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Detecting flogged ground with the Minelab GPZ 7000

This article is aimed at those starting on their GPZ journey, but those with experience may find some benefit also, as will other Minelab GPX and SDC users.

Over many years in store, I was bombarded by new prospectors saying they have spent days in well known areas with no result. These well-known areas have been hammered hard, raked and re raked again and again. At first sight of these areas it is easy to believe there is nothing left- but that is far from the truth!

Why is this? Firstly, everyone has different abilities and skills. They use their detectors in different ways, or are running different settings. Secondly, everyone takes a different path through an area- usually the easiest- and often wander randomly in more or less a straight line. Most importantly- are not being thorough and systematic in how they work the area.

In these well worked spots, it is not about how much ground you cover in a day, rather how thoroughly you work that ground!

With the GPZ 7000 at your disposal, it makes it relatively easy to pull out nuggets in these areas, but the trick is to be very slow and methodical. 

The easy gold is probably gone, so we need to focus on the ‘stealth’ nuggets. These usually odd shaped pieces, or pieces that are in the ground at an odd angle, presenting an audible signal only when approached from a certain angle. 

The key to finding these elusive nuggets is to work systematically- marking out a 20-30m square area, and detecting it like you would mow a lawn, covering every square inch. Once complete, detect the square again at 90 degrees, and again at 45 degrees. This way, sneaky pieces have no way to hide- no matter their shape or orientation in the ground. 

In the accompanying video, you can hear the target is not overly loud, but when disturbed during the first recovery attempt, suddenly begins to scream! This suggests the piece was likely standing on its end in ground, so that only the tiny tip was conveying the signal. When moved, it then presented its broad side- giving off a very loud response.

Now for the GPZ- The best advice I can give a new user, apart from the above information, its to firstly re-set your machine so all prior ground balance information is cleared. Perform your ferrite ground balance with the quick track button and when complete, there should be no signal given off by the ferrite ring, and the audio should stabilize quickly when the coil is pumped up and down- if it does not, or there is still signal from the ferrite- repeat until its perfect.

Next, adjust the detector tone to suit your hearing (there is no right or wrong here) and then…… leave the settings alone! The Gpz is a powerful beast, and unless you know it intimately, changing the settings off the default may hinder things for you. The only setting you may need to change is the sensitivity- only if the machine is very unstable on the default of 9. If it is too noisy, lower the sensitivity a few points and you should find it settles nicely, we are shooting for a stable machine here.

There are many trainers that teach you to crank the sensitivity up- but in doing so you then begin to introduce excessive noise and instability- obvious targets will get louder, but all that extra EMI or ground noise will also become louder and this in turn will drown out the often very subtle response from the stealth gold we are chasing. These same trainers will also tell you to scrub the coil on the ground. This has the same drawbacks as turning the sensitivity right up. Being a constant transmit / receive machine, it is prone to saturating the ground with signal if scuffed on the ground, again introducing excess noise. The best practice to getting a stable machine is to keep the coil slightly off the ground. This allows a nice smooth threshold- the targets will be quieter, however the subtle changes in the threshold now become very easy to hear even for a novice. Any subtle semi repeatable noise should be investigated.

Finally, sweep speed- I have found 4-5 seconds from side to side allows targets to really come through. If you speed up, you may not hear the tiny warble telling you to dig!

On the day the video was taken, 3 pieces of gold weighing 0.06grm, 0.17grm and 0.77grm  (and 3 lead shot) were won in the space of 2hrs working a 20m square area, in a location that has seen hundreds of detectors over it- even a detecting event last year! The best part is, this square is only 50m from the main area people park!

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