cold rocks?

[timberjack]

So aside from all the trash and some pretty cool stuff i have found so far (horse shoes-choker chaines-a moter compartment cover for my fellerbuncher) i have found some hot rocks (arsenopyrite?) ..i have found 2 rocks that when i swing over them the threshold tone dissappeares,,,,any ideas? Thanks for all the great responses to my other posts and helping me learn so much so quickly,,,parker

 

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[Hoser John]

Must know what kind of detector to answer question-John

 

[timberjack]

Gold bug 2

 

[DesertNuggets]

Have a pic of the rock? My GB2 goes off on any rock with high enough iron content. The usual suspects are magnetite or hematite.

 

[Jim Hemmingway]

I have found 2 rocks that when i swing over them the threshold tone disappears,,,,any ideas?

Timberjack... the threshold loss results from passing the coil over hotrocks that have both a sufficient iron mineralization and a more elevated (higher into the non-conductive GB range) ground balance (ground phase) than the GB setting used on your detector to ground balance to the surrounding terrain.

Normally the above scenario results from rocks with abundant magnetite mineralization... a highly magnetic susceptible iron oxide. There are other iron oxides that overlap into the magnetite GB range such as hematite, however hematite normally has little effect on metal detectors because it is only weakly magnetic susceptible and likely not much or any different in that respect than the surrounding terrain / substrates normally encountered in mining / prospecting country.

In short... you are experiencing negative (cold rock) hotrock signals in the example you've described. Some photos below...

Jim.

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[timberjack]

Yesterday i took the goldbug 2 with me while walking a woodlot i cut 10 years ago and will be working on agine later this summer. Aside from the intersting old logging relics (crosscut saw handle, sled irons, square nuts, square nails) i found i noticed that most of the rocks i swung over were cold. I kept ground balancing the machine, but, i would have a clear steady tone, swing over a rock, the tone would dissapear, swing past the rock and the tone would return. This area is down stream as the glaciers flowed from a large exposed rocky hill and a associated fault line. There were several boulders that had very rusty quartz veins running thru them, but, agine the signal would just dissappear..when i hit a beer can the machine would scream.
I did find one rock that gave me a weak signal, when i broke it open it appeared to be composed of red garnet. Very interesting stuff

 

[Hoser John]

Reminds me of the old school tr units where you could reverse tune to look for ferrous objects instead of gold. Great for ID samples and relic hunting old cabin sites-John