If a person were to discover a method to transmute lead into gold easily, would they be required by law to disclose this information when selling it or exchanging it for currency?
The method used costs little energy and resources, and would devalue gold almost completely were the methodology exposed. The Seller would carefully structure their supply and run a mine as a front to obfuscate the gold's origin. They know what they are selling has no true value anymore, but act to prevent their buyers from learning this themselves.