New Whites PI

[Eric Foster]

Changing the subject back to this "hole" problem, Eric Foster has been doing some experiments along the lines of just what size gold does get eliminated. Hopefully, he will post hs results at some time in the near future. Some of the results of his testing is extremely interesting to say the least.

Reg

Hi Reg and Steve,

Yes, I worked out a way of measuring the "hole" in the response of the GS5B. It required finding a metal that I could file down easily in 0.1 - 0.2gm stages and that had enough weight to measure in small quantities on electronic scales. I tried aluminium but the final sizes were going under 0.1gm, which is the minimum I can weigh. Gold would be best, but I was not about to start filing down gold nuggets, so I settled for lead. Lead is considerably less conductive than gold, so a greater mass is required to give the same decay curve. What I was looking for was the point where the low tone changed to a high, and the metal became almost undetectable. Another advantage of lead is that it came be built up again with solder, so that the experiment came be repeated several times.

The results were surprising. The low point of the notch turned out to be 6.0gm but 0.1gm either way and we were back to 50% detection range and either a low (6.1gm) or high tone (5.9gm). You still get 80% range for a 5.7gm and a 6.3gm. This indicates how narrow the notch is, which also gave rise to another surprising effect. I would file the lead say, to a point where the response disappeared. If I left the lead sitting on the bench for a while, the low tone and detection range would come back. I then found that if I held the lead in my fingers and waved it over the coil, the low tone and range would reduce, and then come back as a high tone. This is obviously a temperature effect which was proved by cooling the lead to 0degC in a fridge, measuring it, and then heating it in a cup of boiling water. The otherwise undetectable piece went back to either a low tone or a high tone and full detection range. Physics books tell you that when a metal is heated, its electrical resistance increases, and the opposite when it is cooled. I didn't expect this would show up on a metal detector.

With the GS5B, the notch moves if you alter the pulse delay and re-ground balance. Changing the delay to 15uS (about 1/2 rotation) moves the bottom of the notch to 6.3gm. For gold the equivalent target would be smaller because of gold's higher conductivity. Pure gold is 70, relative to copper at 100, and some Australian nuggets that were recently measured on a conductivity meter, ranged from 20 - 50 This reading is independent of size. USA nuggets are generally thought to be lower conductivity. Lead is about 9 for comparison. So it looks as though for a gold nugget of average conductivity 35, somewhere about 1.6gm would be in the notch.

This raises all sorts of interesting questions as to what happens in the field. Searching on a cold day, compared to a hot day? Not only the ground signal changes (verified in an earlier experiment) but if nugget signals change as well? Hmmm......

Eric.

[Reg]

Hi Eric,

Thanks for the great post. For those people like me who have a technical background and have been running my own tests, your experiments have been a wealth of information. They certainly do answer a lot of unexplained questions

For those of you who are less familiar with the technical aspects, basically what Eric has determined through experiments is many strange gold related things can occur that do have an explanation.

As an example, one may hunt an area to death, be convinced they have cleaned the area out, only to find more nuggets at some later date. The key to why is both complex and simple.

What happens is the ground signals change with temperature as do target responses. Now, the ground balance feature of an PI creates a notch feature that is dependent upon the ground signal, which can change with temperature. Meanwhile, metal objects will change characteristics with temperature. So, all signals are basically changing with temperature. So, if even nothing else changes, just hunting at different days or times when there is a wide temperature swing can make a considerable difference as to what is detected and what is not.

Because the Ground Balance feature (GB) also will create a "hole" in the detection of gold, then this particular range of nuggets that will respond with less than a full signal can vary from day to day, depending again upon the temperature. In other words, the depth capabilities to detect a particular nugget may vary by 50% or more with just a small change.

Now, what was also determined by Eric is this notch or "hole" problem is quite narrow, so it doesn't take that dramatic of a temperature change to go from a strong signal to a very weak signal from the same target. Under the worst case conditions, this feature can cause a decent size nugget to be ignored even if it only a few inches down in the ground.

Now, compound the problem with a form of auto ground balance which can also alter that narrow notch a considerable amount, and something as basic as changing coils just might result in a GB change that allows one coil to detect a particular target better than another.

On detectors such as the GS 5 which has a manual ground balance, then something as basic a small GB change, or even a slight change in delay can make a big difference.

Keep in mind that the explanation as to why we can have strange results and differences in target signals is because of temperature changes and GB changes. Who knows just what happens when moisture variations are analyzed with the same intensity.

In a nutshell, this gold hunting stuff is far more complex than one might think.

Reg

[JW.]

I'm learning stuff!!! This has really been an education and I feel now like I understand a few more things than I did before, thanks to everyone who has added to the topic.

A question for anyone about Eric's findings...

So from Eric's experiments with hot and cold metals and their respected detectability, which one is better? Were the hot metals more prone to being detected or was it the cold or did I miss it in there and in Reg's post? Not that I think it would change when I hunt but I was just curious about which is which...

Reg, "more complex than one might think", no kidding!!

Say on the GPX, when you reground balance, does it start from the point you balanced at last GB or does it reset the whole GB to startup and begin again? I have yet to hunt in tracking GB just from the fear or balancing out a nugget from over investigation, the things you mention happen in fixed GB tracking too right?

Sorry for the basic questions.

HH

JW

[Reg]

Hi JW,

One statement made on the POZ forum is somewhat interesting in the fact, one person mentioned this hot/cold thing was common knowledge. That is really interesting because, the hot/cold gold signal variation is basically true only on a PI with limited ground balance range and only occurs at the GB (ground balance) point.

Here is something interesting, if you have two GB points, you have two holes. What can happen is you will have two shallower or different type holes, but lets forget this for a while.

Move the GB control farther than possible on the ML's such that the GB point is way off and this whole hot/cold thing goes away as do the holes. If the ground balance is adjusted far enough, one can't really tell the difference in signals on different sizes of gold as the result of a temperature change. There might be a very slight difference that might be possible to determine with special equipment, but to the average ear, one couldn't tell a hot nugget signal from a cold one.

When a PI is ideally ground balanced, the ground produces no signal. At that point some gold will have the same response as the ground and produce little or no signal. Adjust the ground balance just a little and that same ground is no longer perfectly ground balanced. What also happens is the gold that produced no signal at the earlier setting will now be heard with a much stronger signal and a slightly different size piece of gold will have a much weaker signal.

Move the ground balance adjustment farther yet, and both the previous pieces of gold just mentioned will now both sound off much louder. Move the GB such that there is no GB as such and ALL gold generates a signal.

All of this happens only as the result of the GB setting. Change the GB, change the gold that gets ignored or partially ignored.

Now, lets say we don't change the GB point, but we do change the temperature of the gold. What can happen is we will see the same change on the gold signals, meaning when we change the temperature, some gold that had a weak signal now has a strong one and visa versa.

So, change the temperature only, change the gold signal and change the size that gets ignored. Because of the GB setting, some hot gold will get louder and some will get weaker. The same holds true for cold gold. Whether the gold gets easier to detect or harder is determined by the GB setting.

The ground signal changes also just a little when the temperature changes, so both can change.

This really gets confusing to try to explain.

As for which is better for detection of gold, hot or cold, the answer is basically neither from an absolute standpoint. The answer lies in the adjustment of the GB control and how the gold it relates to it.

No GB design is perfect, so it will be off just a little but can be off on either side of perfect, meaning it can be a little positive, or a little negative. In most cases, one can't tell the difference just by listening. However, which side it is on and the slightest temperature change will determine which gold has the weakest signal.

The question was asked, if you reground balance do you change things? Yep, most likely if the GB actually changes.

Now, one thing Eric mentioned briefly was conductivity and how it can change just when a piece of gold falls into the 'hole'. What this basically means is change the chemistry of the gold a little and size of gold that falls into the "hole" changes.

Change the characteristic (shape or roughness) of the gold and the same holds true.

Now, if all of this gets confusing, then remember what else was mentioned on the POZ forum about the gold that was ignored for a certain distance and then was detected at a deeper distance. Yes, this holds true at times also.

Now, before people panic, one should realize that the gold or amount of gold that falls into this category is really quite small. So, little gold is missed for this reason only. Normally, other human errors can cause much more gold to be missed.

Reg

[Reg]

Hi All,

With just over 7900 views, one might think this thread is drawing a little interest.

Now, I was trying to figure out a better way to way to try to explain what happens to a signal with heat and how it changes. Well, I will try a simple analogy that may make sense. Lets hope so.

Ok, think of a teeter totter and the balance point. If you sit on that balance point, you don't go up or down, so you don't wee or woo, where a wee is go up and a woo is going down.

Now, the question was asked whether hot or cold causes the best signal, well this is what basically happens. When the ground changes, so it would be like the pivot point changing below you and moving either left or right. So, depending upon which way it shifts, you become a wee or a woo because you are no longer on the center position.

Lets say the ground doesn't change, but the gold temperature does. In this case, the pivot point doesn't move, but you do, you slide left or right, depending upon the temperature, so you again, become a wee or a woo.

Now, to try to explain why some signals get better and others get worse, think of sitting left of center and moving slightly to the right. Now, you have approached the pivot point so you create less of a signal because you move less as the board pivots. This means you have changed from a louder or bigger wee to a smaller one. If you move enough, you will sit on the center and become the null signal that is neither a wee or a woo.

This time, lets sit on the right side of the pivot point. In this case, if the temperature causes you to shift to the right, you will move farther from the pivot so you will move more or get louder as a signal.

The point of all this is some gold right at the point where it is or can fall into the hole, then this same gold can get louder or quieter depending upon which way it moves.

Eric Foster pointed something out to me that when the gold gets colder, the conductivity increase and as such, is easier to detect, so there is a slight advantage. Once again, if no ground balance was used, I highly doubt one could really tell any difference, though.

Ok, lets change the subject again. Since this thread started, I have figured out a way to discriminate higher conductive coins and can actually tell one from another. So, with additional circuitry, we could have a decent discriminator for these items. This would make this PI a great coin hunting detector when looking for older silver and copper coins.

At the time I found this out, I mentioned that iron was still a problem and I was working on it. Well, that problem now has a basic solution. Yes, I can tell the pesky pieces of tin cans from gold.

The key is using the same basic technique used in VLF's where two signals (diferent samples) are compared at different levels or ratios. At the right ratio, gold and other higher conductive objects will cause a negative or no signal, while the pesky ferrous junk will sound off with a positive signal. Just check this signal and you know whether to dig or not.

When time permits, I will use this signal to probably trigger a response on a meter or maybe a LED. I could toggle between ratios using a simple switch to test each item that is detected. So, there are different methods that could be used to let the operator know if the buried object is gold or ferrous junk. Obvoiusly, other non ferrous objects such as shell casings will still be a problem, but they will on the most sophisticated discriminator.

So, a discriminating PI is possible using the basic techniques involved today. BTW, I do have a working model and have verified this works.

Just thought people might want to know.

Reg

[Eric Foster]

Eric Foster pointed something out to me that when the gold gets colder, the conductivity increase and as such, is easier to detect, so there is a slight advantage. Once again, if no ground balance was used, I highly doubt one could really tell any difference, though.

Reg

Yes, nuggets do it too. I found a 4gm nugget that I can tune out with the GB control on the GS5B. This was quite a different point on the control to where the ground balances out, but this should not affect the characteristics of the notch. Adjusting the control carefully for no signal, the nugget was then put into a cup of boiling water. The nugget then gave a wee response. After 10 minutes in the freeze compartment of the fridge, it now gave a woo.

The changes did not seem as great as for the lead, but it was very definite. I have no idea what the temperature coefficient of metal conductivity is, and whether it is different for different metals, but the important thing is that temperature change can make a difference in detectability in an instrument that is notching out the ground response.

One other important point that I have not yet mentioned, is that the tests, both lead and gold, were done with the target being brought down vertically on the coil axis. If you pass the target from side to side, different things happen. The latter of course is what would occur in the normal course of searching. Because the magnetic field from the coil gets more horizontal as you approach the coil edges, and the targets have a certain thickness to diameter ratio, initially you get a wee, followed by a null when the target is on axis. You get another wee as it passes the other side of the coil. So in practice you do not get a situation where the nugget completely disappears. It is still audible but as two responses. You would not get this if the target was spherical as the eddy current decay is the same whatever the orientation to the coil field. If the target's major response is not notched out, then the on-axis signal is dominant and you would hardly notice the coil edge signals.

Eric.

[JW.]

Ok, lets change the subject again. Since this thread started, I have figured out a way to discriminate higher conductive coins and can actually tell one from another. So, with additional circuitry, we could have a decent discriminator for these items. This would make this PI a great coin hunting detector when looking for older silver and copper coins.

I know a slew of turf hunters in California that would jump all over this, granted it gets an inch or more depth than the Explorers...

I think I will have to read the previous posts a few times, lots of great info and knowledge being passed on here!

So Reg, I make custom carbon fiber parts, how about a slick shiny black control box for that PI?

HH

JW

[montana]

Reg. Good stuff on ground balancing. One thing I've learned over the years with PIs is that because of their ability to handle the ground mineralization , we can often be detecting with our GB a little off one way or another without hearing the the ground mineralization manifesting itself as noise in our headphones. It wasn't that way with the VLFs. A tiny bit off and you knew it. Hence the fine ground balance knob on say the Whites GM3. you could adjust for the micro changes in the ground mineralization with that super sensitive machine. The drawback was that moving only a few feet away would mean ground balancing again. The PIs could move through these micro-climates with little audible disturbance making it much easier to use in tough , changable ground. I have experimented a lot with buried weak targets and found that with few exceptions the signal could be improved by reground balancing a few inches away from the target and swinging over it again. On very few occasions the target would become slightly weaker or remain the same, which could be explained by your statements that a slight positive or neg. GB can give a slightly better response on certain nuggets. I believe that a near perfect ground balance is still the best situation for the vast majority of nuggets, and I think that to me the GP3500 was a better machine than the GP3000. Although I don't think there was any significant difference between the two other than the push button GB on the handle of the GP3500. It just made it so easy to GB that it was done far more frequently making it seem more sensitive . This was also when I really started GBing after hearing a target and swinging over it again. It was just so quick and easy. I don't leave an iffy target without re GBing and checking it again. This often results in an iffy target becoming a definate target. I am also quite sure that the GPseries detectors don't start all over again from scratch when reground balancing since when making small adjustments the GB is achieved in one or 2 pumps of the coil as opposed to at startup in a radicly different ground type than detected on the previous outing and it might take many pumps of the coil and several tries starting the GB sequence over again. They also retain the last GB setting indefinately until the GB button is pushed again with the power on. This is not the case with the atmospheric tuning feature of the GPs . You will often have to retune after even a breif turn off.----Bob

[Miner Matt]

I was just wondering if anybody has ever used a Whites Surf PI Pro for nugget hunting?

[grubstake]

I tried once, they will find bigger stuff, but not smaller gold, no ground balance on them. Grubstake

[Reg]

Hi Matt,

Grubstake's right, the Whites PI pro doesn't have a ground balance and the delay is not short enough to easily detect small gold. So, there would be some serious limitations in using this detector.

You can us a PI without ground balance if the unit is low powered, can use a DD coil, and has an adjustable autotune. It isn't perfect, but it will work. Unofortunately, the PI Pro doesn't have some of these, so it would struggle.

Reg

[Reg]

Hi JW,

Thanks for the offer, but my units all look pretty bad and anything nice would be out of place. They look bad because I never get finished before coming up with a new idea, so it is off to the races in a different direction. To make matters worse, I have a few PI's and each one is a little different from the the other so I can try to compare things.

Now, as for this latest design, I have found when discriminating coins, my unit easily beats any VLF I have for depth on coins in the ground where I live. I don't see any reason that wouldn't hold true in other places.

The part I am concentrating on now is the ferrous/non ferrous setup. For the time being, I will have a toggle switch to switch from one to the other to make a quick check. This is simple and easy to do.

When time permits, I will start over and redesign the entire circuit so I don't have to switch. Instead, I will have some form of ID indication as each target is found. This will take a while to get right.

Once the new design is in place, it would work extremely well anywhere since the ground balance would be independent. In places where no ground balance is needed,none would be used. The depth capabilities increase signficantly when no ground balance is used. This is where a new design will really shine.

Right now, my problem is finding time to get the design done. I have too many other things going on at the resent time that interfere with finding time to work on this project.

Reg

[Digger Bob]

Hi JW,

Thanks for the offer, but my units all look pretty bad and anything nice would be out of place. They look bad because I never get finished before coming up with a new idea, so it is off to the races in a different direction. To make matters worse, I have a few PI's and each one is a little different from the the other so I can try to compare things.

Now, as for this latest design, I have found when discriminating coins, my unit easily beats any VLF I have for depth on coins in the ground where I live. I don't see any reason that wouldn't hold true in other places.

The part I am concentrating on now is the ferrous/non ferrous setup. For the time being, I will have a toggle switch to switch from one to the other to make a quick check. This is simple and easy to do.

When time permits, I will start over and redesign the entire circuit so I don't have to switch. Instead, I will have some form of ID indication as each target is found. This will take a while to get right.

Once the new design is in place, it would work extremely well anywhere since the ground balance would be independent. In places where no ground balance is needed,none would be used. The depth capabilities increase signficantly when no ground balance is used. This is where a new design will really shine.

Right now, my problem is finding time to get the design done. I have too many other things going on at the resent time that interfere with finding time to work on this project.

Reg

WOW! Just too much good stuff in this thread to absorb. I'm going to have to print it all out and try to digest it during the winter. Thanks to all the experts who have contributed. Most of it is over my head but some is sinking in.

Digger Bob

[Reg]

Hi Montana,

Sorry to take so long to get back to you and your discussion about the difference between the ground balance on a VLF and that of a PI.

You are absolutely correct, the slightest adjustment on a VLF can make a world of difference, not only to the ground signal but also the signal from hotrocks. This is especially true of rocks primarily made up of magnetite or even have a reasonable amount of this material in it.

Fortunately, PI's basically ignore magnetite. The signal has come and gone way before any samples are taken. Now, when you have stringers of magnetite running through clay, strange things happen. The field is distorted somewhat, but the biggie is the fact the magnetite alters the average ground signal because of the absence of a signal, so the movement across from concentrate black sand to a clay base will normally cause a response.

Now, if a rock is big enough, then it can cause a similar change, but that normally doesn't happen because of the characteristics of the rock itself.

Remember, it is the black sand and magnetite hotrocks that cause the most dramatic signal changes on a VLF, but cause little to no response on a PI. So, generally, a PI is extremely quiet in places that cause a VLF to scream. Generally speaking the worse the ground for a VLF, the better it is for a PI. This is the true claim to fame for a PI. With fewer and milder secondary signals, it is much easier to hear the faint target responses. This, in effect, really assists in the depth differences between the two types of detectors.

You are also right about the GB can be off a little on a PI and not cause much of a problem. If the GB is a little too much, it is almost impossible to tell, yet more and more basalt rocks may be ignored at the same time. On a detector such as the GS 5, adjusting the control to minimize many of the basalt signals will also have little to no ground response. What does change is the size of gold that drops into the hole.

So, what is the significance of this? The answer is easy. To assure the best and most thorough coverage of an area, one can adjust the GB to the ground and then scan the area thoroughly. Then adjust the detector such that a piece of basalt that would normally give a decent response is ignored and the scan the area one more time. This should minimize any losses because the the "hole" effect.

One more thing about PI's and ground balancing. There have been several posts on different forums about PI's detecting charcoal. Unfortunately, that isn't true. A good test is to find a charred board or even take a bunch of charcoal briquette's (BTW, these are nothing more than charred wood) and perform an air test. I think you will find that you will get no response from either.

What does happen at a campfire is something that Eric Foster mentioned some time back on the PI forum and that is the surrounding soil containing magnetite and hematite is changed to maghemite, which is easily detected by a PI. So, intense heat can cause this iron oxide transition which will then cause the response people encounter.

Reg

PS, I couldn't let this thread disappear until it at least hits 10,000 views.

[montana]

Reg. I found that with the GPX4000 while running in the Smooth mode, I could work a certain area very easily that was thoroughly littered with very hot basalt rocks. The response from these basalts could either be a positive or a negative signal. By selecting one of them that gave a strong positive response and ground ballancing on it , I could eliminate all the positives which gave a very nugget like response . The remaining basalts(which were a great minority) that it would pick up were then a very un-nuggetlike negative with a warbly sound thrown in. It was then a piece of cake to pick out the good solid positive sound of a nugget resulting in some great fun in a place that used to leave me with a "hotrock headache". This doesn't work with all basalts , but in this particular place it was the answer to working it easily. This didn't work with the previous GPs or SDs which didn't have the smooth option. Somewhere in your extensive posts above there is probably an answer to why this worked so well. I do know that with your machines, Erics machines, and the GPX4000, the ability to alter timings/delays is the key to closing up any holes if I understand your posts correctly. We , as operators just have to figure out when we need to make those changes . It seems that we've gone full circle from very difficult machines to run , to simple turn on and go machines, and now back to a little more challenging machines. I personally like the fact that Minelab has put us back in the drivers seat so to speak. Now that I see where Minelab has gone, I think that I would be more objective when trying out say a GS5B. The first time I looked at one, I couldn't figure out what Eric was trying to achieve. Reading your posts and now being familiar with the GPX4000, I believe they are both heading in the same direction, but by slightly different routes. I would probably now understand what some of the adjustments are on the GS , and how they correlate to the adjustments on the Minelab.I love to read your posts although a lot of it may be way over my head. Some parts I can really grasp and I've been enlightened. Keep it coming . If only 1/4 of it sticks, I'll know more than I did.----Bob

[Reg]

Hi Montana,

I am curious if on one of the earlier SD's where you could select either channel, you might be able to do the same thing by only selecting the channel that detects the small gold better. I think this is channel 2, but I may be wrong. I would suspect if only one channel is involved, you could ground balance to the most positive basalt and get the results you mentioned.

Now, one thing that has to be cautioned is the positive gold responses are for smaller gold only. I would expect larger solid gold nuggets to generate a negative response.

I can't say what happens on a ML but I suspect that it is true there also, but on the GS 5 and similar detectors, when ground balanced to the typical ground, I have never experienced a negative responding piece of basalt. All basalt generates the wider weak positive response, much like a deep nugget or no response at all. Some pieces of basalt may generate a stronger signal than others, but they are all positive. Generally, this signal is wider softer and smoother than any typical positive sounding gold target. Now, like you said, you can ground balance to the more positive responding basalt and quickly tell if it is a rock or not. The odds are really slim it is a nugget that is switching from a positive to negative signal over this narrow of a range of adjustment, but it could happen.

What might be nice is to have dual GB adjustments that one could switch between. This would allow a person to adjust to the ground with one and a positive responding basalt rock with the other, so one could switch quickly between the two. This is possible.

Reg

[Reg]

Hi Steve and Montana,

Both of you have added specifics about the GPX and what to expect. One thing that caught my eye was something that Steve said. Here it is;

"This may relate to the new smooth mode in the GPX-4000. Smooth changes the tones. Small items go "wee", middle sized items go "woo", and very large items go "wee" again. This combined with the fact that the smooth mode greatly reduces the response from basalt cobbles would seem to indicate some radical change in the ground balance method being used."

The fact object sizes change tones from wee's to woo's and back to wee's, indicates there is the strong possibility of certain sizes that don't respond at all. This is in line with what has been posted on the ProspectinginOZ forum, where they indicated nuggets in the 1 oz and some larger seem to disappear or are ignored for certain depths.

Have either of you, Steve, or Montana, done any specific investigating of this condition where some larger nuggets seem do be ignored at certain depths by trying to verify or dispute what has been found during testing in OZ?

I would initially check using simple air tests first and test various size nuggets over an oz on size by simply checking them from near coil surface to the maximum air test distance they can be detected to see if they do fall into a "hole" and are ignored over any of the range. Knowing this can be very important when hunting.

This multiple tone change is interesting and doesn't occur on the GS 5. As such, the GS 5 does have a "hole" but it is quite defined and limited. Also, tones are basic wee's for small items and woo's for larger ones. Any deviation from this usually is the result of the gold characteristics. Primarily, some larger gold can respond with a wee if the gold is very porous, or simply not a solid mass.

Reg

[montana]

Reg. Not having the analytical mind that you have , I look at this hole as irrelevant in the smooth setting. I only care about one thing. If the ground is so horrible that I can only keep my sanity by running in the smooth mode, and if by doing so , I can then easily hear most nuggets , then I'm a happy camper. This is the only time I use the smooth mode anyway. If I get 5 nuggets that I wouldn't have gotten in other settings, then I could care less if I missed the odd one by running in smooth. I'd have left without the 5 nuggets or the odd one.

The GPs often give a negative or inverted response on certain basalts. It however never seems to be as strong as a large nugget inverted response which generally is on a nugget in the 1/2 ounce range and up . This negative or inverted response to a basalt usually doesn't happen on a rock more than a few inches deep. These are easy to check out . The SD2000 gave a negative or woo signal on almost all nuggets unless it was a real monster near a pound, then it gave a positive or wee response. The SD2100 was the reverse. The detector can be set up to give a response either way at the factory . With the GPX we can do it ourselves with the twist of a knob. I don't know why the GPs only need a 1/2 ounce nugget to make the flip flop, and the SDs need a multi-ounce nugget to do it. Personally I liked the way the SDs were in that respect. As far as multiple flip flops in the smooth mode, I never checked it out. All I've ever found were nuggets under 1/3 ounce while in the smooth and they all gave a normal wee response.-----Bob

[Reg]

Montana,

You are right, I am one who needs to know just what to expect. That way I can try to figure out a way to overcome any limitations I know exist with my detector. Knowing what is happening also helps further understand just how the PI works. On the GS 5 or similar design, there is a hole that is very narrow. It can be shifted a little with the ground balance, or on my personal PI's this hole can be eliminated by reducing the amount of GB applied. So, I know how to overcome the problem.

As for the GPX, for me it is just a matter of curiosity as to what is ignored. I wish one of the guys who was involved in the testing in OZ would have jumped in with a little more info on what they found if for no other reason than to inform new GPX owners.

Now, from what I have read, it is 1 oz and larger gold that can be ignored in the smooth mode, but I am not sure just what was the smallest size they tested either. Maybe Doug of Prospecting in OZ will chime in with that info.

The reason I am curious is right now, much is unknown, so a lot of what if's can prevail. As an example, what if, all gold over a half oz is ignored at least some of the time or over a certain distance in the smooth mode? This may be possible if no one has actually checked? Here in the US, that isn't a big problem since the majority of the gold found is in the gram size. But, what if that is true? That is why I asked the question of both you and Steve H. Both of you seem to have been the ones who have experimented the most. Hopefully, Steve will jump in when he gets back from nugget hunting. He seems to have tested the smooth more more than anyone.

The reason I am curious about what happens in the smooth mode is because of a feature that was on the older GS 4 PI. One could select a certain mode and when in that mode, only the "wee's" would generate a signal. All woo's were ignored. So, any larger solid gold would be ignored.

As for the negative signals from Basalt, that is interesting. That can only happen if the GB adjusted well past the normal ground balance setting. At perfect ground balance all basalt should give a positive indication. At least it does on a GS 5 type detector. Now, on the GP's, since there are two channels, is the ground balance adjusting each one independently or just one and the other is following? That is an interesting possibility because it could explain why some basalt generates a negative response.

The change from a wee to a woo signal occurs when the object is such that the signal from the object and how it relates to the ground signal. Anything that has a signal that decays faster than the ground signal is a wee response and those signals lasting longer are woo's. This is true when the detector is balancing out the ground signal. Generally, this means small gold gives a wee signal and larger gold will cause a woo type response

What I have found on a unit that only has one channel is the change can occur over a fairly wide range, meaning a 1/4 oz might become a woo if the gold is very solid and a half oz could be a wee if it is very coarse. So, on very coarse rough gold, it could take a very large size to make the tone change. On specimen gold, the problem is even worse because it depends on multiple factors. So, it is possible for a very large multi ounce specimen to only give a wee signal. So, this wee/woo thing is more complicated that one might think.

Anyway, trying to figure out just what happens and why is fun.

Reg

[montana]

Reg. I don't know why there is sometimes a negative response from a basalt rock. I do know that in some places there is a very wide amount of response from one basalt hotrock to the next. Some will put the detector into overload and the next one you brace yourself for a blast and there is no response at all. We also tend to lump erupted volcanics into one category and call them all basalts. Some come from flows, some were blown out of the volcano and scattered over a huge area which are often called lava bombs, and then there are the scorrias (spelling?), a very foamy type of eruptive that has many air holes and looks like a sponge. These are often reddish in color and often give a very strong signal. The flow basalts have relatively few gas pockets or air holes, the lava bombs more gas pockets, and the scorrias being the holiest.

I have never talked to anyone who has seen or had an analysy or assay done on them to explain why they bother our detectors. Is it as simple as the iron content ? For some reason I feel that this isn't the only thing going on with these . Most basalts are considered worthless for their mineral content , but our detectors seem to think that they are loaded with metals. We can understand why a lump of magnetite gives a signal, but why doesn't hematite or limonite give a signal? They are all iron ores, and there are other high iron content ores which are also ignored. With the PIs , hotrocks are becoming less and less of a problem, but there are still some that plague us. I visited a place in Ca. where the ironstones were so hot that a walnut size piece gives a very strong nuggetlike response at 18" or more. The very patient detectorists have managed to pick some real nice nuggets from this mess, but they dig as many as 100 or more ironstones to every nugget. The nuggets run with these ironstones and if you aren't digging the ironstones you don't get any gold. Luckily it's an anomoly. I've never experienced hotrocks of this calibur before other than the green turds that John B. made famous. Now those are some world class hotrocks.-----Bob

[Reg]

Hi Montana,

Basalt is an interesting rock. I agree there can be a wide range of signal variations from this type of rock. My best guess is the greater the maghemite content, the more intense the signal from the basalt.

Now, magnetite by itself shouldn't give a response on a PI. The response time is too short and any signal should have been gone for a while before the sample is taken. So, if a rock appearing to be magnetite does sound off, the rock most likely contains secondary materials, probably maghemite, that are causing the signal if the detector is properly aligned.

There may be a way a PI can respond to magnetite because of a magnetic lag type signal if the detector isn't properly adjusted. I suspect this can happen if there is improper or insufficient cancellation of the earth field effect. Swinging the coil through the air will generally let you know if that is the case. There should be no signal when the coil is moved through the air if all is right. Care must be taken on this test to assure the coil lead isn't moving and causing a signal since we have a tendency to sweep the coil faster when testing for this condition.

Your discussion of ironstones in CA intrigues me. If you go back to that location I would appreciate it if you gathered up a few of these rocks for me to experiment with. I suspect Eric Foster might want a couple also. He has designed some interesting equipment to analyze the characteristics of both soil and rocks that helps in determining what is happening.

I am also interested in John B.'s "green turds" also. Where is he finding them? I think I will just shorten the name to John B. turds, or maybe J.B. turds. I would like to test a couple of them also.

If and when I ever get caught up I am going to calibrate one of my PI's so I can check things using a calibrated delay. This will help in evaluating what is happening.

Reg

[Reno Chris]

Reg:

I've seen pictures of JB's rocks and they appear to be largely cuprite, a red metallic copper oxide mineral - the associated green is from secondary oxidation of the copper. In cuprite, unlike most copper minerals, the copper is in a +1 valence, giving it an unbalanced free electron, so it probably has some electrically conductive properties, although I've never read any study of such. Many specimens have a metallic luster with a semi-metallic appearance. It is also sometimes called "ruby copper".

According to John, they sound off rather loudly on metal detectors.

Chris

[montana]

Chris. They are some kind of copper mineral apparently. I gave mine away . They certainly do make a detector sound off. 3 feet deep is no problem for a 2 lb. lump. I have only seen them in the place John showed me. A few miles away I dug the deepest ironstone I've ever dug also. That place is hotrock city.

Reg. That place in Ca. has all the types of eruptive volcanics I mentioned. It was a nasty place to detect before the GPX4000 came out. It eliminates all but the scorria type and those are then only a weird, fluttery gurgle once the detector is set up right. If I go back over there I'll bring back a few samples.---Bob

[nuggethunting]

Hello Reg and Montana,

I have a bunch of those "Green Blobs." I actually found them in a different spot than where John B. and others found theres. I found a small gully that was loaded from one end to the other with them. Some were so freaking large it would take several men to even move them. I also found the vein towards the upper end of the wash, pretty much looked like solid copper!

Someone mentioned that some of these "blobs" have a small percentage of free gold in them.

Take care,

Rob Allison

[Reg]

Hi Chris, Montana, and Rob,

Thanks for the information about the green rocks. Rob, if you think about it bring a decent size one with you to the 24K weekend outing on the 13th and 14th. If you can spare one, I would like one to play with to see what I can find out. I doubt I will have time to set my detector up to tell me much by then. So, if you have a spare, I would appreciate it. That way I can work on it when I get a chance.

Montana, I would appreciate some of the worst volcanic or other hotrocks you run into. It helps me to know what is out there and if there are ways to eliminate them as a problem.

Reg