Minelab GPX-4500, Instruction Manual

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The GPX-4500 is capable of rejecting many
ferrous (iron) targets while still detecting
non-ferrous targets.
While detecting in littered goldfields much of the
shallow iron rubbish may be ignored with a high
probability that valuable targets will not be missed.
When Iron Reject is turned off no iron targets will be
rejected. Therefore, all types of metals will produce
a target response. This is known as 'All Metal' and is
the preferred setting for most situations.
In All Metal the detector will give varying volume
and pitch signals. This information does not indicate
the type of metal in the object.
If you are Pinpointing a target prior to digging, the
best results will be obtained with Iron Reject Off.
Iron Reject
When Iron Reject is activated the detector rejects
ferrous objects by blanking the normal target signal.
You will notice the Threshold tone goes silent as the
coil passes across the ferrous target.
Discrimination is dependent on target signals being
strong enough for the GPX-4500 to determine if the
target is ferrous or non-ferrous. If the signal is weak
the detector will give a non-ferrous response until
the signal becomes stronger, i.e. due to a hole being
dug and the coil getting closer to the target. The
Iron Reject function is designed this way to allow
maximum accuracy, while limiting the chances of
rejecting a desirable target.
You can choose less cautious levels of discrimination
for appropriate areas. Possibly there is a mining
camp that has not been detected due to the high
level of rubbish. Iron Reject now gives you the ability
to increase the amount of rejection while knowingly
accepting more risk of rejecting a low grade nugget.
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Note: When a target has
been located the coil should
be passed back and forth
over the target centre
several times. Remember to
set Ground Balance to Fixed
for this and keep the sweep
across the target at an even
height and as close to the
ground as possible.
Range Off (All Metal), 1–10
Caution: Do not attempt
to discriminate by
raising and lowering
the coil on a deep or
partially dug target. An
accurate discrimination
requires an even side-
to-side coil motion. It is
recommended to dig all
targets that do not give an
obvious rejection.
Tip: To improve
discrimination accuracy
you should always test the
target from at least two
directions (90˚ to each
other) so that the detector
'sees' the target from
different profiles.