COIL FOR DEPTH

I have a small patch where I have found some gold at depth ,the largest 80gms at a measured 20inches.
I was using a GPX 4000 with a 16" NF round mono coil, it has been suggested that I go back over the patch
with a 25" NF round mono[ which I will have to buy]. Would the 25" be much of an advantage over the 16" ?
Hopefully some of you that chase deep gold can give your opinions.
Cheers Greg.

Hi Greg, sounds like a nice patch..well done.

Yeah if you have dragged out an 80 grammer and its a patch its definitely worth it. A 25 inch should get you a few more inches especially if there are big nuggets down there,(unless the ground noise is bad and maybe a 20 inch would give the best depth?). Maybe also worth a go with a 11 inch mono as well if you got a fair few smaller nuggets off the spot.

The coil will cost a bit. i would try to borrow one if possible. But i may be handy to have a big coil for the deeper big gold areas you may come across in your travels.

Depending where you are, a shop may hire you out one for a day or 2 . There are a few bigger coils (30 inch and +) floating around some of the main gold areas that you could ask around about also.

If you can drive close to the spot you may also want to throw a crowbar in the vehicle if you use a big coil. they can save you heaps of energy.

Hope there are a few potatos down there waiting for you.
Tributer

Gday Greg


I have always believed that there is such a thing as an optimum sized coil, what I mean by that is the coil that best suits the output capacity of the detectors electronics, has anybody else wondered why Minelab only produces coils up to the 18" size?? ( I dont recall seeing anything bigger than that )

From what I a can gather it appears that the 18" coil seems to be the optimum sized coil for these detectors, especially on mineralised ground, the way I see it is the only advantage that you would have using a 25" coil over an 18" coil is the ground coverage and not a depth advantage as most would think, the disadvantages of the operating conditions would remove any advantage, for a start a bigger coil atrracts more emi, the detectors electronics have to work harder to compensate for this added noise and also the added feedback from the greater ground coverage.

The output from the detectors electronics to the coil remains constant regardless of the size of the coil as far as I know, so having this in mind then I would tend to believe that the pulse that emits from the coil into the ground would have to vary from coil to coil, previously I told of how when using the 4500 I detected a specimen nugget with approx 16 grams of gold in it with minelab 8" mono that was at about 18" down, at the time I was surprised by this but now have new faith in the capability of that combination.

I think that if we were able to see a visual representation of the signals that were emitted from each type and size of coil we would be surprised and have to re consider what we believe that some of these coils are capable of.

The 16' mono that you are using is a capable coil as well, and experimenting with the detectors settings would I believe give you a better advantage than shelling out for bigger coils, one other thing is that you have to forget about is hearing "definate signals" and start concentrating on "murmurs" and anything resembling unusual ground noises.

Deep gold very rarely gives a good signal but is more likely to be no more than a "waver" in the threshold, learning to recognise this is more important than bigger and bigger coils.


cheers

stayyerAU

Hi, Thanks for your replies, the area where we found the gold is mostley gravel type ground about15" deep sitting on a layer of
laterite[I think that"s what it is].My wife found the first bit a 5gm sunbaker with a GPX Extreme with a 8'' mono coil,and yes the
deep pieces were really more of a break in the threshold than a rise in noise which made me think that the machine was near it's
maximum depth.I have just bought a B & Z speaker /booster combo and as soon as the weather cools down over here I will give it
another going over,I think I'l stay with the 16'' coil and see what happens. A mate of mine has got a 24x12 mono ,perhaps I can
borrow it for a comparison.It all gives me some thing to think about until the weather is cool enouth for me to head off again.
Cheers Greg.

Hi Greg
Jack Lange told me that the 24 x12" coil has approx the same depth capability as the 16" round coil, obviously the sensitivity at the toe & heel are an advantage as is ground coverage but for outright depth the round coils are best.
cheers
Lee