Pre-Cambrian geology of the Galena-Roubaix district, Black Hills, South Dakota

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PKE-CAMBRIAW GEOLOGY OP’JO T GAt®'-ROUBAlX DISTRICT, BLACK HILLS, ; SOfcOT, DAKOTA

by

R o b ert Berg

A d i s s e r t a t i o n s u b m itte d in p a r t i a l f u l f i l l m e n t o f th e re q u ire m e n ts f o r th e d e g re e o f D o cto r o f P h ilo so p h y i n th e D epartm ent o f Geology I n th e G raduate C o lle g e o f th e S ta te U n iv e r s ity o f Iowa May, 1942

ProQuest Number: 10598676

All rights re s e rv e d INFORMATION TO ALL USERS The quality o f this re p ro d u c tio n is d e p e n d e n t u p o n t h e qu ality o f t h e c o p y s u b m itte d . In t h e unlikely e v e n t t h a t t h e a u th o r did n o t s e n d a c o m p le te m a n u sc rip t a n d th e r e a r e missing p a g e s , th e s e will b e n o te d . Also, if m a te ria l h a d to b e re m o v e d , a n o te will in d ic a te t h e d e le tio n .

uest, P ro Q u est 10598676 P ublished by P ro Q u e st LLC (2017). C opy rig h t o f th e D issertation is h e ld b y t h e A uthor. All rights re se rv e d . This work is p r o te c te d a g a in s t u n a u th o riz e d c o p y in g u n d e r Title 17, U nited S ta te s C o d e M icroform Edition © P ro Q u e st LLC. P ro Q u est LLC. 789 East E isenhow er Parkw ay P.O. Box 1346 A nn Arbor, Ml 48106 - 1346

ii B r? C0

Ores

1 .5

1.0

C h lo rite

0.0

2.0

Z o i s i t e and c l l n o z o i s l t e

5 .0

3 0 .0

C arbonaceous m a t e r i a l

0.8

1.0

G arn et^ tit a n it © > a p a t i t e # e t al* a c c e s s o r ie s

0.00

1.0

M in e ra l C o n s titu e n t

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and c a l c i t e o f t e n show a g ra n o b la s t i c t e x t u r e *

I n ro o k s

c o n ta in in g a lo w e r p e r c e n ta g e o f am p h ib o le , a d i a b l a s t i c te x t u r e i s o c c a s i o n a lly o b serv ed # D e ta ile d d e a e r ip tlo .u a o f th e a m p h ib o lite m in e ra ls A m phibole 3 :

The m ost common am phibole fo u n d i n th e

a m p h lb o lite s i s h o rn b len d e *

The h o rn b le n d e i s u s u a l l y h ig h ly

p le o e h r o ie from d a r k g re e n (IS) to l i g h t e r sh a d e s o f g re e n (X) *

Somev a r i e t i e s e x h i b i t a b lu is h - g r e e n and g re e n

p le o c h ro is m j o th e r s a r e g re e n t o y e llo w is h -g re e n * T here ar© so many d i f f e r e n t m o le c u le s i n h o rn * b le n d e t h a t c a u se v a r i a t i o n s i n o p t i c a l p r o p e r t i e s t h a t i t i s d i f f i c u l t t o d e r i v e t h e i r c h e m ic a l c o m p o s itio n by c o r r e l a ­ t i o n o f o p t i c a l p r o p e r t i e s fo u n d i n p u b lis h e d g r a p h s .

The

u s u a l p r o p e r t i e s fo u n d i n d i c a t e a h o rn b le n d e o f th e com posi­ t i o n % ( Mg) ( HajCagFegA lgSigO a*•«*

(W in o h e ll, 1934, p . 251)*

% arca* 1*690$ Ng ~ Hp « *020$ -2V - 70-80°$ % r d a r k g r e e n , X s l i g h t g re e n j Z A o a 14° • T hese p r o p e r t i e s i n d i c a t e a c o m p o s itio n h ig h e r i n Ca and F e , and lo w er i n Mg and Ha th a n th e h o rn b le n d e o f th e S o u th e rn B lack H i l l s .

(H a m ilto n , 1935)*

Th© am p h ib o les have

a p p a r e n tly d e v e lo p e d from th© r e e r y e t a l i i n a tio n and r e a c t i o n o f b a s ic p la g io e la s © f e l d s p a r and an ir o n r i c h c a lc iu m c a r ­ b o n a te *

Some h o rn b le n d e may have d e v e lo p e d fro m c h l o r i t e o r

o th e r m in e r a ls .

The h o rn b le n d e u s u a l l y shows a p o i k i l o b l a s t i c

t e x t u r e , c a r b o n a te s o r q u a r ts o c c u r r in g a s r e l i c t s i n th e s i e v e - l i k e te x tu r e *

45

Two o th e r am phibole s found le e s commonly i n th e a m p h lb o lite s ar© o f th© o ia m m ln g to n ite-g ran erit© s e r i e s , and o f th© a c t l n o l l t e - t r e m o l l t © s e r i e s *

The m in e ra l o f th e

. fo rm e r s e r i e s i s a g r u n e r i t e r i c h i n iro n *

O p tic a l p r o p e r ­

t i e s i n d i c a t e th© c o m p o s itio n (OHjgCFe, Mg* Mn, Ca)^Sl@Ogg | th e r a t i o FesMgiCaiMn * 81311*4*4** *

(L a rs e n and Berman*

Mp - l# 5 7 0 j % * l* 6 9 0 j J?g s l* 7 0 5 j Hg - Np a .035$ Z/\© s 1 3 °| Z « p a le y ello w * X and Y « c o l o r l e s s j -2V s ecu 8 0 ° .

1954* p# 186)*

The g r u n e r i t e o c c u rs i n th e hand specim en

n o t as a g g r e g a te s b u t as r o s e t t e - l i k e r a d i a t e s from a common c e n te r * t h e i r c o l o r i s g re y to brown w ith a s i l k y l u s t e r * I n t h i n s e c t i o n th e y show a w e ll d e v e lo p e d 110 c le a v a g e and a r e o n ly w eakly p le o c h r o io •

The c r y s t a l s and c le a v a g e

fra g m e n ts c h a r a c t e r i s t i c a l l y show b o rd e rs and s u r f a c e s c o v e re d w ith llm o n ite and h e m a tite s t a i n s *

The co m p arab le

am phibole o f th© S o u th e rn B lack H i l l s i s cujm alngtonlt© , a v a r i e t y much r i c h e r i n Mg and p o o re r i n Fe* Members o f th e a c t i n o l i t e - t r e m o l i t e s e r i e s a r e r a r e I n th© a m p h lb o lite s o f th e G alena-K oubaix D i s t r i c t * I t a p p ro x im a te s th© c o m p o s itio n of a c t i n o l i t e c o n ta in in g 60 mol p e r c e n t HgCa^FegSlQOg^ m olecu le* low Mg v a r ie ty *

T his I s a h ig h F e ,

I t o c c u rs as lo n g , b la d e d , a e ie u l& r c r y s t a l s .

I t s p le o c h r o io c o lo r s ar© u s u a lly weak b l u i s h - g r e e n , Z >X*

46

E x p la n a tio n o f P la to XI Z o i s i t e ( a t to p ) r e p la c in g l a b r a d o r i t e ; h o rn b le n d e and q u a rtz * x 14 S hredded h o rn b le n d e i n groun&mass o f andesin© f e l d s p a r (An3g ) ; opaque m in e ra l i s p y r rh o f c ite . x 14 P o l k i l o b l a s t l c h o rn b le n d e w ith r e l i c t s o f q u a r t z ; q u a r tz and a n d e sln e i n whit© a r e a s ; d a r k e r m in e ra l ( I n whit© a r e a s ) w ith h ig h e r r e l i e f I s c h l o r i t e * A ll c o n s t i t u e n t s e x p e c t h o rn b len d e show a m arked d i r e c t i v e te x tu r e * x 14 Z o is it e has h e re a lm o st c o m p le te ly r e p la c e d p l a g l o c l a s e f e l d s p a r ; some h o rn b le n d e a t l e f t * T h is s e c t i o n i s from th e c e n te r o f an o r b i c u l a r c o n c r e t i o n - l i k e mass i n th e a m p h ib o lite * x 14 L ab rad o r I fee p a r t l y r e p la c e d by z o i s i t e ; h o rn b le n d e i n u p p e r l e f t c o r n e r ; c h l o r i t e a f t e r h o rn b le n d e i n u p p e r h a l f o f s e c t i o n , x 32 Z o i s i t e has p a r t l y r e p la c e d p la g lo c l a s e f e l d s p a r (Aas o ) | and n e e d le - lik e h o rn b len d e p rism s* x 32

47

5

P l a t e XI

6

48

E x p la n a tio n o f P la te XIX 1*

H ornblende show ing d e c u s s a te t e x t u r e i n groundm ass o f p la g lo c l a s e f e l d s p a r s o lid * tw in n e d e a l c i t e I n u p p e r l e f t c o m e r , x 32

3.

P o ik H o b la s t ic h o rn b le n d e I n ab u n d an t e h lo r I te * * c a lc ite groundm ass• x 32

3.

P o i k l l o b l a s t i c h o rn b le n d e p o r p h y r o b la s ts w ith r e l i c t s o f q u a r ts and e a l c i t e f h ig h r e l i e f m in e ra l I n w h ite q u a r tz a r e a s I s c a l c l t e * x 32

4.

fte ifta to b la stic h o rn b len d e p rism s I n groundm ass o f q u a r tz and p la g lo c la s e f e l d s p a r (Ango)* & 14

5.

Bedding p re s e rv e d by g r a p h i t i c o r ca rb o n a ce o u s m a t e r i a l I n a m p h lb o llte • x 32

6* P e n n in ite has h e re c o m p le te ly r e p la c e d a m p h lb o le .

R e lic ts from am phibole a r e s t i l l e v i d e n t; p la g lo c l a s e f e l d s p a r ( l a b r a d o r i t e ) i n l i g h t c o lo re d a re a s # T h is ro c k h as alm o st been c o n v e rte d to a m ica s c h i s t #

49

5

P la te XII

6

50

Til© u s u a l l y h ig h e r Ca-Fe p e rc e n ta g e (low Mg-Na) I n th e am p h ib o les o f th e G alena-H oubaix a r e a i n co m p ariso n w ith th e lo w e r Oa-Fe (h ig h Mg«*Na) p e r c e n ta g e i n th e am phih o le s o f th e S o u th e rn B lack H i l l s i s i n t e r e s t i n g b u t lo g ic a l*

The h ig h e r Ca-*F© p e rc e n ta g e i s shown i n a l l th e

am phibo les J u s t d e s c r ib e d when com pared w ith H am ilton*s (1955) d e s c r i p t i o n s o f th e am p h ib o les h ig h e r i n Mg and Na from th e S o u th e rn B lack H ills *

The h ig h e r Mg*Ha p e r c e n ta g e

i n th e am p h ib o les o f th e S o u th e rn B lack H i l l s i s a p p a r e n tly r e l a t e d to th e i n t r u s i o n o f th e g r a n i t e th e re *

The i n t r u s i o n

o f th e a c i d i c g r a n i t e mass h as r e s u l t e d t h e r e i n th e a d d i t i o n o f so d a and th e fo rm a tio n o f s o d ic m in e ra ls j th e a d d i t i o n o f much s i l i c a w ith th e i n t r u s i o n o f th e g r a n i t e h as r e s u l t e d i n a r e a c t i o n w ith m agnesian m in e ra ls a lr e a d y p r e s e n t i n th e ro c k and th e p r e c i p i t a t i o n o f m ag n esian m in e ra ls *

In

t h i s way th e t o t a l c o m p o s itio n o f th e am p h ib o les o f th e S o u th e rn B la c k H i l l s i s se e n t o be h ig h e r i n Mg and Na, end lo w er i n Ca and Fe* F e ld s p a r ra n g e s I n c o m p o s itio n from andesin© to la b ra d o rite *

Most o f t e n th e more c a l c i c f e l d s p a r i s u n tw in n e d ,

and o c c u rs i n m in u te g r a i n s , s i m i l a r i n a p p e a ra n c e t o q u a r t s , e x c e p t t h a t th e f e l d s p a r has h ig h e r r e l i e f *

The more s o d ic

f e l d s p a r s (An3o*"An45) a r e more o f te n I n l a r g e r c r y s t a l s and o f t e n e x h i b i t a l b i t e tw in n in g .

The f e l d s p a r s form w ith th e

q u a r t s a g r a n o b l a s t i c t e x t u r e , and o f te n e x h i b i t a m o r ta r s tru c tu re *

The f e l d s p a r s as w e ll as th e q u a r t z , a p p e a r to

have b e e n g ra n u la te d *

51

Q u a rtz c o n s t i t u t e s a v a r i a b l e p e r c e n ta g e o f th e © m p h ib o lite s •

I t e x h i b i t s w ith th e f e l d s p a r s a g r a n o b l a s t l e

t e x t u r e o r m o rta r s t r u c t u r e #

I n many in s ta n c e s th e g r a in s

a p p e a r mashed and m y lo n itiz e d *

The i n d i v i d u a l q u a r tz g r a in s

a r e I n v a r i a b l y m in u te , u s u a lly l e s s th a n *06 mm*

(jb sp h ib o le

c r y s t a l s i n th e same ro c k a r e u s u a l l y many tim es t h i s s i z e , —fro m 1 mm* to .25 mm.)*

The q u a r tz o f t e n shows s e p a r a te d

is o g y r e s I n th e I n t e r f e r e n c e f i g u r e , wavy e x t i n c t i o n . I r r e g u l a r c r o s s f r a c t u r e s , and o th e r a p p e a ra n c e s o f h a v in g b ee n s t r a i n e d .

However, i n some in s ta n c e s q u a r tz I s com­

p l e t e l y n orm al and has a p p a r e n tly b een r e c r y s t a l l i z e d * C alciu m c a rb o n a te I s a m ost common c o n s t i t u e n t o f th e a m p h ib o llte s , som etim es c o m p risin g 40 p e r c e n t o f th e rook* Mg.

The CaC0$ u s u a l l y c o n ta in s some Pe b u t v e ry l i t t l e I t o c c u rs u n ifo rm ly d i s t r i b u t e d I n I r r e g u la r - s h a p e d

m asses th ro u g h o u t th e s e c t i o n s , as r e l i c t s I n h o rn b le n d e , o r , I n l a r g e r m asses show ing good tw in n in g ( g r a in s from *5 to *25 mm. d ia m e t e r ) .

These l a r g e r m asses a p p e a r to be

c o n c e n tr a te d i n b le b -lik © fo rm s .

I n one a m p h lb o lite i n

w hich th e am phlbole had b e e n r e p la c e d by c h l o r i t e , th e c a l c l t e I s fo u n d s t r e t c h e d o u t i n marked p la n e s o f la m in a ­ t i o n ; th e s e c t i o n th e n a p p e a rs as a l t e r n a t e la y e r s o f e l l i p s o i d a l - s h a p e d c a l c l t e m asses and l a y e r s o f q u a r t z c h lo r it© a g g r e g a te s .

T h is v a r i e t y shows much i r o n s t a i n

( llm o n l te ) a s s o c i a t e d w ith th e c a l c l t e .

I t I s p o s s i b le

t h a t i n some c a s e s th e 1 im o n ite - s t a i n e d CaC03 r e p r e s e n ts

52

th e d i s i n t e g r a t i o n o f s i d e r o p l e s i t e rhombs*

Some exam ples

p r e s e r v e a ro u g h ly © u hed ral rhomb o f c a l c l t e th e p e r ip h e r y o f w h ich i s form ed o f l i m o n l t e « A lm ost e v e ry t h i n s e c t i o n o f s m p h lb o llte w i l l show some p e r c e n ta g e o f th e v a r io u s o r e s , ev e n th o u g h i t be sm a ll*

P y rr h o tit© i s m ost common; p y r i t e , m a g n e tite ,

and ilm e n it e a l s o o c c u r accom panied b y th e h y d r a tio n p r o d u c ts , -llm o n lt© and le u c o x e n e • A d eep o l i v e - g r e e n p e n n i n ite i s o f t e n fo u n d r e p la c in g h o rn b len d e *

I t shows th e c h a r a c t e r i s t i c

anom alous i n t e r f e r e n c e c o lo r s *

I n p la c e s th e p e n n i n ite i s

ab u n d an t enough to form a c h l o r i t e s c h i s t * C l i n o z o i s i t e commonly r e p la c e s p l a g l o c l a s e f e l d s p a r , s ta n d in g o u t i n b o ld r e l i e f a g a i n s t th e o th e r m in e ra ls o f th e s e c t i o n , and c h a r a c t e r i s e d b y i t s b lu e anom alous I n t e r f e r e n c e c o lo r s * G a rn e t o c c u rs v e r y r a r e l y i n th e a m p h ib o lite s o f th e G alen a-R o u b alx D i s t r i c t *

G arn et was fo u n d I n a s i n g l e

I n s ta n c e I n an am p h ib o lit© from w est o f th e town o f G alena* T his g a r n e t d o es n o t show a p o i k l l o b l a s t i c t e x t u r e , i s p e r f e c t l y © u h e d ra l, and i s c r o s s e d b y i r r e g u l a r f r a c t u r e s . C arbonaceous and g r a p h i t i c m a t e r i a l o c c u rs as a b la c k opaque m a t e r i a l . a m p h ib o lite s .

I t i s p e r s i s t e n t I n many o f th e

( R e f . m ic ro p h o to g ra p h , P la te X I I , f ig * 5 ) .

M e g a sc o p lc a lly th e m a t e r i a l I s b la c k i n c o l o r , and has a b la c k s t r e a k ; I t i s s o f t and f r i a b l e *

In th in s e c tio n I t

53

I s o p aq u ej i t i s b la c k and n o n - m e ta llic I n r e f l e c t e d l i g h t # As s e e n i n th© m ic ro p h o to g ra p h i t o c c u rs i n p a r a l l e l bands t h a t a r e somewhat wavy#

L ess o f te n i t o c c u rs s p o r a d i c a l l y

d is s e m in a te d th ro u g h o u t th© t h i n s e c t i o n .

I t i s b e lie v e d

t h a t t h i s m a t e r i a l may r e p r e s e n t c a rb o n a ce o u s m a t e r i a l o f an o r i g i n a l l y s e d im e n ta ry ro ck #

54

DISCUSSION OF M S OKI GIN OF THE AMPHIBOLITES A m p h ib o lite s and o th e r ro c k s o f s i m i l a r c h e m ic a l and m ln e r a lo g ic a l c o m p o s itio n ( I n c lu d in g g r e e n s to n e s , e p i d i o r l t e s , m e ta -g a b b ro s , e tc * ) a r e b e lie v e d to have b een d e v e lo p e d i n on© o r more o f th e f o llo w in g ways s 1*

G r a n ltl& a tio n o f lim e s to n e s (Adams and Barlow* 1909)*

2*

M etamorphism o f b a s ic t u f f s o r la v a s (numerous Lake S u p e r io r and E uropean w r i t e r s ) *

3#

Metamorphlam o f b a s ic ig n eo u s I n t r u s i v e r o o k s , ( T i l l e y , 1923; P a ig e , 1 9 2 4 , 1 9 2 5 ).

4*

M etemorphism o f se d im e n ta ry beds (W iseman, 1934f R u n n er, 1936)* F u rth e rm o re , th© o c c u rre n c e o f th e s e k in d s o f

ro c k s 3ms b e e n n o te d a lo n g f a u l t p la n e s j b e c a u se o f t h i s s e v e r a l w r i t e r s have s u g g e s te d a r e l a t i o n s h i p b etw een th© r e g io n a l t e c t o n i c s and th© d evelopm ent o f t i l l s ty p e o f ro c k (B eck e, B e r tr a n d , H a rk e r, P r i o r , Benson)*

R unner ( p e r s o n a l

com m unication) h as s u g g e s te d t h a t th e s e ro c k s may have d e v e lo p e d I n s i t u a lo n g f a u l t p la n e s * An a l t e r n a t i v e e x p la n a ­ t i o n h as b e e n o f f e r e d to a c c o u n t f o r th e c h a r a c t e r i s t i c o c c u rre n c e o f a m p h ib o lite s and s i m i l a r ro c k s i n s i l l s and i n a s s o c i a t i o n w ith c a lc a re o u s ro ck s*

I t ha® b een s u g g e s te d

t h a t c a lc a r e o u s beds may have l o c a l i z e d b a s ic In tru s iv e © and c a u s e d t h e i r p r e c i p i t a t i o n (R u n n er, 1 9 3 3 ).

55

P a ig e s t a t e s t h a t m ost o f th e a m p h ib o lite ro c k s o f th e B la c k H i l l s a r e ^m etam orphosed ig n e o u s ro c k s o f d i o r l t e - g a b b r o c o m p o s itio n ” *

However, o f one l e n t i c u l a r

mass o f am p h ib o lit© w e st o f H i l l C i t y , he s t a t e s t h a t ® alth o u g h no r e s i d u a l s o r c a rb o n a te o c c u r , th© bed p ro b a b ly r e p r e s e n t s an im pure a i d e r ! t i c d o lo m ite * tt P a ig e , 1925)*

(B a rto n and

However, a c c o rd in g to R unner ( p e r s o n a l

c o m m u n ic atio n ), r e s i d u a l s o f c a rb o n a te a r e v e ry ab u n d an t i n t h i s ro ck #

On th© g e o lo g ic map i n th e same p u b l i c a t i o n

(B a rto n and P a ig e , 1 9 2 5 ), t h i s r o c k , d e s ig n a te d as an am p h ib o l© -g arn et s c h i s t , s t r i k e s i n t o and c o n tin u e s a t i t s n o r th e r n end as a mass o f w hat P a ig e c o n s id e r s t o b© ig n e o u s a m p h lb o lite # I n th e G alen a-R o u h aix D i s t r i c t , th e f i e l d r e l a t i o n ­ s h ip s o f th e a m p h ib o lite s alw ays show two c h a r a c t e r i s t i c s t h a t a r e more t y p i c a l o f s e d im e n ta ry ro c k s th a n o f igneous ro c k s s 1*

The a m p h ib o lite s a lm o st ev ery w h ere o c c u r i n c o n c o rd a n t l e n t i c u l a r m a s se s , p a r a l l e l t o th© b e d d in g o f th® s e d im e n ta ry ro ck s*

2*

The a m p h ib o lite s a r e fo u n d a t on© s tr a f c lg r a p h lc h o riz o n * I n a d d i t i o n t o th© p o in ts c i t e d a b o v e , two o th e r

c h a r a c t e r i s t i c s may b e p o in ts o f s i g n i f i c a n c e as to t h e i r o r i g i n , a lth o u g h th e y a r e n o t n e c e s s a r i l y d i s t i n c t i v e o f s e d im e n ts * 3*

The a m p h ib o lite s o c c u r i n zones a d ja c e n t to ro c k s c h a r a c t e r i z e d by ab u n d an t c a rb o n a te m in e r a ls , o r c a rb o n a c e o u s m a te r ia l*

56

4*

Th© a m p h ib o lite s o c c u r a lo n g p la n e s o f f a u l t s o r sh e a r p la n e s . T hese c h a r a c t e r i s t i c s a re a ls o to a la r g e e x t e n t

t r u e o f th e o t h e r a r e a s o f a m p h lb o lite ro c k s i n th e B la c k U lis *

(B a rto n and P aig e* 1925j Runner* 1934)*

These

a r e a s in c lu d e th© K eystone* R o c h fo rd , Nemo* and B ear Moun­ ta in D is tric ts *

I n th e Bead D i s t r i c t th© a m p h ib o lite s a r e

a l s o w e ll d e v e lo p e d I n a n o th e r s t r a t 1g ra p h ic h o r iz o n .

G ro s s-

c u t t i n g r e l a t i o n s h i p s a re r a r e l y s e e n i n a r e a s o f a m p h lb o lite } th e m ost n o ta b le e x c e p tio n t o t h i s i s i n th e Nemo D i s t r i c t * j u s t n o rth w e s t o f th e town o f Nemo*

I n t h i s same a re a * a

f a u l t h as b e e n mapped a lo n g th e c o n ta c t and s t r i k e of th e o u tc ro p o f th e © m p h ib o llte*

(B a rto n and P aige* 1925}

Runner* 1934)* The mode o f o c c u rre n c e and ro c k s a s s o c ia te d w ith th e a m p h ib o lite s i n th e G alena-R oubaix D i s t r i c t a r e c h a r a c ­ t e r i s t i c s o f th© a m p h ib o lite s t h a t a r e s i m i l a r to th o s e fo u n d i n o t h e r a r e a s in v e s tig a te d *

I n an i n v e s t i g a t i o n o f

th e l i t e r a t u r e on w id e ly s e p a r a te d a r e a s th e w o rld over* s im ila r re la tio n s h ip s e x is t*

to th o se c i t e d above a r e fo u n d t o

However* m ost a u th o rs have I n t e r p r e t e d th e amphibo­

l i t e s and s i m i l a r ro c k s o f th e s e w id e ly s e p a r a te d a r e a s a s ra e ta -ig n e o u s i n o r ig in *

The fo llo w in g t a b l e shows th©

r e l a t i o n s h i p s p r e v a i l i n g i n a p p ro x im a te ly one h u n d red a r e a s , a t v a r io u s l o c a l i t i e s on m ost o f th e c o n tin e n ts *

57

T able I I S tru c tu ra l re la tio n s h ip s

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The w r i t e r does n o t mean to im p ly i n th© e n s u in g d i s c u s s i o n t h a t th e ro o k s o f a l l a r e a s r e p r e s e n te d i n th e above t a b l e a r e m e ta -s e d im e n ta ry i n o r ig in *

Ho d o u b t ro c k s

o f known m e ta -s e d im e n ta ry and known m e ta -ig n e o u s o r i g i n have b e e n in c lu d e d *

The t a b l e m e re ly r e p r e s e n t s th e d a t a

on a r e a s c o n t a in i n g a p a r t i c u l a r k in d o f ro ck * I n c lu d in g a m p h ib o lite s , g re e n s to n e s * e p l d l o r l t e s , m e ta -g a b b ro s , e tc # However* th e t a b l e makes I t c l e a r t h a t g e o l o g is ts w o rk in g i n v a r io u s r e g io n s o f th© w o rld have fo u n d am phibo­ l i t e s , g r e e n s to n e s , and s i m i l a r r o c k s , i n g r e a t num bers, o c e u rln g I n s i l l - l i k e m asses p a r a l l e l t o and i n c o n t a c t w ith s e d im e n ta ry b e d s , o f w hich th e d o m in an t ty p e I s c a rb o n a te o r ca rb o n a c e o u s rock*

I n 75 p e r c e n t o f th© c a s e s , th©

g e o l o g is ts have I n t e r p r e t e d th e a m p h ib o lite s o r g r e e n s to n e s a s e i t h e r i n t r u s i v e o r e x t r u s i v e Ig n eo u s ro ck *

I n o n ly 27

p e r c e n t o f th e o c c u rre n c e s have th e s e ro c k s b e e n i n t e r p r e t e d as m e ta -s e d im e n ta ry i n o r ig in * The p ro b lem th e n may b© s t a t e d th u s :

If a

c o n s id e r a b le p e rc e n ta g e o f th e a m p h ib o lite s and s i m i l a r ro c k s a r e o f i n t r u s i v e Ig n eo u s o r i g i n , why do so many o c c u r as s i l l s ?

F u rth e rm o re , why s h o u ld la v a flo w s o r b a s ic

58

i n t r u s i v e s b e so commonly fo u n d i n zones o f c a lc a r e o u s ro c k s ?

I f on th e o t h e r hand# th e a m p h ib o lite s a r e o f

s e d im e n ta ry o r i g i n , why have th e y so c h a r a c t e r i s t i c a l l y b e e n m etam orphosed to ro c k s c l o s e l y re s e m b lin g b a s ic ig n e o u s r o c k s , w hereas th e m etam orphosed s h a le s and sand** s to n e s a r e s t i l l I d e n t i f i a b l e as su ch ? Inasm uch as th e G alena~R oubaix D i s t r i c t f u r n i s h e s good exam ples o f a m p h ib o lite s In th e t y p i c a l o c c u r r e n c e s , a c o n s id e r a ti o n o f th e o r i g i n o f th e s e ro c k s seems p e r tin e n t#

l?hat a d e f i n i t e p ro b lem d o es e x i s t i n r e l a t i o n t o th© o r i g i n o f t h i s ty p e of ro c k has lo n g b e e n re c o g n is e d # Wiseman (1934) a p t l y sum m arises some o f th e e a r l y works and o p in io n s , e s p e c i a l l y I n r e l a t i o n t o th® m etam orphism o f b a s i c ig n e o u s ro c k s# “E v er s in c e th® p u b l i c a t i o n o f T © all*s d e s c r i p t i o n o f th e S c o u rle d ik e (1 8 8 5 ), and i t s p a s sa g e fro m a d o l e r i t e i n t o a f o l i a t e d amphibo^ l i t ® by th e o r d in a r y p r o c e s s e s o f m etam orphism , p e t r o l o g i s t s have fro m tim e t o tim e d i r e c t e d t h e i r r e s ©archies #•«•#*# to th® s tu d y o f th© m etam orphism o f b a s i c ig n e o u s ro c k s# “ *>«***# among th e e a r l i e r w r i t e r s may be m e n tio n e d M acu llo ch (1 8 2 1 ), D© l a Beeh© ( 1 8 3 4 ), and S t a r r y Bunt (1875)# A lth o u g h f r e q u e n t l y th e w ork o f th e s e a u th o r s was a m odel o f c a r e f u l and a c c u r a te d e s c r i p t i o n , t h e i r I n f e r e n c e t h a t h o rn b le n d ic ro c k s w ere c h e m ic a l p r e c i p i t a t e s from a th e rm a l o cean c a n to * d a y be r e g a r d e d as o f h i s t o r i c a l i n t e r e s t only* I t was l e f t f o r Jukes (1862) to s u g g e s t t h a t h o rn ­ b le n d ic ro c k s w ere a l t e r e d t u f f s o r l a v a s . D e a lin g w ith th e a m p h ib o lite s c h i e f l y from so u th w e s t E n g la n d , A l l p o r t ( 1 8 7 6 ), P h i l i p s (1 8 7 8 ), and Bonney (1 8 8 5 ), e x p re s s e d th© view t h a t th e y w ere m etam orphosed

59

Ig n e o u s r o c k s . S h o r tly a f te r w a r d s , th e S c o t t i s h G e o lo g ic a l S urvey ( G e ik le , 1 8 8 4 ), i n th© c o u rs e o f t h e i r i n v e s t i g a t i o n s on th© a m p h ib o lite s o f A b e rd e e n s h ire and B a n f f s h ir e can© to a s i m i l a r c o n c lu s io n .* E a r l i e r th a n Wiseman1s summary, Benson (1926) p re p a re d a co m p reh en siv e memoir on th e ttT e c to n ic C o n d itio n s Accompanying th e I n t r u s i o n o f B a sic and U ltr a b a s ic R ocksn . Benson I n v e s t i g a t e d numerous a r e a s a l l o v e r th© w o rld I n th e l i g h t o f Suess* g e n e r a l i z a t i o n t h a t Hth e g re e n ro c k s form s i l l s i n d i s l o c a t e d m o u n tain s t h a t som etim es fo llo w th e b e d d in g p la n e s and som etim es th e p la n e s o f m ovem ent.* Benson c o n c lu d e d t h a t a r e l a t i o n s h i p e x i s t e d b etw een t e c t o n i c c o n d itio n s and th e i n t r u s i o n o f b a s ic ig n eo u s ro c k s s *fhus we may b e lie v e t h a t th© e v id e n c e her© c o l l e c t e d te n d s to th e c o n c lu s io n t h a t e a c h o f th© s e v e r a l m o rp h o lo g ic a l ty p e s o f b a s ic and u l t r a b a s i c ro c k s i s v e ry g e n e r a lly a s s o c ia te d w ith a s d e f i n i t e a s e t o f t e c t o n i c c o n d i t i o n s , and o f t e n w ith as d e f i n i t e a group o f l e s s b a s ic ig n e o u s r o c k s . w Benson v i s i t e d many o f th e a r e a s on w hich he b a se d h i s c o n c lu s io n s , b u t much o f h i s d a t a I s b a se d on r e f e r e n c e to l i t e r a t u r e only*

He assumed t h a t a l l th e a r e a s

he i n v e s t i g a t e d w ere a r e a s o f b a s ic and u l t r a b a s i c Ig n eo u s ro ck .

Ho d o u b t many o f th© a r e a s i n v e s t i g a t e d by Benson

a r e a r e a s o f b a s ic Ig n eo u s r o c k s .

However, many o f th e s e

r e g io n s show c e r t a i n r e l a t i o n s h i p s w hich r a i s e a q u e s tio n a s t o a p o s s i b le a l t e r n a t i v e mode o f o r i g i n o f th e r o c k s .

60

T hese r e l a t i o n s h i p s a re s i m i l a r to th o s e c i t e d i n T able I I * A l a r g e number o f th© 11a r e as o f b a s ic and u l t r a b a s i c Ig n eo u s r o c k s " show p a r a l l e l and c o n c o rd a n t r e l a t i o n s to th e a d ja c e n t s e d im e n ts , and a d ja c e n t c o n t a c t ro c k s a re o f te n c a lc a r e o u s ro ck s*

We a g a in q u e s tio n why ro c k s o f t h i s g e n e r a l com posi­

t i o n sh o u ld so o f te n show c o n c o rd a n t r e l a t i o n s to th e a d j a c e n t s e d im e n ts , and why th© c o n t a c t ro c k s sh o u ld so o f t e n be c a lc a re o u s * I n o r d e r t o a c c o u n t f o r th e c o n c o rd a n t n a tu r e o f a m p h lb o lite ro c k s and to e x p la in t h e i r c h a r a c t e r i s t i c o c c u r ­ re n c e I n zones o f c a lc a r e o u s r o c k s , R unner (1933) d e v e lo p e d an h y p o th e s is w hich m ig h t b e I n k e e p in g w ith th e d a t a s e c u re d i n th e f i e l d *

The a b s t r a c t o f t h i s p a p e r i s q u o te d i n f u l l s

" S e v e ra l w o rk ers I n th© B la c k H i l l s p r e C am brian have n o te d a re m a rk a b le c o in c id e n c e i n o c c u rre n c e o f a m p h ib o lite s d e r iv e d from b a s i c i n t r u s l v e s w ith o th e r s d e r iv e d from p u re c a rb o n a te ro c k s* R e ce n t s t u d i e s i n t h i s r e g io n have r e v e a le d f u r t h e r exam ples o f t h i s phenomenon, to g e t h e r w ith a c l o s e a s s o c i a t i o n o f th e s e ro c k s w ith f e r r u g in o u s q u a r tz v e i n s . T here a r e many th o u sa n d s o f f e e t o f p re-C am b ria n I n w hich Ig n eo u s a m p h lb o lite and q u a r tz v e in s a re l a c k i n g , b u t much o f th© g r e a t e s t d e v e lo p ­ m ent o f th e b a s ic In tru s iv e © i s I n th© h o riz o n s o f c a lc a r e o u s ro c k s* V a rio u s e x p lan atio n ® f o r t h i s a s s o c i a t i o n a r e s u g g e s te d w ith th e em phasis l a i d upon th e p o s s i b le e f f e c t o f c a lc a r e o u s b ed s I n l o c a l i z i n g th© in tru s iv e ® by c a u s in g t h e i r p r e c i p i ­ t a t i o n . Th© s i l i c a o f th© accom panying q u a r tz v e in s i s b e lie v e d to b e d e r iv e d from th e ig n eo u s ro c k s a t th e tim e of t h e i r c o n s o l i d a t i o n ." L a te r (1 9 3 5 ), Runner s u g g e s te d an a l t e r n a t i v e e x p la n a tio n on th© o r i g i n o f c e r t a i n o f th© a m p h ib o lite s o f th e B la c k H i l l s •

61

”I n th© p re-C am b ria n o f th e B lack S i l l s , a m p h ib o lite s q u i t e c l e a r l y d e r iv e d from se d im e n ts have th e c h e m ic a l c o m p o sitio n o f r a t h e r b a s ic ig n e o u s ro c k s and l o c a l l y show i n t r u s i v e r e l a t i o n ­ s h ip s * The s e d im e n ta ry a m p h ib o lite s w ere form ed fro m c a l c a r e o u s , m a g n e sia n , and f e r r u g in o u s s h a le s by r e c r y s t a l l i s a t i o n u n d e r g r e a t p r e s s u r e * The I n t r u s i v e a m p h ib o lite s r e p r e s e n t p o r tio n s o f th e s e d im e n ta ry a m p h ib o lite s t h a t have m ig ra te d as p l a s t i c m asses a lo n g zones o f w eakness I n th e e n c lo s in g ro ck s* T here seems to be l i t t l e o r no e v id e n c e t h a t f u s io n was in v o lv e d , h e n c e , p ro c e s s i s n o t p r o p e r ly r e g a r d e d as a n a te& Is o r sy n te s& s* ” I n an e f f o r t to b r i n g o u t th e s i m i l a r i t i e s and d i f f e r e n c e s b etw een h o rn b le n d e o f m e ta -s e d im e n ta ry o r i g i n and h o rn b le n d e o f m e ta -lg n e o u s o r i g i n , T i l l e y (1938) com pared th e h o rn b le n d e ”i n lo w -g ra d e met am orphic zones o f th e G reen S c h i s t s ” *

T h is i n v e s t i g a t i o n and co m p ariso n was

made on two g ro u p s o f B r i t i s h r o c k s ,

”th© G reen Beds o f

th© H ig h lan d s ( P h i l i p s , 1 9 3 0 ), and th e G reen S c h is t s o f th© S t a r t A rea o f s o u th Devon ( T i l l e y , 1 9 2 3 ), th e fo rm e r s e d im e n ta ry and th e l a t t e r g en u in e d e r i v a t i v e s o f b a s i c ig n e o u s r o c k s •” More r e c e n t l y , T em perley (1938) d is c u s s e s th e p r e s i d e n t i a l a d d r e s s o f Head t o th© B r i t i s h S o c ie ty (1939)* T em perley was p a r t i c u l a r l y p e r tu r b e d by two p o in ts I n R ead1® a d d re s s *

Th© s i m i l a r i t y o f th e s e p o in ts t o c h a r a c t e r i s t i c s

o f a m p h ib o lite s c i t e d e a r l i e r I n t h i s d is c u s s io n i s n o ta b le s ”1# 2*

How was th e b u lk o f th e d o l e r i t e s i l l c o n v e rte d t o a m p h lb o lite ? Why i s th e p la n e o f f o l i a t i o n o f th e a m p h ib o lite s p a r a l l e l to th e s u r f a c e s o f th e s i l l s a t w h a te v e r a n g le th e y l i e ? ”

62

T hese q u o ta tio n s on th© problem s o f c e r t a i n m etsm orphlc ro c k s and sum m aries o f t h e i r i n t e r p r e t a t i o n by v a r io u s r e s e a r c h e r s makes c l e a r c e r t a i n p o in ts s 1*

M etam orphlc ro c k s c l e a r l y d e r iv e d by th© m etam orphism o f c e r t a i n s e d im e n ts , and th o s e d e r iv e d by th e raetam orphlsm o f b a s ic ig n e o u s r o c k s , a r e d i s t i n g u i s h e d o n ly w ith d i f f i c u l t y *

2*

A m p h ib o lite s , g r e e n s to n e s , and s i m i l a r ro ck s e i t h e r show c e r t a i n c h a r a c t e r i s t i c s t h a t a r e u n iq u e t o th e i n t r u s i o n o f b a s ic ig n eo u s r o c k s , o r , th e r e i s so m eth in g in h e r e n t i n th e p h y s ic a l and c h e m ic a l c o n s t i t u t i o n o f c e r t a i n s e d im e n ta ry ro c k s to e a s i l y m etam orphose them to ro c k s o f se e m in g ly d i o r i t l c o r g a b b ro ic c o m p o s itio n and te x tu re *

O rig in o f th e G alen a-R o u b aix A m p h ib o lite s I t i s th e b e l i e f o f th e w r i t e r t h a t th e a m p h ib o lite s o f th e G alen a-R o u b alx D i s t r i c t a r e metam or­ p h o sed c a l c a r e o u s , d o l o m i t i c , and f e r r u g in o u s s h a l e s , r a t h e r th a n m etam orphosed Ig n eo u s ro c k s o f g a b b ro ic o r d i o r i t l c co m p o sitio n *

Some o f th e re a s o n s f o r t h i s b e l i e f

have a lr e a d y b e e n s u g g e s te d ; th e s e and o th e r e v id e n c e s w i l l be h e r e p re s e n te d * 1* a* I n no I n s ta n c e s a r e c r o s s - c u t t i n g o r d is c o r d a n t r e l a t i o n s found* The a m p h ib o lite s o c c u r w ith t h e i r s t r i k e ( e lo n g a tio n ) p a r a l l e l to th e s t r i k e o f a d j a c e n t known s e d im e n ta ry b e d s* b* The a m p h ib o lite s everyw here o c c u r a t th e same s t r a t i g r a p h l c h o riz o n * o* The a m p h ib o lite s ev eryw here o c c u r i n zones o f c a lc a r e o u s ro c k s o r ro c k s c o n ta in in g c a rb o n a c e o u s m a te r ia l*

63

0* Th© w r i t e r b e l i e v e s t h a t p ro p o u n d ers o f th e th e o r y o f d e r i v a t i o n o f a m p h ib o lite s from g a b b ro ic and d i o r i t l c ro c k s h av e f a i l e d t o ta k e i n t o a c c o u n t a n o th e r f a c t o r # Such d e r i v a t i o n i s a h ig h e r g rad e m etam orphlc change th a n t h a t w hich p ro d u ced th e c h l o r i t i c - p e l i t i c assem b lag e o f m in e ra ls w ith w hich th e a m p h ib o lite s a r e a s s o c ia te d # I f th e a m p h ib o lite s w ere d e r iv e d by th© m etam orphism o f ig n e o u s ro c k s o f d i o r i t l c o r g a b b ro ic compo­ s i t i o n , one w ould e x p e c t to f i n d some e v id e n c e o f th® a l t e r a t i o n o f a u g ite to h o rn b le n d e o r p e rh a p s th e rem a in s o f zoned p la g lo c l a s e f e l d s p a r s • B oth o f th e s e c o n s t i t u e n t s ( a u g i t e and zoned p la g lo c l a s e f e l d s p a r ) a r e c h a r a c t e r i s t i c o f ro c k s o f t h i s compo­ s i t i o n ( d i o r i t e - g a b b r o ) # However, a c c o rd in g to P a ig e , (B a rto n and P a ig e , 1 9 2 5 ), MAugit© was n o t re c o g n iz e d w ith c e r t a i n t y # m etam orphism h a v in g p ro c e e d e d to o f a r to le a v e any o r t h i s common c o n s t i t u e n t o f d i o r i t e s and d ia b a s e s # 1* T h is s ta te m e n t i s made on th e b a s i s o f p e tr o g r a p h ic e x a m in a tio n o f a m p h ib o lite s o f numerous a r e a s of th e B la c k H ills * He 1th© r w ere any e v id e n c e s o f a u g i t e fo u n d i n any o f th© p e tr o g r a p h ic e x a m in a tio n s made o f th© a m p h ib o lite s o f th e G alen a-R o u b aix D i s t r i c t • 3* W ith in th e a m p h lb o lite a re a s a r e la y e r s re s e m b lin g q u a r t s i t e o r c h e r t • These l a y e r s w ere d e s c r ib e d I n th e s e c t i o n on s t r a t i g r a p h y , and in c lu d e th© f e r r u g in o u s - q u a r t ss-am phlbole ro c k s (Home® ta k e fm#) and th e s i l i c e o u s lim e s to n e s (Poorman fm*)* These ro c k s w ere mapped as q u a r t z i t e s by P aig e (B a rto n and P a ig e , 1 9 2 5 ), and w ere a p p a r e n tly re g a rd e d as o f s e d im e n ta ry o r ig in * These l a y e r s o c c u r w h o lly e n c lo s e d by th e ©mphlbolit© In p la c e s w here th e fo rm a tio n s a r e te r m in a te d norm al t o t h e i r s t r i k e by s h e a rin g * These l a y e r s now c o n t a in g r a n u la r q u a r t z ! t e , a l t e r e d a m p h ib o le s, and c a rb o n a c e o u s m a t e r i a l , i n a d d i t i o n t o o th e r m inor c o n s t i t u e n t s , in c lu d in g p l a g l o c l a s e f e l d s p a r , c a l c l t e and o r e s . These s i l i c e o u s la y e r s everyw here m a in ta in a p a r a l l e l and c o n c o rd a n t r e l a t i o n w ith r e s p e c t to th© s t r i k e o f th© a m p h ib o lite s * 4* C e r t a in p e tr o g r a p h ic e v id e n c e I t seems i s a l s o s i g n i f i c a n t i n t h i s problem } a# T h in s e c tio n s o f some a m p h ib o lite s show q u a r t z , p l a g l o c l a s e f e l d s p a r , o r e , and c h l o r i t e , I n a m arked d i r e c t i v e t e x t u r e . G ro ss c u t t i n g th© d i r e c ­ t i v e t e x t u r e , a re ab u n d an t p o i k l l o b l a s t s o f h o rn b len d e* I n some i n s t a n c e s , th e h o rn b le n d e now c o n s t i t u t e s o v e r f i f t y p e r c e n t o f th e r o c k . I t I s th© b e l i e f o f th e w r i t e r t h a t th© m in e ra ls show ing th© d i r e c t i v e t e x t u r e r e p r e s e n t th e m etam orphosed c o n s t i t u e n t s o f an o r i g i n a l l y f e r r u g in o u s and d o lo m itlc s h a le # A

64

s u b s e q u e n t p e r io d o f m etam orphism h as r e s u l t e d i n th e d ev elo p m en t o f th e h o rn b le n d e fro m p l a g l o c l a s e f e l d s p a r , q u a r t s , and th e im pure c a rb o n a te s * ( P l a t e XX, f i g * 3 . ) b* O th er t h i n s e c t i o n s o f b o th a m p h lb o lite and th© l a y e r s b e l ie v e d to r e p r e s e n t th e Homestake fo rm a­ t i o n c o n t a i n a b u n d a n t c a rb o n a c e o u s and g r a p h i t i c m a te r ia l * The p r e s e n c e o f th e c a rb o n a c e o u s m a tte r I s c e r t a i n l y an e x c e l l e n t c r i t e r i o n f o r th e s e d im e n ta ry o r i g i n o f th e ro c k s I n w h ich i t i s p r e s e n t* I t i s t r u e t h a t g r a p h ite m ig h t o c c u r as a c o n t a c t m etam orphlc m in e r a l i n ig n e o u s r o c k s , b u t i t i s d o u b tf u l t h a t c a rb o n a c e o u s m a tte r w ould be g e n e r a lly d i s t r i b u t e d th ro u g h o u t th e ro c k as shown i n P l a t e I I , f i g * 6* The p a r a l l e l a s p e c t o f th e ca rb o n a ce o u s b an d s may p o s s i b ly r e p r e s e n t th e b e d d in g o f an o r i g i n a l l y s e d im e n ta ry r o c k . c* o th e r t h i n s e c tio n s ta k e n from th e a r e a s o f a m p h lb o lite c o n t a in as much as f o r t y p e r c e n t c a lc iu m c a r b o n a te and o t h e r c a rb o n a te s (Pe > Mg)« The abundance o f c a rb o n a te m in e r a ls in th e ro c k s s h o u ld n o t a lo n e b© ta k e n a s a c r i t e r i o n o f s e d im e n ta ry o r ig in # B ut th e c o n s i s t e n t l y h ig h p e r c e n ta g e s o f c a rb o n a te m in e ra ls I s a t l e a s t s u g g e s tiv e o f a s e d im e n ta ry o r ig in * O th er t h i n s e c t i o n s from ro c k s w hich a p p e a r m e g a s c o p lc a lly to b e v e r y s c h i s t o s e a m p h ib o lite s , a r e fo u n d to c o n t a in l a r g e l y c h l o r i t e and e a l c i t e as th e d o m in an t c o n s t i t u e n t s * L enses o f pur© c a l c l t e a r e a l s o fo u n d j i n th e f i e l d th e s e a r e o f t e n many m e te rs I n le n g th * d* T h at h o rn b le n d e c a n and does d e v e lo p i n c a lc a r e o u s s h a le s i s a p t l y i l l u s t r a t e d I n th e m etam or­ p h o sed e l l i p s o i d s i n th e R oubaix ro ck s* Prom th© f i e l d re la tio n © and p e tr o g r a p h ic d e s c r i p t i o n s ( r e f e r p* ) th e r e a d e r s h o u ld h av e no d o u b t t h a t th e e l l i p s o i d s have d e v e lo p e d In a s e d im e n ta ry ro ck * I n c a lc a r e o u s p o r t i o n s o f t h i s r o c k , le n s e s o f c a lc a r e o u s m a t e r i a l have b e e n " r o l l e d ” I n t o th e sh a p e s o f e l l i p s o i d s * D u rin g t h i s s h e a r in g and m etam orphism ab u n d an t ho rn * b le n d e h as d e v e lo p e d ( r e f e r P lat© X, f i g s * 3 and 4 )*

65

HETAMOKPHXSM The m etam orphlc changes w hich th e pre«*Csmbrian ro c k s have u n d erg o n e a r e c l o s e l y a l l i e d to th e s t r u c t u r a l c o n f i g u r a t i o n o f th e re g io n *

I n f a c t , th e s t r u c t u r e g iv e s

a h e l p f u l k ey to d e c ip h e r in g th e dynam o-m etam orphle h i s t o r y w hich c o n c e rn s th e s t r a t a *

The c r o s s - f o l d i n g s u g g e s ts t h a t

t h e r e may have b een more th a n one p e r io d o f dynam ic m et am orphism *

T hat t h e r e h as b ee n a n o th e r p e r io d o f m etam orphism

o f th© th e rm a l ty p e I s n o t as w e ll I l l u s t r a t e d i n t h i s d i s ­ t r i c t as i t I s c o n tig u o u s to l a r g e g r a n i t e m asses I n th e S o u th e rn B la c k m i l s *

But t h i n s e c tio n s o f th e ro c k s o f

G alen a-R o u b alx D i s t r i c t show m in e ra ls w hich c o u ld have o n ly b e e n I n tro d u c e d by th e em an atio n s o f a g r a n i t i c mass* The o r i g i n a l c o m p o sitio n o f th e s e d im e n ta ry beds was p ro b a b ly n o t g r e a t l y d i f f e r e n t th a n th e l i t h o l o g y o f many o f th© P a le o z o ic and M esosoic s e d im e n ta ry beds o f th e B lack H ills *

The o r i g i n a l b ed s p ro b a b ly In c lu d e d g r i t s ,

s a n d s to n e s , lim e s to n e s , c a rb o n a ce o u s s h a l e s , aren a ce o u s s h a l e s , and c a lc a r e o u s s h a le s * Th® e a r l i e s t p e r io d o f m eism orphiam o f w hich th e r e I s any r e c o r d was a m etam orphism c h a r a c t e r i s e d by g r e a t s t r e s s , and accom panying r e l a t i v e l y h ig h te m p e ra tu re s * T h is mefcamorphism was p ro b a b ly th e r e s u l t o f and contem por­ aneous w ith th© f o l d i n g w hich form ed th© m a jo r s t r u c t u r a l f e a t u r e s now p r e s e n t , i* ©*, th© t i g h t l y c lo s e d i s o c l i n a l fo ld s *

66

Mmes to n e s and s a n d s to n e s w ere p r o b a b ly r e c r y s t a l l i z e d I n to m a rb le s and q u a r tK ite s r e s p e c tiv e ly * I n im pure s h a le s , b i o t i t © , q u a r t z , p la g lo c l a s e f e l d s p a r , and s u l f i d e s w ere th e new ly c r y s t a l l i z e d m in e ra ls *

I n a d d i­

t i o n t o s e v e r e l y c o n t o r t i n g th© s e d im e n ta ry s t r a t a I n to a s e r i e s o f t i g h t l y c lo s e d I s o c l i n a l f o l d s , t h i s p e r io d o f g r e a t s t r e s s was r e s p o n s i b le f o r th e d ev elo p m en t o f c h a r a c ­ t e r i s t i c m in e ra ls *

ftm r e l a t i v e l y h ig h te m p e ra tu re s may have

d e v e lo p e d from f r i c t i o n due t o s t r e s s o r h e a t c r e a te d by th e f r i c t i o n , o r i t may b e r e l a t e d to some b o d y , em placed co n ­ te m p o ra n e o u sly w ith t h i s p e r io d o f f o ld in g *

I t i s n o t known

w h e th e r a seco n d p e r io d o f f o l d i n g was contem poraneous w ith th e f i n a l p e r io d o f th e rm a l metamorphism*

However, s t r e s s

m in e r a ls a r e fo u n d t h a t a r e l a t e r th a n th e e a r l i e s t p e r io d o f m etam orphism d e s c r ib e d i n th e l a s t p a ra g ra p h *

MLs i s

th e p e r io d o f dynam ic m etam orphism o c c u r r in g w ith th e f o l d ­ in g t h a t p ro d u ced th e c r o s s f o ld s *

Inasm uch as b o th u n ­

o r i e n t e d m in e ra ls have d e v e lo p e d a t t h i s tim e ; a r e l a t i v e l y h ig h te m p e ra tu re was p ro b a b ly © x ite n t* H ornblende and o th e r am phiboles a r e fo u n d t o be l a t e r th a n th e e a r l i e r group o f m in e ra ls d e v e lo p e d ( b i o t i t © , q u a r t z , f e l d s p a r , e t a l« )*

I t i s p o s s i b le t h a t th e s e

am p h ib o les may have b een form ed d u r in g t h i s p e r io d o f s t r e s s metam orphism* I t I s th e b e l i e f o f th e w r i t e r t h a t th e p e r io d o f th e rm a l metam orphism may b e r e l a t e d t o th e i n t r u s i o n o f

67

g r a n i t e i n th© S o u th e rn B la c k H ills *

A lth o u g h th© g r a n i t e

m a s s if i s more th a n t h i r t y m ile s d i s t a n t fro m th e G alena* R o u b aix D i s t r i c t * i t i s p o s s i b le t h a t s m a ll i n j e c t i o n s em an atin g fro m th e g r a n i t e may have p e n e tr a te d to w ith in a s h o r t d i s t a n c e from th© G alen a-R o u b aix D i s t r i c t *

These

i n j e c t i o n s have e i t h e r b e e n in tr u d e d as v e in s i n th© s c h i s t s * o r h y d ro th e rm a l v o l a t i l e c o n s t i t u e n t s from th© g r a n i t e have had c o n t a c t m etam orphic e f f e c t s on th e s c h i s t s * Such seems to have b ee n th e c a s e i n a number o f s m a lle r a r e a s w ith in th e G alen a-R o u b alx D i s t r i c t .

The

i n t r o d u c t i o n o f soda* s i l i c a * and v a r io u s v o l a t i l e con* s t i t u e n t s (F* B* H2O* S) h as p ro d u ced c h a r a c t e r i s t i c m in e ra l a ssem b lag es o f g r a n ite *

M icro p h o to g rap h s ( P l a t e X II* f ig s *

1 and 2 ) show a lb it© d e v e lo p e d due to th e i n t r o d u c t i o n o f q u a r tz and soda* c ry s ta ls *

The a lb it© o c c u rs i n la rg e * w e ll tw inned

B i o t i t e I s more ab u n d an t and b e t t e r d e v e lo p e d th a n

i n any o f th e o th e r c h l o r i t i e - p e l l t l e se d im en ts*

I n th® same

sr o c k from w h ich t h i s t h i n s e c t i o n was made t i t a n l t e , a p a t i t e * and l a t e s u l f i d e s w ere a l s o a p p a r e n tly In tro d u c e d m a t e r i a l s . The v e in s I n th e v i c i n i t y o f G alena show p a r t i c u l a r l y w e ll th e e f f e c t s o f th e I n t r u s i o n o f g r a n i t i c m a te ria l•

C e r t a in v e in s i n Ruby G ulch a t G alena c o n t a in

v e i n q u a r tz c o n ta in in g la r g e b la c k tourm alin© c r y s t a l s * T hese a r e commonly 4 t o 5 cm* lo n g and 4 to 6 mm* I n d ia m e te rs some a re as l a r g e as 10 cm* long*

I n a d ja c e n t

s c h i s t s o f th© n o rth w e s te rn fo rm a tio n l a r g e g a r n e ts ar© found* commonly 3 t o 4 cm* I n d ia m e te r ; on© p o r tio n o f a

68

g a r n e t c r y s t a l show ing th r e e d o d ecah ed ro n f a c e s was 7 cm* I n d ia m e te r*

I t was a ls o i n t h i s g e n e r a l v i c i n i t y t h a t

th e o n ly a m p h lb o lite c o n ta in in g g a r n e t was fo u n d . E a s t and s o u th o f R o u b aix , i n th e s c h i s t s and a m p h ib o lite s , v e in s a r e fo u n d c o n ta in in g q u a r t z , z o i s i t e , to u r m a lin e , and some h o rn b len d e *

The tourm alin© i s b la c k

and w e ll s t r i a t e d i n th© hand specim en* i n t h i n s e c t i o n i t i s h ig h ly p le o e h r o le , 0 > 33*

0 i s d a r k b lu s lh - g r e e n * E I s

r e d d i s h - v i o l e t j t h i s I s a to u rm a lin e h ig h I n i r o n . O th er v e in s a r e q u a r tz - o lig o c la s © v e i n s •

They

c o n ta in c r y s t a l l i n e , g la s s y - a p p e a r in g q u a r t z , and w h ite to pal® y e llo w f e ld s p a r * Some v e in s i n th© a m p h ib o lite s c o n ta in abundant m u sco v ite*

I n d iv id u a l a g g r e g a te s o f m icaceous p l a t e s a r e

as l a r g e as on© cm. i n d ia m e te r*

Many o f th e s e were found

i n sec* 29 e a s t o f R o u b aix , and on th e e a s t e r n b o r d e r o f th e l a r g e s t a m p h lb o lite a r e a , i n sec* 2 6 , T* 4 N ., H. 4 E* B e sid e s th o s e m in e ra ls d ev e lo p ed from th e I n t r o d u c t i o n o f m a t e r i a l , t h i n s e c tio n s show th e e v id e n c e o f a l t e r a t i o n o f m in e ra ls and developm ent o f new m in e ra ls fro m th o s e a lr e a d y p r e s e n t in th e r o c k .

Some o f th e s e have

b e e n d e s c r ib e d u n d e r th© m in e ra lo g y o f th© a m p h ib o lite s* Z o i s i t e h as commonly r e p la c e d p la g lo c la s e f e ld s p a r * h o rn ­ b le n d e has a l t e r e d t o p e n n in ite and o th e r v a r i e t i e s o f c h lo rite *

69

STRUCTURAL GEOLOGY

General Most; f o l d s o f th e p re-C am b rian ro o k s o f th e H o rth e m B lack H i l l s a r e o f th e i s o c l i n a l ty p e#

A x ia l-

plane© # s e h i s t o s i t y # and beds have# as a r u le # r e l a t i v e l y s t e e p d ip s # -fro m s i x t y t o n in e ty d e g r e e s ; some o f th e s e a r e o v e r tu r n e d f o ld s * P lan e flo w c le a v a g e i s w e ll developed# © s p e c ia lly i n th e ab u n d an t s c h is t© and s m p h ib o lite s • commonly show a weak l i n e a r cleav ag e*

These ro c k s

D uring th e f o ld in g

o f th e ro ck s i n p re-C am b rian tim es# ro c k flow age m ust have ta k e n p la c e u n d e r th e c o n d itio n s o f r a t h e r h ig h te m p e ra tu re # and g r e a t p r e s s u r e and s t r e s s # r e s u l t i n g i n th e developm ent o f many m in e ra ls n o t p r e s e n t in th e o r i g i n a l rock*

D uring

f o ld in g # p la n e and l i n e a r c le a v a g e a r e d ev e lo p ed by th e fo rm a tio n o f new m in e ra ls ( s t a b l e u n d e r th e e x i s t i n g con­ d i t i o n s o f te m p e ra tu re # p r e s s u r e and s t r e s s ) # from chem i­ c a l c o n s t i t u e n t s a lre a d y p r e s e n t i n th e rock# and# i n some c a s e s from in tro d u c e d m a te r ia l*

The m icas and c h l o r i t e

b e s t e x h i b i t p la n e c leav a g e# w h ile th e am phiboles quit© commonly show l i n e a r cleav ag e* Inasm uch a s p la n e c le a v a g e i s commonly p a r a l l e l t o th e a x i a l plan© o f f o ld s # th© c le a v a g e i s n e a r ly p a r a l l e l to th© s t r i k e o f th e beds on th© lim b s o f th© lo n g I s o c l i n a l f o ld s # and i s norm al to th® s t r i k e o f th© beds on th e a x is

70

o f th e f o ld s *

T hus, th e r e I s a g r a d a t io n a l change b etw een

th e lim b s and th e a p i c e s , from c le a v a g e t h a t i s p a r a l l e l , to c le a v a g e t h a t i s norm al to th e s t r i k e o f th e s t r a t a * P la n e c le a v a g e i s b e s t e x e m p lifie d i n th e m icaceous and c h l o r i t i c s c h i s t s w hich c o n ta in an abundance o f p l a t y m in e ra ls *

M uscovite r a r e l y p ro d u ces p la n e c le a v a g e

s in c e i t i s an added c o n s t i t u e n t and c r o s s - c u t s th e d i r e c t i v e t e x t u r e d e te rm in e d by th e o th e r p l a t y m in e r a ls ,

L in e a r

c le a v a g e I s som etim es e v id e n t i n th e s c h i s t s , b u t i t I s m ost c h a r a c t e r i s t i c o f th e a m p h ib o llte s due to th e e lo n g a te d c h a r a c t e r o f th e am phiboles*

L in e a r c le a v a g e e v id e n c e s th©

develop m en t o f m in e ra ls i n one d i r e c t i o n o n ly , - o r i n a l i n e , a t th e i n t e r s e c t i o n o f two p la n e s*

L in e a r c le a v a g e has much

th e same r e l a t i o n to th© ele m e n ts o f a f o l d and th e s t r a t a as d oes p la n e c le a v a g e * I n th e S o u th e rn B lack H i l l s , Runner and H am ilton (1934) fo u n d t h a t th e m ajo r a x is o f e l l i p s o i d a l c o n c r e tio n s , f l a t t e n e d b o u ld e r s , and th e m ajo r a x is o f e lo n g a te d c r y s t a l s t o be i n th e d i r e c t i o n o f and n e a r ly i f n o t q u ite p a r a l l e l t o th e p i t c h o f th e f o ld s *

I n th e G alena-R oubalx D i s t r i c t

m in e ra ls show ing l i n e a r p a r a l l e l i s m , s t r e t c h e d s t r u c t u r e s , and s t r u c t u r e s h av in g th e shape© o f t r i a x i a l e l l i p s o i d s , a r e found a l s o t o be o f a id I n d e te rm in in g th© p i t c h o f f o l d s . T his p r i n c i p l e was o f much h e lp i n c o n firm in g th e d i r e c t i o n o f p i t c h as d e te rm in e d by o th e r m eans.

71

I n th e G alen a-R o u b aix D i s t r i c t numerous p r i n c i p l e s w ere u s e d t o d e te rm in e th e age o f b e d s , and i n d e c ip h e r in g th e s t r u c t u r e *

No one o f th e s e p r i n c i p l e s a lo n e would be

s u r e p ro o f o f th e ag© o f b e d s , o r w h e th e r th e y w ere f o ld e d i n t o a n t i c l i n e s o r s y n c lin e s ; b u t th e c o n f ir m a tio n o f e a c h o f th e c r i t e r i a b y e a c h o th e r i n t o a l o g i c a l w hole s u g g e s ts th e c o r r e c t o r d e r o f s u p e r p o s itio n and th© n a tu r e o f th e f o ld s # 1* Assuming t h a t th e p i t c h i s n o t o v e r tu r n e d , we know t h a t an a n t i c l i n e apex es i n th e d i r e c t i o n o f p i t c h , and a s y n c lin e apexes o p p o s ite t o th e d i r e c t i o n o f p itc h # 2* The d i r e c t i o n o f p i t c h i s i n th© d i r e c t i o n o f th e l i n e a r c le a v a g e # 5# C e r t a in seq u en ces o f r e p e t i t i o n s o f beds i n d i c a t e a n t i c l i n e s and s y n c lin e s i f th© age o f th© b ed s i s p r e v io u s ly d eterm in ed # 4* The r e l a t i o n o f c le a v a g e t o b e d d in g and th e r e l a t i o n o f m inor d r a g f o ld s t o b e d d in g i s su c h t h a t th© r e l a t i v e d i r e c t i o n o f movement o f a d ja c e n t b eds may be d eterm in ed # 5# From th e d i r e c t i o n o f s h e a r on th e lim b s o f f o l d s i n a d ja c e n t b ed s th e p o s i t i o n o f ax es o f a n t i * c l i n e s and sync l i n e s may be d eterm in ed # 6# O pposing d ip s o v e r la r g e a r e a s i n d i c a t e s t r u c t u r e i n g e n e ra l# B*g#, i n g e n e r a l th e d ip s ta k e n on th e w e st s id e o f th e a r e a , i n th e n o rth w e s t p o r t i o n o f T . 3 N#, R* 4 £ # , a r e to th e e a s t ; d ip s on th e e a s t e r n b o rd e r of th e R oubaix ro ck s a r e t o th e w est# T h is , i n g e n e r a l i n d i c a t e s a s y n c lin e h e re # 7# C o a rs e r m a te r ia l s more o f t e n o c c u r a t th e b a s e o f a c e r t a i n d i v i s i o n , g ro u p , o r member# £*g*, th e c o a rs e g r i t s to n e s o f th e H oubalx Group o f ro c k s o c c u r n e a r th e b a s e o f th e f o r m a tio n , th u s i n d i c a t i n g r e l a t i v e s u p e r p o s itio n #

Th© Gal©na~Koubaix D i s t r i c t i s lo c a te d a t th e n o r th e r n ap ex o f a s y n c lin o r lu m .

The a x is o f t h i s s t r u c t u r e

ru n s i n a g e n e r a l north**®onth d i r e c t i o n s l i g h t l y w est o f th® c e n t e r o f R, 4 E *, T , 3 N», and T# 4 N# G eo lo g ic map w i l l

R e fe re n c e to th©

show t h a t th e a x is ru n s th ro u g h th e c e n t e r

o f th e mapped o u tc ro p o f R oubaix ty p e o f ro ck s*

S uperposed

on t h i s l a r g e r s t r u c t u r e a re a n tic !5 ,n e s and s y n c l i n e s , o f te n i n th© fo rm o f d r a g f o ld s *

P r o g r e s s iv e ly su p e rp o se d on th©

l a r g e r f o l d s a r e s m a lle r d ra g f o l d s down to s t r u c t u r e s c e n tim e te r s i n d im en sio n s*

I n a d d i t i o n , a n t i c l i n e s and sy n ­

c l i n e s a r e a f f e c t e d by c r o s s f o ld s w ith a x i a l p la n e s c r o s s i n g th© f i r s t form ed o n e s . and 3 5 , T , 4 N#, R* 4 B,

T h is 3.® b e s t I l l u s t r a t e d i n se c s* 28 Th© a x i a l plan© o f th e a n t i c l i n e

i n d i c a t e d th e r e i s i t s e l f f o ld e d i n t o an S*shape& c u r v e , J a g g a r m en tio n s th® p e c u l i a r change o f s t r i k e i n th e v i c i n i t y o f th e Anaconda M ine, i n an e a r l y r e p o r t on th© econom ic g e o lo g y o f th© B lack H i l l s ( I r v i n g , Bamon® and J a g g a r , 1904) ,

,rSumming up th e Algonki&n s e c t i o n a lo n g th©

rldg© n o r t h e a s t o f th© C lo v e r L eaf (Anaconda) M ine, we s e e t h a t th e w e s t-s o u th w e s t s t r i k e i s u n u s u a l, s u g g e s tin g t h a t th e r e i s some sudden change i n s t r u c t u r e e a s t and w est o f th e r id g e i n q u e s tio n .

T his change on th e w e st ta k e s p la c e

i n th© im m ediate v i c i n i t y o f th© G lo v e r L eaf (A naconda) o re body,*1 F a u lts a r e q u e s tio n a b ly r e p r e s e n te d I n th e O ale n aR oubalx D i s t r i c t ,

No m a jo r f a u l t s a t any g r e a t a n g le to th®

b e d d in g o r s c h i s t o s l t y wore o b serv ed #

However, i n th e

s o u th e a s t e r n p o r t i o n o f th e a r e a th e ab se n c e o f th e E l l i s o n q u a r t s i t e and th e t r u n c a t i o n o f c e r t a i n bed® w ith in th e a m p h ib o llte s u g g e s ts f a u l t i n g o u t o f some b ed s* The w hole p a t t e r n o f s t r u c t u r e o f th© r e g io n u n d e r c o n s i d e r a t i o n shows a s h e a r in g o f th© w e st s id e o f s t r u c t u r e s i n a n o rth w a rd ly d i r e c t i o n , to th o s e on th e e a s t i n a s o u th ­ w a rd ly d i r e c t i o n #

T hat fa u lt® may be p r e s e n t a lo n g b ed d in g

p la n e s i s p o s s i b l e ; i t i s d i f f i c u l t to d is c o v e r th e m ag n itu de o r ev en th© p re s e n c e o f s t r i k e - s l i p f a u l t s #

However, th e

c r o s s - f o l d i n g d o es g iv e some e v id e n c e o f r e l a t i v e movement o f th e b ed s a lo n g a n o r th - s o u th p la n e# S p e c i f ic s t r u c t u r e s ^ As m en tio n ed i n th e g e n e r a l d is c u s s io n o f s t r u c t u r e , th e l a r g e s t s i n g l e s t r u c t u r e I n th e r e g io n i s th e l a r g e s y n c lln o r iu m , th e a x i a l p la n e o f w hich tr e n d s i n a n o r th - s o u th d i r e c t i o n s l i g h t l y e a s t o f th e c e n te r o f th e a re a *

T his i s

a p p a r e n tly th e same s t r u c t u r e w h ich P aig e m en tio n s (B a rto n and P a ig e , 1 9 2 5 ); P aig e trace® th e a x i a l p la n e o f t h i s s t r u c ­ t u r e so u th w a rd to th e g r a n ite # o f th e R oubaix Group i n th e

The g r e a t th ic k n e s s o f beds o f T# 3 N*, R . 4 E* P i s due

t o r e p e t i t i o n s by fo ld in g # Vilest o f th e a r e a o f R oubaix rock® I s a m inor a n t i c l i n e in v o lv in g th© N o rth w e ste rn and G a r f ie ld fo rm a tio n s #

Th© w estern m o st m inor s y n c lin e o f th e R oubaix s y n c l l n o r i m apex es i n th e SBj. o f sec# 18f ! , 4 H ,, H 4 E# T here a r e h e re some good exam ples o f th e b e d d in g b e in g n orm al t o th© c le a v a g e #

The e a s t lim b o f t h i s s y n c lin e

may b e t r a c e d tow ards Roubaix#

Th© apex o f a m inor a n t i ­

c l i n e i s i n d i c a t e d a t th e Anaconda Mine*

I r v i n g , Emmons,

and Jh g g a r (1904) i n an e a r l y econom ic r e p o r t on th© Anaconda M ine, m e n tio n th e p e c u l i a r change o f s t r i k e a t t h i s p o in t# The apex o f a n o th e r s y n c lin e i s p resu m ab ly u n d e r th e C am brian c o v e r i n se c* 2 1 , T. 4 N*, K# 4 K# The n e x t a n t i c l i n e t o th® e a s t in v o lv e s m ost o f th e b ed s r e p r e s e n te d i n th e a re a # i s o c l i n a l fo ld #

I t i s a t i g h t l y c lo s e d

I t s a x i a l p la n e d ip s s t e e p l y to th e e a s t ,

and tr e n d s g e n e r a lly n o r th - s o u th i n th© c e n t e r o f se c# 28# The a x i a l p la n e th e n assumes an e a s t- w e s t tr e n d i n th© S9f% o f se c* 2 8 , and l a t e r resum es th e n o r th - s o u th tr e n d a lo n g th e b o r d e r o f s e c s * 32 and 3 3 , T* 4 N*, R# 4 E* The a x i a l plan® of a m inor s y n c lin e p a s s e s betw een th© a m p h ib o lite a re a s I n th e s i o f sec# 2 8 , tr e n d ­ in g i n a n o r th - s o u th d ir e c tio n *

The s t r u c t u r e s e a s t o f t h i s

p o in t in v o lv in g th e R oubaix Group o f r o c k s , a r e l e s s e a s i l y d e fin e d *

I n g e n e r a l , th e b ed s a re p ro b a b ly r e p e a te d on© o r

more tim es i n th© a n t i c l i n e , s o u th o f th© la r g e amphlbol© mass*

P resu m ab ly , th e g r e a t th ic k n e s s o f b ed s w ith in th©

l a r g e a m p h ib o lite a r e a i s due to r e p e t i t i o n s by f o ld in g #

75

A m in o r s y n c lin e apex es t o th e e a s t o f th e la r g e a m p h ib o lite m a ss, i n th e m i o f s e c , 2 2 , T# 4 H*, R# 4 E# Th© b e d s to th© e a s t o f th© R oubaix Group o f ro c k s r e p r e s e n t th e o ld e r ro c k s on th© e a s t lim b o f th e l a r g e s y n e lin o rlu m t h a t oe cup l a s th e c e n te r o f th e a re a * E a s t o f th e G stlena-K oubaix D i s t r i c t , R unner (1934) h as d e s c r ib e d a d o u b ly ^ p itc h in g a n t i c l i n e , th e w est lim b o f w hich i s composed o f ro c k s o f th e Lead System#

The e a s t

lim b o f th© R oubaix s y n e lin o rlu m i s th e n i d e n t i c a l w ith th© w e st lim b o f R u n n er1© d o u b ly ^ p itc h in g a n t i c l i n e # However, th© s i t u a t i o n i s n o t q u ite so sim p le# I n o r d e r t o e x p l a in th e r e p e t i t i o n and o m issio n o f c e r t a i n b ed s i n t h i s g e n e r a l a r e a (s e c s # 1 4 , 1 1 , 2 , T* 3 N#, R# 4 1 # ) , one m ust co n c lu d e t h a t s h e a r in g and f a u l t i n g w ith in th e a m p h ib o lite a r e a s , h as r e s u l t e d I n th© r e p e t i t i o n o f c e r t a i n b eds and th e o m issio n ©f o th e rs #

7©

BIBLIOGRAPHY 1880

Hewt o n , H enry, "G eology o f th e B lack H i l l s o f s o u th D a k o ta ," U* S . Geog. and G e o l. S urvey o f th e Rooky M ountain R e g io n , 1880#

1388

C ro sb y , W* 0 , , "G eology o f th e B lack H i l l s o f S o u th D a k o ta ," Bos# Soc* N a t, H is t# , Proo# v o l . X X III, p p . 488*517, 1 8 8 8 .

1890

Van H is e , C . R . , "The Pr© -Cam brian Rooks o f th© B lack H i l l s , " G eo l, S o c. A m er., B u l l . , v o l . 1 , p p . 2 0 3 845, 1890,

1899

I r v i n g , John D u er, "A C o n tr ib u tio n t o th e Geology o f th© N o rth e rn B lack H i l l s , " A n n a ls, N. Y* Acad# S c i . , X II , No. 9 , p p . 1 8 7 -3 4 0 , 1899.

1904

i "Economic R eso u rces o f th© N o rth e rn B lack H ills ', w ith c o n t r ib u t io n s b y S* P . Emmons and T* A. J a g g a r , j r . , " U. s . G e o l. S u rv . P r o f . P ap er 2 6 , 1904.

1913

P a ig e , S id n e y , "P re-C am b rian S tr u c tu r e o f th e N o rth B lack H i l l s , S o u th D ak o ta , and I t s b e a r in g on O rig in o f Horae s ta k e Or© B ody," G eo l. S o c. Amer*, B u l l *, v o l . 2 4 , p p . 293*300, 1913.

1921

R u n n er, J . J * , "E vidences o f an U nconform ity w ith in th© p re-C am b rian o f th e B lack H ills o f S o u th D a k o ta ," G eo l. S o c. Amer. B u l l . , v o l . 3 2 , p p . 3 7 -3 8 , 1921.

1923

H o ste d , J* 0* and W rig h t, L. B ., "G eology o f th e Homestake Or© B odies and th e Lead A rea o f S o u th D a k o ta ," Eng. and M in. J o u r . - P r e s s , v o l . 1 1 5 , p p . 793—99 and 8 3 6 -4 3 , 1 923.

1923

P a ig e , S id n e y , H o ste d , J . 0 . , and W rig h t, L . B ., "The Geology o f th e Homestake M ine," E con. G e o l., v o l . 1 8 , p p . 2 0 5 -5 7 , 1923.

1923

T i l l e y , 0 • E . , "Th© P e tro lo g y o f th© M etamorphosed Rocks of th© S t a r t A rea ( S o u th Devon) , ” Q u a rt. Jour# G eo l. S o c ., l x x i x , p . 1 7 2 , 1923.

1924

P a ig e . S id n e y , H o ste d , J . 0 . and W rig h t, L. B ., "G eology o f th© R egion aro u n d L ead, S . D. and i t s b e a r in g on th e Homes ta k e Ore Body," U. S . G e o l. S u r v ., B u l l. 7 6 5 , 1924.

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1925

B a rto n , N. H* and P a ig e , S id n e y , " C e n tr a l B la c k H i l l s f o l i o , S o u th D a k o ta ," U. S* Geol* S u rv • , Geol* A tla s f o l i o No* 2 1 9 , 1925*

1926

B enson, W* N ., "'The T e c to n ic C o n d itio n s Accompanying th e I n t r u s i o n o f B a sic and U l tr a b a s le Ig n eo u s H o ck s," N a t1I* Acad* S c l . , v o l* XIX, 1 s t m em oir, O ov*t. P rtg * O f f ic e , W a sh in g to n , 1926*

1926

B la c k w e ld e r, E l i o t , "P re-C am b rian G eology o f th e M ed icin e Bow M o u n tain s, 11 Geol* S o c . Amer*, B u ll* , v o l . 3 7 , p p . 6 1 5 -5 B, 1920*

1926

Emmons, W* H* and L aney, P* B*, "G eology and Ore D e p o s its o f th e Duektown M ining D i s t r i c t , Ten­ n e s s e e ," TJ* S* Geol* S u rv * , P ro f* P a p e r, No* 139, 1926.

1950

P h i l i p s , F* C *, "Some M in e r a lo g ic a l and C hem ical Changes in d u c e d by P r o g r e s s iv e M etamorphism I n th e G reen Bed o f th e S c o t t i s h D a lr a d i a n ," Min* Mag*, a s c ii, 1 9 3 0 , p* 239*

1951

M cL aughlin, D. H*, "The Homestake E n t e r p r i s e - Ore G en esis and S t r u c t u r e , " Eng* and Min* J o u r * , v o l . 1 3 2 , p p . 3 2 4 -2 9 , 1 9 5 1 .

1932

Thomas, L . C *, " S tr a tig r a p h y and S t r u c t u r e o f th e P re-C am b rian Hocks o f th e S o u th e a s te r n B la c k H i l l s , " S t a t e U n iv . o f Io w a, unpub1 • P h . D. d i s s e r t a t i o n , 1932*

1933

G u s ta fs o n , I* X*, "M etam orphism and H y d ro th erm al A l t e r a t i o n o f th e Homestake G o ld -B e a rin g f o r m a tio n ," Eeon* G eo l* , v o l . 2 8 , p p . 1 2 3 -1 6 5 , 1933.

1933

B u rn e r, J* I * , " A s s o c ia tio n o f C e r t a i n Ig n eo u s and S e d im e n ta ry A m p h lb o lite s ," G e o l. soc* A m er., Proc* f o r 1 933, n o . 4 5 , p* 443 ( a b s t r a c t ) , 1 9 3 3 .

1934

R u n n e r, J* J * , and H am ilto n , R* G ., "M etam orphosed C a lc a re o u s C o n c re tio n s and t h e i r G e n e tic and S t r u c t u r a l S i g n i f i c a n c e ," Am* Jo u r* S c l* , v o l* 2 8 , p p . 5 1 -6 4 , 1934.

1934

R u n n er, J . J * , "P re-C am b rian G eology o f th e Nemo D i e t . , B lack H i l l s , S o u th D a k o ta ," Am. J o u r . S c i# , v o l . x x v l i l , November, 1934, p p . 3 5 3 -7 2 , 19 3 4 .

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1935

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1935

T a y lo r , G arv in I*., "Th© P re-C am b rian G ra n ite s o f th© B lack H i l l s , " Amer* Jour* S c i* , v o l* 2 2 9 , pp* 2 7 8 -2 9 1 , 1935*

1936

R u n n er, J* J * , " I n t r u s i v e S ed im en tary A m p h ib o lite s ," Geol* Soc* Amer*, Proe* f o r 1 9 3 6 , p* 99 ( a b s t r a c t ) , 1936.

1936

W rig h t, Lawrence B«, "Gold D e p o s itio n i n th e B lack H i l l s o f S o u th D akota and Wyoming,0 A, I* M* M. S . , T ech . Publ* Ho* 6 9 9 , 1 936.

1938

T i l l e y , G* s#, "The S ta tu s o f H ornblende i n Low-grade M etam orphic 55on©s of th© G reen S c h i s t s , " Geol* Mag*, v o l . Ix x v , p . 4 9 7 , 1938*

1939

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1939

B e rtra m , John G«, " C l a s s i f i c a t i o n and N om enclature o f Rock D n its ," B u ll* A* A* P* G*, v o l* 2 3 , Ho. 7 M l y , 1 939.

1942

T em p erley , B. H«, "Some Problem s o f th© A rchean Rocks o f th© T anganyaika T e r r i t o r y , ” Geol* Mag*, n o . 1 , p p . 67 f f . , 1 9 4 2 .

79

Plate XIII

GEOLOGIC MAP of th e

Pre -Cambrian Formations

GALENA-ROUBAIX DISTRICT SOUTH DAKOTA

LEGEND Sedimentary Rocks

D ip & SrptRE

SCHEMATIC

STRUCTURE

SECTION ALONG UNE A-X