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

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GEOLOGY OF THE DEPOSITS 13 mens from 2 other localities (SA-2 and VB-116a, table 4), but the fine-grained mica from 4 localities was identified as muscovite (VB-115, NP-15, VC- 27b, and SY-2a, table 4), and as margarite from 1 locality (VB-116b, table 4). It is interesting that fine-grained paragonite (NP-24) and muscovite (NP-15) both occur at Hagers Mountain, and finegrained muscovite (VB-115), paragonite (VB- 116a), and margarite (VB-116b) all occur at the same locality on Willis River in Buckingham County, Va. Chemical analyses of the two fine-grained micas at Hagers Mountain are given in table 5. Three samples of flake mica all proved to be muscovite (VB-W19-22, SN-5, VPE-101). Samples of green mica from three localities, both coarse- (VPE-101) and fine-grained (VC-27b and SY-2a), were determined as chromian varieties of muscovite. Dietrich (1956) describes paragonite from kyanite veins at a locality in Campbell County, Va., and another in Franklin County, Va. Fine-grained micas replace kyanite at several localities (figs. 9, 10, 11). Formation of these finegrained micas probably took place in the declining stages of metamorphism. Hydrothermal clay minerals occur in some abundance in kyanite quartzite in parts of the Crowders Mountain and Clubb Mountain deposits and in minor amounts at Willis Mountain and several other deposits. The clay mineral at Crowders Mountain is dickite ;2 both dickite and kaolinite occur at Willis Mountain.3 The clay minerals vein and replace both kyanite and quartz (fig. 11). Dickite replaces diaspore and kyanite at Willis Mountain (fig. 12). TABLE 5. Chemical analyses of paragonite and muscovite from Hagers Mountain, Person County, N.C. SiO 2.............. A1 20 S............. Fe 20 s............. FeO........ ....... MgO.............. CaO............... Na 2O ............. K 20.............. H 20.............. H 20+............ Ti0 2.............. C0t .. ............. P&s ... ........... F. ................ MnO.............. BaO .............. Total..... . .. Less O for F. . Total..... ... [Lucille M. Kehl, analyst] Paragonite Muscovite (NP-24) (NP-15) (Lab. No. 52-1678CDMW) (Lab. No. 52-1679CDMW) 46.78 38.99 .44 .01 .00 .12 5.10 3.05 .14 4.80 .11 .01 .09 .05 .00 .07 99.76 .02 99.74 46.55 36.97 .74 .10 .15 .00 1.90 8.33 .06 4.28 .36 .04 .06 .06 .00 .19 99.79 .03 99.76 Samples were prepared for chemical analysis by Donald H. Richter, who also determined the following optical properties: N« Nfl N7 . ................ (-)2V............. N T-N«............ 1.572 1.595 1.602 38° .030 1.570 1.593 1.599 36° .029 FIGURE 9. Photomicrograph of kyanite-paragonite rock from Hagers Mountain, Person County, N.C. Shows kyanite (k) veined and partly replaced by fine-grained paragonite (pa) and minor amount of'clay mineral (cl). Plane-polarized light. Pyrophyllite is most abundant in the nonfoliated kyanite-quartz deposits. It is common in veins and masses of radiating crystals at two of the nonfoliated deposits (Corbett deposit, North Carolina, and Graves Mountain, Ga.), and also in the southern part of the foliated deposit at Clubb Mountain, N.C. Pyrophyllite seems to replace kyanite and quartz in the same manner as the clay minerals and the fine-grained micas do. Fine grains of topaz occur locally in very small amounts in several of the foliated deposits. It is rather abundant in parts of the nonfoliated deposit at the Corbett property (fig. 13). The iron-aluminum phosphate lazulite, is common as large dark-blue crystals with pyrophyllite and quartz at Clubb Mountain and with kyanite at Graves Mountain, two well-known localities for this mineral. Other aluminum phosphate minerals found in minor amounts are the strontium-aluminum phos- 2 Identified by R. L. Smith. 3 Identified by X-ray determination by F. A. Hildebrand and electron microscopy by C. P. Da vis and E. J. Dwornik.
14 KYANITE, SILLIMANITE, AND ANDALUSITE DEPOSITS, SOUTHEASTERN UNITED STATES very rare occurrence are corundum, diaspore (fig. 12), sillimanite, and zunyite. Other accessory minerals are listed in table 2. SIULJMANITE-QUAKTZ DEPOSITS Deposits of sillimanite-quartz rock have been found only in the Kings Mountain district, North FIGURE 10. Photomicrograph of kyanite quartzite, from about 0.3 mile west of Madisonville, Charlotte County, Va. Shows characteristic gneissic structure, with kyanite (k) partly replaced by finely fibrous chromian muscovite (m.); quartz (q), rutile (r), limonite (1), holes in section (h). Planepolarized light. phate goyazite, at Clubb and Crowders Mountains; the calcium-aluminum phosphate crandallite, at Clubb Mountain; and the aluminum phosphate variscite found in one thin stringer in drill core from Willis Mountain. FIGURE 12. Photomicrograph of kyanite (k) and diaspore (d) veined by dickite (di), Willis Mountain, Buckingham County, Va. Rutile (r) ; hole in section (h). Plane-polarized light. Carolina-South Carolina. Their structure and petrography are discussed but briefly here, because they are described more fully in the section on the Kings Mountain district. The sillimanite quartzite deposits are relatively small; most of them are between 10 and 30 feet FIGURE 11. Photomicrograph of kyanite quartzite cut by clay veinlets, from diamond-drill hole 6 (at 116 ft), Willis Mountain, Buckingham County, Va. Shows kyanite (k), and quartz (q) veined by clay mineral (cl). Rutile (r). Two types of clay have been identified in specimen by X-ray and electron microscope: (1) dickite and (2) kaolinite and (or) hallosyite. Holes in section (h). Plane-polarized light. Other aluminous minerals in kyanite-quartz rock (found in moderate amounts in several deposits in the Kings Mountain district) are chloritoid (fig. 14), staurolite, and andalusite. Aluminous minerals of FIGURE 13. Photomicrograph of topaz (to) and kyanite (k) in fine-grained quartz (q), from Corbett deposit, about 5 miles west of Smithfield, Johnston County, N.C. Rutile (r). Specimen contains about 70 percent quartz, 20 percent topaz, and 10 percent kyanite. Plane-polarized light.
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