CONTENTS OF JULY, 2012, Vol.XXXIII   No.3

 

Geophysical Study of the Gas Show Area in the South Western Region of the Proterozoic Cuddapah Basin.

Y. Sreedhar Murthy, S.V.S. Sarma, S. Murali and M. Preeti

 

Mineral Potential of the Dhanjori Metavolcanics, East Singhbhum, Jharkhand.

L.K. Das, K.K.Dasgupta and M.K. De

 

Electrical and PEXMEL Responses over a Sulphide Body in Shyami-ki-Dhani Area, Sikar District, Rajasthan.

Dinesh Gupta, B.Banerjee and B.B.Bhattacharya

 

Interpretation of Gravity and Magnetic Profiles in the Bay of Bengal and Inferences on the Anomalous Crustal Structure.

M.Subrhamanyam and N.Vasudeva Rao

 

A Re-Examination of the Crustal Structure Across Narmada-Son-Lineament (NSL), Madhya Pradesh, Central India using Magnetotelluric and Gravity Modeling.

D.C. Naskar, L.K. Das, K.K. Roy**, R.K. Majumdar*, K. Choudhury

 

Estimation of total Dissolved Solid in Ground Water of Tarai Area of Shahjahanpur, Bareilly and Pilibhit Districts, Uttar Pradesh.

H.P.Mishra*, M.K.Rai, S.K.Mishra, Amar Singh, N.Singh, R.K.Singh, and S.K.Singh

 

 

Geophysical Study of the Gas Show Area in the South Western Region of the Proterozoic Cuddapah Basin

 

Y. Sreedhar Murthy*, S.V.S. Sarma**, S. Murali* and M. Preeti***
*Professor of Geophysics (Retd.), Osmania University, Hyderabad
**Scientist (Retd.), National Geophysical Research Institute, Hyderabad
***Project Scientist, Geo Resources Technologies Consultants Private Limited,, Hyderabad

 

 Abstract

   In the western Cuddapah basin several bore wells were identified to be associated with methane gas gushing out along with the ground water in the Tadipatri area. In order to gain insights in to the subsurface structure and lithology in the gas show area, deep electrical soundings together with resistivity scanning along a 4.5 Km. long traverse was carried out. Magnetic field measurements were also carried out along the resistivity scanning traverse. The subsurface model obtained from the inversion of electrical data brought out in general a three layer structure with the top and the bottom layers being conductive (50-100 ohm.m) representing the Tadipatri shales and a middle intermediate moderately resistive layer (a few hundread Ohm.m) interpreted to be a hidden sill. The intermediate layer exhibited conspicuous discontinuities/breaks, which are also observed to be associated with well defined sharp magnetic anomalies. Interestingly all the bore wells located along the scanning traverse and which exhibited gas shows fall very close to these segments of breaks in the intermediate layer suggesting that these features represent fault/fracture zones. These structures are inferred to facilitate the outward movement of the gas that remained presumably trapped underneath with the sill itself acting as a cap rock. The area of gas shows falls over the unique “gravity high” in the south western region of the basin which is interpreted to be a zone of magmatic intrusion. It is inferred that the source for the observed gas shows has a generic link to the hidden magmatic intrusive feature which might have created conditions favourable for thermogenic origin of the CH4 through low-temperature fluid-rock interactions in the crustal layers related to active magmatism and metamorphism.

 

 

 

Mineral Potential of the Dhanjori Metavolcanics, East Singhbhum, Jharkhand

 

L.K. Das, K.K.Dasgupta*and M.K. De**
Deputy Director General, MW, GSI, Kolkata,
*Geophysicist(Sr.),GSI, Coal Wing, Salt lake, Kolkata.
**Gcophysicist (Jr.) GSI, ER. Salt Lake, Kolkata.

 


Abstract

   Deep Electrical Profiling (DEP) has proved to be very useful in identifying buried conductive anomalies in Dhanjori basin. 2-D modeling of such anomalies indicated a near vertical conductive body (80 ohm m) within the metabasics of Dhanjoris. A deep stratigraphic cum structural borehole drilled vertically upto a depth of 768 m over this anomaly zone revealed flat lying metavolconic assemblages grading from acidic to ultra basic in composition with interlayering of tuff and sediments. At least four different flows have been identified following the classical top and bottom criteria followed in stratigraphy. The bore hole lithology is in itself a revealation as it is different from the expected lithostratigraphy of Dhanjori basin. The metabasics are highly sheared and striated and the propensity of shearing increases with depth.

 

   Deep Electrical Sounding (DES) has been successful in estimating the thickness of the lithopackage which is within 1 km. SP, resistance, natural gamma ray logs run up to 750 m depth indicate 37 distinct conductive zones, varying from a fraction of a meter to several meters. Some of these are sulphides with pyrite, chalcopyrite, covellite and arsenopyrite assemblages. Density and chargeability values measured in the laboratory on selected core samples corroborate the above findings.

 

 

 

 

Electrical and PEXMEL Responses over a Sulphide Body in Shyami-ki-Dhani Area,

Sikar District, Rajasthan.

 

Dinesh Gupta, B.Banerjee*and B.B.Bhattacharya**
GSI, SR, Hyderabad, * Director (Geophysics) Retd., GSI Kolkata.
** Director (Retd.), Indian School of Mines, Dhanbad.
E-mail: dineshguptagsi@yahoo.com.in, dinesh.gupta@gsi.gov.in

 

Abstract

 

   Massive sulphide mineralisation with total sulphide content (TSC) about 25-30% in visual estimate was reported from the debri of a dug well dump near village Shyami­ki-Dhani in Neem-ka-Thana tehsil of Sikar district of Rajasthan. Integrated geological, geophysical and eochemical surveys were carried out in the area. In addition, to identify the type and abundance of metallic mineral present in the study area, PEXMEL (Partial Extraction of Metallic Ions by Electrolysis) survey was also carried out over the geophysical & geochemical anomaly zone. The results of the synergistic approach are presented in this paper.

 

   Results of PEXMEL survey over test traverse in this area are indicating 1025 NCC units for Zn over a background of 100 NCC units; and 150 NCC units of Pb over a background of 30 NCC units. A rock sample analyzed from well dump gives the following values: 1.3% Zn and 0.3% Cu. Surface Geophysical surveys employing electrical methods along with PEXMEL method were successful in identifying sulphide body’s extension and type of metallic sulphide.


 

 

Interpretation of Gravity and Magnetic Profiles in the Bay of Bengal and Inferences on the Anomalous Crustal Structure

 

M.Subrhamanyam and N.Vasudeva Rao
Department of Geophysics, Andhra University, Visakhapatnam - 530003

 

Abstract

 

   The paper deals with the gross structure of magnetic crust as deduced along six transects across the Bay of Bengal. The broad variations in the oceanic basement depth, Curie Point geotherm depth and sea bed attitude in the Bay of Bengal are discussed in terms of anomalous crustal structure. Two W-E trending transects, of which one is in the vicinity of 150 N latitude and the other along 130 N latitude, besides two NW – SE trending and two SW- NE trending transects are considered. Oceanic basement and Curie Point geotherm depth are determined using spectral method and the results are found to be in good agreement with the free- air gravity based crustal models. The SW - NE transects revealed rise in sea bed and dipping magnetic basement towards NE while the Curie Point geotherm depth changes very little. Results of the investigation revealed similarity in the models of gross magnetic crust and those derived from free- air gravity data along the six transects across the Bay of Bengal.


 

 

A Re-Examination of the Crustal Structure Across Narmada-Son-Lineament (NSL),
Madhya Pradesh, Central India using Magnetotelluric and Gravity Modeling

 

D.C. Naskar, L.K. Das, K.K. Roy**, R.K. Majumdar*, K. Choudhury**
Central Geophysics Division, Geological Survey of India, Kolkata
*Department of Geological Sciences, Jadavpur University, Kolkata
**Retired Dy.D.G. GSI, Kolkata.

Abstract

 

   The Narmada–Son–Lineament (NSL) in the Central Indian Shield (CIS) is a profound crustal discontinuity, reactivated several times in the geologic past with left lateral transcurrent motion. These episodic reactivations have produced many graben/horst structures. The bounding faults of some of these younger morphotectonic units viz. the Narmada South Fault (NSF), have produced earthquakes of (M 6.0) in Jabalpur and swarms of earthquakes in Pandhana. Abnormally high heat flow is seen over the Satpura horst, south of NSL. High heat flow is normally accompanied by higher crustal electrical conductivity at depth. This paper is an attempt to re–examine the crustal structure of the northern part of the CIS, through MT and gravity studies, over a few selected transects in the area.

 

 

 

Estimation of total Dissolved Solid in Ground Water of Tarai Area of Shahjahanpur, Bareilly and Pilibhit Districts, Uttar Pradesh

 

H.P.Mishra*, M.K.Rai, S.K.Mishra, Amar Singh, N.Singh, R.K.Singh, and S.K.Singh

*Geophysicist (Sr), GSI Complex, Sector-E, Aliganj, Lucknow – 226024

Abstract

 

   Tarai area of Ganga basin is a potential prospect for fresh ground water aquifer as it acquires fine/coarse sand beds under alluvium and Siwalik sediments. Deep electrical resistivity survey has demarcated fresh and saline water interfaces at deeper level. Unconfined shallower aquifer bears saline water whereas deeper confined aquifer contains potable water, underlain by thick zone of salinelbrackish water, Fresh and saline water have shown resistivities ranging from 20-45 Ohm-m and 2-10 Ohm-m respectively. The depth of the fresh and saline water interface has been interpreted as 1859m at Puranpur, 1944m at Shahjahanpur, 1050m at Baheri and 2600m at Nigohi. An analytical approach has been made to estimate the total dissolved solid in fresh water at deeper level, which falls between 150 and, 180 mg/lt ofNaCI equivalent at the aquifer temperature. Under the prevailing geohydrological conditions the incursion of saline. water into the fresh water-bearing horizon cannot be ruled out due to over drawal of ground water in the area. This poses geoenvironmental hazards with regard to ground water management in the tract.

 

 

 

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