GEOCHEMISTRY AND ECONOMIC POTENTIAL OF PEGMATITES IN THE THOMASTON-BARNESVILLE DISTRICT, GEORGIA Mark D. Cocker Georgia Department of Natural Resources Environmental Protection Division Georgia Geologic Survey GEOLOGIC REPORT 7 GEOCHEMISTRY AND ECONOMIC POTENTIAL OF PEGMATITES IN THE THOMASTONBARNESVILLE DISTRICT, 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 1992 Geologic Report 7 TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS......................................................................................................................................................iv ABSTRACf................................................................................................................................................................................. 1 Acknowledgements................................................................................................................................................................... 1 INTRODUCTION...................................................................................................................................................................... 1 Purpose of investigation............................................................................................................................................ 1 GRANITIC PEGMATITES ...................................................................................................................................................... 2 Composition and classification................................................................................................................................. 2 Pegmatite provinces, belts and districts, fields and groups................................................................................. 2 THE THOMASTON-BARNESVILLE DISTRICf.................................................................................................................. 2 Past mining activity.................................................................................................................................................... 5 Location and size......................................................................................................................................................... 5 Terrain and exposure.................................................................................................................................................. 6 Vegetation.................................................................................................................................................................... 6 Previous work ............................................................................................................................................................. 6 SAMPLING AND ANALYTICAL PROCEDURES.............................................................................................................. 6 Locations of mines, prospects and samples........................................................................................................... 6 Sampling techniques................................................................................................................................................... 7 Sample analysis........................................................................................................................................................... 7 GENERAL GEOLOGIC SETTING.......................................................................................................................................... 7 The Pine Mountain belt ............................................................................................................................................. 7 The Uchee belt ............................................................................................................................................................ 11 The Inner Piedmont .................................................................................................................................................. 11 The Piedmont ............................................................................................................................................................. 11 The Berner Mafic Complex ...................................................................................................................................... 11 PEGMATITES OF THE THOMASTON-BARNESVILLE DISTRICT................................................................................ 12 Physical characteristics ............................................................................................................................................. 12 Mineralogy ................................................................................................................................................................. 12 Internal zoning of the pegmatites ........................................................................................................................... 12 Geochronology........................................................................................................................................................... 18 PEGMATITE GEOCHEMISTRY ................ ............................................................................................................................ 18 Pegmatite fractionation and trace element geochemistry ................................................................................... 18 Muscovite geochemistry .......................................................................................................................................... 20 Discussion of pegmatitic muscovite geochemical zoning ................................................................................... 38 Feldspar geochemistry ............................................................................................................................................. 38 GENESIS OF THE THOMASTON-BARNESVILLE PEGMATITES..................... ............................................................ 38 Physical conditions ................................................................................................................................................... 38 Source of the pegmatites .......................................................................................................................................... 40 ECONOMIC POTENTIAL OF THE THOMASTON-BARNESVILLE PEGMATITE DISTRICf ................................. 40 Rare metals ................................................................................................................................................................. 40 Mica ............................................................................................................................................................................. 41 Feldspar ....................................................................................................................................................................... 41 SUMMARY ............................................................................................................................................................................... 41 REFERENCES CITED .............................................................................................................................................................. 42 APPENDICES ........................................................................................................................................................................... 45 I. Locations of pegmatite mines, prospects and samples .......................................................................... 47 II. Muscovite geochemistry ............................................................................................................................ 57 III. Feldspar geochemistry ............................................................................................................................... 69 IV. Analytical parameters ................................................................................................................................ 74 V. Attitudes of pegmatites .............................................................................................................................. 76 VI. Attitudes and lithologies of country rocks............................................................................................... 77 Ill Figure 1. Figure 2. Figure3. Figure 4. Figure 5. Figure 6. Figure7. 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. Figure 26. Figure 27. Figure 28. Figure 29. Figure30. Figure 31. Figure 32. Figure 33. LIST OF ILLUSTRATIONS Page Pegmatite belts and districts in Georgia.................................................................................................. 3 Pegmatite fields within the Thomaston-Barnesville district............................................................... 4 Sample location map................................................................................................................................. 8 Generalized geologic map of the Thomaston-Barnesville district...................................................... 9 Cross-section through the Thomaston-Barnesville district............................................... ................... 10 Pegmatite trend map of the Thomaston-Barnesville district.............................................................. 13 Primary forms of pegmatites in the Thomaston- Barnesville district ............................................... 14 Regional mineralogical zoning in the Thomaston- Barnesville district.. .......................................... 15 Generalized zoning in muscovite-bearing pegmatites. A) Simple zoned pegmatites. B) Complex zoned pegmatites................................................................................................................. 16 Types of mica deposits within the Thomaston-Barnesville district................................................... 17 Pegmatite districts and granitic plutons in Georgia ........................................................................... 19 Scatter plot ofF versus Rb/K in pegmatitic muscovite....................................................................... 21 Scatter plot of Nb versus Rb/K in pegmatitic muscovite .................................................................. 21 Scatter plot of Be versus Rb/K in pegmatitic muscovite ................................................................... 23 Scatter plot of Li versus Rb/K in pegmatitic muscovite..................................................................... 23 Scatter plot of Rb versus K20 in muscovite.......................................................................................... 24 Scatter plot of Ta versus Rb/K in muscovite............. ........................................................................... 24 Scatter plot of Zn versus Rb/K in muscovite....................................................................................... 25 Scatter plot of Ba versus Rb/K in pegmatitic muscovite..................................................................... 25 Scatter plot of V versus Rb/K in pegmatitic muscovite...................................................................... 26 Scatter plot of log K/Rb versus log Li in pegmatitic muscovite ................................. ...................... 26 Map of the distribution ofF in muscovite ............................................................................................ 27 Map of the distribution of Be in muscovite .......................................................................................... 28 Map of the distribution of Li in muscovite .......................................................................................... 29 Map of the distribution of Nb in muscovite ......................................................................................... 30 Map of the distribution of Rb in muscovite .......................................................................................... 31 Map of the distribution of Ta in muscovite .......................................................................................... 32 Map of the distribution of Zn in muscovite ..................................................... ... .......................... ....... 33 Map of the distribution of Rb/K20 in muscovite ............................................................................... 34 Map of the distribution of Ba in muscovite .......................................................................................... 35 Map of the distribution of Ba/Rb in muscovite ................................................................................... 36 Map of the distribution of V in muscovite ............................................................................................ 37 Relation of pegmatites to metamorphic facies series ........................................................................... 39 IV GEOLOGY AND ECONOMIC POTENTIAL OF PEGMATITES IN THE THOMASTON-BARNESVILLE DISTRICT, GEORGIA by Mark D. Cocker ABSTRACT The Thomaston-Barnesville district is one of twelve presently recognized pegmatite districts in Georgia which form part of the Appalachian pegmatite province. The pegmatites of the Thomaston-Barnesville district are predominantly mica (muscovite)- rich. During World War II, this district was the largest producer ofsheet and punch mica in the southeastern Piedmont of the United States. No mica has been mined in the Thomaston-Barnesville district for approximately 30 years. The current investigation evaluates this district's potential for rare metals and to a lesser extent its potential for mica and feldspar. The present evaluation is based on minor and trace element geochemistry of muscovite collected from the Thomaston-Barnesville district's pegmatites. Over a period of nearly 50 years since the latest investigations in this district, cultural activities, natural reforestation, and rapid degradation of mine exposures left a poor physical record of the formerly known pegmatites. The resistance of muscovite to weathering combined with the presence of indicator elements in the muscovite for rare metals make muscovite an ideal sampling medium in this district. Geochemical results show that anomalous indicator elements(Be,F,Ga,Li,Nb,Sn,Rb, Ta,andZn)inmuscovite coincide with the recorded occurrences of rare-metal bearing pegmatites. Anomalous indicator elements in muscovite helped identify other pegmatites which may contain raremetal bearing minerals. Most of the pegmatites with anomalous indicator elements are concentrated in the central part of theThomaston-Barnesvilledistrictalthough some pegmatites in other parts of this district also appear to have potential for containing rare-metal bearing minerals. The potential for additional undeveloped sheet and punch muscovite deposits is good in parts of the district along the continuation of apparent structural trends; however, the difficulty of finding these relatively small targets may preclude additional work. Further development of some of the larger, partially mined pegmatites at depth or along strike and processing of mine dump material for scrap mica may be economically feasible for small operations. A few pegmatites in the Thomaston-Barnesville district contain unweathered feldspar, but most near-surface, pegmatitic feldspar is weathered to clay. The potential ofthis district for sodic and potassic feldspar is low. ACKNOWLEDGEMENTS The author gratefully acknowledges the permission and interest of the numerous property owners to inspect and sample the old pegmatite workings. The author wishes to thank the reviewers of this manuscript for their thoughtful insights and efforts. INTRODUCTION PURPOSE OF INVESTIGATION The current investigation evaluates the pegmatites in the Thomaston-Barnesville district for their rare- metal potential. Because the Thomaston-Barnesville district is the largest pegmatite district in Georgia, it was regarded as having a better than average potential for containing raremetal bearing pegmatites. Rare metals which are commonly concentrated in pegmatites include beryllium, cesium, gallium, germanium, lithium, niobium, rubidium, tantalum, thorium, uranium, and zirconium. Uses for many of these metals has increased significantly since the last major pegmatite mining in Georgia. Strategic demand and high prices encouraged the mining of pegmatites in Georgia for feldspar, sheet mica and punch mica, particularly during World War I and World War II. During World War II, mica production in the Georgia Piedmont accounted for 41 percent (over 146,000 lbs.) ofthe mica produced in the southeastern Piedmont (Jahns and others, 1952). The largest portion of this mica production was from the Thomaston-Barnesville district. Investigations prior to 1950 concentrated on the mica content and not the potential for rare metals in these pegmatites. 1 GRANITIC PEGMATITES COMPOSITION AND CLASSIFICATION Pegmatites of the Thomaston-Barnesville district are generally granitic in composition. Granitic pegmatites are coarse-grained, lensoidal, dike-like intrusions generally composed of various proportions of quartz, mica (generally muscovite), and potassic or sadie feldspar. Accessory minerals such as tourmaline, garnet, and beryl may also be present Granitic pegmatites are classified on the basis of geological-petrogenetic criteria developed by Ginsburg and others (1979) and recently introduced into North America by Cerny (1982a). The four basic types of granitic pegmatites are: 1) miarolitic pegmatites, 2) rare-element pegmatites, 3) mica-bearing pegmatites, and 4) maximal depth pegmatites (Cerny, 1982a). Brief descriptions of each type given below are based on Cerny (1982a). Miarolitic pegmatites occur as pods in the upper parts of epizonal granite intrusions that are emplaced into low-grade metamorphic country rocks. These pegmatites are characterized by crystal-lined cavities containing such minerals as quartz, feldspar, fluorite, beryl, tourmaline and topaz. These cavities are the sources of many museum quality specimens and gemstones such as aquamarine (beryl), tourmaline and topaz. Rare-elementpegmatites generally occur in cordieriteamphibolite facies metamorphic rocks peripheral to differentiated allochthonous granites. Thesepegmatites are formed at pressures equivalent to intermediate depths (3.5-7 km). These pegmatites are enriched in one or more of the following elements: lithium, cesium, rubidium, tantalum, tin, and niobium. In addition to quartz, sadie and potassic feldspar, lepidolite, beryl, cassiterite and tantalite may be present. Mica-bearingpegmatites occur in almandine-amphibolite facies metamorphic rocks and are formed at pressures equivalent to depths of7 to 11 kilometers. Typical mineralogy includes quartz, muscovite, and sadie and potassic feldspar. Additional minerals which may be present include biotite, tourmaline, beryl and garnet. Although pegmatites of this class are primarily important for their mica conteui, some like the Cochran mine in north Georgia and the giant rare-element bearing Greenbushes pegmatite in Australia (Partington, 1990) may be important sources ofrare-element bearing minerals. The source intrusions for mica-bearing pegmatites are commonly not apparent. The genesis of mica-bearing pegmatites may be due to anatexis or by separation from an anatectic, more or less autochthonous granite (Cerny, 1982a). Maximal depth pegmatites occur in upper amphiboliteto granulite-facies terranes, and commonly grade into migmatites. Maximal depth pegmatites are believed to form at pressures equivalent to depths greater than 11 kilometers (Cerny, 1982a). These pegmatites consist mainly of sadie and potassic feldspar with lesser amounts of quartz and minor amounts of muscovite and biotite. The pegmatites of this class may be barren, allanite plus monazite-bearing or ceramic (feldspar-rich). In the southeastern United States, the most abundant pegmatites are the mica-bearing and the maximal depth types. These pegrnatites have been principally mined for mica or feldspar. Several groups or districts of rare-element bearing pegmatites occur in the southeastern United States. These have been important producers of lithium (King's Mountain district, North Carolina), beryllium (Troup County district, Georgia) (Furcron and Chancey, 1954: Furcron, 1959), and tin and tantalum (Rockford district, Alabama) (Foard and Cook, 1989). Miarolitic pegmatites are currently unknown in the southeastern United States. PEGMATITE PROVINCES, BELTS, DISTRICTS, FIELDS AND GROUPS Granitic pegmatites occur in spatially and/or genetically definable groups. Such distributions have been defined by Ginsburg and others (1979) and Cerny (1982a). The largest defined entity is a pegmatite province which includes the entire group of pegmatite fields or belts within a single metallogenic province. A pegmatite belt consists ofpegmatite fields or districts which are related to each other by a large scale linear geologic structure and occur in a common structural position and geological environment. A pegmatite district contains several associated pegmatite fields, which are separated from other pegmatite fields either territorially or geologically. A pegmatite field is an area containing pegmatites which include a single formation type with a common geological-structural environment, age and igneous source. The smallest definable occurrence ofpegmatites is a pegmatite group defined in a similar manner to a pegmatite field except that it is a spatially distinct part of a pegmatite field (Ginsburg and others, 1979; Cerny, 1982a). Isolated pegmatites may only appear to be isolated because of the lack of known additional occurrences in the area. THE THOMASTON-BARNESVILLE DISTRICT The Thomaston-Barnesville district is one of twelve pegmatite districts presently recognized in Georgia (Cocker, 1990). These pegmatite districts are concentrated in two distinct belts (Figure 1): the Blue Ridge belt and the Piedmont belt, which form part of the southernmost segment of the Appalachian pegmatite province (Jahns and others, 1952). The Thomaston-Barnesville district, as referred to in this report, is principally that district of the same name as described by Furcron and Teague (1943) and by Heinrich and others (1953). This district was defined by those authors principally on the basis of mining or prospecting of the 2 GRIFFIN KILOMETBRB 0 50 I Fl F3 i 0 XILBS 50 IE"3E3! EXPLANATION ~ PEGMATITE DISTRICT A THOMASTON-BARNESVILLE B TROUP c JASPER D PUTNAM E CRAWFORD-JONES-BALD~N F CHEROKEE-PICKENS G CARROLL-PAULDING H HARTWELL I RABUN J LUMPKIN-UNION-TOWNS K HABERSHAM L OCONEE Figure 1. Pegmatite belts and districts in Georgia. The Thomaston-Barnesville district lies within the Piedmont pegmatite belt. (Modified from Cocker, 1992). 3 / ~ ...-. ::. .. LIGHTHOUSE FIELD . . . .. ( .: . ~. " i ~UNT FIELD CONCORD FIELD LY 01 INDIAN GRAVE FIELD ~ (_,/ Thomasto:!J . ~ .(.;;.',1v., . .. YATESVILLE FIELD ' ... .. ; ~ ~ ~~MANVILLE FIELD LAZER CREEK FIELD 0:/ - . ~Fo~ FIELD FIELD I e SCALE ~ 0. 5. 1.0 KILOMETERS Figure 2. Pegmatite fields within the Thomaston-Barnesville district. Pegmatites in the two largest fields - Waymanville and Yatesville yielded most ofthe known mica production. The cities - Forsyth, Thomaston and Barnesville are included as geographical references. Figures 3 and 4 provide more geographical references. muscovite-bearing pegmatites within Monroe, Lamar and Upson counties. The present study extends the district to include nearby muscovite-bearing pegmatites which have similar physical and compositional characteristics, and are in close spatial proximity to those pegmat.ites which have previously been included in the district. The Thomaston-Barnesville district can be divided into a number of pegmatite fields based on the spatial distributions of the currently known pegmatites. These fields are outlined on Figure 2. The majority of known pegmatites occur in a broad band that extends from a point south of Thomaston northeast through Yatesville (yVaymanville and Yatesville fields). The Indian Grave, Concord, Lighthouse, Blount, Juliette, Russellville, and Lazer Creek pegmatite fields appear to be geographically isolated from each other. The Lazer Creek field may be an extension of the Waymanville field. PAST MINING ACTIVITY Past mining activity within the Thomaston-Barnesville district focussed on high-quality mica. All of the mica that was mined in the Thomaston-Barnesville district apparently was muscovite. The term mica includes a number of distinctly different mineral species; however, muscovite is the most important species for its physical properties. The term "mica" is retained in this publication in the circumstances in which muscovite is referenced as mica in the publications cited. Mica is important for its physical properties. Mica is graded by: size, color, clearness, uniform perfect cleavage, flexibility, electric power factor, and freedom from intergrowths with other minerals and from clays, spots and stains (yVhitlatch and others, 1962). Sheet and punch mica are large, principally defect-free muscovite crystals or parts of large muscovite crystals found only in pegmatites. Sheet and punch mica are used for a variety ofpurposes, including: electrical insulation and specialty window panes. Good quality sheet and punch mica command high prices because of their rarity. Scrap, flake and ground mica are derived from the smallerand commonly defect-ridden micas and are more abundant than the sheet and punch mica. Dry ground mica is used in concrete, stucco, backing for asphalt, roofing, dusting powder for rubber tires, fireproofing material, lubricants, and in molded insulation (yVhitlatch and others, 1962). Jahns and Lancaster (1950) provide a detailed study of commercial sheet muscovite properties. During World Wars I and II, the restriction of strategic sheet illld punch mica supplies caused an increase in demand and price. Higher, subsidized prices encouraged prospecting and mining of mica-bearing pegmatites within Georgia. Mica production in Georgia was initially centered in the northern part of the Blue Ridge pegmatite belt. Until about 1918, most of the mica production in Georgia was from hard- rock mines in the Lumpkin-Union-Towns and the Cherokee-Pickens districts. Because of dwindling reserves in the Blue Ridge, the discovery of rich, mica-bearing pegmatites in the Piedmont, combined with the ease and low-cost of saprolite versus hard-rock mining, the bulk of mica production shifted to the Thomaston-Barnesville and Hartwell districts in the Piedmont pegmatite belt. Systematic mining in the Thomaston-Barnesville district began about 1916 with the most extensive mining confined to the periods, 1917-24 and 1941-45 (Heinrich and others, 1953). During the period 1917-24, output from the Thomaston-Barnesville district is estimated at several hundred thousand pounds of trimmed mica (Heinrich and others,1953). During World War II, the Thomaston-Barnesville district was the leading producer of sheet and punch mica in the southeastern Piedmont of the United States with 114,165 pounds or 32 percent of the total production (Jahns and others, 1952). Sixty-two percent of this production came from 4 mines: Adams, Battles, Earley Vaughn and Mitchell Creek (Heinrich and others, 1953). Although published, comprehensive data is incomplete following World War II, production ofsheet mica apparently continued in a few of the larger mines at a decreased level into the early 1960's when price subsidies were discontinued (yVhitlatch and others, 1962). Yearly production of sheet mica in Georgia ranged from 9,000 to 17,000 lbs./year during this period (Cocker, 1992). Several of the mines described by Heinrich and others (1953) have been significantly enlarged in the time between World War II and the present investigation. Early, underground mining in this district involved selective removal of mica. After World War II, mining concentrated on the larger pegmatite bodies. Open-pit mining of the larger pegmatites probably involved the used of steam shovels, bulldozers and backhoes. Most mining activity was confined to the upper, weathered portion of a deposit (the upper 13 to 20 meters - 40 to 60 feet). The mica was trimmed by hand at the mine site or in the nearby towns of Thomaston, Barnesville, Yatesville, Culloden, and Forsyth. High quality sheet mica of the type mined here in the past still commands premium prices. Within the United States, which imports nearly all of its sheet mica, no major source of sheet mica is being mined. In 1988, the United States imported approximately $2 million worth of sheet mica (Davis, 1988). The United States also produces and consumes considerable amounts of scrap, flake and ground mica. In 1988, the United States producedabout$23 million worth of scrap, flake and ground mica and imported about $5.5 million dollars worth of scrap, flake and ground mica (Davis, 1988). LOCATION AND SIZE The Thomaston-Barnesville district is located approximate!y halfway between Macon and Griffin (Figure 1). Most 5 of the pegmatites considered to be part of this district are located within the counties of Monroe, Upson and Lamar, but mica-rich pegmatites also occur in Pike, Talbot, Jasper and Butts Counties. The total area of this district is approximately 2000 square kilometers. TERRAIN AND EXPOSURE The terrain is generally gently rolling to flat with some of the major drainages cutting deeply into the more gentler terrain. Elevations range from 100 to 250 meters above sea level. The western side of the district is bounded by the elongate ridges of Pine Mountain. The gentle terrain is controlled mainly by deep saprolitization. Natural exposures are most common along deep drainages or hill tops. Road cuts locally expose bedrock. Exposures of pegmatites are rare. Most pegmatites were apparently discovered by farmers when they plowed up chunks of weathering-resistant mica. VEGETATION The vegetation of the region is governed principally by land-use. Much of the flat terrain is in pasture. The gently rolling terrain may also be in pasture, but is more commonly forested. Vast tracts of land have been clear-cut and replanted with pines one or more times. Recently reforested (5 to 15 years) land contains thick underbrush and is extremely difficult to traverse. Many previously farmed tracts have been abandoned and are now overgrown with climax forest flora (oaks, hickory, sweetgum). Land-use requirements in this district commonly resulted in the filling-in or bulldozing of open-pits, shafts and mine dumps. Combined with rapid revegetation, many old mines and prospect pits have literally disappeared. Some of these former mines may be detectable by the presence of muscovite concentrated on the land surface. PREVIOUS WORK Galpin's (1915) study appears to be the first to locate and describe numerous feldspar and mica pegmatites as well as aplite dikes. Most of these descriptions and locations are generalized, and some of the described locations were difficult to verify. Because of the lack of prospecting activity prior to Galpin's investigations, many pegmatites had not been discovered. Smith (1931-1933) located and briefly described a significantly larger number of mica-bearing pegmatites that were discovered and developed during World War I. Smith's field notes are keyed numerically to pre1920's soil maps. Furcron and Teague (1943) published many of Smith's descriptions along with their descriptions of mica-bearing pegmatites that were discovered and developed during the initial stages of World War II. Furcron and Teague (1943) published the first maps which show locations of individual pegmatite mines in Georgia. Subsequent investigations by the United States Geological Survey (Jahns and others, 1952; Heinrich and others, 1953) and the United States Bureau of Mines (Beck, 1948) during World War II coincided with the extensive prospecting and mining of mica-bearing pegmatites throughout the southeastern Piedmont. Many of the locations and descriptions in Heinrich and others (1953) are based on Furcron and Teague (1943) and ultimately Smith (1931-1933). The studies by Jahns and others (1952) and Heinrich and others (1953) brought a wealth of data from other pegmatite districts in the United States and an expanded understanding of pegmatites. These earlier investigations provide critical information on the mineralogy, internal zoning and structure of the pegmatites in the southeastern Piedmont Much of this information was nearly impossible to verify or elaborate on because of the poor physical condition of the olderpegmatite mines and outcrops. Physical information on the pegmatites in this district which are contained in this report are principally based on descriptions obtained during the earlier studies. The geologic setting of the district was poorly known at the time of the earlier studies. Subsequent investigations by Clarke (1952), Grant (1967) and Smith and others (1969), and more recently, by Schamel and others (1980), Higgins and others (1988), Hooper (1986) and Stieve(1984) contributed to an increased understanding of the lithologies and major structures in and adjacent to the district. Despite these efforts, the basic geologic framework within the ThomastonBarnesville district remains poorly known. These later geologic contributions reflect the lack of recent interest in pegmatites and a lack of knowledge of the potential that the pegmatites' geology and geochemistry can contribute to the understanding of the regional geology. SAMPLING AND ANALYTICAL PROCEDURES LOCATIONS OF MINES, PROSPECTS AND SAMPLES As previously described, the Thomaston-Barnesville district covers a large area and includes numerous mines and prospects which have been documented by Smith (19311933), Furcron and Teague (1943), Beck (1948), Heinrich and others (1953), Koch and others (1984 and 1987). It was difficult to find the mines and prospects located by the above authors due in part to the lack of map coverage or the relatively poor quality of the maps available at that time. Also, the occasional erroneous transcription of mine locations (Furcron and Teague, 1943; Beck, 1948; Heinrich and others, 1953; Koch and others, 1984 and 1987) initially described by Smith (1931-1933) was perpetuated by later 6 authors. Text descriptions of the locations occasionally did not match the map locations. In addition, subsequent human activity or natural reforestation obliterated or obscured the former mining activity. Because one of the major goals ofthe present investigation is the evaluation of this district's pegmatites, the inspection and sampling of the known pegmatites required their location in the field. This investigation succeeded in finding most of these mines and prospects. Pegmatites, which belong to this district, are located on nineteen United States Geological Survey 7.5 minute quadrangle sheets. These 7.5 minute quadrangle maps (1:24000 scale) show the most accurate locations of these mines, prospects and sample points and are on file at the Georgia Geologic Survey. The locations of these mines, prospects and sample points are also given in Appendix I as UTM coordinates (in meters). The accuracy of most of the points actually located in this investigation in UTM coordinates is plus or minus 10 to 50 meters (about 30 to 150 feet). The locations of those mines and prospects which could not be found in the field during the present study are based on the descriptions by the previous authors, but the accuracy of these locations is uncertain. The mine and sample point locations were compiled from the 7.5 minutequadranglemapsontofour 1:100000 scale map sheets (Thomaston, Griffin, Milledgeville, and Macon) which are also on file at the Georgia Geologic Survey. A single sample location map was compiled from these four maps and reduced for this publication (Figure 3). SAMPLING TECHNIQUES The southeastern Piedmont in Georgia presents a difficult sampling situation. Prolonged and intensive subtropical to tropical weathering since the Late Cretaceous, has altered much of the near surface rock to saprolite. Hard bedrock exposures are locally abundant, but are generally rare. Most of the pegmatites within this district contain quartz, muscovite and a potassic and/or sadie feldspar. Quartz and muscovite are commonly the only minerals at or near the surface which have resisted the chemical weathering. The trace element geochemistry of muscovite and feldspar is useful in identifying pegmatites which may contain rare-metal bearing minerals. Muscovite concentrates and feldspar concentrates (where present) were collected. Mineral concentrates were collected randomly at a dump, exposure or outcrop in an attempt to achieve an average or representative sample of the entire pegmatite. This sampling procedure aLtempted to minimize the effects of mineralogical and chemical zoning within each pegmatite. The lack of exposed workings in nearly all of the pegmatites and the apparent mixing of dump material during and after mining necessitated this type of sampling procedure. Any regional comparisons of pegmatite geochemistry should be based on a representative sample from each pegmatite. In a few instances, the scarcity of pegmatitic material restricted the diversity of samples which were collected. SAMPLE ANALYSIS Samples were analyzed by two different geochemical labs over the duration of this project Twelve samples, which were collected during the initial stages of this investigation were analyzed by Skyline Labs in Wheatridge, Colorado. The remainder of the samples were analyzed by BondarClegg, Inc. in North Vancouver, B.C. and Ottawa, Ontario. Two duplicates of the samples analyzed by Skyline Labs were also analyzed by Bondar-Clegg. The results were comparable. Skyline Labs used inductively coupled plasma spectroscopy to analyze the submitted samples. BondarClegg used inductively coupled plasma spectroscopy, direct coupled plasma spectroscopy, atomic absorption spectrometry, gravimetric analysis, x-ray fluorescence, and specific ion analysis to analyze the submitted samples. The muscovite and feldspar analyses are presented in Appendix II and III respectively. Specific methods, extraction techniques, and lower detection limits for each element are given in Appendix IV. Minor changes in the lower detection limits for some elements by Bondar-Clegg during thecourseofthis investigation did not affect the interpretation of the results because of the emphasis on high geochemical concentrations. GENERAL GEOLOGIC SETTING THE PINE MOUNTAIN BELT The Thomaston-Barnesville district lies principally within the eastern end of the Pine Mountain belt (Figure 4). Muscovite-bearing pegmatites of this district also occur outside of the Pine Mountain belt to the north andeastofthe Towaliga and Box Ankle faults (Figure 4). Rocks in the eastern end of the Pine Mountain belt are mainly Middle Proterozoic orthogneisses of the Wacoochee Complex and younger, metasedimentary rocks (Schamel and others, 1980). The most widespread lithology of the Wacoochee Complex is a strongly foliated granitic gneiss called the Woodland Gneiss (Hewett and Crickmay, 1937; Rankin and others, 1989). Orthogneiss which contain biotite, garnet and prominent hypersthene in the central part of the Thomaston-Barnesville district is known as the Jeff Davis Granite. A 1,051 MaRb-SrisochronfortheWoodland Gneiss (Rankin and others, 1989) indicates a Grenville age for the metamorphism of the orthogneiss. Charnockitic rocks indicate that the metamorphic grade was granulite facies. Late Proterozoic orearly Paleozoic age metasedimentary clastic rocks of the Pine Mountain Series overlie the 7 351-12 351-11 351-13 m=u~ ~ -m=l~ - - -- - - -- --1A"9-IJ 1(9- 6 149-H 9-1 I 1A91S )AI- 16, lC99 ,I 349-22 349-5l 1n-u 1 - - 349-2~ )A!I- 3 349-1 ~!:-} JlU 151-7 m=~~ ~m=~ g JU - 10 H12"4' ;11 351-U l5!-ZS 351-26 376-7 376-8 376-9 376-10 376-11 376-2 .. 376-1 376-3 376-4 376-5 376-6 .376-12 376-13 379-ll 379-14 a ~8-Z m:~ . ll(-z 5 37. . 0J lil!-~9-Zr ~=, 378-6 3787 .3 ~ IIARNESYILLE 378-l .m:t~ 378-4. 3711 79-5 h9-6 319-17 }79-18 379-1~ 0 >7H7 a e3ao-7 379-9 179-10 )1;-25 380,; )80-11 80-12 379-3179-11 -)19 - 22 . Z3! '9-26 338800--113 e380-10 8 e ~1-7 ~1-5 Hl:l - ' l&l-1 lHatl:-1~ Alat-4 ~1-JZ 38110 341-U e 381-13. Q] '39-35 439-36 PUE CO. LAllA I CO. oa-' 4011-7 ... 4081 uPs~ co. of-to o;- tt 4~0!91--2U0 &08-2 4081 :g.,:u \ :z;~ m:u .m:~ ~m:u 439-30 40lH m:n ~ ~. 408-5 409-11 :g:IS 40912'-.. A 16 m:~: (m)=I-~5r5 J!:~- ~::;:jji~i,ft:Jn'"-o' -~m1=0~-2~ 3l:ff-n-"-. . m:i 0 m- 379-2 ' 179-23)7!2J l7Nl .09-25 -.;-,o,:~~ 409-26 <0490-9z370 L- ot 3 e 41o- 2 ___. . . 0 44110~3~1 l:U 3804- )80-2 380-3 411-1 411-Z Ul-3 e411- "' 441111--56 411-7 a C0 4091 9 6 409 -36 :g9- 5 0 0 u>u . 4 41100--4l 411-98 411-11 e4ll-l8 ljg:! ...... e411-ll 411-12 4 09-25 04JJ - SA U44Q0--5009 /4(09093-4l1: 41029 410-27 10-25 Ullt9 (Cerny, 1982a). The geochemical trends observed in pegmatite fractionation are similar to and extend those trends observed in plutonic gnmitcs. The ratios: K/Rb, K(fl, Ba/Rb, Rb/Sr, and Nb(fa all tend to decrease to extremely low values with increasing pegmatite fractionation (Cerny, 1982a). Plots of these ratios versus trace elements illustrate the differences in pegmatite groups and demonstrate trends in pegmatite fractionation. In the U.S.S.R. and more recently in Canada (Cerny, 1982a, 1982b; Cerny and others, 1986; Trueman and Cerny, 1982), pegmatite invesligations have emphasized regional mineralogical and geochemical zoning along with the pctro- genesis of the different types of pegmatites as a means of locating and identifying potentially economic pegmatites. The trace element geochemistry of pegmatitic K-feldspar and muscovite has repeatedly demonstrated that trace element geochemistry is an effective means of determining fractionation trends within pegmatite districts and in assessing the economic potential of the individual pegmatites (Trueman and Cerny, 1982). Trace element geochemical analysis of muscovite and feldspar is particularly useful in the southeastern United States because of the extensive weathering. Of the common minerals present in a typical pegmatite, muscovite is the only mineral structurally favorable to include a variety of the incompatible trace elements as substitutions in its structure. Also, muscovite is essentially unaffected by weathering and commonly is the only surface indicator of a mica-bearing pegmatite. In the uncommon pegmatites which are feldsparrich and mica-poor, feldspar is unaffected by weathering, and can be used instead of muscovite. It is critical, however, to compare muscovite and feldspar analyses separately. Current and recent investigations by the Georgia Geologic Survey have established that the trace-element geochemistry ofpegmatitic muscovite is a powerful and practical tool in the economic evaluation of granitic pegmatites in Georgia (Gunow and Bonn, 1989; Cocker, 1990; Cocker, 1991). Gun ow and Bonn (1989) demonstrated thatmuscovites within the more strongly fractionated pegmatites of the Cherokee-Pickens district are enriched in the rare elements (Be, Nb, Li, F and Rb/K). Also, the muscovite in the berylrich pegmatite of the Cochran mine in the Cherokee-Pickens district is geochemically distinct from the muscovite in other beryl-bearing and beryl-poor pegmatites within the same pegmatite field. MUSCOVITE GEOCHEMISTRY The following discussion is based on the geochemical results contained in Appendix II, scatter plots of trace clements, and district-scale geochemical maps. The scatter plots (Figures 12 to 21) illustrate the correlative variations between the trace elements and the relative amount of differentiation exhibited by each pegmatite. Where possible, the trace element chemistry from the Cherokee-Pickens district(Gunow and Bonn, 1989) is included in several of the scatter plots for a relative comparison. Use of that data (Gunow and Bonn, 1989) assumes the accuracy and precision of the geochemical data from the two different projects are approximately similar. Although some of the data obtained in this study was obtained from the same commercial geochemistry lab used by Gunow and Bonn (1989), several years separated the analyses and no duplicates ofGunow and Bonn's samples were available to correlate the results of Lheir work with that of the present study. The geochemical maps (Figures 22 to 32) illustrate 20 8000 ~----~----~--~----~----~----~----~~----~ l .. . . . . . . t + . ~ 7000 ...............-r-..ttor-~. ...... .. . ~ -r-j.. : :t=: \ 1 ~1:--t r: t:: >< CP Be-poor + CP Be-rich D Thorn-Bam !........ ;......... p. ck;... .:.. E~ : i 4000 ............... j............ I o ...... D i i f...... .... .... ... l !i........ . J. ....... I u. i i b ! I 3000 io. ................ ~----1..---k--------~--J............... : ++ j................. P0 b 1 i i i i IJ :.! : :t:~I: :t:J : [J . .""2" + i. .w.... j l 0 ! i ! : . : ! . l 1 ! : 0 50 100 150 200 250 300 350 400 Rb/K (ppmx1 0000/ppm) Figure 12. Scatter plot ofF versus Rb/K in pegmatitic muscovite. Results (Appendix II) from the Thomaston-Barnesville district (boxes) are compared with beryl-absent and beryl-poor pegmatites (exes) and beryl-rich pegmatites (crosses) of the Cherokee-Pickens district (data from Gunow and Bonn, 1989). 400 ~----~----~, ----~, ----~----~----~----~----~ ~------~ j L.. + : l ['" ' ; >< 350 CP Be-poor + 300 CP Be-rich CJ 250 Thom-Barn E ~ + ::.,~-.l;~t~Dr ~ f :~I 1I : SO'b........ 0 0 50 j. ...............i,................. j.............;..................;..................;................... . i - ! i, 6. D !_ : I ! ! i ._1 !, 100 150 200 250 300 350 400 Rb/K (ppmx1 0000/ppm) Figure 13. Scatter plot ofNb versus Rb/K in pegmatitic muscovite. Results (Appendix II) from the Thomaston-Barnesville district (boxes) are compared with beryl-absent and beryl-poor pcgmatites (exes) and beryl-rich pegmatites (crosses) of the Cherokee-Pickens district (data from Gunow and Bonn, 1989). 21 geochemical values or ratios coded with symbols in order to simplify the appearance of each map and to focus attention on the location ofgeochemical anomalies and trends. Circles represent the lowest values; squares represent intermediate values; and stars are the highest values. Because of the extreme diversity in geochemical values, and these figures are not contoured. Groups ofpegmatites containing the most anomalous values are oullined by dashed lines. The major faults on the north and south sides of the Pine Mountain terrane and the approximate location of the kyanite-sillimanite isograd (after Smith and others, 1969) are indicated. The F and Nb concentrations in the muscovites from the Thomaston-Barnesville district overlap those of the berylabsent pegmatites of the Holly Springs field and of the berylpoor pegmatites of the Ball Ground field and extend across the range between those pegmatites and the beryl-rich pegmatites of the Ball Ground field (Figures 12 and 13). Muscovite from the beryl-bearing pegmatite of the Reynolds mine in the Thomaston-Barnesville district contains a similar Nb content (334 ppm) as that from the Cochran mine. Muscovite in the beryl-rich pegmatitesofthe CherokeePickens district are enriched in Be relative to pcgmatites of the Thomaston-Barnesville district and the beryl-poor and beryl absent pegmatites of the Cherokee-Pickens district (Figure 14). The major implication of Figure 14 is that the potential for beryl-rich pegmatites in the ThomastonBarnesville district is small. The Li content of the muscovites in the ThomastonBarnesville district is similar to that of the muscovites in most of the pegmatites of the Cherokee-Pickens district (Figure 15). The Cochran mine is enriched in Li relative to the other pegmatites in that district. In the Thomaston-Barnesville district, Rb increases (wFiitghurienc1r6e)a.sEinngricKhm2oentfoorfRRbbregleantievrealtloyKb2eoloowccu7r0s0abpopvme 700 ppm to over 1500 ppm Rb principally within the 8 to 9 weight percent K20 range. Muscovite in the beryl-rich pegmatites of the Cherokee-Pickens district is enriched in Rb and K20 relative to the most Rb-enriched muscovites in the Thomaston-Barnesville district. Seven muscovite samples are distinctly enriched in Ta (95 to 189 ppm) compared to the other muscovite samples in the Thomaston-Barnesville district (Figure 17). Zn values progressively increase up to 120 ppm with increasing Rb/K (Figure 18). Zn values which range up to 226 ppm do not appear to be related to theRb/K ratio. NoTa orZn values are reported for the Cherokee-Pickens district (Gunow and Bonn, 1989). The Ba concentration increases dramatically at low Rb/ K ratios in muscovite from the Thomaston-Barnesville district, the Holly Springs field and the beryl-poor pegmatites of the Ball Ground field of the Cherokee-Pickens district (Figure 19). Muscovite samples which have low Ba contents have a significantly higher Rb/K ratio principally because of an increase in Rb. Although Ba and Rb compete for the same structural site in muscovite, the Ba concentration is significantly greater in muscovite from less fractionated or muscovite-bearing pegmatites (Shmakin, 1984; Gunow and Bonn, 1989) than from more highly fractionated or rare-element pegmatites. This relation is demonstrated by higher Ba concentrations in whole-rock analyses of less fractionated granites compared with more fractionated granites (El Bouseily and El Sokkary, 1975). Because V also competes for the same structural sites asK, Rb, and Ba, V is higher at low Rb/K ratios (Figure 20). The Ba/Rb ratio is also used as an indicatorof the degree of pegmatite fractionation. The Ba/Rb ratio is in the range 0.3-0.7 in muscovite-bearing pegmatites, and this ratio is in the range 0.002-0.02 in rare-element pegmatites (Shmakin, 1984). Muscovite from the Cochran mine in the CherokeePickens district has a Ba/Rb ratio of 0.1 (Gunow and Bonn, 1989) which lies between the Ba/Rb ratios for muscovitebearing and rare-element pegmatites (Shmakin, 1984). The Ba/Rb ratios for muscovites in the Thomaston-Barnesville district are in the range 0.02-5.59. Thirteen pegmatitic muscovite samples have a Ba/Rb ratio in the range 0.02-0.09 which overlap the range for rare-element pegmatites. Geochemical data for a variety of pegmatite classes from around the world compiled by Cerny and Burt (1984) show that each pegmatite class appears to have distinctive trace element signatures. Most of the pegmatites in the Thomaston-Barnesville district, Holly Springs field and beryl-poor pegmatites of the Ball Ground field in the Cherokee-Pickens district lie in or near to the muscovite class of pegmatites as depicted on a scatter plot (Figure 21) of the log K/Rb ratio versus log Li (Cerny and Burt, 1984; Gunow and Bonn, 1989). A few pegmatites from the ThomastonBarnesville district as well as the Cochran mine pegmatite (Gunow and Bonn, 1989) occur in or beyond the rareelement pegmatite field shown by Cerny and Burt (1984). The geochemical maps (Figures 22 to 28) indicate that the highest concentrations ofF (2000 to 7076 ppm), Be (10 to266.5 ppm),Li (40to greaterthan 100ppm),Nb(70to 334 ppm), Rb (600 to 1534 ppm), Ta (95 to 189 ppm), Zn (70 to 226 ppm) are concentrated in the central part of the district. The more highly fractionated pegmatites (higher Rb/K20 ratios) are located within the central part of the district and in the northwestern part of the district (Figure 29). The highest Ba concentrations (400 to 1456 ppm) are located peripherally to the central part of the district (Figure 30). The more highly fractionated pegmatites (based on the lowest Ba/Rb ratios- 0.02 to 0.39 ppm) are mainly located within the central part of the district (Figure 31). A second zone of more highly fractionated pegmatites appears to be located in the northwestern part of the district. Three northeast-trending zones containing the highest V values (30 to 186 ppm) extend along the center and edges of the Pine Mountain terrane (Figure 32). The higher V 22 45 ~----~----~----~----~~----~----~----------~ r--------~ ! : ! j +l : j ; + >< 40 :jt....ji... j-!+""''''"' CP Be-poor ::::i:=:r.~;t=.~l ~:~:t::::~:~: + CP Be-rich CJ l : j-:: : Thom-Barn t J:::t=J:::=I + ! ; 20 ~~ ; ~ ~ I i :: - 'c~~::~:J 5 F t:l ! l 0 ..... .. (................. ciiJ.....9 .........;............ ......,i.. .. ....... ... j ~ ................... j j ................. . !~ : j I! O+-----~------~= ------+' ------r' ------'r-----~'------4!------4 0 50 100 150 200 250 300 350 400 Rb/K (ppmx1 0000/ppm) Figure 14. Scatter plot of Be versus Rb/K in pegmatitic muscovite. Results (Appendix II) from the Thomaston-Barnesville district (boxes) are compared with beryl-absent and beryl-poor pegmatites (exes) and beryl-rich pegmatites (crosses) of the Cherokee-Pickens district (data from Gunow and Bonn, 1989). 700 I )( i. . . . . . . .. l. . . . . .. . ..i.. . . . . .... 600 .................-J.-................t--1* [-- ..---:_,,............tt--"''''""" + ! i ' : : 500 ... . .... . l... : ..... : l...... . !.. 1:.... t ..........J,.................. ! l : : : CP Be-poor + CP Be-rich CJ I..... .....;. . .... L........ L........ E 400 ..................;..................l.................. J.. ................ Thom-Bam .as. ::J 300 200 100 CJ e i b + a+c!P i CJ : tJ : : i ! : 100 150 200 250 300 Rb/K (ppmx1 0000/ppm) + i ! : 350 400 Figure 15. Scatter plot of Li versus Rb/K in pegmatitic muscovite. Results (Appendix II) from the Thomaston-Barnesville district (boxes) are compared with beryl-absent and beryl-poor pegmatites (exes) and beryl-rich pegmatites (crosses) of the Cherokee-Pickens district (data from Gunow and Bonn, 1989). 23 3500 3000 i ,, ,,,,,,,,,,,,,,.,...... .................... +! I , I , a ;~ . .r-" -- r ~u ! H )( CP Be-poor 1 ' + i : + : I: : : 2500 :r1' r:...................:~ -----...................i~....................... i I ; : : ~ i : i : + - , : l r- Eaa.. 2000 ! . l ............... .. ...... . l """"~ -- - ---"" "' i' """"""" " " "" ""'" f -l"'' """ '"'' ''"" ''" t" " ...... ....... ..... .1~ .................. ~ - .............l............ t........o...~.....,............. a.D: 1500 l- ----- .................. CP Be-rich D Thorn-Bam ! 1 io D ! ~ 1000 ! ! .. -................... ! j................... ..... ti oU --+-. . . ..........!fD.. --.......+....f; ...................... . ' I 1 i I D : i 500 ........................!......................!--rnflo.. : D 0 D ~; j D :D ~ 0 6' + -~s.P....w..-- O+-------~--------,'.--------;r-;3-----r--------T--------1 5 6 7 8 9 10 11 K20 (weight percent) Figure 16. Scatter plot ofRb versus K20 in muscovite. Results (Appendix II) from the Thomaston-Barnesville district (boxes) are compared with beryl-absent and beryl-poor pegmatites (exes) and beryl-rich pegmatites (crosses) of the Cherokee-Pickens district (data from Gunow and Bonn, 1989). 300.-----~----~----~----~----~----~----~---. i i ! ' i 250 .................:....-.g : ........~ ................ .. . ~ .... .......... .... ~ .. ................lI ....... (l...... ........... .~. ..... .. .......... j l ~ l ! ~ ; 200 E sa. 150 100 ... rSl.., Do ! I : i ; 0 ~~',-t~ .': .,~l~r6Di_~OD ~bb: ~D4I' ~~'f ---I~'~----+--~;---~ 0 50 100 150 200 250 300 350 400 Rb/K (ppmx1 0000/ppm) Figure 17. Scatter plot of Ta versus Rb/K in muscovite. Results (Appendix II) from the Thomaston-Barnesville district are indicated. NoTa analyses are available from the Cherokee-Pickens district for comparison. 24 2 501~----~--~~--~----~--------------~----~ ! i D 200 . . 000000 0 0 00000 0 0 0 00 ~ 00000 0+ oo o o 0000 00 ! 000 ! . . . 000000 0 0 00o .. !0 000000000 00 000000 0;0ooooooo0 0 0000000 0; 0 0000000000000 o0o O~ O ........ ._.M~OO OO O O O O O0; .OOOooooo o ooo o oO a .i=, ' 0 : : l r. . .. .. rI. . . . . rI . . I TI......... ! ~ 150 T!' "~ 0e!r- ! D [] ' i ' I T: ............... : : oo''- - ~ ~ ~ I )- L I _). . . .. . .. !c~ o ! D ;c P l: 0 1 ! : : : i : : zor r I 1P ~cP b 1 ' l ~ ~ 50 '"+-J 1 Ci@f'c:P: i ~ ~ ; ~ ~o 1 . i l l 0 +---0 ~ 0 ,:0~-0 -~-----+-----4----~f------~----~--~ 0 50 100 150 200 250 300 350 400 Rb/K (ppmx1 0000/ppm) Figure 18. Scatter plot of Zn versus Rb/K in muscovite. Results (Appendix II) from the Thomaston-Barnesville district are indicated. No Zn analyses are available from the Cherokee-Pickens district for comparison. ~ ~----~--~----~----~----~----~--~----~ >< 2500 .................!...........--r- ........... L...............~.................;..................!.................:............... j I li l l : ~ l i ; ~ 2000 E + a. .9:: 1500 1'0 Ill >< CP Be-poor + CP Be-rich D Thorn-Barn 1000 ............ I ! I I I l 500 i- 5!! ... b ~ 1 ~ + !+ ! l I ++ 0 +---~~---~~~~~~~~F-~~+-----4-----~----~ 0 50 100 150 200 250 300 350 400 Rb/K (ppmx1 0000/ppm) Figure 19. Scatter plot of Ba versus Rb/K in pegmatitic muscovite. Results (Appendix II) from the Thomaston-Barnesville district (boxes) are compared with beryl-absent and beryl-poor pegmatites (exes) and beryl-rich pegmatites (crosses) of the Cherokee-Pickens district (data from Gunow and Bonn, 1989). 25 200~----~----~--~----~----~----~----~--~ i I :: -~r~ t ~ - - ~ t!: :t:iJi : i! I l :: r: r:J ~ :~- ~~~ 1: ::!-~] > ao~ ............~m~-a~- -L-.............L....... . . .)........... .j..................~...................~.........._...... : o~~ ~[: ~]: ~ I 1 1! : ; r : :::r:= 20 ........cfl ..;............oo-------cr..b -...............;..................!- ...............;...--- a~ iJ fli=n1J i : : i : : l : : : 0 +-----~-~~QF~- ~--~,~~~+' ----~'r-----+' ----~'----~ 0 50 100 150 200 250 300 350 400 Rb/K (ppmx1 0000/ppm} Figure 20. Scatter plot of V versus Rb/K in pegmatitic muscovite. Results (Appendix II) from the Thomaston-Barnesville district are indicated. No V analyses are available from the Cherokee-Pickens district for comparison. .B, EAYL ~:OOR , / CHEAO\(EE.f'ICKENS 2.5 ,....................... ,~ ......,... JE..:l:tW'r '""''~ .........................;............................ +, I"' "' ~ l i E-.aEaaa--..., 2 1.5 ~: .!) a: ~ 0) 0 ...J 0.5 >< CP Be-poor + CP Be-rich 0 Thorn-Barn 0 0 2 3 4 5 Log Li (ppm) Figure 21. Scatter plot of log K/Rb versus Li in pegmatitic muscovite. Results (Appendix II) from the Thomaston-Barnesville district (boxes) are compared with beryl-absent and beryl-poor pegmatites (exes) and beryl-rich pegmatites (crosses) of the Cherokee-Pickens district (data from Gunow and Bonn, 1989). Also represented are fields for rare-element pegmatites, muscovite-rich pegmatites (after Cerny and Burt, 1984), and the rare-element Harding and Tanco pegmatites (data from Jahns and Ewing, 1976; Renaldi and others, 1972; diagram modified from Gunow and Bonn, 1989). The direction of increasing differentiation is from the upper left to the lower right in this diagram. 26 ' ,._/ '\ , ' 5S;OIISVTH / i * 1\) ....... / '\ --I *"- I / / / I / \* I ** I I , T~Sd) I / * '-.- ' .,. , o~ ._ * FLUORINE IN I