Your analogy has a flaw: gold is a commodity with a known price. If I discover a rare artifact in my backyard, I can't be taxed on that because no one has any i

Your analogy has a flaw: gold is a commodity with a known price. If I discover a rare artifact in my backyard, I can't be taxed on that because no one has any idea what it's worth— arguably it doesn't have worth unless someone pays me for it.