Contents of January 2003 - Vol. XXIV No.1

INTEGRATION OF GEOLOGICAL, GEOPHYSICAL AND GEOCHEMICAL STUDIES TO IDENTIFY NEW POTENTIAL TARGET AREAS FOR LEAD-ZINC AND COPPER MINERALISATION IN COVERED TERRAINS OF RAJPURA-DARIBA GROUP, WITH SPECIAL EMPHASIS TO BETHUMBI-BHUPALSAGAR AREA, SOUTHERN RAJASTHAN
K.N.Mathur, R.S.Goyal and Dinesh Gupta

PRESENCE OF ANOMALOUS CRUSTAL ROOT BENEATH SAURASHTRA PENINSULA - INFERENCE FROM GRAVITY MODELLING
Bijendra Singh, S.K.Prajapathi and D.C. Mishra

GEOELECTRICAL IDENTIFICATION OF PALAEOCHANNELS OF RIVER YAMUNA FOR FRESH GROUNDWATER IN PARTS OF MATHURA AND AGRA DISTRICTS, UTTAR PRADESH
P.C. Chandra, B.B.Trivedi, M.M.Srivastava, Mohd.Adil and M.K.Bhowmic

SEISMIC TOMOGRAPHY FOR EARTHQUAKE SOURCE AREAS
J.R. Kayal

MT SURVEY OVER THE GEOTHERMAL REGION OF BAKRESHWAR FOR INVESTIGATION OF DEEPER GEO-ELECTRICAL STRUCTURE
Bimalendu B. Bhattacharya, Rajib K. Sinharay and Shalivahan

IDENTIFICATION AND DEPTH-DETERMINATION OF SUBSURFACE MAGNETIC CAUSATIVES IN LANKA-KAKI AREA OF KOPILLI VALLEY, ASSAM
S.K.Laskar, A.K.Bhattacharya and Pallabee Choudhury


INTEGRATION OF GEOLOGICAL , GEOPHYSICAL AND GEOCHEMICAL STUDIES TO IDENTIFY NEW POTENTIAL TARGET AREAS FOR LEAD-ZINC AND COPPER MINERALISATION IN COVERED TERRAINS OF RAJPURA-DARIBA GROUP, WITH SPECIAL EMPHASIS TO BETHUMBI - BHUPALSAGAR AREA, SOUTHERN RAJASTHAN

K.N.Mathur*, R.S.Goyal** and Dinesh Gupta**

*Geological Survey of India, NRO, Aliganj, Lucknow
**Geological Survey of India, Jhalana Doongri Jaipur

Abstract

Rajpura-Dariba Group of rocks is linearly spread between Satdhudhia in the north to Bhinder in the south, over an area of 100 km long (North-South) and on an average 3 km wide (east-west). The belt is endowed with rich lead-zinc mineralisation at Dariba-Rajpura, Sindesar, Bamania; copper mineralisation at Satdhudhia, Dariba-Rajpura, Bari-Lunera, Akola and Tana-Bhagol and silver mineralisation at Baghera (Bharak). Some of the lead zinc deposits are under active exploitation, whereas, others are in various stages of development for mining. The belt in the central part got faulted and displaced into two with a movement of about 15 km. As a result, now there are two belts namely Dariba-Rajpura-Sindesar-Bamania-Bethumbi-Bharak-Satdhudhia being northern belt- Belt-1 (names are from south to north) and Chhatrikhera-Jashma-Bhupalsagar-Akola-Tana-Bhinder is southern belt- Belt-2, which is an autochthonous (names from north to south). Owing to the presence of gossans and ancient mining at Rajpura-Dariba, the northern belt is very well explored, resulting in rich Pb-Zn deposits, whereas southern belt being soil covered could not be explored in detail, except in small ancient old mining zones meant for copper, such as at Bari-Lunera, Rawatiya, Pari, Akola and Tana. The integrated studies have revealed that before faulting the two belts were contiguous and Dariba-Rajpura of Belt-1 was in contact with Chhatrikhera of Belt-2, hence mineralisation similar to that of Dariba-Rajpura is also expected at Chhatrikhera-Jashma. This thesis is further supplemented by detailed geological, structural, airborne and surface geophysics, geochemistry and aerial photography data. The study is a successful case of integration of all the branches of earth sciences resulting into delineation of new potential target areas for further detailed exploration by drilling, in the covered terrain.

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PRESENCE OF ANOMALOUS CRUSTAL ROOT BENEATH SAURASHTRA PENINSULA - INFERENCE FROM GRAVITY MODELLING

Bijendra Singh, S. K. Prajapati and D. C. Mishra
National Geophysical Research Institute, Hyderbad

Abstract

Bouguer anomaly map of Saurashtra is characterized by a large number of circular gravity high associated with known volcanic plugs of Deccan magmatism. It also depicts a large wavelength gravity low centered over Jasdan in central Saurastra which bears an inverse relation with the topography. This low has been interpreted due to mass deficiency resulting from thickening of crust caused by isostatic compensation. Deep seismic sounding (DSS) result along Navibander-Amreli profile clearly indicates variation of Moho depth from 35 Km towards the coast to 42 Km beneath the high lands. Assuming that the compensation is at Moho level, modeling of isostatic regional anomalies in terms of Moho variation along DSS profile has yielded a density contrast of - 0.15 g/cm3 which is much less than the expected density contrast of - 0.40 g/cm3 across the Moho in normal region. This feature points to (i) either the crustal root is anomalously dense (ii) or the upper mantle is anomalously light. DSS result has not indicated any anomalous velocity structure across the Moho. In the absence of conclusive evidence this issue can not be resolved. However, it may be argued that like Saurastra which had experienced extensive volcanism, an increase in crustal root density may be more plausible explanation for its thickening. 

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GEOELECTRICAL IDENTIFICATION OF PALAEOCHANNELS OF RIVER YAMUNA FOR FRESH GROUNDWATER IN PARTS OF MATHURA AND AGRA DISTRICTS, UTTAR PRADESH

P.C. Chandra, B.B. Trivedi, M.M. Srivastava, Mohd. Adil and M.K. Bhowmick
Central Groundwater Board, Northern Region, Lucknow

Abstract

Districts Mathura and Agra are replete with brackish to saline groundwater. About 525 electrical resistivity soundings conducted over an area of 2200 sq.kms in the western and southeastern parts of these districts respectively, that is towards west of river Yamuna, helped define the spatial disposition of the palaeo-channels as elongated resistive bodies. In Mathura district it is oriented in a general NNW-SSE direction, almost parallel to the present day course of river Yamuna, while in Agra it is quite wide and oriented in NNE-SSW. The palaeo-channel delineated towards east and south of Agra hold material of better granularity as compared to those in Mathura district. Also, the channel in Agra district is deeper. These conform with the palaeo-course/abandoned channels of the eastward migrating river Yamuna picked up from satellite imageries. The area covered by these inferred palaeo-channels is about 260 sq.kms. Water wells could be constructed upto a depth of 30-40m in parts of Mathura and upto about 100m in Agra in the succinctly defined coarse-grained sediments in the channels containing fresh groundwater zones to suitably cater to the drinking water demand of these cities.

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SEISMIC TOMOGRAPHY FOR EARTHQUAKE SOURCE AREAS

J.R. Kayal
Geological Survey of India, Central Geophysics Division, 27 J.L. Nehru Road, Kolkata

Abstract

Seismic tomography structures of source areas of the two recent damaging earthquakes, the 1993 Killari earthquake (mb 6.3) in central India and the 2001 Bhuj earthquake (MW 7.6) in western India are presented. Large number of aftershocks followed the main shocks. The seismic phases (P and S arrivals) of the aftershocks are used for the tomography study. The tomography images revealed lateral heterogeneities in velocity structure; the earthquakes occurred in the high velocity zones at the fault ends.

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MT SURVEY OVER THE GEOTHERMAL REGION OF BAKRESHWAR FOR INVESTIGATION OF DEEPER GEO-ELECTRICAL STRUCTURE

Bimalendu B. Bhattacharya*, Rajib K. Sinharay** and Shalivahan*
* Department of Applied Geophysics, Indian School of Mines, Dhanbad.
** Geophysics Division, Central Water and Power Research Station, Pune

Abstract

Bakreshwar geothermal system is one of the most promising geothermal resourse in India. The surface manifestation of this system is a cluster of hot springs with temperature of the thermal fluid varies from 350C to 880C (Majumdar et al., 2000). Bakreshwar (23052'48" N; 87022'40" E) is located in Birbhum district, West Bengal. (Fig. 1). The heat flow of the area is very high with values vary from145 mW/m2 to 200 mW/m2. This is more than double of the average global heat flow and similar to the young oceanic ridges. The geothermal gradient near the hot spring is 900C/km (Chandrasekharan, 2000). The area shows a considerable gravity high with highest anomaly +40 mgal. Several investigations have been made over that region but failed to locate any probable reservoir for geothermal fluid and source of the heat. Detailed audio magnetotelluric (AMT) survey was carried out by Indian School of Mines over the close vicinity of the hot spring (Sinharay et al., 2000). The results showed the absence of any probable reservoir or source below the hot spring. In present study, magnetotelluric (MT) survey has been carried out along approximately a 12 km long profile to study the distant and deeper subsurface geoelectrical structure to study the geothermal system broadly.

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IDENTIFICATION AND DEPTH-DETERMINATION OF SUBSURFACE MAGNETIC CAUSATIVES IN LANKA-KAKI AREA OF KOPILLI VALLEY, ASSAM

S.K. Laskar, A.K.Bhattacharyya and Pallabee Choudhury
Tezpur University, Napaam, Assam

Abstract

A vertical component magnetic profile extending from Shillong massif to Mikir hills at northwest of Lanka - Kaki line in Kopilli Valley is analysed for identification and depth determination of subsurface magnetic causatives lying across it. The analysis reveals that a basaltic trap lies concealed in the area. The maximum depth to the basement is about 3.25 km over a span of about 4km and it is covered by the trap extending over a span of about 10km at an average depth of about 1.75km in middle of the basin.

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