[en] Geratiyon-ki-Dhani (GKD) area is located in Khetri sub-basin of North Delhi Fold Belt and exposes metasediments of Ajabgarh Group. The Ajabgarh Group comprises quartz-biotite schist which is intruded by albitite and granite. The primary uranium phases viz. davidite and brannerite occurring with calcite and /or quartz veins are common in albitite. Quartz and calcite from mineralised albitite have been selected for characterization of the ore-forming fluid, which makes a promising uranium deposit. Fluid inclusion petrography indicated presence of three (03) types of fluid inclusions (FIs) based on phases present at room temperature and mode of occurrence; polyphase (type 1a and 1b) and biphase (type 2) inclusions. Type 1a FIs are primary in nature and are composed of vapour bubble, salt crystals with <50% liquid phase and are irregular or negative crystal in shape varying in size between 12-23µm and occasionally contain hematite grain. The type 1a inclusions homogenised mostly by dissolution of salt crystal between 243-382°C (mode=340°C, n=30) corresponding to salinity of 34.32-46.13 wt% NaCl-eq (mode=42wt% NaCl-eq, n=30). Type 1b FIs have vapour bubble, salt crystal with >50% liquid phase, occur as trans-granular trails and in clusters, having irregular shapes with size varying from <5-12µm. The inclusions homogenised by disappearance of salt crystals at 209 to 294°C (mode= 280°C, n=35) corresponding to salinity range from 29.03-38.59 wt% NaCl-eq (mode=36wt% NaCl-eq, n=35). A wide range of overlap is noted in salinity (34.32-38.59 wt% NaCl-eq) and homogenization temperature (243-294°C), histograms of type 1a and 1b inclusions suggest them to be part of a common fluid activity. Polyphase inclusions show simple cooling and follow halite saturation curve in salinity-temperature diagram. Biphase inclusions are invariably associated with type 1b and also show a cooling trend. On the basis of fluid characteristics, it is concluded that magmatic albitite has provided single mineralising solution resulting in davidite enriched mineralisation. The gradual cooling of high temperature (243-382°C), high saline (34.32-46.13 wt% NaC-leq) hydrothermal fluids has ensued U-mineralisation in GKD. The evidences presented here are significant as magmatic albitite hosted mineralisation is found for the first time in North Delhi Fold Belt of Khetri sub-basin of northwest india. it has opened a new concept for exploration which will help more resource addition. (author)

[en] A number of uraniferous albitite occurrences have been reported in Rajasthan associated with Archaean basement and Meso-proterozoic rocks of Delhi Supergroup. Albitite bodies in Geratiyon ki Dhani are located along NE-SW trending eastern albitite zone in Khetri sub-basin of North Delhi Fold Belt. The albitite occurs as a NNW -SSE trending linear ridge extending over 1.5 km strike length intruding metasediments of Ajabgarh Group represented by quartzite, quartz-biotite schist and calc-silicate rock. The magmatic origin of albitite is characterised by sharp (intrusive) contact of albitite with metasediments, xenoliths of quartz-biotite schist and presence of igneous textures and absence of replacement textures in albitite. Subsurface exploration in the area has established uranium mineralization over 1200 m strike length and 300 m vertical depth, occurring as steeply dipping low grade lodes with varying thickness. The uraniferous albitites are dominantly pink to red coloured fine- grained rocks, composed of albite (85-90%), quartz (5-10%), K-feldspar (1-2%), minor biotite «1 %) and secondary chlorite and calcite. Davidite is the most abundant radioactive phase with minor brannerite and U-Ti complex. REE mineral assemblages such as monazite, xenotime, bastnaesite and zircon were identified. Geochemical studies of the uraniferous albitite recorded high Na₂O (av. 9.67 %) and low K₂O (av. 0.40 %) content. Albitites are enriched in REE (av. 1249 ppm), especially LREE (av. 1143 ppm) leading to high LREE/HREE ratio (av. 12.27). Recognition of uraniferous albitites with distinct magmatic characteristics around Geratiyon ki Dhani has enhanced the uranium potentiality of eastern albitite zone and has strengthened the scope of exploration activities in the adjacent ares. (author)

[en] 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 675-834Ma. In view of inter-growth textures, high ThO₂ content and association with quartzofeldspathic 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. (author)

[en] Uranium mineralization at Umra, Udaipur district, Rajasthan is hosted by carbon and siliceous phyllite (with minor calcareous components) of the Paleoproterozoic Aravalli Supergroup. The mineralized zone trends NE-SW to N-S, dipping 45-55° towards SE to E. Uraninite, coffinite and brannerite are the main uranium phases observed that occur in association with sulphides (pyrrhotite, pentlandite, gersdorffite, chalcopyrite and pyrite), magnetite and ilmenite. Uraninite is found to occur as veins and disseminated ultrafine grains. Colloform and botryoidal texture with shrinkage/ synaeresis cracks indicate the presence of pitchblende also, formed at relatively low-temperature. Textural features suggest remobilization of disseminated syngenetic and / or diagenetic uranium minerals during low-grade metamorphism and deformation. Textural features suggest multiple phases of sulphide mineralization also. Mineral chemical data indicate that uraninite and pitchblende are compositionally similar containing 80.09-87.17 wt.% UO₂ (av. 84.45 wt.%) and 11.37-11.82 wt.% PbO (av. 11.58 wt.%) with negligible SiO₂, CaO, TiO₂, FeO, ThO₂ and RE2O₃. High U/Th ratio (>1000) in uraninite/ pitchblende indicates limited cationic substitution and therefore low temperature (<350°C) hydrothermal origin of mineralization. Chemical age, calculated on the basis of UO₂, ThO₂ and PbO concentration in uraninite, indicates the minimum age of mineralization is 956±12 Ma. S isotopic data of pyrite suggest syn-sedimentary or diagenetic origin by bacterial reduction of seawater or pore water sulphate under anoxic conditions (-24.7‰ to -16.2‰), as well as hydrothermal (-3.7‰ to +8.8‰) origin. Similarity of S isotopic composition of hydrothermal pyrite with that of pyrite (+5.2‰) from meta-basic rock indicates that a component of S has been derived from the associated basic/meta-basic rocks in the area. Signatures of multiple generations of uranium mineralization, and multiple episodes of deformation, metamorphism and hydrothermal alteration reveal a complex metallogenic history in Umra. Compositional details of uraninite and their occurrence in the form of veinlets in association with hydrothermal pyrite suggest dominantly epigenetic hydrothermal mineralization events coeval with deformations of the Aravalli sediments. (author)

[en] Khetri Sub Basin of North Delhi Fold Belt of Delhi Supergroup is favourable locale for uranium mineralization. Concealed ore grade uranium mineralisation has been located at Jahaz along the 'albitite zone'. Mineralization is hosted by brecciated and sheared quartz biotite schist and quartz amphibole schist of Ajabgarh Group over a strike length of 2.10 km with average thickness of 3.78m. Mineralised zone is confined between 360m to -18m RL. Common alteration features recorded in mineralised rocks are silicification, chloritization and albitisation. The principal ore minerals are uraninite, molybdenite, pyrite, pyrrhotite and chalcopyrite. Geochemical studies indicate average content of U₃0₈ 357 ppm, Mo 274 ppm, V 117 ppm, Cu 584 ppm (n=100) in mineralized rock. Principal component analysis (PCA) has revealed U-Cu-Mo, U-V and Ni-Co association. Uranium mineralisation is structurally controlled, 'metasomatite' type. Age of this mineralisation is 841±26 Ma by Pb-Pb method. (author)

[en] The South Khetri sub-basin (KSB) in North Delhi Fold Belt (NDFB) along Narsinghpuri-Khandela-Rohil tract exposes Ajabgarh Group of metasediments of Delhi Supergroup. The Ajabgarh Group comprises impure carbonate sequence with volcanics in the lower part and psammopelitic assemblage with minor lenses of carbonate and siliceous rocks in the middle and upper part. The NNE-SSW trending wide spread zone of albitisation in KSB forms a mega lineament, which can be traced from north of Sior-Siswali to south of Kishangarh, covering approximately 170 km length along strike with 6-10 km width. Integrated exploration approach by AMD has led to the establishment of sizeable uranium deposit at Rohil, Sikar district, Rajasthan; thereby NDFB has now been established as uranium potential province. The study area is mostly soil covered baring N-S to NNE-SSW trending quartzite ridge exposed in the northwestern part of Rohil village