CHIRIA IRON ORE MINE
The iron ore deposits at Chira are reported to have been discovered by M/s P.N. Bose and R.Saubolle, prospectors for M/s Martin and Company. The Bengal Iron & Steel Co. started mining operations on a very small scale in Pansiraa Buru near Chiria in 1901 under the name of Manoharpur Ore Mines, which is considered one of the oldest mines in the country. A light railway was established in 1910 and commercial exploitation of the iron ore started in 1910 at Duia (Banalata Buru) and adjoining areas and at Chiria (Budha Buru) in 1916.
Geology and Structure
Geologically, the terrain forms a part of the oldest meta-sedimentary and metavolcanic formations of the Chhotanagpur plateau considered as homotaxial with the Dharwars in the Indian geological column. Generally it is believed that the iron rich formations of the Bonai-Keonjhar range form part of the Iron Ore Series.
In a generally accepted opinion, iron ore bearing Banded Iron Formations (BIF) lie between the two discretely argillaceous environments of shales, phyllites, sandstones, lavas, ash and tuff beds, with the basal sandstone conglomerates, occurring at the base of iron ore group which unconformably overlies the older metamorphics. Profuse volcanic activity in the form of tuff beds, has also been noticed in the banded iron formations and within the iron ore body itself. The Iron Ore Group of rocks occur around the Singhbhum granite body.
The geographical placement of the Iron Ore Group is confined between Manoharpur in the north to Gandhamardan in the south. It has an elongated horse-shoe shape, trending in NNE-SSW, open on NNE and spread over a surface area of 100 x 30 km. The Budha Buru hill with the Chiria iron ore deposit, falls on the north-western edge of the area.
The regional structural configuration of the iron ore group has been interpreted as a NNE-SSW trending synclinorium plunging NNE. The northern periphery of this basin shows abuttal against the ENE-WSW Satpura-Mahanadi strike.
The Chiria iron ore deposit is banded limonite – goethite – hematite assemblage, capping the Budha Buru hill sloping down to 530 m. MSL resting on a shale BHQ country rock of the Iron Ore Group. Trending parallel to the major structure, the longest axis of the deposit is N250E – S250W, spread on a visible strike length of over 6.5 km. and an average outcrop width of about 3.5 km.
The oblong tabular iron ore body is bound by BIF. Lateristisation is extensive all over, which obliterates the exact delineation of ore boundary on surface. The mineralised area of all the four deposits in 13.4 sq.km of which the non-mineralised patches of shale / BHQ account for a cummulative total of 3.4 sq. km on surface.
The lithological types encountered from top to bottom in and around the deposit are as follows:
Laterite and Canga
|Iron Ores||Massive and thickly laminated ore
Thinly laminated and biscuity ore
Blue and red powdery ore
Banded Iron Formations
(Intertonguing shale and BHQ)
Formational contracts are always gradational. The thickness of these beds is found to be variable. The above succession is normal as indicated by indirect evidence.
The average general strike of the Chiria iron ore deposit is N250E – S250E with a general dip of 500 in N650W direction. However, the strike varies from E-W to N-S and dip from 00 to 900 mainly due to development of intricate folds and cross folds and to a lesser extent due to solution slumping.
Two sets of folds an done or more sets of cross folds are observed in the area. The first set of folds is parallel to major Dharwarian trend of the Bonai-Keonjhar-Singhbhum belt and the second is roughly parallel to the later Satpura-Mahanadi trend. The major fold axis of the ore body which is generally NE-SW. The axis trend of second set of folds is roughly in N650W – S650E direction.
It has not been easy to locate and trace the faults within the ore body because of the effects of residual concentration and lateritisation. The faults have been interpreted on the basis of lithological repetitions / omissions, the presence if restricted zones of brecciation and some geomorphological indications like linear scarps etc. The main fault which can be traced on the surface runs roughly in N-S direction across the entire deposit. Brecciation, silicificatrion and shearing are noticed in some bore holes. The hade of the fault is about 350 towards east. A number of smaller faults oblique to the longer axis of the deposit are present and have been traced over distances varying from 100 to 1500 m. and their hades vary from 400 to 700.
The other structural features are development of foliation, joints, striations and pucker lineations. Thin orientation with respect to the structural disposotion are mostly of the usual type and therefore fabric study on microscopic scale corroborates to the field interpreations.
It may be concluded that structurally the deposit has a basin like configuration with an undulating floor marked by a BHQ horizon. The BHQ horizon, stratigraphically older to the ore bearing horizon, is exposed all around the deposit except for the south-western and extreme southern portion of the deposit. In these areas conglomerates older to the BHQs are exposed. Although BHQs are not exposed in the south-western corner, thin continuity below the cover of laterite has been established by the sub-surface explorations. The synclinal configuration and a north-easterly plunge in the southern part of the area is demonstrated by a closure involving the older beds. On the basics of a generally centrifugal dips of the maker horizon (BHQ), the structure is concluded as a basin.
Within the basin, there are anticlines and synclines. A prominent anticlinal configuration is seen in the central and northern parts of the area near the central axial line. Synclinal configuration are quite common towards the peripheries of the deposit. The plunge directions in the northern and southern peripheries vary from 150 to 200 while in the central party they are almost horizontal. These are indications of cross folding, with cross fold axes of the deposit. The synclinical disposition with cross-folds has given rise to certain culminations and depressions, where the ore bottom crops out selectively in the upward portions.
Nature of Mineralisation
Chiria iron ore deposit comprises mainly hematite-goethite ore with varying amounts of other secondary derivatives such as lipidocrocite and earthy limonitic minerals. On surface hematite and goethite are almost in equal proportion whereas in the deeper horizons due to lack of weathering and formation of secondary minerals, hematite appears to be predominant.
Mineragraphic studies were carried out on a few random surface samples by MECL and according to them the average values of the approximate model percentage of the different mineral constituents of these samples are-
– Hematite – specularite … 34%
– Goethite … 35%
– Lepidocrocite … 10%
– Magnetite … 3.5%
– Meghenite … 2.5%
– Earthy limonite … 15%
Classification of Ore types
The litho-units in bore holes have been grouped under the following classification:
Soil, float ore and canga;
Laterite and lateritic ore;
Limonite, limonitised and goethetised ore including yellow ochre;
Hard (massive and laminated) ore;
Biscuity, friable and powdery ore;
Shale (Ferruginous, clayey often highly siliceous)
Soil, float ore and canga
This represents the top soil and the loose boulders of any ore type. The float ore occurs as rounded to sub rounded or pieces of ore scattered in loose soil or lateritic dust or clay on the slopes. The iron ore contents of float ore vary depending upon the type or ore.
Canga is a variety which holds broken pieces of hard ore in a lateritic matrix to impart a brecciated look on surface. This iron content of this ore is generally less than 56% and as such included under this category.
Sometimes it analyses more than 57% Fe and then it is included in lateritic ore.
Laterite and lateritic ore
Laterite occurs as top capping zone of the deposit, generally hard and irregular, formed by intense lateritisation of iron ore or outcropping shales and transitional ore. Laterite formed from shale is low in iron content and high in alumina while the ore formed from iron ore is relatively higher in Fe content and when Fe% is 57% and above it has been termed as lateritc ore. The lateritic ore is derived from the lateritisation of hard and soft ores. It ranges in hardness from soft to almost compact and generally form a surface capping of the deposit. It displays highly irregular patches/lenses of red, brown and yellowish limonite with intermixed clayey substances which grades hematite patches equally irregular in shape and size. The ore is generally found to be low in Fe% and high in Al203%. At places due to intense weathering it grades into laterite. The iron content varies from 50% to 62%.
Limonite, limonitised and geothised ore including yellow ochres :
The limonite and limonitised ores are hydrdated ores (Fe203.3H20) and of yellow shades. They are low in Fe content varying from 52% to 57%. Gowthite (FeO(OH)) occurs as medium to fine grained. Most of the goethite is formed by alteration of massive earthy hematite. It generally occurs as cavity/ fracture fillings and also as disseminations in the ore. The Fe content varies from 57% to 63%.
Yellow ochre occurs as a fine to very fine grained ore with equigranular texture. The fine grains are disseminated throughout the ore type. The major minerals are hematite, goethite and gibbesite and minor minerals are specularite and lepidocrocite.
Hard (massive and laminated) Ore
This is a massive, fine to medium grained, hard and compact hematite (Fe2O3) ore with minimal porosity. Its colour ranges from dark brown to brownish grey. The fine elongated cavities present are filled with earthy hematite and goethite. Massive variety shows very insignificient laminations while laminated ore shows clear laminations of varying thickness. The iron content of this variety varies from 61% to 68.4%. Physically the ore having ½ cm. thick or more laminations has been included in this category.
Porous and soft laminated ore
The characteristic feature of this ore type is its lamination which may range in thickness from 10 to 25 mm in thickly laminated ores mostly due to alteration of hematite rich and goethite rich bands. Sometimes this ore becomes porous because of the removal of mostly siliceous material. The size of the open cavities ranges from a micron t several millimetres. The cavities are filled sometimes by goethite or limonite. The iron content of this type of ore varies from 57% to 68.8%.
Biscuity, friable and powdery ore
The characteristic feature of this ore type is its lamination which may vary from 5 to 10 mm in biscuity ore and 1 to 5 mm in thinly laminated ore. The ore is very friable and quickly pulvarised to a powder. The iron content of this ore type varies from 57% to 65%.
This is a fine to very fine grained ore, made up of well crystallised minerals. Blue dust often shows a thinly banded nature which is mostly a relict feature. It is frequently inter-layered with shale or hard hematite bands. It occurs in the form of pockets and lenses of varying dimensions with friable and soft ore, often traversed by secondary quartz-veins and commonly bearing thin ochre and kaolinous bands and pockets. The ore is high in iron and low in alumina contents. The iron content varies from 57% to 69.10%.
Practically all the non-lateritic iron-ore bearing formations in direct contact with the iron ores contain abundant amounts of iron minerals in a banded form, mostly as oxides or hydro-oxides. With the preponderance of visible silica, they pass on to the Banded-Hematite-Quartzite incorporating all siliceous and cherty formations with visible iron oxides. They generally occur in purer form but when weathered, as horses, within iron ore zones, wherever they are clayey and clastic in nature they are grouped under general term shale in a direct non-genetic sense.
Shale and Clay
The shales are purple to buff in colour when ferrifginous. They are fine grained, argillaceous and indurated sediments with phyllitic sheen. They also have a considerable amounts of iron oxides. They are mainly silicated and iron content varies in iron content from 0.5 to about 20%. The powdery ores having less than 57% Fe contents have also been included in this category for reserve calculation purpose. At many places, they are highly siliceous inclusive of silica bands.
This is not exposed anywhere in the Chiria iron ore deposit on the surface. However, it has been encountered in adits.
There are at present six mining leases at Chiria. These are (a) Budhaburu (Mcllellan) (b) Ajitaburu, (c) Dhobil, (d) Sukri – Lutur, (e) Ankua and (f) Tatiburu. The iron ore deposits are concentrated in two ridges. Leases such as Budhaburu (Mcllellan), Ajitaburu and Dhobil are located on the main ridge and Sukri – Lutur, Ankua and Tatiburu leases are located in the adjacent ridge.
The mining lease at Chiria was initially with the Bengal Iron and Steel Company (BISC) from 1901. After liquidation of BISC in 1935, the mining lease was taken over by Indian Iron and Steel Co. (IISCO), which have since been merged with SAIL.
At present mining is concentrated at BudhaBuru (Mclellan), Dhobil and Sukri-Lutur leasehold areas. Raising and sizing of iron ore is done with contractual semi-mechanized system of mining from small quarries. All the quarries spread over in the above mentioned three leaseholds produce around 5 lac ton of lump ore annually. Fine ore produced during mining operation are stacked separately.
In general, the height of ore benches vary between 4 to 6 m whereas width is maintained at about 6 – 10 m. Bench slope is kept at 700. Overall slope angle is maintained at 400. For primary drilling, 110 mm diameter crawler drills are deployed.
Cartridge of slurry explosives is used in conjunction with electric detonators and fuse for blasting purpose. There is a 5 t explosives magazine, located at the foothill near the Chiria Township for safe storage of explosives, detonators & fuses.
Excavator – dumper combination is used for excavation & loading of ore as well as overburden/waste. Smaller size excavators are deployed for excavation & loading on the dumpers. Some time excavator stacks the ore at the same bench floor for manual sizing. Excavated overburden / waste is dumped separately at a suitable location.
Sizing of run-of-mine (ROM) ore is done either by manual breaking on the quarry floor or by a crusher of 50 t/h capacity. Crushed / sized ore is loaded into tipper trucks by loaders / manually.
Dispatchable ore in the desired size fraction is sent to the loading yard at Purnapani near Manoharpur station through tipper trucks. In the railway siding the sized ore is loaded into the rakes by Front-end loader.