Where Did My Signal Go?

[Jim Hemmingway]

Yep... a very handsome 'character' piece, congratulations LipCa.  

 

Jim. 

[LipCa]

Steve, 

 

I have never had ground go from good to bad like you mentioned in your first post.  Was that with a PI or VLF or both?  If it was with a PI, I probably haven't used one enough to experience it.

[Steve Herschbach]

In two locations in California I have been on very, very hot ground with the SDC 2300. Extremely red and loaded with magnetite. The SDC struggled with it, kind of groaning as the ground balance tried to keep up. I would get a faint signal I would think was a possible nugget, and scratch into the stuff. It would go all kinds of "sparky" for lack of a better term. After messing with it I decided these were basically patches of almost pure magnetite. Soil sitting in place does actually end up with the particles being magnetically aligned and stirring it up is kind of like stirring up a hornets nest.

Luckily these places are more like small patches and so not something I had to deal with overall.

From Bruce Candy at https://www.minelab.com/__files/f/11043/METAL%20DETECTOR%20BASICS%20AND%20THEORY.pdf

"Thus, USA goldfields are typically different from Australian goldfields:

• The USA soils are mostly mildly mineralised but in some areas may contain either nearly pure magnetite black sands or rocks, which are problematic for metal detectors as they have very high X components (strongly attracted to magnets).

• Australian gold fields have highly mineralised soils, but very few black sands or rocks that contain nearly pure X magnetite. The magnetic materials are in the forms of magnetite-rich small pebbles and rock coatings, clays and general “sandy” soils. These all contain magnetic materials that produce high levels of X signals as well as R. The ratio of X and R is random, and the R component arises from extremely small magnetic particles called superparamagnetic materials..."

Predicting Soil Influence on the Performance of Metal Detectors: Magnetic Properties of Tropical Soils http://www.jmu.edu/cisr/journal/13.1/rd/igel/igel.shtml

Influence of Soil Properties on the Performance of Metal Detectors and GPR http://www.jmu.edu/cisr/journal/17.1/RD/takahashi.shtml