TITLE:
Apatite Microstructure and Composition in Manganese Formation of Eastern Ghats, Orissa, India
AUTHORS:
Subhasmita Jena, B.K. Mohapatra, P. P. Singh
KEYWORDS:
Apatite, Eastern Ghats rocks, Manganese ore
JOURNAL NAME:
Journal of Minerals and Materials Characterization and Engineering,
Vol.10 No.5,
April
20,
2011
ABSTRACT: Apatite grains in a stratabound manganese ore body from Eastern Ghats in Leliguma, Koraput
district south Orissa, India were studied under optical and electron microscope. Apatite shows
bimodal occurrence: one associated with granite/pegmatitic phase and other with manganese
phase, and exhibits different microstructure and composition. Apatite in pegmatitic association
(occurring as inclusion in quartz and feldspar) is small in size and occurs as subhedral grains
having irregular boundaries and poor in manganese content (MnO: 0.16%). Apatite associated
with manganese mineral phases (cryptomelane / romanechite) is mostly euhedral, relatively
larger in size, contains higher manganese value, and exhibits some peculiar features like
twinning, zoning, overgrowth, and occasionally contains inclusion of quartz and feldspar grains.
Apatite grains occurring as inclusions within quartz and feldspar are of hydrothermal origin and
formed along with pegmatitic minerals. Such apatite is almost devoid of manganese but
relatively enriched in Sr, F and LREE content. The apatite in manganese mineral association
formed during supergene process. The apatite of latter generation appears as idiomorphic
crystals; contains up to 6.85% of MnO in solid solution and shows relatively higher HREE
values. The higher HREE values may be due to its derivation from stratiform Mn-ore bodies and
associated granitised rock during remobilization, solution and precipitation of Mn –rich fluid
along structurally weak planes resulting in development of a stratabound ore body.