Energy & Fuels 2001, 15, 817-829
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Oxidation of Organic Matter in the Transition Zone of the Zechstein Kupferschiefer from the Sangerhausen Basin, Germany Yu-Zhuang Sun*,†,‡ and Wilhelm Pu¨ttmann§ Hebei Institute of Architectural Science and Technology, 056038 Handan, Hebei, P. R. China, and Johann Wolfgang Goethe-Universitaet Frankfurt, FB 17 Geowissenschaften-Umweltanalytik, Georg-Voigt-Str. 14, D-60054 Frankfurt a. M., Germany Received October 5, 2000
Thirteen samples of the Permian Kupferschiefer (Sangerhausen Basin, Germany) were studied by microscopy, stable isotope analysis, Rock-Eval analysis, Fourier transform infrared (FT-IR) spectroscopy, and additional geochemical methods in order to understand the oxidation processes of organic matter in a profile of mineralized Kupferschiefer. Relatively intense oxidation occurred at the bottom of the profile, where bitumens were oxidized by ascending brines, and altered to pyrobitumen and “kir” bitumen. Because of organic matter oxidation Corg-values, extract yields, and HI values decrease at the bottom of the profile. The oxidation resulted in release of δ12Crich organic constituents and enrichment of the residual organic matter in δ13C organic carbon in the extracts of the oxidized Kupferschiefer. In the bottom sample, major IR absorption bands between 1207 and 900 cm-1 (C-O-C, C-O-H) were caused by oxidation of saturated hydrocarbons. A reduced absorption at 2955-2869 cm-1 relative to less oxidized samples indicates oxidation of aliphatic compounds. The intensity of the carbonyl band at 1700 cm-1 (CdO) relative to the band at 1600 cm-1 (CdC) decreases from the bottom to the top of the profile, indicating a preferential oxidation in the bottom part of the profile. Results from the analysis of extracts by gas chromatography-mass spectrometry (GC-MS) indicate that these major absorption bands are due to the oxidation of long-chain saturated hydrocarbons and alkylated aromatic hydrocarbons. The oxidation products from alkylated aromatic compounds include naphthalene, biphenyl, phenanthrene, and dibenzofuran. The oxidation products of saturated hydrocarbons include aliphatic acids, alcohols, and esters. The oxidation may have occurred after Kupferschiefer deposition.
1. Introduction Kupferschiefer mineralization has been studied for many years.1-3 The importance of oxidizing brines for copper mineralization in the Kupferschiefer has been documented in previous studies.4-6 In several studies, the metal accumulation process has been attributed to a single event during sedimentation.1,7 Large et al.8 * Author to whom correspondence should be addressed. † Hebei Institute of Architectural Science and Technology. ‡ Present address: Basin and Reservoir Research Center, University of Petroleum, Beijing, Shuiku Road, Changping, Beijing, 102200, P. R. China. § Johann Wolfgang Goethe-Universitaet Frankfurt. (1) Wedepohl, K. H. Soc. Mining Geol. Jpn.; IMA-IAGOD Spec. Issue 1971, 3, 263-273. (2) Jowett, E. C. Econ. Geol. 1986, 81, 1823-1837. (3) Pu¨ttmann, W.; Merz, C.; Speczik, S. Appl. Geochem. 1989, 4, 151-161. (4) Pu¨ttmann, W.; Heppenheimer, H.; Diedel, R. Org. Geochem. 1990, 16, 1145-1156. (5) Rentzsch, J. Zbl. Geol. Palaeont. 1991, Teil 1, 945-956. (6) Cathles, L. M., III; Oszczepalski, S.; Jowett, E. C. Econ. Geol. 1993, 88, 948-956. (7) Haranczyk, C. In Geology and Metallogeny of Copper Deposits; Friedrich, G., Genlin, A. D., Naldrett, A. J., Ridge, J. D., Sillitoe, R. H., Vokes, F. M., Eds.; Springer-Verlag: Heidelberg, 1986; pp 461476. (8) Large, D. J.; MacQuaker, D. J.; Vaughan, D. J.; Sawlowicz, Z.; Gize, A. P. Econ. Geol. 1995, 90, 2143-2155.
studied the Kupferschiefer of southwest Poland and suggested that some of the copper was concentrated at low temperatures during early diagenesis. On the other hand, Jowett,2 Pu¨ttmann et al.,3,4,9 and Cathles et al.6 argued that the oxidizing brines and significant copper enrichment occurred during the late diagenesis or epigenesis of the Kupferschiefer, and introduced metals into the Kupferschiefer from the Rotliegend sediments. This secondary organic matter oxidation was proposed to mediate copper accumulation by the Kupferschiefer.3,5,6 The oxidation of organic matter in Kupferschiefer has (9) Pu¨ttmann, W.; Merz, C.; Speczik, S. Zbl. Geol. Palaeont. 1991, Teil 1, 957-974. (10) Kucha, H. Tschermaks Min. Petr. Mitt. 1981, 28, 1-16. (11) Hammer, J.; Roesler, S.; Gleisberg, B. Chem. Erde 1988, 48, 61-78. (12) Sawlowicz, Z. Mineral. Pol. 1989, 20, 69-89. (13) Sawlowicz, Z. Mineral. Pol. 1991, 22, 49-68. (14) Sawlowicz, Z. In Bitumens in Ore Deposits; Parnell, J., Kucha, H., Landais, P., Eds.; Special Publication of the Society for Geology Applied to Mineral Deposits, 1993; Vol. 9, pp 431-446. (15) Oszczepalski, S.; Rydzewski, A. Zbl. Geol. Palaent. 1981, Teil I, H.4, 975-999. (16) Oszczepalski, S. Geological Quarterly 1994, 38, 651-672. (17) Bechtel, A.; Gratzer, R.; Pu¨ttmann, W.; Oszczepalski, S. Int. J. Earth Sci. 2000, 89, 72-89.
10.1021/ef0002187 CCC: $20.00 © 2001 American Chemical Society Published on Web 05/02/2001
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Energy & Fuels, Vol. 15, No. 4, 2001
Sun and Pu¨ ttmann
the Lubin district, southwest Poland10,12,13,19 and Sangerhausen Basin.11 Organic geochemical methods have been used by Pu¨ttmann et al.3,4,18 on oxidized samples from Poland and Germany. Kucha,10,20 Speczik and Pu¨ttmann,21 and Wolf et al.22 studied preferentially kerogen in Kupferschiefer by microscopy. Bechtel and Pu¨ttmann23 analyzed oxidized samples by isotopic methods. In the present study, these methods were combined to clarify the oxidation processes in the weakly oxidized Kupferschiefer from the transition zone in the Sangerhausen Basin, Germany. Figure 1. Location map of the Sangerhausen Basin, Germany (after Borg).50
Figure 2. Lithological profile of the Kupferschiefer section, Sangerhausen Basin.49
been investigated in many studies.3,4,10-17 Most of the studies, however, have concentrated on the strongly oxidized Kupferschiefer in the so-called Rote Fa¨ ule. The Rote Fa¨ ule is a hematitic red zone,5 adjacent or crosscutting the Kupferschiefer horizon. In some areas, however, the Kupferschiefer section was not influenced by Rote Fa¨ ule and consequently the degree of oxidation must have been low (transition facies11). Previously, only a few samples of Kupferschiefer transition facies have been studied geochemically by Hammer et al.11 The transition zone was for the first time microscopically identified by Oszczepalski and Rydzewski15 and was further recognized by Oszczepalski.16 To clarify the oxidation processes in Kupferschiefer from the transition facies, nine Kupferschiefer samples (T1) and four Zechstein carbonate samples (Ca1) were selected in a 0.58 m profile from the Niederroeblingen mine, Sangerhausen Basin (Figures 1 and 2). Rote Fa¨ ule is not observed in this profile. In previous studies, FT-IR has been performed on the highly mineralized Kupferschiefer and Rote Fa¨ ule from
2. Analytical Methods The sample material has been described by Sun and Pu¨ttmann.24 Maceral and ore mineral investigations were carried out on polished blocks. The reflected light microscope was a Leitz MPV2 with a halogen lamp (oil 32/0.65, 548 nm, 3 × 3 µm, EMI9592 S-11). The organic carbon content (Corg) of finely ground (
