Geology and origin of the Chilean nitrate deposits.

Abstract

The unique nitrate-rich caliche deposits in the Atacama Desert owe their existence to an environment favourable to accumulation and preservation of the deposits, rather than to any unusual source of the saline materials. The essential conditions are: 1) extremely arid climate similar to that of the present-day Atacama Desert; 2) slow accumulation during late Tertiary and Quaternary time; and 3) paucity of nitrate-utilizing plants and soil microorganisms. The wide distribution of the deposits without systematic relationship to topography or rock type can be explained only by atmospheric transport and deposition. Ore-grade nitrate deposits evidently formed in 3 ways: 1) slow accumulation on old land surfaces that have had little or no modification since the Miocene; 2) accumulation on lower hillsides and at breaks in slopes as the result of leaching and redeposition by rainwater; and 3) accumulation in saltpans and saline ponds.-from Author