The Rio Tinto Borax Mine (also known as the U.S. Borax Boron Mine) in Boron, CA is California's largest open-pit mine and the largest borax mine in the world, producing nearly half the world's borates. It is operated by the Rio Tinto Group.[1][2]
The borax deposit here was discovered in 1913, by Dr. John K. Sukow, who when drilling for water found a deposit of what he believed to by gypsum, but further testing revealed that it was the colemanite form of borax. Francis Marion "Borax" Smith quickly bought the claim for his Pacific Coast Borax Company.[3][4] Mining at the site by shafts began in the 1920s. Pacific Coast Borax later became U.S. Borax, which subsequently opened the current open pit mine in 1957. U.S. Borax was later acquired by Rio Tinto Group, which continues to operate the mine today.