It's a spear tip form the ancient tribe Maribubta that came to the American Island from the land just north of Tyriniba. Looks like one of the tribes elder braves property.
Getting on a military base is not so unusual. I have been hunting one here for the past 15 years on and off. Also hunted on Alameda air base in Ca. and bases in KS, KY, and in Europe. Food for thought.
I think you have the best answer. I've seen these types of hinges quite a few times. I believe I've seen them on china-cabinet doors or kitchen cabinet doors.