Mixed precious-metal sweepings — such as those from jewelry polishing floors containing both gold and platinum-group metals — have a different commercial value profile and are classified under the heading for the predominant precious metal or under a mixed precious-metals scrap heading. Separating them prevents misvaluation and ensures the correct statistical tracking of each metal's secondary supply.

Refiners generally require a pre-shipment assay or lot analysis stating estimated gold content (in troy ounces or grams per unit weight), a description of the scrap source (e.g., electronic components, dental alloy, plating bath), and a commercial invoice reflecting the agreed value based on that assay. CBP may also request this documentation to verify that the declared customs value is consistent with the precious-metal content.