On vacation near Poitiers, I took advantage of this scorching day to visit the famous Melle mines with my family (13°C all year in the mine).
During 400 years, the Frankish kings had 35 km of tunnels dug there, in harsh conditions, to extract the silver needed to mint our dear denarii and obols. The technique used was fire cutting: a wood fire weakened the calcified limestone (too hard for iron tools) and then the miners could scrape 10 cm of wall to find the galena geodes. With 1 kg of galena, we make 2 grams of silver, so barely more than one denier!
The mines were condemned around the year 1000, not for lack of ore but for lack of wood...
An exciting guided tour that I recommend, which includes videos on experimental archeology as to metallurgy and coinage.
