GPZ Low-high Signals And High Yield Vs General

[robby_h]

Steve,
You seem to have a very good handle on it. I used simple PI GB in my example where the late ground sample is amplified to equal the first ground sample. Minelab use a more efficient method but the high and low tones still follow normal timing convention and pivot around a point determined by the GB setting, but all bets are off with enhance/fine gold/difficult soil timings because the tones can go high for say a 4 grammer in normal and low in enhance etc and then reverse again, this is because the difficult soil algorithms combine more samples than normal timings.

Before the GPX it was rather alarming to hear about the number of large nuggets found in half dug holes abandoned by mostly novices because the tone went low. This usually occurred because most gold they normally found gave a high tone and a low tone usually meant junk. It's silly at the best of times but became ridiculous when they walked away from a low tone in ground that had never been disturbed.

Jasong mentioned the fact that the ZED has to deal with an additional ground component that the GPX does not. This is the so-called X component but it's separate to the VRM signal (magnetic decay signal) common to both technologies and cancelling VRM is responsible for the tone change. It's rather interesting to note that X discrimination can be reasonably reliable, especially when combined with time constant discrimination. The CTX 3030 uses both.

One thing that can occur if the VRM signal is very weak is the VRM GB might settle on a different setting to another detector of the same make and model in the same ground simply because there is little to cancel and this might make a selected nugget respond with a high tone on one detector and a low tone on the other detector. This can actually happen on dry clean golden beach sand where the auto GB settles anywhere and then gets way out of whack when swept over a ferrous target. In this case you would have to carry a ferrite and a VRM ground sample to obtain the same result with two ZEDs or a VRM sample for SDs/GPs and GPXs. Shows why air tests are unreliable.
 

[Steve Herschbach]

Thanks Robby, I have always enjoyed your knowledgeable posts. I wish it was just novices; I am quite sure I have missed a big nugget passing on a low tone somewhere along the way. The problem for me is most of my digging career was in Alaska in dragline, bulldozer, and bucket line dredge tailing piles. The amount of large junk at depth is unbelievable to people who have never experienced it. Imagine 55 gallon fuel drums buried 6 feet deep and you start getting the picture. I have seen people invest half a day in digging one target, only to find a can. It wears a person down at some point with a PI and all but forces a certain amount of picking and choosing your best bets.

I am extremely appreciative of wide open desert country and the type of ground I encounter there by comparison!

[Lunk]

 

I'm assuming we all have equally functioning machines so the difference is either in the nugget, the ground, or the machine algorithms iteself. And I can eliminate the ground in experiments easily enough by keeping it constant and testing different nuggets in the exact same spot with the same settings.

Have you considered that perhaps since Aussie ground is generally so much more mineralized than ours that the GB point for their ground allows more nuggets to reverse than it does ours?

[jasong]

Yes, see my previous reply:

 

I've just gone back and retested all 13 of the nuggets I've found this trip over 1/4 oz and every one of them goes high-low, even if I balance the detector to a big chunk of magnetite or to sand, I can't force them to reverse. 7 to 39 grams, 13 nuggets. Bit more than a statistical oddity.

 

 

I've tested on a ton of different types of ground too in addition to just trying to "force" them to reverse via the above method.

[Steve Herschbach]

Oh well, last try. If the nuggets refuse to go lo-hi then by definition they are of a size/shape/purity that puts them on the other side of the ground balance/setting equation. Mixing gold and silver dramatically drops conductivity putting the nugget farther from the balance point than the size would suggest. Most Alaska gold I have dealt with will not go low tone until we are talking an ounce or more in weight and multi ounce specimens will still go high tone. But as Robby has noted I have seen all sorts of weird shifts with GPX units depending on the timing selected.

Unless you are frequenting areas where there is a lot of large gold (multi-ounce) the vast majority of gold will give a hi-lo tone. In spots I have hunted in Nevada where grammers are the bread and butter it all goes hi-lo and that is that.

I am not speaking for the Aussies or their gold or ground, just what I have experienced in the U.S. Forcing a ground balance on magnetite may not replicate the situation they face with maghemite.

[Lunk]

That does make things interesting, Jasong. I have also noticed that different combinations of Gold Modes and Ground Types can alter the tones; for example in High Yield\Normal and High Yield\Difficult most all the nuggets I have found respond with a high-low, whereas in General\Difficult most reverse.

[Sourdough Scott]

A long shot. But might different hemispheres make a difference?

[jasong]

I wish it was cheap to ship about 500lbs of genuine, A-1 grade, fiery hot Aussie dirt over here so I could test my machines out on it and see how it compares to some of the hotter parts of Arizona.

[Lunk]

SS, not unless the coriolis effect is somehow involved, lol!

Jasong, sounds like a good excuse to go hunt Australia to me...

[Sourdough Scott]

Just wondering. Different polarities from northern to southern hemispheres. ZVT switches polarities. Very interesting discussion. Way above my brain payscale.