DISTRIBUTION OF heavy mineraLS IN BEACH SAND DEPOSITS: AN OVERVIEW
India is endowed with valuable resources of beach sand minerals. Indian beach-line along Kerala, Tamil Nadu, Andhra Pradesh, Orissa where significant deposits of different minerals are available from beach sands, made this country one of the leading producers of heavy minerals in the world. The beach sand minerals constitute a group of important economic minerals such as - Ilmanite (FeO.TiO2), Rutile (TiO2), Monazite (Ce,La,Y,Th)PO4, Garnet, Sillimanite (Al2O3.SiO2) and Zircon (ZrO2.SiO2). The adjacent map shows the locations on the Indian beach-line where significant deposits of these minerals occur in varying size, concentration and grade ranging from 5% to 45%.
Fig: Indian beach-line showing locations of heavy mineral deposits in beach sands.
Australia and Brazil are other major producers of these minerals. Most of the Australian occurrences are along the parts of coasts of New South Wales, Queensland and Western Australia. The Australian deposits contain about 45% rutile while the Indian deposits have about 5% rutile. Around 90% of the world’s supply of rutile comes from Australia. However, the ilmanite content of the Australian deposits is quite low (around 20%). Further the high chromium content bars the usage of the Australian ilmanite in pigment industry. Brazil supplied around half of the world’s monazite till recently. The deposits occur mainly along 1600 km. of the coast which covers Rio de Janerio, Bahia, Espirito Santo, Parabyba and Rio Grande do Norte.
In India the heavy mineral deposits of west coast are largely concentrated as high-grade beach and low-grade dune deposits extending from Kanyakumari to Malabar Coast with interruptions. The main deposits are around Kayamkulam - Neendakara coast (popularly known as Quilon deposits) in Kerala and in the Manavalakurichi region in Tamil Nadu. The Quilon deposits extend for about 20 km in length while at Manavalakurichi the deposits spread over 2 km. Along the eastern coast a large resource of beach sand minerals was established near Chatarpur - Gopalpur Block having a coastal length of about 18 km and width of about 1.5 km where IRE is operating the mine for Orissa Sand Complex (OSCOM) plant. This Block alone has a resource of 62 million tonnes of heavy minerals having a grade of 18.50% in raw sand. According to a recent report titled “Recovery of Sillimanite from beach sand of Chatarpur, Orissa and its thermal treatment for refractory applications” published by Inder Science Publishers, in the beach sand of Chatarpur, sillimanite which has refractory applications accounts for 8% of these heavy minerals. The Chavara (Kerala) and Manavalakurichi (TN) are considered to be among the richest deposits in the world. On average basis Indian beach sand deposits contain about 9% rutile, 6% garnet, 3% sillimanite, and 1% monazite and zircon. While ilmanite dominates the Indian beach sand to an extent of 60% to 82%, the Australian sands have only about 20% of the same. However, in the latter rutile and zircon are comparatively in considerable amounts.
The heavy mineral deposits found in the beach sand comes under the category of Placer Deposits, have a special mode of occurrence along the sea coast, mostly influenced by the prevailing geological conditions in that region over a long period. Geologically speaking ‘Placer Deposits’ are those deposits which are found near or around the off-shore regions and have formed from rock alteration and little chemical and biogenic activities of pre-existing pegmatite rocks. The heavy minerals are thought to be derived from the crystalline basement rocks, chiefly of granitic and dioritic nature and also partly from Tertiary sediments. Khonadalites constitute the principal source rock of the Indian beach sand deposits of heavy minerals. These deposits are a product of river action which carried these to the sea where sorting and repeated wave action have resulted in concentration of heavy minerals along the sand bars. Deposits occur on present beaches, barrier beaches and old elevated inland beaches buried below sand dunes. The localization of some of these deposits is a result of changes in surface level and diversions of the complicated stream networks.
industrial uses of heavy minerals
The opaque, black, mineral is important source of Titanium and its compounds (alloys). It serves as a source of titania for special glasses, a colouring agent for producing black coatings on brick and for developing speckled effects on ceramic tile and in pottery glazes.
Sillimanite (Al2O3 SiO2)
It is used as an important raw material for high alumina refractories for Cement, Iron and Steel, Ceramic, Petrochemical and Electrical industries. An important use of sillimanite refractories is in construction of glass melting tank furnace, because of the high resistance of sillimanite refractories towards corrosion and erosion of due molten glass. Sillimanite is used both as sand as well as in fines (pulverized in Ball Mill etc.). The fine grained material is especially suitable for the production of monolithic refractory. More about properties and uses of Sillimanite have been discussed in separate posts Sillimanite - Properties and Occurrence in India [Read] and Use of Sillimanite in Refractories [Read].
It is used as coating of welding electrodes and manufacture of titanium dioxide. Rutile is also used to stain pottery bodies and glazes. Artificial teeth are among the ceramics so tinted.
This mineral is mainly used for abrasives and in glass and optical industries.
Zircon is used as raw material for the production of zirconium metal, other ferro-alloys and special refractories. Zircon nozzles of different shapes are for continuous casting of steel. Zircon-alumina (AZS), zircon-mullite (zirmul) refractories in different shapes are widely used as feeder refractories in the glass industries, in steel ladle, blast furnace etc. Due to the high hardness and abrasive resistance, zircon is used for making high density grinding media. The major uses of zircon can be categorized as follows:
(a) Refractories, Steel and Glass : 35%
(b) Ceramics : 25%
(c) Foundry : 21%
(d) Others : 19%
Monazite is used as a source of Thorium and Rare-Earth.
BEACH-SAND MINERAL INDUSTRY IN INDIA: AN OUTLOOK
The beach sand mineral industry in India dates back to the beginning of the 20th century. The growth of this industry has been relegated to three distinct periods: 1. between 1909 and 1919 when largely the discovery of the deposits was followed by German exploitation, 2. between 1918 and 1959 with the British control, and 3. the subsequent period in which the important events are the mining agency agreement and the nationalization. The exploitation of beach sand minerals and processing were earlier restricted to only Public sector Undertakings mainly by Indian Rare Earths Limited (IRE), which was set up by the Atomic Energy Commission with four divisions comprising Rare Earths Division at Alwaye, Minerals Division at Quilon, Thorium Division at Trombay and Orissa Sand Complex (OSCOM) at Matikhal near Chatarpur. The OSCOM was set up in 1977 with a target of annual production:
Ilmanite - 2,20,000 tonnes
Rutile - 10,000 tonnes
Sillimanite - 30,000 tonnes
Zircon - 2,000 tonnes
Monazite - 4,000 tonnes
The commercial production at OSCOM started at 1986 but the production could never match the desired level for a long period due to various reasons. Indian Rare Earth also set up a Synthetic Rutile Plant to convert the ilmanite to Synthetic Rutile, with an annual capacity of 96,000 tonnes. However, due to some technical problem this plant could not run for long and the entire production of ilmanite from OSCOM plant is being exported to USA, Norway, Japan and South Korea while the garnet, sillimanite and zircon are sold in the domestic market and monazite is kept for Atomic Energy Department.
Considering the vast potential of beach-sand mineral industry in India, the Government of India has recently relaxed certain provisions and Private Companies have been allowed for the first time to participate in exploitation of these minerals. [To refer to these Policies and Statutory Provisions relating to exploitation of beach sand minerals from Government of India, Department of atomic Energy logon: http://www.sipcot.com/policies2_4.htm]. Moreover, there are other things which make mining of heavy minerals from Indian beach sand deposits favourable such as -
=> Deposits are easily accessible and free from human settlements.
=> As these heavy minerals are available in a shallow depth, it is easy to mine the raw sand.
=> There is no over-burden removal required before mining.
=> Beach-sand mining is eco-friendly unlike other mining operations. The original landscape is restored after mining, without radio-active mineral.
Hence, after considering all these favourable factors as well as the encouraging policies adopted by the Government of India in this regard, the prospects of beach sand mineral industry in India appear to be very bright.