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Origin of Potash Deposits

  • Donald E. GarrettAffiliated withSaline Processors, Inc.University of California

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Large, deeply buried potash deposits are found in many marine evaporite and other formations throughout the world, and occur in every continent and most geological epochs from the Cambrian to the present (Sonnenfeld 1985). The predominant mineral form is sylvite (KCl), found in almost every deposit with halite (NaCl) to form the mixture called sylvinite. In most occurrences fairly pure sylvinite exists with essentially no soluble sulfate or other salts, and in some zones of many deposits carnallite (KCl · MgCl · 6H2O) is also found, occasionally being massive and similarly crystallized with halite nearly free from other soluble salts. In only a few deposits do soluble sulfate salts occur with the potash, such as zones of the Zechstein Basin where “hartsalz” (sylvite with kieserite, MgSO4 · H2O, or anhydrite and halite) is common; double salts such as zones in Sicily and Ethiopia where kainite (KCl · MgSO4 · 2.75H2O) is predominant; and in areas of Carlsbad, New Mexico where langbeinite (K2SO4 · 2MgSO4) occurs extensively. In some deposits various other potash double salts are also present in trace to minor quantities, as well as occasionally quite extensive formations of the insoluble mineral poly halite, K2SO4 · MgSO4 · 2CaSO4 · 2H2O. In a few locations carnallite and some sylvinite occurs with halite and tachyhydrite (CaCl2 · 2MgCl2 · 12H2O.)