Gold has 1 naturally occurring isotope, of which 197Au is the most abundant at 100 %. Averaged over those abundances the atomic weight is 196.966569 Da.
A mass spectrum does not show that average: it shows one peak per isotope, at the exact mass below, in the ratio of the abundances. That pattern is what identifies the element in a spectrum.
The periodic table, read every way a chemistry course asks for. This tool needs JavaScript; these are the pages it offers: