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

ORIGIN 25
matism in areas extending over tens of square miles
could hardly have been so selective that deposition
of aluminum was vertically restricted to sandstone
beds, only a few feet thick in many places, and nowhere
formed discordant replacement masses in
sandstone or adjacent beds. In addition to the
quartzose rocks, aluminous schists occur in the
Kings Mountain district; the aluminous minerals
are not distributed irregularly through these
schists, but occur in layers that probably represent
the original bedding. If the Al2Si0 5 minerals in
these two districts are the result of aluminum metasomatism,
no evidence whatever remains of the
means by which this pervasive replacement took
place. In both districts, quartz veins and peg­
matites are present, but the Al2Si0 5 minerals are
absent from the pegmatites and are present in the
quartz veins only where these veins cut the highalumina
rocks. In the Kings Mountain district,
quartz veins occur in most of the metamorphic
rocks; a quartz-kyanite vein that cuts kyanite
quartzite at Clubb Mountain is definitely later than
the kyanite quartzite (fig. 25). Pegmatite bodies in
the Kings Mountain district are restricted to the
margin of the Yorkville quartz monzonite, and
show no relation to the distribution of most of the
beds of high-alumina quartzite. Pegmatites are more
widely distributed in the Farmville district; however,
they do not contain kyanite and they are not foliated,
indicating that they are younger than the
well-foliated kyanite (or sillimanite) quartzite.
Tourmaline is very common in many quartz veins
in the Farmville district, and occurs sparingly in
quartz veins in the Kings Mountain district. However,
tourmaline is an extremely rare mineral in the
quartzose high-alumina deposits in these districts,
and kyanite was not found in any of these tourmaline-quartz
veins. Evidently the tourmaline mineralization
had nothing to do with the formation of
kyanite in these two districts. This is in contrast
to the Bhandara district, India, where tourmalinequartz
veins are associated with kyanite deposits;
Chatterjee (1931) has suggested that borates or
boric acid accompanying the tourmaline mineralization
acted as mineralizers to mobilize aluminum
from chlorite-muscovite schists.
Mobilization of aluminum by metamorphic differentiation
or other means in the Farmville and
Kings Mountain districts seems to have been restricted
to the formation of lenticular aggregates of
coarse unoriented kyanite in kyanite quartzite and
minor amounts of kyanite in some quartz veins that
cut kyanite quartzite.
The weight of the evidence seems to us to point
to an origin of these high-alumina quartzites in
both the Farmville and Kings Mountain districts by
the recrystallization of clay-quartz sand sediments.
In the Kings Mountain district, sillimanite was
formed instead of kyanite in the highest temperature
zones near the Yorkville quartz monzonite.
REPLACEMENT DEPOSITS
Quartzose deposits of Al2Si0 5 minerals that seem
to be of replacement origin are the deposits of kyanite-quartz
rock at Hagers Mountain, N.C., the
Corbett property, North Carolina, Little Mountain,
S.C., and Graves Mountain, Ga.; the andalusitepyrophyllite-quartz
deposits of the North Carolina
pyrophyllite belt; and the Brewer mine and Boles
Mountain, S.C. These replacement deposits all occur
in the belt of volcanic flows, tuffs, and slates in the
eastern Piedmont.
These replacement deposits are each made up of
many lenticular segments, which are generally
conformable to the enclosing schists, but which are
partly discordant at Graves Mountain, Ga., and at
the Brewer deposit, South Carolina. This discordance
is one evidence of replacement origin.
Relict minerals or structures of the original rock
are strong evidence of replacement in some deposits.
Large grains of blue quartz, some being well-formed
bipyramidal crystals, are abundant in some of the
kyanite-quartz rock at Graves Mountain (p. 98; fig.
1). They are most likely relict quartz phenocrysts
in an igneous rock that has been almost completely
replaced by silicon and aluminum. At the Brewer
deposit, South Carolina, the original structures of
breccia tuffs and of bedding or foliation are preserved
in silicified rock (Pardee and Park, 1948).
Similar features are found in some of the North
Carolina pyrophyllite deposits (Stuckey, 1928);
masses or lenses of unaltered or only partly altered
country rock are also found in some of these pyrophyllite
deposits.
The quartz that forms the matrix is extremely
fine grained in all these deposits, similar to much
quartz of replacement origin. Silicification was the
first stage of mineralization; the aluminous minerals
vein and replace quartz. Kyanite occurs in
irregular bodies and crosscutting veins in kyanitequartz
rock. Topaz forms irregular masses and networks
of veins in the Brewer deposit; it also occurs
in the Bowlings Mountain deposit, North Carolina.
Pyrophyllite is invariably the latest aluminous mineral;
it replaces quartz, kyanite, andalusite, diaspore,
and topaz (figs. 17,18,19).