If you thought that a metal detector is a "magic stick" I have to disappoint you..
The discrimination depends on conductivity, which is quite limited none the less.
As such there is no way to just dig treasure and leave all scrap behind.
Gold has a similar conductivity as Nickel and smaller Aluminium pieces (i.e. Pull tabs) so that's the area you should focus on, but still the best is without a doubt to dig it all.
As for the DFX, its a nice detector. Got one myself.
However it is not really intended for prospecting as such, then the V3 is quite a bit better as an all-rounder.