Mining salt on the saltflat of the Danakhil Depression, Ethiopia. A) lifting the salt slab prior to cutting. B) loading the cut slabs of salt pavement onto a camel for transport out of the saltflat.
Around 6,000 BC on the margins of Lake Yun Cheng in Northern China’s we see the first evidence of an industry designed to harvest and produce salt, via the evaporation of lake brines in purpose-built salt pans. In Europe, the first recorded industrial production of pan salt took place in Italy some 2500 years ago when Ancus Martius, one of the early Roman kings, began letting seawater into an enclosed basin, then allowing the sun to evaporate the water to create a salt residue. The importance that Rome attached to the salt works and port at Ostia was such that the main highway along which the salt was carried to Rome was called the Via Salaria. Like Venice after it, the city of Rome based much of its early commerce on trading salt. Special salt rations paid to early Roman soldiers were known as “salarium argentum”, the forerunner of the English word “salary.” With a near-monopoly on supply to Rome, the traders in the port of Ostia raised the salt price so high that the state was forced to take over the industry in 506 BC.
When Julius Caesar landed in Britain in 55 BC, he brought his salinators with him, but found that even the backward Britons were extracting salt by pouring brine on to hot stones. The Romans, however, used iron pans in which they boiled the brine, and Caesar established a brine-based salt works in Cheshire and subsequently in other localities where ancient salt occurred at shallow depths. The towns in Britain where salt was made from brines extracted from shallow buried ancient salt beds can be distinguished to this day by the termination “wich”, an Anglo-Saxon descriptor for a place where salt was made and includes towns like Greenwich, Ipswich, Droitwich, Northwich and Middlewich. Likewise, within regions of shallow salt and brines in Austria and Germany, names containing “salz” and “halle,” such as Salzburg (“salt city”), Salzkammergut, Reichenhall, Halle, Hallein, and Hallstatt, as well as the old Austrian/Polish province of Galicia, identify some of the salt-bearing areas.
In 12th-Century Timbuktu in Africa, the gateway to the Sahara Desert was the seat of renowned scholars and merchants, who valued salt extracted from salt lakes to north in the vicinity of Taoudenni, Mali, as highly as books or gold. The Taoudenni mines are located on the bed of an ancient erg-edge salt lake and have been actively quarried for more than a 1,000 years. Today, the miners use crude axes to dig pits that usually measure 5 m by 5 m with a depth down to around 4 m. The miners first remove up to 1.5 m of red clay overburden, in contrast to the salt miners in the Danakil who work at the active pan surface. Then several layers of poor-quality salt are removed before reaching three layers of high-quality salt. The salt is cut into slabs that are 110 cm x 45 cm by 5 cm in thickness and weigh around 30 kg. Two of the high-quality layers are of sufficient thickness to be split in half, so that five slabs can be produced from the three layers. Having removed the salt from the base area of the pit, the miners excavate horizontally to create galleries from which additional slabs can be obtained. As each pit is exhausted, another is dug so there are now thousands of pits spread over a wide area on the lake.
Over the centuries salt has been extracted from three distinct areas of the lake depression, with each successive area located further to the southwest. The areas can be clearly seen on satellite photographs (22.606519°E, 4.030660°S). Until recently salt was transported south by huge camel trains, now more and more salt is carried out by 4-wheel drive trucks, south to Timbucktu and on to the river port of Mopti. Among the some of the nomadic tribes of the Sahara and Ethiopia’s Danakil Plains, salt is carried by camel trains and is still used occasionally as money or bartered for a cash equivalent. When the camel trains of Mali carried the salt, each animal typically carried four blocks of salt. On reaching the salt market, three blocks sold off the back of each animal went to the camel train owners, and the profit of the sale of the remaining block to the salt miner.
Blocks of Taoudenni salt at the port of Mopti in Mali, Africa (information in accompanying text and this image "Mopti sel" by Taguelmoust downloaded at the French language Wikipedia. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Mopti_sel.jpg#/media/File:Mopti_sel.jpg)
Salt has been harvested from these salt ponds at Maras Peru, since the time of the Inca Empire. The site has around 3000 ponds of 5 square metres (54 sq ft) each. As the location is surrounded by halokinetic subcrop, saline springs feed the ponds that then are allowed time to evaporate. After around a month, the thickness of salt in the concentrator pans reaches 10 centimetres (3.9 in) and is then removed in sacks.
The ancient Incas made salt at Maras in Peru, and the Maya at Salinas de los Nueve Cerros in Guatemala. Bot are regions area where natural salt springs flow into a river gully, giving easy trading access to downstream customers. This Nueve Cerros site was the only large-scale source of salt for the interior Lowland Maya. Maya technology included solar evaporation and firing of brine from salt springs in special large ceramic bowls that are the largest receptacles ever found in any Maya site.
The Chinese produced salt by many methods: they evaporated brine in salt lakes, boiled seawater, or pumped and processed brine from wells drilled into salt beds. Modern oil-drilling traces its roots back to Chinese methods of bamboo-based drilling technology that originally evolved for salt production from ancient subsurface brine sources.
The Chinese have been using brine wells and a form of salt solution mining, for more than 2,000 years. Designed-use shaft wells were sunk as early as 220 BC in the Szechuan and Yunnan provinces (Warren, 2016, Chapter 13). By 1035 AD, the Chinese in the Szechuan area were using percussion drilling to recover deep brines, a technique that would not come to the West for another 600-800 years. European travellers to China in 1400-1700 AD reported salt and natural gas production from dense networks of brine wells. Some of the wells had been sunk deeper than 450 metres, and at least one well was more than 1,000 metres deep. Salt production in China at that time was prodigious, with more than 10,000 wells in operation. Marco Polo reported annual output in a single province of more than 30,000 tons.
The highly organised salt trade of China was observed by Marco Polo, who recorded that the major item of commerce on the Yangtze River was salt, shipped upstream from the coast (especially from the city of Hangchou) to the interior cities. In Tibet, Marco Polo noted that tiny cakes of salt, manufactured from salt lakes in the high plains of Tibet were pressed with images of the Grand Khan and used as coins.
Solution mining and brine recovery technology in saltworks of the Szechuan region of China in the mid-eighteenth century. A) Man-powered percussion drilling using a human weighted lever system to raise the drill bit. Inset shows typical spade-like iron drill bit that was suspended on bottom of a bamboo drill string. B) Animal-powered hoisting of brine from a salt well showing the use of flexible bamboo cable wrapped on a spindle. C) Transfer of brine to iron pans for boiling of the brine product and recovery of salt. Boiling plants often using piped natural gas (No bamboo piping from wellhead to boiling house is shown in this image). (from the annals of Salt Law of Sichuan Province).