Metal detectors And hot Rocks

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Post  adrian ss on Mon Oct 28, 2019 8:54 am

If you had to select a metal detector that can see through hot rocks and find gold which would you go for?
I can think of several vlf & Pi but all of them still bang on the occasional HR.
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Post  PeterInSa on Tue Oct 29, 2019 12:23 pm

Definitely not a ML 3000 or earlier Pi machine, years ago had to travel across country to pick up a vehicle part in Laverton WA, on the return stopped at an old patch and using a borrowed 3000 detected for 5 minutes prior to putting the 3k back in mates vehicle, the hot rocks were everywhere, on the 4500 the same signal would be a small nugget. At the time had a 2200 as a backup to my 45, Back in Adelaide sold the 2200 along the lines of, if am not prepared to use a 3000 in WA, less enthusiastic to use a 2200.

Incidentally came back to the old patch this year and we still picked up small nuggets with a 4500, 2300 x 2 and a 7K.

Having said the above, however, its what you get used too, if I had never owned a 45 probably would be quiet happy using the 3000 or the 2200.

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Post  Kon61gold on Tue Oct 29, 2019 2:02 pm

With discrimination, always comes a trade off Adrian. I know not of any current hand held pulse out there, that can completely see through hot rocks, even though it might have or offer discrimination capabilities, without a trade off & that trade off is on depth.
The best discriminating capabilities on any hand held detector would have to be on a single frequency VLF, but VLF's suffer the greatest of depth loss as the degree of in ground mineralization increases.
A majority of todays VLF's discriminate well the iron from a non metallic target, but again, at the cost of depth & since most the easy gold has already been found in many a current gold producing locality, all that is left are the smaller nuggets or the occasional larger slug at depth. So any form of discrimination used out on any gold field today, would only be good for separating the ferrous junk from the odd bit of aluminium bottle cap (less there be a nice size slug of gold, shallow buried in amongst that junk)
Even the newly designed PI Ground Expert Pro (from DRS Electronics Germany) having the best discrimination ever seen on any a pulse induction detector, comes at a great cost to loss of depth & depth (or more of it) is all that is left today, in the hope of finding more gold. It is something we cannot afford to lose.

Cheers Kon. T25
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Post  adrian ss on Tue Oct 29, 2019 2:59 pm

Guess I agree with you blokes.

With a VLF I still use the ole Boing sound to id neg hot rocks and lift the coil a bit on the positive rocks. The signal drops away quickly on these. and tends to not repeat in the same position every time. It is still possible for gold to be blanked out beneath these hot rocks. It really is a matter of knowing your machine and that takes practice, practice, practice.
My Finny is pretty quiet on HRs. Also I am led to believe that the 5000 has some good settings and timings (Smooth, Enhance, Fine) that chill the hot rocks quite well??.....But is that at the expense of loosing small nuggs??
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Post  Nightjar on Tue Oct 29, 2019 3:10 pm

adrian ss wrote:But is that at the expense of loosing small nuggs??

Yep! The hotrocks with a lump of gold hanging on. Wink







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Post  joe82 on Tue Oct 29, 2019 6:33 pm

i can run over hotrocks with the 7 and have hardly a murmur where the gpx detectors sound off like a nuggy I have tested many a target with my mates 4500 and had the 7 not make a sound????????

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Post  PeterInSa on Tue Oct 29, 2019 7:52 pm

Re (I have tested many a target with my mates 4500 and had the 7 not make a sound????????)

And with a small change in the Threshold tone maybe a nugget............or.....

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Post  hugh62 on Tue Oct 29, 2019 10:00 pm

adrian ss wrote:If you had to select a metal detector that can see through hot rocks and find gold which would you go for?
I can think of several vlf & Pi but all of them still bang on the occasional HR.

     Mmm I think there'd be quite a few of us that would like to know as well ,be helluva break thru in detector technology . Tried years ago a little experiment with my 5k on some ground smothered in hematite and magnetite ,with the odd banded iron thrown in ,so I set the 5 up so it would only respond to what I thought were more positive target signal response's , (  with me keeping in mind that the high possibility's that they would just be more enriched with iron of course  ,but optimistically hoping they may also have a high Gold content also Rolling Eyes ) and picked up any hematite and magnetite rocks ,with the intentions of dollying them up and panning them off ,well after dollying up one or two lots I gave it up as a bad joke ,my god those rocks are hard Neutral
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Post  Kon61gold on Tue Oct 29, 2019 11:14 pm

Hey Joe, may I ask what type of coil was used on your mate's 4500 at the time of testing over hot rocks (was it of mono configuration or DD?) If he had any type of mono coil on, that would explain why hot rocks were sounding off like gold nuggets.

Cheers Kon.  T25
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Post  joe82 on Wed Oct 30, 2019 6:28 am

yeah kon the 12 evo if there wer iffy signals he got I would run the 7 over them love the way 7 handles that type of hot ground but yeah the evo range sings out, I had the 19 evo out on my 5k for something different last weekend (managed a 12gm solid at depth) but had a couple of ground (hot rock) noises aswell dig down balance on waste pile for them to disappear

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Post  adrian ss on Wed Oct 30, 2019 7:45 am

What Kon said; The DDs are better in hot rock territory although not so flash on the tiny nuggs.
    I tried a 12 x 8 DD on my TDI but it did not like it at all. On the other hand I find the TDI to be fairly good over hot ground with the mono's.
Whether in Hi or Lo conductivity mode the TDI is quiet over hot ground but the diff is that nuggs between very small up to around the 5-6 g mark will give a High tone in Lo conductivity mode and nothing in Hi. There is a point somewhere between 5g and 7 g that the tone will change to Low and then Hi conductivity mode is required. If you search in "All Conductivity' then the tecta can get a bit noisy but it won't miss much  gold. So I guess if you are just chasing the small stuff below 6g with the TDI in hot ground then Low Conductivity might be the idea.
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Post  moredeep on Wed Oct 30, 2019 5:22 pm

I know with the 5000 if I ground balance next to a suspected hot rock and get say a 25% or 50% reduction in response I'll leave it confident that its hot rock/mineralisation.
To be double sure I'll balance directly over the target if i get a reduction in response I'm fairly confident the it's not a metal target as such.
If I'm still not sure I'll scrape a few cm off and balance again over the ?hotrock
Some fully sick iron stone won't balance out or reduce in response so its dig dig dig .
Some say I might balance out a gold nugg but I have experimented ,its very hard to balance out a "REAL" target.

Cheers moredeep
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Post  Kon61gold on Wed Oct 30, 2019 7:51 pm

T04  Fellas, the only time in 30 odd years of detecting, I'v ever seen a positive in ground target signal, be cancelled out by a detector, was when using a Gold Bug 2.
I got a very faint in ground signal when working in All Metal, only to have that same signal dis-appear on me the moment I flicked the switch into discrimination.  Showed a mate where I got the signal & he went over it with at the time the newly released SD2000, only to receive a clear distinct signal response right over the same spot. To cut a long story short, the target responce turned out to be a 4.5 gram nugget, sitting vertically almost 9 inches down, in mineralized clay. Shocked

Cheers Kon. T25
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Post  moredeep on Wed Oct 30, 2019 10:15 pm

I still have the sound embedded in my head to this day of my first nuggi I ever got,that was with the sd2000 kon,
I tried and tried to balance it out thinking it was ground noise,it sounded like a deep whoa whoa noise,
I Just couldn't balance the bloody thing out ,had me baffled being a novice with the 2000,so I dug it , it started making that classic 2000 big target growling noise .
And bingo down 18' in the beautiful white pipe clay soil a 15 ozer .
I ventured out tonight to my favorite mongrel hot rock spot and still got sucked into digging a noise that would not balance out or reduce in response to balancing right on top of it.
Down about 6 inches some of the best PINK mineralised clumps you'll ever see,ONCE THE BIG CLUMP WAS OUT IT WAS ALL OVER, a very quiet hole indeed.
Overall I can confidently balance out most hot rock but there is still that little sucker that will suck me and make me dig a bloody big hole on a hot evenings night.
The cold frosty beer took away the disappointment of the tricky little hot rock:lol:

cheers moredeep
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Post  Kon61gold on Wed Oct 30, 2019 10:43 pm

Agree with that one moredeep. There will always be that hot section or pocket of ground, that cannot cancel out no matter what we do, necessitating a dig, only to lose or weaken all form of signal response, the moment the hot pocket of whatever, is taken out of the ground & evenly spread out.
Count our lucky stars those type of signals, ain't one in every two, or we would have packed in detecting a long time ago. Shocked Q35

Cheers Kon. T25
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Post  Nightjar on Wed Oct 30, 2019 11:18 pm

Here is a very hot hot rock detected with my 4500 + 11" Commander Mono out Ora Banda way.
This little beauty jumped out of the spoon to cling onto the magnet. A close examination revealed a tiny glimmer of gold.
Later I managed to prise a piece of the iron stone away to reveal that this was a nugget completely encased with ironstone.
Dig every target and check hot rocks carefully especially the shiny ironstone ones.
I never fiddle around with ground balancing etc around or over a target.
We are very fortunate in the area we go too, majority of gold is only a few scrapes deep and bed rock is a mere 150mm/200mm deep.

Metal detectors And hot Rocks Ggt910






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Post  butch on Tue Dec 10, 2019 3:35 pm

adrian ss wrote:If you had to select a metal detector that can see through hot rocks and find gold which would you go for?
I can think of several vlf & Pi but all of them still bang on the occasional HR.

Detect in the cooler months; They are heated up by the sun that's why they're called hot rocks.
My SD2000 was unusable with a mono coil in November in WA, put on the DD and eliminated most of them. Just hanging around now till April.
Getting exited..  bounce

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