Marriage with my Malagasy partner

Hello everyone! I am a French retiree currently living in Tunisia in Monastir. My main goal is to contract marriage with my Malagasy partner, in front of the authorities in Gibraltar, where, if my information is correct, we can do it without going through a French embassy or consulate. After this event, we want to settle in the area, if life there suits us. Thank you for your welcome! Marie Claire and Jean-Claude.