I wouldn't call that a gold standard; I'd call it currency freedom. A gold standard is when a government coercively decrees how gold must and must not be used.

"But whether the Constitution really be one thing, or another, this much is certain--that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist." --Lysander Spooner, 1867