  We explore heavy-element nucleosynthesis by rapid neutron capture (r-process)
in the decompressing ejecta from the surface of a neutron star. The
decompression is triggered by a violent phase transition to strange quark
matter (quark-nova scenario). The presence of neutron-rich large Z nuclei
(40,95) < (Z,A) < (70,177), the large neutron-to-seed ratio, and the low
electron fraction Ye ~ 0.03 in the decompressing ejecta present favorable
conditions for the r-process. We perform network calculations that are adapted
to the quark-nova conditions, and which mimic usual (n-gamma) equilibrium
r-process calculations during the initially cold decompression phase. They
match to dynamical r-process calculations at densities below neutron drip
(4.10^11 g cm-3). We present results for the final element abundance
distribution with and without heating from nuclear reactions, and compare to
the solar abundance pattern of r-process elements. We highlight the
distinguishing features of quark-novae by contrasting it with conventional
nucleosynthetic sites such as type II supernovae and neutron star mergers,
especially in the context of heavy-element compositions of extremely
metal-deficient stars.
