Integrated Analysis and Interpretation of Helicopter Borne Aeromagnetic and Gamma Ray Spectrometric Data of the South Meleka (Adola Greenstone Belt, Southern Ethiopia)
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Date
2015-07-07
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Addis Ababa University
Abstract
This work uses part of an airborne survey data of Adola belt generated by Geological
Survey of Ethiopia in 1994. The belt has been studied by different researchers to explain the structural
pattern and mineralization. Here, the different enhancing filters are applied on the aeromagnetic and
gamma ray spectroscopic data and the geophysical signatures gleaned are used to explain the rock units
and structural features associated to mineralization. In addition, the airborne coverage data of Ethiopia
is updated with new coverage data gathered for petroleum exploration.
The Upward Continuation (UWC) filter at different height shows the effects of deeper regional
source by removing the shallower effects and possible noises. Upward continued TMI (up to 500m)
above the flight height of the magnetometer showed a WNW-ESE trending linear structure at the
southern parts of the area. Further enhancement using tilt derivative reveals some more geological
features.
The Gamma ray spectrometric data is regridded with a cell size of 15m and a bi directional line
gridding is applied using Oasis Montaj, and filtered and shaded maps of the individual radio elements
(U, TH, K, and TC) and a ternary image are produced. The ternary map demarcated major geological
units such as basalts, gneisses and central volcano sedimentary terrain. These are peculiar signatures
well marked at the eastern, western and central part of the area. The ratio map of Th/K is prepared to
select the alteration zones favourable for mineralization. The Total Count map mapped the central
volcano sedimentary belt with a low total count from northern end up to the southern covering a wide
part of the study area. It also portrayed area around Kilenso Babicho, Meleka and north Sakaro with a
high total count.
The analysis and interpretation from the ground magnetic and radiometric surveys are
compared with that of the aeromagnetic and gamma ray spectrometric data on selected areas and are
found to be well corroborated. From the result of all the enhanced maps the trends and dispositions of
the inferred faults at the southern part are modified. Power spectrum technique is applied to estimate
the depth to source of the magnetic body. The average depth for both the shallower source and deeper
source anomalies using the FFT analysis method are estimated to be 11.98m and 43.54m respectively.
From all the interpreted maps composite map is produced which show the magnetic lineaments,
altered zone, and selected target area for further study and follow-ups.
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Keywords
Integrated Analysis, Interpretation, Helicopter Borne, Aeromagnetic, Gamma Ray Spectrometric, South Meleka, Adola Greenstone Belt, Southern Ethiopia