Effect of Dolerite Dyke on the Sediments of Motur Formation of Polapathar Area, Satpura Basin, Betul District, M.P. and its Implication for Uranium Mineralization

Satpura Gondwana Basin around Polapathar contains feldspathic and subfeldspathic quartz arenites of the Motur Formation, with minor intercalations of shale and conglomerate, resting over the Barakar Formation. These sediments are intruded by a number of dolerite dykes trending NE-SW and E-W. The arenites, when close to the contact of dolerite dykes, are reddish brown coloured, rich in heavy minerals like ilmenite, monazite and zircon, have higher concentration of REE, especially LREE and devoid of uranium mineralization (<50 ppm uranium); hence, they are designated as non-mincralized arenaceous rocks (NMARs). The alteration of plagioclase to a mixture of sericite, calcite and clay minerals, and pronounced negative europium anomaly in these samples indicate europium fractionation in a high-temperature condition, possibly related to dolerite intrusion. The reddish grey coloured arenaceous rocks away from the contact of these dykes are rich in hematite, biotite and pyrite, host uranium mineralization (≥100 ppm U) and are termed as uranium mineralized arenaceous rocks (UMARs). These rocks contain a few grains of ilmenite, monazite and zircon, and, therefore, have low concentration of TiO₂, and REE. The relatively flat chondrite-normalized REE pattern with slightly negative to positive europium anomaly in UMARs indicates preferential mobilization of other LREE in comparison to europium. Uraninite, brannerite, U-Ti complex, traces of coffinite and pitchblende are the uranium minerals. Besides, uranium is in adsorbed state on goethite, limonite and organic matter. The localized concentration of uranium in UMARs, confined between two NE-SW trending dykes, is suggestive of the re-mobilization of uranium from the sediments by heated groundwater and its concentration in suitable locales, with the dolerite dykes supplying the required thermal gradient for such re-mobilization.