60 ounces missed by ML4500 and 5000

Here's our story of woe from this years operations. This patch was originally found about three years ago when we heard about it. It was on company ground but we decided to apply for a Special Prospecting Licence and give it a good pushing. Of the 60 ounces found by the orginal finder, very few of the species could be heard with a ML 5000. 95% of the gold was found with a Whites GM2. These White's machines are not pulse induction. They belong to the "outmoded" (?) VLF type of detector.

We knew of this phenomenon so we bought a Whites for the job. After getting the SPL and all the permits from the DMP and DIA, we pushed in 4 spots to a depth of 400mm,,,,,,,,,and came up empty on every scrape. After this disappointment we decided we'd "surf the surface" with the Whites. With this we found 8 species,,,,,,,,,only one of which could be heard with a ML4500/5000 when tested. All the species were on the top when found and all screamed at me with the Whites.

Not one specie was under the surface. They were all sunbaking, but the ML machines went clean over the top of 'em. All were very well rounded and worn. As you can see, the gold was extremely fine and this is the reason that an ML Pulse Induction machine can't "see" it. More with the next photos.


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Here's another. This one was very similar to one that was found in a creek line on the lease next door, about one km away. That one contained 3 ounces and would fit easliy into the palm of your hand. This one contains about 2 ounces. Again this one couldn't be heard with an ML machine, but screamed on the Whites.

Cat

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Here's another that my wife found after I'd inadvertently run it over with the 'dozer. Note the jagged edge where it snapped. I found the other half next day about 5 mtrs away! So I musta picked it up and dropped it in slewing!

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Cat

I dont fully understand metal detectors but know there is a difference between PI and VLF machines. I found this specimen at Sandstone earlier this year with a GP 3000 it was lying on the surface and gave a low signal possibly because the specimen only had 5 grams of gold in it. The gold was'nt visable until I chipped a piece of the specimen.


Cheers Kevurl=https://servimg.com/view/17477758/26][You must be registered and logged in to see this image.][/url]

Leonora?

Depends who's asking,,,,,,,,,, 

Cat

I'm still pondering whether to dryblow the dirt on the area, but the gold looks a bit too fine for a dryblower. Maybe a sluice would be better, but then water would be a problem even with a recirculating sluice. There's a reef somewhere, obviously, but I reckon it's either shed and vanished or it's a long way from the end of my lease.
I think the latter is the case as these species were all on top and have had the hell belted out of 'em. Old river bed? I plotted the run of the species using Ozi-Explorer's "blank map" function. The results were a very clear picture of where the gold was running - and it was practically in a wide, but straight line about 40 mtrs wide by 250 mtrs long in a ellipse. I love Ozi-Explorer for mapping.

The ground is wide valley between two granite ridges with quartz intrusions. The species show that the gold was dead set on the interface of these two rock types.


If I can get a copy of the map out of Ozi-Ex I'll put it on here.

Cat

thanks for sharing Cat great stratergy running the VLF pitty there were no deeper ones for you, is there a reason that they settled on the patch? if not i recon the reef cant be to far away?
unless it was eroded away completely

G'day cat, Jason here. I spoke with someone with exact same story as yours. I too have recently found something similar but by no means as a larger patch. So am pretty interested somewhere down the track in trying a different detector to see if it picks up much more species.

Very interesting Cat- makes me want to head to a few spots I know and give my goldbug 2 a swing- ive barely used it since getting it, as its basically a back up or for the missus to play with. Definitely have to start using it more  

Chad,

Check yer PM about that book ya wanted. I've been crook.

Cat

UTBN wrote:G'day cat, Jason here. I spoke with someone with exact same story as yours. I too have recently found something similar but by no means as a larger patch. So am pretty interested somewhere down the track in trying a different detector to see if it picks up much more species.

Jason, it was around Leonora and there's a a fair few people around there that know me and the story.

Cat

Biggest Kev wrote:I dont fully understand metal detectors but know there is a difference between PI and VLF machines. I found this specimen at Sandstone earlier this year with a GP 3000 it was lying on the surface and gave a low signal possibly because the specimen only had 5 grams of gold in it. The gold was'nt visable until I chipped a piece of the specimen.


Cheers Kev

Kev,

The rule of thumb with metal detectors is "The lower the frequency, the deeper the signal penetrates into the ground - but with less sensitivity",,,,,,,,,"The higher the frequency, the shallower the frequency but with far more sensitivity". So the low freqs are for big bits down deep and the high freqs are for tiny bits near the top. In this respect the old Fisher Gold Bug at the high freq of 60 Khz (?) was a killer on small bits but had no depth. The Whites GM2 that I used on this patch has a freq of 48khz. The old Minelab 16000 VLF had a fixed freq of 16 khz. These are known as "VLF/TR" machines or "VLF" for short. They operate by sending EMI transmission (Electro Magnetic Impulse) into the ground at ONE FIXED FREQUENCY. They transmit and listen at the same time. Because they have only one single freq, they can be used with a very fast swing. They went out if fashion when the Minelab SD came along with the Pulse Induction Technology.

A pulse induction machine works by transmitting a series of different frequencies into the ground, not just one signal at one freq. These frequencies have a wide range. I'm not sure what that range is but it could be from as low as 4khz up to 80khz. The circuitry works by firstly transmitting the whole range of freqs into the ground. This is known as the "Transmit" stage. When this transmitted signal hits a metallic object, the EMI generates an eddy current across the whole surface of that object. Remember that bit.

The "Transmit" stage then switches off and a "silent" gap occurs. The "Recieve" freuency then switches "ON" and "Listens" for the (now) decaying eddy current on the surface of the metal object. When it hears the eddy current, it sounds off as an audible tone in your earphones. That sound is your target.

Now as you can see, the Pulse Induction machine has a huge advantage over a VLF machine. It can detect over many nugget sizes at many different and deeper depths. That's why it was so successful when Minelab first introduced it. But it also has a downside.

More in the next post.

Cat

Thanks Cat, for puting it simple to make it easier to understand. Can't wait for your next post.

Cheers Kev

Cat,
 
I recently built a small foldable 12v dryblower to use for testing ground. I used very good quality dryblower cloth and was very suprised at how much very fine gold it traps. Might be worth a go on your above mentioned ground.
 
Cheers,
 
Driller.

Hi Cat ,
I can't believe the results you mentioned.
I do know driving these minelabs (4500 and5000)Varys hugely from user to user.
I've seen pin head size gold found with both many times over.
Also seen plenty of new 5000 users walking around with wandering thresholds missing lots and unable to read 1/2 gram test pieces.
My advise to these folks still stands as to take out a test piece ,small as fly shite and make the machine read it .bark as loudly most audible as possible.
Interesting post though
Thanx

driller wrote:Cat,
 
I recently built a small foldable 12v dryblower to use for testing ground. I used very good quality dryblower cloth and was very suprised at how much very fine gold it traps. Might be worth a go on your above mentioned ground.
 
Cheers,
 
Driller.

Gday Driller- im interested in seeing your dryblower- any chance of throwing up some pics or even the plans???

decanfrost wrote:Hi Cat ,
I can't believe the results you mentioned.
I do know driving these minelabs (4500 and5000)Varys hugely from user to user.
I've seen pin head size gold found with both many times over.
Also seen plenty of new 5000 users walking around with wandering thresholds missing lots and unable to read 1/2 gram test pieces.
My advise to these folks still stands as to take out a test piece  ,small as fly shite and make the machine read it .bark as loudly most audible as possible.
Interesting post though
Thanx

Decan,

I didn't believe it at first either. The species from this patch were tested by me and two other operators of 4500s and 5000s. One of those operators were previously unknown to me, but the other is a smart, young guy that detects for a living and finds all kinds of "fly-schitt" gold. Both of them tried every combination of settings and both of 'em failed to get even the faintest lift in threshold, let alone a signal. Nothing. Zilch. Silence except for background threshold noise.

I've been using detectors since 1983 and it was the same when I tried. But with a VLF Whites, they were screaming!

Prior to buying the Whites for this pushing, I called Nenad, the tech at Minelab. After much evasion, he finally admitted that I was correct in my assertion about this flaw and why it happens. You can read why in the next "lesson" about PI vs VLF detectors. 

Cat

This thread could not have come at a better time for me.
I've been looking at the best detector to take on a short trip. I have two available either a White's Goldmaster 3 or a Minelab i-trak. The alternative is to rent one of the Minelab GPX models. Suggestions please?

Wow cat sounds unbelievable.
However one other thing that screams out to me is settings .
8 inch commander mono or 6 inch Sadie and set up by these mount magnet guys and if a fail I will except defeat and buy you two beers.
But very interesting story.
I've just bought a French made wireless machine (Deus)which is very interesting to say the least.have you heard of them?.
First wireless detector.
Check em out you might like.
(aren't as sensitive on salt/extremely mineralized ground)but scream at the .2targets
Cheers
Decan

scotgold wrote:This thread could not have come at a better time for me.
I've been looking at the best detector to take on a short trip. I have two available either a White's Goldmaster 3 or a Minelab i-trak. The alternative is to rent one of the Minelab GPX models. Suggestions please?

Scotty,

The ML E-Track is a treasure hunting machine. It's not a prospecting machine as is the SD/GPX series or the Whites. Although the Whites, being a VLF is good for treasure hunting. How good the E-Track would handle the ubiqitious iron mineralisation in the WA Goldfields, I wouldn't know as I've never tried one out there. An E-Track wouldn't be my choice by a long way, unless I was in the local park looking for coins.

I'd go the GPX 5000 if cost isn't an issue but they do take some handling if you've never used one before. However, the ML manuals are very good and the factory pre-sets will get you 90% of the gold - if it's there. If the Whites comes to you at no cost and you can't go the hire of the GPX, I'd go the Whites, The Whites GM was "king of the hills" prior to the introduction of the ML SD series in 1994. The GPX is now top-dog but as I've pointed out here, it does miss gold. You might just find what the GPX misses.

Having said all this, I still reckon the GPX with it's Pulse Induction is the best there is currently.

HTH.

Cat

Decan,


I had a look at at the advertising for that Deus machine. They make a lot out of the "wireless" headphone and remote operation. For me, I'd love the wireless headphones as I wear two hearing aids that use "Bluetooth" connectivity. I wish Minelab would put this in thier machines. However, the Deus is simply another VLF machine with a switching system to select different operating frequencies. These can only be used one at a time. They run 4Khz, 8Khz, 12Khz and 18Khz, which are all low range. That would give them some depth but nowhere near a PI machine such the ML. I don't know how good they are in practical terms as I've never used one. But other than the "wireless" thing, they are old technology. But so is the Whites!

Minelab had a machine like this about 20 years ago. It was called the "Eureka". It had two switchable freqs of 8khz and 32 Khz.  I had one and gave it to someone. I didn't like it.

HTH

Cat

About the downside to a Pulse Induction (PI) machine and why the ML can’t “hear” species with fine gold.

The problem with PI machines is that in “transmitting” several freqs in rapid succession into the ground, switching off and then switching on another “Listening” circuit, is that these things, these switchings take time. It’s only nanoseconds because it’s all done with the usual “microchip” that’s in all computers these days. But it does take time,,,,,,,,,”switch on, transmit, switch off, gap, switch on, listen”. Unlike the VLF Transmit and Receive which are both “On” at the same point in time.

The speed of how these things occur with a PI machine depends on how fast the chip can operate. This is known as “The Clock Speed”. On an ML machine it’s pretty rapid but even then we need to allow “time” for the PI detector to do the job for us and give it a chance to “transmit, switch off, gap, switch back on, listen”. That means we have to swing slower than we would with a VLF machine. As we hear all the time “low and slow is the go”. Now we know the reason why.

Long ago, we calculated the optimum swing speed of an SD machine over ground. Some assumptions needed to be made but we worked out that roughly speaking “one metre a second” is about the right speed for the coil over ground. That was with an SD machine but I doubt it’d much faster than this with the newer GPX series. If you try this speed next time you’re out bipping, you’ll find it’s a bit slower than is your natural pace. That is, you need to make a conscious effort to “slow it down” and you’ll find yourself travelling faster than this if you’re not aware. It doesn’t help if you’re constantly thinking about what’s over the next hill either! As the old parachutist saying goes,,,,,,,”one second is one thousand, two seconds is two thousand” so just keep saying to yourself “one thousand, two thousand” and you’ll be talking in seconds. “One thousand – left, one thousand – right”.

So why does the PI miss these species? In order to generate a large enough eddy current such that it can “sense” or “hear it”, the surface area of the metal object has to be “big enough”. Even a pinhead nugget can be big enough if you’re swinging slow enough – as above. If you’re swinging faster, then the machine doesn’t have sufficient time to “switch on, transmit, switch off, gap, switch on, listen” – because you and the coil (which is the listening device) have moved on.  The signal was very faint to start with as the pinhead was only small, so the eddy current would have been only small. So not much to listen to as the eddy was nearly dead and you’d moved too fast. Ya missed it!

These species contain gold that is extremely fine. They’re typical primary source gold or reef gold. If you ever get the chance to look at some ore from a gold mine, chances are you’ll see nothing at all, just rock. That’s because the gold is so fine that it’s sub-microscopic.  As the gold in these species of mine is so fine and surface area of each bit of gold is so small, the PI machine can’t generate a sufficiently large eddy current that can be “heard” by the listening circuit. The eddy effect is not cumulative. Just because there’s a “lot” of gold in the specie doesn’t mean they all combine and make one big signal. The fine gold just makes a lot of very tiny ones, so tiny that they amount to being “silent” to the machine. This was all confirmed when I spoke to Minelab last year.

It’s a bit like going over a solid piece of copper wire that’s big enough to generate a large eddy current on its surface. Try shredding or pulverising the wire into almost invisible, tiny, microscopic bits and the signal won’t be generated such that it can be heard by the PI listening circuit.

Species have always been a problem for Minelab PI machines even from back in the days of the SD. I had a few “magical mystery moments” even back then, but I didn’t know the cause. If the specie has sufficient gold particles that are in some way joined together, then right there is your “surface area” for the eddy current. But if they are all separate particles there’s no “connectivity” and hence no “surface area” and hence no signal.

All very technical but - HTH

Cat

Many thanks Cat,
Your advice has confirmed my intuitive feelings. It will certainly be a rental Minelab GPX model!

Cat,


re reading your original post regarding this strange 4500-5000 specific experience I can see a bit more in it and it truly is an interesting set of circumstances .

Thanx for sharing.