Undetectable GOLD!

[Moneybox]

In my opinion it has little to do with the detector. It's all in the form of the gold. This is not alluvial gold even though Liz found it in a river it is best described as elluvial gold. We've found a couple of patches of it recently.

https://www.prospectingaustralia.com/forum/viewtopic.php?id=21526&p=2

This patch was so difficult that we got the Jackwinder out to extract the gold that we was sure was there.

The gold is very sharp so you'd expect it to go off like a bit of wire but the GPX just ignores it and the SDC only picks up the bigger bits. The GPZ7000 has the same problem. It was not detectable with the GPX4500 and even though the SDC found some it was only bigger bits over 0.2g when the SDC is quite capable of finding alluvial gold 1/10th of that size.

This gold averaged 0.25g each. I doubt that's all that was there but that's as small as the SDC would detect and the GPX4500 only found the largest one at 1.95g.

Quite a lot of this gold was the same. We only got the bigger bits with the GPX4500 and the SDC failed to get anything very small as it usually would. You can see that there's a lot of rock still stuck to the gold becuse it hasn't been cleaned by alluvial action.

 

[Ridge Runner]

WTG MB, that's a heck of a hall, :Y:

Do you own a VLF ? because it would be good to know if they could see any of them bits,

thanks for posting them.

John.

 

[Moneybox]

We have a GMT but it's not all that good in WA's mineralization.

 

[Ridge Runner]

Yeah tough ground always has the last word aye,

thanks again,

John.

 

[hAyyoUinAU]

Interesting.

 

[BigWave]

Hi MB, I believe that the gold in WA is of two types:
1. Alluvial/Elluvial gold, which has moved from reefs, and
2. Grown gold, which has grown due to precipitation of minute traces of gold dissolved in subterranian waters.

I reckon (IMHO) it is this second type of gold that is hard to detect because it was never solid to start with and grows in a crystalline form that does not offer strong eddy current loops..

You can tell by pictures of WA gold that some are chunky (reefy) type gold, whereas that shown by MB has a totally different look.
I reckon that if it was rumbled, where the surface gold was mashed together, it would then be easily detectable.

Whilst the article of below references the GT, I believe that it likely better describes this WA gold

http://www.google.com.au/url?sa=t&r.../thread/2938&usg=AOvVaw24g46_0gscrNT0pSYrQy8d

Just speculation? Maybe, but food for thought.

 

[hAyyoUinAU]

I think it has to do more with the fact that Australia is the oldest land in the world.

Anything else is speculation. The whole lightning bolts making big nuggets was another theory I have heard too.
God knows. I just like the fact that its there in the first place.

I appreciate a plate full of nuggets that are said to not be detectable by GPX, SDC or GPZ, however, video of this happening would be a lot better.
That was the idea of this topic, to upload video of gold that won't detect with one machine but will maybe with another.

Well at least you got the undetectable gold and a lot of it, so well done either way.

 

[hAyyoUinAU]

Also, stupid question but, what is a Jackwinder? Sorry, I just never heard of it before

 

[Moneybox]

Also, stupid question but, what is a Jackwinder? Sorry, I just never heard of it before

The Jackwinder is made by Jack , Outback on this site, from Broken Hill. It's still in prototype form so I'm not free to show it here but I'm sure Outback can give you more information.

 

[Moneybox]

Hi MB, I believe that the gold in WA is of two types:
1. Alluvial/Elluvial gold, which has moved from reefs, and
2. Grown gold, which has grown due to precipitation of minute traces of gold dissolved in subterranian waters.

I reckon (IMHO) it is this second type of gold that is hard to detect because it was never solid to start with and grows in a crystalline form that does not offer strong eddy current loops..

You can tell by pictures of WA gold that some are chunky (reefy) type gold, whereas that shown by MB has a totally different look.
I reckon that if it was rumbled, where the surface gold was mashed together, it would then be easily detectable.

Whilst the article of below references the GT, I believe that it likely better describes this WA gold

http://www.google.com.au/url?sa=t&r.../thread/2938&usg=AOvVaw24g46_0gscrNT0pSYrQy8d

Just speculation? Maybe, but food for thought.

BW most of this gold seems to come from calcrete, I guess that's really limestone with a WA name :/

 

[BigWave]

Hi MB, If you read of supergene enrichment, you will note that the gold is very slowly leached from its source at an oxidising layer (acidic), and precipitating from solution in a reducing layer (basic). Such a layer would be calcrete.
There are many very rich supergene enrichment deposits of gold (and many other minerals) around Australia.
That is not theory.
The article that I referenced was just a simple explanation. There's much greater depth reading of supergene enrichments in geological and other scientific papers.
What I was hypothesising was that maybe it's this type of gold that is more difficult to detect than chunky eluvial and alluvial gold from reefs (which were formed in a hypogene process).

 

[Bjay]

got this little one a few days ago with the sdc, only barely picked it up and was basically on the surface. Not the best pic but weighs just under .2 and should have screamed on sdc. Rubbed on coil of a z and much the same, only faint, 5000 with 12 inch evo nothing, 5000 with 14 x9 evo nothing. Never seen it before but some golds just hard to pick up i geuss.

 

[BigWave]

Moneybox was kind enough to send me two samples of his undetectable gold after their latest Pilbara pilgrimage.
0.7 and 0.6g - they should howl on most detectors.
Whilst I haven't tried the samples under any detectors, I have noted:
1. They are light for their size compared to nuggety gold (little heft),
2. Appear finely crystalline to the naked eye,
3. The gold is dispersed in a quartz host (see image below),
4. Good electrical conductivity was evidenced with a multimeter over most areas.
So, certainly these are not Lateritic (forming in laterites) due to the strong presence of quartz. I was hoping they were supergene enrichments.
I'm no geo, but I believe that this is eluvial primary gold coming from an orogenic process but likely not secondarily enriched to form larger solid nuggets.
The gold is heavily interspersed in quartz to the point that, whilst conductive across large areas, the tortuous shape that eddy currents would have to take around the quartz inclusions would not permit any significant "back emf" (and a very quickly decaying one) that would be easily detectable.
Will be interesting to try with both PI and VLF detectors over the next few weeks when I can get out again.
Any real geos out there - please correct me if I have goofed in my understanding.
I'd really like to explore undetectable supergene gold - anyone got any?

 

[hAyyoUinAU]

So I gather a pin pointer would not pick it up either?

Would be interesting to know the actual percentage of gold in that sample.

 

[BigWave]

Good point. I'll try a pin-pointer and SG tonight.

 

[Ridge Runner]

If you are going to test it with a VLF of any brand try using one with a 5 or 6 inch concentric coil because they are normally pretty hot on bits like that, Also LF (vlf) machines should get it under normal conditions,

Good luck with the test and thanks for making the effort, looking forward to your results,

J.

 

[BigWave]

1. Detecting the "undetectable gold" with MineLab Pro-Find Pinpointer
The MineLab Pro-Find (turned up full bore) detects them both from ~1cm, but chunky gold around the same physical size was consistently detected from ~ 2cm (very close to double the range) using pieces of varying shape.

Then tried a chunky nugget about half the size, and picked it up at around 1.5cm (to be expected - I guess).

2. Detecting the "undetectable gold" with a Garret "Carrot" Pinpointer
The Garret Pro-Pinpointer AT (again on full bore) detects the specimens at ~1.5cm, and similar sized chunky gold at ~ 3cm (again - close to double the range), so considerably better than the MineLab, but I rarely use this pin-pointer as it drives my 4500 nuts (even when turned off) so I either leave it behind or have daughter carry it.

3. Pinpointer Conclusion
Significantly poorer detection performance on the undetectable gold with pinpointers than on chunky nuggets, but at least they're detectable with the pin-pointers.

4. Specific Gravity Testing
I did a rough SG (rough due to small specimen sizes around 0.7g) showing ~37% Au by volume and ~80% Au by weight.

5. Next Up
I will try on both a 4500 (say 14"*9" Evo) and an eTrak (around an 11" coil) this weekend (that's all I have), and will try later with friends' Zed and SDC detectors.

PS:
If anyone has some secondary gold sourced from a known laterite field that is difficult to detect (the nuggets - not the field), I'd like to buy a few please (or at least loan a sample or two) to try.

 

[Ridge Runner]

5. Next Up
I will try on both a 4500 (say 14"*9" Evo) and an eTrak (around an 11" coil) this weekend (that's all I have), and will try later with friends' Zed and SDC detectors.

PS:
If anyone has some secondary gold sourced from a known laterite field that is difficult to detect (the nuggets - not the field), I'd like to buy a few please (or at least loan a sample or two) to try.

I am pretty sure that you will find that E-trac will not pick it up because they are not sensitive enough, most single frequency machine should/might ?

Great report, thanks again.

J.

 

[hAyyoUinAU]

1. Detecting the "undetectable gold" with MineLab Pro-Find Pinpointer
The MineLab Pro-Find (turned up full bore) detects them both from ~1cm, but chunky gold around the same physical size was consistently detected from ~ 2cm (very close to double the range) using pieces of varying shape.

Then tried a chunky nugget about half the size, and picked it up at around 1.5cm (to be expected - I guess).

2. Detecting the "undetectable gold" with a Garret "Carrot" Pinpointer
The Garret Pro-Pinpointer AT (again on full bore) detects the specimens at ~1.5cm, and similar sized chunky gold at ~ 3cm (again - close to double the range), so considerably better than the MineLab, but I rarely use this pin-pointer as it drives my 4500 nuts (even when turned off) so I either leave it behind or have daughter carry it.

3. Pinpointer Conclusion
Significantly poorer detection performance on the undetectable gold with pinpointers than on chunky nuggets, but at least they're detectable with the pin-pointers.

4. Specific Gravity Testing
I did a rough SG (rough due to small specimen sizes around 0.7g) showing ~37% Au by volume and ~80% Au by weight.

5. Next Up
I will try on both a 4500 (say 14"*9" Evo) and an eTrak (around an 11" coil) this weekend (that's all I have), and will try later with friends' Zed and SDC detectors.

PS:
If anyone has some secondary gold sourced from a known laterite field that is difficult to detect (the nuggets - not the field), I'd like to buy a few please (or at least loan a sample or two) to try.

Great stuff. And good to see that the pin pointers picked it up. The reduced distance would make sense if the gold content is less as well.

Will be interested in the results from ZED. :Y:

 

[Heatho]

Pro pointer AT operating frequency 11.5khz

Couldn't find the operating freq or the pro find 25

I doesn't surprise me that VLF pinpointers will detect those species.

Detectors like the Goldmonster, Equinox (in 40khz mode) GB2 and other high frequency VLF's would certainly detect them as well I'd say. They must just fall into the timing holes of the GPX units, I'm really interested to see if the ZED and SDC can detect them, I'll be surprised if they don't, especially if the SDC doesn't.

Looking forward to the next results BW. :Y: