northwest Are big coils throughly feasible for gold detectors and up to what point?
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australian electronic gold prospecting forum.com  |  Detector Technology and Electronics and new detectors  |  Detector Coils (Moderator: Goldman)  |  Topic: Are big coils throughly feasible for gold detectors and up to what point? 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: Are big coils throughly feasible for gold detectors and up to what point?  (Read 895 times)
bugwhiskers
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« Reply #40 on: Sunday January 27 2019 18:26:53 AEDT PM »

One rock regardless of how big does not a real test make. Get on a plane or put a detector on one.
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« Reply #41 on: Sunday January 27 2019 18:52:30 AEDT PM »

  
  
The image below is a Hot Rock being suspended by the edge of a square Super Magnet.

It serves to demonstrate just how much Iron can be in rocks in the Victorian goldfields.
Nice. Hand it over... happy face
Do you have a big one, let say 4-5 kg or so?

Also is the soil littered with small particles of these rocks or are the rocks rather contained and the soil less Iron loaded?

I am asking because on one of our mineral test sites in BG the rocks represent very well the real conditions with the exception of conductivity. The rocks are not conductive, but the soil is on top of been loaded with millions of nasty magnetic rocks. So after it rains is the big fun. smile

our worst soils are full of  magnetic  minerals (mainly  superparamagnetic materials; magnetite, maghemite and titano-hematite) and assorted magnetic rocks and some  particularly in   WA are conductive as well!
The R/X%  varies from 0.5% in our worst ground to 10% in milder soils.
doug smile
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« Reply #42 on: Sunday January 27 2019 20:20:20 AEDT PM »

  


our worst soils are full of  magnetic  minerals (mainly  superparamagnetic materials; magnetite, maghemite and titano-hematite) and assorted magnetic rocks and some  particularly in   WA are conductive as well!
The R/X%  varies from 0.5% in our worst ground to 10% in milder soils.
doug smile

In those worse soils what can you expect to find considering that after ground compensation every last big gold nuggets is busted?

My point been it could be more productive to think where we can dig some huge gold chunks undetectable with PI so far because of their unusually long time constant, rather than where we can get every detector destroyed from impossible hassle.  happy face

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« Reply #43 on: Sunday January 27 2019 22:13:39 AEDT PM »

  
In those worse soils what can you expect to find considering that after ground compensation every last big gold nuggets is busted?
When ****X candy came out with the SD2000 he said i believe that the depth it was getting was perhaps about 90-95% of what is maximally possible with any hand held detector.An sd 2000 he modified for the late Jim stewart which  had a lower clock frequency (ie a much longer Tx pulse)  from testing  done i believe is still  on large targets the deepest seeking metal detector.The sharp timing in the GPX series may go as deep but cannot be used over very mineralized ground.
If we are serious about getting more depth on very  large nuggets at the expense of all smaller ones then i think we must take our   clues from what is being done in the area of UXO detection.ie large transmit coils, high coil currents  to maximize TX field strengths and  multiple Rx coils.Even then "difficult"  ground is still a major problem because deep target  signals may only be a tiny fraction of the huge  R+X ground signal.
I think that the TD is easier to overcome  some of ground problems because your can wait for most of the X signal to dissipate before sampling  whereas in the FD you not only have to deal with a variable ground R but a variable and often unpredictable X signal as well!!
these are just my thoughts,
doug smile
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« Reply #44 on: Sunday January 27 2019 22:52:55 AEDT PM »

Here is an example of what has to be done to detect/discriminate UXO in magnetic soils using FD methods.
Inversion of frequency domain data collected in a magnetic setting for the detection of UXO
Nicolas Lhomme*ab, Leonard R. Pasionab, Stephen D. Billingsa, Douglas W. Oldenburgb
aSky Research Inc., Suite 112A, 2386 East Mall, Vancouver, BC, Canada, V6T1Z3
bGeophysical Inversion Facility, Dept. of Earth & Ocean Sc., The University of British Columbia,
6339 Stores Rd, Vancouver, BC, Canada, V6T 1Z4
ABSTRACT
Magnetic soils are a major source of false positives when searching for landmines or unexploded ordnance (UXO) with electromagnetic induction sensors. The viscosity effects of magnetic soil can be accurately modeled by assuming a ferrite relaxation with a log-uniform distribution of time constants. The frequency domain response of ferrite soils has a characteristic negative log-linear in-phase and constant quadrature component. After testing and validating that assumption, we process frequency domain electromagnetic data collected over UXO buried in a viscous remanent magnetic host. The first step is to estimate a spatially smooth background magnetic susceptibility model from the sensor. The response of the magnetically susceptibility background is then subtracted from the sensor data.The
 background removed data are then inverted to obtain estimates of the dipole polarization tensor. This technique is demonstrated for the discrimination of UXO with hand-held Geophex GEM3 data collected at a contaminated site near Denver, Colorado.
  
and
  
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« Reply #45 on: Sunday January 27 2019 23:12:06 AEDT PM »

Another key factor that is going to hinder the development of a  detector that will go deeper on big nuggets is that any commercial product must comply with Australia's emission standards for EMC.
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« Reply #46 on: Monday January 28 2019 01:13:23 AEDT AM »

  
Another key factor that is going to hinder the development of a  detector that will go deeper on big nuggets is that any commercial product must comply with Australia's emission standards for EMC.
doug smile
This is where VLF is so much better, because it does not need the power output of PI to do the job as it is far more energy efficient and it does not shed any near the amount of EMI that PI does.

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« Reply #47 on: Monday January 28 2019 10:08:42 AEDT AM »

  
  
Another key factor that is going to hinder the development of a  detector that will go deeper on big nuggets is that any commercial product must comply with Australia's emission standards for EMC.
doug smile
This is where VLF is so much better, because it does not need the power output of PI to do the job as it is far more energy efficient and it does not shed any near the amount of EMI that PI does.



That may well be true but i am yet so see any VLF that can match a PI for depth in highly mineralized ground.
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« Reply #48 on: Wednesday January 30 2019 03:01:33 AEDT AM »

  


That may well be true but i am yet so see any VLF that can match a PI for depth in highly mineralized ground.
doug smile

Since I got no access to gold nuggets what other targets would you suggest to use for a demo on this one? I will be on highly mineralised ground with the GPX4500 on Friday and I have prepared MP with 13"DD.

On my test site the soil is not magnetic, BUT when it is very wet/muddy (winter/early spring) as it is now the phase shift is only 3 degrees away from magnetite. So what ground would you call that?
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australian electronic gold prospecting forum.com  |  Detector Technology and Electronics and new detectors  |  Detector Coils (Moderator: Goldman)  |  Topic: Are big coils throughly feasible for gold detectors and up to what point? « previous next »
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