The 1.4-billion-year-old deposit formed on the seafloor around hot springs system similar to the “black smoker” type known on today’s ocean floors. In the ancient sea bottom hot springs at Black Butte, hot water with high concentrations of dissolved metals and sulfur vented onto the seafloor and encountered very cold seawater. The change in temperature and chemistry caused the metallic elements including copper to bond with other elements including sulfur and precipitate onto the seafloor as metal-bearing sulfide minerals. The precipitated minerals built up into sheet-like layers later buried under thousands of feet of sediment. After formation of the Rocky Mountains, erosion exposed the deposits near the earth’s surface so that they can be mined.