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(δF/δθ) are expressed in nT/km. Consequently the anomalous value of the total field (δF)
can be calculated from
F
F
FF
(nT)
(F
)
(2)
obs
o
Geophysical (Magnetic) traverses over the delineated area are as shown in Figure 6b. In this
survey, the total magnetic field was measured. The data reduction involved removing the
regional field, reduction to the pole and vertical continuation before the plot of profile along
the traverse. Removing the regional field helps to emphasize the magnetic anomaly of
interest and this was done by subtracting the known regional field from the measured value.
The reduction to the pole helps to change the actual inclination to the vertical. It was
performed by convolving the magnetic field with a filter whose wave number response is
the product of a polarization-orientation factor and the field -orientation factor (Baranov,
1957; Gunn, 1975; Spector and Grant, 1985). Also the field upward continuation attenuates
anomalies caused by local, near - surface sources relative to anomalies caused by deeper
more profound sources.
5.4.1 The magnetic models
Information available from the magnetic profiles along the four West - East traverses, VLF -
EM, VES data and the geochemical anomaly are used in the modeling of magnetic data to
confirm the existence of the linear features, basement depth (and topography) and the
basement tectonic framework which are revealed in the area. The magnetic profiles were
modeled using the 2. 5D modeling algorithm of the WingLink software programme (version
1. 62. 08). The profiles which are along the West - East include: Olorombo to Ibode, Gada to
Iwikun, Okeipa to Eyinta and Itagunmodi to Aiyetoro. The modelling of these profiles
shows very reasonable fit between the observed and the calculated magnetic profiles.
Figure 9A shows the observed and the calculated anomaly for the magnetic profile along
Olorombo to Ibode and the corresponding geologic section in Figure 9B. Three model bodies
are involved in the computation and these include the Amphibolite (s = 280 SI unit),
Gneiss/Migmatite Undifferentiated (s = 300 SI unit) and Schist Epidiorite Complex (s = 100
SI unit) together with the overburden (s= 5 SI unit). The contact between the rock types may
represent structural or lithological contacts especially in the area of basement outcrops (El-
Shayeb, Personal communication). The model lithological contacts when correlated with the
known geology shows that the contact between the Amphibolite and the Gneiss/Migmatite
Undifferentiated partly correlated but the contact between the Gneiss/Migmatite
Undifferentiated and the Schist Epidiorite does not correlate with the known geology. An
overburden thickness of 2m is observed on theGneiss/Migmatite Undifferentiated rock at
station 750m while the thickness is 1. 5m in the Schist Epidiorite Complex rock. The
overburden is deepest (14m) in the Gneiss/Migmatite Undifferentiated rock at station
1350m.
Figure 10A shows the observed and the calculated anomaly for the magneticprofile along
Gada to Iwikun and the corresponding geologic section in Figure 10B which is on the central
part of the delineated area. Three model bodies are involved in the computation and these
include the Amphibolite (s = 250 SI unit), Gneiss/Migmatite Undifferentiated (s = 130 SI
unit) and Schist Epidiorite Complex (s = 150 SI unit) together with the overburden (s= 10 SI
unit) and a Quartz vein (s=35 SI unit). The model has three bodies representing the three
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