Potash Resources: Occurrences and Controls

Abstract

Natural potash evaporites are a typical part of a brine evaporation series, crystallizing at the higher concentration or bittern end, either at the surface (primary salts) or in the shallow subsurface (secondary salts). Today, bedded accumulations of primary potash evaporites are a relatively rare occurrence. Extremely high solubility of most potash salts means they accumulate in highly restricted, some would say highly continental, modern depositional settings (Cendon et al. 2003). Wherever Quaternary potash does occur naturally, as in the playas of the intermontane Qaidam Basin in China and in the Danakil Depression in the Afar Rift of Africa, carnallite, not sylvite, is the dominant potash salt. This has led some to postulate that carnallite is the archetypal primary marine potash phase, while sylvite is a secondary diagenetic mineral formed by incongruent dissolution of carnallite. Others have argued that ancient sylvite was sometimes a primary precipitate, deposited by the cooling of highly saline surface or near surface brines and from seawater with ionic proportions different to those of today (Hardie 1996).