Preliminary mineralogical investigation of Leicestershire low-rank coal

A preliminary mineralogical/geochemical investigation of low-rank coals from Leicestershire, England, has been carried out with a view to their future beneficiation. Analytical scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) have been used to identify and assess the distribution of mineral phases likely to give corrosion-producing or slag-forming materials during combustion, and those minerals which would be potentially valuable by-products of beneficiation processes. Differences in the mineral petrography of borehole samples from the Vale of Belvoir Prospect and coal from Bagworth Colliery are compared. Samples from both areas contain substantial amounts of epigenetic minerals: calcite, dolomite, kaolinite and fluor-apatite are important phases in the Bagworth sample, whilst gypsum, illite, quartz, kaolinite, barytocelestine, pyrite, chalcopyrite, anatase, galena and sphalerite occur in the Vale of Belvoir samples. Whereas the presence of halides in the Bagworth coal would seem to be a possible source of boiler-corrosion problems, the major undesirable characteristic of the Vale of Belvoir coal is the presence of significant amounts of metal sulphides. However, extraction of sulphides from this coal prior to combustion could provide a valuable source of metals as a by-product. Certain trace element concentrations in the Vale of Belvoir samples have also been determined by instrumental neutron activation analysis (INAA) and higher levels of lanthanide elements are present in the whole coal relative to mineral veins (mainly gypsum). Trace-element signatures may provide a useful distinction between syngenetic and epigenetic mineral formation.     

Mineral matter in triassic and tertiary low-rank coals from South Australia

The minerals and non-mineral inorganic constituents in Triassic and Tertiary low-rank coals from various coal deposits in South Australia were studied using selective chemical leaching and oxygen-plasma ashing techniques. Although gypsum may be present in some samples, most of the sodium, calcium and magnesium, as well as part of the sulphur, appears to occur as a combination of dissolved ions in pore water and exchangeable ions attached to carboxylate groups. Significant concentrations of iron and aluminium occur in acid-soluble form, probably as organometallic complexes within the hydrocarbon structure.Quartz is the dominant mineral in the Tertiary coal samples. It appears to be mainly detrital, but doubly terminated euhedral crystals suggest an authigenic origin in one of the deposits. Well crystallized kaolinite is common in the Triassic coals, while poorly crystallized kaolinite occurs in the Tertiary samples. Siderite, calcite and possibly collophane occur in the Triassic coals; sparse pyrite is present in both the Tertiary and the Triassic samples.The differences in minerals and other inorganic constituents between the Tertiary and Triassic deposits can be explained partly by variations in the composition of the pore waters permeating the strata, and partly by mobility of silica and alumina from different sources within the peat deposit. The relative mobility of the different inorganic constituents is also significant in beneficiation of the coal for use in combustion processes.     

考虑滑脱效应的低阶煤动态渗透率预测新模型

为准确预测低阶煤动态渗透率变化规律,在煤岩立方体模型基础上,考虑基质孔隙和滑脱效应对渗透率的影响,建立低阶煤动态渗透率预测新模型,并对影响绝对渗透率和滑脱系数的因素进行敏感性分析,讨论了甲烷和氮气对基质收缩与滑脱效应的影响。研究表明：基于“火柴棍”假设建立的模型是新模型不考虑基质孔隙时的一个特例,P-M、S-D模型与新模型相比基质收缩作用更加明显,考虑基质收缩与滑脱效应的新模型更具实用性。气体郎格缪尔应变是影响基质收缩的关键,煤岩绝对渗透率能否反弹是割理压缩、基质孔隙膨胀、基质弹性形变和基质收缩4个因素共同作用的结果。相同条件下,甲烷的基质收缩强于氮气,氮气的滑脱效应强于甲烷,影响滑脱系数的因素包括内因和外因,滑脱系数与割理宽度随孔隙压力变化时呈现相反规律。滑脱效应和基质收缩效应共同提升气测渗透率,煤岩孔隙压力越低,二者对渗透率的提升作用越明显。     

低煤级煤与UO22+的吸附络合及亲煤型铀矿成矿过程

针对中国亲煤(煤系)砂岩型铀矿床成矿过程,以不同氧化程度的低煤级煤为研究对象,采用分光光度法研究煤对铀酰离子的吸附络合作用.结果表明,煤对铀酰离子(UO22+)的吸附作用受煤氧化程度、煤种、溶液pH值、环境温度和铀溶液初始浓度等因素影响.脱附实验和红外光谱分析进一步证明,煤中活性官能团与铀酰离子发生了明显的化学吸附/络合作用.基于上述结果,提出了亲煤型砂岩铀矿的成矿过程,为揭示煤与铀矿共伴生关系提供了基础数据.     

Delineation of the distinctive nature of tertiary coal beds

Floral character in mires has changed progressively through time. In the Carboniferous, pteridophytes, sphenophytes and lycophytes were dominant but by the Permian gymnosperms were an important component of mire flora. During the early Mesozoic gymnosperms remained the characteristic mire vegetation, together with pteridophytes, and conifers became dominant during the Jurassic. Cretaceous and Paleocene vegetation are similar, with taxodiaceous flora being important in mire vegetation. From the Eocene onwards, however, angiosperms were increasingly dominant in mire communities and in the Miocene herbaceous vegetation began to play a significant role. Together with these changes in floral character at least three aspects of coal character also appear to vary sequentially with time and are distinctive in the Tertiary: (1) proportions and thickness of vitrain banding, (2) coal bed thickness and (3) proportions of carbonised material. A compilation has been made of data from the coal literature comparing older coals with those of the Tertiary, in order to give a perspective in which to examine Tertiary coals. It was found that only Tertiary coals contain significant proportions of coal devoid of vitrain bands. In addition, Tertiary coals are the thickest recorded coal beds and generally contain low percentages of carbonised material (many less than 5%) as compared to older coals. It is interesting to note that Paleocene coal beds are similar to Cretaceous coals in that they tend to be thinner and contain higher proportions of carbonised material than do younger Tertiary coals.The absence of vitrain bands in some Tertiary coal beds is thought to result from the floras dominated by angiosperms, which are relatively easily degraded as compared to gymnosperms. The thickness of Tertiary coals may be related to an increase in biomass production from the Carboniferous through to the Tertiary, as plants made less investment in producing lignin, an energy-intensive process. In addition, with less lignin in plants, easier degradation of biomass may have facilitated nutrient recycling which, in turn, led to greater biomass production. Increased biomass production may have also ‘diluted’ the carbonised material present in some Tertiary peats, leading to lower proportions in the coal. Another possible cause of decreased carbonised components in Tertiary coal is that decreasing lignin content resulted in decreased charring during fires, as lignin is particularly prone to charring. A third possibility is that the carbonised component of peat may be concentrated during coalification so that Tertiary coals, generally of lower rank than Mesozoic or Paleozoic coals, contain a smaller fraction of carbonised plant material. It is not at present clear which of these mechanisms may have affected carbonised material in peat and coal but it is clear that lignin type and content has had an important role in determining peat and coal character since the Paleozoic.     

Diagenetic history of a North Sea chalk

A study of the petrofabrics of Danian and uppermost Maastrichtian chalk from the North Sea was undertaken to investigate its particulate components and diagenetic history. Danian and Maastrichtian chalks are intensely mottled and burrowed globi-gerinid lime mudstones. The Danian chalk matrix is composed of coccolith and thoracosphaerid debris, whereas the Maastrichtian chalk matrix contains mainly coccoliths. The lower part of the Danian is often argillaceous. Three modes of lithification are evident—a spot-welding of adjacent grains (important in Danian chalk), selective overgrowths (prolific in Maastrichtian chalk), and a sparry calcite pore filling associated with Maastrichtian stylolitization. Not only does the scant cementation of chalk stem from an inadequate source of metastable calcium carbonate in the form of aragonite, but also indirectly in that extensive pressure-solution is impeded by certain pore fluid compositions. Pressure-solution can occur only at point contacts where a threshold linear pressure is exceeded and so allows an increase in calcite solubility. It is proposed that through the formation of spot-welds an initial rigid intergranular framework is constructed in chalk relatively early during diagenesis. Subsequent increases in overburden eventually permit extensive stylolitization and the late diagenetic reprecipitation of a sparry calcite pore filling adjacent to stylolites. The time and genesis of selective overgrowths is less clear.     

准噶尔盆地彩南地区深层低阶煤吸附特征及其影响因素

现有数据表明我国1 000 m以浅低阶煤层含气量普遍偏低,而深层低阶煤试采效果显示较好。基于Langmuir方程开展了低阶煤高温高压环境下等温吸附模拟实验,结果表明：褐煤吸附量约占长焰煤、气煤吸附量的1/3,吸附能力最弱,随着煤阶的升高,吸附量逐渐增大;实验发现低阶煤在55℃、12 MPa以下吸附量随温度、压力增大而增加较快,并建立了基于煤阶-温度-压力条件下的深层低阶煤饱和吸附模型;煤层随着埋藏深度的增加,吸附量呈现出快速增加-缓慢增加-缓慢递减的过程,即深层煤层吸附量存在吸附临界深度带,为1 400~1 700 m。1 400 m以浅吸附量受压力正效应大于温度负效应,吸附量随埋深增加而增加,临界深度带内吸附量达到极限,不再增加,1 700 m以深温度负效应大于压力正效应,吸附量随深度增加而减小。实验结果为深层低阶煤层气资源评价及开发潜力提供理论依据。     

某些颗粒灰岩的成岩环境标志和成岩序次

追朔至19世纪,首次将成岩作用术语引入文献要推Moresby (1835)和Gumbeel (1868),后经Walther (1894)及其后很多学者研究才得以广泛使用。而有关碳酸盐成岩作用的专题研究仅是三十多年的历史。开始是成岩阶段分析,侧重在“时间”上研究成岩作用。本世纪五十年代以后,随着开展大量现代碳酸盐沉积工作,对碳酸盐矿物学和流体化学研究的日益深入,才从“空间”变化和分布上讨论碳酸盐成岩作用,即进行成岩环境研究。     

Diagenetic trends in the phenolic constituents of Sphagnum-dominated peat and its corresponding humic acid fraction

Models of peat accumulation assume that peat decomposition occurs mostly above the water table, with little or no decomposition once it enters the deeper, saturated, anoxic zone. Few studies have used molecular biomarkers for tracing post depositional, decomposition-related trends in peat deposits. We studied the major diagenetic changes in the phenolic constituents within a Sphagnum-dominated ombrotrophic bog deposit. The yield of lignin-derived phenols and degree of decomposition, measured using alkaline cupric oxide oxidation of bulk peat samples and their corresponding humic acids, revealed that most of the degradation takes place in the surface layers corresponding to the acrotelm. In fact, total phenolic constituents of peat samples decrease from 36.1 to 21.6 mg g⁻¹ OC (organic carbon) over the first 36 cm, whereas in the deeper anoxic layers, phenolic constituents tend to accumulate, reaching a highest concentration of 71.0 mg g⁻¹ OC. The diagenetic alteration of these phenolic constituents during peat accumulation involves significant demethoxylation and an increasing yield of vanillyl oxidation products despite the low redox potential. Syringyl phenols tend to be particularly resistant to diagenetic alteration and are significantly enriched within the humic acid fraction (twofold) with respect to the bulk peat. This, together with the higher degree of oxidation, suggests that this organic matter fraction is enriched in more resistant, but nonetheless diagenetically altered, phenolic constituents. This suggests that humic acids constitute a refractory pool of organic C with a relatively low turnover rate. Our results confirm that the major processes involved in the variation in phenolic constituents with depth are strongly related to the post depositional environment and that evaluation of diagenetic trends in phenolic constituents may provide molecular-level information on the changes that fresh biomass undergoes during early diagenesis in peatlands.     

Diagenetic trends in the siliceous facies of the Monterey Shale in the Santa Maria region, California

X-ray diffraction and oxygen isotopic analyses of outcrop and subsurface samples of siliceous rocks were used to reconstruct thermal and diagenetic histories of the Miocene Monterey Shale near Santa Maria, California. Within many stratigraphic sections soft, porous diatomaceous rocks change gradationally to underlying hard and brittle chert, porcellanite, and siliceous shale; the accompanying silica mineral zones are, in descending stratigraphic order: (1) biogenic silica (opal-A), (2) cristobalitic silica (opal-CT), and (3) microcrystalline quartz. Boundaries between silica mineral zones and stratigraphic horizons are often discordant. Within the opal-CT zone, the d(101)-spacing of opal-CT decreases in a smooth non-linear fashion from about 4 10 Å to 4-04 Å. In the Santa Maria Valley and Bradley oil field areas the thicknesses of the opal-CT zones are greater and the present thermal gradients less than in the adjacent Orcutt oil field. Thin opal-CT zones at shallow maximum burial depths apparently correlate with higher thermal gradients. Using present thermal gradients and reconstructed maximum burial depths from well data in the Santa Maria region, the ranges in temperatures for the top and base of the opal-CT zone are 38–54 °C and 55–110 °C, respectively. The temperature difference between these two boundaries ranges from 17 to 60 °C. In comparison, temperature ranges for these two boundaries computed from oxygen isotopic compositions of opal-CT and quartz, extrapolated experimental quartz-water fractionations, and assuming δO¹⁸= 0%_o for the isotopic composition of the equilibrating fluid are 18–56 °C and 31–80 °C for the top and base of the opal-CT zone, respectively. The temperature difference between these boundaries is 11–36 °C using this method. Thermal gradients and sedimentation rates strongly influence rates of silica transformations. Reconstructed thermal and diagenetic histories of siliceous rocks of the Monterey Shale at four well sites in the Santa Maria region demonstrate that most silica conversions probably occurred during the last 3–4 Myr in response to accelerated rates of sedimentation (and therefore burial heating) during the Pliocene.     

Diagenetic trends of fluorine concentration in Negev phosphorites, Israel: implications for carbonate fluorapatite composition during phosphogenesis

An electron probe and chemical study of bulk phosphorite samples and separated constituents from various Negev deposits was carried out together with XRD, FTIR spectroscopy and textural analysis. The results allow a better understanding of the distribution of fluorine in these Upper Cretaceous phosphorite sequences and shed light on variations in the composition of the carbonate fluorapatite (CFA) phase during phosphogenesis. Two facies are recognized: (1) a pristine, microbially generated phosphorite facies; (2) a recycled, peloidal and biodetrital facies. Fluorine distribution in the Negev phosphorites is facies controlled: F/P₂O₅ is much lower in the pristine facies (0·090–0·107) than in the recycled facies (0·107–0·120). In addition, F/P₂O₅ varies considerably between the various constituents of the phosphate fraction; F‐poor francolites (F/P₂O₅ as low as 0·080) co‐exist with F‐rich francolites (F/P₂O₅ as high as 0·135) in the same phosphorite bulk sample. A lower F/P₂O₅ in francolite is associated with higher Cd and Zn concentrations in the phosphorite, an increase in Fe‐rich smectites in the clay fraction and the presence of structural OH in the francolite. The lower F/P₂O₅ ratios in the pristine facies are attributed to high organic deposition rates during the formation of these matted sediments, leading to rapid burial of the in situ‐forming CFA. This is possibly coupled with diffusion of F from sea water into bottom sediments being hampered by microbial mat coatings. These conditions resulted in O₂‐depleted porefluids, inducing the precipitation of Cd‐rich Zn sulphides and the formation of Fe‐rich smectites. F‐enrichment probably takes place when the earlier formed F‐poor ‘primary’ CFA is relocated close to the sea floor and bathed with interstitial sea water solutions of higher F concentrations. Oxidation and removal of the sulphide‐bound Cd and Zn apparently occurred together with enrichment in F of the francolite. Combining chemical data with XRD and FTIR results suggests a multistage growth for the Negev phosphate constituents in shifting formational sites and porefluids of varying F concentrations. This multiphase growth is reflected in the patchy distribution of F in the Negev constituents and might explain the inverse correlation between mean CO₂/F and F/P₂O₅ ratios of the analysed phosphorites in the two facies. It also suggests that CFA (or an amorphous precursor) initially formed with some OH groups in the apatite structure, which were subsequently substituted by F ions in recycled francolite through re‐equilibration with porefluids of higher F concentrations.     

长春市白垩纪煤系及煤矿特征

介绍了早白垩世营城组煤系与营城子组有关的岩浆岩、构造,煤盆地地球物理特征,煤矿床概况,煤矿床类型,煤炭资源现状。     

Volcanogenic tonsteins from tertiary coal measures,East Kalimantan,Indonesia

Laterally persistent tonsteins, up to 30 cm thick, occur in coal seams and associated sediments in the Tertiary Kutei Basin of East Kalimantan, Indonesia, where Neogene strata which form a generally eastward-prograding, marginal-marine to fluvio-deltaic sequence, are disposed in a north-northeast to south-southwest striking fold belt, centred on Samarinda. Eight tonsteins have so far been recorded in the middle to upper Miocene of the Badak syncline, some 40 km south-southwest of Samarinda, and range from tonsteins in the strict sense (kaolinite-mudstones of wide stratigraphical extent) including graupen and kristall varieties, to smectite-mudstones. They may pass laterally into each other. Most contain pyroclasts in varying stages of alteration and are regarded as volcanogenic. Primary textures include microscopic vitroclastic aggregates completely argillised to smectite, graded crystal-tuffs with abundant sanidine, glass shards and secondary vermiform kaolinite crystals, and argillised lithic tuffs. Texturally and compositionally these Tertiary tonsteins are closely similar to European Carboniferous tonsteins and this strengthens the conclusion of a volcanogenic origin even where pyroclastic textures have been removed through alteration. The East Kalimantan tonsteins are of economic and stratigraphic significance in providing distinctive horizons which have proved useful in aiding correlation of boreholes drilled in a coal-resource project in this area.     

Diagenetic and very low-grade metamorphic characteristics of the Paleozoic series of the Istanbul Terrane (NW Turkey)

The Istanbul Terrane along the Black Sea coast in NW Anatolia, is a Gondwana-derived continental microplate, comprising a well-developed Paleozoic succession. Petrographic and X-ray diffraction studies were performed on rock samples from measured sections throughout Ordovician?CCarboniferous sedimentary units. Diagenetic-very low-grade metamorphic clastic (shale/mudstone, siltstone, sandstone) and calcareous rocks (limestone, dolomite) mainly contain phyllosilicates, quartz, feldspar, calcite, dolomite, hematite and goethite minerals. Phyllosilicates are primarily represented by illite, chlorite, mixed-layered chlorite?Cvermiculite (C?CV), chlorite?Csmectite (C?CS) and illite?Cchlorite (I?CC). Feldspar is commonly present in the Ordovician and Carboniferous units, whereas calcite and dolomite are abundant in the Silurian and Devonian sediments. The most important phyllosilicate assemblage is illite?+?chlorite?+?I?CC?+?C?CV?+?C?CS. Illite and chlorite-bearing mixed layer clays are found in all units. The amounts of illites increase in the upper parts of the Silurian series and the lower parts of the Devonian series, whereas chlorite and chlorite-bearing mixed-layers are dominant in the Ordovician and Carboniferous units. Kübler index values of illites reflect high-grade anchimetamorphism for the Early Ordovician rocks, low-grade metamorphism to high-grade diagenesis for the Middle Ordovician?CEarly Silurian rocks and high-grade diagenesis for the Late Silurian?CDevonian units. The K-white micas b cell dimensions indicate intermediate pressure conditions in the Early Ordovician?CEarly Silurian units, but lower pressure conditions in the Middle Silurian?CDevonian units. Illites are composed of 2M ₁?±?1M _d polytypes in all units, except for Upper Ordovician?CLower Silurian units which involve 1M polytype in addition to 2M ₁ and 1M _d polytypes. The 2M ₁/(2M ₁?+?1Md) ratios rise from Devonian to Ordovician together with the increasing diagenetic-metamorphic grade. Chlorites have IIb polytype. In general, crystal-chemical data of clay minerals in the Istanbul Terrane show a gradual increase in the diagenetic/metamorphic grade together with increasing depth. The new data presented in this work indicate that the diagenetic/metamorphic grade of the Paleozoic of the Istanbul Terrane is higher than that of the neighboring Zonguldak Terrane and generated by a single metamorphic phase developed at the end of Carboniferous. This finding contrasts with the metamorphic history of the neighboring Zonguldak Terrane that displays a distinct Early Devonian unconformity and a thermal event.     

Diagenetic development of a Precambrian limestone as interpreted from a modern analogue

A strong correlation in the geometry and mineralogy of two cement generations of a Quaternary with a Precambrian calcarenite enables us to reconstruct the diagenetic history of the Precambrian limestone. Both calcarenites contain two cement generations (A and B) of which A consists of dolomite, B of calcite. The following diagenetic stages can be recognized: after deposition of the allochems in a shallow marine environment, cementation in the intertidal zone with magnesian calcite (cement A) led to the formation of beachrock (Stage 1). By lowering of the sea level, the beach rock was shifted into the supratidal zone, but still remained under the predominant influence of the sea water (breakers, spray). During longer periods of aridity, the magnesian calcite of cement A and of the allochems was transformed into dolomite by brines derived from sea water with very high Mg/Ca ratio (> 15), whereas aragonite and calcite remained unaffected. After further lowering of the sea, an increasing influence of meteoric water caused the wet transformation of aragonitic allochems to sparry calcite and to the precipitation of sparry calcitic cement B.     

梵王寺井田含煤岩系沉积环境分析

从收集整理以往资料入手,以梵王寺井田地质资料为基础,分析梵王寺井田含煤岩系、沉积环境与聚煤特征。本井田含煤岩系与沉积体系主要为：滨海弱障壁泻湖潮坪体系、有潮汐影响的浅水三角洲（水下）体系、多河系浅水三角洲（水上）、体系以及由曲流河为主的冲击平原体系。其中,在滨海弱障壁泻湖潮坪和浅水三角洲（水上）成煤期成煤环境较好,利于成煤。     

Diagenetic metal profiles in recent sediments of a scottish freshwater Loch

Integrated total elemental, phase-specific, and pore-water analyses of sediment cores from Loch Ba, Scotland, show that early diagenetic processes have promoted extensive metal enrichment immediately beneath the sediment-water interface. The accumulation of Mn, Pb, Zn, Cu, and Co in sedimentary solids upward of 3 cm depth is accompanied by an increasing residence of these elements in adsorbed and hydrous oxide phases. Such phases are formed through oxidative precipitation from the interstitial pore fluids, following the upward migration of metals from more deeply buried, anaerobic sectors of the sediment pile. There is good evidence that Fe and Ni are subject to similar influences, although their total abundances near the sediment surface are less conspicuously modified. In the Loch Ba sediments, the oxic conditions promoting metal precipitation are entirely confined to strata of postindustrial age. In the absence of fully diagnostic pore-water and sequential chemical data, similar diagenetic profiles could plausibly be misinterpreted as the product of anthropogenic contamination.     

The crystallisation trends of spinels in tertiary basalts from Rhum and Muck and their petrogenetic significance

Spinels are commonly observed in alkali olivine basalts and olivine basalts that form the Plateau Magma Series of the British Tertiary Province. The spinels are either partly or wholly enclosed within olivine or may have adhered to olivine surfaces, and have undergone cation exchange and reaction with the cooling basaltic melt. Detailed microprobe traverses indicate complex exchanges involving Fe-Mg, Cr-Al, Fe³⁺-R³⁺ and Fe²⁺ Ti-R³⁺ substitutions. Some of these changes are due to a reaction with liquid that produced plagioclase and resulted in Al depletion in the spinel. A complex series of solid solutions between hercynite-magnesioferrite-chromite and Al-Cr-titomomagnetite, is indicated in a combination that precludes the disappearance of spinel by a simple peritetic reaction with the melt. The initial spinels are compositionally distinct from the chromites found in the Rhum layered series and underline the great compositional variability of liquidus spinels that can crystallise from basaltic liquid. Some of this variability may relate to the changing solubility of Cr, which behaves as a trace element, in basaltic liquids in response to slight changes in the structure of the melt.LDGO Contribution no. 2575