Well done Nobby that made it as clear as um, well, fog
mineralisation is as it says minerals or tiny particles that are of a metallic origin whether from natural ores or rust particles. These particles exist in lesser or greater degrees in all soils and have an accumulative effect on a metal detector, meaning that the deeper the signal travels then the greater the mineralisation and with some coils this effect would follow the inverse square law and if you double the distance you would in fact multiply the effect by a factor of 4.
While at low levels these "Metals" are below the sensitivity of most machines, as their density increases, so the machine starts to see the effect as an actual target, thus small targets with a low conductivity that stand out "unique" on the surface, once buried begin to merge with their background, untill eventually the signal from the target and that of the surrounding ground is the same.
Ground balancing a machine basically calibrates "zero" on the machine but of course small burried targets can also be "zeroed" out
While the more expensive machines can be fine tuned to mineralisation and can be run "on the edge", all VLF motion machines suffer from it regardless of price
PI machines on the other hand work in a different way and are not effected by naturally occurring mineralisation which is why they can find small targets and a far greater depth.
