Ore mineralogy and mineral-chemistry of uranium mineralisation, and geochemistry of metasomatised calc-silicate rocks at Raghunathpura, Mahendragarh district, Haryana

Abstract

Uranium mineralization at Raghunathpura, Mahendragarh district, Haryana is confined to a major shear zone within the metasedimentary lithounits which is marked by prominent alkali metasomatism. The metasedimentary lithounits of the area belong to the Ajabgarh Group of Delhi Supergroup and form part of the Khetri basin. Alkali metasomatised calc-silicate rock is the main host for anomalous uranium mineralisation and is mainly composed of tremolite-actinolite, diopside, scapolite (mariolite type), wollastonite, calcite, quartz, graphite and sphene. Hydrothermal/metasomatic alterations are manifested as multiple episodes of albitisation with minor microclinisation, carbonitisation, silicification and U-Th-sulfide-clay formation. The radioactive mineral phases are uraninite (uraninite I and II), coffinite, brannerite, U-Ti complex, uranothorite, thorite, allanite, monazite and associated sulphides are pyrrhotite, pyrite, chalcopyrite, molybdenite and galena. Repeated hydrothermal alterations in this shear zone has remobilised the uranium as seen by the alteration of uraninite, metamictised uranothorite and formation of remobilized graphite. Mineral chemistry of uraninites and their chemical ages indicate two distinct phases of formation of which the rounded uraninite I, rich in Th and REE represents the earliest phase with a chemical age of 809 Ma. Uraninite II with a chemical age of 745Ma is Thpoor and the mineral chemistry indicates its origin from a relatively low temperature fluid. Th-bearing and Th-poor coffinite are recorded, of which Th-bearing coffinite is the product of alteration of uraninite I and Th-poor is of remobilized origin. The observed mineralogical and chemical features are suggestive of a hydrothermal mineralisation associated with one or more episodes of alkali metasomatism.