Once the oil is on the surface, it passes through separators to remove any admixed gas from the oil. The gas is sent into pipelines while the oil is sent to storage tanks called _tank batteries_. Periodically, the oil is drawn from the tank batteries where it is transported by pipeline or rail to refineries. The great bulk of the crude oil leaves New Mexico for refining via a major pipeline network extending through Texas to both the Gulf and East coasts. Some oil is refined in New Mexico, however. Oil refineries in Artesia, Bloomfield, Ciniza, Farmington, and Monument have a combined capacity to treat some 30,000 barrels (42 gallons a barrel) of crude oil a day. On the other hand, practically all the natural gas is treated in New Mexico so as to recover its liquid petroleum constituents before sending it out of the state by pipeline. MINING The mining industry of New Mexico dates back to the days of Spanish rule. Copper was mined from the Santa Rita mine as early as 1800 for shipment to Mexico for use in coinage. Significant mining in New Mexico did not commence, however, until the late 1800’s. There are three major centers today: Carlsbad, potash; Silver City area, copper, zinc, and lead; and Grants, uranium. [Illustration: Question: where are the other oil pumps and tanks in the San Juan Basin?] The potash mining east of Carlsbad, a $75 million-a-year industry employing more than 3600 persons, is the largest operation of its kind in the world. Six mining companies are active in the area, and a seventh is developing yet another mine. _Potash_ is a word used to denote various potassium compounds. The principal ore mineral at Carlsbad is sylvanite, a mixture of potassium chloride and sodium chloride (common salt). The ore contains the equivalent of 21 to 25 per cent potassium oxide (K₂O).[6] Another ore mineral, known as _langbeinite_, a double salt of potassium and magnesium sulfate, is also mined. The potash ores occur as horizontal beds sandwiched between thick salt and anhydrite layers. These beds are the result of evaporation of large quantities of salt waters during the latter part of the Permian period some 240 million years ago. The potash-bearing horizons now are buried from 900 to 1800 feet below the surface. The discovery of potash in southeast New Mexico was almost by accident. In 1925, the Snowden and McSweeny Company drilled a wildcat oil test a few miles east of Carlsbad. The hole was dry, but potash minerals were detected in the drill cuttings. The discovery generated considerable interest because the United States was forced to import most of its potash prior to this time. Further drilling proved the existence of tremendous deposits of potassium salts in that area.