c\
NORTH CAROLINA
DEPARTMENT OF CONSERVATION AND DEVELOPMENT
GEORGE R. ROSS, DIRECTOR
DIVISION OF MINERAL RESOURCES
JASPER L. STUCKEY, STATE GEOLOGIST
Bulletin Number 65
Geology and Structure of Part of the
Spruce Pine District,
North Carolina
A PROGRESS REPORT
BY
JOHN M. PARKER, III
Geological Survey, U. S. department of the interior
PRESENTING THE RESULTS OF A COOPERATIVE UNDERTAKING BETWEEN THE U. S.
GEOLOGICAL SURVEY AND THE NORTH CAROLINA DEPARTMENT OF
CONSERVATION AND DEVELOPMENT.
North Carolina
Department of Conservation and Development
George R. Ross, Director
Division of Mineral Resources
Jasper L. Stuckey, State Geologist
Bulletin Number 65
Geology and Structure of Part of the
Spruce Pine District,
North Carolina
A PROGRESS REPORT
By
John M. Parker, III
Geological Survey, U. S. Department of the Interior
Presenting the Results of a Cooperative Undertaking
Between the U. S. Geological Survey and the North
Carolina Department of Conservation and Development
MEMBERS OF THE BOARD OF CONSERVATION
AND DEVELOPMENT
Governor W. Kerr Scott, Honorary Chairman Raleigh
Miles J. Smith, Chairman Drawer 751, Salisbury
Walter J. Damtoft, Vice Chairman Canton
Charles S. Allen Box 409, Durham
W. B. Austin Jefferson
Aubrey L. Cavenaugh Warsaw
Ferd Davis Zebulon
Staley A. Cook Times-News, Burlington
C. Sylvester Green Box 31, Chapel Hill
Charles H. Jenkins Ahoskie
Fred P. Latham Belhaven
Mrs. Roland McClamroch 514 Senlac Rd., Chapel Hill
Hugh M. Morton Box 839, Wilmington
J. C. Murdock Route 1, Troutmans
W. Locke Robinson Mars Hill
Buxton White Elizabeth City
ii
LETTER OF TRANSMITTAL
Raleigh, North Carolina
October 22, 1952
To His Excellency, Honorable W. Kerr Scott
Governor of North Carolina
Sir:
I have the honor to submit herewith manuscript for publica-tion
as Bulletin 65, "Geology and Structure of Part of the Spruce
Pine District, North Carolina."' This Bulletin is another in the
series being made possible by the cooperation of the U. S. Geologic-al
Survey.
This report covers a part of the most important pegmatite
district in the United States, It is believed that the information
contained herein will be of considerable value to those interested
in pegmatites and pegmatite minerals.
Respectfully submitted,
George R. Ross,
Director
in
CONTENTS
Page
Abstract ...... 1
Introduction 1
Location of district 1
History 3
Summary of investigations in the district 3
Scope of present report 4
Acknowledgments 4
General geology of the district 4
Rock types 4
General statement 4
Metamorphic rocks : — . 6
Mica gneiss 6
Muscovite schist 6
Dolomitic marble 6
Hornblende gneiss, hornblende schist, and amphibolite 7
Igneous rocks 8
Dunite 8
Pyroxenite 8
Pegmatite 8
Aplite 10
Basalt 1
1
Altered metamorphic and igneous rocks 11
Mica injection gneiss 11
Chloritic amphibolite 12
Chlorite-biotite schist 12
Soapstone and talcose schist 13
Asbestos rock 13
Superficial deposits 14
Terrace deposits 14
Floodplain alluvium 14
Talus and landslide deposits - 14
Structure 14
Interlayering 14
IV
Page
Foliation and lineation 15
Folding 15
Faulting 1
G
Jointing 1
6
Deformation by intrusions .___ 16
Economic geology of the district 17
General statement 17
Pegmatite mineral products 17
Beryl 17
Columbium—tantalum minerals 17
Feldspar 17
Kaolin 18
Mica 19
Sheet mica '. 19
Scrap mica 20
Quartz 21
Rare earth minerals 21
Uranium minerals 21
Other mineral and rock products 21
Amphibole asbestos 21
Building stone and crushed rock 22
Chromite . 22
Garnet . 22
Kyanite 23
Mica schist .. _ 23
Olivine T . 23
Vermiculite 24
ILLUSTRATIONS
Plate 1. Geologic map of part of the Spruce Pine district,
North Carolina In Pocket
Figure 1. Index map of the Spruce Pine district, North Carolina 2
Table 1. Subdivisions of the Spruce Pine district 5
Digitized by the Internet Archive
in 2013
http://archive.org/details/geologystructure1952park
GEOLOGY AND STRUCTURE OF PART OF THE SPRUCE PINE DISTRICT,
NORTH CAROLINA
A PROGRESS REPORT
By John M. Parker, III
ABSTRACT
General geologic mapping and detailed studies of many mica, feldspar, and kaolin deposits have been
made by the U. S. Geological Survey since 1939 in the Spruce Pine pegmatite district, North Carolina. Much
of this work has been in cooperation with The North Carolina Department of Conservation and Develop-ment.
The area is near the western border of the state, in Avery, Mitchell, and Yancey Counties.
The district is underlain by crystalline metamorphic and igneous rocks that may be grouped as follows
:
(1) metamorphic rocks derived by regional dynamic metamorphism from interbedded sedimentary and per-haps
volcanic rocks of pre-Cambrian or early Paleozoic age; (2) metamorphic and igneous rocks altered by
hydrothermal solutions or by injection of magma; and (3) intrusive igneous rocks of early (?) and late
Paleozoic age. The metamorphic group includes mica gneisses and mica schists, and dolomitic marble of
sedimentary origin, and hornblende gneiss and schist that may have been derived from impure dolomite,
from mafic volcanic rocks, or possibly from mafic sills. The altered rocks include feldspathic mica injec-tion
gneiss developed mainly from mica schist and gneiss impregnated with pegmatitic material, and chlo-rite
amphibolite, chlorite-biotite schist, soapstone, talc schist, and asbestos rock formed largely by altera-tion
of hornblendic rocks and, to a lesser extent, of dunite. The igneous group includes a few bodies of
dunite and pyroxenite, probably of early or middle Paleozoic age, a great number of fine- to coarse-grained
pegmatite bodies that range in size from stringers to stocklike masses, of Carboniferous age, a few aplite
dikes apparently related closely to pegmatite, and a few diabasic basalt dikes, probably of Triassic age.
Bedrock is generally mantled with residual soil and in many places is covered with unconsolidated surficial
deposits that include terrace sediments, floodplain alluvium, and talus and landslide deposits.
The schists and gneisses are interlayered with one another in bands that range from a fraction of an
inch to several hundred feet in thickness. The layers pinch out or thicken along their strike so that they
interfinger complexly. Few isoclinal folds are recognized. Foliation (flow cleavage) is parallel to the lay-ering
almost everywhere. The general strike is northeast and the dip is southeast, but locally diverse atti-tudes
are common. Drag folds commonly plunge south or southwest. Faults of small displacement are
numerous ; no large ones are surely known. Regular tectonic joints are confined almost entirely to horn-blendic
rocks. Large bodies of fine-grained pegmatite have deformed their walls slightly ; they contain many
inclusions.
The major mineral products of the area are feldspar, kaolin, scrap mica, and sheet mica. Other minor
or potential mineral products include beryl, columbium-tantalum minerals, quartz, rare earth and uranium
minerals, amphibole asbestos, building stone and crushed rock, chromite, garnet, kyanite, mica schist, olivine,
and vermiculite.
INTRODUCTION
LOCATION OF DISTRICT
The Spruce Pine pegmatite district in North Carolina (fig. 1) is near the middle of the western boun-dary
of the state, in Avery, Mitchell, and Yancey Counties. It lies just west of the Blue Ridge drainage
divide in rugged mountain country of the upper reaches of the Toe River, a tributary of the Tennessee
River system.
The district includes about 250 square miles; it extends about 25 miles in a northeasterly direction
and is about 12 miles wide. The town of Spruce Pine, midway of the district near its southeast side, is the
Geology and Structure of Part of the Spruce Pine District, North Carolina
ea^o'
36°0O'-
Burnsville
ve pegmatites
the district described in text
and 1941
No I of Nortn Carolina
nservation ond Development
and 1948
ent report
Figure 1 Index Map of the Spruce Pine District, North Carolina
commercial center. The Carolina, Clinchfield, and Ohio Railroad ; U. S. Highway 19-E ; and State Highway
26 cross the area.
The district is covered by parts of the following topographic maps of the U. S. Geological Survey:
Mount Mitchell, Morganton, Roan Mountain, and Cranberry 30-minute quadrangles, and by the Bakersville,
Carvers Gap, Newland, Burnsville, Micaville, Spruce Pine, Linville Falls, Black Brothers, Celo, and Woods
Mountain 7 1 -^-minute quadrangles.
Geology and Structure of Part of the Spruce Pine District, North Carolina 3
HISTORY
Mining of various nonmetallic minerals has been a major industry in the district for some 80 years.
The district has, in fact, been the principal mining center in the Southeast for mica, feldspar, and residual
white clay. Sheet mica has been mined since about 1868, and in the years since then the district is estimated
to have yielded nearly half of the Nation's total production of this mineral. Since about 1893 scrap mica
for grinding has been an important byproduct, and in later years a primary product. Feldspar was first
shipped in 1911, and in most years since 1917 North Carolina has ranked first among the feldspar-produc-ing
states. The greater part of the state's production has been in the Spruce Pine district. White china
clay has been produced since about 1904, and during the past 30 years the district has been almost the sole
source of residual kaolin in eastern United States. In addition there has been a relatively small production
of amphibole asbestos, beryl, columbium-tantalum minerals, kyanite, ground mica from schist, olivine, quartz,
vermiculite, and, for local use, soapstone, various gneissic building stones, and crushed rock.
SUMMARY OF INVESTIGATIONS IN THE DISTRICT
Geologic investigations in the Spruce Pine district; by the U. o. Geological Survey began in 1893 with
the small-scale (1/125,000) mapping of the mountain areas by Arthur Keith (1903; 1905; 1907). In 1904-
1906 and again in 1914 some of the mica and feldspar deposits were examined and mapped by D. B. Ster-rett
(1923) ; part of this work was supported by the North Carolina Geological and Economic Survey.
Watts (1913) studied the feldspar and kaolin deposits about 1912 for the U. S. Bureau of Mines. The kaolin
deposits were again investigated in 1918 by W. S. Bayley (1925), also in cooperation with the North Caro-lina
Geological and Economic Survey.
Intensive investigations of the pegmatite deposits were begun in 1939 by the U. S. Geological Survey
with the economic studies of Kesler and Olson (1942). General areal geologic mapping of the Spruce Pine
district on a larger scale (1/24,000) was commenced in 1940 by J. M. Parker, III, and continued in 1941
by Parker, J. C. Olson, and J. J. Page. The U. S. Geological Survey's work in the district after July 1941
was in cooperation with the North Carolina Department of Conservation and Development. The results of
this mapping and of some later work were published under Olson's authorship (1944) in a bulletin that
included a colored geologic map on a scale of approximately 1/17,000 of two areas totalling about 37 square
miles near Spruce Pine and near Bandana in Mitchell County. In 1942 the kaolin deposits were reexam-ined
as possible sources of aluminum ore by J. M. Parker, III, (1946) and some additional mapping was
done.
During World War II detailed examinations and large-scale maps (1/240 to 1/600) were made for
several hundred mica deposits. This work was carried on at different times by a total of 19 geologists and
assistants, under the local supervision of J. C. Olson from December 1942 to May 1944, and of J. M. Parker,
III, from then until October 1945. Many of these mine maps are available on open file in the U. S. and State
Geological Survey offices. All of this material on mica deposits in the Blue Ridge areas of southeastern
United States is in preparation for publication by the Geological Survey (Jahns et al.)
General geologic mapping of parts of the Spruce Pine district on a scale of 1/12,000 was resumed by
R. H. Jahns between November 1945 and February 1946, and was continued by J. M. Parker, III, in August-
September 1947, and by a party of five under Parker's direction between June and September 1948. At the
close of the 1948 field season a total of about 72 square miles (fig. 1) had been mapped; of this about 37
square miles has been published (Olson, 1944, pi. 1). Within the 31 square miles mapped during 1948 some
450 pegmatites were examined ; of these about 280 seemed to have economic value and their inferred re-sources
were estimated. Thin sections of about 40 rocks were examined microscopically by D. A. Brobst
in the University of Minnesota petrographic laboratories during the winter 1948-1949. His descriptions
are incorporated in this report. Studies of decomposed rocks were made by thermal and spectographic
methods at Columbia University by J. L. Kulp during the same period; these results will be published sep-arately.
In addition to the U. S. Geological Survey's work, several other studies of economic minerals have been
made in the district. The results of these recent significant investigations are given in the publications
listed among the references at the end of this report.
4 Geology and Structure of Part of the Spruce Pine District, North Carolina
SCOPE OF PRESENT REPORT
The present report is a summary of current knowledge of the general geology and structure of the
district. To date (June 1949) a little less than one-third of the district has been mapped geologically and
this work is to be continued. Petrographic investigations of the rocks by microscopic and other laboratory
methods have been started and much remains to be done. Consequently this progress report is preliminary
and its interpretations are tentative.
The economic results of recent investigations have in part already been made available in the publica-tions
cited above, and others are now in preparation. Additional economic information obtained during
the continuing postwar investigations will appear on the final geologic map and in the final report when the
district has been completely mapped. In this report, therefore, the economic geology of the district is sum-marized
very briefly.
ACKNOWLEDGMENTS
The information compiled in this report was obtained by many coworkers and from many sources. It
is literally impossible to assign detailed credit in an undertaking which has extended over so long a time
and in which so many geologists have participated. The writer is pleased to acknowledge his indebtedness
to all the geologists and assistants with whom he has been associated during the work in the district over
the 9-year period 1940-1949. These include, during the prewar period, H. K. Dupree, T. L. Kesler, J. C.
Olson, and J. J. Page; during World War II, E. Ellingwood, III, V. C. Fryklund, Jr., P. W. Gates, Jr., L.
Goldthwait, W. R. Griffitts, J. B. Hadley, J. E. Husted, W. P. Irwin, R. H. Jahns, D. M. Larrabee, R. W.
Lemke, J. J. Norton, J. C. Olson, J. J. Page, L. C. Pray, L. W. Seegers, W. C. Stoll, R. A. Swanson, and J. R.
Wolfe, Jr. ; and during the postwar period, D. A. Brobst, H. S. Johnson, Jr., J. L. Kulp, and J. A. Redden.
The work has been supervised successively by G. R. Mansfield, H. M. Bannerman, R. H. Jahns, E. N. Cam-eron,
and L. R. Page. Most of the credit for the information contained in this report should go to these men.
The author of course assumes responsibility for errors and dubious interpretations.
Detailed petrographic descriptions of about 40 specimens of some of the principal rock types were pre-pared
by D. A. Brobst. This information has been included at appropriate points in the report. Mr. Brobst
also compiled the map of plate 1. Much published material has been incorporated, in part by citation and in
part sub-consciously by assimilation.
The mapping has been greatly aided by the friendly cooperation of miners, mine operators, and local
residents, who have freely supplied information about earlier operations, inaccessible workings, and the
location of exposures hidden by vegetation. During World War II the officials and employees of the Colonial
Mica Corporation gave invaluable assistance.
The Division of Mineral Resources, North Carolina Department of Conservation and Development,
financed part of the work and Dr. J. L. Stuckey, State Geologist, participated in planning the work and pub-lishing
the results.
GENERAL GEOLOGY OF THE DISTRICT
ROCK TYPES
GENERAL STATEMENT
The Spruce Pine district is underlain by a considerable variety of rocks of diverse histories and com-plex
structure. During recent large-scale mapping 14 principal varieties of bedrock have been distinguish-ed;
subvarieties and unusual phases of several of these exist. These have been divided, on the basis of
modes of origin into three groups : (1) metamorphic rocks resulting from high-rank regional dynamic
metamorphism ; (2) metamorphic and igneous rocks that have been altered by hydrothermal solutions or
by injection of magma; and (3) intrusive igneous rocks.
Most of the first group of gneisses and schists were originally a thick series of bedded rocks that appar-ently
consisted mainly of fine-grained, water-laid sediments such as sandy shales and shaly limestones
;
others may have been mafic lava flows or volcanic tuffs, or sills intruded into the sediments. All of these
traditionally have been assigned to the pre-Cambrian (Keith, 1905, pp. 2-3), but available evidence does
not preclude their being early Paleozoic. These rocks were completely recrystallized on a regional scale by
Geology and Structure of Part of the Spruce Pine District, North Carolina 5
intense stress and high temperature while they were deeply buried. This metamorphism perhaps occurred
in pre-Cambrian times, but it may have occurred, as suggested by King (1950, p. 16), in early or middle
Paleozoic time.
The metamorphic rocks were intruded by several types of igneous masses that range in size from thin
sills and dikes to large stocklike bodies. The principal intrusions are of late Paleozoic age ; some may have
been pre-Cambrian and some are probably Triassic.
Many of the earlier rocks were altered during the intrusion of the igneous rocks, either by the injection
of fluid magma or by hot solutions or gases. Thus parts of several of the high-rank, regionally metamor-phosed
rocks have been transformed locally into low-rank metamorphic rocks.
In addition to the mantle of residual soil that overlies much of the area, the bedrock has been buried
in many places—mainly along and near the valley bottoms—by superficial deposits of unconsolidated ma-terial.
Most of these deposits have been laid down by streams, but others accumulated by gravity.
The district may be subdivided into nine areas, distinguished by differences in the predominant coun-try
rock, the structure, and the typical pegmatites. The boundaries are shown in figure 1 and the features
characteristic of each area are given in Table 1. The general geology of that part of the district mapped
in 1947 and 1948 is shown on plate 1. The part mapped previously has been published by Olson (1944,
Pi. 1).
Plate 1. Geologic map of part of the Spruce Pine district, North Carolina. In Pocket.
Table 1.
—
Subdivisions of the Spruce Pine District 1
Area
Predominant
country rock
Predominant
structure
Plumtree Hornblende Low, variable
gneiss (and
mica gneiss).
dips.
Ingalls Injection
gneiss
Moderate,
variable dips.
Spruce Pine Injection
gneiss
Moderate to high
dips in all di-rections.
Crabtree
Creek
Injection
gneiss
Moderate to high
dips in all di-rections.
Ledger-Kona-
Micaville
Mica gneiss,
injection
gneiss.
High to moderate
dips to south-east.
South Toe
River
Injection
gneiss and
mica gneiss.
Moderate to high
dips to southeast
and southwest.
Typical pegmatites
Thin lenses in series; many
elongate. Medium- and
coarse-grained.
Stocks, thick dikes, and sills. Kaolin
Economic products from, pegmatites
Brown, reddish, and green sheet mica
(Potash block spar).
Fine- to coarse-grained.
Irregular stocks, thick sills,
and dikes. Fine- to
coarse-grained.
Irregular stocks, very thick
sills, and dikes. Fine-to
coarse-grained.
Thick, irregular sills, and
stocks. Fine- to coarse-grained.
Tli in gently plunging
elongate lenses. Medium-to
coarse-grained.
High dips to
southeast.
Moderate to high
dips to south-east.
Sills and thin lenses in
series. Medium- to
coarse-grained.
Thin sills. Medium to
coarse-grained.
Ground mica
Potash block spar
Green sheet mica; "A" structure
Soda spar (flotation)
Potash block spar
Kaolin
Green and brown sheet mica; "A" struc-ture
Ground mica
Potash block spar
Soda block spar
Green—"A" structure (and brown) sheet
mica; stained
( Ground mica)
Soda spar (flotation)
Potash block spar
Soda block spar
Ground mica
Brown, green (and reddish) sheet mica;
stained
(Kaolin)
Brown, green (and reddish) sheet mica;
stained
Ground mica
Potash block spar
Soda block spar
Reddish, brown (and green) sheet mica
(Potash block spar)
( Soda block spar)
Brown and green sheet mica; stained
(Potash block spar)
Hawk-Bandana- Mica gneiss
Shoal Creek and hornblende
gneiss.
Green Mountain Mica gneiss
and hornblende
gneiss.
Black Mica gneiss
Mountains and hornblende
gneiss.
1 Stained mica or "A" structure noted only where common. Potash spar (perthitic microcline) is hand-sorted as blocks from coarse
pegmatite. Soda spar (plagioclase) is in part produced similarly (block spar) but most is separated with admixed potash spar
by froth flotation. Ground mica includes small flakes obtained from kaolinized fine-grained pegmatite and larger books too de-fective
to yield sheet mica. Items are listed in order of estimated abundance or importance; minor items in ( ).
Steep dips to north- Thin to thick sills; steeply
west, southwest, plunging pipes. Medium-and
southeast. to coarse-grained.
I Soda block spar)
Reddish sheet mica;
(Potash block spar)
'A" structure
6 Geology and Structure of Part of the Spruce Pine District, North Carolina
METAMORPHIC ROCKS
Mica gneiss.—Mica gneiss is probably the most abundant metamorphic rock in the district, and is pre-dominant
or fairly common in all subdivisions. Ordinarily it is interbedded with hornblende gneiss in layers
ranging in thickness from a fraction of an inch to scores of feet, but in places it forms unbroken masses
several hundred feet thick. Dikes and sills of pegmatite, and quartz veins are common. The foliation in
places is nearly planar, but elsewhere it has been gently warped or closely folded.
The typical rock is a moderately fine-grained even-textured gneiss composed of layers of quartz and
feldspar alternating with layers of muscovite and biotite. Mica is sufficiently abundant in places to render
the rock schistose. Either muscovite or biotite may locally dominate to the practical exclusion of the other.
The banding is commonly regular, and quite thin layers may persist long distances. The feldspar in most
specimens is oligoclase or sodic andesine; microcline is uncommon. Biotite is partly altered to chlorite.
Small red garnets (0.5 to 2.0 mm in diameter) are common and in places are very abundant. Kyanite
needles and blades are especially abundant in a northeast-trending belt near Bandana in Mitchell County
and also over most of the Black Mountains area. Some layers of gneiss are exceedingly rich in kyanite and
have blades as much as 4 inches long. Common minor constituents include magnetite, allanite, clinozoisite,
zircon, apatite, sphene, rutile, leucoxene, and pyrite. In some places quartz seems to have crowded aside and
invaded the micas, suggesting it may have been introduced. Thin streaks of graphite in mica gneiss were
noted at the Carson Rock mine in Yancey County.
Mica gneiss weathers to light or moderately dark brown soil that is sandy and is rich in tiny flakes of
muscovite and bleached biotite. Because mica is unaltered even in gneiss where the feldspar has been en-tirely
weathered to clay, decomposed gneiss has a misleading appearance and may be mistaken for mica
schist where only the foliation surfaces are observed; its true character is most apparent on cross breaks.
The common regularity of the lamination of mica gneiss, its mineral composition, and the fact of its
being interbedded with marble at one locality indicate a sedimentary origin for much of it. Presumably it
was originally sandy shale. These deposits may have been formed during pre-Cambrian or possibly during
early Paleozoic time. Regional dynamic metamorphism transformed the sediment to its present condition
during a pre-Cambrian or Paleozoic orogeny.
Mica gneiss was the principal rock type included by Keith (1903, p. 2) in the Carolina formation on his
geologic quadrangle maps.
Muscovite schist.—Bands of muscovite schist ranging in thickness from a few feet to about 600 feet are
interbedded with mica gneiss in several parts of the district. It crops out in several narrow strips near
Bandana in Mitchell County and near Blue Rock church in Yancey County, as well as elsewhere in the dis-trict.
The rock is relatively coarse textured. Muscovite, the dominant mineral, occurs in flakes commonly a
quarter of an inch wide. In places a little biotite is associated with the muscovite. Small quartz grains and
minor amounts of feldspar probably constitute about a quarter of the rock. The schist grades into mica
gneiss by increase in the abundance of feldspathic layers. Red garnet crystals ranging from 0.02 to 0.5 inch
in diameter generally are abundant. Kyanite occurs in the Bandana area, and small black tourmaline
prisms were observed in the schist near quartz and pegmatite stringers along the highway l 1 /> miles south
of Bakersville. Muscovite schist weathers to a light-brown soil in which coarse, yellow, iron-stained mus-covite
flakes are abundant.
Muscovite schist probably was formed by metamorphism of the more shaly layers in the sedimentary
series, which gave rise to mica gneiss. It, like the mica gneiss, was included by Keith in his Carolina forma-tion.
Dolomitic marble.—Coarsely crystalline dolomitic marble is interbedded with mica gneiss along lower
Sinkhole Creek in Mitchell County. It can be traced about 1700 feet northeast from the Toe River but is
not known to the southwest. No other marble is known in the district. Apparently there are two layers,
about 10 and 40 feet thick, separated by about 20 feet of mica gneiss ; but the structure has been so disturbed
by faulting and by the intrusion of an irregular, crosscutting pegmatite that perhaps one layer has been
Geology and Structure of Part of the Spruce Pine District, North Carolina 7
repeated. Individual grains of dolomite are as much as 0.3 inch across. The magnesia content of a sample
is reported by Hunter1 to be nearly as high as that of the mineral dolomite.
Hornblende gneiss, hornblende schist, and amphibolite.—Gneisses, schists, and amphibolites composed
largely of hornblende are abundant in the Spruce Pine district. They are probably second in abundance
—
possibly even first—among the foliated rocks. They are common in all parts of the district and ordinarily
are interbedded with mica gneiss or schist. In the northeastern part of the district especially, in Avery
County, these rocks are several thousand feet thick and are almost free of other, interbedded rocks. The
type locality of the Roan formation of Keith (1903, p. 2)—comprising mainly hornblendic rock—is just
north of the district in Roan Mountain. Another area underlain almost exclusively by hornblendic rock
extends north and northwest from I^statoe to the North Toe River, and includes Simmons Knob and Baileys
Peak.
The hornblendic rocks form layers from a fraction of an inch to many feet in thickness that are gen-erally
interbedded with mica gneiss or schist. As in the mica gneiss, the foliation may be planar, warped,
or tightly crumpled. Where hornblendic and micaceous gneisses are interbedded, the bedding and foliation
of both are strictly parallel; no definite crosscutting relations have been seen. Keith (1903, p.2) reports
that the Roan formation "appears to cut the Carolina gneiss" but chat the contacts have been so metamor-phosed
that proof of the relationship is impossible. Regular joint fractures are more common in the horn-blende
gneiss and schist than in the less brittle mica gneiss.
The hornblendic rocks include (1) distinctly banded gneisses with alternating hornblendic and felds-pathic
layers, (2) schistose rock consisting almost exclusively of fine to coarse hornblende needles with
roughly parallel orientations, and (3) nearly massive amphibolites that lack distinct foliation and consist
dominantly of feldspar and quartz. The gneisses and schists are black to dark green, and are medium to
fairly coarse grained. The hornblende needles, which range from about 1 to 20 mm in length, are in parallel
planes, but linear parallelism in these planes is not common. The gneisses and schists grade into one another
by variation in feldspar content. Most of the feldspar is oligoclase or andesine. In some phases feldspar
forms elongate, augenlike lenses. Quartz ordinarily composes 10 to 20 per cent of the rock but rarely may
compose nearly 50 percent. Garnet is ordinarily less abundant than in mica gneiss but in places forms lenses
half an inch thick. On Fawn Mountain in Yancey County garnet crystals as much as half an inch in
diameter locally compose more than half of the rock. Biotite and chlorite in places, especially in the vicinity
of pegmatitic bodies, are mixed with hornblende and form as much as a quarter of the rock; these minerals,
as well as epidote and allanite, formed by alteration of hornblende. Thin layers and veinlets of epidote are
common. Other minor constituents include magnetite, ilmenite, pyrite, chalcopyrite, sphene, rutile, zircon,
apatite, and leucoxene. Staurolite was observed in a garnet-rich specimen from Upper Blue Rock Branch
valley.
Associated and interbedded with the hornblendic gneisses and schists are other similar gray to green
rocks in which actinolite-tremolite and possibly anthophyllite take the place of hornblende.
These rocks have been noted in the Boonford, Kona, Double Island, and Bandana areas. In some of these
rocks scattered grains of carbonate are cut and embayed by tremolite and chlorite.
The more massive amphibolite, described by Olson (1944, p. 19) is fine-grained and is commonly light
brown or yellow. It is much less abundant than the other two rock types and occurs in relatively thin layers
interbedded with hornblende gneiss or schist.
The hornblendic rocks decompose to a dark-brown, commonly a reddish-brown, very plastic, heavy, and
generally grit-free soil. Partly decomposed fragments resemble old weathered bricks. These soils resemble
those derived from diabase, but may be distinguished by the traces of foliation and by the residual boulders
in the subsoil.
The Roan formation (hornblendic rocks) was believed by Keith (1903, p. 2) to be intrusive into the
Carolina gneiss and thus younger, though also of pre-Cambrian age. The only observation made by the
writer that might possibly support this view is a relationship noted near a small creek just south of the
Carolina Mineral Company No. 20 mine in upper Crabtree Creek valley. Here a layer of hornblende gneiss
'Hunter, C E., oral communication.
8 Geology and Structure of Part of the Spruce Pine District, North Carolina
about a foot thick and enclosed in mica schist ends abruptly in a flat surface perpendicular to the bedding;
the foliation of the schist bends sharply around the square end of this layer. Though this relationship might
have resulted from intrusion, it can also be interpreted as a deformational feature. The outstanding feature
of the hornblendic rocks is the regularity of the layering where they are interbedded with mica gneiss. Even
very thin layers persist long distances. In an outcrop along the South Toe River about 2 miles north of
Micaville, 10 bands of alternating mica and hornblende gneiss are exposed in a distance of 4.64 inches across
the layering. The layers range in thickness from 0.04 inch to 1.22 inches. All but one of these thin layers are
continuous with almost uniform thickness the full length of the exposure, a distance of about 4 feet. Such
uniformity and persistence of layering suggest a sedimentary origin. Gradation of grain size across a single
hornblende gneiss bed has been observed. These thin, interbedded hornblende gneisses and the actinolite-tremolite
rocks may have been impure dolomitic limestones. The mafic mineralogic composition, however,
coupled with the conformable relations to mica gneiss, has led most workers to believe that the ordinary horn-blende
rocks are metamorphosed mafic volcanic extrusives, and perhaps, in part at least, are conformable
intrusive sills. Chemical data are lacking and the relationship to the marble is not known. Consequently,
origin is still in doubt. Perhaps some of the hornblendic rocks are sedimentary in origin and some are
igneous.
IGNEOUS ROCKS
Dunite.—Intrusive masses of dunite in the Spruce Pine district are known in the vicinity of Frank in
Avery County, on Mine Creek and Whiteoak Creek south and southeast of Bakersville in Mitchell County,
and on Mine Branch near Newdale and on Mine Fork north of Burnsville in Yancey County. They have
been investigated by Hunter (1941) and by Hunter, Murdock, and MacCarthy (1942).
In plan the dunite masses are irregularly round or elliptical, and are as much as 2000 feet long. They
commonly cut across the foliation of the enclosing gneisses.
The dunite is medium- to coarse-grained, and consists mainly of olivine with accessory enstatite and
chromite, as well as the alteration products antigorite, talc, tremolite, and chlorite. It weathers to an ex-ceedingly
infertile, gray-brown soil and is characteristically exposed on rocky surfaces nearly barren of
vegetation.
The dunite bodies have not undergone the regional dynamic metamorphism that has affected the older
gneisses and schists which they intrude. The Newdale mass seems to have been intruded by pegmatite,
though the contacts are not well enough exposed for the relationship to be certain. Hunter (1941, pp. 61-62),
however, reports that several pegmatites cut the Democrat dunite body in Buncombe County just southwest
of the Spruce Pine district. Dunite has been greatly affected by hydrothermal solutions, which may have
been related to the pegmatites. Consequently, the dunite intrusives are considered to be younger than the
mica and hornblende gneisses and schists and older than the late Paleozoic ( ?) silicic intrusives.
Pyroxenite.—Ultramafic rocks underlie small areas scattered throughout the district. Most of these have
been considerably altered so that their original composition is in doubt. They seem to have been largely
pyroxenite, but they probably also include peridotites. At present they consist mainly of soapstone and/or
asbestos rock, and are described under those headings.
At the J. W. Autry mica mine a mile southeast of Burnsville there is a small mass of coarse-grained,
black pyroxenite which is almost unaltered.
The age of pyroxenite is probably similar to that of dunite, and the two rocks may be variants from the
same magma. Both have been greatly altered by hydrothermal solutions apparently derived from the peg-matitic
intrusives, but they have not been regionally metamorphosed.
Pegmatite.—A large variety of closely related silicic igneous bodies, ranging from very large stocklike
granitic masses, through large and small pegmatite sills, lenses, and dikes, to quartz veins, intrude most of
the rocks of the Spruce Pine district. Slightly younger aplite dikes are probably part of the same series.
These intrusives, collectively called pegmatite in the present report, are distributed generally though uneven-ly
over the district. Large bodies of fine-grained pegmatite ("alaskite" and "granite" of other reports) are
commonest along the southeast side of the district in the Ingalls, Spruce Pine, and Crabtree areas especially.
(See Table 1 and Figure 1.) The coarser-grained pegmatite occupies a curved belt 4 to 6 miles wide on the
Geology and Structure of Part of the Spruce Pine District, North Carolina 9
north, northwest, and southwest sides. Almost no pegmatite bodies occur southeast of the big fine-grained
pegmatite masses. Within the district several areas contain almost no pegmatite.
The pegmatites consist primarily of various proportions of plagioclase, quartz, perthitic microcline, and
muscovite. On the average it is estimated that plagioclase forms about 45 per cent of the rock, quartz about
25 per cent, microcline about 20 per cent, and muscovite about 10 per cent. Microcline is lacking in many
pegmatites or pegmatite units and muscovite is low or is lacking in a few ; plagioclase and quartz are nearly
ubiquitous. The plagioclase is mostly oligoclase but ranges, according to Maurice (1940, p. 160), from
Ab.,4 to Ab7n . A tentative classification of the pegmatites used in current areal mapping groups the possi-ble
combinations of the principal constituents into major types depending on the mineral proportions. Four
types were mapped, as follows: (1) plagioclase-quartz-muscovite pegmatite, (2) plagioclase-quartz pegma-tite,
(3) plagioclase-quartz-perthite-muscovite pegmatite, and (4) perthite-quartz-plagioclase-muscovite. 1 A
quantitative estimate of the proportions of the essential minerals was made for each pegmatite examined, and
the relative order of abundance is given in the name. In addition to the essential minerals, the pegmatites
commonly contain garnet, biotite, and apatite in small quantities, and still less commonly beryl, tourmaline,
epidote, allanite, thulite, various sulphides, tantalite-columbite, and uranium minerals.
Pegmatite weathers to light-colored sandy soils. It is distinguished by abundant quartz, partly in large
blocks, very small amounts of iron stain, and large quantities of muscovite in small or large flat flakes.
In the early reports by Keith (1903; 1905; 1907) the silicic intrusives were referred to as granite and
pegmatite, and were mapped with the Carolina gneiss. Later Watts (1913, p. 106) distinguished granite
from pegmatite in the district, but the difference was not generally appreciated. Hunter (1940, p. 98) in-troduced
F. L. Hess' term "alaskite" for the finer-grained granitic rock (average grain diameter, 0.25 to 0.5
inch) occurring in large irregular bodies, as distinguished from the coarse pegmatite that forms smaller
sills and dikes. This called attention to an economically important difference, inasmuch as the "alaskite"
bodies by supergene decomposition had become deposits of residual kaolin with very large reserves as com-pared
with the small deposits worked during the earlier days of the clay industry, which were derived from
coarser and smaller pegmatite sills and dikes. The term "alaskite" has been rather widely adopted in the
district but is not retained here because the dominant feldspar does not correspond to that of the rock type
to which the name was originally applied (see Spurr, 1900, p. 231).
The finer-grained pegmatite has also been referred to as granite, granodiorite, and leucotonalite. The
term "granite" is objectionable because the dominant feldspar is not microcline, orthoclase, or albite but is
mostly oligoclase. The remarkably low iron content (averaging less than 1 per cent) and the high silica
content (about 75 per cent) show a resemblance to granite. The virtual absence of mafic minerals was the
reason for Hess and Hunter's proposal (Hunter, 1940, p. 98) of "alaskite." Granodiorite or leucotonalite or
quartz monzonite and quartz diorite are not entirely satisfactory names because the silica is too high, the
iron too low, and the plagioclase too sodic for typical rocks in these categories. The texture of the Spruce
Pine rock, though finer grained than that of typical pegmatite mined for feldspar and mica, is still much
coarser than that of average granite or granodiorite ; most of the grains are half an inch across and many
are more than an inch. Thus, though the terms "granodiorite," "leucotonalite," and "leucoadamellite" may
be mineralogically correct, they may be misleading. For these various reasons it is thought best to refer to
"alaskite," "granite," or "granodiorite" as leucogranodioritic, fine-grained pegmatite.
Though a practical difference does exist between the larger bodies of finer-grained rock that yield
kaolin in commercial quantities and the smaller bodies of coarser rock that are sources of hand-picked feld-spar
and sheet mica, yet the gradations in texture and mineral composition between these two extremes indi-cate
that the finer- and the coarser-grained bodies must have resulted from local variations in the crystallization
of the same magma. The large "alaskite" bodies contain irregular parts of more coarsely pegmatitic texture
from which block spar and book mica may be obtained ; the contacts between these parts are so completely
gradational that no line can be drawn between them. In fact, many of the largest and most valuable peg-matites
from which feldspar has been mined, as at the Gusher Knob and Deer Park mines, have "walls" of
"alaskite" into which they grade by decreasing grain size. Conversely, in many rather small mica-bearing
pegmatites there are zones of rock identical in texture and composition with the "alaskite" and grading in-x
It has not proved feasible to show these types separately on the geologic map, plate 1.
10 Geology and Structure of Part of the Spruce Pine District, North Carolina
sensibly into typical coarse pegmatite. For these reasons, during recent field work by the U. S. Geological
Survey, both types have been considered variants of a single rock, to which the name pegmatite is applied.
The different pegmatites are distinguished by textural and mineralogical modifiers.
Individual mineral grains in the pegmatites range from about 0.1 inch to about 6 feet in thickness. Those
pegmatites or pegmatite units in which more than half the rock consists of grains hajf an inch thick or less
are referred to as fine-grained ; where more than half ranges between half an inch and 6 inches, as medium-grained
; and where more than half exceeds 6 inches, as coarse-grained. All of the minerals may occur in
grains near the lower size limit. Masses of plagioclase attain a maximum thickness of about a foot, and
subhedral crystals of microcline about 6 feet. Quartz forms solid masses of small grains as much as 20 feet
thick. Muscovite books more than a foot wide are uncommon; the largest obtained in the district, taken
many years ago from the Fannie Gouge Mine, is said to have weighed 4300 pounds.
In some pegmatites the grain size is rather uniform, except for a slight increase in average grain size
from the wall inward, but in others great differences in texture exist from one part to another. Some peg-matites
have lenticular masses of microcline a foot or more long scattered through rock averaging half an
inch in grain size. Many have a rude foliation resulting from the parallel orientation of mica flakes and
elongate masses of feldspar or quartz.
Nearly half of the pegmatites in the Spruce Pine district are essentially homogeneous in mineral com-position
and texture. The remainder comprise several rock units. The most common units are called zones,
and are distinguished by contrasting mineralogy or texture or both. These zones are roughly concentric
shells around a central core ; the outside shape of each roughly approximates that of the whole pegmatite.
The simplest type of zoned pegmatite has two zones—a thin border zone of distinctly finer grain and a
coarse-grained core—both commonly consisting of plagioclase, quartz, and muscovite. A little more than a
quarter of the pegmatites carefully investigated had three or more zones. The cores are commonly of mas-sive
quartz or of coarse perthitic microcline and quartz, the wall zones are of plagioclase-quartz-muscovite
rock, and the border zones are of finer-grained rock of similar composition.
In addition to zones, which are considered to be primary units formed during the crystallization of the
pegmatitic fluid, some pegmatites have rock units formed by the filling of fractures with later pegmatitic
material, and a very few have units resulting from replacement of earlier rock by hydrothermal solutions
derived from pegmatitic fluids.
A detailed description of the internal structure of pegmatites generally, with many references to those
in the Spruce Pine district, may be found in a paper by Cameron, Jahns, McNair, and Page (1949).
The variety of form of the pegmatites is very great. Fine-grained pegmatite forms very large masses
whose shapes in plan are highly irregular and whose extensions in depth are entirely unknown. They may
be stocks or huge sills. They tend to be elongated northeastward and are as much as 2 miles long and a
mile wide. Numerous sills, dikes, and stringers extend from them. Inclusions of country rock, ranging
from a fraction of an inch to scores of feet in thickness, are common within them, especially near the con-tacts.
The inclusions are commonly slablike and tend to parallel the walls, but irregular masses and dis-cordant
orientations are numerous.
Typical coarse-grained pegmatite forms smaller bodies which, though irregular, tend to be tabular or
lenticular. At least three-quarters of these are conformable to the foliation of the enclosing gneisses. They
include thin tabular sills, pinch-and-swell sills, irregular thick sills, more or less discoidal lenses, consider-ably
elongate lenses, and irregular pipelike masses. Elongate lenticular pegmatites plunge parallel to the
axes of neighboring minor folds, generally at moderate angles to the south or southwest. The discordant
bodies range from tabular to lenticular to irregular. The coarse pegmatites range in thickness from a few
inches to more than a hundred feet.
The age of the pegmatitic intrusives probably is late Paleozoic. Radioactive determinations (Holmes,
1931, pp. 342-344; Alter and McColley, 1942, p. 213) on uranium minerals have given various ages ranging
from 251 million to about 370 million years. A thorium determination (Bliss, 1942, p. 215) on monazite,
however, gave 600 million years, presumably pre-Cambrian.
Aplite.—Small dikes of aplite are fairly common in the western part of the district and less common
elsewhere. The rock is quite fine grained (averaging 1/50 inch) and is composed of oligoclase, quartz,
Geology and Structure of Part of the Spruce Pine District, North Carolina 11
and muscovite or biotite. It is usually equigranular, though some is porphyritic. Much is plainly foliated,
with small green muscovite flakes aligned parallel to the dike walls. Minor accessory and secondary min-erals
include apatite, rutile, sphene, zircon, chlorite, sericite, and epidote. The dikes cut across pegmatites
and have sharp contacts with both pegmatite and the metamorphic rocks. Though distinctly later than peg-matite,
they probably represent the same magmatic invasion.
A large body of apparently similar rock has been mined on a small scale for halloysite clay on the north-east
slope of Carters Ridge V/o miles southeast of Spruce Pine. The body trends roughly north and is at
least 40 feet thick and 150 feet long. It consists almost wholly of fine-grained feldspar, with little musco-vite
and apparently no quartz. The feldspar has been completely kaolinized to depths of more than 25 feet,
forming a very plastic, grit-free, white clay. Paralleling the body just to the west is a ledge of massive
quartz at least 20 feet thick that crops out for a distance of about a hundred yards. This deposit has re-cently
been investigated by Hunter and Hash (1949, pp. 10-14).
Basalt.—Thin dikes of basalt cut pegmatites and their wall rocks at several places in the Plumtree area
in Avery County. The dikes consist of labradorite, augite, and olivine in part altered to serpentine. They are
fine-grained to aphanitic and in part at least have ophitic texture. Veins of calcite, zeolites, and sulphides
are associated with the dikes. Keith (1905, pp. 5-6; 1907, pp. 7-8) mapped similar gabbro just north and
northwest of the Spruce Pine district. Petrographic similarity to the late Triassic dikes and sills (see
Campbell and Kimball, 1923, p. 45; Prouty, 1931, pp. 480-481; Reinemund, 1949) in the North Carolina
Piedmont indicates that the basalt dikes in the Spruce Pine district are also Triassic in age.
ALTERED METAMORPHIC AND IGNEOUS ROCKS
Mica injection gneiss.—Mica injection gneiss occurs in wide areas around the large intrusives of fine-grained
pegmatite, where granitic material has been injected into and has permeated mica schist and to a
lesser extent mica gneiss, and even hornblende gneiss and schist. This rock is most abundant along the
southeast side of the district, especially near the large intrusives of the Spruce Pine and Crabtree Creek
areas, and in the northern part of the South Toe River valley. The large Brushy Creek and Threemile
Creek intrusives in Avery County have produced thinner and less extensive injection gneiss, apparently be-cause
of the preponderance of hornblende gneiss over mica schist in this part of the district.
Mica injection gneiss is coarse grained and is characterized by silvery muscovite flakes separating and
enclosing small pods of feldspar and quartz. On surfaces parallel to the foliation the rock looks like mica
schist, but on cross breaks the dominance of feldspar and quartz is apparent. Veins of quartz and stringers
of pegmatite abound. The feldspar is oligoclase or andesine (An, L. to An,,,) and composes 20 to 50 per cent of
the rock; quartz is in reciprocal amounts. Muscovite is the usual mica but commonly biotite is abundant
and locally is predominant. Minor constituents include apatite, sphene, magnetite, zircon, staurolite, allan-ite,
clinozoisite, chlorite, and pyrite. Textural relationships observed under the microscope, such as crum-pled
mica foliae and inclusions of mica in quartz and feldspar, tend to confirm the field interpretation of the
origin of this rock. Much of the rock, especially that associated with hornblendic rocks, is highly garnet-iferous.
Near some intrusives the mica foliae are separated into shreds isolated in feldspar and quartz, and
the injection gneiss grades into normal fine-grained pegmatite. At greater distances from the intrusive
the amount of injected material may be so small that the typically lumpy foliation is not developed and the
injection gneiss grades into normal schist or gneiss.
Injection gneiss weathers to light-yellow sandy soil much like that derived from fine-grained pegmatite.
It may ordinarily be distinguished by the presence of curved bunches of muscovite flakes in the soil, rather
than the flat and coarser mica flakes yielded by pegmatite. In many places, however, the amount of intro-duced
material is so great that, if exposures are poor, doubt exists as to whether the area is underlain by
injection gneiss or pegmatite.
This distinctive kind of mica gneiss, or migmatite, is partly of metamorphic and partly of igneous ori-gin.
The injection of magmatic material between the foliation planes was accompanied by partial solution
and recrystallization of the original constituents of the rock. Mica schist seems to have been the most readily
injected of the earlier rocks. Practically every exposure of mica schist shows at least a little introduced
material. The hornblendic rocks evidently were less permeable than schistose micaceous ones, as unaltered
12 Geology and Structure of Part of the Spruce Pine District, North Carolina
layers remain in the injection gneiss formed from hornblende schist and gneiss. In places, however, horn-blende
gneiss or schist has been intruded lit-par-lit and the hornblende changed to biotite. These injection
gneisses are rich in biotite. Where the change was not complete, red garnets are common in the altered
part and lacking in the original. Elsewhere only metacrysts of feldspar or eye-shaped spots of feldspar or
granitic material were added to hornblende schist. ,
Chloritic amphibolite.—Complexly metamorphosed, nonfoliated amphibolite characterized by curved
plumose aggregates of chlorite or actinolite underlies wide areas in upper Brushy Creek valley near Estatoe
in Mitchell County and extends northeastward beyond Penland. Smaller areas were observed near Rock-house
Creek in Grassy Creek valley, near Bear Creek Church, and just west of Crabtree Creek north of
U. S. Highway 19-E. These amphibolite bands range in thickness from a few feet to at least a third of a
mile, and invariably are adjacent to hornblende gneiss or schist on at least one side. Within the amphibolite
are numerous masses of hornblende gneiss or schist with greatly contorted foliation, suggesting that the am-phibolite
was derived from such hornblendic rocks. Some exposures contain closely packed ellipsoidal
masses, a few inches to 2 or 3 feet thick which resemble pillow structure of lava.
The chloritic amphibolite is exceedingly variable in character from place to place. Most of it is essen-tially
massive, but in places it shows contorted foliation. In the typically massive rock curved sheaves and
veinlets of chlorite or actinolite divide the rock into rough lenses from half an inch to 3 or 4 inches thick.
These lumpy masses consist mainly of fine-grained plagioclase (oligoclase or andesine) and quartz with
minor amounts of hornblende, biotite, and garnet. The ends of the curved sheaves of chlorite and actinolite
fray out into the feldspathic part. Faint parallel orientation of biotite and hornblende is observed in thin
sections of some of the feldspathic, fine-grained material. Other parts of this rock consist of irregularly
matted aggregates of dark amphibole needles and fine-grained micaceous minerals, apparently including
biotite, chlorite, and muscovite or possibly talc, with very little feldspar and quartz. In places irregular bod-ies
of massive quartz—possibly quartzite—occur. Sulphide minerals, principally pyrite and pyrrhotite, are
abundant and in the fine-grained feldspathic parts may form as much as 1 or 2 per cent of the rock. Out-crops
are knobby because of the curved surfaces of chlorite and are pitted and heavily iron-stained from
weathering of the sulphides. The dark-brown plastic soil derived from chloritic amphibolite closely resem-bles
the soil formed from hornblende gneiss and schist.
Detailed petrographic information is not available and therefore, the origin of this rock is not well
understood. The chloritic amphibolite is perhaps migmatitic rock derived from hornblende gneiss by pro-found
physical and chemical alteration. The intense contortion of the foliation indicates local deformation.
The ellipsoidal masses resembling pillow lava probably are broken gneiss fragments in a wide fault zone,
somewhat rounded by abrasion during displacement and by subsequent chemical alteration. The brecciated
rock apparently was altered by hydrothermal solutions and probably also by the injection of aplitic magma.
The fine-grained feldspathic parts seem to represent aplitic material added to the original constituents that
were recrystallized by hot solutions or magmatic fluids to form actinolite and chlorite.
Chlorite-biotite schist.—Chlorite-biotite schist occurs in eastern Mitchell County on the northeast end of
Tempa Mountain and on Hanging Rock Knob three-quarters of a mile to the north, and in Avery County on
the east side of the North Toe River at the mouth of Brushy Creek. This schist forms irregularly lenticu-lar,
conformable layers, one to about 20 feet thick, in mica injection gneiss. The schist is closely crumpled
in small and large sigmoid, chevron, and irregular folds. In the micaceous rock are numerous relic strips
of hornblende gneiss and schist in which some amphibole crystals are as much as 8 inches long and half an
inch thick. The schist layers are irregularly and complexly veined by quartz and fine-grained pegmatite
similar to that in the mica injection gneiss. The schist consists mainly of chlorite and biotite, with long-hornblende
needles, fine-grained talc, minor quartz, feldspar, apatite, and sulphides. It contains hundreds
of ellipsoidal, spheroidal, and irregular bodies ranging from an inch to 6 feet in diameter and from a quarter
of an inch to 18 inches in thickness. Most of these ellipsoids are composed of hornblende schist, in which
much of the hornblende is in needles 3 or 4 inches long. Others consist of subhedral white and smoky quartz
crystals irregularly packed together. These bodies are conformable to the foliation of the schist, and some
grade laterally and longitudinally from hornblende schist into chlorite-biotite schist. Others, especially the
quartz ellipsoids, have sharp boundaries. Though the shape of the ellipsoids might suggest an origin from
Geology and Structure of Part of the Spruce Pine District, North Carolina 13
pillow lava, the composition of the quartz ellipsoids, and the gradational contacts of the hornblendic ones,
together with their association with hornblende gneiss layers, seem unfavorable to the possibility.
Weathering bleaches and iron-stains the rock so that near the surface it is dull brown instead of glassy
green and black.
Microscopic examination reveals the presence of titanite, magnetite (?), and zircon inclusions in horn-blende
and biotite. In places carbonate forms a fifth of the rock. In some specimens chlorite predominate-and
in others biotite. The feldspar is mainly oligoclase, though some orthoclase appears to be present. Horn-blende
has been altered to interleaved biotite and chlorite, which appear in part to be contemporaneous.
Elsewhere chlorite and some talc seem to be secondary after biotite. Quartz and feldspar replace horn-blende
and biotite; quartz and carbonate replace feldspar.
This schist apparently was formed through hydrothermal alteration of hornblende-rich rocks by solu-tions
coming from underlying pegmatite magma. To form biotite presumably some potash had to be intro-duced.
The large number of ellipsoids and veins of quartz seems to indicate that the solutions were siliceous,
though silica would have been released by the change of hornblende to biotite. Carbonate indicates the
addition of carbon dioxide. The result was mainly a recrystallization of the original material into new
minerals, and to a lesser extent the development of larger grains oi original minerals such as hornblende.
Chlorite-biotite schist is distinguished from chloritic amphibolite by its strongly schistose texture and
predominance of micaceous minerals. The amphibolite is largely massive, the only well-foliated parts being
hornblende gneiss ; chlorite is a characteristic but not a dominant mineral.
Soapstone and talcose schist.—Bodies of impure soapstone and talcose schist are numerous in the Spruce
Pine district. They are distributed rather generally over the district and most are relatively small. They
have been derived from dunite and hornblende gneiss, and possibly from pyroxenite.
The dunite bodies, previously described, have to a considerable extent been altered. The bulk of some
bodies now consists largely of serpentine rather than the original olivine. Near their outer edges, however,
talc schist or soapstone has been commonly formed. In fact, Hunter (1941, pp. 45, 50, 54) shows a talc-vermiculite
fringe, which is commonly schistose and slickensided, around all the dunite bodies. The impure
soapstone bodies in the Grassy Creek area in Mitchell County, which occur within fine-grained pegmatite,
apparently as inclusions, are reported by Olson (1944, p. 22) to have centers of dunite.
Most of the soapstone in the Spruce Pine district, however, seems to have been formed by alteration of
hornblende gneiss. Small bodies of impure soapstone, mostly from about 5 to 25 feet thick, are numerous
throughout the district within areas of hornblende gneiss. The largest body mapped is on the east side of
Crabtree Creek about half a mile northwest of Crabtree Falls. In many places the gneiss can be traced
along strike into soapstone that may retain the foliation of the gneiss. Much of the rock is fine grained and
massive but in places it is rather schistose. Actinolite, chlorite, serpentine, and vermiculite commonly are
mixed with the talc. Soapstone is resistant to local weathering and commonly crops out conspicuously.
Loose fragments of the rock are numerous in the overlying soil.
The talcose rocks have been formed by local secondary hydrothermal alteration of rocks rich in mag-nesian
minerals. Olivine and hornblende by hydration have been converted into talc, commonly with asso-ciated
serpentine, chlorite, and actinolite. This probably was caused by solutions emanating from the peg-matitic
intrusions.
Asbestos rock.—Amphibole asbestos rock occurs in at least half a dozen places in the Spruce Pine district.
mainly in Yancey County. Probably the best deposits are that on a ridge 1 mile northeast of Micaville near
the Googrock mine and that on the northwest side of the South Toe River opposite the mouth of Blue Rock
Branch. The latter deposit occurs in a band of hornblende gneiss, from which it evidently was derived, and
forms an irregular zone some 20 feet wide trending northeast parallel to the local foliation. The rock
consists in part of matted groups of diverging amphibole blades or coarse needles from 0.5 inch to 6.0 inches
long, and in part of closely packed rosettes or radiating groups of finer fibers 0.5 to 1.0 inch long. A small
deposit half a mile west of Young's Chapel in Yancey County contains gently dipping irregular veins that
strike about perpendicular to the foliation and are composed of cross fibers as much as 38 inches long.
Amphibole asbestos has also been formed along the contact between the Newdale dunite body and horn-blende
gneiss. Small amounts of actinolite, talc, and chlorite occur in most deposits.
14 Geology and Structure of Part of the Spruce Pine District, North Carolina
Chrysotile asbestos is reported by Hunter (1941, p. 57) in the Whiteoak Creek dunite mass a mile
southeast of Bakersville.
The asbestos deposits have not been studied in detail, but they seem to have resulted from local hydro-thermal
alteration of mafic rocks, mainly hornblende gneiss.
SUPERFICIAL DEPOSITS
Terrace deposits.—Old erosion surfaces throughout the district are represented by flat-topped ridges
and adjacent gently rolling country along the rivers and larger tributaries. These are about 50 to 200 feet
above the present valley bottoms. Most of these fairly level, elevated areas are underlain by unconsolidated
stream sediment that rests unconformably on the eroded edges of the various bedrock formations. The low-est
few feet of this capping of sediment is commonly gravel, in places containing well-rounded boulders
more than a foot in diameter. The bulk of the deposit is brown silt and clay, with recurrent layers of
sand and gravel. The deposit is heavily stained and in part is loosely cemented by iron oxide. Its max-imum
thickness is about 30 feet, but the thickness may vary considerably in any one deposit. Stratification
is quite irregular; scour and fill or cross-bedding are common.
These deposits are the remnants of old floodplain alluvium, laid down when the whole region was at a
lower elevation and before the streams had worn down to their present levels. Regional uplift in stages
has allowed the formation of at least three terrace levels, each uplift causing the streams to destroy part of
the higher deposits. The ages of the several high-level deposits are not known ; they are probably all
Pleistocene or at the oldest Pliocene.
Floodplain alluvium.—All of the larger streams have by lateral erosion developed flat floodplains along
much of their length that range in width from only a few feet to a quarter of a mile. These flat bottom
lands are underlain by gravel, sand, and impure clay that probably range in thickness from about 5 to 10
feet. This sediment lies unconformably on the eroded bedrock formations, completely burying them ex-cept
for occasional exposures in the stream channels. These deposits are of very recent origin.
Closely related to floodplain alluvium are the comparatively large alluvial-fan deposits made by the
steeper tributaries where they pass off the mountain sides into the valley bottoms. The upper surfaces of
these slope gently but irregularly toward the main valley and are crossed by numerous abandoned stream
channels. The deposits consist of poorly sorted gravel, sand, and clay and contain many boulders of large
size. They merge into the flat floodplain deposits at their outer edges. Large areas along the lower moun-tain
slopes are mantled with this material. An especially large one has been formed by Jones Creek a
mile north of Ingalls in Avery County.
Talus and landslide deposits.—Talus and landslide deposits occur along the lower parts of many steep
mountain slopes, as on the east side of Buck Hill Mountain in Avery County. These deposits of broken and
weathered rock, now largely decomposed to soil, have crept, slid, or fallen into their present positions
mainly by the influence of gravity. They are not related to any present-day stream but form where the
mountain side is concave outward. Temporary runoff in such broad hollows was doubtless an important
factor in the transportation of this material, but it probably moved mainly by flowing and sliding downhill
when thoroughly wet. The upper surface slopes gently to rather steeply and is commonly hummocky. Ex-tremely
large masses of rock, large enough to be mistaken for outcrops of the bedrock, are included. The
thickness of the talus and landslide material is not known, but topographic evidence indicates that it may
be as much as 50 feet in places.
STRUCTURE
INTERLAYERING
The gneisses and schists of the Spruce Pine district are complexly interlayered and succeed one another
apparently without systematic repetition. Mica gneiss and hornblende gneiss or schist are by far the most
abundant types, and these are interbedded on both a large and a small scale. The individual layers range
from a fraction of an inch to several hundred feet in thickness, but they rarely exceed 50 feet in thickness.
The layers taper gradually, and in places rather abruptly, along their strike, so that various types inter-
Geology and Structure of Part of the Spruce Pine District, North Carolina 15
finger with one another. Sequences only a few hundred yards apart along strike differ markedly. As a
result of this interfingering and the scarcity of rock exposures, contacts can not be traced with any assur-ance
; in fact, most boundaries are inferred. In addition, since most outcrops include more than one rock
type in layers which are too thin to map separately, it is possible to map only the dominant type. It can
be taken for granted that each rock type designated on the map includes smaller amounts of one or more
of the other rocks.
Most of this complex interlayering and interfingering is probably an original structure formed by suc-cessive
deposition of contrasting sedimentary, and perhaps volcanic layers of different areal extents. The
uniformity of layering on a small scale seems to be a sedimentary feature and the interfingering resembles
that generally noted in extensive terranes of unmetamorphosed sediments. If the hornblende gneiss and
schist were derived from mafic intrusives, at least part of the interfingering may result from thin, tapering
sills intruded into stratified rocks.
FOLIATION AND LINEATION
Foliation is well developed in all metamorphic rocks of the district. A large proportion of almost all
rocks consists of mica flakes or needlelike hornblende crystals. These inequidimensional minerals are
oriented in parallel planes so that schistose cleavage is marked. In almost all localities this cleavage is
parallel to the layering of the different interbedded rocks. In a few localities where mica gneiss has a small
proportion of mica, most of the flakes are at an appreciable angle to the banding of the rock.
Linear fabric resulting from parallel alignment of the long dimensions of hornblende needles in horn-blendic
rocks is not common. Though these needles generally are parallel to the layers, they seldom line
up in one direction on these layers but point in diverse directions. In some localities, however, such linea-tion
has been noted.
FOLDING
The older metamorphic rocks of the Spruce Pine district have been subjected to at least two periods of
folding. The earlier deformation is recorded chiefly in the development of foliation and lineation. In addi-tion,
at a few places the layers can be seen to have been sharply folded isoclinically on a small scale. The
difference in dip or strike of the opposite limbs of the folds is commonly not more than 5°. The beds are
reversed in a strip along the fold axis only a few inches wide, and in this area it is uncertain whether
the foliation is at a high angle to the bedding or whether it too is reversed. These tight folds probably
were formed during the ancient deformation that resulted in regional dynamic metamorphism.
The foliated rocks have been tilted more or less steeply. The diverse attitudes in different parts of the
district seem to indicate that this folding was later than the regional dynamic metamorphism. The tilting
is presumably an effect of large-scale folding. The absence of key beds makes it impossible to trace out the
large structures and to delineate definite anticlines and synclines ; fold axes are recognizable in only a few
places. Inasmuch as the large-scale general geologic map has been completed for only a part of the dis-trict,
conclusions regarding such structures remain tentative and general.
The general strike is to the northeast and most dips are steep to the southeast, in conformity to the
Appalachian regional structure. In the northeastern part of the district near Plumtree the rocks are rela-tively
flat and are irregularly but gently warped. Across the northern and western sides of the district the
dips are rather uniformly steep to the southeast. South and southwest of Newdale moderate to steep dips
to the southwest and west are common though not general. The structure of the metamorphic rocks alon^;
the southeast side of the district, in the belt of large intrusives of fine-grained pegmatite, is highly irreg-ular.
Most dips are moderate to steep but may be in any direction and vary abruptly from place to place.
Locally in all parts of the district the foliated rocks have been bent into small upright or overturned
anticlines and synclines with flank lengths of a few feet. In places the foliation has been closely crumpled
into tiny crenulations that commonly have V-shaped crests and troughs. The axes of most of these small
folds plunge gently or moderately to the south or southwest, but other attitudes are not rare. These small-scale
folds are presumably drag folds associated with larger structures and so probably indicate the general
attitude of the major features. Some may be related to faults.
16 Geology and Structure of Part of the Spruce Pine District, North Carolina
The regional dip of the foliated rocks to the southeast seems to have controlled the distribution of peg-matites.
The large bodies of fine-grained pegmatite are all near the southeast side of the district. The
bodies of coarse-grained pegmatite are abundant in a curved belt extending from the north, along the north-west
and west sides of the big intrusives. Almost none occur to the southeast. The fine-grained pegma-tite
presumably represents the parent magma from which the other pegmatites wer«e derived or is itself a
derivative of a hidden subjacent mass. The general scarcity of systematic joints and of discordant pegma-tites
in the district indicate that the role of fractures in conducting magma upward must have been minor.
Cleavage planes were the easy passageways. Since on the whole the foliation dipped southeast, coarse peg-matites
would necessarily be asymmetrically distributed with respect to the large bodies of fine-grained
pegmatite because of the greater ease of passage of magma along rather than across the layers.
FAULTING
Many faults with diverse attitudes offset all the rocks of the district, except possibly aplite and basalt.
The fault surfaces are slickensided and generally coated with manganese oxide. Similar striations on
foliation planes and pegmatite contacts attest to other shearing movements. Lack of key beds makes it
impossible to determine most displacements, but some are certainly only a few inches or a few feet and
probably most of them are small. The spatial relations of large rock masses encountered during mapping
have not been such as to necessitate the postulation of major faults to account for the structure. The chlo-ritic
amphibolite may be evidence of a large shear zone.
Many of the minor faults may be due to the emplacement of the larger pegmatites and others may have
occurred during later regional uplifts.
JOINTING
Systematic tectonic joints are rare in the district. Locally they are well developed in hornblendic
rocks, which seem to be more brittle than micaceous ones. Irregular fractures extending in all directions
are common. Expansion joints parallel to the local land surface are numerous, particularly in the large
bodies of more massive, fine-grained pegmatite.
DEFORMATION BY INTRUSIONS
The intrusion of dunite seems to have caused little deformation in the wall rocks. The contacts cross-cut
the older rocks in part, and elsewhere the walls seem to have been shoved apart as the magma rose
between steeply dipping foliation planes.
The pegmatite magma penetrated upward and laterally mainly along the layers of the earlier foliated
rocks. Most of the coarse-grained intrusives are conformable, and elongate parallel to the strike of the
metamorphic rocks, though fine details of the contacts show all to be discordant. Thus their positions and
forms seem to have been controlled mainly by pre-existent structure. Some of the smaller conformable
pegmatitic lenses, particularly those in flat-lying gneiss in the northeast part of the district, have been
completely mined away without revealing any trace of the channelway through which the magma entered.
In these places the country rock must have been opened along the foliation planes by tectonic forces or
magma pressure to allow the fluids to pass and then to have closed without trace of the movements.
The larger bodies of fine-grained pegmatite, however, did cut across the foliation on a large scale, and
displaced and crumpled the older rocks. Many of the small faults seem to have been caused by the magma
making room for itself. Hundreds of inclusions of various wall rocks were broken off and engulfed in the
intrusives. These range in length from a few inches to half a mile and are common throughout the big
pegmatites, though concentrated near their borders. They commonly parallel the walls from which they
were derived but may be diversely oriented. Many are considerably crumpled, and most contain considerable
pegmatitic material. Many masses of gneiss within pegmatites may have been roof pendants now isolated
from the country rock by erosion. These perhaps are essentially in their original positions, but the rock
formerly continuous with them along their sides was completely removed to higher or lower levels by the
intrusions.
Aplite and basalt seem to have filled open fractures without disturbing their wall rocks.
Geology and Structure of Part of the Spruce Pine District, North Carolina 17
ECONOMIC GEOLOGY OF THE DISTRICT
GENERAL STATEMENT
Most of the mineral products of the Spruce Pine district are derived from pegmatites. The recent in-vestigations
have been directed toward those rocks and have been focused especially on mica and, to a
lesser degree, on feldspar deposits. Other mineral resources have received only incidental consideration.
Pegmatites in the district have yielded the following industrial minerals : beryl, columbium-tantalum
minerals, feldspar, kaolin, mica, quartz, rare earth minerals, and uranium minerals. Other actual or poten-tial
mineral products of the district include amphibole asbestos, building stone and crushed rock, chromite,
garnet, kyanite, mica schist, olivine, and vermiculite. The distribution of the main pegmatite mineral
products in the district is indicated in Table 1.
The four principal mineral products, listed in the order of their usual importance, are feldspar, kaolin,
ground mica, and sheet mica. These are estimated to account for more than 90 per cent of the district's
total mineral production.
PEGMATITE MINERAL PRODUCTS
BERYL
Beryl is a comparatively rare constituent of Spruce Pine district pegmatites. Most occurrences are
along the southeast side of the district, especially toward the southwest end. The most notable localities are
probably at the Biggerstaff Branch and Poteat mines in Mitchell County, and especially at the Ray Mine in
Yancey County. Beryl occurs as fairly well formed, pale-green, hexagonal prismatic crystals, ranging from
a small fraction of an inch to about 3 inches in diameter. It seems to occur mainly in pegmatites of moderate
size which contain considerable perthitic microcline and to occupy inner positions near the core. Produc-tion
has been incidental to feldspar and mica mining, and the total is probably of negligible commercial im-portance.
No regular production of beryllium ore appears to be possible.
Gem beryl was mined years ago at two localities in Mitchell County and at one in Yancey County, but
the total production seems to have been small. Small emeralds were obtained at the Grindstaff Emerald
mine on Crabtree Mountain, and considerable aquamarine was found at the Grassy Creek Emerald mine.
Aquamarine and golden beryl have also been obtained at the Ray Mine. Further information is contained
in a report by Kunz (1907).
COLUMBIUM-TANTALUM MINERALS
Columbite-tantalite and samarskite occur in small quantities principally at a few feldspar mines in the
Spruce Pine and Crabtree Creek areas, but also at several localities in the Mine Fork area (as Randolph
mine) north of Burnsville. The most notable deposit is doubtless the McKinney mine in upper Crabtree
Creek valley. These minerals seem to occur in association with replacement units in large pegmatites
rich in perthitic microcline. A few hundred pounds of both minerals have been produced as by-products
of feldspar operations but resources appear to be inconsequential. Other known localities include the Deake.
Pink, and Wiseman mines in Mitchell County and the Ray mine in Yancey County.
FELDSPAR
The value of feldspar produced in the Spruce Pine district has exceeded that of any other mineral
product in almost every year since 1920. The first shipments were made in 1911, from the Deer Park
mine. North Carolina has been the leading producer in the United States each year since 1917. and most
of its production has come from the Spruce Pine district. The economic geology of the feldspar deposits
has been considered in detail by Olson (1944, pp. 41-51) so only a summary emphasizing recent develop-ments
will be included here.
Most of the feldspar produced in the district is of two general types: (1) "potash spar" for pottery
manufacture chiefly, and (2) "soda spar" for glassmaking. The former consists mainly of perthitic micro-cline
with quite small amounts of plagioclase feldspar (mostly oligoclase) and quartz. Because of the ad-mixture,
"potash spar" has several percent of soda, but the potash-to-soda ratio is ordinarily 3 to 1 or
18 Geology and Structure of Part of the Spruce Pine District, North Carolina
higher. Because in making pottery the feldspar is mixed with clay, it is ground to 200-mesh or finer. Soda
spar consists mainly of plagioclase (mostly oligiclose) with smaller amounts of perthitic microcline and a
little quartz, so that the soda content slightly exceeds the potash. Granular soda spar is mixed with sand
in glassmaking and so is ground to about 20-mesh size. The two types are thus not sharply distinct. Most
shipments are made up by blending various batches and are strictly controlled to specified composition by
chemical analyses of samples. A third type, "corduroy spar," is the intergrowth of plates and wedges of
quartz in microcline, or less commonly in plagioclase, called graphic granite. The quartz usually amounts
to about 25 per cent of the rock and the resulting ground spar is especially siliceous.
High-potash spar is produced mainly from thick coarse-grained pegmatites that are well zoned. Micro-cline
is the dominant feldspar in very few of the pegmatites. Only large and well-zoned pegmatites contain
concentrations of commercial value. These occur as coarse microcline-quartz cores or intermediate zones
adjacent to massive quartz cores or discontinuous central quartz pods. These zones are mined selectively,
and blocks of perthitic microcline larger than about 2 inches are sorted out, cobbed, and loaded by hand.
The distribution of such deposits in the district is indicated in Table 1 as potash block spar. They occur
mainly in a belt along the southeast side of the district, enclosed in the big bodies of fine-grained pegmatite.
Resources of minable high-potash block spar are generally believed to be low, though it is probable that
other good deposits exist but fail to crop out.
Soda spar is produced in two ways. Some soda block spar is mined selectively, cobbed and sorted by
hand from pegmatites less clearly zoned and less coarse than those which yield potash spar. The blocky
plagioclase is usually in an inner zone where it is mixed with small amounts of microcline and quartz. Though
plagioclase forms nearly half of most pegmatites, it generally occurs in grains and masses too small for
economical hand-sorting. Deposits with block plagioclase have been worked mainly in the central part of
the district. (See Table 1.)
Most soda spar in the district is now produced by large-scale milling of fine-grained pegmatite ("alas-kite").
The rock is quarried, crushed, and ground, and the component minerals separated mainly by froth
flotation. The feldspar concentrate comprises plagioclase with less microcline, and the soda content is a
little higher than the potash content. Byproducts include ground mica and quartz sand. Enormous quan-tities
of rock suitable for such milling exist along the southeast side of the district, though sites favorable
for quarrying and convenient to transportation are not numerous.
KAOLIN
The production of kaolin (white china clay) has in recent years been in either second or third place
in value of the mineral products of the Spruce Pine district; mica for grinding has competed with kaolin
for second place after feldspar. The Spruce Pine kaolin is residual clay formed by decomposition in place
of feldspar-rich rock originally low in iron-bearing minerals. Surface waters containing carbonic and or-ganic
acids have percolated into all of the rocks to variable depths and have converted feldspar into clay.
The large stocks or sills of fine-grained pegmatite ("alaskite") , where favorably located, have been partially
changed to white clay in places to depths of about 100 feet. Other rock types, though altered similarly, have
not yielded commercially valuable kaolin deposits; coarse pegmatite occurs in masses too small to be
economically mined for clay, and all other types of rock have such a high proportion of mafic minerals
that the clay is too iron-stained for ceramic use.
The primary factor controlling the location of kaolin deposits is thus the presence of large bodies of
fine-grained pegmatite. Not all such bodies, however, have been converted to clay. Kaolin deposits are
restricted to pegmatites that crop out in areas of a well-developed strath along the major drainage lines.
This strath consists of wide, flat valley bottoms along the upper reaches of streams and of sediment-capped
flat terraces or gently rolling country along the rivers and major tributaries farther downstream. During1
a previous period of erosion, while the strath was being formed, circulation of ground water in these areas
kaolinized the underlying rocks. The low altitude of the deposits and the gentle land slopes above them
have favored their preservation from recent erosion.
The kaolin deposits consist of clay (apparently kaolinite mainly) with undecomposed feldspar (both
plagioclase and microcline), quartz, and muscovite. Under the local conditions, microcline is more resistant
to weathering than plagioclase and so has a higher ratio to plagioclase in kaolinized rock than in fresh rock.
Minor amounts of biotite and decomposed garnet are present in places. Recoverable clay usually amounts
Geology and Structure of Part of the Spruce Pine District, North Carolina 19
to 15 to 20 per cent of the deposit. It is separated by a complex procedure involving grinding, washing,
screening, settling, and flotation. Scrap mica is an imjortant byproduct. The feldspar and quartz are
wasted in existing plants. Reserves of recoverable washed kaolin in the district are estimated to be be-tween
3 million and 7 million short tons.
Detailed reports on the kaolin deposits by Bayley (1925), Hunter (1940), and Parker (1946) are avail-able.
MICA
Sheet mica.—The mining of sheet mica is the oldest mineral industry of the Spruce Pine district. Pre-historic
mining was carried on, presumably by Indians, and modern mining has continued since 1868. The
annual and total values of sheet-mica production have in recent years been exceeded by those of other prod-ucts
but the importance of the industry continues to be great because of the strategic character of better-quality
sheet mica in war time. For this reason most of the recent work of the U. S. Geological Survey in
the district has been focused on sheet-mica-bearing pegmatites. As a consequence, several detailed reports
on these deposits are available or in preparation; these include reports by Sterrett (1923), Kesler and Olson
(1942), Olson (1944), Cameron, Jahns, McNair, and Page (1949), Jahns and Lancaster (1950) , and Jahns
et al. The present description is of a summary character ; for more comprehensive and detailed information
the reports cited should be consulted.
The range of color, quality, and size of sheet mica produced is considerable, and the different kinds are
not uniformly distributed over the district. The colors of thin plates range from pinkish brown through
brown and greenish brown to dark and light green. The mica in any single pegmatite is either of one color
throughout or of two colors, each of which is limited to a distinct structural unit. Certain colors dominate
in each part of the district (see Table 1), though some mica,, of each color is found in practically all areas.
In the Ingalls, Spruce Pine, and Crabtree Creek areas, where large fine-grained pegmatite bodies prevail,
most mica is green, brownish green or greenish brown. In the areas just north, northwest, and southwest of
this belt (i.e., Ledger-Kona-Micaville and South Toe River areas) brown mica predominates, though green-ish
brown is common. Still farther northwest and west (Hawk-Bandana-Shoal Creek and Black Mountain
areas) reddish-brown mica is most abundant, but is accompanied by light-brown and a very little green
mica. Green mica generally occurs in association with massive quartz cores or in perthitic microcline-rich
pegmatites. Reddish-brown mica is commonest in perthitic microcline-poor pegmatites that have calcic
oligoclase. In pegmatites having two colors of mica, green mica is usually near the core margins and brown
in the wall zone.
Much mica is stained by specks, spots, and streaks of hematite and magnetite. These impurities may
be arranged randomly or in lines crossing each other in regular patterns. Stained mica occurs throughout
the district and is most common in areas where there are large bodies of fine-grained pegmatite.
Inclusions of small intergrown crystals, plates, and grains of many minerals are common between the
sheets of mica books. Inclusions of quartz, plagioclase, garnet, muscovite, biotite, apatite, epidote, tour-maline,
and kyanite have been noted. Inclusions seem to be common in all types of mica from all parts of
the district but they are probably most abundant in green mica.
Structural defects that reduce the yield of trimmed mica include "A" structure, wedge-shaped books,
"locky" cleavages, ruling, reeves, and bent and broken books. Green mica is especially apt to occur in
wedge "A" books. These defects are so common throughout the district that perfect mica books are prac-tically
unknown.
Mica books yielding trimmed sheet must be at least 2 inches in diameter; most range from 5 to 8
inches. The size of mica books or the proportion of large books does not seem to vary geographically or
with the type of deposit.
The fine-grained pegmatite of the large stocks (?) contains abundant flake mica but no books large
enough to yield sheet. The smaller tabular or lenticular bodies of coarse-grained rock within fine-grained
pegmatite and gneissic wall rocks may contain large mica books.
Books of a size, quality, and concentration to be of commercial importance are confined for the most
part to pegmatites that consist dominantly of medium-grained plagioclase and quartz, or to zones of this
20 Geology and Structure of Part of the Spruce Pine District, North Carolina
composition within more complex pegmatites. Rock containing small to moderate amounts of perthitic
microcline intermixed with plagioclase may be mica-rich also, but if perthitic microcline predominates most
of the muscovite is green and has "A" structure. The mutual exclusion of important amounts of blocky per-thitic
microcline and of book muscovite in the same rock mass is the basis for the common division of com-mercially
important coarse-grained pegmatites into mica deposits and feldspar deposits. Some pegmatites,
however, yield both products, but ordinarily the value of one greatly exceeds that of the other and the two
occur in different zones.
Though muscovite is irregularly distributed through practically all parts of every pegmatite, concentra-tions
of commercial value are restricted. In the many pegmatites in which no zoning is apparent, mica is
ordinarily disseminated throughout the body. The mica is not uniformly concentrated in all parts, but
neither do the richer parts seem to be systematically distributed. Such deposits usually are in relatively
thin lenses or sills in foliated rocks. The mica may be of any color except dark green, and it is generally flat
and clear.
In pegmatites having only a thin border zone and a core, book mica is scattered through the core. A
few pegmatites having two or more zones of subequal thickness likewise contain deposits of mica in the core.
In most zoned pegmatites book mica is concentrated in the wall zone. This distribution prevails in
those having feldspathic cores, in those having massive quartz cores, and especially in the more distinctly
zoned pegmatites having three or more units. Mica is about equally abundant throughout the thickness of
the wall zones, but ordinarily the hanging-wall zone is substantially richer than the foot wall zone. The mica
is generally flat, and is reddish brown, brown, or brownish green.
Mica concentrations along the margins of massive quartz cores or central quartz pods are of little
importance in the district. They occur mainly in coarse pegmatites enclosed in large bodies of fine-grained
pegmatite. The mica is invariably green, and "A" structure is moderate to extreme. Much of this mica
is stained.
In a small proportion of pegmatites mica is especially abundant in shoots, which consist of fairly well
defined, narrow, elongate parts of unzoned pegmatites or of particular zones. Such concentrations are com-monest
in the larger tabular and lenticular bodies. Shoots ordinarily plunge obliquely down the dip of the
pegmatites at moderate to low angles, the most common directions being southerly. Some appear to be
localized by outward rolls or sharp bends in the hanging wall, or by the crests in elongate lenticular pegma-tites.
Many doubtless reflect a thicker part of the pegmatite, and their elongate shape and plunging atti-tude
probably indicate similar features for the whole body.
Available evidence indicates that the likelihood of any particular deposit being rich in mica does not
depend on pegmatite shape, character of zoning, or type of mica distribution within the pegmatite. Corre-lation
with mineralogy of the pegmatite has already been described.
In pegmatites that have been mined commercially, book mica generally constitutes about 2 to 6 per cent
of the rock. Large volumes of pegmatite tend toward the lower figure. The recovery of salable sheet mica
is commonly about 5 per cent of the mine-run book mica, the remainder, except for losses, going into scrap
for grinding.
The geologic conditions in the district indicate that at least as much unmined mica exists as has been
produced to date. The outlook for actual discovery of deposits not now exposed is, of course, not encourag-ing.
It is hoped that completion of the geologic mapping of the district will make clearer the factors con-trolling
the localization of productive pegmatites. Additional prospecting by exposing outcrops over wider
surfaces and by core drilling should uncover further supplies. Future production can be maintained at a
high level only at times of high prices or substantial subsidies.
Scrap mica.—Much scrap accumulates during rifting and trimming book mica to obtain sheet; in fact,
well over 90 per cent of mine-run book mica necessarily becomes scrap. In mining for either sheet mica or
feldspar, additional amounts of scrap mica are recovered from broken and bent books or books too small to
trim, though much of this material goes to the dumps. In refining kaolin a large quantity of fine mica in the
form of flakes and small books is recovered by froth flotation as a valuable byproduct. Similarly the pro-duction
of feldspar by milling and flotation of fresh or little-altered fine-grained pegmatite has yielded very
large amounts of scrap for grinding.
Geology and Structure of Part of the Spruce Pine District, North Carolina 21
In recent years mining of scrap mica as a primary product has become commercially important. Weath-ered
bodies of fine-grained pegmatite, similar to those worked for kaolin but also some less thorough kaolin-ized
ones, are mined hydraulically or by power shovel and the mica is separated by washing and screening.
These masses are commonly large and irregular, and may contain 10 to 20 per cent muscovite in flakes and
small books. They occur mainly in the belt along the southeast side of the district. In most of these opera-tions
the kaolin and feldspar are not recovered, and the mica recovery in the fine sizes is very low.
Nonpegmatitic sources of material for ground mica include mica schist and byproduct mica from kyan-ite
mining.
Resources of mica for grinding seem to be large, though the best deposits have been exploited. The
rate of depletion of any one deposit is rapid. Because the easily mined and processed material is confined to
the zone of weathering, the long-term outlook is less favorable than for mineral products obtained from
unaltered rock.
QUARTZ
Quartz is a plentiful constituent in all Spruce Pine pegmatites, but only two types of occurrence are
of economic importance. Many of the larger pegmatites have cores or large discontinuous central pods of
massive gray, smoky, or white quartz. These bodies are most common in the perthitic microcline-rich
pegmatites of the Spruce Pine and Crabtree Creek areas near the southeast border of the district. Per-thitic
microcline and green "A" mica are associated with the quartz, but they can ordinarily be cobbed out
to yield quartz of high purity. Though large quantities of such material are available as a byproduct from
feldspar mining, not much has been sold because of the great shipping distance to glassmaking centers.
Uses demanding high purity, however, have accounted for small production. Thus, quartz from the Chestnut
Flat mine in Mitchell County was used for the glass mirror of the 200-inch reflecting telescope for the Mount
Palomar Observatory in California.
With the advent of froth-flotation production of feldspar, a fairly high-silica quartz byproduct has re-sulted
from the separation of the disseminated quartz in fine-grained pegmatite. The rock being milled
occurs near the southeast margin of the district near Spruce Pine and along the South Toe River near Kona.
The quartz sand thus produced is used in plaster, concrete aggregate, and for road surfacing.
RARE EARTH MINERALS
Minerals containing metals of the rare earth group, mainly cerium, which occur in the Spruce Pine
district include allanite and monazite, Allanite is a fairly common, though minor, constituent of pegma-tites,
especially along the north, northwest, and west sides of the district. It is associated with calcic oligo-clase.
Most of it is in small needlelike crystals, though blades as much as 6 inches long occur at the Tantrough
mine a mile southeast of Burnsville. Because it is sparse and intergrown with feldspar, allanite is noncom-mercial
even as a byproduct.
Monazite is extremely rare in the pegmatites, and no placer deposits are known.
URANIUM MINERALS
Uraninite, uranophane, gummite, autunite, cyrtolite, clarkeite, and torbernite, in addition to samarskite,
occur in exceedingly small quantities in a few pegmatites. These are mainly rather large pegmatites, rich
in perthitic microcline, mostly along the southeastern margin of the district. These minerals are so sparse
as to yield small rare specimens only. Radioactivity in these pegmatites, except actually next to the min-erals
mentioned, is of such low intensity as to be barely detectable. Known localities include the Deake,
Flat Rock, McKinney, Pink, and Wiseman mines in Mitchell County and the Carolina Mineral Company No.
20 and Ray mines in Yancey County.
OTHER MINERAL AND ROCK PRODUCTS
AMPHIBOLE ASBESTOS
Amphibole asbestos has been mined on a small scale from at least three deposits in the district. The
principal production probably has been from the Frank dunite mass in Avery County, where small-scale
mining has been carried on intermittently for years. Slip-fiber anthophyllite asbestos is reported by Hunter
22 Geology and Structure of Part of the Spruce Pine District, North Carolina
(1941, pp. 43-45) to occur along the contact of the olivine rock with hornblende gneiss and along shear zones
within the dunite.
Mining was undertaken about 1943 at the Blue Rock deposit in Yancey County on the northwest side
of the South Toe River opposite the mouth of Blue Rock Branch. Two kinds of rock occur there, one con-sisting
of matted groups of diverging coarse needlelike crystals from 0.5 inch to 6,0 inches long and the
other of closely packed rosettes of radiating groups of fine fibers 0.5 to 1.0 inch long. The latter type has
been mined selectively from a northeast-trending, nearly vertical zone about 20 feet wide in hornblende gneiss.
Two irregular open cuts in line, one at about 40 feet higher than the other, have been worked ; each is 15 to
25 feet wide, about 50 feet long, and as much as 20 feet deep.
Smaller production has also come from a similar deposit on a prominent rocky ridge about a mile north-east
of Micaville.
Small amounts of asbestos are common in most dunite bodies and in many soapstone masses derived
from hornblende gneiss.
BUILDING STONE AND CRUSHED ROCK
Various gneisses have been quarried on a small scale at numerous points in the district for local use as
rough building stone or as crushed stone for road metal. Hornblende gneiss and small quantities of mica
gneiss have been utilized in masonry for walls, houses, and larger buildings. These rocks are widely dis-tributed
throughout the district. The quarries are small and are worked sporadically as need arises. Many
are enlargements of highway cuts.
Evenly layered mica gneiss with hornblende gneiss beds has been quarried beside the road a quarter
of a mile north of Penland in Mitchell County. An unusually tough, massive, fine-grained mica gneiss was
formerly quarried for crushed stone a quarter of a mile southeast of Normansville in Mitchell County.
Evenly laminated hornblende gneiss is quarried intermittently a mile west-northwest of Rebels Creek be-side
the road to Kona. Ellipsoidal masses of hornblende schist from the chlorite-biotite schist on the north-east
end of Tempa Mountain have been used in masonry of a business building in Spruce Pine. Waste rock
from the dumps of various feldspar and mica mines, especially from the very large dumps of the McKinney
mine on the east fork of Crabtree Creek, is much used to surface secondary and mine-access roads. This
material consists mainly of feldspar and quartz fragments with fine-grained pegmatite and some gneissic
wall rock. The value of much of it is lessened by considerable scrap mica, which gives poor traction for
vehicles.
Soapstone was formerly obtained from many quite small openings scattered over the district. It seems
to have been used nearby for house piers, chimneys and fireplaces and for grave markers. The deposits ap-parently
are too small to sustain continuing production even if demand warranted it.
CHROMITE
Chromite occurs commonly as veins and irregular lenses in dunite in the Spruce Pine district, in suffi-cient
quantities to excite interest in the commercial possibilities. The deposits have been investigated care-fully
by Hunter, Murdock, and MacCarthy (1942), who concluded that they are so small and of such low
grade as to be workable only under abnormally high price conditions or as a byproduct of possible future
production of olivine for manufacture of magnesium metal or salts.
GARNET
Garnet is a common mineral in several kinds of rocks in the district. Very few pegmatites lack garnet
but in none is it more than a minor constituent. Mica gneiss is commonly garnetiferous and hornblende
gneiss may be so, especially near large silicic intrusives and where associated with biotite-rich injection
gneiss.
The only commercial production of garnet has been as a byproduct of kyanite mining from a deposit 2
miles southeast of Burnsville in Yancey County.
The most garnet-rich rock observed in the district is hornblende gneiss on the northeast slope of Fawn
Mountain and along upper Blue Rock Branch in Yancey County. In places here garnet crystals as large
as half an inch compose about half the rock. No production from this rock is known to have been attempted.
Geology and Structure of Part of the Spruce Pine District, North Carolina 23
A zone of massive garnet rock occurs on a ridge crest 1.2 miles S. 84" E. of the highway bridge across
the South Toe River in Newdale, Yancey County, on property of Thad Young. The zone, in altered horn-blende
gneiss, is perhaps 8 to 10 feet thick and trends west-northwest. Massive brownish-red garnet (al-mandite)
composes most of the rock; small separate crystals and fine granules are less common. Fine
granular epidote and matted fine actinolite needles as long as half an inch occur in small irregular masses.
White quartz forms irregular veins and masses several inches across. A small prospect pit has been opened
but no mining has been undertaken.
KYANITE
Kyanite is a common accessory mineral in mica gneiss and schist at many places in the Spruce Pine
district and is especially abundant near Bandana in Mitchell County and in much of the Black Mountains
area in Yancey County. It also occurs less commonly in pegmatite and in quartz veins near Bandana. At
least one shaft more than 30 feet deep was sunk about 1926 by E. B. Ward near Bandana in pegmatite or
vein rock containing coarse kyanite blades, but little seems to have been produced. Further details are
reported by Stuckey, (1932, pp. 665-669).
The only commercial development of kyanite in the district was undertaken 2 miles southeast of Burns-ville,
outside of the area mapped to date. Celo Mines, Inc. (later Mas-Celo Mines and Yancey Kyanite Co.)
operated a large quarry, underground mine, and mill from late 1934 until early 1944. Dark-gray mica
gneiss containing 10 to 15 per cent disseminated kyanite needles and blades up to 4 inches long was worked.
The rock is reported by Mattson (1936, pp. 313-314) to have contained kyanite, quartz, biotite, muscovite,
garnet, albitic feldspar, apatite, beryl, pyrite, pyrrhotite, chalcopyrite, galena, sphalerite, bornite, and chal-cocite.
In addition to the low-iron kyanite concentrate, byproduct abrasive garnet and thermally luminescent
quartz were turned out. The value of scrap mica recovered was reduced by the predominance of biotite over
muscovite. Details of the operation are reported by Mattson (1936, pp. 313-314) and by Trauffer (1936,
pp. 46-48). A detailed investigation of the deposit was made in 1943 by N. E. Chute of the U. S. Geological
Survey for the Reconstruction Finance Corporation ; the results have not been published.
MICA SCHIST
Two types of mica schist have been mined for grinding. Muscovite schist has been mined from numer-ous
small pits over a considerable area on Tempa Mountain a mile east of Spruce Pine. It consists of fairly
coarse flakes of muscovite with minor biotite, quartz, and feldspar. The schist has been injected by many
quartz veins ranging from thin stringers to masses as much as 7 feet thick. Near these veins the schist has
been coarsened by recrystallization and the veins contain groups of flakes and small books of muscovite.
Much of the mica produced has come from the veins. This material was dry-ground for many years by the
Victor Mica Co.
Chlorite-biotite schist has been mined on the northeast end of Tempa Mountain and on Hanging Rock
Knob. The open cuts extend along the hillsides a little more than 100 feet and have a maximum depth of
about 30 feet. Since the dip is into the hill, the depth of overburden is becoming great and underground
mining will have to be undertaken. The rock has been dry-ground without beneficiation to give an impure
ground mica containing actinolite, which has been in demand for rolled asphalt roofing.
OLIVINE
Olivine of refractory grade occurs in five dunite masses in the Spruce Pine district. It has been pro-duced
intermittently on a small scale by the United Feldspar and Minerals Corp. since about 1935 from the
Daybook deposit 4 miles north of Burnsville in Yancey County. The fine-grained olivine has been extensively
altered to serpentine and in addition contains deleterious bronzite and talc, so that careful hand cobbing
and sorting is necessary to maintain refractory grade. The iron content of the olivine is said1 to be unde-sirably
high. More than 3.000,000 tons of relatively unaltered olivine has been estimated by Hunter (1941,
p. 52) to exist in the Daybook deposit. The other deposits have been worked little or not at all but could
supply much additional material.
'McDowell, J. S., Harbison-Walker Refractories Co., Pittsburgh, Pa., oral communication.
24 Geology and Structure of Part of the Spruce Pine District, North Carolina
vermiculite
Vermiculite occurs in the dunite bodies in the Spruce Pine district, and is especially common in the
Frank deposit in Avery County and in the Daybook deposit in Yancey County. Murdock and Hunter (1946,
pp. 17 and 39) report that in the Frank deposit it is associated with anthophyllite asbestos along interior
faults and with talc in a marginal zone; similar interior and marginal vermiculite Ozones exist in the Day-book
deposit. The vermiculite appears to have been formed by alteration of chlorite, which in turn is a
secondary mineral derived from the original dunite. A little vermiculite has been produced from the Frank
area.
Vermiculite of quite different association occurs in many pegmatites as a result of alteration of pri-mary
biotite. This vermiculite, or biotite, usually forms either subhedral books or narrow strips as much
as 5 feet long. A deposit of possible commercial value is reported by Murdock and Hunter (1946, p. 37) at
the head of Little Bear Creek in Mitchell County.
Geology and Structure of Part of the Spruce Pine District, North Carolina 25
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