Is a corsage appropriate at a black tie affair?

Yes it can be. It's best to buy a pin-on corsage for an adult female that is dainty and not too showy. Have the florist make the corsage in paler shades to suit the dress your date is wearing (you won't know the color in most cases.) If it's a teen then get a wrist corsage that is dainty and the same applies as far as color unless you know the color of her dress.