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

Aniruddha Basu ¹, L. K. Das ¹, M. Moitra ¹, D. Bhattacharya ¹, A. K. Lahiri ¹

Affiliations
1 Marine Wing (HQ). GSI, Kolkata, Bhubijnan Bhawan, Karunamoyee, Salt Lake, Kolkata - 700 091, IN

Abstract

This note records the occurrence of a lamproitic body traversing the Archaean greenstone belt in Singhbhum craton near Rajnagar-Tiring area in east Singhbhum district of Jharkhand. This discovery opens up new vistas of search for similar rocks in this region.

Keywords

Lamproites, Singhbhum Granite, Rajnagar Tiring Area, Jharkhand.

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D. C. Naskar ¹, L. K. Das ², A. K. Lahiri ¹

Affiliations
1 Central Geophysics Division, Geological Survey of India, 27 J.L. Nehru Road, Kolkata-700016, IN
2 Central Geophysics Division, Geological Survey of India, 27 J.L. Nehru Road, Kolkata -700016, IN

Abstract

Gravity, magnetic survey and deep resistivity soundings along three profiles in Ulia-Hargawan area, Surguja district, Chhatisgarh provide the basement topography beneath the outcropping coal bearing Gondwana rocks. Deep resistivity soundings confirm that the overlying Gondwana rocks represents the Barakars with resistivity range of 50 Ohm-m to 400 Ohm-m, and thickness varies from 1 m to 442 m. The Archean basement is characterized by still higher order of resistivity in the area. The magnetic vertical field anomaly brought out some lower order magnetic response over the Gondwana rocks which is represented by the Barakars, because the overlying sediments are non magnetic. The amplitude of magnetic anomaly over the Gondwana lying between Ulia-Jagima is 200 nT to 230 nT in the area. One high amplitude magnetic anomaly of 500 nT has been observed just to the immediate west of Jagima which may be due to an intrusive body. Higher amplitude of magnetic anomaly is observed over the basement. Fluctuations in magnetic responses are observed at a few locations which may be due to the presence of basement faults. These are also corroborated with resistivity results.

The gravity profile and the resultant 2-D gravity modeling along Ulia-Patna-Nawapara brought out one basin a! structure which is corroborated by magnetic and resistivity results. The extension of this basin has also been inferred, whose probable direction is south of Ulia to north of Jagima. The thickness of Gondwana is interpreted to be 1 m to 450 m which is more or less corroborated with resistivity results. Two sharp contacts have been interpreted, one to the immediate west of Ulia village and the other to the immediate east of Jagima village respectively which are the boundaries between the Permo-carboniferous Gondwana and the Archaean metamorphic basement. High gravity values are observed over the high density metamorphic rocks.

Keywords

Gondwana, 2D model, Chhatisgarh.

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