Kupferschiefer

The Kupferschiefer is a thin but widespread layer of copper bearing black shale of Late Permian age, roughly two hundred and fifty seven million years old, extending across parts of present day Germany, Poland and neighboring countries, deposited on the floor of an ancient restricted sea under low oxygen conditions that preserved both fish fossils and, economically, one of the richest sedimentary copper and silver deposits in the world. The formation has been mined for metal since medieval times and remains a major source of copper ore in Poland today.