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.
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.
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.
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.
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.
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.
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.