What is more metal than exploring a dungeon for the priceless bones of mammoths long dead? CARVING a dungeon to explore for the priceless bones of mammoths long dead. All of these credit to Amos Chapple, here and here.
Obviously, mostly, dungeons exist already. But I can see the applications here. Perhaps there is a patron back in town, far away from the fly-rich, endless, bear-haunted woods, who will provide a magical tool for carving out the lands of your ancestors, in return for the spoils. Perhaps you can hire such tools nearby even, in the vicious, watch-your-tusks-and-your-back shanty town on the nearest patch of stable land. Perhaps your party druid has a plausible water spell that could be used on suitable landscapes (if they don't object on principle to this practice).
Adventurers can grow rich in this way, selling raw materials to collector far away for their gaudy baubles, and to enchanters who know well the properties of ancient ivory. But adventurers can die in this way too. Not all things buried by time were dead when they were buried, and not all of them are dead - or fully dead - when they are unburied.