I've got a bunch of smokies and quartz crystals, most of them aren't great but a few are good size and really really clean inside and I also managed a nice little colorless topaz \ diamond??? (not 100% sure what it is, the SG was 3.532). Can't say I've got any real method for finding them, I just dig and classify for gold and these things turn up in the sieve. I also managed to land a nice quartz crystal cluster\cave which I took to the local gem club, apparently these things from that area are incredibly rare especially in the condition I found mine in. I'm guessing if you move enough material and try and reach the hard to get to spots these things will turn up from time to time.
Never had any luck with sapphires or garnets or big topaz or anything yet. The best I've seen is shards in my sluice cons, 99& of which are yellow, orange and red, and even then from all the digging I've done I've only picked out 3 tiny little blue gemstone shards.
Cheers
Adam