Several radioactive quartz-pebble conglomerate (QPC) occurrences at the western margin of Archaean Bonai granite and overlying Iron Ore Group (IOG) rocks have recently been located over a total strike length of 8-10 km intermittently in a NE-SW to E-W trend with steep dips due north-west to north in parts of Sundargarh district of Orissa. The QPC samples have analysed up to 0.039% U 3 O 8 and 0.035% ThO 2 with high concentration of Y (74 to 518 ppm), La(<100 to 880 ppm), Cr ( 126 to 633 ppm), Zr (137 to 1250 ppm) and Pb (31 to 581 ppm). Cellulose Nitrate (CN) film studies of few QPC samples indicated adsorbed uranium over goethite and infiltrated ferruginous material (limonite), secondary uranium as encrustation and fracture filling and discrete sub-rounded grains of monazite, zircon, allanite and rare xenotime in the matrix of QPC as radioactive phases. Higher content of Th over U, elevated concentration of Y and La in QPC eliminates the possibility of its low temperature product by epigenetic processes. Poor correlation of U with elements like Pb, Y, Zr, La and Cr can be explained due to surficial leaching of uranium from QPC after its deposition as reflected by adsorbed U over iron-oxides and low U/Th ratio in QPC in the area.

Geological and radiometric studies of outcrops aided by extensive subsurface exploration through drill holes in an otherwise soil-covered terrain revealed the existence of low grades, medium tonnage, and metasomatite types of polymetallic uranium deposits at Rohil in India. Microscopic studies, electronprobe micro analyses, and geochemical analyses of samples from lodes indicate the polymetallic nature of mineralisation involving copper and molybdenum, in addition to uranium. Wide variations in the composition of fluid (S-, F-, P-, and O-rich) led to the formation of sulphides, fluorite, U-phosphosilicate, quartz, and magnetite, respectively, and are associated with uraninite. Litho-geochemical analyses from the Rohil deposit indicate multifarious metasomatic alterations associated with polymetallic mineralisation occurring in veins. The major mineralogical and metasomatic controls on rock compositions and the extent of material transfer processes that influenced the host rocks and mineralisati on are quantified by molar element ratio studies and alteration plots. General element ratio (GER) diagrams on chemical analyses of rock samples reveal albitisation and chloritisation as major and microclinisation, sericitisation, carbonatisation, and silicification as minor wall rock alterations associated with ore mineralisation. The alteration box plot between the chlorite–carbonate–pyrite index (CCPI) and the Ishikawa alteration index (AI) indicates the influence of hydrothermal activity and dominance of both albitisation and chloritisation. The ore zone is controlled by meso- and microstructures and the geometry of the soda- and potash-metasomatised zone around hydrothermal veins. This zone contains several anastomosing mineralised veins defined by a prominent joint that is set in quartzite that strikes subparallel to the axial surface of the F2 isoclinal folds and the pervasive schistosity S1 in the quartz–feldspar–biotite schist. Aventurisation of albite and microcline, established through electron probe micro analyses, can be considered as a pathfinder for uranium mineralisation. The close association of uranium and metallic sulphide mineralisation with microstructural, mineralogical (albitisation, chloritisation, and microclinisation), and geochemical variations can be applied as suitable exploration guides in a similar geological set-up worldwide.

Kanchankayi is located in the central part of the 55 km long Kurlagere-Gogi-Gundanahalli (KG) fault of Meso-Neoproterozoic Bhima basin of Southern India. Intensive integrated exploration in Kanchankayi has established a concealed, fracture-controlled, low-grade uranium deposit. Uranium mineralisation is mostly confined within the fractured limestone of Shahabad Formation and partly within fractured basement granite. Tectonic movements along the KG fault in Kanchankayi area have resulted in the northward thrusting of basement granite over the Bhima sediments forming a reverse fault geometry. Structural mapping and sub-surface exploration has established that the uranium mineralisation is mainly confined to the fault zone. In general, the fault zone is characterised by steep southerly dipping to vertical limestone beds. Iso-dip contouring was attempted on the beds having equal angle of dip, with the premise that steep southerly dipping and vertical beds will reveal the trend and location of the fault zone on the surface. The iso-dip contour map reveals that the contour depicting the fault zone initially follows the basement-sediment contact and further NE i.e. towards Kanchankayi and transgresses into the Bhima sediments. This suggests that the fault zone, instead of following the basement-sediment contact, moves within the basin in Kanchankayi. Recent sub-surface exploration in Kanchankayi has corroborated this interpretation. The innovative approach in utilizing structural mapping and isodip contouring has not only given a new dimension to the exploration programme at Kanchankayi but also provided a model technique for exploration of concealed, structure-controlled, hydrothermal, vein-type uranium mineralisation in parts of Bhima basin.

The southern basement of the Cuddapah Basin comprises the Dharwar Batholith and greenstone belt complex. Granitoids of the batholith exhibit extensive variation in terms of geomorphology, age, mineralogy, and micro/meso scale structures. The eastern part of Dharwar Craton along 13°50′ to 14°8′N latitude and 78°45′ to 79°05′E longitude was studied to enlighten the rheological influence on crustal evolution. Frequent occurrences of migmatites of restricted dimension are observed in the south of 14°10′N latitude. The granite‐migmatite contacts are not sharp in general. Different types of migmatite complex and their relationships with granitoids as well as older country rocks represent an exhumed segment of the crustal catazone. The widespread group of migmatitic rocks are classified in a composite manner on the basis of morphology and structure. Furthermore, genetic implication vis‐a‐vis anatexis history is also evaluated. Static and dynamic modes of migmatites are recognized with reference to geothermal gradient and tectonics. Based on the degree of anatexis, two categories of migmatites are identified in the field, that is, metatexites and diatexites. In addition, metatexites are classified into four sub‐types (viz, patch, dilatant, net, and stromatic) and diatexites are also sub‐divided into two categories (viz, schollen or raft and schlieren). The hybrid nature of migmatitic rocks with both metamorphic and igneous characteristics are used to analyse pre‐ and post‐anatectic events. The preserved evidences of partial melting are marked as leucocratic patches. In situ stagnation of the melt or subsequent separation from the remaining solid provides different morphology of static mode. Importance of dihedral angle at solid–liquid contacts is also considered in the present context to describe the grain boundary penetration by partial melt. Folds, veins, and boudins of different styles and generations played significant role in dynamic mode migmatitization. The syn‐ and post‐metamorphic deformation events and granite melt generation from migmatites are schematically defined. Spatial and temporal relationships of schist‐gneiss‐migmatites of both static as well as dynamic mode reveal initiation of the crustal development by vertical accretion of ultramafic‐mafic lava and TTG. Cyclic partial remelting of the metabasic lava and TTG and underplating led to development of the lithospheric plate. Later upwelling material at convergent plate and associated heat transfer led to generation of granitic magma. The established prograde and retrograde cycle of metamorphism were possibly interrupted by crustal reworking events. This study confirms about the crustal catazone segment (with >15 km depth and >500°C) in which physical processes control generation, segregation, ascent, and emplacement of juvenile granite from migmatites.

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