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A detrital zircon U–Pb laser ablation–inductively coupled plasma–quadrupole mass spectrometry (LA-ICP-QMS) provenance study was undertaken on samples selected from the Lower Gondwana successions preserved in the fault-bounded Bokaro and Jharia basins in India to investigate the provenance of the sediment and determine whether the strata were deposited in isolated syn-depositional graben basins or formed part of a wider regional depositional system. A total of 730 concordant U–Pb detrital zircon ages revealed six distinct age fractions: (i) a latest Neoproterozoic to earliest Cambrian age fraction (530 to 510 Ma), which tails down in some samples to older Neoproterozoic ages (650 to 630 Ma); (ii) a major age fraction with an age peak of earliest Neoproterozoic (950 Ma), accompanied in some samples by a twin Mesoproterozoic peak (1000 Ma); (iii) a middle Mesoproterozoic age fraction (1330 to 1300 Ma); (iv) a prominent earliest Mesoproterozoic zircon age fraction (1600 Ma); (v) a less well-defined late Palaeoproterozoic zircon age fraction (2100 to 1700 Ma, or 1600 Ma); and (vi) an Archaean zircon age fraction that typically comprises two zircon age fractions, namely zircons with early Neoarchaean ages (2800 to 2750 Ma) coupled with zircons with ages older than 3100 Ma. Comparison of these newly obtained age fractions with detrital zircon age data presented by Veevers & Saeed (2009) shows similarities with the Gondwana strata of the Mahanadi and Pranhita–Godavari basins, implying that strata preserved in the fault-bounded Gondwana basins in central east India formed part of a much wider regional depositional system and that they were not deposited in isolated half-graben or graben basins. Potential source regions to the Gondwana strata of the Bokaro and Jharia basins include the Eastern Ghats Mobile Belt and rock units in Antarctica. [ABSTRACT FROM AUTHOR]

Analysis of the grain-scale deformation mechanisms in folded rocks of the Dongargarh Supergroup, central India, reveals that deformation was accomplished by a combination of pressure solution, microfracturing and dislocation creep processes. The finite strain was assessed using the [R.sub.f]/[PHI] method (X/Z [approximately equal to] 2). Partitioning of strain into various deformation mechanisms revealed that dislocation creep and pressure solution were the major contributors to the finite strain, followed by microfracturing. Analyses of microstructures suggest a sequence of dislocation creep followed by pressure solution and microfracturing, that ultimately gave way to microfracturing and limited crystallization or recrystallization. Overall constancy in volume during deformation is suggested from the balance between fracture-related grain-scale dilatancy and solution-related volume loss. Observations on cleavage spacing within various lithologies in a specific structural setting suggest that lithology played a vital role in cleavage development. Cleavage development in sandstones of the Dongargarh Supergroup required thin shale interbeds (for competency contrast) and grain size < 0.036 mm (4.75 [PHI]). Keywords: cleavage, grain scale deformation, Palaeoproterozoic, shallow crustal processes.

The Kolhan Group in the Singhbhum Craton of eastern India is a passive margin siliciclastic shelf to deep‐water carbonate ramp platform succession. It occupies a unique position in respect of the Central Indian Tectonic Zone (CITZ), widely considered as the suture joining the northern and southern Indian cratonic blocks at the time of amalgamation of the Mesoproterozoic supercontinent Columbia. The Kolhan succession is closely comparable to other Late Proterozoic 'Purana' successions of India including the siliciclastic‐carbonate Suasar Group from the central part of the CITZ. We report here the first U–Pb detrital zircon ages from the Kolhan Group. The youngest age population obtained from basal siliciclastics suggests it is not older than ca. 1,158 Ma. The absence of any concordant detrital zircon <1,000 Ma which is well represented in the adjoining Singhbhum Shear Zone and CITZ extensions, suggests that the sedimentation took place prior to ca. 1,000 Ma. The Kolhan Group, therefore, records an extensional event between two major episodes of supercontinent assembly (i.e., Columbia and Rodinia). A similar motif of extension and passive margin sedimentation across Mesoproterozoic Peninsular India together with the widespread Mesoproterozoic lamproite and kimberlite emplacement event suggests an episode of extension and major basin development across the Indian Shield in between the two supercontinent amalgamation cycles of Columbia and Rodinia. [ABSTRACT FROM AUTHOR]

The quartz-pebble conglomerate (QPC)-hosted detrital uranium mineralization is unique in character in terms of their restricted distribution before 2.2 Ga atmosphere during pre-Great Oxidation Event (pre-GOE). Such QPC paleoplacer deposits over the world are good targets for moderate to high tonnage and low grade uranium deposits and more importantly for their gold content. The Mahagiri Quartzite, dated c. 3.02 Ga for their youngest detrital zircon population, is developed unconformably over the Mesoarchean Singhbhum Granite (3.44 Ga to 3.1 Ga). The Mahagiri Quartzite includes a conglomerate-pebbly sandstone dominated subaerial alluvial fan to coastal braided plain sequence in the lower parts and shallow marine mature quartz arenite in the upper parts. The alluvial fan-braided plain deposits in the lower parts host a number of pyritiferous and uraniferous conglomerate and pebbly sandstone beds. The uraninite grains are rounded to subrounded in outline suggesting mechanical transport and detrital origin. Together with detrital pyrite and uraninite constitute the example of > 3.0 Ga paleoplacer closely comparable to the Witwatersrand Au–U deposits. EPMA and SEM-EDS studies suggest that the uraninite grains are rich in Th (> 4 wt.%), S and REE-Y. Chemical formula calculations from EPMA analyses suggest uraninite grains belong to two populations with different oxidation states as revealed from Y/REE and cation U 4 + : U 6 + [apfu] ratios. The U contents of the detrital uraninite grains from Mahagiri are significantly lower than that of the ideal stoichiometric composition of UO 2 . This is mainly due to higher amount of heterovalent cationic substitution by Th, REE, Y, Pb, and Ca in Mahagiri QPC uraninite structures, and partial alteration and metamictization of uraninites. Alteration due to metamictization resulted in elevated concentration of Si, Al, P, and Ca in more altered and metamict uraninite grains. The REE pattern is typically flat with comparable LREE–HREE concentration. The high Th content flat REE-pattern suggests that the uraninitere presents high temperature phases (> 350 °C) and are magmatic in origin. The Mahagiri detrital uraninite grains suggest existence of highly felsic and K-rich (richer than TTG) granodiorite–granite–monzogranite suites (GGM) of rocks older than 3.1 Ga in the Singhbhum craton. [ABSTRACT FROM AUTHOR]

High-precision SHRIMP U–Pb zircon dating yields a late Palaeoarchaean age (3290 ± 8.6 Ma) for a large, unmetamorphosed, weakly peraluminous TTG body (the Keonjhargarh–Bhaunra pluton) in the Singhbhum craton of eastern India. One inherited subhedral zircon grain gave a concordant age of 3495.9 ± 5.3 Ma and Nd isotope characteristics show a juvenile trend with εNdt ~ 0 and TDM 3395–3453 Ma. The data support a model of typical Archaean crustal evolution until late Palaeoarchaean times for the Singhbhum craton, which is in contrast to the more southerly Bastar craton where Palaeoarchaean non-TTG granites have been identified. These data demonstrate the diachronous development of continental crustal blocks now forming the basement of the eastern and central peninsular of India. [ABSTRACT FROM PUBLISHER]

High-grade hematite ores of the Iron Ore Group in the Noamundi area, Jharkhand state, India, are hosted by a laterally extensive, 220-m-thick banded iron formation (BIF) in a folded greenstone belt succession of Paleoarchean age. Single orebodies, which are up to 3 km long along strike and several hundred meters wide, depending on dip of the beds, are strata bound and composed of two major ore types--namely, hard hematite ore that is of ancient geologic origin and ores related to recent weathering along a lateritized Cretaceous- Cenozoic land surface. The ancient hard hematite orebodies comprise laminated hematite ores in which microplaty hematite is dominant, and massive ores composed almost entirely of martite. Supergene ores, in contrast, are comprised of goethite-rich duricrust and soft saprolitic hematite ores representing the leached zone of the Cretaceous-Cenozoic laterite profile. Hard hematite-martite ores formed by hydrothermal replacement of BIF protolith, not only through leaching of silica but possibly 'also through introduction of iron by hydrothermal fluids of meteoric origin. Hematite iron ore pebbles in a conglomerate at the base of the Meso- to Neoproterozoic Kolhan Group near Noamundi attest to the antiquity of the hard hematite orebodies. Soft saprolitic iron ores formed as a product of lateritic weathering processes in Cretaceous-Cenozoic times. Supergene alteration took place under the influence of reducing and acidic meteoric water, which is typical for lateritic soil profiles developed under humid tropical climatic conditions with lush plant cover. Goethitic duricrusts capping the laterite profile suggest alternating wet and dry seasons in this environment. [ABSTRACT FROM AUTHOR]

The late Mesoproterozoic to Neoproterozoic sedimentary successions on the southern Indian craton are described from the Dharwar and Bastar cratonic blocks and the intervening Pranhita-Godavari rift valley. These successions include a characteristic lime-mudstone-shale assemblage that has been deposited in a deep-water cratonic depositional setting beyond the reach of coarser detritus. The Kolhan Group occurring on the Singhbhum craton at the northeastern corner of the southern Indian craton also includes similar lime-mudstone and shale deposits that can be lithologically correlated with the late Meso-Neoproterozoic successions from other cratonic blocks of the peninsula. The correlation attempted here, based on the lithology and depositional setting, leads to the reconstruction of a major deep-water basin on the southern Indian craton during the late Mesoproterozoic to Neoproterozoic transition. The large-scale subsidence of the Indian craton leading to the development of a vast deep-water cratonic basin is likely to be related to terminal Mesoproterozoic fragmentation of parts of the supercontinent Rodinia. [ABSTRACT FROM AUTHOR]

Detrital uraninite bearing QPCs are restricted in pre-GOE Archean rocks (Cuney, 2010). U+4 state in these uraninites is highly unstable in surficial environment even at very low oxygen concentration. Uraniferous QPCs are preserved in strata below supergene profile. Our study from Mesoarchean siliciclastics of the Singhbhum craton India reveals significant variations in mineralogy, major and trace element composition from subsurface and supergene alteration levels. The QPCs from below the weathering profile still preserve detrital uraninite grains (Mukhopadhyay et al., 2016). In contrast the QPCs from the weathering profile mostly contain U in Ti-bearing phases such as brannerite and leucoxene. Uraniferous QPCs from below weathering profile show enrichment of Cr, Ni, Cu, Zn, LREE, Y, U, Th, Pb, depletion or low variation of V, Co, Rb, Ba, Sc, Sr, Cs, Eu anomaly, and flat HREE pattern with respect to non-uraniferous QPCs. Elemental correlation between U-Th with respect to other elements show positive correlation with Fe2O3, Sc, Co, Ni, Y, Ta, Pb and HREE and negative correlation with SiO2, Al2O3, MgO, MnO, Na2O, K2O, Zr, Hf, Rb, Ga, Cs, Zn and LREE. It is obvious that in surface samples within supergene weathering profile, chance of survival of uraninite is very rare. The correlation of other elements with U and Th indicate positive values with MnO, TiO2, Zr, Ti, Hf, Sr, Ba and LREE and negative correlation with respect to SiO2, Al2O3, Na2O, V, Co and Ta. There exists slight negative or no correlation with respect to Fe2O3, K2O, Sc, Cr, Cu, Ga, Y, Nb, Rb, Pb and HREE within QPC samples from supergene profile. The enrichment of redox elements (Cr, Cu and Ni) and their positive correlation with U-Th clearly point to the reduced nature of the uraniferous QPCs from subsurface beyond the supergene profile. The redox-sensitive trace elements indicate the presence of detrital pyrites. On the other hand the QPCs from the supergene zone show definite U mobilization and complexation mainly with Ti. Such mobilization may have taken place during diagenesis or during surficial oxidative weathering at low atmospheric oxygen level below the threshold of complete oxidation of U+6 state. A low positive correlation of U with redox sensitive elements (V, Cr, and Cu) may indicate that U- here is not associated with redox sulphides. U also reveals positive correlation with LREEs indicating preferential U-concentration in supergene phosphate phases. The elemental correlations of U with Ti and LREE are likely to suggest that the U-concentration in QPCs took place in the diagenetic to supergene weathering profile through alteration of Ti-bearing phases (Pronto Reaction) and phosphates. Such signature may be important in understanding hidden redox U-paleoplacers below supergene weathering profile. ReferencesCuney, M., 2010. Evolution of Uranium Fractionation Processes through Time: Driving the Secular Variation of Uranium Deposit Types. Economic Geology, 105, 553–569.Mukhopadhyay, J., Mishra, B., Chakrabarti, Kalyan., De, S., and Ghosh, G., 2016. Uraniferous paleoplacers of the Mesoarchean Mahagiri Quartzite, Singhbhum craton, India: Depositional controls, nature and source of >3.0 Ga detrital uraninites. Ore Geology Reviews, 72, 1290-1306. [ABSTRACT FROM AUTHOR]