  We present a study of phase separation from supersaturated 3He-4He liquid
mixtures at low temperatures addressing both the degree of critical
supersaturation Dx and the thermal-to-quantum crossover temperature T* for the
nucleation process. Two different nucleation seeds are investigated, namely 3He
droplets and 4He vortex lines with cores filled with 3He. We have found that
the experimental T* is reproduced when we consider that nucleation proceeds
from 3He droplets, whereas Dx is reproduced when we consider 4He vortex lines
filled with 3He. However, neither nucleation configuration is able to
simultaneously reproduce the current experimental information on Dx and T*.
