field Excursion The Georgia .Marble District W. ROBERT POWIR 4ncl IRNIST W. READ ANNUAL MEETING Sotttheastern Section The Geological Society of America APRIL 14, 19b2 GUIDEBOOK NUMBER 1 Department ofMines, .M-ining and Geology GARLAND PEYTON, DIPECTOR Atlantn, Geor9ia COVER PAGE Creole Marble Photograph courtesy Georgia Marble Company, Tate, Georgia. TABLE OF CONTENTS Introduction _________________ Page 5 Whitestone Area Rocks west of the Murphy marble_________________________________ 7 Meta-graywacke _______ _________ _ _ _ _ _ _ _ _ _ _ __ 8 Quartz-sericite phyllite______________________________ 8 Spotted chlorite-sericite phyllite___________________________________ _ _____________________ _ 8 Meta-conglomerate___________________ 8 Quartz-sericite phyllite________ _ __ - - - - ----------------------------------------------------------------------------------- 8 Graphite slate_______ ____________________________ _ 8 Chlorite-sericite phyllite____ ______________ - - - - - - -------- -- - - - - 8 Murphy marble__________________ _ _ _ _ _ _ _____________ 9 Rocks east of the Murphy marble__________ 9 Biotite-quartz schist________________ __ _ ------------------------------------------------------------------------------------ 9 Garnet-graphite schist_____________________________ ______ _ ____ 9 Staurolite-graphite schisL____________________ _ _ ____ _ ----- 9 Graphite schist_____________________ 9 Sericite-chlorite schist - - - - - - - ---------- - -- 9 Structure_______________________________________________________________________________________________________________________________________________________________ 10 Tentative Correlation with other Metasediments in North Georgia _________________________________ ------------------------------------- 12 Structural Implications _---------------------------______________________---------------------------____ ____________________________________________________ _____ 13 Tate Quarries------------------------------------------------------------------------------------------------------------------------------------------------------------ 14 Tate Mi11 ______________________________________________----------------------------------------------------------- ----------------------------------- ______________________ 19 BibliographY-------------------------------------------------------------------------------------------------------- - -- - - - - - - - - - - - - 20 LIST OF FIGURES Figure Page Geologic Sketch Map of the Whitestone Area ________________________________________ --------------------------------------------------------- 6 2 Cross-sections of the Goble Mine_________________ _ _ _ _____ _ _ _ _ _____ _ 11 3 Correlation of Metasediments in North Georgia_______________________________________________________ 12 4 Generalized Cross-section of the Whitestone Area_______________________________ _ 13 5 Tate Area______________________________________________________________________________________________ --------------------------------------------------------- 15 6 Etowah Quarry_____________________________________ ______________ 16 7 Etowah Quarry, Looking South_____________________________________________________________ _ 17 8 Columns for the U.S. Capitol Building from Cherokee Quarry No. 13__________________________________________________________ 18 9 Tate MilL _____________ ____ -- 21 3 I INTRODUCTION The Murphy marble was named by Keith (1907, p. 5) for the town of Murphy, North Carolina. It has been mapped in Georgia by LaForge and Phalen (1913), Bayley (1928), Hurst (1955), and Fairley (in prep.). It has generally been assigned a Cambrian Age (Hurst, 1955, p. 7). The Murphy marble in North Georgia underlies a long narrow valley that extends northeastward from Whitestone, Georgia, to and beyond the North Carolina border. The towns of Ellijay, Blue Ridge, and Mineral Bluff lie in the valley. Between Ellijay and Blue Ridge, the valley splits into two nearly parallel parts with an intervening ridge. Both parts of the valley are underlain in part by the Murphy marble. South of Whitestone the marble is offset to the east. With only scattered intervening exposures, it picks up in the valley of Long Swamp Creek about one mile east of Jasper, Georgia, and underlies the valley of that creek to and beyond Ball Ground, Georgia. At Tate, Georgia, the marble is thickest and best developed. It underlies the valley of East Branch eastward to a point about one mile east of Marble Hill. The outccrop pattern here appears peculiar on the map in that it forms a hook branching eastward off the main marble belt, the open part of the hook facing south. South of Tate, several elongate bodies of marble are isolated from the main belt. Bailey ( 1928) interpreted them as infolds. Outcrops along the main belt are discontinuous; the discontinuity in most cases has been ascribed to thrust faulting from the east. Detailed mapping of the Murphy marble from Whitestone, Georgia, to Nelson, Georgia, was begun by the Geology Department of the Georgia Marble Company during 1961. The mapping is far from complete. The Georgia Marble Company has contracted with Surdex Corporation of St. Louis, photogrammetrists, to map 19 square miles in the Tate area and four square miles in the Whitestone area at a scale of 1:2400 and a contour interval of fiv~ feet. Large scale aerial photographs of the intervening area are also contracted for. These maps and photographs will be available during the spring of 1962, and at that time, systematic mapping of the marble belt in this area will begin. The present Geology Department of the Georgia Marble Company has existed only since June, 1961. It has concentrated on collecting old records, locating and logging old drill cores, and has made a few reconnaissance surveys. Its present contributions to the knowledge of the Murphy Marble are therefore few and tentative. E. H. Reade is primarily responsible for mapping and correlations in the Whitestone area; W. R. Power, for the Tate area; and M . C. Joyce, for descriptions of the Tate milL 5 GEOLOGIC MAP 0~ TNE WHITESTONE AREA --IMPROVED ROAD --UNIMPROVED ROAD _ ...- ORAINA6 RAILROAD --- G01-DGIC CONTACT - u 0 FAULT .J- BEDDING ~ '"01./AT/ON . I Figure 1 6 .H. Rcadc,Jr. Rocks West of the Murphy Marble. The field trip will leave Georgia Highway 5 and cross the ridge that borders the marble valley on the west. The rocks under this ridge dip east, are believed to be right side up, and therefore, underlie the marble. Stops will be made to inspect the rocks (see fig. 1) . LaForge and Phalen (1913) mapped the Ellijay quadrangle which lies immediately east. They show the Mur- phy marble to be underlain by the Valleytown formation. Northeast of Whitestone, they describe the Valleytown as "a narrow strip of talcose and siliceous slates" (1913, p. 6). Southeast of Whitestone, they describe the Valleytown as "being siliceous mica slate, curly phyllite, or augen gneiss ... (having) an appearance very similar to that of a bird's eye maple, the "eyes" being lumps of quartz and feldspar of apparently extraneous origin." LaForge and Phalen report the Valleytown formation south of Ellijay to be underlain by the Nantahala slate consisting chiefly of "graphitic schist with more or less staurolite throughout its thickness and containing few or no siliceous beds." The section from Georgia Highway 5 to the Murphy marble shows the following sequence of rock types. Although none of the units have been "walked out", the sequence shows along five different roads extending to within two miles of Jasper, and it is reasonably certain that they are mappable units. 7 1. Meta-graywacke. The meta-graywacke is a medium to fine grained rock composed predominantly of quartz, feldspar, and biotite. The biotite is distributed throughout and gives the rock a weak foliation which is parallel to bedding. The bedding is well defined and ranges in thickness from ca 2" to ca 12". Beds are generally separated by thin slaty layers. The rock is distinguished by the conspicuous bedding and by the presence of biotite. 2. Quartz-sericite phyllite. The quartz-sericite phyllite is composed predominantly of sericite and fine granular quartz. Chlorite occurs on foliation planes and in thin layers, but is much less conspicuous than in the chlorite-sericite phyllites. The color is predominantly buff to gray rather than green. Garnets occur in some layers. Foliation planes are more widely spaced than in the chlorite-sericite phyllites and do not curve and branch conspicuously. The rock is distinguished by fine granular quartz and less conspicuous chlorite. 3. Spotted chlorite-sericite phyllite. The spotted chlorite-sericite phyllite contains tiny black spots one to three mm across, partly rhombic and partly equidimensional or irregular in outline. The spots appear to be composed of hematite and other iron oxides. Foliation planes are curved and branching so that in the "b" direction the rock has an augen appearance. In places the curved folia are crenulated. The rock is distinguished by the conspicuous green colored folia and the presence of black spots. Some layers of the spotted phyllite contain elongate pebble-size fragments of quartz. These are believed to be I meta-conglomerates as they increase in abundance toward the next unit which is clearly a meta-conglomerate. 4. Meta-conglomerate. The conglomerate contains elongate pebbles of blue quartz, milky to smoky quartz, and feldspar. Quartz predominates and quartz pebbles are generally larger than feldspar fragments. The matrix is feldspathic in places, elsewhere it is composed predominantly of sericite and chlorite. In places the conglomerate contains cobble-size fragments of fine-grained blue quartzite and fine-grained white to gray quartzite. Thin beds and lenses of chlorite-sericite phyllite are common within the conglomerate. A principle distinguishing feature of the rock is the presence of abundant blue quartz fragments. 5. Quartz-sericite phyllite. This unit is similar to # 2. 6. Graphite slate. The graphite slate is a black fine-grained slate or phyllite. Foliation planes curve slightly and in places are slightly crenulated, but they do not branch and intersect as do folia in the chlorite-sericite phyllite. At the top (eastern edge) thin beds of almost pure quartzite, one to two inches thick, are interlayered with the slate and the amount of chlorite in the slate increases. The rock is distinguished by its color and even foliation. 7. Chlorite-sericite phyllite. The chlorite-sericite phyllite contains lenticular pods and irregular bodies of milky vein quartz and minor amounts of calcite. In places it contains beds or lenses of black, micaceous marble. Epidote occurs sparingly in small vugs. Foliation planes are curved and branching so that in the "b" direction the rock has an augen appearance. In places the foliation planes are crenulated and branching on the curved surface. At one locality the foliation is markedly discordant to the general trend. This outcrop is unusually rich in epidote and may mark a fault. The rock is distinguished from the spotted chlorite-sericite phyllite by the absence of tiny black spots and by the presence of vein quartz and calcite. It is easily distinguished from other units by the conspicuous green colored, curved folia. 8 8. Murphy Marble. Core drilling has shown that the Murphy Marble in the Whitestone area can be subdivided into five well-defined units. In places these units can be further subdivided. The stratigraphy from top to bottom is as follows: (a) 265-350' Fine-grained dolomitic marble ranging in color from almost pure white to gray. The top ten feet or so of this unit is transitional into the overlying schist. The transition zone contains alternating bands of dolomite and talc-phlogopite schist. The dolomite immediately below the transition zone is generally light gray to gray in color. In most of the area there is a second zone of alternating dolomite and talc-phlogopite schist anywhere from 17 feet to 150 feet below the transition zone. This zone also contains layers of pink marble a few inches thick. Below the second schist zone the color of the dolomite is white to light gray. (b) 70-180' Fine-grained, white to light gray tremolite-quartz marble. This unit is also talcose in part, but the distinguishing feature is the presence of abundant white to light gray tremolite and of quartz. (c) 215-280' Fine-grained, light gray to gray dolomite marble. This unit is similar to unit (a) except there is less white colored material. (d) 0-50' Medium-grained white to light gray banded calcite marble. (e) 110-130' Coarse-grained, light gray to gray, banded graphite marble. This unit and unit (d) are easily distinguished as being the only calcite marbles in the area. Dolomite is being mined by the Willingham-Little Stone Co., a division of the Georgia Marble Co., for use as terrazzo chips, agriculturai lime, roofing chips, road aggregate, and so on. White dolomite for terrazzo chips is the premium product and attempts are made to mine dolomite for other uses so as to develop reserves of white stone. Mining is by the room-and-pillar method and shovels are used underground to load trucks which deliver to the primary crusher. The crushing and screening plants are located on the Louisville and Nashville Railroad by which most of the products are shipped. Three mines and two plants are being worked. Two other mines are inactive and are awaiting further exploration before being reopened. Rocks East of the Murphy Marble. The following sequence of rocks is exposed in a section along Fasset Creek east of the Murphy Marble. Contacts have not been traced in the field nor has any attempt yet been made to correlate them with other sections. 9. Biotite-quartz schist. This is a fine to medium-grained gray to brownish gray rock with distinct, thin compositional banding. It contains varying amounts of chlorite, sericite feldspar, and garnet. The light colored bands are rich in quartz and feldspar; the dark colored bands, rich in biotite. The unit also contains layers of fine to medium grained spotted sericite-chlorite-quartz schist and fine to medium-gr;:tined, brown, biotite quartzite. Several thin bands of amphibolite were found on the hillside above the mines, but attempts to trace them more than a few feet failed. 10. Garnet-graphite schist. A steel-gray, graphite schist with sericite, chlorite, and porphyroblasts of garnet and muscovite. The rock has regular even foliation and some crinkling on foliation planes. 11. Staurolite-graphite schist. Identical with (10) except for the presence of staurolite and the absence of garnet. 12. Graphite schist. Identical with (10 and (11) except for the absence of garnet and staurolite. 13. Sericite-chlorite schist. This is a silvery white and greenish gray sericite-chlorite schist mottled with small dark spots. Foliation planes are crinkled giving the appearance of button structure in the upper parts; contains elongate knots of chlorite, muscovite, and quartz that apparently pseudomorph kyanite or staurolite. 9 STRUCTURE The rocks in the Whitestone area dip consistently east. A major normal fault trending about N 15 W cuts through the area. The trend of rocks west of the fault is arcuate and the continuity of the strata is interrupted by the fault. Less is known of the rocks east of the fault, but they apparently trend parallel or nearly parallel to it. The fault can be seen in the mines at Whitestone and its attitude has been determined by drilling. The crosssections (fig. 2) show the relationships. The biotite-quartz schist is on the hanging wall, the Murphy marble and the biotite-quartz schist are on the foot wall. Large drag folds can be seen in the mines. The rock is brecciated and discolored up to 100 feet from the fault. No deep holes have been drilled in the hanging wall, but the dip-slip displacement is believed to be at least 500 feet. The normal fault is cut by a number of low angle thrusts in which the biotite-quartz schist was thrust over the Murphy marble. These faults are of relatively small displacement, but are clearly outlined by core drilling. Discordant structures within units 7 and 13 suggest the presence of other faults in the area, but they are not traced out or proved. Small folds having the appearance of drag folds are common in the biotite-quartz schist. They suggest relative upward and westward movement of rocks from the east. Foliation cuts across compositional layering at a steeper angle than the layering in these folds. Nearly all the rocks in the area are strongly foliated. In some rocks the folia are curved and branching, elsewhere crinkles are even. Except in the drag folds of the biotite-quartz schist the general trend of foliation is parallel to bedding. 10 .uve :1 to ci z.0, X 0 \- .0z.. ~r ; 0 .I. I .;.. / ./ /J f/ ~