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In recent years, the new environmental problem are arising due to industrial hazard wastage, global climate change, ground water contamination and etc., gives an attention to protect environment.one of the major source of contamination of ground water is improper discharge of industrial effluents these effluents contains so many heavy metals which are cause more effects the human life. The present study about contamination of ground water due to trace metals in and around the Vijayawada. 60 samples are collected industrial area around the Vijayawada. The study area divided into five zones depending on the nature of industries are present in the study area .The following trace metals are analyzed Al, As, Cd, Cr, Cu, Fe, Pb, Mn, Hg, Ni, Se, and Zn were analyzed in all the sample. In some ground water sample are found to be more concentration of metals are exceeds maximum limits values of WHO, ISI standards. The result gives important information of ground water quality.

Organic-rich shale rocks from the Paleocene–Eocene Palana Formation in western Rajasthan, India, were systematically investigated based on inorganic and organic geochemistry combined with microscopic examinations to evaluate the sedimentary paleoenvironmental conditions and volcanic activity and their impact on the high organic carbon accumulation. The Palana shales are categorized by high organic matter (OM) and sulfur contents, with total values up to 36.23 wt.% and 2.24 wt.%, respectively. The richness of phytoplankton algae (i.e., telalginite and lamalginite) together with redox-sensitive trace elements further suggests a marine setting and anoxic environmental conditions during the Paleocene–Eocene. The significant low oxygen conditions may contribute to enhancing the preservation of organic matter during deposition. The mineralogical and inorganic geochemical indicators demonstrate that the Palana organic-rich shale facies was accumulated in a warm and humid climate with moderate salinity stratification conditions in the water columns, thereby contributing to the high bioproductivity of the phytoplankton algae blooms within the photic zone. The presence of significant contents of zeolite derived from volcanic material together with silica minerals such as apophyllite and tridymite in most of the Palana organic-rich shales indicates a volcanic origin and supports hydrothermal activities during the Paleocene–Eocene period. These volcanic activities in this case are considered the influx of large masses of nutrients into the photic zone due to the ash accumulation, as indicated by the presence of the zeolites in the Palana shales. Therefore, the high bio-productivity associated with effective OM preservation led to the organic carbon accumulation in the Palana Formation during the Paleocene–Eocene. [ABSTRACT FROM AUTHOR]

This work describes the mineralogy of dolomite carbonatite occurring at the Newania carbonatite complex, Rajasthan, north-western India. The mineralogy records the textural and compositional features of magmatic and post-magmatic stages of carbonatite evolution. Ferroan dolomite is the principal constituent and displays variable degrees of deformation, ranging from brittle-to-ductile deformation regimes. Apatite exhibits textural and compositional evolutionary trends from early-to-late stages of carbonatite evolution. Two varieties of amphibole are reported for the first time from this complex, ferri-winchite and cummingtonite; the former is magmatic and the latter is metamorphic in origin. The columbite–tantalite-series minerals are columbite-(Fe), and their paragenesis evolves from composite grains with pyrochlore to individual crystals. Pyrochlore is magmatic with U–Ta–Ti-rich compositions and shows evolution from calciopyrochlore to kenopyrochlore, followed by alteration during late-stages of carbonatite evolution. Monazite and baryte constitute the post-magmatic mineral assemblage; the former is hydrothermal and crystallised after precursor apatite, whereas the latter is associated exclusively with columbite–pyrochlore composites. On the basis of the mineralogy of the carbonatite, it is concluded that the parent magma was generated by low-degree partial melting of magnesite–phlogopite-bearing peridotite. [ABSTRACT FROM AUTHOR]

After being subjected to geometallurgical evaluation, the iron ores from Singhbhum Bonai-Keonjhar region, eastern India, have been designated as dense martite microplaty hematite high-strength ore (dM-mH-hs ore), massive dense martite microplaty hematite high-strength ore (mdM-mH-hs ore), schistose microplaty hematite low-strength ore (smH-ls ore), microplaty hematite powdery ore (mH-p ore), vitreous goethitic ore (vG ore), and ochreous goethitic ore (oG ore) end members, with varied strengths attributed to the microporosity levels. The first four variants form typical high-grade run-of-mines (ROMs) (hard, soft and powdery iron ore variants, e.g., ROM-HIO, ROM-SSIO, and ROM-PBD, respectively) with better amenability to beneficiation. In contrast, oG and vG ore end members form ROM lateritic iron ore (ROM-LIO) with poor amenability to beneficiation, having relatively higher concentrates of alumina (~3–6 wt%) due to the complex mineral chemistry of goethite and altered hematite. Banded hematite jasper (BHJ) is a very low-grade siliceous end member. In a mining operation, the ROMs may have the attributes of several combinations of the above-stated end members and ROM variants. The designated end members present in the ROMs determine their liberation, mineralogical processes, geometallurgical characteristics, amenability to beneficiation, product grade and recovery. [ABSTRACT FROM AUTHOR]

The end-Cretaceous (ca. 66 Ma) Phenaimata alkaline igneous complex, associated in space and time with the Deccan large igneous province (LIP) in Western India, consists of bimodal (tholeiitic to alkaline) differentiated plutonic to volcanic igneous rocks. Mineralogy and petrology of variably fractionated alkaline lamprophyre and dolerite dykes of the complex are the focus of this study. The two lamprophyre dykes (termed as camptonite-I and camptonite-II) which intrude the host basalt/olivine dolerites and gabbro, differ in their liquidus minerals and crystal size distribution. Their respective rare earth element (REE) and trace element patterns suggest the lamprophyres to be genetically related, with the camptonite-II being relatively more evolved than that of the camptonite-I. Binary mixing model involving trace elements as well as the Sr˗Nd isotopic data in case of the camptonite-I, brings out involvement of crustal contamination in the generation of the lamprophyres. The two dolerites mostly consist of the liquidus phases, with the exception of olivine antecrysts created during early stages of the host gabbro formation but subsequently inherited into their magma. In terms of their trace element composition, the dolerites of this study show a strong similarity with that of the alkali basalts of the complex. The normal compositional zoning of pyroxene and amphibole from the lamprophyres shows that their parental magma initially experienced a closed system fractionation to form a large crystal mush zone and subsequently developed a smaller magmatic chamber where biotites of the camptonite-II first crystallised. Reverse zoning, resorption of crystals, disparity in crystal size distribution and their composition also reveals that a newer batch of magma was introduced from the feeding zone into the initially developed crystal laden magmatic chamber. This replenishment led to the disaggregation of crystals from the mush zone and the resulting magma subsequently evolved to form camptonite-I. Later on, the successive lateral spreading of the newly generated magma increased its buoyancy to rise through the smaller crustal chamber (with biotites) to generate camptonite-II. Our study demonstrates not only the operation of diverse open and closed system processes such as fractionation, replenishment and mush capturing that have occurred within inter-connected plumbing magmatic chambers beneath the alkaline complexes associated with the flood basalt volcanism in large igneous provinces but also their significant role in influencing the ultimate composition of the associated diverse rocks. [ABSTRACT FROM AUTHOR]

The Pakkanadu carbonatite-alkaline complex (PCAC) is one of the nine carbonatite-alkaline complexes, situated along the NE-SW trending Dhramapuri Rift Zone in Southern Granulite Terrain in South India. This oval-shaped intrusion comprises of syenite–carbonatite–dunite–pyroxenite association. The carbonatites of this deformed complex are dominated by calcite carbonatite over dolomite carbonatite and ankerite. The present study mainly focuses on identifying evidence of rare-earth element (REE) remobilization and enrichment based on petrography, mineral chemistry and whole-rock geochemistry of the PCAC carbonatites and associated rocks. Chief rare-earth and rare metal bearing minerals in these rocks include monazite-(Ce), allanite-(Ce), chevkinite-(Ce), pyrochlore, besides strontianite and barite. Geochemically, the studied carbonatites and fenites have enriched, but variable Ba (5300–236,900 ppm), Sr (4360–98,700 ppm), La (84–11,500 ppm), Ce (155–17,200 ppm) and Nd (55–3000 ppm), and Sr/Ba (0.06–3.23) molar ratio. The ΣREE range from 3508 to 32,300 ppm, dominantly contributed by light rare-earth elements (LREE). Presence of a component geochemically similar to benstonite carbonatite is reported during the present study. Geochemically the studied rocks are characterised by enrichment of LREE and elevated concentrations of incompatible, with positive spikes Ba, Sr and strong depletion of Nb, Ta, Ti, Zr and P in primitive mantle-normalized spider diagram. Besides these characters, the presence of phlogopite, amphibole, early magmatic monazite-group minerals and fluorapatite in the Pakkanadu carbonatites indicate that the initial carbonatite magma was enriched in REE, and generated by a low degree of partial melting of a metasomatised fertile mantle in intra-plate rift setting. In addition, low Nb/Y ratio (≤ 1.0), Zr/Sm (up to 6.4) and Hf/Sm (up to 0.12), very high Ba content is indicative of fluid-related metasomatism. The textural relations and mineral chemistry of REE-bearing mineral phases indicate that carbo-hydrothermal processes resulted in remobilization and enrichment of REE. All these factors point towards REE fertility in the PCAC carbonatites and associated fenites. [ABSTRACT FROM AUTHOR]

[Display omitted] • A detailed mineralogical characterization study. • A feasibility study for the potential utilization of coal gasification ash. • First time study of a coal gasification waste generated from an Indian plant. • Optical and stereomicroscopy, FESEM with EDS, XRF, SEM-EDX, XRD, and TGA applied. This work aims to perform the applied mineralogical characterization of coal gasification ash (CGA) generated from a commercial fixed bed downdraft gasification plant in eastern India. Analytical and characterization techniques such as stereomicroscopy, optical microscopy, field emission scanning electron microscopy (FESEM) with energy dispersive spectroscopy (EDS) attached, X-ray fluorescence (XRF), energy dispersive x-ray spectrometer associated scanning electron microscope (SEM-EDX), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were applied for analyzing the coal and the corresponding gasification ash sample. These analytical techniques illustrate that SiO 2 and Al 2 O 3 are the major gasification ash phases, accounting for almost 85% of the entire CGA composition. The dominant mineral phases, such as quartz, mullite, and other aluminosilicates, provide an opportunity for utilization in construction and refractory material manufacturing. Moreover, confirming the presence of rare and valuable earth elements (RVEEs) in the CGA sample with SEM-EDX analysis unearths a new application window in meeting the requirement of the RVEEs starved nation like India, where very few commercial-scale coal gasification units are operational. [ABSTRACT FROM AUTHOR]

The East coast bauxite deposits of Odisha are well known in the mineral map of India. Some such deposits exposed at Nunapaimali, Sasubohumali and Baphlimali overlying khondalite of the Precambrian Eastern Ghats belt have been studied in respect of petrology, mineralogy and microstructure with a view to find out their genetic evolution. Bore hole samples from two former deposits and mine profile samples from Baphlimali revealed a good profile differentiation, in terms of three horizontal zones of variable thickness, which in descending order are: 1 to 29m laterite zone, 2 to 28m bauxite zone, 9 to 36m saprolite zone, comprising of lithomarge and partially lateritised khondalite [PLK] developed over host khondalite. Petrographic and mineralogical difference between these three zones, brought out through optical microscopy and XRD studies, further confirms the differentiation. Genetic evolution of bauxite is interpreted from the study of a large number of samples and results are collated from the photomicrographs appended in the paper. The authigenic bauxitisation was brought about by gradual dissociation of Al-silicate to Al-hydroxide minerals through different weathering cycles as indicated from their microstructural manifestations and mineral assemblages. Primary gibbsite is formed in the initial stage of weathering directly from Al-silicate minerals. Advanced stage of prolonged weathering converts the Al-silicate to kaolinite and then to secondary gibbsite. Grain size enlargement and recrystallisation showing mosaic habit, grain boundary migration and grain orientation are the outcome of digenesis. The weathering/lateritisation process continues, resulting in colloidal precipitation of gibbsite from pore water of lateritic residuum and is in progress even in recent period The Fe-oxide phases, represented by goethite and hematite are youngest in the paragenesis, and formed due to solution, precipitation and dehydration. Iron is mostly contributed by almandine garnet present in the host khohdalite. During chemical leaching, Fe gets released from garnet and occur either as FeOOH along its fractures or fill the weak planes/inter-granular space as secondary goethite. The goethite dehydrates to hematite during digenesis. Goethitisation and limonitisation particularly in the laterite zone are the results of supergene alteration. [ABSTRACT FROM AUTHOR]

Lithomargic clay is generally found below the lateritic soil along the coastal belt of Karnataka. It is rich in silt content and dispersive in nature. This type of soil is liable to erosion and landslides. The lithomargic clay is largely found in the western coast of South India. At present, coastal belt of Udupi district is witnessing a lot of developments in terms of industry, infrastructures, and other activities. Lithomargic clay is a type of problematic soil, which needs a thorough study to make it suitable to sustain any engineering structure such as buildings, pavements, railways, dams. A characterization and mineralogical study is conducted to identify the presence of minerals and compounds for the various soil samples collected along the coastal belt of Udupi regions using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) analysis. The primary minerals observed in majority of the regions are quartz, feldspar such as orthoclase, muscovite, and the secondary minerals formed by the decomposition and chemical alteration of primary minerals include sheet minerals such as kaolinite, halloysite, dickite, gibbsite, and illite in high proportions. The study also shows the presence of iron compounds such as fayalite, goethite, and siderite. The majority of the elements observed are oxygen, silicates, aluminum, potassium, and iron which confirms the presence of the compounds identified through XRD analysis. [ABSTRACT FROM AUTHOR]

A spectacular chain of radiating mafic dykes with precise Pb–Pb and U–Pb baddeleyite ages (~2087–2080 Ma) are reported from the Dharwar Craton, southern India. These radiating dykes are spatially disposed over an extent of 70,000 km2 and flank the northern and western flanks of the Cuddapah Basin in the Eastern Dharwar Craton. Here, we present the geochemical results of four precisely dated dykes and 15 similar trending dykes (N134ºW–N28ºE), which gives first insight into the geochemical behaviour, mantle source characteristics, and geodynamic history of the mafic magmatic event at ~2.08 Ga. Field observations, mineralogy and textures classify them as fine to coarse-grained dolerites, exhibiting insignificant post-magmatic alterations. Basaltic komatiite to high-Fe tholeiitic character, variation in Mg-number (Mg#) (50–75) and crystallisation trends suggest their primary to evolved nature. Enriched light rare earth element (LREE) patterns, negative Nb–Ti anomalies and moderate Th/Nb values (0.5–0.7) in few samples suggest crustal input in the genesis. Petrogenetic modelling using batch melting equation and elemental proxies (La/Yb, Dy/Yb) indicate derivation of these dykes from a heterogeneous spinel to spinel-garnet lherzolitic source. The study postulates that a mantle plume activity at ~2.08 Ga, led to mantle upwelling, causing domal uplift beneath the Cuddapah Basin and emplacement of the Cuddapah dyke swarm (~2.08 Ga). This magmatism was followed by crustal extension and thinning, supervened by thermal relaxation and subsidence, that ultimately led to the formation of the Cuddapah Basin. Several geophysical surveys also concur a high-density material peculiar to a mafic volcanic province present beneath the southwest Cuddapah Basin. The Cuddapah dyke swarm is coeval with Fort Frances dykes, Cauchon Lake dykes and Lac Esprit dykes of the Superior Craton, but their paleolatitudes and geochemical behaviour do not represent an obvious match for the two cratons. The study highlights the significant role of ~2.08 Ga mafic dyke swarm in the evolution of the Cuddapah Basin. [ABSTRACT FROM AUTHOR]

The heavy mineral assemblage (HMA) of sandstones belonging to Mesoproterozoic Kaimur Group in the eastern Son valley, Central India, was investigated. The present communication is aimed at assessing mineralogical maturity, quantifying the contribution of heavy fraction to the bulk rock and its REE budget, sediment recycling and provenance. The transparent heavies record a relative decreasing trend upwards from 63 to 36.4% and on the contrary, opaque heavies show gradual increasing trend upwards from 36.4 to 65.4%. Tourmaline in the transparent heavy fraction reveals an overall decreasing trend of 59–22.8%. Whereas, zircon registers an increasing trend of 3.3–9.5% stratigraphically upwards. The contribution of opaque detrital clasts of ferruginous material composed of hematite and magnetite increases in the Upper Kaimur Sandstone. Tourmaline and zircon grains are characterised by etched, pitted and grooved surfaces. Zircon is also present as tiny inclusion within tourmaline and zircon itself. Heavy fraction of Upper Kaimur sandstone from the lower stratigraphic horizon exhibit lower ∑REE as compared to higher levels. The heavy fraction exhibit LREE/HREE < 1 as compared to bulk rock which has 8–10 times higher ratio. Heavy fraction exhibits enrichment in HREE and [Gd/Yb]N = 0.36–0.43, stratigraphically upwards, which is consistent with increasing Zr values suggesting zircon to be the major contributor to the REE budget of Upper Kaimur Sandstones. The percentage contribution of the zircon to the REE budget of bulk rock could have been ~50–60%. ZTR index (99–100) reveals mineralogically mature nature of Kaimur sandstones. Dominance of zircon amongst the heavies and Th/Sc vs. Zr/Sc plot shows the effect of zircon addition and sediment recycling. The plausible explanation for dominance of opaque minerals in HMA in the Upper Kaimur reflects their contribution from Paleoproterozoic metasedimentary rocks of Mahakoshal Group. HMA of Kaimur sandstones suggests derivation from granitic source. Nb/Yb vs. U/Yb diagram indicates that zircon was derived from magmatic arc source, which is in conformity with inference that Bundelkhand Granite Complex and Chhotanagpur Granite complex dominantly contributed to the Lower and Upper Kaimur Groups, respectively. Research highlights: The paper deals with the study of heavy mineral assemblage of the Kaimur Group sandstones, Vindhyan Supergroup, Son Valley, Central India. Provenance, sorting and recycling of the sediments were inferred. The ferruginous clasts found in the Dhandraul Quartzite/Sandstone also have been studied to understand their mineralogy and texture. Tourmaline and zircon dominate the Lower and Upper Kaimur Sandstones, respectively. The provenance of the Lower Kaimur sandstones is Bundelkhand granite, and Upper Kaimur sandstone is Chhotanagpur Gneissic Complex. The dominance of zircon in HMA and Th/Sc vs. Zr/Sc plot shows the significant effect of zircon addition and sediment recycling. The occurrence of ferruginous detrital clasts in Upper Kaimur sandstones can be attributed to increasing detrital input from adjoining Mahakoshal Group that has the presence of BIFs/BHQ/BHJ in the Agori Formation. The heavy fractions from sandstones of Mangesar Formation and Dhandraul Quartzite from different horizons exhibit an increase in Zr and HREE stratigraphically upwards. This suggests remarkable enrichment of HREE, low LREE/HREE, [La/Yb]N <1 and [Gd/Yb]N <1. HREE enrichment is proportional to the Zr concentration signifying the dominant role of zircon amongst the heavies in managing the ΣREE budget of the bulk rock. The percentage contribution of the zircon is calculated to be ~50–60%. [ABSTRACT FROM AUTHOR]

This study aims to thoroughly examine the distribution, concentration, and occurrence of a broad selection of REEs and major elements in coal samples from Samaleswari coal block, IB valley, Odisha, India using advanced geochemical tools. A total of 85 coal samples from four boreholes were characterized using proximate analysis and calorific value measurements. The corresponding ash samples were examined using X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Electron Probe Microanalyzer (EPMA), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS).The coal ash samples were delineated to be rich in SiO2 (42–65%) along with a lower proportion of Al2O3 (24–41%), Fe2O3 (5–6%), and TiO2 (1–2%). The average concentration of REEs in the four boreholes was found to be 510 ppm, with the distribution pattern being Ce > La > Nd > Y > Pr > Sc > Sm > Gd > Dy > Er > Yb > Eu > Ho > Tb > Tm > Lu. The concentration of critical REEs varied in the range of 100–300 ppm, and outlook coefficient (Coutl) ranged from 0.7 to 1.0, demonstrating our coal seams' suitability as a promising source of REEs. A higher concentration of REEs in BH1 was correlated with a relatively higher proportion of apatite. The increment in REE concentration with depth was speculated to be due to their close association with hematite, especially in BH1 and BH2. A strong positive correlation of all the REEs with clay minerals and specifically TiO2 reinstates their abundance in fine-grained clastic sedimentary rocks which are not significantly affected by weathering. Point analysis using EPMA and Scanning Electron Microscope–Energy Dispersive Analysis X-ray (SEM–EDAX) confirmed the co-existence of La, Ce, Pr, and Nd in the Fe-containing aluminosilicate matrix. In addition, the major oxide ratio and their plot entail terrestrial depositional environment in the basin during coal formation and deposited in semi-arid climatic conditions. [ABSTRACT FROM AUTHOR]

The dolomites of Lakshanhatti Dolomite Member of Simikeri Subgroup of the Proterozoic Kaladgi Basin of Karnataka are medium to fine grained, compact and massive crystalline rocks, and are characterized by stromatolitic and cherty laminations. They are composed mainly of dolomite mineral with traces of calcite and quartz. The MgO content of these dolomites is almost uniform, and varies between 19.57 and 21.35%, while their CaO content varies widely from 30.24 to 38.39%. They are characterized by low SiO2 (av. 0.47%) and Al2O3 contents, indicating negligible amount of detrital quartz and clay fractions in dolomites. The higher contents of Fe (av. 5225 ppm) and Mn (av. 179 ppm) suggest for their substitution in Mg/Ca cations during dolomitization. The values of MgO (av. 20.47%), CaO (av. 35.07%) and insolubles like SiO2, Al2O3 and Fe2O3 (av. 1.31%) categorize these dolomites as refractory grade. It is inferred that the dolomites with stromatolitic structures were formed as primary precipitates due to microbial activity and minor evaporation in a tidal flat shallow marine environment, while the secondary dolomites were formed by the replacement of limestone during burial and diagenesis. [ABSTRACT FROM AUTHOR]

The radioactivity levels of natural radionuclides 226Ra, 232Th, and 40K in the rocks of Dakshina Kannada region of southern India were measured by NaI (Tl) gamma-ray spectrometer. The specific activities of 226Ra, 232Th, and 40K ranged from 4.2 ± 0.4 to 74.5 ± 1.7 Bq kg−1, 14.5 ± 0.7 to 83.5 ± 1.6 Bq kg−1, and 172 ± 3 to 964 ± 7 Bq kg−1 with the mean of 25.1 ± 1.0 Bq kg−1, 36.1 ± 1.0 Bq kg−1, and 502 ± 5.0 Bq kg−1, respectively. The normality of the frequency distribution curves of 226Ra, 232Th, and 40K was tested using the Kolmogorov–Smirnov test. The radiological hazard indices were computed from the measured activity concentration of natural radionuclides in rocks and these were found to be within acceptable levels. To investigate the sources of radioactivity, the minerals involved in the rocks were detected using XRD and FTIR. The mineralogical studies reveal that the principal sources of gamma radiation in the study area are 232Th-rich phosphates and 40K-bearing feldspars. [ABSTRACT FROM AUTHOR]

The Marepalli dyke of the Vattikod cluster of the Ramadugu Lamproite Field, Nalgonda district, Telangana, India consists of pseudomorphed leucite, phlogopite (Al-poor, Ti-rich zoned phlogopite micas), pseudomorphed olivine, fluorapatite and Al-poor diopside embedded in groundmass consisting mainly of poikilitic Fe-rich titanian phlogopite and potassic amphibole. Other groundmass minerals are Al-Na-poor diopside, Al-poor spinels (titanian magnesian chromites to titanian chromites), Sr-rich fluorapatite and late-stage interstitial anhedral crystals of titanite and K-feldspar. The late-stage deuteric minerals present are REE-rich allanite, pyrite, magnetite, chalcopyrite, galena, hydro-zircon, carbonates (calcite, witherite and strontianite), baryte and cryptocrystalline SiO2. Apatite is an early crystallising phase and is present as inclusions in phlogopite and pyroxene. Phlogopite and amphibole occur as inclusions in titanite and K-feldspar. The compositional trends of phlogopite are of almost constant Al2O3 content with FeOT and TiO2 enrichment, and are typical of lamproitic micas. The FeOT enrichment is accompanied additionally by MgO depletion (reflecting VIFe2+ enrichment) from core to rim together with a slight increase in the tetraferric iron component. Diopside is characterised by <0.4 wt.% alumina and <0.6 wt.% sodium contents and exhibits typical lamproitic affinity. The spinels are alumina-poor with un-evolved titanian magnesian chromite to titanian chromite compositions. The presence of K-richterite, as an abundant amphibole, indicates a lamproite affinity, and on the basis of the typomorphic mineralogy, this rock is classified as a 'pseudoleucite-amphibole-phlogopite lamproite'. The Marepalli lamproite shows significant difference in compositional ranges of phlogopite, amphibole, pyroxene and spinel in comparison to those reported from the Vattikod, Gundrapalli, Ramadugu, Somavarigudem and Yacharam lamproites of Ramadugu Lamproite Field. These lamproites are considered to form from a common parent magma under reducing conditions as evidenced from: (1) low tetraferric iron content in phlogopite; (2) low Fe3+# and Ti# in spinels; and (3) high F content in phlogopite and apatite. [ABSTRACT FROM AUTHOR]

We study the deformation features preserved in basement granitoids recovered by scientific core drilling from an active seismic zone in the Koyna region, Deccan Traps, India. The region is characterized by recurrent reservoir triggered seismicity for the past 55 years, including the 1967 M6.3 Koyna earthquake, which produced the Donichawadi fissure zone. We investigate the basement granitoids down to a depth of 1.5 km in a set of four boreholes. Salient findings are as follows: (1) Basement rocks are composed of granite, granite-gneiss and migmatitic gneiss, characterized by greenschist to amphibolite facies metamorphism, (2) Distinctive brittle deformation features, such as fault breccias, fault gouge, prominent slickenlines and slickensides on fractures and pseudotachylites indicate proximity to a fault zone, (3) Fault zones are enriched with secondary precipitations of ferruginous and calcium-rich material which are the evidences of fluid-filled fractures at depth, (4) Fault breccia and gouge are preserved along with intense shattering of cores in zones of near-vertical fractures. Combined with information from downhole geophysical logs in a 3 km deep scientific borehole and the distribution of hypocentres, the study provides strong constraints for the subsurface extension of the Donichawadi fissure zone that is active to this day. The new datasets provide evidence for multiple episodes of fracturing and fault rock formation in an intraplate, near-vertical, fault zone and chemical changes of the fault rocks in the presence of water at seismogenic depth. [ABSTRACT FROM AUTHOR]

The long arcuate Singhbhum Shear Zone (SSZ) of around 160 km length having roughly an E-W trend hosts many uranium deposits and working uranium mines viz., Mohuldih, Bandhuhurang, Turamdih, Narwapahar, Bhatin, Jaduguda and Bagjata from west to east in addition to Cu deposits viz., Rakha, Mosabani etc. REE is well known from Kanyaluka area. Recent sub-surface exploration for uranium by AMD unravelled occurrence of thorite (ThSiO4)-bearing bands in a number of locations in western, central and eastern sectors of uranium mineralisation in SSZ, spanning over the entire shear zone. Thorite is observed in various host rocks involving metapelites of Dhanjori and Singhbhum Group and also in the Soda Granite/ feldspathic schist unit emplaced along the shear zone at the contact between the two groups. The individual lithounits that host thorite-bearing bands are restricted along the Singhbhum Shear Zone and include feldspathic schists (possible derivative of Soda Granite), albite veins, quartz-chlorite schists, quartz-biotite schists and sericite/muscovite-quartz schists. The thorite bearing zones transgresses lithology, stratigraphy as well as uraniferous zones along the shear zone evidently placing them as epigenetic hydrothermal mineralisation possibly later to major uranium metallogeny. Thorite occurs as discrete, rounded as well as subhedral to euhedral grains in various metapelites. They also form veins of their own besides occurring as phases within veins of albite and magnetite-apatite along the shear zone. Such multiple modes of occurrence and varied associated mineralogy suggest hitherto unknown thorium related hydrothermal mineralisation in SSZ. Presence of secondary thorium phases such as brockite (Ca-Thphosphate) as well as post tectonic vein-type occurrence, points towards the mobility of thorium under a hydrothermal regime as well. However, present study thus, for the first time, establish the occurrence of thorite along with REE-Th minerals showing definite evidences of thorium mobilisation in several sectors of the well know U-Cu province of Singhbhum Shear Zone. Thorium-REE mobility is a widely understudied domain and the present findings place the SSZ as an ideal ground for exploring the concept with more understanding of this metal. [ABSTRACT FROM AUTHOR]

Gneiss is medium to high grade metamorphic rock present in one third part of Thana. These rocks have been formed by the metamorphism of pre-existing granites under medium to high P/T conditions and it consist essential min like quartz, k-feldspar, plagioclase, biotite, hornblende, epidote, garnet and iron metaluminous in nature and similar to I also clear that they are formed by the highly fractionated magma. This paper records the petrography, geochemical character and probable origin of this gneiss. [ABSTRACT FROM AUTHOR]

The sandstones of the Bhuban Formation (Miocene) exposed in the Jampui hills of Tripura Fold Belt, India has been studied for provenance, tectonic setting and paleoclimate using the petrography, heavy mineral assemblage and clay mineral studies. The detrital mode of the sandstones indicate that the sediments consists predominantly of detrital quartz (avg. 92.19%), with subordinate proportions of feldspar (avg. 4.55%) and rock fragments (avg. 3.25%). The provenance discrimination diagrams depict the derivation of the detritus from both plutonic and metamorphic source rocks having affinity to continental block provenance. The plots of QFR and semi quantitative weathering index of the clastics support a moderate degree of paleoweathering in the source area under humid climatic condition. The presence of zircon, tourmaline, rutile, kyanite, epidote, sillimanite and garnet in the Bhuban sandstones is ascribed to the provenance of plutonic and metamorphic rocks. Dominance of zircon in the heavy mineral assemblage and the ZTR index values (75.13% avg.) indicate towards moderate degree of maturity with long distance of transport. The study of the shale samples by XRD and SEM analyses shows the dominance of illite over kaolinite and montmorillonite. The presence of minor amount of montmorillonite may suggest the addition of tuff and volcanic ash in the sediments under alkaline environment. [ABSTRACT FROM AUTHOR]

We present multi-proxy records of bulk chemistry, clay mineralogy, stable isotope composition of soil organic matter (δ13C SOM) and pedogenic carbonate (δ18O SC), and mineral magnetic parameters of a loess-paleosol sequence from Kashmir Valley, India, to infer paleoclimate and paleovegetation during Late Pleistocene. 14C AMS dating brackets the age of paleosols between 40 and 19.6 ka and suggests loess to be > 40 ka. Our study shows that a cold/dry climate prevailed at >40 ka (Late Pleistocene), during which the loess accumulation took place, and a warm/humid climate after that led to the development of soil units, with a prominent warm/humid phase around 35 ka. The range of Chemical Index of Alteration (72–78) and significant amounts of illite and chlorite in the section indicate moderate weathering. High kaolinite content, low chlorite, increased K/C, I/C, K/(I + C) ratio, and presence of poorly crystalline and Al-rich illite by ∼36 ka indicates increasing weathering intensity, likely due to an enhanced Indian Summer Monsoon (ISM). High magnetic susceptibility during 35–32 ka indicates enhanced pedogenesis due to a warm-humid climate. Paleotemperature estimates reveal a relatively warmer (by ∼7 °C) climate during pedogenesis than that at >40 ka. δ13C SOM values (−17‰ to −22.2‰) suggest C 3 plants dominated the Kashmir Valley through the Late Pleistocene, however, a short period of enhanced summer monsoon at ∼35 ka favored C 4 plant growth. The paleoclimate variability in the loess-paleosol sequence presented here agrees with the Guliya Ice Core δ18O record and high lake water levels in the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Radiological hazards due natural radioactivity in rocks were assessed in the Udupi district on the south west coast of India. The activity of radionuclides 226Ra, 232Th and 40K in rocks, as a commonly used construction material were estimated. The radiological hazards to the population of the region were evaluated. The 232Th activity concentration in granitic rocks was found to be high. To trace the sources of radioactivity in rocks, the mineralogical studies were carried out using XRD and FTIR technique. The studies indicated that the thorium phosphates and potassium bearing feldspars minerals are the main source of radioactivity in rocks. [ABSTRACT FROM AUTHOR]

The greater demand for high-quality iron ores has forced the iron and steel industries to utilize low-grade iron ores, such as banded hematite quartzite (BHQ). In the present work, a striped hematite quartzite sample from the Haraginadoni area, in the Sandur schist belt, Ballari District, Karnataka, India, was subjected to characterization studies and conventional mineral processing methods to produce pellet-grade concentrate, assayed as Fe > 63.0%, SiO2 + Al2O3 < 7%, (Al2O3/SiO2 < 0.5). The sample was analyzed as 35.70% Fe, 47.44% SiO2, 0.75% Al2O3, 0.06% Mn, 0.07% TiO2, 0.03% P, 0.02% S, and 0.83% LOI. We focused on two routes of beneficiating BHQ samples: (1) conventional gravity followed by reverse floatation and (2) magnetic separation followed by cleaning of magnetic concentrate by reverse floatation. Route 1, achieved pellet-grade concentrate through assaying, and was 63.73% Fe, 6.20% SiO2, 0.19% Al2O3, 0.03% Al2O3/SiO2, and 0.23% LOI, D80 45 µm, with 70.1% Fe recovery and 62.8% concentration efficiency at 39.6 wt% yield. Using Route 2, the process consisted of WHIMS at −74 µm, D80 54 µm, 10,000 Gauss, and with a 3 mm ball matrix, followed by flotation of the WHIMS concentrate, which produced a concentrate through assaying and was 63.34% Fe, 6.30% SiO2, 0.20% Al2O3 (0.03 Al2O3/SiO2), and 0.20% LOI with 77.4% Fe recovery, achieving a 68.8% concentration efficiency at 44.0 wt% yield, meeting pellet-grade specifications. Comparing and analyzing both routes for the concentration methods, Route 2, i.e., WHIMS and the reverse flotation of WHIMS concentrate, was amenable compared to Route 1. [ABSTRACT FROM AUTHOR]

The present paper investigates the mineralogy of fluvial and coastal sediments, with special attention to the heavy mineral placers between Vijaydurg and Redi Point along the 105 km stretch of the coastal area of Sindhudurg District, Maharashtra India. We present the distribution, depositional environment, mineralogy, geochemistry, replenishment and reserve potential of the heavy minerals. The heavy minerals (up to 98 wt%, avg 27 wt%) identified are opaque (ilmenite, magnetite, chromite), pyroxenes, amphiboles, rutile, tourmaline, kyanite, staurolite, zircon, garnet, epidote, sillimanite and olivine, while quartz and feldspar form the light fractions. It is observed that the concentration of heavy minerals is more in the supratidal zone as compared to intertidal zone. The provenances for the minerals are igneous, metamorphic rocks and recycled sediments of Pre-Cambrian Age along with Deccan Trap basalts. Twelve sites were identified in which the inferred reserves of heavy minerals, ilmenite, magnetite and chromite were estimated on a conservative basis. In Area 1 (7 sites), the heavy minerals are 2.33 million tonnes (MT), ilmenite 0.55 MT, magnetite 0.98 MT and chromite 0.032 MT. In Area 2 (5 sites), the inferred reserves of heavy minerals are 0.031 MT, ilmenite 0.008 MT and magnetite 0.004 MT. In the future, these resources could be further explored and thus be useful to the mining industries. [ABSTRACT FROM AUTHOR]

Karimati, a single stone, weighing ∼1 kg, fell on the mid-day of May 28, 2009, in Karimati village, Tahsil Hamirpur, Uttar Pradesh, India. Based on textures and mineralogy, Karimati is classified as brecciated, L5 (S2), ordinary chondrite. Petrologically, the chemical group, L has been assigned based on the typical mean compositions of olivine (Fa:25.5) and low-Ca pyroxene (Fs:21.6). The bulk chemical composition also resembles L chondrite as Mg/Si ratio ∼0.82. Finally, the oxygen isotopic ratios of bulk meteorite sample yielded δ17O (+3.78‰ and +4.07‰) and δ18O (+4.95‰ and +5.52‰), respectively further confirmed Karimati as L-chondrite. The Karimati appears to have been subjected to single fragmentation in the atmospheric flight and it is evident from similar characters of all the lateral faces except the base of the pyramid in terms of its uniform colour, homogeneous fusion crust and shallow regmaglypts. The metamorphic equilibration temperature for Karimati chondrite using two different thermometers (olivine-chromite and two pyroxene thermometry) has been estimated and ranges 655°C and 770°C, respectively with a mean value of ∼710°C and corresponds to the Type 5 thermal equilibration event. [ABSTRACT FROM AUTHOR]

The polymetallic mineral district in the Singhbhum shear zone (SSZ), eastern India, hosts some of the most important Palaeoproterozoic uranium, copper and apatite–magnetite deposits in India. Although the shear zone had been the locale of profuse hydrothermal alteration and there is general consensus about hydrothermal mineralisation, the alteration types vis-à-vis ore mineralisation are not amply clear. In this paper, we describe ore mineralogy and multiple alteration types vis-à-vis uranium-rare earth element (U-REE) mineralisation in the Narwapahar uranium deposit located in the SSZ. Uranium mineralisation is hosted by intensely deformed and metamorphosed tourmalinite, albite schist and chlorite schist, which are mineralogically heterogeneous showing extreme variations in constituent minerals and their modal abundances in the outcrop, hand specimen and microscopic scales often grading to nearly monomineralic rocks. Thorium-poor uraninite is an ubiquitous ore mineral of uranium. High uranium content is also noted in ilmenorutile and some unidentified U silicates. Allanite is the most abundant REE-bearing mineral whereas monazite and xenotime are subordinate. Low-Ti magnetite is nearly ubiquitous in the U ores. Based on locally preserved cross-cutting hydrothermal veins and frozen-in mineral replacement textures, the sequential metasomatic events deciphered from the Narwapahar deposit are B (boron) → Na–Fe (±Ca)→ K–Fe (±Ca)→ K→ H+. Uranium mineralisation is associated with B, Na–Fe and H+ metasomatism and perhaps with K–Fe metasomatism too whereas REE mineralisation is associated with K–Fe metasomatism and resultant hydrothermally altered rocks. The alteration types, especially the well-known pervasive regional-scale alkali metasomatism, the alteration paragenesis as described here and metal association (Fe–Cu–U–REE–Co–Ni–Mo–Au) are akin to Fe oxide (Cu–U–REE) (IOCG)-type mineralisation. The presence of a substantial amount of uranium in ilmenorutile and very fine-grained inclusion of uraninite in magnetite may potentially affect the recovery of uranium during beneficiation leading to low leachability of some uranium ores. The close association of REE-bearing minerals with the U ores requires focused study to examine the potential of U ores as a source of by-product REEs. [ABSTRACT FROM AUTHOR]

This paper presents an insight on major ion chemistry and identification of solute sources in meltwater of Chaturangi glacier throughout the ablation period 2015 and 2016. The results indicate that meltwater is slightly acidic with Ca–HCO3 and Mg–HCO3 dominated hydrochemical facies. In meltwater, Ca2+ and HCO3− are the most dominant cation and anion, respectively. The Water Quality Index values show that the quality of meltwater is good for both the ablation seasons. An important factor governing the quality of water is the residence time for dissolving minerals from the rocks. Mineralogy of surrounding rocks and Gibbs plot suggest that the meltwater ionic concentration is mostly controlled by weathering of rocks with slight contribution from atmospheric aerosols. For meltwater, the average equivalent ratios of Na/Cl and K/Cl were calculated as 3.36 ± 1.29 and 2.29 ± 0.62 in 2015 and 1.39 ± 0.6 and 0.8 ± 0.2 in 2016, which are considerably higher than the marine aerosols (Na/Cl = 0.85 and K/Cl = 0.017), it also confirmed the less contribution of atmospheric input in meltwater. The petrographic analysis of surrounding rocks indicate positive relationship among the cations (Ca2+, Mg2+, Na+ and K+) and mineral abundance. Our observations suggest that the bedrock mineralogy and weathering reactions together with amount and composition of atmospheric inputs are the main sources of ions, dissolved in the glacier meltwater. It might be due to rate of chemical reaction which leads decomposition of rocks and leaching of minerals into the meltwater. Additionally, the geology of the area plays a significant as the influence of geology and climate on water quality is observed by the quantity and types of dissolved materials and amount of the sediment carried by the streams. The elevated proportion of Ca + Mg in total cations and high Ca + Mg/(Na + K ratios, 1.47 ± 0.14 in the year 2015 and 1.44 ± 0.28 in 2016 clearly reveal that the ionic composition is primarily controlled by carbonate weathering and partly by silicate weathering. Further, the low Na + K/TZ− ratio (0.41 ± 0.02) and (0.22 ± 0.05) in 2015 and 2016, respectively also supports that carbonate weathering is main geochemical process controlling the hydrochemistry of meltwater. In addition, the ion denudation rate was calculated for both the years. The results show that the cation denudation rate of meltwater was 32.84 and 22.30 ton/km2/ablation during 2015 and 2016, respectively, whereas the anion denudation rate was found to be 205.43 in 2015 and 170.24 ton/km2/ablation in 2016. [ABSTRACT FROM AUTHOR]

The excellent exposures of plentiful Proterozoic granitic bodies in the north‐east Himalaya offer a chance to explore the evolution of continental crust in the Early Proterozoic period. The present comprehensive study from Bomdila area, western Arunachal Pradesh, NE India documents petrogenesis of Palaeoproterozoic Bomdila granite gneiss and metamorphic history of the region using the whole rock and mineral chemistry, and suitable mineral thermobarometry. The gneisses, with quartz, k‐feldspar, plagioclase, and mica mineralogy, are characterized by enrichment in rare earth elements (total REE up to 290 ppm), Rb, Ba, Th, and depletion in mafic elements (Ni, Cr, V, Sc). The gneisses are subalkaline and peraluminous with A/CNK (Al2O3/CaO + Na2O + K2O) > 1.1, indicating S‐type nature of the granites. The gneisses show fractionated REE patterns (LaN/YbN = up to 22) with LREE enrichment and HREE depletion. Geochemical characteristics such as enriched SiO2, Al2O3, alkalis, LREE, high incompatible element ratios (Rb/Sr and Ba/Sr), and depleted mafic contents with noticeable negative Eu anomalies (Eu/Eu* = 0.2 – 0.6) suggest an origin of gneisses through high‐temperature (>800°C) shallow crustal melting of a pelitic source similar to the metasedimentary enclaves within the gneisses. Mineral thermobarometric calculations suggest a tightly constrained P–T condition of 7.5–8.6 kbar and 560–590°C for the gneiss and schist from the study area. Almost identical P–T conditions of metamorphism from different lithologies attests that the Bomdila area may have attained an upper amphibolitic facies condition, possibly concomitant to the Himalayan Orogeny. Though rudimentary, temperature estimates from Ti‐in biotite thermometer suggest an increase in metamorphic grade towards the Main Central Thrust. [ABSTRACT FROM AUTHOR]

Glauconites occurring within the Ukra Member of Kutch Basin have remained unexplored in terms of their economic significance. The present study aimed to present a detailed physicochemical characterization of glauconite occurring in the siliciclastic rocks of Guneri and Umarsar area of the Kutch district, Gujarat, India to explore their economic potential. The study involved an integrated petrographical, mineralogical, and geochemical investigation of glauconitic rocks to highlight the occurrence, nature, and maturity of glauconite. The characterization was carried out using X-ray diffraction (XRD), X-ray fluorescence (XRF), and electron probe microanalysis (EPMA) combined with energy dispersive X-ray (EDX), Field emission gun scanning electron microscopy (FEG-SEM), Fourier-transform infrared spectroscopy (FTIR), and inductively coupled plasma mass spectroscopy (ICP-MS). Petrographic and bulk XRD analysis revealed that the glauconite occurs as green pellets constituting ~30 and 40% of the glauconitic sandstone and shale, respectively. Whole-rock analysis showed that the value of K2O varies considerably from 3.93 wt.% (sandstone) to 5.63 wt.% (shale). Mineral chemistry indicated the distinctive chemical composition of glauconite pellets containing 7.4–8.4 wt.% of K2O. The parameters, such as the distance between the (001) and (020) peaks and the large K2O content (~8 wt.%) of the glauconite fraction reflect an evolved to highly evolved stage of maturation. The morphological and spectral signatures further support the high degree of maturation in glauconites. Trace-element analysis implied that the glauconitic sandstone and shale contain elements such as Zn, Mn, Cu, Co, Mo, and Ni, which serve as essential micronutrients for plants. These data sets collectively constitute part of a preliminary study which is prerequisite to beneficiation, but further evaluation of its potential as a potash fertilizer also is needed. [ABSTRACT FROM AUTHOR]

The Corbyn's Cove area in south Andaman Island exposes a ~ 30 m thick sequence of sheet lavas, pillows and hyaloclastite deposits related to the Andaman Ophiolite, India. The upper sheet lavas are emplaced as tabular forms with thick, jointed core, vesicular crust and patchy hyaloclastite. The sheet lavas are criss-crossed by a network of calcite veins. The pillows constitute a modest flow field at the base of the sheet lavas and contain small (4.55 x 5.18 cm) to large (60.89 x 113.86 cm), spherical, non-vesicular, glassy entities. Pillow interiors contain radial and concentric joints. Absence of vesicles suggests that the pillows have been emplaced subaquaeously at depths greater than 4 km. The pillow lavas are fed by dykes. Thick hyaloclastite deposits containing sporadic patches of pillow breccias are intricately associated with the pillows in mound-like progradational bird foot deltas. In thin sections, the pillow lavas are characterized by lanceolate plagioclase and fretted pyroxene quenched morphologies in a holohyaline texture indicating high degrees of undercooling (ΔT ~ 100 to 200°C). Plagioclase compositions range from Anorthite (An97-99) in the core to Albite (An1-9) in the glassy margin. Individual plagioclase phenocryst in the dyke and pillow interior show tabular forms (ΔT ~ 50°C), with effects of albitization of the margin (An1-10; S-D index - 1.89 to 65.57) and variable alteration in the core (PI - 20.84 to 37.14; CIA - 70.92 to 99.34). Geochemically, the dyke-pillow lavas are hypersthene-normative tholeiites that have undergone variable degrees of spilitization and alteration. The sheet lavas have higher concentrations of Cs, Rb, Ce, U, K, Sr, P, Zr and Yb relative to N-MORB due to post emplacement cryptic metasomatism related to the calcite stockwork. These episodes of alteration have influenced the mineralogy and geochemistry of the original lavas. The geochemistry of the lavas indicates that they were deposited in a MORB-like environment, with a possible back-arc affinity. We envisage that the entire sequence from Corbyn's Cove was emplaced subaqueously during the Late Cretaceous in the Indo-Sino Burmese sea along the flanks of a rising mid oceanic ridge where the magma (1222 to 1230°C; 6 to 8 kbar) was generated at shallow depths (~ 20 km) and erupted to the surface as dykes that fed the pillow lava flow fields. Spilitization of the pillow lavas to various degrees occurred at temperatures between 1218 to 1164°C and even lower while the hydothermal alteration took place at temperatures well below 300°. [ABSTRACT FROM AUTHOR]

Lower Gondwana Kommugudem Formation of the Krishna‐Godavari (KG) Basin in the eastern coast of India records the deglaciation sequences of the Early Permian and is characterized by well‐preserved sandstone—shale—coal cyclothems. Kommugudem shales from six deep borewells of the KG Basin were studied for the organic petrological and geochemical compositions. The objective was to elucidate its source rock properties and depositional settings, which provide significant insights on the shifts in the Gondwanan palaeoenvironment and its climatic controls during the Early Permian. Maceral identification reveals the abundance of vitrinite that is distinctive to organic‐rich Permian Gondwana sediments. SiO2 enrichment with the dominance of quartz and clay minerals suggests moderate to strong weathering with palaeoclimate shift from cold, arid to hot, and semi‐arid during the Early Permian. The occurrence of higher short and mid‐chain alkanes with predominant n‐C18 and important biomarker ratios suggest a transitional fluvio‐marine environment of deposition, which is also supported by the enrichment of redox‐sensitive trace elements. Prevailing anoxia enhanced the preservation of organic matter, despite reduced primary productivity, as indicated by low P/Ti ratios. A depleted δ13Corg (mean = −21.55‰) in the shales, distinct to the interglacial period, reflects the changes in pCO2 of the Early Permian atmosphere. Sedimentary biomarkers, carbon isotopes, and trace elements explicate the palaeoceanographic conditions and sea‐level changes, indicative of marine influence in the dominantly fluvial regime. The deposition and preservation of organic‐rich sediments under anoxic (possibly euxinic) water‐column took place, forming the prolific Pre‐trappean Lower Gondwana Kommugudem source rock in the KG Basin. [ABSTRACT FROM AUTHOR]

• Clockwise P–T paths with considerable heating during decompression were first reported in mafic granulites from the Sittampundi Complex. • Zircon U–Pb age of 2513 ± 29 Ma represents the peak or near-peak metamorphic time. • The NSGT experienced collision/subduction and subsequently mantle diapirism processes. The dispute of tectonic environments such as subduction-collision setting versus extension tectonic setting, is a common phenomenon in the Precambrian. Despite the ongoing controversy, the pressure–temperature (P–T) paths recorded by metamorphic rocks are often used as an indicator for distinguishing between subduction-collision and extension tectonic settings in the early Precambrian. It is widely acknowledged that high-pressure (HP) granulites may have formed in crustal-thickening-dominated collision/subduction environment. Conversely, ultra-high temperature (UHT) granulites may have formed in the elevated mantle heat flux environment. The Sittampundi Complex (SC), where HP granulites and UHT granulites coexist, plays a crucial role in unraveling the late-Neoarchean to early-Paleoproterozoic tectonic evolution of northern South Granulite-facies Terrane (NSGT) of India. In this study, we present new P–T paths from three HP mafic granulites overprinted by UHT granulite facies metamorphism in the SC and provide more data to unravel metamorphic evolution of NSGT. Phase equilibria modeling and traditional thermobarometry calculations illustrated that clockwise metamorphic pressure–temperature (P–T) paths were yielded, passing from 3.3 to 9.3 kbar/631–669 °C (prograde stage) through 11.9–18.5 kbar/828–986 °C (pressure-peak stage), and through 6.6–11.1 kbar/1019–1085 °C (temperature-peak stage) to 4.4–8.1 kbar/845–930 °C (retrograde stage). The HP mafic granulites exhibit clockwise P–T paths with a considerable heating process (ca. 150–180 °C) from the pressure-peak stage (HP-granulite sub-facies) to the temperature-peak stage (UHT-granulite sub-facies). Zircon U-Pb dating yields an age of 2513 ± 29 indicates that the metamorphism took place in the Neoarchean. The uncommon P–T paths from Neoarchean HP granulite in the NSGT suggest that during late Neoarchean, the NSGT had experienced the crustal-thickening dominated collision/subduction (assembly of micro-blocks of Dharwar Craton) and subsequently mantle diapirism process. [ABSTRACT FROM AUTHOR]

The Western Dharwar Craton (WDC) exhibits numerous exposures of NNW–SSE to NW–SE trending mafic dykes. Geochemistry of four 2.21 Ga NNW–NW trending dykes and 21 other similar trending dykes provides new insights into the geochemical behaviour, mantle source characteristics, and tectonic history of mafic magmatic event, which have also affected the Eastern Dharwar Craton (EDC). Based on modal mineralogy and texture, these dykes can be classified into dolerite, olivine dolerite, gabbro, and olivine gabbro. They show basaltic to basaltic‐andesitic composition and have sub‐alkaline tholeiitic nature. LaN/LuN ratio classifies the dykes into two groups: Group I, with values close to 2, shows relatively flat REE patterns while, Group II, with values 4–6, has inclined REE patterns. In general, both groups show LREE enrichment and most of the samples exhibit negative Nb–Ta and Ti anomalies, indicating crustal contamination. However, negative Zr–Hf anomaly and low Th/Nb values (0.14–0.73) noticed within the samples preclude significant crustal inputs. Petrogenetic modelling using batch melting equation suggests that the dykes fractionated from two distinct mantle melts and had slightly different sources, both within the spinel–garnet transition zone. The overall composition of these 2.21 Ga dykes is consistent with a mantle plume‐induced heterogeneous source that was previously modified by some ancient subduction event. Coeval dykes from EDC exhibit similar geochemical behaviour, mantle source characteristics, and tectonic history. These and other synchronous dykes from distant cratons, viz. Superior, Slave, Greenland, represent a 2.21 Ga large igneous province event, which is linked with the Sclavia/Superia supercraton. [ABSTRACT FROM AUTHOR]

The mineralogical composition of nano-clays (NCs), and their potential implications in soil bulk properties of Indian Vertisols are unexplored. In this study, we have isolated NCs (<100 nm) from Deccan basalt (DB) alluvium derived Vertisols (Typic Haplusterts) of central India and characterized them for their mineralogy and crystalline behavior. The soils are clayey (>60%) in texture, rich in smectite mineral (60–80% in <2 μm fraction), alkaline (pH 7.8–8.5), calcareous, and contain <1.0% organic carbon. The clay fraction (<2 μm) is dominated by smectitic NC (40–60%) followed by hydroxy-interlayered vermiculite (HIV), pedogenic chlorite (PCh), kaolinite, and mica. The smectite is little hydroxy-interlayered (HIS), and hydroxy-interlayering is less pronounced in NC smectites than in the coarser clay smectites. The NC smectites are of smaller crystallite size (3.5–5.5 nm) and higher in crystal strain (15–22%) than coarser size clays because of its low lattice charge. The abundance of smectitic NCs considerably reduces the saturated hydraulic conductivity (<1 cm hr–1) of the soils due to high dispersion and swelling (COLE ≥ 0.20) of smectite clays even at the low level of exchangeable sodium percentage (ESP ≤ 5) and a moderate amount of exchangeable magnesium. The report on nano clays (<0.1 μm) highlights the unique role of nano smectites in some selected soil properties, as well as in the origin of SAT Vertisols of the Indian subcontinent. [ABSTRACT FROM AUTHOR]

Mineralogical and geochemical (major, trace and rare earth elements) studies were carried out on the clay samples of the Terani Formation, South India to investigate the paleoweathering, source rocks characteristics and tectonic setting. The chemical index of alteration (CIA), plagioclase index of alteration (PIA) values and A-CN-K diagram indicate that clays were generated from source rocks of the upper continental crust affected by intense chemical weathering. The chondrite-normalized REE patterns show considerable LREE enrichment, HREE depletion with significant negative Eu anomalies. The REE patterns, elemental ratios like Al2O3/TiO2 Cr/Ni, Eu/Eu*, (La/Lu)cn, La/Sc, Th/Sc, La/Co, Th/Co, and Cr/Th, discriminant function diagram, various bivariate and ternary plots indicate the contribution of sediments from felsic and intermediate source rocks. The discriminant-function-based tectonic setting diagrams reveal passive margin setting for the source area of the Terani Formation. [ABSTRACT FROM AUTHOR]

Coking/metallurgical coal is one of the essential raw materials for steel industries. The metallurgical coal in India contains high ash content (mineral matters), is rich in inertinite, and requires optimization before its proper utilization. Distribution of mineral matter in coking coal plays a significant role in achieving the desired product for blast furnace and coke-making operations. The present paper reports a case study on the distribution and nature of mineral matter in Indian coking coals at varying densities with respect to the coal's beneficiation behavior. The maceral analysis indicated the maximum liberation of reactives at the relative density (RD) of 1.2–1.3 g/cm3 while maximum inerts concentrated at the highest density (RD > 1.8 g/cm3). The most dominating mineral matter found in the coal is argillaceous minerals containing substantial amounts of quartz followed by carbonate and sulfides existing as cavity fillings or in disseminated form. X-ray diffraction (XRD), X-ray fluorescence (XRF), and electron-probe microanalysis (EPMA) techniques were used to study the mineral distribution and transformation behavior of coke produced from the coking coal during carbonization process. A case study on the reactivity of dispersed mineral matter in coke and the implication of mineral transformation behavior on coke is also discussed in this paper. [ABSTRACT FROM AUTHOR]

Studies were undertaken to produce reactive pozzolana i.e. metakaolin from four kaolinitic clays collected from different sources in India. This paper reports an investigation on the effect of mineralogy on the pozzolanic activity of fired kaolin clay samples. Samples are characterized by X-ray diffraction (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) in order to determine their mineralogical composition and structural differences. Calcination of samples are carried out at 700°C and 800°C for one hour. The decomposition of kaolinite is recorded using methods of thermal analysis and FTIR. The resultant products are identified by XRD. The pozzolanic activity of the thermally treated samples is evaluated based on electrical conductivity. Pozzolanic activity of metakaolinite is strongly related to the crystallinity of the original kaolinite. Well-ordered kaolinite is transformed into less reactive metakaolinite. [ABSTRACT FROM AUTHOR]

The Krishna Godavari offshore basin to the east of India is a proven reserve, rich in natural gas hydrate. The impact of sediment characteristics on the hydrate formation has already been well established in open literature. In the present study, we have attempted to investigate the mineralogy of sediments collected from KG basin by elemental analysis (energy dispersive spectroscopy) and x-ray diffraction. Various physicochemical characteristics of the clayey sediments such as TDS, salinity, pH, conductivity and resistivity were analysed at various concentrations and compared together. Also, this paper highlights the rheological behavior of the sediment samples with concentrations of 20, 35 and 50 wt% at different experimental temperatures (278.15 K, 283.15 K and 288.15 K). Viscosity measurements were performed for a wide range of shear rates for all concentrations and comparative studies have been conducted on their exhibited behavior. The viscosity of sediment sample were found to be varying from 76.3 to 0.003 Pa s depending on the sediment concentration, temperature and shear rate. In addition, viscoelastic measurements were carried out at various angular frequencies for all the sediment samples. The work aims to characterise the sediments of KG basin and analyse the rheological behavior of sediment solution which has not yet been reported in open literature. This will provide vital information for possible methane recovery from KG basin hydrate reservoir by manipulating the host sediment behavior. • Analysis of physico-chemical properties of the KG basin sediment samples. • Mineralogy of KG basin sediment samples were analysed. • Rheological studies with different sediment concentrations at various temperatures. • Viscoelastic properties of KG basin sediment samples were analysed. [ABSTRACT FROM AUTHOR]

Most continental flood basalt (CFB) provinces of the world contain silicic (granitic and rhyolitic) rocks, which are of significant petrogenetic interest. These rocks can form by advanced fractional crystallization of basaltic magmas, crustal assimilation with fractional crystallization, partial melting of hydrothermally altered basaltic lava flows or intrusions, anatexis of old basement crust, or hybridization between basaltic and crustal melts. In the Deccan Traps CFB province of India, the Barda and Alech Hills, dominated by granophyre and rhyolite, respectively, form the largest silicic complexes. We present petrographic, mineral chemical, and whole-rock geochemical (major and trace element and Sr–Nd isotopic) data on rocks of both complexes, along with 40Ar–39Ar ages of 69.5–68.5 Ma on three Barda granophyres. Whereas silicic magmatism in the Deccan Traps typically postdates flood basalt eruptions, the Barda granophyre intrusions (and the Deccan basalt flows they intrude) significantly pre-date (by 3–4 My) the intense 66–65 Ma flood basalt phase forming the bulk of the province. A tholeiitic dyke cutting the Barda granophyres contains quartzite xenoliths, the first being reported from Saurashtra and probably representing Precambrian basement crust. However, geochemical–isotopic data show little involvement of ancient basement crust in the genesis of the Barda–Alech silicic rocks. We conclude that these rocks formed by advanced (70–75 %), nearly-closed system fractional crystallization of basaltic magmas in crustal magma chambers. The sheer size of each complex (tens of kilometres in diameter) indicates a very large mafic magma chamber, and a wide, pronounced, circular-shaped gravity high and magnetic anomaly mapped over these complexes is arguably the geophysical signature of this solidified magma chamber. The Barda and Alech complexes are important for understanding CFB-associated silicic magmatism, and anorogenic, intraplate silicic magmatism in general. [ABSTRACT FROM AUTHOR]

The spatial and temporal association between lamprophyres and kimberlites provides unique opportunities to explore their genetic relationships. This paper explores such a relationship by detailing mineralogical and geochemical aspects of Korakkodu lamprophyre dykes located within the well‐known Mesoproterozoic diamondiferous Wajrakarur Kimberlite field (WKF), towards the south‐western margin of Paleo–Mesoproterozoic Cuddapah Basin, Eastern Dharwar Craton, southern India. Mineralogy reveals that these dykes belong to calc‐alkaline variety of lamprophyres, but their geochemistry display mixed signals of both alkaline and calc‐alkaline lamprophyres. These lamprophyres are highly potassic, and their high Al2O3 and low‐TiO2 content implies a shoshonitic character. Low Mg#, Ni, and Cr concentration highlight their evolved nature. High (La/Yb)N and (Gd/Yb)N content is consistent with their derivation from low degrees of partial melting, whereas highly fractionated nature suggests the presence of garnet in their source. Absence of prominent Nb‐Ta anomaly implies to the dilution of lithospheric mantle source by melts rich in HFSEs and low La/Nb ratio compared to those of the calc‐alkaline island arc volcanics and suggests an asthenospheric overprint on lithospheric mantle source. Carbonatite metasomatism in the source region of these lamprophyres is apparent from conspicuously high‐Zr/Hf ratio, and the HFSE budget of these lamprophyres are principally controlled by the presence of phlogopite veins in their lithospheric source. An extremely heterogeneous and layered lithospheric mantle beneath Eastern Dharwar Craton has been inferred from the divergent genetic history of Mesoproterozoic lamprophyres and kimberlites in the Wajrakarur field. [ABSTRACT FROM AUTHOR]

Mineralogy and bulk-rock geochemistry (including Sr and Nd isotopes) of two ultramafic (pyroxenite) intrusions at Gurramkonda, situated adjacent to the southwestern margin of the Paleo-Mesoproterozoic Cuddapah Basin within the Eastern Dharwar Craton, southern India, are presented. The pyroxenites have a characteristic cumulate texture, with a predominance of pyroxene (augite) and amphibole (hornblende and actinolite), whereas chromite is present mostly as inclusions in pyroxene. Mineral chemistry of these ultramafics is akin to that of arc cumulate rocks, particularly those associated with the Alaskan-type complexes, formed in suprasubduction zones. High Mg#'s (72–74), coupled with high bulk-rock Ni (830–1130 ppm) and Cr (1110–1,360 ppm), strikingly correspond to those of continental arc cumulates. The enrichment of large ion lithophile elements over high field strength elements, conspicuous negative Nb-Ta, Zr-Hf, and Ti anomalies, and chondrite-normalized light rare earth element patterns highlight their arc affinity. Fluid-related modification of the mantle source is apparent from the various trace-element ratios. Negative ɛ Nd2.15Ga values (−0.93 to −2.90) also support contribution of an enriched-mantle reservoir in their genesis. Partial melting of this fertile mantle source has been attributed to the Paleoproterozic lithospheric extension with heat contributions from a mantle plume or convective asthenosphere. Ultramafic intrusions of arc-related geochemical affinity thus constitute rare, but genetically important, occurrences within the Eastern Dharwar Craton. We propose that, together with the recently studied calc-alkaline lamprophyres occurring immediately toward the western margin of the Cuddapah Basin, the Gurramkonda pyroxenites are manifestations of a long-lived and major subduction system of Neoarchean age in the Eastern Dharwar Craton, southern India. [ABSTRACT FROM AUTHOR]

This article reviews the information regarding potassium (K) status of Indian soils based on research conducted since 1929. The patterns and lacunae regarding potassium consumption in India are also mentioned. The role of minerals in potassium availability vis-à-vis forms of potassium is discussed and elucidated with suitable clay mineralogical evidences. The article also highlights the problems of potassium availability to plants in Indian shrink-swell soils. We have pointed out the inefficacy of the universal method used for assessing plant-available K (1N NH4OAc) in Indian shrink-swell soils, as observed from extensive K response studies. The current practices of assessing only plant-available K is not adequate to detect native changes in soil potassium. This paradoxical situation necessitates revision and revalidation of the existing potassium fertilizer recommendations, which are being adopted since four decades. A holistic research envisaging soil test crop response and mineralogical studies will help in revising potassium evaluation methods in India, leading to judicious fertilizer application by the farmers. [ABSTRACT FROM AUTHOR]

We describe the mineralogy of a lamproite dyke from Gundrapalli village (Nalgonda district), Telangana, India. The dyke consists of a mineral assemblage characteristic of lamproites in terms of the presence of amphiboles (mainly potassic-richterite together with potassic-arfvedsonite, magnesio-riebeckite, Ti-rich potassic-magnesio-arfvedsonite, potassic-magnesio-arfvedsonite, katophorite and potassic-ferri-katophorite), Al-poor pyroxene, phlogopite (Ti-rich, Al-poor), pseudomorphed leucite, spinel (chromite-magnesiochromite), fluorapatite, baryte, titanite, rutile, barytocalcite, calcite, ilmenite, hydro-zircon, baotite, strontianite, allanite, quartz and pyrite. The absence of wadeite and priderite have been compensated for by the presence of baotite, rutile, titanite, baryte and hydro-zircons. The presence of the secondary phases: allanite, hydro-zircon, chlorite, quartz and cryptocrystalline silica, implies that the dyke has undergone deuteric alteration. On the basis of its typomorphic mineralogy the Gundrapalli dyke has been classified as a pseudoleucite-phlogopite-amphibole-lamproite. We report the presence of the rare mineral baotite from this lamproite, the first recognition of baotite from a lamproite in India. The mineralogy of the baotite-bearing Gundrapalli lamproite is analogous to the baotite-bearing Kvaløya lamproite from Troms, Norway. [ABSTRACT FROM AUTHOR]

A new occurrence of lamprophyre dyke is being reported from Saurashtra peninsula of Gujarat, north-western Deccan trap. The paper presents and discusses the detail mineralogy, field setting and whole rock major and trace element geochemistry. The newly discovered lamprophyre dyke intruded into the porphyritic olivine basalt flow. It is E-W trending dyke paralleling with Narmada rift trend, 200 m long and ∼1 m in width. Petrographic observations suggest the lamprophyre dyke is fine grained, porphyritic and shows typical panidiomoprphic texture. It contains phenocrysts of euhedral to subhedral amphibole (kaersutite), subhedral clinopyroxenes (diposide augite) and olivine pseudomorph enveloped in the groundmass composed of plagioclase, clinopyroxene and amphibole with carbonate, Ti-magnetite, zeolite and apatite occurring as accessory phases. Few clinopyroxenes show reaction and embayed margins thus indicating xenocrystic orgin. The normative chemistry of the lamprophyre dyke suggests alkaline nature with significant amount of olivine and nepheline. Whole rock geochemical data shows comparatively higher SiO2 than the other lamprophyres of the Deccan and similar to the MgO depleted lamprophyres of the Chhota Udepur alkaline province. The primitive mantle normalized multielements pattern shows absence of any high field strength element (HFSE) anomaly. Studied dyke displays more similarity with the earlier reported pre- Deccan alkaline lamprophyres and more particular with the Chhota Udepur lamprophyre. Occurrence of this new lamprophyre dyke from the Saurashtra region extends and confirms the presence of lamprophyre magmatism in the far north-western part of the Deccan. [ABSTRACT FROM AUTHOR]

Detrital mineralogy of the sandstone of Fort Member of Jurassic Jaisalmer basin has been investigated with respect to provenance, the influence of palaeoclimate, distance of transport and effects of diagenesis on the detrital mineralogy. Petrographic studies based on quantitative analysis of the detrital minerals revealed that the sandstones are composed mostly of quartz, feldspar, mica, chert, rock fragments and heavy minerals. The detrital modes of the studied Fort Member sandstone, which are indicative of mature stable cratonic blocks and recycled orogen provenance, where sediments are likely to be derived from collision orogen under semi-humid to humid climatic conditions. Petrographic data coupled with the palaeocurrent analysis results indicate a mixed provenance including granites, granite-gneisses, low and high-grade metamorphic rocks of the Aravalli craton. [ABSTRACT FROM AUTHOR]

Distinctly different groundmass mineralogy characterise the hypabyssal facies, Mesoproterozoic diamondiferous P3 and P4 intrusions from the Wajrakarur Kimberlite Field, southern India. P3 is an archetypal kimberlite with macrocrysts of olivine and phlogopite set in a groundmass dominated by phlogopite and monticellite with subordinate amounts of serpentine, spinel, perovskite, apatite, calcite and rare baddeleyite. P4 contains mega- and macrocrysts of olivine set in a groundmass dominated by clinopyroxene and phlogopite with subordinate amounts of serpentine, spinel, perovskite, apatite, and occasional gittinsite, and is mineralogically interpreted as an olivine lamproite. Three distinct populations of olivine, phlogopite and clinopyroxene are recognized based on their microtextural and compositional characteristics. The first population includes glimmerite and phlogopite-clinopyroxene nodules, and Mg-rich olivine macrocrysts (Fo 90-93) which are interpreted to be derived from disaggregated mantle xenoliths. The second population comprises macrocrysts of phlogopite and Fe-rich olivine (Fo 81-89) from P3, megacrysts and macrocrysts of Fe-rich olivine (Fo 85-87) from P4 and a rare olivine-clinopyroxene nodule from P4 which are suggested to have a genetic link with the precursor melt of the respective intrusions. The third population represents clearly magmatic minerals such as euhedral phenocrysts of Fe-rich olivine (Fo 85-90) crystallised at mantle depths, and olivine overgrowth rims formed contemporaneously with groundmass minerals at crustal levels. Close spatial association and contemporaneous emplacement of P3 kimberlite and P4 lamproite is explained by a unifying petrogenetic model which involves the interaction of a silica-poor carbonatite melt with differently metasomatised wall rocks in the lithospheric mantle. It is proposed that the metasomatised wall rock for lamproite contained abundant MARID-type and phlogopite-rich metasomatic veins, while that for kimberlite was relatively refractory in nature. [ABSTRACT FROM AUTHOR]

Abstract: Small rivers commonly drain in a few lithologies making their sediments as a good candidate for investigating provenance and weathering environments. We investigated spatial variation in compositional changes in the sediments of a modern river (Khurar River) from its source to sink for 35 km in Khajuraho area, Madhya Pradesh, India. The Khurar River in its entire course is surrounded by the Bundelkhand granitic complex that provides uniform source to the sediments. The possible physical and chemical controls on the bed-load sediments i.e. grain-size, mineralogy, geochemistry and their climatic control are investigated in detail here. Bed- load sediments of the Khurar River are very coarse to coarse sand-size ranging from -0.63 to 0.80 phi and they are devoid of fine sediments such as clay. The mineralogy of the sediments suggests that they are arkosic in composition. The spatial variation in the chemical composition of the sediments is negligible in the river basin from source to sink in the very coarse to coarse sand size range. The sediments are rich in SiO2 (≤82.93) and Al2O3 (≤11.03 wt %) and they have lower values of TiO2 (≤0.27), Fe2O3 (≤1.49), CaO (≤1.12), MgO (≤0.77), K2O (≤5.25) and Na2O (≤3.48 wt %). The trace elements such as Cr (≤66), Co (≤8), Cu (≤19) and Ni (≤12 ppm) have lower values than UCC; but the Pb (≤21) and Rb (≤142 ppm) have higher values than UCC. Lower concentrations of transition elements, such as V, Ni and Cr imply enrichment of felsic minerals in these sediments, a feature also confirmed by the mineralogical study. The high Zn content at some stations suggests anthropogenic contamination in the sediments. A-CN-K ternary plot suggests total alteration of plagioclase resulting in more removal of CaO and Na2O due to continuous weathering in the catchment area. Also, in this plot, sediments lie near to the albite concentration above the anorthite-albite line with gradual depletion in anorthite indicating that they are the weathering products of albite-enriched parent material. The A-CNK-FM ternary plot shows that all the samples plot close to the feldspar apex indicating higher abundance of feldspars. Further, the CIA (54 to 57), PIA (58 to 64) and CIW (70 to 78) values of the sediment samples suggest low to intermediate weathering environment. Chondrite-normalized pattern of REE (Rare earth elements) exhibits depletion of HREE with weak positive Eu anomaly suggesting low fractionation of the plagioclase feldspar. Thus, the major, trace and rare earth elements geochemistry of the bed-load sediments from the Khurar River suggest that they are derived from the weathering of felsic rocks and the original signatures of the granitic provenance remain there even after weathering under sub-humid climatic conditions in the river basin. [ABSTRACT FROM AUTHOR]

Systematic studies were carried out to understand the influence of mineralogy and physico-chemical parameters on the behavior of natural radionuclides in the riverine environs of Hemavathi, one of the important rivers of South India. The physico-chemical parameters, granulometric content, magnetic susceptibility and mineral compositions were measured in the soil and sediment samples to understand the factors affecting the activity concentration of radionuclides in the river ecosystem. The mean activity of 226 Ra, 232 Th, and 40 K in the soil was found to be 37.65 Bq kg −1 , 36.79 Bq kg −1 , and 301.47 Bq kg −1 , respectively. The mean activity of 226 Ra, 232 Th, and 40 K in the sediment was 64.26 Bq kg −1 , 100.43 Bq kg −1 , and 379.02 Bq kg −1 , respectively. Elevated level of radionuclide concentration was observed in the sediment samples. In order to trace the source of the radionuclides, the mineral composition of the soil and the sediment was studied using FTIR and extinction coefficient of major minerals were calculated. Multivariate statistical analyses were carried out to determine the possible correlation between radionuclides, Physico-chemical parameters and the minerals. In particular, Magnetic susceptibility shows significant correlation with 226 Ra in both soil and sediment. The statistical analyses suggested that quartz and clay mineral kolanite play a major role in enhancing the radionuclide content in soil and sediment. [ABSTRACT FROM AUTHOR]

Recent offshore exploration by the Geological Survey of India (GSI) located ferromanganese crusts (Fe Mn) along the Chagos-Laccadive Ridge (CLR) offshore western continental margin of India. CLR Fe Mn crusts grew on phosphorite substrate rock (phosphorite cemented sand/silt with moderate carbonate fluorapatite (CFA) cement and goethite). Phosphorite precipitation is the product of intense upwelling and phosphorus regeneration due to organic matter degradation and fish debris dissolution. CLR Fe Mn crusts are of hydrogenetic origin precipitated in an oxic environment. As a result of hydrogenetic processes under oxic conditions, Fe-vernadite dominated the mineral phase of Fe Mn crusts. CLR Fe Mn crusts formed when the North Indian deep-water layer mixed with oxygen-depleted waters from the Arabian Sea, Persian Gulf, and Red Sea. Three genetic layers are identified in the Fe Mn crusts; Type-I, Type-II, and Type-III developed in response to fluctuation in dissolved oxygen during periods of intensified suboxic bottom waters and monsoon maxima associated with past climatic events in the Arabian Sea. Type-I layers are columnar showing low Mn/Fe ratio (∼1), reflectivity, Mg (average 1.24%), and Ni (average 0.29%). Dendritic Type-II layers show high Mn/Fe ratios (average 12.29), reflectivity, Mg (average 3.51%) and Ni (average 1.69%). Type-III layers show very low Mn/Fe ratios (average 0.21), reflectivity, Mg (average 1.4%) and Ni (average 0.01%) and contain a substantial amount of terrigenous debris of aeolian origin. Elements of economic interest such as Mn, Co, Ni, Cu, Mo, Li, Te, and REY in CLR Fe Mn crusts are depleted owing to terrigenous contribution. • New occurrences of Fe Mn crusts found along Chagos-Laccadive Ridge. • Hydrogenetic Fe Mn crusts formed on phosphatized siltstone substrate. • Fe Mn crusts formed in response to mixing of North Indian deep water with Arabian Sea, Persian Gulf, and Red Sea waters. • Formation of phosphatized siltstone was triggered by intense upwelling and regeneration of phosphorus. • The elements of economic interest are depleted in Laccadive Fe Mn crusts. [ABSTRACT FROM AUTHOR]

The Nidar ophiolite is one of the well-preserved and almost complete ophiolite sections of the Neo-Tethyan oceanic lithosphere, obducted along the continental margin between the Indian and the Eurasian plate. This ophiolite sequence is mostly dominated by ultramafic rocks, consisting of forearc-related refractory, mainly harzburgite, dunite, and serpentinite, with minor intrusions of lherzolite, chromitites, and pyroxenites. In this present study, detailed mineralogical, whole rock geochemistry (major oxides, trace elements, PGE), and Nd isotopic composition of mantle-derived peridotites have been carried out to constrain the petrogenesis and melt evolution. These peridotites are depleted in nature due to the low modal composition of clinopyroxene, high forsterite content in olivine, and wide variation in Cr# and bulk rock chemistry, indicating variable degree of partial melting. The spoon-shaped rare earth element (REE) patterns indicate metasomatism by fluids derived from a subducting slab enriched in light REEs. Geochemical composition of the studied peridotites rocks is marked by high ratio of Al 2 O 3 /TiO 2 , LILE-LREE enrichment, HFSE depletion, and spoon-shaped chondrite-normalized REE patterns and (La/Sm) N > 1 and (Gd/Yb) N < 1, indicates some involvement of boninitic mantle melts and validate a subduction initiation process. The total PGE of the peridotites (ΣPGE = 33–337 ppb) is much more enriched than that of the primitive mantle and other ophiolite peridotites. The PGE distribution displays a concave upward pattern with higher PPGE/IPGE ratios (i.e., 0.11–1.45), suggesting that partial melting is not the only process for the evolution of the Nidar ophiolite peridotites. Enrichment of PPGE and incompatible elements (like LREE) and higher Pd/Ir ratio (0.69–8.26) indicates that these peridotites have undergone fluid/melt interaction in a supra-subduction zone (SSZ) tectonic setting. PGE concentrations of these depleted harzburgites and dunites, formed by partial melting of cpx–harzburgites in an SSZ that produced the boninitic-like melt. The enrichment of incompatible elements like the PPGE is mainly due to the circulation of fluids in the subduction zone, which leads to the PGE fractionation in mantle peridotites. Also, these peridotites have 143Nd/144Nd ratios (0.51148–0.51262) and εNd(t) (t = 140 Ma) values (i.e., +0.97 to −21.3), indicating derivation from depleted mantle sources within an intra-oceanic arc setting. The geochemical behavior exhibited by the Nidar ophiolite peridotites suggests the evolution of a highly depleted fore-arc mantle wedge significantly modified by various fluids and melts during subduction. The mineralogical, geochemical, and Nd isotopic composition of these peridotites and dunites mutually depict the diverse mantle compositions, suggesting insights into the interactions between the oceanic crust and mantle as well as associated geochemical cycling in an SSZ environment. • The peridotites are highly depleted and extremely modified. • These peridotites are enriched with PGE and Nd isotopic compositions. • A two-stage process is suggested for the Nidar ophiolite peridotites. [ABSTRACT FROM AUTHOR]