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
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
D. Bhaskara Rao and C. P. V. N. J. Mohan Rao
INTERCOMPETENT TRANSFORMATION OF MAGNETIC ANOMALIES BY EQUIVALENT
SOURCE TECHNIQUE
DETERMINATION OF IN SITU DENSITY AND ASSESSMENT OF EFFICACY
OF GROUTING BY GAMMA-GAMMA LOGGING AT BARVI MASONRY DAM, MAHARASHTRA
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 2½ 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 2½ 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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