Comparison of Metasomatic and Pegmatite Type of Mineralization in and near Rohil Uranium Deposit, Sikar District, Rajasthan, India: An Insight from Field Relations, Petrography and Mineral Chemistry

Abstract

A new type of uranium mineralization, associated with late stage pegmatitic activity and quartzo-feldspathic injections has been identified in Rohil West that lies at about 500 m west of main Rohil uranium deposit. The injections have caused extensive deformation and silicifications of host quartz-muscovite-biotite schist. Uranium mineralization is represented by uranitite occurring in association with high temperature phases like allanite, monazite and zircon. Uranitite forms coarse to medium euhedral - subhedral grains showing intergrowth textures with minerals like quartz, feldspar and biotite of quartzo-feldspathic injections. Uraninites contained high ThO₂ 2.67-7.21wt% (av. 4.78%, n=30) and high Re₂O₃ (2.35-4.31 wt.%, n=30). Chemical age of uranitite is calculated as 675-834 Ma. In view of intergrowth textures, high ThO₂ content and association with quartzo-feldspathic injections uranium mineralization in Rohil West block is interpreted as Pegmatitic Type.

The recognition of granite-pegmatite related uranium mineralization in Rohil West has opened up another dimension for the exploration, in addition to the largely Metasomatite Type uranium mineralization at Rohil. The possible extensions of newer type of uranium mineralization in NDFB need to be interpreted from heliborne geophysical data for the search of satellite deposit to Rohil.