The Khewra Salt Mine (or Mayo Salt Mine) is in Khewra, north of Pind Dadan Khan, an administrative subdivision of Jhelum District, Punjab Region, Pakistan. The mine is in the Salt Range, Potohar plateau, which rises from the Indo-Gangetic Plain, and is the second largest in the world. The mine is famous for its production of pink Khewra salt, often marketed as Himalayan salt, and is a major tourist attraction, drawing up to 250,000 visitors a year. Its history dates back to its discovery by Alexander's troops in 320 BC, but it started trading in the Mughal era. The main tunnel at ground level was developed by H. Warth, a mining engineer, in 1872 during British rule. After independence, the BMR took possession until 1956 and then PIDC owned the mines till 1965. After India-Pakistan war in 1965, the WPIDC took over the administration of salt mines and in 1974, the Pakistan Mineral Development Corporation took over the mine, which still remains the largest source of salt in the country, producing more than 350,000 tons per annum of about 99% pure halite. Estimates of the reserves of salt in the mine vary from 82 million tons to 600 million tons. Geology The Khewra Salt Mine is excavated within the base of a thick layer of highly folded, faulted, and stretched Ediacaran to early Cambrian evaporites of the Salt Range Formation. This geological formation consists of a basal layer of crystalline halite, which is intercalated with potash salts. This basal layer is overlain by gypsiferous marl, which is covered by interlayered beds of gypsum and dolomite with infrequent seams of oil shale. These strata are overlain by of Neoproterozoic to Eocene sedimentary rocks that have been uplifted and eroded along with the Salt Range Formation to create the Salt Range at the southern edge of the Pothohar Plateau. The Ediacaran to early Cambrian evaporites of the Salt Range Formation have been thrust southward over Neoproterozoic to Eocene sedimentary rocks by many kilometers, which tectonically incorporated fragments of the underlying younger strata within these evaporites. The Salt Range is the southern edge of a well-described fold-and-thrust belt, which underlies the entire Pothohar Plateau and developed south of the Himalayas as a result of ongoing collision between India and Eurasia. Palynomorphs (organic microfossils) have been used to make inferences about the ages of the Salt Range Formation and its salt layers that are