Abstract

The boron resources of Chile are all located in the northern part of the country mainly in the evaporitic basins known as 'salares' (salt flats) and are genetically related to Upper Tertiary-Quaternary volcanic activity. The most important deposits are located in the Andean basins of the Altiplano at Surire, Ascotan, Aguas Calientes Norte, Quisquiro, Aguas Calientes Sur, Maricunga and Pedernales. In addition other Altiplano basins may have boron resources, but have yet to be evaluated. The borates are present primarily in horizons known as 'barras' and usually form lenses which interdigitate with evaporitic and clastic detrital sediments. In other instances boron minerals form modules referred to as 'papas' which are up to decimeters in diameter. Economic accumulations of boron are always located within the first few meters of the saline deposits. The only Chilean economic boron-bearing mineral is ulexite, a Ca-Na borate: other minerals appear in minor amounts. Boron is also present in the lithium-rich brines of the Salar de Atacama from which boron can be recovered as by-product of lithium extraction (0.84 g/l as polyborates). A third, and far less important type of deposit, is present in the Pampa del Tamarugal within borate-rich horizons associated with paleosols. Finally, other boron accumulations, currently not exploitable, are associated with geothermal brines and the nitrate industry, both as by-products.