Covering Ground Vs Going For Depth

[fredmason]

Jonathan;

For deep targets are you saying, in part, that a short swing over the target is not optimal?  If I understand correctly, the coil swing must begin before the target and continue beyond the target...then swing at right angles. While doing this the coil must be kept in the same plane- or level?

Merry Christmas to you and the family

fred

[Jonathan Porter]

1 minute ago, fredmason said:

Jonathan;

For deep targets are you saying, in part, that a short swing over the target is not optimal?  If I understand correctly, the coil swing must begin before the target and continue beyond the target...then swing at right angles. While doing this the coil must be kept in the same plane- or level?

Merry Christmas to you and the family

fred

Hi Fred, the coil swing must pass through the center of the plume of the target to clear the two Rx windings so the signal is manifest properly, otherwise only a partial groan like response will occur. Quite often a deep target is only recognizable as being a target because the zone associated with the response is different to the ground signal response in the immediate area. There is a center to the response as Steve has quite rightly said, but the actual response is so much than that and I feel a lot of this information is lost through poor coil control and too high sensitivity and Volume settings. The volume difference on targets is more subtle with the GPZ due to the coil design, so it is best to be conservative.

JP

[jasong]

I'm making a vid right now breaking down the actual field of a mono coil in a finite element analysis program (I'm not to trying to spam I promise, it just happens this discussion coincides with what I'm working on). I can't model anything without axial symmetry since I'm just using a free FEA program so DD and Super D is out of my ability. Anyways, even with a mono coil, i suspect, the "cone" effect isn't as small as some rules of thumb present. it's more like a "U" depending on a number of factors.

[Jonathan Porter]

1 minute ago, jasong said:

I'm making a vid right now breaking down the actual field of a mono coil in a finite element analysis program (I'm not to trying to spam I promise, it just happens this discussion coincides with what I'm working on). I can't model anything without axial symmetry since I'm just using a free FEA program so DD and Super D is out of my ability. Anyways, even with a mono coil, i suspect, the "cone" effect isn't as small as some rules of thumb present. it's more like a "U" depending on a number of factors.

I think we need to think of the coils physical receive shape as being the governing factor about target signal effects. A round mono is what dictates the uniformity of the response, hence appearing like a cone, in actual fact it is more to centering of the coil as a whole that dictates the response once the sweet spot is found.

The actual field of the target is very large when it is at depth, the receive part of the coil needs to be optimised positionally by the operator to get signal uniformity.

JP

[Flyrock]

Hi all

Fantastic information here. Re: Covering Ground Vs Going For Depth

My wife and I are semi-pro prospectors and I exclusively use the covering ground method (patch hunting), while my wife does a bit of both.

I have put in 1150 hours coil-time in this last season with my 4500 and the new elite 18" coil, only dropping down to the 14" for chaining a new patch. My wife swings a 5000 with a 14" elite coil, dropping down to a 11" elite when we are chaining. (she has put in approx. 900 hrs this year).

We will be buying an SDC 2300 for next season.

We spent 7 months in the West Australian bush, 5 of those months alongside our friends/partners who swing (he) 7000 and she 5000 with 11" minelab.

My wife has found 3 times the amount of pieces than I, although I have just over double the weight.

Many, many comparisons of undug targets have been done between the 4500/18" elite and the 7000/14".

Some targets can be heard by one machine and not the other. Its an approx. 60%/40% split in favour of the 7000/14".

Our friends do more cleaning up/going for depth than patch hunting.

We ended up with 63 Oz, they 32 Oz.

Hope this helps with the discussion.

Cheers

Phil

[Steve Herschbach]

Welcome to the forum Phil. Those are impressive sums and your relaying of your experiences is quite appreciated! I have often seen similar results where going for larger gold results in half the finds but twice the weight of another person cleaning up patches.

[Steve Herschbach]

2 hours ago, Jonathan Porter said:

Steve I have to disagree in some part with these comments. In my opinion the deeper larger gold with the GPZ is a broader response with an epicenter that requires accurate coil sweep centering to manifest properly. The centering is not down to the targets field only being pinpoint small but more the requirement of the swing position of the two Rx's of the coil needing to be equalized over the plume of the faint field thrown out by the target. The two Rx's of the DOD coil need to be dead center to manifest a deep target response fully and equally, but the coil needs to pass though the complete broad plume of the target to fully manifest a response.

The target basically becomes a Tx, so logic would say the further the coil is from the target the more spread out the targets Tx field will be, just like the Tx of the coil plumes outwards from its transmission point. The Twin Rx windings of the SuperD coil need to pass through the Tx field of the target to generate a response, if the target is deep then both Rx's of the coil need to be even relative to the target to manifest a clear signal hence requiring accurate coil sweep speed and control. The ability to tap into the full noise floor information of the GPZ is very beneficial in zoning in on deep nugget responses, I'm constantly amazed how far a target can be pulled away from the coil and still generate a recognizable response over ground noise response with the GPZ, which is why I always advocate using conservative settings when chasing deep gold.

I don't mean to be controversial just my 2 cents.

JP

Absolutely JP, your advice and opinions are not only respected but highly sought after. I was talking about metal detectors in general and not the GPZ specifically, and should have said so. Anything you have to say about the GPZ I am all ears!

I suspect also you are talking much larger deep nuggets than I would be thinking about - mine measured in multiple grams and yours in multiple ounces.

[mn90403]

My recent discussions and readings with some of you here on the forum and some not here has been a focus on 'hot settings' vs 'conservative' settings of the GPZ 14".  As a user I have to satisfy myself with a 'discussion' of taking a conservative setting(sensitivity 6,7,8) and increasing the volume of the deep, weak signal vs finding with a hot setting(sensitivity 15+) trying to hear the deep signal among the chatter.  One school of thought is that the conservative settings will sense deeper because you are not 'exciting' the first 10" of ground as much as you do with the hot settings.  The hot settings are said to find more shallow, small gold but miss deeper targets depending on the ground.  (It always depends on something, doesn't it?  haha)

Now JP comes along and tells us with the GPZ we are swinging 'double cones' that should be controlled correctly with the swing in order to get the deep targets we have been missing.  This seems to require a bit slower speed because the brains of the GPZ can't keep up with the ground if you go too fast.  I'll have to remember this for the 19" when it comes.

Jason reminds me of beach detecting and my early days of hunting in the desert.  Go fast and find the good stuff!  You can find more good stuff if you don't spend time digging everything and you let your machine discriminate.  In the desert you can discriminate with speed because the small stuff will be ignored.  You can also discriminate with depth. (Give a surface scrape and if it is still there dig!)  Another beach analogy works here when you find a couple of good rings in an area you need to slow down because you might be in a 'pocket' which would be similar to a patch.  Pockets are produced by water, waves, tide and wind.  Patches are produced by geologies outside of this discussion.

My experiences of large and deep objects so far with the GPZ suggests that it 'sees' well beyond its coil size.  When I bring the coil near a can it senses it many inches (if not feet) before I get there.  When I swing my pick over or near it as in an air test I know the direction of the target. (I haven't experimented with pinpointing and sensitivity yet.)  Large targets (not gold yet) that I have dug are not only heard under the coil but off to the side.  I think this has helped me to find gold under bushes I did not find with the GPX.

I'm enjoying this thread and thought I would include some non-professional user observations.

Mitchel

[Norvic]

MN, You will not have to concern yourself to much with swinging the 19 slowly, I doubt it could be swung any other way. Be a wee hard and tiring to stop the momentum of a fast swing. My time with the 19, firstly in my hot 14 settings for ziltch then switching to JPs conservative settings over the same ground was a eye opener for me. So much so that once (if) I get back to using the 14 I`ll be back to conservative settings for a bit for sure. So many different factors influence our chances of success, even when we are swinging over gold. Which we are every time we swing...........

[jasong]

58 minutes ago, Steve Herschbach said:

I suspect also you are talking much larger deep nuggets than I would be thinking about - mine measured in multiple grams and yours in multiple ounces.

This here is a good point, semantically speaking since we have both US and AUS prospectors here. I see some really astounding stuff coming from Australia that may be average finds for some over there but would be bigger than anything I could ever reasonably expect to find here in the US.

I guess to me anything under 1 gram is "small", 1-10 grams is medium, and 10+ grams are big nuggets...I've dug somewhere around 2500 nuggets since I started detecting and the biggest I've ever found is 1.17 ounces, which incidentally didn't happen until last year.

1 hour ago, Flyrock said:

We ended up with 63 Oz, they 32 Oz.

For a second point of reference from over here in the US, I spent 9 months living full time in the field in 2015. My total take with a detector was a little over 17 ounces, plus some high quartz specis, that was my 5th (and final) year doing it more or less full time. In Australia I think that'd be kinda average (or even subpar?) results - but over here it's hard to even convince people it's real without being a big name in prospecting.  Still, it's not enough to support me, but that's why I am so rigorous about efficiency and maximizing production with my technique.