  Spectrum of the doubly heavy tetraquarks, $bb\bar q\bar q$, is studied in a
constituent quark model. Four-body problem is solved in a variational method
where the real scaling technique is used to identify resonant states above the
fall-apart decay thresholds. In addition to the two bound states that were
reported in the previous study we have found several narrow resonant states
above the $BB^*$ and $B^*B^*$ thresholds. Their structures are studied and are
interpreted by the quark dynamics. A narrow resonance with spin-parity
$J^P=1^+$ is found to be a mixed state of a compact tetraquark and a $B^*B^*$
scattering state. This is driven by a strong color Coulombic attraction between
the $bb$ quarks. Negative-parity excited resonances with $J^P=0^-$, $1^-$ and
$2^-$ form a triplet under the heavy-quark spin symmetry. It turns out that
they share a similar structure to the $\lambda$-mode of a singly heavy baryon
as a result of the strongly attractive correlation for the doubly heavy
diquark.
