The codex entry on lyrium says the following:
Even though dwarves have a natural resistance, raw lyrium is dangerous for all but the most experienced of the Mining Caste to handle. Even for dwarves, exposure to the unprocessed mineral can cause deafness or memory loss. For humans and elves, direct contact with lyrium ore produces nausea, blistering of the skin, and dementia. Mages cannot even approach unprocessed lyrium. Doing so is invariably fatal.
Thus I find it baffling that touching a raw lyrium vein (as a mage no less) doesn't kill me outright, but rather heals me. I can kind of reason that raw lyrium has different properties when you encounter it in the Fade, but this also happens while underground in the Frostback Mountains.
So why do lyrium veins heal you when the codex says that they are fatal?