Geochemical Characteristics of a Veinlet Kupferschiefer Profile from the Lubin Mine, Southwestern Poland

Previous studies have shown that the ascending, oxidizing brines play a very important role in Kupferschiefer mineralization. Fractures could be the pathway of the brines. In order to clarify the influences of the brines on bulk organic matter, aromatic hydrocarbons and Kupferschiefer mineralization, one veinlet Kupferschiefer profile from the Lubin mine, southwestern Poland was studied with the microscopic, geochemical and Rock-Eval methods. The microscopic results indicate that organic matter of the veinlet sample consists dominantly of bitumen. Its extract content is higher than in other samples. The dominant aromatic compounds are naphthalene and alkylated naphthalenes (Na-PAH), which have migrated into the veinlet sample from other sediments. The content of phenanthrene and its methylated derivatives (Ph-PAH) is much lower than in other samples. The reason may be due to their heavier mass than Na-PAH. It is more difficult for Ph-PAH to migrate. The Na-PAH was probably removed from the shale by dist     

The Role of Organic Matter During Metal Enrichment in Permian Kupferschiefer of the Rudna Mine,Southwest Poland

The bulk composition of organic matter and saturated and aromatic hydrocarbons extracted from 16 samples collected from two Kuperschiefer profiles in the Rudna mine,Southwest Poland has been analyzed to study the role of organic matter during base metal enrichment in the Kupferschiefer shale.The results indicated that the extract yields and saturated hydrocarbon yields decreased with increasing base metal contents.GC and GC/MS analyses indicated that n -alkanes and alkylated aromatic compounds were depleted and may have served as hydrogen donators for thermochemical sulfate reduction.The enrichment of base metal is closely connected with the destruction of hydrocarbons.     

Geochemical and isotopic composition of organic matter in the Kupferschiefer of the Polish Zechstein basin: relation to maturity and base metal mineralization

max vs the present depth of the Kupferschiefer, soluble organic matter (SOM) yields, and relative proportions of saturated and aromatic hydrocarbons of the SOM provide evidence for an oxidative alteration of organic matter in highly mineralized Kupferschiefer samples near the Rote F?ule zones. This is confirmed by differences in the composition of the saturated and aromatic hydrocarbon fractions of the soluble organic matter: Saturated hydrocarbons from Rote F?ule samples are dominated by short-chain n-alkanes and higher abundances of pristane and phytane relative to heptadecane (n-C17) and octadecane (n-C18), respectively, compared with samples more distant to the Rote F?ule zone. Compositional changes of the aromatic hydrocarbon fractions with decreasing distance to that zone are characterized by the occurrence of polycyclic aromatic hydrocarbons and elevated ratios of phenanthrene to methylphenanthrenes that are attributed to demethylation reactions and resulted in a decrease of the methylphenanthrene index (MPI 1). Kupferschiefer samples from the barren zone of the Polish Basin do not show these alteration patterns. The observed variations in organic matter composition with burial depth are consistent with changes due to increasing thermal maturation. Maturity assessment is achieved from MPI 1 and the methyldibenzothiophene ratio (MDR). From the relationship between the maturity of organic matter in terms of vitrinite reflectance values and depth of the Kupferschiefer strata, a continuous increase in reflectance of vitrinite is obtained within the Polish Basin. The alteration pattern of organic matter related to base metal mineralization of the Kupferschiefer corresponds to changes in the isotopic composition of organic carbon and calcite. Kerogen within, or close to, Rote F?ule zone is enriched in ¹³C caused by the preferential release of isotopically light organic compounds through progressive degradation of organic matter. The opposite tendency towards lower δ ¹³C and δ ¹⁸O values of calcite provides evidence for isotopic exchange between carbonate and the oxidizing, ore-bearing solutions and for organic matter remineralization. In contrast, organic matter and calcite from the Kupferschiefer do not show regular trends in δ ¹³C with increasing thermal maturation. Received: 25 June 1999 / Accepted: 1 December 1999     

Uranium and thorium in the Kupferschiefer formation,Lower Zechstein,Poland

The Kupferschiefer in Poland has an increased U content. The facies high in organic matter are significantly enriched in U. The maximum values of U are mostly in the lower part of the Kupferschiefer sequence. The mean (x) U content in the Kupferschiefer from the Lubin-Sieroszowice district is 61.5 ppm and from the rest of the Polish Zechstein basin is about 26 ppm. Thorium occurs only in small quantities (x) = 1.5 and 5 ppm respectively). The high variance of U and Th in the Kupferschiefer is due to multistage diagenetic processes. The main U carrier is thucholite. The investigated thucholite showed a Th-content below 0.36 ppm. Thucholite with uraninite exolutions showed small (up to 1.0 wt.%) admixtures of U and thucholite without microscopically visible exsolutions (up to 37.85 wt.% U). The phosphates showed significant amounts of U (up to 0.24 wt.). The U content in the Kupferschiefer is significantly lower than in black shales from other part of the world. Uranium in the Lubin district is not economic.     

Influences of the Basin Brines on Hydrocarbons of the Anthracosia Shales from Southwestern Poland

Previous studies have shown that the oxidizing brines from the Early Permian Rotliegende sequence have influences on the organic matter of Kupferschiefer. However, inside the Rotliegende sequence there are two other black shales: the Lower and Upper Antracosia shales, which have not been studied as much in detail as in Kupferschiefer. In the present study 12 samples from the Lower and Upper Antracosia shales were analyzed by organic geochemical methods in order to clarify the influences of the oxidizing brines on organic matter. The results indicate that the organic matter of the samples from the Upper Antracosia shale and the bottom of the Lower Antracosia shale was oxidized under the influences of the oxidizing brines. The oxidation resulted in a depletion of saturated hydrocarbons and the alky Is of the aromatic compounds.     

滇黔交界地区玄武岩铜矿中有机质的生物标志物特征及其地质意义

滇黔交界地区玄武岩中赋存的自然铜矿化与沥青密切相伴,玄武岩层间含碳沉积岩中的自然铜矿化发育大量碳质。本文采用有机质抽提、族组分定量及饱和烃色-质分析等方法对这两种产状的铜矿石中有机质的族组分含量和生物标志物进行了研究,并对其地质意义进行了探讨。通过研究取得如下认识：①含沥青铜矿石和含碳质铜矿石虽然产状明显不同,其有机质成因有明显差异,但其有机质族组分含量及生物标志物特征十分类似,反映它们经历了类似的地质作用;②有机质族组分及其生物标志物提供的来源信息较混乱,这可能是成矿流体循环改造导致的;③生物标志物特征表明,含沥青铜矿石及含碳质铜矿石中有机质经历了类似的较还原的高盐度环境,这可能是高盐度成矿流体及还原的成矿条件的指示;④生物标志物特征及氯仿沥青“A”低含量特征表明两类铜矿石中有机质成熟度高,这可能是成矿流体的热力对有机质改造的结果;⑤有机质生物标志物特征显示两类铜矿石中有机质生物降解作用不强,表明沥青的形成是原油受成矿热液热力影响发生热裂解的结果。     

Metal accumulation during and after deposition of the Kupferschiefer from the Sangerhausen Basin,Germany

A densely sampled profile (58 cm in thickness) composed of 13 samples of the Kupferschiefer and overlying Zechstein carbonates from the Sangerhausen Basin, Germany has been analysed by various geochemical and microscopic methods in order to clarify the mechanism of base metal accumulation. In this location, the Kupferschiefer is only slightly influenced by the hematite-bearing, oxidized fluids calledRote Fäule.The determination of facies-dependent parameters along the profile indicates that Kupferschiefer from the Sangerhausen Basin was largely deposited in a marine environment; only at the beginning of Kupferschiefer sedimentation did euxinic conditions prevail. The bottom part of the profile is significantly enriched in trace elements such as Cu, Ph, Zn, As, Co, Ag and U. The Cu concentration amounts to 19.88 wt.%. Post-depositional oxidation of the organic matter is observed only in the transition zone between the Kupferschiefer and the Zechstein conglomerate indicating the influence of ascending, oxidizing brines. Microscopic analyses show that only Fe sulfides form framboidal textures; Cu minerals are present along the total profile preferentially in fractures and as patchy structures composed of chalcocite, chalcopyrite and bornite. In the highly mineralized bottom section, Cu sulfides are associated with pyrobitumen, sparry calcite and arsenopyrite. Results from maturation studies of organic matter suggest that the maximum temperature affecting the Kupferschiefer was approximately 130°C.A 3-step-process of metal accumulation is proposed. During deposition of the sediment, framboidal pyrite and pyrite precursors were precipitated by bacterial SO₄²⁻ reduction (BSR). During diagenesis the pyrite and pyrite precursors were largely replaced by mixed Cu/Fe minerals and by chalcocite (PR). In the section with very high Cu contents (> 8%) reduced sulfur from Fe-sulfides was not sufficient for precipitation of Cu and other trace metals from ascending solutions. In this part of the profile, thermochemical SO₄²⁻ reduction (TSR) occurred after pyrite replacement as indicated by the presence of pyrobitumen and sparry calcite.     

Influences of the basin brines on extractable bitumen of Kupferschiefer from southwestern Poland

A study of the influences of the basin brines on hydrocarbon generation of the Kupferschiefer in southwestern Poland has been carried out.The samples from the Konrad and Polkowics mines were analyzed by orgainc geochemical,microscopic and FTIR methods.The results indicate that organic matter of Kupferschiefer tends to decrease with the ascending,oxidizing brines,In the Konrad profile,the Kupferschiefer was strongly oxidized.The extract yields were depleted up to 50mg Ext/g Corg.Gas chromatography(GC) and gas chromatography-mass spctrometry(GC/MS) data indicate that the depletion occureed predominantly in saturated hydrocarbon compounds.The identified n-alkanes in smpale KD1 were depleted at least to 5000μg/g Corg.The aromatic compounds show a fidderent trend of variation.The concentrations of phenanthrene alkylphenanthrenes(Ph-PAH) and naphthalene alkylnaphthalenes(Na-PAH) show a decrease,whereas sulfur polyaromatic hydrocarbons(S-PAH)and oxygen polyaromatic hydrocarbons(O-PAH) show an incrase under the influences of oxidizing brines,In the Polkowice profile,organic matter under the influences of oxidizing fluids shows a simlar trend of varation as in the Konrad mine.Analyses of polar compounds shed light on the oxidation processes at the molecule level.The dominant products of oxidation are aliphatic acid.alcohol and ester.FTIR results indicate that the oxidation of organic matter led to a decrease in aliphatic CH3 and an increase in C-O,C=O bands.     

The Werra cyclotheme (Upper Permian,Fore-Sudetic Monocline,Poland): Insights into fluctuations of the sedimentary environment from organic geochemical studies

A study of the extracts of samples recording a transgressive–regressive succession of the Werra cyclothem, Zechstein (Upper Permian), from the southern margin of the European Permian Basin (the Fore-Sudetic Monocline, Poland) provides an insight into major sources of organic matter and diagenetic processes. The studied cross-section comprises all lithologies representative for the European basin, including transgressive sandstones (Weissliegend) and organic-rich shales (Kupferschiefer) followed by carbonates as well as regressive anhydrites with intercalations of rock salt. Due to the variable influence of overlapping diagenetic processes that affected the organic matter, i.e. maturation and late diagenetic oxidation related to base metal mineralisation, a reliable comparison of the biomarker results is only possible for the major upper part of the section (ca. 38 m, including carbonates and evaporites) but not for the oxidised first 2–3 m from the base of the Kupferschiefer.The transition from carbonate to evaporate sedimentation is associated with a shift to predominant even C-numbered n-alkanes, increased abundance of carotanes and high homohopane index reflecting enhanced reducing conditions. The presence of the C₂₅ regular isoprenoid, squalane, biphytane and the rapid decrease in the pristane/phytane ratio in the evaporites are mainly controlled by the important contribution from both halophilic and methanogenic archaea. The occurrence of gammacerane in the anhydrites suggests development of water column stratification at some stages of the sea regression. This is associated with appearance of specific aryl isoprenoids with a lycopane carbon skeleton most likely related to Botrycoccus braunii race L algae. Lycopane derivative occurrence suggests that such an algal race could have occurred since Permian (currently known Recent-Eocene). The presence of the abundant freshwater/brackish algal biomarkers in evaporititic deposits can be envisaged in the costal part of the Zechstein basin with temporary salt wedge estuary water stratification. The algae bloomed in the top fertile fresh/brackish water layer fed by rivers, and the algal biomass was deposited on the sea floor covered with evaporitic brine. The stratification periodically broke down during precipitation of the rock salt, presumably due to a decrease in riverine water input, as revealed by characteristic disappearance of gammacerane and hopane distributions similar to those observed for the carbonate rocks.The methylphenanthrenes/phenanthrene ratio was used together with methyldibenzothiophenes/ dibenzothiophene ratio to assess maturity. These maturity estimations indicate that the peak of oil window has been reached, which is confirmed by other biomarker maturity parameters based on sterane and hopane distributions. The maturity stage of oil generation and expulsion was further confirmed by the presence of solid bitumen as cements in the sandstone underlying Kupferschiefer and bitumen veins and lenses in the carbonates.     

Comparative studies of organic matter petrography of the late palaeozoic black shales from Southwestern Poland

There are at least two sapropelic units associated with Late Palaeozoic black shales in Central Europe. The older unit, of Late Carboniferous age, is the lower part of the Anthracosia Shales in the Intrasudetic Basin, and the younger one is the well-known Zechstein Kupferschiefer in both the Foresudetic Monocline and the Northsudetic Basin. The first unit is of lacustrine origin, while the second one represents deposition in a shallow marine depositional environment. Both units contain high amounts of organic matter, thus being typical black shales.The organic matter dispersed in these shales was studied petrographically. In general, the vitrinite reflectance of the shales studied indicates variable, but moderate organic matter maturity (0.68–1.25%), equivalent to the oil window. Detailed microscopic studies of the organic material dispersed in the lower unit of the Anthracosia Shales showed that liptinite, especially alginite is the most abundant component. Secondary altered organic matter, i.e. solid hydrocarbons, rarely occurs. Organic components together with mineral matter constitute a lacustrine sapropelic association, a humic (terrestrial) association and an intermediary association. The character and predominance of alginite and lacustrine sapropelic association are indicative of an open-lacustrine depositional environment. In general, this organic composition is typical of type I kerogen.Microscopic analysis of the Kupferschiefer revealed a mixture of liptinite, vitrinite and inertinite macerals, and other organic components such as amorphous sapropelic mass (ASM) and solid bitumens. The most common organic components are liptinite macerals. Bituminite and alginite predominate, and are diagnostic macerals of this unit. The amount of bituminite locally exceeds 85 vol.%. Other liptinite macerals such as sporinite and liptodetrinite, are present in significantly lower amounts, one exception being ASM, which may be present in higher amounts. Humic constituents (vitrinite and inertinite) are rare, present in small amounts in the Kupferschiefer beds. The organic matter composition points to type II kerogen for this unit.     

Geochemical features of re-deposited organic matter occurring in fluvioglacial sediments in the Racibórz region (Poland): A case study

The erosion of rocks rich in organic matter typically leads to the complete mineralization of the organic material. However, in some cases, it is re-deposited to become a part of sediments once more. This process should be considered to be a part of global carbon cycle, possibly much more significant than assumed to-date. The research presented here aims to characterize re-worked organic matter occurring in post-glacial sediments of southern part of Poland, in the Oder river valley (the Racibórz town region, Miocene, Pleistocene and Holocene age). Organic substances extracted from the sediments originated from organic matter that had resided in rocks eroded by glaciers. Sediments were sampled in two boreholes which sediments were correlated. Sediments were extracted and extracts analyzed with gas chromatography-mass spectrometry (GC-MS) to assess distributions of biomarker groups. Organic matter of selected samples was pre-concentrated and analyzed with Py/GC-MS. In the extracts several biomarker parameters of source/environment and thermal maturity were calculated. Organic substances in the investigated sediments come from variable re-deposited organic matter occurring in rocks eroded by glaciers. Three main parent types of re-deposited organic material are identified showing variable geochemical features: 1) organic matter of recent or almost recent age being the source of polar labile compounds; probably formed in situ, 2) re-deposited organic matter of the middle diagenesis showing features similar to lignites (huminite reflectance Rf ~ 0.25–0.35%) deriving from angiosperm remains, mainly monocotyledons and to the lower extend also deciduous trees, 3) re-deposited organic matter at the middle catagenesis (Rf ~ 0.65–0.75%) being the source of most of aromatic hydrocarbons and biomarkers such as steranes, hopanes of the more thermally advanced distribution type. Its geochemical properties and assumed directions of sediment transport indicate bituminous coals of Upper Silesian Coal Basin together with coaly shales as a possible source of this organic matter. Such mixed origin of organic matter caused large discrepancies in values of thermal maturity parameters depending on input from the particular sources and occurrence both geochemical biomarkers and their biochemical precursors in the same samples.     

Accumulation of copper in the Permian Kupferschiefer: A result of post-depositional redox reactions

Within the Central European Zechstein Basin the Permian Kupferschiefer has been deposited under anoxic conditions. In most parts of the basin, the metal content does not exceed values commonly observed in black shales. However, in areas near to the Zechstein sea-shore which are simultaneously related to rift zones a significant base metal enrichment is observed. Organic geochemical analyses of the copper-mineralized sections in the Kupferschiefer from Southwest Poland show that significant changes in the composition of organic matter are associated with the metal enrichment processes. Porphyrins, commonly abundant constituents of the shale, have been decomposed by oxidizing fluids. Additionally, aliphatic hydrocarbons have been largely removed from the bitumen and alkylated aromatic systems were affected by side-chain degradation. This particular type of alteration is explained by ascending oxidizing solutions which transported high amounts of base metals from Lower Permian red beds into the Kupferschiefer horizon acting as a geochemical trap. The metal precipitation is suggested to be a result of thermochemical sulphide production with organic matter acting as hydrogen source. In areas such as the Lower Rhine Basin in the bottom section of the Kupferschiefer the base metals lead and zinc as well as barium have been accumulated from basinal Carboniferous formation waters. Copper enrichment is not observed because potential source rocks are missing in this area. However, the observed compositional changes of the organic matter do not point towards thermochemical redox processes.     

Relationship of polycyclic aromatic sulfur compounds and gold enrichment in the Kupferschiefer from Poland and Germany

1INTRODUCTION ORGANICALLY BOUNDSULFURCOMPOUNDSWEREPREVI OUSLYDETECTEDINTHEKUPFERSCHIEFER(P櫣TTMANNAND GO EL,1990;ROSPONDEKETAL.,1994).P櫣TTMANN ANDGO EL(1990)INVESTIGATEDTHEEXTRACTABLEORGANIC MATTERINTHEKUPFERSCHIEFERFROMTHENORTH SUDETIC SYNCLINEANDPROPOS…     

Hydrogeochemical characteristics of mine water in the Harz Mountains,Germany

Water samples (springs, creeks, mine adits) from different former mining districts of the Harz Mountains and the nearby Kupferschiefer (copper shale) basin of Sangerhausen were analysed for major ions and trace metals. Due to more intensive water rock interactions including the ore minerals, the mine water concentrations of main components and trace metals are generally higher compared to non mining affected surface waters of the mountain range. Furthermore, the content of major ions in mine water is enriched by mixing processes with saline waters from Permian layers in the Kupferschiefer district and at the deeper levels of the mines in the Upper Harz Mountains. The waters of the different mining districts can be distinguished by trace metal occurrences and concentrations derived from the different ore bodies. Water from the Kupferschiefer mines shows the highest Na, Cl, Cu, Mo and U concentrations, whereas a combination of elevated As and Se concentrations is typical for most of the samples from the mines around St. Andreasberg. However, there are exceptions, and some water samples of all the investigated mining districts do not follow these general trends. Despite the influence of mining activities and ore mineralisation, hydrochemical effects due to rain water dilution can be seen in most of the waters. According to the elevation of the mountain range, higher precipitation rates decrease the ion concentrations in the waters of springs, creeks and mine adits.     

甘肃省阳山超大型金矿床的有机地球化学特征研究

甘肃省文县阳山金矿是我国地质勘查储量最大的卡林-类卡林型金矿床,赋矿地层为泥盆系一套碳-硅-泥质地层.矿区发育了大量碳质千枚岩,富含有机碳.本文研究了矿石和围岩可溶有机质的生物标志物、有机质的来源和成熟度、干酪根的碳同位素等,论述了阳山金矿床的有机地球化学特征及有机质与成矿的关系,查明了参与成矿的有机质主要是菌藻类等低等生物.生物标志化合物参数和干酪根的H/C-O/C原子比值指示阳山金矿有机质成熟度较高,达到了无烟煤的演化阶段.在热演化的过程中,有机质裂解产生的CH_4和C-2H_6等进入成矿流体中,参与了成矿过程.阳山金矿赋矿地层中含有生物成因的草莓状黄铁矿,显示生物-有机质参与了地层的预富集作用.有机碳含量、有机质的类型和金的丰度之间相关性不明显,说明在阳山金矿的成矿过程中有机质对金的沉淀贡献不大,但是有机质可能参与了金的预富集和运移.     

Biomarker geochemistry of marine organic matter in the Hushan and Chaohu areas,Lower Yangtze region

Marine strata are widely exposed in the Hushan and Chaohu areas, Lower Yangtze region. As biomarker geochemistry of the strata has not been well documented, this paper deals with the biomarker composition of representative samples collected from the Silurian, Carboniferous and Triassic systems and their geological implications, thus providing clues to marine organic matter. On the basis of experimental results, it is shown that abundant biomarkers (e.g. n-alkanes, isoprenoids, terpanes and steranes) were detected. As organic matter in the strata is highly to over mature in general based on petrologic microobservation, some biomarkers (mainly n-alkanes) except terpanes and steranes cannot reflect the source, depositional environment and maturity of organic matter. Thus, primarily based on analyses of the terpanes and steranes, it is suggested that organic matter in the Silurian and Carboniferous strata is derived mainly from lower organisms, while higher plants are predominant in the Triassic organic matter. This further indicates that the depositional environment may have transformed from the marine to continental facies in the Late Triassic. These results provide new evidence for the study of regional depositional evolution, and have enriched the study of biological composition of organic matter. In addition, the biomarker geochemistry of organic matter at high to over maturation stage is addressed.     

The origin of rhythmic sulphide bands from the Permian sandstones (Weissliegendes) in the footwall of the Fore-Sudetic “Kupferschiefer” (Poland)

Rhythmic copper sulphide bands occur in the Weissliegendes sandstones, in the footwall of the Kupferschiefer in the mining district of SW Poland. The δ ³⁴S values of sulphides vary from −39 to — 44‰ (6–7‰ lighter than Kupferschiefer sulphides). The copper sulphides are represented mainly by digenite and chalcocite. According to microprobe results their Pb, Ni, Zn and Ag contents are similar to those in the Kupferschiefer. The bands are assumed to be formed by diffusion of bacterially produced hydrogen sulphide from the Kupferschiefer into the porous volume of the white sandstones containing dissolved copper. The sulphides were precipitated in almost equidistant bands, from top to bottom, probably according to the Ostwald-Prager supersaturation theory. The increase of isotopically heavier sulphur towards the lower levels in the sandstone might be explained by closing of the bacterial sulphate reduction system. Contribution to the IGCP Project No. 254     

Organic geochemistry and petrography of Lower Cretaceous Wealden black shales of the Lower Saxony Basin: The transition from lacustrine oil shales to gas shales

Ninety-seven Wealden black shale samples from three wells in the Lower Saxony Basin have been studied by organic geochemical and organic petrographical methods to determine their maturity, organic facies and depositional environment. The maturities of the three wells range from early mature (Ex-A), late to postmature (Ex-C) to overmature (Ex-B) as determined by vitrinite reflectance measurements, diamondoid ratios and other geochemical maturity parameters. Ex-C and Ex-B show distinct petrographic features related to oil generation and migration. In particular, the occurrence of dispersed solid bitumen replacing initial type I kerogen suggests a formerly active petroleum system. Structural and textural differences between early mature alginites and solid bitumen in postmature to overmature samples show an alteration of the pore system with increasing maturity. A freshwater depositional environment is indicated by widespread occurrence of botryococcus algae and other small alginite particles predominating in the immature well. These alginites are absent in the more mature gas shales of wells Ex-C and Ex-B. Geochemical evidence of algae and phytoplankton in general is provided by numerous biomarker parameters, while the occurrence of β-carotane in some samples indicates events of increased salinity, although no hypersaline conditions are inferred due to very low gammacerane indices. Increased amounts of vitrinite and inertinite in samples of Ex-B suggest locally significant terrigenous input of organic matter for some periods during Wealden Shale deposition. High sulfur/organic carbon ratios provide evidence for sulfate rich waters and (partly) anoxic bottom water conditions. While the lower mature lacustrine source rocks generate paraffinic/waxy oils, gas and condensates are produced at post-mature stages. Furthermore, maturity distribution maps from 3D numerical petroleum systems modeling reveal substantial differences in respect to petroleum generation.     

Organic geochemical evaluation of Cretaceous shale samples from the Orange Basin,South Africa

Organic geochemical evaluation of thirty-two Aptian to Campanian shale samples from seven wells drilled on the shelf of the Orange Basin (southwestern Atlantic margin) was carried out in order to determine their origin, depositional environment, thermal maturity and hydrocarbon potential. The shale samples, selected to represent highstand, lowstand and transgressive systems tracts, were analysed by Rock–Eval pyrolysis for total organic C characteristics and by gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) for n-alkanes, aliphatic isoprenoid hydrocarbons and biomarkers (steranes, hopanes and tricylic terpanes). For most of the shale samples Rock–Eval data, hydrogen (HI) and oxygen index (OI) point to mainly Type III terrigenous organic matter. Only a few samples of Turonian age reveal a higher proportion of marine organic matter being classified as Type II/III or Type II. Biomarker parameters suggest that the samples are deposited under suboxic to oxic environmental conditions. Rock–Eval data and biomarker maturity parameters assign for most of the samples a maturity level at the beginning of the oil window with some more mature samples of Aptian, Albian and Cenomanian age. The hydrocarbon generation potential is low for most of the shelf shales as indicated by the S2/S3 ratio and HI values. Exceptions are some samples of Turonian and Aptian age.     

Georadiochemical evidence to weathering of mining residues of the Mansfeld mining district,Germany

Mining heaps are used as archives for the investigation of weathering processes. Aim of this work was to investigate the different weathering behavior of heap materials derived from Kupferschiefer mining with respect to environmental hazard. For this purpose, Kupferschiefer and slag material of two heaps of different age were examined regarding to the radionuclide distribution and geochemical composition. By measuring of the local dose rate, performing digital autoradiography and gamma spectrometry the radiological load of the heaps and the heap materials was determined. The geochemical characterization of the samples was performed by XRF, ICP–OES and ICP–MS. The results show a clear higher radionuclide load of the younger slag heap. A depletion of chalcophile and lithophile elements in the older slag was determined. Apart from a homogeneous radionuclide distribution, considerable radionuclide enrichments in fossil fragments could be proven. The results reveal a different weathering behavior of slag material in comparison to the Kupferschiefer depending on the chemical binding of the elements on organic and inorganic species. Natural organic matter as well as apatite in Kupferschiefer act as retention barrier for some metals.