Progression in sulfur isotopic compositions from coal to fly ash: Examples from single-source combustion in Indiana

Sulfur occurs in multiple mineral forms in coals, and its fate in coal combustion is still not well understood. The sulfur isotopic composition of coal from two coal mines in Indiana and fly ash from two power plants that use these coals were studied using geological and geochemical methods. The two coal beds are Middle Pennsylvanian in age; one seam is the low-sulfur (< 1%) Danville Coal Member of the Dugger Formation and the other is the high-sulfur (> 5%) Springfield Coal Member of the Petersburg Formation. Both seams have ash contents of approximately 11%. Fly-ash samples were collected at various points in the ash-collection system in the two plants. The results show notable difference in δ³⁴S for sulfur species within and between the low-sulfur and high-sulfur coal. The δ³⁴S values for all sulfur species are exclusively positive in the low-sulfur Danville coal, whereas the δ³⁴S values for sulfate, pyritic, and organic sulfur are both positive and negative in the high-sulfur Springfield coal. Each coal exhibits a distinct pattern of stratigraphic variation in sulfur isotopic composition. Overall, the δ³⁴S for sulfur species values increase up the section in the low-sulfur Danville coal, whereas they show a decrease up the vertical section in the high-sulfur Springfield coal. Based on the evolution of δ³⁴S for sulfur species, it is suggested that there was influence of seawater on peat swamp, with two marine incursions occurring during peat accumulation of the high-sulfur Springfield coal. Therefore, bacterial sulfate reduction played a key role in converting sulfate into hydrogen sulfide, sulfide minerals, and elemental sulfur. The differences in δ³⁴S between sulfate sulfur and pyritic sulfur is very small between individual benches of both coals, implying that some oxidation occurred during deposition or postdeposition.The δ³⁴S values for fly ash from the high-sulfur Springfield coal (averaging 9.7‰) are greatly enriched in ³⁴S relative to those in the parent coal (averaging 2.2‰). This indicates a fractionation of sulfur isotopes during high-sulfur coal combustion. By contrast, the δ³⁴S values for fly-ash samples from the low-sulfur Danville coal average 10.2‰, only slightly enriched in ³⁴S relative to those from the parent coal (average 7.5‰). The δ³⁴S values for bulk S determined directly from the fly-ash samples show close correspondence with the δ³⁴S values for SO₄^− 2 leached from the fly ash in the low-sulfur coal, suggesting that the transition from pyrite to sulfate occurred via high-temperature oxidation during coal combustion.     

Isotopic and molecular composition of coal-bed gas in the Amasra region (Zonguldak basin—western Black Sea)

Previous studies on the coal-bed methane potential of the Zonguldak basin have indicated that the gases are thermogenic and sourced by the coal-bearing Carboniferous units. In this earlier work, the origin of coal-bed gas was only defined according to the molecular composition of gases and to organic geochemical properties of the respective source rocks, since data on isotopic composition of gases were not available. Furthermore, in the western Black Sea region there also exist other source rocks, which may have contributed to the coal-bed gas accumulations. The aim of this study is to determine the origin of coal-bed gas and to try a gas-source rock correlation. For this purpose, the molecular and isotopic compositions of 13 headspace gases from coals and adjacent sediments of two wells in the Amasra region have been analyzed. Total organic carbon (TOC) measurements and Rock-Eval pyrolysis were performed in order to characterize the respective source rocks. Coals and sediments are bearing humic type organic matter, which have hydrogen indices (HI) of up to 300 mgHC/gTOC, indicating a certain content of liptinitic material. The stable carbon isotope ratios (δ¹³C) of the kerogen vary from −23.1 to −27.7‰. Air-free calculated gases contain hydrocarbons up to C₅, carbon dioxide (<1%) and a considerable amount of nitrogen (up to 38%). The gaseous hydrocarbons are dominated by methane (>98%). The stable carbon isotope ratios of methane, ethane and propane are defined as δ¹³C₁: −51.1 to −48.3‰, δ¹³C₂: −37.9 to −25.3‰, δ¹³C₃: −26.0 to −19.2 ‰, respectively. The δD₁ values of methane range from −190 to −178‰. According to its isotopic composition, methane is a mixture, partly generated bacterially, partly thermogenic. Molecular and isotopic composition of the gases and organic geochemical properties of possible source rocks indicate that the thermogenic gas generation took place in coals and organic rich shales of the Westphalian-A Kozlu formation. The bacterial input can be related to a primary bacterial methane generation during Carboniferous and/or to a recent secondary bacterial methane generation. However, some peculiarities of respective isotope values of headspace gases can also be related to the desorption process, which took place by sampling.     

Molecular and carbon isotopic analysis of individual biological markers: evidence for sources of organic matter and paleoenvironmental conditions in the Upper Ordovician Maquoketa Group, Illinois Basin, U.S.A.

Variations in the carbon isotopic composition (δ¹³C) of pristane, phytane, n-heptadecane (n-C₁₇), C₂₉ ααα 20R sterane, and aryl isoprenoids provide evidence for a diverse community of algal and bacterial organisms in organic matter of the Upper Ordovician Maquoketa Group of the Illinois Basin. Carbon isotopic compositions of pristane and phytane from the Maquoketa are positively covariant (r = 0.964), suggesting that these compounds were derived from a common source inferred to be primary producers (algae) from the oxygenated photic zone. A variation of 3‰ in δ¹³C values (−31 to −34‰) for pristane and phytane indicates that primary producers utilized variable sources of inorganic carbon. Average isotopic compositions of n-C₁₇ (−32‰) and C₂₉ ααα 20R sterane (−31‰) are enriched in ¹³C relative to pristane and phytane (−33‰) suggesting that these compounds were derived from a subordinate group of primary producers, most likely eukaryotic algae. In addition, a substantial enrichment of ¹³C in aryl isoprenoids (−14 to −18‰) and the identification of tetramethylbenzene in pyrolytic products of Maquoketa kerogen indicate a contribution from photosynthetic green sulfur bacteria to the organic matter. The presence of anaerobic, photosynthetic green sulfur bacteria in organic matter of the Maquoketa indicates that anoxic conditions extended into the photic zone.The δ¹³C of n-alkanes and the identification of an unusual suite of straight-chain n-alkylarenes in the m/z 133 fragmentograms of Ordovician rocks rich in Gloeocapsomorpha prisca (G. prisca) indicate that G. prisca did not contribute to the organic matter of the Maquoketa Group.     

Geochemistry of Sulfur and Hazardous Elements in Late Paleozoic Coals and Partings from Taozao Coalfield, Shandong Province, China

Intermsoftheharmfulmattersincoalandcoalminingwastes,thefirstisabouthazardouselements ,theotherin cludessulfurandhazardousorganicmatter.Muchresearchontracetoxicelementsandtheirimpactsonenvironmenthasbeeninvestigatedinmanycountries (Goodarzi,1995 ;Finkelman ,1994 ;Chouetal.,1982 ) .Althoughthere searchconcerningthisaspectwasstartedmuchlaterinChi na ,manystudieshavebeenstrengthenedsince 1980 ,andmuchprogresshasbeenmade ,alargenumberofdatahavebeencollected ,andthecomparisonshavebeenmadeforthedata…     

Sulphur and carbon isotopic composition of power supply coals in the Pannonian Basin, Hungary

The present work is an attempt to establish the stable isotope database for Mesozoic to Tertiary coals from the Pannonian Basin, Hungary. Maceral composition, proximate analysis, sulphur form, sulphur isotopes (organic and pyritic), and carbon isotopes were determined. This database supports the assessment of the environmental risks associated with energy generation, the characterization of the formation and the distribution of sulphur in the coals used.The maceral composition, the sulphur composition, the C, S isotopic signatures, and some of the geological evidences published earlier show that the majority of these coals were deposited in freshwater and brackish water environments, despite the relatively high average sulphur content. However, the Upper Cretaceous, Eocene, and Lower Miocene formations also contain coal seams of marine origin, as indicated by their maceral composition and sulphur and carbon chemistry.The majority of the sulphur in these coals occurs in the organic form. All studied sulphur phases are relatively rich in ³⁴S isotopes (δ³⁴S_organic = + 12.74‰, δ³⁴S_pyrite = + 10.06‰, on average). This indicates that marine bacterial sulphate reduction played a minor role in their formation, in the sense that isotopic fractionation was limited. It seems that the interstitial spaces of the peat closed rapidly during early diagenesis due to a regime of high depositional rate, leading to a relative enrichment of the heavy sulphur isotopes.     

Geological and Isotopic Constraints on the Metallogenic Evolution of the Proterozoic Sediment-Hosted Pb-Zn (Ag) Deposits of Brazil

Integrated studies of seven Proterozoic sediment-hosted, Pb-Zn-Ag sulfide deposits of Brazil, permit the estimation of the age of the hosting sequence and the mineralization, the nature of the sulfur and metal sources, the temperature range of sulfide formation and the environment of deposition. These deposits can be classified into three groups, according to their ages. (a) Archean to Paleoproterozoic: the Boquira deposit, in Bahia state, consists of stratiform massive and disseminated sulfides hosted by parametamorphic sequences of grunnerite-cummingtonite+magnetite that represent a silicate facies of the Boquira Formation (BF). Lead isotope data of galena samples indicate a time span between 2.7 and 2.5 Ga for ore formation, in agreement with the stratigraphic position of the BF. The relatively heavy sulfur isotope compositions for the disseminated and stratiform sulfides (+8.3 to +12.8 ‰ CDT)suggest a sedimentary source for the sulfur. (b) Paleo to Mesoproterozoic: stratiform and stratabound sulfides in association with growth faults are present in the Canoas mine (Ribeira, in Paraná state) and in the Caboclo mineralization (Bahia state). They are hosted by calcsilicates and amphibolites in the Canoas deposit, whereas in the Caboclo area the mineralization is associated with hydrothermally altered dolarenites at the base of the 1.2 Ga Caboclo Formation. The interpreted Pb-Pb age of the Canoas mineralization is coeval with the 1.7 Ga host rocks. Sulfur isotopic data for Canoas sulfides (+1.2 to +16 ‰ CDT) suggest a sea water source for the sulfur. The range between −21.1 and +8.8 ‰ CDT for the Caboclo sulfides could suggest the action of bacterial reduction of seawater sulfates, but this interpretation is not conclusive. (c) Neoproterozoic: stratiform and stratabound sulfide deposits formed during the complex diagenetic history of the host carbonate rocks from the Morro Agudo (Bambui Group), Irecê and Nova Redenção (Una Group), yield heavy sulfur isotope values (+18.9 to +39.4 ‰ CDT). The uniform heavy isotope composition of the barites from these deposits (+25.1 to +40.9 ‰) reflect their origin from Neoproterozoic seawater sulfates. The late-stage, and most important, metallic concentrations represent sulfur scavenged from pre-existing sulfides or from direct reduction of evaporitic sulfate minerals. Lead isotope data from the Bambui Group suggest focused fluid circulation from diverse Proterozoic sediment sources, that probably was responsible for metal transport to the site of sulfide precipitation. (d) Late Proterozoic to Early Paleozoic: lead-zinc sulfides (+pyrite and chalcopyrite) of Santa Maria deposits, in Rio Grande do Sul, form the matrix of arkosic sandstones and conglomerates, and are closely associated with regional faults forming graben structures. Intermediate volcanic rocks are intercalated with the basal siliciclastic members. Lead isotope age of the mineralization (0.59 Ga) is coeval with the host rocks. Sulfur isotopic values between −3.6 and +4.1 are compatible with a deep source for the sulfur.Geological, petrographic and isotopic data of the deposits studied suggest that they were formed during periods of extensional tectonics. Growth faults or reactivated basement structures probably were responsible for localized circulation of metal-bearing fluids within the sedimentary sequences. Sulfides were formed by the reduction of sedimentary sulfates in most cases. Linear structures are important controls for sulfide concentration in these Proterozoic basins.     

Isotopic evidence for the origin of sulfur in the Herrin (no. 6) coal member of Illinois

The sulfur isotopic composition of the Herrin (No. 6) Coal from several localities in the Illinois Basin was measured. The sediments immediately overlying these coal beds range from marine shales and limestones to non-marine shales. Organic sulfur, disseminated pyrite, and massive pyrite were extracted from hand samples taken in vertical sections.The $\text{δ}{}^{34}\text{S}$ values from low-sulfur coals (< 0.8% organic sulfur) underlying nonmarine shale were +3.4 to +7.3%₀ for organic sulfur, +1.8 to +16.8%₀ for massive pyrite, and +3.9 to +23.8%₀ for disseminated pyrite. In contrast, the $\text{δ}{}^{34}\text{S}\text{values from high-sulfur coals}$ (> 0.8% organic sulfur) underlying marine sediments were more variable: organic sulfur, ?7.7 to +0.5%₀, pyrites, ?17.8 to +28.5%₀. In both types of coal, organic sulfur is typically enriched in ³⁴S relative to pyritic sulfur.In general, δ ³⁴S values increased from the top to the base of the bed. Vertical and lateral variations in δ ³⁴S are small for organic sulfur but are large for pyritic sulfur. The sulfur content is relatively constant throughout the bed, with organic sulfur content greater than disseminated pyrite content. The results indicate that most of the organic sulfur in high-sulfur coals is derived from post-depositional reactions with a ³⁴S-depleted source. This source is probably related to bacterial reduction of dissolved sulfate in Carboniferous seawater during a marine transgression after peat deposition. The data suggest that sulfate reduction occurred in an open system initially, and then continued in a closed system as sea water penetrated the bed.Organic sulfur in the low-sulfur coals appears to reflect the original plant sulfur, although diagenetic changes in content and isotopic composition of this fraction cannot be ruled out. The wide variability of the δ ³⁴S in pyrite fractions suggests a complex origin involving varying extents of microbial H₂S production from sulfate reservoirs of different isotopic compositions. The precipitation of pyrite may have begun soon after deposition and continued throughout the coalification process.     

The stable isotope geochemistry of Australian coals

D/H, ¹³C/¹²C, ¹⁸O/¹⁶O and ³⁴S/³²S ratios in the organic matrix and organic solvent extracts of Australian coals, and in the fluids and minerals associated with these coals, are reported and reviewed against similar isotopic data for coals from other regions.Where coals are immature, original isotopic differences between macrolithotypes, and between solvent extracts (lipid concentrates) and insoluble residues, are largely preserved. However, with increasing maturity these characteristic differences, particularly those between macrolithotypes, are rapidly erased. Conversely, where, as indicated by low total sulfur contents, coals of Cretaceous to Permian age were deposited under essentially freshwater conditions, δ³⁴S values^* for the organically-bound sulfur remain remarkably constant at +4 ± 3‰ relative to meteoritic sulfur. In similar, younger Tertiary coals, the organic sulfur is markedly enriched in ³⁴S.Five distinctive isotopic patterns, which may be interpreted in terms of the environment of sulfate reduction, can be recognized from ³⁴S/³²S ratio measurements on the various forms of sulfur in Australian coals.Isotopic studies of seam gas hydrocarbons collected in situ show these to be unexpectedly strongly depleted in the heavier isotopes of hydrogen and carbon relative to natural gases from proposed humic sources. Furthermore, no pronounced increase in the ¹³C content in methane with increase in rank of the parent coal was observed. In addition, several sources of associated carbon dioxide have been delineated, including normal maturation processes, invasion of the seams by magnetic carbon dioxide, and interaction of the coal with intrusive magma.Isotopic exchange between free seam gases is not accepted as an explanation for some unusual isotopic fractionations seen, rather the data suggest that these gases may be formed in a state approaching isotopic equilibrium. This argument also satisfactorily explains the isotopic compositions of primary siderite and secondary calcite associated with bituminous coal seams. However, where seams are invaded and permeated with externally derived carbon dioxide, usually of magnetic origin, carbonates are frequently absent, presumably as a result of the action of carbonic acid.     

Carbon isotopes of Middle–Lower Jurassic coal-derived alkane gases from the major basins of northwestern China

Coal-derived hydrocarbons from Middle–Lower Jurassic coal-bearing strata in northwestern China are distributed in the Tarim, Junggar, Qaidam, and Turpan-Harmi basins. The former three basins are dominated by coal-derived gas fields, distributed in Cretaceous and Tertiary strata. Turpan-Harmi basin is characterized by coal-derived oil fields which occur in the coal measures. Based on analysis of gas components and carbon isotopic compositions from these basins, three conclusions are drawn in this contribution: 1) Alkane gases with reservoirs of coal measures have no carbon isotopic reversal, whereas alkane gases with reservoirs not of coal measures the extent of carbon isotopic reversal increases with increasing maturity; 2) Coal-derived alkane gases with high δ¹³C values are found in the Tarim and Qaidam basins (δ¹³C₁: − 19.0 to − 29.9‰; δ¹³C₂: − 18.8 to − 27.1‰), and those with lowest δ¹³C values occur in the Turpan-Harmi and Junggar basins (δ¹³C₁: − 40.1 to − 44.0‰; δ¹³C₂: − 24.7 to − 27.9‰); and 3) Individual specific carbon isotopic compositions of light hydrocarbons (C_5–8) in the coal-derived gases are lower than those in the oil-associated gases. The discovered carbon isotopic reversal of coal-derived gases is caused by isotopic fractionation during migration and secondary alteration. The high and low carbon isotopic values of coal-derived gases in China may have some significance on global natural gas research, especially the low carbon isotope value of methane may provide some information for early thermogenic gases. Coal-derived methane typically has much heavier δ¹³C than that of oil-associated methane, and this can be used for gas–source rock correlation. The heavy carbon isotope of coal-derived ethane is a common phenomenon in China and it shed lights on the discrimination of gas origin. Since most giant gas fields are of coal-derived origin, comparative studies on coal-derived and oil-associated gases have great significance on future natural gas exploration in the world.     

From in-situ coal to fly ash: a study of coal mines and power plants from Indiana

This paper presents data on the properties of coal and fly ash from two coal mines and two power plants that burn single-source coal from two mines in Indiana. One mine is in the low-sulfur (<1%) Danville Coal Member of the Dugger Formation (Pennsylvanian) and the other mines the high-sulfur (>5%) Springfield Coal Member of the Petersburg Formation (Pennsylvanian). Both seams have comparable ash contents (11%). Coals sampled at the mines (both raw and washed fractions) were analyzed for proximate/ultimate/sulfur forms/heating value, major oxides, trace elements and petrographic composition. The properties of fly ash from these coals reflect the properties of the feed coal, as well as local combustion and post-combustion conditions. Sulfur and spinel content, and As, Pb and Zn concentrations of the fly ash are the parameters that most closely reflect the properties of the source coal.     

Modes of occurrence of minerals in the Carboniferous coals from the Wuda Coalfield,northern China: with an emphasis on apatite formation

The mineralogical compositions of the Nos. 9 and 13 coals, which are medium-volatile bituminous coals in rank, from the Wuda Coalfield at the northwestern margin of the Ordos Basin in northern China, were investigated by optical microscopy, field emission-scanning electron microscopy in conjunction with energy-dispersive X-ray spectrometry (SEM-EDX), and X-ray powder diffraction techniques. The minerals in the Wuda coals are mainly represented by quartz, kaolinite, illite, pyrite, marcasite, apatite, dolomite, and ankerite, with trace amounts of anatase, calcite, boehmite, jarosite, gibbsite, anhydrite, and bassanite in some samples. The rod-like pyritized bacteria have been identified with SEM-EDX in Wuda coals. Moreover, the slightly reducing and alkaline environment in the original peat swamp favored bacterial action and propagation. The average concentrations of P₂O₅ in the Nos. 9 and 13 coals are 0.47 and 0.18 %, respectively. Phosphorus is not uniformly distributed within the Wuda coal seam. The maximum content of apatite in Wuda coals in certain horizon can reach up to 91.4 % (on an organic matter-free basis), corresponding to the fluorine and P₂O₅ concentrations of 2803 μg/g and 5.96 %. The high proportion of fluorine and P₂O₅ in the Wuda coals is mainly due to the authigenic apatite. The phosphorus in Wuda coals was probably derived mainly from phospho-proteins in the organic matter of the original peat deposits.     

Petrology and isotopic geochemistry of dawsonite-bearing sandstones in Hailaer basin, northeastern China

The CO₂ gas reservoir sandstones in the Hailaer Basin contain abundant dawsonite and provide an ideal laboratory to study whether any genetic relationship exists between dawsonite and the modern gas phase of CO₂. The origins of dawsonite and CO₂ in these sandstones were studied by petrographic and isotopic analysis. According to the paragenetic sequence of the sandstones, dawsonite grew later than CO₂ charging at 110–85 Ma. The dawsonite δ¹⁸O value is 7.4‰ (SMOW), and the calculated δ¹⁸O values of the water present during dawsonite growth are from −11.4‰ to −9.2‰ (SMOW). This, combined with the NaHCO₃-dominated water linked to dawsonite growth, suggests meteoric water being responsible for dawsonite growth. The δ¹³C values of gas phase CO₂ and the ratios of ³He/⁴He of the associated He suggest a mantle magmatic origin of CO₂-rich natural gas in Hailaer basin. Dawsonite δ¹³C values are −5.3‰ to −1.5‰ (average −3.4‰), and the calculated δ¹³C values of CO₂ gas in isotopic equilibrium with dawsonite are −11.4‰ to −7.3‰. These C isotopic values are ambiguous for the dawsonite C source. From the geological context, the timing of events, together with formation water conditions for dawsonite growth, dawsonite possibly grew in meteoric-derived water, atmospherically-derived CO₂ maybe, or at least the dominant, C source for dawsonite. It seems that there are few relationships between dawsonite and the modern gas phase of CO₂ in the Hailaer basin.     

内蒙古西部乌达矿区煤层自燃的控制因素

煤层自燃是一个复杂的物理、化学和环境作用过程,是多种内在原因和外在条件综合作用的结果.本文分析了内蒙古乌达矿区煤层自然发火的内在原因和外在条件,揭示了煤层自燃的各种控制因素.影响煤层自燃的内在原因包括煤层厚度、变质程度、灰分含量、发热量、硫含量和有机显微组分含量等;外在条件包括地质构造、气候、水文地质、地形地貌、煤层的赋存状况、大矿和小煤窑的开采情况等.最后探讨了对不同成因的煤层自燃采取不同的预防和治理方法,为今后煤火的研究和治理奠定了理论基础.     

Sulfur geochemistry of Jurassic high-sulfur coals from Egypt

Jurassic high-sulfur coals from the Maghara area in Egypt were analyzed for the abundance and isotopic composition of different forms of sulfur. Analyses indicated that the sulfur occurs in the form of organic, pyrite, and sulfate forms. Pyrite sulfur represents the major fraction, while sulfate sulfur is minor and could be formed during sample preparation for the analyses.The δ³⁴S CDT values of the organic sulfur are positive ranging between 1.0‰ and 13.5‰ with an average of 9.1‰. Pyrite δ³⁴S values are also positive ranging between 1.5‰ and 15.4‰ with an average of 6.6‰. The high δ³⁴S values of the organic sulfur in the Maghara coals suggest a freshwater origin of the organic components of these coals. The lack of correlation between pyrite and organic sulfur isotopes implies different incorporation mechanisms of sulfur. The high-sulfur contents along with the positive and high δ³⁴S values suggest a marine origin of pyrite sulfur and support the geological interpretation of marine invasion after the peat formation that was responsible for the incorporation of the pyrite sulfur.The occurrence of pyrite as euhedral crystals as well as the high and positive δ³⁴S values of the pyrite sulfur indicates the formation of pyrite during diagenesis as a result of marine water invasion of the preexisting peat in a brackish coastal plain environment.     

Coalbed methane in the Ruhr Basin, Germany: a renewable energy resource?

Around the globe underground hard coal mining leads to a release of methane into the atmosphere. About 7% of the global annual methane emissions originate from coal mining. In the year 2002, 16 countries used coal gas to generate heat and electricity. In many cases, the exact size of coalbed methane reservoirs is not identified. The possibility of a long-term gas production and its profitability at single sites are unknown. To clarify these points, the processes of gas generation as well as the gas-in-place volume have to be determined. Both issues are tackled here for the Ruhr basin. Within this basin, coal gas samples were taken at 13 gas production sites, spread over three samplings within 14 months. There were virtually no changes in the concentrations of gas components at single sites within this period. The isotope composition of methane (δ¹³C-methane: −40.0 to −57.3‰ vs. PDB) revealed that the produced methane is a mixture of gases of thermogenic and microbial origin. The microbial contribution of methane seems to be more pronounced at sites of active and especially abandoned coal mining than at unmined places. Ethane and propane are of thermogenic origin, with ethane's isotopic composition tending to heavier values (richer in ¹³C) with time. This time-dependent phenomenon is interpreted as being caused by desorption. In addition, living methanogenic archaea were detected in mine water samples from depths down to 1200 m.     

Fluid inclusion and stable isotope study of the Cobre–Babilonia polymetallic epithermal vein system, Taxco district, Guerrero, Mexico

The Cobre–Babilonia vein system formed during a single major hydrothermal stage and is part of the Taxco district in Guerrero, southern Mexico. Homogenization and ice melting temperatures range from 160 to 290 °C and from − 11.6 to − 0.5 °C, respectively. We determined an approximate thermal gradient of 17 to 20 °C per 100 m using fluid inclusions. A thermal peak marked by the 290 °C isotherm is interpreted as a major feeder channel to the veins. The highest content of Zn + Pb in ore coincides with the 220 and 240 °C isotherms. Salinities of mineralizing fluids range from 0.8 to 15.6 wt.% NaCl equiv, and are distributed in two populations that can be related with barren or ore-bearing vein sections, with 0.8 to 6 wt.% NaCl equiv and 7 to 15.6 wt.% NaCl equiv, respectively. δ¹³C and δ¹⁸O water values from calcite from the Cobre–Babilonia vein system and the Esperanza Vieja and Guadalupe mantos range − 5.4‰ to − 10.4‰ and 9.9‰ to 13.4‰, respectively. δ³⁴S values range from 0‰ to 3.2‰ and − 0.7‰ to − 4.3‰ in sphalerite, − 4‰ to 0.9‰ in pyrite, and − 1.4‰ to − 5.5‰ in galena. Both fluid inclusion and stable isotope data are compatible with magmatic and meteoric sources for mineralizing fluids. Also, sulfur isotope compositions suggest both magmatic and sedimentary sources for sulfur.     

潮控与河控下三角洲平原成煤的岩石学和地球化学特征

从显微煤岩组成特征、不同显微组分中有机硫的含量、伴生元素组成、硫同位素的分布特征等方面对内蒙古乌达矿区潮控下三角洲平原形成的高硫煤 9煤层和河控下三角洲平原形成的低硫煤 13煤层进行了研究。结果表明 ,潮控下三角洲平原形成的煤层较之河控下三角洲平原形成的煤层具有较高的镜质组含量 ;伴生元素中 Na、K、V、Mg等含量偏高 ,而稀土元素含量较低 ,稀土元素的含量与煤中的粘土矿物含量成正比 ;黄铁矿和有机硫同位素都比较轻 ,表明高硫煤中硫的来源主要是海水中细菌还原的硫酸盐。     

Groundwater transformation of a low-sulfur to a high-sulfur coal, the Harlem coal of the northern Appalachian basin

The Harlem coal is postulated to have been deposited in raised-bog settings. It was initially deposited as low-sulfur peat, but groundwater of a later origin altered portions of it to high-sulfur coal. The total sulfur content of 172 samples from 31 locations on a moisture- and ash-free basis have a quadrimodal distribution with two major modes at 0.75% S and 2.0%S. Multiple sampling and analyses at specific mine sites indicate that the addition of sulfur of a later origin occurred either laterally adjacent to sandstone channels or vertically adjacent to faults. Significant sulfur addition also occurred above clay partings at these sites. The original low-sulfur nature is preserved where the coal bed is isolated from descending groundwater by a thick impervious layer. Trace-element analyses show high concentrations of mobile elements such as Na and Mn in the high-sulfur coals.     

Relations of petrographical and geochemical parameters in the middle Miocene Lavanttal lignite (Austria)

Samples from two lignite seams (Lower Seam, Upper Seam) of the Lavanttal basin (Austria) and additional xylite were investigated for variations in maceral composition, petrography-based facies indicators, bulk geochemical parameters, and molecular composition of hydrocarbons. Both seams originated in a topogenous mire and evolved within a transgressive setting. The final drowning of the mire is indicated by sapropelic shales. Whereas the sapropelic shale overlying the Lower Seam was deposited in a freshwater lake, the sapropelic shale above the Upper Seam represents a brackish lake.Numerous relationships are found between petrography-based facies indicators and the geochemical composition of organic matter. The contents of macerals of the liptinite group are positively correlated with soluble organic matter (SOM) yields and hydrogen index (HI). Consistent with maceral composition and high HI values, enhanced proportions of short-chain n-alkanes, which are predominantly found in algae and microorganisms, are obtained from samples of the sapropelic shales. The final drowning of the mire is reflected by decreasing pristane/phytane ratios, due to the rise in (ground)water table and the establishment of anaerobic conditions, as well as by decreasing ratios of diasterenes/sterenes, indicating increasing pH values in the mire. The degree of gelification of plant tissue (gelification index) is governed by the microbial activity in the mire, as indicated by the hopanes concentration. The differences in floral assemblage during the formation of the Lavanttal lignite seams are reflected by major differences in tissue preservation. Preservation of plant tissue (TPI) in the Lavanttal lignite is obviously controlled by the presence/absence of decay-resistant gymnosperms in the peat-forming vegetation, and additionally influenced by the relative contribution of wood to coal formation. The results provide evidence that valuable information for coal facies characterization could be obtained by petrography-based and geochemical facies indicators. An influence of the floral assemblage (gymnosperms/angiosperms ratio) and of the contribution of algal biomass on carbon isotopic composition of the organic matter (δ¹³C = − 24.2 to − 28.6‰) is proposed. Carbon cycling during biogeochemical decomposition of plant tissue by bacteria is suggested to affect the δ¹³C values of the coal. The chemotaxonomical classification of the xylites as gymnosperm remnants, based on the molecular composition of terpenoid biomarkers, is corroborated by the carbon isotopic composition of the xylites (mean δ¹³C = − 24.1‰) and the extracted cellulose (mean δ¹³C = − 20.2‰). The higher isotopic difference of about 3.9‰ between cellulose and total organic carbon of the xylites, compared to the difference between cellulose and wood found in modern trees, is explained by the smaller effect of decomposition on δ¹³C of cellulose.     

Environmental control of carbon isotope variations in Pennsylvania black-shale sequences, Midcontinent, U.S.A.

A reversal of the conventional carbon isotope relationship, “terrestrial-lighter-than-marine” organic matter, has been documented for two Pennsylvanian (Desmoinesian) cyclothemic sequence cores from the Midcontinent craton of the central United States. “Deep” water organic-rich phosphatic black shales contain a significant proportion of algal-derived marine organic matter (as indicated by organic petrography, Rock-Eval hydrogen index and ratios) and display the lightest δ¹³C-values (max −27.80‰ for kerogen) while shallower water, more oxic facies (e.g. fossiliferous shales and limestones) contain dominantly terrestrial organic matter and have heavier δ¹³C_kerogen-values (to −22.87‰ for a stratigraphically adjacent coal). δ¹³C-values for extract fractions were relatively homogeneous for the organic-rich black shales with the lightest fraction (often the aromatics) being only 1‰, or less, more negative than the kerogen. Differences between extract fractions and kerogens were much greater for oxic facies and coals (e.g. saturates nearly 5‰ lighter than the kerogen).A proposed depositional model for the black shales calls upon a large influx of nutrients and humic detritus to the marine environment from the laterally adjacent, extremely widespread Pennsylvanian (peat) swamps which were rapidly submerged by transgression of the epicontinental seas. In this setting marine organisms drew upon a CO₂-reservoir which was in a state of disequilibrium with the atmosphere, being affected by isotopically light “recycled-CO₂” derived from the decomposition of peaty material in the water column and possibly from the anoxic diagenesis of organic matter in the sediments.