  In light of the increasingly heavy UHECR composition at the highest energies,
as observed by the Pierre Auger Observatory, the implications of these results
on the actual source composition and spectra are investigated. Depending on the
maximum energy of the particles accelerated, sources producing hard spectra
and/or containing a considerably enhanced heavy component appear a necessary
requirement. Consideration is made of two archetypal models compatible with
these results. The secondary signatures expected , following the propagation of
the nuclear species from source to Earth, are determined for these two example
cases. Finally, the effect introduced by the presence of nG extragalactic
magnetic fields in collaboration with a large (80 Mpc) distance to the nearest
source is discussed.
