Origin and Distribution of Uranium and Thorium
Deposits in India
India has no significant reserves of Uranium; the need for uranium is met through imports. Uranium is imported from Russia, Kazakhstan, France, Canada and Australia. Uranium resources in India are estimated at various stages of exploration, and the estimates of uranium reserves for planning and commercial exploitation are prepared jointly by the Atomic Minerals Directorate (AMD) and the Uranium Corporation of India Limited (UCIL).
The identified conventional uranium resources in India are hosted by the following type of deposits:
1. Carbonate Deposit 42.24
2. Metamorphite type 31.55
3. Sandstone type 10.33
4. Unconformity type 9.95
5. Metasomatite 3.74
6. Granite Related 1.99
7. Quartz Pebble Conglomerate 0.19
The majority of these resources occur in following 5 uranium provinces.
1. Cuddapah uranium province, located in the Southern and South Central Regions. It contains the Proterozoic unconformity related uranium deposit at Lambapur-Peddagattu in Nalgonda district, Andhra Pradesh. The Cuddapah basin also hosts a unique stratabound uranium deposit associated with siliceous dolostone at Tummalapalle in Cuddapah district, Andhra Pradesh.
2. Singhbhum uranium province, located in the Eastern Region.All the deposits, presently being exploited,such as Jaduguda, Narwapahar, Turamdih, and Bagjata occur in this province.The other deposits in this belt are Mohuldih, Nandup, Rajgaon, and Garadih.All these occurrences are of vein type.
3. Mahadek uranium province, located in the Northeastern Region. The Cretaceous Mahadek Formation in Meghalaya contains the largest and richest sandstone-hosted uranium deposit of the country at Domiasiat (KPM deposit) in West Khasi Hills district. Another deposit of similar nature is at Wahkyn where exploration activities are in progress.
4. Albitite belt of Rajasthan and Haryana, located in Western and Northern Regions. The Meso-proterozoic Delhi Group of metasediments in parts of Rajasthan and Haryana holds potential for metasomatic and unconformity type of uranium mineralisation. A small deposit hosted by albitised metasediments of Delhi Supergroup has been established at Rohil and its extension.
5. Bhima basin, located in Southern Region. Comprising arenaceous and calcareous metasediments of Bhima Group deposited over basement granite, affected by number of East-West trending major fault zones. A small sized medium grade uranium deposit has been established in one such fault zone at Gogi.
Apart from these economically feasible occurrences, a number of geological situations occur, which may host potential uranium mineralization. Efforts are underway to augment the uranium resource base of the country by undertaking exploration activity in the following geological domains.
1. Proterozoic Basins: Nearly 33% of world uranium resources are found in the Proterozoic rocks. Particularly the unconformity contact zones between the Lower Proterozoic rocks with those of Middle-Upper Proterozoic ages have been the prime locales for the Uranium mineralisation. In India, a number of Proterozoic basins such as (i) Cuddapah basin, Andhra Pradesh (ii) Aravalli-Delhi fold belt, Rajasthan (iii) Gwalior-Vindhyan basin, Madhya Pradesh (iv) Bhima basin, Karnataka (v) Chhattisgarh basin in Chhattisgarh & Orissa exist where multidisciplinary investigations have been taken up in search of unconformity related uranium deposits.
2. Phanerozoic Basins: Similarly nearly 18% of world uranium resources are associated with Phanerozoic sandstones. In India too, the Phanerozoic sandstones, particularly the Cretaceous basin of Meghalaya has been one of the main targets for uranium exploration. One deposit has already been established and the entire basin has been considered as one of the thrust areas for uranium investigation. Other Phanerozoic basins considered potential are (i) Siwalik basin of the Himalayas, (ii) Gondwana basins of Central India.
3. Fe-oxide breccia type deposits: Particularly after the discovery of the Olympic Dam deposit in Australia which alone constitutes 31% of world uranium resources (RAR+EAR under <US $40/Kg U category - as per WNA publication), attention has been given worldwide to look for uranium mineralisation elsewhere in similar geological environment. In Indian scenario, such environments exist in parts of Madhya Pradesh, Jharkand and Meghalaya where investigations have been initiated with this objective.
4. Quartz pebble conglomerate deposits: Known Quartz-pebble conglomerate (QPC) type of U-deposits constitute 13% of total world uranium resources. They occur as basal Lower proterozoic beds unconformably lying above Archaean basement rocks. In India such environments are observed at a number of places like Walkunji in South Kanara District and Arbail in North Kanara district in the Western Ghat Belt, Karnataka, Dhanjori and Iron basins of Singhbhum district, Jharkand and Sundergarh district, Orissa. Based on the number of anomalies located in these areas survey has been intensified for locating QPC type of deposits.
5. Vein and Metasomatic type deposits: In recent past, Metasomatic/ vein type mineralisation associated with albitite type of rocks emplaced in tectonised domains have been located in many parts of the world, particularly in Russia and Kazakhastan. They owe their origin to both magmatic and metasomatic processes. Such geological set up also exists in India particularly in parts of Rajasthan (Aravallis) and Andhra Pradesh. Extensive efforts are being made for locating such deposits.
6. Placer Deposits: An important source of uranium is the mineral monazite in which uranium occurs as a trace constituent. Placer deposits of monazite occur in abundance as beach sands occur on east and west coasts and in some places in Bihar. But the largest concentration of monazite sand is on the Kerala coast. Other minerals like apatite, zircon and sphene which occur in these placers, also contain traces of uranium. Over 15,200 tonnes of uranium is estimated to be contained in monazite placers.
The Atomic Minerals Directorate for Exploration and Research (AMD) has established the presence of 1,71,672 tonnes of Uranium ore (U308) as on 30.06.2011. One tonne of uranium ore yields 0.848 tonnes of uranium metal. State-wise details of uranium resources are given in the following table:
The UCIL is presently operating five underground mines (viz. Jaduguda, Bhatin, Narwapahar, Turamdih and Bagjata), one open cast mine (Banduhurang) and two Processing Plants (Jaduguda and Turamdih) in East Singhbhum District and one underground mine at Mohuldih is under construction at Saraikela Kharswan District (all in Jharkhand State). An underground mine and ore processing plant at Tummalapalle (Tummalapalle Uranium Project) in Andhra Pradesh with a capacity to process 3000 tonnes per day (tpd) ore is in advanced stage of construction. An underground mine and process plant at Gogi in Yadgir District of Karnataka is under pre-project stage.
Some common minor primary constituents of igneous rocks carry uranium and thorium in isomorphous substitution for Ca, some REE and other elements.
Thorium Deposits in India
Monazite is the chief source of thorium in the world. Though it is a constituent of some granites and pegmatites, these rocks are not economically workable. Monazite is concentrated by weathering into economically workable deposits in beach sands in the coastal tracts of Australia, Brazil, Ceylon, Malaysia and India. Other common accessory minerals of igneous rocks which carry thorium (and uranium) in trace amounts as isomorphous substitution are monazite, apatite, zircon and sphene. Most of these minerals are resistant to weahering, but they differ greatly in their resistance to attrition during transportation with clastics. Monazite, apatite and xinotime are most easily reduced by attrition, but under favorable conditions these minerals become enriched in sands and gravels which have been transported short distances. They are found frequently in heavy mineral resistate fraction of terrestrially deposited clastics. Hence stream and beach monazite-bearing placers are found in many parts of the world. Zircon, which also carries a large portion of U and Th contents of felsic rocks, is a common constituent of the resistate fraction of all kinds of clastic sediments. These resistant minerals (monazite, apatite, xinotime and zircon) may be removed from erosional terranes of igneous rocks and become concentrated in placer deposits in environments where rock destruction by decomposition is predominant over that by disintegration, viz. the tropical climatic zones. The thorium content of minerals contained in these placers is considerably greater than the uranium content; therefore the deposits are classified primarily as thorium-bearing placers.
In India monazite is found in the coastal tracts of Cuttak and Ganjam districts of Orissa where the thickness of the placer is about 30 cm with a monazite content of 2.5 percent. Minor occurrences have been noticed between Chilka Lake and Chicacole River also. Thick ilmenite and monazite placers are found around Vishakhapatnam and Bhimunipatnam in Andhra Pradesh. The beach sands of the coastal tracts of Kerala and Tamil Nadu are also very rich in monazite. They also contain ilmenite and rutile. Monazite bearing sands are best developed along the beaches of the southwest coast of India between Quilon and Kanyakumari (Lipuram, Pudur, Kovalam, Varkala and Neendakarai) and between Chowghat and Ponnani. On the east coast of India, monazite concentrations are not as good as on the western and southwestern coasts, nevertheless small deposits are found along the Vishakhapatnam and Tanjore coasts. Monazite bearing black sand deposits occur in the coastal tracts of Waltair, Bimlipatnam and Narasipatnam.
According to the Atomic Minerals Directorate for Exploration and Research (AMD), a constituent Unit of the Department of Atomic Energy (DAE), India has 10.70 million tonnes of Monazite which contains 9,63,000 tonnes of Thorium Oxide (ThO2). According to a 2011 estimate by the US Geological Survey, the global reserves stand at 1,913,000 tonnes. India's thorium is mostly located in a contiguous belt of eastern coastal states as placer sands.
The following table shows the distribution of thorium reserves in the country according to a 2016 reserve estimates :
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