It's pretty competitive with granite: If you would otherwise train magic with plank make you'd get 160k magic xp/h and -410k gp/h. If you would otherwise train smithing with adamant platebodies you'd get 175k smithing xp/h and -5.1m gp/h. That means an hour of gold mining saves 0.5 hours of mining and smithing, as well as 1.3m in the associated costs. Concentrated gold: 50k mining xp, costs 130k, saves 0.5 hours, saves 1.3m Granite: 70k mining xp Although you can alch while you mine granite. But that's really really painstaking.