GP 3000 settings?


Recommended Posts

I had something odd happen this last weekend. Maybe someone out there can enlighten me as to what caused this.

While testing a new machine in the field, we buried a large nugget (about 1/4 oz.) about 8 inches deep. Normally this is a no brainer as far as the signal strength from my 3000. But this time when I went over it, there was virtually no signal. Going slower and scrubbing the ground produced a weak low signal like deep iron. I usually hunt in Deep and Sensitive to pick up the small ones. I now started fooling with the controls to try to figure out what was wrong. As soon as I switched to Normal from sensitive, the signal boomed through, even several inches above the ground. The same thing happened in salt mode.

So, my question is what does that say about the ground? Highly mineralised or low. Why such a pronounced difference on a relatively shallow target? The ground was damp mud and the nugget setting on hard pan bedrock, bluish-grey in color. Up on the bank where we usually hunt, it's red and fairly hot ground. I was using the stock 11" DD loop and all the usual settings that have produced many deep nuggets over the years. It's shaken my confidence a bit and may have to go back over some ground I thought was cleaned out.

Digger Bob

Link to comment
Share on other sites

Hi Bob,

Regarding the situation in Deep and Sens. I regret to report that the same thing happened to me. Did this happen to you on Saturday? I was at the Placerites, I got a good weak signal which turned out to be tin foil about 6 inches down. After retrieving the target and found out what it was, I burried it and tried different settings as I knew it should have sounded louder than it originally did. I switched from Deep, Sens to Deep, Normal and there was a world of difference. I thought It might have been atmospheric conditions interfering with the machine. After switching to Deep Normal I found a .6 dwt. shortly after that. Onion Gold

Link to comment
Share on other sites

Hi Bob,

What you experienced doesn't surprise me. I haven't used the 3000 but I suspect the sensitive mode is simply one channel of the two channel system, much like switching to channel 2 on the SD's. (I think channel 2 is the channel more sensitive to smaller gold. It has been a long time since I used the SD, so I might have it backwards.)

Anyway, when using the one channel sensitive to small gold, it is very possible that nuggets in the 1/4 oz range appear to sort of disappear. I had one particular nugget that was only detectable down a couple of inches when using one channel only.

The reason has to do with the ground balance circuitry and how ground balance is obtained. At least, that is my best guess.

Here is the kicker, change the GB just a little, and the same nugget might sound much louder, but one about the same size, might generate a weaker signal. At least, that is what I found to be true.

My best guess is what you experienced is related to what I found to be true on the SD. Fortunately, what happens appears to be limited to a small range of nuggets around a certain size and that size just happens to be about 1/4 oz.

So, it does pay to search an area using different techniques, settings and possibly different types of coils. All can have an influence and alter things a little.

Reg

Link to comment
Share on other sites

  • Admin

Hello Bob,

This is an interesting subject since there are so many variables present. Personally I have found my best gold at depth with the Sensitive/Deep settings on the GP Extreme, GP3000 and GP3500. However, I didn't check to see how the other settings would have responded. The deepest nugget was approx. 28-inch deep, while others have been in the 20-24 inch range.

I know I have found 1/4 ouncers at 18-inch deep with the GP3000 and GP3500, but they were just faint whispers and could easily be missed if I wasn't paying close attention. The coils used were the Coiltek 14-inch round mono and Coiltek 17-inch elliptical Wallaby mono.

I believe the shape, density and overall matrix of the nugget/specimen plays an important role in detection. The Minelab PI's don't detect very porous gold well, but love the solid slug type gold.

I also like the Sensitive setting since I know it can find smaller gold and smaller gold at depth over the "Normal" mode. However, running is "Sensitive/Deep" is more erratical then "Normal/Normal" or "Normal/Deep."

Hope to hear more feedback from others on this subject.

Rob Allison

Link to comment
Share on other sites

First of all, thanks to all who responded. I've gotten a wide range of opinions on the various forums from many respected sources. Let me see if I can summerize and expand on what happened.

The area has two distinct gold bearing "fields". The first is brick hard clay ranging up to 12 inches deep with decomposing granite bedrock under it. "Large" nuggets up to 6 dwt have been found on the bedrock with nothing but trash in the overburden. The over burden is fairly warm and the bedrock mild. This is where I hunted first and got no good signals deep. And it is here where I suspect I may be missing something using these settings. I'll now have to go back after some rain softens things up and try some different settings to test these theorys. I find it hard to believe that I just happened to hit on the right size, shape, and depth of nugget to be undetectable at the usual settings. I'm hoping that is the case, since I know there are more there. But that brings up even more questions.

The second area is the same bedrock covered by only an inch of dirt. Nothing large has ever been found there, but there are lots of .1 and .2 dwt pieces imbedded in it. Working in Sensitive makes these little ones pop even with a 11" loop. I've had these little ones "disapear" when hunting in Normal.

I've found large and small, shallow and deep, using the Sensitive and Deep and the ground usually doesn't cause an instability problem. That's why I was so mystified with the response this time.

I ground balanced each time after changing settings. I even changed to fixed before going over it.

One of the problems of course, is that in a new area you don't know what size gold is there or how deep until you start finding something (if there even is anything) So, hunting the same ground twice or even three times with different settings becomes time consuming when there is more ground to check out.

My favorite loop is the DD Wallaby but was using the stock loop this trip. I'll now have to play with other loops and nuggets and see if I can duplicate this with monos and well as the pro coils. The nugget was solid, not porous nor quartzy. A 3 ozer buried 12 inches boomed as did a 1 ozer in the same ground with the same settings.

Strange... well, back to the drawing board

Digger Bob

Link to comment
Share on other sites

I had something odd happen this last weekend. Maybe someone out there can enlighten me as to what caused this.

While testing a new machine in the field, we buried a large nugget (about 1/4 oz.) about 8 inches deep. Normally this is a no brainer as far as the signal strength from my 3000. But this time when I went over it, there was virtually no signal. Going slower and scrubbing the ground produced a weak low signal like deep iron. I usually hunt in Deep and Sensitive to pick up the small ones. I now started fooling with the controls to try to figure out what was wrong. As soon as I switched to Normal from sensitive, the signal boomed through, even several inches above the ground. The same thing happened in salt mode.

So, my question is what does that say about the ground? Highly mineralised or low. Why such a pronounced difference on a relatively shallow target? The ground was damp mud and the nugget setting on hard pan bedrock, bluish-grey in color. Up on the bank where we usually hunt, it's red and fairly hot ground. I was using the stock 11" DD loop and all the usual settings that have produced many deep nuggets over the years. It's shaken my confidence a bit and may have to go back over some ground I thought was cleaned out.

Digger Bob

Hi Bob,

As I understand it, sensitive mode on your GP is a timing change that switches the "Receive" circuit on a bit faster than normal to allow the eddy currents generated in smaller targets to be more easily heard. Salt mode switches later to allow eddy currents from the ground/salts, time to dissapate. Deep mode is an audio boost and not a timing change at all, so when you run in sensitive and deep you effectively turn the receive circuit on faster and boost the response. You will let more ground noise in especially with a mono coil.

Because of the way the 2 detectors channels are set up in normal mode, the null position shifts when sensitive mode is selected (and I presume salt mode as well) and that allows some targets about the size of the one you tested to slip through the net, so to speak, and avoid detection.

Also, some coils do not perform as well in sensitive mode as well as they do in normal. This is found out by testing each particular coil which is time consuming to say the least. Sensitive and deep combined should be used when the chances of the nuggets being smaller and shallower, outweigh the chances that bigger deeper ones are about. I generally prefer to use sensitive mode when I am after the smaller bits in shallow ground and deep mode when the depth of ground to the rubble layer is over 12" deep, but hardly ever combine the two. Sensitive mode also gives a DD coil a real boost as they tend to be on the quiet side in comparison to my favourite, the mono.

I reckon that you have a bit of work ahead of you to recover your ground and see what may turn up. Best of luck with it. As a final thought, when we cover the ground from 3 different direction as recommended, and combine the multiple coil/settings configurations as well, and then throw in the variety of different detectors available, then we have Centuries of detecting ahead of us. Regards to all from Qld Sandy in Oz.

Link to comment
Share on other sites

  • Admin

Hello All,

Digger Bob - Makes you wonder if you have missed faint targets in the past with the settings you run. I know for the most part I use "Sensitive" mode to find the dinks in shallow ground conditions or on exposed bedrock. The "Sensitive" mode really makes a difference on small gold.

I have ran "Sensitive/Deep" and "Normal/Deep" over some of the same ground and really haven't found anything different in several patches that have good depth. However, now the questions is, "Are there more nuggets at depth even in the patch?"

For the most part, I think you will have better results and wouldn't have to second guess yourself if you run "Normal/Deep" over the deep zones. Although, then you might miss some of the small nuggets at depth .... :mellow:

I've personally found some very sizeable nuggets at depth in the "Sensitive/Deep" mode, so I know it can punch down there.

Qld Sandy - Thanks for joining the forums. Read your posts over on the Aussie forums all the time. Hope to see you posting here more in the future.

Take care,

Rob Allison

Link to comment
Share on other sites

Hello All,

Digger Bob - Makes you wonder if you have missed faint targets in the past with the settings you run. I know for the most part I use "Sensitive" mode to find the dinks in shallow ground conditions or on exposed bedrock. The "Sensitive" mode really makes a difference on small gold.

I have ran "Sensitive/Deep" and "Normal/Deep" over some of the same ground and really haven't found anything different in several patches that have good depth. However, now the questions is, "Are there more nuggets at depth even in the patch?"

For the most part, I think you will have better results and wouldn't have to second guess yourself if you run "Normal/Deep" over the deep zones. Although, then you might miss some of the small nuggets at depth .... :mellow:

I've personally found some very sizeable nuggets at depth in the "Sensitive/Deep" mode, so I know it can punch down there.

Qld Sandy - Thanks for joining the forums. Read your posts over on the Aussie forums all the time. Hope to see you posting here more in the future.

Take care,

Rob Allison

Ok, then, one last question. I think I know the answer already but let's if you agree with me.

I'm heading out to Nevada next weekend. I'm going to an area where a couple of 2 and 3 ozers have been found lately. I'm only interested in locating those deep types of signals, even though there may be smaller ones nearer the surface. I plan on using the big 24" UFO loop, as that's the biggest mono I have.

Given this, I would want to hunt in Deep/Normal mode and fixed GB, right? As I said before, I'm no rookie at this but my confidence is a bit shaken by this latest experience.

Digger

Link to comment
Share on other sites

It's sure got me wondering! I've done pretty well keeping the skunk at bay, but usually with little bitty dinks; in sensitive and deep. I've found larger pieces in this mode at some depth, but it's got me curious. I'm going to retrace my steps (and crawls)of last week, in normal/deep and normal/normal. If a biguns found, then I'm gonna have to drive all the way back up to Rye Patch and Sawtooth, before the snows ;)

Link to comment
Share on other sites

Shep, If they're real big you will most likely here them in sensitive or any setting for that matter. In my limited detecting, I'v found some 2gr to 1/4oz ers that didn't sound off, at depth, when in sensitive, but in normal were a nice sweet sound. I started to play with the settings a little, this summer, when there was a good target underfoot, and was pretty surprised that a few nuggets dissapeared when switched over to sensitive.

Oh well I dont mind going over a patch a few times.

Link to comment
Share on other sites

That's exactly what I'm going to do this Saturday! I know the area I've been and have have been over it before and still can edge out a bit; if a huge one (and I mean, huge one) shows up, I'll be sold. Well can't be sold, I'm old and dig holes; like an old hound that likes chickens, only one way to get rid of them ;)

Link to comment
Share on other sites

Hi Guys,

My prospecting buddy and I generally run larger mono elliptical coils over the 17" x 11" size on the 3500's in our areas and find deep mode to be a tad annoying on ground that is less than 12"deep because of the feedback generated. DD coils may be better in this department but we rarely use them. We will run deep on the deeper ground of course until the above happens. Generally we find normal/normal/tracking medium mode to be our patch finding settings, and sensitive mode saved for the smaller coils and smaller gold around the 1/2 dwt or less. Fixed is the preferred mode for chaining or carefully doing a patch obviously.

There are times that sensitive can highlight a signal as shown when RD got a very confused signal over a target in normal/normal. The detectors 2 channels were trying to respond equally in this case but a shift to sensitive/normal gave a nice clear signal, I presume because the timing change made the channel for smaller gold respond better on the eddy currents that were greater with the faster receive sampling. It ended up a 1 ouncer sitting on its edge, presenting a smaller surface area to the detector, from around the 14"mark. It never hurts to check different settings when a target is presented as it gives you a better idea of what your machine/coil choice is capable of in the conditions you are detecting in. I find salt mode will lose most of the smaller signals with the later receive sampling and as a rule do not use it, preferring to go to a DD coil instead if the conditions call for it. RD and I constantly check signals between us that we suspect are gold, as we generally run different coils.

Interestingly in our area we get a lot of chattery interference with some loud pips, and as our Summer is warming up, so is the noise (solar flares?). When it gets annoying I find that detecting in fixed mode stops the auto ground balance from drifting as it tries to tune the interference out, thinking it is ground balance out of whack. The bigger the coil the worse it is and as we prefer the bigger coils, we suffer the consequences.

Regards from Qld Sandy.

Link to comment
Share on other sites

Bob and all,

Ran the GP3K yesterday, retracing where I have gone before, only this time switching between normal/normal and normal deep. Got one little 1dwt'r with the wallaby till noon, then went back to the Platypus in the same settings. Both were a little quieter in the above settings, but don't believe I was missing any thing.

Heres a question to put out,when running discrimination and level at 12 o'clock, is there any loss of depth or sensitivity or just the null? I dig all ,most the time anyway. We have one area where we're hunting that is loaded with nails, wire and rusty cans. At the end of the day or walking back to the quad, I get a little lazy. Anyone run in discrimination and get a null and find a nugget? I would assume if it did, it could be a larger nugget.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share