Summary:
The lron ore deposit of Jilling Langalota Iron Block leasehold area forms a part of 'Horseshoe Synclinorium', near to the closure of the major Synclinorium. The major lithological units of the area comprised of mainly Banded Iron Formation (BIF) with several major granitic intrusive e.g. Singhbhum, Bonai, Mayurbhanj Granite etc. along with the volcano Sedimentary sequences. The rocks of the lron Ore Group underwent the green schist facies of metamorphism and were characterized by the presence of some schistose rocks in the area. The metamorphic rocks observed In the area are mostly the product of regional metamorphism.
The area is a part of the westerly dipping eastern limb of the NNE plunging asymmetric Synclinorium, The general trend of the rock is N-S with a variation between NNW-SSE to NNESSW with rolling dip. The structure of the rock of this area is complicated due to several fold movements. The axis of the major fold is N-S. The ore bodies are laid down In the Syn- form with their axes plunging due to south and north.
• The strike of ore body varies from NNE-SSW to NNW-SSE with dip varying from 18 to 40° towards west and as well as towards east;
• BHJ has a strike mostly varying between 150-300 and at some places with 1450 160° and dip varying from 27° -35° towards ESE-SSE;
• Shale has a strike which varies from 10° -300 towards East. Shale anticlines were discernible on the bench faces;
• 5-6 joint sets present in ore body;
• 2-3 vertical type of joints, with strikes varylng from 55° -80º and 160° -180° (mainly 750 and 175") forming Rhombohedra blocks of ore. 6. 1-2 horizontal type of joints.
Lower Shale Formation:
The Lower Shale Formation (LSF) overlies the volcanic formation and underlies the sedimentaries of BIF conformably. This formation mainty comprises of variegated shale members underlying browh and grey shales, The different colored shale members exhibit gradational contact with cach other. This unit Is considered as weathering product of volcanics. This shale at many places contains well-preserved relics of vesicles and Amygdules, which obviously suggest its primary Tuffaceous/voicanic parentage. The members of this formation often exhibit fine lamination inherited from parent Tuff/tuffites. Close interbedded interrelationship of lava flows with the overtying tuff indicates a sub- aqueous origin for the lava.
Upper shale formation
The cessation of the chemical serdimentation is marked by the beginning of deposition of argillaccous group of rocks known as Upper Shale Formation (USF). This formation is divided into two members. Lower member is purple, brown and grey;thinly laminated and encloses lenticular /irregular shaped bodies of manganese ores.The upper member of USF is yellow, maroon and white coloured and devoid of manganese mineralization.
Banded Iron Formation (BHJ & BHQ)
On the basis of field disposition and broad composition of different members, the BIF in the study area can be classified broadly in to following three categorias:
Banded Hematite Jasper: BHJ is red /buff in color and show distinct banding. Often the bands are gradational. The jasper and hematite are more or less similar in thickness, Such litho units are predominantly seen in this area.
Banded Chert/Ferruginous Chert: The exposures of Banded Chert/ Ferruginous Chert are seen in thís area. Often banding is recognized by the fine color difference. They are very poor in iron content.
Bonded Hematite Shale (BHS): The Banded Ferruginous Shale is often overlain by banded hematite jasper, This unit is characteristically banded with iron minerals and shale. This is locally called as transitional ore, It is persistently noticed throughout the Iron ore mines. In this unit the banding is thinner and sharper than those in BHJ.
Banded Shale (B5)/Ferruqinous Shale (FS): Ferruginous shale /Bandod shale is a type of shale that is rich in iron. In the study area the rock typically exhibits a reddish tint if the iran present is ferric or a green tint if the iron is ferrous. Dark gray or black shale, however, often results from the presence of appreciable manganese content.
Laterites: Most part of the area is covered by laterite of various types. The laterites have been developed mostly over the shate unit of the area and depending upon the composition of the shale, different types of laterites have been developed. The shale rich in alumina has given rise to bauxitic laterite and thuse rich in iron have developed ferruginous laterites respectively. Ferruginous laterite occuples most of the high lands in the vicinity and is wide-spread.
Alluvial Soil: The low lying areas are filled up mostly with alluvial soil.
Massive Ore
Massive ore is usually fine grained, dense and compact. It often exhibits fine laminations paraliel to the bedding plane. The thickness of the laminae ranges from microscopic dimension to as thick as 0.7cm. Perpendicular set of joints is well developed in massive ore. The massive ore does not exhibit much evidence of slumping. It is seen in the topographic highs and show gradationa! relation with the underlying laminated ore/blue dust.
Laminated ore (HLO/SLO)
The laminated ore exhibits well developed layering due to alternate iron rich and clay. / tuffaceous shale rich bands. This type can be grouped into hard laminated ore (HLO) and soft laminated ore (SLO) dopending on its compactness and thickness of clay layer.
Primary modified type
The primary modified ore is friable, flaky in nature and possess considerable amount of void space. It is the modified form of primary type resulted due to removal / leaching of gangue materials from the original bulk, Two ore types, viz., biscuity ore and blue dusts are categorized under this group.
Biscuity/Friable ore
The Biscuity/Friable ores are usually seen associated with BHJ/BHQ and laminated ore.
Blue dusts:
The fine-grained iron ore powder with characteristic metallic blue color is well known as blue dusts (BD). This ore occurs as pockets passing laterally or vertically into one of the primary ore types. Occurrence of blue dust is neither related to topography nor confined to any stratigraphic sequence.
Reworked type
The 'reworked type' ores are formed when the primary ore/ rock types (BHJ/BHQ/iron ores etc.) arc subjected to internal changes under environmental variation. it develops due to chemical weathering through supergene enrichment processes. Litho facies of reworked types occur either as blankets / floats or locally along fracture planes. This can be further divided Into two types.
Lateritic ore: Laterite / lateritic ore in the region occur as blankets over almost all the members of iran formations. When it is developed in contact with some ore bodies, its grade is proved to be relatively high (Fe: Av. 59%), while with contact of shaly horizan, it is of low grade (Fe: Av. 56%) nature and contain more alumina (6-7% -A203). When it is of commercial / economic grade it Is termed as lateritlc are.
Detrital ore: Detrital ore appears like a sedimentary conglomerate. The difference between primary modified and reworked ore types are the modified type mostly retains structure and texture of the primary type while the reworked type show different features, li) the mineralogy of modified type remains same as primary type except that the percentage of iron minerals increases in latter type. On the contrary, the reworked type exhibitsa distinctly different mineralogy.
The strike length of the iron ore body available within the lease hold area is 900 meter. The width of the lron ore body varies from 400 meters to 600 meters. The maximum and minimum thickness of the iron ore body within the lease hold area is 90 meters and 30 meters respectively.