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

66 KYANITE, SILLIMANITE, AND ANDALUSITE DEPOSITS, SOUTHEASTERN UNITED STATES
eral, tightly compressed northeast-trending isoclinal
folds with steeply dipping axial planes distinguish
this belt from more open folds to the
west. The Yorkville quartz monzonite was emplaced
into the rocks along the east side of the belt in
Early Mississippian(?) time. The age of the metamorphic
rocks is not certain. The lowest rank
metamorphism in this part of the Piedmont is recorded
in some of these rocks, yet near the Yorkville
quartz monzonite the rocks are strongly deformed
and highly metamorphosed, indicating that the sedimentary
and igneous rocks in the belt were formed
before Mississippian time. Some structural and
mineralogical evidence (see "Structure" and "Metamorphism")
can be interpreted as indicating that
these rocks are older than a far-reaching Ordovician
orogeny that metamorphosed the rocks to the west
(Overstreet and Griffitts, 1955). Diabase dikes of
Triassic age cut all the rocks in the belt.
The Crowders Mountain-Henry Knob area is
situated about midway north and south, on the east
side of this belt, in a zone involving two major converging
structures: the northeast-trending belt of
metamorphic rocks and the north-trending contact
of the Yorkville quartz monzonite (fig. 41; pi. 7).
Except for marble, all the metamorphic rock types
characteristic of the belt are found in the Crowders
Mountain-Henry Knob area.
The metamorphic rocks of the Reese Mountain-
Clubb Mountain area, on the east side of the Yorkville
quartz monzonite, are probably a continuation
of a part of the belt of metamorphic rocks of the
Crowders Mountain-Henry Knob area.
Two large plunging folds are suggested by the
distribution of beds of manganiferous schist and
high-alumina quartzite in the Crowders Mountain-
Henry Knob area (fig. 42). These folds are here
named the Sherrars Gap syncline, after Sherrars
Gap on the east limb of this fold, and the South
Fork anticline, after the South Fork of Crowders
Creek and its northern tributary, which drain the
central part of the area. Primary sedimentary and
volcanic textures and structures are evident in some
of the rocks in the western part of the area, but,
as very few primary features diagnostic of tops
and bottoms of beds were found, the anticlinal and
synclinal nature of the folds is not well established.
The rocks exhibit a marked increase in grade of
metamorphism from the greenschist and albite-epidote
amphibolite facies (Turner, 1948) in the western
part of the Crowders Mountain-Henry Knob
area to the higher subfacies of the amphibolite
facies in the eastern part of the area near the Yorkville
quartz monzonite (fig. 42). The only pegmatite
bodies in the area are within the main body of
the Yorkville quartz monzonite and in the metamorphic
rocks within about 2,000 feet of the quartz
monzonite contact. Pegmatite bodies are somewhat
more abundant in the metamorphic rocks of
the Reese Mountain-Clubb Mountain area.
The interstream areas in the Kings Mountain district
define a gently sloping surface of low relief
whose altitude is between 750 and 950 feet. In
the Crowders Mountain-Henry Knob area several
long hills and ridges rise abruptly 100 to 800 feet
above this surface. Some of these hills, such as
Crowders Mountain, The Pinnacle, and the north
end of Kings Mountain, are prominent regional
landmarks. Henry Knob is an isolated hill in the
southeastern part of the area. In the Reese Mountain-Clubb
Mountain area the hills and ridges are
lower, and the maximum relief is 150 feet.
Most of the prominent hills in the district are underlain
by kyanite quartzite, fine-grained quartz
schist, schistose conglomerate, and sillimanite
quartzite. The trend and extent of the kyanite
quartzite beds are accurately indicated by the size
and shape of the hills. The crests of these hills are
usually craggy, precipitous cliffs are common, and
the slopes are heavily mantled with talus of kyanite
quartzite. The hills underlain by sillimanite
quartzite are generally lower and shorter than the
ridges underlain by kyanite quartzite.
ROCK TYPES
STRATIGRAPHY
The stratigraphic order of the metamorphic rocks
in the district is not well known but is inferred
from the somewhat poorly established major folds
in the Crowders Mountain-Henry Knob area. The
best clues to the stratigraphy and structure are the
beds of manganiferous schist, kyanite quartzite, and
sillimanite quartzite (fig. 42; pi. 7). Two major
folds, the South Fork anticline and the Sherrars
Gap syncline, are suggested by the distribution of
these marker beds, but the anticlinal and synclinal
nature of the folds is not well established because
of the paucity of primary sedimentary structures.
Questionable crossbedding in quartzite on the
northwest side of Lake Montonio, 1 mile southwest
of The Pinnacle, and graded bedding in a thick
bed of schistose conglomerate on Yellow Ridge indicate
the tops of the beds face southeast and that
these beds are on the northwest limb of a synclinal
fold (the Sherrars Gap syncline). The axial plane
of the southwestern half of this fold dips steeply