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I had something odd happen this last weekend. Maybe someone out there can enlighten me as to what caused this.
While testing a new machine in the field, we buried a large nugget (about 1/4 oz.) about 8 inches deep. Normally this is a no brainer as far as the signal strength from my 3000. But this time when I went over it, there was virtually no signal. Going slower and scrubbing the ground produced a weak low signal like deep iron. I usually hunt in Deep and Sensitive to pick up the small ones. I now started fooling with the controls to try to figure out what was wrong. As soon as I switched to Normal from sensitive, the signal boomed through, even several inches above the ground. The same thing happened in salt mode.
So, my question is what does that say about the ground? Highly mineralised or low. Why such a pronounced difference on a relatively shallow target? The ground was damp mud and the nugget setting on hard pan bedrock, bluish-grey in color. Up on the bank where we usually hunt, it's red and fairly hot ground. I was using the stock 11" DD loop and all the usual settings that have produced many deep nuggets over the years. It's shaken my confidence a bit and may have to go back over some ground I thought was cleaned out.
Digger Bob
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GP 3000 settings? Very odd
#1
Digger Bob 
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Posted 25 September 2006 - 01:47 PM
MultiQuote
#2
Jonathan Porter
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Posted 25 September 2006 - 04:37 PM
QUOTE (Digger Bob @ Sep 26 2006, 06:47 AM)
I had something odd happen this last weekend. Maybe someone out there can enlighten me as to what caused this.
While testing a new machine in the field, we buried a large nugget (about 1/4 oz.) about 8 inches deep. Normally this is a no brainer as far as the signal strength from my 3000. But this time when I went over it, there was virtually no signal. Going slower and scrubbing the ground produced a weak low signal like deep iron. I usually hunt in Deep and Sensitive to pick up the small ones. I now started fooling with the controls to try to figure out what was wrong. As soon as I switched to Normal from sensitive, the signal boomed through, even several inches above the ground. The same thing happened in salt mode.
So, my question is what does that say about the ground? Highly mineralised or low. Why such a pronounced difference on a relatively shallow target? The ground was damp mud and the nugget setting on hard pan bedrock, bluish-grey in color. Up on the bank where we usually hunt, it's red and fairly hot ground. I was using the stock 11" DD loop and all the usual settings that have produced many deep nuggets over the years. It's shaken my confidence a bit and may have to go back over some ground I thought was cleaned out.
Digger Bob
While testing a new machine in the field, we buried a large nugget (about 1/4 oz.) about 8 inches deep. Normally this is a no brainer as far as the signal strength from my 3000. But this time when I went over it, there was virtually no signal. Going slower and scrubbing the ground produced a weak low signal like deep iron. I usually hunt in Deep and Sensitive to pick up the small ones. I now started fooling with the controls to try to figure out what was wrong. As soon as I switched to Normal from sensitive, the signal boomed through, even several inches above the ground. The same thing happened in salt mode.
So, my question is what does that say about the ground? Highly mineralised or low. Why such a pronounced difference on a relatively shallow target? The ground was damp mud and the nugget setting on hard pan bedrock, bluish-grey in color. Up on the bank where we usually hunt, it's red and fairly hot ground. I was using the stock 11" DD loop and all the usual settings that have produced many deep nuggets over the years. It's shaken my confidence a bit and may have to go back over some ground I thought was cleaned out.
Digger Bob
G'day Digger, I am not surprised you experienced this. By using either Sensitive mode or Salt mode you alter the TIMINGS of your GP, using Sensitive the receive circuit is turned on at a much earlier stage and Salt turns on the receive at a later stage. The GP's are optimised to work best in Normal mode where both channels of the detector are at their optimum performance. In some ground types certain sized nuggets will produce a very weak signal depending on where the GB ends up when using Sensitive, most of this is explained in our first video "Unleashing the GP Series".
I would only ever recommend using Sensitive mode when the ground is shallow and the potential targets small. Also keep in mind if you use Sensitive mode you leave yourself vulnerable to more ground noise.
Hope this helps
JP
BTW I noticed on another forum the 24K club are having a communal push up at Rich Hill, members of this forum who will be present should look into one of the Nugget Finder XP coils, by running in XP mode in conjunction with Mono mode you could cut out on a huge amount of interference, this might come in handy with all the other Minelab machines in the area when they open the ground up for detecting
.
#3 Guest_Spinifex_*
Posted 26 September 2006 - 07:55 AM
Hi Digger Bob
I not trying to go head to head with JP on this as he has the superior knowledge and experience on all things detector related, but I must say I am a bit surprised by this.
I have been investigating and testing the differences between sensitive and normal for some time now and to try and generalizing my findings; Sensitive mode will give an equal or better response on small nuggets (under 10 grams) down to 12 inches deep. Normal mode can give a more defined response on larger nuggets beyond this range.
(Note: The improved response on smaller nuggets is more significant when using a DD coil.)
I would be interested to know if you could duplicate this result again. One thing that springs to mind is when you switch from sensitive to normal it shifts your ground balance considerably; the detector would need to be reground balanced using the same technique and location when testing between the modes for everything to be equal.
I have had plenty of small weak signals diminish further in Normal mode but am yet to get one the other way around as you describe. Apparently there is always a dead spot in the range and you may have hit it with this particular test nugget but I am doubtful of this going from the size and depth descriptions and particularly as you were using a DD coil.
Ha, your post has shaken up my confidence too.
Regards
Spinifex
I not trying to go head to head with JP on this as he has the superior knowledge and experience on all things detector related, but I must say I am a bit surprised by this.
I have been investigating and testing the differences between sensitive and normal for some time now and to try and generalizing my findings; Sensitive mode will give an equal or better response on small nuggets (under 10 grams) down to 12 inches deep. Normal mode can give a more defined response on larger nuggets beyond this range.
(Note: The improved response on smaller nuggets is more significant when using a DD coil.)
I would be interested to know if you could duplicate this result again. One thing that springs to mind is when you switch from sensitive to normal it shifts your ground balance considerably; the detector would need to be reground balanced using the same technique and location when testing between the modes for everything to be equal.
I have had plenty of small weak signals diminish further in Normal mode but am yet to get one the other way around as you describe. Apparently there is always a dead spot in the range and you may have hit it with this particular test nugget but I am doubtful of this going from the size and depth descriptions and particularly as you were using a DD coil.
Ha, your post has shaken up my confidence too.
Regards
Spinifex
#4 Guest_Guest_Digger Bob_*_*
Posted 26 September 2006 - 09:53 PM
First of all, thanks to all who responded. I've gotten a wide range of opinions on the various forums from many respected sources. Let me see if I can summerize and expand on what happened.
The area has two distinct gold bearing "fields". The first is brick hard clay ranging up to 12 inches deep with decomposing granite bedrock under it. "Large" nuggets up to 6 dwt have been found on the bedrock with nothing but trash in the overburden. The over burden is fairly warm and the bedrock mild. This is where I hunted first and got no good signals deep. And it is here where I suspect I may be missing something using these settings. I'll now have to go back after some rain softens things up and try some different settings to test these theorys. I find it hard to believe that I just happened to hit on the right size, shape, and depth of nugget to be undetectable at the usual settings. I'm hoping that is the case, since I know there are more there. But that brings up even more questions.
The second area is the same bedrock covered by only an inch of dirt. Nothing large has ever been found there, but there are lots of .1 and .2 dwt pieces imbedded in it. Working in Sensitive makes these little ones pop even with a 11" loop. I've had these little ones "disapear" when hunting in Normal.
I've found large and small, shallow and deep, using the Sensitive and Deep and the ground usually doesn't cause an instability problem. That's why I was so mystified with the response this time.
I ground balanced each time after changing settings. I even changed to fixed before going over it.
One of the problems of course, is that in a new area you don't know what size gold is there or how deep until you start finding something (if there even is anything) So, hunting the same ground twice or even three times with different settings becomes time consuming when there is more ground to check out.
My favorite loop is the DD Wallaby but was using the stock loop this trip. I'll now have to play with other loops and nuggets and see if I can duplicate this with monos and well as the pro coils. The nugget was solid, not porous nor quartzy. A 3 ozer buried 12 inches boomed as did a 1 ozer in the same ground with the same settings.
Strange... well, back to the drawing board
Digger Bob
--------------------
"In Gold We Trust"
The area has two distinct gold bearing "fields". The first is brick hard clay ranging up to 12 inches deep with decomposing granite bedrock under it. "Large" nuggets up to 6 dwt have been found on the bedrock with nothing but trash in the overburden. The over burden is fairly warm and the bedrock mild. This is where I hunted first and got no good signals deep. And it is here where I suspect I may be missing something using these settings. I'll now have to go back after some rain softens things up and try some different settings to test these theorys. I find it hard to believe that I just happened to hit on the right size, shape, and depth of nugget to be undetectable at the usual settings. I'm hoping that is the case, since I know there are more there. But that brings up even more questions.
The second area is the same bedrock covered by only an inch of dirt. Nothing large has ever been found there, but there are lots of .1 and .2 dwt pieces imbedded in it. Working in Sensitive makes these little ones pop even with a 11" loop. I've had these little ones "disapear" when hunting in Normal.
I've found large and small, shallow and deep, using the Sensitive and Deep and the ground usually doesn't cause an instability problem. That's why I was so mystified with the response this time.
I ground balanced each time after changing settings. I even changed to fixed before going over it.
One of the problems of course, is that in a new area you don't know what size gold is there or how deep until you start finding something (if there even is anything) So, hunting the same ground twice or even three times with different settings becomes time consuming when there is more ground to check out.
My favorite loop is the DD Wallaby but was using the stock loop this trip. I'll now have to play with other loops and nuggets and see if I can duplicate this with monos and well as the pro coils. The nugget was solid, not porous nor quartzy. A 3 ozer buried 12 inches boomed as did a 1 ozer in the same ground with the same settings.
Strange... well, back to the drawing board
Digger Bob
--------------------
"In Gold We Trust"
#5 Guest_Guest_*
Posted 28 September 2006 - 09:10 PM
QUOTE (Guest_Digger Bob_* @ Sep 26 2006, 09:53 PM)
First of all, thanks to all who responded. I've gotten a wide range of opinions on the various forums from many respected sources. Let me see if I can summerize and expand on what happened.
The area has two distinct gold bearing "fields". The first is brick hard clay ranging up to 12 inches deep with decomposing granite bedrock under it. "Large" nuggets up to 6 dwt have been found on the bedrock with nothing but trash in the overburden. The over burden is fairly warm and the bedrock mild. This is where I hunted first and got no good signals deep. And it is here where I suspect I may be missing something using these settings. I'll now have to go back after some rain softens things up and try some different settings to test these theorys. I find it hard to believe that I just happened to hit on the right size, shape, and depth of nugget to be undetectable at the usual settings. I'm hoping that is the case, since I know there are more there. But that brings up even more questions.
The second area is the same bedrock covered by only an inch of dirt. Nothing large has ever been found there, but there are lots of .1 and .2 dwt pieces imbedded in it. Working in Sensitive makes these little ones pop even with a 11" loop. I've had these little ones "disapear" when hunting in Normal.
I've found large and small, shallow and deep, using the Sensitive and Deep and the ground usually doesn't cause an instability problem. That's why I was so mystified with the response this time.
I ground balanced each time after changing settings. I even changed to fixed before going over it.
One of the problems of course, is that in a new area you don't know what size gold is there or how deep until you start finding something (if there even is anything) So, hunting the same ground twice or even three times with different settings becomes time consuming when there is more ground to check out.
My favorite loop is the DD Wallaby but was using the stock loop this trip. I'll now have to play with other loops and nuggets and see if I can duplicate this with monos and well as the pro coils. The nugget was solid, not porous nor quartzy. A 3 ozer buried 12 inches boomed as did a 1 ozer in the same ground with the same settings.
Strange... well, back to the drawing board
Digger Bob
--------------------
"In Gold We Trust"
The area has two distinct gold bearing "fields". The first is brick hard clay ranging up to 12 inches deep with decomposing granite bedrock under it. "Large" nuggets up to 6 dwt have been found on the bedrock with nothing but trash in the overburden. The over burden is fairly warm and the bedrock mild. This is where I hunted first and got no good signals deep. And it is here where I suspect I may be missing something using these settings. I'll now have to go back after some rain softens things up and try some different settings to test these theorys. I find it hard to believe that I just happened to hit on the right size, shape, and depth of nugget to be undetectable at the usual settings. I'm hoping that is the case, since I know there are more there. But that brings up even more questions.
The second area is the same bedrock covered by only an inch of dirt. Nothing large has ever been found there, but there are lots of .1 and .2 dwt pieces imbedded in it. Working in Sensitive makes these little ones pop even with a 11" loop. I've had these little ones "disapear" when hunting in Normal.
I've found large and small, shallow and deep, using the Sensitive and Deep and the ground usually doesn't cause an instability problem. That's why I was so mystified with the response this time.
I ground balanced each time after changing settings. I even changed to fixed before going over it.
One of the problems of course, is that in a new area you don't know what size gold is there or how deep until you start finding something (if there even is anything) So, hunting the same ground twice or even three times with different settings becomes time consuming when there is more ground to check out.
My favorite loop is the DD Wallaby but was using the stock loop this trip. I'll now have to play with other loops and nuggets and see if I can duplicate this with monos and well as the pro coils. The nugget was solid, not porous nor quartzy. A 3 ozer buried 12 inches boomed as did a 1 ozer in the same ground with the same settings.
Strange... well, back to the drawing board
Digger Bob
--------------------
"In Gold We Trust"
Interesting discussion on this subject (sensitive,normal and salt mode) from Reg Sniff and others and on coils on: http://groups.yahoo....rospectinginOz/
#7
Montana
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Posted 30 September 2006 - 10:20 AM
Digger Bob. Too bad you didn't switch to a mono coil and try it again with the nugget still in the ground at the same depth. I have had nuggets boom through after a coil change that weren't detectable before with another coil on the same settings. For this reason after I have established that there are nuggets there, I will try at least three different coils before I consider the patch done. Some coils just outperform others on certain types of ground. Don't doubt your detector when something like this happens until you have tried different coils. Also , as J.P. says , sensitive setting may not always be the best choice. I use it most of the time in the places that I hunt , but it isn't always the best choice. It usually is though for small nuggets at less than 8". I am guilty of not switching to the normal mode when I probably should at times. -----Bob
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