It needs more communication to understand the topic. My wife was born in this city and often used to play and visit the underground passages under the whole city from school.
It was the first ever large-scale silver mining and coinage. Brectates and denarii:
Jihlava – the oldest mining town in the Czech Republic Jihlava became the first mining town around 1240, in the vicinity of which silver veins were discovered. In total, over 20 ore-bearing veins were known here, the thickness of which was very variable, from a few cm to 2 m.
a charter giving the town the right to mine silver
there you can see what the corridors under the city look like, and an illustration of how the rock was mined, where there was a silver vein.
Found a punch for breccias in the underground of the city during building modifications.
silver denarius found underground where the mint was