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

More documents

Recommendations

Info

KYANITE DEPOSITS 35 EXPLANATION Kyanite deposits 3? Kyanite mine 1. North end, East Willis Ridge 2. South end, East Willis Ridge 3. Willis Mountain (main ridge) 4. Willis Mountain (Round Mountain) 5. Carwile property 6. Woods Mountain 7. Falling Creek 8. Baker Mountain 9. Madisonville 10. Leigh Mountain 11. Southern Prince Edwards County Area mapped geologically FIGURE 27. Index map of kyanite deposits in Farmville district, Buckingham, Charlotte, and Prince Edward Counties, Va.
36 KYANITE, SILLIMANITE, AND ANDALUSITE DEPOSITS, SOUTHEASTERN UNITED STATES to the west were recently mapped by Brown and Sunderman (1954). GENERAL GEOLOGY The principal rocks in this part of the Piedmont metamorphic belt include several varieties of mica schist and gneiss, hornblende gneiss, and kyanite quartzite, all of probable Precambrian age. Pegmatites and quartz veins are abundant. Bodies of granite occur to the north and east but not in the vicinity of the kyanite deposits. Slate of Ordovician age occurs in a narrow north-trending syncline at Arvonia, a few miles north of the district; the southern end of this syncline may extend into the mapped area. Conglomerate, sandstone, shale, and coal beds of Triassic age occur in a basin about 15 miles long just east of the northern part of the mapped area. Diabase dikes of Triassic age cut all rock formations in the region. The rocks of pre-Triassic age have been highly deformed and metamorphosed. The trends of the rock formations and the foliation are variable because of complex folding, but in general lie between north and east. The grade of metamorphism is uniform, and belongs to the amphibolite facies (Turner, 1948, p. 76-88), as exemplified by such assemblages as biotite-oligoclase-quartz (with epidote-garnet in places) and hornblende-oligoclase or andesinequartz (with biotite-epidote-garnet locally). Erosion since Triassic time has produced a gently rolling- surface and deep weathering of the underlying rocks. The highly resistant beds of kyanite quartzite form ridges and knobs (Willis Mountain and neighboring ridges, and Woods, Baker, and Leigh Mountains) that rise 100 to 500 feet above the general peneplain surface. ROCK TYPES STRATIGRAPHY The dominant rocks in the mapped area are biotite gneiss, hornblende gneiss, and muscovite-quartz schist (pis. 2, 3). Kyanite quartzite is a distinctive rock that forms conspicuous outcrops but underlies only a small part of the entire district. The thickness of kyanite quartzite is less than 40 feet at most places, and exceeds 50 feet only at Willis and Baker Mountains. Garnetiferous kyanite schist is exposed beneath kyanite quartzite at several localities. Thinner and less extensive rock units in the metamorphic series are quartzite, ferruginous quartz rock, and garnet-quartz rock. These rocks are probably late Precambrian. The graphitic schist exposed in the headwaters of Whispering Creek (pi. 2) probably is in the southern extension of the syncline of Arvonia slate of Late Ordovician age. The Ordovician age for the Arvonia slate was originally assigned to fossils found in one of the slate quarries at Arvonia (Darton, 1892; Watson and Powell, 1911); Stose and Stose (1948) have recently questioned this age determination, and suggest that these slates may be Silurian. Igneous rocks intruding the metamorphic series are pegmatite, biotite-quartz syenite, a few thin dikes of aplite, and diabase. Small bodies of pegmatite occur throughout the region; biotite-quartz syenite is known only at three localities at the northern end of the district. The pegmatites and syenite may be Ordovician or later Paleozoic in age. Diabase dikes of Triassic age cut the metamorphic rocks of the mapped area and the Triassic sedimentary rocks to the east. Quartz veins are widely distributed in the metamorphic rocks; some veins contain abundant tourmaline. The key to the stratigraphic order of the metamorphic series is found in a large anticline lying east and northeast of Willis Mountain. Biotite gneiss is the major rock type exposed in the core of this anticline (herein called the Whispering Creek anticline); kyanite quartzite lies on both flanks of the fold (pi. 2). This thick sequence of biotite gneiss, containing a few thin layers of hornblende gneiss, is evidently older than the kyanite quartzite. Biotite gneiss also lies beneath kyanite quartzite in an anticline at Woods Mountain, and is exposed to the north of (and stratigraphically beneath?) kyanite quartzite at Baker Mountain (pi. 3). In the Whispering Creek anticline, a thin sequence of biotite gneiss lies just above the kyanite quartzite, and is overlain by a thick series of hornblende gneiss. In the anticline at Woods Mountain, hornblende gneiss appears to lie directly above kyanite quartzite. In the Baker Mountain area, the thickest sequence of hornblende gneiss seems to be just below the kyanite quartzite horizon, but some hornblende gneiss lies above the quartzite, and is overlain by muscovite-quartz schist. The similarity, though not strict identity, of the apparent stratigraphic order in the different parts of the district strongly suggests that the thick series of biotite gneiss is the oldest formation. Kyanite quartzite occurs in the upper part of the biotite gneiss, and is overlain by hornblende gneiss in the Willis Mountain-Woods Mountain area and by muscovite schist in the Baker Mountain-Madisonville area. This interpretation of the stratigraphic order is shown diagrammatically in figure 28.
Page 1 and 2: Kyanite, Sillimanite, and Andalusit
Page 3 and 4: UNITED STATES DEPARTMENT OF THE INT
Page 5 and 6: IV Page Kyanite deposits Continued
Page 7 and 8: VI CONTENTS TABLES TABLE 1. Major d
Page 9 and 10: KYANITE, SILLIMANITE, AND ANDALUSIT
Page 15 and 16: 8 KYANITE, SILLIMANITE, AND ANDALUS
Page 17 and 18: Type of mica Muscovite . . . Do....
Page 19 and 20: 12 KYANITE, SILLIMANITE, AND ANDALU
Page 41: 34 KYANITE, SILLIMANITE, AND ANDALU
Page 93 and 94:
86 KYANITE, SILLIMANITE, AND ANDALU
Page 95 and 96:
KYANITE, SILLIMANITE, AND ANDALUSIT
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
100 KYANITE, SILLIMANITE, AND ANDAL
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
120 KYANITE, SILLIMANITE. AND ANDAL
show all

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

Create successful ePaper yourself

Delete template?

Save as template?