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#1

Bush
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Joined: 24 January 2016
Posts: 404
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27 December 2020 08:20 am

Question to PA. Members & Guests.
When using a magnet over a target to help to facilitate and decipher the material to extract.
Why or How does a Metal Detector register the difference between iron ore stone and small pieces of steel when the iron stone also sticks to the magnet.
In other words why does the detector ignore the iron stone yet signals smaller pieces of man made iron / steel amongst it when their both of the same or
similar composition.
``I`m finding this difficult to phantom. sad

Last edited by Bush (27 December 2020 08:35 am)


The Needs of Necessity Rides Over Legislative Law. No PHD or Masters Degree then my say is regarded irrelevant.
Knowledge is not Wisdom. Common Sense you were Born with.

#2

nucopia
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From: Gone Bush
Joined: 07 July 2015
Posts: 3,623
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27 December 2020 08:33 am

Dig every target is always a good habit to have and yeah iron stone will usually stick to a magnet similar to other Ferris metals.
I had that experience with an ironstone encased nugget in Maryborough sticking to a magnet ..almost tossed it but it was heavy so I didn’t .I had to scratch off some ironstone to see the gold ..6.15 grams before an acid bath 5.1 grams after..


every day is an adventure

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#3

Bush
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Joined: 24 January 2016
Posts: 404
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27 December 2020 08:50 am

Yeh `i` started using the magnet to try and speed up the extraction process but so much iron stone sticking to the magnet became an ordeal.
Still just don`t understand why the detector ignores the iron stone but detects steel smaller than the iron stone.
Question still remains unanswered.


The Needs of Necessity Rides Over Legislative Law. No PHD or Masters Degree then my say is regarded irrelevant.
Knowledge is not Wisdom. Common Sense you were Born with.

#4

Deepseeker
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Joined: 13 August 2018
Posts: 1,701
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27 December 2020 09:09 am

I had a piece just last week from near Rheola, about the size of a large pea. It was dark rusty brown like an Ironstone, and the 5000 loved it loud and clear. However, when I turned on the Iron Reject function and set it to 10, it didn't reject it hmm The Iron reject works as I had been using it on and off all day in a trashy area.

Thinking that maybe there might be some of the good stuff inside, I brought it home with me to test with a magnet (I took the magnet off of the end of my pick handle some time ago, as it was interfering with the NF 25" DD-X as I walked along and it hung down off of my belt near my feet).

When I got home, I got out of the car and took it over to one of our raised garden beds where I use a larger rare earth magnet as part of the system I use to hold the shade cloth down. I was some inches away from the magnet when the rock flew out of my hand and stuck to the magnet. I binned the rock and walked inside, still none the wiser as to what that was all about neutral


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#5

nucopia
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From: Gone Bush
Joined: 07 July 2015
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27 December 2020 09:10 am

What detector are you using ?
I’m no expert but some one on here is sure to have an answer.


every day is an adventure

#6

mbasko
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From: Central West NSW
Joined: 27 January 2015
Posts: 4,815
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27 December 2020 09:29 am

Iron stone & steel aren't the same or similar compositions.

Basically iron stone contains iron compound/s in various levels over 15%. Depending on how rich in iron compound it is it might stick to a magnet but won't signal on a detector. Other pieces will signal on a detector & are commonly referred to as hot rocks.
Most sedimentary rocks contain iron to some degree but not enough to be "iron stone".

Steel is a man made alloy that is predominantly made from pure iron & carbon.

p.s. metal detector timings & ground balancing/tracking is designed to remove most of the ground signal. It will also remove some of the target signal too but steel & other metal targets being pure metal will still have a good signal.
That's why it's important to maintain a good ground balance (fixed or manual) or not keep waving an auto tracking detector over a faint signal. If your ground balance is out it can mask faint signals or auto tracking can in some cases balance it out.
In short & in most cases if the ground balance is good it will remove unwanted noise from the ground effects but leave a clear target response on metals.

Last edited by mbasko (27 December 2020 09:49 am)


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#7

Bush
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Joined: 24 January 2016
Posts: 404
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27 December 2020 09:34 am

Deepseeker wrote:

I had a piece just last week from near Rheola, I was some inches away from the magnet when the rock flew out of my hand and stuck to the magnet. I binned the rock and walked inside, still none the wiser as to what that was all about neutral

Poltagist Lol.
There a pretty powerful magnet them new earth magnets.
When i said to speed up the extraction process `i` mean to identify the object in case it is iron.
but from what you guys are saying is extract the target in any event.

SDC2300 Nucopia.


The Needs of Necessity Rides Over Legislative Law. No PHD or Masters Degree then my say is regarded irrelevant.
Knowledge is not Wisdom. Common Sense you were Born with.

#8

Bush
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Joined: 24 January 2016
Posts: 404
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27 December 2020 09:40 am

mbasko wrote:

Iron stone & steel aren't the same or similar compositions.

Basically iron stone contains iron compound/s in various levels over 15%. Depending on how rich in iron compound it is it might stick to a magnet but won't signal on a detector. Other pieces will signal on a detector & are commonly referred to as hot rocks.
Most sedimentary rocks contain iron to some degree but not enough to be "iron stone".

Steel is a man made alloy that is predominantly made from pure iron & carbon.

Thanks mbasko.
It`s not in my field of expert`ae & i know you know that.
cheers mate. smile


The Needs of Necessity Rides Over Legislative Law. No PHD or Masters Degree then my say is regarded irrelevant.
Knowledge is not Wisdom. Common Sense you were Born with.

#9

goldierocks
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Joined: 10 January 2015
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27 December 2020 12:56 pm

Bush wrote:
mbasko wrote:

Iron stone & steel aren't the same or similar compositions.

Basically iron stone contains iron compound/s in various levels over 15%. Depending on how rich in iron compound it is it might stick to a magnet but won't signal on a detector. Other pieces will signal on a detector & are commonly referred to as hot rocks.
Most sedimentary rocks contain iron to some degree but not enough to be "iron stone".

Steel is a man made alloy that is predominantly made from pure iron & carbon.

Thanks mbasko.
It`s not in my field of expert`ae & i know you know that.
cheers mate. smile

It is not a function of the iron content but on the iron minerals present (broadly grouped as limonite. hematite, maghemite and magnetite), and their abundance.
Limonite = non-magnetic
Hematite = non=magnetic
Maghemite = moderately magnetic
Magnetite = highly magnetic

Often more than one iron mineral is present in a sample. For example, bushfires can convert non-magnetic limonite and hematite to magnetic maghemite on the surface of the ground.


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

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#10

Deepseeker
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27 December 2020 01:41 pm

In an branch of science that continually confounds me, thank you for the above explanation goldierocks thumbsup


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#11

mbasko
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From: Central West NSW
Joined: 27 January 2015
Posts: 4,815
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27 December 2020 02:27 pm

goldierocks wrote:

It is not a function of the iron content but on the iron minerals present (broadly grouped as limonite. hematite, maghemite and magnetite), and their abundance.
Limonite = non-magnetic
Hematite = non=magnetic
Maghemite = moderately magnetic
Magnetite = highly magnetic

Often more than one iron mineral is present in a sample. For example, bushfires can convert non-magnetic limonite and hematite to magnetic maghemite on the surface of the ground.

You forgot the carbonates & silicates?
Siderite = non-magnetic unless heated
Chamosite = weakly magnetic
smile thumbsup


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#12

goldierocks
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27 December 2020 02:33 pm

Deepseeker wrote:

In an branch of science that continually confounds me, thank you for the above explanation goldierocks thumbsup

One other bit of information might also be useful. The different iron oxides form in different ways, which one could group as PRIMARY and SECONDARY. It has relevance to the occurrence of gold in them. Primary being those that form before or simultaneously with the gold. secondary being those formed later by weathering of primary gold deposits.

(1) All of the iron minerals can be primary (e.g. sedimentary limonite, hematite and maghemite iron ores, magnetite banded iron formation, Hamersley-type hematite ores)
(2) Limonite is the most common (abundant) form of secondary iron oxide formed during weathering. It forms usually within 30 m of surface by oxidation of other iron minerals and by oxidation of sulphide minerals in primary gold deposits. Rainwater high in oxygen from the atmosphere, percolates down into the ground and alters the earlier minerals. Gold can occur in the iron-rich ferricrete of the laterite, usually derived from within the earlier minerals.
(3) Hematite can form from hot, gold-bearing waters when gold deposits first form (e.g. at Tennant Creek). Magnetite can also (e.g. Ernest Henry in the Cloncurry district, at Olympic Dam)

1609041502_mt-cpy_ernest_henry.jpg

(4) Gold can be deposited when hot waters containing gold hit EARLIER iron minerals such as hematite and magnetite (e.g. banded iron formation (magnetite) at Tennant Creek, magnetite bodies at Tennant Creek).

1609041468_banded_iron_formation_hamersley.jpg

(5) Ferricrete (iron-rich laterite, usually hematite and limonite) has formed at surface by weathering over much of Australia during fairly recent times geologically (the last 30 million years or so). If laterite forms over earlier gold deposits of any type, the surface water in cracks can dissolve gold from it, which then moves sideways until it hits iron oxide minerals such as magnetite and maghemite of any age, including ferricrete duricrusts formed at the same time as the laterite, and gold will crystallize out in these iron oxides. Much of the "noisy" ground in central Victoria is of this type - the gold can be primary or secondary, but much of the iron oxide is secondary limonite and maghemite formed at surface from iron weathered out of the iron-rich sedimentary rocks such as slate, or from granite, or from oxidised sulphide minerals..

1609041526_ferricrete_hill_cap.jpg
1609041526_ferricrete.jpg

1609041788_pisolitic_ironstone_gravel.jpg

So you might have a lump of gold in a mixture of different iron oxides in a single district. For example around Cloncurry, a sample of fresh rock might contain primary magnetite and primary gold. Nearby at the same deposit you might have primary gold associated with secondary limonite that formed by weathering of magnetite and sulphide minerals such as pyrite and pyrrhotite. Further along the outcrop might be a lump of secondary limonite as part of a laterite, which contains secondary gold derived b y weathering of a primary magnetite-rich gold deposit (with probably a bit of primary gold still within it as wll, perhaps a few lumps of primary magnetite).

No wonder that you are confused!

However it is worth trying to learn the iron oxides. For example, if gold is on a lump of fresh magnetite in say the Mt Magnet district (such as at Watertank Hill mine), there might be a primary gold deposit in banded iron formation nearby. So if you see a banded iron formation on the ridge above you, it might be worth checking it for gold. Alternatively, sometimes in central Victoria of you are having trouble with noisy ground, it might be worth focussing on areas where most of the lateritic ironstone has been washed away, leaving fresher unweathered rock such as slate and sandstone (the gold will not have necessarily have washed away - it is six times heavier than the rock and four to six times heavier than limonite).

Why I say that learning a bit of geology can improve your chances of finding gold.

Last edited by goldierocks (27 December 2020 03:03 pm)


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

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#13

XLOOX
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From: Inglewood Fault, QLD
Joined: 21 August 2019
Posts: 99
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27 December 2020 04:23 pm

Bottom line - Iron is both magnetic & very conductive ( just not as conductive as more precious metals), ironstone is magnetic but not very conductive.

Regardless of whether VLF or PI ,your metal detector Transmit field produces tiny electric currents in high conductivity materials and these currents cause their own tiny electromagnetic fields a fraction of a second later that the detector Recieve coil picks up & the detector then identifies as metal.Beep !

In low conductivity materials there is nearly no current generated so the return fields are nearly too weak to be picked up at all but more importantly the timing of the return field from ground/ mineral is also different to that from a normal metal target ( very little delay for ground/minerals) so a good detector can still tell the difference.... up to a point.

There is another effect with VLF detectors and that is a highly magnetic mineral in the ground distorts the transmit field, which is then picked up by the recieve coil and unless it is a really good detector it will confuse it as the distorted transmit field is 1000x stronger than the return from a target.. This is why a PI is much better when lots of ironstone around.

PS Goldierocks that is the best info on ironstone gold relationship I have seen. It is a keeper in my permanent collection

Last edited by XLOOX (27 December 2020 04:31 pm)


1985-2005 Garretts ADS Deepseeker x 2- now THATS a slow learner !
2017-2021 Whites TDI SL 16V+Sadie, Makro Gold Kruzer, QED PL3+14x9 Evo, Elite18

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#14

goldierocks
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27 December 2020 04:28 pm

Strictly, SOME (in some areas most) ironstone is magnetic. But a bit irrelevant to your operational description I realise.


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

#15

steve f
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Joined: 15 August 2018
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27 December 2020 04:32 pm

so after all that, like nucopia said in a previous post - dig every target

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#16

mbasko
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From: Central West NSW
Joined: 27 January 2015
Posts: 4,815
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27 December 2020 05:14 pm

steve f wrote:

so after all that, like nucopia said in a previous post - dig every target

Dig every target is very good practice in theory but if you get back to the original question:

Why or How does a Metal Detector register the difference between iron ore stone and small pieces of steel when the iron stone also sticks to the magnet.
In other words why does the detector ignore the iron stone yet signals smaller pieces of man made iron / steel amongst it when their both of the same or
similar composition.

To just say dig every target doesn't really answer the question.
Got a bit long winded on the why's of magnetic iron stone & iron oxide formation side of it but good knowledge to have on board regardless. thumbsup
In a nut shell it's what good detectors are designed to do - ignore ground signal & give a response to metal. Unfortunately there are some "hot rock" compositions even the best detectors can't cancel out.
I'd more take on board this from Nucopia:

I had that experience with an ironstone encased nugget in Maryborough sticking to a magnet ..almost tossed it but it was heavy so I didn’t .I had to scratch off some ironstone to see the gold ..6.15 grams before an acid bath 5.1 grams after..

I'm more than sure that's got more than a few people over the years & some have even tossed away golden "hot rocks".

Last edited by mbasko (27 December 2020 05:16 pm)


Everything we use comes from mining or farming.

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#17

goldierocks
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27 December 2020 06:22 pm

mbasko wrote:
steve f wrote:

so after all that, like nucopia said in a previous post - dig every target

Dig every target is very good practice in theory but if you get back to the original question:

Why or How does a Metal Detector register the difference between iron ore stone and small pieces of steel when the iron stone also sticks to the magnet.
In other words why does the detector ignore the iron stone yet signals smaller pieces of man made iron / steel amongst it when their both of the same or
similar composition.

To just say dig every target doesn't really answer the question.
Got a bit long winded on the why's of magnetic iron stone & iron oxide formation side of it but good knowledge to have on board regardless. thumbsup
In a nut shell it's what good detectors are designed to do - ignore ground signal & give a response to metal. Unfortunately there are some "hot rock" compositions even the best detectors can't cancel out.
I'd more take on board this from Nucopia:

I had that experience with an ironstone encased nugget in Maryborough sticking to a magnet ..almost tossed it but it was heavy so I didn’t .I had to scratch off some ironstone to see the gold ..6.15 grams before an acid bath 5.1 grams after..

I'm more than sure that's got more than a few people over the years & some have even tossed away golden "hot rocks".

Be warned that manganese oxide (very black) coats some gold nuggets, and they have been discarded (e.g. St Arnaud in Victoria).

1609053702_mn_gold_nugget.jpg


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

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#18

goldierocks
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27 December 2020 06:40 pm

mbasko wrote:
goldierocks wrote:

It is not a function of the iron content but on the iron minerals present (broadly grouped as limonite. hematite, maghemite and magnetite), and their abundance.
Limonite = non-magnetic
Hematite = non=magnetic
Maghemite = moderately magnetic
Magnetite = highly magnetic

Often more than one iron mineral is present in a sample. For example, bushfires can convert non-magnetic limonite and hematite to magnetic maghemite on the surface of the ground.

You forgot the carbonates & silicates?
Siderite = non-magnetic unless heated
Chamosite = weakly magnetic
smile thumbsup

Quite true - but I was concentrating on the dark iron oxides that cause people trouble and are associated with gold - I should have said iron oxide minerals. Siderite and chamosite are not very relevant in that sense, although they often also occur in banded iron formation and can weather to iron oxides. There are other iron minerals as well, such as all the sulphides - pyrite, pyrrhotite, troilite, greigite and mackinawite, and the rare iron silicate fayalite, and these can all weather to iron oxides. Also, I wanted to keep it simple (e.g. what I call "limonite" I am using as a loose term for the hydrous iron oxide minerals, that include ferrihydrite, akaganéite, feroxyhyte, goethite, lepidocrocite and limonite). But people know these hydrous iron oxides as typically brown to yellow-brown and often rather "earthy" looking, and usually loosely call them limonite or goethite. Let's not confuse people with detail - for metal detecting, limonite,

1609055528_limonite.jpg

hematite (red),

1609055555_hematite.jpg

maghemite (red)

1609055651_maghemite.jpg

and magnetite (black)

1609055498_magnetite.jpg

are sufficient ops

Last edited by goldierocks (27 December 2020 06:54 pm)


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

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#19

mbasko
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From: Central West NSW
Joined: 27 January 2015
Posts: 4,815
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27 December 2020 06:42 pm

goldierocks wrote:

Be warned that manganese oxide (very black) coats some gold nuggets, and they have been discarded (e.g. St Arnaud in Victoria).

https://www.prospectingaustralia.com.au … nugget.jpg

Seen similar from around Hill End (Tambaroora) NSW in places too.
An old mate of mine found a handful & was disgusted at the "ugly" gold. I offered to take them off his hands but he declined the offer. lol
I've also seen a few examples of "magnetic" gold (specimens) including one I found myself.
Bottom line if a rock gives a signal on a detector it needs to be investigated.

Last edited by mbasko (27 December 2020 06:45 pm)


Everything we use comes from mining or farming.

#20

goldierocks
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Joined: 10 January 2015
Posts: 3,260
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27 December 2020 06:56 pm

mbasko wrote:
goldierocks wrote:

Be warned that manganese oxide (very black) coats some gold nuggets, and they have been discarded (e.g. St Arnaud in Victoria).

https://www.prospectingaustralia.com.au … nugget.jpg

Seen similar from around Hill End (Tambaroora) NSW in places too.
An old mate of mine found a handful & was disgusted at the "ugly" gold. I offered to take them off his hands but he declined the offer. lol
I've also seen a few examples of "magnetic" gold (specimens) including one I found myself.
Bottom line if a rock gives a signal on a detector it needs to be investigated.

So easy to remove the black coating - a rinse in weak hydrochloric acid would do it, and will not touch the gold. Just don't use aqua regia!


Robert Benchley...
I have kleptomania, but when it gets bad, I take something for it.

#21

Bush
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Joined: 24 January 2016
Posts: 404
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27 December 2020 07:03 pm

Hi Buoys & Gulls,
Just wondering if any one knows anything about The Goldseeker 12000 VLF /TR/3D.
Just acquired one for some exchange of welding rust repairs.
Tried the internet & search bar on PA but not much info about the creatures.
Interesting old relic `i` must say.
Cheers Bush.


The Needs of Necessity Rides Over Legislative Law. No PHD or Masters Degree then my say is regarded irrelevant.
Knowledge is not Wisdom. Common Sense you were Born with.

#22

mbasko
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From: Central West NSW
Joined: 27 January 2015
Posts: 4,815
Member
27 December 2020 07:06 pm

goldierocks wrote:

So easy to remove the black coating - a rinse in weak hydrochloric acid would do it, and will not touch the gold. Just don't use aqua regia!

After he declined my kind offer lol I told him to give them a soak in brickies acid. They came out nicely.
I don't play around with acids much at all these days with the kids around. Can't go to the shed without at least the 4yo following me.
Aqua regia would be a definite no go for me full stop. Nowhere near set up for using that or reclaiming the gold. tongue lol

p.s. just a caution to. Cleaning an old shed up last year & found some Alibrite that was leaking out the container. Don't know how long it had been there, looked like years, but the original container appears to have deteriorated.

Last edited by mbasko (27 December 2020 07:58 pm)


Everything we use comes from mining or farming.

#23

Bush
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Joined: 24 January 2016
Posts: 404
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27 December 2020 07:19 pm

Sorry guys `i` didn`t mean to interrupt you were All on a Great Roll of information above.
Keep going invaluable info i must say.
My Q could be answered later at your discretion.
Cheers .
.


The Needs of Necessity Rides Over Legislative Law. No PHD or Masters Degree then my say is regarded irrelevant.
Knowledge is not Wisdom. Common Sense you were Born with.

#24

mbasko
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From: Central West NSW
Joined: 27 January 2015
Posts: 4,815
Member
27 December 2020 07:23 pm

Bush wrote:

Hi Buoys & Gulls,
Just wondering if any one knows anything about The Goldseeker 12000 VLF /TR/3D.
Just acquired one for some exchange of welding rust repairs.
Tried the internet & search bar on PA but not much info about the creatures.
Interesting old relic `i` must say.
Cheers Bush.

Can't help with the 12000 Bush but you might be able to use the 15000 manual to help a bit?
https://www.google.com/url?sa=t&source= … mQn0qdIyRA
Someone like Reg Wilson or Nenad might be able to help with it?


Everything we use comes from mining or farming.

#25

Bush
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Joined: 24 January 2016
Posts: 404
Member
27 December 2020 07:28 pm

Their both Top Blokes .
Thank mbasko ~i` know i`m sometimes a bit impulsive.
Keep going with the above Great stuff.

Last edited by Bush (27 December 2020 07:29 pm)


The Needs of Necessity Rides Over Legislative Law. No PHD or Masters Degree then my say is regarded irrelevant.
Knowledge is not Wisdom. Common Sense you were Born with.


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