Introduction to the resistivity surveying method. The resistivity of ...

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same depth with more data points in the pseudosection plot (Figure 21c). This phenomena is
basically due to the shape of the contours in the sensitivity function of the dipole-dipole array
(Figure 8c). This example illustrates the danger of only using the distribution of the datum
points in the pseudosection to constrain the position of the model blocks (Loke and Barker,
1996a). If the model blocks are placed only at the location of the datum points, the high
resistivity body will be missing from the inversion model, and an important subsurface
feature would not be detected!
Figure 21. (a) Apparent resistivity pseudosection for the survey to map holes in the lower clay
layer. (b) Inversion model and (c) sensitivity values of the model blocks used by the inversion
program.
2.7.7 Magusi River Ore Body - Canada
This is an example of a combined resistivity and induced polarization (I.P.) survey.
This survey was conducted over the Magusi River ore body where dipole spacings (the “a”
factor in Figure 2) of 30.5 meters (100 feet), 61.0 meters (200 feet) and 91.4 meters (300 feet)
were used (Edwards 1977). For each dipole length, measurements were made with values of 1
to 4 for the dipole separation factor “n”. The I.P. measurements were given as metal factor
values. The resulting resistivity and I.P. pseudosections have a very complex distribution of
Copyright (1999-2001) M.H.Loke