It has been many long years since Minelab set of the last great gold rush with the release of the old SD2000 pulse induction metal detector. This detector was a huge improvement over the existing vlf and ib type detectors that had great difficulty in trying to work in Australia’s highly mineralised goldfields. The SD2000 was followed up with the likes of the SD2100 and SD2200 detectors and these detectors found hundreds of thousands of ounces of gold, some are still being used today as the owners have tried newer detectors and do not like them. I have asked a lot of questions as to why these prospectors refuse to upgrade and here are some of the answers. The newer detectors through various means attempt to remove the ground noise via some electronic filters or analogue to digital signal processing that is attempting to allow the target signal through the detector while at the same time squashing out the ground noise. 

Is ground noise the enemy? the answer is not so straight forward, it depends on the detector and what you are looking for, many articles ago i wrote about using a detector for finding paleochannels, these are buried creeks and other low lying area’s that have collected a lot of heavy reactive minerals that give a different ground response in relation to the surrounding ground. Many prospectors searching for these old river and creek beds will not use a newer detector as they say the sound is too processed for them to be able to understand or detect the ground noises that they are hunting.

They prefer to use the SD2000 and SD2100 mainly due to the detectors having manual ground balance. The way they use the manual ground balance is to offset the balance as the coil is lowered to the ground the controls are set to make the detector a little bit more noisy and then just back off the ground balance just a small amount so that any increase in ground noise is easily detected. Some prospectors go the other way to make the detector on the edge of over compensation of the ground balance that makes the detector very quiet, they then pick the rise in threshold. The latter method will lose you some gold but works well for picking up an area with increased minerals. The fact is the newer detectors are designed to get rid of the ground noise, removing as much of the peaks and troughs as possible and trying to allow only the target signals to get through.

One thing that is very interesting is that under some conditions a target is not detected by one model of detector but a different model can pick it up easily. This is mainly to do with the electronics that remove the ground noise and sometimes the baby gets thrown out with the bath water. The older detectors in the hands of a very skilled operator can usually hear every target and ground noise but after many years of experience they can work out the difference between gold and ground noise, the best discriminator is between you’re ears and it takes a lot of practice over the years to get good at it.

There are a lot of GPZ , SDC and GPX detectors out and about being used in the goldfields and many have ditched their GP series detector in favour of the newer detectors, if you are using a GP or GPX in normal timings there is next to no difference in performance, it is only the extra timings that are aimed at smaller gold that is the main difference. There are many that rave about the SDC2300 as they find gold each time they use it, the combination of a very small coil and being able to fast sample means it will be like a vacuum cleaner on small gold. This detector does find pin head sized gold but here is my question, How many pin heads make a gram? Years ago many a professional prospector would ignore 0.1 grams and continue on looking for larger gold.

The next detector to look at is the GPZ7000 , it is a heavy detector weighing in at 3.1Kg but the question is was it pushed out to market too soon without being properly tested? There were many complaints of ground balance issues and sounding off over voids, and a non steady threshold. After some months the stop gap solution to this problem was to place a ferrite torroid on the ground and use this to force the detector to ground balance. Recently it seems that ML have done some changes to the software and the problem has gone away. It looks like the field testers should take a bit more care while testing the detectors in my own humble opinion.

Time to digress, one of our customers found a nice 25 oz nugget with a GPX-5000 detector, the article is on the abc.net site, just search for gold and it will lead you to the article, or you can follow the link on my website detectormods.com. We are currently working on ways to get even greater depth out of the SD GP and GPX detectors by reducing the noise even further, we are testing out capacitive reduction using negative impedance, i probably lost you on that one but what it means is that when you reduce noise you lose performance but the new technique means greater depth with less noise.

As there are a lot of prospectors using the modded gpx detectors and some have found a way of pulling more undetected gold from old patches, Most detectorists do not use “sharp mode” and many people tell me that it it cannot be made to work on hot ground. Well a few of our customers using both the 4500 and 5000 detectors are pulling lots more gold from old ground using sharp mode, by using the using high frequencies with the frequency mod and running a lot more input gain using the modded front end with the 10 turn adjustment. Please note ( This only works with the Gain and Frequency mod)

Sharp mode seems to punch down nice and deep with increased frequency while reducing ground noise with the shorter pulse times. Sharp timings is a mode that is definitely worth exploring. It is also worth remembering that by changing just one condition, either the setting up of a detector, coil size or time of day (ground temperature) that hidden nuggets can be found. There have been very good reports that by using the sharp timing with a higher frequency and extra gain that excellent depth can be achieved by using big DD coils. If you use older coils they may not work, you need the DD to be made from litz wire, some early ones had magnet wire in the receiver coil and this reduces the performance to such an extent that trying to detect becomes a waste of time.

Coils and static, the input stage of our detectors are very sensitive and one of the problems yet to be addressed is static build up, it can cause noise as it slowly discharges into or across the coil or when you get the ping from some vegetation, the way to reduce static is to mist the coil with water or coat it with a static reducing compound. A cheap way to protect against static and also keep your coils looking good is to find an antistatic car polish and use it on your coils, there are antistatic floor treatments available as well but they are expensive due to the fact that they come in large amounts. You can buy a chemical named Behentrimonium Chloride and make your own anti static solution, it is cheap and you can mix it with methylated spirits and spray or brush it onto your coils. I found it on Ebay, it is not expensive. I have a major amount of new information on using the GP and GPX series of detectors, I am in the middle of collating a lot of test data and will be putting it up on detectormods.com