When many first hunted and foraged in roving bands across Africa and Europe the salt that individuals required was usually supplied by the foods that they consumed. However, as people settled in larger communities and began the cultivation of crops and the raising of cattle and other animals for consumption the need for external sources of salt became urgent. There were two main sources of this salt – on the coast evaporated seawater (and the still water of marshes) provided a ready source of salt for those with the patience to let the sun do its work and inland were salt mines became increasingly important.
The exploitation of rock salt has without a doubt been going on for thousands of years. The oldest evidence for salt mining has been found in the Araxes Valley in modern day Azerbaijan. The salt mines in this area were being exploited as long ago as 3500 BC, and it is no coincidence that these mines were situated alongside the ancient Silk Road linking Tabriz in Iran with Constantinople. However – there is tantalizing evidence for salt mines far older than this elsewhere in the world, including China.
Although in ancient times men labored deep in caves and mines to bring rock salt (known as halite) to the surface today the process is heavily industrialized. Today China, India and the United States are the top three producers of rock salt in the world. However, strangely enough, even though these countries have some of the largest salt mines in the world the prize for the most massive goes to the Sifto Salt Mine in Goderich, Ontario – Canada. The salt that is mined here was deposited on the bed of a long-gone ocean that once covered the basin of Lake Huron around 400 million years ago.
This mine is 1,800 feet below Lake Huron and is 1.5 miles wide and 2 miles long. It covers a vast area of around 2.7 million square miles and produces about 7 million tons of rock salt every year.
There are two main methods of extracting the salt from the mine. The first is a traditional method where shafts are driven sometimes thousands of feet below the ground. Salt is first removed leaving behind pillars to support the roof of the safe and then a slot is cut at the bottom of the salt wall. Explosives are inserted into holes in this undercut and detonated. The resultant blocks of salt are then transported to a conveyor belt which will take them to the surface. The second method uses evaporation to produce very high-quality salt. Wells are drilled into the salt-bearing strata and water is pumped down the wells. The salt dissolves in this water and the brine is then pumped to the surface to be stored into a series of huge vessels where successive stages of greater vacuum conditions cause pressure drops that continually refine the salt until the final product emerges from the end of the process.
Salt is today as important to civilization as it was in ancient times. Although the great salt roads such as Roman Via Salaria (Salt Route) no longer exist salt remains an essential part of modern life – although thankfully now more readily available than it was in the past – due to both the industrial scale evaporation of sea salt and salt mining.