We report on topographical and electrical properties of an evaporated (as-prepared) thin gold film before and after irradiation with 200 keV Ar+ ions. TEM-investigations reveal for the as-prepared film voids and channels of small size, and a pronounced percolative structure with large scale inhomogeneities after irradiation. Magnetoresistance measurements carried out before and after irradiation yield the temperature dependence of the phase coherence lengthLψ, when analysing the experimental data within current theories for 2-dimensional (2d) weak localization. The results can be explained by normal electron diffusion if-for the as-prepared film-Lψ is larger than the size of structural inhomogeneities, and-for the irradiated film-by anomalous electron diffusion ifLψ becomes smaller. The analysis ofLψ(T) for the irradiated film yields critical exponents for 2d-percolation, in good agreement with predictions of percolation theory.