Radioactive waste also plays a significant role. Uranium tailings are waste by-product materials left over from the rough processing of uranium-bearing ore. They are not significantly radioactive. Mill tailings are sometimes referred to as 11(e)2 wastes, from the section of the Atomic Energy Act of 1946 that defines them. Uranium mill tailings typically also contain chemically hazardous heavy metal such as lead and arsenic. Vast mounds of uranium mill tailings are left at many old mining sites, especially in Colorado, New Mexico, and Utah. Although mill tailings are not very radioactive, they have long half-lives. Mill tailings often contain radium, thorium and
Uranium mining in Colorado consists of Tertiary hydrothermal veins filling fracture zones oriented predominantly NNW-SSE in gneiss, schist, and quartzite of the Precambrian Idaho Springs Formation. The chief ore mineral is pitchblende, which occurs with adularia and ankerite. Schwartzwalder could interest no one in his discovery, so he drove the first adit of the Schwartzwalder mine by himself, made the first ore shipment in 1953, and sold the mine in 1955. The Schwartzwalder mine was the source of more than 99% of the uranium produced from the Front Range province. The mine operated until 1995, producing 17 million pounds (7700 metric tons) of uranium