Alright, I've been getting questions about rules, so I'll post the system which I'm most confident about.
Everyone who wants to mine will be assigned one or a few mines, which will have a mineral or minerals assigned as well as a "richness" value. Rich mines have lots of the mineral in one place, while poor mines have less mineral or less pure mineral.
Each month, each mine will mine an amount of mineral equal to the lode richness times a special modifier based on the mineral times the number of miners working there, times a number equal to around 1/100. Copper and marble both have a special modifier equal to 100; iron's is 50, gold's is 15, and so on. Metal ores need to be smelted, typically at a rate of 10 ore plus one fuel to one bar of metal. Fuel can be coke (derived from coal) or charcoal (derived from wood), or occasionally omitted in special cases probably involving magic. As the years go on, mines become less efficient as miners need to spend more time moving the minerals than mining; this takes the form of a drop in a few tenths of a percentage point in mineral gain every year, although this mechanic will be the first tossed if the whole thing is too complex. A single smelter can smelt four loads of ore per month.
Alloys can also be smelted. It takes three iron, one unit of charcoal, and fuel to make two (or maybe one) bar of steel. Two copper plus one tin plus fuel equals three bronze. I'll come up with other alloys on request.