208 



UNITED STATES MINERAL RESOURCES 



of the world, but available data suggest that most 

 deposits are in areas characterized by above-average 

 amounts of boron in spring waters and sediments and 

 are in Cenozoic nonmarine basins formed by tectonic 

 processes. 



Prospecting for boron minerals starts with the 

 identification of basins that were, during the geo- 

 logic past, favorable for the accumulation of borate- 

 rich waters. Some basins and their sediments are 

 undeformed whereas others are folded, faulted, part- 

 ly eroded, and concealed to an extent that their 

 original shape can be inferred only by geologic re- 

 construction. Exploration generally requires drilling. 

 Sodium borate minerals (for example, borax) are 

 soluble and therefore are soon leached from outcrops 

 except in very arid regions. Calcium borate minerals 

 (for example, colemanite) and sodium-calcium bor- 

 ates (for example, ulexite) are less soluble but are 

 not well preserved in outcrop. 



Reserves and known resources of borates are large. 

 One published estimate of world indicated reserves 

 is 72 million short tons B2O3; one-half of this is in 

 domestic deposits and one-sixth is in Turkish de- 

 posits (MacMillan, 1970a, p. 882). Conservative esti- 

 mates of the sodium borate reserves in California 

 alone show that they are sufficient for 300 years at 

 present domestic consumption rates and 100 years at 

 present world consumption rates (Smith, W. C, 

 1966). Recently discovered Turkish sodium borate 

 reserves increase this supply fivefold (Industrial 

 Minerals, 1970). Calcium borate reserves in Cali- 

 fornia, Turkey, and South America further add to 

 the supply. At present consumption rates, world re- 

 serves and known resources thus are adequate for 

 many hundreds and possibly thousands of years. The 

 geologic settings of boron deposits are relatively well 

 understood, and prospecting during the last decade 

 for new deposits has been correspondingly effective. 

 New deposits are likely to be found if economic in- 

 centive exists, and world resources might ultimately 

 be increased 2-10 times. 



NITRATES 



Nitrogen compounds are essential to modern in- 

 dustry and agriculture. Production of nitrogen com- 

 pounds by "fixation" of nitrogen from the atmos- 

 phere began during World War I and now accounts 

 for all United States, and nearly all world, produc- 

 tion of nitrogen compounds. In 1968, world produc- 

 tion was 35.4 million tons of contained nitrogen, and 

 U.S. production was 10.1 million tons (Lorenz, 1971). 

 Nitrogen from the atmosphere will supply world 

 needs for the foreseeable future. For nearly 100 

 years before World War I, however, the chief source 



of fixed nitrogen was the Chilean nitrate caliche 

 deposits, and even today no comparable source of 

 solid nitrates is known in the world. The source of 

 nitrates before discovery of the Chilean deposits was 

 animal wastes. The Chilean deposits are still being 

 exploited but production is small; in 1968, NaNOg 

 and KNO3 production from there was equivalent to 

 0.12 million tons of nitrogen (Lewis, 1970a). Never- 

 theless, their importance as a potential resource is 

 large, and they supply other valuable coproducts. 



Caliche layers containing nitrates are extensive in 

 the Atacama Desert of northern Chile and are 

 known to occur in the coastal desert of Peru as far 

 north of Arequipa. The caliche layer is at or near 

 the surface and generally is 3-12 feet thick. Evapo- 

 rite minerals occur as cementing material in regolith 

 (the cement commonly makes up about a third of 

 the caliche) and as veins and impregnations in bed- 

 rock. The principal minerals are soda-niter (NaNos) , 

 halite (NaCl), and several sulfate minerals; the 

 deposits are unique in also containing iodate 

 minerals. 



Reserves of Chilean nitrate ore containing 7 per- 

 cent (present cutoff grade) or more NaNOa are esti- 

 mated to be about 2.5 billion tons. Contained in this 

 ore are an estimated 220 million tons of NaNOa, 1 

 million tons of iodine, 9 million tons of B2O3, and sub- 

 stantial amounts of less valuable components. Ca- 

 liche that is similar but contains less than 7 percent 

 NaNOa is even more widespread in northern Chile 

 and probable resources are more than 25 billion tons. 



STRONTIUM 



Strontium and its compounds are used chiefly for 

 pyrotechnics and similar purposes that utilize the 

 red coloration of its flame, but some is used for 

 vacuum tubes, greases, ceramics, color television 

 tube glass, and other purposes. In 1968, about 6,500 

 tons of strontium was consumed in the United States. 



Most production comes from celestite (SrS04), al- 

 though strontianite (SrCOa) is locally abundant. 

 Current production of strontium minerals comes 

 chiefly from Mexico and the United Kingdom. The 

 United States has sources of strontium, but all pres- 

 ent consumers utilize imported ore (Park, 1971). 



Bedded deposits of celestite and strontianite in 

 California were mined during World Wars I and 

 II. They consist of concretionary layers of the min- 

 erals in Cenozoic lacustrine deposits made up chiefly 

 of tuff and shale. Both celestite and strontianite 

 deposits contain gypsum and some include halite; 

 the strontianite beds are also associated with lime- 

 stone. The strontium minerals formed largely by 

 replacement of preexisting clastic sediments, but 



