Mineral Resources of Assam - Limestone : Assam Geography Study Materials & Notes
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Mineral Resources of Assam – Limestone: Assam Geography
Limestone in Assam
The high-grade fossil limestone or ‘nummulitic’ limestone deposits of Assam are geologically known as ‘Sylhet limestone’ as these belong to that groups of rocks. The limestone deposits are confined in areas of Garo hills, united Khasi and Jaintia hills, Cachar hills and Mikir hills. One of the largest outcrops of limestone is at the foot of the Khasi hills. Vast deposits of high-grade limestone are best observed in the Jowai area. Lime stones of the Khasi and Jaintia hills can be used for manufacture of cement and for lime-burning purposes. It can be used in chemical industries and for metallurgical purposes. The limestone deposits of the state offer vast scope for developing innumerable industries where limestone is required.
Limestone occurrence in Assam are confined to North Cachar Hills and Karbi Anglong districts. The Sylhet limestones continue into the North Cachar Hills across the Kharkor and Kopili rivers. They are found to cover an extensive area near Garampani to The north-east of the confluence of the two rivers. In Karbi Anglong, the principal occurrences are Silbheta-Meyong Disa,Chopung Hills,Jarapagaon,Koilajan Bar Harihajan and Doigrung. Of these the first two are rather high in iron even though the reserves are large;reserves in Silbheta-Meyong Disa are 38 million tonnes,in Chopang Hills 17 million tonnes and in Jarapagaon 6.5 million tonnes. The total reserves between Koilajan and Kidimithapa are of the order of 81 million tonnes of which 43 million tonnes are reckoned as being high in silica.
The State Directorate of Geology and Mining has proved that 3 million tonnes of these limestones are of cement grade. Average composition of the samples analysed gave,Ca0 47.20 per cent and Mg0 1.30 per cent. Silica varies between 8 and 12 per cent and alumina and ferric oxide 1 and 3 per cent and 2 and 4 per cent respectively. In Bar Harihajan of Karbi Anglong district,about 4.5 million tonnes are likely to be available at Saini Langso,Chota Harihajan and Disai Nala analysing.
Exposures of limestones are known along the Doigrung river 19 kms. south of Golaghat but the quantity of reserves have not been estimated. One available analysis estimates CaCo3 72-90 per cent,MgCo3 7.33 per cent,Mg0+Al203 +Fe203 9.0 per cent and Insolubes 10.70 per cent.
Cement Manufacture constitutes the most important use of limestone. Next in order of importance is its use as a fluxing agent in the metallurgical industry. Other uses, apart from lime for building mortar,are in the manufacture of various chemicals,glass,refining of sugar,oil and as a filler.
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