Contents of January, 1999 - Vol. XX No.1

 

A NEW KIMBERLITE DISCOVERY FROM A STRUCTURAL ELUCIDATED OF GRAVITY DATA, MADDUR - NARAYANPET FIELD, MAHBUBNAGAR DISTRICT, ANDHRA PRADESH
N. Sreeram Murthy, R. Ananda Reddy, M. V. R. K. Rao, B. Sunder Raj, N. V. S. Murthy and K. P. R. Vittal Rao

 

STATISTICAL MODELING OF LINEAMENTS: AN EXPERIMENTAL STUDY
Aklesh Kumar Jain

GEOLOGICAL AND STRUCTURAL INFERENCES OF SHILLONG MASSIF FROM AEROMAGNETIC DATA
J. V. Rama Rao

INTERPRETATION OF AEROMAGNETIC ANOMALIES OVER BIDA SEDIMENTARY BASIN, NIGERIA
S. C. Garde and L. A. Sunmonu

THREE DIMENSIONAL MODELLING OF GRAVITY ANOMALIES OVER GODAVARI BASIN
D. Bhaskara Rao and C. P. V. N. J. Mohan Rao

 

INTERCOMPETENT TRANSFORMATION OF MAGNETIC ANOMALIES BY EQUIVALENT SOURCE TECHNIQUE
V. Radhakrishna Murthy and K. V. Swamy

DETERMINATION OF IN SITU DENSITY AND ASSESSMENT OF EFFICACY OF GROUTING BY GAMMA-GAMMA LOGGING AT BARVI MASONRY DAM, MAHARASHTRA
R. K. Kamble and S. D. Vaidya

 


A NEW KIMBERLITE DISCOVERY FROM A STRUCTURAL ELUCIDATED OF GRAVITY DATA, MADDUR - NARAYANPET FIELD, MAHBUBNAGAR DISTRICT, ANDHRA PRADESH

 

N. Sreeram Murthy, R. Ananda Reddy, M. V. R. K. Rao, B. Sunder Raj, N. V. S. Murthy and K. P. R. Vittal Rao

Geological Survey of India, Hyderabad

Abstract

 

Regional gravity and magnetic maps are of immense use in identifying the most favourable areas in Kimberlite exploration. The study of gravity linears, second order trends, flextures, terminations and their intersection points is significant, in that they indicate the zones of density / magnetic susceptibility changes the underlying rocks had undergone due to fracturing, several phases of magmatic episodes, deformation events and intrusive activity etc. Since these form a favourable structural setting for the emplacement of kimberlites, delineation of these features from an appraisal of regional gravity / magnetic maps is the first step in Kimberlite exploration. Regional gravity and magnetic maps are prepared on a 1:50,000 scale in Maddur-Narayanpet Field. Kamusanpalli block is selected for semi-detailed geophysical coverage on the basis of structural information inferred from the regional maps. The significant geophysical indications recorded are ground checked and then resistivity profiling was carried out to test the individual geophysical anomalies. The methodology thus followed has resulted in the discovery of a 'concealed Kimberlite pipe' M-11 of size 60 * 20m (semi-weathered) in Kamusanpalli block. Further petrologic and chemical studies confirmed the geophysical findings.

 

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STATISTICAL MODELING OF LINEAMENTS: AN EXPERIMENTAL STUDY

Aklesh Kumar Jain

ONGC-Schlumberger Joint Research Centre, 7 - Floor, 8 - Core, SCOPE Complex, 7 - Lodhi Road, New Delhi - 110 003.

 

Abstract

The paper embodies important findings based on Landsat analysis and Photogeomorphological studies of the southern part of Pranhita - Godavari Graben in the south-eastern quadrant of Indian peninsula. Lineament modeling has revealed two dominant trends in NE-SW and NW-SE directions. Their trend analysis has helped reconstruct following stress-strain regime active in this area:

- tensile stresses in the direction of 35 - 215 and

- comprehensive stresses in the direction of 10 - 190 and 100 - 280.

These stresses appear to have been responsible for the generation of two dominant lineament trends as mentioned above. The tensile stresses operating in the direction of 35 - 215 were responsible for the origin of the graben. An experimental work has been carried out with a statistical approach on lineament intersection points, which seem to follow the Normal Distributing or Gaussian Distribution. This work has brought out the relationship between lineaments and geomorphology, implying thereby that high terrain show high concentration of lineament intersection points and low lying areas show less number of lineament intersection points. Thus majority of landforms in this area appear to be dominated by endogenic process. Numerous evidence of neo-tectonic activities in this area seem to confirm this. An extension of the previously mentioned experiment has given a lead in deciphering the basement below the sedimentary fill. Though the results everywhere do not corroborate the existing gravity data on basement configuration.

 

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GEOLOGICAL AND STRUCTURAL INFERENCES OF SHILLONG MASSIF FROM AEROMAGNETIC DATA

J. V. Rama Rao

Geophysics Division, Geological Survey of India, Shillong

 

Abstract

A qualitative interpretation of Aeromagnetic map of Meghalaya - Assam has revealed a number of features giving the structural fabric of Shillong massif. From west to east, the shillong plateau has been brought out in a general strike of NW-SE to NE-SW through E-W. While in the western part of the plateau the NW-SE lineaments appear to control the disposition of lithology, the E-W lineaments in the central part and NE-SW lineaments in the eastern part are predominant, probably due to the north to south Himalayan thrust. Further three zones of N-S lineaments orthogonal to Shillong massif, at the swerves, from NW-SE to E-W and E-W to NE-SW are indicated possibly representing crustal breaks. These are parallel to 90 E ridge and their association with magnetic bipolar anomalies relate to intrusive plug like bodies. As one of them is associated with carbonatite body, such as bipolar N-S trending anomalies warrant ground check for their mineralization potential.

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INTERPRETATION OF AEROMAGNETIC ANOMALIES OVER BIDA SEDIMENTARY BASIN, NIGERIA

S. C. Garde* and L. A. Sunmonu**

*Department of Physics, University of Ibadan, Nigeria
**Department of Pure & Applied Physics, Ladoke Akintola University of Technology, P.M.B. 4000, Ogbomoso Oyo state, Nigeria

Abstract

 

The depth of the basement complex underlying the Bida sedimentary basin has been estimated from the aeromagnetic anomaly contour map (sheet 184) published by the Geological survey of Nigeria (1976). The complex nature of the anomalies and the elegance and ease of the Fourier transform method incited us to use the FFT (Fast Fourier Transform) subroutine for the calculation of the basement depth along fifty-four south-north profiles. These profiles are spaced at 1.0 km and data were picked up at an equal interval of 0.5 km. A maximum depth of 3.0 km in the northwestern part of the basin has been estimated, where as the average depth is 1.81 km. Although, certain structural and geological considerations suggest possible occurrence of iron ore, gold and tin deposits as well as a remote possibility of diamond pipes in some areas. Further detailed geophysical investigation has been suggested in selected areas for mineral exploration.

 

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THREE DIMENSIONAL MODELLING OF GRAVITY ANOMALIES OVER GODAVARI BASIN

D. Bhaskara Rao and C. P. V. N. J. Mohan Rao

Department of Geophysics, Andhra University, Visakhapatnam - 530 003

 

Abstract

The methods developed earlier for 2 D and 3D gravity modelling using quadratic density contrast function are used for analysis of gravity anomalies over Chintalapudi and Godavari sub-basins. The decrease of density contrast with depth in Chintalapudi sub-basin is approximated by a quadratic function. The regional gravity field in this sub-basin is estimated to be - 30 mgal based on borewell and DSS data. Two gravity profiles across the Chintalapudi sub-basin are interpreted by 2 D modelling methods using a quadratic density function. The depths interpreted to the basement compare very well with the depths obtained to the basement by drilling and DSS methods. The residual gravity anomaly map for the Chintalapudi sub-basin is constructed and interpreted by 3D modelling methods using a quadratic density contrast function, and the resulting basement map is presented. A quadratic density contrast function is assumed for Godavari sub-basin based on a stratigraphic data. The regional is assumed to be -40 mgal. The residual gravity anomaly map of the Godavari sub-basin is interpreted by 3D modelling methods, and the resulting basement map is presented.

 

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INTERCOMPETENT TRANSFORMATION OF MAGNETIC ANOMALIES BY EQUIVALENT SOURCE TECHNIQUE

V. Radhakrishna Murthy and K. V. Swamy

Dept. of Geophysics, Andhra University, Visakhapatnam - 530 003, India

Abstract

The method equivalent source is adopted to transform magnetic anomalies in any one component into the other two components. An equivalent source is worked out which can generate the observed anomalies; and the anomalies of the equivalent source are calculated in the other two components. The equivalent source that can favourably transform the anomalies of two-dimensional bodies is found to be a model of a number of vertical sheets of infinite depth extension, all located at the same depth and magnetized in the same direction. The magnitudes of magnetization of the hypothetical sheets are calculated in the method of equivalent source. For the three-dimensional bodies, the equivalent source constitutes several vertical rods of infinite depth extension, all located at the same depth and magnetized in the same direction. The method is extended to calculate the anomalies reduced to the plot or equator in the case of two-dimensional bodies.

 

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DETERMINATION OF IN SITU DENSITY AND ASSESSMENT OF EFFICACY OF GROUTING BY GAMMA-GAMMA LOGGING AT BARVI MASONRY DAM, MAHARASHTRA

R. K. Kamble and S. D. Vaidya

Central Water and Power Research Station, Pune - 411 024

Abstract

Excessive leakage was observed from drainage holes of Barvi Masonry dam in spite of grouting and guniting. Doubts were therefore raised about the stability of dam and efficacy of grouting was required to be assessed. This paper deals with gamma-gamma logging adopted at Barvi masonry dam for assessing efficacy of grouting. These studies helped in determining bulk density and identifying weak zones in the masonry. The values of bulk density thus determined were utilized for dam stability analysis and adopting remedial measures.

 

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