of igneous olivines and pyroxenes. The presence of olivine and orthopyroxene pseudomorphs, the whole-rock chemistry, and the differentiation trends exhibited by their normative vertical distribution strongly suggests that olivine and orthopyroxene were the primary constituents of the original rock.
Serpentinization of Fe-bearing olivine or pyroxene releases iron to form magnetite. This fine-grained magnetite is concentrated during development of a mesh-texture pseudomorphic after the original olivine or pyroxene creating an outline of the mesh-texture (Fig. 11 and 14). This magnetite pattern is preserved in silicified serpentinites but is destroyed in steatized serpentinite (Fig. 38). A decrease in modal magnetite with increasing talc (Fig. 39) and the absence of finegrained magnetite in talc that has replaced lizardite implies dissolution of the fine-grained magnetite duringsteatization.Thelargermagnetite(orferritchromite) masses show no sign of dissolution perhaps due to compositiona! differences or reaction thermodynamics.
Previous studies described the Burks Mountain serpentinite as consisting of antigorite with thin veinlets of chrysotile (McLemore, 1965). Antigorite generally is formed during prograde metamorphism and reflects the high temperatures attending the upper greenschist to lower amphibolite facies (Evans and Frost, 1975; Wicks and O'Hanley, 1988). Because formation of antigorite is non-pseudomorphic, its development would have destroyed the igneous textures observed in thin sections and hand samples. Lizardite is the only serpentine mineral observed in thin-sections and identified by XRD (Cocker, 1989a; Sacks and others, 1989). Lower temperatures for the formation and preservation of lizardite (Wicks and O'Hanley, 1988), and the absence of antigorite suggest that serpentinization occurred substantially after peak metamorphism. Textural evidence (pseudomorphic mesh-textures) indicates that this occurred in a static environment.

Serpentinization in a static environment differs significantly from that in a dynamic environment. A static environment is characterized by the lack of a penetrative fabric in the hand sample or thin-s ction, and is inferred for the isotropic, grid-like framework of fractures that surround olivine and pyroxene fragmentsin partially serpentinized ultramafic rocks (Wicks and O'Hanley, 1988). These fractures establish sites for the initial lizardite alteration that eventually forms pseudomorphic textures. Thepseudomorphic process preserves the outlines of the original grains, textures, fracture patterns and cleavages of the parent minerals. This geometry is compatible with a water-diffusion controlled process (MacDonald, 1984). A dynamic environment is characterized by a penetrative fabric (Wicks and O'Hanley, 1988).
AI though Sacks and others (1989) describe apparently foliated chromite from the Burks Mountain complex, this investigation did not find any indication of a penetrative fabric inoutcrop,drill core,or thin-section. One sample collected by Vincent and others (1990) is penetratively deformed but this is probably localized. A penetrative fabric (Sacks and others, 1989) should have destroyed the lizardite mesh-texture. Also, the high-grade, progressive metamorphism accompanying the defonnation should have recrystallized the lizardite into antigorite. Tl1e lack of a penetrative fabric, the presence of lizardite instead of antigorite, the preservation of lizardite mesh-texture, the preservation of acicular amphiboles (tremolite and anthophyllite), and the preservation of mineralogical layering, stronglyindicat no widespread penetrative defom1ation. Penetrative d formation may have occurred locally during a post-serpentinization adjustment event.

ALTERATION OF SERPENTINITE

Movement of fluids and elements between the

country rock, generally gneisses and amphibolites,

and the serpentinite caused the development of exten-

sive alteration of the serpentinite and subtle alteration

of the country rock. Locally, the serpentinites are per-

vasively altered to tak, chlorite, carbonate, and quartz.

Silicification preserved the lizardite mesh-texture,

whereas the talc, chlorite-and carbonate generally form

non-pseudomorphic aggregates. AI terationof the coun-

try rocks involved chloritization, biotitization and per-

haps form

atiltbaintiizteat+ioIn-;ilTmie0n2itaep. pears

to

be

remobilized

to

Although spatial and temporal overlap of alter-

ation phases has obscured some textural and mineral-

ogical reiations, alteration zoning is present. The alter-

ation zoning from unaltered serpentinite to unaltered

46

Figure 38. Photomicrograph of magnetite destruction in talc. Right half of picture is lizardite serpentinite plus finegrained (black specs) magnetite derived from olivine and enstatite during serpentinization. Left half contains coarsebladed talc that has replaced the lizardite and most of the secondary magnetite. Large black grains in upper center and upper right are magmatic spinels altered to Cr-magnetites during prograde metamorphism. The Cr-magnetite in the talc is not visibly affected by steatization. Sample is PC87-4-67. Width of field of view is 2.65 mm.
47

J
12
-

10

+J

~

~

Q)
u 8

~

C)

P..

-~

C)
.w
.-i
.w

6
.

Q) ~
tJ'I

4 0

liS
::

-

2 h

0 b
0

0
ooo n

0
8 fl v
0

0

,...

p~

0 0
I
20

~
\....
0
0
0

u
r{
0

I

40

60

Talc (percent)

0
'-
I
80

0
I
100

Figure 39. Modal magnetite~ talc diagram. Diagram illustrates an overall decrease in total modal magnetite with increasing modal talc in serpentinite. The few percent magnetite in +60% talc is Cr-magnetite. The scatter in the abundance of magnetite may be attributed to the distribution of primary, magmatic Cr-magnetite.

48

country rock is: 1) "fresh" serpentinite containing disseminated patches of talc, carbonate and Type II chlorite (types of chlorite are discussed below); 2) thin zone of Type II chlorite; 3) talc +carbonate; 4) massive talc; 5) foliated talc; 6) Type III chlorite; 7) altered country rock; to 8) country rock. This zonation is similar to metasomatic alteration sequences commonly developed at ultramafic-country rock contacts: ultramafic assemblage/ talc + carbonate/ talc/ Ca-amphibole + chlorite/ chlorite/ transitional country rock/ country rock (Sanford, 1982).
Talc
Talc occurs: 1) as coarsely bladed, fibrous-appearing rinds, about 1 em wide, along the edges of fissures and around the rims of ultramafic clasts in the multilithic breccias (Fig. 23,24 and 26);2) as a massive, fine-grained replacement of serpentinite adjacent to fractures in the serpentinite, in breccia zones, and in the margins of the serpentinite; and 3) as small, disseminatedaggregatesinmassiveserpentinite(Fig.36). It generally replaces liiardite, enstatite, tremolite and anthophyllite. Lizardite (Fig. 40), tremolite and anthophyllite decrease with increasing talc content. Steatization also causes dissolution of fine-grained secondarymagnetitewhichoutlined the lizardite mesh texture (Fig. 38).
Carbonate
Magnesite, dolomite and calcite are texturally and temporallydistinct from each other in the Burks Mountain serpentinites. Cross-cutting veins and replacement textures indicate that the carbonates are younger than lizardite, tremolite, and anthophyllite, but overlap with talc, quartz and chlorite. Carbonates are most abundant in rocks with low talc (<25 modal percent) and with 30-50 modal percent lizardite.
The most abundant carbonate is an early stage magnesite with a very fine- to medium-grained (<.01 0.1 rom) sugary texture. Magnesite commonly occurs replacing lizardite in the center of the mesh texture of the lizardite, as a patchy replacement of talc and chlorite, and in veinlets cutting talc and chlorite. Dolomite, the next most abundant carbonate, is coarser grained and occurs as euhedral grains or aggregates also in the center of the mesh texture. Dolomite also appears to replace fine-grained carbonate in veins and in the mesh texture. Calcite, the least abundant carbonate, occurs as clean, generally coarse grains rimming tremolite, replacing the centers of the lizardite mesh texture, and as younger veinlets cutting all other veinlets. The veinlets commonly consists of large elongate grains

with an unidentified opaque mineral locally in the center of the veinlet.
Chlorite
Chlorite developed in the Burks Mountain serpentinites in three distinct modes which are indicative of different paragenesis. These are referred to in this report as types I, II, and III. Type I chlorite, discussed earlier, developed as a reaction rim around spinel (Fig. 12 and 13) during progressive metamorphism. Type II chlorite is concentrated along the talcserpentine contact and is disseminated in serpentinite and talc. Type III chlorite, which is the most conspicuous and abundant chlorite, occurs as coarse-grained flakes filling fractures and forming the matrix of the multilithic breccia (Fig. 24, 25 and 26). Type III chlorite (Fig. 5 and 9) is also commonly known as chlorite blackwall developed between serpentinite and country rock (Chidester, 1962). Type II and III chlorites are more Mg-rich (based on their birefringence) than the Type I chlorite.
Type II and III chlorite replaces talc and to a lesser extent lizardite, tremolite and anthophyllite. These chlorites generally occur as anomalous medium to dark blue birefringent blades elongate up to 3 rom in length and as radiating sprays localized in massive talc near and adjacent to the talc-lizardite contact. Type II chlorite also forms single, dark blue birefringent crystals disseminated in serpentinite, minor light bluegraybirefringent spraysand rosettes replacinglizardite and medium blue-gray birefringent veinlets cutting and replacing lizardite. Some type III chlorite is a coarse-grained (0.5-2 rom) gray chlorite, and it is replaced by light blue birefringent chlorite and possibly by dark blue to brown birefringent chlorite. Finegrained, light blue birefringent chlorite occurs along fractures and cleavages in gray birefringent chlorite. In drill core and outcrop type III chlorite forms massive, coarse-grained, non-foliated, platy intergrowths in open structures. Type III chlorite consists of poorly bound coarse flakes which are very susceptible to weathering and washout by drilling fluids.
Silicification
Silicification and quartz veining are widespread in the northern Burks Mountain serpentinite, but are only locally developed in the southern serpentinite. Attempts to drill through the silicified and veined northern serpentinite to examine the distribution of silicification and veining with depth were unsuccessful because of loss of circulation and caving during drilling. The much greater abundance of silica in the

49

100

80

-+J

!::

Q)
u

60

~

Q)

0..

u 40
l""'i ~
8




20


-



0

20

40

60

80

Lizardite (percent)

Figure 40. Modal talc-lizardite diagram. Diagram illustrates a strong negative correlation between talc and lizardite reflecting the replacement of lizardite by talc.

50

northern serpentinite and its virtual absence in the southern serpentinite is unexplained. Silicification was not observed in any country rocks from drill core, outcrop or float. Also, resistant ridges or hills which might indicate silicified country rock are not present.
Quartz veins cut across talc, chlorite, and serpentine, with quartz commonly replacing these minerals. The intensity of silicification is directly related to the density of quartz veining. The above relations suggest silicification and quartz veining are probably simultaneousand directly related. Veiningis multistagebased on the following observations: 1) quartz-veining consists of banded quartz veins; 2) quartz veins cross-cut other quartz veins; and 3) vein mineralogy changes from quartz to chalcedony to opal? in progressively younger veins. Crustiform vein quartz is common, indicating open-space filling.
The Si02 content increases dramatically from an average of about 40 weight percent in normal serpentinite to 80-90 weight percent in silicified serpentinite. No major volume changes are evident, for the modal magnetite and weight percent Fe203 are essentially the same in unsilicified and silicified rocks.
ALTERATION OF COUNTRY ROCKS
Secondary biotite
Secondary biotite (8 modal percent) occurs as numerous anastomosing veinlets cutting hornblende (Fig. 41), biotite, quartz and plagioclase and as irregular aggregates replacing plagioclase in an amphibolite (Fig. 42) 5 feet (1.5 m) below the lower serpentinitegneisscontact (PC 1-175). Closer to the serpentinite the veinletsarecomposed ofchlorite instead ofbiotite. The secondary biotite is similar to the pleochroic, yellowish-brown (resembling rust in thin-section) secondary biotite occurring as irregular branching patterns in country rock schist in many localities in New England (Chidester, 1962; Sanford, 1982) and Virginia (Burfoot, 1930).
The formation of secondary biotite begins with chloritization of biotite in the country rock immediately adjacent to the ultramafic body. Chloritization mobilizes potassium which diffuses further into the country rock. Biotite forms at the expense of calcic amphibole (hornblende (Fig. 41)) or plagioclase (Fig. 42) (Sanford, 1982; Chidester, 1962). At Newfane, Vermont, epidote replaces chlorite which, in turn, replaces biotite. Further out in the country rock, biotite, albite and minor chlorite replace hornblende. This may be the origin of biotite blackwall zones around many ultramafic bodies (Sanford, 1982).

Secondary albite
Extensive albitization of plagioclase occurs along fractures and commonly forms irregular masses to euhedral porphyroblasts within the plagioclase (Fig. 43).Albitizationprobablywasinitiatedbychloritization of plagioclase. Chloritization mobilized Na20 further into the country rock immediately adjacent to the chlorite zone. Albitization of plagioclase mobilized CaO, some of which may have formed secondary titanite. Albitization resulting from chloritization of plagioclase is a commonly reported phenomenon developed adjacent to Alpine-type serpentinites in the eastern United States (Chidester, 1962; Jahns, 1967).
Ti- bearing phases
Titanite is an abundant but minor phase occurring as individual grains and as overgrowths on Ti-oxides in gneisses and amphibolites adjacent to the serpentinite. Similar occurrences adjacent to New England ultramafics consist of: 1) ilmenite with overgrowths of leucoxene or of rutile and/or titanite; 2) rutile with overgrowths of titanite; and 3) ilmenite, rutile and titanite with no overgrowths (Chidester, 1962). A pronounced increase inTi and titanite in the chlorite zone was recognized by Sanford (1982). The chloritization of biotite plus the chloritization and albitization of plagioclase probably mobilized the Ti and Ca necessary to form the secondary Ti-oxides and titanite. Metamorphosed chlorite blackwall at PaddyGo-Easy Pass, WA contains spinel enclosing rutile suggesting a reaction of chlorite+ ilmenite= olivine+ spinel+ rutile+ water (Frost, 1975). Ilmenite replaces amphibole, and titanite rims ilmenite and replaces ilmenite, epidote and amphibole in association with talc deposits in Virginia (Burfoot, 1930). Recrystallized aggregates of anhedral titanite, commonly up to 2 mm in size, occur in hornblende schists and gneisses, amphibolitesand hornblende gabbro associated with talc and asbestos deposits in Georgia (Hopkins, 1914).
PETROCHEMISTRY
Petrochemistry can be used to determine: the origin of a rock or a suite of rocks; igneous differentiation trends; the effects of metamorphism; and the effects of alteration. The data discussed in this section are presented in Appendices I-VI. Additionally, some ratios discussed in this section are derived from the data in those appendices.
FELSIC AND MAFIC ROCKS

51

Figure 41. Photomicrograph of secondary biotite cutting and replacing hornblende. Minerals include hornblende (H) and biotite (B). Sample is from DDH 87-1, 175 feet. Width of field of view is 1.13 mm.
Figure 42. Photomicrograph of secondary biotite cutting and replacing plagioclase. Minerals include biotite (B), plagioclase (P), and hornblende (H). Sample is from DDH 87-1, 175 feet. Width of field of view is 1.13 mm.
52

Figure 43. Photomicrograph of secondary albite. Albite (A} veinlet cuts plagioclase (P). Also apparent are patches of secondary albite replacing plagioclase. Other mineral is biotite (B). Sample is from DDH 87-1,175 feet. Widthoffield of view is 1.13 mm.
53

Primary igneous or sedimentary textures are not preserved in the felsic and mafic rocks in the vicinity of the Burks Mountain complex. The nature of these rocks may be suggested by their petrochemistry. Studies of amphiboli tes indicate that variation trends can be used to distinguish between ortho- and para-amphibolites (Leake, 1964).
Trends in the Niggli values of igneous rocks differ from those trends caused by mixingpeliticand carbonate sedimentary rocks (Leake, 1964). Niggli values are:
o mg = (Mg0/(Fe0 + MnO + 2Fe2 3 + MgO)), c = = (CaO),and al-alk (AJ 20 3+Na20+K20)(Leake, 1964).
Igneous rocks show a systematic decrease in mg with a subsequent increase in al-alk. On a triangular plot of mg, c and al-alk, the mixing line joining dolomite and typical pelite and semi-pelite is perpendicular to a typical basic igneous series trend. Mixtures of pelite and semi-pelite with limestone should plot in a different part of the diagram and should show a characteristic trend of their own. The mafic gneisses/amphibolites in the Burks Mountain area follow a normal igneous trend (Fig. 44) indicating that they may have igneous (including volcanic) protoliths. The felsic gneisses also plot along this trend suggesting that they may also have igneous(including volcanic) protoliths. The inclusion of several granitic rocks in these trends tends to support, but does not prove an igneous parentage for the felsic gneisses.
A Ca0-Na20-K20 diagram (Fig. 45) shows several distinct dusters of rock analyses. Field A consists of very high-CaO metagabbros. Field B consists of high-CaOmetabasalts. Field Cis composed ofgranites and felsic gneisses with high Na20 and K20.
The CaO and Na20+K20 contents of these rocks are about equal at 58 weight percent Si02 suggesting that they may be part of a calc-alkaline rock series (Peacock, 1931). On an AFM diagram (Fig. 46), the felsic gneisses and granites from the Burks Mountain area occur along a calc-alkaline enrichment trend. Mafic gneisses/ amphibolites (metabasalts) from the Burks Mountain area lie on a tholeiitic Fe-enrichment trend.
On a normative SiOTNaAISi30 8-CaA12Si20 8 (quartz-albite-anorthite) diagram the analyses define a trend intersecting at about 750C (Fig. 47). This defines the minimum m lting temperature at 5 kb pressure and is reasonable for generation of partial melting associated with migmatitization. This temperature is similar to the anticipated maximum temperature (700C) proposed for peak metamorphism in this part of the Kiokee belt (see discussion on conditions of metamorphism).
The Ti02 contents of the mafic rocks range from

1.1 to 1.3 weight percent, and appear to be greater than those indicative of a subduction-related environment (Feiss, 1982).
Rare earth element(REE) analyses of lhe amphiboIites (Cocker, 1989c) show a slight enrichment in light REE suggesting an island-arc or continental margin origin.
The Kiokee belt rocks analyzed in this study are markedly different from the Little River Series rocks (Carolina Slate belt) analyzed by Whitney and others (1978). The Kjokee belt rocks display a variation in Al203 from <13 to >17wcightpercentinmafic to felsic rocks while the Little River Series rocks show no variation. TheKiokeebeltrocksanalyzedin thisstudy show a strong enrichment in K20; rocks with 70-75 weight percent Si02 contain 2.5 to 4.7 weight percent K20 versus 0.5-1.5 weight percent in Little River Series rocks. Despite the limited number of analyses, a continuous trend in Si02content (unimodal) appears tobe present the Kiokec belt rocks.
The spatial association of abundant felsic rocks with the mafic rocks (metabasalts), the light REE enrichment, and the calc-alkaline trend suggest, but do not prove a continental margin environment(+/- a minor island arc component) for the Kiokee belt rocks in this area. Another, alternative explanation for the Kiokee belt rocks is the mixed environment intermediate between continental margins and island arcs (Rogers, 1982). This mixed environment has characteristics of both the continental margin and island arc setting and is believed to have developed over a crust intermediate, both in thickness and in composition, between continental and oceanic crust.
ULTRAMAFIC ROCKS
Magmatic trends
Concentrations of major and trace elements in the Burks Mountain serpcntinHes are generaJJy related to their stratigraphic height in the serpentinite, which is the elevation above the lower serpentinite-country rock con tact. Vertica Ichemical variation trends within the serpentinite are interpreted as: 1) metasomatic changes towards the edges of the serpentinite, and 2) vertical primary differentiation trends which have persisted despite metamorphism and metasomatism. Where present, pervasive silicification severely changed the whole-rock chemistry of the altered ultramafite on a broader scale apparently unrelated to present contacts.
o Variations in the concentrations of Si02, MgO,
MnO, Fe2 3, and CaO probably reflect primary igneous differentiation trends in the ultramafic body from

54

mg ~ mafic gneiss/amphibolite b. felsic gneiss/granite
Typical pelite and semipelite

c
Limestone

al-alk

Figure 44. Niggli mg-c-(al-alk) triangular diagram. The mafic gneisses/amphibolites plot along the igneous rock trend and suggest these have igneous protoliths. The felsic gneisses and granites also plot along this trend and may suggest that they also have igneous protoliths. Calculation of c, mg, al-alk are explained in the text. Rock fields and the igneous rock trend are from Leake (1964).

55

CaO
Figure 45. Ca0-Na20-K20 triangular diagram of felsic and mafic gneisses and granites. Analyses of felsic and mafic rocks included in the appendicies are shown as dots. Three fields are evident: A) a high CaO field corresponding to the metagabbros; B) an intermediate field containing mafic gneisses/amphibolites; and C) an Na20 + K20 field containing felsic gneisses and granites.
56

Figure 46. AFM triangular diagram of serpentinites,felsic and mafic gneisses and granites. Analyses of serpentinites, felsic and mafic rocks included in the appendicies are shown as dots. The felsic and mafic rocks follow two wellestablished trends: the mafic gneisses follow the tholeiitic Fe-enrichment trend; the felsic gneisses and granites follow the calc-alkaline trend. The serpentinites plot in the lower right corner (Mg0).
57

Q Quartz
2.Q90
FAibgu=raelb4i7t.eN. TohremnaotrivmesAofbt-hAense-Qrodckiasgcrlaumstefronr efealrstihceginneteisrsseecstaionndogfrtahneittwesoaltiPqvuai~.s=s5ukrfba.cAesna=nadntohreth7i5t0e0, CQi=soqtuhaerrmtz.,
Several of these norms appear to lie on a path which intersects the boundary curve at this point. Diagram modified from Yoder (1968).
58

an olivine-richbase to an orthopyroxene-rich top. Si02 shows two subparallel enrichment trends (Fig. 48): 1) in the more silica-rich trend, Si02 increases from about 38 weight percent near the base to 41-42 weight percent in the upper part of the serpentinite; 2) in the more silica-poor trend, Si02 increases from about 33-35 weight percent near the base to about 36-37 weight percent in the upper part of the serpentinite. The increase in Si02 content may reflect a change from SiOTpoor olivine (Mg2Si04) to SiOTricher enstatite (MgSi03).Mg0exhibitsagradualincreasefromabout 35 weight percent near the base to about36.5-37 weight percent near the top of the serpentinite (Fig. 48). Sharp increases between 20-30 feet and about 57 feet may reflect local increases in the magmatic olivine content. FeO also shows a sharp increase between 20-30 feet above the base. Concentrations of MnO generally decrease from about 0.12 weight percent to about 0.055 weight percent toward the upper part of the
serpentinite. Fe2o3 decreases slightly fromabout6-7.5
weight percent to about 5 weight percent possibly reflecting a decrease in the overall magnetite/chromite content of the original igneous body.
A distinct decrease in CaO from 3.5 weight percent to less than 0.1 weight percent with increasing stratigraphic height (Fig. 49) may result from a decrease in primary Ca-pyroxene (represented by a small diopside (CaMgSi20 6) component). A similar concentration of Ca along the borders of a harzburgite from Burro Mountain, CA is attributed to release of Ca from pyroxenes through progressive serpentinization (Coleman and Keith, 1971). Because Ca is not compatible with the crystal structure of serpentine minerals, it will leave serpentinite to form rodingite or remain to form tremolite ordiopside (Wicks and O'Hanley, 1988). In the Burks Mountain serpentinite, influx of carbonate-bearing solutions from the country rock is suggested by the increase in the C02 content of the serpentinite towards its base (Fig. 50).
The average Ti02 content of the Burks Mountain serpentinites and talc is nonnally 0.01 weight percent. Near the top ofBurks Mountain is a layered, magnetite + ilmeno-hematite (38.2 weight percent Fe20 3) rock
o enriched in Ti02 (92 weight percent), V (750 ppm),
P2 5 (0.34 weight percent) and rare earth elements (REE)(273 ppm La to 1.9ppm Lu) (Cocker, 1989c). The Cr content of this rock is unusually low (100 ppm) especially when compared to thcrestoftheserpentinite body (550-4500ppm). Textural reiations and geochemical datasuggestseparation ofan immisciblcTi02-V-PREE-Fe-rich melt in the upper part of the ultramafite which subsequently sank to the base of a crystal mush (Fig. 17). Below the crystal mush the remainder of the harzburgite was apparently crystallized and was not

penetrated by the sinkingof theTiOTV-P-REE-Fe-rich melt. The V content of serpentine and talc is normally on the order of 5-15 ppm and ~20 ppm Tespectively. Challis (1965) noted thatV tends to concentrate in the pyroxenes (90-200 ppm) in New Zealand ultramafic rocks. In disseminated chromite in dunite and harzburgite, Vis 180 ppm but is concentrated in massive chromite at 900-1400 ppm (Challis, 1965). Polished sectionsofthisrockindicateaminoramountofstrongly resorbed chromite with the remainder being magnetite and ilmeno-hematite. The REE, Ti and V are probably concentrated in these latter minerals.
Vanadium also tends to concentrate along with apatite and REE in the later crystallizing titan-magnetites in the Stillwater (Helz, 1985) and Bushveld layered mafic intrusions (Reynolds, 1985). The similar association of V, Ti, P and REE in iron oxide-rich rocks in the upper levels of the Burks Mountain complex suggests a similar paragenesis to iron oxide-rich rocks in the layered mafic intrusions.
In the Burks Mountain ultramafites, Ni generally ranges from 0.2 to 0.25 weight percent in serpentinite and from 0.12 to 0.19 weight percent in talc, chlorite and silicified serpentinite. If most of the Ni is assumed to be in one phase common to the talc, chlorite and silicified serpentinite, the Ni is probably in Cr-magnetite. The higher Ni content of the serpentinite suggests that Ni may occur in lizardite in addition to the Crmagnetite.
The behavior of Ni and Co in ultramafic rocks is dependent on olivine. At high temperatures during crystallization from an ultramafic magma, Ni substitutes for Mg in the olivine lattice. During the serpentinization of Ni-bearing olivine, Ni tends to partition into oxides, sulfides or alloys rather than into lizardite. This is attributed to the low water fugacity during serpentinization of olivine (Wicks and O'Hanley, 1988). Co tends to follow Ni in olivine, so their distribution in the serpentinite should reflect that of normative olivine. In Figure 51, Co and Ni show a positive correlation to each other. In the southern Burks Mountain serpentinite, Co, Ni, and Cr tend to increase toward the base of the serpentinite. This is best illustrated by Co (Fig. 52). The serpentinite contains two Cr populations: one greater than Ni (0.2550.45 weight percent), and the other lower than Ni (0.055-0.2 weight percent). Cr tends to have a greater degree of variability than Co and Ni within the serpentinite.
Effects of serpentinization
The chemical aspectsofserpentinizationarequantified using a method devised by Shteinberg (1960)

59

42

-

--~ 40

I:

Q)

0
~ Q)
p.

-
__.

.__.



4. . . .



41

~ .c: 38

. ..C...".>
(I) ~

36

N

.0.....
til

-

~



34 0



I

I

20

40

60

I

I

80

100

120

Height above base of serpentinite (in feet)



37



.......

~



I:

(I)
0
~ 36
(I)
p.

.~ c:
...C..".> (I) 35

-

'


"



41

~

-
0 C">
:E 34

-

33



I

I

I

I

0

20

40

60

80

100

120

Height above base of serpentinite (in feet)

Figure 48. Si02 and MgO versus height above base in the serpentinite. The main SiOz trend shows an increase from about 38 weight percent to about 41 weight percent with increasing height. A lower trend is subparallel to the up-
per trend. The general trend in MgO shows an increase from about 35 weight percent to about 36.5-37 weight percent.
Variations above and below these trends may reflect primary, magmatic variations and/ or alteration of the serpentinite.

60



3
-+I
J:
- Q)
,0...
Q)
~ 2
.+.cJ:
M
"'Q)
- - ~
0ro 1
()
-
0 0



.-.,


20

40


'


I

I

60

~-

80 ' 100 I


120

Height above base of serpentinite (in feet)

Figure 49. CaO versus height above base in the serpentinite. TheCaOshowsa definitedecreaseof3.5 weight percent to 0.1 weight percent from the base to the top of the serpentinite. This trend may be related to a higher concentration of carbonates toward the base or to a primary, magmatic distribution. The latter may be due to a higher diopside component toward the base of the ultramafite.

61

6

...,
s::
Q)
0,....

Q)

~
...,

4

.r::

t1'l

r-i

-Q)
~

N
u 0

2

0

20

40

60

80

100

120

140

Height above base of serpentinite (in feet)

Figure SO. C02 versus height above base in the serpentinite. The carbonate content is distinctly higher,4-6.5 weight percent, near the base of the serpentinite than in the upper part of the serpentinite, 0-2.3 weight percent. This may
reflect the influx of C02 from the basal country rock-serpentinite contact.

62

140

~
..0....
r-1

-
-

.r.-..1..

a 100

~

Q)

p.

Ul

-

~ ~
pS .

-

~ 50

r-1

S ,.Q

-

0

(.)

-

10 0






I 1000

I

I

' 2000 ' I

Nickel (parts per million)

Figure 51. Co versus Ni in serpentinite. Co shows a positive correlation with increasing Ni.

140

s::

-

...0... 120

r-1

.r..-.1.. a

~ 100

Q)
p.

-

Ul
~ 80
~ llj
p.

60

~ r-1 llj

-

,.Q
0 40
(.)
-

20



,.

~





"






0

20

40

60

80 100 120 140

Height above base of serpentinite (in feet)

Figure 52. Co versus height above base in serpentinite. Co shows a well defined decrease with increasing height above the base of the serpentinite.

63

and employed by Coleman and Keith (1971). In Shteinberg's chemographic plot, the ratios RO' /Si02 and H20/Si02 (in molecular amounts) are employed in a triangular diagram (Fig. 53) with apices RO'(representing the molecular sum of the amounts of MgO, total Fe as FeO, CaO, MnO, and NiO reduced by
o Hth2eom.oIlfesciulilcaar,aimroonuonrtsmoafgCnre2sia3daondnAotl2c0ha3n),gSeia0p2parned-
ciably during progressive serpentinization of dunites and harzburgites, the RO' /Si02 ratio should be rela-
o tively constant with only H20/Si02 increasing to-
ward serpentine which has a H2 /Si02 ratio equa1to 1. Variations in the RO' /Si02 ratio for harzburgHes result from variations in the odginal orthopyroxeneolivine contents (RO' /Si02=2 for olivine, 1.6 for serpentine, and 1.0 for enstatite).
When the Burks Mountain serpentinites are plotted using loss-on-ignition (LOI) for H20, they are sea ttered over a wide range oH-I20/Si02 between 1.0 and 1.8. Because other components, principally C02, contribute to the LOI component, an adjustment could be made to the LOI if the proportion of C02 is estimated. The LOI content for the Burks Mountain serpentinites increases proportionally with increasing carbonate content above 10 weight percent LOI. The 10 weight percent LOI can be attributed mainly to the H20 content of serpentine. Subtraction of an increasing percentage of C02 with increasing LOl provides a closer estimate for H20. Most of the data then plots to within +0.1 H20 / Si02 of serpentine (Fig. 53). Additional data scatter may be due to analytical error, contamination by phases other than serpentine, or a correction factor for C02 which is slightly too low.
Variation in the RO' /Si0 2 ratio (Fig. 54) may be related to the original orthopyroxenc:-olivine content. As discussed earlier, the relatively orthopyroxene-rich harzburgite becomes increasingly olivine-rich with increasing depth. The shift in RO' /Si02 towards higher metal content with progressive serpentinization might suggest metal enrichment or silica depletion with increasing serpentinization; however, neither is known to occur. The orthopyroxene (enstatite) content of the harzburgite ranges from 20 percent to 62 percent. Serpentinization generally appears to increase with depth. Increasing olivine content, which is usually more susceptible to serpentinization than orthopyroxene (Coleman and Keith, 1971), with depth may account for the increase in serpentinization.
The decrease in H20/Si02 with increasing stratigraphic height in the serpentinite (Fig. 55) may be related to the increasing Si02 content reflecting the change in olivinc:-enstatite content and to a decrease in H20 content away from the wallrock-serpentinite contact. A decreasing RO' /Si02 ratio with increasing

height suggests that the variation in the primary mineralogy may be the controlling factor.
The oxidation ratio (100xFe20 3/(Fe20 3+Fe0) should increase with increasing degree of serpentinization. The increase in Fe+3 is taken up by serpentine and an increase in modal magnetite. Coleman and Keith (1971) suggested the oxidation ratio would not be a good estimate for the degree of serpentinization because of the uncertainty in the oxygen activity and other factors. However, the oxidation ratios of Burks Mountain serpentinites increase as the H20/Si02 ratio moves toward 1.0 =serpentine (Fig. 56).

Effects of metasomatism

Metasomatic alteration of the serpentinite is sug-

gested by changes in Al20 3, Na20, K20 and possibly FeO from the center to the outer edges (top and base)

of the serpentinite. Al20 3 decreases from about 0.40.46 weight percent in the core of the serpentinite to

about 0.32-0.37 weight percent near the upper and

lower margins of the serpentinite (Fig. 57). Near the

present contacts, the Al20 3 content increases sharply -up to 0.58 weight percent. From the core to the upper

and lower margins of the serpentinite, Na20 increases from 0.005-0.01 to 0.02-0.04 weight percent (Fig. 58),

and K20 increases from 0.01-0.012 to 0.02-0.03 weight percent (Fig. 58). Circulating fluids may have leached

lAela2c0he3dfNroam2othaendseKrp2e0ntfirnoimte

to the

form chlorite country rocks

and and

transported them into the serpentinite. Because the

amountofvariationinA120 3,Na20,andK20israther minimal (and may be more apparent than real),

mineralogic changes are not detectable in modal analy-

ses of these rocks. The Al20 3 required to form the abundant chlorite present in the fractures and the

monolithic breccia matrix must have come from the

country rock, because the normal Al20 3 content of the serpentinite is too low.

The FeO content of the serpentinite is generally

lower in the core (about 0.4-0.7 weight percent) and

increases toward the upper and lower margins (about

0.8-2.3 weight percent). The FeO content decreases

near the lower margin of the serpentinite body. As

noted earlier, the FeO content may be related to the

distribution of magmatic olivine, or the FeO content

may be related to the relative abundance of talc and

serpentine. As the H20 /Si02 ratio increases above 1.0 (H20/Si02 is equal to 1.0 for serpentine), the amount of serpentine decreases. In the Burks Mountain

serpentinite, the FeO content does increase with an

increase in the H20/Si02 ratio (Fig. 59) and thus is related to a decrease in serpentine. The increase in FeO

64

1.8 1.6 1.4 1.2
1.0

0.6 0.4 0.2

2.0 1.8 1.6 1.4 1.2 RO I /Si02

o Orthopyroxene
1.0

Figure 53. RO' versus Si02-H20. RO' represents the molecular sum of MgO, total Fe as FeO, CaO, MnO and NiO reduced by the molecular amounts of Crz03 and Alz03. The Burks Mountain complex serpentinites (represented by dots) all plot near the ideal serpentinite composition (5). Ideal olivine, orthopyroxene and serpentine compositions are denoted by squares. Assuming isochemical serpentinization, except for addition of H20, the original rock should range from about 80-30% olivine and 20-70% orthopyroxene (After Shteinberg, 1960).
65

2.0

1.8

.-.

-



1.6

N

.0....
U)
........



~ 1. 4



'


- - -.-

1.2
-

1.0 0

I

I

20

40

60

r

80

100

Height above base of serpentinite

120

140

(in feet)

Figure 54. RO'/Si02 versus height above base in the serpentinite. Decrease in this ratio with increasing height probably reflects an overall change in normative mineralogy with height.

. 1. 20
1.18 ~
-
1.16

1.14

-

1.12 -

N
.0....

-

U) 1.10

........

0

::::N 1. 08
-

- 1. 06

1. 04
1. 02 -

0

-





~





20

40

60



t

80

100

120

140

Height above base of serpentinite (in feet)

Figure 55. H20/Si02 versus height above base in the serpentinite. See text for discussion.

66

..- - 1.2

0

-

~
+l Ill l-1
N
0
~ U)

- 1.15
---

......... 1.1
0 N
:I:

---

1. 05

--

-

I

I

70

74

78

'



82

86

90

9-1

Oxidation ratio (Fe2o3 x 100/ (Fe2o3 + FeO)) Figure 56. Oxidation ratio versus H20/Si02. The oxidation ratio increases as the ideal ratio (H20/Si02 = 1) for
serpentine is approached.

0 ,....."' 0. 40
<

0.32 0

20

40

60

100

120

Height above base of serpentinite (in feet)

Figure 57. Al203 versus height above base in the serp en tini te.ln the core of theserpenti:ni te theAI203 content varies from about 0.39 to 0.46 weight percent. It decreases to about 0.32 weight percent t_owards the upper and lower margins, and then itincreasesto0.58 weightpercentnearthelowcrand uppercontacts. Thevariationnearthecontacts may reflect migration of Al203 to form chlorite.

67

0.04

-4-J
s::

0.03

ual

~

al

Q.

.4c-J:
"".-4 0.02
a:.l

0 N
:Izl;l
0.01

LOWER
MAimN


urrER
MARGIN
,


0

20

40

60

80

100

120

0.030~-------r------~------~------~----~~~------~~

UPPER MARGIN


'

0

20

40

60

80

100

120

Height above base of serpentinite (in feet)
Figure 58. Na20 and K20 versus height above base in the serpentinite. In the core of the serpentinite the Na2o
content ranges from 0.05-0.1 weight percent. Towards the upper and lower margins, the Na20 content increases to 0.02-0.04 weight percent. This slight increase towards the base may reflect influx ofNa20 associated with chloritization of plagioclase in the country rock. In the core of the serpentinite K20 ranges from 0.01-0.012 weight percent. Jn the upper and lower margins of the serpentinite, the K20 content ranges from 0.02-0.03 weight percent. This may reflect an influx ofK20 associated with chloritization of biotite in the adjacent country rock.

68

1.2

-~

--

"c("1')

{) ).j

-

(1)

0.

-

.."..0."c..'':1. 1.1

-(1)
~

-



~

0
(1) ~

' -

-
-





1.0

I

I

I

1-

I

I

T

T

I

I

I

0

1

2

3

Figure 59. FeO versus H20/Si02 ratio. Increase in FeO may reflect increasing steatization and subsequent destruction of secondary magnetite.

69

may be caused by the substitution of Fe+2 for Mg+2 in

talc and/or an increase in the talc content toward the

outer edge of the serpentinite. The presence of second-

ary magnetite in the serpentinite and its absence in talc

causesa generally higheroxidation ratio in serpentinite

(72-95 percent) than in talc (42-82 percent).

The change in major and trace element chemistry

accompanying alteration of serpentinite to talc, chlo-

rite and quartz is illustrated by a series of graphs

(Figures 60-62). The oxides Si02 and MgO (total70-90 weight percent), reflect the changes in mineralogy

accompanying each type of alteration (Fig. 60). MgO

(34-37.5 weight percent) is relatively constant in

serpentinite, and Si02 varies from 33.4-41.6 weight percent. In talc-rich rock, Si02is significantly enriched (up to 61 weight percent) but is highly variable due to

different amounts of carbonate in the analyzed rocks.

In chlorite-rich rock, the Si02 content is generally similar to that of serpentinite. The decrease of MgO in

talc-rock is related to increases in silica or carbonate. In

chlorite-rock, the decrease in MgO is caused by an

increase in AI20 3 (Table 2). The highercontentofCaOand C02 near the base
of the serpentinite (Figs. 49 and 50) suggests influx of

CaOand COTbearingsolutionsfrom the countryrocks.

The CaO content increases from less than 3 weight

percent in serpentinite to as much as 8.5 weight per-

cent (average 4.06 weight percent) in talc and to 4.2

weight percent in silicified talc (Fig. 61). The associa-

tion of talc and carbonate commonly is attributed to

addition The

oFfe2Co032atnodsFeerpOecnotninteen. ts

(generally

5-8

weight

percent and 0.3-2.3 weight percent respectively) vary

considerably in serpentinite (Fig. 60) suggesting a

wide range in the amount of magnetite, both metamor-

phic and secondary (serpentinization-related). The
decrease in Fe2o3 content from serpentinite (gener-
ally 5-8 weight percent) to talc {1-5 weight percent)

resulted from dissolution ofsecondary magnetite dur-

ing steatization. The decrease in modal magnetite with

increasing talc content is shown by Fig. 38 and 39. In
chlorite, the Fe2o3 content is highly variable (1.8-9.5
weight percent) but on average is equal to that in

serpentinite. The small variation of FeO in talc (1.1-1.5

weight percent) may reflect the relatively stable meta-

morphic magnetite content and lack of secondary

magnetite.

Several major element-oxides (Al20 3, Ti02, Na20, and K20) are significantly enriched in chlorite relative to serpentinite, talc, silicified serpentinite, and

silicified talc. Al20 3 is enriched from <0.5 weight percent up to 12.3 weight percent (Fig. 61). Because the

Al20 3 content of the Burks Mountain serpentinites are uniformly very low, it is likely that the Al20 3 was

introduced by Al-bearing solutions which then re-

acted with serpentine and talc. The fluids migrated

along fractures extending well into the serpentinite

and through the relatively porous multilithic breccia.

The Ti02 content increases sharply from 0.01 weight percent in serpentinite and talc to 5.1 weight percent in

chlorite (Fig. 62) also suggests mobilization and trans-

port ered

of Ti02 from the country rock. immobile, significantamounts

Normally consid-
of both Al2o3 and

Ti02 have migrated considerable distances along frac-

tures and through the multilithic breccia. Both Na20

and K20 (Fig. 62) increase from less than 0.05 weight

percent talc and

in to

serpentinite 0.28 weight

ptoer0c.1enwt Neiag2hot paenrcde0n.7t5Nwa2e0ighint

percent K20 in chlorite. These six- to fifteen-fold en-

richments further suggest influx of major oxide-bear-

ing fluids from the enclosing country rocks.

In general, the major chemical changes accompa-

nying metasomatism of serpentinite include enrich-

ment of Si02, FeO, and CaO enrichment of Si02, Al20 3,

during
Na2o,

steatization and K20, and Ti02

during chloritization relative to average Burks Moun-

tain serpentinite. During steatization, Fe2o3, MgO,

LOI, Ni and Cr decrease, and during chloritization,

CaO, MgO, LOI, Ni and Crdecreaserelative to average

Burks Mountain serpentinite.

Effects of silicification

In the silicified ultramafites, silicification is nearly complete. TheSi02contentincreases to 85.8-90.4 weight percent (Fig. 60) and most of the other oxides are reduced to minimal levels (Figures 60, 61 and 62). Preservation of metamorphic and secondary magnetite in serpentinite noted in thin sections is further
demonstrated by similar concentrations of Fe2o3 (5.4-
6.7 weight percent) in silicified serpentinite and nonsilicified serpentinite (5-8 weight percent).

Chemical Effects of Weathering

The geochemistry of a weathered serpentinite clast (sample D139) from the Old Petersburg Road roadcut shows significant depletion of certain elements and an apparent enrichment in others when compared to fresh serpentinite from the drill core.
The decrease of CaO and in the loss-on-ignition (LOI) component reflect the weathering and removal of carbonate. The absence of carbonates in all thinsections of exposed serpentinites examined in this study might suggest that carbonate is absent in unweathered serpentinite at depth; however, these chemical analyses confirm that carbonates are removed almost completely by weathering. Deep-weathering

70

- 10

~ c

-

s

T

c

ss ~T

<II 0
).I
<II 04
.~ .c: ..t.J..'I
-<II
~
...,
0 N
<II
~
'tS I:
ttl

. 8
~
6 ~
-

Fe203



4

-

~
2

1\






--


Ill





!:::..

.I

!:::..

0 <II
~

6. FeO

Qt:::..t:::..l:::..

~

6.

6 . !:::..

!:::..!:::..

!:::..

l:::..t:::..

!:::..!:::.. !:::..!:::..

6. l:::..t:::.. 6. 1.6

0

100
~

s

T

I:
Q)

-

0

).I

Q)
04

80

.j.)
..c:

-

..0..."

-Q)
~

60

N

-

-

iQ ---- .0....
Cl) 40

i~~!6~ZZZ



c ss)T


Si02

t:::..



'tS

I:

~

ttl

6.6. ~
6.

~'1 !:::..
!:::..t:::..

0 20

0"

- ~

6.

!:::..

0

!:::..!:::..

.6

o Figure 60. Si02 and MgO, Fe2 3 and FeO versus serpentinite alteration type. Weight percent of oxide is plotted
versus the principal rock type. Each rock type is essentially a monomineralogic alteration "assemblage". Variations in compositions of each rock type are due principally to trace amounts of other minerals such as talc, chlorite and carbonate in serpentinite. S = lizardite serpentinite, T =talc, C =chlorite, SS =silicified serpentinite, ST =silicified talc.

71

s
8

T

c

ss ;T

- - ~c
Q)

6

u

~ Q)
~

-

.~ .c:
0'1

4

~

-:Q.)



0
"'()

2 0

--


I



I IIIII

12



s

T

c

ss ,1

-10



~ c

Q)
u

"'

~ Q)

8

. ~

.~.c:

- . 0'1
-~

6

:Q.)

--

.., 4
- 0 N ~



<

2

0 .

I~

Figure 61. AI2o3 and CaO versus serpentinite alteration type. Weight percent of oxide is plotted versus the principal
rock type. Each rock type is essentially a monomineralogic alteration "assemblage". Variations in compositions of each rock type are due principally to trace amounts of other minerals such as talc, chlorite and carbonate in

serpentinite. S = lizardite serpentinite, T =talc, C =chlorite, SS =silicified serpentinite, ST =silicified talc.

72

0.6

s

-+sJ::

Q)

0
~

0.4

Q)
c.

.+c:J:
0\
r-l
-:Q:.) 0.2
N
0
.-l ~

o.o

T

c ss




0.8

.oJ
::

CJ

0

~

Q)
c.

0.6

.+c:J:
0\
r-l
-Q)
~
0.4

0 N
~

's0:: l 0.2

0 N
zl

o.o

s

T

c

ss

K20

/:).



Na 20

Figure 62. Na20 and K20, and Ti02 versus serpentinite alteration type. Weight percent of oxide is plotted versus the principal rock type. Each rock type is essentially a monomineralogic alteration "assemblage". Variations in compositions of each rock type are due principally to trace amounts of other minerals such as talc, chlorite and carbonate in serpentinite. S = lizardite serpentinite, T =talc, C =chlorite, SS =silicified serpentinite, ST =silicified talc.

73

Table 2.

Average Chemical Composition of Ultramafic Rocks Burks Mountain Complex (this study)

Serpentine

AVG STD

VAR

Chlorite

Talc

AVG STD

VAR AVG

STD

VAR

Si02 Al203 Fe203 FeO MgO CaO
Na20 K20 LOI
Ti~
P205 MnO StO
Rb20 Ni Cr

38.28 0.39 5.89 0.99 36.26 0.99 0.02 0.02 15.29 0.01 0.01 0.10 0.002 0.001 0.221 0.235

2.60 0.05 1.31 0.64 0.78 0.83 0.01 0.01 1.92 0.00 0.00 0.03 0.00
O.D19 0.108

6.76 42.17 5.22

0.00

7.85 2.81

1.72

5.45 2.28

0.41

1.13 0.63

0.60 27.72 4.86

0.70

0.64 0.78

0.00

0.15 0.11

0.00

0.20 0.25

3.68 13.43 3.10

0.00

0.23 0.14

0.00

0.08 0.16

0.00

0.12 0.08

0.00

0.00 0.116

0.157 0.115 0.108 0.045

27.27 7.90 5.19 0.39 23.60 0.61 0.01 0.06 9.58 0.02 0.02 0.01
0.013 0.002

47.52 0.58 3.05 1.35 28.22 4.06 0.06 0.02 12.72 0.01 0.01 0.14 0.0005 0.0005 0.163 0.215

11.53 0.26 1.32 0.17 2.48 3.68 0.02 0.01 7.68 0.00 0.00 0.14
0.032 0.005

132.85 0.07 1.75 0.03 6.13 13.57 0.00 0.00 59.06 0.00 0.00 0.02 0.00 0.00 0.00 0.00

TOTAL 98.720

99.426

98.144

AVG =average STD =standard deviation VAR =variance
The original analyses for serpentinite, chlorite and talc are presented in Appendix II.

Table 3.

Chemistry of Fresh and Weathered Serpentinite (values are in weight percent)

Average Fresh Serpentinite Weathered Serpentinite

Si02

MgO

36.26

Al203

0.39

Fe203

5.89

FeO

0.99

Na20

0.02

K20

0.04

CaO

0.99

LOI

15.29

Ni

0.22

Cr

0.24

Ti~

0.01

Average fresh serpentinite is from Table 2.

9.70 11.10 24.70 0.38 0.04 0.06 0.03 9.90 0.19 0.46 0.26

74

of serpentinites in many parts of the world produces Ni-rich saprolites which are an important source of that metal. The results of this study do not suggest that weathering enriched Ni in the study area.
The weathering index of a silicate rock provides a chemical index for quantifying the intensityofweathering (Parker, 1970). The weathering index is calculated from the expression:
100 X [(Na)a/0.35 + (Mg)a/0.9 + (K)a/0.25 + (Ca)a/0.7] (where (X)a is the atomic percentage of element X divided by its atomic weight). The weathering index, normally 96-104 for fresh serpentinites, decreases to 27 for serpentinite in the roadcut.
GEOPHYSICS
Rocks with different physical properties can be distinguished by measuring those properties with geophysical instruments. Serpentinites and other ultramafic and mafic rocks are commonly significantly different from felsic rocks in their physical properties. Generally, they differ most in density and/or magnetic susceptibility. Geophysical methods aided in the subsurface delineation of the Burks Mountain complex serpentinites because of their extremely poor exposures; especially of the southern serpentinite. Initial geophysical work conducted by Long (1987) used gravity methods. A second survey by Cocker (1989a) employed ground magnetic methods.
GRAVITY
Unaltered ultramafic rocks are generally very dense with a specific gravity of 3.3 for dunite and harzburgite. Alteration of ultramafic rocks changes their mineralogy and hence their density. Specific gravity of serpentine minerals ranges from 2.55 for chrysotile and lizardite to 2.61 for antigorite (Coleman, 1971). The presence of antigorite instead of lizardite, massive talc (specific gravity 2.7-2.8, average 2.71, Telford and others, 1976), as well as other minerals such as magnetite, carbonate, chlorite and actinolite will affect the density of an ultramafite to different degrees. Amphibolites have densities ranging from 2.90 to 3.04 with an average of 2.96 (Telford and others, 1976) and may be misinterpreted as ultramafic rocks.
Long (1987) attributes a subtle gravity anomaly in the Burks Mountain area to talc mineralization but found the anomaly to be indistinguishable from an anomaly over higher density mafic rocks. This lack of a distinctive gravity signature is attributed to similar densities of the talc and mafic rocks. However, the densities of talc and serpentine should be less than the densities of the mafic rocks and, in principle, should be

distinguishable from them. Similaritiesin the densities of talc and serpentinite
to felsic rocks may significantly increase the difficulty in distinguishing the ultramafic from the felsic rocks. Felsic rocks have densities which are normally lower
than ultramafic rocks. Granite has a: density range of
2.50 to 2.81 with an average of 2.64, and gneiss has a range of 2.59 to 3.0 with an average of 2.80 (Telford and others, 1976). The densities of serpentinite and talc can range from 2.55 to 2.8 overlapping that of granite and gneiss.
MAGNETICS
The abnormally higher concentrations of magnetite in serpentinite compel the choice of magnetics as the most highly suitable geophysical technique to delineate serpentinites associated with ultramafic rocks (Breiner, 1980). Primary magmatic magnetite and/or chromite is commonly significantly more abundant in mafic/ultramafic rocks than in more felsic rocks. Prograde amphibolite facies metamorphism of mafic/ ultramaficrocksproducesamoremagnetite-richspinel which is more magnetic than the magmatic spinel. Also, serpentinization of Fe-Mg silicates releases additional iron to form finely disseminated magnetite.
The ground magnetic survey consisted of two main parts: an initial orientation survey followed by the main survey. The orientation survey was run alongside of the Old Petersburg Road with stations every 50 feet. The orientation of the line was chosen to cross the previously mapped regional geologic trends (McLemore, 1965). The interval was chosen to determine the minimum spacing required to detect the serpentinite.
The orientation survey identified a very prominent anomaly coincident with the serpentinite (Fig. 63). A grid was constructed to cover the serpentinite and subsequently was expanded to cover additional areas of interest. Numerous N-S and E-W ground magnetics profile lines were constructed and the results are similar to the orientation survey line in defining the serpentinite. A ground magnetic map (Fig. 10) compiled from these data successfully delineated the subsurface extent of the serpentinite. The subsurface presence of serpentinite was confirmed by drill testing. Discontinuities in the magnetic anomalies suggest the presence of faults which break the serpentinite into smaller segments. Smaller anomalies correspond with isolated ultramafi te masses identified by surface float. Extension of the survey to a wider line spacing over the western end of Burks Mountain uncovered currently unexplained discontinuities in the magnetic expression of the serpentinite. These discontinuities include

75

53800

3:

0

0

~

53000

North

Ul ttl
1=: 1=: ttl t!l
52000

South

51000~----r----.-----r----~----~--~-----r----~----+---~

2000

1000

0

1000

2000

Distance (in feet)

Figure 63. Ground magnetic survey line. This line (400W) is oriented north (left) to south (right) with the view towards the east. Pronounced positive magnetic anomaly (greater than 52,100 gammas) is associated with the underlying serpentinite. Relatively non-magnetic Kiokee gneisses and granites occur north of the serpentinite.

76

exceptionally high and narrow magnetic anomalies and serpentinite with an abnormally low magnetic response. The scale of the ground magnetic map (Fig. 10) prohibits the inclusion of these narrow anomalies.
The ground magnetic anomaly over the southern serpentinite is roughly coincident with a positive anomaly detected in anairborne survey (Daniels, 1974). These results suggest that the southern serpentinite extends to the southwest at a relatively shallow level for approximately several thousand feet.
DISCUSSION AND CONCLUSIONS
PHYSICAL CONDITIONS DURING PROGRADE METAMORPHISM
Studies in the northeastern portion of the Kiokee belt in the vicinity of Lake Murray, S.C. (Dallmeyer and others, 1986) provide a framework for estimating the physical conditions during the metamorphism in and adjacent to the Burks Mountain complex (Fig. 64). Maximum metamorphic conditions during Alleghanian metamorphism are suggested to be approximately 4.5 kb with a minimum temperature of 530C (Secor and others, 1986a), although a more recent study (Snoke and Frost, 1988) indicates pressures of up to 7 kb and 575C were attained in Kiokee belt rocks located in South Carolina. Subsequent rapid cooling from above 500C to below 300C is attributed to rapid uplift from mid-crustal depths and erosion in the Ia test Carboniferous and Early Permian (Dallmeyer and others, 1986). Slower cooling to about 100-125C occurred over the following 170 million years (Zimmerman, 1979; Naeser and Cebula, 1978; Dallmeyer and others, 1986).
Mineral equilibrium relations suggest peak metamorphic conditions were probably much higher than the minimum 530C. Dallmeyer and others (1986) show a maximum temperature on their thermal evolu-
tion curve of 600C with an error of +I- 70C. During
amphibolite facies metamorphism, temperatures are between 600 and 700C (Ehlers and Blatt, 1982). The relict upper amphibolite assemblages identified in the serpentinized metaharzburgite (Cocker, 1989a) are similar to upper amphibolite facies assemblages in other serpentinites (Springer, 1974; Frost, 1975; and Pinsent and Hirst, 1977). Maximum temperatures estimated for these similar assemblages are: 775C (Springer, 1974); 750C (Frost, 1975);and 725C (Pinsent and Hirst, 1977). The presence of anthophyllite places a minimum temperature of formation at 2-4 kb of approximately 600C (Evans and Guggenheim, 1988).
The clustering of granite and granite gneiss (migmatites) compositions near 750C at 5 kb pressure

(Fig. 47) is in reasonable agreement with the 700C estimated from the above metamorphic relations. Intrusion of the granites in association with or subsequent to the migmatization during the Lake Murray deformation event (discussed earlier) is thought to have produced the amphibolite facies metamorphism in the Kiokee belt (Secor and others, 1986a and 1986b; Dallmeyer and others, 1986; and Secor, 1987).
PHYSICAL CONDITIONS DURING SERPENTINIZATION
Physical conditions during serpentinization can be determined through the use of phase diagrams, textures, mineralogy and chemical analyses. As discussed in previous sections, the only recognized serpentine mineral is lizardite; the lizardite forms a pseudomorphic mesh textureafter olivine and enstatite;
and the lizardite is relatively low in AI2o3.
Using these parameters, the physical conditions during formation of the Burks Mountain lizardite serpentine can be estimated from P-T phase diagrams. The stability fields of each of the three primary serpentine minerals, lizardite, chrysotile and antigorite, can be shown in P-T space, because each is known to replace or be replaced by the other two serpentine minerals.
Two types of P-T phase diagrams, which are constructed from experimental relations and thermodynamic data, include the MSH (Mg0-Si02-H20) and the MASH (Mg0-Al20 3-SiOTH20) diagrams (Wicks and O'Hanley, 1988). The MSH diagram contains six phases: lizardite, antigorite, chrysotile, brucite, forsterite, enstatite, talc and water, and 3 components (MgO-SiOTH20). The MASH diagram includes a seventh phase, clinochlore, through the addition of a fourth component (AI20 3). Reactions involving two serpentine minerals have not been calibrated experimentally, so only the topologic relations can be shown (Fig. 65 and Fig. 66). These phase diagrams are for lowAI (less than 1 weight percent AI20 3) lizardite and high-Al (greater than 3.5 weight percent Al20 3) lizardite respectively.
Lizardi te should be the stable serpentine phase at pressures above 500 bars and at temperatures below 200C(WicksandO'Hanley, 1988). Theinvariantpoint [LT] in Figures65 and 66 is at500bars and 200C. The stability of lizardite is dependent on its Al-content as illustrated by the intersection of the following two reactions. The equilibrium lizardite = forsteri te + talc+ clinochlore + water and antigorite= forsterite + talc+ water intersect at 700C and 35 kb for a(H20)=1 with a lizardite containing 9 weight percent A120 3. A decrease in Al-con tent to 3.5 weight percent moves this

77

IGNEOUS

METAMORPHIC

ALTERATION

PROGRADE

RETROGRADE

800
w
t: 600
:::l
~ 400
w

' "\ '

~ -----
/

RAPID UPLIFT
~
\ \
\

Q.
~ 200
t-

' ~ ---- -

00

......

Early Paleozoic

M

p

Pe

Tr

J

(X)

TIME

<modified from Dallmeyer and others, 1983)

Figure 64. Time-temperature diagram for Alleghanian metamorphism. Graph illustrates relative cooling for the ultramafic complex during the Early Paleozoic. After emplacement into the Kiokee section, the ultramafites were heated and metamorphosed during the Mississipian (M) and Pennsylvanian (P). This was followed by rapid uplift and cooling during the Permian. Serpentinization probably occurred below 2500C during the Late Permian (Pe). Alteration to talc, chlorite, carbonate and quartz may have occurred during the Triassic (Tr) and/ or Jurassic (J). Time and temperature constraints are presented by Dallmeyer and others (1986). Temperature is in Centigrade.

L T

-- ----f- :c----------:----=-----=-------:-:-=-----:.-.-

B
PHASES A Antigorite B Brucite
c Chrysotile
Cl Clinochlore F Forsterite L Lizardite T Talc
w Water
METAMORPHIC REGIMES A Retrograde F + W - A
B Retrograde F ( + El + W - L (PH2<) < Pgl
c Prograde L - C =Cl
0 Prograde L .... A + F + Cl + W (PH20 = Pgl
Figure 65. P-T phase diagram for MSH system. This is a schematic phase diagram illustrating the relative reactions and metamorphic regimes (after Wicks and O'Hanley, 1988). Retrograde metamorphism under most conditions should result in the formation of Iizardite in regime B. The retrograde formation of antigorite is rare (only 1 or 2 occurrences are documented).
79

l I

I" "v'

Q_<FTl

\

\

t-=--x---- J~-:t-._-~. -
'\ -----+---~---:--_-:~
!:--.:----::-:-::---=--=~-:-=--=---==
\ -:..-. -~-----....:c----= O:SF_-_-~_-:...
/' ~- --- --- --- -----

Figure 66. P-T phase diagram for MASH system. This is a schematic phase diagram illustrating the relative reactions and metamorphic regimes (after Wicks and O'Hanley, 1988).
80

intersection to 550C and 5 kb for a(H20)=1 (Wicks and O'Haruey, 1988; Caruso and Chernosky, 1979).
With an average Al2o3 content of less than 0.5 weight
percent for the Burks Mountain serpentinites, this

intersection should shift to still lower temperatures

and pressures.
The reaction lizardite = chrysotile+I -clinochlore

(Fig. 66) controls the P-T coordinates of the stability

field oflizarditeand is critical to the stability oflizardite

during retrograde serpentinization. This reaction is

displaced towards lower temperatures if the Al-con-

tent of lizardite increases. At pressures above those of

invariant points [CT] and [BC], this reaction is stable,

and lizardite is metastable during retrograde

serpentinization. From these relations, low-Al, pseudo-

morphic lizardite is probably metastable (Wicks and

O'Hanley, 1988).

During serpentinization, if water pressure,

P(H20), is less than geostatic pressure, P(g), the system is under a hydrostatic head and depth becomes an

important factor. With increasing depth, P(H20) will increase more rapidly than P(g) until they are equal. At

any given depth, reactions with a positive slope will

plot at a lower temperature and those with a negative

slope will plot at a higher temperature if P(H20) < P(g) thanifP(H20)=P(g)(BrutonandHelgeson, 1983). The geometry of the phase diagrams will remain un-

changed, because a(H20)=1 (a is the activity of a component). If lizardite and chrysotile form at tem-

peratures less than 250C, and P<H20)<P(g) with thermal gradients of 30-100C/km, fluid pressure would

be 800 bars at 7.5 km or 300 bars at 2.5 km for a fluid

density oft glcm3 (Bruton and Helgeson, 1983; Wicks

and O'Hanley, 1988).

The Burks Mountain lizardite serpentinites can

be placed within one of four major types or regimes of

serpentinization (Wicks and O'Hanley, 1988). These

regimes are defined by the relation of serpentine min-

eralogy and textures to reactions on the phase dia-

grams (Fig. 65 and 66). The Burks Mountain

serpentinites developed in the retrograde regime B

which involves the alteration of forsterite and enstatite

to lizardite at low water pressure (P(H20)<P(g)) with production of pseudomorphic textures. This is prob-

ably a metastable reaction due to suppression of the

forsterite to chrysotile reaction at low water pressures

(Wicks and O'Hanley, 1988). The other regimes in-

volve: A) the retrograde hydration of olivine to pro-

duce antigorite with decreasing temperature with

Pch(Hry2s0o)t=ilPe (+g)I;-

C) the prograde reaction lizardite = clinochlore characteristic of chrysotile

asbestos deposits; and D) the prograde reaction lizardite

=antigorite+ forsterite + clinochlore +water at higher

temperatures and pressures with P(H20)=P(g) (Wicks

and O'Hanley, 1988). Maximum temperature of formation for lizardite
seq>entine is generally believed to occur below 2002500C and may be as low as 100C (Wenner and Taylor, 1971). Serpentinization at temperatures near 100C may be possible by a non-equilibrium process of dissolution of olivine and pyroxene and the precipitation of brucite, serpentine and talc (Nesbitt and Bricker, 1978).
The age of serpentinization can not be determined directly, but within the context of a metamorphic-structural model developed for the Kiokee belt certain constraints may be placed on the timing of serpentinization. Using the time-temperature curve (Fig. 64) of Dallmeyer and others (1986), the first time that the metaharzburgites would cool from a higher temg;rature regime into a temperature range of 200250 C for retrograde formation of lizardite, would be approximately 285 Ma. This Early Permian age is a maximum age of serpentinite formation.
Oxygen and hydrogen isotopic investigations of serpentinized oceanic and continental ophiolites indicate that most of the lizardite-chrysotile in continental ophiolites probably formed from hot, exchanged meteoric ground waters, mixed meteoric-magmatic waters,ormixedmeteoric-connatewatersinsteadofocean or connate waters (Wenner and Taylor, 1973). the presence of lizardite in the Burks Mountain complex suggests but does not prove that meteoric waters were involved in formation of the Burks Mountain serpentinite.
PHYSICAL CONDITIONS DURING SERPENTINITE ALTERATION
Two distinctly different types of alteration affected the serpentinite: 1) talc + carbonate + chlorite alteration, and 2) silicification. Type 1 alteration is commonlydeveloped as a sequenceofrelativelysimple, essentially monomineralic zones. The origin of these zones has been investigated in detail as a chemical mass transport process (Chidester, 1962; Jahns, 1967; and Sanford, 1982) and as a process related to the mineralogic stability relations (Hemley and others, 1977). Silicification of the Burks Mountain serpentinite involved the near total replacement of the serpentinite by quartz and certainly involved extraordinary amounts of chemical mass transport.
Origin of type 1 alteration by chemical mass transport involves movement of significant volumes of oxides between the country rock and ultramafic rock. The free energy or chemical potential differences between the country rock and ultramafite act as driving forces for diffusion ofchemical components. Chemi-

81

cal potential differences calculated from compositional variations and equilibria among components indicate directions of mass transfer (Sanford, 1982). Some studies suggest that mass transfer involved the introduction of Si, Fe and C02 into the ultramafic body accompanied by the loss of H20 and Mg (Sanford, 1982). During low-grade metamorphism Ca and C02 are transferred in, but at higher grades, they are removed from the ultramafic body and Na introduced. Generally, Na and K migrate into the country rock in front of the advancing chlorite zone (Sanford, 1982). Other studies suggest that AI moves outward in front of the outward growing talc zone. This conclusion is based on evidence that talc has replaced the chlorite (Jahns, 1967) but is opposite to Sanford's (1982) observations.
AIthough Cr2o3and Ti02are considered immo-
bile by Sanford (1982), magnetite-titanite intergrowths which replaced ilmenite and titanite which replaced rutile at lower greenschist facies metamorphism are petrographicevidenceofthemobilityofTi02.Numerous occurrencesin New England, Virginia, North Carolina and Georgia of secondary titanite associated with chloritic alteration correlate with geochemical patterns that indicate Ti02, is in fact, highly mobile in this environment. Significant enrichment of Ti02 in chloritic fractures within the Burks Mountain serpentinite also demonstrate considerable mobility of Ti02. Sanford (1982) attributes smaller Cr concentrations in the talc, talc-carbonate and actinolite-chlorite zones than in the original rock to a net volume increase. A similar decrease of Cr in the talc and chlorite zones in the Burks Mountain serpentinite is attributed in the present study to leaching of Cr from these rocks by the altering solutions. Similar modal concentrations of magnetite in the talc and chlorite zones in the Burks Mountain serpentinite suggest that volumes did not increase significantly.
An increase in silica activity or a decrease in temperature during metamorphism can also effect the observed zonation (Fig. 67). In ultramafites, talc can form from serpentine, olivine, enstatite, or amphibole (anthophyllite) with an increase in the activity of Si02 or a decrease in temperature. Calculated silica-activity diagrams (Fig. 67) indicate that talc could form from serpentine (antigorite) at temperatures down to at least 100C. Because lizardite is the stable phase below 200-250C, talc probably formed at or below that temperature. An increase in Si02 activity can result from an influx of SiOTsaturated fluids, removal of MgO, or an increase in the Si/Mg ratio of the silicate fraction of the rock due to the conversion of Mg-silicate to Mgcarbonate. Influx of C02 to form MgC03 (Fig. 68) from serpentine releases silica which increases the activity of silica. The frequent association of carbonates and

talc in steatized serpentine favors this mechanism as

the most common mode of steatization.

The stabilities of chlorites with different compo-

sitions enables estimations to be made concerning the

physical conditions during chlorite formation. Chlo-

rite is stable and will form under a broad range of

metamorphic conditions from the prehnite-

pumpellyite facies into the amphibolite facies. The

upper limits of chlorite are defined by its breakdown to

form forsterite + enstatite + green spinel + H20 in the sillimanite zone of the amphibolite facies. The devel-

opment of chlorite in a metamorphosed ultramafite
requires a source of AI2o3.
In low-Al ultramafites like the Burks Mountain

serpentinites, the most common sources of AI203 are spinels and the adjacent country rocks. The source for
the AI2o3 in the chlorite which formed adjacent to the
spinels was probably the spinels themselves. The

amount of chlorite thus formed is minor compared to

the large amounts of coarse-grained chlorite found in

fractures in the serpentinite and in the matrix of the

mul tilithic breccia. The formation of the coarse-grained

chlorite requires an influx of solutions bearing Al20.J

and
+/-

may require removal of FeO which is facilitated

Si02 or addition of Mgu by fractures and breccias

open to exchange with the surrounding rocks.

If the system is open to AI, the amount of Al

substituting for Si and Mg will principally depend on

the stability of the chlorite of that particular composi-

tion (Bailey, 1988b). The Al20 3 content of chlorites obtained from whole-rock and microprobe chemical

analyses of chlorites demonstrate a strong correlation

with metamorphic grade.

Within contact metamorphosed peridotite and

blackwall rock, chlorite becomes more Al-rich with

increasing metamorphic grade (decreasing distance)

toward the heat source (Fig. 69). In the Blue River
Peridotite, Cassiar, B.C., the Al2o3 content of chlorite
increases from 1.1 weight percent 4 km (2.5 miles)

away to over 19 weight percent adjacent to the batho-

lith/peridotite contact(Pinsent and Hirst, 1977). Chlo-

ri tes in thermally metamorphosed blackwall at Paddy-

Go-Easy Pass in the central Cascades, Washington

increase in Al20 3 from 12.1 weight percent in a forsterite-talc assemblage (equivalent to lower amphi-

bolite facies) to over 20 weight percent in a chlorite-

forsterite-enstatite-spinel assemblage (equivalent to

upper amphibolite facies) near the batholith/ perido-

tite contact (Frost, 1975). The estimated maximum

temperatures near the contacts are 700-750C (Pinsent

and Hirst, 1977) and greater than 700C at 2 to 3 kb

pressure (Frost, 1975).

Chlorites in ultramafic rocks subjected to regional
metamorphism show a similar increase in AI2o3 con-

82

1

2

<S 3
(j)
ns
01 0
T 4

Lizardlte

Antigorite

5
Brucite 6

Forsterite Periclase

100

200

300

400

500

600

700

8 0

Temperature (C) P=2 kb

Figure 67. Silica activity versus temperature phase diagram for the MSH system. This diagram illustrates the relation of the talc stability field to those of lizardite, enstatite, forsterite (olivine). The disseminated patchy talc is anticipated to have formed at high temperatures during the retrograde alteration of enstatite+/- forsterite +/anthophyllite. The principal mechanism for the formation of this talc is probably a decrease in temperature. The formation of the massive talc resulted from the alteration principally of lizardite at low temperatures. Talc probably formed from an increase in silica activity resulting from carbonate alteration of lizardite. The lizardite field is inserted in the antigorite field shown by Evans and Guggenheim (1988) based on the phase diagrams by Wicks and O'Hanley (1988) and the temperature anticipated for lizardite formation (see text). The boundary between lizardite and antigorite is independent of temperature (see Fig. 65 and 66).

83

An+Oz+W
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 X(C02l P-2kb
PHASE An Ant hophylllte A! Antigorite Dol Dolomite En Enstatite Fo Forsterlte Mst Magnlllte
az Quartz
Tc Talc Tr Tremollte
w Water
Figure 68. T-XC02 phase diagram. No similar diagrams have been constructed for lizardite at lower temperatures where lizardite would be stable. This phase diagram is constructed for antigorite with a minimum calculated temperature of 350C. This diagra m does illustra te the point that, with a slight increase in X(C02), antigorite (and probably liza.rdite) is unstable and will r act, in general, to form talc plus magnesite, dolomite or calcite.
84

20

+sJ::

Ql

0
j...j

-

Ql

~

I

- .+sJ:: 15
0'1

-~
I . (l)
... ;3:

-
-

(l)

-

- +J
-~

10

j...j

'

-

0

.r.-c1:
0

-

4-1

-

0

5

+sJ::
Ql
+sJ::
0

-
-

0 1

I

I

.-.



I

I



0 ""

0

1

2

3

4

N
r-1

Distance from igneous contact (in kilometers)

~

Figure 69. Chlorite AI2o3 content versus distance from igneous contact, WA. The intrusion of a younger batholith
metamorphosed a peridotite and caused the growth of metamorphic chlorite in that peridotite. This diagram illustrates the dependence of the Al20 3 content of chlorite in that peridotite on temperature as reflected by the distance from the contact with the batholith. Chlorite formed at a higher temperature (and metamorphic grade) has a distinctly higher Al203 content than chlorite formed at a lower temperature (and metamorphic grade). Data is from Pinson and Hirst (1977).

85

tent with increasing grade. When plotted with chlorites from thermally and regionally metamorphosed ultramafites (Fig. 70), the coarse-grained chlorites from the Burks Mountain complex with low Al20 3 (average 7.85 weight percent) are in the range of the greenschist facies. This is compatible with the formation oflizardite under greenschist facies conditions.
Based on the evidence presented in this investigation, the conditions prevailing during the formation of lizardite and its alteration to talc, carbonate and chlorite include low temperatures, <200-250C, and low pressures, <2.5 kb, and low P(H20), <300 bars. Alteration of the lizardite to carbonate, talc and chlorite probably resulted from fracturing and brecciation leading to or resulting from a decreasein pressure plus the introduction of C02, Si02 and A120 3. These conditions contrast with the suggested development of metasomatic reaction rims around the lizardite serpentinite bodies during amphibolite facies metamorphism (Sacksand others, 1989).The lizarditeshould have re-equilibrated to antigorite during upper greenschist to epidote amphibolite facies, and subsequently antigorite should break down to form olivine, enstatite and amphibole in the amphibolite facies. The second type of alteration, silicification, involves significant addition of silica and removal of most of the other oxides (see discussion under petrochemistry). The intimate association of multistage quartz veining with the silicification of Burks Mountain serpentinites is similar to other occurrences of extensive silicification and quartz veining commonly documented as hydrothermal in origin. The source of the hydrothermal silica-bearing solutions is presently unknown, but constraints on the conditions at the time of silicification can be estimated.
Sacks and others (1989) suggest that silicification occurred prior to or during amphibolite facies metamorphism; however, petrographic and field relations demonstrate silicification occurred after steatization and at low temperatures and pressures. Phase relations in the system serpentine + quartz also suggest that conditions of silicification were under relatively low temperatures. The assemblage serpentine+ quartz reacts to form talc above 310C at 1 kb. This asse~n blage is slightly more stable at hi!bher pressures where the reaction takes place at 350 C at about 6.5 kb. Pressures were probably low (<3 kb) as suggested by the widespread association ofopen-space quartz veins with the silicification. These estimated temperature and pressure conditions plus the pebographic and field relations indicate conditions during or after silicification were well below the minimum 600C of the amphibolite facies.

PARAGENESIS AND ORIGIN
PARAGENESIS
The paragenesis of the Burks Mountain ultramafites, detailed in Fig. 71, is inferred from petrographic, petrochemical and field relations to be:
1) intrusion and crystallization of an ultramafic/ mafic magma or magmas;
2) emplacement of the Burks Mountain ultramafites into the Kiokee belt rocks;
3) prograde metamorphism of a harzburgite ultramafite to an upper amphibolite grade-
assemblage of enstatite + chlorite +I-tremolite +I- anthophyllite+ ferritchromite or Cr-
magnetite with primary or recrystallized olivine + orthopyroxene stable; 4) retrograde metamorphismofolivine, enstatite, anthophyllite and tremolite to lizardite serpentine plus secondary magnetite; 5) fracturing/brecciation of the serpentinite and enclosing Kiokee rocks possibly by low-angle, small-scale thrusting; 6) influx of C02, which may be accompanied by Si02 and/or loss of MgO through a fracture system resulting in alteration of lizardite to carbonate + talc; C02 addition may extend beyond #7;
7) influx of Al2o3 along fractures and breccias
to form coarse-grained chlorite from talc and lizardite; this may accompany or overlap #5; chloritization, albitization and biotitization of the country rocks immediately adjacent to the serpentinites also occurred at this time; 8) localized fracturing of the serpentinite with
numerous periods of quartz +I- chalcedony
deposition in veins and by pervasive silicification replacement of talc, serpentine, amphibole and chlorite; 9) further fracturing of serpentinite and Kiokee gneisses during Late Jurassic extensional te-e tonics(?) with little or no accompanying alteation.
GEOCHRONOLOGY OF METAMORPHISM AND ALTERATION
The age of the metamorphism and alteration that affected the metaharzburgites of the Burks Mountain complex is not known because of the lack of datable minerals in the metamorphic and alteration assemblages. However, certain events can be used to bracket the metamorphism and alteration of the Burks Mountain complex. The suggested model for the Burks Mountain complex is that it was emplaced into its present

86

10
9

..s!<:: 8
ta
~ 7

CJ

r-1
.t::

6

Q.

~
0

5

J:l

ta +J

4

(1)

~

3

2

1

-
- ---- -- ---

~

-- - -

--

-- ......

- - ~
-- - - - - - ... ~ I""

~

-- - - - - -- -~

r-

-
_-..._ ......
--

I

I

I

~

I

0

2

4

6

8 10 12 14 16 18 20

Al 2o3 content of chlorite (weight percent)

EXPLANATION

Metamorphic Rank

Primary Phases

1 2 3 4 5 6 7 8 9 10

Chrysotile Lizardite Antigorite Forsterite- Talc Forsterite- Anthophyllite Forsterite- Enstatite Biotite Gamet Kyanite Sillimanite

o Figure 70. Chlorite AI2 3 content versus metamorphic grade. A compilation of chlorite analyses from ultramafic
rocks with documented metamorphic grades indicates a progressive increase in the Al20 3 content with increasing
metamorphic grade. The metamorphic facies equivalents are summarized in Table 1. Data from Chidester (1962), Cocker (this report), Frost (1975), Pinsent and Hirst (1977), and Tracy and others (1984).

87

PARAGENESIS OF BURKS MOUNTAIN COMPLEX

Early

Paleozoic

M

p

Pe

Tr

IGNEOUS

METAMORPHIC

J ALTERATION

Present

PROGRADE

RETROGRADE

ENSTATITE (1) OLIVINE (1) SPINEL (2) Ti-MAGNETITE ILMENO-HEMATITE CHLORITE (1) MAGNETITE (1)

--~ -= -

, ___ ,__

X

---1 -------X j ==::J========x ---- ----- --X

TREMOLITE

ANTHOPHYLLITE

OLIVINE (2)

CXI CXI

I ENSTATITE (2)

TALC (1)

LIZAROITE

MAGNETITE (2)

BRECCIATION

CARBONATE

---

---- --------X

-- -

- -----------X

----

-- -- ------

-~-

- --- r-~ -- :r-------------X . -X -------x - ----x

TALC (2)

-

----X

CHLORITE (2)

-

---X

BIOTITE

-

---X

ALBITE

-

---X

TITANITE

-

---X

QUARTZ

---X

Figure 7L Paragenesis of Burks Mountain complex. The developmentof each mineral (or event) is illustrated by a thick solid or dashed bar. The thin dashed lines illustrate probable preservation of that phase during that time. The large X's indicate the mineral is presently preserved. Time symbols are the same as in Fig. 64. The numbers after the mineral phase refer to the relative temporal position of each phase when more than one of the same phase may have developed.

position within the Kiokee belt at some point during the Alleghanianorogeny. It wasprobablynotemplaced prior to the Alleghanian orogeny as little evidence exists of penetrative deformation which affected the Kiokee rocks in this area during the Alleghanian orogeny.
The preserved mineral assemblages suggest that the Burks Mountain complex was subjected to middle to upper amphibolite facies prograde metamorphism. Because penetrative deformation that would accompany emplacement is absent in the metamorphic silicates, this metamorphism appears to have occurred after emplacement of the ultramafites. It is suggested that the age ofpeak metamorphism of the Burks Mountain complex is thus similar to the age of prograde Alleghanian metamorphism which has been established as 295 to 315 Main rocks from the northwest limb of the Kiokee antiform (Dallmeyer and others, 1986).
A period of rapid cooling from above approximately 500C to below approximately 300C as defined by retention of Ar in hornblende and biotite apparently occurred between 295 and 285 Ma (Dallmeyer, and others, 1986). This was followed by slower cooling through about 100-125C at 130-150 Ma as defined by apatite fission ages (Zimmerman, 1979; Naeser and Cebula, 1978; Dallmeyer and others, 1986). Rapid cooling followed by slower cooling is interpreted as recording a period of rapid uplift from mid-crustal depths followed by erosion in the latest Carboniferous and Early Permian.
It is probable that the retrograde formation of lizardite serpentine occurred at some time following the period of rapid cooling. The maximum age of serpentinization may be constrained by the last cooling of the metaharzburgites through a temperature of approximately 250C. The intersection of the slope of the time-temperature curve for the Kiokee belt rocks (Dallmeyer and others, 1986) with a temperature of approximately 250C suggests a maximum age of about 270-280 Ma.
The youngest event which can be directly correlated is the chloritization in the multilithic breccia, the serpentinite, and in the immediately adjacent Kiokee rocks. This event includes the extensive development of coarse grained chlorite in fractures and breccias in the serpentinite and along the contact between the serpentinite and the country rock, and the chloritization, albitization, biotitization and Ti02 remobilization of the country rock immediately adjacent to the serpentinite. Dating of this event does not presently exist, but the abundant secondary titanite and biotite formed at this time present an opportunity to constrain what may be the waning stages of Alleghanian meta-

morphism. Silicification appears unrelated, chemically and
structurally, with any previous metamorphism oralteration events and may be related to the initial stages of extensional tectonics associated with Jurassic-Triassic rifting.
ORIGIN OF THE BURKS MOUNTAIN ULTRAMAFIC ROCKS
The Burks Mountain complex contains an assemblage of serpentinite, amphibolite and metagabbro interpreted as harzburgites, basalts and gabbros (Sacks and others, 1989; Cocker, 1989a and 1989c). The complex may be part of a cumulate mafic and ultramafic intrusive and extrusive complex formed within or below the Carolina slate belt or tectonically incorporated from an exotic terrane (Sacks and others, 1989). The gneisses and schists of the Kiokee belt have been interpreted as part ofan accretionary complexcontaining fragments (BurksMountain complex) of the Iapetus oceanic crust (Higgins and others, 1988; Sacks and others, 1989).
Clusters of ultramafic and mafic rocks near the Inner Piedmont-Kings Mountain belt boundary, and in the Raleigh and Kiokee belts (the Burks Mountain complex) are interpreted to be a regionally distinct group of ophiolitic complexes or ophiolitic melanges (Butler, 1989). Other ultramafites in South Carolina and North Carolina are interpreted as Alpine-type or island-arc intrusive complexes (Butler, 1989). Zoned mafic-ultramafic intrusions in the Kings Mountain belt are suggested to indicate a period of intra-arc rifting during development of the Carolina terrane (Dennis and Shervais, 1988).
Ophiolites are considered to be oceanic lithosphere which may occur in midocean ridges, back-arc basins and island arcs. Ophiolites may be incorporated into continental rocks during thrusting associated with collisions involving continents or continents and arcs.
Harzburgi te tectonites are a common component of the lower part of ophiolites found incorporated into continental rocks. Evidence for a tectonized harzburgi te in rocks studied in this part of the Burks Mountain complex was not found in any of the core drilling and in surface outcrops examined in this investigation. A relic fabric, defined by flattened chromite grains in the serpentinized harzburgite, which would indicate that the protolith is a harzburgite tectonite is described by Sacks and others (1989). Some of the large Cr-magnetites disseminated in the serpentinite might appear to be flattened. Detailed petrographic studies in this study indicate extensive resorption and/or metamorphic reaction has deeply embayed the Cr-magnetites re-

89

suiting in a wide variety of shapes. Most of the shapes

of these spinels are rather ornately developed and

probably would not have survived penetrative defor-

mation. Where observed in thin-sections, olivine and

pyroxene pseudomorphs are not deformed. However,

the high-grade metamorphism and the complete

serpentinization of the harzburgite could have ob-

scured any metamorphic fabric that might have devel-

oped in the olivine and pyroxene textures.

Current evidence does not indicate the mode of

emplacement of the Burks Mountain complex.

Ultramafites can be emplaced originally as ultramafic

melts or as solid masses of serpentinite. As solid masses

they may be squeezed into their final sites during the

last stages of folding or as brecciated masses along

post-orogenic faults (Chidester, 1962; Jahns, 1967;

Chidester and Cady, 1972). High-temperature contact

aureoles indicate that some large ultramafic masses

are emplaced as melts that differentiated and cooled in

place (Challis, 1965; Green, 1964a and 1964b). The

relative ease of serpentinite remobilization commonly

separates the ultramafic bodies from their former con-

tact aureoles. Subsequent metamorphism may also

obscure contact relations. The behaviorofserpentinites

as competent, relatively strong masses may obscure

more extensive tectonism.

The lack of penetrative metamorphic textures,

the preservation of delicate prograde metamorphic

textures (Cocker, 1989a), and the preservation of a

probable igneous differentiation sequence (Cocker,

1989c) strongly suggest that the ul tramafi te has under-

gone little internal tectonic deformation since it was

emplaced as a melt or solid mass and subsequently

metamorphosed.

The Burks Mountain complex has similarities to

ophiolite complexes such as the Marum ophiolite com-

plex in Northern Papua New Guinea (Jaques, 1981)

and to layered mafic complexes such as the Stillwater

in Montana and the Bushveld in South Africa. The

overall poor exposure and intense weathering, in ad-

dition to the high grade metamorphism and subse-

quent serpentinization, steatization and silicification

severely limit a more rigorous mineralogical and pet-

rological comparison. In general, the ultramafic/ mafic

rock suite of the Burks Mountain complex is more

similar to that of ophiolitic complexes.

Whole rock analyses suggest that the composi-

tion of the parental magma that produced the

harzburgite K20,Al203

might have been very andREE's. The100M

low in g/(Mg

+TiFOe~2N)raa2toio,

was probably 80 +I- 2 (Fig. 72) which is similar to that

of the Marum ophiolite parent magma (Jaques, 1981).

The magma must have been Cr- and Ni-rich with 2250-

2350 ppm Ni and 2000-2950 ppm Cr in the

stratigraphically lowermost harzburgites. Differentiation of a single magma probably pro-
duced the observed SiOTenrichment trend manifested as an increase in normative enstatite and a decrease in normative olivine with increasing stratigraphicheight. The rather sudden appearance of fine-scale, rhythmic igneous layering followed by separation of an immiscible liquid which formed Ti02-V-P-REE-richmassive magnetite segregations (Cocker, 1989c), is best interpreted asan influxofa new, moredifferentiated magma or magmas. The extreme enrichment in Ti-V-P-REE in an Fe-rich liquid is commonly developed within layered mafic intrusions and is not known to be associated with ophiolitic complexes.
The present investigation suggests that the Burks Mountain complex was emplaced into a more mature, differentiated, calc-alkaline suite of rocks than ha~ previously been assigned to the Kiokee belt. The petrochemical results obtained from fresh core samples indicate that the gneisses and amphibolites enclosing the Burks Mountain serpentinites are not geochemically similar to the Carolina Slate belt volcanics which have been proposed as correlative rocks. The Na20rich, Carolina Slate belt volcanics are interpreted as a primitive volcanic arc (Whitney and others, 1978). The Kiokee belt rocks are considerably higher in K20 and may represent a more mature island arc or continental setting. The amphibolites are enriched in REE's compared with rna fie volcanics commonly associated with ophiolitic complexes (Snoke and others, 1981) suggesting they are part of the Kiokee belt suite described above. The unusual enrichment of REE, Ti and V in certain layered rocks of the Burks Mountain complex suggests a subsequent intrusion of a magma enriched in those elements. Concentration of those elements may have been cause by contamination from country rocks enriched in these elements, extreme differentiation of a parent magma, or dynamic partial melting of crustal material.

90

20

18

16

Ophiolite Metamorphic

14

Peridotite

12

10

ol

8

6

(Coleman, 1977)

4

2

0

.eo

.e5

.90

.95

14

12

Papua Harzburgite

10

Tectonite

e

6

ol + opx + cpx

4

(England & Davies,

> 2

1973)

0 0

z

.eo

.e5

.90

.95

w

::I

0 w
a: 5

1&. 4

Papua Harzburglte

3

Cumulate

2

ol + opx + cpx

1

0

.eo

.e5

.90

.95

5-r------------------------------

4

3

Burks Mountain Serpentinite

2

whole rock

1

o-r-Lp~~~~~~4-,-~~~+-~

.eo

.85

.90

Mg/(Mg +Fe)

Figure 72. Frequency versus Mgi(Mg+Fe) in selected ultramafites. The high MgO content and narrow concentration of analyses distinguish residual metamorphic peridotite/harzburgite tectonite from the lower MgO content and broader range in composition ofharzburgite cumulates. The distributionofanalyses ofBurks Mountain serpentinites is similar to that of the harzburgite cumulates.

91

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94

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96

APPENDICES
97

98

Si02 Al203 Fe203 FeO MgO CaO Na20 K20 LOI
Ti~
P205 MnO SrO Rb20 Ni Cr
v
Co Ba
TOTAL
Si02 AI203 Fe203 FeO MgO CaO Na20 K20 LOI
Ti~
P205 MnO SrO Rb20 Ni Cr
v
Co Ba
TOTAL

APPENDIX I.

Whole Rock Chemistry- Mafic and Felsic Rocks (values are in weight percent, except for V, Co and Ba which are in ppm)

A

B

c

D

E

F

G

H

I

J

46.1 43.9 19.6 17.2 9.40 7.2 2.0 4.0 0.45 8.3 19.0 14.5 0.74 1.6 0.2 0.37
1.4 0.9 1.1 1.1 0.23 0.22 0.17 0.18
0.14 0.001 0.0002 0.0295 285.0

50.7 16.0 5.3 3.8
7.0 4.3 3.2 1.2 7.1 1.3 0.24 0.18 0.053 0.006

47.9 16.6 7.2 5.8 5.2 6.9 4.0 0.77 2.8 1.9 0.27 0.21 0.001 0.001

65.5 14.8 3.6 1.5 2.3 3.1 4.0 1.6 1.9 0.77 0.14 0.11

70.0 50.6 14.5 16.3 0.73 6.2 3.3 5.1
1.2 4.9 3.0 7.5 3.5 3.5 2.5 1.2 0.4 2.8 0.54 2.1 0.1 0.56 0.13 0.25 0.03 0.008 0.0015 0.0145 200.0

76.1 75.3 14.1 0.9 0.4 10.2 0.26 2.7 0.11 6.3
1.5 1.2 4.2 0.03 4.1 0.02 0.3 1.2 0.05 0.01 0.01 0.14 0.029 0.17
25.0

74.0 14.0 0.01 0.85 0.56
1.2 4.0 4.5 0.07 0.08 0.03 0.09 0.007 0.0005 0.001 0.003 15.0

90.0

280.0

20.0 150.0

100.418 99.611 100.379 99.552 99.32 99.938 100.019 101.159 98.17 99.331

K

L

M

N

0

p

Q

R

s

72.1 15.0 0.94
1.8 0.64 2.3 3.9 4.5 0.5 0.36 0.11 0.038 0.034 O.D15

71.3 14.7 1.3 1.3 0.56 2.0 3.5 4.2 0.5 0.34 0.09 0.042
0.009

76.7 12.7 0.65 0.81 0.39
1.1 4.2 3.2 0.4 0.18 0.03 0.036 0.016

62.5 15.6 5.0 0.3 2.7
1.7 2.2 1.9 6.4 0.62 0.02 0.072

70.5 14.4 1.2 1.5 0.68
1.8 3.3 4.7 1.0 0.33 0.11 0.048

58.0 16.1 5.3 2.4 3.6 5.8 3.8
1.6 1.9 1.2 0.32 0.16

65.6 18.9 3.6 0.23 0.31 0.032 0.08 1.4 7.9 0.35 0.01 0.029

70.0 64.4 16.8 15.0 2.4 3.6 0.26 0.83 0.33 2.6 0.019 3.2 0.15 4.0 3.0 3.2 6.0 1.7 0.28 0.78 0.01 0.29 0.038 0.058

55.0 30.0 155.0 35.0 25.0 80.0 51.0 105.0 33.0 20.0 41.0 105.0 102.237 99.832 100.421 99.012 99.568 100.18 99.441 99.287 99.331

99

APPENDIX I. (cont.)

Sample

Location

A PC 88-2,60' B 51-43
c 51-175
D 54-225 E 52-81 F 51-231 G PC88-2, 61' H 52-88 I E900-5500
J PC88-2, 222'
K 51-282 L 52-43
M 51-208 N 0230-240 0 E300-NOO p E50-52275 Q E50-N70 R E50-N310
s E50-S2410

DDH88-2 60 feet DOH 87-1 43 feet DOH 87-1 175 feet DOH 87-4 225 feet DOH 87-2 81 feet DOH 87-1 231 feet DOH 88-2 61 feet DOH 87-2 88 feet surface DOH 88-2 222 feet DOH 87-1 282 feet DOH 87-2 43 feet DOH 87-1 208 feet surface surface surface surface surface surface

Surface samples are located in Figure 73.

100

Si02 Al203 Fe203 FeO MgO CaO Na20 K20 LOI TiO:l P205 MnO SrO Rb20 Ni Cr
v
Co
TOTAL
Si02 AI203 Fe203 FeO MgO CaO Na20 K20 LOI TiO:l P205 MnO SrO Rb20 Ni Cr
v
Co
TOTAL

APPENDIX II.

Whole Rock Chemistry- Ultramafic Rocks (values are in weight%, except for V, Co and Ba which are in ppm)

A

B

c

D

E

F

G

H

I

J

K

41.6 0.34 6.4 0.73
36.80 0.076 0.03 0.03 13.4 0.01 0.01 0.17 0.001 0.001 0.230 0.310

40.6 0.47 5.3 0.78
35.90 0.08 0.03 0.02 15.2 0.01 0.01 0.085 0.001 0.001 0.170 0.310

70.0

40.8 0.46 6.5 0.39
36.10 1.10 0.01 0.01
13.2 0.01 0.01 0.067 0.001 0.001 0.225 0.445

40.8 38.6 0.37 0.32 2.5 6.2 0.89 0.30
36.70 35.00 0.60 2.90 0.01 0.02 0.02 0.02 12.4 16.0 0.01 0.01 0.01 0.01 0.056 0.12 0.001 0.004 0.001 0.001 0.245 0.230 0.280 0.200

35.1 0.34 7.2 1.4
37.10 2.00 0.02 0.01
16.0 0.01 0.01 0.12 0.006 0.001 0.225 0.285

90.0 85.0

90.0

36.2 33.4 0.40 0.35 5.1 5.9 0.41 2.30
37.50 36.90 0.48 0.84 0.04 0.04 0.01 0.02 17.3 18.5 0.01 0.01 0.01 0.01 0.11 0.12 0.001 0.002 0.001 0.001 0.235 0.220 0.175 0.295 5.0
95.0 105.0

36.9 0.38 5.386 2.10
35.10 0.45 0.005 0.024 15.2 0.01 0.01 0.12
0.210 0.099 15.0

37.0 0.46 7.655 0.75
35.60 1.70 0.005 0.011
17.6 0.01 0.02 0.09
0.235 0.110 5.0

40.1 0.42 6.658 0.81
36.20 0.69 0.005 0.012
13.4 0.01 0.01 0.10
0.205 0.077

100.138 98.967 99.329 94.893 99.935 99.827 97.982 98.908 95.994 101.246 98.697

L

M

N

0

p

Q

R

s

T

u

61.0 0.37 1.1 1.5
30.1 0.022 0.01 0.02 5.00 0.01 0.01 0.033 0.001 0.001

55.5 1.0 3.4 1.3
30.2 0.82 0.04 0.02 6.40 0.01 0.01 0.047

42.1 0.62 4.8 1.1
24.1 8.4 0.04 0.036 15.40 0.01 0.01 0.37
0.130 0.210 20.0

31.5 41.2 0.35 3.8 2.9 1.9 1.5 0.96
28.5 36.9 7.0 0.23 0.04 0.05 0.024 0.03
24.10 13.80 0.01 0.09 0.01 0.01 0.13 0.024
0.195 0.070 0.220 0.020 5.0

39.7 7.8 9.4 0.89
26.2 0.03 0.07 0.03 14.70 0.12 0.01 0.07
0.410 0.170

37.6 10.4 6.0 0.41 25.5 0.04 0.01 0.05 18.10 0.30 0.01 0.074
0.140 0.120

43.7 5.9 3.9 0.6
31.0 0.71 0.28 0.15 14.10 0.16 0.01 0.085
0.093 0.120

37.9 12.3 5.9
1.7 24.1
2.3 0.25 0.75 12.10 0.51 0.43 0.22

52.9 6.9
12.3 2.2
22.6 0.51 0.23 0.18 7.80 0.21 0.04 0.23

0.110 0.120 0.105 0.113

99.266 98.747 97.326 96.479 99.084 99.600 98.754 100.808 98.675 99.633

101

Si02 Al203 Fe203 FeO MgO CaO Na20 K20 LOI Ti02 P205 MnO SrO Rb20 Ni Cr
v
Co
TOTAL

APPENDIX II. (cont.)

v wX y

z

AA AB AC AD

41.8 11.1 24.7 0.38 9.70 0.031 0.04 0.06 9.90 0.26 0.19 0.042
0.195 0.460 100.0

89.0 0.12 5.8 0.30 2.30 0.091 0.0 0.024 1.4
O.ot
0.01 0.066
0.165 0.260 5.0

89.2 0.43 6.7 0.43 1.80 0.021 0.03 0.02 1.6 0.01 0.02 0.060
0.165 0.220 5.0 35.0

90.4 85.8 0.21 0.45 5.4 4.3 0.43 0.26 2.00 7.70 0.022 0.017 0.01 0.03 0.04 0.02 1.3 1.9 0.01 0.01 0.05 0.02 0.025 0.069
0.110 0.094 0.180 0.125 5.0 5.0

75.1 15.0 0.21 11.2 2.1 38.2 0.65 2.7 10.80 15.80 4.20 0.10 0.02 0.02 0.02 0.05 7.6 6.4 0.01 9.20 0.01 0.34 0.110 0.300 0.059 0.125
750.0 15.0

43.9 46.1 17.2 19.6 7.2 9.398 4.0 2.0 8.30 0.45 14.50 19.00
1.60 0.74 0.37 0.20 0.9 1.4 1.10 1.10 0.22 0.23 0.180 0.170 0.140 0.001 0.021 0.0 0.01 0.030
285.0

98.858 99.546 100.706 100.187100.795 101.014 99.341 99.611 100.418

Sample
A 51-74
c 54-140
E 51-160 G 55-205 I PC88-2, 115' K PC88-2, 176' M 55-163 0 PC88-2, 128' Q 54-23
s 54-170
u PC88-2, 104' w PC88-3, 18'
y PC104-1 AA 55-103 AC 51-43

Location

Sample

DDH 87-1 74 feet DDH87-4 140 feet DDH87-1 160 feet DOH 87-5 205 feet DDH88-2 115 feet DDH88-2 176 feet DDH87-5 163 feet DDH88-2 128 feet DDH87-4 23 feet DDH87-4 170 feet DDH88-2 104 feet DDH88-3 18 feet surface DDH87-5 103 feet DOH 87-1 43 feet

B 54-90
D 55-158.5 F 54-196
H 55-236
J PC88-2, 151'
L 51-132
N PC88-2, 203' p 55-177
R 54-47
T PC1-173
v D-139
X BM-1
z B-825
AB B-850 AD PC88-2, 60'

Surface samples are located in Figure 73.

Location
DDH87-4 90 feet DDH87-4 158.5 feet DDH87-4 196 feet DDH87-5 236 feet DDH88-2 151 feet DOH 87-1 132 feet DDH88-2 203 feet DDH87-5 177 feet DDH87-4 47 feet DOH 87-1 173 feet surface surface surface surface DOH 88-2 60 feet

102

APPENDIX III.

Norms- Mafic and Felsic Rocks

A

B

c

D

E

F

G

H

Corundum 2.298 0.0 1.221 0.798 0.0 0.052 0.0 0.985

Quartz

8.686 0.637 27.132 30.052 5.166 32.295 25.364 29.821

Orthoclase 7.603 4.703 9.706 14.842 7.221 24.023 26.139 24.987

Albite

29.028 29.028 34.982 34.742 29.752 30.148 35.235 32.436

Anorthite 21.341 25.917 14.848 14.377 25.69 7.313 9.968 9.397

Diopside

0.0 6.040 0.0 0.0 6.707 0.0 0.526 0.0

Hy(En)

18.690 10.910 5.879 3.000 9.570 0.270 1.450 1.400

Hy(Fs)

0.840 1.650 0.0 4.830 0.970 0.120 1.820 0.840

Magnetite 8.238 10.790 3.040 1.063 9.142 0.575 1.340 1.897

Chromite

0.0 0.0 0.0 0.0 0.022 0.0 0.0 0.0

Hematite

0.0 0.0 1.599 0.0 0.0 0.0 0.0 0.0

Ilmenite

2.647 3.730 1.501 1.030 4.061 0.094 0.672 0.650

Apatite

0.596 0.646 0.333 0.233 1.321 0.023 0.250 0.210

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

Anorthite 40.930 41.120 28.720 31.290 44.540 16.360 22.460 22.900

Albite

59.070 58.880 71.280 68.710 55.460 83.640 77.540 77.100

Di(En)

0.0 44.850 0.0 0.0 46.420 0.0 25.540 0.0

Di(Fs)

0.0 5.150 0.0 0.0 3.580 0.0 24.460 0.0

Di(Wo)

0.0 50.0 0.0 0.0 50.0 0.0 50.0 0.0

Hy(En)

96.680 89.690 100.0 44.960 92.840 75.270 51.090 68.830

Hy(Fs)

3.320 10.310 0.0 55.040 7.160 24.730 48.910 31.170

Di+En+Fo 18.690 16.950 5.879 3.00 16.277 0.270 1.976 1.400

Di

0.0 35.634 0.0 0.0 41.205 0.0 26.619 0.0

En

100.0 64.366 100.0 100.0 58.795 100.0 73.381 100.0

I

J

K

L

M

N

0

p

Q

Corundum 0.386 0.891 0.0 0.0 19.020 14.254 7.431 0.0 0.0

Quartz

36.814 28.570 14.098 19.465 65.470 61.252 37.595 66.084 0.0

Orthoclase 18.906 28.177 9.621 19.307 9.136 19.005 12.126 0.124 2.215

Albite

35.531 28.329 32.721 34.548 0.745 1.362 20.104 0.262 13.159

Anorthite

5.303 8.327 22.543 13.815 0.102 0.027 8.964 2.331 38.429

Nepheline 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.301

Diopside

0.0

0.0

3.587 0.358 0.0

0.0

0.0

2.231 26.087

Hy (En)

0.970 3.046 7.459 6.443 0.852 0.882 7.259 15.145 0.0

Hy (Fs)

0.720 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Fo (01) Fa (01)

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.761

0.0

0.0

0.0

0.0 0.0

0.0

0.0

0.0 0.0

Magnetite 0.942 1.765 4.863 0.615 0.0 0.164 0.0 9.514 8.238

Chromite

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Hematite

0.0 0.0 2.039 3.251 3.976 2.460 3.24 3.957 0.0

Ilmenite

0.342 0.636 2.319 1.512 0.605 0.570 0.851 O.o19 2.647

Apatite

0.070 0.259 0.755 0.686 0.025 0.025 0.051 0.334 0.0

Rutile

0.0 0.0 0.0 0.0 0.069 0.0 0.221 0.0 0.0

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

103

APPENDIX III. (cont.)

I

J

K

L

M

N

0

p

Q

Anorthite Albite Di (En) Di (Fs) Di (Wo)
Forsterite Fayalite Hy (En) Hy (Fs) Di+En+Fo Di En Fo

12.33 21.70 39.37 27.37 11.42 1.86 29.59 89.34 73.35 87.67 78.30 60.63 72.63 88.58 98.14 70.41 10.66 26.65
0.0 0.0 50.0 50.0 0.0 0.0 0.0 50.0 48.55 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.45 0.0 0.0 50.0 50.0 0.0 0.0 0.0 50.0 50.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 97.09 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.91 63.930 62.980 100.0 100.0 100.0 100.0 100.0 100.0 0.0 36.070 37.020 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.970 3.046 11.046 6.081 0.852 0.882 7.259 17.376 32.848 0.0 0.0 32.473 5.264 0.0 0.0 0.0 12.840 79.417 100.0 100.0 67.527 94.736 100.0 100.0 100.0 87.160 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 20.583

Sample

Location

A 51-175 B 54-225
c 52-81
D 51-231 E PC88-2,61' F 52-88 G 51-282 H 52-43 I 51-208
J E300-NOO
K E50-52275 L E50-52410 M E50-N70 N E50-N310 0 0230-240 p E900-5500 Q PC1-43

DDH87-1 175 feet DDH87-4 225 feet DDH87-2 81 feet DDH87-1 231 feet DDH88-2 61 feet DDH87-2 88 feet DDH87-1 282 feet DDH87-2 43 feet DDH87-1 208 feet surface surface surface surface surface surface surface DDH87-1 43 feet

Surface samples are located in Figure 73.

104

APPENDIX IV. Norms- Ultramafic Rocks

A

B

c

D

E

F

G

H

I

J

K

Corundum 0.165 0.330 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Quartz

0.0

0.0

0.0

0.0 0.0

0.0

0.0 0.0 0.0

0.0

0.0

Orthoclase 0.204 0.141 0.069 0.143 0.141 0.070 0.073 0.147 0.177 0.077 0.083

Albite

0.293 0.303 0.098 0.102 0.201 0.201 0.420 0.421 0.051 0.051 0.051

Anorthite

0.361 0.399 1.371 1.098 0.863 0.965 1.094 0.892 1.167 1.436 1.274

Diopside

0.0

0.0 3.809 1.895 12.621 8.418 1.385 3.283 1.182 6.613 2.074

Hy(En)

52.991 53.673 46.283 49.733 30.281 16.004 29.570 17.40 40.620 30.288 46.400

Hy(Fs)

Fo (01)

36.907 37.180 39.476 42.172 47.451 63.287 59.941 66.827 46.970 50.90 40.87

Fa (01)

Magnetite 3.569 3.274 1.56 3.025 2.134 6.117 2.713 9.932 9.446 3.878 4.015

Chromite

0.769 0.796 1.112 0.730 0.513 0.732 0.467 0.789 0.181 0.194 0.133

Hematite

4.917 4.069 6.471 0.944 5.915 4.370 4.450 0.488 0.151 6.476 5.036

Ilmenite

0.022 0.023 0.022 0.023 0.023 0.023 0.023 0.024 0.023 0.023 0.023

Apatite

0.027 0.028 0.027 0.028 0.028 0.028 0.029 0.029 0.028 0.056 0.028

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Anorthite 53.76 55.41 92.94 91.00 80.16 81.87 71.07 66.65 95.59 96.38 95.95

Albite

46.24 44.59 7.06 9.0 19.84 18.13 28.93 33.35 4.41 3.62 4.05

Di (En)

50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0

Di (Fs)

Di (Wo)

50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0

Forsterite 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Fayalite

Hy (En) 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Hy (Fs)

Di+En+Fo 89.898 90.853 89.568 93.80 90.353 87.709 90.896 87.510 88.772 87.801 89.344

Diopside

0.0

0.0 4.253 2.02 13.969 9.598 1.524 3.752 1.332 7.532 2.321

Enstatite

58.946 59.077 51.674 53.020 33.514 18.247 32.532 19.883 45.758 34.496 51.934

Forsterite 41.054 40.923 44.074 44.959 52.517 72.156 65.945 76.365 52.911 57.972 45.745

L

M

N

0

p

Q

R

s

T

Corundum 9.039 12.788 4.637 3.863 0.234 12.78 0.373 0.410 12.635

Quartz

0.133 0.0 0.0 0.0 88.481 31.804 87.804 74.964 0.0

Orthoclase 0.210 0.368 1.025 0.208 0.236 0.396 0.118 0.118 0.319

Albite

0.702 0.105 2.739 0.497 0.0

0.0 0.204 0.167 0.0

Anorthite

0.100 0.166 3.996 1.263 0.0

0.0 0.048 2.697 0.0

Diopside

0.0

0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0

Hy(En)

77.38 76.040 65.310 50.22 5.038 27.155 4.522 19.39 18.507

Hy(Fs)

0.0

0.0 0.0 0.05 0.0

0.0 0.0 0.0 0.0

Fo (01)

2.07 16.780 0.0 40.39 0.0

0.0 0.0 0.0 16.698

Fa (01)

0.0

0.0 0.0 0.04 0.0

0.0 0.0 0.0 0.0

Magnetite 3.260 0.862 2.02 3.324 1.521 0.575 1.745 1.15 0.0

Chromite

0.0

0.0 0.0 0.0 0.0

0.761 0.327 0.186 0.016

Hematite

8.899 6.868 3.115 0.0 0.0 27.155 5.556 3.555 41.101

Ilmenite

0.270 0.709 0.351 0.201 0.019 0.555 0.002 O.Q19 6.862

Apatite

0.027 0.029 0.027 0.027 0.118 0.496 0.046 0.046 0.848

Na-carbonate 0.0

0.0 0.0 0.0 0.085 4.66 0.010 O.D18 0.706

Rutile
---

-

-

-0.0-

-

-0.0-

-0-.0

-

-0.0-

- -0.0 - -0-.0 - -0.-0 - -0.0- - - - 6.286

105

APPENDIX IV. (cont.)

L

M

N

0

p

Q

R

s

T

Anorthite Albite Di (En) Di (Fs) Di (Wo) Forsterite Fayalite Hy (En) Hy (Fs) Di+En+Fo Diopside Enstatite Forsterite

11.79 59.88 88.21 40.12 0.0 0.0 0.0 0.0 0.0 0.0 100.0 100.0 0.0 0.0 100.0 100.0 0.0 0.0 77.38 78.11 0.0 0.0 100.0 97.35 0.0 2.65

57.90 70.55 42.10 29.45
0.0 0.0 0.0 0.0 0.0 0.0 100.0 99.93 0.0 0.07 100.0 99.93 0.0 0.07 82.09 90.61 0.0 0.0 79.559 55.42 20.441 44.58

0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 100.0 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.0 0.0 0.0 0.0 0.0 5.038 27.155 4.522 19.32 35.205 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 52.569 0.0 0.0 0.0 0.0 47.431

Sample

Location

A 51-74
B 54-90
c 54-140
D 55-158.5
E 51-160
F 54-196
G 55-205 H 55-236 I PC88-2, 115'
J PC88-2, 151'
K PC88-2, 176' L 54-23
M 54-47 N 54-170 0 55-177 p PC104-1
Q D-139 R BM-1
s B-825
T B-850

DDH87-1 DDH87-4 DDH87-4 DDH87-4 DDH87-1 DDH87-4 DDH87-5 DDH87-5 DDH88-2 DDH88-2 DDH88-2 DDH87-4 DDH87-4 DDH87-4 DDH87-5 surface surface surface surface surface

74 feet 90 feet 140 feet 158.5 feet 160 feet 196 feet 205 feet 236 feet 115 feet 151 feet 176 feet 23 feet 47 feet 170 feet 177 feet

Surface samples are located in Figure 73.

Note:

Hy (En)= enstatite component of hypersthene; Hy (Fs) = ferrosalite component of hypersthene; Di (En)= enstatite component of diopside; Di (Fs) = ferrosalite component of diopside; Di (Wo) = wollastonite component of diopside; Fo = forstersite component of olivine; Fa= fayalite component of olivine.

106

APPENDIXV.

Modal Analyses - Mafic and Felsic Rocks

A

B

c

D

E

F

G

H

Hornblende Epidote Plagioclase Magnetite Apatite Zircon Quartz Plagioclase Microcline Biotite Zircon Opague Biotite(sec) Muscovite Titanite Orthoclase

50.6 25.45 18.26 5.09 0.3
0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 33.22 44.63 19.22 2.28 0.33 0.33 0.0 0.0 0.0 0.0

32.55 0.0 0.0 0.0 0.26 0.0 3.15 43.57 0.0 8.4 0.0 3.67 8.4 0.0 0.0 0.0

1.55 0.0 0.0 0.0 0.0 0.0 23.6 40.37 26.71 5.9 0.0 0.0 0.0 1.86 0.0 0.0

0.0 0.65 0.33 0.33 0.0 0.0 30.94 28.99 29.64 7.82 0.0 0.0 0.0 1.30 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 29.77 23.41 0.0 24.75 0.67 0.0 0.0 0.0 0.67 20.74

0.0 0.0 0.0 0.0 0.0 0.0 36.16 26.71 33.88 2.93 0.0 0.33 0.0 0.0 0.0 0.0

43.45 0.0 2.24 2.24 1.28 0.0 0.0 46.96 0.0 6.07 0.0 0.0 0.0 0.0 0.0 0.0

TOTAL

100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Note: Biotite (sec) is biotite formed during chloritic and albitic alteration.

Sample
A PC1-43 B PC1-208
c PC1-175
D PC1-282 E PC2-43 F PC2-81 G PC2-88 H PC4-225

Location
DDH87-1 43 feet DDH87-1 208 feet DDH 87-1 175 feet DDH87-1 282 feet DDH87-2 43 feet DDH87-2 81 feet DDH87-2 88 feet DDH87-4 225 feet

107

APPENDIX VI.

Modal Analyses - Ultramafic Rocks

A

B

c

D

E

F

G

H

I

J

K

L

Lizardite

84.89

Talc

0.64

Carbonate 9.65

Chlorite(b) 0.0

Chlorite(gy) 0.0

Chlorite(tot) 0.0

Tremolite

2.57

Anthophyllite 0.0

Magnetite

2.25

Picotite

0.0

Quartz

0.0

Chalcedony 0.0

Gamierite

0.0

Zoisite

0.0

79.63 13.27 3.4 0.31 0.0
0.31 0.0 0.0 3.4 0.0 0.0 0.0 0.0 0.0

76.42 12.26 0.0
2.52 0.31 2.83 0.0 0.0 8.49 0.0 0.0 0.0 0.0 0.0

70.10 17.36 3.54 0.64 0.0 0.64 0.0 0.0 8.36
0.0 0.0 0.0 0.0 0.0

67.97 25.82
0.0 1.96 0.0 1.96 0.0 0.0 4.25 0.0 0.0 0.0 0.0 0.0

67.17 16.41 5.17 1.82 0.0
1.82 0.0 0.0 9.42 0.0 0.0 0.0 0.0 0.0

65.31 0.94
26.25 0.0 0.0 0.0 0.94 0.0 6.56 0.0 0.0 0.0 0.0 0.0

62.88 22.71
0.0 10.48 0.0 10.48 0.0
0.0 3.93 0.0 0.0 0.0 43.23 0.0

48.05 10.71 29.55
8.44 0.0 8.44 0.65 0.0 2.6 0.0 0.0 0.0 0.0 0.0

42.26 37.10
8.06 9.35 0.0 9.35 0.0 0.0 3.23 0.0 0.0 0.0 0.0 0.0

42.12 27.58 18.48
3.64 0.0 3.64 0.0 0.0 8.18 0.0 0.0 0.0 0.0 0.0

40.91 14.55 35.45
0.3 0.0 0.3 0.0 0.0 8.79 0.0 0.0 0.0 0.0 0.0

TOTAL

100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

M

N

0

p

Q

R

s

T

u v

w X

Lizardite

37.05

Talc

24.26

Carbonate 33.77

Chlorite(b) 3.93

Chlorite(gy) 0.0

Chlorite(tot) 3.93

Tremolite

0.0

Anthophyllite 0.0

Magnetite

0.98

Picotite

0.0

Quartz

0.0

Chalcedony 0.0

Gamierite

0.0

Zoisite

0.0

35.74 22.95 35.74
2.95 0.0 2.95 0.66 0.0 1.97 0.0 0.0 0.0 0.0 0.0

27.72 59.41
0.66 6.60 0.0 6.60 0.0 0.0 4.29 0.0 1.32 0.0 0.0 0.0

12.58 75.48 0.97 3.23 0.0
3.23 0.0 0.0 7.74 0.0 0.0 0.0 0.0 0.0

6.29 57.86
6.29 25.47
0.0 25.47 0.0 0.0 4.09
0.0 0.0 0.0 0.0 0.0

5.14 93.57
0.0 0.0 0.0 0.0 0.0 0.0 1.29 0.0 0.0 0.0 0.0 0.0

1.27 36.62 10.51 46.82
0.0 46.82
0.0 0.0 4.78 0.0 0.0 0.0 0.0 0.0

0.0 21.12 20.5 47.2
0.0 47.2
0.0 0.0 1.55 0.0 9.63 0.0 0.0 0.0

0.0 22.57
0.0 0.31 0.0 0.31 0.0 0.0 0.31 0.0 68.03 8.78 0.0 0.0

0.0 45.37
0.0 0.31 0.0 0.31 0.0 0.0 2.16 0.0 46.91 5.25 0.0 0.0

0.0 53.4 22.22
0.62 0.0 0.62 0.0 0.0 5.86 0.0 17.90 0.0 0.0 0.0

0.0 17.1 0.0
0.0 0.0 0.0 0.0 0.0 4.84 0.0 78.06 0.0 0.0 0.0

TOTAL

100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

108

APPENDIX VI. (cont.)

y

z

AA AB AC AD AE AF AG

Lizardite

0.0

Talc

1.0

Carbonate 0.0

Chlorite(b) 20.6

Chlorite(gy) 0.0

Chlorite(tot) 20.6

Tremolite

0.0

Anthophyllite 0.33

Magnetite

4.32

Picotite

0.0

Quartz

73.75

Chalcedony 0.0

Gamierite 0.0

Zoisite

0.0

0.0 16.61 0.0 13.74 64.54 78.27 0.0 0.0 5.11 0.0 0.0 0.0 0.0 0.0

0.0 15.41 0.0 0.0 0.0 0.0 0.0 0.0 5.66 0.0 78.93 0.0 0.0 0.0

0.0 0.0 39.2 0.0 0.0 0.0 0.31 0.0 0.0 87.5 0.31 87.5 0.0 0.0 0.0 0.0 5.86 12.5 0.0 0.0 54.63 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 79.0 0.0 2.82 0.0 2.82 0.0 16.3 1.88 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 59.59 59.59 0.0 30.81 6.69 2.91 0.0 0.0 0.0 1.74

0.0 0.65 0.0 0.0 67.1 67.1 0.0 31.94 0.32 0.0 0.0 0.0 0.0 0.0

0.0 56.86 0.0 0.33 0.0 0.33 0.0 39.54 3.27 0.0 0.0 0.0 0.0 0.0

TOTAL

100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

.J
Note: (b) = blue birefringent chlorite; (gy) = gray birefringent chlorite; (tot)= total chlorite.

Sample

Location

A PCt-78
c EV5
E PCt-88 G PC4-196 I PC5-195 K PC4-90 M PC5-219 0 PC4-67 Q PC5-158
s PCI-144
u PC5-122
w PC5-149
y AP2 AA APt AC EVtA AE EV4 AG EV5

DDH87-1 surface DDH87-1 DDH87-4 DDH87-5 DDH87-4 DDH87-5 DDH87-4 DDH87-5 DDH87-1 DDH87-5 DDH87-5 surface surface surface surface surface

78 feet
88 feet 196 feet 195 feet 90 feet 219 feet 67 feet 158 feet 144 feet 122 feet 159 feet

Surface samples are located in Figure 73.

Sample
B PC4-140 D PC4-185 F PCS-156 H EV 11
J PC4-210
L PCS-236 N PCS-209 p PC4-73 R PCI-132 T PCS-103
v PCS-147
X AP5
z AP3
AB APIA AD EV7 AF EV9

Location

DDH87-4 DDH87-4 DDH87-5 surface DDH87-4 DDH87-5 DDH87-5 DDH87-4 DDH87-1 DDH87-5 DDH87-5 surface surface surface surface surface

140 feet 185 feet 156 feet
210 feet 236 feet 209 feet 73 feet 132 feet 103 feet 147 feet

109

EXPLANATION

Sample Site

Sample Number

Sample Site Sample Number

1

D230-240

2

E300-NOO

3

E50-S2275

4

E50-N70

5

E50-N310

6

E900-S500

7

E50-S2410

8

D-139

9

BM-1

10

PC104-1

11

B-825

12

B-850

13

EV 1A

14

EV4

15

EV 5

16

EV 7

17

EV9

18

EV 11

19

AP 1

20

AP 1A

21

AP2

22

AP3

23

AP4

Figure 73. Sample Location Maps. Maps are portions of the northwestern corner of the Evans 7.5 Minute and northeastern corner of the Appling 7.5 Minute Quadrangle Maps of the United States Geological Survey. Samples include those collected during this investigation and some which were collected by Vincent and others (1990). The EV and AP series were collected by Vincent and others (1990).

110

APPUNG QUADRANGLE
GEOROIA-COLUMBIA CO. 7.5 MINUTE SERIES (TOPOGRAPHIC)
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