Honestly haven't tried it much. I am generally searching for mid conductive relics in my mineralized soil so if I go single, I am generally using the higher frequencies (15 or 20 khz) in Field or Gold mode, but have had the most success in Field 2 multi.
BTW - in mineralized ground there are no absolutes as far as frequency choice is concerned - that is really a function of the targets of interest, their depth, site iron and trash density, and a bunch of other variables. In general, lower frequency signals travel further in in the ground (regardless of mineralization) and are ideal for picking up larger targets and high conductors. But mineralization (depending on the type and the constituency of other components of the soil see below) can also cause more scattering of low frequency signal more than high frequency signals. Small mid conductors can be more readily acquired using higher frequencies in all soil types but higher frequency signals will still travel only so far in soil due to soil signal attenuation. So the bottom line is there is no pat answer on the ideal frequency to use in mineralized ground. Multi-frequency detectors, like Equinox, tend to handle mineralization best, and typically in Multi IQ mode.
Note also that "mineralization" is a very imprecise term, knowing the type of mineralized ground is important if you really want to adjust the detector to handle it - and unfortunately, Equinox provides no clues as to mineralization type because the ground balance number is basically meaningless and Equinox provides no Fe3O4 meter.
Another thing I forgot to mention previously, when shifting Equinox to single frequency, you also lose Iron Bias functionality altogether (the user setting adjustment disappears) and you may notice that the Equinox is less forgiving of a less than optimal ground balance as multiIQ is more stable under a wider range of ground balance settings that deviate from the actual soil conditions. HTH.
