Mineragraphic Studies of Upper Carboniferous —Upper Permian Phosphate Nodules from Chamba Basin of Chamba District, Himachal Pradesh, India

Phosphate nodules from the Upper-Carboniferous to Upper-Permian period were discovered in the Chamba District of Himachal Pradesh. They are hosted by the Salooni formation and are sporadically found in black carbonaceous slate. They are grey to black coloured and vary from sub-round to oval shape, often exhibiting sharp conchoidal fractures. The petrography, X-ray diffractometry (XRD), and scanning electron microscopy (SEM) reveal that the phosphate mineral assemblages are dominated by cryptocrystalline apatite, namely collophane (carbonate fluorapatite or CFA) in studied samples. Quartz veins are often found in the nodules, along with associated gangue minerals, including, microcrystalline silica, carbonate and pyrite as minor constituents. The findings of the textural study show that the phosphates are present in both the pelletal form as well as apatite-rich matrix together with microfossil remnants. Clay minerals fillings suggest the intense chemical weathering of continental sources. The outcomes of this study suggest that the variations in the mineral morphologies, texture, and presence of organic matter within the phosphate nodules may be a result of early diagenesis precipitation of Carbonate Fluorapatite (CFA) crystals in the porewater with the help of activity of microorganisms at the sediment-water interface.