Chromite.docx
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Chromite is an oxide mineral composed of chromium, iron, and oxygen that is an important source of chromium. It is used to produce stainless steel and other alloys. India has significant chromite resources, around 2% of the world total. The largest deposits are found in Odisha associated with ultramafic intrusions into ancient greenstone belts. Chromite deposits form in three main types - stratiform layers, podiform disseminations in ophiolites, and placer deposits in beach sands. India has estimated reserves of 344 million tonnes.
Chromite.docx
- 1. Chromite: - Introduction: Chromium is an important metal and has a wide range of industrial uses. Chromite is a metal used to induce hardness, toughness and chemical resistance in steel. The alloy produced is known as “stainless steel”. Elemental chromium (Cr) does not occur in nature, but is present in ores. Chromite is an oxide mineral composed of chromium, iron, and oxygen (FeOCr2O3). Chromite ore mostly consists of chromite with subordinate amounts of ferrichromite, magnetite, ilmenite and secondary silicates like serpentine, talc, tremolite, uvarovite and kammererite. Physical Properties: Chromite is dark gray to black in color with a metallic to submetallic luster and a high specific gravity (4.0 to 5.1, Harness-5.5 to 6, Clevage-None, Streak- Dark brown. Small amounts of chromite are found in many types of rock. 1) Stratiform deposits (large masses of igneous rock such as Peridotite, Dunite that slowly crystallized from subsurface magma); 2) podiform deposits (Serpentines and other metamorphic rocks derived from the alteration of Dunite and Peridotite); and, 3) Beach sands (derived from the weathering of chromite-bearing rocks). Chromite is used in the manufacture of alloys along with other metals, such as, nickel, cobalt, molybdenum, copper, titanium, zirconium, vanadium, columbium and selenium. Indian chromite deposits amount to about 2% of total world resources. In India, stratiform chromites are found in ultramafics intrusive into Archaean or Precambrian lithosequences of low or high metamorphic grade. Stratiform complexes were emplaced in the low grade greenstone sequences in Odisha, Jharkhand and Karnataka and in high grade granulite lithopackages in Tamil Nadu and Andhra Pradesh. Tertiary ophiolite sequences having ultramafic rocks and podiform chromite are known to occur in Manipur, Nagaland and Ladakh sectors of Himalayan belt and in Andaman Islands of Indo-Burma arc. Indian Occurrences: The Indian chromite deposits have been classified into the following categories based on their association with different stratigraphic horizons of different geological ages. A. Associated with Ultramafic intrusive into: (a) Archaean supracrustals (greenstone belts): 1. Sukinda and Boula-Nuasahi in Odisha, 2. Jojohatu-Roroburu belt in Jharkhand 3. Sinduvalli and Byrapur in Karnataka 4. Bhandara-Nagpur, Sindhudurg and Chandrapur belts in Maharashtra (b) Precambrian Eastern Ghats Granulite Belt and Southern Granulite terrains: 1. Andhra Pradesh 2. Tamil Nadu B. Associated with Tertiary Ophiolite sequences in Himalayan orogenic belt: (1) Manipur (2) Nagaland (3) Jammu & Kashmir Himalayas and (4) Andaman & Nicobar Islands. The major economic deposits in the country occur in association with ultramafic intrusive intruding Iron Ore Group rocks in Odisha and Sargur Group in Karnataka, both of Archaean age. Type of Deposits: Chromite deposits are generally of two types viz., a) Stratiform b) Podiform and c) Beach Placer A. Stratiform Deposits: Stratiform deposits are large masses of igneous rock that cooled very slowly in subsurface magma chambers. During this slow cooling, chromite and associated minerals crystallized early while the magma was still at a very high temperature. Their crystals then settled to the bottom of the magma chamber to form a layered deposit. The world's known chromite occurs in the Bushveld Complex in South Africa and the Great Dyke in Zimbabwe. Other important stratiform deposits include the Stillwater Complex in Montana, the Kemi Complex of Finland, the Sukinda Complex of India, the Goias in Brazil, the Mashaba Complex of Zimbabwe and small deposits in Madagascar. These deposits are Precambrian in age. Stratiform deposit have low Cr/Fe ratio.
- 2. B. Podiform Deposits: Podiform deposits are large slabs of oceanic lithosphere that have been thrust up onto a continental plate. These slabs of rock, also known as "ophiolites," can contain significant amounts of chromite. In these deposits the chromite is disseminated through the rock and not highly concentrated in layers. Podiform deposits are known in Kazakhstan, Russia, the Philippines, Zimbabwe, Cyprus, and Greece. Podiform deposit have High Cr/Fe ratio. C. Beach Sand: Chromite is found in beach sands derived from the weathering of chromite-bearing rocks and laterite soils that developed over peridotite. Two facts allow these chromite sands to occasionally contain economic deposits of chromite. First, chromite is one of the more weathering-resistant minerals of peridotite. That causes it to be concentrated in residual soils that form in the weathering zone above chromite-rich rocks. Second, chromite has a higher specific gravity than other minerals in peridotite. This causes it to be selectively transported and deposited by wave and current actions, concentrating it in certain locations at streams and beaches. These deposits are sometimes rich enough and large enough that they can be mined for chromite. Reserves/Resources: As per NMI database based on UNFC system, the total reserves/resources of chromite in the country as on 1.4.2015 has been estimated at 344 million tonnes with 102 million tonnes as “Reserves" (30%) and 242 million tonnes as "Remaining Resources" (70%). (Source: IBM Year Book 2019) More than 96% resources of chromite are located in Odisha, mostly in Jajpur, Kendujhar and Dhenkanal districts. Minor deposits are scattered over Manipur, Nagaland, Karnataka, Jharkhand, Maharashtra, Tamil Nadu, Telangana and Andhra Pradesh. Depending on compositional variation, chromite ore can be divided into the following three categories: Ore Type Cr2O3 Percentage Al2O3 Percentage Cr:Fe High Chromium 46-55 --- >2 High Iron 40-46 --- 1.5-2 High Aluminium 32-38 22-34 2-2.5 Use of Chromium: