Limestone,dolomite,Gypsum and Anhydrite

Limestone: Limestone is by far the most abundant mineral commodity in Pakistan. With its unlimited reserves, limestone forms many ranges and is exposed in the Indus Basin, Axial Belt right from Karachi in the south to Khyber in the north and further north at several places in the Northern Montane Area. Balochistan Basin is deficient in limestone since surface outcrops are mostly of Late Tertiary elastics. Limestones of the Indus Basin and Axial Belt are Late Palaeozoic to Tertiary in age,while in the Northern Areas, Early Palaeozoic limestones are also found. Due to the widespread development of limestone deposits, it is not possible here to list the individual occurrences, but a glance over the geological map of Pakistan and through the description of stratigraphy would reveal that the formations listed below, where exposed, are good resources of limestone.

Chemical composition of the limestone varies from bed to bed and place to place. Geochemical evaluation has to be made before putting them to use in a specific industry. Details may be seen in Master(1963)and Ahmad and Siddiqi (1993).

Dolomite: Dolomite deposits are mostly associated with limestone and are of diagenetic origin. In fact the process of dolomitization is so common in the rocks that most of the limestones of the country are observed to have been dolomitised to a lesser or greater degree. In the Upper Indus Basin, the major dolomite bearing formations are in Salt Range (Precambrian), Jutana (Cambrian), Khisor (Cambrian), Kingriali (Triassic), and Samana Suk (Jurassic). Some detailed work has been done on Kingriali Dolomite in the Surghar Range, where four deposits of dolomite have been located.About 900 million tonnes of reserves have been established in beds averaging 80 metres in thickness.
Dolomite is of good grade, close to the theoretical value of dolomite. Datta Formation especially of Trans Indus ranges contains one of the best dolomitedeposits. Details on other dolomite horizonsare not available but, generally the dolomite is of good quality and large reserves are available. In southern part of Lower Indus Basin, near Jhimpir, about 0. 5 million tonnes of dolomite reserves are established in two beds measuring 2.5 m and 7 m in the Laki Formation (Eocene), MgO content is 17%and CaO 36%, as determined in two samples (Khan and Gauhar, 1966). Good quality of dolomite has been discovered in the Axial Belt near Quetta (Ahmad, 1974).

Dolomite is present in beds up to 80 m thick at the base of Jurassic Takatu Formation in the Chiltan Range. The dolomite is saccharoidal in texture and of good quality. Representative chemical analyses have given an average of about 20% MgO and 32% CaO with negligible insoluble (S. H. Gauhar personal communication). Reserves for a strike extension of 5 km are estimated at 250 million tonnes. These reserves are conservative estimates, however, it may be much more than indicated.
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In the northern areas near Sherwan, about 16 km west of Abbottabad and within the Abbottabad Formation(Cambrian),here it is bedded,but the dolomite is associated with soapstone at some localities near the villages of Khanda Khirand Chalethar. It is small but fine quality deposit.
In the Northern part of Axial Belt, large dolomite deposits arc described from Khyber Agency. The dolomite occurs in Shagai limestone and Khyber limestone, both of probable Precambrian age. Larger and better grade deposits are found in the upper part of Khyber limestone.The dolomite has saccharoidal texture. It is present in the defilesof Khyber Pas area. Further north in the Northern Sedimentary Province, numerous dolomite deposits of Devonian age are present in the Chitraldistrict,where massive dolomite in lower part of the Shogram formation and bedded dolomite in the middle part of Shogram formation is present. Further northeast in the northern Karakoram Guhjal formation is mostly dolomite. Other formations, which contain dolomite within are Chilmarabad formation, Kilik formation,Aghil limestone formation and many others.
' Gypsum and Anhydrite: The gypsum deposits range from Precambrian to Mioccne-Plioccne in age. Mostly theyare small deposits. Only gypsum deposits of Sargodha and Kohat division are larger (3to15m) deposits of widely distributed in the Upper Indus Basin,which have practically inexhaustible reserves. Precambrian gypsum and anhydrite deposits are confined to the Salt Range Formation exposed along the southern escarpment of the Salt Range. Cambrian gypsum and anhydrite deposits are locally developed in Khisor Range in the Khisor Formation; they are more than 200 m thick. Eocene gypsum-anhydrite deposits occur in Ghazij Group in Middle Indus Basin all along the Sulaiman Range and in Kirthar formation in Marri-Bugti hills, in Jatta Gypsum in Kohat area of Upper Indus Basin and in Sakesar Limestone (facies change) near Deduce in the Salt Range.Studies of representative sections of gypsum-Anhydrite deposits by(H.A. Raza, 1977) at Cheri (Salt
Range), Saiyiduwali (Khisor Range), Jatta (Kohat) and Rakhimunh (Sulaiman Range) have shown that the gypsum is associated with dolomite and organic laminite in acyclic sequence and possesses
characteristics which point to its formation in sabkha type supratidal flat environment (Shearman,
1963, 1966; Kinsmall, 1969). The available generalized composition of gypsum from various1 localities is given as under (Ahmad, 1969).

Besides, the above-mentioned gypsum occurrences, small layers of gypsum up to one metre thick have been reported from several places in hallows amongst the sand dunes in the Thar Desert (Ahmad, 1969).