EVAPORITES AND BRINES 



203 



KNOWN RESOURCES OF EVAPORITES 

 AND BRINES 



POTASSIUM COMPOUNDS 



Potassium (commonly referred to as its oxide, 

 "potash," KoO) is a plant nutrient that is essential 

 to maintain and expand food production for both 

 man and animal. About 95 percent of the potassium 

 compounds produced in the world are used as fer- 

 tilizers ; the remaining 5 percent are used in manu- 

 facturing drugs, dyes, and chemical reagents (U.S. 

 Bur. Mines, 1970) . Polyhalite (2CaS0,-KoS04-MgS04 

 •2H2O) deposits in New Mexico and Texas are not 

 now used, but may someday be, as a combination soil 

 conditioner and fertilizer ; coarsely ground polyhalite 

 in contact with water forms solutions containing 

 potassium, magnesium, and sulfate, and leaves gyp- 

 sum as a soil-conditioning residue. 



World production of potassium compounds in 

 1970-71 was equivalent to 17.8 million tons of K2O, 

 and production capacity is considerably larger. East- 

 ern Europe supplied 37 percent of this quantity; 

 North America, 31 percent ; Western Europe, 27 per- 

 cent ; and South America, Africa, and Asia, the bal- 

 ance. Countries providing major sources are the 

 U.S.S.R., East Germany, West Germany, France, 

 Canada, and the United States. Israel, Spain, Italy, 

 China, Chile, and Congo (Brazzaville) provided small- 

 er amounts. Potash-producing facilities are under 

 development in Australia and the United Kingdom 

 (Eilertsen, 1971; Lewis, 1970b; British Sulphur 

 Corp., 1971) . 



In the United States in 1970, potassium compounds 

 were produced by 13 companies which operated 

 plants in five States. About 87 percent of production 

 in the United States comes from crystalline deposits 

 in southeastern New Mexico and eastern Utah ; the 

 remaining 13 percent comes largely from brine op- 

 erations in northwestern Utah, California, and Michi- 

 gan. Production declined from a maximum of 3.3 

 million tons of KoO equivalent valued at $122 million 

 in 1966 to 2.7 million tons valued at about $71 million 

 in 1970 (Lewis, 1970b). This decline is expected to 

 continue as the domestic industry faces serious prob- 

 lems of dwindling reserves of high-grade ores and 

 loss of markets to Canadian sources of supply. 



Sources of potassium compounds in the United 

 States and elsewhere in the world are of two main 

 types: (1) crystalline deposits of saline rocks of 

 marine origin containing sylvite, langbeinite, and re- 

 lated potassium minerals, and (2) concentrated 

 brines from wells or in relict lakes and lacustrine 

 sediments of continental origin in arid regions. The 

 crystalline deposits are by far the richest in potassi- 



um and the simplest to exploit; the concentrated 

 brines are lower grade but generally allow production 

 of other substances such as sodium carbonate, sodi- 

 um sulfate, borates, magnesium, lithium, or bromine 

 as coproducts of the potassium compounds. 



Most potassium ores in marine evaporite deposits 

 have the potassium concentrated in sylvite (KCl) or 

 a potassium-magnesium mineral, and all occur with- 

 in the sodium-rich (halite) facies of evaporite de- 

 posits. Although not now considered ore, large and 

 nearly pure deposits of the potassium mineral poly- 

 halite (K2MgCa2(S04)4-2HoO) occur in or near the 

 calcium-rich facies of evaporite deposits. In North 

 America, polyhalite deposits occur only in south- 

 eastern New Mexico and western Texas near the 

 boundary of the halite and anhydrite facies. 



The greatest concentrations of sylvite in most 

 evaporite basins are in tabular bodies that may be 

 primary or replacement in origin. Such deposits are 

 mostly tens of feet thick and several square miles 

 in area, and generally contain at least twice as much 

 halite as sylvite. Smaller concentrations of sylvite 

 (or carnallite) occur in markedly discordant replace- 

 ment lenses and veins that contain little or no halite. 

 Both types of concentrations ordinarily have sharp, 

 clear-cut boundaries (Jones and Madsen, 1968) . 



Brines are also a source of potassium compounds 

 in the United States. Most productive brines are from 

 inland lakes but some are from deep wells. Most al- 

 low production of other commodities along with the 

 potassium salts so that the costs of processing are 

 shared, a practice that contributes to the commercial 

 feasibility of such low-grade sources of the element. 

 In other respects, however, brines that yield potassi- 

 um have little else in common, either geologically or 

 chemically. Production from California is from alka- 

 line near-surface brines in an upper Quaternary sa- 

 line deposit ; Utah production is from nearly neutral 

 surface waters of a saline lake ; Michigan production 

 is from acidic deep-well brines; production from 

 Israel is from brines in the Dead Sea. 



Exploration for potassium deposits is difficult be- 

 cause the deposits are soluble and consequently do 

 not crop out at the surface. Before extensive drilling 

 for petroleum, potassium deposits were mostly en- 

 countered accidentally in mines being worked for 

 salt. Analysis of near-surface brines from relict lakes 

 has been used with some success to locate exploitable 

 deposits in arid regions, but it has not been used 

 with success elsewhere. Analysis of cuttings, cores, 

 and gamma-ray and other logs from exploratory 

 boreholes drilled primarily for petroleum has been 

 responsible for most potash discoveries in recent 



