GPZ 7000 Discrimination

[wirelessguy]

I am starting a thread on GPZ discrimination.  In this missive I use “discrimination” with reference to both hot rock and junk identification. 

Let me start with my hypothesis then describe how I got there.   I am very much asking for corroborating or contradictory evidence to my hypothesis and other notes as well as any other useful info on GPZ 7000 discrimination.

Hypothesis:

Natural gold from small, barely perceptible signal return, to huge enough to provide overload, always produces a high-to-low tone when in high yield gold mode / general ground type settings.  Natural Gold can sound either high-to-low or low-to-high in difficult or severe ground type settings.  Ground type is the only user changeable setting that effects tone changes high-to-low or low-to-high on a particular target.

Required Conditions:  negligible EMI, negligible other metal or overriding hot rock present.

The one thing that has been true to date in my field experience and experiments, is that every natural gold find or test nugget from small, barely perceptible to huge enough to provide overload, had a high-to-low tone when in high yield/general.  I understand this hypothesis is no giant breakthrough enabling classification of the Zed as anything other than an all-metal machine as the Minelab manual and advertising clearly classify it.  Nonetheless, it’s the entire useful conclusion I’ve come to in as few words I can make it.  (I have trouble with writing few words.  J  )   Minelab makes no mention of discriminating sounds yet the pitch change of high-to-low or low-to-high is impossible to ignore, and naturally causes the curious to explore.* 

Early in my experimentation and Zed education, I spent hours determining what controls affected a reliable pitch change in different junk materials and hot rocks and gold.  All kinds of elaborate charts in my notebook.  I am glad I have not posted on this topic earlier because I have been through many cycles where experiments and field experiences would give me some preliminary beliefs which would soon thereafter be disproved by another experiment or field experience.

What has emboldened me to make this post (as simple as the hypothesis is) is that I was fortunate recently to experiment on a very large gold in quartz specimen.  Not certain on the mass of gold (> several ozs for sure) yet the return signal easily produces overload response on all gold type/ground type combinations. (No, not my gold.  L )   The specimen produced high-to-low on high yield/general, low-to-high for difficult and severe ground types.  Always true as I backed the Zed coil away from the specimen.

This was enlightening and counter to my early Zed experimentation on aluminum where size of aluminum changed pitch direction.  I found that the Zed, with no change in settings, will respond high-to-low on small pieces of aluminum foil (several mm x several mm) yet respond low-to-high on large (>100 mm x >100 mm) keeping high yield/general constant as well as all other settings.   Zed responds low-to-high on soda and beer cans with high yield/general.    So, I have wandered about assuming the same for gold (size of metal can affect pitch change) and hence I have NO DISCRIMINATION at all.   I “convinced” myself of this when I tested a 1 gram nugget (high-to-low) then a very large men’s gold wedding band (low-to-high) keeping high yield/general constant as well as all other settings.   Hence my hypothesis states “natural gold” to distinguish from alloys.

Hot rocks, iron or mineral based, produce a symphonic range of return sounds and can be high-to-low or low-to-high on any ground type or gold mode setting.   (another thread necessary on hot rock strategies.)  My hypothesis of “Ground type is the only user changeable setting that effects tone changes high-to-low or low-to-high on a particular target.” is not in conflict with the fact that you can put audio smoothing on high and totally eliminate a return from a weak target.   Audio smoothing setting does not change the pitch direction on a target.

Iron.  Man made iron and high % iron alloy objects produce low-to-high on all ground types only if the iron is not rusted heavily.  If the iron is rusted it can produce high-to-low or low-to-high.   This of course is near useless info for the prospector because most all iron stuff we find is rusted. 

Since I work in a hard rock environment, "dig it all" is just not practical.   Hence, my experiments and documentation on the GPZ7000 tones to try and get any possible discrimination info out of it. In my environment, that mostly means hot rock.  In my environment, I can prospect in high yield/general at least 90% of the time.  Mineralization puts me in difficult or severe less than 10% of the time.  I also have the “luxury” to mark interesting signal location first located by GPZ, then come back with my Whites MXT to try and discriminate.  (Also have GMT, GB II and GB Pro available.)  This works well on strong signals, or near-surface hot rock, however weaker GPZ signals produce inadequate response for any accurate discrimination from the VLFs.

Even if your environment requires you to mostly search in difficult or severe ground type settings, you could always go high yield/general as a discrimination test right over the target.  Of course then you might have "overriding hot rock" condition.   I think the most opportunity for uselessness of my hypothesis, even if it's accurate, is that I just don't have much experience of gold in difficult or sever ground environments whereas that is much the norm elsewhere.

* My previous Minelab experience is just ~ 80 hours with a GP3000, so I come to GPZ 7000 without much Minelab audio discrimination experience.  I’m told on other posts in this forum that is a Zed education advantage.

[Norvic]

Interesting subject, but I have found signal responses in the PI`s and the GPZ much similar, deeper nuggets are often a null directly over target same as ferrous targets, with a signal on each side and those warbley signals just love them.

 Also contrary to what seems the consensus the GPZ is a easy machine to use straight out of its box I believe, would recommend it to a beginner over the GPXs. Why the GPZ has been portrayed as a difficult machine to use for those who used a PI before is beyond me, and with the finds that are being made by previous GPXs users who have switched over to the GPZ that belief is certainly not universal. GB is simply different but just follow the manual.

 

Too many times I`ve thought this is gold and its ferrous and vice versa. Maybe I`m not hearing properly but feel neither the PI`s or GPZ are capable of discrimination to a degree that you could trust. But I stress my belief is simply if you get a signal dig it up and am keen to save some digging if the GPZ is capable of discriminating.

[jasong]

I did a bunch of experiments as you did Wireless guy, but there is always outliers to the data, piece that don't follow the patterns. In the end I don't think there is enough of a pattern anywhere to reliably discriminate unless you are in such a trashy location that there is no choice but to do so. After realizing that though there is honestly not much reason to keep using the GPZ over a good discriminating VLF.

While iron discrimination is a bit touch and go and sometimes in the head, I think it is possible to discriminate hotrocks or lenses of mineralization. 

Most lensy mineralization whether ferrous or salt that I ran into in NV was low-high and I got into a bad habit of avoiding digging low-high's altogether for a short time. But there is a solution to that problem, if a piece of gold is big enough to give a low-high signal in HY then it's going to be big enough to give a signal on Extra Deep as long as the original signal wasn't really faint (try it out). So I generally rechecked every low-high with Extra Deep mode and if the signal disappeared, which was basically every time, then I didn't bother digging it. It's not iron discrimination, but it is mineralization/salt lens discrimination. It's not 100%, but when you are digging 100's of low-highs every day all of which are ground noise then it's pretty useful. Of course you still have to dig the faint ones since this isn't reliable on them. I don't suggest anyone tries this unless they test it first for a month and dig all those signals and see it for themselves in action before just passing them over and not digging them.

This is also one of the reasons I have been almost begging Minelab to make the autotrack trigger multifunction so that we can easily switch between presets or combinations of multiple modes quickly, it takes too long how they have it set up in the software now.

One thing that may worth looking into, I've mentioned it a couple times here before but no one else seems to notice it but me so maybe its just in my head, is that Difficult may be less sensitive to iron objects than the reduction in sensitivity it experiences in gold (after switching from Normal). Let me try to explain that better: Difficult is without a doubt less sensitive to iron targets than Normal is, just like it is less sensitive to (most) gold targets than Normal is. But the *amount* Difficult is less sensitive to iron is greater than the amount it is less sensitive to gold. If that makes sense. Iron target sensitivity seems to drop off greater in Difficult than it does with Gold.

Even in the field the people I've talked to haven't noticed this. But I swear, it's not in my head. And if it isn't (ok, I'm willing to admit I'm crazy though if I am) then that may be a consistent pattern of discrimination that can be used - especially if we are given a quick track trigger multifunction so we can switch between modes quickly. You could switch between Normal/Difficult and listen to the rate the signal drops off. I've had success doing this, I can generally tell when it's iron. It works less with smaller bits of tin and better with larger metal.

[Norvic]

Dave, Your not wrong our ground is much quieter than WA, although we do have some that compares but not with your salt ground. But regardless the ground would be just as big a problem to the PI to GPZ user as it is to the new user who hasn`t used a PI is my belief, but the consensus seems that it is the user who goes from the PIs to the GPZ who is having the most problems. That I find hard to comprehend because the GPZ is as you pointed out is easy to set and understand how to set.

Remarkable that it was introduced and cannot handle WA mineralisation, because the OZ market I feel would be largest in WA, with a lot of GPZs purchased over this way heading to WA in winter. But it certainly is a gold magnet in our ground, straight out of the box.

[LuckyLundy]

Tones are very important to learn. I have a handful of preferred signal tones...but not all nuggets will give these sounds. Now in Northern California in the Goldfields, we deal with tons of trash. You can spend all day dig'n trash and hot rocks...until there is a perfect gold detector, dig them all and let the scoop sort them out!

LuckyLundy

[klunker]

 I just don't know what to think about trying to "discriminate" with a detector not designed to do so. Even the best VLF with the best operators are wrong a lot of the time (Steve H. excepted). What I do know is I have dug a lot of holes, thinking as I dug "tonight I'll be able to afford my beer in a bottle instead of a can" and then be sorely disappointed with another piece of iron. I have also dug obvious iron trash targets that are now in someones nugget collection. Every time I think I'm clever I only out smart myself. The nugget responses on the Z are all over the place and are not to be trusted. You get warbley signals, double beeps, tiny nuggets making a LOUD signal. and faint whispers from something that you think should have screamed. However if anyone has some discrimination tricks to try with the Z I would certainly try them.

[strick]

The nugget responses on the Z are all over the place and are not to be trusted.

 

Words of Wisdom for sure.

 

With every target there is hope.  How much one chooses to dig depends upon how hopeful the individual is. Some targets sound more hopeful then others. My little terrier "Buddy" in my avatar is a digging machine. He helps to keep me motivated to move some dirt while we are out detecting.

 

strick

[normmcq]

I don't cherry pick the signals that I dig, I dig everyone. except in a very trashy area and have always wondered if the ones I left behind were the big one. With having said that, I always try to imagine what I am digging in relation to what I was hearing. I have been fooled by very small pieces of gold that were very shallow, but have been fairly accurate on my assessment of target id. I did have an interesting experience recently on a trip to Nevada. I got a very nice broad, smooth down up signal and was running in High Yield with auto signal off and Normal. The more I dug, the louder the signal got. I was in  an area that had no trash. At about 15 inches, I thought this going to be the biggest  piece I have ever found, at just over twenty inches, I got a 2.1 dwt. It was a very smooth flat piece and must have been positioned in a way that afforded the best signal response. Don't trust your intuitions. just dig your targets.   Norm

[Steve Herschbach]

I just don't know what to think about trying to "discriminate" with a detector not designed to do so. Even the best VLF with the best operators are wrong a lot of the time (Steve H. excepted). What I do know is I have dug a lot of holes, thinking as I dug "tonight I'll be able to afford my beer in a bottle instead of a can" and then be sorely disappointed with another piece of iron. I have also dug obvious iron trash targets that are now in someones nugget collection. Every time I think I'm clever I only out smart myself. The nugget responses on the Z are all over the place and are not to be trusted. You get warbley signals, double beeps, tiny nuggets making a LOUD signal. and faint whispers from something that you think should have screamed. However if anyone has some discrimination tricks to try with the Z I would certainly try them.

I am wrong all the time. The problem is we never know exactly when we leave a target in the ground if we were wrong or not. I figure I have left more gold in the ground than most people ever find. I like the basic concept of dig it all. But I get into places where there is just too much trash, or when I am just too tired at the end of the day and out of steam. At that point I will dig targets that sound "sweet" to me and my percentage of non-ferrous to ferrous does improve. But at the very same time doing this I know I have walked away from good targets. Just the way it is.