Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

M. W. Y. Khan ¹, A. Mukherjee ¹

Affiliations
1 School of Studies in Geology, Ravishankar University, Raipur 492010 (M.P.), IN

Abstract

This paper documents the geochemical and mineralogical characters of the phosphorite of Charmuria Formation (Chhattisgarh Basin). X-ray diffraction studies have revealed presence of carbonate fluorapatite as the only apatite mineral in this phosphorite, along with quartz as major gangue, and kaolinite-illite, calcite and pyrite in subordinate amounts. Structural formula of this apatite closely resembles carbonate fluorapatite. Further, CaO/P₂O₅ ratio (1.37 - 1.99) suggests that this phosphorite has not been affected by weathering. Quartz dominance over clay minerals and low CIA (24.79 - 46.87) is attributed to the tuffaceous nature of siliceous clays (lithofacies-A). The depletion of Sr, and trace elements of organic association in siliceous clays, phosphorite and phosphatic siliceous clays point to a common provenance.

Keywords

Geochemistry, Phosphorite, Carbonate Fluorapatite, Chhattisgarh Basin.

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D. Subba Rao ¹, A. Mukherjee ², M. W. Y. Khan ³, D. N. Sridhar ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN
2 central Ground Water Board, Raipur (CG), IN
3 Pandit Ravi Shankar Shukla University, Raipur (CG), IN

Abstract

A new occurrence of Within-Basin pyroclastic flow rocks (welded felsic tuffs and ignimbrites) is reported for the first time from Sukda area in the NE part of the Chhattisgarh basin. The flows are characterized by the presence of microporphyritic textures, feldspars, quartz, glass shards, volcanic rock fragments and magmatic garnet. High concentrations of Na₂O (-6.61 wt%), low K₂O (0.01 to 1.0 wt%) and high Sr contents (416 ppm) are found in these rocks. REE show a Well-Fractionated trend with high LREE enrichment, sloping HREE patterns and absence of Eu anomalies. Major, trace and REE geochemistry of the Chhattisgarh welded tuffs indicate that they are Na- Rhyolites. The characteristic high Sr/Y and La/Yb_N, ratios and low HREE contents suggest that the parental magmas of these rocks were produced by extensive partial melting of a mafic source in deeper crustal levels (lower crust) where garnet and or hornblende are residual phases.

Keywords

Felsic Tuffs, Na-Rhyolites, Ignimbrites, Chhattisgarh Basin, Chhattisgarh State.

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