The tunnel bores deep into the mountain, wooden supports placed periodically along the length of the passage. Torches illuminate a set of rails leading into the distance, and what appears to be a journal lays on top of a mine cart filled with iron ore.
I look at the most recent entry
It takes you a moment to interpret the chicken scrawl, but you read yesterday's yield was clocked in at 1700lbs of ore.
Effectively I am trying to find out how many workers would need to be employed in the mine-shaft to produce 1700lbs in the average day. Each worker is a healthy human male with a steel pick-axe. Most are experienced in their trade.
Edit: The technology level is mid-medieval European I believe