The solid state reaction between a nickel thin film and a silicon substrate leads to the sequential formation of Ni2Si, NiSi and NiSi2. The growth of the two first silicides occurs at low temperature (200-300°C) and is controlled by nickel diffusion. NiSi2 is only formed in a brutal manner at high temperature which indicates a nucleation controlled formation. We show that the addition of gold to the nickel film drastically affects these characteristics : Ni2Si and NiSi appear simultaneously and the nucleation temperature of NiSi2 is lowered. The solubility of gold in the three silicides is limited which induces a precipitation of gold. Depending on temperature this precipitation takes various forms : gold enriched surface layer or gold clusters at inner interfaces.