Low-grade cannot have gold on them. If they do have any gold that would make them mid or hi grade depending on the amount of it and any IC chips.I actually have a box of stuff that is as you describe as low grade boards but seem to have gold on them.
If your still curious about refining and want to at least read about it this place probably has more experts and wanta-be's than anyplace else on the web.
http://goldrefiningforum.com/phpBB3/index.php
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