Rare-earth element and oxygen isotope studies of altered Variscan granites: The western Harz (Germany) and southern Sardinia (Italy)

Chemical Geology, 54 (1986) 53--68 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

53

RARE.EARTH ELEMENT AND OXYGEN ISOTOPE STUDIES OF ALTERED VARISCAN GRANITES: THE WESTERN HARZ (GERMANY) AND SOUTHERN SARDINIA (ITALY) G. M O R T E A N I 1, P. M O L L E R 2 a n d J. H O E F S 3 1Institut fiir Mineralogie der Technische UniversitEt Miinchen, 8046 Garching (Federal Republic o f Germany) 2A. G. Geochemie, Hahn--Meitner-Institut fiir Kernforschung G. m.b.H., 1000 Berlin 39 (Federal Republic o f Germany) 3 Geochemisches Institut der UniversitEt G6ttingen, 3400 GSttingen (Federal Republic o f Germany)

(Received December 3, 1984; revised and accepted July 31, 1985)

Abstract Morteani, G., MSller, P. and Hoefs, J., 1986. Rare-earth element and oxygen isotope studies of altered Variscan granites: the western Harz (Germany) and southern Sardinia (Italy). Chem. Geol., 54: 53-68. Studies on whole-rock samples and mineral separates from granitoids of the Harz Mountains, Germany, and southern Sardinia, Italy, have revealed postmagmatic changes of rare-earth element (REE) concentrations and isotopic composition of oxygen. The REE distribution patterns of the altered rocks do not deviate significantly from the unaltered samples, but the REE patterns of the feldspars and biotites show characteristic changes. Some of the feldspars lost their typical positive Eu anomalies, whereas some of the biotites gained negative Ce anomalies. In the altered samples the quartz--feldspar oxygen isotopic fractionation is either too low or even reversed relative to primary magmatic pairs. The observed effects are discussed as the interactions of the cooling granitoids with either surface or magmatic waters. It is concluded that a high-temperature water--rock interaction with essentially magmatic waters best explains the observed phenomena.

1. Introduction and problem The Variscan g r a n i t o i d s o f t h e B r o c k e n a n d O k e r p l u t o n s (Harz, G e r m a n y ) a n d of t h e Sarrabus, San Vito, Quirra and A r b u r e s e i n t r u s i o n s (Sardinia, Italy) have b e e n selected for a s t u d y o f p o s t m a g m a t i c alterations. In t h e s u r r o u n d i n g s o f these granitic bodies h y d r o t h e r m a l vein d e p o s i t s are k n o w n a n d 0009-2541/86/$03.50

m i n i n g activities are r e p o r t e d since medieval times a n d c o n t i n u e in a few places. T h e B r o c k e n - - O k e r p l u t o n i c c o m p l e x (Fig. 1) is s u r r o u n d e d b y P b - - Z n and f l u o r i t e - b a r y t e vein deposits. Their z o n i n g a r o u n d t h e B r o c k e n a n d t h e Oker p l u t o n s has previously b e e n explained b y decreasing temp e r a t u r e o f t h e o r e - f o r m i n g fluids (ErdmannsdSrfer, 1908; Hesemann, 1930;

© 1986 Elsevier Science Publishers B.V.

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16

Fig. 1. Geological sketch map of the sampling area in the western Harz Mountains with sampling points in squares; details in Table I (after Hinze. 1972). DG = roof granite; PD = porphyrie roof granite; IG = Ilsenstein granite; GD = granite--diorite zone; MG = micropegmatitic granite. Figures in the legend: I = Mesozoic carbonaceous sediments north of the Harz border fault; 2 = Oker granitoids; 3 = gabbro of Bad Harzburg; 4 = granitoids of the Brokken plutons; 5 = Ecker gneiss; 6 = Paleozoic units (after Mohr, 1978). Sampling points represent the analyses as indicated in Table I.

S c h n e i d e r h S h n , 1 9 4 1 ; Wilke, 1 9 5 2 ; Oelsner et al., 1 9 5 8 ) . M o r e r e c e n t l y Nielsen ( 1 9 6 8 ) , W e d e p o h l et al. ( 1 9 7 8 ) a n d MSlier e t al. ( 1 9 7 9 ) discussed a n o n - m a g m a t i c s o u r c e of t h e sulphide m i n e r a l i z a t i o n s . T h e vein calcites, h o w e v e r , have b e e n e x p l a i n e d as crystall i z a t i o n p r o d u c t s o f essentially m a g m a t i c w a t e r s (MSller et al., 1 9 7 9 , 1984}. In t h e immediate surroundings of the outcrops o f t h e O k e r p l u t o n significant mineralizat i o n s are u n k n o w n . S o u t h e r n Sardinia is o n e o f t h e m o s t i m p o r t a n t m i n i n g districts o f Italy. T w o m i n i n g areas c a n b e distinguished, o n e o f t h e m in t h e a r e a b e t w e e n t h e t o w n s o f M o n t e v e c c h i o a n d Iglesias, t h e o t h e r j u s t n o r t h o f t h e S a r r a b u s (Fig. 2). I t is p r o b a b l e t h a t t h e s e g r a n i t o i d s are g e n e t i c a l l y r e l a t e d

:;+-.L

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2. G e o l o g i c a l

.... sketch

map

of souther~

Sardinia

with sampling points indicated in squares: details in Table II (after Biste. 1979). Figures in the legend: 1 = post-Carboniferous rocks: 2 = Paleozoic units: 3 = granitoids of Variscan age: 4 = faults.

t o t h e i m p o r t a n t P b - - Z n vein d e p o s i t s o f M o n t e v e c c h i o a n d G e n n a m a r i - - I n g u r ~ o s u as well as s o m e o t h e r s o f s u b o r d i n a t e importance, the antimony and the fluorite vein d e p o s i t s n o r t h o f t h e Sarrabus, a n d various m o l y b d e n i t e (Salvadori, 1 9 5 9 ) , cassiterite (Biste, 1 9 8 2 ) a n d w o l f r a m i t e (Venerandi, 1 9 6 8 ) o c c u r r e n c e s . In s o u t h e r n Sardinia important sedimentary lead--zinc deposits o f p r e - V a r i s c a n age are also k n o w n (Di Colbertaldo, 1973). Since t h e m e n t i o n e d g r a n i t o i d s w h i c h m a y be r e l a t e d w i t h m i n e r a l i z a t i o n s are " s p e c i a l i z e d " a n d altered t o v a r y i n g degrees, it is t h e goal o f t h e p r e s e n t p a p e r t o discuss w h e t h e r t h e late o r p o s t m a g m a t i c alterat i o n s o f t h e s e m a g m a t i c r o c k s are t h e result o f either surface or m a g m a t i c wa~ers interacting w i t h t h e cooling granitoids. This is done by studying the fractionation of the r a r e ~ a r t h e l e m e n t s ( R E E ) a n d o x y g e n isot o p e s b o t h in w h o l e - r o c k s a m p l e s a n d m i n e r a l separates. R E E a n a l y z e s have b e e n carried o u t b y n e u t r o n a c t i v a t i o n at t h e r m a l f l u x e s o f 1012 c m -2 s -1 at t h e B E R II r e a c t o r , Berlin. The methods of data evaluation have been r e p o r t e d b y Dulski et al. (1977). O x y g e n was e x t r a c t e d w i t h B r F , according t o t h e m e t h o d describ4
55 and Mayeda (1963). 6lSO-values are given relative to SMOW. The analytical reproductibility is within + 0.2%o. 2. Geology

2.1. The granitoids o f the western Harz, Germany The Harz Mountains, northern Germany, mainly consist of strongly folded Silurian to Carboniferous unmetamorphosed sedimentary rocks. Their northern margin is formed b y the Variscan granitic intrusions o f Oker, Brocken, Ramberg, and the gabbro b o d y of Bad Harzburg. Along the northern contact the Permo-Mesozoic rocks transgressively overlie the Paleozoic strata. The Harz Mountains are therefore considered to be a semi-horst, the northern part of which is uplifted by at least 2000 m relative to the sub-Variscan Cretaceous anticline (Mohr, 1978). The Oker pluton outcrops as many small apophyses intercalated with metasediments showing contact metamorphism (Fig. 1). According to Dengler (1956) and Fuchs (1969) the Oker pluton mainly consists of a grey granophyric granite and subordinate amounts of augite-bearing granites, granodiorites, quartz diorites, and biotite augite quartz diorites. Fuchs {1969) concluded that there is no genetic relationship between the granitoids of the Oker pluton and the gabbroic rocks of Bad Harzburg. No conclusive indication of a genetic relationship b e t w e e n the Oker and the Brocken plutons has been established so far (Fuchs, 1969; Vinx, 1982). The granitoids of the Brocken pluton (Fig. 1) form a more or less continuous mass outcropping within an area of ~ 12 × 14 km 2. Seven types of granitic and three types of dioritic rocks were distinguished b y ErdmannsdSrfer (1908) and Chrobok {1965). Granitic rocks form the overwhelming part of the outcrops, the youngest intrusion being the Ilsenstein granite (Miiller, 1978).

In thin sections the granites very often show clouded alkali feldspars, granophyric intergrowths between alkali feldspar and quartz, chloritization of biotites and epidotization of plagioclases. Miarolitic cavities are frequently observed. The granites look pinkish to brick red in discrete parts. The gabbro and norite of Bad Harzburg form a b o d y of ~ 8 km N--S length and 3 km E--W width (Fig. 1). A direct contact between the Brocken pluton and the gabbro and norite complex of Bad Harzburg is found north and south of the Eckergneiss b o d y which shows features of an older medium-grade regional metamorphism, as well as of a younger contact metamorphic overprint (Chatterjee et al., 1960). The age of the Brocken and Oker granites has been found to be 285 + 13 Ma according to a Rb/Sr whole-rock isochron (Schoell, 1970a, b) with an (S~Sr/S6Sr)in ratio of 0.714 + 0.002. The age of the gabbro and norite complex of Bad Harzburg seems to be slightly older than that of the granitic rocks. Schoell (1970b) mentioned that these rocks are possibly ~ 30 Ma older than the granite intrusions. This age relationship is confirmed by gabbro xenoliths found in the Brocken pluton by Sohn (1956). An intrusive contact o f granitic rocks with the gabbro of Harzburg was recently disclosed in the Radau--Oker tunnel near its eastern adit. The high Sr initial ratios of the granitoids favour a crustal origin by anatexis. Other criteria proposed b y Chappell and White (1974), White and Chappell (1977) and Takahashi et al. (1980) do not allow a clearcut differentiation into either I- or S-type granites. According to Sohn (1956) and Miiller (1978) the granitoids are considered to be cogenetic with the gabbroic rocks. Both authors postulated that the granitoid magma was completely molten during the intrusion. Relic minerals are absent. The sampling localities in the Harz area and the respective sample numbers for the granitic rocks are given in Fig. 1 and Table I.

56

TABLE I R E E a n d 6 ~aO d a t a o f w h o l e - r o c k s a m p l e s , feldspars, b i o t i t e s a n d q u a r t z f r o m t h e O k e r a n d B r o c k e n p l u t o n s ; G e r m a n : : Ref. Fig. 1

Sample No,

Material analyzed*

Rock type and c o m m e n t s

REE (ppm)

: ~,7©

La

Ce

Sm

Eu

Tb

Yb

Lv

~ )j(~ ~s~

124 14,5 41.5 185 51.2 12.2 11.9 405 52.2 12.2 15.9 320 61.5 8.5 13.7 207 49.7 8.9 17,5 358 98.6 11.5 15.2 162 90.7 14.6 13.5

240 23.6 78 370 101 19.4 23.7 855 101 19.6 30,8 661 105 13.6 25.6 430 95 15.1 35.1 754 171 15.5 23.7 279 139 20.5 23.3

18.6 1.7 5.4 28.8 9.0 1.7 1.9 74.2 8.9 1,3 2.6 57.8 8.2 0.9 2.4 40.2 8.9 1.0 3.1 70.3 15.1 1.3 2.2 24.1 11.5 1.4 2.0

3.4 4.2 0.19 0.44 1.2 1.9 0.08 0.96 1.5 2.3 0.08 0.5 1,7 2.4 0.23 0.25 I.I 1.6 0.27 0.44 1.9 2.9 0.29 3.4 4.5 4.0 0.2

2.4 0.14 0.46 1.6 1.3 0.21 0.22 I0 1.3 0.12 0,25 6.5 1.3 0.1 0.29 5.1 1.5

0.7

+10,5 ~12 ÷11.4 ~;,7

0.41 10 1.6 0.14 0.19 2.6 0.86

5.8 0,3 ].1 6.1 3.7 0.8 0.99 29 3.5 0.25 0,57 17 3.5 0.25 0.83 14 4~5 0.2 1.5 :~1 3.5 0.35 0.43 6.0 2.2

0.2

0.49

140 13.1 14,1 206 3,0 4.3 3.7

242 17.1 23.3 417 3.6 3.0 6.0

20.5 1.2 2.0 34.6 0.9 0.9 1.0

3,1 4.3 0.5 1.2 0.18 0.15 0.09

2.4 0.18 4.9 0.36 0.26 0.28

7.4 0,38 0.44 9,0 2.9 2.1 2.0

1.0 0.2 0.2 0.~

31.7 59.6 21 16.8 4.0 10.2 244 507 48,6 81.2 11.6 19.2 5.5 9.5 518 1,120 45.8 85.5 17.2 27.2 6.8 13.7 48.3 98.2 10.6 16.7 8.6 17 54.7 98.5 9.8 13.8 7.4 11,1

6,5 3.3 1.2 61.4 9.0 2.1 1.0 98.3 7.5 2.5 1.2 9.3 1.5 1.5 I0.I 1.6 1.2

0.48 0.54 0.04 1.71 0.81 0.97 0.27 1.33 0.82 0.77 0.I 0.85 0.85 0.16 0.88 0.77 0.5

1.4 0.71 0.31 14 1.59 0.46 0.18 12.4 1.3 0,3 0.18 2.0 0.59 0.26 1.7 0.46 0.22

4.6

0.6

1.53 56 5.24 2.88 0.7 45.7 4.2 0,6 0.8 6.8 1.2 1.28 5.6 2.5 t.0

9.9 1.4 3.4

0.99 0.89 0.17

1.7 0.37 0.49

5.2 1.5 1,7

(a) O h e r p I u t o n : 1

2

3

4

5

77.106 77,106 77.106 77.106 77.96 77.96 77.96 77,96 77.95 77.95 77.95 77.95 77.108 77.108 77.108 77.108 77.98 77.98 77.98 77.98 80.27 80.27 80.27 80.31 80.31 80.31 80.31 80.31A 80.31B 80.34 80.34 80.34 80.34 80.37 80.37 80.37

GG KFS QZ BI GG KFS QZ BI GG KFS QZ BI GG KFS QZ BI GG KFS QZ BI GG KFS QZ GG GKFS RKFS QZ BI BI GG KFS QZ BI GG KFS QZ

sy e n o g r a n i t e

syenogranite

syenogranite

syenogranite

syenogranite 19 vol.% Q Z - - F S g r a p h i c intergrowth granite, i m m e d i a t e contact to diabase g r a n i t e , g r e e n i s h plagioclase, r e d d i s h K-feldapax, b i o t i t e c h l o r i t i z e d ( 8 0 , 3 1 A) or intensely chlorltized ( 8 0 . 3 1 B) granite, K-feldspar, reddish

g r a p h i c q u a r t z - - f e l d s p a r intergrowth from a miarole

0.1 1.3 0.45 0.08 4.7 0.46 0.06 2.8 0.4 0.1 2.4 0.5 0,1 4.0 0.4

0.8 0.2

0.7

+10.6 +11.4 +6.1 +14) +9.5 +11.6 +8,0 +9.9 4-10.7 +11.4 ,~6,2 +10.:5 +11.9 +6.0

-12.6 +13.5 ~13.4 +11.8 +9.0 *ID.4 +12.5 ÷13.6 ,,12.0 ~7.5

(b) B r o c k e n p l u t o n : 6

7

8

77.126 77.126 77.126 77.126 80.48 80.48 80.48 80.48 77.123 77.123 77.123 77.127 77.127 77,127 79.4 7 79.47 79.47 79.47 79.48 79.48 79.48

GG KFS QZ BI GG KFS QZ BI GG KFS QZ GG KFS QZ GG FS QZ BI GG FS QZ

I l s e n s t e i n granite~ grey

r o o f g r a n i t e , grey

porphyric roof granite, pink

porphyric roof granite, pink

p o r p h y r i c r o o f g r a n i t e , grey

porphyric roof granite, brick red

51,2 9,8 19.6

87 14.1 30.8

0.17 8.6 0.63 0.22 0.09 8,12 0.57 0.12 0.94 0.13 0.16 0.6 0.2 0.1 0.6 0.1 0.2

+8.8 +8.8 +10.5 +3.7 +11.0 +10,9 +10.8 +10,6 +9.2 +9.5 +9,6 +4.2 -11.2 +12,1 +10.6

57 TABLE I (continued) Ref. Fig. 1

Sample No.

Material analyzed*

Rock type and comments

180

REE (ppm) La

Ce

Sm

Eu

Tb

Yb

bu

(°/00 vs. SMOW)

(b) B r o c k e n p l u t o n ( c o n t . ) : 77.112 77.112 77.112 79.52 79.52 79.52 79.52 79.53 79.53 79.53 79.53 79.54 79.54 79.54 79.54

GG FS QZ GG FS QZ BI GG FS QZ BI GG FS QZ BI

33.5 17 1.4 54.5 11.2 18.7

72.2 34.9 6.6 96 14.1 24.8

7.1 3.0 0.4 10 1.3 1.9

0.72 0.57 0.05 1.0 1.1 0.52

1.6 0.7 0.15 1.7 0.22 0.2

6.2 3.3 0.73 4.9 0.82 0.47

0.86 0.38 0.11 0.6

roof granite, grey

59.6 8.6 7.3

100 11.5 11.6

10.4 1.3 1.4

1.0 0.74 0.35

1.8 0.42 0.25

4.9 2.3 1.2

0.62 0.22 0.15

r o o f g r a n i t e , b r i c k red

50.2 18.4 9.7

84.1 21.5 19.1

9.7 2.5 1.9

0.87 0.85 0.32

1.7 0.3 0.35

5.0 1.1 1.7

0.65 0.11 0.2

roof granite with traces of fluoride roof granite, red

+12.9 +11.2 +11.7

0.08 +4.9 +11.2 +12.4 +10.4 +4.0 +12.3 +13.5 +10.6 +4.6

B l a n k s f o r R E E = b e l o w d e t e c t i o n l i m i t s ; b l a n k s f o r 61SO = n o t d e t e r m i n e d . * G G = w h o l e r o c k ; BI = b i o t i t e ; F S = f e l d s p a r ; K F S = K - f e l d s p a r ; G K F S = g r e e n i s h K - f e l d s p a r ; R K F S = r e d K - f e l d s p a r ; Q Z = quarz.

The ability to sample the Brocken granite is limited by b o t h p o o r outcrops and the border to the German Democratic Republic. Therefore, most of the samples were collected in the western marginal zone. This comprises the Ilsenstein granite (IG), the r o o f granite (DG) and the porphyritic roof granite (PD). A detailed petrographic description of these granites can be found in ErdmannsdSrfer (1908) and Chrobok (1965).

2.2. The southern Sardinian granitoids, Italy The Variscan granites of Sardinia and Corsica form the "massiccio cristallino Sardo--Corso" (crystalline massif of Sardinia and Corsica) (Blasi, 1973). They intrude into pre-Variscan, mainly Cambrian to Lower Carboniferous, metasediments and metavolcanics. Post-Permian faults intersect older structures and produce grabens of varying sizes, the most significant of which is the Campidano. The various granitic rocks form two-third of the crystalline basement of Sardinia. These granitoids are considered to be the source of Sn, W, Mo, F, Pb and Zn mineralizations found in their surroundings (Heetveld and Pretti, 1975). According to Di Simplicio et al. {1974)

three groups of rocks can be distinguished within the Variscan intrusives: Group 1. Gabbros grading into diorites and tonalites. They form rather small bodies enclosed b y larger granitoid masses. In the basic rocks amphibole and biotite predominate over pyroxene and olivine. Their plagioclases often show strongly corroded basic cores and the pyroxenes are surrounded b y amphibole rims. Group 2. Quartz diorites to granodiorites which were formed b y repeated intrusions (D'Amico, 1960; Negretti, 1966; Ghezzo et al., 1973). These rocks host many xenoliths. Group 3. Monzogranitic to leucogranitic rocks are most common. Their only mafic mineral is biotite. White mica is found occasionally. In this study only samples of leucogranitic composition from the Sarrabus, Monte Linas, Arburese and Quirra massifs have been studied. These bodies are located in the south of the island of Sardinia, east and west of the Campidano (Fig. 2). According to Biste (1979) the granitic b o d y of Sarrabus, the largest one in southern Sardinia, is deeply eroded and shows no or only very weak postmagmatic alterations.

58

in contrast to the more basic ~'an:itoids and gabbroic rocks. In the Q--A---P diagram after Streckeisen (1967) they ploi; i~ t,he center of the monzogranitic field. The gram,diorites and the quartz diorites of the second group have a Rb/Sr whole-rock age of 297 ± 6 Ma, whereas the leucogranites show a~ age of only 279 ± 1 Ma (Del Moro e~ ai.. 1975). The (S~Sr/86Sr)in ratio of the rocks o f group 2 is 0.7099 ± 0.0006, that of the leucogranites is 0.7085 :~ 0.0005, The radiometric age dates confirm the i'ield reia-

The Monte Linas massif consists of muscovite-bearing two-mica granites and leucogranites. Greisenization associated with cassiterite, molybdenite and chalcopyrite mineralizations indicate a strong postmagmatic alteration. The Monte Linas granitoids are more highly differentiated than those of the Sarrabus (Biste, 1979). According to Di Simplicio et al. (1974), the leucogranites from Sardinia form a rather distinct group in the A - - F - - M as well as in the K20--Na20--CaO diagram,

OKER whore rock

biotite

3

K -fetdspor

2

E c 0 0

~

(

8

WWI-

LLI LU

o

i

i

i

I

i

~

0

i

i

Lo Ce NdSmEuTb Yb

I

i

I i

i

r

0

r

La Ce Nd SmEuTb Yb

:

La

i i

IONIC radii of REE 3+

i

Yb

©

@

@

~

Ce SmEuTb

BROCKEN whol.e rock

o

3

biotite

3

K -fe[dspar

c o

~5 w1 ~l ~ UJ W*

]

.

0

~

9 79,52

i

i

i

i

i

Lo Ce Sm Eu Tb

i

i

Yb

Lo Ce SmEu Tb

Yb

LO

i Ce

-

, ,

NdSmEuT3

Yb

ionic radn of REE 3+

©

@

@

Fig. 3. REE distribution patterns of whole rocks, biotites and feldspars from the Oker ptuton (a--c) and Brocken pluton (d--f).

59

tions showing the intrusion sequence: gabbro--granodiorites--monzogranites--leucogranites. From isotopic data and petrological considerations Di Simplicio et al. ( 1 9 7 4 ) r e j e c t e d older ideas that the intrusive masses as a whole are formed b y magmatic differentiation processes and suggested that these rocks, at least those of groups 2 and 3, represent undifferentiated, anatectic minima. Again, Brotzu et al. (1983) have already mentioned that the criteria proposed b y Chappell and White (1974), White and Chappell (1977),

and Takahashi et al. (1980) do not allow a differentiation between I- and S-granites. The sampling localities of the southern Sardinian granites of Sarrabus, Monte Linas, Quirra and Arburese are indicated in Fig. 2 and Table II. The sample numbers are identical to those in Biste (1979). 3. Results 3.1. REE distribution patterns 3.1.1. Whole rocks. The five REE distribu-

biotite

MONTE LINAS whore rock

K fe[dspa_~r_r -

(8) 1-

2-

Z®~E u~

0

"~255/256 194

1-

L,U'W LLI

LIJ

o~ 0

I

I

La

Ce

r

[

r

I

Sm Eu Tb

f

I

Yb

La

Ce

i

i

Sm Eu Tb

i

i

Yb

Lo

i

Ce

i

r

i

SmEu Tb

i

Yb

ionic rodii of REE 3÷

@

©

biotite

SARRABUS

4~

whore rock 2-

1-

~ r

I

La

Ce

©

(5

K -feldspar (11)

24'

0-4 i

F

i

SmEu Tb

1

Yb

0

i

I

La

Ce

I

I

I

r

SmEu Tb

Yb

La

Ce

SmEu Tb

Yb

Lonlc radii of REE 3+

@

@

@

Fig. 4. R E E d i s t r i b u t i o n p a t t e r n s o f w h o l e rocks, b i o t i t e s a n d feldspars f r o m t h e M o n t e Linas p l u t o n (a--c) a n d S a r r a b u s p l u t o n (d--f).

60 T A B L E II R E E a n d 6180 data o f w h o l e - r o c k s a m p l e s , feldspars, b i o t i t e s a n d q u a r t z f r o m t h e S a r r a b u s a n d M o n t e Linas p l u t o a s , italy" Ref.

Sample

Material

Fig. 2

No.

analyzed*

(a) S a r m b u s 4 5

6

7

045 048 017 017 017 017 018 018 018 018 027 027 027 011 012 012 012 012 013 014 014 030 031 004 004 025 025 (b) M o n t e

1

2

3

138 138 167 167 167 141 141 141 158 158 158 1 71 139 139 149 149 149 150 150 150 160 160 163 163 164 164 164 194 194 255 255 296 296

Rock types and c o m m e n t s

REE (ppm) La

Ce

,' ~ ( ) Sm

Eu

Tb

Yb

L~

87 83.3 30 24.7 t 2.4 28,9 4.48 8.15 3.09 7.63 343 114 16.9 38 1.84 3.17 2.31 5,91 172 286 1,53 2.89 ].64 4.3 257 556 41.7 69 41,3 71.4 4.3 6.82 4.04 8.56 48 72.6 244 522 26.8 50.3 4.43 8.34 515 1,100 121 267 22.6 44.9 i.57 3.09 2.16 2,13 811 801

26.4 11.7 5.5 1.24 1.51 252 4.1 0.23 2.67 57.8 0.19 0.62 100 13.2 7.4 0.58 0.81 14.1 54.8 5.7 0.82 42.9 50 5.1 0.26 0.24 144

0.76 1.38 0.11 0.07 0.02 0.84 0.35 0.66 0.02 0.9 0.65 0.02 0.86 0.54 0.44 1.17 0,07 0.3 1.64 0.45 0.86 2.61 0.56 0.31 0.52 1.5 1.38

1.2 0.7 1.2 0.3 0.32 22 0.72

11 10 7 4.1 0.58 3.95 0 . 5 6 170 4.9

0.66 11.6

3.43 0.51 61

3.4 3.7 0.35 0.51 28.8 52 2.95 3.1 3.0 6.84 5.37 6.9 2.94 6.78 139 375 22.2 53.4 3.52 4.14 612 1,010 76.8 240 2,48 2.97 0.27 0.72 25.6 55.1 4.37 5.91 244 341 24 44.8 3.32 4.71 469 517 3.64 5.53 0.38 0.54 4.84 8,18 194 430 22.5 56.6 4,77 8.42 367 321 5.81 3.47 0.22 0.53 6.55 7.2 0.26 0.5 4.13 3,84 0.45 1.33

0.42 0.06 10.3 0.5 0.99 0.89 1.54 98 9.2 0.39 300 54 0.47 0.05 13.4 0.62 364 9.0 0,30 238 0.65 0.09 0.89 77 8.3 0.78 215 0.23 0.03

0.12 0.02 0.45 0.84 0.02 0.38 0.03 0.21 0.26 0.54 0.38 0.82 0.06 0.01 0.18 0.61 0.51 0.20 0.58 0.87 0.12 0.03 0.48 0.64 0.31 0.65 1.37 0.69 0.01 0.08 0.01 0.06 0.02

( '/~0 vs~ SMOW)

pluton:

BI BI GG KFS QZ BI GG KFS QZ BI KFS QZ BI BI GG KFS QZ BI BI GG KFS BI BI GG KFS KFS BI

q u a r t zdiorite granite leucogranit~

leucogranite

monzogranite

leucogranite leucogranite

leucogranite leucogranite monzogranite granodiorite l e u c o g r a n i t e , alkali f e l d s p a r rich monzogzanite

0.16 2.7 7.1 0.89 0.14 4.47 9.71 0.75

2.32 77 16 7.0 0.7 t.03 22 28 6.0 1.0 14 41 4.0

5,7

26

20,6 2.1 0.81

0.4~

+10.2 -8,5 +9.1 +11~4 +8.4 +9.6 ÷lO

1,8

0,15 2_3

e9.7 +10.2

0.12

58

+8.3 +4.8

Linas pluton:

KFS QZ GG KFS QZ KFS QZ BI GG KFS BI BI KFS QZ GG KFS BI GG KFS BI KFS QZ KFS BI GG KFS BI KFS QZ KFS QZ KFS QZ

*See n o t e to T a b l e I.

h y d r o t h e r m a l altered granite leucogranite

l e u c o g r a n i t e , alkali f e l d s p a r rich leucogranite

aplite alkali-rich l e u e o g r a n i t e leucogranite

leucogranite

leucogranit e leucogranite leueogranite

granite granite granite

0.05 0.53 0.11

+12.6 +12 1.5

0.22 0.39 20.1 1.5 0.15 24 10.6

9.0 1.0 0.9 2.5 74 6.0

0.18 0.39

0,16 140 38

~11.~ +10 +11.8 +11.3

+11.9 +7 +11.3 -11.5

2,1 0.14 38 1.5

12 1.4 210 11

19

150

0.22 17.2 1.8 0.15 16

0,6 0.4 71 9.0 130

0.1 0.02

0.1

+10.8 +6.7

+12.2 +11,5 +10.8 +6.8 +11.3 +7.2 ÷1].6 +11.7 +10.9 +11.4 +11.7 ÷11.6

61

much more conspicuous negative Eu anomalies. In addition, negative Ce anomalies appear in some of the samples of the Monte Linas granite.

tion patterns of the whole-rock samples from the Oker pluton are all subparallel (Fig. 3a). The absolute REE contents vary within a factor of 3 (Table I). Fig. 3a also includes three REE distribution patterns of granitoid samples which have been collected at the contact with the Harzburg gabbro massif in the Radau--Oker tunnel. The two groups of samples are sympathetic. All patterns are characterized b y a small negative Eu anomaly. The REE distribution patterns of samples from the Brocken pluton are also subparallel (Fig. 3d). Compared to the Okef samples t h e y are less steep and exhibit an increased negative Eu anomaly. The distribution patterns of the Brocken granitoids are definitely different from those of the Oker pluton and the Radau--Oker tunnel. The REE distribution patterns from the Sarrabus and Monte Linas granite samples are rather similar (Fig. 4a and d). They differ from those of the Harz granites by

3.1.2. Biotite. In comparison to the concentration levels in the respective wholerock samples all REE except Eu are enriched in biotite {Figs. 3b, e and 4b, e). The ratio of individual REE concentrations in biotite and the respective whole rock is rather uniform in the Harz granitoids, but varies considerably with those from Sardinia (Table III). Eu ratios of < 1 are only observed in the Oker samples. In all the other samples the Eu ratio is > 1, indicating that Eu is relatively enriched in these biotites, b u t still to a less extent than all the other REE. In the samples from the Harz Mountains Ce behaves like the other trivalent REE whereas it is deficient in the patterns of most of the samples from the Sardinian granitoids.

T A B L E III

l?lBiO Ratio of concentrations of R E E between biotite and melt: ~'WR La

Ce

Nd

Sm

Eu

Tb

Yb

Lu

Oker pluton, Harz: 77.95 77.96 77.98 77.106 77.108 80.34

6.1 7.9 7.2 1.5 3.4 1.5

6.6 8.5 8.0 1.5 4.1 1.7

2.0

6.5 8.2 7.9 1.6 4.9 1.7

0.33 0.8 0.4 0.13 0.15 0.39

6.4

9.4 3.8

3.6 1.5

46 14

27 33 26

5.0 7.7 6.7 0.67 3.9 2.0

4.9 7.8 6.9 1.1 4.0 1.2

6.1 10 8.0 1.4 5.0 1.4

10 3.1

12 1.7

14 30

7.6 2.6

18 16

24 13

2.8 1.5 4.4

18 16 8.9

18 23 14

Brocken pluton, Harz: 77.126 80.48

7.7 4.2

8.5 5.1

Sarrabus pluton, Sardinia: 17 18

28 10

4.0 7.5

Monte Linas pluton, Sardinia: 149 158 164

9.6 28 16

6.2 19 5.7

~2 K-feldspar. The REE distribution p a t t e r n s in K - f e l d s p a r s a r e m u c h m o r e varia b l e t h a n t h o s e in b i o t i t e s ( F i g s . 3c, f a n d 4 c , f). T h e c o n c e n t r a t i o n l e v e l s o f R E E in K - f e l d s p a r s a r e l o w e r t h a n in t h e w h o l e - r o c k samples. The Eu anomalies are either posit i v e , n e g a t i v e o r e v e n z e r o in s a m p l e s f r o m t h e s a m e a r e a ( F i g s . 3c, f a n d 4c~. The patterns of samples 80.35, 80.37 (Fig. 3c) represent K-feldspars from miarolitic c a v i t i e s . T h e s e p a t t e r n s a r e e n t i r e l y d i f f e r e n t f r o m t h e o t h e r R E E p a t t e r n s in t h e 3.1,3.

K - f e l d s p a r s f r o m t h e O k e r p l u t o n shaman ~:, a b a n d in F i g . 3c. T h e r a t i o o f t h e i n d i v i d u a l R~_:~I m ~ f e l d s p a r a n d t h e w h o l e r o c k a r e a l w a y s tess t h a n u n i t y e x c e p t f o r Eu. T h e E u ~ i ~ r a t i o ( T a b l e I V ) is r a t h e r u n i f o r m f o r t h e s a m p l e s of the Oker pluton and varies increasmgly in t h e B r a c k e n , M o n t e L i n a s a n d S a r r a b u s Kf complex. The ElwR ratios (El L a , (_b~ Sm, Tb, Yb and Lu) vary much more than t h o s e o f E u in all c o m p l e x e s .

TABLE IV Kf Ratio of concentrations of REE between K-feldspar and melt: ElwR

La

Ce

Nd

Sm

Eu

Tb

Yb

0.15 0.19 0.11 0.091 0.12 0.086 0.058 0.48 0.059 4.0 0.93

1.5 1.6 1.5 1.2 1.4 1.5 1.2 1.3 1.,1

0.09 0.16

0.07 0.22 0.05 0,052 0,07:1 0.10

0.83

0.72

0.13 0.13 0.26 0.23 0,16 0.14 0.50 0.16 0.33 0.43

1.1 0.74 0.98 1.2 0.88 0.90 1.1.3 1.0 0.94 0.79

0.13 0.23 0.18 0.29 0.27 0.22 0.51 0.30 0.23 0.44

0.18 0,14 0.53

0.23 0.056

0,68 1.9

0.25

0.59

0.049 0.042 0.11

3.1 2.1 2.1

0.067 0.10 0.11

0.08

Lu

Oker pluton, G e r m a n y 77.95 77.96 77.98 77. I06 77.108 80.27 80.31R 80.31G 80.31 80.35 80.37

0.23 0.24 0,1~ 0,12 0.12 0.090 0.56 0,094

0.19 0.19 0.16 0.098 0,13 0.091 0.073 0.50 0.071

1..!

~.2

0,~,~

0.45

0.058 0.077 0.088 0.33

0.37 0.05 0.2a 072

0.25 0.15 !.0

Bracken pluton, Germany: 79.52 79.53 79,54 80.48 79.47 79.4~ 77.126 77.127 77.123 77.! 12

0.2] 0.14 0.37 0.2-1 0.18 0.19 0.66 0.22 0.38 0.51

0.14 0.I2 0.26 0.24 0,14 0.16 0.25 0.17 0.32 0.4~

0.17 0.47 0,22 0.56 0.45 0.29

Sarrabus plut~m, Italy:

17

0.36 0.3 l

18

0.28 0.083

Monte Linas pluton, Italy: 149 158 164

0.15 0.16 0.20

0.11 0,077 0.13

0.11

0.36 0.17 0.35 0.33 0.17 0.14 0.44

63

3.2. Oxygen isotope data 3.2.1. Harz area. Samples 77.95, 77.96, 77.98 and 77.108 from the Oker pluton show a relatively constant oxygen isotope composition, both in whole rock and in its minerals (Fig. 5). In detail the isotope composition of the minerals exhibit the following features: quartz is rather constant (11.7 + 0.3 wt.%), while biotite and especially K-£eldspar show some scattering. Q u a r t z biotite fractionations are normal with respect to magmatic pairs in general (except 77.95 and 80.31), in contrast to quartz--K-feldspar fractionation, where only samples 77.95 and 77.98 are normal. In all other samples the quartz--feldspar fractionation is either too small or even reversed, such that Kfeldspar is isotopically heavier than quartz. This would indicate the absence of i s o t o p e equilibria at magmatic temperatures. Samples 80.31 and 80.34 from the Radau--

I&- OKER 12lOB

BffOCEN

lI lI

I

6

~L c l&

SARRABUS

I~ l

5~

9°

10-

B6-

I

ill. ° QUIRRA ARBURESE Mt. LkNAS

o quertz • K-fe(dspar ~ biotite Fig. 5. ~)1SO-values of quartz, K-feldspar and biotite from the Oker, Brocken, Sarrabus, Quirra, Arburese and Monte Linas plutons.

Oker tunnel macroscopically indicate hydrothermal alteration by the presence of green feldspar and strongly chloritized biotite. The 61SO-values of the whole-rock samples from the Brocken pluton vary between +8.8 and +12.3°/00 . Since only sample 80.48 is from the deepest eroded level of the intrusion, all other samples are from the marginal zone (Fig. 1); this sample may represent the oxygen isotope composition of the bulk granite. All rocks macroscopically look relatively fresh. Quartz and biotite 6~SO-values are quite constant (except sample 77.126), the feldspars vary by more than 5%°. Especially n o t e w o r t h y are the reversals between quartz and feldspar, the feldspar being heavier by nearly 3%° in sample 79.54. The 6 ~SO-values may be related to the colour of the K-feldspar: the redder the feldspar, the higher the 6~sO enrichment.

3.2.2. Sardinian granites. In a recent paper Brotzu et al. (1983) reported oxygen isotope data on Sarrabus leucogranites which show quartz--feldspar fractionations between 0.8 and 2.1. The lower values are normally not observed at magmatic temperatures and may already indicate some isotopic disequilibrium. The samples with low quartz-feldspar fractionations either originate from the northern margin of the Sarrabus body where mineralizations do occur in the country rocks or the sample itself is fluorite-bearing. The Sarrabus samples analyzed are exclusively from the northern margin and show even more disturbed quartz--feldspar fractionations. Furthermore, our data from the Monte Linas, Arburese and Quirra massifs show similar features to those already observed in the marginal parts of the Brocken. Their quartz, biotite and K-feldspar 6180 values are relatively constant in each body, but again quartz--K-feldspar fractionations are either too low or even reversed.

i ::-'~,D B~O

4. Discussion

Hat

Z

..........

Although the extent of losses of REE from the melts b y volatile phases is unknown, it is assumed that the REE contents of the granitic melts are reflected by the whole-rock samples. The REE pattern in Figs. 3 and 4 suggest that biotite collects REE, with the exception of Eu, from the melts leaving behind a residual melt relatively enriched in Eu, b u t considerably depleted in all the other REE. The K-feldspar crystallizing from such a residual melt should show a positive Eu anomaly. This is shown in the K-feldspars from the Oker pluton d o c u m e n t e d b y the continuous band in Fig. 3c, and found in some of the K-feldspars from the Brocken and the Sardinian granites (Figs. 3f and 4c, f). However, some of the K-feldspar samples from the Brocken and the Monte Linas K-feldspars show no or even negative Eu anomalies. The ~.lBi° ~'WR and E1Kf. reflect the different behaviour of Eu and the other REE during crystallization. Since the amount of Eu entering biotite and the absolute amount of biotite is rather small, nearly all Eu of the melt remains available for coprecipitation with plagioclase and K-feldspar. Therefore, the Eu~v~ is expected to be uniform and largely independent of the amount of biotite that crystallized from the melt. This is in contrast to the EtwRKf for E1 = La, Ce, Sm, Tb. Yb and Lu, which is expected to decrease with increasing amounts o f early crystallized biotite. Under conditions of undisturbed batch crystallization and absence of postmagmatic alteration the ElwR Kf and ElwR Bio should show a systematic and intercorrelated trend with the exception of Eu. Any postmagmatic alteration, however, will affect the REE distribution between minerals such as biotite and K-feldspar and thereby the ~:~Bio ~'WR and E lKf ~ - r a t i o s . In Fig. 6 E I ~ is plotted vs. EI~/R. Systematic intercorrelation is only observed for the samples from the Oker pluton. All the other plots show erratic relationships which are assumed to be a strong

,~

.~ ~

Bio

EIwR

~

Southern

.~.~

Sardmla

-

~~.~@~

ROc

!!Jl

020

E

3.2~ Kf ~VtR

"3~,

-:

%2

'50

-

Fig. 6. Plot of ~'WR ~lBio vs. ElwR Kf indicator of alteration processes. Among the samples analyzed those of the Oker pluton appear to be least altered. The relative constancy of the 5 ~80-values of quartz implies that the temperature of hydrothermal interaction was low enough to leave quartz unaffected, probably lower than 450°C. From the measured oxygen isotope composition of the feldspars the oxygen isotope composition of water can be calculated to be between +8 and +11%o at 400°C (O'Neil and Taylor, 1967) (Fig. 7). A lower-temperature estimate may be obtained by the following consideration. Temperature conditions during Carboniferous and Permian times suggest a rather warm climate in the northern hemisphere, limiting the isotopic composition of meteoric waters to be only slightly negative in the 180 ratios, near the oceanic value o f that time and probably of today. Using the experimentally determined fractionation factors of O'Neil and Taylor (1967), the necessary

65

A ~

"ZO: [(]GULS~e:

,n %'°°

Fig. 7. Oxygen isotope fraetionations between K-feldspars (measured) and a coexisting fluid phase (calculated). The used fraetionation factors are from Friedman and O'Neil (1971). For comparison 180 ranges of different water types are schematically shown. temperature of a meteoric water interaction should be slightly above 100°C in order to produce the observed isotopic composition of feldspar. In summary, temperatures of alteration should be restricted to the range between 100 ° and 450°C (Fig. 7). Principally three different processes can be assumed to m o d i f y the original REE contents and oxygen isotope ratios of rockforming minerals: (1) intercrystalline redistribution; (2) alteration by fluids supplied from outside the pluton; (3) alteration by fluids emanating from the residual magma. These alternatives will now be discussed: (1) The intercrystalline redistribution of REE and oxygen isotopes in a quasi-closed system would not require large amounts of fluids. With respect to the REE such a process may be acceptable since the REE show a strong t e n d e n c y to become enriched only in biotite. The source of the supplied REE could be the huge reservoir of REE in the feldspars. However, the drastic changes in :sO contents in K-feldspars contradicts a closed-system mechanism, since the wholerock samples increased in 1sO content (Tables I and II). For example, sample 80.48 which is assumed to represent the least altered material shows an 6 ~80-value which is lower than all the other samples from the Brocken

(Table I). Therefore, water--rock interaction with large amounts of fluids have to be postulated. (2) In the presence of a fluid phase, a retrograde redistribution of lanthanides and oxygen isotopes can be expected until it ceased for kinetic reasons. It has been abundantly documented, for example by Taylor (1974, 1977, 1978), that fluids from outside the plutons are frequently responsible for alteration in granitoids. In most of these cases the interaction results in an lSO depletion of the feldspars. However, as observed in our study, a few cases of an lSO enrichment have been reported (Taylor, 1974; Wenner and Taylor, 1976). As mentioned above, this necessitates rather low temperatures (~ 100°C) for the water-rock interaction (Fig. 7). The granitoids of the Harz and of southern Sardinia intruded at quite shallow levels (Bederke, 1962; Abraham and Schreyer, 1973; Di Simplicio et al., 1974; Winkler, 1978) into highly folded and fractured, unmetamorphosed rocks. This aspect of the geological situation favours an interaction with surface waters. In addition, the reddening of the feldspar and the observed Ce anomalies require oxygen-rich fluids such as surface waters. (3) In a recent paper MSller et al. (1979, 1984) emphasized that the calcite from Pb--Zn vein mineralizations in the Harz area crystallized from essentially magmatic fluids. An admixture of non-reducing metamorphic or even surface water, however, cannot be excluded. The arguments for the presence of magmatic waters in calcite genesis are: (a) very high absolute REE contents of vein calcites and REE distribution patterns characteristic for high temperatures; (b) absence of Eu and Ce anomalies similar to occurrences in carbonatites; (c) absence of negative Eu anomalies in calcite intercalated with sphalerite which strongly suggests different sources for the CO2 and the H2S; if the H2S is derived from

surface waters, the carbonates originate from a deep non-reducing source; fd) 5~3C-values of carbonates correspond with magmatic carbon; a mixture of 5t3C from organic material and marine calcites, however, could result in similar values pointing to a metamorphic source. Arguments against a low-temperature alteration are the following: (1) the presence of coexisting K-feldspar and plagioclase in all granitoid samples; (2) undisturbed 87Rb/STSr ratios in wholerock samples, resulting in good-quality isochrons; (3) kinetic reasons. With reference to Helgeson (1974) plagioclase is only stable in solutions with unrealistically high Ca :÷ ion concentrations at low temperatures I~ 100°C). At these temperatures albite wilt form. Therefore, water--rock interactions at such low temperatures should lead to extensive destruction of calcic plagioclase. At higher temperatures (say 300--400°C) plagioclase is thermodynamically favoured. Thus, the presence of both K-feldspar and plagioclase in all samples analyzed demands a hightemperature alteration process. The published Rb--Sr age determinations and their rather small standard deviations (Schoell, 1970a, b; Del Moro et at., 1974) indicate that. the granitoids were not depleted in Sr due to destruction of the plagioclase. Under conditions of low-temperature alteration the Rb--Sr distribution is expected to be disturbed resulting in a large scatter of data points in the respective Nicolaysen diagrams. The third argument is a very general one. With decreasing temperatures the exchange of isotopes and ions decreases drastically. It becomes difficult to understand the extent of the oxygen isotope and REE exchange observed in the samples. The above geochemical considerations favour a high-temperature water--rock interaction. Since magmatic fluids in equilibrium with granitic rocks are generally character-

ized by ~ L~O-values between +6 an(i ~]()!~-,,~ an alteration temperature between :~00~ anti 400°C results from Fig. 7 5. Conclusion The observed phenomena of ~teration in the granitoids from the Harz Mountains and southern Sardinia can be explained by: (1)low,temperature water--rock interaction with surface waters, or (2) high-temperature water--rock interaction with essentially magmatic waters. The REE and oxygen isotopic distribution of minerals separated from altered granites alone do not allow one to unequivocally differentiate between the two possibilities. Arguments in favour of a high-temperature alteration are the presence of coexisting K-feldspar and plagioclase as well as an undisturbed Sr--Rb distribution in all granitoid samples analyzed. Furthermore, as in the Harz area contributions o f magmatic waters are indicated by characteristic features in the vein mineralizations of the country rocks, the high-temperature interaction seems to be more probable. The emanating fluids must have passed through the outer portions of the solidified granites. The most altered samples from Sardinia were collected in areas where mineralizations are well known in the surroundings. If a genetic link is assumed between miner, alization and alteration (Biste, 1982), then in Sardinia also the high-temperature water-rock interaction appears to be most likely. References Abraham, K. and Schreyer, W., 1973. Petrology of a ferruginous hornfels from Riekensgliick, Harz Mountains, Germany. Contrib, Mineral: Petrol., 40: 275--292. Bederke, E., 1962. Das Alter der Harzfaltung. Neues Jahrb. Geol. Palaeontol., pp. 24--27. Biste, M., 1979. Die Anwendung geochemischer tndikatoren auf die Zinn-HSffigkeit herzyniseher Granite in S/id-Sardinien. BerL Geowiss; Abh., Dietrich Reimer, Berlin, No. A/18, 111 pp.

67 Biste, M., 1982. Geochemistry of South Sardinian granites compared with their tin potential. In: A.M. Evans (Editor), Metallization Associated with Acid Magmatism. Wiley, New York, N.Y., pp. 37--49. Blasi, A., 1973. Batolite granitico Sardo. In: A Desio (Editor), Geologia dell'Italia. Unione Tipografico--Editrice Torinese, Torino, pp. 770--773. Brotzu, P., Ferrini, V. and Masi, U., 1983. Stableisotope geochemistry of Hercynian granitoid rocks from the Sarrabus massif (southeastern Sardinia, Italy). Isot. Geosci., 1: 77--90. Chappe]l, B.W. and White, A.J.R., 1974. Two contrasting granite types. Pac. Geol., 8: 173--174. Chatterjee, N.D., Plessmann, W. and Wunderlich, H.G., 1960. Zur Altersstellung des Eckergneisses im Harz. Neues Jahrb. Geol. Palaeontol. Monatsh., pp. 368--379. Chrobok, S.M., 1965. Untersuchungen zur Geologie des Brockenmassivs (Harz). Beih. Geol., No. 48, 82 pp. Clayton, R.N. and Mayeda, T.K., 1963. The use of bromine pentafluoride in the extraction of oxygen from oxides and silicates for isotopic analyses. Geochim. Cosmochim. Acta, 27: 43. D'Amico, C., 1960. La massa dioritico--quarzifera di Bitti--Onani (Sardegna). Acta Geol., 8: 129-180. Del Moro, A., Di Simplicio, P., Guasparri, G., Rita, F. and Sabatini, G., 1975. Radiometric data and intrusive sequence in the Sardinian batholith. Neues Jahrb. Mineral. Abh., 126; 28--44. Dengler, H., 1956. Der Okergranit im Harz. Geol. Jahrb., 72: 85--116. Di Colbertaldo, D., 1973. Principali risorse del sottosuolo. In: A. Desio (Editor), Geologia dell' Italia, Unione Tipografico--Editrice Torinese, Torino, pp. 956--1008. Di Simplicio, P., Ferrara, G., Ghezzo, C., Guasparri, G., Pellizzer, R., Ricci, C.A., Rita, F. and Sabatini, G., 1974. I1 metamorfismo ed il magmatismo paleozoico nella Sardegna. Soc. Ital. Mineral. Petrogr., 30: 979--1068. Dulski, P., Parekh, P.P. and MSller, P., 1977. Resolution of the two phases of limestones with respect to their trace element contents. J. Radioanal. Chem., 38: 315--325. Erdmannsd6rfer, O.H., 1908. Bau und Bildungsweise des Brockenmassivs. Jahrb. Preuss. Geol. Landesanst., 26: 379--405. Friedman, I. and O'Neil, J.R., 1977. Compilation of stable isotope fractionation factors of geochemical interest. U.S. Geol. Surv., Prof. Pap. 440-KK. Fuchs, W., 1969. Untersuchungen zur Geologie und Petrographie des Okerplutons im Harz. Clausthaler Tekton. Hefte, 9: 111--185. Ghezzo, C., Guasparri, G. and Sabatini, G., 1973. Relationi fra rocce granitiche e metamorfiche

nella Sardegna centro-settentrionale, Nota III. Le introsioni della zona Orotelli--Bolotana-Bultei: Rilevamento con studio mojale. Mineral. Petrogr. Acta, 19: 155--186. Heetveld, H. and Pretti, S., 1975. Geochemical exploration in Sardinia. Geochemical Exploration 1974. Developments in Geology, Vol. 1. Elsevier, Amsterdam, pp. 119--129. Helgeson, H.C., 1974. Chemical interactions of feldspars and aqueous solutions. In: W.S. MacKenzie and J. Zussmann (Editors), The Feldspars. Manchester University Press, Manchester, pp. 184-217. Hesemann, J., 1930. Die Erzbezirke des Rambergs und von Tilkerode im Harz. Arch. Lagerst~/ttenforsch., No. 46, 92 pp. Hinze, C., 1972. Geologische Karte vom Harz. R.V. Reise- und Verkehrsverlag, Berlin (scale 1:40,000). Mohr, K., 1978. Geologie und Minerallagerst~tten des Harzes. E. Schweizerbarth'sche Verlagbuchhandlung, Stuttgart, 388 pp. MSller, P., Morteani, G., Hoers, J. and Parekh, P.P., 1979. The origin of the ore-bearing solution in the Pb--Zn veins of the western Harz, Germany, as deduced from rare-earth element and isotope distributions in calcites. Chem. Geol., 26: 1 9 7 215. M611er, P., Morteani, G. and Dulski, P., 1984. The origin of the calcites from Pb--Zn veins in the Harz Mountains, Federal Republic of Germany. Chem. Geol., 45: 91--112. Mfiller, G., 1978. Die magmatischen Gesteine des Harzes. Clausthaler Geol. Abh., 92 pp. Negretti, G.C., 1966. Ricerche petrografiche sul complesso granitoide del settore di susachi (Sardegnacentrale). Boll. Serv. Geol. Ital., 87: 145-247. Nielsen, H., 1968. Schwefel-Isotopenverh~:ltnisse aus St. Andreasberg und anderen Erzvorkommen des Harzes. Neues Jahrb. Mineral. Abh., 109: 289--321. Oelsner, O., Kraft, M. and Schfitzel, H., 1958. Die Erzlagerst~/tten des Neudorfer Gangzuges. Freiberg. Forschungsh. C, 52: 1--114. O'Neil, J.R. and Taylor, H.P., 1967. The oxygen isotope and cation exchange chemistry of feldspars. Am. Mineral., 52: 1414--1437. Salvadori, I., 1959. Segualazione di una manifestazione a molibdenite nella zona di Villacidro contributo alla conoscenza della mineralizzazioni a molibdenite in Sardegna. Resoconti Assoc. Min. Sarda, 63: 5--27. Schneiderh6hn, H., 1941. Lehrbuch der Erz-Lagerst~:ttenkunde. Gustav Fischer, Jena, 858 pp. Schoell, M., 1970a. Untersuchungen zur Altersstellung des Brocken-Intrusionskomplexes im Harz. Thesis, Technological University of Clausthal, Clausthal, 72 pp.

Schoell, M., 1970b. K/Ar and Rb/Sr age determinations on minerals and total rocks of the HarzMountains/Germany. Eelogae Geol= HEN., No. 63, 229 pp. Sohn, W., 1956. Der Harzburger Gabbro Geol. Jahrb., 72: 1t7--172. Streckeisen, A.L., 1967. Classification and nomenclature of igneous rocks -- Final report of an enquiry. Neues Jahrb. Mineral. Abh.~ 107: 144-214. Takahashi, M., Aramaki, Sh. and Ishihm-a, Sh., 1980. Magnetite-series/ilmenite-series vs. t-type/S-type granitoids. Min. Geol. Spec. Issue, 8: 13--28. Taylor, H.P., 1974. Oxygen and hydrogen isotope evidence for large-scale circulation and interaction between ground waters and igneous intrusions with particular reference to the San Juan Volcanic Field, Colorado. In: A.W. Hofmann, B.J. Giletti, H.S. Yoder and R.A. Yund (Editors), Geochemical Transport and Kinetics. Carnegie inst. Washington, Publ., 634: 299--324. Taylor, H.P., 1977. Water/rock interaction and the origin of H,O in granitic batholiths. J. Geol. Soc., London, 133: 509--558. Taylor, H.P., 1978. Oxygen and hydrogen isotope studies of plutonic granitic rocks. Earth Planet.

Sci. Lett., 3 8 : 1 7 7 - 2 1 0 . Venerandi, I., 1968. I1 giacimento a molibdeni~e ~ wolframite di Perda Mahori. ]st L o m b a r d o (Rend. Sei.) A, 102: 678--716. Vinx, R., 1982. Das Harzburger (~abbrornassi,,' eine orogenetisch gepr~igte "layered int,r u s i m ( . N. Jahrb. Mineral. Abh., 144: 1--28. Wedepohl, K.H., Delavaux, M.H. and Doe, B.i~, 1978. The potential source of lead in the Permian Kupferschiefer Bed of Europe and some selected Paleozoic mineral deposits in the Federal Republic of Germany. Contrib. Mineral. Petrol_ !35: 2 7 3 281. Wenner, D.B. and Taylor, H.P., 1976. Oxygen and hydrogen isotope studies of a Precambrian granite-rhyolite terrane, St. Francois Mountains, southeastern Missouri. Geol. Soc. Am. Bull.. 8 7 : 1 5 8 7 1598. White, A.J.R. and Chappell, B.W., 1977. bq~rametamorphism and granitoid genesis. Tectonophysics, .13: 7--22. Wilke, A., 1952. Die Erzgiinge yon St. Andreasberg ~m Rahmen des Mittelharz:Ganflgebietes. Beih: Geol. Jahrb., 7: 1--228. Winkler, H.G.F., 1978. Der Pluton des Brockengranit. Aufschluss, Sonderh., 28: 38--45.