Black sand is an indicator that gold may be near. The reason is, is because black sand is heavy, and so is gold. Just imagine when high water runs in a stream or river the bottom actually suspends. This causes the stream bed/river bottom to classify itself by weight (just like panning), thus the black sand theory. That?s one of the ways to think in order to find gold (what will the heavy martial do in that situation).
This is no secrete, all you have to do is check out a few books from the library, like how to find gold.
From what I understand even the best VLF machine won?t handle black sands, it?s almost like detecting on a metal plate, most of it is magnetic. PI machine dedicated to gold will cut through black sands like butter. All out electronic prospectors normally have a few detectors and coils in their arsenal to find the places that gold hides. Different gold hunting situations will require a different detector. High frequencies do find small nuggets like the 72 Hz GB-2, but less depth is achieved. Lower frequencies go deeper, smaller coils find small nuggies too as well as read between close targets better.
Just my HO