  The concept of harmonic metallic structure on a metallic pseudo-Riemannian
manifold is introduced. In the case of compact manifolds we prove that
harmonicity of a metallic structure $J$, with $J^2=pJ+qI$ and $p^2+4q\neq 0$,
is equivalent to $dJ=0$. Conditions for a harmonic metallic structure to be
preserved by harmonic maps are also given. Moreover, we consider harmonic
metallic structures on the generalized tangent bundle, provide a
Weitzenb\"{o}ck formula for the dual metallic structure and express the
Hodge-Laplace operator on $TM \oplus T^*M$.
