Geological Survey of India

This study evaluates the hydrogeochemical status of the aquifers within the Chhattisgarh Basin overlying the concealed, metallogenic Sonakhan Greenstone Belt. By integrating pH, electrical conductivity (EC), major ions, and heavy metals (As, Cu, Fe, Mn, Ni, and Zn) from 53 groundwater samples, we evaluate the influence of mineral-rich basement within the shallow hydrologic regime. The findings indicate that the groundwater quality for both drinking and irrigation is primarily governed by silicate weathering and secondary carbonate dissolution, which remains well within the permissible limits. Localized enrichments of Na+, Cl−, and F− near Churela and Sarsiwa suggest limited anthropogenic overprints and evaporative effects, implying that the regional hydrological system is in a state of natural rock-water equilibrium. Non-carcinogenic health hazard from heavy metals for both adults and children is negligible, which reveals a total absence of heavy metal mobilization into the overlying aquifers, despite the presence of hydrothermal mineralized zones in the basement. Our findings suggest that the dense, hydrogeologically competent Mesoproterozoic sedimentary cover functions as a robust geochemical barrier, sequestering the mineralized basement and hindering the upward migration of toxic solutes.

Landslide susceptibility assessment in basaltic terrain of the Deccan Volcanic Province, India, remains challenging due to complex geomorphic controls and limited evaluation of integrated modelling approaches. This study aims to compare commonly used statistical and heuristic models and to examine whether their integration improves susceptibility prediction. Bivariate statistical models of Modified Frequency Ratio (MFR), Statistical Index, Weight of Evidence and the heuristic Analytic Hierarchy Process (AHP) models were applied using six conditioning factors: slope inclination, slope aspect, slope curvature, geomorphology, land use and land cover and slope forming material. A landslide inventory comprising 99 documented landslides was used for model development and validation. Landslide Susceptibility Index and Landslide Occurrence Favourability Scores were calculated to generate four susceptibility maps, which were evaluated using Receiver Operating Characteristic analysis. Binary classification using mean, median and Natural Breaks (Jenks) thresholds enabled accuracy assessment through contingency tables, including Type I and Type II errors. Among individual models, MFR showed the best performance and was therefore integrated with AHP. The integrated model achieved an Area Under the Curve of 0.827, representing improvements of 4.9

Crustal assimilation is a fundamental process that significantly contributes to magmatic evolution and diversification. Distinguishing between crustal contamination and source contamination (subduction-related recycling of the crustal material), largely based on geochemical data, presents significant challenges and often leads to misleading petrogenetic interpretations. In this study, we evaluate the role of crustal assimilation in the magmatic evolution of mafic dyke swarms through petrological, geochemical, and multi-isotopic (Sr-Nd-Pb-Hf) study on NNW to NW and E-W trending mafic dykes from the tectonic contact between the Bastar Craton and the Eastern Ghat Mobile Belt, India. All the studied dykes show ophitic texture, and the major mineralogy includes compositionally zoned clinopyroxenes, plagioclase, and hydrous mafic silicates such as amphiboles and mica. The presence of significant amounts of myrmekitic intergrowths of quartz and plagioclase in the groundmass indicates the assimilation of granitic country rock into the evolving magma. Geochemical data classify these rocks as basaltic/gabbroic to basaltic andesitic/gabbroic diorite. The NNW to NW trending mafic dykes exhibit substantial geochemical similarity to the similar to 1.88 Ga Narayanpur Kondagaon mafic dykes of the Bastanar swarm, while the E-W trending mafic dykes resemble the spatially proximal E-W trending similar to 2.25 Ga Churra dyke swarm. All the mafic dykes show arc-related geochemical signatures, including negative Nb, Ta, and Ti anomalies on primitive mantle-normalized multi-element patterns, as well as an enrichment of large ion lithophile elements over high field strength elements. Our petrological and geochemical study reveals a strong influence of crustal contamination on magmatic evolution. Geochemical indicators of crustal input, such as prominent negative Nb anomaly (Nb/Nb*), low Ce/Pb and Nb/U ratios, demonstrate a strong correlation with increasing silica content in these rocks, indicating the assimilation of granitic country rock. The initial Sr-87/Sr-86 ratios in the studied dykes show an increasing trend with silica, while the initial Nd-143/Nd-144 and Hf-176/Hf-177 ratios decrease with increasing silica, reflecting the strong control of crustal assimilation on the geochemistry of these rocks. A similar trend with silica is observed in the initial Pb-208/Pb-204 and Pb-206/Pb-204, further supporting a strong control of crustal assimilation. AFC modelling using alpha-MELTS also reveals crustal contamination during magma evolution, with modelling results consistent with late-stage assimilation of the cold continental crust. We suggest that the arc-related signatures of the mafic dykes can be potentially deceptive and have been significantly influenced by the assimilation of continental crust during their ascent to the surface. The presence of magmatic amphiboles in the least contaminated dykes points towards the derivation of primary melts from a hydrous sub-continental lithospheric mantle enriched by ancient subduction/accretion-related processes during the Archean evolution of the craton.

Intertrappean bole horizons occurring between successive basaltic lava flows represent periods of volcanic quiescence during which weathering and soil formation took place. These horizons preserve geochemical signatures that can be used to reconstruct paleoclimatic conditions. Twenty-eight samples of red bole and green bole horizons were analyzed for major oxides, trace elements and rare earth elements. Chemical Index of Alteration (CIA), trace-element relationships (Cr–Ni, V–Cr, Sr–CaO, Zr–TiO₂) and REE correlations (La–Ce) were used to evaluate weathering intensity and paleoclimate. Red bole horizons show higher CIA values and enrichment of immobile elements, indicating intense chemical weathering under humid climatic conditions, whereas green bole horizons represent comparatively less weathered material formed under moderate weathering conditions. The results suggest that bole horizons represent paleosol layers developed during warm and humid climatic intervals between basaltic eruptions.

Introduction: The layer-wise morphology, mineralogy and geochemistry of Fe-Mn crusts and nodules from the West Sewell Ridge (WSR) in the Andaman Sea were analyzed. Materials and methods: We have investigated exploration and geochemical methodologies, statistical input, and cobalt chronometry to understand the genesis of Fe-Mn crusts and nodules. Results: The dominant hydrogenetic input during the inner layer development with a slower growth rate (GR) has enriched the trace elements in the inner layers, in comparison to those in the outer layers. The mineralogy and geochemistry of nodules and crusts reveal that these precipitates are dominantly hydrogenetic in origin; however, diagenesis also contributes to their growth, especially for the nodules. Cobalt chronometry showed that the heterogenetic growth of the crusts and nodules started from ~10 Ma and continued up to ~2.5 Ma with an average GR of ~7 mm/Ma. However, from 2.5 Ma to the present time, a higher diagenetic input and an increase in GR (~11 mm/Ma) were noticed due to the increased supply of sediments in the WSR. The hydrogenetic growth is more dominant in the inner layers, and is progressively altered to both hydrogenetic and diagenetic in the outer layers. Conclusions: We infer that the WSR crusts and nodules developed on the ridge top in a continental margin environment. A detailed internal morphological study establishes the presence of an intensified oxygenated deepwater flow which is responsible for the deposition of oxyhydroxides. Due to the increased GR and development in a continental margin environment with continental sediments supplied primarily from the continental margin of the Andaman Accretionary Prism, the bulk trace metal concentrations are depleted in the crusts and nodules in comparison to the open ocean crusts and nodules. However, WSR crust/nodules are economically viable due to the high contents of nickel and rare earth elements present in the inner layers.