Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Mahendra P. Singh ¹, Prakash K. Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN

Abstract

The coals are sub-bituminous to high volatile bituminous in rank and show evidences of "bituminization" stage of maturation. They have distinctive petrographic characteristics being rich in secondary liptinites such as exsudatinite (nil to 7.66%), bituminite (0.94 to 28.88%) and fluorinite (nil to 0.99%). The rock-eval data suggest that they are hydrogen-rich and have immature organic matter-kerogen type 1II. The study corroborates the earlier contention regarding the onset of 'oil window' at Rom of 0.5% and suggests that the paleodepth of burial of the coal bearing horizon in the Rajmahal basin was from 1890 to 2970m. The loss of cover has been estimated to range from 1440 to 1720m

Keywords

Coal Petrology, Permian, Rajmahal Basin, Bihar.

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Mahendra P. Singh ¹, R. M. Singh ¹, D. Chandra ²

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi 221 005, IN
2 Department of Applied Geology, Indian School of Mines, Dhanbad, IN

Abstract

Scanning Electron Micrography of the Jharia Coals has been attempted with a view to decipher the enigmatic microstructural features and diversities in distribution of mineral matter in the banded constituents and coal. A wide variation has been observed in the distribution of mineral matter in coal lithotypes. The mineral matter is most abundant in durain; abundant in c1arain and dull clarain, less abundant in bright clarain and vitrain; and rare in fusain. The order of abundance of the mineral matter may be put as; Durain > Dull Clarain > Clarain > Bright Clarain > Vitrain > Fusain.

The microstructural relation of mineral. matter with coaly substances reveals that in durain and elarain, mineral matter is associated as massive impregnation, superficial infilling of micropores and filling of cavities. In vitrain, this occurs mainly iS superficial inlilling of pores, superficial mountings, and in and around cavities. In c1arain mineral matter is mainly confined to dull bands, while bright bands contain sporadic mineral matter. Fusain is almost devoid of inorganic contamination. At places, however, mineral matter is observed filling the cavities of cell fibres and cell lumina.

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Mahendra P. Singh ¹, D. Chandra ², Y. V. S. Prasad ³

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi, IN
2 Department of Applied Geology, Indian School of Mines, Dhanbad, IN
3 Quality Control Department, CCL, Ranchi, IN

Abstract

The Scanning Electron Micrography of bulk coal samples from Dishergarh, Sirpur and Kajora areas of Raniganj Coalfield has been attempted with a view to find out the role of microstructures in promoting the spontaneous combustion of these coals. Microanalysis of vitrain and c1arain has shown that these bands of R-VIII seam are highly porous as compared to the overlying and underlying seams. Further, finely dispersed pyrite has also been observed filling these micropores. It is concluded that the occurrence of ubiquitous micropores could be a prevalent factor responsible for the spontaneous combustion property of these coals in different ways.

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Mahendra P. Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi 221 005, IN

Abstract

Three types of crystal morphology; viz., stacks or books, elongated crystals, and card-house structure are observed. These morphological forms characterise the kaolinite as free slacking type. The occurrence of stacks or books as well as elongated crystals in vitrain suggest formation of vitrain and development of these morphological forms under a low electrolyte water condition, whereas, the dominance of card-house structure in durain is suggestive of coagulative processes and flocculation and high electrolyte concentration during the development of dull bands.

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Mahendra P. Singh ¹, R. M. Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi 221 005, IN

Abstract

Heavy mineral analyses of Talchir, Barakar and Kamthi sediments (Lower Gondwana) have been carried out with a view to elucidate their distribution, relative abundance, nature and behaviour. The heavy mineral separates show the presence of garnet, zircon, tourmaline, rutile, epidote, staurolite, chlorite, kyanite and opaques-including ilmenite, magnetite and hematite. It is inferred that the Talchir sediments are mainly the disintegrated products of high-rank metamorphic terrains, granitic plutons and pegmatitic veins. The heavy mineral associations of Barakar and Kamthi sediments reflect the dominance of basic and acidic igneous plutons together with the possibility of pegmatitic veins in the source area.

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Mahendra P. Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi 221005, IN

Abstract

The fusain fragments separated from the Tertiary coals of Meghalaya were studied under a high performance Scanning Electron Microscope. The transverse view (across the bedding plane) of these charcoalified plant tissues shows the preservation of micro anatomical details together with complete absence of middle lamella leading to cell-walls homogenization. The homogenization of cell-walls suggests that fusain of these coals has originated due to the pyrolysis of woody tissues. Pyrolysis took place during the intermittent dry seasons by the generation of forest fires in the basin. Disappearance of middle lamella zone from the cell-wall points that charcoalification temperature was 400°C. Further, charring of wood at a high temperature is indicative of the high oxygen level during the development of coal facies.

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Mahendra P. Singh ¹, Prakash K. Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN

Abstract

Application of Fluorescence microscopy to the organic petrological study of Rajmahai Coals has been done with a view to have a correct qualitative and quantitative assessment of the Liptinite constituents of these low rank coals. The study has revealed the presence of hydrogen rich constituents which were recorded as mineral matter under white incident light due to their greater resemblance to clay minerals, being dark grey to black in colour. These constituents are bituminite, flourinite and exsudatinite which occur in considerably high concentrations and are proved to be a kind of expelled hydrocarbons. Further, it has been observed that the concentration of these expelled secondary constituents is much higher in the basal parts of the coal seams suggesting high activity of their generation in the over-pressured zones of the coal seams. Besides, the study suggests that the "birthline" or maturation level desired for the generation of liquid hydrocarbon is 0.5% Ro mean.

Keywords

Rajmahal Basin, Hydrocarbon, Fluorescence, Coal, Bihar.

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Mahendra P. Singh ¹, Prakash K. Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi-221005, IN

Abstract

The Lower Gondwana coals of the Rajmahal group of coalfields have been studied, in detail, under the Petrological and the Scanning Electron Microscopes to elucidate the mode of occurrence of mineral matter and their microstructural relations with organic constituents. Observations of both the methods reveal the occurrence of mineral matter as massive impregnation, intimate inter growth, superficial mounting, superficial blanketting, pore filling and solution cavity filling. The absence of microstructures, when observed via incident light microscopy such as superficial blanketting and superficial mounting in the macerals and microlithotypes, in general. suggests their elimination during the course of grinding and polishing of the coal pellets. This suggests skewing of the mineral matter assessment through microscopic examination. The quantitative distribution of mineral matter in the coal lithotypes as observed in SEM is Durain> Clarain > Vitrain > Fusain while the ash analysis of different lithotypes shows the order of dominance of ash (equivalent to mineral matter) as Durain > Fusain> Vitrain > Clarain.

Keywords

Mineral Matter, Rajmahal, Scanning Electron Microscope.

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Mahendra P. Singh ¹, Alok K . Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 22 1 005, IN

Abstract

This paper is an attempt to focus on the Micro-Morphological characterization of pyrite and its quantitative distribution in the Tertiary coal deposits of Northeast India with the help of improved incident light microscopic techniques. The coal deposits of this region occur in the states of Meghalaya, Assam, Arunachal Pradesh and Nagaland, and are known to have originated in two distinct Tectono-Sedimentary settings. The coal bearing sequences of Meghalaya are Eocene in age and have evolved over platform areas under stable shelf conditions. On the other hand, the coal deposits of Assam, Arunachal Pradesh and Nagaland are Oligocene in age and have originated in the foreland basins Pillar coal samples from all the coal seams (Measuring a metre or more in thickness), either exposed as outcrops or in mine workings, have been subjected to this study.

The results of petrographic examination reveal that the coals of platform areas in Meghalaya are comparatively rich in pyrite. The mode of occurrence of pyrite identified are disseminated, cavity filling, framboidal, fissure and cleat fillings, Discrete-Grains and massive replacement (Dendritic form). In the coals of platform areas, the dominant form of pyrite is massive replacement whereas framboidal pyrite is the most common form in the coals of foreland basins. The study indicates that the concentration of Framboidal(>5 to 50 μm size), massive replacement (>lo to >15O μm size) and disserninated forms (

Keywords

Pyrite, Morphology, Mode of Occurrence, Classification, Tertiary Coals, Northeast India.

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Mahendra P. Singh ¹, Alok K. Singh ²

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 22 1 005, IN
2 R & D Division, The Tata Iron and Steel Company Limited, Jamshedpur - 831 007, IN

Abstract

Petrographic examination of Oligocene coals of Upper Assam has shown some morphological changes in the Maceral-Resinite, which is suggestive of their pyrolysis due to thermal maturation. It has been observed that the resinites of these coals resemble in optical properties, including the microstructures, to the artificially pyrolyscd resinite (up to 330°c/72hr) of Middle Jurassic coals of northeast Greenland. Since the Upper Assam crudes are high wax oil, this observation seems to be one of the potential evidences in support of the growing perception that coals of this basin (of the Barail Group) have acted as source for the oil in the same geological horizon.

Keywords

Pyrolysis, Resinite, Hydrocarbon Generation, Oligocene Coals, Upper Assam.

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Mahendra P. Singh ¹, Prakash K. Singh ¹, Alok K. Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, U P, IN

Abstract

In the present paper an attempt has been made to carry out the petrographic characterization of coals from the Deoghar basin and to reconstruct the palaeoenvironmental conditions of coal formation using macerals and microhthotypes as tools For this purpose a large number of pillar coal samples from the Karharban and Barakar seams were collected and were subjected to detailed petrographic examination The results indicate that the Karharban coals are rich in inerlimte while the Barakar coals are comparatively rich in vitnmte The rank of Deoghar coals (as per ASTM system), on the basis of the mean of random vitnnite reflectance, has been found to range between Sub-Bituminous 'B' and High Volatile 'C Bituminous The quantitative relationships of macerals, microhthotypes and mineral matter show that these coals have originated from the transitional plant communities in open to forest moor and under limno-telmatic to hmnic conditions Moreover, the Karharban coals have evolved under oxic moor conditions with sudden high flooding while the Barakar coals have evolved under comparatively wet moor conditions with intermittent moderate to high flooding Low values of TPI and GI indicate periodic dryness in the basin This contention is supported by the dominance of inertodetnnite particularly in the coals of Karharban Formation.

Keywords

Permian coals, Petrography, Depositional environment, Deoghar basin Bihar.

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Mahendra P. Singh ¹, Alok K. Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN

Abstract

Borjan coalfield is situated on the western flank of the Naga Hills in the Mon district of Nagaland. Pillar coal samples from Watking and Kongan seams were subjected to detailed petrographic and geochemical investigations for the assessment of their source rock characteristics. During petrographic examination, emigration of exsudatinite (waxy oil) from a microfracture in vitrinite (telocollinite/collotelenite) has been observed. This is a rarely reported visible evidence of primary migration of oil in coal through microfracturing.

Keywords

Oligocene Coals, Hydrocarbon Emigration, Microfracturing, Vitrinite, Borjan Coalfield, Nagaland.

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Mahendra P. Singh ¹, Alok K. Singh ¹

Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN

Abstract

A large number of coal samples from the Palaeogene coal deposits of Northeast India were subjected to detailed chemical (proximate, ultimate and Rock-Eval pyrolysis) and petrographic (maceral, microlithotype and vitrinite reflectance) analyses to examine their source rock characteristics and to explore their participation in hydrocarbon generation. The results show that these coals are sub-bituminous 'C' to high volatile bituminous 'C' in rank and have requisite petrographic characteristics to act as a potential source for the generation of significant amount of normal hydrocarbons. The values of'vitrinitc reflectance, particularly of the coals of Meghalaya and Assam, suggest a maturation close to the 'top oil window' (birth line). This indicates the possibility of expulsion of oil and condensates in the basin. However, this contention needs to be supported by organic geochemical data, maturation modelling and time of hydrocarbon generation.

Keywords

Palaeogene Coals, Petrography, Source Rock Potential, Maturation, Oil Window, Northeast India.

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