MATERIAL COMPOSITION OF BROWN COALS FROM THE KHARANOR DEPOSIT

O. A. Dulzon

(Presented by Professor A. V. Aksarina)

The Kharanor brown-coal deposit is located in the Kharanor-Turga depression in the southern part of Eastern Transbaikalia. According to studies of the coal-bearing deposits of Transbaikalia by N. F. Karpova and L. P. Nefed’eva [5], the brown coals of the Kharanor deposit were assigned to the Lower Cretaceous. The first petrographic description of the coals of the Kharanor deposit was carried out from exploratory boreholes by O. G. Rumyantseva in the 1940s. A detailed petrographic description of the material composition of the coals was carried out by the author according to the new terminology established by GOST 9414-60 [1].

The macroscopic description of the coal was carried out in a trench of the Kharanor open-pit mine. The coal of the Moshchnyi seam is black with a brownish tint and has an angular fracture. By luster, the Kharanor coals may be divided into dull and semidull. Dull coals make up 80.1%, and semidull coals 19.9%.

The striated, striated-banded, and banded structure of the coal is due to the presence of small lenses and bands of vitrain and fusain. The coal also contains frequent inclusions of lignite measuring \(0.5 \times 1.0 \div 5 \times 30\) cm. The lignites of the Kharanor coals are characterized by good preservation of the woody tissue.

To study the material composition of the coal-forming plants of the Kharanor deposit, 273 coal samples were examined in polished sections and polished blocks. The percentage content of microcomponents in the Moshchnyi coal seam was also counted. Counting of microcomponents was carried out on an ISA-type integration table. Conversion of microcomponents in polished sections and polished blocks to the content of microcomponents in the coal seam was carried out according to the method of Z. V. Ergol’skaya [3].

According to GOST 9414-60 [1], the Kharanor coal of the Moshchnyi seam is composed predominantly of microcomponents of the following three groups:

vitrinite, fusinite, and liptinite. The vitrinite group of the Kharanor coals is characterized by a diversity of microcomponents.

The microcomponents of the semivitrinite group in the Kharanor coals are isolated and are combined with the fusinite group, to which it is close in chemical-technological properties and origin.

The penultimate group in the GOST 941-60 nomenclature [1]—the alginite group—is not distinguished, since the amount of algotellinite is present in an extremely small quantity (0.05–1.0% per polished section). Therefore it is not reflected in the overall calculations of the microcomponents and properties of humic brown coal. Yu. A. Zhemchuzhnikov and A. I. Ginzburg [4] also classified coals with such a small content of algae as humic.

Microcomponents of the mineral-impurity group are observed in polished sections of Kharanor coals only in isolated cases. However, the weighted average ash content of the Moshchnyi seam lies within the limits of 1.04–29.8%. In all probability, this ash content and the dullness of the vitrene lens bands can be explained by the fact that the mineral impurities are closely associated with the organic mass of the coal. Similar assumptions were made by O. G. Rumyantseva in studying coal deposits of Transbaikalia.

Thus, the entire petrographic composition of the organic mass of the Kharanor coals is reduced to the characterization of three principal groups of microcomponents, differing in properties and genesis: vitrinite, fusinite, and liptinite.

Vitrinite Group

The vitrinite group comprises two subgroups of microcomponents: structureless collinite and structured telinite, which in transmitted light have a red and dark-brown color; in reflected light they are gray and have a smooth surface.

Vitrene (lithotype) and collinite (microcomponent).

Vitrene in the Kharanor coals is observed in the form of dull lenses and bands measuring 0.8 × 1.0 to 0.3 × 30 cm. The vitrene lenses are cut by endogenous cracks running along the lenses and at right angles to the bedding. The dullness of the vitrene lenses is apparently explained by the close association (formed already at the stage of peat accumulation) of the solidified organic colloid with the mineral colloid.

The collinite subgroup is represented by collinite “B.”

Collinite “B” makes up the principal mass of the Kharanor coals and more often has a xylovitrenous and very rarely a vitrenous structure. The color of the main mass in transmitted light is reddish-brown; in ash-rich coals it is dirty brown, and in reflected light it is dark gray. The principal mass of the coal predominates in the vitrinite group.

The telinite subgroup unites plant fragments of several varieties: telinite “A,” telinite “B,” and telinite “V.”

Telinite “A” includes fragments of the wood of conducting and mechanical plant tissues of reddish-brown, dark-brown, and often yellowish-brown color.

In the Kharanor coals, microcomponents with a xylene and xylovitrenous structure predominate. Fragments of wood with transverse sections and clearly expressed growth rings are often observed; their cell openings are filled with resinite. Also present are fragments of wood with a stellate structure and pores bordered in an araucaroid manner.

Telinite “B” is cork tissue of orange-brown color, the intercellular openings of which are filled with suberinous material of dark-orange color. Cork tissue occurs fairly often in the Kharanor Moshchnyi seam.

Telinite “B” has two varieties. They have the form of lenses and consist of parenchymatous tissue, bordered by thin or thickened cutinite. The size of the bands and lenses of telinite “B” ranges from \(0.30 \times 1.40\) to \(0.12 \times 2.60\) mm. In reflected light, telinite “B” has a clearly expressed cellular structure, sharp relief, and a gray color.

The material of the first variety was, in all probability, leaves of ginkgo and fern plants, which is confirmed by the size of the fragments and also by the conclusions of O. G. Rumyantseva, who studied the material composition of the Kharanor coals.

The second variety is represented by tissue of coniferous plants containing thin resin canals filled with resinite and bordered by more thickened cutinite. It must be supposed that these microcomponents formed from needles of coniferous plants.

Fusinite Group

Microcomponents of the fusinite group occur in all petrographic types of Kharanor coal. The fusinite content varies from 10.43 to 17.53% of the seam thickness. The following microcomponents are included in this coal-petrographic group of fusinite: semifusinite, micrinite, fusinite, and sclerotinite.

Semifusinite consists of plant fragments of dark-brown, almost black color with xylem, xylem-tracheid, and stellate structure. In reflected light, semifusinite is grayish white.

Micrinite is a structureless black microcomponent with smooth outlines. In reflected light it is grayish white.

Fusinite has every possible cellular structure of plant tissue. It is sometimes represented by isolated fragments with a coarse cellular structure with annual growth rings. This variety of fusinite consists of fragments of conducting tissues of coal-forming plants. Another variety of fusinite has fragments of plant tissue with large cellular openings, which are the pith part of the stem and have a disordered arrangement. As V. V. Drushchits [2] indicated, the same picture is given by transverse sections of ginkgo vegetation. In the Kharanor Thick Seam, such scraps of plant fragments were observed rather often.

The third variety of fusinite has the structure of araucarioid-bordered pores, which is an obligatory feature of coniferous vegetation and is confirmed by the works of V. E. Moskaleva [6].

Sclerotinite consists of black rounded-angular and oval bodies of reticulate structure. In reflected light they are white, with high relief. Sclerotinite occurs in the coal mass as isolated inclusions and in clusters. The size of the fragments is \(0.17 \times 0.42\) mm; that of clusters, \(1.00 \times 3.00\) mm.

Yu. A. Zhemchuzhnikov, A. I. Ginzburg [4], and other researchers believe that the presence of sclerotinite of such a structure indicates the Mesozoic age of the coal, which is fully confirmed also by other factors listed earlier.

Leiptinite Group

The group of leiptinite microcomponents of the Kharanor coals includes the following kinds: sporinite, cutinite, resinite, and suberinite. For them

are characterized by a distinctive structure and an orange-golden color. In reflected light they have a dark-gray color and a sharp relief in comparison with the cementing main mass of coal that contains them.

Sporinite is observed in the form of exine shells of microspores. They have the form of yellow strokes or hooks measuring \(0.06 \times 0.20\) mm. Sometimes microsporinite forms small accumulations of oval shape measuring \(0.06 \times 0.60 \div 0.12 \times 0.36\) mm. The content of microsporinite in the polished sections ranges from \(0.4 \div 2.06\%\).

Macrospores were not found in the coal.

Cutinite is usually observed in the form of thin toothed linear and closed bodies of yellow, yellowish-orange color, whose thickness is \(0.03 \div 0.2\) mm. More often, cutinite rims lenses of parenchymatous tissue of telinite “B.” Rarely, accumulations of cutinite are observed in the form of matting measuring \(1.00 \times 4.00\) mm. In a single specimen, a yellow thick cutinite with a wavy structure measuring \(0.60 \times 22.60\) mm was encountered.

Resinite occurs in the form of small angular bodies; more often it forms small chains of them. These bodies have a light-orange, yellowish-orange color. Usually they are distinguished by clear contours and bright coloration. The resinite bodies have cracks in all possible directions in the form of a fine network. Often resinite fills cell cavities in telinite “A.” The size of the resinite bodies ranges within \(0.04 \times 0.04 \div 0.30 \times 2.00\) mm, and their content per polished section is \(0.04 \div 4.89\%\).

Suberinite includes fragments of the walls of cork tissue, which is a secondary covering tissue of both woody and some herbaceous plants. The cell walls of cork during the life of the plant are impregnated with a special fat-like substance—suberin. When they die, the cavities of the cork-tissue cells are filled with air or with destroyed protoplast of brown or yellow color and give the plant remains of the cork tissue the corresponding coloration.

In section, cork tissue has a tabular or reticulate structure. Often, in the process of gelification, the humic part of the plant matter is removed and only the resin-bearing substance—suberinite—of yellow, yellowish-orange color and tangled-fibrous structure remains. Suberinite cells are resistant to decomposition, are well preserved, and are clearly expressed in the main mass.

Studying under the microscope the material composition of the Kharanor coals, the author established that the coal-formers were remains of woody-stem and herbaceous vegetation. The coal was composed essentially of woody forms of fern-like and gymnosperm plants. Particularly often, among the gymnosperm plants in the Kharanor coals, fragments of conducting and bark tissues of conifers, represented by pine and partly by ginkgo, were encountered.

O. G. Rumyantseva [7], studying the coals of Kharanor, found in them pollen of conifers and spores of fern-like plants.

LITERATURE

1. I. I. Ammosov and Tan Syu-n. Stages of Coal Alteration and Paragenetic Relationships of Combustible Minerals. Publishing House of the USSR Academy of Sciences, Moscow, 1961.

2. V. V. Drushchits, T. A. Yakubovskaya. Paleobotanical Atlas. Moscow State University Press, 1961.

3. Z. V. Ergolskaya. Methodology of petrographic study of a coal seam for determining coal quality. Materials on the Geology of Western Siberia, No. 59, 1947.

4. Yu. A. Zhemchuzhnikov, A. I. Ginzburg. Fundamentals of Coal Petrology. Publishing House of the USSR Academy of Sciences, Moscow, 1960.

1. N. F. Karpov, L. P. Nefed’eva. The history of Upper Mesozoic coal accumulation on the territory of the Buryat ASSR and the southeastern part of the Lena Basin. — Transactions of the Coal Geology Laboratory. Issue XVIII. Publishing House of the Academy of Sciences of the USSR, Moscow–Leningrad, 1963.

2. V. E. Moskaleva. The structure of wood and its changes under physical and mechanical influences. Publishing House of the Academy of Sciences of the USSR, Moscow, 1957.

3. O. G. Rumyantseva. Petrography and spore-pollen composition of the coals of Transbaikalia. Irkutsk University Press, Irkutsk, 1947.