I think probably the better way to go is to horn in on the supply of raw iron to the guilds that use it as a raw material. Then you cut deals with the crafts guilds to protect you from the miners legally and physically in exchange for a regular source of iron. Since you, as a single wizard, are doing this strictly to have a steady income of easy money, you take care not to put the miners out of business. Then, hopefully, the combination of craft guild protection and a lack of a truly DIRE economic threat means that the miners don't go aggro.
