[en] The Mahadek Basin of Meghalaya is well known for sandstone type uranium mineralization hosted by Upper Cretaceous Lower Mahadek Sandstone. The Mahadek Basin is elongated in east-west direction and covers an area of 1800 sq km. It is 180 km long from Jayantia in the east and Balphakram in the west and 5 to 20 km wide. Over five decade of extensive exploration effort in the basin, AMD has established more than 20000 te of uranium oxide from this belt which contribute about 11% of total Indian reserves. So far two major deposit, Domiasiat and Wahkyn-Wahkut and five satellite deposit at Umthongkut, Gomaghat, Tyrnai, Lostoin and Phallangdilon have been identified in this basin. The average grade of uranium mineralization is around 0.10% eU₃O₈

[en] Significant uranium mineralization hosted in feldspathic sandstone of Upper Cretaceous Lower Mahadek Formation has been located at Laitduh, East Khasi Hills district, Meghalaya. Two mineralized horizons have been identified within Lower Mahadek Formation with vertical separation of 30 m. Samples from upper horizon have assayed upto 0.17% U_3O_8, whereas samples from lower mineralized horizon have assayed upto 0.50% U_3O_8. The radioactive minerals identified are coffinite and pitchblende occurring in association with carbonaceous matter. (author)

[en] The albite rich pegmatoid leucosomes at Naktu, Son valley, host uranium mineralisation and form a major part of the early proterozoic migmatised arkosoic to psammopelitic sedimentary rocks. These leucosomes occur as repeated, concordant lenses and bands in association with melanosomes, measuring 10 m x 5 m to over 1000 m x 160 m with thickness varying from few centimeters to over 30 m. The migmatites show combination of phlebitic, surretic, opthalmitic, and stromatic structures. The uranium minerals are dispersed mainly within the albite rich leucosomes containing disseminations of recrystallized and unaltered biotite selevages. U₃O₈ values range from 0.012% to 0.20% with traces of ThO₂. The mineralised zone is also locally enriched in Mo, Cu, and Y minerals. Uraninite (mostly euhedral) is the main ore mineral; other radioactive minerals include zircon, and xenotime in association with molybdenite, pyrite chalcopyrite, apatite, and fluorite. (author)

[en] Pegmatitic injections within the magnetite bearing granitoid host rare metal and rare earth mineralisation at Jaurahi, Sonbhadra district, Uttar Pradesh. The ore minerals identified are columbite, eschynite, samarskite, fergusonite, monazite, thorite, uranothorite and zircon in association with magnetite, ilmenite and rutile. Samples of mineralised pegmatite have analysed 0.65 to 4.42 % Nb and 0.55 to 4.85 % Y. (author)

[en] Provenance studies on the basis of U, Th and K reveal that the sediments of the Gulcheru formation were derived from a minor heterogeneous but dominantly granitoid provenance, which often underwent moderate chemical weathering. Mixing of reworked and heavy mineral bearing matured sediments with newly generated detritus took place at different times. Sedimentation took place in three different phases. Initially the sediments were deposited in fluvioaeolian environment. Later, subsidence of the depo-centre along basinal growth faults led to the transgression of seawater over earlier sediments. The last phase of the sedimentation history continued in the marginal marine domain. The depocentre most possibly experienced semi-arid climate. (author)

[en] The eastern Arunachal Himalayas abuts against Trans Himalayan range along Tidding suture which is considered to mark the boundary between the Indian and Central-Burmese plates. The present study in the proximity of Tidding Suture is a preliminary geochemical study to understand intrinsic radioelemental and REE distribution. The radioelemental distribution (n=34) in different litho-units indicate Ra (eq) ranging from <5 to 20 ppm and ThO_2, ranging from <5 to 104 ppm. The granite assayed up to 76 ppm eU_3O_8, upto 20 ppm Ra (eq) with 104 ppm ThO_2, indicating high intrinsic content of radioelements. The preliminary geochemical study of the Trans Himalayan YSC and associated rocks in the proximity of Tidding Suture indicates that the granitic injections, occurring at its base have an affinity for S-type and have anomalous radioelemental concentration. The graphite schist contains high REEs due to the presence of allanite

[en] Uranium mineralization in Madyalabodu area, Cuddapah district, Andhra Pradesh, is spatially related to chloritized and brecciated quartzite of the Gulcheru Formation in the immediate vicinity of E-W to ESE-WNW trending basic dyke. Chloritization transgresses the lithological boundaries. Whole-rock geochemical data indicate enrichment of MgO and Al₂O₃ coupled with depletion of SiO₂, Na₂O, K₂O, CaO and TiO₂ in the chlorite-rich zone. Fe₂O₃ and FeO do not vary significantly in the altered and the unaltered zones. Electron Probe Microanalysis (EPMA) data reveal that the chlorites in contact with uranium minerals are enriched in MgO and depleted in FeO than in the others. Considering the petrological evidence, geochemical signature and structural constraints, it appears that chlorite acted more as an adsorbent rather than as a reductant in facilitating uranium mineralization. Uraninite crystallized later from the uranium originally adsorbed on chlorites. Chloritization might also have facilitated mineralization through the generation of nascent hydrogen, H₂S and lowering pH of uranium-bearing solution. (author)