Electrical and electromagnetic methods - Geophysics for the Mineral Exploration Geoscientist - page 285

Low High

Surface projection of source body

Resistivity Polarisation

High Low

Pseudosections Earth models

0
1
2
3
4
5

n =1
n =2
n =3
n =4
n =5
n =6
n =7
n =8

Source
body

Depth = 0.5 dipole length

0
1
2
3
4
5

n =1
n =2
n =3
n =4
n =5
n =6
n =7
n =8

Source
body

Depth = 2.0 dipole lengths

0
1
2
3
4
5

n =1
n =2
n =3
n =4
n =5
n =6
n =7
n =8

Source
body

Dip = 45°

0
1
2
3
4
5

Source
body

n =1
n =2
n =3
n =4
n =5
n =6
n =7
n =8

Source
body

Separation = 3.0 dipole lengths

0
1
2
3
4
5

n =1
n =2
n =3
n =4
n =5
n =6
n =7
n =8

Dip = 90°

Figure 5.51 Computed dipole - dipole array resistivity responses of some simple 2D conductivity models. Horizontal scale is one dipole length

per division.

drillhole geology available. In addition it is a good example
of conductive overburden response in resistivity data.
The deposit was discovered using EM methods and
investigated further with a time domain resistivity/IP
survey using a pole

overburden (see below), with the lateral variations usually
reflecting changes in overburden thickness and/or resistiv-
ity. However, in this area they may also be due to the
conductive mineralisation being in contact with the over-
burden (see Section 5.3.4 ). In contrast, the apparent char-
geability pseudosection has no obvious relationship to the
overburden. It shows a clear positive

dipole array ( Fig. 5.53 ) . The apparent
resistivity pseudosection shows high conductivity at low
n values. This is the typical response of conductive

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' pants-legs ' anomaly