Kyanite, Sillimanite, and Andalusite Deposits of the Southeastern ...

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KYANITE DEPOSITS 37 BAKER MOUNTAIN- MADISONVILLE AREA Symbol f q hg qt kq ks ms bg EXPLANATION UNMETAMORPHOSED ROCKS Red conglomerate, sandstone, and shale with coal beds (exposed just east of area mapped near Willis Mountain) UNCONFORMITY Pegmatite Biotite-quartz syenite METAMORPHOSED ROCKS Present character Graphitic schist WILLIS MOUNTAIN- WOODS MOUNTAIN AREA Probable original nature Siliceous black shale UNCONFORMITY Garnet-quartz rock with Thin layers of sandy and abundant amphibole (anthophyllite, actinolite) clayey dolomite in basaltic flows Ferruginous quartz rock (contains magnetite and hematite) Hornblende gneiss and schist, commonly -garnetif erous Quartzite Kyanite quartzite Kyanite-quartz-mica schist Muscovite-quartz schist Biotite-quartz-feldspar gneiss, commonly garnetif erous Ferruginous chert beds in basaltic flows Basaltic or andesitic lava flows Sandstone Clay-bearing sandstone Shale with high clay content Shale, or silicic volcanic rocks Graywacke Age TRIASS ORDOVICIANf?) ORDOVICIANt?) YOUNGER OR FIGURE 28. Diagrammatic sections of sequence of formations in the Farmville district, Virginia. The chemical composition of the biotite gneiss (discussed below) suggests that the parent rock was probably a graywacke (Pettijohn, 1949, p. 250). The character of the hornblende gneiss indicates that it was a basaltic or andesitic lava poured out at irregular intervals during deposition of the thick series of graywacke. The distribution pattern of the kyanite quartzite is that of a folded sedimentary formation; it was probably originally a clay-bearing sandstone. The biotite gneiss closely resembles and is possibly correlative with the Lynchburg gneiss of Precambrian(?) age, which is widely distributed in a northeast-trending belt about 30 miles to the west (Furcron, 1935; Jonas and Stose, 1939; Brown and Sunderman, 1954; Espenshade, 1954). The hornblende gneiss may be equivalent to the basalt flows of the Catoctin formation occurring above the Lynchburg gneiss on the flanks of the Catoctin-Blue Ridge anticlinorium. The Catoctin may be late Precambrian or early Cambrian in age (Bloomer and Werner, 1955; Reed, 1955). No rocks similar to the kyanite quartzite are known in the Lynchburg gneiss or Catoctin formation. Most of the areas mapped as biotite gneiss on plates 2 and 3 were mapped by Jonas (1932) as the Wissahickon formation of Precambrian age; however, some areas of biotite gneiss were mapped as granodiorite. Jonas mapped the kyanite quartzite as a separate unit in the Wissahickon formation. BIOTITE GNEISS The biotite gneiss is typically a gray rather finegrained gneiss made up largely of quartz, feldspar, and tiny flakes of black biotite. The rock generally has a finely banded gneissic structure and a pronounced lineation formed by elongated biotite flakes. At a few localities the minerals are coarse grained and the rock resembles somewhat a granitic gneiss. Coarse gneiss in the core of the Whispering Creek anticline, about 3 miles southeast of Dillwyn, was considered by Taber (1913, p. 80-82) to be granite and was mapped as granodiorite by Jonas (1932, pi. 2). Chemical and spectrochemical analyses of two samples of the biotite gneiss are given in table 6. Plagioclase, whose composition is generally about An20-3o, is the most abundant feldspar and the only variety present in some of the specimens examined. Microcline also occurs in some of the rock; it is in both of the analyzed specimens (table 6). Biotite is an abundant mineral; in some places it is altered slightly to chlorite. Epidote is commonly associated with biotite; it is an abundant constituent
38 KYANITE, SILLIMANITE, AND ANDALUSITE DEPOSITS, SOUTHEASTERN UNITED STATES in specimen VPE 102, containing 4.31 percent CaO (table 6), but is absent in specimen VB 118, containing 1.91 percent CaO. Garnet, in small crystals 1 to 2 mm across, is present in much of the gneiss. Muscovite is rather common, and hornblende is found in small amounts in some places. Minor accessory minerals are calcite, apatite, pyrite, sphene, rutile, and zircon. Biotite gneiss is widely exposed in the region. The greatest thickness of biotite gneiss lies beneath the kyanite quartzite, as in the core of the Whispering Creek anticline, at Woods Mountain, and north of Baker Mountain. Biotite gneiss also occurs at several horizons above the kyanite quartzite. The biotite gneiss is probably a metamorphosed sedimentary rock because it seems to occur most abundantly at a definite stratigraphic position and because it nowhere shows intrusive relations. Its chemical composition suggests that it was originally graywacke. MUSCOVITE-QUARTZ SCHIST AND GNEISS Muscovite-quartz schist and gneiss are commonly light gray and rather coarse grained; the muscovite flakes are 3 mm or larger. Plagioclase (An 5_15 ) and microcline are present in some of the more gneissic varieties. A little garnet and kyanite are found at some localities. The more common accessory minerals are tourmaline, magnetite, pyrite, apatite, and zircon. The rock is well foliated; elongated muscovite flakes are arranged in linear orientation. Muscovite-quartz schist and gneiss are exposed most extensively in the Baker Mountain-Madisonville area (pi. 3) to the south of, and structurally above (as well as stratigraphically above?), the kyanite quartzite. Thin layers of muscovite schist and gneiss are interbedded in the thick biotite gneiss series in the Willis Mountain-Woods Mountain area. The muscovite-quartz schists were probably shales or silicic volcanic rocks originally. KYANITE SCHIST Garnetiferous mica schist containing about 5 percent kyanite is exposed beneath kyanite quartzite at the south end of Willis Mountain and east of the Baker Mountain kyanite deposit. The foliation of the schist is closely crinkled, and kyanite, biotite, and muscovite are arranged in linear orientation parallel to the crinkles. Quartz and plagioclase (generally An25_3 5 ) are the other essential constituents. Biotite is replaced to a minor extent by chlorite. A little staurolite occurs locally. Kyanite schist may be rather widespread beneath kyanite quartzite in TABLE 6. Chemical and spectrochemical analyses of biotite gneiss and hornblende gneiss from Farmville district, Virginia Si0 2............. AlsOs. ........... Fe 80............. FeO ............. MgO...... ....... CaO ............. Na 2O ............ K 2O. ............ H 20- ........... H 20+........... Ti0 8............. C0 2............. P 20 5...... ....... F.... ............ MnO ............ Total .......... Less O for F .... Total .......... Chemical analyses [L. D. Trumbull, analyst] Biotite-quartz-feldspar gneiss VPE 102 64.85 14.86 2.31 3.70 2.03 4.31 3.44 2.58 .07 .84 .68 .01 .14 .04 .14 100.00 .02 99.98 VB 118 68.06 14.54 .91 3.92 2.53 1.91 3.02 3.07 .08 1.02 .58 .00 .13 .05 .09 99.91 .02 99.89 Garnet-hornblende gneiss VB 111 50.45 15.19 3.63 8.79 5.49 8.58 3.98 .10 .05 1.11 1.68 .39 .16 .03 .25 99.88 .01 99.87 VB 112 51.66 15.27 5.39 7.16 3.90 12.01 1.58 .08 .04 1.40 1.11 .01 .13 .01 .31 100.06 .00 100.06 Spectrochemical analyses [P. R. Barnett, analyst. Zeros in unit colum signify that the elements were not detected ; sensitivity limits for these elements are: B, 0.003 ; La, 0.005 ; Mo, 0.0001 ; and Zn 0.01. Elements not detected in any of the samples, together with their sensitivity limits, are: Ag, 0.0005 ; As, 0.05 ; Au, 0.003 ; Be, 0.0001 ; Bi, 0.001 ; Cd, 0.005; Ge, 0.0005; In, 0.001 ; Nb, 0.001; Pt, 0.003 ; Sb, 0.01 ; Sn, 0.001 ; Ta, 0.05 ; Th, 0.05 ; Tl, 0.01 ; U, 0.05 ; and W, 0.01] B. ...... ......... Ba............... Co............... Cr... ............ Cu .............. Ga.............. Mo.............. Ni............... Pb............... Sc............... Sr. .............. V.......... ...... Y. .............. Yb .............. Zn............... Zr............... 0 .09 .002 .0008 .0006 .002 .005 0 .0004 .002 .004 .2 .02 .007 .0005 .01 .02 0 0 .07 .005 .001 .003 .002 .003 .0007 .004 .001 .002 .003 0 .0006 0 .0009 .002 .001 .001 .0007 .009 .1 .1 .008 .05 .004 .01 .0004 .0007 0 .03 .02 .01 0.001 .002 .004 .0005 .002 .002 0 0 .001 .002 .008 .3 .07 .006 .0005 .02 .005 Location of samples: VPE 102, Lab. No. 53-831SCD. Outcrop in stream about 1 mile east of Baker Mountain, Prince Edward County, Va. VB 118, Lab. No. 53-832SCD. Large ledges just east of Willis River, 2 miles N. 31° W. from Curdsville, Buckingham County, Va. VB 111, Lab. No. 53-833SCD. Medium-grained variety of garnet-hornblende gneiss from outcrop just below Arcanum dam on Willis River, Buckingham County, Va. VB 112, Lab. No. 53-834SCD. Fine-grained variety of garnet-hornblende gneiss from outcrop just below Arcanum dam on Willis River, Buckingham County, Va. the region, but exposures are few. Ledges of similar kyanite-bearing schist are exposed along Virginia Highway 626 at Falling Creek, Prince Edward County (fig. 27).
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Page 3 and 4: UNITED STATES DEPARTMENT OF THE INT
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