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L. K. Das ¹, D. C. Mishra ², D. Ghosh ¹, B. Banerjee ¹

Affiliations
1 Central Geophysics Division, Geological Survey of India; P-49; C II Road, Beliaghata, Calcutta-700 016, IN
2 National Geophysical Research Institute, Hyderabad-500 007, AP, IN

Abstract

Ground magnetic survey of part of central India covering the Vindhyan Basin of the upper Son valley region has delineated some subsurface vsolcanogenic Proterozoic rifts below the Vindhyan cover and several faults which have controlled the tectonics of the region. The magnetic map in general shows four distinctly different domains with magnetic anomalies differing both in amplitude and their nature. In general, the Vindhyan basin is characterized by low amplitude broad anomalies while the Mahakoshal (lower Proterozoic) Group depicts large amplitude sharp anomalies due to the presence of high susceptibility (2-19 × 10^-3 CGS units) ferruginous rocks in them. The domain boundaries are either faults or indicate formational contacts between the different types of rocks with contrasting susceptibility values.

The subsurface basement relief map of the Pre-Vindhyan topography determined by 2-dimensional Harmonic Inversion of the magnetic data reveals an asymmetric graben structure with the southern boundary fault between the Vindhyans and the Mahakoshals as the most prominent linear structure.

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Buddhadeb Banerjee ¹, S. S. De ¹, L. K. Das ¹

Affiliations
1 Geophysics Division, Geological Survey of India, 27, J. L. Nehru Road, 4th Floor, Calcutta 700 016, IN

Abstract

Partial electrolytic extraction of metals can be effectively utilised for direct detection of polymetallic minerals in addition to their discrimination which is a difficult task by other geophysical exploration techniques. The principle lies in trapping the metallic cations from the electrolyte formed by leaching of the ore body at depth by a direct current supply impressed on ground surface and analysing the electrolyte chemically for determination of different metallic contents diagonising the target.

Field tests have been successfully carried out with this approach over known and unknown mineralised bodies at Kendadih, Seraikella areas in Singhbhum district, India.

Keywords

Electrolysis, PEXMEL, Singhbhum.

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L. K. Das ¹, B. P. Pal ¹, B. K. Nandi ¹, R. Singh ¹, K. Ghatak ¹, K. K. Mukhejee ¹

Affiliations
1 Geological, Survey of India, Marine Wing Kolkata - 700 09 1, IN

Abstract

No Abstract.

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B. J. Sengupta ¹, S. K. Ghatak ¹, B. K. Nandi ¹, R. Singh ¹, P. C. Das ¹, S. C. Biswas ¹, L. K. Das ¹, B. P. Pal ¹

Affiliations
1 Geological Survey of India, Marine Wing, DK-6, Karunamayee, Sector-II, Salt lake, Kolkata - 700 091, IN

Abstract

No Abstract.

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L. K. Das ¹, B. Das ², S. N. Chowdhury ³, D. C. Naskar ³, G. Karunakar ³, S. K. Dey ²

Affiliations
1 GSI, Marine Wing, DK 6, Salt Lake, Kolkata - 91, IN
2 GSI, seminary Hills, Nagpur, IN
3 GSI, CGD, 27 JLN Road, Kolkata - 16, IN

Abstract

Gravity-Magnetic mapping and resistivity sounding have been conducted in a grid pattern of 50 m × 100 m and 200 m × 200 m respectively over one square km area between Tokapal and Duganpal villages on Jagdalpur-Gidam road about 18-20 km from Jagdaipur township. The objective has been to map the eastern and the northern extension of an already known kimberlite sill in the area which is exposed in a pit and intersected in some drill holes at shallow depth to the west of the area surveyed.

The Bouguer anomaly (BA) map reveals a near circular peak marginal high of + 0.5 mGal around 0/N100 station over the background value of -59 mGaI in the area surrounded by an envelope of +0.3 mGal, almost in a N-S disposition between the traverses W350 and E100 stretching from the northern end down to S400 grid. Another such N-S feature, somewhat subdued (+0.3m Gal), is recorded in the BA map, in the northeastern part of the area bounded by traverses E200 and E400 and the base line. It is interesting to note that this sill like body is exposed around station E200/S300 where no BA high is detected. However, in the magnetic (VF) map, this sill body is picked up as a dipolar anomaly. Joining the axes of the dipolar lows and highs, the magnetic kimberlite body is yet again resolved into two near circular bodies as recorded in the gravity map. A gap in the continuity of the kimberlite sill around E200 is also indicated.

3D Euler's deconvolution solutions arrived from both the gravity and the magnetic (VF) data assuming a sill type body have been extremely useful in demarcating the geometry of the causative body at three different depth levels.The resistivity in a grid pattern shows the evidence of buried kimberlite in the area characterized by a marginal resistivity high (30-130 0hm.m). A 3D subsurface map of the kimberlite sill using ROCK WORKS has been prepared from the resistivity data.

Several 2-D G-sMe ctions have also been presented constraining these from the results of resistivity survey. Such sections will immensely help in targetting future drill holes in the area. The 3D Euler's deconvolution solutions and the 3-D configuration of the Kimberlite body have lent the third dimension in prospecting the covered kimberlites through geophysical mapping.

Keywords

Kimberlites, 3D Configuration, Gravity-Magnetic Mapping, Resistivity, Indravati Basin, Bastar District, Chhattisgarh.

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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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