Rare Earths From Lighter Flints To X-Rays ? Discovery

Mountain Pass, California is located 96 km southwest of Las Vegas, Nevada, and has an exposed surface orebody within view of Interstate Highway 15. Mineral prospecting in this region dates back to about 1860 followed by the discovery and subsequent mining (1870-1895) of silver bearing veins on the north slope of nearby Clark Mountain. In contrast to the four lane divided interstate highway of today, all supplies needed for mining during this early history were transported by wagons from San Bernardino which is 320 km west. Many small lead mines were active in the area during 1917-20, and a small gold mine operated in 1941-42 within 100 m of the orebody presently being worked. In 1949 two prospectors searching for uranium with a Geiger counter discovered a radioactive vein outcrop at Mountain Pass. Further investigation revealed the presence of a large amount of a light-brown, heavy mineral to a depth of about 2 m. A sample of this unidentified mineral was submitted to the Boulder City, Nevada, U.S. Bureau of Mines where a spectroscope examination shoved high level rare earth oxides, carbon dioxide, and fluorine. These results indicated the mineral was bastnasite.