MAJOR EVAPORITE POTASH DEPOSITS IN EXTENSIONAL TERRAINS

The world’s largest marine evaporite potash deposits including the Devonian Elk Point Basin in Canada (200,000 km²-area underlain by potash salts, the Permian Salado Basin in the western United States (91,000 km²), and the Zechstein Basin in northern Europe (approximately 150,000 km²) are in large, intracratonic basins developed on stable continental platforms. Although deposits in extension-related basins are generally smaller, the third and fifth largest potash producers - the Devonian Pripyat Basin in Belarus (15,000 km²) and the Pliocene Dead Sea Basin in Israel and Jordan (2,500 km² are found in extension-related basins. Other important potash deposits are in extension-related basins including the Holocene Danakhil Basin in Ethiopia and Eritrea (2,000 km²), the Cretaceous Gabon and Congo Basins in west central Africa (approximately 50,000 km²), and the Cretaceous Sergipe Basin in Brazil (10,000 km²) also contain important potash deposits. Numerous potash horizons in these basins (up to 60 creates a total average mineralized thickness of over 200 m as compared to 4 to 12 horizons and a total average thickness of 30 m to 50 m in the intracratonic basins. Increased basin aridity caused by adjacent rift-related mountain building facilitated extreme evaporation, brine concentration, and deposition of salt and potash as sylvite, carnallite, kieserite, langbeinite, and polyhalite. Episodic extensional activity found in these continental rift basins and its associated crustal thinning, basin deepening, and recurring marine invasion were responsible for the thick, repeated potash sequences. During marine rifting, hydrothermal emanations from spreading centers may increase brine concentrations of Cl, S, K, Na, and Ca facilitating deposition of potash salts. Extension-related basement faulting may help initiate halokinesis in the thick salt sequences. Halokinesis is well-known to bring potash salts to the near-surface from deeper, uneconomic levels. Salt diapirs may also be responsible for structural traps for oil and gas and related sulfur deposits.