Coil selection for noisy ground

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Coil selection for noisy ground Empty Coil selection for noisy ground

Post  MS on Mon Apr 06, 2009 11:24 am

Hi All
I was taken to an old patch by a friend who used to work an area for big gold and they pulled heaps out close to the surface 17 years ago with a proscan. I was told the area was heavy iron mineralization and it sure was {nothing like I have seen before}
I tried my Gp3500 with a coiltek 17” elliptical DD pro and had a lot of trouble penetrating the ground, with the machine very noisy with it imposable to distinguish between ground noises and deep targets.
I don’t know what coil to use in this situation and I know the depth was greatly reduced in comparison to other areas I have worked with this coil.
Someone said to try a large anti-interference coil or a 18” round DD pro but thought I would ask here first to see what others think before I make a purchase.

Regards Mark
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Coil selection for noisy ground Empty coils

Post  buck06 on Mon Apr 06, 2009 7:54 pm

myself and juppman detect in the same sort of areas juppman has a 3000 he has tryed heaps of coils but he swears by the standard d/d coil he got with the 3000 8inch coil he said it the only coil he can get to run smooth but he still gets signals from hotrock but has learnt to pick the different sounds cheers buck Very Happy
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Coil selection for noisy ground Empty Coil selection for noisy ground

Post  MS on Mon Apr 06, 2009 10:08 pm

buck06 wrote:myself and juppman detect in the same sort of areas juppman has a 3000 he has tryed heaps of coils but he swears by the standard d/d coil he got with the 3000 8inch coil he said it the only coil he can get to run smooth but he still gets signals from hotrock but has learnt to pick the different sounds cheers buck Very Happy

Thanks buck
I have both those coils and didn't try them as thought they would be noiser than what I was using.
I thought the smaller the coil the noiser it would be especially 8" mono , ie larger coil deeper pen and less sensitive to surface min but then again is it trying to read a too larger surface area with more Mineralisation
Mark
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Coil selection for noisy ground Empty Re: Coil selection for noisy ground

Post  echidnadigger on Mon Apr 06, 2009 11:15 pm

MS wrote:Hi All
I was taken to an old patch by a friend who used to work an area for big gold and they pulled heaps out close to the surface 17 years ago with a proscan. I was told the area was heavy iron mineralization and it sure was {nothing like I have seen before}
I tried my Gp3500 with a coiltek 17” elliptical DD pro and had a lot of trouble penetrating the ground, with the machine very noisy with it imposable to distinguish between ground noises and deep targets.
I don’t know what coil to use in this situation and I know the depth was greatly reduced in comparison to other areas I have worked with this coil.
Someone said to try a large anti-interference coil or a 18” round DD pro but thought I would ask here first to see what others think before I make a purchase.

Regards Mark
Mark,
I am starting to wonder about ellipticals in that sort of situation. The centre is like a standard round coil but the tight windings on the nose and rear of an elliptical could upset the electronics. The super sensitive nose and rear, could be looking at shallow ground and the machine is trying to balance things according to the messages sent from the sensitivity of the elliptical shape. Maybe depth is lost as a result, I'm not sure.
However elliptical coils do have a habit of magnifying mineralisation and ironstone. A little like a mono but not working with the same dynamics.
What I have said here is speculation born from experiences and may be wrong.
In that type of ground with a 3500 I would go the dd for sure. With all due respect I would also suggest that your setting are in the right spot for that type of ground. Trying to balance on the hottest spot and then flick to fixed may be one thing, Another may be switch to slow tracking and swing slow ( let the machine keep up ) Or fast and swing slow letting the machine keep up. Try all the tricks that your machine gives you but please auto tune you machine on this spot, before you try anything else, and don't forget about the manual tune if things aint right after the auto tune, it does help.
Brett.
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Coil selection for noisy ground Empty Re: Coil selection for noisy ground

Post  MS on Mon Apr 06, 2009 11:43 pm

echidnadigger wrote:
MS wrote:Hi All

Regards Mark
Mark,
I am starting to wonder about ellipticals in that sort of situation. The centre is like a standard round coil but the tight windings on the nose and rear of an elliptical could upset the electronics. The super sensitive nose and rear, could be looking at shallow ground and the machine is trying to balance things according to the messages sent from the sensitivity of the elliptical shape. Maybe depth is lost as a result, I'm not sure.
However elliptical coils do have a habit of magnifying mineralisation and ironstone. A little like a mono but not working with the same dynamics.
What I have said here is speculation born from experiences and may be wrong.
In that type of ground with a 3500 I would go the dd for sure. With all due respect I would also suggest that your setting are in the right spot for that type of ground. Trying to balance on the hottest spot and then flick to fixed may be one thing, Another may be switch to slow tracking and swing slow ( let the machine keep up ) Or fast and swing slow letting the machine keep up. Try all the tricks that your machine gives you but please auto tune you machine on this spot, before you try anything else, and don't forget about the manual tune if things aint right after the auto tune, it does help.
Brett.

Thanks Brett
That makes perfect sence of the problem I was having with the elliptical DD coil , I thought a larger DD would be better in this hot ground and I now think the extra sensitivity of the coil ends form the Elliptical made it too sensitive for the ground I was working. I will get a larger round ie 14 or 18 "DD and give that a try when I get back over there.
I did find when I went slower it was a bit better but still not enough to pick the deep signals from the ground noise.
Thanks for your help and I wouldn't have thought of looking from that perspective.
Regards Mark
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Coil selection for noisy ground Empty Re: Coil selection for noisy ground

Post  echidnadigger on Mon Apr 06, 2009 11:53 pm

Cheers Mark,
I think I'm on the money but I am still learning and always will be. Other members input on your inquiry, may help both of us.

Brett.
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Coil selection for noisy ground Empty Re: Coil selection for noisy ground

Post  Guest on Tue Apr 07, 2009 5:18 am

Gday Mark

I have worked similar ground to the type you describe, its sounds a bit like theres banded ironstone and probably magnatite, most of the interference would more than likely be from the magnetic composition of the rock, so therefore the coil is picking up on the magnetics and the mineralisation.

I have also used a 8" mono in that ground and all though it squeeks and squarks a it it will handle it better than a larger coil, as it is not picking up the interference as much, I found that any other larger mono coil was just simply swamped by it and all they would do was moan and groan and give you the s...s! in a few minutes.

In the end the best coils I found to use in those conditions are the standard 11" dd coil, and the coiltek 14" round dd pro, I used the old terracotta coloured one but you could try the newer cream coloured one as they are supposed to work better on the 3500, of course you will need to make sure to have it set on dd and use either a slow or medium timing setting, you could also try cancel mode as well, but you would be better to tune it and try to get it to run as stable as possible and then keep it in fixed.

You will just have to experiment with the settings, and keep your swing speed slow, you may even try have to keep the coil a bit higher above the ground as well, you may think that you are losing depth this way but if you cant get the machine to run quietly then you wont hear any target signals above the noise so your not going to get anything anyway.

Also I cant say for sure but a friend told me he likes the black 11" or 18" minelab coils that come with the gp extreme for this, he might be right, I didnt use the black coils much with the extreme as I always felt that they lacked sensitivity, but for your purpose they might be just the thing.

cheers

stayyerAU

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Coil selection for noisy ground Empty Coil selection for noisy ground

Post  MS on Tue Apr 07, 2009 11:12 am

Thanks stayyerAU
You have given a few good points there such as lifting the coil up a bit to reduce ground noise and try cancel mode.I didn't try these
The ground was very mineralized with the normal ironstone and quartz but also a black nearly gloss carbon type
banding through red/pink quartz.Also there was what looked like a grey to redish shale stone but it was very hard and heavy and slightly magnetic .The area where my friend got the gold from years ago was very hard ground to dig with shallow soil off around the exposed bedrock .They were lucky and got to work this area first and found a lot of gold on and close to the surface but now it would take hard rock mining to get to it. I was hoping to pick up a bit that they missed and it was obvious others had been all over the area since, but my advantage was my old friend new the exact spot to detect but as I said before I got signals from ground noise all over the place and digging was very hard ie crowbar and pick.Its a long trip for me to get back over there so I just want to get everything together and worked out before I give it a second crack.
Thanks for your help and it's been great to get advice and idea's from others with more experience than me.
Mark
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