http://localhost:8081/jspui/handle/123456789/6 2026-11-14T06:22:58Z http://localhost:8081/jspui/handle/123456789/21760 Title: GENESIS OF URANIUM MINERALIZATION IN JAHAZ, KHETRI BELT, ARAVALLI CRATON, INDIA Authors: Mishra, Priyanka Abstract: Jahaz, a uranium deposit along the "albitite line" of Rajasthan, India, is hosted within the Meso-Proterozoic metamorphic rocks of the Delhi Supergroup. The mineralization is confined to brecciated and sheared metasediments and extends over a ~ 2 km strike length with an average thickness of 3.78 meters. The Jahaz deposit is medium tonnage (3570 tons) with a 0.01 cut-off grade of U3O8. The principal metallic minerals in the mineralized zones are uraninite, molybdenite, pyrrhotite, pyrite, chalcopyrite, and minor brannerite. Quartzite, amphibolite, garnetiferous quartz biotite schist, and graphite schist are the major rock types in this area. The garnetiferous quartz biotite schist and amphibolites are sheared/albitized, and U-mineralization is mostly confined to the albitized zones. The metamorphic mineral assemblage found in host rocks are annitemagnesiohornblende- ferrohornblende-bytownite-quartz-anorthite with almandine-staurolitecorundum- ilmenite. Four hydrothermal-metasomatic stages have been established: (i) early hydrothermal, (ii) Na±K, (iii) Na-Ca-Mg, and (iv) late hydrothermal. The study area experienced a ductile, ductile-brittle transition to a brittle shear deformation, where the early hydrothermal and Na±K metasomatic alteration stage is correlated to ductile deformation (700 °C-500 °C), Na- Ca-Mg metasomatic stage is with ductile-brittle transition to brittle deformation (500-280 °C) and late hydrothermal stage with brittle deformation (≤ 280 °C). The quartzo-feldspathic, milky quartz and gray quartz veins developed during early hydrothermal stages and are unrelated to mineralization. The fluid responsible for the first (Na±K) metasomatic stage was rich in Cl, and albite-1, amphibole-1, chlorite-1, calcite-1, biotite-1, quartz-1, and sericite formed due to the replacement of the parent metamorphic minerals. The occurrence of albite-2, amphibole-2, chlorite-2, calcite-2, titanite-2, quartz-2, and apatite along veinlets/cavities due to the precipitation of dissolved components from F-rich fluids related to second (Na-Ca-Mg) metasomatic stage. The quartz-3, calcite-3, and muscovite-1 veinlets represent the last hydrothermal activity and overprinted the earlier hydrothermal-metasomatic stages. The Na+, Cl- , H2O, CO2, Mg2+, S2-, F-, and PO4 3- bearing hydrothermal fluids were responsible for different stages of metasomatic-hydrothermal alteration and associated U-mineralization. The Na-Ca-Mg metasomatic stage is considered the main mineralization stage and is controlled by the ductilebrittle shear regime. 2024-11-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/21759 Title: CRUST AND UPPER MANTLE STRUCTURE IN NORTHEAST INDIA Authors: Shukla, Neeharika Abstract: The North East Region (NER) of India is one of the world's most seismically active and tectonically complex regions, forming a continent-continent triple junction joining the Indian plate with the Asian plate and the Burmese plate. The NER of India and adjoining areas exhibit complex tectonics owing to India-Asia collision/convergence and rotational tectonics in the Eastern Himalayan Syntaxis. Such complex tectonics can alter and reshape the crustal composition and structure, playing a key role in deciphering the region's geodynamics. The complex tectonics of the region not only changed the crustal configuration but also caused several devastating earthquakes, such as the 1897 Great Shillong Plateau earthquake (revised Mw 8.1), the 1950 Great Assam earthquake (revised Mw 8.4), and about 25 large (Mw > 7.0) earthquakes in the region. The diverse subsurface structures of the region play a key role in generating destructive earthquakes. To understand the seismogenesis and geodynamic evolution of NER India, studying the crustal configuration and upper mantle structure is crucial. While several studies have addressed crustal thickness, fewer studies have explored crustal composition based on physical parameters like the Poisson’s ratio. Furthermore, a significant portion of the region remains unexplored due to the limited availability of geophysical data. This region possesses significantly different tectonic domains, such as Pop-up tectonics in the Shillong Plateau, collision tectonics in the Himalaya, subduction tectonics in the Indo-Burma Ranges, and rotation tectonics in the EHS. Although the surface geology of these tectonic units was well-studied, a complete understanding necessitates examining the spatial variations in the subsurface structure. Thus, one of the primary motivations of the present study is to investigate such changes in the crustal configuration and shallow upper mantle structure by application of receiver function analysis of teleseismic earthquakes. Moreover, this study attempted to study crustal deformation in the IBR and adjoining areas with the help of seismic anisotropy investigations. The results obtained in this study have been interpreted in association with similar results available to provide a more comprehensive perspective. 2025-01-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/21758 Title: Modeling two-dimensional Stress Field evolution and its role in reservoir-induced seismicity of Koyna Warna region and general seismicity of Northwest Himalayas Authors: Panwar, Anshul Abstract: Reservoir-triggered seismicity (RTS) has emerged as a critical subject in earthquake science following the devastating 1967 Koyna-Warna earthquake (Mw 6.3), underscoring the complex interplay between anthropogenic reservoir loading and natural fault systems. This thesis presents a comprehensive investigation into RTS, primarily focusing on two geologically distinct regions in India: the Koyna-Warna region in Maharashtra and the Tehri region in Uttarakhand. A detailed static stress modeling approach, employing analytical solutions and numerical simulations, has been developed to evaluate stress perturbations induced by reservoir water level fluctuations. Our findings reveal distinct responses based on fault mechanisms— strike-slip faulting near the Koyna reservoir exhibits in-phase Coulomb stress changes with sinusoidal water loading. In contrast, normal faulting near the Warna reservoir shows out-ofphase behavior. These theoretical insights are supported by earthquake catalogue analysis, including temporal patterns and variations in seismicity. A comparative study of the b-value, a statistical measure of earthquake magnitude distribution, has been conducted over four decades (1980–2022) for both the Koyna and Tehri regions. Results show a significant stress release in the Koyna region in the most recent decade, with comparatively subdued seismicity in the Tehri region, where the RTS potential remains under speculative observation. The spatial extent of RTS has also been assessed by categorizing seismic responses into local (within 30–50 km of the dam) and remote (beyond 50 km) zones, revealing notable differences in the triggering mechanisms between the two regions. Further, the thesis delves into the broader seismicity of the Indian plate boundaries, characterized by high tectonic activity and complex earthquake behavior. Special emphasis is given to the North-West Himalayas, where an upward trend in seismic activity has been observed between 2018 and 2023. An innovative analytical technique—Chaos Game Representation (CGR) using driven iterated function systems—has been introduced to better understand the temporal evolution of seismicity in this region. This fractal-based approach enables visualization of nonlinear and self-similar patterns in seismic time series data, offering insights beyond traditional methods. 2025-08-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/21757 Title: Characterization of Geomechanical Controls on Flow Behaviour in Tight Reservoirs Authors: Kukshal, Ankita Abstract: This research details the characterization of geomechanical properties which is further utilized to scrutinize applications such as wellbore stability and the risk of sanding, and also to study the enhancement of fluid flow rates without compromising on sanding tendencies, ensuring safe production. This becomes even more critical for complex petroleum systems, particularly when the formation of interest is a predominantly unconventional reservoir characterized by subsurface heterogeneity and complexities. Elastic parameters (Poisson's ratio, Young’s modulus, shear modulus, bulk modulus) and strength parameters (cohesion, unconfined compressive strength, friction angle) were calculated using a basic well log suite and laboratory-based wave velocity measurement using the ultrasonic pulse wave velocity technique. Regression models were observed for the dynamic measurements obtained from a well log dataset and ultrasonic pulse measurement, which was further validated and correlated. Pore pressure is calculated using Eaton’s slowness which is based on Terzaghi’s principle. These parameters were applied in the poro-elastic strain model to compute the minimum horizontal stress gradient (Sh) and the maximum horizontal stress gradient (SH) of 0.78 psi/feet to 0.85 psi/feet and 0.89 psi/feet to 0.99 psi/feet, respectively. These parameters were further validated using Zoback’s stress polygon, reducing the range between the upper and lower bounds in estimating maximum horizontal stresses, thereby improving reliability. The ratio of minimum to maximum principal stress was calculated based on the frictional strength of pre-existing fractures and faults, which is affected by the underlying subsurface lithology. Mogi-Coulomb was utilized as a failure criterion to determine wellbore stability and to predict mud weight window ranging from 15.5-16 ppg for Raghavapuram shale and from 14.4-16.8 ppg for Nandigama sandstones has been ascertained as a safe window. This study uses quantified estimates of laboratory measured mineralogy and observation on the arrangements of these constituents and establishes a procedure to detect the wellbore failure. I thoroughly investigated overpressure generation in these formations, linked to clay diagenesis, compaction, and water expansion, using a velocity-density cross-plot and variation of porosity with increasing depth. Sanding tendencies in these formations were studied by analysing the critical drawdown pressure (CDDP), which depends on both critical bottom hole pressure and reservoir pore pressure at varying depletion rates. Wellbore with oriented perforations and formation with similar petrophysical properties were simulated using finite element modelling at field scenarios to calculate the fluid flow rates. The influence of oriented perforations, ranging from 0 to 360 degrees with a phase angle of 36 degrees, on fluid flow rates to minimize sanding tendencies was examined, and the critical fluid flow rates at drawdown were analysed. This thesis offers a novel approach by bridging the gap, combining laboratory-measured mineralogy and observations of constituent arrangements with numerical simulations and geomechanical parameters obtained from well log datasets in the studied formations. 2025-08-01T00:00:00Z