Why not avoid the whole issue and just reclaim the gold by selling the contents of your solder pot to a reclaimer. Solder analysis is under $ 50 while the solder can be reclaimed at a value of at least 50 % of your virgin metal cost, plus a concentration of gold of .2-.3 percent will cover the balance of the new charge. Check with your reclaimer, get an independent assay, negotiate the price up front..... and agree on a standard size of mold to pour your ingots. Do not list your shipment as gold bearing bars, but do special tag them. We never had a project that got a pot that far, but our planning indicated that reclaim would actually make money if we did.