Any deep iron can throw off, and lie to even the best of detectors...all detectors. If I get a straight, full on, iron tone from every direction, I will not dig it. Yet, most relic hunters would gladly do so, as it could be an old ax head, a rusted out gun, etc. As a coin hunter though, I'll only dig the deeper iron if I'm totally fooled (it sounds like a coin), or if it sounds like iron sporadically, but there's high tones breaking through on certain swings/directions. This can mean a coin is too deep, and it can't be read cleanly, or, it might be there's iron in the hole, with a good target nearby. Or it's just iron falsing a high tone.
Also, as Ed said, there could be tiny iron particles in the soil, which can sound like a deep signal. Once you open the hole and disturb the soil, it breaks the iron particles up, and you don't hear the signal anymore. Many people call these "ghost holes" or "phantom holes".
I don't know of too many hunters who chase the deeper signals who
don't dig a ton of iron every outing. It's the way it is. I literally dig probably a half pound (if not more) of old nails, whatsits, spikes, etc. each time I detect. But here's the thing...
If there's iron down that deep, there's gotta be non-iron targets, too
As you grow with your detector, you'll be able to correctly predict much of the deeper iron, but not all of it. Nobody can, nor can any detector. If you wanna get the goodies, you gotta go through the junk.
Joe
