Badania petrograficzne węgla pokładu Otto, kopalnia Radzionków, Górny Śląsk

Adam Drath, Stanisław Jaskólski


Petrographical investigations of the Otto coal bed, Radzionków mine, Upper Silesia

Review of the geological literature pertaining to the coal mines situated on the Northern wing of the Trough of Beuthen L1, 38, 45] and on its prolongation to the East [151 showed that the correlation of the coal beds belonging to the „Sattel“Group, and especially the correlation of the Otto coal bed on the Radzionków mine with the coal beds exploited on the neighbouring mines is an open question. Conducting that correlation from the Western boundary of the Upper Silesian Coal Basin, the Otto coal bed should be included in the strata of the Ruda („Mulden“ Group). Investigations made in the mines showed that the Otto coal bed on the Radzionków mine should be correlated with the „1“, or with the „1“ and "11" coal beds on the Andaluzja mine. The last named coal beds Doktorowicz-Hrebnicki [15] compares with the „Fanny“ coal bed („Sattel“ Group) of the mines Jowisz and Grodziec II, which are situated on the Eastern prolongation of the Trough of Beuthen. In order to solve this problem and to give the pétrographie characteristic of the high volatile noncoking coal in that part of the Polish Coal Basin, detailed megascopic and microscopic pétrographie investigations and chemical analyses were made, as the first stage of the pétrographie coal research of the Polish Coal Basin initiated by professor Charles Bohdanowicz . The division of labor during the working out of this problem was conducted in such a way, as to utilise fully the main domains of research of both authors. S. Jaskólski , one of whose special domains of research is the petrography of the anorganic rocks and mineralogy, made pétrographie investigations (by means of heavy liquides) of the mineral substance occuring in the Otto coal bed, and also chemical investigations; and after becoming acquainted with the morphology of macérais, he counted under the microscope the lower half of the microscopic profile. A. Drath one of whose special domains of research is coal petrography collected the literature pertaining to the total performed work, and, on the basis of the scheme of coal research established by him [16], worked out the megascopic profile of the investigated coal seam, and also the morphology of the microscopic constituent of that coal, and counted under the microscope the upper half of the microscopic profile and was occupied with the putting together and designing of the total megascopic and microscopic profile of the investigated coal seam. The text of the work was written by A. Drath with the exception of chapter VIII „Chemical investigations“ and chapter IX „Investigations of the anorganic mineral substances“ which were written by S. Jaskólski. Microphotographs were made by both authors. In chapter I the scheme of the conducted investigations is given. Chapter II is devoted to the geological description of the Radzionków mine, situated in the NW part of the Polish Coal Basin (see fig. I). On the area of Radzionków mine, coal beds belonging to the Marginal Group were encountered only in boreholes (see fig. II). Actual exploitation of the Radzionków mine is confined merely to the coal seams belonging to the „Sattel“ Group (seams: Podkładowy, Serio, Grapow, Otto (?) ) and to the „Mulden“ Group (Edgar, Barbara, Paweł, Louis, Nadkładowy I and Nadkładowy II). Carboniferous in the Radzionków mine is overlaid by Permian (?), Triasie and Pleistocene. Tectonic conditions are very simple (fig. I), the Radzionków mine is situated on the Northern wing of the Beuthen Trough, the strike of the coal seams is N 112° S and the dip 25° to the South. There are only a few faults on the area belonging to the Radzionków mine. In chapter III the reasons are given for the choice of the Otto coal seam as the object of the conducted research, and the manner of taking the samples for pétrographie investigations and chemical analyses ils described. Aqualitative megascopic description of the rock types encountered in the Otto coal bed and the principles of the new international nomenclature used in coal petrography [7, 13, 29] form the contents of chapter IV. The results of the quantitative megascopic investigations (chapter V) are shown on fig. I ll, left hand side. The Otto coal seam is rather weakly differenciated as far as the pétrographie composition is concerned, because it is composed chiefly of durain. But never the less it is possible to distinguish in the profile of the investigated coal bed eight layers having somewhat different megascopic composition. From the quantitative megascopic profile the following probable history of the formation of the Otto coal bed may be deduced: The footwall layer having the thickness of 0,75 m corresponds to the autochtonie stage of the formation of the described coal bed. Forest growing in situ furnished material for the formation of this layer. The vitrain encountered in it derived from trunks of trees, and the durain mainly from spores which partly fell from the local trees, and were partly blown in from the farther regions. In this autochtonie layer vitrain should prevail above the spores and leaf cuticles, which in fact is evident from the megascopic profile. In the next stage the terrain subsiding rather rapidly wTas covered by a thick layer of water, under which began the sedimentation of the material transported from the farther regions. Thus the second layer was formed (actual thickness 0,44 m), which consists of solid durain (without any vitrain lenses). As time went on the subsidence was smaller and smaller, which may be deduced from the larger amount of fusain, which appears in the third layer (1,02 m). The uppermost part of this layer consists of a fusain band 43 mm thick. This fu sain was probably formed during the elevation of the terrain, when a fire destroyed the upper part of the growing coal seam (it is generally believed that fusain was formed by fires). After this time of elevation, a violent subsidence took place, giving rise to a shale deposit (38 mm thick). The first cycle of the formation of the Otto coal bed consists of two phases: 1) autochtonie phase: coal rich in vitrain is formed; 2) allochtonic phase: a) subsidence, the thickness of the water cover is growing and rather thin plant material is supplied (spores—durain); b) elevation, the thickness of the water cover diminishes, this (tree trunks) and thin (spores) plant material is supplied, giving rise to the formation of vitrain and durain lamina. The upper pa rt of the coal bed, from the shale up to the hanging wall, was formed also probably in an allochtonic phase, but during the continual subsidence of irregular amplitude: a) During the formation of the layer (thickness 2,32 m) immediately above the shale the subsidence was probably concordant to the supply of the plant material. Besides spores also fragments of tree trunks were supplied, the former forming durain and the later vitrain bands. b) When the next layer was formed (thickness 1,26 m) the subsidence was not so uniform. In some periods the water cover was so thick, that formation of solid durain took place, but in other periods the water cover was thinner and more vitrainous material was deposited. c) After th a t the subsidence became less intense, under relatively thin water cover, plant material with a larger amount of wood (vitrain) was laid down and gave rise to the last but one layer (1,5 m thick). d) When the hanging wall layer was forming, the oscillation of the area was again more intense. At first began the sedimentation of the alternating lamina of solid durain, finely banded durain, and coarsely banded durain, but finally the subsidence was so great and the supply of the plant material so small, that the hanging wall shale was deposited. The results of the qualitative microscopic investigations (chapter VI) may be summarised as follows: a) Durain, the main megascopic constituent of the Otto coal bed, is composed of several macerals: micrinite, collinite, exinite, semifusinite. Micrinite prevails only in solid durain, but in the other types of durain (micro-, finely-, and coarsely banded) the main constituent is collinite. In the upper part of the profile semifusinite plays the most important role. b) There are several types of megaspores in the Otto coal bed (see Plate X and XI), but as far as the quantity is concerned microspores prevail largely above megaspores, and in some parts of the profile they form even up to 90% of durain lamina. c) Cuticles of sporangia may also be observed in the polished sections of the Otto coal bed. They are not only empty but also filled up with microspores, which very often are p a sted together forming nearly an uniform mass. Sometimes even cones with sporangia may be seen (Plate XII fig. 1—9). d) Leaf cuticles belong to the comparatively rare plant remains in the investigated coal, as a rule are very much decomposed and very thin (Plate XII fig. 10, Plate XIII fig. 1, 2, 3). On the contrary sometimes these cuticles are not only very thick, but also contain beautifully preserved, fine mesophyll structure (Plate XIII fig. 4, 5, 6). e) Resinite or resinous and waxen substance plays a subordinate role among the macerals of the Otto coal seam. It a p pears not only in durain and clarain but also in telinite, filling up certain cell lumina (Plate XIII fig. 7—10, Plate XIV fig. 1—9). Besides the true resinites there were also found pseudoresinites, that is spores very intensively pasted together (Plate XIV fig. 10, Plate XV fig. 1, 2, 3). f) In certain layers of the Otto coal bed fungous tissue plays an important role. It may be subdivided into sclerotia (PI. XVI fig. 4—10, PL XVII fig. 1—6) and other fungous tissue, which could not be exactly defined, because the anatomy of the Carboniferous fungi is scarcely known. Abundant accumulation of sclerotia in certain layers proves th at during the formation of the Otto coal bed there were periods of rather low humidity, (then sclerotia were formed) and periods of comparatively high humidity, favorable for the development of fungi. This statement does not agree with the generally accepted opinion, that during Carboniferous there were uniform, humid climatic conditions. Fungous tissue may be observed only in durain and clarain and it is probable that fungi destroyed not only wood, but also other plant tissues. Fungous remains contained in coal are formed from chitine. It is believed that a comparatively great abundance of these remains in coals is a sufficient reason for the creation of new maceral composed of fungous tissue, for which the name „chitinite“ is proposed. g) The anorganic mineral substance contained in the Otto coal bed may be subdivided into the following two groups: 1) syngenetic, which is supplied together with the plant matter; 2) epigenetic, which is supplied to the coal seam after its consolidation and which fills up fissures caused by the dessication of the colloidal material of coal and by tectonic movements. A microscopical investigation of the polished sections from the Otto coal bed proved that the most important syngenetic substances in that coal were: kaolinitic-clayey substance, pyrite and siderite; these substances may be observed above all in fusinite and durain, in clarain and vitrain they are less common. To the epigenetic substances belongs: calcite, ankerite, dolomite, siderite and pyrite. The abundance of carbonates as epigenetic minerals is comprehensible, when one takes into account, that Carboniferous on the area of the Radzionkow mine is overlain by „Muschelkalk“. Epigenetic minerals fill up the contraction fissures (mainly in vitrain) and tectonic fissures (mainly in durain and clarain). h) Collinite occuring in the coal of the Otto bed is a colloidal, amorphous matter and forms the fundamental substance of clarain and to some degree of durain. In the last named rock types there are also very small fragments of the plant tissues preserved as telinite, but they form only a small fraction of the collinitic mass. i) Telinite in the investigated coal bed forms definite la mina up to the thickness of 38 mm (solid antraxylon of Thiessen), or rather thin (usually less than 1 mm), elongated lenses in durain which may be seen only under the microscope (fibrous antraxylon of Thiessen). The main mass of telinite is derived from the woody tissue, but also other plant tissue may give rise to telinite: mesophyll (phyllinite, or phyllovitrain see Plate XIII figure 4, 5, 6) and cork (suberinite, Plate XX fig. 4, 5). There are two ways in which telinite may originate: 1) from the plant tissues by their compression, without any supply of the outside material (compression type of telinite); 2) by filling up the cell lumina with collinite, which forms a colloidal, fluid mass impregnating the whole coal seam at the time of its formation (impregnation type of telinite). In the first case it is necessary to etch the polished section of telinite in order to make evident the cell structure. In the second case the difference between the chemical composition of the plant tissue (forming a sort of scaffold in that type of telinite) and the collinite (impregnating the cell lumina) is generally sufficient to make evident the cell structure of that type of telinite by simple polishing. Compression type of telinite ought to have comparatively low volatile matter content, because the plant tissue making this type of telinite (mainly wood) is formed from lignine, which has rather low volatile matter content. Collinite originates from the decomposition of all plant remains, therefore also of spores in spore coals, and this fact may explain the high volatile matter content of collinites and also telinites (impregnation type) in the spore coals (flamy and gas-flamy coals). These observations and deductions enabled the first of the authors to explain why the eight samples taken from the entire thickness of the Otto coal bed (Table No. 3) have almost similar chemical composition and volatile matter content, in spite of rather different content of individual macerals. In the same way one may also explain the small difference in the volatile matter content between durain and vitrain stated by R. Potonie [37] in the flamy and gas-flamy coals of the Ruhr Basin, and the great difference (9%) in the volatile matter content in the two layers of vitrain in the same block of coal. j) Fusinite has almost always very distinct cell structure. Very often fusinite is impregnated with anorganic mineral matter, sometimes also fusinite impregnated with collinite may be seen. Results of the quantitative microscopical investigations (chapter VII) are shown on table no. 1 and fig. III right hand side. The content of individual macerals varies in the whole profile rather regularly, except semifusinite, which is the main constituent in the uppermost part of the profile, and telinite, in the lowest part. Micrinite is a subordinate constituent in the investigated coal; only this part of the profile which shows greater than the average content of spores (solid durain) has a larger amount of micrinite (up to 70%). This conformity of micrinite content with spores corroborates the genetic connection between the spores and the micrinite. The most uniformly distributed macerals in the profile are collinite and fusinite. In order to make clearer the changes in the microscopical composition of the entire coal bed, table no. 2 and fig. IV were made, which give the microscopical composition of each meter of the, entire thickness of the investigated bed. The lowest row on table no. 2 gives the average microscopic composition of the Otto coal bed. Three macérais play the most important role as far as the microscopic composition of this coal bed is concerned: collinite, telinite and exinite; therefore one may name the coal of the Otto bed: collinitic-teliniticexinitic coal. Chemical analysess how (chapter VIII, table no. 3) that the investigated coal bed has an average volatile matter content of 37,9% and gives sandy coke; on this basis one may characterize this coal as gas-flamy coal. The comparison of the chemical analyses of samples ta ken from the total thickness of the coal bed, with the results of the microscopic analyses of the same samples (table no. 3) show that a microscopic analyse of a coal bed is a more sensitive tool, than the exact chemical analyses. Pétrographie investigations of the anorganic mineral matter (chapter IX) were conducted in such a way, that the mineral matter was separated from the coal by means of heavy liquids and determined under the microscope. The main anorganic constituents are calcite, pyrite and kaolinitic-clayey substance. Siderite (ankerite), dolomite and quartz appear only as accessory minerals; heavy minerals, very common in sedimentary rocks, form a fraction of one percent of the total mineral content and therefore have no practical importance. Only 38% of the total mineral matter content were separated by means of heavy liquids. The quantity of separated mineral matter content is not proportional to the total amount of mineral matter but depends from such factors as mineralogical composition, coarseness of grains, degree of dissemination in coal, pétrographie structure of coal etc. Therefore not the total amount of mineral matter in coal decides about the commercial value of a given coal bed, but the ease with which this mineral matter content may be separated. A coal bed having a larger, but easily separable amount of mineral matter may be commercially more valuable, than a bed having a lesser amount of mineral matter but which cannot be so easily separated. From the three main mineral constituents pyrite and calcite are the most injurious, because they lower the fusibility point of ash. But fortunately they occur in coarse grains and therefore may be easily separated by the flotation process. Kaolinitic-clayey substance forms very small grains in coal, and is very disseminated, but it raises the fusibility point of ash and therefore is an advantageous component of ash. Similar investigations of one coal bed were made in U. S. A. (State of Illinois), and the same three main components of anorganic mineral matter were found. Therefore one may conclude that calcite, pyrite and kaolinite-clayey substance are main components of anorganic mineral matter in coals in general. From the Illinois coal only 30°/o of the total mineral matter could be extracted, therefore still lesser amount. Each coal bed has its characteristic quantity of extractable mineral matter.

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