Detectors for Big Deep gold versus Detectors for Small Shallow gold

There is one thing that I never fully understood and that is why some PI detectors are considered good for Big Deep gold ( SD2200, 7000Z, GPX5000) and others are considered Small Shallow gold detectors ( SDC2300, GPX6000 & now AF-E1500).

I get that for small gold you need a small coil & very small pulse delay timing and for big deep gold you need a big coil and slightly longer pulse delay but naively I assume that any detector that can separate the target signal from the ground signal for 0.1g at 100mm could do the same for 100g at 1m, if it had a bigger coil.

It seems that is not the case else the SDC & 6000 should be great deep detectors when coupled with +18" round coils but no-none is even making coils that big for them.

So there must be more to what it takes to make a good deep gold detector than sensitive electronics and a big coil but I dunno what the other differences are .

Anyone have any knowledge on this topic?

XLOOX said:

There is one thing that I never fully understood and that is why some PI detectors are considered good for Big Deep gold ( SD2100, 7000Z, GPX5000) and others are considered Small Shallow gold detectors ( SDC2300, GPX6000 & now AF-E1500).

I get that for small gold you need a small coil & very small pulse delay timing and for big deep gold you need a big coil and slightly longer pulse delay but naively I assume that any detector that can separate the target signal from the ground signal for 0.1g at 100mm could do the same for 100g at 1m, if it had a bigger coil.

It seems that is not the case else the SDC & 6000 should be great deep detectors when coupled with +18" round coils but no-none is even making coils that big for them.

So there must be more to what it takes to make a good deep gold detector than sensitive electronics and a big coil but I dunno what the other differences are .

Anyone have any knowledge on this topic?

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Hello XLOOK,
Re, your questions about the detector models suited for finding big deep nuggets; over the years there have been a few M/Lab detectors that had a better chance of finding big nuggets in that situation.

Here is my take on those models, the first deep PI they made is the SD 2000, and it was certainly a deep gold getter, nothing matched it until the SD 2200 d came along. With a big coil it found lots of deep big gold.

My next model to get large deep gold in red hot mineral ground was the GPX 4500, this opened up those old patches once more.

The 2100 and the Extreme, plus the GPX 5000 were all tuned to find the smaller gold mainly, yes, they could go fairly deep, but not as deep as those others I have mentioned.

The Z 7000 was a hybrid that went deeper on specimen gold, and also the rough, porous, and ragged nuggets. Therefore, for finding gold laden quartz leaders and reefs, the Z is the go.

The Later machines that find the tiny gold, just do not have the right Timings in them to do the job.

Once we went away from using Normal timings, the big deep nuggets dropped off, thus that tells me, this is the timing to aim to use whenever you can.

So, really the mineralisation dictates if you can use Normal timing, the only other option for you, is to select the right coil for the area and ground type you are working.

You are right in saying that the Pulse Delay Timing, has everything to do with getting deep nuggets in hot ground. An example is; years ago, Bruce Candy altered an SD detector for a mate of mine, what he done was to alter the timing on the clock to lengthen the transmit signal, so the Timing then fully charged the nuggets with eddy currents at depth, with their much longer time constants.

Of course, he always used large Coils, and found some very sizable nuggets that others could not get to.

All I can suggest is to use one of the deep seeking detector models, and maybe have it worked on to lengthen the transmit signal. Without the right timing to suit those deeper big nuggets, they will stay in the ground.

Looking at the best coil to use for this helps enormously too, the size of say a 20” inch to 25” inch DD round coil, is the way to go.

Cheers ozziegold.

ozziegold said:

Hello XLOOK,
Re, your questions about the detector models suited for finding big deep nuggets; over the years there have been a few M/Lab detectors that had a better chance of finding big nuggets in that situation.

Here is my take on those models, the first deep PI they made is the SD 2000, and it was certainly a deep gold getter, nothing matched it until the SD 2200 d came along. With a big coil it found lots of deep big gold.

My next model to get large deep gold in red hot mineral ground was the GPX 4500, this opened up those old patches once more.

The 2100 and the Extreme, plus the GPX 5000 were all tuned to find the smaller gold mainly, yes, they could go fairly deep, but not as deep as those others I have mentioned.

The Z 7000 was a hybrid that went deeper on specimen gold, and also the rough, porous, and ragged nuggets. Therefore, for finding gold laden quartz leaders and reefs, the Z is the go.

The Later machines that find the tiny gold, just do not have the right Timings in them to do the job.

Once we went away from using Normal timings, the big deep nuggets dropped off, thus that tells me, this is the timing to aim to use whenever you can.

So, really the mineralisation dictates if you can use Normal timing, the only other option for you, is to select the right coil for the area and ground type you are working.

You are right in saying that the Pulse Delay Timing, has everything to do with getting deep nuggets in hot ground. An example is; years ago, Bruce Candy altered an SD detector for a mate of mine, what he done was to alter the timing on the clock to lengthen the transmit signal, so the Timing then fully charged the nuggets with eddy currents at depth, with their much longer time constants.

Of course, he always used large Coils, and found some very sizable nuggets that others could not get to.

All I can suggest is to use one of the deep seeking detector models, and maybe have it worked on to lengthen the transmit signal. Without the right timing to suit those deeper big nuggets, they will stay in the ground.

Looking at the best coil to use for this helps enormously too, the size of say a 20” inch to 25” inch DD round coil, is the way to go.

Cheers ozziegold.

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Thanks for sharing that history ozziegold, I learnt a lot.

I have never used the SD or GP detectors as back then I was stupidly still persevering with the ADS and swearing a lot ! Barely had to dig for any gold found with that detector but at least it had decent size coz that was all it could see

I wonder why the 6000 doesnt have a longer timing option & yet the 5000 is pretty much discontinued ?

With a VLF it is simple. Lower frequency (i.e. 5 kHz) means the transmitting and receiving is oscillating a lot slower than say high frequency (60 kHz), which is oscillating very quickly. The slower/lower frequency is not as good at detecting very small and low conductive targets, but it has the advantage of punching down deeper on larger/higher conductive targets. With 60 kHz, it is happening so fast that it can pick up the tiniest metals, but just can't penetrate. Also because it is so sensitive, ground minerals act as a barrier, so it just can't punch through it. That is why VLF's can be woeful or awesome depending on the type of ground you use them in.

With Pulse Induction detectors it is a lot more complicated, especially when Minelab introduced Dual Channel PI back on the SD2000. There is just a lot going on. Different numbers of pulses, the voltages used, is the input voltage regulated, and then when DVT came out, different voltages on different pulses, and also how is all the information presented as audio. With a pulse detector there is a certain OFF time between the Transmit pulse and the Receive pulse, i.e. they are not continually operating like on a VLF. The advantage of that is that a big chunk of ground signal dissipates before the Receive pulse comes on, so pretty much all PI machines will handle bad ground better than a VLF. BUT, as was the case when the SD2000 came on the scene, the one disadvantage was the loss on very small gold sensitivity. But no one really cared, as people were pulling 10g plus nuggets out regularly. So as the big gold became less and less available, detectors had to keep getting more and more sensitive in order for prospectors to keep finding it.

By manipulating the Pulses, ground balance, transmit power and other internal goodies, detectors got a little better, but at some point the only way forward was to offer specialised Modes (soil/timings) to optimise the detector for specific tasks, i.e. Sensitive, Normal, Salt etc. This was basically the evolution of the GP extreme to the GPX5000. Now as good as the 5000 was/is in Fine Gold (and Sensitive Extra in milder soils) where the VLF's still had an advantage was on "hard to see" gold. This is gold that is rough/flaky/prickly or still in host rock, i.e. specimens. The VLF's could see this type of gold just fine, but couldn't penetrate in bad mineralisation......enter the SDC2300. By being specifically geared towards this "hard to see" gold, and being basically switch on and go, it was dynamite on this small stuff, but the drawback is it won't punch as deep on bigger multi gram bits. But don't let anyone tell you it won't find big gold, that's just nonsense.

So that covers big deep gold and small shallow gold, so then what's next? GPZ - it could have almost SDC sensitivity and GPX depth on the same swing with a 14" coil. But this required different technology, not the usual Pulse tech of the 5000. The GPZ still remains the best unit on the widest range of target sizes and gold types in my opinion. But in talking to many customers over the years, they are not getting any younger, and back and shoulder issues or bad knees is common place, and they just can't handle the bigger machines anymore, and digging multiple deep holes in one day is out of the question. This is what made the 6000 a big hit, with a lot of used GPZ's coming up for sale.

So yes, you can probably put an 18" coil on an SDC, but it just won't perform as well as putting the same coil on a GPX4500 running in Normal. At the same time, you could increase the sensitivity of the SD2000 by putting on an 8x6" sadie coil, but put that Sadie on a GPX5000 or now the AlgoForce E1500, and it will blow the SD2000 away on small gold sensitivity.
The way I look at it is this: I'm the prospector, and the detector is the main tool. These tools have many different attachments that do different jobs better than others. So when I'm looking to do a specific task, I want to pick the best tool and best attachment for the job.

XLOOX said:

Thanks for sharing that history ozziegold, I learnt a lot.

I have never used the SD or GP detectors as back then I was stupidly still persevering with the ADS and swearing a lot ! Barely had to dig for any gold found with that detector but at least it had decent size coz that was all it could see

I wonder why the 6000 doesnt have a longer timing option & yet the 5000 is pretty much discontinued ?

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G/day XLOOK.

Now I understand why you were asking, yes you had to move with the times in those days. The old VLF detectors had their limitations, but found plenty of gold in those earlier days.

After the first initial jump up to the SD 2000 PI. Which we thought cost an arm and a leg at the time, you could immediately see the benefit, the detectors paid for their cost in a few weeks for many.

Now having a pocket full of dollars, this set you on the road to move along through the new detector releases as they changed, some for the better and others tweaked for smaller gold, although there were more small bits to be found.

Then again, we liked chasing the large deep stuff. That’s where the big money kept many in the game for years. We soon went back to an older model when this happened, as coupled with the development of new after-market coils, these helped us find more deep gold.

A few new models were missed purposely by being in the know, this helped to avoid those. The new 4500 was a top detector, although noisy at times, it had the raw guts to go deep to satisfy our needs, like the SD 2200’d had done.

It was just like the jump we had earlier from the VLF detectors to the SD 2000, PI once again. These 45’s satisfied us until the new 5000 releases.

I did buy a GPX 5000, but once more M/Lab had mostly targeted the smaller end of the gold range, it did a fair job at finding much gold for many.

But I and others, went back and bought another 4500. Luckily, I got one of the last ones, that’s before they started using the 5000-circuit board in those newer models of the 4500’s.

The Z 7000, was a huge jump up in price at their release, and a lot held off to see how it went, I held off for years, but finally bought a second hand one, but being careful, I kept the 4500.

The Russian X coils had changed my mind, with the 7000 showing that extra depth when using those new X Concentric Coils.

Minelab’s SDC 2300 and GPX 6000 found heaps of tiny pieces of gold and lead shot, they satisfied a lot of people. Yet these models were not made to find really deep gold, mostly the small shallow targets, there has been the odd bigger piece found with them, but not consistently.

A mate and I bought a 6000 between us in the first week of its release, we gave it a good try, and sold it a week later.

XLOOK, If there is no break-through in technology, once again our only option is to go back to the models that done the job. Now there are new detector modifications today that have a proven out in the field record, and also new style coils of larger size and lightness for our needs.

So, that’s where we are at presently, maybe the new Z 8000 will be the answer, but then again at that price, perhaps not so many takers for quite some time, I recon.

Thank you, Nenad, for your in-depth write up it is very enlightening, and I’m sure many will benefit from your knowledge written here. I had thought XLOOK was mostly interested in finding out about large deep gold, and the how to and what it requires to do so.

Cheers to you both. ozziegold.

ozziegold said:

Thank you, Nenad, for your in-depth write up it is very enlightening, and I’m sure many will benefit from your knowledge written here. I had thought XLOOK was mostly interested in finding out about large deep gold, and the how to and what it requires to do so.

Cheers to you both. ozziegold.

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Likewise! A great read

I don't think the GPZ is the best detector, probably the best price tag! And Nobel prize for its weight. But thats all i think its got going for it. It has failed to see multi ounce nuggets at depth on multiple occasions (in an area) that a GPX 5000, a 4800, and a 4500 could detect noticeably. It didn't have any faults, has been tested by other people aswell and it has found mutli gram gold consistently, but for some reason the deeper multi ounce gold is invisible regardless of settings, modes used, or coils used, even the 19 coil. Have tried a few GPZ and I have given up, maybe others have worked out the same and maybe thats why there's more GPZ on the 2nd hand market.