It is currently legal to barter goods or services in exchange for gold or silver bullion in the United States.
Gold and silver do not have to be registered or certificated, although a prudent person would usually seek evidence confirming their authenticity and it would be common practice to keep gold and silver in a repository such as a bank or Fort Knox, and to conduct the transaction via negotiable certificates evidencing ownership of the gold or silver (basically warehouse receipts whose transfer is governed by the Uniform Commercial Code) rather than to physically transfer the gold or silver, in a large dollar value transaction.
There have been periods of time in the United States where this was not allowed, unless done by a state government (which has a constitutional right to do so), or by a local government authorized by a state government to do so. But those laws are not currently in force and haven't been for a long time.
Transfers conducted with gold or silver bullion in excess of $10,000 per transferee per year, probably have to be reported to the same officials to whom a cash transaction in that amount is reportable on IRS Form 8300, because it is considered a collectible cash substitute, even though it is legal to do so and no tax is specific to barter transactions in gold or silver. IRS Publication 1544 explains the rule.
