I understand that the Xterra 70 and 705 has a prospecting mode, and i read somewhere people r using it to tell if its worth digging your target up. My question is, what about haloed iron? Will the prospecting mode still go off with haloed iron or a bigger piece of iron? 2nd question, whats the deal with a 3mhz coil? Does it see silver and NOT iron better? Im not to worried that it goes deeper.Im just hoping it can see conductive (coins or buttons) and ignore iron without having any discrimination. thanx