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

KYANITE DEPOSITS 45
anticline, kyanite quartzite is exposed for a distance
that is less than half its length of exposure on the
east limb, but the outcrop width is considerably
wider on the west limb and the ridge is much more
prominent. The principal belt of kyanite quartzite
on the west extends for about 2y% miles north from
the south nose of the anticline and consists of several
discontinuous segments (pis. 2, 4). The longest
segment of kyanite quartzite forms Willis Mountain,
a ridge about 1^4 miles long that rises over 500
feet above the surrounding countryside and makes
the most conspicuous landmark in this part of the
Virginia Piedmont. Steep cliffs of kyanite quartzite
from 100 to 150 feet high form the upper part of
the mountain along most of its length; the lower
slopes are mantled with talus containing large blocks
of kyanite quartzite. Round Mountain, a ridge about
1,500 feet long and having cliffs up to 100 feet high,
is formed by a body of kyanite quartzite whose
northern end is about one-third of a mile south of
Willis Mountain. At the northern end of Round
Mountain and the southern end of Willis Mountain
kyanite quartzite is exposed in oppositely curved
belts formed by a syncline whose axis reverses its
direction of plunge between these ridges and
plunges gently northward along Willis Mountain
and southward along Round Mountain (pi. 2). Kyanite
quartzite on the west limb of each syncline is
exposed for only short distances, the probable extensions
to the north and south being covered by
heavy talus from the main ridges. Probably the
kyanite quartzite in the west limb of the synclines
beneath the talus-covered areas either becomes very
thin or is cut out by steep thrust faulting; both
inferences are shown on plate 2.
There is considerable close folding (fig. 30) on
the east limb of the syncline (west limb of the
Whispering Creek anticline), and the shapes and
widths of the kyanite quartzite exposures on Willis
Mountain are probably related to this folding. The
hook-shaped segment at the south end of Willis
Mountain lies several hundred feet to the west of
the main ridge. This offset probably was caused
by folding or faulting, or possibly both; northplunging
folds have been assumed here on plate 2,
section A-A'.
Along the high part of Willis Mountain north of
this gap, kyanite quartzite is exposed over widths of
between 200 and 300 feet for a distance of about
2,000 feet; this part of the ridge trends N. 5° to
10° E. (pi. 4). For about 3,000 feet farther northeast,
the ridge declines gently in elevation, and the
quartzite outcrop becomes narrower, ranging be-
FIGURE 30. Minor folds and pitted weathering in kyanite quartzite near south
end of Willis Mountain. View looking north in direction of plunge of fold
axes.
tween 100 and 150 feet; the trend of the ridge
changes rather abruptly to N. 15° to 20° E. The
kyanite quartzite beds in the widest and highest
part of the ridge have been thickened considerably
by drag folds; such folds may be few or absent in
the lower and narrower part of the ridge to the
north.
A thin diabase dike has been inferred to cut
through the gap between these two segments of
kyanite quartzite (pi. 2). This inference is supported
by the facts that the gap is about 3,000 feet
northwest along the strike from an exposed diabase
dike, and that a diabase boulder was found on the
west slope of Willis Mountain a few hundred feet
below the gap; diabase crops out along a creek
about 1 mile northwest from the gap along this
trend. Diabase has been exposed on the west side
of the gap by recent mining operations.
Short thin bodies of kyanite quartzite and schist,
and quartzite that is nearly barren of kyanite,
occur on the south nose of the Whispering Creek
anticline (pi. 2). These isolated segments may be
the remnants of formerly continuous beds that have