FLUID INCLUSION STUDIES OF QUARTZ - CALCITE VEINS ASSOCIATED WITH URANIUM MINERALISATION IN ROHIL URANIUM DEPOSIT, NORTH DELHI FOLD BELT, RAJASTHAN, INDIA

Abstract

Rohil Prospect of South Khetri Copper Belt (SKCB), Rajasthan is a house of polymetallic, metasomatic hydrothermal vein type uranium mineralization. The mineralization is mostly restricted to a narrow but extended zone of albitization known as albitite line. The major uranium minerals present in the Rohil deposit include uraninite, coffinite, and brannerite, along with Copper-Molybdenum sulfides. The host rocks are metasedimentary rocks metamorphosed in greenschist to amphibolite facies condition and bear the footprint of brittle deformation. The metasedimentary rocks associated with mineralization include quartz biotite schist, quartz amphibole schist, quartzite, graphite schist etc., which are further intruded by multiple veins of quartz, calcite, pegmatite etc. They show the signature of hydrothermal alteration in terms of chloritization, silicification, albitisation, actinolization, etc. The mineralization and alteration features are restricted along the fractures, shear zone, and fold axis of the deformed and altered metasedimentary host rocks, indicating an association of intense hydrothermal fluid activity. The detailed fluid inclusion study of wafers prepared out of quartz and calcite reveals that it contains four types of inclusion viz., Type I (Aqueous Biphase in quartz), Type II (Monophase in quartz), Type III (Aqueous Biphase in calcite) and Type IV (Halite bearing polyphase). Based on the phases present at room temperature and microthermometric data, it has been suggested that the fluid involved is probably a high salinity, high density, moderate temperature fluid, and the probable source is either magmatic or connate water. The salinity Vs homogenization diagram shows that the fluid has undergone cooling and/or fluid mixing, reflected by the considerable salinity variation. The calculated salinity and temperature data for Type IV inclusions suggest that some inclusions are clustered below halite saturation curve, indicating re-equilibration of inclusions during or after trapping in the host mineral.