Selected Papers Arising from the EEC Primary Raw Materials Programme (1978-81)

Commission of the European Communities environment and quality of life

Selected papers arising from the EEC primary raw materials programme (1978-81)

Commission of the European Communities

Selected papers arising from the EEC primary raw materials programme (1978-81)

PARL EUROP. Blblioth.

N. C.

ZOO- 9, ,n J ^8om-. ^(o^t T-&N- Directorate-General Science, Research and Development

1984 EUR 8617 EN-FR Published by the COMMISSION OF THE EUROPEAN COMMUNITIES Directorate-General Information Market and Innovation Bâtiment Jean Monnet LUXEMBOURG

LEGAL NOTICE Neither the Commission of the European Communities nor any person acting on behalf of the Commission is responsible for the use which might be made of the following information

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.moO, Luxembourg, Office for Official Publications of the European Communities, 1984 ice for C ISBN 92-825-4086-3 Catalogue number: CD-NO-83-037-2A-C

reprinted from Mineralium Deposits

Foreword

This special issue of Mineralium Deposita is devoted to certain aspects of the 1978-1981 Research and Development programme of the European Communities in the field of "Primary Raw Materials". A major aim of this programme was to increase the E.C. potential for self-supply of a number of mineral raw materials, prin• cipally non-ferrous metals. The main research areas were: (1) Exploration, with emphasis both on economic geology and on the improvement of geochemical, geo• physical and remote sensing techniques; (2) ore processing, and (3) mining technology. In keeping with the orientation of this journal, the papers presented here concern the geology and geochemistry of ore-bearing formations, problems of ore genesis and potential applications to prospecting. Although they do not cover the entire range of research activities that have been sponsored by the E.C. in these particular fields, they do highlight a number of topics of great interest to economic geologists: - Investigations on fluid inclusions in granites and other rocks - Stable isotope studies - Geochemical proximity indicators for massive sulphide deposits - Trace element patterns in black shales and carbonates - The origin of base-metal vein-type deposits in carbonates - A statistical multivariable approach to regional prospecting - Diagenesis in red beds and its bearing on mineralizing processes More papers on these and other themes may follow in subsequent regular issues of the journal. On behalf of the Commission, I wish to thank the president of the Society for Geology Applied to Mineral Deposits as well as the editors of Mineraliwn Deposita for their invaluable assistance in preparing this special issue. May , I also express the hope that this is but a first step, a first experiment which will be continued and perhaps amplified upon the completion of the new Raw Materials programme sponsored by the E.C. for the period 1982-1985.

J. Boissonnas Commission of the European Communities Directorate General for Science, Research and Development

Mineral.Deposita 18, 303-313 (1983) MINERALIUM DEPOSITA © Springer-Verlag 1983

Thallium, Nickel, Cobalt and Other Trace Elements in Iron Sulfides from Belgian Lead-Zinc Vein Deposits

J. C. Duchesne1, A. Rouhart1, C. Schoumacher1 and H. Dillen2

1 Laboratoires associés de Géologie, Pétrologie et Géochimie, Université de Liège, Sart Tilman, Belgique 2 Département Scheikunde, Universitaire Instelling Antwerpen, Wilrijk, Belgie

Fe-sulfides associated with Belgian Pb-Zn vein deposits have been analysed by DC arc spectrometry and XRF for Tl, Ni, Co, Mn, Zn, Pb, Ge, Cd, and As. They show high Tl contents (from >30 ppm upt to 6800 ppm) and Co:Ni ratios <1. These features permit to distinguish them from Fe-sulfides of sedimentary and high temperature occurrences. The Tl distribution in a botryoidal marcasite of Vedrin (average Tl content of 0.68%) has been investigated by ion microprobe. It displays a pattern similar to colloform texture. Principal component analysis shows that the behaviour of Tl is partly controlled by a factor opposing Tl to all other elements. This is interpreted as reflecting the influence of sorption mechanisms by contrast with direct precipitation. Tl and the other elements are not considered of magmatic origin because no acidic magmatism is known during or after Variscan times. Extraction from sedimentary rocks by hydrothermal brines is favoured.

INTRODUCTION 1964), and discussed (Bernard, 1965; Duchesne, 1965). The present study cor• roborates these first results with the A systematic study of the trace element help of more powerful analytical tech- geochemistry of pyrite and marcasite niques and statistical methods of in- has been undertaken in order to charac- terpretation. terized iron sulfides associated with Pb-Zn vein deposits, and to examine whether trace elements could help to ANALYTICAL METHODS understand the conditions of formation of the ore, and thus facilitate the de- As a general rule, the specimens were tection of hidden deposits. A prelimi- carefully investigated under the re- nary study by Duchesne (1964) showed fleeted light microscope to select the the presence of relatively large amounts homogeneous Fe-sulfide parts of the ore. of thallium in marcasite from the Vedrin The purity of the sampled parts was ore deposit (Belgium) and pointed to the checked under the binocular after re- similarities with Pb-Zn deposits from duction to small fragments. When neces- the Cevennes border in France. The pure- sary hand-picking of impurities was fur- ly syngenetic origin of these latter ther done and remains of calcite remov- deposits proposed by Bernard (1961) was ed by a brief HC1 2N attack. Though questioned on this basis (Duchesne, greatest care was exercised in the ope- 304 J.C. Duchesne et al.

ration, the method - like any other se• calibration of Co, Ni, Mn, Zn, Cu. The paration method - cannot however war• four standards provide excellent work• rant the absolute purity of the analys• ing curves for Co, Ni, Mn and Zn, and ed aliquots of the samples. This fact a good one for Cu. Only one standard was taken into consideration in the out of the four available can be used interpretation of data by means of for Cd, Ag, Sb, Bi, Sn and Cr. There• statistical methods (see below). The fore, 45° slope working curves, passing use of Clerici's solution (Tl formate through the standard values, in log- and malonate) as a density liquid has log coordinates, are used for these been prohibited to avoid contamination elements (Ahrens and Taylor, 1961). For by Tl. The final grinding to about -150 Ge synthetic standards obtained by mix• mesh was done in agate mortars. ing Ge to a Fe2Û3 matrix are used. Tl, Pb and As are calibrated with values Three different analytical methods are measured by X-ray fluorescence. The used: detection limits are: 0.2 ppm Ag; 1 ppn Pb, Mn, Cu, Ge; 5 ppm Co, Ni, Sb, Bi, 1. DC arc spectrography Sn, Cr; 10 ppm Tl; 15 ppm As, Cd. 2. X-ray fluorescence spectrometry 3. Ion microprobe analysis (SIMS) 2. X-ray fluorescence analysis is used for the determination of relatively 1. DC arc spectrography is used to de• high contents of Tl, Pb and As. A CGR termine Co, Ni, Mn, Cd, Ge, Sb, Bi, Sn, alpha 2020 semi-automatic spectrometer Cr as well as low contents of Tl, Pb working with a Mo-tube at 50 kV and and As. The method is inspired from He- 50 mA and a LiFlOO analysing crystal is gemann and Leybold (1954). The powdered used. Analytical lines are Tl Lgj, sample is mixed with 2 parts of "spec- As KBi and Pb L3i- Standard samples pure" graphite, and loaded in the coni• ASK-3 and PS-1 are used to calibrate cal cavity of a graphite electrode the method for Pb and As. Synthetic (SCHRIBNER type - National Carbide samples made by mixing various amounts L4024). A 3 mm diam-rod (Le Carbone- of TI2O3 to a pyritic matrix are used Lorraine type 207) is used as an upper for Tl. It must be noted that the Tl electrode. A drop of Elvacite 2044 di• content of 100 ppm, given by Schron et luted in toluene is placed on the load• al. (1975) for PS-1, is highly over• ed electrode and dried in order to form estimated. No Tl is detected by DC arc a cake. This procedure prevents loss of spectrography, which means that the Tl material during the first seconds of content is lower than 10 ppm. Inspec• arcing and regularizes burning. An tion of the most sensitive line at optimum reproductibility (± 5%) can 5350 Â with ICP spectrography also re• thus be obtained. veals no Tl. The limits of detection A stabilized DC arc of 6.5 A and (LD), following Currie (1968), are 30 220 V from a PHILIPS Multisource is ppm Tl and Pb and 45 ppm As. used to burn the sample (anode) during 30 sec. All analyses are duplicated. 3. Secondary ion mass spectrometry The spectrograph is a FUESS 110 H (4 (SIMS) in the ion microscope mode is prisms) equivalent to the HILGER large used to study the distribution pattern spectrograph. The densitometer is mod C of Tl through polished sections of about 1285 from FUESS. The spectra are record• 1 cm in diameter, with a spatial resol• ed on KODAK plates (type) SA 1 in the ution of 1-10 pm. Quantitative analyses range of 2760 & to 3480 ft. The analyti• with a spatial resolution of 250 um is cal lines (Â) are the following: Co possible for e.g. Mn, Co, Ni, Cu and Tl. 3044; Ni 3051; Mn 2933; Zn 3822; Cd The instrument used is a Cameca IMS- 3261; Cu 3274; Ge 3039; Sb 3878; Bi 3068 ;300 ion microscope, and a 6 KeV Ar+ Sn 2840; Cr 3015; Tl 2768; As 2780; Fe primary beam is used with a current den• 3053 is used as an internal standard. sity of 12 A/mm2. For quantitative anal• Four international standard samples of yses an electrostatic sector is used to pyrite: PS-1 (Schron et al., 1975), P-l select 140-160 eV ions for Mn, Co, Ni and P-2 (Robinson and Walshe, 1977) and Cu, and 60-80 eV ions for Tl. The and ASK-3 (Christie, 1975) are used for analysed surface is 250 pm in diameter. Thallium, Nickel, Cobalt and Other Trace Elements in Iron Sulfides 305

For calibration of Mn, Co and Cu the iron and acids. A concentration of 6800 four already mentioned reference samples ppm is found by that method for the are used in the form of pellets, as Vedrin sample. A massive part of the described by Dillen and Gijbels (1981). specimen is used to determine a sensi• No certified standards being available tivity factor for SIMS, with 32S as an for quantitative Tl analyses, a sample internal standard. from Vedrin, which has been examined by SIMS and found virtually homogeneous at the 250 um-scale (standard deviation for 14 different measuring sites of 250 ym diameter each: 11%), is used as SAMPLING a reference sample after determination of its Tl content by ICP-AES, in nitric acid solution, using the 5350 Â Tl-line. The instrument is calibrated by Tl-so- 84 samples belonging to 36 occurrences lutions containing the same amount of of marcasite or pyrite have been anal-

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Fig. 1. Geological sketch map of South Belgium showing the provenance of the various iron sulfide samples from Pb-Zn vein deposits. 4. Post-Variscan ter• rains; 3. Devonian and Carboniferous terrains; 2. Cambrian and Silurian ter• rains; 1. Numbered stars refer to the investigated occurrences: 1, 2, 3 and 11: Poppelsberg, Stuck, Lontzen and Moresnet, respectively; 4: Vedrin; 5: Hayes- Monet; 6: Corphalie; 7: Engis; 8: Angleur; 9: Heure; 10: Villers-en-Fagnes; 12: Chaudfontaine 306 J.C. Duchesne et al.

ysed. The main occurrences come from DISCUSSION East Belgium (Fig. 1): Poppelsberg (11 samples) and Stuck (2 samples) are The results usually show a wide dis• small post-Variscan Pb-Zn vein deposits persion in the various Pb-Zn occurrence! cutting across Dinantian carbonate rocks They can however be summarized as fol• and Famennian rocks of the Vesdre Mas• lows : sif. They were recently drilled by the 1. The Co content is low - usually close Union Minière Company. Lontzen (15 sam• to or below 5 ppm - in the Belgian Pb- ples) also belongs to the same type of Zn type and contrasts with the sedimen• mineralization and comes from the same tary and high temperatures occurrences, area, but is entirely situated in siltic which show averages of 332 ppm and 2180 to pelitic rocks of Famennian age. ppm respectively. The Ni content of the Another well documented site - the Pb-Zn type is higher than the Co and Vedrin Mine, near Namur - has also been can be compared to the sedimentary or investigated. It is a vein deposit in high temperature sulfides. Therefore, Dinantian carbonate rocks of the Namur the Co:Ni ratio is < 1 in the Pb-Zn synclinorium (Evrard, 1943). Two types type. According to classical interpre• of sulfides are studied. The first and tations (see e.g. the reviews by Loftus- most common one is the vein type (12 Hills and Solomon, 1967 and Bralia et samples): a fibro-radiated marcasite al., 1979) this would indicate a sedi• associated with some blende and galena mentary origin. However, the various in a calcite gangue. The second type authors usually consider that this cri• (5 samples) is a marcasite, filling terion is poorly significant when used small veins and veinlets of a brecciat- alone. The present data on sedimentary ed dolostone, at a distance of 10-20 m occurrences also confirm that the Co/Ni from the main vein. ratio has to be used with caution. In• Other Belgian Pb-Zn occurrences have deed, 5 out of 12 sedimentary occurren• also been included: Hayes-Monet, Cor- ces which are studied here show phalie, Engis and Angleur (2 samples) Co:Ni > 1, an inverse relation to what from the Namur synclinorium; Heure and should be expected since they all con• Villers-en-Fagnes in Devonian strata from cern typical cubic pyrites in black the Dinant synclinorium; Moresnet and shales or slates. It is likely that re- Chaudfontaine in the Vesdre Massif, the crystallization due to incipient meta- latter is a cubic pyrite associated with morphism can lead to an enrichment of G a baryte stratiform deposit (Dejonghe, with respect to Ni, in such a way that 1979) in Devonian strata. an original Co:Ni < 1 might be modified Two occurrences from the Cévennes to a Co : Ni > 1 . border - Soulier and St Félix de Pal- It can be concluded that, in Pb-Zn lière - previously studied by Duchesne deposits, the Co:Ni ratio in iron sul• (1964) have also been reinvestigated. fides has no genetic significance since Moreover, 12 occurrences from sedi• the observed relation ( < 1) is not in mentary rocks, mainly pyrite cubes from agreement with the geological evidence. shales, have been included for the sake It must however be noted that the low of comparison (Rochelinval, Bayehon, Co content of the Pb-Zn occurrences Deville, Grand-Halleux, Longfaye, Huc- appears to be a feature restricted to corgne, Ronquière, Grufflingen, Boux- this type of deposits and is likely to harmont, Visé, Gris-Nez - France, Balla- have a promising genetic meaning. chullish - Scotland) as well as pyrites formed at high temperature (Agrokipia- 2. Thallium is always present (from Cyprus, Calamita and Rio Marine - I. > 30 ppm up to 6800 ppm) in the Belgian Elba, Pamour-Canada, Luzenac-France and Pb-Zn type, whatever the geological unit Buranga-Ruanda). to which they belong (Dinant or Namur synclinoria, Vesdre Massif) or the age The results of the analysis are sum• of the enclosing rocks (Dinantian or marized in Table 1 which gives the aver• Devonian). It is also present in the age and the range of variation of each Cevennes border (Duchesne, 1964) where trace element in each occurrence. Aubagne and Leleu (1981) have recently Table 1. Trace element contents (ppm) of iron sulfides

VENDRIN OTHER BELGIAN CEVENNES POPPELSBERG STUCK L0NTZEN SEDIMENTARY HIGH TEMP OCCURRENCES OCCURRENCES OCCURRENCES OCCURRENCES MAIN VEIN BRECCIA

Number of 11 2 15 12 5 12 samples 9 3 7

Tl X 235 90 83 517 78 229 806 <10 <10 range 30-1600 30-150 30-190 73-6800 54-88 55-650 460-1080 Co X ? (7)d> I (O 36 <5 <5 1 (6) <5 332 2180 range <5-90 <5-48 8-98 <5-220 <5-1470 47-6600 Ni X 370 300 448 17 10 200 5 374 145 range 45-1650 10-600 42-1010 <5-42 5-17 <5-620 <5-6 8-2050 8-440 Co/Ni X <0.04-0.14 <0.1-0.5 0.05-0.15 <0.1-0.5 <0.3-

Mn X 23 7 22 245 2 73 113 310 35 range 1-125 3-11 3-290 1-1000 ■ (ID <15 100 2720 283 273 range <10-2450 500-4500 50-1010 <10-40 <10-310 1300-5000 20-625 <10-850 Sb X 19 54 <5 <5 ? (7) 310 27 ? (6) range <5-65 10-100 15-150 <5-25 20-660 <5-180 <5-10 Bi X <5 <5 <5 <5 <5 <5 <5 ? (8) range <5-35 (50) Cr range <5 <5 <5 <5 <5 <5 <5 <5-250 (350)

(1) average not significant: the figure into brackets gives the number of values below the detection limit (2) with two additional values >50000 ppm Detailed data can be obtained from the authors 308 J.C. Duchesne et al,

mentioned Tl-rich (0,5 to 1%) melniko- contents in the Vedrin marcasite from vites and marcasites in Pallière. the brecciated dolostone are lower than On the other hand, Tl is absent in the main vein occurrences; they also ( < 10 ppm) from all sedimentary and display less dispersed values. In Lon- high temperature occurrences. According tzen, almost all trace elements are en• to Ivanov et al. (1960), Tl is commonly riched relative to the Poppelsberg- found in numerous varieties of poly- Stuck type. Since the deposits all be• metallic deposits. It is usually more long to the same fault system, it is enriched in sphalerite or galena than likely that this difference is due to in iron sulfides, e.g. from some Cauca• the siltic to pelitic nature of the sus deposits. Shaw (1952) and Albuquer• Famennian enclosing rocks at Lontzen que and Shaw (1972) also report high Tl as compared to the carbonate rocks at content in marcasite from several local• Poppelsberg and Stuck. ities (Japan, Caucasus, Central Asia, etc...). In Western Europe, since Stoi- 4. In addition to the variations be• ber (1940), Tl is mentioned in Pb-Zn tween the different occurrences, the deposits of Belgium, Westphalia, and trace elements display large intervals Silesia. Except for the data of Thein of variation within the different de• (1975) on the Meggen deposit (see be• posits. In order to investigate these low), no modern analyses have been made variations in detail, the statistical available on sulfides and this hampers method of principal component analysis the study of the chalcophile behaviour has been applied to the Pb-Zn type. The of Tl. computing has been performed by the In the Belgian Pb-Zn occurrences the Fortran IV program of Davis (1973) maximum Tl content in iron sulfides is adapted for a Heathkit Z89 microcomputer found in a radiated botryoidal marcasite with a memory of 64 K of RAM and two from the Vedrin mine (0,68%). The dis• 5.25 inch floppy discs. tribution of Tl, as revealed under the Fig. 2 summarizes the results obtain• ion microprobe, is shown on Plate 1. ed on 40 samples from Pb-Zn deposits, Tl is not incorporated as independent representing the whole population of phases larger than 1 urn (the resolution this type except the samples from the power of the ion microprobe) and can Vedrin mine. Bi and Cr which are absent thus be considered regularly distribut• from the Pb-Zn type were not considered. ed troughout the marcasite phase. At a The reason for discarding the Vedrin larger scale thin alternating bands samples is that the contents in Co, Cd, (from 1 to 50 ym) of contrasting Tl As and Sb are currently below the limit contents are disposed perpendicular of detection of the method. A large num• to the radiating directions of the tex• ber of data below the detection limit ture. The overall picture is quite sim• can indeed artificially modify the true ilar to the so-called colloform texture correlation between the elements. and can be put together with the fact Four factors can explain 72 % of the that Tl is notably enriched in collo• variance of the population. They can be form varieties of iron sulfides (Ivanov interpreted as follows. et al., 1960). In a second specimen Factor 1 opposes Tl to a group of from Vedrin an inclusion of a Tl and Pb several elements which comprises ele• bearing mineral-possibly hutchinsonite ments such as Ni, Co, Zn, Cu and Ge (Pb, Tl)2(Cu, Ag)As5S10 - was also which have an ionic radius close to found, thus indicating that trace min• that of Fe and therefore are compati• erals can also control the distribution ble with their entering in the crystal• of Tl. lizing iron sulfide by isomorphism. On the other hand, the opposite sign of 3. Some variations can be observed be• the Tl factor loading can indicate a tween the different Belgian deposits or different controlling mechanism, possib• even within the same deposit. The Vedrin ly related to the higher value of the marcasites are low in Co, Ni, As, Sb, ionic radius (T1+ = 1.40 &) (Sahl, Cu, Ag compared to the East Belgium oc• 1974). As already mentioned, Tl is en• currences. The Tl, Zn, Mn, Cu and Ag riched in minerals presenting a collo- Thallium, Nickel, Cobalt and Other Trace Elements in Iron Sulfides 309

Plate 1. Tl distribution in a botryoidal marcasite from the Vedrin mine (Namur, Belgium) as revealed by secondary ion mass spectrometry (ion microprobe). Thin alternating bands (1 to 50 um) of contrasting Tl contents - the higher the con• tent, the darker the intensity - are perpendicular to the radiating directions (well displayed in photo 2) of the texture in a pattern similar to colloform texture

form structure, such as Schalenblende obtained under the ion microprobe and or in various "gel"-like or amorphous colloform texture is striking and strong minerals, such as melnikovite (see ly suggests that adsorption on colloids Ivanov et al., 1960). Moreover, its is the mechanism which controls the be• size and chemical similarity with large haviour of Tl. This is not in agreement alkali ions is consistent with its ex• with Roedder's view (1968), in which traction from solutions by adsorption colloform texture cannot be formed bv processes (Albuquerque and Shaw, 1972). material in a colloidal state when de• The similarities between the pic• posited, but by direct crystallization ture of the Tl distribution which is from a fluid. We however believe that 310 J.C. Duchesne et al.

] Factors 1 2 3 4 blende which can be rich in Tl (Evrard, 1945) and in GeCd. .10 - Factor 2 is difficult to interpret. •Mn It probably results from the combinatior .08 ■ of several mechanisms. Mn might come • So from inclusions of blende. It is how .06 • As ZnlCo •Cd ever hard to understand why Mn, which • Ag •G* •Tl could easily substitute for Fe, is main .M •Tl ly controlled here by its substitution in THCu en -SbiAs with Zn and also why CdGe, classically c .02 diadochic of Zn (see factor 4) appears a _o here with factor loadings of sign dif 0 ferent from Zn. The grouping of Pb with o o Ag is classical in galena and might -02 also indicate inclusions of trace •Mn amounts of this mineral. Cdl*9 -a* • Zn Though some points are still some • Pb ■ Ml what obscure, principal component anal •Zn-Cu •Cu -06 ysis clearly shows that several possi ' AQ-G.I& ble mechanisms can account for the pre • Co sence of Tl in the population: sorption -as phenomena and inclusions of sulfosalts and also possibly of blende. This is in "/■of variance 25 18 15 U agreement with the modes of occurrences cumulate'/* of variance 25 43 58 72 of Tl observed under the ion microprobe and in conformity with what is known Fig. 2. Graphical representation of the of its chalcophilic behaviour. principal component analysis of the trace element contents of iron sulfides from PbZn vein deposits. Factor load ings less than 0.22, below the level SOURCE OF THALLIUM: AN OPEN QUESTION of significance following Harman (1967), are not represented Polymetallic deposits which show the highest amount of Tl are related to acidic magmatism either volcanic or plutonic such as in the classical reg our factor 1 is an indication that two ion of Caucasus (Ivanov et al., 1960) oi different mechanisms play a role in the in Turkey (Jankovic and Le Bel, 1976). deposition of the iron sulfides and The enrichment of Tl in the late stages that, all things being equal, the Tl of the magmatic differentiation is well content of a sample is a measure of the in agreement with its similarity of be relative importance of sorption effects haviour with K. in the process of formation of the par The source of Tl in PbZn deposits ticular sample. in carbonate environment is however a Factor 3 groups together SAsAg and debatable question. In the Meggen de is also loaded with Cu and Tl. We inter posit (Westphalia), the distribution of pret this as due to inclusion of trace Tl in and around the stratiform ore minerals of sulfosalts, some of them body is considered to be due to the containing Tl, which is known to have exhalative origin of the elements (Thei' geochemical affinities with Sb and As 1975; Gwosdz and Krebs, 1977) and can (Jankovic and Le Bel, 1976). thus be linked to a synsedimentary Factor 2 is positively loaded with event. In Belgium however, except for Mn and Zn and negatively with PbAgCd some thin Kbentonites of Dinantian age Ge. Factor A groups Tl with CdGe which (Thorez and Pirlet, 1979), volcanic are opposed to NiCu, and might indi rocks are not known interbedded in the cate the influence of inclusions of Variscan sedimentary pile. In the area, Thallium, Nickel, Cobalt and Other Trace Elements in Iron Sulfides 311 acidic plutonism is restricted to the permits to distinguish them from all small granitoids of La Helle and Lam- other occurrences (Tl < 10 ppm). The Co mersdorf (Germany) (Corin, 1965). They content is lower than in sedimentary are situated far away from important occurrences. deposits, such as the Vedrin Mine, and since they have suffered a deformation 2. The mode of occurrence of Tl in iron of Variscan or Caledonian age, they are sulfides is either in the form of trace certainly older than the post-Variscan minerals or is dispersed in the iron tectonic event which controls the em• sulfide phase according to a zoned and placement of the veins. The presence recurrent pattern, similar to a collo- of a granitic batholith at depth under form texture. Several lines of evidence the Ardennes has been surmised by Four- indicate that sorption phenomena and marier (in Dewez and Lespineux, 1947) inclusions of sulfo-salts can account to account for the distribution of the for most of the behaviour of this ele• Belgian ore deposits. But no evidence ment in the deposition of the iron sul• in favour of such an hypothesis has fides. ever been put forward. 3. The paucity of acidic magmatism in Tl, if not magmatic, must find its Belgium during Devonian and Carboni• source in sedimentary rocks from which ferous sedimentation or in post-Varis• it was scavenged by hydrothermal brines. can times makes the hypothesis of a When taking the data of Heinrichs et magmatic source for the Tl difficult al. (1980) on sedimentary rocks, it is to accept. The hypothesis that Tl to• noted that the Tl content (average: gether with other elements was scaveng• 0.41 ppm; black shales: 2.5 ppm) is ed from sedimentary rocks by hydrother• high relative to the Pb content (aver• mal solutions is favoured. age: 16.7 ppm, black shales: 82 ppm). The Tl/Pb ratio varies between 1/50 Acknowledgements. The present investi• and 1/30, values which are higher than gation is part of a research program those commonly found in sulfides from supported by the EEC (111-79-7-MPPB) Pb-Zn deposits. Therefore it is not and the Belgian SIPS (MP-CE-5) (Pro• unlikely that any process which would ject Leaders: P. Evrard and J. Belliere). extract and concentrate Pb would also The authors wish to express their grati• be active for Tl. tude to the Union Minière, for giving access to drilled samples of Poppels- berg, Stuck and Lontzen; to L. Dejonghe, A.M. Fransolet and F. Dimanche for CONCLUSIONS donating various samples; and to R. Gijbels for the use of the SIMS instru• ment and for interesting discussions. Distribution of trace elements in vari• ous occurrences of iron sulfides indi• cates: 1. The iron sulfides related to Belgian REFERENCES Pb-Zn vein deposits, mainly in carbonate environment, belonging to different geological units (Namur Synclinorium, Ahrens, L.H., Taylor, S.R.: Spectro- Dinant Synclinorium, Vesdre Massif) or chemical analysis (2nd Ed) Addison- situated in Devonian or Dinantian strata, Wesley, 454 p (1961) form a group along with two occurrences Albuquerque de, C.A.R., Shaw, D.M. : from the Cévennes border; this group Thallium. In: "Handbook of Geochemis• can be distinguished from iron sulfides try". Wedepohl, K.H. (ed) Springer, of various origins by their Ni, Co and Berlin. Vol. II-5 section 81, 1972 Tl contents. Their Co:Ni ratio ( <1) Aubagne, M., Leleu, M.: Recherche de can be compared with sedimentary occur• guides de prospection pour les gites rences but is distinctly lower than in Pb-Zn liés aux strates en environne• high temperature occurrences (Co:Ni>l). ment carbonate. Deuxième phase: Le Their Tl content ( >30 ppm up to 0,6%) gite de la Croix de Pallières (Bor- 312 J.C. Duchesne et al,

dure Cévenole, Gard), B.R.G.M.Compte Soc. Géol. Belgique, 66, M181-202 rendu de fin d'étude, 1981 (1943) Bernard, A.: Contribution à l'étude de Evrard, P.: Minor elements in sphaler• la province métallifère sous-Cévenole ites from Belgium. Econ. Geol. 40, Sci. Terre, 7, 3-4, 123-403 (1961) 568-574 (1945) Bernard, A.: Comments on "Présence de Gwosdz, W., Krebs, W.: Manganese halo thallium dans les sulfures de fer de surrounding Meggen ore deposit, Ger• la mine de Palliêre (Gard, France)" many. Trans. Inst. Min. Metal., sect. by J.C. Duchesne. Ann. Soc. Geol. B, 86, 73-77 (1977) Belgique 88, 151-152 (1965) Harman, H.H.: Modern factor analysis Bralia, A., Sabatini, G., Troja, F.: (2nd ed) University of Chicago Press, A réévaluation of the Co/Ni ratio in 1967 pyrite as geochemical tool in ore Hegemann, F., Leybold, C: Eine Méthode genesis problems. Miner. Deposita, zur quantitativen spektrochemischen 14, 353-374 (1979) Analyse von Pyrit. Zeitschr. Erzberg- Christie, O.H.J.: Three trace element bau u. Metallhiittenwesen, v. 7, geological materials certified as a 108-113 (1954) result of a cooperative investigation. Heinrichs, H., Schulz-Dobrick, B., Talanta, 22, 1048-1050 (1975) Wedepohl, K.H.: Terrestrial geochem• Corin, F.: Atlas des roches êruptives istry of Cd, Bi, Tl, Zn and Rb. de Belgique. Mém.Expl.Cartes Géol. Geochim. Cosmochim. Acta 44, et Min. de Belgique, no 4, 190 p, 1519-1533 (1980) 1965 Ivanov, V.V., Volgin, V.Y., Krasnov, Currie, L.A.: Limits for qualitative A.A., Lizunov, N.V.: Thallium: Basic and quantitative determination. Anal. geochemical and mineralogical proper• Chemistry, 40, 586-592 (1968) ties, genetic types of deposits and Davis, J.C: Statistics and data anal• geochemical provinces (in Russian), ysis in Geology. John Wiley, 420 p, Moscow Academy of Sciences, Transi. 1973 International Geology Review, Book- Dejonghe, L.: Discovery of a sedimen• section. Published by the American tary Ba (Fe, Zn, Pb) ore body of Geological Institute, 1960 Frasnian age at Chaudfontaine, Pro• Jankovic, S., Le Bel, L.: Le thallium vince of Liège, Belgium. Mineral. dans le minerai de Bôzcukur près Deposita, 14, 15-20 (1979) Kitahya, Turquie. Bull.Suisse Minéral Dewez, L., Lespineux, G.: Les minerais Pétrol. 56, 69-77 (1976) du sol belge. In: "Centenaire de Loftus-Hills, G., Solomon, M.: Cobalt, l'A.I.Lg - Congrès 1947 Section Géo• Nickel and Selenium in sulfides as logie". Ed. AILg, Liège, 73-120 indicators of ore genesis. Mineral. (1947) Deposita, 2, 228-242 (1967) Dillen, H., Gijbels, R.: Etude de quel• Robinson, P., Walshe, J.L.: Trace-ele• ques éléments en traces dans la py• ment analysis of pyrite - an inter- rite par analyseur ionique. J. laboratory survey. Trans. Inst. Min. Microsc. Spectrosc. Electron., 6, Metal. 5, B216-218 (1977) 179-194 (1981) Duchesne, J.C: Présence de thallium Roedder, E.: The noncolloidal origin of dans les sulfures de fer de la mine "colloform" textures in sphalerite de Palliêre (France). Ann. Soc. Géol. ores. Econ. Geol. 63, 451-471 (1968) Belgique, 87, 1-7 (1964) Shal, K.: Thallium. In: Handbook of Duchesne, J.C: A reply to A. Bernard's Geochemistry. Wedepohl, K.J. (ed) comments on "Présence de thallium vol. II-5 section 81A. Springer, dans les sulfures de fer de la mine Berlin, Heidelberg, New York, 1974 de Palliêre (Gard, France)". Ann. Schrbn, W., Rossler, H.J.: Drei neue Soc. Géol. Belgique, 88, 153-155 geochemisch-mineralogische Komplex- (1965) standards Galenit GF-1, Sphalerit Evrard, P.: La minéralisation de Vedrin SF-1 and Pyrit PS-1. Z. Angewandte (Province de Namur, Belgique). Ann. Géologie, 21, 17-25 (1975) \ Thallium, Nickel, Cobalt and Other Trace Elements in Iron Sulfides 313

Shaw, D.M.: The geochemistry of thal• stages of Belgium. In: "Intern. Clay lium. Geochim. Cosmochim. Acta, 2, Conference 1978", Mortland & Farmer 118-154 (1952) (eds), Elsevier, 323-332 (1979) Stoiber, R.E.: Minor elements in sphal• erites. Econ. Geol. 35, 501-519 (1940) Thein, J.: Geochemische Untersuchungen Received: October 7, 1982 im Sulfiderz im Nebengestein und in Accepted: January 4, 1983 den B6den der Lagerstatte Meggen-West- falen. Doctorate thesis - Rheinische Prof. J.C. Duchesne Friedrich-Wilhelms-Universitat zu Laboratoires associés de Géologie, Bonn, 70 p (unpublished), 1975 Pétrologie et Geochimie, Thorez, J., Pirlet, H.: Petrology of Université de Liège K-Bentonite beds in the carbonate B-4000 Sart-Tilman series of the Visean and Tournaisian Belgique

Mineral.Deposita 18, 315-333 (1983) MINERALIUM DEPOSITA © Springer-Verlag 1983

Scheelite Mineralization in Central East Greenland

C. P. Hallenstein and J. L Pedersen

Nordisk Mineselskab A/S, The Northern Mining Co. Ltd., Copenhagen, Denmark

Numerous scheelite-mineralized areas have been located in the Caledonian fold belt of Central East Greenland (70°- 74 1/2° N). The fold belt comprises Archaean and Proterozoic metamorphic complexes flanked by Late Proterozoic and Lower Palaeozoic sediments, and intruded by Upper Proterozoic and Caledonian granitic rocks. Scheelite mineralization occurs in: marble-skarns in Upper Pro• terozoic metasediments often spatially associated with Caledonian or older granitic intrusives; skarns and quartz veins in Late Proterozoic sediments (Lower EBG quartzite) up to 7 km from outcropping Caledonian granites; veins in fault zones cutting late Proterozoic sediments (Upper EBG limestones). In this paper, the three types are described with emphasis on structural setting, min• eralogy and trace-element chemistry. It is concluded that most scheelite min• eralization is associated with Caledonian igneous activity, either at or near granite contacts or as mineralization distal to granites at depth. Of the vari• ous types described, the scheelite veins in Late Proterozoic limestone are con• sidered to be of the best economic potential.

INTRODUCTION ternational Geological Correlation Pro• gram by Ghisler et al. (1980). They described scattered scheelite grains of The work of this paper formed part of detrital origin in quartzitic sediments. the project "Study of Scheelite Miner• Furthermore, tungsten as wolframite oc• alization in Central East Greenland" curs at the Malmbjerg porphyry molyb• which was supported by "The program denum (Kirchner, 1964) (Fig. 1). for Research and Development of the Geochemical exploration during the European Community in the Field of Pri• course of the project (Hallenstein et mary Raw Materials". The project was al., 1981) enabled the finding of num• initiated in 1979 and completed early erous scheelite-mineralized areas which in 1982. are described and discussed in this Minor scheelite mineralization in paper. float and outcrop was known in the area The East Greenland project area lies prior to the start of the project (Hint- between 70°00'N and 74°30'N and is bound• steiner, 1977). Scheelite had also been ed to the west by the Greenland ice cap, observed in the area during a regional and to the east by the Greenland Sea survey in 1974-1975 as part of the In• (Fig. 1). The physiography is dominated 316 C.P. Hallenstein and J.L. Pedersen

CALEDONIAN AND OLDER GRANITIC m ROCKS LATE PROTEROZOIC AND LOWER L/ THRUS PALEOZOIC SEDIMENTS

UPPER PROTEROZOIC METASEDIM E NTS SCHEELITE MINERALIZED AREA H ANO MIGMATITES ARCHEAN AND MIDDLE PROTEROZOIC CE, GLACI EHS m BASEMENT (PARTIALLY OVERLAIN BY UPPER PROTEROZOIC M E TASEDI MENTS) □ POST-CALEDONIAN ROCKS

Fig. 1. Geological map of Central East Greenland showing scheelite-mineralized areas. 1. Kalkdal, 2. East Milne Land, 3. Knivbjergdal, 4. Gemmedal, 5. Roslin Gletscher, 6. Eremitdal, 7. Bersaerkerbrae and Skjoldungebrae, 8. Trekantglet- scher, 9. Galenadal and Scheelitdal, 10. Randenaes, 11. North Margeries Dal, 12. South Margeries Dal, 13. Panoramafjeld and Eleonores Bugt and 14. Noa Dal Scheelite Mineralization in Central East Greenland 317

by mountainous terrain, varying from Milne Land, South Stauning Alper and in glacier-dissected alpine regions with West Andrées Land. They comprise foli• peaks nearing 3000 m above sea level, ated augen and muscovite granites. to less rugged mountains, often topped by plateaus with an elevation of 1000 to 2000 m, and cut by deep U-shaped Late Proterozoic and Lower Palaeozoic valleys. Numerous, long, deep fjords Sediments dissect the entire area. The climate of the area is arctic, The metamorphic complexes are flanked with average yearly precipitation of by Late Proterozoic sediments of the 400 mm, and average temperatures for Eleonore Bay Group (EBG) and Tillite Juli and January of 5°C and -20°C Group, and by Cambro-Ordovician sedi• respectively. ments (Fig. 1). The main belt of these sediments stretches from Alpefjord to northeast of Andrées Land. GEOLOGY The oldest sediments are the Lower EBG, which is sub-divided into the Arenaceous-Argillaceous "series", the The Caledonian fold belt occupies most Calc-Argillaceous "series", and the of the investigated area (Fig. ]). It Argillaceous-Arenaceous "series". The comprises Archaean and Proterozoic crys• Lower EBG is best known in the Alpe- talline rocks, flanked by Late Protero• fjord region, and exceeds 8000 m in zoic and Lower Palaeozoic sediments. thickness. The sediments comprise Proterozoic and Caledonian granitic quartzites, siltstones and minor carbo• rocks intrude the fold belt (Henriksen nate horizons. The overlying Upper EBG and Higgins, 1976, and Higgins et al., is about A000 m thick, and has been 1981). Post-Caledonian rocks include divided into three "series", the 2000 m Devonian to Lower Permian molasse sedi• thick Quartzite "series", which is over• ments, Upper Permian to Cretaceous most• lain by the 1000 m thick Multicoloured ly marine sediments, and Tertiary plu- "series" and the over 1000 m thick tonic and volcanic rocks (Haller, 1971). Limestone-Dolomite "series". The Quartz• ite "series" consists of red and white quartzites and black to green quartzitic Archaean and Proterozoic Metamorphic shales. The Multicoloured "series" com• Complexes prises up to 100 m thick, dark lime• stone units and interbedded yellow, Archaean and Middle Proterozoic high- red and green dolomitic and quartzitic grade-metamorphic basement complexes shales and light-coloured dolomites. occupy the western-most parts of the The Limestone-Dolomite "series" is a area (Fig. 1). Isotopic age determina• 1200 m thick sequence of white to black tions have yielded dates of 2935 to dolomites and limestones. Fossil stud• 2300 m.y. and 1980 to 1705 m.y. for the ies have indicated a very late Riphean basement complexes (Steiger et al., or Vendian age for the Upper EBG (i.e., 1979; Rex et al., 1976; Rex and Gled- 700 to 600 m.y. old) (Vidal, 1979). hill, 1981). The Upper EBG is slightly unconformably The basement complexes are overlain overlain by Tillite Group tillites and and bordered to the east by Upper Pro• dolomitic shales, and Cambro-Ordovician terozoic metasediments and migmatites limestones and dolomites. These are the (Fig. 1). These rocks consist of quartz- youngest sediments which were deposited ites, mica schists and some marbles, prior to Caledonian deformation. and were metamorphosed 1100 m.y. ago (Hansen et al., 1978; Rex and Gledhill, 1981). They were subjected to a stage Caledonian Ovogenesis and Granitic of migmatization and granitic intru• Intrusion sion around 1000 m.y. ago (Steiger et al., 1979). Upper Proterozoic granitic During the Caledonian orogeny, metamor- rocks have been identified in West phism was widespread but variable 318 C.P. Hallenstein and J.L. Pedersen throughout the fold belt. Amphibolite on Fig. 1. It is possible to divide facies was reached in some of the Upper the scheelite-mineralized areas into Proterozoic metasediments, and the three groups on account of their geo• western-most EBG sediments of the Alpe- logical setting. The groups and their fjord-Andrées Land belt have been weak• respective areas are as follows: ly metamorphosed in the greenschist - Scheelite mineralization in Upper facies (Thyrsted, 1978). Proterozoic metasediments, often spati• Caledonian deformation occurred most• ally associated with Caledonian or ly as broad, N-S trending fold struc• older granitic intrusions. The areas tures. Both the metasedimentary com• assigned to this group are Kalkdal, plexes and the EBG sediments have been East Milne Land, Knivbjergdal, Gemmedal affected by the folding. The folding Roslin Gletscher and Eremitdal. is interpreted as having formed as a result of vertical forces accompanying - Scheelite mineralization in the Lower the updoming of crystalline rocks EBG sediments, up to 7 km from out• (Haller, 1971; Higgins et al., 1981). cropping Caledonian granites. The areas The fold axes exhibit alternating cul• of this group comprise Bersaerkerbrae, minations and depressions. Skjoldungebrae, Trekantgletscher, Ga- Normal faulting along N-S, E-W and lenadal, Scheelitdal and Randenaes. NW-SE trends also developed during the - Scheelite mineralization in fault deformation (Eha, 1953). The largest zones in Upper EBG sediments without displacements are associated with the spatial relation to granitic rocks. E-W and NW-SE faults, and may exceed The areas of this group comprise 1000 m. North and South Margeries Dal, Panora• Caledonian granitic rocks occur in ma Fjeld, Eleonores Bugt and Noa Dal. East Milne Land, the Stauning Alper, Work in the areas has included geo• West Andrées Land and Liverpool Land. logical mapping at scales from They span a wide range of ages and 1:10,000 to 1:500 and systematic samp• compositions (Steiger et al., 1979; ling. Samples have been subjected to Rex and Gledhill, 1981). The oldest pétrographie and chemical studies. Un• Caledonian granitics, with ages from less otherwise specified, chemical anal 560-475 m.y. have the compositions yses of tungsten, antimony and arsenic granodiorite, monzonite, and two-mica were by XRF and of other elements by granite. The intrusions which accom• semi-quantitative emission spectroscop; panied the peak of the orogenesis, from The results of this work are summariz• 455-430 m.y. ago also have compositions ed in the following descriptions of from granodiorite to muscovite granite. the mineralized areas of each group. The latest phases of Caledonian activi• ty resulted in late to post orogenic intrusions with an age of 420-375 m.y. These dated rocks comprise biotite Mineralization in Upper Proterozoic granite, aplite and pegmatite. Metasediments

Kalkdal DESCRIPTION OF SCHEELITE MINERALIZATION Kalkdal is an E-W trending valley in Liverpool Land, and scheelite mineral! zation occurs at several localities Numerous scheelite-mineralized areas within a 20 km2 area of the valley have been found in a 350 km long belt (Fig. 2). in Central East Greenland. Outcropping The geology of Kalkdal comprises scheelite mineralization is known in ESE-striking metasediments intruded by 12 areas, which vary from 1 to 20 km2 pinkish biotite granite in the west an in size, and scheelite-bearing boulders grey foliated granodiorite in the east have been located in a further two areas The granite has been dated at 434 m.y. The location of all areas is indicated (Hansen and Steiger, 1971) and the met Scheelite Mineralization in Central East Greenland 319

^ | Skarn Quarternary deposits Ê||jt|] Shear zone

|co8|5| Amphibole gneiss Y^S* | Ice, glaciers y Fault

p''l'i|i;| Dolomite marble I:•:•:I Granite < Strike/dip

| | Schist and paragneiss fr-r-^H Granodiorite A Scheelite locality

Fig. 2. Geological and scheelite-mineralization map of Kalkdal

sediments at 1183 m.y. (Hansen et al., lite skarns, and also contains diopside, 1973). The metasediments are dominated actinolite, plagioclase and scapolite; by biotite-hornblende-garnet schist - reddish-green garnet skarn, which is and paragneiss, with some dolomitic a subordinate type and is irregularly marble beds and amphibole gneiss. Skarn distributed. It contains epidote, has developed in marble when in contact augite, quartz, humite and fluorite in with granodiorite and in a marble hori• addition to garnet. zon several kilometres from outcropping intrusive rocks. Skarn does not occur Only the actinolite and garnet skarns at granite-marble contacts. contain scheelite. Tungsten contents Scheelite mineralization in Kalkdal in hand-sized samples may reach 1%, has been located in the skarns (Fig. 2) but the overall content of the skarns and in a few pegmatite and quartz veins is less than 100 ppm. The scheelite is which cut the skarns. molybdeniferous. The skarns at the granodiorite con• In the marble horizon which is dis• tact are from a few centimetres to sev• tal to the granodiorite, skarn has de• eral metres thick, and can be grouped veloped where the horizon is cut by into four principal assemblages: small faults. Both diopside and actino• - green diopside skarn, which is formed lite skarns occur, and they are inter• from forsterite marble and also con• sected by plagioclase-scapolite vein- tains plagioclase and scapolite lets. Lenses of molybdenum-free schee• lite mineralization, up to several - dark green actinolite skarn, which metres long, occur in these skarns, forms as a replacement of diopside and are accompanied by sericitization skarn; of plagioclase and scapolite. The lenses - grass-green epidote skarn, which contain up to 2% W, but the tungsten alternates with the diopside and actino• content of the entire skarn is less 320 C.P. Hallenstein and J.L. Pedersen than 500 ppm. The scheelite-bearing Knivbjergdal skarns are enriched in lithium (up to 100 ppm) and beryllium (up to 100 ppm) Mineralization has been located in an area of a few square kilometre in Kniv• bjergdal, West Andrées Land (Fig. 1). The geology of the area consists of East Milne Land Upper Proterozoic metasediments which are dominated by quartzites, with an Scheelite mineralization is known in a interbedded, 100 to 200 m thick horizon 2 km long zone at the northern contact of schists and marbles. The metasedi• of an over 100 km2 granodiorite-dominat- ments have been intruded by granite, ed intrusive complex in East Milne Land and the schists now occur in the top of (Fig. 1). the granite as large lenses up to The geological setting of East Milne 1000 m long and 100 m thick (Fig. 3). Land is similar to that of Kalkdal. The schists comprise biotite, quartz E-W striking metasediments, comprising and plagioclase with accessory sphene marble, quartzite and mica schist, are and apatite. They are calcareous in intruded by a plutonic complex. The places and may contain diopside, tremo• oldest, and principal intrusive phase, lite and clinozoisite. The marbles are was granodiorite, which has a radio• calcitic and often bituminous. The main metric age of 453 m.y. (Hansen and granite intrusion is a grey two-mica Tembusch, 1979). The next phase was granite, although a red, potassium-rich mafic quartz syenite and the youngest granite also occurs. Pegmatites cross• was biotite granite. Biotite granite cut the entire area. The granites have has been dated at 386 and 373 m.y. not been dated. Two types of skarn - a (Hansen and Tembusch, 1979). pale brown zoisite-clinozoisite skarn Scheelite-bearing skarns have formed and a green diopside skarn - have form• at contacts between granodiorite and ed in the marble near the contact to marble. The skarns occur either as len• the granite. The zoisite skarn envel• ses, up to 2 m wide and 10 m long, in opes the diopside skarn. dolomitic marble within 50 m of the Scheelite mineralization occurs in granodiorite or as a continuous band both the schist and marble lenses at at the granodiorite-marble contact. the top of the granite (Fig. 3). In The band has been traced for 150 m, mineralized schist, scheelite occurs is 40 cm thick, and is scheelite-bear• in clinozoisite-rich layers, in crossing in the 20 cm closest to the marble. cutting shear zones and disseminated ii The scheelite-bearing skarn consists biotite-rich schistose layers. Minerali of tremolite, idocrase, quartz and zation is typically restricted to centi calcite, together with minor biotite, metre-thick bands in the schist with u| diopside, chlorite and native bismuth. to 0.3% W. The overall tungsten content Diopside, tremolite and scheelite are of the schist is less than 100 ppm. early minerals of the assemblage. Ido• Studies of the schist mineralization crase represents an intermediate stage, have revealed that the more intense and quartz and calcite fill the final scheelite mineralization is accompaniei interstices. Hand samples of skarn may by increasing contents of fluorite (up contain up to 3% W, 0.5% Bi, 200 ppm to 10% by vol.) and apatite (up to 2% Sn and 30 ppm Mo. The average tungsten by vol.), by bleaching of the biotite, content of the skarn lenses is about and by enrichment in tin (200 ppm) and 500 ppm, and of the skarn band about beryllium (70 ppm). 0.5%. In the marbles, scheelite minerali• It is evident from field relation• zations has developed with zoisite- ships that the formation of the skarn clinozoisite skarn. The skarn also con• postdates the intrusion of the grano• tains minor diopside, quartz, plagio• diorite. Pegmatite veins in the grano• clase, fluorite, calcite and apatite. diorite do not continue into the skarn This type has only been observed in or marble, which indicates a pre-skarn boulders. The boulders contain skarn truncation of the veins. bands up to 20 cm wide, in which the Scheelite Mineralization in Central East Greenland 321

A Scheelite locality

Fig. 3. Geological and scheelite-mineralization map of Knivbjergdal

tungsten content is about 1%, and which Other Areas are also enriched in copper (150 ppm), lead (150 ppm), tin (400 ppm), beryl• Scheelite mineralization in Upper Pro- lium (70 ppm), lithium (700 ppm) and terozoic metasediments is also known bismuth (50 ppm). from Gemmedal, Eremitdal and Roslin 322 C.P. Hallenstein and J.L. Pedersen

Gletscher (Fig. 1). Outcropping marble/ area, and at Scheelitdal and Galenadal calc-silicate lenses with minor schee- which respectively are 1 km and 3 km lite occur in biotite-muscovite schist stratigraphically higher than the sedi at Gemmedal. The calc silicates com• ments at Trekantgletscher, and which prise diopside, clinozoisite, idocrase are 5 to 7 km east of the outcropping and garnet. As well as containing up granite (Fig. 1). to 3.4% W in hand samples, the calc- At Trekantgletscher, scheelite oc• silicate rocks are enriched with up to curs in centimetre to metre dimensione 400 ppm Sn and 200 ppm Bi. The meta- lenses of contact metamorphosed calca• sediments have been intruded by garnet reous quartzite - the skarnoid rocks. and tourmaline-bearing, two-mica granite The lenses are often zoned, with an veins, and have been subjected to post- approximately 1 cm thick, greenish hor mineralization deformation. blende-diopside-clinozoisite rim and a Boulders of forsterite marble, with calcareous core usually dominated by scheelite in dark green, massive skarn garnet-hornblende skarnoid. The garnet have been found at Roslin Gletscher. hornblende skarnoid comprises quartz, They stem from the migmatized metasedi- grossularite, diopside, hornblende, ments of the area. The skarn is compos• clinozoisite, plagioclase, scapolite ed of diopside, plagioclase, scapolite and calcite. Fluorite and scheelite oc and scheelite. Post-mineralization de• cur in minor amounts, and sphene, apa• formation of the skarn is evident. A tite and opaque minerals are accesso• hand sample of skarn contained 2% W and ries. In some cases, a zone of garnet- minor tin (80 ppm) and beryllium idocrase skarnoid occurs within the (200 ppm). garnet-hornblende skarnoid. The garnet The Eremitdal mineralization is also idocrase skarnoid comprises quartz, known only in skarn boulders. The boul• grossularite, idocrase, fluorite, cal• ders are of marble cut by veins of cite, diopside and clinozoisite. Schee tourmaline-bearing, two-mica granite. lite, sphene and opaque minerals are A scheelite-bearing, up to 0.5 m thick accessories. Most scheelite occurs in calc-silicate assemblage has developed the garnet-hornblende skarnoid. Tung• at the granite-marble contact. The calc- sten contents of hand samples vary silicate rock comprises diopside, gar• from 0.1 to 0.8% W. The average conter net and idocrase, with minor clinozoi• of an entire skarnoid lens is only a site, sphene, plagioclase, muscovite, few hundred ppm tungsten. The skarnoid actinolite, quartz, calcite, apatite, are also enriched in beryllium (300 pp fluorite and scheelite. The skarn has tin (200 ppm) and bismuth (100 ppm). a low tungsten content ( <100 ppm), At Scheelitdal, scheelite is associ and is enriched in tin (300 ppm). ated with concordant quartz veins. The veins are from fifty to several hundre metres apart, are up to 3 m thick, and Mineralization in the Lower EBG can be followed for up to 500 m. In Sediments addition to coarse-grained quartz, the veins contain coarse-grained arsenopyrite and rare scheelite as centimetr Alpefjord large idiomorphic crystals. The schee• Scattered scheelite mineralization has lite occur near the contact to the wal been located along 15 km of the west rocks. coast of Alpefjord. The geological set• In an approximately 5 km2 area sout ting of this area comprises quartzitic of Galenadal, quartz veins and fractun sediments of the Arenaceous-Argilla• zones are mineralized with arsenopyrit ceous "series" (Frankl, 1951) and Cale• and scheelite. The mineralized veins donian intrusive granites (Fig. 1). and fracture zones occupy 1 to 2% of Scheelite mineralization has been the volume of the sediments. At one studied at three localities - Trekant- locality, more intense scheelite min• gletscher at the contact of the lower• eralization has been located in 2 to most-preserved sediments of the Lower 6 m wide, E-W striking quartz-vein EBG and granite in the south of the swarms (Fig. 4). The swarms are not co Scheelite Mineralization in Central East Greenland 323

Fig. 4. Quartz-vein swarm, Galenadal

tinuously exposed, but it appears as if 150 m thick Calc-Argillaceous "series", one continues for 800 m along its strike. and the rusty shaly quartzites of the Detailed field observations in the Argillaceous-Arenaceous series (Frânkl, swarms have revealed the existence of 1953). Large-scale folding has resulted several generations of quartz veins. in tilting of the sediments at about The oldest veins contain most of the 50° to the northeast. The granites scheelite, whereas arsenopyrite, galena, have intruded to a level about 500 m chalcopyrite, pyrrhotite and bismuthi- below the Calc-Argillaceous "series". nite occur in the youngest veins. Some calc-silicate minerals have devel• Systematic sampling of the vein oped in calcareous rocks during con• swarms indicates an average content of tact metamorphism. 0.1% W and 0.2% As. The contents of The principal scheelite mineraliza• other elements in sulphide-rich samples tion at both localités is associated are 1500 ppm Pb, 200 ppm Bi, 15 ppm Ag, with quartz veins. Minor mineralization 12 ppm Sb, 50 ppm Cu, 25 ppm Zn and 0.1 in calc-silicate rocks has also been ppm Au (Stendal, 1982). seen, but only in boulders. At Bersaerkerbrae, 0.5 to 5 cm thick veins occur in the Calc-Argillaceous Bersaerkerbrae and Skjoldungebrae "series". The centre of the veins con• Scheelite mineralization has been found sists of muscovite with accessory fluo- at these two localities in the North rite, apatite and cassiterite, and is Stauning Alper, some 10 km from each enveloped by an up to 1 cm thick zone other. Both are near the contact be• of fluorite, muscovite, quartz, plagio- tween Lower EBG sediments and Caledo• clase and minor scheelite. In the Arena• nian granite (Fig. 1). ceous-Argillaceous "series", sub-con• The geology of both areas consists cordant quartz veins from 0.2 to 1 m of grey quartzites of the Arenaceous- thick and up to several hundred metres Argillaceous "series", overlain by al• long are mineralized. Mineralization is ternating limestones and shales of the principally in an up to 5 cm thick, 324 C.P. Hallenstein and J.L. Pedersen greisen-like, muscovite-rich selvage lite mineralization is known in two of the veins, which comprises cassiter- areas about 12 km from each other - ite, apatite, fluorite and scheelite. North and South Margeries Dal (Fig. 1) The quartz core of the veins contains In Margeries Dal, Upper EBG sedi• accessoric bornite, chalcopyrite, cas- ments are cut by large E-W striking siterite, hematite, galena, bismuthinite faults, over 10 km long and with throw: and stannite. The average tungsten con• of 100 to 1000 m (Fig. 6). The northen tent of the veins is less than 100 ppm, blocks are generally downthrown. Many but the muscovite selvage contains on second-order faults, up to a few hun• average about 0.5% Sn. dred metres long, branch off the main Scheelite mineralization at Skjol- faults (Fig. 5). The throws of the dungebrae occurs in a few, up to 2 cm second-order faults are up to 100 m, thick quartz-muscovite-fluorite veins, but diminish on going away from the and in more frequent, up to 1 m thick main faults. The sediments of Margerie: quartz-fluorite-carbonate veins. Tung• Dal form part of the easterly dipping sten contents of the veins average less flank of an open anticline. On the than 100 ppm. structural contour map (Fig. 6), it ca; be seen that the anticline forms a domi Randenaes culmination in West Ymers 0. Lamprophyi dykes intrude the sediments and contaii Randenaes is situated on the south coast fragments of quartzite and granite. of Lyells Land just east of the contact Mineralization in North and South zone between Proterozoic metasediments Margeries Dal occurs in the 100 m thicl and Lower EBG sediments (Fig. 1). The lowermost limestone unit of the Upper contact zone is intruded by Caledonian EBG as veins in second-order structure: two-mica granites and by pegmatites. At North Margeries Dal (Fig. 5) the The oldest pegmatites are sub-concor• largest vein contains both scheelite dant to the easterly dipping Lower EBG and stibnite in a breccia zone strik• sediments, and are rimmed by millimetre ing 080° and dipping 75°N. Stibnite to centimetre-thick muscovite greisen. predominates in the 65 m of the brec• Younger pegmatites are sub-vertical and cia zone nearest the main fault. It without associated greisen. The meta• occurs as decimetre-thick massive vein sediments are contact metamorphosed and and as thin veinlets in the hanging comprise interbedded quartzite, biotite wall of the breccia zone in the lime• schist and garnet-biotite schist, with stone. Scheelite has been observed in some metre-sized lenses of calc-silicate the brecciated limestone of this 65 m (skarnoid) rocks. long zone, but only as scattered grain; Most of the scheelite mineralization West of the stibnite-dominated zone of the area is associated with the grei• the brecciated limestone is mineralizei sen rims of the oldest pegmatites. The along strike for 110 m, mostly with greisen may also contain cassiterite, scheelite, but also with stibnite. arsenopyrite, tourmaline and fluorite. Scheelite occurs as irregularly dis• The greisen contains up to 3000 ppm W, tributed fillings in the 1-2 m thick 800 ppm Sn and enhanced contents of breccia zone. Stibnite occurs in a few lithium (200 ppm) and beryllium (50 ppm) millimetre to decimetre-thick veins in Traces of scheelite also occurs in both the footwall and hanging wall of joints in the wall rocks of mineraliz• the breccia zone. Sampling of the en• ed pegmatites and in lenses of skarnoid tire 110 m long zone indicates content! rocks. of 0.8% W and 2.4% Sb with a thickness averaging 3 m. Dolomitization and sili cification of the limestone is also Mineralization in the Upper EBG present in the breccia zone. Magnesia Sediments contents are up to 5% and silica from 10 to 60%, compared with <1% MgO and North and South Margeries Dal 1-5% SiÛ2 in unmineralized limestone. Margeries Dal is a 20 km long, NNE- There are slight enrichments in bis• striking valley on West Ymers 0. Schee• muth (up to 10 ppm), mercury (up to Scheelite Mineralization in Central East Greenland 325

Fig. 5. Geological and scheelite-mineralization map, North Margeries Dal

Fig. 6. Structural contour map of the Upper EBG, Andrées Land and Ymers (after Haller, 1971) 324 C.P. Hallenstein and J.L. Pedersen greisen-like, muscovite-rich selvage lite mineralization is known in two of the veins, which comprises cassiter- areas about 12 km from each other - ite, apatite, fluorite and scheelite. North and South Margeries Dal (Fig. 1) The quartz core of the veins contains In Margeries Dal, Upper EBG sedi• accessoric bornite, chalcopyrite, cas- ments are cut by large E-W striking siterite, hematite, galena, bismuthinite faults, over 10 km long and with throi and stannite. The average tungsten con• of 100 to 1000 m (Fig. 6). The norther tent of the veins is less than 100 ppm, blocks are generally downthrown. Many but the muscovite selvage contains on second-order faults, up to a few hun• average about 0.5% Sn. dred metres long, branch off the main Scheelite mineralization at Skjol- faults (Fig. 5). The throws of the dungebrae occurs in a few, up to 2 cm second-order faults are up to 100 m, thick quartz-muscovite-fluorite veins, but diminish on going away from the and in more frequent, up to 1 m thick main faults. The sediments of Margerie quartz-fluorite-carbonate veins. Tung• Dal form part of the easterly dipping sten contents of the veins average less flank of an open anticline. On the than 100 ppm. structural contour map (Fig. 6), it ca be seen that the anticline forms a doqi Randenaes culmination in West Ymers 0. Lamproph) dykes intrude the sediments and contai Randenaes is situated on the south coast fragments of quartzite and granite. of Lyells Land just east of the contact Mineralization in North and South zone between Proterozoic metasediments Margeries Dal occurs in the 100 m thic and Lower EBG sediments (Fig. 1). The lowermost limestone unit of the Upper contact zone is intruded by Caledonian EBG as veins in second-order structure two-mica granites and by pegmatites. At North Margeries Dal (Fig. 5) the The oldest pegmatites are sub-concor• largest vein contains both scheelite dant to the easterly dipping Lower EBG and stibnite in a breccia zone strik• sediments, and are rimmed by millimetre ing 080° and dipping 75°N. Stibnite to centimetre-thick muscovite greisen. predominates in the 65 m of the brec• Younger pegmatites are sub-vertical and cia zone nearest the main fault. It without associated greisen. The meta• occurs as decimetre-thick massive ve'i sediments are contact metamorphosed and and as thin veinlets in the hanging comprise interbedded quartzite, biotite wall of the breccia zone in the lime• schist and garnet-biotite schist, with stone. Scheelite has been observed in some metre-sized lenses of calc-silicate the brecciated limestone of this 65 m (skarnoid) rocks. long zone, but only as scattered gran Most of the scheelite mineralization West of the stibnite-dominated zone of the area is associated with the grei• the brecciated limestone is mineralize sen rims of the oldest pegmatites. The along strike for 110 m, mostly with greisen may also contain cassiterite, scheelite, but also with stibnite. arsenopyrite, tourmaline and fluorite. Scheelite occurs as irregularly dis• The greisen contains up to 3000 ppm W, tributed fillings in the 1-2 m thick 800 ppm Sn and enhanced contents of breccia zone. Stibnite occurs in a fev lithium (200 ppm) and beryllium (50 ppm) millimetre to decimetre-thick veins in Traces of scheelite also occurs in both the footwall and hanging wall of joints in the wall rocks of mineraliz• the breccia zone. Sampling of the en• ed pegmatites and in lenses of skarnoid tire 110 m long zone indicates content rocks. of 0.8% W and 2.4% Sb with a thickness averaging 3 m. Dolomitization and sili cification of the limestone is also Mineralization in the Upper EBG present in the breccia zone. Magnesia Sediments contents are up to 5% and silica from 10 to 60%, compared with <1% MgO and North and South Margeries Dal 1-5% SiÛ2 in unmineralized limestone. Margeries Dal is a 20 km long, NNE- There are slight enrichments in bis• striking valley on West Ymers 0. Schee• muth (up to 10 ppm), mercury (up to Scheelite Mineralization in Central East Greenland 325

Fig. 5. Geological and scheelite-mineralization map, North Margeries Dal

Fig. 6. Structural contour map of the Upper EBG, Andrées Land and Ymers (after Haller, 1971) 326 C.P. Hallenstein and J.L. Pedersen

3 ppm), silver (up to 2 ppm) and gold (up to 0.15 ppm). Gold analysis was by fire assay, other elements were analyzed by atomic absorption. The breccia zone can be traced for a further 50 m to the west. It is 0.5-1 m wide with no visible scheelite or stibnite, but the contents of tung• sten and antimony are still elevated with 4-100 ppm W and 2-100 ppm Sb. Several other mineralized lenses oc• cur in an overlying limestone unit up to 40 m north of the main fault (Fig. 5). They are up to 1 m thick, 10 to 15 m long, contain about 1% W but no anti• mony. The tungsten, as scheelite, oc• curs as breccia fillings in second- order fault structures. Similar small Fig. 7. Scheelite-mineralized limestoa scheelite-mineralized lenses have been breccia, South Margeries Dal. Photo in located in second-order structures in UV-light with scheelite shining white the overlying limestone approximately 200 m east of the main mineralization (Fig. 5). The main mineralization of South Margeries Dal is a vein in a breccia zone, striking ENE, dipping 80°N, and veins. Post-mineralization deformation without any appreciable amount of dis• has caused deformation twinning and placement. The zone is up to 3 m wide fracturing of the scheelite grains, and can be followed from the bottom and shearing of stibnite into very to the top of the 100 m thick, lower• fine-grained aggregates. most limestone unit. Scheelite occurs as breccia fillings in the limestone Other Areas (Fig. 7), and is particularly concen• trated in the breccia zone in the lower Minor scheelite mineralization as thin half of the unit. The tungsten content veinlets in joint planes in Upper EBG averages nearly 3% over an average sediments is known at several other width of 2.5 m. Dolomitization and si- localities (Fig. 1.). At Panorama Fjell licification are pronounced and cor• the veinlets occur in the lowermost relate well with the distribution of limestone unit of the Upper EBG and an scheelite. Stibnite has not been ob• associated with a major, SE-striking, served, but antimony can be detected normal fault zone. The mineralization as a trace element (up to 19 ppm Sb). is antimony free, and was accompanied Pétrographie studies of the North by silicification and dolomitization oi and south Margeries Dal veins have the limestone. At Eleonore Bugt, dolo• enabled the description of the textural mites underlying the lowermost lime• and mineralogical development during stone unit host the few scheelite vein- vein formation in the limestone. After lets. They occur a few hundred metres cataclastic deformation of the lime• east of a SE-striking fault. The vein- stone, very fine-grained quartz, dolo• lets of Noa Dal occur in calcareous mite and scheelite replaced calcite quartzite beds of the Upper EBG Quart- in the fractured limestone. During pro• zite "series", and are associated with gressive replacement, large subhedral an E-W striking fault. Panorama Fjeld scheelite grains formed. Fine-grained and Eleonore Bugt occur on the east quartz occurs as inclusions in the flank of a domal culmination in East rims of the scheelite grains. At a Andrées Land, and Noa Dal on 'the east late stage, calcite and stibnite (if flank of the West Ymers 0 culmination present) precipitated in the centre of (Fig. 6). Scheelite Mineralization in Central East Greenland 327

DISCUSSION skarn, which has not been subjected to further skarn or hydrothermal processes. The Kalkdal and Milne Land skarns are Mineralization in Upper Proterozoia also characterized by the early forma• Metasediments tion of diopside, but without accompany• ing scheelite. Under a continuing Relationship between mineralization and skarn-forming process, the diopside of granitic rocks these areas was replaced by actinolite or tremolite or epidote or idocrase. The mineralization in Upper Proterozoic Actinolite, tremolite and idocrase may metasediments is typically associated be accompanied by minor scheelite, with calcareous units in the metasedi• whereas scheelite has not been observed ments, and is often spatially associat- with epidote. In Kalkdal, a final hydro- d with granitic intrusion. The schee- thermal phase occurred, with sericiti- lite-bearing skarns of Kalkdal, Milne zation of plagioclase and the precipi• Land and Eremitdal all occur at the tation of significant scheelite. The contacts of intrusive rocks - granodio- scheelite-bearing skarns of Gemmedal rite for the first two and granite for and Eremitdal contain garnet and ido• the last. However, the skarn of Milne crase in addition to diopside, but a Land is clearly post granodiorite, paragenetic sequence of calc-silicate whereas those of Kalkdal and Eremitdal minerals is not apparent. were formed at the same time as the intrusion of the igneous rocks with The Knivbjergdal calc-silicate as• which they are in contact. semblage is principally zoisite, clinozoisite and diopside,and was accompanied The relationship between mineraliza• by scheelite. In a second, and apparent• tion and granitic intrusion in Kniv- ly subsequent phase, the formation of bjergdal is uncertain. No signs of skarn diopside predominated. It is probable or scheelite have been observed at the that the mineralization in schists de• exact metasediment-granite contacts, veloped during the phase of zoisite- but there is a general spatial relation• skarn formation. ship between granite and mineralization. There are also several features evi• The scheelite-bearing calc-silicate dent in the trace-element chemistry of rocks of Gemmedal and Roslin Gletscher the various skarns. The scheelite of are not clearly associated with granitic the diopside skarn of Roslin Gletscher, rocks although the metasediments of the tremolite skarn on Milne Land, and each area are characterized by granite the actinolite skarn in Kalkdal is al• veining and migmatization respectively. ways molydeniferous. Enhanced contents Skarn Formation of tin occur in the skarns of all areas except Kalkdal. Bismuth, lithium and The calc-silicate assemblages of Kalk• beryllium are enhanced in the skarns dal, Milne Land, Gemmedal, Eremitdal of many of the areas. and Roslin Gletscher have been formed Age of Mineralization in dolomitic marble, and are dominated by magnesian minerals. Those of Kniv- There are no clear dates for the for• bjergdal, however, have been formed in mation of the various skarns. The best calcic-carbonate rocks and are magne• age information exists for the Kalkdal sium poor. Furthermore, the calc sili• and Milne Land areas. The Kalkdal min• cates of all areas are generally iron eralization postdates the metamorphism poor. of its host sediments (1183 m.y.: Han• The calc-silicate assemblages which sen et al., 1973), is associated with have developed in dolomitic marble all the intrusion of granodiorite which has contain diopside. Some diopside, as well not been dated, and predates the intru• as forsterite, have been observed in sion of the granite (434 m.y.: Hansen unaltered marble, but most diopside and Steiger, 1971). The Milne Land skarn developed as a first stage of the postdates the intrusion of the grano• skarn-forming process. The scheelite of diorite with which it is in contact, Roslin Gletscher occurs in a diopside and is thus younger than 453 m.y. 328 C.P. Hallenstein and J.L. Pedersen

(date from Hansen and Tembusch, 1979). gletscher and Randenaes. The zoned The intrusive history of Kalkdal and skarnoid assemblages are interpreted East Milne Land is similar, there being as having been formed by a combination an early granodiorite phase which was of metamorphism and metasomatism. The subsequently intruded by granite. If calc-silicates grossularite, diopside the Kalkdal granodiorite is of similar and hornblende developed during meta• age to the Milne Land granodiorite, the morphism. Idocrase, scapolite, fluoritf skarns which formed at the contacts of and scheelite were formed during later the Kalkdal granodiorite would be of an reaction with skarn-forming fluids. age corresponding to the peak of Cale• The third mineralization type occurs donian orogenesis (455-430 m.y.). If it either in quartz veins as at Randenaes is presumed that the Milne Land grano• and Galenadal, or in quartz-fluorite diorite and the post-granodiorite skarns veins, as at Bersaerkerbrae and Skjol• were derived from a common magmatic pa• dungebrae. Mineralized veins have been rent, an age corresponding to the main observed up to seven kilometres from Caledonian orogenesis may also be at• the granite contact. tributable to the Milne Land skarns. All three mineralization types are The scheelite occurrences of Kniv- enhanced in bismuth. Tin is associated bjergdal, Gemmedal, Eremitdal and Roslin with the greisen type, and arsenic witl Gletscher occur in Upper Proterozoic the quartz-vein type. metasediments intruded by Upper Protero• It is assumed that all scheelite zoic and Caledonian granites. It is mineralization in the area is of simi• thus possible that the occurrences are lar age. Direct age evidence does not of Upper Proterozoic and/or Caledonian exist, but the intrusion of the gran• age. The post-mineralization deforma• ites, which appear to have controlled tion which is evident in Gemmedal and the mineralization, was during the Roslin Gletscher suggests that the min• main Caledonian orogeny (455-430 m.y.) eralization of these two areas may be A granite intruding the Lower EBG souti older than that of the other areas. of Randenaes has been dated at 445 m.y (Rex et al., 1976) . Mineralisation in Lower EBG Sediments The Lower EBG sediments of the Alpe- Mineralization in Fault Zones in Upper fjord and North Stauning Alper region EBG Sediments are intruded by Caledonian two-mica The mineralization of this group occurs granites. Scheelite or other mineraliza• as veins in fault and breccia zones in tion has not been observed at the actual folded Upper EBG sediments, and in par• granite-sediment contacts, even when ticular in the lowermost limestone unii the granites cut the thick limestone of the Upper EBG. The development of beds of the Calc-Argillaceous "series". the folds and of culminations along There is, however, a clear zoning of anticlinal axes are believed to be a the scheelite-mineralization type from function of granitic upwellings at within a few hundred metres of the con• depth. The presence of granite stocks tact to up to 7 km from the contact. is supported by the occurrence of gran• One type of mineralization generally ite xenoliths in the lamprophyre dykes occurs within 1 km of the granite con• of the domal areas. Anticlinal culmina• tact, and is associated with muscovite- tions occur in West Ymers 0 and in East greisen formation at the borders of Andrées Land (Fig. 6). All the known pegmatite and quartz veins. This situ• fault-associated scheelite mineraliza• ation is known at Randenaes and Bersaer- tion occurs on the flanks of these two kerbrae. domal structures within 20 km of the The second mineralization type also apices of the domes. In addition to occurs within 1 km of the granite con• updoming and faulting the sediments, tact. It is restricted to skarnoid de• the granitic stocks are considered to velopments in lenses of calcareous have been the source of epithermal so• quartzites. This type is known at Ber- lutions, from which the mineralization saerkerbrae, Skjoldungebrae, Trekant- was precipitated. Scheelite Mineralization in Central East Greenland 329

Most of the mineralization occurs tures up to 150 m from the main fault in the lowermost limestone unit of the structure, and generally becomes less Upper EBG, which is of obvious potential intense on going away from the main as a chemical trap for ascending solu• fault. Stibnite, which is also present tions. The unit is furthermore physical• in North Margeries Dal, occurs only in ly competent, and production of open the zone nearest the main fault. Trace fracture, fault and breccia zones, contents of tungsten and antimony are i.e. suitable physical traps, is thus detectable as a halo in the breccia possible in the limestone. Similar zone for 50 m beyond the visible miner• chemical and physical conditions exist alization. Movement of ore-forming in overlying limestone units, and some fluids along the main fault and into scheelite-mineralizing fluids have second-order structures is thus implied. reached overlying units in North Mar- Pétrographie studies have indicated geries Dal. Minor occurrences of schee• that the first stage of vein develop• lite have been observed in quartzites ment involved replacement of calcite in and dolomites below and above the lower• limestone by quartz and dolomite. As most limestone unit (Noa Dal, Eleonores replacement progressed, scheelite, and Bugt and North Margeries Dal). finally calcite and stibnite (if pre• In North Margeries Dal, the minerali• sent) were precipitated. Pétrographie zation occurs in second-order struc• and chemical studies have confirmed

Table 1. Comparison of East Greenland tungsten occurrences with a world-scale classification of tungsten occurrences

CLASSIFICATION OF TUNGSTEN OCCURRENCES ( BURNOL ET AL. 1978) OCCURRENCES IN EAST GREENLAND

I DEPOSITS ASSOCIATED WITH THE PLUTONIC ENVIRONMENT

A SKARN MILNE LAND. KALKDAL, KNIVBJERGDAL ETC.

B PEGMATITES RANDEN£S

C VEIN TYPE 1 STOCKWORK MINERALIZATION JUST ABOVE AN INTRUSION WITH NO APPARENT RELATION TO AN INTRUSION 2 DISSEMINATION IN PLUTONIC CUPOLAS MALMBJERG 3 INDIVIDUAL VEINS OUTSIDE OR WITHIN A PLUTONIC INTRUSION OUARTZ VEINS WITH WOLFRAMITE QUARTZ VEINS WITH CASSITERITE AND WOLFRAMITE OUARTZ VEINS WITH SCHEELITE GALENADAL AND NORTH STAUNING ALPER OUARTZ VEINS WITH SCHEELITE AND GOLD 1 PIPE MINERALIZATION

II DEPOSITS ASSOCIATED KITH THE SUBVOLCANIC ENVIRONNENT

A TUNGSTEN AND TIN TOGETHER 1 TUNGSTEN-TIN-BEARING POLVMETALLIC VEINS RICH IN SULPHIDES 2 TUNGSTEN-TIN MINERALS DISSEMINATED IN RHVOLITE

B TUNGSTEN WITHOUT TIN 1 OUARTZ VEINS WITH HUEBNER1TE AND SULPHIDES 2 OUARTZ VEINS WITH FERBERITE OR SCHEELITE,AND STIBNITE NORTH AND SOUTH MARGERIES DAL 3 QUARTZ VEINS WITH FERBERITE

III TUNGSTEN ASSOCIATED WITH MANGANESE OXIDES

IV STRATABOUND TUNGSTEN DEPOSITS

V PLACER DEPOSITS WITH TUNGSTEN 330 C.P. Hallenstein and J.L. Pedersen that silica, tungsten, antimony, sul• zoic to Upper Cretaceous ages. They oc• phur and magnesium have been introduced cur in carbonate rocks, which for most during the mineralization process. Some exploitable tungsten deposits are cal• post-mineralization faulting has affect• cific and not dolomitic limestones. Thi ed the veins, resulting in fracturing skarn mineralogy is typified by early- of scheelite grains, shearing of stib- stage, magnesium-aluminium-rich, iron- nite, and recrystallization of calcite. poor calc-silicates (diopside, grossu- The metallogenetic model which is larite, idocrase), by middle-stage iroi proposed above for this mineralization rich calc-silicates (hedenbergite, an- type invokes a main Caledonian orogeny dradite, almandine), and by late-stage age. The post-mineralization deforma• hydrous assemblages (tremolite, actino- tion which has occurred is attributed lite, hornblende, epidote). The early to fault reactivation in post-Devonian stage is generally tungsten-poor, wherf times. as the middle, and particularly the late stages are generally tungsten ricl The skarn occurrences of East Green• land exhibit some, but not all of the THE EAST GREENLAND OCCURRENCES COMPARED above-mentioned characteristics. Grano• WITH A WORLD-SCALE CLASSIFICATION OF diorite is associated with the skarns TUNGSTEN DEPOSITS of Kalkdal and Milne Land, whereas the other occurrences either are associatei with granite or are without obvious In the past, tungsten deposits have plutonic association. The intrusion of been divided into vein deposits, often most of the granodiorites and granites together with tin, and skarn deposits. is believed to have accompanied the However, during the last 20 years, the main Caledonian orogeny (455-430 m.y.) finding of new types and new areas of - the end of the Lower Palaeozoic. Onl; tungsten mineralization has resulted in the skarn of Knivbjergdal has developei the need for a more detailed and compre• in calcitic marble. The other skarns oi hensive classification scheme. Such a the Upper Proterozoic metasediments ha scheme for tungsten occurrences has been developed in dolomitic marbles, and th( proposed by Denisenko (1975), and re• skarns in the Lower EBG of Alpefjord vised by Burnol et al. (1978). This re• and the North Stauning Alper are in vised scheme is summarized in Table 1. calcareous quartzites. The East Green• It has been possible to classify the land skarns generally exhibit an early, East Greenland scheelite occurrences in diopside-rich phase, which was often accordance with this scheme, into the followed by a stage of hydrous-mineral categories skarns, pegmatites and quartz development (amphiboles, idocrase, epi• veins in the plutonic environment, and dote) . The hydrous phase was typically into scheelite plus stibnite veins in accompanied by minor scheelite miner• the subvolcanic environment (Table 1). alization. A final stage of more in• This categorization of East Greenland tense alteration and rich scheelite scheelite is discussed below. The wolf• mineralization occurred locally in ramite-bearing porphyry molybdenum de• Kalkdal, but not at any of the other posit at Malmbjerg is furhtermore clas• known skarn occurrences. None of the sifiable into the category of dissemina• East Greenland skarns exhibit an iron- tion in a plutonic cupola. rich stage of calc-silicate developmeni Skarns Pegmatites In their comprehensive review of skarn deposits, Einaudi et al. (1981) have Burnol et al (1978) point out that characterized tungsten skarns according scheelite or wolframite-bearing peg• to associated plutonic rocks, host rocks matites are a relatively unimportant and skarn mineralogy. Tungsten skarns source of tungsten. Such pegmatites an are typically associated with plutonic characterized by enrichment in the ele• rocks of granodiorite to quartz monzon- ments beryllium, lithium, niobium and ite composition, and of Middle Palaeo• tantalum and by the minerals topaz, Scheelite Mineralization in Central East Greenland 331 tourmaline, beryl, apatite, etc. The CONCLUSIONS scheelite and cassiterite-bearing pegmatites at Randenaes are quite com• parable with this characterization. Numerous scheelite occurrences have been discovered in a 350 km long belt of Quartz Veins with Scheelite Central East Greenland. It has been Tungsten-bearing quartz veins are the possible to group the occurrences into source of 70-75% of the worlds tungsten three main geological settings: (Burnol et al., 1978). Most of these - scheelite in Upper Proterozoic meta• veins occur in argillaceous and arena• sediments, often associated with grano- ceous sediments (or metasediments) and diorite or granite intrusion; contain wolframite. However, scheelite - often with gold - occurs in quartz - scheelite in Lower EBG sediments, as• veins in more calcareous host rocks, sociated with granite, pegmatite and or even in granitic host rocks. The quartz-vein intrusion; tungsten deposit of Barruecopardo in - scheelite in Upper EBG sediments, Spain comprises scheelite-bearing quartz without direct magmatic association. veins in granites (Arribas, 1979). The veins are from 1 to 50 cm thick, and Metallogenetic models have been con• are traceable over several hundred structed for the groups, and Caledonian metres. Arsenopyrite accompanies the magmatic activity is a common factor in scheelite. The tungsteniferous quartz each of the models. The geological en• veins of East Greenland (in the Alpe- vironment of the first group is con• fjord and North Stauning Alper areas) sidered to represent a deeper level of occur in argillaceous and arenaceous Caledonian magmatic activity. Several sediments with a minor calcareous com• of the scheelite occurrences suggest ponent. However, scheelite is the only that minor tungsten mineralization may tungsten mineral which has been observ• have been present in the Upper Protero• ed in the veins. Arsenopyrite and base zoic rocks prior to the Caledonian oro• metals accompany the scheelite. The geny. The second geological environment quartz-vein swarm of Galenadal is of represents an upper level of Caledonian similar dimensions and mineralogy to magmatism, whereas the third environ• the veins of Barruecopardo. ment is considered to be distal to Cale• donian granite at depth. The metallogenetic models are of use Quartz-Scheelite-Stibnite Veins as exploration aids: Quartz veins of the subvolcanic environ• ment with scheelite, ferberite and - The contact zones of granodioritic stibnite are an important source of intrusives and marble-bearing metasedi• tungsten in Bolivia. The veins typical• ments are the best targets in the Upper ly occur in fault and fracture zones, Proterozoic metasedimentary belts. The contain small lenses which are rich scheelite-bearing skarns of the Upper iii tungsten, and are not accompanied by Proterozoic metasediments contain en• any obvious magraatic source (Burnol hanced contents of tin, bismuth, lithi• et al., 1978). Arribas (1978) has de• um and beryllium, which also may be scribed a similar scheelite-stibnite useful as exploration aids. vein deposit - that of the Codosera - Exploration for scheelite in the con• mine in Spain. This vein occurs in a tact zones of Caledonian granites and breccia zone in limestone, and is also the Lower EBG sediments should take in• without direct association with magma- to account the zoning of mineralization tism. The East Greenland scheelite- type from skarn and greisen type nearest stibnite veins (Margeries Dal) are the granites to quartz-vein type up to quite comparable with these examples, several kilometres from the granites, as they occur in fracture/breccia zones as well as the minor element contents in limestone, contain small lenses of - bismuth in all types, tin nearest rich mineralization, and are without the granites and arsenic furthest from direct association with magmatism. the granites. 332 C.P. Hallenstein and J.L. Pedersen

- The metallogenetic model for the third REFERENCES group involves mineralization in the lowermost limestone unit of the Upper Arribas, A.: Mineral paragenesis in th EBG when cut by E-W trending fault Variscan metallogeny of Spain. zones, and on the flanks of anticlinal Stvdia Geologica 14, 223-260 (1978) culminations. Exploration in such poten• Arribas, A.: Le gisement de tungstène tial areas could furthermore utilize de Barruecopardo (60°31'W et 41°08'N the tungsten and antimony haloes in Chronique Recherche Minière, FRA 450 the fault zones around the mineraliza• 42-49 (1979) tion. Burnol, L., Geffroy, J., Soler, P.: Le tungstène, ses principaux types It is also possible to draw some de gisement. Chronique Recherche conclusions about the economic poten• Minière, FRA 441, 27-43, et n° 443, tial of the various mineralization 27-44 (1978) types in East Greenland based on the Denisenko, V.K.: Classification des comparison with the world-scale classi• gisements de tungstène à des fins fication of tungsten deposits: prévisionnelles. Zap. Vses. min. - The skarn-type occurrences on East obshch. 104, vyp 5, 526-538 (in Rus• Greenland are probably not of great sian). (Translation B.R.G.M. 5, 493) economic potential because: they are (1975) generally of limited extent and rela• Eha, S.: The pre-Devonian sediments of tively low tungsten content, they Ymers 0, Suess Land and Ella 0 (East mostly are developed in dolomitic mar• Greenland) and their tectonics. Medd ble, and they lack the iron-rich for• Gr<

Hansen, B.T., Frick, U. Steiger, R.H.: logical investigations in the crystal• The geochronology of the Scoresby line complexes of the East Greenland Sund area. 5: K/Ar mineral ages. Rapp. Caledonian fold belt between 72° and Gr^nlands geol. Unders. 58, 59-61 74°N. Rapp. Gr^nlands geol. Unders. (1973) 80, 127-133 (1976) Hansen, B.T., Higgins, A.K., Bar, M.-T.: Steiger, R.H., Hansen, B.T., Schuler, Rb-Sr and U-Pb age patterns in poly- Ch., Bar, M.T., Henriksen, N.: metamorphic sediments from the Polyorogenic nature of the Southern southern part of the East Greenland Caledonian fold belt in East Green• Caledonides. Bull. geol. Soc. Den• land. An isotopic study. J. Geol. 87, mark 27, 55-62 (1978) 474-495 (1979) Henriksen, N., Higgins, A.K.: East Stendal, H.: Geochemistry and genesis Greenland Caledonian Fold Belt. In: of arsenopyrite mineralization in Geology of Greenland, Escher, A., late-Precambrian sediments in Central Watt, W.S., (eds) pp 182-246, Copen• East Greenland. Trans. Instn. Min. hagen: Geol. Surv. Greenland 1976 Metall. (Sect. B: Appl. Earth. Sci.) Higgins, A.K., Friderichsen, J.D., 91, B187-B191 (1982) Thyrsted, T.: Precambrian metamorphic Thyrsted, T.: Structural and metamorphic complexes in the East Greenland Cale• studies in the East Greenland Cale• donides (72°-74°N) - their relation• donides between 72° and 74° N. Rapp. ships to the Eleonore Bay Group, and Gr^nlands geol. Unders. 90, 94-99 Caledonian Orogenesis. Rapp. Gr^n- (1978) lands geol. Unders. 104, 5-46 (1981) Vidal, G.: Acritarchs from the Upper Hintsteiner, E.A.: Scheelitprospektion Proterozoic and Lower Cambrian of in Ostgronland. Berg-Huttenmann. East Greenland. Bull. Gr^nlands geol. Monatsh. 122, 2a, 31-35 (1977) Unders. 134, 55 pp (1979) Kirchner, G.: Die Molybdanlagerstatte des Erzberges bei Mesters Vig, Ost• gronland. Berg- Huttenmann. Monatsh. Received: June 15, 1982 109, 162-173 (1964) Accepted: January 13, 1983 Rex, D.C., Gledhill, A.R.: Isotopic studies in the East Greenland Cale• C.P. Hallenstein donides (72°-74°N) - Precambrian and Northern Territory Department of Caledonian ages. Rapp. Gr^nlands geol. Mines and Energy Unders. 104, 47-72 (1981) P.O. Box 2901 Rex, D.C., Gledhill, A.R., Higgins, Darwin, Northern Territory A.K.: Progress report on geochrono- Australia 5794

Mineral.Deposita 18, 335-347 (1983) MINERALIUM DEPOSITA © Springer-Verlag 1983

Fluid Inclusion Petrography of SW England Granites and its Potential in Mineral Exploration

A. H. Rankin1 and D. H. M. Alderton2

1 Department of Geology, Imperial College, London, England 2 Department of Geology, Chelsea College, London, England

Fluid inclusions in granite quartz from SW England provide a record of the com• plex and protracted hydrothermal history of this important metallogenic pro• vince. Regional variations in terms of the different types of inclusions can be correlated on an inter-pluton scale with both the texture of the host gran• ite and the extent to which it is mineralized. On an intra-granite scale those areas where mineralization is particularly pronounced show a higher overall in• clusion abundance than areas where little or no mineralization is known to oc• cur. The types of fluid inclusion most commonly related to Sn-W-Cu mineraliza• tion are halite-free, moderate temperature inclusions. Inclusions containing visible CO2 at room temperature are restricted to two localities in SW England. Both of these contain stockwork/vein-swarm tungsten mineralization. These re• gional 'fluid inclusion anomalies' show that fluid inclusion petrography using a simple pétrographie microscope has potential application in the field of min• eral exploration.

INTRODUCTION 1979) or vein deposits on a mine scale (Roedder, op. cit.). The idea that fluid inclusion petro• This paper reports on the distribution graphy might prove useful as a regional and abundance of fluid inclusions in exploration tool in SW England was en• quartz from mineralized granite of SW couraged by Sorby's early observations England with the primary aim of assess• (1858) which clearly demonstrated mark• ing the value of fluid inclusion petro• ed variations in the fluid inclusion graphy in regional mineral exploration assemblage in granite quartz. Several in this area. fluid inclusion studies have recently A number of accounts of fluid in• been undertaken in SW England on a lo• clusions as tools in mineral explora• cal scale mostly on vein material (for tion already exist in the Russian lite• summaries see Charoy, 1979; Jackson et rature. These have recently been re• al., 1982; Rankin et al., 1982; Rankin viewed by Roedder (1977). Studies in and Alderton, 1982). the West are limited and with few ex• There has been little interest since ceptions are concerned either with por• Sorby's early work in studying fluid phyry copper deposits (Nash, 1976; Chi- inclusion populations in the granites vas and Wilkins, 1977; Evans et al., themselves. Our own data, presented 336 A.H. Rankin and D.H.M. Alderton here, is only a beginning and should GRANITES AND MINERALIZATION OF SW not be considered an exhaustive account. ENGLAND We have concentrated on methods which are simple and rapid to use and there• fore potentially useful in exploration. The geology has recently been reviewed by Charoy (1979) and Edmonds et al. From Sorby's early description and (1975). Five main granite masses are from our own initial observations it intruded into a sequence of Devonian is clear that most of the inclusions and Carboniferous sediments which were in granite quartz are secondary. These regionally metamorphosed to green- represent late-stage, post-consolida• schist faciès prior to granite in• tion fluids that have passed through trusion. and (sometimes) altered and mineralized the granites. Primary inclusions are Geophysical evidence suggests that rare but when present may either re• the five main masses of granite are present magmatic fluids generated from part of a larger batholith buried at the early magma (in the case of magmat• depth. A series of minor granite in• ic quartz) or later fluids (in the case trusions also occur and these are pre• of hydro thermally recrystallised quartz) .sume d to be similarly connected at depth. In theory, it should be possible to The granites were intruded towards study the fluid inclusion paragenesis the end of the Hercynian orogeny and and hence build up a picture of the have been dated at about 280 m.y. (for progressive stages in the thermochem- details see Jackson et al., 1982). Geo ical evolution of hydrothermal fluids chemically they show only minor varia• associated with these granites. In prac• tions and are sensu stricto biotite- tice, magmatic and hydro thermal quartz muscovite granites. Textural variation are very difficult to distinguish. Mat• are more pronounced (Dangerfield and ters are further complicated because Hawkes, 1981). samples from different plutons show marked differences in their fluid in• The main variations are in terms of: clusion populations as do samples from i) overall grain size different areas of the same pluton. ii) size of K-feldspar megacrysts Thus, even from a cursory examination it is apparent that hydrothermal acti• Regional variations also occur in vity, as recorded by the fluid inclu• the distributions and abundance of sion assemblages in the granites them• late-magmatic minor and trace minerals selves, was non-uniform in its distri• such as topaz, tourmaline and fluorite bution and episodic. This is entirely Fractures initiated by regional stres• compatible with the complex nature and ses before and during granite emplace• non-uniform distribution of alteration ment were exploited by subsequent hydi and ore mineralization as discussed thermal and late-stage magmatic pheno• below. The rationale behind the present mena (Moore, 1975). The linear frac• study is to establish whether it is pos• tures are in general parallel to the sible to relate differences in the fluid axis of the batholith (Fig. 1), tend• inclusion populations to different de• ing to occur on one particular margin grees or types of hydrothermal activity of a pluton. Some portions of the associated with the granites. The re• granite are much more extensively min- sults for four of the five major plu• eralizd whilst others are almost barn tons are presented here. The St. Austell of mineralization. pluton is associated with intensive Ore mineralization occurs mostly ii kaolinisation. This process has, in veins or vein swarms. The ore mineral• many places, obscured the earlier hydro- ogy is complex and variable but domini thermal events, and further complicated ed by cassiterite, wolframite and sul• the fluid inclusion populations. Because phides of Cu, Fb, Zn, As and Fe. Gang) of this we will not consider this plu• minerals and alteration products of tl ton in the present paper. The results granite are dominated by quartz, tour• are published in detail elsewhere (Al• maline, fluorite, muscovite, chlorite, derton and Rankin, 1983). alkali-feldspar and kaolinite. Fluid Inclusion Petrography of SW England Granites 337

Fig. 1. Geological map of SW England (adapted from Alderton, 1976)

SW England is a classic example of Stable isotopic evidence (Sheppard, temporal and spatial mineral zonation 1977; Jackson et al., 1982) indicates (Moore, 1982). The earliest minerali• that the fluids involved in ore miner• zation, closest to the granite, is alization and hydrothermal alteration characterized by Sn-W-Cu veins. Later contained a large component of meteoric mineralization is dominated by Pb-Zn water. Simpson et al. (1979) and Moore and tends to occur further away from (1982) have suggested that areas of in• the granites. Early mineralization has tense mineralization are where convec- been dated about 270 m.y., which is tive hydrothermal cells, involving very close to the age of granite large volumes of meteoric water, were emplacement (Jackson, et al., 1982). extensively developed. A number of later hydrothermal events The origin of the ore metals is the have been postulated on isotopic evi• subject of much speculation. Leaching dence (op. cit.). Uranium mineraliza• from the surrounding country rocks or tion and extensive kaolinisation are consolidated granites is plausible, but almost certainly related to these later a magmatic origin cannot be excluded events. Warm springs in underground on the basis of available evidence. workings (Alderton and Sheppard, 1977) and high heat flow (Tammemagi and Wheil- don, 1974) show that even today the METHODOLOGY AND APPROACH region is hydrothermally active. Thus a number of separate hydrothermal events have affected the areas from the time Normal pétrographie thin sections were of emplacement of the granite to the used to study the size, shape, abun• present day. dance and types of inclusions present 338 A.H. Rankin and D.H.M. Alderton in quartz from samples of unaltered and effective. The general features of granite collected at about 1-3 km in• each inclusion type are listed below. tervals from each of the four major plutons. Only the last two parameters showed significant variations and these Type 1 were studied in detail. The usual size of the inclusions ranged from about 5 Monophase aqueous inclusions sometimes to 20 um and shapes ranged from highly containing a small vapour bubble. Thesi irregular through to rounded or nega• are highly irregular, usually flattene tive crystal cavities. Fluid inclusions and occur in distinct planes. Their were also observed in feldspars, and homogenisation temperatures range up certain accessory minerals (apatite, to about 200°C. topaz, fluorite) within the granite, but were seldom as well-developed as in the quartz, and were therefore not con• Type 2 sidered further. A limited amount of heating and Aqueous inclusions containing a moder• freezing stage work on polished wafers ate to large vapour bubble. Generally, was conducted during the initial stages these inclusions are more regular in of this research to determine the over• shape and show less of a tendency to all range of salinities and homogenisa- occur in planar groupings. An arbitrar tion temperatures (Th) for the inclu• subdivision based on the proportion of sion populations. Routine determination vapour (2a, 2b) has sometimes been maq of Th and salinity were not attempted Th range is from about 200°C to 600°C. for all samples because of the inordi• nate length of time required to accumu• late data and the concommitant unlikeli - Type 3 hood that this approach would find ap• plication as a rapid, routine explora• Aqueous inclusions characterised by tion technique. chloride daughter minerals (e.g. hal• ite) . The vapour bubble is variable in size but typically occupies between 10% and 30% of the inclusion volume. CLASSIFICATION OF INCLUSIONS IN SW Vapour-liquid homogenisation tempera• ENGLAND GRANITES tures are generally between 200°C and 350°C. Halite solution temperatures are variable but may be as high as Fluid inclusions may be classified in 500°C. a number of ways. Most obvious is a genetic classification (P, PS, S) but this is very subjective and in granite Type 4 quartz, as previously indicated, may be impossible. An alternative is to clas• Gaseous inclusions, either totally fil sify the inclusions according to gross led with vapour or, more rarely, to• composition. A six-fold classification gether with a small rim of liquid. The scheme is proposed. The inclusions are often occur in planes and are charac• classified according to the volumetric teristically rounded or equant in shap proportion of vapour and aqueous sol• Homogenisation is to the vapour phase ution and whether the inclusions con• but it is rarely possible to determine tain liquid CO2 or chloride daughter the exact temperature at which this minerals (halite) at room temperature. occurs. Solidified melt inclusions are includ• ed in this scheme. The subdivisions are somewhat arbitrary and considerable Type 5 overlap can occur between each inclu• sion type in some samples. In general, C02~rich inclusions, containing a vari however, the classification is useful able proportion of aqueous solution ai Fluid Inclusion Petrography of SW England Granites 339

characterised by a CC^-rich phase DETERMINATION OF THE RELATIVE PROPOR• (C02£ and/or C02v). TIONS OF DIFFERENT FLUID INCLUSION TYPES Type 6

Our final inclusion type is essentially At a fixed interval during the abun• crystalline or possibly glassy. A small dance estimates (depending on the ab• amount of vapour is usually present undance of inclusions) a count of the and we tentatively identify these as various inclusion types was made. About trapped silicate melts. 100-150 inclusions were counted overall and the results expressed as percent• ages of the total population. The main problem with this procedure is that it DETERMINATIONS OF THE OVERALL ABUNDANCE is sometimes difficult to unambiguously OF INCLUSIONS classify an inclusion and this intro• duces a certain amount of subjectivity. For total fluid inclusion abundance Tests were however carried out to assess estimates, the most accurate (and time- the within sample and operative varia• consuming) method would be to actually bility. A variability of 10-15% is typ• count the number of inclusions in a re• ical when assessing the overall abun• presentative volume of quartz. The dance of inclusions. For the individual other extreme would be to make a rapid types the variability can be up to visual estimate of the overall inclu• ± 30% in some samples, probably because sion density. We have adopted an ap• about 100 inclusions are not truly re• proach between these two extremes as a presentative of the sample. These vari• compromise between time and accuracy. ations could be reduced by increasing The use of pétrographie sections of the number of observations. For our pur• standard thickness (30 um) meant that poses, where we are only concerned with a standard volume of quartz was compar• broad differences these numbers are ed at each operation, and that samples considered sufficient. in other collections could also be studied. In addition, the petrography of the rock could be assessed at the RESULTS same time. Six standard charts were prepared illustrating the range of overall fluid inclusion abundances in The main results are summarised in quartz as seen under x 280 magnifica• Figure 2. tion. These were chosen for the ease in visually distinguishing the differ• ent abundances. The thin section was Type 1 Inclusions scanned at x 280 magnification, 100 to 150 half fields of view were observed These comprise about 10-20% of the to• at random, and the individual overall tal population for most samples. They abundance score estimated each time by show no systematic spatial relation• comparison with the standard charts. ship to mineralization but are especial• The mean abundance score was then cal• ly abundant (up to 50%) in areas of in• culated. This method became quite rapid tense kaolinisation, as already noted with practice and soon took about 20 in the St. Austell mass (Rankin and minutes per sample. Routine checks were Alderton, 1982; Alderton and Rankin, made by comparing the counts obtained 1983). by estimation with the values obtained by absolute counting methods and the results compared favourably. One neces• Type 2 Inclusions (a and b) sary factor to be considered is the size of the inclusions. Counting was They show a wide variation, between restricted to those inclusions which about 5% and 80%. They are especially were >2 um in size. common in the Carnmenellis granite and 340 A.H. Rankin and D.H.M. Alderton

Dartmoor

Carnmenellis

10-1 5 L o , r-T -—H-ITn 01234567T I I I 1 1 1 1 1 1 1 1 1 8 0 10 20 30 40 50 60 Abundance score 7. Type 1

4 °-a Dartmoor Dartmoor 15- 10-

0 -i—ri—i—r

15- Bodmin 30Q Bodmin 10- 10' ' 5- 5- 0- nnn ■ 0' 30 Carnmenellis H Carnmenellis 10 5-1 i—i—i—i—i 0 ^-^—i—i—i—i—i—r

Land's End 15- Land's Ends 10- 5 0 k^Ui? W 0 10 20 30 40 50 0 10 20 30 40 50 60 70 80 % Type 2b 7. Type 3

Fig. 2. Histograms of the distribution of inclusion types and overall abundance for four of the major plutons from SW England (n=number of separate granite sampl Fluid Inclusion Petrography of SW England Granites 341

least abundant in the Dartmoor granite. A high percentage of these inclusion types sometimes correlates with regions where extensive mineralization occurs (e.g. Land's End, Fig. 3c and the small mineralized stocks of Cligga and Kit Hill).

Type 3 Inclusions

These show the most marked variations of all inclusion types between the var• ious plutons. The Dartmoor and Land's End populations contain up to 75% of this inclusion type whilst the Bodmin and Carnmenellis granites typically only show a trace ( <1%). A noteworthy exception is in the Carnmenellis gran• ite where a small 'stock' of fine• grained granite within the main mass contains an enhancement (~20%) of this inclusion type. This enhancement is also noted in the normal, coarse gran• ' 0 lb 2'0 3*0 40 5"o 6'0 70 80 ite close to this stock. % Type 2a

Type 4 Inclusions Dartmoor These show a very wide spread between samples from the same granite and be• tween granites. Large variations occur (5% to 80%) but no regional trends are apparent.

Type 5 Inclusions

Carnmenellis These are exceptionally rare and have only been identified at two localities; 10' Hemerdon Bal, to the south of Dartmoor, and Goonbarrow, in the kaolinised mass 0' -i—I—I—r i r i of St. Austell. Both these localities are host to sheeted vein systems con• Land's End taining W mineralization (Wolframite). However this relationship is not con• 5- sistent; several other W-bearing locali• rJW1 ties (e.g. Cligga) contain no C0 -bear- 0- 'l-, 2 0 10 20 30 40 50 60 70 80 90 ing inclusions. %. Type l>

Fig. 2 Type 6 Inclusions

These are very difficult to identify but have been recorded tentatively from all the granites. 342 A.H. Rankin and D.H.M. Alderton

• £0.3 o 0 - trace

• 1.6 - 2.0 O 1 - 5 9 3.1 - 3.5 o 6 - 20 £ £.6 - 5.0 o 21 - 35 ^ 6.1 - 6.5 o 36 - 50 A 7.6 - 8.0 o »51 Overall abundance V. Types

Fig. 3a-c. Distribution of veins (a), fluid inclusion abundances (b) and Type 2a inclusions (c), Land's End granite. Key for figures 3 to 6 (d)

Overall Inclusion Abundance (Figs. 3-6) ly typify these areas in the Bodmin, Land's End, and Carnmenellis granites. This parameter is perhaps the best for In these granites the regions of high distinguishing broad areas in the gran• abundance extend away from the areas ol ite where mineralization is known to oc• known mineralization but do follow the cur. High inclusion abundances general• overall trend of the vein systems Fluid Inclusion Petrography of SW England Granites 343

Fig. 4a and b. Distribution of veins (a) and fluid inclusion abundances (b), Bodmin Moor granite

I"*'

Fig. 5a and b. Distribution of veins (a) and fluid inclusion abundances (b), Carnmenellis granite

(Figs. 3, 4). This could indicate con• Although mineralized areas within a cealed mineralization or could repre• granite may show increased fluid in• sent broad zones of fluid migration. clusion abundances, such differences We are surprised by the lack of cor• may not occur between a mineralized relation between high abundances and and a non-mineralized granite. In fact all the mineralized areas in the Dart• the Dartmoor granite (least mineralized) moor granite (e.g. around Birch Tor). probably contains the highest overall There is however the possibility that fluid inclusion abundances in SW Eng• the style of this mineralization is dif• land . These abundances are presumably ferent to that in most of the other related to factors concerned with the areas. granites crystallisation and evolution. 344 A.H. Rankin and D.H.M. Alderton

Fig. 6a and b. Distribution of veins (a) and fluid inclusion abundances (b), Dartmoor granite

DISCUSSION they occur in planar groupings or ar• rays) . Several generations are generally The approach used in this study has present but age relationships are almo been simple and empirical. We have not impossible to establish, except for concerned ourselves with comprehensive Type 1 inclusions. These clearly post• heating and freezing stage studies nor date all others and represent the fina with establishing a detailed chronology phase of hydrothermal activity in the for the fluids in different areas of region. These general observations arc the SW England granites. This is pur• compatible with the conclusions from poseful because if fluid inclusion isotopic and age dating studies (Jack• studies are to be used routinely in son et al., 1982) that hydrothermal ac regional mineral exploration, the tech• tivity in SW England was a complex, niques need to be relatively inexpen• protracted process made up of a number sive, rapid and cheap to use by persons of separate events. who are perhaps unfamiliar with estab• It is also clear from the overall lished fluid inclusion methods. The distribution of inclusions (Fig. 2) parameters of abundance and distribu• that different plutions developed dif• tion of inclusion types have been ferent types of fluids. This is shown chosen to fulfill these requirements. by variations in the proportions of They can be determined routinely during Type 2a and Type 3 inclusions. Type 3 normal pétrographie microscopy. halite-bearing inclusions seem to cor• In granite the distinction between relate with the texture of the granite P, PS and S inclusions is usually very Based on the classification of Danger- difficult and subjective. This is why fields and Hawkes (1981) those with we have chosen not to consider it in large K-feldspar megacrysts (Dartmoor too much detail. As a generalization, and Land's End) contain a high propor• however, most of the inclusions have tion of halite-bearing inclusions, the appearance of S or PS types (i.e. whereas those with smaller megacrysts Fluid Inclusion Petrography of SW England Granites 345

(Bodmin and Carnmenellis) have little fluids presumably migrate via micro• or no halite-bearing inclusions. fractures and may be trapped as fluid Previous ore production figures inclusions. They may well be unable to (Dines, 1956) for each granite may be alter the host rock (e.g. granite) but taken as a guide to their degree of may form distinctive fluid inclusion mineralization (Sn-W-Cu). Carnmenellis assemblages beyond the visible litho- has by far the most mineralization, logical or geochemical anomalies in the Bodmin and Land's End have intermediate rocks. This is presumably what is seen amounts and Dartmoor the least. Halite- in the SW England granites. bearing inclusions show no relation• The rare occurrence of inclusions ship to mineralization, but Type 2a containing liquid CO2 at two localities inclusions do. They are most abundant in SW England is especially relevant in in the Carnmenellis granites and least the context of mineral exploration be• abundant in Dartmoor. This is consistent cause at both localities extensive vein with published fluid inclusion data for swarms carrying tungsten mineralization vein quartz and cassiterite referred are known to occur. The origin of these to in the Introduction; the fluids re• CC"2-bearing fluids is unknown but the sponsible for main-stage mineralization association of such fluids and tungsten generally have the character of a Type mineralization elsewhere in the world 2a inclusion. is well established (Higgins, 1980). It therefore seems probable that, It is, however, emphasised that Type 5, although the chemistry of the granites C02_liquid bearing are not always as• is very similar, their associated fluids sociated with tungsten deposits in SW varied during their final stages of England. Fluid inclusions associated evolution. The generation of saline with the Cligga Sn-W-Cu deposit, for fluids was not associated with exten• example, have been extensively studied sive Sn-W-Cu mineralization. At present by Jackson et al. (1977) and Charoy it is not clear whether these fluids re• (1979) neither of whom were able to present the same stages of evolution in detect CO2 in the inclusions even dur• the separate granites or for instance ing cooling studies. whether the less saline assemblages in the Bodmin and Carnmenellis granites are indicative of later influx of dilute SUMMARY AND CONCLUSIONS (perhaps meteoric) fluids. However it is clear that those granites with a Fluid inclusion populations in SW Eng• dominant assemblage of Type 2a inclu• land granites provide a record of the sions are more favourable as regards complexity and episodic nature of hydro- Sn-W-Cu mineralization. thermal events in the area. The other major feature emerging Low temperature, Type 1 inclusions from our data is that within these represent the final phase of hydrother• granites areas of higher total inclu• mal activity, related to kaolinisation sion abundance can often be correlated of the granite. On a broad, inter-plu- with areas of mineralization. In addi• ton scale the proportion of moderate tion these areas of increased fluid in• to high temperature Type 2 inclusions clusion abundance are often more exten• correlates with the extent to which sive than the actual areas of minerali• each pluton is mineralized. • zation. This could indicate that the Halite-bearing, Type 3 inclusions fluids responsible for hydrothermal are unrelated to mineralization but mineralization were able to penetrate overall show a distinct relationship the granite well beyond the confines of to the texture of the granite. The the visible mineralization. Yermakov land's End and Dartmoor granite can be (1966) has formulated the concept of distinguished from the Bodmin and Carn• the 'steam aureole* or 'steaming- menellis granites on this basis, through aureole', whereby fluids caus• though the reasons for this distribu• ing mineralization are able to migrate tion are unclear. Perhaps they repre• away from the channelway and pervade sent two separate though petrochemical- the surrounding, solid rock. These ly similar phases of intrusion with 346 A.H. Rankin and D.H.M. Alderton different hydrothermal systems associ• Alderton, D.H.M., Rankin, A.H.: Fluid ated with them. inclusion studies in the St. Austell Type 4 gas-rich inclusions show no granite. (Jl. Geol. Soc. Lond., 140, variation between plutons, but do dem• 297-310 (1983) onstrate that the hydrothermal phase Alderton, D.H.M., Sheppard, S.M.F.: did in fact boil at stages during its Chemistry and origin of thermal waten evolution. from southwest England. Trans. Instn, Type 5 CC^-bearing fluid inclusions Min. Metall. (sect. B: Appl. earth are only found associated with two W- Sci.) 86, B191-194 (1977) bearing vein swarm deposits. In view of Charoy, B.: Definition et importance the known association with tungsten des phénomènes deuteriques et des deposits elsewhere in the world, and fluides associes dans les granites, their extremely rare occurrence in SW consequences metallogeniques. England it is recommended that future Science Terre, Nancy, Mem. 37, 364 finds be viewed with interest as indi• (1979) cators of the proximity of potential Chivas, A.T., Wilkins, R.W.T.: Fluid ore deposits of tungsten. inclusion studies in relation to Thus fluid inclusion petrography hydrothermal alteration and minerali• does hold some promise as a tool in zation at Koloula porphyry copper mineral exploration in this region. The prospect. Guadalcanal. Econ. Geol. overall abundance of the fluid inclu• 72, 153-169 (1977) sion population is often effective at Dangerfield, J., Hawkes, J.R.: The distinguishing areas within a particular Variscan granites of south-west pluton where hydrothermal activity is England: additional information. pronounced. However, it is not possible Proc. Ussher Soc. 5(2), 116-120 (1981 to compare abundances between different Dines, H.G.: The metalliferous mining plutons because each probably developed region of southwest England. Mem. its own particular hydrothermal system. Geol. Surv. U.K. 2 vols, HMSO (1956) It is believed that routine fluid Edmonds, E.A., McKeown, M.C., Williams, inclusion petrography and abundance de• M.: British regional geology: south• terminations could become part of gen• west England (fourth edition). HMSO, eral exploration strategy for Sn-W-Cu London (1975) deposits in granitic areas elsewhere Evans, A.M., Haslam, H.W., Shaw, R.P.: in the world especially during the re• Porphyry style copper-molybdenum connaissance and target selection mineralisation in the Ballachulish stages of exploration. The methods are igneous complex, Argyllshire, with simple and rapid to use and should be special reference to the fluid in• considered a routine part of normal clusions. Proc. Geol. Ass. 91, pétrographie examination of granite (1 & 2), 47-51 (1979) samples. Higgins, N.C.: Fluid inclusion evidence Acknowledgements. This work was jointly for the transport of tungsten by car• funded by European Economic Communities bonate complexes in hydrothermal sol• as part of their R&D programme on utions. Can. J. Earth Sci. 17, Primary Raw Materials and by the Natu• 823-830 (1980) ral Environment Research Council. DHMA Jackson, N.J., Moore, J.McM., Rankin, gratefully acknowledges the support A.H.: Fluid inclusions and minerali• provided by these organizations during zation at Cligga Head, Cornwall, the tenure of a post-doctoral research England. Jl. geol. Soc. Lond. 134, assistantship at Imperial College. 343-349 (1977) Jackson, N.J., Halliday, A.N., Sheppari REFERENCES S.M.F., Mitchell, J.G.: Hydrothermal activity in the St Just mining dis• Alderton, D.H.M. : The geochemistry of trict, Cornwall. In: Metallization mineralisation at Fendarves, and associated with acid magmatism, other Cornish areas. Unpubl. PhD Evans, A.M. (ed) John Wiley and Sons, thesis, University of London (1976) New York, 385, 137-179 (1982) Fluid Inclusion Petrography of SW England Granites 347

Moore, J.McM.: Mineral zonation near Simpson, P.R., Brown, G.C., Plant, J., the granite batholiths of south-west Ostle, D.: Uranium mineralization and northern England and some geo- and granite magmatism in the British thermal analogues. In: Metallization Isles. Phil. Trans. R. Soc. Lond. associated with acid magmatism. A291, 385-412 (1979) Evans, A.M. (ed) John Wiley and Sons, Sorby, H.C.: On the microscopical struc• New York, 385, 229-241 (1982) ture of crystals, indicating the Rankin, A.H., Alderton, D.H.M.: Fluid origin of minerals and rocks. Q. J. inclusion studies on mineralized geol. Soc. London 14, 453-500 (1858) granites of the British Isles: an Yermakov, N.P.: Use of gas-liquid in• assessment of their use in the explo• clusions in prospecting and explora• ration for mineral deposits associated tion for postmagmatic ore deposits with granitic rocks. Final Report, and blind ore bodies. Sovetskaya Contract 041 MPP UK 168 p. EEC R & Geologiya 9, 77-90 (in Russian, D programme on 'Primary Raw Materials' translated in International Geology (1982) Review 9 (7), 947-956, listed as P Rankin, A.H., Alderton, D.H.M., Thomp• P Ermakov) (1966) son, M., Goulter, J.E.: Determination of uranium: carbon ratios in fluid inclusion decrepitates by inductively- coupled plasma emission spectroscopy. Miner. Mag. 46, 179-186 (1982) Roedder, E.: Fluid inclusions as tools in mineral exploration. Econ. Geol. Received: August 30, 1982 72, 503-525 (SEG distinguished lec• Accepted: February 16, 1983 ture in scientific research) (1977) Sheppard, S.M.F.: The Cornubian batho- A.H. Rankin lith, SW England: D/H and 180/160 Department of Geology studies of kaolinite and other al• Imperial College teration minerals . Jl. geol. Soc. London SW 7 3BP Lond. 133, 573-591 (1977) England

Mineral.Deposita 18, 349-363 (1983) ...... MINERALIUM DEPOSITA © Springer-Verlag 1983

Caractère Epigénétique-Etranger des Gîtes Filoniens Pb-Zn (Ba-F) du District du Bord Sud du Synclinorium de Dinant (Belgique)

A. Préat, S. Cauet et A. Herbosch

Laboratoires Associés de Géologie-Pétrologie, Université Libre de Bruxelles, Bruxelles, Belgique

Numerous vein mineralizations occur in the carbonate series of the Middle and Upper Devonian located in the Pb-Zn (F-Ba) metalliferous district of the South border of the Dinant Synclinorium. A regional lithogeochemical study (major and trace elements) of the Givetian limestones reveal the low potential of heavy metals in these platform sediments. These results are confirmed by the distri• bution of 13 elements present in a vein mineralization and its close surrounding. Finally, the comparison of the isotopic composition of the lead in the galenas of the vein mineralization and the traces of lead in the host rocks add decisive important arguments. These results seem to be sufficient to reject the hypothesis of the origin of the metals by lateral secretion and are in favor of an "epigenetic-foreign" character for these mineralizations.

De nombreux indices et anciennes exploitations de faible tonnage pour Pb-Zn-Ba-F s'observent dans les séries carbonatées du Dévonien moyen et supérieur du SW du Synclinorium de Dinant où elles délimitent un district métallifère. Une étude li- thogéochimique régionale des calcaires givétiens montre le faible potentiel mé• tallifère de ces sédiments de plateforme. Ces résultats sont confirmés par l'étude de la distribution de 13 éléments présents dans un filon et son encais• sant immédiat. Enfin la comparaison des compositions isotopiques du Pb des ga• lènes du filon et du Pb en trace dans les calcaires encaissants apporte des ar• guments décisifs. Ces résultats sont suffisants pour rejeter l'hypothèse de l'ori• gine des métaux par sécrétion latérale et militent en faveur du caractère "épi- génétique-étranger" de ces minéralisations.

I. INTRODUCTION L'élaboration de modèles génétiques cohérents, but ultime de la métallo- Les relations systématiques générale- génie, comporte la reconstitution des ment observées entre les concentrations différentes étapes qui, de l'aval vers métallifères et les milieux rocheux au l'amont, sont le milieu de dépôt, le sens large constituent des guides logi- transport et la source des métaux. De ques en exploration et les bases de cette trilogie, c'est le problème de toutes typologies. Au delà de ces rela- la source qui est le plus difficile tions figées, les processus génétiques â aborder car le plus éloigné des ma- peuvent cependant être reconstitués. nifestations du dépôt (Routhier, 1967). 350 A. Préat et al.

A ce sujet, la connaissance du de• dizaine de kilomètres en largeur, de• gré de familiarité (Routhier, 1969, puis Beaumont à l'ouest jusqu'à Bornai 1980) du contenu des minéralisations à l'est (Fig.1). On y observe deux par rapport à leurs terrains encais• types de minéralisations: sants constitue un guide majeur dans - des amas et disséminations d'appa- la recherche de la source des élé• rance stratiforme liés aux phénomènes ments présents dans le corps minérali• de dolomitisation des récifs frasniens sé. appartenent aux dômes anticlinoriaux La présente étude a pour principal de la partie médiane du Synclinorium objectif d'envisager certains aspects de Dinant (Massifs de Beaumont et de de ce problême, et d'établir les re• Philippeville). Des filons sont égale• lations entre les minéralisations fi- ment présents et semblent liés à ces loniennes du bord sud du Synclinorium amas. Ces minéralisations n'ont, à ce de Dinant et l'ensemble des terrains jour, encore jamais fait l'objet d'étu sédimentaires formant leur cadre géo• des mêtallogéniques détaillées; logique. - des filons transverses recoupant les L'évaluation du degré de familiari• séries carbonatées du Givétien et du té de ces minéralisations par rapport Frasnien, plus rarement du Couvinien. aux roches encaissantes s'appuiera Ces derniers, également peu étudiés d'abord sur l'étude régionale de la jusqu'ici, recoupent soit la bordure distribution des éléments majeurs et méridionale du Synclinorium de Dinant, en traces dans ces dernières. Une soit les brachyanticlinaux secondaires étude des profils de distribution des à noyaux de calcaire givétien qui ac• mêmes éléments présents dans un filon cidentent sa partie centrale. plombo-zincifère et son encaissant im• Ce sont ces dernières minéralisa• médiat permettra ensuite d'écarter tions de type épigénétique qui font l'hypothèse d'une origine des métaux l'objet du présent travail. par sécrétion latérale sensu stricto. Il s'agit de minéralisations discor Une étude isotopique comparative du dantes liées à un grand nombre de pe• plomb des galènes du filon et du plomb tites failles transversales et quasi en traces dans les sédiments situés à verticales de direction moyenne NNW- proximité immédiate confirmera les ob• SSE. Les filons, de faible épaisseur servations précédentes et permettra, (0,1-0,9 m), sont le plus fréquemment vu la convergence des arguments, de associés aux calcaires givétiens situe conclure au caractère étranger du con• de part et d'autre de la localité de tenu du corps minéralisé. Givet (Fig.1). La paragenèse est sim• La comparaison de ces résultats iso• ple: marcasite, galène, sphalerite, topiques avec ceux déjà publiés (Cauet barytine, fluorine, calcite, dolomite, et al., 1982; Herbosch et al., 1983) quartz. L'ensemble de ces minéralisa• permettra enfin d'étendre cette con• tions se distingue par l'absence de clusion à l'ensemble des minéralisa• structures collomorphes à rubanèes à tions filoniennes du bord sud du Syn• schalenblende et de minéraux accessoi• clinorium de Dinant. res de nickel, bien connus dans l'im• portant district de Bleiberg-Moresnet situé au nord-est de la Belgique (de II. CONTEXTE GEOLOGIQUE ET METALLO- Magnée, 1967). Par contre, la barytine GENIQUE est localement abondante (Vierves, Ave et Auffe). Les bandes calcaires de la partie centrale du district recèlent De nombreux indices et anciennes exploi• également des gîtes à fluorine exclu• tations de faible tonnage en Pb-Zn-Ba-F sive (Calembert et Van Leckwijck, 1942 sont connus depuis longtemps et délimi• dont les liens avec les concentrations tent au sud-ouest du Synclinorium de plombo-zincifères sont inconnus. Dinant un district métallifère (de Mag• Malgré leurs nombreux caractères née, 1967; Bartholomé et al., 1979) géologiques communs, ces minéralisa• d'axe est-ouest s'étendant sur une cen• tions ne sont pas similaires du point taine de kilomètres en longueur et une de vue de la composition isotopique du Caractère Epigénétique-Etranger des Gîtes Filoniens 351

Fig.1. Localisation des principales minéralisations filonienne plombo-zincifères du bord sud du Synclinorium de Dinant plomb des galènes: Cauet et al.,(1982) L'importance prise par cette derni• ont montré qu'une partie de ces der• ère phase dans l'ensemble de la sédimen• nières (Beauraing, Revogne, Resteigne, tation carbonatêe, tout particulière• Tellin, Jemelle au "Bois de Lamsoule", ment dans la Formation de Fromelennes, Masbourg) présentent des compositions a généralement conduit à l'idée que isotopiques similaires et significati- cette Formation pourrait constituer la vement différentes des autres minérali• source des métaux pour les minéralisa• sations filoniennes du district (Fig.1). tions de la région. Dans ce contexte, Elles définissent un petit groupe ho• les phénomènes de compaction et de mogène, à la fois isotopiquement (grou• diagenèse seraient à l'origine de l'ex• pe 2 de la Fig.2) et géographiquement pulsion physique et chimique de l'eau (est de Givet, Fig.1). intersticielle présente dans les sys• C'est dans cette région que le Givê- tèmes poreux de ces sédiments et con• tien, épais d'environ 500 mètres, a stitueraient ainsi le principal facteur été divisé sur base lithostratigraphi- responsable de la migration des flui• que en trois formations: Formation de des. Ces derniers peuvent alors être Trois-Fontaines à la base, Formation piégés dans des formations perméables du Mont d'Haurs et enfin Formation de relativement proches ou lorsque celles- Fromelennes au sommet (Errera et al., ci n'existent pas ou sont inaccessib• 1972). Chacune de ces Formations cor• les, rester associés sous forme d'un respond à la répétition d'un phénomène aquifère lié aux sédiments d'origine. simple se déroulant en quatre phases, Dans le détail, ces mécanismes sont avec prédominance d'une phase à sédi• évidemment très complexes et concer• mentation essentiellement lagunaire et nent également les circulations des continentale ou de sebkha (Errera,1975). eaux météoriques, des eaux de compac- 352 A. Prèat et al.

207pb/204pb erreur analytique

-15.7

X O x o / / 3 -,/ /«O *7 + -15.6 / + • +

206 18.2 18.3 18.4 18.5 Pb/2(* Pb I l

Fig.2. Diagramme 20/Pb/204Pb _ 206pb/204pb pour les gaiènes des minéralisations. In Cauet et al., 1982

tion expulsées par tassement des for• reconnus au Givétien mais sont locali• mations argileuses suivant des circu• sés dans la prolongation septentrionale its paléohydrologiques dont il manque du Bassin de Namur (Van Tassel, 1960); encore de nombreuses données pour leur Legrand, 1962; Coen-Aubert et al., reconstitution (de Magnée, 1967; Bar- 1980). Il faut également noter l'associ tholomé et Gérard, 1976) . ation d'indices de galène avec des fa• De tels modèles génétiques faisant ciès récifaux et lagunaires du Fras- soit appel au blocage rapide des mé• nien (Pel et Monseur, 1979). taux sur une bordure littorale et dans En conclusion, les sédiments givé- des conditions climatiques particuli• tiens de la région étudiée se sont dé• ères (développement d'une sebkha ou posés en climat tropical sur une plate• d'une plaine supratidale en climat forme carbonatée peu profonde et sub- tropical), ou bien faisant appel â sidente essentiellement dominée par des des circulations paléohydrologiques environnements lagunaires et de sebk- de saumures ont déjà été invoqués de has évaporitiques ayant pu constituer nombreuses fois pour expliquer certains un métallotecte pour certains métaux gisements d'origine sêdimentaire (Bush, lourds dont le Pb et le Zn. 1970; Dozy, 1970; Renfro, 1974; Lagny, Dans le but de vérifier ces hypo• 1975; Routhier, 1980; etc. ...). thèses, une série de coupes situées La découverte, il y a une dizaine dans l'axe du district (Fig.1) ont été d'années, d'un niveau d'anhydrite dans étudiées du point de vue sédimentolo- la Formation de Fromelennes au sondage gique et géochimique. de Focant (Graulich et al., 1967) ef• fectué â proximité immédiate de la zone étudiée (Fig.1), ne pouvait que renfor• III. ETUDE SEDIMENTOLOGIQUE ET LITHO- cer cette hypothèse et rendre compte du GEOCHIMIQUE caractère sursalé des fluides évoluant à partir d'eaux marines connées par III.I Sédimentologie filtration osmotique (Dunham, 1970) ou â partir d'eaux météoriques par dis• L'analyse sédimentologique fine per• solution des évaporites. D'autres fa• met de définir pétrographiquement plus ciès évaporitiques ont également été de 20 microfaciès essentiellement car- Caractère Epigénétique-Etranger des Gîtes Filoniens 353 bonatés caractérisant des milieux de dé• de la position des différentes coupes pôts comparables â ceux que l'on ren• étudiées, on constate que la sédimenta• contre aujourd'hui dans les plateformes tion carbonatée du Givêtien s'est ef• carbonatées (Purser, 1980). fectuée dans un domaine peu profond re• Ces différents paléomilieux de sédi• lativement limité sur la partie in• mentation permettent de définir un pro• terne de la plateforme en relation di• fil paléogéographique théorique; ils recte avec la mer ouverte. L'environne• s'étendent du domaine marin ouvert le ment le plus représentatif est celui plus externe et subtidal avec dévelop• d'un lagon (Préat et Boulvain, 1982). pement d'épisodes récifaux, puis dans Dans ce milieu, pouvant être particuli• les domaines intertidaux caractérisés èrement abrité, les eaux sont alors par plusieurs hauts-fonds oolitiques confinées et au niveau du fond les et les domaines subtidaux internes es• sédiments sont réducteurs. L'extension sentiellement lagunaires, et enfin dans des faciès supratidaux y est relative• les zones les plus internes du domaine ment faible et leur isolement de l'in• supratidal où se développent de nom• fluence marine jamais suffisamment du• breux platiers algaires accompagnés de rable pour que de véritables précipi• dépôts parfois émergés de laminites tés salins s'y développent. En consé• ayant subi une diagenèse dans les eaux quence, aucun faciès évaporitique franc, phréatiques ou vadoses. ni même aucune dolomie primaire n'ont En tenant compte de la succession pu être mis en évidence lors de cette des différents microfaciès ainsi que étude sédimentologique.

Tableau 1. Teneurs moyennes des calcaires givétiens

GROUPE DE GIVET

FORMATION TROIS-FONTAINES FORMATION FROMELENNES

RESTEIGNE* VAUCELLES OLLOY S. D'AVE DOURBES N=99 N=75 N=83 N=40 N=87

CaO (%> 45.338.5 50.3±3.0 51.314.0 51.7+4.5 55.013.0 MgO 2.1±1.6 2.0±0.7 1.710.5 0.8+0.2 1.2+1.0

K20 1.0±0.8 0.4+0.3 0.510.6 0.5+0.4 0.2+0.3

A1203 2.4±2.4 1.210.7 1.211.0 1.111.2 0.610.7

Si02 8.0+7.2 4.312.0 3.912.7 4.5+4.1 2.012.1

Fe203 1.010.7 0.510.3 0.510.4 0.510.4 0.310.6

(ppm) Mn 378+350 1701122 275+149 1801140 1601154 Sr 298167 250192 244+90 308149 240154 S 4269±2714 1607+1286 Pb 17 + 17 20 + 30 8±4 Zn 22±47 11119 21126 17+33 817

Formation de Trois-Fontaines et du Mont d'Haurs pro-parte 354 A. Préat et al.

Tableau 2. Comparaison des teneurs moyennes en Pb et en Zn de différentes roches carbonatées

Pb Zn

CLARKE : calcaires de plateforme 9 20 (TUREKIAN et WEDEPOHL, 1961) "world" average limestone 8 26 (WOLF et al, 1967, table II)

MASSIF SCHISTEUX RHENAN : roches carbonatées dévono- 11 50 carbonifère (HEINRICH et al, 1980)

SYNCLINORIUM DE DINANT : - Formation de Trois-Fontaines, Givétien, Resteigne, (cette étude) n = 99 (1) 17 22 - Formation de Fromelennes, Givétien, Sourd d'Ave, (cette étude) n = 40 (1) 8 17 - Roches carbonatées Tn3-VA Salet - Pont-de-Bonne - Martinrive (VAN ORSMAEL et al, 1980) (2) n = 236 2 17 - calcaires n = 153 2 22 - dolomies n = 56 1 14

BASSINS DE LA VESDRE ET NAMUR - Calcaires de Schmalgraf Carbonifère (SWENNEN et al, 1981) n = 21 (2) 10 77 - Calcaires de Plombières Carbonifère (SWENNEN et al, 1981) n - 101 (2) 3 44 - Dolomies (type Sovet) Carbonifère (VAN ORSMAEL«et al, 1980) (2) - bassin Vesdre 16 146 - bassin Namur 28 213 - Calcaires frasniens (FRIEDRICH et SCHEPS, 1981) (1) - rêcifaux n = 110 7 65 - noduleux n = 43 20 98

(1) analyses sur roches totales

(2) analyses de la phase soluble à l'acide

III.2. Lithogêochimie A1203, Fe203 total, MgO, CaO, Na20, K20, Mn, Sr, S, P, Pb et Zn (Tableau I Plus de 300 échantillons calcaires ap• Tous ces éléments ont été analysés par partenant aux coupes étudiées (Resteig• spectrofluorescence des rayons X, par ne, Sourd d'Ave, Olloy, Vaucelles, Nis- calibration linéaire sur cru pour les mes, Dourbes, Fig.1) ont été analysés éléments majeurs (Leake et al., 1969) en roche totale pour 13 éléments ma• et par une méthode mathématique de cor• jeurs, mineurs et en traces: SiOn, rection des effets de matrice pour les Caractère Epigénétique Etranger des Gîtes Filoniens 355

traces (Vie Lesage et al., 1979). carbonatées du Dinantien (analyse de L'étalonnage est basé dans les deux la phase soluble à l'acide) et du Fras- cas sur des standards internationaux. nien (analyse sur roche totale) met en Ces analyses correspondent à un évidence le faible fond géochimique en échantillonnage particulièrement dense Pb et en Zn du Synclinorium de Dinant de l'ordre du mètre, à raison d'un et en particulier du Givétien de son échantillon tous les 3 ou A bancs en• bord sud. viron, ce qui est suffisant pour dé• Ces observations, purement descrip• finir un fond continu régional et tives, permettent déjà de conclure au mettre en évidence d'éventuels niveaux faible potentiel métallogênique des porteurs d'anomalies en métaux lourds. roches givêtiennes du bord sud du Syn• L'ensemble des résultats (Tableau I) clinorium de Dinant. révèle d'une manière générale l'homo• généité gêochimique des sédiments étu• Une analyse factorielle en mode R diés, qui se marque par l'absence de a été effectuée sur les données des variations importantes des teneurs au deux coupes-types de Resteigne (Fig.3) sein de chacune des Formations, aussi et du Sourd d'Ave dans le but d'éluci• bien pour les éléments majeurs que der les processus géologiques fonda• ceux en traces. On notera également mentaux qui contrôlent la distribution la très grande pureté de ces calcaires des éléments dans ces calcaires. Les dont les teneurs moyennes en CaO dé• résultats, assez semblables pour les passent souvent 50%. En ce qui concerne deux coupes, montrent que le comporte• le Pb et le Zn, on remarque immédiate• ment géochimique du Pb et du Zn ne sem• ment les faibles teneurs moyennes, la ble pas obéir à des lois simples, leurs faible amplitude de leurs variations: communautés assez faibles (h2 < 0.6) Opk = 17 ppm, O^n = 47 ppm pour la témoignent de l'importance des phéno• coupe de Resteigne mènes aléatoires parmi les processus qui contrôlent leur distribution. Ces ^p, = 4 ppm, Ozn = 33 ppm pour la coupe du Sourd d'Ave faits s'expliquent et par les très ainsi que l'absence d'anomalies notab• faibles teneurs observées et par l'ab• les, les valeurs maximales ne dépas• sence de variations importantes. sant pas 100 ppm pour le Pb et 200 ppm Néanmoins dans la Formation de Trois- pour le Zn. Les teneurs en soufre, Fontaines (Fig.3), le Pb co-varie sys• assez élevées pour des calcaires, sont tématiquement avec le Mn et plus faible• nettement plus fortes dans la Forma• ment avec le Zn (facteur III). Dans la tion de Trois-Fontaines (x = 4270 ppm) Formation de Fromelennes, ces trois ce qui s'explique par des teneurs en éléments sont regroupés au sein d'un S systématiquement plus élevées dans même facteur s'opposant fortement au les faciès lagon qui y représentent Mg, traduisant leur expulsion lors l'essentiel de la sédimentation. des phénomènes de dolomitisation qui On constate donc qu'en ce qui con• existent localement. cerne les métaux lourds, leurs teneurs moyennes sont faibles dans l'ensemble L'opposition avec le S (facteur III), des coupes étudiées: elles sont in• ainsi que la présence d'un facteur IV férieures au Clarke pour le Zn, égales s'identifiant avec la diagenèse des sul• ou légèrement supérieures au Clarke fures en milieu réducteur conduisant pour le Pb (Tableau II). Il en est de à la seule formation de pyrite, sont même si on les compare aux valeurs ex• révélatrices de la pauvreté en métaux trêmement bien documentées concernant lourds de l'environnement sêdimentaire. les calcaires du Massif Schisteux Rhé• L'interprétation de l'analyse fac• nan (Heinrich et al., 1980; Tableau II), torielle montre clairement que si les dont les Ardennes constituent le pro• conditions nécessaires au "piêgeage" longement occidental. Malgré les ap• des métaux lourds existaient (milieu proches analytiques différentes, la anaêrobique à sédimentation ralentie), comparaison des teneurs observées dans par contre la disponibilité en Pb et les calcaires givétiens (analyse sur en Zn sous forme d'ions en solution roche totale) avec celle des roches n'existait pas. 356 A. Prêat et al.

SCHÉMA FACTORIEL DE LA MATRICE VARIMAX : 5 FACTEURS RENDANT COMPTE DE 74% DELA VARIANCE TOTALE. FORMATION DE TROIS FONTAINES, GROUPE DE GIVET, CARRIÈRE DE RESTEIGNE. (99 ÉCHANTILLONS). FACTEURS I II III IV V % variance 35.0 16.9 12.3 6-1 3.7 + 1.0 AI2O3 | Si02 K2O .8 . Sr P .6 l Na2 0 • CaO S Fe203f , s . Zn Fe 0 t .4 . MgO #Na20 2 3 .P

S .2 ■Mn Sr 2' 2 0.0 } Al £>. Na^ .2 ■MMn , 2°3_. ISi02 .4 •s

6 - .Fe203t • CaO Pb .8 - •MgO |Mn -1.0 20 40 60 80 100 % cumulés de la variance en facteurs communs

Fig.3. Schéma factoriel de la matrice varimax. Formation de TroisFontaines, Resteigne

IV. ETUDE GEOCHIMIQUE ET ISOTOPIQUE dans un même banc recoupé par le filon. D'UN FILON Les figures 4 et 5 représentent en or donnée la gamme des teneurs observées Il s'agit d'un filon de faible épais pour chacun des éléments analysés le seur (10 à 20 cm), visible sur une long du profil filonencaissant, ainsi quinzaine de mètres dans les deux ni que la moyenne arithmétique des te veaux supérieurs de la carrière de neurs (x) pour l'ensemble des calcaires Resteigne, où il présente une direction analysés dans la coupe de Resteigne générale N45°E et un pendage 45°SE net (Tableau 2). Cette moyenne définit ain tement sécant par rapport aux calcai si pour chacun de ces éléments son fort res de la Formation de TroisFontaines continu. en succession normale. I est essentiel L'examen de ces figures montre im lement constitué d'hydroxydes de fer médiatement que la longueur du profil et de manganèse et on y observe locale est bien suffisante, aussi bien vers ment des rognons et mouchetures de ga l'ouest que vers l'est, puisqu'on re lène. trouve à quelques mètres seulement les fonds continus de tous les éléments analysés. De plus, une série d'anoma IV. I. Etude gêoehimique d'un profil lies positives apparaît très nettement filon-encaissant pour les éléments suivant le Pb et le Zn présentent une migra Les profils de distribution de 13 élé tion du filon vers l'encaissant, les ments ont été établis pour le filon et pics étant surtout localisés dans les son encaissant carbonaté immédiat sur premiers mètres audelà desquels on re une longueur voisine de 15 mètres et trouve immédiatement les fonds continus Caractère Epigénétique-Etranger des Gîtes Filoniens 357

ANOMALIES POSITIVES (X.n =99) —1500 ppm

Fig.4. Profils de distribution du Zn, Mn, Fe2Û3, SiC^, MgO et Cl dans les cal• caires encaissant le filon de Resteigne

- le Fe, Mn, Mg, Si et Cl présentent leurs comportement s'explique facile• le même type de variations et délimi• ment par des phénomènes de dolomiti- tent ainsi sur plusieurs mètres de vé• sation hydrothermale, par contre pour ritables halos accompagnant le filon. le soufre aucune explication n'a pu En ce qui concerne le Mn, les rapports être trouvée. Les profils de distri• pics sur fonds continus sont très éle• bution de KoO, A120_ et P sont très vés de sorte que cet élément pourrait semblables et ne montrent pas de rela• représenter un excellent indicateur tions évidentes avec ceux des éléments de minéralisation. Des anomalies néga• précédents. Remarquons également que tives, indiquant un appauvrissement les halos observés sont essentielle• du filon et de son encaissant, s'ob• ment développés à l'ouest du filon et servent pour le Ca, le Sr et le S. En sont donc dissymétriques. Malgré la ce qui concerne les deux premiers, localisation de cette partie ouest en 358 A. Prêat et al.

PROFILS DE DISTRIBUTION DE CaO,Sr,S ANOMALIES NÉGATIVES ET DE IÇO, Al203,P DANS LES CALCAIRES ENCAISSANT LE FILON DE RESTEIQNE (X/i =99)

ppm -■80 X

Fig.5. Profils de distribution de CaO, Sr, S, K20, AI2O3 et P dans les calcaires encaissant le filon de Resteigne

aval pendage et la possibilité d'alté Une analyse factorielle effectuée ration météorique avec percolation des sur ces données (malgré le faible nom éléments les plus solubles, il nous bre d'échantillons) fait apparaître semble que cette dissymétrie est pri quatre facteurs (Fig.6): le premier maire vu sa remarquable régularité pour rend compte manifestement des phéno tous les éléments y compris la silice mènes hydrothermaux tandis que les (insoluble dans les conditions super trois suivants sont identiques â ceux ficielles) . déjà identifiés sur la coupe de Res Caractère Epigénétique-Etranger des Gîtes Filoniens 359

SCHÉMA FACTORIEL DE LA MATRICE VARIMAX 4 FACTEURS RENDANT COMPTE DE 87 % DE LA VARIANCE TOTALE. FILON DELA CARRIÈRE DE RESTEIGNE (23 ÉCHANTILLONS) FACTEURS I II III IV %variance 33.0 28.5 25.7 12.5

i.u ■ • S AI2O3 • K2O .8 - Sr • P • • CaO •Pb .6 - • CaO • Si02 Sr • •Zn

.4 - • Mn .2 -

u.u ■ .2 - l/) Pb Mn .4 - : Si 02 Fe203 • c, ,go 3 •P • MgO ^ • Si 02 • 6 -

8 - Mn M » Fe203 Cl 1 9° 10 - i 1 1—' 0 20 40 60 80 100 % cumulés de la variance en facteurs communs

Fig.6. Schéma factoriel de la matrice varimax. Filon de Resteigne teigne (facteurs I, II et III de la met en évidence son homogénéité isoto Fig.3) et correspondent â la roche pique (Fig.7). Les compositions iso saine. Le premier facteur, représen topiques du Pb en roches totales ont tant 33 % de la variance totale, op également été mesurées sur trois échan pose les éléments fortements appauv tillons lithologiquement représenta ris (CaO, Sr, S) dans le filon et son tifs de l'encaissant du filon. halo aux éléments enrichis (Pb, SiC^, A la différence des galènes, une MgO, Fe203, Mn). roche ne peut être considérée comme En conclusion, l'allure des pro un système fermé visàvis du Pb, sa fils et en particulier l'absence de composition isotopique évolue après sa zone de drainage (dépression par rap formation suite à la désintégration de port au fond continu) à l'approche du l'uranium présent in situ. Afin de filon semble exclure l'origine des mé mettre en évidence d'éventuelles fili taux par sécrétion latérale sensu stric ations entre le Pb de la minéralisation to. et celui des roches, il convient dès lors d'effectuer des corrections afin de connaître leur composition isotopi que au moment de leur formation. Ces cor IV. 2. Gêochimie isotopique du Pb rections, fonction des teneurs en U, L'évaluation du degré de familiarité Pb des échantillons, sont cependant de la minéralisation par rapport aux difficiles car ces éléments peuvent sédiments hôtes a également été ap avoir migré, en particulier l'uranium prochée par une étude isotopique com qui est très mobile lors des phénomènes parative du Pb des galènes de la mi d'altération. Ces corrections, et par néralisation et du Pb en trace au sein conséquent l'incertitude associée, ont des sédiments. beaucoup d'influence sur le rapport La mesure des compositions isoto 206pb/204pb et extrêmement peu sur le 207 204 piques du Pb de trois galènes du filon rapport Pb/ Pb. 360 A. Prêat et al.

207 Pb 204 Pb

-15.7 Erreur sur Erreur analytique la discrimination (T = ± 1 %o / + de masse

+ galènes du filon o roches totales: encaissants + du filon -15.6

_^.. correction pour la désintégration "in situ „ 206 Pb -15.5 183 18.4 185 18.6 18.7 18.8 204 Pb " i " i i Fig.7. Géochimie isotopique de Pb du filon de Resteigne et de son encaissant

Relativement aux rapports 2°6pb/2°4pb exclut la possibilité de sécrétion la• de la minéralisation, les rapports térale sensu lato. 206pb/204ptj ,jes sédiments sont nette• IV. 3. Conclusions ment plus élevés (Fig.7). Malgré l'in• certitude sur la correction, il est L'allure des profils de distribution fort probable que les rapports de 13 éléments dans un filon et son 206pt,/204pb de ces sédiments devaient encaissant immédiat, ainsi que la com• être plus élevés que ceux de la miné• paraison des compositions isotopiques ralisation à l'époque permo-triasique. du Pb des galènes du filon et du Pb en L'hypothèse d'une sécrétion latérale trace dans les calcaires encaissants, â cette époque ou plus tard est donc permettent d'écarter l'hypothèse d'une exclue car dans ce cas les compositions origine des métaux du filon par sécré• isotopiques des galènes de la minérali• tion latérale, ce qui milite en faveur sation devraient obligatoirement être du caractère épigénétique-êtranger de plus radiogéniques. Bien plus, le fait la minéralisation du filon de Resteigni d'avoir des rapport 2°7pb/204pb signi- Vu les caractères minéralogiques et ficativement différents entre minérali• structuraux très semblables des autres sation et sédiments hôtes rend impos• filons présents dans ce district (Fig.l sible toute idée de filiation. ainsi que le très faible potentiel mé• La source principale du Pb de la tallifère de l'encaissant carbonaté minéralisation de Resteigne ne se givétien (Tableaux 1 et 2), il nous trouve certainement pas dans les sédi• semble possible de généraliser cette ments encaissants (Formations de Trois- conclusion â tous les filons du distrii Fontaines et du Mont d'Haurs), ce qui du bord sud du Synclinorium du Dinant, Caractère Epigénétique-Etranger des Gîtes Filoniens 361

V. CONCLUSIONS GENERALES nes affectant le Givétien du district V.l. Résultats du bord sud du Synclinorium de Dinant. L'étude sêdimentologique montre que V. 2. Perspectives malgré la présence importante des en• vironnements confinés et supratidaux, Dans ce contexte, un modèle épigêné- aucun faciès êvaporitique n'est présent tique-étranger peut être envisagé non dans le Givétien des coupes étudiées. seulement pour le Givétien mais d'une De plus, les phénomènes de dolomitisa- façon plus générale pour le Dévonien tion y sont mineurs et secondaires. moyen et supérieur du bord sud du Syn• L'analyse des éléments majeurs et clinorium de Dinant qui s'est déposé en traces permet de conclure d'une part sur la bordure méridionale d'une large à la très grande pureté (CaO > 50%) et plateforme s'étendant depuis le bord homogénéité de ces roches carbonatées sud du Massif du Brabant jusqu'au moins et, d'autre part â leur faible poten• Givet. Les sédiments de cette localité tiel métallogénique: les teneurs moyen• appartenaient probablement dès le Gi• nes en Pb et Zn sont très proches, si vétien et beaucoup plus certainement pas inférieures â leurs Clarkes respec• dès le Frasnien au talus continental tifs et les variations autour de leurs assurant la transition entre les fa• moyennes très faibles. ciès de plateforme et ceux de bassin. L'étude des facteurs contrôlant la Dans ce cas, la présence d'êvapori- distribution des éléments dans ces tes â Focant pourrait présenter un in• calcaires, effectuée par analyse fac- térêt particulier par sa position pa• torielle en mode R, permet en outre de léogéographique de bassin qui, si elle montrer quantitativement et objective• se confirme par l'étude sêdimentologi• ment que si les conditions nécessaires que en cours, rendrait compte de l'ori• au piêgeage des métaux lourds existai• gine des saumures sur la bordure de ent (milieux lagunaires réducteurs à la plateforme. Entraînés à de grandes sédimentation ralentie), par contre profondeurs par les mouvements de sub• la disponibilité en métaux lourds fa- sidence, ces fluides pourraient alors sait défaut. migrer le long du talus en système re• Compte tenu de la convergence de lativement fermé sous forme d'aquifères ces résultats, il apparaît fort peu longeant les discontinuités sédimentai- probable que les calcaires givétiens res structurellement liées à l'évolu• du bord sud du Synclinorium de Dinant tion de la marge continentale. Ce sont aient pu constituer la source des mé• les mouvements orogéniques qui, en rom• taux des gisements filoniens qui leur pant les conditions d'équilibre litho• sont cependant préférentiellement as• statique établies au cours de la phase sociés. précédente, permettent l'ouverture du L'étude gêochimique et isotopique système et la remontée des fluides des relations entre un filon minéra• qui peuvent alors précipiter leurs lisé en galène et son encaissant cal• métaux. caire permet d'écarter définitivement Un modèle basé sur une activité vol• l'hypothèse d'une origine des métaux canique dévonienne peut également être par sécrétion latérale. L'argument iso• envisagé pour expliquer l'origine d'une topique révèle, en particulier, l'im• partie des minéralisations filoniennes possibilité d'une filiation entre le du bord sud du Synclinorium de Dinant, Pb en trace dans les roches et celui celui-ci étant effectivement coupé de des galènes, dont la composition iso• ses racines par un charriage impor• topique moins radiogénique traduit né• tant de 40 â 100 km suivant une direc• cessairement une autre provenance. tion septentrionale (Bless et al., 1980), L'ensemble de tous ces résultats La présence plus au sud et â l'est permet d'infirmer l'hypothèse de dé• (Nord du Massif Armoricain, Massif part, à savoir les sédiments givétiens Schisteux Rhénan) d'un volcanisme al• en tant que mêtallotecte-source, et calin intra-plaque connu dès le Dévo• traduit le caractère épigénétique- nien inférieur (Bebien et al.,1980) étranger des minéralisations filonien- pourrait étayer cette hypothèse. Ceci 362 A. Préat et al,

permettrait également de rendre compte Min. Metal..(sect. B), 79, 137-144 de la similitude des compositions iso• (1970) topiques du Pb d'une partie des miné- Calembert, L., Van Leckwijck, W.: Les rations de la région étudiée et de cel• gisements de fluorine belges et les du Dévonien inférieur (Fig.2). français, du bord méridional de Syn Afin de tester la validité de ces clinorium de Dinant. Bull.Soc. Géol modèles, desêtudes sêdimentologiques de Belgique, 65, 64-75 (1942) et palêogêographiques devraient s'as• Cauet, S., Herbosch, A., Weis, D.: surer que le sud de la région étudiée Genetic study of belgian lead-zinc soit un équivalent possible de la zone mineralizations in carbonate en• rhéno-hercynienne bien connue plus à vironments through lead isotopic l'est dans la région de Marburg en Al• geochemistry. Actes du Symposium lemagne (Franke et al., 1978). sur les gîtes filoniens Pb, Zn, Ba, F du domaine varisque. Bull.BRGM (2 Remerciements. Cette étude a pu être II, 329-341 (1982) réalisée grace à l'aide financière de Coen-Aubert, M., Groessens, E., Legran la C.E.E. (contrat n° 110-79-7 MPPB) R. : Les formations paléozoi'ques des et des Services Interministériels de sondages de Tournai et de Leuze. la Politiques Scientifique (contrat Bull.Soc.belge Géol. Paléont. Hydro MP/CE/6). Une partie des analyses ont 89, 241-275 (1980) été réalisées sur l'installation de Dozy, J.J.: A geological model for the Fluorescence X appartenant au Collec• genesis of the lead-zinc ores of tit tif Interuniversitaire de Gêochimie Mississippi Valley, U.S.A. Trans. Instrumentale, subventionné par le Inst. Min. Metall.(sect. B), 79, F.R.F.C. (convention no 2.4521.76). 163-170 (1980) L'un de nous (Cauet S.) bénéficie Dunham, K.C.: Mineralization by deep d'une bourse de recherche du F.N.R.S. formation waters: a review. Trans. Nos plus vifs remerciements à F. Boul- Inst. Min. Metall. (sect.B), 79, vain, G. Ceuleneer et F. Alderson pour B127-136 (1970) leur participation à l'étude de terrain. Errera, M.: La sêquostratigraphie: dé• veloppement théorique et applicatio: BIBLIOGRAPHIE au Givétien franco-belge. Thèse de doctorat. Université Libre de Bru• Bartholomé, P., Ek, C., Batacchi, A., xelles, 401 p. 1975 Catalono, M., Pellegrini, L.: Dos• Errera, M., Mamet, B., Sartenaer, P.: siers II. Lead and Zinc. Commission Le Calcaire de Givet et le Givétien of the European Communities DGXII, à Givet. Bull. Inst. Roy. Sci. Nat. vol. 1, 492 p., 1979 Belgique, 48, 1-59 (1972) Bartholomé, P., Gérard, E.: Les gise• Franke, W., Eder, W., Engel, W., Lange ments plombo-zincifères d'Engis, strassen, F. : Main aspects of geosyi province de Liège, Belgique. Annales clinal sedimentation in the Rhenohei des Mines de Belgique, 11e livraison: cynian zone. Z.dt.Geol. Ges. 129, 901-917 (1976) 201-216 (1978) Bebien, J., Gagny, Cl., Rocci, G.: Friedrich, G., Scheps: Prospection of La place du volcanisme dévono-di- stratabound sulfide mineralization nantien dans l'évolution magmatique in the western part of the Rhenish et structurale de l'Europe moyenne Schiefergebirge. Contact group "Geo varisque au Paléozoique. Mémoire du logy of ore deposits and of their BRGM, 108, 213-225 (1980) host rocks", Liège, discussions et Bless, M.J.M., Bouckaert, J., Paproth, communications personnelles, 1981 E.: Environmental aspects of some Graulich, J.M., Bouckaert,J., Delmer, Pre-Permian deposits in N.W.Europe. A.: Le sondage n° 27 - Neuville Meded. Rijks. Geol.Dienst, 32-1, (1967-1973) P. 185 W n° 407. Notes 3-13 (1980) de débitage. Rapport Service Géo• Bush, P.R.: Chlorid-rich brines from logique de Belgique, 1967-1973 sabkha sediments and their possible Heinrich, H., Schulz-Dobrick, B., role in ore formation. Trans. Inst. Wedepohl, K.H.: Terrestrial geocheir Caractère Epigénétique-Etranger des Gîtes Filoniens 363

istry of Cd, Bi, Th, Pb, Zn and Rb. Routhier, P.: Essai critique sur les Geochim. Cosmochim. Acta 44, 1519— méthodes de la géologie (de l'objet 1533 (1980) â la genèse) Paris, Masson (éd.), Herbosch, A., Cauet, S., Préat, A.: '202 p. 1969 Recherche de métallotectes de na• Routhier, P.: Où sont les métaux pour ture géochimique pour la prospection l'avenir? Mémoire du BRGM, 105, de gîtes Pb-Zn belges. Prof.Paper, 409 p. 1980 197, Service Géologique de Belgique, Swennen, R., Viaene, W.: Lithogeo- 117p. 1983 chemistry of some carbonate sec• Lagny, P.: Les gisements stratiformes tions of the Dinantian in the Ves- associés aux évaporites: position dre region (Belgium). Bull.Soc. dans le temps et place dans l'es• Belge de Géologie 90, 65-80 (1981) pace des bassins sédimentaires éva- Turekian, I.K., Wedepohl, K.H.: Distri• poritiques. Bull. Centre Rech. Expl. bution of the elements in some major Pau 4, 445-476 (1975) units of the Earth's crust. Bull. Leake, B.E., Hendry, G.L., Kemp, A., Geol. Soc. Amer. 72/2, 175-192 Plant, A.G., Harvey, P.K., Wilson, (1961) J.R., Coats, J.S., Aucott, J.W., Van Orsmael, J., Viaene, W., Bouckaert, Liinel, T., Howartz, R.J.: The chemi• J.: Lithogeochemistry of upper Tour- cal anaysis of rock powders by auto• naisian and lower Visean carbonate matic X-ray fluorescence. Chem. Geol. rocks in the Dinant basin. Meded. 5, 7-86 (1969/1970) Rijks. Geol. Dinst, 32-12, 96-100 Legrand, R.: Données nouvelles sur le (1980) Tournaisien grâce aux forages de Van Tassel, R.: Anhydrite, cêlestine Tournai et de Leuze. C.R.Acad.Sc. et barytine du Givétien du sondage Paris 254, 3878-3880 (1962) de Tournai. Bull.Soc. Belg. Géol. De Magnée,I.: Contribution â l'étude Palêont. Hydrol. 69, 351-361 génétique des gisements belges de Vie le Sage, R., Quisefit, J.P., De- Pb, Zn et barytine. In: Genesis of jean de la Bâtie, R., Faucherre, J.: stratiform lead-zinc barite fluorite Utilisation du rayonnement primaire deposits. Ed.J.S.Brown. Econ.Geol. diffusé par l'échantillon pour une Mon. 3, 255-266 (1967) détermination rapide et précise des Pel, J., Monseur.G.: Minéralisations éléments traces dans les roches. de galène et de pyrite dans le ré• X-Ray Spectrometry, 8-3, 181-184 cif Fnh du Frasnien de Frasnes (Bel• (1979) gique). Annales Soc.Géol.de Belgique Wolf, K.H., Chilingar, G.V., Beales, 101, 389-397 (1979) F.W.: Elemental composition of car• Preat, A., Boulvain,F.: Etude sêdimen- bonate skeletons, minerals and sedi• tologique des calcaires givêtiens ments. In: G.V.Chilingar, H.J.G.Bis- â Vaucelles (Bord sud du Synclino- sell and R.W.Fairbridge (eds.), rium de Dinant). Ann. Soc. Géol. Carbonate rocks, physical and chemi• Belgique, 105, 273-282 (1982) cal aspects. (Developments in Sedi- Purser, B.A.: Sédimentation et diage- mentology, 9B) Elsevier, Amsterdam, nèse des carbonates néritiques ré• 413 p. 1967 cents. Inst. Français Pétr., Ed. Technip, 366 p. (1980) Renfro, A.R.: Genesis of Evaporite - Received: August 3, 1982 Associated Stratiform Metalliferous Accepted: February 16, 1983 Deposits - A Sabkha Process. Econ. Geol. 69, 33-45 (1974) A.Herbosch Routhier, P.: Le modèle de genèse: Laboratoires Associés de Géologie, quelques concepts fondamentaux en Pêtrologie et Gêochronologie Pêtrologie et Métallogênie. Modèle Université de Bruxelles des théories mêtallogéniques. Chron. Avenue F.D.Roosevelt, 50 Mines et Rech. minière, 177-190 B-1050 Bruxelles (1967) Belgique

Mineral.Deposits 18, 365-377 (1983) MINERALIUM DEPOSITA © Springer-Verlag 1983

Diagenetic Processes and the Mineralization in the Triassic of Central England

I. Holmes, A. D. Chambers, R. A. Ixer, P. Turner and D. J. Vaughan

Department of Geological Sciences, University of Aston, Birmingham, England

Continental red beds are the host rocks of a characteristic style of minerali• zation which suggests a genetic link between red bed formation and ore forma• tion. Samples of unmineralized and mineralized Triassic sediments from Central England have been studied sedimentologically, petrographically and geochemically with the aim of clarifying this link which may provide valuable guides for exploration. On the basis of sedimentological and pétrographie observations it is suggested that these red beds were formed as a result of diagenetic altera• tion whereby detrital silicates and oxides are progressively dissolved and the iron released is deposited as hematite. A model for mineralization is proposed involving the release of trace metals from detrital minerals during diagenesis, their retention in saline interstitial solutions, migration to suitable sites of precipitation and deposition by reaction with trapped hydrocarbons or reduc• ed sulphur.

INTRODUCTION aspect of ore formation in this environ• ment. This aspect of red bed minerali• zation has not yet been investigated in Continental red beds are the host rocks detail. In this work, the mineraliza• of a characteristic style of mineraliza• tion in the Triassic rocks of Central tion which is dominated by the metals England has been studied together with copper, lead, zinc, uranium and vanadium, the petrology and geochemistry of the although not all these metals are neces• host rocks both adjacent to and dis• sarily present in any one deposit or tant from mineralization. The objectives region of mineralization (Stanton, of this preliminary survey have been to 1972). This distinctive association sug• clarify the relationship between min• gests a genetic link between red bed eralization and diagenesis. formation and the processes of ore for• mation, a link which still remains to be properly explained and may provide valuable clues in the search for ore GEOLOGICAL SETTING deposits of this type. Many of the mineralogical and textural features of red The Triassic of Britain was deposited beds are a product of diagenesis and in a number of fault-bounded, avolcanic, the relationships between mineraliza• often deep sedimentary basins. A num• tion and diagenesis may be a crucial ber of separate depositional basins can 366 I. Holmes et al,

Post-Triassic Mercia Mudstone & Penarth Group Sherwood Sandstone Group Pre -Triassic Mineralization locality with main elements present Sampling location

Fig. 1. Geological map of Central England showing the Triassic sedimentary basins. Areas in which mineralization has been exploited in the past are shown along with the major elements known to occur

be identified in Central England and prising the Stafford, Needwood, Hinck• these are shown in Fig. 1. These basins ley, Knowle and Worcester basins. may be divided into two broader over• The stratigraphy of the British Tri• all areas - Northwest Central England, assic has been recently reviewed by including the Cheshire (-Shropshire) Warrington et al. (1980) who recommend basin and the Central Midlands, com• subdivision into three lithostrati- Mineralization in the Triassic of Central England 367 graphic divisions the Sherwood Sand Cheshire Basin and further south in the stone Group, the Mercia Mudstone Group Midlands. and the Penarth Group. In Northwest The Sherwood Sandstone Group is com Central England the Sherwood Sandstone posed of a variety of conglomerates, Group is diachronously conformable pebbly sandstones and mudstones. The with underlying dominantly argillaceous conglomerates and pebbly sandstones Permian strata, while in the Central lower in the sequence are generally Midlands this junction is unconformable. interpreted as the deposits of an allu The junction between the Sherwood Sand vial fan/braided river system, whilst stone Group and the Mercia Mudstone the overlying finergrained sandstones Group is conformable and diachronous. represent alluvial deposits of low sin Both groups are of considerable thick uosity stream channels (AudleyCharles, ness in Central England, as shown by the 1970). In addition, in the Helsby Sand representative sections in Fig. 2. The stone Formation, Thompson (1969) identi overlying Penarth Group is seen in the fied aeolian dune deposits. In general,

South Cheshire Hereford and Worcester and North Shropshire West Midlands

RHAETIAN ra Westbury Fm Blue Anchor Fm Blue Anchor Fm

NORIAN

Wilkesley Halite Fm Arden Sst. Mbr CARNIAN Droitwich Halite Fm t/> ™ LADINIAN Northwich Halite Fm <

ANISIAN Tarporley Sltst. Fm Bromsgrove Sst. Fm Helsby Sst. Fm

Wilmslow Sst. Fm SCYTHIAN Chester Pebble Beds iïw Kinnerton Sst. F m Kidderminster Fm

PERMIAN

Penarth Group

Mercia Mudstone Group

■£::'!: Sherwood Sandstone Group

Fig. 2. Representative stratigraphie sections of the Triassic sediments of Central England 368 I. Holmes et al.

the grain size of the Sherwood Sand• increase in igneous influences (Ali, stone Group decreases in a northerly 1982). During deposition of the Mercia direction through Central England, which Mudstone Group, local topography was is the general direction of alluvial apparently reduced to the extent that transport in the British area. Central England was a low plain subject The Mercia Mudstone Group commences to variable marine influences, with in Northwest-Central England with the limited detrital supply. Tarporley Siltstone Formation, which, with its lateral equivalents in the Cen• tral Midlands, represents deposition in intertidal conditions (Ireland et al., 1978). This is followed by a very thick SAMPLE COLLECTION succession comprising dominantly mudstones, but in places with very thick halite deposits. The origin of these Samples representative of unmineralized deposits is controversial since carbo• Triassic sediments were obtained from nate and sulphate faciès of comparable the core of the Wilkes ley borehole stor significance are absent. Detailed sedi- ed by the Institute of Geological Scien mentological study of parts of the ces. Samples were also collected from Mercia Mudstone Group by Arthurton exposures in Central England, mainly (1980) led to the conclusion that the in the vicinity of known mineralization layered halite and associated laminated These samples were collected so as to mudstones were the result of marine represent both mineralized and unmin• flooding due to eustatic rise in sea eralized material. Sampling locations level. The more blocky mudstones were are shown in Figure 1. considered to represent emergent condi• tions during periods of regression. At the top of the Mercia Mudstone Group, the Blue Anchor Formation appears to PETROGRAPHY be transitional between the underlying mudstones and the marine Penarth Group and may be a marginal marine deposit. Sediments from the Wilkesley borehole Palaeogeographic reconstructions for range in grain size from coarse sand• the Triassic of Central England (Aud- stones to mudstones. They are dominant• ley-Charles, 1970), show that the Sher• ly red in colour, but occasionally grey wood Sandstone Group was laid down on a or green. The sandstones frequently sho north-west sloping piedmont. Most of carbonate and sulphate cements, togethe the sediment influx was thus from the with a varied suite of authigenic min• Hercynian mountain chain of North Eu• erals including quartz, potash feldspar rope and Southwest England, although plagioclase feldspar, hematite and TiOj isolated upstanding blocks centred on minerals (Fig.3). Sediments obtain• Wales, the Lake District and the Pen- ed from areas adjacent to mineraliza• nines would have been important local tion range from mudstones to conglomer• sources. The source rocks were probably ates. They may be red in colour but are varied, including a mixture of sedimen• frequently bleached. Sulphate and car• tary, low-grade metamorphic and igneous bonate cements are absent, except in rocks. The unconformity at the base of areas where barium mineralization is the Helsby and Bromsgrove Sandstone prevalent, when barite cements are com• Formation is thought by Warrington mon. Authigenic feldspar is not as com• (1970) to be a possible equivalent of mon as in the unmineralized material, the Hardegsen discontinuity in Germany. but authigenic quartz and hematite are This unconformity is followed by an in• widely distributed. Particularly in the crease in coarse-grained detritus and sediments associated with mineralizatio an increase in the content of perthitic but also in the unmineralized sediments feldspar and heavy minerals (particular• iron and copper sulphides occur within ly mica, apatite and garnet), possibly quartz overgrowths, indicating their indicating source area uplift and an formation during diagenesis. Fia. 3a-f. Photomicrographs of sediments from the Wilkesley borehole: (a) quartz grain showing an authigenic overgrowth of quartz and anhydrite pore-filling cement; (b) authigenic overgrowth of plagioclase feldspar showing twins in optic• al continuity and forming a triple junction with an authigenic overgrowth of quartz; (c) authigenic potash feldspar grain surrounded by anhydrite cement; (d) dolomite rhombs blocking pore connections; (e) scanning electron photomicro• graphs showing rounded quartz grain with barite cement; (f) scanning electron photomicrograph showing anhydrite cement 370 I. Holmes et al.

There is a general discrepancy in GEOCHEMISTRY the petrological characteristics of sur• face exposures and subsurface drill cores in the Triassic of Central Eng• Samples have been analysed by a combi• land. Carbonate and sulphate cements nation of X-ray fluorescence spectro• are often absent in surface and near- metry, atomic absorption spectrophoto• surface rocks and have presumably been metry and delayed neutron activation dissolved in the present-day ground• analysis. In Table 1 and 2 are listed water zone. Detrital and authigenic sili• results of the analysis of samples from cates, particularly K-feldspar, also the Wilkesley borehole. Analysis was by show dissolution textures within this X-ray fluorescence spectrometry, with zone and kaolinite is frequently abun• the exception of Cd and Co which were dant, filling secondary pore spaces. determined by atomic absorption spectro• This kaolinite may have been precipi• photometry. Certain of the major element tated in equilibrium with the present values are shown graphically in Figure * groundwater which is usually mildly Major element contents will obvious• oxidizing and slightly acid to neutral. ly reflect mineralogical changes in the Walker (1976) proposed that the for• succession and it can be seen from Fig• mation of continental red beds was a ure 4 that while SiC>2 increases general• result of diagenetic alteration. He con• ly towards the base of the sequence, sidered that the Permo-Triassic red the other major elements show a broad beds of Europe formed under similar decrease. This reflects the increasing• conditions to those observed at the ly arenaceous character of the lower present time in south-western USA. part of the succession. In more detail, There, due to the aridity of the area, whereas AI2O3 and Fe2Û3 show a reason• unstable ferromagnesian silicates are ably steady decrease down through the not destroyed by surface weathering but sequence, CaO and MgO show large fluc• are supplied to the depositional basin. tuations (Table 1) due to variations in These minerals are then progressively the content of carbonate and sulphate dissolved during diagenesis by oxygenat• cements. The alkalis, Na2Û and K2O, ed groundwater and the iron thus releas• show reasonably constant values through ed is deposited as hematite, or precur• the sequence, except for high K2O con• sor minerals to hematite. With time tents in the muds tones at the top of (possibly tens of millions of years) the sequence and in sample 9826 (which the unstable ferromagnesian minerals contains a large reduction spot) and a are completely destroyed, leaving no high Na2Û content in sample 9828, from direct evidence for their former exis• within a halite bed. tence . The trace element contents in Ta• Walker's (1976) proposed mechanism ble 2 show similar distributions to the for the genesis of red beds fits well major elements in that they are deplet• with the data already outlined for the ed in samples with the highest SiÛ2 con• Triassic of Central England. The pres• tents. Concentrations of most trace ence of aeolian dunes indicates that elements are similar to those reported arid conditions were common, while the from the analysis of sedimentary rocks, formation of authigenic quartz, feld• with the main exception of Cu, which in spar and hematite would be expected to several samples is much higher than the follow the dissolution of unstable fer• published average values of ~30 ppm romagnesian silicates. The formation of (Wedepohl, 1978). Ba and Sr show signi• authigenic minerals is, of course, de• ficant enrichment in two samples each, pendent upon the prevalence of suitable in the case of Sr this is probably due conditions of Eh and pH. Thus, for ex• to Sr substitution in calcite and an• ample, the occurrence of authigenic hydrite. plagioclase and of sulphate cements in In Table 3 are shown results of the sediments from the upper part of the inalysis of samples from three mineral• Sherwood Sandstone Group may indicate ized areas - Alderley Edge, Gallantry that interstitial conditions were more Bank and Grinshill. All of these anal• alkaline than at other horizons. yses were performed by atomic absorp- Mineralization in the Triassic of Central England 371

Table 1. Geochemical analysis of samples from Wilkesley Borehole

Major elements as % weight

Sample Si02 A1203 Fe203 MgO CaO Na20 Ti02 MnO P so CI L.O.I. it Total V 2°5 3

9355 41.54 12.58 5.81 8.77 9.48 1.03 4.26 0.53 0.09 0.12 0.05 N.D. 16.00 100.26 9356 44.15 11.99 5.61 7.72 9.77 1.12 3.70 0.60 0.11 0.14 0.03 N.D. 15.10 100.04 9361 45.10 13.59 3.84 13.19 5.68 1.31 2.92 0.67 0.10 0.14 0.04 N.D. 1-3.30 99.88 9369 53.46 13.88 4.13 7.44 4.21 1.63 3.83 0.73 0.09 0.13 0.20 0.04 10.10 99.86 9728 29.51 5.48 1.37 0.59 3.47 19.40 1.04 0.28 0.02 0.05 5.63 13.41 22.00 99.21 9770 43.89 13.98 6.49 8.31 6.82 2.41 3.36 0.60 0.06 0.13 2.36 0.09 11.80 100.28 9772 40.88 12.23 5.23 7.20 9.87 1.44 3.17 0.62 0.07 0.15 4.60 0.07 14.20 99.77 9776 46.19 10.61 4.12 9.45 8.53 0.95 2.46 0.54 0.07 0.12 2.71 0.01 14.40 100.15 9781 41.83 12.26 3.68 8.87 10.43 1.41 2.42 0.60 0.10 0.11 0.45 0.05 18.40 100.59 9782 45.22 10.76 3.39 7.84 10.89 1.43 2.50 0.66 0.08 0.12 0.76 N.D. 16.60 100.27 9792 69.84 3.35 0.94 1.78 8.84 0.52 1.07 0.25 0.04 0.06 5.37 N.D. 7.70 99.76 9792A 66.15 7.82 2.50 4.28 5.88 0.71 2.14 0.48 0.03 0.10 1.55 N.D. 8.60 100.24 9799 61.90 3.78 1.19 1.56 11.69 0.70 1.13 0.32 0.05 0.06 8.34 N.D. 9.00 99.72 9799A 61.27 4.00 1.97 3.52 10.57 0.75 1.08 0.38 0.11 0.08 4.48 N.D. 11.40 99.61 9803 74.15 2.16 0.32 0.17 8.99 0.25 1.13 0.05 0.02 0.02 7.22 N.D. 5.30 99.79 9807 86.65 6.40 1.20 0.60 0.38 1.37 2.55 0.35 0.02 0.09 0.11 0.01 0.90 100.63 9810 87.85 4.59 0.72 0.74 0.87 1.20 2.02 0.15 0.03 0.05 0.11 0.01 1.90 100.24 9815 87.28 4.77 0.99 0.76 1.05 1.01 1.94 0.20 0.03 0.06 0.00 N.D. 2.20 100.29 9817 87.00 5.25 0.92 0.71 0.54 1.18 2.08 0.22 0.03 0.07 0.11 0.01 1.50 99.62 9821 80.83 7.77 2.12 1.08 1.02 1.43 2.60 0.53 0.05 0.11 0.07 N.D. 1.80 99.41 9826 58.29 18.50 5.14 3.54 0.54 1.06 6.03 0.87 0.04 0.18 0.12 0.01 4.70 99.02 9828 72.03 8.15 2.60 1.86 4.17 1.19 2.57 0.55 0.06 0.11 0.42 N.D. 6.20 99.91 9831 50.81 13.86 5.76 5.94 6.22 0.74 4.63 0.65 0.13 0.12 0.16 0.01 10.70 99.73 9853 83.23 4.30 1.02 0.31 3.52 0.98 1.85 0.25 0.03 0.07 1.08 N.D. 3.70 100.34

L.O.I. - Loss on ignition N.D. - Not determined * Total corrected for 0 = CI

Table 2. Geochemical analysis of samples from Wilkesley Borehole

Trace elements in ppm

Sample Ba Sr Rb Zr Cu Co Pb Zn Cd Ni Cr V Y La

9355 292 213 158 121 157 29 14 46 3 45 87 85 24 29 9356 261 241 138 176 21 34 23 55 3 47 91 86 28 33 9361 364 172 135 180 17 33 15 122 2 47 94 118 30 39 9369 539 161 14 45 26 83 4 54 73 136 9728 241 1325 5 19 22 25 3 22 32 40 9770 251 321 6 48 33 92 3 86 112 124 9772 257 456 4 47 35 71 4 65 88 110 9776 316 344 9 31 27 66 2 38 60 94 9781 317 120 21 43 32 57 3 44 71 118 9782 115 231 107 274 122 28 13 46 4 33 53 49 30 23 9792 147 361 32 211 12 12 10 13 N.D. 31 29 18 14 10 9792A 221 289 77 259 5 25 12 54 1 35 65 57 20 19 9799 228 463 31 337 70 16 11 11 N.D. 26 31 20 18 12 9799A 1438 640 33 440 323 13 13 16 N.D. 36 40 34 24 19 9803 165 304 31 33 7 2 11 0 N.D. 36 7 5 5 3 9807 361 57 0 83 11 12 5 19 19 27 9810 302 45 1 70 8 12 0 9 9 10 9815 290 58 53 155 31 11 12 2 N.D. 78 22 16 11 14 9817 294 210 13 20 15 N.D. 82 18 9821 321 77 73 348 25 23 12 15 N.D. 55 56 45 23 25 9826 438 59 3 77 20 74 8 74 97 177 9828 284 158 75 370 120 23 13 21 N.D. 49 62 56 25 26 9831 314 100 5 53 21 58 3 56 77 121 9853 212 172 40 265 24 6 10 3 N.D. 56 24 14 11 12

N.D. - Not determined 372 I. Holmes et al.

% for SiC>2 40 60 80

Lithology Depth in Sample borehole number (m) Red mdst. 188 9355-

Red mdst. 194 9356.

Red mdst. 229 9361-

Red mdst. 300 9369-

Grey mdst. 709 9728-

Red mdst 890 9770-

Red mdst. 978 9772 ■

Red mdst. 1154 9776-

Grey mdst. 1304 9781-

Grey sltst. 1305 9782-

Red sltst. 1487 9792-

Red slst. 1511 9799-

Red sndst. 1535 9803-

Red sndst. 1602 9807-

Red sndst. 1618 9810-

Red sndst. 1628 9815-

Red sndst. 1648 9817-

Red sndst. 1652 9821-

Green sltst. 1662 9826-

Red sltst. 1664 9828-

Red sltst. 1667 9831-

Red sndst. 1685 9853-

Fig. 4. Plot showing the variation in concentration (weight %) of certain major elements in samples from the Wilkesley borehole Mineralization in the Triassic of Central England 373

Table 3. Geochemical analyses and descriptions of samples from mineralised areas

Major elements as Z Trace elements in ppm Sample no. A1203 Fe203 MgO CaO Na20 V Mn Cu Co Pb Zn Cd Ni CI 5.33 1.24 0.32 0.19 0.22 2.81 153 7 18 14 0 0 40 G3 2.42 0.20 0.08 0.03 0.34 1.58 54 60 6 23 20 1 65 GB1 2.66 0.36 0.11 0.28 0.23 1.80 100 11 9 14 0 0 40 GB3 3.14 0.63 0.12 0.07 0.22 1.72 55 14 9 9 4 0 37 GB4 2.42 0.18 0.09 0.06 0.17 1.41 38 11 5 9 4 1 1 AE1 18.27 7.42 1.64 0.39 0.61 6.05 266 1347 98 26 454 8 100 AE2 17.53 3.20 1.48 0.30 0.44 5.50 301 2595 177 916 345 8 80 AE31 1.04 0.17 0.05 0.16 0.09 0.42 168 356 50 6 355 4 40 AE32 2.25 0.26 0.10 0.75 0.44 1.21 172 4973 40 15 546 6 80 AE5 1.53 0.30 0.07 0.04 0.10 0.66 67 81 35 11 26 1 6 AE8 2.31 0.65 0.06 0.04 0.15 1.28 18 19617 104 31 1517 14 44 AE9 4.38 0.42 0.09 0.06 0.28 2.48 33 386 26 84 129 7 39 AE11 3.00 0.26 0.08 0.04 0.20 1.59 38 30 20 6 7 0 19 AE13 2.95 4.37 0.05 0.03 0.20 1.61 84 51822 248 9252 1380 47 456

Gl Red sandstone, Grinshill G3 Indurated bleached sandstone, Grinshill GB1 Red sandstone with barite, Gallantry Bank GB3 Red sandstone, Gallantry Bank GB4 Bleached sandstone, Gallantry Bank AE1 Red mudstone, Alderley Edge AE2 Green mudstone, Alderley Edge AE31 Bleached sandstone, Alderley Edge AE32 Bleached sandstone with malachite, Alderley Edge AE5 Red sandstone with barite, Alderley Edge AE8 Malachite stained conglomerate with barite, Alderley Edge AE9 Light-brown pebbly sandstone, Alderley Edge AE11 Light-brown sandstone, Alderley Edge AE13 Vein material, Engine Vein Mine, Alderley Edge

tion spectrophotometry. It can be seen by the delayed neutron activation method that the tabulated major element con• showed uniformly low U contents, com• tents are generally lower than those for monly in the range 1-3 ppm, with a high• the Wilkesley samples. This is a reflec• est value of 5.5 ppm. U values tend to tion of the coarser-grained nature of be slightly higher in the finer-grained the sediments and their correspondingly sediments. Analysis of ore material higher quartz contents. Especially no• from Alderley Edge similarly showed U table are the low CaO and MgO contents, contents below 3 ppm. which reflect the almost complete ab• sence of carbonate and sulphate cements (except for barite). The trace element values for the samples from Gallantry ASPECTS OF THE MINERALIZATION Bank and Grinshill are similar to those for the Wilkesley sediments, while those Numerous examples of mineralized sedi• from Alderley Edge are frequently much ments occur in the Triassic rocks of higher, indicative of the more exten• Central England and the more significant sive mineralization occurring at Aider- occurrences are shown on Figure 1. The ley Edge. The trace element contents of dominant mineralization appears to be the Alderley Edge sample show the min• of copper and barium, with more re• eralization to be dominantly copper, stricted lead and zinc occurrences. Co• with subsidiary enrichment in lead and balt and nickel also occur, as does zinc. manganese. Vanadium has been reported Analysis of samples for uranium from from a few localities but uranium has both Wilkesley and the mineralized areas not been recorded to any great extent, 374 I. Holmes et al.

although it has not been searched for able sandstone horizons and then depo• systematically. Many of the areas of sited metals in suitable environments. mineralization were mined on a small Similar solutions are also responsible scale in the 18th and 19th centuries for the diagenesis of the sediments, (Carlon, 1979, 1981). suggesting that a link between mineral• Most of the metalliferous deposits ization and diagenesis may exist. in the Triassic of Central England It has already been stated that the have a broadly similar geological set• diagenetic history of the Central Eng• ting. The mineralization is commonly land Triassic sediments is thought to associated with a fairly major fault be similar to that shown by Walker and is largely limited stratigraphical- (1976) for Tertiary red beds in south• ly to the sediments of the upper part western USA and north-western Mexico. of the Sherwood Sandstone Group. In The proposed sequence of diagenetic particular, the mineralization is more changes is shown in generalised form common in the porous conglomerates and in Table 4. Detrital silicates, clays coarse sandstones, especially where and oxides are subject to dissolution these underlie or are faulted against during early diagenesis and authigenic mudstone bands, to form stratigraphie mineral grains or overgrowths are form• traps. The mineralization tends to be ed by later precipitation when these better developed down-dip from the fault solutions meet suitable conditions. zone. Barite is far more widespread More complete cementation (and possib• than the metalliferous mineralization, ly mineralization) can be regarded as but in general follows the same form, an extension of this process. The major being especially widespread in the more element redistributions which may be permeable horizons expected to occur during this diageneti The Alderley Edge deposit may be cit• sequence are shown in Table 4. ed as an example of the ore mineral As well as possibly releasing large paragenesis of the deposits in the Tri• amounts of major elements, the dissolu• assic of Central England. This has been tion stage will also result in the re• studied by Ixer and Vaughan (1982) who lease of the trace metals located in found the following sequence. Detrital the detrital minerals. As an example of opaque phases including iron-titanium the trace metal contents to be expected oxides and pyrite in clastic grains are copper averages 100 ppm in pyroxenes followed by iron and copper sulphides and biotites but may reach 1000 ppm and found in quartz overgrowths and there• 11,600 ppm respectively (Wedepohl, 1976 fore associated with the diagenesis of These and other ranges of expected cop• the sediments. The main phase of mine• per contents for detrital phases are ralization consists of sulphides cement• shown on Table 4. ing the clastic grains and forming in Walker (1976) has shown that during the order iron/nickel - copper - zinc - diagenesis and red bed formation, fer- lead. This primary assemblage has under• romagnesian silicates, feldspars and gone substantial alteration, resulting detrital oxides are often completely in the formation of secondary copper dissolved, thus releasing the major sulphides and carbonates and sulphates and minor element contents into solu• of copper, zinc and lead. Reactions tion. These elements will only remain within the present groundwater zone are in solution as long as the chemical probably responsible for this altera• conditions are suitable for them to do tion. so, once conditions become unsuitable the element will precipitate. Taking again the example of copper, it has been shown that copper will be releas• DISCUSSION ed into solution following the dis• solution of detrital silicates and The mineralisation occurring in red beds oxides. As the solubility of copper in of the type found in Central England normal terrestrial groundwater is less has clearly been deposited from solu• than 1 ppm at near neutral pH, it may tions which have passed through perme• be expected that either diagenetic sol" Mineralization in the Triassic of Central England 375

Table 4. Scheme for the main diagenetic reactions occurring in red bed formation

Detrital supply Early diagenesis - Authigenie Cementation Mineralization dissolution precipitation

Silicates Quartz Quartz Barite K-feldspar (Cu x 5ppmt <20ppm) K Al Si Bs Pb K-feldspar Galena Plagioclase (Cu x 62ppm; <840ppm) Ca Na Al Si Plagioclase Pyrite Ferromagnesians (Cu x 100ppra;

Ti02 Anatase

pH =7, Eh +ve co3- so4" pH <7, Eh -ve + +

tions would be extremely dilute with of trace metals in red beds, the ex• respect to copper or that copper would ample of the Cheleken Peninsula (USSR) be quickly precipitated from solution. may be considered. Lebedev (1972) re• Rose (1976), however, has shown that ported that hot brines derived from the solubility of copper is dramatical• the Neogene red beds of the Cheleken ly increased in saline waters, through Peninsula commonly contain 2 ppm copper the formation of CuClJ and CuCl^- com• and lead and 4 ppm zinc in solution. In plexes. He found solubilities of 100 ppm extreme cases the lead content ranges copper for approximately 10g/l dissolv• to 77 ppm and the copper content to ed chloride. Of more direct importance 15 ppm. Lebedev et al. (1971) showed to red bed mineralization studies is that the lead was mainly present in that a complex such as CuCl§- is stable solutions as PbCl^ and PbCl^- complexes. at a pH of about 7 and in the presence These brines produce on average 300 tons of hematite, conditions comparable to of lead, 50 tons of zinc and 30 tons of those prevailing during the diagenesis copper annually at the surface. This of red beds. modern evidence supports the hypothesis Having shown that possible mechanisms of derivation of metalliferous solu• exist for the dissolution of trace me• tions from red beds. tals during diagenesis and for their In the case of the Triassic rocks transportation and concentration in of Central England, there is abundant solution, it remains only to consider halite within the sedimentary sequence means for their precipitation from sol• to produce saline interstitial waters ution. Metals such as copper, lead and capable of dissolving and transporting zinc are all precipitated from solution significant quantities of trace metals. as sulphides, presumably in a reducing It was shown in Table 2 that the copper environment with the presence of dis• contents of an unmineralized Triassic solved sulphur. Such environments would sequence showed several anomalously occur if the metal-rich brine solutions high values. This may well be an indi• encountered trapped hydrocarbons, hydro• cator that redistribution of trace me• gen sulphide or sediments rich in sul• tals, especially copper, has occurred phides such as pyrite. during the diagenetic formation of the As a modern analogue of the dissolu• red bed sequence. The amounts of metal tion, transportation and concentration involved may be roughly estimated by 376 I. Holmes et al. making an assumption of the amount of Arthurton, R.S.: Rhythmic sedimentary the original copper content of the se• sequences in the Triassic Keuper Marl diment removed during diagenesis. Con• (Mercia Mudstone Group) of Cheshire, sidering the Sherwood Sandstone Group northwest England. Geol. J. 15, sediments in the Cheshire Basin, the 43-58 (1980) area involved is approximately Audley-Charles, M.G.: Triassic palaeo- 3.4 x109m2, in which the Sherwood Sand• geography of the British Isles. Q.J. stone Group ranges up to 1000 m in geol. Soc. Lond. 126, 49-89 (1970) thickness. Taking a thickness of only Carlon, C.J.: The Alderley Edge mines. 100 m gives a rock volume of J. Sherratt & Son, Altrincham 1979 3.4 x lO11!3. Assuming an average ini• Carlon, C.J.: The Gallantry Bank coppei tial copper content of 30 ppm and re• mine, Bickerton, Cheshire. British moving from this during diagenetic al• Mining No. 16, 1981 teration only 1 ppm produces 884,000 Ireland, R.J., Pollard, J.E., Steel, tons of copper metal. It is evident, R.J., Thompson, D.B.: Intertidal se• therefore, that the potential exists diments and trace fossils from the for deriving substantial metalliferous Waterstones (Scythian-Anisian?) at deposits from the diagenetic processes Foresbury, Cheshire. Proc. Yorks. involved in red bed formation. As a geol. Soc. 41, 399-436 (1978) comparison with the above figure, the Ixer, R.A., Vaughan, D.J.: The primary total tonnage of ore removed from Alder- ore mineralogy of the Alderley Edge ley Edge is estimated to have yielded deposit, Cheshire. Min. Mag. 46, approximately 5000 tons of copper 485-492 (1982) metal. Lebedev, L.M. : Minerals of contemporary hydrothenns of Cheleken. Geochem. Acknowledgements. The work described in Int. 9, 485-504 (1972) this paper was supported by the Primary Lebedev, L.M., Baranova, N.N., Nikitin; Raw Material Research and Development I.B., Vernadskiy, V.I.: On the forms Programme of the Commission of the Euro• of occurrence of lead and zinc in the pean Communities under Contract No. Cheleken thermal brines. Geochem. Int MPP. 155.81 UK(H). 8, 511-516 (1971) The Director and Staff of the In• Rose, A.W. : The effect of cuprous chlo• stitute of Geological Sciences, partic• ride complexes in the origin of red- ularly Dr. A.A. Wilson, are thanked bed copper and related deposits. for providing access to samples and Econ. Geol. 71, 1036-1048 (1976) data from borehole material. Dr. R.J. Stanton, R.L.: Ore Petrology. McGraw King of Leicester University is thank• Hill, New York 1972 ed for his advice and the loan of sam• Thompson, T.B.: Dome shaped aeolian ples from the East Midlands areas and dunes in the Frodsham Member of the Dr. C.J. Carlon for access to his un• so-called "Keuper" Sandstone Forma• published Ph.D. thesis. tion (Scythian-?Anisian: Triassic) We thank Pam Minor for preparation at Frodsham, Cheshire (England). of the typescript and Beverley Parker Sed. Geol. 3, 263-289 (1969) for drafting the diagrams. Walker, T.R.: Diagenetic origin of continental red beds. In: Falke, H. (ed.) The Continental Permian in Central, West and South Europe. D. REFERENCES Reidel Publishing Co., Dordrecht- Holland, p. 240-282 (1976) Warrington, G.: The stratigraphy and Ali, A.D.: Triassic stratigraphy and palaeontology of the "Keuper" Series sedimentology in central England. of the Central Midlands of England. Unpublished University of Aston Ph.D. Q.J. geol. Soc. Lond. 126, 183-223 thesis (1982) (1970) Mineralization in the Triassic of Central England 377

Warrington, G., Audley-Charles, M.G., Received: July 27, 1982 Elliott, R.E., Evans, W.B., Ivimey- Accepted: April 5, 1983 Cook, H.C., Kent, P.E., Robinson, P.L., Shotton, F.W., Taylor, F.M.: A correlation of Triassic rocks in Dr. D.J. Vaughan the British Isles. Geol. Soc. Lond. Reader in Mineralogy Spec. Report No. 13, 78 p. (1980) The University of Aston Wedepohl, K.H.: Handbook of Geochemis• Department of Geological Sciences try. Springer, Berlin Heidelberg Gosta Green, Birmingham B4 7ET New York, 1978 England

Mineral.Deposita 18, 379-386 (1983) MINERALIUM DEPOSITA © Springer-Verlag 1983

Inclusions Fluides dans les Calcites Associées à la Mineralisation Pb-Zn de Poppelsberg (Est de la Belgique)

A. Darimont

Chercheur IRSIA, Laboratoire de Géologie Appliquée, Liège, Belgique

Les inclusions fluides des calcites prélevées dans un filon plombo-zincifêre dans l'Est de la Belgique montrent une grande dispersion des températures d'ho• mogénéisation Th (30°C à plus de 360°C) et sont caractérisées par deux types de températures de fin de fusion Tf2(-14°C et -21°C). L'ébullition n'a pu être démontrée. En raison de la dispersion des températures d'homogénéisation non expliquée à ce jour, la profondeur de mise en place du gisement reste difficile à estimer. Toutefois, les propriétés thermométriques des inclusions fluides permettent de distinguer les calcites issues d'un site fertile (Poppelsberg) des calcites provenant d'un site stérile (Belle Roche, Th=150°C, Tf2 variable avec un mode à -8°C): Fluid inclusions in calcites sampled in a Pb-Zn mineralized vein in East Bel• gium are characterized by a large dispersion of filling temperatures Th (30°C to more than 360°C) and by two groups of freezing points Tf2 (-14°C and -21°C). Boiling has not been proved. According to the still unexplained dispersion of the filling temperatures, this study does not permit an estimation of the depth of the ore formation. Nevertheless, fluid inclusions thermometric properties make possible the distinction between calcites associated with a mineralization (from the fertile locality of Poppelsberg) and calcites from sterile area (Belle Roche, Th=150°C, Tf2 variable around a mode of -8°C).

SITUATION GEOLOGIQUE La minéralisation de Poppelsberg (Fig.1) jalonne une faille NNW-SSE re• dressée, transverse aux structures her- Les minéralisations plombo-zincifères cyniennes NE-SW (Fig.2). Le filon re• exploitées jadis (Moresnet, La Calamine, coupe des couches arêno-pélitiques fa- Schmalgraf...) se répartissent dans menniennes et carbonatées dinantiennes. une bande de terrains carbonifères qui La minéralisation se compose de ga- s'êtend de Namur à l'ouest à Aachen à lène, blende colloforme et marcasite l'Est (Fig.1). Les gisements Pb-Zn de en zonages disséminés dans une gangue l'Est de la Belgique (massif de la Ves- calcitique. L'absence de dissolution dre) se situent généralement au contact majeure aux êpontes de l'encaissant calcaire dinantien-schiste houiller, carbonate indique que les solutions de- à l'intersection des coeurs synclinaux vaient être saturées en carbonates hercyniens et des failles transversa- avant d'arriver sur le site du dépôt. les anté-crêtacêes (Timmerhans, 1905). La présence de calcites précoces par 380 A. Darimont

MATERIELS ET METHODES D'INVESTIGATION

La calcite a été échantillonnée sys• tématiquement en veines, filon et géo• Aachen des dans les sondages et carrières de Poppelsberg (Fig.2); elle a été pré• levée dans les niveaux dolomitiques ou bréchiques de la carrière de La Bel• le Roche. Les calcites clivées en esquilles V7A Carbonifère millimétriques, sont observées au 1 POPPELSBERG moyen d'un microscope Leitz Ortholux 2 BELLE ROCHE polarisant muni d'une platine chauf• fante 350. Le principe et la méthode i .20 km d'étalonnage correspondent à ceux de Fig.1. Position des niveaux carboni• la platine Chaixmeca (Hollister L.S., fères belges; localisation des sites 1981, p.293). L'intervalle de tempéra• de Poppelsberg et Belle Roche tures se situe entre -100°C et +350°C. Toutes les inclusions biphasées ob• servées (789 mesures) ont été chauf• fées. Certaines (146 mesures) ont été congelées. Des problêmes optiques ont rapport aux sulfures démontre la sta• souvent empêché de faire les lectures bilité de la calcite pendant le trans• de températures d'homogénéisation et de port du Plomb et du Zinc (Giordano and fin de fusion sur la même inclusion. Barnes, 1981). Des calcites broyées et calibrées, La calcite est le seul minéral trans• diamètre compris entre 420 et 590 mi• parent omniprésent sur le site. On la crons, ont été écrasées à la platine rencontre en gangue de la minéralisa• à écrasement de façon à apprécier le dé tion (filon), en veines millimétriques gagement en C02. Î9 d'entre elles ont à centimétriques (veines) et en remplis• été étudiées au spectromêtre de masse sage de cavités dans certains niveaux par M.F.Miller et T.J.Shepherd de l'Ins dolomitiques (géodes). titute of Geological Sciences, à Lon• La calcite du filon est rubannée dres. transparente à opaque; la calcite des veines est microgrenue ou spathique souvent translucide; la calcite des géodes est présente sous forme de cris• TYPES D'INCLUSIONS taux idiomorphes millimétriques à cen• timétriques transparents implantés sur A température ambiante, les inclusions une croûte de calcite microgrenue. fluides sont monophasées (liquide) ou De façon à comparer les caractéris• biphasées (liquide-gaz). Aucune phase tiques thermométriques des inclusions solide n'a été observée. fluides des calcites prélevées dans le Les variétés morphologiques rencon• site fertile avec celles de calcites trées peuvent se résumer en trois types provenent d'un site stérile, des cal• (Fig.3): cites ont été prélevées dans une région I inclusions claires à contour géo• vierge de minéralisation plombo-zinci- métrique (cristal négatif) contenant un fère connue et dans le même contexte li• bulle de gaz transparente; remplissage thologique et stratigraphique. Elles gazeux faible. proviennent de la carrière de la Belle II inclusions claires à contour Roche, située le long de l'Amblève dans régulier contenant une bulle de gaz le synclinorium de Dinant (Fig.1). Il transparente ou sombre; remplissage s'agit essentiellement de calcites en gazeux faible. géodes dans des niveaux dolomitiques III inclusions claires ou sombres ou bréchiques; les veines sont rares. à contour irrêgulier contenant une bull* Inclusions Fluides dans les Calcites Associées à la Minéralisation Pb-Zn 381

BLOC DIAGRAMME POPPELSBERG -RABORATH.

S2Î sondage sX faille

^^^ dinantien h ' i ' \\ calcaire

dolomitique

t-1""1 ■■! crinoidique famennien

échelle

Fig.2. Description géologique du site de Poppelsberg; localisation des carriè res et sondages

TYPES MORPHOLOGIQUES

Fig.3. Types morphologiques d'inclusions fluides les plus fréquents. 382 A. Darimont de gaz à halo noir; remplissage gazeux fréquence des inclusions change d'une variable. calcite à l'autre ou d'une plage à La taille des inclusions varie de l'autre dans la même calcite. 5 microns à plusieurs centaines de mi Le taux de remplissage gazeux varie crons. La taille des bulles de gaz de 3/100 à 70/100. Les mesures au spec varie de 5 microns â 200 microns. La tromètre de masse indiquent un taux en

D site stérile

■ site fertile

Fig.4. Distribution des températures d'homogénéisation Th et des températures de fin de fusion Tfj observées dans les calcites en géodes, veines et filon, provenant du site fertile (Poppelsberg) et du site stérile (Belle Roche) Inclusions Fluides dans les Calcites Associées â la Minéralisation Pb-Zn 383

C02 inférieur à 0.25 moles%. Aucune généisation se produit en phase liquide. phase liquide CO2 n'a été observée. La calcite éclate vers 370°C. Certaines Les inclusions biphasées â carac• inclusions ne se sont pas homogénéisées tère nettement secondaire sont ali• â cette température; parmi celles-ci gnées le long des plans de clivage. quelques-unes contiennent une bulle de Elles se sont homogénéisées â des tem• gaz qui s'expanse pendant la chauffe pératures inférieures à 100°C. (après refroidissement à 20°C, la bulle reprend sa taille initiale). La répartition des températures d'ho• RESULTATS THERMOMETRIQUES mogénéisation est reproduite à la Figure 4 suivant l'appartenance de la calcite Les températures d'homogénéisation va• aux groupes filon, veines, géodes pour rient de 30°C à plus de 360°C. L'homo• les sites fertile (Poppelsberg) et sté-

Tf2 -15 géode a D site stérile -9 8 D

3 D R] Th 60 90 120 150 180

O O 30 géode site fertile

-18 O -12 O

- 6 O 8 8° 8 n. Th 90 150 210 filon 21 M

A 15 A AA A A Â A A A 9

Th 60 120 180 240 300 360 Fig.5. Corrélations entre les températures d'homogénéisation Th et les tempé• ratures de fin de fusion Tf_ observées dans trois échantillons: une géode du site stérile, une géode du site fertile et une calcite du filon 384 A. Darimont rile (Belle Roche). Plusieurs pics se température d'homogénéisation de 150°C, dessinent dans les histogrammes: 60°- température minimale de piègeage, cor• 90°, 150°, 210°. Les températures les respondant vraissemblablement aux tem• moins fréquentes voisinent 105°C. Il pératures régionales lors de l'enfouis• n'existe aucune relation évidente entre sement des couches dolomitiques hôtes. les variétés morphologiques et les tem• Les variations des températures de fin pératures d'homogénéisation. de fusion (à Th constante) font penser Lors de la congélation, plusieurs à la présence d'un fluide localement comportements sont observés: certaines dérivé, contrôlé par la minéralogie inclusions se craquaient, les cristaux encaissante. La température de fin de de glace sont nettement visibles; fusion la plus fréquente est voisine d'autres restent homogènes (un seul cris• de -8°C. tal?). Lorsqu'il n'y a pas de craque• b- les calcites du site fertile lures, l'évolution de la fusion est per• sont caractérisées par une grande dis• çue à travers la déformation de la bulle persion des températures d'homogénéisa• de gaz. tion. Les températures de première fusion Parmi les calcites de ce site, les (first melting point) généralement in• calcites associées à la minéralisation férieures à -50°C, attestent de la pré• plombo-zincifère se distinguent par sence d'autres sels que NaCl dans la l'existence d'inclusions fluides dont solution, tels que CaCln, MgCl2.... les températures de fin de fusion se Les températures de fin de fusion répartissent en deux groupes: -21°C et (freezing point) varient de -33°C à -14°C. Certaines calcites en veines +1CC (Fig.4.). Trois pics s'individuali• prélevées autour de la minéralisation sent: -21°, -14°, -3° â Poppelsberg; et sont apparentées aux calcites filonien• un pic à Belle Roche: -8°. nes (même Tf _). Quant aux calcites is• sues des niveaux dolomitiques encais• sants la minéralisation, elles contien• CORRELATIONS TEMPERATURES D'HOMOGE• nent des inclusions fluides dont les NEISATION-TEMPERATURES DE FIN DE FUSION températures de fin de fusion varient de -33°C à 0°C. Cette variation peut résulter d'un mélange de fluides. Les corrélations entre les températures d'homogénéisation Th et les températures de fin de fusion Tf2 au sein d'un même individu s'expriment de différentes fa• INTERPRETATION çons (Fig.5): 1- Th variables, Tf~ constantes 2- Th variables, Tf2 variables La dispersion des températures d'homo• 3- Th constantes, Tf variables. généisation observée dans les inclu• 2 sions fluides des calcites du site Le cas 1 s'observe dans les calcites fertile pose un problème. Pour discer• filoniennes de Poppelsberg (30°C < Th ner les températures significatives < 360°C; Tf2 = -21°C et Tf = -14°C), d'un point de vue génétique ou utili• C ou en veines (30 C < Th < 360°C; Tf2 = sables sous l'angle de la prospection, -21°C, -14°C, -3°C); il est indispensable de connaitre les le cas 2 s'observe dans les calcites processus responsables des dispersions en géodes de Poppelsberg (30CC < Th < enregistrées. 360°C; -33°C < Tf2 < 0°C; Plusieurs processus peuvent être envi• le cas 3 s'observe dans les calci• sagés: tes en géodes du site stérile de Belle 1- fuites après piègeage (leakage) Roche (Th = 150°C; -14°C < Tf2 < 0°C). 2- variations des conditions pres• Les corrélations Th-Tf~ permettent sion-température pendant la cristalli• de distinguer les calcites provenant sation du site stérile des calcites du site 3- mélange de plusieurs fluides fertile: 4- division par étranglement des a- les calcites géodiques du site inclusions (necking down) stérile sont caractérisées par une 5- ebullition (boiling). Inclusions Fluides dans les Calcites Associées â la Minéralisation Pb-Zn 385

1- Les inclusions logées dans des CONCLUSIONS zones fissurées peuvent avoir été vidées de leur contenu totalement ou en partie. Toutefois, certaines plages Les caractéristiques thermométriques non fissurées d'inclusions isolées des inclusions fluides des calcites pei- montrent des dispersions de tempéra• mettent de distinguer les calcites tures d'homogénéisation énormes. "fertiles" des calcites "stériles": 2- Les conditions pression-tempé• - A Belle Roche, site stérile, les rature peuvent varier au cours du calcites en géodes dans les niveaux dépôt de la calcite. Il n'est cepen• dolomitiques ou bréchiques ont cristal• dant pas possible de mettre en évi• lisé à des températures proches ou su• dence un gradient de température lors• périeures à 150°C. La salinité des qu'on examine des calcites prélevées fluides piégés, exprimée en tempéra• dans le filon à partir de l'éponte jus• ture de fin de fusion, bien que vari• qu'au coeur: toutes contiennent une able, se situe le plus souvent autour large gamme de températures d'homo• de -8°C. généisation. - A Poppelsberg, site fertile, les 3- Le mélange de plusieurs fluides inclusions fluides des calcites â con• influence autant les salinités, c'est- tenu C0? faible (< 0.25 moles %) se à-dire les températures de fin de fu• sont formées à des températures cer• sion, que les températures d'homo• tainement supérieures à 110°C. Sans généisation. Les calcites en géodes évidence d'ébullition, on peut consi• contiennent des inclusions fluides dont dérer que les fluides minéralisateurs les températures de fin de fusion mon• sont des fluides "chauds". Les homo• trent une grande dispersion qui pour• généisations en phase liquide se font rait effectivement s'expliquer par le à des températures pouvant dépasser mélange de fluides de salinités diffé• 360°C. rentes. Au sein du site fertile, les calci• 4- La recristallisation du minéral tes filoniennes se distinguent par hôte peut conduire à la division d'in• deux types de températures de fin de clusions en plusieurs inclusions. Il fusion: -21°C et -14°C. Certaines cal• en résulte une grande dispersion des cites en veines y sont apparentées températures d'homogénéisation. (Dari- (même Tf ~). Les températures de fin tnont et Coipel, 1982). de fusion rencontrées dans les calcites Sans l'appui de renseignements mor• gêodiques sont variables. phologiques, la signification des dif• En raison du doute qui pèse sur 1'in• férents domaines de températures ob• terprétation de la dispersion des tem• tenus est difficile à élucider. De pératures d'homogénéisation des inclu• plus, la recristallisation n'affecte sions fluides des calcites de Poppels• pas nécessairement toutes les inclu• berg, il est prématuré de poser des li• sions; et elle peut se produire à dif• mites quant aux mécanismes de dépôt, férentes températures. ou d'essayer d'envisager une origine 5- L'êbullition est le processus le quelconque. plus séduisant: il conduit â la con• Les investigations dans d'autres naissance de la température de piêga- sites, et sur d'autres minéraux, sou• ge sans correction de pression. Mal• tenues par une étude isotopique s'avè• gré la présence de bulles de gaz qui rent indispensables pour situer les in• s'expansent pendant la chauffe, non clusions dans un contexte génétique. homogénéisées à 360°C, l'êbullition n'a pu être mise en évidence. La non détection d'inclusions à très fort Remerciements. Cette étude a été sub- remplissage gazeux nous empêche d'ap• sidiee par la Communauté Economique précier les températures d'homogénéi• Européenne et par les Services Belges sation minimales, correspondant aux de la Politique Scientifique. Elle a températures probables de formation. été menée dans les laboratoires de 386 A. Darimont

Géologie Appliquée et de Géologie, Hollister, L.S.and others: Practical Pétrologie, Géochimie de l'Université aspects of microthermometry. In: de Liège. Short Course in fluid inclusions. L'Union Minière nous a permis d'échan• Hollister, L.S., Crawford, M.L.(ed tillonner les sondages de la zone miné• 278-304 (1981) ralisée de Poppelsberg. Timmerhans, Ch.: Les gîtes métalli• Nous remercions J.Coipel, B.Kreulen et fères de la région de Moresnet. T.Shepherd pour leur collaboration, Congrès international des mines, de J.Touret pour son acceuil à Amsterdam la métallurgie, de la mécanique et et ses critiques positives. de la géologie appliquée, Liège, 1905

BIBLIOGRAPHIE

Darimont, A., Coipel, J.: Dispersion des températures d'homogénéisation: Received: July 27, 1982 ebullition ou division par étran• Accepted: March 24, 1983 glement? Chem.Geol. 37, 151-163 (1982) Anne Darimont Giordano, T.H., Barnes, H.L.: Lead Laboratoire de Géologie Appliquée, transport in Mississippi Valley Type 45, avenue des Tilleuls Ore solutions. Econ.Geol. 76, 2200- B-4000 Liège 2211 (1981) Belgique Mineral.Deposita 18, 387-398 (1983) „_^ ,...„. MINERALIUM DEPOSITA © Springer-Verlag 1983 Geochemical Proximity Indicators of Massive Sulphide Mineralization in the Iberian Pyrite Belt and the East Pontic Metallotect P. Moller1, M. A. Dieterle2, P. Dulski1, K. Germann2, H.-J. Schneider2 and W. Schutz2 1 Geochemie, Hahn-Meitner-lnstitut fur Kernforschung Berlin GmbH, Berlin, Germany 2 Institut fur Angewandte Géologie, Freie Universitat Berlin, Berlin, Germany

\ comparative lithogeochemical study of mainly surface rocks of the Iberian Pyrite Belt (volcanic-sedimentary sequence) and the East Pontic metallotect (volcanic island arc system with few intercalations of marine sediments) has been performed in order to find facies-independent proximity indicators of mas• sive sulphide mineralizations. As, Sb, Tl, and Na seem to be the most promis• ing indicator elements for primary hydrothermal exhalation and/or alteration haloes. The size of the alteration haloes largely depends on the permeability of the country rocks and is best defined by ratios such as As/Na, Sb/Na, and ri/Na.

INTRODUCTION chemistry of the rocks (e.g. the well documented footwall alteration pipes During geochemical prospecting for or stockwork zones with intensive chlo- strata-bound volcanogenic massive sul• ritization, sericitization and silifi- phide deposits increasing emphasis is cation), but they should also determine being placed on lithogeochemical me• the development of geochemical zona- thods (e.g. Govett & Pwa 1981, Large tions on the sea floor around the sites 1981, Pirie & Nichol 1981, Selinus of discharge. 1981, Sopuck et al. 1980, van den Boom The purpose of this study was to et al., 1980). In contrast to conven• develop lithogeochemical proximity in• tional soil geochemistry, litho- or dicators of general applicability for rockgeochemistry (Govett 1983) may strata-bound base metal deposits by supply information about the primary analyzing mainly the distribution pat• geochemical environment of ore deposi• terns of some highly mobile elements tion, and is less sensitive to secon• such as Sb, As, Tl, and F in different dary contaminations. Proximity indi• geological environments. cators derived from lithogeochemical patterns thus directly reflect the path• ways of the mineralizing solutions. Analytical Methods Lithogeochemical exploration con• Neutron activation analysis, atomic ab• cepts for volcanic-sedimentary sulphide sorption spectrophotometry, and poten- deposits stem from models that regard tiometry have been applied as analyti• such mineralization as the product of cal methods. The behaviour of 42 elements submarine hydrothermal activity. Not has been studied, but only results on As, only would perculating hydrothermal Sb, Na, Tl, F, and Au will be reported fluids alter the mineralogy and geo• here in detail. 388 P. Moller et

GEOLOGICAL SETTING AND MINERALIZATION dolerites) are quantitatively much important and do not indicate genet relations with the sulphide mineral] Iberian Pyrite Belt zations. In general the sulphide-bea ing horizons are topped by jaspery o In the Pyrite Belt massive stratiform die Mn-Fe rich sediments which, togei pyrite orebodies associated with dis• with the sulphides, mark the waning seminated sulphides of copper, lead stage of the felsic volcanic activity and zinc are hosted by a Lower Car• Using the assumption that the manga• boniferous volcanic-sedimentary se• nese-iron mineralization should have quence of marine origin (Fig.l). These been fed from nearly the same hydro- sulphide mineralizations are spatially thermal volcanic sources as the undei and temporally related to felsic cyc• lying sulphide bodies we interpret les of a bimodal volcanism. The host them as genetically associated exhala rocks at proximal locations are main• tive Mn-Fe aureoles. Our lithogeochem ly quartz-keratophyric pyroclastics cal investigation concentrated on thi and rarely lavas, whereas in more dis• marker horizon. The whole volcanic- tal locations they are slates, includ• sedimentary pile is overlain by non- ing black slates. The products of ma• mineralized slates and graywackes of fic volcanism (spilites, spilitic tuffs, the Culm group.

slates,graywackes

,hematitic slates manganese - jaspers basic volcanics

acid tuffs, tuffites/ •slates, black slates, chloritites massive sulfides stockwork

basic sills m

u acid lavas

acid tuffs

phyllites, siltstones, quartz wackes, quartzites

Fig.1. Schematic lithostratigraphic column for the ore-bearing sequence at the northern flank of the Rio-Tinto Syncline bhemical Proximity Indiactors of Massive Sulphide Mineralization 389

/Geological and metallogenetical Leitch 1981, and Sawa et al. 1970). bblems of the SW-Iberian Pyrite The entire metallotect extends over Lt (the type area of Iberian type more than 350 km in an east-west direc• volcanogenic polymetallic pyritic tion and constitutes the mobile belt iposits according to Schermerhorn between the Pontic and the Anatolian D81) recently have been dealt with in plate (Fig.3). The ratio of economi• bpth by Bernard and Soler (1980) and cally interesting base metals is chang• outhier et al. (1978). Previous stu- ing in the general striking of the me• jies of lithogeochemical haloes in the tallotect from east (Cu »Pb+Zn) to rail rocks around orebodies (Kersabiec west (Pb+Zn >Cu). tnd Roger 1976, Strauss et al.1981) Volcanic activity in the East Pon• tsing trace element distributions (main• tic Belt began in the Upper Jurassic- ly Cu, Pb, Zn, Co, Ni) stressed the lack Lower Cretaceous with the extrusion of if any relationship between the ore and a 4000 m thick sequence of various j)ts volcano-sedimentary environment, basic volcanics onto crystalline base• [here are, however, indications of ment (Fig.4) (Akin 1979, Aslaner 1977, iydrothermal alterations located main• Buser et al. 1973, Maucher et al. 1962). ly in footwall zones which resulted in A locally exposed disconformity separa• lg and K enrichment and Na impoverish• tes this sequence from Upper Cretace• ment (e.g. Garcia Palomero 1980, Ber- ous dacitic volcanics of approximately sard and Soler 1980, Straus et al. 1000 m thickness which consist mainly 981). In general previous explora- of lava flows and intercalated pyro- ion for sulphide deposits in the Py- clatics. Mineable mineralization is ite Belt has mainly been based on con- confined to a distinct phase of daci- entional geological and geophysical tic-rhyolitic eruptives within the Up• ethods (Strauss et al. 1977). Cu-Pb-Zn per Cretaceous (Maucher 1969, Tugal oil geochemistry did not prove to be 1969). Volcanic products are extremely f much practical use, because suit- variable from place to place and the ble soils were either lacking or were presence of interfingering lava flows feavily contaminated by the extensive and pyroclastic layers as well as ag• fining and smelting activities. How- glomerate pipes suggests the existence yer, mercury surveys of soils and soil of a number of eruptive centers. It £ses have yielded more promising re- may be possible to correlate these ults (Robbins, 1975). variable sequences using a distinc• The northern flank of the Rio Tinto tive series of tuffs and small lenses incline (Rambaud 1969), where both sul• of sandstone at the top of the sequence fide and associated manganese minerali- which can be identified everywhere by ations occur, has been chosen as the their intensive alteration (e.g. sili- lain study area (Fig.2). About 1000 fication and kaolinitization). It is (amples were taken along strike from a noteworthy that according to our ob• (6 km long section of the most promi• servations the mineralization nowhere rent manganese-bearing horizon over• traverses this "marker bed", and that lying the uppermost sulphide level.Also in addition to being barren the trans- lampled were sections across the sul- gressive rocks do not exhibit any geo- )hide-bearing volcanic-sedimentary se- chemical dispersion haloes (e.g. "flysch [uence in the vicinity of some known ore- limestones" at Akarsen, dacite at Mur- >odies. gul, andésites and basalts at Maden- koy etc.). Therefore, the volcanic hy• drothermal mineralization must have test Pontic Metallotect been limited to a relatively short time interval during the Upper Creta• Lccording to plate tectonic concepts, ceous. It was regionally confined to :he East Pontic metallotect represents isolated spots. This feature is also L volcanic island arc system of Creta• substantiated by the geochemical re• ceous to Tertiary age which hosts a sults. A lesser mineralizing event ;reat number of base metal deposits seems to be linked to dacitic and an- [Akin 1979, Akinci 1980, Aslaner 1977, desitic volcanics of Paleocene to Eo-

A A A Basalt Pliocene A A

+ f ■*• *■-*■ + 4 Eocene,- vulcanics ••• f - Granodiorite

Eocene,"fiysch" A Cu-deposits

▲ Cu- deposits Cretaceous, "flysch "

■'-'-V-1 -, Cretaceous,- vulcanics

t » »\ 1 W i- Jurassic

Paleozoic,- metamorphics

*■'++•

Fig.3. Geological setting of the East Pontic metallotect generalized after various authors; Main deposits: 1 Mur gul, 2 Akarsen, 3 Baskoy, 4 Hotmaden, 5 Madenkoy, 6 Kutlular, 7 Lahanos 392 P. Moller et al.

XBaskôy , ' X Lahanos (Giresun) X Madenkôy (Rize) y Murgul (Artvin) !

basalt/andesite basalt/andesite andesite/basa ♦ pyroclast limestone,marl granodiorite dacitic ♦ granite andesitic tuff diorite + pyroclast limestone.marl limestone.marl sandstone, conglomerates &&:; ♦basalt sills limestone.marl. sandstone ♦ dacite basalt, conglomerates andesite(UBS) dacite andésite,basalt andesite(UBS) spilite(UBS) dac.tuff ♦ dacitelDS) pyroclastics(DS). limestone dacpumice tuff ♦ sandstone pyroclasticslDS rhyodacite ♦ ♦ limestone ♦ basalt sills pyroclastics(DS) dac.sandy tuff limestone

dacite(DS) dacite ♦ dacitelDS) pyroclastics(DS) marl limestone L

Fig.4. Simplified lithostratigraphic columns for the East Pontic metallotect; Cubase metal mineralization in general, cross hatching alteration zone, mainly kaolinization and silicification; UBS Upper Basic Series; DS Dacitic Series; LBS Lower Basic Series cene age (e.g. Baskoy, Fig. 3 and 4), of authors have confirmed this con but the results reported here are re cept (e.g. Akin 1979, Akinci 1980, As stricted to the Upper Cretaceous group. laner 1977, Cagatay et al. 1980, Leite Comprehensive geologic investiga 1981, Tugal 1969). We would suggest tions of the entire belt are still that the semistratabound character of lacking and the "stratigraphie" corre these mineralizations could be used as lation of the mineralized members is a tool for further prospecting activi somewhat uncertain since most of the ties. isolated mining areas have only been The sampling programme has been surveyed locally (Aslaner 1977, Buser confined to the vicinity of the numer et al. 1973, Cagatay et al. 1980, ous known mineralizations (abandoned Leitch 1981, Tugal 1969, Sawa et al. mines) and the area of the working 1970). Nevertheless, a semistrata Murgul mine in order to obtain a re bound nature of the mineralization gional comparison. Commonly surface seems to be acceptable and leads us rocks have been sampled, in 100 to to propose a common mode of genesis. 600 m profiles cutting the whole rock Some additional observations support sequence from the unmineralized base this hypothesis. Maucher (1969) and to the barren overlying members (Fig.6) Maucher et al. (1962) have pointed out As a whole about 1400 host rock and the stratiform and syngenetic nature ore samples were taken from 25 pro of the Upper Cretaceous base metal files. The results discussed here re deposits in the western part of the fer to only about 50% of the analyti metallotect and an increasing number cal work. Geochemical Proximity Indicators of Massive Sulphide Mineralization 393

MnBa

Tl/Na

As/Na

Sb/Na

10km

Fia. 5. Distribution of F/Na, Tl/Na, As/Na and Sb/Na ratios in hematitic slates along a 36 km striking profile at the northern flank of the Rio-Tinto Syr.cline. X-axis : Sampling locations as indicated in Fig. 2

For improvement of the hard rock modal frequency distributions of their geochemistry at some places additional• most characteristic major, minor, and ly soil and stream sediment samples trace elements. Based on these litho- have been analyzed indicating unknown logies, geochemical profiles for dif• base metal anomalies (e.g. south of the ferent indicator elements have been Murgul deposit and south of Sirtkôy). worked out of which one selected ex• ample is discussed below. In the hematitic slates of the man• ganese-iron formation the proximity of DISCUSSION jasper/manganese ore bodies (e.g. La Grulla, El Pocito, Soloviejo, Pépita) and a barite ore body W of San Miguel Iberian Pyrite Belt is indicated by anomalously high con• centrations (compared to the regional By combining pétrographie and geochemi• background) of the mobile elements As, cal analysis a detailed petrologic Sb, Tl, and F, and by lowered concen• classification has been established trations of Na. Using elemental ratios, foi the most important rock types of the anomalies of As/Na, Sb/Na, Tl/Na, the volcanic-sedimentary complex. Al• and F/Na (Fig.5) are most prominent together 16 rock types can be distin• near manganese ore bodies, but some of guished which exhibit exclusively uni- the stratigraphically lower sulphide 394 P. Moller et al.

100m

i - -location of sampling

L L -1 I t-l-2 ra. 2rL^-4 Fig.6. Akarsen deposit, Murgul area. Combination of two N-S sampling profiles crossing the deposits. Observe the positive Sb-Au-As anomalies and the negativf Na anomaly in the mineralized areas in contrast to the barren transgressive sec. ments in the northern part 1 - dacite, 2 - dacite tuff, 3 - marine sediments (limestone), 4 - "flysch", 5 - mineralization

ore bodies (Poderosa, Chaparrita) are In the slates of the overlying clearly detectable, too. Additional Culm group underlying ore bodies can anomalies occur away from known depo• be traced by the same geochemical in• sits e.g. W of Chaparrita; they possib• dicators, although with less contrast. ly indicate blind ore bodies. These anomalies can be considered as In similar geochemical sections in secondary dispersion haloes from the the stratigraphically lower acid vol- underlying accumulations which result• canics, which are the immediate host ed from diagenetic or metamorphic so• rocks of the sulphide ore bodies, the lution transport. In all cases Zn does elemental ratios clearly indicate not show significant anomalies. zones of hydrothermal fluid-rock inter• Anomalous Cu and Pb contents seem actions in the vicinity of sulphide to be restricted mainly to host rocks ore bodies (e.h. San Miguel, Pena del in the immediate vicinity of sulphide Hierro). bodies or sulphide-bearing horizons. Geochemical Proximity Indicators of Massive Sulphide Mineralization 395

Hence Cu anomalies observed in the est F values delineate lineaments which footwall of Mn-Fe formations could in• may be considered as the feeder veins dicate blind sulphide bodies. for the ascending hydrotherms. Outside The geochemical contrast of the of this area, as well as in the over• anomalies of major and trace elements lying barren dacite member, the F va• as evaluated from regional background lues decrease rapidly. Since the F con• ratios taken from partitioned probabi• tents vary over nearly one order of lity frequency distributions decreas• magnitude, the F data could be applied es in the order: Cu - As - Tl - Na - as a local geochemical indicator for Sb - Pb - Ba. Enrichment factors for covered mineralizations. As and Tl are about 10, for Sb~5, Within the silicified dacitic-ande- and the depletion factor for Na is~8. sitic tuffaceous sequence As, Sb, Tl, The spatial dimensions of the ano• Na have been found to behave like F in malies have been studied by geostat- Murgul and change their concentration istical methods. One-dimensional vario- levels only in the near vicinity of grams exhibit mean horizontal diameters mineralizations (Fig.6). This indicates of haloes between around 700 m for Sb that geochemical contamination caused and 1500 m for Na. The spatial dimen• by the ascending metal-bearing solu• sions of the anomalies increase in the tions did not permeate the host rocks order: Cu - Sb, As, Tl - Pb - Na - Ba - to any large extent, whereas the sili- Mn. cification and propylitization affected In addition to Mn-enrichment the the whole rock body. The primary alter• geochemical faciès of the Mn-Fe for• ation haloes are in the order of 10-50m mation is characterized by regionally wide. A second stage of spatially re• elevated contents of Ba which locally stricted silicification is strictly culminate in stratiform low-Sr barite bound to the sulphide mineralization. bodies. These are accompanied by F ano• The occurrence of anomalous Au va• malies . lues in the altered country rock seems Footwall zones of autochthonous sul• to be linked to zones of positive Sb phide bodies (e.g. San Miguel) and lo• and As and negative Na anomalies (Fig. cally hanging-wall or lateral peripheral 6). The Au concentrations range up to positions of host rocks may be charac• 8 ppm with typical values of about terized by intensive chloritic alter• 30 ppb. Enhanced concentration of ations resulting in Mg and Fe anomalies. either Au or Mo is of general genetic Also, silicification and sericitization interest. Since Mo in all samples ana• (Rio Tinto, La Zarza) may accompany lyzed has been found to be below the pyrite ore bodies. In summary, the geo• detection limit of about 100 ppb, the chemical pattern of the ore-bearing elevated Au values probably indicate volcanic-sedimentary sequence of the a genetic relationship of the E-Pontic Pyrite Belt is characterized by broad copper deposits with the copper porphy• anomalies which may attain regional ries of the island-arc type. size as in case of manganese. In the studied area the anomalies of the elements As, Sb, Tl, F, Au, and Na are rather narrow and restrict• East Pontic metallotect ed to the vicinity of the ore bodies probably due to a spot-like exhalative The data on trace elements in bedrock mineralization in a prevailing non- samples from the overlying and under• marine environment. lying volcanic formations do not indi• cate extensive geochemical dispersion haloes and anomalies except within the near vicinity of the ore bodies. Here, CONCLUSIONS conspicuous increases in mobile elements as Tl, As, Sb, Au, and F, and a decrease In both areas very similar geochemical in Na are observed. wall rock alterations have been ob• Within the mineralized area of the served which involve loss of Na and well exposed Murgul deposit, the high• gain of As, Sb, Tl, and F. However, 396 P. Moller et al, the spatial extent of these phenomena In conjunction with geologic map• differs considerably in the two areas. ping and pétrographie analysis, litho- Loss of Na during hydrothermal al• geochemistry of mobile elements such teration is a well known phenomenon as As, Sb, and Tl can therefore be (Spitz and Darling 1978, Ramsden and used as an effective technique in the Ryall 1979). Grigorjan (1976) reports exploration for strata-bound sulphide that the largest dispersions in wall deposits particularly in mixed volcanii rocks of hydrothermal deposits are those sedimentary environments. of Sb and As.Furthermore, he points out that these elements are some of the most important indicators of poly- Acknowledgements. The authors are in• metallic deposits. Tl is enriched in debted to the Commission of the Euro• hydrothermal alteration zones where it pean Communities for their financial is preferentially hosted by micas (De support under contract No. 117-80 MPÏ Albuquerque and Shaw 1969). F species D. The help of the following companies are common constituents of volcanic and organizations is gratefully acknov gases and are easily adsorbed and in• ledged: Comisiôn Nacional de Geologia, corporated by various clay minerals Madrid, M.T.A. and Etibank, Ankara. and micas. In this way anomalous F in We are also indebted to Prof.G.K.Muecfc clay minerals may be used to define (Halifax) and Prof.G.Friedrich (Aachen marker horizons of ancient hydrother• for their criticism and improvement of mal or fumarolic activity (Schneider the text. et al.1975). The elements As, Sb, Tl, and F cha• racterize hydrothermal solutions by REFERENCES their enhanced concentrations. During cooling As, Sb, and Tl will be copre- Akin, H.: Géologie, Magmatismus und cipitated with or adsorbed by the min• Lagerstattenbildung im ostpontiscti erals near the discharge area. Gebirge/Turkei aus der Sicht der Plattentektonik. Geol.Rdsch. 68, Following Large's (1977) hypotheti• 253-283 (1979) cal solution recycling convective Akinci, O.T.: Major copper metallogemi model most of the metals could have unites and genetic igneous complex• been leached from the volcanic host es of Turkey. In: European Copper rocks at depth. The heating of the Deposits, S. 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identifying favourable areas for Tugal.H.T.: The Pyritic Sulphide De• the discovery of volcanogenic mas• posits of the Lahanos Mine Area, sive sulphide deposits. Can.Inst. Black Sea Region, Turkey, Doct. Min.Metall.Bull. 73, 152-166 (1980) Thesis, 182 pp., Univ. Durham 1969 Strauss,G.K., Madel, J., Fernandez Van den Boom,G., Rehder.S., Kottrup, Alonso.F.: Exploration practice G.: Geochemical patterns in the for strata-bound volcanogenic sul• rocks surrounding the Woodlawn phide deposits in the Spanish-Por• volcanogenic ore deposit, New South tuguese Pyrite Belt: Geology, geo- Wales, Australia. Geol.Jb.D 40, physices and geochemistry. In: 169-200 (1980) Time- and Strata-Bound Ore Depo• sits, D.D.Klemm, H.-J.Schneider, Received: March 15, 1983 Eds., 55-93. Berlin, Heidelberg, Accepted: April 21, 1983 New York: Springer 1977 Strauss, G.K., Roger,G., Lecolle,M., Prof.Dr.H.-J.Schneider Lopera,E.: Geochemical and geo• Institut fiir Allgemeine Géologie der logic study of the volcano-sedi• Freien Universitât Berlin mentary sulphide orebody of La WichernstraBe 16 Zarza, Huelva Province, Spain. D-1000 Berlin 33 Econ.Geol. 76, 1975-2000 (1981) FRG Mineral.Deposita 18, 399-410 (1983) MINERALIUM DEPOSITA © Springer-Verlag 1983 Stable Isotope Studies of Sulphide Mineralisation on the Leinster Granite Margin and some Observations on its Relationship to Coticule and Tourmalinite Rocks in the Aureole F. M. Williams and P. S. Kennan

Department of Geology, University College, Belfield, Dublin, Ireland

Galena and sphalerite occur in brecciated veins along the eastern margin of the Caledonian Leinster Granite in south-east Ireland. This mineralisation is spa• tially related to the occurrance of spessartine quartzites (coticules) in the aureole rocks. Tourmalinites are closely associated with these coticules. A de• crease in the temperature of mineralisation from about 500°C in the northern Unit I to 250°C in the central Unit III to possibly less than 200°C in the southern Unit V of the intrusion is suggested by decreasing sulphide 63l*S val• ues, increasing sulphate 63I+S values and sulphide-sulphate fractionation values. Sulphur, carbon and oxygen isotope data suggest the involvement in the vein min• eralisation of sulphur, carbon and mineralising fluids at least partially deriv• ed from the coticule and tourmaline bearing aureole schists.

INTRODUCTION recognised a relationship between the siting of sulphide deposition and the occurrence in the aureole of garnet The late-Caledonian Leinster Granite in quartzites and suggested that the source SE Ireland (Fig. 1) intrudes a sequence of the metals might lie in the aureole. of slates, greywackes, quartzites and The mechanism of metal transport envis• calc-alkaline volcanic rocks ranging aged aureole-derived hydrothermal waters from Cambrian to Silurian in age. Pb-Zn set in motion as a result of the em• sulphide mineral deposits occur at in• placement nearby of hot granite. Briick tervals along the eastern margin of the and O'Connor (1980, 1982) arrived at a intrusion. Though there has been no similar conclusion and proposed, in ad• doubt for many years concerning the age dition, that a suite of major trans• of the granite itself, that of the min• verse fractures-faults acted as selec• eralisation has been a matter of some tive channelways for circulating ground debate. Finlayson (1910), for instance, waters and governed the siting of the favoured a Hercynian age. Tremlett base-metal deposits. Elsdon and Kennan (1959) related the mineralisation to (1982) presented additional evidence the granite emplacement. Lead isotope supporting a Caledonian age for the data (Moorbath, 1962) appear to favour mineralisation. the former opinion; the interpretation Stable isotope and ore textural stud• of the data is, however, open to doubt ies were undertaken (by F.W.) in order regarding the model used. Kennan (1978) to further refine models explaining the 400 F.M. Williams and P.S. Kennati

Location

5KmK> 15

+ + H LEINSTER GRANITE, Units numbered • Sampled locality + + 4

KILCULLEN GROUP, greywackes,-slates ; L.Ordovician - Wenlock

hjj DUNCANNON GROUP, acid, intermediate and basic votcanicS; Llandeito - Ashgill

\^ RIBBAND GROUP, slates, sandstones, siltstsones, basic votcanics(black), coticule and ^-J tourmalinite bearing Irthotogies(stippled);M.Cambrian - Llandeilo BRAY GROUP,graywackes, slates, quartzites ; Precambrian L. - M.Cambrian

Fig. 1. Location and general geology (Based on Fig. 1 of Briick et al., 1979) Stable Isotope Studies of Sulphide Mineralisation 401 origin of the sulphide deposits on the The veins are often associated with granite margin. In this paper the re• the occurrence of red feldspar bearing sults of this work are related to con• pegmatites (Kennan, 1978). These pegma• tinuing studies on certain aureole litho- tites occur as narrow veins and ill- logies (by P.S.K.). The aim is the cre• defined aggregates of coarse crystals ation of a model enabling the predic• (Kennan, 1974). The red feldspar is tion of sites of significant mineralisa• characteristic as is the absence of tion. the tourmaline, spodumene, beryl and garnet, common in other Leinster peg• matites . MINERALISATION Many of the veins show clear evidence of brecciation before and after sulphide Sulphide mineralisation in the granite deposition. This brecciation is likely occurs along the eastern contacts of to have been a factor contributing to Units I, III and V (Fig. 1.). The sul• both the migration of the ore bearing phides occur in veins that often trend fluids and the provision of large sur• perpendicular to the granite contact. face areas on which the sulphides and Some continue into the aureole schists their gangue minerals crystallised. for several metres. They are most abun• dant in Unit III. Some individual veins continue along strike for up to 3 km. They rarely exceed a width of 6 m. STABLE ISOTOPE STUDIES In typical veins coarse grained ga• lena and sphalerite with minor chalco- Analytical Methods pyrite and pyrite occur in a quartz and baryte gangue. Calcite is a common Sulphur, carbon and oxygen isotope de• gangue mineral in Unit III only. Baryte terminations were carried out on sul• is absent in Unit V. A generalised para- phide and sulphate minerals and whole genetic scheme is shown in Figure 2. rock samples. Sample localities are shown on Figure 1. Results are present• ed in Tables 1 and 2 and Figure 3. A Table giving the values of the 82 sul• Quartz phur isotope analyses will be provided on request. Haematite — Extraction of sulphur dioxide from Pyrite — sulphides followed the method of Robin• Calcite son and Kusakabe (1975), from baryte that of Coleman and Moore (1978) and Chalcopyrite — 7- from whole rock samples that of Thode Sphalerite and Monster (1965). Samples were run on Galena a VG Micromass 602C double collector mass spectrometer at The Institute of Tetra hed rite Geological Sciences, London. Results Fluorite 9— have been corrected for instrumental crosstalk and isobaric interference Rammelsbergite (Coleman, 1980) and are expressed as Cassiterite °/oo differences from the troilite Jamesonite phase of the Canyon Diablo meteorite standard. Scheelite Carbon dioxide was extracted from Baryte calcite and whole rock samples by re• acting them with 100% phosphoric acid Native Silver ?- at 25°C (McCrea, 1950). Samples were run on a VG Micromass 903 triple col• lector mass spectrometer. Results have Fig. 2. Generalised paragenesis of the been corrected for instrumental cross• vein mineralisation talk and isobaric interference (Craig, 402 F.M. Williams and P.S. Kennan

0? Unit I H3

H Schist fll H Granite an 3 H Galena mn □ 3 1 1 Baryte 0 10 20 H Sphalerite 30 «V* 40 VA Chalcopyrite \S\ Pyrite 1 I X, X « No. of analyses Hi y2 Unit III m*

B|l8|3 3

0 10 20 30 34 nt 40

h Unit V g* 1 1 -10 0 e-s.%010

Fig. 3. Sulphur isotope results. All ô31*S values determined are included

1957) and are expresses as °/oo differ with the exception of three values, and ences from the Chicago PDB standard those from Unit V fall between 1.0 for carbon and Standard Mean Ocean and 0.2°/oo with one exception. Baryte "Water for oxygen. from Unit I has values in the range 19.7 to 23.0°/oo, while those from Unit III range between 24.6 and 31.9°/oo. Sulphur Isotope Determinations No baryte was found in Unit V. A control on the variation in the A systematic difference in the 631*S <534S values of tip heap samples was values can be seen in galenas from the established using additional samples three mineralised granite units (Fig. collected at varying spacings along 3) . 631*S values of the galena from several outcroping veins. The maximum Unit I fall within the range +5.0 to variation between different sulphide +8.9°/oo, those values from Unit III samples from the same sulphide vein is fall within the range 0.8 to 5.0°/oo, 2.6 /oo. The analytical error was Stable Isotope Studies of Sulphide Mineralisation 403

Table 1. Sulphur isotope values uses d to calLculat e s ulphur iscitop e equilibration temperatures

34 Location Sample No. Gang. Min. 6 s A34S T. Err. 0 /oo °/oo T°C ±( )

Unit 1 Ballycorus 810662.2 None Ga + 6.2 + 5.7 166(4) Ballycorus 810662.1 Py + 11.9 Ballycorus 810654.81 Qtz Ga + 5.0 + 14.8 490(30) Ballycorus 810654.83 Ba + 19.8 Ballycorus 810654.84 Qtz Ga + 6.3 + 13.4 529(35) Ballycorus 810654.82 Ba + 19.7 Killiney 810704.2 Ba Ga + 8.0 + 15.0 485(29) Killiney 810704.1 Ba +:23. 0 Killiney 810704.3 Ba Ga + 8.9 + 14.1 509(32) Killiney 810704.1 Ba +23.0 Killiney 810703.2 Qtz Ga + 6.3 + 2.1 450(18) Killiney 810703.1 Py + 8.4

Unit 3 Glendalough 810678.2 Ba Ga + 2.7 +21.9 335(12) Glendalough 810678.1 Ba +:24. 6 Glenmalure 802668.33 Ba Ga + 7.0 - 0.5 Ds. — Glenmalure 802668.31 Sph + 6.5 Glendasan 810687.4 Qtz Ga + 0.8 + 5.2 157(4) Glendasan 810687.5 Sph + 6.0 Glendasan 810682.3 Qtz Ga + 3.0 + 4.9 170(5) Glendasan 810682.4 Sph + 7.9 Glendasan 810689.2 Qtz Ga + 3.5 + 4.1 211(6) Glendasan 810689.3 Sph + 7.6 Glendasan 810689.6 Qtz Ga + 4.3 + 2.3 278(13) Glendasan 810689.5 Sph + 6.6 Glendasan 810689.8 Qtz Ga + 4.0 + 3.4 259(8) Glendasan 810689.9 Sph + 7.4 Glendasan 810693.5 Qtz Ga + 4.1 + 2.6 335(12) Glendasan 810693.4 Sph + 6.7 Glendasan 810672.2 Qtz Ga + 3.3 + 2.9 303(10) Glendasan 810672.1 Sph + 6.2 Glendasan 810684.6 Qtz Ga + 3.9 + 2.0 297(14) Glendasan 810684.2 Cpy + 5.9 Glenmalure 802668.313 Cal Sph + 7.8 + 0.3 434(159) Glenmalure 802668.314 Cpy + 7.5 Glendasan 810687.12 Cal Ga + 8.2 - 2.3 Ds. — Glendasan 810687.13 Sph + 5.9 404 F.M. Williams and P.S. Kennan

Table 1 (continued)

Location Sample No. Gang. Min. S34S A34S T. Err. °/oo °/oo T°C ±( )

Glendasan 810693.3 Cal Ga + 2.3 + 1.5 385(23) Glendasan 810693.2 Cpy + 3.8 Glendasan 810695.4 Cal Cpy + 5.3 +2.4 Ds. — Glendasan 810695.3 Sph + 7.7 Glendasan 810694.2 Cal Ga + 4.9 + 4.6 102(5) Glendasan 810694.4 Cpy + 9.5 Glendasan 810670.5 Cal Ga + 8.6 0.7 Ds. — Glendasan 810670.4 Sph + 7.9

Unit 5 Brownsford 810699.1 Qtz Ga - 0.9 + 7.2 92(3) Brownsford 810699.2 Sph + 6.3 Brownsford 810699.3 Qtz Cpy + 1.9 +4.4 Ds. Brownsford 810699.2 Sph + 6.3 Brownsford 810699.1 Qtz Ga - 0.9 + 2.8 208(9) Brownsford 810699.3 Cpy + 1.9 Brownsford 810699.5 None Ga + 9.0 -6.4 Ds. — Brownsford 810699.4 Sph + 2.4

The quoted error reflects analytical errors, not published fractionation factor uncertainties. Temperatures were calculated using fractionation factors determined for the sphalerite-galena pair experimentally by Cha- manske and Rye (1974) and theoretically by Sakai (1968). The chalcopyrite- sphalerite, pyrite-galena and chalcopyrite-galena fractionation factors used were those determined by Kajiwara and Krouse (1971). The baryte- galena fractionation factor used was that of Ohmoto and Rye (1979). Ds. = Inferred disequilibrium

0.1°/oo. The whole rock granite 634S that they formed contemporaneously and values obtained from Units I and III in equilibrium with each other. Mineral are similar (+9°/oo), as are the values pairs provide reasonable temperatures of two schist samples from widely sepa• as long as both formed in equilibrium rated localities on the margin of Unit with solutions of uniform temperature I. They differ markedly from the 63l*S and chemical states (Ohmoto and Rye, values of +18.3 and +20.9°/oo obtained 1979). from two schist samples collected from In Unit I, the fractionation values the margins of Unit III. obtained from galena-baryte pairs are considered the most reliable (see Rye and Ohmoto, 1974). They give an average Sulphur Isotope Fractionation Values temperature of mineralisation of 500°C (Table 1). The 634S values of the ga• The fractionation of sulphur isotopes lena in the galena-pyrite pairs is with• between sulphide pairs depends on their in the same range as that of the galena- temperature of crystallisation provided baryte pairs. This suggests that the Stable Isotope Studies of Sulphide Mineralisation 405

S34S values of the pyrite are heavy; In Unit I, the essentially equal galena and pyrite are not in equilibri δ34S Σ s values of trace sulphur in the um. Ore textural evidence suggests granite, the aureole schist and the that the pyrite formed earlier in the postulated vein sulphur source suggest a δ paragenetic sequence. a common sulphur source with 34 SΣs In Unit III, the galenasphalerite value of about +9°/oo. In Unit III, pairs in a quartz gangue give scattered the essentially equal δ34S values of positive fractionations; these are, the trace sulphur in the granite and however, adequate to indicate deposi the postulated vein sulphur source s¬ tional temperatures of 200350°C. The gest that they also shared a common s¬ δ34 disequilibrium shown by sulphides in a phur source with a SΣ s value of calcite gangue suggests that the fluid about +9°/oo. However, the δ34 SΣ s values was at too low a temperature to allow of the schist are very high (+18.3 and isotopic equilibration. This suggests +20.9°/oo) and are not consistent with a depositional temperature of less than Ssuggest bacterial reduction of sulphate 200°C for the calcite (see Rye, 1974). in a closed basin and may reflect c¬ In the galenasphalerite pairs which ditions that were restricted. In Unit show disequilibrium the galena δ34S V the vein sulphur could have been ¬ values lie outside the normal 0.8 to rived from a source with a δ34SΣs value +5°/oo range for Unit III and all are of +9 /oo by low temperature sulphide heavy. sulphate fractionation. The higher than 3 The Unit V fractionation values im normal δ 4S values of one galena sample ply disequilibrium and may reflect a from Unit V and of three galena samples temperature of deposition which was in disequilibrium with sphalerite in probably less than 200°C. Thus the de Unit III may also reflect partial re positional temperature appears to drop equilibration from a +9°/oo source. Al¬ from about 500°C in Unit I to about hough the data do not establish a 4S 250°C in Unit III and to possibly less source with a δ3 Σs value of +9°/oo for than 200°C in Unit V. all three Units, such is plausible.

Thus it may be that the granite, the Source of Sulphur sulphide veins, and the aureole schists of Unit I shared the same sulphur source. The data for Units I and III show a The aureole rocks are suggested as the systematic decrease in the δ34S values source of sulphur for the granite and of galena with a corresponding increase the veins. The same source is plausible Σ3 in those of baryte with falling tem¬ for Units III and V. The δ 4 SΣs value erature. This strongly suggests that of +9°/oo in the aureole rocks could the change in δ34S values is due to have originated by bacterial reduction equilibrium fractionation between sul¬ of seawater sulphate in an earlier open hide and sulphate species at decreas¬ system. Assuming an average fractiona ng temperatures while the δ34S value tion between bacteriogenically reduced of the sulphur source remained constant sulphide and sea water sulphate of (Fig.3; see Coleman, 1977). 15°/oo (Sangster, 1976) the fi31+S value The δ34S values obtained from sul¬ of the corresponding sea water sulphate hides in Unit V could be due to low would be expected to be about +24°/oo. temperature sulphidesulphate fractio¬ This lies in the lower end of the range 4S ation from a source with a δ3 Σs val¬ of values for Lower Palaeozoic sea wa of +9°/oo. No sulphate minerals are ter given by Nielsen (1979). known to be associated with the sul¬ ide minerals implying that if a sul¬ ate phase was present it was deposit¬ Oxygen Isotope Determinations elsewhere. The observed values could also be due to the influence of The δ 18 0 values of calcite gangue in a magmatic sulphur source with a the sulphide in Unit III have a narrow SΣ δ34 s of 0°/oo or to a combination of range of 4.4°/oo, from +14.2 to both a 0°/oo and a +9°/oo source. 18.6°/oo (Table 2). Secondary trace 406 F.M. Williams and P.S. Kennan

Table 2. Carbon and oxygen isotope results

18 Location Sample No. Description ô13C°/oo 6 0°/oo

Unit 1

Killiney 810709 Grani te -11.3 + 15.2 Lough Tay 810659C Schist -18.5 "

Unit 3

Glendasan 810687.11 Calcite - 6.8 + 17.5 Glendasan 810670.3 Calcite - 6.9 + 17.6 Glenmalure 802668.317 Calcite - 7.1 + 16.0 Glendasan 810694.3 Calcite - 7.8 + 15.6 Glendalough 810678.3 Calcite - 8.3 + 14.2 Glendasan 810693.1 Calcite - 8.9 + 15.3 Glendasan 810689.7 Calcite -12.8 + 15.4 Glendasan 810689.1 Calcite -13.0 + 17.8 Glendasan 810695.2 Calcite -14.6 + 18.6

carbonate from a bulk granite sample the range +5.5 to +10°/oo (Taylor, from Unit I has a <5180 value of 1974). At temperatures below about +15.2°/oo. The analytical error was 180°C, the equilibrium fractionation 0.05°/oo. between calcite and water assumed to have retained its magmatic signature is such that the measured range of carbo• Source of Oxygen nate 6180 values would not be attained (see 0'Neil et al., 1969). The implica• The narrow range of 6180 values tion is that non-magmatic water (e.g., (4.4°/oo) suggests that both the tem• hydrothermal-meteoric or formation perature of the fluid and the source of waters), was likely to have been pre• its oxygen remained constant. Any tem• sent during calcite deposition in the perature variation would have produced sulphide veins and in the granite. large variation in the 6180 values. A change of oxygen source would also pro• duce a large range of values. The <5180 Carbon Isotope Determinations value of trace oxygen in calcite in a bulk granite sample from Unit I also The 613C values of calcite samples lay within the narrow range shown by from sulphide veins in Unit III have the gangue calcite suggesting that a large range (from -14.5 to -6.8°/oo). they shared the same oxygen source. No There is no systematic correlation be• carbonate is present in association tween 613C and 6180 values of the same with mineralisation in Units I and V. calcite samples. A bulk aureole schist Sulphur isotope values suggest that sample and a bulk granite sample from the calcite was deposited at tempera• Unit I analysed for trace carbonate tures less than 200°C (see above) . have <513C values of -18.5 and -11.3°/oo, Given this conclusion, the 6180 values respectively. Analytical error was of the carbonate (Table 2) may con• 0.05 /oo. Due to lack of suitable ex• strain the nature of any waters involv• posure the samples could not be placed ed. Magmatic 6180 water values fall in in paragenetic sequence. Stable Isotope Studies of Sulphide Mineralisation 407

Source of Carbon They are themselves closely associated with other quartzites and more pelitic Oxygen isotope data indicate that the rocks all of which are unusually rich temperature of deposition of calcite in tourmaline. The use of tourmaline remained constant. Sulphide disequi• as a guide to mineralisation has been librium assemblages suggest a tempera• recently documented by Slack (1980, ture of less than 200°C. If carbon was 1982). Both of these rather unusual present in the system not only as dis• rock types are a distinctive feature of solved carbonate species but also as some otherwise largely pelitic sequences 13 methane, graphite or C02, then the 6 C of the Cambro-Ordovician Ribband Group values for the carbonate minerals will of SE Ireland as defined by Briick et 13 represent maxima for the ô jc of the al. (1974). 13 system (Fritz, 1976). Thus the 6 Cj;c In SE Ireland, tourmaline has often value for the system may have been con• been noted in the Leinster Granite and siderably less than the -14.6 to in the aureole rocks. In the granite -6.8°/oo values observed but it could it is a constituent of some pegmatite, not have been higher. aplite and quartz veins (Brindley, Organic matter has typical 613C val• 1954) and of hydrothermally altered ues between -15 and -30 /oo (Fritz, granite (Briick and O'Connor, 1977). In 13 1976). A 6 Cyc value equal to or less the aureole the mineral is especially than the observed 613C values of the obvious as fringes to some cross-cut• lighter carbon (-14.6 to -12.8°/oo) ting aplite veins and as an apparently strongly suggests a biogenic source for late addition to the metamorphic as• this carbon. Small changes in the pH or semblages (Brindley, 1957). To date, f02 of the system could produce the the conclusion drawn from these facts total range of observed 613C values has been the common one that the aure• 13 from a biogenic source with a 6 Cjc ole tourmaline reflects post-intrusion of -15°/oo or less (see Ohmoto, 1972). pneumatolysis; the implication has been The total range of values could also that the necessary boron derived, as have been produced by the mixing of a late magmatic concentrate, from the biogenically derived carbon nearby granite. No evidence has been 13 (6 Cjc « -18°/oo) with magmatically presented in support of an external 13 derived carbon (<5 Cj-c fa -5°/oo, source although Briick and O'Connor Ohmoto, 1972). A biogenic source for (1980, p. 361, 1982, p. 156) include some of the carbon present in the gran• tourmalinisation in a list of alter• ite and the veins is implied. The source ations related to thermally induced of this biogenic carbon is very likely circulation of ground waters in the to have been the aureole schists, which envelope. 13 have a 6 C value of -18.5 /oo. Recent observations show that the amount of tourmaline in the aureole far outweighs that present in the granite or its veins ; some aureole rocks con• .THE AUREOLE ROCKS: COTICULES AND tain in excess of 75% tourmaline. TOURMALINITES Rocks composed of tourmaline and quartz only are prominent. A soda rich feld• spar occurs as an additional constitu• The isotope data do not, by themselves, ent. These tourmalinites sometimes show allow an unambiguous conclusion regard• layering on a fine scale. Some small ing the origin of the mineralisation. folds defined by tourmaline rich layers They do, however, serve to refocus at• are typical pre-intrusion structures. tention on the aureole rocks. A spatial Tourmalinites occur in those partic• association between the sulphide depo• ular parts of the aureole where the sits on the granite margin and the pre• coticules are a distinctive feature. sence of spessartine quartzites in the The coticules and tourmalinites may be adjacent aureole has been noted (Ken- partial lateral equivalents; the cotic• nan, 1978). These quartzites are coti- ules are especially common adjacent to cules as defined by Renard (1878). Units I and III whereas the tourmalini- 408 F.M. Williams and P.S. Kennan

tes are more often encountered close to CONCLUSIONS Units IV and V. These tourmalinites are in every way comparable with such rocks in volcanic 1 . The sulphides in Unit I of the sequences elsewhere. Of special inter• Leinster Granite were deposited at a est to this study is the fact that they temperature of about 500°C, those of are associated with massive exhalative Unit III at about 250°C and those of Pb-Zn ores at Broken Hill, New South Unit V at possibly less than 200°C. Wales (Plimer, 1980) - ores sited in The aureole rocks are suggested as the ironstones that have, as further later• source of sulphur for the granite and al equivalents, manganese-garnet quart- veins, particularly for Unit I. The zites that compare closely with those data suggest the involvement in the of Leinster (see Stanton, 1976). The vein mineralisation of sulphur, carbon recently discovered metal and manganese and mineralising fluids at least parti• bearing sediments in the south-west ally derived from the aureole rocks. Pacific island arc may be modern analog• 2. It is likely that the emplacement of ues (Cronan et al., 1982). the granite resulted in the mobilisa• In the Aldridge Formation, British tion of base metals previously resident Columbia, rip-up clasts of laminated in the aureole rocks to form sulphide quartz-tourmaline rock in an intrafor- mineral deposits near to and on the mational conglomerate serve to estab• granite margin. lish the early, probably syngenetic, introduction .of boron (Ethier and Camp• 3. The rocks of the pelitic Cambro- bell, 1977). In SE Ireland, it is not Ordovician Ribband Group containing yet possible to prove a synsedimentary coticules, tourmalinites or related origin; however, the quantity and the sediments are prospecting targets for distribution of the tourmaline make it base metals in SE Ireland. This is es• very difficult to envisage the neces• pecially so where later intrusions are sary boron as other than a constituent present. of the original sediments. Tourmaline rich rocks have not been Acknowledgements. The substance of this recognised in and around the volcano- paper derives from studies undertaken genie Cu-Fe-Pb-Zn sulphide ores at as part of EEC Research Contract MPP- Avoca (Piatt, 1977 and Fig. 1.) nor at 126-EIR(G). We wish to thank Dr. M. the nearby Ballard magnetite deposit Coleman (IGS, London) for his help (Dowries and Piatt, 1978). However, to with the mass spectrometry and for both NE and SW along strike, coticules stimulating discussion, Dr. C. Halls occur in Ribband Group sediments. Al• (Imperial College, London) for his help though the stratigraphie-structural in the study of ore textures and their relationship between the coticule bear• interpretation, Mr. P. McArdle and Dr. ing sequences and Avoca-Ballard ores C. Williams (Geological Survey of Ire• remains to be established, it is a land) for their continuing support and fact that these distinctive quartzites our colleagues at University College are confined to narrow elongate tracts Dublin, notably T. Culligan and of ground in SE Ireland where signifi• G. Doyle. cant ore deposits occur. This regional pattern and the lithologies present identify the coticule and tourmalinite bearing rocks in the granite aureole as a potential source for the metals REFERENCES now deposited on the granite margin. Analyses of stream sediments support this conclusion (Briick, 1977). It is Brindley, J.C.: The Geology of the interesting to speculate that the ulti• northern end of the Leinster Granite: mate source of the metals at Avoca may Part I - internal structural features. also be coticule bearing Ribband Group Proc. R. Ir. Acad. 56B, 159-190 strata. (1954) Stable Isotope Studies of Sulphide Mineralisation 409

Brindley, J.C.: The Aureole Rocks of McDougall, J.C.: A submarine hydro- the Leinster Granite in South Dublin, thermal manganese deposit from the Ireland. Proc. R. Ir. Acad. 59B, 1-18 south-west Pacific island arc. (1957) Nature 298, 456-458 (1982) Briick, P.M.: Stream sediment base metal Czamanske, G.K., Rye, R.O.: Experimen• geochemistry on one-inch sheets 120 tally determined sulfur isotope frac• and 121. Geol. Surv. Ireland Rept. tionation between sphalerite and Ser. RS 77/1, 15-23 (1977) galena in the temperature range 600° Briick, P.M., O'Connor, P.J.: The Lein• to 275°C. Econ. Geol. 69, 17-25 ster Batholith: geology and geochemis• (1974) try of the northern units. Geol. Surv. Dowries, K.M.J., Piatt, J.W.: The Avoca- Ireland Bull. 2, 107-141 (1977) Ballard mineralised belt, County Briick, P.M., O'Connor, P.J.: Major Wicklow. J. Earth Sci. R. Diibl. Soc. transverse and other linears in the 1, 121-133 (1978) Leinster Granite. Geol. Surv. Ire• Ethier, V.G., Campbell, F.A.: Tourmaline land Bull. 2, 349-370 (1980) concentrations in Proterozoic sedi• Briick, P.M., O'Connor, P.J.: Relation• ments of the southern Cordillera of ship of hydrothermal phenomena within Canada and their economic signifi• the Leinster Granite to crustal frac• cance. Can. J. Earth Sci. 14, tures delineated from Landsat Imagery. 2348-2363 (1977) Photogrammetria 37, 151-159 (1982) Elsdon, P., Kennan, P.S.: Age of Sul• Briick, P.M., Potter, T.L., Downie, C: phide Deposits on the Margin of the The Lower Palaeozoic stratigraphy of Leinster Granite, Ireland. In: Metal• the northern part of the Leinster lization Associated with Acid Magma- Massif. Proc. R. Ir. Acad. 74B, tism, A.M. Evans (ed) John Wiley, 75-84 (1974) 1982 Briick, P.M., Colthurst, J.R.J., Feely, Finlayson, A.M.: The Metallogeny of the M., Gardiner, P.R.R., Penney, S.R., British Isles. Q. Jl. geol. Soc. Reeves, T.J., Shannon, P.M., Smith, London 66, 281-296 (1910) D.G., Vanguestaine, M.: South-east Fritz, P.: Oxygen and carbon isotopes Ireland: Lower Palaeozoic strati• in ore deposits in sedimentary rocks. graphy and depositional history. In: In: Handbook of Strata-bound and The Caledonides of the British Isles . Stratiform ore deposits. K.H. Wolf, - Reviewed. A.L. Harris, C.H. Holland, (ed), Vol. 2, pp 191-215. Amsterdam- B.E. Leake, (eds), pp 533-544. Edin• Oxford-New York, Elsevier 1976 burgh: Scottish Academic Press, Ltd., Kajiwara, Y., Krouse, H.R.: Sulfur iso• 1979 tope partitioning in metallic sulfide Coleman, M.L.: Sulphur isotopes in systems. Can. J. Earth Sci. 8, petrology. J. Geol. Soc. Lon. 133, 1397-1408 (1971) 593-608 (1977) Kennan, P.S.: The petrography of some Coleman, M.L.: Corrections for mass- red-feldspar pegmatites and their as• spectrometer analysis of sulphur sociation with late hydrothermal dioxide. Stable Isotope Report No. changes in the Leinster Granite. Sic. 45, Pub. by Institute of Geological Proc. R. Dubl. Soc. 5A, 77-84 (1974) Sciences, London (1980) Kennan, P.S.: The origin of the sul• Coleman, M.L., Moore, M.P.: A method phide deposits in the Leinster Gran• for the direct reduction of sulphates ite. J. Earth Sci. R. Dubl. Soc. 1, to sulphur dioxide for isotopic anal• 41-47 (1978) ysis. Analyt. Chem. 50, 1594-1595 McCrea, J.M.: On the isotope chemistry (1978) of carbonates and a palaeotemperature Craig, H.: Isotopic standards for car• scale. Jour. Chem. Phys. 18, 849-857 bon and oxygen and correction factors (1950) for mass-spectrometric analysis of Moorbath, S.: Lead isotope abundance carbon dioxide. Geochem. Cosmochem. studies on mineral occurrences in the Acta 12, 133-149 (1957) British Isles and their geological Cronan, D.S., Glasby, G.P., Moorby, significance. Phil. Trans. R. Soc. S.A., Thomson, J., Knedler, K.E., (London) 254A, 295-360 (1962) 410 F.M. Williams and P.S. Ketman

Nielsen, H.: Sulfur isotopes. In: Sangster, D.F.: Sulphur and lead iso• Lectures in Isotope Geology, E. topes in strata-bound deposits. In: Jager, J.C. Hunziker, (ed), Handbook of Strata-bound and Strati• pp 283-312, Berlin-Heidelberg-New form ore deposits. K.H. Wolf (ed), York, Springer, 1979 Vol. 1, pp 219-266. Amsterdam-Oxford- Ohmoto, H.: Systematics of sulfur and New York, Elsevier 1976 carbon isotopes in hydrothermal ore Slack, J.: Tourmaline - A prospecting deposits. Econ. Geol. 67, 551-578 guide for massive base-metal sulphide (1972) deposits in the Penobscot Bay Area, Ohmoto, H., Rye, R.O.: Isotopes of sul• Maine. Maine Geol. Surv. Special phur and carbon. In: Geochemistry of Economic Studies Series No. 8, Hydrothermal Ore Deposits. H.L. Bar• 1-25 (1980) nes (ed) pp 509-561, 2nd éd., New Slack, J.: Tourmaline in Appalachian- York-Chichester-Brisbane- Toronto, Caledonian massive sulphide deposits Wiley-Interscience 1979 and its exploration significance. O'Neil, J.R., Clayton, R.N., Mayeda, Trans. Inst. Min. Metall. B91, 81-89 T.K.: Oxygen isotope fractionation (1982) in divalent metal carbonates. J. Stanton, R.L.: Petrochemical studies of Chem. Phys. 51, 5547-5558 (1969) the ore environment at Broken Hill, Piatt, J.W.: Volcanogenic mineralisa• New South Wales : 3-banded iron for• tion at Avoca, Co. Wicklow, Ireland mations and sulphide ore bodies: and its regional implications. In: constitutional and genetic ties. Volcanic Processes in Ore Genesis, Trans. Inst. Min. Metall. B85, pp 163-170, London, Inst. Min. Metall. 132-141 (1976) and Geol. Soc. 1977 Taylor, H.P.: The application of oxygen Plimer, I.R.: Exhalative Sn and W Depos• and hydrogen isotope studies to prob• its Associated with Mafic Volcanism lems of hydrothermal alteration and as Precursors to Sn and W Deposits ore deposition. Econ. Geol. 69, Associated with Granites. Mineral. 843-883 (1974) Deposita 15, 275-289 (1980) Thode, H.G., Monster, J.: Sulphur iso• Renard, A.: Sur la structure et la com• tope geochemistry of petroleum eva- position mineralogique du coticule. porites and ancient seas. Am. Assoc. Mém. Cour, et Mém. des Sav. Acad. Petrol. Geol. Mem. 4, 367-377 (1965) Roy.de Belg. 16 (1878) Tremlett, W.E.: Thé Pre-Çambrian Rocks Robinson, B.W., Kusakabe, M.: Quantita• of Southern Co. Wicklow (Ireland). tive preparation of sulphur dioxide Geol. Mag. 96, 58-68 (1959) for ô^S analyses from sulphides by combustion with cuprous oxide. Analyt. Chem. 47, 1179-1181 (1975) Rye, R.O.: A comparison of sphalerite- galena sulphur isotope temperatures with filling temperatures of fluid inclusions. Econ. Geol. 69, 26-32 Received: September 14, 1982 (1974) Accepted: May 5, 1983 Rye, R.O. Ohmoto, H.: Sulphur and car• bon isotopes and ore genesis: A re• F.M. Williams view. Econ. Geol. 69, 826-842 (1974) Department of Geology Sakai, H.: Isotopic properties of sul• University College phur compounds in hydrothermal pro• Belfield, Dublin 4 cesses. Geochem. J. 2, 29-49 (1968) Ireland Mineral.Deposita 18, 411-421 (1983) MINERALIUM DEPOSITA © Springer-Verlag 1983

GeochemJcal Investigations of Paleozoic Shales and Carbonates in the Aachen Region

V. Scheps and G. Friedrich

Institut fur Minéralogie und Lagerstâttenlehre, Aachen Technical University, FRG

In the western part of the Rheinisches Schiefergebirge geochemical investiga• tions were carried out on Paleozoic black shales and carbonates in the Aachen region. Primary and secondary metal distributions were determined in selected units of sedimentary rocks by XRF-analysis and in stream sediments by AAS-analysis. The primary geochemical pattern and the results of geological studies re• veal that Frasnian (Upper Devonian) black shales and nodular limestones were deposited in a restricted environment under euxinic conditions of a swell and basin faciès. Black shales and nodular limestones are enriched in Zn and Cu resp., possibly indicating stratiform sulphide mineralization. Geochemical ano• malies in stream sediments with increased values of Pb, Zn, Cd, Cu, Co, and Ni were found in areas of Lower Paleozoic sedimentary rocks and associated acid intrusives which are known to contain low grade sulphide mineralization of the "porphyry copper-type".

INTRODUCTION Investigations of the secondary dis• persion of trace elements in surface waters, stream sediments and soils in During the last years detailed geochem• selected areas were started in an ear• ical studies were carried out in the lier phase of our research projects: eastern part of the Rheinisches Schie- Kulms and Friedrich (1970), Hermann fergebirge, especially near the strati• (1979) and by other groups e.g. Emmer- form sulphide-baryte deposit of Meggen mann et al. (1981). (e.g. Hilmer, 1972; Friedrich et al., Subject of the present study is 1977, 1979; Gwosdz and Krebs, 1977; the investigation of primary and sec• Brinkmann et al., 1978). Facies and ondary metal distributions in two areas stratigraphy of the Paleozoic area of different geological setting, the south of Aachen in the western part of Venn Massif and the Inde Syncline the Rheinisches Schiefergebirge were (Scheps, 1982). Rock geochemistry was also studied in detail by different re• carried out in selected lithological search groups (e.g. Kasig et al., 1978), units: but there was still a lack of lithogeochemical data, especially concerning in the Venn Massif the primary trace element distribution. Revinian 4 and 5 (Cambrian), 412 V. Scheps and G. Friedrich

in the Inde Synaline mentary rocks of a thickness of about Frasnian (Upper Devonian), 4000 to 5000 m. The sedimentation was Visean (Lower Carboniferous). highly influenced by the Old Red Conti• nent in the north and was interrupted Due to contamination by former min• by two main periods of transgression ing industries in the Inde Syncline (Hollerbach and Kasig, 1980): area (vein-type Pb-Zn-deposits near Aachen, Stolberg and Moresnet) the in• 1. A large carbonate platform was form vestigation of stream sediments was ed in the Givetian and the early Fras• restricted to the Venn Massif. nian, followed by a sequence of nodulai limestones and black shales up to the end of the Frasnian. GEOLOGICAL SETTING 2. A second carbonate platform was formed during the Lower Carboniferous. The area south of Aachen is character• The whole sequence was folded and ized by a thick series of Paleozoic thrust-faulted during the Asturian oro rocks including black shales and mar• geny (Upper Carboniferous). ginal reef faciès which are known to be Detailed lithogeochemical investiga• favourable environments for the forma• tions were carried out in the following tion of stratiform sulphide mineraliza• units: Frasnian (Upper Devonian) reef tion. Geology and stratigraphy of the limestones, nodular limestones and two investigated areas (Venn Massif and black shales. Inde Syncline) are shown in Fig. 1 Generally the Devonain carbonate and 2. platform has a total thickness of about 250 m. The cyclic growth of the bio- Venn Massif stromal reefs started in the Givetian. During the Frasnian the reefs were ovet The anticlinal core of the Venn Massif lain by nodular limestones and black consists of a series of Cambrian (Re- shales (Kasig, 1967, 1980a). South of vinian) and Ordovician (Salmian) black Aachen the reef limestones represent a shales, sandy shales, quartzitic sand• part of the southeastern flank of the stones and quartzites with a thickness Inde Syncline. of about 2000 m. This sequence was de• Within this sequence several profils formed by the Caledonian orogeny and were sampled (Figs. 2, 3 and 4): pro• discordantly overlain by Lower Devonian file 8 which comprises a shaly interca• sediments (Gedinnian). The Revinian and lation at the basis of the Frasnian Salmian sedimentary rocks are locally reefs of about 4 m thickness (the so- intruded by tonalités and tonalité por- called "Grenzschiefer"), a tuffaceous phyrites, e.g. in the area near Lam- bed of 1 m thickness (profile 5) within mersdorf (Fig. 1). the Frasnian reefs, and a sequence of Lithogeochemical studies were car• 120 m thickness (profiles 1 and 2) con- ried out on samples from the Lower Pa• prising the upper part of the reefs and leozoic strata: Revinian 4 and 5 (Cam• the transition zone from the reef facie brian). The Revinian 4 (Fig. 1, profile to nodular limestones and black shales. 9) is characterized by alternating Due to the lack of outcrops, the upper quartzites, quartzitic sandstones and part of the Frasnian black shales and black phyllitic shales of 300 to 400 m nodular limestones could not be sampled thickness (Knapp, 1978). The Revinian 5 continously (profile 3 and 6). (Fig. 1, profile 11) mainly consists of black phyllitic shales with minor quart• zites of 300 to 500 m thickness. Visean Limestones (Lower Carboniferous)

Inde Synaline The Visean limestones were deposited in a shallow lagoonal environment (Boonen The Inde Syncline consists of Lower and Kasig, 1979; Kasig, 1980b, 1981). Devonian to Upper Carboniferous sedi• In contrast to the Devonian reefs, the Geochemical Investigations of Paleozoic Shales 413

Y///X U. Cretaceous Ert&Syl U.Carboniferous L. Carboniferous ] Famennian Upper II111111 ! I Frasnian Devonian t^^^l M.Devonian ] L.Devonian Salmian (Qrdov.) o Tonalité « Tonalité Porphyrite Revinian (Cambr.) 1

Fig. 1. Geological map (after Knapp, 1978) showing the Inde Syncline, the Venn Massif and the rock sampling locations 1 to 11 414 V. Scheps and G. Friedrich

Profile the "Coated Grain Succession" (V3a?) U.Carboniferous with a thickness of 110 m'. L.Carboniferous TïiïiTi JC Tournaisian ■ ■ ■ : ■ ; ■ ; ■ Pb/Zn Deposits U.Devonian 1,2.2a.3. The veintype Pb/Zn deposits in the ill,!, 4.5.6.8 StolbergAachenMoresnet area are ^TW^ structurally controlled and connected to Devonian and Lower Carboniferous car M.Devonian bonate rocks (Gussone, 1964). The genet Eifiliin ic interpretation of these epigenetic, hydrothermal mineralizations is still Emjlin being discussed. They may be of magmat L. Devonian Siegeniin —^'- ^—: ——'• — ichydrothermal origin related to deep seated structures or were mobilized Gedinniin from older sedimentary rocks by hydro thermal activity.

Ordovician GEOCHEMISTRY OF SELECTED SEDIMENTARY ROCKS Cambrian Reiiniln 4 ind 5 9.10.11

A total of698 rock samples was analyze) for 20 elements by XRF. Pure carbonate rocks, which contain trace element con ra ■ ^ » centrations below the detection limit o; the XRF measurement method (e.g. Na) ^ v l£75] VI were decomposed with HF, HNO, and HC1 and analyzed by AAS. The geochemical ESI »« h~ 1 VIII data were evaluated by statistical methods. In addition to the statistical Fig. 2. Stratigraphy of the Inde Syn interpretation of geochemical data the cline and the Venn Massif (simplified geological setting of every profile was after Knapp, 1978). The black lines studied in detail. According to their show the stratigraphie position of the relative stratigraphie position, the investigated sedimentary rock profiles average metal concentrations (x) and the (nos. 1 to 11), the dotted line indi standard deviations (s) of the profiles cates the area of the stream sediment are given in Figs. 3 and 4. survey. I = Carbonates, II = Sandy Generally two types of sedimentary shales, III = Sandy shales and black rocks were investigated in the course shales, partly metamorphosed, IV = of this study: shales and limestones. Sandstones, V = Shales, VI = Black The evaluation of geochemical data of shales and quartzites, partly metamor these rock types has indicated clearly phosed, VII = Acid intrusives (Tona that most of the analyzed elements are lité of Lammersdorf), VIII = Unconfor dominantly related to clay minerals and mity organic matter due to the adsorption capacity of these compounds . In addi tion elements as Ba and Pb, Zn and Cu Lower Carboniferous sediments mainly consist of chemical precipitates and clastic carbonates. The investigated The profile was studied in detail by profile (Figs. 3 and 4; profile 7) com Kasig (1981). The sample material was prises a section from the upper part kindly placed at the authors' disposal of the "Vaughanites Oolith" (Via) to for further geochemical studies Geochemical Investigations of Paleozoic Shales 415

may be bound in specific minerals as cline), they form a remarkable poten• baryte and as sulphides, respectively. tial for hydrothermal metal mobiliza• From the analyzed 20 elements, Co is tion. This potential could be increased always below the detection limit of the by the duplication of beds in the Paleo• XRF measurement method ( < 20 ppm) and zoic area south of Aachen. According to was not analyzed by AAS. According to recent geophysical studies this area our own results and data from litera• (s. Fig. 1) was overthrusted to the NW ture (e.g. Gwosdz and Krebs, 1977; along the "Aachener Oberschiebung", a Large, 1980; Swennen et al., 1982) the thrust fault at the northwestern rim of following elements are especially suit• the Inde Syncline (Meissner et al., able as indicators for certain sedimen• 1981, Bless et al., 1980). tary environments: increased Na and Sr concentrations may indicate hypersaline conditions during the formation of car• Frasnian Reef Limestones, Nodular bonate sediments, increased V contents Limestones and Black Shales indicate an euxinic environment, high K The sequence of the Upper Devonian reef concentrations and increased K/Rb ratios limestones locally contains small, epi• point to volcanic activities during the genetic sphalerite mineralizations bound deposition. Pb, Zn, Cu, Co, Ni, Ba and to veinlets and bedding planes. Signi• Mn are used as pathfinder elements for ficant stratiform mineralization could stratiform sulphide mineralization, and not be detected within the reefs. The in comparison with the distribution pat• cyclic growth of the biostromal reefs terns of the other elements it can be is generally not reflected by geochem• distinguished, if the enrichments are istry, in a few cases only the clay con• of syngenetic or of epigenetic origin. tent increases slightly towards the top A "manganese halo" is a well known of the cycles. The uppermost 15 m of proximity indicator for stratiform sul• the reef sequence are characterized by phide mineralization. an increase of Mg, Na and Sr, indicat• ing a hypersalinar environment that probably caused the end of the reef Results and Discussion growth. In general the investigated Upper Devonian reefs were not suitable for stratiform sulphide formation. The Revinian 4 and 5 (Cambrian) black biostromes were deposited in a relative• phyllitic shales ly shallow water (Kasig, 1980a). Rather Compared with other shales the Lower uniform extending over large distances, Paleozoic black phyllitic shales of they did not form any structures suit• the Revinian 4 and 5 are characterized able as "sulphide traps". by a significant lack of Ca, Na, Mn Profile 8 (Figs. 3 and 4) which re• and Ni (Figs. 3 and 4; <0.5% CaO, presents a transgressive phase of shale <0.1% Na20, <0.04% MnO, <25 ppm Ni). sedimentation within the reefs ("Grenz- This probably indicates extreme depos- schiefer"), is slightly increased in itional conditions with low pH and Eh Zn and Cu (300 ppm Zn, 180 ppm Cu) values. Cu is slightly increased in the bound to tuffaceous layers of some mil• Revinian 4 and 5 (up to 150 ppm) and limeters thickness. Pb in the Revinian 4 (up to 130 ppm). Another tuffaceous horizon of nodular High concentrations of V within the limestones of about 1 m thickness oc• same samples (up to 200 ppm) indicate curs in the middle of the reef sequence that these Cu and Pb contents are relat• (Figs. 3 and 4; profile 5). In contrast ed to an euxinic black shale environ• to other Upper Devonian rocks the clay ment. fraction is characterized by anomalous Anomalous metal enrichments could K contents ( > 7% K2O) and increased not be detected within the Revinian K/Rb ratios ( >200), possibly pointing black phyllitic shales, but considering to volcanic activities during the de• the extension of these wide spread position of this horizon. rocks and the grea't depth of burial (at At the end of the reef growth the least 3000-4000 m below the Inde Syn- sedimentary environment changed to the Si02 Al203 CaO MgO Na20 K,0 TiO, Fe203 MnO P*0, ± ■ 20 60 100| 20 40 20 40 60 1 3 5 2 4 6 0.4 0.6 1.2 2 6 10 0.0 S 0.15 0.25 0.05 015 0.25 —i—i——i i_ - —i—i—i—i__i V3|1 III Viséan 1 1 1 7 111- i i i 1 1 1 «Il

Famennian 1 1 • 1 • 1 ■ Fa 1-2 3 2» 1 o 1 o 1 T T \ T T F3 '-r~-T~-r~-:-c-:-: II' I

I°I° i oI çîI o oI oI o I o I o I I Frasiian T 'I o I ° I 0 I o I o ^ / F2 1 olo I 1 r I I I a I » I I 5 I 1H- I -V |

115 ii a T Revinian _ (Cambr.) «« h-; I I 4S i 1

(î-s) i (x-s) 1 ---- 2 1 ToTt S~nT

Fig. 3. Distribution of major and minor elements in selected Paleozoic sedimentary rocks of the Aachen region (concen trations in percent); arithmetic mean (x) ± standard deviation (s). 1 = Shales, 2 = Sandy shales, 3 = Limestones, 4 = Nodular limestones, 5 = Sandy limestones Pb Zn Cu Sr Ba V Ni Rb Cr 2 0 6 0 100 140 50 ISO 250 350 20 60 100 200 400 600 400 600 100 200 100 200 300 5 0 150 i i i__i i i i_ i i i i i i- i i i L- ■ —i—i ■ V3i?

Viséan

«u

Famennian 1 t~r ' — * ..• —1 • 1. —■ Fa H 1 1 0 1 o 1 1 F3 :>:>:>: I o I o I / l°i°l T o 1 o I o / \ ni*** Frasnian £1 H

■«.- I

g i » 11 s i im<2o l<30 |<20 I -r- l

K 11 I n

Revinian I (Cambr.) *< 9 I 45

Fig. 4. Distribution of trace elements in selected Paleozoic sedimentary rocks of the Aachen region (concentrations in ppm, explanation see Fig. 3) 418 V. Scheps and G. Friedrich

deposition of nodular limestones and lateral secretion of stratiform low black shales in a swell and basin fa• grade sulphides probably leads to the ciès which is in particular favourable formation of epigenetic mineralization for the formation of sulphides (Figs. in veins. A similar genetical model, 3 and 4; profile 6): syngenetic chalco- based on mobilization of sulphides from pyrite in markasite nodules was found Frasnian sediments, could recently be within nodular limestones which are proved in Belgium by Dejonghe et al. generally enriched in Cu (profile 6; (1982). x = 55 ppm Cu). A stratiform Zn anomaly up to 1000 ppm of 4 m thickness was found within the underlying black shales (profile 6). The Mn content of the nod• ular limestones and black shales (on GEOCHEMISTRY OF STREAM SEDIMENTS the average 0.11% to 0.15% MnO), is generally increased, but due to the vertical profiles a stratabound "manga• The hot extractable contents of Pb, Zn, nese halo" could not be detected. Evi• Cd, Cu, Co, Ni, Mn, and Fe from the -80 dence for the swell and basin faciès is mesh fraction of 347 stream sediment given by field observations and litera• samples were analyzed by AAS. As shown ture (e.g. Knapp 1978) showing extreme in Table 1, the average concentrations variations of the thickness within the of Pb and Zn are about two times higher Frasnian black shales and nodular lime• than those in other parts of the Rhei- stones at the south-eastern rim of the nisches Schiefergebirge. The first eval Inde Syncline. uation of data has shown that this in• Further evidence for stratiform min• crease is caused by the Pb-Zn-Cd-con- eralization on the stratigraphie level tamination derived from the ancient of Frasnian black shales is given by mining industries near Aachen and Stol- the Ba (Fe, Zn, Pb) mineralization near berg, which is obviously not only re• Chaudfontaine in Belgium (Dejonghe, stricted to the area of the Inde Syn• 1979). The F2/F3 transition zone, where cline where the epigenetical ore depos• the Chaudfontaine mineralization occurs, its were exploited. Waste materials could not be investigated in this study containing traces of sphalerite and as this section is not exposed at the galena were frequently used for road surface. constructions. In this way contamina• tion was also spread over the Venn Mas• sif. This made it very difficult to Visean Limestones separate anomalies of mineralized bed• rock from false anomalies due to anthro The Visean limestones studied in this pogenetic contaminations. Therefore program contain the highest Pb-Zn-val- the numerous anomalies found in the ues of all profiles (Fig. 4; profile 7). Venn Massif had to be studied in de• Positive correlations of Pb and Zn with tail by additional methods: V and Sr show that the enrichments of Pb (up to 630 ppm) and Zn (up to 1300 - determination of metals and pH-values ppm) are bound to euxinic conditions in stream waters by AAS, and increased salinity of an evaporitic - determination of major, minor and environment. According to Kasig (1980b) trace elements in selected stream sedi• the stratigraphie position of these en• ment samples by XRF. richments is the "Upper Cyclic Succes• sion" of V2b. In a lower section of As a result of these studies it can Visean limestones similar metal enrich• be shown that "true" anomalies are due ments were found by Swennen et al. to the following reasons. (1982) in the adjoining Vesder Basin/ Belgium. Sedimentary enrichments as proved Variation of pH-Values in Visean limestones may be the poten• tial source for vein-type Pb-Zn-deposits Large areas of the Venn Massif are of the Inde Syncline. Mobilization by covered by swamps which causes low pH- Geochemical Investigations of Paleozoic Shales 419

Table 1. Pb, Zn, Cd, Cu, Co, Ni, Mn, and Fe in stream sediments of the Venn Anticline (hot extractable contents from the -80 mesh fraction, n=347, AAS) max = maximum x = arithmetic mean min = minimum s = standard deviation

Pb Zn Cd Cu Co Ni Mn Fe (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (%)

max 2820 7400 60.0 326 813 251 16750 35.30 min 20 18 0.1 9 3 3 5 0.63 £ 188 574 6.6 33 59 43 1848 4.02 s 239 836 9.7 24 88 45 2632 3.05

A 73 132 - 25 18 55 - -

B 105 207 - 34 - - - -

C 80 270 - 40 - - - -

A) Average metal content of stream sediments (about 660 samples from the vicinity of the Meggen ore deposit (Hilmer 1972) B) Average metal content of stream sediments (about 4000 samples) of the eastern part of the Rheinisches Schiefergebirge (Friedrich et al. 1977) C) Anomalous metal contents of 5200 stream sediments in the Eifel/Hunsriick area (Emmermann et al. 1981) values (pH 2-4) especially in the cen• trations in stream sediments ( > 7000 tral regions of the Venn Massif. To• ppm Mn) depending on pH-values. Several wards marginal areas the pH-values in• metal enrichments, especially of Co, crease (pH 4-7) caused by dilution with Ni and Cd, are due to their adsorption water of higher pH-values and carbonate by Mn-hydrolysates. Contrary to Mn the supply by carbonate rocks. This increase frequently occurring precipitates of of pH-values effects the precipitation Fe-hydroxides do not play any role con• of metals which were in solution before cerning metal enrichment. and leads to the formation of anomalies in marginal areas of the Venn Massif. Vein-type Baryte-Sulphide Mineralization

Mn-Rioh Sedimentary Rooks Baryte mineralization is known on NW-SE striking faults at the northern rim of The sedimentary rocks of the Ordovician the Venn Massif northeast of Zweifall (s. Fig. 2) are enriched in Mn (up to (Holzapfel 1910, Fig. 1). The occurren• 25% MnO, Kramm, 1980). This is in sharp ces are characterized by distinct Ba- contrast to the Cambrian shales forming anomalies in stream sediments ( >700 the anticlinal core which are relative• ppm Ba). Pb and Zn anomalies correspond• ly poor in Mn ( <400 ppm Mn, see above). ing to the Ba-enrichments show, that This increased Mn-content of Ordovician the faults may contain Pb-Zn-sulphides rocks may lead to increased Mn-concen- besides baryte. 420 V. Scheps and G. Friedrich

Mineralization of Acid Intrusives ical anomaly in stream sediments relat• The most important anomaly (Pb > 700 ed to Lower Paleozoic (Revinian and ppm, Zn > 2000 ppm, Cd > 25 ppm, Cu > Salmian) sedimentary rocks which are 80 ppm, Co > 250 ppm, Ni > 140 ppm) was associated to acid intrusives ("Ton• found at the southeastern rim of the alité of Lammersdorf" and tonalité por- Venn Massif in the drainage system of phyrites). These intrusives may con• the "WeiBer Wehbach" NE of Lammersdorf tain a "porphyry copper-type" mineral• (Fig. 1). The anomaly corresponds to ization similar to the igneous rock outcrops of acid intrusive rocks of complex of "La Helle" in Belgium. uncertain Paleozoic age, the "Tonalité Acknowledgements. of Lammersdorf" and the tonalite-por- The authors are in• phyrites NE of Lammersdorf in the valley debted to Drs. U. Hack and P. Mol1er of the "WeiBer Wehbach". Another igne• who critically reviewed the manuscript. ous rock complex in the adjoining Bel• Funding of the research work was provid gium, the tonalité of "La Helle" (Fig. ed by the "Commission of the European 1), which is similar to the Tonalité of Communities" and the "Deutsche For- Lammersdorf, contains mineral associa• schungsgemeinschaft". tions similar to those of the porphyry copper deposits (Weis et al. 1980). Further investigation of this anomaly REFERENCES is limited due to the widespread thick weathering crust covering the Venn Mas• sif and requires shallow core drilling. Bless, M.J.M., Bouckaert, J., Papproth, The "Tonalité of Lammersdorf" for ex• E.: Environmental aspects of some ample was discovered during the con• Pre-Permian deposits in NW Europe. struction of a railway track. The ex• Meded. Rijks Geol. Dienst 32 (1), posure is deeply weathered and fresh 3-13 (1980) material cannot be sampled at the sur• Boonen, P., Kasig, W.: Das Dinantium face. zwischen Aachen und Luttich. Z. dt. Geol. Ges. 130, 123-143 (1979) CONCLUSIONS Brinkmann, J. (ed): Projekt Rhenoher- As result of this research work two zynikum; Untersuchung der Metal'lver- geological structures in the Aachen teilung in geosynklinalen Sedimenten region are recommended for further des Rhenoherzynikums in stratiformen exploration. Konzentrationen. Bundesanst. f. Geow. u. Rohstoffe, pp 133, 1978 1. The Upper Devonian Black Shale Dejonghe, L.: Discovery of a Sedimen• Faaies of the Inde Synoline tary Ba (Fe, Zn, Pb) Ore Body of Frasnian Age at Chaudfontaine, Pro• The black shales and nodular limestones vince of Liège, Belgium. Mineral. were deposited under euxinic conditions Deposita 14, 15-20 (1979) in a restricted environment of a swell Dejonghe, L., Rye, R.O.. Cauet, S.: and basin faciès on top of an irregular Sulfur isotopes of barite and lead subsiding shelf platform. This sedimen• isotopes of galena from the strati• tary environment is favourable for sul• form deposit in frasnian carbonate phide mineralization. Further evidence and shale host-rocks of Chaudfontaine for the existence of sulphides on this (Province of Liège, Belgium). Ann. stratigraphie level is given by the Soc. Géol. Belgique 105, 97-103 mineralization of Frasnian beds near (1982) Chaudfontaine (Belgium). Emmermann, K.-H., Fauth, H., Hindel, R., Ree, C: Geochemische Obersichts- 2. Lower Paleozoic Sediments of the prospektion im linksrheinischen Venn Massif associated with Acid Schiefergebirge. Erzmetall 34, Intrusives 152-159 (1981) The southeastern rim of the Venn Massif Friedrich, G., Katsch, A., Plûger, is characterized by a distinct geochem- W.L., Horion, B., Keller, C: Unter- Geochemical Investigations of Paleozoic Shales 421

suchung der Metallverteilung in geo- Kasig, W., Spaeth, G., Stoltidis, J. synklinalen Sedimenten des Rhenoher- Walter, R.: Stratigraphie, Palaogeo- zynikums in stratiformen Konzentra- graphie und Tektonik des nordlichen tionen. Teilprojekt Aachen. Abt. liriksrheinischen Schiefergebirges. angew. Lagerst. Lehre RWTH Aachen Exkursionsfiihrer 130. Hauptversammlung (unpubl.) 1977 DGG Aachen, pp 1-26, 1978 Friedrich, G., Katsch, A., Keller, C: Knapp, G.: Erlauterungen zur geologi- Geochemische und explorationsgeo- schen Karte der nordlichen Eifel chemische Untersuchungen im Rhenoher- 1:100.000. 2. Aufl., pp 152, 1978 zynikum, Nachfolgeuntersuchungen. Kramm, U.: Herkunft und Ablagerungs- Inst. f. Minéralogie u. Lagerst. milieu der manganreichen ordovizi- Lehre RWTH Aachen (unpubl.) 1979 schen Gesteine des Stavelot-Venn- Gussone, R.: Untersuchungen und Be- Massivs, Ardennen. Z. dt. Geol. Ges. trachtungen zur Paragenesis und Ge• 131, 867-888 (1980) nesis der Blei-Zink-Erzlagerstatten Kulms, M., Friedrich, G.: Geochemische im Raume Aachen-Stolberg. Diss. RWTH Untersuchungen der Boden im Lager- Aachen, pp 130, 1964 stattengebiet Bleialf/Eifel. Geol. Gwosdz, W., Krebs, W.: Manganese halo Mitt. 10, 305-332 (1970) surrounding Meggen ore deposit, Ger• Large, D.E.: Geological parameters as• many. - Appl. earth sc, Trans. Inst. sociated with sediment-hosted, sub• Min. Met. 86, B73-B78 (1977) marine exhalative Pb-Zn-deposits: Hermann, R.: Untersuchungen zur Bestim- an empirical model for mineral ex• mung von Pb, Cu, Zn, As, Se and Sb in ploration. Geol. Jb. D40, 59-129 Boden und deren Ausgangsgesteinen (1980) mit ausgewahlten Beispielen aus der Meissner, R., Bartelsen, H., Murawski, nordlichen Eifel. Diss. RWTH Aachen, H.: Thin-skinned tectonics in the pp 124, 1979 northern Rhenish Massif, Germany. Hilmer, E.: Geochemische Untersuchungen Nature 290, 399-401 (1981) im Bereich der Lagerstätte Meggen, Scheps, V.: Geochemische Untersuchungen Rheinisches Schiefergebirge. Diss. in der nordlichen Eifel - Ein Beitrag RWTH Aachen, pp 162, 1972 zur Geochemie der FluBsedimente und Hollerbach, A., Kasig, W.: Organic mat• der palaozoischen Schwarzschiefer und ter in Paleozoic sediments of the Karbonatgesteine des Venn-Massivs und Aachen Region, east of the Brabant der Inde-Mulde. Diss. RWTH Aachen, Massif. Meded. Rijks Geol. Dienst pp 104, 1982 32, 106-110 (1980) Swennen, R., Boonen, P., Viaene, W.: Holzapfel, E.: Die Géologie des Nordab- Stratigraphy and lithogeochemistry of falles der Eifel mit besonderer Be- the Walhorn section (Lower Visean; riicksichtigung der Gegend von Aachen. Vesder Basin, E.-Belgium) and its Abh. Kgl. Preuß. Geol. Landesanst., implications. Bull. Soc. Belg. Geol. n.F., 66, pp 218, Berlin, 1910 91, 239-258 (1982) Kasig, W.: Biofazielle und feinstrati- Weis, D., Dejonghe, L., Herbosch, A.: ' graphische Untersuchungen im Givetium Les associations des minéraux opaques und Frasnium am Nordrand des Stavelot- et semi-opaques de la roche ignée de Venn-Massivs. Diss. RWTH Aachen, la Helle. Ann. Soc. Géol. Belgique pp 177, 1967 103, 15-23 (1980) Kasig, W.: Cyclic sedimentation in a Middle-Upper Devonian shelf environ• ment in the Aachen Region, F.R.G. Received: May 5, 1983 Meded. Rijks Geol. Dienst 32, 26-29 Accepted: May 26, 1982 (1980a) Kasig, W.: Dinantian carbonates in the Prof. Dr. G. Friedrich Aachen Region, F.R.G. Meded. Rijks Institut fur Minéralogie und Geol. Dienst 32, 44-52 (1980b) Lagerstattenlehre der TH Kasig, W.: Zur Géologie des Aachener WiillnerstraBe 2 Unterkarbons. Habilitationsschrift D-5100 Aachen RWTH Aachen, pp. 253, 1981 FRG

Exploration for Antimony Deposits in Southern Tuscany, Italy

R. M. Dehm, D. D. Klemm, C. Muller, J. Wagner and K. Weber-Diefenbach

Institut fur Allgemeine und Angewandte Géologie der Universitat München, Munchen, FRG

The idealized prototype of a southern Tuscan antimony deposit can be described as follows: The irregular mineralization is situated in the upper part of the highly porous Calcare Cavernoso, overlain by an impermeable unit, normally a flysch-type rock. The deposits are bound to the edge of horst positions and also to areas of elevated geothermal gradient and resulting hydrothermal activi• ty. These observations were used as variables for statistical probability cal• culations for antimony-deposit formation. Within the areas determined to be of high probability, 47 target areas were selected for geochemical soil sampling. Positive correlation of antimony with barium, strontium and lead, corresponding to gangue and accessory ore minerals in the deposit was found. Local distribu• tion of Sb of 3 representative areas are discussed in detail. Although no high anomalies so far unknown were identified, known mineralizations were extended or neighbouring anomalies found. Regional correlation with horst structures and especially their fault margins (e.g. eastern margin of the ridge of Monticiano) was confirmed. The high density of mineralizations in the Tafone area is also reflected in the geochemical results of the soil sample prospection. A possible explanation for this accumulation may be seen in the large outcrops of pre-Car- boniferous rocks, which generally are expected to be the primary source of antimony. From these pre-Variscan units antimony was remobilized and transport• ed hydrothermally to its present position.

I. GEOLOGICAL SETTING AND ic interest by means of geochemical MINERALIZATION prospection in addition to those al• ready knwon.

Southern Tuscany was already famous for 12 stratigraphy it's variety of ore deposits during Etruscan times. Besides the antimony _, , . j . . .. , . The stratigraphie unit sr present in deposits, the provinc e^-^ homes massive _ .. _ , , ... . •.. i_ j ^-^ Southern Tuscan 1)y can be grouped as pyrite deposits, hematite and magnetite followfollowss (fig(Fig. . 1), deposits, mixed sulfide vein deposits and disseminated Hg-mineralizations . AAN _ _ Ai..m orf _thi. • s stud,.!y was.t..o shei_ jd more ) Tuscan Basement light on the genesis of the antimony This group includes all pre-Sudetian deposits and to define areas of econom- rocks known in the area. Whereas in 424 R.M. Dehm et al.

Northern Tuscany a variety of old Paleo• clastic sediments. More details see zoic units is exposed in the Pisan Moun• Sestini (1970) and Giannini et al. tains and even more so in the Apuan (1971). Alps, Southern Tuscany contains only a The Plio- to Pleistocene period is small number of pre-Sudetian rocks in also characterized by widespread mag- mostly limited and separated outcrops. matic activity represented by grano- The oldest fossil-dated rock is of De• dioritic intrusions in the west (e.g. vonian age (Bagnoli & Tongiorgi, 1979). Elba) and rhyolitic to intermediate It is however generally accepted that volcanites in the east (e.g. Mte. older rocks are also involved. Accord• Amiata). Locally large covers of tra• ing to Rau et al. (1974), Bagnoli et vertine are associated with hydrother• al. (1978) and (1979), the basement com• mal activity. See also Pichler (1970) prises a variety of rock types, mainly and Marinelli (1975). phyllites with occasional evaporite lenses, black schists, metasandstones and scarce metabasites and porphyroids. 1.2 Structural Geology Carbonates are very rare, only few len• ses or thin layers occur. Two orogenic cycles are known in South• ern Tuscany: the Variscan and the Al• B) Tuscan Series pine cycle. The sediments of the Tuscan series range A) Variscan Orogenesis from the Upper Carboniferous to the lowermost Miocene. Since Carnian the Due to the few outcrops of old Paleo• sequence is complete but, because of zoic rocks, the knowledge of the Varis• the complex tectonic situation, can can orogeny in Southern Tuscany is lim• hardly ever be found in one profile. A ited. The Sudetian phase is generally synopsis is given in Giannini et al. taken as the culmination. Nappe-type (1971). The Permotriassic clastic Ver- structures were identified and the rucano is followed by carbonate deposi• autochthony of the basement is there• tion during the Triassic and Jurassic. fore a point of debate. Important for Sb deposit formation is the evaporite-rich dolomitic Calcare B) Alpine Orogenesis Cavernoso (Carnian to Norian). Creta• ceous and Tertiary sediments are clays The compressional phase leads to the and marls with occasional carbonates. gliding of the Ligurian nappe onto the The miogeosynclinal cycle ends in the Tuscan series, which in turn is being Miocene with clastic deposition (Macigno compressed and, particularly in the sandstone). portion above the Calcare Cavernoso shows also nappe-type movements and the intensive development of small C) Ligurian Nappe scale wedges. Where still present, the The eugeosynclinal deposition started Ligurian nappe forms a rather imperme• in the upper Jurassic with well devel• able cover over the generally more per• oped ophiolites, followed by some car• meable Tuscan series. The tensional bonates and thick flyschtype sediments. phase, starting in the Miocene and Occasionally clastic deposits (e.g. probably still continuing results in Pietraforte Sandstone) can be found. a well developed horst-graben system For a more detailed description see which generally runs WNW-ESE. The Mio• Abbate et al. (1970) and Giannini et cene to recent magmatism is strongly al. (1971). correlated with this structural pattern

D) Neoautochthonous and Quarternary 1.3 Geothermal Activities The Miocene, Pliocene and Quarternary sediments reflect repeated re- and The magmatic phase leads to a variety transgressions resulting in quick of geothermal phenomena which may still changes between high and low energy be observed in the area. The geother- Exploration for Antimony Deposits in Southern Tuscany 425

mal gradient in Southern Tuscany is wells, steam and gas emanations are regionally about 5°C/100m. In some par spread all over the area. See also Ben ticularly "hot" areas it rises to over venuti et al. (1971). 30°C/100m and is economically used for the production of electricity (e.g. Lardarello, TravaleRadicondoli, Mte. 2. THE ANTIMONY DEPOSITS Amiata). The Triassic and Jurassic car bonates, in particular the Calcare Today, the antimony deposits are gener Cavernoso with their highly permeable ally accepted to be epigenetic. The rocks form the main aquifer in Southern ore mineral content of the deposits Tuscany. A large number of thermal consists of

QUARTERNARY NEOAUTOCHTHONOUS and QUARTERNARY

TERTIARY MacignoSandstone **

Scisti policromi/ Calcare Nummulltiche H W CRETACEOUS Majolicalimestone * * D PJ O < Chert * JURASSIC 1 Posidonomyamarls co H Calcare Massiclo * Pi co ? ' Calcare ad Avicula u Calcare Cavernoso/ *** D Grezzoni EH TRIASSIC Formazione di Tocchi

Verrucano

PERMIAN ? Poggio al Carpino •> Série di Farma CARBONIFEROUS 0> Série di Carpineta CD 0) X -Sudetian phase ■a S 8 iH M m Ol Rni 4J •H •P D) Formazione di Risanguino ■U 0 DEVONIAN ? id

Fig. 1. Schematic stratigraphy of rocks relevant for ore formation and outcrop ping in Southern Tuscany, which are dated with a certain reliability. Uncertain ties are indicated by questionmarks 426 R.M. Dehm et al.

- main components: antimonite (up to dependence on the geothermal gradient. 10% in the ore), pyrite and marcasite Generally however, Sb-mineralizations (absent to about 10%) are found in areas of elevated thermal - accessories: metastibnite, cinnabar, activity or their former equivalents. orpiment, realgar, sphalerite, galena, Concerning these factors the views arsenopyrite, tetrahedrite, chalcopyrite of different authors are unanimous. - some secondary alteration products. The point of discussion however is the The gangue is formed by quartz, cal- source of the deposit-antimony. In con• cite, gypsum; subordinate are barite trast to a number of articles by Dessai and fluorite. Most deposits show intense (e.g. 1974 and 1977) and his colleagues silification of the host rocks. The (e.g. Dessau et al. 1969 and 1972) the genesis of the near-surface formed min• authors of this article do not considei eralizations is controlled by the fol• the deposit-antimony to be derived fror lowing parameters. the young magmatism or from in situ remobilization within today's host rocj The authors' studies lead to the A) Stratigraphie-Pétrographie Control following genetic model: Mobilization of Sb-Concentrations from deeper seat• Sb-minralizations are limited to high• ed series; transport in hydrothermal ly permeable units within the Tuscan convection cells and near-surface pre• series, except for some minor minerali• cipitation in permeable rocks. The mag• zations in Ligurian rocks (s. Fig. 1). matism and the correlated rise of the The Calcare Cavernoso is the most fre• geothermal gradient deliver the neces• quent and the only economically impor• sary energy. Primary Sb-concentrations tant host rock. The high permeability are expected in pre-Carboniferous rocks results from the dissolution of the In Southern Tuscany however undoubted• anhydrite component of the evaporitic ly primary concentrations could not yet sediment. The typical position for the be identified with certainty. mineralization is just below the con• tact to the impermeable cover, which is mostly formed by Ligurian flysch. Occasionally clay-rich members of the Tuscan series may take the same func• 3. SAMPLING AND ANALYTICS tion (e.g. Schisti Policromi). Neumann (1979) carried out a multivari• ate statistical analysis to identify B) Structural Control areas of high probability for Sb-deposit-formation in Southern Tuscany. Ad• The Miocene nappe phase often trans• ditional geological studies lead to the ported impermeable Ligurian onto per• selection of 47 target areas (Fig. 2). meable Tuscan rocks. The following A total of 5840 soil samples were block tectonics generated the faults taken between autumn 1979 and spring necessary for hydrothermal convection 1982. The samples were taken with a between different stratigraphie levels. drilling rod, max. depth 100 cm, from The Sb-mineralizations are concentrat• the B-horizon. During the sampling ed in highly faulted areas at the mar• several field variables, dealing with gins of horst structures. Occasional the sample itself and the geological mineralizations along the faults empha• underground were documented in a data sizes their function as transport media. sheet. For local scale exploration sampling was usually carried out in a rectangular grid with point distances C) Ore Genesis and Magmatism of 50 x 100 m or 100 x 200 m. In special cases denser grids for mine scale ex• There is no obvious correlation between ploration or on the other hand recon• Plio-Pleistocene magmatism and ore de• naissance profiles for regional scale position, neither is there a simple exploration were taken. Exploration for Antimony Deposits in Southern Tuscany 427

Fig. 2. Simplified geological map of Southern Tuscany with sampling areas. (NQ: Quarternary and Neoautochthonous; VSV: Plio- and Pleistocene volcanic and subvolcanic rocks; MG: Pliocene intrusive rocks; LIG: Ligurian nappe; T-TC: Ter• tiary and Cretaceous of Tuscan series; T-J: Jurassic of Tuscan series; T-CC: Calcare Cavernoso of Tuscan series; T-VC: Verrucano of Tuscan series; PVC: All units older than Verrucano; n: Nappe contact; f: Fault 428 R.M. Dehm et al.

Table 1. Average antimony contents (ppm) of total data and separated sampling areas (N = number of samples)

No Sampling grid Sb No Sampling grid Sb

Total data 5841 209 22 Capalbio SE 33 194 23 Marrucherone 145 70 1 Bagni di Petriolo 137 48 24 Scaroncia W 50 87 2 Fonderia di S.Martino 79 614 25 Scaroncia E 42 62 3 Cetine South 370 498 26 Montebuono 136 3 4 Cetine North 54 6 27 Venturi 65 8 5 Frassine I 303 295 28 Paganico 393 145 5A Frassine Special 693 14 29 Cappuccini 93 4 6 Frassine II 85 91 30 Mte. Cetona 51 3 7 Montauto 146 203 31 Mte. Rotondo 157 45 8 Tafone 213 42 32 Montieri 140 17 9 Pelagone 156 215 33 Micciano 27 9 10 Poderi del Bufalo 58 1299 34 Massa Marittima 164 55 11 La Campigliola 157 488 35 Casa Bianca 68 140 12 S. Gerolamo 106 1951 36 Prunicce 45 9 13 Bottro del Inferno 40 231 37 Pomonte 93 47 14 Poggio Costone 71 349 38 Mte. Labbro 45 1 15 La Pianaccia 25 2 39 Magliano 107 28 16 Lagaccioli 275 189 40 Manciano 132 200 17 Poggio Vaccaro 112 337 41 Selvena 80 22 18 Poggio Capraio 129 181 42 Poggio Capanne 34 111 19 Poggio Castellaccia 78 735 43 S. Martino sul Flora 100 329 20 Capanelle I 21 1380 44 Campiglia d'Orcia 108 1 21 Capalbio SW 95 274 45 Casa Vogli 120 4

The samples were transported to Field and chemical data were compu• Munich in plastic bags, dried in the terized, using the data base management oven at max. 70°C for three days. They system SIR (Robinson et al. 1979). For were then ground in a powder mill with statistical analyses the program pack• widia or silit inserts to less than ages SPSS (Nie et al., 1975) and BMDP 100 microns. For XRF-analysis, the pow• (Dixon et al., 1981) were used. In ad• der was mixed homogeneously with a dition programmes for special require• polymerisation chemical in the ratio7:3 ments and computer plots were developed and was pressed in aluminum caps to powder pellets. The 13 trace elements, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Sb, Ba, Pb were 4. RESULTS analyzed by energy dispersive X-ray analysis (EDXRF). Control-measurements by atomic absorption analysis were car• 4.1 Regional Distribution Patterns ried out especially for Sb. Major and minor elements in selected samples were The regional distribution pattern analyzed with EDXRF. (Fig. 2) indicates that the Sb-deposits Exploration for Antimony Deposits in Southern Tuscany 429

or anomalies are connected to the elon• there is evidence of a hydrothermal gated horst structures, which also cause system in the ridge of Montepulciano the outcropping of paleozoic rocks. the geothermal gradient established may The remarkable accumulation around not be high enough to allow near-sur• the Tafone Graben extends to the SW to face precipitation of antimony. Capalbio and possibly into N. Latium. Although the geology of the Tafone area - In the Mte. Amiata area a large num• is expected to continue into N. Latium, ber of Hg-mineralizations occur, some detailed knowledge is not available be• also containing antimonite as accessory cause of the thick Pleistocene volcanic mineral. There are also some smaller Sb cover. All deposits presently being ex• mineralizations. Grids sampled in this ploited are situated in the Tafone area area generally show elevated Sb values. The majority of all grids in this area With the exception of S. Martino sul have anomaleously high Sb-contents (see Fiora (grid No. 43) however, the ano• Table 1). malies are rather low. The Sb-anomalies of other areas are The following target areas are re• also associated with tectonic struc• commended as economically attractive: tures : Cetine South (3), Frassine (5), La Campigliola (11), S. Gerolamo (12), - Elevated values are found along the Poderi del Bufalo (10), Pelagone (9), Monticiano ridge and in its southern Le Capanelle (20) and Paganico (28). and northern prolongation (grids No. 1, In some of these areas detailed work 2, 3, 28, 36) in particular at its such as: dense grid sampling, geophysic• eastern margin. Further to the west, in al studies for better transparency of the pyrite and mixed sulfide containing the local structure and finding of anti- "Colline Métallifère", a number of monite-accompagnying pyrite ore have smaller horsts contain locally elevated begun. Sb-values. Except for one single grid (Frassine I, grid No. 5) the values are, Another group of high anomalies although clearly anomaleous, not com• need further investigation: Lagaccioli . parable with some of the really high (16), Poggio Vaccaro (17), Poggio anomalies. Capraio (18), Poggio Castellaccia (19) and Manciano (4). - Sb-mineralizations are not known in the area north of Siena. The sampling grid Casa Vagli (No. 45) although struc• 4.2 Local Distribution Patterns turally and petrographically favourably situated, contains no Sb values above Cetine (Fig. 3): This locality is known the background. This may be explained for the abandoned Sb-mine of the same by the general absence of geothermal name. According to the knowledge of the anomalies. local geology gained by superficial The area Cappuccini (No. 29) and and mining works, the mineralization Monte Cetona (No. 30) situated on the is bound to a NW-SE running fault which ridge of Montepulciano, do not contain brings the Calcare Cavernoso in contact values above the background, although with a widespread flysch-type rock, their position is theoretically very the Galestri e Palombini. The ore de• favourable. Numerous fault systems, posit was mined in the Calcare Caver• permeable aquifers and thermal wells as noso. indicators of geothermal activity are According to the results of the geo- present. There are two possible reasons chemical sampling (Fig. 3) there is a for the absence of Sb mineralizations: clear separation between areas of high a) primary Sb-enrichments are not avail• and low Sb contents. The Sb-anomalies able in the underlying rocks. however do not coincide with the fault. b) According to Wagner (1980) the for• Two possible explanations may be g?ven: mation of ore deposits depends on the a) The fault mapped is not the main con• development of hydrothermal convection trolling factor for ore formation, cells in connection with the from W to b) the fault mapped is part of a series E prograding igneous activity. Although of faults oblitterated by the flysch, 430 R.M. Dehm et al.

IHHHâSS «rC--J---ji—j-lnn;^^---"-.^ QUARTERNARY and NEOAUTOCHTHONOUS TUSCAN SERIES ■ Waste dump Calcare Cavernoso Detrital

|:;|jj:|;| Miocene sediments -— Fault LIGURIAN NAPPE **—*' Fault (hypothesized) Galestri e Palombini 0 400m

Sb isolines: / / 20ppm .• 100ppm 500ppm lOOOppm SOOOppm / / Fig. 3. Geological map and isoline plot of Sb contents in soil samples of the Cetine South area (grid No. 3). Geology: Enlargement of survey maB 1:100.000; No. 120. Grid indicated at map margin. The hypothesized fault is based on the pattern of geochemical Sbdistribution which may all have acted as transport hydrothermal activities are evident. media for ore solution. Under these Soil samples were taken in a 100 by circumstances it may be hypothesized 350 m grid. The isoline plot shows large that to the SW of the fault mapped areas with more than 1000 ppm and four there is only a thin layer of flysch centers with values higher than 3000 covering a mineralized zone of the ppm. Two of these are in alluvial ter Calcare cavernoso. rain. The two others are in a contact area of Calcare Cavernoso/Santa Fiora La Campigliola (Fig. 4): This locali flysch and in Macigno sandstone respec ty is situated within a large area of tively, both in a strongly faulted zone numerous known and partly exploited and should be sampled in a denser grid. Sbmineralizations, just S of the aban Additional geophysical methods should doned mine Macchia Casella. be carried out. The Tafone graben extends to the SE Cappuccini (Fig. 5): No Sb anomalies to the Tafone mine, presently together were found. This may be due to a) hydro with the nearby Montauto, the only Sb thermal convection cells causing ore productive localities. Tectonic and formation have not yet been established Exploration for Antimony Deposits in Southern Tuscany 431

QUARTERNARY and NEOAUTOCHTHONOUS TUSCAN SERIES u u * Alluvial a 0 0 Macigno sandstone

vX'V'^ Silification -z-z-: Calcare nummulitiche

Calcare ad Avicula LIGUr: S. Fiora Fly sen ?}j& Calcare Cavernoso 0 250 500 750m i _ ™ Verrucano Sb - isolines / Fault / / lOOOppm/ 3000ppm / / jS Thrust plane Fig. 4. Geological map and isoline plot of Sb contents in soil samples of the Campigliola area (grid No. 11). Geology: R. Siegert 1982. Grid indicated at map margin or b) the ridge of Montepulciano is not expected that the ridge of Montepulci- underlayn by Sb-containing Paleozoic ano will be the area affected next by series. igneous and thermal activity. Thermal Taking into consideration the W to wells as first indicators of rising E prograding Plio- to Pleistocene mag- temperatures in the lower levels sup- matism of Southern Tuscany, it may be port this extrapolation. Two areas 432 R.M. Dehm et al.

F—i » r > 1 »— E-----3( ■*'-•>.{?-'■ ?.--:-> ;

NEOAUTOCHTHONOUS 400m Pliocene sediments Fig. 5. Geological map and isoline TUSCAN SERIES Fault plot of the Cappuccini area (grid No. ---_-: Jurassic carbonates Sb- isolines: 29) near Montepulciano; geology: En largement of Survey map 1:100.000; 20 ppm gvjyj; Calcare Cavernoso No. 121. Grid indicated at map margin

RNTIM0NY * FREQUENCY DISTRIBUTION * T0TRL DRTR 5B41 SAMPLES

1 1 1 1 1 1 1 —i 1 1 1—r i ■ i i i i —

FC*: ia.ate mM

7.5^ -

5.eg? -

z'*v/ WÊÊÊMÊMA^ WËÊÊËÊÊM wm 1 2 3 4 G 10 16 25 40 2! il2 iae 53 100 1S8 251 39G 631 1000 Sb FC543 : RELATIVE FREQUENCY V/.Ï Sb : ANTIMONY CONCENTRATION [PPM; LOGSCALED Fig. 6. Frequency distribution of antimony contents (ppm) in 5840 soil samples. Semiquantitative range below 20 ppm Sb Exploration for Antimony Deposits in Southern Tuscany 433

(Cappuccini and Monte Cetona) were cause of their suitability, judged on therefore sampled in favourable posi• the basis of conventional geological tion to identify Sb-anomalies which observation. None of the grids sampled might be interpreted as signs of pre• in these areas however showed Sb-values sent ore deposit formation. above the average. On the other hand, some areas, indicated with a high prob• ability by the statistics, appeared un• 4.3 Data Analysis suitable by conventional geological standards. These areas, too, contained Data collected and processed as describ• only low Sb-values. No highly anomalous ed in 3.5 were treated with uni-, bi- areas so far unknown were found. How• and multivariate statistical methods. ever, quite a few extensions of known Aim of this study was to reveal the mineralizations were detected. The geo• geochemical behaviour of the analyzed chemical methods applied can be regard• elements, especially the trace elements ed as appropriate. Geared for the aim and their dependence of the different of the study, the point distances of geological situations. Fig. 6 shows fre• the grids can be adjusted according quency distribution for Sb of all to the subsequent steps: finding and 5840 samples. Whilst the overall dia• delineation of the mineralizations. gram in Figure 6 shows a chi-square dis• The mobility of Sb and the near- tribution, areas with elevated Sb-values surface formation typical for these de• produce a binominal distribution, which posits also favour the method applied. is characteristic for mineralized and Transferred to other metals, the sys• hydrothermally altered areas. This ob• tem has to be adjusted accordingly. servation also applies to the elements Still problematic is the detection of Sr, Ba and Pb, which generally can be anomalies through impermeable cap rocks, correlated with Sb. The observation in this case the clay-rich flysch-type that these elements were transported rocks. and precipitated together with Sb is The extensive study produced a de• supported by the variety of accessory tailed picture of the Sb-distribution minerals (galena, sphalerite, Pb-Sb of southern Tuscany. The potentially sulfosalts) and the gangue minerals mineralized zone was narrowed down to (baryte, calcite) within the known ore the area south of Siena and west of the deposits. A detailed analysis of the ridge of Montepulciano. To the South, geochemical aspects will be published the area is bordered by the thick cover in a geochemically orientated paper. of Pleistocene tuff in Northern Latium. Within this zone mineralization is petrographically bound to permeable rocks of the Tuscan series and overly• 5. CONCLUSIONS ing impermeable covers. The ore depos• its are structurally controlled by The results of the geochemical soil sur• fault zones of Pliocene to subrecent vey show that the statistical probabili• block tectonics. ty determinations were satisfactory and The accumulation of Sb-deposits and that the statistical treatment of geo• mineralizations in the Tafone area was logical data can be used as a powerful also veryfied by geochemical prospect• tool in exploration. It should be men• ing. A possible explanation for this tioned however that southern Tuscany may be an underlying particularly Sb- offers very favourable conditions for rich formation as primary source. Pre- statistical analysis since the density Carboniferous rocks with primary Sb en• of data available in the area exceeds richments are considered to be the that of an average prospection area source of the deposit antimony. Unusual• remarkably. ly large outcrops of paleozoic rocks in Besides the areas indicated with the area do contain antimony in small high probability for Sb-ore formation amounts (up to 20 ppm), which are how• by the statistics, some more areas were ever not yet proven to be of primary selected for geochemical sampling be• origin. 434 R.M. Dehm et al.

Acknowledgements. The authors wish to Dixon, W.J., Brown, M.B., Engelmann, thank RI.MIN. S.p.A., Follonica, for L., Frane, J.W., Hill, M.A., Jennrich cordial cooperation and the Commission R.I., Toporek, D.D.: BMDP statistical of the European Communities for finan• software. Berkeley, 736 pp, 1981 cial support. Giannini, E., Lazzarotto, A., Signorini R.: Lineamenti di stratigrafia e di REFERENCES tetonica. In: Autori Vari: La Toscana Méridionale. Rend. Soc. Ital. Mineral Abbate, E., Sagri, M. : The eugeosyn- Petrol. 27, 33-168 (1971) clinal sequences. Sed. Geol. 4, Marinelli, G.: Magma evolution in Italy 251-340 (1970) In: Squyres, C.H. (ed) Geology of Bagnoli, G., Gianelli, G., Puxeddu, M., Italy. Tripolis, 165-219, 1975 Rau, A., Squarci, P., Tongiorgi, M.: Neumann, N.: Geologische und geochemi- The Tuscan Paleozoic: A critical re• sche Bildungsparameter der Hg-/Sb- view. In: Tongiorgi M. (ed) (1978): Lagerstatten der Slid toskana, Italien. Report on the Tuscan Paleozoic base• Unpublished Ph.D. thesis. University ment. CNR: Rapporto interno del Sotto- of Munich, 132 pp, 1979 progetto Energia Geotermica, Progetto Nie, N.H., Hull, C.H., Jenkins, J.S., Finalizzato Energetica. Pisa, 9-26,1978 Steinbrenner, K., Bent, D.H.: SPSS. Bagnoli, G., Tongiorgi, M.: New fossili- Statistical Package for the social ferous Silurian (Mt. Corchia) and sciences. New York, 675 pp, 1975 Devonian (Monticiano) layers in the Pichler, H.: Italienische Vulkangebiete Tuscan Paleozoic. Mem. Soc. Geol. It. I. Stuttgart, 248 pp, 1970 20, 301-313 (1979) Rau, A., Tongiori, M.: Geologia dei Bagnoli, G., Gianelli, G., Puxeddu, M., Monti Pisani a sud-est della Valle Rau, A., Squarci, P., Tongiorgi, M.: del Guappero. Mem. Soc. Geol. It. A tentative stratigraphie reconstruc• 13, 227-408 (1974) tion of the Tuscan Paleozoic basement. Robinson, B.N., Anderson, G.D., Cohen, Mem. Soc. Geol. It. 20, 99-116 (1979) E., Gazdzik, W.F.: SIR - Scientific Benvenuti, G., Brondi, M., Aglio, M. information Retrieval. Evanston, dall, Roit, R.da, Cassan, P.de, 488 pp, 1979 Ghiara, E., Gigli, C, Marinelli, G., Sestini, G.: Postgeosynclinal deposi• Martini, M., Gragnani, R., Orlandi, tion. Sed. Geol. 4, 481-520 (1970) C, Paganin, G.: L'idrologia. In: Siegert, R. : Bericht uber die Kartie- Autori Vari: La Toscana. Méridionale. rung, sowie petrografische, lager- Rend. Soc. Mineral. Petrol. 27, stâttenkundliche und bodengeochemi- 211-316 (1971) sche Bearbeitung eines Gebietes bei Dessau, G.: Die Lagerstâtten Toskanas La Campigliola (Sudtoskana, Italien). im Lichte der Geologischen Entwick- Unpublished Diploma thesis, Universit; lung des Landes. Archiv f iir Lager- of Munich, 150 pp, 1982 stattenforschung in den Ostalpen, Wagner, J.: Die Eisen- und Kupfersulfid Sonderband 2, 51-77 (1974) lagerstâtten der Toskana in ihrem Dessau, G.: Die Quecksilber- und Anti- geologischen Rahmen. Unpublished Ph. monlagerstatten der Toskana. Frei- D. thesis, University of Munich, 9 p, berger Forschungshefte, Reihe C, Nr. Received: March 24, 1983 328, 47-71 (1977) Accepted: May 26, 1983 Dessau, G., Stefanis, A.,de: Studio geologico-minerario della zona mer- Dipl.-Geol. R. Dehm curifera di Cerreto Piano (Scansano, Prof.Dr.D.D.Klemm Provincia di Grosseto). Mem. Soc. Dipl.-Geol.C.Mûller Geol. It. 8, 289-323 (1969) Dr.J.Wagner Dessau, G., Duchi, G., Stea, B.: Prof.Dr.K.Weber-Diefenbach Geologia e depositi minerari della Institut fur Allgemeine und Angewandte zona Monti Romani - Monteti (Communi Géologie der Universitât di Manciano e Capalbio (Grosseto) e LuisenstraBe 37 Ischia di Castro (Viterto)), Mem. D-8000 Mûnchen 2 Soc. Geol. It. 11, 217-260 (1972) FRG European Communities - Commission EUR 8617 — Selected papers arising from the EEC primary raw materials programme (1978-81) Luxembourg : Office for Official Publications of the European Communities 1984 — reprinted from Mineralium Deposita, Springer-Verlag : pp. 301-434 —16.5 x 24 cm Environment and quality of life series EN-FR ISBN 92-825-4086-3 Catalogue number: CD-NO-83-037-2A-C Price (excluding VAT) in Luxembourg : ECU 8.71 BFR400 IRL6.40 UKL 5 USD 7.50

This special issue of the journal Mineralium Deposita contains papers on the following topics, all relating to the field of economic geology and its ultimate application to mineral prospecting : (i) fluid inclusions of south-west England granites and their use in prospecting for tin, tungsten and copper; (ii) diagenetic processes and mineralization in the Triassic of central England ; (iii) the relationship between sulphide mineralization on the margin of the Leinster granite (south-east Ireland) and its aureole rocks: evidence from stable isotope studies; (iv) geochemical prospecting for antimony deposits in Tuscany ; (v) tungsten mineralization in central East Greenland; (vi) isotope and trace element studies on the lead-zinc vein-type deposits of Belgium ; (vii) geochemical investigations of shales and carbonate rocks in the Aachen region ; (viii) geochemical proximity indicators of concealed sulphide mineralization in the Iberian pyrite belt.

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