Hi Alain,
A pity Matchlock will be absent for a while.
Your piece is very interesting; its dimendions are similar to my example posted
HERE
While mine was considered a hand cannon and not a signal mortar, having to do with particular details for which Matchlock (for one) is a better judge,
i wouldn't advance on what yours is. The caliber and barrel thickness would suggest a cannon but the basis and touch hole with that slight lip (a repair?) suggest a (standing up) mortar.
I would agree is an old and very nice piece in any case. Naturaly cannons (handgonnes) are more rare, being much earlier than mortars; also the value depends on that.
I hope this helps and that i am not talking nonsense.