Better to keep that magic unlock scroll for when you find the three chests in your armoury. At least those chests have a chance of giving high level loot.
Small spoiler:
You can find at least two more magic unlock spells. One is in a mound in the temple of dead, near the spot where you find some guy's journal, along with a lot of ingredients. The other rests in a mound in the 'crypt' area of the mines.
