Clay Domes; Charcoal - Minelab Eureka Gold Instruction Manual

Page 15
11.2

Clay Domes

A common occurrence in nugget-bearing country is soil mineralisation
commonly known as 'clay domes'. These are regions of rather broad sound
which could be confused with the sound which would come from a large
deep nugget.
The following procedure will quickly establish whether or not the sound
comes from clay or a metal target:
a) Pinpoint the target as best you can.
b) Remove about 4 cm (1.5") depth of soil from over the target response.
Dish the hole so that there are no sharp edges around the hole.
c) Sweep the coil across the target from a few directions, keeping the
coil as low as possible. Listen to the signal and note if it is:
— Any louder or more defined than before. By bringing the coil closer
to a metal target the signal should become louder.
— Note if the signal seems to come from one direction only
(a mineral signal will often come from one direction only, or at
least be less defined from the return sweep).
d) If you are still not sure, continue to dig deeper and again, note the
points above.
e) Be sure to dish the hole when digging to ensure there are no sharp
edges. Sweeping the coil across the sharp edge of a hole can cause
false spurious signals due to the change in distance between the
ground and the coil.
11.3

Charcoal

Charcoal can sound loud and rather like a metallic target when close to
the surface. Charcoal is usually created by farmers burning off tree stumps
or by bushfires. The growth is burnt below the ground level, so it is not
always obvious what the sounds are until you have actually dug up the
causes of these noises a few times. Again, experience will teach the
operator how to read the ground efficiently and gain understanding of the
detector's response to the ground.
An indication of charcoal is that the sound seems very spread out and
becomes patchier as the ground is dug. Inexperienced operators should
continue to dig until the reason for the signal becomes clear.
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