Uranium mining in Colorado the Slick Rock, Gypsum Valley, Uravan, and Gateway mining districts. Uranium mining in southwest Colorado goes back to 1898, when a miner dug ten tons of yellow ore that tested high in uranium and vanadium out of a deposit at Roc Creek in Montrose County, Colorado, and shipped it to France, where M. M. C. Friedel and E. Cumenge identified the new mineral that they named carnotite. The mineral was mined for its vanadium, with uranium as a byproduct. Although radium had been discovered in 1898, it had been derived from pitchblende, and the radium content of carnotite was not
Stephanie Horovitz radiochemistry. It predicted that lead resulting from the radioactive decay of uranium or thorium would have different atomic weights than typical lead. Early experimental data was not considered authoritative by analytical chemists. Hönigschmid had studied under leading expert Theodore Williams Richards at Harvard and his work in determining precise atomic weights was well respected. Horovitz isolated lead from uranium-rich pitchblende samples from the St. Joachmistal mine. Her gravimetric analysis to the thousandth of a gram proved that lead created from the radioactive decay of uranium had a lower atomic weight than typical lead. This was the first widely-accepted experimental proof