||2,55,000 sq km
||Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland,and Tripura.
||Regional Centre for Exploration and Research, AMD Complex, Nongmynsong,PO : Assam Rifles, Shillong – 793 011.
||Dr. Prakhar Kumar
Deputy Regional Director
Ph. : 0364-2537656
Fax : 0364-2534855
Northeastern Region of AMD with Regional Headquarters at Shillong shoulders the responsibilities for the exploration of atomic minerals in the Northeastern part of the country. Exploration for atomic minerals in this part of the country began way back in the 1950's;initially, in Meghalaya and later extended to other states of Northeast India. Based on the outcome of exploration, AMD has concentrated its efforts mainly in the states of Meghalaya, Arunachal Pradesh and Assam, which have been identified as the most potential states. These states hold the potential for sandstone-type, hydrothermal vein-type and unconformity related uranium deposits, besides rare metal and rare earth deposits.
The country’s largest and richest sandstone-type uranium deposits are located in Domiasiat and Wahkyn areas of West Khasi Hills district,Meghalaya and are hosted by Lower Mahadek sandstone of Upper Cretaceous period. The Mahadek sediments are exposed along the southern fringe of Meghalaya Plateau over 180 km from east to west in Jaintia,East Khasi and West Khasi and Garo Hills.
Nearly 131 km of drilling by completing about 1,800 boreholes has resulted in proving of 16,000 tonnes U3O8 accounting 14% of the country’s total uranium reserve. This includes, 9,500 tones U3O8 at Domiasiat, 5,300 tonnes U3O8 at Wahkyn, 570 tonnes U3O8 at Tyrnai and 760 tonnes U3O8 at Lostoin.
Secondly the interface between Lower Proterozoic Tyrsad metapellites and Middle Proterozoic Barapani quartzites of the Shillong basin of Meghalaya and Assam holds promise for unconformity-related uranium mineralisation. Similarly Garo crystallines of Meghalaya are potential for hydrothermal vein- type of mineralisation.
In Arunachal Pradesh, hydrothermal vein-type of uranium mineralisation has been located in Proterozoic Siang Group in brecciated silicified and sericitised quartzites in parts of West Kameng and West Siang districts. Economically viable deposit of uranium is yet to be found in this state.
Broad Geological Features: Broadly following geological domains occupy major part of the region
i. Archaean basement rocks mostly exposed in Meghalaya and Assam.
ii. Proterozoic supracrustals comprising Shillong group of metasediments in Meghalaya and extra peninsular rocks of Arunachal Himalayas comprising Bomdilla gneiss, Dirang schist, Sela groups of rocks, etc.
iii. Mesozoic rocks represented by Mahadek sandstones and Carbonatites of Cretaceous period and Sylhet traps of Jurassic period.
iv. Tertiary sediments exposed in the states of Arunachal Pradesh, Assam, Meghalaya, Manipur, Tripura, Nagaland and Mizoram. Oil wells are located in some of these areas.
v. Younger granites of 479 to 881 m.y. emplaced into Proterozoic and Archaean rocks.
Summary of Investigations:Important Uranium Deposits
DOMIASIAT/KYELLENG-PYNDENGSOHIONG, MAWTAHBAH (KPM) URANIUM PROJECT
The Domiasiat uranium deposit now known as Kyelleng-Pyndengsohiong-Mawtahbah (KPM) located in West Khasi Hills district of Meghalaya was discovered in 1984 as a result of reconnaissance survey. Exploration drilling and all geological studies in the area were completed in 1992. Subsequently exploratory mining was undertaken and pilot scale testing of flow sheet for recovery of uranium was also carried out. Uranium mineralisation is hosted by arkose to sub-arkose and feldspathic wacke associated with organic matter and pyrite. Pitchblende and coffinite are ore minerals. The ore body is tabular and occurs within a vertical depth of 50 m. A total of 9,500 tonnes uranium oxide contained in 9.22 million tonnes of ore with av. Grade 0.104%e U3O8, av. thickness 4.07m have been estimated at Domiasiat.
WAHKYN URANIUM DEPOSIT
The Wahkyn Uranium Deposit located at the confluence of Wahblei and Kynshi rivers, about 12 km west of Domiasiat in West Khasi Hills District of Meghalaya is another sandstone-type of uranium deposit. This deposit has gross similarity with Domiasiat uranium deposit in respect of geological set up and host rock characteristic and uranium mineralisation. Detailed investigations in Wahkyn area,have established mineable ore reserve of 5,300 tonnes U3O8 with an average grade of 0.130% eU3O8 contained in 3.58 million tonnes of ore.
TYRNAI : Tyrnai area is SW of Shillong and 5.5 Km SSW of Mawkyrwat connected by all weather motorable roads. A reserve of 570 tonnes of uranium oxide contained in 0.609 million tonnes of ore at 0.094 %eU3O8 average grade and 1.53m average thickness was estimated in inferred category.
LOSTOIN : The Lostoin block is located just 800m NW of Wahkyn deposit. A total of 760 tonnes of U3O8 in 1.18 million tonnes of ore have been proved in inferred category.
PRESENT THRUST AREAS
UMTHONGKUT : Significant uranium mineralisation hosted by Lower Mahadek sediments was located at Umthongkut area in the western fringe of West Khasi Hills district. This is considered highly potential block and is under active exploration at present.
WAHKUT : Southern continuity of Wahkyn deposit is being taken up for sub-surface exploration for augmenting additional uranium resources.Wahkut block is to the immediate south of Wahkyn ore body, which is open towards this block. This is also considered to be potential for uranium mineralisation and is under active exploration.
GARO CRYSTALLINES, MEGHALAYA : The Precambrian crystalline terrain of West Garo Hills district in the western part of Meghalaya Plateau has geological and tectonic features favourable for hosting hydrothermal vein-type uranium mineralisation. The migmatitic terrain of Garo Hills has witnessed anorogenic alkali granitic, pegmatitic and mafic igneous activities and shows extensive alteration of iron oxide along shear zones. The alkali granite has at places appreciable concentration of iron oxides (up to 12.5%), Cu (up to 2004 ppm), Pb (up to 242 ppm),Zn (up to 190 ppm) and total REE (up to 1233ppm).
The terrain is known to host a number of radioactive anomalies.Since 1959, more than 100 anomalies mostly uraniferous in nature have been recorded in the Garo crystalline around Rasubelpura,Ringi nala, Dasol nala, Dumal nala, Madarigiri in Simsang river section hosted by pegmatoids, quartzo-feldspathic injections and sheared granites at Anek.
ARUNACHAL PRADESH : Arunachal Pradesh, is the second significant state for uranium exploration wherein the rock formations from Precambrian to Miocene are exposed. The Meso Proterozoic Siang Group (Eq. Daling Group) hosts Fe-U mineralisation. The Group consists of a lower volcano-argillaceous sequence and an upper psammo-pelitic sequence. Significant uranium occurrences associated with sulphide mineralisation have been located at a number of places along 400 x 400 km belt extending from Kameng in the west to Siang in the east.
Hydrothermal vein-type of uranium mineralisation hosted by quartzite-phyllite sequence of Siang Group has been located in West Kameng and West Siang districts at Jamiri – Rukhu (silicified and sericitised phyllitic quartzite, 0.036-0.27% U3O8), Tai (brecciated silicified and sheared quartzite, up to 37.95% U3O8) and Kaying (sheared silicified phyllitic quartzite). The main uranium minerals identified are uraninite,brannerite and secondary uranium minerals such as uranophane, beta uranophane and torbernite.
Hydrothermal vein-type of uranium mineralisation associated with Fe-Cu-REE hosted by metavolcano-sedimentary rocks (Iron Formation) of Siang Group has been located in West Siang and Upper Subansari districts at Gamak (quartzo feldsphathic veins traversing the fractured and brecciated iron stones, 0.008–0.170% U3O8), Kau nala (quartzo-feldsphathic veins following foliation planes of the muscovite magnetite-quartz schist, 0.010 – 0.020% U3O8), Maro-Baririjo area (brecciated pyrite-magnetite-quartz-chlorite-phyllite and iron stone, 0.010 – 0.130% U3O8) and in New Badak area (magnetite and sulphide bearing quartz-sericite schist, 0.011 – 0.58% U3O8).Uranium occurs as uraninite, brannerite and absorbed in iron hydroxide.Detailed radiometric checking, geological mapping and drilling of all these areas are envisaged to probe the sub-surface continuity of uranium mineralisation and identifying the uranium reserves.
RARE METALS AND RARE EARTHS
Rare earths and rare metals are mainly hosted by Carbonatites and associated alkaline rocks.In North eastern Region, carbonatite and alkaline complexes are identified at Jasra and Sung valley of Meghalaya and Barpung & Samchampi of Assam.
SAMCHAMPI ALKALINE COMPLEX :
The samchampi-alkaline carboantite complex forms part of the carbonatite–alkaline province emplaced along the ENE-WSW Tyrsad – Barapani- Kalyani lineament in the Mikir Hills Massif of Assam (FIG. 5).Pyroxinites, titano- hematite rock, syenite, carbonatite and phosphatic rock bodies are present at Samchampi.
Detailed exploration has indicated 12,124 tonnes niobium, 2,685 tonnes tantalum and 1,821 tonnes yttrium in the soils. The titano-hematite rocks source of iron and titanium contains about 400 million tonnes of iron ore with 61% Fe and 3.4% TiO2. Moderate reserve of about 15 million tonnes of phosphate ore has also been estimated besides 4,364 tonnes of uranium oxide and 17,738 tonnes of REE.
In Sung Valley, rare earths and rare metals are hosted by carbonatites which occurs mainly as dykes or sheet like bodies intruding the pyroxenite, peridotie and ijolite. The carbonatite bodies range in size from 40 x 60m to 400 x 120m with NE trend. Fission track dating of apatite in carbonatite indicated 84±13-90±10Ma.Chemically,carbonatite contain 34.7 to 53.2% CaO, 31 to 40.10% CO2. The trace elements analysed are Ba (513-622 ppm), Sr (1399-3396 ppm), Ce (149-471 ppm),U (0.5-29 ppm), Th(<0.6-65.1 ppm),La (30-100ppm),Y (10-100ppm) and Zr (10-628ppm). Exploration by hand auger drilling at 250m grid interval upto a average depth of 1.0m over an area of 11 sq km has indicated 1,600 tonne of niobium in the soil.
The region is equipped with facilities such as