What's the deal with Harkon's Ancient Vault?

[Coldhands]

I thought there'd be more of a story to the quest for fixing Luthor's mind, but the Slann Gold quest ends with, "You found some magic gold. It's probably important." And then the main quest just says get the Slann gold and build the Ancient Vault, then, "Congrats, Luthor got his magic back."

Is there a Warhammer lore explanation for what the cave was and how the gold helped put his mind back together? Or did he not put his mind back together, and just got his magic back?