  Along with binary neutron star mergers, the in-spiral and merger of a black
hole and a neutron star is a predicted site of $r$-process nucleosynthesis and
associated kilonovae. For the right mass ratio, very large amounts of neutron
rich material may become unbound from the post-merger accretion disk. We
simulate a suite of four post-merger disks with full-transport general
relativistic neutrino radiation magnetohydrodynamics. We find that the outflows
from these disks are very close to the threshold conditions for robust
$r$-process nucleosynthesis. For these conditions, the detailed properties of
the outflow determine whether a full $r$-process can or cannot occur, implying
that a wide range of observable phenomena are possible. We show that on average
the disk outflow lanthanide fraction is suppressed relative to the solar
isotopic pattern. In combination with the dynamical ejecta, these outflows
imply a kilonova with both blue and red components.
