Coal seam, variations

Local and regional variation in petrographic character of specific coal beds have been investigated actively for more than forty years. Roos (9) initiated comprehensive studies demonstrating that the character and quality of a coal seam change from place to place and that detailed sections were necessary for insight into the composition of coal. This important type of study has been continued and extended by several workers (3, 4, 5, 8, 10). In the Australian coals, Taylor and Wame noted that changes in microlithotype... 

I find it interesting that in the strata studied by Schopf and Long, the sills lay above the coal seams. This means that the temperature gradient owing to the sill was of opposite sign to the geothermal gradient, and therefore in sequences of samples like those in the table on pp. 166-7, it is the coals that were initially of lowest rank that were more intensely subjected to thermal alteration. This situation may account for the observed variations in H/C-O/C relations with depth below the sill (which are complex) however, since the samples were not taken from vertical boreholes, some lateral variations in the strata no doubt also affect the relations. 

Coal seams display two different modes of variation rank and type. The rank of the material under consideration is anthracite. Regarding type, coal is composed of different bands of materials, distinctly contrasted in regard to physical and chemical composition. These bands are termed lithotypes in this paper, after the word coined by Seyler (2) in 1954. 

The preparation of maceral concentrates for study has been achieved by one of two approaches, either by hand picking or by a variety of techniques which exploit the variation in density between the various maceral groups. The first level of hand picking is the judicious sampling of lithotypes. This term is used to identify the various layers found in a coal seam. For humic coals there are four main designations of lithotypes vitrain, clarain, durain, and fusain (42). Vitrain bands are sources of fairly pure vitrinite group macerals while fusinite and semi-fusinite can be obtained from fusain. These are the... 

In addition to the variation of chemical properties within coal seams, significant variation also occurs between different coal fields in Victoria. An extensive research program in which this variation was investigated has been conducted by the State Electricity Commission of Victoria on behalf of the Victorian Brown Coal Council. 

Rhenish brown coal consists of a variety of lithotypes which are already discernible in the coal seam by brightness variations. 

Variation Within Major Coal Seam. The distribution of elements within the coal seam can be summarized by four general trends 1) concentration of elements in the margins, 2) concentration in the lower part of the seam, 3) even throughout the seam or minor distribution patterns, and 4) irregular distribution. 

During the long period required for the accumulation of sufficient plant debris to form a thick coal seam [estimated as 100,000 years per 100 m (26)], the environment of deposition will show significant changes at any given locality. Variations in the prevailing botanical community, in the depth and nature of the swamp water, and in the conditions of decay and decomposition of plant material result in the formation of coals with different characteristics, i.e., lithotypes. A thick coal seam, therefore, will have a stratified or layered structure, where each layer can be... 

These chemical data support the concept of lithotype variation and demonstrate heterogeneity within a thick coal seam. 

Coal, by virtue of its origin, is quite heterogeneous its mineral content varies considerably both vertically and laterally within coal seams. Vertical variation has resulted from changes through time in the content of mineral detritus introduced into the peat swamp, in the pH, and to some extent in the species of vegetation that inhabited the swamp at any one place or time. This variation has been measured by determining the differences in mineral content in different layers or benches of the seam at particular places. Lateral variation has been measured by analysis of the whole coal seam (channel samples) from one locality to another. 

Variations Between Benches of the Herrin (No. 6) Coal. Variations of mineral matter in bench samples collected from the Herrin Coal seam at five different mines in Illinois were reported by Gluskoter et al. (2.) The total mineral matter (%LTA) varied between benches at one site from 9.2 to 26.5 percent (Figure 5). The variations of several mineral components at the same site are also shown in this figure. The amount of arsenic is related to or is a function of the amount of pyrite. Organic sulfur, silica, and calcium contents varied only a little. Molybdenum ranged from 1 to 49 ppm and was concentrated at the top and bottom of the coal seam (Figure 6). At four of the five sites analyzed, Ge and Mo were enriched in the top and bottom benches. 

Identification and correlation of petrologic benches within the coal seam by Johnson (69) provided a basis for detailed study of the minerals in the coal ( ). The variation of the minerals is distinctly correlated along the traverse (Figure 6). 

Inorganic element concentrations in coal show variations from a microscopic to a worldwide scale. From a resource evaluation perspective, the most significant variations occur within and between coal seams and basins. The rest of the paper will discuss factors that cause these variations. 

The self-developed mining-induced stress testing system can accurately test the variation of mining-induced stress in front of the working face with the advance of working face under three soft coal seam geological conditions. 

Make use of the FLAC ° software to simulate the variation rule of the stress and displacement in coal seam 13-1 during the panel 1311(1) extraction. The height of the model is up to the roof of coal seam 13-1, the mining direction (strike direction) is defined as x-axis, the vertical strike direction of coal seam is y-axis, and the vertical direction of panel is z-axis. The size of the... 

The best analogy for the macroscopic structure of coal is a fruitcake. The dough corresponds to the principal maceral, vitrinite, while the various goodies correspond to the different macerals spread throughout. The ground nnts play the role of the mineral matter. The composition of the fruitcake is not rank dependent, but rather is due to the original coal deposition and depositional enviromnent. The mac-erals become more like one another as rank increases, but their proportions are not rank dependent. In fact, their relative proportions vary with both vertical and horizontal positions in a coal seam, with the vertical variation occur-ing over a much shorter distance scale. 

Seam correlations, measurements of rank and geologic history, interpretation of petroleum (qv) formation with coal deposits, prediction of coke properties, and detection of coal oxidation can be deterrnined from petrographic analysis. Constituents of seams can be observed over considerable distances, permitting the correlation of seam profiles in coal basins. Measurements of vitrinite reflectance within a seam permit mapping of variations in thermal and tectonic histories. Figure 2 indicates the relationship of vitrinite reflectance to maximum temperatures and effective heating time in the seam (11,15). 

The petrography of brown coals differs from that of black coals and is less well developed. However, evidence is mounting that brown coals can vary significantly, even within the same seam, and that these variations may effect their conversion behaviour. 

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