Potash:

Potassium salts deposits are few and found only in the Indus Basin especially in the KohatPotwar Province. There arc three known potential sources of potash in Pakistan. They are the potash beds associated with rock salt in the Salt Range Formation, subsurface brines encountered in a drill hole in the Salt Range and the green sand of Chichali Formation in the Surghar Range. Potash minerals occur interbedded in the Salt Range Formation and have been described from the Khewra salt mines (Alam and Asrarullah, 1973). The potash occurs as specks thin streaks, thin seams and lenticels of limited extent in the rock salt and the salt-marl separating the salt seams. Seven potash bearing salt-marl beds have been recognised of which two contain thicker scams varying between 1 to 5 m in thickness and 250 to 400 m in their lateral extent.Chemical and mineralogical variations are significant. The ore is either clay bearing or clay free. In addition to halite, it is mostly composed of sulphate minerals like kainite, langbeinite, kiescrite and polyhalite. Presence of sylvitc has only been noticed in one instance. The proved reserves of ore containing 7.83% potassium oxide are estimated at12,500tonnes.

                 Another source of potassium is subsurface brines. In an exploratory drill hole by an oil company at Dhariala, 15 km, NW of Khewra. Saturated artesian hot brines were encountered at a depth of about 2600 m. The brine contained chlorides of potassium, magnesium, sodium and calcium, and bromine and boron in small quantity. The flow of brines at a high pressure was found to be 4,500 litres per minute (Richards,1963).

                Chichali Formation of Jurassic-Cretaceous age contain yet another potential source of potash in which the glauconitic sandstone(or green sand) is exposed in the Surghar Range from north of Kalabagh to Makerwal for a distance of 45 km.Beds of green sand are 3 to 20 m thick and at places, make up a cumulative thickness up to 30 m. Total reserves of about 23 million tonnes of green sand are available(Kidwai,1963).Experiments have been made to utilize the green sand as water softener

and potasic fertilizer (Bakhsh ct al., 1963).The result so obtained indicated that the potash contents are
rather low (KÿO 1.28% to 4.28%) and all the potassium is not readily available for nutrition to plants as only a small fraction of it is in exchangeable form. For this reason and because of high transportation cost, the green sand is not presently considered useful for direct application as a fertilizer. It may become of economic significance if a method for extraction of potassium from the green sand is successfully evolved. However, Bakhsh andothers (op.cit.) have recommended its use as an effective water softener; they have calculated that one tonne of green sand with exchange capacity of 16 m.eq. per 100gm. will completely remove the hardness of 35,500 litres of water with a hardness of 250 ppm calculated as calcium carbonate. It may be further added that the potash content of green sand are low to consider its use as fertilizer, however, it is very effective as a water softener.