KNOWLEDGE BASE ARTICLE
GPZ 7000 Tips & Tricks

Gold Detecting in Difficult Ground Conditions
Why noise occurs and what you can do about it.
Even after ground balancing, some soils produce un-ground-balanced 'noises' when moving the coil across the ground. This is due to interference fromdifferent chemicals or 'minerals' in the ground, and no metal detector can ever completely be immune to them. Commonly used terms to describe such'noisy' soils are: ‘difficult’, ‘mineralised’ , ‘hot’ , ‘salty’, ‘variable,’ or ‘saturable.' The problem is that this un-ground-balanced 'ground noise' may obscure thefainter signals from deeper gold nuggets. However, it is possible to reduce this ground noise to better hear the fainter nugget signals by selecting suitabledetector control settings, and by the way you swing the coil, in particular; how high above the soil’s surface you swing the coil, and how fast.

General Advice.
In all soils that produce ground noise use the ferrite that is available from Minelab for the GPZ 7000 to ground balance. The method of ground balancing
with the ferrite is given in KBA 26 'Tips for Better Ground Balance.' In noisy soils, the first thing to try is both ground balancing and swinging the coil at leasta few centimetres above the soil, and when doing so check whether this clearly reduces the ground noise or not. The specifics are given below.

The greatest absolute depths are possible in Normal, followed by Difficult, followed by Severe. Always try to use the deeper setting, but, in noisy
soils, you will probably find more nuggets using Difficult or in extremely noisy soils, using Severe, because these reduce the ground noise relative
to the fainter nugget signals.

Identifying Types of Difficult Groundnoise effectgreater than

200 cmnoise effect lessthan or equal tonoise effect lessthan or equal to

3 cm

1 cm

Variable (Hot) Ground

Saturable Ground

Salty Ground (Conductive Soils)

This term has 2 different
meanings. One meaning is
the ground balance requires
a different ground balanceadjustment from one patch of soil to anotherrelatively close patch of soil. The other meaning
is variable hot ground has alternating patches oflow (L) and high (H) concentrations of soil signal
interference that produces noise, and such soils
are often red and/or black in colour. In either
case, when the detector coil is moved across theground, the ground balance required for optimal
adjustment changes often, and sometimes fairlyabruptly. In this type of ground, use the Difficult
Gold modes and use the ferrite every time you
ground balance (see KBA 26), and after groundbalancing, use either Auto or Manual Ground
Balance depending on which seems to work
best for that particular soil. It may pay to swing
the coil at least a centimetres above the more
noisy patches.

Some soils can ‘saturate,’ whichmeans that whilst it is possible
to get near zero signal when
the coil is raised and lowered
down to several centimetres above the groundsurface, lowering the coil below a certain height
produces an un-ground-balanced signal. Refer toKBA 24 'Basics of the GPZ 7000 Technology: Zero
Voltage Transmission (ZVT)' for further details on
saturation and Viscous Remanent Magnetism.

The presence of 'salty' (or'saline' or 'conductive') soil iseasy to determine. If an
un-ground-balanced signal
occurs when you raise and lower the coilbetween 50 cm and a metre (or more) above
the soil surface, the soil is conductive.
Unfortunately, the ground balance required forthe conductive soil component is different to
the 'usual' magnetic ground signal component,
and both are not properly balanced out
simultaneously; hence the ground noise fromconductive soils.

(Remember though, do not ground balance
moving the coil up and down; only use this up-anddown coil movement to check what type of noisy
soil you happen to be detecting in.)In saturable (or severe) soils, the height below which
an un-ground-balanced signal occurs is dependent
on the soil’s chemistry and detector settings. In
such soils, this saturation noise 'threshold height' isusually, but not always, less that about 3 cm above
the soil surface for the Difficult setting, and usually a
bit less than this for the Severe setting, but maybe as
high as 15 cm for the General setting.

KNOWLEDGE BASE ARTICLE | KBA 27-2

Combinations
It is possible to have any combination of anyof the above; that is, variable, saturable, andconductive (saline) soils.

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How best to operate your detector for thesedifferent noisy soils:
Electromagnetic Interference (EMI)
If the detector happens to be noisy when the coil is being
held still; and therefore this noise is not caused by a signal
from the soil; this noise is probably caused byElectromagnetic interference (EMI); the source being fromthe mains electricity or signals from lightning; the latter maybe eventhousands of kilometres away. Use either Manual or Auto Noise Cancel tominimise this noise.

Default settings and Quick Start method
The GPZ 7000 default settings have been designed for use
in typical mineralised goldfields soils and it is recommended
that you start with these. But, you may well find more goldusing different settings and by changing how you swing
the coil, especially in noisy soils. Below are tips for noisy soil conditions.

Variable Hot Ground
For these soils, regularly use the recommended side-to-side
ground balancing technique preferably using the ferrite(see KBA 26). It may be advantageous to raise the coil atleast to 1 cm above the surface for patches of ground that
produce more ground noise for this sort of soil.

Saturable (Severe) Ground
The important controls for prospecting in saturable soils are
the Ground Type selected settings, and swinging the coil atapproximately (or a bit above) the threshold height below
which saturation noise signals significantly occur. Further, it
is important always to ground balance (with Quick­‑Trak) using the ferrite
and with the coil swung at this threshold height. It may also help to set thedetector to Manual Ground Balance (which fixes the ground balancesetting) after each ground balancing.

Select the Ground Type as a compromise between tolerable saturationnoise signals and Ground Type, that is to say; if Normal is impracticallynoisy, then try Difficult, but if this is also impractical, select Severe.

Conductive (Saline) GroundIn these soils, High Yield produces the most ground noise,
and General less, and Extra-Deep yet less still. Many
conductive soils also produce substantially more groundnoise when Normal is used (often from 'hot rocks'), and forthese soils, it is better to use Difficult.
In conductive (saline) soils, ground balance using the ferrite
as instructed in KBA 26, and thereafter, set the detector’s
ground balance to Fixed using the Manual Ground Balance
mode. It is important to swing the coil at a consistentheight and slower sweep speed to help reduce the soil
generated noise level. As a rule salty ground tends to be shallow, andbecause the GPZ 7000 is designed mainly for bigger targets at depth, you
may be better off prospecting in deeper ground away from the salty areas.

Adjusting other detector controls
For any of the above conditions, there is the option of
making further adjustments to the detector controls. The
Sensitivity control can be adjusted lower than the default
setting of 9 and the Audio Smoothing control can bechanged from Low to High to assist reduce noisy soil
ground signals to a more practical level.

KNOWLEDGE BASE ARTICLE | KBA 27-2

Expert Tips from Jonathan Porter
Jonathan Porter is a well known Australian
professional prospector with over twenty
five years of gold detecting experience. He
has been sharing valuable knowledge via
the Minelab Treasure Talk blog since 2010.

Jonathan worked in close association
with Minelab to evaluate and field test
the GPZ 7000. Here he brings you his
top detecting tips to help you get themost out of your GPZ 7000 in difficult ground.
Jonathan describes the steps he takes in salty and saturable soils toachieve and maintain a good ground balance:
1. If you don’t have a dust iron ferrite, perform a walk‑and‑sweep
ground balance at start up or after a ‘Reset Audio and Detection
Settings’ via Quick Start. I highly recommend you perform thisin ground that is not too noisy (i.e. low level of 'waa waa' sound)and keep the coil at least 3 cm above the ground to avoid
saturation signals.
2. If you have a dust iron ferrite and the area you are in is salty,
perform the octopus‑sweep ground balance technique overthe ferrite placed on the ground, but limit the speed of thesweep to reduce salt signals and also minimise the amount ofsweep distance (tighten the sweep up to ensure that signals
from the ferrite are frequently sensed by the coil).
3. Once the above procedures have been performed go intothe Ground Balance Mode menu and select Manual. This willlock the ground balance so that saturation and salt signals do
not affect the ground balance setting after that point. You canconfigure the User Button to take you directly to the Ground
Balance Mode menu option to save on time.
4. Go detecting, just like you would with a GPX 5000 in Fixedmode when using Fine Gold or Enhance. If you feel the need toground balance, place the dust iron ferrite on the ground andperform the octopus-sweep ground balance for 3 to 5 secondsor until the unit is quiet (this should be checked regularly). There
should be minimal or no noise over the ferrite, but you need theferrite there once the Quick‑Trak button is pressed to get a goodground balance. Even if the ferrite part of the ground balance isgood (i.e. quiet when swept over the ferrite), all further groundbalancing in the same area should use the ferrite.
5. For those without a ferrite you should do a miniwalk‑and‑sweep ground balance holding the Quick‑Trak button,
preferably where the noisy salt signal ('waa waa' noise) is less,keeping the coil at least 3 cm above the ground to avoid
saturation signals.
To read Treasure Talk blogs by Jonathan Porter, Visit
www.minelab.com/treasure-talk?author=24957
Click here to see KBA 26‘GPZ 7000 Tips for Better
Ground Balance’ for more
information on groundbalancing the GPZ 7000
using the walk‑and‑sweep
or ferrite‑assisted groundbalance methods.

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