The old copper mines in Southern Arizona like Bisbee and Morenci were started to process copper ore which was essentially low content ore found in the soil however before the open pits they were underground and much Turquoise was removed mostly by the miners with the blessing of the owners because looking for the Turquoise made the miners work harder and faster. Up in Alaska during the Klondike years initially they had problems refining the Gold because typical mercury processing didn't work because the ore was fouled by this heavy black sand. Once they modified the process they separated this nuisance sand and threw it away. It turned out that stuff was Platinum. it's very common a mining operation produces way more than one targeted product. often times many separate operations are going on in differing locations within the deposit and sometimes everything is all together in one small spot.