Pyrophyllite deposits in North Carolina

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Norih ouroiina Stare Library
Raleigh
North Carolina jyj e Q,
Department of Conservation and Development
Dan E. Stewart, Director
Doc.
Division of Mineral Resources
Stephen G. Conrad, State Geologist
Bulletin 80
Pyrophyllite Deposits
in North Carolina
by
Jasper L. Stuckey
Raleigh
1967
Digitized by the Internet Archive
in 2013
http://archive.org/details/pyrophyllitedepo1967stuc
North Carolina
Department of Conservation and Development
Dan E. Stewart, Director
Division of Mineral Resources
Stephen G. Conrad, State Geologist
Bulletin 80
Pyrophyllite Deposits
in North Carolina
by
Jasper L. Stuckey
Raleigh
1967
MEMBERS OF THE BOARD
OF CONSERVATION AND DEVELOPMENT
James W. York, Chairman Raleigh
R. Patrick Spangler, First Vice Chairman Shelby
William P. Saunders, Second Vice Chairman Southern Pines
John M. Akers Gastonia
John K. Barrow, Jr. Ahoskie
J. 0. Bishop Rocky Mount
David Blanton Marion
Harry D. Blomberg Asheville
Robert E. Bryan Goldsboro
William B. Carter Washington
Arthur G. Corpening, Jr. . High Point
Moncie L. Daniels, Jr. Manteo
Koy E. Dawkins Monroe
Dr. J. A. Gill Elizabeth City
John Harden . Greensboro
Gilliam K. Horton Wilmington
Dr. Henry W. Jordan Cedar Falls
Petro Kulynych Wilkesboro
William H. Maynard Lenoir
W. H. McDonald Tryon
Jack Pait Lumberton
John A. Parris, Jr. Sylva
Oscar J. Sikes, Jr. Albemarle
T. Max Watson Spindale
11
LETTER OF TRANSMITTAL
Raleigh, North Carolina
March 1, 1967
To His Excellency, HONORABLE DAN K. MOORE
Governor of North Carolina
Sir:
I have the honor to submit herewith manuscript for publication as
Bulletin 80, "Pyrophyllite Deposits in North Carolina," by Jasper L.
Stuckey.
This report contains detailed information on the occurrence, distri-bution
and geology of pyrophyllite in North Carolina and should prove
to be of considerable value to those interested in the mining and
processing of this valuable mineral resource.
Respectfully submitted,
DAN E. STEWART
Director
m
CONTENTS
Page
Abstract 1
Introduction 1
Previous work 1
Geology of the Carolina Slate belt 4
General statement 4
Distribution and character of the rocks 4
Felsic volcanic rocks 5
Mafic volcanic rocks 6
Bedded argillites (volcanic slate) 6
Igneous intrusive rocks 7
Environment of deposition 7
Structural features 7
Age of the rocks 8
Geology of the pyrophyllite deposits 9
Introduction 9
Distribution 10
Geologic relations 11
Form and structure 11
Mineralogy of the deposits 12
Pyrophyllite 12
Quartz 12
Sericite 12
Chloritoid 12
Pyrite 13
Chlorite 13
Feldspar 13
Iron oxides 13
High alumina minerals 13
Petrography 13
Origin of the pyrophyllite deposits 14
Earlier theories 14
Analyses of rocks 16
Origin of North Carolina pyrophyllite 18
Source of mineralizing solutions 18
Conditions of pyrophyllite formation 19
Reserves 19
Mining methods 20
Processing 21
Uses of pyrophyllite 21
Mines and prospects 23
Granville County 23
Daniels Mountain 23
Bowlings Mountain 23
IV
Long Mountain 24
Robbins prospect No. 1 24
Jones prospect 24
R. E. Hilton property 24
E. C. Hilton property 24
Robins-Uzzell property 25
Robbins prospect No. 2 25
Orange County 25
Murray prospect 25
Hillsborough mine 25
Teer prospects 25
Alamance County 27
Snow Camp mine 27
Major Hill prospects • 27
Chatham County 28
Hinshaw prospect 28
Randolph County 28
Staley deposit 28
Pilot Mountain prospects 28
Moore County 29
McConnell prospect 29
Jackson prospect 30
Bates mine 30
Phillips mine 30
Womble mine . .31
Reaves mine 31
Jones prospect 33
Currie prospect 33
Ruff prospect 33
Hallison prospect 33
Standard Mineral Company 33
Tucker and Williams pits 35
Sanders prospect . .35
Montgomery County 36
Ammons mine 36
North State property 1 36
North State property 2 36
Cotton Stone Mountain 37
Standard Mineral Company 37
References cited 37
ILLUSTRATIONS
Facing
Page
Plate 1. Pyrophyllite deposits in North Carolina 23
2. Piedmont Minerals Company 26
A. Mill
B. Open pit mine
3. Glendon Pyrophyllite Company 32
A. Mill
B. Open pit mine (Reaves)
4. Standard Mineral Company 34
A. Mill
B. Open pit mine
VI
Pyrophyllite Deposits of North Carolina
By
Jasper L. Stuckey
ABSTRACT
All the known occurrences of pyrophyllite in North Carolina are found in Granville, Orange,
Alamance, Chatham, Randolph, Moore and Montgomery counties where they are associated with vol-canic-
sedimentary rocks of the Carolina Slate Belt. These rocks consist of lava flows interbedded with
beds of ash, tuff, breccia and shale or slate that vary in composition from rhyolitic, or acid, to andesitic,
or basic, and fall into three natural groups : Felsic Volcanics, Mafic Volcanics, and Bedded Argillites
(Volcanic Slate). They have been folded, faulted and metamorphosed to the extent that they contain
a well defined cleavage that strikes northeast and dips, in general, to the northwest.
The pyrophyllite deposits which are irregular, oval or lens-like in form occur in acid volcanic rocks
that vary from rhyolite to dacite in composition. The field, microscopic and chemical evidence indicates
that the pyrophyllite bodies were formed by metasomatic replacement of the host rocks through the
agency of hydrothermal solutions under conditions of intermediate temperature and pressure.
Pyrophyllite has a variety of uses chief of which are in paints, rubber goods, roofing materials,
ceramic products and insecticides. Reserves, while not large, are ample for several years.
INTRODUCTION
The pyrophyllite deposits of North Carolina are
associated with volcanic-sedimentary rocks of the
Carolina Slate Belt. Volcanic-sedimentary and
similar rocks form a belt or zone along the east-ern
border of the Piedmont Plateau and parts
of the Coastal Plain all the way from the vicinity
of Petersburg and Farmville, Virginia, southwest
across North Carolina, South Carolina and into
Georgia, as far as the southern part of Baldwin
County south of Milledgeville—a total distance
of over 400 miles. In North Carolina the zone
occupied by volcanic-sedimentary rocks is known
as the Carolina Slate Belt. It is in this belt that
the pyrophyllite deposits of the state are found.
The western border of the Carolina Slate Belt
lies a few miles east of Charlotte, Lexington and
Thomasville, crosses Guilford County southeast
of Greensboro and continues northeast across the
northwest corner of Alamance and Orange coun-ties
and the center of Person County to the Vir-ginia
line. The eastern limits of this belt are
marked, by the cover of Coastal Plain sediments.
PREVIOUS WORK
Due to the presence of a wide variety of min-erals
in them, the rocks of the Carolina Slate
Belt have been of interest for approximately 150
years. These rocks, because of their complex
character and well developed cleavage, were
called slates by a number of investigators over a
period of 70 years before their true nature began
to be recognized. The first published report on
that part of the slate belt in which pyrophyllite
deposits are known to occur was a descriptive list
of rocks and minerals from North Carolina by
Denison Olmsted (1822). In this list he de-scribed
novaculite, slate, hornstone, whetstone
and talc and soapstone from several counties in-cluding
Orange and Chatham. He stated that the
talc and soapstone were extensively used for
building and ornamental purposes and added that
Indian utensils of the same materials were com-mon.
In 1823, Olmsted was appointed by the Board
of Agriculture to make a geological survey of the
State. In his first report (1825) he called atten-tion
to the "Great Slate Formation which passes
quite across the State from northeast to south-west
covering more or less of the counties of
Person, Orange, Chatham, Montgomery —." The
presence of talc and soapstone was noted in
Orange, Chatham and other counties together
with beds of porphyry in the eastern part of the
formation and bands of breccia consisting of
rolled pebbles interbedded in a ferruginous green-stone
in different places.
Ebenezer Emmons (1856), one of the most
competent geologists of his time, considered the
Carolina Slate Belt rocks to be among the oldest
in the country and placed them in his Taconic
system which he divided into an upper and lower
member. The upper member consisted of clay
slates, chloritic sandstones, cherty beds and brec-ciated
conglomerate. The lbwer member consisted
of talcose slates, white and brown quartzites and
conglomerate. He did not recognize the presence
of volcanic rocks in what is now known as the
Carolina Slate Belt. In his lower unit, Emmons
found what he considered to be fossils and named
them Paleotrochis major and Paleotrochis minor.
Diller (1899) recognized these as spherulites in
rhyolite.
Emmons described in some detail the phyro-phyllite
deposits near Glendon, Moore County,
then known as Hancock's Mill and classed the
talcose slates, or those containing the pyrophyl-lite,
as the basal member or oldest rocks of his
Taconic system. He further pointed out that pyro-phyllite
occurred in the same position in Mont-gomery
County.
Prior to this time the pyrophyllite had been
considered as soapstone, but Emmons tested it
before the blowpipe and found it to contain alumi-num
and classed it as agalmatolite. He gave the
physical properties of this mineral together with
its uses and the methods of mining near Han-cock's
Mill. Brush (1862) analyzed some of the
material from Hancock's Mill, Moore County and
showed it to be pyrophyllite.
Kerr (1875) placed the rocks of the slate belt
in the Huronian, which in his classification is a
division of the Archean and considered them to
be sedimentary. He mentioned talc and soapstone
from Orange and Chatham counties but added
nothing to the description already published by
Emmons.
Kerr and Hanna (1893) in "Ores of North
Carolina," described some old gold mines in the
Deep River region and stated: "It is worthwhile
to add that part of what passes for talc is pyro-phyllite
and even hydromicaceous."
Williams (1894) recognized for the first time
the occurrence of ancient acid volcanic rocks in
the slate belt. He studied a small area in Chatham
County and applied for the first time modern
petrographic methods to the study of these rocks.
He described this area in part as follows : "Here
are to be seen admirable exposures of volcanic
flows and breccias with finer tuff deposits which
have been sheared into slates by dynamic agen-cies."
He classed the slate belt rocks as Precam-brian
in age.
Nitze and Hanna (1896) first used the name
Carolina Slate Belt for the rocks Olmsted (1825)
had designated the "Great Slate Formation."
They recognized the occurrence of volcanic rocks
in the slate belt and suggested that there had
been more than one volcanic outbreak and during
at least one period of inactivity slates had been
deposited. They did not mention pyrophyllite but
described in some detail the Bell, Burns and
Cagle gold mines, all of which are in the pyro-phyllite
area along Deep River in Moore County
and pointed out that there had been much silicifi-cation
at all of these and some propylitic altera-tion
at the Bell mine in particular.
Pratt (1900) described the pyrophyllite de-posits
near Glendon and showed by chemical
analysis that the mineral is true pyrophyllite. He
described the pyrophyllite deposits as follows:
"They are associated with the slates of this region
but are not in direct contact with them, being
usually separated by bands of siliceous and iron
breccia which are probably 100 to 150 feet thick.
These bands contain more or less pyrophyllite
and they merge into a stratum of pyrophyllite
schists." He offered no suggestion as to the origin
of either the slates, breccia or pyrophyllite.
Weed and Watson (1906) in a report on "The
Virgilina Copper District," concluded that the
rocks of that area were Precambrian volcanics,
chiefly an original andesite that had been greatly
altered by pressure and chemical metamorphism.
Laney (1910) presented a report on the "Gold
Hill Mining District of North Carolina," in which
he stated: "The rocks here included under the
general term slates while having many local vari-ations
seem clearly to represent a great sedi-mentary
series of shales with which are inter-bedded
volcanic flows, breccias and tuffs. In their
fresh and massive condition the slates are dense,
bluish rocks which show in many places well
defined bedding planes and laminations. The vol-canic
flows, breccias and tuffs which are inter-bedded
with the slates apparently represent two
kinds of lava, a rhyolitic and an andesitic type."
Pogue (1910) presented a report on the "Cid
Mining District of Davidson County," in which
he described the rocks of that area as follows:
"Wide bands of sedimentary, slate-like rock, com-posed
of varying admixtures of volcanic ash and
land waste have the greatest areal extents. Inter-calated
with these occur strips and lenses of acid
and basic volcanic rocks, represented by fine and
coarse-grained volcanic ejecta and old lava flows."
Laney (1917) in a report on the Virgilina dis-trict
classed the rocks in the area studied as
volcanic-sedimentary and stated: "Under this
group are placed both the acid and basic flows
and tuffs and the water laid tuffs and slates."
Stuckey (1928) presented a report on the Deep
River region of Moore County in which he di-vided
the rocks of the Carolina Slate Belt in that
area into slates, acid tuffs, rhyolites, volcanic
breccias and andesite flows and tuffs. He noted
that the schistosity dipped to the northwest and
interpreted the structure as a closely compressed
synclinorium with axes of the folds parallel to the
strike of the formations. In addition, he pointed
out that metamorphism is not uniform through-out
the area.
Bowman (1954) studied the structure of the
Carolina Slate Belt near Albemarle, North Caro-lina,
and recognized sedimentary rocks, volcanic
tuffs and flows, and mafic intrusives in the area.
He interpreted the structure as a series of undu-lating
open folds.
Conley (1959); Stromquist and Conley, 1959;
and Conley (1962 b) divided the rocks in the
Albemarle and Denton 15-minute quadrangles
into (1) a lower volcanic sequence consisting
largely of felsic tuffs that have been folded into
an anticline plunging to the southwest, (2) a
volcanic-sedimentary sequence consisting of a
lower argillite unit, an intermediate tuffaceous
argillite unit and an upper graywacke unit which
have been folded into a syncline also plunging to
the southwest and (3) an upper volcanic sequence
consisting of mafic and felsic volcanic rocks which
unconformably overlie the first two sequences.
According to Conley (1962 a), "In Moore
County only the lower and middle units appear to
be present; however, some rhyolite in the area
might belong to the upper unit. The exact strati-graphic
relationships of some of the rocks in the
county are in doubt because of the gradational
nature of the contacts, a condition further com-plicated
by intense folding and faulting and lack
of outcrops."
Conley and Bain (1965) suggested that the
rocks of the Carolina Slate Belt in North Carolina
can be divided into natural, mappable rock units.
They proposed and named a set of rock units or
formations into which these rocks might be
divided, gave their areal extent and described
their structure and lithology. From oldest to
youngest these proposed formations are:
Morrow Mountain rhyolite
Badin greenstone Tater Top Group
Unconformity
Yadkin graywacke
McManus formation
Tillery formation
Efland formation
Uwharrie formation
Albemarle Group
The Uwharrie formation is composed chiefly of
subaerially deposited felsic pyroclastic rocks.
These are felsic tuffs consisting of interbedded
lithic, lithic-crystal and devitrified vitric-crystal
tuffs, welded flow tuffs and rhyolite.
The Efland formation is a water-laid sequence
consisting of andesitic tuffs with interbedded
greenstones, conglomerates, graywackes and
flows.
The Albemarle Group is a water-laid sequence
of pyroclastics and sediments which is divided
into the Tillery formation, the McManus forma-tion
and the Yadkin graywacke.
The Tillery formation is composed in part of
finely laminated argillite exhibiting graded bed-ding
and in part of andesitic tuff and greenstone.
The McManus formation is predominantly a
felsic tuffaceous argillite formerly known as the
Monroe slate.
The Yadkin graywacke is a dark-green gray-wacke
sandstone containing interbeds of mafic
tuffaceous argillite, mafic lithic-crystal tuff and
felsic lithic tuff.
The older rocks are in part unconformably
overlain by subaerially deposited pyroclastics and
flows known as the Tater Top Group. From base
to top the group is composed of basaltic tuffs and
flows overlain by rhyolite flows. The Tater Top
Group is divided into the Badin greenstone and
Morrow Mountain rhyolite.
The Badin greenstone is composed of lithic
crystal tuffs and a basal unit of flows and flow
tuffs of andesitic composition.
The Morrow Mountain rhyolite consists of
dark-gray to black porphyritic rhyolite contain-ing
prominent flow banding.
Conley and Bain described the Troy anticli-norium,
with a northeast-southwest trend, as the
major structural feature of the Carolina Slate
belt. West and southwest of the Troy anticlinori-a
um, northeast trending open folded synclines and
anticlines predominate. East of the Troy anticli-norium
the rocks are more intensely folded. They
are compressed into northeast trending asym-metric
folds whose axial planes usually dip
steeply to the northwest. In many places, argil-lite
has been converted into slate and phyllite.
They considered the age of Carolina Slate Belt
rocks to be early Paleozoic.
GEOLOGY OF THE CAROLINA
SLATE BELT
GENERAL STATEMENT
In North Carolina rocks of the Carolina Slate
Belt actually form two belts that are separated
by sedimentary rocks of the Durham, Deep River
and Wadesboro Triassic basins and by the Roles-ville
granite pluton and associated gneisses and
schists. The first and most important of these and
the one Olmsted (1825) first called the "Great
Slate Formation" and Nitze and Hanna (1896)
first called the Carolina Slate Belt lies to the west
of the belt of Triassic rocks and varies in width
from 20 to 60 miles. It is widest between Sanford
and Lexington and narrows to the north and
south. It crosses the central part of the State in
a northeast-southwest direction from Anson and
Union counties on the southwest to Granville,
Person and Vance counties on the northeast and
underlies all or parts of Anson, Union, Mecklen-burg,
Cabarrus, Stanly, Montgomery, Moore,
Chatham, Randolph, Davidson, Rowan, Guilford,
Alamance, Orange, Durham, Person, Granville
and Vance counties. This belt contains all the
known pyrophyllite deposits in North Carolina
and will be considered in detail below.
The second belt in which Kerr (1875) first
recognized metavolcanic rocks lies to the east of
the belts of Triassic, igneous and metamorphic
rocks. It begins in Anson County on the south,
varies greatly in width and regularity and con-tinues
in a northeast direction to Northampton
County on the north. It is exposed at the surface
in all or parts of Anson, Richmond, Moore, Har-nett,
Lee, Wake, Johnston, Wayne, Wilson, Frank-lin,
Nash, Halifax and Northampton counties.
The eastern limits of this belt are unknown due
to the cover of Coastal Plain sediments. A deep
well in Camden County about 8 miles north of
Elizabeth City, the county seat of Pasquotank
County, penetrated rocks that are apparently of
the Carolina Slate Belt. Two deep wells—one a
few miles southeast of Kelly, Bladen County and
the other 4 miles south of Atkinson, Pender Coun-ty—
both penetrated Carolina Slate Belt rocks.
West of a line from Elizabeth City to Atkinson,
of the few wells that reached basement, some
penetrated granite, some penetrated gneiss and
schist and a few penetrated rocks of the Carolina
Slate Belt.
It is possible that if the crystalline floor be-neath
Coastal Plains sediments was exposed, the
types and percentages of rocks in this floor
would not differ greatly from those found west
of Coastal Plain sediments in Harnett, Johnston,
Wake, Wilson, Franklin, Nash, Vance, Warren,
Halifax and Northampton counties, where
gneisses and schists, granites and rocks of the
Carolina Slate Belt occur in about equal amounts.
Pyrophyllite has not been found in this eastern
zone of Carolina Slate Belt rocks and they are
not considered further in this report.
DISTRIBUTION AND CHARACTER
OF THE ROCKS
The rocks of the Carolina Slate Belt, west of
the Durham, Deep River, and Wadesboro Triassic
basins, consist of lava flows interbedded with
beds of ash, tuff, breccia and shale or slate. All
of these except the flows contain much nonvol-canic
material in the form of mud, clay, silt, sand
and conglomerate. (Also present is much non-descript
material, some of which may be vol-canic,
which for the lack of a better term has
been designated land waste) . The flows, breccias,
tuffs and ash beds and beds of shale or slate are
all interbedded and in general do not appear to
occupy definite stratigraphic positions in the
series. The flows vary from rhyolite through
andesite to basalt. The rhyolites and andesites
vary from fine grained to coarsely porphyritic
whereas the basalts are often amygdaloidal. The
breccias vary from rhyolitic to andesitic in com-position
and in fragment size from one-half inch
to nearly a foot in diameter. The fragments of
the breccias are in turn fragmental, apparently
pyroclastic in origin. Some of the fragments in
the breccias are sharply angular, although many
are rounded, indicating transportation and de-position.
The tuffs, while containing both acid
and basic materials, are in general of an acid
composition and composed of fragments less than
half an inch in diameter. These fragments which
vary from angular to rounded are often embedded
in much fine-grained material apparently of non-volcanic
origin.
Beginning in the vicinity of the Randolph-
Chatham county line, 15 to 20 miles south of
Siler City, and continuing northeast through
Siler City to the northern part of Orange County
and the southeastern part of Person County are
a number of beds of quartz conglomerate varying
in width from a few inches to as much as 250
feet and of unknown length. The quartz pebbles
in this conglomerate are generally less than an
inch in diameter, well rounded and embedded in
silt and sand, further indicating sedimentary
processes.
The shales and slates, which are generally well
bedded, are composed of fine-grained volcanic
materials (and much land waste) in the form of
clay, silt and fine sand. Finally, much of the fine-grained
materials in the breccias, tuffs and por-tions
of the shales and slates strongly resemble
metasiltstone and metagraywacke of some of the
metagraywacke rocks in other areas, further indi-cating
sedimentary processes.
A wide variety of rocks are present in the
Carolina Slate Belt and various attempts have
been made to divide them into units or forma-tions.
Conley (1959) and Stromquist and Conley
(1959) proposed a three fold division of the
rocks of the Albemarle and Denton 15-minute
quadrangles, while Conley and Bain (1965) pro-posed
a set of nomenclature for the rock-strati-graphic
units and their areal extent in the Caro-lina
Slate Belt. Since these proposals are not well
known and generally accepted and since the rocks
of the Carolina Slate Belt fall into three natural
divisions, it appears that these three natural divi-sions
are to be preferred in this discussion. These
three divisions are Felsic volcanic rocks, Mafic
volcanic rocks and Bedded argillites (volcanic
slate).
FELSIC VOLCANIC ROCKS
Felsic. volcanic rocks occupy about half of the
Carolina Slate Belt in the central part of the
State and are the predominating rocks in the
eastern part of the Piedmont Plateau. In this area
they occupy much of the Carolina Slate Belt
west of the Durham and Deep River Triassic
basins and northeast of Anson, Union and Stanly
counties.
The felsic volcanic rocks consist largely of ma-terials
of volcanic flow or fragmental origin. The
flows are essentially rhyolite, while the frag-mental
materials vary from rhyolitic to dacitic in
composition. The fragmental rocks consist of
breccias and coarse and fine tuffs, with coarse
and fine tuffs making up the greater portion of
the occurrences. Lenses of mafic volcanics and
bedded slate of limited extent are also present.
The fragmental rocks consist of fine and coarse
tuffs and breccias. The coarse tuffs predominate
and contain the fine tuffs and breccias as inter-bedded
bands and lenses. The fragments compos-ing
these rocks are angular to well rounded and
vary in size from nearly a foot to a fraction of an
inch in diameter.
The fine tuff occurs interbedded with both the
slate and coarse tuff and grades into each of them.
It has no wide areal extent but occurs as narrow
bands and lenses in the coarse tuffs.
Microscopically the fine tuff shows a crypto-crystalline
ground mass with fragments of quartz
and feldspar (orthoclase, albite, oligoclase) as
well as secondary minerals epidote, clinozoisite,
chlorite and calcite. Iron oxides are sparingly
present. Some sections show small rock frag-ments
containing original flow structure while
others exhibit a parallel arrangement of the par-ticles
due to metamorphism.
The coarse tuff varies from a massive to a
highly schistose type of rock, that in places has
been so slightly changed as to show some of its
original characters. There is every gradation to
a fine tuff on one hand and to a breccia on the
other. The freshly broken rock proves to be made
up of quartz and feldspar grains and rock frag-ments
of less than one-half an inch in diameter
set in a bluish or greenish-gray groundmass, the
whole often resembling an arkose.
In thin section the coarse tuff shows fragmental
phenocrysts of quartz, orthoclase and acid plagio-clase
with fragments of different kinds of rocks,
some of which show definite flow structure, all
embedded in a fine-grained groundmass. Kao-linite,
epidote and calcite form secondary prod-ucts.
Biotite and muscovite are rare. Grains of
hematite and limonite as well as small particles
of titanite and apatite are found in most sections.
Flows of rhyolite occur as narrow bands and
lenses in the tuff into which they appear to grade
at places. This apparent gradation is possibly due
to the fact that some material classed as silicified
fine tuff may be partially devitrified rhyolite. The
rhyolite is dense and indistinctly porphyritic,
with a dark gray to bluish color, and in fresh
fracture shows a greasy luster. Flow lines have
developed in numerous places and are best seen on
weathered surfaces, while amygdaloidal structure
may be found in a number of outcrops.
In thin section the rhyolite shows phenocrysts
of plagioclase (chiefly oligoclase) orthoclase and
quartz, named in the order of relative abundance.
Kaolinite, epidote and chlorite have developed
commonly from the weathering of the feldspars,
and calcite is frequently found along fractures in
the rocks.
Acid volcanic breccia includes all felsic rocks
that exhibit a fragmental character sufficiently
well defined to attract attention in the hand speci-men,
and in which the fragments are over one-half
inch in diameter. The size of the fragments
(observed) varies from one-half inch to several
inches in diameter. These rocks consist partly of
brecciated tuff and partly of brecciated rhyolite.
When freshly broken the breccia often shows a
greenish or mottled-gray color, produced by vari-ous
colored fragments in a finer groundmass. In
places the breccia has been strongly sheared and
it nearly always shows some mashing and schis-tosity,
but on the whole is more massive than the
finer tuff rocks.
Thin sections show little difference from the
regular coarse tuffs. The fragments are chiefly
of tuffaceous or rhyolitic character with occa-sional
slate fragments. Phenocrysts of quartz,
orthoclase and plagioclase (chiefly oligoclase) are
abundant. The fragments of the brecciated rhyo-lite
phase show a flow structure. In all phases of
the breccia the groundmass is altered and kao-linized.
Grains of iron oxide chiefly hematite are
present, while the secondary minerals epidote and
calcite and secondary quartz are plentiful.
MAFIC VOLCANIC ROCKS
Mafic volcanic rocks are scattered throughout
the northern two thirds of the Carolina Slate
Belt, but are most abundant along the western
side. The rocks of this unit consist of volcanic
fragmental and flow materials. The fragmental
materials are chiefly normal tuffs and breccias of
andesitic composition, while the flows vary from
andesite to basalt.
The tuffs are generally andesitic in composi-tion.
In places they are fine grained and lack the
fragmental appearance. In such areas, one of
which may be seen along U.S. Highway 64, for a
mile west of Haw River in Chatham County, the
rock strongly resembles a graywacke. The tuffs
contain much epidote and often have a greenish
color. Other colors vary from dark gray to nearly
black. In addition to epidote, plagioclase, quartz
and secondary calcite, iron oxides are present.
The mafic fragmental rocks are not as strongly
metamorphosed as the felsic fragmental rocks,
but contain a cleavage that strikes northeast and
dips northwest in the southern part of the area
and to the southeast in the northern part.
The mafic breccia is distinctly more basic than
the felsic breccias and appears to be mainly ande-sitic
in composition. It consists chiefly of brec-ciated
tuffs and flows, but ranges all the way
from a fine and highly mashed tuff to a massive
coarse breccia with fragments up to several inches
in diameter. It varies from a dark gray through a
chlorite and epidote green color.
In thin section this rock appears more uniform
than in the hand specimen. Fragmental materials
embedded in a feldspathic groundmass make up
most of the rock. The following minerals are
present: orthoclase, plagioclase (oligoclase and
andesine) chlorite, epidote, zoisite, clinozoisite,
quartz, calcite, iron oxides, kaolinite and sericite.
The andesite and basalt occur as bands and
lenses interbedded with the fragmentals. The
andesite is dark green in color, usually massive
or fine grained, but occasionally coarsely por-phyritic.
A coarse porphyritic variety, with horn-blende
crystals up to two inches long occurs in
western Randolph County. The basalt is dark to
nearly black and often amygdaloidal. Both the
andesite and the basalt are characterized by the
lack of a well defined cleavage. The minerals pres-ent
include epidote, plagioclase, quartz, secondary
calcite and iron oxides. Epidote is the most abun-dant
mineral present, giving the rock its green
color. The name greenstone is often used for this
rock.
BEDDED ARGILLITES (VOLCANIC SLATE)
Bedded argillites (volcanic slate) commonly
referred to as slate, bedded slate, or volcanic
slate, occur in the southern part of the Carolina
Slate Belt and extend as far north as the central
part of Davidson and Randolph counties. A few
small areas occur on the east side of the belt in
Montgomery, Moore and Chatham counties. There
are, also, some small areas east of the Jonesboro
fault in Anson and Richmond counties.
The bedded argillites (volcanic slate) consist
chiefly of dark colored or bluish shales or slates,
which are usually massive and thick bedded. How-ever,
the beds occasionally show very finely
marked bedding planes. Contacts between the
slates and tuffs are usually gradational and often
a single hand specimen will show gradation from
a bedded slate to a fine-grained tuff. In composi-tion
the bedded argillites vary from felsic tuffa-ceous
argillite to mafic tuffaceous argillite inter-mixed
with varying amounts of weathered
material and land waste. Much of the slate is
massive and jointed showing little effects of meta-morphism
while in other places it has been
strongly metamorphosed and shows a well defined
slaty cleavage. The cleavage or schistosity does
not in most places correspond to the bedding
planes of the rock. In places, especially near
igneous intrusives and mineralized zones, the slate
is often highly silicified and resembles chert.
IGNEOUS INTRUSIVE ROCKS
The Carolina Slate Belt is bordered on the
west by an igneous complex composed of gabbro,
diorite and granite and intruded at many places,
particularly in the northern half by granitic-type
rocks. These igneous intrusives apparently vary
from late Ordovician to early Permian in age.
ENVIRONMENT OF DEPOSITION
The occurrence of volcanic-sedimentary rocks
along the western edge of the Coastal Plain and
eastern edge of the Piedmont Plateau, in a long
narrow belt that extends from southeastern Vir-ginia
to central Georgia, with a length of more
than 400 miles and width up to 120 miles, sug-gests
deposition under geosynclinal conditions.
As indicated above, these rocks consist of a great
volcanic-sedimentary series varying from felsic
to mafic in composition and composed of lava
flows, beds of breccia, coarse tuff, fine tuff and
ash, and feeds of shale or slate now designated as
bedded slates or argillites. The lava flows and the
coarse angular tuff and breccias could have been
formed on land or under water. Conclusive evi-dence
for one as opposed to the other is lacking.
Many of the tuffs and breccias consist largely of
subangular to rounded fragments that were cer-tainly
reworked and deposited in water. The
bedded slates and argillites were definitely water
laid. Their composition, both chemical and physi-cal,
and their texture indicate that they were not
transported great distances. Finally, the presence
of varying amounts of nonvolcanic materials or
land waste in the form of mud, clay, silt, sand
and at places rounded quartz pebbles up to an
inch in diameter indicate that varying amounts of
materials were brought into the area from ad-jacent
land masses.
There seems to be little doubt that the rocks of
the Carolina Slate Belt were formed in a eugeo-syncline.
The volcanic materials in this geosyn-cline
came largely from beneath the surface by
volcanic eruptions, while the nonvolcanic sedi-ments
came from narrow belts of uplift that were
present in or adjacent to the trough.
The thickness of these rocks is variable but un-known.
It appears possible, however, that in cen-tral
North Carolina, west of the Durham, Deep
River and Wadesboro Triassic basins, the vol-canic-
sedimentary series may have a thickness up
to 20,000 or 30,000 feet. The period of volcanic-activity
during which this great series of volcanic-sedimentary
rocks were being formed must have
continued through a very long time, perhaps
hundreds of thousands or even millions of years.
During this time, there were innumerable alter-nations
between quiet upwelling of lava, explo-sive
activity piling up great amounts of tuff,
breccia and ash and periods of comparative quiet
accompanied by weathering, erosion and deposi-tion
of the bedded deposits. Between successive
outbursts the magma probably underwent some
degree of differentiation so as to give rise to
more acid rocks at one time and more basic at
another. Such changes were not great for at no
time did the products depart far from the general
type which was a relative acid magma rich in
soda.
STRUCTURAL FEATURES
The chief structural features of the rocks of
the Carolina Slate Belt are cleavage planes,
joints, folds and faults. The first of these to be
of interest was the cleavage planes. Olmsted
(1825) designated these rocks as the Great Slate
Formation because of the well developed, slate-like
cleavage which he observed over most of the
area. In general, rocks of the Carolina Slate Belt
south of U.S. Highway 70 from Durham to
Greensboro have a well defined cleavage that
strikes northeast and dips steeply to the north-west.
North of this line the cleavage continues
to strike northeast but much of the dip is to the
southeast and at a lower angle than that which
dips to the northwest. No explanation for this
change in dip is readily available.
The metamorphism which produced the cleav-age
was not as intense as was originally thought
and also varied widely from place to place. At
places, metamorphism was so severe that the
cleavage has become schistosity and the rocks are
essentially schists. At other places, the cleavage
apparently grades into jointing. As a result, the
massive rocks are highly jointed and contain
poorly developed cleavage planes.
Recent work has revealed that folding is better
developed than was formerly thought. It is now
established that the rocks are in general well
folded into a series of anticlines and synclines.
The largest and most important fold is the Troy
anticlinorium which trends in a northeast-south-west
direction and whose axis lies a short dis-tance
west of Troy. West and southwest of the
Troy anticlinorium, northeast-trending open fold-ed
synclines and anticlines predominate. The
most important of these is the New London syn-cline.
East, southeast, and northeast of the Troy
anticlinorium the intensity of the folding in-creases.
The rocks are tightly compressed into
northeast-trending, asymmetric folds whose axial
planes usually dip steeply to the northwest.
The bedded argillites (volcanic slate) seem to
have consolidated readily and folded like normal
sediments while the tuffs and breccias remained
in a state of open texture and tended to mash and
shear instead of folding. This is indicated by the
mashed and sheared condition of practically all
the tuffs while in numerous cases more or less
well preserved bedding planes in the slates indi-cate
definite folding.
Numerous insignificant faults occur in nearly
all parts of the Carolina Slate Belt. These in gen-eral
never amount to more than a few feet and
are doubtless only the adjustments due to the
folding of the rocks and are not of any great
structural importance. However, along the east-ern
border of the belt where the Carolina Slate
Belt rocks have been compressed into northeast-trending
asymmetric folds whose axial planes dip
steeply to the northwest, thrust faults are present.
The abundance and importance of these faults
in relation to the overall structure of the Carolina
Slate Belt are not yet fully established, but recent
geologic mapping has revealed the presence of
such faults in Moore and Orange counties.
AGE OF THE ROCKS
Emmons (1856), the first worker to date the
rocks of the Carolina Slate Belt, considered them
to be mainly slates and quartzites of sedimentary
origin as shown by the presence of rounded peb-bles.
He divided these rocks into a lower and
upper series and placed them in his Taconic
system which was early Paleozoic in age. He con-sidered
the talcose slates of the lower series to
have essentially the same composition as the
underlying primary series and stated: "The tal-cose
slates may be regarded as the bottom rocks,
the oldest sediments which can be recognized,
and in which, probably, no organic remains will
be found."
Later Emmons found near Troy, Montgomery
County, two or three species of fossils in the
lower series of the Taconic system. These fossils,
which belonged to the class of zoophites, the low-est
organisms of the animal kingdom, were found
through about 1000 feet of rock and occurred
from a few in number to abundant.
The fossils were considered to be corals of a
lenticular form that varied in size from a small
pea to two inches in diameter. At first, Emmons
considered the difference between the small and
the larger forms to be the result of age but
later decided that they were specific and named
the small form Paleotrochis minor and the large
form Paleotrochis major.
These forms were of interest to Emmons main-ly
in showing that lower Taconic rocks were fos-siliferous
rather than in actually dating the rocks.
Paleotrochis major and Paleotrochis minor were
later identified as spherulites in rhyolite and not
fossils, Diller (1899).
Kerr (1875) classed the rocks of the Carolina
Slate Belt as Huronian in age, which in his classi-fication
is a division of the Archean. Williams
(1894) classed them as Precambrian in age. Wat-son
and Powell (1911) on the basis of fossils,
considered the Arvonia slates of the Piedmont of
Virginia to be Ordovician in age. Laney (1917)
on the basis of the work by Watson and Powell,
classed the volcanic-sedimentary rocks of the
Virgilina district of the Carolina Slate Belt as
Ordovician in age.
In recent years the trend has been to place the
age of these rocks as early Paleozoic, probably
Ordovician. According to the U.S. Geological Sur-vey,
Professional Paper 450A, Research 1962,
"Lead-alpha measurements by T. W. Stern on
zircon collected by A. A. Stromquist and A. M.
White from felsic crystal tuffs in the Volcanic
Slate belt of the central North Carolina piedmont
have confirmed a previously inferred Ordovician
age for these unfossiliferous rocks." White, et. al.
(1963) gave the details on the collection and
evaluation of two samples of zircon from the
Albemarle quadrangle and stated: ". . . the indi-cated
age for each is Ordovician according to
Holmes time scale (Holmes, 1959, p. 204) ."
Recently, St. Jean (1964) reported the first
authentic discovery of fossils in the Carolina
Slate Belt of North Carolina. The discovery con-sisted
of two abraded and moderately distorted
thoraxes and pygidia of a new trilobite species.
The specimens were collected from a piece of
stream rubble in Island Creek at Stanly County
Road 1115. The type rock in which the fossils
occurred is present in outcrops upstream. St.
Jean classed the specimens as a new species ques-tionably
assigned to the Middle Cambrian genus
Paradoxides and stated: "Although the generic
assignment is questionable, the morphologic char-acters
of the two specimens indicate an age no
younger than Middle Cambrian and no older than
the age of the oldest known Early Cambrian tri-lobites."
"The specimens are significant because they
represent the first authentic fossil material from
the Piedmont south of Virginia and provide
paleontological documentation of the age and
marine nature of a lithologic unit in the area.
Micropygous Cambrian trilobites are more com-mon
in eugeosynclinal belts, which part is in
keeping with the paleogeographic and lithologic
setting."
Granites of post-Ordovician but Paleozoic age
and diabase dikes of Triassic age both intrude the
Carolina Slate Belt rocks. The granites apparently
furnished the solutions that produced the pyro-phyllite
and associated minerals, and are con-sidered
further below. The diabase dikes have
no relations to the pyrophyllite deposits and are
not discussed further.
GEOLOGY OF THE PYROPHYLLITE
DEPOSITS
INTRODUCTION
Just when pyrophyllite was first discovered in
North Carolina is not known. Olmsted (1822) in
a report entitled, "Descriptive Catalogue of Rocks
and Minerals Collected in North Carolina" listed
talc and soapstone from several counties includ-ing
Chatham and Orange and stated that fhey
were extensively used for building and orna-mental
purposes, and added that Indian utensils
of the same materials were common. In 1825 he
called attention to the "Great Slate Formation"
which passes across the State from northeast to
southwest and again noted the presence of talc
and soapstone in Chatham and Orange counties.
Since no talc and soapstone are known to occur
in rocks of the Carolina Slate Belt and since
pyrophyllite is found at a number of localities in
the belt it is quite probable that the deposits
mentioned by Olmsted were pyrophyllite.
Emmons (1856) described a material which
was locally known as soapstone at Hancock's Mill,
(Now Glendon) Moore County and near Troy,
Montgomery as follows : "A rock, which occurs in
extensive beds, and known in the localities where
it is found as a soapstone, can by no means be
placed properly with the magnesium minerals. It
is white, slaty, or compact translucent, and has
the common soapy feel of soapstone, and resem-bles
it so closely to the eye and feel that it would
pass in any market for this rock. It has, how-ever,
a finer texture, and is somewhat harder;
but it may be scratched by the nail, so that it
ranks with softest of minerals: it scratches talc,
and is not itself scratched by it; it is infusible
before the blowpipe, and with nitrate of cobalt
gives an intensely blue color, proving thereby the
presence of alumina in place of magnesia." He
classed the mineral as agalmatolite, the figure
stone of the Chinese, and described the methods
used in quarrying it at Hancock's Mill.
Brush (1862) analyzed some of the material
from Hancock's Mill, Moore County and showed
it to be pyrophyllite.
Pratt (1900) described the deposits and pub-lished
further analyses of the pyrophyllite. He
stated that : "While the talc deposits of Cherokee
and Swain counties are pockety in nature and of
limited depth, the pyrophyllite formation is con-tinuous
and of considerable, though of unknown
depth."
Pratt described the pyrophyllite as follows:
"While possessing many of the physical proper-ties
of talc and often being mistaken for it, the
pyrophyllite is quite different in its chemical com-position,
and is a distant mineral species. Al-though
this mineral probably cannot be put to
all the uses of talc, it can be used for the larger
number of them, and those for which the talc is
used in the greatest quantity. Some of this might
be of such quality that it could be cut into pencils,
but the most of this mineral would only be of
value when ground. It is soft with a greasy feel
and pearly luster, and has a foliated structure.
The color varies from green, greenish and yel-lowish-
white to almost white; but when air-dried
they all become nearly white. Very little compact
pyrophyllite has been observed that would be
suitable for carving, as is used in China, although
considerable of this has been used in the manu-facture
of slate pencils."
Pratt presented three chemical analyses of
pyrophyllite from Moore County that were very
close to the theoretical composition of that min-eral.
He, also, pointed out that the deposits had
been worked almost continuously since the Civil
War.
Hafer (1913) noted that the pyrophyllite did
not differ greatly from the sericite found in the
old gold mines of the slate belt and may have
originated in the same manner. He, also, called
attention to the masses of pyrite-bearing quartz
that are often found associated with the pyro-phyllite
deposits.
Stuckey (1928) presented the first detailed re-port
of the pyrophyllite deposits of North Caro-lina.
He described their distribution, geological
setting, form or shape, mineralogy, origin and
possible continuation with depth. He classed the
deposits as hydrothermal in origin and thought
that they might continue to considerable depths.
DISTRIBUTION
Pyrophyllite occurrences are known along the
eastern half of the Carolina Slate Belt from the
vicinity of Wadesville in the southwestern part
of Montgomery County northeastward to the
northern part of Granville County near the Vir-ginia
line. These occurrences may consist of a
single deposit or they may contain several pros-pects
or deposits.
In Montgomery County pyrophyllite is known
to occur near Wadesville ; on Cotton Stone Moun-tain,
3.5 miles north of Troy; just east of State
Road 1312 near Abner; and northeast of Asbury
in the northeastern corner of the county. Consid-erable
prospecting has been done near Wadesville
and the area appears promising for mining.
Limited prospecting has been done on Cotton
Stone Mountain but no mining has been carried
out. Limited prospecting and some mining have
been carried out on the deposit near Abner but
the property is currently idle. One deposit north-east
of Asbury appears to have been worked out,
but another is promising for future development.
In Moore County, pyrophyllite is found ap-proximately
four miles southwest of Spies near
the point where Cotton Creek enters Cabin Creek
;
near Robbins; and in a zone several miles long
that lies along Deep River north of Glendon. The
Robbins area contains the only underground
mine, which is the largest pyrophyllite mine in
the State, and several open pit prospects. The
Glendon zone contains three active open cut mines
and a number of prospects.
Pyrophyllite is known to occur in Randolph
County in the vicinity of Pilot Mountain about 8
miles southeast of Asheboro, just north of State
Highway 902, and near Staley in the northeastern
part of the county. In the Pilot Mountain area
there are four prospects, one of which has been
explored and considerable iron-stained pyrophyl-lite
is reported to be present. No mining has been
carried out in this area. The deposit near Staley,
which at one time contained the second largest
mine in the State, has been worked out and aban-doned.
The only known pyrophyllite area in Chatham
County is located near the Chatham-Alamance
county line on the Hinshaw property. This prop-erty
is about 2 miles east of State Road 1004 and
a short distance north of State Road 1343. Pyro-phyllite
crops out at three places in the area, one
of which has been prospected to a limited extent.
No mining is being carried out in the area.
Pyrophyllite is known to occur at two localities
near Snow Camp in southern Alamance County.
On Pine Mountain southeast of Snow Camp is a
major open pit mine from which pyrophyllite
has been mined for more than 20 years. About 2
miles east of Snow Camp there are several pyro-phyllite
exposures on a prominent hill known as
Major Hill. Major Hill lies south of State Road
1005 and between State Roads 2356 and 2351.
The outcrops in Major Hill are promising and
prospecting is currently underway.
In Orange County pyrophyllite is known to
occur in the vicinity of Teer in the southwestern
part of the county; near Hillsborough; and on
the Murray estate about 6 miles northeast of
of Hillsborough. In the vicinity of Teer, prospect-ing
has been carried out at three or more places
10
and limited mining was done at one time. This
area has been abandoned at least temporarily.
South and southwest of Hillsborough are three
prominent hills which trend northeast and parallel
the major geologic structure of the area. The
northern most of these hills contains a major open
cut pyrophyllite mine that is an important pro-ducer
of pyrophyllite, andalusite, sericite and
silica. The deposit in the Murray property north-east
of Hillsborough lies south of State Road 1538
and west of State Road 1548. Considerable pro-specting
has been carried out on this property,
but no mining has been done.
In Granville County, pyrophyllite deposits are
found on Bowlings Mountain northwest of Stem
;
at several places on Long Mountain which lies to
the northwest of Bowlings Mountain; and on
Daniels Mountain about 9 miles north of Oxford.
On Bowlings Mountain, which is located about
three miles slightly northwest of Stem, prospect-ing
and some mining have exposed a major pyro-phyllite
deposit. To the northwest of Bowlings
Mountain is a northeast trending series of irregu-lar
hills that occupy an area a mile or more in
width and some 4 miles long, known as Long
Mountain. Prospecting and some exploration have
demonstrated the presence of pyrophyllite at sev-eral
places on Long Mountain, but no mining has
been done. About 9 miles north of Oxford and 1.5
miles northeast of State Highway 96 and east of
Mountain Creek is Daniels Mountain on which
pyrophyllite is known to occur. No prospecting or
mining has been done on this mountain.
GEOLOGIC RELATIONS
All the pyrophyllite deposits of North Carolina
occur in acid volcanic rocks, chiefly in medium
to fine-grained tuffs and to a less extent in an
acid volcanic breccia. They are not found at any
place in a basic andesitic type of rock or asso-ciated
with a typical water-laid slate. At the
Phillips, Womble and Reaves mines, which are
found in the Deep River pyrophyllite zone north
of Glendon, Moore County, the footwall side of
the pyrophyllite bodies is an acid volcanic breccia.
Next to the footwall is a highly mineralized pyro-phyllite
zone that grades into a fine-grained acid
tuff. At places the pyrophyllite grades into and
replaces parts of the brecciated footwall. Where
the band of volcanic breccia is absent from the
footwall side of the deposits, in this zone, the
pyrophyllite bodies are much nearer the slate
than where the breccia is present, but they are
never found in normal slate. On the hanging wall
side the pyrophyllite grades into medium to fine-grained
acid tuff.
The geologic distribution of the pyrophyllite
deposits is probably controlled in part by the
composition of the rocks and in part by rock
structures. As indicated above (page 8), the
tuffs and breccias remained in a state of open
texture and tended to mash and shear instead of
folding. As a result, the acid tuffs and breccias
developed shear zones along which the pyrophyl-lite
mineralization was later concentrated. A few
shear zones, particularly those along Deep River
near Glendon and near Robbins (both in Moore
County) were developed along major thrust
faults. However, the great majority of the pyro-phyllite
deposits are found in shear zones that
do not show any evidence of containing faults.
FORM AND STRUCTURE
A prominent feature of the pyrophyllite bodies
is their irregular, oval, or lens-like form. This
structure is observed along the strike and also
vertically to the depths reached in mining. In
nearly every deposit that has been developed
enough to show the true structure, bodies and
lenses of pyrophyllite are found along with lenses
of tuffaceous rocks that exhibit various stages of
alteration. Most pyrophyllite deposits occur as
narrow bands or zones aligned with the cleavage
strike and dip of the country rock. They range
in size from those measured in inches up to 500
feet wide and 1500 to 2000 feet long. The strike
of the cleavage in both the country rock and the
pyrophyllite bodies is northeast-southwest, while
the dip is steeply to the northwest.
In most cases the larger mineralized zones con-sist
of a very siliceous footwall, a well developed
mineralized zone and a highly siliceous and seri-citic
hanging wall. Where these conditions exist
contacts between the mineralized zone and the
footwall and the hanging wall are gradational.
Contacts between the footwall and country rock
and the hanging wall and country rocks are, also,
gradational. When the siliceous footwall and the
sericitic hanging wall are absent, as they fre-quently
are, contacts between the mineralized
zones and the country rocks are gradational.
Excellent examples of the siliceous footwall
may be seen at the Bowlings Mountain deposit,
11
Granville County, at the Hillsborough deposit,
Orange County, at the Staley deposit, Randolph
County, and at the mine of the Standard Mineral
Company, Moore County. In general, it consists
of a light blue-gray to white, fine-grained to
medium-grained rock having the general appear-ance
of quartzite. Selected samples from the more
massive portions of this rock consist almost en-tirely
of silica. The rock has been fractured con-siderably
at places and contains varying amounts
of sericite and pyrophyllite. When fresh, the rock
is hard and dense and breaks with a conchoidal
fracture. When weathered, it breaks down to a
sandy friable material that is usually white, but
is often stained various shades of yellow and red
by iron oxide.
The siliceous footwall ranges from less than 5
to more than 50 feet in thickness and in many
cases extends the entire length of the deposit.
When it occurs as a massive unit, it often crops
out as bold ledges near the crest of the hill as at
the Staley and Hillsborough deposits. However,
as at the mine of the Standard Mineral Company
near Robbins, Moore County, it may not crop out
at all. From the footwall mineralization increases
inward to rich zones and lenses of pyrophyllite
and then decreases towards a schistose and seri-citized
hanging wall.
MINERALOGY OF THE DEPOSITS
The minerals most commonly observed in the
pyrophyllite deposits in the apparent order of
their abundance are pyrophyllite, quartz, sericite,
chloritoid, pyrite, chlorite, feldspar, iron oxides,
zircon, titanite, zeolites and apatite. Of these,
only the first eight are present in important
amounts or related to the development of the
pyrophyllite. The other minerals are present in
small amounts to the extent they might occur as
accessory constituents of an igneous rock or as
products of regional metamorphism or weather-ing.
In addition, small amounts of fluorite have
been found with quartz veins intruding the fault
zone at the Phillips mine. Also, varying amounts
of the high-alumina minerals andalusite, dia-spore,
kyanite and topaz have been found in sev-eral
pyrophyllite mines and prospects. The posi-tion
of these high-alumina minerals in the
mineral sequence of the pyrophyllite deposits is
not clear and they are discussed below.
Pyrophyllite
Pyrophyllite is a hydrous aluminum silicate
with the general formula H2Al2Si40i2. It crystal-lizes
in the orthorhombic system, but good crys-tals
are rare. It commonly occurs as (1) foliated,
(2) granular and (3) radial or stellate masses.
The color varies from nearly black through yel-lowish
white, green, and apple green to pure
white. It has a specific gravity of about 2.8 to 2.9,
and a hardness less than the finger nail. It has a
pearly luster, a greasy feel and commonly occurs
as masses, lenses and pockets associated with
quartz, sericite and chloritoid. The pyrophyllite in
the deposits near Glendon and Robbins, Moore
County, consists almost entirely of the foliated
variety. That in the other major deposits consists
largely of massive granular and radial fibrous
forms with occasional small amounts of the foli-ated
variety.
Quartz
Quartz is an oxide of silicon with the general
formula Si02 . It crystallizes in the hexagonal
system, and good crystal specimens are common.
Quartz is colorless when pure, has a conchoidal
fracture, a viterous luster, a hardness of 7 and
a specific gravity of 2.65. It is abundant through-out
the deposits everywhere except in the very
purest pyrophyllite and occurs (1) as large
masses of cherty or milky appearance, (2) as
clear veins and stringers in the deposits and
along the walls, and (3) as small masses and
nodules in the altered or only partly altered rock.
Sericite
Sericite is a fine-grained variety of mica, usual-ly
muscovite, occurring in small scales and having
the composition (H,K)AlSi04 . It crystallizes in
the monoclinic system, has a basal cleavage, a
hardness of 2-2.25, a specific gravity of 2.76-3
and a vitreous luster. The color varies from color-less
through gray, pale green, and violet to rose-red.
Sericite is often concentrated as bands or
zones along the hanging wall of the pyrophyllite
bodies and to a lesser extent along the footwall.
It is, also, present as finely divided scales and
flakes and as zones through good pyrophyllite.
Chloritoid
Chloritoid probably crystallizes in the triclinic
system but rarely occurs in distinct tabular crys-
12
tals. It often occurs in the form of sheaves or
rosettes. The general formula is H2 (Fe,Mg)
Al2Si07 . It has a basal cleavage, a pearly luster,
a hardness of 6.5 and a specific gravity of 3.52-
3.57. The color varies from dark gray through
greenish black to grayish black. Chloritoid is
found in varying amounts in all the pyrophyllite
deposits but is most abundant in those along
Deep River north of Glendon, Moore County
where an acid iron breccia forms part of the
footwall.
Pyrite
Pyrite has the formula FeS2 , crystallizes in the
isometric system and often occurs as good crys-tals.
It has a conchoidal fracture, a hardness of
6-6.5, a specific gravity of 4.95-5.10, a metallic
luster and a brass-yellow color. It is present in
small amounts associated with the silicified tuff
along the walls of the pyrophyllite bodies and in
the lenses of silicified country rock included in
the deposits.
Chlorite
Chlorite, probably clinochlore, has the formula
H8Mg5Al2Si3 18 , crystallizes in the monoclinic sys-tem
and usually occurs as flakes or scales. It has
a hardness of 2-2.5, a specific gravity of 2.65-2.78,
a pearly luster, and a grass-green to olive color.
Chlorite occurs rather commonly in the impure
portions of the pyrophyllite bodies and in the
altered wall rocks.
Feldspars
Feldspars, orthoclase (KAlSi3 8 ), albite
(NaAlSi3 8 ), and in one case andesine, a mixture
of albite (NaAlSi3 8 ) and anorthite
(CaAl2Si2 9 ), were found in small amounts in
the less silicified portions of the wall rock of the
pyrophyllite bodies. Orthoclase and albite are
more abundant due to the fact that they are com-mon
constituents of the rhyolitic and dacitic rocks
in which the pyrophyllite was formed.
Iron Oxides
Iron oxides, chiefly hematite Fe2 3 and magne-tite
Fe3 4 , occur in small amounts in each pyro-phyllite
deposit studied, but most abundantly in
the footwall of the mines along Deep River north
of Glendon, Moore County, where an acid iron
breccia is present.
High Alumina Minerals
One or more of the high-alumina minerals an-dalusite
(Al2Si05 ), diaspore (A12 3H20), kyanite
(Al2Si05 ) and topaz (AlF) 2Si04 , are present in
varying amounts in most of the pyrophyllite de-posits
except those in Moore County, and Conley
(1962a) reported collecting a specimen from the
fault zone in the Phillips mine that contained
pyrophyllite, diaspore, topaz and fluorite.
The occurrence of high-alumina minerals in the
pyrophyllite deposits is quite irregular, with the
greatest concentrations near the footwall and
lesser amounts along the hanging wall and asso-ciated
with lenses of only partly altered country
rock included in the deposits. Andalusite is abun-dant
in the Hillsborough deposits. In the deposit
on Bowlings Mountain, Granville County, there
is considerable topaz as well as small amounts of
andalusite and kyanite. Some blocks of topaz are
in the pyrophyllite deposits today and represent
material that was not replaced or destroyed dur-ing
pyrophyllite formation.
PETROGRAPHY
A careful study of a number of thin sections
cut from specimens collected at the various mines
and quarries shows that the pyrophyllite deposits
have been formed in volcanic tuffs and to some
extent in a volcanic breccia that varied from
dacitic to rhyolitic in composition.
Sections from specimens of tuff and breccia col-lected
along the walls of the pyrophyllite bodies
and from partly altered country rock included in
them show that the minerals of the pyrophyllite
bodies were formed in the order of quartz, pyrite,
chloritoid, sericite, and pyrophyllite; and that
these minerals have definite relations to each
other and to the feldspars and iron oxides in the
country rock.
The first change was a marked silicification of
the enclosing rocks accompanied by a rapid de-crease
in their normal mineral content. The feld-spars,
rock fragments, and fine-grained ground-mass
of the rocks were readily replaced by quartz
to the extent that the altered rocks became masses
of cherty and milky quartz.
At the Womble and Phillips mines north of
Glendon, Moore County and at the Staley mine 3
13
miles west of Staley, Randolph County, the silici-fication
was accompanied or immediately followed
by the development of pyrite, as this mineral is
found in the silicified wall rocks of the mines and
in included masses of silicified country rock but
not in good pyrophyllite.
Chloritoid is found in varying amounts at all
the prophyllite prospects and mines but is more
abundant at some including the Womble and
Phillips mines north of Glendon, Moore County
and the Murray prospect 5 miles northeast of
Hillsborough, Orange County and the Staley mine
3 miles west of Staley, Randolph County. At the
Womble and Phillips mines it is apparently re-lated
to an acid iron breccia which contains con-siderable
magnetite and hematite and forms the
football of these deposits. The chloritoid at the
Murray prospect and the Staley mine seems to
be related to bands and zones of greenstone in
the wall rocks of the bodies near the pyrophyllite.
The chloritoid was not observed replacing the
iron oxides but the marked increase and close
association of chloritoid with the iron oxides at
every point where the latter are present suggests
a close genetic relation between the two. The
chloritoid was developed along with or soon after
the silicification of the tuff and in thin sections
is seen to have partly replaced the quartz.
Sericite is often concentrated as bands or zones
along the hanging wall of the pyrophyllite bodies
and to a lesser extent along the footwall. It is
also present as finely divided flakes and scales
and as zones through good pyrophyllite. Thin sec-tions
cut from silicified and partly prophyllitized
masses from the various pyrophyllite deposits
show sericite associated with pyrophyllite and
having about the same relations to the quartz.
The cherty or flinty masses of quartz in the pyro-phyllite
bodies are cracked and shattered and
partly replaced by sericite.
The microscope shows pyrophyllite to be the
last mineral formed. In every case silicification
preceded the development of pyrophyllite.
The feldspars diminish with silicification so
that feldspar and pyrophyllite are seldom found
in the same section. Where pyrophyllite is found
in sections with chloritoid, it occurs in every
crack and opening in the sheaves and bundles of
chloritoid as a replacement of the chloritoid. Prac-tically
all specimens except those from the purest
pyrophyllite, contain some quartz, the amount of
the latter depending upon the purity of the speci-men
in terms of pyrophyllite. In sections from
such specimens the pyrophyllite is replacing the
quartz. Sections from the masses of cherty or
milky quartz associated with pyrophyllite show
both sericite and pyrophyllite replacing the quartz
with sericite apparently earlier than the pyro-phyllite.
The position of the minerals andalusite,
diaspore, kyanite and topaz in the sequence is not
clear, but they appear to have been formed before
or early in the pyrophyllitization process as they
have been replaced partially by sericite and pyro-phyllite.
ORIGIN OF THE PYROPHYLLITE
DEPOSITS
In considering the origin of the pyrophyllite
deposits, it has been necessary to take into ac-count
their shape and distribution, their relations
to the enclosing rocks, their mineralogical com-position,
the relations of the associated minerals
to each other, and the relations of the pyrophyl-lite
to the associated minerals and the enclosing
rocks. Over the years, ideas as to the origin of
pyrophyllite have changed and future develop-ment
of the deposits may disclose new informa-tion
that may require new explanations. This is
especially true since the deposits are associated
with metamorphic rocks and ideas on the origin
of metamorphic rocks and their contained miner-als
are in a state of change.
EARLIER THEORIES
Before discussing the origin of North Carolina
pyrophyllite, reference should be made to the
views expressed by other writers on the origin of
this mineral and the chloritoid and sericite asso-ciated
with it.
Emmons (1856) considered pyrophyllite (agal-matolite)
as a sedimentary rock near the base of
his Taconic system. Levy and Lacroix (1888)
stated that pyrophyllite occurs in metamorphic
rocks while Dana (1909) classed it as a mineral
formed at the base of schists or as a mineral of
the crystalline schists and Paleozoic metamor-phics.
Clapp (1914) described pyrophyllite deposits
on the west side of Vancouver Island, British
Columbia. Both alunite and pyrophyllite occur
in andesite, dacite and associated pyroclastic
rocks. This series and in particular its fragmental
parts, has been metasomatically altered to quartz-sericite-
chlorite rocks, quartz-sericite rocks,
14
quartz-pyrophyllite rocks and quartz-alunite
rocks. Clapp concluded that most of the minerali-zation
was caused by hot sulphuric acid solutions
of volcanic origin which were active during the
accumulation of the pyroclastic rocks, and as a
result of relatively shallow depths and low pres-sures.
He postulated little change in the bulk
composition of the original volcanic rocks and
interpreted most of the new minerals as having
been developed from feldspars. In general, how-ever,
the quartz-pyrophyllite rocks show a net
gain in alumina, a loss of potash and either a loss
or a gain in silica.
Buddington (1916) and Vhay (1937) have
described in detail the pyrophyllite deposits in
the Conception Bay Region of Newfoundland.
These deposits occur in a thick series of Pre-cambrian
rhyolite and basalt flows which contain
interlayered breccias, tuffs and some waterlaid
materials. These volcanic rocks were altered re-gionally
with the development of abundant chlo-rite
and silica. Locally, some of the rocks were
pyrophyllitized, some pinitized and some silici-fied.
Some of the pyrophyllite concentrations are
found in rhyolite breccias and conglomerates, but
most are limited to the rhyolite flows. The pyro-phyllite
itself forms single, well defined veins, as
well as series of inter-connecting veins, lenses
and pockets. The development of the pyrophyllite
evidently involved the introduction of large
amounts of alumina, the replacement of alkalies
by hydroxyl, and the removal of silica, both that
occurring as free quartz and that in the other
minerals. Much of the pyrophyllitized rock may
once have been a relatively homogeneous glass.
Buddington (1916) concluded that these de-posits
were formed by the metasomatic replace-ment
of previously silicified rhyolites by thermal
waters under conditions involving dynamic stress
and intermediate temperatures and pressures.
The solutions evidently moved along fault or shear
zones, and the deposits have a marked schistosity.
Vhay (1937) concluded that the individual flakes
of pyrophyllite have a random orientation and
that the schistosity of the deposits represent an
inherited feature preserved by differential re-placement
along schistose structures already
established.
The pyrophyllite deposits in the San Dieguito
area of San Diego County, California, have been
described in detail by Jahns and Lance (1950).
These deposits were formed by the alteration of
volcanic flows, breccias and tuffs that ranged in
composition from andesite to rhyolite.
Jahns and Lance (1950) described the origin
of these deposits as follows : "The mode of occur-rence
of the San Dieguito pyrophyllite, particu-larly
its distribution with respect to fractures
and shear zones in the host volcanic rocks, indi-cates
that it was formed by replacement of these
rocks. Its development was accompanied by intro-duction
of Si02 , A12 3 and probably OH. The
phyrophyllite bearing rocks, including those of
highest grade, contain fresh pyrite and other sul-fide
minerals at depths in excess of 20 feet in
most parts of the area. Both pyrophyllite and
sulfides appear to be hypogene, and are plainly
earlier than the widespread iron oxides, man-ganese
oxides and clay minerals of supergene
origin.
"Under the microscope both pyrophyllite and
quartz replace feldspars and other original min-erals
of the volcanic rocks, and in many places
the two replacing minerals are of the same gen-eral
age. As pointed out by Bastin and others,
(1931) aggregate, rather than sequential replace-ment,
is characteristic of hypogene processes.
Zonal distribution of replacing minerals with
respect to remnants of earlier minerals, a feature
so common in supergene replacement, is con-spiciously
absent from the pyrophyllite-bearing
rocks. Moreover, the replacement is not particu-larly
selective; the pyrophyllite, although first
attacking parts of the groundmass in the volcanic
rocks is generally distributed throughout the
phenocrysts and groundmass minerals."
They conclude : "The metamorphism of the vol-canic
rocks in the San Dieguito area, and the
subsequent introduction of silica and pyrophyl-lite
almost certainly took place during late Trias-sic
or Cretaceous time. A considerable thickness
of volcanic rocks was removed by erosion prior
to deposition of the latest Cretaceous sediments
in the region, so that it is impossible to establish
a maximum depth at which the pyrophyllite de-posits
were formed. At no place is the total thick-ness
of the Santiago Peak volcanics known, but it
may well have amounted to several thousand feet.
On the basis of the general geologic relations and
the indirect evidence from laboratory investiga-tions,
it seems likely that the San Dieguito pyro-phyllite
deposits were formed hydrothermally
under conditions of intermediate temperatures
15
and pressures. This is in accord with conclusions
reached by Buddington (1916) for somewhat
similar deposits in the Conception Bay region of
Newfoundland, and by Stuckey (1925) for the
deposits in the Deep River region of North Caro-lina.
In contrast, the deposits on Vancouver Is-land,
British Columbia, appear to have been
formed under near surface conditions."
Based on a study of samples collected from
various pyrophyllite deposits of North Carolina,
Zen (1961) tended to disregard the effect of
hydrothermal replacement solutions on the forma-tion
of the pyrophyllite bodies. He considered the
presence of the three phase mineral assemblage
of the ternary system A12 3 — H2 —Si02 to
indicate that water acted as a fixed component.
He further noted, however, that to say water
acted as a fixed component did not completely
imply the absence of a free solution phase (hy-drothermal
solutions). Such a phase could have
existed, but certainly did not circulate freely
through the system destroying the buffering
mineral assemblages.
Conley (1962a) concluded: "The bulk chemical
composition of the pyrophyllite deposits is essen-tially
the same as that of the country rock. All
of the chemical elements present in the pyrophyl-lite
deposits are present in the country rock, with
the exception of fluorine, copper and gold. These
elements are associated with quartz veins and
silicified zones and were obviously brought in
from an outside source. The pyrophyllite deposits
could have formed in place with either addition
or substraction of chemical elements if the ele-ments
were properly segregated and recrystallized
into new minerals."
LeChatelier (1887) determined the tempera-ture
at which pyrophyllite loses its water and
found two points of marked loss, one at 700° and
the other at 850° C. Stuckey (1924) made a com-parative
dehydration test of pyrophyllite and
sericite and found that sericite lost its water much
faster than pyrophyllite at lower temperatures
and at 750° C was practically dehydrated while
the pyrophyllite held about 1 percent of its water
which was finally lost at approximately 900° C.
Rogers (1916) classed sericite as a typically
low temperature mineral associated with the last
stages of hydrothermal alteration while Lindgren
(1919) classed it as a mineral common to hydro-thermal
alterations at shallow and intermediate
depths and pointed out that in acid rocks of the
rhyolitic type silicification and sericitization are
common near the surface, but did not agree with
Rogers that sericite is a late mineral.
While much has been published regarding the
nature of chloritoid there is little definite infor-mation
on its genesis. Clark (1920) stated that
chloritoid is formed in schists where much iron
and water are present, and that it is intermediate
between the micas and chlorite and may alter
into either. Manasse (1910) described a schist of
sericite, quartz, rutile, tourmaline, chlorite and
epidote from the Alps of Italy, closely associated
with and occurring on both sides of a marble, in
which chloritoid is abundant.
Niggli (1912) in a study of the chloritoid and
ottrelite groups of the Swiss Alps decided that
the two minerals are identical. He pointed out
that chloritoid is abundantly developed in schists
that were originally high in clay content and
thought that its formation was directly due to
pressure and relatively independent of tempera-ture.
He gave a diagram showing that regardless
of temperature, chloritoid is formed with an in-crease
in pressure and conversely it drops out
when the pressure diminishes.
ANALYSES OF ROCKS
In Table 1, on page 17, there are a number of
chemical analyses of rocks and minerals from the
Carolina Slate Belt of North Carolina and for
comparison, several analyses of similar rocks
from other regions. Number 1 is a rhyolite from
Flat Swamp Mountain in the Carolina Slate Belt
of Davidson County, North Carolina, while Num-ber
2 is a devitrified rhyolite from South Moun-tain,
Pennsylvania. Number 3 is an average of
115 analyses of rhyodacite and rhyodacite-obsidian
obtained from widespread areas. Num-ber
4 is dacite from Kemp Mountain in the
Carolina Slate Belt of Davidson County, North
Carolina. Number 5, is dacite tuff, 1 mile south-east
of Monteith Bay, Vancouver Island, while
Number 6, is the same type of rock a short dis-tance
away that has been silicified and altered
to a cherty quartz-sericite rock. Numbers 7, 8,
9 and 10, represent commercial pyrophyllite from
4 mines in North Carolina.
Analyses Number 1 through 5, Table 1, page 17,
represent normal or average rhyolite and dacite
rock types, and as is to be expected the bulk com-position
of these analyses is remarkably uniform.
Si02 varies from 66.27 to 74.67 percent, A12 3
16
from 10.78 to 15.39 percent, CaO from 0.34 to
3.68 percent, Na2 from 3.40 to 5.46 percent, K2
from 1.74 to 3.01 percent, and H2 from a trace
to 0.68 percent. Analyses number 7 through 10,
represent average commercial pyrophyllite, and
as might be expected the bulk composition of
these analyses is remarkably uniform. Si02 varies
from 57.58 to 64.68 percent, A12 3 from 28.34 to
33.31 percent, CaO from a trace to 0.72 percent,
Na2 from 0.06 to 0.38 percent, K2 from a trace
to 3.90 percent, and H2 from 5.40 to 5.86 per-cent.
This change in bulk composition from rhyolite
and dacite to pyrophyllite was brought about by
silicification of the rhyolite and dacite to a cherty
quartz rock as shown in analysis number 6, fol-lowed
by replacement to pyrophyllite. As silicifi-cation
advanced there was a decrease in alumina
and alkalies and an increase in silica. Replace-ment
by pyrophyllite, in some cases, preceded or
accompanied by sericite, resulted in a decrease in
silica and an increase in alumina, potash increas-ing
with the sericite content, while water in-creased
from about 1 percent to an average of
5.59 percent.
The conditions indicated by the above analyses
may be observed at many of the pyrophyllite de-posits
in the area. Beginning in walls of unaltered
rhyolitic or dacitic tuff there is a gradual transi-tion
through silicification, sericitization and pyro-phyllitization
to lenses and masses of practically
pure pyrophyllite in the interior of the bodies.
As a result, the mineral bodies contain walls of
silicified country rock that on the interior por-tions
have been more or less sericitized and par-tially
to completely pyrophyllitized.
Table 1. Analysis of Rhyolite, Dacite and Pyrophyllite
1 2 3 4 5 6 7 8 9 10
Si02 74.67 73.62 66.27 72.33 73.22 87.80 64.53 57.58 64.68 64.54
A12 3 10.78 12.22 15.39 14.56 13.46 9.08 29.40 33.31 28.34 28.88
Fe2 3 1.25 2.08 2.14 0.15 2.33 0.40 0.33 0.60 0.45
FeO 2.11 2.23 2.22 0.96 nd 0.67 nd nd nd
MgO trace 0.26 1.57 0.91 0.42 trace trace trace trace
CaO 1.47 0.34 3.68 2.55 1.50 trace trace 0.72 0.36
Na2 5.31 3.57 4.13 3.40 5.46 0.62 0.28 0.06 0.38 0.12
K2 2.68 2.57 3.01 2.82 1.74 1.70 trace 3.90 0.01 0.18
H2 0.59 0.68 0.30 0.62 1.04 5.86 5.56 5.54 5.40
C02 1.30
Ignition 0.40
Total 100.16 99.09 99.26 99.24 99.71 100.04 100.33 100.74 100.27 99.33
1. Rhyolite from Flat Swamp Mountain, North Carolina, Pogue (1910) p. 54
2. Devitrified rhyolite from South Mountain, Pennsylvania, Williams (1892) p. 494
3. Average of 115 analyses of rhyodacite and rhyodacite-obsidian, Nockolds (1954) p. 1014
4. Dacite from Kemp Mountain, Davidson County, North Carolina, Pogue (1910) p. 57
5. Dacite tuff 1 mile southeast of Monteith Bay, Clapp (1914) p. 120
6. Silicified dacite tuff (cherty quartz-sericite rock) Monteith Claim, Clapp (1914) p. 120
7. Pyrophyllite from Rogers Creek Mining Company's mine, Pratt (1900), p. 26
8. Pyrophyllite from Standard Mineral Company's mine, Stuckey (1928), p. 36
9. Pyrophyllite from Womble mine, Stuckey (1928) p. 36
10. Pyrophyllite from Gerhard Bros., Staley, North Carolina, Stuckey (1928) p. 36
17
ORIGIN OF NORTH CAROLINA
PYROPHYLLITE
The field, microscopic and chemical evidence
indicates that the pyrophyllite deposits in North
Carolina have been formed through the metaso-matic
replacement of acid tuffs and breccias of
both rhyolitic and dacitic composition. The de-velopment
of pyrophyllite was accompanied by
the introduction of Si02 , A12 3 and water. The
quartz, pyrite, chloritoid, sericite and pyrophyl-lite
in the mineralized bodies are apparently of
hypogene origin.
Evidences that the deposits have been formed
by replacement are as follows
:
(1) Gradational contacts between pure pyrophyllite
and the unaltered country rocks.
(2) The preservation of structures of the primary rocks
in the mineralized rocks, such as bedding planes
of the finer tuffs, and fragmental outlines of the
coarser tuffs and breccias.
(3) The presence of masses and lenses of practically
pure or only partly altered country rock, appar-ently
unattached and completely surrounded in the
mineral bodies.
(4) The introduction of some elements and the removal
of others.
(5) The lack of any noticeable change in the volume
of the original rocks during the mineralization
processes.
(6) The massive and homogeneous structure of the py-rophyllite.
The following sequence of events is deduced
:
(1) The metamorphism of the volcanic fragmental and
flow rocks in which the mineral bodies were later
formed.
(2) The silicification of the volcanic fragmental and
flow rocks by metasomatic processes as is indicated
by the presence of original structures of the vol-canics
in the silicified materials, and by the pres-ence
of entirely surrounded fragments of only
partly silicified volcanic rocks in the quartz areas.
(3) The development of pyrite in the silicified areas,
accompanying or immediately following the silci-fication
of the volcanics.
(4) The development of chloritoid to some extent in all
the pyrophyllite bodies and in abundance in parts
of these deposits that are near iron rich forma-tions.
(5) The development of sericite by the replacement of
the previously silicified volcanic fragmental and
flow rocks.
(6) The development of pyrophyllite by replacement of
the previously silicified and mineralized tuffs and
breccias, closely associated with or immediately
following the formation of the sericite.
SOURCE OF MINERALIZING SOLUTIONS
The pyrophyllite forming solutions were evi-dently
of hypogene origin, but their source is not
so easily demonstrated. The only intrusive igneous
rocks that are exposed near any pyrophyllite de-posits
in the area are diabase dikes, which are
clearly later than the pyrophyllite mineralization.
While none of them are known to be exposed in
or near a pyrophyllite deposit there are a great
many granite type intrusive rocks exposed at
widely scattered localities in the pyrophyllite
area.
During the latter half of the nineteenth cen-tury
there were a number of active gold and cop-per
mines throughout the Carolina Slate Belt that
were important enough to receive considerable
attention in reports of the North Carolina Geolog-ical
Survey between 1856 and 1917. Nitze and
Hanna (1896) pointed out that the gold and cop-per
deposits throughout the Carolina Slate Belt
are very similar and that much silicification had
accompanied the formation of the ores. They at-tributed
this mineralization to hot carbonated,
alkaline waters of deep seated origin. Laney
(1910) found much silicification associated with
the ore bodies (gold and copper) at Gold Hill,
and concluded that the mineralization had been
produced by hot solutions given off from a granite
that had been intruded into the volcanics in the
immediate vicinity of the ore bodies. Pogue
(1910) found practically the same conditions in
the Cid district of Davidson County, except that
there were no known intrusive igneous rocks to
have furnished the solutions. He concluded, how-ever,
that there were large igneous masses in-truded
into the rocks of the district from below,
but that these rocks did not reach the surface.
If Nitze and Hanna are correct in their state-ments
that the gold and copper mines of the en-tire
slate belt are in general alike, and if Pogue
is correct in assuming a large intrusive magma
below the Cid district that belonged to a period
when large amounts of igneous rocks were in-truded
into the Piedmont Plateau and brought
near the surface, it seems that the same condi-tions
must have existed in the pyrophyllite re-gion
and that the gold ores of the various mines
were formed by hot solutions from igneous mag-mas
below. There is a close relation between the
pyrophyllite deposits and the metalliferous de-posits
at a number of places. One that may be
used as a type example is the mine of the Stand-ard
Mineral Company near Robbins, Moore Coun-ty,
where the pyrophyllite schist grades directly
into the silicified tuff at the old Cagle gold mine.
This seems to indicate that the same source that
18
furnished the hot solutions to deposit the gold and
copper ores in the slate belt also furnished the hot
solutions to produce the pyrophyllite bodies.
CONDITIONS OF PYROPHYLLITE
FORMATION
Different investigators have indicated that py-rophyllite
may form under conditions varying
from high temperature and pressure to low tem-perature
and pressure such as exist near the
surface.
The information available on the origin of
chloritoid. seems to indicate that it forms at fairly
high temperatures and according to Niggli
(1912) is directly dependent upon fairly high
pressure.
Graton (1906) classed the gold-quartz veins of
the Southern appalachians as high temperature
in origin, while Laney (1910) and Pogue (1910)
both indicated that the gold and copper ores of
the Gold Hill and Cid districts were formed under
conditions of temperature and pressure varying
from high to intermediate. That the pyrophyllite
bodies were formed by hot solutions given off
from the same source and acting at about the
same time is indicated by the close association of
the pyrophyllite bodies with the old gold mines,
especially the Cagle gold mine near Robbins,
Moore County and at the Brewer gold mine
(Powers, 1893) in South Carolina. Hafer (1913)
noted the presence of copper bearing pyrite in
the mine of the Southern Talc Company at Glen-don,
Moore County.
It is possible that at the pyrophyllite deposits
there was a gradual change from high tempera-ture
and pressure to low temperature and pres-sure
of hydrothermal alteration near the surface
during the period of activity of the hot solutions.
The writer, however, agrees with Buddington
(1916) and Jahns and Lance (1950) and believes
that the pyrophyllite deposits of the Carolina
Slate Belt in North Carolina were formed under
conditions of intermediate temperature and pres-sure.
While considering the source of the solutions
and the conditions under which the pyrophyllite
was formed the problem of a line of entrance for
rising solutions should not be overlooked.
As has been stated above, the pyrophyllite de-posits
occur as elongate bodies or lenses several
times as long as they are wide. In at least four
localities, near Robbins, Moore County, along
Deep River north of Glendon in Moore County,
near Hillsborough in Orange County, and north
of Stem in Granville County, the pyrophyllite
bodies occur as a long zone of lenses from 50 feet
to 500 feet wide and from 250 feet to 2000 feet
long that can be traced for considerable distances
along strike. The mineral bodies are all found in
acid tuffaceous rocks and in some cases, particu-larly
along Deep River north of Glendon in Moore
County, on the limbs of anticlines (as they were
worked out and mapped in the field).
It seems unreasonable for a special type of vol-canic
tuff to have been formed as long narrow
bands so widely separated while at all other points
there were such wide variations in the material.
The conclusion, therefore, is that there was either
faulting or some lines of weakness developed
along which the solutions entered to form the
mineral deposits.
Recently, Conley (1962 a) has shown that the
pyrophyllite deposits along Deep River, north of
Glendon, and those southwest of Robbins in Moore
County, were formed along fault zones. There has
not been enough detailed mapping carried out to
determine the true conditions at the other de-posits
in the slate belt. Stuckey (1928) pointed
out that the pyrophyllite bodies were formed by
the replacement of acid tuffs and breccias of both
dacitic and rhyolitic composition and that the
tuffs and breccias remained in a state of open
texture and tended to mash and shear instead of
folding. It is logical to assume, therefore, that all
the pyrophyllite bodies were formed along lines
of weakness, either fault zones or shear zones.
RESERVES
Sufficient evidence is not available to determine
accurately the reserves of pyrophyllite in North
Carolina, but there is sufficient information to
establish the presence of fairly dependable indi-cated
reserves. Of some 15 known occurrences of
pyrophyllite in North Carolina only 5 or 6 have
been developed enough to indicate important re-serves
of mineable pyrophyllite. These major
deposits occur near Robbins and Glendon, Moore
County, near Snow Camp, Alamance County, near
Hillsborough, Orange County and near Stem,
Granville County. All of these deposits, with two
exceptions occur along prominent hills or ridges.
The Glendon deposits occur in gently undulating
topography, while that near Robbins occurs in a
relatively flat area covered largely by a thin
veneer of Coastal Plain sand.
19
To-date, with one exception, all the pyrophyl-lite
mining in the State has been carried out
largely from shallow pits and open cuts that have
seldom reached a depth greater than 50 or 75
feet. The one exception to these conditions is at
the mine of the Standard Mineral Company at
Robbins, Moore County, where a shaft 650 feet
deep and drifts and stopes are being used. In
none of these pits, open cuts, or mines has there
been any major change in the pyrophyllite or
associated minerals with depth.
Even though pyrophyllite should not be found
in commercial amounts to depths of over 200 feet,
there is enough available to that depth, in the
more promising deposits, to support an important
industry for many years under efficient mining,
milling and concentration practices.
The processes of milling have been such that
everything that went into the mill had to be pure
enough to make a good finished product. It is only
recently that any attempt has been made to use
separating and concentrating machinery in the
removal of grit and other impurities. This has
meant that a large amount of material which con-tained
50 percent or more of pyrophyllite has
been going on the dumps as waste. If the methods
of milling could be improved to the point where
all material containing as much as 40 to 50 per-cent
pyrophyllite could be utilized, it would prac-tically
double the available amount on the basis of
milling practices formerly carried out.
Pratt (1900) pointed out that the pyrophyllite
is continuous and of considerable, though un-known
depth. Hafer (1913) suggested that pyro-phyllite
should be found to the same depths that
the gold mines of the area have reached, and in-dicated
that gold had been mined to a depth of
500 feet. This statement seems very reasonable
when it is realized that there is a close relation
in the distribution of the gold and pyrophyllite
mines, and also a strong possibility that the solu-tions
forming both come from the same source.
Stuckey (1928) stated: "Taking into consider-ation
the mineralogy and origin of the deposits,
the source of the solutions and the relations in
the distribution of the gold and pyrophyllite de-posits,
it seems reasonable to expect pyrophyllite
in commercial amounts to a minimum depth of
500 feet. This statement does not mean that every
pyrophyllite deposit can be developed into a mine
at that depth. It does mean, however, that all
indications point to a depth of that magnitude
for the larger bodies which really show promise
at the surface."
The results obtained in exploring for pyrophyl-lite
over the intervening years have borne out
this statement. Some small prospects have been
explored that did not prove continuous with
depth, but drill holes more than 500 feet deep
have failed to reach the limits of the major de-posits.
The pyrophyllite deposits occur as irregular
lenses 50 to 500 feet wide and 500 to 1500 or more
feet long. The bodies of workable pyrophyllite
usually occur near the center of the deposits and
vary in width from a few feet to more than 100
feet. Pyrophyllite has a specific gravity of 2.8 to
2.9 and weighs 175 pounds per cubic foot. Each
100 feet of length and depth of a pyrophyllite
body 100 feet wide should yield 50,000 tons allow-ing
for a 60 percent recovery. Using these figures
and assuming recovery to a depth of 400 to 500
feet, a reserve of some 10 to 12 million tons of
pyrophyllite is indicated in North Carolina.
During the past 15 years it has been frequently
stated that all the really promising pyrophyllite
deposits in North Carolina had been discovered
and were controlled by three or four major min-ing
companies. Recently, detailed prospecting by
two major companies has resulted in the discovery
of promising occurrences of pyrophyllite in three
new areas. These deposits have not been explored
and detailed information on them is not available.
These discoveries are interesting, however, as
indicating that undiscovered bodies of pyrophyl-lite
are still available in North Carolina to those
willing to do the necessary prospecting to find
them.
MINING METHODS
The first reference to pyrophyllite mining in
North Carolina was by Emmons (1856, p. 217)
who stated: "Large quantities have been ground
the last year in Chatham County for the New
York market." He, also stated (p. 53) "The rock
does not split readily with gunpowder; when
quarried in this mode, as at Hancock's, it breaks
out in illshapen shattered masses. Hence it should
be cut out with a sharp pick or an edged instru-ment
of suitable form."
At first prospecting and mining were carried
out by pits, shallow shafts, drifts and open cuts.
As demands for larger quantities increased and
off color material became salable, open cuts
—
20
made possible by information from diamond drill-ing
and by modern earth-moving machinery have
furnished most of the production. The largest,
and only modern underground pyrophyllite mine
in North Carolina, is operated near Robbins,
Moore County, through a 650 foot shaft, drifts
and stopes.
PROCESSING
The processing of pyrophyllite has changed
slowly through the years as demands and uses for
the mineral have increased and changed. Prior to
about 1855 it was used only locally—for stove
linings, fireplaces, chimneys, mantels and grave-stones—
and was cut and shaped to fit the par-ticular
need. The production of pyrophyllite
crayons was started about 1880 and continued
until about 1920. Ground pyrophyllite was first
produced in 1855, (Emmons 1856, p. 217) . From
1855 to 1913 grinding was carried out, first at
Hancock's Mill and later at Glenn's Mill, both
located on Deep River near the present village of
Glendon, Moore County. The grinding stock was
carefully selected, air dried, and crushed. It was
then crushed by hand, ground with millstones and
passed through bolting cloth.
In 1902 the first mill constructed exclusively
for grinding pyrophyllite was built near a deposit
along Deep River, north of Glendon. This was
followed in 1904 by a second mill on another de-posit
about a mile away. Both mills were alike
in that the grinding stock was air dried and
crushed. In one mill the crushed material was
passed through a hammer mill, ground with mill-stones,
fed into a ball mill, ground 8 hours and
screened. In the other mill, the crushed material
was ground with millstones, the fines removed by
air, and the coarse material fed into a ball mill,
ground, and screened. Both of these mills were
abandoned by the end of 1921.
Before 1918, all the known pyrophyllite de-posits
of any importance were located along the
north side of Deep River, in the general vicinity
of Glendon, Moore County. In that year, what
later proved to be the largest known pyrophyllite
deposit in the state was discovered about 2 miles
southwest of Robbins, Moore County, when wagon
wheels brought up a fine white material that
proved to be pyrophyllite. The first modern grind-ing
plant was built on this property about 1921.
The process first used consisted of crushing,
grinding in a hammer mill and screening. The
hammer mill did not prove satisfactory for grind-ing,
and after some modifications, the process
was abandoned. A new process was installed, con-sisting
of crushing and grinding in a roller mill,
and screening. As the ceramic market for pyro-phyllite
has become more important, conical peb-ble
mills for fine grinding have been installed in
this and other plants in the State.
At the present time three companies—the
Standard Mineral Company at Robbins, the Gen-eral
Minerals Company at Glendon, and the
Piedmont Mineral Company at Hillsborough are
mining and processing pyrophyllite for market.
A fourth company, the North State Pyrophyllite
Company at Greensboro is mining pyrophyllite
and producing a variety of pyrophyllite refrac-tories
but is not selling pyrophyllite as such.
None of these companies is carrying out benefi-ciation
or true mineral dressing on crude pyro-phyllite.
By selective mining, blending, grinding
and screening, a wide variety of grades, stand-ardized
both as to grain size and chemical com-position,
is being produced for fillers and specialty
products and for use in ceramic bodies and re-fractories.
In the processes used to-date, only pyrophyllite
pure enough to make a salable finished product
has been used. As a result, much good material
containing 40 to 60 percent pyrophyllite has been
discarded. In view of the somewhat limited re-serves
and increasing demands, too much good
material is being left in the ground or thrown on
the dumps. However, as demands have increased,
improved methods of grinding and screening have
reclaimed much material formerly discarded. Re-search
on the removal of iron, free silica and
other impurities has been carried out. As a result,
larger tonnages of pyrophyllite of higher quality
than that now being produced should be made
available to industry as demands increase.
USES OF PYROPHYLLITE
Pyrophyllite has a wide range of uses which
are dependent largely upon the remarkable physi-cal
properties of the mineral. Most of these uses
are similar to those of talc, to the extent that the
two minerals are often used interchangeably. Py-rophyllite
is a hydrous aluminum silicate with the
formula H2Al2Si40i2. It occurs in several common
habits, the best known, perhaps, being the rosette-like
aggregates of radially disposed fibers and
elongate flattened crystals. A flaky or foliated
21
variety with a slaty cleavage is common along
the north side of Deep River and near Robbins
in Moore County. A third variety consists of
masses of grains and fibers that lack orientation
or layering. In some of the finer-grained occur-rences,
the pyrophyllite individuals are rosette-like
in detail although this is rarely apparent to
the unaided eye.
While the chemical formula of theoretically
pure pyrophyllite is rather simple, most commer-cial
pyrophyllite contains varying small quanti-ties
of the elements, iron, calcium, magnesium,
sodium, potash and titanium. The chemical com-position
can be useful in predicting the behavior
of pyrophyllite where very exact controls are
required in the manufacture of certain products.
In ceramic bodies, for example, such properties
as color, shrinkage and absorption of tile bodies
can be predicted in terms of the raw pyrophyllite
used in them.
The nature and uses of several types of pyro-phyllite
from North Carolina have been effec-tively
summarized in a booklet published by the
R. T. Vanderbilt Company (1943) of New York.
For further details on the properties of pyro-phyllite
the reader should consult Grunner
(1934), Hendricks (1938), and Ross and Hend-ricks
(1945).
Prior to about 1855, pyrophyllite was used
locally for tombstones, and such stones, still well
preserved, may be seen in two or more cemeteries
near Glendon. Emmons (1856) described it as an
excellent substitute for soapstone in stove linings,
fireplaces, chimneys and mantles. He stated that it
was not suitable for paint as it became translu-cent
when mixed with oil, but described it as a
filler that helped retain the perfume in soap and
added that large quantities were ground for the
New York market in 1855. He described it as
suitable for anti-friction powder and use in cos-metics
and quoted Dr. Jackson to the effect that
it would make a very refractory material for
stoneware and crucibles.
At present, pyrophyllite is used chiefly in the
manufacture of insecticides, rubber, paint, ceram-ics,
refractories, plastics, and roofing paper. It
has a number of minor uses for products including
cosmetics, wallboard, rope and string, special
plaster, textile products, paper, linoleum and oil-cloth,
and several types of soap. The best pro-duction
figures available indicate that about one
half of the current annual production goes into
insecticides, rubber and paint, one third into
ceramics and refractories and the remainder into
plastic, roofing paper, linoleum, cosmetics and a
host of minor uses.
According to Jahns and Lance (1950) : "A
large part of the domestic production of pyrophyl-lite
is incorporated into paints and particularly
non-reflecting and other special types in which
flake pigments of light color are desired. High oil
absorption of ground pyrophyllite and its free-dom
from grit also are desirable properties for
paint use. Ground material is employed as a filler
in rubber goods, certain roofing and flooring ma-terials,
special plasters, plastics, insecticides, tex-tile
products, paper, linoleum and oilcloth, rope
and string, several types of soap and in some
fertilizers. It serves as a "loader" in paper and
textile fabrics, where its whiteness and resistance
to the effects of fire and weather are particularly
desirable. This resistance also partly accounts for
its use in roofing papers and other asbestos and
asphalt goods. Its corrosion resistance makes it
an especially satisfactory filler in battery cases.
There are indications that it also may serve effec-tively
as a low noise filler in phonograph records.
"With a low bulk density and slight acidity in
ground form, high absorptive characteristics, and
superior qualities as a flake-form dusting agent,
pyrophyllite is an excellent carrier for such active
insecticides as DDT, nicotine, pyrethrum and
rotenone. The flakiness of the mineral leads to
desirable adhesion on leaves and other parts of
dusted plants, and its softness and freedom from
grittiness when finely ground make for reduction
of wear on nozzles and other parts of mechanical
insecticide dispensers.
"Pyrophyllite of great purity and whiteness has
been used as a base for cosmetics and toilet prep-arations,
but the total amount is not large. The
lubricating properties of the mineral underlie its
use in some greases, in tires and other rubber
goods, on machine-driven box nails, and in vari-ous
kinds of dies. On the other hand, it also is
employed as a fine, "soft" abrasive in the scour-ing
and polishing of certain foodstuffs, as well
as some painted or lacquered surfaces. It serves
as a high-quality packing and insulating material,
as a constituent of adhesive, corrosion-resistant
covering compounds, and as an absorbent for oil
substances in a wide variety of products. It,
also, can be processed for use in crayons and
pencils.
22
"As a constituent of ceramic bodies, pyrophyl-lite
is being more and more widely used. It is a
good substitute for feldspar and quartz in wall-tile
bodies, as it decreases their shrinkage and
their crazing by thermal shock or moisture ex-pansion.
It also is employed as a source of alumi-num
in enamels, and as a raw material for semi-vitreous
dinnerware and some types of refrac-tories."
Uniformity of grain size and mineral content
is becoming important for all uses. For ceramics,
whiteware, and wall tile, where the size of the
finished product must be controlled accurately,
pyrophyllite is one of the best materials available
provided it is perfectly uniform in grain size and
composition. For use in special refractories, such
as car tops for tunnel kilns, monolithic furnace
lining and furnace lining requiring rapid tem-perature
changes, pyrophyllite makes an excel-lent
body that is shock-resistant.
MINES AND PROSPECTS
Beginning on the northeast in Granville Coun-ty,
near the Virginia line, and continuing in a
southwesterly direction to the southwestern part
of Montgomery County is an irregular zone, along
the eastern part of the Carolina Slate Belt, that
contains all the known occurrences of pyrophyl-lite
in North Carolina. Prospects, outcrops and/or
mines are known to occur in Granville, Orange,
Alamance, Chatham, Randolph, Moore and Mont-gomery
counties.
GRANVILLE COUNTY
Daniels Mountain
Pyrophyllite bodies occur in three localities in
Granville County. One of these is on Daniels
Mountain, a prominent ridge that rises nearly
200 feet above the surrounding countryside.
Daniels Mountain is located approximately 9
miles slightly northwest of Oxford, about 1.5
miles east of North Carolina Highway 96 and
just south of Mountain Creek. The area is un-derlain
with acid volcanic rocks. Small amounts
of pyrophyllite occur on the north end of this
ridge. No prospecting had been done at the time
the writer visited the ridge. Espenshade and Pot-ter
(1960) described Daniels Mountain as fol-lows
: "Another deposit of pyrophyllite occurs on
a prominent ridge rising nearly 200 feet above
the surrounding countryside, about 14 miles
northeast of Bowlings Mountain deposit, 9 miles
northwest of Oxford, and about l 1/^ miles east
of North Carolina Highway 96. Float and low
outcrops of dense siliceous rock are abundant for
about three-quarters of a mile along the ridge.
Chloritoid occurs in some rock, disseminated
hematite and magnetite are also present. Blocks
of massive pyrophyllite, 1 to 2 feet long, are dis-tributed
along a distance of 600 to 700 feet at
the north end of the ridge. Other aluminous min-erals
have not been discovered."
Bowlings Mountain
A major pyrophyllite deposit is present on
Bowlings Mountain, a prominent hill that is lo-cated
about 3 miles northwest of Stem and 10
miles southwest of Oxford, Granville County. The
hill rises to an elevation of about 700 feet above
sea level (approximately 200 feet above the sur-rounding
countryside), has a trend of about N
15° E and conforms to the pattern of a series of
rather pronounced ridges to the northwest. The
pyrophyllite deposit which lies along the crest
and northeastern slope of the mountain is ap-proximately
500 feet wide and more than 1500
feet long. The strike is N 15° E and the apparent
dip is 70° to 80° to the northwest, paralleling
the strike and dip of the country rock.
Prospecting was first carried out on the south-west
end of the ridge and near the western slope,
about the turn of the century, when a pit known
as the Harris prospect was opened. This pit which
was 15 to 20 feet long, 6 feet wide and 6 to 10
feet deep was opened on an outcrop of radiating
or needle-like crystals of iron-stained pyrophyl-lite.
About 1940 a shaft was sunk to a depth of
approximately 80 feet near these old pits. The
phyrophyllite found in this shaft did not differ
materially from that found in the surface pits and
the work was abandoned.
About 1949 or 1950, Carolina Pyrophyllite
Company began exploration and development
work here, consisting of pitting and trenching
followed by drilling, during the course of which
a large tonnage of pyrophyllite was discovered.
Following this exploration work, 2 opencuts were
developed from which considerable pyrophyllite
was mined and shipped by truck to a grinding
plant at Staley, some 80 miles to the southwest,
before that mill was closed in 1960.
23
On the southeast or footwall side of the deposit
is a medium-grained, dense, quartzitic rock con-taining
pyrite that seems to represent the foot-wall
of the deposit. Northwestward from the
quartzitic rock mineralization is quite apparent.
Massive and crystalline pyrophyllite occurs in
very fine-grained schistose zones in sericite schist.
Tough, white, granular rock containing coarse-grained
andalusite, quartz, and pyrophyllite is
present in parts of the deposit. Massive topaz
identical in appearance with the dense topaz from
the Brewer mine in South Carolina is abundant
as float adjacent to the quartzitic footwall. Here,
it is found concentrated in a series of rather
poorly defined zones covering an area more than
100 feet long and 200 feet wide. Individual pieces
range from less than one-fourth inch to 3 feet
in diameter. Outcrops in the area are rare, but, in
recent road cuts along the northern end of the
mountain, topaz is exposed as a series of narrow,
irregular veinlike masses in sericite schist. It
also occurs as stringers a few inches thick in
phyrophyllite in the southernmost open cut. The
topaz occurs as boulders in the quartzitic rock,
filling cracks and fractures, as small knotty
masses disseminated throughout the rock and as
large massive pieces which in some cases appear
to grade into the host rock. The andalusite and
topaz, older than the pyrophyllite, appear to re-place
the country rock and in turn are replaced
by pyrophyllite.
Long Mountain
About a mile or two to the northwest of Bowl-ings
Mountain is a zone of irregular hills from 1
to 1.5 miles wide and 4 to 5 miles long that is
known as Long Mountain. This ridge trends
about north 20 degrees east and lies partly to
the north and partly to the south of State Road
1139. The highest point on Long Mountain is a
knob north of State Road 1139 and along the
western side of the ridge that is known as High
Rock Mountain. It rises to an elevation of some
150 to 200 feet above the surrounding country-side
and 700 feet above sea level. Pyrophyllite
outcrops of varying size and promise, some of
which have been prospected and some of which
have not, are widely scattered throughout Long
Mountain.
Robbins Prospect 1
On the Robbins property, in the vicinity of
High Rock Mountain is an area about 1000 feet
wide and 2000 feet long on which radiating pyro-phyllite,
associated with quartz veins, is common
but not abundant. No prospecting has been done
in this general area and the potential for commer-cial
deposits of pyrophyllite is unknown. Most of
the pyrophyllite visible is badly iron stained.
Jones Prospect
To the east of the Robbins tract and about 1500
feet north of State Road 1139, some 4 or 5 pros-pect
trenches that varied in length from 150 to
300 feet and up to 8 or 10 feet deep were opened
on the Jones land some 8 or 10 years ago. Details
of this prospecting are not available but indica-tions
for pyrophyllite are good. The country rock
is a medium to fine-grained felsic volcanic tuff
that has a cleavage which strikes north 20 to 30
degrees east and dips steeply to the northwest.
Both foliated and radiating pyrophyllite, some
of which is iron stained, is farily common.
R. E. Hilton Property
Adjoining the Jones land on the east is the land
of R. E. Hilton on which there is a zone varying
from 250 to 500 feet wide and about 1000 feet
long that contains promising outcrops of pyro-phyllite.
No prospecting has been done on this
property but bold outcrops of good pyrophyllite
make it appear promising.
E. C. Hilton Property
Along the east side of Long Mountain and
south of State Road 1139 there are two interest-ing
areas of pyrophyllite on the land of E. C.
Hilton. The first of these, which is about 1500
feet south of State Road 1139 and near a recent
sawmill site, consists of about three acres on
which bold outcrops of pyrophyllite mixed with
similar outcrops of felsic volcanic rocks are abun-dant.
No prospecting has been done here but the
outcrops indicate the possible presence of im-portant
amounts of good pyrophyllite. The other
area is on a prominent hill about 1500 feet farther
southeast and beyond a small stream. Surface
exposures of pyrophyllite are not extensive but
some interesting outcrops of radiating crystals
may be seen. Considerable prospecting in the form
of drilling, the results of which are not known,
was carried out here about 8 or 10 years ago. The
country rock at both of these prospects is a medi-um
to fine-grained, felsic volcanic tuff.
24
Robbins-Uzzell Property
About 1500 feet south of State Road 1139 and
to the southeast of High Rock Mountain is an
unnamed ridge that ranges between 500 and 600
feet above sea level. This ridge which begins near
the head of an east flowing stream continues in a
south 20 degrees west direction to and beyond
Dickens Creek a distance of 1.5 to 2 miles. The
northeast end of this ridge is a part of the Rob-bins
tract while the southwest end is a part of
the Uzzell land. No prospecting has been done on
this ridge but outcrops of excellent pyrophyllite
remarkably free of iron stain make it promising
as a source of pyrophyllite.
Robbins Prospect 2
Just east of Knap of Reeds Creek and a short
distance south of State Road 1139 is a power
transmission line tower. Beginning near this
tower and extending to the southwest for a dis-tance
of 800 to 1000 feet is a pyrophyllite body
that is 300 to 400 feet wide. The cleavage in this
mineral body strikes about north 35 to 40 degrees
east and dips steeply to the northwest. The rocks
surrounding this deposit consist of medium- to
fine-grained acid volcanic materials. The north-west
150 to 200 feet of the deposit consists largely
of good quality pyrophyllite that varies from mas-sive
to foliated. The southeast or footwall portion
to a width of 75 or 100 feet appears to be in part
sericite. This is a promising deposit that could
contain considerable high-grade pyrophyllite.
ORANGE COUNTY
Murray Prospect
Pyrophyllite deposits occur in three localities in
Orange County. One of these known as the Mur-ray
property is located on a ridge about 5 miles
northeast of Hillsborough near the intersection
of State Roads 1538 and 1548. State Road 1538
passes just to the north of the property while
State Road 1548 lies just to the east. Here along
a ridge in an area of medium to fine-grained acid
volcanic rocks are old prospect pits up to 30 feet
long by 10 feet wide and 6 feet deep. Most of the
pits are about 10 feet long by 4 feet wide and 6
feet deep. The pits are scattered over an area 75
to 100 feet wide and 500 feet long. Pyrophyllite
of the foliated or schistose variety is present on
the dumps and in the sides of the pits as well as
in an occasional outcrop. Chloritoid is abundant
in the walls of some of the pits, especially near
narrow bands of greenstone in the felsic volcanics.
This area probably contains pyrophyllite of value.
Hillsborough Mine
Immediately south of Hillsborough are three
prominent hills which trend northeast and paral-lel
the major geologic structure of the area. From
northeast to southwest these hills are often desig-nated
Hill No. 1, Hill No. 2 and Hill No. 3. Al-though
the three hills appear to be much alike in
many ways, the developed mineralization is
limited to Hill No. 1, the northeastern most of
the three. Here, prospecting was started in 1952
by the North State Pyrophyllite Company fol-lowed
by mining a few years later. The zone of
mineralization as exposed by the open cut mining
operations is some 1500 feet long and from 100 to
250 feet wide. It strikes approximately N. 50° E.
and dips from 60 to 80 degrees to the northwest.
The mineral body has a footwall of dense siliceous
rock that forms the crest of the hill or ridge and
a hanging wall of sericite schist. The chief min-erals
in the deposit in the order of decreasing
abundance are silica, massive and crystalline or
radiating pyrophyllite, sericite, andalusite and
topaz. Minor amounts of diaspore have been re-ported.
Andalusite is abundantly disseminated
throughout the deposit and seems to be consider-ably
more abundant than pyrophyllite in much of
the deposit. It is light blue, greenish blue or gray
in color, has a pronounced blocky appearance, and
occurs as small fragments about one-fourth inch
in diameter, disseminated sparingly to abundant
throughout the quartzose rock. Topaz occurs spar-ingly
in the deposit, apparently being limited
largely to disseminated grains and masses in the
fractured quartzose footwall rock.
Recent field work indicates that to the south-west
mineralization similar to that on Hill No. 1,
now being worked by Piedmont Minerals Com-pany,
may be present in workable amounts on the
northwest side of Hill No. 2 and in a prominent
knob on the northwest side and near the north-east
end of Hill No. 3.
Teer Prospects
In the southwestern part of Orange County,
approximately 10 miles southwest of Hillsbor-
25
A. Mill
B. Open Pit Mine
Plate 2. Piedmont Minerals Company
26
ough, and in the general vicinity of Teer, there
are a number of pyrophyllite outcrops, at least
three of which have been prospected. On the north
end of Mitchell Mountain and about one-half mile
southwest of Teer, North State Pyrophyllite Com-pany
carried out prospecting and produced a small
amount of pyrophyllite. A pit 100 feet long, 30
feet wide at the top and 15 feet deep was exca-vated.
The strike of the cleavage is N. 55° E. and
the dip is 75 degrees to the northwest. The
amount of good grade pyrophyllite was too low
for economic mining and the prospect was ban-doned.
About 3 miles almost due north of Teer
and between State Road 1117 and Cane Creek, on
the farm of Salina Sykes is a small prospect pit
that contains minor amounts of radiating pyro-phyllite.
No production was made and the pit is
now abandoned.
About one mile almost due north of Teer and
between State Roads 1115 and 1116, considerable
prospecting and some mining for pyrophyllite
was carried out on the land of Clarence Bradshaw
by the Carolina Pyrophyllite Company, between
1958 and 1961. A pit 200 feet long by 100 feet
wide at the top and about 80 feet deep was exca-vated.
The pyrophyllite content of the rock was
originally 24 percent. The cleavage of the rock
strikes about N. 55° E. and dips 75 degrees to the
northwest.
ALAMANCE COUNTY
Snow Camp Mine
The Snow Camp pyrophyllite deposit being
worked by the North State Pyrophyllite Com-pany,
is located on Pine Mountain about 3.5 miles
southeast of Snow Camp. Prospecting was started
in 1935 and over the intervening years the de-posit
has been a major producer of massive pyro-phyllite.
The pyrophyllite is shipped by truck to
the company's plant at Pomona, North Carolina
where it is used in the manufacture of firebrick,
brick-kiln furniture and other refractory prod-ucts.
The deposit is a lenticular body of massive
pyrophyllite and fine-grained quartz about 35
feet long and 250 feet wide. Open pit mining had
developed walls nearly 100 feet high in the east
and south sides of the pit until parts of them
were removed for safety reasons in 1965. A rib of
high-silica rock is present near the center of the
deposit. This rib has been quite heavily mineral-ized
in places and parts of it have been mined out.
Coarse-grained andalusite was reported to have
been found in a zone several feet wide in the
northern part of the deposit, but it did not seem
to be very abundant. This deposit still appears to
contain a large reserve of high-grade pyrophyl-lite.
Major Hill Prospects
About 2 miles east of Snow Camp there are
several pyrophyllite outcrops on a prominent hill,
known locally as Major Hill. Major Hill lies south
of State Road 1005, between State Roads 2356
and 2351, and north of State Road 2348. This hill
is somewhat irregular in shape, but slightly elon-gate
in a direction a little north of east. Two
small exposures of pyrophyllite are to be seen in
old prospect pits near the west end of the hill,
but they do not appear to be of commercial size.
Beginning about midway of the hill from west to
east and along the southern slope some 250 feet
from the crest is a zone of pyrophyllite about
1000 feet long and 50 to 100 feet wide that ap-pears
from outcrops to contain a considerable ton-nage
of high-grade massive pyrophyllite. Due to
wooded conditions and lack of outcrops the geolog-ical
setting could not be satisfactorily determined.
It appears, however, that the pyrophyllite is in
an area of medium- to fine-grained tuffaceous
rocks of volcanic origin and acid composition. This
deposit is on land belonging to the North Carolina
National Guard.
Immediately to the east of the deposit on the
National Guard land is a deposit 100 to 150 feet
wide and 350 to 500 feet long on lands of the
Holliday estate. This deposit contains both pyro-phyllite
and sericite which have a cleavage that
strikes N. 50° to 60° E. and dips steeply to the
northwest. This deposit appears to contain a con-siderable
tonnage of minable material.
To the northeast of this deposit and near the
east end of Major Hill is another deposit of
promise on the Holliday estate. The outcrop is
irregular in shape but appears to be 150 to 300
feet wide and 400 to 500 feet long. Pyrophyllite
and sericite, both of which have a cleavage that
strikes N. 50° to 60° E. and dips steeply to the
northwest, are present in varying amounts in this
deposit.
To the south and southeast of the above de-scribed
deposits is another deposit on the south-east
tip of Major Hill and on lands of the Holliday
estate. This deposit is 150 to 250 feet wMe and
27
400 to 500 feet long. It contains both pyrophyllite
and sericite which have a cleavage that strikes
N. 50° to 60° E. and dips steeply to the north-west.
Because the above described three deposits, on
the Holliday estate are all in wooded areas and
rock outcrops are not too abundant it was not
possible to establish completely the geological
setting. It appears, however, that all three are in
areas of medium- to fine-grained tuffaceous rocks
of volcanic origin and acid composition. In the
spring and summer of 1966 these deposits were
under option to and being prospected by the North
State Pyrophyllite Company.
On the Richardson land, a short distance north-east
of Major Hill and just west of State Road
2351, is an interesting occurrence of pyrophyllite.
The outcrop area which is elongated in a north-east
direction appears to be about 100 feet wide
and 350 to 500 feet long. Both massive and radiat-ing
pyrophyllite are present.
About 2 miles east of Snow Camp and a short
distance north of State Road 1005, the Carolina
Pyrophyllite Company is quarrying sericite on a
small ridge on a hill adjacent to the Foust lands.
The sericite is being shipped by truck to Glendon
where it is ground and blended with pyrophyllite.
Open pit mining indicates a large tonnage of rock
which may extend into the Foust lands to the
north.
CHATHAM COUNTY
Hinshaw Prospect
The only known pyrophyllite deposits in Chat-ham
County are on the farm of Don Hinshaw in
the northwestern corner of the county. This prop-erty
is about 2 miles east of State Road 1004 and
a short distance north of State Road 1343. It can
be reached by leaving State Road 1004 at State
Road 1343 about 2.5 miles south of the Chatham-
Alamance line. Follow State Road 1343 about 1.5
miles northeast to the Hinshaw farm. The out-crops
are in a wooded area a short distance north
of the Hinshaw home. Here, some years ago,
Carolina Pyrophyllite Company opened a pit some
10 feet wide, 15 feet deep and 25 to 40 feet long.
Near this pit, pyrophyllite is scattered through
rocks over a distance of 100 feet long and 25 to
50 feet wide. To the northeast are other outcrops
that look promising. Enough pyrophyllite out-crops
are present in the area to indicate that it
is worth prospecting.
RANDOLPH COUNTY
Pyrophyllite is known to occur in Randolph
County in two areas. One of these is in the north-eastern
corner of the county about 3.5 miles west
of Staley. The other is on the southern slopes of
Pilot Mountain just north of State Highway 902
and about 8 miles east of Asheboro.
Staley Deposit
The Staley deposit, now worked out, was at one
time the second largest pyrophyllite mine in the
State. The main part of the deposit lay along the
crest and northwest side of a rather steep hill as
a lenticular body 100 to 200 feet wide and 350
feet long. The cleavage strike was approximately
N. 50° E. and the dip was 60 to 70 degrees to the
northwest. When abandoned the open cut was
about 180 feet wide, 300 feet long and 250 feet
deep. The hanging wall of the deposit consisted
of a volcanic ash largely altered to a sericite
schist. A central zone