Customs value for polymetallic concentrates is typically based on the transaction value of the shipment as invoiced, which in turn reflects the payable metal content (silver, gold, copper, lead, or zinc) minus treatment and refining charges. Importers should retain the commercial invoice, assay certificate, and offtake contract terms as supporting documentation, since CBP may request these to verify that the declared value accurately reflects the contained silver and co-product credits.

Silver concentrates are produced directly from ore by physical beneficiation (flotation, gravity separation) and retain the mineralogical character of the original ore. Slags and residues arise from smelting or refining operations and are classified under separate headings for metallurgical residues. The distinction affects both the applicable SITC/HTS heading and, in some jurisdictions, export licensing requirements, so the processing history of the material should be documented clearly in shipping records.