Iron Ore Deposits of Eastern India (With Map) | Metals | Metallurgy

In this article we will discuss about:- 1. Introduction to Iron Ore Deposits 2. Overview of the Iron Ore Group 3. Iron Ores of the Singhbhum Era.

Introduction to Iron Ore Deposits:

Rich iron ore deposits of high grade where the iron percentage is more than 60 per cent, eastern India account for more than half of the total current annual production of more than 180 million metric tonnes of iron ore in India. After nearly a century of active mining the estimated remaining iron ore resource of the eastern Indian deposits is in the order of five billion metric tonnes at > 60wt per cent Fe.

The best grade and largest East Indian deposits are virtually all hosted by Precambrian banded iron formation (BIF) of the Iron Ore Group (IOG).

The following description is from Mukhopadhyay et al, (2008). Major strata bound ore deposits occur in the BIFs of the eastern IOG in the Gorumahishani-Badampahar range, western IOG in the Noamundi-Joda-Malangtoli-Bursua-Gua-Chiria ranges, and in the southern IOG in the Daitari-Tamka range.

Relatively minor amounts of low-grade ores occur as ancient colluvial detrital conglomeratic ore deposits in the Late Mesoproterozoic Kolhan successions around Chamakapur and Baljori villages as well as Quaternary alluvial deposits close to major BIF-hosted deposits.

There are differences in opinion regarding the origin of the BIF-hosted iron ore deposits of eastern India. They are generally believed to have formed through preferential leaching of silica from BIF/BHQ (banded hematite quartzite) in response to supergene weathering and tropical lateritization processes. A syngenetic hypothesis for the origin for the BIF- hosted high-grade iron ores has also been invoked.

An alternative hydrothermal model or combinations of supergene and hydrothermal processes have been put forward. In more recent times Beukes et al. (2008) and Mukhopadhyay et al. (2008) proposed a supergene-modified hydrothermal model for the deposits of the Noamundi area based on field relationship, petrographic and geochemical proxies.

Overview of the Iron Ore Group:

The iron ores of eastern India are virtually restricted to the BIF-bearing Paleo-Mesoarchean greenstone successions of the Singhbhum craton. The craton is one of the oldest Paleo-Mesoarchean cratonic nuclei of the peninsular India. It is a composite mosaic of Archean greenstone-granitoids and Proterozoic supracrustal successions.

The oldest granitoid is referred to as the Older Metamorphic Tonalite Gneiss (OMTG, 3,400 m.y.) that includes enclaves of metasedimentaries of the Older Metamorphic Group (OMG, 3,500-3,800 m). The OMTG is intruded by several granitic plutonnes collectively referred to as the Singhbhum Granitoid with three phases of emplacement between 3300 m.y. and 3100 m.y.

The Singhbhum Granitoid is the aerially most extensive unit and encases the BIF-bearing Iron Ore Group (IOG). Younger Neoarchaean to Mesoproterozoic volcano-sedimentary successions un-conformably overlie the granite-greenstone successions.

The IOG low grade metamorphic greenstone belt successions comprise banded iron formation (BIF), mafic-felsic volcanic rocks, chert, shale and minor carbonate. The greenstone belts occur as three large detached enclaves within Singhbhum Granitoid.

These enclaves are informally referred to as the western (Noamundi-Joda- Koira-Malangtoli-Bursua-Chiria), eastern (Gorumahisani-Badampahar) and southern (Malaygiri-Tamka-Daitari) IOG. Iron ore deposits occur in BIF host units in all three areas of greenstone belts.

However, the economically most important deposits are located in the western IOG, in the Noamundi-Joda-Koira-Malangtoli-Bursua-Chiria range. From base to top, it includes thick, massive, or pillowed rhetabasalt, lower phyllitic shale-tuff (locally with thin carbonate and supergene manganiferous mineralization), BIF, and upper phyllitic.

The main regional structure controlling the outcrop belt has been described as a northeasterly plunging synclinorium-the ‘horseshoe synclinorium’, with overturned western limb. The name comes from the fact that the resistant BIF results in a range of hills with a typical horseshoe-shaped outcrop pattern. The synclinorium has been later cross-folded along an east-west axis. The high-grade iron ores of the Western IOG are mainly composed of hematite.

In contrast the smaller deposits of the Eastern IOG are mainly composed of magnetite-rich stratabound bodies in a thick BIF unit. These deposits are located along the Gorumahishani-Bdamapahar range. The eastern IOG is folded into several steep anticlines and synclines with early steep isoclinal folds trending NNE-SSW and late open folds with axis trending WNW-ESE.

The BIF-bearing metavolacnics succession of the southern IOG is well exposed along the Tomka-Daitari Ranges. The succession consists from the base upwards of massive and pillowed basalts with a few thin greys to green chert interbeds, felsic to intermediate volcanic and volcaniclastic rocks (tuffs), bedded chert and BIF.

The BIF unit here is more than 120 m thick and hosts the Daitari and Tomka hematite-rich iron ore deposits. A podiform chromiferous ultramafic body that forms the most important chromite resource of India in the Sukinda Valley overlies the BIF with a thrust contact.

The ultramafic body and the greenstone succession of the Daitari-Tamka range are un-conformably overlain by a thick siliciclastic shelf succession, the Mahagiri Quartzite that includes detrital chromite grains in its lower parts.

Until recently there was no direct age for the IOG successions. A minimum age of ˜3,200 m.y. was provided for the Iron Ore Group by granitoids intrusive into the three outcrop belts. Mukhopadhyay et al (2008) obtained 3,506 ± 2 Ma U-Pb SHRIMP zircon age from the dacitic lava from the southern IOG around Daitari.

Iron Ores of the Singhbhum Era:

Iron ores of the Singhbhum era ton (Figures 4.1 and 4.2) occur as stratabound orebodies within the BIF protolith or else in subordinate amount as detrital colluvial ores in ancient geological formations or Quaternary to recent alluvial deposits.

The detrital ores are seemingly derived from the stratabound mother orebodies. The main stratabound orebodies are essentially hematitic in mineralogy, though magnetite/martite dominated orebodies occur in the Gorumahishani-Badampahar range of the eastern IOG.

The stratabound orebodies are hosted by the prominent BIF-units in each of the IOG outcrop belts. Thickness of the BIF protoliths may range from 120 to 220 m. Besides the major BIF-bearing unit, several thinner (a few metres) BIF units in the lower manganiferous shale of the western IOG are also mineralized and are locally mined.

Megascopically the ores are of two major types, namely, hard massive/laminated ore and soft/friable ore that can grade to completely incoherent blue dust variety. The high-grade hard orebodies have been found to near completely replace the BIF protolith or might grade to unmineralized BIF through partly mineralized BIF both vertically and laterally. Locally, the orebodies include patches of partly mineralized BIF.

The orebodies strictly follow the folded form surfaces of the BIF protolith and consequently the attitude of the orebodies varies with the changing attitudes of the BIF units. Although relative timing of ore genesis with respect to the deformation is yet to be resolved, lack of pervasive deformation fabrics in platy hematite-rich orebodies and intricate fold patterns locally preserved in essentially monomineralic orebodies without appreciable viscosity difference among strata suggest that ore formation might have postdated the deformation of the host BIF.

Soft orebodies are also stratabound to specific units in the BIF host and closely associated with hard ore bodies. These are considered orebodies that resulted from supergene alteration of originally partly mineralized BIF by the same hydrothermal fluids that formed the associated high-grade hard hematitemartite ores.

Both hard and soft ores contain on average 64 to 67 wt per cent Fe, 1 to 2.8 wt per cent Al₂O₃, 0.5 to 3.6 wt per cent SiO₂, and 0.05 to 0.1 wt per cent P₂O₅. The hard ore mineralogically may include associations of martite -hematite ± magnetite or hematite ± martite or hematite ± goethite. The soft ores and blue dusts are predominantly hematitic with subordinate amount of martites and goethite.

In general the martite- rich hard ores occur at the lower/deeper levels. This type of ore commonly grades to either soft friable/blue dust ore or laminated hematitic ores. The goethitic ores commonly occupy the upper levels of deposits and are distinctly the products of oxidation in the present-day weathering profile.

Contrary to the existing idea of origin of these orebodies by supergene process of leaching of silica from the BIF and hence residual enrichment of Fe-ore minerals, recent investigations suggest a supergene-modified hydrothermal process of ore formation. The presence of excess magnetite/martite in orebodies compared to their relative abundance in the BIF-protolith provides the major evidence of early hydrothermal ore-forming process.

The presence of partly mineralized BIF relicts, the existence of orebodies below unmineralized BIF (e.g., in the Gandhamardan ore deposit, OMC, Orissa) and lateral gradation of one ore type into the other support the hydrothermal ore genesis as primary ore-forming process. The magnetite-martite ores are believed to be the products of hypogene hydrothermal ore genetic process.

The hard hematitic ore have been explained as the product of replacement of the BIF-protolith in relatively low- temperature hydrothermal system peripheral to magnetite/martite-rich ore-bodies. The soft ores have been related to various degrees of dissolution of Fe²⁺ during supergene oxidation in acidic groundwater in Cenozoic times.