Geology of the northern part of the Cherry Creek metamorphics, Madison Co., Montana
by Willard D Tompson
A THESIS Submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree
of Master of Science in Applied Science at Montana State College
Montana State University
© Copyright by Willard D Tompson (1959)
Abstract:
Kyanite and sillimanite occur in the Precambrian schists, gneisses, and pegmatites of the Cherry Creek
(Archean ?) metamorphics south of Ennis, Montana. The metamorphic rocks were formed as a result of
the regional metamorphism of a thick sequence of sedimentary rocks—mostly limestones and shales.
The stratigraphic section of metamorphic rocks is about 3,050 feet thick and consists of interlaminated
dolomite-marble, dolomitic marble, kyanite-bearing schists and gneisses, amphibolites, and gneisses
and schists, undivided. The rocks are tightly folded and a large isoclinal syncline, which plunges
steeply to the east, repeats the section in the map area.
Three types of pegmatites occur in the area and each type displays a preference for certain host rocks:
kyanite pegmatites occur in kyanite schist or gneiss; feldspar-quartz-muscovite-tourmaline pegmatites
occur in marble and in kyanite schist; and feldspar-quartz pegmatites are most prominent in
quartz-feldspar gneiss.
The kyanite pegmatites apparently formed by processes of metamorphic differentiation, in which
aluminum ions were added to a quartz segregation and probably grew on kyanite nuclei already present
in the quartz.
The inversion, sillimanite replacing kyanite, occurs repeatedly in the kyanite pegmatites and is
probably due to increased temperatures subsequent to the formation of the kyanite. According to
equilibrium diagrams by Miyashiro (1949) and Hietanen (1956), pegmatitic kyanite forms at low
temperatures and pressures and inverts to andalusite at higher temperatures and is stable,at higher
pressures. The fact that in these pegmatites, sillimanite was produced with increased temperatures,
suggests that kyanite possesses no low TP stability field. GEOLOGY OF THE NORTHERN PART OF THE CHERRY CREEK
METAMORPHICS, MADISON CO., MONTANA
by
WILLARD D. TOMPSON
A THESIS
Submitted t o the Graduate F a c u l t y
in
p a r t i a l f u l f i l l m e n t of t h e require me nts
f o r the degre e of
Master of Science in Applied Science
at
Montana S t a t e College
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t
I
/
Approved;
Head, Major Department
I.
Bozeman, Montana
May 1959
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CONTENTS
Text
Page
A b s t r a c t ....................................................................................................................................
5
I n t r o d u c t i o n and g e n e r a l g e o lo g y ...............................................................................
6
P u r p o s e ......................................................................................................................................
6
Acknowledgments....................................................................................................................
6
F i e l d work...............................................................................................................................
6
Summary of p re v io u s work.................................................................................................
6
D e s c r i p t i o n of r o c k s ..........................................................................................................
Dolomite-marble and d o l o m i t i c m a r b l e ...........................................................
Kyanite s c h i s t , k y a n i t e g n e i s s and a s s o c i a t e d r o c k s ...........................
G n e i s s .............................................................................................................................
S t r a t i g r a p h y of the metamorphic r o c k s .........................................................
10
10
11
11
12
P e t r o l o g y of the p e g m a t i t e s ..........................................................................................
B a s is f o r d i v i s i o n of p e g m a t i t e s ....................................................................
Kyanite p e g m a t i t e s ...................................................................................................
The si I l i m a n i t e group of m i n e r a l s .......................................................
S t a b i l i t y r e l a t i o n s of the s i l l i m a n i t e g r o u p ...............................
Mineralogy of the k y a n i t e p e g m a t i t e s ................................................
D e s c r i p t i o n of k y a n i t e p e g m a t i t e s .......................................................
O p t i c a l p r o p e r t i e s o f k y a n i t e and p e t r o g e n e s i s ...........................
I n v e r s i o n s and s t a b i l i t y r e l a t i o n s of the aluminum
s i l i c a t e m i n e r a l s in the p e g m a t i t e s ..............................................
O r ig in of k y a n i t e p e g m a t i t e s ..................................................................
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14
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17
20
20
21
31
32
Fe Id s p a r - q u a r t z - m u s c o v i t e - t o u r m a l i n e p e g m a t i t e s ...................................
M in er al ogy .........................................................................................................
D e s c r i p t i o n .......................................................................................................
P e g m a ti te s in marble l a y e r s ....................................................................
Rim Rock p e g m a t it e and V e t t e r P r o s p e c t ............................................
Control of l o c a l i z a t i o n of the Rim Rock p e g m a t i t e ....................
35
35
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36
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36
F e l d s p a r - q u a r t z p e g m a t i t e s .................................................................................
D e s c r i p t i o n of p e g m a t i t e s ........................................................................
Mineralogy of p e g m a t i t e s ...........................................................................
P e g m a t i t e - h o s t rock c o n ta c t r e l a t i o n s h i p s and
o r i g i n of p e g m a t i t e s ...............................................................................
37
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39
133412
3
Text
Page
S t r u c t u r e ..................................................................................................
Co ntact r e l a t i o n s between Precambrian rocks and P a l e o z o i c ro c ks .
F o ld in g of th e metamorphic r o c k s .........................................
S t r u c t u r a l i n t e r p r e t a t i o n ........................................................................
Boudinage s t r u c t u r e s in th e marble l a y e r s ................................................
40
40
41
41
44
P r i n c i p l e of th e metamorphic f a c i e s a p p l i e d to the rocks o f the
n o r t h e r n p a r t of th e Cherry Creek metamorphics..........................................
47
P o t e n t i a l f o r economic development of the Ennis k y a n i t e d e p o s i t ...........
The volume of k y a n i t e - b e a r i n g rocks in thg map a r e a ..........................
49
49
I n d u s t r i a l uses of k y a n i t e ............................................................................................
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4
ILLUSTRATIONS
F ig u r e
1.
Page
A real map showing l o c a t i o n of map a r e a in t h i s r e p o r t
and type a r e a of Cherry Creek me tamorp hics............. ..........................
7
2.
Map of k y a n i t e - b e a r i n g p e g m a t i t e ..................................................................
15
3.
Diagram showing p o s s i b l e s t a b i l i t y r e l a t i o n s
of th e aluminum s i l i c a t e m i n e r a l s ................................... .......................
17
Diagram showing s t a b i l i t y r e l a t i o n s h i p s of k y a n i t e , s i l l i manite and a n d a l u s i t e under 15,000 p s i w a te r p r e s s u r e ...............
18 ^
E q u i li b r iu m diagram of the aluminum s i l i c a t e m i n e r a l s , i l l u s ­
t r a t i n g the pro p o s a l t h a t k y a n i t e may have no lo w -p r es su r e
s t a b i l i t y f i e l d . .....................................................................................
32
4.
Map of Rim Rock' p e g m a t i t e ........ .......................................
38
5.
Geologic map of th e n o r t h e r n p a r t of th e Cherry Creek meta­
morphics, Madison C o . , Mont., w it h s t r u c t u r a l i n t e r p r e t a t i o n .
42
6.
Map of f o l d s in d o l o m i t e - m a r b l e ...........................................................
43
7.
Boudin in d o l o m i t e - m a r b l e . ...............................................................................
46
8.
AKF diagram of am ph ib ol it e f a c i e s . . . . ; ......................i.............................
48
9.
AKF diagram of e p i d o t e - a m p h i b o l i t e f a c i e s .....................................
48
3A.
SB.
Plate
-■
1. Geologic map and c r o s s - s e c t i o n of the n o r t h e r n p a r t of the
FrontisCherry Creek metamorphics, Madison C o . , Mont............................... .. pie ce
2.
Ph o to m ic r o g ra p h s .....................................................................................................
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3.
P h o to m ic r o g ra p h s ............................................................................................ ...... .
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4.
Ph o to m ic r o g ra p h s .....................................................................................................
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5.
P h o to m ic r o g ra p h s........... ..........................................................
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6.
Ph ot o m ic r o g ra p h s .....................................................................................................
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7.
Photomicrographs.................................... "................................................................
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8.
Ph ot o m ic r o g ra p h s ..........................
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5
ABSTRACT
K yanite and s i l l i m a n i t e occur in th e Precambrian s c h i s t s , g n e i s s e s ,
and p e g m a t it e s of the Cherry Creek ,(Archean ?) metamorphics south of
Ennis, Montana. The metamorphic rocks were formed as a r e s u l t of the
r e g i o n a l metamorphism of a t h i c k sequence of sedimentary r o c k s —mostly
li m e s to n e s and s h a l e s . The s t r a t i g r a p h i c s e c t i o n of metamorphic rocks
i s about 3,050 f e e t t h i c k and c o n s i s t s of i n t e r l a m i n a t e d dolo m it e marble, d o l o m i t i c marble, k y a n i t e - b e a r i n g s c h i s t s and g n e i s s e s , amphi­
b o l i t e s , and g n e i s s e s and s c h i s t s , u n d iv id e d . The rocks a r e t i g h t l y
fo l d e d and a l a r g e i s o c l i n a l s y n c l i n e , which plunges s t e e p l y to the
e a s t , r e p e a t s th e s e c t i o n in the map a r e a .
Three type s of p e g m a t it e s occur in th e a re a and each ty pe d i s p l a y s
a p r e f e r e n c e f o r c e r t a i n ho s t r o c k s : k y a n i t e pe gm at ite s occur in
k y a n i t e s c h i s t or g n e i s s ; f e l d s p a r - q u a r t z - m u s c o v i t e - t o u r m a l i n e pe gmatites
occur in marble and in k y a n i t e s c h i s t ; and f e l d s p a r - q u a r t z peg mat ites
a re most prominent in q u a r t z - f e l d s p a r g n e i s s .
The k y a n i t e p e g m a t it e s a p p a r e n t l y formed by p r o c e s s e s of metamorphic
d i f f e r e n t i a t i o n , in which aluminum ions were added t o a q u a r t z segreg a­
t i o n and p r oba bly grew on k y a n i t e n u c l e i a l r e a d y p r e s e n t in th e q u a r t z .
The i n v e r s i o n , s i l l i m a n i t e r e p l a c i n g k y a n i t e , occurs r e p e a t e d l y in
t h e k y a n i t e pe g m a t it e s and i s prob ab ly due to in c r e a s e d t e m p e ra t u re s
subsequent t o the f or m at io n of the k y a n i t e . According to e q u i l i b r i u m
diagrams by Miyas hiro (1949) and Hietanen (1956), p e g m a t i t i c ky a n it e
forms a t low te m p e r a t u r e s and p r e s s u r e s and i n v e r t s to a n d a l u s i t e at
h i g h e r t e m p e r a t u r e s and i s s t a b l e , a t h i g h e r p r e s s u r e s . The f a c t t h a t in
t h e s e p e g m a t i t e s , s i l l i m a n i t e was produced w it h in c r e a s e d t e m p e r a t u r e s ,
s u g g e s ts t h a t k y a n i t e p o s s e s s e s no low TP s t a b i l i t y f i e l d .
6
INTRODUCTION AND GENERAL GEOLOGY
The aluminum s i l i c a t e m i n e r a l s , k y a n i t e and s i l l i m a n i t e , occur in
s c h i s t s , g n e i s s e s and pe g m at it es on th e n o r t h e a s t f l a n k of th e G rave ll y
Range, Montana, about 12 m ile s south of Ennis, Montana, and 5 miles no rt h
of and continuous w it h th e type a re a of th e Cherry Creek metamorphics
( P e a l e , 1896) ,(See F ig u r e I) .
Precambrian rocks in th e a re a i n c l u d e :
dolom ite -m arble and dolo m it i c
marble, s c h i s t s , g n e i s s e s , a m p h i b o l i t e s , and p e g m a t i t e s .
R e l i e f i s moderate and outc rops of Precambrian rocks a re l i m i t e d ;
th e marble l a y e r s u s u a l l y form low r i d g e s , and the s c h i s t s commonly are
covered by s o i l or a llu vi um .
To th e west the Precambrian rocks d i s a p p e a r under P a l e o z o i c rocks
and d i s p l a y a marked nonconformity with th e Middle Cambrian Fl a th e a d
f o r m a ti o n , o l d e s t of th e P a le o z o i c rocks in th e r e g i o n .
To th e e a s t
t h e y are covered by l a r g e T e r t i a r y t r a v e r t i n e d e p o s i t s and by alluvium
of the Madison R iv e r ,
Evidence of T e r t i a r y hot s pr in g a c t i v i t y is
widesp read in t h e a r e a and t h e presence of p y r o l u s i t e in t h e hot spring
d e p o s i t s has encouraged some p r o s p e c t i n g f o r t h a t m i n e r a l .
PURPOSE
The purpose of t h i s i n v e s t i g a t i o n i s twofold:
(I ) to determine in
some d e t a i l the l i t h o l o g i c ty p e s, t h e i r e x t e n t , and th e s t r u c t u r e of a
p a r t of th e Cherry Creek metpmorphics, and (2) t o det ermi ne the o r i g i n
of th e k y a n i t e p e g m a t i t e s .
7
\ '\ W
O
After U.S.G.S.
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4
S CALE
S
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IO MI LES
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i
Areol Mop Showing Locotion of Mop Areo in This Report
ond Type Area of Cherry Creek Metamorphics.
Map Area in This Report
W.OT.,1959
Type Area of Cherry Creek
FIGURE I
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ACKNOWLEDGMENTS
The w r i t e r wishes t o acknowledge th e a s s i s t a n c e of s e v e r a l i n d i v i d u a l s
as w e ll as a l l members of th e s t a f f of th e Department of Geography and
Geology, Montana S t a t e C o ll e g e .
Dr. Robert F o s t e r was c o n s u l t e d f r e ­
q u e n t l y d u ri n g a l l phases of th e i n v e s t i g a t i o n and c o n t r i b u t e d numerous
v a l u a b l e s u g g e s t i o n s ; Dr. TVilliam McMannis v i s i t e d the a r e a and was
h e l p f u l in the i n t e r p r e t a t i o n of s t r u c t u r e s ; Dr. N ic hola s Helburn made
s c h o l a r s h i p funds a v a i l a b l e f o r c e r t a i n phases of the i n v e s t i g a t i o n ; Mr.
Dan A n d r e tt a a s s i s t e d capably in the f i e l d work; the s t a f f of the L i b ra r y
of Montana S t a t e College ob ta in e d many p u b l i c a t i o n s which were not
immediately a v a i l a b l e ; Mr. Sumner Gerard provide d f i n a n c i a l su pport f o r
t h i n s e c t i o n s ; and Mrs. I r e n e Kukkola and Mrs. N i t a Nickerson typed the
manuscript.
F i e l d equipment was s u p p li e d by th e Department of Geography
and Geology, Montana S t a t e C o ll e g e.
FIELD WORK
F i e l d work was c a r r i e d out over a p e r i o d of about t h r e e months duri ng
th e summer and f a l l of 1958.
Mapping was done w it h pla ne t a b l e and a l i d a d e , and Brunton, d i r e c t l y
on a to p o g r a p h ic base map with a s c a l e of I inch eq ual s 300 f e e t .
The
ba se map was developed by e n l a r g i n g a p o r t i o n of the U. S. Ge olog ical Survey,
Varney and Cameron q u a d r a n g l e s .
Air photos were used as an aid in i n t e r ­
p r e t a t i o n and in th e l o c a t i o n of s i g n i f i c a n t outc ro p s .
SUMMARY OF PREVIOUS WORK
Most w r i t e r s agree t h a t th e s e rocks had a sedimentary o r i g i n ; however,
9
views d i f f e r on the p r o c e s s e s involved in t h e i r metamorphism.
P e a l e (1896, p.2) named t h e Cherry Creek rocks and a s s ig n e d them to
Algonkian age.
They were d e s c r i b e d as c o n s i s t i n g of
"a s e r i e s of marbles or c r y s t a l l i n e li m e s to n e s and i n t e r l a m i n a t e d mica
s c h i s t s , q u a r t z i t e s , and g n e i s s e s . . . They are a l l h i g h l y i n c l i n e d and
are p e r f e c t l y conformable to one a n o th e r , occupying an a r e a of 30 to 40
square m ile s . . . They are fo ld e d , but th e f o l d s are somewhat obscure
so t h a t i t i s im p o s si b le to e s t i m a t e a c c u r a t e l y the t o t a l t h i c k n e s s , but
i t i s c e r t a i n l y not l e s s than s e v e r a l thousand f e e t . Between Cherry Creek
and Wigwam Creek, on the west s id e of th e Madison Val ley , the unchanged
beds of th e Cambrian r e s t upon the upturned edges of t h i s g r o u p . "
Runner and Thomas (1928, p. 202-203) recog nize d a sedimentary o r i g i n
f o r th e rocks of th e Cherry Creek and a t t r i b u t e d the a l t e r a t i o n s l a r g e l y
to
" t h e e f f e c t s of i n t r u s i v e g r a n i t e s and s i l e x i t e . " "Dynamic metamorphism
i s regarded as having been of minor im p o r ta n c e ." " S e l e c t i v e metamorphism
i s w e l l d i s p l a y e d . - Highly a l t e r e d sediments l i e in te rb e d d e d with c r y s t a l ­
l i n e l im e s to n e s , showing l i t t l e or no chemical ch an ges ."
R a b b i t t (1946, p. 124) noted,
"The t h i n banding, the concordancy w it h o t h e r rock u n i t s in th e s e c t i o n ,
and th e composition le ad me t o b e l i e v e t h a t t h e g n e i s s e s a re metamor­
phosed s h a l e s and s a n d s to n e s; th e metamorphism being e f f e c t e d by the
soaking of th e sediments w it h hot s o l u t i o n s . I t i s pro b a b le t h a t th e re
was not much movement of m a t e r i a l . "
He l a t e r noted (p. 125),
"The a m p h ib o li te s are concordant w it h th e g n e i s s e s , d o lo m ite s and p h y l l i t e s
w it h which they are in c o n t a c t . No c r o s s c u t t i n g has been observed . . . .
The a m p h ib o li te s of the a r e a seem to have been o r i g i n a l l y sediments which
have been th oro u g h l y r e c r y s t a l l i z e d w i t h o u t the i n t r o d u c t i o n of much
m a t e r i a l ."
Reid (1957, p , 20) in propos ing a sedimentary o r i g i n f o r the Cherry
Creek metamorphics s t a t e d ,
"The complex i n t e r g r a d a t i o n a l n a tu re of th e metamorphic r o c k s , the wide
v a r i e t y of rock types p r e s e n t and t h e i r complex s t r u c t u r e seem, to the
10
p r e s e n t w r i t e r , to r e q u i r e the pro p o s a l of a sedimentary o r i g i n f o r both
th e Pony and Cherry Creek metamorphic r o c k s . E a r l i e r works, of course,
have p o s t u l a t e d t h a t th e Cherry Creek i s of sedimentary o r i g i n
In h i s study of th e k y a n i t e pe g m a t it e s in the Cherry Creek area,
H e i n r i c h (1948, p. 14) no te d,
"The c o a r s e s t k y a n i t e and t h e r i c h e s t c o n c e n t r a t i o n s occur in the unmeta­
morphosed p e g m a t i t e s . "
He concluded,
"Most of the k y a n i t e in' th e g n e i s s i s g e n e t i c a l l y r e l a t e d to the i n t r u ­
s io n s of the p e g m a t i t e s . The for matio n of k y a n i t e does not appear t o r e ­
p r e s e n t mere r e c r y s t a l l i z a t i o n of m a t e r i a l s a l r e a d y p r e s e n t in th e gn e is s
a t the time of p e g m a t i t i c i n t r u s i o n , bu t pro ba bly in volv e s t h e a d d i t i o n
of aluminum to the w a ll rock by p e g m a t i t i c s o l u t i o n s . "
Thus, most workers agree on the sedim enta ry o r i g i n of the Cherry
Creek r o c k s ; in view of th e n a t u r e of t h e s e rocks i t could h a r d l y be o t h e r ­
wise.
However, t h e r e i s no g e n e r a l agreement on p r o c e s s e s involved in
t h e i r metamorphism.
One th e o r y a s c r i b e s the metamorphism t o a r e c o n s t i t u ­
t i o n of m a t e r i a l s at hand w hi le th e o t h e r n e c e s s i t a t e s t h e i n t r o d u c t i o n of
new m a t e r i a l s .
F i e l d evidence does not su pport a t h e o r y f o r the i n t r o d u c t i o n of lar,ge
amounts of m a t e r i a l and t h e rocks in th e a r e a could p r ob a bly have been
formed by th e r e c r y s t a l l i z a t i o n of m a t e r i a l s p r e s e n t in t h e sedimentary
rocks w it h the a d d i t i o n of l i t t l e or no new m a t e r i a l .
DESCRIPTION OF ROCKS
Dolomite-Marble and Dolomi tic Marble
Dolomite-marble and d o l b m i t i c marble are the most abundant rocks in
t h e map a r e a .
They are very c o a r s e l y c r y s t a l l i n e and, on th e f r e s h s u r f a c e ,
are w h it e , grey, cream,, pink or v i o l e t in c o l o r .
The weathe red outcrop ■
.11
i s u s u a l l y tan or brown.
The marble i s r e s i s t a n t to w e a th e ri n g and forms th e r i d g e s of low
hills.
I t s t r i k e s e a s t e r l y and has a n e a r l y v e r t i c a l d i p .
I t is
l o c a l l y s i l i c e o u s and c o n t a i n s boudins of q u a r t z i t e and w o l l a s t o n i t e q u a r t z - d o l o m i t e ro c k .
Amphibolite pods and pe g m a t it e s occur l o c a l l y in th e m a r b l e .
At the
Rim Rock p e g m at it e of S t o l l (1950, p . ' 5 9 ) ( P l a t e I) a l a r g e m i c r o c l i n e q u a r t z - t o u r m a l i n e - m u s c o v i t e p eg ma ti te i s a s s o c i a t e d with a small amphi­
b o l i t e pod and both a re conformable t o th e f o l i a t i o n of th e host ro^ek.
A marble specimen taken from t h i s l o c a l i t y was found to c o n t a i n :
93
p e r c e n t d o l o m i t e , 6 p e r c e n t c a l c i t e , and I p e r c e n t o t h e r m i n e r a l s .
Kvanite S c h i s t s , Kyanite Gneiss and A s s oc ia te d Rocks
These rocks are l a r g e l y k y a n i t e - b i o t i t e - g a r n e t s c h i s t and k y a n it e b io tite-feld sp ar-q u art'z gneiss.
They c o n ta i n va ri ou s amounts, of k y a n i t e .
Mapped w it h t h e s e rocks a r e some g n e i s s e s , amphibolites, and pe gmatites
which are not d i f f e r e n t i a t e d due to in a d eq u a te exposures or small s i z e . .
In out crops of k y a n i t e g n e i s s , k y a n i t e bla des stand out in r e l i e f and
generally exhibit l i t t l e ,
or no, l i n e a t i o n .
Kyanite b l a d e s in the s c h i s t
have a s t r o n g to weak l i n e a t i o n and t h e s c h i s t p o s se ss e s moderate f o l i ­
ation.
Gneiss.
Near th e s outhe rn l i m i t of the, map a r e a are a group of g n e i s s e s ,
s c h i s t s , p e g m a t i t e s , a m p h i b o l i t e s , and i r o n formation (a t h i n l a y e r ,
a ppr ox im a te ly 10 f e e t t h i c k , Pe rs ona l Communication, Dan Robertspri', 1958)
12
which a re no t d i f f e r e n t i a t e d by t h i s w r i t e r .
The f o l i a t i o n of th e s e rocks
i s p a r a l l e l to th e f o l i a t i o n of o t h e r rocks in the a r e a .
L i t h o l o g i c a l l y , the rocks are q u a r t z - b i o t i t e - m u s c o v i t e - f e l d s p a r g n e i s s ,
q u a r t z - b i o t i t e s c h i s t s , a m p h i b o l i t e s , and a m ph ibo le -ga rnet g n e i s s .
They
c o n t a i n l a r g e t a b u l a r p e g m a t it e bodie s which a re composed of f e l d s p a r
(mos tly mi c r o c l i n e ) and q u a r t z , and are concordant w it h th e f o l i a t i o n of
th e h o s t rock, e xce pt f o r a few small p e g m a t it e s which cut the l a r g e peg­
m atites.
S t r a t i g r a p h y of the Metamorphic Rocks
The s t r a t i g r a p h y of t h e s e Precambrian rocks i s most c onv e n ie n tl y ex­
p r e s s e d in terms of broad u n i t s , co rre sp ond in g to the u n i t s as de fi n e d in
t h e legend on the map ( P l a t e I ) .
S t r u c t u r a l evidence must be employed in th e d e t e r m i n a t i o n of the r e l a ­
t i v e ages of the rock u n i t s si nce t h e r e i s no g e ner al agreement among g e o l o ­
g i s t s as t o which u n i t s are o l d e s t or y o u n g e s t , or to j u s t how many u n i t s
e x i s t (complex f o l d i n g has caused r e p e t i t i o n of u n i t s ) .
»
The s t r u c t u r a l evidence (see S t r u c t u r e . p . 40 to 45) i n d i c a t e s t h a t
th e g n e i s s e s and s c h i s t s a t the s outhe rn l i m i t of the map a r e a are the
oJ.des t of th e Precambrian rocks in the a r e a .
Furthermore, t h e r e i s evidence
f o r the pr es enc e of an i s o c l i n a l f o l d (see Figure 5 ) .
The c a l c u l a t e d s t r a t i g r a p h y i s measured along the l i n e Af-A (see P l a t p
i
I) from t h e southernmost c o n ta c t of the k y a n i t e - b e a r i n g ro c k s w ith the
g n e i s s e s and s c h i s t s , t o the c e n t e r of th e u n i t in which th e mica p r o s p e c t
(P r o s p e c t No. 2) occurs ( t h i s u n i t appea rs t o be the core of th e i s o c l i n a l
13
f o l d , see F ig ure 5 ) .
The rock u n i t s are l i s t e d in o r d e r of t h e i r r e l a t i v e
ages w it h th e o l d e s t rocks a t the bottom of the l i s t :
Rock Type
Thickness
Kyanite-bearing s c h i s t , s c h is ts ,
g n e i s s e s , and a m p h ib o li te s ........................... 430 f e e t
Dolomitp-marble and d o lo m it i c marble
w it h some q u a r t z i t e , w o ll a s t o r i i t e
rock and a m p h i b o l i t e . Contains
many b o u d i n s .......................... ' ............................ 360 f e e t
G ne iss es, s c h i s t s , and marble,
un div id e d. .............................................................
Dolomite-marble and d o l o m i t i c
marble . .
K y a n i t e - b e a r i n g s c h i s t .......................................
Dolomite-marble and d o l o m i t i c
marble . .
Kyanite-bearing s c h is ts , s c h is ts ,
g n e i s s e s , and a m p h ib o li te s
210 f e e t
. 100 f e e t
100 f e e t
.1180 f e e t
. ......... 670 f e e t
T o t al Thickness of S e c ti o n
3050 f e e t
Local t h i c k e n i n g and t h i n n i n g i s common in th e s e r o c k s , so the t h i c k ­
ne ss of any u n i t i s no t n e c e s s a r i l y c o r r e l a t i v e with th e t h i c k n e s s of the
same u n i t in a n o th er l o c a l i t y .
PETROLOGY OF THE PEGMATITES
i
The map a re a i s c h a r a c t e r i z e d by t h e occurrence of many pe gmatites
which vary w id e ly in composition, s i z e , and shape.
B a s i s f o r D iv is io n of Pegmatites
The pe g m at it es p o s s e s s c e r t a i n c h a r a c t e r i s t i c s which are unique and
which, when p r o p e r l y i n t e r p r e t e d , may p r o v id e a clue to th e pegmatite
origin.
These c h a r a c t e r i s t i c s a r e :
(I ) th e mineralogy of the pe gm at ite ,
14
(2) the type of p e g m at it e h o s t ro ck , (3) t h e c o n ta c t r e l a t i o n s h i p between
t h e pe g m a t it e and i t s ho s t rock, and (4) th e shape of the p e gm at ite body.
Although much u s e f u l i n fo r m a t io n may be gained from a study of the
p e g m a t i t e , the d e t e r m i n a t i o n of the c o n t r o l s of pe gm at ite l o c a l i z a t i o n r e ­
quires fu r th e r inform ation.
Bamberg (1956, p. 188) in h i s stu dy of the
Greenland pe g m a t it e s no te d,
nThe l o c a l i z a t i o n of p e g m a t it e s i s ( I ) r e l a t e d to the degre e of re g i o n a l
metamorphism in the a r e a . . . (2) determine d by the mechanical p r o p e r t i e s
of the h o s t r o c k s , and (3) c o n t r o l l e d by th e c h a r a c t e r of th e t e c t o n i c
e v o l u t i o n of th e re g i o n s ( j o i n t s and f a u l t s g e n e r a l l y l o c a l i z e p e g m a t i t e s ) .
The l o c a l i z a t i o n of s p e c i a l types of p e g m a t i t e s ( i . e . , c h a r a c t e r i z e d by a
c e r t a i n m in e ra l composition; f o r example, g r a p h i t e - b e a r i n g p eg ma ti tes or
p e g m a t i t e s w it h d i o p s i d e ) seems t o have been c o n t r o l l e d by a combination
of the m in e r a l- c h e m ic a l composition of the ho s t rocks and th e temperature
and p r e s s u r e a f f e c t i n g the complex a t th e time of emplacement of the peg­
m atite."
Most p e g m a t it e s in th e a r e a can be pla c e d i n t o one of t h r e e groups,
each group being somfewhat l i m i t e d in i t s oc currence t o a p a r t i c u l a r kind of
ho s t ro c k .
The three, groups may be b r o a d l y regarded a s ;
(I) kyanite-
q u a r t z p e g m at it e which commonly occur in k y a n i t e s c h i s t and k y a n i t e g n e i s s ,
(2) f e l d s p a r - q u a r t z - m u s c o v i t e - t o u r m a l i n e pe g m at it es which occur in both
marble and in k y a n i t e s c h i s t and k y a n i t e g n e i s s , and (3) f e l d s p a r - q u a r t z
p e g m a t i t e s which are most prominent in the gn e is s ne ar th e s outhe rn l i m i t of
th e map a r e a .
Kyanite P e g m a ti te s
Kyanite pe g m a t it e s are r e s t r i c t e d in occurrence to h o s t rocks which
c o n ta i n k y a n i t e .
The p e g m at it e bodie s are g e n e r a l l y i r r e g u l a r in shape and
have at l e a s t a p a r t of the p eg ma ti te body concordant w i t h th e f o l i a t i o n
of the ho s t rock (F ig ure 2 ) .
■
15
Sc a le I
F o l i a t i o n of Kyanite S c h i s t
Large Kyanite Blades
Quartz
Figu re 2
Kyanite b e a r i n g p eg ma ti te in Precambrian k y a n it e s c h i s t , lo c a t e d a t
p r o s p e c t No. I (See P l a t e I ) . Pegma tite body is amoeba-I ike in shape and
i s p a r t l y concordant and p a r t l y d i s c o r d a n t w it h host r o c k . C o n c e n tr a ti o n s
of l a r g e k y a n i t e b la d e s occur l o c a l l y n e a r the margins of the pegmatite
body.
16
The l a r g e s t c o n c e n t r a t i o n of the k y a n i t e pe gm at ite s occurs in the n o r t h
c e n t r a l p a r t of the map a r e a .
Local t h i c k e n i n g of the s c h i s t in t h i s l o ­
c a l i t y and th e l i n e a t i o n of minor f o l d axes sugg est s t h e p resen ce of an
" a n t ic li n a l" fold.
Thus, th e l o c a l i z a t i o n of th e s e k y a n i t e p eg ma ti tes may
be p a r t l y r e l a t e d t o the f o l d .
H e in r ic h (1948, p. 15) noted c o n c e n t r a t i o n s of k y a n i t e
" i n a u re o le s
around the q u a r t z - r i c h p e g m a t it e s " and s t a t e d , "Outward from th e pegmatite
c o n t a c t s the grade d im in is h e s r a p i d l y . "
This i s i n c o n s i s t e n t w ith ob s er -
v a t i o n s made by t h i s w r i t e r because t h e q u a n t i t y of the k y a n i t e in any given
l a y e r may i n c r e a s e , d e c r e a s e , or remain c o n s t a n t — independent of the p r o x i ­
mity of a p e g m a t i t e .
Kyanite b l a d e s in t h e s c h i s t and. g n e i s s are g e n e r a l l y l e s s than one
inch in l e n g t h , bu t many are over two inc hes in l e n g t h .
The s i z e of k y a n i t e
b l a d e s in t h e s c h i s t does not n e c e s s a r i l y i n c r e a s e in th e v i c i n i t y of a
p e g m a t i t e ; b u t c e r t a i n l y th e l a r g e s t k y a n i t e b la d es occur in th e p e g m a t i t e s .
The S i l l i m a n i t e Group of M i n e r a l s . - Kyanite, s i l l i m a n i t e , and an dal us i t e are polymorphs of th e compound AlgSiOg.
A n d a lu s it e and s i l l i m a n i t e
c r y s t a l l i z e in t h e orthorhombic system; k y a n i t e in t h e t r i c l i n i c system.
They a l l belong to the c l a s s , n e s o s i l i c a t e s , (Winchell and Winchell, 1951,
pp. 241, 250-258).
The s i l i c o n - o x y g e n t e t r a h e d r a in n e s o s i l i c a t e s e x i s t s
as s e p a r a t e e n t i t i e s ,
(Mason
1958, p. 77 ), i . e . , the oxygen atoms in the
SiO^ t e t r a h e d r a are not shared w it h o t h e r t e t r a h e d r a .
A ll t h r e e m i n e r a l s d i s s o c i a t e to form m u l l i t e (Al&SigOig), plu s l i q u i d
or g l a s s , when h e a te d t o high te m p e r a t u r e s .
Sillim an ite in v e rts t o 'm ullite
17
a t about 1545° C. and k y a n i t e and a n d a l u s i t e i n v e r t a t about 1300° C . ,
(Winchell and W i n c h e l l , 1951, pp. 520, 521 and 528).
S t a b i l i t y R e l a t i o n s of the S i l l i m a n i t e Group. - The s t a b i l i t y r e l a t i o n s
of the aluminum s i l i c a t e m in e r a ls are not w e ll known because the e n v i r o n ­
ment in which the m i n e r a l s are formed i s d i f f i c u l t to reproduce in the
laboratory.
Given the p ro p e r m a t e r i a l s w it h which to form the aluminum
s i l i c a t e m i n e r a l s , t h r e e v a r i a b l e s i n f l u e n c e t h e i r c r y s t a l l i z a t i o n — temper­
a t u r e , p r e s s u r e ( p l u s s t r e s s ? ) , and the w a te r vapor p r e s s u r e in the system.
I t i s the q u a n t i t a t i v e d e t e r m i n a t i o n of t h e s e th re e v a r i a b l e s which w i l l
make p o s s i b l e the r e c o g n i t i o n of the s t a b i l i t y f i e l d s of th e th r e e alum­
inum s i l i c a t e m i n e r a l s .
P e t r o g r a p h i c evidenc e and p e t r o l o g i c evidence are used to e s t i m a t e
th e s t a b i l i t y r e l a t i o n s o f th e aluminum s i l i c a t e m in e ra ls and are summar­
iz ed in an e q u i l i b r i u m diagram (see F ig ur e 3 ) .
Kyanite
Sillim anite
A n d a lu si t e
Mullite
Temperature
Fig ur e 3. Diagram showing p o s s i b l e s t a b i l i t y r e l a t i o n s of
the aluminum s i l i c a t e m in e r a ls ( a f t e r Miyashiro, 1949).
Hietanen (1956) b e l i e v e s the t r i p l e p o i n t to be about 400°.
16
Raraberg (1952, p. 7 4 ) ( a f t e r Yoder, 1952) i n d i c a t e d ( i n e q u i l i b r i u m
diagrams) t h a t a t 15,000 ps i w a te r vapor p r e s s u r e , the t r i p l e p o i n t is
about 660°, as shown in Fig ur e 3A.
Sillim anite
Andalusite
Kyanite
_______________________
430°
660°
Temperature
990°
Fi g u r e 3A. Diagram showing s t a b i l i t y r e l a t i o n s h i p s of
k y a n i t e , s i l l i m a n i t e , and a n d a l u s i t e under 15,000 ps i
w a te r p r e s s u r e .
S i l l i m a n i t e i s u s u a l l y con sid ered t o be the h i g h e s t temperature
form of the AlgSiO^ polymorphs.
Mason (1956, p. 244) has suggested t h a t
because s i l l i m a n i t e i s t h e commonest of the t h r e e m i n e r a l s , i t may
possess the la rg e st s t a b i l i t y f i e l d .
This p o i n t is perhaps c l a r i f i e d by
Turner and Verhoogen (1951, p. 412):
" I t i s h ig h l y pro bab le t h a t s i l l i m a n i t e , u s u a l l y assumed t o be s t a b l e
only a t high te m p e r a t u r e s , i s a c t u a l l y th e s t a b l e form of AlgSiOg over a
much b ro a d e r range, from normal s u r f a c e te m pe ra t ure s almost to the m e l t ­
ing p o i n t a t atmos phe ri c p r e s s u r e . "
They a l s o su gge st t h a t some high te mp erat ure r e a c t i o n s , e . g . , the formation
of s i l l i m a n i t e a t extreme t e m p e r a t u r e s , may be i r r e v e r s i b l e :
" . . . s i l l i m a n i t e , formed only a t maximum metamorphic t e m p e r a t u r e s , at
high p r e s s u r e s , or under c a t a l y t i c i n f l u e n c e of deformatio n or pore
f l u i d s , would remain s t a b l e and show no tendency to i n v e r t to any oth e r
form d u ri n g subsequent c o o l i n g . "
A n d a l u s i t e a p p a r e n t l y i s s t a b l e a t high te m pe ratu res and low p r e s s u r e s
(Ramberg, 1952, p. 45) and, in p a r t i c u l a r , i t does not form in rocks which
19
are S t r e s s e d ( B a r t h , 1951, p . 256) (Mason, 1958, p . 244) ( H i e t a n e n ,, 1956,
p . 26) .
B arth (1951, p. 256) n o te s " .
; . t h a t th e l a t t i c e of andalu-
s i t e i s h i g h l y s u s c e p t i b l e t o , and e a s i l y d e s tr o y e d by s t r e s s f o r c e s . "
"Writers g e n e r a l l y agree t h a t k y a n i t e develops in aluminous rocks
which have undergone metamorphism a t high p r e s s u r e s and i n t e r m e d i a t e tem­
p e r a t u r e s (Mason, 1958, p. 244) (H ie ta nen , 1956, p. 26) (Griggs and
Kennedy, 1956).
Some w r i t e r s p r e f e r to i n c l u d e s t r e s s as a c o n t r i b u t i n g
f a c t o r in the fo rm ati on of k y a n i t e , mostjly because k y a n i t e has a very
high d e n s i t y (B a rt h , 1951, p. 256) (Hi e ta nen , 1956, p. 26).
Barth (1951,
p . 257) n o te s t h a t
" a l t h o u g h s t r e s s may f a v o r the development of k y a n i t e , i t i s not n e c e s s a r y ;
k y a n i t e can grow in a p e g m a t it e where n-o s t r e s s seems t o have been p r e s e n t . "
M i y a s h i r o (1949a, a b s . ) c r i t i c i z e s t h e id e a t h a t s t r e s s i s n e c e s s a ry
foy the fo rm ati on of c e r t a i n m i n e r a l s and c o n s id e rs te m p e r a t u r e , hydro­
s t a t i c p r e s s u r e , and c o n c e n t r a t i o n of the components as " t h e only e s s e n t i a l
f a c t o r s c o n t r o l l i n g metamorphism."
M u l l i t e i s no t common as a n a t u r a l I y - o c c u r r i n g m i n e r a l , bu t i t is
produced a r t i f i c i a l l y .
Kennedy (1955) has found t h a t a s o l i d s o l u t i o n e x i s t s between m u l l i t e
and s i l l i m a n i t e a t t e m p e r a t u r e s of 550°-6000 and 400 b a r s t o 3000 bars
(5000 p s i t o 43,500 p s i ) w a t e r p r e s s u r e .
M u l l i t e i s formed a t the low
p r e s s u r e s ; s i I limarrire a t the high p r e s s u r e s .
!
The s i g n i f i c a n c e of the s t a b i l i t y r e l a t i o n s of the s i l l i m a n i t e group
and t h e i r b e a r i n g on the k y a n i t e p e g m a t it e s in the map a r e a i s d i s c u s s e d
below under "O ri g in of Kyanite P e g m a t i t e s . "
,
20
Mineralogy of th e K yanite P e g m a t i t e s . - Quartz i s t h e most abundant
m in e ra l in t h e kyani t e - b e a r i n g p e g m a t i t e s .
The p eg ma ti te a t P r o s p e c t ,
No. I ( P l a t e I ) in th e n o r t h c e n t r a l p a r t of S e c ti o n 6 was mapped in some
d e t a i l and c o n c e n t r a t i o n s of k y a n i t e are noted on the map of the peg mat ite
(F ig u re 2 ) .
C a l c u l a t i o n s based on s u r f a c e o b s e r v a t i o n s i n d i c a t e t h a t
k y a n i t e and s i l l i m a n i t e comprise about o n e - h a l f p e r c e n t t o 1% p e r c e n t of
th e volume of the p e g m a t i t e .
is quartz.
Approximately 98 p e r c e n t of th e pegmatite
In th e a r e a s of k y a n i t e c o n c e n t r a t i o n q u a r t z makes up about
45 p e r c e n t of the t o t a l rock; k y a n i t e and s i l l i m a n i t e , 35 p e r c e n t ; s e r i c i t e ,
15 p e r c e n t ; and t h e remaining 5 p e r c e n t may c o n s i s t of any of the fo ll ow ­
ing m i n e r a l s :
p l a g i o c l a s e , m u s c o v i t e , g a r n e t , to u rm al in e , b i o t i t e ,
g r a p h i t e , and a p a t i t e .
Other k y a n i t e p e g m a t i t e s in the a r e a c onta in about
th e same m ine ral assemblage, but p r o p o r t i o n s vary in d i f f e r e n t p e g m a t i t e s .
D e s c r i p t i o n of Kyanite P e g m a t i t e s . - Kyanite pe g m a t it e s d i s p l a y many
k y a n i t e b la d e s up t o t h r e e inch es in l e n g t h and s e v e r a l are n e a r l y e i g h t
inches.
At th e southwest c orn e r of the p e gm at ite at P r o s p e c t No. I
(F ig ur e 2) are a group of l a r g e i n t e r s e c t i n g bla des up t o te n inches long
which are th e l a r g e s t seen in th e a r e a .
I t i s i n t e r e s t i n g to note t h a t
in t h i s p e g m at it e a l l c o n c e n t r a t i o n s of k y a n i t e occur n e a r th e margin of
th e p e gm at ite body, and b la d e s of k y a n i t e are not o r i e n t e d and g e n e r a l l y
i n te r s e c t other blades.
The b la d es i n t h e pe gmatite are t r a n s p a r e n t ,
w h i t e or bl ue in c o l o r , and s i n g l e b l a d e s may e x h i b i t v a r i a t i o n s of a l l
three colors.
A b r i l l i a n t b lu e , which i s noted in some c r y s t a l s , i s
g e n e r a l l y r e s t r i c t e d t o the c e n t r a l p a r t of the b l a d e .
S i l l i m a n i t e occurs
(
21
as s m al l, w h it e , f e l t e d m a s s e s .
At P r o s p e c t No. 5 ( P l a t e I) massive w h it e and brown s i l l i m a n i t e occurs
in a smal l, i r r e g u l a r pod a s s o c i a t e d w it h a k y a n it e p e g m a t i t e .
The c o n t a c t s
are obs cur e, but the pod appears t o be about ten f e e t long and t h r e e f e e t
wide and i s exposed in a small draw a t t h e s i t e .
A b u l l d o z e r p i t has ex­
posed a s p e c t a c u l a r k y a n i t e - q u a r t z - s i I l i m a n i t e peg mat ite a t t h i s l o c a t i o n .
Some of the q u a r t z in t h i s p e gm at ite b e a r s deep s t r i a t i o n s where i t has
been in c o n t a c t w it h k y a n i t e b l a d e s .
The s t r i a t i o n s a p p a r e n t l y were imposed
upon th e q u a r t z by k y a n i t e .
Small g a r n e t s , s p e c i e s p y r a l s p i t e ,
(a mixture of a lm a n d it e and s p e s s a r -
t i t e as d e f i n e d by Winchell & W i n c h e l l , 1951, p . 483) occur in the s c h i s t
and in th e pe g m at it es and commonly occur as i n c l u s i o n s in k y a n i t e b l a d e s .
G r a p h it e i s a l s o an abundant (up t o one p e r c e n t ) mine ral i n th e s c h i s t and
occurs commonly in the pe g m at it es and as i n c l u s i o n s in k y a n i t e and s i l l i ­
m a n it e .
S i l v e r y - w h i t e s e r i c i t e occurs along the cleavage p l a n e s of kyan ite
and appea rs to r e p l a c e k y a n i t e .
Massive, yellow s e r i c i t e occurs in some
of th e pe g m a t it e s and r e p l a c e s k y a n i t e , Quartz, p l a g i o c l a s e , and b i o t i t e .
B i o t i t e , which i s a major c o n s t i t u e r i t of the k y a n i t e s c h i s t , i s not
common in th e k y a n i t e p e g m a t i t e s .
O p ti c a l P r o p e r t i e s of Kyanite and P e i t r o q e n e s i s . - A k y a n i t e bla de,
which was ta ke n from th e p eg ma ti te at P r o s p e c t No. 5, was mounted on a
s l i d e w it h th e 100 c le av ag e p a r a l l e l to th e pla ne of th e s l i d e .
The ex­
t i n c t i o n a ng le , which was determined by t a k i n g the average of s ev e ra l
■22
measurements on t h i s b l a d e , was ZAc = 3 0 . 2 ° .
Under t h e microscope s i l l i m a n i t e appea rs in small, f i b r o u s masses
and as long, s t r a i g h t , or s l i g h t l y curving ne ed le s p r o j e c t i n g from the
fibrous masses.
Groups of n e ed le s are g e n e r a l l y p a r a l l e l t o s u b p a r a l l e l .
I s o l a t e d s i l l i m a n i t e n e e d l e s occur, b u t are not as common as ne ed le s which
p r o j e c t from f i b r o u s s i l l i m a n i t e .
Almost w i t h o u t e x c e p t i o n , the s i l l i ­
ma nit e n e e d le s appear t o r e p l a c e q u a r t z or k y a n i t e .
Some n e e d le s show
an i n c l i n e d e x t i n c t i o n , and t h e s e , presumably, are n e e d le s of k y a n i t e —
p o s s i b l y pseudomorphs a f t e r s i l l i m a n i t e .
Hietanen (1956, p . 17-19), in
h e r stu dy of the aluminum s i l i c a t e s in t h e Boehls B utte quadran gle,
Idaho, noted "pseudomorphs of k y a n i t e and a n d a l u s i t e a f t e r s i l l i m a n i t e . "
G ra p h it e i s found between the m in e ra l g r a i n s and as i n c l u s i o n s in
some of th e m i n e r a l s .
Kyanite commonly has g r a p h i t e i n c l u s i o n s and s i l l i ­
ma nit e may have g r a p h i t e w i t h i n the f i b r o u s masses.
Graphite generally
a pp ear s t o have been fo r c e d i n t o an " o r i e n t a t i o n " by th e c r y s t a l l i z a t i o n
f o r c e s of the su rro und in g m i n e r a l s .
P l a g i o c l a s e i s n o t abundant in the k y a n i t e pe gm at ite s and when
p r e s e n t , i t i s commonly s e r i c i t i z e d .
P l a g i o c l a s e from th e pe gmatite at
P r o s p e c t No. I has been i d e n t i f i e d as a ndes in e (Ab^y, Angg), as determined
by measurement of e x t i n c t i o n angles from the t r a c e of COIQ} in a l b i t e
t w in s .
S e v e ra l m in e ra l re pla cem en ts occur r e g u l a r l y in the p e gm at ite s and
are worth n o t i n g :
s i l l i m a n i t e — k y a n i t e ( s i l l i m a n i t e r e p l a c e s kya nit e)
(s e e P l a t e ' l l , Fi g u r es I and 2, and P l a t e V I I I , Figu re I ) ,
sillim anite
23.
q u a r t z (see P l a t e ¥■, Fi gu re I ) , s i l l i m a n i t e ->- kya nit e and p l a g i o c l a s e
(s e e P l a t e VI, Fig ur e I ) ,
s i I l i m a n i t e —^-tourmaline (see P l a t e V, Figure I ) ,
s i l l i m a n i t e and k y a n i t e —^ g a r n e t (see P l a t e IV, Figure I ) , s e r i c i t e - ^ - k y a n i t e and q u a r t z (see P l a t e I I I , Fig ur e I and 2), m u s c o v i t e - ^ k y a n i t e (see
P l a t e VII, Figure.,.2), s i l H m a n i t e — b i o t i t e ( i n minor amounts) , k y a n i t e —
b i o t i t e ( i n mi nor amounts) and c a l c i t e may r e p l a c e any of the p e t m a t i t e
/
m i n e r a l s ( c a l c i t e i s a p p a r e n t l y a secondary m i n e r a l ) .
''
The or d e r in which th e m in e ra ls formed,may be summarized as
follows:
q u a r t z and b i o t i t e , k y a n i t e , s i l l i m a n i t 4 , s e r i c i t e and c a l c i t e .
I n or d e r to avoid ambiguity, i t should be noted t h a t a lt hough q u a r t z is
r e p l a c e d by k y a n i t e and s i l l i m a n i t e ,
some q u a r t z a p p a r e n t l y formed l a t e r
than the aluminum s i l i c a t e m in e ra ls and b e f o r e s e r i c i t e .
Hence, th e re i s
p ro b a b ly e a r ly - f o r m e d q u a r t z and l a t e - f o r m e d q u a r t z in t h e p e g m a t i t e s .
24
P la te
F ig u r e I . Large k y a n i t e bla de being r e p l a c e d by
s i l l i m a n i t e . Specimen taken from ky a n it e p e gm at ite
a t p r o s p e c t No. I . Crossed n i c o l s , 67X. K = k y a n i t e ;
Q = quartz; S = s illim a n ite .
F ig ure 2. S i l l i m a n i t e r e p l a c i n g k y a n i t e and q u a r t z .
Specimen from p eg ma ti te a t p r o s p e c t No. I . Crossed
n i c o l s , 67X. K = k y a n i t e ; S = s i l l i m a n i t e ; Q = q u a r t z .
PHOTOMICROGRAPHS
II
25
P la te
Fi gu re I . S e r i c i t e with g r a p h i t e i n c l u s i o n s . Some
k y a n i t e being r e p l a c e d by s e r i c i t e . Crossed n i c o l s ,
67X. K = k y a n i t e ; G = g r a p h i t e ; Q = q u a r t z ; S = s e r i c i t e .
Specimen from p eg ma ti te a t p r o s p e c t No. I .
F ig ure 2. Kyanite and s e r i c i t e with g r a p h i t e i n c l u ­
s i o n s . S e r i c i t e and k y a n it e being re p la c e d by s e r i c i t e .
Crossed n i c o l s , 67X. K = k y a n i t e ; Q = q u a r t z ; G =
g r a p h i t e ; S = s e r i c i t e . Specimen from p eg ma ti te at
P r o s p e c t No. I
PHOTOMICROGRAPHS
III
26
P la te
F ig u r e I . S i l l i m a n i t e and k y a n i t e r e p l a c i n g g a r n e t .
Garnet has q u a r t z i n c l u s i o n s . Crossed n i c o l s 67X.
K = kyanite; S = s illim a n ite ; G = garnet; Q = quartz.
Specimen from p eg ma ti te a t p r o s p e c t No. I.
F ig u r e 2. Quartz r e p l a c i n g p l a g i o c l a s e , k y a n i t e r e ­
p l a c i n g q u a r t z . Crossed n i c o l s , 67X. P = p l a g i o c l a s e ;
Q = q u a r t z ; K = k y a n i t e . Specimen from k y a n i t e - q u a r t z
g n e i s s n e a r p r o s p e c t No. 7.
PHOTOMICROGRAPHS
IV
27
P la te
F ig u r e I . S i l l i m a n i t e n e e d le s p r o j e c t i n g from f i b r o u s
s i l l i m a n i t e and r e p l a c i n g q u a r t z . Crossed n i c o l s , 67X.
S = s i l l i m a n i t e ; Q = q u a r t z . Specimen from p e gm at ite
n e a r p r o s p e c t No. I .
F ig ure 2. S i l l i m a n i t e n e e d le s and f i b r e s r e p l a c i n g
to u r m a l i n e . Plane l i g h t , 67X. Specimen from peg­
m a t i t e a t p r o s p e c t No. 5. S = s i l l i m a n i t e ; T = t o u r ­
m a lin e .
PHOTOMICROGRAPHS
V
2b
P la te
VI
Fi g u r e I . S i l l i m a n i t e r e p l a c i n g k y a n it e and p l a g i o c l a s e . Specimen from p r o s p e c t No. 5. Crossed n i c o l s ,
67X. P = p l a g i o c l a s e ; K = k y a n i t e ; S = s i l l i m a n i t e .
Fi g u r e 2. Q ua rtz r e p l a c i n g p l a g i o c l a s e , k y a n i t e r e ­
p l a c i n g q u a r t z . Specimen from q u a r t z - k y a n i t e g n e i s s
n e a r p r o s p e c t No. 7. P = p l a g i o c l a s e ; K = k y a n i t e ;
Q = q u a r t z . Crossed n i c o l s , 67X.
PHOTOMICROGRAPHS
136412
29
P la te
Fi g u r e I . Large k y a n it e bla de w it h q u a r t z and
g r a p h i t e i n c l u s i o n s . Specimen from k y a n it e g n e i s s
n e a r p r o s p e c t No. 4 . Crossed n i c o l s , 67X. Q = q u a r t z ;
K _ kyanite; G = g rap h ite.
Fi g u r e 2. Kyanite blade be in g r e p la c e d by mu s co vi te .
Specimen from V e t t e r Mica p r o s p e c t ( p r o s p e c t No. 2 ) .
Crossed n i c o l s , 67X. Q = q u a r t z ; K = k y a n i t e ; M =
mus cov ite.
PHOTOMICROGRAPHS
V II
30
Fi g u r e I . S i l l i m a n i t e r e p l a c i n g q u a r t z and k y a n i t e
(along edge of b l a d e ) . Specimen from k y a n i t e peg­
m a t i t e a t p r o s p e c t No. I . Crossed n i c o l s , 67X. S =
s i l l i m a n i t e ; Q = quartz; K = kyanite.
Fig ur e 2. T ypi cal f i e l d of k y a n i t e - b i o t i t e s c h i s t .
Specimen from p r o s p e c t No. 4 . Plane l i g h t , 67X. B =
b i o t i t e ; K = kyanite; Q = quartz; G = grap h ite.
PHOTOMICROGRAPHS
P la te
V III
31
I n v e r s i o n s and S t a b i l i t y R e l a t i o n s of th e Aluminum S i l i c a t e M inerals
in t h e Kyanite P e g m a t i t e s . - Kyanite and s i l l i m a n i t e are t h e two aluminum
s i l i c a t e m i n e r a l s which occur in the k y a n i t e pe g m a t it e s ; no a n d a l u s i t e
was found in th e p e g m a t i t e s .
The most common i n v e r s i o n of th e aluminum s i l i c a t e m i n e r a l s in the
p e g m a t i t e s i s s i l l i m a n i t e —=^kyanite ( s i l l i m a n i t e r e p l a c i n g k y a n i t e ) , and
t h i s i n v e r s i o n i s noted r e p e a t e d l y in t h i n s e c t i o n s (see P l a t e I I , Fi gure s
I and 2 ) .
The i n v e r s i o n , k y a n i t e - 5- s i l l i m a n i t e , may a l s o e x i s t because
t h e r e are a few n e e d l e s which look l i k e s i l l i m a n i t e but have an i n c l i n e d
e x t i n c t i o n , and hence, may be k y a n i t e —p o s s i b l y pseudomorphs a f t e r s i l l i ­
m a n it e .
The c o n s i s t e n c y w i t h which the i n v e r s i o n , s i l l i m a n i t e —s-kyanite,
occurs in th e k y a n i t e pe g m a t it e s may sug ges t t h a t a change i s in order f o r
the e q u i l i b r i u m diagram, as shown in F ig u r e 3.
The l o c a t i o n of the lower
p a r t of th e k y a n i t e s t a b i l i t y f i e l d i s based on the f a c t t h a t ky a n it e may
occur in a p e g m a t i t i c environment and presumably c r y s t a l l i z e s in a manner
s i m i l a r to t h a t of most m i n e r a l s which are t y p i f i e d by p e g m a t i t i c occur­
rences, i . e . ,
c r y s t a l l i z a t i o n a t low t e m p e r a t u r e s and p r e s s u r e s .
If this
were t h e case, i . e . , i f the k y a n i t e in the peg ma ti tes ' c r y s t a l l i z e d at low
t e m p e r a t u r e s and p r e s s u r e s , then i t s p o s i t i o n in the e q u i l i b r i u m diagram
( F ig u r e 3) should be a t th e lower end of t h e k y a nite s t a b i l i t y f i e l d .
According to the diagram (Figure 3) t h e n , an i n c r e a s e in p r e s s u r e should
no t a f f e c t th e k y a n i t e s in ce i t i s s t a b l e a t high p r e s s u r e s .
An in c r e a s e
in te m p e r a t u r e , however, should cause t h e k y a n i t e t o i n v e r t to a n d a l u s i t e ,
32
an in v e r s i o n which did not occur in the pe gm at ite s d i s c u s s e d in t h i s
paper.
The i n v e r s i o n i s s i l l i m a n i t e —* -k ya nite , as noted above.
Thus, the
e q u i l i b r i u m diagram would pro bably be more a p p l i c a b l e to the k y a n i t e - s i l l i manite s t a b i l i t y r e l a t i o n s which were observed in the k y a n i t e pe gma ti te s,
as d i s c u s s e d in t h i s pap er, i f the diagram were c o n s t r u c t e d as in Figure 3B.
Kyanite
Sillim anite
A n d a lu si t e
Temperature
Figure 3B. E q u i li b ri u m diagram of the Aluminum s i l i c a t e
m i n e r a l s , i l l u s t r a t i n g the p ro p o s a l t h a t k y a n i t e may have
no lo w -p r es su r e s t a b i l i t y f i e l d .
The p o s i t i o n of a n d a l u s i t e in t h i s e q u i l i b r i u m diagram i s taken from
Miyashiro (1949) and s in ce no a n d a l u s i t e was i d e n t i f i e d in th e p e gm at ite s ,
i t s s t a b i l i t y f i e l d can be given no comment.
The evidence o u t l i n e d above s t r o n g l y su gg est s t h a t the k y a n it e in
t h e s e pe g m at it es did not form under low TP c o n d i t i o n s , but formed under
c o n d i t i o n s of moderate p r e s s u r e s and i n c r e a s i n g t e m p e r a t u r e s .
O rig in of the Kyanite P e g m a t i t e s . - Occurrence of rocks composed of
q u a r t z and l a r g e k y a n i t e b la d e s ( g e n e r a l l y r e f e r r e d to as k y a n i t e pegma­
t i t e s ) have been d e s c r i b e d many times in t h e l i t e r a t u r e , and t h e i r o r i g i n
33
has been a t t r i b u t e d to v a r i o u s p r o c e s s e s which range from p r e c i p i t a t i o n
from a hydrothermal s o l u t i o n to p r o c e s s e s i n v o l v i n g metamorphic d i f f e r e n ­
tiation.
The f a c t t h a t k y a n i t e does occur in pe g m at it es has led many w r i t e r s
to th e co nc lu si on t h a t k y a n i t e i s s t a b l e a t low PT c o n d i t i o n s as we ll as
a t m o d e r a t e - t o - h j g h PT c o n d i t i o n s (see Fi gure 3 ) .
S e v e r a l l i n e s of ev ide nc e le ad t o t h e co nclusion t h a t t h e p eg ma ti tes
in th e map a r e a of t h i s i n v e s t i g a t i o n formed as a r e s u l t of metamorphic
d i f f e r e n t i a t i o n ; p o s s i b l y a combination of p r o c e s s e s i n v o l v i n g re c r y s t a l ­
l i z a t i o n and c o n c r e t i o n ( see Ramberg, 1952, p . 220-226, 237-261).
evidence may be summarized as fo l l o w s :
The
( I ) k y a n i t e - q u a r t z p eg ma ti tes
occur only in ho s t rocks which c on ta in k y a n i t e and q u a r t z ; ( 2 ) k y a n it e
( and s i l l i m a n i t e ) a re commonly shared between the p e gm at ite and host rock;
(3) th e aluminum s i l i c a t e m in e r a ls commonly r e p l a c e o t h e r m in e r a ls in t h e
p e g m a t i t e s ; (4) t h e r e has been no g r e a t enrichment of AlgOg ( s e e Figure 2
and p . 20), bu t r a t h e r a r e l a t i v e d e p l e t i o n of (Fe, Mg)D and g r e a t e n r i c h ­
ment of .SiO2 w i t h , p e rh a p s , s l i g h t l o c a l enrichment of AlgOg (replacement
of, b i o t i t e by k y a n i t e a n d /o r s i l l i m a n i t e r e p r e s e n t s a r e l a t i v e l o c a l en­
richme nt of about 40 p e r c e n t AlgOg); and (5) th e p eg ma ti te bodie s pos se ss
no r e g u l a r shape.
Qu artz i s commonly r e p l a c e d in t h e p e g m a t it e s by k y a n i t e and s i l l i ­
m a n it e .
Thus, i t may be re a s o n a b le t o b e l i e v e t h a t th e f i r s t s ta ge in
th e for matio n of th e p e g m a t it e oc curred w it h the development of a q u a r t z
segregation, i . e . ,
th e for matio n of a q u a r t z " v e i n " .
The for mation of .
/
34
t h e q u a r t z body could be i n i t i a t e d by d i l a t i o n or sh e a r, and. d uri ng i t s
growth could pro ba bl y i s o l a t e some of th e m in e r a ls from th e ho s t rock as
inclusions.
The for matio n of a s e g r e g a t i o n in ro c ks which are in chemical e q u i ­
l i b r i u m w i l l r e s u l t in chemical d i s e q u i l i g r i u m , e . g . , a space which was
occupied by rocks w i t h , pe rh a p s, 60 p e r c e n t SiOg, 20 p e r c e n t AlgOg, and
10 p e r c e n t KgO w i l l , a f t e r the s e g r e g a t i o n , be occupied by rocks with
nearly
100
p e r c e n t SiOg.
In o r d e r t o r e - e s t a b l i s h e q u i l i b r i u m , new mineral a s s o c i a t i o n s are
formed in t h e ho s t r o c k s , and c e r t a i n ions ( t h e more mobile ions) may
m i g r a t e t o the s i t e of d i s e q u i l i b r i u m and e s t a b l i s h a new assemblage of
m i n e r a l s — in t h i s i n s t a n c e , k y a n i t e and q u a r t z , which are s t a b l e under the
p r e v a i l i n g PT and chemical c o n d i t i o n s .
The development of l a r g e c r y s t a l s in a metamorphic environment is
w e l l e x p la i n e d by Ramberg (1952, p . 223):
"The p r o b a b i l i t y of nuc le us formation a t given P and T and a given degree
of s u p e r s a t u r a t i o n i s determined by th e c h a r a c t e r of the p r e - e x i s t i n g
m i n e r a l s [kyanite in t h i s case] and t h e i r i n t e r f a c e s . The new n u c l e i w i l l ,
t h e r e f o r e , p r e f e r a b l y tend t o form in or on one of the p r e - e x i s t i n g
m i n e r a l s or in an i n t e r f a c e between two p a r t i c u l a r s p e c i e s of old m i n e r a l s .
. . . I f th e most f a v o r a b l e pla ce of n u c l e i formation i s an i n t e r f a c e
between m i n e r a l s which are r a r e in the ho s t rock, then only a few n u c l e i
w i l l form and th e growth of ' g l o m e r o b l a s t s ' ( p o l y c r y s t a l l i n e monomineralic
c l u s t e r s ) around th e n u c l e i thu s c r e a t e s a c e r t a i n type of metamorphic
d ifferentiation."
Thus, i f the above t h e o r y i s a p p l i e d to the for mati on of the k y a n i t e q u a r t z p e g m a t it e s as d i s c u s s e d in t h i s p a p er , we may p o s t u l a t e t h a t a few
k y a n i t e c r y s t a l s , i s o l a t e d in a q u a r t z - r i c h s e g r e g a t i o n , could a ct as
n u c l e i f o r a d d i t i o n a l aluminum and s i l i c o n io ns , and when t h e aluminum and
/
35
s i l i c o n ions became a v a i l a b l e , t h e i r growth on th e n u c l e i could promote
th e development of l a r g e c r y s t a l s of k y a n i t e .
The i n v e r s i o n , s i l l i -
m a n i t e Jcyanite, which i s noted r e p e a t e d l y in t h i n s e c t i o n s , may be due
t o an i n c r e a s e in te m p e ra t u re subsequent to the formation of k y a n it e (see
Fi g u r e SB).
S e r i c i t e r e p l a c e s k y a n i t e and s i l l i m a n i t e in most t h i n
s e c t i o n s and appears t o have formed as a r e s u l t of r e t r o g r e s s i v e metamor­
phism, p o s s i b l y accompanied by the i n t r o d u c t i o n of HgO and KgO t o the
pegmatite.
I t has been shown t h a t the k y a n i t e pe g m at it es do n o t r e p r e s e n t a re a s
of aluminum enric hme nt; and t h e r e f o r e , t h e r e i s no need t o suppose t h a t
aluminum was in tr o d u c e d by hydrothermal s o l u t i o n s or p e g m a t i t i c s o l u t i o n s ,
as proposed by H e in ri c h (1945, p. 14 -1 5) .
F u r t h e r , t h e r e i s no evidence
of Precambrian i n t r u s i o n s in th e a r e a from which s o l u t i o n s might emanate.
N e i t h e r i s t h e r e re aso n to b e l i e v e t h a t th e pe gm at ites are r e l a t e d to the
T e r t i a r y e x t r u s i v e rocks in th e G r a v e l ly Range, since none of the peg­
m a t i t e s i n t r u d e rocks which are younger than Precambrian in a g e .
r
.-•Feldspar-Quartz-Muscovite-Tourmaline Pe gma tit e s
M in er al og y. - These pe g m at it es occur in marble or s c h i s t and c ontai n
m i c r o c l i n e , q u a r t z , p l a g i o c l a s e (Abgg, Ang), to urm al in e , b i o t i t e , g a r n e t ,
and" m u s c o v i t e .
Kyariite and s i l l i m a n i t e may occur in minor amounts i f the
ho s t rock c o n ta i n s k y a n i t e or s i l l i m a n i t e .
M ic r ocl in e i s g e n e r a l l y the
most abundant mi ne ral in t h e s e p e g m a t i t e s ; however, some pe gm at ite s which
c o n ta i n q u a r t z , m us cov it e, and to u rm al in e c o nt ai n l i t t l e or no m i c r o c l i n e .
D e s c r i p t i o n . - The p e gm at ite bodie s are len s- sh a pe d or i r r e g u l a r and
36
are conformable w it h th e f o l i a t i o n of th e ho s t r oc k.
S e v e r a l of th e se
p e g m a t i t e s c on ta in small c o n c e n t r a t i o n s of muscovite and some have been
p r o s p e c t e d ; however, no s u c c e s s f u l mining program has d e v e l o p e d .
.P e g m a ti te s in Marble L a v e r s . - S e v e r a l f e l d s p a r - q u a r t z - m u s c o v i t e - t o u r ­
maline p e g m a t it e s occur in marble l a y e r s in t h e n o r t h e r n o n e - f o u r t h of
Section
6
( P l a t e I ) , and a few are found in o t h e r p a r t s of th e map a re a ,
e . g . , th e p eg ma ti te which occurs in S e c t i o n
of the southernmost marble u n i t .
6
along the -.southern boundary
These pe g m a t it e s l i e w i t h i n the marble
u n i t s and along th e margins of s c h i s t s and a m p h i b o l i t e s , which suggests
t h a t t h e pe g m a t it e - fo rm in g m a t e r i a l s may have been d e r i v e d from the
s c h i s t s and a m p h i b o l i t e s .
Rim Rock Pegma tite and V e t t e r P r o s p e c t . - S t o l l (1950, p. 59) mapped
t h e Rim Rock pe g m a t it e ( l o c a t e d in n o r t h c e n t r a l S e c ti o n
t h e V e t t e r mica p r o s p e c t (P fo sp e c t No. 2, P l a t e I ) .
6
, P l a t e I) and
He r e p o r t e d t h a t the
southwest end of th e Rim Rock p e g m at it e i s in f a u l t c o n t a c t w it h a r e d d i s h brown, th in - b e d d e d q u a r t z i t e .
No f a u l t i s e v i d e n t a t the l o c a t i o n of the
p e g m a t i t e , and th e q u a r t z i t e which i s in c o n t a c t w ith the p eg ma ti te i s
t a l u s from th e Middle-Cambrian F l a t h e a d for mation t h a t crops out about 350
f e e t t o the n o r th w e s t.
Co ntrol of L o c a l i z a t i o n of the Rim Rock P e g m a t i t e . - The presence of
a small am ph ib o li te boudin a d j a c e n t to th e Rim Rock p e g m a t it e suggests t h a t
th e boudin may have in f l u e n c e d the l o c a l i z a t i o n of the p e g m a t i t e .
During
metamorphism t h e boudin could a ct as a r i g i d body c r e a t i n g a p r e s s u re
shadow t o which th e peg m at it e- fo rm in g m a t e r i a l s could m i g r a t e .
Ramberg
(1956, p. 197) no te d,
;
" P e g m a t i t i c m i n e r a l s w i l l grow in p r e s s u r e shadows in l e 6 .. of r i g i d i n ­
c l u s i o n s in much th e same f a s h io n t h a t q u a r t z grows in p r e s s u r e shadows
of g a r n e t p o r p h y r o b l a s t s . "
The s t r i k e of f o l i a t i o n of th e ho s t rock sugg est s t h a t d i l a t i o n ,
r e s u l t i n g from the f o l d i n g of the hos t ro ck , may a l s o have i n f l u e n c e d the
l o c a l i z a t i o n of th e Rim Rock p e g m a t i t e , i . e . ,
a low p r e s s u r e a re a produced
d u r in g f o l d i n g could c o nce iv a bly be an a r e a of accumulation f o r the peg­
m a t i t e - f o r m i n g m a t e r i a l s (F igu re 4 ) .
F e l d s p a r - Q u a r t z Pe gma tit e s
These pe g m a t it e s occur ne ar t h e so u th er n l i m i t of th e map area and
are a s s o c i a t e d w it h t h r e e main host r o c k s :
orthoclase-quartz-m icrocline-
b i o t i t e g n e i s s , a m p h ib o le -q u a rt z g n e i s s , and a m p h ib o li te .
The p e g m a t it e s were no t examined m i c r o s c o p i c a l l y and t h i s d i s c u s s i o n
i s based on megascopic o b s e r v a t i o n s .
D e s c r i p t i o n of P e g m a t i t e s . - The pe g m a t it e bodies are long and t a b u l a r
and appear t o be m os tly concordant w it h th e f o l i a t i o n of t h e ho s t ro ck .
They are th e l a r g e s t pe g m a t it e s in th e a r e a , but t h e i r e x a c t s i z e i s
d i f f i c u l t to deter mine due t o in a d eq u a te e x p o su r e s .
One of t h e s e peg­
m a t i t e s i s i n d i c a t e d on th e map (see P l a t e I ) ; however, i t s e x ac t s i z e i s
no t shown because of i t s l i m i t e d ex posu re.
be about
100
The p eg ma ti te body appears t o
f e e t t h i c k , i n c l u d i n g some t h i n l a y e r s of g n e i s s , and may be
n e a r l y a h a l f - m i l e long.
Mineralogy of P e g m a t i t e s . - The p e g m a t i t e s are composed l a r g e l y of
mi c r o c l i n e and m i c r o c l i n e - p e r t h i t e , and va ry in g amounts of q u a r t z .
T a b u la r
3b
50 f t .
Sc a le
Fi g u r e 4 .
Map of Rira Rock Pegmatite
Map showing p o s i t i o n of pe gm at ite body (X) and a m phib olit e (black) and
t h e i r r e l a t i o n to f o l i a t i o n of marble (wavy l i n e s ) . Dip of f o l i a t i o n is
n e a r l y v e r t i c a l . Arrows i n d i c a t e d i r e c t i o n of fo r c e s t h a t may have pro ­
duced a s t r e s s couple, thus c r e a t i n g a d i l a t i o n which could a c t as a sink
f o r pe g m a t it e - fo rm in g m a t e r i a l s . Modified a f t e r S t o l l (1950, p. 59).
39
q u a r t z ve in s occur p a r a l l e l to the f e l d s p a r p e g m a t i t e s .
Pe gm at ite -H os t Rock Contact R e l a t i o n s h i p and O ri g in of P e g m a t i t e s . The c o n t a c t between t h e pe g m at it es and t h e i r host rocks i s d i f f u s e , and
s h a r i n g of m i n e r a l s between hos t rocks and p e gm at ite s i s me ga sc op ic a lly
v isible.
Small g a r n e t s occur in the p e g m a t it e s and e x h i b i t no p a r t i ­
cular d is trib u tio n , i . e . ,
th e y are no t confined to the margins or the
c e n t e r of the p e g m a t i t e s , but occur randomly throughout th e p e g m a t it e s .
Such a random d i s t r i b u t i o n of the g a r n e t s would not be ex pec te d i f the
p e g m a t i t e s were formed from aqueous s o l u t i o n s .
In such c as e , the
g a r n e t s would be p r e s e n t as i n c l u s i o n s which were picked up by the
s o l u t i o n s from th e a d j a c e n t country ro c k .
They would be ex pec te d to con­
c e n t r a t e , due t o t h e i r h i g h e r s p e c i f i c g r a v i t y , and t h e r e f o r e , would be
found in c l u s t e r s r a t h e r than as i s o l a t e d i n d i v i d u a l s .
A s l i g h t d e p l e t i o n of f e l d s p a r and q u a r t z a d j a c e n t to " a p l i t e ' 1
( h e re used t o i n d i c a t e small s t r i n g e r s of f i n e - g r a i n e d f e l d s p a r - q u a r t z
rock of ap pr ox im at el y th e same composition as t h e p e g m at it es ) s t r i n g e r s
would seem to i n d i c a t e t h a t a t l e a s t p a r t of the f e l d s p a r and q u a r t z may
have been d e r i v e d from th e host r o c k .
The chemical composition of the
q u a r t z - m i c r o c l i n e - b i o t i t e - o r t h o c l ase g n e i s s , as c a l c u l a t e d from the mode
of one t h i n s e c t i o n was ap pro xim at el y:
70.1 p e rc e n t Siog; 11.2 p e rc en t
AI 2 O3 ; 3 . 7 p e r c e n t ( a l , F e ) 2 O3 ; 3.1 p e r c e n t (Fe, Mg)0; 11.6 p e rc e n t
(Na, K^O and .3 p e r c e n t HgO.
The high p e r c e n ta g e (1 1.6 p e r c e n t ) of
(Na, KjgO may i n d i c a t e t h a t some of t h i s m a t e r i a l was in t r o d u c e d duri ng
metamorphism.
•Ji
The d i f f u s e c o n t a c t s between th e pe g m at it es and host rocks
40
would seem to i n d i c a t e t h a t th e (Na, K) 2 O was in tr o d u c e d by metasomatic
processes.
C o n c e n tr a ti o n of th e s e c o n s t i t u e n t s , which r e s u l t e d in the
fo rm ati on of p e g m a t i t e s , may have oc cu rr ed a t the time of i n t r o d u c t i o n
of t h e m a t e r i a l , or subsequent t o i n t r o d u c t i o n .
The occurrence of l a r g e a m p h ib o li te l a y e r s ne ar t h e pe g m at it es may
p r o v id e an e x p l a n a t i o n as t o the source of the p e gm at ite - fo rm in g
m a t e r i a l s s in ce t h e more v o l a t i l e c o n s t i t u e n t s of the a m p h ib o li te s may
have mi gr at e d from th e a m p h ib o li te s t o s i t e s f a v o r a b l e f o r p r e c i p i t a t i o n ,
th us e n r i c h i n g c e r t a i n rocks w it h f e l d s p a r and q u a r t z and d e p l e t i n g o t h e r
ro c ks of th os e m a t e r i a l s .
This type of metamorphic d i f f e r e n t i a t i o n was
a l s o noted by Reid (1957, p. 20),
" . . . the most a bund ant ly developed u l t r a b a s i c rocks l i e on the margins
of the l a r g e s t metamorphic p e gm at ite b o d i e s . "
STRUCTURE
C o n ta ct R e l a t i o n s Between Precambrian Rocks and P a l e o z o i c Rocks
The c o n t a c t between t h e Precambrian ro c ks and th e P a l e o z o i c rocks i s
c l e a r l y v i s i b l e a t a few p l a c e s in t h e map a r e a and i s o th e r w is e covered
by t a l u s from the P a l e o z o i c sedimentary r o c k s .
The s t r i k e of the P a l e o z o i c rocks i s about N IO0 E and t h e dip i s
about 5° 1W to IO0 Hf.
The f o l i a t i o n of t h e Precambrian ro c ks s t r i k e s gen­
e r a l l y N 80° E, but has c o n s i d e r a b l e l o c a l v a r i a t i o n .
The d ip v a r i e s
from about 45° S t o 65° N, b u t, in g e n e r a l , i s n e a r l y v e r t i c a l .
The f o l i ­
a t i o n of th e Precambrian rocks was t h e r e f o r e e s s e n t i a l l y v e r t i c a l at the
time of d e p o s i t i o n of th e P a l e o z o i c r o c k s .
Fol di ng of the Metamorphic Rocks
The r e p e t i t i o n of d i s t i n c t l i t h o l o g i c types s ug ges ts t h a t the rocks
may have been fo ld e d or f a u l t e d .
There i s some ev ide nc e f o r r e p e t i t i o n by f o l d i n g , i . e . , minor f o l d s ,
m o d e r a t e - s i z e f o l d s , and r e p e t i t i o n of d i s t i n c t rock t y p e s ; but evidence
f o r r e p e t i t i o n by f a u l t i n g was not o b s e r v e d .
Minor f o l d s ( l e s s than 12 inches) occur in g n e i s s i c rocks in two
l o c a l i t i e s , and a few minor f o l d s occur in marble l a y e r s .
M oder at e -s iz e
f o l d s ( l a r g e r than two f e e t ) a l s o occur in the marble, p a r t i c u l a r l y in the
southernmost l a y e r (see F i g u r e s 5 and
6
and P l a t e I ) .
S t r u c t u r a l I n t e r p r e t a t i o n . - The s t r u c t u r a l i n t e r p r e t a t i o n i s based
upon th e a p p ar en t r e p e t i t i o n of c e r t a i n rock l a y e r s , th e l i n e a t i o n of f o l d
a x e s , and the a t t i t u d e s of f o l i a t i o n of th e ro c k s .
The g e n e r a l s t r u c t u r a l p a t t e r n a ppea rs t o be t h a t of an i s o c l i n a l
s y n c l i n e (?) whose a x i s plunges about 60° to 70°, N 80° E (see Figure 5 ) .
I f t h e s t r u c t u r e i s i n t e r p r e t e d t o be an ove rtu rne d a n t i c l i n e , i . e . ,
an a n t i c l i n e in which th e a x i s plunges HO 0 or 120°, N
c r o s s - f o l d i n g should occu r.
8 0
° E, then some
No c r o s s - f o l d i n g i s observed in th e map a r e a .
I f the s y n c l i n a l i n t e r p r e t a t i o n i s c o r r e c t , the o l d e s t of the Pr ecambrian rocks in t h e map a re a are the g n e i s s e s and s c h i s t s which occur
a t the so uth er n l i m i t of the a re a, and th e youngest Precambrian rocks
( n o t n e c e s s a r i l y i n c l u d i n g pe gm at ite s) occur in the core of th e f o l d .
7
/ ‘ Ii
/ /
pCm
Geologic Mop of the Northern Port of
the Cherry C reek M etomorphics,
Madison Co., M ontana with
Structural Interpretation.
EXPLANATION
SCALE
O
3 0 0 0 Feet
I
I
WOiT., 1959
Ip € m
| D o l o m i t e - M a r b l e a n d D o lo m itic M a r b l e
Ip C k s I K y o n ite S c h i s t .
S c h is ts , G n e is s e s
|p € g s | G n e is s e s a n d
S c h i s t s , U n d iv id e d
^ 5 ^
and
F o lia tio n o f M e t a m o r p h i c R o c k s
C o n ta c t o s M a p p e d
FIGURE 5
^ ,7 0
S tru c tu r a l In te r p re ta tio n
P lu n g e o f F o ld A x e s
of
C o n ta c t .
A m p h ib o lite s
Map of Folds in
Dolomite-Marble.
See Location " F " , Plate I .
W.D.T.,1959
SCALE
O______________ 5 0 FEET
I
I
FIG U R E 6
44
Boudinaqe S t r u c t u r e s in Marble Lavers
Boudinage s t r u c t u r e s , which occur l o c a l l y in the ro c k s , are most f u l l y
developed in s i l i c e o u s marble (see a re a d e s i g n a t e d "b oudin s" , P l a t e I ,
Section
6)
and commonly have t h e i r X and Y axes p a r a l l e l and t h e i r Z a x i s
p e r p e n d i c u l a r , or n e a r l y p e r p e n d i c u l a r , t o the f o l i a t i o n of th e e n c l o s i n g
rock (see Ramberg, 1955, p. 522).
The boudins are t y p i c a l l y b a r r e l - s h a p e d
( i n two dimensions) and are composed of q u a r t z , dolom ite , c a l c i t e , and
w b l l a s t o n i t e (see F ig u r e 7 ) .
Ramberg (1955, p. 512, 513, 517) has p o i n t e d out t h a t
"Boudins are u s u a l l y oblong bodies wit h t h e s h o r t e s t dimension p e r p e n d i c u l a r
t o th e s c h i s t o s i t y in th e e n c l o s i n g rocks and th e l o n g e s t dimension p a r a l l e l
to the s c h i s t o s i t y . "
'
As t o the o r i g i n of boudinage s t r u c t u r e s , he s t a t e s ,
" . . . th e b a s i c re aso n f o r boudinage s t r u c t u r e i s d i f f e r e n c e s in com­
p e te n c y between th e boudin l a y e r and t h e a d j a c e n t ro c k s , th e l a t t e r be ing
r e l a t i v e l y incompetent or d u c t i l e , the former competent or b r i t t l e .
"The b a r r e l - s h a p e of boudins i s . . . r e a d i l y e x p l a i n e d by compression
p e r p e n d i c u l a r t o the l a y e r i n g and a consequent e l o n g a t i o n p a r a l l e l to the
layering . . . "
In r e g a r d t o the fo rm ati on of an e l o n g a t e body he s t a t e s (p . 517),
" E lo n g a ti o n of a body of m a t t e r in one or more d i r e c t i o n s can be caused
by, (I ) s t r e t c h i n g under t e n s i l e s t r e s s , ( 2 ) compression in a d i r e c t i o n
p e r p e n d i c u l a r , t o the d i r e c t i o n ! s) of e l o n g a t i o n , or (3) a s t r e s s couple
a t about a 45° angle t o the e l o n g a t i o n . "
However, he concludes t h a t most boudins are produced by compression in a
d i r e c t i o n p e r p e n d i c u l a r t o boudin e l o n g a t i o n :
" . . . th e s t r u c t u r e of the incompetent rocks a d ja c e n t t o boudins . . .
shows t h a t th e b a s i c re a so n f o r the e l o n g a t i o n of the incompetent roc ks ,
in by f a r th e most c a s e s, must have been a compressive s t r e s s p e r p e n d i c u l a r
( o r at an obtuse angle) t o the boudin l a y e r . "
45
The q u a r t z - d o l o m i t e - c a I c i t e - w o l l a s t o n i t e rock i s a p p a r e n t l y more
b r i t t l e than th e marble, and thu s i t y i e l d e d t o s t r e s s by r u p t u r e ;
whereas t h e marble y i e l d e d by f lowage.
The l i n e a t i o n of th e boudins i s p a r a l l e l to the f o l i a t i o n of the
e n c l o s i n g ro c k s , or about N 80° E, i n d i c a t i n g t h a t the compressive
f o r c e s which formed t h e boudinage s t r u c t u r e s were p e r p e n d i c u l a r t o (or
a t an obtuse angle to) t h e long a x i s of th e boudins.
Such compressive f o r c e s could a l s o be employed t o e x p l a i n th e f o l d ­
ing of the ro c k s , as proposed in t h i s p a p e r .
46
Ol
I
Boudin in dolom ite-m arble.
See Boudins ,P late I .
Drawn a ft e r photograph.
W.D.T., 1 95 9
i
SCALE
6
I
12 Inches
I
Ruptures
Foliation (vertical)
Figure 7
Competent
rocks
47
PRINCIPLE OF THE METAMORPHIC FACIES APPLIED TO THE ROCKS
" OF THE NORTHERN PART OF THE CHERRY
CREEK METAMORPHICS
The rocks in th e map a r e a appear t o have been metamorphosed under
c o n d i t i o n s ap proximating th o s e of the e p i d o t e - am phi bolit e f a c i e s or the
a m p h ib o li te f a c i e s .
This i n t e r p r e t a t i o n i s based upon th e o b s e r v a ti o n of
s e v e r a l c r i t i c a l m in e ra l assemblages which occur in the a r e a :
(1)
Kyanite-sillim anite-m uscovite-plagioclase-quartz
(2)
Kyani t e - s i l l i m a n i t e - b i o t i t e - q u a r t z
(3)
K yanite-andalusite-pyralspite-biotite-quartz
(4)
C alcite-dolom ite-w ollastonite-quartz
(5)
Kyanit e - s i l l i m a n i t e - b i o t i t e - p y r a I s p i t e - m u s c o v i t e - q u a r t z
(6)
Mi c r o c l i n e - o r t h o c l a s e - b i o t i t e - q u a r t z
(7)
Amphibole (h o r n b le n d e ) - p l a g i o c l a s e
F ig u r e
8
r e p r e s e n t s a s t a b l e m in e ra l assemblage^
of th e amp hibo lite
f a c i e s ; F ig ure 9, a s t a b l e assemblage of th e e p i d o t e - a m p h ib o li te f a c i e s .
I t i s noted t h a t specimens taken from w id e ly s ep a ra te d p o i n t s in the map
a r e a may be c o n v e n i e n t l y p l o t t e d on t h e s e diagrams.
4b
A
Muscovite
Staurolite
\ — E-56-4-1
B iotite
Almandine
V-Vacant f i e l d
M i c r o c li n e
Figure b . Amphibolite f a c i e s : AKF diagram f o r rocks
w it h excess Si&g and AlgO^. P o i n t E - 5 b - 4 - l r e p r e s e n t s
p o s i t i o n of specimen of k y a n i t e - b i o t i t e s c h i s t taken
from P r o s p e c t No. 4 ( a f t e r Tur ner and Verhoogen, 1951,
p. 45 3) .
Kyanite
Staurolite
Muscovite
,Garnet
\ Chlorite
E-Sb-GOrthdclase
Biotite
Figure 9. E p i d o t e - a m p h i b o l i t e f a c i e s : T a lc , k y a n i t e pota sh f e l d s p a r (AKF) diagram of the high e p id o te - a m p h i­
b o l i t e f a c i e s ( a f t e r Ramberg, 1952, p. 149). P o in t
E-Sb-G-Gl i n d i c a t e s p o s i t i o n of b i o t i t e - p o t a s h f e l d s p a r q u a r t z g n e i s s . Specimen taken from gn e is s n e a r southern
l i m i t of map a r e a .
49
POTENTIAL FOR ECONOMIC DEVELOPMENT OF THE ENNIS KYANITE DEPOSIT
The economic p o t e n t i a l of t h i s d e p o s i t of k y a n it e and s i l l i m a n i t e i s
dependent upon s e v e r a l f a c t o r s :
(I)
th e a c t u a l volume of k y a n i t e - b e a r i n g
ro c ks in t h e a r e a and t h e p e r c e n t of k y a n i t e and s i l l i m a n i t e in the r o c k s ,
(2) the ea se w it h which t h e k y a n i t e - b e a r i n g rocks can be mined, (3) the
e a s e w it h which th e k y a n i t e and s i l l i m a n i t e can be c o n c e n t r a t e d i n t o a mar­
k e t a b l e p r o d u c t, ( 4 ) t h e pro x im it y of a market f o r th e f i n i s h e d produ ct ,
( 5 ) th e world market s i t u a t i o n f o r th e r e f r a c t o r y m a t e r i a l s , and ( 6 ) th e
a b i l i t y of th e k y a n i t e and s i l l i m a n i t e t o convert t o m u l l i t e .
The scope of t h i s pa per does not i n c l u d e a study of th e above f a c t o r s ,
w i t h th e p o s s i b l e e x c e p t i o n of the f i r s t , which w i l l be d i s c u s s e d b r i e f l y .
The Volume of K va n it e- B e a ri n q Rocks in th e Map Area
An a c c u r a t e e s t i m a t e of th e volume of k y a n i t e - b e a r i n g rock in the a r e a
and t h e p e r c e n t of k y a n i t e in t h e rock can be made only a f t e r e x t e n s i v e
t r e n c h i n g and sampling.
The depth t o which t h e k y a n i t e - b e a r i n g rocks p e r s i s t
can be de termined by s e l e c t i v e d r i l l i n g .
is correct, i . e . ,
I f the s t r u c t u r a l i n t e r p r e t a t i o n
i f th e s t r u c t u r e i s a s y n c l i n e (see p. 41 and Fig ur e
6
)
“'h
th e k y a n i t e - b e a r i n g ro c ks may p e r s i s t t o c o n s i d e r a b l e d e p t h s .
Ttiere jis no
i
re a s o n t o b e l i e v e t h a t t h e q u a n t i t y or q u a l i t y (massive k y a n i t e i s con- , , , ,
s i d e r e d t o be high q u a l i t y , and d i s s e m i n a t e d k y a n it e i s co n si d e re d t o be
low q u a l i t y —both s u b j e c t t o t h e i r m u l l i t e - f o r m i n g a b i l i t i e s ) of the k y a n i t e ,
J
in any l a y e r of th e k y a n i t e - b e a r i n g r o c k s , should i n c r e a s e or d e cr ea se w i t h
depth.
I
50
INDUSTRIAL USES OF KYANITE
Kyanite has an i n d u s t r i a l a p p l i c a t i o n in the pro d u c ti o n of m u l l i t e - m u llite (plus free s i l i c a )
i s formed when k y a n i t e i s heat ed t o a tempera­
t u r e of about 1300° C.
M u l l i t e i s used in th e manufacture of h i g h l y r e f r a c t o r y m a t e r i a l s
which p o s s e s s a low c o e f f i c i e n t of ex pa ns io n, r e s i s t a n c e t o loads at high
t e m p e r a t u r e s , and r e s i s t a n c e t o thermal shock and th e c o r r o s i v e a c t i o n of
r e a c t i v e s l a g s (Haw, 1954).
According t o Gunsallus and Tucker (1957, p.2)
. . -about 90 p e r c e n t of a l l m u l l i t e r e f r a c t o r i e s have been employed
t o l i n e fu r n a c e s o p e ra te d by th e m e t a l l u r g i c a l and g l a s s i n d u s t r i e s . . .;
. . 1 0 p e r c e n t . . . consumed in m i s c e l l a n e o u s a p p l i c a t i o n s , c h i e f l y in
t'he ceramics i n d u s t r y . "
{
51
BIBLIOGRAPHY
B a r t h , T. F. Ttf., 1952, T h e o r e t i c a l p e t r o l o g y : John Wiley
387 p .
&
Sons, I n c . ,
Bowen, N. L . , 1924, The system A^Og-SiOg (Abs.) : G e o l. Soc. America
B u l l . , v. 35, no. I , p. 123.
&
Campbell, I . ,
Wright, L.A., 1950, Kyanite p a r a g e n e s i s a t Ogilby, C a l i f .
( A b s . ) : G e o l. Soc. America B u l l . , v . 61, no. 12, p. 1520-1521.
Chadwick, R. A., 1958, Mechanisms of pe g m a t it e emplacement: G e o l . Soc. of
America, v. 69, no.7 ,p. 803-836.
Dunn, j . A . , 1929, The aluminous r e f r a c t o r y m a t e r i a l s ; k y a n i t e and s i l l i manite and corundum in n o r t h e r n I n d i a : I n d i a G eo l. Survey, Mem. 52,
( 2 ) , p. 145-274.
F y f e , W. S . , Tu rn er, F. J . , and Verhoogen, J . , 1958, Metamorphic r e a c t i o n s
and metamorphic f a c i e s : G e o l . Soc. America, Mem. 73, 259 p.
G rig gs , D. T , , and Kennedy, G. C., 1956, A simple a p p a r a tu s f o r high
p r e s s u r e s and t e m p e r a t u r e s : Am. J o u r . S c i . , p. 722-735.
&
G u n s a l l u s , B. L.,
Tucker, G. E., 1957, K yanite and r e l a t e d m i n e r a l s : U. S.
Bureau of Mines Yearbook, 1957, 4 p.
Haw, V. A., 1954, Kyanite in Canada: Canadian Min. M e t a l l . B u l l . , no. 501,
p. 27-35.
H e i n r i c h , E. W., 1948, D e p o si ts of the s i l l i m a n i t e group of m in e ra ls south
of Ennis, Madison C o . , with no te s on o t h e r oc cur rence s in Montana:
Mont. Bureau of Mines, Misc. C o n t r i b u t i o n no. 10, 22 p.
________________ , 1949, P e gm a tit e s of Montan'a: R e p r in t from Economic G e ol.,
v. 44, no. 4, 43 p.
H ietanen, A., 1956, K ya ni te, a n d a l u s i t e and s i l l i m a n i t e in t h e s c h i s t
in Boehls B u t t e q ua dra ng le , Idaho: R e p r i n t from Am. M i n e r a l o g i s t 41,
p. 1-27, 27 p .
J e f f e r y , J . A., 1944, The s i l l i m a n i t e group of m i n e r a l s : C a l i f . J o u r , of
Mines and G e o l. , v. 39, no. 3, p. 383-390.
Kennedy, G. C., 1955, P y r o p h y l I i t e - s i I l i m a n i t e - m u l I i t e e q u i l i b r i u m r e ­
l a t i o n s t o 20,000 b a r s and 800° C.: G e o l. Soc. America, V. 6 6 , no. 12,
p . 1584.
52
Mason, B., 1 9 5 8 , , P r i n c i p l e s of g e och e m is tr y: John Wiley & Sons, 310 p.
M iy a s h ir o , A., 1949a, A not e on s t r e s s m i n e r a l s CAbs. ) : G e o l. Soc. Japan
J o u r . , 55, p . 216-217.
______________ , 1949b, The s t a b i l i t y r e l a t i o n s of k y a n i t e , s i l l i m a n i t e and
a n d a l u s i t e , and t h e p h y s i c a l c o n d i t i o n s of the metamorphic p ro ce sse s
(Abs. ) : G e o l. Soc. Japan, 55, p. 223.
Nordstrom, C., 1947, Geology of a k y a n i t e d e p o s i t ne ar Ennis, Montana:
T h e s is (B.S ) Montana School of Mines, B u tt e , Mont.
P e a l e l A. C., 1896, Three Forks, Mont.: U. S. G e o l. Survey F o l i o #24,
7 p . , 4 maps.
B a b b i t t , J . C., 1946, S t u d i e s of t h e Cherry Creek s e r i e s and anthop h y l l i t e in Montana; T h e s is (Ph.D.) Harvard U n i v e r s i t y .
Ramberg, H., 1952, The o r i g i n of metamorphic
Chicago P r e s s , 3T7 p.
&
metasomatic r o c k s : Univ. of
____________ , 1955, N a t u r a l and e x per im en ta l boudinage and pinc h and swell
s t r u c t u r e s : J o u r . G e o l. , v . 63, no. 6, p. 512-526.
,________ , 1956, P e gm a tit e s in west Greenland: G e b l . Soc. America B u l l . ,
v. 67, p . 185-213.
Read, H. H., 1933, Q u a r t z - k y a n i t e rocks in Unst, Sh et la nd I s l a n d s : Mineral
Mag., v. 23, p. 319-328.
Reid, R. R., 1957, Bedrock Geology of th e n o r t h end of th e Tobacco Root
Mts. , Madison C o . , Montana: Mont. Bur. Mines G G e o l . , Mem. 36, 25 p.
Runner, J . J . , and Thomas, L. C., 1928, S t r a t i g r a p h i c r e l a t i o n s of the
Cherry Creek group i n th e Madison V a ll e y , Mont. ( A b s .) : G e o l . Soc.
America B u l l . , v. 39, no. 2, p. 202-203.
S t o l l , W. C., 1950, Mica & Heryl p e g m a t it e s in Idaho
Survey P r o f . Paper 229-, 64 p .
&
Montana: U. S. G e o l.
Stu ckey, J . L ., 1932, Cy an it e d e p o s i t s of North C a r o l i n a : Econ. G e ol., v. 27,
no. 7, p . 661-674.
Turner,' F. J . , and Verhoogen, J . ,
McGraw-Hill Book Co., I n c .
1951, Igneous and metamorphic p e t r o l o g y :
W i n c h e l l , A. N., 1914, Mining d i s t r i c t s of t h e D il lo n quad rangle and ,
a d j a c e n t a r e a s : U. S . G e o l. Survey, B u l l . 574, 191 p ., 8 p i .
53
WinchelI, A. N., and Win che ll, H., 1951, jSlements of o p t i c a l mineralogy,
p a r t 2: John Wiley and Sons, p. 483-^28.
T
PLATE I
R l W.
EXPLANATION
Alluvium
18 l/2°i
Quaternary
Talus
72 66
T.7S.
Travertine
Tertiary
Sedimentary Rocks, Undivided
r
Paleozoic
p€Kp I \ '
/
Middle Cambrian Flathead Formation
Dolomite Marble and Dolomitic Marble
Kyanite Bearing Schist Prominent. Includes
Some Gneiss and Amphibolite
Gneisses and Schists,Undivided
Precambrian
Amphibolite
/' Pol
Kyanite Bearing Pegmatite
Pegmatites,Undivided. Generally Contain Quartz,
Feldspar, Tourmaline and (or) Muscovite
Mica Protpact
X2
Contact
Qt
a
Contact
Approximately
Located
P tg i
x IO
Attitude of Bedding in
S edim entary Rocks
^60
Attitude of Foliation in
C rys ta llin e
-V-
Strike of Vertical Foliation in C rystalline
^rVo
Attitude of Foliation
Ar
Strike of V ertical
T.8S.
I
Il
Carbonates
5840
'
I- /
6042
+ 5 746
X
6000
Prospect
in Kyonite
Bearing
/.5 0
Plunge o f Axes of M o d e r a t e - S iz e
L in ea tio n
H orizontal
Anticlinal
Folded
A---- A'
Cross
S ection
- •••___
Large
Interm ittent
Gneisses
Joints
Plunge of
Trace of
and
Relative Movement
Strike and Dip of
I
Gneisses
Rock
"eo
\
/ _o
and
Foliation in Schists
Fault. Arrows Indicate
y
L\
in Schists
Carbonates
of
Minor
Folds
Fold
Axes
Axis
Foliation
SCALE
9- T - - T - ^
IOOO___________________________ 2 0 0 0
I
I
1 0 0 0 FEET
Stream
)
----CONTOUR
IN T E R V A L
40
GEOLOGIC MAP
6000
S m all Draw
FEET
AND CROSS SECTION
A'
of
THE NORTHERN PART OF THE CHERRY CREEK METAMORPHICS
MADISON COUNTY, MONTANA
5800
5600
pCm
BASE
MAP
TOPOGRAPHY
EY US. GEOL
SURVEY, VARNEY
5400
GEOLOGY BY
Cross Section
WI L L A R D
D. TOMPSON, JR.
JANUARY, 1959
AND
CAMERON
QUADRANGLES
MONTANA STATE UNIVERSITY LIBRARIES
C S T ^
136412