hi there,
not so sure on really fine stuff. as i recently posted i got 4 bits totalling 0.14 grams. these were still bigger than flour sized. and i've got a gold bug 2 that can detect some small stuff.
if you had a lot of flour gold then that might produce a bit better result. a bit like when you detect a drift of black sand. detector picks it up but it won't detect so well the general amount of black sand spread over the area.
if you have a small bottle of gold then this can be good to do some tests with. just try not to lose any gold over the ground.