I have at least one of every detector you mentioned except for the GMZ. I don't have one of those.
Now, it is been many years since I hunted for gold in the Gunnison area so I am also rusty on particular places in that area.
Now, with that said, most gold found in CO is small, thus the VLF's are usually the best choice. The SL isn't as good for the really small gold when compared to the GMT or the GB 2. I like the SL but don't use it as much here in CO when I am nugget hunting.
As for which is best, the GMT or the GB 2, well that is more of a personal preference. Both work well. If you know how to use the ground balance to your advantage the GMT in auto tracking works extremely well.
If you rely on the display, you probably will leave gold behind. I have yet to find a display that is accurate all of the time or most of the time in some places. Specimen gold quite often is in rock containing ferrous oxides that can cause readings that will cause one to ignore the rock. Remember, the signal from a ferrous oxide is many times stronger than the weaker signal from gold. As such it doesn't take much iron oxide in a rock to cause the rock to be ignored even though it may have a stringer of gold in it. This is why it is important to know as much about the gold in the area where you are hunting.
A friend of mine uses a GB 2 and mentioned he followed behind a GMT owner and often found gold left behind. He suspected the White's owner was actually detecting much of the gold but assuming it was junk because of the readings he received.
The GB 2 disc feature works well but again isn't perfect. My buddy uses it so often that he broke the toggle, so he is using my GB 2 until he gets his fixed.
So, rather than always rely on any form of discrimination, make sure to check at least some of the signals. In places where actual iron objects are scarce, it is best to check all especially if the signals are weak and smooth signals.
As for the ground balance feature on the GMT, check some of those signals that are quickly tuned out after a few passes over them while the tracking feature is on. Don't be surprised to find that many small pieces of iron junk will be tuned out much like the ground signal. As a general rule, free gold doesn't do that. However, if the gold is locked in a rock, then it is a matter of the rock's makeup.
So, the old saying dig all and the only true discrimination is a person's eyes and a good loupe does hold true.
In areas where the iron oxides are not that bad and the gold is normally in nugget form, then one can use the disc feature with a little more confidence, especially if there is a lot of iron junk to deal with. Again, if this iron junk is rare, then dig all is the best way to go.
So, getting back to your original question, either the GMT or the GB 2 should serve your purpose.
The SL works fine for gold a little larger. Now, in a few years, PI's just may turn out to be the best if some of the features I am aware of are advanced properly.
Reg
