  The analytic structure of the 2 flavour full QCD lattice Landau gauge quark
propagator is investigated with Pad\'e approximants applied to its vector and
scalar form factors. No poles at complex momentum are observed for the
propagator. Moreover, there is clear evidence of a pole at real on-axis
negative Euclidean momentum, i.e. for Minkowski type of momentum. %, with a
positive residuum. This pole occurs at Euclidean momenta $p^2 \sim - 300$ MeV
and it reproduces typical quark mass values used in phenomenological effective
quark models. The Pad\'e approximant analysis also gives hints on the presence
of a branch cut. Our results also show a clear correlation between the position
of this pole, understood as an effective quark mass, and the pion mass that is
compatible with PCAC. Slightly differences between the poles for the two quark
form factors are observed which can be viewed either as a limitation of the
method or as a suggestion that the quark propagator has no spectral
representation.
