The north of Chile has the biggest caliche ore deposits known in the world and the only source of commercially-exploited natural nitrates on the planet.
Their geological origin is not clear. Caliche formation is believed to be the result of sediment deposits of an ancient interior sea or the accumulation of minerals resulting from erosion of The Andes West face.
Caliche is under an overload material layer having a thickness of between 0.5 and 2.5 meters in mineral strata which may have from 0.2 to 5 meters of power. Mineral concentrations in the caliche vary between a mine and another. In total SQM operates annually around 30 million tons of caliche.
Caliche overload is removed using bulldozers. Then, explosives are used to break the mineral, which is installed in trucks with front loaders. In Pedro de Valdivia, trucks haul and accrue mineral on piles or stocks near temporary railroad stations, where it is loaded on wagons bound to the production plant. In María Elena, Nueva Victoria and Pampa Blanca (located in Sierra Gorda), the mineral is leached in piles, obtaining solutions destined, as a first term, to iodine production. Subsequently, they are taken to solar evaporation ponds, where salts are crystallized using high nitrate concentrations transported by truck to the Coya Sur plants, where they are used as a supply in potassium nitrate production.
In the plants, caliche is ground mechanically until reaching a size of about ½ inch. Ground mineral is then transferred to a batch leaching plant, where its nitrate, iodine, and sulphate contents are extracted.