After the decentralisation of GSI a circle Office viz. the Assam Circle under the Eastern region, Calcutta was set up at Shillong in 1961 with eight Officers to accelerate GSI's activities on mapping and mineral assessment in Assam, NEFA, Nagaland, Manipur and Tripura. In 1968 a separate circle Office of GSI for NEFA Arunachal was established at Tezpur.
Simultaneous with the birth of the new states and union territories in the northeastern India two more circle offices of GSI came up in 1972 to cover its activities independently in Tripura - Mizoram with headquarters at Agartala and Manipur - Nagaland with headquarters at Dimapur. The former Assam and NEFA Circles were then rechristened as the Assam Meghalaya Circle and Arunachal Pradesh Circle, separately.
As a result of the above mentioned developments, the Northeastern Regional Office was established at Shillong with Mr. D.R.S Mehta as its first Deputy Director General.
Each office has different laboratories and divisions performing various activities. Information about some of these units is provided below:
MMIP carries out mineral assessment of Meghalaya state through regional integrated surveys. The work includes geological mapping on suitable scale, systematic integrated sampling including rock, mineral, soil, plant and water, supplemented by geobotanical studies and subsurface exploration by geophysical methods and exploratory drilling followed by interpretation and coordination of all field and laboratory data. One such investigation for limestone in Lum Syrmun Block, west of Litang river Valley, Jaintia Hills revealed a total combined reserve of 7723.0 mt (indicated ) and 599.8 mt (inferred) which includes Cement, SMS, LD and Chemical Grade limestone
Work on similar lines has also been done by the Assam Mineral Investigation Project operating from Guwahati.
Introduction: The Division is engaged in investigation of the geological aspects of all engineering projects in the Northeastern Region. It renders geological advice in dam construction, road and railway alignment, slope stability, tunnel alignment, heavy engineering installation etc. At present several geologists are actively engaged in various projects as detailed below:
Year of starting
Kameng Hydroelectric Project, West Kameng district
Talong NE Project, East Kameng district (Feasibility Stage)
Dibbin HE Project West Kameng district (Feasibility Stage)
Kapak leyak HE Project West Kameng district (Feasibility Stage)
Nyukcharong Chu HE Project East Kameng district (Preliminary stage)
Investigation for Water Resource Development Project in Tawang Chu, Tawang district
Bharali -1 (Kameng 1)HE Project East kameng district
Jiadhal Dam Project, West kameng District
Thoubal multipurpose River project, Senapati District
I & FCD, Manipur
Tapimukh HE MultipurposeProject Mani pur-Mizoram Border (feasibility stage)
Tuivai HE Project Charuchandpur district (Preliminary stage)
Electricity Deptt., Manipur
Irang He Project, Tamenglong district (Preliminary stage)
Electricity Deptt., Manipur
Myntdu-Leshka HE Project Stage-II Jainia Hills District
Mawhu HE Project, East Khasi Hills district (feasibility stage)
Geological Survey of India being the 'Nodal Agency' for landslide related studies is engaged in Landslide Hazard Zonation mapping, Site specific studies of landslides and preparation of Landslide inventory in different parts of the country. This includes Land Slide Hazard Zonation in parts of Manipur, Nagaland, Mizoram, and specifically the Geological and Geotechnical Site specific study of Sonapur Landslide and Landslide Inventory of Jaintia Hills, Meghalaya.
The study revealed that the rocks exposed along the Sonapur landslide consist of a banded sequence of sandstone, silt and shale belonging to Barail Group of Oligocene age. The shale bands exhibits splintery character and disintegrates easily upon exposure and is source of huge quantity of debris. Four faults trending NW-SE and N-S are recorded in the area along with eight sets of joints. These are close to moderately spaced. Studies further revealed that slide is a combination of planner and wedge failure, together with debris movement triggered by heavy rainfall. Monitoring of Sonapur Landslide is important due to passing of National Highway through this slide zone.
Geophysical Division: The Division makes use of sophisticated instruments to locate the hidden sub-surface mineral resources and also subsurface structures by highly trained Geophysical personnel. Their knowledge is also utilized in ascertaining various rock types in depth for foundation work of engineering projects. The division also engages in studies involving earthquakes mechanism and prediction in the earthquake prone region.
Chemical Division: The Chemical Division plays a very important role in chemical analysis of rock and mineral samples collected by field geologists to ascertain their elemental contents. The Division uses highly sophisticated precision instruments for analysis of samples like Atomic Absorption spectrometer at its laboratory at Shillong. Recently X-Ray Florescence Spectrometer and one Atomic Absorption Spectrometer including Graphite furnace and Hybrid Generator unit (GF-AAS) has been installed.
Drilling Division: After systematic mapping, geophysical and geochemical exploration are over, indicating the possibility of mineral deposit at depth, their presence or absence, extent etc are physically verified by drilling. The quality/quantity and grade of minerals are obtained by analyzing and interpreting the drill cores.
Petrology Division: This Division is concerned with study of rock and minerals in the field and laboratory under microscope and with other instruments for the purpose of identification of different constituents required for proper evaluation of field data, relating to geology, genesis and structure. Gem Testing has been started in Northeastern Region with the establishment of small laboratory at Shillong to render service to interested parties. Gemstones are identified based on standard non destructive methods employing both physical and optical properties followed by their mineralogical identification.
Palaeontology Division: This Division studies fossils - identification of which help in deciphering the condition of deposition, palaeogeography and the age of the rock where they are embedded. This also helps in correlation of rocks exposed in different geographic areas. Palaeontological studies in this region proved that the coal forming plant existed along the Himalayan foot hills of Arunachal some 280 million years ago and an arm of sea invaded part of the area in the same period. The southern part of Meghalaya Plateau was under sea at about 100 million years ago. Existence of large reptiles in this region has been indicated by remains of Dinosaurs in the rocks of this region.
Photogeology and Remote Sensing Division: This Division studies aerial photograph and satellite imagery for delineating geological structure, rock type, drainage pattern etc. and structural aspects for identifying potential mineral bearing areas. Considering the inaccessible nature of this terrain this work is of supreme significance.
Map and Compilation Division: This Division is engaged in catering to the map requirement, toposheet, sale of geological and mineral maps, atlas, maintenance of map stock, dissemination of map information through exhibition, book fair etc. Cartographic requirements, archival and updating of maps database and coordination among various operational units are also dealt by this unit. The division is also involved in preparation of quadrangle geological mineral map and digitization of compiled geological maps on 1:50,000 scale.
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