  We consider the reduced dynamics of a small quantum system in interaction
with a reservoir when the initial state is factorized. We present a rigorous
derivation of a GKLS master equation in the weak-coupling limit for a generic
bath, which is not assumed to have a bosonic or fermionic nature, and whose
reference state is not necessarily thermal. The crucial assumption is a
reservoir state endowed with a mixing property: the n-point connected
correlation function of the interaction must be asymptotically bounded by the
product of two-point functions (clustering property).
