Petrochemistry of Bhuban Formation rocks in and around Aizawl City, Mizoram, India
Authors: K. Lalduhawma and Shiva Kumar
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The area in and around Aizawl City is dominated by Middle and Upper Bhuban rock formations. Geologically and petrologically the area has not been so far explored therefore the present study was initiated. The study area is composed of sandstone and shale belonging to Middle and Upper Bhuban formation and lies in between 92°60’ E longitude and 23°58’ N latitude. Rock samples collected from different sections in the study area were analyzed to study the mineralogical compositions of the rocks and determination of the multi-elemental distribution using high precision X- ray fluorescence analysis. The study shows that the area is dominated by different rock units such as sandstone, shale, siltstone and shaly sandstones belonging to middle and upper Bhuban formation. Petrological studies reveal that sandstone is greywacke exhibiting argillaceous matrix mainly siliceous, ferruginous and calcareous (due to presence of fossils) and rock fragments. The oxide and silica weight percentage observed from the geochemical analysis indicate Na2O, K2O and MgO have the maximum variation in the study area. The trace elements Sc, Co, Ni, Cu, Zn, Ga, Pb, Th, Rb, U, Sr, Y, Zr, Nb, Ba, Cr, V in parts per million (ppm) show a different variation in sandstone, shale and siltstone. Ba is having maximum value >500 ppm followed by Zr in sandstone whereas Cr is maximum in shale. Prominent feature is a persistently higher amount of uranium (~4 ppm) in the rocks of Middle Bhuban rocks in contrast to the average abundance in sandstone i.e. 2 ppm.