Abstract
Several small lensoidal bodies of felsic volcanics are exposed in a curvilinear pattern within the brecciated granitoids of Bundelkhand Gneissic Complex (BGC) at Mohar. Sub-surface data reveals extensive presence of these felsic volcanics below the sediment of Vindhyan Supergroup. It occurs like a sheet with thickness varying from 12 m to 134 m. Its lateral extent has been traced upto 4.8 km. Multiple flows of felsic magma are identified based on colour, granularity, cross cutting relations and cyclic distribution of multiple vesicular bands along the entire thickness of felsic magma. The felsic rock contains upto 13.21% K2O. Chemical composition of these felsic volcanics varies across the column. Petrographically and chemically all these felsic volcanics are identified as rhyolite or rhyolite tuff.
Significant uranium mineralisation of 0.0165% eU3O8 average grade has been intercepted for 11.10 m thick with <0.005% ThO2 within the felsic rock. Radiometric assay of a mineralised intercept (15 cm length) has revealed up to 0.15% U3O8 with disequilibrium in favour of parent. Uranium occurs as disseminated grains of coffinite — (Y) associated with pyrite, chalcopyrite, galena, molybdenite, hematite, fluorite, anglesite and cerrusite. Mineral assemblage and mode of occurrence of the uranium and other minerals in the host rock indicates its hydrothermal nature. This is the first reported uranium occurrence from the volcanogenic environment of Bundelkhand.
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Bhattacharya, D., Joshi, G.B. & Sharma, R. Uranium mineralisation associated with felsic volcanism at Mohar, Shivpuri district, Madhya Pradesh. J Geol Soc India 78, 57–62 (2011). https://doi.org/10.1007/s12594-011-0067-7
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DOI: https://doi.org/10.1007/s12594-011-0067-7