genesis of the precambrian copper-rich caraiba

8/9/2019 Genesis of the Precambrian Copper-rich Caraiba

1/23


2/23


3/23

353

Fig. 2. Simplified geology of

part of the Salvador-Curaq/t

Orogen showing the high-grade

terrains of Curaqfi (CT ) and

Jacurici (.IT) and their m afic

ultramafic bodies. Geo logy after

Inda and Barbosa (1978), Gava

et al. (1983) and Mascarenhas et

al. (1984)

indicating that the age of development of the precursor sources of

the two complexes may not have been very different.

Mod els for the araiba mineralisation

T h e Ca r a i b a mi n e ra l i s a t i o n i s b a si ca l l y o f d i s s emi n a t ed

t y p e . T h e m a i n o r e mi n e ra l s - ch a l co p y r i t e an d b o rn i t e

- a r e h o s t ed i n c en t i me t r e t o t en s -o f -me t r e s t h i ck h y p e r -

s then i t i c and nor i t i c bod ies enc losed wi th in the h igh-

g rad e g n e i s s e s . T h e h y p e r s t h en i t e s a r e b y f a r t h e mo s t

Cu - r i ch ro ck s (Cu = 2 -5 w t ; n o r i t e s < 0. 5 w t ) . Ma g -

net i t e , and to l esser ex ten t i lmeni t e , a re the main accessor -

i es i n t h e d i s s emi n a t ed mi n e ra l i s a t i o n , t h e i r ab u n d an c e

corre la t ing pos i t ive ly wi th the main o re minera l s , i . e . , t he

r i ch e r t h e o r e t h e mo re mag n e t i c i t i s (Sa an d Re i n h a rd t

1984) . Veins and ve in le t s o f rem obi l i sed o re a re very

c o m m o n , a n d c o n si s t m o s t l y o f c h a l c o p y r it e a n d b o r n i te

w i t h mi n o r cu b an i t e , mag n e t i t e an d N i - t e l l u r i d e s . So me

v e i n s a r e r i ch e r i n N i an d ca r ry p en t l an d i t e , p y r rh o t i t e ,

mack i n aw i t e , ch a l co p y r i t e an d cu b an i t e . T h es e p a r a -

geneses , a long wi th ch lo r i t e , ep ido te , carbonate , an -

thophyl l i t e and t a l c , ind ica te tha t the ve in su lph ides have

b een r emo b i l i s ed u n d e r amp h i b o l i t e - t o g r een s ch i s t- f ac ie s

m e t a m o r p h i c c o n d it i on s .

T h e o r i g i n o f t h e Cu - b ea r i n g m af i c -u l t r amaf i c r o ck s o f

the Cura~/~ t e r ra in has long been con t rovers i a l . Le inz

(1948) and Schneider (1951) descr ibed the su lph ide-bear -

i n g p y ro x en i te s a s mag m a t i c . L ad e i r a a n d Bro ck es (1 96 9)

a s c r i b ed t h e maf i c -u l t r amaf i c r o ck s t o an i g n eo u s s u i t e


4/23

354

the sulphides. Mandetta (1982) later extended Linden-

mayer's model to suggest that the Caraiba deposit is

a layered intrus ion composed of cycles of igneous differ-

entiation, with a bottom-to-top sequence of: (i) massive

hypersthenite with minor olivine-pyroxenite, (ii)mela-

norites, (iii) norites and leuconorites with hypersthenite

streaks, and (iv) norite to leuconorite with interleaved

gabbros to gabbronorites, locally banded.

Subsequent field and mineralogical studies on out-

crops as well as drill-cores (Oliveira 1990a,b) failed to

confirm the layered intrusion model of Mandetta (1982).

Instead, crosscutting relationships suggested that the

Caraiba complex may be a multiple sequence of intrusions

of dykes, veins, and breccias. Here, field, mineralogical

and geochemical data are integrated to provide a better

petrogenetic model for the complex and for the min-

eralisation.

Fig. 3. Simplifiedgeologyof part of the Cura~fi high-grade terrain

(modified from Delgado and Souza 1981, and the Caraiba Mine

stare

representing the initial magmatism of a geosynclinal pile.

Suszczynski (1972) suggested that the mafic-ultramafic

rocks resulted from metamorphism of pure- to impure-

carbonates , locally highly magnesian. Delgado and Souza

(1975) presented trace element data for some mafic-ultra-

mafic rocks and concluded that the mean Cr, Ni, Ti, Cu,

Co, and V values found are more compatible with an

igneous origin for these rocks. Townend et al. (1980),

reviewing previous models for Caraiba, proposed an ig-

neous origin, the available data favouring a sequence of

basic to ultrabasic sills metamorphosed at granulite grade.

Figueiredo (1981), noting the similarity between the REE

patterns of an iron-rich hypersthenite from the Caraiba

mine and some regional iron formations, suggested a sedi-

mentary origin for parts of the Caraiba ore-body. Linden-

mayer (1981) described relict cumulus textures in some

gabbros associated with the Cu-bearing norites-hyper-

sthenites and found possible clinopyroxene exsolution

lamellae in hypersthene. On the basis of chemical data and

cross-cutting relationships deduced from drill cores, she

concluded that the ore-hosting rocks are intrusive and

evolved through fractional crystallization of a previously

differentiated Fe-Ti-rich tholeiitic liquid, and that the

hypers thenite-norite-gabbro-anorthosite sequence might

well represent the original igneous stratigraphy. She also

suggested that some anhydrite-bearing marble and calc-

silicate rocks could have supplied sulphur to form part of

ield and p etrographic aspects

As with many igneous complexes in Precambrian high-

grade terrains (cf. Windley et al. 1981), the Caraiba ore-

bearing mafic-ult ramafic rocks still preserve a good pro-

portion of their primary igneous features. Cross-cutting

relationships with the country gneisses, and between the

different rock types within the complex, can be observed

in the Caraiba open pit. These clearly suggest emplace-

ment of the complex as multiple intrusions of norite and

hypersthenite as dykes, veins and igneous breccias. The

associated peridotites and gabbroic rocks are interpreted

as xenoliths.

ypersthenites and norites

These rocks account for more than 94 of the Caraiba

mafic-ultramafic complex, and are found mostly as dykes,

veins, and magmatic breccias. Observations on

9 boreholes suggest the proportion of hypersthenite to

norite is ca. 60:40. The contact between these rock-types is

mostly sharp, but a complete gradation from hyper-

sthenites to melanorites, norites, and to the less abundant

noritic anorthosites may occasionally be observed. Some-

times a homogeneous rock, either hypersthenite or norite,

can be traced for some tens of metres. Centimetre-thick

folded dykes of hypersthenite or norite may sporadically

be found cross-cutting the ore-grade rocks. Similar situ-

ations occur in the southern part of the open-pit where

off'shoots of coarse-grained hypersthenite clearly transect

the metamorphic banding of hornblende-pyroxene

granulite and migmatitic gneiss. The igneous breccias

comprise fragments of norite enveloped by hypersthenite.

This feature, and the offshoots described above, suggest

that some hypersthenites originated from liquids of the

same composition, rather than from another parental

magma.

Field observations on chalcopyrite-bearing hyper-

sthenite dykes from the southern part of the Caraiba open

pit (Oliveira and Lacerda 1993) demonstrate tha t some

hypersthenites have been emplaced synkinematically dur-

ing the most prominent deformational event (F3):


5/23

355

Fig. 4. Simplifiedgeology of the

Caraiba open-pit with location

of studied outcrops an d

boreholes. Geology after Silva

1985)

1. Dr ag folds in count ry- roc k granuli te-facies gneiss indi-

ca te tha t a s teeply d ipping hypers theni te dyke in t rude d

along a dextral t ransten siona l shear zone Fig. 5a);

2 . A se t o f narrow and para l le l melanori te to hyper-

sthenite dykes cut across the steep fol iat ion of the

migmat i t ic gneiss , whereas another se t , conformable

in ter leaved wi th the gneiss , has been boudinaged and

broken apart , somet imes c lear ly showing a s igmoidal

shape indicat ive of a dextral sense of mo tio n Fig. 5b);

3 . A cm-th ick hypers theni te dyke , a branch of a th icker

and adjacent one, cross-cuts the migmati t ic gneiss fol i-

a t ion and was subsequent ly t ransposed a long the

gneiss fo l ia t ion ; the a d jacent dyke i s nearly conform -

able in the host gneiss and shows anti thet ic sl ip on


6/23

356

a

W

I I

E

~

9 1

Fig. 5a--c. Cross-sections, Cara iba open-pit, showing evidence of

hypersthenite emplacement controlled by shearing in a) and b) and

concurrent dyking and deformation in c). Grey hypersthenite; sub

parallel lines foliation of migmatitic gneiss

f r ac t u re p l anes , s ugges t i ng dex t r a l d i s p l acem en t

F ig . 5c ) . The t r ans pos ed dyk e con t a i n s hyper s t hene

t r ans ec t ed by b i o t i t e , wh i ch i s a t yp i ca l am ph i bo l i t e -

g rade F 3 m i ne ra l .

The s t ruc t u ra l f ea t u res, des c r i bed by Ol i ve i r a and Lace rd a

1993 ) and s u m m ar i s ed he re , s ugges t tha t a t l eas t s om e o f

t h e C a r a i b a r o c k s m a y h a v e t h e ir e m p l a c e m e n t c o n t r o l l e d

by a r eg i ona l s hea r be l t t ha t r eached s en il it y in t he wan i ng

9 5

8 5

X

O • 7

65

4 5

l ow T - - ~

h i g h T

3 5

0 5

9

. o ~ . + & . w - . ,+ ~ . r + +

0 % ~ 0 o + ~ + 6 + + o

o +

+

H y p e r s t h e n i t e

9

M e l a n o r i t e

o

N o r i t e

I I I ~ I

1 2 3 4

M o l e A I 2 0 3 I n O p x

Fig. 6. Mg-number versus alumina content in orthopyroxenes from

Caraiba norites and hypersthenites. SK Skaergaard trend after

Hoover 1989). Also shown is the low- and high-T trend of the

Josephine peridotite after Dick 1977)

8 5

8O

x

O .

o

_c

s

z

IE

7

65

C o n t a c t C o a r s e

P e r l d o t l t e T r a n s i t i o n H y p e r s t h e n l t e

Fig. 7. Variation of orthopyroxene composition across the contact

between a per idotite xenolith and the host hypersthenite. Sample

380-C from outcrop 380

s t age o f evo l u t i on o f the P a l eop ro t e rozo i c S a l vado r -

Cura~/t orogen.

The hyp er s t hen i te s and no r i te s a r e com pos e d o f hyper -

s thene, p lag ioclase , su lphides , Fe-Ti oxides , ph logopi te

and apa t i t e i n va ry i ng p ropo r t i ons . Under t he m i c ro -

s cope , hyper s t hene and p l ag i oc l as e a re ve ry f r e s h , s om e

s howi ng t r i p l e -j unc t ion con t ac t s i n r e s pons e t o s ubs o l i dus

recrys ta l l i za t ion; but several pr imary features are s t i l l

p res e rved . P lag i oc l as e and h yper s t hene i n t he no r i te s a r e

in propor t ions cons i s ten t wi th eu tect ic crys ta l l i sa t ion . In

t he hyper s t hen i t e s , however , hyper s t hene m ay o f t en con -

t a i n anhed ra l t o s ubh ed ra l i nc l u si ons o f p lag i oc l as e in

op t i ca l con t inu i t y , i m p l y i ng t ha t p l ag i oc l as e m ay be bo t h

a cum ul us o r a pos t cum ul us phas e ; m ore r a re l y p r i s m a t i c

hyper s t hene fo rm s an apa t i t e -hyper s t hene cum ul a t e

o r , t oge t he r w i t h p l ag i oc l as e , s hows c ro s s -bedd i ng l i ke


7/23

357

i g n e o u s l a m i n a t i o n . W h a t m a y h a v e b e e n t r a p p e d o r

i n t e r st i ti a l no r i t i c li qu i d s a re com m o n l y found wi t h i n t he

hyper s t hen i t e s ; i n t hes e pa t ches , hyper s t hene m ay s how

s ubhed ra l c ro s s - s ec t i on and p l ag i oc l as e is r eve r s e ly zoned .

Mi no r s u l ph i des , ox i des and ph l ogop i t e g ra i n s a l s o occu r

as i nc l u s i ons i n hyper s t hene , t hough m os t a r e t ex t u ra l l y

in ters t i t i a l . They have recrys ta l l i sed to d i f ferent ex tent s

d u r i n g d e f o r m a t i o n / m e t a m o r p h i s m s o th a t i n t e r g ra n u l a r

s u l ph i des and ox i des d i s p lay a l l s tages f rom hav i ng eq u i -

l i b r ium t ex t u res w i t h hyper s t he ne (= annea l ed co n t ac t s )

t o hav i ng c ro s s -cu t t i ng r e l a t ions h i p s ( s ec ondary g rowt h ) .

A l t h o u g h p h l o g o p i t e f r e q u e n t ly s h o w s s e c o n d a r y g r o w t h ,

p r i m ary i n t e r s t i t i a l ph l ogop i t e a round hyper s t hene can be

obs e rved . P h l ogop i t e i s a l s o found as a p r i m ary phas e i n

t he hype r s t hen i t e ve i n (no t ed i n (3) above) a s we l l a s i n t he

pe r i do t i t e -hos t ed hyper s t hen i t e s .

Apa t i t e is a ub i qu i t ous m i ne ra l , be i ng g ranu l a r i n s hape

i n t he hyper s t hen i t e s , where i t m ay r each ove r 30 m o-

da l , and g ranu l a r t o p r i s m a t i c i n no r i te s . P h i l po t t s

(1967) no t ed t ha t h i gh conce n t r a t i ons o f apa t i t e and F e -T i

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

exp l a i ned t he a s s oc i a t i on i n t e rm s o f im m i s c ib l e li qu id s . In

s o m e a n o r t h o s i te s t h e p r o p o r t i o n o x i d e : a p a t i t e i s 2 : 1

wh i ch P h i l po t t s (1967) i n t e rp re t ed i n t e rm s o f eu t ec t i c

c ry s t a l l i za t i on . In t he C ara i ba ano r t hos i t i c rocks , apa t i t e

do es no t s ho w s uch a d i r ec t r e l a t i ons h i p wi t h F e -T i

oxides ; none theless the pe t rogen es i s of P +_ (Fe + T0-r ich

l i qu id s i n m as s i f ano r t hos i t e s r em ai ns en i gm at ic .

Ultramafic xenoli ths

Ul t ram a f i c xeno l i th s a r e loca l l y com m o n , c ropp i ng o u t a s

f i ne -g ra i ned d i s con t i nuous rounded t o ova l s haped ba l l s

i n a g round m a s s o f hyper s t hen i t e and no r i te ; com po s i -

t i ona l l y t hey com pr i s e du n i t e , ha rzbu rg i te , o l iv i ne o r t ho -

py roxen i t e , o l i v i ne -ho rnb l ende o r t hopy roxen i t e and o l i -

v i n e - o r t h o p y r o x e n e h o r n b le n d i t e w i th m i n o r a m o u n t o f

b ro wn t o b l ac k s p i ne l and ph l ogop i t e . I t i s ve ry d i ff i cu l t t o

es t ab l i s h whe t he r t he xeno l i t h s occu r dom i nan t l y a t one

s t r a t i g raph i c l eve l becaus e t hey a re abs en t i n s om e

boreho l es , even i n t hos e d r i l l ed a l ong t he s am e ve r t i ca l

c ro s s - s ec t i on t h rough t he m af i c -u l t r am af i c com pl ex . The

x e n o l i th - g r o u n d m a s s c o n t a c t s a r e s h a r p a n d , f ro m p e t r o -

g raph i c ev i dence , the pe r i do t i t e s c l ea r l y c ry s t a ll i zed be fo re

t he hyper s t hen i t e s and no r i t e s . De t a i l ed exam i na t i on o f

a con t ac t be t we en a pe r i do t i t e xeno l it h and t he g rou nd -

m as s hyper s t hen i t e s hows a f i ne -g ra i ned hyper s t hen i t e

o f f s hoo t i n jec t ed i n t o t he pe r i do t i t e , a s l igh t dec reas e o f

t he hyper s t hen i t e g ra i n s i ze t owards t he pe r i do t i t e , and

e l onga t ed hyper s t henes pe rpend i cu l a r t o t he con t ac t w i t h

t he pe r i do t i t e . Th i s l a s t r em arkab l e f ea t u re i s cons i s t en t

wi t h g row t h o f m i ne ra l s a t a co o l ed s u rf ace . M oreov er , t he

hos t hyper s t hen i t e i s com pos e d o f ph l ogop i t e , apa t i t e and

i n t e r s t i t i a l m agne t i t e , bo rn i t e and cha l copy r i t e , wh i ch

l e av e s n o d o u b t t h a t t h e m a g m a w a s h y d r o u s a n d t h a t

two immiscib le l iqu ids , v iz . s i l i ca te and su lphide-oxide,

coexis ted .

T h e p e r i d o t i te o r t h o p y r o x e n e c o m p o s i t i o n s h o w s a g a p

b e t w e e n 8 - 1 8 E n c o m p a r e d w i t h p y r o x e n e s f r o m

hyper s t hen i t e s and no r i t e s (O l i ve i r a 1990b ; O l i ve i r a and

Ta rney 1994 ), wh i ch aga i n ru l e s aga i n s t de r i v i ng t he l a t t e r

9 0

8 0

i 70

6 0

9 Se t 1 [

5 0

E d g e C e n t r e E d g e

Fig. 8. Compositional variation in reverse zoned plagioclase of

norite 380 1D

Phlogopite Eastonite

100

8O

A

~ . 60

5

9

40

8

20

P h l o g o p i t e

+ -H - +o + 0 ~ o

o So

+ . ~ . o t o r

~ l r

B i o t i t e

+ Norl tes

o Hypersthenites

0

0.44 0.46 0.48 0. 0 0. 2 0.54 0.56

Annite Siderophyllite

AI/ Mg+Fe)

Fig. 9. Composition of biotite phlogopite series in hypersthenites

and norites from the Caraiba mine

f rom t he fo rm er by f r ac t i ona l c ry s t a l l i s a t i on . No t ab l y ,

ca l c ic py roxen e occu r s i n t he m o s t f f ac t i ona t ed pe r i do t i te ,

bu t i s ab s en t i n t he C u- r i ch hyper s t hen i t e s .

abbroic xen ol i ths

X e n o l it h s o f g a b b r o n o r i t e s , g a b b r o s , a m p h i b o l e - g a b b r o s ,

a n d l es s o ft e n a m p h i b o li te s , a r e c o m m o n i n t h e C a r a i b a

m af i c -u l t r am af i c rocks . L i ke t he u l t r am af i c xeno l i t h s t hey

occu r i n cm -s i ze roun ded ova l o r e l onga t e b l ocks . B ecaus e

s om e s i m i l a r l i t ho l og i es occu r i n t he s up rac rus t a l s e -

quence and / o r a s dykes i n t he o r t hogne i s s es G1 and G2 i t

i s potent ia l ly poss ib le that a few xenol i ths could be local .

T h e x e n o li th s a r e c o m p o s e d o f p la g i o c la s e a n d C a - p y r o -

x e n e w i th v a r i e d p r o p o r t i o n s o f a m p h i b o l e , h y p e r s th e n e ,

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

ra re l y i n te rg ranu l a r , t ex t u re . In s o m e g abb ro i c xeno l it h s ,

C a-py roxenes a re pa r t i a l l y t o t o t a l l y r ep l aced by ho rn -

b l ende , wh i ch i n t u rn m a y d i s p l ay s ym pl ec t i c i n t e rg rowt hs


8/23

T

e

1

R

e

a

v

m

n

a

c

m

o

o

m

h

C

a

b

c

m

e

O

S

m

e

F

C

N

F

C

N

F

C

D

h

2

8

5

1

3

9

9

0

2

8

R

H

H

N

e

N

e

H

M

i

n

a

O

O

O

O

P

a

%

O

5

1

5

6

5

6

5

3

5

9

T

O

0

0

-

-

-

A

z

O

3

0

1

6

1

9

1

7

2

8

C

O

-

-

-

F

O

2

2

2

2

2

2

2

3

0

0

M

n

O

0

4

0

5

0

4

0

6

-

M

g

O

2

4

2

8

1

1

2

5

-

C

O

0

1

0

4

0

3

0

4

9

2

N

-

-

0

0

6

1

K

2

.

.

.

.

T

a

9

5

1

2

9

8

1

1

9

2

C

o

p

o

o

O

6

6

6

6

3

S

1

9

1

9

1

9

1

9

1

2

T

0

0

A

0

1

0

0

0

0

0

0

5

7

C

r

F

2

+

0

7

0

6

0

8

0

7

0

0

M

n

0

0

0

0

0

0

0

0

-

M

g

1

2

1

2

1

0

1

2

-

C

0

0

0

0

0

0

0

0

1

7

N

-

-

-

0

0

2

1

K

S

m

4

0

4

0

3

9

4

0

1

9

X

M

0

6

0

6

0

5

0

6

-

X

0

0

0

0

0

0

0

0

-

m

6

2

6

7

5

5

6

2

-

%

A

-

-

4

2

F

C

2

2

N

e

P

a

5

3

2

1

9

8

5

7

0

0

9

1

3

1

1

5

7

1

9

2

0

0

0

1

9

4

6

N

5

1

H P

a

5

7

2

5

1

2

4

8

9

3

3

9

9

6

0

2

1

1

7

1

9

5

0

N 8

3

N

e

P

a

5

3

2

7

8

6

5

9

0

5

9

1

3

1

4

5

5

1

6

2

1

0

1

1

9

4

1

N 8

9

A

h

P

a

5

2

2

6

8

0

6

4

0

4

9

8

3

1

5

5

4

1

5

2

2

0

0

1

9

4

0

N

9

2

H P

o

3

1

4

6

1

1

0

3

1

9

1

3

9

4

9

0

2

5

5

0

5

2

6

0

0

1

3

3

6

1

7

1

5

7

7

F

C

2

7

N

e

P

o

3

0

4

1

1

1

1

7

1

8

0

4

9

2

9

5

2

5

6

0

4

2

5

1

7

3

3

0

1

1

7

1

6

6

7


9/23

Table

2. Representative analyses of sulphide and oxides from hyper-

sthenites and norites in Drillcores FC2516 and NO 33, Ca raib a mine

Mineral Cpyr Pyrr Born Cpyr

Fe 30.7 59.76 12.64 26.41

Co 0.01 0.04 0.0 0.06

Ni 0.01 0.35 0.02 0.0

Cu 33.8 0.02 60.07 39.59

Zn 0.03 0.03 0.02 0.02

S 34.21 38.77 26.7 32.57

To tal 98.76 98.97 99.44 98.65

Ni /Cu 0.0 15.7 0.0 0.0

Continued

Magn Spin Magn Spin

TiO2 0.33 0.01 0.24 0.04

A12Oa 1.53 53.04 1.22 49.93

CrzO3 5.63 7.51 5.59 7.42

Fe2 03 56.31 - 57.38 0.79

Fe O 29.37 23.64 29.52 23.66

MnO 0.13 0.28 0.12 0.28

MgO 0.07 8.66 0.09 7.86

To tal 93.37 93.14 94.16 89.98

Cation proportions

Ti 0.08 0.002 0.08 0.006

A1 0.587 14.728 0,464 14.486

Cr 1.45 1.399 1.425 1.443

Fe 3+ 13.8 14.0 0.148

Fe 2 + 8.0 4.657 7.96 4.871

Mn 0.036 0.056 0.032 0.059

Mg 0.033 3.041 0.042 2.891

Born

11.60

0.01

0.02

61.15

0.02

26.60

99.40

0.0

Cpyr, Chalcopyrite; Pyrr, pyrrhotite; Born, bornite; Magn, magne-

tite; Spin, spinel

o f h y p e r s t h en e an d p l ag i o c l a s e a t g r a i n b o u n d a r i e s . T h i s

f o r m a t i o n o f a m p h i b o l e a t t h e e x p e n s e o f p y r o x e n e a n d

i t s fu r ther re crys ta l l i sa t ion , sugges t re -equ i l ib r ium of the

h y d ra t ed g ab b ro i c x en o l i t h i c r o ck t o t h e h i g h e r t em-

p e ra t u r e s o f t h e h o s t n o r i t i c -h y p e r s t h en it i c mag m a . T h e

g ab b r o i c x en o l it h s h av e few co u n t e rp a r t s i n t he s u r ro u n d -

ing coun t ry rocks (Ol ive i ra and Tarney 1994) , bu t the i r

d i s ti n c t n eg a ti v e N b an o ma l i e s o n man t l e n o rma l i s ed

d i ag rams co u p l ed w i t h t h e i r f r a c t i o n a t ed RE E p a t t e rn s

sugges t a con t inen ta l in f luence/ inpu t .

359

yroxene

O r t h o p y r o x e n e r a n g e s f r o m En68_54 i n h y p e r s t h en i t e s

through 1~n67.63 i n me l an o r i t e s t o En66_56 i n nor i t es . In

t h e an o r t h o s i t e s t h e r e i s v e ry l i t t l e v a r i a t i o n i n co mp o s i -

t i o n (E n 6 1 -E n 6 2 ) . Co mp ar i n g s amp l e s f r o m d r i l l h o l e s

F C 2 5 1 6 a n d N O 3 3 , o r t h o p y r o x e n e s f r o m t h e f o r m e r a r e

s l igh t ly more i ron r i ch En61.56 c o m p a r e d w i t h En66_6o .

T h e a l u mi n a co n t en t o f p y ro x en es f al ls w i th i n t h e r an g e

3 .6 -1. 1 mo l e , th o s e f ro m t h e h y p e r s t h en i t e s b e i n g mo re

a l u mi n o u s an d l e s s f r a c t i o n a t ed t h an t h o s e f ro m t h e

melanor i t es and nor i t es (Fig . 6 ) . Pyroxenes f rom a l l rocks

fo l l o w a t r en d p e rp en d i cu l a r t o t h e t r en d o b s e rv ed i n

l o w -p re s s u re i g n eo u s i n t ru s i o n (e .g . Sk ae rg aa rd ) b u t p a r -

a l le l t o t h e t r en d d e f i ned b y l o w - t e mp e ra t u r e - h i g h - t em-

p e ra t u r e A l p i n e p e r i d o t it e s an d h i g h -p re s s u re p e r i d o t i te s .

T h e A 1 2 03 c o n t en t o f p y ro x en e s i n c r eas e s w i t h i n c r ea s i n g

t emp e ra t u r e an d p r e s s u re (G reen an d R i n g w o o d 1 9 6 7 ,

G ree n 1 96 9) , h en ce t h es e p a r a me t e r s ma y h av e co n t ro l l ed

A 1 2 0 3 en t e r i n g i n t o o r t h o p y ro x en e . H o w ev e r , t h e h i g h e r

A l zO 3 ab u n d an ces i n p y ro x en es f ro m t h e h y p e r s t h en i t e s

may b e d u e t o o t h e r f a c t o r s . Bo t h h i g h t o t a l an d w a t e r

p r e s s u re i n h i b i t t h e c ry s t a l l iz a t i o n o f p l ag i o c l a s e (Y o d e r

and Ti l l ey 1962) , so i f the hype rs then i t es re prese n t h igher

p r e s s u re mag m as , t h en C a a n d A1 w o u l d b e av a i l ab l e to

en t e r t h e p y ro x en e s t r u c t u r e . H o w ev e r , t h e co ex i st en ce o f

n o r i t e an d h y p e r s t h en i t e mag mas mak es p r e s s u r e d i f f e r -

en ces an u n l i k e l y ex p l an a t i o n . Ca l c i c p y ro x en es o ccu r i n

n o n e o f t h e se ro ck s an d t h e Ca co n t en t o f t h e an a l y s ed

o r t h o p y ro x e n es i s v e ry lo w ( < 0. 60 mo l e ) . I t ap p ea r s

t h a t t h e A 1 20 3 co n t en t o f o r t h o p y ro x en e i s d e t e rmi n ed b y

t h e p r e s en ce o r ab s en ce o f p lag i o c l a se , co u p l ed w i t h

a r e l a ti v e l y A l - ri ch, Ca - p o o r n a t u r e o f t h e p a r en t a l ma g -

mas .

ineral chemistry

Mi n e ra l g r a i n s o f n o r i t e s an d h y p e r s t h en i t e s f r o m

b o reh o l e s F C2 5 1 6 an d N O 3 3 ( see F i g. 4 f o r l o ca t i o n ) w e re

an a l y s ed w i th a J E O L Su p e rp ro b e a t L e i ce s t e r U n i v e r s i t y

t o a s ce r t a i n an y co mp o s i t i o n a l t r en d s t h a t mi g h t s u p p o r t ,

o r o t h e rw i s e , t h e l ay e r ed s i l l s mo d e l o f L i n d en may e r

(1981) and Mandet t a (1982) . These two cores were chosen

b ecau s e t o g e t h e r t h ey co n t a i n r ep r e s en t a t i v e s o f a l l r o ck

t y p es . E x t r a s amp l e s f r o m O u t c ro p 3 8 0 i n t h e o p en -p i t

(Fig . 4 ) he lped c la r i fy the p lag ioc la se and pyro xen e com -

p o s i t i o n a l r e l a t i o n s h i p s i n t h e p e r i d o t i t e -b ea r i n g h y p e r -

s then i t e . Represen ta t ive minera l ana lyses a re g iven in

Table 1.

Fig. 10. Com positional varia tion of pyroxene and plagioclase from

the Caraiba complex compared with island-arc cumulates (Burns

1985), layered intrusions (Wager a nd Brown 1967), massif-type anor -

thosites (Emslie 1985) and the K ope rber g Suite (Mclve r et al. 1983;

Conradie and Schoch 1986)


10/23


11/23

1 2

1 0

361

1 0

8

0

o 6

4

.O_2

I -

0 . 4

0 . 3

0

-

= E 0 . 2

0

0 0

0 0 0 0 0 O 0

0 0 0 0 0

0

0 0

e H y p e r s t h e n i t e s

o o N o r i t es

0%*o

0

o 8

0 8 0 o

9 9 ooO 9

I , O0 I

0 0

o% 9~

O O o

9 0 O 0 ~ 0 ~

~ i

~

o o a : i .

, I , 0 ~ I @ , I

9 9 9 0 9

9 9 0 0 O 9

9 o .

0 O ~ 9

0 oO- 9

0 0 0

0 O 0

0 0 0

0 0 9

0

8 o

0 O 8 0 0

O 0 0 0

0 0

b

i

d

O

0 9

0 0

8o o ~ 76 76 76 o

9 9

9 o O o o o O o e~ e

9 9 9 O ~ w

e o .

9 O 0 ~ O

@

O O

0 O 0 O @ O O

9 9 9

I , O' I , 2 1 ,

0

0

0 O 0 0 0

0

O 0 0 O 0 9

o

0 0 ~ @ 9

0 O 0 O 0 u ~ -

9 .' rp

r I O , O 9 I O Q r

I

o e o o d l

o 9 O ~ I a

0 0

0 0 0 0 o O ~ @ 0

o ~

0 0 0 O 0

0

0

0 0

0

0

I I

0 . 4 0 . 5

mg

0 . 1 8~

0

0 . 0

' ' ' ' ' ' ' ' ~

0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 . 7 0 . 3 0 . 6 0 . 7

mg

to

0

.1

. 01

1 0

n

z

5

1 0 0 0

,m

Z

1 0 0

10

Fig. 12a-f. Summaryof major and trace element variation versus rag-number (rag*) in hypersthenitesand norites from Caraiba (drillholes

FC2516 and NO33, and outcrops 380 and 365N)

All three types may be variably layered.

In Archaean high-grade metamorphic terranes, the

complexes are layered and can be grouped into a mafic-

ultramafic type and a gabbro-anorthosite type (Windley

et al. 1981). The geotectonic environment of format ion of

these ancient complexes is uncertain, but various authors

have suggested similarity with island-arc (Windley et al.

1981), ocean floor (Weaver et al. 1981, 1982) or cont inental

margin (Srikantappa et al. 1984) environments.

In the Proterozoic, the major ity of the mafic-ultramafic

complexes have been emplaced on to the cratons along

megafractures (Windley 1984). They are represented by

mafic dyke swarms, large layered tabular bodies such as

the Great Dyke of Zimbabwe, and layered complexes such

as the Bushveld in South Africa and the Niquelgmdia in

Brazil. An important type of plutonism characteristic of

the Mesoproterozoic is that represented by massif-type

anor thosites (Herz 1969, Emslie 1985, Ashwal 1988) which

may have been emplaced into the continental crust in

orogenic or anorogenic environments (Emslie 1985). Can

any links be drawn with Caraiba?

In Fig. 10, pairs of coexisting orthopyroxene and pla-

gioclase from the Caraiba hypersthenites and norites are

compared with island-arc cumulates, layered intrusions

and anorthosites of the massif-type. Data for the South

African Koperberg Suite (Schoch and Conradie 1990), the


12/23

362

1 5 0 0

1 0 0 0

C

N

5 O

0

0

N N~

9 Hypersthenites

o Norites

o O

~ 0 0 O 0

I t I J

1

2 0

F e 2 0 3

I

3

4 0 0

b

0 0 ,

o % ~

o o 9

o

q j

9 9 9

o 0 0 ( % ) ~ I I ' .

O O o ~ 9 .

o ~ F e 2 0 3

~ 0 0 o o 9 @

I I f

1 0 2 0 3 0

1 2 0 0

1 0 0 0

8OO

6 0 0 >

4 0 0

2 0 0

0

4 0

O

O,I

O

M .

4O

0

3O

O

o

o o

o O o

1 0 o

0

o

o o

o

o

. . . . . . . . i

1 1 0 0

. o.

9 ~ ' ~ I E "

9

o o 0

O o o

9 @ @

~ o ~

0 0

0 0 O 0

Cr

i i

1 1 1 1 O 1

Fig. 13a-d. Major and trace element variation n hypersthenitesand norites from the Caraiba mine

1 0 0 0 0

1 0 0 0

1 0 0

C r

. . . . . . . 1 0

1 0 0 0 0

closest analogue of Caraiba, are also plotted for compari-

son. Most of the Caraiba rocks plot on the fields for

massif-type anorthosites and the Koperberg Suite. The

orthopyroxene compositions of the Caraiba samples va-

ries less than the plagioclase but no marked positive

correlation is seen like that commonly observed in layered

intrusions. The mineral chemistry of the Caraiba hyper-

sthenites and norites then is similar to that observed in

massif-type anorthosites, and unlike that seen in island-

arc cumulates and tholeiitic layered intrusions. Analogy

between the Koperberg Suite and massif-type anor-

thosites has already been drawn Conradie and Schoch

1986), hence it is useful to test whether models for the

petrogenesis of massif-type anorthosites can be applied to

the Caraiba rocks. First we examine the constraints from

whole rock geochemistry.

G e oc h e m is t r y

Major, trace and rare-earth element analyses of represen-

tative hypersthenites, melanorites and norites from drill-

holes FC2516 and NO33, and outcrops on benches 380,

365N and 395S see Fig. 4 for location) are given in Tables

3a and 3b. It is evident that the typical hypersthenite

or norite rocks from the different localities within the

complex are not significantly different from each other,

and that the chemical variations observed are mostly

controlled by the relative proportions of contained min-

erals. The hypersthenites have higher Fe203, MgO, Cr,

Cu, Mn and Ni, and less A1203, CaO, Na20, Sr and Zr

than the norites. Also, the former are generally more

enriched in Rb, K 20 , Ba, Zn and V, and more depleted in

Nb, TiO2, rare earth elements REE) and P205 than the

latter. Hypersthenites and norites from FC2516 are slight-

ly richer in MgO, Cr, Ni, V, Rb, Ba and K20 than the

equivalent rocks from NO33, reflecting the mineral chem-

istry.

The calculated CIPW norms using Fe203/FeO = 0.15)

of all rocks show very low contents of diopside. Indeed,

the hypersthenites and norites contain significant propor-

tions of normative corundum, indicating saturation with

respect to A1203, and further implying derivation from an

Al-rich magma, as also suggested by the pyroxene com-

positions. The Al-rich characteristic of the Caraiba rocks

is further shown by a plot of A1203

vs

tFeO Fig. 11),

which also emphasises their Fe-rich nature. Plots of

rag

number [MgO/ FeO + MgO) using FezO3/FeO = 0.15]

against major and trace elements Fig. 12), and the posi-

tive correlation between element pairs Zn-Fe, V-Fe, Cr-Fe

and Cr-Ni Fig. 13) reveal that Ni, Cr, MnO, Zn, V and

Fe203 decrease with fractionation, whereas Nb, TiO2,

P2 5

and CaO increase.

Good positive correlation not illustrated here) is


13/23

3 6 3

4 0

3 0

2 0

0

1 0

1 0 0 0

t O 0

1 0

1

0

1

.01

0

0

0

0

0

.-

0

~0

0

4

0

0 0

0

* s

0

0

0

0

0

0

O 0

s

0

* FC2516-Hypersthenites I

9

NO33-Hypersthenites

o FC2516-Nori tes ]

o NO33-Nori tes J

. , , . . , . . , < > = :

o

9 0 ~ 0

O 0

0 0 0

9 0

O 0 0 0

0

0 O

0

0

0

8

~

0

0

0

,I

,I

@

9 *+>* 9 ~ 9 M

~ o*o 00o . .

,01, 0

0

O 0

0

0

@ @

@

o : o

9 o o .

0 0 $ 9 1 4 9

o41, I. e 9

O 9

0 9 O 9 0 0

0

b

1 0 0 0

0

9

d

0

i

f

@

@ O 0

e

9 9

0

@ 9

0 0 @ 0 ~ ' ~ 0 0 " ' ~ 0 0 " "

3

o . ~ ~o r o

o

0 9

0 0

t . ,+ :

S * * r 1 6 2

o+>. ~ . o+O . d ,.

0 0

+,,41

0 Q 0

0

0

o

o 0

o 8

0 0

0

r i i i I

,I

0 0 9 ~ 9

O e ~ 9 0 0 0

0 0 0

0

0 0

o

0 0

~ 0

~

, =

E

0 . 5

F i g . 1 4 a - f . V a r i a t i o n o f r a g -n u m b e r ( m g * ) , m a j o r a n d t r a ce e l e m e n t s i n r e l a ti o n t o c o p p e r c o n c e n t r a t i o n i n s a m p l e s f r o m d r i l l h o l e s F C 2 5 1 6

a n d N O 3 3

observed between e lement pairs Nb-Ti , A1-Ti , K-Ba, Rb-

Ba, Mg-Fe , K-Rb, Ca-Sr and to le ss extent a lso Ti-P. T i

corre lates negat ive ly with V and Zn. Al l these observa-

t ions indicate that Nb is main ly he ld in i lmenite and

poss ib ly a lso in the brown mica ( see h igh Nb value in

biot i t i te 395S-B2 in Table 3 b) . V, Cr and Zn are mo st ly

partit ioned into magnetite, K, R b and Ba into bro wn mica,

and Sr into plagioclase (Ba also in norite plagioclases) .

The increase of T i with increas ing A1 also suggest s that the

amount of i lmenite increases in the most fract ionated

rocks , i. e. the nor i tes. Th e negat ive corre lat ion betw een T i

and V and Zn, on the other hand, indicates that ma gnet i te

is an ear ly fract ionat ing phase a lon g w ith hypersthene and

sulphides . This agrees very we l l with the h igh modal

propo rt ions o f su lphides an d ma gnet i te in hypersthenites .

Foc using o n the behaviour o f copper in the hypersthenites

and nor i tes , p lot s of Cu vs Fe , Ni , Cr , V, K and rag*

(Fig. 14) reveal the following:

1 . The h ighest Cu contents are found in the hyp er-

sthenites as expected from f ie ld and petrograp hic evid-

ence;

2 . T h e C u vs m g* an d C u vs F e 203 p lo t s sh ow t h e N O 33

hypersthenites are geochemica l ly s l ightly more evolv ed

and more Cu-r ich than the ir FC2516 counterparts .

This i s in agreement with the enhanced su lphur so lubi l -

i ty with increas ing Fe content in maf ic magmas, as

determined exper im ental ly (Haugh ton e t a l. 1974) .


14/23

T

e

3

R

a

v

a

y

o

h

h

e

H

y

a

n

e

N

o

,

~

C

o

F

2

F

N

O

3

N

O

3

N

o

2

7

3

3

8

0

9

2

T

H

y

H

y

H

y

H

y

S

O

2

4

5

4

4

3

2

4

7

T

O

2

0

3

0

3

0

8

0

1

A

1

3

4

9

4

1

4

5

2

6

F

2

3

2

2

3

7

1

6

M

n

O

0

3

0

3

0

4

0

4

M

g

O

2

0

2

7

1

6

1

6

C

a

O

0

9

0

6

1

4

7

8

N

a

O

0

9

0

1

0

5

0

2

K

2

0

6

0

8

0

5

0

1

P

O

5

0

0

0

1

0

2

5

2

T

a

9

8

9

7

9

8

9

4

T

e

e

m

e

p

m

)

d

e

m

i

n

b

X

R

F

V

2

3

6

1

C

r

1

1

2

4

N

i

9

1

9

3

C

u

1

1

4

4

Z

4

4

6

3

G

a

2

2

2

1

R

b

2

4

1

6

S

5

1

7

7

Y

1

1

1

1

Z

6

2

4

1

N

b

1

1

3

5

0

8

3

B

3

1

1

5

L

<

2

1

0

4

3

1

6

C

4

8

5

0

2

3

3

N

d

0

6

2

4

8

5

2

T

1

2

2

3

4

8

3

N

i

C

u

0

0

0

0

0

0

0

0

R

e

h

e

e

m

e

d

e

m

i

n

b

C

P

E

3

N

7

B

H

y

4

6

0

4

4

4

2

7

0

3

1

6

1

6

0

3

0

3

0

2

9

5

3

2

1

4

4

2

1

3

1 1

1

5

8

1

8

8

1

1

5

0

0

3

N

1

2

H

y

2

2

1

2

6

3

7

0

3

1

3

0

9

<

0

2

0

1

0

1

8

2

1

6

2

1

1

3

3

6

1 1

2

3

7

4

9

7

6

3

0

4

3

6

0

0

3

1

A

H

y 4

5

0

7

7

8

2

1

0

2

2

0

1

9

0

3

1

6

6

0

0

9

4

4

1

6

9

3

2 9

3

1

2

O

2

1

3

1

6

3

1

0

4

0

3

0

0

3

1

B

H

y

4

7

0

8

3

6

2

0

0

3

1

5

1

5

0

1

1

1

0

6

9

4

3

2

1

2

4

2

4

1

1

2

O

1

1

6

1

3 2

1

7

0

0

3

C

H

y

4

2

0

2

3

9

2

0

0

3

2

4

0

4

0

2

0

3

0

0

9

8

2

2

2

1

4

2

1

1

8

2

1

2

1

5

2

3

0

1

F

2

2

N

o

4

2

0

6

6

3

2

0

0

3

1

0

2

3

0

8

0

2

0

3

9

9

3

3

1

2

4

2

4

1

1

8

2

6

5

6

2

4

1

7

1

5

0

0

F

2

2

2

N

o

4

4

1

1

2

7

1

3

0

1

4

0

8

2

4

0

0

5

0

5

9

9

1

2 3

5

1

2

1

7

1

2

5

3

1

3

6

4

5

0

0

L

4

0

3

4

1

2

1

0

4

9

2

7

3

9

1

3

2

7

1

5

3

9

C

7

4

6

8

2

9

3

0

1

3

6

7

9

1

3

7

5

2

2

7

6

7

P

0

8

7

1

3

2

4

5

1

7

1

0

1

2

5

4

0

6

3

3

9

0

N

d

3

2

2

3

1

8

1

0

7

5

3

9

5

5

2

1

2

1

1

1

3

2

S

m

0

8

4

4

2

9

4

6

2

0

1

3

1

6

4

9

0

6

3

2

7

9

E

0

2

0

2

0

6

5

2

0

3

0

1

0

3

0

6

0

0

0

8

2

5

G

d

0

7

3

4

2

4

3

8

1

9

1

0

1

6

4

3

0

6

2

8

6

4

D

y

0

9

2

2

2

2

9

1

5

0

9

1

5

2

6

0

7

2

3

3

6

E

0

7

1

1

1

0

9

2

0

9

0

6

1

1

1

4

0

5

1

5

1

5

Y

b

0

9

1

2

1

3

6

4

1

1

0

8

1

1

1

2

0

8

1

4

0

9

L

0

1

0

1

0

2

0

8

0

1

0

1

0

1

0

1

0

1

0

2

0

1

(

L

Y

b

N

2

8

1

5

5

0

1

8

3

0

2

3

2

4

8

8

2

1

5

0

2

8


15/23

T

e

3

R

e

a

v

a

y

n

e

N

o

a

h

e

A

n

p

d

e

P

a

m

p

b

e

A

m

p

a

b

o

e

B

o

C

o

F

N

O

3

N

O

3

3

N

3

N

3

3

3

N

o

3

6

1

6

A

8

A

2

A

2

C

2

D

T

N

o

N

o

N

o

N

o

N

o

N

o

N

o

N

o

S

O

z

4

0

4

8

4

7

4

9

4

9

4

1

4

4

4

6

T

O

2

1

1

1

8

1

2

1

0

0

2

1

7

1

4

1

2

A

1

1

3

1

1

1

2

1

5

2

6

1

3

1

3

1

F

O

3

1

6

2

8

1

5

1

3

8

0

1

8

1

9

1

2

M

n

O

0

1

0

2

0

1

0

2

0

1

0

1

0

2

0

2

M

g

O

9

6

1

5

5

3

1

6

6

0

6

5

1

9

1

2

C

a

O

5

6

2

7

7

8

7

5

9

4

9

5

6

2

5

0

N

a

2

5

1

4

3

3

1

5

3

0

2

8

1

1

1

2

K

2

2

1

1

2

0

7

0

1

0

2

0

1

0

3

0

3

P

0

1

0

0

0

4

0

1

0

5

1

5

0

3

0

6

T

a

1

0

9

7

9

4

1

9

9

1

9

6

9

2

9

7

T

e

e

m

e

p

m

)

d

e

m

i

n

b

X

R

F

V

2

7

2

2

9

2

3

3

C

r

2

1

1

3

2

6

7

1

N

i

2

3

4

2

2

2

3

5

C

u

5

6

2

1

8

3

5

1

Z

1

3

1

1

1

1

2

2

G

a

2

4

3

2

2

2

2

2

R

b

1

4

2

2

5

3

1

1

S

3

2

5

2

5

4

2

2

Y

9

9

2

7

1

3

1

1

Z

4

5

2

1

1

3

2

3

N

b

7

1

6

4

5

3

3

2

1

8

2

5

4

6

8

B

a

8

6

2

2

8

i

0

1

1

L

1

8

9

2

3

5

9

6

2

3

6

3

1

7

2

1

C

3

7

1

1

7

9

7

6

5

1

1

6

2

7

5

3

N

d

1

2

2

9

4

7

4

5

2

1

7

1

1

4

2

3

T

5

4

3

8

0

2

<

2

6

6

4

8

3

5

1

5

N

i

C

u

0

4

0

0

0

0

0

1

0

0

0

0

0

0

0

0

R

a

e

h

e

e

m

e

p

m

)

d

e

m

i

n

b

C

P

E

L

1

8

1

3

3

7

5

2

0

7

8

1

0

2

1

C

3

4

1

3

7

9

1

6

4

5

1

3

2

5

0

P

4

2

1

6

9

5

1

8

6

1

2

2

4

3

6

5

N

d

1

4

5

8

3

3

6

8

2

2

8

3

1

5

2

7

S

m

2

6

0

9

8

1

4

5

3

1

1

3

6

5

7

E

1

1

0

8

2

1

0

7

1

7

3

0

1

0

1

1

G

d

2

0

0

8

6

6

1

3

4

6

1

8

3

1

4

8

D

y

1

1

0

8

4

1

0

9

2

6

7

2

2

0

2

9

E

0

6

0

5

1

8

0

6

1

1

2

9

1

1

1

3

Y

b

0

6

0

8

1

5

0

6

0

8

1

7

0

9

1

2

L

0

1

0

1

0

2

0

1

0

1

0

2

0

1

0

1

L

Y

b

N

1

7

1

0

1

9

7

7

1

9

2

1

1

1

1

9

N

O

3

9

A

n

5

9

0

0

2

1

4

4

0

1

3

3

8

6

5

0

0

6

6

1

0

2

9

2

2 3

3

6

7 2

5

6

2

O

<

1

2

2

3

3

8

5

4

5

3

9

5

8

3

1

7

6

9

9

4

1

8

6

2

5

7

2

4

3

1

9

3

1

2

0

1

2

1

3 3

G

P 4

5

0

3

3

3

1

3

0

1

3

1

1

4

0

2

0

2

0

0

9

6

7

4

1

1

2

1 1 1 8 5 0

4

2 6 8 5 0

4

3

4

9

5

1

2

8

4

8

1

2

7

0

2

1

2

1

2

0

8

0

7

0

1

3

3

3

N

B

A

m

p

4

9

0

6

1

6

1

2

0

1

1

2

1

3

1

3

0

4

0

0

9

8

2

5

1

4

8

1

4

1

1

1

2

5

3

1 1 1

0

3

0

1

8

6

2

6

3

5

1

7

3

9

1

1

3

5

2

7

1

5

1

6

0

2

3

7

3

B

B

i

o

4

2

3

1

1

8

1

2

0

1

1

0

0

6

0

5

7

5

0

0

1

1

7

1

9 2

3

4

4

6

1

2

1

6 2

7

0

2

5

4

1

2

1

4

5

5

3

0

8

0

1

0

6

0

5

0

2

0

2

0

0

1

3


16/23

366

F

/ ~ o Norites

9 Hypersthenites

A M

Fig. 15. AF M diagram for hypersthenites and nori tes of the Caraiba

com plex. The peridoti tes are show n for compa rison. Fie lds after

Ku no 1968) and Irvine and Baragar 1971)

It had been suggested that the Caraiba complex has the

major element chemistry of tholeiitic suites (Lindenmayer

1981). Fig. 15 shows the AFM diagram for hyperstheni tes

and norites of Caraiba. The rocks clearly plot along

a trend of relatively constant Fe/Mg ratio and increasing

total alkalis, a characteristic of the calc-alkaline series.

The tholeiitic trend obtained by Lindenmayer (1981) re-

sults from the over-emphasis given to peridotites and

gabbroic rocks. Although some hypersthenites and norites

have cumulate textures, which might artificially extend

supposed 'liquid' trends, it is important to note that it

would be difficult to explain the dykes and veins of norites

and hypersthenites, and the mobility of the hypersthenite

groundmass to the breccias, with a liquid component.

Current hypotheses cited to explain the origin of calc-

alkaline suites (or trends), include magneti te fractionation

(Osborn 1959; Gill 1981) and combined assimilation with

fractional crystallization (AFC: DePaolo 1981, Grove and

Baker 1984), while Cawthorn and O'Hara (1976) sugges-

ted that early fractionation of amphibole can generate

calc-alkaline trends. The la tter seems not to be applicable

to the Caraiba norites-hypersthenites as no primary am-

phibole has been observed. The relations between Fe, Ti,

V, and Zn suggest that fractionation involving magnetite

(plus sulphide) could account for the calc-alkaline trend

observed on the AFM diagram. However, the Caraiba

complex is not a normal calc-alkaline suite because

the late 'differentiates' are norites and anorthosites, not

granites.

The mantle normalized multi-element diagrams for the

average compositions of hypersthenite and norites and

various selected samples (Fig. 16) emphasise the strong

mineralogical control on the whole-rock chemistry. Thus,

those hypersthenites and norites with high modal abund-

ances of apatite generally contain high contents of REE,

Y and P (e.g. sample NO33-92.29 in Table 3a and

Fig. 16b, d) confirming that apatite concentrates most of

the REE. Similarly, high modal phlogopitic mica corre-

lates with high contents of Rb, Ba, Ti, Nb and K (e.g.

sample 395S-B2 in Table 3b and Fig. 16b). The coarse-

grained and intrusive hypersthenite of bench 395S (ana-

lyses 395S and 395S-C in Figs. 16a, b) has one of the

lowest modal apatite contents and consequently has low

P and REE abundances on mantle normalized diagrams.

Conversely, it has up to 3 primary phlogopite, reflected

by the high Rb, Ba and K on these diagrams.

In Fig. 16, the plagioclase-poor hypersthenites have

a marked negative Sr anomaly whereas the plagioclase-

rich norites do not. Although Sr partitions strongly into

plagioclase (Philpotts and Schnetzler 1970), it is not easy

to account for the negative Sr anomaly in the hyper-

sthenites unless plagioclase had been involved in their

petrogenesis, for instance through earlier removal of a pla-

gioclase-rich melt from the hyperstheni te source. Both the

hypersthenites and, to a lesser extent, the norites show

marked depletion in Nb relative to the light rare earth

(LREE) and low-field strength elements (LFSE). Such

negative Nb anomalies are characteristic of island-arc

lavas, many continental flood basalts and of the continen-

tal crust i tself(Saunders et al. 1980; Thompson et al. 1983;

Weaver and Tarney 1983,1984). Proterozoic dolerite

dykes commonly show this anomaly (Weaver and Tarney

1983), as do Phanerozoic flood basalts thought to be

derived from the subcontinental lithospheric mantle, such

as the Paran~ from southern Brazil (Mantovani et al.

1985, Hawkesworth et al. 1986). It is reasonable to suspect

then tha t the Caraiba ultramafic/mafic hypersthenites and

norites with this geochemical signature could also be of

sub-continental lithosphere derivation. Rare earth ele-

ments (REE) can be useful petrogenetic indicators in this

regard.

The REE patterns of hypersthenites and norites are

quite fractionated (Fig. 17, Table 3a, b), but variable, with

(La/Yb)N ratios ranging from 2 to 13 in hypersthenites and

from 7 to 27 in norites. The hypersthenites with the

highest and lowest REE abundances are, respectively, the

apatite-rich samples from borehole NO33 (sample 92.29)

and the coarse-grained and intrusive pyroxenite from

bench 395S in the open-pit (sample 395S-C). The hyper-

sthenite dished REE patterns with consistent negative Eu

anomalies (Fig. 17c) would be consistent with removal of

phases such as plagioclase and apatite which normally

concentrate Eu + LREE and MREE respectively. The

norites (Fig. 17a) are more variable regarding the Eu

anomaly, but it is clear that removal of plagioclase from

either the source (i.e. earlier melting episode, as noted

above) or a magma has played a significant role in the

evolution of the Caraiba rocks.

Interesting comparisons can be made with the Koper-

berg Suite in South Africa, and massif-type anorthosites

(Fig. 17b, d). REE pat terns for the Caraiba and the Koper-

berg Suite rocks are much more fractionated than for the

massif-types, especially with respect to the middle- to

light-REE. While this may be because the source for the

Caraiba and Koperberg rocks contained residual phases

with low distr ibution coefficient for these elements, a more

likely explanation is tha t the Caraiba/Koperberg source

had suffered metasomatism that had left it enriched

in more easily fusible LREE- to MREE-rich mineral

phases such as mica and amphibole +_ apatite. The lack of


17/23

367

5 0 0

2 0 0

1 0 0

5 0

2

g s

2

1

[ a A v e r a g e s o f H y p e r s t h e n i t e s

3 9 5 S

0 . 5 - - 9 3 6 5 N

o 3 8 0

0 . 2 9 N O 3 3

t~ FC2516

0 . 1 I I I I I I I I I I I I

C A v e r a g e s o f N o r i t e s

2 0 0

1 0 0

5 0

2

l O

g

2

1

9 ~ 5 N

0 . 5 -

9 3 8 0

o N 0 3 3

0 . 2 -

[ ] FC2516

0.1 t ~ ~ ~ i i ~ i ~ ~ ~

R b B a K N b L a C e S r N d P Z r T i Y

b R e p r e s e n t a t i v e H y p e r s t h e n i t e - B i o ti ti te

z~ 395S-B2

o 395S-C

o NO33-92.29

d R e p r e s e n t a t i v e N o r i t e s

1 3

- - o N 0 3 3 - 9 3 . 2 6

c= FC2516-265.20

i

R b B a K N b L a C e S r N d P Z r T i Y

F i g . 1 6 a -d . M a n t l e n o r m a l i s e d m u l t i - e l e m e n t d i a g r a m s o f C a r a i b a C o m p l e x r o c k s : a a v e r a g e c o m p o s i t i o n s o f h y p e rs t h e n i te s f r o m d i f f er e n t

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

M c D o n o u g h 1 9 8 9 )


18/23


19/23

369

20

15

10

3 .

0 3

~ 5

o 3

~

Q

5

10

Nori lsk Duluth

I = I ~ I

len et al. (1990). A more recent study of the Koperberg

Suite sulphides by Boer et al. (1994) has shown a weak

negative correlation of mean 034S with mean Cu/S ratios

which is interpreted in terms of sulphur devolatilisation

during the high-grade metamorphism. They also recorded

modest 180 enrichment in the mafic host rocks (range in

61SOrock = + 5.9 to + 8.3 0, compared with a 'normal

mantle' value of ca. + 5.7 ___0.3 0), which was taken to

indicate some crustal contamination of mafic magmas.

The correspondence between Caraiba and the Koperberg

suite is close, despite the ca. 1000 Ma difference in age;

Boer et al. (1994) also favour mantle derivation. Crustal

geochemical or isotopic signatures are present in both

suites, and the ques tion remains as to what processes are

responsible for this.

Fig 18 Sulphur isotope data for mafic complexes and the upper

mantle in comparison with the Caraiba sulphides (data after Kyser

1986; Ohmoto 1986; Von Gehlen et al. 1990)

significant HREE depletion suggests that garnet was not

a residual phase during melting. The Koperberg rocks

have higher abundances of REE but both suites exhibit

similar patterns.

Sulphur i sotopes

Sulphur isotopic compositions of the Caraiba sulphide

minerals were used by Oliveira and Choudhuri (1993) to

evaluate the crustal contribution in the genesis of the

sulphides (cf. Lindenmayer 1981). Fourteen samples of

remobilised and disseminated chalcopyrite or chal-

copyrite + bornite from the Caraiba open-pit were ana-

lysed for sulphur isotopes at the University of Calgary,

Canada. They show 634S in the range - 1.495 to + 0.643

with an average value of - 0.604.

Because the isotopic fractionation factors among all

sulphide species are probably within 0.5 o, magmas for-

med by partial melting of the mantle or rocks crystallized

from such magmas should have 6348 values similar to

those of the parental mantle material (Ohmoto 1986).

Sulphur derived from mantle has an isotopic composition

very similar to meteorite sulphur and it is assumed that

the upper mantle as a whole has 634S = 0 _ 3 0 and

the primitive upper mant le an average of + 0.5 0 (e.g.

Ohmoto 1986; Chaussidon et al. 1989). However, many

mantle derived mafic igneous rocks have 6a*s outside this

range (Ohmoto 1986, and references therein), such as the

Duluth complex (0 to + 17 o, Noril' sk intrusive ( + 6 to

+ 16 o), and the Bushveld complex ( - 9 to -6 o).

Although the mantle might be slightly heterogeneous

(Chaussidon et al. 1989), assimilation of crustal sulphur

has been evoked to explain such anomalous values (e.g.

Naldrett 1981; Ohmoto 1986).

Figure 18 shows the Caraiba sulphur isotope data fall in

the range predicted for the mantle and appear not to have

inherited significant amounts of heavy 3 from supra-

crustal rocks. Moreover, the sulphur isotope ratios from

Caraiba are very similar to sulphide sulphur from the

Okiep copper district, South Africa reported by Von Geh-

D i s c u s s i on

Petrogenetic models for the Caraiba complex are con-

strained by the following observations:

1. Field evidence indicates that the complex consists of

multiple dyke-like intrusions and igneous breccias of

hypersthenite, norite and minor anorthosite with

peridotite and gabbro xenoliths, and tha t it is younger

than most high-grade country-rocks: supracrustals,

banded gneisses, migmatitic gneiss, tonalitic ortho-

gneisses, garnet- and pyroxene granulites. It may be

coeval with the youngest granitic to syenitic sheets.

Several hypersthenites and norites are likely to have

been liquids judging from their mode of occurrence.

2. The peridotitic and gabbroic xenoliths have few

counterparts in the surrounding country rocks and are

not linked to the hypersthenites and norites by frac-

tional crystallization, though may conceivably be re-

lated to them by some other process/processes at some

earlier stage of evolution of the complex;

3. The similarities with massif-type anorthosites suggests

a common petrogenesis.

4. The hypersthenites and norites display a major element

calc-alkaline signature and may be linked theoretically

by fractionation processes involving plagioclase, or-

thopyroxene and magnetite ( + sulphide). Local crus-

tal contamination seems not to have been important.

Field, petrographic and geochemical evidence indi-

cates that there have been several episodes of magma

injection, each having different degrees of enrichment

(e.g. hypersthenites associated with the anorthosites

are richer in incompatible trace elements, Fe and Cu);

5. The primary magma(s) must have had a basic composi-

tion, low calcium content, high Fe /Mg ratio and rela-

tively high alumina; also hydrous and enriched in

Ti, Cu, S, K, REE and P to account for the presence of

primary copper sulphides, ilmenite, phlogopite and

apatite, sometimes in large modal proportion. The

source must have been enriched in incompatible

elements, most likely the subcontinental mantle or

lower crust as suggested by the fractionated REE

(LaN/YbN = 2-27), and by negative Nb anomalies on

mantle-normalized diagrams;


20/23


21/23

371

tend to favour a mantle origin. However, in both these

mecha nisms there is the potential to s ubduct mafic ocean

floor with hydrot herma l copper enrich ment into the deep

crust or upper man tle to create the right source character-

istics for a future Caraiba deposit.

Finally, the Car aiba rocks, especially the hyper-

sthenites may have their emplacement controlled by

a regional shear belt. A coarse-grained hypersthenite

dyke has given a Sm- Nd min eral isochron of

1890 _+ 60 Ma (Oliveira 1990b) which is rema rka bly sim-

ilar to faul t-co ntrol led granites (1889 _+ 64 Ma) report ed

by Padi lha a nd Melo (1991) in the Salvador-Curagfi Oro-

gen south of the Caraiba area. Metasomatism in the

mantle or crust is enhanced within shear zones. It is

possible that the Caraiba Complex may result from re-

mobil isa t ion of metasomatised contaminated mantle or

mafic + sediment lower crust during the waning stage of

evolut ion of the early Proterozo ic Salvador-Curaqfi colli-

sional orogen.

Acknowledoements The Cara iba Mine Ltd., and its staff, are warmly

thanked for field logistic support, and Rob Wilson and Nick Marsh

for laboratory support with microprobe and XRF analyses at

Leicester. The Brazilian CNPq and the British CVCP are gratefully

acknowledged for providing financial support for EPO at Leicester.

e f e r e n c e s

Ackermand, D., Herd, R.K., Reinhardt , M., Windley, B.F. (1987)

Sapphir ine parageneses from the Caraiba complex, Bahia, Brazil.

The influence of Fe 2+-Fe3+ distribution on the stability of sap-

phirine in natura l assemblages. J. Metamorphic Geol. 5 : 323-339

All6gre, C.J., Minster J.F. (1978) Quantitative models of trace ele-

ment behaviour in magmatic processes. Earth Planet. Sci. Lett.

38:1 25

Alt, J.C., Shanks, W.C., Jackson, M.C. (1993) Cycling of sulfur in

subduction zones: the geochemistry of sulfur in the Mariana

Island Arc and back-arc trough. Earth Planet. Sc i. Lett.

119:477-494

Andreofi, M.A.G., Hart, R.J., Andersen, NJ.B., Moore, J. (1988) Th,

U, REE-fich anorthosite from Namaqualand, S. Africa. Implica-

tions for metallogenesis and KREEP-basalt . Chem. Geol. 70 : p.69

Ashwal, L.D. (1982) Mineralogy of mafic and Fe-Ti oxide-rich

differentiates of the Marcy anorthosite massif, Adirondacks, New

York. Am. Mineral. 67 : 14-27

Ashwal, L.D. (1988) Anorthosites: classification, mythology, trivia,

and a simple unified theory. J. Geol. Soc. India 31:6-8

Ashwal, L.D., Wooden, J.L., Emslie, R.F. (1986) Sr, Nd, and Pb

isotopes in Proterozoic intrusives astride the Grenville front in

Labrador: implications for crustal cont aminati on and basement

mapping. Geochim. Cosmochin. Acta 50:2571-2585

Barbosa, J.S.F. (1986) Cons titution lithologique et metamorphique

de la region granulit ique du Sud de Bahia, Br+sil. Univ. Paris,

Mem. de Sciences de la Terre 86-34: 401pp

Barbosa, J.S.F. (1990) The granulites of the Jequi6 complex and

Atlantic Coast mobile belt, southern Bahia, Brazil - and expres-

sion of Archean/Early Proterozoic plate convergence. In: Viel-

zeuf, D., Vidal, P. (eds.) Granulit es and crustal evolut ion. Kluwer,

Amsterdam, pp. 195-221

Barbosa, J.S.F., Fonteilles, M. (1989) Caracterizac~o dos prot61itos de

regi~o granulitica do Sul da Bahia-Brasii. Rev. Bras. Geoc. 19: 3-18

Berg, J.H., (1980) Snowflake troctolite in the Hettasch intrusion,

Labrador: evidence for magma-mixingand supercooling in a plu-

tonic environment. Contrib. Mineral. Petrol. 72 : 339-351

Boer, R.H., Meyer, F.M., Cawthorn, R.G. (1994) Stable isotopic evid-

ence for crustal contamination and desulfidation of cupriferous

Koperberg Suite, Namaqualand, South Africa. Geochim. Cos-

mochim. Acta 58 : 2677-2687

Burns, L.E. (1985) The Border Ranges ultramafic and mafic com-

plex, south-central Alaska: cumulate fractionates of island-arc

volcanics. Can. J. Earth Sci. 22:1020-1038

Carlson, R.W., Wiebe, R.A., Kalamarides , R.I. (1993) Isotopic s tudy

of basaltic dikes in the Nain Plu tonic Suite: evidence for enriched

mantle sources. Can. J. Earth Sci. 30:1141-1146

Cawthorn, R.G., O Hara, M.J. (1976) Amphibole fractionation in

calc-alkaline magma genesis. Am. J. Sci. 276:309 329

Chaussidon, M., Albarede, F., Sheppard, S.M.F. (1989) Sulphur

isotope variations in the mantle from ion microprobe analyses of

micro-sulphide inclusions. Earth Planet. Sci. Lett. 92 : 144-156

Clifford, T.N., Gronow, L., Rex, D.C., Burger, A.J. (1975) Geo-

chronological and petrogenetic studies of high-grade meta-

morphic rocks and intrusives in Namaqualand, South Africa. J.

Petrol. 16:154-188

Clifford, T.N., Barton, E.S., Retief, E.A., Rex, D.C. (1990) New

isotope data from the Koperberg Suite and some associated

rocks, O okiep district, Namaqualand, South Africa (abstract).

Geocongress 90, Geol. Soc. South Africa. Cape Town, pp. 96-98

Clifford, T.N., Barton, E.S., Retief, E.A., Rex, D.C., Fanning, C.M.

(1994) A crustal progenitor for the intrusive anorthosite-char-

nockite kindred of the cupriferous Koperberg Suite, O okiep

District, Namaqualand, South Africa. New isotope data for the

country rocks and the intrusives. J. Petrol. (in press)

Coleman, R.G. (1977) Ophiolites. Springer, Berlin Heidelberg, New

York, 229 pp

Conradie, J.A., Schoch, A.E. (1986) Petrographical characteristics of

the Koperberg Suite, South Africa - An analogy to massif-type

anorthosites? Precambrian Res. 31 : 157-188

Conradie, J.A., Schoch, A.E. (1988) Rare earth element geochemistry

of an anorthosite-diorite suite, Namaqua mobile belt, South

Africa. Earth Planet. Sci. Lett. 87:409-422

Czamanske, G.K., Bohlen, S.R. (1990) The Stillwater Complex and

its anorthosites: an accident of magmatic underplating? Am.

Mineral. 75 : 37-45

Delgado, I.M., Souza, J.D. (1975) Projeto Cobre Curar Rel. final.

Goel. Economica do distrito cuprifero do Rio Curar

Brasil. CPRM /DNP M, vol. 30

Delgado, I.M., Souza, J.D. (1981) Projeto Cobre-Cura~fi-Parte 1. In:

Brasil. DNPM-Cobre no Vale do Rio Curaga, Estado da Bahia.

Geologia 20. Se~fio Geologia Economica 3 : 7 149

DeMaiffe, D., Hertogen, J. (1981) Rare earth element geochemistry

and strontium isotopic composition of a massif-type anor-

thositic-charnockit ic body: the Hidra massif (Rogaland, SW

Norway). Geochim. Cosmochim. Acta 45:1545-1561

DePaolo, D.J. (1981) Trace element and isotopic effects of combined

wallrock assimilation and fractional crystallization. Earth

Planet. Sci. Lett. 53:189-202

Dick, H.J.B. (1977) Part ial melting in the Josephine Peridotite. I.

The effect on mineral composition and its consequence for

geobarometry and geothermometry. Am. J. Sci. 227 : 801-832

Emslie, R.F., (1985) Proterozoic anorthosite massifs. In: Tobi , A.C.,

Touret, J.L.R. (eds.) The deep Proterozoic crust in the North

Atlantic Provinces. Reidel, Dordrecht, pp. 39-60

Figueiredo, M.C.H. (1981) Geoquimica das rochas metamorficas de

alto grau do nordeste da Bahia-Brasil. In: Inda, H.A.V.,

Marinho, M.M., Duarte, F.B. (eds) Geologia e Recursos Minerais

do Estado da Bahia, Textos Bfisicos, vol. 4, pp. 1-71

Figueiredo (1989) Geochemical evolution of eastern Bahia, Brazil:

a probable Early Proterozoic subduction-re lationmagmatic arc.

J. South Am. Earth Sci. 2:131-145

Foley, S. (1992) Vein-plus-wall-rock melt ing mechanisms in the

lithosphere and the origin of potassic alkaline magmas. Lithos

28 : 435-453

Fourcade, S., Maury, R.C. , Defant, M.J ., McDermott, F. (1994)

Mantle metasomatic enrichment versus arc crust contamination

in the Philippines: oxygen isotope study of Batan ultramafic

nodules and northern Luzon arc lavas. Chem. Geol.

114:199-215


22/23

372

Fr os t , B . R. , L i nds l e y , D . H . , S i mm ons , C . (1989 ) Or i g i n a n d e vo l u t i o n

o f a no r t h os i t e s a n d r e l a t e d r oc ks . Pe n r os e C onf e r e nc e Re po r t .

G e o l o g y 1 7 : 4 7 4 - 4 7 5

Ga va, A. , Na scim ento , D.A. , Vidal , J .L .B., G hig no ne , J .I ., Ol ive i ra ,

E.P. , Sant iago Fi lho , A.L. , Teixei ra , W. (1983) Geologia . In :

P r o j e t o R A D A M B R A S I L . F o l h a s S C . 2 4 / 2 5 A r a c a j u / R e c i f e .

L e v a n t a m e n t o de R e c u r s o s N a t u r a i s 3 0 : 2 7 3 76

Gi l l , J . B . ( 1981 ) Or oge n i c a nde s i t e s a nd p l a t e t e c t on i c s . Sp r i nge r ,

B e r l in H e i d e l b e r g N e w Y o r k , 3 9 0 p p

Go l dbe r g , S . A . ( 1984 ) Ge oc he mi c a l r e l a t i ons h i p s be t we e n a no r -

t h o s i te a n d a s s o c ia t e d i r o n - r i c h ro c k s , L a r a m i e R a n g e , W y o m -

i ng , Co n t r i b . Mi ne r a l . Pe t r o l . 87 : 376 387

Gr e e n , D . H . , R i ngwo od , A . E . (1967 ) The ge ne s i s o f ba s a l t i c ma gma s .

Co n t r i b . Mi ne r a l . Pe t r o l . 15 : 103 190

Gr e e n , T . H . (1969 ) H i gh - p r e s s u r e e xpe r i m e n t a l s tud i e s on t he o r i g i n

o f a no r t hos i t e . C a n . J . Ea r t h Sc i. 6 : 4 27 - 440

Gr ov e , T . L ., Ba ke r , M. B . (1984 ) Pha s e e qu i l i b r i um c on t r o l s on t he

t ho l e i i ti c ve r s us c a l c - a l ka l i ne d i f f e r e n t i a t ion t r e nds . J . G e ophys .

Res . 89 : 3253 -3274

Ha sui , Y. , S i lva , L . J .H.D. , S i lva , F . J .L. , M an de t ta , P . , M oraes ,

J .A .C .

Ol i ve i r a , J . G ., Mi o l a , W . (1982 ) Ge o l ogy a nd c oppe r mi ne r a l i z a -

t i on o f Cu r a q~ R i ve r Va l l e y , Ba h i a . Re v . Br a s. Ge oc . 12 : 46 3 - 474

Ha ugh t on , D . R . , Roe de r , P . L . , Sk i nne r , B . J . ( 1974) So l ub i l i t y o f

s u l f ur i n m a f ic m a g m a s . E c o n . G e o l . 6 9 : 4 5 1 - 4 6 7

Ha w ke s w or t h , C . J. , Ma n t ov a n i , M. S . M. , Ta y l o r , P . N . , Pa l a c z , Z .

( 1986 ) Ev i de nc e f r om t he Pa r a n~ t o f s ou t h Br a z i l f or a c on t i ne n t a l

c o n t r i b u t i o n t o D u p a l b a s a l t s . N a t u r e 3 2 2 : 3 5 6 - 3 5 9

He r g t , J . M. , Pe a t e , D . W. , Ha wke s wor t h . CJ . ( 1991 ) The pe t r oge n -

e s is o f M e s o z o i c G o n d w a n a l o w - T i f lo o d b a s a l ts . E a r t h P l a n e t .

Sci . Let t . 105:13 4 148

He r z , N . ( 1969 ) Ano r t hos i t e be l t s , c on t i ne n t a l d ri f t, a nd t he a n o r -

t hos i t e e ve n t . Sc i e nc e 164 : 944 947

Hoove r , J . D . ( 1989 ) Pe t r o l ogy o f t he ma r g i na l bo r de r s e r i e s o f t he

Ska e r g a a r d i n t r u s i on . J. Pe t r o l . 30 : 399 - 440

I nda , H . A . V . , Ba r bos a , J . F . ( 1978 ) Ma pa ge o l og i c o do Es t a do da

Bahia . (Escala 1 : 1 .000.000) . Secre tar ia de Minas e Energia da

Ba h i a , Ba h i a

I r v i ne , T . N . ( 1974 ) Pe t r o l ogy o f t he Du ke I s l a nd u l t r a ma f i c c ompl e x ,

s ou t h e a s t e r n A l a s ka . Ge o l . Soc . Am. Me r e . 138 , 240 pp .

Irvine , R.N. , Barag ar, W .R.A. (1971) A gu ide to the ch emica l classifica-

t ion o f the com m on volcan ic rocks . Ca n. J . Ear th Sci . 8 : 523~548

Kh a n , M. A. , J a n , M . Q. , Wi n d l e y , B . F ., Ta r ne y , J ., Th i r l wa l l , M. F .

( 1989) The C h i l a s ma f i c i gne ous c ompl e x : t he r oo t o f t he Koh i s -

t a n I s l a n d A r c i n t h e H i m a l a y a s o f N . P a k i s t a n . G e o l . S oc . A m .

Spec . Pa p. 23 2 : 75 94

Kuno, H. (1968) Dif ferent ia t ion of basa l t magmas. In : Hess , H.H. ,

Pold ervaa r t , A. (eds .) Basal ts , vol. 2 , Wiley New York, pp . 6 23 ~8 8

Kys e r , T . K . ( 1986) S t a b l e i s o t ope va r i a t i on s i n t he m a n t l e . I n : Va l le y ,

J . W. e t a l . (e d s. ) S t a b l e i s o t ope s i n h i gh t e mp e r a t u r e ge o l og i c a l

p r oc e s s e s . Re v . Mi ne r a l ogy 16 : 141 - 164 . Mi ne r a l og i c a l Soc i e t y

o f A m e r i c a

La de i r a , E . A ., B r oc ke s , J .R . H . ( 1969 ) Goe l o g i a da s Qu a d r i c u l a s de

P o c o d e F o r a , E s f o m e a d o , T a n q u e N o v o e L a j e s , D i s t r i t o c u -

p r i f e ro do R i o Cur a q / t , Ba h i a , B r a s i l. Re l a t. Ge os o l s ubm e t i do a o

D N P M , 2 0 9 p p

L a m b e r t , D . D . , S i m m o n s , E .C . ( 19 88 ) M a g m a e v o l u t i o n i n t h e

S t i l l wa t e r c ompl e x , M on t a na . I I . R a r e e a r t h e l e m e n t e v ide nc e f o r

t he f o r m a t i on o f t he J - M r ee f. Ec on . G e o l . 83 : 1109 - 1126

Le a ke , B . E ., Fa r r ow , C . M. , Tow ne n d , R . ( 1979) A p r e - 2000 M yr o l d

g r a nu l i t e f ac ie s me t a m or ph os e d e va po r i t e fr om Ca r a i ba , B r a z i l?

N a t u r e 2 77 : 4 9 - 5 0

Le i nz , V . (1948 ) Ge ne s e da j a z i da de c ob r e de Ca r a i b a , Ba h i a . M i ne r .

Me t a l . 12 : 277 - 278

L i nde nm a ye r , Z . G . (1981 ) Evo l uc ~o ge o l 6g ic a do Va l e do R i o C ur a q fi

e dos c o r pos mf i f i co - u l tr a m~f i c os mi ne r a l i z a dos a c ob r e . I n : l nda ,

H.A.V. , Mar inho, M.M. , Duar te , F .B. (eds . ) Geologia e Recursos

Mi ne r a i s do Es t a do da Ba h i a . Te x t o s Bf is ic os, vo l. 4 : 72 - 1 10

Loferski , P . J. , Arculu s , R.J . (1993) M ul t ip has e inc lu s ion s in p lagio-

c l a s e f r o m a n o r t h o s i t e s i n t h e S t i l l w a t e r C o m p l e x , M o n t a n a :

i mp l i c a t i ons fo r t he o r i g i n o f t he a no r t hos i t e s . Co n t r i b . Mi ne r a l .

Pe t r o l . 114 : 63 - 78

Lof g r e n , G . ( 1974 ) Te m pe r a t u r e i nduc e d z on i ng i n s yn t he t i c p l a g io -

c lase fe ldspar . In : MacK enzie , W.S. , Zu ssm an, J . (eds. ) The Feld -

s pa r s . Ma nc he s t e r Un i v . P r e s s pp . 362 - 375

L o m b a a r d , A . F ., E x p l o r a t i o n D e p a r t m e n t S t af f o f th e O o k i e p C o p -

pe r Compa ny L t d . ( 1986 ) The c oppe r de pos i t s o f t he Ok i e p

d i s t r i c t , Na ma qua l a nd . I n : Anha e us s e r , C . R . , Ma s ke , S . ( e d s . )

Minera l deposi t s of southern Afr ica . Vols . I , I I . Geol . Soc . S .

Africa, pp. 1421-1445

Ma a l oe , S . ( 1976 ) The z o ne d p l a g i oc l a s e o f t he S ka e r ga a r d i n t r u s i on ,

Ea s t Gr e e n l a nd . J . Pe t r o l . 17 : 398 - 419

M a c Le a n , W. H. , Sh i m a z a k i , H . (1976 ) The pa r t i t i o n o f Co , N i , Cu ,

a nd Zn be t we e n s u l f i de a nd s i l i c a t e l i qu i d s . Ec on . Ge o l .

71 : 1049 1057

M a nd e t t a , P . (1982 ) As pe c t o s ge o l og i c os e pe t r oge ne t i c os da s a s s o -

c i a c oe s ma f i c o - u l t r a ma f i c a s de r e g i a o de C a r a i ba , V a l e do

Cura q /~ . B . A . Un pub l i s he d M a s t e r t he s is , Fe de r a l U n i ve r s i t y o f

Ba h i a , Ba h i a

M a n t

genesis of the precambrian copper-rich caraiba

Documents