Salt mining

Salt mining extracts natural salt deposits from underground. The mined salt is usually in the form of halite (commonly known as rock salt), and extracted from evaporite formations.^[1]

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.

The earliest found salt mine was in Hallstatt, Austria where salt was mined, starting in 5000BC.^[2]

As salt is a necessity of life, pre-industrial governments were usually keen to exercise stringent control over its production, often through direct ownership of the mines. Whereas the collection of most taxes generally required at least the grudging cooperation of the upper classes, ownership of salt mines could provide monarchs with a lucrative source of income for which they did not need to rely on the goodwill of other strata of society such as the nobility to remit to the monarch. For example, Polish king Casimir the Great relied on salt mines for over a third of his revenue in the 14th century.^[3]

Ancient China was among the earliest civilizations in the world with cultivation and trade in mined salt.^[4] 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.^[5] 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.^[6] The Chinese made use of natural crystallization of salt lakes and constructed some artificial evaporation basins close to shore.^[4] 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.^[5] In Southwestern China, natural salt deposits were mined with bores that could reach to a depth of more than 1,000 m (3,300 ft), but the yields of salt were relatively low.^[6] Salt mining played a pivotal role as one of the most important sources of the Imperial Chinese government's revenue and state development.^[6]

Most modern salt mines are privately operated or operated by large multinational companies such as K+S, AkzoNobel, Cargill, and Compass Minerals.

Some notable salt mines include:

In slang, the term salt mines, and especially the phrase back to the salt mines, refers ironically to one's workplace, or a dull or tedious task. This phrase originates from c. 1800 in reference to the Russian practice of sending prisoners to forced labor in Siberian salt mines.^[18][19]

Salt mines

• Khewra
• Schacht Asse II
• Turda
• Wieliczka
• Windsor

General

• Salt evaporation pond
• Brine mining
• Injection well
• Salt lake
• Salt dome
• Miner
• Coal mines and saltworks of Gouhenans
• Grozon coal and saltworks
• Coal mines and saltworks of Saulnot

Wikimedia Commons has media related to Salt mines.

• Mohammedia Rock Salt Company