EDITORIAL Exploitable minerals in North East — Arpan Dutta
The North-Eastern Region (NER) of India can claim to be a potential source for many valuable minerals. But, practically, they lack substantial evidences to prove that claim excepting well exhibited existance of a few minerals like petroleum, coal, limestone and base-metal deposits of copper and zinc in the region, now-a-days. Still, the available data relating to old workings of some of the minerals like common salt, iron, gold, silver, sillimanite and chromite yielded prosperity of mineral resources. Common salt was harnessed from brine springs mostly occurred around Sadiya and Borhat areas of Assam. In this regard Capt R Boileu Pemberton’s report of 1835 is enough to gather information wherein he stated as “The springs most generally known are those of Boorhat and Sadiya ... salt obtained from the springs was said to much more pure and higher price than that imported from Bengal ...” As regard iron, Pemberton pointed out that it was found north of Dergaon, south of Kacharihat and under the Naga Hills. Iron was reportedly extracted from Garo Hills of Meghalaya and Loharghat of Kamrup district, Assam. Similarly, gold and silver were said to be extracted from gold-silver bearing placer deposits found abundantly in most of the rivers of Assam. Likewise, sillimanite and chromite were mined from Sonapahar of Meghalaya and Ukhrul of Manipur respectively in the region.
Minerals of NER could be categorised on the basis of their characteristics as metallic, non-metallic, fuel along with energy group of minerals and constructional as well as decorative stones. Metallic minerals are found in rocks as ores, wherefrom different metals could be extracted economically. Non-metallic minerals are regarded as raw materials for various industries for obtaining processed products and application in furnaces as lining bricks. Fuel minerals have wide application in generation of power besides being used in manufacture of POL, oil, gas, LPG and coal based products. The workable metallic minerals found available in the region are iron, gold, copper and chromium. In general, iron ores occure in two seperate mineral assemblage zones in Archean Gneissic Complex giving rise to Banded Haematite Quartzite (BHQ) and Banded Magnetite Quartzite (BMQ) havinf exception with the deposit of Samchampi of Karbi Anglong district, Assam where it is found in Carbonatite Complexes.
The deposits of iron are well exposed in Chandardinga Hills of Dhubri district and Lengupara and Kumri of Goalpara district, Assam whose reserves are estimated to be of 11.24 million tonnes, 7.50 million tonnes and 9 million tonnes, respectively. The iron content of the reserves varies from 46.09 per cent to 51.23 per cent. It is to be noted that the deposits may not be suitable for beneficiation at present, yet it has been opined by experts that there is likelihood of extraction of iron from the ores through advanced technology. Significantly, the iron ore of Chandardinga is claimed to be upgraded through mixing of high assayed iron ores, which will have wide application in various iron industries.
In contrary to the above deposits, a fairly good deposit of iron has been discovered around Samchampi area of Karbi Anglong district few years back. The deposit is located by Geological Survey of India (GSI) and Atomic Mineral Division (AMD), Government of India. It occurs in alleged Samchampi Carbonatite Complex (SACC) in the Archean Massif. As reported, the most important resource of SACC is iron ore. Two large stock-like out crops of titano haematite occupy an area of 2.5 km in the central and western part of the complex. The ores contain an average of 83 per cent Fe2O3, 0.7 per cent FeO, 3.7 per cent TiO2, 2.77 per cent Al2O3 excluding some other substances. The reserve of the deposit has been calculated as 3x108 tonnes (inferred).
The gold along with the silver became the prime minerals in Assam during Ahom’s reign. They occur as placer deposits in most of the rivers of the State. Still major emphasis on extraction was given on four rivers – the Subansiri, the Bhoroli, the Disoi and the Janglupani. Out of which Subansiri’s share was maximum. Inspite of that then British government temporarily suspended the gold washing with a view to make necessary arrangements for carrying out the investigation and exploitation systematically. But due to prevailing disturbed political situation and other reasons the government gave a deaf ear to extraction and ultimately gold washing getting closure from the year of 1875. Apart from the placer gold of Assam, small quantity of gold reported to have been occurred in Sidang (Arunachal Pradesh), the Dhansiri (Nagaland) and Jyrsad (Meghalaya).
It may be stated that out of the metallic deposits, only a workable copper-lead-zinc deposit is found at Bhotang-Rangpo and Dikchu in East Sikkin district, Sikkim. This polymetallic deposit bears a reserve of 803x103 tonnes, 803x103 and 803.90 tonnes respectively of copper, lead-zinc and silver ones. Apart from this a similar polymetallic zone in Khasi and Jaintia Hills, Meghalaya and copper-zinc mineralised zone in Subansiri and Sidang districts, Arunachal Pradesh are encountered. Similarly, in case of chromium, the region is not rich enough barring a 2000 tonne reserve of refractory grade chromite of Ukhrul, Manipur. Further, a minor deposit of chromite has also been reported from Pukhpur area of Nagaland.
The non-metallic deposits confined to this region are limestone, dolomite, sillimanite, graphite, chinaclay, fire clay and asbestor. So far as the deposit of limestone is concerned the State of Meghalaya received prime importance as it bears a maximum quantity of 133978x103 tommes. Both cement and lime grade limestone bearing suitability to use in cement and chemical industries are available in the State.
Out of the eight States of the region, Assam, Meghalaya and Arunachal Pradesh are the treasure houses of decorative granite in general and marble in particular. Granite of attractive colours like grey, pink and black being suitable for preparations of decorative tiles, slabs and poished/unpolished blocks of various sizes are available in the States. As a whole, the reserve of the granite in the States of Assam and Meghalaya respectively are 58350m3 and 286467x103m3. The marble is confined only to certain localities of Arunachal Pradesh viz Hanli and Dora having a total reserve of 76112 million tonnes.
