206 



UNITED STATES MINERAL RESOURCES 



ties are very large and adequate for centuries to 

 come. Synthetic gypsum is produced as a byproduct 

 of the manufacture of several other compounds, but 

 the economics of production probably will prevent 

 these sources from being exploited solely for the 

 value of the gypsum. 



SODIUM CARBONATE 



Sodium carbonate (NasCOn, which is known indus- 

 trially as "soda ash") is an important industrial 

 chemical because of its own chemical properties, and 

 because of its use in the manufacture of other com- 

 pounds such as sodium bicarbonate, sodium hydrox- 

 ide, and sodium nitrate. In 1970 the United States 

 consumed 6.8 million tons of sodium carbonate and 

 exported an additional 0.3 million tons. Present 

 domestic consumption is as follows: 50 percent for 

 manufacture of glass, 40 percent for making other 

 chemicals, 8 percent in paper and pulp manufacture, 

 and 2 percent in miscellaneous uses such as soap, 

 detergents, and water softeners (MacMillan, 1970d; 

 Lansche, 1971b). A potentially large use of one of its 

 derivatives, sodium bicarbonate (NaHCOa), is as a 

 cleanser of sulfur dioxide from stack gases of power- 

 rlants. 



Most of the sodium carbonate and bicarbonate now 

 produced in the United States is manufactured from 

 sodium chloride, ammonia, and carbon dioxide by the 

 Solvay process, but this production is gradually de- 

 clining because of the high cost of new plants and 

 follution problems. This chapter discusses natural 

 deposits whose 1971 production was valued at $56 

 million and constituted 38 percent of the U.S. total. 

 Before 1950, sodium carbonate from natural sources 

 in California supplied only about 6 percent of U.S. 

 needs. In that year, however, production commenced 

 from an immense deposit of bedded trona (NaoCO:; 

 •NaHCOa -21120) in southwestern Wyoming. By 

 1970, this deposit furnished about one-third of the 

 Nation's sodium carbonate. It will probably become 

 the major domestic source within a few years ; plan- 

 ned increases in the mining and refining capacity of 

 three plants producing from the Wyoming deposit 

 v/ould raise annual production to about 5 million tons 

 of sodium carbonate (70 percent of present consump- 

 tion) and a possible fourth plant would raise produc- 

 tion even further. 



Core drilling is virtually required in prospecting 

 for natural sodium carbonate and other saline de- 

 posits. All valuable saline minerals are soluble and 

 so are rarely exposed in outcrop, but some geologic 

 indications help narrow the target before drilling 

 (Smith, 1966c; Culbertson, 1971). For example, 

 sodium carbonate minerals dissolved from outcrops 



may be indicated by identifiable cavities or pseudo- 

 moi-phs, a high sodium carbonate content in ground 

 or surface water may indicate concealed deposits 

 undergoing such solution, and certain lithologic tex- 

 tures and less soluble evaporite minerals in outcrop- 

 ping rocks may indicate nearby buried salines. 

 Gamma-ray, neutron, sonic, and density geophysical 

 logs from oil and gas test holes generally indicate the 

 presence of any trona layers that were penetrated, 

 although it is difficult to distinguish them from some 

 other evaporites. 



The domestic resources of sodium carbonate are 

 immense. Not only are there nearly inexhaustible 

 supplies of salt and limestone from which sodium 

 carbonate could be manufactured by the Solvay 

 process, but the trona deposits in the Green River 

 Formation of Eocene age in southwestern Wyoming 

 that are now being mined would supply the Nation's 

 needs for more than 3,000 years at the present rate 

 of consumption. These deposits underlie an area of 

 about 1,300 square miles at depths of 400-3,500 feet 

 (Bradley and Eugster, 1969; Culbertson, 1971). Re- 

 sources of trona in beds more than 3 feet thick total 

 about 85 billion tons; some beds, however, locally 

 contain halite as an impurity. Between 30 and 40 

 billion tons of trona are contained in halite-free beds 

 more than 6 feet thick. Marlstone and oil-shale beds 

 between the trona beds contain submarginal re- 

 sources in the form of disseminated sodium carbon- 

 ate minerals such as shortite (Na2C03-2CaC03) and 

 northupite (Na^COs • NaCl • MgCO.) . 



In northwestern Colorado, the Green River For- 

 mation contains additional resources of sodium car- 

 bonate in the form of nahcolite (NaHCO.^). These 

 resources add substantially to the nation's supply. 

 The mineral occurs as lenses, nodules, and beds in a 

 thick sequence of rich oil shale that also contains 

 large amounts of dawsonite and some halite. Nahco- 

 lite-bearing oil shale, 100 or more feet thick, under- 

 lies an area of about 255 square miles in the northern 

 part of the Piceance Creek basin at depths of 1,100- 

 2,000 feet. The average nahcolite content in repre- 

 sentative core holes ranges from 13 to 26 weight per- 

 cent. The area is estimated to contain 32 billion tons 

 of nahcolite, making this the second largest sodium 

 carbonate deposit known in the world (Trudell and 

 others, 1970; Dyni and others, 1970). Nahcolite is a 

 potential source of soda ash, but it may also gain use 

 in its natural form as a chemical agent for removing 

 oxides of sulfur and nitrogen from hot industrial 

 stack gases and as a low-cost means of increasing 

 the yield of alumina from interbedded dawsonite- 

 bearing oil shales with which the nahcolite neces- 

 sarily would be mined. 



