  The building blocks of Titan and Enceladus are believed to have formed in a
late-stage circumplanetary disk around Saturn. Evaluating the evolution of the
abundances of volatile species in this disk as a function of the migration,
growth, and evaporation of icy grains is then of primary importance to assess
the origin of the material that eventually formed these two moons. Here we use
a simple prescription of Saturn's circumplanetary disk in which the location of
the centrifugal radius is varied, to investigate the time evolution of the
icelines of water ice, ammonia hydrate, methane clathrate, carbon monoxide and
dinitrogen pure condensates. To match their compositional data, the building
blocks of both moons would have had to form in a region of the circumplanetary
disk situated between the icelines of carbon monoxide and dinitrogen at their
outer limit, and the iceline of methane clathrate as their inner limit. We find
that a source of dust at the location of centrifugal radius does not guarantee
the replenishment of the disk in the volatiles assumed to be primordial in
Titan and Enceladus. Only simulations assuming a centrifugal radius in the
66--100 Saturnian radii range allow for the formation and growth of solids with
compositions consistent with those measured in Enceladus and Titan. The species
are then able to evolve in solid forms in the system for longer periods of
time, even reaching an equilibrium, thus favoring the formation of Titan and
Enceladus building blocks in this region of the disk.
