  We study equilibrium states of an infinite system of interacting particles in
a Euclidean space. The particles bear `unbounded' spins with a given symmetric
a priori distribution. The interaction between the particles is pairwise and
splits into position-position and spin-spin parts. The position-position part
is described by a superstable potential, and the spin-spin part is attractive
and of finite range. Thermodynamic states of the system are defined as tempered
Gibbs measures on the space of marked configurations. We derive sufficient
conditions of the existence and uniqueness of these Gibbs measures.
