The White's GMT is a good choice for a low end gold detector. By using the term low end I don't mean cheap quality, just low price. The GMT can be purchased for about $800.00 new and $500.00 used. It does have some problems with Arizona's heavily mineralized areas but can handle them decently with effort and practice. It can find gold as small as .02 gram with my experience and of course larger pieces. The fact that the GMT is a VLF or very low frequency detector means it can discriminate iron trash very well. In fact from my experience I'd say the discrimination is 99.9% accurate on trash. The digital scale normally shows gold at 25 or lower. What I am referring to is the digital "scale" called "Probability of Iron". You can see the scale below in the picture, the ground balance is set at 77, the amount of mineral is 00, and the one little rectangular bar over the 0 to the right of 25 is what I am referring to.
The real upside to this unit is if you hunt old mine dumps or tailings piles. This is where the true dual purpose of this gold detector comes into play. While the more expensive pulse induction (PI) gold detectors will outshine the GMT or any VLF for the most part in the washes and hillsides they won't be able to match the GMT's performance in mine dumps and tailings. Not only will the GMT find more gold in old mine tailings and mine dumps it will also tell you when a target is just an old nail or piece of iron junk accurately. It is also not affected by power lines like the more expensive PI units. It is also much lighter in weight than the more expensive PI units if that is a concern for you.
So if you are looking for an entry level gold metal detecting gold prospecting machine that will do ok hunting washes and hillsides for gold and will absolutely shine in old mine dumps and tailings the GMT might just be the ticket. If you want to ask questions of other users of the GMT please join our online forum.