This just means that the various radioisotopes of gold are pretty unstable.

AU197 is the non radioactive stable version. Radioactive atoms have a half life but AU197 isn’t radioactive.

Any atom will probably not have a half life.

Either @flutherother is correct, or all your gold is about to wither away to dust…

All isotopes of an element are, chemically speaking, still that element. However you can have radioactive isotopes that have a half-life. When a radioactive atom “decays”, it gives up energy through a variety of mechanisms, usually specific to that isotope. When that happens, typically it is no longer that chemical element.
Not all isotopes of an element are radioactive. In other words, they are happy where they are. They don’t have extra energy to give up…the balance of neutrons, protons, and electrons is proper and no energy is needed to be given up to hit stability. So when a radioactive isotope of gold decays, it stops being gold. But that doesn’t mean all gold isotopes react the same way.