Might need some fine tuning but in theory the gold should displace the black sand as it packs out.
I run a Mackirk Boss and after each clean out on the creek I do a quick pan-off to get rid of most of the junk and small rocks and finish the rest up at home in the pan, I tried the cleanup sluice thing once upon a time but found I always ended up having to use the pan to some degree anyway so I just do the whole lot in the pan these days
Cheers
Adam