Systematic geological mapping on scale 1:50,000 is the most fundamental and basic among various activities of GSI, providing National Geoscientific Information and knowledge base, for undertaking almost all earth-science related programmes.
Out of the total mappable areas of 3.146 million sq.km. of the country, 3.0906 million sq.km. has so far been covered by systematic mapping, bringing the total coverage to 98.245%.
The areas left for systematic mapping are inaccessible areas of North Eastern Himalayas in the States of Arunachal Pradesh, Nagaland,Manipur and a portion of the Meghalaya plateau bordering Bangladesh; the Northern Himalaya in the states of Jammu & Kashmir and Uttaranchal; the Jarwa inhabited islands of Andaman & Nicobar and Abujhmar Plateau of MP and left out portions of Andhra Pradesh.
Specialised thematic Mapping is undertaken at scale 1:25000 to resolve problems pertaining to stratigraphy, structure and tectonics, ore localisation and conceptual modelling on various aspects including crustal evolution and metallogeny. Considering the fact that a large number of mineral occurrences with surface expressions and old workings have already been either located or proved, it is essential to not only probe the deeper levels of the crust by geophysical integration but also prognosticate by identifying every minor litho-member through mapping.
The geological database established by systematic geological mapping is further enriched through incorporation of additional parameters, enhancement in quality and quantity and also refinement of the data element/data subsets. This involves integration of airborne geophysical data, regional gravity data, geological and geochemical data replete with high precision laboratory data.
Geochemical mapping serves as an aid to mineral exploration, soil fertility assessment, human and animal health, establishing valid environmental baseline and understanding the chemistry of the environment. National Geochemical Mapping initiated during X plan period, is an all India programme, aimed at generating base line geochemical database through reconnaissance scale survey. This will enable identifying primary and secondary dispersion pattern as well as possible pay off zones of hidden or deep-seated mineralised areas. NGM commenced in 2000-01 fs and will continue to run for more than 20 years till the entire surface area of the country is covered by geochemical sampling. The main media of sampling will be ‘fluvial’ or ‘slopewash’ material in 1km2 cells (unit cells); water (flowing) and soil at 5 minute interval. Other media of sampling include ‘humus’ and ‘flood plain’ samples. Sampling will be carried out with 1: 50,000 toposheet as the base map. These samples will be analyzed for 68 elements using ‘Clarke’ as the lower level of detection. The processed data will be produced in the form of toposheets-wise contoured maps depicting elemental variation. An area of 21,556.80 sq. km. was covered under the National Geochemical Mapping Programme during the F.S. 2004-2005 (upto July, 2005).
Geophysical Mapping activity at GSI includes Regional geophysical mapping programmes; surveys for mineral investigations mainly by resistivity and induced polarization methods, search for minerals / coal especially in concealed terrain and identification of subsurface features.
Apart from these, studies on environment and ecology, glacial mass balance, archeology applications, earthquake precursors and preventive measures against natural hazards, aftershock studies, land subsidence and void identifications; Geotechnical problems; Borehole geophysics; Seismotectonics studies, active fault mapping, tectonic studies and studies on urban development are also undertaken by the geophysics divisions.
Geological Survey of India (GSI) is engaged in airborne geophysical surveys for data acquisition employing magnetic and gamma ray spectrometric techniques. The surveys are followed up by data processing, preparation of aero-geophysical maps and interpretation. The interpreted aero-geophysical maps are used in ground evaluation, aimed at adding information to geological maps and for prospecting and exploration for minerals. Processing of aerogeophysical data is carried out in the Geophysical Mapping Centre (GMC) of AMSE for generation of total intensity magnetic maps and elemental distribution maps for U, Th, K and the total count.
Since the acquisition and induction of TOASS till date, a total of 3,73,636 line km over an 1,80,185 sq km was covered by multi-sensor survey by the Twin Otter Airborne Survey System, involving magnetic, spectrometric, radiometric and electromagnetic methods till the end of June,2005 in different areas of the country.
The interpretation of the aerogeophysical data, supplemented by ground follow-up is a concurrent exercise that follows the airborne geophysical surveys. It aims at collecting ground truth for the corresponding aerogeophysical anomalies by geological and geochemical studies.
Highlights of achievement during the first four years of the Tenth Five Year Plan (April, 2002 to December, 2005)
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