Oh, and then it stops being gold, right?
Earth contains an element called Thorium. It is slightly radioactive and has a half life of over 14 billion years. That means that pretty much all of it is still around.
It breaks down into what are called rare earths.
What you are imagining is that the ATOM is a fixed item. It's not. It has electrons, protons and neutrons. Those objects, in turn, are made up of quarks.
We use the term "element" to refer to combinations of electrons, protons and neutrons that react in certain ways "chemically".
As you have guessed we can have an element that has billions of years of stability and another that has only days of stability, yet they are chemically reactive in the same way.
Do not confuse the term "element" with the term "atom" ~