I have heard of roasting black sands to separate fragments of gold from the black sand.  Recently I have been using another method that I have employed successfully.  This method does not involve heating or treating the black sands with chemicals.

First I process the concentrates through a Gold Cube and pan the gold from the Gold Cube's concentrates. Then I run the black sands through a rock crusher (I use the Cobra Rock Crusher) to further separate gold from black sands.  I use the rock crusher to reduce the black sands down to 20 mesh or finer.  After crushing all the black sands, I run the material through the Gold Bandit and pan the Gold Bandit's concentrates a final time to retrieve the fine gold.

Another method I have seen from MakeYourOwnGoldBars is to simply smelt the black sands to recover any gold.