Axiom Tests On Extreme Black Sand

[Knomad]

 

 This test was on the worst Black Sand Ground I have seen, although it is not as bad as it was a few years ago, I suspect the Black Sand has sunk deeper. Years ago NO detector could even see a Brass Shotgun Shell deeper than even with ground level.!

 

I tested 3 detectors, My Equinox 800, My Whites Goldmaster GMT, and the new Garrett Axiom.  The first two are very good VLF detectors, the Axiom is the latest technology Pulse Detector.  Pulse Detectors are almost always better in really bad ground conditions.

  ALL 3 detectors would not ground balance fully on this ground, at least at anywhere near normal sensitivity, the GMT did at reduced sensitivity.

 

Interesting Axiom testing --

  I tested with 3 coils, The 11 x 13 DD, The 7 x 11 DD and The 7 x 11 Mono.

NONE of the coils would fully ground balance at even a sensitivity setting of 3, and was noisy at 2.  The exception was in Salt Mode, it at least came close to balancing, so was the quietest with a low threshold setting.

  Fine Mode, was basically non usable with ALL coils and a sensitivity above 2.

  Normal was usable but noisy at 3, But really hard on the ears.

  Large, about the same as Normal, just not as clear on the target.

  Salt, was by far the quietest but with depth loss of 1 to 2 inches.

  Target - a piece of lead, likely a banged up 22 bullet, just 6 inches deep, NO coil would detect this target in this ground at less than a sensitivity setting of 3, and was Very Noisy at 3.

 

INTERESTINGLY -- ALL modes, except Fine, could be run at FULL Sensitivity, but with the Threshold OFF at -9..!

  AND detect the target.!

The ONLY other way to run it was with sensitivity below 3 (and miss the target) or go insane from ground noise.

( NOTE - I usually run my detectors slightly hot, with minimal threshold, so am used to background noise, But that is NOT possible here.)

 

The 11 x 13 DD had the clearest and strongest target response.

  The 7 x 11 DD was OK, But Surprisingly More Noisy. I had expected it to be less noisy looking at less ground, but maybe it is more sensitive, so reacts more to the ground that is not fully balanced out.

  The 7 x 11 Mono was as expected, slightly more sensitive than the same size DD, But substantially noisier.

 

Strange, But with no threshold it has to break past a zero point to signal anything, But it will in this extreme ground.

  Normally there is a substantial sensitivity loss with no low threshold, but with ground this noisy it seems to filter the noise, with a smaller sensitivity loss.

 

Unfortunately the Dual Balance did not seem to work, even holding the button until it goes into dual balance, I suspect because it was not hot Rocks, Just Black Sands, so couldn't tell the difference, and balance numbers were inconsistent and all over the place.

 

 

BTW, neither VLF could see the target deeper than 2 inches.

[Steve Herschbach]

That’s some bad stuff. Here at Lake Tahoe I have similar material. The GPX 6000 and GPZ 7000 won’t fully ground balance on most of it, but they are useable with steady coil control. By that I mean maintain a steady height more than anything, and move at a moderately slow pace to let the autotune keep up.

The Axiom on the other hand will get a clean ground balance on most of it, though mono coils are usually out of the equation - use the DD. However, in extreme places even the DD will not balance, and if you try to the machine goes into an overload state. The solution is to just do a partial ground balance - easiest way is to do the procedure higher off the ground and do let it hit the overload point. Then simply use it like the GPX or GPZ and through good coil control it will work fine. All three in those conditions act more like a regular non-ground balancing PI as any rapid up and down coil motion will signal. Luckily PI in general was designed for this kind of stuff and so is far more forgiving than a VLF when it comes to being out of balance. In some cases NOT being ground balanced will actually give you more depth as this TDI demo shows.

A similar situation exists with the ATX and might be applicable to the Axiom….

This issue is something I’ve been working on for years. The main problem with the Axiom, GPX 6000 and GPZ 7000 are that believe it or not they are too hot on small gold, which accentuates the issues with magnetite. Same issue you saw with the Axiom small FC DD - I wish there were a regular DD for the Axiom as the FC DD are hotter but that hurts with extreme ground issues, the main reason for DD in the first place. I recently got an old Infinium with 14x10 mono coil that will cleanly ground balance in places where these other machines can’t even balance with a DD, let alone mono. This oddly enough is because it’s not as jacked up as the other units, and in the end that works in its favor. That old machine is currently putting a smile on my face as I’d forgot just how unique and fun to use that 14x10 mono is. I can read targets with it better than with almost any other PI combo I’ve used.

There are also spots I nugget hunt in the Sierras like you describe. Serpentine bedrock with magnetite soil. A VLF will call a 30-06 brass shell casing on the surface as ferrous and lose the target at two - three inches. People who have never experienced this stuff think it’s all BS but it’s real all the same.

The GPX 5000 is still the best machine made for this type of conditions as it has some special timings for handling it. They cut the machine way back in some ways but that is what you have to do in the worst ground. This chart is for the 5000 but looked at it another light it shows how less sensitive modes can work better in bad ground than hotter modes, and that applies to all detectors, not just the 5000.

Minelab Mineralization and Timing Example

The following chart illustrates the procedure for finding the correct timing for each situation. In general, always start with the Normal timing. If the detector is stable and quiet, try timings on the left - Sensitive Extra, Sharp, or in rare cases, Coin/Relic. If ground noise or hot rocks present problems in Normal, then try timings on the right - Fine Gold, Enhance, or Sensitive Smooth. Salt settings should generally only be used on alkali ground (salt flats) or salt water beaches, but may have applications in other ground. The goal is always to find the most powerful setting that allows for stable operation. Each timing can be adjusted within certain parameters, primarily through the use of the Gain and Stabilizer settings. Adjusting for a lower Gain, for example, may be preferable to going to a less powerful timing.

Minelab GPX Timing Selection Chart - Click on image for larger version

Finally, each timing may work best with a certain type of coil (DD or Mono) and the timings have varying level of resistance to Electro Magnetic Interference (EMI). The matrix below attempts to show which timings offers which benefits and strengths/weaknesses.

Minelab Timing Coil EMI Matrix - Click on image for larger version

The simple chart below can be printed out and taped or glued on your detector shaft as a reminder in the field as to which timing may be best. Click on the image to download a large version.

Minelab Timing Decal - Click on image for larger version

 

Details Here

Final note on all this is I wish I could get a standard DD epoxy filled water coil for the Axiom for wading, just like one Garrett already has the mold for!

[phrunt]

Yes, I've done beaches where a large coin on the surface is reported as junk, and bury it an inch or two and it just blends into the sand's response being iron effectively not being detected at all, with the Equinox constantly having its overload icon on the screen.

The GPX works to a degree on these beaches, better than anything else I've tried anyway but can't ground balance the ground out so I need to experiment more with settings to try get it working better, and I'm not even at the worst of the black sand beaches further up the country which are just pure black sand, mine at least around here have a mixture.  The ones on the West Coast further up the country are next to impossible to detect.  My 4500 went up there to a guy that wanted to detect them, didn't work out for him.

Tarsacci made a coil they claimed was a NZ coil for detecting these beaches, needless to say it doesn't work, the guy that tried my 4500 had no luck with the Tarsacci setup with the "NZ Coil" and declared it a waste of money.

It's good to hear the Axiom working to a certain degree in this sort of ground.  I intend to make a trip up to these beaches sometime this year as they would have to be an untapped gold mine, very popular beaches for swimming yet nobody can detect them very well at all.  I was hoping the 15" CC for the GPX by X-coils may help, sadly I can't see it resolving the problem with my attempts at the local semi black sand beaches, it appeared worse than the DD at handling the ground, perhaps being spiral didn't help with that.

The QED where you were able to dumb it down by changing the pulse delay and a DD coil worked quite well on the semi black sand beaches so as Steve was saying the weaker the detector is on small targets the better it works in the bad ground.  Maybe I should have kept it.

My question is how does the Axiom compare to the GPX 5000 in heavy concentrations of black sand? 

[Steve Herschbach]

1 hour ago, phrunt said:

My question is how does the Axiom compare to the GPX 5000 in heavy concentrations of black sand? 

My bet is in the 5000 due to the multitude of settings and coil options. Just need to dumb it down until it works. As noted an old school non-ground balancing PI with an available long pulse delay like the Garrett Sea Hunter will work better sometimes. But there is another reality also. I have some large blocks of pure magnetite ore. No detector can balance to them or see through them because you may as well try to detect through a steel plate. There is a point where magnetite black sand is thick enough it gets close to that same level of concentration, and then all bets are off. There is such a thing as undetectable soil, though it’s extremely rare.

[phrunt]

Thanks Steve, just trying to be prepared for my trip. as it seems even the guys living at these beaches have had little to no success so I want to be as prepared as possible.

Much like Knomad saying the larger 13x11 DD is better than the 11x7 DD on the Axiom I've been finding the same, larger DD's appear to work better than smaller ones on the GPX 5000, I put it down to them being less sensitive to smaller targets.  I think this was the downfall of the 15" CC spiral too, the less sensitive something is the better it seems to work.

 

[Luis]

the 18" concentric from the detech brand could be a very good option with the 5000 on that type of beach Simón

[phrunt]

16 minutes ago, Luis said:

the 18" concentric from the detech brand could be a very good option with the 5000 on that type of beach Simón

I thought similar but now I've tried a 15" Concentric I don't think this is the case, one of the positives of Concentrics is they have a smaller inner receive winding, this makes them more sensitive than a similar size coil on smaller targets, however, being more sensitive they will have trouble with the black sand, at least the 15" CC is that way.

[Steve Herschbach]

I’d be looking more at standard DD or one of the old anti-interference or salt coils as they were called. Something with a reputation for being mild and therefore probably not as popular. Commander 15x12” DD might be a good option.

We keep this up I’m going to talk myself into a 5000. 

[Knomad]

When I first went to this location a few years ago it was Virtually Undetectable, a Nox 800 in any mode with any settings, a Whites GMT, a Fisher Goldbug Pro, and a Whites TDI SL, could not even detect a Brass Shotgun Shell even level with the surface.

This time I think the Black Sand has sunk, But is near pure iron and in both concentrated areas as well as small spots everywhere, so any coil movement detects another glob it seems.

If I did not know where the test target was, it is highly unlikely I would find it with sensitivity high enough to detect it, even moving slow, the threshold was way too noisy even at minimal setting, like it was Mixing Threshold with target sound. BUT with threshold Completely OFF somehow it filtered the background noise sound but still allowed the Target Sound, in ALL except fine mode that was unusable. What was heard was an occasional clipping of target sound, but basically silent other than that. NOTE- This ONLY worked well at FULL sensitivity of 8.!   Anything below 6 and the target was lost,  So Silent Searching AT MAXIMUM sensitivity..!  When otherwise a sensitivity of 3 was REQUIRED to detect the target BUT was Unbearably Noisy.

 

[phrunt]

I have the 11" Coiltek AI coil for the GPX, I will give it a serious try on the crazy black sand when I go there, that coil is surprising in the fact it loses little sensitivity over the 11" DD coil, very similar performance there but it's absolutely awesome in high EMI, quiet as a mouse.  I also have the 15x12" DD Commander so I'll give it a shot and compare.