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W
E
a)
198,000
200,000
202,000
204,000
206,000
Apparent resistivity
n =1
n =2
n =3
n =4
n =5
n =6
198,000
200,000
202,000
204,000
206,000
Apparent phase angle
n =1
n =2
n =3
n =4
n =5
n =6
b)
198,000
200,000
202,000
204,000
0
250
500
750
1000
1250
Resistivity
200,000
202,000
204,000
198,000
0
250
500
750
1000
1250
Phase angle
c)
Figure 5.55 Dipole
-
dipole array
ΒΌ
Low
High
(dipole length
400 m) resistivity/IP
data from the Olympic Dam IOCG
deposit. Pseudosections of (a) the
survey data and (b) the inversion
models. (c) The geological section.
See text for details. Redrawn, with
permission, from Esdale et al.( 2003 ) .
0
1000
Resistivity
Polarisation
s
s
s
s s
s
Metres
v
v
v
v
v
v
High
Low
v
v
bn
v
v
v
v
Sedimentary cover sequence
Granite and granitic breccias
Granite-haematite breccia complex
Bornite-chalcopyrite interface
model. Petrophysical measurements showed that zones of
low resistivity are due to saline groundwater within highly
porous haematitic breccias. The strongest IP sources occur
within the conductive body. Their origin is uncertain but it
may be haematite within the breccia complex. Clearly,
resistivity/IP surveys are capable of de
the nature of the gradients, steeper gradients being on the
up-dip side of the source body (see Section 2.10.2.3 ) . The
following two examples demonstrate electrical mapping in
mineralised terrains using the gradient array.
ning responses
from deep targets, but there is no response from the
economic component of the Olympic Dam deposit.
Example - Pine Point carbonate-hosted massive sulphide
The first example demonstrates the detection of sulphide
ores in contoured chargeability data. The data are from the
Pine Point region in the Northwest Territories, Canada,
where there are numerous small carbonate-hosted zinc-
lead deposits (Rhodes et al., 1984 ). The host sequence is a
Devonian reef complex, and there is glacial overburden
with an average thickness of about 15 m. The orebodies
consist of sphalerite, marcasite, galena, pyrite and some-
times pyrrhotite. Gangue is calcite and dolomite. The
ores are not electrically conductive and do not produce
5.6.6.4 Maps
The interpretation of electrical parameter maps mainly
involves identi cation of anomalous responses. The
gradient array is commonly used for mapping an area
and anomalies are chie y coincident with their source,
with strike of the source corresponding with the orienta-
tion of the response, if elongated. Dip may be inferred from
 
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