If you take a look at my video “The Outback Prospector – Unleashing the GP Series” you will notice a common theme throughout, “do not detect in Auto Ground Balance or you could miss gold”. I have mentioned this so many times since the GP extreme was released that it has almost become a mantra.
Now the big problem is that not all areas are conducive to running in fixed GB, especially if you want to maximize your chances on deep targets in highly variable ground. A good example of this is in the majority of ground found in Victoria’s Golden Triangle (in fact anywhere where there is a high concentration of ironstone), if you were to take a magnet and rub it anywhere in the soil strata from surface to bedrock you would find it would become covered in iron stone fragments.
It is these fragments that resist the magnetic field of your coil or to be more precise it is these fragments that cause extreme duress to your GB circuit as it tries to compensate to the variations from one area to another (sometimes only a few feet apart).
 Obviously you cannot detect these areas effectively by relying on manual GB alone because you would be on the button all the time trying to keep it in tune. I have been warning about the use of Auto GB for years now because of the too fast GB that has been present on the GP series since late 2000. But tell that to the poor prospectors who have no choice, they either put up with the noise or plain and simply accept the fact they will be blowing the odd nugget at depth but at least maintain some sort of sanity.
The auto GB on the GP extreme and GP 3000 is too fast and has been a sore point with me for a very long time. But you have to realise I do not represent the average prospector, in fact I probably only represent a minute percentage of the market (maybe 1%) and as such even though I can offer good advice from a usability point of view and also a technical point of view, the units Minelab make still have to cater to the majority.
Thankfully after a lot of discussions and hopefully on my part, education of the majority, Minelab have decided to give us the end user a larger range of choices by offering three GB speeds on the GP 3500. I can now with a clear conscience tell end users out there in the real world that they can now without any fear detect in Auto GB without compromising too much on outright depth.
You can now head into those extreme areas and feel confident your machine will not GB out a good target at the extreme range of your machines ability unless the ground is dead quiet or has no variability at all. To prove this point I headed out to an ironstone laden site yesterday and smack bang in the middle of a hand cleared patch I lobbed onto a 3 ˝ OZ nugget at only 14 inches. The nugget was in a previous operators dig hole and was missed I am sure because of one of two reasons, either they were in fixed GB and discounted it as ground noise (the area is rife with them) or they were in Auto and it was Ground Balanced out all together.
I myself was unconvinced when I first heard it, but it would not balance out so I dug off a few inches, by this stage it improved slightly but it was not till I had gone down at least 10 inches that it really started to boom. I was in Tracking/Medium setting the whole time and at no time did the machine act up or become unstable. It should be noted here that the Level adjust (Discrimination control) function of the GP is no longer tied in with the Ground Balance on the 3500, so now you can just switch on and go and rely on your machine to do the job while you concentrate on the more important things. Minelab have factory pre-set the pausing effect function of the GP 3500 at the optimum setting for the Tracking speed you select (see my video for info about pausing effect), this should save on a huge amount of confusion.
 The purpose of this post is to inform those of you interested in the immediate differences of the
GP 3500 over the GP 3000 and what it means to us as prospectors. I would also like to add, all dealers worldwide were made aware via e-mail of the new machine within hours of each other. Only a handful of people have actually tried a GP 3500 and it is for this reason I am posting my experiences and results to better inform the public as we get closer to the machines actually being made available.
Jonathan Porter
Edited by - Jonathan Porter on 04/03/2005 17:28:35
Minelab GP 3500 Review by
aurumaustralis
 |