Ground mineral does have an effect at times on what results you get.
Here the ground is near neutral. I have hit high coins deeper with a Compass X-100 at 13.77 kHz than units at 3 kHz like a V3i.
But some areas like Shiloh Tenn. with strong negative ground, the Compass would not go as deeply as my Mk-1, at 6.592 kHz on say buttons which are low conductors.
(Jerry Tyndall said the DMC-4 (kHz) in bad ground was better than a DMC-2B at 14kHz.)
Wet salt adds another angle; a Fisher 1280X Aquanaut at 2.4 kHz hits very deep on high conductors (the lowest frequencies are much less affected by salt) and will hit very small gold
at least to a certain point. The higher frequency units from 12-19+ kHz are severely affected in salt on all targets and depth is modest.
Two and three frequency units seem to work extremely well and get great depth in salt or any mineral on any conductors, until you come to black sand.
Gold nuggets, especially the size of fine bird shot may not respond to dual/multis, or the lowest range of VLF'S, but get up to 40-60 kHz and they will hit nuggets so small they are difficult to see.
Take a vintage unit TR-IB like a Compass 77B at 100 kHz and while they do not offer much depth at best, will hit a high or low conductor completely obscured by nails.
There is much more than frequency though, number of ground filters, quality; loop design and size, and TX power and recovery speed have huge effects on depth. (that's just the detector, before your expertise level is factored in) Its hard to tune detectors so they are equal to see how they will perform against each other (NASA Tom has written on this too.)
Generally higher frequencies produce more energy at less battery drain (filling the Q of the loop.)
In most places where I hunt here, the mid range seems to offer the best depth in my (very) low mineral ground on the widest range (or a CZ or say, SE Pro.)
(Troy Galloway's X-5 at 19 kHz seems to hit high conductors as deeply as low-he claims there is a circuit he added to do this, and results from many people seem to bear it out.)
(((The PI operating at a very broad range of frequencies may have the best depth on all targets in any condition, but its ability to identify or discriminate is very primitive at best-and iron is its bane.)))
Units with more than one single frequency, or selectable filters started with the Compass X units.
Maybe the best option today are units with up to several separate frequencies to opt from, depending on target choice, or iron saturation-like the Impact or Kruzer, or Deus; Nokta, Makro & XP are known
for excellent ability to work to hit targets that are iron masked.
Its often a crap shoot because luck is a Huge factor: to find all the goodies, you have to dig all the trash--and that takes time.
Bon chance mes amies!
