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

Abhijeet Mukherjee ¹, Amitabh Tripathi ¹, Prakash K. Singh ¹, E. V. S. S. K. Babu ²

Affiliations
1 National Mineral Development Corporation Limited, Khanij Bhawan, Masab Tank, Hyderabad - 500 028, IN
2 Atomic Minerals Division, Begumpet, Hyderabad - 500 016, IN

Abstract

Garnet concentrates from the Bahradih kimberlite pipe were analysed by electron microprobe and found to be mostly of the pyrope-almandine variety with significant amount of Na₂O and a pyrope content in the range of 48.76-61.45%, almandine 30.82-41.97% and grossular 2.313-9.983%, indicating eclogitic paragenesis. Their Mg# ranges from 53.92 to 66.59. The presence of traces of Na and Ti in these garnets indicates that substitution of these elements into the garnet structure is feasible at high pressure. Five out of 50 garnets analysed from Bahmdih show Na₂O = 0.07 wt.% which indicates that they are from the diamond stability field, as confirmed further by the recovery of diamonds from the pipe.

Keywords

Kimberlite, Garnet, Pyrope, Almandine, Diamond, Raipur District, Madhya Pradesh.

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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

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, 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, 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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Abhijeet Mukherjee , Amitabh Tripathi , Prakash K. Singh , E. V. S. S. K. Babu

Abstract

No Abstract.

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