Metal detector testing

[xcvator]

Another newb dumb question I've watched various "airtests" and depth tests on Y/T etc and they all say what a great M/D this is

So my question is does it matter if the soil/dirt is disturbed or not in a field depth test, do the "impulses ?" penetrate disturbed earth better than undisturbed earth ?

I probably shouldn't be thinking at this time of night, it hurts 8.(

 

[Davent]

I reckon it matters in a lot of different ways. Sometimes an air test might give you LESS depth than you would get in undisturbed ground, depends on shape of the nugget, the way its sitting,I.e. flat, on its edge etc, wether the soil is dry or damp, if the nug is in damp clay under dry top soil....lots of variables.

I tend to think air tests rip you off a little. Recently did an air test on a .2 gram nug with my 4500 and 14x9 evo v a z7000, and there wasn't much difference, yet in the field the z gets a lot more than me in the same ground. And occasionally, I pull a small nug at a stupid depth, dug one a few days ago, .8 of a gram that screamed like a shopping trolley and was 1/2 a pick handle deep. I had been over that spot at least 4 times and I know a z and an SDC had missed it too.

Why? Different conditions? Just missed it?

 

[Ramjet]

I don't put much faith in air tests. Coins can be different numbers or tones from location to location. assume it depends on the different conditions.... Different minerals n the soil, moisture etc etc.

 

[condor22]

The only thing an air test will tell you is that the detector has picked up the target (or not). I have a small test piece I use at about 0.7gr, when I get to an area I haven't detected before or if changing coils, I'll GB first, then maybe play with the settings to see what the different responses are to the test piece. Particularly when using a small coil (I have a 5000)

Sometimes the ground can be noisy and it won't respond, other times I feel like moving it aside because something bigger might be below, lol.

The bottom line is, re gold, every nugget is different and the ground can be so variable in chemistry, moisture content, density, hardness etc etc. All you can do is have the detector run as smooth as possible at the maximum power punch practicable, to give you the best chance of finding something.

 

[Heatho]

You'll get a better signal if a metal object is in situ due the "halo effect", a small target that is just on the verge of detection can give a better signal when it is in the undisturbed ground, dig it out and it may not be detectable after being disturbed as the halo effect will disappear.

I've seen this happen a few times, last time it happened to me started up my SDC to find it but the batteries were dead and it kept shutting down.....

From the GPX5000 manual.

"A halo effect, which may be built up around a buried metal
object, makes the object appear to be larger to the detector
than it actually is. This will be reduced once the target is
disturbed from its position in the ground (e.g. a small object,
detected at a substantial depth, may be more difficult to
detect once disturbed from the ground and lying in the
loose dirt. If the object is re-buried the halo effect will not
be present).

Also.
Halo Effect
After a metal object has remained undisturbed
in the soil for a considerable amount of time
a diffusion occurs around the object. This
has the effect of the object appearing to the
detector to be a larger size.

 

[Ridge Runner]

Metals like Copper, Bronze and Brass can be found at greater depths than they air test at whether it is a VLF or a PI because they leach in to the ground making a much larger target in undisturbed ground,

VLF's will go deeper in damp ground than they do in the dry ground, also add the halo effect and they will go deeper or match PI machine under those conditions if the Ground conditions are not too mineralized.

 

[as5672]

Hi all
I am not sure if it was on this site or another that I read to buy a few small nuggets off eBay to test the metal detector. I am not sure what size to get as I can't find the site. I was thinking 0.10 0.20 0.40 0.60 and 1gram.
Would like to hear from people if I should or shouldn't buy them and the size of the nuggets.
I have a minelab 705 gold.

Thanks
Anthony

 

[Pro-oz]

You could also use bits of lead cut to size

 

[as5672]

Ok nice, I have lots of lead.
I will try that.
Thanks Prooz

 

[Ridge Runner]

I agree with Prooz, And that you want to use bits half of those weights that you have listed, Because most detectors can find big'uns it's those little bugga's that are hard to track down and they are your bread and butter Gold,

Hope this helps, Good Luck.

John.

 

[as5672]

Ok John I will do that.
Thank you

 

[Magilla]

I made some test pieces from aluminium as I read somewhere that to a detector it is closer to gold. It is amazing how small you can go and still pick it up with a small coil.

 

[as5672]

Thanks all for your help.
I used lead and what I got from my 705 gold was these.

0.10g 1.5 cm
0.26g 2 inches
0.63g 3 inches
1.12g 4 inches

Is that good or bad for a 705 gold.
Not sure how I feel about the depth.

Thanks
Anthony

 

[Ridge Runner]

Thanks all for your help.
I used lead and what I got from my 705 gold was these.

0.10g 1.5 cm
0.26g 2 inches
0.63g 3 inches
1.12g 4 inches

Is that good or bad for a 705 gold.
Not sure how I feel about the depth.

Thanks
Anthony

That's fine, those depths will change depending on the soil but most of all is how much you are paying attention so you can expect those depths to go deeper and or not so deep, You have a good machine and it is Ideal, keep up the testing with targets, settings and locations and you should do well with it.

John.

 

[Davent]

not bad depths there mate.

 

[as5672]

Ok thanks guys.

 

[polky]

That's good for a 705, had one for 12 mths and deepest target was a boot tack at 4 inches. Fella that's been swinging for 30 yrs told me most gold is found in the 4 to 6 inch range. Not the biggest just the most targets.

 

[Smoky bandit]

Hi mate i just done a test with a half grm gold nugget at 4 inches ....burried in a hole with dirt from gympie gold feilds...the xterra 705 in prospecting mode...using 18.75.oliptical coil...sensitivity at 26.....threshold at 14 volume at 30...and it screemed everytime i pased the coil over it...Hope that helps :Y:

 

[retroenduro]

one advantage of buying a gold nugget of ebay to test the 705 is you can wind up your mates/family...its amazing where a gold nugget can pop up reckon my father in law will have the whole garden dug up by next week

 

[gef12]

Air tests and in ground tests...
Air tests are pretty much a bench mark as where a machine sits in comparison to others whilst in air .. nothing more.

In ground tests would be a more proven testing method if comparing apples to apples. And yes greater depths can be achieved on certain targets within ground.
This is mainly due to what is termed Halo Effect.
The Halo Effect is a kin to an increase in a targets size on the returning signal to a detector. This is achieved via the differening ground types that consist of minerals, sulfides, salts and acids that lie within the ground. So an oxidising metalic target will create a "Halo" around itself due to acids and the multitude of minerals and salts reacting to it. So you say Gold doesnt oxidise .. correct 100% per gold doesn't.. but we rarely find nuggets that are pure .. they also contain silver, copper and other alloys and also may contain iron stone.
You may find also that damp ground may increase your detection range due to an increase in the ground conductance. Also as explained previously a target in undisturbed ground will be detected deeper than if the same target were to be placed in the ground at same depth.