I'm curious if a regular medical centrifuge might work. Maybe one of the 10k rpm ultrafuges.
And would the material need to be wet?
Heaven knows the density and specific gravity of gold is far higher than black sands.
I think somewhere in my wanderings I saw one invention, but it might not be hard to rig something else.
Medical equipment (used) is often available on ebay.
Cheers!
Mary