Minelab Gpx17 (17x13) Mono Coil Now Or Wait For Nf 16x10 Mono

[Dutchman4]

On 1/9/2024 at 12:22 PM, Jonathan Porter said:

Not so sure about my ability to be too technical 😊 but in essence conductive signals are salt signals created by moisture in the ground. Even in the desert there is sub soil moisture and particularly in goldfields because gold weathering from host rock involves a lot of clays being formed. The rocks on the land contain minerals, those minerals get absorbed by water after rain, the water then flows to the sea and evaporates leaving the minerals behind, that is why the earths oceans are salty. 

During rain events in the goldfields the weathered country also has concentrations of minerals on the surface of the ground this is due to oxidation just like rust on your car, when those concentrated minerals get damp the conductive signal increases dramatically and in some instances to the point that a metal detector is unusable or a coil that can handle conductive signals has to be used (like the DD coil supplied with the GPX6000).

When conductive signals are present the response they create masks or hides edge of detection deep signals, the detector also becomes very swing speed dependant so a slow Motion filter becomes problematic (called recovery on a lot of coin machines), the GPZ 7000 has a Motion filter called Ground Smoothing when applied you can hear the threshold becoming more erratic and unstable but depth is lost so I never use it and instead focus on my coil control.

Conductive signals are made worse by larger coils, this is because the conductive signal is seen from a very long way away from the coil. In wet conditions you can see this for yourself by lifting/raising the coil from ground height to above your waist, you will hear a loud long drawn out moaning sound as the coil is moved through an arc. So a smaller coil is recommended when the ground is damp which does not help ground coverage when patch hunting in wide open spaces.

The other issue is damp mineralised clays, those can have a complicated effect on a metal detector, especially a highly sensitive machine like the GPX 6000, or GPZ 7000. They produce a combination of conductive signals and another effect on micro magnetic particles in the soils which are impossible to ground balance out, these signals can sound very target like both sharp and shallow sounding and also broad and edge of detection deep sounding. The wetter the ground the worse they are.

A key to identifying these is coil control and sweep speed. There are a few immutable things about a motion detector, if using a consistent range of motion relative to the depth of a target (that’s the amount of distance the coil needs to be swept relative to the ‘lead in’ and ‘tail out’ positions of a target, basically from the point the threshold starts to change from the left to right and the other point going back the other way from right to left), then two factors have a bearing on a “real” target over a ground generated one.

One is the height of the coil relative to target, in other words the closer you get to a target the louder it should get (very dependant on ground effect (for another discussion another day)) and the speed of the sweep. If the range of motion is maintained but the sweep speed is halved then theoretically the target response should effectively double. A conductive target like response will not do this and will get quieter not louder. In other words, in damp conditions slow down.

The reason we move the coil is because the detectors are motion detectors (coil needs to move relative to the target to generate a response), the coil movement is all about the receive aspect not the transmit, moving the coil allows you to investigate any weak fields created by a target, the receive coil of the detector needs to move through the field created by the target, these fields will be thousands of times weaker than the transmit so require careful coil control to manifest properly. Hence why it’s so important to have good coil control, being prepared to vary and control the sweep speed and maintain a good range of motion when investigating edge of detection targets.

Accurate ground balance, consistent coil height, good range of Motion and constantly tweaking the swing speed are all vital skills for working successfully with a metal detector, especially in conductive areas. You get all these things into alignment and deep targets jump out at you.

Hope this helps
JP

So based on this information, am I correct to think that using the 6000 (with a mono coil) in wet or damp soil, from lets say a recent rain event in the deserts of the western US, would hinder the performance of the detector and it would be best to wait some days for the soil to dry out again?

[RONS DETECTORS MINELAB]

All soils can react differently, I would say try lowering the gain and see if you can get a smooth threshold, if no success then try the DD coil.

A large signal should stand out from ground noise in most cases, but not all.

[Dutchman4]

1 hour ago, RONS DETECTORS MINELAB said:

All soils can react differently, I would say try lowering the gain and see if you can get a smooth threshold, if no success then try the DD coil.

A large signal should stand out from ground noise in most cases, but not all.

Thanks Ron,

My real question is this:

I don't like to metal detect for gold during or after it rains in the desert for a number of reasons but mainly I don't like to dig and recover targets in wet or damp soil and I don't like to walk around with muck on my boots.  I am retired so I can choose when to go prospecting based on if I like the weather or not.

So I just want confirmation that some wet or damp soils can increase ground noise, requires lowering of the gain and results in reduced depth and performance.  From your response it appears that you confirm this to be the case and this will be yet another reason for me to plan my prospecting trips so as to avoid wet or damp soil when I can.

[RONS DETECTORS MINELAB]

34 minutes ago, Dutchman4 said:

So I just want confirmation that some wet or damp soils can increase ground noise, requires lowering of the gain and results in reduced depth and performance.  From your response it appears that you confirm this to be the case and this will be yet another reason for me to plan my prospecting trips so as to avoid wet or damp soil when I can.

yes, some saturated ground conditions do adversely affect the overall performance, sometimes moderately.

[phrunt]

or in mild ground they enhance performance.  Nothing is more exciting here than hitting a gold area after fresh rain, rains pretty infrequent in my gold areas however once a good dumping has taken place the ground lights up.

[Dutchman4]

17 minutes ago, phrunt said:

or in mild ground they enhance performance.  Nothing is more exciting here than hitting a gold area after fresh rain, rains pretty infrequent in my gold areas however once a good dumping has taken place the ground lights up.

Is this because of the mechanics of water erosion removing overburden or is there a technical explanation?

[snakejim]

1 hour ago, Dutchman4 said:

Thanks Ron,

My real question is this:

I don't like to metal detect for gold during or after it rains in the desert for a number of reasons but mainly I don't like to dig and recover targets in wet or damp soil and I don't like to walk around with muck on my boots.  I am retired so I can choose when to go prospecting based on if I like the weather or not.

So I just want confirmation that some wet or damp soils can increase ground noise, requires lowering of the gain and results in reduced depth and performance.  From your response it appears that you confirm this to be the case and this will be yet another reason for me to plan my prospecting trips so as to avoid wet or damp soil when I can.

My experience in highly mineralized ground is that it becomes very conductive when wet or damp and especially affects the VLFs performance. The ground not only becomes noisy, but a great deal of depth is lost due to the signal being reflected or suppressed. I have proven this time and time again. The drier the ground, the greater the depth is attained with the VLF detector.

However, with the pulse detectors the effects are not that noticeable except maybe more ground noise. Depth is not affected as much as with a VLF detector. snakejim

[phrunt]

29 minutes ago, Dutchman4 said:

Is this because of the mechanics of water erosion removing overburden or is there a technical explanation?

No, nothing to do with erosion, just something to do with the milder ground I think, I'm not the only one here to notice it either.  Targets just light up more in damp ground here.

[mn90403]

Given a choice in most of my areas (Rye Patch excluded) if the ground is damp and it was not previously a dry lakebed with many salts, I would prefer damp ground over dry ground.

Why?  As Simon said you hear things you don't when the ground is dry.

An explanation might be as simple as conductivity.  The damp ground seems to carry the pulses better and if I can't cite an increase in depth, I attest to an increase in clarity of the nuggets in wet/damp vs dry.

[geof_junk]

1 hour ago, phrunt said:

or in mild ground they enhance performance.  Nothing is more exciting here than hitting a gold area after fresh rain, rains pretty infrequent in my gold areas however once a good dumping has taken place the ground lights up.

Simon I found that the moist ground because of salt signal tended to partly neutralize the negative ground that was very hot when the ground was extremely dry in Victoria.  Anyway whether I a'm right or wrong I still did better in moist ground than in bone dry ground.