If you are a nonresident visiting the U.S. with gifts, your personal belongings or goods for resale there is a possibility you will not have to pay duty. For instance, if you are visiting the U.S. for 72 hours or more you are allowed to bring up to $100 worth of goods duty-free. If the value of the gift exceeds $100, you will be required to pay duty.

Note that Gold Coins count as "money" (if they are negotiable currency) and there is no duty on "money". Travelers entering or leaving the USA are required to declare amounts of "money" over $10,000, but there is no duty, regardless of the amount/value.