coveney & chen 1991

8/3/2019 Coveney & Chen 1991

http://slidepdf.com/reader/full/coveney-chen-1991 1/6

Mineral. Deposita 26, 83-88 (1991)

i ep 'oe r a l i u msl ta

9 Springer-V erlag 1991

N i- M o- P G E- A u - r i c h or e s in C h in e s e b lac k s h a le s an d s p e c u la t ion s

on poss ib le analogues in the Uni ted States

R . M . C o v e n e y , J r 1 a n d C . N a n s h e n g 2

1 Depa rtment o f G eosciences, University of Missouri-Kansas City, Kansas City, M issouri 64110-2499, United States2 Institute of G eochemistry, Acad emia Sinica, Guiyan g, Guizhou Province, People's Republic of C hina

Received: March 1990/Accepted: Dece mbe r 1990

Ab st rac t . M o l y b d en u m - r i ch b l ack s h a l e s f r o m t h e C am -

b r i an o f s o u t h C h i n a co n t a i n s u l fi d e b ed s w i th > 2 w t . %M o , > 2 w t . % N i a n d 2 0 0 - 7 0 0 m g / T e a c h f o r A u , P t a n d

P d . S i m i l a r d ep o s i ts o ccu r in C an ad a . I n t h e U .S . M i d -

w es t , P a l eo zo i c b l ack s h a l e s co n t a i n an ex t en s i v e M o

an o m al y an d s p o r ad i c en r i ch m en t s f o r P t g r o u p e l e -

m en t s , s u g g es ti n g t h e p r e s en ce o f N i - M o - P G E - A u s u l -

f ide depos i t s l ike those be ing mined in China .

Che n e t a l. ( 1982) r epor ted enr iche d values fo r N i , M o, V ,

C u , U , B a an d A g f r o m l o w er C am b r i an b l ack s h a l e s i n

ten p rov inces in sou th China , inc lud ing Yunnan ,

G u i zh o u , H u n an , J i an g x i an d Z h e j i an g ( F i g . 1 ). B l acki l l i t i c Cambr ian shales f rom these occur rences average

3 5 0 p p m M o a n d 1 50 p p m N i ( F a n 1 98 3). M o r e o v e r ,

v a l u es ex ceed i n g 4 w t. % V 2 0 5 h av e b een r ep o r t ed f r o m

c a r b o n a c e o u s a n d p h o s p h a t i c C a m b r i a n b l a c k s h a le s o f

sou th China (Zhang 1983) . A l l together , the meta l - r ich

s h a l e s d e f i n e an ex t en s i v e M o an o m a l y ex t en d i n g f o r

h u n d r ed s o f t h o u s an d s o f s q u a r e k i l o m e t e r s ( C h en e t a l.

1982) . The Cambr ian b lack shales con ta in th in su l f ide

l ens es an d b ed s w i t h o r e - g rad e en r i ch m en t s o f M o an d N i

an d l e ss e r v a l u es o f P G E an d A u . S u l f id e l en s e s a r e m i n ed

f o r M o i n G u i zh o u an d s i m i la r d ep o s i ts w e r e on ce m i n ed

f o r M o a n d N i i n H u n a n . A n a l o g o u s d e p o s i ts a re k n o w n

f r o m a t l e a s t o n e o t h e r l o ca t i o n , t h e S e l w y n B as i n o fC an ad a . T h ey m ay o ccu r e l s ew h er e , f o r ex am p l e i n t h e

P a l eo zo i c o f t h e cen t ra l U n i t ed S t a t e s (C h en an d

Coveney 1989) .

Z u n y i , G u i z h o u

Discovered in 1979 and mined s ince 1985 , the Zuny i Modepo s i t s a r e located near Son g l in , c lose to Zuny i (Tsuny i )

i n t h e p ro v i n ce o f G u i zh o u . O r e o ccu r s a s th i n ( 5 - 1 5 cm )su l f ide lenses and b eds in near ly f ia t - ly ing b lack shales o f

t h e lo w e r C a m b r i a n N i u t i t a n g F o r m a t i o n a f e w m e t e rs

ab o v e i t s co n t ac t w i t h t h e P r o t e r o zo i c Z ( S i n i an )

D o u s h a n t u o F o r m a t io n .

T o o u r k n o w l ed g e t h e Z u n y i d ep o s i t s a r e t h e o n l y

m i n es i n t h e w o r l d w h e r e M o i s t h e p r i m ar y p r o d u c tr eco v e r ed f r o m s h a l e . T h e Z u n y i M o m i n es an n u a l l y

y ie ld ,~ 1000 tonnes o f o re averag ing , -~4 w t .% M o and

co n t a i n i n g u p t o 4 % N i , 2 % Z n , 0 .7 p p m A u , 5 0 p p m A g ,

0 .3 ppm Pt , 0 .4 ppm Pd , and 30 pp b I r (Chen e t al . 1982 ,

Fan 1983 , Fan e t a l . 1984 , Chen 1988 , Chen and Coveney

1 98 9) . P eak v a l u es a re n ea r 7 .7 % M o , 2 7 0 0 p p m S e an d

2 .5 % A s . P r ec i o u s m e t a l s a re n o t ex t r ac t ed f r o m t h e o r e s ,

bu t mine ta i l ings ar e s tockp i led fo r even tual r ecovery .

The su l f ide o re (F ig . 2 ) cons i s t s main ly o f a mix tu re o f

n o d u l a r p y r i te , n o d u l a r p h o s p h o r i t e an d p e l le t s o f s o li d

organ ic mat ter ( so -ca l led s tone coal ) , quar tz and shale .

R e l a t i v e l y co a r s e ( ~ 1 m m - d i am e t e r ) n o d u l a r t ex t u re s

g r ad e t o co a t i n g s o f su l fi d e s o n t i n y ( 1 - 1 0 m i c r o m e t e r )spheru les o f o rgan ic m at ter (F an 1983).

Ore m inera l s inc lude jo rd is i te , pyr i te , vaes i te , ger s -

dor f f i t e , po ly dym i te and mi l ler it e (Fan 1983). Som e

m as s i v e s u l f i d e s am p l e s a r e v e r y d en s e b u t o t h e r s a r e

s u p r is i n g ly l ig h t b ecau s e o f ab u n d an t o r g an i c m a t t e r an d

l a rg e am o u n t s o f p o re s .

P r e l i m i n a ry S E M / E D A X s t u d ie s o f s ev e ra l su l fi d e

nodu les cons is t ing ch ief ly o f pyr i te ind ica te th a t the po-

r o u s r i m s o f n o d u l e s co n t a i n m u ch m o r e N i ( F ig . 3 ) t h an

t h e i n te r io r s . T h e ex t e r i o r p o r t i o n s o f s o m e n o d u l e s co n -

t a i n m o r e S e an d A s t h an t h e in t e r i o r p o r t io n s . S o m e a r e

r i m m ed w i t h a r e l a t i v e l y l a t e M o - r i ch p h as e , p r o b ab l y

j o r d is i te . M o m a y ev en b e p r e s en t in t h e r i m o f t h e n o d u l es h o w n i n F i g . 3 b ecau s e s m a l l am o u n t s o f M o ( < ,-~ 1 % )

a r e o b s cu r ed b y i nt e r fe r en ce b e t w een t h e K - a l p h a p eak o f

S an d t h e L - a l p h a p eak f o r M o an d b ecau s e o f t h e r el a -

t iv e l y h i g h ex c i t a ti o n p o t en t i a l f o r M o K - a l p h a .

Su l fu r i so to pe values (6 34S) fo r fo ur samp les d r i l l ed

f r o m p y r i t e n o d u l e s f r o m Z u n y i av e r ag e - 9 .9 8 p e r m i lr e la t iv e t o t h e C an o n D i ab l o T r o i li te s t an d a r d ( r an ge o f

v a l u e s = - 7 . 3 t o - 1 1 . 2 ). A n a l ys i s o f o ne ri m o f p o r o u s(and p oss ib ly cor rode d) p yr i te f rom Zuny i y ie lds a 6 34S

value o f + 3 .7 per mi l , appreciab ly heav ier than the in te-

r i o r o f t h e n o d u l e w h i ch m eas u r e s - 1 0 .2 p e r m i l (F i g . 3 ).

S i l i c eo u s v en t i n g t u b es an d ch e r t b ed s f o u n d i n t h e

u n d e r l y in g ( l at e S i n ian ) D o u s h an t u o F o r m a t i o n o f n o r t h

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Fig. 1. Locations of Ni-Mo deposits in Cambrian black shales,south China. Ni-M o sulfide bed occurrences include Dezhe (De),Zhejin (Zh), Zunyi (Zu), Dayon g (Da), Cili (Ci), Duchang (Du) and

Lizhe (Li). Locations of major suture zones, flysch terrane, andophiolites (irregular black) generalized from H su et al. (1988). Karstareas generalized from various sources

T h e p r o v i n c e o f G u i z h o u ( i n cl u d i ng t h e i m m e d i a t e

a r e a o f t he Z u n y i M o m i n e ) c o n t a i n s s o m e o f th e f i n e st

k n o w n e x a m p l e s o f t o w e r k a r s t t o p o g r a p h y . E x t e n di n g

t h r o u g h o u t t h e p ro v i n c es o f Y u n n a n , G u i z h o u , G u a n g x i

a n d H u n a n , t h e sp e c t a c u l a r k a r s t re g i o n o f s o u t h C h i n a

i s a p r o d u c t o f d e ep m o d e r n w e a t h e r i n g w h i c h , a s d i s-

c u s s e d b e lo w , m a y h a v e i n f l u e n ce d d e v e l o p m e n t o f t h e

ores .

Fig. 2. Ore Slabs from Zunyi and Dayong. Similar nodular texturesare shown by the N i-Mo sulfides in samples collected 350 km apart

G u i z h o u ( C h e n 1 9 8 8 ) s u g g e s t a h y d r o t h e r m a l s o u r c e o f

meta l s in some cases . Quar tz c rys ta l s f rom the vent tubes

c o n t a i n s f l u i d i n c l u s i o n s w i t h h o m o g e n i z a t i o n t e m p e r a -

tures be tween 158 and 172~

Other locat ions in South China

M e t a l - r i c h C a m b r i a n b l a c k s h a l e s o c c u r i n n i n e o t h e r

p r o v i n c e s i n s o u t h C h i n a b e s id e s G u i z h o u ( C h e n e t a l.

1 98 2 ). A b o u t 3 0 0 - 4 0 0 k m n o r t h e a s t o f Z u n y i ( F ig . 1 ),

C a m b r i a n s h a l e s n e a r D a y o n g a n d C i l i , H u n a n , c o n t a i n

s imi la r nodula r N i -M o sul f ide beds (F ig . 2) wi th enr iched

va lues for Ni , Mo, Au and PG E (Fa n 1983) . Sulf ide beds

n e a r D a y o n g w e r e f o rm e r l y m i ne d f o r N i a n d M o . O t h e r

N i - M o d e p o s i t s o c c u r i n C a m b r i a n s h a l e s n e a r D e z h e ,

Yun nan (Chen e t a l . 1982), a t Ducha ng, J i angxi (Fa n

1 9 8 3 ) , a n d i n m e t a m o r p h o s e d l o w e r C a m b r i a n b e d s n e a r

Lizhe , Zhe j i ang (Chen and Yang 1987) . Al l known occur -

rences of the Ni - Mo sul f ide beds a re found c lose to the

P r e c a m b r i a n - C a m b r i a n b o u n d a r y . T h e a r e a l d i s tr i b u ti o n

8/3/2019 Coveney & Chen 1991


S o ~ I l tn ~ -6 Py o u ~ . ]OkU

FeKO.I t Ni K(2

~

U i t l ,9 i l l Ni K~As K(Z

S o ~ I x r~ Py I n

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F'As KG,

B

28803 CNT 6.40K EU 10eV/ch B EDA• ~76G1 CNT 6 . 4 1 K E U 10eV/eh A

85

Fig. 3. SEM views of pyrite nod-ule in Ni-Mo ore bed from EarlyCambrian black shale, Zunyi,Guizhou. Elemental analyses byenergy dispersive X-ray spectrom-etry (EDAX ); S-isotype analysesby mass spectrometric techniques(Krueger Enterprises) on samplesdrilled from nodule with a 1 mmmicrodrill. The late (Ni-rich) py-rite rim contains relatively heavysulfur ( 6 3 4 S = + 3.7 per mil, con-trasting with -10.2 per mil forpyrite in the interior of the nodule

o f s o m e o f t h e h i g h est g r ad e o ccu r r en ces o f N i - M o s u l-

f ide o re fo rms a l inear be l t , poss ib ly con t ro l led by base-

m en t f r ac t u r e s , w h i ch ex t en d s E N E f r o m Y u n n an

t h r o u g h G u i zh o u , H u n an , an d J i an x i t o Z h e j i an g

(Fig . 1 ) . Desp i te many s imi lar i t i es , there are d i f f erences

am o n g t h e d ep o s i ts . Fo r ex am p l e , a t s o m e d ep o s i ts , Fan

(1983) no tes the p rese nce o f sphaler i te , pen t land i te , t en -

nan t i te and v io lar i te as wel l as the o re minera ls l i s ted

above fo r Zunyi . Tuf f s ar e associa ted wi th the minera l -

i zed h o r i zo n s a t s o m e l o ca t i o ns .

Origins of the ores

J u d g i n g f r o m s u r f ace ex p o s u r e s , few o f th e N i - M o d e -

p o s i t s can h av e t h e g en e t ic co n n ec t i o n s w i t h t h e m ar i e o r

u l t r am af i c s o u r ce / h o s t r o ck s ch a r ac t e r i s t i c o f co n v en -

t ional ( igneous-af f i l i a ted) PGE depos i t s . Smal l l a te Pale-

o zo i c o r M es o zo i c o p h i o l i t e m e l an g es co n t a i n i n g p e r i -

do t i tes , gabbros and sp i l i t es (Hsu e ta l . 1988) occur

s p a r s el y n ea r t h e zo n e o f N i - M o o r e s h a le o ccu r r en ces .

Y e t o n l y t h e D u ch a n g o ccu r r en ce h as o p h i o l i te s n ea r b y

(Fig. 1).

O n t h e b as is o f e l ev a t ed Ir v a l u es Fan ( 1 98 3 ) an d Fan

eta l . (1984) have sugges ted ex t r a ter r es t r ia l source fo r

some co n s t i t u en t s o f t h e o re s . Wh e t h e r o r n o t a b o l i d e i s

invo lved , the character i s t ic nodu lar tex tu res o f the su l f ide

beds impl ies a syngenet ic o r ig in (Fan 1983 , Chen e t a l .

1982).

I t s eem s m o r e l i k e l y t h a t s u b m ar i n e s p r i n g s o r s o m e

o t h e r t e r r e s t r i a l s o u r ce p r o v i d ed s u p p l i ed m e t a l s t o t h e

shales , perhaps dur ing sed imenta t ion . The l inear d i s t r i -

b u t i o n o f k n o w n o r e s m ay r e fl ec t m i g r a t i o n o f m i n er a l i z-

i n g f l u i d s t h r o u g h d eep f r ac t u r e s f r o m d eep - c r u s t a l o r

man t le sources . An oth er poss ib i l i ty is expu ls ion o f f lu ids

dur ing o rogen ic even ts r ef lec ted by th ick f lysch o r s la teter r ane (H su e t a l . 1988) located s ou th o f the main o re-

g r ad e o ccu r r en ces .

H o w ev e r t h e r e m ay a l s o h av e b een an ep i g en e t ic co m -

p o n e n t o f m i n e r a li za t i o n . O u r p r e l i m i n a r y d a t a i n d i ca te

t h a t l a t e p y r i t e co n t a i n s m o r e N i , Se an d M o t h an ea r l y

pyr i te . I t a l so con ta ins d i s t inc t ly heav ier su l fu r than the

i n t e r io r s o f n o d u le s . T h e s eco n d s t ag e m ay , o f co u rs e ,

mere ly r epresen t the las t even ts o f syngenes is , bu t we do

not th ink tha t th i s is the case because o f the sharp d i f f er -

ences between ear ly and la te pyr i te (F ig . 3 ). The ages and

cau s e (s ) o f t h e i n f e r r ed s eco n d s t age o f m i n e r a l i za t i o n a r e

u n k n o w n b u t t h e g eo l o g i c se t t in g o f s o u t h C h i n a s u g ges ts

at least two possibil i t ies .

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T h e s e c o n d s t a g e m a y h a v e b e e n c a u s e d b y a n e p i g e -

n e t ic h y d r o t h e r m a l e v e n t . F o r e x a m p l e , s u t u r in g o f t e c -

t o n i c p l a t e s d u r i n g t h e M e s o z o i c ( H s u e t a l. 1 9 8 8) m a y

h a v e i n d u c e d m i g r a t i o n o f h y d r o t h e r m a l f lu id s t h r o u g h

t h e a d j a c e n t t e r r a n e . D i a g e n e t i c f l u id s a n d b a s i n a l b r i n e s

r e s p o ns i b le f o r M V T P b - Z n m i n e r a l iz a t i o n a r e c a p a b l e

o f m o b i l i zi n g P G E ( M a c d o n a l d 1 98 7, L e c h l er a n d H s u

1 9 89 a ) a n d M o ( E r i c k s o n e t a l . 1 98 1 , 1 98 7 , C o v e n e y a n d

G l a s c o c k , 1 9 8 9 ) .A s e c o n d p o s s i b i l i t y i s s u g g e s t e d b y t h e u n u s u a l l y

w i d e s p r e a d a n d w e l l- d e v e lo p e d Q u a t e r n a r y k a r s t o f

s o u t h C h i n a . D i s n a r ( 1 9 8 1 ) a n d o t h e r s h a v e s h o w n t h a t

M o a n d S e a r e r e a d i l y f i xe d b y o r g a n i c m a t t e r a t a m b i e n t

t e m p e r a t u r e s a n d a c i d p H c o n d i ti o n s a l t h o u g h t h e y a r e

q u i t e m o b i l e a t h i g h p H v a l u e s . P o s s i b l y M o a n d S e w e r e

m o b i l i z e d a t l o w t e m p e r a t u r e s b y h i g h p H s o l u t i o n s eq u i -

l i b r a t e d w i t h c a r b o n a t e b e d s a n d w e r e t h e n p r e c i p i t a t e d

w h e r e v e r t h e p r e g n a n t s o l u t i o n s i n f i l t r a t e d s u l f i d e b e d s .

T h i s m e c h a n i s m w o u l d r e a d i l y e x p l a in t h e j u x t a p o s i t i o n

o f w e l l - d e v e l o p e d k a r s t w i t h b e d s t h a t a r e e x c e p t i o n a l l y

e n r i c h e d i n M o .

F i n a l l y it s h o u l d b e n o t e d t h a t t h e m i n e r a l i z a t i o n m a yb e r e l a t e d t o a n c i e n t w e a t h e r in g . U n c o n f o r m i t y U d e-

p o s i t s , a s s o c i a t e d w i t h t h e e a r l y - m i d d l e P r o t e r o z o i c

s t r a t i g r a p h i c b o u n d a r y , c a r r y e n r i c h e d v a l u e s f o r N i ,

M o , A u a n d P G E ( H u l b e r t e t a l. 1 9 88 ). G r a u c h ( 1 98 9 )

a n d G r a u c h a n d M o s i e r ( 1 9 8 7 ) n o t e t h a t s u c h d e p o s i t s

o r i g i n a t e b y c o m p l e x p r o c e s s e s th a t p r o b a b l y i n v o l v e

d e e p w e a t h e r in g , m e t a m o r p h i s m a n d m i g r a t i o n o f ba s i-

n a l b r in e s a l t h o u g h t h e r e la t i v e i m p o r t a n c e o f e a c h f a c t o r

r e m a i n s u n a s s e s s e d. S u c h d e p o s i t s h a v e m a n y f e a t u r e s in

c o m m o n w i th t he N i - M o - P G E - A u d e p o s it s o f C h i n a

( e .g . , a n i d e n t i c a l s u i t e o f m e t a l s a s s o c i a t e d w i t h a m a j o r

s t r a t i g r a p h i c u n c o n f o r m i t y ) . I n v e s t i g a t i o n s i n p r o g r e s s i n

o u r l a b o r a t o r i e s s h o u l d c l a r if y w h e t h e r o r n o t t h e s e re -s e m b l a n c e s h a v e g e n e t i c s i g n i f i c a n c e .

U n c o n v e n t i o n a l se d i m e n t a r y P G E o c c u r r e n c e s i n C a n a d a

O f a l l k n o w n d e p o s i t s N i - M o s u l fi d e b e d s in b l a c k s h a l e s

o f t h e S e l w y n b a s in ( C a n a d i a n Y u k o n ) m o s t c l o s e ly r e -

s e m b l e t h o s e o f C h i n a . L i k e t h e C h i n e s e d e p o s i t s , t h o s e

i n C a n a d a h a v e b e d t hi c k ne s s e s o f ~ 5 - 1 5 c m , c o n t a i n

a b u n d a n t v a e s i t e , a p p r e c i a b l e v a l u e s f o r N i , M o , P G E

a n d A u a n d s p a ti a l a ss o c i a ti o n w i th a m a j o r u n c o n f o r m i -

t y a t th e e d g e o f a s e d i m e n t a r y b a s i n . T h e s e b e d s c o n t a i n

a s m u c h a s 5 . 8 % N i , 1 % Z n a n d 8 0 0 m g / t P G E ( L .J .

H u l b e r t , p e r s o n a l c o m m u n i c a t i o n 1 9 8 8 ; P a r r y 1 9 8 9 , R . C .C a r n e p e r s o n a l c o m m u n i c a t i o n 1 99 0 ). D i f f e r e n c e s i n -

c l ud e s o m e w h a t l o w e r v a l u es f or M o ( < 0 . 4 % M o ) a n d

D e v o n i a n h o s t s t ra t a .

T h e C h i n e s e a n d C a n a d i a n d e p o s i t s w e r e b o t h d i s c o v -

e r e d a l i t t l e m o r e t h a n a d e c a d e a g o , a n d i t i s e n t i r e l y

p o s s i b le t h a t s i m i l a r d e p o s i t s h a v e b e e n o v e r l o o k e d e l se -

w h e r e . E n r i c h e d P G E v a l u e s a re k n o w n f r o m o t h e r s e d i-

m e n t a r y o c c u r r e n c e s ( T a b l e 1 ), s u c h a s t h e K u p f e r -

s c h i e fe r o f P o l a n d ( K u c h a 1 9 82 ), M n - m i n e r a l i z e d p i p e s

i n l i m e s t o n e s i n N e v a d a ( L e c h l e r a n d H s u 1 98 9 b ) a n d t h e

C a r b o n i f e r o u s o f t h e U . S . M i d w e s t ( C h y i 1 9 82 ). P G E

v a l u e s i n ex c e s s o f 1 0 0 p p b ( m g / t ) a r e c o m m o n i n s u c h

o c c u r r e n c e s ( T a b l e 1 ) .

Table 1. Peak values for Au, P GE an d Ni in non-placer sedim enta-ry deposits com pared with conventional (igneous-hosted) PG E ores

ppb (mg/T) w t%

Au Pt Pd IrNi

B l a c k s h a l e s

Polan d ~ 3 000 000 340 000 1 600 000 - 0.4

Chin a 2 700 300 380 20 5.1Yukon Ca nad a 3 86 540 210 5.8O k l a h o m a U S A 4 19 150 - 0.7 0.2Nev ada USA 5 - 30 10 - -Ind iana USA 6 4 <20 <20 1 .0 0 .04Indiana USA 7 - 63 16 -

O t h e r s e d i m e n t s

Kentucky 8 2 200 - -Australia 9 5 620 1 330 - -Ca na da 10 36 000 12 000 14 000 - -

C o n v e n t i o n a l o r e s 11

Bushveld RSA 260 4 800 3 000 200 0.18Stillwa ter US A 120 4 200 14 800 530 0.24Sudbury Ca nad a 120 340 360 10 1.30

1 Permian Kupferschiefer (Kucha, 1982)2 C am brian sulfide bed (Fan, 1983)3 Devonian sulfide bed (Parry, 1989)4 Mississippian (Orth et al., (1988)5 Devonian (Lechler and Hsu, 1989b)6 Pennsylvanian (Coveney and Glascoek, 1989)7 Devonian-Mississip. (Lechler and Hsu, 1989b)8 Pennsylvanian, Num ber 9 Coal (Chyi, 1982)9 Proterozoic, Coronation Hill (Grauch, 1989)

10 Proterozoic, Atha basc a (Grauch, 1989)11 Average values, from Hulbert et al. (1988)

C a r b o n i f e r o u s be d s o f t h e C e n t r a l U n i t e d S t a t e s

I n t h e c e n t r a l U n i t e d S t a t e s , a n o m a l o u s v a l u e s f o r P G E

a r e k n o w n f r o m D e v o n i a n - M i s s i s s ip p i a n b l a c k s h a le s o f

I n d i a n a ( L e c h l e r a n d H s u 1 9 8 9 b ) , M i s s i s s i p p i a n b l a c k

s h a le s o f O k l a h o m a ( O r t h e t a l . 19 8 8) , a n d P e n n s y l v a n i -

a n ( U p p e r C a r b o n i f e r o u s ) c o a l s o f K e n t u c k y ( C h y i 1 98 2)

(F ig . 4 ) .

B l a c k m a r i n e s h a l e s f r o m t h e D e v o n i a n - M i s s i s s i p p i a n

b o u n d a r y a n d in th e P e n n s y l v a n i a n a r e m a r k e d l y e n -

r i c h e d i n h e a v y m e t a l s . L i k e t h e C h i n e s e b l a c k s h a l es t h e y

r o u t i n e l y c o n t a i n v a l u e s b e t w e e n t e n s a n d t h o u s a n d s o f

p a r t s p e r m i l li o n M o ( S h a f f e r e t a l. 1 9 81 , C o v e n e y a n d

M a r t i n | 9 8 3, C o v e n e y e t al . 19 87 , C o v e n e y a n d G l a s c o c k1 9 8 9 ) . F o r e x a m p l e , t h e P e n n s y l v a n i a n M e c c a Q u a r r y ,

E x c e ll o, L o g a n Q u a r r y a n d H o l l a n d s h al e s o f I n d i a n a

c o n t a i n a v e r a g e v a l u e s > 1 00 0 p p m i n I n d i a n a . S o m e o f

t h e s e s a m e b e d s c a n b e t r a c e d t o I l l i no i s , I o w a , K e n t u c k y

a n d M i s s o u r i w h e r e t h e y ty p i c a l ly c o n t a i n h u n d r e d s o f

p p m M o . C o n c e n t r a t i o n s g r a d u a l l y d i m i n i s h t o t e n s o f

p p m M o i n K a n s a s a n d O k l a h o m a ( C o v e n e y e t a l. 1 98 7,

C o v e n e y a n d G l a s c o c k 1 98 9) . O t h e r P e n n s y l v a n i a n b l a c k

s h al es c o n t a in h u n d r e d s o f p p m M o i n K a n s a s a n d M i s -

s o u r i ( C o v e n e y a n d G l a s c o c k 1 9 8 9 ) . U . S . s h a l e s c o n t a i n

e n r i c h e d v a l u e s f o r M o c o m p a r a b l e i n m a g n i t u d e a n d

a r e a l e x t e n t ( F i g . 4 ) t o t h o s e o f t h e C h i n e s e b l a c k s h a l e s

(Fig . 1 ) .

8/3/2019 Coveney & Chen 1991


Fig. 4. Locations of PGE enrichments in Carboniferous beds, cen-tral Uni ted States. Distr ibution of Pennsylvanian coals and shalesis approximated by extent of Mecca Quarry Shale and equivalent

beds (modif. from Wanless and Wright, 1978). Coals in Kentucky(1) cont ain up to 210 ppb Pt (Chyi, 1982). Heavy stippling shows

original distribution of Chattanooga Shale and equivalents (fromConant a nd Swanson, 1961; Nuelle, 1988; Amsden, 1988) whichconta in PGE enrichments in Oklahoma (2, from Orth et al., 1988)

and Indiana (3, from Lechler and Hsu, 1989b). The Midwest con-tains extensive karst and major Pb-Zn deposits (MVT) formed bybasinal brines that may have been derived from the Illinois,

Anadarko and Arkoma basins (e.g., Leach and Rowan, 1986). Base-ment features (e.g., Humbol dt fault, the Reelfoot rift, and the mid-

cont inent geophysical anomlay) are from Bickford et al. (1986)

Black shales may have ore grade enrichments in the

vicinity of the Reelfoot Ri ft where Chyi (1982) reportsenhanced values for Pt in Pennsylvanian coals. Lechler

and Hsu (1989b) find lesser but still appreciable values

for PGE in equivalents of the Devonian-Mississippian

Chat tanoo ga Shale (up to 63 ppb Pt in Indiana).

Ore-grade enrichments may also be associated with

the Humboldt fault of Kansas or elsewhere near faults

bounding the Midcontinent geophysical anomaly. Orth

et al. (1988) have reported whole-rock values as large as

160 ppb for Pt in beds near the Devonian-Mississippian

boundary near Ada, Oklahoma, for example. The base-

ment near this location is intensely faulted and structural-

ly complex as it lies on an extension of the Humboldt

fault (Fig. 4). Distal to this major basement structure, ineastern Kansas and western Missouri, what may be mi-

nor expulsion vents are found in limestones next to the

metal-rich Pennsylvanian shales. These take the form of

Pb-Zn mineralized pipes such as the one at the Jumbo

mine (Blasch and Coveney 1988) and minor structuressuch as mineralized animal burrows or root casts con-taining ferroan dolomite with or without calcite, barite,

petroleum or sphalerite (Raga n 1987). Because of poorexposure, it is unclear whether or not major hydrother-

mal venting and mineralization occurred near major

basement structures such as the Humbold t fault, thoughthe possibility exists. The likelihood that PGE ores or

unconformity-re lated U deposits may be associated with

87

the Central North American rift system (Midcontinent

geophysical anomaly) has been suggested by Berendsen

(1989).

At present it is impossible to say whether or not Ni-

Mo-PGE-Au deposits similar to those of China exist in

the central United States, where many of the most critical

areas associated with major basement structures are

buried. Nevertheless the question is sufficiently impor-

tant that we will briefly summarize the evidence.There are important similarities between the central

United States and southern China. Most notably both

areas contain broad expanses of metalliferous Paleozoic

black shales with very enriched values for Mo (> 100 to

2000 ppm). Both have broad regions of karst and both

border sedimentary basins. Know n PGE anomalies in the

Carboniferous beds of the central United States are of the

same order of magnitude as the values in the Ni-Mo beds

in China. These anomalies are located in the vicinity of

major basement structures tha t could have acted as feed-

er zones.

On the other hand, the Chinese deposits are located in

a tectonically active area rather than a craton. At leastsome are associated with tuff beds suggesting the possi-

bility of a critical genetic role for igneous activity which

can probably be ruled out in the central United States. If

this is the case, other places in the Unit ed States such as

Nevada, where Lechler and Hsu (1989 a, b) report signif-

icant PGE values associated with sediments, would clear-

ly be more suitable areas than the Midwest for prospect-

ing.

Conclus ions

The Ni-Mo-PGE-Au sulfide beds of south China proba-bly originated as exhalites from submarine springs during

the Cambrian. Some metals of economic interest may

have been added later by circulating basinal brines or by

modern supergene events related to deep karst weather-

ing. A genetic role for deep ancient weathering,

analogous to unconformity U deposits, is also conceiv-

able. Extraterrestrial sources for PGE are an interesting

possibility, but probably need not be invoked without

addit ional evidence.

Discovered only recently, the Ni-Mo-Pt-Au deposits

of China and Canada may be only the first indications of

a globally significant source for Ni, Mo and PGE. Similar

deposits may well exist in Poland or elsewhere in associa-tion with metalli ferous black shales. Although evidence is

inconclusive concerning the existence of Ni -Mo-PG E-Au

sulfide beds in the Paleozoic of the U.S. Midwest, there

are sufficient similarities in the settings - major Mo

anomalies, possible feeder fractures in the basement, ex-tensive kars t - to justi fy exploration.

Acknowledgements.We appreciate the support of the Nationa l Sci-ence Foundations of the United States (Grant EAR89-17322) and

the People's Republic of China. Travel and seed grants from theSchool of Gradua te Faculties and Research, the Center for Interna-tional Affairs, and the College of Arts and Sciences at the Univer-sity of Missouri-Kansas City were essential. Discussions with

Zhang Aiyun, R.C. Carne, Fan Delian, G.A. Desborough, E.D.

8/3/2019 Coveney & Chen 1991


88

Goebel, R.I. Grauch, J.B. Maynard, J.B. Murowchick, B.E. Nesbittand D.F. Sangster have been invaluable. We particular ly wish tothank L.J. Hulbert for calling atten tion to the Selwyn Basin. Profes-

sors D.P. Hopkins and J.B. Murowchick provided helpful com-

ments on the m s . Some analyses were supplied by M.D. Glascock(University of Missouri Research Reactor). Sulfur isotope analyseswere performed by Krueger Enterprises. Scott Robinson of theUMKC School of Dentistry coordinated SEM studies. This paper

is a contribution to International Geological Correlations Pro-gramme Project Number 254, "Metalli ferous Black Shales and Re-lated Ore Deposits". Jan Pasava and Richard I. Grauch organized

the IGC session at which these results were first reported (Chen andCoveney 1989).

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