ionic metal detector

let say you have a (loop) coil.
your elctrik source is AC. but you use diod.
so you get one way current at loop which is not costant.
if you can omit opposite current at decays ,and make this at low frequency with powerfull waves,can you collecet positive and negatif ions around loop.
now apply this to earth.
north south fileds lines generally travels in ground with high density of flux than on earth surface.
when it crushes to diamagnetic substances and/or cavities needs to travel around it.
some of them has to be come up to surface and cause to increase of density at that spots(areas)
this will be powerfull source to pull ions on surface of earth than normal consantration flux areas.like magnet pulls iron .it will collect ions.
which ions ?
it is up to whaether and ionic properties of that region.

how is this rudy
maybe I can not give answer for weeks cause of job travel.