Is it possible to protect molten magnesium with Butane
if it might pull the oxygen out of sand , try using magnesium oxide, surely it won't pull the oxygen from its own self. Or using burnt lime, surely it won't pull oxygen away from calcium. 
It might react with butane to form magnesium hydride and carbide ....which would be fun to play with . Also magnesium easily reacts with nitrogen to make the nitride...which is an excellent way to make ammonia