The probable results of the below (in my imagination) would be a toss-up between asphyxiation, blindness, and/or molten magnesium in uncomfortable places but I'm not entirely sure. So given this scenario what would be the outcome:

An angry fire mage is fighting a crafty metal mage: how much of a bad day will the fire mage have when hit with a face full of magnesium dust that has passed through a fireball?