Well, changing canmount=noauto did not do the trick, still that's what mount returns:
[root@system /usr]# mount
zroot on / (zfs, local, nfsv4acls)
devfs on /dev (devfs)
zroot/usr/jails on /usr/jails (zfs, local, noatime, nfsv4acls)
zroot/usr/jails/basejail on /usr/jails/basejail (zfs, local...