I will clarify just in case that the miner dude must have full Industry belief.
Full Nature belief: 0-4% chance of metal bar
Neutral/default Nature-Industry belief: 10% chance of metal bar
Full Industry belief: 20% chance of metal bar
After your miner has full Industry, I recommend going full barbarism for maximum strength. After that max life to increase chances of survival in the event of cave-in.
Mining doenst really need LP investment but you may want to sudy throwaway curios with him and put points in smithing since all metalworking is STR*Smithing and your miner will double as smith. UA is also viable investment, it may allow you to escape troll -I repeat escape, not fight. You should have escape route planned whenever you mine, you must run into minehole or cave exit.
http://ringofbrodgar.com/wiki/Personal_Beliefshttp://ringofbrodgar.com/wiki/Troll