I like mining. I found my copy of the Complete Book of Dwarves and decided to make up some mining rules for ACKS.
They are fairly long and have a lot of tables. I’ll provide a summary here, but for the full thing, I set up a quick wiki page just so I would have somewhere to post tables, and you can read it here: http://aryxymaraki.pbworks.com/w/page/76091609/Mining
Also available as a download on the Downloads page on this site: http://autarch.co/downloads (in the Supplemental Rules section)
For summary, I have rules for finding mineral veins in a hex, then accessing them, then extracting ore, then smelting it.
Mines come in various flavors (copper, tin, lead, iron, silver, electrum, gold, platinum, mithril). The first four listed there are common metals, the last five are precious metals. Each has a varying amount of ore that you can extract per week of work (I used weeks because Complete Book of Dwarves does, but you can easily translate it to months by just multiplying by 4).
Each mine has a quality rating (1-10, or 10% to 100%) which is the percentage of its ore that is metal. Once you smelt your ore, you end up with metal equal to ore weight * quality. Once you know your metal weight, you move over to simply using the mercantile system; 100 stone of common metals is a load, 4 stone of precious metals is a load.
Smelting it requires you to buy a smelter (which come in three sizes, each of which can handle varying amounts of ore per week) and pay for the operation of the smelter (which is much more expensive for precious metals than for common metals).
Mines have a duration before they run empty and you have gotten all the ore. There are also some tables I stole from CBOD to determine which direction the vein goes, so you can properly describe your underground adventures as you accidentally break into a cavern full of lava and screaming.
If you like fun numbers like “Minimum Quality for Profit” and “What happens if you hire umber hulks to mine for you”, there’s a link to the Mining Math page on top of the Mining page. The Mining page is written to be read, the Mining Math page is more me doing random math then posting it.