Unlike the mineral deposits of the Upper Harz, the ore deposits at the Rammelsberg were caused by the escape of hot, metal-bearing, thermal springs on the sea floor in the Devonian period. This formation is referred to as a sedimentary exhalative deposit. At the bottom of the Devonian sea, two large lenses of ore were formed that were later caught up in the folding of rocks during the Carboniferous period and so lie overturned at an angle in the mountain.