The rare weapon enchantments, Fire Aspect, Looting, and Sweeping Edge, are all fairly simple concepts, but that also means a lot of potential candidates. Thankfully, the nature of alumentum means it should work as a catch-all material for Fire Aspect. As for Looting, gold seems to be the logical starting point. And for Sweeping Edge, I would prefer to use raw lightning but the destructive properties of TNT shall have to suffice.