COMMONWEALTH OF VIRGINIA DEPARTMENT OF CONSERVATION AND ECONOMIC DEVELOPMENT DIVISION OF MINERAL RESOURCES GEOLOGY AND MINERAL RESOURCES OF FLUVANNA COUNTY Jomes W. Smith R. C. Milici S. S. Greenberg BULLETIN 79 VIRGINIA DIVISION OF MINERAL RESOURCES Jomes L. Colver Commissioner of Minerol Resources ond Stote Geologist CHARLOTTESVILLE, VIRGI N IA 1964 COMMONWEALTH OF VIRGINIA DEPARTMENT OF CONSERVATION AND ECONOMIC DEVELOPMENT DIVISION OF MINERAL RESOURCES GEOLOGY AND MINERAL RESOURCES OF FLUVANNA COUNTY Jomes W. Smlth R. C. Milici S. S. Greenberg BULLETIN 79 VIRGINIA DIVISION OF MINERAL RESOURCES Jomes L. Colver Commissioner of Minerol Resources ond Stote Ceologist CHARLOTTESVILLE, VIRGIN IA 1964 Couuoxwn.rr,r:s on Vrncrxr.l DnpenruoNt or Puncneses ,tNn Suppt,v RrcnlroNo 1964 DEPARTMENT OF CONSERVATION AND ECONOMIC DEVELOPMENT Richmond, Virginia Menyrw M. Surnpnr,tNa, Director A. S. Recner,, JR., Ereantiae Assistant BOARD G. Ar,vrrv MAsspNsunc, Hampton, Chairman Svnmnv F. Suer,r,, Roanoke, Viee-Chairman Anonpw A. F,Lnr,nv, Danville Wonrnrncron Feur,rwon, Glasgow Cenr,rsr,p H. Hulror,srxr, Williamsburg Genr,enu E. Moss, Chase City EnNnsr Lno Slrrrn, Grundy Vrcron W. Srnwlnr, Petersburg Jonx S. TnonNroN, Culpeper CONTENTS Plco Abstract. ......... 1 Introduction. 1 Location and size of area 1 Present investigation. .. ,2 Acknowledgements.... : Previous work. 3 Geography 4 6 a Lower chlorite-muscovite unit. I Middle muscovite unit. ... 1t Upper chlorite-muscovite unit. .. 12 Metaribrphosed volcanic and sedimentary rock unil,.... 12 Arvonia Formation l4 Granodiorite unit. l8 Triassic dikes. 2I Structural geology. 23 Folds. 24 Faults 26 Minor structural features 26 Foliation. 27 Minor folds 27 Lineations. 29 Metamornhism. 29 Regional metamorphism. 29 Contact metamorphism. 31 Geologic history 32 Economic geology. DD Building stone. 33 Talc... 34 Slate. 35 Asbestos.... 35 Crushed stone 35 Garnet........ JJ Gemstones. 38 Iron-bearinq minerals. 38 Vermiculite. 39 Sand and qravel. 39 CIay materials. 39 Gold. 40 Ground water.. 44 Magnetie survey. 52 Appendix I: Chemical analyses. 53 Appendix II: Analytical age determinations.. 56 References trt Index..... 61 ILLUSTRATIONS Prarn Peen l. Geologic map of Fluvanna County, Virginia. .In pocket 2. Mineral resorirces map of Fluvanna County, Virginia. ' . .In pocket 3. Vertical magnetic intensity profiles, Fluva,nna County, Virginia. .In pocket Frcunn l. Index map showing location of Fluvanna County. 2 , Alluvial terrace boulders 5 3. Quartzite at the base of the Arvonia Formation. 15 4. Negative photomicrograph of almandine-amphibole-quartz schist from the Arvonia Formation. l6 5. Negative photomicrograph of almandine-amphibole-quartz schist from the Arvonia Formation. l6 6. Photomicrograph of euhedral garnet containing graphite (?) inclusions' . r7 Photomicrograph of oolites composed of goethite in a matrix of chlorite and quartz. t7 8. Bremo Member of the Arvonia Formation. 18 o Cross-bedding within the Bremo Member...... 19 10. Lineation resulting from stretching of crinoid columnals (?). ' .. .. r9 11. Elongated crinoid columnal from the Bremo Member. .. n 12. Elongated brachiopod or pelecypod shell in Arvonia quartzite. n ,q 13. Granodiorite gneiss. .....i. 9' 14. Photomicrograph of granodiorite. 15. Biotite'rich xenolith within granodiorite. 23 16. Steeply dipping beds of subgraywacke z5 t7. Minor folds and flow cleavage developed in quartzose slate of the Bremo Member % 18. Quartz vein and main pit at the Davis quarry 36 TABLES Pecn 1. Geologic formations in Fluvanna County. 8 2. Data on Fluvanna County clay materials tested for ceramic and light- weight-aggregate purposes. 4I 3. Data for water wells in Fluvanna County. 46 VII GEOTOGY AND MINERAL RESOURCES OF FLUVANNA COUNTY By Jeups W. Surrn, R. C. Mrr,rcr, exn S. S. Gnppnnonc ABSTRACT Fluvarrna County is situated in the central Virginia Piedmont on the southeast limb of the BIue Ridge anticlinorium. The rocks range from the Cambrian or Precambrian Catoctin Formation through the Upper Ordovician Arvonia Formation. The aggregate thickness of this metamorphosed sequence is about 21,000 feet. The lower 13,000 feet of strata are composed of paragonitephyllites andchlorite-muscovite- or muscovite-bearing graywackes, subgraywackes, argillites, phyllites, and quartzose phyllites interbedded with minor amounts of greenstone (metabasalt). The upper 8,000 feet of strata consist of a metamorphosed volcanic and sedimentary rock unit and the Arvonia Formation. The sequence was folded into asymmetrical and overturned anti- clines (Rivanna River, Hardware) and synclines (Columbia, Arvonia, Long Island) near the end of Ordovician time, and the granodiorite batholith was intruded between the time of folding and the end of the Devonian Period. All units were subjected to regional metamorphism near the end of the Mississippian Period. In the western portion of Fluvanna County formations are within the greenschist facies, and in the eastern portion formations are within the almandine-amphibolite facies. Metamorphic grade generally increases from west to east across the county; biotite and garnet isograds were mapped. Triassic diabase dikes generally trend northwestward across northeastward-trending Paleozoic structures. The dikes are composed principally of labradorite, pyroxene, and olivine. Stone, talc, asbestos, quartz, garnet, gemstones, iron minerals, vermiculite, sand and gravel, clay, and gold occur within the area. INTRODUCTION LocerroN eNo Srzu oF AREA Fluvanna County includes an area of approximately 282 square miles in the central portion of Virginia (Figure 1). The county lies VrncrNre Drvrsrox oF MTNERAL Rnsouncos between lines of longitude 78"04' and 78"30'W. and lines of latitude 37"42'and 38o01'N. This area is shown on portions of five l5-minute quadrangle maps: Charlottesville, Scottsville, Columbia, Dillwyn and Lakeside Village. Counties bordering 'S'luvanna'are louisa orr .the north, Goochland and Cumberland on the east, Buckingham on the south, and Albemarle on the west. Palmyra, Fork Union, Columbia, and a portion of Scottsville are the towns in the county. The nearest city is Charlottesville, l0 miles to the west. Figure l. Index map showing location of !'luva,nna County. PnnsnNr INvusrrclrtoN The purpose of this report is to describe the rock and mineral resources, and to discuss the geology of the county. J. W' Smith mapped in the eastern portion of the county from June 1960 to Sep- tember 1962 and prepared the major portion of the report. R. C. Milici mapped and sampled the formations in the western portion of Fluvanna County between the period April 1962 and April 1963, and S. S. Greenberg studied the petrography of the formations in the area during this period; they wrote portions of the stratigraphy, structural geology, metamorphism, and geologic history and prepared Appendix I. About 2500 rock samples were collected. One hundred twenty-five thin sections, 2000 X-ray diffraction traces, 8 X-ray spectrographic traces, and several rock slabs were made to study the composition and texture of the samples. The X-ray traces were made on a General Electric XRD-5 direct-recording X-ray diffraction unit. Acrxowr,aocEMENTS During the preparation of this report the Virginia Division of Mineral Resources employed the following persons whose work has Gnor,ocy or Itr,uveNNA CouNTy been incorporated in this report: H. Robert Hopkins, C. T. Spiker, and Clarke Jones mapped in portions of the county; Villard S. Griffin, Jr" -and Richsrd .F. Pharr made a magnetometer survey. William R. Brown of the University of Kentucky visited the writers in the field and contributed many ideas concerning the geology of Fluvanna County. James L. Calver, State Geologist, contributed materially to the improvement of the manuscript. The Rb-Sr and lead-alpha age determinations were obtained through the courtesy of the United States Geological Survey. J. T. Nuckols III of the Solite Corporation, Richmond, Virginia, supplied information and cores that, were collected in Fluvanna Countv in search of highway aggregate. Pnpvrous Wonr Darton (1892), Watson and Powell (1911), Stose and Stose (1948), and Applegate (1955) reported on fossils in the Arvonia slate in Bucking- ham County which extends on strike into Fluvanna County. Extensive petrographic work was done by Taber (1913) in his consideration of the gold belt, and his maps include the eastern half of Fluvanna County; his discussion of gold mining in the area is the most comprehensive to date. Jonas (1927, 1932) mapped the county. Stose and Stose (1948) investigated the structure and stratigraphy of the Arvonia Formation. Brown and Sunderman (1954) mapped the southern half of the county in more detail than previous workers. Brown (1951, 1953, 1962), Espenshade (1954), and Redden (1963, 1964) discussed the stratigraphy and structural geology of the Virginia Piedmont, particularly in the area southwest of Fluvanna County. Four formations are indicated in Fluvanna County on early State geologic maps published by the Virginia Geological Survey (1911, 1916): Precambrian crystalline schist and gneiss, Precambrian granite and granite gneiss, undifferentiated Cambrian, and the Ordovician (Cinn- cinnatian) Arvonia Formation. On the 1928 edition of the "Geologic Map of Virginia" (Virginia Geological Survey) no Cambrian rocks are shown in Fluvanna County, and small areas of hornblende gneiss or hornblende gabbro and aporhyolite are indicated. Cline, Watson, and Wright (1921) mapped two formations in the northeast corner