Mineralogy and Geochemistry of Beldih apatite, Purulia district, West Bengal

Abstract

The apatite deposit in Beldih, 'Purulia District, West Bengal, occurs along the east-west trending Beldih-Kutni shear zone or Northern shear zone (north or Singhbhum Shear Zone) belonging to Precambrian Singhbhum Group of Satpura Orogeny. The poly metamorphic sequence of the area consists of phyllites, mica-schists, ortho-quartzites, amphibolites, granites, gneisses, calc-silicates and migmatites. The apatite ore occurs as apatite-quartz-magnetite vein within the chlorite-phyllite. The ore body is a composite lens separated by phyllite partings. The mineralization is controlled by lithology and structure. The comprehensive mineralogical study by microscope, X-ray diffraction and infra-red spectroscope, besides chemical analysis reveals that the apatite is mixed fluor-hydroxyl-apatite in composition having fluorapatite in structure. The main impurities that are associated with the apatite mineral are quartz, chert, magnetite, hematite (martitised), goethite and ilmenite. The major element chemistry of Beldih apatite mineral resembles closely with that or igneous apatite from different parts of the world. The ore body contains considerable proportion of some trace elements and rare earths (REE). The REE distribution pattern displays a negative slope with negative europium (Eu) anomaly indicating an introduction of REE in hydrothermal fluids.