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Petrological and geochemical characteristics of Palaeogene low-rank coal on the Faroe Islands: Restricted effects of alteration by basaltic lava flows
Abstract
The first combined petrographic and geochemical investigation of coal from the Faroe Islands was performed as a case study to understand thermal effects from basaltic lava flows on immature coal. The samples were divided into two distinct groups: “normal” coal (xylite and detroxylite) and “altered organic matter” (charcoal and organic particles dispersed in samples rich in altered clastic mineral components or enriched via hydrothermal fluids). The “normal” coal consists primarily of huminite-group material dominated by ulminite. The proportions of material from inertinite and liptinite groups vary from sample to sample. The studied macerals are anisotropic with no observed reaction rims or vacuoles. According to the mean ulminite reflectance in combination with ultimate and proximate analyses, the coal reached the lignite and subbituminous stages. The maceral compositions together with coal palynology indicate a predominance of gelified wood-derived tissues and demonstrate that the coal evolved in wet forest swamps under limno-telmatic to telmatic conditions.
... The Faroe Islands Basalt Group has been divided into seven lithostratigraphic formations, namely, (from bottom to top): Lopra Fm., Beinisvørð Fm., Prestfjall Fm., Hvannhagi Fm., Malinstindur Fm., Sneis Fm. and Enni Fm (Passey and Jolley, 2009). The individual basaltic flows are often separated by volcaniclastic sediments (occasionally coal-bearing tuffitic claystone, sandstone or conglomerate of terrestrial origin) deposited between individual volcanic eruptions (Andersen et al. 2002;Waagstein et al. 2002;Passey and Jolley 2009;Pokorný et al. 2015;Kuboušková et al. 2016). ...
... Relatively uniform distribution of interstitial tachylyte is indicative of rapid cooling during the dyke emplacement without dramatic changing of P-T-X conditions (e.g. Kuboušková et al. 2016;Ulrych et al. 2017). Petrographic thin sections made from marginal pseudo-hieroglyphs revealed that they do not texturally or compositionally deviate from the host basaltic rock (Fig. 5c, d). ...
Volcanic landforms resulting from Cenozoic volcanism represent the most peculiar features of global geodiversity and provide eminent narratives for geoeducation. Among them, however, relict volcanic forms and site-specific landforms in remote areas have received less attention. In this paper, we provide the first description of unique volcanogenic features (hereinafter referred to as pseudo-hieroglyphs) developed on a summit rock wall at the Sandfelli ridge near the village of Gjógv in the N Eysturoy Island (Faroe Islands). The geomorphic evolution of the ridge and rock wall during the Quaternary is described and detailed petrographic analyses of the volcanogenic features are provided. Based on observed petrographical features, we interpret the pseudo- hieroglyphs to probably represent unique examples of chaotic horizontal columnar jointing. Following the geomorphological and petrographic examination of the study site, we analyse current Faroese legislation aiming at nature conservation and use this case to discuss broader implications of geoheritage conservation and geotourism in distant regions.
... These abundances reflect complex peat-forming conditions ( [31] ; O'Keefe et al. 2013). The ternary diagrams of Mukhopadhyay [36] have been applied to many low-rank coals [4,28,52,61] to examine the variations in the depositional environment, primarily in terms of mire type and oxygenation. Application of this method ( Fig. 11 a) to the Sonari lignite samples highlights the fluctuating water table during peat accumulation. ...
Lignite samples from the Sonari mines of Barmer Basin, Rajasthan, India have been studied for the first time by applying advanced petrochemical techniques. The objective of the study was to reconstruct Paleomire conditions and to examine the source rock potential of the lignite-bearing sequence. Based on the mean huminite/vitrinite reflectance values (0.24–0.31%Ro), all of the samples studied are lignite B in rank. Geochemical analysis results show, the atomic ration H/C and O/C ranges from 0.03–0.15 and 0.27–0.61 respectively, hydrogen index (HI) and oxygen index (OI) ranges from 173 to 256 mg HC/g TOC and 29–55 mg CO2/g TOC respectively, with Tmax value (415–416 °C), entails these lignites are thermally immature and contain type III kerogen. The studied lignites have total organic carbon (TOC), and S2 values vary from 41.24–49.19wt% and 78.53–119.81 mg HC/g rock, respectively, which indicate that these lignites may be served as good hydrocarbon source rock.
The lignites are principally composed of huminite (mean 47.5 vol%) and inertinite (mean 31.4 vol%) group of macerals with a low concentration (mean 8.5 vol%) of liptinite macerals. The predominance of attrinite in the Sonari lignite samples suggests that woody vegetation has undergone significant degradation. Petrographic indices such as TPI (Tissue preservation index; 0.92–2.13), GI (Gelification index; 0.97–8.25), GWI (Groundwater influence index; 0.34–1.50), and VI (Vegetation index; 0.16–1.84) indicate deposition in a wet forest paleomire and peat formation under ombrotrophic to mesotrophic hydrogeological conditions. Ternary plots based on maceral and microlithotype entails fluctuating water table condition during peat deposition.
The GC-MS (Gas chromatography–mass spectrometry) data shows that the ratios, Pr/Ph pristine/phytane (˂1), Pr/C17 (0.57), Ph/C18 (0.25) and carbon preference index (CPI) value 3.73 along with δ¹³C (−25.04%) values indicate that the Sonari lignites are composed primarily of gymnosperms taxa which formed under relatively dry and cold paleoclimatic conditions. Besides, FT-IR (Fourier-transform infrared spectroscopy) spectra give the signature of a C–H aliphatic stretching region and predominate methylene group in the aliphatic carbon region, which is also observed in the NMR (Nuclear magnetic resonance).
... The geological basement of the Faroe Islands (61°20 0 N-62°24 0 N and 6°15 0 W-7°41 0 W; Fig. 1A, B) consists of Palaeocene basaltic lava flows of the North Atlantic Igneous Province, often interbedded with volcaniclastic layers, mostly tuffitic sandstones, while less common are siltstones and locally coal-bearing claystones Pokorn y et al. 2015;Kubou skov a et al. 2016). The Quaternary sedimentary cover is represented by unconsolidated or weakly consolidated glacial deposits, such as tills, glaciofluvial and glaciolacustrine deposits, Pleistocene blockfields and aeolian sands, and abundant Holocene peat deposits. ...
Iceland and Faroe Islands represent a classical example of an area fully formed by volcanic activity. Their geological history goes back to the Lower Palaeogene when the northern part of Mid-Atlantic Ridge was active in the area of hotspot expression. Thick effusions and sheet intrusions of tholeiitic plateau basalts of Palaeogene age are characteristic for the Faroe Islands. Undersea volcanism which continuously cropped up and extruded the surface began in the Middle Miocene. The sequence of volcano-stratigraphic units with numerous volcaniclastic sedimentary layers is typical for both regions. However, there is one significant difference – in Iceland the marine and coastal deposits dominate but in the Faroe Islands mostly freshwater sediments are concerned.
Marine fauna is often preserved in the Icelandic sediments, for example Bivalvia, Gastropoda, Scaphopoda, Cirripedia, Annelida etc. In non-marine ecosystems, fossil plants, which locally form coal layers, dominate. Freshwater and terrestrial animals are much rarer. Fossil records of animal activities have not been studied there yet; however, their information potential has a great potential. Before the research presented in here, only three ichnologic papers were published and in several others the traces are only marginally mentioned.
No animal fossils from the Palaeogene age have been discovered in the Faroe archipelago yet, the same goes for the trace fossils. The only knowledge relates to the fossil plants. From the period after the end of the volcanic activity the finds of fossils are mostly limited to the Holocene age, except the Eemian wood fragments from the unique locality on the Borðoy Island.
In 2012–2018, a detailed paleontological research was carried out in the above mentioned European part of Arctic and Subarctic. Various bioerosion traces of Weichselian age were identified in the glaciomarine sediments, which remained after mechanic damages on shells of mollusc or barnacle, caused by the activity of predators; or after attachment of epibiotic organisms (e.g. Anellusichnus, Caulostrepsis, Centrichnus, Clionolithes, Finichnus and Oichnus), a lot of traces of locomotion were also found on the surface or inside sediment (will be published in the coming years). Resting traces and escape traces were also found here in the marine and also freshwater environments (Miocene).
It is not surprising that the marine ichnoassemblages show the worldwide geographic range; on the other hand, the lacustrine trace fossils are mostly endemic (Helminthoidichnites, Mammillichnis, Thorichnus igen. nov. and Vatnaspor igen. nov.).
In the Faroe Islands, the character of the Palaeogene landscape and ecosystems was quite well known based on the knowledge about the fossil plants and lithology of the volcaniclastic sediments. However, the proof of the animal presence was still missing. Although expected, the finding of Helminthoidichnites isp. and ?Palaeophycus isp. on the Eysturoy Island was important. Another but significantly younger trace fossils (Teredolites) were identified in the wood fragments comes from gyttja coastal cliffs of Eemian age. Terminal deposit place of driftwood in the lake basin connected with sea allows a big discussion about principal directions of sea currents in the last interglacial, despite their origin in high seas. The youngest confirmed traces come from the late Holocene soil profile. These are rhizoliths that testify the change of the landscape in the age of first human settlement of Faroe Islands. At present, the trace fossils mentioned above represent the first and only occurrence of trace fossils on the Faroe Islands.
... The geological basement of the Faroe Islands (61°20 0 N-62°24 0 N and 6°15 0 W-7°41 0 W; Fig. 1A, B) consists of Palaeocene basaltic lava flows of the North Atlantic Igneous Province, often interbedded with volcaniclastic layers, mostly tuffitic sandstones, while less common are siltstones and locally coal-bearing claystones (Storey et al. 2007;Pokorn y et al. 2015;Kubou skov a et al. 2016). The Quaternary sedimentary cover is represented by unconsolidated or weakly consolidated glacial deposits, such as tills, glaciofluvial and glaciolacustrine deposits, Pleistocene blockfields and aeolian sands, and abundant Holocene peat deposits. ...
The coastal cliffs in Klaksvík (Borðoyar Bay), is the only known locality with Eemian sediments in the Faroe Islands. Previous studies carried out there were focused on the sedimentology, tephra chemistry, paleoecology including aquatic environment or the age of the deposits. In the lacustrine, clayey to silty gyttja we collected scattered wood fragments, identified as Larix sp., Pinus sp., Taxus sp. and Betulaceae?. In addition, these wood remains contain numerous trace fossils, made by marine wood-boring bivalves (Teredolites longissimus), which together with a discussion about the areal extent of the identified tree species leads us to conclude that they are non-native, i.e. driftwood. Northern Siberia is usually regarded as the most likely source area for driftwood in the eastern North Atlantic region. However, we combined the approximate transport distance from the areal extent of the wood with the main directions of marine currents in the relevant section of the North Atlantic. By adding the known average marine current velocities during the penultimate interglacial it results in 130–200 days for transport from North America and 350–1100 days from Siberia. Comparing this with the maximal buoyancy period for the identified tree species, we conclude that the Faroese driftwood may originate not only from Siberia, but also from the eastern coast of North America, especially from the region around the Great Lakes, as well as from western Europe.
... Megascopic glass of tachylytic composition only rarely occurs in volcanic provinces. Mechanism for the production of basaltic glass is exclusively connected with rapidly cooled basaltic lavas (e.g., the North Atlantic Igneous Province; Kuboušková et al. 2016). Origin of megascopic basaltic glass from basaltic volcanic products of the Pacific Plate was discussed by Nichols et al. (2014). ...
Tachylytes from rift-related volcanic rocks were recognized as: (i) irregular veinlets in host alkaline lava flows of the Kozákov volcano, Czech Republic, (ii) (sub)angular xenoliths in alkaline lava of the feeding channel of the Bukovec volcano, Czech Republic, and (iii) paleosurface of a tholeiitic lava flow from Hafrafell, Iceland. The tachylyte from Kozákov is phonotephrite to tephriphonolite in composition while that from Bukovec corresponds to trachyandesite to tephriphonolite. Both glass and host rock from Hafrafell are of tholeiitic basalt composition. The tachylyte from Kozákov, compared with the host rock, revealed a substantial enrichment in major elements such as Si, Al and alkalis along with Rb, Sr, Ba, Nb, Zr, REE, Th and U. The tachylyte from Bukovec displays contrasting trends in the incompatible element contents. The similarity in composition of the Hafrafell tachylyte paleosurface layer and parental tholeiitic basalt is characteristic for lavas. The host/parent rocks and tachylytes have similar initial Sr–Nd characteristics testifying for their co-magmatic sources. The initial εNd values of host/parent rocks and tachylytes from the Bohemian Massif (+3.4 to +3.9) and those from Iceland (+6.3) are interpreted as primary magma values. Only the tachylyte from Bukovec shows a different εNd value of −2.1, corresponding to a xenolith of primarily sedimentary/metamorphic origin. The tachylyte from Kozákov is a product of an additional late magmatic portion of fluids penetrating through an irregular fissure system of basaltic lava. The Bukovec tachylyte is represented by xenoliths originated during the interaction of ascending basaltic melt with granitoids or orthogneisses, whereas the Hafrafell tachylyte is a product of a rapid cooling on the surface of a basalt flow.
The composition characteristics of altered coals in the Huaibei Coalfield, China, was investigated through a comparative analysis between altered and unaffected coals from the Wolonghu, Taoyuan and Renlou coal mines. Results indicated that the altered coals in Wolonghu coal mine are mostly anthracite coals, with a maximum vitrinite reflectance of 1.6–3.9% (average of 2.9%). Coals from Wolonghu coal mine were mainly consisted of vitrinite (66.2–97.0%), followed by inertinite (2.0–4.0%) and exinite (0.4–6.9%). Differences in volatile matter content were observed between the altered coals in Wolonghu coal mine and unaffected coals from neighboring coal mines, im-plying that the chemical composition and maturity of coals were changed after magmatic altera-tion. In addition, differences in hydrogen element were noted among the coals from Wolonghu, Renlou and Taoyuan coal mines, and the phenomenon of “deficient in hydrogen element” was observed in Wolonghu coals. The aliphatic hydrocarbon structure parameters suggested that the aliphatic chain lengths of Wolonghu coals are shorter than those of coal samples from the Renlou and Taoyuan coal mines. In addition, maturity is positively correlated with hydrogen enrichment degree, but negatively related with aliphatic hydrocarbon structure. Coals from Renlou and Taoyuan coal mines showed great weight loss with various heating rates at temperatures of 0–1000 °C, whereas those from Wolonghu coal mine had less weight loss.
Multiplicative relations are one of most powerful techniques to express the preferences over alternatives (or criteria). In this paper, we propose a wide range of hesitant multiplicative fuzzy power aggregation geometric operators on multiattribute group decision making (MAGDM) problems for hesitant multiplicative information. In this paper, we first develop some compatibility measures for hesitant multiplicative fuzzy numbers, based on which the corresponding support measures can be obtained. Then we propose several aggregation techniques, and investigate their properties. In the end, we develop two approaches for multiple attribute group decision making with hesitant multiplicative fuzzy information and illustrate a real world example to show the behavior of the proposed operators.
Interlava volcaniclastic sediments, mostly sandstones, from the Palaeogene Faroe Islands Basalt Group (Malinstindur and Sneis Formations) contain rare ichnofauna and well-preserved pseudo-fossils in the form of linear structures. Five specimens of two ichnogenera have been identified, which include Helminthoidichnites isp. and ?Palaeophycus isp. The linear structures are interpreted to be desiccation cracks. This association indicates an environment with low to moderate hydrodynamic energy, which confirms a mosaic landscape of floodplains with rivers and shallow lakes.
The effects of igneous intrusions have proved to be important for the exploration and development of coalbed methane in many coal basins. However, the studies of the influences of localized intrusions on coalbed methane reservoirs are still insufficient. In the context of five typical dike/sill intrusion patterns (i.e., dike cut-through, dike cut-in, floor intrusion by sill, roof intrusion by sill, and dual intrusions of roof and floor by sills), this study investigates the changes of coal organic composition and pores/fractures resulting from igneous intrusions. The influences of igneous intrusions on coal composition mainly include the decrease of vitrinites (especially telocollinite) and the increase of inertinites contents, as well as the formation of secondary devolatilization vacuoles and of exogenous desiccation microfractures. The vacuoles have size of 0.1–10 μm, and the microfractures are commonly developed with a wide space and a significantly short length. The microfractures typically have irregular dendritic, filamentous, and turtleback textures, and densities of hundreds per 9 cm2. The influences of igneous intrusions on coal pores and fractures vary significantly depending on the intrusion patterns, the coal ranks after the intrusion, and the nature of the adjacent formation surrounding the intrusion. For the coals with a VRr > 4.2%, the intrusion significantly reduced the coal pore development. For the coals with a VRr from 2.1%–4.2%, the development of the coal pores improved with decreasing distance to the contact. For the coals with a VRr < 2.1%, the intrusion resulted in a slight improvement of the coal pore development. A possible explanation for the increasing gas content near the intrusion is that the secondary vacuoles and microfractures induced an increase in the gas storage capacity and in the permeability of the coal reservoir. The detailed intrusion patterns of sills and dikes contribute to the formations of the coalbed methane accumulation in coal seams, and to the coal-generated gas accumulation in the reservoir of the highly permeable surrounding-rocks.
Med det færdige geologiske kort over Færøernes prækvartære dannelser foran os skal vi i lag med at skildre den geologiske udvikling af et rent vulkansk område, kort og godt et, der så at sige i alle måder adskiller sig fra dem, Danmarks Geologiske Undersøgelse plejer at belyse med sine kort.Vi vil derfor indlede vor kortbladsbeskrivelse med nogle korte afsnit, der omtaler 1. vulkanismen som fænomen, 2. den vigtigste blandt lavabjergarterne: basalt, 3. den særlige udformning basalten har i plateaubasaltområder og endelig 4. Færøernes placering i det nordatlantiske basaltområde.
We report on the leaves, fruits, inflorescences, and pollen of two fossil species in the genus Platycarya. The association of these dispersed organs has been established by their repeated co‐occurrence at a large number of localities, and for two of the organs (fruit and pistillate inflorescence, and pollen and staminate inflorescence) by apparent organic attachment of compression fossils. Each of the two species can be distinguished by characteristics of all the known megafossil organs. We also review the fossil record of dispersed platycaryoid fruits and inflorescences, recognizing three additional species of Platycarya and two of Hooleya. Two of the fossil Platycarya species are morphologically very different from the living Platycarya strobilacea Sieb. et Zucc., but they show the diagnostic features of the genus. Hooleya is a generalized member of the Platycaryeae that is probably close to the ancestry of Platycarya.
The two Platycarya species known from multiple organs provide a remarkable example of mosaic evolution in which fertile and foliar structures have attained different levels of morphological specialization. The leaves, often considered the most plastic of plant organs, retain several features that are otherwise seen only in the Engelhardieae. These similarities in leaf architecture between the fossil Platycarya species and Engelhardieae are advanced features for the Juglandaceae, and thus indicate a sister‐group relationship between the two lines. In contrast to the leaves, the fruits, inflorescences, and pollen of the fossil Platycarya species are almost as specialized as those of the extant P. strobilacea and bear little resemblance to the same structures in other genera of the family.
The morphology, taphonomy, sedimentary setting, and geographic and stratigraphic distribution of three of the fossil platycaryoid species suggest that they were wind‐dispersed, early successional plants that grew in thickets. This habit is retained by Platycarya strobilacea and is typical of many of the amentiferae (e.g. Myricaceae, Betulaceae). The r ‐selected life‐history pattern of the Platycarya line may well have contributed to its low diversity through geologic time.
The preceding chapter has shown that in the course of undisturbed sedimentation the various depositional environments produce specific orders of superposition of lithofacies which are recognisable in the stratigraphic column as either rhythmic or cyclic patterns. The strongest cyclicity results from coastal settings, where on either side of the shoreline several contrasting depositional environments coexist which can be shifted readily by relative sea level variations. Coal measures interbedded with marine sediments therefore provide particularly good examples of cyclic sedimentation and were used by Weller (1930) to formulate the concept of cyclothems, which for many decades strongly influenced research into coal measure sedimentation (Fiege 1937, 1952; van Leckwijck 1948; Wanless 1931, 1950; Wanless and Weller 1932; Wanless and Shephard 1936; Weller 1956, 1958; Moore 1950; Moore 1959; Jessen 1956a–c, 1961; Jessen et al. 1952, and others). A comprehensive summary of the early work is given by Duff et al. (1967).
Mineralogical and chemical examination of Tertiary interbasaltic clays from the Faeroe Islands revealed three types of alteration of volcanic tuffs and basalts: 1) Argillization of volcanic tuffs within a lacustrine environment results in the formation of aluminous beidellites and metahalloysites; these clays are associated with extensive coal layers at Suduroy. 2) Argillization of volcanic tuffs due to hydrothermal action resulted in the formation of thick layers of ferriferous beidellites associated with small amounts of hematite and zeolite (e.g. at Nolsoy). 3) Meteoric alteration of volcanic tuffs and basalts, which took place under hot climatic conditions and contrasting seasons, led to the development of ferriferous and aluminous-ferriferous beidellites, metahalloysite, kaolinite, hematite and goethite in low (Hov profile) or high (Oravik profile) topographical positions. The three processes occurred individually or were superimposed.-D.J.M.
The coalfields of South Africa contain numerous dolerite intrusions, which affected the quality of the surrounding coal through thermal processes, commonly believed to be controlled by the size of the magmatic body. Data gathered from a working coalfield in Secunda, South Africa, suggest that the relationship between intrusive sills and coal is complex and factors other than intrusion width must be considered in relation to the contact metamorphic effect. The study area contains multiple dolerite intrusions of Karoo age, of which three intrusions occur as sills intruded close to the main coal seam of the. A large database (>8000 boreholes) of coal quality data was used to investigate the presence or absence of a change in coal quality relative to dolerite proximity. Reduction in coal quality was defined using three proximate analysis values, namely the ash, volatile content and dry ash free volatile (DAFV) as defined in the coal industry. The resultant investigation showed no correlation between the position and thickness of the dolerites, and changes in coal quality as measured by proximate analysis. In the absence of a linear relationship between coal quality and dolerite proximity, two processes are proposed to explain the absence of the contact metamorphic effects expected from previous studies. Firstly dolerite emplacement dynamics may influence the size of the metamorphic aureole produced by an intrusion, invalidating intrusion size as a measure of thermal output. Secondly, hydrothermal fluids mobilised by the dolerite intrusions, either from the country rock or the intrusion itself may percolate through the coal and act as the metamorphic agent responsible for changing coal quality, by dissolving the volatile and semi-volatile components of the coal and transporting them to other locations. These two processes are sufficient to explain the lack of a clear “metamorphic effect” related to the dolerite intrusions. However, the perceived lack of a clear correlation between the coal quality parameters and the metamorphic effects associated with dolerite intrusion may also reflect the inadequacies of proximate analysis techniques in quantifying geological processes within the coal.
Focusing on today's major fuel resources – ethanol, biodiesel, wood, natural gas, petroleum products and coal – this book discusses the formation, composition and properties of the fuels, and the ways in which they are processed for commercial use. The book examines the origin of fuels through natural processes such as photosynthesis and the geological transformation of ancient plant material; the relationships between their composition, molecular structures, and physical properties; and the various processes by which they are converted or refined into the fuel products appearing on today's market. Fundamental chemical aspects such as catalysis and the behaviour of reactive intermediates are presented, and global warming and anthropogenic carbon dioxide emissions are also discussed. The book is suitable for graduate students in energy engineering, chemical engineering, mechanical engineering and chemistry, as well as professional scientists and engineers.
In the new classification (ICCP System 1994) the maceral group inertinite has been enlarged to include seven macerals by replacing the former maceral sclerotinite by two others, called funginite and secretinite. Funginite consists of fungal remains only, whereas secretinite comprises inert residues that are similar to fungal sclerotia in their optical characteristics but are, in fact, oxidized and subsequently coalified plant excretions. This revision necessitated a redefinition of the maceral macrinite in order to establish a clear division between secretinite and macrinite. The definitions of the remaining inertinite macerals, although upgraded and enlarged, remain largely unchanged.
This study has investigated the effect of small igneous intrusions on Early Cretaceous carbonaceous fluvial sediments of the Gippsland Basin of south-eastern Australia, based on outcrops in the onshore western part of the basin. Vitrinite reflectance measurements, quantitative mineral phases and clay mineralogy were carried out on twenty two samples of organic-rich mudstone up to 25. m east and west of a 1. m wide dyke. Samples of the dyke allowed classification as an alkali-basalt, based on its optical characteristics, and major- and trace-element properties.Background vitrinite reflectance of 0.75%-0.80% [Rmax] in the sediments is elevated up to 6.67% [Rmax] close to the dyke margin, with slightly different patterns on each side of the intrusion. Analysis of seven selected organic-rich mudstone samples shows that they all have very similar XRD patterns, with the main minerals in all cases being quartz, feldspar (mainly plagioclase), chlorite, illite and interstratified illite/smectite. These observations suggest that the thermal maturity of the organic matter in the sediments was locally elevated by heating due to emplacement of the dyke, but no significant changes were observed in host-rock mineralogy that could be related to the heat generated by the dyke and the associated vitrinite reflectance variations.
This chapter reviews the present-day composition of the continental crust, the methods employed to derive these estimates, and the implications of the continental crust composition for the formation of the continents, Earth differentiation, and its geochemical inventories. We review the composition of the upper, middle, and lower continental crust. We then examine the bulk crust composition and the implications of this composition for crust generation and modification processes. Finally, we compare the Earth's crust with those of the other terrestrial planets in our solar system and speculate about what unique processes on Earth have given rise to this unusual crustal distribution.
The Donglin Coal Mine, an important mine in the Nantong coalfield in southwestern Chongqing, is immediately adjacent to the Songzao coalfield. To investigate the mineralogy and geochemistry of Donglin coals, profile channel samples from the mineable Nos. 4 and 6 coals were collected. The minerals, major element oxides, and trace elements were analyzed by LTA-XRD in combination with Siroquant software, XRF, ICP-MS, ICP-CCT-MS (As and Se), ISE (F), and DMA-80 Hg analyzer (Hg). The results indicate that the Donglin low volatile bituminous coals were characterized by low ash yields and high total sulfur contents. The minerals varied between the Nos. 4 and 6 coals, differentiated by montmorillonite, calcite, ankerite, and pyrite. Despite the low boron concentration, Donglin coals were influenced by brackish water during coal accumulation. Selenium (10.9 mg/kg), F (431 mg/kg), Hg (0.350 mg/kg), Nb (20.7 mg/kg), and Ta (3.68 mg/kg) in the No. 4 coals, and F (425 mg/kg), Be (7.11 mg/kg), Ga (14.5 mg/kg), Ge (22.5 mg/kg), Zr (218 mg/kg), Nb (35.5 mg/kg), and Ta (4.42 mg/kg) in the No. 6 coals are slightly enriched. Four vertical distributions of elements were demonstrated, i.e., roof, floor, roof and floor, and middle enrichments. The slightly enriched trace elements and UCC-normalized REY distribution patterns of the Donglin coals jointly eliminated the impact of various volcanic ashes and terrigenous input from the Kangdian Oldland during the Late Permian. However, the roof rock samples shared the geochemical feature of mafic tonstein (enriched Sc, V, Cr, Co, and Ni), while the floor rock of the No. 6 coals resembles alkali tonsteins (enriched Ga, Zr, Nb, Ta, Hf, and REY). Lithium, Ga, Zr, Ag, Cd, In, Sn, Cs, Hf, Bi, Th, and U occurred in kaolinite and/or montmorillonite in the No. 4 coals, while Li, Nb, Ag, Cd, In, Cs, Ba, and Th occurred in kaolinite in the No. 6 coals. Vanadium, Sr, and Mo in the No. 4 coals, and Sr and Sc in the No. 6 coals were associated with calcite and/or ankerite. Arsenic, Se, Hg, Sb and Tl, and Hg and Mo were associated with pyrite in the Nos. 4 and 6 coals, respectively. Lithium, Be, Ge, and Sb in the No. 4 coals and Be and Ge in the No. 6 coals might be of organic affinity.
A thin sill-like body, probably andesitic, intrudes a coal seam within the Collinsville coal measures (Permian) of the Bowen
basin, eastern Queensland, and is altered to albite, kaolinite, chalcedony, ankerite, siderite, calcite, and leucoxene. Textural
relations suggest that it was partly crystalline when intruded. The coal was converted to coke at the contact, and coal, made
plastic up to two feet from the contact, injected the coke and intrusive along cracks. Liquid tarry products were carbonized
and formed masses of small spheres 1-200 microns in diameter. Gases deposited carbon in open spaces. Pyrite from the coal
was mobilized to form replacements and veinlets.
The North Atlantic Igneous Province (NAIP) is a large igneous province (LIP) that includes a series of lava suites erupted from the earliest manifestations of the (proto)-Icelandic plume, through continental and ultimately oceanic rifting. The lavas of one of these sub-provinces, the British Palaeogene Igneous Province (BPIP), were some of the first lavas to be erupted in the NAIP and overlie a thick crustal basement and sedimentary succession with abundant S-rich mudrocks. We present the first platinum-group element (PGE) and Au analyses of BPIP flood basalts from the main lava fields of the Isle of Mull and Morvern and the Isle of Skye, in addition to a suite of shallow crustal dolerite volcanic plugs on Mull, and other minor lavas suites. BPIP lavas display both S-saturated and S-undersaturated trends which, coupled with elevated PGE abundances (> MORB), suggest that the BPIP is one of the most prospective areas of the NAIP to host Ni-Cu-PGE-(Au) mineralisation in conduit systems. Platinum-group element, Au and chalcophile element abundances in lavas from West and East Greenland, and Iceland, are directly comparable to BPIP lavas, but the relative abundances of Pt and Pd vary systematically between lavas suites of different ages. The oldest lavas (BPIP and West Greenland) have a broadly chondritic Pt/Pd ratio (~ 1.9). Lavas from East Greenland have a lower Pt/Pd ratio (~ 0.8) and the youngest lavas from Iceland have the lowest Pt/Pd ratio of the NAIP (~ 0.4). Hence, Pt/Pd ratio of otherwise equivalent flood basalt lavas varies temporally across the NAIP and appears to be coincident with the changing geodynamic environment of the (proto)-Icelandic plume through time. We assess the possible causes for such systematic Pt/Pd variation in light of mantle plume and lithospheric controls, and suggest that this reflects a change in the availability of lithospheric mantle Pt-rich sulphides for entrainment in ascending plume magmas. Hence the precious metal systematics and potential prospectivity of a LIP may be affected by contamination of plume-derived magmas by subcontinental lithospheric mantle at the margins of cratons that has been enriched by Palaeoproterzoic orogenesis.
Igneous intrusions in coal seams are found in 80 % of coal mines in the Huaibei coalfield, China, and coal and gas outburst accidents have occurred 11 times under a 120-m-thick sill in the Haizi mining field. The magma's heat had a significant controlling effect on coal seam gas occurrence. Based on theoretical analysis, experimental tests and site validation, we analyzed the temperature distribution following magma intrusion into coal measure strata and the variations in multiple physical parameters and adsorption/desorption characteristics between the underlying coal seams beneath the sill in the Haizi mining field and coal seams uninfluenced by magma intrusion in the adjacent Linhuan mining field. The research results show that the main factors controlling the temperature distribution of the magma and surrounding rocks in the cooling process include the cooling time and the thickness and initial temperature of the magmatic rock. As the distance from sill increases, the critical effective temperature and the duration of sustained high temperatures decrease. The sill in the Haizi mining field significantly promoted coal seam secondary hydrocarbon generation in the thermally affected area, which generated approximately 340 m3/t of hydrocarbon. In the magma-affected area, the metamorphic grade, micropore volume, amount of gas adsorption, initial speed of gas desorption, and amount of desorption all increase. Fluid entrapment by sills usually causes the gas pressure and gas content of the underlying coal seams to increase. As a result, the outburst risks from coal seams increases as well.
The Huainan coalfield, where magma is commonly intruded into the coal measures in the northern section, (e.g., the Zhuji, Dingji, Pansan, and Panbei mines), is the largest energy base in eastern China.
To investigate the mineralogical and geochemical responses of coal to igneous intrusion, minerals, major and trace elements in sandstone, thermally-altered coal, igneous rock, sandy mudstone, and unaltered coal samples were collected from a representative profile of the No. 1 Coal of the Pansan Coal Mine. The samples were analyzed using an optical microscope, powder X-ray diffraction, scanning electron microscopy in conjunction with X-ray energy dispersive spectroscopy, X-ray fluorescence, inductively coupled plasma atomic emission spectrometry and mass spectrometry. The results indicated that the thick sill transformed from mafic rocks at the bottom, via intermediate rocks in the middle to felsic rocks at the top of the profile. The moisture, total sulfur, and carbon contents of the coal increased, whereas volatile matter, hydrogen, and nitrogen decreased during contact metamorphism caused by igneous intrusion. Epigenetic minerals (i.e., dolomite, quartz, and pyrite) occurred in the thermally-altered coals. Three stages of hydrothermal fluids (i.e., Ca-, Mg-, and Fe-rich; Si-rich; and Fe- and/or H2S-rich solutions) were identified. Iron, Ca, S, Si, Mg, Zn, Cd, and Pb were transported into the thermally-altered coal by hydrothermal fluids. The concentrations of Co and Ni in the thermally-altered coal increased in relation to the increase of ash yields that were caused by contact metamorphism, whereas the B in the coal was volatilized. Manganese directly related to the intrusive magma. Phosphorus, Ge, and Sr might be introduced into the coal by groundwater; however, K, Na, Ga, and Ba were leached out. Titanium, Sc, Cr, V, Cu, Zr, Nb, and rare earth elements and yttrium (REY) in the coals originated from terrigenous input and were not influenced by igneous intrusion.
Siderite spherules are described and chemically analysed from two localities (Holið í Helli section and Rókhagi coal mine) within the coal-bearing Prestfjall Formation. The formation marks a significant hiatus in the eruption of lava flows of the Paleogene Faroe Islands Basalt Group and shortly follows the Paleocene-Eocene Thermal Maximum. The spherules are chemically pure, although FeCO3 (80.6-99.2 mol.%) shows a marked substitution for MnCO3 (0.1-13.9 mol.%). The low concentrations of MgCO3 (0.0-0.4 mol.%) and the lack of associated sulphide minerals (e.g. pyrite) confirms the freshwater lake environment affinity of the formation. The siderite spherules from the Holið í Helli section contain significantly higher concentrations of MnCO3 (< 13.9 mol.%) than those from the Rókhagi coal mine (< 2.5 mol.%) suggesting the presence of a stratified water column. The Holið í Helli section most likely represents the margin of the lake basin, whereas the Rókhagi coal mine the central area, where sedimentation rates were low and saw the thickest accumulations of coal. The high concentrations of MnCO3 may also account for the abundance of siderite spherules formed by the split crystal process in the Holið í Helli section, whereas prefect spherules consisting of individual crystals growing concentrically around a cryptocrystalline centre are dominant from the Rókhagi coal mine.
The fly ashes derived from three giant coal-hosted Ge deposits, Lincang (Yunnan of southwestern China), Wulantuga (Inner Mongolia of northern China), and Spetzugli (Primorye, Russian Far East), are unique because they are highly enriched in elements, including up to (on an organic-free basis): 4.66% Ge, 2.12% As, 1.56% F, 1.22% Sb, 0.56% W, 0.56% Zn, 0.55% Pb, 0.13% Sn, 0.12% Ga, 0.056% Bi, 0.04 % Be, 0.028% Cs, 0.017% Tl, and 0.016% Hg. These high element concentrations in the fly ashes are due both to their high levels in the raw coals from which they were derived and their high volatility during the coal combustion process.
Rare earth elements and yttrium (REY) were fractionated during coal combustion. They are more enriched in fly ashes than in slag from the respective coals. Maximum REY enrichment may occur either in fine-grained fly ash from baghouse filters or in coarse-grained fly ash from electrostatic precipitators. Cerium and Eu are more enriched in the fly ashes than other REY, and yttrium is relatively depleted in the fly ashes in comparison with the slag.
Three types of unburnt carbon can be identified in the fly ashes: (1) carbon with well-preserved initial maceral structures (fusinite and secretinite), (2) isotropic and anisotropic carbon, and (3) secondary fine-grained carbon. The last type of unburnt carbon is characterized by embedded fine-grained Ge-bearing and other mineral phases.
Ge oxides (e.g., GeO2) are the major Ge carrier in the fly ashes. Other Ge-bearing mineral phases, however, were also identified, including glass, Ca ferrites, solid solutions of Ge in SiO2, and probably elemental Ge or Ge (Ge-W) carbide, as well as previously-unknown complex oxides including (Ge,As)Ox, (Ge,As,Sb)Ox, (Ge,As,W)Ox, and (Ge,W)Ox. Some portion of the Ge occurs as adsorbed species in different types of unburnt carbon (Types 1 and 2) in the ash particles.
Geochemical studies of sulfur in coals comprise several major aspects relating to the nature and origin of sulfur in coals, including the abundance and distribution of sulfur in coal seams, abundance of sulfur in coal lithotypes and macerals, characteristics and geochemical significance of sulfur-containing organic compounds, sulfur isotopic studies relating to the sources of sulfur in coals, and sedimentary environments controlling the geochemistry of sulfur in coal. A review of the evidence suggests that the variation of sulfur in coals is closely related to the depositional environments of coal seams. For low-sulfur coal (< 1% S), sulfur is derived primarily from parent plant material. For medium-sulfur (1 to < 3% S) and high-sulfur (≥ 3% S) coals, there are two major sources of sulfur: 1) parent plant material, and 2) sulfate in seawater that flooded peat swamps. Abundances of sulfur in coal are largely controlled by the degree of seawater influence during peat accumulation and by postdepositional changes (diagenesis). In high-sulfur coals, seawater sulfate diffuses into the peat, which is subsequently reduced by bacteria into hydrogen sulfide, polysulfides, and elemental sulfur. Reaction of hydrogen sulfide with ferrous iron generates fine pyrite crystals and mackinawite [FeS0.9]. Mackinawite reacts with elemental sulfur to converts to greigite [Fe3S4] and then to framboidal pyrite. The reduced sulfur species in the peat (hydrogen sulfide, elemental sulfur and polysulfides) react with the organic matter to form organic sulfur compounds. During coal diagenesis, nodular pyrite forms. Permineralized peat was formed during diagenesis which contains appreciable fraction of pyrite. After coal is solidified, pyrite can deposit in the cleats from circulating groundwater. Epigenetic pyrite veins may be deposited from basinal fluids. Thus, pyrite forms during various stages of coal formation from peat to coal, as well as late epigenetic activity.
The Junggar coal basin, with enormous coal reserves, is one of the largest coal basins in Xinjiang Province, Northwest China. According to the exploration data, there is one to dozens of workable coal seams developed in the Xishanyao Formation of Middle Jurassic across the whole basin, with the maximum accumulated coal thickness of over 100 m. Ninety-six bulk coal samples from six exploration boreholes in the Southern and Eastern Junggar Coalfields were collected to investigate the coal qualities of the Junggar coals. The mineralogical characteristics of the studied coals were determined by Powder X-ray diffraction (XRD) and geochemical analyses are performed by means of inductively-coupled plasma atomic-emission spectrometry (ICP-AES) and inductively-coupled plasma mass spectrometry (ICP-MS). The Eastern and Southern Junggar bituminous coals are all characterized by low ash yields, low S contents, and low mineral contents. Furthermore, the concentrations of most major and trace elements in both the Eastern and Southern Junggar coals are relatively low with respect to other Chinese and worldwide coals, with the exceptions of Sr and Ba. The results show that elements including K, Li, Ti, Sc, V, Cr, Ga, Rb, Zr, Pb, and rare earth elements (REEs), have aluminosilicate affinities. Ca-bearing and Fe-bearing carbonate affinities are deduced for Ca, Mg, Fe, Mn, Sr, and Ba. Sulfur (Fe), Zn, Pb, Cu, and As show a partial sulfide affinity in some coals. An apatite and/or crandallite affinity is deduced from relatively high correlation of P, Sr, and Ba. The very high coal quality of Junggar coals is attributed to very low detrital supply in very stable shallow-lake sedimentary facies during peat accumulation. Slight differences of peat bog accumulation rate, water table, and oxidizing-reducing condition account for the merging and splitting of coal seams in different coal exploration areas and the slight differences of mineral, S, ash, and trace element contents. In summary, the Eastern and Southern Junggar coals with very enormous reserves are characterized by high quality, which is significantly and environmentally relevant to coal combustion by-products (CCPs) and potential emissions of gaseous pollutants/particulate matter during the large coal consumption in pulverized coal combustion power stations in Xinjiang Province. The high coal quality of the Junggar coals is expected to generate CCPs that can be reused for various purposes with low environmental threat.
The Early Cretaceous Wulantuga high-Ge coal deposit in Inner Mongolia is one of the major coal-hosted Ge deposits in China. This paper reports new data on the petrological, mineralogical, and geochemical compositions of 13 bench samples of the high-Ge No. 6 coal from the Wulantuga deposit, and provides new insight into the origin and modes of occurrence of the minerals and elements present.The No. 6 Coal has a low rank (Ro,max = 0.45%) and is a low-ash coal (8.77%). The total content of inertinite (52.5 vol.% on average) in most coal benches is higher than that of huminite (46.8 vol.% on average). The dominant huminite maceral is textinite (averages 43.9%), and the dominant inertinite macerals are mainly fusinite (averages 33%) and semifusinite (12.5%), along with trace portions of intertodetrinite, secretinite, funginite, and macrinite. Fungus, seen as the maceral funginite, played a role in the development of degraded maceral forms in the Wulantuga coals. Funginite is present in samples examined in this study, but is not easily extracted during palynological studies; recovered fungal taxa are saprophytes, indicating woody decomposition prior to incorporation in the mire. Palynology revealed a sparse flora that is consistent with the early Cretaceous age.Minerals in the coal include quartz, kaolinite, illite (and/or illite/smectite), gypsum, pyrite, and traces of rutile and anatase. A varying proportion of bassanite was observed in the low-temperature ashes (LTAs). Bassanite in the LTAs was derived both from the dehydration of gypsum in the raw coals and from the interaction between organically-associated Ca and S during the low-temperature ashing. In addition to a proportion of detrital quartz, fine-grained and cell-filling quartz of authigenic origin is also present. Pyrite is of syngenetic origin and derived from sulfate-rich hydrothermal fluids.Compared to common Chinese and world low-rank coals, the No. 6 Coal is enriched in Be (25.7 μg/g), F (336 μg/g), Ge (274 μg/g), As (499 μg/g), Sb (240 μg/g), Cs (5.29 μg/g), W (115 μg/g), Hg (3.165 μg/g), and Tl (3.15 μg/g). Germanium in the coal is organically associated, and its enrichment is attributed to hydrothermal fluids from the adjacent granitoids. Beryllium is probably associated with Ca- and Mn-bearing carbonate minerals and to a lesser extent with clay minerals, rather than with organic matter. Fluorine largely occurs in clay minerals (kaolinite and illite). The elevated concentrations of Tl, Hg, As, and Sb are mainly distributed in pyrite and were derived from the same hydrothermal source. The high W in the coal occurs in both the organic matter and the authigenic quartz. Illite is the major carrier of Cs in the coal.The accumulation of rare earth elements (REE) in the coals had a polygenetic and multistage nature, including two syngenetic stages (early hydrothermal and terrigenous) and one diagenetic (late hydrothermal) stage. The REE distribution patterns of the early hydrothermal and terrigenous stages were characterized by the enrichment of medium REE (M-type REE) and light REE (L-type REE), respectively. A H-type REE distribution pattern (HREE enrichment) occurred in the late diagenetic hydrothermal stage.The high-Ge Wulantuga coals are also abnormally enriched in precious metals. Gold, Pt, and Pd in the coals, calculated from their concentrations in the LTAs, are 3.5–25.8, < 4–25.5, and < 2.5–15.5 times higher in comparison with those in the continental crust. The highest concentrations of precious metals occur in the pyrite contained in the coal and are 18 (Pd), 130 (Au), and 725 (Pt) times higher than those of the continental crust. The pyrite is probably the basic carrier of the Pt and some portion of the Au in the coal; additionally, a portion of precious metals may be organically (halogen-organic) bound in the coal.
MORPHOLOGICAL studies of the North Atlantic Ocean show a heterogeneous
ocean floor between the continental shelves of Europe and Greenland.
Submarine ridges and banks divide it into several basins. Geophysical
studies indicate that the Mid-Atlantic Ridge, Jan Mayen Ridge, and Mohns
Ridge play important roles in the evolution of the ocean floor using the
concept of seafloor spreading and continental drift. In the past few
years the Iceland-Faeroe Ridge has also been of interest.
The present book is designed as an introduction to the geology of the Faeroe Islands and as an aid to the understanding of the geological map of the Faeroe Islands, which was recently published with an accompanying description in Danish by the Geological Survey of Denmark (Danmarks Geologiske Undersøgelse 1. Række Nr. 24. Beskrivelse til Geologisk Kort over Færøerne i malestok 1:50,000 ved Jóannes Rasmussen og Arne Noe-Nygaard. English Summary). The Danish account will be referred to hereafter as the Memoir. During the geological investigation of the Faeroe Islands it was attempted to produce a map showing a naturally delimited part of the North Atlantic basalt province at a scale larger than that normally used in an area of plateau basalts. This was possible because the area concerned was small and the rocks were well exposed.
In this study, petrographic examinations along with proximate, calorific value, ultimate, sulphur form and XRD analyses were performed in order to determine the coal characteristics and the depositional environment of the Miocene Çan coals. Seventy coal samples were taken from cores and open pit mines.The investigated Çan coals are humic coals and classified as lignite to sub-bituminous coal based on the random huminite reflectance (0.38–0.54% Rr), volatile matter (45.50–62.25wt.%, daf) and calorific value (3419–6479kcal/kg, maf). The sulphur content of the Çan coals changes from 0.30 up to 12.23wt.%, and a broad range of ash contents was observed varying between 2.46wt.% and 41.19wt.%. Huminite is the most abundant maceral group (74–95vol.% mmf) consisting of mostly humocollinite (gelinite) which is followed by relatively low liptinite (2–18vol.% mmf) and inertinite content (2–13vol.% mmf). In general, major mineral contents of coal samples are clay minerals, quartz, mica, pyrite and feldspar.The Çan–Etili lignite basin consists of mainly volcano-clastics, fluviatile and lacustrine clastic sediments and contains only one lignite seam with 17m average thickness. In order to assess the development of paleo-mires, coal facies diagrams were obtained from maceral composition. According to the Vegetation Index (VI) and Ground Water Index (GWI), the Çan coal accumulated in inundated marsh, limnic and swamp environments under a rheotrophic hydrological regime. In general, the facies interpretations are in accordance with the observed sedimentalogical data.
A B STR ACT: Mineralogical and chemical examination of Tertiary interbasaltic clays from the Faeroe Islands revealed three types of alteration of volcanic tufts and basalts: (1) Argillization of volcanic tufts within a lacustrine environment resulted in the formation of aluminous beidellites and metahalloysites; these clays are associated with extensive coal layers at Suduroy. (2) Argillization of volcanic tufts due to hydrothermal action resulted in the formation of thick layers of ferriferous beidellites associated with small amounts of hematite and zeolite (e.g. at Nolsoy). (3) Meteoric alteration of volcanic tufts and basalts, which took place under hot climatic conditions and contrasting seasons, led to the development of ferriferous and aluminous-ferriferous beidellites, metahalloysite, kaolinite, hematite and goethite in low (Hov profile) or high (Oravik profile) topographical positions. The three processes occurred individually or were superimposed.
The Paleocene flood basalts of the Faroe Islands form a central part of the North Atlantic Igneous Province, but have proven difficult to date because of very low-grade burial metamorphism in the chabazite-thomsonite to the laumontite zeolite zone. We present 17 replicated K/At and 8 Ar/Ar whole-rock analyses of basalts from the >3 km thick lower basalt formation, the age of which has been debated for years. Samples are from the massive core of thick, exposed flows, and two boreholes (Vestmanna-1 and Lopra-l). Six samples are drill cuttings. Extensive microprobe work and mass balance calculations show that roughly 60% of the potassium of the dated basaits resides in plagioclase, interstitial cryptocrystalline rhyolite and smectitic clay, the rest mainly forming thin rims of alkali feldspar on plagioclase. Six basalts fulfil the following criteria: (1) they are almost homogeneous in K and Ar (ages on different splits vary by <4Ma); (2) the only low-temperature phase present is smectite (saponite ± minor inter-stratified chlorite-smectite); and (3) max. c. 6% of total K occurs in smectite. This smectite replaced metastable interstitial glass during early burial and has a trivial effect on measured ages. The six basalts give mean K/Ar whole-rock ages of 56.5 ± 1.3 to 58.9 ± 1.3 Ma (1σ), which are interpreted as igneous ages consistent with mapped palaeomagnetic reversals and unpublished Ar/Ar dates. They suggest that the oldest drilled lavas erupted at 58.8 ± 0.5 Ma (lσ) in the later part of magnetochron C26r accumulating at >2kmMa-1, and that the volcanism came to a slow end at 56.4 ± 0.5 Ma in the beginning of chron C24r. The Lower Basalt Formation is overlain by 10 m of coal-bearing sediments and 2 km syn-breakup iavas, deposited in early C24r (>55 Ma). The remaining 11 basalts are either inhomogeneous, carry > 10% of the total K in clay, have C/S > saponite or contain traces of zeolites, secondary quartz, dioctahedral smectite or celadonite as probable indicators of prolonged alteration, and they give low or variable K/Ar ages. The Ar/Ar analyses include five of these poor samples plus three of the first group. They give a plateau age of 55.7 ± 0.9 Ma (1σ) for two exposed flows assigned to chron C25n, but of 60-63 Ma for six drilled lavas assigned to C26r. We argue that the later Ar/Ar ages are too high due to 39Ar recoil loss out of the sample (0-25%) or relocation during irradiation and should be ignored.
Unexpected Early Namurian (Namurian A) sediments were identified in several boreholes in the vicinity of Němčičky (the Němčičky basin), south Moravia. Coal fragments were recovered from the boreholes Něm 1, 2, 5 and 6. These fragments come partly from in situ coal seams, partly from eroded coal seams and partly from coalified logs. Although these fragments were recovered from depths of 2690.9m (Něm 5) to 4803m (Něm 1), their mean reflectance (R 0) is 0.57% up to 0.9% which corresponds to subbituminous to high volatile bituminous coal. The very low rank of the coal at these depths argues for very fast coalification of the coal fragments most likely during the Carboniferous. The rank of the coal is believed not to have been affected by later burial beneath Jurassic sediments or by tectonic burial under Carpathian nappes.
Changes in high-volatile bituminous coal (Pennsylvanian) near contacts with two volcanic intrusions in Illinois were investigated with respect to optical properties, coal chemistry, and coal pore structure. Vitrinite reflectance (Ro) increases from 0.62% to 5.03% within a distance of 5.5 m from the larger dike, and from 0.63% to 3.71% within 3.3 m from the small dike. Elemental chemistry of the coal shows distinct reductions in hydrogen and nitrogen content close to the intrusions. No trend was observed for total sulfur content, but decreases in sulfate content towards the dikes indicate thermochemical sulfate reduction (TSR). Contact-metamorphism has a dramatic effect on coal porosity, and microporosity in particular. Around the large dike, the micropore volume, after a slight initial increase, progressively decreases from 0.0417 cm3/g in coal situated 4.7 m from the intrusive contact to 0.0126 cm3/g at the contact. Strongly decreasing mesopore and micropore volumes in the altered zone, together with frequent cleat and fracture filling by calcite, indicate deteriorating conditions for both coalbed gas sorption and gas transmissibility.
In Jharia coalfield, nearly 1250 Mt of coking coal has been devolatilized due to igneous intrusives and ∼ 1900 Mt due to mine fires. This paper is an effort to investigate the effect of carbonization in two intrusive affected coal seams of Ena (seam XIII) and Alkusa (seam XIV) collieries of this coalfield. Through petrographic studies by microscopy, characterization of normal and heat-affected coals was carried out. The microstructures and microtextures produced due to extraneous heat have been related to nature and extent of heat, location of heating source, and quality and quantity of natural coke produced. Based on the results of this study and earlier studies, an effort has been made to study the classification scheme for microtextures of natural cokes generated through in-situ carbonization of the coal seams. It has been observed that in case of such heat effects under overburden pressure, the anisotropy is much more pronounced as compared to laboratory-carbonized cokes. In the mildly carbonized coals (pre-plastic phase, < 300 °C) the vitrinite attained higher reflectance than normal vitrinite, liptinite started disappearing, and inertinite remained unaffected. In the moderately affected coals (plastic phase, 300–500 °C), mesophase spheres and fused natural cokes were generated from the reactives (vitrinite and liptinite maceral groups), the liptinites disappeared, and structurally, the inertinites remained almost unchanged with slight increase in the reflectance value. In the severely heat-affected coals (post plastic phase, > 500 °C) the identified microtextures were mesophase spheres, different shapes and sizes of natural cokes, graphitic sphaeroliths, pyrolytic carbons, inerts with morpho-structural changes and slightly higher reflectance values, and altered and unaltered mineral matters. A gradual change in the heat-affected coals with increasing temperature was observed with respect to location of intrusive body.
The elemental composition of macerals in high-volatile bituminous coals from the Gunnedah Basin, New South Wales, Australia, has been analysed by light-element electron microprobe techniques. The results have been evaluated in relation to maximum vitrinite reflectance trends in vertical section, including the effects of marine influence and igneous intrusions on the coal-bearing sequence. Mean maximum vitrinite (telocollinite and desmocollinite) reflectance for the analysed samples ranges from 0.63% to 0.99%, and to 2.2% for coal affected by igneous intrusions. The carbon content of the vitrinite, as determined by electron microprobe, ranges from 79.74% to 86.07%, and up to 89.06% for the heat-affected coal studied.
An early Miocene (Ottnangian) lignite seam up to 36 m thick occurs in the Oberdorf trough at the northwestern margin of the Styrian Basin. It forms part of the fluvial Köflach–Voitsberg Formation. Petrographic and palynologic data, together with ash yield and sulphur content of samples from two boreholes and two surface profiles have been used to study vertical and horizontal coal facies variations. Numerous partings and a high ash yield show that the lignite originated in a topogenous mire. Petrographic indices and palynological data suggest a wet-forest swamp paleo-environment. A fluvial main parting with channel sediments at the eastern margin of the Oberdorf trough and overbank sediments in its central part splits the lignite into a lower and an upper seam. The lower seam consists of a lower high-ash part with frequent splittings and a higher low-ash part. The upward decrease in number and thickness of silty–clayey partings, interpreted as crevasse splay deposits, reflects the withdrawal of the fluvial sediment source. Coal composition is characterized by an upward increase in (detro-)xylitic coal and in tissue preservation. A good correlation between tissue preservation and percentages of Taxodiaceae–Cupressaceae pollen suggests that this is mainly a result of an increasing contribution of decay-resistant gymnosperms (conifers). The upper seam is also ash-rich. Abundant inertinite at the eastern margin of the Oberdorf trough is related to fire episodes inside or outside the mire. Main features of the upper seam in the central basin are an upward increase in tissue preservation and in percentages of Taxodiaceae–Cupressaceae pollen. High sulphur contents in the fresh-water lignite are a result of a concentration of sulphate-rich waters above the impermeable floors of the lower and upper seams. Carbonate-rich surface waters from the Graz Palaeozoic and Raasberg-Sequence raised the pH value and controlled sulphur (and ash) contents in those parts of the lower seam, which are uninfluenced by the basal sulphur enrichment. Palynomorph spectra are dominated by Taxodiaceae–Cupressaceae pollen and pollen from plants living in a mixed mesophytic forest. Pollen from aquatic and reed plants are rare. The ratio between arctotertiary and paleotropic pollen is close to one and supports the early Miocene age of the lignite. The detected pollen spectra point to warm–temperate subtropic and humid conditions.
We combine new and published 40Ar/39Ar age determinations from incremental heating experiments on whole rocks and mineral separates to assess the timing, duration and distribution of volcanic activity during construction of the North Atlantic Igneous Province. We use these ages together with volume estimates of erupted magmas and their cumulates to calculate melt production rates for the early Tertiary flood basalts of East Greenland and the Faeroes Islands. The lavas lie at opposite ends of the Greenland–Iceland–Faeroes Ridge, the postulated Iceland hotspot track, and record volcanic activity leading up to, during and following continental breakup between Greenland and Europe.
The Faroe Islands Basalt Group (FIBG) is a continental flood basalt province with four proven lithohorizons that have abundant spot height data. The spline interpolation method was used to construct spatial surfaces for the lithohorizons. The resultant surfaces conform to dip and strike estimates that were previously modelled by hand and confirm the methods reliability. The surfaces should be used as guides only, but can be quickly and easily updated as new information becomes available. The surfaces have been used for a variety of different tasks, for example, obtaining gross thickness estimates, producing isopach maps and constructing geological cross-sections. An additional benefit of the spatial surfaces is the ability to constrain disparate observations in a stratigraphic framework, which will be particularly important for future studies attempting to understand, for example, the temporal and spatial development of continental flood basalt volcanism. The spline interpolation method applied in this study can be equally used for other stratigraphic horizons (e.g. chemohorizon, chronohorizon, biohorizon) and in other continental flood basalt provinces (e.g. Deccan Traps, Columbia River Basalt Group).
The Culver-Baer mercury deposit is located within the strike-slip Mercuryville fault zone. Silica-carbonate rock is silica rich at the centre of the deposit and consists of the assemblage quartz+magnesite+pyrite. This assemblage is cut by numerous quartz-chalcedony veins and breccia veins composed of quartz+chalcedony±cinnabar±millerite±barite. Geochemical modelling indicates that the mineralogical zonation from serpentinite to silica-rich silica-carbonate rock in the centre of the deposit can arise from the interaction of serpentinite with a CO 2-rich, H 2O-CO 2 fluid (PCO 2≥30 bars at 200°C). The association of petroleum and cinnabar, particularly along the hanging walls of breccias, is most likely due to a common source and transport in a relatively buoyant fluid rather than due to a direct chemical link. Because there is no evidence for the introduction of any other components, these data suggest that the Culver-Baer deposit may be a fossil condensate zone. -from Authors
Despite the common association between mercury deposits and liquid hydrocarbons, the effects of mercury organic interactions on mercury transport have received little attention. In this study, we estimate the extent of aqueous mercury complexation, and the partitioning of mercury among aqueous liquid, aqueous vapor, and an organic phase, quantifying the relative importance of each phase in mercury transport. The calculations suggest that significant mercury transport in the aqueous liquid, predominantly as Hg (aq)0, is only possible under relatively oxidizing and alkaline conditions. The frequent occurrence of liquid hydrocarbons in mercury-depositing hydrothermal systems, however, implies that conditions are reducing and that aqueous liquid transport of mercury is relatively unimportant. High concentrations of mercury also can be dissolved in aqueous vapor. However, boiling rarely occurs at the depths at which the ore solutions originate, and thus, the presence of a vapor phase is unlikely during mercury transport. Extrapolation of low-temperature experimental measurements of mercury solubilities in organic phases enables quantitative estimates of mercury concentrations in liquid hydrocarbons under hydrothermal conditions. Our calculations suggest that extremely high concentrations of mercury can dissolve in the organic phase and that organic phase transport may control mercury mobilities in many mercury ore- forming hydrothermal systems.
A comparative study based on a nongenetic classification of mercury ore deposits from around the world suggests that mercury is derived from sediments rather than from magmas and is mobilized by volcanic heat. Under favorable circumstances the metal may be concentrated in hydrothermal fluids of superficial origin. The amount of mercury liberated by igneous processes can be estimated by numerical application of the heat transfer theory on a model based on geologic data. Results of such calculations suggested that quantities of mercury sufficient to form most ore deposits can be generated by this process.