Field occurrence of the volcanic rocks

In the Sonakhan greenstone belt, a thick sequence of mafic volcanic rocks along with associated felsic variants constitutes the Baghmara Formation. The basaltic rocks are well exposed in the western part of the belt near Baghmara and Jangla Pahar. The lower part of the Baghmara Formation contains pillow basalts, referred to as, lower unit basalts. Individual pillows range in size from <10 cm to >40 cm in elongation. The overlying unpillowed massive basalts, referred to as, upper unit basalts, are well developed around Baya-Deopur-Deogarh hill road. Felsic rocks of rhyolitic composition and associated intermediate rocks occur as hillocks towards northwest of Runjhuni and west of Thelkadabri near Golajhar. They are generally greenish in colour and can be distinguished easily in the field. There is no unconformity between the two basaltic units.