As a follow up, another important consideration is the type and quantity of magic available to the miners. Placer mining in which gold, as flakes and nuggets, is taken from the gravel can be boosted by various sorting cantrips or spells, but while the spells instantly affect a small area manual labor is likely to be the norm (though the scene of several weary miners watching as a wizard merely points at a gravel bar, mumbles with a flourish, and gold flakes appears in a nice pile has some possibilites).
Hard rock ming is another issue. Soft sedimentary stone can be cut by normal tools but the granite where gold veined quartz is normally found is extremely hard and rapidly wears down iron tools. Prior to the advent of dynamite most tunnels were barely large enough to crawl in, were usually worked by short lived slave and convict labor, and progress was measured by a few feet per week. The only alternantive was water power - do a search on Californian Hydro mining or Roman techniques in Illyria and Iberia to see devastation comparable with modern open pit mining. With magic the rock can be broken into manegable ore with directed explosion spells or by allowing water to seep into cracks and instantly freezing it with a variety of cold spells.
