Detrital type manganese ore bodies in the iron ore group of rocks, Orissa, Eastern India |
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| Authors: | B K Mohapatra P P Mishra and P P Singh |
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| Abstract: | Detrital type of manganese ore bodies in the Precambrian Iron Ore Group of rocks occur in the Bonai-Keonjhar belt, Orissa
besides stratiform (bedded type) and stratabound-replacement types of deposits. These ores appear in form of large boulders
within lateritised aprons at various depths, often reaching beyond 30 m from the surface. Overprinting of primary structures,
presence of mixed Fe-clasts and Mnooliths/pisoliths, mineral species of different generations and wide chemical variation
amongst morphological varieties and from boulder to boulder are the characteristic hallmarks of such ore bodies. Features
associated with ores occurring in different morphologies, namely: spongy, platy, recemented, and massive varieties from a
typical profile of Orahari Mn-ore body in Keonjhar district are described. Recemented variety may be further classified into
sub-varieties such as canga, agglomerate, and mangcrete. Common primary Fe-minerals are hematite, martite with relict magnetite.
The secondary Fe-Mn phases are goethite, specularite, cryptomelane, lithiophorite, chalcophanite, manganite, and pyrolusite.These
are ore bodies of allochthonous nature developed through a number of stages during terrain evolution and lateritisation. Secondary
processes such as reworking of pre-existing crust through remobilisation, solution, precipitation, cementation, transport,
etc. are responsible for the development of such detrital ore bodies in the Bonai-Keonjhar belt of Eastern India. |
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