Fe doping of GaN is gaining increasing interest in the recent years for the realization of diluted magnetic semiconductors for spintronic applications as well as to obtain high-resistivity layers in GaN-based heterostructures. For all these applications high concentrations of Fe atoms have to be introduced in substitutional sites in the GaN crystalline matrix. Among the different incorporation techniques, ion implantation proved to be a very powerful tool and it is being more and more employed. Nonetheless several problems and effects have to be addressed in this case, mainly concerning the implantation damage and its annealing recovery, and possible Fe redistribution effects upon thermal treatments. In this work we present the results of an investigation on the evolution upon rapid thermal annealing of the lattice site location of implanted Fe centers, as a function of the implantation conditions (fluence and temperature). The aim was to study the role of the implantation damage on the thermal stability of the Fe centers. For this study commercial GaN substrates grown on sapphire have been implanted with Fe ions at fluences in the range 2x10¹⁵ – 1x10¹⁶ cm^-2, both at room temperature and at 350 °C. Isochronal annealings have been performed by RTA at different temperatures up to 1000 °C. The implanted samples have been then analyzed  by means of SIMS to extract the Fe concentration profiles, RBS-channeling to study the implantation damage evolution while PIXE-channeling was used to determine the Fe lattice site location as a function of the annealing temperature.