How Deep question

[oldkoot]

went out detecting today where I detect is my own property which is located in north eastern Arizona its a 40 acre property in a vary remote area.

I have two detectors one is the AT PRO and the other is the X-Terra 705 with three coils the 705 is the detector I use the most. I have three coils for the 705 I have the 5x10 hf coil, the 6 inch hf coil and the 9 inch mf coil I use the 5x10 on the 705 the most.

I also run in prospecting mode all the time with it set to all metal the 705 ground balances in the 20s to sometimes in the mid 30s I ALSO USE THE TRACKING AND A GROUND BALANCE OFFSET OF -3

anyway my question is today I went out to an area of my property and started detecting after I did the ground balance had a faint target that was different from everything else this signal was so faint that I could barely hear it in my headphones it would not pinpoint I dug down about 4 inches and checked the hole again with the detector it got louder so I dug down another 2-3 inches the target sound got louder but I still could not locate the item when I finally gave up because it started raining I was down about 12-14 inches in the hole and the 705 was still telling me there is a target there my question is can the 705 pick up targets that deep I was also using a Garrett pin pointer the pin pointer was not sounding off but the 705 kept getting louder and louder the deeper I dug.

 

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[oldkoot]

Maybe it's a frequency thing as the 705 does run at a slightly higher frequency depending on coil choice? What coil are you running on the 705? 18.75Hz I'd assume. If so does it exhibit the same behavior with a lower frequency coil?

I'm leaning towards it just a rock instead of a meteor. Doesn't really look meteorish too me.

Kenmitch I am running the 5x10 DD 18.75 KHz coil (football shaped) and yes I tend to agree with you as to it being just a rock just puzzling as to the reactions I get from both detectors

I had not thought about changing to the mid frequency coil on the 705 and see what it does over it or the 6 inch DD 18.75 which I would think I would get the same reaction from the 6 inch coil since it is the same frequency as the 5x10 will check and see.

 

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[oldkoot]

Well now I am totally confused I took the rock outside with the same coil I had been using still got the same response after I ground balanced and set it up in prospecting AM no discrimination set still got the same thing took it off of AM but still in prospecting mode with a discrimination of 5 same thing still kept raising the discrimination one notch at a time all the way to ten notches still the same thing so I shut the 705 down and went through the same things as described and still had the same results with the 9 inch concentric coil 7.5 KHz both the 5x10 18.75 and the 9 inch 7.5 gave me the same sounds in prospecting mode tried switching to coin and treasure with both coils and same results as posted I got no response in coin and treasure from either coil so I do not believe it has anything to do with the frequency.
I also after trying the 705 with both coils tried the AT Pro again and to no avail no response what so ever took some quarters,dimes and nickel's and threw them out on the ground and both the 705 and the AT PRO were hitting on them so I do not know this is baffling as you know what I don't know what to think now.

I believe the 705 is hitting on something just what is the question.

 

[Kenmitch]

The mystery goes on. I can't really think of any reason why the 705 would see a false target on different frequency coils.

What we've learned so far:
The rock is heavy.
No response from a pinpointer....No big surprise as they are not really that sensitive to smaller targets unless close.
The 705 gets a hit using 2 different frequency coils.
The AT Pro sees nothing but seems to be functioning correctly.

How tough is the rock? Does it scratch easy with a knife or a nail?

 

[sqaush]

I followed the link on post 27. I think I would file a spot and see what it looks like below the surface.

Sent from my SAMSUNG-SM-G891A using Tapatalk

 

[arizau]

I followed the link on post 27. I think I would file a spot and see what it looks like below the surface.

Sent from my SAMSUNG-SM-G891A using Tapatalk

Or on a grinding wheel and do a scratch test on underside of tile or a porcelain toilet reservoir cap. One thing is that it doesn't pass a visual test from looking at the picture.

 

[oldkoot]

Or on a grinding wheel and do a scratch test on underside of tile or a porcelain toilet reservoir cap. One thing is that it doesn't pass a visual test from looking at the picture.

I did a scratch test on a ceramic tile it was like you were drawing on the tile with a piece of chalk when I did that I thought it had scratched the tile but the mark wiped rite off I also used a file on one edge and it appears to be like a carbon looking under the surface.
Can carbon set off a metal detector?

think i will take a angle grinder to it with a carborindum blade and cut it in half maybe that will tell me something if the blade don't explode on me

 

[Jim Hemmingway]

I did a scratch test on a ceramic tile it was like you were drawing on the tile with a piece of chalk when I did that I thought it had scratched the tile but the mark wiped rite off I also used a file on one edge and it appears to be like a carbon looking under the surface.
Can carbon set off a metal detector?

think i will take a angle grinder to it with a carborindum blade and cut it in half maybe that will tell me something if the blade don't explode on me

Hi Oldkoot… rocks that generate signals from metal detectors come in a wide variety of shapes, compositions and sizes depending on the locality, and those rocks that generate a signal are referred to as hotrocks. Most hotrock signals result from the type of iron minerals present within their structure, but there are other substances that can also produce signals as well… such as conductive graphite.

The rock in your photo appears to be a hotrock… typically characterized by extra weightiness and some discernible magnetism. Both these properties would result from the iron minerals present within the rock.

Different detectors or even individual detector searchmodes sometimes process target signals in different ways. So just because one detector won’t signal over this rock doesn’t imply that one or the other detector is somehow not functioning properly. It simply means that they process signals differently.

Now what you have overlooked is that your AT Pro does not possess a true motion all-metal mode as does your Minelab 705. Discrimination modes even in zero discrimination still filter out some types of signals and this is exactly what is happening with your AT Pro. Your 705 is working just fine. In the 705’s true motion all-metal prospecting mode, the unit does recognize that the rock produces a signal, whereas the AT Pro discrimination mode ignores that same hotrock signal.

If you would like more information about such things, I can provide you with some brief, understandable reading material that will be helpful.

Jim.

 

[oldkoot]

thank you Jim it does make since what you are saying
I just never had this happen to me where one detector would sound off and the other would not
I would appreciate any info you can provide me with always like reading and learning something new

 

[Kenmitch]

https://www.minelab.com/treasure-talk/hot-rocks-part-1

https://www.minelab.com/usa/treasure-talk/hot-rocks-part-2

Hot Rocks - Meteorite Identification

Here's a thread about AT Pro and hot rocks. Might be able to experiment and try detuning too see if it will see it.

http://www.treasurenet.com/forums/garrett/344573-pro-vs-hot-rocks.html

Did you try the " ground tracking offset " on the 705 to see if it makes the rock not detectable?

http://www.treasurenet.com/forums/metal-detecting-gold/126682-xt705-hot-rocks.html#post2246913

 

[oldkoot]

Thanks Kenmitch that info was vary helpful I actually went to another area on my property yesterday that I had to climb up the side of a mountain, detected all the way up it and down the other side.
It ran into a wash just above this wash I encountered all kinds of hot rocks brought a couple down with me because they were giving me the same sounds with the 705 that I got off of the first rock, I wanted to see if the AT PRO would see them but it did not so my property seems to have these all over it, the area I was in yesterday was like a mine field with them probably 50 ft by 50 ft area had these rocks all over it gonna have to go back and spend more time in that spot but it might just be worth the effort to do so guess I better put on my mountain goat shoes LOL

 

[Kenmitch]

I'd smash it up then and see whats inside of it. Would be an interesting rainy day project while killing some time. I'd try to whack it in half and see if you get a signal from either side of it. If so I'd whack that side into smaller pieces and check again. If you still get a signal I'd smash the rock into dust if possible and pan it out to see what's in it.