Radioactive quartz-pebble conglomerates from western margin of Bonai granite pluton, Sundargarh district, Orissa — A new find

Abstract

Several radioactive quartz-pebble conglomerate (QPC) occurrences at the western margin of Archaean Bonai granite and overlying Iron Ore Group (IOG) rocks have recently been located over a total strike length of 8-10 km intermittently in a NE-SW to E-W trend with steep dips due north-west to north in parts of Sundargarh district of Orissa. The QPC samples have analysed up to 0.039% U 3 O 8 and 0.035% ThO 2 with high concentration of Y (74 to 518 ppm), La(<100 to 880 ppm), Cr ( 126 to 633 ppm), Zr (137 to 1250 ppm) and Pb (31 to 581 ppm). Cellulose Nitrate (CN) film studies of few QPC samples indicated adsorbed uranium over goethite and infiltrated ferruginous material (limonite), secondary uranium as encrustation and fracture filling and discrete sub-rounded grains of monazite, zircon, allanite and rare xenotime in the matrix of QPC as radioactive phases. Higher content of Th over U, elevated concentration of Y and La in QPC eliminates the possibility of its low temperature product by epigenetic processes. Poor correlation of U with elements like Pb, Y, Zr, La and Cr can be explained due to surficial leaching of uranium from QPC after its deposition as reflected by adsorbed U over iron-oxides and low U/Th ratio in QPC in the area.

Geochemistry of detrital zinc-rich chromite in conglomerates from eastern India

“…Uraninite, zircon and chromite are well-rounded and detrital, similar to other Late Archaean to Palaeoproterozoic quartz-pebble conglomerate-hosted uranium mineralisation. Previous studies report up to 0.039 wt.% U 3 O 8 (Kumar et al , 2009) and 100 ppb to 2.25 ppm Au in the radioactive conglomerates (Jana et al , 2016). Both well-rounded and sub-rounded to angular zircons are present; the latter exhibit evidence for fluid-induced alteration to quartz and xenotime.…”

“…The clasts are at places stretched and fractured implying post-depositional deformation of the conglomerates. The matrix is composed of quartz, chlorite, sericite and heavy minerals such as uraninite, zircon, chromite, ilmenite, rutile, apatite, monazite, xenotime, pyrite and zircon (Kumar et al, 2009;Pal et al, in preparation). Uraninite, zircon and chromite are very well-rounded and detrital in nature similar to Late-Archaean-Palaeoproterozoic quartz pebble conglomerate-hosted uranium mineralization globally.…”

“…Previous studies report up to 0.039 wt. % U 3 O 8 (Kumar et al, 2009) and 100 ppb to 2.25 ppm Au in the radioactive conglomerates (Jana et al, 2016). Both well-rounded and sub-rounded to angular zircon grains are present; the latter shows lines of evidence of fluid-induced alteration to quartz and xenotime.…”

“…The study area around Birtola and Bagiyabahal is located on the west of the Bonai granite (marked by a dashed rectangular box). (b) Geological map around the study area (modified after Kumar et al , 2009) with the sample locations.…”