A note on the occurrence of altered thorite in proterozoic Bijawar sediments, Chhattarpur District, Madhya Pradesh, India

Petromineralogical studies of highly radioactive ferruginous arkose from the lowermost unit of Bijawar Group near the contact with the Bundelkhand granite in Bijawar area, indicate abundant discrete detrital thorite with subordinate monazite as the chief radioactive phases. Pale to dark brown, translucent thorite is variably altered with rare evidence of leaching of uranium into surrounding fractures. EPMA data of such altered grains also support the above observation. This micron scale hydrothermal alteration phenomenon has large-scale metallogenic importance, whereby leaching of uranium from a substantial volume of thorite is likely to remobilize sufficient uranium in the system. Thus, the detrital resistate minerals, viz., thorite and monazite within the lowermost Bijawar sediments could be one of the important sources of uranium for later mineralisation episodes in various stratigraphic horizons in the environs of Bijawar basin. (author)