Geology Reference
In-Depth Information
Drillhole PDS1
Drillhole DS1
Time
Scale
Time
Scale
1.22 ms
1.53 ms
2.08 ms
2.71 ms
3.80 ms
5.05 ms
7.24 ms
9.74 ms
14.11 ms
19.11 ms
27.86 ms
37.86 ms
x500
x500
x500
x500
x200
x200
x50
x10
x5
x2
x2
1.22 ms
1.53 ms
2.08 ms
2.71 ms
3.80 ms
5.05 ms
7.24 ms
9.74 ms
14.11 ms
19.11 ms
27.86 ms
37.86 ms
x200
x100
x50
x20
x10
x5
x2
80
80
60
60
40
40
20
20
0
0
Station no.
20
45
70
95
120
170 m
Station no.
30
55
80
105
130
155
180
205 m
145
Drillhole DS2
W
E
Time
Scale
PDS1
DS1
EMP loop
1.22 ms
1.53 ms
2.08 ms
2.71 ms
3.80 ms
5.05 ms
7.24 ms
9.74 ms
14.11 ms
19.11 ms
27.86 ms
37.86 ms
DS2
x50
x10
x2
x2
80
best fit
current loop
1% zinc
60
40
0.2%
copper
20
Shale
Sericitized tuffs
Black shale
Semi-massive sulphides
End of EMP survey
0
disseminated
pyrite
Station no. 115
140
165
190
215
240
265
290 m
0
100 m
Fig. 9.14
Drillhole TDEM profiles and geological section over Single Tree Hill, NSW, Australia. (Redrawn from Boyd & Wiles 1984.)
angle methods.They are, basically, ground mobile trans-
mitter-receiver systems lifted into the air and interfaced
with a continuous recording device. Certain specialized
methods, described later, have been adopted to over-
come the specific difficulties encountered in airborne
work. Active systems comprise two main types,
fixed
separation
and
quadrature
.
9.8 Airborne electromagnetic surveying
Airborne EM techniques are widely used because of
their speed and cost-effectiveness, and a large number of
systems are available.
There is a broad division into
passive systems
, where
only the receiver is airborne, and
active systems
, where
both transmitter and receiver are mobile. Passive systems
include airborne versions of the VLF and AFMAG
methods. Independent transmitter methods can also be
used with an airborne receiver, but are not very attractive
as prior ground access to the survey area is required.
Active systems are more commonly used, as surveys
can be performed in areas where ground access is diffi-
cult and provide more information than the passive tilt-
9.8.1 Fixed separation systems
In fixed separation systems the transmitter and receiver
are maintained at a fixed separation, and real and imagi-
nary components are monitored as in ground surveys.
The coils are generally arranged to be vertical and either
coplanar or coaxial. Accurate maintenance of separation
