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

KYANITE, SILLIMANITE, AND ANDALUSITE DEPOSITS, SOUTHEASTERN UNITED STATES
Well-developed foliation (fig. 48) is parallel to
bedding, and, in general, dips steeply and conforms
to the shape of the quartzite outcrop. This is particularly
true at the south end of the deposit.
Small randomly oriented folds, with amplitude
and wave length from 1 to 15 feet, are abundant
throughout the kyanite quartzite of this deposit.
The gently plunging and horizontal small fold axes
in the high southern half of the mountain (fig. 52)
suggest that the anticlinal axis there may be virtually
horizontal. The northern half of the mountain,
lying some 150 to 200 feet below the summit,
is underlain by chloritoid schist which is surrounded
by kyanite quartzite. In the northern half
of the deposit, linear elements in kyanite quartzite
plunge inward towards the enclosed chloritoid
schist, suggesting that the quartzite beds converge
at depth.
Figure 52 shows that the kyanite content is
highly variable throughout the deposit. The boundaries
between quartzite containing 5 to 30 percent
kyanite and quartzite containing 0 to 5 percent kyanite
are not well defined. The largest concentration
of kyanite is at the northeast end of the
deposit where kyanite seems to constitute more
than 20 percent of the rock.
Kyanite quartzite at The Pinnacle contains abundant
limonite. At some places limonite forms a
hard outer rind which promotes cavernous weathering
of softer rock beneath. Most of the limonite
was derived from the weathering of small disseminated
crystals of pyrite.
Thin-section study of kyanite quartzite from this
deposit indicates that kyanite occurs as subhedral
to irregular anhedral crystals. Individual blades or
grains of kyanite hold few quartz inclusions, but
generally have irregular contacts with quartz; not
uncommonly the kyanite blades are bent, fractured,
and faulted. Some lenticular bands of coarsegrained
quartz in the groundmass may represent
highly flattened quartzite pebbles. Accessory minerals
include white mica, pyrite, magnetite, rutile,
zircon, and apatite.
CHOWDERS MOUNTAIN
Crowders Mountain, located in the northern part
of the Crowders Mountain-Henry Knob area and
about 4 miles east of the city of Kings Mountain, is
a long high craggy ridge. The relief ranges from
about 25 feet at the south end of the ridge where
the kyanite quartzite outcrop is narrow (pi. 7; fig.
42) to about 750 feet at the middle of the ridge
where the quartzite outcrop is widest. The shape
of the ridge is accurately shown by the shape of the
quartzite outcrop. The north nose of Crowders
Mountain has a relief of about 550 feet. Sheer cliffs,
100 to 150 feet high, occur along the east and west
side of the mountain north of the radio tower.
Two principal types of quartzite are interlayered
at Crowders Mountain, kyanite quartzite and massive
ferruginous quartzite with generally only minor
amounts of high-aluminous minerals. The individual
outcrops have a northerly strike and very
steep dip, and are intensely folded. The amplitude
and wave length of these folds range from a few
inches (fig. 47) to several hundred feet. In the southern
half of the mountain the small fold axes and
kyanite blades plunge consistently to the south;
throughout the northern part most linear elements
plunge to the south, but some plunge north and
some are horizontal.
As the overall structure of the quartzites in the
vicinity of Crowders Mountain is not well known,
two structural interpretations are given. Both interpretations
assume that the thick quartzite outcrops
mark the approximate position of the nose of
the north-plunging South Fork anticline.
Interpretation 1 (pi. 7) presupposes that the
quartzite outcrops represent a single quartzite bed
repeated by faulting and folding. These folds,
steeply plunging anticlines and synclines with
nearly vertical axial planes, were presumably superposed
on the South Fork anticline.
Brecciated schist, cemented with limonite, occurs
at the north end of Crowders Mountain along the
fault that borders the mountain on the east.
Shear zones occur in the zone of dickite alteration
on the east side of the mountain and along the
fault one-quarter mile west of the radio tower.
Interpretation 2 presupposes the presence of
three quartzite beds at different stratigraphic positions
(fig. 42). Bed A, the oldest, crops out at the
Shelton property and along a low ridge southwest
of the Lawton barite mine; bed B crops out about
one-half mile west of the Shelton property and constitutes
the main thick outcrops in the southern
and central part of Crowders Mountain; bed C is
represented by the long lenses of kyanite quartzite
in the northern part of the mountain.
Most of the quartzite exposed in the central and
southern parts of Crowders Mountain is a massive
gray ferruginous quartzite with little or no kyanite.
Magnetite and staurolite are locally very abundant
in this rock. Two thin sections of the staurolitic
quartzite have the following estimated modal range: