Gold (specie) that completely discriminates on the GMT!

[Infiniumexplorer Excalibur]

I was scanning some gold that I found with my 3000, over the GMT, and I found a specie that completely discriminates!

You can see the black ironstone on it which is why. In WA gold is very closely associated with ironstone.

To be carefuI with discrimination... know people keep saying it, but it's scarier in a way when it's a personal truth All though I've known this myself regarding other detectors, but not so much with the GMT.

The disc on the GMT so far has been very disapointing to say the least, but I thought that when it reads as 100% iron then there would be at least decent confirmation.

 

[fredm]

Back when I started with a vlf/tr the machine had a null point which would indicate metal or mineral...depending if there was more metal or more mineral...looks like your sample had enough iron to overlook the metal...never trust descrimination if you want 99% certainty...

Fred

 

[Digger Bob]

I've run into the same thing here in N. California on certain nuggets. These come from hydraulic pits and the gold has a black manganese coating. It causes the gold to chatter just like iron. Clean the black off and the signal is clean. Same thing happens with bad dirt sometimes. A small nugget in half a scoop of this Nevada dirt chatters too. As you remove more and more dirt the signal becomes clean. I have probably lost some nuggets thinking they were trash. The black gold looks just like iron unless you look close. That's why the pros are always stressing, dig everything!

Digger Bob

 

[Infiniumexplorer Excalibur]

I think mineralisation plays havoc with the iron readout. I have only used the GMT a few times and it is hardly accurate, about 4% of the time, even if the target is on top of the dirt. This was dissapointing for me, at least it is still sensitive. The disrim on the minelab pi's and the infinium is way more accurate, and they're pi's.

 

[B.T]

Sounds odd, some yeah like any disc machine can now and then get fooled especially small gold in really bad ground, but by the sounds of your experience's its nearly all the gold you check or trial on discs out! It nearly all reads 100% iron, is that right? I know of quite a few people using GMT's in WA, NT, QLD and VIC and they have never reported it being like that. All machines can disc out gold, two of my mates were out about three years ago with good SD2200's detecting near Maryborough. One gets a target and digs down about 10" in rock hard ground, the other checks with his in Disc and it discriminates out full on. He calls it for a horseshoe, 8 more inches and out comes a 14 ounce slug!
So effectively the PI at just 8 inches read 14 ounces as iron!
Before you write it off try this, just holding it in the air, naturally away from metal and interference, turn the sens up flat out, it should get a little chattery but should not overload or squeals out of control. If it does then the coil is crook and would be why its unreliable in disc. Try this several times as it can show up intermittently.
Too high a gain in bad ground can throw things as well. Yes some gold will disc on all machines but your percentages sound more like a coil problem.
I was detecting with this mate just recently using the GMT near Dunolly in noisy ground and his disc, tracking and everything worked just fine. You can see the quartz too was pretty mineralised and associated with ironstone!

 

[Infiniumexplorer Excalibur]

Hi BT, thanks for the advice. My gripe with the GMT is not that is reads 100% on gold, (only the one in the photo), but that it reads all over the place on any target, junk, gold etc, out in the field. When doing air tests in my room then the iron readout is consistent, so I figured that ground mineralisation is probably affecting the readout.

I still need to use it more and I'll try experimenting with turning the gain up or down and other settings but I don't think I used the gain too high out in the field. I have two coils, the standard and the shooter. The shooter is very hard to use, it picks up lots of signals everywhere unless I lower the gain to around 3. The standard coil is much more stable. I live in Adelaide and used the GMT in three different areas. See how I go next time out.

 

[B.T]

Just try turning the gain flat out in the air a few times to see if it overloads. On the rare occasion it has been the coil and on those occasions the iron disc was thrown out.

 

[Infiniumexplorer Excalibur]

Doesn't seem to overload. I'll try to take it out next week.

 

[David]

Did either you(Infiniumexplorer Excalibur) or B.T. ever compare head to head a (GPX machine or your GP-)3000 vs GMT on small gold nuggets and fine specimens ?? Which detector won, marginally or by a long shot ?

The 3000 using the stock 11"DD in mono mode(psuedo mono), Commander 5x10" DD, CT or NF 5x10" mono, NF Advantage 7x12" mono, or with a CT GoldStalker round 6" mono coil.

 

[Nugget Hunter Smith]

The GMT has no discrimination! It is an all metal mode detector so you must not have it ground balanced properly or maybe the SAT is set to high and it is missing the tiny pieces of gold in the iron ore. Check the batteries and the coil connection as these can also cause problems. Because of its operating frequency, it is one of the most sensitive detectors on the market.

 

[B.T]

n/t

 

[B.T]

Have tried that. Must admit that the 45 running a good mono, cranked up in sens xtra in quiet ground is a rocket. Put a little C/tek 6 on it and damn its good at specie stuff shallow.
But have had the GMT get stuff that even that combo couldn't hear. Found some nice stuff in quartz a couple of months back that when I finished cracking out the gold I could hear with the 45 i tested bits on the GMT, the left over silent to the 45 ones, and there were still some highly visible small gold veins the GMT barked on. A couple of very nice looking little species too. In those situations they sort of compliment each other. You wouldn't get all the gold with either of them alone.

 

[Infiniumexplorer Excalibur]

I know that a 4000/3000 is very sensitive. Doesn't really matter what model, except you can use the GPX's in smooth/enhance which might get rid of the jitters that you get when you use a tiny coil. So any GP model will get down to .05 grammers with a small enough coil at efficiency, maybe smaller. That's why it's not worth getting a vlf detector that's not high enough in frequency IMO! Although a vlf at 17 khz might still be better for crystaline gold, but why not get the GMT/GB2 and get gold that no other detector (theoretically) can get.

You need to get something that is excellent at what it does, getting gold at certain situations that no other detector can get. The Minelab PI's cover most bases, from the largest nuggets, all the way down to about .05 gramms efficiently, that is, at depth and quietly. I'm not sure what the smallest gold the GMT will be able to get in moderate ground, but it better be <.05 gramms!

 

[Infiniumexplorer Excalibur]

n/t

To BT, it reads 50, although I have only tried it indoors. I'll try and take it out this weekend.

 

[Neilo]

The GMT will definately find smaller gold than the GP4500 I have used both. I have used the GP4500 with the little 6 inch Coiltek coil. I t will pick up under 0.1 grm nugget but wont pick up much smaller. I have picked up pin head nuggets 10 of them did no weigh 0.1 grms in total.