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Lead and sulfur isotope evidence for the origin of the Inler Yaylası lead–zinc deposits, Northern Turkey
Journal of Asian Earth Sciences 26 (2006) 91–97 www.elsevier.com/locate/jaes
Lead and sulfur isotope evidence for the origin of the Inler Yaylası lead–zinc deposits, Northern Turkey Ahmet Go¨kc¸e*, Gu¨lcan Bozkaya Department of Geological Engineering, Cumhuriyet University, Sivas, Turkey Received 15 April 2004; accepted 20 October 2004
Abstract The Eastern Black Sea Region of Turkey contains over 400 massive (Kuroko type) and vein type Cu–Pb–Zn deposits. The Inler Yaylası lead–zinc deposits are typical examples of the vein type and have been economically mined for 15 years. Three ore veins were identified along E–W trending fault zones, hosted by extensively altered, Upper Cretaceous volcano-sedimentary rocks. A Tertiary granitoid intrusion occurs near the area of mineralization. The ore veins contain sphalerite, galena and minor amounts of pyrite, chalcopyrite, fahlore, chalcocite and covellite as ore minerals, with quartz and calcite as gangue minerals. The measured d34S values of galena (K3.9 to K1.9 ‰V-CDT) and sphalerite (K2.0 to C0.4 ‰V-CDT) and calculated d34S values of H2S in equilibrium with these mineral (K2.14 to K0.73 ‰V-CDT) are slightly lower than the magmatic sulfur values and suggest an indirect magmatic source, that would involve the leaching of isotopically lighter sulfur from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit. Lead isotope ratios, for galena samples are dispersed in a narrow range from 18.639 to 18.676 (206Pb/204Pb), 15.671–15.698 (207Pb/204Pb) and 38.761–38.870 (208Pb/204Pb). These lead isotope data are close to those of an orogene reservoir and are very different from those of a mantle-related reservoir. In the light of these observations it may be assumed that the sulfur and lead concentrated in the studied deposits was leached by deep circulated meteoric water from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit which contained light magmatic sulfur and orogenic lead. q 2004 Elsevier Ltd. All rights reserved. Keywords: Northern Turkey; Inler Yaylasi; Lead-zinc vein deposits; Sulfur and lead isotopes
1. Introduction The Eastern Black Sea Region of Turkey contains over 400 massive (Kuroko-type) and vein-type Cu–Pb–Zn deposits. The lead–zinc deposits are located in the Tutakdag˘i area (Fig. 1) and are typical examples of the vein type deposits. Mining activities in the area have been continuing for over 20 years. Three ore veins were identified along the E–W trending fault zones, hosted by extensively altered volcano-sedimentary rocks, which were intruded by a granitoid intrusion.
* Corresponding author. Tel.: C90 346 2191010; fax: C90 346 2191171. E-mail address: [email protected] (A. Go¨kc¸e). 1367-9120/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2004.10.001
The ore veins consist mainly of quartz and sulfide minerals such as sphalerite, galena and minor amounts of pyrite, chalcopyrite, fahlore, chalcocite and covellite. Gossan zones with limonite, malachite and azurite have developed at the surface. The thickness of the veins varies from 0.4 up to 8 m. In previous studies Karaog˘lu (1992) and C¸alapkulu and Karaog˘lu (1987) reported varying temperatures of the oreforming fluids between 150 and 290 8C. According to S¸as¸maz (1993) and S¸as¸maz and Sag˘irog˘lu (1994a,b) the deposits developed as ore veins along faults in a large alteration zone in the Upper Cretaceous volcano-sedimentary unit, and hydrothermal fluids from Paleocene granitoids possibly caused the alteration and ore deposition. Demirkiran (1993) and Demirkiran et al. (1995) pointed out
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A. Go¨kc¸e, G. Bozkaya / Journal of Asian Earth Sciences 26 (2006) 91–97
Fig. 1. Location map and simplified geology map of the study area (after S¸as¸maz and Sag˘irog˘lu, 1994a).
that the deposits occur in the altered upper levels of the volcano-sedimentary units. Authors of the present paper have carried out various geological investigations, including field geology, ore microscopy, fluid inclusion, stable—(O, H and S) and lead—isotope geochemistry in recent years. Microthermometric studies of the fluid inclusions (Go¨kc¸e and Bozkaya, 2003) showed that hydrothermal fluids contain MgCl2– CaCl2–NaCl at the early stage, NaCl dominated at the later stage. In addition, the salinity and temperature of the hydrothermal fluids decreased from early to later episodes of mineralization; from 14.8 to 0.2% NaCl equiv. and from 377.2 to 105.5 8C, respectively. The salinity and temperature of the hydrothermal fluid acting during the sulfide mineralization episode ranged from 7.3 to 0.4% (average; 4.0%) NaCl equiv. and from 311.1 to 212.9 8C (average; 272.0 8C), respectively. Oxygen and hydrogen isotope results from water trapped in fluid inclusions (d18O; C 4.2–C6.7 ‰V-SMOW and d D; K83.0 to K59.0‰V-SMOW)
suggest that hydrothermal fluids contained either magmatic water mixed with small amounts of meteoric water (and/or formation water of meteoric origin), or meteoric water that was isotopically modified by deep interaction with the surrounding magmatic rocks. The latter type of fluid has been suggested for the Kurs¸unlu and Murgul deposits in the eastern Black Sea region (Go¨kc¸e et al., 1993; Go¨kc¸e and Spiro, 2002). This paper reports sulfur and lead isotope characteristics in sulfides from Inler Yaylası lead–zinc deposits, and discusses the origin of the metals and sulfur in these deposits.
2. Geological background The Eastern Black Sea Region is covered by volcanosedimentary units that formed over a long period of time, from the Liassic to the Pliocene; plutons intruded these units
A. Go¨kc¸e, G. Bozkaya / Journal of Asian Earth Sciences 26 (2006) 91–97
during the Paleocene, and flysch-like sediments were laid down during the Eocene. These volcano-sedimentary units are classified as the Lower Basic Series (Liassic to Lower Cretaceous), the Dacitic Series (Upper Cretaceous), Tertiary Granitoids (Paleocene ?), Flysch-like Sediments and the Upper Basic Series (Eocene), the Young Basic SeriesCLate Dikes (Oligocene–Pliocene) and the Eastern Anatolian Terrestrial Volcanics (Miocene–Pliocene). A widely accepted view is that the region developed along a convergent plate boundary, possibly as a volcanic arc (e.g. Tokel, 1973; Pejatovic¸, 1979; Akıncı, 1980, 1985; Bektas¸, 1983; Bektas¸ et al., 1984). In the study area, the Upper Cretaceous volcanosedimentary rocks consist of lavas and pyroclastics of rhyodacitic, dacitic and andesitic composition. This unit may be part of the ‘Dacitic Series’ which hosts most of the sulfide deposits in the Eastern Black Sea region. Volcanic rocks of this series include extensive alteration zones with distinctive pale colours, which are not typical of the younger units. The alteration is most profound around the Tertiary granitoids and in the mineralised areas. The Tertiary granitoids are of alkali granitic, granitic and syenitic composition. Dike-like subvolcanic equivalents are also present. These rocks intruded Upper Cretaceous volcano-sedimentary units during the Paleocene(?) and are overlain by Eocene sediments. The Eocene volcanics consist of lavas and pyroclastics of andesitic, basaltic and trachy-andesitic compositions and occur in outcrops as slightly altered massive rocks. They overlie Upper Cretaceous volcano-sedimentary rocks and Tertiary granitoids and are overlain discordantly by PlioQuaternary volcanic rocks. Eocene sediments consisting of alternating yellowishgray, thinly bedded sandstone–siltstone and claystone beds discordantly overlie the Upper Cretaceous volcano-sedimentary rocks and Tertiary granitoids. Plio-Quaternary volcanic rocks occur in the study area as fresh outcrops of basaltic rocks, and these rocks overlie discordantly all the older units mentioned above.
3. Ore geology 3.1. Depositional style and ore–host rock relationship In the study area, three parallel E–W-trending ore veins were identified during the field work. These veins are cut and offset by younger faults (Fig. 2). The ore veins were designated V1, V2 and V3. The dip of the V1 vein is nearly vertical (varying between 858 to the N and 858 to the S), and those of V2 and V3 vary between 458 and 608 to the N. The parts of the V2 and V3 veins between the F1 and F2 faults were being mined at 1910, 1880, 1802 and 1715 m levels during the course of our field studies. The ore veins consist mainly of quartz and sulfide minerals. Gossan zones with limonite, malachite and azurite
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have developed at the surface. The thickness of the veins varies from 0.4 up to 8 m. These ore veins are hosted by older volcano-sedimentary rocks in an area near to a granitoid intrusion. The volcanic host rocks show extensive alteration characterized by quartz, limonite, chlorite, clay minerals and epidote occurrences around the ore veins. 3.2. Ore mineralogy Thin sections and polished blocks of representative ore samples were investigated under a polarising microscope. Sphalerite and galena are the dominant ore minerals, accompanied by variable amounts of pyrite, chalcopyrite, fahlore, chalcocite and covellite. The amount of pyrite and chalcopyrite increases throughout the deeper levels. In addition to these common minerals, Sasmaz (1993) and Sasmaz and Sagiroglu (1994a,b) reported the presence of enargite, pyrrhotite, linnaeite, tetradymite, altaite, magnetite and native gold. Barite was observed in outcrops, but was not detected in the deeper levels of the veins. Quartz crystals are found in three different sizes: the largest is in the outer zones of the veins, while the smallest occurs in the innermost zones. Sulfides are observed among the smallest quartz crystals, indicating that the sulfide mineralization developed later than the quartz crystallization. Calcite is generally present as thin veinlets which cut the quartz and sulfide zones and seem to be formed during the latest episode of mineralization.
4. Sulfur- and lead-isotope studies 4.1. Samples and methods Sulfur isotope compositions were determined for galena and sphalerite samples, while the lead isotope compositions were determined only on the galena mineral seperates, handpicked from samples collected from the V2 and V3 ore veins at the 1802 and 1715 m levels. Samples ST-101 to ST109 were taken from the V2 vein at the 1803 m level, samples ST-110–ST-119 were taken from the V3 vein at the 1725 m level and samples ST-120–ST-129 were taken from the V2 vein at the 1725 m level. Sulfur isotope analyses were performed at the Isotope Geochemistry Laboratories of NERC (Keyworth, Nottingham, UK) and at the Department of Geological Sciences of University of Nevada, Reno, USA. The results are reported in the d notation as per mil (‰) deviations relative to the Vienna CDT standard (d34S V-CDT) in Table 1, with an overall analytical reproducibility of G0.2 ‰ at both laboratories. Lead isotope composition of the galena samples were analysed in static mode (simultaneous measurement of all isotope ion currents) using Finnigan MAT-261 thermal ionization multicollector mass spectrometer at the Institute
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Fig. 2. Position of the Pb–Zn veins in the study area.
for Precambrian Geology and Geochronology, St Petersburg, FL, USA and presented in Table 2. Lead isotope ratios have been corrected for mass fractionation of 0.13% per atomic mass unit, calculated from replicate analyses of Pb isotope composition in the US National Institute of Standards (NIST) standard SRM-982. An external reproducibility of lead isotope ratios of 0.1% for 206Pb/204Pb, 0.15%
for 207Pb/204Pb, and 0.2% for 208Pb/204Pb has been demonstrated at the 2s confidence level through multiple analyses of BCR-1 standard. In order to minimize the mass fractionation effects, the measurements of the galena Pb isotope compositions were carried out at constant (and equal to those measured in NIST SRM-982) lead quantities. This was accomplished through the separation of lead from
A. Go¨kc¸e, G. Bozkaya / Journal of Asian Earth Sciences 26 (2006) 91–97 Table 1 Sulfur isotope values of the analysed samples from Inler Yaylası area Sample no.
Location (veinaltitude) (m)
Mineral
d34S‰ CDTG 0.2
ST-01 ST-106 ST-106 ST-110 ST-120 ST-120 ST-121 ST-124 ST-125 ST-125
V2-1803 V2-1803 V2-1803 V3-1725 V2-1725 V2-1725 V2-1725 V2-1725 V2-1725 V2-1725
Galena Sphalerite Galena Sphalerite Sphalerite Galena Sphalerite Sphalerite Sphalerite Galena
K3.9 K2.0 K3.9 C0.4 0.0 K1.7 K0.4 K0.5 K0.8 K1.9
(*) (*) (*) (**) (*) (*) (**) (**) (**) (**)
(*) Analysed at NERC Stable Isotope Laboratory; (**) Analysed at Stable Isotope Laboratory of the Nevada Reno University).
the galena using ion-exchange columns with a calibrated resin capacity. The NIST standard was run twice with each series of samples. All uncertainties are quoted at the 2s level. 4.2. Results The d34S values of sphalerites and galenas range from K 2.0 to C0.4 (average K1.8) ‰V-CDT and K3.9 to K1.7 (average K2.85) ‰V-CDT, respectively (Table 1). Lead isotope data for six galena samples from various levels of the ore veins are dispersed in narrow ranges from 18.639 to 18.676 ( 206 Pb/ 204Pb), 15.671 to 15.698 (207Pb/204Pb) and from 38.761 to 38.870 (208Pb/204Pb) and presented in Table 2. These data are shown on 207Pb/204Pb vs 206Pb/204Pb and 208Pb/204Pb vs 206Pb/204Pb diagrams in Fig. 3. 4.3. Discussion d34S values of H2S in equilibrium with a sulfide mineral are estimated in the range of K2.14 to K0.73 ‰V-CDT using the average d34S values of sphalerite (K1.8 ‰V-CDT) and galena (K2.85 ‰V-CDT), and the average temperature of the hydrothermal fluid during the sulfide mineralization episode (272.0 8C) in the related equations proposed by Ohmoto and Rye (1979). These d34S values of H2S are slightly below typical magmatic sulfur values. Either a direct magmatic source,
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depleted in 34S (from granitoid intrusion) or an indirect magmatic source may be assumed, involving leaching of isotopically lighter sulfur, either from the Upper Cretaceous volcano-sedimentary rocks or from a deep-seated older ore deposit. Previously published fluid inclusion and stable isotope results (Go¨kc¸e and Bozkaya, 2003), that suggested hydrothermal fluids contained either magmatic water mixed with small amounts of meteoric water (and/or formation water of meteoric origin) or meteoric water isotopically modified by deep interaction with surrounding magmatic rock, increase the probability of an indirect magmatic source, with leaching from the surrounding rocks. The differences between the d34S values of galena and sphalerites from the same samples are in accordance with isotopic fractionation trends for these two mineral pairs. But the textural characteristics, show that galena precipitated slightly later than sphalerite, and the higher isotope fractionation temperature values (calculated as 343.6 and 378.9 8C using the d34S values of the sphalerite–galena pairs of samples ST-106 and ST-120, and the related equation suggested by Ohmoto and Rye, 1979) compared with the microthermometric homogenization temperatures measured in fluid inclusions (in the range of 212.9–311.1 8C, average; 272.0 8C), which represent the fluid responsible for sulfide mineralization (Go¨kc¸e and Bozkaya, 2003), indicate that these two mineral pairs were not precipitated in equilibrium. Lead isotope data are close to those of a orogene reservoir and are very different from a mantle-related reservoir of the Plumbotectonics Model by Zartman and Haines (1988). These data plot above the Stacey and Kramers (1975) model curves for average crustal Pb-isotope evolution on 207Pb/204Pb vs 206Pb/204Pb and 208Pb/204Pb vs 206 Pb/204Pb diagrams (Fig. 3). These observations mean that the galena Pb was derived from sources with slightly higher than average crustal 238U/204Pb (m) and 232Th/204Pb ratios, similar to the orogenic reservoir proposed by Zartman and Haines (1988). No isotopic evidence was obtained for lead derived from a mantle-related reservoir. Calculated Pb-isotope model ages for these deposits, using the ISOPLOT program of Ludwig (1997), range from 174 to 123 Ma (average; 154G34 Ma) and indicate that the model parameters used in calculations do not exacly correspond to potential sources of lead in the galena samples studied.
Table 2 Lead isotope composition of the analysed samples from Inler Yaylası area Sample
206
Pb/204Pb
2s error
207
Pb/204Pb
2s error
208
Pb/204Pb
2s error
Model238U/204Pb
Model Age (Ma)
ST-101 ST-106 ST-110 ST-111 ST-114 ST-125
18.660 18.669 18.663 18.665 18.639 18.676
0.1 0.1 0.1 0.1 0.1 0.1
15.671 15.691 15.697 15.691 15.672 15.698
0.15 0.15 0.15 0.15 0.15 0.15
38.761 38.838 38.850 38.835 38.771 38.870
0.2 0.2 0.2 0.2 0.2 0.2
9.93 10.0 10.0 10.0 9.94 10.0
123 157 174 160 140 167
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magmatic sources and indicate a possible indirect magmatic source, involving leaching of isotopically lighter sulfur from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit. 206 Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios for galena samples show a narrow range from 18.639 to 18.676, 15.671 to 15.698 and 38.761 to 38.870, respectively. These lead isotope data are close to those of an orogene reservoir and are very different from the mantlerelated reservoir of the Plumbotectonics Model by Zartman and Haines (1988). These data plot above the Stacey and Kramers (1975) model curves on 207Pb/204Pb vs 206Pb/204Pb and 208Pb/204Pb vs 206Pb/204Pb diagrams. In the light of these observations and previously published fluid inclusion and stable isotope results (Go¨kc¸e and Bozkaya, 2003), it may be presumed that the sulfur and lead concentrated in the studied deposits was leached by deep circulated meteoric water, the isotopic composition of which had been modified by the interaction with surrounding magmatic rocks, from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit which contained light magmatic sulfur and orogenic lead derived from a reservoir with higher 238 U/204Pb (m) and 232Th/204Pb ratios compared to average crustal values. A lead source derived from a mantle-related reservoir does not seem to have been involved.
Acknowledgements Fig. 3. Lead isotope composition of galena seperates from the Inler Yaylası Pb–Zn veins.
5. Summary and conclusions Although, sulfur- and lead-isotope and other geochemical data, to identify the composition and origin of the surrounding plutonic and volcano-sedimentary rocks are lacking, which makes it difficult to identify the source of the sulfur and lead in ore veins, the following conclusions may be proposed, using the presently available data. Lead–zinc deposits in the Inler Yaylası area occur in three parallel ore veins displaced by E–W-trending faults. These ore veins are hosted by extensively altered Upper Cretaceous volcano-sedimentary rocks, and a Tertiary granitoid intrusion is located near the area of mineralization. The alteration zone is marked by an assemblage of quartz, limonite, chlorite, clay minerals and epidote. The ore veins contain sphalerite, galena and minor amounts of pyrite, chalcopyrite, fahlore, chalcocite and covellite as ore minerals, and quartz and calcite as gangue. The measured d34S values of galena (K3.9 to K1.7; average K2.85‰V-CDT) and sphalerite (K2.0 to C0.4; average K1.8‰V-CDT) and calculated d34S values of H2S in equilibrium with these minerals (in the range of K2.14 to K0.73 ‰V-CDT) are slightly lower than the values of direct
The Research Foundation of Cumhuriyet University supported this study (Project No: M-194). Thanks are due to Dr Baruch Spiro (Natural History Museum, London, UK) and Dr Greg B. Arehart (Nevada Univ., Isotope Geoch. Lab.) for sulfur isotope analyses. We also thank to Dr Leonid A. Neymark (US Geological Survey) for critical readings and useful comments. Dr David Lowry (Royal Holloway, University of London) provided a helpful review.
References ¨ .T., 1980. The major copper metallogenic units and genetic Akıncı, O igneous complexes in Turkey. In: Jankovich, S., Sillitoe, R.H. (Eds.), European Copper Deposits, pp. 199–208. ¨ .T., 1985. The Eastern Pontide volcanosedimentary belt and Akıncı, O associated massive sulfide deposits. In: Dixon, J.E., Robertson, A.H.I. (Eds.), The Geological Evolution of the Eastern Mediterranean Special Publication 17. Geological Society, London, pp. 415–428. Bektas¸, O., 1983. I-type granites and their geotectonic position in the northeastern Pontian magmatic arc. Abstracts of the 37th Geological Congress of Turkey, pp. 49–50. Bektas¸, O., Pelin, S., Korkmaz, S., 1984. Mantle uprising and polygenetic ophiolites in the Eastern Pontide (Turkey) back arc basin. Abstracts of the Ketin Symposium Geological Society of Turkey, Ankara, pp. 175–188.
A. Go¨kc¸e, G. Bozkaya / Journal of Asian Earth Sciences 26 (2006) 91–97 C ¸ alapkulu, F., Karaog˘lu, N., 1987. Metallogenic investigation of lead– zinc–copper mineralization of the Inler Plateau. Abstracts of the Geological Congress of Turkey 1987, 31. Demirkiran, Z., 1993. Mining geology and mineralization of Inler Yaylasy´ (Sebinkarahisar-Giresun) Pb–Zn mine, Unpublished Master Thesis, Dokuz Eylu¨l University, 336p. ¨ ., 1995. Mining geology and Demirkiran Z., C¸alapkulu F., Pis¸kin, O mineralization of Inler Yaylasy´ (Sebinkarahisar–Giresun) Pb–Zn mine, International Earth Sciences Colloquium on the Aegean Region, IESCA-1995, V-II, pp. 505–518. Go¨kc¸e, A., Bozkaya, G., 2003. Fluid-inclusion and stable-isotope characteristics of the Inler Yaylasi Lead–Zinc deposits, Northern Turkey. International Geology Review 45, 1044–1054. Go¨kc¸e, A., Spiro, B., 2002. Fluid-related characteristics of the C ¸ akmakkaya and Damarko¨y copper deposits, northeast Turkey. International Geology Review 44, 744–754. Go¨kc¸e, A., Spiro, B., Miller, M.F., 1993. Stable-isotope (O, H, and C) geochemistry and origin of the mineralising fluid in the Kursunlu (Koyulhisar–Sivas) vein-type Pb–Zn–Cu deposits. Geological Bulletin of Turkey 36, 73–79 (in Turkish with English Abstract). Karaog˘lu, N., 1992. The fluid inclusion study on Inler Pb–Zn–Cu mineralizations (Sebinkarahisar-Eastern Black Sea-Turkey). Proceedings of the International Conference of Environment and Mineral Processing, Ostrava, Czech Republic 1992;, 102–113. Ludwig, K.R., 1997. ISOPLOT: a plotting and regression program for radiogenic-isotope data; Version 2.95 (July 1997 rev.). USGS OpenFile Report 91-445.
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Ohmoto, H., Rye, R.O., 1979. Isotopes of sulfer and carbon. In: Barnes, H.L., (Ed.), Geochemistry of Hydrothermal Ore Deposits. Wiley, New York, pp. 506–567. Pejatovic¸, S., 1979. Metallogeny of the Pontid-type massive sulfide deposits, Publications of Mineral Research and Exploration Institution of Turkey 177, 100p. S¸as¸maz, A., 1993. Pb–Zn Deposits in the Tutakdagi Area, Unpublished PhD Thesis, Fırat University Science Institute, 98p. S¸as¸maz, A., Sag˘irog˘lu, A., 1994a. Geology of the Pb–Zn deposits in the Tutakdagi area (S¸ebinkarahisar–Giresun). Bulletin Mineral Research and Exploration Instution of Turkey 116, 51–64 (in Turkish with English Abstract). S¸as¸maz, A., Sag˘irog˘lu, A., 1994b. Geology of the Inler Yaylasy´ (S¸ebinkarahisar–Giresun) Pb–Zn deposits. Geological Bulletin of Turkey 37, 13–28 (in Turkish with English Abstract). Stacey, J.S., Kramers, J.D., 1975. Approximation of the terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters 26, 207–221. Tokel, S., 1973. Evaluation of the eastern Pontides during Mesozoic and Tertiary, and possible relation to the North Anatolian seismic zone. Abstract, in Symposium of Earth Sciences, 50th Anniversary Republic of Turkey, pp. 1–4, MTA-Turkey. (in Turkish with English Abstract). Zartman, R.E., Haines, S.M., 1988. The Plumbotectonic model for Pb isotopic systematics among major terrestrial reservoirs—a case for bidirectional transport. Geochemica et Cosmochimica Acta 52, 1327– 1339.
Lead and sulfur isotope evidence for the origin of the Inler Yaylası lead–zinc deposits, Northern Turkey Ahmet Go¨kc¸e*, Gu¨lcan Bozkaya Department of Geological Engineering, Cumhuriyet University, Sivas, Turkey Received 15 April 2004; accepted 20 October 2004
Abstract The Eastern Black Sea Region of Turkey contains over 400 massive (Kuroko type) and vein type Cu–Pb–Zn deposits. The Inler Yaylası lead–zinc deposits are typical examples of the vein type and have been economically mined for 15 years. Three ore veins were identified along E–W trending fault zones, hosted by extensively altered, Upper Cretaceous volcano-sedimentary rocks. A Tertiary granitoid intrusion occurs near the area of mineralization. The ore veins contain sphalerite, galena and minor amounts of pyrite, chalcopyrite, fahlore, chalcocite and covellite as ore minerals, with quartz and calcite as gangue minerals. The measured d34S values of galena (K3.9 to K1.9 ‰V-CDT) and sphalerite (K2.0 to C0.4 ‰V-CDT) and calculated d34S values of H2S in equilibrium with these mineral (K2.14 to K0.73 ‰V-CDT) are slightly lower than the magmatic sulfur values and suggest an indirect magmatic source, that would involve the leaching of isotopically lighter sulfur from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit. Lead isotope ratios, for galena samples are dispersed in a narrow range from 18.639 to 18.676 (206Pb/204Pb), 15.671–15.698 (207Pb/204Pb) and 38.761–38.870 (208Pb/204Pb). These lead isotope data are close to those of an orogene reservoir and are very different from those of a mantle-related reservoir. In the light of these observations it may be assumed that the sulfur and lead concentrated in the studied deposits was leached by deep circulated meteoric water from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit which contained light magmatic sulfur and orogenic lead. q 2004 Elsevier Ltd. All rights reserved. Keywords: Northern Turkey; Inler Yaylasi; Lead-zinc vein deposits; Sulfur and lead isotopes
1. Introduction The Eastern Black Sea Region of Turkey contains over 400 massive (Kuroko-type) and vein-type Cu–Pb–Zn deposits. The lead–zinc deposits are located in the Tutakdag˘i area (Fig. 1) and are typical examples of the vein type deposits. Mining activities in the area have been continuing for over 20 years. Three ore veins were identified along the E–W trending fault zones, hosted by extensively altered volcano-sedimentary rocks, which were intruded by a granitoid intrusion.
* Corresponding author. Tel.: C90 346 2191010; fax: C90 346 2191171. E-mail address: [email protected] (A. Go¨kc¸e). 1367-9120/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2004.10.001
The ore veins consist mainly of quartz and sulfide minerals such as sphalerite, galena and minor amounts of pyrite, chalcopyrite, fahlore, chalcocite and covellite. Gossan zones with limonite, malachite and azurite have developed at the surface. The thickness of the veins varies from 0.4 up to 8 m. In previous studies Karaog˘lu (1992) and C¸alapkulu and Karaog˘lu (1987) reported varying temperatures of the oreforming fluids between 150 and 290 8C. According to S¸as¸maz (1993) and S¸as¸maz and Sag˘irog˘lu (1994a,b) the deposits developed as ore veins along faults in a large alteration zone in the Upper Cretaceous volcano-sedimentary unit, and hydrothermal fluids from Paleocene granitoids possibly caused the alteration and ore deposition. Demirkiran (1993) and Demirkiran et al. (1995) pointed out
92
A. Go¨kc¸e, G. Bozkaya / Journal of Asian Earth Sciences 26 (2006) 91–97
Fig. 1. Location map and simplified geology map of the study area (after S¸as¸maz and Sag˘irog˘lu, 1994a).
that the deposits occur in the altered upper levels of the volcano-sedimentary units. Authors of the present paper have carried out various geological investigations, including field geology, ore microscopy, fluid inclusion, stable—(O, H and S) and lead—isotope geochemistry in recent years. Microthermometric studies of the fluid inclusions (Go¨kc¸e and Bozkaya, 2003) showed that hydrothermal fluids contain MgCl2– CaCl2–NaCl at the early stage, NaCl dominated at the later stage. In addition, the salinity and temperature of the hydrothermal fluids decreased from early to later episodes of mineralization; from 14.8 to 0.2% NaCl equiv. and from 377.2 to 105.5 8C, respectively. The salinity and temperature of the hydrothermal fluid acting during the sulfide mineralization episode ranged from 7.3 to 0.4% (average; 4.0%) NaCl equiv. and from 311.1 to 212.9 8C (average; 272.0 8C), respectively. Oxygen and hydrogen isotope results from water trapped in fluid inclusions (d18O; C 4.2–C6.7 ‰V-SMOW and d D; K83.0 to K59.0‰V-SMOW)
suggest that hydrothermal fluids contained either magmatic water mixed with small amounts of meteoric water (and/or formation water of meteoric origin), or meteoric water that was isotopically modified by deep interaction with the surrounding magmatic rocks. The latter type of fluid has been suggested for the Kurs¸unlu and Murgul deposits in the eastern Black Sea region (Go¨kc¸e et al., 1993; Go¨kc¸e and Spiro, 2002). This paper reports sulfur and lead isotope characteristics in sulfides from Inler Yaylası lead–zinc deposits, and discusses the origin of the metals and sulfur in these deposits.
2. Geological background The Eastern Black Sea Region is covered by volcanosedimentary units that formed over a long period of time, from the Liassic to the Pliocene; plutons intruded these units
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during the Paleocene, and flysch-like sediments were laid down during the Eocene. These volcano-sedimentary units are classified as the Lower Basic Series (Liassic to Lower Cretaceous), the Dacitic Series (Upper Cretaceous), Tertiary Granitoids (Paleocene ?), Flysch-like Sediments and the Upper Basic Series (Eocene), the Young Basic SeriesCLate Dikes (Oligocene–Pliocene) and the Eastern Anatolian Terrestrial Volcanics (Miocene–Pliocene). A widely accepted view is that the region developed along a convergent plate boundary, possibly as a volcanic arc (e.g. Tokel, 1973; Pejatovic¸, 1979; Akıncı, 1980, 1985; Bektas¸, 1983; Bektas¸ et al., 1984). In the study area, the Upper Cretaceous volcanosedimentary rocks consist of lavas and pyroclastics of rhyodacitic, dacitic and andesitic composition. This unit may be part of the ‘Dacitic Series’ which hosts most of the sulfide deposits in the Eastern Black Sea region. Volcanic rocks of this series include extensive alteration zones with distinctive pale colours, which are not typical of the younger units. The alteration is most profound around the Tertiary granitoids and in the mineralised areas. The Tertiary granitoids are of alkali granitic, granitic and syenitic composition. Dike-like subvolcanic equivalents are also present. These rocks intruded Upper Cretaceous volcano-sedimentary units during the Paleocene(?) and are overlain by Eocene sediments. The Eocene volcanics consist of lavas and pyroclastics of andesitic, basaltic and trachy-andesitic compositions and occur in outcrops as slightly altered massive rocks. They overlie Upper Cretaceous volcano-sedimentary rocks and Tertiary granitoids and are overlain discordantly by PlioQuaternary volcanic rocks. Eocene sediments consisting of alternating yellowishgray, thinly bedded sandstone–siltstone and claystone beds discordantly overlie the Upper Cretaceous volcano-sedimentary rocks and Tertiary granitoids. Plio-Quaternary volcanic rocks occur in the study area as fresh outcrops of basaltic rocks, and these rocks overlie discordantly all the older units mentioned above.
3. Ore geology 3.1. Depositional style and ore–host rock relationship In the study area, three parallel E–W-trending ore veins were identified during the field work. These veins are cut and offset by younger faults (Fig. 2). The ore veins were designated V1, V2 and V3. The dip of the V1 vein is nearly vertical (varying between 858 to the N and 858 to the S), and those of V2 and V3 vary between 458 and 608 to the N. The parts of the V2 and V3 veins between the F1 and F2 faults were being mined at 1910, 1880, 1802 and 1715 m levels during the course of our field studies. The ore veins consist mainly of quartz and sulfide minerals. Gossan zones with limonite, malachite and azurite
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have developed at the surface. The thickness of the veins varies from 0.4 up to 8 m. These ore veins are hosted by older volcano-sedimentary rocks in an area near to a granitoid intrusion. The volcanic host rocks show extensive alteration characterized by quartz, limonite, chlorite, clay minerals and epidote occurrences around the ore veins. 3.2. Ore mineralogy Thin sections and polished blocks of representative ore samples were investigated under a polarising microscope. Sphalerite and galena are the dominant ore minerals, accompanied by variable amounts of pyrite, chalcopyrite, fahlore, chalcocite and covellite. The amount of pyrite and chalcopyrite increases throughout the deeper levels. In addition to these common minerals, Sasmaz (1993) and Sasmaz and Sagiroglu (1994a,b) reported the presence of enargite, pyrrhotite, linnaeite, tetradymite, altaite, magnetite and native gold. Barite was observed in outcrops, but was not detected in the deeper levels of the veins. Quartz crystals are found in three different sizes: the largest is in the outer zones of the veins, while the smallest occurs in the innermost zones. Sulfides are observed among the smallest quartz crystals, indicating that the sulfide mineralization developed later than the quartz crystallization. Calcite is generally present as thin veinlets which cut the quartz and sulfide zones and seem to be formed during the latest episode of mineralization.
4. Sulfur- and lead-isotope studies 4.1. Samples and methods Sulfur isotope compositions were determined for galena and sphalerite samples, while the lead isotope compositions were determined only on the galena mineral seperates, handpicked from samples collected from the V2 and V3 ore veins at the 1802 and 1715 m levels. Samples ST-101 to ST109 were taken from the V2 vein at the 1803 m level, samples ST-110–ST-119 were taken from the V3 vein at the 1725 m level and samples ST-120–ST-129 were taken from the V2 vein at the 1725 m level. Sulfur isotope analyses were performed at the Isotope Geochemistry Laboratories of NERC (Keyworth, Nottingham, UK) and at the Department of Geological Sciences of University of Nevada, Reno, USA. The results are reported in the d notation as per mil (‰) deviations relative to the Vienna CDT standard (d34S V-CDT) in Table 1, with an overall analytical reproducibility of G0.2 ‰ at both laboratories. Lead isotope composition of the galena samples were analysed in static mode (simultaneous measurement of all isotope ion currents) using Finnigan MAT-261 thermal ionization multicollector mass spectrometer at the Institute
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Fig. 2. Position of the Pb–Zn veins in the study area.
for Precambrian Geology and Geochronology, St Petersburg, FL, USA and presented in Table 2. Lead isotope ratios have been corrected for mass fractionation of 0.13% per atomic mass unit, calculated from replicate analyses of Pb isotope composition in the US National Institute of Standards (NIST) standard SRM-982. An external reproducibility of lead isotope ratios of 0.1% for 206Pb/204Pb, 0.15%
for 207Pb/204Pb, and 0.2% for 208Pb/204Pb has been demonstrated at the 2s confidence level through multiple analyses of BCR-1 standard. In order to minimize the mass fractionation effects, the measurements of the galena Pb isotope compositions were carried out at constant (and equal to those measured in NIST SRM-982) lead quantities. This was accomplished through the separation of lead from
A. Go¨kc¸e, G. Bozkaya / Journal of Asian Earth Sciences 26 (2006) 91–97 Table 1 Sulfur isotope values of the analysed samples from Inler Yaylası area Sample no.
Location (veinaltitude) (m)
Mineral
d34S‰ CDTG 0.2
ST-01 ST-106 ST-106 ST-110 ST-120 ST-120 ST-121 ST-124 ST-125 ST-125
V2-1803 V2-1803 V2-1803 V3-1725 V2-1725 V2-1725 V2-1725 V2-1725 V2-1725 V2-1725
Galena Sphalerite Galena Sphalerite Sphalerite Galena Sphalerite Sphalerite Sphalerite Galena
K3.9 K2.0 K3.9 C0.4 0.0 K1.7 K0.4 K0.5 K0.8 K1.9
(*) (*) (*) (**) (*) (*) (**) (**) (**) (**)
(*) Analysed at NERC Stable Isotope Laboratory; (**) Analysed at Stable Isotope Laboratory of the Nevada Reno University).
the galena using ion-exchange columns with a calibrated resin capacity. The NIST standard was run twice with each series of samples. All uncertainties are quoted at the 2s level. 4.2. Results The d34S values of sphalerites and galenas range from K 2.0 to C0.4 (average K1.8) ‰V-CDT and K3.9 to K1.7 (average K2.85) ‰V-CDT, respectively (Table 1). Lead isotope data for six galena samples from various levels of the ore veins are dispersed in narrow ranges from 18.639 to 18.676 ( 206 Pb/ 204Pb), 15.671 to 15.698 (207Pb/204Pb) and from 38.761 to 38.870 (208Pb/204Pb) and presented in Table 2. These data are shown on 207Pb/204Pb vs 206Pb/204Pb and 208Pb/204Pb vs 206Pb/204Pb diagrams in Fig. 3. 4.3. Discussion d34S values of H2S in equilibrium with a sulfide mineral are estimated in the range of K2.14 to K0.73 ‰V-CDT using the average d34S values of sphalerite (K1.8 ‰V-CDT) and galena (K2.85 ‰V-CDT), and the average temperature of the hydrothermal fluid during the sulfide mineralization episode (272.0 8C) in the related equations proposed by Ohmoto and Rye (1979). These d34S values of H2S are slightly below typical magmatic sulfur values. Either a direct magmatic source,
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depleted in 34S (from granitoid intrusion) or an indirect magmatic source may be assumed, involving leaching of isotopically lighter sulfur, either from the Upper Cretaceous volcano-sedimentary rocks or from a deep-seated older ore deposit. Previously published fluid inclusion and stable isotope results (Go¨kc¸e and Bozkaya, 2003), that suggested hydrothermal fluids contained either magmatic water mixed with small amounts of meteoric water (and/or formation water of meteoric origin) or meteoric water isotopically modified by deep interaction with surrounding magmatic rock, increase the probability of an indirect magmatic source, with leaching from the surrounding rocks. The differences between the d34S values of galena and sphalerites from the same samples are in accordance with isotopic fractionation trends for these two mineral pairs. But the textural characteristics, show that galena precipitated slightly later than sphalerite, and the higher isotope fractionation temperature values (calculated as 343.6 and 378.9 8C using the d34S values of the sphalerite–galena pairs of samples ST-106 and ST-120, and the related equation suggested by Ohmoto and Rye, 1979) compared with the microthermometric homogenization temperatures measured in fluid inclusions (in the range of 212.9–311.1 8C, average; 272.0 8C), which represent the fluid responsible for sulfide mineralization (Go¨kc¸e and Bozkaya, 2003), indicate that these two mineral pairs were not precipitated in equilibrium. Lead isotope data are close to those of a orogene reservoir and are very different from a mantle-related reservoir of the Plumbotectonics Model by Zartman and Haines (1988). These data plot above the Stacey and Kramers (1975) model curves for average crustal Pb-isotope evolution on 207Pb/204Pb vs 206Pb/204Pb and 208Pb/204Pb vs 206 Pb/204Pb diagrams (Fig. 3). These observations mean that the galena Pb was derived from sources with slightly higher than average crustal 238U/204Pb (m) and 232Th/204Pb ratios, similar to the orogenic reservoir proposed by Zartman and Haines (1988). No isotopic evidence was obtained for lead derived from a mantle-related reservoir. Calculated Pb-isotope model ages for these deposits, using the ISOPLOT program of Ludwig (1997), range from 174 to 123 Ma (average; 154G34 Ma) and indicate that the model parameters used in calculations do not exacly correspond to potential sources of lead in the galena samples studied.
Table 2 Lead isotope composition of the analysed samples from Inler Yaylası area Sample
206
Pb/204Pb
2s error
207
Pb/204Pb
2s error
208
Pb/204Pb
2s error
Model238U/204Pb
Model Age (Ma)
ST-101 ST-106 ST-110 ST-111 ST-114 ST-125
18.660 18.669 18.663 18.665 18.639 18.676
0.1 0.1 0.1 0.1 0.1 0.1
15.671 15.691 15.697 15.691 15.672 15.698
0.15 0.15 0.15 0.15 0.15 0.15
38.761 38.838 38.850 38.835 38.771 38.870
0.2 0.2 0.2 0.2 0.2 0.2
9.93 10.0 10.0 10.0 9.94 10.0
123 157 174 160 140 167
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magmatic sources and indicate a possible indirect magmatic source, involving leaching of isotopically lighter sulfur from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit. 206 Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios for galena samples show a narrow range from 18.639 to 18.676, 15.671 to 15.698 and 38.761 to 38.870, respectively. These lead isotope data are close to those of an orogene reservoir and are very different from the mantlerelated reservoir of the Plumbotectonics Model by Zartman and Haines (1988). These data plot above the Stacey and Kramers (1975) model curves on 207Pb/204Pb vs 206Pb/204Pb and 208Pb/204Pb vs 206Pb/204Pb diagrams. In the light of these observations and previously published fluid inclusion and stable isotope results (Go¨kc¸e and Bozkaya, 2003), it may be presumed that the sulfur and lead concentrated in the studied deposits was leached by deep circulated meteoric water, the isotopic composition of which had been modified by the interaction with surrounding magmatic rocks, from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit which contained light magmatic sulfur and orogenic lead derived from a reservoir with higher 238 U/204Pb (m) and 232Th/204Pb ratios compared to average crustal values. A lead source derived from a mantle-related reservoir does not seem to have been involved.
Acknowledgements Fig. 3. Lead isotope composition of galena seperates from the Inler Yaylası Pb–Zn veins.
5. Summary and conclusions Although, sulfur- and lead-isotope and other geochemical data, to identify the composition and origin of the surrounding plutonic and volcano-sedimentary rocks are lacking, which makes it difficult to identify the source of the sulfur and lead in ore veins, the following conclusions may be proposed, using the presently available data. Lead–zinc deposits in the Inler Yaylası area occur in three parallel ore veins displaced by E–W-trending faults. These ore veins are hosted by extensively altered Upper Cretaceous volcano-sedimentary rocks, and a Tertiary granitoid intrusion is located near the area of mineralization. The alteration zone is marked by an assemblage of quartz, limonite, chlorite, clay minerals and epidote. The ore veins contain sphalerite, galena and minor amounts of pyrite, chalcopyrite, fahlore, chalcocite and covellite as ore minerals, and quartz and calcite as gangue. The measured d34S values of galena (K3.9 to K1.7; average K2.85‰V-CDT) and sphalerite (K2.0 to C0.4; average K1.8‰V-CDT) and calculated d34S values of H2S in equilibrium with these minerals (in the range of K2.14 to K0.73 ‰V-CDT) are slightly lower than the values of direct
The Research Foundation of Cumhuriyet University supported this study (Project No: M-194). Thanks are due to Dr Baruch Spiro (Natural History Museum, London, UK) and Dr Greg B. Arehart (Nevada Univ., Isotope Geoch. Lab.) for sulfur isotope analyses. We also thank to Dr Leonid A. Neymark (US Geological Survey) for critical readings and useful comments. Dr David Lowry (Royal Holloway, University of London) provided a helpful review.
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