Are some claims (Minelab) just hype?

[Anonymous]

Just wondering 'cause I spent part of the summer up in northern Alaska prospecting. Two guys on the creek had ML SD2200d's. Now, in the Minelab literature, they claim that an SD will get 3-4 times the depth that a VLF unit will. Judging from what I saw, this seems to be a load of kife. I decided to bring up my Fisher CZ6 W. 10" coil and, in salt mode due to the mineralization, was pulling up nuggets as deep as the SD's were. The only trouble I had was with the large sheets of Galena (and the small chunks) that gave an iron signal. Would a P.I. machine be able to see through these and sound off on underlying nuggets? Has anyone performed a test wherein different machines in each category (P.I. & V.L.F.) with THE SAME SIZED COILS are are compared re. target size & depth? I'm particularly interested in how the SD's stack up. The reason I used the CZ6 was 'cause the weird mineralization made higher frequency machines (except the Gold Bug 1) go totally bonkers when trying to hunt in the water. The CZ didn't have this problem. I was pressed for time, so I had to cherry pick and therefore hunted in 3 tone disc. mode set at zero disc. This way I could just get the larger nuggets (largest at 2oz & smallest about 1dwt) but I was still picking up the small ones. Unfortunately, the small ones would read as iron, so I didn't dig 'em.

 

[Anonymous]

The Minelab SD2200D was designed for use in the Australian gold fields. The soil conditions there are without doubt the worst in the world. Most if not all VLF's are rendered useless due to the kind of mineralization one encounters there. However, a good VLF design may well equal or outperform a PI in Alaskan soil. The new higher frequency VLF's are also more sensitive to smaller nuggets than a Minelab PI. It is a safe bet that future PI designs will become available which are designed for world wide prospecting use. Life will then become a lot more exciting for the prospector.

 

[Anonymous]

So, in other words, the Minelab claims hold true for that specific soil and for any other are pure hokum? I've cruised the forums and no-one else (reputable)is making such inflated claims. Often, a few inches of added depth are claimed, not up to 4x. I've hunted side by side and also checked the depth of the SD holes and didn't notice any huge depth advantage. BTW.. there are targets all the way to bedrock where I was hunting.

 

[Anonymous]

Hi Dave and Will
The Minelabs certainly work well here in Australia where as Dave says the ground conditions are so bad. The proof of the pudding is in the eating and the SD's have unearthed tons of gold under conditions that VLF detectors can't handle at all. The ground is that bad that VLF detectors have a very limited range where as the SD's are capable of working almost to the full extent of their in air detection depth. The huge amount of gold we walked over when using the old Garretts etc is almost too much to contemplate. Had I had the new technology 20 years ago I would be a wealthy man by now.
Cheers
Steve D

 

[Anonymous]

No rat's involved. Your ground minerals are almost non existant in alaska compared to the ironstone hell hole that Steve works in Australia. No question about it, a Minelab SD or GP will not give you any depth advantage in Alaska. Go try a side by side depth test with Steve down there in Victoria!!! I assure you that you will change your mind. The place is one huge field of ironstone, hot rocks, magnetic and conductive clay. Minelab make VLF's The famous Sovereign and the new XS mult-frequency detectors are most likely the best VLF,s in the world yet Minelab do not advertise them for prospecting use in Australian soil. All the best, Dave. * * *

 

[Anonymous]

Actually, were I was hunting (in Alaska)the mineralization was severe enough to essentially shut down the higher frequency machines whenever thjey got near water.. or at least I'd think it was mineralization. My main beef with Minelab is that they say out & out that their machines go 2-3x deeper without saying that this ONLY applies to a certain type of soil matrix. I just hate less than honest advertizing.

 

[Anonymous]

OK, That's a different kind of rat. Minelab are famous for hype! Their PI detectors are also vastly overpriced. If you make a study as to why Minelab PI's have made such an impact in the Australian goldfields, you will find the following:
PI detectors in general, have great depth capabilities. PI's do not respond to certain ground minerals and some types of hot rocks which are certain to give a VLF a lot of trouble.
Minelab's chief engineer, a gentleman by the name of Bruce Candy observed that the decay time of a received PI waveform due to iron mineral signals varies with the transmitted pulse duration. A long transmit pulse provides a longer signal decay time than does a short transmit pulse.
In contrast to this, a conductive target such as a coin or a gold nugget provides the same receive decay time for both the long and the short transmit pulses.
This observation made possible a PI detector which was capable of working in the Australian goldfields. The SD series detectors transmit a long pulse followed by three shorter pulses which are a quarter as long as the long pulse. The sequence of these four pulses is repeated.
Electronic circuits compare the ratios of the signals received from both the long and the short pulses. Receive signals which have different timing for the long and the short pulses are caused by ground minerals. Circuitry causes these signals to cancel. Signals with the same timing are accepted as good targets.
The result of all this was a new gold rush in Australia. Tens of thousands of beautiful gold nuggets were harvested in areas where VLF's were completely unusable.
Today, the goldfields have been well detected. Vast quantities of nuggets are still there but many are beyond the reach of the present detectors. I can assure you though that there are people around the world who are working hard on a new prospecting PI detector. Dave. * * *

 

[Anonymous]

I'm just waiting for the new Garrett PI. At least it's supposed to be reasonably priced. Aside from that, would you know if a PI machine can see through sheets of galena to pick up a nugget?

 

[Anonymous]

Somewhere I have a fairly large specimen of galena. I know I have tried it in the past with PI's and got no response. However, present machines are more sensitive to poorer conductors, so the test wants doing again. If I can find the chunk I will test and report.
Eric.

 

[Anonymous]

Hi Dave,
I'm puzzled by the statement that for non-ferrous objects, the decay time is the same for long and short pulses. From my tests, and also PI theory, this is not the case, except in special circumstances. e.g. if the transmitter pulse width is shorter than the object time constant, then you will only excite skin effect eddy currents and see a shorter decay than if the pulse was longer than the time constant. In the latter case the pulse is there long enough to fully penetrate the object. The special circumstance is where the short pulse is long enough to give the full signal, then a longer one will give the same result.
Eric.

 

[Anonymous]

Eric,
Candy's patent does not talk about non ferrous objects. Candy talks about ferrites etc. The exact term that he has coined is "Ferrous Relaxation Delay" or "FRD" The method is not one of iron discrimination but one of ground mineral cancellation. You can read about it if you have an extra week or two to decipher it all, in US patent number 5,576,624. Dave. * * *

 

[Anonymous]

When I was up north prospecting with my CZ the big slabs of galena gave off a nice BIG solid iron signal. I didn't want to shift them unless I was pretty sure something good was underneath. The 2 other SD2200d's had gone over the same slabs in the creek. I couldn't help but wonder if, even though the SD's didn't sound off on the galena, it might have interfered with the signal from underlying gold: kinda like a faraday shield. If a PI COULD see through galena, I might just have to cart one up there next year. Maybe that new PI Garrett's coming out with.

 

[Anonymous]

Eric,
Candy's patent does not talk about non ferrous objects. Candy talks about ferrites etc. The exact term that he has coined is "Ferrous Relaxation Delay" or "FRD" The method is not one of iron discrimination but one of ground mineral cancellation. You can read about it if you have an extra week or two to decipher it all, in US patent number 5,576,624. Dave. * * *

 

[Anonymous]

Eric, The long and short pulses cause different delays from ferrites etc. I got the bit about the signals from metal targets providing identical signals from a Minelab write up about their mine detector. I too doubt if they are identical. Still, the important thing is that the long and short pulses provide a method to cancel the ground signal. Reading Candy's patents is like trying to put the Dead Sea Scrolls back together. Dave. * * *

 

[Anonymous]

Hi Will,
I found my galena specimen. It weighs 4lbs and consists of a sandwich of calcite with two 1/2in thick continuous layers of galena. It is about 2.5in thick and approximately 4in x 3in in area. I tried this on an Aquastar, which is more sensitive to lower conductivity objects than the SD detectors. Result, no signal, even when up against the coil. A 0.9gm nugget was detected, with no loss of range, through the Galena; just as though the Galena wasn