Geology of potash
Potash is recovered from both Quaternary lacustrine and ancient marine evaporite targets. Canada, historically the world’s largest potash producer, holds more than 45% of the world’s known potash reserves and recovers potash by mostly conventional underground mining of bedded sylvinite deposits. Production is centred on the Devonian Prairie Evaporite in the Elk Point Basin in Saskatchewan, with lesser production in the Carboniferous New Brunswick sub-basin in the Maritime Provinces. Russia is the other major potash producer at the world scale, it holds some 35% of known world reserves including significant potential for new discoveries in the East Siberian region. Currently, Russia extracts most of its potash from the Cis-Urals region, where sylvinite is conventionally mined from the Permian Upper Kama Basin in the Solikamsk region west of the Urals. Devonian potash is also mined in the Pripyat depression of Belarus, which holds 9% of the world’s known reserves.
In terms of world potash resource, Canada once again tops the bill. A combined U.S. Geological Survey and Saskatchewan Geological Survey assessment (Cocker, Orris, Yang and Dunlap, 2010) estimate known potash resources in the Prairie Evaporite Deposit to be around 88.8 billion tonnes of potassium oxide (K2O). This estimate is higher than various previous estimates ranging from 56 to 67 billion t of K2O. If correct, the potash resource in Saskatchewan would be sufficient to mine for several thousand years at the current production level.
Significant volumes of Permian potash are still mined from the Zechstein of NW Europe (Germany, UK and the Netherlands), while smaller amounts are mined from the northern margin of the Delaware Basin in New Mexico, USA. Oligocene potash was formerly extracted from the Rhine Graben (Alsace Basin) in France, while Miocene potash is still mined in the Stebnik area in the western Ukraine. In Spain, in the northern part of the Ebro Basin near the border with France, potash is produced from Eocene-Oligocene lake sediments.
In Utah, potash is solution mined from the Carboniferous Paradox Formation deposits and recovered from Great Salt Lake brines by solar evaporation and flotation (figure) Israel and Jordan use similar solar technology to produce large volumes of potash from Dead Sea brines created naturally from recycled marine Miocene evaporites and connate waters buried beneath the floor of the Dead Sea (figure). In China, various combinations of KCl and/or K2SO4 are recovered by processing of saline lake brines from the Qarhan and Lop Nur salt flats. In California, potash and coproducts, borax pentahydrate, soda ash and saltcake, have been recovered from various subsurface playa brines using mechanical evaporation. KCl and K2SO4 are byproducts of lithium processing from salar brines in the Atacama Desert of Chile, South America (figure).
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