Element and isotope geochemical investigations of the Kupferschiefer in the vicinity of “Rote Fäule”, indicating copper mineralization (Sangerhausen basin, G.D.R.)

Chemical Geology, 85 (1990) 345-360 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

345

[4]

Element and isotope geochemical investigations of the Kupferschiefer in the vicinity of "Rote F iule", indicating copper mineralization (Sangerhausen basin, G.D.R. ) J. Hammer j, F. Junge 2, H.J. R6sler 3, S. Niese 4, B. Gleisberg a and G. Stiehl 2 1WB Geochemie, Sektion Geologische Wissenschaften, Ernst-Moritz-Arndt-Universitiit, GreifswaM 2200 (German Democratic Republic) 2Zentralinstitut fiir lsotopen- und Strahlenforschung, Akademie der Wissenschaften der D.D.R.. Leipzig 7050 (German Democratic Republic) 3WB Geochemie Sektion Geowissenschaften, Bergakademie Freiberg, Freiberg 9200 (German Democratic Republic) 4Zentralinstitut J~r Kernforschung Rossendorf Akademie der Wissenschaften der D.D.R., Dresden 8051 (German Democratic Republic) (Received February 10, 1989; revised and accepted February 28, 1990 )

ABSTRACT Hammer, J., Junge, F., R6sler, H.J., Niese, S., Gleisberg, B. and Stiehl, G., 1990. Element and isotope geochemical investigations of the Kupferschiefer in the vicinity o f " R o t e F~iule", indicating copper mineralization (Sangerhausen basin, G.D.R.). Chem. Geol., 85: 345-360. Based upon extensive data on the elemental and isotopic compositions of Kupferschiefer of the Sangerhausen basin and according to results of trace-element and structural investigations of bitumen extracts trends of lateral and vertical distribution of various elements and genetic assertions are presented. Irregular positions of F, V, Se, Au and U in the correlation diagram, peculiarities of the lateral distribution of these elements, abnormally high elemental concentrations in the rocks and in the bituminous extracts as well as alterations discovered in the composition of hydrocarbon groups and their structures support the idea of an influx of oxidizing, metalrich waters moving through the "Rote F~ule" from the Rotliegendes basin into the Kupferschiefer sediment. Isotope geochemical investigations (carbon, nitrogen and oxygen of organic, carbonate and silicate fractions were carried out in order to characterize more precisely the conditions of sedimentation and the regime of diagenesis. The contrary 5~3C curves of Pb-Zn facies and "Rote F~iule" facies and the J3C enrichment in the organic matter of"Rote F~iule" can be explained by different redox conditions during sedimentation and/or diagenesis. Furthermore the decreasing d~SO-values of carbonates of the Rote F~iule also suggest an influx of meteoric waters. The results oppose a final syngenetic to early diagenetic fixation of the metal contents in Kupferschiefer areas in the vicinity of Rote F~iule. The established model of influx of metalliferous fluids, which arose from the Rotliegendes, is of local interest for element input and element redistribution.

1. Introduction The Kupferschiefer of the Central European Upper Permian marine sediments can be regarded as a classic example for a non-ferrous metal-mineralized black shale. Despite the economically important Kupferschiefer exploitation lasting for 800 years, this rock represents today the economically 0009-2541/90/$03.50

most important copper ore of Poland and the G.D.R. Besides Cu also other elements are additionally extracted, such as e.g. S, V, Co, Ni, Zn, Se, Mo, Pd, Ag, I, Re, Pt, Au and Pb. At present, finding and mining of Kapferschiefer deposits in Poland show the existing perspectives in the exploitation of potential ore deposits in the Kupferschiefer horizon. Compared to the total areal extent of Kup-

© 1990 Elsevier Science Publishers B.V.

346

ferschiefer, the number of ore-bearing zones is rather low. Thus, Cu concentrations of > 0.3% occur according to Wedepohl et al. (1978) probably only in 1% of the 600,000-km 2 total area of the Upper Permian basal sediment. Cu ores of economic grade are mainly restricted to near-shore regions of the Zechstein sea and to barren red-colored rocks (Rote F~iule="red rot" hereafter abbreviated as RF) in the Kupferschiefer horizon and in the Zechsteinkalk. Therefore, the establishment of scientific geochemical prospecting criteria is very important from the practical point of view. This paper gives information about the lateral and vertical distribution and about the enrichment of facies-critical elements in order to obtain criteria for successful future exploration. Moreover, a contribution to the clarification of the genesis of anomalous amounts of various elements in the Kupferschiefer horizon shall be presented. The Kupferschiefer is a finely laminated bituminous marl with a mean thickness of ~ 3540 cm. It is the oldest marine platform sediment of the Variscan fold belt of northern Central Europe. It superposes Late Variscan molasse sequences (reaching several thousand meters in thickness) and, in the southern marginal zone of its distribution range, Variscan or pre-Variscan folded basement. A general review of the ore-bearing zone in the Upper Permian sediments is given by Rentzsch (1974) and Wedepohl et al. ( 1978 ). According to a strong lateral zonation of the Cu, Pb and Zn mineralization and barren areas, the Kupferschiefer horizon is divided in the following facies ranges: RF (barren), Cu facies and Pb-Zn facies. In addition to the lateral zoning from areas of an oxidizing environment, the metals follow the well-known vertical zoning pattern of the Kupferschiefer, with Cu lower in the section than Pb and Zn. The lateral and vertical gradients correspond well with the increasing solubility of the sulphides of Cu, Pb and Zn in saline solutions. The finely dispersed sulphide mineralization at the Upper

J. HAMMER ET AL.

Permian basis is not limited to the Kupferschiefer layer, but it is also found in the clastic and in part in the sandy-carbonatic basement rocks as well as in the roof rocks. Proximal to RF the mineralization is concentrated within the Zechsteinkalk and higher parts of the Kupferschiefer, whereas distal to the RF the lower parts of the Kupferschiefer and the Weissliegendes are mineralized. The rocks of the Upper Permian basis show economically important Cu concentrations only in the case of superposing intramontane troughs of the Variscan orogen (Rentzsch, 1976). The regular and spatial association of Cu-rich ore zones and the RF ranges within the seam (yon Freiesleben, 1815; Erzberger et al., 1968; Rentzsch, 1976, 1981; Rydzewski, 1978) is of great interest for clarifying the genesis of non-ferrous metal mineralizations and also of practical importance in prospecting. Among the different possibilities for the origin of oxidized zones are: (a) RF facies resulting from syngenetic and/or dia-epigenetic inflow of oxidizing waters from bottom walls or hanging rocks, respectively; and (b) RF as a syngenetic silent and/or shallow-water facies within the normally developed Kupferschiefer. This complicates the use of RF as a promising mining guide. Only few RF ranges contain ore-enriched zones at their flanks. The following features are believed to be essential indicators of a syngenetic genesis of the RF: seam convergences, decreasing contents of organic carbon and sulphide sulphur, the presence of corals and brachiopoda faunal associations within the Kupferschiefer, characteristics of landslips and variations of thickness within the Upper Permian limestone (Jung et al., 1974; Paul, 1982). On the other hand, variations in the primary metallogenic distribution [e.g., formation of cementation zones, layer oxidation ("Schichtoxidation")], the existence of replacement fabrics and replacement paragenesis and the non-equilibrium of the sulphur isotope chemistry for pyrite and the copper sulphides (Marowsky, 1969; Rentzsch,

KUPFERSCHIEFER IN THE VICINITY OF "ROTE FAULE", INDICATING Cu MINERALIZATION

1976, 1981 ) indicate characteristic features of a diagenetic to epigenetic formation of the RF. The latter may be caused by an inflow of oxidizing waters in the Kupferschiefer or in a preexistent syngenetic RF facies. The close association between the RF and metal zones [after Jowett ( 1987 ) regular zoning parallels the RF contact ] suggests that RF is an integral part of the metal zoning and was a part of the oreforming process. Various interpretations with respect to the time of the non-ferrous metal mineralizations as well as to the source of the giant metal resources accumulating in the Kupferschiefer [after Rentzsch (1974) > 109 t* o f C u , Pb and Zn] are given by Wedepohl, 1964; Brongersma-Sanders, 1968; Erzberger et al., 1968; Baumann et al., 1984; Kulick et al., 1984. Wedepohl (1964) and Wedepohl et al. ( 1978 ) favoured a syngenetic sulphide precipitation of Cu, Pb and Zn in anoxic marginal basins of Upper Permian seawater. This model of syngenetic origin of Kupferschiefer mineralization includes early diagenetic recrystallization. Most modern genetic models agree that parts of base and precious metals were introduced from an external source and describes a syn- to diagenetic inflow of meteoric metalliferous waters, although much controversy still exists over the timing of Kupferschiefer mineralization (Eugster, 1985; Kucha and Pawlikowski, 1986; Sawlowicz, 1986). Eugster (1985) pointing to the absence of anomalously high element contents in other black shales of the Central European Upper Permian (e.g., fetid shale (Stinkschiefer) and grey salt pelite ) calls for special attention to the important role of the "red-bed" formation superposed by Kupferschiefer as element source. Rentzsch and Kampe (1979) directed the attention to the clear relation between the geochemical specialization of Pb and Zn in the Permo-Silesian molasse sediments and the predominance of Pb and Zn in the Kupferschiefer. Investigations on *1 t = 1 metric tonne= 103 kg.

347

paleomagnetic dating of RF copper marl samples indicate a Triassic age (Jowett et al., 1987) and, according to the authors, pointed to an inflow of waters via RF lasting until the late-diagenetic stage of the Kupferschiefer formation. After Jowett (1986) metalliferous fluids rose up along the flanks of basement highs and overturned in a convective pattern within the Rotliegendes. 2. Samples and analyzing methods Samples were taken from the "Bernhard Koenen" pit, Niederr/Sblingen, Sangerhausen basin, G.D.R. Six profiles were selected by considering the usual facies differentiation for the southeastern piedmont of the Harz Mountains, depending on predominant redox relations during the sedimentation and/or diagenesis of Kupferschiefer. Corresponding to traditions lasting for hundreds of years, the Kupferschiefer includes, with regard to colour, hardness and fabric structure the following seam layers: "Feine Lette" (FL), "Grobe Lette" (GL), "Kammschale" (KS), "Schieferkopf" (SK) and "Schwarze Berge" (SB). A detailed sampling of the Pb-Zn facies (strongly reducing conditions, profiles 1-3 and 1-4), of the Cu facies (moderate reducing conditions, profiles 1-5 and 1-6) and of the RF facies (oxidizing conditions, profiles 5-6 and RF) was carried out. The analysis of Kupferschiefer profiles of different facies positions makes the study of accumulation and dispersion processes of element possible under different redox conditions in the sedimentation and diagenesis environment. Additional, vertical trends of element distribution were observed. The immediate subjacent bed ("Sanderz", SE, up to 3 cm below the sole of the seam ) and the hanging bed ("Dachklotz", DK, up to 20 cm above the top side of the seam) of the non-ferrous metal-bearing layer were also analysed. Jaw-breaker, planet-ball mills and agate-ball mills were used to pulverize the samples up to a particle size of < 63/tm. The following ana-

348

lytical methods were applied for sample investigations: instrumental neutron activation analysis (INAA) (Na, K, Sc, Cr, Fe, Co, Ni, As, Se, Br, Rb, Mo, Ag, Sb, Cs, La, Ce, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Au, Th and U); radiochemical neutron activation analysis (Re); atomic emission spectrometry (Be, B, Ti, V, Cr, Mn, Co, Ni, Ga, Zr, Mo, Ag and Pb); atomic absorption spectrometry (AAS) (Li, Na, K, Ca, Mn and Sr); spectral photometry (P205); energy-dispersive X-ray fluorescence analysis (Cu, Zn, Sr, Y, Zr, Nb and Pb); chemical analysis (SiO2, A1203, FeO, MgO, CaO, S2-, Corg, CO2, Ge, F, Norg , Ninorg); mass spectrometry (isotopes of Pb, C, O and N); column chromatography and infrared (IR) spectroscopy (characterization of bituminous fraction ). Information about the reproducibility and accuracy of the analytical data is given in Hammer et al. (1987). 3. Results

3. I. Element geochemical investigations of whole-rock samples Increasing contents of chemically precipitated CaO and decreasing concentrations of organic carbon within the uppermost layers of the Kupferschiefer have been demonstrated by Hammer et al. (1987). The contents of the chemically precipitated and reducing components decrease in a horizontal direction as the RF facies is approached. In contrast, the contents of SiO2 and A1203 reach maximal values in the investigated RF facies profile. The analytical results for the major and 39 trace elements are given in Tables I and II. Systematic data of the distribution of those geochemically interesting elements like U-Th, Au-Ag, rare earth-elements (REE), Br, Cs, Ta and Hf among the several metallogenic types of Kupferschiefer have been determined for the first time. For comparison Table II also shows averages for ordinary shales and black shales

J. HAMMER ET AL.

(see also Fig. 1 ). The concentration ranges of the elements in the narrow neighbouring Kupferschiefer profiles and the extent of vertical zoning of the element distribution are remarkable. The comparison (Fig. 1 ) shows many elements with considerably higher concentrations in the Kupferschiefer (e.g., Co, Ni, As, Se, Ag, Sb, Re, Au, U, but also Cu, Pb, Zn). The higher concentrations of these sulphophile, biophile and oxyphile elements compared with the "black shale average" signify geochemical peculiarities of the environment, the source and the mineralization processes of the Kupferschiefer. The REE (La, Ce, Sm, Eu, Tb, Yb and Lu ) as well as the elements Sc, Cr, Ga, Rb, Sr, Mo, Hf, Ta and Th occur in normal concentrations in comparison to black shales. The elements Li, Be, B, F, Mn, V, Y, Zr, Nb and Cs show concentrations in the Kupferschiefer with a little higher level. From the graph of the correlation coefficients calculated for the elements with Th and organic carbon (Fig. 2 ), it is possible to distinguish the following groups: (A) Detrital elements and elements adsorptively bound at clay minerals, e.g. Na, K, Rb, Cs, Hf, Ta, Th. (B) Organic- and/or sulphidic-fixed elements, such as Fe, Co, Ni, As, Br, Mo, Ag, Sb, U. (C) Carbonate-fixed group of elements (Mn, Sr). REE and F, Cr, V, Se and also Au could not be unequivocally included into one of the classified groups of elements. A separation of the bonding types "organic" and "sulphidic" is not possible on the basis of the above-mentioned correlations, because both bonding mechanisms have strong relations in space and time. Considerable differences in the contents of Cor~ and S2- are observed in relationship with the RF facies. Thus, the zone of maximal sulphur concentration moves into the handing roof of the Kupferschiefer seam in the immediate vicinity of the RF facies. In contrast, the

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J. HAMMER ET AL.

T A B L E II R e s u l t s o f t h e t r a c e - e l e m e n t i n v e s t i g a t i o n s o f t h e K u p f e r s c h i e f e r s a m p l e s o f S a n g e r h a u s e n b a s i n ( v a l u e s in p p m ) a n d t h e i r c o m p a r i s o n w i t h t h e c o n t e n t s o f a c l a y s c h i s t s a v e r a g e ( V i n o g r a d o v , 1962 ) a n d o f a b l a c k s h a l e a v e r a g e ( H a m m e r et al., 1 9 8 8 b ) E l e m e n t C o n c e n t r a t i o n r a n g e in t h e s e a m l a y e r s F L t o SB Kupferschiefer

P b - Z n facies

Cu facies

R F facies

C l a y schist

Black shale

average

average

(Vinogradov,

(Hammer

1962)

etal., 1988b) 50 2.5 70

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57

-

108

70

-

86

62

-

108

57

-

97

60

Be

2

-

10

2

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7

2

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6

5

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10

3

290

160

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300

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130

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390

130

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1,980

490 750

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-

20.6 5,800 3,700

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-

390 3,000

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21 42

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1,750 470

Cu

20

-76,900

Zn Ga

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-12,100 44

270 100 10

Ge As

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14.5 2,000

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11.4 25 120 < 50 22

-

163 225 270 280 290

Zr Nb

160 13

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320 75

Mo

11

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730

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1,800

Ag Sn

1.6

Sb Cs

1.0 15.5

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29.2

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52

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66.8 37.4 71.1 105

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Pb U

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data.

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3,800 500

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3,800

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2,800

330

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3,300

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370 3,000

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390 - 2,900

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122

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27

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450

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470

42

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95

95

65

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1,400 110

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57 80

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2.5 20.5

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29 11.6 31

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530 9.9

150 500

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9

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3.6 0.48 7.2 1.6 27.3 0.275 15.1 1,100 670

2.6 0.43 5.7 1.2 0.24 <0.02611.1 90 19 -

9.0 2.1 1.4 3.6 0.55 8.5 2.0 4.6 7.3 17.2 580 200

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351

K U P F E R S C H I E F E R IN T H E V I C I N I T Y O F " R O T E F A U L E " , I N D I C A T I N G Cu M I N E R A L I Z A T I O N

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distribution of organic carbon reaches its highest concentration in the subjacent bed of the Kupferschiefer seam, independent of the facies (Figs. 3 and 4). Elements with a clear sulphophile character (Fe z+, Co, Ni, Cu, Zn, As, Mo, Ag and Sb) follow the trend of maximal sulphide sulphur content but the biophile elements (V, Se, Br, Au and U) conform to the vertical distribution curves of organic carbon. The lateral (only partly the vertical) distribution curves of several elements, e.g. V, Se, Au and U, contradict established geochemical laws in the field of exogenous processes. So the elements Au and Se show a distinct lithophile character (Fig. 2) in contrast to their common, clearly biophile or sulphophile characters (Keltsch, 1983; Vilor, 1983; Dissanayake and Kritsotakis, 1984; Judovi~ and Ketris, 1984). The lateral distribution curves of Au show increasing contents in direction to RF facies despite of decreasing concentrations of organic carbon and sulphide sulphur approach-

352

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KUPFERSCHIEFER

IN THE

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INDICATING

ing the oxidizing facies (Fig. 5). The lateral distributions of U differ also from organic carbon curves (Fig. 6). Obviously, the mobility of U during an oxidizing diagenesis is the reason for the lateral and vertical U redistributions within the seam. The existence of cementation zones in the immediate environment of the RF ranges was indicated by Rentzsch (1981) of the basis of detailed ore microscopic and geochemical investigations. The elements V, Se and Br show a behaviour

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r';J ;;''~

SB

k

SK

--

--sBt~l sK

KS

i

GL

°

61.

Cu MINERALIZATION

353

similar to Au and U (Hammer et al., 1987, 1988b). The Kupferschiefer of the Cu and Pb-Zn facies shows higher Co/Ni ratios with values of 0.30-4.90 compared to those of other black shales (Hammer et al., 1988b). The selective concentration of Co compared with the geochemically similar Ni may be caused by peculiarities of supply (source) and by variability of ore mineral paragenesis in the vicinity of RF zones (J. Rentzsch, pers. commun., 1988). The RF profile shows a lower thickness and lower Corg and S2- concentrations than the profiles of Pb-Zn and Cu facies (22 cm instead of 41 cm of profile 1-3). The decrease of thickness especially in layers GL, SK and SB is caused by a decreasing intensity of carbonate precipitation. The more reducing conditions in the Cu and Pb-Zn facies lead to an increasing release of carbon dioxide controlled by bacteria. Fig. 7 shows the diluting effect of carbonate portions for detritally controlled elements, which are fixed to clay minerals. Therefore the indicated three cycles of sedimentation with the Kupferschiefer seam of the Thuringian basin described by Gerlach and Knitzschke (1978) are not caused by epirogenic movements and by related variations in the erosion intensity in the distributive province. Rather, they are a consequence of fluctuations in the position of a chemical barrier which regulates carbonate precipitation (Paul, 1982 ).

FL I

1.4

1.0

0.6

1.4

i

i tO

r i O.6

Sc Sc' Th Th' ~ o---o

~

3.2. Geochemical investigations of the bituminous fraction of Kupferschiefer

' ,~..' ' 1'5' '1'5'

$C I ~"c =14. 2) Sc'(~'~= 22.5)

~'--" Th ('f"-h =12.9 } Th' {1"h'= 20.6)

Fig. 7. Distribution curves of the elements Sc and Th in the Kupferschiefer (Sc, Th = natural concentrations; Sc', Th' = concentrations calculated with respect to a sample composition free of carbonate, sulphide sulfur and organic carbon). The contents which were normalized to the RMS values have been calculated from the values of the five seam layers of the six investigated profiles. A steady distribution for all seam layers, being independent of facies, is observed for the calculated values of composition free of carbonate, sulphide sulfur and organic carbon.

In order to investigate the composition and structure of organic matter in the Kupferschiefer and its role in element precipitation and in the modification of the sedimentary and diagenetic regime, we have carried out benzeneethanol and chloroform bituminous extracts of Kupferschiefer samples. For these investigations INAA, column chromatography and IR spectroscopy were used (Hammer et al., 1988a). In Fig. 8 the results of element geochemical

354

J. HAMMERET AL.

CO

-~

As

Au

Br

Se

Lo

Na

oO

Mo Cr

• •

3

•

,,,

, • o

-¢::

oO

o 0

~

o

o~

•

°°

o

®-2

o .

o°

I •

÷

+

•

+

ooOO

o÷

41

,

®

• •

o o

,b +c ®d

- I

eeo

o

+-3 °00°

+

o

o

•°

O0

=

0

4

o

o o o ®

°o°

o°~

Mn

g

•

~

o °"

o

o

o O0

•

Zn

• S"

°o

•

o

.o

Fe

1

l,

@

Eu

-0

° °

o°

o

o

÷ o o -2

-3

o

r

r

•

T

•

T

®

T

°

1;

Fig. 8. Contents of some trace elements in bituminous extracts of Kupferschiefer samples of different facies [ 1 = P b - Z n facies; 2 = Cu facies; 3 = transition profile; 4 = " R o t e F~iule" facies; a = element content of the chloroform extract; b = element content of the benzene-ethanol extract; c = C l a r k e value; d = m a x i m a l concentration of the recent plankton (calculated with regard to dry residue); e = recent seawater concentration ].

reduced facies

Rote Fdute facies

Fig. 9. Investigated relative portions of bituminous substances in Kupferschiefer samples of different facies using column chromatography ( 1 = acid asphalthenes; 2 = neutral asphalthenes; 3 = p a r a f f i n s / n a p h t h e n e ; 4=low-level aromatics; 5 = polyaromatics; 6 = resins).

investigations of the non-incinerated bituminous extracts are compared with corresponding contents of ocean water and Clarke concentrations and also with maximal concentrations observed in marine plankton (Bowen, 1966; Martin and Knauer, 1973; Bostrrm et al., 1974; Fowler, 1977; Moore and Bostrrm, 1978). The chemical elements Co,

Sb, Au, Se, Mo and Eu show considerably higher concentrations in the Kupferschiefer bitumen than in marine plankton (referring to dry residue). These element accumulations can be explained by diagenetic redistribution and accumulation processes in the sediment (Volkov and Fomina, 1971; Cholodov et al., 1983 ). Another possibility of explanation may be an anomalous external element source, most likely metalliferous fluids which arose from the Rotliegendes continental volcanic and siliciclastic sequences below. The significant increase of the Au and Se contents in the bituminous extracts in direction to oxidizing facies is striking. An increase of more highly polymerized hydrocarbons (resins) and of highly-oxidized components (asphalthenes) in the RF facies may be understood from Fig. 9 and Table III. These show the results of column chromatography of the bituminous components, soluble in chloroform, of one KS sample of the Pb-Zn shale and RF facies. This observation fits with

355

KUPFERSCHIEFER IN THE VICINITY OF "ROTE FAULE", INDICATING Cu MINERALIZATION

TABLE III

Results of the bituminous investigations of the Kupferschiefer samples of different facies position using column chromatography

Amount of bitumen A Total asphalthenes

Reducing facies

Oxidizing facies

(mg)

(%)

(mg)

(%)

202.9 104.1

100 51.3

140.2 99.1

100 70.7

20.8 83.3 98.8

10.2 41.1 48.7

62.7 36.4 41.1

44.7 26.0 29.3

84.5 2.9 4.9 6.5

41.7 1.4 2.4 3.2

22.3 1.5 8.9 8.4

15.9 1.1 6.3 6.0

whereof. acid asphalthenes neutral asphalthenes Hydrocarbon compounds

whereof. paraffins/naphthenes low-level aromatics polyaromatics resins % (paraffins/naphthenes) + % aromatics % resins + % asphalthenes

0.83

'-"-I DK: I

,58 SK

I

KS ..~

GL o ~ I

FL

.-,=

ii~.

SE •

Non:j

ppm

10[)0

0 DK

20C)0 L I I

s~

30[)0 o

4000 -

•

o.,\

\

SK

;4,

KS

,

/

&-,

Gt.

/.,'

\

/

b,Y"

FL SE

/

-4-

•

~pm Nor,ore! "° I 2~o 460 o 1'o 2'0

(C/N)o% 3'0 4'o 50

Fig. 10. Vertical distribution of organic and inorganic nitrogen contents and the (C/N)org ratios in the investigated profiles of Kupferschiefer (for explanations see Fig. 3, further: @ . . . . . . . . . F~iule" facies ).

• = P b - Z n facies; © - - - O

= "Rote

the experience of Timofeev (1968) and Voroncov et al. ( 1986 ), according to which an increase of the relative concentrations of resins

0.30

and asphalthenes is observed in the case of oxidizing diagenesis and catagenesis. However, the expected decreases in the Se and Au concentrations in the oxidized bituminous fractions of the RF facies were not observed. From this fact Au and Se precipitation is deduced, which took place syngenetically and/or epigenetically with respect to the oxidizing processes. The oxidation of organic substance in the RF detected by column chromatography was not supported by the determination of (C/N)org ratios of whole-rock samples (Fig. 10). In contrast to the results of Borchert and Krejci-Graf ( 1959 ), according to which oxidative alterations of organic matter result in the degradation of peptides and in consequence in an increase of (C/N)org ratios, we observed lower values in the RF samples than in the samples of Pb-Zn facies. This observation can be explained only by a primary sapropelitic character of the investigated RF profile and by an oxidation of organic matter after complete conservation of peptides. Investigations by means of IR spectroscopy of the bituminous fractions of the Kupferschiefer show a relative increase of oxygencontaining functional groups and higher-aro-

356

J. HAMMERETAL.

matic structural elements towards the RF facies (Hammer et al., 1988a).

3.3. Stable isotopes In addition to investigations of the oxygen and carbon isotope geochemistry of Kupferschiefer from R6sler et al. (1968) and Marowsky (1969), isotope investigations of organic matter (carbon and nitrogen), of the carbonate fraction (carbon and oxygen) and of the silicate fraction (nitrogen) in facial different Kupferschiefer profiles were carried out. A detailed interpretation of these isotope resuits is reported by Hammer et al. ( 1989 ). The ~3C-values of organic matter in the samples of the Pb-Zn facies are generally lower than the corresponding ~t3C-values of the RF facies (Fig. 11; Table IV). Oxidation processes which have caused a destruction of organic groups rich in 12C are believed to be the essential cause of the increasing 813C-values in the RF facies. The relative ~2C enrichments in carbonates of RF facies, formed or altered by

oxidizing conditions, support this inference (Fig. 11 ). The relatively wide variation range of the ~80 PDB values of the Kupferschiefer carbonates ( - 10 to + 4%0, Fig. 12) can be explained only by an inflow of meteoric water enriched in lighter isotopes via the RF facies. This inference is consistent with small temperature variations during sedimentation and diagenesis, with the existence of constant overburden pressure, and with the absence of dynamometamorphic processes. Fig. 12 shows that the ~ ~3C- and 8 lSO_values of the carbonates of the Pb-Zn facies lie without exception in the range of the marine carbonates. In contrast, the RF samples lie in the range of freshwater limestones in the diagram of Keith and Weber (1964). This and the decreasing 8180-values in the RF point to an inflow of meteoric groundwaters enriched in lighter isotopes through the RF and ascending from the Rotliegendes basin. Table IV contains the isotope variations of nitrogen measured for the first time for the Kupferschiefer

TABLE IV

Oxygen, carbon and nitrogen isotope ratios of the investigated Kupferschiefer samples (values in %o) Seam layer

613Corg

613Ccarb

~ 1SOcarb

~ J5Nots

816Ninorg

+0.7 +1.7 +1.7 -0.5 -1.1 -1.0 -2.7

+31.9 +34.6 +32.2 +28.1 +25.5 +24.8 +21.4

+9.1 +6.6 +7.2 +10.9 +21.3 +22.0 +5.4

+5.9 +5.9 +2.8 +2.4 +3.7 +4.2 +7.1

Pb-Zn facies: DK SB SK KS GL FL SE

-26.0 -26.1 -26.8 -26.6 -25.8 -25.5 -25.6

(+0.9) (+0.1) (+0.4) (+0.0) (+0.6) (+0.0)

(+0.1) (+0.0) (+0.0) (+0.3) (+0.0) (+0.0) (+0.1)

(+0.5) (+0.4) (+0.1) (+0.0) (+2.3) (+0.0) (+0.3)

(+ 1.5) (+0.0) (+0.2) (+1.1) (+0.6) (+0.7) (+1.0)

(+0.1) (+0.8) (+0.1) (+2.1) (+1.7) (+0.3)

"Rote Fiiule" facies: DK SB SK KS GL FL SE

-24.5 (+ 0.2) -24.5 (+ 0.4) -24.7(+0.0) -25.3 (+0.2) -24.5 (+0.1) -22.9 (+0.1) -25.3 (+0.6)

+0.4 (+0.4) - 4 . 3 (+0.8) -5.0 - 2 . 8 (+0.4) -2.6 -2.2 -3.2 (+0.3)

+30.3 (+0. 7) +26.0 (+0.3) +25.5 +23.8 (+ 0.0) +25.3 +25.8 +20.8 (+0.2)

+6.8 (+3.4) + 14.3 (+0.4) +15.7(+0.5) + 18,2 (+0.1) + 17.4 (+0.0) + 12.2 (+0.8) + 7.6

+ 10.1 (+ 1.6) + 7.3 (+2.2) +5.9(+0.2) + 7.0 (+0.9) + 7.1 (+0.1) +6.2 (+0.5) + 7.3 (+0.3)

The determination of No,~ was carried out by Kjehldahl exposure and the determination of Nino~gby HF-H2SO4 exposure. 0t sOand 813C-values are vs. SMOW and PDB, respectively.

KUPFERSCHIEFERIN THE VICINITYOF "ROTEFAULE', INDICATINGCu MINERALIZATION

DK

0',

SB /

,

¢

357

',:

DKI' SB

f

\

SK

SK KS \

GLI

GL

FL

FL

~c~

SE

o

SE

lq

Y4

I'7 zb

z'3

6" ISNorg[%oi

DK

DK

p.

SB SB

/ ./

f

/ ~

/

~--

I

! \

SK

KS KS \\

\.

GL

/

GL ,,,

FL

\

I

FL

~l.

~tIO~

.

.

.

.

SEI

SE -29

'

'

"

-2'3

'

"

613Corg 1%0] Fig. 11. Carbon isotope variations of the carbonates and the organic substances in the investigated Kupferschiefer profiles. For explanations see Fig. 10.

6 ~C [*/u PI:IB ] -6

-2 SK o

-7 -10 -,a ---SE

SEo

"

~

-4

FL.GL

K'S

~

~'

G ~0

4

ro 1./** PDBI

-z

- - - - - - .,,Q.FL

~S %L

,SB

• DK

-2

~

~ ~

oSB

z= ~.-,... "6

Fig. 12.6 ~3C~a~b-6~80 variations of the investigated Kupferschiefer carbonates [dividing line between marine and freshwater carbonates according to Keith and Weber (1964) ]. • = Pb-Zn facies; O = "Rote F~iule" facies. For explanations see Fig. 3. A distinct division into facially different carbonates is observed.

~rSNinorg [ %] Fig. 13. Variation of nitrogen isotope values of organic and inorganic components in the seam layers of the Kupferschiefer. For explanation see Fig. 10.

of the Central Europe. The 615Norg_values range from +5.4 to +22.0%o and show significant differences between oxidizing and reducing facies when comparing particular seam layers (Fig. 13). In contrast with the monotonically decreasing t~lSNorg-values from bottom to top of the Pb-Zn facies, the curves of the RF facies show increasing d 15Norg.values to the KS seam and small decreasing 615No,g-values to the roof. The contrary trends of the ~13Co~g-and 315Norgvalues in the RF facies, in comparison with the Pb-Zn facies, point to different conditions of diagenesis and/or epigenesis in both facies ranges. The isotope variations of inorganic nitrogen (NH4-nitrogen, fixed in clay minerals and phosphates) are significantly lower than the corresponding 6~SNorg data (Table IV). The t~lSNinorg-values of the RF facies generally lie

358

higher than the fi~SNinor~-valuesof the Pb-Zn facies. This can be explained by the assumption that the nitrogen of the RF facies was released during oxidation of organic matter and subsequently fixed in layer-lattice silicates and authigenic phosphates, and this nitrogen was richer in 15N than the inorganic nitrogen of the Pb-Zn facies (Hammer et al., 1989).

J. HAMMERET AL.

lication. The authors are indebted also to colleagues Drs. H.K. Bothe, M. Geisler, W. Klemm, J. Pilot, W. Schr/Sn, K.H. Rentrop and K.-H. Elert for their analytical helps. Colleagues Drs. G. Knitzschke, R. Gerlach, J. Rentzsch, P. Beuge, C.-D. Werner and Mr. J. Luge were friendly debating partners with their special knowledge. The paper benefited from critical remarks by two anonymous reviewers.

4. Conclusions References The investigations yielded numerous indicators for an inflow of meteoric waters from the Rotliegendes basin into the Kupferschiefer sediment. The analytical results prove an inflow of metalliferous oxygen-rich waters via the Rote F/iule (RF) facies lasting until the late diagenesis of the Kupferschiefer. The inflowing solutions derived from Rotliegendes basin sediments are saline waters which moved along ruptured zones and along the margins of the intramontane molasse troughs from the hanging beds to the subjacent bed of the Kupferschiefer. Regarding the high cation solution capacity of oxidizing groundwaters (Lisicin, 1975 ) and the sudden change of the redox conditions from positive values in the transport medium to negative values in the sediment and the presence of bonding partners and geochemical barrieres of sorption, an intensive element accumulation from the inflowed waters takes place, presumably due to high flow rate and long circulation times. Our model of element supply by waters introduced from the Rotliegendes basins applies only to the portions of the Kupferschiefer lying nearest the RF zones. The inflowing brines were not able to penetrate Kupferschiefer areas over distances of kilometers.

Acknowledgements The authors are indebted to the VEB Mansfeld-Kombinat for the possibility of sampling of Kupferschiefer in the Sangerhausen basin and for the granted kind possibilities for pub-

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KUPFERSCHIEFER IN THE VICINITY OF "ROTE FAULE", INDICATING Cu MINERALIZATION

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J. HAMMER ET AL.

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