Abstract
Detailed field and petrological studies revealed the presence of phosphatic bands at the interface of khaki-green and variegated shale and within the khaki-green shale of Owk Formation in Neoproterozoic Kurnool basin. The phosphatic bands which are encountered as thin individual layers (10–40 cm) within the Owk shale have formed due to sedimentary processes. A maximum of seven phosphatic bands including two variants hard, compact, fine grained jet-black type and soft friable, grayish white to greenish white type are discontinuously exposed at the surface but are laterally persistent throughout the hillocks of the area. Petrographic examination reveals that the phosphatic bands are composed of cryptocrystalline apatite occurring as isotropic phosphate and minor anisotropic phosphate. Chemical analysis of selected samples of the phosphatic bands indicate that the P2O5 content ranges from 5–19.8% whereas the P2O5 content determined by the EPMA ranges from 1.76–38.11%. Apatite, quartz, clinochlore, muscovite and traces of xenotime are the mineral constituents of the phosphatic bands identified by XRD. The apatite mineral is identified as fluorapatite.
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Gopakumar, B., Waghmare, M. Nature of occurrence of phosphatic bands in Owk Formation, Neoproterozoic Kurnool basin, Andhra Pradesh. J Geol Soc India 88, 213–221 (2016). https://doi.org/10.1007/s12594-016-0480-z
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DOI: https://doi.org/10.1007/s12594-016-0480-z