Before the advent of the modern internal combustion engine and earth-moving equipment, mining salt was one of the most expensive and dangerous of operations because of rapid dehydration caused by constant contact with the salt (both in the mine passages and scattered in the air as salt dust) and of other problems caused by accidental excessive sodium intake. Salt is now plentiful, but until the Industrial Revolution, it was difficult to come by, and salt was often mined by slaves or prisoners. Life expectancy for the miners was low.
In ancient Rome, salt on the table was a mark of wealth; those who sat nearer the host were "above the salt", and those less favored were "below the salt". The Roman historian Pliny the Elder stated as an aside in his Natural History's discussion of sea water, that "in Rome ... the soldier's pay was originally salt and the word 'salary' derives from it ..."
Ancient China was among the earliest civilizations in the world with cultivation and trade in mined salt. They first discovered natural gas when they excavated rock salt. The Chinese writer, poet, and politician Zhang Hua of the Jin dynasty wrote in his book Bowuzhi how people in Zigong, Sichuan, excavated natural gas and used it to boil a rock salt solution. The ancient Chinese gradually mastered and advanced the techniques of producing salt. Salt mining was an arduous task for them, as they faced geographical and technological constraints. Salt was extracted mainly from the sea, and salt works in the coastal areas in late imperial China equated to more than 80 percent of national production. The Chinese made use of natural crystallization of salt lakes and constructed some artificial evaporation basins close to shore. In 1041, during the Song dynasty, a well with a diameter about the size of a bowl and several dozen feet deep was drilled for salt production. In Southwestern China, natural salt deposits were mined with bores that could reach to a depth of more than 1000 m, but the yields of ground and salt were relatively low. As salt is a necessity of life, salt mining played a pivotal role as one of the most important sources of Imperial Chinese government revenue and state development.
Mining regions around the world
Some notable salt mines are:
|Austria||Hallstatt and Salzkammergut.|
|Bosnia and Herzegovina||Tuzla|
|Bulgaria||Provadiya; and Solnitsata, an ancient town believed by Bulgarian archaeologists to be the oldest in Europe and the site of a salt production facility approximately six millennia ago.|
|Canada||Sifto Salt Mine in Goderich, Ontario, which, at 1.5 miles (2.4 km) wide and 2 miles (3.2 km) long, is one of the largest salt mines in the world extending 7 km2 (2.7 sq mi) .|
|England||The "-wich towns" of Cheshire and Worcestershire.|
|Ethiopia, Eritrea, Djibouti||Danakil Desert, where manual labor is used.|
|Germany||Rheinberg, Berchtesgaden, Heilbronn|
|Italy||Racalmuto, Realmonte and Petralia Soprana within the production sites managed by Italkali.|
|Morocco||JMS salt mine in Khemisset.|
|Northern Ireland||Kilroot, near Carrickfergus, more than a century old and containing passages whose combined length exceeds 25 km.|
|Pakistan||Khewra Salt Mines, the world's second largest salt-mining operation, spanning over 300 km.|
|Poland||Wieliczka and Bochnia, both established in the mid-13th century and still operating, mostly as museums. Kłodawa Salt Mine.|
|Romania||Slănic (with Salina Veche, Europe's largest salt mine), Cacica, Ocnele Mari, Salina Turda, Târgu Ocna, Ocna Sibiului, Praid and Salina Ocna Dej.|
- Salt mines
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