 Estimates of the total reserves of salt in the mines range from 82 million tons to 600 million tons . In raw form it contains negligible amounts of Calcium , Magnesium , Potassium , Sulfates and moisture , with Iron , Zinc , Copper , Manganese , Chromium and Lead as trace elements . Salt from Khewra , also known as Himalayan salt , is red , pink , off @-@ white or transparent . In the early years of British rule , the Khewra mine produced about 28 @,@ 000 to 30 @,@ 000 tons per annum ; it increased to about 187 @,@ 400 tons per annum for the five fiscal years ending 1946 – 7 and to 136 @,@ 824 tons for the two years ending 1949 – 50 with the systematic working introduced by Dr H. Warth . The mine 's output was reported in 2003 to be 385 @,@ 000 tons of salt per annum , which amounts to almost half of Pakistan 's total production of rock salt . At that rate of output , the tunnel would be expected to last for another 350 years . 
