Thorium concentration in Ranchi plateau and other parts of Jharkhand State,

Rivers flowing through Ranchi plateau may also contain thorium.

By

Dr. Nitish Priyadarshi

Thorium deposits in India.

River flowing near Ranchi city.

Pegmatite intrusions in host rocks in Ranchi plateau.

Thorium is a naturally occurring radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 by the Norwegian mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius and named after Thor, the Norse god of thunder. Thorium produces a radioactive gas, radon-220, as one of its decay products. Secondary decay products of thorium include radium and actinium. In nature, virtually all thorium is found as thorium-232, which undergoes alpha decay with a half-life of about 14.05 billion years.

Berzelius was quite unaware of the tremendous amount of power that this element stores within it. Subsequent development in the field of nuclear science and technology, however, revealed that thorium might well prove to be equal to the god after whom it was named.

Thorium, which is transmutated U-233 in a breeder reactor, can be used as a nuclear fuel. It is presumed that with the development of breeder technology, thorium will come to play a vital role in providing electric power to millions.

Thorium is widely distributed in the earth’s crust with an average abundance of 8 ppm (parts per million) and is usually associated with uranium or the rare earth-earth elements. The principal mode of occurrence is in the form of veins in granites, synites, pegmatites and other acidic intrusions containing thorium- bearing minerals, such as thorite, thorianite, uranothorite and monazite. Detrital monazite occurs in quartz-pebble conglomerates, beach placers, inland placer deposits and dunes.

The largest known reserves of the thorium are contained in the beach and inland placer deposits of monazite, which are exploited for their rare-earth and ThO₂ contents. Placer deposits of monazite are found in Australia, Egypt, India, Liberia, Brazil, Malaysia and the USA (Florida).

Among the inland placer deposits containing heavy mineral there are two appreciable concentrations of monazite, which are located in the Ranchi plateau of Jharkhand and the Purulia planes of West Bengal.  These occurrences cover an area of about 608 sq. km. forming a thin cover of an average depth of about 50 cm (which may be locally up to 2m.). These deposits have been formed due to the weathering and erosion of Precambrian gneisses and schists, intruded by pegmatites and porphyritic granites, which are enriched in monazite and other associated heavy minerals. 

The placer minerals are released from their matrix by weathering. The comminuted materials are washed slowly down slope to the nearest stream or to the seashore. Moving stream water sweeps away the lighter matrix, and the heavier placer minerals sink to the bottom or are moved downstream relatively shorter distances. The sands of the rivers like Swarnrekha, Jumar, Potpoto, kanchi, etc. flowing through Ranchi plateau may contain thorium in considerable amount.

Thorium present in the river streambed sediments are mostly of terrestrial origin and their concentrations are related to the type of parent rocks and to the genesis of the sediments. The river sediments generally exhibit large variation in composition. This variation can be related to the chemical and mineralogical evolution of these sediments along the river, influence of tributaries, or different properties of drained soil. The mobility of radionuclides in the aqueous system is an important factor influencing the content of radionuclides in river sediments. Surface run-off waters in the tributaries wash down a part of deposited radionuclides and finally store them in the river sediments.

Most of the radioactive anomalies in the Damodar Valley basins are confined to the Panchet  sandstones with the preponderance of thorium over uranium. A similar pattern has also been observed in the Barakar sediments of the Hutar basin.

The granites of the provenance areas fir the Hutar-Daltonganj basins contain anomalous uranium values. Uranium mineralization has also been observed in the granitic rocks comprising the southern periphery of the Hutar basin. The Proterozoic granitoids, forming the provenance for the Hutar and Auranga sub basin (Jharkhand), have been analysed which revealed uranium content up to 520 ppm, while the clays and sandstones of Barakar Formations have revealed anomalous uranium-thorium values of the order of 120-150 ppm uranium and less than 100-800 ppm thorium.

Reference:

Bateman, A.M. 1955. Economic mineral deposits. John Wiley & Sons, Inc. New York.

Virnave, S.N. 1999. Nuclear geology and atomic mineral resources. Bharti Bhawan, Patna.

Viswanathan, G., Badri, N.S.R., and Virnave, S.N. 1989. Radioelement distribution in the Lower Gondwana sediments of Hutar basin, Palamau district, Jharkhand; its bearing on uranium exploration. Exploration Research Atomic minerals Vol. 2 , pp 121-131.

http://dae.nic.in/writereaddata/lssq%20379.pdf

http://large.stanford.edu/courses/2012/ph241/bordia1/

Rare earths elements are in increasingly short supply as world demand surges.

Jharkhand State of India can play major role in Rare Earth Elements production.

by

Dr. Nitish Priyadarshi

China has been steadily reducing export quotas since 2005 for rare earth elements, which consist of 17 metals used in crucial new green technologies like hybrid cars, wind turbines and superconductors, as well as in missile guidance systems and mobile phones.

According to Chinese experts, “Mass extraction of rare earth will cause great damage to the environment and that's why China has tightened controls over rare earth production, exploration and trade,".

Overseas buyers have expressed concern about China's policies to restrict rare earth exports, which have driven up global prices. Rare earths are in increasingly short supply as world demand surges, with industry officials predicting a global shortfall of 30,000 to 50,000 tonnes by 2012.

The automobile industry uses tens of thousands of tons of rare earth elements each year, and advanced military technology depends on these elements, too. Lots of "green" technologies depend on them, including wind turbines, low-energy light bulbs and hybrid car batteries. In fact, much of western civilization depends on rare earth elements such as terbium, lanthanum and neodymium.

If that happens, the western world will be crippled by the collapse of available rare earth elements. Manufacturing of everything from computers and electronics to farm machinery will grind to a halt. Electronics will disappear from the shelves and prices for manufactured goods that depend on these rare elements will skyrocket.

Seeing the possible scarcity of rare earth elements in coming future, India can play major role in REE production. Especially Jharkhand and West Bengal State, which has the potential of good REE in its rocks and inland placers.

Rare earth elements or rare earth metals are a collection of seventeen chemical elements in the periodic table, namely scandium, yttrium, and the fifteen lanthanides. Scandium and yttrium are considered rare earths since they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties. Rare earth minerals occur chiefly in association with alkalic plutons and in placers derived from them. Specific minerals mined for their rare earth or thorium content are monazite and bastnaesite. Despite their high relative abundance, rare earth minerals are more difficult to mine and extract than equivalent sources of transition metals (due in part to their similar chemical properties), making the rare earth elements relatively expensive.

Common Properties of the Rare Earths.

1. The rare earths are silver, silvery-white, or gray metals.
2. The metals have a high luster, but tarnish readily in air.
3. The metals have high electrical conductivity.
4. The rare earths share many common properties. This makes them difficult to separate or even distinguish from each other.
5. There are very small differences in solubility and complex formation between the rare earths.
6. The rare earth metals naturally occur together in minerals (e.g., monazite is a mixed rare earth phosphate).

Indian reserves are predominantly of monazite ore. Monazite contains about 60% of the rare earths of the cerium group expressed as oxide plus an average 7.2% thorium and minor yttrium. It is yellowish to reddish brown mineral. In India, it occurs in commercial concentrations in beach sands.

The pegmatite veins in crystalline rocks contain a few rare earth minerals as their accessory constituents. The most common of these are columbite and tantalite, torbernite, aeschynite, allanite etc. which occur in the mica pegmatite of Hazaribag in Jharkhand State of India. Other places in India are Nellore, Andhra Pradesh and Tranvancore in Kerala and Rajasthan. Gadolinite is found associated with cassiterite in a tourmaline pegmatite in Palanpur; and molybdenite in the crystalline rocks of Chota Nagpur in Jharkhand state.

Geological Survey of India (GSI), during field season 1993-94, carried out detailed study of the north Singhbhum shear zone, in Jharkhand State, with a view to establishing mineral potential including rare earth elements (REE). The results obtained, being not encouraging, similar study in parallel north Purulia shear zone, which is also known as Jhalda shear zone is to be taken up. It extends westward in Ranchi district and is associated with apatite and magnesite mineralization. Recently, some carbonatites with high REE values are reported from this shear zone in West Bengal in India.

In the course of specialized thematic mapping of Chota Nagpur gneissic complex in parts of West Bengal, a few rare metal pegmatites bodies have been identified .Chemical data of these samples show high cesium (1.72 to 13.73%), rubidium (0.27 to 0.33%) and lithium (0.07 to 1.36%).

The world reserve base in terms of rare earth oxides content is estimated at 110 million tones. Although a certain degree of rare earth’s processing exists in a number of countries, the industry is dominated by a few main players like USA, France, Japan and China.

Mineable concentrations of source elements of the rare earth group of metals are uncommon. Bastnaesite is mined extensively in China and the USA. Monazite is recovered largely as a by-product of processing heavy mineral sands in various parts of the world, primarily Australia and India.

Among the inland placer deposits containing heavy mineral, there are two appreciable concentrations of monazite, which are located in Ranchi plateau of Jharkhand and the Purulia planes of West Bengal in India. These occurrences cover an area of about 608 km² , forming a thin cover of an average depth of about 50 cm (which may be locally up to 2 m). These deposits have been formed due to the weathering and erosion of Precambrian gneisses and schists, intruded by pegmatites and porphyritic granits, which are rich in monazite and other associated heavy minerals.

The rare earths are constituents of more than 100 minerals, but only few are recovered. Bastnaesite, monazite, xenotime and rare earth-bearing clays are the principal sources of rare earth supply in the world.

REE are strategic resources upon which entire nations are built. In many ways, they are similar to rubber -- a resource so valuable and important to the world that many experts call it the "fourth most important natural resource in the world," right after water, steel and oil. Without rubber, you couldn't drive your car to work or water your lawn. Many medical technologies would cease to work and virtually all commercial construction would grind to a halt.