Khewra Salt Mine

Khewra is the second largest salt mine in the world, in the Jhelum District of Punjab, Pakistan, cut into the Salt Range of the Pothohar Plateau where it rises out of the Indus plain. It is also the source of the pink salt sold worldwide as Himalayan salt, and it draws up to 250,000 visitors a year.

The salt was found, by tradition, by Alexander's troops in 326 BC, when the horses were seen licking the rocks. Trading in it began under the Mughals. The main tunnel at ground level was driven in 1872 by a British mining engineer, H. Warth, and that tunnel is still how you get in.

After independence the mine passed through a succession of state bodies: the BMR until 1956, then the Pakistan Industrial Development Corporation until 1965, then the West Pakistan Industrial Development Corporation after the 1965 war with India, and since 1974 the Pakistan Mineral Development Corporation. It remains the country's largest source of salt, producing over 350,000 tons a year of roughly 99 percent pure halite. Estimates of what is still down there range from 82 million to 600 million tons, which is a wide enough spread to tell you how hard the deposit is to measure.

Geologically it is remarkable. The mine works the base of a thick, heavily folded and faulted sequence of Ediacaran to early Cambrian evaporites of the Salt Range Formation: crystalline halite interleaved with potash salts, overlain by gypsiferous marl and then beds of gypsum and dolomite.

Salt comes out of the mine the way it has since the British era, on a two foot narrow gauge railway laid through the tunnel, and rail cars still run it. Inside, the temperature holds between about 18 and 20 degrees Celsius all year, and part of the mine has been used to treat respiratory illness with salt therapy. Pakistan Railways has run special tourist trains to Khewra from Lahore and Rawalpindi.