198 



UNITED STATES MINERAL RESOURCES 



valuable components of nearly all of these materials 

 were at one time dissolved in large bodies of water. 

 Their present geologic settings reflect the one or 

 more processes by which those dissolved components 

 were concentrated or crystallized into deposits that 

 can, or might be, commercially exploited. 



Some of the commodities described in this chapter 

 come from more than one type of evaporite or brine 

 deposit. The largest quantities, however, generally 

 come from one of three types of deposits that have 

 fundamentally similar geologic histories. Potassium 

 compounds, salt, gypsum, and anhydrite mostly come 

 from sediments formed by the evaporation of sea 

 water during the geologic past. Sodium carbonate, 

 sulfate, borate, nitrate, and some iodine and stronti- 

 um compounds come from sediments and near-sur- 

 face brines formed by the evaporation of inland 

 bodies of water. Bromine, iodine, calcium chloride, 

 magnesium, and magnesium compounds are mostly 

 extracted from brines derived from sea water, wells, 

 and inland salt lakes. Lithium is also extracted from 

 brines, but is discussed in a separate chapter. 



The existing quantities of evaporites and brines 

 provide theoretical resources that are much larger 

 than the amounts that .are likely to ever be used. It is 

 diflScult, however, to predict this limit. This is true 

 of all commodities, but some unusual factors are 

 involved in assessing commodities extracted from 

 evaporites and brines. One factor is that some com- 

 modities can be derived from both evaporites and 

 brines. Future resources of these commodities are 

 thus represented by extremely diverse forms of 

 "ore" which may vary in grade by one or two orders 

 of magnitude. Obviously, they require quite different 

 technologies for processing and therefore very dif- 

 ferent bases for projecting future use. Brines, in 

 essence, are very low grade ore bodies that are ex- 

 ploitable only because they are very large and can be 

 inexpensively processed. Many brines contain less 

 than 5 percent of the desired substance, and some 

 contain only a few tenths or hundredths of a per- 

 cent. Solid salts, in contrast, are generally mined 

 from very high grade ore bodies ; operating potash 

 mines normally extract ore containing more than 20 

 percent potassium mineral, and salt, sodium carbon- 

 ate, and borate mines normally extract ore that is 

 75-95 percent mineral. 



Another reason that resources of commodities ob- 

 tained from evaporite and brine deposits are difficult 

 to assess is that the price is determined largely by 

 the cost of transporting the commodities to markets. 

 Deposits nearest rail and highway systems now have 

 an advantage over those that are more remote; de- 

 posits near seaports have advantages over all others 



in shipping to some domestic and most international 

 markets. Proximity to markets and efficiency of 

 transportation will probably remain important fac- 

 tors in the economic potential of most deposits, but 

 consideration of these factors is beyond the scope of 

 this study so cannot be included in its conclusions. 



Still other uncertainties must be considered in the 

 evaluation of the resources of certain commodities. 

 Some are compounds, not elements, and new techno- 

 logical developments may provide ways in which 

 some of them can be synthesized from abundant and 

 low-cost sources of their ingredients. Still others are 

 present in significant amounts in sea water, and new 

 processes may someday allow them to be extracted 

 from it ; sea water would then be an unlimited source 

 of those commodities. 



In the following discussion, the geologic settings of 

 evaporite and brine deposits are first outlined. Com- 

 modities derived from evaporites and brines are then 

 described individually so that their uses, production, 

 economics, geologic settings, and known resources 

 can be outlined. Speculation follows as to the outlook 

 for existing but undiscovered resources of geological- 

 ly related commodities ; future resources are dis- 

 cussed in genetically related groups because evalua- 

 tion of them is based more on their general char- 

 acter and on the prevalence of broadly favorable 

 areas than on specific targets. Salient problems and 

 examples of the research necessary to help solve 

 them are suggested in the final section. 



GEOLOGIC SETTING OF EVAPORITE AND 

 BRINE DEPOSITS 



The deposits that serve as sources of commodities 

 derived from evaporites and brines are grouped in 

 this chapter both by the geologic setting in which 

 they originated and by their present form. Crystal- 

 line deposits are separated into two groups according 

 to their marine or nonmarine origin ; surface and 

 subsurface waters containing unusual quantities of 

 valuable inorganic components are combined into a 

 group called brines, regardless of their probable geo- 

 logic origin. Although deposits within each group dif- 

 fer in many respects, they have features in common. 

 The following summaries emphasize the common fea- 

 tures but also note some of the differences. 



MARINE EVAPORITES 



The group of sedimentary rocks known as marine 

 evaporites consists of halite, gypsum, anhydrite, and 

 commonly some interbeds of limestone and dolomite. 

 Some limestone and either gypsum or anhydrite are 

 present in all major and many minor evaporite basins 

 of the United States (fig. 24, table 42) ; halite and 



